Wafer defect inspection system detects physical defects (foreign substances called particles) and pattern defects on wafers and obtains the position
coordinates (X, Y) of the defects. Defects can be divided into random defects and systematic defects.
Random defects are mainly caused by particles that become attached to a wafer surface, so their positions cannot be predicted. The major role of
a wafer defect inspection system is to detect defects on a wafer and find out their positions (position coordinates).
On the other hand, systematic defects are caused by the conditions of the mask and exposure process, and will occur in the same position on
the circuit pattern of all the dies projected. They occur in locations where the exposure conditions are very difficult and require fine adjustment.
The wafer defect inspection system detects defects by comparing the image of the circuit patterns of the adjacent dies. As a result, systematic
defects sometimes cannot be detected using a conventional wafer defect inspection system.
Inspection can be performed on a patterned process wafer or on a bare wafer. Each of these has a different system configuration. Below is an
explanation of typical inspection systems; Patterned wafer inspection system and Non-patterned wafer inspection system.
Wafer inspection, the science of finding defects on a wafer, is becoming more challenging and costly at each node. This is due to process shrinks,
design complexities and new materials.
The idea is to find a defect of interest on a wafer. In the inspection process, a wafer inspection tool takes a photo of a die. Then, the tool takes
a photo of another die and compares them. If there’s a change, that’s generally a defect.