Photoresist Film Research Articles

Comparison of the spatial statistics of random and defined-sequence photoresist films

Comparison of the spatial statistics of random and defined-sequence photoresist films

Effect of the initial viscosity and substrate corner geometry on edge beading of photoresist films

Effect of the initial viscosity and substrate corner geometry on edge beading of photoresist films

Relationship between the surface free energy of underlayers and the dissolution kinetics of poly(4-hydroxystyrene) partially protected by t-butoxycarbonyl groups in tetramethylammonium hydroxide aqueous developer

In the lithography used for the high-volume production of semiconductor devices, the photoresist film becomes thin with the reduction in pattern size to prevent the pattern collapse due to the surface tension of rinsing liquids. The interfacial effect becomes strong with the reduction in photoresist film thickness. In the development process, it is of importance to clarify the relationship between the photoresist and the underlayer for fine patterning. In this study, the dissolution kinetics of poly(4-hydroxystyrene) (PHS) partially protected by t-butoxycarbonyl (t-Boc) groups in tetramethylammonium hydroxide (TMAH) aqueous solution was found to be related to the surface free energy of the underlayer. The attenuation rate of developer viscosity first decreased and then increased with the polar-to-dispersion component ratio. An inflection point with the lowest rate existed. The TMAH concentration affected not only the attenuation rate but also the ratio of polar to dispersion components at the minimum attenuation rate.

Inkjet Printing Photoresist with Ultralow Viscosity on Silicon Wafers for Uniform Coating.

Inkjet printing is introduced into the photoresist coating process for uniform photoresist film formation on silicon wafers with the in-house inkjet experimental prototype. The optimization of a dual negative voltage waveform is proposed to achieve stable droplet jetting for the ultralow viscosity (0.71 mPa·s) photoresist with a 1:10 dilution ratio employed in the semiconductor packaging processes. Moreover, the maximum droplet jetting velocity can reach 9.51 m/s, and the droplet volume is controlled at ∼6.5 pL with excellent droplet concentration. The uniform film of the AZ P4620 photoresist is coated on silicon wafers by quantitatively exploring and optimizing the printhead driving frequency and movement velocity utilizing the droplet deposition model and experimental analysis. Results show that the optimal inkjet parameters with 5 kHz in jetting frequency and 6 mm/s in motion velocity can obtain a film evenness index of 4.81% with the thickness of 0.945 μm, which exhibits a more uniform photoresist film than the spray coating method. The study not only expands the application of the inkjet printing technique but also offers an alternative for photoresist coating in the photolithography process.

Fabrication of pyrolytic carbon interdigitated microelectrodes by maskless UV photolithography with epoxy-based photoresists SU-8 and mr-DWL

Maskless UV photolithography is increasingly used, especially in research environments where low turn-around time for new designs improves productivity. Here, we fabricate pyrolytic carbon interdigitated microelectrodes with small interelectrode gaps, good adhesion to the carrier substrate, high surface area and excellent electrochemical properties using maskless UV photolithography with two negative epoxy-based photoresists, namely the commonly used SU-8 and the recently developed mr-DWL. The minimum realizable trench width in 15 μm thick photoresist films is 2.4 ± 0.15 μm for mr-DWL 5 and 3.1 ± 0.10 μm for SU-8 2035. After pyrolysis, the two resulting pyrolytic carbon materials show similar electrochemical properties. However, shrinkage during pyrolysis is significantly lower for mr-DWL compared to SU-8, which is beneficial for the fabrication of interdigitated microelectrodes. Furthermore, delamination of the electrodes during processing and operation is prevented due to the introduction of poly silicon adhesion structures. This work provides valuable insights into maskless UV lithography as well as into the pyrolytic carbon process to increase the yield, performance and productivity for fabrication of microelectrodes.

Ultradurable Embedded Physically Unclonable Functions.

Physically unclonable functions (PUFs) have attracted growing interest for anticounterfeiting and authentication applications. The practical applications require durable PUFs made of robust materials. This study reports a practical strategy to generate extremely robust PUFs by embedding random features onto a substrate. The chaotic and low-cost electrohydrodynamic deposition process generates random polymeric features over a negative-tone photoresist film. These polymer features function as a conformal photomask, which protects the underlying photoresist from UV light, thereby enabling the generation of randomly positioned holes. Dry plasma etching of the substrate and removal of the photoresist result in the transfer of random features to the underlying silicon substrate. The matching of binary keys and features via different algorithms facilitates authentication of features. The embedded PUFs exhibit extreme levels of thermal (∼1000 °C) and mechanical stability that exceed the state of the art. The strength of this strategy emerges from the PUF generation directly on the substrate of interest, with stability that approaches the intrinsic properties of the underlying material. Benefiting from the materials and processes widely used in the semiconductor industry, this strategy shows strong promise for anticounterfeiting and device security applications.

A 3D nanoscale optical disk memory with petabit capacity.

High-capacity storage technologies are needed to meet our ever-growing data demands1,2. However, data centres based on major storage technologies such as semiconductor flash devices and hard disk drives have high energy burdens, high operation costs and short lifespans2,3. Optical data storage (ODS) presents a promising solution for cost-effective long-term archival data storage. Nonetheless, ODS has been limited by its low capacity and the challenge of increasing its areal density4,5. Here, to address these issues, we increase the capacity of ODS to the petabit level by extending the planar recording architecture to three dimensions with hundreds of layers, meanwhile breaking the optical diffraction limit barrier of the recorded spots. We develop an optical recording medium based on a photoresist film doped with aggregation-induced emission dye, which can be optically stimulated by femtosecond laser beams. This film is highly transparent and uniform, and the aggregation-induced emission phenomenon provides the storage mechanism. It can also be inhibited by another deactivating beam, resulting in a recording spot with a super-resolution scale. This technology makes it possible to achieve exabit-level storage by stacking nanoscale disks into arrays, which is essential in big data centres with limited space.

Adhesion of Electron-Irradiated Diazoquinone–Novolac Photoresist Films to Single-Crystal Silicon

Adhesion of Electron-Irradiated Diazoquinone–Novolac Photoresist Films to Single-Crystal Silicon

Flexible Manipulated Interference Lithography Incorporating Modulated Optical Fourier Transform System

AbstractSpatial‐variant micro/nano‐structures are widely utilized in metasurfaces to modulate optical wave‐fronts into arbitrary shapes, performing as a new generation of flat optics. To flexibly fabricate micro/nano‐structures in real time, an optical Fourier transform system modulated by a diaphragm and a binary optical element (BOE) is proposed. Theoretical analysis shows that light field at image plane is a multiple result of twice Fourier transform of diaphragm and BOE's transmission field, with its amplitude and phase distribution independently manipulated by diaphragm and BOE. Inversely, diaphragm and BOE can be designed to get customized interference fields, where four fields with different vectors are generated for instance. Utilizing these four fields for time division multiplexing exposure, fringes inside circle/ring shapes with variant orientations are produced in photoresist film. Furthermore, multiple spatial variant fields can be obtained simultaneously while more symmetric distributed apertures acted as diaphragm, which shows great potential for the fabrication of segmented or interleaved spatial‐variant micro/nano‐structures in addition.

Вплив тонких плівок Se на ефективність збудження поверхневих плазмон-поляритонів в срібних та алюмінієвих голографічних решітках

In this paper, we study the effect of thin selenium layers up to 3 nm thick on the efficiency of excitation of surface plasmon polaritons (SPPs). The Se layers were deposited by thermal evaporation in vacuum on the surface of silver and aluminum gratings. Gratings with a groove profile close to sinusoidal and a period equal to а = 694 nm were formed on chalcogenide photoresist films using interference lithography. Then they were coated with layers of the above metals with a thickness of 80–85 nm using thermal evaporation. Registration of SPP excitation on the gratings was carried out by measuring the angular dependences of the intensity of specularly reflected or diffracted p-polarized He-Ne laser radiation on a stand mounted on the basis of a G5M goniometer and a Fedorov table. An atomic force microscope was used to determine the shape of the groove profile and the depth of the grating relief. It has been found that for silver gratings with a relief modulation depth h/a less than the optimal value (which ensures maximum plasmon absorption, i.e., the maximum efficiency of SPP excitation), selenium deposition causes significant degradation of the plasmon resonance: a decrease in the depth of the minimum of the total reflection Rpt (i.e., a decrease in the efficiency of plasmon absorption), a shift of the Rpt minimum towards larger angles, and its widering. For silver gratings with h/a greater than the optimal value, a similar shift and widering of the plasmon resonance is also observed. However, at the same time, a significant deepening of the Rpt minimum is recorded, that is, an increase in the efficiency of SPP excitation. Such changes in the plasmon characteristics also appear on aluminum gratings, however, in this case the effect of the selenium layers is weaker by an order of magnitude. The obtained results allow us to propose a method of correcting the plasmonic characteristics of silver gratings in which the value of h/a is higher than optimal.

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

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

Pyrolyzed photoresist thin film: Effect of electron beam patterning on DC and THz conductivity

Pyrolyzed photoresist films (PPFs), which are formed via vacuum annealing of a photoresist without a catalyst, can be employed for fabrication of graphitic nanostructures by using conventional lithographic techniques. Such approach allows for reduction of technological steps required for fabrication of conductive micro- and nanoelectrodes for different applications. However, the operation frequency range of PPF electrodes is still unknown. Here, we report the results of the comparative study of PPF structures fabricated by electron beam lithography prior and after the annealing process with preference to the first approach. By performing the comparative measurements of PPF transport properties we found that both pre-and post-processed PPFs possess the same conductivities at dc-current and in the frequency range from 0.2 to 1.5 THz. Moreover, we achieved the sheet resistance of 150 nm thick PPFs as low as 570 Ω/sq, which is comparable to that of commercially available chemical vapour deposited (CVD) graphene. These findings open a path for a simple, reproducible and scalable fabrication of graphitic nanocircuits, nanoresonators and passive components suitable for applications in frequencies up to few terahertz.

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.

STRENGTH PROPERTIES OF ELECTRON IRRADIATED FILMS OF NEGATIVE NOVOLAC
 PHOTORESISTS ON MONOCRYSTALLINE SILICON

The adhesive and strength properties of electron-irradiated NFR 016D4 photoresist films for explosive lithography
 deposited on the surface of KDB-10 single-crystalline silicon wafers by centrifugation have been studied.
 It has been experimentally established that electron irradiation leads to warping and partial detachment of the
 NFR 016D4 photoresist film from the silicon substrate. Irradiated photoresist films behave like brittle materials.
 A significant decrease in crack resistance and adhesion to the silicon substrate of irradiated photoresist films was
 observed. caused by radiation-induced processes at the photoresist/silicon interface.

Enhanced Removal of Photoresist Films through Swelling and Dewetting Using Pluronic Surfactants.

Organic photoresist coatings, primarily composed of resins, are commonly used in the electronics industry to protect inorganic underlayers. Conventional photoresist strippers, such as amine-type agents, have shown high removal performance but led to environmental impact and substrate corrosiveness. Therefore, this trade-off must be addressed. In this study, we characterized the removal mechanism of a photoresist film using a nonionic triblock Pluronic surfactant [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] in a ternary mixture of ethylene carbonate (EC), propylene carbonate (PC), and water. In particular, the removal dynamics determined by using a quartz crystal microbalance with dissipation monitoring was compared with those determined by performing confocal laser scanning microscopy and visual observation to analyze the morphology, adsorption mass, and viscoelasticity of the photoresist film. In the absence of the Pluronic surfactant, the photoresist film in the ternary solvent exhibited a three-step process: (i) film swelling caused by the penetration of a good solvent (EC and PC), (ii) formation of photoresist particles through dewetting, and (iii) particle aggregation on the substrate. This result was correlated to the Hansen solubility parameters. The addition of the Pluronic surfactant not only prevented photoresist aggregation in the third step but also promoted desorption from the substrate. This effect was dependent on the concentration of the Pluronic surfactant, which influenced diffusion to the interface between the photoresist and the bulk solution. Finally, we proposed a novel photoresist stripping mechanism based on the synergy between dewetting driven by an EC/PC-to-water mixture and adsorption by the Pluronic surfactant.

Self-organized submicron structures in photoresist films by UV-laser irradiation at water-confined conditions

A new kind of self-organized pattern formation process has been found during laser irradiation of polymer films in water confinement just below the laser ablation threshold, resulting in a randomly oriented pattern with a period of about 475 nm. The morphology, orientation, period, and amplitude of these patterns are inconsistent with both laser-induced periodic surface structures that typically consist of linear grooves with periods smaller the laser wavelength and wrinkling patterns that feature a much larger period and appear at layered systems. Excimer laser (λ = 248 nm, tp = 25 ns) exposure of 650 nm thick photoresist films on silicon wafers cause the growth of irregular submicron patterns. The pattern morphology that is examined with imaging techniques is correlated to processing parameters. The amplitude of these laser-induced self-organized (LISE) submicron structures are strengthened with pulse number and laser fluence. The experimental results are discussed together with simulations of laser heating the photoresist film in water confinement. The proposed pattern formation mechanism of such laser-induced self-organized submicron structures at temporal excitation of a confined polymer surface comprises the formation of an oriented roughness based on LIPSS that are developed to wrinkled structures due to the transient formation of a soft subsurface area that provides conditions for wrinkling of the water cooled, stiff polymer surface by laser-induced stress fields. Size, amplitude, and morphology of the LISE pattern provide good properties for applications in such fields as wetting, friction, optics, and bioactivity.

Multiple-beam colloidal quantum dot lasers in a waveguide-grating-waveguide microcavity

In this work, multiple-beam colloidal quantum dot lasers are achieved in a double waveguide-grating (waveguide-grating-waveguide, W-G-W) microcavity. The grating is fabricated simply using interference lithography, and CdSe/CdS/ZnS colloidal quantum dots (CQDs) are spin-coated as the gain to form an active waveguide-grating structure. The photoresist film, which is not completely etched to the bottom, provides another waveguide-grating structure. In the W-G-W structure, low-threshold multiple-beam laser output is realized under optical pumping with emission peaks at 664.6 and 645.2 nm. The oblique laser is derived from a quasi-propagation mode. The thresholds of the two laser modes are 22.7 and 28.3 μJ/cm2, respectively, and both laser modes are TE0 modes. In addition, the emission wavelengths of the two modes of the designed distributed feedback laser can be flexibly tuned by changing the thickness of the CQDs' waveguide layer. The presence of quasi-propagation modes provides another method for designing compact laser sources, which could help in the design of wireless communication networks, hyperspectral 3D sensing, and color laser displays.

Mean Free Path of Electrons in Organic Photoresists for Extreme Ultraviolet Lithography in the Kinetic Energy Range 20-450 eV.

The blur caused by the nonzero mean free path of electrons in photoresists exposed by extreme ultraviolet lithography has detrimental consequences on patterning resolution, but its effect is difficult to quantify experimentally. So far, most mean free path calculations use the dielectric formalism, which is an approximation valid in the optical limit and fails at low kinetic energy. In this work, we used a modified substrate-overlayer technique that exploited the attenuation of the Si 2p core level originating specifically from the native silicon dioxide to evaluate the attenuation of electrons traveling through 2 and 4 nm of photoresist overlayers to provide a close estimation of the inelastic mean free path relevant for photoresist lithography patterning and for electron microscopy. The photoemission spectra were collected in the proximity of the Si 2p edge (binding energy ∼101 eV) using synchrotron light of energy ℏω ranging between 120 and 550 eV. The photoresist films were prototypical chemically amplified resists based on organic copolymer of poly hydroxystyrene and tertbutyl methacrylate with and without triphenyl sulfonium perfluoro-1-butanesufonate photoacid generator and trioctylamine quencher. The inelastic mean free path of electrons, in the range that is relevant for photoresist exposure in extreme ultraviolet lithography (20-92 eV), was found to be between 1 and 2 nm. At higher kinetic energy, the mean free path increased, consistently with the well-known behavior. The presence of the photoacid generator and quencher did not change the mean free path, within experimental error. Our results are discussed and compared with the existing literature on organic molecules measured via dielectric formalism and electron transmission experiments.

Design and fabrication of patterned high performance quantum-dot color conversion films for μLED full color display applications

The fabrication and performance of patterned quantum dot color conversion films are of great significance for μLED full color displays. In this work, TiO2 nanoparticles was designed and introduced to mix with quantum dots (QDs) as well as photoresist polymer to prepare the patterned quantum-dot photoresist (QDPR) films using direct photolithography, and to improve the color conversion efficiency (CCE) of QDPR. The results show that uniform QDPR films with controllable thickness and size could be achieved by optimizing the photolithography process parameters, whose minimum dimension can reach 12 μm. And the maximum CCE of patterned QDPR films was up to 67.46% with the thickness of only 4.28 μm. In addition, distributed Bragg reflector (DBR) and black matrix (BM) were employed to regulate the outgoing light and reduce the optical crosstalk, respectively. A color conversion device using a blue μLED and the QDPR films incorporated with DBR and BM have been demonstrated, with the color gamut of 120.53% NTSC, exhibiting the potential application for the next-generation high resolution full-color displays.

INDENTATION OF ELECTRON-IRRAUDED FILMS OF DIAZOQUINONE NOVOLAC
 PHOTORESISTS ON SILICONE

The strength properties of FP9120, SPR 700 and S1813 G2 SP15 diazoquinone novolac photoresist films
 on silicon irradiated by 5 MeV electrons with a fluence of 3 1016 cm-2 were studied by indentation. Misprints of
 the microindenter in films of diazaquinone novolac photoresist are barrel-shaped, which indicates the presence
 of tensile stresses that form during film drying. A destruction zone with radial and lateral cracks was observed
 around the indenter prints, forming a pattern in the form of "butterflies". It has been established that during longterm
 storage and irradiation of films of diazoquinone novolac photoresists, an increase in the values of the true
 microhardness of the films takes place, which is due to the cross-linking of novolac macromolecules in the bulk
 of the polymer.