2-D Target Lithographic Focus and Dose Measurement
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Solution Overview
Problem
Current methods for measuring focus and dose in lithographic processes using one-dimensional structures are ambiguous, as multiple combinations of focus and dose can result in similar critical dimension and sidewall angle measurements, leading to difficulties in unique determination and increased measurement time and substrate area usage.
Innovation Solution
A method and system involving a mask with a pattern comprising an array of structures, where one pitch direction is resolvable by the exposure apparatus and another is not, allowing for unique focus and dose determination from reflected radiation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If one-dimensional structures are used for focus and dose measurement, then measurement can be performed, but measurement precision is reduced due to ambiguity where multiple combinations of focus and dose produce similar critical dimension and sidewall angle measurements
Solution Approach 1:
The patent transitions from one-dimensional measurement structures to two-dimensional target structures. The 2-D target comprises an array of structures with different orientations (e.g., first set of lines in one direction, second set of lines in perpendicular direction), enabling unique determination of both focus and dose parameters by measuring properties in multiple directions. This dimensional expansion provides additional measurement information that resolves the ambiguity inherent in one-dimensional measurements.
2Measurement precision
If multiple one-dimensional structures are used to reduce measurement ambiguity, then measurement precision improves, but substrate area usage increases
Solution Approach 1:
The patent combines multiple measurement functions into a single integrated 2-D target structure. Instead of using separate one-dimensional structures for different measurements, the 2-D target merges focus measurement and dose measurement capabilities into one compact array of structures with different orientations. This consolidation achieves the same measurement precision as multiple separate structures while using significantly less substrate area.
3Measurement precision
If multiple one-dimensional structures are used to reduce measurement ambiguity, then measurement precision improves, but measurement time increases
Solution Approach 1:
The 2-D target is segmented into multiple sets of structures with different orientations (e.g., first set at 0 degrees, second set at 90 degrees). Each segment responds differently to focus and dose variations, allowing simultaneous extraction of both parameters from a single measurement of the entire segmented target. This segmentation enables parallel information extraction, reducing measurement time compared to sequential measurement of multiple one-dimensional structures.
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 focus and dose with reduced substrate area usage and measurement time, improving the ambiguity and efficiency of the process.
Implementation Method 1
detecting radiation reflected from the marker on the substrate
Data Source
AI summary
In order to determine whether an exposure apparatus is outputting the correct dose of radiation and its projection system is focusing the radiation correctly, a test pattern is used on a mask for printing a specific marker onto a substrate. This marker is then measured by an inspection apparatus, such as a scatterometer, to determine whether there are errors in focus and dose and other related properties. The test pattern is configured such that changes in focus and dose may be easily determined by measuring the properties of a pattern that is exposed using the mask. The test pattern may be a 2D pattern where physical or geometric properties, e.g., pitch, are different in each of the two dimensions. The test pattern may also be a one-dimensional pattern made up of an array of structures in one dimension, the structures being made up of at least one substructure, the substructures reacting differently to focus and dose and giving rise to an exposed pattern from which focus and dose may be determined.