REACTOR-CHARACTERISTICS PARAMETERS FOR LOW-PRESSURE CVD PROCESSES

Three dimensionless parameters for a hot wall multiple-disk-in-tube LPCVD reactor have been presented. The first CVD parameter, CVD1, is defined as the ratio of a gas dynamic to a diffusion characteristics time. The gas dynamic characteristics time is the time taken for a carrier gas to pass through the reactor by a macroscopic forced convection flow, namely a reactor tube length divided by an average macroscopic velocity of a carrier gas in the reactor. The diffusion one is the time required for a reactant gas to diffuse through the carrier gas in the radial direction of the reactor. The second CVD parameter, CVD2, is the ratio of the diffusion to a chemical reaction rate characteristics time. The chemical reaction rate one is the time needed for a wafer surface to be covered with reactant gas molecules by a monolayer, considering the collision of the molecules with the wafer surface and a heterogeneous reaction efficiency. The third CVD parameter, CVD3, is made up of the ratio of a convection to a diffusion mass flux rate. The CVD3 is a function of a mass density, Reynolds number, Schmidt number, a radius ratio of a wafer to the reactor, and a non-dimensional spacing in the axial direction between the wafers. CVD1 and CVD3 are evaluated greater than 1, on the other hand, CVD2 equals nearly 1 at low reactor temperatures for practical deposition conditions.