Foamed Urethane Polishing Pad with Mixed Cell Structure
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Solution Overview
Problem
Existing polishing pads fail to maintain high flatness and prevent scratches, especially on larger substrates like wafers with diameters of 200 mm or more, due to uneven temperature distribution and rapid clogging, leading to uneven polishing and edge roll-off.
Innovation Solution
A polishing pad with a foamed urethane sheet comprising closed and open cells, specifically adjusted open cell ratios, loss factor ratios, and Shore DO hardness, which allows for efficient slurry retention and distribution, reducing scratches and maintaining flatness across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polishing pad with substantially closed cells is used, then the polishing pad structure is simple and manufacturing is easy, but the amount of slurry held is small, cooling effect is insufficient, and polishing temperature distribution becomes uneven
Solution Approach 1:
The polishing pad employs a composite cell structure where different regions serve different functions: closed cells provide structural support and ease of manufacture, while strategically positioned open cells provide slurry retention and cooling. This local differentiation resolves the contradiction by allowing each cell type to optimize its specific function rather than requiring the entire pad to be one uniform structure.
Solution Approach 2:
The invention uses a composite foam structure combining both closed cells and open cells within the same polishing pad. This composite approach allows the pad to simultaneously achieve the manufacturing simplicity of closed-cell foams while incorporating the slurry-holding and cooling capabilities of open-cell regions, thus resolving the temperature distribution issue.
2Temperature
If a polishing pad with connected open cells is used, then the amount of slurry held increases and cooling effect improves, but the resin deforms easily under polishing load, reducing flatness
Solution Approach 1:
The polishing pad uses closed cells in regions requiring structural rigidity to maintain flatness under load, while using open cells in regions where slurry retention and cooling are prioritized. This spatial differentiation of cell types allows the pad to simultaneously achieve good cooling effect and maintain polishing flatness.
Solution Approach 2:
The composite foam structure combines closed-cell and open-cell regions, where closed cells provide mechanical strength and resistance to deformation under polishing load, while open cells provide enhanced slurry capacity and cooling. This composite approach resolves the contradiction between cooling effectiveness and structural rigidity.
3Quantity of substance
If the open cell ratio is increased to improve slurry retention, then cooling effect improves, but the polishing pad deforms more easily under load, deteriorating flatness
Solution Approach 1:
The polishing pad concentrates open cells in specific regions where slurry retention is most beneficial for cooling, while maintaining closed cells in load-bearing regions to preserve structural rigidity. This localized distribution optimizes both slurry retention and flatness maintenance simultaneously.
Solution Approach 2:
The composite cell structure allows the pad to achieve adequate slurry retention through open-cell regions while maintaining overall structural integrity through closed-cell regions, thus resolving the contradiction between slurry capacity and deformation resistance.
4Productivity
If polishing is performed on large substrates (200mm or more diameter), then productivity increases, but temperature distribution becomes highly uneven, making uniform polishing extremely difficult
Solution Approach 1:
The polishing pad uses a non-uniform distribution of open and closed cells tailored to match the thermal profile of large substrates, with higher open-cell content in regions experiencing higher temperatures to enhance local cooling capacity, thereby maintaining temperature distribution uniformity across the entire large substrate surface.
Solution Approach 2:
The composite foam structure with combined open and closed cells provides both the slurry capacity needed for cooling large substrate areas and the structural stability required for uniform polishing across the entire surface, enabling high productivity while maintaining temperature uniformity.
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 polishing pad effectively maintains high flatness and prevents scratches on both center and outer circumferential portions of substrates, even during repeated polishing, by ensuring consistent temperature distribution and slurry exchange, thus stabilizing the polishing rate and preventing clogging.
Implementation Method 1
a polishing pad comprising a foamed urethane sheet which is provided on a surface thereof and which includes closed cells and open cells
Implementation Method 2
the polishing pad and a substrate are rubbed against each other, and thus the surface of the substrate to be polished is processed into a flat surface with the abrasive grains in the slurry. In the polishing with loose abrasive grains, a tendency is observed in which the temperature of the substrate is raised from moment to moment by the frictional heat during the polishing
Data Source
AI summary
Provided is a polishing pad which is capable of providing a high flatness to a polishing workpiece and suppressing the formation of scratches, and a method therefor. The polishing pad comprises a foamed urethane sheet on the surface which includes closed cells and open cells and which satisfies the following requirements: (1) an open cell ratio is 20-80 vol% where the total volume of closed cells and open cells is taken as 100 vol%, (2) the ratio [tanδ (wet/dry) ratio] of a loss factor tanδ in a water-absorption state to that in a dry state is 1. 3-1. 7, the loss factors being measured according to JIS K7244-4 with an initial load of 20 g at a measuring frequency of 1 Hz at a temperature of 26°C in a tensile mode over a strain range from 0.01 to 0.1%, and (3) the Shore DO hardness according to ASTM D2240 is 60-80.