Strange alignment mark example: silicon nitride windows

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Here is a case where both standard alignment and correlation alignment fail. Silicon nitride windows provide high contrast “marks” but these windows are usually larger than 100 um, the maximum mark size on the EBPG. Instead of using standard mark detection, we collect images of each side, then analyze these images with “find_edge”. The sequence is defined in a script (align_window.sh) that you can plug into an exposure job. 

Alternatively, the EBPG has an imprecise alignment mode in which the operator simply points to a location to indicate where the “mark” is. This type of marker is called “joy” for the use of a virtual “joystick”. You don’t know what a joystick is? Don’t worry, it won’t be on the test. 

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This is the test: THE CRUEL WORLD OF ALIGNMENT MARKS. Yes, you have to answer these questions.