Real-time generation of circular patterns in electron beam lithography

Electron beam lithography(EBL)involves the transfer of a pattern onto the surface of a substrate byfirst scanning a thin layer of organicfilm(called resist)on the surface by a tightly focused and precisely controlled electron beam(exposure)and then selectively removing the exposed or nonexposed regions of the resist in a solvent(developing).It is widely used for fabrication of integrated cir-cuits,mask manufacturing,photoelectric device processing,and otherfields.The key to drawing circular patterns by EBL is the graphics production and control.In an EBL system,an embedded processor calculates and generates the trajectory coordinates for movement of the electron beam,and outputs the corresponding voltage signal through a digital-to-analog converter(DAC)to control a deflector that changes the position of the electron beam.Through this procedure,it is possible to guarantee the accuracy and real-time con-trol of electron beam scanning deflection.Existing EBL systems mostly use the method of polygonal approximation to expose circles.A circle is divided into several polygons,and the smaller the segmentation,the higher is the precision of the splicing circle.However,owing to the need to generate and scan each polygon separately,an increase in the number of segments will lead to a decrease in the overall lithography speed.In this paper,based on Bresenham’s circle algorithm and exploiting the capabilities of afield-programmable gate array and DAC,an improved real-time circle-producing algorithm is designed for EBL.The algorithm can directly generate cir-cular graphics coordinates such as those for a single circle,solid circle,solid ring,or concentric ring,and is able to effectively realizes deflection and scanning of the electron beam for circular graphics lithography.Compared with the polygonal approximation method,the improved algorithm exhibits improved precision and speed.At the same time,the point generation strategy is optimized to solve the blank pixel and pseudo-pixel problems that arise with Bresenham’s circle algorithm.A complete electron beam deflection system is established to carry out lithography experiments,the results of which show that the error between the exposure results and the preset pat-terns is at the nanometer level,indicating that the improved algorithm meets the requirements for real-time control and high precision of EBL.

Nano-Level Electron Beam Lithography

The JEOL JBX-5000LS is a vector type machine.The system hardware features an ion-pumped column,a LaB 6 electron emitter,25kV and 50kV accelerating voltage,and a turbo-pumped sample chamber.The resolution,stability,stitching and overlay of this system are evaluated.The system can write complex patterns at dimensions down to 30nm.The demonstrated overlay accuracy of this system is better than 40nm.

A New Method to Retrieve Proximity Effect Parameters in Electron-Beam Lithography

A new method for determining proximity parameters α,β ,and η in electron beam lithography is introduced on the assumption that the point exposure spread function is composed of two Gaussians.A single line is used as test pattern to determine proximity effect parameters and the normalization approach is adopted in experimental data transaction in order to eliminate the need of measuring exposure clearing dose of the resist.Furthermore,the parameters acquired by this method are successfully used for proximity effect correction in electron beam lithography on the same experimental conditions.

Effects of electron beam lithography process parameters on structure of silicon optical waveguide based on SOI

Electron beam lithography(EBL) is a key technology in the fabrication of nanoscale silicon optical waveguide. The influence of exposure dose, the main process parameter of EBL, on the structure profile of poly-methyl methacrylate(PMMA) after development was studied using a silicon on insulator(SOI) wafer with 220 nm top silicon as the substrate. The relationship between exposure dose and structure pattern width after development was analyzed according to the measurement results. The optimum exposure dose of 220 μC/cm^(2) was found to obtain a final structure consistent with the designed mask value through subsequent processes. At the same time, according to the image segmentation curve tracking technology, the contour extraction process of the dose test results was carried out, and the relationship among mask design value, exposure dose and two-dimensional roughness of boundary contour was analyzed, which can provide reference for the subsequent electron beam lithography of the same substrate material.

Fabrication and Characteristics of a Si-Based Single Electron Transistor

Si based single electron transistor (SET) is fabricated successfully on p type SIMOX substrate,based on electron beam (EB) lithography,reactive ion etching (RIE) and thermal oxidation.In particular,using thermal oxidation and etching off the oxide layer,a one dimensional Si quantum wire can be converted into several quantum dots inside quantum wire in connection with the source and drain regions.The differential conductance (d I ds /d V ds ) oscillations and the Coulomb staircases in the source drain current ( I ds ) are shown clearly dependent on the source drain voltage at 5 3K.The I ds V gs (gate voltage) oscillations are observed from the I ds V gs characteristics as a function of V gs at different temperatures and various values of V ds .For a SET whose total capacitance is about 9 16aF,the I ds V gs oscillations can be observed at 77K.

Chemically Amplified Resist Based on Dendritic Molecular Glass for Electron Beam Lithography

A novel dendritic molecular glass(MG)containing adamantane core(AD-15)was synthesized and characterized.It exhibits good solubility in common organic solvents and a stable amorphous state at room temperature,which contributes to forming films with different thicknesses by spin-coating.The thermal analysis of AD-15 indicates that no apparent glass transition temperature(Tg)is observed before the thermal decomposition temperature(Td=160℃).The good thermal resistance suggests that it can satisfy the lithographic process and is a candidate for photoresist materials.The patterning properties of AD-15 resist were evaluated by electron beam lithography(EBL).By optimizing the lithographic process parameters,AD-15 resist can achieve 40 nm half-pitch patterns with a line-edge roughness of 4.0 nm.The contrast and sensitivity of AD-15 resist were 1.9 and 67µC/cm^(2),respectively.Compared with the commercial PMMA(950k)electron beam resist,the sensitivity of AD-15 resist increases by 6 times.This study provides a new example of molecular glass resist with high resolution and sensitivity for EBL.

Fabrication of a 256-bits organic memory by soft x-ray lithography

This paper reports a procedure of soft x-ray lithography for the fabrication of an organic crossbar structure. Electron beam lithography is employed to fabricate the mask for soft x-ray lithography, with direct writing technology to the lithograph positive resist and polymethyl methacrylate on the polyimide film. Then Au is electroplated on the polyimide film. Hard contact mode exposure is used in x-ray lithography to transfer the graph from the mask to the wafer. The 256-bits organic memory is achieved with the critical dimension of 250 nm.

Latest developments in EUV photoresist evaluation capability at Shanghai Synchrotron Radiation Facility

Evaluating the comprehensive characteristics of extreme ultraviolet(EUV)photoresists is crucial for their application in EUV lithography,a key process in modern technology.This paper highlights the capabilities of the Shanghai Synchrotron Radiation Facility(SSRF)08U1B beamline in advancing this field.Specifically,it demonstrates how this beamline can create fringe patterns with a 15-nm half-pitch on a resist using synchrotron-based EUV lithography.This achievement is vital for evaluating EUV photoresists at the advanced 5-nm node.We provide a detailed introduction to the methods and experimental setup used at the SSRF 08U1B beamline to assess an EUV photoresist.A significant part of this research involved the fabrication of high-resolution hydrogen silsesquioxane mask gratings.These gratings,with an aspect ratio of approximately 3,were created using electron beam lithography on an innovative mask framework.This framework was crucial in eliminating the impact of zeroth-order light on interference patterns.The proposed framework propose offers a new approach to mask fabrication,particularly beneficial for achromatic Talbot lithography and multicoherent-beam interference applications.

Development of massively parallel electron beam direct write lithography using active-matrix nanocrystalline-silicon electron emitter arrays

Nanoscale lithographic technologies have been intensively studied for the development of the next generation of semiconductor manufacturing practices.While mask-less/direct-write electron beam(EB)lithography methods serve as a candidate for the upcoming 10-nm node approaches and beyond,it remains difficult to achieve an appropriate level of throughput.Several innovative features of the multiple EB system that involve the use of a thermionic source have been proposed.However,a blanking array mechanism is required for the individual control of multiple beamlets whereby each beamlet is deflected onto a blanking object or passed through an array.This paper reviews the recent developments of our application studies on the development of a high-speed massively parallel electron beam direct write(MPEBDW)lithography.The emitter array used in our study includes nanocrystalline-Si(nc-Si)ballistic electron emitters.Electrons are drifted via multiple tunnelling cascade transport and are emitted as hot electrons.The transport mechanism allows one to quickly turn electron beamlets on or off.The emitter array is a micro-electro-mechanical system(MEMS)that is hetero-integrated with a separately fabricated active-matrix-driving complementary metal-oxide semiconductor(CMOS)large-scale integration(LSI)system that controls each emitter individually.The basic function of the LSI was confirmed to receive external writing bitmap data and generate driving signals for turning beamlets on or off.Each emitted beamlet(10×10μm^(2))is converged to 10×10 nm^(2) on a target via the reduction electron optic system under development.This paper presents an overview of the system and characteristic evaluations of the nc-Si emitter array.We examine beamlets and their electron emission characteristics via a 1:1 exposure test.

Electron-beam lithography for polymer bioMEMS with submicron features

We present a method for submicron fabrication of flexible,thin-film structures fully encapsulated in biocompatible polymer poly(chloro-p-xylylene)(Parylene C)that improves feature size and resolution by an order of magnitude compared with prior work.We achieved critical dimensions as small as 250 nm by adapting electron beam lithography for use on vapor deposited Parylene-coated substrates and fabricated encapsulated metal structures,including conducting traces,serpentine resistors,and nano-patterned electrodes.Structures were probed electrically and mechanically demonstrating robust performance even under flexion or torsion.The developed fabrication process for electron beam lithography on Parylene-coated substrates and characterization of the resulting structures are presented in addition to a discussion of the challenges of applying electron beam lithography to polymers.As an application of the technique,a Parylene-based neural probe prototype was fabricated with 32 recording sites patterned along a 2 mm long shank,an electrode density surpassing any prior polymer probe.

A method to restrain the charging effect on an insulating substrate in high energy electron beam lithography

Pattern distortions caused by the charging effect should be reduced while using the electron beam lithography process on an insulating substrate. We have developed a novel process by using the SX AR-PC 5000/90.1solution as a spin-coated conductive layer, to help to fabricate nanoscale patterns of poly-methyl-methacrylate polymer resist on glass for phased array device application. This method can restrain the influence of the charging effect on the insulating substrate effectively. Experimental results show that the novel process can solve the problems of the distortion of resist patterns and electron beam main field stitching error, thus ensuring the accuracy of the stitching and overlay of the electron beam lithography system. The main characteristic of the novel process is that it is compatible to the multi-layer semiconductor process inside a clean room, and is a green process, quite simple, fast, and low cost. It can also provide a broad scope in the device development on insulating the substrate,such as high density biochips, flexible electronics and liquid crystal display screens.

Heterometallic Ti-Zr oxo nanocluster photoresists for advanced lithography

Extreme ultraviolet lithography(EUVL)and electron beam lithography(EBL)are considered to be crucial lithography techniques utilized in the fabrication of nanoscale semiconductor devices.However,the industry currently faces a scarcity of EUV photoresists that meet the increasingly challenging standards in terms of resolution,sensitivity and roughness.Metal oxo nanoclusters have garnered significant interest in the field of EUV photoresist due to their relatively stronger absorption cross-section for extreme ultraviolet light and lower dimensions.In this study,we utilize a heterometallic nanocluster strategy by a combination of titanium and zirconium metals to investigate their solubility,assess the suitability of various developers,and evaluate their performance in electron-beam and EUVL,as well as study their etch resistance for pattern transfer.We demonstrate that R-4 is able to get a critical dimension(CD)of 25 nm at low doses under EBL,as well as 50 nm resolution at EUVL with a remarkable sensitivity of 19.7 mJ cm−2.This study offers an efficient heterometallic method for optimizing the lithographic performance of metal oxo nanocluster photoresists,which can benefit the development of commercially viable next-generation EUV photoresists.

200nm Gate Length Metamorphic In_(0.52)Al_(0.48)As/In_(0.6)Ga_(0.4) As HEMTs on GaAs Substrates with 110GHz f_T

200nm gate-length GaAs-based InAlAs/InGaAs MHEMTs are fabricated by MBE epitaxial material and EBL （electron beam lithography） technology. Ti/Pt/Au is evaporated to form gate metals. A T-shaped gate is produced using a novel PMMA/PMGI/PMMA trilayer resist structure to decrease parasitic capacitance and parasitic resistance of the gate. Excellent DC and RF performances are obtained and the transconductance （gm） ,maximum saturation drain current density （Joss）, threshold voltage （ VT）, current cut-off frequency （fT） , and maximum oscillation frequency （fmax） of InAlAs/ InGaAs MHEMTs are 510mS/mm,605mA/mm, -1.8V, 110GHz, and 72GHz, respectively.

Fabrication of Sub-20nm Metal Nanogaps from Nanoconnections by the Extended Proximity Effect

We describe the fabrication of metal nanogaps of sub-20nm in feature size using the proximity effect in electron beam lithography （EBL）. The proximity effect is extended to develop a flexible and practical method for preparing metal （e. g. Au or Ag） nanogaps and arrays in combination with a transfer process （e. g., deposition/lift-off）. Different from the direct gap-writing process,the nanogap precursor structures （nanoconnections） were designed by GDSII software and then written by electron beam. Following a deposition and lift-off process, the metal nanogaps were obtained and the nanogap size can be lowered to -10nm by controlling the exposure dose in EBL.

Selection of isolated and individual single-walled carbon nanotube from a film and its usage in nanodevices

Individual and isolated single-walled carbon nanotubes （SWNTs） are important for fabricating relevant nanodevices and studying the properties of the SWNT devices. In this work, we demonstrate that individual and isolated SWNT can be selected and obtained from a film containing a huge number of SWNTs. By using both the polymethylmethacrylate （PMMA） as a negative resist and the electron beam lithography, the selected SWNT can be fixed on a substrate, while the other SWNTs in the film can lift off. The selected SWNT can be used to fabricate nanodevice and a gas sensor of oxygen is demonstrated in this work.

Three-step lithography to the fabrication of vertically coupled micro-ring resonators in amorphous silicon-on-insulator

A simple method to fabricate vertically coupled micro-ring resonators in amorphous silicon-on-insulator is created by a three-step lithography process. First, the linear loss at 1.55 μm of the a-Si：H film is calculated to be 0.2 =k 0.05 dB/cm. Then, the bottom line waveguide of Su-8 with a flat top surface of 300 nm is created by etching. The thickness of Su-8 can easily be controlled by the etching time. Finally, by opening the window pattern and etching several layers, the first layer marks made by electron beam lithography are found with a 50 nm resolution, and the high quality of the micro-ring resonator is demonstrated.

Super-long longitudinal magnetization needle generated by focusing an azimuthally polarized and phasemodulated beam

Based on the inverse Faraday effect, a super-long longitudinal magnetization needle can be induced by a trans- versely polarized needle-shaped electric field. This needle-shaped electric field can be obtained in the focal vol- ume of the objective by focusing an azimuthally polarized vortex beam that is modulated both radially and azimuthally by a specifically designed annular phase filter. The numerical calculation shows that the full widths at half-maximums in longitudinal direction and in transverse direction of the magnetization needle are 282 and 0.27λ. The corresponding needle aspect ratio of 103 is more than ten times larger than that of the magnetization needle fabricated by electron beam lithography.

Alternating Copolymerization of Epoxides and Isothiocyanates to Diverse Functional Polythioimidocarbonates and Related Block Polymers

Synthesis of diverse polythioimidocarbonates via ring-opening copolymerization of epoxides and isothiocyanates catalyzed by organoboron catalyst was reported herein.Both aromatic and aliphatic isothiocyanates underwent successful copolymerization with terminal and internal epoxides,allowing for the precise tuning of the performance of the resultant copolymers over a broad range.The wide scope of available isothiocyanates and epoxides enables the direct construction of sulfur-containing functional polymers featuring both high glass transition temperature and refractive index.Additionally,it was observed that aromatic isothiocyanates polymerize much faster than aliphatic ones,and the reactivity difference facilitated the one-step synthesis of block polymers from mixed aromatic isothiocyanates,aliphatic isothiocyanates and epoxides due to the preferential incorporation of aromatic isothiocyanates over the aliphatic analogues during their alternating copolymerization with epoxides.The produced polythioimidocarbonates can be used as positive resists for electron beam lithography(sensitivity of 130μC/cm^(2) and contrast of 1.53 for poly(CHO-alt-EITC)).Coupling with their high refractive index(1.58—1.68),polythioimidocarbonates might find functional applications in optics.These results render ring-opening copolymerization of epoxides and isothiocyanates a facile route to enrich functional polymer library.

Fabrication and measurement of optical characterization of one dimensional photonic crystal with defect

Numerical calculations based on the transfer matrix method are carried out, and the results of band gap with resonance peaks are obtained. The electron beam lithography technology （EBL） and induction coupling plasma （ICP） etching are used to make the photonic crystal （PC） structures, and from several scanning electron microscope images, the PC structures are observed with features closing to the design. In order to create the tiny PC structures in the right places of the waveguide by the EBL technology at different time, some alignment markers are deposited on the chip, which are made of gold that deposited on titanium for its good adhesion to the underlying Si. An optical testing bed is designed for measurement of the optical characterization of PC structures. Through the analysis of the measured data, a △λ value of 0.8 nm is obtained and for the centre frequency of 1547 nm, a very high quality factor value of 1933 can be obtained. The 3-rim difference represents only a 0.2% error from the theoretical centre.

InP-base resonant tunneling diodes

We have fabricated In0.53Ga0.47As/AlAs/InP resonant tunneling diodes（RTDs） based on the air-bridge technology by using electron beam lithography processing.The epitaxial layers of the RTD were grown on semiinsulating（100） InP substrates by molecular beam epitaxy.RTDs with a peak current density of 24.6 kA/cm^2 and a peak-to-valley current ratio of 8.6 at room temperature have been demonstrated.