CMP Retaining Ring Segmented Bottom Surface
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing retaining rings for carrier heads in chemical mechanical polishing (CMP) systems wear away quickly due to contact with the polishing pad, leading to uneven polishing and potential substrate edge issues, such as increased radial non-uniformity and substrate edge chipping, due to the 'pad rebound effect'.
Innovation Solution
A retaining ring with a generally annular body featuring a bottom surface with multiple channels and islands that provide a controlled contact area of 15-40% of the plan area, reducing the pad rebound effect by distributing pressure uniformly and using a combination of materials like polyphenylene sulfide for the lower portion and a harder material for the upper portion, which is secured with an adhesive or screws, to manage wear and prevent substrate damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the retaining ring contacts the polishing pad to retain the substrate, then the substrate is securely held, but the retaining ring wears away quickly
Solution Approach 1:
The bottom surface of the retaining ring is segmented into multiple discrete contact areas (islands) separated by channels, rather than having a continuous contact surface. This segmentation reduces the total contact area with the polishing pad while maintaining effective substrate retention through distributed pressure points.
Solution Approach 2:
Different regions of the retaining ring have different properties: the contact areas are designed with specific hardness and friction characteristics to engage the polishing pad, while the channels provide wear relief and pressure distribution. The contact areas constitute only 15-40% of the total bottom surface area, concentrating the wear to specific locations.
2Reliability
If the retaining ring has full contact with the polishing pad, then the substrate is well retained, but the pad rebound effect causes uneven polishing and substrate edge chipping
Solution Approach 1:
The continuous contact surface is divided into multiple discrete contact islands separated by channels. This segmentation reduces the total contact area to 15-40% of the bottom surface, which minimizes the pad rebound effect while maintaining adequate substrate retention through the distributed contact points.
Solution Approach 2:
Instead of full contact between the retaining ring and polishing pad, only a partial contact area (15-40% of the bottom surface) is designed to contact the pad. This partial action is sufficient for substrate retention while reducing harmful rebound effects that occur with complete contact.
3Duration of action of stationary object
If the retaining ring is made of hard material to resist wear, then the lifespan is extended, but the substrate edge may be damaged due to increased hardness
Solution Approach 1:
The retaining ring exhibits spatial variation in material properties: the contact areas have higher hardness and friction coefficients to resist pad wear, while the channels and non-contact regions have lower hardness to prevent substrate damage. This local differentiation allows the ring to be wear-resistant where needed without being overly harsh on the substrate.
Solution Approach 2:
The retaining ring is constructed as a composite structure with regions of different material properties. The contact areas use harder, more wear-resistant materials, while other regions use softer materials that are less likely to damage the substrate during handling and polishing operations.
Data Source
AI summary
A retaining ring includes a generally annular body having an inner surface to constrain a substrate, an outer surface, and a bottom surface. The bottom surface has a plurality of channels extending from the outer surface to the inner surface and a plurality of islands separated by the channels and providing a contact area to contact a polishing pad. Each channel includes a recessed region adjacent the outer surface such that the channel is deeper in the recessed region than in a remainder of the channel. The recessed region and the remainder of the channel each have substantially uniform depth.