Dynamic Focus Oblique Laser Illumination for Spinning Wafer Inspection
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Solution Overview
Problem
Current spinning wafer inspection systems face challenges in maintaining focus at high frequencies due to wafer and chuck motion, limiting sensitivity and throughput, as existing autofocus methods have slow response times that are inadequate for state-of-the-art defect detection systems operating at frequencies up to 10000 RPM.
Innovation Solution
A high-frequency dynamically focused oblique laser illumination system that adjusts the beam direction incidence angle to maintain focus, combined with automatic beam shaping and steering, using a module with piezo actuators and high-order PID controllers, along with precise beam monitoring and measurement systems to correct for laser and thermal drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shorter wavelength illuminating light and smaller spot size are used to achieve higher sensitivity, then sensitivity is improved, but depth of focus decreases making the sample go out of focus more easily
Solution Approach 1:
The patent implements a dynamic focus adjustment system that continuously changes the focal position of the laser beam to track the wafer surface topography. This dynamic adaptation allows the system to maintain focus on the actual sample surface even when using short wavelengths and small spot sizes, thereby preserving both high sensitivity and adequate depth of focus through real-time compensation of surface variations
Solution Approach 2:
The system incorporates a feedback mechanism using a position-sensitive detector to monitor beam position and a focus detection system to sense the actual focal position on the wafer surface. This feedback information is used to adjust the beam delivery system in real-time, ensuring that the focus remains on the sample surface despite using shorter wavelengths that inherently have smaller depth of focus
2Manufacturing precision
If beam focusing optical element or target surface is moved to maintain focus, then focus is maintained, but response time becomes very slow (0-100 Hz) which is inadequate for high-speed wafer inspection (up to 10000 RPM)
Solution Approach 1:
The patent replaces the slow mechanical focusing system with an optical beam delivery system that uses acousto-optic or electro-optic modulators to dynamically adjust the beam focal position at high frequencies. This substitution of mechanical adjustment with optical control enables focus tracking at frequencies compatible with high-speed wafer inspection (up to 10000 RPM), achieving both precise focus maintenance and fast response time
Solution Approach 2:
The system dynamically changes the optical parameters of the laser beam, specifically the focal position and incidence angle, using high-speed controllable optical elements. By modulating these parameters at high frequencies through electronic control rather than mechanical movement, the system achieves rapid focus adjustment capable of tracking wafer surface variations during high-speed spinning inspection
3Productivity
If wafer spinning frequency is increased to improve throughput, then productivity is improved, but maintaining focus becomes more difficult due to increased motion effects
Solution Approach 1:
The patent implements a dynamic focus tracking system that operates at frequencies synchronized with high-speed wafer spinning (up to 10000 RPM). The system continuously adapts the beam focal position to follow the moving wafer surface, enabling maintainment of focus stability even at high rotational speeds where traditional static or slow-response focusing systems would fail
Solution Approach 2:
The system employs a high-frequency feedback loop that uses position-sensitive detectors and focus sensors to monitor beam position and focal accuracy in real-time during high-speed wafer spinning. This feedback information drives high-speed actuators or optical modulators to correct focus deviations, enabling throughput improvement through increased spinning frequency while maintaining focus stability through active compensation
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
Enables rapid focus adjustments in the range of milliseconds, enhancing sensitivity and maintaining focus during high-speed wafer inspection, thereby improving defect detection capabilities and system throughput.
Implementation Method 1
An embodiment of the apparatus which controls the inventive autofocus employs a piezo actuator 330
Implementation Method 2
The focus is changed by changing the beam direction incidence angle so as to bring focal spot onto the wafer surface
Data Source
AI summary
A method and apparatus for producing high frequency dynamically focused oblique laser illumination for a spinning wafer inspection system. The focus is changed by changing the beam direction incidence angle so as to bring focal spot onto the wafer surface.Disclosed herein is a system and method for automatic beam shaping (i.e., spot size) and steering (i.e., position) for a spinning wafer inspection system, combined into a single module. Also disclosed is a method and system for measuring the beam position/size/shape and angle with sufficient resolution to make corrections using feedback from the monitor.