Scanning Interference Lithography Phase Locking
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Solution Overview
Problem
Existing scanning interference photolithography systems face challenges in achieving high-precision control of interference patterns due to limitations in vibration resistance, air disturbance, and poor anti-interference ability, which affects the fabrication of high-performance gratings with nanometer-level precision and sub-10,000-level grid line density.
Innovation Solution
A scanning interference photolithography system utilizing a heterodyne optical path with a heterodyne phase meter and displacement measurement interferometer, where the phase between exposure beams is measured using a heterodyne measurement principle, and phase modulation is controlled to lock the interference pattern, while a vibration isolator and motion platform ensure stability and precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a beam splitter near the substrate is used to extract left and right exposure beams to form two interference signals for homodyne locking, then the interference pattern can be locked to prevent drifting, but the measurement signal is a DC signal with poor anti-interference ability and difficulty in phase retrieval, subdivide and direction judgment
Solution Approach 1:
The patent changes the measurement signal type from DC signal (homodyne) to AC signal (heterodyne) by introducing a frequency shift between reference and measurement beams. This parameter change fundamentally improves anti-interference ability and enables precise phase measurement through frequency discrimination, directly resolving the contradiction between locking reliability and measurement precision.
Solution Approach 2:
The patent replaces the homodyne detection mechanism with a heterodyne detection mechanism, substituting the measurement principle itself. By introducing acoustic optical modulators to create frequency shifts, the system transforms the detection approach from direct intensity measurement (DC) to frequency-modulated measurement (AC), thereby achieving both reliable locking and high-precision phase measurement.
2Reliability
If the piezoelectric ceramic is used to drive the mirror base to adjust the phase of the interference pattern, then the interference pattern can be locked, but the piezoelectric ceramic has a relatively large modulation range but a relatively low modulation speed, making it difficult to achieve high-performance grating fabrication
Solution Approach 1:
The patent replaces the mechanical piezoelectric ceramic actuation system with an optical phase modulation system using acoustic optical modulators. This substitution eliminates the mechanical inertia and slow response characteristics of piezoelectric ceramics, achieving high-speed phase modulation through electrical control of acoustic waves in the modulator material, thereby resolving the speed limitation while maintaining locking reliability.
3Area of stationary object
If a motion platform carrying a substrate is used for scanning exposure, then large-area grating fabrication is enabled, but motion error during scanning-stepping process causes dynamic drift of the grating pattern with respect to the substrate
Solution Approach 1:
The patent implements a real-time feedback system where the heterodyne phase meter continuously monitors the phase of the interference pattern during motion platform scanning. The measured phase information is fed back to the phase modulation system, which dynamically adjusts the reference beam phase to compensate for motion-induced drift, thereby maintaining precise grating pattern positioning over large areas despite platform motion errors.
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 system achieves high fringe pattern locking accuracy and high laser utilization, enabling the production of large-area, high-precision, dense grating lines with improved resistance to beam offset and dynamic drift, effectively addressing the limitations of prior art.
Implementation Method 1
a laser light emitted by a laser is split into a zero-order diffracted light and a first-order diffracted light by a first phase modulator
Implementation Method 2
the phase between exposure beams is measured using a heterodyne measurement principle
Implementation Method 3
The photolithography system forms interference pattern exposure by interfering two beams of collimated small-size light
Implementation Method 4
the exposure beam is focused by a lens to change the exposure angle
Data Source
AI summary
Disclosed is a scanning interference photolithography system, comprising a heterodyne optical path, a first interference optical path, a second interference optical path, a motion platform and a control subsystem, wherein a substrate is carried on the motion platform, a displacement measurement interferometer is used to measure the displacement of the motion platform, a first light beam and a second light beam are focused on the substrate for interference exposure; the control subsystem generates instructions according to various measurement information, adjusts angles of corresponding devices or the phase of a light beam, and locks the phase shift of interference exposure fringes of the first light beam and the second light beam. The system has a high precision of fringe pattern locking and a high laser utilization rate, and can be used for producing a large-area high-precision dense grating line gradient periodic grating.