Positive Photoresist Research Articles

Generation of arbitrarily patterned polarizers using 2-photon polymerization

Patterned polarizers are prepared using liquid crystals (LC) doped with a black dichroic dye and in combination with a linear polarizer. The pattern is achieved with a nanostructured LC alignment surface, that is generated using a two-photon polymerization direct laser write (2PP-DLW). This technique creates a pattern of high-resolution grooves in the photoresist at any arbitrary angle. The angle governs the LC orientation at any substrate surface point, determining the transmitted light linear polarization angle. This paper presents the first use of a 2PP-DLW cured positive tone photoresist for dichroic dye-doped LC alignment. Two complementary photoresists have been employed: conventional negative tone SU-8 photoresist and, in this context novel, positive tone S1805 photoresist. The alignment quality of the polarizers has been assessed by analyzing the transmission using an additional polarizer. For SU-8, the resulting grayscale pattern and a contrast ratio (CR) of 14 has measured. The uniformity of the alignment has been measured to be 65% using normalized Shannon entropy (H). For S1805, a CR of 37 was measured, and a uniformity of 63% was obtained. 2PP-DLW allows for shaping complex patterns in submicron dimensions and for the fabrication of arbitrarily patterned polarizers and other LC devices.

Nondestructive Demolding of Structure-Designable High-Aspect-Ratio Nanoimprint Template.

Demolding is a crucial step in nanoimprint lithography (NIL) for successfully transferring template structures onto resist materials. The process, however, is often hindered by the adhesion and friction between the template and resist, leading to inevitable defects on the replicas and posing challenges in replicating templates with high-aspect-ratio (HAR) structures. Here, we introduce a novel approach using the dissolvable template method to achieve the nondestructive demolding of structure-designable HAR nanoimprint templates. The templates were fabricated by the 3D lithography technology, employing a positive photoresist that can be easily dissolved in alkaline solutions after exposure to ultraviolet (UV) radiation. By implementing this method, we successfully transferred dense arrays of pillars with a minimal diameter of 1.2 μm and a significant aspect ratio of 18, as well as a microlens array diffuser with randomly distributed structural parameters. The dissolvable template method paves the way for stress-free demolding, broadening NIL's application range.

Comparative Analysis of Positive Photoresist and Negative Photoresist in Nanoimprint Lithography Technology

Comparative Analysis of Positive Photoresist and Negative Photoresist in Nanoimprint Lithography Technology

Fabrication of microchannels and through-holes in Borofloat glass using Cr thin film with positive photoresist as the masking layer through wet etching

The present work investigates the efficiency of the masking layer, composed of Cr thin film and positive photoresist (AZ1512HS), to fabricate microchannels and through-holes in Borofloat glass wafers via wet etching, utilizing 20 % HF. The initial phase of the work emphasizes microchannel fabrication. ∼50 µm deep and well-defined microchannels are accomplished with no discernible surface defects on the wafer. In the later phase, predominantly sharp-edged through-holes are successfully fabricated in the wafer, without any observable pinholes, during etching for 300 min. The masking layer constantly exhibited robust adhesion to the wafer throughout the etching process, affirming its effectiveness. This work demonstrates the first instance of fabricating 500 µm deep through-holes in glass with Cr thin film and photoresist as a masking layer.

Расчет параметров теплового взрыва нафтохинондиазидных фоторезистов на основе экспериментальных данных

The study is focused on the applied task of determination of self-ignition (flash) temperature of unstable substances in order to facilitate occupational safety without conducting large-scale experiments. For two representatives of a number of naphthoquinonediazides, semi-products of production of positive photoresists—monosodium salt 1,2- naphthoquinondiazide(2)-5-sulfonic acid (Dye M) and 1,2-naphthoquinondiazide(2)-5-sulfochloride (Dye N2), the applicability of the thermal explosion classic theory has been proved. Using experimental kinetic parameters and the heat of decomposition of dyes, parameters of a thermal explosion in adiabatic conditions and convective heat transfer conditions have been calculated. As the analysis of obtained dependences shows, the linear dependence of slow growth (induction period) with time transforms into exponential dependence for each substance. Notably, the heat resistance of Dyes М and N2 is rather low. It has been shown that the slow decomposition of substances in conditions of the missing heat sink can transform into the stage of thermal explosion. The design temperature of self-ignition (flash) of the substance calculated considering the heat sink and the geometry of process equipment is 135 °C for Dye М and 93 °C for Dye N2, which complies with the experimental data. The recommendations on the selection of safe temperatures for drying modes of the studied compounds have been provided.

Cryogenic DRIE processes for high-precision silicon etching in MEMS applications

Cryogenic deep reactive ion etching (Cryo DRIE) of silicon has become an enticing but challenging process utilized in front-end fabrication for the semiconductor industry. This method, compared to the Bosch process, yields vertical etch profiles with smoother sidewalls not subjected to scalloping, which are desired for many microelectromechanical systems (MEMS) applications. Smoother sidewalls enhance electrical contact by ensuring more conformal and uniform sidewall coverage, thereby increasing the effective contact area without altering contact dimensions. The versatility of the Cryo DRIE process allows for customization of the etch profiles by adjusting key process parameters such as table temperature, O2 percentage of the total gas flow rate (O2 + SF6), RF bias power and process pressure. In this work, we undertake a comprehensive study of the effects of Cryo DRIE process parameters on the trench profiles in the structures used to define cantilevers in MEMS devices. Experiments were performed with an Oxford PlasmaPro 100 Estrelas ICP-RIE system using positive photoresist SPR-955 as a mask material. Our findings demonstrate significant influences on the sidewall angle, etch rate and trench shape due to these parameter modifications. Varying the table temperature between −80 °C and −120 °C under a constant process pressure of 10 mTorr changes the etch rate from 3 to 4 μm min−1, while sidewall angle changes by ∼2°, from positive (<90° relative to the Si surface) to negative (>90° relative to the Si surface) tapering. Altering the O2 flow rate with constant SF6 flow results in a notable 10° shift in sidewall tapering. Furthermore, SPR-955 photoresist masks provide selectivity of 46:1 with respect to Si and facilitates the fabrication of MEMS devices with precise dimension control ranging from 1 to 100 μm for etching depths up to 42 μm using Cryo DRIE. Understanding the influence of each parameter is crucial for optimizing MEMS device fabrication.

Recent Advances in Positive Photoresists: Mechanisms and Fabrication.

Photoresists are fundamental materials in photolithography and are crucial for precise patterning in microelectronic devices, MEMS, and nanostructures. This paper provides an in-depth review of recent advancements in positive photoresist research and development, focusing on discussion regarding the underlying mechanisms governing their behavior, exploring innovative fabrication techniques, and highlighting the advantages of the photoresist classes discussed. The paper begins by discussing the need for the development of new photoresist technologies, highlighting issues associated with adopting extreme ultraviolet photolithography and addressing these challenges through the development of advanced positive-tone resist materials with improved patterning features, resolution, and sensitivity. Subsequently, it discusses the working mechanisms and synthesis methods of different types and subtypes of photoresists, starting from non-chemically amplified, organic, and inorganic-organic hybrid photoresists and progressing to dry film resists, with an emphasis on the upsides of each. The paper concludes by discussing how future research in the field of lithography-prioritizing concerns related to environmental impacts, improved photoresist material and properties, and utilization of advanced quantum technology-can assist with revolutionizing lithography techniques.

Enhancing light extraction efficiency of the inclined-sidewall-shaped DUV micro-LED array by hybridizing a nanopatterned sapphire substrate and an air-cavity reflector

In this work, we hybridize an air cavity reflector and a nanopatterned sapphire substrate (NPSS) for making an inclined-sidewall-shaped deep ultraviolet micro light-emitting diode (DUV micro-LED) array to enhance the light extraction efficiency (LEE). A cost-effective hybrid photolithography process involving positive and negative photoresist (PR) is explored to fabricate air-cavity reflectors. The experimental results demonstrate a 9.88% increase in the optical power for the DUV micro-LED array with a bottom air-cavity reflector when compared with the conventional DUV micro-LED array with only a sidewall metal reflector. The bottom air-cavity reflector significantly contributes to the reduction of the light absorption and provides more escape paths for light, which in turn increases the LEE. Our investigations also report that such a designed air-cavity reflector exhibits a more pronounced impact on small-size micro-LED arrays, because more photons can propagate into escape cones by experiencing fewer scattering events from the air-cavity structure. Furthermore, the NPSS can enlarge the escape cone and serve as scattering centers to eliminate the waveguiding effect, which further enables the improved LEE for the DUV micro-LED array with an air-cavity reflector.

Radiation-Induced Alteration of the Reflection Spectra of Diazoquinone–Novolac Photoresist Films by Implantation of Ag+ Ions

FP9120 diazoquinone–novolac positive photoresist films 1.5 μm thick implanted with Ag+ ions and supported on the surface of KDB-10 (111) silicon wafers by centrifugation have been studied by measuring reflection spectra. It has been shown that ion implantation leads to a decrease in the refractive index of the photoresist due to radiation crosslinking of novolac resin molecules and a decrease in the density ρ and the molecular refraction RM of the photoresist. It has been established that the reflection coefficient in the opaque region of the photoresistive film increases with the Ag+ implantation dose. The changes observed in the optical properties of the films under ion implantation conditions are explained taking into account radiation-chemical processes in the phenol–formaldehyde photoresist.

Indirect nanoscale characterization of polymer photoresist wetting using ultra-high frequency acoustic waves

The wetting of surfaces with patterns in the order of a hundred nanometers is often a complex phenomenon to analyze and control. In the semiconductor industry, whether it is during the surface cleaning steps or the deposition of the protective mask (photosensitive liquid resin that is then cross-linked), the conformity of the deposit of the liquid layer on the patterned surface must be perfect or else the functionality of the targeted electronic component will be compromised. Thus, understanding the surface wetting of these liquids allows the implementation of optimized processes. In this paper, we present a method of indirect wetting characterization of a photoresist based on ultra-high frequency (# GHz) acoustic waves. This resin is a commercial product called GKR 4602 (belonging to the KrF series of positive photoresists), which is coated in two different ways: either directly onto the surface of a patterned silicon wafer, or after application of a solvent, Propylene Glycol Ethyl Ether (PGEE), which then acts as a pre-wetting layer. The patterned wafer, playing the role of electrical insulation (Deep Trench Isolation, DTI) are 200 nm wide, deep trenches with a high aspect ratio (> 50). The originality of this paper lies in the validation of the acoustic characterization by direct observation of the wetting of the cross-linked resin. To do so, we used a FIB (Focused Ion Beam) microscope which allowed us to make cuts and capture localized images of the wetting state of the photoresist. Moreover, all the results obtained (resins and patterned silicon surfaces) are directly from the microelectronics industry (STMicroelectronics), showing that our method is fully compatible with an industrial approach.

Cross-Scale Topography Achieved by MOPL with Positive Photoresist to Regulate the Cell Behavior.

Cross-scale micro-nano structures play an important role in semiconductors, MEMS, chemistry, and cell biology. Positive photoresist is widely used in lithography due to the advantages of high resolution and environmental friendliness. However, cross-scale micro-nano structures of positive photoresist are difficult toflexibly pattern, and the feature resolution is limited by the optical diffraction. Here, cross-scale patterned micro-nano structures are achieved using the positive photoresist based on the femtosecond laser maskless optical projection lithography (MOPL) technique. The dependence between exposure dose and groove width is comprehensively analyzed, and a feature size of 112nm is obtained at 110 µW. Furthermore, large-area topography considering cell size is efficiently fabricated by the MOPL technique, which enables the regulation of cell behavior. The proposed protocol of achieving cross-scale structures with the exact size by MOPL of positive photoresist would provide new avenues for potential applications in nanoelectronics and tissue engineering.

High-Resolution Multicolor Patterning of InP Quantum Dot Films by Atomic Layer Deposition of ZnO

This paper presents the high-resolution (>2000 PPI) multicolor patterning of InP quantum dot films using a conventional photolithography process with a positive photoresist (PR). The solvent resistance of the quantum dot (QD) film is achieved by depositing an ultrathin ZnO layer through atomic layer deposition. This is different from previous studies, which lack high-resolution patterning or compatibility with indium phosphide (InP) QDs owing to chemical weaknesses. By employing a positive PR with a photoacid generator, the side-by-side patterning process yields multicolor patterns of red- and green-colored InP-based QDs. Additionally, the stacking of each color QD film is achieved. The patterning process can be used to fabricate QD light-emitting diode devices without degrading their performance. This process can be used not only for thin (<100 nm) QD films, which are used in QD-LED devices, but also for thick (>1 μm) QD films, which can be used in the color-conversion layer with a backlight.

Investigating the Core Parameters to Fabricate V-Shaped Diffraction Grating via MA-P 1215 Positive Photoresist

In this study, the core deposition parameters for the MA-P1215 positive photoresist, namely; spin-coating speed, baking temperature and exposure fluence, have been investigated and optimized using a mask aligner, thermogravimetric and a spectroscopic ellipsometry. The optical properties, specifically, the refractive index n and extinction coefficient k for the films have been calculated via changing the fluence of the energy. The reduction in the thickness of the films with the increase in the spin-coater speed reflects the low viscosity of the MA-P photoresist. The relation between the weight reduction of the film via baking temperature and time reveals that the optimized baking temperature is 120 °C for 2 min, in which the weight of the film is reduced by 51%. We found that the values of both n and k depend on the exposure fluence. At small fluence values, both n and k decreased linearly with the increase in the wavelength. However, by increasing the fluence, the values of n and k became like those for silicon wafer, revealing that the developed film was totally removed. The contrast curve shows a decrease in the film thickness when the fluence of the exposure is increased, and the optimized fluence is found to be 35 mJ/cm2.

Stable electrospray signal on a microfabricated glass chip with three-dimensional open edge and tiered depth geometries

This paper presents the microfabrication and performance of a three-dimensional electrospray ionization (ESI) emitter tip made from glass, which achieves stable current signals important for chemical analysis. Our novel microfabrication process and custom-built signal conditioning hardware provides the advantage of providing accurate features and steady signals. The fabrication process relies on standard microfabrication techniques (i.e., deposition, photolithography, and wet etching). This fabrication method involves the novel application of two layers of positive and negative photoresists in addition to Parafilm® wax tape. Open edge and tiered depth details were successfully created from a multilayer planar mask. This is a benefit for integrated miniaturized and microfluidic systems that often require micro features for their functionality but relatively large millimeter size features for their physical periphery. We demonstrate the fundamental performance of electrospray with this microfluidic chip. The emitter tip was fixed on a linear axis stage with high resolution (10 μm) to finely control the tip distance from a metal counter electrode plate. A custom printed circuit board system was built to safely control four voltages applied to the microchip ports from a single high voltage power supply. To readily form the electrospray, non-aqueous solvents were used for their low viscosity and a constant voltage of +2.7 kV was applied to the sheath electrospray microchannel. The liquid being sprayed was 80/20 (v/v) methanol/acetonitrile with 0.1% acetic acid in the sheath microchannel and with ammonium acetate (10–40 mM) in its remaining microchannels. The electrospray signal was measured in response to varying the distance (1.4 to 1.6 mm) between the electrospray emitter tip and a metal counter electrode plate in addition to the varying concentration of the background electrolyte, ammonium acetate. Stable and repeatable electrospray signal showed linear relationships with emitter tip distance and concentration (r2 ≥ 0.95).

Abstract 3297: Deep reactive ion etched microneedle array for in-vivo melanoma cancer monitoring via cancer exosome isolation

Abstract This study reports a deep-reactive-ion-etched microneedle device (ExoNeedle chip) coated with a hybrid hydrogel that can directly capture cancer-associated extracellular vesicles (EVs) in interstitial fluid (ISF) in a minimally invasive manner, as opposed to conventional liquid biopsy methods involving sample extraction and EV isolation in-vitro or tissue biopsies for melanoma. Tumor derived EVs give insight into a tumor’s mutational burden and provide both prognostic and diagnostic value as a liquid biopsy tool. Melanoma is an aggressive cancer with a lack of promising markers for early detection, onset of metastasis, and monitoring of recurrence. The ExoNeedle chip is intended to pierce through the epidermis and parts of the dermis to isolate melanoma secreted EVs from the ISF to alleviate these unmet needs. The microneedle arrays were created through the Deep Reactive Ion Etching (DRIE) process and a subsequent wet etching step to sharpen the needles. A 4 inch silicon wafer spin coated with 3 microns of positive photoresist was lithographically patterned and etched by DRIE using the standard Bosch processes to expose arrays of cylindrical pillars. Next, the cylindrical features were sharpened using an isotropic wet etch consisting of a mixture of hydrofluoric and nitric acid. The microneedle arrays were made and cleaved into individual patches. Meanwhile, hybrid hydrogel solution was made from Polyvinyl alcohol (PVA) and alginate by dissolving each of them separately in water under heat, followed by mixing the solutions. After centrifuging and filtering the hydrogel, it was conjugated with Annexin V (Av) protein to give it affinity for cancerous exosomes. Lastly, this hydrogel complex was added onto the microneedle patches and gelated with the help of a humidifier that deposited Ca2+ ion vapor over the hydrogel. The microneedles were first optimized and validated using melanoma cell line secreted EVs. Melanoma EVs were successfully isolated and quantified to evaluate the efficacy of the microneedle patches yielding above an 80% capture efficiency from purified serum samples. The microneedle patches were DiO stained, fluorescently imaged, visualized in a scanning electron microscope, and protein concentration was determined respectfully. Additionally, the functional hydrogel coatings on the microneedles are dissolved in ethylenediaminetetraacetic acid (EDTA), subsequently unbinding EVs from Av due to EDTA-based Ca2+ chelation. The dissolved solution is then used for enumeration and quantification of EVs by nanoparticle tracking analysis. We are further validating these patches in skin mimicking models and patient derived xenograft models of melanoma. The technology developed in this study for the isolation of melanoma EVs can broadly pave the way for minimally invasive point of care cancer diagnostics and tracking for melanoma patients. Citation Format: Scott M. Smith, Abha Kumari, Thiago Reis, Yoon-Tae Kang, Sunitha Nagrath. Deep reactive ion etched microneedle array for in-vivo melanoma cancer monitoring via cancer exosome isolation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3297.

Biobased Epoxy Resin with Inherently Deep-UV Photodegradability for a Positive Photoresist and Anticounterfeiting

Biobased epoxy resins have received widespread attention due to their substitution for petroleum-based ones in conventional fields but are rarely reported in functional materials. Herein, a biobased epoxy resin with inherently deep-UV photodegradability was reported. The strategy was based on the [2 + 2] photocycloaddition of trans-cinnamic acid, a renewable resource, to generate a cyclobutane structure in the backbone, which was cleaved upon <280 nm light irradiation. The as-prepared epoxy resin showed high thermal stability and good thermomechanical properties. Meanwhile, owing to the ozonosphere blocking the UV light with a wavelength of <290 nm, the stability of this epoxy resin was guaranteed under a normal environment. When exposed to deep-UV light irradiation, degradation occurred. The degradation mechanism study demonstrated that molecular packing (crystalline/amorphism) was important in determining its degradability. Based on its photoresponsive features, the feasibility of this epoxy resin in the fields of a positive photoresist and anticounterfeiting was well explored. This work provides an attractive strategy for developing biobased epoxy resins to expand their potential application fields.

New Chemically Amplified Positive Photoresist with Phenolic Resin Modified by GMA and BOC Protection.

In this paper, a chemically amplified (CA) i-line photoresist system is described including a phenolic resin modified with glycidyl methacrylate (GMA) addition and protected with di-tert-butyl dicarbonate (BOC group), here called JB resin. JB resin with different degrees of BOC protection was synthesized and characterized with ultraviolet spectrophotometry, Fourier transform infrared spectroscopy and gel permeation chromatography. These resins were also evaluated in CA resists by formulating the JB resin with a photoacid generator (PAG) and tested at 405 nm and 365 nm exposure wavelengths. The BOC protection ratio at approximately 25 mol% of the Novolak phenol group showed the best performance. The resist showed high sensitivity (approximately 190 mJ/cm2), high resolution and good alkali developer resistance with reliable repeatability, indicating the great practical potential of this JB resist system.

Two-photon nanolithography of positive photoresist of AZ 5214E with a spatial resolution at nanoscale

The authors investigated two-photon nanolithography (TPNL) of positive AZ 5214E photoresist thin film with a spatial resolution at nanoscale. A continuous trench with average width of 101 nm was obtained, and a trench with several break points but feature width of 19 nm was fabricated by further increasing the scanning speed. Hole arrays composed of holes with diameters of about 451 nm and period of 800 nm were also fabricated with this photoresist. These results not only reveal that the TPNL of positive photoresist can obtain similar spatial resolution to that of negative photoresists, but also have extensive application prospection in fabrications of integrated circuits, microfluidic devices, surface-enhanced Raman scattering (SERS) substrates, catalyst, and biosensor substrates.

Two-photon shape-modulated maskless lithography of positive photoresist of S1813

The authors systematically investigated influence factors for two-photon maskless lithography of S1813 photoresist. A trench with a width of 155 nm, about 1/5 of the laser wavelength, was fabricated by accurate tuning the scanning speed. Two-photon shape-modulated maskless lithography, a method which employs different combined scanning and exposing approaches was proposed and studied. The patterns of rectangle, parallelogram, rice grain, arc, and “x” letter, and the quatrefoil hole patterns with different shape hearts, were all fabricated by using this method. This work is a protocol for lithography of S1813 photoresist with a high spatial resolution and flexibility. The fabricated trenches and diverse micro/nano patterns can be applied in the fabrication of integrated circuits, metamaterials structures, and SERS and biosensor substrates. This work will be conducive to the development and application of the two-photon maskless lithography of S1813.

Removal Analysis of Residual Photoresist Particles Based on Surface Topography Affected by Exposure Times of Ultraviolet and Developer Solution

Particle removal from the surface of a substrate has been an issue in numerous fields for a long time. In semiconductor processes, for instance, the formation of clean surfaces by removing photoresist (PR) must be followed in order to create neat patterns. Although PR removal has been intensively investigated recently, little is known about how ultraviolet (UV) and developer solutions alter the PR resin (and in what manner) near the surface. While varying the exposure times of UV and developer solution, we investigated the topographic changes on the surfaces of PR resin films and particles. The measured surface properties were then correlated with the detachment force determined using films, and eventually with the residual PR particle removal percentages obtained in a microchannel. Using a positive PR and a base developer solution, we demonstrated that UV causes the surface of PR resin to become hydrophilic and wavy, whereas the developer solution produces a surface with a larger degree of roughness by swelling and partially dissolving the resin. Ultimately, the increased roughness decreased the effective contact area between PR resins, hence decreasing the detachment force and increasing the particle removal percentages. We anticipate that our findings will help understand residual particle issues, particularly on the removal mechanism of PR resins based on surface topography.