Plasma silane concentration as a determining factor for the transition from amorphous to microcrystalline silicon in SiH₄/H₂discharges

Abstract

In this work, the microstructure transition from amorphous to microcrystalline silicon is defined in terms of the silane concentration in the plasma as opposed to the silane concentration in the input gas flow. In situ Fourier transform infrared absorption spectroscopy combined with ex situ Raman spectroscopy has been used to calibrate and validate this approach. Results show that a relevant parameter to obtain µc-Si : H from SiH 4 /H 2 mixtures is the plasma composition, which is determined not only by the gas dilution ratio but also by the silane depletion fraction. It is also shown that µc-Si : H can only be deposited efficiently, in terms of gas utilization, at a high rate by using high input concentration and depletion of silane.

The silane depletion fraction as an indicator for the amorphous/crystalline silicon interface passivation quality

“…2,11 Here, an infrared laser-based plasma diagnostic tool is used in order to measure in situ the silane ͑SiH 4 ͒ depletion fraction during deposition. 12 Silane depletion measurements have provided useful insights such as the origin of higher deposition rates when using very high frequency ͑VHF͒, 13 the determination of the transition region between a-Si:H and c-Si: H depositions, 14 and the optimization of reactor configurations for fast equilibration at ignition. 15 In this paper, the authors study the influence of the silane depletion on a-Si:H layers used for c-Si wafer passivation.…”

Probing the phase composition of silicon films in situ by etch product detection

“…Briefly, the method is based on a short H 2 plasma treatment step during which the gas phase density of SiH 4 ͑i.e., the main etch product released from the film surface͒ is detected. Atomic hydrogen preferentially inserts into strained Si-Si bonds 11,12 resulting in a higher etch rate of a-Si: H relative to c-Si: H. 13,14 The SiH 4 density in the plasma is observed directly by infrared absorption spectroscopy 15 or, alternatively, indirectly by OES. In the latter method, the SiH * emission is detected as originating from SiH 4 etch product dissociation by electron impact, as also reported by Westlake and Heintze.…”

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

“…At 2.0 mbar, silane and hydrogen flows were both 75 sccm (50% silane concentration). As has been shown previously [6,11], microcrystalline material can be deposited at high initial silane concentrations c, provided that the depletion D in the plasma discharge is sufficiently large so that the ratio between the silane radical and atomic hydrogen c p remains small [12]: High depletion can be achieved either by increasing the RF input power or by increasing the residence time of the gas molecules in the reactor (i.e. decreasing the hydrogen flow).…”