Polishing Endpoint Detection via Spectral Index
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Solution Overview
Problem
Existing polishing endpoint detection methods struggle with accurately detecting the endpoint in substrates with low polishing rates, leading to errors due to minimal fluctuation in reflection intensity and variations in initial film thickness between substrates.
Innovation Solution
A method and apparatus that monitor the change in reflection intensity by calculating differences in spectral profiles at predetermined wavelengths, determining the polishing endpoint based on a predetermined threshold value, and using spectral indices to reduce noise and stabilize the detection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical polishing endpoint detection is used with low polishing rates, then the polishing process can be controlled, but the detection accuracy deteriorates due to minimal fluctuation in reflection intensity
Solution Approach 1:
The patent transitions from monitoring reflection intensity at a single wavelength to analyzing spectral profiles across multiple wavelengths. This dimensional expansion allows detection of subtle changes in film thickness by examining the overall spectral shape rather than relying on large intensity fluctuations at individual wavelengths, thereby maintaining detection accuracy even at low polishing rates
Solution Approach 2:
The patent changes the monitoring parameter from absolute reflection intensity to spectral index (ratio of reflection intensities at different wavelengths). This parameter transformation enhances sensitivity to film thickness changes by comparing relative changes across wavelengths, enabling accurate endpoint detection when polishing rates are low and intensity fluctuations are minimal
2Measurement precision
If reflection intensity monitoring is used for endpoint detection, then the polishing endpoint can be detected, but detection errors occur due to variations in initial film thickness between substrates
Solution Approach 1:
The patent transforms the detection parameter from absolute reflection intensity to spectral index, which is a ratio of intensities at different wavelengths. This parameter change normalizes the measurement, making it insensitive to variations in initial film thickness while maintaining sensitivity to the endpoint condition, thereby improving reliability across different substrates
Solution Approach 2:
The patent continuously monitors spectral profiles during polishing and dynamically calculates the spectral index. This real-time feedback mechanism allows the system to track changes in film thickness relative to the starting point, compensating for variations in initial thickness and providing consistent endpoint detection across substrates with different starting conditions
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
This approach allows for accurate detection of the polishing endpoint by emphasizing changes in reflection intensity, reducing false detections, and compensating for variations in initial film thickness, thereby improving the precision of the polishing process.
Implementation Method 1
applying light to a surface of a substrate and receiving reflected light from the substrate
Implementation Method 2
The spectroscope decomposes the reflected light from the substrate according to wavelength and measures reflection intensity at each wavelength
Implementation Method 3
the light, applied to the substrate, is reflected off an interface between a medium and a film and an interface between the film and an underlying base layer of the film. The light waves reflected from these interfaces interfere with each other
Data Source
AI summary
Method and apparatus for detecting an accurate polishing endpoint of a substrate based on a change in polishing rate are provided. The method includes: applying a light to the surface of the substrate and receiving a reflected light from the substrate; obtaining a plurality of spectral profiles at predetermined time intervals, each spectral profile indicating reflection intensity at each wavelength of the reflected light; selecting at least one pair of spectral profiles, including a latest spectral profile, from the plurality of spectral profiles obtained; calculating a difference in the reflection intensity at a predetermined wavelength between the spectral profiles selected; determining an amount of change in the reflection intensity from the difference; and determining a polishing endpoint based on the amount of change.