Reaction Mechanism for Deposition of Silicon Nitride by Hot-Wire CVD with Ultra High Deposition Rate(>7 nm/s)
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0910-A03-03
Reaction Mechanism for Deposition of Silicon Nitride by Hot-Wire CVD with Ultra High Deposition Rate(>7 nm/s) Vasco Verlaan, Zomer Silvester Houweling, Karine van der Werf, Hanno D Goldbach, and Ruud Schropp Utrecht University, Princetonplein 5, PO Box 80.000, Utrecht, NL-3508 TA, Netherlands ABSTRACT The deposition process of silicon nitride (SiNx) by hot-wire chemical vapor deposition (HW CVD) is investigated by exploring the effects of process pressure and gas-flow ratio on the composition of the deposited SiNx films. Furthermore, experiments with D2 and deuterated silane were performed to gain further insight in the deposition reactions taking place. It appeared that the N/Si ratio in the layers determines the structural properties of the deposited films and since the volume concentration of Si-atoms in the deposited films is constant with N/Si ratio, the structure of the films are largely determined by the quantity of incorporated nitrogen. Because the decomposition rate of the ammonia source gas is much smaller than that of silane, the properties of the SiNx layers are largely determined by the ability to decompose the ammonia and to incorporate nitrogen into the growing material. It appeared that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high value of 7 nm/s for dense transparent SiNx films, much faster than conventional deposition techniques for SiNx can offer. Despite this high deposition rate good control over the composition is achieved by varying the flow ratio of the source gasses. Depositions performed with deuterated silane as a source gas reveal that almost all hydrogen in N-rich films originates from ammonia, probably caused by SiNx matrix formation by cross linking reactions INTRODUCTION Hydrogenated silicon nitride (SiNx) is an intensively studied material caused by its diversity of applications. For its use as passivating layer good results are reported for thin SiNx films deposited with methods like PE-CVD, expanding thermal plasma and sputtering. In recent years also a more gentle deposition technique, Hot-Wire CVD, attracted much interests and various studies have shown that excellent passivation properties can be obtained with HW CVD deposited SiNx [1,2,3]. With the HW CVD technique, also known as Hot Filament (HF) CVD or Cat-CVD, the source gasses are catalytically decomposed to radical species only at heated wires. This decomposition takes place with high efficiency [4] and no additional plasma is needed. The absence of any plasma offers HW CVD the benefit that no substrate damage is caused by ion bombardment. Furthermore, the HW CVD technology can be applied at a large scale [5]. The deposition of high quality SiNx films at low substrate temperature is possible [6]. We have investigated SiNx deposited by HW CVD for application as passivating antireflection coating (ARC) on multicrystalline silicon solar cel
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