Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Patent
1998-02-26
2000-02-29
Berman, Jack I.
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
359355, G03F 720, G02B 1314
Patent
active
060312386
DESCRIPTION:
BRIEF SUMMARY
INDUSTRIAL FIELD OF THE APPLICATION
The present invention relates to a projection aligner suitable for fabrication of 64 Mbit to 256 Mbit memory integrated circuits and, more particularly, a projection aligner comprising ArF excimer laser and an optical system composed of quartz glass optical members.
PRIOR ART
An optical lithography, in which a pattern on a mask is transferred on a wafer using light, has widely been used for integrated circuit fabrication with a projection aligner, because the optical lithography is better evaluated in an aspect of cost, as compared with other techniques using such exposing radiation as an electron beam or X-rays.
A projection aligner using an "I-line" having a wavelength of 365 nm emitted from a high-pressure mercury lamp as an optical source has been developed to form a pattern image with a linewidth of 0.5 to 0.4 .mu.m on a wafer. Such a projection aligner can be used for fabrication of 16 Mbit integrated circuits.
However a resolution power in the range of 0.25 to 0.35 .mu.m is required in fabrication of 64 to 256 Mbit integrated circuits, which are of a next generation, and even a higher resolution power in the range of 0.13 to 0.20 .mu.m is required in the case of 1 Gbit integrated circuits. In order to achieve such resolution an ArF laser, especially an ArF excimer laser is used.
However, an optical lithography using an ArF excimer laser as a light source has a various problems and one problem is to achieve optical material good enough to make a lens, mirror and prism, which compose an optical system for image projection.
A choice of optical material for ArF laser light having a wavelength of 193 nm is substantially limited to quartz glass, especially high-purity synthetic quartz glass, because of its excellent transmittance of the ArF laser light. The ArF laser light gives more than 10 times as great a damage to the mass of quartz glass during exposure as KrF light does.
Durability of quartz glass to irradiation of an excimer laser depends on the hydrogen molecule concentration contained in the quartz glass, as disclosed in EP-A2 401 845t. It is disclosed that quartz glass has a sufficient durability to excimer laser irradiation for practical use in a projection aligner with a KrF excimer laser as a light source, when the quartz glass has a concentration of hydrogen molecules of 5.times.10.sup.16 molecules/cm.sup.3 or more. In experiments it has been found that, to minimize the degree of the damage caused by an ArF laser, the hydrogen molecule concentration in the glass should be higher, for example more than 5.times.10.sup.18 molecules/cm.sup.3.
Synthetic quartz glass as material to fabricate optical members, such as a mirror, lens and the like, in various optical systems for optical lithography can be said to have generally been of one kind when considered in terms of hydrogen molecule concentration, since the concentration is a physical quantity to be determined by conditions of synthesis of raw material and/or a following heat treatment (including hydrogen doping) and the physical quantity should generally have a single magnitude, if fluctuations in magnitude thereof, which are ascribed to unintentional minor changes in operational conditions, are neglected due to their smallness.
There are two methods in which hydrogen molecules are incorporated into synthetic quartz glass. A first method is to incorporate hydrogen molecules in an hydrogen containing atmosphere at atmospheric pressure. By this method a maximum concentration of hydrogen molecules in the order 5.times.10.sup.18 molecules/cm.sup.3 can be achieved. A second method is to heat the synthetic quartz glass in a pressurized hydrogen atmosphere to dope with hydrogen molecules. Using this method the maximum concentration of hydrogen molecules can be increased over the value of 5.times.10.sup.18 molecules/cm.sup.3 only by applying a pressure higher than 10 at.
A temperature of a heat treatment in the range of 200 to 800.degree. C. for doping with hydrogen is preferred to a heating/remelting treatment
REFERENCES:
patent: 5488229 (1996-01-01), Elliott et al.
patent: 5719698 (1998-02-01), Hiraiwa et al.
patent: 5908482 (1999-06-01), Komine et al.
Fujinoki Akira
Mori Toshiki
Nishimura Hiroyuki
Berman Jack I.
Heraeus Quarzglas GmbH
Shin-Etsu Quartz Products Co. Ltd.
Tiajoloff Andrew L.
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