Eddy Current Sensor Offset Correction for Polishing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing substrate polishing systems face challenges in accurately measuring film thickness due to the influence of underlayer wiring patterns, leading to inaccurate detection of the polishing end point, especially as the film thickness decreases.
Innovation Solution
A substrate polishing system and method that utilize a first and second polishing apparatus, where the first apparatus calculates and stores an offset value between sensor outputs with and without an underlayer, and the second apparatus corrects sensor outputs using this offset to accurately determine the polishing end point by adjusting the film thickness measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If eddy current sensor is used to measure film thickness, then film thickness measurement is enabled, but measurement precision deteriorates due to influence from underlayer wiring patterns
Solution Approach 1:
The system performs preliminary measurement of the underlayer wiring pattern's influence before the actual polishing measurement. By measuring the sensor output when only the underlayer is present (without the metal film to be polished), the system establishes a baseline that represents the harmful influence of the wiring pattern. This preliminary value is then used to correct subsequent measurements during polishing, effectively removing the wiring pattern's interference from the measurement results.
Solution Approach 2:
The patent introduces an intermediary correction mechanism that mediates between the raw sensor output and the actual film thickness measurement. The correction value, derived from preliminary underlayer-only measurements, acts as an intermediary that compensates for the wiring pattern's influence. This intermediary correction allows the eddy current sensor to accurately measure film thickness even in the presence of conductive underlayer patterns that would otherwise distort the measurement.
2Object-affected harmful factors
If threshold cutting is applied to reduce noise influence, then noise reduction is achieved, but measurement precision deteriorates when film thickness is small
Solution Approach 1:
Instead of using threshold cutting that may eliminate valid small-thickness signals, the patent introduces a correction-based intermediary approach. The correction value, derived from underlayer-only measurements, is added to the raw sensor output to compensate for wiring pattern influence. This intermediary correction preserves the full dynamic range of sensor outputs, including those corresponding to small film thicknesses, while still eliminating the harmful wiring pattern influence.
3Productivity
If multiple substrate polishing operations are performed, then productivity is improved, but device complexity increases due to need for data management
Solution Approach 1:
The patent applies the copying principle by storing correction values obtained from one substrate polishing operation to be used in subsequent operations. Instead of performing time-consuming preliminary measurements for every single polishing cycle, the system creates a reusable correction value copy from the first measurement that can be applied to multiple subsequent polishing operations. This copying approach maintains measurement accuracy across multiple batches while significantly reducing the overall measurement time and system complexity.
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 effectively reduces the influence of underlayer wiring patterns, enabling more precise detection of the polishing end point and improving the accuracy of film thickness measurement throughout the polishing process.
Implementation Method 1
an eddy current sensor is widely used as film thickness measuring devices to measure film thicknesses of substrates
Implementation Method 2
each of which comprises a film thickness sensor for measuring a film thickness of a layer to be polished of a substrate
Data Source
AI summary
A first and a second substrate polishing apparatus and are provided with a film thickness sensor for measuring a film thickness of layer to be polished and polish the layer by pressing the substrate against a polishing pad. The first substrate polishing apparatus outputs difference between output value of the film thickness sensor when an underlayer is exposed and output value of the film thickness sensor when the substrate is not present, as a first offset value. The second substrate polishing apparatus has a storage unit that stores information of the first offset value, an output correction unit that corrects the output value from the film thickness sensor based on the first offset value, and an end point detection unit that outputs control signal indicating end point of substrate polishing when measured value of the film thickness of the layer calculated based on the corrected output value reaches target value.