Pivotable Substrate Retaining Ring for CMP Edge-Effect Control
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face the 'edge-effect' issue, where the edge of semiconductor substrates are polished at a different rate than the center, leading to damage and non-uniformity, and wear on the retaining ring due to collisions during planarization.
Innovation Solution
A carrier head design featuring a pivotally connected retaining ring or a collet retaining ring with a vertically movable outer ring that tightly clamps the substrate, reducing collisions and eliminating the gap between the substrate and the retaining ring, thereby minimizing edge-effect and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retaining ring is used to prevent lateral movement of the substrate, then substrate stability is improved, but collisions between the substrate and retaining ring cause edge-effect damage and wear
Solution Approach 1:
The retaining ring is designed with pivotable segments that can dynamically adjust their position. The segments are connected via pivots allowing them to swing between a first position (during polishing) and a second position (during substrate loading/unloading). This dynamic capability enables the retaining ring to adapt to different operational phases, preventing collisions during polishing while facilitating easy substrate handling.
Solution Approach 2:
The retaining ring is divided into multiple discrete segments rather than being a continuous rigid structure. Each segment can independently pivot about its connection points, allowing localized adjustment and reducing the transmission of forces that would cause collisions. The segmented design provides flexibility while maintaining the overall retaining function.
2Manufacturing precision
If the retaining ring is rigidly fixed to prevent substrate movement, then substrate positioning is improved, but the retaining ring suffers from wear and reduced lifespan
Solution Approach 1:
The retaining ring transitions from a static rigid structure to a dynamic articulated structure. The pivotable segments allow the ring to flex and absorb impacts, reducing wear on individual components. The ability to swing between positions means the retaining ring can accommodate substrate positioning requirements while minimizing contact forces that cause wear.
Solution Approach 2:
The pivotable segment design inherently provides cushioning by allowing controlled movement and absorption of impact forces. Rather than rigidly transmitting collision forces that cause wear, the pivots act as shock-absorbing joints, protecting the retaining ring structure from damage and extending its operational life.
3Manufacturing precision
If the retaining ring is designed to tightly clamp the substrate, then edge-effect is reduced, but the complexity of the retaining ring mechanism increases
Solution Approach 1:
The retaining ring is segmented into multiple independent units, each capable of tight clamping against the substrate edge. This segmentation allows the complex clamping function to be distributed across multiple simple, identical components. Each segment can be independently positioned and adjusted, achieving uniform clamping pressure around the entire substrate perimeter without requiring a complex monolithic structure.
Solution Approach 2:
The dynamic pivotable segment design allows the retaining ring to achieve tight clamping through controlled movement rather than complex mechanical adjustments. The segments can swing into position to contact the substrate edge, providing tight clamping automatically through their motion sequence, thereby reducing the need for additional complex positioning mechanisms.
Data Source
AI summary
A carrier head includes a base assembly, a substrate mounting surface connected to the base assembly, a plurality of segments disposed circumferentially around the substrate mounting surface to provide a collet retaining ring to surround a substrate mounted on the substrate mounting surface, and an outer ring that is vertically movable relative to the plurality of segments. An inner surface of the collet retaining ring is configured to engage a substrate, and the collect retaining ring and outer ring are configured such that vertical motion of the outer ring controls motion of the collet retaining ring between a clamping and unclamping position.