The behavior of fine particles in a low-pressure parallel plate chemical vapor deposition reactor was investigated by constructing a system that permits particle motion in the reactor to be visualized. The test spherical silica aerosol particles, which were 1.0 mum in diameter and dispersed in argon gas, were fed into the reactor from the outside and particle motion was detected by a laser light scattering method. The effect of operating conditions, such as pressure and temperature, on particle transport in the reactor was investigated. The pressure was varied from 2.0 to 4.0 Torr and the wafer-substrate plate temperature was varied over the range of 25degreesC to 300degreesC. A three-dimensional numerical simulation was performed using the commercially available computational fluid dynamics code Fluent. A detailed configuration of the reactor, including the showerhead structure was considered when investigating this mechanism. It is found, both experimentally and by numerical simulation that, when the wafer-substrate plate is not heated, the effect of pressure on particle trajectory in the space between plates cannot be observed. However, at elevated temperature, i.e. when the wafer-substrate plate is heated, the particle trajectory is apparently influenced by pressure. In addition, the effect of thermophoresis, as the result of a temperature gradient by heating of the wafer-substrate plate is very pronounced for gas pressures of both 2.0 and 4.0 Torr. The experimentally observed phenomena were satisfactorily reproduced by simulation.