The role of the silyl radical in plasma deposition of microcrystalline silicon

Abstract

Expanding thermal plasma chemical-vapor deposition has been used to deposit microcrystalline silicon films. We studied the behavior of the refractive index, crystalline fraction, and growth rate as a function of the silane (SiH4) flow close to the transition from amorphous to microcrystalline silicon. It was found that the refractive index, a measure for film density, increases when the average sticking probability of the depositing radicals decreases. Furthermore, we studied the influence of the position at which SiH4 is injected in the expanding plasma on the film density. It was found that the film density becomes higher when the SiH4 is injected closer to the substrate. Both findings strongly suggest that the film density benefits from a high contribution of the SiH3 radical to the growth of microcrystalline silicon.

New insights in microcrystalline silicon deposition with expanding thermal plasma chemical vapor deposition

“…Finally, the 4-mm arc data do not show a clear dependence on the injection-ring position. This last observation seems to be in contrast with our model published before [5]. In that model we argued that by moving the injection ring towards the substrate, the interaction time between the species emanating from the arc (mainly atomic H) and the SiH 4 was reduced.…”

“…In another article we gave an explanation for the different slopes in Fig. 1(c) [5]. It could be argued that this is due to the varying mass density of the films, as suggested by the varying refractive indices in Fig.…”

“…1(b) the depletion is shown as a function of SiH 4 flow. For small SiH 4 flows (<3 sccm) the depletion is almost 100%, because there is a surplus of atomic H available in the plasma to dissociate all the injected SiH 4 (The atomic H flow is expected to be in between 1.8 and 24 sccm [5]). When the SiH 4 flow increases the depletion decreases because gradually there is not enough H to decompose all SiH 4 .…”

“…In this technique, described in more detail below, silane (SiH 4 ) is injected into an atomic-hydrogen plasma beam emanating from a cascaded arc. We reported that lc-Si:H with the highest refractive index could be obtained when the growth was dominated by SiH 3 radicals [5]. We argued that this growth condition was obtained by reducing the interaction time between SiH 4 and atomic H, which is achieved by moving the SiH 4 injection point towards the substrate.…”

RF power density dependent phase formation in hydrogenated silicon films

“…The plasma diagnostics reveals that the density of neutrals in the RF plasma is much higher than the ions. Among the various radicals present in plasma, the SiH 3 density exceeds over SiH and SiH 2 radicals [34,35]. Drevillon et al [36] studied silane plasma using mass spectroscopy and found that SiH 3 + and SiH 3 were responsible for growth of a-Si:H at lower (b5 mTorr) and higher (N100 mTorr) pressure, respectively.…”