Extended marker search routine in the EBPG “Cjob” software
Raith’s EBPG Series systems are fully automated electron beam lithography tools providing automatic focus, stigmation, and field size calibrations. Once a holder is loaded into the airlock, no further manual operator intervention is required.
An extended backup marker procedure, featuring automated alignment control and exposure, has now been introduced to make the alignment registration procedure even more robust when running multiple overnight exposure jobs. It is now also possible to use a wider range of marker types in a single cell.
The marker is the registration position to which the pattern has to be aligned. This can comprise metal squares or etched structures on the substrate surface. For maximum flexibility, the shape of the marker can vary from a square, rectangle, or cross to any shape desired. (This last option is also known as image marker recognition, and can be referenced to a location in the design.)
Normally the same type of markers are used within a given cell. Markers may be damaged during sample processing, which may lead to inability to perform registration.
As a result, when a marker list is used the EBPG system will automatically look up the next possible marker in the list. If this marker is the same type as the damaged general marker, only the new design position of this marker is required.
If the marker is a different type, the position of the new marker type name can be added to the list. In the example (right), the general marker is the 20µm square (A) located in the corners of the design. If the EBPG system cannot find the marker due to marker damage during sample processing or other reasons, it automatically searches for the 10um square marker (B) - here located more towards the middle.
As backup, if required the same routine can be applied as a next step to search for the cross marker (C) in the corner of the design. If this is also not found for some reason, an image marker (D) (e.g. a letter image) can be used.
The system offers you the flexibility to decide how long your marker list should be. Of course, once the first marker is found the system will automatically continue to the next corner.
This extended marker search option, now a standard feature in the EBPG BEAMS software, further reduces the probability of having to abort a job.