Results are presented for the etching of W and WSix in Cl2 and Cl2/BCl3 plasmas. Etch rates were measured for conditions ranging from 0.1 to 1.0 torr pressure, 30° to 170°C electrode temperature, 0.2 to 1.0 W/cm2 power density, and 3 to 200 sccm flow rate. Etch rates varied from below 10 nm/min to 90 nm/min for tungsten and to 450 nm/min for the silicide. Residence time effects on tungsten etching were also studied. Small additions of BCl3 significantly increased the etch rates of both W and WSix and improved the reproducibility. Results suggest that chemical processes have a significant effect on etch characteristics, despite the low vapor pressure of WCl5 and WCl6 .

Thin films of molybdenum were etched both within and downstream from a Cl2 plasma at 200-mTorr pressure and temperatures below 180 °C. When samples were positioned downstream from the discharge, etching proceeded solely by chemical reaction of the film with chlorine atoms. Without a discharge, molecular chlorine did not etch molybdenum. Downstream and in-discharge etch rates were <20 nm/min and etching by atoms was not observed below 100 °C. The chemical reaction between chlorine atoms and molybdenum was proportional to the gas phase Cl atom mole fraction.

The reactions of atomic and molecular chlorine with tungsten were studied by modulated beam‐mass spectrometric methods over the temperature range 300–1350 K. The atomic beam was generated by an RF plasma discharge. With both atomic and molecular beams, the main reaction product up to about 1000 K was WCl4 . The reaction probability with atomic chlorine was a factor of approximately ten higher than that obtained with molecular chlorine. The reaction was nonlinear with respect to Cl2 intensity at low beam fluxes but approached linearity at high beam intensities. Above 1000 K the main reaction product was atomic chlorine. Its reaction probability increased rapidly with temperature; at 1300 K nearly complete dissociation of Cl2 was observed. A kinetic model based on the Eley‐Rideal mechanism was proposed and compared with the data.

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