Comment stsetch2 SNF 2011-05-26 11:04:33: STS2 Wafer Temperature Problem

mcvittie at snf.stanford.edu mcvittie at snf.stanford.edu
Thu May 26 11:04:33 PDT 2011


We still have a significant wafer temperature problem. For the last 3 months or so I have consistently found the wafer temperature to be over 99C when I run the std STS temperature test recipe. Note that the STS spec is T < 77C, and we were running at a peak wafer temperature of 71C before this problem began. I ran the temp test again yesterday and again got T > 99C. I also did a test of my temperature indicator labels on a digital hotplate and found they are accurate to within 1C. The main process impact of the higher temperature is lower resist selectivity. The resist etch rate is running at about 2.5 times higher than it did before the problem. A month or so ago, we found that the problem is not the lip seal or the backside He in that a wafer put on to the chuck after a test run indicated the chuck was over 70C, so the whole chuck is getting hot and staying hot for some time after a run. The chuck assembly consists of the wafer, the lip seal, the chuck, a indium heat transfer gasket, a copper block with passages for coolant flow and the connection to the coolant system. We have placed a TCs on both the incoming and outgoing coolant lines. The outgoing coolant only increases by 0.9C during a test run where the wafer temperature increases from 0C to over 99C. So the problem is either in the way we have installed the indium gasket or in how the chuck is insulated from other heat sources in the chamber. Note that the chamber has a number of heaters to control polymer deposition. Tomorrow, my plan is to open the chamber, to look at the indium gasket, process kit (the insulators around the chuck) and  to measure the temperature around the chuck. We have contacted STS for them to come out and look at this problem.  Jim 




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