Eddy Current Sensor Calibration Using Product Wafer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional calibration methods for eddy current sensors in semiconductor polishing processes require peeling off polishing pads and using calibration wafers, leading to increased costs, low positional precision, and potential errors due to manual handling and oxidation.
Innovation Solution
A calibration method that uses an actual product wafer with known film thickness, eliminating the need for multiple polishing pads and calibration wafers, and automating the process to improve precision and reduce errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration method using multiple polishing pads and calibration wafers is employed, then calibration data can be obtained, but polishing pad must be peeled off and discarded, resulting in increased cost
Solution Approach 1:
The calibration wafer is prepared in advance with a known film thickness that is thicker than the maximum polishing depth. This preliminary preparation allows the calibration to be performed without needing to peel off the polishing pad, as the wafer can be directly placed on the polishing pad for measurement
Solution Approach 2:
Instead of using multiple physical calibration wafers with different thicknesses, the invention uses a single calibration wafer with a known thick film that replicates the calibration conditions for various thickness measurements through controlled polishing depth, reducing the need for multiple physical copies
2Ease of operation
If manual placement of calibration wafer on polishing pad is performed, then calibration can be executed, but positional precision is low and errors may occur due to dust or oxidation
Solution Approach 1:
The manual mechanical placement operation is replaced with an automated pickup and placement mechanism that uses suction or clamping to grasp the calibration wafer and precisely position it on the polishing pad, eliminating human error and improving positioning accuracy
Solution Approach 2:
The calibration process is performed in a controlled environment that prevents oxidation and contamination of the calibration wafer and polishing pad, ensuring measurement accuracy by eliminating harmful environmental factors
3Productivity
If calibration wafer is repetitively used, then calibration can be performed multiple times, but oxidation or deterioration occurs causing measurement errors
Solution Approach 1:
A thick protective film is formed on the calibration wafer before calibration, which serves as a sacrificial layer that prevents oxidation and deterioration of the underlying measurement surface during repeated calibration operations
Solution Approach 2:
The thick film on the calibration wafer acts as a cushioning protective layer that absorbs the harmful effects of repeated handling and environmental exposure, preventing damage to the actual measurement surface and maintaining reliability over multiple calibrations
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
The method allows for accurate calibration of eddy current sensors without peeling off polishing pads, reducing costs and errors, and maintaining precision through automated operation, using a single product wafer for calibration.
Implementation Method 1
The eddy current sensor causes the polishing target such as a conductive film to induce eddy current therein, and detects variation of the thickness of the polishing target from variation of magnetic field occurring due to the eddy current induced in the polishing target
Implementation Method 2
detects variation of the thickness of the polishing target from variation of magnetic field occurring due to the eddy current induced in the polishing target
Data Source
AI summary
In a first step, an output of an eddy current sensor is measured while a polishing target whose film thickness has been known is in contact with the polishing face, thereby obtaining a measurement value of the eddy current sensor which corresponds to the film thickness. In a second step, an output of the eddy current sensor is measured when the polishing target is polished while pressed against the polishing face, thereby obtaining a measurement value of the eddy current sensor that corresponds to a film thickness during polishing. A correspondence relationship between the film thickness of the polishing target and the measurement value of the eddy current sensor is determined from the measurement value obtained in the first step and the measurement value obtained in the second step.