Eddy Current Gain Compensation for CMP Endpoint Detection
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes in semiconductor manufacturing face challenges in determining the endpoint of planarization, as variations in material removal rates due to initial thickness, slurry composition, polishing pad conditions, and load on the substrate make it difficult to determine when a desired thickness or flatness is achieved, leading to potential over- or under-polishing issues.
Innovation Solution
An in-situ eddy current monitoring system is implemented, using a sensor that generates signals based on its proximity to the substrate and a metal body, allowing for real-time adjustment of the signal gain to compensate for environmental and thickness variations, enabling accurate detection of the polishing endpoint by correlating phase difference signals with conductive layer thickness.
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 variations in material removal rate cause inaccurate endpoint detection leading to over- or under-polishing
Solution Approach 1:
The patent replaces the mechanical/time-based endpoint determination method with an eddy current sensing system that uses electromagnetic induction to detect conductive layer thickness in real-time. The eddy current sensor measures the electrical properties of the conductive layer, providing accurate thickness data regardless of variations in material removal rate, thereby eliminating the need to rely on polishing time alone.
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 signals to the control system. This feedback allows the polishing process to be dynamically adjusted based on actual layer thickness, ensuring precise endpoint detection and preventing both over-polishing and under-polishing.
2Measurement precision
If eddy current sensor signal is used directly for thickness measurement, then real-time monitoring is achieved, but signal drift and variations due to environmental factors reduce measurement precision
Solution Approach 1:
The patent introduces a reference conductive layer as an intermediary standard for signal comparison. The eddy current sensor measures both the unknown conductive layer and the reference layer, and the control system compares these signals to compensate for environmental variations. This reference-based approach acts as a mediator that cancels out common-mode noise and drift, improving measurement reliability.
Solution Approach 2:
The patent employs parameter changes by adjusting the gain of the eddy current sensor signal based on reference measurements. The control system dynamically modifies signal parameters (gain adjustment) to compensate for environmental factors such as temperature changes, pad wear, and slurry composition variations, thereby maintaining stable and reliable thickness measurements throughout the polishing process.
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 allows for precise and automatic adjustment of the eddy current signal gain, reducing signal drift and variations, thereby ensuring accurate detection of the polishing endpoint, preventing over- or under-polishing and maintaining optimal circuit performance.
Implementation Method 1
An eddy current sensor is used to generate a signal that is correlated to a thickness of the conductive layer
Data Source
AI summary
In-situ monitoring during processing of a substrate includes processing a conductive film on a substrate in a semiconductor processing apparatus and generating a signal from an eddy current sensor during processing. The signal includes a first portion generated when the eddy current sensor is adjacent the substrate, a second portion generated when the eddy current sensor is adjacent a metal body and not adjacent the substrate, and a third portion generated when the eddy current sensor is adjacent neither the metal body nor the substrate. The second portion of the signal is compared to the third portion of the signal and a gain is determined based at least on a result of the comparing, and the first portion of the signal is multiplied by the gain to generate an adjusted signal.