Phosphorous Gettering by Rapid Thermal Processing
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PHOSH
GErIERflE BY RAPID THEL PROSCSSIM
BXJCHAIB HARTITI, ABDEEIIAH SLA=UI, JEAN-CLAUDE MULLER and PAUL SIFFERT Centre de Recherches Nucldaires (IN2P3), Laboratoire PHASE (UPR du CNRS n0292), BP 20, F-67037 Strasbourg Cedex 2, France
We have investigated the rapid thermal diffusion of phosphorus into ptype silicon from a spin-on coated film as a function of the process tenperature and time duration. The electron diffusion length Lb measurements performed by the Surface PhotoVoltage (SPV) method present evidence for a gettering phenomena since the L. values of the diffused samples are significantly improved. This result is important for the future of RTP in the area of silicon devices where carrier transport is controlled by the bulk lifetime.
Rapid Thermal Processing (RTP) using radiation from tungsten halogen lamps as a heat source has been seen for over five years as a very promising candidate to replace conventional furnace annealing. The RTP is probably better adapted to the fabrication of micron and submicron ICs than the other investigated alternative methods such as lasers, electron beams, resistance heaters and ion beam annealing technologies [1, 2]. However, up to now, there is one major handicap related to this technique, which impedes a larger utilization in microelectronics and avoids applications in the field of power diodes, solar cells or nuclear detector devices. This main drawback concerns the degradation of the bulk carrier transport properties due to the recombination-generation centers which are induced by the fast quenching step at the end of the RTP thermal cycle. In previous works, we have proposed that these defects have their origin in the presence of metallic impurities existing in the starting material and/or diffused from the surface during the thermal processing [3, 4]. In the case of implantation, it has been shown that the activation of metals which are co-implanted with the main implanted species due to sputtering in the implantation system is the main responsible for the degradation of the bulk diffusion length [5]. During the quenching step, a higher percentage of metal atoms is frozen in electrically active state. It is especially important to reduce or eliminate these contaminants in silicon wafers by a gettering effect. Combining dopant diffusion and gettering effect in one thermal cycle could spread the application of RTP to the processing of devices, such as photovoltaic cells and bipolar transistors. Dopant diffusion frcn a doped oxide film or a solid dopant source using RTP seens to be an interesting alternative to avoid problems due to implantation damage. Recently, the use of RTP for doping fran doped glass films [6, 7] has been reported. However, no significant studies have concerned the bulk properties. In this study, we describe the diffusion of phosphorus into silicon from phosphorus-doped spin-on glass (SOG) films using RTP. The resulting diffused samples were characterized by measuring sheet resistance, phosphorus concentration profiles and minority carrier diffu
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