Zone Melting Recrystallization of Patterned Films and Low-Temperature Graphoepitaxy
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ZONE MELTING RECRYSTALLIZATION OF PATTERNED FILMS AND LOW-TEMPERATURE GRAPHOEPITAXY
HENRY I. SMITH(a), C.V. THOMPSON(b), M.W. GEIS(c), H.A. ATWATER(a), T. YONEHARA(d), C.C. WONG(bi, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
ABSTRACT Zone melting recrystallization (ZMR) of Si films on SiO2 has produced large-area films with electrical properties approaching those of bulk wafers. The mechanisms of film formation and the use of patterning to control orientation and defect distribution are briefly reviewed. Some examples of the use of patterning are: single-grain films have been produced by means of planar constrictions; subboundaries and impurities have been entrained to lie along straight lines separated by -100pm through the use of lithographicallydefined grating patterns; a vertical-constriction technique has enabled (100) texture to be achieved in 50pm-thick Si films; a lithographically-defined orientation filter, which takes advantage of growth-velocity anisotropy, has been used to select a predetermined azimuthal orientation. Patterning is also fundamental to graphoepitaxy. Current research emphasizes low temperature processes based on solid-state surface-energy-driven secondary grain growth.
INTRODUCTION This paper deals with the use of patterning to control the location of defects and to influence the crystallographic orientation of thin films formed on amorphous substrates. The subject was reviewed recently in detail [1]. Here we provide a brief review and a guide to the most recent literature.
ZONE MELTING RECRYSTALLIZATION (ZMR)
OF PATTERNED FILMS
In zone-melting recrystallization (ZMR) of Si on Si0 2 , the transition region at the beginning of the recrystallization region provides a multitude of seeds that have a predominance of (100) texture (i.e., (100) planes parallel to the substrate surface) and random in-plane orientations [2,3]. Through a process of occlusion, grains with non-(100) texture and in-plane orientations that deviate by more than -250 from the direction of zone motion are eliminated [2]. This is rather fortuitous since (100) is the (a) (b) (c) (d)
Department of Electrical Engineering and Computer Science Department of Materials Science and Engineering Lincoln Laboratory, Lexington, MA 02173 Center for Advanced Engineering Study
gat. Rs. soc. Symp.
Proc. Vol.
23 (1984)CElsevier Science Publishing
Co.,
Inc.
460
If the Si is thicker than -5gm, preferred orientation for Si MOS devices. the predominance of (100) disappears, and random texture is observed [4].
FACETING AND SUBBOUNDARY ENTRAINMENT Under normal conditions for ZMR, the solidification front is faceted and subboundaries form at interior corners. This experimentally observed phenomenon (see Fig. 6 of Ref. [5]) can be explained by a simple theoretical model [5] in which subboundary spacing is a function of the thermal gradient at the liquid-solid interface and the crystal orientation. We believe that only in very heavily doped or contaminated films of Si are the subboundary spa
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