Overlay Measurement Correction via Stack Difference Isolation
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Solution Overview
Problem
Existing overlay measurement techniques in lithographic processes are inaccurate due to structural asymmetry and stack differences between periodic structures, which are not effectively distinguished from overlay errors, leading to unreliable measurements.
Innovation Solution
A method involving the use of multiple measurement radiation pairs and target designs to determine stack difference parameters, allowing for the correction of overlay measurements by isolating the contributions from structural asymmetry and stack differences, enabling more accurate overlay determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay measurement techniques are used, then measurement process is simple, but measurement precision deteriorates due to inability to distinguish structural asymmetry and stack differences from overlay errors
Solution Approach 1:
The measurement process is segmented into multiple distinct measurement steps using different radiation pairs (e.g., first radiation pair for initial overlay measurement, second radiation pair for stack difference characterization). This segmentation allows separate determination of overlay errors and stack differences, improving measurement precision while managing complexity through systematic breakdown of the measurement process
Solution Approach 2:
The invention changes measurement parameters by using multiple radiation pairs with different wavelengths or energies. By varying the radiation parameters, the system can selectively characterize different structural aspects (overlay vs. stack differences) and obtain corrected overlay measurements that account for stack variation
2Measurement precision
If multiple measurement radiation pairs are used to correct for stack difference, then overlay measurement accuracy improves, but measurement time increases
Solution Approach 1:
Stack difference parameters are determined in advance using radiation pairs before final overlay measurement correction is applied. This preliminary characterization of stack differences allows for efficient correction of overlay measurements without requiring repeated full measurement sequences, thereby reducing overall measurement time while maintaining accuracy
Solution Approach 2:
The measurement process uses continuous illumination with multiple radiation pairs to simultaneously or sequentially gather data for both overlay and stack difference characterization. This continuous measurement approach minimizes idle time and maintains productive measurement action throughout the process
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 provides more accurate overlay measurements by directly addressing structural asymmetry and stack differences, improving the reliability of overlay error detection and process control in lithographic processes.
Implementation Method 1
the measurement beam generates a spot that is smaller than the periodic structure (i.e., the periodic structure is underfilled)... Diffraction-based overlay using dark-field detection of the diffraction orders enables overlay measurements on smaller targets
Implementation Method 2
These devices direct a beam of radiation onto a target and measure one or more properties of the redirected (e.g., scattered) radiation—e.g., intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of reflected angle
Data Source
AI summary
A method including: obtaining a measurement of a metrology target on a substrate processed using a patterning process, the measurement having been obtained using measurement radiation; and deriving a parameter of interest of the patterning process from the measurement, wherein the parameter of interest is corrected by a stack difference parameter, the stack difference parameter representing an un-designed difference in physical configuration between adjacent periodic structures of the target or between the metrology target and another adjacent target on the substrate.