UV Laser Processing of Semiconductor Devices
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UVLASER PROCESSING OF SEMICONDUCTOR DEVICES T. W. Sigmon Stanford Electronics Laboratories, Stanford, CA 94305 ABSTRACT The use of a pulsed UVexcimer laser based process for the incorporation of dopant impurities into Si is described. The process can result in high concentration shallow box like profiles suitable for submicron VLSI device fabrication. The process consists of exposure of the clean silicon surface to a doping gas (B2 H6 , AsH 3 , PH3 ) then driving the adsorbed monolayers of dopant into the Si by a melt-regrowth process initiated by a pulsed XeCl excimer laser. Modeling of the process allows prediction of the resulting doping profiles and electrical properties of the doped layers. Excellent crystal quality of the doped layers is found even without a postdoping anneal. Also, recent results indicate that post doping annealing may not be needed for improvement of the electrical characteristics of the doped layers provided certain conditions are met. Detailed descriptions of the process, results, modeling and device fabrication are presented. INTRODUCTION In the past several years the generalized concept of "in-situ" processing has emerged among several major research laboratories [1,2]. Work has been reported ranging from "in-situ" etching [3], direct write metalization for gate array interconnects [4] and planarization of semiconductor device structures [5] using lasers of various wavelengths. Several groups have also focused on a single process important to an overall "in-situ" process such as epi growth [6], etching [7-9], metal deposition [10-13] photolithography [14] and lastly doping [15-18]. It is this last aspect, doping, upon which this paper intends to focus. Although the above reported processes have used different types of lasers, several of those of prime importance to "in-situ" processing reported the use of UV laser energy. In Fig. 1 we show an artist's conception of a laser based "in-situ" processing station. Although an actual system might consist of several chambers connected by a load lock system, the general idea can be seen. For the laser station both pyrolysis (offen done using vertical laser irradiation) and photolysis (offen done using horizontal laser irradiation) are allowed, with a fine beam (for direct write applications) or a flood beam (for large scale processing) being used either in parallel or sequentially. The UV laser doping process to be discussed could easily be incorporated into such an overall processing system. Development of UV pulsed laser techniques for silicon process technology has required two research directions. One direction emphasizes the fundamental mechanisms of pulsed laser processing, including the laser/ material interactions involved in the process and the second in obtaining actual device results by incorporating the laser process into a device fabrication process. In the following, we will discuss our work into investigating the fundamental mechanisms with the aid of detailed computer modeling of experimental results and the initial application o
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