Pulse Laser Defect Inspection with Narrow Bandwidth
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Solution Overview
Problem
Current defect inspection technologies for semiconductor manufacturing struggle to detect defects smaller than one-tenth of the inspection wavelength with sufficient sensitivity, requiring improved illumination light sources and detection optics to enhance sensitivity and resolution.
Innovation Solution
The use of a pulse oscillation type laser with wavelength conversion to generate high output at short wavelengths, combined with large numerical aperture detection optics and a narrow spectral bandwidth to achieve high sensitivity and resolution, while minimizing chromatic aberration and maintaining necessary surface accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wavelength of illumination light is reduced to detect smaller defects, then measurement precision is improved, but chromatic aberration increases and manufacturing precision deteriorates
Solution Approach 1:
The patent applies parameter changes by utilizing a pulse oscillation type laser with wavelength conversion to generate high output at short wavelengths (e.g., 266nm, 355nm, 532nm). By converting the laser wavelength through nonlinear optical processes and synchronizing the pulse timing with the inspection cycle, the system achieves high measurement precision for sub-10nm defect detection while managing chromatic aberration through controlled spectral bandwidth and synchronized detection timing.
2Measurement precision
If the numerical aperture of detection optics is increased to improve resolution, then measurement precision is improved, but chromatic aberration increases
Solution Approach 1:
The patent resolves this contradiction by using a pulse oscillation type laser with controlled spectral bandwidth and narrow linewidth. The laser's coherent light properties and monochromaticity reduce chromatic aberration effects in high numerical aperture optics, enabling the use of large NA detection lenses to achieve high resolution for sub-10nm defect detection without suffering from severe chromatic aberration that would normally plague broadband light sources.
Solution Approach 2:
The patent replaces conventional broadband illumination systems with a pulse oscillation type laser system. This substitution provides highly monochromatic, coherent light with controllable pulse duration and timing, which dramatically reduces chromatic aberration in high-NA optical systems while enabling precise temporal gating to isolate defect scattering signals from pattern diffraction.
3Measurement precision
If the output power of illumination light source is increased to enhance sensitivity, then measurement precision is improved, but chromatic aberration and surface accuracy requirements worsen
Solution Approach 1:
The patent employs periodic action by using a pulse oscillation type laser that emits light in synchronized pulses rather than continuous wave. The pulse timing is synchronized with the inspection cycle, allowing high peak power illumination to enhance defect scattering signal strength while the pulsed nature and temporal gating reduce the impact of chromatic aberration and relax surface accuracy requirements by isolating the measurement window from environmental and system instabilities.
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 enables the detection of defects with enhanced sensitivity and resolution, improving the detection of small defects and reducing chromatic aberration, thus addressing the limitations of existing technologies.
Implementation Method 1
a pulse oscillation type laser with wavelength conversion to generate high output at short wavelengths
Implementation Method 2
In this wavelength region, the amount of light scattered from a defect can be approximated using a Rayleigh scattering coefficient, and is proportional to the sixth power of the defect size and inversely proportional to the fourth power of the wavelength
Data Source
AI summary
Method for realizing an inspection with short wavelength, high power light source and large numerical aperture, high performance optics to improve defect inspection sensitivity is disclosed. Short wavelength high power laser is realized by using a pulse oscillation type laser suitable for generation of high output power in a short-wavelength region. In addition, a spectral bandwidth of the laser is narrowed down so that amount of chromatic aberration of detection optics with single glass material (i.e. without compensation of chromatic aberration) is lowered to permissible level. Using highly workable glass material to construct the detection optics enables necessary surface accuracy or profile irregularity conditions to be met, even if the number of lenses is increased for large NA or the lens doesn't have a rotationally symmetrical aperture.