Laser-focused Atomic Deposition Research Articles

Two-dimensional sub-200 nm pitch Si gratings with natural orthogonality

As a standard for length and angle, two-dimensional (2D) grating reference materials can be used for performance verification and calibration of various microscopes and 2D stages. This paper proposes a 2D nanoscale reference grating manufactured by combining laser-focused atomic deposition (LFAD) and extreme ultraviolet interference lithography. The theoretical pitch of the 2D grating is 150.46 nm, which is only times the pitch of the Cr grating manufactured by LFAD which can be traceable to the resonance transition frequency of Cr. Moreover, the angle between two periodic directions of the 2D nanograting has natural orthogonality.

Fabrication of 53.2 nm pitch self-traceable gratings by laser-focused atomic deposition combined with extreme ultraviolet interference lithography

The period of the self-traceable grating has extremely high accuracy and minimal uncertainty due to its traceability to natural constants. It is an essential task to shorten the period of self-traceable grating to below 100 nm. In this paper, the self-traceable Cr grating with a period of 212.8 nm prepared by laser-focused atomic deposition (LFAD) is used as the mask, and the second-order frequency doubling (k=2) of the Cr grating is performed by extreme ultraviolet interference lithography (EUV IL). The Cr grating is designed for the best second-order diffraction efficiency. By optimizing the orthogonality between the laser standing wave and the atomic beam, a Cr grating with a peak-to-valley height of 60 nm is prepared. After exposure and development with PMMA 672.01 photoresist, the Si grating is finally obtained by pattern transfer. And its average pitch is evaluated as (53.2 ± 0.1) nm. The exposure results of different photoresists and the uniformity of grating patterns are discussed. The peak-to-valley height of the Si grating is about 50 nm, and the full width at half maximum is about 20 nm. This research provides the possibility for the wider application of self-traceable gratings in advanced nanofabrication and precision measurement.

Critical-dimension scanning electron microscope characterization of smoothly varying wave structures with a Monte Carlo simulation

Scanning electron microscopy (SEM) characterization of a smoothly varying nanograting structure (a Pt-coated Cr grid on a Si substrate) with a sinusoidal waveform has been carried out by a Monte Carlo (MC) simulation technique. Previous studies with critical-dimension (CD) SEM (CD-SEM) have mostly concerned line structures with sharp edges so that there is an obvious edge bloom in the linescan profile of secondary electrons. In contrast, the present grating structures prepared by a laser-focused atomic deposition technique have a smoothly varying waveform in the cross-sectional profile, which pose greater difficulty for quantitative structural characterization by SEM. The grating structure, with a fixed pitch of λ/2 as the period of the standing-wave laser light field, where λ is the wavelength of the corresponding laser light, can be used as an ideal nanoscale metrological length tool; therefore, it is important to characterize its structural features over a large deposited area by SEM imaging for quality control, with the aim of mass reproduction. The present work extends the CD characterization of MC simulation methods to more complex structures. Taking into account different experimental factors, i.e. primary electron beam parameters, geometrical parameters and material properties, the unknown geometrical parameters (i.e. base height, peak height, linewidth shrinkage and peak tilt angle) of the grating lines have been successfully extracted from the experimental linescan profiles of SEM images.

A new type of nanoscale reference grating manufactured by combined laser-focused atomic deposition and x-ray interference lithography and its use for calibrating a scanning electron microscope

Calibration of magnification and nonlinearity of scanning electron microscopy (SEM) is an essential task. In this paper, we proposed a new type of 1D grating sample fabricated by combining laser-focused atomic deposition and x-ray interference lithography as a lateral standard for calibrating SEMs. The calibrations of the grating pattern by a metrological large-range atomic force microscope indicate that the grating sample exhibits outstanding pattern uniformity that surpasses conventional samples fabricated by e-beam lithography: (1) the nonlinear deviation of the grating structures is below +/- 0.5 nm over a measurement range of 5 µm; (2) the maximal variation of the calibrated mean pitch values is lower than 0.01 nm at different locations randomly selected all over the pattern area. The proposed new sample is applied for accurately calibrating the magnification and nonlinearity of a commercial SEM, showing its advantages of easy-of-use and high accuracy. The influence of the defocus level of SEM on the calibration result is also demonstrated. This research offers a feasible solution for highly accurate SEM calibration needed for 3D nanometrology and hybrid metrology demanded in metrology of modern nanoelectronics devices and systems.

Hybrid application of laser-focused atomic deposition and extreme ultraviolet interference lithography methods for manufacturing of self-traceable nanogratings

A novel hybrid method that combines the laser-focused atomic deposition (LFAD) and extreme ultraviolet (EUV) interference lithography has been introduced. The Cr grating manufactured by LFAD has advantages of excellent uniformity, low line edge roughness and its pitch value determined directly by nature constants (i.e. self-traceable). To further enhance the density of the Cr grating, the EUV interference lithography with 13.4 nm wavelength was employed, which replicated the master Cr grating onto a Si wafer with its pitch reduced to half. In order to verify the performance of the gratings manufactured by this novel method, both mask grating (Cr grating) and replicated grating (silicon grating) were calibrated by the metrological large range scanning probe microscope (Met.LR-SPM) at Physikalisch-Technische Bundesanstalt (PTB). The calibrated results show that both gratings have excellent short-term and long-term uniformity: (i) the calibrated position deviation (i.e. nonlinearity) of the grating is below ±1 nm; (ii) the deviation of mean pitch values of 6 randomly selected measurement locations is below 0.003 nm. In addition, the mean pitch value of the Cr grating is calibrated as 212.781 ± 0.008 nm (k = 2). It well agrees with its theoretical value of 212.7787 ± 0.0049 nm, confirming the self-traceability of the manufactured grating by the LFAD. The mean pitch value of the Si grating is calibrated as 106.460 ± 0.012 nm (k = 2). It corresponds to the shrinking factor of 0.500 33 of the applied EUV interference lithographic technique. This factor is very close to its theoretical value of 0.5. The uniform, self-traceable gratings fabricated using this novel approach can be well applied as reference materials in calibrating, e.g. the magnification and uniformity of almost all kinds of high resolution microscopes for nanotechnology.

Fabrication of nanostructures with complex spatial frequency via laser-focused atomic deposition

In this paper we report on experiments generating complex one-dimensional nanoscale patterns with the laser-focused atomic deposition technique. A beam of collimated chromium atoms intersect with an exact on-resonant laser standing wave at 7S3 → 7 transition of 52Cr. With the usage of proper laser intensity and reflectivity of the retroreflecting mirror, which are used to form the standing wave, nanolines with complex spatial frequencies (both λ/2 and λ/4) can be fabricated in one-step deposition. The proportion of the two structures could be 1:1.

Laser-focused Cr atomic deposition pitch standard as a reference standard

A chromium (Cr) grating pitch standard is fabricated by a technique of laser-focused atomic deposition. Cosine errors of the grating standard are analyzed and controlled under a relative error of 6×10−6 after 10-times iterative calibration. The dimension properties of the standard are measured and analyzed by a calibrated metrological atom force microscope (AFM) with large range. The experimental results show the grating standard has a good uniformity and structural periodicity. Hence, the laser-focused Cr atomic deposition grating can work as a reference standard.

Nano-Traceability Study of a Cr Standard Grating Fabricated by Laser-Focused Atomic Deposition

A dimensional artifact is developed, which is a chromium (Cr) deposition grating fabricated by a laser-focused atomic deposition technique. The mean pitch of the grating is measured by using a metrological atomic force microscope with a large range, where a series of reference signs have been performed to locate the deposition area. Cosine error of the measurement result is analyzed and eliminated by the iterative angle calibration. The measurement result shows that the mean pitch of the grating is 212.66 ± 0.02 nm, which is very close to half of the standing laser wavelength (λ = 425.55 nm). This means that the grating has traceability with high accuracy and can substitute the laser interference technology for instrument calibration. Moreover, using the Cr deposition grating as a nano standard can shorten the traceability chain and improve the practical application.

Investigation of shadow effect in laser-focused atomic deposition

The feature width broadening and height increasing of the Cr nanostructure have been experimentally observed in the gradual atom flux distribution divergent area on one sample along the standing wave direction in laser-focused atomic deposition. By applying an optimized ballistic deposition surface growth model to simulate this situation, it is demonstrated that the shadow effect of the forming nanostructure influences the deposition sites of the subsequent incident atoms, which leads to feature broadening and contrast decreasing of the nanostructures. The shadow effect theory provides a new understanding for the explanation of the discrepancy between the calculated results and the experimental observations.

Feature width miniaturization in atom nanolithography with double standing wave layers

Periodic nanostructures spaced by half of the wavelength can be obtained by the technology of laser-focused atomic deposition. Experimental result with single standing wave layer is presented, with a periodicity of 213 ± 0.1 nm, a height of 4 nm, and a feature width of 64 ±6 nm. To further minimize the feature width,focusing and depositing characteristics of double standing wave layers are numerically simulated with optimized particle optics model. It is shown that the spherical aberration is reduced significantly. The predicted feature width is 18.2 nm and the height is approximately 12.6 nm when the powers of the two standing wave layers are 6 and 14 mW, respectively. Well-defined line occurs even when the full-width at half-maximum (FWHM) of transverse angular spread reaches 0.5 mrad. OCIS codes: 140.3325, 220.3740, 220.4241. doi: 10.3788/COL201210.S21403. The fabrication of nanoscale structures by neutral atom lithography has the potential to significantly put forward the nanotechnology, ranging from device miniaturization in electronic industry to nanometrology. Over the last two decades, one-dimensional (1D) structures with this direct deposition technique have been grown with sodium [1] , chromium [2,3] , cesium [4,5] , aluminum [6] , ytterbium [7] , iron [8] , barium [9] , and metastable helium [10] . Focusing and depositing char

Laser-Focused Atomic Deposition for Nanascale Grating

Laser-focused atomic deposition is a technique with which nearly resonant light is used to pattern an atom beam. To solve the problem that the result of laser-cooled atoms cannot be monitored during the 30-min depositing time, we present a three-hole mechanically precollimated aperture apparatus. A 425 nm laser light standing wave is used to focus a beam of chromium atoms to fabricate the nanoscale grating. The period of the grating is 213±0.1 nm, the height is 4 nm and the full width at half miximum is 64±6 nm.

Nanoscale Pitch Standards Sample Fabricated using Laser-Focused Atomic Deposition

Problem statement: Nanotechnology is already a large sector of industry and science research and it is expected to continue to grow at very fast rate. The determination of absolute measurements of length at the nanometer scale and below is very difficult and expensive. So the nanoscale metrology standard is needed. Approach: The laser-focused atomic deposition is a new way to establish nanoscale pitch standards. When the atoms pass though laser standing wave field, the atoms will change the moving trajectory and be focused to the node (or antinode) of the laser standing wave according to the detuning of laser frequency and atomic resonant frequency. Because of the period of the laser standing wave, laser mask will form the anologue of an array of cylindrical lense. If a substrate is positioned at the focal plane of this lens array, a periodic structure is depositing onto the surface. The period of this structure is λ/2 of laser. Results: In this letter, a 425 nm laser light standing wave is used to focus a beam of chromium atoms to fabricate the nanoscale pitch standards sample of 213±0.1 nm. The height was 4 nm. The (FWHM) width of 64±6 nm. Conclusion/Recommendations: The period of this structure is λ2 of laser, whose spatial period can be traced directly to an atomic transtition frequency and the uncertainty possibility is 10-5, which is fitted to be as the nanopitch standards.

激光会聚铬原子光栅三维特性分析

激光会聚铬原子光栅三维特性分析

激光会聚原子沉积技术的原子沟道化研究

激光会聚原子沉积技术的原子沟道化研究

Broadening of Cr nanostructures in laser-focused atomic deposition

This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition. The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm. Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events: the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position; the other is that adatom diffuses by considering two major diffusion processes, namely, terrace diffusion and step-edge descending. Comparing with experimental results (Anderson W R, Bradley C C, McClelland J J and Celotta R J 1999 Phys. Rev. A 59 2476), it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave, the other two simulated trends are the same in the initial stage. These results demonstrate that some surface diffusion processes play important role in feature width broadening. Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.

A novel method to realize the nanometer scale grid deposition

The technology of laser-focused atomic deposition can be used to develop the nanostructure transfer standard of length. In this paper, a novel method is used to fabricate the nanometer structure through chromium atomic deposition. By the designed pre-collimated hole with three apertures, the chromium atomic beam may be divided into three parts. The middle part is for the atom beam to react with the standing wave and the deposition on the substrate with periodic distribution and the other two parts which can not be blocked by the substrate are for the atom beam to react with the detecting laser beam, and can be used to inspect the characteristic of atomic beam. This can provide some guidance for the progress of deposition. The simulatiion results show that the full width of half maximum is 6.2 nm and the contrast is 28:1 by using this special pre-collimated hole. On the other hand, the full width of half maximum and contrast are 32 nm and 8∶1 without using this special hole.

The preliminary result of laser- focused Cr atomic deposition for fabricating nanostructure

The technology of laser-focused atomic deposition can be used to develop the nanostrucrure transfer standard of length. When the frequency of laser standing wave is higher than the resonant frequency of atoms, the atoms will be focused on the wave node of the standing wave. The collimated Cr atoms are focused by a standing-wave laser field as they are deposited on a silicon substrate. Atomic force microscopy measurements shows a spacing of 215nm.

Analysis of Cr atom trajectory and focusing deposition in the standing wave field

The laser-focused atomic deposition is a new way to build the nano transfer standard of high reliability adequate for application. Based on the semi-classical model, this paper starts from the motion equation of chromium atom in the laser standing wave field to get the trajectory of the atoms in the standing wave field by analytical simulation. The effects on focal line features are discussed as a result of the angular collimation, velocity spread in the atomic beam and the spherical aberration. The effects from different deposition positions are also discussed. This paper also gives a sample of the grating structure nanofabricated by laser focusing of Cr atoms.

Nanotechnology with atom optics

A brief review of atom optics is presented, with emphasis on how it can be applied in the field of nanotechnology. Two specific examples are discussed: laser-focused atomic deposition and deterministic production of single atoms. Results are summarized for these two techniques, and discussion is presented on how they can impact progress in the development of nanotechnology.

Accuracy of Nanoscale Pitch Standards Fabricated by Laser-Focused Atomic Deposition.

The pitch accuracy of a grating formed by laser-focused atomic deposition is evaluated from the point of view of fabricating nanoscale pitch standard artifacts. The average pitch obtained by the process, nominally half the laser wavelength, is simply traceable with small uncertainty to an atomic frequency and hence can be known with very high accuracy. An error budget is presented for a Cr on sapphire sample, showing that a combined standard uncertainty of 0.0049 nm, or a relative uncertainty of 2.3 × 10−5, is readily obtained, provided the substrate temperature does not change. Precision measurements of the diffraction of the 351.1 nm argon ion laser line from such an artifact are also presented. These yield an average pitch of (212.7777 ± 0.0069) nm, which agrees well with the expected value, as corrected for thermal contraction, of (212.7705 ± 0.0049) nm.