In-situ Acoustic Emission Monitoring for CMP Endpoint Detection
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in determining the polishing endpoint due to variations in slurry distribution, polishing pad condition, and load on the substrate, leading to inconsistent material removal rates and difficulty in determining the completion of planarization based solely on polishing time.
Innovation Solution
An in-situ acoustic emission monitoring system is integrated into the CMP apparatus, featuring an acoustic emission sensor supported by the platen with a waveguide that extends through the polishing pad to detect acoustic events caused by substrate deformation, and a processor that analyzes the signal to determine the polishing endpoint by performing frequency analysis and triggering endpoint detection based on intensity thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polishing time is used to determine endpoint, then the process is simple to control, but the endpoint detection accuracy deteriorates due to variations in material removal rate
Solution Approach 1:
The patent replaces the mechanical/time-based endpoint determination method with an acoustic emission monitoring system. The acoustic sensor detects acoustic signals generated during polishing, and the system determines endpoint based on acoustic signal characteristics rather than polishing time, thereby improving accuracy while maintaining operational simplicity
Solution Approach 2:
The patent introduces acoustic signals as an intermediary to detect the polishing endpoint. The acoustic emission sensor captures signals from the polishing interface, which serve as an intermediate indicator of the polishing state, allowing indirect but accurate detection of endpoint conditions
2Measurement precision
If acoustic sensor is placed in direct contact with slurry or mechanically decoupled from polishing pad, then signal attenuation is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the acoustic sensor from direct contact with the polishing pad and places it in contact with the slurry or a mechanically decoupled structure. This separation removes the source of mechanical noise and vibration from the sensor, reducing signal attenuation and improving detection accuracy
Solution Approach 2:
The patent uses the slurry or a mechanical decoupling structure as an intermediary between the acoustic sensor and the polishing interface. This intermediary transmits acoustic signals from the polishing zone to the sensor while isolating the sensor from harmful mechanical disturbances
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 solution provides more accurate endpoint detection and improves wafer-to-wafer uniformity by reliably halting the polishing process when the desired layer is exposed, enhancing the precision and consistency of the CMP process.
Implementation Method 1
an in-situ acoustic emission monitoring system configured to detect acoustic events caused by deformation of the substrate and transmitted through the waveguide
Data Source
AI summary
A chemical mechanical polishing apparatus includes a platen to support a polishing pad, and an in-situ acoustic emission monitoring system including an acoustic emission sensor supported by the platen, a waveguide configured to extending through at least a portion of the polishing pad, and a processor to receive a signal from the acoustic emission sensor. The in-situ acoustic emission monitoring system is configured to detect acoustic events caused by deformation of the substrate and transmitted through the waveguide, and the processor is configured to determine a polishing endpoint based on the signal.