Line Scan Spectroscopic White Light Interferometry for Semiconductor Metrology
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Solution Overview
Problem
Current 3D inspection and metrology techniques for semiconductor wafers, such as triangulation, geometric shadow, confocal microscopy, and white-light interferometry, face limitations in precision and throughput, especially in back-end of line applications, and are sensitive to environmental conditions like vibrations.
Innovation Solution
A device and method utilizing a spectrometer with a 2D imaging capability to determine surface height profiles on semiconductor wafers by combining test light reflected from the sample with reference light, eliminating the need for z-direction scanning and improving light utilization efficiency, using a line of light instead of a point, and incorporating an optical chopper for short-duration illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If scanning white-light interferometry is used to achieve high-resolution 3D inspection, then measurement precision is improved, but productivity deteriorates due to slow scanning speed and sample movement requirements
Solution Approach 1:
The patent replaces mechanical scanning in the z-direction with optical path length modulation using a reference mirror that moves along the optical axis. This substitution eliminates the need for mechanical sample scanning while maintaining interferometric measurement capability, thereby improving throughput without sacrificing measurement precision
Solution Approach 2:
The patent transforms the measurement approach by scanning the reference mirror along the optical axis (z-dimension) instead of scanning the sample laterally. This dimensional change allows the entire sample area to be measured simultaneously at each reference mirror position, converting a slow point-by-point measurement into a parallel area measurement that significantly improves productivity
2Productivity
If point-scan spectroscopic devices are used to eliminate z-direction scanning, then productivity is improved, but measurement precision deteriorates due to sensitivity to environmental vibrations
Solution Approach 1:
The patent merges multiple point measurements into a comprehensive area measurement by capturing interferometric data across the entire sample field of view simultaneously. This merging of measurement points into a unified area measurement provides sufficient data redundancy to distinguish true surface height variations from environmental noise, thereby maintaining precision while achieving high throughput
Solution Approach 2:
The patent employs phase-shifting interferometry that captures multiple interferograms at different reference mirror positions and uses computational algorithms to extract surface height information. This feedback-based computational approach filters out environmental vibrations by comparing phase differences across multiple measurements, maintaining measurement precision without requiring mechanical stabilization
3Reliability
If multiple frames are taken at specific z-values in SWI devices, then measurement completeness is improved, but loss of time increases due to repeated sampling requirements
Solution Approach 1:
The patent maintains continuous measurement by moving the reference mirror continuously along the optical axis while simultaneously capturing interferometric data across the entire sample area. This continuous action eliminates the stop-and-go nature of traditional SWI that requires pausing at discrete z-positions, thereby maintaining measurement completeness while reducing total measurement time through uninterrupted data acquisition
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 enhances accuracy and throughput by reducing environmental sensitivity, achieving high-resolution surface height profiling without z-direction scanning, and providing improved robustness against environmental factors, with a dynamic range suitable for semiconductor inspection applications.
Implementation Method 1
The objective lens is configured to illuminate a sample with test light from the source and to combine test light reflected from the sample with reference light reflected from the reference surface to form combined light
Implementation Method 2
The spectrometer is configured to image the combined light as a 2-dimensional ('2D') image. The 2D image has a first dimension of wavelength and a second dimension of position along a length of the entrance slit
Data Source
AI summary
A device and method for surface height profiling are presented. The device has a source with a source slit through which light is provided. The device includes an objective lens having a reference surface. The objective lens is configured to illuminate a sample with test light from the source and to combine test light reflected from the sample with reference light reflected from the reference surface to form combined light. A spectrometer is positioned to receive the combined light at an entrance slit. The spectrometer is configured to image the combined light as a 2D image with a wavelength dimension and a spatial position dimension. A processor in electrical communication with the spectrometer is programmed to receive a signal representing the 2D image and to determine a surface height profile of the sample based on the signal.