Retaining-ring-less CMP Carrier Head with Segmented Gripping Elements
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Solution Overview
Problem
Conventional chemical mechanical polishing (CMP) systems face challenges in uniformly polishing the entire surface of a substrate, often resulting in film non-uniformity and reduced die yield due to uneven polishing rates at the substrate's edge regions.
Innovation Solution
The use of a carrier head with a flexible membrane that includes a substrate-receiving surface with numerous small gripping elements, which replace or supplement the retaining ring, to securely hold the substrate during polishing, thereby reducing side loads and ensuring uniform polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inner retaining ring is used to hold the substrate during CMP, then the substrate is securely retained, but side loads are generated at the trailing edge causing non-uniform polishing
Solution Approach 1:
The patent divides the continuous retaining ring into discrete gripping elements distributed across the substrate surface. These segmented gripping elements (protrusions or adhesive regions) provide retention functionality while eliminating the concentrated side loads generated by a continuous ring, thereby preventing edge non-uniformity.
Solution Approach 2:
The patent removes the inner retaining ring component entirely from the carrier head design. Instead of using a physical ring structure, the invention extracts the retention function and implements it through gripping elements on the flexible membrane, eliminating the source of side load problems.
2Reliability
If a continuous retaining ring is used, then substrate retention is achieved, but slurry agglomeration occurs and polishing uniformity deteriorates
Solution Approach 1:
The continuous retaining ring is segmented into discrete gripping elements spaced across the substrate. This segmentation prevents slurry from accumulating in a continuous ring structure, eliminating agglomeration while maintaining retention through distributed gripping points.
Solution Approach 2:
The retaining ring structure that causes slurry agglomeration is completely removed. The retention function is extracted and reimplemented using gripping elements that do not create the harmful agglomeration effect, allowing slurry to flow uniformly across the polishing surface.
3Strength
If gripping elements with large lateral dimensions are used, then substrate gripping strength is improved, but side loads increase causing edge non-uniformity
Solution Approach 1:
The gripping function is divided into numerous small gripping elements rather than a few large contact points. This segmentation distributes the gripping force across many locations, maintaining overall gripping strength while preventing concentrated side loads that would cause edge non-uniformity.
Solution Approach 2:
Each gripping element is designed with specific local characteristics (small size, appropriate spacing) to provide sufficient gripping force at its location without generating harmful side loads. The distributed arrangement ensures uniform pressure distribution across the substrate edge.
Data Source
AI summary
Exemplary carrier heads for a chemical mechanical polishing apparatus may include a carrier body. The carrier heads may include a flexible membrane coupled with the carrier body. The flexible membrane may include a substrate-receiving surface that faces away from the carrier body. The substrate-receiving surface may include a plurality of gripping elements that protrude away from the substrate-receiving surface. Each of the plurality of gripping elements may have a maximum lateral dimension that is no greater than 2 mm.