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

摘要

In order to form the deep PN junctions 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 of 2um. The double-pulsed laser annealing is characterized by the deep penetration depth due to a green wavelength of DPSS lasers and by precisely and widely controlling the annealing temperature and time. In the IGBT's structure the deep PN junction at a collector (the rear face) should be formed without thermally damaging 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 level of 40keV; and/or phosphorus (P) implant at 1E+13/cm~2 at an energy level of 400keV. The double-pulsed laser irradiation was carried out at the constant first and second pulse energy density of E_1=E_2=1.8J/cm~2 at the delay time of t_d= 0-500ns and the overlap ratio of 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 of 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 of 1.8um to 1.9μm and the high activation ratio of 82% was maintained. The high ratio of electrical activation is supported by the defect-free two-step crystallization process where the majority of the B dopants were annealed in the liquid phase and that of the P dopants in the solid phase.