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, and other parameters, making it difficult to achieve consistent material removal rates and desired flatness or thickness in substrates.
Innovation Solution
The method involves using an eddy current monitoring system to generate signals based on the thickness of conductive layers, calculating a gain and offset to adjust the signal, and determining the polishing endpoint or adjusting parameters to ensure consistent polishing across substrates, incorporating temperature compensation for variations in resistivity across different polishing stations.
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 non-uniformity occurs within a wafer or from wafer to wafer
Solution Approach 1:
The patent implements in-situ monitoring during polishing using eddy current sensors that detect changes in conductive layer thickness in real-time. The system continuously monitors the polishing process and provides feedback signals to determine the actual endpoint based on measured thickness changes rather than predetermined time, resolving the contradiction between simple control and precise uniformity
Solution Approach 2:
The patent replaces time-based mechanical control with electromagnetic sensing. An eddy current sensor generates an alternating magnetic field that induces eddy currents in the conductive layer, and changes in the sensor signal indicate material removal and endpoint, substituting the simple time-based mechanism with a precise electromagnetic measurement system
2Reliability
If in-situ eddy current monitoring is used to monitor substrates during polishing, then endpoint detection reliability improves, but the system complexity increases
Solution Approach 1:
The eddy current sensor system serves multiple functions: it monitors conductive layer thickness during polishing, detects the polishing endpoint, and provides data for process control. This multi-functionality justifies the system complexity by consolidating multiple measurement and control functions into a single integrated monitoring system
Solution Approach 2:
The eddy current sensor acts as an intermediary between the polishing process and the control system. It non-contactly measures thickness changes through the polishing pad by detecting eddy currents induced in the conductive layer, providing reliable endpoint detection without interfering with the mechanical polishing process
3Measurement precision
If gain is determined based on starting value and initial thickness measurement, then signal accuracy improves, but the processing complexity increases
Solution Approach 1:
The system performs preliminary measurements of the initial conductive layer thickness using an in-line or stand-alone monitoring system before polishing begins. This preliminary data is used to calculate the appropriate gain factor for the eddy current sensor, ensuring accurate thickness measurements throughout the polishing process while automating the calibration process to minimize manual intervention
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 endpoint detection, reduces within-wafer and wafer-to-wafer thickness non-uniformity, and allows for automatic adjustments to compensate for environmental and equipment parameters affecting the eddy current signal, ensuring more precise control over the polishing 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
Implementation Method 2
induce an eddy current in the conductive layer and detect the change in the eddy current
Data Source
AI summary
In one aspect, a method of controlling polishing includes receiving a measurement of an initial thickness of a conductive film on a first substrate prior to polishing the first substrate from an in-line or stand-alone monitoring system, polishing one or more substrates in a polishing system, the one or more substrates including the first substrate, during polishing of the one or more substrates, monitoring the one or more substrates with an eddy current monitoring system to generate a first signal, determining a starting value of the first signal for a start of polishing of the first substrate, determining a gain based on the starting value and the measurement of the initial thickness, for at least a portion of the first signal collected during polishing of at least one substrate of the one or more substrates, and calculating a second signal based on the first signal and the gain.