Faceted CMP Retaining Ring for Wear and Polishing Uniformity
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Solution Overview
Problem
Conventional retaining rings used in chemical mechanical polishing (CMP) wear away quickly due to contact with the polishing pad, leading to uneven substrate polishing and reduced lifespan.
Innovation Solution
The retaining ring features an annular body with a faceted inner surface, including planar facets, inwardly-extending projections, or serpentine paths, and varying surface textures or tilts, which distribute pressure and reduce wear, enhancing polishing uniformity and extending the ring's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the retaining ring contacts the polishing pad during CMP, then the substrate can be retained and polished, but the retaining ring wears away quickly and needs frequent replacement
Solution Approach 1:
The inner surface of the retaining ring is divided into multiple facets with different orientations and surface properties. Each facet contacts the substrate at different locations and angles, distributing the wear and contact stress across multiple localized regions rather than a single continuous surface, thereby extending the retaining ring's service life while maintaining effective substrate retention
2Ease of manufacture
If the retaining ring is made of a single plastic material, then manufacturing is simple, but the ring wears away quickly due to uniform softness
Solution Approach 1:
The retaining ring is constructed from multiple materials with different properties - typically a harder, more wear-resistant material for the inner surface facets that contact the substrate, and a softer, more compliant material for the outer structure. This composite construction provides enhanced wear resistance and extended lifespan while maintaining manufacturability through techniques like injection molding with inserts or multi-layer molding
3Shape
If the inner surface is smooth and continuous, then substrate contact is uniform, but polishing uniformity deteriorates due to pressure concentration
Solution Approach 1:
The inner surface is segmented into multiple discrete facets rather than being continuous. Each facet is a separate planar surface oriented at different angles, which segments the contact pressure into multiple discrete contact zones. This segmentation prevents pressure concentration at any single point, distributing the load across multiple facets to achieve more uniform substrate thickness during polishing
4Ease of manufacture
If the retaining ring has a simple cylindrical inner surface, then manufacturing is easy, but angular asymmetry occurs in the polished substrate
Solution Approach 1:
The inner surface employs asymmetric facet orientations and configurations rather than a symmetric cylindrical geometry. The facets are arranged with varying angles and positions that intentionally break rotational symmetry, allowing the retaining ring to compensate for asymmetric wear patterns and pressure distributions that would otherwise cause angular asymmetry in the polished substrate, thereby improving polishing uniformity
Data Source
AI summary
Some implementations of a retaining ring has an inner surface having a first portion formed of multiple planar facets and a second portion that adjoins the first portion along a boundary and includes a frustoconical surface that is sloped downwardly from outside in. Some implementations of the retaining ring have a crenellated or serpentine inner surface, and/or an inner surface with alternating region of different surface properties or different tilt angles.