An overview of X-ray lithography

Current achievements and future prospects of SR base x-ray lithography are explained through an account of research and development efforts made by NTT LSI Laboratories. The SR lithography system, including the compact SR light source Super-ALIS and beamlines with efficient mirrors, is now at the stage of practical use. The vertical x-ray steppers SS-1 and SS-2 have attained a repeatability of overlay accuracy as high as 25 nm (3σ). High-accuracy x-ray masks can be fabricated by applying the multiple-exposure method. Further improvement in pattern placement accuracy is expected with application of distortion compensation writing. Intense efforts made in development of x-ray mask inspection and repair technology resulted in the fabrication of defect-free x-ray masks. Test fabrication of CMOS/SIMOX LSIs has yielded fully functional devices, with an improved overlay accuracy of 0.1 to 0.15 μm (3σ), and a CD control of ±10% in 0.2 μm regions. Further application of SR lithography to the test fabrication of future LSIs will prompt the implementation of this technology into the practical process.     

E-beam lithography by using an STEM with integrated laser interferometer stage

A high resolution e-beam lithography instrument has been developed consisting of an STEM (Zeiss EM 910) equipped with a laser interferometer stage, an electrostatic beam blanker, and “ELPHY Plus”. This new system now allows to perform high voltage e-beam lithography on small samples with highest resolution and precise stitching.     

Accurate Litho Model Tuning Using Design-Based Defect Binning

Advanced lithography optical proximity correction (OPC) techniques rely on accurately tuned process models. Although through-process OPC models are being used for critical layers at the 65-nm node, typically an initial model is created at a single optimized process setting. Such “best condition” models often produce process-window limiting structures that can impact yield. A new methodology is presented for identifying misprinted structures during the qualification of a new photomask and optimizing the process model based on those structures. Instead of the traditional approach which employs repeater analysis, the new technique bins the process-limiting structures according to their design. This method enables efficient data reduction and identification of a new feature set for lithography process model tuning.      

Exposure latitude and CD control study for additively patterned X-ray mask with GBit DRAM complexity

40 kV electron beam lithography has been used to pattern gold plated x-ray masks containing GBit DRAM complexity layouts. The two commercial e-beam resists used, namely PMMA and SAL 601, both showed 0.12 μm resolution capability in dense and large layouts patterning and also, under optimised exposure and development conditions, exhibited good exposure latitudes which were also evaluated for two different beam spot sizes. Futhermore, a study of development technique and effect of e-beam spot size indicated a marked dependence of ultimate resolution and exposure latitude on such parameters. A statistical analysis of 0.12 μm resolution SAL patterning on large chip dies (30 × 30 mm²) resulted in a dimensional control of 10 nm (3σ value).     

Properties of the Stimulus Router System, a Novel Neural Prosthesis

Various types of neural prostheses (NPs) have been developed to restore motor function after neural injury. Surface NPs are noninvasive and inexpensive, but are often poorly selective, activating nontargeted muscles and cutaneous sensory nerves that can cause discomfort or pain. Implantable NPs are highly selective, but invasive and costly. The stimulus router system (SRS) is a novel NP consisting of fully implanted leads that “capture” and route some of the current flowing between a pair of surface electrodes to the vicinity of a target nerve. An SRS lead consists of a “pick-up” terminal that is implanted subcutaneously under one of the surface electrodes and a “delivery” terminal that is secured on or near the target nerve. We have published a preliminary report on the basic properties of the SRS [L. S. Gan , “A new means of transcutaneous coupling for neural prostheses,” IEEE Trans. Biomed. Eng., vol. 54, no. 3, pp. 509–517, Mar. 2007]. Here, we further characterize the SRS and identify aspects that maximize its performance as a motor NP. The surface current needed to activate nerves with an SRS, was found to depend on the proximity of the delivery terminal(s) to the nerve, electrode configurations, contact areas of the surface electrodes and implanted terminals, and the distance between the surface anode and the delivery terminal.      

Optical Phase Add–Drop for Format Conversion Between DQPSK and DPSK and its Application in Optical Label Switching Systems

We propose and experimentally demonstrate an optical phase “add–drop” scheme to enable the format conversion between a 20-Gb/s differential quadrature phase-shift keying (DQPSK) and 10-Gb/s differential phase-shift keying. Meanwhile, the incoming DQPSK could be directly forwarded to another wavelength through the proposed optical phase “drop” scheme, which is implemented by four-wave-mixing effect in highly nonlinear fiber. By orthogonally encoding the label and payload of the optical packet on the in-phase ( $I$) and quadrature ( $ Q $) components of DQPSK, the proposed scheme could be applied in the optical label switching networks. The label erasing and rewriting of optical packets can be achieved through the proposed optical phase “drop” and “add” schemes, respectively.      

FPGA-Based Real-Time Power Converter Failure Diagnosis for Wind Energy Conversion Systems

This paper discusses the design, implementation, experimental validation, and performances of a field-programmable gate array (FPGA)-based real-time power converter failure diagnosis for three-leg fault tolerant converter topologies used in wind energy conversion systems (WECSs). The developed approach minimizes the time interval between the fault occurrence and its diagnosis. We demonstrated the possibility to detect a faulty switch in less than 10 $muhbox{s}$ by using a diagnosis simultaneously based on a “time criterion” and a “voltage criterion.” To attain such a short detection time, an FPGA fully digital implementation is used. The performances of the proposed FPGA-based fault detection method are evaluated for a new fault tolerant back-to-back converter topology suited for WECS with doubly fed induction generator (DFIG). We examine the failure diagnosis method and the response of the WECS when one of the power switches of the fault tolerant back-to-back converter is faulty. The experimental failure diagnosis implementation based on “FPGA in the loop” hardware prototyping verifies the performances of the fault tolerant WECS with DFIG.      

Large-Scale In Situ Fabrication of Voltage-Programmable Dual-Layer High-$kappa$ Dielectric Carbon Nanotube Memory Devices With High On/Off Ratio

In this letter, we report on measurements of carbon nanotube (CNT) field-effect transistors with high on/off ratio to be used as nonvolatile memory cells operating at room temperature. Thousands of memory devices have been realized using a complete in situ fabrication method. The self-aligned fabrication process allows large-scale production of CNT memory devices with high yield. The memory function is obtained by the threshold voltage shift due to the highly reproducible hysteresis in the transfer characteristics. The ratio of the current levels between a logical “1” and a “0” is about $hbox{10}^{6}$.      

Threshold and Filament Current Densities in Chalcogenide-Based Switches and Phase-Change-Memory Devices

Threshold current density of switching was found to grow several decades at constant threshold electric field with reducing interelectrode distance. Data are compared with predictions of various switching theories. Experimental estimate of current density in an electronic filament is reported based on a programming “dead-space” observation in a ring contact device with one subcritical bottom contact dimension. Significance of the shape of S-type negative differential conductivity curve and, namely, the slope of the second part with positive differential conductivity for the programming of phase-change memory is discussed.      

A technique for calibrating an electron-beam evaporator x-ray source

An electron-beam metal evaporator was modified to act as an x-ray source for simulating x-ray lithography induced radiation damage in semiconductor devices. Besides x-rays, such a set-up generates secondary and backscattered electrons. Simulation of radiation damage induced during a typical x-ray lithography processing step requires that secondary and backscattered electrons be removed from the incident radiation. A common method to separate the electrons and x-rays is to block the electrons with a thin beryllium film. However, thin beryllium films are expensive and are not commercially available in large sizes. Instead, a relatively inexpensive polymer pellicle was used to block the electrons. A disadvantage of the pellicle is that its x-ray transmission characteristics are unknown and must be determined experimentally. Previous works calibrated the pellicle x-ray transmission and system electron/x-ray flux ratios using the known x-ray transmission characteristics of beryllium film. To check the accuracy of the beryllium calibration results, a new calibration method employing two pellicles was developed. A comparison of the calibration data found a large discrepancy between the two calibration methods. The discrepancy was attributed to ultraviolet light absorption in the radiation dosimeters. A correction for the ultraviolet light absorption is presented for determining the true electron/x-ray flux ratios and pellicle x-ray transmission.     

Good and bad aspects of traps for neutral particles

We exhibit a configuration of magnetic fiedls which has a field minimum at its center and is therefore suitable for trapping paramagnetic neutral atoms or molecules. The trap has a large field component along the axis and is therefore conducive to high resolution spectroscopy. We propose an RF-laser cooling cycle which appears to be capable of attaining ultimate temperatures of 10^-6K. Limits to the attainable resolution due to this temperature are discussed.

In order to label the properties of traps for neutral particles as “good” or “bad” it is necessary to have some value system. Mine is that good properties enhance the utility of these traps for studies of properties of the trapped atoms: precise spectroscopy of their levels, collision studies using a dense cold target, and possibly the “solid state” physics of their mutual interaction at high density. (From the contrasting perspective of interesting and/or challenging physics relating to slow atoms, the labels good and bad may well be reversed!)     

On the Discontinuity of the Shannon Information Measures

The Shannon information measures are well known to be continuous functions of the probability distribution for a given finite alphabet. In this paper, however, we show that these measures are discontinuous with respect to almost all commonly used “distance” measures when the alphabet is countably infinite. Such “distance” measures include the Kullback–Leibler divergence and the variational distance. Specifically, we show that all the Shannon information measures are in fact discontinuous at all probability distributions. The proofs are based on a probability distribution which can be realized by a discrete-time Markov chain with countably infinite number of states. Our findings reveal that the limiting probability distribution may not fully characterize the asymptotic behavior of a Markov chain. These results explain why certain existing information-theoretical tools are restricted to finite alphabets, and provide hints on how these tools can be extended to countably infinite alphabet.      

94-GHz Imager With Extended Depth of Field

We describe a computational imaging technique to extend the depth-of-field of a 94-GHz imaging system. The technique uses a cubic phase element in the pupil plane of the system to render system operation relatively insensitive to object distance. However, the cubic phase element also introduces aberrations but, since these are fixed and known, we remove them using post-detection signal processing. We present experimental results that validate system performance and indicate a greater than four-fold increase in depth-of-field from 17” to greater than 68”.      

Low energy electron proximity printing using a self-assembled monolayer resist

A simple method for high resolution (<100nm) lithography is reported. We use electrons with energies ranging from 100–300eV emitted by tungsten field emission tips for proximity printing of stencil masks. A comparison with other parallel fine line techniques, like proximity printing and projection lithography with x-rays, high energy electrons or ions, reveals the specific advantages and restrictions of our method.

The masks are made of ≈ 100nm thick silicon membranes structured by e-beam lithography and reactive ion etching (RIE). Free standing gratings with periods down to 100nm serve as test patterns for proximity printing with gaps of ≈15μm. due to the short penetration depth of the low energy electrons, ultrathin resist systems are needed. We have chosen self-assembled monolayers (SAMs) of hexadecane thiol on gold. The monolayer resist is degraded by the exposure, the structures can be transferred by wet chemical etching. Periodic gold structures below 100nm lines and spaces have been generated this way. It was found, that the SAM resist of hexadecane thiol can be used as a positive or negative tone resist depending on the exposure dose.     

Optimum path planning using convex hull and local search heuristic algorithms

Whether in improving quality or productivity the impact of mechatronic systems such as robots in industry is unquestionable. One aspect of interest in robotics is planning the optimum path for a mobile robot or the optimum trajectory for link movements of a stationary robot in order to increase their efficiency. However, for a given set of points complete enumeration of all the possible paths to establish an optimal one is not feasible as the search space increases exponentially (explodes combinatorially) as the number of points increases. This problem, traditionally known as the “Traveling Salesman Problem” (TSP) has attracted a great deal of attention for a long time. Proven enumerative techniques such as “nearest neighbour algorithm”, “branch and bound”, “cutting planes”, and “dynamic programming” as well as approximation methods such as “tabu search”, “greedy algorithm”, “simulated annealing” and “genetic algorithm”, have had only a limited success in solving this problem. Recently “convex hull”, a minimum area and perimeter shape, has been used as an initial sub-tour along with enumerative techniques such as minimising insertion costs to solve the TSP problem. We present a system which uses heuristic rules to augment the convex hull initial sub-tour created by the Graham scan algorithm. The system is able to provide a solution in a polynomial time.     

Tech Talk: An Investigation of Blogging in Technology Innovation Discourse

Web logs, or “blogs,” are fast developing in diverse social and business contexts as influential sources of discourse, knowledge, and community development. In this paper, we investigate an aspect of blogging highly relevant to professional communication: the fast-developing world of “tech blogging.” Tech blogs are blogs that focus on information technology innovation and the high-tech industry. We examine nine months of blog entries gathered by an internet aggregator site dedicated to technology news and commentary. Our analysis provides insights on the discourse of tech bloggers and an elite subgroup (“A-list bloggers”), on the discursive practices of this virtual community, and on issues of identity and legitimacy. Our findings hold implications for tech bloggers as well as for managers who need to navigate the expanding blogosphere and for technical communicators who can benefit from using the information that tech bloggers produce.      

Design and Fabrication of FlexConnects: A Cost-Effective Implementation of Compliant Chip-to-Substrate Interconnects

Compliant free-standing structures can be used as chip-to-substrate interconnects. Such “compliant interconnects” are a potential solution to the requirements that will be imposed on chip-to-substrate interconnects over the next decade. However, cost of implementation and electrical performance limit compliant interconnects. This paper presents two concepts to address this. First, an innovative, cost-effective fabrication process to realize compliant interconnects is proposed. Sequential lithography and electroplating processes with up to two masking steps are utilized. Such an approach potentially reduces the cost of fabricating compliant interconnects. Second, an innovative approach to designing compliant interconnects is proposed to improve electrical performance without compromising on mechanical reliability. The new approach uses parallel/multiple electrical paths as part of the compliant interconnect design. These concepts are integrated to realize a new compliant interconnect technology called FlexConnects. Utilizing the proposed fabrication process parallel-path FlexConnects are realized at a 100- $mu{hbox {m}}$ pitch. Numerical simulations are used to demonstrate that the electrical performance of parallel-path FlexConnects (self inductance of $sim$ 37 pH) is enhanced without compromising on mechanical performance, validating the use of parallel/multiple electrical paths in the interconnect design.      

Radiation damage and its effect on hot-carrier induced instability of 0.5 μm CMOS devices patterned using synchrotron x-ray lithography

The device characteristics and the radiation damgae ofn-channel andp-channel MOSFETs patterned using synchrotron x-ray lithography are examined. The effect of radiation damage caused by x-ray lithography on the device reliability during hot electron injection is investigated. In addition to neutral traps, large amounts of positive oxide charge and interface states, particularly acceptor-like interface states, which cause degradation of MOSFET characteristics are found to be created by x-ray irradiation during the lithography process. Although several annealing steps are performed throughout the entire fabrication process, the radiation damage, particularly neutral traps, is not completely annealed out. The hot-electron induced instability inp-channel MOSFETs is significantly increased due to the enhanced electron trapping in the oxide by residual traps. The effect of radiation damage on hot electron induced instability is found to be more severe inn ⁺-poly buried-channelp-MOSFETs than inp ⁺-poly surface-channel p-MOSFETs. However, the degradation inn-channel MOSFETs due to channel hot carriers is not significantly increased by x-ray lithography. These results suggest that the major degradation mechanism due to hot-carrier inp-channel MOSFETs is electron trapping and inn-channel MOSFETs is interface state generation. It also suggests thatp-channel MOSFETs, in addition ton-channel MOSFETs, needs to be carefully examined in terms of hot carrier induced instability in CMOS VLSI circuits patterned using x-ray lithography.     

下一代光刻技术的设备

下一代光刻技术是指≤32nm工艺节点的光刻技术。介绍了下一代光刻技术与设备,包括X射线光刻技术、极紫外线光刻技术和纳米压印光刻技术等。     

The Structure of General Interference Functions and Applications

This paper provides a theoretical framework for the analysis of interference-coupled multiuser systems. The fundamental behavior of such a system is modeled by interference functions, defined by axioms “nonnegativity, ”scale-invariance,” and “monotonicity.” It is shown that every interference function has an interpretation as the optimum of a min-max problem, where the optimization is over a closed comprehensive positive coefficient set. This provides new insight into the structure of general interference functions and its elementary building blocks. Conversely, it is shown that every closed comprehensive positive set can be expressed as a level set of an interference function. This shows a close connection between the analysis of interference functions and multiuser performance regions, which are typically closed comprehensive. The generality of this framework allows for a wide range of potential applications. As an example, we analyze the problem of interference balancing.