Two Axis Encoder Head Assembly Using Multi-Wavelength Interferometry
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Solution Overview
Problem
Current measurement systems in semiconductor processing lack the necessary accuracy and sensitivity while maintaining a compact design, which is crucial for precise positioning of reticles and wafers during exposure processes.
Innovation Solution
A measurement system utilizing a stage grating and an encoder head that directs multiple measurement beams at different angles and wavelengths, interfering them to create measurement signals along specific axes, allowing for precise positioning and improved sensitivity with a minimal component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurement beams at different angles and wavelengths are used to improve measurement precision, then the accuracy and sensitivity of position measurement is enhanced, but the device complexity increases
Solution Approach 1:
The patent combines multiple measurement beams (first measurement beam at first wavelength and second measurement beam at second wavelength) into a single encoder head assembly. These beams are directed at the stage grating simultaneously or sequentially, and their interference patterns are detected to create measurement signals. This merging approach achieves high measurement precision through multi-wavelength interferometry while containing the structural complexity within an integrated encoder head design.
Solution Approach 2:
The encoder head is designed as a multi-functional device that handles multiple measurement beams of different wavelengths, redirects diffracted beams using redirectors, adjusts beam paths using beam adjusters, and processes interference patterns to generate measurement signals for both X and Y axis positioning. This universal design allows a single component to perform multiple functions necessary for precise two-axis positioning without requiring separate measurement systems for each function.
2Volume of moving object
If a compact encoder design is used to maintain small package size, then the device complexity is reduced, but the measurement precision and sensitivity are compromised
Solution Approach 1:
The encoder head employs a nested arrangement where redirectors and beam adjusters are positioned within the compact encoder head structure. The measurement beams pass through multiple optical elements (redirectors, beam adjusters, polarization beam splitters) that are nested or closely integrated within the limited space of the encoder head. This nested configuration allows the complex optical path required for high-precision measurement to be contained within a small package volume.
Solution Approach 2:
The patent utilizes the third dimension (Z-axis) to arrange optical components vertically within the encoder head, allowing multiple beam paths and optical elements to coexist in a compact footprint. The measurement beams propagate along the Z-axis through the stage grating and interact with redirectors and beam adjusters positioned at different heights, enabling complex measurement functionality without increasing the X-Y plane footprint of the encoder head.
3Measurement precision
If multiple beams are interfered with one another to create measurement signals, then the sensitivity is improved, but the difficulty of detecting and measuring increases
Solution Approach 1:
The patent introduces polarization beam splitters as intermediary optical elements that facilitate the detection of interference patterns between multiple measurement beams. These beam splitters separate and recombine beams with different polarizations, creating measurable interference signals that indicate the relative position of the stage grating. The intermediary role of the polarization beam splitters simplifies the detection process by converting complex multi-beam interference into separable signal components that can be independently measured and processed.
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 enhances the accuracy and sensitivity of position measurement, enabling the precise positioning of wafers and reticles, thus improving the manufacturing of high-density semiconductor wafers while maintaining a compact and simple construction.
Implementation Method 1
the first measurement beam being diffracted by the stage grating creates at least a +1 first order beam and a −1 first order beam
Implementation Method 2
at least a portion of the first measurement beam and at least a portion of the second measurement beam are interfered with one another to create a measurement signal along a signal axis
Implementation Method 3
the first redirector redirects the +1 first order beam back at the stage grating
Data Source
AI summary
A measurement system for measuring the position of a work piece (28) includes a stage grating (234) and an encoder head (236). A first measurement beam (38A) is directed at the stage grating (234) at a first angle, the first measurement beam (38A) being at a first wavelength. A second measurement beam (38B) is directed at the stage grating (234) at a second angle that is different than the first angle, the second measurement beam (38B) being at a second wavelength that is different than the first wavelength. At least a portion of the first measurement beam (38A) and at least a portion of the second measurement beam (38B) are interfered with one another to create a measurement signal along a signal axis.