Combined Overlay Focus Target for Simultaneous Metrology
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Solution Overview
Problem
Current metrology techniques require separate targets and measurement steps for overlay and focus measurements, which are time-consuming and inefficient, reducing productivity and accuracy due to the need for multiple positioning and alignment steps and limited substrate area for product features.
Innovation Solution
A combined target is introduced that includes a first periodic structure and a second periodic structure with intentional positional offset and focus-dependent structural asymmetry, allowing for simultaneous measurement of overlay and focus using a single measurement radiation recipe, enabling the separation of asymmetry components from unintentional mismatch, intentional offset, and focus settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate overlay and focus targets are used with separate measurement steps, then measurement precision can be maintained, but productivity decreases due to multiple positioning and alignment steps
Solution Approach 1:
The patent combines separate overlay and focus targets into a single combined target structure that includes both overlay grating features and focus target features. This allows both overlay and focus measurements to be performed simultaneously in a single measurement step, eliminating the need for multiple positioning and alignment operations while maintaining measurement precision through the integrated target design.
Solution Approach 2:
The combined target serves multiple functions: it provides overlay measurement capabilities through its grating structure and focus measurement capabilities through its focus target features. This multi-functional design allows a single target to replace what were previously two separate targets, improving productivity by reducing the number of measurement steps required.
2Measurement precision
If multiple separate targets are used for overlay and focus measurements, then measurement precision is maintained, but substrate area available for product features is reduced
Solution Approach 1:
By merging overlay and focus targets into a single combined target, the patent reduces the total substrate area occupied by metrology features. The combined target integrates both measurement functions in one location, freeing up substrate area that would otherwise be consumed by separate targets, thereby increasing the area available for product features.
3Measurement precision
If separate measurement steps are used for overlay and focus, then measurement precision can be maintained, but setup time increases
Solution Approach 1:
The combined target enables both overlay and focus measurements to be performed in a single measurement step, eliminating the need for sequential measurement operations. This reduces setup time by avoiding repeated positioning and alignment operations that would be required if separate targets and measurement steps were used, while maintaining precision through the integrated target design.
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 efficient simultaneous measurement of overlay and focus, reducing setup time and substrate area requirements, improving measurement accuracy and productivity by using a single measurement recipe and target, while maintaining high sensitivity to structural asymmetry.
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; intensity at one or more wavelengths as a function of reflected angle; or polarization as a function of reflected angle—to obtain a 'spectrum' from which a property of interest of the target can be determined.
Implementation Method 2
scatterometers have been developed for use in the lithographic field. These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Implementation Method 3
The intensity asymmetry, a comparison of these diffraction order intensities, for a given overlay target provides a measurement of target asymmetry, that is asymmetry in the target. This asymmetry in the overlay target can be used as an indicator of overlay error
Data Source
AI summary
Disclosed is a substrate comprising a combined target for measurement of overlay and focus. The target comprises: a first layer comprising a first periodic structure; and a second layer comprising a second periodic structure overlaying the first periodic structure. The target has structural asymmetry which comprises a structural asymmetry component resultant from unintentional mismatch between the first periodic structure and the second periodic structure, a structural asymmetry component resultant from an intentional positional offset between the first periodic structure and the second periodic structure and a focus dependent structural asymmetry component which is dependent upon a focus setting during exposure of said combined target on said substrate. Also disclosed is a method for forming such a target, and associated lithographic and metrology apparatuses.