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Graduate Student Seminar - 11/18/2011

"He Plasma Pretreatments of Organic Masking Materials for Performance Improvements during Plasma Pattern Transfer"

by Dominik Metzler

Friday, November 18, 2011 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor Gottlieb Oehrlein

Plasma-based pretreatments (PPT) of organic masking materials have been shown to offer significant potential for reduction of surface, line edge, and line width roughness during the subsequent pattern transfer process. Since one of the underlying mechanisms of roughness formation has been reported to be a synergistic effect of energetic ion bombardment, ultraviolet (UV) / vacuum ultraviolet (VUV) plasma radiation and increased temperature, a possible mechanism of organic mask curing may be the elimination of the above synergism by sequential exposures to VUV plasma radiation followed by ion bombardment-dominated plasma etching. To examine this question and establish the impact of pretreatments on roughness introduction, etch resistance, and pattern transfer fidelity during the subsequent pattern transfer process, we have studied pretreatments of 193nm PR and several other organic masking materials in Ar and He discharges with pronounced UV/VUV emission. The impact of pretreatments and subsequent pattern transfer processes on the organic materials were monitored in real-time by in situ ellipsometry. Modeling of these data allows for precise determination of optical material density and film thickness of various layers, i.e., the surface layer densified by ion bombardment, the UV/VUV modified layer in the material bulk, and the rough surface layer. Additionally, post plasma characterization by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) provides information on bulk material modifications and surface roughness improvements, respectively. Pretreatments in a He discharge successfully reduced roughness introduction in a C4F8/Ar pattern transfer process by ~50% (RMS = 4nm) while increasing film etch resistance by ~30% leading to only a slight increase in the total material removal (PPT + pattern transfer) when compared to the uncured material (pattern transfer only). Time-resolved studies of this process allow detailed investigation of distinct stages and underlying mechanisms of materials modification, such as radiation-induced changes in the material's bulk, ion crust formation at the film surface, and surface roughness development. Correlating these observations with post plasma characterization by AFM and FTIR allows for a mechanistic understanding the plasma-based pretreatments or organic materials and their impact on the subsequent pattern transfer process. The dependence of improvements in masking performance on He plasma-based pretreatments and a description of the underlying mechanisms will be presented.

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