Grating Measurement Apparatus for Extended Vertical Range
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Solution Overview
Problem
Existing grating-based measurement systems for photolithography face challenges such as limited vertical displacement measurement range, susceptibility to interference, and complexity in installation due to bulky structures and angular offsets, which hinder high-precision and stable multidimensional measurements.
Innovation Solution
A grating measuring device utilizing dual-frequency light beams with a dual-frequency light reception module, vertical measurement module, and signal processing to calculate vertical displacement, featuring all-fiber optic transmission, high resilience to interference, and a compact design suitable for tight spaces, enabling precise two-dimensional measurements in the X, Y, and Z directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a corner reflector is used to reflect diffracted beams back for two-dimensional position measurement, then horizontal and vertical position data can be determined, but the vertical measurement range is limited by the spot size and any vertical relative displacement causes deviation between reference and measuring spots
Solution Approach 1:
The patent introduces a specific optical path configuration where the measuring beam is diffracted by the grating and reflected back by the corner reflector to form a measuring spot, while the reference beam directly forms a reference spot. The optical system acts as an intermediary that maintains the spatial relationship between reference and measuring spots independent of vertical displacement, thereby extending the vertical measurement range while preserving measurement precision.
2Measurement precision
If a dual-band heterodyne grating-based measurement system is used with fiber transmission, then measurement precision is increased, but the structure becomes bulky and complex to assemble
Solution Approach 1:
The patent employs a dual-band heterodyne detection system where a single optical path configuration serves multiple measurement functions (horizontal and vertical position measurement). The grating and corner reflector assembly performs both diffraction and reflection functions simultaneously, reducing the number of separate components needed and simplifying the overall system structure while maintaining high measurement precision.
3Measurement precision
If any Rx/Ry angular offset exists between the grating and the read head, then the interferometric performance is degraded, but achieving perfect alignment is difficult
Solution Approach 1:
The patent utilizes the asymmetric optical path created by the corner reflector geometry to compensate for angular offsets. The corner reflector's unique property of reflecting incoming beams back parallel to their incident direction (regardless of the angle of incidence) creates an asymmetric optical configuration that is inherently tolerant to misalignment, thereby maintaining interferometric performance even when perfect alignment between grating and read head is not achieved.
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
The solution provides high measurement precision, repeatability, and stability, allowing for picometer-level measurements with reduced errors and a compact, easy-to-install design, suitable for high-precision applications in photolithography and other nanometric metrology needs.
Implementation Method 1
a laser, an isolator, a beam-splitter, frequency shifters
Implementation Method 2
frequency shifters to have different frequencies
Implementation Method 3
the zeroth-order diffracted beam interferes with the reference beam in the vertical detection module, thereby forming a vertical interference signal
Implementation Method 4
a vertical measurement module... collects a zeroth-order diffracted beam resulting from double diffraction at the grating
Implementation Method 5
double diffraction at the grating
Implementation Method 6
a corner reflector reflects the resulting diffracted beams back
Data Source
AI summary
A grating measuring device includes: a light source module (300) for generating two light beams having different frequencies, one of which serves as a measuring beam and the other as a reference beam; a grating (200); and a grating measuring probe (100) including a dual-frequency light reception module, a vertical measurement module, a vertical detection module and a reference detection module. The dual-frequency light reception module is configured to receive the measuring and reference beams, and the vertical measurement module is adapted to project the measuring beam onto the grating (200), collect a zeroth-order diffracted beam resulting from double diffraction occurring at the grating, and feed the zeroth-order diffracted beam to the vertical detection module. The zeroth-order diffracted beam interferes with the reference beam in the vertical detection module, resulting in a vertical interference signal. In addition, the measuring and reference beams interfere with each other also in the reference detection module to result in a reference interference signal. The vertical and reference interference signals are received by a signal processing module and serve as a basis for calculating a vertical displacement of the grating (200). This grating measuring device allows a great vertical displacement measurement range at any working distance.