Retaining Ring Channels for Slurry Flow Control
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Solution Overview
Problem
Chemical mechanical polishing of substrates often results in non-uniform polishing rates across the substrate, with the edge portion polishing at a higher rate than the central portion, leading to uneven surfaces and 'hot spots' of over-polishing.
Innovation Solution
A retaining ring with a plurality of channels extending from the inner diameter to the outer diameter is used to hold the substrate in place during polishing. These channels preferentially expel polishing liquid from the region below the substrate's outer edge, reducing the polishing rate at the edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polishing is used, then the substrate can be planarized, but the edge portion polishes at a higher rate than the central portion, resulting in non-uniform polishing
Solution Approach 1:
The retaining ring incorporates channels with varying geometries at different locations to create localized slurry flow control. The channels have different widths, depths, or orientations in radial vs. tangential directions, enabling differential slurry distribution to achieve uniform polishing across the substrate surface
Solution Approach 2:
The retaining ring uses hydraulic principles by channeling polishing slurry through controlled pathways. The slurry flow is directed through channels in the retaining ring to create specific flow patterns under the substrate, using fluid dynamics to control polishing rate distribution
2Manufacturing precision
If the retaining ring channels are designed to expel slurry from the edge region, then edge polishing rate is reduced, but the channel geometry becomes more complex
Solution Approach 1:
The retaining ring is segmented into multiple channels instead of using a single complex flow path. Each channel handles a specific portion of the slurry flow, and the channels can be arranged in patterns that simplify individual channel geometry while achieving overall flow control objectives
Solution Approach 2:
Instead of trying to control slurry flow into the polishing zone, the invention controls flow out of the polishing zone by expelling slurry through channels in the retaining ring. This inverted approach simplifies the channel geometry by working with natural slurry pressure buildup during polishing
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 solution effectively controls and corrects radial polishing non-uniformity, reduces polishing 'hot spots', and maintains throughput by integrating the adjustment within the polishing station rather than requiring a separate module.
Implementation Method 1
rotating the carrier head about an axis of rotation such that polishing liquid is preferentially expelled from a region below an outer edge of the substrate through the plurality of channels
Data Source
AI summary
A method for chemical mechanical polishing includes bringing a substrate into contact with a polishing pad, causing relative motion between the substrate and polishing pad, dispensing a polishing liquid onto the polishing pad, holding the substrate in a lateral position with a retaining ring secured to a carrier head, and rotating the carrier head about an axis of rotation. The retaining ring has a plurality of channels extending from an inner diameter surface of the retaining ring to an outer diameter surface of the retaining ring such that rotation cause the polishing liquid to be preferentially expelled from a region below an outer edge of the substrate through the plurality of channels.