Sources and scaling laws for LER and LWR

Abstract

LER (line edge roughness) is becoming increasingly critical for manufacturers and efforts to understand and control it have given disappointing results. We propose that LER is due to a combination of coherent optical effects, mask LER, and chemical processes during exposure, PEB (post exposure bake) and development. Different sources of LER have similar scaling laws and PSD (Power spectral density) distribution, and the causes of LER are easily misidentified. High sensitivity, thin resist, and low image log-slope generally give more LER. No single-effect model is going to be adequate to give quantitative predictive guidance how to reduce LER. Since LER is shared between chemistry, optics and metrology, a cross-disciplinary model is needed. We propose such an LER budget model with a unified analysis of the metrology and consequences of LER, but with models for source effects plugged in by experts from the relevant domains.

Mitigating mask roughness via pupil filtering

“…It can originate from a myriad of factors such as the photon or chemical shot noise, molecular stacking, development process, and low image contrast [1,[13][14][15][16][17][18][19][20][21]. Recently, mask roughness gained significant attention as one of the contributors to the wafer LER [2-9, 22, 23].…”

“…It can originate from the aerial image or the photoresist chemistry/processing [1]. The latter remains to be the dominant group in ArF and KrF lithography; however, the roughness originating from the mask transferred to the aerial image is gaining more attention [2-9], especially for the imaging conditions with large mask error enhancement factor (MEEF) values.…”