To align the mask the 3 different capacitances are usually insufficient, since there, is large cross capacitance terms, sometimes all 3 will show essentially the same data scaled by different factors. To still align the sample and the mask a different approach is used. First the sample is aligned optically with the mask using the camera. The using all 3 motors the sample is approached with the mask until the resulting capacitance curve starts flattening. This marks the spot, where part of the mask has collided with the sample. The difference in capacitance values is then noted down and the mask is retracted for some steps. Now the noted down capacitance values becomes the criteria for determining if sufficient alignment is present and upon further approach the steps are stopped when the criteria is exceeded.
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