CMP Polishing Pad Window with Elastomeric Bottom
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Solution Overview
Problem
Conventional polishing pads with windows for endpoint detection in chemical mechanical polishing face issues such as refraction and reflection of signal waves at the solid/gas interface, differential compression leading to deformation, and increased scratch defect rates due to differences in modulus and thermal expansion coefficients between the polishing layer and the window material.
Innovation Solution
A polishing pad design featuring a window that extends through the pad with a top portion made of a conventional window material and a bottom portion made of elastomeric material, allowing for compressibility and reducing stress, thereby avoiding bulging and improving signal transmission and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rigid window material is used for endpoint detection, then signal transmission is improved, but differential compression leads to deformation and protrusion of the window area
Solution Approach 1:
The patent changes the material parameter of the window from rigid to elastomeric, allowing the window to deform elastically under compression rather than maintaining a fixed rigid shape. This parameter change enables the window to accommodate differential compression without protruding or causing scratching defects.
Solution Approach 2:
The patent uses an elastomeric window material that functions as a flexible element, allowing the window to flex and deform elastically during polishing. This flexibility accommodates the differential compression between the window region and surrounding pad material, preventing window protrusion and maintaining surface contact uniformity.
2Measurement precision
If a transparent window material is used for signal transmission, then endpoint detection is enabled, but refraction and reflection at the solid/gas interface create noise
Solution Approach 1:
The patent introduces a fluid (gas or liquid) into the window region to replace the solid/gas interface with a fluid/polishing layer interface. This pneumatic approach eliminates refraction and reflection noise because the fluid conforms to the pad surface and maintains optical contact without creating sharp interfaces that cause signal interference.
Solution Approach 2:
The patent uses a fluid as an intermediary medium between the window material and the external environment. This fluid intermediary eliminates the problematic solid/gas interface by providing a conforming optical path that reduces refraction and reflection, thereby reducing signal noise while maintaining transparency for endpoint detection.
3Strength
If the window material has higher modulus and stiffness than the polishing layer, then structural integrity is improved, but differential thermal expansion and compression cause scratching defects
Solution Approach 1:
The patent changes the mechanical parameters of the window material from high modulus and stiffness to low modulus and high elasticity. This parameter change enables the window to deform elastically under thermal and mechanical loads, matching the compliance of the surrounding polishing layer and preventing differential deformation that causes scratching defects.
Solution Approach 2:
The patent makes the window material homogeneous with the surrounding polishing layer in terms of mechanical compliance by using an elastomeric material with similar elasticity and compressibility. This homogeneity ensures that the window region deforms uniformly with the rest of the pad during polishing, preventing localized stress concentrations that lead to scratching.
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 design enhances the accuracy of endpoint detection by minimizing signal interference and deformation, leading to reduced scratch defects and extended pad lifetime by matching the compressibility of the window region with the rest of the pad, thus improving the uniformity and reliability of the polishing process.
Implementation Method 1
the bottom portion... comprises an elastomeric material wherein there is a gap between side edges of the bottom portion and the sub-pad material
Implementation Method 2
Transmittance of a signal wave through a boundary between a gap (e.g., air) and a surface of the window can lead to refraction or reflection of the signal wave
Implementation Method 3
Since the upper surfaces of the pad and window are frictionally heated during CMP
Implementation Method 4
Differences in the coefficient of thermal expansion (CTE) and thermal conductivity (K) between the polishing material and the window can further exacerbate problems
Data Source
AI summary
A polishing pad for chemical mechanical polishing comprises a polishing layer having a top polishing surface, a sub-pad located opposite from the top polishing surface, the sub-pad comprising a sub-pad material and having a bottom sub-pad surface defining a bottom surface of the polishing pad, and a window for transmitting a signal wave through the polishing pad to a substrate to be polished and back through the polishing pad for endpoint detection, the window having a top window surface, a bottom window surface, and side edges, wherein the top window surface is recessed from the top polishing surface, the bottom window surface is substantially coplanar with the bottom sub-pad surface, and the side edges are in contact with the polishing material and the sub-pad material.