RESUMEN
To improve the exposure contrast of the scanning beam interference lithography (SBIL) system, a mathematical model of scanning exposure that includes the direction error of the measurement mirror is established. The effect of the angle between the interference fringe direction and the X-axis measurement mirror direction on the exposure contrast is analyzed. An accurate method for interference fringe direction measurement based on the heterodyne interferometry measurement method of the metrology grating and phase shift interferometry is proposed. This method combines the diffraction characteristics of the metrology grating and the phase shift algorithm to calculate the angle between the interference fringe direction and the measurement mirror direction accurately and adjust it. Experiments show that this angle reaches 0.6777 µrad, which meets high-precision grating fabrication requirements. Exposure comparison experiments performed at various angles show that a smaller angle between the interference fringe direction and the measurement mirror direction leads to better grating groove production by scanning exposure, which is consistent with the theoretical analysis. The accuracy of the theoretical analysis and the feasibility of the interference fringe direction adjustment method are verified, laying a foundation for high-quality grating fabrication by the SBIL system.
RESUMEN
We propose a 3D measurement method based on 2D grating dual-channel and Littrow equal-optical path incidence to detect the 3D displacement of a 2D grating in the X-, Y-, and Z-directions. The 2D grating is combined with the Littrow incidence method and a turning element to cause the Littrow diffracted light with frequency f1 to interfere with the reference light at frequency f2, and the displacement data in the X-, Y-, and Z-directions are obtained using the separation-dual-channel phase decoupling algorithm. A corresponding test experimental platform is constructed, and linear error evaluation and step error evaluation experiments are performed to determine the displacements in the X-, Y-, and Z-directions. The results obtained show that all linearity errors are within ±60 nm in the 10 mm measurement ranges in the X-, Y-, and Z-directions, and the test resolution is within ±5 nm. The proposed method can thus realize nanoscale synchronous measurement of X-, Y-, and Z-direction 3D displacements.
RESUMEN
The grating interferometer in the Littrow configuration uses quarter wave plates (QWPs) to modulate the polarization in the measurement system to determine the autocollimation optical path. Fabrication errors and mounting errors of the QWPs lead to phase changes in the grating interferometer that generate measurement errors. As an alternative, we propose a grating interferometer that produces conical diffraction. Using the grating instead of QWPs to modulate the beam's polarization bypasses this source of error. A 45 mm range experiment was performed that yielded a repeated measurement error of 40 nm. Experiments show that the system has a simple structure and good repeatability and is capable of high-precision displacement measurements.
RESUMEN
We propose a new symmetrical heterodyne grating displacement measurement method, based on 2D grating and single diffraction quadruple subdivision method. Using a dual-frequency laser with a wavelength of 632.8â nm, output power of 2.2â mW, and a 1200â l/mm 2D grating, eight diffracted light beams interfere in pairs in the X and Y directions through a turning element. The detection system's measurement accuracy was assessed experimentally. The system measurement resolution in the X and Y directions is better than 3â nm; the grating displacement measurement errors within a 10â mm range are better than ±30â nm and ±40â nm, and the repeatability error is better than ±25â nm. The method is not only applicable to nanoscale 2D displacement measurement technology but also can be used for ultra-precision positioning and ultra-precision processing, with the potential for picometer-level improvement.
RESUMEN
To fabricate plain holographic gratings with high wavefront quality and to obtain the wavefront required in varied line-space grating, an active control technology of a diffraction grating wavefront by modulating the phase distribution of the scanning-beam interference lithography system was proposed. Sinusoidal wavefront control is simulated, and the controlled wavefront being almost the same as the target wavefront. A photoresist grating was fabricated whose surface is uniform and the wavefront is ideally sinusoidal. The theoretical analysis and experimental results confirmed that the wavefront of the diffraction grating can be actively controlled by modulating the phase distribution of the scanning-beam interference lithography system.
RESUMEN
To improve grating manufacturing process controllability in scanning beam interference lithography (SBIL), a novel method for exposure dose monitoring and control is proposed. Several zones in a narrow monitoring region are fabricated on a grating substrate by piecewise uniform scanning. Two monitoring modes are given based on the different widths of the monitoring region. The monitoring curve of the latent image diffraction efficiency to scanning velocity is calculated by rigorous coupled wave analysis. The calculation results show that the exposure dose in SBIL can be monitored by the shape change of the monitoring curve, and an optimized scanning velocity can be selected in the monitoring curve to control the exposure dose.
RESUMEN
The interference fringe period is an important phase-locking parameter in the scanning beam interference lithography (SBIL) system. To measure the interference fringe period accurately, a heterodyne period measurement method is proposed. Compared with traditional methods, the requirements for the stage motion characteristics are greatly reduced. In this paper, the theoretical error of the period measurement method is analyzed and relevant experiments are performed. The results show that the average period measurement value is 555.539 nm and the standard deviation of measurement repeatability is 2.5 pm. This method is significant for holographic grating fabrication using the SBIL system.
RESUMEN
Grating-based interferometers play important roles in precision displacement measurements. Gratings are the core components of grating-based interferometers, and grating surface errors and line errors seriously affect measurement accuracy, especially in systems with Littrow configurations. A fast, accurate method to calculate displacement errors caused by grating surface errors and line errors in a grating-based interferometer with a Littrow configuration is proposed. Displacement errors are calculated using the diffracted wavefronts at the ±1st orders of the grating. Experimental comparison of the displacements of a grating-based interferometer and a laser interferometer verifies the correctness of the proposed method. The differences between the calculated and measured displacement error results are within 40 nm. The method is accurate, fast, and low cost and is highly significant for system error compensation and improvement of the measurement accuracy of grating-based interferometers.
RESUMEN
We propose a simple and compact reading head with the Littrow configuration that will increase measurement range and reduce the complexity of a two-dimensional grating-based interferometer. The reading head contains only a beam splitter, two polarizing beam splitter modules, and two mirrors. The theoretical resolutions in two directions are 0.27 nm and 0.18 nm, respectively. In comparison with a dual-frequency laser interferometer, the proposed interferometer can measure displacement from 3 nm to 10 mm with high accuracy. The 3σ values in two directions for the difference are 1.67 nm and 1.35 nm for a displacement of 9 nm. Repeatability for a displacement of 1 µm is better than 2 nm.
RESUMEN
A profile of an X-axis stage mirror results in a phase error of gratings in Scanning Beam Interference Lithography. Traditional methods of measuring the profile require extra probes and another large stage mirror on Y-axis, or requires other operations such as rotating measured object to adjust the zero-adjustment errors. This paper introduces a three-probe system removing the need for Y-axis optical path structure and proposes a bidirectional integration model to solve the problem of zero-adjustment error, simplifying the optical path structure and the measurement process. This method is confirmed by theoretical analysis and experimental results, which is better than traditional methods and can also be used in other application fields of three-point method.
RESUMEN
We designed a new system that eliminates deviations by correcting uncertainty in optical distance measurements in the laser two-color heterodyne interferometer. In simulations, eliminating the uncertainty from the atmosphere, the deviation in the uncertainty of the optical distance was 50 times greater with the two-color method than with the one-color method. Adding a correction arm reduces the deviation caused by the uncertainties in measured optical distances. The uncertainty in the measured path length is reduced to 20 nm over a path length of 1500 mm, giving a relative uncertainty of 1.34 × 10 -8.