APPLICATION OF DYNAMIC INSITU ELLIPSOMETRY AND QUADRUPOLE MASS-SPECTROMETRY TO PLASMA-ASSISTED ETCHING - POLYMER FORMATION AND REMOVAL

The application of in-situ ellipsometry and quadrupole mass spectrometry to the monitoring of plasma-assisted etching processes of oxdized silicon wafers is described. Ellipsometry is used to determine, quantitatively, the rates of build-up and removal of surface layers, whilst mass spectrometry provides complementary information about the composition of the plasma. CHF3 was used as the etchant gas, under reactive ion etching (RIE) conditions, at gas pressures in the range 100-200 mtorr. The discharge was maintained at 13.56 MHz at rf powers from 50 to 200 W. Conditions are identified where a transition from silicon dioxide etching to polymer deposition on the wafer occurred. The polymer layers may be removed by a simple change in plasma power, by subjection to an oxygen discharge in the plasma etching configuration, or by argon reactive ion etching. The polymer film is shown to be non-uniform in thickness across the wafer diameter. It is believed that this variation is related to the energy of ions bombarding the substrate. © 1990.