Sub-resolution imaging target for overlay error measurement
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Solution Overview
Problem
Current semiconductor circuit metrology tools face challenges in accurately measuring overlay errors due to the large dimensions of conventional proxy targets, which differ from actual device features and cannot be inserted within the device area, leading to discrepancies in measured overlay errors.
Innovation Solution
The development of optical inspection apparatus and methods using target features with dimensions less than the optical diffraction limit, allowing for precise measurement of overlay errors by processing scattered optical radiation and analyzing the angular distribution, enabling the measurement of overlay errors between patterned layers with high precision and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional proxy targets with large dimensions are used for overlay measurement, then the targets can be clearly resolved by optical metrology tools, but the targets cannot be inserted within the device area and the measured overlay errors differ from actual device overlay errors
Solution Approach 1:
The patent changes the dimensional parameter of target features from conventional large sizes (e.g., 1-10 μm) to sub-diffraction-limit sizes (e.g., 10-100 nm). This parameter change enables the targets to be inserted within the device area while still allowing accurate overlay measurement through scattered light analysis, resolving the contradiction between target size and measurement accuracy.
Solution Approach 2:
The patent replaces conventional direct imaging methods with scattered light analysis methods. Instead of relying on direct optical imaging of large targets, the system analyzes the angular distribution and intensity of scattered light from sub-diffraction targets, enabling accurate overlay measurement of features smaller than the optical diffraction limit.
2Measurement precision
If target features are reduced to sub-diffraction-limit dimensions, then the targets can be inserted within the device area for accurate measurement, but the targets become difficult to detect and image
Solution Approach 1:
The patent replaces direct imaging with scattered light analysis. By measuring the angular distribution and intensity patterns of light scattered from sub-diffraction targets, the system can detect and measure overlay errors of features that are too small to be directly imaged by conventional optical systems.
Solution Approach 2:
The patent utilizes changes in the optical scattering characteristics (analogous to color changes) of sub-diffraction targets. By analyzing the angular distribution and intensity of scattered light at different angles, the system can detect the presence and position of sub-diffraction targets, making them detectable despite their small size.
3Measurement precision
If conventional overlay measurement methods are used, then multi-frame imaging and complex processing are required, but this reduces measurement efficiency and increases complexity
Solution Approach 1:
The patent merges the measurement of overlay error with a single imaging operation. By capturing both the zeroth-order transmitted light and scattered light in a single frame and processing them together, the system eliminates the need for multiple frames and complex sequential processing, thereby improving measurement efficiency while maintaining accuracy.
Solution Approach 2:
The patent enables continuous overlay measurement by capturing all necessary information in a single frame. The simultaneous capture of zeroth-order and scattered light allows for immediate overlay error calculation without requiring sequential imaging or waiting for multiple frames, thus maintaining continuous measurement capability.
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 allows for accurate and precise measurement of overlay errors within the device area, reducing measurement sensitivity to focus and enabling single-frame imaging, thus improving the precision and efficiency of semiconductor circuit metrology.
Implementation Method 1
An imaging assembly is configured to capture at least one image of the semiconductor wafer including the optical radiation that is scattered from the at least one of the first and second target features
Data Source
AI summary
An optical inspection apparatus includes an illumination assembly, configured to direct optical radiation to illuminate a semiconductor wafer on which first and second patterned layers have been deposited in succession, including a first target feature in the first patterned layer and a second target feature in the second patterned layer, such that at least one of the first and second target features has at least one dimension in the plane of the wafer that is less than an optical diffraction limit of the apparatus. An imaging assembly is configured to capture at least one image of the wafer, and a controller is configured to process the at least one image in order to identify respective locations of the first and second target features in the at least one image and to measure an overlay error between the first and second patterned layers responsively to a displacement between the respective locations.