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.

[1]  A. Heuberger,et al.  Resolution limits in x‐ray lithography calculated by means of x‐ray lithography simulator XMAS , 1986 .

[2]  Henry I. Smith,et al.  Fabrication of sub‐100‐nm linewidth periodic structures for study of quantum effects from interference and confinement in Si inversion layers , 1986 .

[3]  Henry I. Smith,et al.  Fabrication of x‐ray masks using anisotropic etching of (110) Si and shadowing techniques , 1981 .

[4]  Henry I. Smith,et al.  Spatial period division—A new technique for exposing submicrometer‐linewidth periodic and quasiperiodic patterns , 1979 .

[5]  Dimitri A. Antoniadis,et al.  X-ray lithography for sub-100-nm-channel-length transistors using masks fabricated with conventional photolithography, anisotropic etching, and oblique shadowing , 1985 .

[6]  Dale C. Flanders,et al.  Replication of 175‐Å lines and spaces in polymethylmethacrylate using x‐ray lithography , 1980 .

[7]  Henry I. Smith.  A statistical analysis of ultraviolet, x-ray, and charged-particle lithographies , 1986 .

[8]  T. J. Tanaka,et al.  Low-energy x-ray interaction coefficients: Photoabsorption, scattering, and reflection: E = 100–2000 eV Z = 1–94☆ , 1982 .

[9]  K. Suzuki,et al.  High flatness mask for step and repeat x‐ray lithography , 1986 .

[10]  R. Azzam,et al.  Ellipsometry and polarized light , 1977 .

[11]  Henry I. Smith,et al.  Gold transmission gratings with submicrometer periods and thicknesses ≳0.5 μm , 1981 .