title: Improving feature size uniformity from interference lithography systems with non-uniform intensity profiles.
abstract: The non-uniform intensity profile of Gaussian-like laser beams used in interference lithography (IL) leads to a non-uniform dose and feature size distribution across the sample. Previously described methods to improve dose uniformity are reviewed. However, here we examine the behavior of the non-uniformity from the viewpoint of photoresist response rather than the IL system configuration. Samples with a fixed intra-sample dose profile were exposed with an increasing average dose. A line/space pattern with a period of 240 nm across an area of 2 × 2 cm(2) was produced using IL on identical samples using a HeCd laser operated at 325 nm and a Lloyd's mirror IL system. A binary model of photoresist response predicts that the absolute range of line widths in nanometers should be significantly reduced as the overall sample dose is increased. We have experimentally verified a reduction in the range of line widths within a given sample from 50 to 16 nm as the overall dose is increased by only 60%. This resulted in a drop in the narrowest line width from 120 to 65 nm. An etch process is demonstrated to increase the line width by generating a wider secondary chrome hard mask from the narrowly patterned primary chrome hard mask. The subsequent fabrication of a silicon nanoimprint mold is used as a demonstration of the technique.
authors.affiliation: Institute of Nanoengineering and Microsystems, National Tsing-Hua University, No. 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan.
authors.forename: En-Chiang
authors.initials: EC
authors.lastname: Chang
authors.forename: David
authors.initials: D
authors.lastname: Mikolas
authors.forename: Pao-Te
authors.initials: PT
authors.lastname: Lin
authors.forename: Tony
authors.initials: T
authors.lastname: Schenk
authors.forename: Chien-Li
authors.initials: CL
authors.lastname: Wu
authors.forename: Cheng-Kuo
authors.initials: CK
authors.lastname: Sung
authors.forename: Chien-Chung
authors.initials: CC
authors.lastname: Fu