CMP Platen Sensor Rings for Accurate Eddy Current Endpoint Detection
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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, and load variations, leading to non-uniformity within and between wafers.
Innovation Solution
An eddy-current monitoring system with multiple sensors is used to generate thickness traces by identifying minima in the signal, compensating for noise from underlying layers, and adjusting polishing parameters based on calculated layer thickness values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single sensor is used for eddy current monitoring, then the device complexity is low, but the measurement precision and reliability of polishing endpoint detection deteriorates due to insufficient spatial coverage and signal accuracy
Solution Approach 1:
The monitoring system is segmented into multiple sensors arranged in different rings at different radial distances from the rotation axis. Each sensor independently monitors a specific radial zone of the substrate, allowing the system to achieve high measurement precision through distributed measurement points while maintaining manageable device complexity through modular sensor placement
Solution Approach 2:
The system transitions from single-point monitoring to multi-dimensional spatial monitoring by arranging sensors in concentric rings at different radial distances. This dimensional expansion provides comprehensive coverage of the substrate surface, enabling accurate detection of thickness variations and polishing endpoint across the entire wafer area
2Reliability
If multiple sensors are used to improve measurement precision, then the reliability of polishing endpoint detection improves, but the device complexity increases
Solution Approach 1:
The sensor system is divided into multiple independent sensing elements distributed in concentric rings. Each sensor provides independent reliability data for its specific radial zone, and the combined information from all sensors provides comprehensive reliability assessment. This segmentation allows the system to achieve high reliability without creating a single complex interconnected system
Solution Approach 2:
Multiple sensors serve universal monitoring functions across different radial zones of the substrate. Each sensor performs the same basic eddy current measurement function but at different locations, providing both redundant reliability data and comprehensive spatial coverage. This multi-functionality approach increases reliability without proportionally increasing system complexity
3Manufacturing precision
If eddy current monitoring is performed through the polishing pad, then the manufacturing precision of layer thickness is improved, but the object-affected harmful factors increase due to noise from underlying layers and polishing variations
Solution Approach 1:
Sensors are strategically positioned at specific radial distances from the rotation axis to monitor specific local zones of the substrate. By selecting optimal radial positions, the system can distinguish between signal variations caused by actual thickness changes in the target layer versus noise from underlying layers or polishing pad variations, thereby maintaining high manufacturing precision while filtering out harmful interference
Solution Approach 2:
The eddy current field acts as an intermediary that penetrates through the polishing pad to interact with the conductive layer on the substrate. The system uses the changes in this intermediary field to indirectly measure layer thickness without direct physical contact, allowing precise measurement while the polishing pad serves as a transparent medium rather than a source of interference
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 enhances the reliability of determining the polishing endpoint, reduces within-wafer non-uniformity, and improves fabrication yield by 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
Implementation Method 2
the sensor generates a magnetic field that at least intermittently impinges the substrate
Data Source
AI summary
A chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a substrate such that a layer on the substrate contacts the polishing pad, an actuator that controls a radial position of the carrier head over the platen, an eddy current monitoring system, and a controller. The eddy current monitoring system includes a first plurality of eddy current sensors supported by the platen and arranged in a first ring at a first distance from an axis of rotation of the platen and a second plurality of eddy current sensors supported by the platen and arranged in a second ring at a larger second distance from the axis of rotation of the platen. The controller is configured to control the actuator such that the second plurality of sensors sweep only across an edge portion of the substrate held by the carrier head.