Naoki Wakabayashi

PN Junction Formation for High-Performance Insulated Gate Bipolar Transistors (IGBT); Double-Pulsed Green Laser Annealing Technique

In order to form the deep PN junction demanded for the next generation IGBTs, the double-pulsed laser annealing technique as the low-thermal budget heat treatment has been introduced to activate a B-implant layer and a P-implant layer within the wafer surface to the depth 2μm. The double-pulsed laser annealing is characterized by the deep penetration depth due to a green wavelength of DPSS lasers and precisely and widely controlling of the annealing temperature and time. In the IGBTs structure the deep PN junction at a collector (the rear face) should be formed without damaging thermally circuit elements made of low melting point materials at a gate and an emitter (the front face). Ion-implant samples using eight-inch (100) Si wafers were prepared as follows: Boron (B) implant was performed at a dose of 1E+15/cm 2 at an energy of 40keV and/or phosphorus (P) implant at 1E+13/cm 2 at an energy of 400keV. The double-pulsed laser irradiation was carried out at the constant first and second pulse energy density E1=E2=1.8J/cm 2 at the delay time td= 0-500ns and the overlap ratio OR=67-90%. The melt depth was up to about 0.3μm. The electrical activation ratio of the B-implant layer within the depth of about 0.6μm was improved from 91% to about 100% with the delay time increase of 0ns to 500ns. The activation ratio of the P-implant layer within the depth of about 2μm was drastically improved from 48% to 82% with the same delay time increase and the carriers in the P-implant layer were distributed deeply from the depth 1.1μm to 1.8μm. Furthermore, with the overlap ratio increase of 67% to 90% the carriers in the P-implant layer were distributed deeply from the depth 1.8μm to 1.9μm and the high activation ratio of 82% was maintained. The high ratio of electrical activation is supported by the defect-free epitaxial regrowth where the majority of the B dopants was diffused in the liquid phase and that of the P dopants in the solid phase.