Accurate pre-alignment of wafers is key for each individual processing step. Contactless wafer edge measurement requires a dedicated vision system. Demcon focal has developed an image-based measurement system that can detect statically and dynamically the edge of the wafer with respect to the gripper and wafer marker. Using custom optical design, can image the gripper marker, the wafer maker, and the wafer edge into one image.
This resulted in sub-micron accuracy in all three dimensions with extended depth of focus and a flat field. One of the key enablers for such performance is the use of custom optical and opto-mechanical designs for imaging and through-the-lens-illumination in combination with vision algorithms.
● Up to 6mm out-of-focus, precision XY< 1mµ
● Up to 12mm out of focus, precision XY < ~2mµ
● 24mm field-of-view with TTL illumination
Sub-µm accurate alignment comes down to understanding what is happening in the process. How are all elements in the system connected to each other, how is the tolerance table structured, etc. Knowledge, experience and our system engineering approach are central to these challenges.
