Patent Application
20110157573
The present invention relates to spectral purity filters, lithographic apparatus including such spectral purity filters, a device manufacturing method and a device manufactured thereby.
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 steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and 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.
In addition to Extreme Ultra-Violet (EUV) radiation, an EUV source emits many different wavelengths of light and debris. This non-EUV radiation may be harmful for the EUV lithography system, so it is desirable to remove it with a spectral purity filter. Present spectral purity filters are based on blazed gratings. These gratings may be difficult to produce, since the surface quality of the triangular shaped pattern should be very high. The roughness of the surface should be lower than 1 nm RMS. Moreover, use of (e.g. Zr) thin filters transmissive for EUV may be difficult due to the fragility of the filters and low heat-load threshold. In addition, glue that is used for filters on mesh is not desirable for high-vacuum systems.
A further challenge with existing reflective spectral purity filters is that they change the direction of the light from the EUV source. Therefore, if a spectral purity filter is removed from an EUV lithography apparatus, a replacement spectral purity filter should be added or a mirror at a proper angle should be introduced to compensate. The added mirror may introduce unwanted losses into the system.
U.S. Patent Application Publication 2006/0146413, incorporated herein by reference, discloses a spectral purity filter (SPF) comprising an array of apertures with diameters up to 20 μm. Depending on the size of the apertures compared to the radiation wavelength, the SPF may suppress unwanted radiation by different mechanisms. If the aperture size is smaller than approximately half of the wavelength, the SPF reflects virtually all radiation of this wavelength. If the aperture size is larger, but still of the order of the wavelength, the radiation is at least partially diffracted and may be absorbed in a waveguide inside the aperture.
It is an aspect of the present invention to provide an EUV spectral purity filter which improves the spectral purity of a radiation beam.
According to an embodiment of the present invention, a lithographic spectral purity filter includes an aperture, wherein the spectral purity filter is configured to enhance the spectral purity of a radiation beam by being configured to absorb radiation of a first wavelength and to allow at least a portion of radiation of a second wavelength to transmit through the aperture, the first wavelength being larger than the second wavelength. Desirably, the spectral purity filter is configured to absorb a substantial portion, e.g. 80% or more, of radiation of the first wavelength. Desirably, the spectral purity filter comprises a radiation-facing front surface, the front surface being configured to absorb the radiation of the first wavelength. The second wavelength may be a wavelength of about 5-20 nm. More specifically, the spectral purity filter may be configured to filter EUV radiation with a wavelength of about 13.5 nm.
Embodiments of the present invention relate to two main types of spectral purity filters. In the first type of spectral purity filters, the aperture (e.g. pinhole/slit) may absorb radiation having wavelengths that should be suppressed, while transmitting radiation with sufficiently low wavelengths such as EUV. The diameter of the aperture may be below the diffraction limit for the wavelength range that should be suppressed, while being sufficiently above the diffraction limit of radiation, such as EUV, that should be transmitted. In this case, suppression is controlled by the diameter of the aperture. In the second type of spectral purity filters, waveguiding is used for suppressing unwanted ranges of wavelengths. In this case, the diameter or width of the aperture may be above the diffraction limit and the suppression may be controlled by both the diameter and the depth of the aperture.
The diameter or width of the apertures may be equal to or smaller than about 20 μm. For instance, the diameter or width of the apertures may be within range of about 1-2 μm.
The spectral purity filter may comprise an absorptive material configured to absorb radiation of at least the first wavelength. The absorptive material may be doped Si, such as n-type silicon, more specifically P-doped silicon and/or As-doped silicon. However, any semiconductor material may be suitable, for instance Si, Ge, diamond, or diamond-like carbon.
The spectral purity filter may be configured to absorb light with wavelengths larger than about twice the diameter of the aperture, allowing at least a portion of smaller wavelength radiation to be transmitted through the at least one aperture.
Embodiments of the present invention may therefore use a sub-wavelength aperture as a spectral purity filter. The spectral purity filter absorbs light with wavelengths larger than twice the diameter of the aperture.
In an embodiment, there may be only a single aperture.
In an embodiment, there may be at least two or more apertures or a plurality of apertures forming a patterned array. The apertures may form a regular pattern with a high degree of symmetry or an irregular pattern on the spectral purity filter. The apertures may extend from one side of the spectral purity filter to another side.
The shape of the apertures may be adapted for different wavelengths of light. For example, the apertures may be in the form of elongated slits or may be substantially circular (e.g. pinholes). Typically, there may be a plurality of slits or a plurality of substantially circular apertures (e.g. pinholes).
In embodiments where there may be only a single aperture, the aperture may have a diameter of about 0.1-10 μm, for example about 1-2 μm. Furthermore, the spectral purity filter may have a thickness of about 1-20 μm, for example about 10 μm. In these embodiments there is substantially no waveguiding.
In embodiments where there may be a plurality of apertures, the diameter of the apertures may range from about 10-500 nm, about 50-200 nm, or about 100 nm. In these embodiments, the spectral purity filter may have a thickness of about 1-50 μm, for example about 10 μm. The diameter of the apertures ranging from about 1 μm to about 5 μm is suitable for suppression of infrared radiation.
In embodiments where there may be a plurality of apertures, the transparency of the spectral purity filter to different wavelengths may be determined by an aspect ratio between an area formed by the apertures (e.g. the part of the spectral purity filter with holes) and the remaining surface area of the spectral purity filter. The surface area preferably includes about 80% apertures. However, the surface area may include between about 50% and about 95% apertures.
The spectral purity filter may be configured to transmit at least 50%, for example at least about 90%, EUV radiation. The radiation of the first wavelength may at least be one of the group consisting of DUV, UV, visible, and IR radiation. Thus, spectral purity filter may act as an effective filter for DUV, UV, IR and/or visible radiation. The amount of DUV, UV, IR and/or visible radiation transmitting therethrough may be less than about 5%, less than about 1%, or less than about 0.5%.
The spectral purity filter may be an inline optical element and therefore not change the direction of light from an EUV source. The spectral purity filter may therefore be removed from a lithographic apparatus without the need of replacing it by, for example, a mirror.
The at least one aperture in the spectral purity filter may be formed using micro-machining techniques.
According to an embodiment, a spectral purity filter is combined with a waveguide, for example a EUV waveguide. Such a spectral purity filter comprising an EUV waveguide may have a high transmission for EUV, for instance transmission of about 90% for EUV. The transmission for larger wavelengths may be lower. Once again, this spectral purity filter may be an inline optical element allowing the spectral purity filter to be removed from the lithographic apparatus without the need for replacement by, for example, a mirror. The aperture may have a diameter of about 0.1 to 20 μm, for example about 1 μm followed by the waveguide.
The waveguides may be made of a material configured to absorb radiation in a wavelength range to be suppressed. The waveguide may be used to suppress light with wavelengths larger than EUV. The waveguide may be made from Si3N4 which has a high absorption for DUV: −400 dB/cm for a wavelength of 150 nm.
The waveguide may have a length of about 50-500 μm, 100-200 μm, specifically about 100 μm or about 150 μm. There may be one aperture or a plurality of apertures forming a patterned array as previously described. The apertures may be any suitable shape.
The performance of the spectral purity filter with the waveguide may be improved by varying and adapting the diameter of the aperture and the length of the waveguide. A cavity within the waveguide structure may have the same shape as the opening aperture or may be adapted to have a different shape and size depending on the wavelength of radiation which is being filtered out.
To improve the mechanical strength of the spectral purity filters, and without compromising the EUV transmission, at least one patterned layer and at least one unpatterned layer may be used in combination. The unpatterned layer may be in the form of a continuous sheet with no apertures therethrough. The patterned layer may include a plurality of apertures. The plurality of apertures may be in the form of a regular or irregular pattern. The diameter or width of the apertures may be about 0.1-10 μm, for example about 1 μm in diameter. The thickness of the unpatterned layer may be about 10-500 nm, for example about 50 nm. The thickness of the patterned may be about 10-500 μm, for example about 100 μm.
The patterned layer may act as a support for the unpatterned layer and the unpatterned may act as a substrate/support for the patterned layer. The patterned layer and unpatterned layer may be formed from a single piece of material. Alternatively, the patterned and unpatterned layer may be formed separately and thereafter adhered to one another.
There may be only a small reduction in the EUV transmission due to the combination of patterned and unpatterned layers. The combination of the patterned and unpatterned layers may have higher IR-suppression than an unpatterned layer. As both the unpatterned layer and patterned layer act as a spectral purity filter, this results in improved optical performance of the filter.
The spectral purity filters may be used in combination with any other type of mirror or with at least one grazing incidence mirror, for instance in a lithographic apparatus.
The spectral purity filter may be located at any position between a collector in the lithographic apparatus and a focal point in the radiation beam after the collector. Alternatively, the spectral purity filter may be located at any suitable position in the illumination system or the projection system.
According to an embodiment of the invention there is provided a lithographic apparatus including an illumination system configured to condition a radiation beam; a support configured to support a patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table configured to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a spectral purity filter comprising an aperture, wherein the spectral purity filter is configured to enhance the spectral purity of the radiation beam by being configured to absorb radiation of a first wavelength and to allow at least a portion of radiation of a second wavelength to transmit through the aperture, the first wavelength being larger than the second wavelength.
The spectral purity filter may be configured to absorb light with wavelengths larger than about twice the diameter of the aperture, allowing at least a portion of smaller wavelength radiation to be transmitted through the aperture.
The spectral purity filter may be situated behind a collector in the lithographic apparatus.
At least one grazing incidence filter may also be present in the lithographic apparatus.
According to an embodiment of the present invention, a lithographic apparatus includes a spectral purity filter comprising an aperture, the aperture having a diameter, wherein the spectral purity filter is configured to enhance the spectral purity of the radiation beam by absorbing radiation of a first wavelength and allowing at least a portion of radiation of a second wavelength to transmit through the aperture, the first wavelength being larger than the second wavelength.
The spectral purity filter may be configured to absorb light with wavelengths larger than about twice the diameter of the aperture, allowing at least a portion of smaller wavelength radiation to be transmitted through the aperture.
According to an embodiment of the present invention, a device manufacturing method includes providing a radiation beam; patterning the radiation beam; projecting a patterned beam of radiation onto a target portion of a substrate; and enhancing the spectral purity of the radiation beam by absorbing radiation of a first wavelength and allowing at least a portion of radiation of a second wavelength to transmit through an aperture, the first wavelength being larger than the second wavelength.
The spectral purity filter may be configured to absorb light with wavelengths larger than about twice the diameter of the aperture, allowing at least a portion of smaller wavelength radiation to be transmitted through the aperture.
According to an embodiment of the present invention, there is provided a device manufactured according to a method that includes providing a radiation beam; patterning the radiation beam; projecting a patterned beam of radiation onto a substrate; and filtering the radiation beam with a spectral purity filter configured to enhance the spectral purity of the radiation beam by absorbing radiation of first wavelengths and allowing at least a portion of radiation of second wavelengths to transmit through the at least one aperture, the radiation of the first wavelengths having a larger wavelength than the radiation of the second wavelengths.
According to an embodiment of the present invention, a device is manufactured according to a method including providing a radiation beam; patterning the radiation beam; projecting a patterned beam of radiation onto a target portion of a substrate; and enhancing the spectral purity of the radiation beam by absorbing radiation of a first wavelength and allowing at least a portion of radiation of a second wavelength to transmit through an aperture, the first wavelength being larger than the second wavelength.
The spectral purity filter may be configured to absorb light with wavelengths larger than about twice the diameter of the aperture, allowing at least a portion of smaller wavelength radiation to be transmitted through the aperture.
According to an embodiment of the present invention, a device is manufactured according to a method comprising patterning a radiation beam, projecting a patterned beam of radiation onto a substrate, and filtering the radiation beam with a spectral purity filter configured to enhance the spectral purity of the radiation beam by absorbing radiation of first wavelengths and allowing at least a portion of radiation of second wavelengths to transmit through the at least one aperture, the radiation of the first wavelengths having a larger wavelength than the radiation of the second wavelengths. The device may be selected from a group consisting of an integrated circuit, an integrated optical system, a guidance and detection pattern for a magnetic domain memory, a liquid crystal display, and a thin-film magnetic head.
The manufactured device may be an integrated circuit, an integrated optical system, a guidance and detection pattern for a magnetic domain memory, a liquid crystal display, or a thin-film magnetic head.
Embodiments of the present 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 various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape, or control radiation.
The support supports, e.g. bears the weight of, the patterning device. It 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, for example whether or not the patterning device is held in a vacuum environment. The support can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support may be a frame or a table, for example, which may be fixed or movable as required. The support 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 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.
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, for example, between the projection system and the substrate during exposure.
Referring to
The illuminator IL may include an adjusting device AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-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 support (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which projects the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and a position sensor IF (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 positioning device PM and another position sensor (which is not explicitly depicted in
The depicted apparatus could be used in at least one of the following modes:
1. In step mode, the 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. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
2. In scan mode, the 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 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.
3. In another mode, the 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.
One of the reflective elements 19 has in front of it an NA disc 20 having an aperture 21 therethrough. The size of the aperture 21 determines the angle αi subtended by the patterned radiation beam 17 as it strikes the substrate table WT.
The aperture 102 absorbs substantially all radiation with wavelengths for which the aperture diameter is below the diffraction limit, the diffraction limit being half the wavelength in the medium that fills the aperture 102. The medium may be a vacuum. For aperture diameters above the diffraction limit, a substantial fraction of the radiation is transmitted through the aperture. In order for the spectral purity filter to have advantageous absorptive properties, the spectral purity filter may comprise an n-type doped silicon, such as P-doped Si or As-doped Si. Generally, an advantage of using doped silicon is that such materials may be patterned more easily than for example metals.
As an example, for a slit with a 100 nm diameter, substantially all light with wavelengths larger than 200 nm and a polarization direction along the length of the slit is absorbed.
For EUV (having a wavelength of 13.5 nm) a diameter d of about 100 nm is still about 7 wavelengths. Using a numerical analysis, the transmission for EUV of a slit made of 10 μm thick material is estimated to be about 90%. This transmission value refers to the fraction of the radiation that enters the “open” area of the aperture. Depending on the ratio between the aperture and the surrounding material, the transmission should be corrected. As an example, for a slit with an open to closed ratio of 1:1, the transmission is 50%×90%=45%.
A suppression of light is therefore obtained by using an aperture size such as a sub-wavelength diameter slit which blocks substantially all the light with a wavelength larger than twice the diameter without the need of a waveguide structure for additional suppression.
Although
In certain circumstances, it may be advisable to vary the spacing between the slits in order to avoid unwanted diffraction effects due to the periodicity of constant spacing between the slits.
Using a single slit with a diameter of about 1-2 μm, visible-infrared wavelengths may be suppressed by a few orders of magnitude while still having an EUV transmission of −3 dB (50%). In addition, UV wavelengths can be suppressed as well, but require a smaller slit diameter resulting in higher propagation losses for EUV. For a 1 μm wide slit, a UV suppression better than −10 dB is attainable for −3 dB EUV transmission. If more losses can be tolerated, then UV suppression better than −40 dB is attainable.
The length and depth of the slit is a parameter to consider because the slit acts as a diffracting element increasing the (grazing) angle of incidence and by consequence reducing the reflection at vacuum-material interfaces. The height of the slit H controls the number of reflections for a given grazing angle of incidence and as a consequence the length of the slit L can control the suppression. The length of the slit L depends on the desired suppression and on the diameter of the slit.
For a filter that suppresses DUV by absorbtion, the diameter/width of the pinhole/slit is below the diffraction limit of DUV light and typically 100 nm. For a filter that suppresses DUV by waveguiding (waveguide has strong attenuation for DUV light), the diameter of the pinhole/slit is above the diffraction limit and the suppression can also be controlled by the depth L of the slit. Typically, the diameter is 1-2 μm and depth of the slit is in order of 100 μm.
However, the array of slits as shown in
In contrast to the array of elongate slits in the spectral purity filter 200 of
The slits and pinholes in the spectral purity filters as shown in
A further parameter to be considered is the aspect ratio between transparent and non-transparent regions shown in
Using an array of slits (as shown in
Using a spectral purity filter including a large number pinholes may be more desirable because:
An alternative to the spectral purity filters shown in
The spectral purity filter 400 shown in
For proper operation of the spectral purity filter 400, the material of the waveguides should be absorbing for the wavelengths that one wants to suppress with the spectral purity filter. There are no specific requirements for the EUV transmission of the material.
As an example, for a filter that is used to suppress DUV wavelengths, Si3N4 is a good candidate, because it has a high absorption for DUV: −400 dB/cm for a wavelength of 150 nm.
For a single slit pinhole, thickness can in principle be infinite. For an array of slits/pinholes, the thickness should preferably be larger than decay length of light in the absorbing cladding material in order to avoid optical coupling between the light in adjacent pinholes/slits, which is for a sufficiently absorbing material in the order of a few 100 nm.
The pattern of the spectral purity filter 200, 300 shown in
In an embodiment, the diameter of the aperture is around 1 μm. As an example, consider a transmission for a 1 μm wide slit having a length and an input beam with a realistic angular spread of ±7°. After 150 μm propagation along the waveguide, the EUV transmission is 50% while the UV suppression relative to EUV is better than −10 dB. Visible infrared wavelengths will be suppressed even more due to their wavelength.
Taking into account that in practice the image in the intermediate focus of a lithographic apparatus has a diameter in the order of 10 mm, it follows that an array, for example an a-periodic ray, of apertures should be used in order to reduce the propagation losses for EUV.
The overall transparency of a spectral purity filter consisting of an array of slits and/or pinholes is determined by the ratio between the transparent and non-transparent area of the filter. As an example, consider a 1 μm wide slit with a length of 150 μm having an EUV transmission of −3 dB (50%) per slit. In this case, 80% of the spectral purity filter area is transparent, resulting in an overall transmission of 40%.
An analysis of heat load on the spectral purity filter shown in
Concerning the heat load, it can be concluded that a spectral purity filter at elevated temperatures behind a collector is a desirable configuration.
In a further embodiment, there is provided spectral purity filters with improved mechanical strength. When improving the mechanical strength of the spectral purity filters, it is desirable not to compromise the EUV transmission.
It has been found that a thin Si3N4 slab, with no apertures, can be used as a spectral purity filter. However, a thin thickness of a layer stack, for example about 100 nm, may be used to achieve acceptable EUV transmission, which may make the structure fragile for bending in the vertical (i.e. parallel to the optical axis) direction and eventually may lead to cracking of the layer. However, the embodiments shown in
A combination of patterned layers 502 and unpatterned layers 504 as shown in
It should be noted that by using a patterned layer 502 and an unpatterned layer 504, the apertures 506 can be used to suppress longer wavelengths, such as infrared, while the unpatterned layer can be used to suppress UV wavelengths.
In this embodiment, the patterned layer 502 acts as a substrate/support for the unpatterned layer 504. Moreover, the spectral purity filter acts as a cascade of an unpatterned filter and a patterned filter. Therefore, the suppression will be better than the suppression of an unpatterned filter with, for a sufficiently sparsely patterned layer, only a small reduction in the EUV transmission. The suppression by a patterned filter is a geometric effect and improves with increasing wavelength. Therefore, the combination of a patterned and unpatterned layer/stack has the potential of a higher IR-suppression than an unpatterned layer/stack. To suppress infrared wavelengths, the apertures 506 can have a diameter of about 1 μm. The thickness of the unpatterned layer 504 may be about 50-100 nm and the thickness of the patterned layer may vary between about 1-100 μm, depending on whether or not a waveguide-effect is used.
Using an unpatterned layer and a patterned layer may therefore improve the mechanical strength compared with spectral purity filters which are only unpatterned (e.g. a thin slab) or patterned (e.g. spectral purity filters as shown in
Due to the improved strength of the spectral purity filter shown in
As previously described, the filter can be manufactured by known lithographic and/or micro-machining techniques. As an example, a Si-wafer with on top a Si3N4 layer may be used. By etching from the backside of the Si-wafer up to Si3N4 layer, the patterned layer can be defined. The patterned and unpatterned layers may be formed form the same piece of material or alternatively formed separately and thereafter attached to one another.
The spectral purity filters as described above may be used in any suitable type of lithographic apparatus. Moreover, the spectral purity filters according to the present invention may be used in combination with at least one grazing incidence mirror in a lithographic apparatus.
Yet a further embodiment of the spectral purity filter 600 is depicted in
Again, a potential advantage of using doped silicon is that such materials may be patterned more easily than for example metals. Silicon may be micromachined and etched using a variety of lithographic techniques. Grid structures can be etched in silicon for instance using an etching method referred to as deep reactive-ion etching. This method has been described by S. Tachi et al. in an article in Applied Physics Letters titled “Low-temperature reactive ion etching and microscope plasma etching of silicon”.
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. It should be appreciated that, in the context of such alternative applications, any use of the term “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 descriptions above are intended to be illustrative, not limiting. Thus, it should be appreciated that modifications may be made to the present invention as described without departing from the scope of the claims set out below.
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 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), X-ray 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.
While specific embodiments of the present invention have been described above, it should be appreciated that the present invention may be practiced otherwise than as described. For example, the present invention may take the form of a computer program containing one or more sequences of machine-readable instructions that are executable to cause an apparatus to perform 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.
This application claims the benefit of U.S. provisional applications 61/136,347 and 61/193,255, which were filed on Aug. 29, 2008 and on Nov. 12, 2008 respectively, and which are both incorporated herein in their entirety by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/005489 | 7/29/2009 | WO | 00 | 2/25/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61136347 | Aug 2008 | US | |
| 61193255 | Nov 2008 | US |
