AWC Sensor Function and Principle Explanation

AWC Sensor Function and Principle Explanation

In this system, there are two sets of AWC (Auto Wafer Centering) sensors installed at the bottom of the Loadport or Chamber door.
Each sensor is paired with a reflector, forming an optical detection pair.
 

Operating Principle

When a wafer is transferred by the robot arm into the chamber, it passes through the optical path of the sensors.
Since the wafer is circular, it will sequentially block the light of the left and right sensor pairs as it passes.
The system determines whether the wafer is centered on the fork based on the time difference between the two sensors being blocked.
 

Detection Condition System Judgment and Action

Both sensors blocked for the same duration Wafer is centered → No compensation needed
Left sensor blocked for a longer time Wafer is offset to the left → Robot performs rightward offset compensation
Right sensor blocked for a longer time Wafer is offset to the right → Robot performs leftward offset compensation
This method automatically corrects the wafer’s center position during chamber insertion, ensuring no offset or collision occurs.
 

AWC Offset Trend Analysis and Teaching Judgment

The compensation amount of the AWC offset is recorded by the system as a trend.
If a significant drift is observed in the AWC offset trend over a certain period following possible issues (i.e., increasing offset amount or unstable direction), it indicates the following situations may occur :

1. Sensor position abnormality
2. Accumulated robot error
3. Mechanical deviation or thermal drift

At this point, Teaching (re-teaching) should be performed to recalibrate the robot's transfer center coordinates and ensure accuracy.
 

Conclusion

Although the design of this type of AWC mechanism is simple, it is critical for maintaining stable transfer precision.
Through real-time compensation and trend monitoring, it is possible to greatly reduce misalignment-related wafer defects and system errors.