Wafer Sorter Cassette Mapping for Deformation Detection
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Solution Overview
Problem
Current semiconductor wafer fabrication processes face challenges in accurately measuring and addressing wafer cassette deformation, which leads to wafer damage and reduced process yield due to mishandling caused by warped, compressed, or tilted cassettes, as existing systems only verify flatness off-line and lack comprehensive in-line monitoring.
Innovation Solution
A wafer sorter cassette mapping system using a light-emitting diode and photo transistor sensor scans wafers to measure their positions, coupled with a modeling system to evaluate cassette integrity, determining slot positions and triggering disposition based on deformation levels, including replacement decisions, and storing data for trend analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a prior art cassette checking system is used to verify flatness off-line, then the flatness of the lower surface of the cassette housing can be verified, but it cannot provide comprehensive in-line monitoring of cassette deformation and slot position accuracy
Solution Approach 1:
The system performs preliminary measurement of wafer positions using the fiber optic scan head before the wafer sorting operation. By measuring wafer positions in advance and comparing them to expected positions, the system can detect cassette deformation and slot position errors before they cause wafer damage, enabling preventive action rather than reactive correction.
Solution Approach 2:
The patent uses the wafer itself as an intermediary object to indirectly measure cassette deformation. Instead of directly measuring the cassette structure, the system measures wafer positions within the cassette and infers cassette deformation from these measurements. This intermediary approach enables in-line monitoring without requiring direct contact with or modification of the cassette structure.
2Productivity
If wafer cassettes are used without in-line monitoring, then the sorting process can proceed quickly, but wafer damage occurs due to undetected cassette deformation
Solution Approach 1:
The system implements a feedback mechanism where wafer position measurements are continuously taken during the sorting process, compared to expected positions, and used to generate alerts when deformation exceeds thresholds. This feedback loop enables real-time detection of cassette deformation without significantly slowing down the sorting process, as measurements are integrated into the existing wafer handling workflow.
Solution Approach 2:
The patent replaces direct mechanical measurement of cassette structure with optical measurement of wafer positions. By using a fiber optic scan head to measure wafer positions rather than mechanically probing the cassette structure, the system achieves non-contact, rapid measurements that maintain sorting speed while detecting deformation through wafer position variations.
3Difficulty of detecting and measuring
If fixed sensors are used to identify missing or protruding wafers, then basic wafer presence can be detected, but no information about cassette deformation or slot position accuracy is obtained
Solution Approach 1:
The system transitions from two-dimensional wafer presence detection (present/absent) to three-dimensional position measurement by adding Z-axis height measurement capability. The fiber optic scan head measures not only whether a wafer is present but also its precise vertical position, enabling detection of wafer protrusion, depression, and cassette deformation that cannot be detected by presence sensors alone.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables in-line evaluation and improved wafer handling by identifying and mitigating cassette deformation, enhancing device yield and reducing costs by preventing wafer damage and mishandling, while providing data for forecasting and trend analysis.
Implementation Method 1
a fiber optic scan head used to scan over the wafers in the cassette to obtain position measurement data
Implementation Method 2
The vacuum securely holds the bottom surface of the wafer down to the top of the end effector during the pick and place or sorting operations
Data Source
AI summary
A system and methods for the evaluation of the integrity of a wafer cassette and the disposition thereof are based upon evaluation of wafer measurement data obtained using a wafer sorter cassette mapping system utilized in-line during wafer sorting operations. In one embodiment, wafers are placed into slots in the wafer cassette. A wafer sorter cassette mapping sensor is scanned over the wafers in the wafer cassette. The positions of the wafers are measured while scanning the sensor over the wafers. The wafer position measurements are evaluated using a modeling system to determine slot positions, and a determination of the integrity of the cassette is generated. If the integrity determination indicates that the cassette is deformed beyond a predetermined value, the cassette is replaced. The measurement data may be stored in a data base for further trend analysis or for replacement forecasting.