摘要
The forbidden pitch ＂dip＂ in the critical dimension （CD） through the pitch curve is a well-known optical proximity effect. The CD and CD process window near the ＂dip＂,usually found near a pitch range of 1.1 to 1.4 wavelength/ NA （numerical aperture）,is smaller when compared with other pitches. This is caused by inadequate imaging contrast for an unequal line and space grating. Although this effect is relatively well-known, its relationship with typical process condition parameters,such as the effective image blur caused by the photo-acid diffusion during the post exposure bake or the aberration in the imaging lens, has not been systematically studied. In this paper, we will examine the correlation between the image blur and the effect on the CD, including the decrease in the CD value （the depth of the ＂dip＂） and the CD process window. We find that both the decrease in the CD value and the focus latitude near the forbidden pitch correlate very well with the effective Gaussian image blur. Longer effective diffusion length correlates well with a smaller process window and a deeper CD ＂dip＂. We conclude that the dip depth is very sensitive to the change in image contrast.
禁止光学空间周期“Forbidden Pitch”是光学临近效应修正（0PC）中必须要面对并解决的问题之一．它主要出现在1．1～1．4倍（曝光波长／数值孔径）的范围内．由于在此范围内空间图像对比度的削弱，这种效应会导致图形的线宽明显小于其他空间周期．目前业界常用的规避手段主要是通过采集大量的数据校正光学临近效应修正模型，但随着半导体进入深亚微米时代，数据的采集量、置信度越发重要和关键．因此，成功地采用光学临近效应修正技术的关键和前提是建立一套成熟的相关工艺．本文着重研究空间光学和光刻工艺技术的相互关系．我们发现在禁止光学空间周期附近的光学表现与有效高斯模糊息息相关．较长的有效光酸扩散长度将显著地消弱光刻表现，进而影响禁止光学空间周期的图形表现．
基金
上海市科委国际合作资助项目(批准号:075007033)~~
