Hydrogen in amorphous and microcrystalline silicon films prepared by hydrogen dilution

Abstract

Hydrogen incorporation in silicon layers prepared by plasma-enhanced chemical-vapor deposition using silane dilution by hydrogen has been studied by infrared spectroscopy ͑IR͒ and elastic recoil detection analysis ͑ERDA͒. The large range of silane dilution investigated can be divided into an amorphous and a microcrystalline zone. These two zones are separated by a narrow transition zone at a dilution level of 7.5%; here, the structure of the material cannot be clearly identified. The films in/near the amorphous/microcrystalline transition zone show a considerably enhanced hydrogen incorporation. Moreover, comparison of IR and ERDA and film stress measurements suggests that these layers contain a substantial amount of molecular hydrogen probably trapped in microvoids. In this particular case the determination of the total H content by IR spectroscopy leads to substantial errors. At silane concentrations below 6%, the hydrogen content decreases sharply and the material becomes progressively microcrystalline. The features observed in the IR-absorption modes can be clearly assigned to mono-and/or dihydride bonds on ͑100͒ and ͑111͒ surfaces in silicon crystallites. The measurements presented here constitute a further indication for the validity of the proportionality constant of Shanks et al. ͓Phys. Status Solidi B 110, 43 ͑1980͔͒, generally used to estimate the hydrogen content in ''conventional'' amorphous silicon films from IR spectroscopy; additionally, they indicate that this proportionality constant is also valid for the microcrystalline samples.

Optical and Electrical Properties of Undoped Microcrystalline Silicon Deposited by the VHF-GD with Different Dilutions of Silane in Hydrogen

“…It has already been shown [3] that the transition from microcrystalline to amorphous material is abrupt and typically takes place around 7.5% dilution for the deposition conditions used here. The optical absorption spectra measured on the present series (represented in figure 1) confirms the drastic change of optical absorption with a variation of the dilution ratio.…”

“…On the other hand, CPM absorption, which is not masked by the substrate, interface and surface absorption, can detect the changes in the defect-connected absorption: the subbandgap absorption connected to defects is found to increase with increasing dilution ratios. This can indicate an increased number of dangling bonds, unsaturated by hydrogen, at the grain boundaries [3]. The possible role of oxygen impurities on the optical spectrum has not yet been studied, experiments are under preparation.…”

“…The absorption properties of such material is almost "crystalline-like" [2], but can also be tuned by changing the deposition parameters [3].…”

Evolution of the microstructure in microcrystalline silicon prepared by very high frequency glow-discharge using hydrogen dilution

“…3 This series has already been extensively characterized by infrared spectroscopy, elastic recoil detection analysis ͑ERDA͒, and x-ray diffraction. 7,8 These previous studies allowed us to determine the growth rate 7 and the hydrogen incorporation in the deposited layers, 8 as well as to locate the amorphousmicrocrystalline phase transition. 7,8 Electron-transparent samples for TEM characterization are usually prepared by the ion-milling thinning method.…”

Silane depletion dependent ion bombardment and material quality of microcrystalline silicon deposited by VHF-PECVD

“…Efficiencies of micromorph tandem cells and modules well above 10% have thus been demonstrated [3]. However, due to its complex structure that depends on deposition conditions [1,4] and substrate properties [5], and due to the difficulty of characterizing plasma deposition regimes, the impact of these parameters on the microcrystalline material quality is still an open field of research. In this paper, microcrystalline silicon thin films are deposited in different conditions of silane depletion following a recent publication [6] and the material quality is investigated.…”