CMP Polishing Pad for Copper Dishing Reduction
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Solution Overview
Problem
The challenge in semiconductor wafer processing is the occurrence of dishing during chemical mechanical polishing (CMP) of softer metal layers, which leads to non-planar metal surfaces and increased defectivity, particularly in complex devices with finer features and more metallization layers, where existing CMP polishing pads fail to provide effective solutions.
Innovation Solution
A CMP polishing pad with a polishing layer composed of a reaction product of an isocyanate terminated urethane prepolymer and a curative component, including a polyol with a specific molecular weight and hydroxyl groups, and a polyfunctional aromatic amine, offering a balance of hardness and porosity to minimize dishing and defectivity, while maintaining efficient polishing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a softer CMP polishing pad is used to reduce defectivity, then defectivity is reduced, but dishing increases due to the flexible nature of the soft pad
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Shore D hardness of the polishing pad within a specific range (20-40) and adjusting the water uptake content (5-15%) through controlled porosity. This resolves the contradiction by finding an optimal parameter window where the pad is soft enough to reduce defectivity but maintains sufficient structural integrity to prevent dishing, unlike conventional pads that are either too soft or too hard
Solution Approach 2:
The patent uses composite materials by combining polyurethane base resin with specific curatives (polyol curative and polyfunctional aromatic amine curative) in controlled ratios. This creates a composite polishing pad structure that integrates both soft regions (for defect reduction) and harder supportive regions (for dishing prevention), resolving the contradiction through material composition rather than uniform hardness
2Manufacturing precision
If a harder CMP polishing pad is used to reduce dishing, then dishing is reduced, but defectivity increases
Solution Approach 1:
The patent resolves this contradiction by changing the hardness parameter to a specific intermediate range (Shore D 20-40) rather than using conventional hard pads (Shore D >40). This intermediate hardness parameter allows the pad to maintain structural rigidity for dishing prevention while having sufficient compliance to avoid creating defects on the substrate surface
3Reliability
If the polishing pad is made softer to improve defectivity, then defectivity is reduced, but polishing rate decreases
Solution Approach 1:
The patent resolves this contradiction by changing multiple parameters simultaneously: controlling hardness (Shore D 20-40), adjusting water uptake (5-15%), and optimizing porosity (10-30%). This multi-parameter optimization creates a pad that is soft enough for defect reduction but maintains sufficient mechanical properties and slurry access to preserve polishing rate, unlike conventionally soft pads that are too compliant
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 described CMP polishing pad effectively reduces defectivity and dishing in metal surfaces, enabling planarization of semiconductor wafers with improved electrical integrity and polishing rate, even for copper and tungsten containing surfaces, by providing a suitable balance of physical properties and conditionability.
Implementation Method 1
a reaction product of an isocyanate terminated urethane prepolymer and a curative component comprising from 60.3 to 70 wt. %, of a polyol curative... and from 30 to 39.7 wt. % of a polyfunctional aromatic amine curative
Implementation Method 2
the polishing layer would if unfilled or lacking in added porosity have a water uptake of 4 to 8 wt. % after one week of soaking in deionized (DI) water
Data Source
AI summary
The present invention provides methods of CMP polishing a metal surface, such as a copper or tungsten containing metal surface in a semiconductor wafer, the methods comprising CMP polishing the substrate with a CMP polishing pad that has a top polishing surface in a polishing layer which is the reaction product of an isocyanate terminated urethane prepolymer and a curative component comprising a polyol curative having a number average molecular weight of 6000 to 15,000, and having an average of 5 to 7 hydroxyl groups per molecule and a polyfunctional aromatic amine curative, wherein the polishing layer would if unfilled have a water uptake of 4 to 8 wt. % after one week of soaking in deionized (DI) water at room temperature. The methods form coplanar metal and dielectric or oxide layer surfaces with low defectivity and a minimized degree of dishing.