BUILDING ON THE PAST, READY FOR THE FUTURE: - MEMC

In external gettering, a fine-grain layer of
polysilicon is grown on the backside of the wafer to
draw impurities away from the critical regions of
the wafer where devices are built. Wafers with this
backside EG layer yield better and are less sensitive
to process upsets that might ordinarily degrade or
destroy devices. Monsanto (MEMC) was the first
wafer manufacturer to offer external gettering, a
process developed under the lead of Dr. Dale Hill.
By the late 1980s, almost 50 percent of all wafers
made by Monsanto had the polysilicon gettering
layer applied to them.
Another external gettering process adopted by
MEMC was called custom-designed gettering
or CDG. Sandblasting of the wafer backside can
create damage points at the back surface. These
damage points would also effectively trap metallic
impurities. By changing the sandblasting conditions
A product brochure describing the benefits of
granular polysilicon as produced at the MEMC
Pasadena plant.
MEMC 300mm wafer.
to control the density of damage points, a wide
range of damage levels could be created in order to
provide the correct gettering effect to optimize the
customer’s device yields.
MEMC’s process of internal gettering is featured in
the November 2003 issue of Solid State Technology.
Great Strides in Technology 41