Patent Number: 046655417
Section: summary

DESCRIPTION The present invention relates to x-ray lithography, and particularly to submicron x-ray lithography using an ultraviolet, laser produced plasma as a source of x-rays. The present invention is especially suitable for use in producing high-resolution, submicron patterns in resist material for use in constructing integrated circuits. The invention also has application wherever high resolution, submicron patterns are needed, which photolithography is incapable of producing. X-ray lithography has been proposed wherein the x-rays are generated by the interaction of an electron beam and a metal target (see U.S. Pat. No. 3,743,842, issued July 3, 1973). The production of pulses of x-rays for lithography using a laser produced plasma has also been suggested (see U.S. Pat. No. 4,184,078, issued Jan. 15, 1980). Relatively long exposures of the x-ray sensitive material (e.g., x-ray resist) have, however, been required. For example, the system proposed in U.S. Pat. No. 4,184,078 requires the use of 90 laser shots to obtain sufficient absorbed x-ray energy to obtain an acceptable pattern after exposure and developing (see D. J. Nagel, et al., Electronic Letters, 14, 24, p. 781 (1978)). The minimum exposure which has been reported is a multi-nanosecond laser shot (a ten nanosecond pulse followed by a one nanosecond pulse) (see P. J. Mallozzi, et al., in Advances in X-ray Analysis (Plenum Press, New York, 1979)). It has been found, in accordance with the invention that high resolution, submicron x-ray lithography can be carried out using an ultraviolet-laser produced plasma as a source of x-ray pulses. Only a single shot of about one nanosecond (ns) duration of UV laser energy is necessary to produce x-ray flux sufficient for exposure of conventional x-ray resist material. The exposure with the x-ray flux has been carried out with the aid of a shield which blocks the high temperature plasma in the form of debris from the target on which the UV laser pulse is incident. The shield is in thermally coupled relationship with the resist and causes the resist to be heated upon exposure by the x-ray flux. While shields have been used, they have not been used to heat the resist (see U.S. Pat. No. 4,184,078 and the Electronic Letters article, referenced above). The x-ray flux which is incident upon the resist is about an order of magnitude smaller than what has heretofore been required in order to obtain comparable exposures with x-rays from a laser produced plasma. While the invention is not limited to any theory of operation, the increased efficiency of transfer of x-ray energy to the resist enabling the reduction in the required x-ray flux may be due to an abrupt rise in the resist temperature contemporaneous with or after exposure and prior to the development of the resist to produce the pattern. It is therefore a feature of the present invention to provide an improved method and apparatus for x-ray lithography wherein high resolution submicron patterns may be produced with a minimum of exposure by x-ray energy. It is another feature of the invention to provide an improved method and apparatus for submicron, high resolution x-ray lithography through the use of conventional x-ray resists and conventional methods of developing such resists after exposure wherein the amount of x-ray energy which is generated is minimized. It is a still further feature of the invention to provide an improved method of and apparatus for x-ray lithography using laser produced plasma as a source of x-rays, wherein long duration or multiple pulses of laser energy are not required for complete exposure of a pattern for lithographic purposes.