Backside activation of power device IGBTs by microsecond-pulsed green laser annealing thermally assisted with CW diode laser

The earlier long-pulsed green laser annealing system had the big issue: a deep n-type layer, namely, a field stop (FS) layer in IGBT's structure was not sufficiently activated when thick wafers with large heat capacity were used. In order to cope with the big issue, we developed the thermal assist type annealing system in which a long-pulsed green laser (λ:515nm) was combined with a near infrared CW diode laser (λ:808nm). Advantages of the new annealing system are as follows: (1) The simultaneous activation of the B and P implant layers without interdiffusion of B and P dopants. (2) The deep activation of the P implant layer over a depth of 2um, applicable to changes in the wafer thickness of 100um to 525um. (3) The low thermal budget annealing to suppress the thermal damage caused by the temperature rise on the opposite side when the thin wafer is annealed. The newly developed laser annealing system can adapt more flexibly to the backside annealing for a wide variety of IGBT's applications.