bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass spectrometric studies of remote helium plasma dissociation of silane
Authors: Jasinski Joseph M.
Published: July 2002

Molecular beam sampling mass spectrometry combined with low-energy electron impact ionization has been used to detect and quantitate the stable molecules, ions, and silicon radicals created in the interaction of silane with a helium afterglow produced by a microwave discharge in pure helium. The observations are used to understand the afterglow chemistry and to elucidate some important features of the film growth mechanism in the remote plasma-enhanced chemical vapor deposition of silicon films.
Photodecomposition of poly(methylmethacrylate) thin films by monochromatic soft x-ray radiation
Authors: Tinone Marcia C. K. , Tanaka Kenichiro , Ueno Nobuo
Published: July 2002

The photofragmentation reaction of poly(methylmethacrylate) (PMMA) by soft x-ray irradiation was investigated by measuring the yield of released neutral fragments and the changes in the absorption spectra in the carbon and oxygen K-edge regions. Films of 0.4–1.0 μm thicknesses were irradiated with various doses of monochromatic 300, 400, and 600 eV soft x-rays. The effect of irradiation was monitored by the yield of the fragment products released from PMMA, as a function of dose. The fragments of mass 15, 28, 29, 31, 44, and 60 amu, corresponding to CH3, CO, CHO, CH3O, CO2, and C2H4O2, were chosen for monitoring this irradiation dose dependence. Each fragment showed a distinct response to irradiation. The etching rates, represented by the yield of the released fragments, are dependent on the original thickness of the sample and gradually decrease with dose. From the analysis of the thickness and dose dependencies, we concluded that secondary reactions in the bulk play an important role in the desorption mechanism. The absorption spectrum after irradiation indicates the abstraction of the ester group and the formation of double bonds. All the observations are in agreement with a degradation mechanism involving the ester group abstraction followed by main chain scission and, at large doses, crosslinking and the formation of a protecting overlayer of chemical nature similar to poly(butadiene).
Microstructure of radio frequency sputtered Ag1−xSix alloys
Authors: Leedy K. D. , Rigsbee J. M.
Published: July 2002

A series of thin film Ag1−xSix alloys were fabricated using radio frequency sputter deposition with composite Ag+Si sputter targets and water-cooled and liquid nitrogen–cooled substrate holders. The microstructures of the films were analyzed using x-ray diffraction and transmission electron microscopy. As-deposited films contained fcc Ag and amorphous Si. The Ag grain size decreased as the Si content increased. Films deposited on the liquid nitrogen–cooled substrate holder exhibited grain sizes smaller than films deposited on the water-cooled substrate holder. Despite the negligible Ag and Si mutual solid solubilities, the metastable Ag3Si hcp silver silicide phase was observed in addition to fcc Ag and amorphous Si in a 12 at. % Si alloy deposited on the liquid nitrogen–cooled substrate holder. The Ag3Si phase observed by x-ray diffraction in 5000-Å-thick films was not found in the 250-Å-thick TEM films, suggesting a thickness dependence of stability. During vacuum anneals above 100 °C, the Ag3Si phase partially decomposed.
Evolution of GaSb epitaxy on GaAs(001)-c(4×4)
Authors: Thibado P. M. , Bennett B. R. , Twigg M. E. , Shanabrook B. V. , Whitman L. J.
Published: July 2002

The growth of GaSb films by molecular beam epitaxy on GaAs(001)-c(4×4) at 490 °C has been studied in situ with scanning tunneling microscopy and ex situ with transmission electron microscopy. As the film is deposited, four distinct growth regimes are observed: the first two monolayers grow layer by layer with platelet-like two-dimensional (2D) islands; the next monolayer forms coherently strained three-dimensional (3D) quantum dots; further deposition induces film relaxation and rough 3D growth; for film thicknesses ≳100 nm the growth is again 2D, proceeding via spiral growth around emerging threading dislocations. The atomic-scale mechanisms inherent in the transitions between the growth regimes are discussed. Variations in growth procedures aimed at improving the quantum dot uniformity and reducing the dislocation density are proposed.
Experimental determination of quantum dipoles at semiconductor heterojunctions prepared by van der Waals epitaxy: Linear correction term for the electron affinity rule
Authors: Schlaf R. , Lang O. , Pettenkofer C. , Jaegermann W. , Armstrong N. R.
Published: July 2002

We determined the band offset of eight layered heterocontacts consisting of combinations between SnS2, SnSe2, WSe2, MoS2, MoTe2, InSe, and GaSe. The comparison of offsets predicted by the electron affinity rule (EAR) revealed a systematic deviation. Due to the absence of structural dipoles in layered materials, this deviation corresponds to the magnitude of the quantum dipoles at the interface which allows the development of a quantum dipole correction term for the EAR. The corrected EAR is still a linear rule. The error margin of the corrected EAR lies well within the experimental error of photoemission spectroscopy experiments, thus proving the general applicability of linear rules for the determination of the band offset.
Modeling of Ge segregation in the limits of zero and infinite surface diffusion
Authors: Godbey D. J. , Ancona M. G.
Published: July 2002

A model to treat Ge segregation with simultaneous growth and exchange during Si/SiGe layer growth by molecular beam epitaxy is described. Within this three layer formalism, the segregating layers were treated in two limiting cases, a solid surface model in which no surface diffusion occurs, and a fluid surface model, in which surface diffusion is very fast. Simultaneous treatment of exchange and growth within the fluid surface model was the only one of the two that allowed the accumulation of Ge in the top two layers to significantly exceed that of the bulk in surface alloys, in agreement with experimental observations.
Electron cyclotron resonance plasma etching of oxides and SrS and ZnS-based electroluminescent materials for flat panel displays
Authors: Lee J. W. , Pathangey B. , Davidson M. R. , Holloway P. H. , Lambers E. S. , Davydov A. , Anderson T. J. , Pearton S. J.
Published: July 2002

A number of different plasma chemistries have been investigated for the etching of oxides (indium tin oxide for conductive electrodes; alumina/titania and Al2O3 for insulators) and phosphors (SrS, ZnS) used in thin film electroluminescent displays. Under high ion density conditions, such as in an electron cyclotron resonance source, maximum etch rates above 1500 Å/min are obtained for ZnS in Cl2/Ar, BCl3/Ar, and SF6/Ar, for SrS in SF6/Ar and CH4/H2/Ar, for ITO in CH4/H2/Ar and for ATO in SF6/Ar. The etching is ion activated under most conditions, producing good feature anisotropy. Near-surface stoichiometry could generally be maintained on the etched surfaces of all materials except SrS where we invariably detected strong preferential loss of S. An optimized process for etching a typical metal-insulators-semiconductor-insulator-metal stack would involve switching plasma chemistries for each individual layer, but we have successfully patterned such a stack using only the CH4/H2/Ar chemistry.
Thermal stability of a-SiNx:H films deposited by plasma electron cyclotron resonance
Authors: Martı́nez F. L. , del Prado A. , Bravo D. , López F. , Mártil I. , González-Dı́az G.
Published: July 2002

We analyze the influence of rapid thermal annealing on Al/SiNx:H/Si structures with a nitrogen to silicon ratio of 1.55 in the insulator bulk. The SiNx:H is deposited by the electron cyclotron resonance plasma method and the films were annealed at temperatures ranging from 300 to 1050 °C. We have related the changes of the interface trap density with those of the insulator bulk density of dangling bonds, resistivity, and breakdown field. A sharp dip in the dangling bond density is observed at moderate annealing temperatures, from 1.8×1018 cm−3 for the as-deposited film down to 9.6×1016 cm−3 at the point of inversion of the trend between 500 and 600 °C. The density of interface states is also reduced in this range of temperatures from 3.6×1011 to 1.2×1011 eV−1 cm−2. Resistivity and breakdown field are maintained in the range 5×1014–5×1015 Ω cm and 6.4–6.6 MV/cm, respectively, up to a temperature of 600 °C. We attribute the improvement of the interface characteristics and the decrease of dangling bonds to a thermal relaxation and reconstruction of the SiNx:H lattice and its interface with the silicon substrate. For temperatures above this threshold the electrical properties suddenly deteriorate and the density of dangling bonds increase. At even higher temperatures (above 900 °C) a release of hydrogen from N–H bonds takes place.
Multisource plasma chemical vapor deposition for synthesis of SiNx–SiOy and SiNx–SiCy composite films
Authors: Nonogaki Ryozo , Yamada Suzuya , Wada Tetsuya
Published: July 2002

SiN x – SiO y and SiNx–SiCy composite films have been deposited by a multisource plasma chemical vapor deposition (p-CVD) method. Two plasma generators are implemented to form the precursors of the respective component of the composite films. In each plasma generator, two kinds of source gas are fed into the generator and decomposed by two rf electrodes, respectively. The pressure of the reaction zone of the plasma generator is raised by throttling of the aperture of the plasma generator. With the p-CVD system, SiNx–SiOy and SiNx–SiCy composite films in which clusters of SiOy and SiCy are distributed in the matrix of SiNx were deposited effectively, and then nodules were formed.
Depth distribution of plasma induced damage and dislocation generation due to an interaction of subsequent oxidation
Authors: Yamaguchi T. , Sasaki T. , Nikoh H. , Ito T.
Published: July 2002

Surface damage induced by reactive ion etching (RIE) was investigated in terms of its depth, distribution, and correlation with dislocation generation due to subsequent oxidation. Damage structure was evaluated using transmission electron microscopy, reflection high energy electron diffraction (RHEED), Auger electron spectroscopy, and thermal wave measurement technique. A chemical dry etching and surface analyze technique of RHEED and TW were utilized to profile the damage distribution. It is identified that the surface damaged layer consists of two parts; the upper part from the surface to about 4 nm is a heavily damaged amorphous structure containing carbon and the lower part, between 5 and 30 nm, is a single crystal Si with a lot of lattice defects. It is found that RIE damage may form film edge dislocations by the interaction of subsequent selective oxidation even though damage was minimized to suppress oxidation induced stacking faults generation. High leakage current occurs when n+–p junctions are fabricated on this RIE and selective oxidation because of these film edge dislocations. It seems that generation of film edge dislocations has correlated with this carbon contained amorphous layer.
Electron beam optical system with large field coverage for submicron lithography
Authors: Hosokawa Teruo , Morita Hirofumi
Published: July 2002

A low aberration and low landing error deflective focusing system has been developed for submicron electron beam lithography. The deflection system consists of a one-stage electrostatic deflector and a one-stage magnetic lens, which is simple and desirable for a practical electron beam lithography system. The design method is based upon the low aberration and telecentric properties of the ideal uniform magnetic focusing and uniform electrostatic deflection fields. Fringe fields, which are generated in practice, degrade the optical properties, but their distributions are optimized to minimize additional aberration and landing error. Overall aberration is 0.2 μ and landing error is 20 mrad at a 10 mm field corner with a 5 mrad beam half angle after dynamic focus correction. Eight pole and twelve pole electrostatic deflectors are constructed and their performances are obtained and studied. Studies of higher order aberrations show the importance of fifth order rotational invariance for a large area deflection. Using this system, 0.5 μ rule LSI patterns are successfully exposed over a 10×10-mm field.
A precise and automatic very large scale integrated circuit pattern linewidth measurement method using a scanning electron microscope
Authors: Miyoshi M. , Kanoh M. , Yamaji H. , Okumura K.
Published: July 2002

This paper deals with an automatic linewidth measurement method of photoresist pattern linewidths with high accuracy, which we call ‘‘the linear regression method.’’ In the linear regression method, the secondary electron intensity profile at the photoresist pattern edge is approximated by two lines. One is the average line of the secondary electron intensity profile on the substrate and another is the slope line corresponding to the slope of the photoresist edge. The cross point of the two lines is defined as the pattern edge. The linewidths obtained by this method agree with the linewidths obtained by the cross sectional SEM images which are defined as true values, within 0.009 μm for various photoresist slope angles and within 0.002 μm for variation of the underlying materials. A practical pattern linewidth measuring apparatus which employs a high speed measurement time of 2.34 s is also described.
Influence of heterointerfaces on optical properties of CdTe/(Cd,Mn)Te and ZnSe/(Zn,Mn)Se superlattices
Authors: Nurmikko A. V. , Hefetz Y. , Chang S.-K. , Kolodziejski L. A. , Gunshor R. L.
Published: July 2002

A selective comparison is made of the influence of heterointerfaces on recently observed optical properties of CdTe/(Cd,Mn)Te and ZnSe/(Zn,Mn)Se superlattices in the quantum well limit. Specifically, we draw new conclusions and insight of the role of heterointerfaces on exciton localization phenomena in these strained layer structures. Amongst these II–VI superlattices, large variations are encountered which appear at least in part to be connected with interface related disorder.
An electrohydrostatic analysis of equilibrium shape and stability of stressed conducting fluids: Application to liquid metal ion sources
Authors: Chung M. , Miskovsky N. M. , Cutler Paul H. , Feuchtwang T. E. , Kazes E.
Published: July 2002

An exact mathematical treatment of the problem of an electrically stressed fluid from zero field to the onset of instability gives rise to the nonlinear electrohydrodynamic equations which, in general, are not amenable to analytic solution. To make the problem more tractable, one considers two limiting regimes, the electrohydrostatic (EHS) and the electrohydrodynamic (EHD) limits. In the EHS case, the fields and the velocities are assumed to be small so that quasistatic equilibrium exists and the fluid surface is essentially at rest. In this paper we consider the electrohydrostatic analysis of the equilibrium shape and stability of the electrically stressed fluids. The current work reintroduces the EHS stability criterion due to Zeleny, as well as a new set of equations and numerical procedure for analyzing the stability of an axially symmetric fluid with an arbitrary shaped surface. These are contrasted with a stability criterion, introduced by Taylor, which it is argued, is only an equilibrium condition and not a proper criterion for analyzing the general stability of electrified fluids. The Taylor and Zeleny criteria are applied to fluid sources modeled as simple coordinate surfaces, such as the cone, the cusp, and the hyperboloid. These results lead to a new physical interpretation of the onset of fluid instability in the EHS limit. A set of partial differential equations is derived, whose solution describes the equilibrium shape of a conducting fluid as a function of the applied electric field. Numerical results are presented for the evolution of the equilibrium shapes of several liquid metals as a function of the applied voltage. Values of the critical or breakdown voltage are obtained from these results and found to be in good agreement with experiment. Finally, the EHS analysis indicates that a realistic and accurate treatment of the onset of instability requires fluid flow in a dynamical model.
The thermomechanical stability of ion beam masks
Authors: Randall John N. , Sivasankar R.
Published: July 2002

A computer model has been used to study distortions in Si membrane masks which could be used for proximity printing with ion beams. Thermal distortions which occur during exposure and stress relief distortions which occur during fabrication were calculated separately. The results suggest that distortions can be acceptably low in a regime which allows short exposure times and a reasonable field size.
The use of diffraction techniques for the study of in-plane distortions of x-ray masks
Authors: Ruby R. , Baldwin D. , Karnezos M.
Published: July 2002

We describe the use of gratings, placed on boron–nitride membranes and exposed with electron beam lithography, as a method of obtaining both qualitative and quantitative information about x-ray mask in-plane distortions. The mask is placed at an angle α≂arcsin λ/d0 measured with respect to an incident plane wave front (λ=6328 Å for the He–Ne laser and d0=1.0 μm for our grating pitch). A mirror, placed at right angles to the mask, is positioned so that it also intersects the incident plane wave front. Both the resultant diffracted wave front and the reflected diffracted wave front are then collected by a lens system and video camera. The grating is written on all or part of the active area of the mask. The process of developing and patterning the trilayer resist structure and absorber film is identical to that of processing an x-ray mask. Patterned gratings allow us to observe: 1) stage placement errors to <0.1 μm, 2) in-plane errors induced by the mounting fixture, 3) in-plane distortions due to thermal gradients generated at e-beam write-time, 4) in-plane distortions due to the absorber stress. Results indicate that for a 0.9 μm tungsten film the worst-case strain due to the absorber, ∼20 ppm, is seen at visual endpoint; however, complete etching of the interlayer lowers this strain to ∼2–3 ppm.
Visible-laser photochemical etching of Cr, Mo, and W
Authors: Rothschild M. , Sedlacek J. H. C. , Black J. G. , Ehrlich D. J.
Published: July 2002

Direct halogen etching of metal films by laser-induced photochemical and thermal processes at submicrometer resolution is described. The regimes in which each of the processes is prevalent are readily observed. In addition to direct definition of metal patterns, the etched metal films serve as durable resist layers for conventional etching processes. Cl2 is photochemically dissociated at low laser power density levels, enabling direct-write etching of Cr, Mo, and W films on fragile substrates. NF3-assisted etching is dominated by thermal reactions.
Comparison of data transfer rates of focused electron and ion beam nanometer lithography
Authors: Siegel Benjamin M.
Published: July 2002

Light ions such as protons incident on organic resists (polymethylmethacrylate) deposit their energy very efficiently in well-defined volumes with no backscattering. These characteristics make protons the best medium for writing nanometer structures in the lithographic process. To write nanometer structures with focused electron beams the electrons must be accelerated to energies of 50 to 100 KeV where the interaction cross sections are very small and very large doses of electrons are needed and to avoid backscattering, thin-film substrates have been used. We have taken the dosages of electrons and protons that investigators have found are necessary to write 10- and 30-nm lines and using the characteristics of the very high brightness sources that are now available with field emission electron beams and gaseous field ion beams of H+2 and calculated the data transfer rates for writing these nanometer structures. Focused proton ion beam lithography gives data transfer rates two orders of magnitude faster than focused electron beams for writing 30-nm pixels; 1.6×108 Hz for protons versus 3.0×106 Hz for electrons.
Fine pattern lithography using a helium field ion source
Authors: Horiuchi K. , Itakura T. , Ishikawa H.
Published: July 2002

Despite the many reports on characteristics of hydrogen field ion (FI) sources, there have been only a few reports on focusing experiments. We developed a stable helium FI source and a focusing column with a gimbal assembly for beam axis alignment, and carried out focusing experiments. Scanning ion microscope images of a Au wire were observed using the focusing column. From the image resolution, the ion probe diameter was estimated to be ∼200 nm. We exposed a 260-nm-thick polymethylmethacrylate resist on a Si substrate, which produced 200-nm-wide lines. A 70-nm-wide space was also formed. The proximity effect was negligible even if the space between the lines was 100 nm. Thus, we confirmed that a helium FI source is suitable for fine pattern lithography.
Recent advances with the variable axis immersion lens
Authors: Sturans M. A. , Pfeiffer H. C. , Stickel W. , Groves T. R.
Published: July 2002

The novel variable axis immersion lens (VAIL) magnetic focusing and deflection system has been shown to produce excellent images over large fields. A practical lithography tool, however, requires high throughput (writing speed) which the magnetic deflection alone cannot provide. This paper describes the incorporation of a unique high-speed electrostatic deflection system in VAIL which maintains perpendicular landing everywhere on the target. In order to keep the beam at optimum focus when the target height or spot size is changing, a high-speed focus coil was developed which does not produce any positional errors when excited.
Favorable source material in liquid-metal-ion sources for focused beam applications
Authors: Ishitani T. , Umemura K. , Kawanami Y.
Published: July 2002

The variety of ion species is increased by using alloys as well as pure elements as the source material of liquid-metal-ion sources (LMIS’s) in focused-ion-beam (FIB) technology. Some experiments show that the base elements of the alloy affect the charge and energy distributions of emitted ions. Doubly charged ions, which have a narrower energy spread per charge and smaller energy tail than the singly charged ions, form a finer FIB. The intensity ratio of doubly to singly charged ions is expected to increase with selection of an alloy with higher surface tension, because this will strengthen the electric field at the ion emitting surface. LMIS characteristics in connection with source materials are discussed.
Interband transitions in InxGa1−x As/GaAs strained layer superlattices
Authors: Reddy U. K. , Ji G. , Henderson T. , Huang D. , Houdré R. , Morkoç H. , Litton Cole W.
Published: July 2002

Room-temperature photoreflectance (PR) measurements have been used to investigate the optical transition energies in InxGa1−xAs/GaAs strained layer superlattice structures grown by molecular-beam epitaxy (MBE). Sharp PR features indicating excellent optical quality of these MBE grown structures were observed. The transition energies were calculated and PR spectra fitted to the theoretical line shape expression. By observing the variation of Cl-Lbl (where Cl is the first conduction subband in InGaAs layers and Lbl is the first light-hole subband in the GaAs layers) type II superlattice transition, which cannot be observed with photoluminescence even at low temperatures, a conduction-band discontinuity of 70% was obtained. Further, an important outcome of this study is the observation of strong PR features from the spatially indirect Cl-Lbl transition which indicates that the modulation of band to band transitions can be a dominant PR line shape determining mechanism.
Intrinsic stress and stress gradients at the SiO2/Si interface in structures prepared by thermal oxidation of Si and subjected to rapid thermal annealing
Authors: Fitch J. T. , Bjorkman C. H. , Lucovsky G. , Pollak F. H. , Yin X.
Published: July 2002

This paper reports on a study of the intrinsic stress and strain in thin films of SiO2 prepared by the thermal oxidation of crystalline silicon. We focus on the relationship between the inhomogeneity of thin-film properties and the thermal history of the oxide film, including both film growth and thermal annealing. We show that this film can be inhomogeneous in the sense that oxide formed initially at the silicon–silicon dioxide (Si/SiO2) interface has been annealed at the growth temperature for the time required for film growth, whereas newly formed oxide at the growth interface has not been annealed for any appreciable period. We demonstrate that thermal annealing cannot completely remove the thickness dependence in the strain induced by the mismatch between the molar volumes of silicon and silicon dioxide at the growth interface, subject to constraints introduced by the chemical bonding structure at that interface. Based on laser-beam deflection and photoreflectance measurements, we show that there is alway a substantial residual intrinsic interfacial stress, and that is independent of the growth temperature, and thermal annealing. A time scale for describing thermal relaxation of stress and strain profiles is given by the ratio of process time to the viscoelastic relaxation time at the processing temperatures.
Computation of magnetic deflectors for electron beam lithography
Authors: Lencová B. , Lenc M. , van der Mast K. D.
Published: July 2002

The computation of magnetic deflectors by the finite element method is extended to the computation of tapered saddle coils. A general energy functional for any harmonic component of the field was derived, which enables the computation of any multipole made of saddle and toroidal coils in the presence of rotationally symmetric magnetic materials. In order to get the axial harmonics with high accuracy, a different expression for the cylindrical harmonics of the magnetic scalar potential was used, and analytical formulas for the integration of expressions in the energy functional containing higher powers of the radial coordinate were derived. A program defl for the computation of deflectors and other multipoles for mainframe computers and PC/ATs was written, and also a graphical display of the results is provided.
Chlorine and HCl radical beam etching of III–V semiconductors
Authors: Lishan David G. , Hu Evelyn L.
Published: July 2002

This work presents etch rate versus temperature data for GaAs and InP etched by Cl2 and HCl both with and without a remote plasma. The data is described both qualitatively and quantitatively by a thermodynamic model utilizing reactant-flux-limited and product-desorption-limited regimes. This ‘‘ionless’’ etching technique demonstrates reactant-flux-limited, temperature-independent behavior for HCl etching of GaAs for over five orders of magnitude of flux. InP and GaAs show nearly equirate etching at T>150 °C with both gases. Reactive ion etching (RIE) with Cl2 of InP at elevated temperatures produces only moderate rate enhancements; RIE gave a maximum etch rate of ∼800 Å/min at 175 °C compared to ∼0.5 μm/min obtained with the remote plasma system at the same temperature.
Focused ion beam induced deposition of platinum for repair processes
Authors: Tao Tao , Wilkinson William , Melngailis John
Published: July 2002

Focused ion beam induced deposition of platinum from a gas of (methylcyclopentadientyl) trimethyl platinum has been demonstrated and used for integrated circuit repair. Ga+ ions in the range of 30–40 keV have been used and line widths down to 0.3 μm with resistivities as low as 70 μΩ cm have been observed. The deposition yield as a function of angle of incidence has been measured by scanning the ion beam across a 2.6 μm diameter pyrex rod. The conductors on an actual integrated circuit have been modified by milling and filling a via to connect two Al lines in a sandwiched configuration as well as by milling two vias through passivation and connecting two adjacent Al lines.
A direct method to produce and measure compositional grading in AlxGa1−xAs alloys
Authors: Sundaram M. , Wixforth A. , Geels R. S. , Gossard A. C. , English J. H.
Published: July 2002

We present a method to calibrate the profile of Al mole fraction versus depth, deposited in growth of graded AlxGa1−xAs alloys in a molecular-beam epitaxy machine. A computer is used to either ramp the Al oven temperature (analog alloy), or pulse the Al beam (digital alloy), with a fractional monolayer depth resolution that permits averaged alloy profiles corresponding to a range of different design profiles to be obtained. The profiles are measured in calibration runs by using a fast picoammeter to track the ion-collector current of the beam flux monitor ion gauge (facing the ovens), and integrating the ion current with time. Parabolic quantum wells are grown by either technique and the corresponding measured profiles are compared to each other and to the design profile. The ability of the digital-alloy technique to obtain almost arbitrarily varying graded-alloy profiles is illustrated.
Carrier diffusion effects in III–V semiconductor structures measured by the point contact current voltage technique
Authors: Eldridge G. W. , Berkowitz H. L. , Hillard R. J. , Heddleson J. M. , Rai-Choudhury P. , Mazur R. G. , Stillman G. E.
Published: July 2002

Measurements of electrically active dopant profiles in thin III–V semiconductor structures are critical to the development of high speed and optoelectronic devices. The point contact current voltage (PCIV) technique has previously been demonstrated to be a powerful method for the high spatial resolution carrier concentration profiling of III–V semiconductors, offering improved measurement range and resolution when compared with C-V methods. For thin layers, the on-bevel carrier concentration profile measured with the PCIV technique differs from the electrically active net dopant profile. These differences are due to carrier diffusion. Poisson analysis can account for the diffusion of the carriers away from the dopant atoms and provide a clearer picture of the dopant profile in the material. In this paper we demonstrate application of the Poisson equation to the interpretation of PCIV measurements on thin III–V semiconductor structures of current interest.
Alignment signal failure detection and recovery in real time
Authors: Progler C. J. , Chen A. C. , Hughlett E.
Published: July 2002

One primary detractor in an alignment system’s performance is the corruption of alignment target integrity by thin film processes, metal grain structure, and contamination. While most aligners will acquire even very low contrast signals with sufficient precision, the measured align position is often inaccurate due to process induced asymmetries or dislocation of edges in the targets. If marks are sufficiently corrupted by lithographic processes, all alignment systems will suffer a performance degradation albeit to different degrees depending on the design. This article will present a general methodology and algorithm for the real-time detection and correction of erroneous alignment signal data in an image forming alignment system. An alignment signal figure of merit, based on image symmetry and internal consistency [A. Stankov, A. Lupata, and C. Progler, Proceedings of the KTI Microelectronics Seminar, City, Data 1991 (unpublished)], forms the basis for judging the integrity of alignment data. These two alignment signal quality metrics are computed and checked during each alignment cycle. Based on the signal metrics, the algorithm permits special signal filtering to obtain more robust alignment performance. Moreover, the algorithm has the ability to quantify the ‘‘quality’’ of alignment targets prior to exposure, thus, highlighting potential problem layers, mask errors, and wafer trouble spots due to processing. A description of the algorithm logic and implementation is described along with test bed and exposure-based data demonstrating the many benefits of the algorithm. These include improved overlay, faster alignment convergence, fewer alignment fails, and rapid assessment of alignment target integrity saving both time and money in the early stages of process development. In addition, an extension of the concept to a broader range of alignment system designs is briefly described.
Selective electroless plating on electron beam seeded nanostructures
Authors: Lee K. L. , Thomas R. R. , Viehbeck A. , O’Sullivan E. J. M.
Published: July 2002

Selective electroless plating on electron beam deposited palladium seed catalyst has been used for the fabrication of metallic nanostructures on planar and nonplanar substrates. The palladium seed catalyst was deposited using an allycyclopentadienylpalladium organometallic complex as the precursor. Isolated and proximity palladium seed test structures with linewidths ranging from 50 to 250 nm, with thicknesses ranging from 15 to 100 nm and gap spacing between proximity structures ranging from 50 to 250 nm were used to study the effect of the Pd seed size on metal deposition during the electroless plating process. The observed film growth behavior was apparently consistent with the theory of effect of seed size on the mass transport of dissolved oxygen to the catalytic sites during the plating process. For identical seed structures, differences in film growth behavior were also observed between plating of electroless copper and nickel. Metallic features with sizes as small as 100 nm in width and thickness had been obtained using selective electroless metal deposition on the electron beam seeded palladium catalysts. Proximity metallic structures with 100 nm line, gap, and thickness had also been obtained. This process had also been successfully applied to the fabrication of a magnetic force sensor for use in the atomic force microscope.
Characteristics of ion beam assisted etching of GaAs: Surface stoichiometry
Authors: Kosugi Toshihiko , Iwase Hiroaki , Gamo Kenji
Published: July 2002

Ion beam assisted etching of GaAs has been performed by continuous and pulsed Ga focused ion beam irradiation in Cl2 atmosphere, and etch yield and surface composition have been measured as a function of beam energy and Cl2 flux. It was observed that pulsed irradiation results in a 10 times or more higher etching rate than continuous irradiation. From Auger electron spectroscopy, it was observed that the surface becomes As rich after the etching with the composition depending on the etching condition. The thickness of the surface altered layer extends 7–20 nm depending on the beam energy. These results are discussed based on rate equations.
Controlling the profile of nanostructures
Authors: Tsutsui K. , Hu E. L. , Wilkinson C. D. W.
Published: July 2002

The profiles of etched quantum dots are determined by the etch conditions used, but as well, by the geometry of the array in which the dots are situated. Arrays of 60 nm diam dots in ZnTe were formed, and etched using reactive ion etching in a mixture of methane and hydrogen. Using the same etch conditions, the geometry was systematically modified, either by utilizing increased dot-to-dot spacing in uniform arrays, or by defining successively larger ‘‘clearing areas’’ centered about a single, ‘‘specimen dot.’’ For the uniform array of dots, the degree of undercut of the profile increases with the dot spacing, and is proportional to the etched area. For the specimen dot, the degree of undercut of the profile is proportional to the radius of the clearing. Understanding of the importance of the geometry allows formation of high density arrays of vertical quantum dots in the II–VI materials.
Repair of soft-x-ray optical elements by stripping and redeposition of Mo/Si reflective coatings
Authors: Early K. , Windt D. L. , Waskiewicz W. K. , Wood O. R. , Tennant D. M.
Published: July 2002

Experiments aimed at recovering soft-x-ray projection lithography mirrors that have defective reflective coatings by stripping and redeposition of Mo/Si multilayers are being reported. Two wet etchants were found that would remove the multilayers from composite glass substrates. One etchant is a solution of potassium ferricyanide and sodium hydroxide in water; the other is nitric acid with a minute quantity of hydrofluoric acid. Although each of these solutions offers preferential etch selection of the multilayers over the substrate glass, the selectivities are insufficient. The result is a surface roughening that lowers the reflectance from subsequently deposited multilayer coatings to an unacceptable level. With the addition of a carbon barrier layer between the substrate and the multilayer coating, either etchant can be used to strip the multilayers without damage to the underlying substrate surface.
X-ray mask fabrication using advanced optical lithography
Authors: Tsuboi S. , Suzuki K.
Published: July 2002

A viable method of x-ray mask fabrication using advanced optical lithography is proposed and the results of a feasibility study using conventional optical lithography is presented. This method reduces the proximity effect compared to electron-beam lithography for x-ray masks. Thus, it achieves excellent critical dimension control and offers high productivity and low cost with a single layer resist process. This technology was applied to fabricating x-ray masks with two 64 Mb dynamic random access memory (DRAM) circuit dies. The 64 Mb DRAM pattern on a five time reticle was replicated onto a 1-μm-thick positive resist coated on an extremely flat x-ray mask substrate using a conventional i-line stepper. The resist pattern was directly transferred to an x-ray absorber Ta film using low-wafer-temperature electron cyclotron resonance plasma etching with SF6 gas. The resulting 0.75-μm-thick Ta pattern with vertical sidewalls was fabricated with 20 nm (3σ) critical dimension control. This simple process makes x-ray masks with low defect density.
Evaluation of repair phase and size tolerance for a phase-shift mask
Authors: Ohtsuka Hiroshi , Kuwahara Kazuyuki , Onodera Toshio
Published: July 2002

The conjugate twin-shifter method for alternating phase-shift method provides the flexibility for mask shifter layout, and is applied for both isolated and periodic shifter arrays in conventional i-line positive resist processes. A new mask structure simplifies shifter pattern delineation and reduces the effects of phase defects. The detail of intermediate phase interference has been analyzed by applying the two-dimensional shifter array as the phase defect. The results of this analysis provides the optimum repair element array for the new repair method of phase defects. Then the effectiveness of this simple repair method is examined in the i-line process by using the test arrays that delineated in the XeF2 assisted focused ion beam process.
Key technologies in lower submicron lithography: Ultimate super resolution imaging system and chemically amplified resist using the self-solubility acceleration effect
Authors: Nakase Makoto , Inoue Soichi , Fujisawa Tadahito , Kihara Naoko , Ushirogouchi Tohru
Published: July 2002

A breakthrough in lithography is necessary to realize lower submicron devices beyond 64Mbit dynamic random access memories (DRAMs) due to limitations set by the required depth-of-focus and the k1/√k2 value, which represents the total performance of resist materials. An ultimate super resolution imaging system optimized by using a Monte Carlo-like method has been proposed to meet this point-of-view, which suggests that 64 and 256Mbit DRAMs can be realized by i-line and KrF excimer laser exposures, respectively. In addition, a novel chemically amplified resist has been developed using a newly synthesized dissolution inhibitor, t-butylcarbonate derivatives of o-cresolphthalein, which increases the dissolution rate contrast by the self-solubility acceleration effect.
Multilayer resist process for asymmetric gate recess in field-effect transistors
Authors: Ballegeer D. G. , Nummila K. , Adesida I.
Published: July 2002

A multilayer electron beam resist process for asymmetric gate recess for field-effect transistors (FETs) in compound semiconductors is presented. With this process, it is possible to decrease the drain conductance while maintaining a large source conductance by recessing the highly doped cap of the FET structure to a greater extent in the direction of the drain. This can be accomplished with a single electron-beam exposure process followed by a single step development due to the different sensitivities of the resist layers. A weak sidelobe exposure on the drain side of the gate is also needed during the electron-beam exposure process. This resist process is designed to reduce the number of lithography steps and the critical alignment required in the conventional ‘‘double-gate recess’’ process. InAlAs/In0.7Ga0.3As modulation-doped field-effect transistors (MODFETs) fabricated using the new process were found to have gate-to-drain breakdown voltages of 8.5 V, which was a significant improvement over the 2.25 V gate-to-drain breakdown voltages of the MODFETs fabricated using a conventional symmetric T-gate process.
Schottky field emission based scanning Auger microprobe
Authors: Narum David H.
Published: July 2002

A probe forming electron optical system utilizing Schottky field emission cathode technology has been designed and optimized for application to high spatial resolution scanning Auger microscopy (SAM). This article examines optics design trade-offs driven by the unique requirements of SAM, summarizes the theoretical performance limits of the resulting design, and compares simulation and experimental results over a wide range of operating conditions. Experimental results reported include beam diameter as a function of voltage and current, and beam current stability in various modes of operation (≲1%/h under optimum conditions). Experimental beam size data are compared to limits set by the magnified source, spherical and chromatic aberration, deflection aberrations, diffraction and space charge effects. The optical system is designed to operate at beam voltages ranging from ≤1 to 25 kV, with beam current at the sample of ≤1–100 nA. The operational mode of the instrument is chosen to emphasize either high spatial resolution (at the expense of maximum current) or high throughput (at the expense of spatial resolution) under the discretion of the operator. Switching from one to the other is accomplished by a change in the voltage applied to the extraction anode, resulting in the desired angular emission intensity JΩ. The time required for stabilization of the source after such a change has been found to be acceptable; for example, following a change from 0.25 to 1.0 mA/sr, beam current drift of ≲2%/h is generally achieved in less than 60 min.
Fabrication of a novel split-backgate transistor by in situ focused ion-beam lithography and molecular-beam epitaxial regrowth
Authors: Brown K. M. , Linfield E. H. , Jones G. A. C. , Ritchie D. A. , Thompson J. H.
Published: July 2002

Using the technique of in situ ion beam lithography and molecular-beam epitaxial regrowth high-quality backgate high electron mobility transistor devices were fabricated. In situ gallium ion beam damage has enabled independent contacts to be made to two closely spaced conducting layers. In addition, the lower conducting layer has been divided up into three regions, separated by high energy ion implantation. The combination of these techniques has enabled us to demonstrate the operation of the split-backgate transistor.
Fabrication limits of nanometer T and Γ gates: Theory and experiment
Authors: Maile B. E.
Published: July 2002

Theoretical and experimental investigations of methods to obtain T- and Γ-shaped sub-100 nm gates using electron-beam lithography, multilayer resist schemes and lift-off are reported. A resist profile simulation tool, based on Monte Carlo electron scattering calculation and an adaptive string algorithm, is combined with an experimentally determined solubility database for various resist/developer pairs. This provides a very accurate description of the profile formation process for arbitrary resist/substrate stacks and excellent agreement between simulated and experimental resist profiles is achieved. Limitations due to forward scattering and the influence of development conditions are discussed. Using optimized exposure and development parameters, sub-100 nm T and Γ gates with very low end-to-end resistances can be fabricated without sacrificing process latitudes.
SiGe/Si electronics and optoelectronics
Authors: Wang Kang L. , Karunasiri R. P. G.
Published: July 2002

Recently, there is an increased interest in the use of SiGe layered material for integration with Si technology. SiGe offers the opportunity for the first time to realize the advantages of heterojunctions in Si-based technology. In this article, the present status of the SiGe epitaxial growth techniques will be discussed from the point of view of device application. New directions will be presented. Next, electronic devices to be reviewed include bipolars and field effect transistors. The progress of tunneling devices will also be discussed. Then, the realization of quantum wells and superlattices for optoelectronics will be discussed. These will include Si-based detectors and modulators based on interband and intersubband transitions. One of the focuses will be the normal incidence operation for intersubband devices. Finally, the current status in the quest of light emitters will be briefly addressed.
Edge roughness of a 200-nm pitch resist pattern fabricated by ion projection lithography
Authors: Brünger W. H. , Blaschke J. , Torkler M. , Buchmann L.-M.
Published: July 2002

The edge roughness of test patterns fabricated by ion projection lithography has been investigated to indicate the optimum experimental conditions for sub-100-nm resolution. Direct observation in a scanning electron microscope, electron metrology, and atomic force microscopy has been employed for the evaluation of widths in the resist structures. Imperfections in the open stencil mask give rise to the main part of edge roughness, especially if electrostatic charging occurs. Lines and spaces in PMMA resist developed with high contrast show a roughness of 10 nm per edge if the mask has no defects and the projection system and resist performance have been adjusted satisfactorily. Statistical fluctuations of the ion current have no influence if a medium sensitive resist like PMMA is used resulting in exposure times of 100 ms.
Current-controlled negative differential resistance in InAs/AlxGa1−xSb tunnel structures
Authors: Chow D. H. , Schulman J. N.
Published: July 2002

We report the design and demonstration of a novel resonant tunneling device which displays bistability in operating current over a range of applied voltages. The device is based on an InAs/AlxGa1−xSb double barrier heterostructure. Although similar in design to conventional resonant tunneling structures, the type-II InAs/AlxGa1−xSb heterostructure permits the simultaneous accumulation of electrons and holes in the quantum well/barrier region under an applied bias. The steady-state free-charge distribution, and hence the device current, is strongly dependent upon the bias history of the device. This effect is manifested as a current-controlled (S-shaped) negative differential resistance under conditions in which the device current is specified while the device voltage is measured; a bistable (hysteretic) characteristic is observed under conditions in which the voltage is specified and the current is measured. We have observed current bistability for AlxGa1−xSb barrier compositions in the range 0.4<x<0.6, with high/low state separation in the 105 A/cm2 range. Under current-controlled measurement conditions, peak-to-valley voltage ratios as high as 1.5 have been observed.