352 Crystal Growth and Evaluation of Silicon for VLSI and ULSI
the crystal can be precipitated as SiO
x
clusters that act as trapping sites for impurities. This
process is called internal gettering, and is one of the most effective means to remove unin-
tentional impurities from the near-surface region where devices are fabricated. In addition
to the intrinsic gettering, other treatments can be applied before or during device fabrica-
tion to remove defects and unwanted metallic impurities from regions where devices are
fabricated. Gettering can be achieved by intentionally damaging the back of the silicon
wafer and then subjecting it to high-temperature annealing treatments. Again, the dam-
aged region in the wafer acts as a sink for unwanted ...