Flash-Light Source Intensity for Film Thickness Measurement
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Solution Overview
Problem
The existing optical surface-monitoring systems using xenon flash lamps struggle to effectively measure film thickness due to low light intensity in the short wavelength range, making accurate thickness measurement challenging.
Innovation Solution
The polishing method and apparatus enhance light intensity by emitting the flash-light source multiple times during each exposure time, with the light detector capturing reflected light multiple times, thereby increasing the intensity of the reflected light and enabling accurate film thickness measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a xenon flash lamp is used as the light source in an optical surface-monitoring system, then the system can provide pulsed light covering a broad wavelength range (200 nm to 1100 nm), but the light intensity in the short wavelength range (200 nm to 250 nm) is low, making it difficult to effectively measure film thickness
Solution Approach 1:
The patent applies periodic action by causing the flash-light source to emit light multiple times during a single exposure time of the light detector. Instead of a single pulse, the system uses repeated pulses (e.g., 3-10 times) within the exposure window, which accumulates the reflected light signal and effectively increases the light intensity in the short wavelength range where the xenon flash lamp naturally has low output.
2Illumination intensity
If the flash-light source emits light multiple times during each exposure time, then the reflected light intensity is enhanced, but the system complexity increases due to coordinated control of multiple emissions
Solution Approach 1:
The patent merges the light emission function and detection function into a coordinated sequence within the optical sensor head. The control unit integrates the timing control of multiple flash emissions with the exposure timing of the light detector, combining these functions into a unified control routine that manages the entire measurement cycle without requiring separate complex control systems for each component.
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 effectively enhances the intensity of the reflected light, particularly in low-intensity wavelength ranges, allowing for precise film thickness measurement and improving the accuracy of the measurement process.
Implementation Method 1
causing the flash-light source to emit light plural times in a first exposure time of the light detector
Implementation Method 2
capturing reflected light from the substrate by the light detector via the optical sensor head
Data Source
AI summary
A polishing method capable of accurately measuring a film thickness of a substrate, such as a wafer, by enhancing light intensity of a flash-light source, such as a xenon flash lamp is disclosed. The polishing method includes: while an optical sensor head is moving across a substrate, causing a flash-light source to emit light plural times in a first exposure time of a light detector to direct the light to the substrate via the optical sensor head, capturing reflected light from the substrate by the light detector via the optical sensor head, further causing the flash-light source to emit light plural times in a second exposure time of the light detector to direct the light to the substrate via the optical sensor head, and capturing reflected light from the substrate by the light detector via the optical sensor head; generating a spectrum of the reflected light; and detecting a surface state of the substrate from the spectrum.