I want to make a single mask for multi-layer lithography. This mask will be having different patterns. Now the issue is how to make alignment marks for this.
There are two methods that I known of. The marker could be crosses and should be big enough to be seen under the vision system of your photolithography system.
1) Etched marker
Etch down for about 1 um of the marker and it should be quite visible during the alignment.
2) Metal marker
Use lift-off or other technique to produce metal marker on the wafer. The marker produced in this way is of lower accuracy than (1) normally.
The markers should be present in every mask layers that need alignment.
Hope this helps.
You can have alignment marks designed on each layer/pattern. You have to superimpose one over the other for subsequent patterning.
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