Radiation thermometry of silicon wafers in a diffusion furnace for fabrication of LSI

A radiation thermometry technique suitable for measuring the temperature of silicon wafers in a diffusion furnace has been developed. A principal feature of this technique is that it measures the temperature of wafers that are not in the line of sight of a conventional pyrometer. An optical guide, consisting of two quartz prisms, gives optical access to interior wafers in the load. A measuring wavelength of 0.9 mu m is selected since a silicon wafer is opaque and its emissivity does not depend on temperature at this wavelength. The accuracy of the thermometry is examined by comparing the measured value of the pyrometer with that of a thermocouple. The two measured values agree within +or-2 degrees C in a steady state. When wafers are being inserted into or drawn out from the furnace, however, an error is caused by the veiling glare at the optical guide and the wafer.< >