Wafer Inspection Laser Intensity Control During Rotation
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Solution Overview
Problem
During the inspection of small foreign matters on wafers, existing technologies face challenges in maintaining consistent laser light intensity due to rotation acceleration/deceleration, leading to inaccurate detection and potential thermal damage, especially when large-diameter foreign matters are present.
Innovation Solution
An inspection device with a rotation-and-translation unit, light intensity modulation, and data processing unit that adjusts laser light intensity based on real-time linear speed and rotation speed, ensuring accurate inspection by controlling the stages' movements and light intensity during acceleration and deceleration phases, and specifically weakening light intensity for large-diameter foreign matters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser light intensity is increased to improve detection sensitivity for small particles, then detection sensitivity improves, but thermal damage to large particles and the wafer increases
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the laser light intensity based on the detected foreign matter size. The system transitions from static intensity control to dynamic control where the laser intensity is continuously adapted according to the size of detected particles, allowing high intensity for small particles (improving detection sensitivity) and low intensity for large particles (preventing thermal damage).
Solution Approach 2:
The patent implements parameter changes by modifying the laser light intensity parameter based on foreign matter size classification. The system detects particle size and accordingly changes the laser intensity parameter - using higher intensity for small particles to enhance detection sensitivity and lower intensity for large particles to avoid thermal damage, thus resolving the contradiction between detection sensitivity and thermal damage prevention.
2Productivity
If inspection is performed during rotation acceleration/deceleration to shorten inspection time, then productivity improves, but linear speed deviation occurs leading to inaccurate detection
Solution Approach 1:
The patent applies feedback by continuously monitoring the actual linear speed of the rotating wafer and using this information to adjust the laser light intensity. The system incorporates a speed detection mechanism that provides real-time feedback on linear speed deviations during acceleration and deceleration phases, enabling dynamic compensation through intensity adjustment to maintain constant integrated intensity and ensure detection accuracy throughout the inspection process.
3Device complexity
If laser light intensity is not adjusted during rotation acceleration/deceleration, then device complexity is reduced, but integrated light intensity becomes non-constant causing detection inaccuracy
Solution Approach 1:
The patent implements parameter changes by adjusting the laser light intensity parameter in response to rotation speed changes. Instead of complicating the mechanical control system, the invention modifies the optical parameter (intensity) based on detected linear speed, providing a relatively simple yet effective solution to maintain constant integrated intensity during acceleration and deceleration phases.
4Device complexity
If translation speed is not accurately controlled relative to rotation speed, then device complexity is reduced, but inspection coverage creates gaps reducing reliability
Solution Approach 1:
The patent applies feedback by implementing a coordination control mechanism that monitors both rotation speed and translation speed, using this feedback information to adjust the translation speed dynamically. This ensures accurate synchronization between rotational and translational movements, preventing inspection gaps and maintaining reliable coverage without requiring overly complex mechanical coordination systems.
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 accurate and efficient inspection of small foreign matters during rotation acceleration/deceleration, preventing thermal damage by maintaining consistent light intensity and ensuring thorough coverage without gaps, while effectively managing the inspection of large-diameter foreign matters.
Implementation Method 1
a Pockels cell is used as a unit to dynamically changing the incident laser beam power level delivered to a sample during surface inspection scanning
Implementation Method 2
inspecting a foreign matter or a defect on an object under inspection such as a wafer, a thin film substrate, and a photomask by irradiating the object under inspection with light
Data Source
AI summary
An inspection device capable of inspecting a foreign matter even during rotation acceleration/deceleration of an object under inspection. The inspection device includes a rotation-and-translation unit configured to rotate and translate the object under inspection; a light intensity modulation unit configured to modulate intensity of laser light to irradiate the object under inspection; a light intensity control unit configured to control the light intensity modulation unit; an object-under-inspection-operation detection unit configured to calculate information about a linear speed at a laser irradiation position on the object under inspection; a data processing unit configured to start foreign matter and defect inspection when a rotation speed of the object under inspection reaches a predetermined speed and a rotation-and-translation control unit configured to determine a time required for a next single rotation of a rotation stage, and apply, to a translation stage, a translation control value for moving the translation stage.