Polishing Pad Window Laser Ablation for Optical Measurement
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Solution Overview
Problem
Conventional polishing pads with polyurethane windows for chemical-mechanical planarization suffer from surface roughness that reduces light transmission and increases light scattering, leading to lower measurement resolution and variability in optical end-point detection during semiconductor wafer planarization.
Innovation Solution
The polishing pad features a window with its lower surface treated by laser ablation to remove surface roughness and optionally forms micro-lenses, enhancing light transmission and reducing scattering for improved optical measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyurethane windows are formed by slicing a polyurethane block, then the window can be easily manufactured and integrated into the polishing pad, but the slicing process produces surface roughness that scatters light and reduces measurement resolution
Solution Approach 1:
The patent applies laser ablation to fundamentally change the surface parameters of the window. By using laser energy to remove material layer by layer, the surface roughness is reduced from 10-100 microns to a smooth finish, transforming the optical properties of the window surface to minimize light scattering while maintaining the polyurethane material's ease of manufacture and integration
2Ease of manufacture
If the window has surface roughness from slicing, then manufacturing is simpler, but light scattering increases and signal strength decreases
Solution Approach 1:
Laser ablation changes the surface energy and optical parameters of the window by removing rough surfaces through controlled vaporization and ejection of material. This process reduces light scattering losses and increases the transmission of optical signals through the window, thereby reducing energy loss while preserving the simple polyurethane fabrication process
3Productivity
If conventional slicing is used to create the window, then production is faster and simpler, but the bottom surface roughness scatters light and reduces signal strength
Solution Approach 1:
The laser ablation process rapidly removes surface roughness from the window, transforming the optical parameters in a controlled manner. This post-processing step maintains high production efficiency by being a rapid, automated process that significantly reduces surface roughness depth, thereby improving measurement precision without substantially reducing overall production speed
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 laser-ablation treated surface increases light transmission by up to 3 times, leading to more robust and accurate in-situ optical measurements, improving reliability and extending the pad's lifespan by minimizing signal loss due to surface roughness.
Implementation Method 1
the lower surface has been treated by laser ablation to remove surface roughness present on the lower surface
Implementation Method 2
the lower surface has been treated by laser ablation to remove surface roughness present on the lower surface. The laser-ablation treated surface increases light transmission by up to 3 times
Implementation Method 3
A light beam is directed through the window to the wafer surface, where it reflects and passes back through the window to a detector
Data Source
AI summary
The present invention provides a polishing pad for performing chemical mechanical planarization of semiconductor substrates. The polishing pad comprises a polishing pad body having an aperture formed therein and a window fixed in the aperture for performing in-situ optical measurements of the substrate. The window has a lower surface capable of transmitting light incident thereon. The lower surface has been treated by laser ablation to remove surface roughness present on the lower surface.