Grating Array Wavefront Sensor for Thin Film Thickness and Profile
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Solution Overview
Problem
Current techniques for in-situ real-time monitoring of thin film surface profile and thickness during growth processes are either intrusive, inaccurate, or limited to specific environments and materials, failing to simultaneously measure both parameters effectively.
Innovation Solution
A grating array based wavefront sensor system with a programmable light modulator is used for simultaneous in-situ real-time monitoring of surface profiling and thickness measurement, independent of the substrate and deposition environment, allowing dynamic switching between grating patterns and operating at the highest possible frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intrusive techniques like quartz crystal balance are used for thickness monitoring, then thickness measurement is available, but the technique is not directly in-situ and requires deposition on the sensor rather than the actual substrate
Solution Approach 1:
The patent introduces an optical intermediary system (laser beam, wavefront sensor, and optical path) that enables indirect measurement of substrate parameters without physical contact. The laser beam acts as a mediator carrying information about surface profile and thickness from the substrate to the sensor, resolving the contradiction between non-intrusive measurement and measurement capability
Solution Approach 2:
The patent replaces mechanical/intrusive measurement systems (quartz crystal balance requiring physical deposition on sensor) with an optical measurement system. The wavefront sensor uses light reflection and wavefront analysis to measure thickness and surface profile without mechanical contact or material deposition on the sensor, enabling true in-situ measurement
2Loss of information
If multiple measurement techniques are used for surface profiling and thickness monitoring, then comprehensive parameters are obtained, but the system complexity increases and simultaneous measurement is not achieved
Solution Approach 1:
The patent merges surface profiling and thickness measurement functions into a single integrated wavefront sensor system. By analyzing different aspects of the reflected wavefront (overall wavefront shape for surface profile, optical path differences for thickness), the system simultaneously obtains both parameters without requiring separate measurement devices or techniques
Solution Approach 2:
The wavefront sensor is designed as a multi-functional device that can measure both surface profile and thickness using the same optical path and detection mechanism. The single sensor system performs multiple measurement functions by processing different information from the reflected laser beam, reducing system complexity while maintaining comprehensive measurement capability
3Measurement precision
If conventional wavefront sensors are used, then measurement is possible, but mechanical vibrations and environmental changes affect measurement accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the wavefront sensor continuously monitors the reflected laser wavefront and the system adjusts for disturbances. By comparing wavefront measurements and identifying changes caused by vibrations or environmental factors, the system can compensate for these harmful effects and maintain measurement accuracy during in-situ monitoring
Solution Approach 2:
The patent uses ultrasonic vibration as an active measurement aid. By applying controlled ultrasonic vibration to the substrate and detecting the modulated reflected light signal, the system can distinguish between vibrations caused by the measurement process itself and external environmental vibrations, thereby improving measurement accuracy in vibrating environments
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
Enables accurate and simultaneous measurement of surface profile and thickness without prior calibration, reducing the impact of mechanical vibrations and environmental dependencies, and providing comprehensive information over larger areas.
Implementation Method 1
an array of gratings to diffract the beam incident thereon to form an array of focal spots on a detector
Implementation Method 2
a lens to focus the diffracted beams to form an array of focal spots on a detector plane
Implementation Method 3
a laser beam is made to incident on a substrate in a deposition unit and the beam reflected from the substrate is directed towards a wavefront sensor
Data Source
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AI summary
A system and method for real-time monitoring of surface profile and thickness measurement of thin film using a grating array based wavefront sensor is disclosed. A laser beam is incident on a substrate on which deposition is to be performed and then a reflected beam from the substrate falls directly or after transmission falls on an array of gratings. The direction of a diffracted beam of a particular diffraction order is a function of the orientation and periodicity of the corresponding grating. The diffracted beam is made to pass through a combination of lenses to generate an array of focal spots. The surface profile of the incident laser beam is estimated from the displacements of these focal spots corresponding to the elements in the grating array. The grating array pattern can be altered to avail certain benefits such as simultaneous thickness and surface profiling, higher frame rate, flexible dynamic range and so on. The technique is applicable to uniform as well as non-uniformly deposited thin films on the flat as well as non flat substrates.