Ferrite Core Geometry for High-Resolution CMP Eddy Current Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Eddy current monitoring systems face challenges in achieving high spatial resolution during chemical mechanical polishing of substrates, particularly in detecting the thickness of conductive layers with low conductance metals, due to the spread of the magnetic field, which affects the accuracy of polishing endpoint detection and process control.
Innovation Solution
The design of an electromagnetic induction monitoring system with a specific core configuration, including a nickel-zinc ferrite core and a winding assembly, which reduces the spread of the magnetic field by optimizing the dimensions of the core and winding assembly, allowing for improved spatial resolution and effective monitoring of conductive features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional electromagnetic induction monitoring system is used, then the system can monitor substrate thickness during CMP, but the magnetic field spread reduces spatial resolution and measurement accuracy
Solution Approach 1:
The core is divided into multiple segments including a center post and an annular rim separated by a gap. This segmentation allows the magnetic field to be controlled and confined more effectively, reducing unwanted field spread and improving spatial resolution of the eddy current sensor.
Solution Approach 2:
Different portions of the core have different geometrical properties - the center post has a first width while the annular rim has a second width greater than the first. This local variation in dimensions optimizes the magnetic field distribution at different radial positions, enhancing measurement precision without requiring a completely complex redesign.
2Measurement precision
If the core dimensions are optimized to reduce magnetic field spread, then spatial resolution improves, but the device structure becomes more complex
Solution Approach 1:
The winding assembly is nested within the gap between the center post and annular rim of the core. This nesting arrangement allows the coil to be positioned precisely where it is needed to generate the magnetic field, while the core structure itself provides the positioning framework, reducing overall device complexity.
Solution Approach 2:
The core features asymmetric dimensions where the annular rim has a greater width than the center post. This asymmetric configuration optimizes the magnetic field geometry for reduced spread while maintaining a manufacturable structure that doesn't require overly complex winding patterns.
3Reliability
If the annular rim surface area is increased relative to the center post, then magnetic field control is improved, but manufacturing precision requirements increase
Solution Approach 1:
The design specifies that the annular rim surface area should be at least two times greater than the center post surface area, and the rim width should be 1.1 to 1.5 times the post width. These parameter ranges provide sufficient design flexibility to achieve reliable magnetic field control while allowing for normal manufacturing tolerances.
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 configuration enhances the spatial resolution of the eddy current sensor, enabling more precise monitoring of conductive features, such as metal sheets or lines, and improves the control of polishing parameters, reducing non-uniformity and ensuring accurate detection of the polishing endpoint.
Implementation Method 1
an eddy current sensing system may be used to induce eddy currents in a conductive region on the substrate
Implementation Method 2
induce eddy currents in a conductive region on the substrate to determine parameters such as the local thickness of the conductive region
Data Source
AI summary
An apparatus for chemical mechanical polishing includes a support for a polishing pad having a polishing surface, and an electromagnetic induction monitoring system to generate a magnetic field to monitor a substrate being polished by the polishing pad. The electromagnetic induction monitoring system includes a core and a coil wound around a portion of the core. The core includes a back portion, a center post extending from the back portion in a first direction normal to the polishing surface, and an annular rim extending from the back portion in parallel with the center post and surrounding and spaced apart from the center post by a gap. A width of the gap is less than a width of the center post, and a surface area of a top surface of the annular rim is at least two times greater than a surface area of a top surface of the center post.