Photoresist Layer Research Articles

A low-cost fabrication method of nanostructures by ultraviolet proximity exposing lithography

The lithography contact/proximity printing technique is widely used in the fabrication of microelectronic components, optical devices, and micro-fluidic chips. However, the fabrication of nano-sized structures requires high-cost equipment. This paper proposes a low-cost method to manufacture nanostructures by ultraviolet proximity exposing lithography through a microphotomask on a conventional lithographic aligner. The influence of exposure distance on photoresist pattern size is studied, and the standing wave effect on the photoresist layer is reduced by post-baking. This cost effective method can be widely applied to fabricate patterns with a nanofeature size.

Nano-Patterns of Photoresist Fabricated by Ultraviolet Lithography Technology.

Nanofluidics devices with two-dimensional nano-structures have attracted extensive interests for biological and chemical applications. The fabrication of nanoscale mask patterns with controllable line width is an indispensable process for manufacturing two-dimensional nano-structures. However, a simple and low-cost method for fabricating two-dimensional nano-patterns is still a challenge. In this work, a novel simple and low-cost method for fabricating nanoscale mask patterns with controllable line width, based on the ultraviolet exposure is presented. In the experiment, a layer of AZ5214 reversal photoresist was exposed to the ultraviolet light through the photomask with microscale patterns. After the lithography, nanoscale photoresist mesas patterns instead of microscale patterns were produced. The photoresist mesas with 400~800 nm width were fabricated. Meanwhile, by adjusting the parameters of exposure time, various nanoscale dimensions of photoresist mesas can be obtained. The proposed method overcomes limitations of the conventional ultraviolet lithography technology without the need to the expensive nanolithography equipment. Our novel fabrication method should be a useful tool for two-dimensional nano-structures fabrication due to its advantages of simple fabrication process, well controllability, and low-cost.

Fabrication of concave microlenses on a diamond by a spin coating process.

In this study, to fabricate diamond concave microlenses in a simple manner, an approach that combines a spin coating process with subsequent dry etching was demonstrated. First, photolithography was used to produce cylindrical holes in the photoresist layer on the diamond surface. Then, another photoresist was spin coated to fill the holes, and the concave structures with meniscus shapes were then obtained because of centrifugal force and interfacial tension. Finally, diamond concave microlenses were formed by transferring photoresist concave structures onto a diamond substrate using a dry etching technique. The fabricated diamond microlens exhibits a low surface roughness with nanometers as well as high-quality imaging and focusing performances, which is expected to have a wider range of potential applications under harsh and special conditions.

Rotational UV-lithography using flexible chromium-coated polymer masks for the fabrication of microstructured dental implant surfaces: a proof of concept

The purpose of this work was to demonstrate the technical feasibility for the fabrication of microgrooves or micropits on dental implants or dental implant abutment surfaces using a novel fabrication method derived from common UV-lithographic microfabrication. Instead of using a flat and rigid chromium/glass mask to structure a photoresist layer on a small cylindrical part, a flexible chromium-coated polymer mask was introduced into the lithographic setup. Through an elastic deformation of the polymer mask, it was possible to achieve lateral resolutions as small as 1.5 µm on small cylinders and to structure conical parts. By subsequent controlled under-etching of the structured photoresist layer, microgrooves of different cross-sectional geometries can be generated and applied to the implant or implant abutment surface. Such structures can be used for contact guidance of human gingival fibroblasts or endothelia cells to enhance the wound healing process and the overall soft-tissue integration.

A novel photoresist-based film-profile engineering scheme for fabricating double-gated, recess-channel IGZO thin-film transistors

We reported an experimental fabrication of double-gated (DG) thin-film transistor (TFT) with IGZO recess-channel using a designer photoresist-based thin-film profile engineering approach. In this approach, an organic shadow mask of photoresist (PR) was formed over a p+-Si wafer that was encapsulated by an oxide layer. The lithographically-patterned PR layer is an effective mask for shadowing reactive species during the subsequent deposition steps of IGZO and Aluminum, enabling the formation of IGZO recess-channel and discrete Al source/drain pads at room-temperature. The top-gate or DG configurations with the Si substrate serving as the bottom-gate were investigated. The fabricated DG TFTs show significant improvements in both ION and IOFF as compared with single-gated TFTs. The proposed process scheme is readily applicable to the back-end-of-line of a chip. This work demonstrates the feasibility of IGZO recess-channel TFTs in various gated configurations, enabling a building block for emerging functional devices for More-than-Moore applications.

Directed assembly of nanomaterials using electrospray deposition and substrate-level patterning

We report on the use of electrospray deposition and electrostatic focusing provided by a patterned photoresist layer to direct the assembly of nanomaterials on to a target substrate. Metallic (silver), semiconducting (titanium dioxide), and dielectric (polystyrene) particles were electrospray printed onto silicon and glass substrates with periodic photoresist patterns. The assembly and structure of the deposit was governed by the spray time, print material, substrate electrical properties, and geometry of the photoresist layer. The deposited particles could maintain an excess electric charge that influenced the assembly of subsequent particles. Tall, tree-like structures with high aspect ratio were formed on the silicon substrate when using silver and titanium dioxide particles. The growth of the deposit was inhibited for the polystyrene particles or when the target was glass. This technique was used to build two-layer deposits of different materials without having to align one layer to the next.

Ion beam planarization of optical aluminum surfaces

For fabrication of high-performance mirror devices, technical aluminum alloys Al6061 or Al905 are widely used. The surface error topography after manufacturing by single-point diamond turning is applicable in the infrared spectral range. For increasing demands on the optical surface quality in the shortwave visible and ultraviolet spectral range, further improvement of the surface roughness is required. Hence, a promising alternative process to attain the required surface quality is evaluated. Within the ion beam planarization technique, a photoresist layer is deposited by conventional spin coating or spray coating technologies exhibiting an ultrasmooth surface. When removing the resist by reactive ion beam etch (RIBE) processing using nitrogen process gas, the ultrasmooth surface topography of the resist is transferred into the substrate. We optimized the photoresist thermal pretreatment to realize roughness preservation and a steady-state material removal rate during RIBE machining. The optimum preparation steps are explored based on roughness evaluation, chemical modification, and etch resistance of the negative photoresist. Reactive ion beam etching-based planarization is conducted on single-point diamond turned RSA Al905 and RSA Al6061 samples made of rapidly solidified aluminum (RSA) in a two-step process. The optimum process and the roughness evaluation are explored by topographic analysis applying a combination of white light interferometry and atomic force microscopy measurements.

Plasmonic interference lithography by coupling the bulk plasmon polariton mode and the waveguide mode

Plasmonic lithography based on surface plasmon polariton has been proven to breaking the diffraction limit and deliver the super-resolution patterns. However, most previously reported studies suffer from the low energy efficiency and subwavelength excitation grating that obstructs the application in nanofabrication. In this work, a special plasmonic lithography prototype is proposed based on the coupling of the bulk plasmon polariton mode squeezed through the hyperbolic metamaterial (HMM) and the waveguide mode supported in the coupling layer/HMM/photoresist sandwich structure. The results demonstrate that periodic patterns with strong lithography light intensity (>220%) over the whole photoresist layer compared with incident optical intensity, high aspect ratios (1.5:1) and a half-pitch of 57.5 nm can be generated, under the interference of the fourth-order diffracted light of grating. The lithography linewidth can reach 1/16 of the mask period of 920 nm and ~1/8 of the wavelength of the 436 nm illumination light. This design of period reduction makes the device fabrication much easier, costless and even exhibits good tolerance to the roughness of the multilayer. In addition, theoretical analyses performed are widely applicable to systems working at other ultraviolet wavelengths including 248, 365 and 405 nm.

Three Dimensional Maskless Ultraviolet Exposure System Based on Digital Light Processing

This paper reports the development of a three dimension maskless photolithography system with an oblique scanning method based on digital light processing technology. The system consists of a UV light source, a digital micromirror device (DMD), a microlens/pinhole array, two optical projection lenses, and a three-axis (xyz) servo-controlled stage. The optical system can form a rectangular array of UV spots with a diameter of few μm directly on the surface of a sample sitting on the stage. A photoresist (PR) layer is coated on the sample surface. Using an oblique scanning approach, the whole area of PR layer can be exposed by this UV exposure system in a maskless manner. Since the energy intensity of each UV spot can be independently modulated by a corresponding group of micromirrors in the DMD, and a three-dimensional (3D) UV dosage distribution can be achieved through computer programming on the DMD and the xyz stage. After developing processes, 3D PR microstructures with arbitrary patterns and/or surface profiles can be readily formed by this maskless lithography system. Experimental results will be addressed as well as potential applications for 2D and 3D microfabrication.

Integrated Piezoelectric AlN Thin Film with SU-8/PDMS Supporting Layer for Flexible Sensor Array.

This research focuses on the development of a flexible tactile sensor array consisting of aluminum nitride (AlN) based on micro-electro-mechanical system (MEMS) technology. A total of 2304 tactile sensors were integrated into a small area of 2.5 × 2.5 cm2. Five hundred nm thick AlN film with strong c-axis texture was sputtered on Cr/Au/Cr (50/50/5 nm) layers as the sacrificial layer coated on a Si wafer. To achieve device flexibility, polydimethylsiloxane (PDMS) polymer and SU-8 photoresist layer were used as the supporting layers after etching away a release layer. Twenty-five mM (3-mercaptopropyl) trimethoxysilane (MPTMS) improves the adhesion between metal and polymers due to formation of a self-assembled monolayer (SAM) on the surface of the top electrode. The flexible tactile sensor has 8 × 8 channels and each channel has 36 sensor elements with nine SU-8 bump blocks. The tactile sensor array was demonstrated to be flexible by bending 90 degrees. The tactile sensor array was demonstrated to show clear spatial resolution through detecting the distinct electrical response of each channel under local mechanical stimulus.

Экспериментальные исследования различных полимерных композиций для создания рельефно-фазовых дифракционных решеток для систем дополненной реальности

The possibility of copying high-frequency diffraction gratings obtained in a photoresist layer to glass substrates using polymer compositions (“OKM” and “Tekhnovit”) is shown and their comparative analysis is carried out. The mechanism of copying the relief-phase structure is based on a two-stage process consisting of the following steps: obtaining a nickel master, applying a polymer composition to it and curing under the influence of UV radiation. The copying modes were optimized (time, exposure, thickness of the polymer base), and that allowed to obtain relief phase diffraction gratings with a surface relief depth comparable with the initial structure obtained in the photoresist layer. The diffraction efficiency of the resulting gratings was estimated, as well as the change in the depth of the surface relief of polymer copies obtained from one master.

Theoretical optimization of the photolithography through array of 1.2 μm silica microspheres

Interest in heteroepitaxy of III-V compounds on Si has been growing rapidly in recent years due to the potential of the optoelectronic components integration on silicon. However, most of the semiconductor compounds conventional in optoelectronics cannot be easily integrated on Si substrates due to the formation of the lattice defects. In this paper, we consider the fabrication of the mask consisting of the ordered nanoscale holes with the use of microsphere photolithography for selective epitaxial growth – promising approach for nanostructures fabrication on mismatched substrates. We have carried out the calculation of electromagnetic wave absorption in the photoresist layer through 1.2 μm microspherical silica lenses. The theoretical optimization of the photoresist thickness parameter allowed to obtain a value at which the minimum holes diameter in the photoresist is achieved. These data are necessary for carrying out the process of lithography through microspherical lenses to create a patterned growth mask.

Highly Uniform Plasmonic Interference Lithography Assisted by Hyperbolic Multilayer Graphene

Plasmonic interference lithography (PIL) is able to break the diffraction limit, realizing deep-subwavelength resolution in a large area. However, because the energy of surface plasmon polariton (SPP) wave is mainly confined on the surface of the metallic layer, the interference patterns in the photoresist layer often suffer from shallowness and nonuniformity. In this work, a PIL structure with highly uniform patterns is proposed, working in the wavelength of 193 nm. The structure consists of a silicon substrate and a photoresist sandwiched by two multilayer graphene films. Due to the hyperbolic property of the multilayer graphene, a slot SPP mode which is weakly dependent on the photoresist thickness is stimulated through volume plasmon polaritons in the hyperbolic multilayer graphene. A uniform periodic pattern with a half-pitch resolution of 29 nm (λ/6.7) maintains even the photoresist thickness that is larger than 80 nm. Our findings may provide a new method to realize robust PIL patterns.

Ultrahigh-sensitive plasmonic sensing of gas using a two-dimensional dielectric grating

We demonstrate an ultrahigh-sensitive plasmonic sensing of gas, employing a two-dimensional (2D) dielectric grating fabricated by laser interference lithography. The 2D grating was designed with the period of 500nm and prepared in an AZ1505 photoresist layer on a gold film of 20nm thickness deposited on a fused silica glass substrate. The surface plasmon resonance (SPR) in the Kretschmann configuration with spectral interrogation was utilized to measure the response of the sensor to vapors of aqueous solution of ethanol. Based on measurement of the gas refractive indices with the reference Au/Cr/SF10 sample, the resonance wavelength dependence was obtained. The SPR response of the structure in a spectral range of 1.68-1.85µm with a sensitivity of 8200-111,000nm/RIU was revealed. The sensor provides significantly higher sensitivity in comparison to conventional and grating-based SPR sensors.

Highly sensitive in situ-synthesized cadmium sulfide (CdS) nanowire photosensor for chemiluminescent immunoassays

Highly sensitive in situ-synthesized cadmium sulfide (CdS) nanowires (NWs) for the detection of chemiluminescence in immunoassays with a photoresist (PR) layer to stabilize the CdS NWs before and after coating with a parylene film were developed. The thickness of the PR layer was controlled by adjusting the viscosity of the PR solution used for spin-coating. PR2005 was the optimal PR for passivation of the NW surface. After the addition of a parylene coating on the CdS NWs, the photocurrent increased by as much as 50% over a broad range of light intensities, and the additional PR layer increased the photoresponse over the whole range of light intensities. When the photoresponses of the CdS NWs with and without the parylene film were compared after the addition of a PR layer, significant differences were observed in the photocurrent behavior after the incident light was turned off. For the CdS NWs with a parylene film and PR layer, the photocurrent reached the baseline within milliseconds of the incident light being turned off. However, the CdS NWs without a parylene film but with a PR layer required >60 s to reach the baseline level. This difference was due to the capacitance arising from the contact between the NWs. The in situ-synthesized CdS NW photosensor passivated by the parylene film and a PR layer was used in a chemiluminescence-based immunoassay. Finally, the detection of human immunodeficiency virus antibodies was demonstrated via a chemiluminescent enzyme-linked immunosorbent assay based on the CdS NW photosensor in comparison with the optical-density measurement for the chromogenic reaction of TMB(3,3′,5,5′-Tetramethylbenzidine).

3D hydrodynamic focusing in microscale channels formed with two photoresist layers.

3D hydrodynamic focusing was implemented with channel cross-section dimensions smaller than 10 μm. Microchannels were formed using sacrificial etching of two photoresist layers on a silicon wafer. The photoresist forms a plus-shaped prismatic focusing fluid junction which was coated with plasma-enhanced chemical-vapor-deposited oxide. Buffer fluid carried to the focusing junction envelopes an intersecting sample fluid, resulting in 3D focusing of the sample stream. The design requires four fluid ports and operates across a wide range of fluid velocities through pressure-driven flow. The focusing design was integrated with optical waveguides to interrogate fluorescing particles and confirm 3D focusing. Particle diffusion away from a focused stream was characterized.

Formation and Characterization of Hole Nanopattern on Photoresist Layer by Scanning Near-Field Optical Microscope.

Patterning of lines of holes on a layer of positive photoresist SX AR-P 3500/6 (Allresist GmbH, Strausberg, Germany) spin-coated on a quartz substrate is carried out by using scanning near-field optical lithography. A green 532 nm-wavelength laser, focused on a backside of a nanoprobe of 90 nm diameter, is used as a light source. As a result, after optimization of parameters like laser power, exposure time, or sleep time, it is confirmed that it is possible to obtain a uniform nanopattern structure in the photoresist layer. In addition, the lines of holes are characterized by a uniform depth (71–87 nm) and relatively high aspect ratio ranging from 0.22 to 0.26. Numerical modelling performed with a rigorous method shows that such a structure can be potentially used as a phase zone plate.

Flip Chip Joining with Quaternary Low Melting Temperature Solder Bump Fabricated with Injection Molded Solder

Abstract IBM has developed and has been enhancing the injection molded solder (IMS) technology as an advanced solder bumping technology with flexible solder alloy composition applicable even to fine pitch and small diameter systems. IMS is a simple bumping technology that can form solder bumps by injection of molten solder into via holes patterned in a photoresist layer. IMS is applicable to formation of solder caps for Cu pillar bumping which is a technology widely used for fine pitch applications. One of the advantages of IMS is the capability of using ternary, quaternary, or more compositions solder alloys for bumping, which is not achievable by current plating technology. In this study, the feasibility of IMS bumping and flip chip joining with quaternary solder alloys is demonstrated through assembling of 2.5D package test vehicles using low melting temperature (135°C) SnBi based quaternary alloy solder and associated reliability test. The test vehicles passed the 2250 cycles criteria of thermal cycling test and the observation of microstructures showed that there is no significant crack at the solder joints after flip chip joining or after the 2250 cycles of thermal cycling test. In addition, the tensile test on SnBi based quaternary alloy solder, Sn-58wt%Bi-2.0wt%In with small amount of Pd (less than 1wt%) was conducted using fine diameter specimens. From the SS curve obtained from the test, Young's modulus of the solder was determined as 7.3 GPa and 0.2% proof stress was obtained as 73 MPa both at 25°C. The creep property of the solder was evaluated and the constants for Norton's creep law for the solder were determined at 25, 80 and 110°C. The microstructure observation and Energy Dispersive X-ray (EDX) analysis of the flip chip joints revealed the formation of a thick bismuth (Bi) layer between CuSn intermetallic compound (IMC) layers within a joint. The mechanical simulation of the 2.5D test vehicles showed that the thermomechanical stress of a flip chip joint with Bi/CuSn IMCs at thermal cycling condition is comparable to those of CuSn IMC or Sn-3.0Ag-0.5Cu (SAC305) solder joints consistent with the thermal cycling test result. The advantage of using low temperature quaternary solder materials in flip chip packages is confirmed by mechanical simulation of 2D packages at reflow condition which showed lower stress on low-k dielectric layers for the packages with quaternary solder joints than for the packages with SAC305 solder joints.

Evaporation of water droplets on photoresist surfaces – An experimental study of contact line pinning and evaporation residues

We have systematically studied the interaction of ultrapure, de-ionized water droplets with chemically amplified, deep-ultraviolet photoresist layers during evaporation by means of experiments. The contact lines of the evaporating droplets undergo two pinning events. The footprint diameters during pinning D1,2 scale with the initial droplet diameter D0 approximately as D1,2∼D04/3. Evaporated droplets leave a residue behind, generally in the form of an ultrathin layer (order 1–10 nm) with a sub-micron thick mound in the center. We have systematically characterized the residue dimensions as a function of the initial droplet size, the photoresist composition and process conditions. Post-evaporation rinsing steps were found to be unable to completely remove a deposit, depending on how long after droplet evaporation they were performed. Our results indicate that the occurrence of so-called watermark defects might be related to deliquescence induced by ionic residues.

Broadband infrared plasmonic metamaterial absorber with multipronged absorption mechanisms.

A broadband plasmonic metamaterial absorber with near perfect multiband absorption in the infrared region is designed using a metal-insulator-metal configuration and fabricated using photolithography. The metal-insulator-metal configuration consists of a Ti microdisk array, a SiO2 insulator spacer, and an Al bottom layer. The multiband absorption occurs with near perfect absorption at 4.8-7.5 µm and 9.7-10.5 µm. Ultra-broadband absorption in the mid-IR wavelength range between 3-14 µm is realized by adding a rough photoresist layer on top of the periodic microdisk structures. The multiband absorption is achieved through the combined mechanisms including plasmonic surface lattice resonance, gap plasmon resonance, Fabry-Perot cavity resonance, and the intrinsic phonon-polariton absorption of SiO2.