image: Figure 1 | Framework of a grating interferometer system for 3-DOF measurement. (a) Reading head. (b) Calculation module. (c) Dual-frequency laser source. PPLN: Periodically Poled Lithium Niobate; HWP: Half-Wave Plate; QWP: Quarter Wave Plate; COL: Fiber Coupler; AOM: AcoustoOptic Modulator; P: Polarizer; PBS: Polarizing Beam Splitter; PD: Photo Detector; AD: Analog-to-digital conversion; CLK: Clock signal; FPGA: Field Programmable Gate Array.
Credit: Can Cui, Lvye Gao et al.
The relentless pursuit of higher precision in semiconductor lithography and atomic-scale manufacturing demands measurement systems capable of sub-nanometer accuracy, multi-axis capability, and robust environmental adaptability. Traditional capacitive sensors, time grating sensors, and laser interferometers face limitations in measurement range, stability, or multi-DOF performance.
To address these challenges, a research team led by Prof. Xinghui Li at Tsinghua University’s Shenzhen International Graduate School has developed a novel integrated heterodyne grating interferometer with a zero dead-zone optical path. This innovative design eliminates optical path difference-induced errors, thereby mitigating the effects of laser frequency drift and air refractive index fluctuations at their source.
Key highlights of the study include:
1. Zero Dead-Zone Optical Path Design – Precision optical path matching removes dead-zone errors, significantly improving measurement reliability.
2. Simultaneous 3-DOF Measurement – A dual-frequency laser source and integrated reading head enable simultaneous X/Y/Z displacement measurement within a compact 90×90×40 mm³ module.
3. Global Crosstalk Analysis and Compensation – A wavelet-based filtering algorithm reduces crosstalk errors to below 5%, ensuring high multi-axis accuracy.
4. Outstanding Performance – Achieving 0.25 nm (X/Y) and 0.3 nm (Z) resolution, superior linearity (6.9×10⁻⁵, 8.1×10⁻⁵, 16.2×10⁻⁵), and excellent repeatability (0.8 nm@1000 nm), with ranges exceeding 10 mm in-plane and 2 mm axially.
The authors note that this technology demonstrates clear advantages over existing sensors in precision, integration, and multi-axis capability, making it a promising candidate for future integrated circuit fabrication, atomic-scale production lines, and ultra-precision aerospace systems.
Journal
Light: Advanced Manufacturing
Article Title
Towards multi-dimensional atomic-level measurement: integrated heterodyne grating interferometer with zero dead-zone