Patent Application
20120262690
The present invention generally relates to a lithographic apparatus. The invention has particular application to an illumination system, which may form part of a lithographic apparatus and has particular, although not exclusive, application to an illumination system for adjusting the profile of a beam of extreme ultra violet (EUV) radiation in a lithographic apparatus.
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. comprising 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. A lithographic apparatus often includes an illumination system, which receives radiation from a source and produces an illumination beam for illuminating a patterning device. Such an illumination system typically includes an intensity distribution adjustment arrangement which directs, shapes and controls the intensity distribution of the beam. Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured. A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1):
where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of k1.
In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Possible EUV radiation sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.
EUV radiation may be produced using a plasma. A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector module for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as particles of a suitable material (e.g. tin), or a stream of a suitable gas or vapour, such as Xe gas or Li vapour. The resulting plasma emits radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing structure or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is typically termed a laser produced plasma (LPP) source.
It is well known in the art of lithography that an image of the patterning device projected onto a substrate can be improved by appropriately choosing angles at which the patterning device is illuminated, i.e., by appropriately choosing an angular distribution of radiation illuminating the patterning device. In a lithographic apparatus having a Koehler illumination system, the angular distribution of radiation illuminating the patterning device is determined by a spatial intensity distribution of the illumination beam in a pupil plane of the illumination system. This is because the illumination beam at the pupil plane effectively acts as a secondary or virtual radiation source for producing the illumination beam that is incident on the patterning device. The shape of the spatial intensity distribution of the illumination beam at the pupil plane within the illumination system is commonly referred to as the illumination mode or profile.
Illumination beams with certain spatial intensity distributions at the pupil plane improve a processing latitude when an image of the patterning device is projected onto a substrate. In particular, an illumination beam having a spatial intensity distribution with a dipole, annular or quadrupole off-axis illumination mode may enhance the resolution and/or another characteristic of the projection process, such as a sensitivity to a projection system optical aberration, the exposure latitude and the depth of focus. Certain “soft-pole” illumination modes may also have an advantageous effect on the image of the patterning device projected onto a substrate. Accordingly, an illumination system typically includes one or more devices or structures to direct, shape and control the illumination beam such that it has a desired spatial intensity distribution (a desired illumination mode) at the pupil plane.
Particularly where EUV radiation is used, it is known to provide an illumination system including a field-facet mirror-device having a plurality of primary reflective facets. Hereinafter, these primary reflective elements may also be referred to as field facets. Each field facet receives, in use, an incident beam portion, i.e., a portion of the beam of EUV radiation emanating from the source collector module and incident on the field-facet mirror-device. The orientation of each field facet is controllable over a range of angles relative to the corresponding incident beam portion. Each field facet is effective to direct radiation from its incident beam portion onto a pupil-facet mirror-device having a plurality of secondary reflective facets. These secondary reflective elements may also be referred to as pupil facets. Each pupil facet will act, when irradiated, as a secondary light source for the patterning device such that the beam of EUV radiation incident on the patterning device may have a desired illumination mode.
An example of such an arrangement is shown in the U.S. Pat. No. 6,658,084 from which further information may be gleaned. This particular patent discloses an illumination system, including a field-facet mirror-device in which each field facet can be set at two possible orientations, the first and second orientations being such that either a corresponding first or a corresponding second pupil facet is irradiated. In such a system, there are twice as many pupil facets as there are field facets, and the corresponding first pupil facets define a first illumination mode while the corresponding second pupil facets define a second illumination mode. The radiation reflected from the first or second pupil facet forms part of the respective first or second illumination mode.
Such an arrangement may have the disadvantage that it is not possible to just modify the first illumination mode by having a field facet not irradiate its associated first pupil facet without having that field facet irradiate its associated second pupil facet. Similarly, one may not modify the second illumination mode by having the field facet not irradiate the second pupil facet without having it irradiate the first pupil facet.
It is an aspect of the present invention to alleviate above-mentioned potential disadvantages by enabling illumination mode adjustments per pupil facet.
According to an aspect of the invention, there is provided an illumination system for use in a lithographic apparatus arranged to project a pattern of a patterning device on a substrate using a projection system. The illumination system includes a field-facet mirror-device, and a pupil-facet mirror-device. The field-facet mirror-device includes a plurality of reflective field facets, each field facet being switchable between a first orientation in which an incident extreme ultra violet radiation beam portion traversing the field facet is directed to the pupil-facet mirror-device and from there to the patterning device, and a supplementary orientation in which the beam portion is directed onto an area of the pupil-facet mirror-device disposed within a radial extent corresponding to the numerical aperture of the projection system of the lithographic apparatus, and arranged as a beam dump area effective to collect incident radiation and to avoid that radiation from reaching the patterning device.
According to an aspect of the invention, there is provided a lithographic apparatus that includes an illumination system that includes a field-facet mirror-device and a pupil-facet mirror-device. The lithographic apparatus also includes a support configured to support a patterning device. The patterning device is configured to receive radiation from the illumination system and pattern the radiation. The lithographic apparatus also includes a projection system configured to project the patterned radiation on a substrate. The field-facet mirror-device includes a plurality of reflective field facets, each field facet being switchable between a first orientation in which an incident extreme ultra violet radiation beam portion traversing the field facet is directed to the pupil-facet mirror-device and from there to the patterning device, and a supplementary orientation in which said beam portion is directed onto an area of the pupil-facet mirror-device disposed within a radial extent corresponding to the numerical aperture of the projection system, and arranged as a beam dump area effective to collect incident radiation and to avoid that radiation from reaching the patterning device.
According to an aspect of the invention, there is provided a method for modifying an illumination mode provided by an illumination system of a lithographic apparatus. The illumination system includes a field-facet mirror-device and a pupil-facet mirror-device. The field-facet mirror-device includes a plurality of reflective field facets. The method includes directing a beam of radiation to the field-facet mirror-device, and switching a field facet from a first orientation in which an incident extreme ultra violet radiation beam portion traversing the field facet is directed to the pupil-facet mirror-device and from there to a patterning device of the lithographic apparatus, to contribute to generating the illumination mode, to a supplementary orientation in which said beam portion is directed onto an area of the pupil-facet mirror-device disposed within a radial extent corresponding to the numerical aperture of a projection system of the lithographic apparatus, and arranged as a beam dump area effective to collect incident radiation and to avoid that radiation from reaching the patterning device.
According to an aspect of the invention, there is provided a device manufacturing method that includes modifying an illumination mode provided by an illumination system of a lithographic apparatus. The illumination system includes a field-facet mirror-device and a pupil-facet mirror-device. The field-facet mirror-device includes a plurality of reflective field facets. The modifying includes directing a beam of radiation to the field-facet mirror-device; and switching a field facet from a first orientation in which an incident extreme ultra violet radiation beam portion traversing the field facet is directed to the pupil-facet mirror-device and from there to a patterning device of the lithographic apparatus, to contribute to generating the illumination mode, to a supplementary orientation in which said beam portion is directed onto an area of the pupil-facet mirror-device disposed within a radial extent corresponding to the numerical aperture of a projection system of the lithographic apparatus, and arranged as a beam dump area effective to collect incident radiation and to avoid that radiation from reaching the patterning device. The device manufacturing method also includes patterning radiation received from the illumination system with the patterning device, and projecting the patterned radiation onto a substrate with the projection system.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
The illumination system may include reflective, diffractive or refractive components, for directing, shaping, or controlling radiation.
The support structure MT holds the patterning device MA 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 support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.
The term “patterning device” 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. The pattern imparted to the radiation beam may 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 projection system, like 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, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since other gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.
As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). 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.
Referring to
In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is passed from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.
The illuminator IL may be used to condition the radiation beam incident on the patterning device to have a both a desired intensity uniformity and a desired angular intensity distribution in its cross-section. The illuminator IL may include a field-facet mirror-device having a plurality of reflective field facets and a pupil-facet mirror-device having a plurality of reflective pupil facets. Each of the field facets receives, in use, an incident beam portion being a portion of a beam of incident EUV radiation emanating from the source collector module SO. An illumination-mode selection-system may be constructed and arranged to set a desired illumination mode. For example, each of the field facets may be oriented to reflect EUV radiation to corresponding, different pupil facets belonging to a first group of the reflective pupil facets defining a first illumination mode, or alternatively may be oriented to reflect EUV radiation to corresponding, different pupil facets belonging to a second group of the reflective pupil facets defining a second illumination mode. The selection of an illumination mode is obtained by adjusting an angular intensity distribution of the radiation beam incident on the patterning device MA through adjusting a corresponding spatial intensity distribution of radiation as reflected by the pupil facets and directed towards the patterning device.
The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After being reflected from 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 PS2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT 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 PS1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. Patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.
The depicted apparatus could be used in at least one of the following modes:
1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT 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 WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.
2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT 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 WT relative to the support structure (e.g. mask table) MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS.
3. In another mode, the support structure (e.g. mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT 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 WT 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.
The radiation emitted by the hot plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap) which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 may include a channel structure. Contamination trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure, as known in the art.
The collector chamber 212 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening 219 in the enclosing structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.
Subsequently, the radiation traverses the illumination system IL, which includes a field-facet mirror-device 22 and a pupil-facet mirror-device 24 arranged to provide a desired angular intensity distribution of the radiation beam 21 at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. As explained above a selection of an illumination mode is obtained by optically connecting the field facets (through appropriately orientating the field facets) to a group of corresponding, different pupil facets. The irradiated pupil facets serve as a secondary light source having the desired spatial intensity distribution defining the illumination mode. For example, the group of corresponding, different pupil facets may be chosen to define one or more off axis, bright poles for providing a polar, off axis illumination mode. Alternatively, the group may be chosen to define an annular illumination mode or a conventional illumination mode. For example, an outer radial extent of the intensity distribution in a pupil plane of the illuminator, at or near the pupil facets, can be selected. The outer radial extent is denoted by σ-outer, where σ-outer is defined as the selected outer radial extent divided by an outer radial extent which matches the numerical aperture NA of the projection system. Similarly, an inner radial extent of the intensity distribution, denoted by σ-inner, can be selected. Upon reflection of the beam of radiation 21 at the patterning device MA, held by the support structure MT, a patterned beam 26 is formed and the patterned beam 26 is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by the wafer stage or substrate table WT.
More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 may optionally be present, depending upon the type of lithographic apparatus. Further, there may be more mirrors present than those shown in the Figures. For example, the projection system PS may actually include 6 or 8 reflective elements.
Collector optic CO, as illustrated in
Alternatively, the source collector module SO may be part of an LPP radiation system as shown in
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.
Referring now to
It will be appreciated that as each field facet of the field-facet mirror-device is able to direct incident radiation onto two pupil facets of the pupil-facet mirror-device, the pupil-facet mirror-device will have twice the number of facets compared to the number of field facets. Furthermore, while in
It will be appreciated that in the illumination system described in relation to
According to an embodiment of the present invention, there is provided an illuminator system for use in a lithographic apparatus, including a field-facet mirror-device including a plurality of reflective field facets, each field facet being switchable between an orientation in which an incident radiation beam portion traversing a field facet is directed to a pupil-facet mirror-device effective to direct radiation from the field-facet mirror-device onto a patterning device and an orientation in which said beam portion is directed onto an area of the pupil-facet mirror-device disposed within a radial extent corresponding to the numerical aperture of a projection system of the lithographic apparatus and arranged as a beam dump area effective to collect incident radiation and to avoid it from reaching the patterning device. The latter radiation is therefore not part of any illumination mode.
In
It should be appreciated that other configurations of beam dump areas PBD using the pupil-facet mirror-device can be provided.
Turning now to
It will be appreciated that while it may be advantageous to have the beam dump region between radial extents R and Ri as shown in the arrangements of
It will be appreciated that while the invention has particular application in a lithographic apparatus employing EUV radiation, the invention has also application in a lithographic apparatus having radiation within other wavelength bands.
It will also be appreciated that while in the particular embodiments described before, the facets of the field-facet mirror-device are three state devices, having three possible orientations, the invention is also applicable to field facet mirrors having two states, one of which corresponds to a facet orientation in which the incident radiation is directed into the beam incident on the patterning device MA, and one state corresponding to an orientation in which the beam is directed to a pupil facet like area arranged as a beam dump area on the pupil-facet mirror-device. Similarly the invention is applicable to field facet mirrors positionable at four, five or even more tilts with respect to an incident beam portion.
Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. 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.
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.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. 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.
This application claims the benefit of U.S. provisional application 61/290,533 which was filed on 29 Dec. 2009, and which is incorporated herein in its entirety by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/068395 | 11/29/2010 | WO | 00 | 6/21/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61290533 | Dec 2009 | US |
