Silicon Surface Texturization Mechanism by Hydrogen Radicals Using Tungsten Hot Filament
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0891-EE07-21.1
Silicon Surface Texturization Mechanism by Hydrogen Radicals Using Tungsten Hot Filament Hiroshi Nagayoshi, Hiroaki Sato, Suzuka Nishimura1 and Kazutaka Terashima1 Tokyo National College of Technology, 1220-2, Kunugida-machi, Hachoji, Tokyo, Japan 1 Shonan Institute of Technology, 1-1-25, Nishikaigan, Tsujido, Fujisawa, Kanagawa, Japan ABSTRACT This paper describes a surface texturing mechanism on crystalline Si using hydrogen radicals generated by a tungsten hot filament. The inverted pyramid or labyrinthV groove structure could be obtained by the particle deposition before etching. The mesh like tungsten particle layer, which works as an etching mask against hydrogen radical, was obtained when the silicon substrate was used. On the other hand, the tungstem particles were not deposited as mesh like pattern when the SiO2/Si substrate was used. These results suggest that the evaporation of silicon hydrides from the silicon surface by hydrogen radical etching causes the mesh like pattern deposition of tungsten particles. The increase of filament current enables short time texturing process of less than 1 minute. INTRODUCTION Surface texturing is a common approach in reducing optical loss in silicon solar cells.[1] On multi crystalline silicon, RIE using SF6 or Cl2, mechanical texturing, and acidic solution method have been introduced.[2] However, chemical etching methods generate much chemical waste. In RIE texturing, exhausted SF6 has much higher global warming effect than that of CO2. On the other hand, Cl2 is difficult to handle. In the high efficiency mono crystalline Si solar cell process, photo-lithography technique has been used to control the feature size of an inverted pyramid texture.[3] Although, high ordered and effective anti reflection properties are obtained by this method, many process steps are needed. We have been studied the silicon surface texturing by hydrogen radical etching and found the textured Si surface could be obtained using the tungsten hot filament method. This process only uses hydrogen as source gas and has a potential to be a low cost as well as an environmentally friendly process. The etching reaction by hydrogen radicals against semiconductor materials such as Si, GaAs, etc., has been already reported by some groups. [4-6] Random pyramid structure fabrication on GaAs surface by hydrogen radical has been reported by Nagayoshi et.al.[7] Although, random pyramid texture structure like GaAs crystal has not obtained yet, we obtained the inverted pyramid or labyrinth V groove texture structure by the tungsten particle deposition before etching. The mesh like pattern particle layer was deposited on the silicon surface, working as an etching mask against hydrogen radicals. This paper describes the mesh like tungsten particle layer deposition mechanism and the possibility of short time texturing by this method.
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EXPERIMENTAL Figure 1 shows the schematic of the experimental apparatus. The furnace heater was used as the reaction chamber. The tungsten filament p
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