Phosphorus and Boron Doping of Silicon Thin Films Using ArF Excimer Laser
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PHOSPHORUS AND BORON DOPING OF SILICON THIN FILMS USING ArF EXCIMER LASER
A. SLAOUI', M. ELLIQ'. H. PATTYN 2, E. FOGARASSY', S. DE UNAMUNO' and R. STUCK' ' Laboratoire PHASE (UPR 292 CNRS), CRN. 23 Rue du Loess, F-67037 Strasbourg France.
2
IMEC, Kapeldreef 75, B-3030 Leuven, Belgium
ABSTRACT This work describes phosphorus (P) and boron (B) doping of polysilicon filns deposited on quartz. Doping is achieved by means of a pulsed ArF excimer laser to melt a controlled thickness of amorphous or polycristalline silicon film coated with a spinon silicate glass (SOG) film containing the dopant (P or B). We have investigated the influence of doping parameters such as laser fluence, number of shots and dopant film thickness on the sheet resistance and the incorporation rate. From these results, we have shown that high doped, shallow junctions presenting sheet resistance lower than 5 kfl/O can be obtained. Poly-Si TFT's with good electrical characteristics were successfully fabricated using this doping technique.
INTRODUCTION The use of lasers in the crystallization of amorphous silicon thin films has been investigated extensively during the last years in order to fabricate polycristalline silicon thin film transistors (poly-TFT's) [1 - 7]. The main advantage of this technology is to be a low temperature processing which permits the use of low-cost glass substrate. The second advantage is that peripheral drive circuits with comparable performance to that obtained with separate Si IC chips can be achieved [6]. Thus, it is possible to realize a complete display (addressing TFT with driver circuits) using the same technology on the same substrate. These TFT's also require shallow and high concentration doping for source-drain formation. However, with the conventional ion-implantation process followed by heat treatment in a furnace for times of the order of minutes to hours, it is difficult to achieve a high dose with low-energy doping. In addition, this long heat treatment could be incompatible with a cheap glass substrate and the use of deposited layers for the gate dielectric (self-alignement technology). To overcome these problems, new doping techniques using high power pulsed lasers have been developed [5 - 10]. Among these techniques, laser induced diffusion from a solid doping source deposited onto the silicon surface seem to be a promising tool for the preparation of shallow junctions. In this case, the laser irradiation of Si thin films is used to melt locally near surface region and produce significant incorporation of dopants from the surface into the molten surface [11] by liquid phase diffusion. Since silicon has a large absorption coefficient (-- 10' cm-1 ) in the ultraviolet region [12], the excimer laser light is strongly absorbed in the near surface region. This feature gives an advantage in forming shallow junctions. This paper describes phosphorus and boron doping of amorphous or polycristalline silicon thin films deposited on quartz. Doping is achieved by using a pulsed ArF excimer laser to melt a contr
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