X-ray mask development based on SiC membrane and W absorber

Abstract

We report a detailed description of x-ray mask technology based on SiC membrane and tungsten absorber. Amorphous SiC films were prepared using either a 100 kHz plasma-enhanced chemical vapor deposition (PECVD) system (allowing a high throughput) or a laser ablation deposition (LAD) technique. The PECVD a-SixC1−x:H films have a maximum Si–C bond density at x=0.5, a hydrogen content of 27 at. % and a high-compressive stress (1 GPa). The LAD films are stoichiometric, hydrogen-free, and under high-compressive stress (1.4 GPa). In order to achieve the tensile stress range (20–40 MPa) required for membrane fabrication, we developed a well-controlled rapid thermal annealing (RTA) process. At 633 nm, the resulting PECVD and LAD membranes have an optical transparency of 75% and 40%, respectively, and their corresponding biaxial Young’s moduli are 250±30 and 360±60 GPa. A novel approach using RTA for ‘‘fine tuning’’ of the tungsten stress is also proposed. Low stress (≤10 MPa) is obtained for W layers initially under compressive stress lower than 300 MPa. Finally, using an e-beam patterning process based on a single resist layer and reactive ion etching for the pattern transfer, x-ray masks with linewidths down to 100 nm were developed.