Plasma CVD of hydrogenated boron-carbon thin films from triethylboron.

Mewlude Imam,Jens Birch,Henrik Pedersen,Carina Höglund,Susann Schmidt,Richard Hall-Wilton

doi:10.1063/1.5006886

Abstract

Low-temperature chemical vapor deposition (CVD) of B-C thin films is of importance for neutron voltaics and semiconductor technology. The highly reactive trialkylboranes, with alkyl groups of 1-4 carbon atoms, are a class of precursors that have been less explored for low-temperature CVD of B-C films. Herein, we demonstrate plasma CVD of B-C thin films using triethylboron (TEB) as a single source precursor in an Ar plasma. We show that the film density and B/C ratio increases with increasing plasma power, reaching a density of 2.20 g/cm3 and B/C = 1.7. This is attributed to a more intense energetic bombardment during deposition and more complete dissociation of the TEB molecule in the plasma at higher plasma power. The hydrogen content in the films ranges between 14 and 20 at. %. Optical emission spectroscopy of the plasma shows that BH, CH, C2, and H are the optically active plasma species from TEB. We suggest a plasma chemical model based on β-hydrogen elimination of C2H4 to form BH3, in which BH3 and C2H4 are then dehydrogenated to form BH and C2H2. Furthermore, C2H2 decomposes in the plasma to produce C2 and CH, which together with BH and possibly BH3-x(C2H5)x are the film forming species.

Highlights

Boron carbides (BxC) have electrical and material properties making them interesting for semiconductor devices and neutron voltaics.1–3 Thermal chemical vapor deposition (CVD) methods often employ temperatures above 1000 ◦C for B−−C film deposition using boron trichloride (BCl3) or diborane (B2H6) as B precursors and methane (CH4) as carbon precursors.4 By contrast, plasma CVD methods employ energetic plasma species to decompose precursor molecules, which lead to deposition temperatures typically below 400 ◦C
We have recently demonstrated that Trimethylboron B(CH3)3 (TMB) can be used as a precursor for hydrogenated BxC thin films in plasma CVD with an Ar plasma affording films with B/C ratios of 0.4-1.9 and 10-20 at. % hydrogen
Motivated by the high B/C ratios obtained in films from TEB in thermal CVD and the thermodynamically accessible possibility to split off the alkyl ligands by β-hydrogen elimination, we studied B−−C film deposition from TEB in CVD with an Ar plasma

Summary

Introduction

Boron carbides (BxC) have electrical and material properties making them interesting for semiconductor devices and neutron voltaics. Thermal chemical vapor deposition (CVD) methods often employ temperatures above 1000 ◦C for B−−C film deposition using boron trichloride (BCl3) or diborane (B2H6) as B precursors and methane (CH4) as carbon precursors. By contrast, plasma CVD methods employ energetic plasma species to decompose precursor molecules, which lead to deposition temperatures typically below 400 ◦C. Boron carbides (BxC) have electrical and material properties making them interesting for semiconductor devices and neutron voltaics.. Thermal chemical vapor deposition (CVD) methods often employ temperatures above 1000 ◦C for B−−C film deposition using boron trichloride (BCl3) or diborane (B2H6) as B precursors and methane (CH4) as carbon precursors.. Plasma CVD methods employ energetic plasma species to decompose precursor molecules, which lead to deposition temperatures typically below 400 ◦C. Plasma CVD is a very attractive technique for depositing boron carbide thin films for microelectronics and neutron detectors based on neutron transparent aluminum substrates. Plasma CVD of boron carbides has been studied using boranes, such as diborane (B2H6), pentaborane (B5H9), decaborane (B10H14), and methane (CH4) as the carbon precursor.. Carborane (C2B10H12) has been used as a single source precursor for BxC in plasma CVD. Plasma CVD of boron carbides has been studied using boranes, such as diborane (B2H6), pentaborane (B5H9), decaborane (B10H14), and methane (CH4) as the carbon precursor. Carborane (C2B10H12) has been used as a single source precursor for BxC in plasma CVD.

Results

Discussion

Conclusion