Control of Grain Boundary Location By Selective Nucleation Over Amorphous Substrates
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CONTROL OF GRAIN BOUNDARY LOCATION BY SELECTIVE NUCLEATION OVER AMORPHOUS SUBSTRATES T. YONEHARA, Y. NISHIGAKI, H. MIZUTANI, S. KONDOH, K. YAMAGATA T. ICHIKAWA Research Center, Canon Inc., Atsugi city, Kanagawa, 243-01, Japan
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ABSTRACT A selective nucleation based crystal-growth-technique over amorphous substrates is originated. The method manipulates nucleation sites and periods and hence, controls the grain boundary location by modifing the substrate surface. In Si, small Si N nucleation sites are formed, 1-2 pm in diameter, 100 Pm in period, oer SiG . One Si nucleus is formed exclusively in the small area of Si N by ýVD. The highly faceted and 3 periodically located nuclei grow over iO up to 100 pm in diameter before impingement. A MOS-FET fabricated inside the island operates comparably to the bulk Si control.
INTRODUCTION Overlayers as-deposited on amorphous substrates are amorphous or, at best, polycrystalline. The absence of long range order in the amorphous substrates is reflected in the absence of long range order in the overlayers. Amorphous films maintain only short range order while polycrystalline films are composed of aggregates of single jrystal grains with grain boundaries between adjacent grains. Graphoepitaxy - introduced the new idea that micro patterning over amorphous substrate surface could alter crystallographic structures in overlayers. In this paper, we propose and demonstrate a novel crystal growth technique named Selective-Nucleation-based-Epitaxy (Sentaxy) in which nucleation sites and periods are manipulated by modifing the amorphous substrate surface. This technique enables one to control grain boundary location. It used to be thought that initial film formation procedures randomly occur and are out of control. This method could be in contrast 4 to epitaxial lateral overgrowth seeded from single crystal substrates and Graphoepitaxy in a sense that this method is based on a phenomenon of selective nucleation which is strongly dependent on amorphous materials.
PRINCIPLE Polycrystalline overlayers are composed of grains, the size of which are widely distributed as shown in Fig. 1.(b). The grain size distribution is mainly attributed to the random nucleation over the substrate, because these grain boundaries are formed by impingement with adjacent grains as shown in Fig. l.(a). In other words, the sites of nucleation are not controlled and nuclei are randomly formed over the substrate surface. For example, closely located nuclei result in small grains, while remoter ones form larger grains due to the difference in time before impingement with adjacent grains which are grown from adjacent nuclei if we assume no grain growth after the impingement. If the nucleation sites are manipulated and located at arbitrary points in some period over the surface, the grain boundaries will be formed and aligned at the center of the nucleation sites' period as shown in Fig. 1.(c), (d).
Mat. Res. Soc. Symp. Proc. Vol. 106. ' 1988 Materials Research Society
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