Chromatic Confocal Trench Depth Measurement
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Solution Overview
Problem
Current metrology technologies are unable to accurately and efficiently measure the depth of high aspect ratio trenches, which are crucial in semiconductor fabrication for MEMS devices, as existing instruments face challenges such as contact limitations, signal confusion, and high costs due to the need for bright light sources and complex alignment.
Innovation Solution
An integrated system combining a traditional microscope with a chromatic confocal, single point, height sensor using an axially dispersive, afocal lens system and a spectrometer to provide simultaneous imaging and height measurement without mechanical movement, employing separate wavelength bands for the microscope and height sensor to avoid cross-interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If standard confocal microscopes are used to measure trench depth, then imaging capability is provided, but measurement accuracy deteriorates due to signal confusion from top and bottom of narrow trenches
Solution Approach 1:
The patent divides the optical spectrum into separate wavelength bands: one band dedicated to imaging (microscope) and another band dedicated to height measurement (chromatic confocal sensor). This spectral segmentation prevents signal confusion between imaging and measurement functions, allowing accurate trench depth measurement even in narrow high aspect ratio structures.
Solution Approach 2:
The patent creates a multi-functional system where a single instrument provides both imaging capability (through the microscope portion) and precise height measurement capability (through the chromatic confocal portion). This eliminates the need for separate instruments while maintaining both functions' performance.
2Ease of operation
If white light interferometers are used for height measurement, then non-contact measurement is achieved, but measurement speed deteriorates due to required longitudinal scanning
Solution Approach 1:
The patent replaces the mechanical longitudinal scanning mechanism of white light interferometers with a chromatic confocal optical system. By using wavelength-dependent focal planes, the system achieves height measurement without mechanical movement, dramatically increasing measurement speed while maintaining non-contact operation.
3Measurement precision
If bright light sources are used in chromatic confocal systems, then height measurement capability is provided, but system cost and complexity increase
Solution Approach 1:
The patent merges the chromatic confocal height sensor with a traditional microscope into a single integrated instrument. By combining these functions and using separate wavelength bands, the system achieves accurate height measurement without requiring excessively bright light sources or complex alignment mechanisms, reducing overall system complexity.
4Measurement precision
If contact stylus profilers are used for trench measurement, then depth measurement is achieved, but the stylus breaks when exiting high aspect ratio trenches
Solution Approach 1:
The patent replaces the mechanical contact stylus with a non-contact optical chromatic confocal sensor. This eliminates the mechanical stress and breaking problems associated with stylus profilers when measuring high aspect ratio trenches, while maintaining accurate depth measurement capability.
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 fast and accurate non-destructive measurement of high aspect ratio trenches, replicating stylus profiler functionality with non-contact optical height measurement, improving process control and reducing costs by using off-the-shelf objective lenses and minimizing complex lens designs.
Implementation Method 1
uses axial chromatic aberration with a broadband source to form a focused spot such that the axial distance to the focus varies with wavelength
Implementation Method 2
The objective lens is then free to perform both the imaging required for the microscope and the focusing required for the height sensor
Implementation Method 3
The beam splitter is of a type that passes the wavelength band used by the microscope and reflects the wavelength band used by the height sensor
Implementation Method 4
A spectrometer at the detector measures the signal level for each wavelength
Data Source
AI summary
A system for the measurement of high aspect ratio trenches. The preferred embodiment consists of three elements: a) an integrated microscope and optical height sensor, b) an axially dispersive, afocal lens system, which is included in the optical height sensor, and c) an algorithm for processing the optical height sensor data to produce the depth of the high aspect ratio trench. The present invention combines a traditional imaging microscope with a chromatic confocal, single point, height sensor. This combination instantaneously provides an image of the object and the height value at one point in the image. No mechanical movement is necessary anywhere in the system to achieve that result. The chromatic confocal height sensor is integrated with a traditional microscope through the use of separate wavelength bands such as a wavelength band in the visible part of the spectrum, and a wavelength band in the infrared or ultraviolet part of the spectrum.