POLYSILICON-GERMANIUM GATE PATTERNING STUDIES IN A HIGH-DENSITY PLASMA HELICON SOURCE

High density plasma etching processes using halogen based chemistries have been studied for 0.2 mu m polysilicon-germanium gate patterning. Bilayer gate stacks consisting of 80 nm polycrystalline Si on 120 nm p olycrystalline Si1-xGex (x was varied between 0.55 and 1) were grown o n 4.5 nm SiO2 covered 200 mm diameter p-type silicon wafers. The bilay er gates were masked with oxide patterns. The wafers were etched in a low pressure, high density plasma helicon source. Various mixtures, ba sed on Cl-2, HBr, and O-2 gases, have been used to investigate the etc hing of the Si/SiGe bilayer gates. The gas mixture and the plasma oper ating conditions have been optimized to obtain anisotropic etching pro files for features down to 0.2 mu m, and to minimize the gate oxide co nsumption. Real time process control was achieved using HeNe ellipsome try in blanket areas, allowing the SiGe/oxide transition to be easily detected. A two step etching process using a Cl-2/O-2-He mixture was d eveloped. The first step uses a high energy ion bombardment in order t o obtain a high etch rate, and the second step uses a lower ion energy to achieve high SiGe/oxide selectivity. The second step is started 40 nm before reaching the SiGe/SiO2 interface in order to reduce gate ox ide consumption and structural defects formation at the edges of the g ate. (C) 1997 American Vacuum Society.