Abstract

Sub-quarter-micron features have been produced in a number of organic resists using soft-x-ray projection lithography (SXPL) at 14 nm, including a demonstration of 0.05 um lines and spaces in poly (methylmethacrylate) (PMMA).¹ Unfortunately, the opacity of conventional resists in the soft-x-ray region requires that the resist thickness be reduced to less than 200 nm;² in practice, 70 nm thick layers are often used. Such thin layers lead to several problems. First, spincoating pinhole-free layers becomes increasingly difficult at thicknesses below 100 nm. Second, the etch resistance of thin organic layers may not be sufficient for subsequent pattern transfer operations. Third, they are too thin to function as planarizing layers over preexisting substrate topography. One solution has been to use a trilevel resist composed of a thin top PMMA imaging layer, an intermediate layer of germanium for etch resistance, and a thick hardbaked photoresist for planarization. While the trilevel approach has been successfully demonstrated for producing high resolution features with SXPL at 14 nm,³ the complexity of this process makes it problematic for rapid acceptance in a production environment. An alternative approach, which circumvents the resist opacity issue, involves the use of so-called surfaceimaging resists.⁴ In a surface imaging resist, radiation-induced changes in a thin imaging layer lead to conversion of the exposed region to an etch resistant material.

© 1993 Optical Society of America