Metrology Apparatus Detecting Sub-Order Diffraction for Small Pitch Targets
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Solution Overview
Problem
In lithographic processes, the reduction of metrology target size to match product structures interferes with traditional methods of measuring patterning parameters due to evanescent diffraction orders and unwanted interference effects, particularly in highly coherent illumination scenarios, which disrupt the determination of parameters like overlay and focus.
Innovation Solution
A method and apparatus that utilize sub-order diffraction components of radiation scattered from targets with periodic structures to measure patterning process parameters, where the targets have a principal periodicity between 50 nm and 400 nm, allowing for the detection of asymmetry even when principal diffraction orders are evanescent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If metrology target size is reduced to match product structures, then measurement applicability to smaller pitch targets is improved, but traditional diffraction-based measurement methods become ineffective due to evanescent diffraction orders
Solution Approach 1:
The patent changes the measurement parameter from detecting principal diffraction orders to detecting sub-order diffraction components. This parameter change enables measurement of targets with smaller pitches (50-400 nm) where principal orders become evanescent, while maintaining measurement accuracy through the use of sub-order components that remain propagating.
2Measurement precision
If highly coherent illumination is used for metrology, then measurement sensitivity is improved, but unwanted interference effects such as fringes are introduced that disrupt parameter determination
Solution Approach 1:
The patent extracts the useful sub-order diffraction components from the total scattered radiation while effectively removing the harmful interference effects. By detecting only the sub-order components, the method separates the useful measurement signal from the disruptive fringes generated by highly coherent illumination.
3Ease of operation
If principal diffraction orders are used for measurement, then measurement simplicity is maintained, but measurement capability is lost when pitch becomes significantly shorter than illumination wavelength
Solution Approach 1:
Instead of using the conventional approach of detecting principal diffraction orders, the patent inverts the approach by detecting sub-order diffraction components. This inversion enables measurement capability for small pitch targets while maintaining a relatively simple detection scheme focused on specific sub-order components.
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
Enables accurate measurement of patterning process parameters by leveraging sub-order diffraction components, improving measurement precision and applicability to smaller pitch targets, while reducing interference effects and maintaining measurement accuracy.
Implementation Method 1
detecting a sub-order diffraction component of radiation scattered from the target
Implementation Method 2
radiation scattered from the target
Data Source
AI summary
A technique of measuring a parameter of a patterning process is disclosed. In one arrangement, a target, formed by the patterning process, is illuminated. A sub-order diffraction component of radiation scattered from the target is detected and used to determine the parameter of the patterning process.