CMP Carrier Head Flexure Through Pressure Chamber
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Solution Overview
Problem
In chemical mechanical polishing (CMP) processes, wear of the retaining ring in the carrier head leads to increased downforce on the substrate, causing wafer-to-wafer non-uniformity and reducing the lifespan of the retaining ring and membrane.
Innovation Solution
A carrier head design with a membrane assembly and a flexure that allows for independent loading of the membrane assembly from vertical motion, coupled with a controller that adjusts pressure in the pressurizable chamber based on measured distance changes to maintain consistent total downforce.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the retaining ring is used to apply downforce on the substrate, then the polishing process can be simplified, but wear of the retaining ring leads to increased downforce and wafer-to-wafer non-uniformity
Solution Approach 1:
The downforce application system is segmented into multiple independent components: a flexible membrane assembly with multiple chambers that can be independently pressurized, and a flexure mechanism that provides independent vertical loading. This segmentation allows precise control of downforce distribution across different regions of the substrate, eliminating wafer-to-wafer non-uniformity while maintaining process simplicity through automated control.
Solution Approach 2:
A sensor is integrated to measure the distance between the carrier body and membrane assembly, providing real-time feedback on downforce conditions. The controller uses this feedback to automatically adjust pressure in the pressurizable chamber, maintaining consistent total downforce on the substrate throughout the polishing process and compensating for retaining ring wear.
2Duration of action of stationary object
If the retaining ring wears over time, then the lifespan of the polishing system is extended, but downforce on the substrate increases causing non-uniformity
Solution Approach 1:
The sensor continuously monitors the distance between the carrier body and membrane assembly, detecting changes caused by retaining ring wear. The controller receives this feedback and automatically adjusts the pressure in the pressurizable chamber to compensate for increased downforce from wear, maintaining consistent total downforce on the substrate throughout the retaining ring's service life.
Solution Approach 2:
The system dynamically changes the pressure parameter in the pressurizable chamber based on measured distance changes. As the retaining ring wears and distance decreases, the controller increases chamber pressure to compensate, maintaining constant total downforce. This parameter adjustment extends the effective lifespan of the polishing system while maintaining precision.
3Manufacturing precision
If pressure is applied to the membrane assembly to maintain downforce, then wafer-to-wafer uniformity is improved, but the complexity of the pressure control system increases
Solution Approach 1:
The system uses the membrane assembly's own flexibility and the flexure mechanism to automatically distribute and maintain downforce. The membrane assembly self-adjusts to substrate contours, and the flexure provides inherent compliance, reducing the need for complex external pressure control mechanisms while maintaining uniformity.
Solution Approach 2:
A pressurizable chamber filled with gas or liquid is used to apply and regulate downforce on the membrane assembly. The fluid pressure automatically distributes force uniformly across the membrane surface, simplifying control compared to mechanical linkages. The controller only needs to regulate chamber pressure, a single parameter that directly translates to uniform downforce distribution.
4Reliability
If the membrane assembly is independently loaded from vertical motion, then control over downforce is improved, but the structural complexity of the carrier head increases
Solution Approach 1:
A flexible membrane assembly is used instead of rigid structural components to apply downforce. The membrane's flexibility allows it to conform to substrate contours and accommodate vertical motion while maintaining controlled downforce. This replaces complex rigid loading mechanisms with a simpler flexible membrane system that achieves the same reliability through material properties rather than structural complexity.
Solution Approach 2:
The flexure acts as an intermediary element between the carrier body and membrane assembly, providing controlled vertical motion and loading. The flexure absorbs and distributes vertical forces, enabling independent loading of the membrane assembly without requiring direct mechanical connection. This intermediary component simplifies the overall structure while maintaining reliable downforce control.
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 maintains consistent load on the substrate across multiple polishing operations, improving wafer-to-wafer uniformity and extending the lifespan of the retaining ring and membrane.
Implementation Method 1
A flexible membrane assembly with a plurality of pressurizable lower chambers can be used to apply a downward force on a substrate
Implementation Method 2
The membrane assembly includes a membrane support and a flexible membrane secured to the membrane support
Implementation Method 3
A flexure connects the membrane support to the housing, and the flexure extends through the pressurizable upper chamber
Implementation Method 4
measuring a distance from a sensor in the lower carrier body to the membrane assembly
Implementation Method 5
controlling pressure in the pressurizable chamber based on the measured distances. Controlling pressure in the pressurizable chamber includes maintaining a consistent total downforce on the membrane assembly
Data Source
AI summary
A carrier head for chemical mechanical polishing includes a housing for attachment to a drive shaft, a membrane assembly arranged beneath the lower carrier body, and a flexure. The membrane assembly includes a membrane support and a flexible membrane secured to the membrane support to defining a plurality of pressurizable lower chambers, with the flexible membrane having a lower surface that provides a substrate mounting surface. A flexible seal forms a pressurizable upper chamber between the housing and the membrane support. The flexure connects the membrane support to the housing, and the flexure extends through the pressurizable upper chamber.