Analysis of thin film polysilicon on graphite substrates deposited in a thermal CVD system

Thin films of polycrystalline silicon of 10-30 mu m were grown on graphite substrates. The deposition experiments were conducted in a horizontal, atmospheric pressure RTCVD reactor from 800 to 1200 degrees C employing the precursor trichlorosilane (TCS) and the dopant trichloroborine (TCB) diluted in a hydrogen carrier gas. The polycrystalline Si layers were analyzed by means of Nomarski microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and by high-resolution transmission electron microscopy (HRTEM). The electrical properties of the 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 in 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 the temperature or/and the input partial pressure of the reactant were raised. Additionally, preferred growth orientation conditions were found. Thus, crystallites grown between 900 and 1100 degrees C showed a maximum diffraction peak for the (2 2 0)-orientation. A highly resistive region was also observed at the silicon-graphite interface due to the formation of SiC agglomerates. (C) 1998 Elsevier Science B.V. All rights reserved.