Method to reduce stress from trench structure on SOI wafer.

摘要

In an isolation trench in a silicon-on-insulator wafer, the sidewalls of the trench curve outwardly at the bottom of the trench where the top silicon layer meets the underlying oxide insulating layer. A typical SOI structure is comprised of a semiconductor substrate (10), a silicon-oxide (SiO2) layer 12, and a single crystal silicon layer (14). A suitable masking oxide layer (16) is deposited on the top surface of the silicon layer (14) and a photoresist (30) is formed thereon. The photoresist (30) is developed in the desired trench pattern and an opening for the trench is formed in the oxide mask (16) by means of well-known semiconductor process steps. An isolation trench (20) is formed in the top single crystal silicon layer (14) so that its sidewalls (22), at the bottom of the trench curve outwardly from the center of the trench. Preferably, the top corners (24) of the trench sidewalls are also slightly rounded to further reduce points of stress. After the trench is formed, the photoresist is removed and an oxide layer (31) is grown on the trench sidewalls using a conventional process. The trench is then filled with polysilicon (32) using a conventional chemical vapor deposition process. Finally, the structure is planarized. Optionally a stress relief annealing step is carried out at about 1050 DEG C to 1100 DEG C for about 20 minutes in a forming gas. This sidewall geometry eliminates the sharp corner at the bottom of the trench that are detrimental to device reliability. <IMAGE> <IMAGE>