Characterization method for new resist formulations for HAR patterns made by X-ray lithography

At the Karlsruhe Institute of Technology (KIT), Institute of Micro Structure Technology (IMT) high aspect ratio (HAR) micro structures are manufactured by means of deep X-ray lithography and gold electroplating (LIGA technology). The technology is used to fabricate grating structures for differential phase contrast X-ray imaging (DPCI). Using an epoxy based negative resist material; electroplated grating structures are fabricated having absorber lamellas with heights up to 100 μm and a period down to 2.4 μm. However, in DPCI there is an increasing demand for improved quality gratings with periods down to 1 μm, areas larger than 50 mm × 50 mm with a high homogeneity in terms of the lamella height distribution and defect-free grating patterns. Pattern deformations are due to limited mechanical stability of the resist during the development process as well as to resist shrinkage during crosslinking, affecting mostly gratings with small periods and HARs. The purpose of this contribution is to present a methodology for the characterization of different epoxy based negative resist formulations, aiming to increase the quality of the HAR free standing grating lamellas by increased mechanical stability of the resist.     

The copolymer of methyl methacrylate and methacrylic acid as a sensitive resist for deep-etch X-ray lithography

The copolymer of methyl methacrylate and methacrylic acid was developed as a new sensitive resist for the LIGA (Lithographie, Galvanoformung, Abformtechnik) process. The resist exposures were carried out at the LIGA beamline of a superconducting compact light source NIJI-III. The absorbed energy density required to remove the entire exposed resist and produce a defect-free microstructure was between 0.4 and 7 kJ/cm³ (4 and 20 kJ/cm³ for PMMA). The sensitivity and patterning depth of the copolymer were 10 times and 3.5 times, respectively, those of poly methyl methacrylate (PMMA) assuming that both resists were exposed to synchrotron radiation (SR) of the same wavelength. Moreover, the copolymer showed high contrast and process stability. This work was performed under the management of the Micromachine Center as part of the Research and Development of Micromachine Technology supported by NEDO (New Energy and Industrial Technology Development Organization).     

The copolymer of methyl methacrylate and methacrylic acid as a sensitive resist for deep-etch X-ray lithography

The copolymer of methyl methacrylate and methacrylic acid was developed as a new sensitive resist for the LIGA (Lithographie, Galvanoformung, Abformtechnik) process. The resist exposures were carried out at the LIGA beamline of a superconducting compact light source NIJI-III. The absorbed energy density required to remove the entire exposed resist and produce a defect-free microstructure was between 0.4 and 7 kJ/cm³ (4 and 20 kJ/cm³ for PMMA). The sensitivity and patterning depth of the copolymer were 10 times and 3.5 times, respectively, those of poly methyl methacrylate (PMMA) assuming that both resists were exposed to synchrotron radiation (SR) of the same wavelength. Moreover, the copolymer showed high contrast and process stability. This work was performed under the management of the Micromachine Center as part of the Research and Development of Micromachine Technology supported by NEDO (New Energy and Industrial Technology Development Organization).     

A new removable resist for high aspect ratio applications

A variety of different photo resists are used for fabrication of MEMS. Presently good results were reported for SU-8, a chemically amplified negative tone photoresist. But SU-8 has a disadvantage for some applications in LIGA technique, especially in the X-ray mask fabrication. After processing the finished resist pattern are hardly soluble from the substrate. This paper will briefly describe the current status of the development of the new negative tone photoresist CAR 44 whose big advantage is the easy removableness of the cross linked pattern. This work widely uses the contents of the presentation “A New Removable Resist for High Aspect Ratio Applications” to the High Aspect Ratio Micro Structure Technology workshop HARMST 2005 held in Gyeongyu (Republic of Korea), June 10–13, 2005.     

SU-8 as resist material for deep X-ray lithography

 A new negative tone resist for deep X-ray lithography is presented. This resist is a nine parts to one mixture of the EPON SU-8 resin with 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)propane (Tetrachlorobisphenol A, TCBA), the latter acting as the photoinitiator. The resist was irradiated at the synchrotron source of DCI at LURE. It was dried for 7 to 20 days beforehand over silica gel while under a light vacuum (20 mbar). Best results for a 150 μm high resist were obtained with a X-ray bottom dose of 3 kJ cm⁻³ and a post exposure bake at 33 °C. Differential Scanning Calorimetry measurements (DSC) determined the glass transition temperature of the resist. The glass transition for the undried, loose resist was 34.7 °C, and it was 28.7 °C when the resist was pressed on a silicon substrate. For a sample of the dried resist, the glass transition was 33.4 °C for the loose resist and 29.8 °C when it was pressed on a Silicon substrate. CD measurements were made on top surface of a set of 100 μm long columns structures, which were produced in 150 μm of this resist. These structures have a constant 100 μm pitch, and the structures themselves varied in width from 20 to 17 μm. For these structures, the CD was calculated to be 0.15 ± 0.03 μm. Received: 8 February 2000/Accepted: 3 March 2000     

Large area, cost effective X-ray masks for high energy photons

The cost effectiveness of the deep X-ray lithography and electrodeposition process, LIGA, depends directly on the throughput of the process. The use of high energy photons allows the exposure of stacked photoresist and results in high throughput. High energy X-ray exposures require a different mask than low energy X-ray exposures. The high energy mask allows a large area exposure but requires a thicker X-ray absorber. The cost of generating high energy X-ray masks can be drastically reduced by using a thick optical photoresist process rather than an X-ray exposure process. The cost can be further reduced by using alternatives to the typical X-ray absorber, gold. High atomic weight (high Z) materials are ideal absorbers. Lead has been demonstrated as being a useable alternative as an X-ray absorber. Received: 7 July 1999 / Accepted: 1 September 1999     

Linewidth design rules for microstructures manufactured in PMMA resist using X-ray LIGA

During the past decade, individual simulation modules for the LIGA process have been developed, such as the power spectrum of the X-rays available from a given synchrotron, the effect of various components in the beam line, the image structure in the resist and image development. This has lead to an understanding of the parameters affecting the basic dimensional relationship between the mask and the 3D image in the resist itself. The commercialization of X-ray LIGA now requires knowledge of the parameters affecting the production engineering of micro devices. Foremost among these parameters are the manufacturing tolerances arising from variations in key microfabrication steps. This paper seeks to integrate the various physical simulation models into a single interactive program, whereby the design engineer can see the effect of different synchrotron output spectra, different beamline constructions and different resist parameters on the dimensions of the planned 3D microstructure. A novel approach to estimating the dimensional tolerances to be expected with large scale production is developed and comparison made with data available from the literature. Predicted results from using a particular synchrotron with a beamline designed to approximate to a “standard” exposure spectra at the rest surface are calculated, showing the microstructure shape and tolerance expected in large scale production. From these data a basic set of equations are established from which “Linewidth Design rules for LIGA” can be established. The steps following definition of the resist structure, for example electrodeposition, injection moulding or hot embossing, are not studied here.     

A new Farkas lemma for positive semidefinite matrices

We consider a general linear system over the cone of positive semidefinite matrices. To check consistency, one may not invoke the standard Farkas lemma because the cone of positive semidefinite matrices is not polyhedral, and thus an additional closedness assumption is required. In this note, we provide a modified Farkas lemma with no closedness assumption     

A new measure of consistency for positive reciprocal matrices

The analytic hierarchy process (AHP) provides a decision maker with a way of examining the consistency of entries in a pairwise comparison matrix and the hierarchy as a whole through the consistency ratio measure. It has always seemed to us that this commonly used measure could be improved upon. The purpose of this paper is to present an alternative consistency measure and demonstrate how it might be applied in different types of matrices.     

Microfabrication of thick tungsten films for use as absorbers of deep X-ray lithography masks

 We fabricated thick (5 μm) tungsten (W) film patterns by sputtering and dry etching, and realized a new deep X-ray lithography mask. The X-ray mask with 5-μm-thick W absorbers could expose about 1-mm-thick resist structures. In the deposition process of W films, the column structure of about 0.2 μm grain size, from which pattern edge roughness originates, disappeared by adding nitrogen into the sputtering gas. W film etching was carried out by reducing gas pressure and cooling the substrate (−40 °C), and a side etch width of below 0.2 μm was obtained. From the results of the pattern edge roughness and the side etch width, a pattern fabrication accuracy below ±0.5 μm was achieved. Furthermore, film stress, which induces pattern distortion, was reduced to below 50 MPa by controlling the sputtering gas pressure. The obtained mask achieved a pattern distortion below ±0.3 μm. Received: 7 July 1999/Accepted: 29 May 2000     

A new maximum-likelihood phase estimation method for X-ray pulsar signals

X-ray pulsar navigation （XPNAV） is an attractive method for autonomous navigation of deep space in the future. Currently, techniques for estimating the phase of X-ray pulsar radiation involve the maximization of the general non-convex object functions based on the average profile fxom the epoch folding method. This results in the suppression of useful information and highly complex computation. In this paper, a new maximum likelihood （ML） phase estimation method that directly utilizes the measured time of arrivals （TOAs） is presented. The X-ray pulsar radiation will be treated as a cyclo-stationary process and the TOAs of the photons in a period will be redefined as a new process, whose probability distribution function is the normalized standard profile of the pulsar. We demonstrate that the new process is equivalent to the generally used Poisson model. Then, the phase estimation problem is recast as a cyclic shift parameter estimation under the ML estimation, and we also put forward a parallel ML estimation method to improve the ML solution. Numerical simulation results show that the estimator described here presents a higher precision and reduces the computational complexity compared with currently used estimators.     

A new concept of full-automated equipment for the manufacture of shirt collars and cuffs

The quality requirements in clothing manufacturing have been increasing and consumer pressure on prices has also grown steadily. In fact, the textile industry is continuously seeking for countries practicing low salaries, because this kind of industry is usually based on labour-intensive tasks, to the detriment of task automation. Thus, clothing manufacturers need to be creative in order to improve the manufacturing processes, trying to automate the needed operations to produce each cloth component as much as possible. Automated operations avoid manufacturing mistakes and increase productivity, which are the main concerns of the clothing market. This work intends to develop a new concept of equipment able to produce collars and cuffs for shirts almost fully automatically. The manual movements have been carefully observed, optimized and replicated by the equipment, which successfully sews and cuts collars and cuffs for shirt fabrication. The structure and main systems used in the equipment were studied using the Finite Element Method (FEM), ensuring the required accuracy for all related operations. The result is a functional equipment that is able to be produced in large scale with an affordable cost, overcoming several problems related to the labour usually associated with the sewing and cutting operations required to fabricate collars and cuffs.     

A new method for positive and unlabeled learning with privileged information

Positive and unlabeled learning (PU learning) has been studied to address the situation in which only positive and unlabeled examples are available. Most of the previous work has been devoted to identifying negative examples from the unlabeled data, so that the supervised learning approaches can be applied to build a classifier. However, for the remaining unlabeled data, they either exclude them from the learning phase or force them to belong to a class, and this always limits the performance of PU learning. In addition, previous PU methods assume the training data and the testing data have the same features representations. However, we can always collect the features that the training data have while the test data do not have, these kinds of features are called privileged information. In this paper, we propose a new method, which is based on similarity approach for the problem of positive and unlabeled learning with privileged information (SPUPIL), which consists of two steps. The proposed SPUPIL method first conducts KNN method to generate the similarity weights and then the similarity weights and privileged information are incorporated to the learning model based on Ranking SVM to build a more accurate classifier. We also use the Lagrangian method to transform the original model into its dual problem, and solve it to obtain the classifier. Extensive experiments on the real data sets show that the performance of the SPUPIL is better than the state-of-the-art PU learning methods.

     

Kinetic masks: a new approach and device for dispersing biologically relevant fluids

The controlled dispersion of fluids, particularly biologically relevant solutions in micro-volumes, is of high practical interest in biotechnology and medicine. Pharmaceutical test assays, for example, need a method for the fast and defined deposition of fluid samples. Most current micro-dispensing methods, i.e. contact-based pin printing, have problems such as time delays, limited dosing velocity, minimum volume or high interference that limit biological applications. Spraying techniques suffer from a lack of reproducibility; a defined deposition of samples on targets is not possible. Here, we introduce a new method for the parallel and spatially defined dispersion of many micro-volumes that overcomes disadvantages of common micro-dispensers. The overall approach is that a fluid drop, produced by a droplet generator, falls on a free trajectory with a defined kinetic energy, and is split by a masking unit placed perpendicular to the flight direction into at least two smaller droplets (Zimmermann et al. in Method and device for dosing fluid media, WO/2002/102515, Germany, 2002). On the target, the resulting droplets form reproducible patterns, which are enlarged and scalable images of the grid pattern. Possible applications for this method are non-contact cell patterning, cell encapsulation, cryopreservation and fast mixing processes in micro-volumes. Here, we use this method for the direct and defined parallel positioning of cell suspensions on specific substrates, which can be useful for test assays, tissue engineering and cryopreservation.     

A new splitting and preconditioner for iteratively solving non-Hermitian positive definite systems

A new iteration method for solving a linear system with coefficient matrix being non-Hermitian positive definite is presented in this note. We study the spectral radius and contraction properties of the iteration matrix and then analyze the best possible choice of the parameter. With the results obtained, we show that the new method is convergent for a non-Hermitian positive definite linear system and propose a preconditioner to improve the condition number of the system. The numerical examples show that the new method is much more efficient than the HSS (or PSS) iteration method.     

Vic-dioximes: A new class of sensitive materials for chemical gas sensing

Vic-dioximes, a class of organic chemical compounds, are proposed and characterized for the first time as sensitive materials for volatile organic compound sensing with sorption based chemical gas sensors. Their peculiar sensing properties described in this work originate in the oxime functional group which is a powerful H bond donor interacting strongly but reversibly with H bond acceptors. These specific interactions result in a high preferential enrichment of analyte molecules with H bonding acceptor capabilities in the sensitive material. Accordingly, sensitivity and selectivity for these compounds of vic-dioxime based sensors are high. The advantageous sensing properties are demonstrated in this work with quartz crystal microbalance sensors using 11 selected volatile organic compounds and a set of vic-dioximes varied in their substituents. Vic-dioximes with short alkylthiol substituents were found highly sensitive to such H bond acceptors as organic amines, alcohols, and esters with partition coefficients up to 26,000. At the same time they showed low affinity for aromatic compounds and chlorocarbons. Vic-dioximes are considered powerful sensing materials and interesting for practical use in chemical gas sensor arrays.     

A hybrid histogram/neural network classifier for creating global cloud masks

A histogram method is used to identify the features which are used to classify the scene elements, and a hierarchical neural network with 'don't care' nodes is used to perform the actual classification. Although the ultimate goal is to produce a classifier capable of detecting clouds anywhere in the world, this preliminary system is limited to classifications in three distinct ecosystems: the polar region, desert terrain, and scenes of biomass burning in South America. Classification accuracies of 97.5 per cent for desert data, 98 per cent for polar data, and 99.2 per cent for biomass burning data were achieved. More importantly, manual analysis of classified scenes which had not been previously seen by the classifier show 'very good' to 'excellent' correspondence between the computer generated classifications and the human expert classifications.