Silicon Bipolar Transistors Fabricated Using Ion Implantation and Laser Annealing
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SILICON BIPOLAR TRANSISTORS FABRICATED USING ION IMPLANTATION AND LASER ANNEALING NOBUYOSHI NATSUAKI, TAKAO MIYAZAKI, MAKOTO OHKURA, TORU NAKAMURA, MASAO TAMURA AND TAKASHI TOKUYAMA Central Research Laboratory, Hitachi Ltd.,Kokubunji, Tokyo 185, Japan ABSTRACT Bipolar transistors with laser annealed base and emitter, as well as those with furnace annealed base and laser annealed emitter, have been successfully fabricated using Q-switched ruby laser pulse irradiation. The performance of laser asannealed transistors is rather poor. However, it can be improved, to some extent, by relatively low temperature furnace annealing after laser irradiation. DC and RF characteristics of laser annealed transistors are presented in conjunction with laser irradiation effects on the characteristics of conventionally fabricated transistors. INTRODUCTION Laser annealing is one of the most recent developments in material modification for device fabrication. This annealing technique, if combined with ion implantation, offers the following promising features for designing and fabricating high speed bipolar devices with shallow junctions, although there still remain potential difficulties [1,2,3] to be solved. The technique makes it possible to realize spatially well localized, heavily doped layers while keeping macroscopically extended residual defects much below the level obtained by furnace annealing. Furthermore, lack of solid phase diffusion of conventional dopants in the extremely short annealing time provides flat npn or pnp double junction structures without the so-called emitter pushout or suck-in effects. This is because complicated diffusional interactions between dopants, mainly through lattice defect mediation, can hardly occur. These features hold in both cw and pulse mode laser annealing. The present authors have reported that extended-defect free layers with very high carrier concentration can be obtained by the pulsed laser annealing of P, As and B implanted layers [4]. They have also pointed out the possibility of making flat npn structures by the single laser pulse annealing of both P and B double implanted layers [5]. In this paper, the electrical characteristics of pulsedlaser annealed bipolar transistors, including fully laser annealed transistors with npn structures formed by a single pulse annealing of double implanted layers, are presented. In addition, the effect of low temperature heat treatment after laser annealing is emphasized to improve the performance of transistors degraded by laser irradiation, taking into consideration the rather poor performance of laser annealed bipolar transistors reported so far [6]. FULLY LASER ANNEALED TRANSISTORS Double junction formation. In pulsed laser annealing, doped impurities are known to redistribute through the liquid phase diffusion mechanism within a laser irradiation induced molten layer. This impurity redistribution, even when two kinds of impurities are simultaneously doped, can be estimated by a simple calculation that assumes the in
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