Lithographic Wafer Positioning via Diffraction Orders
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Solution Overview
Problem
Current lithographic methods for calibrating the positioning of a wafer table in lithographic apparatuses are time-consuming, often requiring several hours to accurately measure and record positioning errors using alignment marks and development processes.
Innovation Solution
A method utilizing multiple radiation poles to illuminate a diffraction grating on a mask, projecting and measuring combination diffraction orders to determine the position of a wafer grating, with filtering techniques to isolate desired orders and improve measurement efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional alignment mark imaging and development process is used to calibrate wafer table positioning, then measurement accuracy is improved, but calibration time increases significantly
Solution Approach 1:
The patent replaces the mechanical/chemical alignment mark imaging and development process with an optical diffraction-based measurement system. The system uses diffraction gratings on both mask and wafer, illuminated by multiple radiation poles, with detectors measuring combination diffraction orders to directly determine relative positioning without requiring physical mark development
Solution Approach 2:
The patent creates an optical copy of the alignment information through diffraction patterns. The diffraction gratings encode position information that is read optically through the projection system, allowing non-contact measurement of wafer table positioning errors without physical interaction with the wafer surface
2Productivity
If multiple radiation poles are used to illuminate the mask grating, then measurement speed is improved, but device complexity increases
Solution Approach 1:
The patent makes the illumination system multi-functional by using the same multiple radiation pole configuration for both normal lithographic exposure and calibration measurements. The system can switch between imaging circuit patterns and diffraction gratings without requiring separate dedicated calibration illumination hardware
Solution Approach 2:
The patent introduces diffraction gratings as intermediary elements on both mask and wafer that mediate the measurement process. These gratings convert the multiple radiation pole illumination into distinct combination diffraction orders that carry position information to the detectors
3Measurement precision
If combination diffraction orders are measured, then positioning measurement accuracy is improved, but signal filtering complexity increases
Solution Approach 1:
The patent applies local quality by assigning specific detection zones to different detectors, where each detector is responsible for measuring a particular combination diffraction order from a specific radiation pole. This localized measurement approach simplifies the filtering requirement compared to trying to separate all orders in a single detector
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 faster and more efficient calibration of the wafer table's position, reducing calibration time from several hours to less than an hour, enabling more frequent and cost-effective alignment across the entire wafer.
Implementation Method 1
using multiple radiation poles to illuminate a diffraction grating on a mask at a mask side of a projection system
Implementation Method 2
project the diffraction orders onto a grating on a wafer such that a pair of combination diffraction orders is formed by diffraction of the diffraction orders
Implementation Method 3
coupling the combination diffraction orders back through the projection system to detectors configured to measure the intensity of the combination diffraction orders
Data Source
AI summary
A measurement method including using multiple radiation poles to illuminate a diffraction grating on a mask at a mask side of a projection system of a lithographic apparatus, coupling at least two different resulting diffraction orders per illumination pole through the projection system, using the projection system to project the diffraction orders onto a grating on a wafer such that a pair of combination diffraction orders is formed by diffraction of the diffraction orders, coupling the combination diffraction orders back through the projection system to detectors configured to measure the intensity of the combination diffraction orders, and using the measured intensity of the combination diffraction orders to measure the position of the wafer grating.