Gas Phase Chemistry of Trimethylboron in Thermal Chemical Vapor Deposition

Mewlude Imam,Andreas Stegmüller,Carina Höglund,Jan Herritsch,Susann Schmidt,Richard Hall-Wilton,Henrik Pedersen,Hans Högberg,Ralf Tonner,Laurent Souqui,Jens Birch

doi:10.1021/acs.jpcc.7b09538

Abstract

Alkylboranes, such as trimethylboron (TMB) and triethylboron (TEB), are promising alternative precursors in low-temperature chemical vapor deposition (CVD) of boron-containing thin films. In this study, CVD growth of B–C films using TMB and quantum-chemical calculations to elucidate a gas phase chemical mechanism were undertaken. Dense, amorphous, boron-rich (B/C = 1.5–3) films were deposited at 1000 °C in both dihydrogen and argon ambients, while films with crystalline B4C and B25C inclusions were deposited at 1100 °C in dihydrogen. A script-based automatization scheme was implemented for the quantum-chemical computations to enable time efficient screening of thousands of possible gas phase CVD reactions. The quantum-chemical calculations suggest TMB is mainly decomposed by an unimolecular α-H elimination of methane, which is complemented by dihydrogen-assisted elimination of methane in dihydrogen.

Highlights

Thin film synthesis of boron-containing materials, especially carbides (B4C), nitrides (BN), and metal borides (e.g., TiB2), have been studied by chemical vapor deposition (CVD)methods using boron halides and hydrides as boron precursors in a hydrogen ambient.[1−9] Boron hydrides, mainly diborane (B2H6), have been widely used for semiconductor applications as they require lower deposition temperatures and provide films with a low level of contamination
All films were adherent on silicon substrates, and an interface reaction between substrate and film was observed for depositions at ≥1000 °C, similar to that previously reported for CVD of BxC thin films from TEB.[13]
We found that the gas phase CVD chemistry of TMB is dominated by a unimolecular α-H elimination of methane to form H2CBCH3 in an inert argon carrier gas

Summary

Introduction

Thin film synthesis of boron-containing materials, especially carbides (B4C), nitrides (BN), and metal borides (e.g., TiB2), have been studied by chemical vapor deposition (CVD)methods using boron halides and hydrides as boron precursors in a hydrogen ambient.[1−9] Boron hydrides, mainly diborane (B2H6), have been widely used for semiconductor applications as they require lower deposition temperatures and provide films with a low level of contamination. Boron halides are less problematic to handle but are not considered suitable for film deposition on metallic substrates due to the formation of hydrogen halides such as HCl. BCl3 requires high deposition temperatures making it incompatible for CVD of boron-based thin films on temperature-sensitive substrates. BCl3 requires high deposition temperatures making it incompatible for CVD of boron-based thin films on temperature-sensitive substrates Alkylboranes, such as trimethylboron (TMB), B(CH3)[3], triethylboron (TEB), B(C2H5)[3], and tributylboron (TBB), B(C4H9)[3], have been suggested as highly reactive, nonpoisonous, nonexplosive alternative B-precursors.[10] These alkylboranes were tested as single-source precursors in CVD of B−C films, and TEB was found to be the best-suited, resulting in B/C ratios between 0.1 and 1.6. The CH radicals combine to Received: September 26, 2017 Revised: October 27, 2017 Published: November 13, 2017

Methods

Results

Conclusion