Spherical pinch (soft X-rays/EUV) and vacuum spark (soft/hard X-rays) radiation sources

Abstract

Summary form only given. X-ray microlithography is a well understood technology by now, however, a compact, cost-effective and intense point soft X-ray source is needed to push this technology from research laboratories into production fabs. While conventional rotating-anode X-ray tube has been proven not capable of meeting the throughput requirement (wafers/hour), synchrotron-based soft X-ray microlithography is only economical in large volume production. Among the various schemes of plasma radiation sources, spherical pinch and vacuum spark have been pursued by ALFT (Advanced Laser and Fusion Technology, Inc.) for a number of years as potential candidates for point X-ray sources in future microlithography technology. The spherical pinch is essentially a geometrically modified /spl theta/-pinch. /spl theta/-pinch had been studied in the earlier years of nuclear fusion program as a reactor candidate, but the intrinsic end losses have never been overcome. In the spherical pinch concept the end loss problem has been relieved to a very large extent, and as a result a high temperature plasma can be generated in the center of a spherical vessel with a size smaller than 1 mm. This plasma can emit radiations from visible, UV, extreme UV, and soft X-ray regions of the spectrum. The radiation intensity, source size and spectrum depend on the working gas, the filling pressure, the input electrical energy and other factors. The vacuum spark is a pulsed high current discharge through two properly shaped electrodes in a vacuum. During the discharge hot spots (minute high temperature plasmas) are formed in the vicinity of the anode due to the micropinch phenomenon. As a result, intense pulsed X-rays (around the characteristic lines of the electrode materials) can be generated.