SINGLE-SHOT EXCIMER-LASER CRYSTALLIZATION OF SILICON FILMS DEPOSITED BY LPCVD

The quality of polysilicon obtained from the crystallization of amorph ous silicon films deposited by the low pressure chemical vapor deposit ion technique (LPCVD) in classical furnace, is known to be high. TFT's fabricated from this material show a field effect mobility greater th an 60 cm(2) V-1 s(-1). To improve this quality, single shot very large excimer laser crystallization of LPCVD films is studied using charact erization techniques such as atomic force microscopy observations, X-r ay diffraction, Hall mobility measurements and spectroscopic ellipsome try. Undoped, highly phosphorous and boron doped, amorphous and crysta llized deposited films are used to give a large overview about the pos sibilities of this crystallization technique. Film properties are cont inuously improved when the laser fluence increases. AFM shows an excel lent uniformity of the film whatever the laser fluence. However, a sud den degradation happens above a fluence value. This degradation is owi ng to cracks certainly induced by the mismatch of thermal expansion co efficients of the substrate and the film. (C) 1997 Elsevier Science S. A.