INSITU MEASUREMENT OF WAFER TEMPERATURES IN A LOW-PRESSURE CHEMICAL VAPOR-DEPOSITION FURNACE

Axial and radial temperature profiles within the wafer load of a multiwafer LPCVD furnace have been measured in situ using a pair of instrumented wafers. Our measurements confirm that the wafer load is not in thermal equilibrium with the furnace tube, as has been widely assumed in many modeling studies. The measurements confirm temperature variations predicted previously from a study of polysilicon film thickness profiles. Temperature variations were small for wafers near the center of the 150 wafer load. However, axial variations of up to 25-degrees-C and radial variations of up to 5-degrees-C were measured at the extremes of the wafer load. For a representative polysilicon deposition data set, axial and radial film thickness variations were found to correlate closely with measured temperature variations. The temperature profile was found to be insensitive to gas composition and flowrate, establishing radiation as the dominant mode of heat transfer. A pair of polysilicon coated quartz radiation shields were shown to improve polysilicon film thickness uniformity both down the load (along the furnace axis) and across each wafer.