EXCIMER-LASER CLEANING OF SILICON-WAFER BACKSIDE METALLIC PARTICLES

An excimer laser cleaning system operating at 248 nm was developed to remove micrometer-sized metallic particles from the backside of silico n wafers. Deliberate iron contamination has been performed using iron- oxide particles having a diameter of 0.5-2 mu m. The surface photovolt age (SPV) method was used to characterize the cleaning efficiency thro ugh the change in diffusion length and iron concentration in the silic on bulk. Following a rapid thermal annealing at 1050 degrees C for 4 m in, the SPV measures diffusion lengths down to 40 mu m for the iron-co ntaminated wafer, corresponding to an iron concentration up to 1.55X10 (13) cm(-3). The minimum diffusion length increases to 130 mu m after two steam laser cleanings done at a laser fluence below the silicon th reshold damage of 200 mJ/cm(2). The iron concentration measured in the bulk of the iron-contaminated wafers is reduced by more than 91%, to a concentration of 1.4X10(12) cm(-3). (C) 1998 American Vacuum Society .