Cryogenic etching of n-type silicon with p+ doped walls with the TGZM process through the Al/Si eutectic alloy

The dry etching of n-type silicon with p+ doped walls was studied with the cryogenic etching directly after the thermomigration process. The selectivity between n-type silicon and p+ doped silicon was first considered in SF6/O2 plasma. No selectivity was observed between these two zones. Thereafter, the capacity of the Al/Si eutectic alloy covered with a thin film of Al2O3 to play the role of hard mask for the etching was confirmed, always in the case of SF6/O2 plasma. Finally, the etching of 50 μm deep trenches through the Al/Si alloy was performed using three different types of process.