Boron doping: B/H/C/O gas-phase chemistry; H atom density dependences on pressure and wire temperature; puzzles regarding the gas-surface mechanism

• Published in: Thin solid films Vol. 519; no. 14; pp. 4421 - 4425
• Main Authors: Mankelevich, Yuri A., Ashfold, Michael N.R., Comerford, Dane W., Ma, Jie, Richley, James C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 02-05-2011
• Subjects: Activated; Boron-doped diamond; Density; Deposition process; Diffusion; Doping; Filaments; Gas mixtures; Hot-filament CVD; Mass transfer; Modeling; Wire; Hot-filament CVD; Boron-doped diamond; Modeling; Deposition process
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2011.01.328

Experimental and modeling studies of the gas-phase chemistry occurring in dilute, hot filament (HF) activated B
2H
6/CH
4/H
2 gas mixtures appropriate for growth of boron-doped diamond are reported. The results of two-dimensional modeling of heat and mass transfer processes and the B/H/C chemistry prevailing in such HF activated gas mixtures (supplemented by reactions involving trace O
2 present as air impurity in the process gas mixture) are discussed and compared with measurements of B atom densities as functions of the hot wire temperature
T
w and distance from the wire. Most of the B
2H
6 molecules that diffuse from the cool, near-wall regions into the hot, near wire region are thermally decomposed (yielding two BH
3 molecules as primary products) and then converted into various ‘active’ B-containing species like B, BH and BH
2 — some of which are able to accommodate into the growing diamond film. H-shifting reactions BH
x
+
H
↔
BH
x
−
1
+
H
2 enable rapid inter-conversion between the various BH
x
(
x
=
0–3) species and the BH
x
source is limited by diffusional transfer of B
2H
6. H atoms play several key roles —
e.g. activating the process gas mixture, and driving inter-conversions between the various H
x
B
y
C
z
O
z′
species. We show that the
T
w and gas pressure dependences of the H atom production rate (by H
2 dissociation on the HF surface) can be accommodated by a simple gas-surface reaction model.