Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70425—Imaging strategies, e.g. for increasing throughput or resolution, printing product fields larger than the image field or compensating lithography- or non-lithography errors, e.g. proximity correction, mix-and-match, stitching or double patterning
  • G03F7/7045—Hybrid exposures, i.e. multiple exposures of the same area using different types of exposure apparatus, e.g. combining projection, proximity, direct write, interferometric, UV, x-ray or particle beam
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70283—Mask effects on the imaging process
  • G03F7/70291—Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices

Definitions

• Ceglio and Markle utilizes a "programmable array of binary light switches" that generates a spatially modulated light field. The modulated light field is then relayed optically to the surface of a substrate that receives the desired circuit pattern.
• EUV extreme ultraviolet
• Ceglio and Markle disclose a programmable array comprising active elements that can be digitally programmed via direct electrical connection to a drive circuit.
• To program the pixels it is usually proposed to have a matrix of wires that carry electrical signals to micro-mirrors at the intersections of pairs of wires. This arrangement becomes more difficult to fabricate as the circuit scale size is reduced, and limits the speed with which the whole array can be addressed.
• Prior art optically addressed light modulators depend upon the relatively high refractive index changes that are available in the visible or ultraviolet spectral ranges, at wavelengths longer than the primary optical transitions relating to the first electronic excitation in optically transmissive media.
• the extreme ultraviolet, or soft X-ray region does not afford either high refractive indexes, or transmissive optical media, with which to construct the prior modulator designs.
• practical modulators In the extreme ultraviolet region, practical modulators have to work in the reflective mode, or otherwise involve the use of sub-micron thickness films if they are to work in the transmission mode.
• the present invention provides very rapid spatial addressing of a modulator without requiring a matrix of addressing wires and associated switching circuits. Instead, a desired spatial pattern is imprinted on the modulator by an optical beam.
• the modulator includes multilayer mirrors that reflect with changed amplitude and/or phase when subjected to a temperature impulse.
• the imprinting optical beam supplies a spatial pattern that is absorbed in the modulator structure, becoming a thermal pattern.
• the modulator structure contains at least one layer of optically absorbing material with a high coefficient of thermal expansion.
• this layer expands, modifying the amplitude and/or phase of EUV or soft X-ray radiation reflected by the modulator structure in such regions.
• the modulator of the present invention is passive, in the sense that no electric power is required to drive the modulator, and does not require micro- lenses.
• the thermal expansion principle is much more effective for the modulation of extreme ultraviolet or soft X-ray radiation because in these regions of the spectrum significant phase changes only require motions of the order of one nanometer, which are readily achieved in materials of high thermal expansion coefficient with temperature excursions as small as a few tens of degrees Centigrade. Such small motions are not able to impress significant phase changes on reflected visible or ultraviolet light.
• a modulator for extreme ultraviolet or soft X-ray radiation comprises a modulator structure that is reflective of extreme ultraviolet or soft X-ray radiation, said modulator structure including material having a high coefficient of thermal expansion, wherein said modulator structure expands in response to illumination with a light beam and alters a parameter of reflected extreme ultraviolet or soft X-ray radiation.
• the modulator structure comprises a multilayer mirror and the material having a high coefficient of thermal expansion comprises one or more layers of the multilayer mirror.
• the modulator includes a substrate and the modulator structure comprises a multilayer mirror and a layer of the material having a high coefficient of thermal expansion between the multilayer mirror and the substrate.
• the modulator structure may be configured to modulate the amplitude and/or the phase of the reflected extreme ultraviolet or soft X-ray radiation.
• the modulator includes a substrate and the modulator structure comprises an array of individual modulator elements affixed to the substrate.
• the modulator structure may be configured to produce a thermal pattern in response to a light beam having a spatial intensity pattern.
• a lithography system is provided.
• the lithography system comprises a modulator for extreme ultraviolet or soft X-ray radiation, including a modulator structure that is reflective of extreme ultraviolet or soft X-ray radiation, said modulator structure including a material having a high coefficient of thermal expansion; an optical pattern generator configured to project a light beam carrying a spatial intensity pattern onto the modulator to produce a thermal pattern in the modulator; a photon source configured to illuminate the modulator with extreme ultraviolet or soft X-ray radiation; and a projection assembly configured to image onto a target extreme ultraviolet or soft X-ray radiation reflected from the modulator and modulated in response to the thermal pattern.
• FIG. 1 is a schematic block diagram of a lithography system in accordance with a first embodiment of the invention
• Fig. 1 A is an enlarged, partial cross-sectional view of the modulator shown in Fig. 1
• Fig. 2 is a schematic block diagram of a lithography system in accordance with a second embodiment of the invention
• Fig. 3 is a schematic cross-sectional view of a multilayer mirror in accordance with a third embodiment of the invention, shown before and after heating
• Fig. 4A is a graph of reflectivity as a function of wavelength for a multilayer mirror having peak reflectivity at 13.5nm
• Fig. 4B is a graph of reflectivity as a function of wavelength for the multilayer mirror of Fig. 4A after heating
• Fig. 5 is a simplified cross-sectional view of a modulator in accordance with a fourth embodiment of the invention
• Fig. 6 is a simplified cross-sectional view of a modulator in accordance with a fifth embodiment of the invention
• Fig. 7 is a front view of the modulator shown in Fig. 6.
• FIG. 1 and 1 A A schematic block diagram of a lithography system in accordance with the first embodiment of the invention is shown in Figs. 1 and 1 A.
• a modulator 10 is configured for optical patterning and for reflection of extreme ultraviolet or soft X-ray radiation. While the discussion herein refers to EUV operation, it will be understood that the present invention is applicable to extreme ultraviolet and soft X-ray radiation, typically in a wavelength range of 1 to 100 nm (nanometers).
• modulator 10 includes a light- transmissive substrate 12 and an array of modulator elements 14 affixed to substrate 12. Modulator elements 14 may be arranged in rows and columns and may define pixels of a pattern.
• Each of the modulator elements 14 may include a multilayer mirror 20 and a thermally expandable pad or layer 22 of a material having a high coefficient of thermal expansion. Other embodiments of modulator 10 are described below.
• An optical pattern generator 30 projects one or more light beams 32 having a spatial intensity pattern 34 (Fig. 6) onto modulator 10. Optical pattern generator 30 may operate in the visible or deep ultraviolet wavelength range.
• the pattern 34 may represent, for example, a circuit pattern to be formed on a semiconductor wafer.
• a photon source 40 generates extreme ultraviolet or soft X-ray radiation.
• the EUV or soft X-ray radiation is collimated by collimator optics 42 and is projected onto modulator 10 as a collimated EUV beam 44.
• a reflected EUV beam 50 is projected by projection optics 52 onto a target, such as a semiconductor wafer 54.
• a cooling assembly may provide air and/or liquid cooling 60 of modulator 10.
• radiation, typically at 13.5 nm, from photon source 40 is collimated and projected onto modulator 10, which acts as a "mask”.
• the modulator 10 includes an array of multilayer mirrors reflecting at 13.5nm, each mounted on the thermally expandable pad 22 which is affixed to substrate 12.
• Each pad 22 may be an elastomer, such as a silicon-containing elastomer, which absorbs radiation from visible or ultraviolet pattern-carrying beams incident through the light-transmissive substrate 12.
• the elastomer pads respond with greater thermal expansion, imparting a phase shift to EUV radiation reflected from the multilayer mirrors on those layers.
• the reflected EUV radiation passes through de-magnifying projection optics 52 that image the "mask" onto a wafer.
• the mask is programmed as a spatial phase pattern, but this translates into an amplitude modulation pattern at the wafer.
• Other modulator embodiments provide direct amplitude modulation, as discussed below. As circuit feature sizes decrease, there will be an advantage to using 13.5nm EUV photons to expose a resist on the wafer.
• ki is an empirical process constant
• NA is the numerical aperture of the lithographic projection optic that images the array of modulator elements onto the wafer.
• a very high rate of address is available at what would be the wafer location in a conventional deep ultraviolet (DUV) lithography exposure tool.
• a "hybrid" exposure system shown in Figure 2, has the optically addressed modulator 10 located at the normal wafer location of a DUV exposure tool.
• a conventional transmission DUV mask 100 that carries the circuit pattern is imaged by DUV projection optics 102 onto the modulator 10.
• the pattern is then imprinted by the modulator 10 onto extreme ultraviolet beam 50 which carries the pattern, via EUV projection optics 52, to the wafer 54.
• extreme ultraviolet beam 50 which carries the pattern, via EUV projection optics 52, to the wafer 54.
• the DUV mask 100 As the DUV mask 100 is translated, its image scrolls across the modulator 10, which is held stationary.
• the wafer 54 is moved in synchronism with the scrolled pattern, so that many EUV pulses, from different modulator elements, contribute to the final exposure intensity at each point on the wafer surface. In this way, a single defective modulator element does not significantly degrade the quality of the final pattern at the wafer.
• a pixel size of 20nm at the wafer is assumed in order to compose 35nm minimum features with good fidelity.
• the pulse-to-pulse amplitude stability of this laser is important for accurate modulator movement. However, for patterns based on mixtures of ⁇ and zero phase differences, the image is not very sensitive to errors in phase of up to 10% of this range.
• the Cymer specification is for 3% stability (l ⁇ ). Because 80 pulses contribute to a single wafer pixel, some averaging is achieved, tending to smooth the pulse-by-pulse phase errors.
• the present invention provides a method of simultaneously programming large numbers of micro-mirrors in sub-microsecond times, using the thermal imprint of an optical programming beam. This is considered to be useful in maskless lithography. However, many other uses are possible for this fast and simple method of modulation.
• Fig. 3 shows a modulator structure that can be used for amplitude modulation.
• a multilayer mirror 150 includes alternating layers of high refractive index and low refractive index materials. The materials and thicknesses are selected to reflect radiation of a given wavelength.
• Multilayer mirror 150 shown in Fig. 3 includes high index layers 152 and low index layers 154. In this embodiment, at least one of the low index layers 154 has a high coefficient of thermal expansion. In the embodiment of Fig.
• the high index material is molybdenum, for peak reflection at the EUV wavelength of 13.5nm
• the low index material is a silicon-containing elastomer.
• the composition of the low index layers may be a silicon elastomer having a thermal expansion coefficient in the range of 182 to 330 parts per million per degree centigrade.
• the material having a high coefficient of thermal expansion may include an absorber molecule that preferentially absorbs photons of the light beam.
• the multilayer mirror 150 is typically mounted on a light-transmissive substrate for support. In some embodiments, an array of multilayer mirrors, configured as shown in Fig.
• Fig. 3 is affixed to a substrate.
• Amplitude modulation results from a shift in the peak reflection wavelength of the modulator structure due to expansion of the elastomer layers after a heating impulse from the optical beam carrying the spatial intensity pattern.
• the left side of Fig. 3 shows multilayer mirror 150 before heating, and the right side of Fig. 3 shows multilayer mirror 150 after heating and expansion.
• the fractional bandwidth of EUV radiation incident on the modulator is approximately 2.5% because there are several reflections in the multilayer mirrors of the collimator optics, each of which have a fractional bandwidth of about 4% at 13.5nm.
• Figs. 4A and 4B show the calculated shift in peak reflection wavelength for a 2.5% fractional expansion in a one- wavelength period stack. At 13.5nm the reflectivity drops from 55% without expansion to about 5% with expansion, giving a modulator contrast of 10:1.
• the same principle can be applied to a multilayer stack mounted on a thin substrate, or even free-standing, in order to achieve a transmission modulator. If the substrate is sufficiently thin, it transmits EUV radiation.
• a multilayer stack containing silicone elastomer mounted on the substrate can be tuned to reflect EUV radiation when cool, but to transmit when heated.
• a 20 layer one-wavelength stack has a non-resonant transmission when heated of 57%, and can be mounted on a lOOnm silicon nitride membrane with a transmission of 42%, giving an overall transmission of 24%.
• the stack rejects about 97% of EUV radiation.
• the transmission modulator has the disadvantage of being fragile, and the multilayer stack may not be cooled as rapidly, between pulses, as a reflection modulator mounted on a thick substrate. Modulator structures suitable for phase modulation are shown in Figs. 5 and 6. In Fig.
• a single conventional Mo-Si multilayer mirror 200 of period one half wavelength at 13.5nm is attached via a thermally expandable elastomer layer 202 to a transparent substrate 204. Visible or ultraviolet radiation of an imprint beam 210 is incident on layer 202 after traveling through the substrate.
• the elastomer layer 202 can be designed to strongly absorb the imprint beam 210, causing a temperature increase that is rapidly translated into an expansion ⁇ of layer 202.
• reflected EUV beam 214 has a 4 ⁇ / ⁇ phase change relative to incident EUV beam 212, where ⁇ is the EUV wavelength.
• the principle illustrated in Fig. 5 is applied in Fig.
• Each of the modulator elements 250 may include a multilayer mirror 252 and a thermally expandable pad 254 between multilayer mirror 252 and substrate 204.
• Each of the modulator elements 250 may define a pixel of a pattern. According to the example given above, the pixel size may be 140nm by 140nm, with 1 lOnm square modulator elements separated by 30nm channels. It will be understood that different modulator element dimensions may be utilized within the scope of the invention.
• the pads 254 experience varying expansions, with the result that an intensity distribution in the imprint beam is translated into a corresponding phase distribution in the reflected EUV beam 214.
• the spatial resolution is determined by the transverse scale size of the individual modulator elements. It is preferable to divide the surface into an array of independent modulator elements because otherwise, on short scale length, transverse heat conduction may smooth out the transverse spatial temperature profile, reducing the achievable spatial resolution. Additionally, the stiffness of an undivided multilayer mirror may become an obstacle to deformation on short transverse scale lengths.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
• Preparing Plates And Mask In Photomechanical Process (AREA)

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• 2004
  • 2004-08-19 WO PCT/US2004/027049 patent/WO2005019936A2/en not_active Ceased
  • 2004-08-19 JP JP2006524747A patent/JP2007503723A/ja active Pending
  • 2004-08-19 EP EP04781681A patent/EP1664930A2/en not_active Withdrawn
  • 2004-08-19 US US10/921,567 patent/US7079306B2/en not_active Expired - Fee Related

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