Feedback Control System of Wafer Temperature for Advanced Plasma Processing and its Application to Organic Film Etching

A wafer temperature feedback control system during plasma processing with rapid, precise, and real-time temperature monitoring employing frequency-domain low-coherence interferometry was developed. To keep the temperature within a specific range, plasma was actively switched on and off, controlled by signals from a monitoring system. It was applied to an organic film etching process with an H2 and N2 mixture gas plasma. The organic material etching yield from atomic hydrogen has a relatively high sensitivity to temperature, and a constant temperature is required to achieve precise etching profiles. This system maintained the wafer temperature within a few degrees for H2/N2 plasma discharges. Duty ratios per discharge gradually decreased because the temperature of the chamber component parts around the wafer increased. The trench width etched in the organic film increased with increasing wafer temperature. This is because of a temperature dependence balance between the etching reaction and protection film formation on the trench sidewall.