Aspect Ratio Patterns Research Articles

Nanofabrication of hard X-ray optics by metal electroplating in a dry etched mechanically stable inorganic template

A nanofabrication process for high resolution X-ray optics and X-ray lithography masks was developed. The process is based on the plasma etching of a sacrificial hard inorganic interlayer (Si, Si3N4, SiOx or HSQ) used for pattern transfer and aspect ratio amplification. The structures are first defined on a top thin metal film by electron beam lithography and lift-off; a thin nickel layer at the bottom of the hard interlayer is used as etch stop. A base plating (Cr/Au) under the nickel serves as seed layer for the electroplating of an X-ray absorber or phase shifting material. The fabrication is completed by the stripping of the hard template by wet or dry etching. Compared to methods based on analogous process schemes, in which the aspect ratio of nanostructures is instead amplified by pattern transfer into a sacrificial polymer interlayer by oxygen plasma, the investigated method is advantageous for the higher mechanical stability of the nanostructured hard templates with respect to the polymer ones, thus enabling the realization of higher aspect ratio features.

전기장이 적용된 노광후굽기 공정에 의한 고종횡비 근접장 광 리소그래피

In this paper, we propose an electric field enhanced postexposure baking (EFE-PEB) method to obtain deep and high aspect ratio pattern profile in near-field recording. To describe the photoacid distribution under an external electric field during the PEB, we derived the governing equations based on Fick’s second law of diffusion. From the results of the numerical calculations, it is found that the vertical movement of photoacid increases while the lateral movement is stationary as electric field varies from 0 to 8.0 × 10 6 V/m. Also, it is proven that the profile of near-field recording is improved by using the EFE-PEB method with increased depth, higher aspect ratio and larger sidewall angle.

Comparison of positive tone versus negative tone resist pattern collapse behavior

In this work, e-beam lithography patterns have been specifically designed and fabricated which provide the opportunity to probe the collapse behavior of both positive and negative tone systems. The pattern layout includes adjacent parallel line structures that both vary in the line size and also in the distance by which they are separated by the space between them. This type of structure allows for the control and modulation of the capillary forces, and ultimately the stresses, experienced by the photoresist line pairs during the final rinse and drying steps of the development process. Using such structures, it is possible to determine the critical stress, i.e., the maximum stress experienced by the photoresist lines before collapse, as a function of a variety of parameters including: material type, substrate preparation conditions, resist film thickness, and resist feature width. In this article, such a modular approach has been used to compare the pattern collapse behavior of a prototypical positive tone resist formulated using a protected hydroxystyrene-based copolymer and a prototypical negative tone epoxide-based molecular photoresist (4-EP). It was found that the critical stress at the point of pattern collapse decreased both as the thickness and the feature width of the resist lines decreased, though this trend was observed to a much lesser extent in the negative tone 4-EP material. It is observed that the negative tone resist, whose imaging mechanism involves cross-linking, shows far superior pattern collapse performance as compared to the positive tone deprotection based resist and is in general able to achieve significantly higher aspect ratio patterning at equivalent feature linewidths.

New Top-Down Approach for Fabricating High-Aspect-Ratio Complex Nanostructures with 10 nm Scale Features

We describe a new patterning technique, named "secondary sputtering lithography" that enables fabrication of ultrahigh-resolution (ca. 10 nm) and high aspect ratio (ca. 15) patterns of three-dimensional various shapes. In this methodology, target materials are etched and deposited onto the side surface of a prepatterned polymer by using low Ar ion bombarding energies, based on the angular distribution of target particles by ion-beam bombardment. After removal of the prepatterned polymer, high aspect ratios and high-resolution patterns of target materials are created.

Infinitely high etch selectivity during CH2F2/H2 dual-frequency capacitively coupled plasma etching of silicon nitride to chemical vapor-deposited a-C

For fabrication of a multilevel resist (MLR) structure with silicon nitride (Si3N4) and amorphous carbon (a-C) layers, highly selective etching of the Si3N4 layer using a chemical vapor-deposited (CVD) a-C etch mask was investigated by varying the following process parameters in CH2F2/H2/Ar plasmas: etch gas flow ratio, high-frequency source power (PHF), and low-frequency source power (PLF) in a dual-frequency superimposed capacitively coupled plasma etcher. The results of etching the ArF photoresist/bottom antireflective coating/SiOx/CVD a-C/Si3N4 MLR structure showed the possibility of obtaining an infinitely high selective etch process for the Si3N4 layer using a thin CVD a-C etch mask for high aspect-ratio pattern formation. The CH2F2/H2 gas flow ratio was found to play a critical role in determining the process window for infinite Si3N4/CVD a-C etch selectivity, due to the change in the degree of polymerization on Si3N4 and CVD a-C surfaces.

Effects of Aspect Ratio of Photoresist Patterns on Adhesive Strength between Microsized SU-8 Columns and Silicon Substrate under Bend Loading Condition

The adhesive strength between microsized SU-8 columns and a silicon substrate under the bend loading condition has been studied to clarify effects of the columnar aspect ratio. The maximum tensile stresses at the root are almost the same within the range of high aspect ratios (1.4–2.1) of the SU-8 columns, in which delamination cracks are opened by bend loading (mode I). This result shows that the delamination is induced by the maximum tensile stress at the root. On the other hand, the maximum tensile stress irregularly changes within the range of low aspect ratios (0.8–1.1) of the specimens and features of the delamination surfaces differ from those within the range of high aspect ratios. This result suggests that the delamination mode must change from mode I to mode II or the complex mode. All the results show that the adhesive strength of a SU-8 column with the range of high aspect ratios of 1.4 and more obtained from the adhesive bend test can be analyzed as the maximum tensile stress at the root (the adhesive bend strength) in this study.

Interactions between steady and oscillatory convection in mushy layers

We study nonlinear, two-dimensional convection in a mushy layer during solidification of a binary mixture. We consider a particular limit in which the onset of oscillatory convection just precedes the onset of steady overturning convection, at a prescribed aspect ratio of convection patterns. This asymptotic limit allows us to determine nonlinear solutions analytically. The results provide a complete description of the stability of and transitions between steady and oscillatory convection as functions of the Rayleigh number and the compositional ratio. Of particular focus are the effects of the basic-state asymmetries and non-uniformity in the permeability of the mushy layer, which give rise to abrupt (hysteretic) transitions in the system. We find that the transition between travelling and standing waves, as well as that between standing waves and steady convection, can be hysteretic. The relevance of our theoretical predictions to recent experiments on directionally solidifying mushy layers is also discussed.

Experimental Fabrication of High Efficiency Force Sensor by Cr-Si-C Composite Thin Film

Chromium silicon carbide (Cr-Si-C) composite thin film has been deposited on the stainless steel substrate by radio frequency (RF) sputtering and the possibility of the force sensor is discussed. The characteristic of the Cr-Si-C composite thin film force sensor is also described. Small temperature coefficient of resistance (TCR) dispersion has been obtained by a Cr-Si-C composite thin film force sensor, and the TCR was between -20 and 10 ppm/°C at the aspect ratio of 510 and the film thickness of 15 nm. The force sensor with hysteresis-free and good linearity has been prepared on the stainless steel substrate by using the Cr-Si-C composite film. The gauge factor of force sensor has increased according to the reduction of film thickness and the increase of sensor pattern aspect ratio. The gauge factor reached 14.2 at the aspect ratio of 510 and the film thickness of 15 nm, which is 7 times larger than that of Ni-Cr strain gauge.

Improved red-response in thin film a-Si:H solar cells with soft-imprinted plasmonic back reflectors

The impact of controlled nanopatterning on the Ag back contact of an n-i-p a-Si:H solar cell was investigated experimentally and through electromagnetic simulation. Compared to a similar reference cell with a flat back contact, we demonstrate an efficiency increase from 4.5% to 6.2%, with a 26% increase in short circuit current density. Spectral response measurements show the majority of the improvement between 600 and 800 nm, with no reduction in photocurrent at wavelengths shorter than 600 nm. Optimization of the pattern aspect ratio using electromagnetic simulation predicts absorption enhancements over 50% at 660 nm.

Thermal imprinting on quartz fiber using glasslike carbon mold

The authors are developing an on-fiber device that uses a quartz fiber as a substrate material and a large-area display and a wearable health monitor by woven fibers with embedded electrical circuit. The electrical circuit will be formed by inserting some electroconductive material into the concave pattern by inkjet and electroless-plating after thermally imprinting on the surface of the quartz fiber. To imprint the quartz fiber, a mold should be able to withstand the high temperature of 1400°C. Therefore, a mold for quartz imprinting on quartz fiber was fabricated with a glasslike carbon substrate polished by chemical-mechanical-polishing. Mold patterns with high accuracies were processed by applying microelectromechanical system fabrication techniques such as photolithography and reactive ion etching. Precise patterns with 5μm minimum linewidths were transferred on the front surface of a 200μm square quartz fiber by thermal nanoimprint technology. The width of the imprinted quartz fibers grew from 200to296μm by the loading force, but part of the loading force was also used up in deforming the quartz fibers. Filling rates, defined as the ratio of the height of imprinted patterns to the depth of mold patterns, were calculated and then the relationship between the filling rate and the aspect ratio of mold patterns was investigated. The molding accuracy was found to be independent of the size of the mold patterns, but it did exhibit its dependency on the aspect ratio of the mold patterns. The expected overlay accuracy, which is important for making circuitry in the future, was approximately 5μm judging from the imprinted patterns on the quartz fiber.

Step height removal mechanism of chemical mechanical planarization (CMP) for sub-nano-surface finish

The step height reduction mechanism of chemical mechanical planarization (CMP) was studied to increase the removal rate of ceria (CeO2) abrasive, which is based on slurry application to high aspect ratio patterns. Four kinds of nano-abrasives at 0.5wt% abrasive concentration were prepared, including jet-milled ceria, ball-milled ceria, silica, and colloidal silica. Three kinds of ceria and four kinds of colloidal silica were used to evaluate the removal effect with respect to nano-particle size. The step height reduction was investigated with the edge of a rectangular pattern and the top area of a saw tooth pattern. We found that the removal shapes of the rectangular and saw tooth patterns depended on the nano-particle shapes and sizes. In particular, the spherical abrasive was effective at edge removal in both ceria and silica abrasives, while the smaller abrasive sizes showed good rectangular edge pattern removal after relatively short polishing times. These results can be explained by different friction mechanisms, e.g. rolling and sliding frictions. We conclude that a spherically shaped and small-sized ceria abrasive is effective at increasing the ceria removal rate in high aspect ratio patterns.

Single-crystal silver nanowires: Preparation and Surface-enhanced Raman Scattering (SERS) property

Ordered Ag nanowire arrays with high aspect ratio and high density self-supporting Ag nanowire patterns were successfully prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide (AAO) template. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation. Transmission electron microscopy and scanning electron microscopy investigation reveal that large-area and ordered Ag nanowire arrays with smooth surface and uniform diameter were synthesized. Surface-enhanced Raman Scattering (SERS) spectra show that the Ag nanowire arrays as substrates have high SERS activity.

Fabrication of arbitrary polymer patterns for cell study by two‐photon polymerization process

Topographically patterned surfaces are known to be powerful tools for influencing cellular functions. Here we demonstrate a method for fabricating high aspect ratio ( approximately 10) patterns of varying height by using two-photon polymerization process to study contact guidance of cells. Ridge patterns of various heights and widths were fabricated through single laser scanning steps by low numerical aperture optics, hence at much higher processing throughput. Fibroblast cells were seeded on parallel line patterns of different height ( approximately 1.5-microm, approximately 0.8-microm, and approximately 0.5-microm) and orthogonal mesh patterns ( approximately 8-microm and approximately 4-microm height, approximately 5-microm and approximately 5.5-microm height, approximately 5-microm and approximately 6-microm height). Cells experienced different strength of contact guidance depending on the ridge height. Our results demonstrate that a height threshold of nearly 1 microm influences cell alignment on both parallel line and orthogonal mesh patterns. This fabrication technique may find wide application in the design of single cell traps for controlling cell behavior in microdevices and investigating signal transduction as influenced by surface topology.

Novel Approach of Semiconductor Manufacturing Process on Copper Dual Damascene Processes Integration

Abstract: The performance of the manufacturing process in each of these areas determines the overall manufacturability of the process. As device geometries are reduced, understanding and minimising the sources of process‐induced defects is critical to achieving and maintaining high device yields. This paper presents a comprehensive investigation of a novel metrology on semiconductor process module integration and technology on optimal integrated lithography processes and solution to the problem of defects reduction on semiconductor wafer in sub‐micron processes integration. As dual damascene integration copper process is complicated and critical in semiconductor processes. It has been common knowledge that pattern collapse and missing of this process and numerous defects could be prevented by optimal the process module tuning. To investigate novel semiconductor process integration on deep pattern aspect ratio effects of sub‐micron semiconductor wafer BEOL (Back‐End‐Of‐Line) structure were included in this study. Moreover, the electrical device investigations of device checking were also included.

굴절률 차이와 디지털 홀로그래피를 이용한 큰 단차측정

디지털 홀로그램과 굴절률 차이를 이용하여 사용된 광원의 파장보다 큰 단차를 측정하는 연구를 하였다. 위상차를 측정하여 단차를 측정하는 방식에서는 위상차가 <TEX>$2{\pi}$</TEX>보다 큰 경우에는 원리상 단차를 구하기 어렵다. 이를 보완하기 위하여 굴절률 차이를 이용하여 인위적으로 광경로차를 줄여 파장보다 큰 단차를 측정할 수 있는 디지털 홀로그래피 시스템을 구성하였고, 실험적으로 파장의 약 3배 이상의 단차를 측정하였다. Digital holography and refractive index difference are used to measure a high aspect ratio's patterns. When interference fringes are very closely spaced, the phase data containing high frequencies where <TEX>$2{\pi}$</TEX> ambiguities cannot be resolved. In this technique, the optical path difference is decreased by decreasing the refractive index difference. As a result, we solve the <TEX>$2{pi}$</TEX> ambiguities. Also, this technique is applicable to measure the refractive index if the shape of the sample is known.

Optimal Integration Process for Elimination of Abnormal Striation on Wafer Dual Damascene Processes

This paper is focused on optimal lithography processes using copper back-end-of-line (BEOL) semiconductor wafer integration technology and a solution to the problem of defect reduction on a semiconductor wafer. The pattern collapse observed in this process and numerous defects were prevented by optimizing the process module tuning. A novel semiconductor process on various pattern designs and deep pattern aspect ratio effects of a submicron semiconductor structure were included in this study. In addition to the experimental wafer manufacturing process, the electrical device data and defect reduction checking were also included.

Manufacture of an Integrated Three-Dimensional Structure Nozzle Plate Using Microinjection Molding for a 1200-dpi Inkjet Printhead

This paper presents an integrated microtechnology for the fabrication of a 3-D structure nozzle plate for a 1200-dots-per-inch (dpi) inkjet printhead. The 3-D structure nozzle plate contains a fluidic channel, nozzle chamber, and 432 conical nozzles whose taper angle is about 9deg-11deg to vertical. When the integrated 3-D structure nozzle plate is packaged onto the printhead, there is no need for alignment between the nozzle and the ink chamber, as there is when conventional production methods are employed. Therefore, misalignment of the nozzle and ink chamber is avoided, thereby reducing the cost by up to 50%, as well as greatly improving the print quality. This paper demonstrated the integration of excimer laser technology and microinjection molding to fabricate a 3-D structure nozzle plate. Excimer laser technology was used to create the high aspect ratio pattern with a tapered angle structure, and then, high-hardness Ni-Co alloy microelectroforming technology was used to achieve micromold insertion of the nozzle plate. In the microinjection molding, a variotherm control system was utilized for rapid heating to the mold temperature, which must be close to the glass temperature to ensure a good replication of the nozzle plate. The experiment resulted in the fabrication of a 3-D structure nozzle plate 2.7 mm in width and 10.8 mm in length. The total thickness was not more than 80 plusmn2 mum (ink channels, nozzle chamber, and nozzle plate), and the diameter and pitch of the nozzle holes were 25 plusmn2 mum for the outlet, 43 plusmn2 mum for the inlet, 84 plusmn2 mum in pitch, and 30 plusmn2 mum for the ink channel. Using this 3-D structure nozzle plate improved the competitiveness of the inkjet printhead. We have demonstrated the manufacture of the main parts of the 3-D structure nozzle plate for a 1200-dpi printhead; the aforementioned fabrication process yields satisfactory results and can be applied to commercial production.

Adsorption of Cationic Surfactants onto Photoresist Surfaces-A Way to Reduce Pattern Collapse in High Aspect Ratio Patterning

en

현상공정에서 표면장력에 의한 극미세 3 차원 구조물의 변형거동 분석 및 저감방안에 관한 연구

Dense and fine polymer patterns often collapse, as they come into contact with each other at their protruding tips. Resist pattern collapse depends on the aspect ratio of patterns and the surface tension of rinsing materials. The pattern collapse is a very serious problem in microfabrication, because it is one of the factors which limit the device dimensions. The reasons for the pattern collapse are known as the surface tension of rinse liquid, centrifugal force and rinse liquid flow produced in the developing process. In this work, we tried to evaluate the pattern collapse of three-dimensional microstructures that were fabricated by two-photon induced photopolymerization, and showed the way how to reduce the deformation of microstructures.

빔 위치 관련 제어인자가 집속이온빔 패턴 증착공정에 미치는 영향

Abstract The application of focused ion beam (FIB) depends on the optimal interaction of the operation parameters between operating parameters which control beam and samples on the stage during the FIB deposition process. This deposition process was investigated systematically in C precursor gas. Under the fine beam conditions (30kV, 40㎚ beam size, etc), the effect of considered process parameters - dwell time, beam overlap, incident beam angle to tilted surface, minimum frame time and pattern size were investigated from deposition results by the design of experiment. For the process analysis, influence of the parameters on FIB-CVD process was examined with respect to dimensions and constructed shapes of single and multi- patterns. Throughout the single patterning process, optimal conditions were selected. Multi-patterning deposition were presented to show the effect of on-stage parameters. The analysis have provided the sequent beam scan method and the aspect-ratio had the most significant influence for the multi-patterning deposition in the FIB processing. The bitmapped scan method was more efficient than the one-by-one scan type method for obtaining high aspect-ratio (Width/Height > 1) patterns. 기호설명 A : 수준계AR : 폭에 대한 높이 또는 깊이 비율Lm(An) : 직교 배열 함수m : 실험의 크기 n : 배치 가능한 최대 인자수