Comment stsetch2 SNF 2011-05-28 12:30:05: Solved STS2 Wafer Temperature Problem

mcvittie at mcvittie at
Sat May 28 12:30:05 PDT 2011

I wrote a report/comment last night which I can not find listed so here is a repeat. Yesterday (Friday) I opened up the chamber and took apart the chuck assembly, which is not a hard task. I focused on the two indium gaskets under the chuck which transfer heat from the chuck to the cooled copper block below. In the center, I found 3 indium gaskets stacked on top of each other. I remove all of them and put the best of the 3 back in the center position. The edge gasket was in bad shape. I removed it in 2 pieces. After smoothing it, I put it back in the edge position. I reassembled evedrything, pumped the system down,  did a O2 clean and run a dummy run of the temperature test recipe. I than did the 15 min temperature test using a wafer with temperature indicator labels ranging from 71C to 121C. Since March, this test has consistently given peak wafer temperatures above 100C.  After cleaning up the indium gaskets and going to a single center gasket, I got a peak wafer temperature of 77C. It is at the limit of the STS spec but it is a great improvement over what I have seen seen for the tool. 
Clearly, we need to a get a new set of gaskets and make sure they are installed properly.  The He leak rate was 9 mT/min. Improving this leak rate should also reduce the wafer temp.  I have also been monitoring a TC on the coolant coming out of the chuck.  Until last night, I have been seeing a coolant tempap rise of 0.9C during my std temp test. After the change to the indium gasket, the coolant temp rise was 1.2 C. This shows that monitoring the coolant temp rise may be a good way  of monitoring the wafer temperature.    Jim 

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