Viscoelastic Polishing Pad for Edge Sagging and Step Elimination
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Solution Overview
Problem
Existing polishing pads suffer from edge sagging and insufficient step elimination performance, despite improvements in physical properties and bubble structures, leading to undesirable polishing outcomes in semiconductor devices.
Innovation Solution
A polishing pad with a polishing layer and cushioning layer, characterized by specific ratios of storage elastic modulus to loss elastic modulus (tan δ) and storage elastic modulus at different frequencies, and the inclusion of hollow microspheres, to prevent edge sagging and enhance step elimination performance without altering the polishing layer's composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If foamed polyurethane is used for the polishing layer, then the polishing pad can follow the shape of the workpiece edge, but edge sagging occurs due to excessive polishing at the edge
Solution Approach 1:
The polishing pad is designed with a cushioning layer having a specific bubble structure (average bubble diameter 50-200 μm, bubble density 0.3-0.6 mL/g) that creates local variations in hardness and compressibility. This local quality differentiation allows the polishing layer to adapt to the workpiece shape while preventing excessive edge polishing through controlled mechanical properties in different regions of the pad structure.
Solution Approach 2:
The invention controls the removal rate ratio (edge-to-center) within a specific range (1.05-1.30) by adjusting the cushioning layer's physical parameters including bubble diameter, bubble density, and Shore A hardness (40-70). This parameter optimization resolves the contradiction by tuning the pad's mechanical response to achieve both shape following and edge control.
2Manufacturing precision
If the polishing layer hardness is increased to prevent edge sagging, then edge control improves, but step elimination performance deteriorates
Solution Approach 1:
The invention optimizes the cushioning layer's Shore A hardness within the range of 40-70, which is softer than conventional pads. This softer hardness allows the pad to conform to step structures on the workpiece surface, improving step elimination performance while maintaining edge control through the controlled bubble structure that prevents excessive material removal at edges.
Solution Approach 2:
The polishing pad combines a foamed polyurethane polishing layer with a specially structured cushioning layer containing controlled bubble distributions. This composite structure integrates the hardness needed for edge control with the compliance needed for step elimination, resolving the contradiction between edge precision and step handling capability.
3Manufacturing precision
If the polishing pad structure is modified to improve edge sagging, then edge control improves, but other polishing performance may deteriorate
Solution Approach 1:
The cushioning layer is designed with specific local characteristics including bubble diameter (50-200 μm), bubble density (0.3-0.6 mL/g), and thickness (10-30% of total pad thickness). These localized structural features enable the pad to simultaneously achieve edge sagging control, step elimination, and general polishing performance without compromising any single function.
Solution Approach 2:
The invention establishes specific parameter ranges for the cushioning layer (bubble size, density, hardness, thickness ratio) that create an optimized balance between multiple polishing performance metrics. By controlling these parameters within defined ranges, the pad achieves versatile performance across different polishing scenarios including edge control, step elimination, and flat surface 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 polishing pad effectively prevents edge sagging and improves step elimination performance by maintaining consistent elastic properties across a wide frequency range, ensuring uniform polishing without significant changes in physical properties.
Implementation Method 1
dissipating the high energy during compressing as well as having high rigidity
Implementation Method 2
The polishing pad exhibits reduction of the dishing of the metal feature, excellent flattening performance and a low degree of the occurrence of the defect by especially dissipating the high energy during compressing
Data Source
AI summary
A polishing pad contains: a polishing layer having a polishing surface for polishing a workpiece; and a cushion layer disposed on the side of the polishing layer opposite from the polishing surface. With regard to the ratio (tan δ) of the storage elastic modulus E′ to the loss elastic modulus E″ of the whole polishing pad, as obtained through dynamic viscoelasticity measurement using frequency dispersion (25° C.) in a bending mode, the ratio of the maximum value of tan δ measured at 100-1000 rad/s (tan δmax100-1000) to the maximum value of tan δ measured at 1 to 10 rad/s (tan δmax1-10) is 0.75 to 1.30.