1P23 Decomposition processes of H3NBH3 (borazane) and (BH)3

1P23 Decomposition processes of H3NBH3 (borazane) and (BH)3(NH)3
(borazine) on heated W wire surfaces
(Shizuoka Univ.1, JST CREST2) Atsushi Miyata1,2, and Hironobu Umemoto1,2
([email protected])
Recently, we have reported that B2H6, one of the most widely used dopant gases in semiconductor
industries, can be decomposed efficiently on heated metal wire surfaces [1]. B and BH could be identified
in the presence an excess amount of H2. The direct product on the wire surfaces must be BH3, which
reacts with H atoms formed from H2 to produce B and BH in the gas phase. In the present study, it was
examined if similar production of BH3 is possible from H3NBH3, which is much less toxic and safer
compared to B2H6. (BH)3(NH)3 is not explosive, either, and can be another candidate of a safe B-atom
dopant precursor.
The experimental apparatus was similar to those described elsewhere [1]. The decomposition
efficiencies of the material gases were measured with a quadrupole mass-spectrometer. Stable
decomposition products were also identified mass spectrometrically. The B-atom density was evaluated
by a laser-induced fluorescence (LIF) technique at 249.8 nm, which corresponds to the 2s23s 2S1/2 – 2s22p
2
P3/2 transition. The absolute density was estimated by comparing the LIF intensity with the intensity of
Rayleigh scattering caused by Ar. H3NBH3 was effused from its reservoir, while (BH)3(NH)3 was
introduced into the chamber through a mass flow controller after diluted with He to 2.0%.
According to the mass spectrometric measurements, the decomposition efficiency of H3NBH3 was 86%
when the W wire temperature was 2320 K, which is higher than that for B2H6, around 70%. This
efficiency increased to 97% when H2 was introduced, but no such increase was observed when He was
added. Fig. 1 shows the typical mass spectra. Besides H2, NH3, and N2, H2NBH2 could be identified as a
stable product. B atoms could be observed in the presence of an excess amount of H2. The B-atom
density increased not only with the wire temperature but also with the reservoir temperature. When the
reservoir temperature was 350 K, the B-atom density was comparable to that observed in the B2H6/He/H2
system. The B-atom signal in the absence of a H2 flow was extremely small, suggesting that the direct
production of B atoms on wire surfaces is minor and that B atoms are produced in the secondary reactions
with H atoms in the gas phase. Fig. 2 shows the wire temperature dependence of the B-atom densities.
(BH)3(NH)3 could also be decomposed on heated W wire surfaces, but the production of B atoms could not
be confirmed even in the presence of an excess amount of H2. The production of BHx species must be
minor.
Twire / kK
Ion current
B-atom density / cm-3
1012
0
10
20
30
Mass number
Fig. 1 Mass spectra of H3NBH3 and its
decomposition products. W wire temperatures
were 2230, 1580, and 300 K from up to bottom.
No buffer gases were introduced.
[1] H. Umemoto, T. Kanemitsu, and A. Tanaka, J. Phys.
Chem. A,118, 5156 (2014).
2.3
2.2
2.1
2.0
1.9
1011
1010
0.42
0.44
0.46
0.48
0.50
0.52
0.54
1000 Twire-1 / K -1
Fig. 2 B-atom densities as a function of the
reciprocal of W wire temperature in the presence of
a H2 flow of 20 sccm for B2H6/He/H2 (■) and
H3NBH3/H2 (●, ▲). The B2H6/He flow rate was
10 sccm. The H3NBH3 reservoir temperatures
were 295 (●) and 350 K(▲). Results for pure H2
systems are represented by ○.