Patent Application
20170269480
The present description relates to methods and apparatus for using patterning device induced phase in, for example, optimization of the patterning device pattern and one or more properties of illumination of the patterning device, in design of the one or more structural layers on the patterning device, and/or in computational lithography.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
A patterning device (e.g., mask or reticle) used to pattern radiation may give rise to an unwanted phase effect. Specifically, the topography of the patterning device (e.g., variation of the topography of features of the pattern on the patterning device from the nominal topography of the features) may introduce an unwanted phase offset into the patterned radiation (e.g., into the diffracted orders emanating from the features of the pattern of the patterning device). Such a phase offset may reduce the accuracy with which a pattern is projected onto a substrate.
The present description relates to methods and apparatus for using patterning device induced phase in, for example, optimization of the patterning device pattern and one or more properties of illumination of the patterning device, in design of the one or more structural layers on the patterning device, and/or in computational lithography.
In an aspect, there is a method including measuring properties of a three-dimensional topography of a lithographic patterning device, the patterning device including a pattern and being constructed and arranged to produce a pattern in a cross section of a projection beam of radiation in a lithographic projection system, calculating wavefront phase effects resulting from the measured properties, incorporating the calculated wavefront phase effects into a lithographic model of the lithographic projection system, and determining, based on the lithographic model incorporating the calculated wavefront phase effects, parameters for use in an imaging operation using the lithographic projection system.
In an aspect, there is provided a method including measuring properties of a three-dimensional topography for a plurality of lithographic patterning devices, each patterning device including a pattern and being constructed and arranged to produce a pattern in a cross section of a projection beam of radiation in a lithographic projection system, calculating, for each patterning device, wavefront phase effects resulting from the measured properties, and determining differences between calculated wavefront phase effects for the plurality of patterning devices, and adjusting imaging parameters for the lithographic projection system to account for the determined differences.
In an aspect, there is provided a method including measuring properties of a three-dimensional topography of a lithographic patterning device, the patterning device including a pattern and being constructed and arranged to produce a pattern in a cross section of a projection beam of radiation in a lithographic projection system, calculating wavefront phase effects resulting from the measured properties, comparing calculated wavefront phase effects across different regions of the lithographic patterning device, and applying a correction to a parameter of the lithographic process to account for the compared calculated wavefront phase effects across the different regions.
In an aspect, there is provided a method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including preparing the device pattern using a method described herein and exposing the device pattern onto the substrates.
In aspect, there is provided a non-transitory computer program product comprising machine-readable instructions configured to cause a processor to cause performance of a method described herein.
Embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:
Before describing embodiments in detail, it is instructive to present an example environment in which embodiments may be implemented.
an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. DUV radiation or EUV radiation);
a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters;
a substrate table (e.g. a wafer table) WTa constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and
a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.
The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
The patterning device support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The patterning device support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The patterning device support structure may be a frame or a table, for example, which may be fixed or movable as required. The patterning device support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”
The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.
The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.
As here depicted, the apparatus is of a transmissive type (e.g., employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g., employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g., two or more substrate table, two or more patterning device support structures, or a substrate table and metrology table). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.
The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.
Referring to
The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as CS-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross section.
The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the patterning device support (e.g., mask table MT), and is patterned by the patterning device. Having traversed the patterning device (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g., an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WTa can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in
Patterning device (e.g., mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device (e.g., mask) MA, the mask alignment marks may be located between the dies. Small alignment markers may also be included within dies, in amongst the device features, in which case it is desirable that the markers be as small as possible and not require any different imaging or process conditions than adjacent features. The alignment system, which detects the alignment markers is described further below.
The depicted apparatus could be used in at least one of the following modes:
In step mode, the patterning device support (e.g., mask table) MT and the substrate table WTa are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WTa is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
In scan mode, the patterning device support (e.g., mask table) MT and the substrate table WTa are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WTa relative to the patterning device support (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.
In another mode, the patterning device support (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WTa is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WTa or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
Lithographic apparatus LA is of a so-called dual stage type which has two tables WTa, WTb (e.g., two substrate tables) and two stations—an exposure station and a measurement station—between which the tables can be exchanged. For example, while a substrate on one table is being exposed at the exposure station, another substrate can be loaded onto the other substrate table at the measurement station and various preparatory steps carried out. The preparatory steps may include mapping the surface control of the substrate using a level sensor LS and measuring the position of alignment markers on the substrate using an alignment sensor AS, both sensors being supported by a reference frame RF. If the position sensor IF is not capable of measuring the position of a table while it is at the measurement station as well as at the exposure station, a second position sensor may be provided to enable the positions of the table to be tracked at both stations. As another example, while a substrate on one table is being exposed at the exposure station, another table without a substrate waits at the measurement station (where optionally measurement activity may occur). This other table has one or more measurement devices and may optionally have other tools (e.g., cleaning apparatus). When the substrate has completed exposure, the table without a substrate moves to the exposure station to perform, e.g., measurements and the table with the substrate moves to a location (e.g., the measurement station) where the substrate is unloaded and another substrate is load. These multi-table arrangements enable a substantial increase in the throughput of the apparatus.
As shown in
In order that the substrate that is exposed by the lithographic apparatus is exposed correctly and consistently, it is desirable to inspect an exposed substrate to measure one or more properties such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. If an error is detected, an adjustment may be made to an exposure of one or more subsequent substrates. This may particularly useful, for example, if the inspection can be done soon and fast enough that another substrate of the same batch is still to be exposed. Also, an already exposed substrate may be stripped and reworked (to improve yield) or discarded, thereby avoiding performing an exposure on a substrate that is known to be faulty. In a case where only some target portions of a substrate are faulty, a further exposure may be performed only on those target portions which are good. Another possibility is to adapt a setting of a subsequent process step to compensate for the error, e.g. the time of a trim etch step can be adjusted to compensate for substrate-to-substrate CD variation resulting from the lithographic process step.
An inspection apparatus is used to determine one or more properties of a substrate, and in particular, how one or more properties of different substrates or different layers of the same substrate vary from layer to layer and/or across a substrate. The inspection apparatus may be integrated into the lithographic apparatus LA or the lithocell LC or may be a stand-alone device. To enable most rapid measurements, it is desirable that the inspection apparatus measure one or more properties in the exposed resist layer immediately after the exposure. However, the latent image in the resist has a very low contrast—there is only a very small difference in refractive index between the part of the resist which has been exposed to radiation and that which has not—and not all inspection apparatus have sufficient sensitivity to make useful measurements of the latent image. Therefore measurements may be taken after the post-exposure bake step (PEB) which is customarily the first step carried out on an exposed substrate and increases the contrast between exposed and unexposed parts of the resist. At this stage, the image in the resist may be referred to as semi-latent. It is also possible to make measurements of the developed resist image—at which point either the exposed or unexposed parts of the resist have been removed—or after a pattern transfer step such as etching. The latter possibility limits the possibility for rework of a faulty substrate but may still provide useful information, e.g. for the purpose of process control.
The material of the absorber 302 may be, for example, molybdenum silicide (MoSi) or any other suitable material which absorbs the radiation beam B of the lithographic apparatus (e.g. DUV radiation), i.e. the absorbing material blocks the radiation beam, or which absorbs part of the radiation beam B as it travels through the absorbing material. A patterning device which has absorbing material that blocks the radiation beam may be referred to as a binary patterning device. The MoSi may be provided with one or more dopants which may modify the refractive index of the MoSi. It is not necessary for the radiation to travel through the absorber material 302, and for some absorber materials 302 substantially all radiation may be absorbed in the absorber material 302.
The absorber 302 does not fully cover the substrate 300, but instead is configured as an arrangement, i.e., pattern. Thus, gaps 304 are present between areas of absorber 302. As noted, only a small part of the patterning device MA is shown in
The radiation beam B of the lithographic apparatus (see
As further shown in
Further, besides intensity, the diffraction orders also have a phase. As noted above, the topography of a patterning device MA (e.g., the ideal pattern features themselves, unevenness across the pattern surface of the patterning device, etc.) may introduce an unwanted phase into the patterned radiation.
Such a phase may cause, e.g., a focus difference and image shift. Focus difference arises when the radiation beam suffers even order aberrations (e.g., caused by the topography of the patterning device). That is, even means the phase for the −n diffraction order and the phase for the corresponding +n diffraction orders are substantially the same. When the radiation beam suffers odd order aberrations, a pattern image may move in a direction transverse to an optical axis of the lithographic apparatus. That is, odd means that the phase for the −n diffraction orders and the phase for the corresponding +n diffraction orders have substantially the same magnitude but an opposite sign. This transverse movement may be referred to as image shift. Image shift can lead to contrast loss, pattern asymmetry and/or placement error (e.g., the pattern is shifted horizontally from where expected, which can lead to overlay error). Thus, in general, the phase of the diffracted orders can be decomposed into even and odd phase contributions, where an even phase distribution will typically be entirely an even phase contribution and an odd phase distribution will typically be entirely an odd phase contribution or a combination of even and odd phase contributions.
A focus difference, image shift, contrast loss, etc. may reduce the accuracy with which a pattern is projected onto a substrate by the lithographic apparatus. Accordingly, embodiments described herein may reduce the focus difference, image shift, contrast loss, etc.
In particular, the patterning device topography induced phase and intensity referred to above is a wavefront phase and intensity respectively. That is, the phase and intensity is in the diffracted orders at the pupil and is present for all absorbers. As noted, such wavefront phase and intensity can cause, e.g., a focus difference and/or contrast loss.
The wavefront phase is distinguished from an intentional phase shifting effect at the image plane, i.e., substrate level, provided by a patterning device designed to create such a phase shift (e.g., a phase-shifting mask). Thus, as distinguished from the wavefront phase, the phase shifting effect is typically present for only some absorbers and causes an E-field phase change. For example, in embodiments in which the radiation beam is partially absorbed by the absorber of a patterning device, a phase shift of the radiation beam as it exits the absorber may be introduced between that radiation and the radiation that passes through the adjacent gap. Rather than causing contrast loss, the phase shift effect desirably improves the contrast of an aerial image formed using the patterning device. The contrast may, for example, be at a maximum if the phase of radiation which has passed through the absorber is 90° different from the phase of radiation which has not passed through the absorber.
So, in an embodiment, various techniques are discussed herein to use the patterning device topography induced phase and/or intensity (wavefront phase and/or intensity) information (whether in data form, in the form of a mathematical description, etc.). In an embodiment, the patterning device topography induced phase (wavefront phase) is used to make a correction to reduce the effects of such phase. In an embodiment, such a correction involves (re-)design of the patterning device topography to reduce or minimize the effects of the patterning device topography induced phase (wavefront phase). For example, the patterning device stack (e.g., the one or elements/layers that make up the patterning device and/or the processes to make those one or more elements/layers) is tuned in terms of, for example, refractive index, extinction coefficient, sidewall angle, feature width, pitch, thickness and/or a parameter of a layer stack (e.g., a composition of the stack, a sequence of layers of the stack, etc.), to reduce or minimize the effects of the patterning device topography induced phase (wavefront phase). In an embodiment, such a correction involves application of a correction to one or more lithographic apparatus parameters (e.g., illumination mode, numerical aperture, phase, magnification, etc.) to reduce or minimize the effects of the patterning device topography induced phase (wavefront phase). For example, a compensating phase may be introduced downstream of the patterning device, e.g., in the projection system of the lithographic apparatus. In an embodiment, such a correction involves tuning of the patterning device pattern and/or one or more parameters of the illumination (generally referred to the illumination mode and typically comprises information on the type and details of the intensity distribution of the radiation, e.g., whether it is annular, dipole, quadrupole, etc. illumination) applied to the patterning device by the lithographic apparatus to reduce or minimize the effects of the patterning device topography induced phase (wavefront phase).
In a further embodiment, the patterning device topography induced phase (wavefront phase) is applied in the calculations of computational lithography. In other words, the patterning device topography induced phase (wavefront phase) and optionally patterning device topography induced intensity (wavefront intensity) is introduced into the simulation/mathematical models used to simulate imaging using, for example, a lithographic apparatus. So, instead of or in addition to the physical dimensional description of the patterning device topography used for such simulation/mathematical models, the patterning device topography induced phase and optionally patterning device topography induced intensity is used in those simulation/mathematical models to generate, for example, a simulated aerial image.
So, for these applications, the patterning device topography induced phase (wavefront phase) is needed. To obtain the wavefront intensity and phase of a pattern or a feature of the pattern, the pattern or feature may be programmed into a lithography simulation tool, such as the Hyperlith software, which is available from Panoramic Technology, Inc. The simulator can rigorously calculate a near-field image of the pattern or feature. The calculation may be done by Rigorous Coupled-Wave Analysis (RCWA). A Fourier transformation may be applied to yield intensity and phase values for the diffracted orders. These scattering coefficients may then be analyzed to determine a correction that can be applied to remove or ameliorate the phase. In particular, the analysis may focus on the magnitude of the phase, such as the range of phase across the diffraction orders. In an embodiment, a correction is applied to reduce a magnitude of the phase and in particular, reduce the magnitude of the range of phase across the diffraction orders.
The analysis may focus on the “fingerprint” of the phase and/or intensity across the diffraction orders. For example, the analysis may determine if the phase distribution is generally even across the diffraction orders, for example, generally symmetric about, e.g., the 0th order. As another example, the analysis may determine if the phase distribution is generally odd across the diffraction orders, for example, generally asymmetric about, e.g., the 0th order. Where the phase distribution is generally odd across the diffraction orders, the phase distribution may be, as discussed above, a combination of an odd phase contribution with an even phase contribution. In both cases, a pattern or profile with a shape akin to the “fingerprint” of the phase may be identified. In an embodiment, such a pattern or profile is described by a set of appropriate basis or eigen functions. The suitability of the basis or eigen function(s) may depend on the suitability of the function(s) for use in a lithography apparatus or depend on the phase range within which the main phase variations can be described. In an embodiment, such a pattern or profile is described by a set of polynomial functions being orthogonal over the interior of a circle. In an embodiment, such a pattern or profile is described by a Zernike polynomial (having Zernike coefficients), by a Bessel function, a Mueller matrix or a Jones matrix. The Zernike polynomial may be used to apply an appropriate correction to the phase that will reduce or remove the undesired phase. For example, the m=0 Zernike polynomials cause spherical aberrations/corrections. Thus, they cause feature dependent focus shifts of the image plane. The m=2 Zernike polynomials cause astigmatism aberrations/corrections. The m=1 and m=3 Zernike polynomials are referred to as coma and 3-foil respectively. These cause shifts and asymmetries of image patterns in the x-y image plane.
Referring to
Referring to
So, for normal incidence, the phase distribution is generally even and causes a loss of best focus. Further, the phase has a pattern, which can be generally described by, e.g., Zernike polynomials such as Zernike Z4 (i.e., Noll index 4), Zernike Z9 (i.e., Noll index 9) and/or a higher order Zernike, e.g., Zernike Z25 (i.e., Noll index 25). Such a description of the pattern of the phase can be used, e.g., for making a correction as discussed further.
Referring to
Referring to
Similar to incidence angle, the patterning device topography may have a variation in side wall angles. Side wall angle refers to the angle of the side wall of an absorber feature relative to the substrate. So, for example, referring to
So, for a range of incidence angles and/or side wall angles, the phase distribution is generally odd and causes not only a loss of best focus, but also a contrast loss, a loss of depth of focus, pattern asymmetry and/or placement error. Further, the phase has a pattern, which can be generally described by, e.g., Zernike polynomials such as Zernike Z3 (i.e., Noll index 3) and/or Zernike Z7 (i.e., Noll index 7). Such a description of the pattern of the phase can be used, e.g., for making a correction as discussed further.
Further, besides the incident angle and/or side wall angle, the phase is also significantly dependent on the feature width of the pattern or its feature. In particular, the phase range generally scales according to 1/feature width. Typically, the feature width would be one or more critical dimensions (CD) of the pattern or feature and so the phase range scales according to 1/CD.
So, from the foregoing, the patterning device topography-induced phase effect is not highly dependent on pitch. Further, by selecting an appropriate CD for a pattern and evaluating incident angle, an effective correction or optimization can be applied for the entire pattern of the patterning device, or a portion thereof associated with the selected CD, to enable improved or optimized imaging using the pattern.
Thus, using measured or otherwise known values of the topography of a patterning device for which its phase is to be corrected, the optical wavefront phase may be calculated. The wavefront phase information can then be used to effect a change in, for example, a parameter of the lithographic apparatus or process, and/or the patterning device. For example, the calculated optical wavefront phase information can be incorporated into a model of an optical system of the lithographic projection system (sometimes referred to as a lens model).
One example of a lens model used to correct for aberrations is described in U.S. Pat. No. 7,262,831 which is herein incorporated by reference in its entirety. As described above, the lens model is a mathematical description of the behavior of the optical elements of the projection system.
The overall aberration can be decomposed into a number of different types of aberration, such as spherical aberration, astigmatism and so on. The overall aberration is the sum of these different aberrations, each with a particular magnitude given by a coefficient. Aberration results in a deformation in the wave front and different types of aberration represent different functions by which the wave front is deformed. These functions may take the form of the product of a polynomial in the radial position r and an angular function in sine or cosine of mθ, where r and θ are polar coordinates and m is an integer. One such functional expansion is the Zernike expansion in which each Zernike polynomial represents a different type of aberration and the contribution of each aberration is given by a Zernike coefficient.
Particular types of aberration, such as focus drift and aberrations with even values of m (or m=0) in the angular functions dependent on mθ, can be compensated for by way of image parameters for effecting adjustment of the apparatus in such a manner as to displace the projected image in the vertical (z) direction. Other aberrations, such as coma, and aberrations with an odd value of m can be compensated for by way of image parameters for effecting adjustment of the apparatus in such a manner as to produce a lateral shift in the image position in the horizontal plane (the x,y-plane).
To this end, the lens model further provides an indication of the setting of the various lens adjustment elements that will give optimal lithographic performance for the particular lens arrangement used and can be used together with the to optimize the overlay and imaging performance of the lithographic apparatus during exposure of a lot of wafers. The predicted image parameter offsets (overlay, focus, etc) are supplied to an optimizer which determines the adjustment signals for which the remaining offsets in the image parameters will be minimized according to the user-defined lithographic specification (which will include for example the relative weighting to be allotted to overlay errors and focus errors and will determine to what extent the maximum allowed value for the overlay error (dX) over the slit for example will be counted in the merit function indicating optimal image quality as compared with the maximum allowed value for the focus error (dF) over the slit). The parameters of the lens model are calibrated off-line.
Based on the model incorporating the calculated optical wavefront phase information, one or more parameters for use in an imaging operation using the lithographic projection system may be calculated. For example, the one or more parameters may comprise one or more tunable optical parameters of the lithographic projection system. In an embodiment, the one or more parameters comprise a manipulator setting for an optical element manipulator of the lithographic projection system (e.g., an actuator to physically deform an optical element). In an embodiment, the one or more parameters comprise a setting of a device arranged to provide a configurable phase by local application of heating/cooling to change refractive index such as described in United States Patent Application Publication Nos. 2008-0123066 and 2012-0162620, which are incorporated herein in their entireties by reference. In an embodiment, the calculated optical wavefront phase information is characterized in terms of Zernike information (e.g., a Zernike polynomial, Zernike coefficients, a Noll index, etc.). In an embodiment, the wavefront phase information (such as a representation including, for example, a Zernike representation, of an odd phase distribution) can be used to determine placement of one or more features of the pattern. The placement may yield, e.g., a placement error, which may be an overlay error. The placement or overlay error may be corrected using any known technique, such as changing the location of the substrate relative to the patterned beam.
For example, using measured or otherwise known values of the topography of a patterning device for which its phase is to be corrected, an applicable pattern (e.g., Zernike polynomial) of the phase and a magnitude of the phase (e.g., a magnitude of a phase range across diffraction orders) can be identified. A phase correction based on the magnitude and applied according to the pattern may reduce or remove the undesired phase. In an embodiment, the applicable pattern may comprise a combination of patterns (e.g., a combination of an even phase distribution pattern selected from, e.g., Zernike Z4, Z9 and/or Z25 with an odd phase distribution pattern selected from, e.g., Zernike Z3 and/or Z7). In a combination of patterns, a weighting may applied to one or more of the patterns. For example, in an embodiment, a higher weighting is applied to an odd phase distribution pattern than an even odd phase distribution pattern.
In an embodiment, the correction aims to reduce or minimize the phase range across one or more of the diffraction orders. That is, referring to
Such correction of the phase for normal incidence radiation may improve the best focus. The term “best focus” may be interpreted as meaning the plane in which an aerial image with the best contrast is obtained. Further, such correction of the phase for off-axis illumination (i.e., where radiation is at an angle other than or in addition to normal) and/or side wall angle may improve the best focus. Moreover, the off-axis illumination and/or sidewall angle has a tendency to cause two-beam imaging. Thus, off-axis illumination and/or sidewall angle can be prone to contrast loss, depth of focus loss, and possibly pattern asymmetry and pattern placement errors. Thus, the correction of the phase for off-axis illumination and/or sidewall angle may improve these other effects.
As will be appreciated, the phase for the entire pattern need not be determined if there are one or more “critical” features or “hotspot” patterns that push the imaging of the pattern to or out of the boundary of the process window. Accordingly, the phase may be determined for such “critical” features and the correction may accordingly be focused on those “critical” features. Thus, in an embodiment, where the pattern is design layout for a device, the optical wavefront phase information is specified only for one or more sub-patterns or features of the patterning device pattern (i.e., the design layout).
In an embodiment, the phase may be determined for a number of feature widths, a number of illumination incident angles, a number of sidewall angles, and/or a number of pitches. Values therebetween may be interpolated. The phase information may be “mapped” onto the pattern and thus yield a two-dimensional set of phase information for the pattern. The phase information may be analyzed to identify the applicable pattern (e.g., Zernike polynomial) and a magnitude of the phase (e.g., a magnitude of a phase range across diffraction orders) for correction.
In an embodiment, one or more properties of the pattern topography may be measured, which values may be used to generate the phase information. For example, the feature width, pitch, thickness/height, sidewall angle, refractive index, and/or extinction coefficient may be measured. One or more of the properties may be measured using an optical measurement tool such as described in U.S. Patent Application Publication No. US 2012-044495, which is incorporated herein in its entirety by reference. Thus, metrology of a patterning device may be used to determine the patterning device topography induced phase, which may then be used to create a correction or design (e.g., applied to a lens model of a lithographic apparatus to adapt a lithographic process). The device described in the foregoing Patent Application may be referred to as a scatterometer or a scatterometry tool. An example of such a measuring device include the Yieldstar product, available from ASML of Eindhoven, NL. Alternately, three-dimensional topography of the reticle may be measured using an optical metrology tool, a scanning electron microscope, or an atomic force microscope. Further details of a scatterometry tool are described below, with reference to
When designing a pattern, designing a process for exposing a pattern and/or designing a process for manufacturing a device, computational lithography may be used that simulates various aspects of the device manufacturing process. In a system for simulating a manufacturing process involving lithography and a device pattern, the major manufacturing system components and/or processes can be described by various functional modules, for example, as illustrated in
The properties of the illumination and projection optics are captured in the optical model module 604 that includes, but is not limited to, numerical aperture and sigma (σ) settings as well as any particular illumination source parameters such as shape and/or polarization, where σ (or sigma) is outer radial extent of the illumination source shape. The optical properties of the photo-resist layer coated on a substrate—i.e. refractive index, film thickness, propagation and polarization effects—may also be captured as part of the optical model module 604, whereas the resist model module 605 describes the effects of chemical processes which occur during resist exposure, post exposure bake (PEB) and development, in order to predict, for example, contours of resist features formed on the substrate. The patterning device model module 603 captures how the target design features are laid out in the pattern of the patterning device and may include a representation of detailed physical properties of the patterning device, as described, for example, in U.S. Pat. No. 7,587,704, incorporated by reference herein in its entirety. The objective of the simulation is to accurately predict, for example, edge placements and critical dimensions (CDs), which can then be compared against the target design. The target design is generally defined as the pre-OPC patterning device layout, and will be provided in a standardized digital file format such as GDSII or OASIS.
In general, the connection between the optical and the resist model is a simulated aerial image intensity within the resist layer, which arises from the projection of radiation onto the substrate, refraction at the resist interface and multiple reflections in the resist film stack. The radiation intensity distribution (aerial image intensity) is turned into a latent “resist image” by absorption of photons, which is further modified by diffusion processes and various loading effects. Efficient simulation methods that are fast enough for full-chip applications approximate the realistic 3-dimensional intensity distribution in the resist stack by a 2-dimensional aerial (and resist) image.
Thus, the model formulation describes most, if not all, of the known physics and chemistry of the overall process, and each of the model parameters desirably corresponds to a distinct physical or chemical effect. The model formulation thus sets an upper bound on how well the model can be used to simulate the overall manufacturing process. However, sometimes the model parameters may be inaccurate from measurement and reading errors, and there may be other imperfections in the system. With precise calibration of the model parameters, extremely accurate simulations can be done.
So, when performing computational lithography, the patterning device topography (sometimes referred to as mask 3D) may be included in the simulation, for example, in the patterning device model module 603 and/or the optical model module 604. This may be done by transferring the patterning device topography into a set of kernels. Each feature edge of the pattern is convoluted with these kernels to yield, for example, an aerial image. See, e.g., U.S. Patent Application Publication No. 2014/0195993, which is incorporated herein in its entirety by reference. Accordingly, the accuracy depends on the number of kernels. Trade-offs would be made in accuracy (e.g., the number of kernels used) versus the time to run the simulation. A further, related technique for such simulation is described in U.S. Pat. No. 7,003,758, which is incorporated herein in its entirety by reference.
Accordingly, in an embodiment, the patterning device topography induced phase and optionally patterning device topography induced intensity may be used in computational lithography to determine the imaging effect of the three-dimensional topography of the patterning device pattern. Thus, referring to
Then, instead of or in addition to kernels, such optical wavefront phase and intensity information may be used in the computational lithography calculations at 615. In an embodiment, the optical wavefront phase and intensity information may be represented as a kernel in the computational lithography calculations. Thus, at 620, the imaging effect of the three-dimensional topography of the patterning device pattern may be computed, using a computer processor, based on the optical wavefront phase and intensity information. In an embodiment, calculation of the imaging effect is based on a calculation of a diffraction pattern associated with the patterning device pattern under consideration. So, in an embodiment, computing the imaging effect involves computing a multi-variable function of a plurality of design variables that are characteristics of the lithographic process, wherein the multi-variable function is a function of the calculated optical wavefront phase and intensity information. The design variables may include a characteristic of illumination for the pattern (e.g., polarization, illumination intensity distribution, dose, etc.), a characteristic of the projection system (e.g., numerical aperture), a characteristic of the pattern (e.g., a refractive index, a physical dimension, etc.), or the like.
In an embodiment, computing the imaging effect of the topography of the patterning device comprises computing a simulated image of the patterning device pattern. For example, in an embodiment, “point sources”−δ-functions (having intensity amplitude A and phase Φ as parameters) may be designated at the edges of features of the pattern in the simulation to approximate the patterning device topography. For example, the simulation may use a transmission function of the illumination as follows:
As discussed above, the patterning device topography induced phase depends at least on critical dimension, sidewall angle and/or incidence angle of the radiation. In an embodiment, a range of plots or collections of data of this optical wavefront phase are calculated for a range of incident angles of the pattern or a feature of the pattern and used in the computational lithography calculations. In an embodiment, a range of plots or collections of data of this optical wavefront phase are additionally or alternatively calculated for a range of critical dimensions of the pattern or a feature of the pattern, for a range pitches of the pattern or a feature of the pattern, for a range of sidewall angles of the pattern or a feature of the pattern, etc. and used in the computational lithography calculations. In an embodiment, the optical wavefront phase is rigorously calculated using a simulator such as the Hyperlith software. Where needed, values in between may be interpolated. These phase plots or collection of data may be pre-calculated with high precision and may effectively contain the full physical information of the patterning device topography. The imaging effect of the three-dimensional topography of the patterning device pattern can then be calculated using the diffraction pattern of the pattern (which is feature dependent of the pattern) and adding the computed optical wavefront phase information.
So, in an embodiment, there is provided a method comprising: obtaining calculated optical wavefront phase and intensity information caused by the three-dimensional topography of a pattern of a lithographic patterning device; and computing, using a computer processor, an imaging effect of the three-dimensional topography of the patterning device pattern based on the calculated optical wavefront phase and intensity information. In an embodiment, obtaining optical wavefront phase and intensity information comprises obtaining three-dimensional topography information of the pattern and calculating the optical wavefront phase and intensity information caused by the three-dimensional topography based on the three-dimensional topography information. In an embodiment, calculating the optical wavefront phase and intensity information is based on a diffraction pattern associated with an illumination profile of a lithography apparatus. In an embodiment, calculating the optical wavefront phase and intensity information comprises rigorously calculating the optical wavefront phase and intensity information. In an embodiment, the three-dimensional topography is selected from: an absorber height or thickness, refractive index, extinction coefficient, and/or absorber sidewall angle. In an embodiment, the three-dimensional topography comprises a multi-layer structure comprising different values of a same property. In an embodiment, the optical wavefront phase information comprises optical wavefront phase information for a plurality of critical dimensions of the pattern. In an embodiment, the optical wavefront phase information comprises optical wavefront phase information for a plurality of incident angles of illumination radiation and/or sidewall angles of the pattern. In an embodiment, the optical wavefront phase information comprises optical wavefront phase information for a plurality of pitches of the pattern. In an embodiment, the optical wavefront phase information comprises optical wavefront phase information for a plurality of pupil positions or diffraction orders. In an embodiment, computing the imaging effect of the topography of the patterning device comprises computing a simulated image of the patterning device pattern. In an embodiment, the method further comprises adjusting a parameter associated with a lithographic process using the lithographic patterning device to obtain an improvement in the contrast of imaging of the pattern. In an embodiment, the parameter is a parameter of the topography of the pattern of the patterning device or a parameter of illumination of the patterning device. In an embodiment, the method comprises tuning a refractive index of the patterning device, an extinction coefficient of the patterning device, a sidewall angle of an absorber of the patterning device, a height or thickness of an absorber of the patterning device, or any combination selected therefrom, to minimize a phase variation. In an embodiment, the calculated optical wavefront phase information comprises an odd phase distribution across the diffraction orders, or a mathematical description thereof.
So, whether using the computational lithography supplemented with optical wavefront phase information as described or using traditional computational lithography, it is desirable to make corrections of the patterning device topography induced phase (wavefront phase). Some types of corrections have already been described above and some additional types of corrections include tuning the patterning device stack, tuning the patterning device layout and/or tuning illumination of the patterning device using a patterning device/illumination tuning (sometimes referred to as source mask optimization).
Patterning device/illumination (source mask optimization) typically does not account for the patterning device topography or else uses a patterning device topography library of dimensions. That is, the library contains a set of kernels that are derived from the patterning device topography. But, as described above, those kernels tend to be an approximation and so, accuracy is sacrificed to get desirable runtime.
Accordingly, in an embodiment, the patterning device/illumination tuning calculations involve patterning device topography induced phase (wavefront phase) information. Thus, the impact of the patterning device absorber can be described by phase in the diffracted orders. So, the patterning device topography induced phase (wavefront phase) contains all the necessary information.
In an embodiment, like the computational lithography described above, the patterning device/illumination tuning calculations involve patterning device topography induced phase (wavefront phase) information. That is the mathematical/simulation calculations involve the patterning device topography induced phase (wavefront phase) information. For some basic features, using the phase may be enough to calculate the optimum patterning device/illumination mode combination.
In an embodiment, additionally or alternatively, the patterning device topography induced phase (wavefront phase) information is used as a check or control for patterning device/illumination tuning calculations. For example, in an embodiment, the patterning device topography induced phase (wavefront phase) information is used to limit, or define a limit of, the extent of an illumination, patterning device and/or other lithographic parameter and a traditional patterning device/illumination tuning process is performed within the extent or constrained by the extent. For example, patterning device topography induced phase (wavefront phase) information may be obtained for a plurality of incident angles and analyzed to identify an acceptable angular range within which the patterning device topography induced phase (wavefront phase) is acceptable. A traditional patterning device/illumination tuning process may then be performed within the angular range. In an embodiment, a traditional patterning device/illumination tuning process may yield one or more proposed combinations of patterning device layout and illumination mode. One or more parameters of those one or more combinations may be tested against the patterning device topography induced phase (wavefront phase) information. For example, the graphs of patterning device topography induced phase (wavefront phase) against diffracted orders for various incident angles may be used to rule out a proposed illumination mode if the incident angle for that illumination mode yields a magnitude of phase that exceeds a threshold.
Referring to
At 702, the simulation model that calculates the profile of the pattern is selected. The simulation model may include, in an embodiment, an aerial image model. In that case, the distribution of the incident radiation energy distribution onto the photoresist will be calculated. Calculation of the aerial image may be done either in the scalar or vector form of the Fourier optics. Practically, this simulation may be carried out with the aid of a commercially available simulator such as the Prolith, Solid-C or the like software. The characteristics of the different elements of the lithographic apparatus, like the numerical aperture or specific patterns, may be entered as input parameters for the simulation. Different models like a Lumped Parameter Model or a Variable Threshold Resist model may be used.
In this specific embodiment, relevant parameters to run aerial image simulations may include the distance to the plane where the best plane of focus exists, a measure of degree of spatial partial coherence of the illumination system, polarization of the illumination, the numerical aperture of the optical system illuminating the device substrate, the aberrations of the optical system and a description of the spatial transmission function representing the patterning device. In an embodiment, as described above, the relevant parameters may include patterning device topography induced phase (wavefront phase) information.
It should be understood that the use of the simulation model selected at 702 is not limited to, for example, calculation of a resist profile. The simulation model may be carried out to extract additional/complementary responses like process latitude, dense/isolated feature biases, side lobe printing, sensitivity to patterning device errors, etc.
After defining the model and its parameters (including initial conditions of the pattern and the illumination mode), the method then proceeds to 703 where the simulation model is run to calculate a response. In an embodiment, the simulation model may perform calculations based on the patterning device topography induced phase (wavefront phase) information as described above in respect of computation lithography. Thus, in an embodiment, the simulation model embodies a multi-variable function of a plurality of design variables that are characteristics of the lithographic process, the design variables including a characteristic of illumination for the pattern and a characteristic of the pattern, wherein the multi-variable function is a function of the calculated optical wavefront phase information.
At 704, one or more illumination conditions of the illumination mode (e.g., changing the type of the intensity distribution, changing a parameter of an intensity distribution such as σ, changing dose, etc.) and/or one or more aspects of the layout or topography of the patterning device pattern (e.g., applying a bias, adding an optical proximity correction, changing an absorber thickness, changing a refractive index or extinction coefficient, etc.) are adjusted based on analysis of the response.
The response calculated in this embodiment may be evaluated versus one or more lithographic metrics to judge whether there is, e.g., enough contrast to successfully print the desired pattern feature in resist on the substrate. For example, the aerial image can be analyzed, through a focus range, to provide estimates of the exposure latitude and depth of focus and the procedure can be performed iteratively to arrive at the best optical conditions. Practically, the quality of the aerial image may be determined by using a contrast or aerial image log-slope (ILS) metric which may be a normalized image log-slope metric (NILS), which may be normalized to the feature size, for example. This value corresponds to the slope of the image intensity (or aerial image). In an embodiment, the lithographic metric may comprise a critical dimension uniformity, exposure latitude, a process window, a dimension of the process window, mask error enhancement factor (MEEF), normalized image log-slope (NILS), edge placement error, and/or a pattern fidelity metric
As discussed above, in an embodiment, the patterning device topography induced phase (wavefront phase) information may be used to evaluate or constrain the calculation of the response. For example, in an embodiment, the patterning device topography induced phase (wavefront phase) information is used to limit, or define a limit of, the extent of an illumination, patterning device and/or other lithographic parameter and a traditional patterning device/illumination tuning process is performed within the extent or constrained by the extent to generate the response. For example, patterning device topography induced phase (wavefront phase) information may be obtained for a plurality of incident angles and analyzed to identify an acceptable angular range within which the patterning device topography induced phase (wavefront phase) is acceptable. A traditional patterning device/illumination tuning process may then be performed within the angular range. In an embodiment, a traditional patterning device/illumination tuning process may yield one or more proposed combinations of patterning device pattern configuration and illumination mode as the response. One or more parameters of those one or more combinations may be tested against the patterning device topography induced phase (wavefront phase) information. For example, the graphs of patterning device topography induced phase (wavefront phase) against diffracted orders for various incident angles may be used to rule out a proposed illumination mode if the incident angle for that illumination mode yields a magnitude of phase that exceeds a threshold.
At 705, the simulation/calculations, the determination of the response and evaluation of the response may be repeated until a certain termination condition is satisfied. For example, the adjustment may continue until a value is minimized or maximized. For example, a lithographic metric, such as critical dimension, exposure latitude, contrast, etc., may be evaluated whether it meets a design criteria (e.g., critical dimension less than a certain first value and/or greater than a certain second value). If the lithographic metric doesn't meet the design criteria, the adjustment may continue. In an embodiment, for an adjustment, new patterning device topography induced phase (wavefront phase) information may be used or obtained (e.g., calculated).
Further, in addition to patterning device/illumination tuning, one or more other parameters of the lithographic apparatus or process may be tuned. For example, one or more parameters of the projection system of the lithographic apparatus may be tuned, such as numerical aperture, an aberration parameter (e.g., a parameter associated with a device that can tune aberrations in the beam path), etc.
So, in an embodiment, there is provided a method comprising: for an illumination by radiation of a pattern of a lithographic patterning device, obtaining calculated optical wavefront phase information caused by three-dimensional topography of the pattern; and based on the optical wavefront phase information and using a computer processor, adjusting a parameter of the illumination and/or adjusting a parameter of the pattern. In an embodiment, the method further comprises, for the adjusted illumination and/or pattern parameter, obtaining calculated optical wavefront phase information caused by the three-dimensional topography of the pattern and adjusting the parameter of the illumination and/or adjusting the parameter of the pattern, wherein the obtaining and adjusting is repeated until a certain termination condition is satisfied. In an embodiment, the adjusting comprises calculating, based on the optical wavefront phase information, a lithographic metric and, based on the lithographic metric, adjusting the parameter of the illumination and/or the pattern. In an embodiment, the lithographic metric comprises one or more selected from: a critical dimension uniformity, exposure latitude, a process window, a dimension of the process window, mask error enhancement factor (MEEF), normalized image log-slope (NILS), edge placement error, or a pattern fidelity metric. In an embodiment, the obtaining comprises obtaining the calculated optical wavefront phase information for a plurality of different incidence angles of illumination radiation; and wherein the adjusting comprises defining an acceptable angular range of incident illumination radiation based on the calculated optical wavefront phase information, and adjusting the parameter of the illumination and/or the pattern, within the defined angular range. In an embodiment, the adjusting comprises performing an illumination/patterning device optimization. In an embodiment, the adjusting comprises computing a multi-variable function of a plurality of design variables that are characteristics of the lithographic process, the design variables including a characteristic of illumination for the pattern and a characteristic of the pattern, wherein the multi-variable function is a function of the calculated optical wavefront phase information.
In an embodiment, there is provided a method to improve a lithographic process to image at least a portion of a pattern of a lithographic patterning device onto a substrate, the method comprising: obtaining calculated optical wavefront phase information caused by three-dimensional topography of the pattern; computing, using a compute processor, a multi-variable function of a plurality of parameters that are characteristics of the lithographic process, the parameters including a characteristic of illumination for the pattern and a characteristic of the pattern, wherein the multi-variable function is a function of the calculated optical wavefront phase information; and adjusting characteristics of the lithographic process by adjusting one or more of the parameters until a predefined termination condition is satisfied.
In an embodiment, the adjusting further comprises computing a further multi-variable function of a plurality of design variables that are characteristics of the lithographic process, wherein the further multi-variable function is not a function of the calculated optical wavefront phase information. In an embodiment, the multi-variable function is used for a critical area of the pattern and the further multi-variable function is used for a non-critical area. In an embodiment, the adjusting improves the contrast of imaging of the pattern. In an embodiment, the calculated optical wavefront phase information comprises an odd phase distribution across the diffraction orders, or a mathematical description thereof. In an embodiment, the obtaining comprises obtaining three-dimensional topography information of the pattern and calculating the optical wavefront phase information caused by the three-dimensional topography based on the three-dimensional topography information. In an embodiment, the pattern is a design layout for a device and the optical wavefront phase information is specified only for a sub-pattern of the pattern. In an embodiment, the method comprises adjusting the parameter of the illumination, wherein the adjusting the parameter of the illumination comprises adjusting an intensity distribution of the illumination. In an embodiment, the method comprises adjusting the parameter of the pattern, wherein the adjusting the parameter of the pattern comprises applying an optical proximity correction feature and/or a resolution enhancement technique to the pattern. In an embodiment, the optical wavefront phase information comprises optical wavefront phase information for a plurality of incident angles of radiation and/or sidewall angles of the pattern. In an embodiment, the obtaining comprises rigorously calculating the optical wavefront phase information.
Patterning device stack tuning (e.g., optimization) is mainly done by looking at manufacturability aspects (e.g., etching). If the imaging using the patterning device is part of the tuning this is done using one or more derived imaging figures of merit such as exposure latitude. These derived imaging figures of merit are feature and illumination setting dependent. When using a derived imaging figure of merit (e.g. exposure latitude) for tuning, it may not be clear if the derived tuned stack is fundamentally better on all imaging related topics because the tuning depends on the features, the illumination setting, etc.
Accordingly, instead or in addition to evaluating a derived imaging metric like exposure latitude, the patterning device topography induced phase (wavefront phase) is evaluated. By evaluating the dependency of patterning device topography induced phase (wavefront phase) against one or more patterning device stack properties (e.g., refractive index, extinction coefficient, absorber or other height/thickness, sidewall angle, etc.), an improved patterning device stack can be identified that reduces or minimizes a magnitude of the mask 3D induced phase. The mask stack derived this way may be fundamentally better on a plurality of imaging properties for all features and/or illumination settings.
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As will be appreciated, the same analysis may be applied to patterning device absorbers with different refractive indices, different extinction coefficients, etc. to tune (e.g., optimize) the patterning device stack. Thus, besides the optimizations described above for thickness for a particular combination of refractive index, extinction coefficient, etc., similar optimizations can be performed for different refractive indices for a particular combination of thickness, extinction coefficient, etc., different extinction coefficients for a particular combination of thickness, refractive index, etc., etc. And so, those results may be used in a co-optimization function to arrive at a tuned (e.g., optimal) stack. And while physical parameters of the patterning device topography have been described, parameters of forming the patterning device topography may be similarly considered (such as etching).
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So, in an embodiment, while absorber characteristics may be modified to help correct for patterning device topography induced phase (wavefront phase) of an EUV mask, a further way to correct for the patterning device topography induced phase (wavefront phase) is to provide off-axis illumination that addresses the odd phase distribution associated with the horizontal lines and mitigates fading. For example, dipole illumination (with poles at the appropriate position) can provide illumination for both the horizontal and vertical lines but that is better suited for the horizontal lines.
Further, for EUV illumination for example, patterning device topography induced phase (wavefront phase) effects can be different not only per orientation (e.g., vertical or horizontal features) but also per pitch. For different feature orientations and different pitches, there are best focus differences, a Bossung curve tilt, contrast differences through pitch, and/or depth of focus differences.
In an embodiment, the techniques for evaluation of the phase (e.g., the use of the figures of merit, the co-optimization, etc.) may be applied in the other embodiments herein, where the varied parameter is, instead of or in addition to a patterning device stack property, incident angle of illumination radiation, sidewall angle, critical dimension, etc.
So, in an embodiment, there is provided a method comprising: obtaining optical wavefront phase information caused by a three-dimensional topography of a pattern of a lithographic patterning device; and based on the optical wavefront phase information and using a computer processor, adjusting a physical parameter of the pattern. In an embodiment, the pattern is a design layout for a device and the optical wavefront phase information is specified only for a sub-pattern of the pattern. In an embodiment, the method further comprises, for the adjusted physical parameter of the pattern, obtaining optical wavefront phase information caused by the three-dimensional topography of the pattern and adjusting the parameter of the physical parameter of the pattern, wherein the obtaining and adjusting is repeated until a certain termination condition is satisfied. In an embodiment, the adjusting improves the contrast of imaging of the pattern. In an embodiment, the calculated optical wavefront phase information comprises an odd phase distribution across the diffraction orders, or a mathematical description thereof. In an embodiment, the adjusting comprises determining a minimum of phase caused by the three-dimensional topography of the pattern of the lithographic patterning device. In an embodiment, the physical parameter comprises one or more selected from: refractive index, extinction coefficient, sidewall angle, thickness, feature width, pitch, and/or a parameter of a layer stack (e.g., sequence/composition/etc.). In an embodiment, adjusting the physical parameter comprises selecting an absorber of the pattern from a library of absorbers. In an embodiment, obtaining optical wavefront phase information comprises rigorously calculating the optical wavefront phase information.
Thus, in an embodiment, the patterning device topography induced phase (wavefront phase) is used to tune (e.g., optimize) the patterning device stack. In particular, the wavefront phase effects may be mitigated by absorber tuning (e.g., optimization). In an embodiment, as discussed above, an opaque binary mask may be unfavorable, while a transmissive phase shifting mask with optimized absorber thickness may give the best performance in terms of wavefront phase and lithographic performance on the substrate.
And, for EUV patterning device, contrast loss due to odd phase distribution effects may be best mitigated by illumination mode tuning (e.g., optimization).
In an embodiment, patterning device to patterning device differences may be tuned (e.g., optimized) using the patterning device topography induced phase (wavefront phase). That is the patterning device topography induced phase (wavefront phase) information of each separate patterning device may be compared or monitored to recognize differences between patterning devices and, for example, apply a correction to a parameter of the lithographic process (e.g., a correction to one or more of the patterning devices, a change to an illumination mode, an application of a compensating phase in the lithographic apparatus, etc.) to make them similar in performance (which may involve making the performance “worse” or “better”). Thus, in an embodiment, there is provided a monitoring of differences in phase between different patterning devices (of, e.g., one or more similar critical patterns, features or structures) and tuning the lithographic process to compensate for the determined difference (e.g., a correction to one or more of the patterning devices, a change to an illumination mode, an application of a compensating phase in the lithographic apparatus, etc.). This approach may be usefully applied to patterning devices that are nominally identical. That is, where a fabricator has multiple “copies” of a particular patterning device, it is possible that variations in production or treatment of the patterning devices will result in different phase performance. One copy may be a replacement for another, for example, or in the case of particularly high volume production, there may be many copies being used in parallel on several different lithographic systems. Thus, it may be useful to make the slightly different patterning devices perform more alike though adjustments to the parameters.
In an embodiment, across the patterning device variation may be tuned (e.g., optimized) using the patterning device topography induced phase (wavefront phase). That is the patterning device topography induced phase (wavefront phase) information of different patterns, or regions, on the patterning device may be compared to recognize differences between the regions and, for example, apply a correction to a parameter of the lithographic process (e.g., a correction to one or more of the regions of the patterning device, a change to an illumination mode, an application of a compensating phase in the lithographic apparatus, etc.) to make them similar in performance (which may involve making the performance “worse” or “better”). Thus, in an embodiment, there is provided a monitoring of a difference in phase across the patterning device for, e.g., one or more similar critical patterns, features or structures and tuning the lithographic process to compensate for the determined difference (e.g., a correction to one or more of the patterning devices, a change to an illumination mode, an application of a compensating phase in the lithographic apparatus, etc.). This compensation may be performed dynamically, during a scanning operation of the lithographic apparatus, for example. Such that different regions of the patterning device undergo different phase compensation as the patterning device is relatively scanned and imaged onto the substrate. By way of example, a pattern that is sparse on one side and dense on the other, or one in which in which the critical dimension varies across the mask pattern, may exhibit a change in phase effects as the scan progresses. This type of variation with scan position could be compensated on the fly by adjusting imaging parameters as described herein.
Thus, one or more of these techniques may provide a significant improvement of the accuracy with which the lithographic apparatus may project a pattern, or a plurality of patterns, onto a substrate.
Some of the techniques herein to correct for wavefront phase, e.g., to address focus difference by changing absorber thickness, may reduce the contrast of the aerial image formed using the patterning device. In some application areas this may not be a significant concern. For example, if the lithographic apparatus is being used to image patterns which will form logic circuits then contrast may be considered to be less important than focus difference. The benefit provided by an improvement of focus difference (e.g. better critical density uniformity) may be considered to outweigh the reduced contrast. An appropriate optimization function with, e.g., weighting of the lithographic merits may be used to arrive at a balance (e.g., optimum). For example, in an embodiment, a phase shift provided by the patterning device, and the contrast improvement that this provides, may be taken into account as well as the patterning device topography induced phase when, for example, correcting for the patterning device topography induced phase. A compromise may be found which provides a necessary degree of contrast while providing a reduced patterning device topography induced phase.
In the above described embodiments, the absorbing material has generally been described as a single material. However, the absorbing material may be more than one material. The materials may, for example, be provided as layers, and may, for example, be provided as a stack of alternating layers. To change the refractive index or extinction coefficient, a different material may be adopted having the desired refractive index/extinction coefficient, a dopant may be added to the absorber material, relative proportions of constitute elements of the absorber material (e.g., proportion of molybdenum and silicide), etc.
Referring back to the inspection apparatus described above with reference to
Another embodiment of a scatterometer SM2 is shown in
A reference beam is often used, for example, to measure the intensity of the incident radiation. To do this, when the radiation beam is incident on the partially reflective surface 1816 part of it is transmitted through the surface as a reference beam towards a reference mirror 1814. The reference beam is then projected onto a different part of the same detector 1818.
One or more interference filters 1813 are available to select a wavelength of interest in the range of, say, 405-790 nm or even lower, such as 200-300 nm. The interference filter(s) may be tunable rather than comprising a set of different filters. A grating could be used instead of or in addition to one or more interference filters.
The detector 1818 may measure the intensity of scattered radiation at a single wavelength (or narrow wavelength range), the intensity separately at multiple wavelengths or the intensity integrated over a wavelength range. Further, the detector may separately measure the intensity of transverse magnetic- (TM) and transverse electric- (TE) polarized radiation and/or the phase difference between the transverse magnetic- and transverse electric-polarized radiation.
Using a broadband radiation source 1802 (i.e. one with a wide range of radiation frequencies or wavelengths—and therefore of colors) is possible, which gives a large etendue, allowing the mixing of multiple wavelengths. The plurality of wavelengths in the broadband desirably each has a bandwidth of a and a spacing of at least 2.32 (i.e., twice the wavelength bandwidth). Several “sources” of radiation may be different portions of an extended radiation source which have been split using, e.g., fiber bundles. In this way, angle resolved scatter spectra may be measured at multiple wavelengths in parallel. A 3-D spectrum (wavelength and two different angles) may be measured, which contains more information than a 2-D spectrum. This allows more information to be measured which increases metrology process robustness. This is described in more detail in U.S. patent application publication no. US 2006-0066855, which document is hereby incorporated in its entirety by reference.
By comparing one or more properties of the beam before and after it has been redirected by the target, one or more properties of the substrate may be determined. This may be done, for example, by comparing the redirected beam with theoretical redirected beams calculated using a model of the substrate and searching for the model that gives the best fit between measured and calculated redirected beams. Typically a parameterized generic model is used and the parameters of the model, for example width, height and sidewall angle of the pattern, are varied until the best match is obtained.
Two main types of scatterometer are used. A spectroscopic scatterometer directs a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. An angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity (or intensity ratio and phase difference in case of an ellipsometric configuration) of the scattered radiation as a function of angle. Alternatively, measurement signals of different wavelengths may be measured separately and combined at an analysis stage. Polarized radiation may be used to generate more than one spectrum from the same substrate.
In order to determine one or more parameters of the substrate, a best match is typically found between the theoretical spectrum produced from a model of the substrate and the measured spectrum produced by the redirected beam as a function of either wavelength (spectroscopic scatterometer) or angle (angularly resolved scatterometer). To find the best match there are various methods, which may be combined. For example, a first method is an iterative search method, where a first set of model parameters is used to calculate a first spectrum, a comparison being made with the measured spectrum. Then a second set of model parameters is selected, a second spectrum is calculated and a comparison of the second spectrum is made with the measured spectrum. These steps are repeated with the goal of finding the set of parameters that gives the best matching spectrum. Typically, the information from the comparison is used to steer the selection of the subsequent set of parameters. This process is known as an iterative search technique. The model with the set of parameters that gives the best match is considered to be the best description of the measured substrate.
A second method is to make a library of spectra, each spectrum corresponding to a specific set of model parameters. Typically the sets of model parameters are chosen to cover all or almost all possible variations of substrate properties. The measured spectrum is compared to the spectra in the library. Similarly to the iterative search method, the model with the set of parameters corresponding to the spectrum that gives the best match is considered to be the best description of the measured substrate. Interpolation techniques may be used to determine more accurately the best set of parameters in this library search technique.
In any method, sufficient data points (wavelengths and/or angles) in the calculated spectrum should be used in order to enable an accurate match, typically between 80 up to 800 data points or more for each spectrum. Using an iterative method, each iteration for each parameter value would involve calculation at 80 or more data points. This is multiplied by the number of iterations needed to obtain the correct profile parameters. Thus many calculations may be required. In practice this leads to a compromise between accuracy and speed of processing. In the library approach, there is a similar compromise between accuracy and the time required to set up the library.
In any of the scatterometers described above, the target on the substrate may be a grating which is printed such that after development, the bars are formed of solid resist lines. The bars may alternatively be etched into the substrate. The target pattern is chosen to be sensitive to a parameter of interest, such as focus, dose, overlay, chromatic aberration in the lithographic projection apparatus, etc., such that variation in the relevant parameter will manifest as variation in the printed target. For example, the target pattern may be sensitive to chromatic aberration in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberration will manifest itself in a variation in the printed target pattern. Accordingly, the scatterometry data of the printed target pattern is used to reconstruct the target pattern. The parameters of the target pattern, such as line width and shape, may be input to the reconstruction process, performed by a processing unit PU, from knowledge of the printing step and/or other scatterometry processes.
While embodiments of a scatterometer have been described herein, other types of metrology apparatus may be used in an embodiment. For example, a dark field metrology apparatus such as described in U.S. Patent Application Publication No. 2013-0308142, which is incorporated herein in its entirety by reference, may be used. Further, those other types of metrology apparatus may use a completely different technique than scatterometry.
The metrology targets as described herein may be, for example, overlay targets designed for use with a metrology tool such as Yieldstar stand-alone or integrated metrology tool, and/or alignment targets such as those typically used with a TwinScan lithographic system, both available from ASML. In practice, the patterning device under inspection may include such targets which will themselves induce certain wavefront phase effects. More broadly, however, the features on the patterning device, when illuminated by the scatterometer, will interact with the scatterometer light in a similar way such that an understanding of the application of the measurements to a metrology target apply equally to measuring other characteristics of the patterning device.
In an embodiment, the radiation beam B is polarized. If the radiation beam is not polarized then the different polarizations which make up the radiation beam may reduce or cancel out the patterning device topography induced focus difference such that a significant patterning device topography induced effect (e.g., focus difference) is not seen. But, desirably a polarized radiation beam may be used and if the radiation beam is polarized then this reduction or cancelling out may not occur, and accordingly an embodiment as described herein may be used to reduce patterning device topography induced effects. Polarized radiation may be used in immersion lithography, and so embodiments described herein may therefore be advantageously used for immersion lithography. The radiation beam of a EUV lithographic apparatus typically has an angle of, for example, around 6 degrees for its chief ray, and as a result different polarization states provide different contributions to the radiation beam. Consequently, the reflected beam is different for the two polarization directions and as such can be considered to be polarized (at least to some extent). Embodiments of the invention may therefore be advantageously used for EUV lithography.
In an embodiment, a patterning device may be provided with a functional pattern (i.e. a pattern which will form part of an operational device). Alternatively or additionally, the patterning device may be provided with a measurement pattern which does not form part of the functional pattern. The measurement pattern may be, for example, located to one side of the functional pattern. The measurement pattern may be used, for example, to measure alignment of the patterning device relative to the substrate table WT (see
Contrast as discussed herein includes, for an aerial image, image log slope (ILS) and/or normalized image log slope (NILS) and, for resist, dose sensitivity and/or exposure latitude.
While at points in the description only the patterning device topography induced phase (wavefront phase) may be discussed, it should be understood that such references may include the use of the patterning device topography induced intensity (wavefront intensity). Similarly, where only the patterning device topography induced intensity (wavefront intensity) may be discussed, it should be understood that such references may include the use of the patterning device topography induced phase (wavefront phase).
The terms “optimize”, “optimizing” and “optimization” as used herein mean adjusting a lithographic process parameter such that results and/or processes of lithography have a more desirable characteristic, such as higher accuracy of projection of a design layout on a substrate, a larger process window, etc.
An embodiment of the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed herein, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. Further, the machine readable instruction may be embodied in two or more computer programs. The two or more computer programs may be stored on one or more different memories and/or data storage media.
This computer program may be included, for example, with or within the imaging apparatus of
Any controllers described herein may each or in combination be operable when the one or more computer programs are read by one or more computer processors located within at least one component of the lithographic apparatus. The controllers may each or in combination have any suitable configuration for receiving, processing, and sending signals. One or more processors are configured to communicate with the at least one of the controllers. For example, each controller may include one or more processors for executing the computer programs that include machine-readable instructions for the methods described above. The controllers may include data storage medium for storing such computer programs, and/or hardware to receive such medium. So the controller(s) may operate according the machine readable instructions of one or more computer programs.
Although specific reference may have been made above to the use of embodiments in the context of lithography using radiation, it will be appreciated that an embodiment of the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to lithography using radiation. In imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
Further, although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
The invention may further be described using the following clauses:
1. A method comprising:
measuring properties of a three-dimensional topography of a lithographic patterning device, the patterning device including a pattern and being constructed and arranged to produce a pattern in a cross section of a projection beam of radiation in a lithographic projection system;
calculating wavefront phase effects resulting from the measured properties;
incorporating the calculated wavefront phase effects into a lithographic model of the lithographic projection system; and
determining, based on the lithographic model incorporating the calculated wavefront phase effects, parameters for use in an imaging operation using the lithographic projection system.
2. The method of clause 1, wherein the lithographic model comprises a lens model.
3. The method of clause 1 or clause 2, wherein the parameters comprise tunable parameters of the lithographic projection system.
4. The method of any of clauses 1 to 3, wherein the parameters comprise manipulator settings for the lithographic projection system.
5. The method of any of clauses 1 to 4 wherein the parameters comprise illuminator settings for the lithographic projection system.
6. The method of any of clauses 1 to 5, wherein the measured properties are selected from the group consisting of: height, sidewall angle, refractive index, extinction coefficient, an absorber stack parameter, and combinations thereof.
7. The method of clause 6 wherein the absorber stack parameter comprises a composition of the absorber stack, a sequence of layers of the absorber stack, and/or a thickness of the absorber stack.
8. The method of any of clauses 1 to 7, wherein the calculated wavefront phase effects are characterized in terms of Zernike information.
9. The method of any of clauses 1 to 7, wherein the calculated wavefront phase and information is characterized by one of a Bessel function, a jones Matrix and a Muller matrix.
10. The method of any of clauses 1 to 9, wherein the determined parameters comprise parameters selected to reduce a total range of wavefront phases for the patterning device.
11. A method comprising:
measuring properties of a three-dimensional topography for a plurality of lithographic patterning devices, each patterning device including a pattern and being constructed and arranged to produce a pattern in a cross section of a projection beam of radiation in a lithographic projection system;
calculating, for each patterning device, wavefront phase effects resulting from the measured properties; and
determining differences between calculated wavefront phase effects for the plurality of patterning devices, and adjusting imaging parameters for the lithographic projection system to account for the determined differences.
12. A method as in clause 11, wherein the plurality of patterning devices are nominally identical but have some variation in three-dimensional topography.
13. A method as in clause 12, wherein a first one of the plurality of patterning devices comprises a replacement for a second one of the plurality of patterning devices.
14. A method as in any of clauses 11 to 13, wherein differences in the three-dimensional topography among the lithographic patterning devices are the result of wear or cleaning.
15. A method as in any of clauses 11 to 14, wherein the adjusting comprises selecting imaging parameters for the lithographic projection system selected to reduce differences in imaging among the plurality of patterning devices.
16. A method comprising:
measuring properties of a three-dimensional topography of a lithographic patterning device, the patterning device including a pattern and being constructed and arranged to produce a pattern in a cross section of a projection beam of radiation in a lithographic projection system;
calculating wavefront phase effects resulting from the measured properties;
comparing calculated wavefront phase effects across different regions of the lithographic patterning device; and
applying a correction to a parameter of the lithographic process to account for the compared calculated wavefront phase effects across the different regions.
17. A method as in clause 16, wherein the pattern comprises a plurality of patterns.
18. A method as in clause 12, wherein the applying a correction to the parameter of the lithographic process is performed dynamically during a scanning operation of the lithographic process.
19. A method as in any of clauses 16 to 18, wherein the comparing is performed for sets of structures having one or more similar critical patterns, features or structures.
20. A method as in clause 19, wherein the similar critical patterns, features or structures are similar in two dimensions and comprise features selected from the group consisting of critical dimension, pitch, structure shape, and combinations thereof.
21. The method of any of clauses 1 to 20, wherein calculating the wavefront phase information is based on a diffraction pattern associated with an illumination profile of a lithography apparatus.
22. The method of any of clauses 1 to 21, wherein calculating the wavefront phase information comprises rigorously calculating the optical wavefront phase information.
23. The method of any of clauses 1 to 22, wherein the wavefront phase information comprises wavefront phase information for a plurality of critical dimensions of the pattern.
24. The method of any of clauses 1 to 23, wherein the wavefront phase information comprises wavefront phase information for a plurality of incident angles of illumination radiation and/or sidewall angles of the pattern.
25. The method of any of clauses 1 to 24, wherein the wavefront phase information comprises wavefront phase information for a plurality of pitches of the pattern.
26. The method of any of clauses 1 to 25, wherein the wavefront phase information comprises wavefront phase information for a plurality of pupil positions or diffraction orders.
27. The method of any of clauses 1 to 26, wherein computing the imaging effect of the topography of the patterning device comprises computing a simulated image of the patterning device pattern.
28. The method of any of clauses 1 to 27, further comprising adjusting a parameter associated with a lithographic process using the lithographic patterning device to obtain an improvement in the contrast of imaging of the pattern.
29. The method of clause 28, wherein the parameter is a parameter of the topography of the pattern of the patterning device or a parameter of illumination of the patterning device.
30. The method of any of clauses 1 to 29, comprising tuning a refractive index of the patterning device, an extinction coefficient of the patterning device, a sidewall angle of an absorber of the patterning device, a height or thickness of an absorber of the patterning device, or any combination selected therefrom, to minimize a phase variation.
31. The method of any of clauses 1 to 30, wherein the calculated wavefront phase information comprises an odd phase distribution across the diffraction orders, or a mathematical description thereof.
32. The method of any of clauses 1 to 30, further comprising calculating from the measurements wavefront intensity information caused by the three-dimensional topography of the pattern.
33. A non-transitory computer program product comprising machine-readable instructions configured to cause a processor to cause performance of the method of any of clauses 1 to 32.
34. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including determining the parameters using the method of any of clauses 1 to 32 and exposing the device pattern onto the substrates.
The patterning device described herein may be referred to as a lithographic patterning device. Thus, the term “lithographic patterning device” may be interpreted as meaning a patterning device which is suitable for use in a lithographic apparatus.
The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.
The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
The embodiment(s) described, and references in the specification to an “embodiment”, “example,” etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. For example, one or more aspects of one or more embodiments may be combined with or substituted for one or more aspects of one or more other embodiments as appropriate. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description by example, and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. The breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
This application claims priority of U.S. application 62/093,370 which was filed on Dec. 17, 2014 and which is incorporated herein in its entirety by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/077769 | 11/26/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62093370 | Dec 2014 | US |
