Scan Signal Characterization for Alignment Diagnostics
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Solution Overview
Problem
Current lithographic processes face challenges in accurately detecting alignment errors and variations caused by customer modifications, such as mark damage and deformation, which affect overlay accuracy and wafer quality.
Innovation Solution
Characterizing and dissecting scan signals using local curve fitting techniques to extract additional diagnostic parameters, allowing for improved alignment control and correction of alignment issues, including mark deformation and background signal effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional FFT fitting algorithms are used to process scan signals, then processing speed is maintained, but measurement precision deteriorates due to crosstalk from background content and inability to detect localized mark deformations
Solution Approach 1:
The patent divides the scan signal into multiple local segments and performs curve fitting on each segment independently. This segmentation allows the system to detect localized mark deformations and reduces crosstalk from background content, as each segment is processed separately to extract precise alignment information without interference from other regions.
Solution Approach 2:
The patent applies local curve fitting techniques that adapt to local signal characteristics rather than using a uniform global fitting approach. This local quality approach enables the system to account for variations in mark deformation, background content, and signal quality across different regions of the scan, improving overall measurement precision.
2Measurement precision
If comprehensive signal analysis is performed to detect all alignment issues, then measurement precision improves, but loss of time increases due to extensive processing requirements
Solution Approach 1:
The patent performs preliminary local curve fitting on signal segments to identify regions with potential alignment issues before applying more computationally intensive analysis. This preliminary action allows the system to focus detailed analysis only where needed, reducing overall processing time while maintaining comprehensive detection capability.
Solution Approach 2:
The patent applies curve fitting to a selected number of signal segments rather than processing the entire scan signal uniformly. By applying partial action to the most critical segments, the system achieves sufficient measurement precision without the time cost of exhaustive processing of all signal data.
3Manufacturing precision
If local curve fitting is applied to each signal segment, then manufacturing precision improves through better alignment control, but device complexity increases due to additional processing steps
Solution Approach 1:
The patent extracts alignment information from local curve fitting results of individual signal segments, separating the extraction of alignment parameters from the overall signal processing workflow. This extraction approach simplifies the integration of local fitting results into the broader lithographic process control system.
Solution Approach 2:
The local curve fitting algorithm is designed to serve multiple functions: detecting alignment position, identifying mark deformations, and characterizing background content. This multi-functionality reduces the need for separate specialized processing steps, thereby limiting the increase in overall device complexity despite the enhanced manufacturing precision.
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
Enhances alignment accuracy and wafer quality assessment, enabling better detection of alignment errors and adjustments, thereby improving overlay precision and reducing crosstalk from background content.
Implementation Method 1
a sensor for sensing light from the mark when the mark is being illuminated by the light source and for generating a scan signal indicative of the sensed light
Data Source
AI summary
A system for and method of processing a wafer in which a scan signal is analyzed locally to extract information about alignment, overlay, mark quality, wafer quality, and the like.