Comparison of SOI Technologies
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COMPARISON OF SO1 TECHNOLOGIES
Hon Wai Lam Texas Instruments Incorporated MS 944, P. 0. Box 225621 Dallas, Texas 75265
ABSTRACT Silicon-on-Insulator (SO1) technologies are becoming more important as CMOS becomes the preferred technology for VLSI. The progress of the three most actively researched SOI technologies, beam-recrystallized SOI, implanted buried oxide and Full Isolation by Porous Oxidized Silicon will be summarized in this paper. INTRODUCTION Silicon-on-Insulator (SOI) refers to a generic class of materials where a crystalline silicon film is supported on an insulating substrate. Silicon-on-Sapphire (SOS) is a classic example of an SOI technology. Recently, there are several new approaches for the implementation of SOI. They are, namely, beam-recrystallized SO1 [1-4], implanted buried oxide (also known as SRIOX for Separation by IMplanted OXygen) [5-7], FIPOS (which stands for Full Isolation by Porous Oxidized Silicon) [8], epitaxial overgrowth [9] and graphoepitaxy [10]. The efforts on epitaxial overgrowth and grapoepitaxy have been relatively small due to some fundemental problems that are encountered with these two processes. The efforts devoted to the first three new approaches, however, have grown significantly in the last three years. Although there are increasing interest in the application of SOI to large area display [11], high voltage [12] and stacked CMOS [13] applications, the rapid growth in the interest in the new SOT technologies arises from the fact that CMOS is becoming more important in VLSI, primarily for power consumption and heat dissipation considerations. A CM1OS/SOI technology is superior to a bulk CMOS technology because it eliminates latch-up, increases packing density and increases circuit speed due to reduced parasitic capacitance and reduced chip size. In this review paper, we will explore the development of SOT technologies to date, with primary emphasis on those developments that address applications in VLSI. BEAM-RECRYSTALLIZED SOT Beam-recrystallized SOT, a thin film zone melting process, has progressed from the use of an unseeded approach [1,2] to a seeded approach [3], from using a scanning cw argon ion laser beam [1] to a graphite strip-heater [4], which has resulted in the bility to process a large wafer in a short time. All the different recrystallization approaches start with the deposition of a polysilicon film on top of a dielectric layer, which, in the case of most VLSI applications, is an oxide layer thermally grown on top of a single crystal silicon wafer. In the case where seeding is used, part of the underlying silicon
Mat. Rs. Soc.Symp. Proc. Vol. 23 (1984)@ Elsevier Science Publishing Co., Inc.
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wafer is exposed so that it is in contact with the deposited polysilicon. A heat source is then scanned across the surface of the polysilicon such that the area under illumination is melted. As the heat source is scanned away, the molten silicon freezes and crystallizes, resulting in the formation of large grains. In the case where a seed is used, single cry
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