Beam Interference Lithography Research Articles

High-efficiency three-port beam splitter under normal incidence.

A fused-silica three-port grating under TE-polarized normal incidence is designed and manufactured with improved diffraction efficiency (DE) and bandwidth. A physical explanation of the grating diffraction is provided using the simplified mode method (SMM), and parameters of the grating structure were optimized using rigorous coupled-wave analysis (RCWA). For a given set of optimized parameters, a transmitted three-port grating with an area of 170m m×170m m was fabricated by scanning beam interference lithography (SBIL), and diffraction properties were investigated. The average DEs for the +1, 0, and 1 orders of the 25 sampling points are 29%, 30%, and 31% at a 632.8nm incident wavelength. Additionally, the measured DEs of the +1, 0, and 1 orders all exceed 25% at the wavelength range from 613 to 653nm.

Improving grating duty cycle uniformity: amplitude-splitting flat-top beam laser interference lithography.

Laser interference lithography is an effective approach for grating fabrication. As a key parameter of the grating profile, the duty cycle determines the diffraction characteristics and is associated with the irradiance of the exposure beam. In this study, we developed a fabrication technique amplitude-splitting flat-top beam interference lithography to improve duty cycle uniformity. The relationship between the duty cycle uniformity and irradiance of the exposure beam is analyzed, and the results indicate that when the beam irradiance nonuniformity is less than 20%, the grating duty cycle nonuniformity is maintained below ±2%. Moreover, an experimental amplitude-splitting flat-top beam interference lithography system is developed to realize an incident beam irradiance nonuniformity of 21%. The full-aperture duty cycle nonuniformity of the fabricated grating is less than ±3%. Amplitude-splitting flat-top beam interference lithography improves duty cycle uniformity, greatly reduces energy loss compared to conventional apodization, and is more suitable for manufacturing highly uniform gratings over large areas.

Design and Analysis of a Long-Stroke and High-Precision Positioning System for Scanning Beam Interference Lithography

A macro–micro dual-drive positioning system was developed for Scanning Beam Interference Lithography (SBIL) which uses a dual-frequency laser interferometer as the position reference and exhibits the characteristics of long travel, heavy load, and high accuracy. The macro-motion system adopts a friction-driven structure and a feedforward PID control algorithm, and the stroke can reach 1800 mm. The micro-motion system adopts a flexible hinge–plus-PZT driving method and a PID control algorithm based on neural networks, which achieves sufficient positioning accuracy of this system at the nanometer level. An optical-path-sealing system was used to reduce the measurement noise of the dual-frequency laser interferometer. The static stability of the positioning system, the stepping capacity of the macro-motion system, the stepping capacity of the micro-motion system, and the positioning accuracy of the system were tested and analyzed. Additionally, the sources and effects of errors during the motion process were assessed in detail. Finally, the experimental results show that the workbench can locate at the nanoscale within the full range of travel, which can satisfy the SBIL exposure requirement.

Accurate measurement and adjustment method for interference fringe direction in a scanning beam interference lithography system.

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.

Simple spatially resolved period measurement of chirped pulse compression gratings.

We present an easy-to-implement and low-cost setup for the precise measurement of the period chirp of diffraction gratings offering a resolution of 15 pm and reasonable scan speeds of 2 seconds per measurement point. The principle of the measurement is illustrated on the example of two different pulse compression gratings, one fabricated by laser interference lithography (LIL) and the other by scanning beam interference lithography (SBIL). A period chirp of 0.22 pm/mm2 at a nominal period of 610 nm was measured for the grating fabricated with LIL, whereas no chirp was observed for the grating fabricated by SBIL, which had a nominal period of 586.2 nm.

Large-area silicon photonic crystal supporting bound states in the continuum and optical sensing formed by nanoimprint lithography.

Optical bound states in the continuum (BIC) are found in various dielectric, plasmonic and hybrid photonic systems. The localized BIC modes and quasi-BIC resonances can result in a large near-field enhancement and a high-quality factor with low optical loss. They represent a very promising class of ultrasensitive nanophotonic sensors. Usually, such quasi-BIC resonances can be carefully designed and realized in the photonic crystal that is precisely sculptured by electron beam lithography or interference lithography. Here, we report quasi-BIC resonances in large-area silicon photonic crystal slabs formed by soft nanoimprinting lithography and reactive ion etching. Such quasi-BIC resonances are extremely tolerant to fabrication imperfections while the optical characterization can be performed over macroscopic area by simple transmission measurements. By introducing lateral and vertical dimension changes during the etching process, the quasi-BIC resonance can be tuned over a wide range with the highest experimental quality factor of 136. We observe an ultra-high sensitivity of 1703 nm per RIU and a figure-of-merit of 65.5 for refractive index sensing. A good spectral shift is observed for detecting glucose solution concentration changes and adsorption of monolayer silane molecules. Our approach involves low-cost fabrication and easy characterization process for large-area quasi-BIC devices, which might enable future realistic optical sensing applications.

대면적 나노구조 패턴 제작을 위한 위상 마스크 기반 스캐닝 근접장 홀로그래픽 리소그래피

Near-filed holographic nanolithography is a method to fabricate periodic nanostructures using a phase mask comprised of nanogratings, where this method results in twice the pattern density of the phase mask. However, the practical use of this method has been limited due to low throughput and scalability. In this study, the drawbacks of the conventional holographic nanolithography were overcome by using a scanning laser beam interference lithography for making a large area phase mask, and by utilizing large area exposure with superimposition of laser beam. To confirm the feasibility of the proposed near-field holographic nanolithography, we fabricated a nanograting having a line width of 88.8nm and a pitch of 170nm onto an entire 4-in wafer from a phase mask having a pitch of 338nm.

Fabrication of ultra-high aspect ratio silicon grating using an alignment method based on a scanning beam interference lithography system.

The high-aspect-ratio silicon grating (HARSG) is an important X-ray optical device that is widely used in X-ray imaging and spectrum detection systems. In this paper, we propose a high-precision alignment method based on the scanning beam interference lithography (SBIL) system to realize precise alignment between the <111> orientation on the (110) wafer plane and the grating lines direction, which is an essential step in HARSG manufacture to obtain the high-aspect-ratio grating structure. After the location of the <111> orientation through fan-shaped mask etching and reference grating fabrication, a two-step method that combines static preliminary alignment and dynamic precision alignment is used to align the reference grating lines direction with the interference field fringes of the SBIL system through the interference of the diffracted light from the reference grating near the normal direction, which can realize a minimal alignment error of 0.001°. Through the overall alignment process, HARSGs with groove densities of 500 gr/mm, 1800 gr/mm, and 3600 gr/mm were fabricated through anisotropic wet etching in KOH solution, producing ultra-high aspect ratios and etch rate ratios greater than 200.

Theoretical Exposure Dose Modeling and Phase Modulation to Pattern a VLS Plane Grating with Variable-Period Scanning Beam Interference Lithography

Variable-period scanning beam interference lithography (VP-SBIL) can be used to fabricate varied-line-spacing (VLS) plane gratings. The exposure phase modulation method to pattern a VLS grating with a desired groove density must be carefully devised. In this paper, a mathematical model of the total exposure dose for VLS plane grating fabrication is established. With model-based numerical calculations, the phase modulation effects of the parameters, including the fringe locked phase, fringe density, and step size, are analyzed. The parameter combinations for the phase modulation are compared and chosen, and the optimal coordinate for phase compensation is selected. The calculation results show that the theoretical errors of the groove density coefficients can be controlled within 1e-8. The mathematical model can represent the deposited exposure dose for patterning VLS gratings during the lithography process, and the chosen parameters and proposed phase modulation method are appropriate for patterning VLS gratings with VP-SBIL.

Design on constant coherent light intensity fringe locking system for scanning beam interference lithography

Design on constant coherent light intensity fringe locking system for scanning beam interference lithography

Active control technology of a diffraction grating wavefront by scanning beam interference lithography.

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.

Analysis and design of fringe phase control system for scanning beam interference lithography

Scanning beam interference lithography (SBIL) is an advanced technology developed for manufacturing large-area diffraction grating at a nanometer-scale phase accuracy. To withstand environmental disturbances and maintain the interference fringes still relative to the substrate, SBIL requires high-precision phase control. We proposed a fringe phase control system with homodyne detection for SBIL. First, a homodyne detector is employed to achieve high-precision phase measurement, while ensuring the simplicity of the optics and high laser utilization. The time-varying nonlinear error in the measurement results is corrected by a dynamic ellipse fitting method. To reduce the latency effect, a lead controller is designed using the root locus method based on the model identification result. The lead controller considerably increases the control bandwidth while ensuring a sufficient phase margin, which further suppresses disturbances and stabilizes the interference fringes to within ∼1 / 60 of the fringe period. Wide-range phase tracking for perpendicular scanning with high accuracy is also verified through an experiment.

Method for exposure dose monitoring and control in scanning beam interference lithography.

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.

Design and control of precision work stage with air bearing for large size optical grating fabrication

Scanning Beam Interference Lithography (SBIL) is an advanced large-diameter and high-precision plane grating manufacturing solution, which has very high requirements for the positioning accuracy and running speed of the work stage carrying the substrate. In order to improve the size and accuracy of optical grating manufacturing in scanning interference lithography further, air bearing with high precision, high loading capacity and high stiffness is one of the key components for the work stage. In this paper, in order to design a large stroke work stage which meets the demand, firstly, the air bearing, the core part of the work stage, is analyzed and calculated by finite element method, and the pressure distribution curve of the air bearing of the work stage is obtained. On this basis, the linear air bearing with high bearing capacity and high stiffness is designed by using the omni-directional preloading analysis method of high-precision motion platform. Based on the high-precision position feedback of grating encoder, the high-precision closed-loop control of 20nm (3σ) is realized by using PID control and trap filter, which meets the design and requirements, and provides technical and engineering support for the manufacture of large-scale optical grating.

Heterodyne period measurement in a scanning beam interference lithography system.

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.

Scan angle error measurement based on phase-stepping algorithms in scanning beam interference lithography.

In this paper, a doubled-period grating (DPG) method is proposed to measure the scan angle error in scanning beam interference lithography (SBIL), together with a high-resolution two-dimensional stage and phase-stepping algorithms. A reference grating, which was the doubled period of the interference field, is adapted to diffract the incident left and right beams to form an interferogram captured by a CCD camera. The phase-stepping algorithm was applied to calculate the phase of the interferogram. First, by translating the stage, the reference grating lines were adjusted parallel to the scan direction by comparing the phase of the interferogram between the starting point and the ending point. Next, by rotating the stage step by step, the phase of the interferogram was obtained at each step as well as the phase slope. The scan angle error was considered to be least when the slope was minimum. Finally, a grating mask with a size of 100×100 mm2 was fabricated to verify the feasibility of the method. The scan angle error was measured with a precision of less than 12.65 μrad, which indicates the effectiveness of the proposed method to fabricate high-quality gratings in the future.

Piecewise Linear Weighted Iterative Algorithm for Beam Alignment in Scanning Beam Interference Lithography

To obtain a good interference fringe contrast and high fidelity, an automated beam iterative alignment is achieved in scanning beam interference lithography (SBIL). To solve the problem of alignment failure caused by a large beam angle (or position) overshoot exceeding the detector range while also speeding up the convergence, a weighted iterative algorithm using a weight parameter that is changed linearly piecewise is proposed. The changes in the beam angle and position deviation during the alignment process based on different iterative algorithms are compared by experiment and simulation. The results show that the proposed iterative algorithm can be used to suppress the beam angle (or position) overshoot, avoiding alignment failure caused by over-ranging. In addition, the convergence speed can be effectively increased. The algorithm proposed can optimize the beam alignment process in SBIL.

扫描干涉光刻机的超精密移相锁定系统

扫描干涉光刻机的超精密移相锁定系统

Real-time correction of periodic nonlinearity in homodyne detection for scanning beam interference lithography

Scanning beam interference lithography (SBIL) is an advanced large-area grating manufacturing technology. To produce gratings with nanoscale phase accuracy, the phase detector is demanded for a high precision in SBIL. A well-designed homodyne detector with a four-orthogonal detection is proposed to meet the harsh measurement requirements. However, the phase detection could suffer from periodic nonlinearity error, which changes slowly over time. A real-time correction method based on an extended Kalman filter is applied to estimate and compensate the periodic nonlinearity. The simulation results show that this method has great advantages in eliminating the time-varying periodic nonlinearity, compared with the conventional least squares fitting method. An experimental setup is also established to validate the proposed correction method.

Precision fringe period metrology using an LSQ sine fit algorithm.

High-precision grating fabrication is a precondition of grating-based displacement measurement techniques. Likewise, the value of high-precision fringe period is an essential parameter in the grating fabrication process, especially in scanning beam interference lithography. In this paper, a procedure for measuring the fringe periods of interference beams is introduced. The procedure includes signal acquisition and signal processing. The precisions of both the configuration for acquisition and the algorithm for processing are discussed. Experiments for fringe period measurement are also conducted, and an average value of 564.374nm with a standard deviation of 1.5pm is obtained, reaching a repeatability of 2.6ppm. The value of precision period lays a solid foundation for the fabrication of high-precision gratings.