bluuebunny/crossref_metadata_2025 huggingface dataset:
Low energy electron beam top surface image processing using chemically amplified AXT resist
Authors: Whelan C. S. , Tanenbaum D. M. , La Tulipe D. C. , Isaacson M. , Craighead H. G.
Published: July 2002

High resolution processes are demonstrated with a positive-mode chemically amplified AXT top surface imaging resist system exposed with a low energy electron beam. Top surface imaging is an ideal match to low energy electron beam lithography because it allows thick resist layers to be patterned despite the limited penetration depth of the electron beam. The three key steps of the process are exposure, silylation, and etch development. All three steps influence the final process sensitivity, contrast, and resolution. The AXT has a poly(hydroxy styrene) base resin, and has been formulated both with and without a dye used to enhance optical absorption. We have achieved sub 100 nm resolution both with and without a postexposure bake. Critical area doses below 1 μC/m2 are demonstrated. The edge roughness and density of etch residue from silylation defects have been compared for a variety of oxygen plasma etch systems.
Stress dependent silylation model and two-dimensional profile simulation
Authors: Zuniga Marco A. , Neureuther Andrew R.
Published: July 2002

A new model for polymer silylation is proposed that takes into account three mechanisms: The relaxation of the polymer during silylation, a diffusivity of the silylating agent which increases with resist matrix expansion, as well as a local reaction rate retardation due to stress induced by resist swelling. These mechanisms capture changes in profile shape during silylation. The resulting nonlinear differential equations are solved two-dimensional (2D) using the finite element method and the influence of the main parameters is studied as a function of feature size and feature type, illustrating the effects of initial aerial image and processing conditions on the final resist image. The simulation profiles reproduce the silylation depth reduction with feature size and abrupt encroachment heretofore unexplained in various experimental studies.
Top surface imaging process at and below quarter-micron resolution and pattern transfer into metal
Authors: Irmscher Mathias , Höfflinger Bernd , Reuter Christian , Springer Reinhard , Stauffer Craig , Puttock Mark
Published: July 2002

The use of top surface imaging processes pushes the limits of both deep ultraviolet lithography and e-beam direct writing. However, the flow effect due to silylation with monofunctional aminosilanes prevents the creation of a faithful resist mask of a high resolution. The application of mixed mono- and bifunctional agents causes crosslinking of the silylated resist and eliminates the flow. We investigated details of the silylation of novolak-based chemically amplified resists with a mixture of bis(dimethylamino)methylsilane and dimethylsilydiethylamine. After mixing, new materials evolved until a stable ratio of all components was reached. During silylation the ratio changes again and requires a continuous adaptation of the silylation parameters. The optimized process enables the realization of a 0.15 μm pattern in 0.7 μm thick resist. An inductively coupled plasma etcher was evaluated for transferring of the resulting resist structures into typical aluminium alloys. The developed process enables the etching of subquarter-micron features into 0.6 μm thick AlSiCu layers.
New fabrication techniques for high quality photonic crystals
Authors: Cheng Chuan C. , Scherer Axel , Tyan Rong-Chung , Fainman Yeshayahu , Witzgall George , Yablonovitch Eli
Published: July 2002

We have developed new methods for the fabrication of high quality two-dimensional (2D) and three-dimensional (3D) photonic crystals. These techniques involve anisotropic etching and steam oxidation of AlAs mask layers. We have made manufacturable 2D photonic crystals with high aspect ratios for use as micropolarizers and have measured extinction ratios larger than 800 to 1 between TE and TM modes transmitted through these structures. The new Al2O3 mask fabrication technique also allows us to fabricate 3D structures with up to six repeating layers in depth and over 90% attenuation in the band gap region. Here, we show the fabrication details and performance of 2D and 3D photonic crystals.
Low voltage electron-beam lithography based InGaAs/GaAs quantum dot arrays with 1 meV luminescence linewidths
Authors: Wang K. H. , Pecher A. , Höfling E. , Forchel A.
Published: July 2002

We have developed InGaAs/GaAs quantum dots with diameters down to about 50 nm on shallow quantum wells using low voltage electron-beam lithography and wet chemical etching. Due to the low energy of the e-beam of 2.5 keV the proximity effect is negligible and arrays of quantum dots with a homogeneous diameter could be fabricated. By using low excitation photoluminescence spectroscopy we observe a clear shift of the dot emission to higher energy due to lateral quantization that amounts to 6 meV in the smallest structures. The linewidth of the luminescence of the dot arrays of about 1.5 meV is almost independent of the dot size, i.e., the inhomogeneous broadening due to the patterning induced lateral size fluctuation is found to be negligible in the present structures.
Characterization of Si-doped layer in GaAs fabricated by a focused ion beam/molecular beam epitaxy combined system
Authors: Yanagisawa Junichi , Nakayama Hiromasa , Oka Kenji , Nakai Masaya , Wakaya Fujio , Yuba Yoshihiko , Takaoka Sadao , Murase Kazuo , Gamo Kenji
Published: July 2002

Effect of the regrowth temperature of the cap layer grown successively on a Si focused ion beam (FIB) implanted GaAs surface on the dopant activation was investigated using a FIB/molecular beam epitaxy combined system. Indication of the reevaporation of the implanted Si was observed at high regrowth temperature and the fabrication process was improved by using low regrowth temperature. A high doping efficiency was obtained for the ion dose at about 1×1013 cm−2. Present results indicate the importance of controlling the regrowth condition to obtain high doping efficiency.
Characterization of strained Si/Si1−yCy structures prepared by molecular beam epitaxy
Authors: Joelsson K. B. , Ni W.-X. , Pozina G. , Pettersson L. A. A. , Hallberg T. , Monemar B. , Hansson G. V.
Published: July 2002

Various structures containing Si1−yCy alloy layers have been prepared and characterized by x-ray diffraction, cross-sectional transmission electron microscopy, photoluminescence (PL), Fourier transform infrared spectroscopy, and spectroscopic ellipsometry. A band gap reduction equal to 63 meV/% C has been estimated from PL when taking into account the quantum well (QW) confinement shift using an effective mass calculation. The QW-related emission observed from a multiple QW structure has a temperature quenching behavior with an activation energy equal to 8 meV. Carbon outdiffusion from the QWs has been evidenced by a blueshift of the PL peak and changes in the x-ray diffraction data after furnace annealing at 800 and 850 °C.
Real time in situ composition control of InGaAs lattice matched to InP by an 88-wavelength ellipsometer
Authors: Kuo C.-H. , Boonzaayer M. , DeHerrera M. , Kyong T. , Zhang Y.-H. , Johs B. , Hale J. S.
Published: July 2002

We have compiled the optical constants database for InxGa1−xAs which covers the composition range from 0.51 to 0.55 and the temperature range from 400 to 525 °C. The InP substrate temperature was monitored by diffusive reflectance spectroscopy during the growth of the epitaxial layer. Ellipsometry was used to monitor the InxGa1−xAs composition over the entire temperature and composition range of the database. The composition monitored by ellipsometry is within 0.002 from the high resolution x-ray data with the exception of growth temperature at 400 °C which is 0.005. We have also demonstrated the real time in situ feedback control of the InxGa1−xAs composition during epitaxial growth by using ellipsometry. The absolute accuracy of the InxGa1−xAs composition from the controlled experiment is 0.002. We can use this database to grow thick InxGa1−xAs layers grown on the InP substrates and can also use this as an in situ tool to fine tune the InxGa1−xAs composition before the growth of the complicated structure.
Device design and circuit modeling issues in ultrahigh vacuum/chemical vapor deposition SiGe heterojunction bipolar transistors
Authors: Cressler John D. , Joseph Alvin J. , Salmon Stacey L. , Harame David L.
Published: July 2002

We discuss the physical basis, experimental results, and compact circuit modeling issues associated with neutral base recombination, germanium-ramp effects, and high-injection heterojunction barrier effects in graded-base, silicon-germanium heterojunction bipolar transistors. All three phenomena depend strongly on Ge profile shape and temperature, and are unaccounted for in conventional silicon bipolar transistor compact models such as SPICE.
Fabrication of diamondlike carbon-coated field emitter triode using aluminum parting layer
Authors: Lee Sanjo , Lee Sunup , Jeon D. , Lee K.-R. , Kwon Ju Byeong , Hwan Oh Myung
Published: July 2002

Coating silicon field emitter tips with a thin film of diamondlike carbon (DLC) seems to be a promising way to improve the performance of the silicon emitter tips. If one deposits a DLC film directly onto the gated silicon emitter, DLC will contaminate the side wall of the insulating layer, which can cause a large leakage current to the gate. To prevent the contamination of the side wall, we deposited an aluminum sacrificial layer before coating the DLC film. The gate current measured from the DLC-coated emitters using the sacrificial layer was less than 3% of the anode current.
Vacuum microelectronic pressure sensor with novel “stepped” or “curved” cathode
Authors: Xia S. H. , Liu J.
Published: July 2002

This article proposes two new types of vacuum microelectronic (VME) pressure sensors, in which a “stepped cathode” or a “curved cathode” is used instead of the conventional cathode. The principle and structure of the new sensors are described. The properties of the conventional VME pressure sensor and the novel sensors have been theoretically investigated and compared by computer simulations, and the results are shown in several plots. It is seen that, at the same anode voltage and for the same anode deformation, the novel cathodes produce emission currents more than an order of magnitude higher than the conventional cathode. The obvious advantages are that larger currents are easier to detect and less affected by noise. Furthermore, the novel cathodes can increase the sensitivity of the sensors, improve the linearity of output signals, and enlarge the sensors’ measurement range. It has been shown that the “curved cathode” is an ideal model but it may be difficult to realize in practice at the present stage. The “stepped cathode” can be realized and has been fabricated by the author. The fabrication of the novel stepped cathode emission array and the anode pressure sensing film is briefly reported, and the scanning electron microscopy photographs are shown.
Acetylene gas as a carbon source: An x-ray photoemission spectroscopy and near-edge x-ray absorption fine structure spectroscopy study of its stability on Si(111)-7×7
Authors: Rochet F. , Dufour G. , Stedile F. C. , Sirotti F. , Prieto P. , De Crescenzi M.
Published: July 2002

The electronic structure and bonding geometry of acetylene adsorbed at room temperature on Si(111)-7×7 is studied by a combination of synchrotron radiation x-ray photoemission spectroscopy and of near-edge x-ray absorption fine structure spectroscopy. Then the stability of the molecule, submitted to thermal annealings and to synchrotron white beam irradiation is examined. The possibility of using acetylene gas as a carbon source for the fabrication of silicon-carbon compounds (or for the formation of abrupt carbon/silicon interfaces) is discussed.
Suppression of the base-collector leakage current in integrated Si/SiGe heterojunction bipolar transistors
Authors: Assous M. , de Berranger E. , Regolini J.-L. , Mouis M. , Hernandez C.
Published: July 2002

High leakage currents at the base-collector junction of heterojunction bipolar transistors have been mentioned by several authors. In this article, we compare two pre-epitaxy cleaning procedures which both allow smooth epitaxy without any extended defects. Using our initial cleaning procedure, we obtained leakage current values in the range of the published results. We show that our results were consistent with the presence of defects induced by the low-energy reactive ion etching involved in this procedure. In contrast, we obtain a very significant reduction of the leakage current using our new all-wet chemical cleaning.
Atomic force microscopy study of the morphological modifications induced by laser processing of Si(1−x)Gex/Si samples
Authors: Padeletti G. , Larciprete R.
Published: July 2002

Atomic force microscopy topography and power spectral density analysis of the recorded images were used to obtain a thorough characterization of the morphological modifications determined by laser processing of Si(1−x)Gex/Si (100) structures grown by ultrahigh vacuum chemical vapor deposition (CVD). Two irradiation modalities were considered. In the first case, several samples differing in alloy film thickness and morphology were irradiated by KrF laser pulses at 248 nm after the CVD growth. Alternatively, the laser pulses were used to assist the CVD growth itself. In both cases laser irradiation determined primarily a severe smoothing of the surface roughness. However for the post-growth irradiation the achieved flatness was strictly dependent on the initial surface features (i.e., roughness and grain dimensions). The comparison between the results obtained in the two irradiation modalities demonstrated that, as far as surface flatness is concerned, laser-assisted deposition results a superior technique, since it allows the achievements of structureless surfaces, with roughness as low as 0.3 nm.
Comparison of the structure and electrical properties of thermal and plasma grown oxides on GaAs
Authors: Lefebvre P. R. , Lai L. , Irene E. A.
Published: July 2002

Valence band x-ray photoelectron spectra (XPS) from oxide films grown on GaAs surfaces by thermal oxidation and electron cyclotron resonance (ECR) plasma oxidation are compared. The present work along with previous studies clearly show that the ECR grown oxides are nearly stoichiometric and close to GaAsO4 while thermally grown oxides are closer to Ga2O3 having significant amounts of As+3 oxidation states. Metal oxide semiconductor (MOS) structures were prepared by coating both the thermal and ECR plasma grown GaAs oxides with ECR plasma enhanced chemically vapor deposited (PECVD) SiO2 and then with evaporated Al as top contact. Interface charges in terms of fixed oxide charge and surface electronic states were obtained from conventional capacitance–voltage measurements. Despite the significant difference in the GaAs oxides structure, most notably the GaAsO4 like ECR plasma oxides, the interfaces prepared by both thermal and plasma oxidation were found to be equally unpassivated in terms of high levels of interface electronic states and Fermi level pinning.
Control of etching-product-dependent shape and selectivity in gate polysilicon reactive ion etching
Authors: Sato Masaaki , Arita Yoshinobu
Published: July 2002

In polycrystalline silicon (polysilicon) etching for gate electrodes in high-performance complementary metal-oxide-semiconductor large scale integration fabrication, extremely high selectivity of polysilicon etching to the gate oxide is needed because the thickness of the gate oxide reduces. It is also important to overcome the well-known shape distortion problem, called “notching” or “local side etching,” where the gate side-wall is locally side-etched at the interface between the polysilicon and the gate oxide. We examine the origin of notching and the selectivity to the gate oxide in chlorine- and oxygen-based reactive ion etching of the phosphorous-doped polysilicon gate with an SiO2 hard mask. It is found that the etching product returning to the surface plays an important role in both side-wall and gate-oxide protection, which determines the shape of the electrode and the selectivity. Based on our findings, we developed a novel step-etching method that provides high-performance gate electrode etching that is infinitely selective without notching. This method uses the addition of a SiCl4 gas, which is equivalent to the etching product, as well as oxygen during overetching when the generation of etching product is reduced.
Growth optimization of GaxIn1−xAsyP1−y/GaAs(0.98 μm) quantum wire heterostructures
Authors: Moy A. M. , Pickrell G. W. , Cheng K. Y.
Published: July 2002

The strain-induced lateral-layer ordering technique has proven itself to be a viable method for creating quantum wires (QWRs) via molecular beam epitaxy. In an effort to achieve emission at the technologically important 0.98 μm wavelength, GaxIn1−xAsyP1−y QWRs formed on on-axis GaAs substrates using (GaP)m/(InAs)n short-period superlattices (SPS) are investigated. The growth parameters, such as the growth temperature, the source switching pause scheme, and the group-V source flow sequence are optimized to create QWRs with emission near 0.98 μm. For structures utilizing abrupt switching between constituent layers, it was determined that the optimal temperature at which to grow the (GaP)2.2/(InAs)1 SPS on GaAs was 480 °C. By introducing pause times and additional group-V source coverage to the growth scheme, the quality of the QWR heterostructure is markedly improved. The existence of a lateral composition modulation in the growth plane is evidenced by the low-energy emission (redshift) with respect to the bulk GaxIn1−xAsyP1−y, and the highly polarized nature of the photoluminescence (PL) spectra. Furthermore, the effects of the barrier material between QWR layers (in the growth direction) on the temperature stability of PL peak wavelengths near 0.98 μm were studied. The temperature induced wavelength shift depends on the barrier material, barrier thickness, and the composition of the SPS used in the QWR region. A minimum PL peak wavelength shift of about 200 Å between 77 and 300 K was observed in the GaxIn1−xAsyP1−y QWR system with Ga0.51In0.49P barriers.
Solid source molecular beam epitaxial growth of In0.5Ga0.5P pseudomorphic high electron mobility transistor structures
Authors: Hoke W. E. , Lemonias P. J. , Beaudoin R. M. , Torabi A.
Published: July 2002

InGaP/GaAs heterostructures and InGaP/In0.2Ga0.8As pseudomorphic high electron mobility structures were grown by solid source molecular beam epitaxy using valved arsenic and phosphorus sources. At 450 °C abrupt arsenic/phosphorus heterojunctions were obtained. Charge transfer was demonstrated at both normal and inverted InGaP/GaAs heterojunctions. From capacitance–voltage profiling measurements the InGaP/GaAs conduction band discontinuity was determined to be 0.15 eV with an interface charge density of 8×1010 cm−2. Consistent with a moderate conduction band discontinuity, single pulse doped In0.5Ga0.5P/In0.2Ga0.8As structures were grown with a channel sheet density of 1.5×1012 cm−2. Double pulse doped InGaP/AlGaAs/In0.2Ga0.8As/AlGaAs structures were also grown incorporating AlGaAs donor layers and an InGaP Schottky layer. Appropriate for power devices, high sheet densities (3.5×1012 cm−2 at 77 K) and high mobilities (6620 cm2/V s at 300 K; 16920 cm2/V s at 77 K) were obtained. The InGaAs quantum well photoluminescence intensity was enhanced from the lower surface recombination velocity of InGaP compared to that of AlGaAs. No degradation of AlGaAs quality was observed by incorporating InGaP and AlGaAs into the same structure by solid source molecular beam epitaxy.
On the improvement in thermal quenching of luminescence in SiGe/Si structures grown by molecular beam epitaxy
Authors: Chen W. M. , Buyanova I. A. , Pozina G. , Monemar B. , Ni W. X. , Hansson G. V.
Published: July 2002

Thermal quenching of photoluminescence (PL) from SiGe/Si quantum well (QW) structures grown by molecular beam epitaxy is shown to be more severe when grown at a lower temperature. The mechanism responsible for the thermal quenching of PL is discussed as being due to thermally activated nonradiative recombination channels, related to defects in both Si barriers and SiGe QW. Nonradiative defects in Si can be rather efficiently deactivated by post-growth treatments such as hydrogenation and thermal annealing, leading to a significant improvement in the thermal quenching behavior of PL from single QW structures. Nonradiative defects in SiGe are found to be thermally stable, on the other hand, evident from the experimentally observed minor role played by post-growth thermal annealing in the thermal quenching of PL from multiple QW structures.
Atomic force microscopy observation of the ferroelectric domain structure on the (010) cleavage surface of K2ZnCl4
Authors: Kim D.-Y. , Hong J. W. , Kwun S.-I. , Jeong S.-Y.
Published: July 2002

The ferroelectric domain structure of K2ZnCl4 was studied by atomic force microscopy (AFM). The domain feature was observed on the (010) cleavage surface which is parallel to the polar a axis. This finding demonstrates that the image of ferroelectric domains observed by AFM is not due to the interaction between the tip and the spontaneous polarization, but due to a real deformation of the crystal surface.
Material-wave nanotechnology: Nanofabrication using a de Broglie wave
Authors: Matsui Shinji , Fujita Jun-Ichi
Published: July 2002

An approach for nanofabrication using de Broglie wave has been developed. Line and dot patterns with 100-nm periodicity were delineated on a PMMA resist by electron-beam holography with a thermal field-emitter gun and an electron biprism. This technique allows us to produce nanoscale periodic patterns simultaneously. Furthermore, the possibility of nanostructure fabrication by atomic-beam holography has been demonstrated by using a laser-trap technique and a computer-generated hologram made by electron-beam lithography.
GaAs/AlGaAs heterojunction bipolar transistors with a base doping 1020 cm−3 grown by solid-source molecular beam epitaxy using CBr4
Authors: Micovic M. , Nordquist C. , Lubyshev D. , Mayer T. S. , Miller D. L. , Streater R. W. , SpringThorpe A. J.
Published: July 2002

We show that epitaxial layers suitable for fabrication of AlGaAs/GaAs heterojunction bipolar transistors with a carbon base doping level of up to 1020 cm−3 can be grown by solid-source molecular beam epitaxy using CBr4 as a doping precursor. We have observed that the gain of devices fabricated from these layers is improved using an abrupt conduction-band discontinuity at the emitter–base heterointerface. The observed relationship between current gain and the base width Wb of these devices deviates from the 1/Wb2 dependence predicted by diffusive electron transport for base widths that are shorter than 60 nm. The relationship is better approximated by a 1/Wb dependence, which is in better agreement with the theories of ballistic or quasiballistic electron transport. Current gain of the devices drops rapidly as the base thickness exceeds 60 nm.
Investigation of radiation damage in germanium induced by MeV Si+
Authors: Wang Ke-Ming , Lu Fei , Meng Ming-Qi , Shi Bo-Rong , Liu Xiang-Dong , Liu Ji-Tian , Xu Tian-Bin , Zhu Pei-Ran
Published: July 2002

Polished germanium Ge (100) was irradiated with 1.0–2.0 MeV Si+ at different doses from 4×1013 to 1×1014 ions/cm2 under different angles: 7°, 45°, and 60°. The radiation damage is studied by the Rutherford backscattering/channeling technique. The experimental damage distribution is extracted from the spectrum based on the procedure by Feldman et al. The experimental damage distributions are compared with the result from the TRIM (transport of ions in matter) code. The results show that (1) it is easier to amorphize Ge than Si, and the damage in Ge (100) induced by MeV Si+ depends on the dose, energy, irradiation angle, and annealing temperature also; (2) the shape of damage profile in Ge (100) induced by 2.0 MeV Si+ under 60° irradiation can be described well by the TRIM prediction, except the near-surface region where the experimental damage ratio is higher than that given by the TRIM prediction; (3) after 800 °C annealing, damaged Ge (100) trends to be recrystallized.
Fabrication of heterojunction bipolar transistors with buried subcollector layers for reduction of base-collector capacitance by molecular beam epitaxy regrowth
Authors: Micovic M. , Nordquist C. D. , Lubyshev D. , Mayer T. S. , Miller D. L. , Streater R. W. , SpringThorpe A. J.
Published: July 2002

A process for fabrication of heterojunction bipolar transistors (HBTs) with selectively buried subcollectors by molecular beam epitaxy (MBE) regrowth is described. This process can be used to reduce parasitic base-collector capacitance of HBTs and improve the speed of these devices. In situ etching by iodine prior to the regrowth was used for the first time to improve the quality of the substrate epilayer interface in a semiconductor device grown by MBE. The secondary ion mass spectroscopy depth profiles of regrown HBT structures suggest that the in situ surface cleaning by molecular iodine was not sufficient to remove all contamination from the substrate epilayer interface and that the microwave performance of HBTs fabricated by this process may have been affected by that contamination. The dc performance of devices which were fabricated by our process was not affected, however, by the contamination and was comparable to the dc performance of conventional HBTs. Our results suggest that the described process for fabrication of HBTs with selectively buried subcollectors by MBE regrowth would be feasible in conjunction with a more effective surface treatment.
Optimization of the temperature distribution across stencil mask membranes under ion beam exposure
Authors: Kim B. , Engelstad R. , Lovell E. , Chalupka A. , Haugeneder E. , Lammer G. , Löschner H. , Lutz J. , Stengl G.
Published: July 2002

The pattern placement accuracy of a stencil mask is affected by thermomechanical distortion induced during ion beam exposure. Any temperature gradient across the mask membrane could result in thermal distortions which contribute to the stringent error budget. Therefore, a concept has been proposed to control the temperature across the mask membrane by using radiation heat transfer between exposure station components. This work extends previous efforts by including the effects of the backside radiation loss of the exposure area, the aperture, etc. Here the exposure station which has been proposed by IMS-Ion Microfabrication Systems is investigated and simulated with finite element models. Parametric studies have been performed in order to optimize design variables such as material properties, and the temperature settings of the cooled lens electrodes and aperture.
Plasma polymer films for 532 nm laser micromachining
Authors: Silverstein M. S. , Visoly I. , Kesler O. , Janai M. , Cassuto Y.
Published: July 2002

Laser micromachining with a frequency doubled Nd:YAG laser (532 nm) can replace more complex microlithographic processes for rapid turnaround in the development of prototype application-specific integrated circuits. Plasma polymerization is a rapid, dry, environmentally friendly process that yields crosslinked pinhole-free films. Plasma polymerized films of ethylene and an additional gas [PP(gas/E)] were investigated for their micromachining potential. The deposition rates, molecular structures, physical properties and optical properties of the polymers were characterized. PP(Ar/E), with relatively little oxygen and no nitrogen, with superior substrate adhesion and with no debris generated on laser micromachining was chosen as the optimal laser micromachining film. The PP(Ar/E) coefficient of optical absorption at 532 nm (α532), related to unsaturated group concentration, increased with the ratio of plasma power to ethylene mass flow rate [W/Fm(E)]. α532 reached an asymptote of 2.9 μm−1 at high W/Fm(E) and could be enhanced slightly using postpolymerization ultraviolet exposure. The optimum conditions were using Ar/E=1/1 and 75 W to produce a 0.6 μm thick film for micromachining at 2 J/cm2 focused 0.25 μm beneath the surface. The laser pulse in a 1.2 μm thick film was not fully developed at 2 J/cm2 and exhibited rounded corners at 4 J/cm2, indicating that multiple low energy pulses would be preferable. A complicated and densely packed pattern with several different pulse sizes in which neighboring holes from pulses in close proximity do not merge was accurately reproduced in PP(Ar/E) using laser micromachining.
High throughput electron lithography with the multiple aperture pixel by pixel enhancement of resolution concept
Authors: Kruit P.
Published: July 2002

A new lithography concept for the sub-100 nm generations is proposed. The bulk of the machine is a traditional deep ultraviolet demagnification scanner–stepper. The mask is illuminated by 106–108 almost diffraction limited subbeams formed by a microlens array. After demagnification these subbeams are focused on a photon–electron converter plate. Each photon subbeam triggers the emission of a narrow beam of electrons. The electron beams are focused individually on the wafer, which is at a distance of about 1 mm from the converter plate. By scanning both mask and wafer through the many beams, the whole wafer is exposed.
Performance investigation of Coulomb interaction-limited high throughput electron beam lithography based on empirical modeling
Authors: Han Liqun , McCord Mark A. , Winograd Gil I. , Pease R. F. W.
Published: July 2002

Multibeam direct writing and projection strategies have been proposed for high throughput electron beam lithography; however, the large beam current required may cause severe beam blur due to the stochastic Coulomb interaction effects between the electrons. From viewpoint of both concept proof and practical system design, evaluation of the fundamental system limits and the optimum performance in a large range of multiple system parameter variable space is critical for such high throughput tools. Based on the response surface design approach, well-fitted empirical models of image beam size as a function of various system parameters have been extracted from Monte Carlo simulations of electron interactions for different proposed multi-beam systems. The blurred imaging beam size is examined in a wide range of system parameters: beam currents from 1 to 100 μA, acceleration voltages from 25 to 100 kV, column lengths from 1 to 100 cm, field sizes from 0.5 to 2 mm, and demagnification from 4 to 16. Two general tendencies for such systems were observed: the nonuniformity of image defocusing due to the inhomogeneous interbeamlet space charge effect at large field sizes, and the high sensitivity of maximum beam current to column length at a fixed image beam size. Finally, the throughput versus acceleration voltage is evaluated under different assumptions of resolution, resist thickness, and column length. It is concluded that to achieve the throughput required by manufacturing beyond 0.1 μm resolution, very aggressive design of a short column along with thin resist will be required.
Phase shift microscopes
Authors: Feldman M.
Published: July 2002

We report on a new class of scanning optical microscopes with twice the resolution of conventional microscopes. The new microscopes use standard components to produce high intensity images, with large working distances and large depths of focus, without additional mechanical complexity. The microscopes scan a focused laser beam which has passed through a pattern of phase shifts arranged in a spiral staircase. These phase shifts generate a narrow dark spot in the center of the focused beam. The width of this central dark spot is about half the diffraction limit. The signal from this “phase shifted” beam is subtracted from the signal produced by a conventional Gaussian beam which is simultaneously scanned. The difference between the two detected signals corresponds to the signal from a bright beam of width equal to the width of the dark central area. Since only linear operations on observed optical signals are used, there is a useful improvement in resolution of about a factor of 2. This improves both the accuracy with which feature edges may be located, as well as the resolution of small features such as the corners of narrow lines.
Top surface imaging process and materials development for 193 nm and extreme ultraviolet lithography
Authors: Rao Veena , Hutchinson John , Holl Susan , Langston Joseph , Henderson Craig , Wheeler David R. , Cardinale Greg , O’Connell Donna , Goldsmith John , Bohland John , Taylor Gary , Sinta Roger
Published: July 2002

The maturity and acceptance of top surface imaging (TSI) technology have been hampered by several factors including inadequate resist sensitivity and line edge roughness. We have found that the use of a chemically amplified resist can improve the sensitivity in these systems by 1.5– 2× without compromising the line edge roughness. In addition, we have shown improved line edge roughness by increasing the molecular weight of the polymeric resin in the resist. Using these materials approaches, we have been able to show excellent resolution images with the TSI process for both 193 nm and extreme ultraviolet (13.4 nm) patterning.
At-wavelength detection of extreme ultraviolet lithography mask blank defects
Authors: Jeong Seongtae , Idir Mourad , Lin Yun , Johnson Lewis , Rekawa Seno , Jones Michael , Denham Paul , Batson Phil , Levesque Rick , Kearney Patrick , Yan Pei-Yang , Gullikson Eric , Underwood James H. , Bokor Jeffrey
Published: July 2002

We report the design and operation of an at-wavelength system for extreme ultraviolet lithography mask blank defect detection. Initial results demonstrate sensitivity to submicron size phase defects. The performance of the system is compared with the practical requirements for a mask blank inspection system in terms of the sensitivity and scanning time.
Aspheric collimator for a point source x-ray lithography system
Authors: Singh-Gasson S. , Vladimirsky Y. , Cerrina F.
Published: July 2002

X-ray point sources are an interesting alternative to synchrotrons for small to medium scale production. These sources are by nature highly divergent, and thus require the use of collimation for delivering an acceptable lithographic illumination. We present the design of an aspheric collimator for a point source such as a dense plasma focus system. Designing a collimating mirror for a point source presents different challenges than designing one for a synchrotron source, although both cases require that the radiation be condensed and collimated to deliver the radiation with 1%–2% uniformity and acceptable runout over a large field area. The collimator is 3 cm wide and 31 cm long, accepts 20 mrad in the vertical and 70 mrad in the horizontal, and delivers the x-ray flux to a 3 cm×3 cm field on a mask located 3 m from the source with a runout of 6 mrad. The figure is an asphere, not dissimilar to those developed previously. The scanning mechanism, however, is radically different, since the virtual rotation point is located at the source, rather than at the mirror pole. This design provides excellent uniformity since the mirror is always scanned inside the radiation cone while maintaining a constant nominal incidence angle. The design principles and predicted performance are discussed in detail, together with a consideration of the manufacturing challenge for such a mirror. The collimator design presented has the capability of delivering the required power density and collimation from an x-ray point source to satisfy the requirements of x-ray lithography.
Wafer chuck for magnification correction in x-ray lithography
Authors: Feldman M. , Smith D.
Published: July 2002

Magnification correction has emerged as a critical issue in x-ray lithography for very large scale integrated circuits. We have developed a simple and robust method to correct the magnification, which is suitable for use in a collimated x-ray beam from a storage ring. In our technique the wafer is bent to conform to a chuck whose surface is a portion of a sphere of adjustable radius. Both increases and decreases in the pattern size may be accommodated by using convex and concave spherical surfaces, respectively. The radius of the chuck can be set to achieve desired corrections of up to several parts per million. The maximum attainable correction is determined by the permissible out of plane distortion which accompanies the wafer bending, and is dependent upon the wafer thickness and the field size. The change in the wafer pattern is expected to be very nearly an isotropic magnification; however a limited one-dimensional magnification correction may also be added by differentially scanning the mask and wafer.
Overlay modeling for proximity x-ray lithography
Authors: Chen Alek C.
Published: July 2002

Proximity x-ray lithography is one of the most promising manufacturing technologies for the fabrication of future electronics devices with ground rules of 100 nm and less because of its wide exposure latitude and processing simplicity. However, the ability to make 1× x-ray masks, with high pattern placement accuracy, has continued to be one of the main technical challenges preventing the wide use of this technology by the semiconductor industry. A model has recently been developed to examine the parameters affecting the overall lithographic system overlay performance, such as the mask pattern placement error as well as the error sources from the x-ray aligner. The model treats all of the error sources statistically. The major assumption of the model is that all the error sources are statistically independent. This is a fairly accurate assumption for the error sources under consideration. For example, the mask pattern placement error is and should be independent of the aligner wafer stage stepping errors. Furthermore, the model can simulate error sources that do not follow the normal statistics. The model has three major components: (1) the x-ray aligner machine model that simulates all the major aligner error sources such as mask and wafer alignments, (2) the application parameter component that considers any application-specific setup tool parameters such as the number of wafer alignment marks and the number and location of global alignment sites, and (3) the mask component that accounts for the effects of pattern placement accuracy on alignment marks and overlay metrology targets. A detailed description of the model and the experimental data used to verify its validity will be given. The relative impact of the various subcomponent error contributions on the overall overlay performance will be provided.
Temperature gradients during absorber etching and their effect on x-ray mask patterning
Authors: Pendharkar S. V. , Resnick D. J. , Laudon M. F. , Dauksher W. J. , Mangat P. J. S. , Seese P. A. , Cummings K. D.
Published: July 2002

Pattern transfer in x-ray mask absorbers is often accomplished by reactively etching in chlorine containing plasmas. In this article, we show that the etch rate of one such absorber, TaSi, is a strong function of substrate temperature. We also show that the etch rate versus temperature behavior of TaSi is a result of the Ta in the film. Hence, other Ta based absorbers (Ta, Ta4B, TaGe, etc.) may also exhibit a similar behavior. We use finite element modeling to demonstrate that under certain conditions, significant temperature variations can exist on a National Institute Standards and Technology (NIST) x-ray mask which in turn can lead to etch rate variations. We also present experimental verification of these modeling results. Finally, through modeling, we discuss the effect of this etch rate variation on the pattern placement accuracy of NIST x-ray masks.
High-accuracy interferometry of extreme ultraviolet lithographic optical systems
Authors: Goldberg Kenneth A. , Naulleau Patrick , Lee Sang , Bresloff Cynthia , Henderson Craig , Attwood David , Bokor Jeffrey
Published: July 2002

Recent improvements in extreme ultraviolet (EUV) lithographic imaging with Schwarzschild objectives have come as a direct result of at-wavelength interferometric characterization with the phase-shifting point diffraction interferometer. High accuracy system wave front characterization has led to the determination of the best Schwarzschild objective and subaperture configuration. These investigations and the results of imaging experiments are discussed. Two pinhole null tests have provided an in situ method of demonstrating reference wavefront accuracy of ∼λEUV/300.
Parametric study of the etching of SiO2 in SF6 plasmas: Modeling of the etching kinetics and validation
Authors: Lagarde T. , Pelletier J. , Arnal Y.
Published: July 2002

The uniform distributed electron cyclotron resonance plasma of SF6, excited at either 2.45 or 5.85 GHz, has been applied to study the etching of SiO2 by F atoms as a function of the three relevant plasma parameters: neutral F-atom flux, ion flux, and ion energy. Three saturation effects are observed. At constant ion current density, the etch rate at first increases linearly with F-atom flux, but then it reaches a plateau, which rises when one raises the ion current density. Second, at constant F-atom flux, initially the etch rate also climbs linearly with ion current density, and again, levels out at larger ion current density, and is higher at larger F-atom flux; however, the initial increase is independent of the F-atom flux. Third, the etch rate evolves similarly as a function of bias voltage for constant F-atom flux and ion current density. These results are first interpreted by a simple mechanism of F-atom adsorption on the SiO2 surface, followed by SiF4 formation at, and desorption from the surface, and by assuming a constant density of adsorption sites for fluorine on the SiO2 surface. However, although this model provides the general trends of the etching kinetics of SiO2 as a function of each plasma parameter, it nevertheless fails explaining many details of the observed etch rates. In fact, ion induced desorption of oxygen from the SiO2 surface is mandatory prior to F-atom adsorption on the Si overlayer thus built up on SiO2. The model resulting from this hypothesis is in complete agreement with the experimental results obtained on the etching kinetics of SiO2 in SF6 plasmas.
Effect of light exposure on 1/f noise in a-Si:H
Authors: Johanson Robert E. , Scansen D. , Kasap S. O.
Published: July 2002

We measure the changes induced in the 1/fα conductance fluctuation power spectrum of n-type a-Si:H in the dark after illumination by band-gap light of intensity 0.17 W/cm2. Initially the relative noise power decreases by a factor of 5 over the first 100 min of exposure. For longer exposures, the noise recovers but preferentially at higher frequencies causing α to decrease from 1.1 in the annealed state to between 0.8 and 0.9 after 60 h of illumination. Also after long exposures, the spectrum does not fit a simple power law but has additional weight at higher frequencies. Other aspects are typical of 1/f noise, a linear dependence on applied current and Gaussian statistics, in both the annealed and light soaked states, which are in disagreement with other reports on similar material. Some of the increase in noise beyond the 100 min exposure is attributed to carriers interacting with localized states that become emptied as the Fermi level drops.
Smooth and anisotropic reactive ion etching of GaAs slot via holes for monolithic microwave integrated circuits using Cl2/BCl3/Ar plasmas
Authors: Nordheden K. J. , Hua X. D. , Lee Y. S. , Yang L. W. , Streit D. C. , Yen H. C.
Published: July 2002

A process to produce very smooth and highly anisotropic through-the-wafer slot via holes using reactive ion etching in Cl2/BCl3/Ar mixtures has been developed. In this study, we have extensively investigated the GaAs etch rate and resultant etch profiles as functions of bias voltage, gas ratio, flow rate, chamber pressure, aspect ratio, and etch time. An optimum via hole etching process using a Plasma Therm 790 reactive ion etching system was determined to be 300 V bias voltage, gas flow ratio of Cl2:BCl3:Ar=4:3:10, and chamber pressure of 15 mTorr. The average etch time for 20 μm wide ×60 μm long vias on a 50 μm thick 3 in. diam wafer is 180 min using a total flow rate of 50 sccm, which corresponds to an average etch rate of 0.3 μm/min. This process has been successfully implemented on two-stage Ka-band monolithic microwave integrated circuit driver amplifiers fabricated by TRW. Under a pulsed bias with Vds=5.0 V and an input power of 15 dBm, the average power added efficiency was greater than 40% with a 13–14 dB gain between 32 and 36 GHz. A peak power added efficiency of 44% was achieved at 35 GHz.
Single-mask silicon microtriode
Authors: Garner David M. , Amaratunga Gehan A. J.
Published: July 2002

A single-mask structure for a micrometer-sized silicon triode (microtriode) is proposed. The fabrication of the device has been optimized to produce a suspended chromium gate above a pyramidal silicon cathode. The gate approaches from the side, in the same plane as the anode. Field emission between the anode and cathode in diode-mode operation in atmosphere has been confirmed. Diode-mode operation of the device is suitable for sensor applications.
Sub-100 nm KrF lithography for complementary metal–oxide–semiconductor circuits
Authors: Fritze M. , Astolfi D. , Liu H. , Chen C. K. , Suntharalingam V. , Preble D. , Wyatt P. W.
Published: July 2002

Sub-100 nm metal–oxide–semiconductor field effect transistor gate structures have been fabricated using resolution-enhanced 248 nm optical lithography. We employed the chromeless phase-shift approach together with thin resists and optimized etches to achieve these results. Polysilicon gratings with critical dimension (CD)≈60 nm and TiN (damascene) gratings with CD≈35 nm have been fabricated with good process latitudes. We are applying this process to the fabrication of basic test circuits for an aggressively scaled silicon on insulator complementary metal–oxide–semiconductor technology.
Particulate contamination in tungsten low pressure chemical vapor deposition: An experimental study
Authors: MacGibbon B. S. , Busnaina A. A. , Rasmussen D. H.
Published: July 2002

Particulate contamination is a leading cause for low yields of logic and memory devices. As circuit feature sizes decrease, submicron particles will have a greater effect on the yield. In this article, particulate contamination during the fabrication of tungsten multilevel interconnects is investigated. Particles can be carried into the chamber with the incoming gas or they may be generated due to the reactive chemistry present during processing. Tungsten films are deposited using silane (SiH4) reduction of tungsten hexafluoride (WF6). Higher deposition rates can be obtained by increasing the deposition pressure. However, particle generation has been found to occur at higher pressures. The particle generation occurs at a SiH4:WF6 inlet mole ratio greater than 1. At high pressures and wafer temperatures (>20 Torr, 425 °C), particle deposition is suppressed and the particle exits the chamber with the exhaust gas. The experimental data show that the particle generation is not a result of classical homogeneous nucleation or heterogeneous nucleation. The particles are produced from a gas reaction between Si and W containing species. A theory is developed that explains the observed particle generation, as a function of process pressure, temperature and SiH4:WF6 mole ratios.
Characterization of field emission cathodes with different forms of diamond coatings
Authors: Zhirnov V. V. , Küttel O. M. , Gröning O. , Alimova A. N. , Detkov P. Y. , Belobrov P. I. , Maillard-Schaller E. , Schlapbach L.
Published: July 2002

The emission of different diamond coatings on silicon field emitter arrays were investigated: chemical vapor deposition diamond, high pressure and high temperature synthetic diamond, and shock-synthesized nanodiamond. Practical emission characteristics such as: emission threshold, maximum current, current stability, and reproducibility were tested. The effects of surface modification, the size of diamond crystallites, and hydrogen plasma treatments were also studied.