X-ray lithography at .about.100 A linewidths using X-ray masks fabricated by shadowing techniques

Abstract

A new technique for fabricating high contrast X-ray masks with precisely controlled linewidths of less than 100 A is described. The technique is based on the deposition at an oblique angle ("shadowing") of X-ray absorber material onto relief structures of triangular or square cross-section in a polyimide plastic membrane. Precise linewidth control is possible because shadowing angle, absorber thickness and relief structure can be precisely determined. The smooth and well-controlled triangular cross-section structures required are produced in silicon by anisotropic chemical etching and then transferred to polyimide by molding. The square structures are made by reactive-ion-etching SiO.sub.2 with CHF.sub.3 and are transferred to polyimide by molding. Results of a numerical model of carbon K (45 A) X-ray exposures in PMMA of shadowed triangular profile masks are presented which indicate that linewidth control of .+-.50 A should be possible for submicrometer period gratings. Scanning electron micrographs of PMMA gratings of 1 .mu.m, 3200 A and 1968 A period with linewidths as small as 400 A are shown. The successful replication of <200 A linewidth patterns in PMMA using the carbon K X-ray and shadowed square cross-section masks is reported.

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