Transparent Polishing Pad for Optical End-Point Detection
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Solution Overview
Problem
Conventional polishing pads used in CMP processes are opaque due to the large refractive index difference between the polymeric matrix and gas-filled capsules, which hinders in-situ optical end-point detection, and existing solutions involving separate windows are inefficient and costly.
Innovation Solution
A transparent polishing pad with a polymeric matrix and embedded polymeric capsules having a liquid core, where the refractive indices of the matrix, shell, and liquid core are within 30% of each other, allowing for effective in-situ optical end-point detection without the need for a separate window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gas-filled polymeric capsules are embedded in the polishing pad to create surface asperities, then the polishing pad structure is improved for transporting polishing composition, but the polishing pad becomes opaque due to large refractive index difference, hindering optical end-point detection
Solution Approach 1:
The patent changes the physical state of the capsule filling from gas to liquid, and selects a liquid with refractive index matched to the polymeric matrix. This parameter change eliminates the optical interface between materials with different refractive indices, making the polishing pad transparent while preserving the capsule structure for asperity formation and polishing composition transport.
Solution Approach 2:
The patent creates optical homogeneity by filling the polymeric capsules with a liquid whose refractive index matches that of the polymeric matrix material. This eliminates optical interfaces and refraction effects, making the entire polishing pad structure optically homogeneous and transparent, allowing optical end-point detection to function effectively.
2Measurement precision
If separate windows are added to enable optical detection, then optical end-point detection becomes possible, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the optical detection function directly into the polishing pad structure itself by making the entire pad transparent through refractive index matching. This eliminates the need for separate windows or aperture structures, integrating the optical detection pathway through the pad material and simplifying the overall device architecture.
Solution Approach 2:
The transparent polishing pad structure serves multiple functions simultaneously: it provides mechanical polishing through asperities, transports polishing composition through the capsule network, and enables optical end-point detection through its transparency. This multi-functionality eliminates the need for separate dedicated optical window components.
3Strength
If polymeric capsules with different refractive index are used to maintain structural integrity, then the polishing pad durability is improved, but light refraction and reflection increase, reducing signal strength
Solution Approach 1:
The patent changes the refractive index parameter of the capsule filling material to match the polymeric matrix, eliminating refraction and reflection at the capsule interfaces. This allows light to pass through the polishing pad structure with minimal energy loss, maintaining strong optical signals for end-point detection while preserving capsule structural integrity.
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 provides a transparent polishing pad that enables efficient in-situ optical end-point detection, reduces manufacturing steps, and improves polishing pad characteristics by minimizing light refraction and reflection, enhancing signal strength and planarization ability.
Implementation Method 1
the refractive indices of the matrix, shell, and liquid core are within 30% of each other, allowing for effective in-situ optical end-point detection
Data Source
AI summary
The present invention relates to a polishing pad useful for planarizing a substrate in a CMP process using a polishing composition. The polishing pad is transparent and allows for the use of an in-situ optical end-point detection apparatus without the need for a separate aperture or window in the polishing pad.