Frequency and electrode shape effects on etch rate uniformity in a dual-frequency capacitive reactor

SiO2 was etched on 300 mm wafers in a dual-frequency capacitive plasma reactor to study etch rate nonuniformity as a function of driving frequency and power. It is shown that the etch rate profile shape varies significantly with the driving frequency. It also is shown that for different driving frequencies, the behavior of etch rate profile shape with the power is quite different, namely: (i) for lower frequency (27 MHz), the shape almost does not change with the power; (ii) for higher frequency (100 MHz), the shape considerably varies with the power. These results clearly indicate that the main reason for the etch rate nonuniformity in high-frequency capacitive reactors is the plasma nonuniformity caused by electromagnetic (standing wave and skin) effects. Using a specially shaped top electrode rather than the traditional flat one is shown to considerably improve the etch rate uniformity.