Silicon Surface Treatment of Contact Hole in Memory Devices by Downstream Fluorine-based Plasma

초록

Silicon surface of contact holes was treated by CF4 based plasma using downstream type ICP source. Silicon etch rate and uniformity were measured on 300 mm wafers as a function of process parameters. The etch selectivity of silicon to silicon nitride, which is Self Aligned Contact (SAC) barrier material, was also studied. The etch uniformity on wafer can be changed from center high to edge high under the high gas flow rage. In order to improve the etch uniformity, He gas is added for a roll of carrier gas, the etch uniformity can be achieved over wide range of Si etch rate by adjusting CF4/O2/He gas mixture ratio, which can be optimized by controlling total gas flow. Also, the best etch selectivity and uniformities are obtained under high gas flow rate condition and that etch selectivity of more than 7:1, Si to Si3N4.