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A13.4.1

Investigations on the Real-Time Monitoring of the Crystallinity of Hydrogenated Microcrystalline Silicon Films Christoph Ross, Friedhelm Finger and Reinhard Carius Institute of Photovoltaics (IPV), Forschungszentrum Jülich, D-52425 Jülich, GERMANY ABSTRACT A method for monitoring the evolution of the crystallinity during the deposition of thin hydrogenated silicon films by using in situ spectroscopic ellipsometry is presented. The crystallinity of the topmost 10-20 nm of a film is derived from the analysis of the shape of ellipsometric spectra in the UV range. The values are closely related to parameters of the deposition process and in good agreement with Raman scattering results. Examples of different kinds of microcrystalline silicon films are shown. Improvements of the time resolution and/or accuracy are discussed. The method turns out to be well suited for process control. INTRODUCTION Transitions between hydrogenated microcrystalline silicon (µc-Si:H) and amorphous silicon (a-Si:H) as a function of growth parameters have attracted a lot of interest during the past years [1-4]. For µc-Si:H, growth near the transition has resulted in optimized material for devices such as solar cells [5]. However, growth in this regime very critically depends on the substrate and on other process conditions [5,6]. Therefore, a real-time control of the crystallinity is desired. We present an empirically derived method for extracting information about the crystallinity from ellipsometric data. As will be shown, this approach can be used as a real-time monitoring tool. We first report on as-deposited hydrogenated silicon (Si:H) with different compositions of crystalline and amorphous material. We then discuss the following examples of real-time measurement during the deposition: (1) growth of µc-Si:H on Si:H layers with different crystallinity, where the crystallinity evolution within the µc-Si:H layer is expected to be determined by the crystallinity of the underlying layer, (2) growth of device-grade intrinsic µc-Si:H as a part of a pi-n solar cell, and (3) growth of a-Si:H/µc-Si:H multilayers. EXPERIMENT Silicon films and solar cells are prepared in a multichamber system for RF and VHF plasmaenhanced chemical-vapor deposition by using hydrogen diluted SiH4 [5]. SC = [SiH4]/([SiH4] + [H2]) denotes the silane concentration in the source gas. The substrates for the different kinds of deposition are specified in the next section. Cr coating of glass substrates serves to reduce background signal in Raman spectroscopy measurements. ZnO:Al coated glass substrates are used for solar cells. In contrast to our standard µc-Si:H p-i-n cell preparation, parts of the ZnO:Al surface have not been texture-etched in order to reduce scattering and depolarization in ellipsometry measurements. Film thickness values have been determined after deposition. One of the deposition chambers is equipped with a UV-visible ellipsometer of the rotatingpolarizer type. The angle of incidence amounts to ≈70°. By using a monochromator with a scanning gra