Optical Axis Division for Simultaneous Alignment Mark Sensing
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Solution Overview
Problem
Conventional alignment sensors in lithographic apparatuses are limited in measuring multiple alignment marks simultaneously due to serial measurement methods, which incur a significant time penalty and dynamics issues when trying to increase scan speed.
Innovation Solution
The optical axis of the sensor is divided to allow simultaneous measurement of multiple alignment marks using beam splitters, creating multiple axes with separate illumination and detection systems, enabling demultiplexing of signals based on pitch, frequency, or temporal displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If serial measurement methods are used to measure multiple alignment marks, then measurement coverage is improved, but measurement time increases significantly
Solution Approach 1:
The optical axis of the sensor is divided into multiple segments using beam splitters, allowing simultaneous measurement of multiple alignment marks along the scan direction. This segmentation transforms the serial measurement process into a parallel one, measuring multiple marks at the same time rather than sequentially, thereby reducing measurement time while maintaining comprehensive coverage
Solution Approach 2:
The invention extends the measurement capability from a single optical axis to multiple optical axes by introducing beam splitters that create parallel measurement paths. This dimensional expansion allows the sensor to measure multiple alignment marks simultaneously along the scan direction, converting a time-consuming serial process into a spatially parallel process
2Productivity
If scan speed is increased to reduce measurement time, then productivity is improved, but dynamics issues and measurement accuracy deteriorate
Solution Approach 1:
By segmenting the optical axis into multiple parallel paths using beam splitters, the system can maintain moderate scan speeds while achieving high productivity through simultaneous measurement of multiple marks. Each segmented path operates independently, allowing stable measurements without the dynamics problems that would arise from attempting to measure multiple marks at extremely high speeds
3Loss of time
If multiple alignment marks are measured simultaneously using divided optical axes, then measurement time is reduced, but device complexity increases
Solution Approach 1:
The optical system is segmented using beam splitters to create multiple measurement paths, enabling simultaneous measurement of multiple alignment marks. This segmentation approach adds optical components but maintains a relatively simple overall architecture by dividing rather than multiplying complex subsystems
Solution Approach 2:
The divided optical axes share common components such as the light source, detector, and signal processing electronics, allowing these components to serve multiple measurement functions simultaneously. This multi-functionality reduces the overall device complexity compared to having completely separate measurement systems for each alignment mark
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 enables the simultaneous measurement of multiple alignment marks without increasing scan speed, reducing time penalties and improving alignment accuracy across the wafer field.
Implementation Method 1
The optical axis of the sensor is divided such that the sensor can simultaneously gather information from multiple positions on the wafer... by beam splitters, creating multiple axes
Implementation Method 2
an interferometer arranged to receive the diffracted light gathered by the light gathering system and configured to generate an optical output based on the diffracted light
Implementation Method 3
a diffracted light gathering optical system arranged to gather diffracted light from a plurality of diffracted light beams diffracted from respective ones of the plurality of alignment marks
Data Source
AI summary
An apparatus for and method of sensing multiple alignment marks in which the optical axis of a detector is divided into multiple axes each of which can essentially simultaneously detect a separate alignment mark to generate a signal which can then be multiplexed and presented to a single detector or multiple detectors thus permitting more rapid detection of multiple marks.