bluuebunny/crossref_metadata_2025 huggingface dataset:
Regrowth on molecular-beam epitaxial layers by transferring in ultrahigh vacuum between growth chambers: An assessment of the interface quality
Authors: de Miguel J. L. , Meynadier M.-H. , Tamargo M. C.
Published: July 2002

The effect of transferring in ultrahigh vacuum conditions between molecular-beam epitaxy chambers on the quality of regrown interfaces is addressed. In particular, the Al0.35Ga0.65As/GaAs heterointerface is probed by low-temperature photoluminescence using a single quantum well (SQW) configuration, where the growth of the second interface has been interrupted and resumed after taking the sample back from the UHV transferring modules. Comparison of the emission characteristics of these SQW structures to others grown uninterruptedly indicates the feasibility of the UHV multichamber configuration for the realization of high-quality heterostructures involving incompatible materials or different processing steps.
Molecular beam epitaxial growth of high-quality GaAs on Si using a high-temperature i
n s
i
t
u annealing process
Authors: Kao Y. C. , Liu H. Y. , Tsai H. L. , Duncan W. M. , Kim T. S. , Shichijo H.
Published: July 2002

In this paper, we report a new process for molecular beam epitaxial (MBE) GaAs-on-Si growth. The process involves high-temperature in situ GaAs annealing above 850 °C. The unique points in this new approach are: (1) the thermal cycling layers or so-called thermal strained superlattices (TSL) are inserted in buffer growth and found to be effective in blocking dislocation propagation; (2) a thin Al0.35Ga0.65As cap layer is deposited after GaAs buffer layer growth to prevent the underneath GaAs epitaxial layer from sublimation during annealing. An 850 °C in situ AlGaAs cap annealing (ACA) of the AlGaAs/GaAs buffer layer can eliminate all the twins and stacking faults in the buffer layers and yield high-quality GaAs film. The bulk GaAs overlayers is grown at normal GaAs/Si growth temperature and is never exposed to a high anneal temperature. High-quality GaAs/Si layers with surface dislocation densities 1×106 cm−2 and an x-ray linewidth of 130 arc s have been achieved.
On the optimization of ion microprobes
Authors: Shao Zhifeng , Wang Y. L.
Published: July 2002

The size of an ion probe is determined by many different factors such as virtual source size, magnification, probe current, and aberrations of its optical column. While operating or designing an ion optical system, it is often desirable to choose these parameters such that the optimum probe is obtained for the anticipated application. In this paper, we propose a routine which could be used to find the optimum magnification and aberrations of a system for given ion source parameters and probe requirements.
Description and applications of a graded-thickness growth technique for molecular-beam epitaxy
Authors: Krusor B. S. , Fenner D. B. , Biegelsen D. K. , Yingling R. D. , Bringans R. D.
Published: July 2002

The technique and some applications of a graded-thickness sample deposition method for molecular-beam epitaxy (MBE) are described. We discuss the use of this method for the growth of GaAs on Si and related materials systems. In this method the substrate is translated during growth relative to a fixed, near-sample-plane shutter so that a wedge shaped growth thickness profile is obtained. We have found this method to be especially useful in conjunction with both ex situ and in situ analytical techniques for probing the continuous evolution of thin film growth. The technique offers several advantages over the traditional method of preparing a series of samples of different thicknesses. We have also found it useful for the direct comparison of the evolution of growth of two different surface preparations. We describe the use of Auger for in situ measurement of the composition and structure of the film at various stages of the growth with near monolayer resolution. Rutherford backscattering (RBS) has been used as an ex situ probe of the evolution of the deposited film. In an attempt to understand and control the atomic scale processes during the initiation of growth at the GaAs–Si interface we have used this method to grow graded-thickness samples with total thickness 3.5–10 nm. Analysis of these films has led us to develop a model for the nucleation and initial stages of growth of GaAs-on-Si. We also report on possible device applications of this technique.
Inverted resist multilayer system for high-definition pattern lithography
Authors: Etrillard J. , Izrael A.
Published: July 2002

A multilayer resist system is used to obtain high-definition and high aspect ratio masks by use of electron lithography. This technique overcomes most of the problems of obtaining with a short exposure time a high-definition mask: a lift-off metal deposition is made over a tick bilayer of hard-baked resist which is then patterned by reactive ion etching in pure low-pressure oxygen plasma. This inverted multilayer system can be used for dry etching of many different material sublayers and can be easily stripped away in a dedicated solvent after the etching. An example of application in self-aligned structures is given.
Rapid thermal oxidation of low-pressure chemical vapor deposition amorphous silicon films
Authors: Gualandris F. , Gregori M.
Published: July 2002

The rapid thermal oxidation (RTO) technique has been physically and electrically evaluated on single crystal and amorphous silicon (α-Si). Data on interface width, oxidation kinetics, and recrystallization kinetics as well as the conduction characteristics are reported for oxidized amorphous silicon. Our results indicate the RTO oxide grown on amorphous silicon is a film with peculiar behavior. By the use of a 250 Å thick oxide, no Fowler–Nordheim conduction is activated at ∼5 MV/cm, and no evidence of conduction is registered until a field of 6 MV/cm (breakdown field). The point-to-point film thickness uniformity results are better than that obtained from furnace oxidation on polysilicon. We suggest this to be related both to α-Si used as a starting material, and to the short oxidation time. A special double metal capacitor test has been proposed and successfully used in order to study the electrical characteristics without any drawback on sample morphology. Based on our experimental results we consider RTO on amorphous silicon as a suitable technique to be used in multipolysilicon device application.
Stochastic effects occurring after ion emission from liquid metal ion sources
Authors: Ward J. W. , Kubena R. L.
Published: July 2002

We have made a computer simulation of ion trajectories near the emitter of a liquid metal ion source. From the trajectory data, we have evaluated the full width at half-maximum (FWHM) of the transverse and longitudinal velocity distributions as a function of the distance downstream from the emitter. An extrapolation of the computed FWHM widths to the extraction electrode are in agreement with values inferred from experimental measurements of the target current density in our two-lens microprobe column.
Capillary-type cluster ion source and its application for selective deposition of aluminum film
Authors: Ogura M. , Komuro M. , Shimizu K. , Yabe A.
Published: July 2002

Cluster ions of acetone and triisobutylaluminum (TIBA) are generated from an apex of a capillary tube with an inner diameter of 5 μm and outer diameter of 20 μm, based on the atomization of a semiconductive liquid in high electrostatic field. Ion emission has an onset at a threshold voltage of around 2 kV, which is nearly equal to the value calculated from Taylor’s argument. The averaged charge-to-mass ratio of these cluster ions is determined to be 4.0–4.7 Coulomb/kg from a time-of-flight method. Spatially selected chemical vapor deposition of aluminum films is realized by the cluster ions of TIBA.
A Zn predeposition technique applied to GaAs/AlGaAs heterobipolar transistors
Authors: Shimamoto Y. , Itakura K. , Ueda D.
Published: July 2002

A Zn predeposition technique has been developed for forming the extrinsic base regions of HBTs. Zn ions are implanted in a shallow region of the p-base region, followed by a quick diffusion using rapid thermal annealing (RTA) at a relatively low temperature of 650 °C. The resultant heavily doped extrinsic base region has less defects at the vicinity of the p-base region than those obtained from conventional Be or Mg ion implantation. Experimentally fabricated HBTs using the new technique have shown more than twice the current gain than reference devices fabricated through Be ion implantation owing to reduced recombination centers in the extrinsic base region.
An edge-defined technique for fabricating submicron metal–semiconductor field effect transistor gates
Authors: Strifler W. A. , Cantos B. D.
Published: July 2002

A new technique has been developed to fabricate submicron gates in GaAs metal–semiconductor field effect transistors (MESFETs) using simple contact lithography. The technique employs a multiple layer resist structure and angle evaporation to define a conformal aluminum mask above the wafer surface. The gate length of the aluminum mask is well controlled by an evaporation angle and a resist thickness. The pattern transfer to the wafer surface is compatible with a recessed gate technology. In a production environment, the process is capable of producing quarter-micron MESFETs with less than ±150 Å (1σ) gate length variation across a 2-in. wafer.
Excimer laser planarization of copper deposited over polyimide
Authors: Baseman Robert J. , Turene Frank E.
Published: July 2002

We report an initial attempt to explore the feasibility of using an excimer laser to planarize copper deposited over polyimide. Even though the polyimide is thermally sensitive, a 2.8 μm thick copper film, deposited over polyimide, was planarized with 248 nm, 25 ns, laser fluences from 1.7 to 2.6 J/cm2. Although planar surfaces were readily produced, a variety of defects were observed in the underlying structures.
The optical logic device and GaAs groove grating fabricated by ion technique
Authors: Tao You-song , Liu Jin-sheng
Published: July 2002

This paper describes the work of fabricating optical logic devices and GaAs groove grating by the LKJ-1B ion beam etching machine and the LDJ-2A ion beam sputtering film system developed in our laboratory. The two-dimension multiple optical beam splitter is a device that produces phase delay which is determined by groove depth [Δφ=(2π/λ)(n−1)d]. K9 optic glass was used as the substrate material. The wavelength of the incident light was 6328 Å (He–Ne laser). The etching depth and the accuracy were dπ=λ/2(n−1)=6128 and 100 Å, respectively. The difference in the splitting light intensity between theory and experiment was ±3.6%. The author has fabricated the groove grating with periods of 10, 4, and 2 μm and depths of 3000, 5000, and 7000 Å. The sidewall slope is about over 85°.
Band offsets and electron localization in semiconductor interfaces and superlattices
Authors: Matthai C. C. , Bass J. M , Oloumi M.
Published: July 2002

The long standing problem of determining band offsets at semiconductor interfaces is readdressed. We show that the valence-band discontinuity can be extracted from a knowledge of the local density of states across the interface. This method can also be used to determine the band offsets in superlattice structures. The concept of band offsets in short period superlattices is examined. It is shown that this is intimately connected with the localization of bands in one or other of the superlattice constituents.
Electronic structure of sodium atoms adsorbed on the GaAs(110) surface
Authors: Allan G. , Lannoo M. , Priester C.
Published: July 2002

The electronic structure of Na atoms adsorbed on the GaAs(110) surface is calculated in the tight-binding approximation and the zero charge limit. For a monolayer and half a monolayer coverage, two different adsorption sites are considered. The surface atom and sodium core level shifts are calculated and compared to the experiment. The adatom binding energy is found to be maximum for adsorption on the surface Gallium dangling bonds. Finally the density of states and the interface state dispersion energy are compared with photoemission results.
Low-coverage metal-induced unrelaxation of the semiconductor surface at Ag/InP(110) interfaces: A photoemission extended x-ray absorption fine structure study
Authors: Mangat P. S. , Choudhary K. M. , Kilday D. , Margaritondo G.
Published: July 2002

The atomic geometries of Ag/InP(110) interfaces for 0.5 and 1 Å nominal metal coverages have been determined by photoemission extended x-ray absorption fine structure (PEXAFS). The coverages correspond to 3×1014 and 6×1014 atoms/cm2, if we assume that the Ag atoms are metallic, although we know that the Ag atoms are clustered at these low coverages. P 2p PEXAFS for 0.5 and 1 Å Ag covered InP(110) surfaces were acquired. The data were analyzed by conventional Fourier analysis procedures using the theoretical backscattering phase function of McKale et al. plus absorber phase function of Teo and Lee. For both silver coverages, the P–In bond length at the interface was determined as 2.52±0.04 Å, which is 0.08±0.02 Å greater than its value for the clean surface. For the clean InP(110) surface, the average (first) P–In bond length is 2.43±0.04 Å [Choudhary et al., Phys. Rev. B 38, 1566 (1988)], whereas in bulk InP the P–In interatomic distance is 2.54 Å. Hence, the PEXAFS results for low-coverage Ag/InP(110) interfaces indicate that the relaxation (contraction) of the clean InP(110) surface is mostly removed by the deposited noble metal atoms. The structural results show that the low-coverage Ag/InP(110) interfaces are nonreactive, since the unrelaxation is not a significant reaction. The low-coverage metal-induced unrelaxation in the P–In bond length at Ag/InP(110) interfaces might contribute to Fermi-level shifts during the Schottky barrier formation.
Transport properties and applications of unstrained In0.75Ga0.25As/Al0.6Ga0.4As heterojunctions
Authors: Rossi D. V. , Fossum E. R. , Kirchner P. D. , Woodall J. M.
Published: July 2002

The electrical and structural properties of a severely mismatched MBE-grown InGaAs/AlGaAs heterojunction were investigated. The heterojunction shows rectification and the InGaAs’s mobility is measured to be 142 cm2 /V s. This low mobility InGaAs contact can be used as the resistive, rectifying contact of a heterojunction-resistive-gate charge-coupled device.
Full-zone k⋅p theory of semiconductor superlattice electronic structure
Authors: Mailhiot C. , Smith D. L.
Published: July 2002

The k⋅p theory has been extensively used to describe bulk semiconductors. This theoretical approach has the same basic advantages for describing superlattices that it has for bulk semiconductors. Here, we present a full-zone k⋅p theory of semiconductor superlattice electronic structure. A reference Hamiltonian is defined by averaging the pseudopotentials of the constituent semiconductors. This Hamiltonian is diagonalized at the zone center to provide the k⋅p basis functions in terms of plane waves. The complex band structure is solved for each of the constituent materials in this basis. The periodicity of the bulk Hamiltonian is lost when the k⋅p zone-center basis is truncated to a finite set. As a result, the complex band structure has nonphysical out-of-zone solutions in the finite basis set problem. These spurious solutions appear to enter in the interface matching conditions. Treating the interface matching conditions in the presence of the spurious out-of-zone solutions is the principal difficulty in formulating a full-zone k⋅p theory of superlattices. Similar problems arise in other formulations in which the periodicity of the Hamiltonian is lost when the basis is truncated to a finite set. We solve this problem by constructing correct repeated-zone states using calculated in-zone states and the periodicity of the true bulk Hamiltonian. Orthogonality and completeness relations for the complex band structure eigenvalue equation are used to formulate the interface matching conditions in terms of matrix elements of the current density operator. Flux conservation is analytically ensured.
Electronic properties of NH3 adsorbed on InP(110) surfaces at room temperature
Authors: Salmagne S. Rossi , Baier H.-U. , Mönch W.
Published: July 2002

The interaction of NH3 with cleaved InP(110) surfaces was investigated by using a Kelvin probe, photoemission spectroscopy with monochromatic ultraviolet radiation (UPS), and low-energy electron energy-loss spectroscopy (LEELS). An NH3 -induced buildup of a depletion layer was found on samples doped p type. For exposures larger than 1×1020 NH3 molecules per cm2, the Fermi level becomes pinned 1.3 eV above the top of the valence band at the surface, while the bands remain flat for samples doped n type. The NH3 -induced surface states thus are of donor type. In the same exposure range the ionization energy was found to decrease by up to (0.5±0.05) eV, indicating the presence of NH3 -induced surface dipoles. In UPS the In(4d) core lines excited with 40.8 eV are insensitive to the NH3 uptake within the limits of experimental error while the energy loss at 17.9 eV observed with LEELS, which is attributed to transitions from In(4d) core levels into empty dangling bonds, decreases as a function of NH3 exposure. Therefore, the initially empty dangling bonds at surface In atoms have to become occupied with increasing uptake of NH3. By using temperature programmed desorption spectroscopy, NH3 was established to adsorb as molecules on InP(110) and GaAs(110) surfaces at room temperature. It is concluded that NH3 molecules are forming surface bonds via their lone electron pairs with empty dangling bonds of surface In atoms. In a surface molecule picture, these bonds will act as surface donors. The decrease in ionization energy is consistent with this model because NH3 molecules are polar with the nitrogen atoms being negatively charged.
Selective tungsten filling of sub-0.25 μm trenches for the fabrication of scaled contacts and x-ray masks
Authors: Maluf N. I. , Chou S. Y. , Pease R. F. W.
Published: July 2002

Trenches in a layer of SiO2 on Si, with feature sizes down to 0.125 μm have been filled with tungsten (W) using selective chemical vapor deposition (CVD). The trenches were formed in a fashion similar to contact vias by reactive ion etching the SiO2 to the underlying silicon. The tungsten was then deposited in a cold wall CVD reactor, by silane reduction of WF6, to a thickness of 0.5 μm. The process results in good planarity and uniformity making it suitable for the fabrication of sub-0.5 μm contacts and interconnects, and for the formation of high aspect ratio absorbers in x-ray masks.
Reactive-ion-etch profile evolution determined by a Monte Carlo microtopography model
Authors: Cotler Tina J. , Elta Michael E.
Published: July 2002

A two-dimensional microtopography-etch simulation using Monte Carlo methods presented earlier is used to simulate various reactive-ion etch profiles. The simulation models the topography of an arbitrary, periodic semiconductor surface during plasma-assisted or reactive-ion etching. A plasma-assisted etch process can be dominated by a physical (ion bombardment) mechanism, a chemical (free radical) mechanism or a physical/chemical interaction mechanism. Alternately recombinant surface chemistry can also determine the final etch profile. Examples of profiles generated under these three conditions are presented.
New taper-etching technology using oxygen ion plasma
Authors: Hashimoto Chisato , Machida Katsuyuki , Oikawa Hideo
Published: July 2002

A new and practical via hole taper-etching technology is proposed to obtain excellent step coverage of the upper metallization around the via holes in submicron multilevel interconnections. The technology uses incident-angle dependency of sputter etching and etching selectivity of oxygen ions. A bias electron cyclotron resonance (ECR) plasma-etching method is applied to realize a practical etching rate using oxygen ions. Scanning electron microscopy (SEM) inspection and contact string tests confirm that excellent results are obtained using the technology, including high yields and high reliability of submicron multilevel interconnections.
New process technique of bonding of large area power darlington transistor having lightly N-doped substrate
Authors: Deshwal V. P. , Dixit B. B. , Vyas P. D. , Khokle W. S.
Published: July 2002

Pure aluminum has been utilized as contact material between power darlington silicon wafer (100 A, 500 V) and molybdenum disk as a back side contact for lightly N-doped substrate. Appropriate temperature profile, assembly fixtures, and optimum aluminum thickness has been used during alloying of silicon wafer with moly disk to minimize silicon dissolution so that segregation of silicon at the liquid–solid interface takes place on silicon side and aluminum freezes out towards moly side giving low resistance ohmic contact, low saturation voltage, and low leakage. Metal base disk thickness has been determined optimally with respect to thickness of device wafer to provide minimum bow of fusion. Evaluation of voids at the moly–aluminum and aluminum–silicon interface indicated their absence at 700 °C bonding temperature.
Electrovoltaic effects and symmetric band bending: Inverse photoemission of epitaxial Bi/GaAs(110) between 60 and 300 K
Authors: Hu Yong-Jun , Wagener T. J. , Jost M. B. , Weaver J. H.
Published: July 2002

Electron-induced surface electrovoltaic effects are determined as a function of temperature and dopant concentration for epitaxial Bi/GaAs(110) by using inverse photoemission. Results obtained with an incident electron flux of 1014-1015 cm−2 s−1 show opposite shifts of empty state features of the Bi overlayers on p- and n-type GaAs(110). These shifts depend upon the bulk dopant concentration and overlayer thickness, and they increase as the temperature is cooled from 300 to 60 K. They reveal a nonequilibrium charge distribution associated with electron–hole creation in the GaAs depletion region. Reversible, symmetric steady-state band bending movements for n- and p-type GaAs(110) are determined as a function of temperature for a variety of coverages by using thermal cycling 300→60→300 K. The suppression of electron–hole recombination at low temperature results in significant band flattening similar to that observed in low temperature photoemission studies for metal–GaAs(110) interfaces.
Effects on sidewall profile of Si etched in BCl3/Cl2 chemistry
Authors: Maa Jer-shen , Gossenberger Herman , Hammer Larry
Published: July 2002

The sidewall profile of Si etched in BCl3/Cl2 chemistry from a single-wafer plasma reactor was found to depend on pressure, presence of resist, BCl3 flow rate, and the addition of CHCl3. In a RIE type of single-wafer plasma reactor, higher pressure and higher power density are used to achieve a higher etch rate. In this case features such as corner trenching, sidewall bowing, and tapering occur more frequently. The correlations between these features and the etch parameters are discussed with a particular emphasis on sidewall passivation effect.
Formation of quantum wires and quantum dots on InSb utilizing the Schottky effect
Authors: Sikorski Ch.
Published: July 2002

The formation of quasi-one- and zero-dimensional electron systems on InSb (111) by Schottky barriers has proven to be a very successful method. The lateral confinement underlying these structures is achieved by a metal grating deposited directly onto the surface of the semiconductor. A large number of metals, ranging from strongly reactive alloys like NiCr to less reactive metals like Au is used to study the formation of the lateral confining potential. The confining potentials are characterized by their intraband resonances using far-infrared spectroscopy. Discussing our results we take advantage of previous results for the Schottky barrier formation.
Rapid electron beam annealing of tantalum films on silicon
Authors: Mahmood F. , Cheema O. S. , Williams D. A. , McMahon R. A. , Ahmed H. , Suleman M.
Published: July 2002

The reaction of tantalum with silicon to form tantalum silicide has been studied using rapid electron beam annealing which gives well controlled time–temperature conditions. Tantalum layers were deposited on single crystal silicon substrates, and annealed at temperatures between 750 and 1100 °C for times ranging between 0.1 and 90 s. The films were studied using sheet resistance measurements, Auger electron spectroscopy depth profiling scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The diffusion of silicon into the tantalum film , and subsequent formation of a stable silicide, was investigated as a function of temperature and time of anneal. It was observed that at a peak temperature of 900 °C, lasting for a time of 0.1 s, only partial silicidation of the deposited tantalum layer had taken place. These conditions establish the minimum thermal processing requirement which must be met for complete silicide formation.
The effect of intensity distribution in the reflected beam on the detection error of monochromatic optical autofocus systems
Authors: Tojo Toru , Tabata Mitsuo , Ishibashi Yoriyuki , Suzuki Hitoshi , Takahashi Susum
Published: July 2002

The measurement error induced by the intensity distribution in the reflected beam from the surface of a substrate was studied to improve the focal accuracy of an autofocus system. It is shown that scanning of the probe beam across the wafer surface reduces the effect of nonuniform reflectivity. An accuracy of 0.6 μm can be obtained. A signal processing circuit which accommodates 40 dB of incident intensity range is developed.
A process-related study of the Al/MoSi2–Al double-level metallization system
Authors: Smith U. , Norström H. , Wennström U. , Johansson A. , Engström I. , Tóth-Pál Z.
Published: July 2002

The influence of some important process parameters on the quality of electrical contacts to a silicon substrate has been studied for a double-level metallization system consisting of Al–MoSi2–Al(Cu,Si)–cSi. This double-level metallization scheme is presently used in the production of advanced complementary metal–oxide semiconductor devices. The metal films were produced in two commercially available sputtering systems. A detailed picture of the reactions within the metal films and at the interface to the substrate was obtained by means of Rutherford backscattering spectroscopy, secondary ion mass spectroscopy, x-ray diffraction (diffractometer and Read camera), differential scanning calorimetry, metallographic sectioning, and scanning electron microscopy, in addition to electrical measurements on contact chains and Kelvin contact structures. The dependence of the stoichiometry of the deposited MoSi2 film on the sputtering pressure was determined in the range 1–15 mTorr. The formation of hexagonal MoSi2 from the amorphous as-deposited film was found to occur around 380 °C with an activation energy of 1.9 eV and an enthalpy of crystallization of about 40 kJ/mol. These results are shown to be compatible with theoretical estimates. Depending on the particular conditions during the deposition of the MoSi2 film, Si was found to be taken up or rejected during anneals up to 425 °C. This led to spiking and precipitation, respectively. Diffusion of Mo into the Al films is shown to have resulted in the formation of MoAl12. The contacts were found to be stable during at least 70 min for temperatures up to 450 °C. It is shown that by proper tailoring of the sputtering conditions and a judicious choice of time and temperature for the postanneal cycle, it is possible to avoid the problems of spiking and silicon precipitation inherent in a metallization system based on a combination of aluminum with a near-stoichiometric silicide.
An investigation of the roughening of silicon(100) surfaces in Cl2/CCl4 reactive ion etching plasmas by i
n s
i
t
u ellipsometry and quadrupole mass spectrometry: The role of CCl4
Authors: Thomas D. J. , Southworth P. , Flowers M. C. , Greef R.
Published: July 2002

The reactive ion etching of silicon(100) in Cl2/CCl4 plasmas at 13.56 MHz is described. In situ ellipsometry is used to determine the extent and nature of silicon surface roughening under a variety of plasma conditions. Quadrupole mass spectrometry yields complementary information regarding the composition of the plasma. In contrast to our previous experiments using pure Cl2, we find that no significant roughening of silicon occurs in Cl2/10%CCl4 plasmas at 100 mTorr, irrespective of rf power in the range 50–300 W (0.3–1.8 W cm−2); indeed smoothing of previously roughened surfaces takes place at 100 mTorr and 100 W. When the plasma pressure is reduced to 50 mTorr, considerable roughening occurs at rf powers ≥100 W and a marked dependence on power is recorded. Water vapor has a far less dramatic effect on the etching and roughening of silicon(100) in Cl2/10%CCl4 plasmas, compared to the effects observed in pure Cl2. This suggests that hydroxide micromasks are efficiently removed by reactive species that derive from CCl4. The mass spectrometric data support the hypothesis that it is CCl2 and CCl3 radicals that probably interact with >Si–OH to form COCl2 and expose reactive silicon sites.
Molecular beam epitaxial growth of GaAs on silicon and silicon on sapphire incorporating a low temperature buffer
Authors: Metzger R. A. , Delaney M. J. , McCray L. , Kanber H. , Wang D. C. , Chi T. Y.
Published: July 2002

GaAs has been grown by molecular-beam epitaxy on both silicon and silicon on sapphire. The incorporation of a low temperature buffer has reduced the film stress from 3.0 to 2.2 kbar for GaAs grown on silicon. However, films stress can be completely removed for growth of GaAs with the incorporation of the low temperature buffer when grown on silicon on sapphire (SOS). The orientation dependence of GaAs grown on SOS has been investigated by growing on orientations slightly off axis from the (100) in the [011] direction by 2°, 4°, and 6°. X-ray, mobility and photoluminescence measurements have been made, showing that growth on 6° misoriented SOS produces nearly stress free films, with materials properties similar to those of GaAs on silicon, and mobilities six times higher than those of GaAs grown on on-axis (100) SOS. Metal–semiconductor field effect transistors (MESFETs) have been fabricated on GaAs on silicon showing device characteristics comparable to those of GaAs on GaAs.
Direct-current and radio-frequency properties of InAlAs/InGaAs pseudomorphic modulation doped field effect transistors with graded channels
Authors: Kolodzey J. , Laskar J. , Boor S. , Agarwala S. , Caracci S. , Ketterson A. A. , Adesida I. , Hsieh K. C. , Sivco D. , Cho A. Y.
Published: July 2002

We report comprehensive high-frequency characteristics of pseudomorphic InAlAs/InGaAs/InP modulation doped field effect transistors having thick, dislocation-free channels with an In mole fraction compositionally graded to x=0.65 at the heterointerface. Grading was achieved by reducing the Ga effusion cell temperature during epitaxial growth. High-frequency S-parameter measurements were performed on transistors having gate lengths of Lg=0.25 μm and showed significant increases in both transconductance gm and current gain cutoff frequency fT with increasing graded channel layer thickness. The best devices with a 30 nm channel have gm=720 mS/mm and fT=120 GHz. We give data on growth conditions, layer structure, and device electrical properties.
Phonon assisted tunneling in lattice-matched and pseudomorphic resonant tunneling diodes
Authors: Yoo Hyungmo , Goodnick Stephen M. , Arthur John R. , Reed Mark A.
Published: July 2002

MBE grown resonant tunneling diodes based on the lattice matched AlAs/GaAs and the pseudomorphic AlGaAs/InGaAs systems are investigated. In the presence of quantizing magnetic field, a large number of tunneling peaks in the valley region of the current–voltage curves are observed. The dependence of the peak positions on magnetic field is used to distinguish direct tunneling between Landau levels from that due to phonon assisted tunneling. Shubnikov de-Haas measurements show the evidence of a two-dimensional quasibound state in the accumulation layer of the emitter and LO phonon assisted tunneling through the Landau levels in the well.
Synthesis and lithographic characterization of poly(4-t-butoxycarbonyloxystyrene-sulfone)
Authors: Kometani J. M. , Nalamasu O. , Reichmanis E. , Kanga R. S. , Thompson L. F. , Heffner S. A.
Published: July 2002

Poly(4-t-butoxycarbonyloxystyrene-sulfone) was synthesized by a thermally induced radical copolymerization of 4-t-butoxycarbonyloxystyrene and sulfur dioxide using AIBN as the initiator. The effect of polymerization conditions such as temperature, monomer feed ratio, and monomer concentration on the copolymer molecular weight and composition was studied. Additionally, the lithographic performance of the matrix polymer was evaluated for various copolymer compositions and molecular weights.
Applying deep ultraviolet lithography
Authors: Tipton Mike , Misium George , Garza Cesar , Eguchi Mitsuru
Published: July 2002

This paper discusses the application of a deep wafer stepper and associated photoresist systems to advanced semiconductor processing. It is shown that, even with the limited number of photoresists available, deep UV lithography is a viable candidate for advanced processes requiring half micron and smaller features. First, the performance of the exposure tool is discussed; lens performance data including image field curvature, and distortion is shown. Next, results obtained using two different approaches for photoresist processing are discussed. Single layer wet developed photoresist processing is shown to be useable in those cases where topography is not severe. Surface imaging photoresist approaches using the DESIRE process are shown to be applicable in cases where topography is an issue or broader process latitude is required.
Laser application in packaging of very large scale integrated chips*
Authors: Jee Yong , Woodard Ollie C.
Published: July 2002

We used a pulsed Nd:YAG laser beam in a tape automated bonding (TAB) process. Tin plated copper TAB tapes were bonded to gold bumped and bumpless silicon chips. The wavelength of the laser source was 1.064 μm with a pulse-to-pulse fluctuation of less than 2%. The bonding rate achieved was over 42 bonds per second. The bonding process was analyzed to understand the laser bonding mechanism and to increase bond yield and reliability. Laser bonded chips were evaluated for bond quality and bond interface metallurgy composition using lead pull testing, cross sectioning, scanning electron microscopy, and energy dispersive x-ray spectroscopy (EDX). Laser bonded chip pull test yield was greater than 99.9% for 1390 bonds with an average pull strength of 91 g. The predominant pull test failure mode was lead breaks (indicating good bonds) after optimizing bonding parameters. The incident laser energy, correlated to the bonding morphology, was varied to find an optimum operating window. Examinations of cross sectioned bonds revealed a strong gold-rich intermetallic compound and no substrate damage. Analytical results indicated that bonding was initiated by laser induced thermal energy absorbed through the tin plating on the copper lead. The molten tin acts as a thermal conductor to the copper lead and gold bump or bumpless pad which produces a copper-gold rich intermetallic compound in the bond interface. This paper will present a brief review of the laser bonding system developed and then concentrates on the laser interaction with the microelectronic chip materials involved in inner lead TAB bonding.
Fabrication of GaAs/GaAlAs quantum wires with side gates
Authors: Wakaya Fujio , Kakuta Takeshi , Takagaki Yukihiko , Yuba Yoshihiko , Takaoka Sadao , Murase Kazuo , Shiokawa Takao , Gamo Kenji , Namba Susumu
Published: July 2002

GaAs/GaAlAs quantum wires with a new type of side gates are fabricated. The gate electrodes are made of two-dimensional electron gas (2DEG) and defined by Ar ion beam etching (IBE) or Ga focused ion beams (FIB) in the heterostructure wafers. The geometrical width of the conduction channel and the side gate is about 0.5–1.5 μm, and the side gate is separated by about 0. 5 μm from the conduction channel. It was observed that negative gate voltage could completely deplete the conduction channel, and, from Shubnikov–de Haas oscillation measurements, that both carrier density, and effective wire decreased with increasing the negative gate voltage. It is found that the FIB process can simplify the process steps, but induce more damage in the narrow channel than the Ar IBE process.
Modifying a JEOL 100B for electron-beam lithography
Authors: Andrews C. C. , Kirk W. P.
Published: July 2002

Description of a complete electron-beam lithography system based on a JEOL 100B scanning/transmission electron microscope is given. The system was modified to include computer control of the sample stage, electron-beam position, and beam current measurements. Various lithography results and additional operating comments are included.
Reduction in beam positioning error by modification of dynamic responses in electron beam direct writing system
Authors: Matsukura Hiroyuki , Tsutaoka Takanori , Nakajima Ken
Published: July 2002

The dynamic responses of the electron beam direct writing system (EB direct writing system) are analyzed using the finite element method (FEM). The equipment is found to have a column swing vibration mode around 160 Hz. The column swing is caused by a bending vibration in the upper plate of the chamber. This vibration is initiated by the movement of the stage drive within the chamber. When column swing occurs, the resulting change in angle of the beam line creates a positioning error. FEM is also used to calculate the relative rotation angle of the column top to the stage surface. The maximum amplitude occurring after stage movement has stopped is 0.208 μrad. Since the distance between the upper plate of the chamber and the stage surface is 79 mm, the beam positioning error is 0.208 μrad×79 mm=16.4 nm. This error can be lessened by stiffening the upper plate. Utilizing cross ribs on this plate, the relative rotation angle can be lessened to 0.073 μrad. Thus, beam positioning error can be reduced to 0.073 μrad×79 mm=5.8 nm. Further, the increase in equipment weight is only 2%.
Atomic resolution on the surface of LiF(100) by atomic force microscopy
Authors: Meyer E. , Heinzelmann H. , Brodbeck D. , Overney G. , Overney R. , Howald L. , Hug H. , Jung T. , Hidber H.-R. , Güntherodt H.-J.
Published: July 2002

Atomic force microscopy (AFM) has already demonstrated its usefulness on a nanometer scale surpassing the resolution of conventional profilometers and probing different interactions such as repulsive contact, electrostatic, and magnetic forces. On an atomic scale the fundamental contrast mechanisms are still under investigation. The atomic resolution on layered materials such as graphite, boron nitride, transition metal dichalcogenides, and MnPS3 shows the great potential of this technique. Several experimental and theoretical investigations on these layered materials have shown that the presence of the AFM tip can lead to a significant distortion of the electronic and atomic structure. For small loadings (≤10−8 N) the tip causes long-range elastic deformations while for higher loadings a sharp tip can puncture the sample. To explain the atomic scale features being measured with higher loadings, different mechanisms such as the dragging of flakes or shearing of layers have been suggested. The application of AFM to nonlayered structures gives the opportunity to exclude several of these influences. Here we present atomically resolved images of LiF(100). The measurements are compared to results from different surface sensitive techniques such as helium scattering and low energy electron diffraction (LEED). The contrast mechanisms of AFM are discussed in relation to these experiments.
Experimental evaluation of the two-state alignment system
Authors: Chen G. , Wallace J. , Cerrina F. , Palmer S. , Newell B. , Randall J.
Published: July 2002

In previous papers we have proposed the principle of the two-state alignment method and studied the effect of process coatings on the alignment signal. In this paper, we experimentally evaluate the performance of the two-state alignment system. We found the alignment signal sensitivity to be larger than 3 V/μm with a noise level of <10 mV, which gives a noise equivalent error smaller than 0.003 μm. The alignment signal time response is <10 ms. In a repeatability experiment, we obtained an alignment standard deviation 3σ=0.036 μm from 500 alignment procedures. We also explored the effect of mask-wafer gap change on alignment signals. The results show that the alignment signal is tolerant to gap changes in a range of several microns. The details of experiment and experimental data analysis are described in this paper. The possible error sources to the alignment accuracy are also discussed. On the basis of the analysis, we can expect the alignment accuracy to be much better than the 36 nm we have achieved.
Wafer process-induced distortion study for x-ray technology
Authors: Schmidt Dennis , Charache Greg
Published: July 2002

X-ray synchrotron radiation is a promising source for submicron lithography. For x-ray lithography to be a useful technology, the combined overlay for the mask, stepper, and wafer processes must be less than that required by the product device specification. X-ray lithography uses a 1× proximity printing technique. Unlike n× optical stepper lithography, a lens cannot be varied nor can a reticle be moved to correct for magnification distortions due to wafer processes. Wafer processes (such as film formation) stress the wafer, causing pattern-magnification distortion and wafer warpage. This paper examines the process’ contribution to the overlay tolerance. Several wafer experiments have been performed using simulated 64 Mbit dynamics random access memory (DRAM) processes. Test wafers, etched with periodic ‘‘L’’ image measurement targets, were both hot processed and trench processed. The ‘‘L’’ targets on the wafers were measured using a long-distance xy measurement system and wafer flatness system. The measurements, before and after each process, show the wafer-induced distortion. One of the experiments discussed in this paper is a hot process used for gate oxidation. This rapid-thermal-oxidation-furnace experiment generated less than 2 ppm distortion. Other examples of hot-process distortion and trench-process distortion data are presented.
Synchrotron radiation damage study of lateral pnp transistors in x-ray lithography
Authors: Hsia L. C. , Aitken J.
Published: July 2002

The synchrotron radiation damage of lateral pnp transistors has been investigated using the vacuum ultraviolet (VUV) storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The devices under investigation were exposed to the x-ray radiation in the range of 1–2 keV, coming out of a lithography beam line. The transistor parameters were measured before and after irradiation, and were measured again after the devices were annealed in forming gas at 400 °C for 30 min. The study shows that synchrotron x-ray radiation reduces the current gain by one order of magnitude at small collector currents. The Gummel plot shows that x-ray radiation adds a big recombination component to the base current. This change is primarily due to the interface traps generated at the interface between Si and SiO2 in the base region. The capacitance-voltage (C-V) measurements on metal-oxide-semiconductor (MOS) capacitors indicate that x-ray radiation increases interface trap density from its initial order of magnitude of 1010–1012/cm2 eV. The irradiation also increases the leakage current between the collector and emitter due to the parasitic p-channel field-effect transistor (PFET), by a factor of 10. Upon annealing both the current gain and leakage current recover their initial values.
Control of diamond film microstructure by use of seeded focused ion beam crater arrays
Authors: Kirkpatrick A. R. , Ward B. W.
Published: July 2002

The nucleation densities associated with diamond growth on some nondiamond substrates are so low that it is possible to employ high resolution methods to define every site at which growth will initiate. A technique has been demonstrated on silicon substrates in which diamond growth is initiated on minute diamond seed particles introduced into patterned arrays of microscopic craters formed by focused ion beam milling. Diamond test films with controlled microstructural properties have been fabricated.
Reducing coherence in a fifth-harmonic YAG source (213 nm) for use in microlithography
Authors: Partlo William N. , Oldham William G.
Published: July 2002

The fifth harmonic of the YAG laser represents a possible alternative to the line-narrowed KrF excimer laser for use in deep ultraviolet microlithography. Producing useful amounts of radiation at 213 nm, the fifth-harmonic YAG has a spectral linewidth well within the needs of today’s nearly monochromatic microlithography lenses. This extremely narrow spectral width, combined with nearly single transverse-mode operation, leads to challenging levels of coherence and speckle. Initial measurements of far-field speckle patterns produced by illuminating a diffuser confirm that the speckle contrast is nearly 100%. Rotating the diffuser so that each pulse produced a different speckle pattern would require nearly 10 000 pulses to form an integrated average with 1% rms noise. We have investigated a relatively simple scheme for reducing the speckle contrast produced by a single pulse. This scheme consists of two counter rotating diffusers placed close to each other. It will be shown that for modest rotation speeds (15 K rpm for 100-mm-diam plates) a significant reduction in the single-shot speckle contrast can be achieved. A relation is derived between the noise reduction capabilities of a diffuser and its scattering properties. This relation can be used to predict the maximum speckle reduction possible for a given illumination system numerical aperture.
Silicon on quartz reflective masks for 0.25-μm microlithography
Authors: Lee Y. H. , Hsieh R. L. , Grenville A. , von Bünau R. , Tsai C. C. , Markle D. A. , Owen G. , Browning R. , Pease R. F. W.
Published: July 2002

One approach to 0.25-μm lithography currently being explored is the unity-magnification Markle-Dyson projection system. This system, operating at λ=248 nm, incorporates a reflective mask in its design. This utilizes the internal reflection at the quartz/film interface. To best meet the requirements of high reflectivity and quarter micron processing, amorphous silicon on quartz masks were chosen. Completed masks were used to print 0.19-μm lines and spaces on the prototype Markle–Dyson system, demonstrating the feasibility of silicon reflective masks for lithography.