Control of Etching Selectivity of Gap to photoresist in ICP

초록

High plasma density by ICP offers an effective technique for GaP etching due to higher ion fluxes, which are 2 orders of magnitude higher than that of RIE system. Etch rates of GaP at source power of 600 W and low dc self-bias of -50V can be controlled between 0.3 um/min in Cl2 + O2 + Ar plasma at 20 mTorr and 6 um/min in Cl2 plasma at 30 mTorr. Etch products of GaP in pure Cl2 plasma are known to be GaClx and PClx. Addition of O2 and Ar reduce the etch rate of GaP because of reduced partial pressure of Cl2 and formation of passivation layer by oxygen. However, the addition of O2 and Ar increase the etch rate of photoresist and decrease the selectivity of GaP to photoresist. O2 reacts easily with organic photoresist and Ar provides physical sputtering effect to both GaP and photoresist etching. In this paper, we study the selectivity of the GaP to photoresist selectivity in ICP by changing source RF power, dc self-bias, gas combination, and chamber pressure. The selectivity can be obtained from 1:1 in Cl2/O2/Ar (27/3/10 sccm) at 20 mTorr) to 60:1 in pure Cl2 at 30 mTorr.