Optimizing silicon processing for in-line monitoring of metal contamination
The influence of thermal drive-in and oxidation conditions on minority carrier diffusion length, surface lifetime and density of states at the Si/SiO2 interface is evaluated. The following is found. (a) Wafer-to-wafer variation of crystal-defect concentration leads to a large spread of diffusion length values if furnace anneal is used to drive in metals from the wafer surface into the bulk. The spread is reduced if rapid thermal processing is used instead. (b) Poor Si/SiO2 interface quality (i.e. high density of interface states and low minority carrier surface recombination lifetime) is measured if oxygen contamination during ramp-down is not controlled or test wafers are not protected by dummy wafers during oxidation. The consequences of these results for in-line monitoring of metal contamination and furnace integrity are discussed.