bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of KrF (248 nm) excimer laser irradiation on electrical and optical properties of GaN:Mg
Authors: Kim Dong-Joon , Kim Hyun-Min , Han Myung-Geun , Moon Yong-Tae , Lee Seonghoon , Park Seong-Ju
Published: March 2003

The electrical and optical characteristics of GaN:Mg irradiated by a pulsed KrF (248 nm) excimer laser have been studied. When an as-grown Mg-doped GaN film was irradiated by an excimer laser at an energy density of 590 mJ/cm2 in a nitrogen atmosphere, the hole concentration was drastically increased up to 4.42×1017 cm−3. Furthermore, a GaN:Mg thin film, which was treated by laser irradiation following a conventional rapid thermal annealing process, showed a very high hole concentration of 9.42×1017 cm−3. The GaN:Mg samples, which were activated in a nitrogen ambient by the KrF excimer laser irradiation, showed two photoluminescence peaks at 2.95 eV and 2.7 eV. The intensities of both photoluminescence peaks were increased with increasing laser energy density and number of pulses. The changes in photoluminescence peaks depending on the laser energy density further suggest that the pulsed KrF excimer laser irradiation dissociates the Mg–H complexes and allows the hydrogens to diffuse out, thus significantly enhancing the p-type conductivity of GaN:Mg.
Characterization of vapor deposited poly (ethylene glycol) films on silicon surfaces for surface modification of microfluidic systems
Authors: Popat Ketul C. , Johnson Robert W. , Desai Tejal A.
Published: March 2003

Microfluidic systems have become important platforms for diagnostic and therapeutic applications. However, as channel dimensions decrease within these systems, the surface properties of these microchannels become increasingly important. When biological fluids are flowed through such channels, nonspecific protein adsorption can occur due to surface interactions, often resulting in reduced efficiency of the system. When small quantities of biological sample are involved, any loss of sample through the system can be critical. Poly(ethylene glycol) (PEG) films are known to reduce protein adsorption, but the existing approaches for coupling PEG to surfaces is not always appropriate for the micro/nanoscale features common in microfluidics systems. Therefore, we have developed a vapor deposition technique to modify microchannels with PEG. These films have been extensively characterized by contact angle measurement, x-ray photoelectron spectroscopy, and atomic force microscopy. Results show that film composition can be controlled by controlling the reactant concentrations and that the films are stable up to a period of 4 weeks. Moreover, protein adsorption is decreased by 80%. The vapor deposition technique may be more efficient in coating micro/nanosized features since it forms uniform, conformal, and ultrathin films on the surface. Surface modification using chemical vapor deposition of PEG shows promising results for a variety of bio-micro-electromechanical system applications.
Contact resistance of newly proposed RuTiN and RuTiO diffusion barriers for future high-density memory capacitors
Authors: Yoon Dong-Soo , Roh Jae Sung
Published: March 2003

We suggested a new design concept for the diffusion barrier in high-density memory capacitors. Both RuTiN and RuTiO were proposed as sacrificial diffusion barriers for oxygen. For newly developed RuTiN and RuTiO barriers, oxidation resistance was superior to that of polycrystalline nitride and ternary amorphous barriers reported by others. Moreover, contact resistance, the most important electrical parameter for diffusion barriers in a capacitor structure, was below 5 kΩ for the Pt/barriers/TiSix/n++poly-Si plug/n+ channel layer/Si substrates even after annealing up to 750 °C, although the current–voltage curves showed nonlinear ohmic characteristics. Consequently, RuTiN and RuTiO films, as diffusion barriers for oxygen, were strongly recommended for achieving high-density capacitors.
Modeling the impact of photoresist trim etch process on photoresist surface roughness
Authors: Rauf Shahid , Stout Phillip J. , Cobb Jonathan
Published: March 2003

Evolution of roughness on photoresist (PR) sidewalls during PR trim etching has been investigated using an integrated two-dimensional plasma equipment-feature evolution model. Results show that the PR trim process reduces PR surface roughness as exposure to energetic ions enhances etching of “rough” protrusions while shadowing of neutral etchants within rough cavities reduces the etch rate there. Large amplitude roughness is found to be relatively easier to remove so the roughness reduction rate decreases as the trim etch process progresses. This is because the disparity between the etch rate of rough protrusions and cavities decreases as roughness is reduced and all regions of the surface start etching laterally at similar rates. Low spatial frequency roughness components are more difficult to remove during PR trimming than high-frequency components because there is less neutral etchant shadowing within cavities at low frequencies and rough bumps become too broad to effectively remove through physical sputtering.
Large area direct nanoimprinting of SiO2–TiO2 gel gratings for optical applications
Authors: Li Mingtao , Tan Hua , Chen Lei , Wang Jian , Chou Stephen Y.
Published: March 2003

We demonstrated an economical way of fabricating gel–film-based devices by combining nanoimprint lithography (NIL) and a sol–gel technique. A novel imprinting procedure, new mold surface passivation, and an effective surfactant added to sol were developed. Gratings with 300 nm pitch and 80 nm linewidth and waveguide gratings with varying periods were imprinted in a single step and with excellent uniformity into the gel films coated on a quarter of 4 in. wafers, respectively. Surface roughness measurements of waveguide gratings by atomic force microscope showed smooth profiles with root mean square roughness less than 6 nm. NIL is an excellent patterning technology for gel–film-based optical devices.
Silicon nanowire with programmable conductivity analyzed by scanning Maxwell-stress microscopy
Authors: Matsukawa Takashi , Kanemaru Seigo , Masahara Meishoku , Nagao Masayoshi , Tanoue Hisao , Itoh Junji
Published: March 2003

A novel silicon nanowire with programmable conductivity which utilizes sensitivity of conductance to surface charging has been investigated. The device consists of a nanowire with a width of 10–25 nm and side gates for control of surface charging on to the nanowire. The wire current measured during sweep of the side gate exhibited clear hysteresis characteristics and significant retention of the programmed states for more than 1000 s. Surface potential imaging of the nanowire by means of scanning Maxwell-stress microscopy (SMM) has been carried out for correlating the programmed conductivity to charging on the nanowire. The SMM images clearly exhibited that charging on the nanowire which provided the programmable conductivity was precisely controlled by the side gate sweep.
Properties of ZnO-doped Zr0.8Sn0.2TiO4 thin films by rf sputtering
Authors: Huang Cheng-Liang , Hsu Cheng-Shing
Published: March 2003

Electrical properties and microstructures of ZnO-doped (Zr0.8Sn0.2)TiO4 thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different rf powers and substrate temperatures have been investigated. The surface structural and morphological characteristics analyzed by x-ray diffraction, scanning electron microscopy, and atomic force microscope, were found to be sensitive to the deposition conditions, such as rf power (300–400 W) and substrate temperature (400–450 °C). The x-ray photoelectron spectroscopy further revealed some firm evidence of a molecular orbital that affected the chemical structure. The selected-area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. All films exhibited Zn0.8Sn0.2TiO4 (ZST) (111) and (002) orientation perpendicular to the substrate surface, and the grain size as well as the deposition rate of the film increased with the increase in both the rf power and the substrate temperature. At a rf power level of 400 W and substrate temperature of 450 °C, the ZST films with 7.41 μm thickness possess a dielectric constant of 51 at 10 MHz and a leakage current density of 1.6×10−8 A/cm2 at an electrical field of 1 kV/cm.
Stability improvement of deuterated amorphous silicon thin-film transistors characterized by modified Schottky-contact gated-four-probe method
Authors: Liu Sheng-Da , Shih An , Chen Shen-De , Lee Si-Chen
Published: March 2003

A modified Schottky-contact gated-four-probe structure was applied to study the stability of the hydrogenated and deuterated amorphous silicon (a-Si:D) thin-film transistors under various bias conditions. It was found that after 10 V bias stress, the density of gap states generated in both the upper and lower part of the mobility gap of deuterated amorphous silicon is two to twenty times less than those of hydrogenated silicon. Besides, less density of states at the lower part of mobility gap of a-Si:D is generated after 20, −10, and −20 V bias stress.
Cell behavior on lithographically defined nanostructured substrates
Authors: Teixeira Ana I. , Abrams George A. , Murphy Christopher J. , Nealey Paul F.
Published: March 2003

Lithographically defined substrates offer unique opportunities for the study of cell behaviors, by allowing the presentation of controlled cell stimuli. We have investigated the effects of substrate topography on the behavior of human corneal epithelial cells using substrates patterned with grooves and ridges of well-defined dimensions. On each substrate, we included feature sizes ranging from the micrometer to the nanometer scale. This work was motivated by the fact that the surface that underlies epithelial tissues in vivo, the basement membrane, has a rich topography with features of nanoscale dimensions. We found that cells responded to topographic features as small as 70 nm wide by aligning with the pattern direction. Additionally, substrate topography affected internal organization of the cell, inducing the alignment of cytoskeletal elements (actin filaments) and adhesive structures (focal adhesions). Therefore, synthetic topographies with feature dimensions of the same length scale as the features encountered in native basement membrane profoundly affected epithelial cell behavior. These findings have relevance in tissue engineering and in the design of prosthetic devices.
Room-temperature nanoimprint and nanotransfer printing using hydrogen silsequioxane
Authors: Matsui S. , Igaku Y. , Ishigaki H. , Fujita J. , Ishida M. , Ochiai Y. , Namatsu H. , Komuro M.
Published: March 2003

Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement errors caused by thermal expansion in the conventional nanoimprint lithography (NIL) process. We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of the poly(methylmethacrylate) used in conventional NIL. We demonstrate HSQ-replicated patterns with a 90 nm diameter hole and 50 nm linewidth for room-temperature replications. Furthermore, we have developed new nanotransfer printing technology utilizing the adhesion characteristics of HSQ. We also demonstrate the transfer of photoresist and Au patterns from a mold to a substrate.
Fabrication and electrical characteristics of carbon nanotube-based microcathodes for use in a parallel electron-beam lithography system
Authors: Teo K. B. K. , Chhowalla M. , Amaratunga G. A. J. , Milne W. I. , Legagneux P. , Pirio G. , Gangloff L. , Pribat D. , Semet V. , Binh Vu Thien , Bruenger W. H. , Eichholz J. , Hanssen H. , Friedrich D. , Lee S. B. , Hasko D. G. , Ahmed H.
Published: March 2003

This article presents an overview of the “Nanolith” parallel electron-beam (e-beam) lithography approach. The e-beam writing head consists of an array of microguns independently driven by an active matrix complementary metal–oxide–semiconductor circuit. At the heart of each microgun is a field-emission microcathode comprised of an extraction gate and vertical carbon nanotube emitter, whose mutual alignment is critical in order to achieve highly focused electron beams. Thus, in this work, a single-mask, self-aligned technique is developed to pattern the extraction gate, insulator, and nanotubes in the microcathode. The microcathode examined here (150×150 gates, 2 μm gate diameter, with multiple nanotubes per gate) exhibited a peak current of 10.5 μA at 48 V when operated with a duty cycle of 0.5%. The self-aligned process was extended to demonstrate the fabrication of single nanotube-based microcathodes with submicron gates.
Bias-induced junction displacements in scanning spreading resistance microscopy and scanning capacitance microscopy
Authors: Eyben P. , Duhayon N. , Clarysse T. , Vandervorst W.
Published: March 2003

Scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) are both valuable tools for analyzing the two-dimensional carrier distribution in semiconductor devices. Both tools rely on the application of a bias between tip and sample to probe the relevant property (capacitance or resistance). With respect to SCM, experimental and theoretical evidence has been presented by several authors that the bias leads to a displacement of the mobile carriers and thus creates an ambiguity in the exact junction location among other carriers, leading to the concept of scanning capacitance spectroscopy. For SSRM, which originally employed a very small bias (50–100 mV), no displacement could be observed. With the advent of scanning spreading resistance spectroscopy and diamond-coated tips, higher bias voltages (up to 3–500 mV) are sometimes applied and questions are raised regarding possible distortions being induced in SSRM as well. In this article, detailed studies on the bias-induced junction displacement in SCM and SSRM are described. On cross sections, a larger junction shift is seen for SCM than for SSRM. On bevel sections both techniques show only a rather small displacement. For SSRM, a clear difference could be observed between p-type implants where almost no displacement is observed compared to n-type implants where a small displacement of the junction peak toward the surface is observed for large positive bias (relative to the back contact). A flattening of the SSRM junction peak for large bias voltages (mainly for positive voltages) was also observed. Finally, theoretical understanding of these observations for SSRM obtained through extensive device simulations and the qualitative simulation of the SSRM profiles are presented.
Development of an electron-beam lithography system for high accuracy masks
Authors: Kawano H. , Ito H. , Mizuno K. , Matsuzaka T. , Kawasaki K. , Saitou N. , Ohta H. , Sohda Y.
Published: March 2003

A mask electron-beam writer for production lines beyond 100 nm was developed. The system HL-7000M is equipped with cell projection function for high critical dimension accuracy. The newly developed technologies are a cell projection optics, objective lens optics, a low distortion stage, a highly accurate control electronics, and high accuracy proximity effect correction hardware. This article describes the details of the electron optics and its performances.
High-resolution complex structures for two-dimensional photonic crystals realized by x-ray diffraction lithography
Authors: Businaro L. , Romanato F. , Candeloro P. , Di Fabrizio E. , Patrini M. , Galli M. , Andreani C. , Passaseo A. , De Vittorio M.
Published: March 2003

Two-dimensional photonic band gap structures were fabricated by x-ray lithography combined with ion etching on metalorganic chemical vapor deposition grown GaAs/AlGaAs waveguides. Such structures, more amenable to fabrication than fully three-dimensional photonic crystals, allow the confinement of light in the third direction using index guiding. The feasibility of complex high-resolution (down to 50 nm) unit cell fabrication has been demonstrated by exploiting x-ray diffraction and nonlinear resist response during the development process. Optical characterizations of some samples were performed. These characterizations show the presence of well-defined photonic band gap structures and second harmonic property generation. The results have been discussed and compared with theoretical simulation.
Correlation between current–voltage characteristics and dislocations evaluated with submicrometer Schottky contacts on n-GaN grown by metalorganic chemical vapor deposition
Authors: Shiojima Kenji , Suemitsu Tetsuya
Published: March 2003

We directly evaluated the effect of dislocations on current–voltage (I–V) characteristics of Au/Ni contacts formed on n-GaN grown by metalorganic chemical vapor deposition. The key feature of our evaluation is the combination of submicrometer Schottky dot array formation by electron-beam lithography and I–V measurement by atomic force microscopy with a conductive probe. The sample, which has a free electron concentration of 3×1017 cm−3, showed that neither mixed nor pure edge dislocations affect the I–V characteristics (Schottky barrier height, ideality factor, and reverse leakage current). Possible models to explain the results are discussed. On the other hand, it was found that a large structural defect with a diameter of a few hundred nanometers shorted the contact. The density, however, was less than 4×105 cm−2. These results indicate that, in fabricating short-gate field-effect transistors, gate Schottky contacts containing dislocations should not be considered a problem with respect to uniformity and reproducibility.
Structural study of amorphous vanadium oxide films for thin film microbattery
Authors: Kim Han-Ki , Seong Tae-Yeon , Yoon Young Soo
Published: March 2003

Solid-state thin film batteries (TFBs) consisting of amorphous V2O5/Pt/Ti/Si have been fabricated by specially designed dual target magnetron radio frequency (rf) and direct current (dc) sputtering systems at room temperature. It is shown that the discharge capacity of the TFBs is degraded with increasing cycle number; after 450 cycles, the capacity is dropped by ∼54% of the initial value. To investigate the degradation mechanism, the structural properties of as-deposited and cycled LiPON and a-V2O5 films are characterized by transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements. TEM and XRD results show that the as-deposited LiPON and V2O5 are amorphous. It is, however, shown that cycling causes the occurrence of crystallites (2–6 nm across) not only in the V2O5 film, but also in the LiPON film. Based on the structural and electrochemical results, the cycle-induced degradation of capacity is correlated to the structural change of the LiPON and V2O5.
Multiple-pulse laser annealing of preamorphized silicon for ultrashallow boron junction formation
Authors: Poon Chyiu Hyia , Cho Byung Jin , Lu Yong Feng , Bhat Mousumi , See Alex
Published: March 2003

Advantages of multiple-pulse laser annealing with a moderate energy fluence over a single-pulse annealing with a high energy fluence are demonstrated on the formation of shallow p+/n junction. When the silicon surface is preamorphized, the multiple-pulse laser annealing with a fluence adjusted to a value which can melt the amorphous layer but not crystal silicon shows that the successive pulses do not increase junction depth further but decrease sheet resistance significantly. Under this condition, the junction depth is still controlled by the depth of the preamorphized layer. However, when the laser fluence is high enough to melt the crystal silicon, the successive pulses result in the deepening of junction depth. This is attributed to the increase of surface roughness by the successive pulses, thereby increasing the total absorbed energy.
Electron transport in a submicron-scale AlGaAs/GaAs field-effect transistor with InAs nanodots as the floating gate
Authors: Koike Kazuto , Sasa Shigehiko , Inoue Masataka , Yano Mitsuaki
Published: March 2003

Electron transport in a submicron-scale AlGaAs/GaAs field-effect transistor with self-assembled InAs nanodots as the floating gate is studied. Both the memory effect in current–voltage characteristics and the Coulomb oscillations in transconductance are observed due to the electron trapping at nanodot potentials. Random oscillations in the transconductance in the subthreshold region are also observed due to the Coulomb repulsion by the trapped electrons.
Temperature-dependent characteristics of an Al0.2Ga0.8As/In0.22Ga0.78As pseudomorphic double heterojunction modulation doped field-effect transistor with a GaAs/AlGaAs superlattice buffer layer
Authors: Li Yih-Juan , Hsu Wei-Chou , Wang Sheng-Yung
Published: March 2003

The Al0.2Ga0.8As/In0.22Ga0.78As pseudomorphic double heterojunction modulation doped field-effect transistor with a superlattice GaAs/Al0.2Ga0.8As buffer layer has been successfully grown by a molecular beam epitaxy (MBE) system, and investigated its temperature-dependent characteristics. The use of a superlattice buffer layer improved the degradation of the device performance at elevated temperatures. For a 1.5×125 μm2 gate dimension, a voltage gain as high as 107 is found at 460 K. Besides, the shift in the threshold voltage is about 0.222 V from 300 to 460 K.
Quantitative method of image analysis when drift is present in a scanning probe microscope
Authors: Huerth S. H. , Hallen H. D.
Published: March 2003

We present a quantitative method of image analysis that automatically corrects for system drift in comparisons of images before and after an event under study. The method utilizes two-dimensional correlations followed by automatic z scaling, shifting, and the calculation of a difference image from the before and after images. Optical reflectance near-field scanning optical microscope (NSOM) images that show the effects of oxygen electromigration are used as an example system. The tunnel current that induces the atomic motion is provided by the metallic NSOM aperture in a scanning tunneling microscope mode. The analyzed (difference) image clearly shows the effects that are otherwise obscured by native oxygen concentration variations, demonstrating the utility of the method. The related issues of false positive/negative probabilities for given noise levels and thresholds are also discussed.
Fabrication of monodomain alumina pore arrays with an interpore distance smaller than the lattice constant of the imprint stamp
Authors: Choi J. , Nielsch K. , Reiche M. , Wehrspohn R. B. , Gösele U.
Published: March 2003

Large-area monodomain porous alumina arrays with an interpore distance of 500 nm are fabricated by imprint lithography. A 4 in. imprint master fully compatible with silicon technology was developed, which allows imprint pressures as low as 5 kN/cm2 for direct imprint on aluminum. Due to the self-ordering phenomenon of porous alumina growth, we were able to reduce the interpore distance of the pore array to 60% of the lattice constant of the master stamp. Three lithographically defined pores are sufficient to guide anodization of a new pore in the center.
Characterization of different-Al-content AlxGa1−xN/GaN heterostructures and high-electron-mobility transistors on sapphire
Authors: Arulkumaran S. , Egawa T. , Ishikawa H. , Jimbo T.
Published: March 2003

Al x Ga 1−x N/GaN  (0.20⩽x⩽0.52) heterostructures (HSs) were grown on a sapphire substrate by atmospheric pressure metalorganic chemical vapor deposition with good uniformity and two-dimensional-electron-gas (2DEG) mobilities of 936, 1163, 1310, 1274, and 911 cm2/V s for different-Al-contents of 20%, 27%, 34%, 42%, and 52%, respectively. 2DEG mobility increase up to the Al content of 34% and then it slowly decreases for high Al-content AlGaN/GaN HSs. An increase of sheet carrier density with the increase of Al content has been observed. A small hump photoluminescence peak of e2DEG1–h has been observed in both 34% and 42% Al-content AlGaN/GaN heterostructures. High Al-content (52%) heterostructure has exhibited a distinguished e2DEG1–h peak. The increase of surface roughness and granular size of AlGaN/GaN heterostructures with the increase of Al content is due to the increase of lattice mismatch between GaN and AlGaN layers. High-electron-mobility transistors (HEMTs) have been fabricated and characterized using AlxGa1−xN/GaN heterostructures with different-gate lengths (2.0–5.0 μm). An increase of extrinsic transconductance (gm) and drain current density has been observed up to the Al content of 34% and it slowly decreases for higher Al-content AlxGa1−xN/GaN HEMTs. The maximum gm of 202 mS/mm with maximum drain–source current density of 525 mA/mm has been observed for 2.0-μm-gate-length Al0.34Ga0.66N/GaN HEMT structure. About 3–4 orders of magnitude, low gate-leakage current has been observed on 42% and 52% Al-content AlGaN/GaN HEMTs when compared with the low Al-content (20%) AlGaN/GaN HEMTs.
Experimental studies of the cap structure of single-walled carbon nanotubes
Authors: Dean Kenneth A. , Chalamala Babu R.
Published: March 2003

Carbon atoms forming the cap of a carbon nanotube are selectively removed through a technique that causes field evaporation during field emission. The resulting changes in the spatially resolved electronic structure are imaged in real time using field emission microscopy. We demonstrate that through repetitive field evaporation cycles, a variety of cap states can be produced on the same nanotube. We measure differences in the electrical properties due to the presence of different cap states.
Study of titanium silicide formation using spike anneal for integrated chip manufacturing
Authors: Tan C. C. , Lu L. , Lai C. W. , See A. , Chan L. H.
Published: March 2003

The use of spike anneal in titanium salicide process was studied. The area dependence of C49-to-C54 TiSi2 phase transformation was reduced for deep submicron poly-Si gate by having spike anneal during [rapid thermal annealing (RTA)] RTA1 without the use of preamorphizing implant or implant through metal. It is believed that the spike anneal during RTA1 resulted in varying amounts of C54–TiSi2, which then acts as nuclesus that grows during RTA2. Results showed that the spike anneal in RTA1 did not increase the gate to source/drain leakage current for the spike anneal temperature investigated at less than 900 °C. Results, also, show that a one-step RTA Salicide process is possible for larger linewidth devices using spike anneal.
Deep reactive ion etching characteristics of a macromachined chemical reactor
Authors: Besser R. S. , Shin W. C.
Published: March 2003

While deep reactive ion etching using an inductively coupled plasma (ICP) source has proven to be a boon to the fabrication of silicon-based microelectromechanical systems, the process is highly sensitive to the geometry of any given device and needs to be modified accordingly. For a chemical microreactor involving fluidic structures of highly varying geometry on the same device, the implementation of ICP etching can be especially challenging. We present the results of a study of one such implementation.
Single electron transistors with Nb/AlOx/Nb junctions
Authors: Dolata R. , Scherer H. , Zorin A. B. , Niemeyer J.
Published: March 2003

Deep submicron Nb/AlOx/Nb tunnel junctions and single electron transistors were fabricated by electron beam gun shadow evaporation, using stencil masks consisting of the thermostable polymer polyethersulfone and germanium. The I(U) characteristics of the single electron transistors show special features due to the tunneling of single Cooper pairs and quasiparticles. Significant e-periodic gate modulation is observed in both the superconducting and the normal state and a gap energy Δeff of up to ≈1 meV has been achieved. The special features of using the refractory metal Nb in combination with the shadow evaporation technique are discussed.
Improvement of mechanical properties of nanometer period multilayer films at interfaces of each layer
Authors: Miyake Shojiro
Published: March 2003

By controlling the time period for which the substrate was positioned opposite each of the graphite and boron nitride semicircular targets, nanometer period carbon nitride and boron nitride multilayer films were deposited one after another in an argon and nitrogen atmosphere. Both the nanoindentation hardness and microwear resistance of the multilayer films changed with the layer period. The multilayer film with a 4 nm period had the highest hardness and microwear resistance. To clarify the reason for this, the atomic scale wear was characterized. The rate of increase of wear depth was almost zero at the depth which corresponds to each layer thickness. It is suggested that the interfaces prevent the defect elongation. The preventive effect of the interface on defect elongation of a 4 nm period multilayer film is greater than that of a 2 nm period multilayer film.
Influence of hydrogen plasma treatment on boron implanted junctions in silicon
Authors: Rangan Sanjay , Horn Mark , Ashok S. , Mohapatra Y. N.
Published: March 2003

Alleviation of transient enhanced diffusion (TED) is a critical issue in realizing deep submicron complementary metal–oxide–semiconductor transistors. In this article we present the influence of hydrogen plasma on TED of boron, along with deep level transient spectroscopic (DLTS) studies on defect evolution as a function of anneal temperature. The studies reveal that TED monotonically increases as a function of anneal temperature up to 650 °C, where maximum TED occurs. A further increase in anneal temperature reveals TED reduction. The DLTS shows a corresponding increase in defect density up to 650 °C and then decreases when annealed at 850 °C for the same amount of time.
Organic modified Schottky contacts: Barrier height engineering and chemical stability
Authors: Kampen T. U. , Park S. , Zahn D. R. T.
Published: March 2003

The electronic properties of Ag/GaAs(100) contacts were modified using interlayers of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA). The influence of the organic films on the electronic transport properties was investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. The in situ I–V curves reveal a strong dependence on the PTCDA interlayer thickness dPTCDA. The effective barrier height varies between 0.81 and 0.64 eV by changing dPTCDA between 0 and 60 nm. For a layer thickness above 5 nm space-charge limited currents in the organic layer strongly influence the carrier transport in the diodes. The C–V characteristics do hardly vary upon introducing an organic interlayer with dPTCDA below 30 nm. The capacitance of the organic film is larger than that of the depletion layer within the GaAs substrates, the latter one being unaffected by the PTCDA modification and dominating the C–V characteristics. Therefore, the change in the effective barrier height can be explained by an increasing image-force lowering in the presence of the organic interlayer. Exposure of Ag/PTCDA/GaAs(100) contacts with dPTCDA=30 nm to oxygen results in an increase in effective barrier height to a value comparable to the one of a bare Ag/GaAs(100) Schottky contact. This sensitivity to air is attributed to oxygen induced deep traps. This results in a shift of the Fermi level from its original position of 2 eV above the highest occupied molecular orbital towards the middle of the band gap of PTCDA.
Integrated equipment-feature modeling investigation of fluorocarbon plasma etching of SiO2 and photoresist
Authors: Zhang Da , Rauf Shahid , Sparks Terry G. , Ventzek Peter L. G.
Published: March 2003

As the microelectronics industry continues to shrink feature size and increase feature density in the back-end of integrated circuits, the traditional empirical approach to plasma etch process development is becoming prohibitively expensive and time consuming. Fundamental physics based models can prove useful in driving down process development time and cost. In this article, an integrated equipment-feature scale modeling infrastructure for SiO2 and photoresist (PR) etching in fluorocarbon based plasma discharges is described. The model correlates process conditions with plasma properties, surface interactions, and etch results. A validated plasma chemistry for Ar/c–C4F8/CF4 and detailed plasma–surface reaction mechanisms for SiO2/PR etching have been incorporated in the model. Major surface reactions for SiO2 etching include neutral surface passivation, fluorocarbon radical polymerization, and ion assisted etching of volatile products. The mechanism for PR erosion includes energy/angle dependent ion sputtering, ion activation, F atom etching with ion assistance, and fluorocarbon radical deposition. Computed SiO2 and PR etch profiles and rates have been validated by comparing with experimental results in a commercial inductively coupled plasma (ICP) etch tool. The validated model is used for a detailed investigation of SiO2/PR etching in a representative 300 mm wafer ICP tool. It is found that SiO2 etch rate is a nonlinear function of Ar/c–C4F8 ratio, where the highest etch rate is obtained when sufficient neutral passivation takes place while polymer deposition is still small. Deviating from this condition reduces SiO2 etch rate by either excessive polymerization or insufficient passivation. PR etch rate and facet size, however, increase monotonically with Ar/c–C4F8 ratio due to reduced polymer deposition. The effect of CF4 ratio in the Ar/c–C4F8/CF4 source gas on SiO2 etching depends on the Ar fraction. When Ar fraction is large, replacing c-C4F8 with CF4 reduces surface passivation and thereby decreases SiO2 etch rate. However, at small Ar fractions, CF4 addition reduces polymer formation and increases the SiO2 etch rate. For the range of conditions explored, SiO2 etch characteristics are insensitive to bias frequency as the ion energies are well above the threshold energy for etching. The plasma zone height (PZH) impacts the fluxes of etchants to the wafer and consequently the SiO2/PR etch rates. PZH, however, does not influence etch uniformity noticeably as diffusion is dominant at low gas pressures.
Crystallization and pyroelectric effect of semiconducting YBaCuO thin films deposited at different temperatures
Authors: Yildiz Ali , Butler Donald P. , Çelik-Butler Zeynep , Kim Choong-Un
Published: March 2003

The pyroelectricity and crystallization level of yttrium barium copper oxide (YBa2Cu3O6+x) thin films have been investigated by depositing the thin films by rf magnetron sputtering at different substrate temperatures. A portion of the thin film samples were analyzed by x-ray diffraction (XRD) to investigate the crystallinity while the remainder were processed to fabricate capacitor structures with Au electrodes to study the pyroelectric properties of the thin films. We observed different crystallization levels for samples that were deposited at different substrate temperatures. Pyroelectric behavior was observed to be correlated to the strength of the XRD peaks observed. Samples that lack crystallinity did not display pyroelectric behavior, while samples with observable crystallinity displayed pyroelectric behavior, either as deposited without poling or induced by poling. Samples lacking crystallinity could not be poled to display a measurable pyroelectric behavior. Pyroelectric coefficients on the order of 50 nC/K cm2 were observed in the polycrystalline samples.
Inductively coupled plasma reactive ion etching of GaInAsSb and AlGaAsSb for quaternary antimonide multiple interconnected module thermophotovoltaics
Authors: Peake G. M. , Shul R. J. , Ashby C. I. H. , Cederberg J. G. , Hafich M. J. , Biefeld R. M. , Palmisiano M. N.
Published: March 2003

We report on the inductively coupled plasma reactive ion etching of GaInAsSb and AlGaAsSb for the fabrication of quaternary multiple interconnected module (MIM) thermophotovoltaic devices. A rapid dry etch process is described that produces smooth surfaces using BCl3 for AlGaAsSb and GaInAsSb structures capped with GaSb. Uncapped GaInAsSb was etched by adding an H2 plasma preclean to reduce surface oxides. GaInAsSb etch rate was studied as a function of accelerating voltage, rf power, temperature, and pressure. The etch conditions found for GaInAsSb were used for AlGaAsSb etching to determine the effectiveness for isolation of the MIM cells. Etch rates of 2700 Å/min with rms roughness of 0.40 nm and 3000 Å/min with rms roughness of 2.33 nm were demonstrated for GaInAsSb and AlGaAsSb, respectively.
Properties of reactive-sputtered Ti1−x AlxN films for complementary metal–oxide–semiconductor silicon storage node electrode diffusion barriers
Authors: Kim Sam-Dong , Rhee Jin-Koo , Park Hyung-Moo
Published: March 2003

We examined the effects of process variables on the sputtered Ti1−xAlxN film properties including the oxidation resistance as diffusion barriers for the complementary metal–oxide–silicon metal–oxide–metal capacitor bottom electrode structures. An optimized process window for the TiAlN sputter deposition is proposed, and the examined electrical and physical properties of the films at various deposition conditions are described in this article. The films deposited at an optimized condition of N2 flow rate of 90–110 sccm, Ar flow rate of 10 sccm, substrate temperature of 300 °C, and dc plasma power of 8 kW showed good electrical resistivity of 500–700 μΩ cm, 1σ sheet resistance uniformity of ∼5% and deposition rate of ∼18 Å/s. At this process window, pseudobinary alloy type of Ti1−xAlxN (x∼0.25) films were obtained with mixed crystallographic preferred orientations of (111) and (200). After furnace postannealing the Pt/TiAlN/TiSi2/poly-Si/SiO2/Si stacks at 600 °C for 30 min in O2, interfacial reaction of the electrode barrier layers was also investigated. Conventional TiN barriers showed complete oxidation of both barriers and TiSi2 films after postannealing, whereas the TiAlN barriers deposited at the optimized process condition were oxidized partially only at the top surfaces and give rise to excellent oxidation stability of the bottom electrode structures.
Improving the quality of electroplated copper films by rapid thermal annealing
Authors: Chang Shih-Chieh , Shieh Jia-Min , Dai Bau-Tong , Feng Ming-Shiann , Wang Ying-Lang
Published: March 2003

The leveler, 2-mercaptopyridine (2MP), increases the filling power of copper electroplating electrolytes in plating 0.15 μm vias, but forms the plated copper metals of small-grained column structures with high resistivity. In this study, we used rapid thermal annealing (RTA) to effectively improve the film quality. After RTA at 400 °C for 30 s, the resistivity of Cu deposits was reduced from ∼16.1 to ∼2.4 μΩ cm. Moreover, the Cu(111) intensity of Cu deposits increased after RTA annealing.
Applications of micro-Raman spectroscopy in salicide characterization for Si device fabrication
Authors: Zhao F. F. , Chen S. Y. , Shen Z. X. , Gao X. S. , Zheng J. Z. , See A. K. , Chan L. H.
Published: March 2003

This article demonstrates that micro-Raman spectroscopy is a very powerful technique for the study of a variety of problems related to metal salicides for Si device fabrication. In addition to its versatile nature and ease of use, this technique provides some unique capabilities that complement the commonly used tools for Si device characterization. Phase identification of the TiSi2 C54, C49, and C40 phases as well as NiSi and NiSi2 can be achieved easily using Raman spectroscopy. The phase transition process from NiSi to NiSi2 has also been successfully monitored. Raman band assignments for C40 TiSi2 and NiSi are also made in order to have a better understanding of the Raman spectra. Thickness measurement of ultrathin salicide films from 45 nm down to 6 nm has been accurately performed using attenuation of the Si Raman signal at 520 cm−1, and film uniformity can also be evaluated using the same peak. Local orientations of the NiSi grains are studied by the relative intensity of the NiSi Raman peaks with micron spatial resolution, which provides complementary information to the space-averaged x-ray diffraction result.
Comparative measurements of the piezoelectric coefficient of a lead zirconate titanate film by piezoresponse force microscopy using electrically characterized tips
Authors: Lin Heh-Nan , Chen Sy-Hann , Ho Shu-Te , Chen Ping-Ren , Lin I-Nan
Published: March 2003

We report comparative measurements of the piezoelectric coefficient d33 of a lead zirconate titanate (PZT) film by piezoresponse force microscopy based on tip/PZT/electrode and tip/electrode/PZT/electrode configurations. With the use of electrically characterized Au-coated tips, the obtained values are in good agreement and indicate a negligible methodological effect. It is concluded that the d33 can be reasonably determined without the use of a top electrode as long as the electrical quality of the tip is qualified.
Multilayer diffusion barrier for copper metallization using a thin interlayer metal (M=Ru, Cr, and Zr) between two TiN films
Authors: Kim Soo-Hyun , Nam Ki Tae , Datta Arindom , Kim Hyun-Mi , Kim Ki-Bum , Kang Dae-Hwan
Published: March 2003

A multilayer structure [TiN(5 nm)/interlayer metal(2 nm)/TiN(5 nm)] has been evaluated as a diffusion barrier between copper and silicon. Three metals (M=Ru, Cr, and Zr) were tested as interlayer materials for the multilayer diffusion barrier scheme, expecting that they will stuff the TiN grain boundaries by forming metal oxides therein. The diffusion barrier performance was found to be the best when the Zr was used as an interlayer material. X-ray diffractometry showed that the Zr interlayer diffusion barrier failed only after annealing at 800 °C for 30 min due to the formation of copper silicide while the reference sample without a metal interlayer failed when annealed at 600 °C. The insertion of Cr also was also found to enhance the diffusion barrier performance, whereas, Ru has little effect on the improvement of the barrier performance. High-resolution transmission electron microscopy and energy dispersive spectroscopy showed that Zr significantly diffused into TiN grain boundaries while Ru did not diffuse during annealing. An explanation of the variation of the diffusion barrier performance with the change of an interlayer metal is given in terms of Gibbs free energy change of the respective metal–oxide formation.
NiAuGeAu ohmic contacts for a planar InP-based high electron mobility transistor structure with suppressed drain conductance frequency dispersion
Authors: Arai Tomoyuki , Sawada Ken , Hara Naoki
Published: March 2003

We have fabricated a thermally stable low-contact-resistance Ni/AuGe/Au contact metal for InP-based high electron mobility transistors (HEMTs) without a heavily doped cap layer. The contact resistance is strongly influenced by the amount of Ni. Minimum contact resistance of 0.19 Ω mm was obtained from a Ni (1 nm)/AuGe (50 nm)/Au (99 nm) contact annealed at 300 °C for 5 min in N2. A smooth surface was obtained after contact formation and excellent thermal stability was achieved during isothermal annealing at 350 °C for 1 h in a N2 ambient. This alloyed ohmic contact satisfies the requirements for device fabrication process steps after the ohmic contact formation. It prevents hole accumulation by eliminating the hole barrier at the carrier-supply layer/channel interface. It also suppresses the kink phenomena and drain conductance frequency dispersion of InP-based HEMTs, and therefore will greatly facilitate the fabrication of ultrahigh-speed integrated circuits.
Dry etching of ZnO films and plasma-induced damage to optical properties
Authors: Park J. S. , Park H. J. , Hahn Y. B. , Yi G.-C. , Yoshikawa A.
Published: March 2003

To study the effects of plasma chemistries on etch characteristics and plasma-induced damage to the optical properties, dry etching of ZnO films has been carried out using inductively coupled plasmas of Cl2/Ar, Cl2/H2/Ar, and CH4/H2/Ar. The CH4/H2/Ar chemistry showed a faster etch rate and a better surface morphology than the Cl2-based chemistries. Etched samples in all chemistries showed a substantial decrease in the PL intensity of band-edge luminescence mainly due to the plasma-induced damage. The CH4/H2/Ar chemistry showed the least degradation of the optical properties.
Optical properties of thin film CrxNy–CrOxNy multilayer films for 157 nm optical lithography
Authors: Rack Philip D. , Lassiter Matthew , Bourov Anatoli , Baiko Dennis , Smith Bruce
Published: March 2003

Cr x N y and CrxOyNz thin films and multilayer CrxNy–CrxOyNz thin films have been investigated as a binary masking material for 157 nm lithography. The chemical compositions of commercial photolithography masks were determined to be a bilayer structure of Cr0.85N0.15 with a top anti-reflection layer of graded CrxOyNz with a total thickness of ∼100 nm. To simulate the commercial structures, CrxNy and CrxOyNz thin films were reactively rf sputter deposited from a metal chromium target in various Ar–N2 and Ar–N2–O2 environments and their optical properties examined. After replicating the standard ∼100-nm-thick bilayer structure, the process was scaled to ∼50 and 80 nm by: (1) thinning the CrxNy layer and (2) by thinning both the CrxNy and CrxOyNz layers proportionally. The vacuum ultraviolet optical properties of the thinned masking materials were evaluated and the 80 nm features were determined to have the desired optical density >4 and the reflectivity of <15%. Modeling of the optical properties agreed well with the experimental results.
Chemical topography analyses of silicon gates etched in HBr/Cl2/O2 and HBr/Cl2/O2/CF4 high density plasmas
Authors: Vallier L. , Foucher J. , Detter X. , Pargon E. , Joubert O. , Cunge G. , Lill T.
Published: March 2003

We have used x-ray photoelectron spectroscopy (XPS) to analyze resist patterned silicon surfaces etched in a commercial 200 mm high density plasma etcher. After anisotropic etching using gate etching chemistries based on HBr/Cl2/O2 gas mixtures with or without CF4 addition, wafers are transferred under vacuum to perform chemical topography analysis using XPS in order to measure the element concentration on the silicon surfaces at the bottom of the trenches as well as the silicon sidewalls. Composition of the layers formed on the silicon sidewalls as a function of the plasma operating conditions is reported and discussed. The sidewall layer formation is mainly attributed to the oxidation of silicon etching by-products and the deposition of fluorocarbon species. Depending on the O2 and CF4 amount during a silicon gate main etch step, composition of the layer can be either SiOx-like or fluorocarbon rich. In all cases, the sidewall layer is transformed into a SiOx material during the subsequent fluorine free soft-landing step, as a result of the direct oxidation of silicon combined with the fluorocarbon species removal by oxygen in the plasma.
Low-loss InP-based photonic-crystal waveguides etched with Ar/Cl2 chemically assisted ion beam etching
Authors: Mulot M. , Anand S. , Swillo M. , Qiu M. , Jaskorzynska B. , Talneau A.
Published: March 2003

We demonstrate low-loss photonic-crystal (PC) waveguides realized in InP by Ar/Cl2 based chemically assisted ion beam etching. The waveguides are obtained as line defects in a triangular lattice of holes etched through a three-layer InP/GaInAsP/InP heterostructure. By optimizing the etching parameters so that the physical and the chemical components are balanced we succeed in obtaining holes deeper than 2 μm even for a hole diameter as small as 220 nm. The quality of the PCs etched by two different process conditions is compared by using the shape and the position of one of the mode gaps as an assessment tool. The measured transmissions spectra indicate that the PC waveguides etched with an optimized process exhibit losses smaller than 1 dB/100 μm. This is to date the lowest loss value reported for PC waveguides in semiconductor heterostructures at optical communication wavelengths.