Wafer Stack Beam Analyzer Alignment Correction
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Solution Overview
Problem
Current lithographic alignment systems face challenges in achieving accurate positioning due to variations in the alignment system and substrate properties, leading to 'on-process' accuracy errors that limit the robustness of the alignment process.
Innovation Solution
An alignment system comprising a radiation source, optical modulating unit, splitter, interferometer, detectors, beam analyzer, and processor that generates light, splits it into sub-beams, interferes them, and uses detectors and beam analyzers to determine alignment status and overlay offset errors, creating a correction table to improve alignment accuracy through a self-learning feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional alignment systems are used, then the alignment process is simple, but on-process accuracy errors occur due to variations in alignment system and substrate properties
Solution Approach 1:
The alignment system is segmented into multiple independent measurement channels: a first measurement channel measures the position of a first alignment mark, while a second measurement channel measures the position of a second alignment mark. Each channel operates independently to measure different aspects of alignment, allowing the system to capture comprehensive alignment data without requiring a single complex measurement mechanism.
Solution Approach 2:
The patent introduces intermediary correction factors that mediate between the raw measurements and the final alignment determination. These correction factors account for variations in alignment system properties and substrate characteristics, serving as intermediaries that transform imperfect measurements into accurate alignment information by compensating for systematic errors.
2Reliability
If alignment system variations are not compensated, then the system operation is straightforward, but overlay error increases due to on-process accuracy problems
Solution Approach 1:
The system implements feedback by using the measurements from both alignment marks to determine correction factors, which are then applied to improve subsequent alignment measurements. The position measurements of the first and second alignment marks feed into a calculation process that generates correction factors, which in turn refine the alignment determination, creating a closed-loop system that continuously improves accuracy.
Solution Approach 2:
The patent changes the parameters used for alignment determination by incorporating correction factors that adjust the raw measurement data. Instead of relying solely on direct position measurements, the system transforms the measurement parameters by applying correction factors derived from the relationship between multiple alignment marks, thereby compensating for systematic variations in the alignment system and substrate.
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
The system effectively compensates for variations in the alignment system and substrate, enhancing the accuracy and robustness of the alignment process by continuously correcting overlay offset errors and improving positioning precision.
Implementation Method 1
The optical splitter splits a beam of light diffracted from a pattern on the substrate, or reflected from the substrate into sub-beams of light
Implementation Method 2
The interferometer interferes at least one sub-beams of the light and produces output light from the interference
Data Source
AI summary
An alignment system obtains the characteristics of the light coming back from a wafer stack. A beam analyzer measures changes in wavelength, polarization, and beam profile. This measured information allows for in-line process variation corrections. The correction provides optical monitoring of individual mark stack variations, and in turn provides information to reduce individual mark process variation-induced accuracy error.