X-ray Lithography: Novel Fabrication Process for SiC/W Steppermasks

Abstract

This paper deals with the fabrication of an X-ray stepper mask based on a rigid SiC membrane and an almost stress free W absorber. As a result of extensive process optimization the poly-crystalline SiC membranes can be fabricated with a smooth surface (Rt<15 nm) and a Young's modulus as high as the bulk value (4.6×1011 N/m2). Membranes of 2.5 µm in thickness are being prepared routinely with excellent transparency for synchrotron and optical radiation. A proper stress adjustment of the SiC membrane can be either realized by an implantation of e.g. boron at a dose of 1015 cm-2 or by a thermal oxidation at 1100°C. The W absorber technology enables absorber stresses of less than 1.107 N/m2, resulting in mask distortions of <100 nm for 25×25 mm2 step fields. Precise sub-0.5-micron pattern have been generated by use of e-beam lithography and RIE techniques. High doses SOR experiments indicate an excellent long-term stability of these SiC/W masks.