Wafer Polishing Eccentricity Correction via Sensor Feedback
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Solution Overview
Problem
Conventional wafer polishing apparatuses face challenges in accurately determining the actual position of film-thickness measurement points due to eccentricity caused by frictional forces, leading to suboptimal polishing pressure application, especially in the edge area, which results in deviations from the target film-thickness profile.
Innovation Solution
A polishing method and apparatus that utilize a substrate detection sensor and a film-thickness sensor to calculate the angle of eccentricity and correct the position of measurement points, allowing for precise determination of polishing pressure based on actual film-thickness signals, thereby ensuring accurate pressure application across the wafer surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the film-thickness sensor is positioned to sweep across the center of the polishing head, then measurement coverage includes both center and edge areas, but the actual measurement points deviate from expected positions due to wafer eccentricity, causing inaccurate polishing pressure control
Solution Approach 1:
The system uses a substrate detection sensor to detect the actual position of the wafer center, then feeds this information back to calculate and correct the measurement point positions. This feedback loop compensates for eccentricity effects, ensuring that film thickness measurements are accurately associated with their corresponding radial positions on the wafer, thereby resolving the contradiction between measurement coverage and measurement position accuracy
Solution Approach 2:
The system dynamically changes the parameter of measurement point position based on the detected wafer center position. By calculating the angle of eccentricity and adjusting the measurement point positions accordingly, the system adapts to actual wafer positioning variations, maintaining accurate film thickness profile control despite eccentricity-induced deviations
2Ease of operation
If the retainer ring inner diameter is larger than the wafer diameter, then the wafer can be easily loaded, but frictional forces cause the wafer perimeter to press against the retainer ring, creating eccentricity and measurement position errors
Solution Approach 1:
The substrate detection sensor provides feedback on the actual wafer center position, enabling the system to detect and compensate for eccentricity caused by retainer ring contact. This feedback mechanism allows the system to maintain measurement accuracy despite the operational convenience of having a larger retainer ring inner diameter
Solution Approach 2:
The system converts the harmful effect of eccentricity (caused by wafer-perimeter contact with the retainer ring) into a detectable signal. By using the substrate detection sensor to measure the actual center position and calculating the angle of eccentricity, the system transforms the problematic eccentricity into useful information for correcting measurement point positions, thereby maintaining measurement precision
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 approach enables the achievement of a target film-thickness profile by accurately determining the actual position of measurement points and applying optimal polishing pressure, improving the precision and effectiveness of the polishing process.
Implementation Method 1
calculating an angle of eccentricity of a center of the substrate relative to a center of the polishing head from the number of substrate detection signals
Implementation Method 2
causing the film-thickness sensor to generate a film-thickness signal at a predetermined measurement point during polishing of the substrate
Implementation Method 3
due to a frictional force that acts between the wafer W and the polishing pad 110, the perimeter of the wafer W is pressed against an inner peripheral surface 103a of the retainer ring 103
Implementation Method 4
The polishing head 102 presses a wafer W against the polishing pad 110 to polish the surface of the wafer W in the presence of the slurry between the wafer W and the polishing pad 110
Data Source
AI summary
A polishing method which can acquire an actual position of a film-thickness measurement point, and can therefore apply an optimum polishing pressure to a substrate such as a wafer is disclosed. The method includes: causing a substrate detection sensor to generate substrate detection signals in a preset cycle and causing a film-thickness sensor to generate a film-thickness signal at a predetermined measurement point during polishing of the substrate while the substrate detection sensor and the film-thickness sensor are moving across the surface of the substrate; calculating an angle of eccentricity of a center of the substrate relative to a center of the polishing head from the number of substrate detection signals; correcting a position of the predetermined measurement point based on the angle of eccentricity; and controlling polishing pressure at which the polishing head presses the substrate based on the film-thickness signal and the corrected position of the predetermined measurement point.