Metrology Target Layout for Overlay Accuracy
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Solution Overview
Problem
Conventional scatterometers using small targets for metrology in lithographic processes face limitations in accuracy due to the nature of small targets and measurement techniques, which impairs the precision of overlay and other parameter measurements, making them less accurate than larger targets.
Innovation Solution
A system and method employing a combination of large and small metrology targets distributed across a semiconductor substrate, where the small targets are placed between and within the large targets, allowing for simultaneous measurement and correction to enhance accuracy by comparing values between the two sets, thereby improving the measurement of parameters like overlay within product areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If small metrology targets are used for measuring overlay within product areas, then the density of measurements and real estate utilization are improved, but the measurement accuracy deteriorates
Solution Approach 1:
The patent combines measurements from both large targets (for high accuracy) and small targets (for high density) into a unified measurement system. The scatterometer measures both target types simultaneously, and the system merges their data to provide both accurate and dense overlay measurements across the substrate.
Solution Approach 2:
The patent introduces an intermediary correction model that relates measurements from large and small targets. This model acts as a mediator, using the accurate measurements from large targets to correct and calibrate the measurements from small targets, thereby enabling small targets to achieve accuracy comparable to large targets.
2Measurement precision
If large metrology targets are used for high accuracy measurements, then overlay measurement accuracy is improved, but the substrate real estate consumed increases
Solution Approach 1:
The patent segments the metrology measurement function into two parts: large targets placed in scribe lanes for accurate reference measurements, and small targets distributed within product areas for high-density measurements. This segmentation allows each target type to serve its specific purpose optimally without wasting substrate real estate.
Solution Approach 2:
The patent applies different target sizes to different locations on the substrate based on local requirements. Large targets are placed where high accuracy is needed (scribe lanes, reference areas), while small targets are placed where high density is needed (within product areas). This local differentiation optimizes both accuracy and real estate utilization.
3Productivity
If small metrology targets are placed within product areas, then measurement density and real estate efficiency are improved, but the reliability of measurements deteriorates due to process variations
Solution Approach 1:
The patent uses measurements from large targets as feedback to correct and validate measurements from small targets. The correction model continuously refines small target measurements using the reliable reference data from large targets, thereby maintaining high measurement reliability even when small targets are placed within product areas subject to process variations.
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 more accurate measurement of parameters within product areas on semiconductor substrates, similar to larger targets, by correcting parameter values using the comparison between large and small targets, thus improving the precision and density of overlay measurements without sacrificing real estate.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection as a function of wavelength
Data Source
AI summary
A pattern from a patterning device is applied to a substrate by a lithographic apparatus. The applied pattern includes product features and metrology targets. The metrology targets include large targets and small targets which are for measuring overlay. Some of the smaller targets are distributed at locations between the larger targets, while other small targets are placed at the same locations as a large target. By comparing values measured using a small target and large target at the same location, parameter values measured using all the small targets can be corrected for better accuracy. The large targets can be located primarily within scribe lanes while the small targets are distributed within product areas.