ANALYSIS OF THE ETCHING OF SILICON IN AN INDUCTIVELY-COUPLED CHLORINEPLASMA USING LASER THERMAL-DESORPTION

The etching of silicon by a chlorine inductively coupled plasma (ICP) was studied using laser desorption laser-induced fluorescence (LD-LIF) analysis to determine the surface coverage of chlorine during steady- state etching. Laser interferometry was used to measure etch rates, an d optical emission actinometry and Langmuir probe analysis were used t o characterize the plasma. The ICP operated in the dim mode for radio frequency (rf) powers less than or similar to 350 W and in the bright mode for higher powers. Under typical operating conditions in the ICP bright mode, the ion density was about 4 X 10(11)/cm(3), the electron temperature was 2.8 eV, and about 90% of the Cl-2 was dissociated. The chlorine surface coverage in the dim and bright modes was similar to 2.0X that with chlorine flow and the plasma off, and increased slowly with power. This coverage ratio monotonically increased from similar t o 1.6X to 2.5X that with the plasma off as the ion energy was increase d from 16 to 116 eV by increasing the rf substrate bias voltage during bright mode operation. Since roughly equivalent adlayer chlorine cont ents were measured by LD-LIF under high ion current/fast etch conditio ns (ICP bright mode), and low ion current/slow etch conditions [ICP di m mode and reactive ion etching mode (substrate stage powered and no I CP power)], both the adlayer chlorine content and the etch rate seem b e controlled by the ion current to the wafer. (C) 1997 American Vacuum Society. [S0734-2101(97)01806-X].