LANGMUIR PROBE MEASUREMENTS AND CHARACTERIZATION OF SILICON ETCHING IN SF6/O2 DISCHARGES

The reactive ion etching of silicon in SF6/O2 mixtures is investigated experimentally. Electrical measurements, using a Langmuir probe, provide the plasma density of the discharge, for various settings of pressure and oxygen percentage. The plasma density ranges between 4 x 10(9) and 1.2 x 10(10) cm-3. Information on the chemical composition of the discharge is obtained using a mass spectrometer. The lower electrode self-bias voltage ranges between 0 and 590 V and the etching rate between 100 and 17,000 angstrom/min. The variation of the relative contribution of chemical etching and ion bombardment to the overall etching rate is demonstrated, as the process parameters are changed. Etching uniformity is also studied and the etching rate is found to be higher near the edge of the electrode.