Overlay Measurement Using Infrared Interference
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Solution Overview
Problem
Current optical alignment and overlay measurement methods in lithography face challenges in accurately determining the position of alignment marks buried under varying layers of integrated circuits, particularly due to opaque layers that prevent measurement radiation from reaching the marks, leading to reduced accuracy and increased errors as feature sizes decrease.
Innovation Solution
A method involving irradiating features on a silicon wafer with a radiation beam, combining scattered radiation portions with different diffraction orders, moderating their phase difference, and analyzing the resulting time-dependent intensity signal to determine overlay errors, which allows for improved dynamic range and accuracy in overlay measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical alignment and overlay measurement methods are used to determine the position of alignment marks, then measurement capability is provided, but measurement accuracy deteriorates when marks are buried under opaque layers
Solution Approach 1:
The patent changes the wavelength parameter of the measurement radiation to infrared range (e.g., 1.3 μm, 1.55 μm, or 2.0 μm), which allows the radiation to penetrate through opaque layers that block visible light, thereby enabling measurement of buried alignment marks while maintaining measurement accuracy
Solution Approach 2:
The patent introduces an intermediary mechanism by using infrared radiation as a mediator that can traverse through the opaque layers to reach the alignment marks, effectively bridging the gap between the measurement system and the buried marks without requiring direct line-of-sight access
2Reliability
If conventional overlay measurement methods are used, then overlay detection is provided, but dynamic range and signal detection capability are limited
Solution Approach 1:
The patent transitions from measuring only intensity differences to measuring both intensity and phase information of the scattered radiation. By utilizing the phase dimension in addition to intensity, the system can extract overlay information from weak signals that would be indistinguishable from noise in conventional intensity-only measurements, thereby expanding the dynamic range and improving reliability
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 the dynamic range of overlay measurements, enabling the detection of weak signals and reducing noise interference, thus providing more accurate and reliable alignment and overlay assessments, even for features buried under opaque layers.
Implementation Method 1
receiving at least a portion of the radiation beam scattered from the two features of the object, the at least a portion of the radiation beam comprising: a first portion comprising at least one diffraction order and a second portion comprising at least one diffraction order
Implementation Method 2
combining the first and second portions such that they interfere to produce a time dependent intensity signal
Data Source
AI summary
A method of determining a parameter of a patterning process applied to an object comprising two features (for example an overlay of the two features) comprises: irradiating the two features of the object with a radiation beam and receiving at least a portion of the radiation beam scattered from the two features of the object. The at least a portion of the radiation beam comprises: a first portion comprising at least one diffraction order and a second portion comprising at least one diffraction order that is different to a diffraction order of the first portion. The method further comprises moderating a phase difference between the first and second portions and combining the first and second portions such that they interfere to produce a time dependent intensity signal. The method further comprises determining the parameter of the patterning process from a contrast of the time dependent intensity signal.