Microgap x-ray nanolithography

Abstract

At linewidths of 0.1μm and below, the time required to expose large-area patterns (∼1cm 2) by electron-beam lithography becomes impractically long. Thus, there is a critical need for reliable replication techniques in this linewidth domain. Replication of features as fine as 18nm by x-ray lithography has been demonstrated. However, all sub-0.2μm-linewidth x-ray lithography to date has been done in intimate contact using polyimide-membrane masks. Polyimide is subject to distortion, and contact can cause mask damage. For these reasons we have investigated x-ray nanolithography with inorganic membranes, and mask-sample gaps of ∼4μm. We discuss the resolution-limiting factors of penumbra, diffraction, and photo-electron range, and consider the tradeoffs of gap and wavelength that need to be made to achieve high resolution. With a Cu L source (λ=1.3nm), a linewidth of 0.1μm requires a gap of ∼4μm. We have used stress-controlled SiON 0.5 membranes of 6cm 2 area attached to a narrow rim etched into a Si substrate. The gap was set by small spaces studs. Gaps of 4–6μm were achieved with uniformities of ∼0.5μm. They were measured using an angular fringe counting technique. Microgap nanolithography was used to replicate 100nm lines with the Cu L x-ray. High aspect-ratio PMMA structures were achieved with steep sidewalls, suggesting that 50nm lines could be faithfully printed with the microgap technique.