Deposition of a-Si Films Using Silane Molecular Beams Excited by Heated Wire and ArF Laser
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DEPOSITION OF a-Si FILMS USING SILANE MOLECULAR BEAMS EXCITED BY HEATED WIRE AND ArF LASER *
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S. FURUNO, S. IGUCHI M. HANABUSA,**T. TSUBOI, T. SATO, AND T. INOUE *Department of Electrical Engineering, Toyohashi University of Technology, Tenpaku, Toyohashi 440, Japan **Higashifuji Technical Center, Toyota Motor Co., Susono, Shizuoka 410-11, Japan ABSTRACT Amorphous silicon films were deposited by using silane molecular beams excited either by ArF laser beams or heated tungsten wires. Reaction mechanisms are discussed on the basis of the dependence of deposition rates on substrate temperature and, in the case of the heated-wire method, on wire temperature. INTRODUCTION Molecular beams have been used in various studies to obtain They fundamental knowledge of molecules, atoms, and nuclei [I]. are generated by a nozzle placed in an evacuated chamber, and are characterized by a uniform distribution of molecular velociIn the present work we used the molecular beams to ties. deposit thin films; in particular, amorphous silicon films were The present method is deposited from silane molecular beams. different from normal gas-phase deposition, because molecular collisions are much less frequent in molecular beams at equivalent gas pressure, which should modify the secondary reactions Technically that occur after dissociation of the source gases. For instance, when speaking, there are certain advantages, too. we dissociated source molecules in the molecular beam by laser beams, an optical window that was used to introduce light into the reaction chamber was not covered with deposits, because the source gas molecules were pumped out quickly and almost completely absent from the vicinity of the window. The main problem in the molecular beam deposition method is Originally how to excite and decompose source gas molecules. we employed a dc discharge generated by an externally applied voltage. It was found to be unstable, however, and we switched As the third to photoexcitation by an ArF excimer laser. method, a heated wire placed inside or around the molecular In the present beams was used to deposit films at great speeds. paper, we report the results obtained from the laser-molecular In addition, we double beam method and the heated wire method. carried out CARS (coherent anti-Stokes Raman spectroscopy) measurements to clarify reaction mechanisms related to molecular beam deposition. EXPERIMENTAL The experimental arrangement used for laser excitation of In previous work silane molecular beams is shown in Fig. 1(a). different types of arrangements were used for the laser-molecular beam experiment [2]; however, the present scheme seems to yield the best result in terms of deposition rates and film quality. Mat. Res. Soc. Symp. Proc. Vol. 75. '1987 Materials Research Society
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(a) Fig.
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Experimental arrangement used for laser-molecular double beam deposition scheme (a), and for heated-wire scheme (b).
The nozzle was a modified automobile fuel injector with an The source gas was either Si2H6 opening of 0.7
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