Photolithography Process Simulation for Integrated Circuits and Microelectromechanical System Fabrication

Simulations of photoresist etching,aerial image,exposure,and post-bake processes are integrated to obtain a photolithography process simulation for microelectromechanical system（MEMS） and integrated circuit（IC） fabrication based on three-dimensional （3D） cellular automata（CA）. The simulation results agree well with available experimental results. This indicates that the 3D dynamic CA model for the photoresist etching simulation and the 3D CA model for the post-bake simulation could be useful for the monolithic simulation of various lithography processes. This is determined to be useful for the device-sized fabrication process simulation of IC and MEMS.

Design of Microstructure Parameters on a Small Multi-Throttle Aerostatic Guideway in Photolithography

A compact multi-throttle aerostatic guideway is the preferred structure for high precision and acceleration motion in the variable-slit system(VS)of photolithography.The presence of microstructure,such as recesses and grooves,on the guideway working surface has been found to improve the loading performance.Nevertheless,the effects on the guideway performance of changing the microstructure on the micron level are not yet clear.The mesh adaptation method,which was proposed by the authors,is employed in this paper to quantitatively study the influences of four microstructure parameters.The effect of tuning these parameters on the loading performance is revealed.The level of impact determines the proposed design process of the parameters.The characteristic feature of the proposed design process is that the working points of carrying capacity,stiffness,and rotational stiffness are unified under twoway adjusting by means of recess parameters.According to the proposed design process and tuning method,the restriction of supply pressure is lifted to a certain extent and the mutual tradeoff among the loading performances is relieved.The experimental results show that the rotational stiffness of the designed guideway,based on the tuned parameters,reached 2.14×10^(4) Nmrad1 and increased by 69.8%.In a scanning test of the applied VS on argon fluoride laser(ArF)photolithography,the average scanning acceleration reached 67.5 m·s^(-2),meeting the design specification.

Modeling of photolithography process in semiconductor wafer fabrication systems using extended hybrid Petri nets

To describe a semiconductor wafer fabrication flow availably, a new modeling method of extended hybrid Petri nets （EHPNs） was proposed. To model the discrete part and continuous part of a complex photolithography process, hybrid Petri nets （HPNs） were introduced. To cope with the complexity of a photolithography process, object-oriented methods such as encapsulation and classifications were integrated with HPN models. EHPN definitions were presented on the basis of HPN models and object-oriented methods. Object-oriented hybrid Petri subnet models were developed for each typical physical object and an EHPN modeling procedure steps were structured. To demonstrate the feasibility and validity of the proposed modeling method, a real wafer photolithography case was used to illustrate the modeling procedure. dynamic modeling of a complex photolithography process effectively The modeling results indicate that the EHPNs can deal with the dynamic modeling of a complex photolithography process effectively.

ITO Etched by Photolithography Used in the Fabrication of Flexible Organic Solar Cells with PET Substrates

In this study, the authors have shown the power conversion efficiency of flexible organic solar cells. The structure of the device is PET/ITO/PEDOT： PSS/P3HT： PCBM/AI. P3HT （poly-3-hexylthiophene）. It was used as an electron donor, PCBM （[6, 6]-phenyl C6 l-butyric acid methyl ester） as an electron acceptor and PEDOT： PSS used as a HIL （hole injection layer）. These materials were deposited by spin coating method on the flexible substrates. Photolithography method is used to etch ITO. The electrical parameters of the fabricated cells were investigated by means of J （V）, FF （fill factor）, the efficiency （r/）, photocurrent and IPCE measurement. It was observed that 45% of the absorbed photons are converted into current. The results obtained using etching technology by photolithography is better than that obtained in the clean room.

Application of photocrosslinkable hydrogels based on photolithography 3D bioprinting technology in bone tissue engineering

Bone tissue engineering(BTE)has been proven to be an effective method for the treatment of bone defects caused by different musculoskeletal disorders.Photocrosslinkable hydrogels(PCHs)with good biocompatibility and biodegradability can significantly promote the migration,proliferation and differentiation of cells and have been widely used in BTE.Moreover,photolithography 3D bioprinting technology can notably help PCHs-based scaffolds possess a biomimetic structure of natural bone,meeting the structural requirements of bone regeneration.Nanomaterials,cells,drugs and cytokines added into bioinks can enable different functionalization strategies for scaffolds to achieve the desired properties required for BTE.In this review,we demonstrate a brief introduction of the advantages of PCHs and photolithography-based 3D bioprinting technology and summarize their applications in BTE.Finally,the challenges and potential future approaches for bone defects are outlined.

High-resolution, full-color quantum dot light-emitting diode display fabricated via photolithography approach

Displays play an extremely important role in modern information society,which creates a never-ending demand for the new and better products and technologies.The latest requirements for novel display technologies focus on high resolution and high color gamut.Among emerging technologies that include organic light-emitting diode(OL ED),micro light-emiting diode(micro-LED),quantum dot light-emitting diode(QLED),laser display,holographic display and others,QLED is promising owing to its intrinsic high color gamut and the possibility to achieve high resolution with photolithography approach.However,previously demonstrated photolthography techniques suffer from reduced device performance and color Impurities in subpixels from the process.In this study,we demonstrated a sacrificial layer assisted patterming(SLAP)approach,which can be applied in conjunction with photolithography to fabricate high-resolution,full-colo quantum dot(QD)patterns.In this approach,the negative photoresist(PR)and sacrificial layer(SL)were uilized to determine the pixels for QD deposition,while at the same time the SL helps protect the QD layer and keep it intact(named PR-SL approach).To prove this method's viability for QLED display manufacture,a 500-ppi,full-color passive matrix(PM)-QLED prototype was fabricated via this process.Results show that there were no color impurities in the subpixels,and the PM-QL ED has a high color gamut of 114%National Television Standards Committee(NTSC).To the best of our knowledge,this is the first ull-olor QLED prototype with such a high resolution.We anticipate that this innovative patteming technique will open a new horizon for future display technologies and may lead to a disruptive and innovative change in display industry.

Microstructuring of carbon/tin quantum dots via a novel photolithography and pyrolysis-reduction process

A novel microfabrication process based on optimized photolithography combined with pyrolysis-reduction is proposed to fabricate interdigital porous carbon/tin quantum dots （C/Sn QDs） microelectrodes.C/Sn QDs active microelectrodes are also employed as current collectors of a micro-supercapacitor （MSC）.A uniform dispersion of Sn QDs （diameter of ～3 nm） in the carbon matrix is achieved using our facile and controllable microfabrication process.The as-fabricated C/Sn QDs MSC obtained by carbonization at 900 ℃ exhibits a higher areal specific capacitance （5.79 mF＆#183;cm-2） than that of the pyrolyzed carbonbased MSC （1.67 mF＆#183;cm-2） and desirable cycling stability （93.3% capacitance retention after 5,000 cyclic voltammetry cycles）.This novel microfabrication process is fully compatible with micromachining technologies,showing great potential for large-scale fine micropatterning of carbon-based composites for applications in micro/nano devices.

Enhanced light extraction of InGaN LEDs with photonic crystals grown on p-GaN using selective-area epitaxy and nanospherical-lens photolithography

We report a new method for the fabrication of two-dimensional photonic crystal （PhC） hole arrays to improve the light extraction of GaN-based light-emitting diodes （LEDs）. The PhC structures were realized using nanospherical-lens photolithography and the selective-area epitaxy method, which ensured the electrical properties of the LEDs through leaving the p-GaN damage-free. At a current of 350 mA, the light output power of LEDs with PhC hole arrays of 450 nm and 600 nm in diameter with the same lattice period of 900 nm were enhanced by 49.3% and 72.2%, respectively, compared to LEDs without a PhC. Furthermore, the LEDs with PhC hole structures showed an obviously smaller divergent angle compared with conventional LEDs, which is consistent with the results of finite-difference time-domain simulation.

3D nonlinear photolithography of tin oxide ceramics via femtosecond laser

As a wide band gap semiconductor material,tin oxide(SnO_(2))has been widely used in gas sensing,optoelectronics and catalysis.The complex micro and nanoscale threedimensional(3D)geometric structures endow the conventional SnO_(2)ceramics with novel properties and functionalities.Nevertheless,ceramics cannot be cast or machined easily due to their high mechanical toughness and resistance.The additive manufacturing opens a great opportunity for flexibly geometrical shaping,while the arbitrary shaping of SnO_(2)ceramics at micro and nanoscale is always a challenge.Herein,preceramic monomers which can be polymerized under ultrafast laser irradiation,were utilized to form complex and arbitrary 3D preceramic polymer structures.After calcination treatment,these green-body structures could be converted into pure high-dense SnO_(2)ceramics with uniform shrinkage,and the feature size was down to submicron.Transmission electron microscopy(TEM)analysis displays that the printed SnO_(2)ceramic nanostructures can be nanocrystallized with grain sizes of 2.5±0.4 nm.This work provides the possibility of manufacturing 3D SnO_(2)ceramic nanostructures arbitrarily with sub-100 nm resolution,thus making it promising for the applications of SnO_(2)in different fields.

PMMA-Based Microsphere Mask for Sub-wavelength Photolithography

The authors present a polymethyl methacrylate(PMMA)-based,reusable microsphere mask used in the laser sub-wavelength photolithography.In order to overcome the diffraction limit to achieve nano-structuring using l-|im laser wavelength,the photolithography technique was conventionally characterized by applying a one-off monolayer of silica microspheres serving as Mie scatterers.Addressing the major limitation of this technique,which was that the monolayer of microspheres must be prepared on the sample surface prior to fabrication,the proposed hot press approach could firmly fuse the 1silica microspheres to the PMMA base without the use of adhesives.The PMMA-based microsphere mask could hence reduce the amount of work for the monolayer preparation and was proven reusable for at least 20 times without damage to top or bottom surfaces.Using the mask,dimples that were 0.7 pm in diameter and 40 nm in depth were produced on tool steel by a single pulse of picosecond laser irradiation.

On the profile of frequency dependent interface states and series resistance in Au/p-InP SBDs prepared with photolithography technique

The frequency dependent of the forward and reverse bias capacitance-voltage （C-V） and conductance-voltage （G/w-V） charac- teristics of Au/p-InP SBDs have been investigated in the frequency range of 20 kHz-10 MHz and voltage range of-5 - 5 V at room temperature. The effects of surface states （Nss） and series resistance （R0 on C-V and G/w-V characteristics have been in- vestigated in detail. The frequency dependent Nss and Rs profiles were obtained for various applied bias voltages. The experi- mental results show that the main electrical parameters of Au/p-InP SBD such as barrier height （gOB）, the density of acceptor concentration （NA）, Nss and Rs were found strongly frequency and voltage dependent. The values of C and G/w decrease with increasing frequency due to a continuous distribution of Nss localized at the metal/semiconductor （M/S） interface. The effect of Rs on C and G is found considerably high especially at high frequencies. Therefore, the high frequencies of the values of C and G were corrected for the effect of Rs in the whole measured bias range to obtain the real diode capacitance Cc and conductance Gc using the Nicollian and Goetzberger technique. The distribution profile of Rs-V gives a peak depending on the frequency especially at low frequencies and disappears with increasing frequencies due to the existence of Nss at the M/S interface.

Novel technique for characterizing feature profiles in photolithography process

A novel angle-resolved scatterometer based on pupil optimization for feature profile measurement in a photolithography process is proposed.The impact of image sensor errors is minimized by optimizing the intensity distribution of the incident light using a spatial light modulator.The scatterometry sensitivity of feature measurement at different polarization conditions is calculated using the rigorous coupled-wave and first-order analyses,and the reproducibility of the scatterometer is evaluated.The results show that the sensitivity and reproducibility of the angle-resolved scatterometer increase by 90% and 40% with pupil optimization,respectively.

Mechanical system and dynamic control in photolithography for nanoscale fabrication: A critical review

As one of the most advanced and precise equipment in the world,a photo-lithography scanner is able to fabricate nanometer‐scale devices on a chip.To realize such a small dimension,the optical system is the fundamental,but the me-chanical system often becomes the bottleneck.In the photolithography,the ex-posure is a dynamic process.The accuracy and precision of the movement are determined by the mechanical system,which is even more difficult to control compared with the optical system.In the mechanical system,there are four crucial components:the reticle and wafer stages,the linear motor,the metrology system,and the control system.They work together to secure the reticle and substrate locating at the correct position,which determines the overlay and alignment per-formance in the lithography.In this paper,the principles of these components are reviewed,and the development history of the mechanical system is introduced.

Regulation of actin cytoskeleton via photolithographic micropatterning

Actin cytoskeleton plays crucial roles in various cellular functions.Extracellular matrix(ECM)can modulate cell morphology by remodeling the internal cytoskeleton.To define how geometry of ECM regulates the organization of actin cytoskeleton,we plated individual NIH 3T3 cells on micropatterned substrates with distinct shapes and sizes.It was found that the stress fibers could form along the nonadhesive edges of T-shaped pattern,but were absent from the opening edge of V-shaped pattern,indicating that the organization of actin cytoskeleton was dependent on the mechanical environment.Furthermore,a secondary actin ring was observed on 50μm circular pattern while did not appear on 30μm and 40μm pattern,showing a size-dependent organization of actin cytoskeleton.Finally,osteoblasts,MDCK and A549 cells exhibited distinct organization of actin cytoskeleton on T-shaped pattern,suggesting a cell-type specificity in arrangement of actin cytoskeleton.Together,our findings brought novel insight into the organization of actin cytoskeleton on micropatterned environments.

Missing Via Mechanism and Solutions

Missing via has been a defect in semiconductor manufacturing,especially of foundries. Its solution can be rather attractive in yield improvement for relatively mature technology since each percentage point improvement will mean significant profit margin enhancement. However, the root cause for the missing via defect is not easy to determine since many factors,such as, defocus, material re-deposition, and inadequate development,can lead to missing via defects. Therefore, knowing the exact cause for each defect type is the key. In this paper, we will present the analysis methodology used in our company. In the experiments,we have observed three types of missing vias. The first type consists of large areas, usually circular,of missing patterns,which are primarily located near the wafer edge. The second type consists of isolated sites with single partially opened vias or completely unopened vias. The third type consists of relatively small circular areas,within which the entire via pattern is missing. We have first tried the optimization of the developing recipe and found that the first type of missing via can be largely removed through the tuning of the rinse process, which improves the cleaning efficiency of the developing residue. However, this method does not remove missing via of the second and third type. We found that the second type of missing via is related to local defocus caused by topographical distribution. To resolve the third type of missing via defects, we have performed extensive experiments with different types of developer nozzles and different types of photomasks,and the result is that we have not found any distinct dependence of the defect density on either the nozzle or the mask types. Moreover, we have also studied the defect density from three resists with different resolution capability and found a correlation between the defect density and the resist resolution. It seems that,in general, lower resolution resists also have lower defect density. The results will be presented in the paper.

Moth-eye Structured Polydimethylsiloxane Films for High-Efficiency Perovskite Solar Cells

Large-area polydimethylsiloxane(PDMS)films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells.An approach that incorporated photolithography,bilayer PDMS deposition and replication was used in the fabrication process.By simply attaching the moth-eye PDMS films to the transparent substrates of perovskite solar cells,the optical properties of the devices could be tuned by changing the size of the moth-eye structures.The device with 300-nm moth-eye PDMS films greatly enhanced power conversion efficiency of ~21 % due to the antireflective effect of the moth-eye structure.Furthermore,beautiful coloration was observed on the 1000-nm moth-eye PDMS films through optical interference caused by the diffraction grating effect.Our results imply that moth-eye PDMS films can greatly enhance the efficiency of perovskite solar cells and building-integrated photovoltaics.

Ultrahigh-rate and high-frequency MXene micro-supercapacitors for kHz AC line-filtering

Harnessing energy from the environment promotes the rapid development of micro-power generators and relevant power management modules of alternating current (AC) line-filtering to obtain a stabilized direct current (DC) output for storage and use. Micro-supercapacitors (MSCs) with miniaturized volume and high-frequency response are regarded as a critical component in filtering circuits for microscale power conversion. Here, we reported the fabrication of the wafer-sized planar MSCs (M-MSCs) based on 2D Ti_(2)C_(2)T_(6) MXene using a photolithography technique. The M-MSCs exhibited an areal capacitance of 153 μF cm^(-2) and a frequency characteristic (f_(0)) of 5.6 k Hz in aqueous electrolyte. Moreover, by employing suitable ionic liquid as electrolyte, the voltage window was expanded to 2 V and the f_(0) could be pushed to 6.6 k Hz relying on the electrical double-layer mechanism and lower adsorption energy while maintaining quasi-rectangular cyclic voltammogram curves at 5000 V s^(-1). Furthermore, the integrated MSCs pack was constructed and exhibited excellent rectifying ability by filtering various highfrequency 5000 Hz AC signals with different waveforms into stable DC outputs. Such ultrahigh-rate and high-voltage M-MSCs module for k Hz AC line-filtering would be potentially integrated with customizable electronics to realize on-chip rectifiers in high-density integrated circuit.

Selection of DBO measurement wavelength for bottom mark asymmetry based on FDTD method

A physical model for simulating overlay metrology employing diffraction based overlay(DBO)principles is built.It can help to optimize the metrology wavelength selection in DBO.Simulation result of DBO metrology with a model based on the finite-difference time-domain(FDTD)method is presented.A common case(bottom mark asymmetry)in which error signals are always induced in DBO measurement due to the process imperfection were discussed.The overlay sensitivity of the DBO measurement across the visible illumination spectrum has been performed and compared.After adjusting the model parameters compatible with the actual measurement conditions,the metrology wavelengths which provide the accuracy and robustness of DBO measurement can be optimized.

The Variables and Invariants in the Evolution of Logic Optical Lithography Process

Photolithography has been a major enabler for the continuous shrink of the semiconductor manufacturing design rules.Throughout the years of the development of the photolithography,many new technologies have been invented and successfully implemented,such as image projection lithography,chemically amplified photoresist,phase shifting mask,optical proximity modeling and correction,etc.From 0.25μm technology to the current 7 nm technology,the linewidth has been shrunk from 250 nm to about 20 nm,or 12.5 times.Although imaging resolution is proportional to the illumination wavelength,with the new technologies,the wavelength has only been shrunk from 248 nm to 134.7 nm(193 nm immersion in water),less than 2 times.Would it mean that the imaging performance has been continuously declining?Or we have yet fully utilized the potential of the photolithography technology?In this paper,we will present a study on the key parameters and process window performance of the image projection photolithography from 0.25μm node to the current 7 nm node.

Acidic Polyester Imides as Thermally Stable Binder Polymers for Negative-Tone Black Photoresist

Polyimides are well-known for their high chemical inertness and thermal stability. However, it is usually challenging to synthesize UV-curable polyimides since the imidization reaction requires such harsh conditions that acrylate type double bonds cannot withstand. In this work, synthetic methods are developed to obtain polyester-imide type binder polymers with high thermal stability, high compatibility with the other components of the black photoresist, and fine photolithographic patterning property for the negative-tone black photoresist. The syntheses of diimide-diacid or diimide-diol intermediates for the polyesterification with dianhydride gave polyester imides which meets this requirement. The photolithographic tests have shown that the patterning of the micron-sized PDL of the organic light emitting diode (OLED) panel could be obtained. This work will interest the researchers working on the design and optimization of thermally stable binder polymers.