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National Instruments Corporation
15-1
15
Scanning
The goal of the scanning application is to inspect a wafer under a fixed
laser. Multiple detectors collect the scattered laser light and feed the data to
an analysis system that maps any defects.
The wafer rests on an XY stage that moves in two dimensions.
The objective of the scan is to cover as much space on the wafer as possible
in the shortest amount of time. Scanning a greater area increases the
chances of detecting all defects. Shortening the scan time lowers the cycle
time, and increases the speed of the production or testing.
You can perform a scanning application in one of the following three ways:
•
Move the stage in a raster by connecting several straight-line move
segments.
•
Use blending to perform the scan in a single continuous move.
•
Use contouring to create a custom scanning path for the stage.
Connecting Straight-Line Move Segments
You can cover the entire area of the wafer by varying the size of the raster
area. You can increase the resolution of the scanning path by shortening the
distance of the vertical straight-line moves. However, remember that
increasing the resolution also increases the cycle time.
Figure 15-1.
Raster Scanning Path
