Wafer Inspection Height Control via Feed Forward
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Solution Overview
Problem
Current semiconductor wafer inspection systems face limitations in height control speed due to open loop resonance in feedback control systems, which restricts the ability to maintain precise height control at high scanning speeds.
Innovation Solution
A system and method incorporating a dynamically actuatable substrate stage assembly with a feedback control system and a feed forward control system, utilizing height error detection and displacement sensors to adjust the actuator state, ensuring the substrate surface remains at the imaging plane or focus of the inspection system, thereby increasing control speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control system is used for height control, then height control precision is improved, but control speed is limited by open loop resonance
Solution Approach 1:
The feed forward control system performs preliminary action by predicting and compensating for height errors before they occur during substrate scanning. The system uses a model to anticipate the required height adjustments and applies them proactively, rather than waiting for feedback from height error measurements, thereby increasing control speed while maintaining precision
Solution Approach 2:
The system combines feedback control (using height error measurements from the detection system) with feed forward control (using displacement sensor data and modeling). The feedback component ensures precision by continuously correcting based on actual measurements, while the feed forward component overcomes the speed limitation by pre-calculating necessary adjustments
2Productivity
If scanning speed is increased for wafer inspection, then productivity is improved, but height error increases
Solution Approach 1:
By using the feed forward control system with displacement sensing and modeling, the system pre-calculates and applies height corrections before the substrate reaches positions where height errors would occur during high-speed scanning, enabling fast inspection while maintaining focus precision
Solution Approach 2:
The system dynamically changes the height control parameters by combining feedback from height error measurements with feed forward predictions based on displacement sensor data and system modeling, allowing the control system to adapt to high-speed scanning conditions while maintaining accuracy
Data Source
AI summary
High speed height control of a surface of a substrate within a wafer inspection system includes positioning a substrate on a substrate stage of a dynamically adjustable substrate stage assembly, actuating the substrate perpendicular to the surface of the substrate, measuring a height error value of the surface of the substrate at a position of inspection of the surface, measuring a displacement value perpendicular to the surface of the substrate at the location of the substrate stage assembly, generating a displacement target from the height error value and the displacement value, and adjusting an actuation state of the actuator using the measured height error value and the generated displacement target in order to maintain the substrate surface at an imaging plane of a detector of the inspection system or a focus of illumination of the inspection system.