On-site SiH₄ generator using hydrogen plasma generated in slit-type narrow gap

Abstract

We have been developing an on-site silane (SiH4) generator based on use of the chemical etching reaction between solid silicon (Si) and the high-density H atoms that are generated in high-pressure H2 plasma. In this study, we have developed a slit-type plasma source for high-efficiency SiH4 generation. High-density H2 plasma was generated in a narrow slit-type discharge gap using a 2.45 GHz microwave power supply. The plasma’s optical emission intensity distribution along the slit was measured and the resulting distribution was reflected by both the electric power distribution and the hydrogen gas flow. Because the Si etching rate strongly affects the SiH4 generation rate, the Si etching behavior was investigated with respect to variations in the experimental parameters. The weight etch rate increased monotonically with increasing input microwave power. However, the weight etch rate decreased with increasing H2 pressure and an increasing plasma gap. This reduction in the etch rate appears to be related to shrinkage of the plasma generation area because increased input power is required to maintain a constant plasma area with increasing H2 pressure and the increasing plasma gap. Additionally, the weight etch rate also increases with increasing H2 flow rate. The SiH4 generation rate of the slit-type plasma source was also evaluated using gas-phase Fourier transform infrared absorption spectroscopy and the material utilization efficiencies of both Si and the H2 gas for SiH4 gas formation were discussed. The main etch product was determined to be SiH4 and the developed plasma source achieved a SiH4 generation rate of 10 sccm (standard cubic centimeters per minute) at an input power of 900 W. In addition, the Si utilization efficiency exceeded 60%.

The effect of pretreatment for SiH4 gas by microwave plasma on Si film formation behavior by thermal CVD

“…As shown in Figure 3, the SiH 4 decomposition efficiency () increases and Si 2 H 6 absorbance decreases with the increase of plasma gap. If the gas flow velocity is uniform in a flow path cross‐section surface perpendicular to the gas flow direction, the plasma residence time ( t res ) of the process gas in the slit‐type plasma is expressed using the cross‐sectional area of the flow path [ 29 ] : where p , d , W , l , and Q are the process pressure, plasma gap, slit width, plasma length, and the standard‐state gas flow rate, respectively. However, the gas transit time ( t tra ) from the plasma to FTIR gas cell is expressed as: where V cha and V pipe are the volumes of reaction chamber and piping line, respectively.…”

“…As the electrode wall is chilled by 20°C water, Si deposited on the electrode wall is easily etched by atomic H. [ 32 ] Moreover, it was verified that the SiH 4 generation rate through Si etching by atomic H increases with increasing input power in a previous study. [ 29 ] In addition, the SiH 4 regeneration in the gas phase would be also anticipated through the following processes: …”

“…The details of the apparatus are described elsewhere. [ 29 ] The small‐volume plasma generated in the narrow gap was used for the pretreatment of SiH 4 . This plasma source is known as a slit‐type plasma source.…”

“…This plasma source is known as a slit‐type plasma source. In a previous study, [ 29 ] the narrow gap was constructed using a Si source attached to a water‐cooled copper electrode jig for SiH 4 generation. In the present study, the narrow gap was constructed using two water‐cooled stainless steel electrode jigs whose plasma‐contacting surface was coated with plasma‐sprayed alumina.…”

“…As shown in Figure 3, the SiH 4 decomposition efficiency (η SiH 4 ) increases and Si 2 H 6 absorbance decreases with the increase of plasma gap. If the gas flow velocity is uniform in a flow path crosssection surface perpendicular to the gas flow direction, the plasma residence time (t res ) of the process gas in the slit-type plasma is expressed using the cross-sectional area of the flow path [29] :…”