Highly Selective Removal of Residual Deposited Films and Oxide Hard Masks on Polysilicon Gate Electrodes in Anhydrous HF Gases

Abstract

This paper presents new vapor-phase HF processes, developed for highly selective removal of residual deposited films of etch by-products and oxide hard masks, following polysilicon gate etching. Etching of thin gate oxides in anhydrous HF gases, after exposure to an HBr/O2 plasma in the gate etch process, was investigated by X-ray photoelectron spectroscopy and transmission electron microscopy. During exposure to an HBr/O2 plasma, a SiBrxOy layer was formed at the near-surface region of the gate oxide. The delay or incubation time to start etching in HF gases was different between the SiBrxOy and underlying undamaged SiO2 layers. Moreover, the etch rates of SiBrxOy and chemical-vapor-deposition oxides used as a mask material were much higher than that of SiO2. By utilizing these differences in incubation time and etch rate, sidewall deposition films and oxide masks on poly-Si gate electrodes were completely removed without side etching or notching of thin gate oxides.