Photoresist Materials Research Articles

Reconstructing the three-dimensional latent image of extreme ultraviolet resists with resonant soft x-ray scattering

Extreme ultraviolet (EUV) lithography is one of the most promising printing techniques for high-volume semiconductor manufacturing at the 14-nm half-pitch device node and beyond. However, key challenges around EUV photoresist materials, such as the exposure-dose sensitivity or the line-width roughness, continue to impede its full adoption into industrial nanofab facilities. Metrology tools are required to address these challenges by helping to assess the impact of the EUV materials’ properties and processing conditions along different steps of the nanofabrication process. We apply the resonant soft x-ray scattering (RSoXS) technique to gain insights into the structure of patterned EUV resists before the development step takes place. By using energies around the carbon K-edge to take advantage of small differences in chemistry, the electronic density contrast between the exposed and unexposed regions of the resists could be enhanced in order to image the patterns with subnanometer precision. Critical-dimension grazing-incidence small-angle x-ray scattering is then performed at energies where the contrast is maximized, enabling the reconstruction of the three-dimensional shape of the latent image. We demonstrate the potential of RSoXS to provide a high-resolution height-sensitive profile of patterned EUV resists, which will help in quantifying the evolution of critical features, such as the line-edge roughness, at a key step of the nanofabrication process.

Evolution of photoresist layer structure and surface morphology under fluorocarbon‐based plasma exposure

AbstractIon bombardment of photoresist materials during plasma etching results in the formation of a surface dense amorphous carbon (DAC) layer that contributes to both etch resistance and the development of surface roughness. Real‐time ellipsometric measurements/analysis reveals that a C4F8‐containing plasma interacts with an Ar‐plasma‐formed DAC layer to produce a modified DAC/fluorocarbon (FC) layer by FC deposition/diffusion of fluorine into the surface. The depletion of the DAC layer via modification and ion bombardment causes the etch rate of the bulk layer to increase. As the modified surface layer is formed, a noticeable decrease in surface roughness decrease is observed. These findings provide an understanding of the mechanisms of atomic layer etching processes in photoresist materials.

Preparation of a Water-Based Photoreactive Azosulphonate-Doped Poly(Vinyl Alcohol) and the Investigation of Its UV Response.

Two different azosulphonate dyes were synthesised and purified for the preparation of a water-based photoreactive azosulphonate-doped poly(vinyl alcohol). The aim was the investigation of a novel azosulphonate-poly(vinyl alcohol) photoresist with decreased water solubility after illumination, setting a focus on environmentally benign substances. The electron distribution of the aromatic rings of the two different azosulphonate molecules were changed by the UV-induced cleavage of the –N=N–SO3− groups, which was evidenced by UV spectroscopy. The formation of ester groups was detected by Fourier-transform infrared and 13C nuclear magnetic resonance spectroscopy. UV–Vis spectroscopy was used to investigate the photoreactivity of the prepared films. Photolithographic experiments demonstrated the applicability of these newly produced materials as photoresist materials. In addition, these materials provide high thermal stability.

Femtosecond Laser Microfabricated Microfilters for Particle–Liquid Separation in a Microfluidic Chip

A novel cross-flow based particle sorter is proposed and demonstrated in this study. The filtration structures consist of two groups of micropillars that are fabricated with photoresist material SU-8 using the femtosecond laser induced two-photon polymerization (TPP) technique. Particles can be separated according to the slit sizes of the micropillars. The distributions of flow velocity and particle trajectories in filters of different lengths are simulated with the COMSOL software. The particle sorting efficiencies are calculated and compared. The microfluidic sorter chip is tested with a fluid consisting of mixed microbeads with diameters of 10 μm and 5 μm. The performance of the sorter developed in this study demonstrates its effectiveness and efficiency in sorting particles in a fluid. Furthermore, the femtosecond laser induced TPP microfabrication technique enables the fabrication of customized microstructures with a high degree of integration and low fabrication cost, promising for various biological, chemical, and environmental applications.

Directly written photo-crosslinked fluorinated polycarbonate photoresist materials for second-order nonlinear optical (NLO) applications

With AF-Z-PC MAs and AF-Ali-PC MAs as the functional layer, we successfully obtained straight and Y structure waveguides by a direct writing method for electro-optical modulator devices.

Flexible TEG Using Amorphous InGaZnO Thin Film

We have demonstrated flexible thermoelectric generators (TEGs) using transverse type structure with amorphous InGaZnO/Mo and amorphous InGaZnO/ITO materials. The amorphous-InGaZnO (a-IGZO) film has advantages such as its low thermal conductivity and relatively high carrier mobility. Additionally, the a-IGZO film can form on a flexible substrate using a low temperature fabrication process. The a-IGZO thin films were deposited at room temperature by RF magnetron sputtering on PEN substrate. The thin film TEG can create a temperature difference in the in-plane lateral direction by using a heat guide. For the heat guide, polymer photoresist material (KMPR 1035) was spin-coated and patterned using the standard photolithography process. Metal masks were used for all the deposition steps. A total of 676 a-IGZO/metal paired cells were connected in series. Temperature difference was applied between the heat guide and the back side of the substrate, and it was confirmed that both temperature difference and Seebeck voltage were generated in the IGZO cell. We have shown that the transparent and flexible TEG on PEN substrate can be fabricated using a-IGZO with the standard fabrication process.

Photoresist materials comprising photobase generators and epoxy resins bearing carboxylic acids to lead to marked enhancement of base‐catalyzed cross‐linking reactions

Most of the photopatterning materials based on epoxy resins utilize photoacid generators (PAGs), which generate superacids as catalysts. They have been used for high aspect ratio photoresists in the fabrication of MEMS devices. However, there is a drawback, in that the acidic species from PAGs will induce metal corrosion. One of the approaches to overcome this problem is the use of photobase generators (PBGs) because organic bases would induce no corrosion. Although there have been many previous investigations of PBGs, only a few articles have mentioned photoreactive materials relying on PBGs because of their low photosensitivity. We report here highly sensitive photopatterning materials comprising PBGs and an epoxy resin bearing carboxylic acid groups. As a result, the photopatterning materials showed higher photosensitivity than conventional epoxy resin systems. We obtained high‐photosensitivity (up to 900 mJ/cm2), high‐resolution (10‐μm line‐and‐space) patterning materials in films, 10 μm in thickness.

Relative importance of various stochastic terms and EUV patterning

An error propagation stochastic model is described and used to study the impact of both photon and photoresist material sources of line-width roughness (LWR). Based on typical chemically amplified resist parameters, material sources of LWR are shown to be of equal importance to photon sources. Of the material sources, quencher is shown to be the most important input noise term. The results show that it is not the relative quencher noise that ultimately matters but rather the absolute quencher noise relative to the mean produced acid count. The results also show that chemical yield is critical and that benefiting from increased absorptivity also requires the chemical yield to be maintained.

An Efficient Spraying Method with Cyclodextrine‐drived Aqueous Stripper for Removing of Organic Photoresist on Indium Tin Oxide Surface

The chemical mechanism of inducing polymer breakage in a photoresist layer plays an important role in the photoresist removal from an indium tin oxide substrate. The spray structure for delivering the relevant functional material is involved in the process of binding and dissolving the PR (photoresist) material. This presents an efficient spraying process of removing the photoresist layer formed on a 260‐nm‐thick indium tin oxide substrate with a CD (cyclodextrine)‐drived aqueous stripper, simultaneously implementing proper mass transfer and heat transfer. It was taken to achieve an economical stripper consumption management by limiting the modified Weber number to 200 and the spray distance to 100 mm. As a result, stable removal performance was achieved, with optical and electric properties varying within the range of 1%, in CD drived aqueous stripping conditions (water content of the stripper composition ≤71%, stripper temperature = 40°C, and stripping time = 40 s).

(Invited) The Mechanism of Surface Modifications of Photoresist Material in Plasma Etching Nano Processes

Etching plasmas employed for the fabrication of ultra large scale integrated circuits (ULSIs) have been causing serious damages to photoresist materials such as surface roughness formations and structural changes. So far, there have been many reports on suppressing these damages by some process techniques such as the UV, HBr plasma cure and so on. However, effects of individual species and photons in the plasma on the damages of photoresist materials have not been clarified enough. Especially, the effect of vacuum ultraviolet (VUV) photons on damages have never been quantitatively understood. Furthermore, beside the VUV photons, the synergetic effects of individual species of ion and radicals enhance the damages. As a result, the chemical structure alteration and the surface roughness formation of polymer materials are considered to be brought about. In the fabrication of the sub-45 nm devices and integrated circuits, it is extremely important to clarify the reaction mechanism of surface modification of photoresist materials induced by the plasma etching process. In this article, firstly, we have focused on the effects of VUV photons on damages on the 193 ArF photoresist materials by investigating the absolute density of VUV photon fluxes measured in the range of 115nm and 200nm in HBr plasma etching processes. The etching and measurement of VUV photons in the plasma were performed in the plasma beam system for understanding the fundamental reaction on the photoresists. This plasma beam system consists of an upper chamber (plasma chamber) and a lower chamber (process chamber). This equipment provided the beam source with the HBr plasma. The plasma beam system was pumped down to a base pressure of 10-5 Pa prior to the experiment. During the whole experiment, inductively coupled plasma (ICP) was generated by applying a radio-frequency (13.56 MHz) power of 400 W to the low-impedance antenna. Pure HBr, H2 or Ar gas was introduced into the plasma chamber at a flow rate of 1 sccm. The pressure of the plasma chamber was maintained at approximately 5 Pa. The chemical compositions of the surface of photoresists before and after the plasma beam irradiation were analyzed by in-situ XPS. On the basis of measured results, effects by VUV photons emitted from HBr on the surface modifications of photoresist materials were clarified. The VUV photons cleaved the MAA groups below the photon dosage of 16 × 1016 photons/cm2. The crosslinking of the photoresist and release of volatile products simultaneously generated the surface roughness. The reaction became saturated with high dosages [1]. Secondary, the sequential irradiation by VUV/radicals from HBr or H2 plasma and Ar ions on a photoresist have been performed. The irradiation by VUV and radicals before the ion irradiation (pre-treatment) suppressed the roughness increase by the ion bombardment but the VUV and radical irradiation after the ion irradiation (post-treatment) increased the roughness. The surface morphologies were also analyzed in detail after pre- or post-treatment on the photoresist by using the power spectral density. Such pre-treatment processes generated a dense and hard crosslinked layers which improved the etch resistance of the photoresist and improved the roughness [2]. The enhancement of roughness by post-treatment was correlated with the removal of the MAA groups and the nonuniformity of crosslinking reactions on the roughened photoresist by the ion irradiation. On the basis of these results, the mechanism of photoresist modifications by individual effects of VUV, ions and radicals and their synergetic effects by sequential irradiation experiments were systematically discussed and then perspectives for the damage less processes to be established in the etching nano processes are introduced. [1] Y. Zhang et al., Journal of Vacuum Science & Technology A, 35, 060606 (2017). [2] Y. Zhang et al., Japanese Journal of Applied Physics, 56, 126503 (2017).

Megasonic Enhanced Photo Resist Removal Using Unique Solvent Free Phase-Fluids on an Advanced Single Wafer Resist Processing System

Removal of photoresist materials (resist stripping) is very straightforward in theory, but can be difficult and complicated in practice. Classical methods have included SPM (sulfuric peroxide module) /piranha, ozone and UV ozone, solvent based fluids and plasmas. All of the legacy methods include hazardous and toxic materials and/or high equipment expense as well as multi-step complexity. The stripping process becomes even more challenging by factors such as thick resist, cross-linked resist or sensitive metals or materials under the resist. This study was carried out In order to determine feasibility of the use of a unique phase-fluid based photoresist-stripper in commercial semiconductor resist removal process steps. Due to their highly dynamic inner structure, phase-fluids penetrate into the polymer network of photoresists and lift the material from the surface. As these water-based stripping fluids are non-aggressive, non-toxic, and require no special handling, the ability to apply them to industry standard resists will result in a reduction of toxic and dangerous chemistries and the environmental impact of their disposal. To investigate the impact of megasonic energy on the process time in both the active and rinse steps and therefore throughput, the study included the introduction of megasonics as a process variable in all test combinations. The study was broken down into two phases. Phase one consisted of a broad spectrum screening process incorporating nine standard photoresists Fig. 1 with various standard thermal treatments as well as a selection of five phase-fluid formulations. The tests were carried out in a single substrate stagnant immersion tank incorporating a megasonic transducer illustrated in Fig. 2. Process time was defined as the time from immersion of the substrate until the photoresist was completely removed. Process variables tested for each resist/phase-fluid combination included three process temperatures, ambient, 40c and 60c as well as the addition of megasonic energy at ambient with a frequency of 925KHz at a dosage of 1.5W/cm2 directly coupled. The results achieved in this phase one screening were used to select the best case phase-fluid, and process conditions for each of the screened photo resists. These conditions became the baseline parameters for phase two. Phase two of the study was carried out in actual single wafer production conditions on an EVG®100 Series Resist Processor equipped with a MegPie® large area megasonic transducer. Process recipes were established using phase one parameters and then refined for optimum total process time, including the actual phase-fluid process time and rinse time. Spin off and dry cycles were kept constant in all process recipes. Complete resist strip process times of <20 seconds were achieved with several photoresist phase fluid combinations while other combinations involving BCB based resist resulted in little to no removal. The results achieved in phase two testing demonstrate the feasibility of a phase-fluid based photo resist strip in a single wafer platform with megasonic enhancement for specific photo resists. Figure 1

Comprehensive Simulations for Ultraviolet Lithography Process of Thick SU-8 Photoresist.

Thick SU-8 photoresist has been a popular photoresist material to fabricate various mechanical, biological, and chemical devices for many years. The accuracy and precision of the ultraviolet (UV) lithography process of thick SU-8 depend on key parameters in the set-up, the material properties of the SU-8 resist, and the thickness of the resist structure. As feature sizes get smaller and pattern complexity increases, accurate control and efficient optimization of the lithography process are significantly expected. Numerical simulations can be employed to improve understanding and process design of the SU-8 lithography, thereby allowing rapid related product and process development. A typical comprehensive lithography of UV lithography of thick SU-8 includes aerial image simulation, exposure simulation, post-exposure bake (PEB) simulation, and development simulation, and this article presents an overview of the essential aspects in the comprehensive simulation. At first, models for the lithography process of the SU-8 are discussed. Then, main algorithms for etching surface evolvement, including the string, ray tracing, cellular automaton, and fast marching algorithms, are introduced and compared with each other in terms of performance. After that, some simulation results of the UV lithography process of the SU-8 are presented, demonstrating the promising potential and efficiency of the simulation technology. Finally, a prospect is discussed for some open questions in three-dimensional (3D) comprehensive simulation of the UV lithography of the SU-8.

Ab initio photodynamics of model EUV photoresists

Tin-oxo cages belong to a class of organometallic compounds which were recently recognized as promising photoresist materials for the extreme ultraviolet (EUV) lithography – a method proposed for the new generation of integrated circuits. The EUV exposure of tin-oxo cages causes significant structural changes; however, the molecular mechanism of these changes is to a large extent unknown. In the present work, we focus on the photoionization dynamics of the small tin-oxo molecules: the trimethlytin hydroxide (TMTH) and trihydroxymethyl stannane (THMS) molecules. We employed the surface hopping (SH) dynamics on the Floating Occupation Molecular Orbital Complete Active Space Configuration Interaction (FOMO-CASCI) potential energy surfaces accelerated with graphical processor units (GPU). After the ionization of both molecules, we observed an ultrafast relaxation (∼100 fs) into the ground and first excited electronic states followed by a rapid dissociation yielding the neutral CH3 and OH radicals and a charged remainder. However, the dissociation dynamic does not occur solely on the hot ground electronic state and reaction outcome partially depends on initially ionized state. Our work also demonstrate that the SH+FOMO-CASSCI based dynamics is suitable for electron-rich open-shell systems.

Control of optical nanometer gap shapes made via standard lithography using atomic layer deposition

Atomic layer deposition is an efficient method for coating a few nanometer-thick alumina over a wafer scale. This method combined with the standard photolithography process was presented to fabricate metallic nanometer gaps that optically act in terahertz regimes. However, the cross-sectional view of the gap shape of the metal–insulator–metal nanogap structure varies depending on the conditions from the stepwise procedure. In specific, selecting photoresist materials, adding ion milling and chemical etching processes, and varying metal thicknesses and substrates result in various optical gap widths and shapes. Since the cross-sectional gap shape affects the field enhancement of the funneled electromagnetic waves via the nanogap, the control of tailoring the gap shape is necessary. Thus, we present five different versions of fabricating quadrangle-ring-shaped nanometer gap arrays with varying different kinds of outcomes. We foresee the usage of the suggested category for specific applications.

Ultraviolet Sensor Performance of Nanostructured LaCoO3 Prepared by the Solution-Polymerization Method

LaCoO3 is a p-type semiconductor material with bandgap of ~2.2 eV, which compared with those reported for TiO2 and ZnO (3.2 and 3.3 eV, respectively) make this material a potential candidate for detecting UV radiation. In this work nanostructured LaCoO3 was prepared by the solution-polymerization method, using polyvinyl alcohol as polymerizing agent. The morphology of the powder calcined at 700°C corresponds to nanostructured sheets having abundant porosity. Thick films were prepared by a simple deposition method using a suspension of the powder. The detection of UV (λ = 365 nm) showed a uniform response pattern. When the optical irradiance was varied the results revealed a quantitative detection. Analogous results were obtained using light of larger λ. In conclusion, LaCoO3 may be used as an alternative UV detector material to prevent skin cancer and as photoresistive material for solar photocells, among others.

Maskless Lithography Using Negative Photoresist Material: Impact of UV Laser Intensity on the Cured Line Width

The application of maskless lithography technique on negative photoresist material is investigated in this study. The equipment used in this work is designed and built especially for maskless lithography applications. The UV laser of 405 nm wavelength with 0.85 Numerical Aperture is selected for direct laser writing. All the samples are prepared on a glass substrate. Samples are tested at different UV laser intensities and different stage velocities in order to study the impact on patterned line width. Three cases of spin coated layers of thickness 90 μm, 40 μm, and 28 μm on the substrate are studied. The experimental results show that line width has a generally increasing trend with intensity. However, a decreasing trend was observed for increasing velocity. The overall performance shows that the mr-DWL material is suitable for direct laser writing systems.

Chemical and Molecular Variations in Commercial Epoxide Photoresists for X-ray Lithography

The quality of high aspect ratio microstructures fabricated by deep X-ray lithography is highly dependent on the photoresist material used and the process parameters applied. Even with photoresists more suitable to this process, it is common to face defects in the final optical components, such as in case of X-ray gratings. The gratings need to be fabricated with critical dimensions on a sub-micrometer and micrometer scale, with periods of few micrometers and heights of hundreds of micrometers to be used in X-ray imaging techniques such as Talbot–Lau Interferometry. During the fabrication process, these features lead to challenges such as mechanical stability, homogeneity, and defect-free grating patterns. Usually, an epoxy-based negative photoresist is used in X-ray lithography, which needs to account for the shrinkage that takes place during polymer crosslinking in order to avoid defects in the final pattern. Nowadays, photoresist material still lacks certain suitable properties (chemical and mechanical) to fabricate gratings of high quality and with acceptable reproducibility. This work presents the results of TGA, FTIR, and MALDI-TOF analysis made on photoresists commercially available and suitable for X-ray lithography. The photoresists presented different profiles regarding the solvent content and oligomers composition, and in the case of some samples, there were high amounts of non-epoxidized oligomers.

Development of a direct patterning method for functional oxide thin films using ultraviolet irradiation and hybrid-cluster gels and its application to thin-film transistor fabrication

A gel state exists in the solution–solid conversion process. We found that solidification can be promoted by irradiating the gel with ultraviolet (UV) light. In this study, a patterning method without using a vacuum system or employing photoresist materials has been proposed wherein solidification was applied to a gel by UV irradiation. Indium oxide gel, indium gallium oxide gel, lanthanum zirconium oxide gel, and lanthanum ruthenium oxide gels were successfully patterned by using our technique. Moreover, an oxide thin-film transistor was fabricated by our novel patterning method and was successfully operated.

병렬 노즐 분사의 ITO 표면 포토레지스트 박리 조건에 관한 해석

Chemical stripping mechanisms are important because they are fundamentally involved in the rate of reaction of bonding and decomposition of materials. The stripping mechanism of a spray technology penetrates or removes a photoresist (PR) material on the indium tin oxide surface. It is the impact force produced by the velocity and mass of the stripper reaching the surface. The mechanisms in which a PR material is agitated or removed by proper liquid movement are dependent on material properties (e.g., viscosity) and conditions (e.g., temperature). Simple tests and numerical analysis have been conducted to determine the performance of a spray on PR materials exposed to a solution-type special stripper. The results performed to compare the impact force as varied by nozzle shape, spray distance, velocity, and flow rate to determine the relationship of the impact force to the performance in material removal.

Black Photoresist for Patterning Pixel Define Layer of Organic Light Emitting Diode with Polyimide as Thermal Stabilizer

In order to improve the visibility for outside use of organic light emitting diodes (OLEDs), the polarized film and black matrix pattern have been used in the small and medium sized OLEDs; however, these cause problem of reducing the emission efficiency of OLED. Changing the color of pixel define layer (PDL) from brown to black is an important point for improving the efficiency and visibility of OLEDs. In this work we studied the photoresist material containing black pigment and the photolithographic process for patterning of black PDL on OLEDs. The black PDL patterns made with our synthesized polyimides as thermal stabilizer were found to give high thermal stability over 300°C.