An Easy Method to Measure the Damaged Thickness of Low-k Film after Ash Process

Abstract

A carbon loss of low-k film occurs when O2-contained gas is used for stripping of photo-resist (PR). A modified SiO2-like layer of low-k film after ash process is called as a damaged or modified layer, indicating deterioration of device performance. Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and so on are used for measuring the degree of low-k damage. These analyses, however, have a disadvantage which is difficult to do in-line monitoring, and should have a wafer broken. The key point in this study is that low-k film containing carbon species is not etched by selective SiO2 etching solution. We used wet process such as dilute HF(100:1) and NE14 to remove a damaged layer, that is, SiO2-like layer. Wet- clean method of low-k material after ash process was found to be a powerful and simple method to evaluate the thickness of the damaged layer numerically with small deviation, compared to FTIR, AES and SIMS analyses.