DMD Lens Aberration Detection via Through Focus Curve
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Solution Overview
Problem
Current photolithography systems face challenges in accurately determining lens aberration, which affects circuit pattern quality and accuracy, due to time-consuming and unreliable methods for focus measurement and aberration detection.
Innovation Solution
The method employs a digital micromirror device (DMD) to project optical patterns on a reflective substrate, acquire return images, form through focus curves, and compare them to predetermined curves to detect and determine lens aberrations, utilizing existing hardware for quick and cost-effective diagnostics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lens aberration is determined by inspecting the quality of printed pattern, then measurement can be performed, but the process is time consuming and unreliable
Solution Approach 1:
The patent applies preliminary action by measuring aberration parameters before actual lithography processing occurs. A test pattern is projected and imaged separately to obtain aberration information, which is then used to adjust lens parameters beforehand. This prevents time-consuming post-processing inspections and ensures reliable aberration detection prior to production.
Solution Approach 2:
The patent introduces an intermediary test pattern and imaging system that separates the aberration measurement function from the main lithography process. By using a dedicated test pattern projection and imaging pathway, the system can quickly measure aberration without interfering with or delaying actual substrate processing, thus reducing detection time while maintaining accuracy.
2Reliability
If focus measurement methods are used to determine lens aberration, then some aberration information can be obtained, but the methods are unreliable and time consuming
Solution Approach 1:
The patent replaces unreliable mechanical focus measurement methods with an optical test pattern imaging approach. Instead of relying on mechanical focus adjustment and inspection, the system projects a known test pattern through the lens and captures the image to directly measure aberration characteristics, providing more reliable and faster aberration determination.
Solution Approach 2:
The patent changes the measurement parameter from mechanical focus position to optical image quality parameters. By analyzing the shape, position, and characteristics of the imaged test pattern features, the system extracts aberration information directly from the optical output, improving both reliability and speed of measurement.
3Measurement precision
If traditional aberration detection methods are used, then lens aberration can be identified, but the system complexity and cost increase
Solution Approach 1:
The patent applies universality by using the existing lithography system's projection and imaging capabilities for dual purposes: both for normal substrate processing and for aberration measurement. The same lens, projector, and camera are used to create test patterns and capture images for aberration analysis, eliminating the need for separate dedicated measurement equipment and reducing system complexity.
Solution Approach 2:
The system performs self-service by using its own existing components to measure its own aberration characteristics. The lithography system projects test patterns through its lens and captures images using its camera to self-diagnose optical aberrations, avoiding the need for external measurement instruments and simplifying the overall system architecture.
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 rapid detection and correction of lens aberrations within five minutes, minimizing errors and maintaining low costs, while identifying specific aberration types for precise lens correction.
Implementation Method 1
using a specific digital micromirror device (DMD) pattern to project an optical image on a reflective substrate
Implementation Method 2
acquiring a picture of returned optical image from the substrate using a camera
Data Source
AI summary
A method for qualitatively detecting aberration and determine aberration types in a photolithography system is disclosed. The method includes using a digital micromirror device (DMD) pattern to project an optical signal on a reflective substrate, acquiring a return optical signal reflected from the substrate at different focus heights (ranging from above to below best focus), forming a through focus curve based off of the return optical signal at various focus heights, comparing the through focus curve to a predetermined curve—the predetermined curve being a function of focus, and determining if a lens aberration is present. By using the existing hardware of the photolithography system to determine if a lens aberration exists, costs are maintained at a minimum and the DMD pattern creates a through focus curve (TFC) image in less than five minutes allowing for quick correction.