ABSTRACT
Higher resolution demands for semiconductor lithography may be fulfilled by higher numerical aperture (NA) systems. However, NAs more than the photoresist refractive index (~1.7) cause surface confinement of the image. In this paper we describe how evanescent wave coupling to effective gain medium surface states beneath the imaging layer can counter this problem. We experimentally demonstrate this at λ = 405 nm using hafnium oxide on SiO2 to enhance the image depth of a 55-nm line and space pattern (numerical aperture of 1.824) from less than 40 nm to more than 90 nm. We provide a design example at λ = 193 nm, where a layer of sapphire on SiO2 counters image decay by an effective-gain-medium resonance phenomena allowing evanescent interferometric lithography to create high aspect ratio structures at NAs of 1.85 (26-nm resolution) and beyond.
ABSTRACT
Numerical methods of generating rough edges, surfaces, and volumes for subsequent simulations are commonly employed, but result in data with a variance that is downward biased from the desired value. Thus, it is highly desirable to quantify and to minimize this bias. Here, the degree of bias is determined through analytical derivations and numerical simulations as a function of the correlation length and the roughness exponent of several model power spectral density functions. The bias can be minimized by proper choice of grid size for a fixed number of data points, and this optimum grid size scales as the correlation length. The common approach of using a fixed grid size for such simulations leads to varying amounts of bias, which can easily be confounded with the physical effects being investigated.
