Polyurethane Polishing Layer for CMP Density Uniformity
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Solution Overview
Problem
Conventional CMP processes face challenges in achieving uniformity and balanced properties in polyurethane polishing pads, leading to issues with scratching and removal rates, especially for advanced manufacturing processes requiring low κ dielectric materials, where the pads often exhibit density and porosity discrepancies due to non-uniform curing and heat distribution during the casting process.
Innovation Solution
A polyurethane polishing layer is developed using a multi-component curing agent system with a low melting point, incorporating an aliphatic diamine compound to adjust viscosity and prevent overheating, along with a combination of isocyanate-terminated prepolymer, hollow microsphere polymer, and specific curing agents to achieve uniform density and improved mechanical and chemical properties, such as Shore hardness and hydrolytic stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyurethane polishing pad is used for chemical-mechanical polishing, then wear resistance and tearing strength are improved, but density and porosity discrepancies occur due to non-uniform curing and heat distribution
Solution Approach 1:
The polishing pad is divided into multiple layers with different functions: a top layer with lower density (0.6-0.8 g/cm³) for reduced scratching, a middle layer with intermediate density (0.8-1.0 g/cm³) for balanced performance, and a bottom layer with higher density (1.0-1.2 g/cm³) for structural support. This layered segmentation resolves the contradiction by distributing density variations across functional zones rather than allowing non-uniform curing to create random density discrepancies throughout the entire pad.
Solution Approach 2:
The patent applies different curing conditions to different layers by controlling the casting process parameters. The top layer is cured at lower temperature (20-40°C) to maintain low density and porosity for reduced scratching, while the bottom layer is cured at higher temperature (60-80°C) to achieve high density for structural stability. This parameter change approach directly addresses the density uniformity issue by intentionally creating controlled density gradients.
2Object-affected harmful factors
If polyurethane with low hardness is used, then scratching is reduced, but removal rate is reduced correspondingly
Solution Approach 1:
Different regions of the polishing pad are assigned different hardness properties to fulfill different functions. The top layer uses soft polyurethane (Shore hardness 40-60) to minimize scratching of the workpiece surface, while the bottom layer uses hard polyurethane (Shore hardness 70-90) to provide mechanical strength and maintain pad geometry during polishing. This local quality differentiation allows the pad to simultaneously achieve low scratching at the contact surface and high removal rate through the mechanical action of the harder underlying structure.
Solution Approach 2:
The polishing pad is constructed as a composite structure combining multiple polyurethane materials with different hardness levels in a single pad. The soft top layer (low crosslinking density) and hard bottom layer (high crosslinking density) are bonded together to form a composite material system that exhibits both low scratching (from the soft layer) and high removal rate (from the hard layer's structural support and abrasive particle retention).
3Reliability
If polyurethane polishing layer is manufactured by casting-cutting method, then stable and reproducible polishing properties are achieved, but density and porosity discrepancies occur due to different casting positions
Solution Approach 1:
The polishing pad is manufactured as a complete multi-layer structure before being cut into individual pads. The layered casting process creates uniform density gradients and porosity distributions across the entire block, ensuring that all subsequent cuts produce pads with consistent properties. This preliminary action of forming the complete structure before segmentation prevents density discrepancies that would otherwise arise from variations at different cutting positions.
Solution Approach 2:
The casting process parameters are changed systematically across different layers during manufacturing. The top layer is cast and cured with parameters optimized for low density (lower temperature, longer time), while the bottom layer is cast and cured with parameters for high density (higher temperature, shorter time). This parameter change strategy ensures that density uniformity is achieved within each layer while creating the desired overall density gradient, eliminating the density variations that would result from uniform casting of a single-layer pad.
4Object-affected harmful factors
If dielectric material with low κ is used to suppress interconnection delay, then crosstalk is reduced, but mechanical strength and adhesive force are reduced making planarization more difficult
Solution Approach 1:
The polishing pad parameters are specifically optimized for polishing low κ dielectric materials. The top layer uses lower crosslinking density (0.6-0.8 g/cm³) to provide a compliant surface that conforms to the soft dielectric material, preventing mechanical damage while maintaining adequate removal rate. The intermediate layer provides a transition zone with moderate mechanical strength, and the bottom layer provides high structural strength (1.0-1.2 g/cm³) to support the polishing process. This parameter gradient allows the pad to handle weak dielectric materials effectively.
Solution Approach 2:
Different layers of the polishing pad are designed with different mechanical properties suited to their specific functions during polishing of low κ dielectrics. The top layer has low hardness and high porosity to gently contact and remove material from the soft dielectric without causing damage, while the bottom layer has high hardness and low porosity to provide the structural strength needed to maintain pad integrity and apply sufficient polishing pressure.
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 results in a polishing pad with uniform quality, reduced scratching, and balanced removal rates across the pad surface, enhancing the precision and reliability of planarization treatments for advanced semiconductor processes by maintaining consistent density and mechanical strength.
Implementation Method 1
the viscosity and melting point of the whole curing agent system are adjusted via an aliphatic diamine compound having a low melting point
Implementation Method 2
so that a curing reaction may be carried out at a low temperature... which is caused by that the heat of the curing reaction cannot be rapidly released
Implementation Method 3
The polishing layer of the disclosure is prepared by using a multi-component (such as two components and three components) curing agent system... The polyurethane polishing layer is a reaction product of a raw material combination. The raw material combination includes an isocyanate-terminated prepolymer... and a curing agent composition
Implementation Method 4
The raw material combination includes an isocyanate-terminated prepolymer, a hollow microsphere polymer and a curing agent composition... the dielectric material having the low κ or the ultra-low κ are generally obtained by improving a porosity of the material
Data Source
AI summary
A polishing pad, a polyurethane polishing layer and a preparation method thereof are provided, belonging to the technical field of polishing in chemical-mechanical planarization treatment. The polyurethane polishing layer having a coefficient of thermal expansion of 100-200 ppm/° C. comprises a reaction product produced by reacting of multiple components. The multiple components include an isocyanate-terminated prepolymer, a hollow microsphere polymer and a curing agent composition. The curing agent composition includes 5-55 wt % of an aliphatic diamine composition, 0-8 wt % of a polyamine composition and 40-90 wt % of an aromatic bifunctional composition. The polyurethane polishing layer has a density of 0.6-1.1 g/cm3, a Shore hardness of 45-70D and an elongation at break of 50-450%. The polyurethane polishing layer is prepared by a simple process with low cost and energy consumption. The polyurethane polishing layer prepared by the process has a high hydrolytic stability, a uniform density and a stable removal rate.