Lateral Solid Phase Epitaxy of Silicon Over Oxide
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LATERAL SOLID PHASE EPITAXY OF SILICON OVER OXIDE
J.A. ROTH, G.L. OLSON, AND L.D. HESS Hughes Research Laboratories, 3011 Malibu Canyon Road Malibu, CA 90265
ABSTRACT We review recent progress in the growth of siliconon-insulator films by lateral solid phase epitaxy. The temperature dependence of the rates of random crystallization and solid phase epitaxy are used to predict the maximum growth of Si over oxide achievable by this technique. Actual overgrowth distances of 10 pm obtained in UHV-deposited films are considerably less than the values predicted. Several possible causes of the difference between observed and predicted overgrowth are discussed.
INTRODUCTION Of the many applications being considered for Si-on-insulator (SO1) technology, one of the most interesting is the production of multiple-layer 3-dimensional integrated circuits (3-D ICs). One can easily imagine the potential advantages of multiple, stacked device layers in a highly parallel application like real-time image processing, or in a byte-high RAM cell where eight or more layers of Si would be stacked so as to greatly reduce the number of bit-address lines required to access a given byte. One reason such applications have not received much attention is that most of the currently popular growth methods for producing SOI are not adaptable to the fabrication of multi-layer structures, or are limited to configurations in which only two device planes are possible, one in the single crystal substrate and one in the SOI film. With few exceptions, the most successful SOI techniques employ melting to effect recrystallization of a polycrystalline Si thin film, and it has proven difficult to conduct such melting without simultaneously causing changes in underlying layers that would prove catastrophic to devices present there. There is, however, a unique SOI growth technique which is intrinsically suited to the production of multilayer structures because it takes place entirely in the solid phase. In the present paper we will review the progress achieved with this new technique, lateral solid phase epitaxy (LSPE), and comment on the problems that remain to be solved before it can find application in the fabrication of 3-D integrated circuits.
BACKGROUND Solid phase epitaxial crystallization of an amorphous film can occur when the film is heated while in intimate contact with a single crystal material of similar crystal structure. This process has most often been studied in Si that was ion implanted at fluences sufficient to amorphize a thin layer near the surface [1-51, and has also been investigated in UHVdeposited amorphous films [6-8]. The idea of lateral SPE over oxide is a conceptually straightforward extension of "vertical" SPE and is depicted schematically in Figure 1. An amorphous film is deposited over an oxide which has one or more openings where the underlying single crystal substrate is exposed. Within these openings, where the amorphous film touches the substrate, vertical SPE can occur upon heating. For Si(100) it is only Mat.
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