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Dear Sir.

We have a project to measure the temperature of the wafer. For some other requirements, however, it's required a 8mm electrical isolation between the wafer and sensor. I plan to put a ceramic (AlN with 150 thermo conductivity) pad between the wafer and sensor with 8mm thickness.

To test the response time different w/ and w/o pad. We established an experiment. Heat the wafer from 23 degree to 30 degree and measure the temperature w/ pad and w/o pad. From the result of simulation with ANSYS, the response time should have no difference w/ pad and w/o pad. While, experience results show there is at least 5 second delay w/ pad.

Why are there 5 second delay?

Could we use ceramic pad as thermo translater and have a good response time?

 Thanks and Best Regards

Kyle(Kejun) Zhang
System Design Engineer
kyle.zhang@kla-tencor.com

Kyle,

I don't know why ANSYS would suggest there to be no difference in the response of a thermal system which just added 8 mm of thermal resistance and the additional mass of the ceramic between a heat sink and a temperature sensor. The additional ceramic will impede the flow of heat whether trying to warm up the wafer or trying to measure a cool down.

 Just taking a theoretical wafer size of 300mm, it would take somewhere around 1300 watts of extra heat just to warm the ceramic from 23 to 30 in 5 seconds. That amount of energy would also need to dissipate through the ceramic in order to stabilize at cool down.