Asymmetric Optical Element for Metrology Radiation Utilization
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Solution Overview
Problem
Current metrology tools in semiconductor manufacturing face challenges in achieving high accuracy and efficiency for overlay measurement and critical dimension analysis of nano-scaled features, particularly due to low radiation utilization efficiency, which increases measurement time and reduces throughput.
Innovation Solution
An optical element with a first portion having higher reflectivity and a second portion with higher transmissivity is introduced, positioned within a specific range from the entrance pupil of the objective lens to enhance radiation utilization and prevent vignetting, allowing for improved diffraction pattern capture and analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional optical element with uniform reflectivity and transmissivity is used, then the optical path is simple, but the radiation utilization efficiency is low
Solution Approach 1:
The optical element is divided into two distinct portions: a first portion with higher reflectivity (greater than 50%) for directing illumination light toward the substrate, and a second portion with higher transmissivity (greater than 50%) for allowing diffracted light to pass through to the detector. This local differentiation of optical properties maximizes radiation utilization efficiency by optimizing each portion's function, resolving the contradiction between energy loss and device complexity.
2Measurement precision
If the optical element is positioned far from the entrance pupil, then alignment is easier, but vignetting occurs and diffraction pattern capture is compromised
Solution Approach 1:
The patent positions the optical element within a specific distance range (5mm to 20mm) from the entrance pupil of the objective lens, transitioning from traditional far-field positioning to a near-field configuration. This spatial repositioning in the optical path enables simultaneous achievement of high measurement precision through complete diffraction pattern capture and practical ease of operation through defined positioning parameters that avoid vignetting while remaining alignable.
3Use of energy by moving object
If the optical element has high reflectivity in the first portion, then more light is directed to the substrate, but less light is transmitted in the second portion
Solution Approach 1:
The optical element is segmented into two functionally distinct portions along its diagonal: the first portion (e.g., upper-left quadrant) with high reflectivity (>50%) optimized for reflecting illumination light toward the substrate, and the second portion (e.g., lower-right quadrant) with high transmissivity (>50%) optimized for transmitting diffracted light to the detector. This segmentation resolves the energy trade-off by assigning different optical properties to different segments, allowing each to perform its function optimally without compromising the other.
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 configuration enhances beam utilization efficiency by approximately three times, enabling faster and more accurate overlay and critical dimension measurements, thus improving the overall throughput and yield in semiconductor manufacturing.
Implementation Method 1
an optical element having a first portion configured to reflect the light received from the illumination source towards the substrate
Implementation Method 2
a second portion configured to transmit the light reflected from the substrate or the desired location in the optical tool
Implementation Method 3
the optical element captures a diffraction pattern caused by the light directed from the first portion onto the substrate and diffracted from the substrate
Data Source
AI summary
An optical element, and a metrology tool or system employing the optical element for measurements of structures on a substrate. The optical element includes a first portion configured to reflect the light received from an illumination source towards the substrate, and a second portion configured to transmit the light redirected from the substrate or a desired location, the first portion having a higher coefficient of reflectivity than the second portion, and the second portion having a higher coefficient of transmissivity than the first portion. A metrology tool may include the optical elements and a sensor configured to receive a diffraction pattern caused by radiation redirected from a substrate, and a processor configured to receive a signal relating to the diffraction pattern from the sensor, and determine overlay associated with the substrate by analyzing the signal.