Digital Flashlamp Controller for High Dynamic Range Optical Measurement
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Solution Overview
Problem
Optical measurement systems in the semiconductor industry face challenges in achieving high accuracy and precision due to variable material layers, complex feature sizes, and dynamic processing conditions, which limit their dynamic range and measurement stability.
Innovation Solution
A digital flashlamp controller system with adjustable high voltage power supply, digital control electronics, and homogenization elements is introduced to control the flashlamp's pulsing and spectral output, enhancing dynamic range and channel-to-channel uniformity, and incorporating a spectral flattening filter to improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional flashlamp-based optical measurement system is used, then the system can perform real-time process monitoring, but the dynamic range is limited and measurement precision deteriorates due to sources of variation
Solution Approach 1:
The system dynamically adjusts flashlamp output intensity through multiple pulsing sequences with varying intensities (first, second, and third intensity levels) rather than using a single fixed intensity. This dynamic approach allows the system to adapt to different reflectivity conditions and extend the measurable dynamic range while maintaining precision through computational processing of the multiple measurements.
Solution Approach 2:
The system changes the temporal and intensity parameters of flashlamp operation by implementing multiple pulsing sequences with different intensity levels. Instead of a single continuous or fixed-pulse operation, the system varies the flash intensity parameters across multiple pulses, enabling it to capture signals across a broader dynamic range while maintaining measurement accuracy through the processed combination of these varied measurements.
2Measurement precision
If the flashlamp intensity is increased to improve signal strength, then the signal-to-noise ratio improves, but the dynamic range decreases due to saturation of high reflectivity signals
Solution Approach 1:
The system applies partial action by using multiple pulsing sequences where each pulse operates at a different intensity level rather than using a single excessive (high intensity) pulse. The first pulse uses a higher intensity to capture low reflectivity signals, while subsequent pulses use lower intensities to capture high reflectivity signals without saturation. This partial application of intensity across multiple pulses resolves the contradiction between achieving sufficient signal strength and avoiding saturation.
Solution Approach 2:
The system implements periodic action through multiple flash pulsing sequences instead of a single continuous or single-pulse operation. The flashlamp is pulsed periodically at different intensity levels (first, second, and third intensities) within a single measurement cycle, allowing the system to gather data across the full dynamic range through these periodic variations while maintaining high signal-to-noise ratios at each intensity level.
3Adaptability or versatility
If multiple measurement channels are used to monitor different wavelengths, then comprehensive process monitoring is achieved, but channel-to-channel variation increases measurement complexity
Solution Approach 1:
The system applies homogeneity by using identical flashlamp pulsing sequences and measurement procedures for all measurement channels simultaneously. Each channel receives the same temporal and intensity pattern of flash pulses, ensuring that all channels experience the same illumination conditions. This homogeneous treatment of all channels eliminates differential effects and reduces channel-to-channel variation, simplifying the complexity of multi-wavelength monitoring.
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 increases the dynamic range and stability of optical measurements, achieving high precision and accuracy in film thickness determination, with improved signal-to-noise ratios and reduced channel-to-channel variation, suitable for advanced semiconductor processes.
Implementation Method 1
a pulsed broadband emission source such as a xenon flashlamp
Implementation Method 2
incorporating a spectral flattening filter to improve measurement accuracy
Implementation Method 3
interferometric endpointing to monitor and control the state of a workpiece within a processing tool by using optical signals reflected from a wafer
Data Source
AI summary
A digital flashlamp controller, a flashlamp control system and a method of controlling a flashlamp bulb employing digital control electronics are provided herein. In one embodiment, the digital flashlamp controller includes: (1) a trigger interface configured to provide firing signals to control a trigger element for a flashlamp bulb and (2) digital electronics configured to generate the firing signals and control multiple pulsing of the flashlamp bulb.