Lithography Devices Research Articles

Study on Two-Dimensional Exit Pupil Expansion for Diffractive Waveguide Based on Holographic Volume Grating

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development cycle and complicated processing. In this paper, we first establish a set of two-dimensional (2D) grating ray tracing models, based on which we determine the initial architecture of the dual-region two-dimensional exit pupil expansion (2D-EPE) AR-HMD holographic waveguide diffraction system. Second, we propose a honeycomb coupled grating array and optimize the optical energy utilization and brightness uniformity of the holographic waveguide and use a custom dynamic linked library (DLL) function to implement the ray tracing of the 2D grating and add a probabilistic splitting function to the DLL, which reduces the single simulation time from 11.853 min to 1.77 min. We also propose a holographic lithography device composed of holographic optical elements (HOEs) and a method for preparing HOEs. Finally, in order to obtain the diffraction efficiency preoptimized by the above DLL for the uniformity of the exit pupil brightness and light energy utilization, we inverse design with the preparation process parameters as the optimization variables and develop the adaptable electromagnetic calculation program Holo-RCWA. Using Holo-RCWA with nondominated sorting genetic algorithm II (NSGA-II), we inverse design to obtain the process parameters satisfying the diffraction efficiency distribution, and the optimization time of the whole system is reduced from 2–3 days to 10 h. This work is of great significance for AR/VR applications.

Tetragonally and Rectangularly Packed Hierarchical Cylinders from A1 BA2 C Tetrablock Terpolymer.

Hierarchical cylindrical nanostructures with different diameters (or shapes) have received much attention because of potential applications to next-generation lithography or advanced optical devices. Here, weobserved, via small-angle X-ray scattering and transmission electron microscopy, tetragonally and rectanguarly packed hierachical cylindrical nanostructures by tailoring the volume fraction of polystyrene mid-block in polystyrene-b-polyisoprene-b-polystyrene-b-poly(2-vinylpyridine) tetrablock terpolymer (S1 IS2 V). P2VP becomes the main cylinder, while PI forms satellite cylinders surrounding the main P2VP cylinder. When the length of S2 block is relatively short, tetragonal arrangement of cylinders is observed. But, a rectanguar arrangement of cylinders is formed for larger S2 block. The experimentally observed hierarchical cylindrical nanostructures are in good agreement with the prediction by the self-consistent field theory. This article is protected by copyright. All rights reserved.

Correction of a digital micromirror device lithography system for fabrication of a pixelated liquid crystal micropolarizer array.

The combination of a digital micromirror device (DMD) lithography system and a rotatable polarizer provides a simple and convenient method to achieve the pixelated liquid crystal micropolarizer (LCMP) array for polarization imaging. In this paper, two crucial problems restricting the high-precision fabrication of LCMP array are pointed out and settled: the dislocation of LCMP pixels caused by parallelism error of the rotating polarizer and the grid defect caused by the gap between micromirrors. After correction, the maximum deviation of the fabricated LCMP pixels was reduced from 3.23 µm to 0.11 µm and the grid defect is eliminated. The correction method reported here lays a good foundation for the fine processing of liquid crystal devices with arbitrary photoalignment structure by using the DMD system.

Study of the ordered assembly morphologies of diblock copolymers on the same substrate.

With the development of frontier technology in emerging semiconductor processes, self-assembling (SA) and directed self-assembly (DSA) of block copolymers (BCPs) have attracted great attention from scientific researchers and become promising candidates for advanced photolithography. Using an optimal coating and baking process, highly ordered assembly morphologies (e.g., cylinder and lamella) of two BCPs in thin films were obtained without an additional topcoat material layer. Moreover, the whole experimental study also provides an optimal process for integrating the two BCPs into the same topographic guiding pattern substrate fabricated by electron beam lithography (EBL) to achieve specific self-assembly. This topographic guiding substrate achieves not only lamellar micro-domains aligned perpendicular to the sidewalls of trench edges but also cylindrical micro-domains (PMMA phase in a PS matrix) aligned parallel to trench edges respectively, which provides insights and valuable information for further applications in lithography and electronic devices.

Development of micro/nano structure pattern generation using direct-beam interferometry

To generate periodic patterns with a 300 nm periodicity on PET substrate, a low-cost direct-beam interferometry device with a 405 nm GaN semiconductor laser diode (Nano Materials) is employed. A similar, cost-effective system was utilized to create periodic patterns with periods between 290 and 750 nm over a vast area using an AlInGaN 405 nm diode. While interference lithography devices are inexpensive and simple to use, they have the drawback of only being able to recreate periodic patterns that are defined by the interference patterns of the laser beams. We present a low-cost direct write lithography system that use the optical head assembly from a Blu-ray disc recorder and is capable of producing both periodic and non-periodic, high-resolution structures for use in Macro/micro/nano processes. The optical head assemblies in Blu-ray drives feature a semiconductor laser diode and a 0.85 NA objective lens for reading optical media. We can attain very huge volumes of homogeneity, throughput, process control, and reproducibility using this Direct Beam approach. We optimized simulated patterns with controlled periodicity, density, and aspect ratio by altering different input parameters and was achieved to 51 nm.

Evaluation of permissible pixel positioning errors for displaying computer-generated holograms in projection photolithography

The authors carried out the estimation of the permissible positioning errors when displaying reflective phase holograms intended for application in holographic photolithography on solid media using electron-beam lithography devices. The work deals with the projection of holographic photolithography based on computer generated Fresnel holograms. The synthesis of holograms involved mathematical modeling of the physical processes of hologram recording and reconstruction using the following parameters: the characteristic size of the binary object is 20 × 20 nm or 80 × 80 nm, the wavelength of the radiation is 13.5 nm, the pixel size of the hologram is 20 × 20 nm, the distance between the planes of the object and the hologram is from 20.4 to 31.6 microns, the angle of incidence of the reference wave is 14º42′. For each of the three objects used in the modeling (namely, “Angles”, “Line grid target” and “Enlarged angles”), four computer-generated holograms were synthesized with different values for standard deviation of the pixel positioning error. The simulation of these errors was carried out by violating the equidistance of the points (pixels) on the hologram aperture. The holograms distorted in this way were subjected to the standard procedure of numerical reconstruction in virtual space. Comparison of the quality of the images obtained at different values of the positioning errors of the hologram pixels made it possible to evaluate their influence on the quality of the reconstructed image. It has been shown that the criterion used for estimating the permissible value of the positioning error in analog holography cannot be applied to synthesized holograms, because of the peculiar properties of interference fringes in discrete holograms. The results demonstrated a significant dependence of the permissible (in terms of image quality) pixel positioning errors on the object presentation method. The analysis revealed the impossibility of applying a single tolerance for pixel positioning errors to all possible synthesis conditions of computer-generated holograms and hence indicates the necessity of including a feature for estimating permissible hologram positioning errors into the software package for the synthesis and reconstruction of holograms. Based on the analysis of the technological parameters of modern electron-beam lithography devices, the authors confirmed the possibility of their use for manufacturing computer-generated holograms in modern high-resolution photolithography. Modeling the permissible positioning errors of computer-generated holograms by the proposed method allows evaluating the practical possibility of producing holograms with the required structure and high quality of the reconstructed image with a specific electron beam lithography device.

In-situ study of platinum reaction with oxygen contaminated silicon layer

This work reports the study of platinum silicide formation on reaction with an oxygen contaminated silicon layer. The observed results are potentially a novel approach to use silicide forming metals as a direct contact electrode to the crystalline core-amorphous silicon oxide shell structure of silicon nanowires without the need of hazardous acids, e.g. hydrofluoric acid, which is commonly used during lithography device preparation to remove the oxide shell. The simulation of the in-situ RBS spectra at temperatures above 250 °C showed the reaction of platinum with the oxygen contaminated silicon layer, forming a new layer with a stoichiometry corresponding to the silicide phase containing about 10–15 at.% oxygen (e.g. Pt0.55, Si0.3, O0.15). The presence of oxygen is attributed to the diffusion of its atoms through the silicide layer to the surface. The in-situ XPS data revealed the diffusion of oxygen towards the surface during the reaction of platinum and silicon while in-situ XRD results showed the sequential formation of the Pt2Si and PtSi phases. Therefore, these results present a simple and user-friendly approach applicable in the fabrication of contact structures in the core-shell silicon nanowire based devices.

Modified inverted selective plane illumination microscopy for sub-micrometer imaging resolution in polydimethylsiloxane soft lithography devices.

Moldable, transparent polydimethylsiloxane (PDMS) elastomer microdevices enable a broad range of complex studies of three-dimensional cellular networks in their microenvironment in vitro. However, the uneven distribution of refractive index change, external to PDMS devices and internally in the sample chamber, creates a significant optical path difference (OPD) that distorts the light sheet beam and so restricts diffraction limited performance. We experimentally showed that an OPD of 120 μm results in the broadening of the lateral point spread function by over 4-fold. In this paper, we demonstrate steps to adapt a commercial inverted selective plane illumination microscope (iSPIM) and remove the OPD so as to achieve sub-micrometer imaging ranging from 0.6 ± 0.04 μm to 0.91 ± 0.03 μm of a fluorescence biological sample suspended in regular saline (RI ≈1.34) enclosed in 1.2 to 2 mm thick micromolded PDMS microdevices. We have proven that the removal of the OPD from the external PDMS layer by refractive index (RI) matching with a readily accessible, inexpensive sucrose solution is critical to achieve a >3-fold imaging resolution improvement. To monitor the RI matching process, a single-mode fiber (SMF) illuminator was integrated into the iSPIM. To remove the OPD inside the PDMS channel, we used an electrically tunable lens (ETL) that par-focuses the light sheet beam with the detection objective lens and so minimised axial distortions to attain sub-micrometer imaging resolution. We termed this new light sheet imaging protocol as modified inverted selective plane illumination microscopy (m-iSPIM). Using the high spatial-temporal 3D imaging of m-iSPIM, we experimentally captured single platelet (≈2 μm) recruitment to a platelet aggregate (22.5 μm × 22.5 μm × 6 μm) under flow at a 150 μm depth within a microfluidic channel. m-iSPIM paves the way for the application of light sheet imaging to a wide range of 3D biological models in microfluidic devices which recapitulate features of the physiological microenvironment and elucidate subcellular responses.

Electrical contact considerations for diamond electron emission diodes

The demonstration of diamond devices has substantiated the superior capability of diamond in high power electronics that relied on the preparation of p-type and n-type diamond through boron and phosphorus doping, respectively, and the growth of high purity intrinsic diamond. We present an approach for electrical contacts to homoepitaxial, phosphorus doped, n-type, diamond that utilizes an interfacial layer of highly nitrogen doped, nanostructured carbon grown by plasma enhanced CVD (PECVD). This contact strategy was utilized in a pin diamond diode for electron source applications. The pin-nano-carbon structure was prepared on HPHT type IIb (111) oriented substrates with intrinsic, n-type, and nano-carbon layer grown in dedicated PECVD systems. The nanostructured nitrogen doped carbon layer was synthesized under argon addition to promote re-nucleation. Diodes from this pin-nano-carbon structure were prepared by lithography and mesa-etched devices contacted by Ti/Pt/Au metallurgy. Final processing in a hydrogen plasma established negative electron affinity properties for electron emission. Electrical characterization of the diodes commenced in vacuum after annealing at ~600 °C for 15 min and observation of exciton light emission indicated bipolar transport. At a forward bias of 14 V a current of 0.1A was measured and at 17 V its increase to 0.5A corresponded to a current density >1500 A/cm2. Compared to conventional pin diodes, the introduction of the nano-carbon layer enhanced the diode and electron emission current by more than an order of magnitude. This was attributed to the reduced contact resistivity of 5.5 × 10−3 Ω cm2 at room temperature. Light emission and diode operation at temperatures >750 °C indicated superior stability of the electrical contact. The n-type layer was characterized by SIMS indicating a phosphorus incorporation of ~2 × 1019cm-3 and for the nano-carbon layer a nitrogen incorporation of ~5 × 1020cm−3. Addressing contact limitations to n-type diamond through the growth of moderately phosphorus doped epilayers followed by highly nitrogen doped nano-carbon layers could provide a preferred approach for electronic devices that could also be extended to (100) surfaces.

Achromatic Flat Subwavelength Grating Lens Over Whole Visible Bandwidths

One of the major challenges for emerging planar subwavelength micro lens is the significant chromatic behavior due to phase mismatch of subwavelength phase shifters. In this letter, the achromatic micro grating lens covering the whole visible wavelength is demonstrated by utilizing relatively low index contrast gratings. Based on the unique chromatic phase shift behavior of polymer nanostructure, we have designed and fabricated a broadband subwavelength achromatic microlens that can cover 250 nm of visible bandwidths (from 435 to 685 nm) with focal shift less than 5%. Our works also represent the first time to design, fabricate, and characterize micrograting lens ( $7~\mu$ m in size) promising for compact integrated nanophotonic devices on chip. In addition, there are more advantages of using a polymer-based microlens, such as easy fabrication on flexible substrate and potential applications, including imaging, spectroscopy, lithography, laser fabrication, and future integrated wearable devices.

Discontinuous pinning effect by a hole row to the gas-liquid interface in a parallel gap

Discontinuous contact line pinning phenomenon appears when liquid wets discontinuous sharp features. It provides additional resistance to the gas-liquid interface and sometimes can be used as an effective approach for liquid control, such as avoiding liquid leakage by extraction holes in immersion lithography and other microfluidic devices. The discontinuous pinning effect by a hole row to the gas-liquid interface in a parallel gap was investigated in this study. We designed an experiment to investigate the behavior and the maximum resistance pressure of a hole row blocking the air-water interface in the gap. It was observed that the interface was partially pinned by the hole edges, while the unpinned parts was also stopped by the interface stretching. The pinning effect caused the interface distorted and produced additive Laplace pressure to resist the water pressure. Three failure types of the discontinuous pinning system were found, which were related to not only the hole edge pinning effect, but also the shape and position of the contact line. By analyzing the experimental results, analytical models based on the Laplace equation were built to formulate the pinning effects in the paper. The resistance pressure can be determined dependent on the developed analytical method. The experimental results agreed with the models in the failure types and maximum resistance pressure estimations.

Reduction of Line Edge Roughness of Polystyrene-block-Poly(methyl methacrylate) Copolymer Nanopatterns By Introducing Hydrogen Bonding at the Junction Point of Two Block Chains.

To apply well-defined block copolymer nanopatterns to next-generation lithography or high-density storage devices, small line edge roughness (LER) of nanopatterns should be realized. Although polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) has been widely used to fabricate nanopatterns because of easy perpendicular orientation of the block copolymer nanodomains and effective removal of PMMA block by dry etching, the fabricated nanopatterns show poorer line edge roughness (LER) due to relatively small Flory-Huggins interaction parameter (χ) between PS and PMMA chains. Here, we synthesized PS-b-PMMA with urea (U) and N-(4-aminomethyl-benzyl)-4-hydroxymethyl-benzamide (BA) moieties at junction of PS and PMMA chains (PS-U-BA-PMMA) to improve the LER. The U-BA moieties serves as favorable interaction (hydrogen bonding) sites. The LER of PS line patterns obtained from PS-U-BA-PMMA was reduced ∼25% compared with that obtained from neat PS-b-PMMA without BA and U moieties. This is attributed to narrower interfacial width induced by hydrogen bonding between two blocks, which is confirmed by small-angle X-ray scattering. This result implies that the introduction of hydrogen bonding into block copolymer interfaces offers an opportunity to fabricate well-defined nanopatterns with improved LER by block copolymer self-assembly, which could be a promising alternative to next-generation extreme ultraviolet lithography.

Generation of high-frequency interference patterns of evanescent electromagnetic waves at Fabry-Perot resonances in dielectric photonic crystals

A diffraction structure for generating high-frequency interference patterns of evanescent electromagnetic waves based on the interference of “volume” modes of dielectric photonic crystals at Fabry-Perot resonances is discussed. For the prediction of the angular locations of the Fabry-Perot resonances, a simple approach for the description of diffraction of a plane electromagnetic wave by a finite photonic crystal is proposed, which is based on the representation of the field inside the photonic crystal in the form of superposition of two counterpropagating “volume” modes of the photonic crystal. The results obtained may find an application in the design of new near-field interference lithography devices.

Fan-in WLP: Technology and Market Trends

The semiconductor industry is facing a new era in which device scaling and cost reduction will not continue on the path they followed for the past few decades, with Moore's law in its foundation. Advanced nodes do not bring the desired cost benefit anymore and R&D expenses for new lithography solutions and devices in sub-10nm nodes are rising substantially. Subsequently, new market shifts are expected in due time, with “Internet of Things” (IoT) getting ready to take over pole market driver position from mobile. In these circumstances, where front-end-of-line (FEOL) scaling options remain uncertain and IoT promises application diversification, in order to answer market demands, the industry seeks further performance and functionality boosts in package level integration. Emerging packages such as fan-out wafer level packages, 2.5D/3D IC and related System-in-Package (SiP) solutions together with more conventional but upgraded flip chip BGAs aim to bridge the gap and revive the cost/performance curve. In such an environment, what is the importance of fan-in wafer level packages (FI WLP), the current status of the fan-in WLP industry and how will fan-in WLP market and technology evolve? This work aims to answer these questions by performing an in-depth analysis on fan-in WLP market dynamics and technology trends.

능동 폴리머 펜 어래이를 이용한 미세 패터닝

We design, develope and test a parallel active polymer pen lithography (PPL) device, which consists of individually addressable elastomeric probe tips. The PPL array chip is fabricated using soft lithography method with polydimethylsiloxane (PDMS) material. Individual probe can be pneumatically actuated via a computer controlled interface. We demonstrate parallel writing with 16 individually addressed pens, with each pen producing a different pattern in the same run. The largest proof-of-concept array fabricated is <TEX>$4{\times}4$</TEX> with a spacing of <TEX>$250{\mu}m$</TEX> in both x and y axes.

ADVANCED CONCEPT FOR CREATION OF SECURITY HOLOGRAMS / PROGRESĪVĀ KONCEPCIJA AIZSARDZĪBAS HOLOGRAMMAS IZVEIDEI

Abstract A new concept is proposed for digital hologram production along with the relevant techniques developed in our laboratory. The main idea of the concept is to maximally separate the calculation of hologram from its optical recording on the light-sensitive media. A special file format containing information on each holographic pixel is created at the stage of calculation. The file is a device-independent by structure, and can be employed for recording a hologram using any of the existing techniques (dot-matrix, optical matrix lithography, e-beam lithography). An optical lithography device is applied to calculate the images for a spatial light modulator at the stage of hologram recording in accordance with the data from the file and in conformity with the hardware features of the device. The proposed method was tested and successfully used to record security holograms. For commercial use a software package and an optical recording system have been developed.

Electron irradiation-enhanced water and hydrocarbon adsorption in EUV lithography devices

The accumulation of water and hydrocarbons molecules on pure Au smooth surfaces were monitored during 100eV electron bombardment at various beam current levels. Our studies showed that these low energy electrons could accelerate the physical adsorption processes of the gaseous contaminant molecules on the mirror surface. The 100eV electron beam was used to provide a rough simulation of the secondary electrons generated during the interaction between the EUV beam at 13.5nm wavelength and the mirror surface in an EUVL device. The adsorption enhancement phenomenon was explained in accordance with Langmuir's Adsorption model by the increase of the sticking coefficient of adsorbed molecules onto the mirror surface. We have also shown that a positive biasing of the top of mirror surface can be used for preventing the secondary electron emission from the mirror surface.

Resolving the Chemical Nature of Nanodesigned Silica Surface Obtained via a Bottom-up Approach

The covalent grafting on silica surfaces of a functional dendritic organosilane coupling agent inserted, in a long alkyl chain monolayer, is described. In this paper, we show that depending on experimental parameters, particularly the solvent, it is possible to obtain a nanodesigned surface via a bottom-up approach. Thus, we succeed in the formation of both homogeneous dense monolayer and a heterogeneous dense monolayer, the latter being characterized by a nanosized volcano-type pattern (4-6 nm of height, 100 nm of width, and around 3 volcanos/μm(2)) randomly distributed over the surface. The dendritic attribute of the grafted silylated coupling agent affords enough anchoring sites to immobilize covalently functional gold nanoparticles (GNPs), coated with amino PEG polymer to resolve the chemical nature of the surfaces and especially the volcano type nanopattern structures of the heterogeneous monolayer. Thus, the versatile surface chemistry developed herein is particularly challenging as the nanodesign is straightforward achieved in a bottom-up approach without any specific lithography device.

Computer-aided microfluidics (CAMF): from digital 3D-CAD models to physical structures within a day

In this paper, we introduce computer-aided microfluidics (CAMF), a process that allows the creation of complex microfluidic structures from their concept to the actual chip within a day. During design and testing of new microfluidic systems, rapid and frequent design modifications have to be carried out. For this purpose, a device using maskless projection lithography based on a digital mirror device (DMD) has been developed. Digital mask layouts may be created using any graphics program (Microsoft Paint, Adobe Photoshop) and can be used as such by the custom-written control software of the system. However, we suggest using another approach: direct importing of three-dimensional digital computer-aided design (CAD) models from which mask information can be directly parsed. This process is advantageous as commercial 3D-CAD systems allow the rapid generation of static or parameterized models which can be used for computerized analyses like, e.g., flow simulation. After model validation, the mask information is extracted from these models and directly used by the lithography device. A chip or replication master is then created by means of lithography using curable monomers or resists as, e.g., Accura 60 or SU-8. With CAMF, the whole process from digital 3D model creation to actually running the experiment can be done within a day.

Novel method for intensity correction using a simple maskless lithography device

A simple, cost effective digital micromirror device (DMD) based maskless exposure device with a novel illumination correction is presented. The small scale laboratory setup with the presented construction details can be used with virtually any microscope with a suitable connector port. We demonstrate a technique for equilibration of intensity inhomogeneity which can be measured on the projection plane. The proposed technique enables pixel wise exposure dose manipulation. Consequently, unlike other systems, we are able to use the entire projected area for exposure with a feature size independent finite exposure time for a selected area. The long working distance makes it possible to expose surfaces located in a well or structures with variable heights which otherwise would not be exposable by conventional contact exposure. This simple setup is particularly helpful in fast, inexpensive prototyping of low resolution microstructures and sensor layouts. Features on silicon, glass and metal have been successfully patterned.