New ultrahigh vacuum setup and advanced diagnostic techniques for studying a-Si:H film growth by radical beams
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A9.24.1
New ultrahigh vacuum setup and advanced diagnostic techniques for studying a-Si:H film growth by radical beams J.P.M. Hoefnagels, E. Langereis, M.C.M. van de Sanden, and W.M.M. Kessels Dept. of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
ABSTRACT A new ultrahigh vacuum setup is presented which is designed for studying the surface science aspects of a-Si:H film growth using various advanced optical diagnostic techniques. The setup is equipped with plasma and radical sources which produce well-defined radicals beams such that the a-Si:H deposition process can be mimicked. In this paper the initial experiments with respect to deposition of a-Si:H using a hot wire source and etching of a-Si:H by atomic hydrogen are presented. These processes are monitored by real time spectroscopic ellipsometry and the etch yield of Si by atomic hydrogen is quantified to be 0.005±0.002 Si atoms per incoming H atom.
INTRODUCTION Over the last two decades, the growth mechanism of a-Si:H has widely been studied, even to such an extent that it has become a model system for understanding thin film growth [1,2]. Meanwhile, the investigations have become more advanced and sophisticated although most of the experiments have been carried out under regular, but sometimes rather well-defined operating conditions for a-Si:H deposition [3]. However, to reach the next level of understanding, i.e. insight into the surface reactions at the atomic scale, surface science-like studies under very well-defined and idealized conditions will be required. Such studies can for example be carried out by mimicking a-Si:H film growth using several well-defined radical beams as, e.g., done for Si plasma etching [4] and deposition of hydrogenated amorphous carbon [5]. In this paper, we present a new experimental setup for beam studies of a-Si:H film growth. In the design of this setup, three basic criteria have been taken into account: 1) The substrate, onto which the film is deposited, is the key factor within the setup and should therefore be easily accessible by (optical) diagnostics and the use of different substrate types, materials, and sizes should be possible. The substrate should also remain clean for a sufficiently long time setting strict demands on the level of vacuum reached in the setup. 2) With well-defined radical (and ion) beams it should be possible to mimic film growth under regular deposition conditions and the radical beams should preferentially be mono-radical and accurately quantified in terms of flux. For a-Si:H, radical beams of SiH3 and H are most appropriate. 3) The growth process needs to be investigated by advanced in situ diagnostics with a clear preference for “all-optical” techniques which are able to monitor film growth in real time. Furthermore, the techniques need to be innovative such that key questions of a-Si:H film growth (e.g., “What is exact role of surface Si dangling bonds?”) can be addressed. In this paper, a setup named GALAPAGOS, which meets these requi
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