Digital Grating Height Measurement Resolving Pixel Limits
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Solution Overview
Problem
The resolution of wafer height measurement in semiconductor manufacturing is limited by the pixel size of optical sensors, which restricts the accuracy and precision of focus control for incident light or charged beams, necessitating improved methods for height measurement.
Innovation Solution
The implementation of a digital grating system that generates virtual gratings using pixelized optical sensors, allowing for the determination of sample height based on integrated intensity changes, effectively functioning as an optical vernier caliper to enhance measurement resolution beyond pixel limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical sensors with pixels are used to measure wafer height, then the measurement process is simple and fast, but the measurement precision is limited by pixel size
Solution Approach 1:
The patent applies segmentation by dividing the optical grating image into multiple zones (first zone and second zone) with different pixel weightings. By selectively weighting pixels in different zones, the system achieves sub-pixel measurement precision without requiring more complex hardware. The segmentation of the image processing approach allows precise height measurement while maintaining system simplicity.
2Measurement precision
If smaller pixel sizes are used to improve measurement resolution, then height measurement precision improves, but the device complexity and cost increase
Solution Approach 1:
The patent changes the parameter of pixel weighting rather than physical pixel size. By modifying the computational parameters (weighting factors for different pixel zones) rather than the physical sensor parameters, the system achieves improved measurement resolution without increasing device complexity or cost. This parameter change approach allows high precision measurement using existing sensor hardware.
3Measurement precision
If traditional optical grating imaging is used, then the imaging process is straightforward, but the measurement resolution is constrained by pixel dimensions
Solution Approach 1:
The patent applies preliminary action by pre-defining the zoning structure and weighting factors for the optical grating image before actual measurement. The first and second zones are predetermined with specific weighting schemes, allowing the system to achieve high resolution measurement through simple computational operations during runtime. This preliminary setup enables both high precision and imaging efficiency.
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 achieves higher measurement resolution, up to tiny fractions of pixels, simplifies and accelerates the imaging process, and reduces sensitivity to light intensity variations, enabling precise height measurement and flexible digital grating configurations.
Implementation Method 1
receiving, by an optical sensor having pixels, an optical grating image of an illuminated optical grating reflected by a surface of the sample
Data Source
AI summary
A method, an apparatus, and a non-transitory computer-readable medium for measuring a height of a sample includes: receiving, by an optical sensor having pixels, an optical grating image of an illuminated optical grating reflected by a surface of the sample; determining, by a processor, a digital grating image by keeping values of first pixels of the optical grating image and resetting values of second pixels of the optical grating image; and determining the height based on a relationship between an integrated intensity of a portion of the digital grating image and the height.