Ultrafast Deposition of Crystalline Si Films Using a High Density Microwave Plasma
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1245-A10-04
Ultrafast Deposition of Crystalline Si Films Using a High Density Microwave Plasma Haijun Jia1,2 and Michio Kondo1 1 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan 2 Baoding TianWei SolarFilms Co., Ltd. Baoding, Hebei 071051, People’s Republic of China ABSTRACT A multi-pressure microwave plasma source is developed and is applied for the fast deposition of crystalline silicon films. In this paper, the plasma source is diagnosed firstly. Electron density, electron temperature and discharge gas temperature of the plasmas generated in ambient air are studied using optical emission spectroscopy (OES) method. By using the high density microwave plasma source, depositions of crystalline silicon films from SiH4+He mixture at reduced pressure conditions are investigated systematically. After optimizing the film deposition conditions, highly crystallized Si films are deposited at a rate higher than 700 nm/s. We also find that the deposited films are fully crystallized and crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process. INTRODUCTION Due to the high carrier mobility, strong stability against light exposure and wide-range spectral sensitivity, high quality crystalline silicon thin films have attracted much attention as a promising material for electronic device applications such as thin film transistors and solar cells [1,2]. Among the various approaches for the preparation of crystalline Si films, the most successful technique thus far is the plasma based chemical vapor deposition (PECVD) process either ignited by radio frequency (rf) or by very high frequency (VHF) using SiH4 highly diluted by H2 as reactive source gases [3,4]. For the cost-effective applications of the material, special attention has been addressed in the recent year to increase its deposition rate while maintaining (reasonable) film quality [5].Recently, there is a growing interest in transferring the low-pressure plasma technologies to high pressure or even atmospheric pressure conditions [6]. The enhanced plasma chemistry in the latter case, especially the higher electron density and the lower electron temperature, offers a high potential for material preparation and modification. Taking into account the above points, in this study, a microwave plasma source, which allows the plasmas to be generated in a wide pressure range from ~1 Torr to atmospheric pressure, is used for the fast deposition of crystalline Si films. In this paper, firstly, we diagnose the properties of the plasma source at atmospheric pressure condition. Moreover, we perform the deposition of crystalline Si films from SiH4+He mixture by using this microwave plasma source.
Through optimizing th
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