Structural and Electrical Properties of Gas Immersion Laser Doped Layers in Crystalline Silicon
- PDF / 304,822 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 105 Downloads / 171 Views
STRUCTURAL AND ELECTRICAL PROPERTIES OF GAS IMMERSION LASER DOPED LAYERS IN CRYSTALLINE SILICON
T.W. SIGMON*, P.G. CAREY*, R.L. PRESS**, T.S. FAHLEN ** and R.J. PRESSLEY" *Stanford Electronics Laboratories, Stanford, CA 94305, **XMR, Inc. Santa Clara, CA 95051
ABSTRACT 4
He backscattering and channeling and 4-point probe resistivity measurements are used to characterize the doping of Si directly from the gas phase by using a laser inprocess. Impurity concentraduced melt/recrystallization 3 9 and sheet resistivities as tions from 3x101 to 5x1020 cmlow as 20 0/0 are obtained by variation of the laser energy Diodes fabricated by this density or number of passes. process exhibit near ideal I-V characteristics with sharp Anreverse breakdowns determined by junction edge effects. 0 nealing at 850 C further reduces the generation-recombination centers to values that result in an ideality factor of 1.0.
INTRODUCTION In the past several years pulsed lasers have been used to anneal damage caused by ion implantation of dopant impurities in technologically relevant Apart from the desire to develop a detailed materials such as silicon [1]. understanding of the melt/recrystallization process occurring on a nanosecond time scale, unique properties of these layers useful in semiconductor As a result device fabrication are of interest for commercial exploitation. of this intense research effort, a detailed understanding of the melt/ crystal growth dynamics, including impurity segregation, has emerged [2,3]. Although fabrication of devices in silicon using lasers has been demonstrated, [4] wide scale commercial applications have not yet occurred. This is most likely due to there being no clear cut performance or cost advantages for the ion implant laser anneal process over conventional ones. However, with the advent of very large scale integration more restrictive requirements are placed on the heavily doped junctions used for sourceRecent experiments drain contacts in metal-oxide-semiconductor devices. have indicated difficulty in obtaining high concentration shallow junctions For instance, the channeling tails occurring via the ion implant process. from low energy boron implants are so severe that a Si preamorphizing implant must be performed before the boron implant further complicating the process [5]. In this paper we describe the results of a process utilizing direct step doping of silicon from the gas phase by a melt/recrystallization As will be seen, both high impurity coninitiated by a pulsed laser. centrations and shallow junctions are a compatible result of this approach. EXPERIMENTAL Silicon crystals of orientation and n or p type resistivities of 1-10 0-cm are doped with either As, P or B by immersion of the wafer in a The doping process occurs gas cell filled with the appropriate ambient [6]. when the samples are irradiated with a laser pulse of sufficient energy to In the system depicted cause the near surface region of the silicon to melt. in Fig. 1, the beam from a Q-switched alexandrite laser (X = 745 nm) is
Ma
Data Loading...
