REDUCTION IN MICROLOADING BY HIGH-GAS-FLOW-RATE ELECTRON-CYCLOTRON-RESONANCE PLASMA-ETCHING

High-gas-flow rate electron cyclotron resonance plasma etching was employed to reduce microloading in Si etching with Cl-2 at low pressure. Microloading estimated with a conventional etching system increases with decrease in pressure from 5 to 0.5 mTorr. The increase in microloading is attributed to the increase in the ratio of ion flux to reacting neutrals. The ion/neutral ratio was found to be as large as 6.4 at 0.5 m Torr. This large ratio was caused by both the decrease in reacting neutral density and the increase in reaction products. The high gas flow rate with a high effective pumping speed of 2000 l/s reduces the reaction products, increases the reacting neutrals and reduces the ion/neutral ratio to 0.65. As the result, the microloading is reduced. The relative etch rate at an aspect ratio of 7 increases from 0.65 at 136 l/s to 1.00 at 2000 l/s. Thus high-gas-flow-rate-etching solved the problem of large microloading which is not suppressed even with high density plasma and low gas pressure.