Fabrication of Phase Masks by Immersion Interference Lithography and Study of Bottom Antireflective Coating Layers for Optical Lithography
Date Issued
2004
Date
2004
Author(s)
Cheng, Wei-Chung
DOI
en-US
Abstract
In this thesis, our study contains three parts. The first part is the study of utilizing hexamethyldisiloxane (HMDSO) film as the bottom antireflective coating (BARC) layer for deep ultraviolet (DUV) and vacuum ultraviolet (VUV) lithographies. We report a novel tri-layer bottom antireflective coating (BARC) design based on hexamethyldisiloxane (HMDSO) films working simultaneously at 157, 193 and 248nm wavelengths and a single-layer BARC film working in water at 193 nm wavelength. The required optical constant for each layer can be tuned by varying the gas flow rate ratio of oxygen to HMDSO in an electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) process The swing effect in the resist is experimentally shown to be reduced significantly by adding this BARC structure.
A novel method for producing durable fused silica self-interference phase mask is described in the second part. The grating pattern is formed into I line positive photoresist (EPG510, Everlight) by 351 nm Ar+ laser interference lithography exposure and is transferred to a thin chromium layer via wet etching solution CR7, then reactive ion etching in CHF3/O2 plasma is used to etch the fused silica substrate. For phase masks working in 248 nm wavelength can be generated by using interferometric lithography. The optimized fabrication process allows phase mask of sub-micron period, centimeter long, with the zero-order intensity suppressed down to 8%. For the demonstration of its practicality, one optimized phase mask with 1.08 μm period and 5% zero-order diffraction efficiency is shown capable of fabricating fiber Bragg gratings with 7 dB transmission loss at 1.563 μm wavelength. Furthermore, another 0.44 μm period phase mask is used to produce a photoresist pattern with halved period. For phase masks working in 157 nm wavelength can be made from modified fused silica with 180 nm period by using immersion interference photolithography. The fabrication process of the phase mask is optimized to generate the largest intensity ratio of diffracted ±1-order to zero-order. The phase mask is demonstrated to produce a photoresist pattern with halved period (90 nm) when illuminated with a laser of 157 nm wavelength. The phase masks are also capable of generating two-dimensional patterns of holes and dots and serving as molds for imprint applications. The third part of this thesis is the study of the bubble effect for 193 nm wavelength immersion interference lithography.
Subjects
浸濕干涉微影
次微米光柵製作
底部抗反射層
BARC
sub-micron grating fabrication
immersion lithography
Type
thesis