Asahi Glass Succeeds in Development & Mass-Production of Synthetic Quartz Photomask Substrate (QC-i) for ArF Liquid Immersion Lithography

    TOKYO, June 23 /Kyodo JBN-AsiaNet/ -- Asahi Glass Co., Ltd. (Headquarters:
 Tokyo; President: Masahiro Kadomatsu) has succeeded in the development of "QC-
 i" a synthetic quartz photomask(1) substrate, which complies with the liquid
 immersion technology used in ArF (argon fluoride) laser steppers(2) that use
 ArF lasers as a light source for photolithography in semiconductor production.
 QC-i can be mass-produced due to substantially reduced production costs, which
 makes it the world's first substrate for ArF immersion photolithography(3) to
 be mass-produced.  This development is expected to dramatically advance the
 ultra-fine processing technology that is indispensable for semiconductor
 fabrication.
     As more advanced, sophisticated integration and ultra-fine techniques for
 devices mounted on LSI chips are required for semiconductor manufacturers,
 they seek shorter wavelength light sources for the photolithography process by
 which semiconductor patterns are formed.  These manufacturers recently have
 begun to use 248 nanometer(4) KrF (krypton fluoride) lasers and 193nm ArF
 lasers, as light sources.
     Meanwhile, the semiconductor device manufacturers(5), aiming to further
 advance ultra-fine processing technologies, are developing photolithography
 processes using much shorter wavelength lasers such as the 157nm-F2 (fluoride
 dimmer) and 13nm-EUV (extreme ultraviolet) lasers.  Asahi Glass in 1999
 developed photomask substrate and pellicle materials for F2 lasers, and is
 currently developing photomask materials for EUV lasers jointly with
 International Sematech of the U.S. (Headquarters: Austin, Texas).  Through
 these efforts, Asahi Glass has strived to shorten the wavelength of light
 sources.  Although development of materials for an F2-laser photolithography
 process has progressed much, manufacturing costs, including equipments, are
 still a major barrier to commercialization. It is expected to take from four
 to six more years before mass-production of an EUV photolithography process is
 realized, considering the progress of development of peripheral materials.
 Therefore, the most pressing task for the industry is to develop a
 photolithography process that can be commercialized at an earlier date and
 requires less investment.
     Facing such circumstances, semiconductor device manufacturers began using
 conventional ArF laser steppers to develop a liquid-immersion photolithography
 process that can improve the accuracy of ultra-fine processing, and they are
 nearing commercialization.  In the liquid immersion photolithography process,
 pure water is put between the stepper lens and silicon wafer to significantly
 refract the light passed through the lens, so that ultra-fine processing on
 the wafer is made possible.  Synthetic quartz photomask substrates for liquid
 immersion photolithography require the "low birefringence(6)" property that
 minimizes irregularities in light polarization(7).
     Leveraging development expertise in dealing with lens materials for ArF
 laser steppers that the Company has accumulated for years, Asahi Glass has
 succeeded in the development of synthetic quartz photomask substrate QC-i
 which can be used in the ArF liquid immersion photolithography on a commercial
 basis.  The characteristics of QC-i are as follows:
 
      1. The birefringence is 1nm or less, compared with the 4 to 5nm for
         conventional synthetic quartz photomask substrates for ArF
         lithography.
 
      2. As production costs are remarkably reduced, QC-i can be mass-produced.
         (Annual production at Asahi Glass is estimated at 50,000 substrates of
         6 x 6 inch square, with a thickness of 0.25 inch.)
 
      3. Component technologies include a high-performance planarizing
         technique conventionally applied in photomask materials for the F2
         lithography, and a technique to reduce defects at scales of 100nm or
         less.
 
     Semiconductor stepper manufacturers are expected to launch mass-produced
 ArF liquid immersion steppers in 2005 and 2006, and demand for photomask
 materials for ArF liquid immersion lithography is forecast to grow remarkably.
 Asahi Glass estimates sales of QC-i at 1 billion yen in fiscal 2008, by coping
 with the rising demand through the mass production. The Company will continue
 to develop and produce high quality, high performance materials matching
 various light sources used in the photolithography process, so that it can
 offer optimum solutions to its customers.
 
     (Terms)
 
     (1) Photomask
     An patterned original sheet needed to transfer LSI circuit patterns to
 silicon wafers and others in the photolithography. A copy of the photomask
 pattern forms on the mask blank, which is a substrate for the fabrication of
 photomasks.
 
     (2) ArF laser stepper
     Typical equipment for photographic exposure which is used to transfer
 photomasking patterns to wafers in IC chip manufacturing process.  Also called
 "reduction-projection exposure device." The ArF laser stepper uses an 193nm
 ArF laser for its light source.
 
     (3) Photolithography
     The general term for processes of transferring LSI circuit patterns to a
 silicon wafer and others. Ultraviolet and other short wavelength light sources
 are used to form fine circuits.
 
     (4) Nanometer
     A nanometer is one billionth of a meter.
 
     (5) Semiconductor device manufacturers
     Manufacturers of the fundamental devices that constitute electronic
 circuits, including transistors, ICs and LSIs.
 
     (6) Birefringence
     A phenomenon in which each ray of light entering an object is split into
 two refractions. Quartz glass causes double refraction, birefringence, due to
 the distortion caused by strains in the material and other causes.
 Birefringence disturbs light polarization in ArF liquid immersion exposure
 equipment, resulting in deteriorated performance.
 
     (7) Polarization of light
     Polarization is occurred when light waves are aligned so that they vibrate
 in the same direction.  In the exposing process to transfer photomask patterns
 to wafers, polarization of the light source improves the contrast when resist
 materials are exposed, enabling an easier transfer of finer patterns to the
 wafers.
 
 

SOURCE  Asahi Glass Co., Ltd.