Soft Retaining Ring for Uniform CMP Wafer Polishing
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Solution Overview
Problem
Conventional polishing systems often result in non-uniform material removal from wafers due to the use of harder retaining rings that can damage or distort the polishing pad, leading to thickness variations and reduced production yield.
Innovation Solution
A carrier head with a retaining ring having a hardness ranging from 5 shore A to 80 shore D, made from materials like PVA, PVC, or PU, which is designed to reduce lateral movement and pressure-induced distortion, ensuring a more uniform polishing process by maintaining the integrity of the polishing pad.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If harder retaining rings are used to prevent wafer movement, then wafer stability is improved, but polishing pad damage and distortion increase
Solution Approach 1:
The patent changes the key parameter of retaining ring hardness from conventional high hardness to a specific range (5-80 Shore D). This parameter change allows the retaining ring to be soft enough to avoid damaging the polishing pad while remaining firm enough to prevent wafer movement, thus resolving the contradiction between wafer stability and pad protection.
Solution Approach 2:
The patent specifies composite or specific material compositions for the retaining ring (including polyurethane, silicone rubber, or other elastomers within the specified hardness range). These materials provide a balance of flexibility and structural integrity, enabling the retaining ring to conform to the polishing pad surface without causing damage while maintaining sufficient rigidity to secure the wafer.
2Reliability
If higher pressure is applied to prevent wafer movement, then wafer stability is improved, but polishing pad distortion increases
Solution Approach 1:
The patent changes the hardness parameter of the retaining ring to create a pressure-distributing interface. The softer material (5-80 Shore D) distributes applied pressure over a larger area and reduces peak stresses, preventing localized pad distortion while maintaining sufficient overall pressure to prevent wafer movement.
3Ease of manufacture
If conventional retaining rings are used, then manufacturing simplicity is maintained, but production yield decreases due to thickness variations
Solution Approach 1:
The patent specifies a hardness range (5-80 Shore D) and material composition parameters for the retaining ring that optimize polishing uniformity. While this requires selecting specific materials within the range, it significantly improves wafer thickness uniformity (edge-to-center variation ≤10%), which directly increases production yield by reducing scrap and rework.
Solution Approach 2:
The patent applies the principle of local quality by ensuring the retaining ring material properties are specifically tailored to the contact interface with the polishing pad. The localized use of softer, more compliant material at the pad-contact surface improves polishing uniformity in that critical region, leading to better overall wafer quality and higher production yield.
Data Source
AI summary
Some embodiments relate to a carrier head. The carrier head includes a housing configured to enclose a wafer, wherein the housing includes a retaining ring recess configured to circumferentially surround the wafer. A retaining ring, which includes a first ring-shaped layer and a second ring-shaped layer, is disposed in the retaining ring recess. The second ring-shaped layer is disposed deeper in the retaining ring recess than the first ring-shaped layer and separates the first ring-shaped layer from a bottom of the retaining ring recess. A hardness of the second ring-shaped layer is less than a hardness of the first ring-shaped layer.