Specific Process Knowledge/Characterization/KLA-Tencor Surfscan 6420/Acceptance test results
Calibration wafers
DTU Nanolab has two (earlier tree, but one has disappeared) calibration wafers for the KLA-Tencor Surfscan. The calibration wafers are 6" silicon wafers with a number of polystyrene latex spheres (PLS) uniformily spread over the surface.
Certified mean diameter and number PLS's on each wafer:
Calibration wafer 1:
- PLS mean diameter: 0.204 µm +/- 0.008 µm
- Number of PLS's: 7234 +/- 10%
Calibration wafer 2:
- PLS mean diameter: 1.112 µm +/- 0.018 µm
- Number of PLS's: 7700 +/- 10%
Calibration wafer 3:
- PLS mean diameter: 4.000 µm +/- 0.043 µm
- Number of PLS's: 7587 +/- 10%
Repeatability check
Acceptance criterion:
10 scans are done on each of the three PLS calibration wafers. The wafers are loaded/unloaded to the cassette every time. The repeatbility of +/- 1σ has to be less than 1%.
Results
Calibration wafer 1:
- Measured average PLS diameter: 0.2063 µm. Repeatability: 0,24%
- Average number of PLS's: 7065. Repeatability: 0.11%
Calibration wafer 2:
- Measured average PLS diameter: 1.100 µm. Repeatability: 0%
- Average number of PLS's: 7427. Repeatability: 0.20%
Calibration wafer 3:
- Measured average PLS diameter: 3.970 µm. Repeatability: 0,24%
- Average number of PLS's: 7101. Repeatability: 0.10%
Uniformity check
Acceptance criterion:
Measure the average PLS diameter by boxing an area in five different locations on a PLS wafer. The measurement has to be within 3%.
Results
Calibration wafer 2:
- Non-uniformity: 1,36%
Calibration wafer 3:
- Non-uniformity: 0.38%
Handling test
Acceptance criterion:
Run a cassette of 25 wafers. The machine should be able to error-free handle the cassette 40 times, i.e. it should be able to handle 1000 wafers without failing.
Results
6" cassette":
A cassette of 25 wafers was handled 40 times over night, i.e. the acceptance criterion was meet.
4" and 8" cassette:
A cassette of 25 wafers was handled two times. The scanning was then stopped to save time as handling of more cassettes is not expected to cause problems.