Crystallization of a-Si Films on Low-Melting-Point Glass Substrates
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CRYSTALLIZATION OF a-Si FILMS ON LOW-MELTING-POINT GLASS SUBSTRATES W.K.PARK*, G.S.CHAE*, E.I.GIVARGIZOV**, A.B.LIMANOV**, and A.N.KISELEV** *An-Yang Laboratory, Goldstar Co., Ltd., Kyongki-Do, 430-080, Korea **Institute of Crystallography, Russian Acad.Sci., Moscow 117333, Russia ABSTRACT Results of experiments on crystallization of thin (50 to 200 nm) amorphous Si films initially deposited onto glass substrates by different techniques (PECVD, LPCVD) and treated by different lasers (argon, excimer, or Cu-vapor) are given. The films treated are characterized by in-plane and cross-sectional TEM, and by microdiffraction. Some conclusions about mechanisms of the crystallization are made. 1. INTRODUCTION Polycrystalline silicon films mnlow-elting-point glass substrates are used for applicaticns in active-matrix liquid-crystal displays (LCD's), in thre-dintional circuits, etc 11-5]. Various techniques for preparaticn of such films have been developed in difTerent laboratories: low-pressure CVD, crystallization of initially-deposited amorT•iou films by different lasers or by rapid thermal annealing, etc. In view of the low melting point of the substrates, crystallization of such films by short-elength lasers whose radiation is absorbed in a very thin subsurface layer of the films is rather popular. Further, different kinds of the lasers can be used for this aim: cw Ar laser, pulsed excimer laser, pulsed Cu-vapor laser, etc. The former one is acceptable for this aim only at a hio-o ,otian of the beam, while the latter ones have rather short (in nsec rage) pulses that can exclude damages of the glass substrates. Energy densities (powers) of the lasers are important parnmeters of the processing. Finally, the history of the films intended for crystallization influences strongly the results. In this paper, three kinds of lasers were used for crystallization of amorphous films, aid the films obtained are ccmpared based cn T134studies of the films. Also, the properties of the initial films intended for crystallizatimn (their history, thickness, etc) are taken into account. 2. EXPERIMENTAL 2.1.
Preparation of initial films for crystallization
Coming, Glass 7059 substrates were used in these experiments. To decrease the tempe-
rature in the substrates and to avoid damage, a buffer layer of SiO2 or Si 3 , 0.2
in
thickness was deposited cn them. Three principal techniques for fabrication of the initial films were used in our expe-
riments: LPCVD, PECVD, and PECVD followed by a dehydrogenaticn asnaling. 0 The LPCVD process was performed by Sill decoaposition at a temperature of 570 C. Films prepared at such tarperatures contained cnly the amorphous phase as shown by TEM studies. A principal advantage of these films is the absnce of dissolved hydrogen negatively influencing the crystallization process. We hereafter call such films "a-Si films". 0 'fTe PECVD prooess was performed at a tarperature of 250 C, and the deposited films cntained up to 23 atanic %of hydrogen. We call these films "a-Si:H films". Finally, sane of the PECV
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