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Automated Wafer Metrology System

Solves challenges posed by bowed wafers and achieves less than 1-micron accuracy in 3-D.

 

Custom automation system designed for precision inspection of wafers for the semiconductor industry.This sophisticated, flexible wafer metrology system combines a Micro-Epsilon profilometer with a high-performance, high-resolution vision system and laser interferometers to detect and measure laser-cut features on one side of a wafer relative to features on the other side of the wafer.

Bowed wafers enter the system at two cassette tilt stations. Wafer handling is via a robot fitted with an edge grip end effector. Wafers are oriented on a notch finder, with wafer ID captured by a Cognex OCR camera. Wafers are then inspected at a custom wafer pocket mounted on an open-frame X-Y stage assembly. The wafer on the table is inspected on both the top and bottom by opposing 1392 X 1040 pixel vision cameras. The top and bottom inspections can be referenced to top or bottom fiducials.

Unique three-dimensional features are inspected by the profilometer, providing final resolutions of less than 0.1 micron. The wafer handling and inspection process are fully automated and wafers are automatically tracked throughout the system. In addition, the entire process can be visually monitored with custom touch-sensitive screens at the user interface.

Wafer bowing causes measurement errors as the wafer is scanned.  A unique custom self-calibration tool and algorithm finds very small angular errors in the cameras and the machine uses this information to compensate for the induced errors to achieve the error budget.

The system is mounted on vibration isolated granite supported by a welded steel base for superior stability. All pneumatic, computer, and control hardware is contained within the base structure. This tool is designed for use in a cleanroom environment and features on-board temperature, humidity and barometric pressure monitoring and weather compensation routines.

Technical Specifications
Control System:

PC based

Operator Interface:

Custom GUI in C#.net tracks wafer progress. System was developed with client to provide a user-friendly interface while meeting specific process criteria.

Machine Vision/Optics:

Two 1392 X 1040 pixel vision cameras with Cognex vision board and Cognex VisionPro software tools. High magnification telecentric lens with computer controlled coaxial and ring lighting.

Wafer Handling Robot:

Standard Isel robot with edge grip end effector.

Environment:

Clean room: Class 10 or above.

Motion Control:

Galil

Stage:

Primatics open frame X-Y stack. System is mounted on granite blocking supported by a welded steel base.

Software Compliance:

Fully compliant with SECS/GEM standards.

Wafer Tracking:

Cognex OCR

Inspection:

Micro-Epsilon profilometer and high-resolution vision system using X-Y laser interferometers for position verification. Top and bottom 3D inspection with fiducial reference on top or bottom.

Wafer Orientation:

Standard Isel notch finder.

Storage Capacity:

Two custom tilt-type wafer cassettes, 25 wafers/cassette.

Environmental Monitoring:

Onboard sensors monitor temperature, barometric pressure, and humidity. Software corrects for variations.

Safety:

Fully guarded enclosure with safety interlocks at all entry points.

 

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