Lithographic Wafer Positioning via Diffraction Orders
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Solution Overview
Problem
Current lithographic methods for calibrating wafer positioning in lithographic apparatuses are time-consuming, often requiring several hours and disrupting the throughput of the process.
Innovation Solution
A method utilizing radiation poles to illuminate a mask side diffraction grating, coupling diffraction orders through a projection system to form combination diffraction orders, which are then measured to determine the position of an object grating on the wafer, allowing for efficient calibration during exposure sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods using closely packed alignment marks are used, then measurement precision is improved, but productivity deteriorates due to time-consuming calibration requiring several hours
Solution Approach 1:
The patent replaces the mechanical/optical imaging and development process with a diffraction-based optical measurement system. Radiation poles illuminate a mask-side diffraction grating, and the resulting diffraction orders are coupled through the projection system to an object grating on the wafer. The combination diffraction orders are detected to directly measure wafer position without requiring physical alignment marks to be imaged and developed, thus eliminating the time-consuming steps while maintaining precision.
Solution Approach 2:
The invention extracts the calibration measurement process from the traditional multi-step imaging and development sequence. By using diffraction orders that can be directly detected by a detector system, the method separates the measurement function from the physical marking process, enabling rapid calibration measurements to be performed during exposure sequences without disrupting throughput.
2Productivity
If calibration measurements are performed during exposure sequences, then productivity is improved, but measurement precision may deteriorate due to time constraints
Solution Approach 1:
The patent enables calibration measurements to be performed continuously during the exposure sequence without interrupting the lithographic process. The diffraction-based measurement system operates concurrently with exposure operations, allowing calibration data to be collected throughout production rather than requiring separate dedicated calibration time, thus maintaining both productivity and precision.
3Measurement precision
If multiple diffraction orders are coupled through the projection system, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent utilizes the existing projection system's optical components to serve dual functions: both the lithographic projection of patterns onto the wafer and the diffraction-based calibration measurement. The same projection optics that are already present in the lithographic apparatus are used to couple the diffraction orders from the mask-side grating to the object grating on the wafer, eliminating the need for separate dedicated measurement optics and reducing overall system complexity.
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
Enables accurate and efficient calibration of wafer positioning with minimal impact on the lithographic apparatus's throughput, allowing for quicker and more frequent calibration processes.
Implementation Method 1
using at least one radiation pole to illuminate a mask side diffraction grating
Implementation Method 2
coupling at least two different resulting diffraction orders per illumination pole through the projection system
Implementation Method 3
project the diffraction orders onto an object grating on or adjacent an exposure route of a wafer such that a pair of combination diffraction orders is formed by diffraction of the diffraction orders
Implementation Method 4
coupling the combination diffraction orders back through the projection system to a detector system configured to measure an intensity of the combination diffraction orders
Data Source
AI summary
A measurement method comprising 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.