Highly conductive silicon films via plasma-enhanced chemical vapor deposition at low temperatures

Abstract

The primary advantage of using plasma-enhanced chemical vapor deposition (PECVD) over conventional chemical vapor deposition is lower substrate temperatures, i.e., 200–300 °C. Using heavy hydrogen dilution, highly conductive poly or single-crystal silicon films were deposited in a conventional parallel plate, ultrahigh vacuum, PECVD reactor at temperatures as low as 200 °C. The source gas used was silane mixed with 1% PH3. The hydrogen concentration was varied between 80% and 98% of the total gas flow. The films were characterized both electrically and optically. The optical properties of the films were evaluated using Fourier-transform infrared spectroscopy. The electrical characterization was done by measuring resistivity and activation energy. P–N diodes were fabricated using these hydrogen-diluted films and I–V characteristics were plotted to obtain the diode quality factor. The current conduction mechanism was determined using I–V curves. The results obtained in this work suggest that PECVD can be successfully employed to deposit highly conductive silicon films at temperatures as low as 200 °C, with preservation of the crystalline structure of the underlying substrate.