Interferometric Vibration Compensation in Probe Microscopy
Solution Overview
Problem
Local probe microscopy is limited by environmental mechanical vibrations, which affect the precision and throughput of semiconductor wafer inspection and review processes, especially in large-scale fabrication, where conventional noise compensation methods are costly and inadequate for high-resolution imaging.
Innovation Solution
A method and apparatus for vibration compensation in local probe microscopy, using a scanning probe and a reference beam reflected from a fixed point subject to similar vibrations, combined interferometrically to generate differential probe height data, allowing for adjustments to maintain constant interaction and improve topography measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AFM is used without vibration compensation, then the device complexity remains low, but the measurement precision deteriorates due to mechanical and acoustic noise
Solution Approach 1:
The patent introduces an interferometer as an intermediary measurement system that independently monitors vibrations of the sample stage. This interferometer acts as a mediator between the vibration source and the AFM measurement, providing vibration data that can be compensated for in the final image, thereby improving measurement precision without requiring direct modification of the AFM probe system
Solution Approach 2:
The patent implements a feedback mechanism where vibration data from the interferometer is continuously fed back to the AFM system. This feedback loop enables real-time compensation of vibration effects on the sample stage, allowing the system to maintain high measurement precision despite environmental mechanical vibrations
2Measurement precision
If vibration compensation is implemented using interferometers, then the measurement precision improves, but the device complexity and cost increase
Solution Approach 1:
The patent segments the vibration compensation function into a separate interferometer system that operates independently from the AFM imaging system. This segmentation allows the interferometer to be optimized for vibration measurement while the AFM system remains optimized for imaging, reducing overall system complexity compared to integrating both functions into a single system
Solution Approach 2:
The interferometer system serves multiple functions: it monitors vibrations of the sample stage, provides vibration data for compensation, and can potentially be used for other measurement purposes. This multi-functionality justifies the added complexity by providing versatile measurement capabilities that benefit the overall system
3Productivity
If environmental vibrations are present, then the throughput increases due to reduced settling time, but the measurement precision deteriorates
Solution Approach 1:
The patent implements preliminary vibration monitoring using the interferometer system that continuously tracks vibrations before they affect the AFM measurement. By having vibration data available in advance, the system can pre-compensate for expected vibrations, allowing faster settling times while maintaining measurement precision
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 enhances the resolution and accuracy of local probe microscopy by effectively canceling out external vibrations, enabling high-resolution imaging and improving throughput in semiconductor wafer inspection and review processes.
Implementation Method 1
An optical lever system (laser reflection from the back of the cantilever onto a segmented photodiode)
Implementation Method 2
interferometrically combining the reflected probe beam and the reflected reference beam to generate differential probe height data
Data Source
AI summary
A The local probe microscopy apparatus (1) comprises a probe (3) with translation stages (5a, 5b) for controlling the position of the probe (3) relative to a sample surface. The probe (3) has a feedback mechanism (6, 5 7) for maintaining the deflection of the probe and a height measuring system (9) which includes means for compensating for environmental noise. The local probe microscopy apparatus is particularly suitable for use as a wafer inspection tool in a wafer fabrication plant where the inspection tool is liable to be exposed to significant mechanical vibration.