CMP In-Situ Signal Filtering for Accurate Endpoint Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in determining the polishing endpoint due to variations in slurry distribution, polishing pad condition, relative speed, and load, leading to inconsistencies in material removal rates and time required to achieve desired flatness or thickness, which existing in-situ monitoring techniques fail to adequately address.
Innovation Solution
An in-situ monitoring system generates a signal that is filtered using a linear prediction filter to model periodic disturbances and an underlying signal, allowing for reliable determination of the polishing endpoint or adjustment of the polishing rate by reducing periodic disturbances without significant filter delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing in-situ monitoring techniques are used to determine polishing endpoint, then real-time monitoring is achieved, but measurement precision deteriorates due to periodic disturbances from slurry distribution variations, polishing pad condition changes, relative speed fluctuations, and load variations
Solution Approach 1:
The patent extracts and removes periodic disturbances from the monitoring signal by identifying and eliminating components related to slurry distribution variations, polishing pad condition changes, relative speed fluctuations, and load variations. This extraction process isolates the true endpoint detection signal from interfering periodic components, thereby improving measurement precision without sacrificing signal reliability
Solution Approach 2:
The patent implements feedback mechanisms that continuously monitor the polishing process parameters and adjust the endpoint detection algorithm accordingly. By feeding back information about slurry distribution, pad condition, speed variations, and load changes, the system dynamically compensates for periodic disturbances, maintaining both high measurement precision and signal reliability throughout the polishing process
2Measurement precision
If filtering is applied to reduce periodic disturbances in the monitoring signal, then measurement precision improves, but filter delay increases causing loss of time
Solution Approach 1:
The patent applies partial filtering by selectively removing only the periodic disturbance components from the signal while preserving the transient endpoint detection signal. Instead of applying heavy filtering that would cause significant delay, the system uses targeted disturbance rejection algorithms that eliminate periodic noise without introducing excessive time lag, achieving measurement precision improvement with minimal time loss
Solution Approach 2:
The patent performs preliminary identification and characterization of periodic disturbances before they interfere with endpoint detection. By pre-modeling the expected disturbance patterns from slurry distribution, pad condition, speed, and load variations, the system can proactively compensate for these disturbances in real-time, improving signal accuracy without requiring excessive filtering that would introduce delay
Data Source
AI summary
A method of controlling polishing includes polishing a substrate, monitoring the substrate during polishing with an in-situ monitoring system, filtering a signal from the monitoring system to generate a filtered signal, and determining at least one of a polishing endpoint or an adjustment for a polishing rate from the filtered signal. The filtering includes modelling a plurality of periodic disturbances at a plurality of different frequencies using a plurality of disturbance states, modelling an underlying signal using a plant state, and applying a linear prediction filter to the plant state and the plurality of disturbance states to generate a filtered signal representing the underlying signal.