Scatterometry Overlay Measurement Using Auxiliary Electromagnetic Fields
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Solution Overview
Problem
Standard scatterometry methods for overlay measurements face challenges due to lack of control over topographic phase and diffraction efficiency, leading to measurement errors from target asymmetries and process instabilities, particularly in cases of low diffraction efficiency and high topography, where signal intensity is compromised by detector noise and sensitivity issues.
Innovation Solution
The method involves illuminating a stationary diffractive target with a stationary source, measuring a signal composed of zeroth and first order diffraction signals, and deriving the first order signal from these sums, using phase scanning and partial overlapping of diffraction orders to enhance signal detection and control, allowing for increased sensitivity and accuracy in overlay measurements by utilizing a broader range of angles and topographic phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard scatterometry methods are used for overlay measurements, then the measurement process is simple, but measurement precision deteriorates due to lack of control over topographic phase and diffraction efficiency
Solution Approach 1:
The patent changes the parameter of diffraction order selection by measuring multiple diffraction orders (zeroth and first orders) instead of relying on a single first-order signal. This parameter change enables control over topographic phase and diffraction efficiency, thereby improving overlay measurement accuracy without requiring complex additional hardware
Solution Approach 2:
The patent segments the measurement process into multiple discrete measurements of different diffraction orders (zeroth order and first order signals). By separating and independently measuring these diffraction orders and then combining them through phase scanning, the system achieves precise control over measurement parameters while maintaining a relatively simple optical configuration
2Illumination intensity
If measurements are taken with low diffraction efficiency, then the measurement process is straightforward, but signal intensity deteriorates and becomes compromised by detector noise
Solution Approach 1:
The patent merges the measurement of multiple diffraction orders (zeroth order and first order signals) into a unified measurement approach. By combining these signals through phase scanning and utilizing their interference patterns, the system enhances the effective signal intensity and improves detection reliability, overcoming the limitations of low diffraction efficiency in individual orders
3Measurement precision
If high topography is present in the target structure, then the structural complexity is realistic for advanced devices, but measurement precision deteriorates due to sensitivity issues
Solution Approach 1:
The patent introduces dynamic phase scanning to the measurement process, where the relative phase between zeroth and first order diffraction signals is systematically varied. This dynamic approach allows the system to adapt to high topography variations in the target structure, maintaining measurement precision by finding optimal phase conditions that maximize signal sensitivity despite complex structural features
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 significantly enhances the accuracy of scatterometry overlay measurements, reduces the impact of process variations, and enables detection of multiple diffraction orders, improving the measurement capabilities and extending the applicability to previously challenging layers.
Implementation Method 1
measuring a signal composed of a sum of a zeroth order diffraction signal and a first order diffraction signal
Implementation Method 2
an optical system arranged to direct the measurement beam onto the substrate
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
Metrology measurement methods and tools are provided, which illuminate a stationary diffractive target by a stationary illumination source, measure a signal composed of a sum of a zeroth order diffraction signal and a first order diffraction signal, repeat the measuring for a plurality of relations between the zeroth and the first diffraction signals, while maintaining the diffractive target and the illumination source stationary, and derive the first order diffraction signal from the measured sums. Illumination may be coherent and measurements may be in the pupil plane, or illumination may be incoherent and measurements may be in the field plane, in either case, partial overlapping of the zeroth and the first diffraction orders are measured. Illumination may be annular and the diffractive target may be a one cell SCOL target with periodic structures having different pitches to separate the overlap regions.