Comment AG4100 SNF 2008-12-04 13:37:43: Results of QUAL1150 recipe ...
shott at snf.stanford.edu
shott at snf.stanford.edu
Thu Dec 4 13:37:43 PST 2008
The AG4100 chamber had been completely rebuilt to alleviate blockage in the cooling lines, the door closure mechanism has been adjusted, a pyrometer calibration has been performed, and we've just run a wafer qualification that, I believe, looks reasonable ... Folks with more experience with this tool, however, should look over the results to insure that things look OK to them as well. In particular, there is significant on-wafer (mostly back to front) thickness variation and I don't have enough experience on this tool to know what is expected in this regard.
Here are the results of the 5 test wafers (note: these were all L-prime wafers that had a normal pre-diffusion clean. This was running the 1150 Qual recipe which is basically a 30 second oxidation at 1150 degrees C.
Wafer 1 2 3 4 5 6 7 8 9 Mean StDev
1 107.23 108.77 111.35 121.71 128.61 119.41 114.62 113.18 122.2 116.3422 7.082508
2 109.06 110.39 115.16 125.87 127.66 126.18 117.64 114.47 113.39 117.7578 7.083262
3 109.45 111.27 114.38 123.58 128.21 122.55 118.39 111.98 113.55 117.04 6.475757
4 109.87 110.76 113.57 121.29 125.08 126.33 118.76 111.47 114.48 116.8456 6.245929
5 108.28 109.88 112.32 119.12 119.68 119.45 116.67 110.27 117.71 114.82 4.602293
Note: the 1 through 9 positions are the standard Woollam positions .... 1 is the top of the wafer, 5 is the flat, 6 is the left side and 9 is the right side. The wafers were loaded so that the flat was at the bottom of the cassette in the AG4100 so that when inserted in the oven, the flat sits away from the door and the top of the wafer is nearest the door. As a result, you can see that the oxide thickness is lowest closest to the door and highest at the deepest reaches of the furnace.
I don't know how this compares to normal on-wafer variation in this tool to know whether better uniformity is to be expected, but the wafer to wafer variation seems to be quite good.
If I am not mistaken, for some time this 1150 recipe was giving noticeably thinner results in the AG4100 than observed in the AG4108. These mean thickness of about 115 angstrom is, I believe, quite close to what is observed on the AG4108 for the same recipe.
In any event, pending further discussion, I'm releasing this tool as "green" under the assumption that each of you will evaluate and consider this on wafer uniformity to see how it meets your needs.
p.s. We are expecting the rebuilt AG4108 chamber to be returned early next week ...
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