|Publication number||USRE41220 E1|
|Application number||US 11/880,425|
|Publication date||Apr 13, 2010|
|Filing date||Jul 10, 2000|
|Priority date||Jul 22, 1999|
|Also published as||EP1214718A1, EP1214718A4, US6931097, WO2001008163A1|
|Publication number||11880425, 880425, PCT/2001/18798, PCT/US/1/018798, PCT/US/1/18798, PCT/US/2001/018798, PCT/US/2001/18798, PCT/US1/018798, PCT/US1/18798, PCT/US1018798, PCT/US118798, PCT/US2001/018798, PCT/US2001/18798, PCT/US2001018798, PCT/US200118798, US RE41220 E1, US RE41220E1, US-E1-RE41220, USRE41220 E1, USRE41220E1|
|Inventors||Claude L. Davis Jr., Kenneth E. Hrdina|
|Original Assignee||Corning Incorporated|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (51), Non-Patent Citations (37), Referenced by (6), Classifications (51), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Application Ser. No. 60/145,057, filed Jul. 22, 1999 entitled Extreme Ultraviolet Soft X-Ray Projection Lithographic Method and Mask Devices of Claude L. Davis, Robert Sabia and Harrie J. Stevens, and U.S. Provisional Application Ser. No. 60/149,840, filed Aug. 19, 1999 entitled Extreme Ultraviolet Soft X-Ray Projection Lithographic Method and Mask Devices of Claude L. Davis, Robert Sabia, Harrie J. Stevens and Kenneth E. Hrdina, and U.S. Provisional Application Ser. No. 60/158,813, filed Oct. 12, 1999 entitled Extreme Ultraviolet Soft X-Ray Projection Lithographic Method and Mask Devices of Claude L. Davis and Kenneth E. Hrdina.
1. Field of the Invention
The present invention relates generally to project lithographic methods and systems for producing integrated circuits and forming patterns with extremely small feature dimensions. The present invention relates particularly to extreme ultraviolet soft x-ray based lithography and radiation manipulating lithography elements which reflectively operate on and manipulate extreme ultraviolet soft x-ray radiation to illuminate, project, and reduce pattern images that are utilized to form circuit patterns. The present invention relates to lithography elements and their use for reflecting extreme ultraviolet soft x-ray photons to enable the use of extreme ultraviolet soft x-ray radiation for lithography that surpasses current optical lithography circuit feature dimension performance.
2. Technical Background
The use of extreme ultraviolet soft x-ray radiation provides beneath in terms of achieving smaller feature dimensions but due to the nature of the radiation, it presents difficulties in terms of manipulating and directing such wavelengths of radiation and has delayed the commercial manufacturing use of such radiation. Current optical lithography systems used in the manufacturing of integrated circuits have progressed towards shorter optical wavelengths of light, such as from 248 nm to 192 nm to 157 nm, but the commercial use and adoption of extreme ultraviolet soft x-rays has been hindered. Part of this slow progression to very short wavelengths of radiation such as in the 15 nm range, has been due to the lack of economically manufacturable mirror elements that can withstand the exposure to such radiation while maintaining a stable and high quality circuit pattern image. For the benefits of extreme ultraviolet soft x-rays to be utilized in the manufacturing of integrated circuits, there is a need for stable high quality glass lithography elements, that preferably allow for direct deposition of reflective coatings to the surface of the glass substrate body.
U.S. Pat. No. 5,956,192 describes a four mirror EUV projection system with lithography mirror elements including two convex mirror elements and two concave mirror elements. U.S. Pat. No. 5,353,322 describes a three mirror x-ray projection lens system with lithography mirror elements including a convex mirror and two concave mirrors. As noted from U.S. Pat. No. 5,698,113, current extreme ultraviolet soft x-ray lithographic systems are extremely expensive. U.S. Pat. No. 5,698,113 tries to address such high costs by trying to recover the surface of multilayer coated substrates by etching the multilayer reflective coatings from substrate surfaces of fused silica and ZERODUR type aluminosilicate crystalline glass-ceramics, even though such etching degrades the substrate surface. “Extreme Ultraviolet Lithography” by Richard Stulen and Donald Sweeney, Optics and Photonics News, August 1999, Vol. 10, No. 8, disclose an EUV reflective coating on a Si substrate (FIG. 3).
The present invention provides for economically manufactured lithography element substrates that are stable, ready and receptive to receiving multilayer reflective coatings and provide an improved extreme ultraviolet soft x-ray based projection lithography method/system. The present invention provides a stable high performance lithography element with the reflective multilayer coating directly deposited on the finished glass surface, and avoids costly and cumbersome intermediate layers between the glass substrate surface and the reflective multilayer coating.
One aspect of the present invention is a projection lithographic method/system for producing integrated circuits with printed feature dimensions less than 100 nm, preferably ≦70 nm, and most preferably ≦50 nm, that includes providing an illumination sub-system for producing and directing an extreme ultraviolet soft x-ray radiation λ from an extreme ultraviolet soft x-ray source. The method further includes providing a mask stage and a mask illuminated by the extreme ultraviolet soft x-ray radiation λ produced by the illumination sub-system for forming a projected mask pattern when illuminated by radiation λ. The method further includes providing a projection sub-system, a wafer stage and an integrated circuit wafer which has a radiation sensitive wafer surface wherein the projection sub-system projects the projected mask pattern from the mask onto the radiation sensitive wafer surface. Providing the sub-systems includes providing reflective lithography elements. Providing reflective lithography elements includes providing reflective multilayer coated Ti doped high purity SiO2 glass lithography elements. More preferably providing reflective lithography elements includes providing Ti doped high purity SiO2 glass projection substrates with defect free surfaces with figure and finish that are free of surface figure measurements >0.25 nm rms. Preferably the substrate surfaces have radiation manipulating surface shaped profiles, such as curved surfaces and shapes, preferably concave or convex which manipulate and operate on the radiation such that the mask pattern is projected and reduced. Preferably the substrate surfaces have surface figures are less than 0.25 nm rms, have mid-spatial frequency roughness ≦0.20 nm rms, and high-spatial frequency roughness ≦0.10 nm rms.
In another aspect, the present invention includes a method of making a projection lithographic system and a method of projection lithography that includes providing an illumination sub-system which has an extreme ultraviolet soft x-ray source and providing a mask stage that has a reflective mask Ti doped high purity SiO2 glass mask wafer with an unetched glass mask surface coated with a reflective multilayer coating. The method further includes providing a projection reduction sub-system including a plurality of Ti doped high purity SiO2 glass reflective lithography elements, providing a wafer stage with a radiation sensitive semiconductor wafer; and aligning the illumination sub-system, the mask stage, the projection reduction sub-system, and the wafer stage wherein the extreme ultraviolet soft x-ray source illuminates the mask stage with extreme ultra-violet soft x-ray radiation and forms a circuit printing pattern which is projected, and focussed by the projection reduction sub-system onto said radiation sensitive wafer.
The invention further includes a method of making a reflective extreme ultraviolet soft x-ray lithography element which includes the steps of: providing a Ti doped high purity SiO2 non-crystalline glass substrate free of inclusions and having a shaped element surface with surface figure features <0.25 nm rms, mid-spatial frequency roughness <0.20 nm rms, and high-spatial frequency roughness <0.10 nm rms, and coating the shaped element glass surface with a reflective multilayer coating with uniform multilayer period thickness controlled to at least 0.1% rms to form a uniform reflective coating having a reflectivity of at least 65% to extreme ultraviolet soft x-rays.
The invention also includes a reflective extreme ultraviolet soft x-ray lithography element that comprises a Ti doped high purity SiO2 inclusion-free glass having an unetched polished radiation manipulating shaped surface, with the surface free of printable surface figures.
The invention further includes a method of making a reflective extreme ultraviolet soft x-ray lithography element that has the steps of: providing a high purity Si containing feedstock and a high purity Ti containing feedstock, delivering the high purity Si containing feedstock and the high purity Ti containing feedstock to a conversion site, converting the Si containing feedstock and the Ti containing feedstock into Ti doped SiO2 soot, consolidating the Ti doped SiO2 soot into an inclusion fee homogeneous Ti doped high purity SiO2 glass, forming the glass into a Ti doped high purity SiO2 glass preform, forming the preform into a shaped surface lithography element substrate, measuring the figure and finish of the substrate surface, and coating the substrate surface with an extreme ultraviolet soft x-ray reflective coating.
Additional features and advantage of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended Figures.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying Figures are included to provide a further understanding of the invention, and are incorporated in and constitutes a part of this specification. The Figures illustrate various embodiments of the invention, and together with the description serve to explain the principals and operation of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying Figures. An exemplary embodiment of the projection lithographic method/system of the present invention is shown in FIG. 1 and is designated generally throughout by reference numeral 28.
In accordance with the invention, the present invention for a projection lithographic method includes providing a mask stage illuminated by extreme ultraviolet soft x-ray radiation λ produced by an illumination sub-system, with the mask stage including a mask for forming a projected mask pattern when illuminated by radiation λ. The invention includes providing Ti doped high purity SiO2 glass lithography elements which manipulate radiation λ and operate on the projected mask pattern.
As embodied herein, and depicted in
The projection lithographic method for producing integrated circuits with printed feature dimensions less than 100 nm includes providing illumination sub-system 36 for producing and directing extreme ultraviolet soft x-ray radiation λ. Illumination sub-system 36 includes extreme ultraviolet soft x-ray source 38. In a preferred embodiment, illumination sub-system 36 includes a laser produced plasma such as a 1.064 μm neodymium YAG layer 40 which produces a Xenon gas plasma 42 from pulsed gas jet Xe clusters which outputs extreme ultraviolet soft x-ray radiation λ that is directed by condenser 44. Alternatively, extreme ultraviolet soft x-ray illumination sub-system 36 may comprise a synchrotron, discharge pumped x-ray lasers, an electron-beam driven radiation source drive, or a radiation source based on high harmonic generation based on femto-second laser pulses. Preferably the illumination sub-system includes a plurality of Ti doped high purity lithography elements E which direct the source produced radiation λ and form condenser 44. Lithography elements E of condenser 44 form a funneling radiation λ pipe, preferably with the lithography elements having substantially flat reflecting surfaces, preferably situated to form glancing reflective angels with radiation λ emitting from source 38. Ti doped high purity SiO2 lithography elements E may be utilized in a elliptical geometry to collect radiation λ.
The projection lithographic method includes providing mask stage 22 which is illuminated by the extreme ultraviolet of x-ray radiation λ produced by illumination sub-system 36. Providing mask stage 22 includes providing a patterned reflective mask 24 which forms a projected mask pattern when illuminated by the radiation λ. Providing mask 24 preferably includes providing a Ti doped high purity SiO2 glass wafer 26 which has a patterned absorbing overlay 28 overlaying reflective multilayer coated Ti doped high purity Sio2 glass defect free wafer surface 3.
The method includes providing a projection sub-system 46 and an integrated circuit wafer 48 with a radiation sensitive wafer surface 50, wherein projection sub-system 46 projects the projected mask pattern from mask 24 onto radiation sensitive wafer surface 50. Preferably projection sub-system 46 is a series of Ti doped high purity SiO2 glass lithography elements E which reduce the size of the mask pattern and project the reduced pattern image onto wafer surface 50. A preferred embodiment is shown in
In a preferred embodiment, extreme ultraviolet soft x-ray radiation λ is in the range from about 5 nm to about 15 nm, and most preferably illumination sub-system 36 directs radiation centered about 13.4 nm to reflective mask 24, with the Ti doped high purity SiO2 glass lithography elements E having a reflectivity of at least 65% at 13.4 nm. With extreme ultraviolet soft x-ray radiation λ centered about 13.4 nm, Ti doped high purity SiO2 glass surfaces 32 are coated with reflective multilayer coating 34 comprising alternating layers of Mo and Si. Alternatively it is preferred that extreme ultraviolet soft x-ray radiation λ is centered about 11.3 nm, with Ti doped high purity SiO2 glass surfaces 32 coated with reflective multilayer coating 34 comprising alternating layers of Mo and Be. With λ centered about 11.3 nm, reflective Ti doped high purity SiO2 glass lithography elements E have a reflectivity of at least 70% a at 11.3 nm. Multilayer coating 34 is preferably comprised of alternating layers of a first element and a second element wherein the coating is highly reflective to the extreme ultraviolet soft x-ray radiation λ.
The provided Ti doped high purity SiO2 glass of lithography elements E is defect free in that the glass body is free of bulk glass defects and is free of inclusion, including glass voids the gas filled voids in the glass, and is particularly free of any such defects or imperfections or structures that have a dimension greater than 80 nm. In a particularly preferred embodiment, glass surface 32 is an unetched glass surface that has been finished such as with polishing, to a surface free of surface figure measurement >0.25 nm rms, and preferably finished to at least 0.15 nm rms roughness. The Ti doped SiO2 glass is substantially non-transmissive to extreme ultraviolet soft x-ray radiation λ and the reflectivity of reflective coated wafer surface 30 and the ultra-low roughness of defect free surface 32 is utilized in the invention to inhibit scattering of radiation λ and provide an ultra-stable high quality image during the projection lithography process. The provided Ti doped high purity SiO2 glass is highly stable, homogeneous, chemical attach resistant, is preferably chlorine-free and preferably has an impurity level of less than 10 ppb of alkali and alkaline earth metals. Preferably the Ti doped high purity SiO2 glass contains from 5 to 10 wt. % TiO2 and has a coefficient of thermal expansion in the range from +30 ppb to −30 ppb at 20° C., and more preferably in the range from +10 ppb to −10 ppb at 20° C. Preferably the TiO2 content is from 6 to 8 wt. %, more preferably form 6.5 to 7.5 wt. %, and most preferably about 7 wt %. Preferably lithography elements E have a variation in coefficient of thermal expansion throughout the glass substrate body that is less than or equal to 15 ppb. The lithography element glass preferably has a thermal conductivity K≦1.40 w/(m.° C.) at 25° C., more preferably in the range from 1.25 to 1.38, and most preferably about 1.31. During projection lithography, lithography elements E and mask 24 are heated by the illumination of radiation λ, and even with such irradiation and heating of lithography elements E changes of the patterned circuit projected image are inhibited and the quality of the projected image is maintained. In the inventive method, the Ti doped high purity SiO2 glass is heated to an operating temperature by radiation λ and preferably the glass has an adjusted Ti dopant level adjusted such that the glass has a coefficient of thermal expansion centered about 0 at such operating temperature, preferably with the zero thermal expansion range also including the lithography element manufacturing temperatures and the lithography element non-operating rest temperature. With such a thermal conductivity and coefficient of thermal expansion, the Ti doped high purity SiO2 glass provides appropriate lithographic operation and stability, and provides a highly reliable and economic lithographic method/system in which the lithography elements do not require cooling in addition to economically manufacturable elements. In a preferred embodiment, the lithography elements are not actively cooled and are free of a cooling system such as circulating cooling fluids, thermal electric coolers, or other means for removing heat build up during operation of the lithography system.
The provided Ti doped high purity SiO2 glass defect free surface 32 are free of surface figure measurements >0.25 nm rms. Finishing methods including chemical mechanical polishing are beneficially accepted by the non-crystalline glass. With shaped surface mirror lithography elements, an appropriately shaped and sized curve is generated in the non-crystalling glass body substrate and finished. The defect free glass surface of lithography elements E preferably have a surface figure no greater than 0.25 nm rms, and a high-spatial frequency roughness (at frequencies above 1 μm−1) no greater than 0.10 nm nms. The reflective multilayer coated Ti doped high purity SiO2 glass surface 30 preferably reflects at least 65%, and more preferably reflects at least 70%, of the radiation λ illuminating the reflective multilayer coating. In a preferred embodiment surface 32 is unetched and free of an intermediate barrier layer or release layer so that multilayer reflective coating 34 is directly bonded thereto.
The invention further comprises a method of making a projection lithographic system and the method of projecting lithographic patterns that includes providing an illumination sub-system 36 with an extreme ultraviolet soft x-ray source 38 and providing a mask stage 22 with a mask receiving member 52 and a reflective mask Ti doped high purity SiO2 glass mask wafer 24 with an unetched glass mask wafer surface coated with a reflective multilayer coating having a reflectivity of at least 65% to extreme ultraviolet soft x-rays received in mask receiving member 52. The method further includes providing a projection reduction sub-system 46 with a plurality of Ti doped high purity SiO2 glass lithography elements E; providing wafer stage 56 with a radiation sensitive semi-conductor wafer 58; and aligning illumination sub-system 36, mask stage 22, projection sub-system 46, and wafer stage 56 such that extreme ultraviolet soft x-ray source 38 illuminates reflective mask 24 with extreme ultraviolet soft x-ray radiation and reflective mask 24 reflects the radiation and forms a printing pattern of which is projected, reduced and focused onto radiation sensitive print media 58. The method includes providing a reflective mask 24 with a Ti doped high purity SiO2 glass mask wafer 26 free of inclusions and wafer surface defects that are printable on radiation sensitive print media 58.
The method preferably includes determining operating temperatures of lithography elements when illuminated by radiation λ during operation of system 20 and providing a lithography elements E includes providing Ti doped high purity SiO2 glass having a coefficient of thermal expansion at the determined operating temperature centered about 0. Such turning of the coefficient of thermal expansion is done by controlled turning of Ti dopant content in the SiO2 glass as demonstrated by
In a further embodiment of the method the Ti dopant high purity SiO2 glass is heated to a raised temperature range by the extreme ultraviolet soft x-ray radiation and the Ti doped high purity SiO2 glass has a coefficient of thermal expansion for the raised temperature range that is less than 10 ppb and greater than −10 ppb. Preferably the method includes providing a Ti doped high purity SiO2 glass that is a thermal insulator (low thermal conductivity) with a thermal conductivity K≦1.40 w/(m.° C.), preferably in the range from 1.25 to 1.38, most preferably about 1.31, and allowing the glass to heat up without actively cooling the glass and reflective elements E.
The invention further comprises a method of making a reflective extreme ultraviolet soft x-ray projection lithography element that includes providing a Ti doped high purity SiO2 non-crystalline substrate free of inclusions and having a shaped element surface with surface figure features <0.25 nm rms, mid-spatial frequency roughness <0.20 nm rms, and high-spatial frequency roughness <0.10 nm rms, and coating the element glass surface with a reflective multilayer coating 34 with a uniform multilayer period thickness controlled to at least 0.1% rms to form a uniform reflective surface 30 having a reflectivity of at least 65% to extreme ultraviolet soft x-rays. The method further includes generating a curved surface 30. Coating with a reflective multilayer coating preferably includes forming alternating smooth thin layers (≦4 nm thick) of a first element and a second element, such as Mo/Si or Mo/Be.
The alternating layers provide a soft x-ray extreme ultraviolet reflectivity peak, preferably centered about 13.4 nm and alternatively centered about 11.3 nm. Such an alternating multilayer reflective coating functions similarly to a quarter wave stack, with the thickness of the layers optimized for constructive interference of the photons reflected at each interface and minimal absorption so a large number of interfaces contribute to the high reflectance of the coating. Preferably layer to layer variation in thickness is within 0.01 nm with the multilayer coating 34 controlled in thickness to about 0.1% rms across lithography element surface 32, preferably a uniformity better than 0.01% so that surface shape 32 is maintained. In a preferred embodiment, the coating is alternating layers of Mo and Si with Mo thickness about 2.8 nm and the Si thickness about 4.0 nm. With proper deposition conditions, reflectances of 68% or greater at 13.4 nm are achievable with such alternating layers. The alternating layers of Mo and Si are preferably capped with a capping layer to prevent oxidation of the Mo on exposure to normal atmospheres, with a preferred capping layer being a Si layer.
In the preferred embodiment, the reflective multilayer coating is directly deposited onto the Ti doped high purity SiO2 glass surface. The finished surface and the Ti doped high purity SiO2 glass properties provide for directly depositing and bonding between the glass surface and the reflective mutlilayer coating without the need for additional treatments of a substrate surface such as smoothing coating processes used with glass-ceramic crystalline containing substrate materials and remove the need for intermediate layers between the glass surface and the reflective mutlilayer coating. A superior and stable reflective lithography element is achieved with the direct bonding contact between the finished Ti doped high purity SiO2 glass surface and the multilayer reflective coating.
Preferably providing a Ti doped high purity SiO2 glass preform as shown in
Preferably cup 142 has a circular diameter shape of at least 0.5 meters, more preferably at least 1 meter, most preferably a diameter of about 1.5 meters so that glass body 144 is a cylindrical boule having a respective diameter of at least 0.5 meters, preferably 1 meter, most preferably 1.5 meters, and a height of at least 8 cm, preferably at least 10 cm, preferably about 15 cm thick, with a preferred height in the range from 12 to 16 cm. Forming glass body 144 into a Ti doped high purity SiO2 glass substrate, preferably includes inspecting glass body 144 for any glass defects, such as inclusions, if defect found selecting defect free sections of glass body 144 such as defect free section 62 of glass body 144 shown in
The invention further includes reflective extreme ultraviolet soft x-ray lithography elements. The lithography element E comprises a Ti doped high purity SiO2 inclusion-free glass substrate that preferably is unetched.
The invention also includes a method of making a reflective extreme ultraviolet soft x-ray lithography element that comprises providing a Ti doped high purity SiO2 glass preform 60 free of glass inclusions. Preferably providing a Ti doped high purity SiO2 glass preform includes providing a high purity Si containing feedstocks 114 and high purity Ti containing feedstock 126, delivering feedstocks 114 and 126 to conversion site 100, converting feedstocks 114 and 126 into Ti doped SiO2 soot 101, consolidating soot 101 into an inclusion free homogeneous Ti doped high purity SiO2 glass and forming the glass into a Ti doped high purity SiO2 glass preform 60. Preferably Si feedstocks 114 is chlorine free and Ti feedstock 126 is chlorine free so that soot 101 and glass 144 is chlorine free.
As shown in
In a preferred embodiment such as in
The finishing steps in addition to polishing the preform surfaces includes cleaning the preform surfaces to remove finishing products to provide a clean smooth surface for contact with the reflective multilayer coating. Preferably the step of providing a preform includes adjusting the Ti dopant weight percent level of the Ti doped high purity SiO2 glass prefrom so that the glass has a coefficient of thermal expansion centered about 0 at an operating temperature of the reflective extreme ultraviolet soft x-ray lithography element.
The inventive method of making a reflective extreme ultraviolet soft x-ray lithography element provides an economic means for efficiently manufacturing large quantities of glass substrate bodies which can enable the utilization of extreme ultraviolet soft x-ray projection lithography for the mass production volume manufacturing of integrated circuits with printed feature dimensions less than 100 nm. Additionally, the inventive method of making a reflective lithography element Ti doped high purity SiO2 glass includes the beneficial steps of inspecting and qualifying the finished glass surface 32 to ensure that the surface has proper figure and finish and is defect free, and additionally inspecting and qualifying the CTE of the glass.
During use of the reflective extreme ultraviolet soft x-ray lithography elements E, the Ti doped SiO2 glass substrate has a lithography operating temperature. The operating temperature of the high purity Ti doped SiO2 glass element include a maximum operating temperature. During the making of the reflective extreme ultraviolet soft x-ray lithography element, the high purity Ti doped SiO2 glass is exposed to manufacturing treatment temperatures. The manufacturing treatment temperatures include elevated temperatures during cutting, machining, finishing, and coating. The manufacturing treatment temperature include a maximum manufacturing temperature. Preferably the high purity Ti doped SiO2 glass is crystallization resistant and has a crystallization temperature Tcrystal at which crystallization in the glass is induced, with Tcrystal being substantially greater than the maximum operating temperature and the maximum manufacturing temperature. Preferably Tcrystal is at least 400° C. higher than the greater of the maximum operating temperature and the maximum manufacturing temperature, more preferably at least 700° C. higher, and most preferably at least 800° C. higher. Preferably Tcrystal is ≧1300° C., with the maximum operating temperature and maximum manufacturing temperature not exceeding 500° C. With the high purity Ti doped SiO2 glass, the crystallization of the glass is inhibited at the elevated temperatures experienced during manufacturing and use of the lithography elements E. The glass is thus beneficial in that it has a high temperature crystallization behavior.
Additionally, in view of the manufacturing treatment temperatures and the lithography operating temperatures the high purity Ti doped SiO2 glass maintain its physical dimensions when exposed to thermal cycling. In the use and manufacture of the high purity Ti doped SiO2 glass lithography element repeated thermal cycling between lower temperatures and higher temperatures do not substantially change the physical dimensions of the glass substrate. Preferably the high purity Ti doped SiO2 glass is resistant to thermal cycling hysteresis, and most preferably is free of thermal cycling hysteresis when repeatedly cycled (>100 cycles) from the lowest lithography operating temperature to the highest lithography operating temperature. Most preferably physical dimensions of the glass substrate and lithography element do not measurably change when repeatedly cycled from a low temperature to a high temperature that are below 300° C. with the low temperature proximate to 0° C. and the high temperature proximate to 300° C.
In a preferred embodiment, the high purity Ti doped SiO2 glass lithography element has a birefringence resulting from permanent strain in the glass of less than 10 nm/cm, and more preferable is less than 2 nm/cm. Preferably birefringence less than 2 nm/cm is achieved by providing a constant homogeneous distribution of Ti dopant throughout the SiO2 glass with the coefficient of thermal expansion in the range from +10 ppm to −10 ppb at 20° C., with the maximum fluctuation in the coefficient of thermal expansion being less than 10 ppb, most preferably less than 5 ppb. Additionally, low birefringence may be obtained by annealing the high purity Ti doped SiO2 glass. Preferably the high purity Ti doped SiO2 glass lithography element substrate is annealed at a temperature of at least 900° C. more preferably at least 1000° C., and most preferably at least 1030° C., and preferably at a time after the glass has experienced stress from machining.
Ensuring such low birefringence levels is achieved by monitoring the coefficient of thermal expansion of the high purity Ti doped SiO2 glass by transmitting ultrasonic waves through the glass and measuring the transit time of the ultrasonic waves through the glass to determine the ultrasonic velocity and expensivity characteristics of the glass exposed to the ultrasonic waves. Preferably such measurement and monitoring of the high purity Ti doped SiO2 glass is utilized throughout the glass lithography element manufacturing process. Such ultrasonic measurements are preferably utilized for quality control, inspection, and selection. Such measurement are preferably utilized to insure the manufacturing of glass body 144 is providing a constant homogeneous distribution of Ti dopant. Additionally, such measurements are used in inspecting glass body 144 and selecting sections 62 to be cut from glass body 144. Further such measurements may be utilized to insure that undue stresses are not formed in the glass during later manufacturing stages such as finishing and also used as a determining factor if further annealing of the glass is required.
A preform 60 may be obtained by cutting the prefrom from an inclusion free area of a Ti doped high purity SiO2 glass boule disk 144 that had a cylindrical disk shape of approximately 152 cm diameter and about a 20 cm thickness (height). The boule is preferably produced from octamethylcycloetetrasiloxane and titanium isopropoxide feedstocks in accordance with
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
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|U.S. Classification||378/84, 378/37, 378/85|
|International Classification||G03F1/00, G03F1/24, G03F1/60, G21K1/06, G03F7/20, H01L21/027, G02B5/26, C03C17/36, G02B17/06, G21K5/02, C03B8/04, G02B5/10, C03B20/00, G02B5/08, G02B5/28|
|Cooperative Classification||C03B19/1415, C03B2201/07, C03B2201/42, G03F1/60, G21K2201/064, G02B17/0636, G03F1/14, G02B5/0891, G02B17/0615, G21K1/062, B82Y40/00, G21K2201/067, B82Y10/00, G03F7/702, G03F7/70283, G03F7/70891, G03F7/70958, G03F7/70233, G03F1/24|
|European Classification||B82Y10/00, G03F1/24, G03F7/70F14, G03F7/70F4, G03F7/70D20, G03F7/70P10B, G03F7/70P6D2, G03F1/60, B82Y40/00, G21K1/06B, G02B5/08V, G02B17/06A2, G02B17/06B2, G03F1/14|