CMP Endpoint Detection with Filtered Signal Compensation
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in accurately determining the thickness of layers during polishing, leading to potential overpolishing, dishing, and water-to-wafer non-uniformity, due to noise in eddy current signals from variations in layer thickness and lateral oscillations of the carrier head.
Innovation Solution
A system that includes an in-situ monitoring system using electromagnetic induction to generate signals based on substrate thickness, with a controller that filters these signals using techniques like notch filters and adjusts the threshold values to account for filtering delays, ensuring precise endpoint detection during polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If eddy current sensing is used to monitor substrate thickness during CMP, then real-time thickness measurement capability is improved, but measurement precision deteriorates due to signal noise from layer thickness variations and carrier head oscillations
Solution Approach 1:
The patent extracts and removes the noise components from the eddy current signal through digital filtering techniques. The filter isolates the useful thickness measurement signal from harmful noise caused by carrier head oscillations and layer thickness variations, thereby improving measurement precision while maintaining signal reliability.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the eddy current signal, comparing it against threshold values, and adjusting the polishing process in real-time. The filtered signal feedback enables dynamic endpoint detection that compensates for signal variations, improving both measurement precision and reliability.
2Measurement precision
If signal filtering is applied to reduce noise, then measurement precision is improved, but time delay in endpoint detection increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing multiple threshold values that correspond to different time delays. Before endpoint detection, the system selects the appropriate threshold based on the filtering time delay, thereby compensating for the delay and maintaining accurate endpoint detection timing.
Solution Approach 2:
The patent uses partial filtering approaches where multiple filtering levels or window sizes can be applied depending on the specific measurement conditions. This allows optimization between noise reduction and time delay, applying just enough filtering to achieve acceptable precision without excessive time delay.
3Manufacturing precision
If traditional endpoint detection is used without filtering compensation, then device complexity is kept simple, but manufacturing precision deteriorates due to overpolishing and dishing
Solution Approach 1:
The patent improves manufacturing precision by dynamically adjusting control parameters (threshold values) based on signal filtering characteristics. The system changes the threshold parameter to compensate for filtering time delay, enabling accurate endpoint detection without requiring complex hardware modifications, thus achieving better polishing uniformity with moderate complexity increase.
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 allows for more reliable halting of polishing at target thickness, reduces overpolishing and dishing, enhances throughput, and improves resistivity control, thereby minimizing water-to-wafer non-uniformity.
Implementation Method 1
an eddy current sensing system may be used to induce eddy currents in a conductive region on the substrate to determine parameters such as the local thickness of the conductive region
Implementation Method 2
an eddy current sensing system may be used to induce eddy currents in a conductive region on the substrate
Data Source
AI summary
A method of polishing includes polishing a layer of a substrate, monitoring the layer of the substrate with an in-situ monitoring system to generate signal that depends on a thickness of the layer, filtering the signal to generate a filtered signal, determining an adjusted threshold value from an original threshold value and a time delay value representative of time required for filtering the signal, and triggering a polishing endpoint when the filtered signal crosses the adjusted threshold value.