A Comparison of Internal Gettering during Bipolar, CMOS, and CCD (High, Medium, Low Temperature) Processes

Abstract

Internal gettering during typical bipolar, CMOS, and CCD processes is compared. A direct comparison is rather difficult since these three processes involve different processing temperatures, contamination levels, and sensitivities to warpage. Also, the sensitivity of device performance to crystallographic defects is significantly different in CMOS, bipolar, and CCD circuits. Therefore our comparison is carried out on a relative basis with an emphasis on the optimum levels of precipitated oxygen, precipitate distribution and morphology, and precipitation kinetics which provide the best gettering action. In order to successfully use internal gettering to improve the yield of bipolar, CMOS, CCD circuits it is necessary to optimize these parameters on an individual basis for each processing line and circuit type. Any attempt to increase the amount of precipitated oxygen above the optimum amount resulted in yield reduction. The yield reduction was caused by: changes in defect morphology (from optimum for gettering), increases in amount of residual surface defects, and reduction of mechanical strength of silicon (generation of edge dislocations, warpage).