Radiative lifetime and collisional quenching of carbon monochloride (A 2Δ) in an alternating current glow discharge

Abstract

Glow discharges are widely employed in semiconductor processing but are relatively poorly understood owing to, in part, a lack of reliable, quantitative diagnostics. Laser‐induced fluorescence promises to be a useful in situ, nonintrusive probe for species concentrations and gas‐phase temperatures, but requires the determination of fluoresence yields (i.e., radiative vs nonradiative decay rates) as a function of the plasma state and molecular rotational quantum number. In this work, carbon tetrachloride plasmas, which are used in the dry etching of such materials as Al, Si, GaAs, and InP, are examined using the laser‐induced fluorescence technique. The quantum yield φ of CCl A ²Δ→X ²Π fluorescence is determined as a function of pressure, flow‐rate, power, electrode temperature, and feedstock composition. Total pressure and addition of Cl₂ to the feedstock are found to be most important in reducing the quantum yield; other plasma parameters and addition of O₂, He, Ar, or N₂ are found to be of secondary importance. The radiative lifetime of carbon monochloride CCl, A²Δ (v=0) is found to be 105±3 ns and to be independent of rotational quantum number up to J=45.5. The weak dependence of CCl laser‐induced fluorescence on most plasma variables makes it nearly ideal as a simple, direct, and quantitative temperature and concentration diagnostic.