Wall Temperature Dependence of Boronization Using Decaborane and Diborane

Abstract

A new boronization technique based on pyrolysis of boron hydrides on hot walls was investigated in a laboratory experiment. The deposition rate of boron films through pyrolysis of decaborane was high enough to apply the pyrolysis to actual fusion devices bakable to 300°C. The hydrogen concentration of boron films prepared by the pyrolysis or conventional plasma-assisted boronization at various temperatures was measured with 15N nuclear reaction and/or IR absorption methods. The hydrogen content markedly decreased with increasing wall temperature, where decaborane always gives higher H content than diborane. Oxygen gettering and hydrogen recycling in a boronized vessel were evaluated by pulsed glow discharge in O2/He and D2, respectively. The results were compared between the pyrolysis and the plasma-based boronizations in decaborane or diborane at various wall temperatures.

Modeling studies of the chemical vapor deposition of boron films from B2H6

“…3 where at lower temperatures B 2 H 6 is not fully decomposed while at higher temperatures BH 3 is the dominant gas-phase species. The dependence observed in the low-temperature regime is similar to the experimental results reported by Yamage et al [15] of 22 kcal/mol. Assuming an Arrhenius form, the experimental data yield an activation energy of 20.270.8 kcal/mol for boron deposition in the lower temperature kinetically limited regime.…”

“…Assuming an Arrhenius form, the experimental data yield an activation energy of 20.270.8 kcal/mol for boron deposition in the lower temperature kinetically limited regime. This value compares favorably with the reported value for the activation energy of the gas-phase decomposition of B 2 H 6 (22 kcal/ mol) [15,32] indicating that the reaction limiting the growth of boron films at lower temperatures is the gas-phase decomposition of B 2 H 6 . The effects of kinetic and mass transport-limited growth are also indicated in the data shown in Fig.…”

“…CVD growth of boron films using B 2 H 6 has been reported for semiconductor applications [10][11][12][13][14][15] and material coatings in nuclear reactors [16][17][18]. Yamage et al [15] used a hot-wall chamber to investigate the deposition of boron coatings from B 2 H 6 and observed an Arrhenius dependence of growth rate on temperature over a narrow temperature range of 300-400 1C.…”

“…Yamage et al [15] used a hot-wall chamber to investigate the deposition of boron coatings from B 2 H 6 and observed an Arrhenius dependence of growth rate on temperature over a narrow temperature range of 300-400 1C. Lengyel and Jensen [9] developed a chemical mechanism for in situ boron doping of silicon thin films from B 2 H 6 using quantum chemistry simulations.…”

Development and operation of first wall in JT-60U high-power heated discharges

“…This value is low, even compared with the other tokamak whose boronization has been carried out in low temperature of -150 "C [7]. This agrees enough with the temperature dependence of hydrogen content in boron film [8]. It is, however, necessary to further reduce the hydrogen/deuterium ratio in the main plasma for experiments, and we needed about 100 shots…”