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Gas phase transport in Si epitaxial growth has been investigated by means of in situ mass spectrometry measurements. of reaction gas concentration profiles. Five species, SIC14, SiHC13, SiHfC12, SIC12, and HC1 are observed in the reaction gas. Not only SIC14 (source gas) but the other Si chlorides as well contribute to the surface growth reaction. The primary reaction species shifts from SIC14 to the other Si chlorides with decreasing gas velocity and with increasing temperature and position along the susceptor.Gas phase reactions and transport phenomena in Si epitaxial growth have been studied extensively by a number of authors and reaction models deduced from an equilibrium viewpoint (1-5). However, the actual reaction is not in equilibrium, but rather quasiequilibrium (6), and the Si epitaxial reaction is difficult to describe by a theoretical model, It is necessary to observe the reaction gas species by in situ measurements in a reactor. Recently such measurements have been made and reaction models proposed. Ban and Gilbert observed the reaction gas profiles in a reactor by using mass spectrometry and reported that SIC14 and only a small amount of SIC12 were found (7, 8). A reaction mechanism was proposed in which SiCI~ was transported to the substrate surface by diffusion and the source gas decomposed into solid Si and HCI byproduct. The following heterogenous reaction occurred at the surface SiC14(g) + 2H2(g) --> Si(s) -t-4HCI(g) Sedgwick and Smith observed reaction gas concentration profiles using laser Haman spectroscopy in Si epitaxy with SiH2C12 as source material (9). The SiHfCI2 decomposed into SIC12 in the gas phase, and then SIC12 was transported to the surface where the epitaxial layer grew SiHfC12---> SiCI# + H2 (gas phase) SiCI2 + Hf--> Si + 2HC1 (substrate surface) Nishizawa and Nihira observed reaction gas profiles by using infrared absorption spectroscopy and found SIC14, SiHC!~, SiHfC~2, and HC1 species (10). They proposed the following models SiHClz SiCla § H2 ~ SIC1,2 ~__-Si % SiH2C12 + HC1Duchemin also investigated Si epitaxial reactions extensively by observing reaction gas profiles in a vertical type reactor (11).Recently, Pollard and Newman have reported a model in which multicomponent mass transfer was considered (12). However, they used calculated gas concentration profiles for the calculation of growth rates. We have observed the reaction gas concentration profiles by in situ measurements using mass spectrometry while changing the growth parameters. It is apparent that the three models mentioned above are likely to describe only a part of the actual reaction. In this paper, it is proposed that all the Si chlorides, SiCIly, SiHC13, SiH2C12, and SIC12, participate in the surface reaction, and the primary surface reaction species which contributes to the growth rate is suggested to shift with changing gas velocity, substrate temperature, and position along the susceptor.
Gas phase transport in Si epitaxial growth has been investigated by means of in situ mass spectrometry measurements. of reaction gas concentration profiles. Five species, SIC14, SiHC13, SiHfC12, SIC12, and HC1 are observed in the reaction gas. Not only SIC14 (source gas) but the other Si chlorides as well contribute to the surface growth reaction. The primary reaction species shifts from SIC14 to the other Si chlorides with decreasing gas velocity and with increasing temperature and position along the susceptor.Gas phase reactions and transport phenomena in Si epitaxial growth have been studied extensively by a number of authors and reaction models deduced from an equilibrium viewpoint (1-5). However, the actual reaction is not in equilibrium, but rather quasiequilibrium (6), and the Si epitaxial reaction is difficult to describe by a theoretical model, It is necessary to observe the reaction gas species by in situ measurements in a reactor. Recently such measurements have been made and reaction models proposed. Ban and Gilbert observed the reaction gas profiles in a reactor by using mass spectrometry and reported that SIC14 and only a small amount of SIC12 were found (7, 8). A reaction mechanism was proposed in which SiCI~ was transported to the substrate surface by diffusion and the source gas decomposed into solid Si and HCI byproduct. The following heterogenous reaction occurred at the surface SiC14(g) + 2H2(g) --> Si(s) -t-4HCI(g) Sedgwick and Smith observed reaction gas concentration profiles using laser Haman spectroscopy in Si epitaxy with SiH2C12 as source material (9). The SiHfCI2 decomposed into SIC12 in the gas phase, and then SIC12 was transported to the surface where the epitaxial layer grew SiHfC12---> SiCI# + H2 (gas phase) SiCI2 + Hf--> Si + 2HC1 (substrate surface) Nishizawa and Nihira observed reaction gas profiles by using infrared absorption spectroscopy and found SIC14, SiHC!~, SiHfC~2, and HC1 species (10). They proposed the following models SiHClz SiCla § H2 ~ SIC1,2 ~__-Si % SiH2C12 + HC1Duchemin also investigated Si epitaxial reactions extensively by observing reaction gas profiles in a vertical type reactor (11).Recently, Pollard and Newman have reported a model in which multicomponent mass transfer was considered (12). However, they used calculated gas concentration profiles for the calculation of growth rates. We have observed the reaction gas concentration profiles by in situ measurements using mass spectrometry while changing the growth parameters. It is apparent that the three models mentioned above are likely to describe only a part of the actual reaction. In this paper, it is proposed that all the Si chlorides, SiCIly, SiHC13, SiH2C12, and SIC12, participate in the surface reaction, and the primary surface reaction species which contributes to the growth rate is suggested to shift with changing gas velocity, substrate temperature, and position along the susceptor.
Many practical chemical vapor transport systems are gaseous diffusion limited. For a singlereaction system under moderate supersaturations, the diffusive transport rate is readily expressed in a form which enables the effect of surface kinetic limitations to be included. Attempts to observe surface limitations in a closed-tube experiment are described together with experiments which confirm the diffusion theory. The treatment of multireaction systems is briefly discussed.This paper is concerned primarily with one-dimensional, diffusion-controlled vapor transport in which one reaction is dominant, with some attention, however, being given to multireaction systems. The system under consideration is illustrated in Figure 1. The solute (for example, a metal) dissolves at temperature T" in the vapor phase under the influence of a vapor solvent (for example, a halogen) and is transported by diffusion to the seed at temperature T'. Solute is deposited on the seed while solvent diffuses back to the source. In place of the source, one may postulate a boundary on which the composition of the gaseous mixture is known.In such a system, common sense would seem to suggest that transport should occur from regions where there is a high density of solute atoms (combined or uncombined) to regions where this density is smaller. One's first approach therefore is to attempt to relate the growth rate of the seed to the total concentration gradient of the solute in the vapor phase. That this cannot be done is due to two effects.? The first is what, following Schaefer ( l ) , may be called streaming. The second is due to the fact teat it is not always a valid approximation to treat the gases in contact with the seed as if they were in equilibrium with it. In fact, gaseous transport rates cannot be calculated without allowing for streaming, while the consideration of the overall transport rate should include the effect of possible surface limitations. These two points will be illustrated with reference to a specific example, namely, the silicon-chlorine system in which transport of silicon occurs by means of the reactionf It is shown later that a potential for vapor transport is provided more nearly by the solute-solvent density ratio, not by the solute density alone. MIXTURE Fig. 1. Schematic view of closed-tube, vapor-growth system. SEALED SILICA TUBE REACTIVE GAS Page 1158A.1.Ch.E. STREAMINGSince each molecule present in the gas phase contains one silicon atom, and since the pressure in the system is constant, there is clearly no appreciable concentration gradient of silicon in the system. Indeed, the concentration of silicon will be slightly higher near the seed because of the temperature gradient and the operation of the gas laws. Nevertheless, diffusive transport occurs by means of reaction (1) down the temperature gradient (from hot to cold). This is explained by noting a significant feature of (I), namely, that the number of gaseous species are not conserved in the reaction. For every molecule of silicon tetrachloride that disa...
Treatment of diffusion-controlled chemical vapour deposition (CDV) usually neglects supersaturation a t the gas-solid interface, which is the basic condition for crystal growth. A new approach based on metastable equilibria and on the concept of activit,y, taking into account departure from equilibrium has been given and applied t o the system resulting from SiCl, + H, mixtures. The control of activity a t the gassolid interface should provide a method of controlling the morphology and perfection of CVD films.Die Behandlung der diffusionsbestimmten chemischen Dampfabscheidung (CVD) vernachlassigt gewohnlich die fibersattigung der Gas-fest-Grenzflache, die die Grundbedingung fur das Kristallwachstum darstellt. Die vorliegende Betrachtung grundet sich auf das metastabile Gleichgewicht und auf die Aktivitat. indem die Abweichung vom Gleichgewicht zugrunde gelegt wird. Ein aus (SiC1, + H,)-Mischungeri hestehendes System wird untersucht. Die Beherrschung der Aktivitat der Gasfest-Grenzflache sollte eine Methode zur Regelung der Morphologie und der Perfektion dunner CVD-Schichten ermoglichen. Main steps in chemical vapour deposition (CVD)SiCI, reduction by H, is one of the most frequently used CVD-processes for epitaxial silicon (THEUERER 1960(THEUERER ,1961(THEUERER , 1964 Chemical vapour deposition on substrates or on already present crystal films occurs usually near atmospheric pressure. Excluding reactions in the gas phase, the deposition consists of the following steps:1. Transport of reactants through the gas phase t o the deposition surface. 2. Surface processes, such as adsorption (both physical and activated) of reactants, chemical reactions, nucleation, crystal growth a n d desorption of products.3. Transport of final products away from the deposition surface.Depositions, the rate of which are controlled by steps 1 and 3 or by step 2 are referred t o as "diffusion-controlled" or "kinetically-controlled", respectively.
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