Analysis of the etching of silicon in an inductively coupled chlorine plasma using laser thermal desorption

Abstract

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, and optical emission actinometry and Langmuir probe analysis were used to characterize the plasma. The ICP operated in the dim mode for radio frequency (rf) powers ≲ 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× 1011/cm3, the electron temperature was 2.8 eV, and about 90% of the Cl2 was dissociated. The chlorine surface coverage in the dim and bright modes was ∼2.0× that with chlorine flow and the plasma off, and increased slowly with power. This coverage ratio monotonically increased from ∼1.6× to 2.5× that with the plasma off as the ion energy was increased from 16 to 116 eV by increasing the rf substrate bias voltage during bright mode operation. Since roughly equivalent adlayer chlorine contents were measured by LD-LIF under high ion current/fast etch conditions (ICP bright mode), and low ion current/slow etch conditions [ICP dim mode and reactive ion etching mode (substrate stage powered and no ICP power)], both the adlayer chlorine content and the etch rate seem be controlled by the ion current to the wafer.