Eddy Current Sensor Gain Determination for CMP Endpoint Control
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in determining the endpoint of polishing, leading to non-uniformity due to variations in slurry composition, polishing pad conditions, relative speed, initial thickness, and load on the substrate, making it difficult to achieve desired flatness or material removal.
Innovation Solution
The method involves using an eddy current monitoring system to generate signals based on the thickness of the conductive layer, calculating a gain and offset to adjust the signal, and determining the polishing endpoint or adjusting parameters, such as pressure, to ensure consistent polishing across substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polishing endpoint is determined merely as a function of polishing time, then the process is simple to control, but the manufacturing precision deteriorates due to variations in material removal rate
Solution Approach 1:
The patent replaces time-based mechanical control with eddy current sensing technology to detect the polishing endpoint. The eddy current sensor monitors the thickness of the conductive layer in real-time, substituting the simple time-based control mechanism with a precise electromagnetic detection system that accounts for variations in material removal rate.
Solution Approach 2:
The patent implements a feedback mechanism where the eddy current sensor continuously monitors the conductive layer thickness during polishing and provides real-time data to adjust the polishing process. This feedback loop allows the system to compensate for variations in slurry composition, pad condition, and other factors that affect material removal rate, thereby maintaining thickness uniformity.
2Measurement precision
If eddy current monitoring is implemented to detect polishing endpoint, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The eddy current sensor serves multiple functions: it detects the polishing endpoint, monitors conductive layer thickness in real-time, and provides data for process control. By making the monitoring system multi-functional, the patent reduces the need for separate detection devices, thereby limiting the increase in device complexity while maintaining high measurement precision.
Solution Approach 2:
The patent uses the eddy current sensor as an intermediary device that indirectly measures the conductive layer thickness through electromagnetic field interaction rather than direct physical contact. This intermediary approach allows for precise measurement without requiring complex mechanical measurement systems, thus improving measurement precision while controlling device complexity.
3Manufacturing precision
If gain is determined based on starting value and initial thickness measurement, then the manufacturing precision improves through signal calibration, but the loss of time increases due to additional calculation steps
Solution Approach 1:
The patent performs preliminary measurements of the initial conductive layer thickness using an in-line or stand-alone monitoring system before the polishing process begins. Based on this preliminary data, the gain is pre-calculated and configured for the eddy current monitoring system. This preliminary action allows the system to be ready for precise monitoring from the start of polishing, minimizing additional calculation time during the actual polishing process.
Solution Approach 2:
The patent implements a dynamic gain adjustment mechanism where the gain value is determined based on the actual starting value and initial thickness measurement for each substrate. This dynamic approach allows the system to adapt to variations in initial conditions while maintaining signal accuracy, and the calculation is optimized to be performed efficiently without significant time loss.
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 improves the reliability of detecting the polishing endpoint, reduces within-wafer and wafer-to-wafer thickness non-uniformity, and compensates for environmental and equipment variations, enhancing the consistency of the CMP process.
Implementation Method 1
One monitoring technique is to induce an eddy current in the conductive layer and detect the change in the eddy current as the conductive layer is removed.
Data Source
AI summary
A method of controlling polishing includes polishing a substrate at a first polishing station, monitoring the substrate with a first eddy current monitoring system to generate a first signal, determining an ending value of the first signal for an end of polishing of the substrate at the first polishing station, determining a first temperature at the first polishing station, polishing the substrate at a second polishing station, monitoring the substrate with a second eddy current monitoring system to generate a second signal, determining a starting value of the second signal for a start of polishing of the substrate at the second polishing station, determining a gain for the second polishing station based on the ending value, the starting value and the first temperature, and calculating a third signal based on the second signal and the gain.