Analysis of laser damage and gettering effect induced by laser boron doping

Abstract

In the present work, laser damage on laser boron doped silicon wafers is studied. Direct evidences of two different laser damages are observed with SEM/STEM: pores appearing in the surface and dislocations in the bulk. Statistical pore size distributions illustrate a downtrend of pore size with laser scan speed increasing. The crystallinity of wafer surface before and after laser doping is also characterized and analyzed by using Raman spectroscopy together with the volume fraction of crystalline Xc. The broadened and fitted Raman bands as well as Xc values present consistent evidence of amorphous silicon introduced in the wafer surface after laser doping. Gettering effect induced by laser doping is studied by taking iron concentration as standard. The highest gettering efficiency (~ 99.5%) is achieved at the middle laser scan speed (4 m/s), which most likely results from the joint effect of segregation coefficient and segregation time. Finally, the influence of laser doping on minority carrier lifetime is discussed with respect to a comprehensive consequence affected by laser damage, boron concentration and iron concentration.