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A4.4



FAST DEPOSITION OF MICROCRYSTALLINE SILICON FILMS USING THE HIGH-DENSITY MICROWAVE PLASMA UTILIZING A SPOKEWISE ANTENNA H. SHIRAI, Y. SAKUMA, K. YOSHINO, AND H. UEYAMA*

Department of Functional Materials Science, Faculty of Engineering, Saitama University, 255 Shimo-Okubo, Urawa, Saitama 338-8570, Japan *Nihon Koshuha Co., Ltd. 1119 Nakayama, Midori-ku, Yokohama, 226-0011, Japan ABSTRACT

The high-density and low temperature microwave plasma utilizing a spokewise antenna was successfully applied to fast deposition of highly crystallized and photconductive microcrystalline silicon (  c-Si:H) films at low temperatures. The deposition rate and film crytstallinity significantly depend on the axial distribution of the plasma parameters. Best crystallinity was obtained at the axial distance Z from the quartz glass plate, where the spread of the ion beam energy impinging to the growing surface was minimum. By optimizing the axial distance Z and total pressure, highly crystallized c-Si:H films could be fabricated with a high deposition rate of ~47/s in the SiH4 and Ar mixture plasma with no use of the H2 dilution. An intentional control of the ion beam energy is also attempted using a mesh grid electrode to suppress the ion bombardment to the growing surface. 1. INTRODUCTION Hydrogenated microcrystalline silicon (c-Si:H) has recently been given much attention because it is one of the most promising materials for thin film solar cells of lower cost, higher conversion efficiency and better stability than amorphous-silicon-based solar cells. Most of the works have been performed by using conventional rf and very high frequency (VHF) plasma CVD methods. In reactive plasmas widely used, generally, there are effects of electron density ne and temperature Te on the products obtained from such processing. Higher ne promote the dissociation of mother molecule and it is desirable for enhancing the deposition rate. So far, to this aim, electron cyclotron resonance (ECR) and helicon wave plasma sources were applied for fast deposition of a-Si:H, a-SiGex:H and c-SiCx alloy films.[1,2] However, higher Te promotes excess secondary reactions and ionization in the plasma, which do damage to the growing surface and interface. To overcome this difficulty, a novel high-density and low temperature plasma source is required. Recently, a couple of novel high-density plasma sources with no use of magnetic field have been applied for ultra-large-scale integrated circuits (ULSI) technologies, i.e., inductive coupling plasma (ICP), surface wave plasma (SWP) and ultra high frequency (UHF:500MHz) plasma.[3,4,5] We have developed a novel high density microwave plasma (2.45GHz) utilizing a spokewise antenna for fast deposition of highly crystallized and

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photoconductive c-Si:H films at low temperatures. The plasma maintains a uniform state over ne >1011cm-3 along with Te of 2-2.5eV in the wide pressure range from 5-50mTorr using Ar plasma.[6] . Higher generation efficiency of neutral radicals such as SiH3 is expected in SiH4 pl