Acoustic Wave Alignment Measurement for Buried Lithography Marks
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Solution Overview
Problem
Current optical alignment methods in lithographic apparatuses face challenges in accurately measuring alignment marks buried beneath layers on silicon wafers, as opaque layers obstruct measurement radiation beams, leading to reduced accuracy and increased overlay errors.
Innovation Solution
A method involving pulsed pump radiation beams to generate acoustic waves, which are then used to enhance the signal-to-background ratio by optimizing the temporal intensity distribution of the radiation, allowing for accurate measurement of features beneath the surface through constructive and destructive interference of acoustic waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a measurement radiation beam is used to measure alignment marks beneath layers on silicon wafers, then the position of alignment marks can be determined, but opaque layers obstruct the beam and reduce measurement accuracy
Solution Approach 1:
The patent introduces acoustic waves as an intermediary medium to transmit information from buried alignment marks to the surface. The acoustic waves are generated by pulsed radiation beams and propagate through the opaque layers, reflecting off alignment marks and carrying position information back to the surface where they can be detected, thus bypassing the obstruction problem of opaque layers
Solution Approach 2:
The patent replaces the direct optical measurement system with an acoustic wave-based measurement system. Instead of using measurement radiation beams that are blocked by opaque layers, the system uses acoustic waves generated by pulsed radiation to probe the alignment marks, substituting mechanical/acoustic wave propagation for direct optical transmission through opaque media
2Measurement precision
If a single pulse of pump radiation beam is used to generate acoustic waves, then the process is simple, but the signal to background ratio is low
Solution Approach 1:
The patent employs periodic pulsed radiation beams with specifically designed temporal intensity distributions to generate acoustic waves. By using multiple pulses with controlled timing and intensity profiles, the system accumulates signal from alignment mark reflections while maintaining suppression of background signals, thereby enhancing the signal-to-background ratio through periodic excitation
Solution Approach 2:
The patent optimizes the temporal intensity distribution parameters of the pulsed radiation beam, including pulse duration, pulse separation time, and intensity profile. By carefully adjusting these parameters, the system achieves constructive interference of reflected acoustic waves from alignment marks while maintaining destructive interference of background signals, maximizing the signal-to-background ratio
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 improves the accuracy of feature measurement by maximizing the signal-to-background ratio, enabling precise determination of alignment marks even beneath opaque layers, thereby reducing overlay errors and enhancing the precision of lithographic processes.
Implementation Method 1
irradiating the surface of the object with a pulsed pump radiation beam so as to produce an acoustic wave in the object
Implementation Method 2
signals generated at the surface by reflections of acoustic waves from the feature
Implementation Method 3
receiving at least a portion of the measurement radiation beam scattered from the surface
Implementation Method 4
a temporal intensity distribution of the pulsed pump radiation beam is selected such that in the measurement time period a signal to background ratio is greater
Data Source
AI summary
A method for determining a characteristic of a feature in an object, the feature being disposed below a surface of the object is disclosed. The surface of the object is irradiated with a pulsed pump radiation beam so as to produce an acoustic wave in the object. The surface of the object is then irradiated with a measurement radiation beam. A portion of the measurement radiation beam scattered from the surface is received and a characteristic of the feature in the object is determined from at least a portion of the measurement radiation beam scattered from the surface within a measurement time period. A temporal intensity distribution of the pulsed pump radiation beam is selected such that in the measurement time period a signal to background ratio is greater than a signal to background ratio achieved using a single pulse of the pulsed pump radiation beam. The signal to background ratio is a ratio of: (a) signals generated at the surface by reflections of acoustic waves from the feature to (b) background signals generated at the surface by reflections of acoustic waves which have not reflected from the feature.