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.     

Asymmetric focusing microlens array fabricated using off-axis lithography

An asymmetric microlens with a given inclination angle was fabricated. Two circular pattern masks with different diameters were used to form a metal pattern and photoresist column on the substrate using the photolithography process. The metal pattern on the substrate was used to control the asymmetric microlens profile using thermal reflow. A lift-off process was applied to the first lithography to precisely define the metal pattern. A second lithography used deviation counterpoint exposure to pattern the photoresist column. The photoresist column was converted into a rubbery state when its temperature was increased to its glass transition temperature (Tg) during the thermal reflow. The asymmetric microlens structure was formed by shifting the arc vertex of the microlens toward one direction taking into account the fact that the copper coating surface has superior hydrophobicity to the silicon substrate surface. A 55° asymmetric microlens array was fabricated in this research by properly controlling the copper pattern size and the offset of two centers.     

A novel fabrication method of micro-needle mold by using the micro-lens mask through contact printing

This study presents a novel and precision process for fabricating a microneedle mold. The process includes a microlens array mask with contact printing in ultraviolet lithography. This method can precisely control the geometric profile of a microneedle array without the use of an etching process. The micro tapered cone microneedle mold utilizes the microlens array mask with geometrical optics. The light passes through the microlens and a hole in a Cr film of a mask, and then radiates onto the photoresist film. The light transmitted through the microlens has an aligned focal point on the photoresist film. An optical system is set up to characterize the optical performance of the machined microneedle, and then compared with theoretical data. The results show that the length of the microneedle from the experiment is close to the derived results. Moreover, the length of the microneedle is significantly influenced by the height and diameter of the microlens. Therefore, this method could also simplify the process and reduce the time needed for the fabrication of the microneedle. The micro cone microneedle has have great potential in the area of the drug delivery applications.     

New high fill-factor triangular microlens array fabrication method using UV proximity printing

A simple and effective method for fabricating a high fill-factor triangular microlens array using the proximity printing in lithography process is reported. The technology utilizes the UV proximity printing by controlling the printing gap between the mask and substrate. The designed approximate triangle microlens array pattern can be fabricated in photoresist. This is because to the UV light diffraction deflects away from the aperture edges and produces a certain exposure in photoresist material outside the aperture edges. This method can precisely control the geometric profile of a high fill-factor triangular microlens array. The experimental results showed that the triangular photoresist microlens array could be formed automatically when the printing gap ranged from 240 to 840 μm. The gapless triangular microlens array will be used to increase the luminance for the backlight module of liquid crystal displays. An erratum to this article can be found at     

New high fill-factor dual-curvature microlens array fabrication using UV proximity printing

A new high fill-factor dual-curvature microlens array fabrication method using lithographic proximity printing process is reported. The proposed technology utilizes UV proximity printing by controlling a printing gap between the mask and substrate. The designed microlens array pattern with high density can produce a high fill-factor dual-curvature microlens array in photoresist. Because the UV light diffraction deflects away from the aperture edges and produces exposure in photoresist material outside the aperture edges, this method can precisely control the geometric profile of a high fill factor dual-curvature microlens array. The experimental results showed that the dual-curvature micro-lens array can be formed automatically in photoresist when the printing gap ranged from 360 to 600 μm. The gapless dual-curvature microlens array will be used to enhance the luminance uniformity for light-emitting diodes (LEDs).     

Micromachining process simulation using a continuous cellularautomata method

In this paper, we present results on the development of an anisotropic crystalline etching simulation (AGES) program based on a continuous cellular automata (CA) model. The program provides improved spatial resolution and accuracy compared with the conventional and stochastic CA methods. Implementation of a three-dimensional (3-D) dynamic CA technique provides increased simulation speed and reduced memory requirement. The first AGES software based on common personal computer platforms has been realized for simulation of micromachining processes and visualizing results in 3-D space. The software is uniquely capable of simulating the resultant profile following a series of micromachining steps, including surface passivation, reactive ion etching, as well as wet chemical bulk etching. A novel method for accurately obtaining the etch-rate diagram of anisotropic etching using both experimental and numerical techniques has been developed     

Design, fabrication, and test of an on-chip micro flow cytometer with integrated out-of-plane microlenses

A micro flow cytometer with an integrated three-dimensional hydro-focusing unit and out-of-plane microlenses was successfully fabricated and tested. The entire system was fabricated with SU-8 ultra-violet lithography process. In the hydro-focusing unit, sheath flows pass through a trapezoid-shaped chamber with three 30° slopes to focus the sample flow in both horizontal and vertical directions. As an essential component in the on-chip optical detection system, integrated out-of-plane microlens was embedded in the sidewall of the fluid outlet channel in the detection area. A pre-aligned optical fiber holder was fabricated on chip to fix the output optical fiber in a position aligned to the microlens. Optical simulation and analysis were also conducted using commercial software Zemax. Numerical simulation results confirmed that the use of microlens substantially improved the detection efficiency by focusing the fluorescent light from the sample cells into the output optical fiber. Preliminary cell counting experiment was performed using the fabricated micro flow cytometer system and the experimental results proved the feasibility of the integrated micro flow cytometer design.     

Dual layer photoresist complimentary lithography applied on sapphire substrate for producing submicron patterns

In this study, the combined technologies of dual-layer photoresist complimentary lithography (DPCL), inductively coupled plasma-reactive ion etching and laser direct-write lithography are applied to produce the submicron patterns on sapphire substrates. The inorganic photoresist has almost no resistance for chlorine containing plasma and aqueous acid etching solution. However, the organic photoresist has high resistance for chlorine containing plasma and aqueous acid etching solution. Moreover, the inorganic photoresist is less etched by oxygen plasma etching process. The organic and inorganic photoresist deposit sequentially into a composite photoresist on a substrate. The DPCL takes advantages of the complementary chemical properties of organic and inorganic photoresist. We fabricated two structures with platform and non-platform structure. The non-platform structure featured structural openings, the top and bottom diameters and the depth are approximately 780, 500 and 233 nm, respectively. The platform structure featured structural openings, the top and bottom diameters and the depth are approximately 487, 288 and 203 nm, respectively. The precision submicron or nanoscale patterns of large etched area and patterns with high aspect ratio can be quickly produced by this technique. This technology features a low cost but high yield production technology. It has the potential applications in fabrication of micro-/nanostructures and devices for the optoelectronic industry, semiconductor industry and energy industry.     

Double‐viewing‐zone integral imaging 3D display without crosstalk based on a tilted barrier array

We propose an integral imaging (II) three‐dimensional (3D) display using a tilted barrier array and a stagger microlens array. The tilted barrier array consists of two orthogonally polarized sheets. In the stagger microlens array, the center of the microlens has p/2 shift with the elemental image along the horizontal direction, where p is the pitch of the microlens. The proposed II 3D display produces two different viewing zones and each of them is almost equal to that of the conventional II 3D display, and it has no crosstalk. We verify the feasibility of the proposed II 3D display in the simulation results.     

Microlens array fabrication by backside exposure using Fraunhofer diffraction

In UV-lithography, a gap between photoresist and UV-mask results in diffraction. Fresnel or near-field diffraction in thick positive and negative resists for microstructures resulting from a small gap in contact or proximity printing has been previously investigated. In this work, Fraunhofer or far-field diffraction is utilized to form microlens arrays. Backside-exposure of SU-8 resist through Pyrex 7740 transparent glass substrate is conducted. The exposure intensity profile on the interface between Pyrex 7740 glass wafer and negative SU-8 resist is modeled taking into account Fraunhofer diffraction for a circular aperture opening. The effects of varying applied UV-doses and aperture diameters on the formation of microlens arrays are described. The simulated surface profile shows a good agreement with the experimentally observed surface profiles of the microstructures. The paper demonstrates the ease with which a microlens array can be fabricated by backside exposure technique using Fraunhofer diffraction.     

Concave microlens array mold fabrication in photoresist using UV proximity printing

This paper presents a simple and effective method for fabricating a polydimethyl-siloxane (PDMS) microlens array with a high fill factor. The proposed method utilizes the UV proximity printing and photoresist replication methods. A concave microlens array mold is made using a printing gap in a lithography process. Optical UV light diffraction of UV light is used to deflect light away from the aperture edges to produce a certain exposure in the photo-resist material outside the aperture edges. This method can precisely control the geometric profile of a concave microlens array. The experimental results show that a concave micro-lens array can be formed automatically in photo-resist when the printing gap ranges from 240 to 720 μm. A high fill factor microlens array can be produced when the control pitch distance between the adjacent apertures of the concave microlens array is decreased to the aperture size.     

ICP深硅刻蚀工艺掩模的研究

通过使用深硅等离子刻蚀机,以C4 F8和SF6为刻蚀气体,对以光刻胶与金属铝两种材料作为掩模的深硅刻蚀结果进行对比,研究了深硅刻蚀过程中掩模材料对刻蚀结果的影响。实验结果表明：以光刻胶做掩模,深硅刻蚀后硅侧壁和硅底部表面形貌平整,垂直度较之铝掩模相当;以金属铝做掩模,深硅刻蚀后深槽底部表面不平整,出现长草现象,但是刻蚀选择比大于光刻胶,两种掩模的硅刻蚀速率相当。     

集成电路刻蚀过程三维建模与可视化技术研究

提出了一个新的、适合于三维条件下集成电路刻蚀过程的数学模型,并对其进行离散化处理,使它能够使用数字计算机进行刻蚀过程的仿真;同时研究了刻蚀过程的表面演化过程并给出了相关的数学模型;又研究了刻蚀模型仿真可视化技术的相关算法以及实现;最后给出了仿真结果并对其进行了讨论。     

集成电路刻蚀过程三维仿真模型优化

集成电路三维刻蚀仿真模型的原始方案使用的是可变点阵的三维刻蚀仿真模型。但是在这种模型作用下新的刻蚀点空间坐标的误差会随着刻蚀点间距的不断增大而增大,最终的积累误差会导致仿真的效果变差。改进了原有算法,使用了新的固定点阵的离散化数学模型代替原有可变点阵的模型,大幅改善了刻蚀精度和显示效果。并给出了刻蚀仿真的结果并进行了讨论。     

Design and fabrication of microlens arrays as beam relay for free-space optical interconnection

In this paper we report the design and fabrication of a beam relay for free space optical interconnection using microlens arrays. Multiple microlens arrays with same focal lengths were designed and fabricated in an out-of-plane layout. This design can be easily integrated with silicon-based optical interconnection devices. The beam relay was fabricated using direct lithography of SU-8 photoresist, and then replicated using UV curable polymer molded with a PDMS intermediate mold. The optical performance was tested and the experimental results show that the optical performances are mainly limited by the aberration of microlenses. Further study needs to be conducted to improve the surface quality of the lenses to reduce the aberrations.     

Fabrication of microlens array with graduated sags using UV proximity printing method

A graduated microlens array is presented in this paper. The proposed device has the same aperture microlens with a gradually increasing sag in the substrate. The design produces gradual decrease in the focal length and intensity when the light passes through the graduated microlens array. This paper presents a new graduated microlens array fabrication method that uses a variable printing gap in the UV lithography process. This method can precisely control the geometric profile of each microlens array without using the thermal reflow process. The angles between the mask and photoresist were placed at 5°, 8°, 10°, 15°, and 20° using a fixture designed in this study. The mask patterns were ellipses with an isosceles triangle arrangement to compensate for the partial geometry.     

Rapid soda-lime glass etching process for producing microfluidic channels with higher aspect ratio

This paper presents a simple method to produce microfluidic channels in soda-lime glasses with the aspect ratio >0.5 utilizing a modified wet etching protocol. A low-cost positive photoresist (PR) layer is used as the etching mask for the wet etching process. Prior to the PR and primer coating procedure, a UV activation process is adopted for enhancing the binding strength of the hexamethyldisilazane primer layer and the glass substrate, resulting in an better adhesion for the PR layer. A fast etching recipe is also developed by increasing the acidity and the temperature of the buffered oxide (BOE) etchant. Since the photoresist etching mask does not peel during the etching process shortly, the structure of the etching mask forms a barrier and results in a different diffusion rate for the etchant inside the etched trench structure. A slower etching rate for the glass is observed at the undercut region such that the proposed anisotropic etching pattern can be achieved. Results show that the etching rate of the modified glass etching process is as high as 7.7 μm/min which is much faster than that of pure BOE etchant (0.96 μm/min). Sealed microfluidic channel with the aspect ratio of around 0.62 is produced with the developed method. The method developed in the present study provides a rapid and efficient way to produce microfluidic channels with higher aspect ratio.     

A combinative technique to fabricate hot embossing master for PMMA tunneling sensors

A combinative approach of anisotropic bulk etching and modified plasma etching has been successfully employed in a single wafer to fabricate silicon masters for the hot embossing process. The masters hold both pyramid pits and positive profile sidewalls with smooth surfaces and steep angles. The SiO₂ layer is utilized as a etching mask with the aid of photoresist in three steps of photolithography patterning. The first polymethyl-methacrylate (PMMA)-based tunneling transducer with polymer membrane structures is fabricated by hot embossing replication with the silicon master. Consequently, the exponential relations between tunneling currents and applied deflection voltages are also reported.This work is partially supported by grants NSF/LEQSF (2001–04)-RII-02, DARPA DAAD19–02–1-0338, and NASA (2002)-Stennis-22.     

Influence of residual layer on cross-sectional shape of thermal-reflowed photoresist structures

When photoresist structures are formed by employing various lithography technologies and followed by thermal reflow treatments, the mechanism that transforms the cross-section of a photoresist structure from a rectangular-shape into a circular-shape is seen as an integral constituent of the manufacturing method of microlens arrays. However, in the case, where a residual layer is absent, a photoresist film is completely exposed to the oncoming radiation down to the interface between the photoresist film and substrate. Even in the presence of a residual layer, it has been uncertain to the author if a photoresist structure with a circular cross-sectional shape could be obtained, and be made applicable for the fabrication of a microlens array. The author then executed a set of thermal reflow treatments under various conditions using a positive-tone photoresist AZP4903 known for its capability of forming relatively thick films. As a result, it became clear that the existence of a photoresist’s residual layer has large influence on the transformation of the cross-sectional shapes of photoresist structures. These observations can be attributed to whether the bottom surface of a photoresist structure is firmly fixed on a hard substrate, or if it happens to be in contact with a soft photoresist layer which can flow comparatively freely.     

Analytical, numerical and experimental investigations of mixing fluids in microchannel

This work presents theoretical analysis, numerical simulation, fabrication and test of a micromixer chip for mixing fluids in microchannel. A three-dimensional analytical model is developed using a different mathematical approach to study passive laminar mixing phenomena and predict concentration distribution in a microchannel. The analytical model is validated by comparing with experimental and simulation results. The process of mixing fluids in a microchannel is simulated by solving the continuity, momentum and mass diffusion equations. The simulation results are validated and then parametric studies are performed to investigate the effects of channel aspect ratio, Reynolds number and diffusion coefficient on the mixing performance. The micromixer chip is fabricated with patterned SU-8 photoresist as the microchannel layer on a PMMA substrate using a combination of photolithography and micro-milling. Experiments are performed with different mixing fluids and the results were compared with that obtained from the theoretical model and simulation results.