This is the second in a planned series of editorials covering all aspects of good science writing.

Abstract unavailable.

The implementation of our previously reported chemo-epitaxy method for directed self-assembly (DSA) of block copolymers (BCPs) on 300-mm wafers is described in detail. Some challenges to be addressed include edge bead removal control of the layers forming the exposure stack and uniformity of the deposited films across the wafer. With the fine tuning of the process conditions, this flow provides chemically nanopatterned substrates with well-defined geometry and chemistry. After a film of BCP is annealed on the chemical patterns, high degrees of perfection are achieved. A BCP with natural periodicity of 25 nm was assembled on100-nm pitch prepatterns, obtaining 4X feature multiplication. Top-down scanning electron microscope images show a wide process window with depth of focus >200 nm and exposure latitude >40% for lines and spaces of 12.5-nm half-pitch. We provide a platform for future study of the origin of DSA generated defects and their relationship to process conditions and materials that are amenable to use by the semiconductor industry.

The optimization of a grapho-epitaxy process flow for lamellar phase block copolymer frequency multiplication on full 300 mm wafers is discussed. The process uses a dedicated photoresist that, after hardening, allows direct coating and annealing of the block copolymer over it. Some of the critical parameters for optimization of this process were found to be the selection of the neutral layer material and reduction of the prepattern resist height. Process window analysis was done by determining the best dose and focus settings for generating high quality directed self-assembly structures with the prepattern process. A very small process window for good self-assembly and an offset in the optimum dose and focus settings for these two stages of the process were found. Finally, the sensitivity of the process to programmed prepattern imperfections was studied. Programmed protrusions in the prepattern as small as 6 nm were found to cause self-assembly defects.

Self-assembly of block copolymers is a potential technique to be used in the fabrication of microelectronic devices. In some cases, the self-assembly is directed by means of an additional technique, e.g. photolithography. This paper studies the impact of ArF_i-lithography on the properties of the polymer after the directed assembly. Placement, critical dimension and critical dimension uniformity of the features are analyzed and discussed and compared to an integrated circuit application according to the international technology roadmap for semiconductors roadmap.

A method for using wet development in a directed self-assembly lithography (DSAL) application is reported. For the typical diblock copolymer poly(styrene-block-methyl methacrylate) (PS-b-PMMA), the PMMA area is removed by an oxygen plasma. However, the oxygen plasma has poor selectivity for the PS portion of the block polymer and etches it simultaneously. As a result, the thickness of the residual PS pattern is thinner than desired and creates a challenge for subsequent pattern transfer. A wet development technique is discussed which offers higher selectivity between the PMMA and PS blocks in the assembled pattern. Specifically, a method using a low pressure mercury lamp and conventional tetramethylammonium hydroxide (TMAH, 2.38%) developer is proposed. Using this method, DSA pattern formation is completed in a single track having coating, baking, exposure, and development modules.

Self-organizing block copolymer thin films hold promise as a photolithography enhancement material for the 22-nm microelectronics technology generation and beyond, primarily because of their ability to form highly uniform patterns at the relevant nm scale dimensions. Importantly, the materials are chemically similar to photoresist and can be implemented in synergy with photolithography. Beyond the challenges of achieving sufficient control of self-assembled pattern defects and feature roughness, block copolymer-based patterning requires creation of robust processes for transferring the polymer patterns into underlying electronic materials. Here, we describe research efforts in hardening block copolymer resist patterns using inorganic materials and high aspect ratio plasma etch transfer of self-assembled patterns to silicon using fluorine-based etch chemistries.

Abstract unavailable.

First results obtained with IMS Nanofabrication's 50-keV proof-of-concept electron multibeam mask exposure tool (eMET POC) are presented. The eMET POC was designed from scratch to meet the requirements of the 11-nm half-pitch node and already features the same column as future high volume manufacturing (HVM) tools. All exposures shown in this paper were the result of 262,144 beams of 20 nm beam size working in parallel demonstrating the capability of IMS's multibeam technology. An alpha tool is scheduled for 2014, followed by a beta tool in 2015 and first-generation HVM tools in 2016.

Techniques to appropriately control the key factors for a character projection (CP) based electron beam direct writing technology for mass production are shown and discussed. In order to achieve accurate CD control, the CP technique using the master CP is adopted. Another CP technique, the Packed CP, is used to obtain suitable shot count. For the alignment on the some critical layers which normally have an even surface, the process removing SiO₂ material filled in the alignment marks is added and then the alignment marks can be detected using electron beam. The proximity effect correction using the simplified electron energy flux model and the hybrid exposure are used to obtain enough process margins. As a result, the sufficient CD accuracy, overlay accuracy, and yield are obtained on the 65 nm node device. Due to the proper system control, more than 10,000 production wafers have been successfully exposed so far without any major system downtime. It is shown that those techniques can be adapted to the 32 nm node production with slight modifications. It is expected that by using the Multi Column Cell exposure method, those techniques will be applicable to the rapid establishment for the 14 nm node technology.

Acceptance of imprint lithography for manufacturing will require demonstration that it can attain defect levels commensurate with the defect specifications of high-end memory devices. Defects occurring during imprinting can generally be broken into two categories; random defects and repeating defects. Examples of random defects include fluid phase imprint defects, such as bubbles, and solid phase imprint defects, such as line collapse. Examples of repeater defects include mask fabrication defects and particle induced defects. Previous studies indicated that soft particles cause nonrepeating defects. Hard particles, on the other hand, can cause either permanent resist plugging or mask damage. In a previous study, two specific defect types were examined; random nonfill defects occurring during the resist filling process and repeater defects caused by interactions with particles on the substrate. We attempted to identify the different types of imprint defect types using a mask with line/space patterns at dimensions as small as 26 nm. An Imprio 500 twenty-wafer per hour development tool was used to study the various defect types. The imprint defect density was reduced nearly four orders of magnitude, down to ~ 4/cm² in a period of two years following the availability of low defect imprint masks at 26-nm half-pitch. This reduction was achieved by identifying the root cause of various defects and then taking the appropriate corrective action.

A block copolymer-directed self-assembly was combined with nanoimprint lithography to generate templates with rectangular patterns through an original double imprint process. A rotary e-beam tool was used to separately expose circumferential and radial line/space chemical contrast patterns with periodicities commensurate to the natural period of two lamellae-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymers. Line patterns are formed by directed self-assembly of PS-b-PMMA on chemical patterns on two separate submaster templates, one with circumferential lines to define concentric tracks, and a second template on which the block copolymer is used to form radial lines at constant angular pitch. The patterns are subsequently transferred to their underlying Si substrates to form submaster templates. Using two sequential nanoimprinting steps, the radial and circumferential submaster line patterns were combined into a final quartz master template with rectangular bits on circular tracks.

We present a prototype electron emitter array integrated with an active-matrix driving large-scale integrated circuit (LSI) for a high-speed massively parallel direct-write electron-beam (e-beam) system. In addition, we describe the results of a performance evaluation of it as an electron source for massively parallel operations. The electron source is a nanocrystalline Si (nc-Si) ballistic surface electron emitter in which a 1∶1 projection of the e-beam can resolve patterns 30 nm wide. The electron-emitting part of the device consists of an array of nc-Si dots fabricated on an SOI or Si substrate and through silicon via (TSV) plugs connected to the dots from the back of the substrate. The device consists of an aligned joint of TSV plugs with driving pads on the active-matrix LSI. Electron emissions are driven by the LSI and are boosted to an appropriate level using a built-in voltage level shifter in accordance with a bitmap image preliminarily stored in the embedded memory. Electron emissions from a test array work as intended, showing the possibility of switching on and off the beamlets by changing the CMOS-compatible voltage.

We studied the erosion and feature stability of fused silica patterns under different template cleaning conditions. The conventional sulfuric acid and hydrogen peroxide mixture (SPM) cleaning is compared with an advanced nonacid process. Spectroscopic ellipsometry optical critical dimension measurements were used to characterize the changes in pattern profile with good sensitivity. This study confirmed the erosion of the silica patterns in the traditional acid-based SPM cleaning mixture (H₂SO₄+H₂O₂) at a rate of ~ 0.1 nm per cleaning cycle. However, the advanced nonacid cleaning process only showed critical dimension shift of ~ 0.01 nm per cleaning. Contamination removal and pattern integrity of sensitive 20-nm features under MegaSonic assisted cleaning was also demonstrated.

Radio frequency MEMS switches are key components in low power communication systems. The present paper reports fabrication of MEMS based series and shunt switches for actuation voltage in the range of 30 to 50 V. Focusing on a low cost fabrication approach, the switches were designed for higher isolation of >25  dB and low insertion loss of <0.5  dB. Aluminum was chosen as a cost effective alternative for the fabrication of the transmission line and structural beam. The shunt and series switches were investigated for a frequency range of 1 to 20 GHz. The shunt switch shows the insertion loss of 0.5 dB and isolation of −28  dB and the series switch shows the insertion loss of 0.7 dB and isolation of −27  dB at 20 GHz. The measured actuation voltage was 30 V for the shunt switch and 42 V for the series switch.

Recently, prototype MOEM tunable Fabry-Perot filters operating from 400 to 800 nm were fabricated under a program to design miniature hyperspectral imagers operating from the visible to the longwave infrared. The filter design uses two semitransparent 30 nm thick silver-film mirrors, one fixed and the other moving, on a low-cost thin commercial quartz substrate. The moving mirror is supported by three leaf spring arms, which are fabricated by wet etching of the quartz substrate. The tuning of the transmitted wavelength of light from the filter is achieved by electrostatically actuating the moving mirror to vary the distance between the two mirrors. The size of the device is 18×24  mm². The fixed part has a 6 mm diameter mirror and three electrodes to apply voltages, and the moving mirror is used as a ground electrode. Au bumps deposited on both parts control the initial air gap distance, and an Au-Au bonding is used to bond the two parts together. The spectral imaging performance of the MOEM filter is characterized using a spectrally tunable source and a CCD camera with suitable optics. The authors present a brief description of the filter, its characteristics, spectral imaging characterization experiment and results.

Photolithography is one of the main mass nanoproduction processes. Manufacturing small devices by photolithography is a challenge because of the risk of collapse of patterns during the drying of rinse liquid. Literature models are usable for only long (i.e., LAR, pattern length/spacing greater than 20) two-line parallel patterns. In the current study, a numerical framework is introduced that allows study the collapse of different pattern geometries. In this framework, the rinse interface shape is found using Surface Evolver, and pattern deformation is found using ANSYS through coupled modeling. The results of the new numerical approach, was in agreement with the analytical model results in the range of its applicability (i.e., long two-line parallel pattern). The developed numerical framework was then used to study a few simple geometries where the analytical model was not applicable. One of the findings from the numerical framework results was that, despite the fact that buttresses stiffen the patterns, buttressed patterns deform more owing to the increase in Laplace pressure.

Modern high-resolution lithography, which employs a chemically amplified resist (CAR) at either 193 or 13.5 nm wavelength, is often limited by pattern collapse. While the general concepts of how CAR platforms work are widely understood, the influence of composition on pattern collapse has been studied to a lesser extent. In addition, the subject is often further complicated by non-disclosure of the resist chemistry used in the lithographic evaluation. Open-source photoresist platforms can be beneficial for fundamental studies on how individual components influence pattern collapse. Such platforms should mimic a typical CAR, containing-apart from the polymer-additional components such as photo acid generators (PAGs) and base quenchers. Here, 193 nm and extreme ultraviolet lithography open-source platforms are presented wherein the chemistry, composition, and concentration are all disclosed. With the aim of fundamentally understand how resist composition and behavior influences pattern collapse, the molecular weight of the polymer backbone and the concentration of both PAG and base quencher were varied. These sets of resists were exposed using high-end optical lithography scanners. The results are presented such that the probability of pattern collapse is derived as a function of the exposure wavelength, chemistry, and component concentrations.

The authors investigated finite element (FE) analysis of damped modal vibrations in complex geometries of micro-electromechanical (MEM) resonators. Q-factor values were determined by taking the thermo-elastic damping into account. The basic model created is presented as a system of partial differential equations, which describe the elastic and thermal phenomena in the MEM structure. Mathematically the problem is formulated as a complex eigenvalue problem. Modal properties of square- and ring-shaped bulk-mode MEM resonators were investigated by taking into account the layered structure of the MEM system and the influence of the geometry of the clamping zone. The calculations were performed by employing the COMSOL Multiphysics FE software. The solution method was verified by comparing numerically and analytically obtained damped modal properties of a MEM cantilever resonator.

An out-of-plane electrostatic comb actuator with in situ capacitive position sensing is presented. Asymmetrical vertical combs are used as the comb drives and in differential out-of-plane position sensing capacitors. A spring which can realize out-of-plane translational displacement of high-aspect-ratio structures was designed and analyzed both analytically and numerically. A robust silicon-on-insulator (SOI) process was proposed and verified to successfully fabricate the actuator with asymmetrical combs. The in situ capacitive position sensing capability was realized by the integrated out-of-plane sensing capacitors, and calibrated with the gravity as an acceleration reference. Treated as an accelerometer, the scale factor and nonlinearity of the actuator are evaluated to be 93.4 mV/g and 0.03%, respectively, with the input range of ±1 g. The tested static out-of-plane displacement ranges from -0.88 to 1.39 μm when the actuator is placed horizontally, and -1.16 to 1.25 μm when placed vertically, both with the supply voltage of 12 volts.

Low-energy electron beam lithography is one of the promising next-generation lithography technology solutions for the 21-nm half-pitch node and beyond because of fewer proximity effects, higher resist sensitivity, and less substrate damage compared with high-energy electron beam lithography. To achieve high-throughput manufacturing, low-energy electron beam lithography systems with writing parameters of larger beam size, larger grid size, and lower dosage are preferred. However, electron shot noise can significantly increase critical dimension deviation and line edge roughness. Its influence on patterning prediction accuracy becomes nonnegligible. To effectively maximize throughput while meeting patterning fidelity requirements according to the International Technology Roadmap for Semiconductors, a new method is proposed in this work that utilizes a new patterning prediction algorithm to rigorously characterize the patterning variability caused by the shot noise and a mathematical optimization algorithm to determine optimal writing parameters. The new patterning prediction algorithm can achieve a proper trade-off between computational effort and patterning prediction accuracy. Effectiveness of the new method is demonstrated on a static random-access memory circuit. The corresponding electrical performance is analyzed by using a gate-slicing technique and publicly available transistor models. Numerical results show that a significant improvement in the static noise margin can be achieved.

Design considerations for ultraviolet-nanoimprint lithography resists were investigated focusing on the major issues of ink-jetting performance, pattern formability, release property, and dry etching resistance. Regarding ink-jetting performance, small droplet ink-jetting of 0.7 pl was successfully demonstrated by adjusting the resist fluid property to the ink-jet coater and controlling the resist volatilization. Regarding pattern formability, a resist pattern was imprinted from a mold pattern of 28 nm in width and 60 nm in depth without pattern dimension change. It was thought that modulus control of the resist was more important than resist shrinkage in achieving excellent pattern formability. As for release property, resist with fluorine monomer and with nonreactive fluorine antisticking agent were compared. The results indicated that resist design has the capability to both reduce separation force and maintain a clear mold surface. The mold release agent decomposed with an increasing number of imprint shots, but the low release-force resist with nonreactive antisticking agent was able to control degradation of the mold release agent and thus improve release property endurance. Regarding etching resistance, it was found that increasing the ring parameter of resist is essential for high etching resistance, and resulted in improved etched pattern features of the substrate.

We compare the performances of vibration-powered microelectromechanical system (MEMS) electrical generators using a Pb(Zr,Ti)O₃ (PZT) material. With the aid of a finite element method simulation, we have designed a PZT cantilever-based energy-harvesting system that uses mechanical vibration. We fabricate cantilevers on the MEMS scale with an integrated variable Si proof mass to obtain a low resonant frequency and high current. Based on simulation results, we fabricate cantilever devices with integrated Si proof masses with volumes of about 0.32 and 0.53 mm ³. These devices compare favorably to the data obtained through simulation. Further, by comparing variable mass volumes, we obtain a high current and low resonant frequency. Similar results are obtained by simulation and experiment. Therefore, we offer a new and predictable means of obtaining a low resonant frequency for application to a micropower source area. Furthermore, from the size effect of the proof mass volume, we obtain the current and resonant frequency of these energy harvester systems. The possibility of a MEMS-scale power source for energy conversion experiments is also tested.

We report the fabrication and testing of 30-μm radii circular InGaN blue light-emitting didode (LEDs) grown on sapphire wafers, with cointegrated Fresnel zone plates (FZP) with outermost ring radii of 99.6 μm on the backside of the sapphire substrates to provide a collimated output. After being embedded on a contact lens platform such LEDs with integrated lenses can aid in producing in-focus images on the human retina. We measured an image width of 50 μm created by a FZP f/3 subsidiary focal point at 230 μm from the surface. We also demonstrate the construction and wireless operation of a contact lens with predetermined embedded text.

The crossover of high-speed digital electronics, micro electro mechanical systems, and cost reduction presents an exciting opportunity to extend optical lithography with multiple e-beam direct write systems (MEB DW). Massive parallelism overcomes the throughput limitation of e-beam direct write systems. Many innovative concepts on multiple e-beam imaging have been conceived and are being developed for various applications, such as maskwriting, prototyping, writing critical layers in high volume manufacturing (HVM), and writing all layers in HVM. MEB DW systems are capable to do all of the above. For maskwriting, the writing time can be saved by between a factor of 5 and 10, but it takes similar efforts to develop the maskwriting technology as direct wafer writing. There is insufficient demand for maskwriting and prototyping tools to warrant the development efforts. Writing critical layers in HVM is cost effective for wafer production and makes economic sense to develop the imaging tool. However, using MEB DW for critical and noncritical layers, especially for 450-mm wafers, presents a unique opportunity to save lithography cost. This is the most desirable application for MEB DW. Once this all-layer application is established, any other applications easily follow.