Application of an acousto-optic spectrometer for plasma etching process quality control

Abstract

The solution is proposed to the problem of the relative concentration dynamics control of chemically active particles in the low temperature gas plasma as well as the investigation of their generation and annihilation by means of time-resolved actinometry. A special small-size acousto-optic spectrometer has been constructed capable of spectral resolution of 0.1–0.3 nm in the visible range (430–850 nm) and the maximum time resolution of 2.0 μs. The software package developed allows: 1. (1) measuring of the chronograms of the relative concentrations of various active particles in parallel mode at eight spectral channels; 2. (2) generating impulse plasma modulation and measuring the microdynamics of the generation and annihilation of the active particles in the frame-by-frame mode (1024 points) in four parallel spectral channels, including the two corresponding background values. To shorten the measurement time and to improve the measurement accuracy of the particle annihilation kinetic characteristics in the interval between two stationary (long) pulses, it is proposed to form a series of probing (short) pulses. Some preliminary results are presented of the monitoring of the fluorine radicals (703.7 nm) relative concentration in the SF 6 gas r.f. plasma, containing as an actinometer a small amount (up to 5%) or argon (750.4 nm) at different discharge powers. Using the measurement results of the fluorine radicals, relative concentration in the pulse-modulated noble gas plasma obtained at monosilicon etching, the constants of the radical accumulation, as well as their life time values, are determined for the loaded and unloaded reaction chamber.