CMP Retaining Ring with Variable Width for Edge Polishing
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Solution Overview
Problem
Conventional retaining rings for chemical mechanical polishing (CMP) cause an 'edge effect' leading to uneven edge polishing profiles, impacting the yield and reliability of semiconductor devices due to differential polishing rates between the substrate edge and center.
Innovation Solution
A retaining ring with varying width between its inner and outer surfaces in a radial direction, designed to shift the edge polishing profile toward the center, reducing the edge effect by compensating for the uneven polishing rates through strategic shaping and positioning of the surfaces, with variations ranging from 2% to 50% of the average width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional retaining ring with uniform width is used during CMP, then the substrate is retained securely, but an edge effect occurs causing uneven edge polishing profile
Solution Approach 1:
The retaining ring is designed with non-uniform width where the width varies in the radial direction. Specifically, the width is greater at locations corresponding to the substrate edge and less at locations corresponding to the substrate center. This local variation in geometry creates corresponding variations in contact pressure with the polishing pad, with higher pressure at the substrate edge and lower pressure at the center, thereby compensating for the edge effect and achieving more uniform edge polishing profile.
Solution Approach 2:
The invention changes the geometric parameter of the retaining ring from a uniform width to a variable width in the radial direction. This parameter change is designed to produce corresponding changes in the contact pressure distribution between the retaining ring and the polishing pad. By controlling the width variation (e.g., 2% to 50% of average width), the contact pressure is modulated to compensate for the edge effect, transforming the pressure profile to achieve uniform polishing across the substrate edge.
2Manufacturing precision
If CMP is performed with conventional retaining rings, then the substrate surface is planarized, but the edge effect results in overpolishing or underpolishing at the perimeter
Solution Approach 1:
The retaining ring incorporates local quality variations through its non-uniform width design. The width is specifically increased at radial locations corresponding to the substrate edge to enhance contact pressure in that region, while the width is reduced at locations corresponding to the substrate center. This localized modification of the retaining ring geometry creates a corresponding localized pressure distribution that compensates for the edge effect, ensuring uniform material removal across the substrate perimeter and improving device yield.
Solution Approach 2:
The invention applies preliminary anti-action by pre-compensating for the edge effect through the non-uniform width design of the retaining ring. Before the CMP process begins, the retaining ring is configured with varying width that anticipates the edge effect phenomenon. During polishing, this pre-configured geometry produces a pressure distribution that counteracts the tendency for overpolishing or underpolishing at the substrate edge, thereby preventing the edge effect from occurring in the first place.
3Manufacturing precision
If a retaining ring with varying width is used, then the edge polishing profile is improved, but the device complexity of the retaining ring increases
Solution Approach 1:
The invention manages device complexity by implementing a controlled parameter change in the retaining ring width. The width varies in the radial direction by a specific amount (e.g., 2% to 50% of the average width), which is sufficient to compensate for the edge effect but not so large as to create excessive complexity. The variation can be implemented through simple geometric modifications such as tapered sections or annular grooves, maintaining manufacturing feasibility while achieving the desired pressure distribution for uniform edge polishing.
Data Source
AI summary
The edge effect or variation in polishing edge profile on a substrate undergoing CMP is reduced by structuring a retaining ring, housed in a carrier head for retaining the substrate, such that the polishing edge profile shifts back and forth with respect to the center of the substrate. Embodiments include structuring the retaining ring such that the width between inner and outer surfaces varies by an amount sufficient to compensate for polishing edge profile variation. Embodiments also include structuring the retaining ring such that the distance from the outer surface to the geometric inner surface varies. Embodiments further include structuring the retaining ring such that the distance between the outer surface to the perimeter of the substrate retained by the inner surface of the retaining ring varies.