There is a need for accurate and instant measurement of pH values in a wide range of applications. The research on
miniaturized polymer based pH sensors has recently emerged due to the progress made in polymer materials science.
Novel method of manufacturing micro sensors arrays for biomedical applications using BioForce NanoeNablerTM is
reported. This nanopatterning system uses a liquid dispensing process via specially designed surface patterning tool
(SPT), which is microfabricated cantilever with an integrated passive microfluidic system. During the deposition
process, which typically takes less than 100 msec, SPT end touches the surface and a volume of fluid is instantly
transferred. The NanoeNablerTM can deliver attoliter to picoliter volumes of liquid with a high degree of spatial accuracy,
which resulted in sensor heads measuring 1-2.5 μm to 30 μm. These sensors were developed for biomedical applications,
in particular pH monitoring. It is envisaged that findings of this work would form the basis for miniaturised point-of-care
diagnostic system. The operation of the sensing elements is based on the properties of polymers, which exhibit a change
in their electrical characteristics (such as resistance or capacitance) on exposure to solutions with different concentrations
of pH value.
Biosensor designs are emerging at a significant rate and play an increasingly important role in foodborne pathogen
detection. Conducting polymers are excellent tools for the fabrication of biosensors and polypyrrole has been used in the
detection of biomolecules due to its unique properties. The prime intention of this paper was to pioneer the design and
fabrication of a single-strand (ss) DNA biosensor for the detection of the Bacillus cereus (B.cereus) group species.
Growth of B. cereus, results in production of several highly active toxins. Therefore, consumption of food containing
>106 bacteria/gm may results in emetic and diarrhoeal syndromes. The most common source of this bacterium is found
in liquid food products, milk powder, mixed food products and is of particular concern in the baby formula industry.
The electrochemical deposition technique, such as cyclic voltammetry, was used to develop and test a model DNA-based
biosensor on a gold electrode electropolymerized with polypyrrole. The electrically conducting polymer, polypyrrole is
used as a platform for immobilizing DNA (1μg) on the gold electrode surface, since it can be more easily deposited from
neutral pH aqueous solutions of pyrrolemonomers. The average current peak during the electrodeposition event is
288μA. There is a clear change in the current after hybridization of the complementary oligonucleotide (6.35μA) and for
the noncomplementary oligonucleotide (5.77μA). The drop in current after each event was clearly noticeable and it
proved to be effective.
KEYWORDS: Receivers, Mathematical modeling, Transmitters, Signal processing, Detection and tracking algorithms, Radio propagation, Non-line-of-sight propagation, Algorithm development, Received signal strength, Transceivers
In this paper we consider the problem of tracking the real-time positions of a diagnostic capsule in the gastrointestinal
(GI) tract. Our solution is a fully developed estimation algorithm that utilizes radio frequency signals converted to
voltage on the received signal strength indicator (RSSI) output of an array of transceivers. We employed a modified
form of the traditional radio-map based deterministic model that requires an estimate of initial position vector. Data
capture was implemented with commercial off-the-shelf transceivers featuring RSSI outputs. At the intermediate
processing stages, trilateration was employed as a mathematical tool to determine the approximate 2-D coordinates of
unknown capsule locations by linearizing the resulting equations. This approach facilitates a PC-based implementation
of fully automated real-time position measurements by eliminating the need to measure angles. In the final algorithm
based on non linear least squares approximations, the Newton's iteration of the resulting Jacobian matrices were used to
generate a more accurate position coordinates. Test Results from laboratory experiments demonstrate the accuracy of the
solution in the centimeter range. This results in a position tracking measurements with an average value error of less than
25%. This kind of results guarantees that our solution can be adapted into telemetry capsules for use in diagnosing
intestinal malfunctions.
Due to the demand for accurate, reliable and highly sensitive pH sensors, research is being pursued to find novel
materials to achieve this goal. Semiconducting metal oxides, such as TiO, SnO and SnO2 and insulating oxides such as
Nb2O5 and Bi2O3, and their mixtures in different proportions are being investigated for this purpose. The films of these
materials mixtures are used in conjunction with an interdigitated electrode pattern to produce a conductimetric/capacitive
pH sensor. The advantages of this approach include straightforward manufacturing, versatility and cost-effectiveness. It
was noted that upon contact with a solution, the electrical parameters of the films, such as resistance etc., change. The
correlation of these changes with pH values is the basis for the proposed system development. The ultimate goal is to
find materials composition, which would have the highest sensitivity towards the pH level of the solutions. It was found
that the materials that produced the highest sensitivity either had a long response time or were unstable over a wide pH
range. Those exhibiting lower sensitivities were found to be more stable over a wide pH range. All oxide films tested
demonstrated a change in electrical parameters upon contact with buffers of known pH value.
This work explores the radiation and ozone sensing properties of mixed oxides in the form of thin films. External effects,
such as radiation and ozone, cause defects in the materials it interacts with and, consequently, it causes changes in their
properties. These changes manifest themselves as the alterations in both the electrical and the optical parameters, which
are being measured and employed for dosimetry sensor development.
An Edwards E306A thermal coating system was used for In2O3:ZnO:SnO2 (90% : 5% : 5%) films deposition. For the
electrical properties measurements, Cu electrodes were manufactured on the glass substrate via thermal evaporation of
Cu; then AZ5214 photoresist was spin-coated over it and exposed to UV light via the acetate, containing the desired
electrodes patterns. After the exposure, the substrate was placed in Electrolube PDN250ML developer solution and then
rinsed in water and placed in the etching solution of SEMO 3207 fine etch crystals to reveal the electrode pattern.
The optical properties of In2O3:ZnO:SnO2 thin films were explored using CARY 1E UV-Visible Spectrophotometer. The
values of the optical band gap Eopt are estimated in the view of the Mott and Davis' theory. It was noted that Eopt
decreases with the increase in radiation dose, i.e. the overall disorder of the system is increased. Doping of In2O3 with
5% ZnO and 5% SnO2 dramatically changes the overall structure of the film and thus affected its sensing to gamma
radiation and ozone. Mixing metal oxides in certain proportions provides a tool for controlling the sensors response.
This paper explores the use of mixed oxide materials such as In2O3 and SiO with various compositions in the form of thermally deposited thin films for gamma radiation dosimetry application. 137Cs radiation source with an activity of 370 kBq was used for exposing the samples to γ-radiation. The absorption spectra for as-deposited and γ-irradiated films were recorded using CARY 1E UV-Visible Spectrophotometer. The values of the optical band gap Eopt were obtained in the view of the Mott and Davis’ theory. It was found that the optical properties of thin films were highly affected by composition and manufacturing conditions. For comparison, Eopt of as-deposited thin film with composition 75 wt.% of In2O3 and 25 wt.% of SiO was found to be 0.9 eV, whereas films with 50 wt.% of In2O3 and 50 wt.% of SiO have Eopt=1.15 eV, in all cases assuming indirect allowed transition. It was noted that Eopt decreased with the increase in radiation dose, i.e. the overall disorder of the system has increased. Thin films of In2O3 and SiO mixtures might be regarded as a cost-effective alternative to the existing commercially available radiation detectors.
Focused ion beams (FIB) have been widely used as a patterning lithography technique for advanced ICs and optical masks fabrication. FIB lithography has certain advantages over the direct-write electron beam lithography in terms of resist sensitivity, backscattering and proximity effects. However, combining the FIB exposure with both Top Surface Imaging (TSI) and dry etching will further extend its advantages towards anisotropic processing of thicker resist layers in comparison to those used by the conventional lithography processes. The newly developed NERIME (Negative Resist Image by Dry Etching) process combines these advantages by the incorporation of focused Ga+ ion beam (Ga+ FIB) exposure, near UV exposure, silylation and dry etching. The work described here follows our investigations into the NERIME process for nanostructure applications and outlines a simplified (two-step) process incorporating FIB exposure and oxygen dry development. The two-step modified NERIME process is a negative working TSI system for DNQ/novolak based resists. Results show that Ga+ ion beam dose higher than 800μC/cm2 at 30keV can modify the exposed resist areas as to withstand the subsequent oxygen plasma etching, thus giving formation of negative resist image. In this study, nanometer resist patterns as small as 30nm with high aspect ratio of up to 15 were successfully resolved due to the high resolution ion beam exposure and anisotropic dry development. The proposed two-step lithography scheme could be utilized for the fabrication of critical CMOS process steps, such as sub-100nm gate formations and lithography over substantial topography.
In this work, the authors explore the application of tetramethylammonium hydroxide (TMAH) developer chemical as a staining agent to enhance the top-down contrast of a silylated pattern to optical detection. When examining a silylated latent image top-down, the topographical differences generated due to the swelling of the silylated region are relied upon to identify pattern details. However, for lower exposure energy or shorter silylation times, there may not be sufficient silicon incorporation to allow clear identification of specific structures for cleaving. The authors have used the TMAH staining technique proposed by La Tulipe et al. to enhance the relief top-down, thereby facilitating analysis of even mildly silylated samples. Results will be presented illustrating the contrast enhancement after staining. Cross-sections of film profiles after aqueous silylation of an I-line photoresist with a solution of hexamethylcyclotrisilazane will also be generated.
Top Surface Imaging (TSI) is a well-established technique used to improve resolution for optical, ultraviolet and electron-beam lithography. The Positive Resist Image by Dry Etching (PRIME) is an advanced lithographic process incorporating electron beam exposure, near UV flood exposure, silylation and dry development. In this paper, the liquid-phase silylation process step in PRIME with Shipley SPR500A-series resists has been experimentally investigated as the most critical part of the process. FT-IR spectroscopy, UV spectroscopy, SIM spectrometry and cross-sectional SEM and TEM were used to characterise the silylation process. Electron-beam exposure with dose in the range of 25-100μC/cm2 at 30KeV was used to crosslinks the resist. Results show that an e-beam dose of 50µC/cm2 was sufficient to prevent silylation in the crosslinked areas. Two bifunctional silylating agents, the cyclic Hexamethylcyclotrisilazane (HMCTS) and the linear Bis[Dimethylamino] dimethylsilane (B[DMA]DMS), were examined and found that they silylate SPR505A much more efficiently than the previously reported Hexamethylcyclotrisiloxane (HMCTSx). The silylation contrast of the PRIME process using HMCTS silylating agent and SPR505A resist was found to be 11:1. The obtained silylated profiles of 1mm lines/spaces gratings for Shipley SPR510A resist have almost vertical sidewalls resulting in very high contrast between the silylated and unsilylated parts of the resist.
Focused Ion beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering and proximity effects. However, combining the FIB lithography with Top Surface Imaging (TSI) will extend its advantages by allowing anisotropic processing of thicker resist layers. This paper reports the development of novel single layer lithography process by combining focused Ga+ ion beam (Ga+ FIB) lithography, silylation and oxygen dry etching. The Negative Resist Image by Dry Etching (NERIME) is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. Results show that Ga+ ion beam dose in the range of 1μC/cm2 to 50μC/cm2 at 30keV can successfully prevent silylation of the resist, thus resulting in the formation of positive image after the dry etching. A negative image can be formed by using a second Ga+ ion beam exposure with a dose higher than 900 μC/cm2 at 30keV to pattern lines into the original exposed resist area. It was observed that resist regions exposed to such high doses can effectively withstand oxygen dry development, thus giving formation of negative resist image. In this study, nanometer resist patterns with high aspect ratio up to 15 were successfully resolved due to the ion beam exposure and anisotropic dry development. This novel TSI scheme for ion beam lithography could be utilized for the fabrication of critical CMOS process steps, such as deep isolation trench formation and lithography over substantial topography.
KEYWORDS: Silicon, Photoresist processing, Ultraviolet radiation, Diffusion, FT-IR spectroscopy, Absorbance, Spectroscopy, Scanning electron microscopy, Lithography, Picture Archiving and Communication System
Top Surface Imaging (TSI) is a well-established technique to improve resolution for optical, ultraviolet (UV) and e-beam lithography. The Positive Resist Image by Dry Etching (PRIME) process is a high resolution single layer lithography system incorporating electron beam exposure, silylation and dry development. In this paper, modeling of nanostructures down to 30nm using PRIME with 0.5micrometers thick Shipley SPR505A resist are presented. The simulated profiles have been found to correlate closely with the published experimental data. Moreover, the liquid-phase silylation process step in PRIME has been experimentally characterised using FT-IR spectroscopy, UV spectroscopy, SIM spectrometry as well as cross-sectional SEM and TEM. The impact of different silylating agents on SPR505A is presented for both the UV exposed and e-beam crosslinked regions of the resist. Results show that an e-beam dose of 50(mu) C/cm2 at 30KeV is sufficient to crosslink the resist and prevent silylation. The silylation contrast using Hexamethylcyclotrisilazane (HMCTS) was found to be the highest (11:1) in comparison with other two silylating agents. It was found that the silicon incorporation in SPR505A resist follows Case II diffusion mechanisms.
The physical, electrical, and temperature dependent properties of thick film polymeric materials are presented. It has been shown that the sensitivity of the planar polymer piezoresistive gauges is comparable to that of the metal-foil gauges. Whereas the sandwich (MRM-metal resistor metal) configurations exhibit similar characteristics to those of cermet thick film MRM gauges, The electrical tests were carried out on films in the MRM configuration and have shown the existence of electroforming at voltages exceeding the forming voltage. Further increasing the applied voltage is shown to produce both s-type and N-type negative resistance within the films, depending on the region of operation within the V- I characteristic.
KEYWORDS: Deep ultraviolet, Photoresist processing, Floods, Image processing, Diffusion, Picture Archiving and Communication System, Modeling and simulation, Anisotropy, Semiconducting wafers, Process modeling
In this paper, a new method to calculate the silylation profile in the PRIME process is presented. New software modules have been added to the 2D simulator SLITS in order to simulate the silylation and dry developed profiles in the PRIME process. The silylation and dry developed profiles for the PRIME process are simulated and compared to experimental results. Simulations were carried out for both e-beam and DUV exposures. Under e-beam exposure, the maximum percentage error between the simulated and experimental results was 13%. Under DUV exposure, the silylation depth at the mask edge can be reduced by increasing the dose thus effectively controlling the resist linewidth. The depth of focus was found to be 0.4 micrometers .
DESIM is an exclusive simulator for the DESIRE process. It can model all the three unit processes i.e. surface imaging (projection/contact, conventional/phase-shifted mask), silylation (positive/negative tone, gas/liquid phase, pre-silylation baking), dry development (single and two step). This paper discusses some of the models and then evaluates the performance of the simulator by comparing the simulated results.
In DESIRE process, silylation is probably the most critical step since the final resist profiles are mainly determined by the Si distribution between the exposed and unexposed areas of the upper part of the resist. In the past, the silylation contrast was used to predict the silylation profile for a given silylation condition. In this paper, a new method to calculate the silylation profile is presented. A new module is added in ANKAN simulator to predict the silylated profile using this method. Extensive simulation was carried out for a one dimensional line space object under various process conditions. Change in silylation depth at the center and corner of the line has been computed to study the effect of aerial image on silylation profile for both PLASMASK 200G and 301U photoresists.
This paper attempts to investigate the possible degradation of the ester formed in PLASMASK 200G photoresist during extended silylation times with HMDS (hexamethyldisilazane). The breakdown of the ester results in the formation of a phenolic moiety and an amide. This may lead to silylation of this newly released phenolic OH-group in the unexposed regions, and hence a decrease in the contrast might occur. This would have a detrimental effect on critical dimension (CD) control. It was found that under higher ammonia concentrations, an ester degrades to release a phenolic group and also an amide. The silylation times involved are much greater than that used in the DESIRE process, and as such degradation of the ester in the DESIRE process is itself quite minimal. It is, however, suggested that a silylating agent that does not form a base on cleavage be used instead to reduce the degradation effect.
KEYWORDS: Process control, Plasma etching, Control systems, Rule based systems, Data processing, Integrated circuits, Inspection, Etching, Metrology, Manufacturing
This paper discusses the development and implementation of a rule-based system which assists in providing automated process control for plasma etching. The heart of the system is to establish a correspondence between a particular data pattern -- sensor or data signals -- and one or more modes of failure, i.e., a data-driven monitoring approach. The objective of this rule based system, PLETCHSY, is to create a program combining statistical process control (SPC) and fault diagnosis to help control a manufacturing process which varies over time. This can be achieved by building a process control system (PCS) with the following characteristics. A facility to monitor the performance of the process by obtaining and analyzing the data relating to the appropriate process variables. Process sensor/status signals are input into an SPC module. If trends are present, the SPC module outputs the last seven control points, a pattern which is represented by either regression or scoring. The pattern is passed to the rule-based module. When the rule-based system recognizes a pattern, it starts the diagnostic process using the pattern. If the process is considered to be going out of control, advice is provided about actions which should be taken to bring the process back into control.
The implementation of statistical process control coupled with a failure mode evaluation analysis had failed to produce feature sizes consistently on the target of 5 micrometers . The process was in control but was not capable of delivering product consistently within specification. A Taguchi-type experiment was organized to maximize the process output. Several experiments were conducted varying just one factor at a time. This procedure identified (a) potential nonlinear response factors and (b) appropriate levels for the Taguchi experiment. Six important factors and one potential interaction (exposure and develop time) were identified. The L8 design of Taguchi's arrays was used and each experiment was repeated at both high and low humidities and different ambient temperatures. Significant factors and their appropriate levels were identified and the predicted response was 4.956 micrometers . The confirmatory runs averaged 5.005 microns.
Many designs of misalignment test structures have been developed
to evaluate registration error. It is desirable to compare the
capabilities of these structures. However, a quantitative measure of
comparison for such structures is not available. An attempt has been
made in this paper to evaluate a quantitative comparison criterion.
Technical merit of a test structure can be determined from the
accuracy and precision of the measurement data. A Figure of Merit(FOM)
is described here, for comparing the capabilities of two or more such
test structures quantitatively.
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