Bulk growth source temperature

Chemical Reaction Mechanisms and Kinetics. CVD chemistry is complex, involving both gas-phase and surface reactions. The role of gas-phase reactions expands with increasing temperature and partial pressure of the reactants. At high reactant concentrations, gas-phase reactions may eventually lead to gas-phase nucleation that is detrimental to thin-film growth. The initial steps of gas-phase nucleation are not understood for CVD systems, not even for the nucleation of Si from silane, which has a potential application in bulk Si production (97). In addition to producing film precursors, gas-phase reactions can have adverse effects by forming species that are potential impurity sources. 

Aluminium contamination is seldom observed for low temperature vacuum sublimation. Aluminium has a low capture coefficient at low temperatures and it does not form refractory carbides with a low vapour pressure. Therefore, traces of aluminium can be easily removed by annealing the furnace in vacuum even if contamination occurs. However, if the material source is insufficiently pure, it can result in noticeable aluminium contamination, especially at elevated growth temperatures. For the bulk crystal growth, aluminium contamination is always observed when abrasive silicon carbide is used as source material [20,22]. The abrasive material usually is highly contaminated [1,22]. 

Alternatively, boron contamination can cause serious problems. Unintentional boron doping is observed both for epitaxial layer growth and for bulk crystal growth. Boron forms a highly stable carbide with a very low vapour pressure. Once introduced into the furnace, it is difficult to remove. Boron contamination can result from the graphite parts of the furnace, from the source material and from evaporation from the reverse side of the substrate as well as from occasional sources. The boron content can be decreased by long anneals at elevated temperatures, although this method is not always effective. 

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