Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films
- PDF / 2,503,726 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 214 Views
1066-A01-04
Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films Haijun Jia1, Hiroshi Kuraseko2, Hiroyuki Fujiwara1, and Michio Kondo1 1 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan 2 The Furukawa Electric Co., Ltd., Yawata-Kaigandori,Chiba, 290-8555, Japan ABSTRACT By using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that 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. Systematic study of the deposition process has been performed as a function of the deposition duration. 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 Crystalline silicon thin films are attracting considerable attention as a promising material for cost-effective thin film solar cell fabrications due to their strong stability and wide-range spectral sensitivity [1,2]. Preparation of the crystalline Si films can be realized by using plasma enhanced chemical vapor deposition (PECVD) method [3]. Due to a large thickness of the Si film needed for sufficient sunlight absorption, high rate deposition of high quality Si films becomes a critical issue [4,5]. For the film growth process, it is usually considered that the film deposition proceeds through several specific growth regimes including incubation, nucleation and stable bulk growth [6]. In addition, atomic H plays an essential role for film crystallization [7]. In this letter, by using a high density microwave plasma source, an ultrafast rate over 1000 nm/s is achieved for polycrystalline Si (poly-Si) film deposition. We find that the film crystalline structure evolves during the deposition process. Annealing-assisted plasma enhanced chemical vapor deposition is proposed to describe the evolution. EXPERIMENTS The microwave-induced plasma source used in this study employs a hybrid-mode resonator cavity. Proper design of the cavity based on a mode-switching technique suppresses the impedance variation before and after plasma ignition. Plasmas are generated inside a hollow quartz tube with an inner diameter of 10 mm positioned in the center of the cavity. By using the plasma source, He and/or Ar plasmas can be generated in a wide pressure range between 1 Torr
and atmospheric pressure. Details about the plasma source were described elsewhere [8]. Si film depositions using the microwave plasma source were performed by using SiH4, He and H2 as source gases. A microwave power of ~100 W was supplied during the depositions under a working pressure of 2 Torr. The depositions were continued for 60 seconds and no intentional substrate heating was used. A quartz fiber used as
Data Loading...
