The CVD Process for Epi Silicon

Several features of these curves are significant. At low temperatures, the reactions are considered to be surface controlled, so there is an overabundance 

At the lower temperatures, the films are polycrystalline. Epitaxial films are produced for temperatures at or above values at the knee of each curve. Therefore, epi can be grown from SiH4 at temperatures as low as 800°C. On the other hand, epi films from SiCI4 require deposition temperatures above 1100°C. 

In growing epi films, the most commonly used reactant is SiCI4. It is inexpensive and easily available. Another reason for its popularity is that it leaves relatively little deposit on the cold walls of the reactor bell jar, so that cleaning is less of a problem. Also, when deposits are done at temperatures between 1100° and 1300°C, film quality is excellent in terms of crystallographic defects. 

Where thicker films are needed, SiHCI3 is often used because of its higher deposition rate. In other respects, it is similar to SiCI4. When lower deposition rates become critical, SiCI2H2 is being used. 

Finally, epi films deposited from SiH4 at low temperatures ( 1000°C) are interesting, but difficulties due to the heavier Si deposits on the cold reactor walls has limited interest in this approach. 

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