Wafer Overlay Measurement Using Pupil-Plane Spot Selection
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Solution Overview
Problem
The challenge of accurately measuring overlay in highly stacked and miniaturized semiconductor memory devices, particularly between insulating layers and memory holes, is exacerbated by pattern misalignment, which affects the reliability and yield of these devices.
Innovation Solution
A measuring device and method using a multi-wavelength light source, beam splitter, and imaging units to acquire and analyze pupil plane intensity distribution images, allowing for the selection of measurement spots free from interfering patterns, thereby enabling robust and accurate overlay measurement between specified patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional single-wavelength measuring device is used, then the device complexity is low, but the measurement precision deteriorates due to interference from unwanted patterns in highly stacked semiconductor structures
Solution Approach 1:
The patent divides the measurement process into multiple wavelength channels, using a multi-wavelength light source to illuminate the specimen. By segmenting the measurement into different wavelength components, the system can selectively measure overlay at specific depths corresponding to different pattern layers, thereby improving measurement precision in highly stacked structures while managing device complexity through systematic decomposition of the measurement task
Solution Approach 2:
The patent introduces the wavelength dimension as an additional measurement parameter. Instead of relying solely on spatial resolution in the image plane, the system uses spectral information to differentiate between patterns at different depths. This dimensional addition allows the measuring device to distinguish overlapping patterns from multiple stacked layers, significantly improving overlay measurement precision without requiring proportional increases in spatial resolution hardware
2Measurement precision
If the measurement spot includes all patterns in the stacked structure, then the productivity is high due to fewer measurement spots needed, but the measurement precision deteriorates due to interference from unwanted patterns
Solution Approach 1:
The patent applies local quality by making the measurement process depth-selective through wavelength filtering. Instead of treating all patterns in the stacked structure uniformly, the system can focus the measurement on specific depth regions by selecting appropriate wavelengths. This allows precise overlay measurement of target patterns while excluding interference from other patterns at different depths, improving measurement precision without requiring a proportional increase in the number of measurement spots
Solution Approach 2:
The patent changes the measurement parameter from purely spatial to include spectral information. By utilizing multi-wavelength illumination and analyzing intensity distribution across different wavelengths, the system can selectively measure overlay at specific depths. This parameter change enables the measurement of overlay between specific pattern pairs in highly stacked structures without being affected by other patterns, thereby maintaining high productivity while achieving high 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
Enables precise overlay measurement by excluding interfering patterns, improving the yield and quality of semiconductor memory devices by reducing positional shifts during manufacturing processes.
Implementation Method 1
a light source that irradiates a measurement spot set on the specimen with a multi-wavelength light
Implementation Method 2
a beam splitter that splits reflected light emitted from the measurement spot by the irradiation with the multi-wavelength light into two directions
Implementation Method 3
a first imaging unit that acquires a first pupil plane intensity distribution image of one of the reflected lights split by the beam splitter, a second imaging unit that acquires a second pupil plane intensity distribution image of the other reflected light
Data Source
AI summary
A measuring device includes a light source that irradiates a measurement spot on a wafer formed with memory holes and slits with a multi-wavelength light, a first imaging unit that acquires a first pupil plane intensity distribution image of reflected light from the measurement spot, a second imaging unit that acquires a second pupil plane intensity distribution image of the reflected light, and a detection unit that analyzes the second pupil plane intensity distribution image to measure overlay. The measuring device includes an overlay analysis unit that acquires the first and second pupil plane intensity distribution images while moving a position of the measurement spot and selects a measurement spot not including the slit based on the first pupil plane intensity distribution image, and uses the overlay obtained by analyzing the second pupil plane intensity distribution image of the selected measurement spot as the overlay of the memory hole and a slit.