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Surface Chemistry of Boron-Doped SiO2 CVD: Enhanced Uptake of Tetraethyl Orthosilicate by Hydroxyl Groups Bonded to Boron

Published online by Cambridge University Press:  22 February 2011

Michael E. Bartram  and
Harry K. Moffat
Michael E. Bartram
Affiliation:
Sandia National Laboratory, Albuquerque, NM 87185-5800
Harry K. Moffat
Affiliation:
Sandia National Laboratory, Albuquerque, NM 87185-5800
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Abstract

Insight into how dopants can enhance deposition rates has been obtained by comparing the reactivities of tetraethyl orthosilicate (TEOS, Si(OCH2CH3)4) with silanol and boranol groups on SiO2. This comparison has direct relevance for boron-doped SiO2 film growth from TEOS and trimethyl borate (TMB, B(OCH3)3) sources since boranols and silanols are expected to be present on the surface during the thermal chemical vapor deposition (CVD) process. A silica substrate having coadsorbed deuterated silanols (SiOD) and boranols (BOD) was reacted with TEOS in a cold-wall reactor in the mTorr pressure regime at 1000K. The reactions were followed with Fourier transform infrared spectroscopy. The use of deuterated hydroxyls allowed the consumption of hydroxyls by TEOS chemisorption to be distinguished from the concurrent formation of SiOH and BOH that results from TEOS decomposition at this temperature. It was found that TEOS reacts with BOD at twice the rate observed for SiOD, given equivalent concentrations of BOD and SiOD. This demonstrates that hydroxyl groups bonded to boron increase the rate of TEOS chemisorption. In contrast, additional results show that surface ethoxy groups produced by the chemisorption of TEOS decompose at a slower rate in the presence of TMB decomposition products. Possible dependencies on reactor geometries and other deposition conditions may determine which of these two competing effects will control deposition rates. This has significant implications for microelectronics fabrication since the specific dependencies would be expected to affect process reliability. In addition, this may explain (in part) why the rate enhancement effect is not always observed in boron-doped SiO2 CVD processes.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 334: Symposium W – Gas-Phase and Surface Chemistry in Electronic Materials Processing , 1993 , 57
Copyright
Copyright © Materials Research Society 1994

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