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.
SEH has the epi experience to produce very low defect densities in an epi layer. Stacking faults and other epi defects are minimized through effective substrate cleaning and effective reactor defect controls. Sensitive laser scattering inspection equipment is used to guarantee the surface quality of epi layers, complemented by visual inspection techniques.
SEH has several approaches to effective gettering for image sensor devices;
- P/P+ or N/N+
- P/P- on N/N- with enhanced gettering
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.
SEH also can provide analytical techniques to determine what metallic impurities and process defects are increasing dark current levels. From this analysis, we can recommend the most effective silicon substrate solution.