Investigation of surface polymerization on silicon exposed to C4F8 heliconwave plasmas

Polymer layers formed on silicon wafer during silicon oxide overetching usi ng C4F8 helicon wave plasmas and their properties were investigated using s pectroscopic ellipsometry, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry. Thr degree of overetching and d.c. self-bias voltage were varied to investigate the effects on the characteristics of the polym ers remaining on the overetched silicon surface. The increase of bias volta ge from - 80 V to - 120 V increased the CIF ratio and carbon bonds such as C-C, C-CFx, and C-Si in the polymer while reducing the thickness of the pol ymer layer. However, prolongation of the overetch time from 50% to 100% did not change the chemical composition of the polymer layer and the carbon bi nding states in the polymer layer remained the same even though the polymer thickness was increased. The polymer layer formed at the higher d.c. self- bias voltage was more difficult to remove by the subsequent post-etch treat ments compared to that formed at longer overetch time. (C) 1999 Elsevier Sc ience S.A. All rights reserved.