Autor: |
Randall C. Boehm, Richard L. Martin, P. Jeffrey Hay, Joel D. Kress |
Rok vydání: |
1999 |
Předmět: |
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Zdroj: |
Surface Science. 436:175-192 |
ISSN: |
0039-6028 |
DOI: |
10.1016/s0039-6028(99)00661-5 |
Popis: |
The desorption of hydrogen in the chemical vapor deposition (CVD) of boron-doped silicon (100) surfaces is investigated using density functional theory and cluster models. The cluster models examine reactions of hydrogen atoms bound to adjacent BSi surface sites that would arise during the decomposition of B 2 H 6 and SiH 4 on a B-doped polysilicon film that is being formed by CVD. Comparisons are made with the analogous processes involving desorption of H 2 from Si dimers, as well as with previous studies in the literature. Calculations show a barrier of approximately 25 kcal/mol for desorption of H 2 from Si 8 BH 14 (‘HBSiH’) and Si 8 BH 15 (‘HBSiH 2 ’) clusters. These calculated barriers may be compared to values of (a) 75–85 kcal/mol typically obtained from other cluster calculations for ‘prepairing’ and ‘isomerization pathways’ from Si dimers on the surface; (b) 53–58 kcal/mol for desorption from SiH 2 ‘defects’; and (c) 55–60 kcal/mol from two-dimensional periodic slab calculations of hydrogen desorption from Si surfaces. These results indicate that barriers for desorption of H 2 from BSi-containing surface dimers are lower than desorption of H 2 from Si surface dimers. These lower barriers arise in part because the hydrogen bound to the B surface atom involves four-coordinate B species which have lower bond energies than classical BH or SiH bonds. These lower barriers could play a role in explaining the increased growth rate of Si observed when chemical vapor deposition is carried out using both SiH 4 (or SiCl 2 H 2 ) and B 2 H 6 precursors. Finally we examined briefly the role of subsurface B atoms in the desorption of hydrogen from Si surfaces, as occurs in desorption studies on annealed B-doped Si films. Small lowerings in the hydrogen desorption energy (from 54 to 52 kcal/mol) and activation barrier (from 76 to ∼70 kcal/mol) were found due to the effect of subsurface B atoms in Si clusters. |
Databáze: |
OpenAIRE |
Externí odkaz: |
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