Determining the thermal response time of temperature sensors embedded in semiconductor wafers

We present a non-contact method for the determination of the thermal response time of temperature sensors embedded in wafers. In this method, a flash lamp illuminates a spot on the wafer in periodic pulses; the spot is on the opposite side from the sensor under test. The thermal time constant of the sensor is then obtained from measurement of its temporal response, together with a theoretical model of heat flows both into the sensor and laterally within the wafer. Experimental data on both platinum resistance thermometers (PRTs) and on thermocouples embedded in silicon wafers show good agreement with the heat transfer models. Values of the thermal response time for a wide range of experimental parameters agree to within standard deviations of 8% (PRTs) and 20% (thermocouples), demonstrating the self-consistency of our results. The method is directly applicable to determining the thermal properties of sensors used in instrumented silicon wafers. We anticipate that the method will have use in development of new sensor attachment methods, in verifying the proper attachment of sensors during production, and in confirming that the thermal attachment has not degraded with age or thermal cycling. To simplify the application of the method, we have produced a table of calculated relevant quantities to be used in relating the measured signal to the thermal response time