SEH offers several epi products suitable
for image sensor manufacture. Image sensors are most commonly
manufactured on epi wafers. CMOS and CCD image sensors have in
common two requirements important in the selection of a silicon
starting material. First, the surface quality must be very high,
with few defects which might impair the function of one of more
pixels. Second, the dark current must be low for good signal to
noise performance, and this means that metallic impurities
responsible for forming recombination centers must be very low
in the surface region. The silicon wafer is selected to
effectively getter these metallic impurities.
Heavily doped p-type substrates provide
effective gettering for Fe, Cu, and Ni impurities. Several proprietary
gettering enhancement techniques for P/P- and N/N- wafers are also
available, utilizing nitrogen doping and additional thermal treatments
to enhance oxygen precipitation.