A process for depositing polycrystalline silicon on substrates, including
foreign substrates, occurs in a chamber at about atmospheric pressure,
wherein a temperature gradient is formed, and both the atmospheric
pressure and the temperature gradient are maintained throughout the
process. Formation of a vapor barrier within the chamber that precludes
exit of the constituent chemicals, which include silicon, iodine, silicon
diiodide, and silicon tetraiodide. The deposition occurs beneath the vapor
barrier. One embodiment of the process also includes the use of a
blanketing gas that precludes the entrance of oxygen or other impurities.
The process is capable of repetition without the need to reset the
deposition zone conditions.