Photoresist Materials Research Articles

64-1: Photolithographic Integration of High Performance Polymer Thin-Film Transistors

We demonstrate the development of organic semiconductor and passive material formulations optimized for photolithographic integration using existing photo-resist materials and technology. These materials can be coated and patterned to produce organic thin-film transistors suitable for integration into mass production processes with charge carrier mobility of greater than 2 cm2/Vs.

26-3: Scalability and Homogeneity of Slot-Die Coated Metal Oxide Semiconductor for TFTs

An indium oxide based precursor solution has been developed by spin-coating method. In order to apply this material to a mass production, material, process and equipment optimizations for slot die coating have been implemented. Slot die coating is a cost-effective, scalable process and already applied to photoresist materials in the display industry. The indium oxide based precursor solution has been coated on bare glasses and TFT substrates by a mass production type slot die coater. Mobility of over 10cm2/Vs is achieved for the first time for large area at annealing temperatures of 350°C. The homogeneity of the film will be presented.

Enhanced Lateral Ordering in Cylinder Forming PS-b-PMMA Block Copolymers Exploiting the Entrapped Solvent.

The self-assembly of block copolymer (BCP) thin films produces dense and ordered nanostructures. Their exploitation as templates for nanolithography requires the capability to control the lateral order of the nanodomains. Among a multiplicity of polymers, the widely studied all-organic polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) BCP can easily form nanodomains perpendicularly oriented with respect to the substrate, since the weakly unbalanced surface interactions are effectively neutralized by grafting to the substrate an appropriate poly(styrene-random-methyl methacrylate) P(S-r-MMA) random copolymer (RCP). This benefit along with the selective etching of the PMMA component and the chemical similarity with the standard photoresist materials deserved for PS-b-PMMA the role of BCP of choice for the technological implementation in nanolithography. This work demonstrates that the synergic effect of thermal annealing with the initial solvent naturally trapped in the basic RCP + BCP system after the deposition process can be exploited to enhance the lateral order. The solvent content embedded in the total RCP + BCP system can be tuned by changing the molecular weight and thus the thickness of the grafted RCP brush layer, without introducing external reservoirs or dedicated setup and/or systems. The appropriate supply of solvent supports a grain coarsening kinetics following a power law with a 1/3 growth exponent for standing hexagonally ordered cylinders.

Fabrication of Pt nanowires with a diffraction-unlimited feature size by high-threshold lithography

Although the nanoscale world can already be observed at a diffraction-unlimited resolution using far-field optical microscopy, to make the step from microscopy to lithography still requires a suitable photoresist material system. In this letter, we consider the threshold to be a region with a width characterized by the extreme feature size obtained using a Gaussian beam spot. By narrowing such a region through improvement of the threshold sensitization to intensity in a high-threshold material system, the minimal feature size becomes smaller. By using platinum as the negative photoresist, we demonstrate that high-threshold lithography can be used to fabricate nanowire arrays with a scalable resolution along the axial direction of the linewidth from the micro- to the nanoscale using a nanosecond-pulsed laser source with a wavelength λ0 = 1064 nm. The minimal feature size is only several nanometers (sub λ0/100). Compared with conventional polymer resist lithography, the advantages of high-threshold lithography are sharper pinpoints of laser intensity triggering the threshold response and also higher robustness allowing for large area exposure by a less-expensive nanosecond-pulsed laser.

Investigations on Photoresist-Based Artificial Dielectrics With Tall-Embedded Metal Grids and Their Resonator Antenna Application

Novel photoresist-based artificial bulk dielectrics with tall-embedded metal grids are investigated and their radiation characteristics are studied in detail. The embedded metal grid substantially increases (around six times) the effective permittivity of the low permittivity base photoresist material, and enables excitation with a simple direct microstrip feed to radiate effectively at frequencies similar to a high-permittivity dielectric resonator antenna (DRA). Moreover, the grid changes the near fields inside the resonator and introduces novel modes that are completely different than those of usual DRAs. A set of artificial resonator antennas is designed, lithographically fabricated, and measured to demonstrate the new modes resonating at 17 and 19 GHz with 2% and 6% bandwidth and 7.6 and 6.6 dB broadside gain, respectively, with suitable cross-polarization levels of better than $- {20}\;\text{dB}$ . These new modes do not appear simultaneously, and can be excited separately by varying the length of the microstrip feed.

Formation of nanometer-thick delaminated amorphous carbon layer by two-step plasma processing of methacrylate-based polymer

The authors show that extended He plasma pretreatment (PPT) of methacrylate-based 193 nm photoresist (PR) material in conjunction with a subsequent biased Ar plasma treatment can lead to blister formation at the polymer surface due to delamination of an ultrathin, ion-induced, dense, amorphous carbon (DAC) layer formed by low energy ion bombardment. For our experimental conditions, the delaminated layer is 1–2 nm thick and primarily composed of sp2-hybrized amorphous carbon. A He or Ar plasma process alone will not lead to this phenomenon, and so far the authors have only observed it for a methacrylate polymer. A possible mechanism of the formation of the ultrathin layer that is consistent with all observations is as follows: During He plasma pretreatment, volatile species are produced by ultraviolet/vacuum ultraviolet radiation-induced photolysis of the polymer pendant groups, e.g., adamantyl and chain-scissioning of the polymer backbone to a depth of greater than 100 nm. While volatile products formed close to the polymer surface can diffuse out during He PPT, those formed deep within the polymer bulk cannot and their concentration will become significant for extended He PPT. During the biased Ar plasma treatment step, a DAC surface layer is generated by Ar+ ion bombardment within the first seconds of plasma exposure. The thickness is dependent on ion energy and in the range of one to several nanometers. This layer appears to be impermeable to gaseous products formed in the PR material. Thus, volatile species diffusing to the surface can accumulate underneath the DAC layer, causing a loss of adhesion and subsequent delamination of this layer from the PR bulk film. The authors also report surface and electrical characterizations of the ultrathin DAC layer using optical microscopy, transmission electron microscopy, Raman and x-ray photoemission spectroscopy, and two-point probe techniques.

In situ SU-8 silver nanocomposites.

Nanocomposite materials containing metal nanoparticles are of considerable interest in photonics and optoelectronics applications. However, device fabrication of such materials always encounters the challenge of incorporation of preformed nanoparticles into photoresist materials. As a solution to this problem, an easy new method of fabricating silver nanocomposites by an in situ reduction of precursors within the epoxy-based photoresist SU-8 has been developed. AgNO3 dissolved in acetonitrile and mixed with the epoxy-based photoresist SU-8 forms silver nanoparticles primarily during the pre- and post-exposure soft bake steps at 95 °C. A further high-temperature treatment at 300 °C resulted in the formation of densely homogeneously distributed silver nanoparticles in the photoresist matrix. No particle growth or agglomeration of nanoparticles is observed at this point. The reported new in situ silver nanocomposite materials can be spin coated as homogeneous thin films and structured by using UV lithography. A resolution of 5 µm is achieved in the lithographic process. The UV exposure time is found to be independent of the nanoparticle concentration. The fabricated silver nanocomposites exhibit high plasmonic responses suitable for the development of new optoelectronic and optical sensing devices.

Studying the Mechanism of Hybrid Nanoparticle Photoresists: Effect of Particle Size on Photopatterning

Hf-based hybrid photoresist materials with three different organic ligands were prepared by a sol–gel-based method, and their patterning mechanism was investigated in detail. All hybrid nanoparticle resists are patternable using UV exposure. Their particle sizes show a dramatic increase from the initial 3–4 nm to submicron size after exposure, with no apparent inorganic content or thermal property change detected. XPS results showed that the mass percentage of the carboxylic group in the structure of nanoparticles decreased with increasing exposure duration. The particle coarsening sensitivities of those hybrid nanoparticles are consistent with their EUV performance. The current work provides an understanding for the development mechanism and future guidance for the design and processing of high performance resist materials for large-scale microelectronics device fabrication.

Monolithic, Crystalline MOF Coating: An Excellent Patterning and Photoresist Material

AbstractMetal–organic frameworks, MOFs, are a class of crystalline porous metal–organic hybrid materials which have originally been developed for applications in gas storage and separation. Here, we demonstrate that due to the enormous chemical flexibility of these molecular materials, they also provide an excellent basis for the development of photoresist materials. In particular, we used an epitaxial process with automated systems to grow either homogeneous or patterned SURMOFs (surface‐anchored MOFs) of the type [Zn2(N3BPDC)2(Dabco)] on different solid substrates. The huge flexibility of the MOF chemistry allowed for different variants of photolithography based on the post‐synthesis modification (PSM) of the MOF materials. Here, two particular and popular PSM‐strategies were employed, the azide–alkyne click reaction and thiol–yne click chemistry. The azide–alkyne click reaction was initiated by the photoreduction of CuII to the active CuI catalyst, whereas the thiol–yne click chemistry was induced directly by UV light. Furthermore, heteroepitaxial growth of multilayer systems (Cu‐N3BPDC+Cu‐BPDC+Cu‐N3BPDC+Cu‐BPDC+Cu‐N3BPDC+Cu‐BPDC) was also used to control the localization of subsequent PSM. The results demonstrated that the patterned functionalization of MOF thin film is not limited to the two dimensions of the mounting surface but is indeed possible in 3D.

Fabrication of a high-resolution mask by using variable-shaped electron beam lithography with a non-chemically amplified resist and a post-exposure bake

A high-resolution technique was developed for fabrication of photomasks for 10-nm-technology nodes and beyond. Current mask manufacturing techniques use a chemically amplified resist (CAR) photoresist material that has a complex mechanism of acid generation that obscures the criteria for selecting the polymer, quencher, and crosslinker for industrial purposes. It is therefore important to validate non-CAR materials as alternative solutions for mask fabrication. In this research, diluted ZEP520A was used as a non-CAR material in conjunction with a JBX9000 electron-beam lithography (EBL) tool. Additionally, a post-exposure bake (PEB) is normally used in mask fabrication. The PEB method was also used in this research, and we investigated its temperature dependence. Critical dimensions (CDs) of 1:1 line-and-space, isolated space, and isolated line patterns on a diluted ZEP520A resist were measured and showed CD shrinkage, an extension effect, and retention of the integrity of the shape after the PEB process. A resolution of the order of 20nm was attained and the insights gained from optimization of the PEB process might be usefully applied in advanced methods for fabricating masks of the next generation.

Photopolymers: Photoresist Materials, Processes, and Applications Kenichiro Nakamura

Photopolymers: Photoresist Materials, Processes, and Applications Kenichiro Nakamura

Synthesis of Epoxidised Silsesquioxane Polymer as Negative Photoresist in Photolithography Application

Epoxidised silsesquioxane (EPSQ) polymer was prepared by hydrosilylation process involving epoxy-disiloxane (EDS) and vinyl silsesquioxane (VSQ). They were characterised and analysed using Fourier Transformed Infrared (FTIR) and H-and Si-Nuclear Magnetic Resonance (NMR) spectroscopy. Pattern development was successfully performed affording well defined features of micron scale using suitable solvent developer. It was demonstrated that the feature definition was highly dependent on time of solvent dissolution and stirring rate. Optimization of several parameters such as resist thickness, pre-bake and post-bake time, ultra-violet (UV) intensity and exposure time are still required for the improved performance photo-resist material. However the results proved that the EPS can be potentially used as photoresist in photolithography application.

Fabrication of Cu–Zr–Ti thick film metallic glass structure by double metal mask lift-off process

In micro-electro-mechanical systems (MEMS) technology, one of the conventional patterning methods used for metallic thin films is the lift-off process using a photoresist material. However, there is concern regarding the photoresist material generating gas due to the long-term annealing or the high power used in sputter deposition. Thin-film amorphous alloys, such as thin-film metallic glass (TFMG), when used in the device, become crystallized by such heating and outgassing during sputtering. Unlike photoresist material, a metal mask does not generate gas during sputtering. However, a metal mask is subject to deformation by the stress in the sputtered film on the mask. The pattern shape of the TFMG structure can thus collapse due to this mask deformation. Its cross-sectional shape then deviates significantly from a rectangle. We propose a novel lift-off process using a double metal mask for reducing changes in the cross-sectional shape, and maintaining the amorphous nature of the TFMG structure. The characteristic of the double metal mask lift-off process is duplication of the metal mask for restraint of the lower metal mask deformation. Since nearly all of the sputtered material is deposited on the upper metal mask, the material is only minimally deposited onto the lower metal mask. In this work, the double metal mask lift-off process was compared with the conventional lift-off process, and important points for using the double metal mask lift-off process were elucidated. Using the double metal mask lift-off process, a very thick amorphous TFMG structure could be obtained, as compared to the conventional lift-off process. To maintain the rectangular cross-sectional shape of the structure, it was found to be necessary to decrease the height of the double metal mask, as compared to the conventional lift-off process, in anticipation of upper metal mask deformation.

ALA-induced fluorescence detection with photoresist-based microfluidic cell sorter for bladder cancer diagnosis

We present a photoresist-based microfluidic fluorescence-activated cell sorter (μFACS) for bladder cancer diagnosis and assess its potential for clinical application. In the developed μFACS system, bladder cancer cells in urine sediment are detected using aminolevulinic acid (ALA)-based fluorescence detection, and then sorted at the Y-junction of the microchannel using an off-chip pinch valve. Once cancer cells are collected, they can be analyzed using polymerase chain reaction (PCR) for detailed gene alteration analysis. Generally, time and cost-effective advantages of negative photoresist material and fabrication technologies have been widely pronounced; however, autofluorescence is a significant drawback when negative photoresist is used as a structural material for μFACS applications. To achieve sensitive fluorescence detection, autofluorescence in the detection area is minimized by thinning the photoresist cover layer of the microchannel and inclining the optical angle of the detection system. Through system calibrations and clinical tests using urine sediments, our experimental results demonstrate a combination of ALA-based photodynamic diagnostic tests using μFACS systems and subsequent PCR analysis is a promising diagnostic approach for bladder cancer.

High-speed optical recording in vitreous chalcogenide thin films

Thin films of glassy chalcogenide semiconductor are widely used as recording media in optical data storage. To obtain relief micro- and nanoscale structures on the surface of optical master discs inorganic photoresists based on chalcogenide glassy semiconductors can be used. They have high resolution and allow for exposure by short laser pulses. Implementation of such exposure is promoted by increasing the speed of photostructural transformations at high powers of exposing radiation. This increase in the sensitivity is associated with both local heating by illumination and a high density of excited electron-hole pairs. The exposure mode of the inorganic photoresists based on glassy chalcogenide semiconductor pulses of 10 -8 -10 -9 s is close to the threshold of local photothermal destruction. Significant impact on the value of the threshold of photothermal destruction effects the choice of the substrate material which determines the rate of heat removal from the irradiation area. Moreover, one also needs to consider the effect of pulsed annealing of the inorganic photoresist material on the process of selective etching. We have established an inversion of the selective etching of the inorganic negative photoresist based on As2S3 in the center of the irradiated zone. The diameter of this zone is about 20% of the diameter of exposing beam. After the selective etching in alkaline solution in the center of protrusions being formed on the substrate, there observed are some dimples with the depth of 30-50 nm. Prior to the processing of irradiated inorganic photoresist by the selective etching these dimples were absent and their appearance is not due to possible local material evaporation of the inorganic photoresist. A possible reason for the inversion of solubility of the inorganic photoresist could be pulsed annealing in the recording process.

IMS (Injection Molded Solder) Technology with Liquid Photoresist for Ultra Fine Pitch Bumping

IMS (injection molded solder) is an advanced solder bumping technology with solder alloy flexibility even at very fine pitch and small size. One of key materials for successful fine pitch bumping by IMS is a photoresist material. The photoresist material must be stable at high temperature during the IMS process and be perfectly stripped after the IMS process without any residue on the surface of the substrate. In this study, negative tone liquid photoresist materials were prepared to investigate effects of thermal cure of photoresist on IMS process and stripping performance. With appropriate cure conditions, successful bumping without any film damages at IMS process and any residue at stripping was achieved. Fine pitch bumping down to 40 μm pitch with 20 μm diameter was demonstrated with a Sn-3.0Ag-0.5Cu solder. Also physical and electrical connections for the solder joints of IMS bumps to Ni/Au pads were confirmed using a 80 μm pitch test vehicle.

A Polyurethane-Based Positive Photoresist.

Polyurethane (PU) monomer mixtures containing commercially available o-nitrobenzyl-based photocleavable monomers have been formulated and tested as low-cost positive tone photoresists. The photolysis reaction is studied by UV spectroscopy. Well-defined micropatterns on 2 μm thick photodegradable PU films are obtained using 365 nm light exposure. This strategy is also extended to improved formulations based on synthesized o-nitrobiphenylpropyl derivatives with enhanced photochemical properties for single photon excitation and high two-photon absorption cross-sections. Improved pattern resolution in 2D and the capability of 3D resolution using a scanning laser at 780 nm is demonstrated. This work demonstrates the potential of PUs as readily available, versatile, and easy-to-use photoresist materials for low-cost lithography applications.

Holograms recording with pulsed laser on diazonaphthoquinone-novolac-based photoresists and their nanocomposites

Direct write digital holography technique (DWDH) using a single 440-nm pulsed laser exposure has been proposed to record master holograms on commercially available positive-tone photoresist systems based on a mixture of diazonaphthoquinone and novolac resin (DNQ-novolac) of different thicknesses. The DNQ-novo- lac nanocomposite doped with copper nanoparticles (CuNPs) films was also used. The method for numerical evaluation of hologram quality based on reflected beam diffraction intensity measurements was proposed and verified. It was found that all investigated photoresist nanocomposites were sensitive enough to record holo- graphic structures at low single pulse laser exposures (from 3.3 to 18.0 mJ∕cm 2 ). Moreover, doping DNQ-novo- lac nanocomposite with CuNPs s increases its sensitivity to pulsed laser exposure by more than 30%. The potential of single pulsed laser exposures to record high quality master holograms on commercially available and metal nanoparticles doped photoresists with at least five times lower exposures values as compared to the continuous-wave laser exposures usually used to expose photoresist materials in holographic applications, opens the possibility to use pulsed lasers for quick master-originals origination for embossed holograms applying a DWDH technique or analog methods. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.53.9 .097101)

Advanced photoresist technologies by intricate molecular brush architectures: Diblock brush terpolymer‐based positive‐tone photoresist materials

The reported diblock brush terpolymer displays the fundamental advantages of high macromolecular and regiochemical control in simultaneous top-down/bottom-up construction of advanced positive-tone photoresist materials. By selective partition the substrate adhesion, surface-active migration, and chemically-reactive deblocking functional compositions into the cylindrical polymer brush architectures, large-areas of vertical alignment of the polymers within thin films are realized. The bottom-up premeditated system enables effective top-down lithography to produce near-molecular pixel resolution (2–3 molecules) at low operation dosage.

Emerging trends in precision fabrication of microapertures to support suspended lipid membranes for sensors, sequencing, and beyond

Suspended lipid membranes, also called black lipid membranes (BLMs), are an important model system that approximates the lipid bilayer environment of cell membranes. Increasingly, BLMs are utilized in sensing strategies that harness high sensitivity measurements of ion flux across the membrane, typically facilitated by ion channel proteins. BLMs are suspended across microapertures that connect two otherwise isolated fluidic compartments, and the precision fabrication of such microapertures can contribute to the stability and performance of the resulting BLM. Here, we highlight two emerging trends in the precision fabrication of microapertures for BLM formation: microfabrication in silicon-based thin film substrates, and microfabrication in the negative photoresist material SU-8. Four unique fabrication strategies are outlined, and we project the impact that these microfabrication strategies will have for BLM-integrated bioanalytical technologies.