Endpoint Detection Window for CMP Pad
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Solution Overview
Problem
Conventional polymer-based endpoint detection windows in chemical mechanical polishing pads lack durability and compatibility with softer polishing materials, leading to increased polishing defects and inadequate performance in detecting endpoints for semiconductor wafer planarization, especially with shorter wavelengths and complex device features.
Innovation Solution
A chemical mechanical polishing pad with an endpoint detection window formulated from a reaction product of an isocyanate terminated urethane prepolymer and a curative system, comprising an aromatic polyfunctional isocyanate, a prepolymer polyol, a difunctional curative, and an amine initiated polyol curative, which provides a balance of hardness, elongation, and optical transmission properties, including a Shore D hardness of 35 to 65, elongation to break of <300%, and double pass transmission of 25 to 100% at 400 nm, enhancing durability and defectivity performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymer-based endpoint detection windows are used, then optical transmission is achieved, but durability and compatibility with softer polishing materials are insufficient
Solution Approach 1:
The patent employs a composite material system consisting of an isocyanate-terminated polyurethane prepolymer combined with a polyol curative. This composite formulation creates a window material that integrates both optical transparency and enhanced mechanical durability, resolving the contradiction between achieving optical transmission and ensuring durability while maintaining compatibility with softer polishing materials.
Solution Approach 2:
The patent modifies the chemical and physical parameters of the window material by controlling the isocyanate index (NCO/OH ratio) within a specific range of 0.8 to 1.2, and by selecting polyol curatives with specific molecular weight ranges (200-10,000 g/mol). These parameter changes optimize the balance between hardness, elongation, and optical transmission, thereby improving durability without compromising optical performance.
2Illumination intensity
If aliphatic polyurethane windows are used, then light transmission over broad spectrum is improved, but durability for demanding polishing applications is insufficient
Solution Approach 1:
The patent changes the chemical composition parameters by using isocyanate-terminated polyurethane prepolymers with specific molecular weight ranges and isocyanate content (5-15 wt%). This formulation approach, combined with controlled curing conditions, produces a window material that maintains broad-spectrum light transmission while achieving the durability required for demanding polishing applications.
3Measurement precision
If shorter wavelengths are used for endpoint detection, then detection precision for thinner material layers is improved, but window degradation increases
Solution Approach 1:
The patent selects specific polyol curatives with molecular weights between 200-10,000 g/mol and controls the isocyanate index within 0.8-1.2 to optimize the window material's resistance to UV degradation. This allows the use of shorter wavelengths (330-425 nm) for endpoint detection without causing excessive window degradation, thereby maintaining both detection precision and window stability.
4Object-affected harmful factors
If softer polishing layer materials are used, then polishing defectivity is reduced, but window durability and compatibility are compromised
Solution Approach 1:
The patent creates a composite window material that is mechanically compatible with softer polishing layer materials. The specific formulation using isocyanate-terminated prepolymers and polyol curatives produces a window with optimized hardness and elongation properties, enabling it to work effectively with softer polishing materials without compromising durability or causing increased defectivity.
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 improved durability and optical properties, reducing polishing defects and enabling accurate endpoint detection with reduced window deformation, suitable for demanding semiconductor polishing applications and complex device features.
Implementation Method 1
the endpoint detection window comprises a reaction product of ingredients... double pass transmission of 25 to 100% at 400 nm
Data Source
AI summary
A chemical mechanical polishing pad is provided containing a polishing layer having a polishing surface; and, an endpoint detection window; wherein the endpoint detection window comprises a reaction product of ingredients, comprising: an isocyanate terminated urethane prepolymer having 5.5 to 9.5 wt % unreacted NCO groups, wherein the isocyanate terminated urethane prepolymer is a reaction product of ingredients comprising: an aromatic polyfunctional isocyanate; and, a prepolymer polyol; and, a curative system, comprising: 0 to 90 wt % of a difunctional curative; and, 10 to 100 wt % of an amine initiated polyol curative having at least one nitrogen atom per molecule and an average of at least three hydroxyl groups per molecule. Also provide are methods of making and using the chemical mechanical polishing pad.