SIDEWALL PASSIVATION DURING THE ETCHING OF POLY-SI IN AN ELECTRON-CYCLOTRON-RESONANCE PLASMA OF HBR

The etching of poly-Si (n + and undoped) in a radio-frequency-biased e lectron cyclotron resonance plasma of HBr was studied. Etch rates of S i, oxide, and photoresist were obtained by ellipsometry as a function of the bias voltage and two substrate temperatures (15 and 50-degrees- C) at 5 mTorr pressure. The etch rate of poly-Si depends on the doping level, with n + Si etching faster than intrinsic Si. High selectiviti es of Si over both oxide and photoresist can be achieved at low bias v oltages. Using angle-resolved x-ray photoelectron spectroscopy, it is shown that a carbon and bromine containing layer is deposited on the s idewall of the poly-Si during the etching process when a photoresist p atterned wafer is used. The thickness of the sidewall film decreases w ith increasing substrate temperature and increases at the bias voltage is raised. The thickness of this sidewall film influences the anisotr opy of the process, with some undercutting occurring at high temperatu re and low bias voltage.