X-ray lithography: Status, challenges, and outlook for 0.13 μm

Abstract

X-ray lithography (XRL) has been under development since the early 1980s, and has reached a state of relative maturity. Numerous devices, including dense and complex integrated circuits, have been fabricated using XRL for one or more critical levels. While development of XRL technology itself continues, XRL is in use in several locations around the world for process development of advanced DRAM (1 Gb and beyond) and logic (0.18 μm and below) integrated circuits. Most of the tool set in use today comes from commercial vendors. Resolution using XRL has been demonstrated at dimensions down to 70 nm or below. Excellent critical dimension (CD) control results have been achieved in simple, single-layer, commercially available resists; for example, a total CD variation of 22 nm (3σ) has been achieved using a mask with a CD variation of 18 nm (3σ). Because of these capabilities, along with the experience and relative maturity of the technology, we believe that XRL is the technology best positioned to succeed optical lithography and be available for timely insertion into manufacturing for 0.13 μm ground rules, as well as to be extendible to 0.10 μm and below. In order to be accepted for manufacturing, however, significant work remains to be done. In particular, new e-beam mask writers and wafer aligners are needed, along with improved mask inspection and repair tools. Mask fabrication processes must also be advanced. The ability to satisfy these needs is not expected to be limited by fundamental physics, but rather is expected to depend on skilled engineering design and implementation. © 1997 American Vacuum Society.