Investigation of Glass Polycapillaries for Use in Proximity X-Ray Lithography.

There is predicted growth of the micro-electronics industry in the 1990's and into the early 21^{st} century. In order for manufacturers of IC's to stay competitive in this vast global market, devices will have to be faster, more sophisticated, and more capable. According to the National Technology Roadmap for Semiconductors by The Semiconductor Industry Association (SIA), feature sizes in device structures are required to decrease in size in order for these goals to be realized. Presently, manufacturers use lithography with deep-ultra-violet (DUV) ^{1,2} wavelengths to produce circuit features of 0.30 μm and below. Because the wavelength of radiation used is of the same size as the features, diffraction phenomenon has become a limiting factor. Industry must therefore choose a new lithographic technique that can overcome the difficulties caused by these relatively large wavelengths. Although, some techniques have the ability to produce feature sizes of 0.2 μm and below, such as electron -beam lithography, ion-beam lithography, synchrotron-x-ray lithography, and even some optical techniques, they have not all developed an economically feasible method of mass producing device structures with a variety of geometries ^{3,4,5}. One such technique, point source x-ray lithography (PXRL), using considerably smaller wavelengths than those used by the current state of the art, could assist optical lithography in economically producing future generations of IC's. The characteristics of an x-ray field needed for x-ray lithography (XRL) is critically important to the manufacturing process. The beam must have control over the divergences produced by the finite-wafer-mask distance and the finite source size, the dose must be uniform throughout the field of exposure, the wavelength must be such as to prevent device damage and to maximize the interaction with the photo-resist, and there must be enough intensity to minimize exposure time. Point-source-x-ray-lithography system developers claim that as line widths in circuits are reduced to 0.18 mum, x-ray optics, specifically a collimator, will be needed to produce the required beam characteristics^6. Among a number of designs, arrays of glass polycapillary fibers have the potential of controlling parameters important to point -source lithography. The high absorption of x-rays by air at energies less than 3 keV necessitates the development of such a collimator be done in an atmosphere such as helium or vacuum. Consequently, there has been little research done at energies of 3 keV or lower. An experimental setup that tests glass capillary fibers under such conditions has been developed. It has sufficiently long optical paths in the vacuum chamber to be useful in evaluating the parameters critical for semiconductor lithography. Experimental and simulated transmission characteristics of polycapillary fibers have been studied at 1 keV.^7 Using this data, a collimator has been developed which will help determine the feasibility of using polycapillary optics for point-source-x-ray lithography. ftn ^1Semiconductor Industry Association, The National Technology Roadmap for Semiconductors, p.87 (1994). ^2Semiconductor International, Feb. (1996). ^3H. Loschner, Proc. SPIE 2194, p. 384 (1994). ^4R. Bojko, Proc. SPIE 1924, p. 214 (1993). ^5L. Liebmann, Proc. SPIE 2194, p. 51 (1994). ^6J. Abate, Advanced Lithography Program, Point Source Collimation Workshop II, Scottsdale AZ (1995). ^7I. Klotzko, Proc. SPIE 2523, p. 174 (1994).