Si Film Growth by Supercooling of a Molten Si Alloy Film
- PDF / 2,669,985 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 73 Downloads / 179 Views
Si FILM GROWTH BY SUPERCOOLING OF A MOLTEN Si ALLOY FILM R.L. Wallace,J. Yi,W.A. Anderson, State University of New York at Buffalo, Department of Electrical and Computer Engineering,Bonner Hall, Buffalo, N.Y. 14260 ABSTRACT A method is described for the deposition of large-grain polysilicon films at low substrate temperatures. This technique uses precipitation from a thin molten prelayer of Si-Au or Si-Au which is supersaturated with Si from a DC magnetron sputter gun. Typical growth temperatures are 6000 C for the Si-Al layer, and 5000 C for the Si-Au layer. Growth rates of 6 pm/hr have been achieved, though higher rates seem possible. Films of 20 pm thickness and grain size up to several hundred pm have been grown on Si0 2 and sheet Mo substrates using Au and Al as the "solvent" metals. The proposed model for film growth was confirmed by cross-section EDS studies of the film/substrate interface. Film crystallinity was confirmed by etching studies, X-ray diffraction, and selected area diffraction. Preferential nucleation has been achieved using a patterned silicide forming metal (Cr,Ni) on RuO 2 coated oxidized wafer. A loss mechanism of the solvent metal during growth was observed. INTRODUCTION A low temperature technique for depositing large grain polysilicon films could significantly lower the production costs of a polysilicon photovoltaic device. One route to a large grain film is by melting an existing film and allowing it to solidify. In this case crystallization occurs from the liquid state. Very high temperatures are needed (14150 C), with attendant problems of thermal stress and impurity diffusion. Another way to achieve crystallization of Si from a liquid is to supercool a Si-metal melt of hypereutectic composition. Primary Si will precipitate out onto likely nucleation sites. Epitaxial growth of Si from an alloy melt has been done using the Ga-Al-Si (Girault[l]) and Au-Bi-Si (Lee[2]) ternary systems, and from the In-Si (Blakers[3]), and Sn-Si (Baliga[4]) binary systems. These experiments typically used a bath of molten alloy in a liquid phase epitaxy (LPE) facility. A bath of molten alloy is not necessary. If a thin layer of the melt is formed on the substrate surface it can act as an intermediate step in thin film deposition. An incident flux of Si on the molten alloy surface could keep the melt saturated in Si with the excess Si precipitating onto the substrate in crystalline form (Figure 1). Another technique using the thin liquid layer concept has already been developed. Vapor-liquidsolid (VLS) growth was investigated in the 1960's (Wehyer[5]). EXPERIMENTAL A thin film liquid phase deposition technique has been developed here, with the goal of producing polycrystalline films. The Si delivery mechanism is DC magnetron sputtering. The alloy melt is formed on the substrate surface by two mechanisms. Either direct sputtering of a metal-Si eutectic alloy is done, or filament evaporation of the solvent metal is followed by Si deposition at above the eutectic temperature. Once the molten
Mat. Res. Soc. Sy
Data Loading...
