Fabrication and testing of 0.1-μm-linewidth microgap x-ray masks

Abstract

A technology has been developed for the printing of 0.1-μm-linewidth patterns using a ‘‘microgap,’’ out-of-contact scheme for x-ray nanolithography (as opposed to zero-gap electrostatic contact). Mask-to-wafer gaps of ∼5 μm are maintained by the use of gap-setting aluminum studs fabricated onto the front surface of the mask mesa rim. X-ray mask blanks are fabricated from silicon wafers coated with low-stress, silicon-rich low-pressure chemical vapor deposition SiNx. The resulting 1–2-μm-thick 6×108 dyn/cm2 stress membranes exhibit extreme strength. A novel aluminum-stencil etching procedure—which includes three CF4 RIE and two KOH etching steps—is used to define the mask membrane and ‘‘mesa’’ structure. Mask absorber pattern fabrication is performed by focused-ion-beam lithography (FIBL) and gold electroplating. We present details of the mask fabrication procedure and the results of testing these masks with x rays from a laboratory CuL (λ=1.34 nm) electron bombardment source and a commercial pulsed laser-plasma x-ray source. This marks the first time that FIBL-generated masks have been used with a pulsed laser-plasma source, and also the finest lines that have been printed using a laser plasma. The results of the evaluation of the x-ray resists PMMA, RAY-PF, RAY-PN, and SAL-601 are presented.