Scatterometer Overlay Measurement Using Diffraction Spectrum Analysis
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Solution Overview
Problem
Current methods for measuring overlay errors in lithographic processes are limited by the need for large overlay targets in scribe lanes, which are not representative of in-die conditions, leading to interpolation errors and signal-to-noise ratio issues when trying to measure small targets.
Innovation Solution
A scatterometer system that uses a radiation beam to irradiate a target on a substrate, collimates and focuses the reflected beam, and detects the intensity of diffraction orders in an image plane to determine substrate properties, allowing for accurate measurement of small in-die overlay targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large overlay targets are used in scribe lanes for measurement, then measurement precision is improved, but the targets are not representative of in-die conditions and require interpolation which introduces errors
Solution Approach 1:
The invention applies local quality by making the measurement spot size adaptable to the local target size. Instead of using a fixed large measurement spot for all targets, the system adjusts the measurement spot to match the dimensions of each specific target (in-die or scribe lane), allowing accurate measurement of small in-die targets while maintaining measurement precision.
Solution Approach 2:
The invention changes the parameter of measurement spot size dynamically based on the target being measured. By adjusting the spot size parameter to be larger than the target dimensions, the system improves signal-to-noise ratio while still achieving accurate in-die overlay measurements without requiring interpolation from scribe lane targets.
2Manufacturing precision
If small in-die overlay targets are measured directly, then in-die overlay accuracy is improved, but signal-to-noise ratio deteriorates due to the small target size
Solution Approach 1:
The invention changes the parameter of measurement spot size to be larger than the target size. This parameter adjustment allows the measurement beam to encompass the entire small in-die target, collecting sufficient signal while maintaining spatial resolution to measure the overlay accurately. The larger spot size improves signal-to-noise ratio without sacrificing measurement precision.
3Measurement precision
If the measurement spot size is increased to improve signal quality, then signal-to-noise ratio is improved, but the ability to resolve small target features may deteriorate
Solution Approach 1:
The invention applies local quality by matching the measurement spot size to the specific target dimensions. For small in-die targets, the spot size is increased relative to the target dimensions (but still maintains appropriate resolution), allowing the measurement to encompass the entire target and collect sufficient signal while still resolving the target features needed for overlay measurement.
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 enables precise measurement of overlay errors directly on in-die targets, reducing interpolation errors and improving signal quality by using a larger measurement spot than the target itself, thus enhancing the accuracy and efficiency of lithographic processes.
Implementation Method 1
reflecting the radiation beam from the target
Implementation Method 2
separating first diffraction orders of the reflected radiation beam
Implementation Method 3
collimating and focusing the reflected radiation beam using an optical system
Implementation Method 4
collimating and focusing the reflected radiation beam using an optical system
Data Source
AI summary
The present invention makes the use of measurement of a diffraction spectrum in or near an image plane in order to determine a property of an exposed substrate. In particular, the positive and negative first diffraction orders are separated or diverged, detected and their intensity measured. The intensity of each of the first diffraction orders from the diffraction spectrum are compared to determine overlay (or other properties) of exposed layers on the substrate.