Ion-Assisted Regrowth of Deposited Si Layers Mechanisms and Morphology
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ION-ASSISTED REGROWTH OF DEPOSITED Si LAYERS MECHANISMS AND MORPHOLOGY
F. PRIOLOa), C. SPINELLAa), A. LA FERLAa), A. BATTAGLIAa), E. RIMINIa), G. FERLA6 ), A. CARNERAc) AND A. GASPAROTTOc) a) Dipartimento di Fisica, Universiti di Catania, Catania (ITALY) b) SGS-Thomson, Catania (ITALY) c) Dipartimento di Fisica, Universiti di Padova, Padova (ITALY)
ABSTRACT Ion-assisted regrowth of chemical vapor deposited amorphous Si layers was investigated for different cleaning procedures. The process was directly monitored by transient reflectivity measurements. The c-a interface stops at the deposited layer/substrate interface for doses depending on the effectiveness of the cleaning procedure in removing the native oxide. Small concentrations of twins are found in the regrown layer. Their amount is also correlated to the cleaning procedure. In oxygen implanted bare Si samples the ion-induced growth rate is reduced to 0.3 of the normal value at a peak 0 concentration of 1 X 102 1/cm 3 . The results on the ion-induced regrowth of deposited layers are explained in terms of oxygen profile broadening during irradiation and retardation of the growth for the presence of dissolved 0. INTRODUCTION Several attempts have been made to epitaxially deposit at relatively low temperatures (-•
8000C) Si layers onto single crystal Si substrates.
The
problems are related to the presence of an interfacial native oxide layer. Several procedures have been used to clean the substrates before deposition and in some cases [1] reasonable single crystals were obtained. Alternatively, one can thermally regrow previously deposited amorphous Si (a-Si) layers. Solid Phase Epitaxial Growth (SPEC) by conventional thermal annealing can, however, be inhibited by the contaminants present at the interface. SPEG can be enhanced by ion irradiation[2-4]. In this case the regrowth occurs at temperature as low as 2000C and has an Arrhenius temperature dependence with an apparent activation energy of 0.3 eV. The ion-beam-induced growth rate is less sensitive to the presence of impurities dissolved in the a-layer with respect to pure thermal regrowth[4-5]. Recently[6-7] thin a-Si layers deposited onto single crystal substrates have been epitaxially regrown by a 600 keV Kr irradiation at 4500C . The regrowth occurs by a uniform layer by layer crystallization despite the presence of an interfacial oxide layer thick enough to prevent any regrowth by con-
Mat. Res. Soc. Symp. Proc. Vol. 126. a1989 Materials Research Society
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ventional thermal annealing. In the present work we report a more detailed investigation of this process following the ion-induced regrowth in situ by transient reflectivity measurements. The influence of different cleaning procedures on the growth rate and on the defects present in the regrown layers has been investigated. EXPERIMENTAL Silicon layers, 50 nm thick, were deposited onto single crystal substrates by chemical vapor deposition. Prior to deposition a set of substrates was cleaned with the FPN (H 2 0: (NH4 ) 2HP0 4 : NH 4 F: H 3 P
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