Polishing Apparatus Strain-Based Endpoint Detection
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Solution Overview
Problem
Current methods for determining the polishing end point of substrates during chemical mechanical polishing (CMP) lack precision, particularly in monitoring changes in frictional forces that indicate the exposure of underlying layers, leading to inaccuracies in endpoint detection.
Innovation Solution
A polishing apparatus and method utilizing a strain measuring instrument with dual measurement modes (low and high resolution) to detect changes in strain caused by friction between the substrate and polishing pad, allowing for accurate determination of the polishing end point by switching to high resolution mode after a peak strain value is reached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If motor current monitoring is used to determine polishing end point, then the method is simple to implement, but the measurement precision is insufficient
Solution Approach 1:
The patent replaces electrical measurement (motor current monitoring) with mechanical measurement (strain gauge on polishing table) to detect polishing end point. The strain gauge directly measures mechanical strain caused by friction changes, providing more precise endpoint detection while maintaining relative simplicity of implementation.
Solution Approach 2:
The patent changes the measurement parameter from electrical current to mechanical strain. By placing a strain gauge on the polishing table, the system measures strain variations that occur when the polishing film is removed and underlying layer is exposed, achieving higher precision endpoint detection through parameter transformation.
2Measurement precision
If strain measurement is used to determine polishing end point, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent extracts the strain measurement function from a complex force measurement system and implements it directly on the polishing table using a strain gauge. This simplifies the overall device complexity while maintaining high measurement precision for endpoint detection.
Solution Approach 2:
The polishing table acts as an intermediary between the friction force generated during polishing and the strain gauge measurement system. The strain gauge mounted on the table indirectly measures the friction changes through table strain, providing precise endpoint detection without requiring direct force measurement apparatus.
3Measurement precision
If high resolution strain measurement mode is used throughout polishing, then the endpoint detection precision is maximized, but the energy consumption increases
Solution Approach 1:
The patent implements periodic switching between low resolution and high resolution measurement modes. The system operates in low resolution mode during normal polishing and switches to high resolution mode only when endpoint is approached, reducing overall energy consumption while maintaining precision when needed.
Solution Approach 2:
The measurement system dynamically adjusts its resolution based on polishing stage. The strain measuring instrument switches between measurement modes according to the polishing process state, optimizing energy consumption while ensuring high precision endpoint detection when the film removal occurs.
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 precise detection of the polishing end point by enhancing measurement sensitivity, ensuring accurate exposure of underlying layers and improving the overall polishing process.
Implementation Method 1
a strain measuring instrument which measures a strain of the support structure
Implementation Method 2
A frictional force generated between the substrate and the polishing pad is transmitted to the support structure via the polishing head and the rotating shaft. The strain of the support structure during the polishing of the substrate varies according to the frictional force generated between the substrate and the polishing pad.
Data Source
AI summary
A novel polishing apparatus which determines a polishing end point of a substrate on the basis of a strain of a constituent element of the polishing apparatus caused by friction between a substrate such as a wafer and a polishing pad. The polishing apparatus includes a rotatable polishing table which supports a polishing pad, a polishing head which presses the substrate against the polishing pad, a rotating shaft connected to the polishing head, a support structure which rotatably supports the rotating shaft, a strain measuring instrument which measures a strain of the support structure, and an end point detector which determines a polishing end point of the substrate on the basis of a change in the strain. The strain measuring instrument includes at least one strain sensor fixed to the support structure.