Wavefront Splitting for Pattern Height Measurement
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Solution Overview
Problem
Current methods for measuring pattern heights in plasma deep etching, such as incremental laser interferometry and spectroscopic ellipsometry, are inadequate as they are sensitive to vibrations, difficult to apply to narrow patterns, and limited to periodic patterns, making it challenging to determine the end of etching with the required micron-level depth resolution.
Innovation Solution
A method involving wavefront splitting and modal filtering of reflected light to extract phase difference information, allowing for real-time, in-situ measurement of pattern heights, applicable to both narrow and wide, periodic and non-periodic patterns, using a device with single-mode optical fibers and a Michelson interferometer for precise height determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If incremental laser interferometry is used to measure pattern heights, then measurement capability is provided, but the method becomes sensitive to vibrations and displacements, reducing measurement precision
Solution Approach 1:
The patent replaces mechanical/vibration-sensitive interferometric measurement systems with an optical method that uses wavefront splitting by the pattern itself. The measurement is achieved through optical path difference analysis of reflected light waves, eliminating the need for mechanical displacement measurements that are sensitive to vibrations.
Solution Approach 2:
The patent creates an optical copy of the pattern's wavefront structure by splitting the reflected light wavefront into multiple components that traverse different optical paths. This optical copying allows measurement without direct mechanical contact or vibration-sensitive displacement sensing.
2Measurement precision
If conventional interferometry with large distance between interferometer and object is used, then measurement capability is provided, but the measurement point size increases to tens of microns, making it impossible to measure narrow patterns
Solution Approach 1:
Instead of using a large-distance interferometer that creates large measurement spots, the patent inverts the approach by using the pattern itself to split the wavefront. The measurement is performed with a focused beam where the pattern's own geometry creates the measurement separation, enabling sub-diffraction-limit resolution for narrow patterns.
Solution Approach 2:
The patent transitions from measuring in the spatial domain with large physical separations to measuring in the wavefront phase domain. By encoding height information in the phase difference of split wavefronts rather than in physical measurement point separation, the method can resolve narrow patterns smaller than the incident beam width.
3Measurement precision
If spectroscopic ellipsometry is used for measurement, then periodic pattern structure determination is enabled, but the method is limited to periodic patterns only, reducing adaptability
Solution Approach 1:
The patent creates a universal measurement method that works for both periodic and non-periodic patterns, as well as narrow and wide patterns. The wavefront splitting mechanism is independent of pattern periodicity, allowing the same optical setup to measure any reflective pattern geometry without methodological limitations.
4Productivity
If existing measurement methods are used in plasma etching, then measurement capability is provided, but real-time in-situ measurement with micron-level depth resolution is not achieved
Solution Approach 1:
The patent enables continuous real-time measurement during the plasma etching process by using an optical method that can penetrate or observe through the etching environment. The wavefront splitting measurement provides continuous height data without interrupting the etching process, enabling real-time monitoring and control with micron-level resolution.
Solution Approach 2:
The patent implements a feedback mechanism where real-time wavefront splitting measurements of pattern height during etching provide immediate information about etching progress. This feedback enables precise control of etching depth by comparing measured heights against target values and adjusting etching parameters accordingly, achieving micron-level depth resolution control.
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 precise, real-time measurement of pattern heights during etching, overcoming limitations of existing methods by allowing measurements of patterns smaller than the incident beam width and providing accurate control of etching depth, even in plasma etching environments with significant vibrations.
Implementation Method 1
a transmission means (8) for guiding the reflected light back towards the beam splitting means (3), said transmission means comprising a single-mode optical fiber
Implementation Method 2
a beam splitting means (3) for splitting the reflected light into a plurality of beams
Implementation Method 3
said measurement means comprising a Michelson interferometer
Data Source
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AI summary
The invention concerns a method for measuring the heights of patterns of an object. Incident light comprising a propagation mode of interest for at least one wavelength of interest, is reflected by a surface (18) of an object (14). The reflection comprises a wave front division of the light by at least one pattern (5), into division components (16, 17). The method then consists in collecting the reflected light (7), followed by filtering the collected light; extracting from the filtered light, for wavelengths of interest, data of phase differences between the division components. Such a method enables the heights of patterns to be measured on an object whose surface is structured and reflects light, in particular the patterns on a silicon wafer. Such a measuring method enables the etching of patterns, for example during deep plasma etching, to be monitored in situ in real time. The invention also concerns a device for implementing said method.