CMP Endpoint Control Using Eddy-Current Underlayer Compensation
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Solution Overview
Problem
Existing chemical mechanical polishing (CMP) methods struggle to accurately determine the polishing endpoint due to variations in material removal rates caused by factors like slurry composition, polishing pad condition, relative speed, and load, leading to non-uniformity within and between wafers, especially when underlying conductive layers contribute inconsistently to eddy current signals.
Innovation Solution
An in-situ monitoring system measures the thickness of a conductive layer and underlying layers, calculates an effective starting thickness value, and adjusts the target thickness using a polynomial function to compensate for underlying layer contributions, enabling precise endpoint detection and uniformity control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional CMP endpoint detection based on polishing time is used, then the process is simple to operate, but the manufacturing precision deteriorates due to non-uniform material removal
Solution Approach 1:
The patent replaces time-based mechanical control with electromagnetic sensing. An eddy current sensor detects changes in conductive layer thickness by measuring electromagnetic field interactions, substituting the mechanical time-based endpoint detection with a non-contact electromagnetic measurement system that provides real-time thickness data.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the eddy current signal during polishing and comparing it against reference values. The system adjusts the polishing process based on real-time signal feedback, detecting endpoint when the signal indicates the conductive layer has been removed and underlying layers are exposed.
2Measurement precision
If eddy current monitoring is used to detect conductive layer thickness, then measurement capability is improved, but measurement precision deteriorates due to inconsistent underlayer contributions
Solution Approach 1:
The patent segments the eddy current signal into distinct components corresponding to different layers. By analyzing the signal profile, the system separates the contribution from the conductive outer layer being polished from the contribution of the underlying conductive layers, allowing independent measurement of each layer's thickness.
Solution Approach 2:
The patent introduces signal processing algorithms as an intermediary between the raw eddy current signal and the thickness measurement. The processing system filters and analyzes the signal to extract accurate thickness information while compensating for the inconsistent underlayer contributions, acting as a mediator that transforms the complex signal into reliable measurements.
3Manufacturing precision
If polishing continues until visual exposure of underlying layer, then the outer layer is completely removed, but manufacturing precision deteriorates due to over-polishing
Solution Approach 1:
The patent performs preliminary detection of the endpoint condition by monitoring the eddy current signal for changes that indicate the conductive layer is approaching complete removal. The system detects the endpoint before visual exposure occurs, allowing the process to be stopped at the optimal point and preventing over-polishing of the underlying layers.
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 method improves the accuracy of polishing endpoint detection and reduces wafer-to-wafer and within-wafer non-uniformity by accounting for inconsistent contributions from underlying layers, ensuring consistent layer thickness across the substrate.
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.
Data Source
AI summary
A substrate is monitored during polishing with an in-situ monitoring system so as to generate a sequence of signal values. The sequence of signal values from the zone is converted into a sequence of effective thickness values for the zone with each effective thickness value including contributions of the outer layer and the one or more underlying layers. A function is fit to the sequence of effective thickness values, an effective starting thickness value for the layer at a start of polishing is determined using the fitted function, and an adjusted target thickness value is calculated based on an initial target value, a starting thickness value, and the effective starting thickness value. A polishing endpoint is detected or a polishing parameter is modified based on the sequences of effective thickness values and the adjusted target thickness value.