Nmos Transistors Fabricated by Simultaneous Laser-Assisted Crystallization and Diffusion on Silicon on Electro-Optic PLZ
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NMOS TRANSISTORS FABRICATED BY SIMULTANEOUS LASER-ASSISTED CRYSTALLIZATION AND DIFFUSION ON SILICON ON ELECTRO-OPTIC PLZT J. H. Wang,* T. H. Lin, S. C. Esener, S. Dasgupta and S. H. Lee Dept. of Elec. & Comp. Eng., University of California, San Diego, La Jolla, CA 92093
* Permanent address: Dept of Appl. Phys., Beijing Polytechnic University, Beijing, China ABSTRACT
Simultaneous CW laser assisted crystallization and diffusion for fabricating NMOS is presented. Hall effect measurement (mobility transistors on Si/SiO2/PLZT crystal delineation (grain size 74cm2W-sec-1 at 1.8xl t1cm-3 of phosphorus dopping), 50x3p0m) and Raman spectroscopy (stress 6.0xlO9dynescm-2 ) indicated that good quality doped silicon crystal film can be produced with this method. NMOS transistors fabricated (45 V), small by this technology show good performances such as high breakdown voltage leakage current (2 nA/ptm), reasonable channel carrier mobility (140cm 2 V- sec-1) and photosensitivity (1.5 A/W). 1. INTRODUCTION
Extensive efforts have been recently directed towards the development of Silicon-onInsulator (SO) technology for producing devices and ICs with high performance. The result of these efforts can be applied to VLSI and 3-RD ICs as well as to the field2 of optoelectronics; for example, to large screen displays and spatial light modulatorsI . Up to now sever% methods for producin4 high quality Si films on insulators have belq developed. CW laser crystallization 3 and graphite strips zone melting recrystallization (ZMR) are the most promising ones. ZMR can be used to produce large silicon grains, but the substrate needs to be heated to 1100°C during the recrystallization. In CW laser recrystallization, the surface region illuminated by focused laser beams can be heated to the silicon melting point, while the substrate can be kept at lower (300-500°C), even at room temperatures. This is the key advantage of laser assisted crystallization for integrating device quality silicon with electro-optic materials that cannot tolerate high temperatures. For impurity doping into silicon films ion-implantation is the most general method in SOI device fabrication. However, the wafers have to be annealed at high temperatures to activate a large percentage of the introduced impurity atoms and to eliminate crystal defects produced during the implantation procefl, Another possible method to introduce impurities locally into Si is laser assisted diffusion. Ad In this paper we report a technology that enables the fabrication of NMOS transistors in one step by simul~l~eous laser crystallization and diffusion of impurities into Si/SiO 2 /PLZT. PLZT"' is a ferroelectric ceramic with a high electro-optic coefficient and is prone to damage at temperatures higher than 900'C. Therefore, laser assisted processing becomes essential for producing high quality Si films and fabricating Si devices on PLZT substrates. If transistors can be fabricated in a thin silicon layer deposited on PLZT, their output can control the applied electric field to PLZT light modula
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