Fabrication of intermediate mask for deep x-ray lithography

 This paper presents the fabrication of intermediate x-ray mask for deep x-ray lithography. In order to have working mask with absorbers thickness larger than 10 μm, the intermediate mask should have absorbers of 0.7 μm in thickness. To demonstrate intermediate mask fabrication, x-ray zone plates are fabricated on the 1.2 μm low-stress silicon-rich silicon nitride (SiN_x) membrane with the tri-layer Chromium-Tungsten-Chromium (Cr–W–Cr) as the x-ray absorbers. The chromium layers both 200 angstroms are used as adhesion and for stress relief. The SiN_x film is deposited with low pressure chemical vapor deposition (LPCVD) and the free standing membrane are formed by KOH silicon backside etching. With the e-beam lithography and reactive ion etching, width of 0.8 μm of outmost zone of the x-ray zone plates has been achieved on the membrane. The scanning electron microscopy (SEM) images of the x-ray zone plates and pictures of intermediate masks are demonstrated. Received: 25 August 1997/Accepted: 3 September 1997     

Fabrication of diffraction grating for X-ray Talbot interferometer

Imaging technology using the phase data attracts attention from many researchers as the observation technique of a biomechanical material. We produced a diffraction grating for obtaining high-resolution phase data. We designed the new process flow and developed the fabrication technique composed of MEMS technology, X-ray lithography, and micro electroplating. The X-ray lithography process was performed using the NewSUBARU synchrotron radiation facility. The line and the aspect ratio of this grating were 4 μm and above 5 μm, respectively. We evaluated the diffraction grating in SPring-8.     

Fabrication of a micro-tip array mold using a micro-lens mask with proximity printing

In this study, a mold for a micro-tip array is fabricated using a microlens array mask with proximity exposure. The micro-tip array uses a microlens array mask with geometrical optics. Light passing through a microlens is focused at the focal points. There is microlens on the mask and the pattern that results from the light passing through the mask is directly projected onto the photoresist surface. A concave profile is developed using a positive photoresist and the remaining photoresist microstructures are formed after the development process. By changing the distance between the mask and the photoresist and the radius of curvature of the microlens, various tip shapes can be fabricated. The exposure gap is calculated using the microlens array mask and the geometry of the mold of micro-tip array is established using the irradiance absorption maps for the different levels. These methods respectively use the model of the positive photoresist and optical software. When electroforming a metallic micro-tip copy of the patterned photoresist, masters are created. The metal micro-tip array is used membrane probe card.     

Fabrication of high aspect ratio nano gratings using SR lithography

In this paper, the fabrication technique for high-aspect-ratio diffractive optical element (DOE) is introduced. The 500 nm-width and 1,000 nm-width line-and-space pattern has been successfully fabricated. It was fabricated by synchrotron radiation (SR) lithography for the application of nano gratings, and poly-methylmethacrylate (PMMA) was used as X-ray resist. The nanoscale grating with the aspect ratio of 4.4 and 2.2 was achieved. So far, there are a number of reported techniques for fabrication of DOEs yet the height of those gratings is not sufficient. Therefore, we have attempted to investigate the fabrication of high-aspect-ratio nano gratings by a high-resolution X-ray lithography using SR source at Ritsumeikan University, Japan. Nevertheless, the evaluation of various factors influencing the high-aspect-ratio structure fabricated by our recommended technique is discussed. So far the fabricating process, such as, proximity gap of exposure, the exposure dosage, and the development time have been optimized to fabricate the gratings.     

Fabrication of high precision X-ray mask for X-ray grating of X-ray Talbot interferometer

X-ray imaging is used in many applications such as medical diagnosis and non-destructive inspection, and has become an essential technologies in these areas. In one image technique, X-ray phase information is obtained using X-ray Talbot interferometer, for which X-ray diffraction gratings are required; however, the manufacture of fine, highly accurate, and high aspect ratio gratings is very difficult. X-ray lithography could be used to fabricate structures with high precision since it uses highly directive syncrotron radiation. Therefore, we decided to fabricate X-ray gratings using X-ray lithography technique. The accuracy of the fabricated structure depends largely on the accuracy of the X-ray mask used. In our research, we combined deep silicon dry etching technology with ultraviolet lithography in order to fabricate untapered and high precision X-ray masks containing rectangular patterns. We succeeded in fabricating an X-ray mask with a pitch of 5.3 μm. The thickness of the Au absorber was about 5 μm, and the effective area was 60  × 60 mm², which is a sufficient size for phase tomography imaging. We demonstrated the utility of the Si dry etching process for making high precision X-ray masks.     

Fabrication of a thin plasmonic color sheet embedded with Al subwavelength gratings in parylene

In this study, we developed a thin plasmonic color sheet (TPCS) embedded with Al subwavelength gratings for use in flexible optical transmission filters, and experimentally demonstrated its transmission characteristics. Al subwavelength gratings were formed in a freestanding thin poly-para-xylylene (parylene-N) film less than 1-μm thick by using electron beam (EB) direct writing and sacrificial etching. The fabricated TPCS contained Al subwavelength gratings with periods ranging from 400 nm to 600 nm, and succeeded in shifting the transmission peak wavelength from 510 nm to 650 nm in the visible range. The freestanding thin parylene-N film deposited by room-temperature chemical vapor deposition provided enough flatness to the TPCS with a height difference of 900 nm in a whole filter area, resulting in uniform transmission spectra. The experimentally obtained peak shift dependent on the grating period agreed well with theoretical calculation results.     

Characterization of liquid crystals impregnated micrometric diffraction gratings for an active near-IR light extraction control

Microsystem Technologies - Due to their narrow reflection peak as well as their compact structure, guided mode resonance filters (GMRFs) are attractive for many applications. In this work, we will...     

Joint application of the incomplete Galerkin method and scattering matrix method for modeling multilayer diffraction gratings

A mathematical model of wave diffraction from a one-dimensional multilayer periodic grating is considered. A rigorous mathematical statement is given for the problem where partial radiation conditions are used for domain confinement. A complete formulation of the numerical algorithm based on a combination of the incomplete Galerkin method and the scattering-matrix method is presented. The algorithm’s convergence rate and computational complexity are analyzed and the optimal values of the computational parameters are recommended.     

Low cost transparent SU-8 membrane mask for deep X-ray lithography

Deep X-ray lithography masks require good transparency and mechanical resistance to the intense synchrotron X-ray beam, large active areas (cm)² and compatibility with the standard fabrication processes (optical lithography and gold electroforming). Moreover higher resolution can be achieved with low roughness flat membrane. Furthermore multiple aligned exposures require an optically transparent material. Diamond like Carbon membranes fulfill those requirements but have a prohibitive cost. Our approach consists in using an SU-8 epoxy resin layer as membrane material. In this communication the different steps of the fabrication process will be presented, as well as the results obtained using the mask for particular applications.     

Fabrication of large area diffraction grating using LIGA process

X-ray imaging is a very important technology in the fields of medical, biological, inspection, material science, etc. However, it is not enough to get the clear X-ray imaging with low absorbance. We have produced a diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. In this X-ray Talbot interferometer, diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we succeeded to fabricate a high aspect ratio diffraction grating with a pitch of 8 μm and small area using a deep X-ray lithography technique. We discuss that the diffraction gratings having a narrow pitch and an large effective area to obtain imaging size of practical use in medical application. If the pitch of diffraction gratings were narrow, it is expected high resolution imaging for X-ray Talbot interferometer. We succeeded and fabricated the diffraction grating with pitch of 5.3 μm, Au height of 28 μm and an effective area of 60 × 60 mm².     

Fabrication of a stainless steel shadow mask using batch mode micro-EDM

A metal shadow mask for organic thin-film transistors (OTFTs) has been fabricated by batch mode electro-discharge machining (EDM). Batch mode micro-electro-discharge machining method was applied for productivity improvement. Negative electrode with multiple holes (3 × 3 or 4 × 4) was fabricated using a single tool electrode. With the negative electrode, 3 × 3 and 4 × 4 tool electrode arrays are EDMed; 6 × 6 and 16 × 16 square hole array masks were batch mode EDMed with the fabricated multi-electrodes arrays. With 4 × 4 electrode array, the productivity is improved to five times of that in the case using a single electrode. Source and drain electrodes of OTFTs were successfully patterned on a pentacene active layer through the mask, and the fabricated pentacene TFTs had good output characteristics.     

Fabrication of HARM structures by deep-X-ray lithography using graphite mask technology

The cost-effective fabrication process for high-aspect-ratio microstructures using X-rays depends largely on the availability and quality of X-ray masks. The fabrication of X-ray masks using commercially available graphite sheet stock, as a mask membrane is one approach that is designed to reduce cost and turnaround time. Rigid graphite offers unique properties, such as moderate X-ray transmission, fairly low cost, electrical conductivity, and the ability to be used with either subtractive or additive processes [1, 2]. This paper will demonstrate the potential of a cost-effective, rapid prototyping of high-aspect-ratio microstructures (HARMs) using graphite masks. The graphite wafer accommodates both the intermediate mask and the working mask. In order to allow a direct comparison of the graphite mask quality with other X-ray masks, the primary pattern was derived from a Ti X-ray mask using soft X-ray lithography (XRL). Received: 7 July 1999 / Accepted: 29 September 1999     

Fabrication of electrostatic MEMS microactuator based on X-ray lithography with Pb-based X-ray mask and dry-film-transfer-to-PCB process

Lithographie Galvanoformung Abformung (LIGA) is a promising approach for fabrication of high aspect ratio 3D microactuator for dual-stage slider in hard disk drive. However, this approach involves practically challenging X-ray lithography and structural transfer processes. In this work, electrostatic MEMS actuator is developed based on a LIGA approach with cost-effective X-ray lithography and dry-film-transfer-to-PCB process. X-ray lithography is performed with X-ray mask based on lift-off sputtered Pb film on mylar substrate and photoresist application using casting-polishing method. High quality and high aspect ratio SU8 microstructures with inverted microactuator pattern have been achieved with the interdigit spacing of ~5 μm, vertical sidewall and a high aspect ratio of 29 by X-ray lithography using the low-cost Pb based X-ray mask. A new dry-film-transfer-to-PCB is employed by using low-cost dry film photoresist to transfer electroplated nickel from surface-treated chromium-coated glass substrate to printed circuit board (PCB) substrate. The dry film is subsequently released everywhere except anchor contacts of the electrostatic actuator structure. The fabricated actuator exhibits good actuation performance with high displacement at moderate operating voltage and suitably high resonance frequency. Therefore, the proposed fabrication process is a promising alternative to realize low-cost MEMS microactuator for industrial applications.     

大宽厚比悬空薄膜的制备与性能分析研究

研究了MEMS中的悬空薄膜制备技术.用浓硼扩散自终止腐蚀法和PECVD淀积法分别进行了试验,得到了宽厚比为3000∶1的悬空浓硼Si薄膜和宽厚比为9 000∶1的SiNx薄膜.对它们的力学特性进行了分析,用纳米硬度计测量了薄膜的杨氏模量.比较了两种方法的优劣.     

自旋阀多层膜巨磁电阻的研制

阐述了多层膜巨磁电阻自旋阀的设计原理和采用金属掩膜版磁控溅射的方法研制多层膜巨磁电阻自旋阀的工艺.制造的多层膜巨磁电阻采用[Co/Cu/Co]三重结构.同时分析了制备的Cu、Co纳米膜的形貌以及利用自旋阀GMR传感器测试得到的实验校准数据并绘制出输出-输入曲线.实验结果表明,制造的巨磁电阻提高了低场下的磁灵敏度,可以用来检测不同方位地磁场的大小,用该方法制造巨磁电阻的迟滞为0.01%F.S.文中介绍的多层膜巨磁电阻制造方法具有工艺简单、可与IC工艺相兼容的优点,有推广应用前景.     

Fabrication of glassy carbon microstructures by soft lithography

This paper describes fabrication techniques for the fabrication of glassy carbon microstructures. Molding of a resin of poly(furfuryl alcohol) using elastomeric molds yields polymeric microstructures, which are converted to free-standing glassy carbon microstructures by heating (T ∼500–1100°C) under argon. This approach allows the preparation of macroscopic structures (several mm²) with microscopic features (∼2 μm). Deformation of the molds during molding of the resin allows preparation of curved microstructures. The paper also presents a method of incorporating these structures on a chip by masking and electroplating.     

Fabrication of GaN light emitting diode membrane on Si substrate for MEMS applications

GaN membrane structures are fabricated for micro-electro-mechanical systems (MEMS). The combination of GaN and Si semiconductors is promising for future MEMS. However, due to the different material properties, the fabrication of MEMS using GaN semiconductor is still limited. Here, a simple membrane of GaN semiconductor deposited on Si substrate was investigated. The GaN crystal was grown by molecular beam epitaxy and metal organic chemical vapor deposition. The basic properties of the fabricated GaN light emitting diode (LED) were investigated. Etching the Si substrate from the backside, a freestanding GaN LED membrane was fabricated which can be useful for micro total analysis system. From those experimental results, it was shown that the GaN LED membrane was feasible for MEMS applications.     

LIGA micro-openings for coherence characterization of X-rays

Infinitely thin opaque screens serving for diaphragms as defined in the visible-light optics are not feasible for operation with X-ray beams due to their high penetrability. Micro-openings of predicted sidewall shape in a gold layer up to 140 μm thick which would provide low transparency, are proposed. The proposed micro-openings were made using the LIGA technique and tested successfully at photon energies of up to 25 keV. The micro-openings can be used as targets for coherence X-ray pattern or, if long interference tails are avoided by means of the advanced sidewall shape, as X-ray beam collimators.     

Fabrication of microgratings on PMMA plate and curved surface by using copper mesh as X-ray lithography mask

We demonstrate experimentally the X-ray lithography technique to fabricate microgratings on a PMMA plate and on curved surfaces such as PMMA cylinder lens surfaces with X-ray lithography by copper mesh as mask. Some gratings with 12.7 μm pitches on the plate and on PMMA curved surface with large area (10 mm × 10 mm) by vertically moving or rotating the resist stage exposure are realized.