CMP Retaining Ring with Soft Polyurethane Insert
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Solution Overview
Problem
The existing wafer carriers used in chemical mechanical planarization processes exhibit an 'edge effect' due to the wobble of wafers relative to the retaining rings, leading to non-uniform polishing rates across the wafer surface, particularly near the flat edges.
Innovation Solution
A wafer carrier with a retaining ring featuring a soft inner surface, made of polyurethane or similar materials with a specific hardness, is used in conjunction with a hard outer ring to reduce edge effects by providing a more uniform polishing experience across the entire wafer surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard retaining ring is used to securely hold the wafer, then the wafer is firmly constrained, but edge effects occur due to wafer wobble leading to non-uniform polishing
Solution Approach 1:
The retaining ring is designed with non-uniform wall thickness: a first portion with greater thickness providing higher strength and constraint force, and a second portion with lesser thickness providing flexibility to reduce edge effects. This local variation in physical properties allows the same component to simultaneously achieve firm wafer holding and uniform polishing by adapting its mechanical characteristics to different functional requirements at different locations.
2Manufacturing precision
If the retaining ring is made entirely of soft material to reduce edge effects, then polishing uniformity improves, but the retaining ring loses structural strength and durability
Solution Approach 1:
The retaining ring incorporates spatially varying material properties through non-uniform wall thickness. The thinner second portion provides the flexibility needed to minimize edge effects and improve polishing uniformity, while the thicker first portion maintains the overall structural strength and durability of the retaining ring. This local differentiation resolves the contradiction between softness for uniformity and hardness for strength.
Solution Approach 2:
The retaining ring functions as a composite structure combining regions of different effective stiffness. The non-uniform thickness creates a composite mechanical behavior where hard, strong regions provide structural integrity and soft, flexible regions provide adaptability for uniform contact. This composite approach allows the single component to achieve both strength and polishing uniformity simultaneously.
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
The use of a two-part retaining ring assembly with a soft inner surface and a hard outer ring significantly reduces edge effects, ensuring uniform polishing across the wafer surface, as demonstrated by radar graphs showing consistent film removal rates across all radial positions.
Implementation Method 1
The retaining ring is made from very hard materials such as PEEK, PET or polycarbonate with a hardness in the range of 80 to 85 Shore D, while the inner surface or insert is made of polyurethane or other material with a hardness in the range of 85 to 95 Shore A
Data Source
AI summary
A method of polishing a wafer with a wafer carrier adapted to further reduce the edge effect and allow a wafer to be uniformly polished across its entire surface, with a retaining ring made from very hard materials such as PEEK, PET or polycarbonate with a hardness in the range of 80 to 85 Shore D, while the inner surface or insert is made of polyurethane or other material with a hardness in the range of 85 to 95 Shore A.