ANALYSIS OF THIN-FILM POLYSILICON ON GRAPHITE SUBSTRATES DEPOSITED INA THERMAL CVD SYSTEM

Thin films of polycrystalline silicon of 10-30 mu m were grown on grap hite substrates. The deposition experiments were conducted in a horizo ntal, atmospheric pressure RTCVD reactor from 800 to 1200 degrees C em ploying the precursor trichlorosilane (TCS) and the dopant trichlorobo rine (TCB) diluted in a hydrogen carrier gas. The polycrystalline Si l ayers were analyzed by means of Nomarski microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and by high-resolution tra nsmission electron microscopy (HRTEM). The electrical properties of th e deposited films were evaluated by spreading resistance profiler (SRP ), by Van der Pauw, and by microwave-deduced photoconductivity decay ( MW-PCD) measurements. Deposition rates of the as-grown Si films were i n the range of 1-3 mu m min(-1) resulting in grain sizes varying from 0.1 to 6 mu m. The grain sizes of the deposited layer increases when t he temperature or/and the input partial pressure of the reactant were raised. Additionally, preferred growth orientation conditions were fou nd. Thus, crystallites grown between 900 and 1100 degrees C showed a m aximum diffraction peak for the (2 2 0)-orientation. A highly resistiv e region was also observed at the silicon-graphite interface due to th e formation of SiC agglomerates. (C) 1998 Elsevier Science B.V. All ri ghts reserved.