Laser-Induced Solid Phase Epitaxy of Silicon Deposited Films
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and Materials Processing
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LASER-INDUCED SOLID PHASE EPITAXY OF SILICON DEPOSITED FILMS
J.A. ROTH, G.L. OLSON, S.A. KOKOROWSKI AND L.D. HESS Hughes Research Laboratories, Malibu, California 90265
ABSTRACT A comparative study of solid phase epitaxy (SPE) of deposited and ion-implanted amorphous Si films was conducted The with the use of a newly developed laser technique. effects of interface contaminants and contaminants distributed within a deposited film on the rate of SPE and final crystal quality are reported. In the absence of impurities, deposited Si films crystallize at the same rate as ion-implanted layers and yield epitaxial films with comparable crystal quality. The presence of impurities in deposited films at the interface or distributed within the film can severely retard the SPE growth, causing several deleterious effects which ultimately degrade the film quality. These effects are more severe at high temperatures.
INTRODUCTION It is now well established that an amorphous Si film deposited onto a clean single crystal substrate can be caused to crystallize epitaxially in the solid However, much less is known about the process of solid state by heating [1-4]. phase epitaxy (SPE) in deposited films than about the equivalent recrystallization process in ion implanted amorphous layers. There are two main reasons for the lack of data on deposited film SPE: 1) SPE growth of a deposited amorphous film is very sensitive to contaminants on the substrate surface, and therefore it has been necessary to use ultrahigh vacuum processing to achieve the degree of substrate cleanliness required for growth of high-quality layers [1]; 2) Even when UHV processing is used to deposit contaminant-free films, subsequent exposure of deposited amorphous Si films to the atmosphere results in absorption of large quantities of impurities [5,6] which interfere with SPE growth. Consequently, to obtain data on the intrinsic behavior of depositedfilm SPE in the absence of contaminants, it is necessary to not only perform the sample preparation in UHV but also to measure the growth rates in UHV without intervening exposure to air. This is in contrast to the case of ionimplanted amorphous Si layers, where it is possible to store samples in air for years without any observable effect on the SPE kinetics [7]. Because of the sensitivity of deposited film SPE to impurities and the concomitant requirement to perform measurements in UHV, it has generally not been feasible to use techniques like Rutherford backscattering (RBS) analysis for studies of crystallization kinetics, as has been done extensively for implanted layers [8-10]. Crystallization rate measurements have been reported for deposited films [3,4], but it was necessary to transfer samples into a separate vacuum chamber for analysis, leading to absorption of impurities from the room air [6] during the transfer. The recent development of cw laser techniques [11,12] for simultaneously providing localized heating and SPE crystallization rate measurements now makes it feasible and
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