Metrology Target Alignment in Lithographic Cells
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Solution Overview
Problem
In lithographic processes, it is challenging to accurately align radiation spots with targets positioned in areas with limited space, particularly where high precision is required and optical contrast is low, making it difficult to measure targets effectively using existing metrology apparatuses.
Innovation Solution
A method and apparatus that utilize a first measurement process to detect the position of an alignment structure on a target, and a second measurement process to align a radiation spot within a metrology structure, where the radiation spot is defined such that its zeroth order radiation is outside the alignment structure, allowing for precise measurement even in constrained spaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If targets are positioned in locations with little space available (product areas), then space utilization is improved, but alignment precision deteriorates
Solution Approach 1:
The target is divided into two distinct functional regions: an alignment structure region for determining target position and a metrology structure region for performing measurements. This segmentation allows the alignment and measurement functions to be separated, enabling precise alignment even when the overall target area is constrained.
Solution Approach 2:
The alignment structure serves as an intermediary element that mediates between the radiation source and the metrology structure. By first determining the target position through the alignment structure and then using this position information to align the radiation spot on the metrology structure, the system achieves precise measurements in constrained spaces.
2Difficulty of detecting and measuring
If radiation spots are aligned with small targets in tight spaces, then measurement capability is improved, but optical contrast deteriorates
Solution Approach 1:
Different regions of the target are assigned different functional qualities: the alignment structure region provides high optical contrast for position determination, while the metrology structure region provides the necessary scattering properties for measurements. This local differentiation ensures that each region performs its specific function effectively despite space constraints.
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 alignment and measurement of targets in tight spaces with improved precision and efficiency, overcoming the limitations of existing technologies by using a dual measurement process to ensure the radiation spot intersects with the metrology structure while avoiding the alignment structure.
Implementation Method 1
measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection, or over a range of angles of reflection, as a function of wavelength
Implementation Method 2
intensity at a single angle of reflection, or over a range of angles of reflection, as a function of wavelength
Data Source
AI summary
Methods and apparatuses for measuring a target formed on a substrate. The target includes an alignment structure and a metrology structure. In one method, a first measurement process is performed that includes illuminating the target with first radiation and detecting radiation resulting from scattering of the first radiation from the target. A second measurement process includes illuminating the target with second radiation and detecting radiation resulting from scattering of the second radiation from the target. The first measurement process detects a position of the alignment structure. The second measurement process uses the position of the alignment structure detected by the first measurement process to align a radiation spot of the second radiation onto a desired location within the metrology structure.