bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of substrate bias voltage on the properties of CNx films prepared by reactive magnetron sputtering
Authors: Hajek V. , Rusnak K. , Vlcek J. , Martinu L. , Gujrathi S. C.
Published: July 2002

In the present work, we systematically study the effect of radio frequency induced negative substrate bias voltage, Ub, on the characteristics of CNx films fabricated by direct current (dc) magnetron sputtering of a graphite target in a nitrogen plasma. CNx films, typically 1–2 μm thick, were deposited onto Si(100) substrates at a temperature of 600 °C and at a pressure of 0.5 or 5 Pa. The films’ microstructure and composition were evaluated using elastic recoil detection analysis, Fourier transform infrared spectroscopy, Raman scattering, x-ray diffraction, and atomic force microscopy. The films were found to be amorphous and partially conductive. The nitrogen concentration in the films varied between 12 and 24 at. %. Increasing the |Ub| values from 300 to 700 V resulted in increasing the N/C ratio, while the hydrogen content in the bulk decreased from 5 to 1 at. %. The latter effect clearly demonstrates the sputter-cleaning process during the ion-assisted deposition. Increasing the |Ub| values also resulted in an increase in film density from 1.5 to 2.7 g/cm3, and in a decrease in surface roughness from 13 to 2 nm. This densification was accompanied by an increased hardness (from 2 to 23 GPa), and elastic recovery (from 35% to 74%), and by higher adhesion to the silicon substrate. |Ub| values higher than 700 V lead to the degradation of the films mechanical properties. Even at its low concentration, hydrogen was found to be directly related to the film quality. We suggest that the presence of hydrogen inhibits interconnection of graphite-like planes containing carbon and nitrogen, which may hamper formation of possible fulerene-like microstructure described in recent literature.
Study on surface reaction of (Ba, Sr)TiO3 thin films by high density plasma etching
Authors: Kim Seung-Bum , Kim Chang-Il , Chang Eui-Goo , Yeom Geun-Young
Published: July 2002

Ferroelectric devices are extremely useful for dynamic random access memories applications because of their high dielectric constant. Using ferroelectric device structure, manufacturing cell capacitance of highly integrated memory device is possible. The small feature size requires anisotropic etching. Since the research of (Ba, Sr)TiO3 thin film etching is seriously lacking, we studied the surface reaction of (Ba, Sr)TiO3 thin films by using high density plasma etching. In this study, (Ba, Sr)TiO3 thin films were etched with Cl2/Ar gas combination in an inductively coupled plasma. This was done by varying the etching parameters such as radio frequency power, direct current bias, and chamber pressure. The maximum etch rate of the BST films was 560 Å/min under Cl2/(Cl2+Ar) of 0.2, 600 W/250 V, and 5 mTorr. The selectivity of BST to Pt and SiO2 was 0.52, 0.43, respectively. The surface reaction of the etched (Ba, Sr)TiO3 thin films was investigated with x-ray photoelectron spectroscopy (XPS) using narrow scan spectra. Ba is removed by chemical reaction such as BaCl2 and physical sputtering. Ar ion bombardment is more effective than chemical reaction between Sr and Cl to remove Sr. Ti is removed by chemical reaction such as TiCl4 with ease. The results of secondary ion mass spectrometer analysis were compared with the results of XPS analysis and the results were the same.
Quantitative aspects of spin-polarized scanning tunneling spectroscopy of Gd(0001)
Authors: Bode M. , Getzlaff M. , Wiesendanger R.
Published: July 2002

The Gd(0001) surface is ideally suited in order to demonstrate spin-polarized vacuum tunneling since it exhibits a dz2-like surface state that is exchange split into two parts with opposite spin polarization. Both, the majority as well as the minority spin parts appear as peaks in the tunneling spectra. The use of ferromagnetic probe tips leads to magnetic field dependent asymmetries in the differential tunneling conductivity at bias voltages which correspond to the energies of the spin components. By mapping the asymmetry parameter we can image the magnetic domain structure of the sample. The spin polarization of the differential tunneling conductivity is found to be in excellent agreement with (inverse) photoemission data. Prolonged exposure to the residual gas being present in the vacuum system leads to a significant decrease of spin polarization.
Valence band x-ray photoelectron spectroscopic studies to distinguish between oxidized aluminum species
Authors: Rotole John A. , Sherwood Peter M. A.
Published: July 2002

The determination of the detailed chemical nature of oxidized aluminum species is an essential requirement for the study of many important practical aspects associated with aluminum metal and its compounds. While thick oxidized films of aluminum metal can be easily characterized by x-ray powder diffraction when the films are crystalline, thin amorphous films are very difficult to characterize. In this article, a study of the valence band x-ray photoelectron spectrum of aluminum oxides, hydroxides, and oxyhydroxides is reported using monochromatic aluminum Kα X radiation. The valence band spectra obtained are shown to have significant differences for different oxidized aluminum species, and can be well understood by comparison with spectra generated from cluster and band structure calculations. This study compliments earlier published studies from this research group using achromatic radiation, and demonstrates how the use of monochromatic X radiation allows a more conclusive distinction to be made among oxidized aluminum species.
Metal–insulator–semiconductor Schottky barrier structures fabricated using interfacial BN layers grown on GaN and SiC for optoelectronic device applications
Authors: Starikov D. , Badi N. , Berishev I. , Medelci N. , Kameli O. , Sayhi M. , Zomorrodian V. , Bensaoula A.
Published: July 2002

Metal–insulator–semiconductor Schottky barrier structures on GaN and 6H-SiC using highly stable interfacial BN layers have been investigated. As reported earlier, such structures fabricated with Ti contacts are capable of withstanding up to 350 and 600 °C when based on 6H-SiC and GaN, respectively. In this work we fabricated diode structures using interfacial BN layers and optically transparent Au contacts. Visible–blind photosensitive structures on GaN and 6H-SiC and prebreakdown light-emitting diode (LED) structures on 6H-SiC have been characterized. The radiant and spectral sensitivities of the photosensitive structures were measured in the range of 200–400 nm. The potential barrier heights determined from photoresponse measurements were 2.7 and 2.88 eV for GaN- and SiC-based samples, respectively. The spectrum of 6H-SiC and p-GaN-based prebreakdown LED structures measured through transparent Au electrodes extended to the ultraviolet region. The optical emission power of the 6H-SiC-based LED structures measured in the range 200–1100 nm saturated to about 10−8 W at current densities close to 200 A/cm2. Prospects for applications of the diode structures described in advanced visible–blind optoelectronic sensors are discussed.
Plasma-induced nitridation of gate oxide dielectrics: Linked equipment-feature atomic scale simulations
Authors: Sukharev Valeriy , Aronowitz Sheldon , Zubkov Vladimir , Puchner Helmut , Haywood John , Kimball Jim
Published: July 2002

Quantum chemical calculations were employed to get insight into the mechanisms involved in plasma-induced nitridation of gate oxide that will suppress boron penetration. The roles played by the nitrogen cations and atoms were explored. It was shown that B interaction with siloxane rings that contain incorporated nitrogen yielded a larger energy gain than rings without nitrogen. This explains the chemical nature of the nitrogen-induced barrier effect. Monte Carlo simulations were used to simulate the necessary energy of incident N2 cations to produce the bond cleavage down to a particular depth in the amorphous SiO2 layer. A combination of the hybrid plasma equipment model and plasma chemistry Monte Carlo codes was used to simulate nitrogen atomic and cation fluxes and their angular and energy distributions at the water surface. Combining simulated cation energies with PROMIS Monte Carlo simulation results makes it possible to derive plasma process parameters that will permit a desired level of nitridation to be reached.
Etch characteristics of optical waveguides using inductively coupled plasmas with multidipole magnets
Authors: An K. J. , Lee D. H. , Yoo J. B. , Lee J. , Yeom G. Y.
Published: July 2002

In this study, silica glass etch characteristics of inductively coupled plasmas with and without the multidipole magnets were investigated using CF4 and SF6 as the etch gases. A Langmuir probe and optical emission spectroscopy were used to investigate the characteristics of the plasmas. When the silica glass was etched with the multidipole magnets, a significant increase in etch rate was obtained with the magnets for both CF4 and SF6 together with an increase in ion saturation current as measured by the Langmuir probe. F radicals estimated by Ar actinometry also increased with the addition of the magnets. When the etch characteristics of CF4 and SF6 with magnets were compared at the same etch conditions, SF6 showed the higher etch rates (>800 nm/min) while CF4 showed the higher etch selectivity (>70:1) over the Cr mask material used in the study. With the magnets, a vertical etch profile was obtained with CF4 while the etch profile with SF6 was a little re-entrant. A 10 μm deep anisotropic silica glass etch profile with a smooth sidewall could be obtained using CF4 and with the magnets at 7.5 mTorr of operational pressure, 1000 W of inductive power, and −100 V of dc self-bias voltage. The silica glass etch rate and the etch selectivity over Cr under these etch conditions were 700 nm/min and 70, respectively.
Microloading effect in ultrafine SiO2 hole/trench etching
Authors: Feurprier Y. , Chinzei Y. , Ogata M. , Kikuchi T. , Ozawa M. , Ichiki T. , Horiike Y.
Published: July 2002

In the search of new etchant gas combinations which address the earth’s environmental concerns, a new C3F6-based plasma etch chemistry is investigated and evaluated for patterning fine SiO2 structures. Trimethylsilane and O2 are added first separately to C3F6 to investigate their respective influence. It is shown that both trimethylsilane and O2 additive gases have beneficial effects on the hole etching process but also result in undesired effects such as enhancement of the microloading effect upon trimethylsilane addition, and poor BPSG/resist selectivity upon O2 addition. When trimethylsilane and O2 are combined and mixed with C3F6, the opening of fine deep holes are achieved. For example, 0.15 μm holes with an aspect ratio of 15 are fabricated using C3F6/8% trimethylsilane/20% O2. The plasma conditions employed are a pressure of 10 mTorr, an rf source power of 500 W, a total flow rate of 30 sccm, and a bias power of 150 W. These plasma conditions allow good control of the hole size, practical resist selectivity for deep hole processing, and microloading-free etching of holes down to 0.15 μm. The C3F6-based plasma etch performance is further evaluated for nanometer-scale patterns using the simpler C3F6/O2 gas system. Line and space and mesh hole patterns delineated by electron lithography are fabricated with dimensions as small as 20 and 70 nm, respectively.
Auger electron spectroscopy low energy electron diffraction study of the growth mode of Ag on Au(111), (311), and (554) single-crystal surfaces
Authors: Rooryck V. , Buess-Herman C. , Attard G. A. , Reniers F.
Published: July 2002

Silver deposition onto gold (111), (554), and (311) single crystals was studied by Auger electron spectroscopy and low energy electron diffraction. It is suggested that the growth mechanism depends partly on the atomic roughness of the surface. Growth on the (311) faces seems to follow a Stranski–Krastanov mode, while growth on Au(111) adopts a Frank–van der Merwe mode. The deposition of one monolayer of silver is required to lift the reconstruction of the Au(111) or (554) surface.
New radical control method for high-performance dielectric etching with nonperfluorocompound gas chemistries in ultrahigh-frequency plasma
Authors: Samukawa Seiji , Mukai Tomonori , Tsuda Ken-ichiro
Published: July 2002

A new method for controlling radical generation in the etching of silicon dioxide is described. In an ultrahigh-frequency (UHF) plasma, the mean electron energy is about 2–3 eV and there are a small number of high-energy electrons. The plasma mainly dissociates C–I (2.4 eV), C=C (2.8 eV), C–C (4.3 eV), and C–Br (3.0 eV) bonds in the CF3I, C2F4, CF2Br2, C2F6, and C4F8 plasmas, and it mainly generates CF3 and CF2 radicals because the bond energies of these bonds are lower than the bond energies of C–F (5.6 eV in CF4) bonds. We found that the densities of these radicals were inversely proportional to the bond dissociation energy in these gases. That is, we found that C–I and C=C bonds are ideal for selective radical generation in the UHF plasma. The ratio of each radical density can be precisely controlled by changing the ratio of the mixture of these gases. As a result, etching selectivity and etching rate are improved considerably. From an environmental viewpoint, CF3I and C2F4 are also good alternatives to perfluorocarbon chemistries because they are believed to have a very short life in the atmosphere.
Automated electron cyclotron resonance plasma enhanced chemical vapor deposition system for the growth of rugate filters
Authors: Swart Pieter L. , Lacquet Beatrys M. , Chtcherbakov Anatoli A. , Bulkin Pavel V.
Published: July 2002

We developed a control system for an electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) reactor for the growth of inhomogeneous dielectric thin films for optical applications. The system supervises the growth of films of a required refractive index profile on different substrates including optical fiber ends. It controls the gas flow rates, microwave power, radio frequency substrate bias, and the ECR and extraction magnet power supplies. The system also adjusts the microwave generator to minimize reflected power during deposition. The characteristics of the ECR-PECVD system and the automation of the deposition process are discussed using the growth of a complex rugate optical filter as an example.
Bonding and morphology study of carbon nitride films obtained by dual ion beam sputtering
Authors: Quirós C. , Prieto P. , Fernández A. , Elizalde E. , Morant C. , Schlögl R. , Spillecke O. , Sanz J. M.
Published: July 2002

Thin carbon–nitrogen films (i.e., CNx) have been obtained by dual ion beam sputtering. The chemical composition and the type of bonding of the CNx material have been examined, as a function of the deposition parameters, by Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The high concentration of C≡N bonds present in some of the samples, as stated by FT-IR, allowed us to correlate this type of bonding with some of the features observed in the corresponding XPS and EELS spectra. Nitrogen concentrations of up to 45 at. %, depending on the deposition conditions, have been estimated by XPS and EELS. The films deposited at low energy were rather homogeneous, as demonstrated by Auger electron spectroscopy depth profiling, and show the highest C–N simple bonds concentration. On the contrary, the use of high energy assisting nitrogen ions leads to the formation of carbonitrile groups (i.e., C≡N), as well as resputtering effects that significantly reduce the thickness of the films and even hinder the growth of a film. The topography and morphology of the different films, as determined by atomic force microscopy, were also observed to depend on the conditions of assistance.
Excitons in ultrathin InAs/InP quantum wells: Interplay between extended and localized states
Authors: Paki P. , Leonelli R. , Isnard L. , Masut R. A.
Published: July 2002

We have performed detailed optical measurements of ultrathin InAs/InP quantum wells grown by metalorganic vapor phase epitaxy. Absorption and photoluminescence excitation spectra reveal the excitonic resonances associated with two- and three-monolayer-thick InAs layers. Photoluminescence spectra also show an emission band at intermediate photon energies which is associated with excitons localized in thin InAs quantum dots. Polarization-dependent measurements clearly show the heavy-hole or light-hole nature of the quantum well resonances. Such an identification of both type of transitions provides a test for electronic structure models. We find that the energy positions of the excitonic transitions in ultrathin InAs/InP quantum wells are not consistent with calculations based on the envelope function model.
p-type transparent conducting In2O3–Ag2O thin films prepared by reactive electron beam evaporation technique
Authors: Asbalter J. , Subrahmanyam A.
Published: July 2002

The transparent and conducting oxide thin films are all, so far, n type. In the present article, we report the results of thin films of In2O3+Ag2O which have shown p-type conductivity and transparency in the visible range. These films are prepared on glass substrates by reactive electron beam evaporation technique at a substrate temperature of 180 °C and at a chamber pressure of 2.5×10−4 Torr with oxygen. The evaporation rate is varied by controlling the electron beam current in the range: 30–100 mA keeping the voltage at 3.8 kV. The starting material is a mixture of In2O3 and Ag2O powder (of purity 99.99%). Two compositions of Ag2O in the starting material: 20% and 40% by weight have been studied. All the films grown at higher evaporation rate are polycrystalline. The electrical and optical properties of the films show very interesting behavior. The type of conductivity (p or n) in these films is observed to be dependent upon the evaporation rate. The best values for p-type films observed in the present investigation are for the 80:20 composition at an evaporation rate 42 A/min: Hall mobility: 8.2 cm2/V s, resistivity: 22.5 Ω cm and transparency at 500 nm: 34%. The data are analyzed in the light of electronegativity equalization and partial negative charge concepts to understand the physics of the p-type conduction.
Desorption species from fluorocarbon film by Ar+ ion beam bombardment
Authors: Hayashi M. , Karahashi K.
Published: July 2002

The species that are desorbed from fluorocarbon films by Ar+ ion bombardment were measured. In this study, we constructed a new apparatus in order to investigate desorption species from fluorocarbon films. The measured fluorocarbon films were deposited on a Si wafer by exposing it to a C2F6 plasma in an inductively coupled plasma reactor. The film characteristics were evaluated with x-ray photoelectron spectroscopy (XPS). The C(1s) peak measured in the deposited fluorocarbon films consisted of large chemically shifted peaks produced by C-F3 and C–F2 bonds as well as C–CFx bonds. The species desorbed by Ar+ ion beam bombardment at 1 and 3 keV on the films were detected using a quadrupole mass spectrometer (QMS). The ratios among CF, CF2, CF3, and CF4 species, which were measured with the appearance energies by QMS, indicate that CF4 is a dominant desorption species with the ratio of 80% among them at the beginning of bombardment at 3 keV and 65% at 1 keV. As the ion dose increased, the total amount of desorption species was reduced. XPS measurement indicated that the ion bombardment changed the characteristics of the fluorocarbon films from F-rich to C-rich. This implies that the species desorbed from fluorocarbon films during etching changed gradually.
Generation of <50 nm period gratings using edge defined techniques
Authors: Flanders D. C. , Efremow N. N.
Published: July 2002

A sequence of edge defined techniques has been developed which allows the successive multiplication of the number of lines in a grating pattern. Holographic lithography at 351.4 nm wavelength in a liquid medium has been used as the primary pattern generation technique for producing gratings with periods of ≊160 nm. A shadowing technique is then used to produce x-ray masks with precisely controlled linewidth-to-period ratios. Reactive-ion etching in CHF3 yields a square profile structure in SiO2 with precise linewidth. The basic edge defined technique consisting of CVD deposition, reactive-ion etching, and selective isotropic etching can then be repeatedly applied given a proper choice of materials and etches. Each cycle of the edge defined technique doubles the number of lines in the pattern. Careful linewidth control at each step can result in gratings with one-half of the initial period with minimum fundamental components. Gratings with ∼40 nm period have been fabricated by doubling the number of lines in a 160 nm period grating twice.
Mechanistic studies of the decomposition of trimethylaluminum on heated surfaces
Authors: Squire D. W. , Dulcey C. S. , Lin M. C.
Published: July 2002

The decomposition of trimethylaluminum (TMA) on copper, aluminum, quartz, and gallium arsenide substrates has been studied as a function of substrate temperature from 550–900 K under low pressure conditions. Detection of gaseous products was carried out by laser multiphoton ionization mass spectrometry (MPI/MS) for methyl radical and aluminum species and electron impact mass spectrometry (EI/MS) for stable species. The methyl radical was the sole gaseous reaction product observed above these substrates, with an apparent activation energy for production of 13±2 kcal/mol. Neither ethane nor methane was observed at the low pressures employed in these experiments, with either helium or hydrogen as carrier gases. A mechanism is proposed to explain these results.
Artificial neural networks for computing
Authors: Jackel L. D. , Howard R. E. , Graf H. P. , Straughn B. , Denker J. S.
Published: July 2002

Recent proposals for neural network models indicate that an array of amplifiers coupled to a lattice of wires with resistive components at the crosspoints can perform calculations using collective properties similar to those observed in biological systems. Such a network can perform both memory and processing functions. The promise of the connection matrix processor lies in its very high density, fault tolerance, and massively parallel operation. This paper describes the operation of a neural network and exploratory fabrication techniques for its implementation.
A study of strain-related effects in the molecular-beam epitaxy growth of InxGa1−xAs on GaAs using reflection high-energy electron diffraction
Authors: Berger Paul R. , Chang Kevin , Bhattacharya Pallab K. , Singh Jasprit
Published: July 2002

In this paper we examine the role of strain in the molecular-beam epitaxy (MBE) growth process by studying growth in InxGa1−xAs on GaAs with x varying from 0 to 0.5. This range covers the critical thickness regime for dislocation formation from ∞ to 12 monolayers. We have studied MBE growth for both on-axis (100) and misoriented substrates. The first issue we address in this paper is the role of strain in controlling the atomic-surface migration. We find from reflection high-energy electron diffraction (RHEED) studies during growth of InxGa1−xAs that as x is increased, the surface migration decreases rapidly. The growth front of the growing structure roughens due to this decreased migration and we have studied the recovery time for the growth front to smoothen. The surface recovery time increases rapidly as the strain in the system increases. Conversely, when GaAs growth is resumed, there is a recovery of the RHEED average intensity and oscillations (peak to peak). At higher growth temperatures, layer-by-layer growth is again restored. Dynamic changes in the RHEED pattern were video recorded, and the data indicate that in the three-dimensional island growth mode observed, the lattice constant in the strained overlayer changes monotonically and attains an equilibrium value before the conventionally calculated critical thickness hc is reached. Low-temperature photoluminescence measurements on misoriented (0°–4°) InGaAs/InAlAs MQW grown directly on GaAs indicate that device-quality material can be obtained for growth at high temperatures (∼570 °C).
Growth of HgCdTe epilayers with any predesigned compositional profile by laser molecular beam epitaxy
Authors: Cheung J. T. , Madden J.
Published: July 2002

HgCdTe epitaxial layers with complex composition profiles were grown by laser molecular beam epitaxy. Composition control was achieved by keeping the Te and Hg beams constant while modulating the CdTe evaporation rate by changing the laser conditions. Three approaches for evaporation rate modulation were investigated. Evaporation rate control by means of the laser repetition rate was found the most practical. Various graded composition HgCdTe epilayers were grown. The measured and intended profiles were found to be in good agreement.
Control of cluster size in nozzle jet expansion
Authors: Yang S. -N. , Lu T. -M.
Published: July 2002

Recent reports showed that ultrasmall metal and semiconductor clusters (up to 1000 atoms per cluster) can be produced during the jet expansion of hot vapor through a small nozzle without the use of carrier gas. Cluster beams are potentially useful in very large-scale integrated (VLSI) thin film processing. In this report, the kinetics of the nonsteady state, stepwise cluster growth in a jet beam with metal vapor is solved quantitatively based on the classical liquid–drop theory. In our calculation for the jet expansion of silver vapor, we found that cluster size up to more than 100 atoms can be formed. This result is consistent with the notion that the nucleation barrier for metal and semiconductor cluster formation can still be small despite their high surface tension. We found that the cluster size distribution depends very much on the stagnation pressure (P0) before the expansion and the nozzle geometry, particularly the expansion angle (θ). For sufficiently large P0 (several Torr) and small θ (<30°), the cluster size distribution is peaked at a value which increases exponentially with the terminal Mach number Mt —the parameter characterizing the expansion conditions.
Structural characterization of GaAs/ZnSe interfaces
Authors: Tamargo M. C. , de Miguel J. L. , Hwang D. M. , Farrell H. H.
Published: July 2002

We have studied, using reflection high energy electron diffraction (RHEED), the initial growth stages of ZnSe layers grown by molecular beam epitaxy (MBE) on GaAs exhibiting various surface terminations. The structural quality of the ZnSe layers was assessed by transmission electron microscopy (TEM). We have observed a preference for two-dimensional nucleation on As-terminated GaAs substrates, whether epitaxial or bulk. On Ga-terminated surfaces a transitional region of three-dimensional growth forms initially. The different behaviors may reflect the electronic imbalance present in the growing GaAs/ZnSe interface. While defect free, thin layers of ZnSe are best obtained on As-terminated GaAs, the initial three-dimensional growth region on the Ga-rich surfaces appears to reduce the density of extended faults formed in thick ZnSe layers due to the lattice mismatch with GaAs.
Test of band offset commutativity by photoemission from an i
n s
i
t
u grown ZnTe/CdS/ZnTe quantum well
Authors: Wilke W. G. , Maierhofer Ch. , Horn K.
Published: July 2002

We have characterized the ZnTe–CdS heterojunction by valence and core level photoemission with synchrotron radiation, using quantum wells grown in situ on ZnTe(110) substrates. The valence band offset of∼ΔEv=0.9 eV shows that this heterojunction is of the staggered type (type II), rarely encountered in experimental studies. We find evidence for chemical reaction involving Te at the interface. The band offsets at both sides of the CdS quantum well exhibit small differences on the order of 0.1 eV, which are also reflected in the dipole contribution at the interfaces. This study, while reporting only small deviations from commutativity, suggests that dipole contributions of varying magnitude, caused by interface reactions, influence the magnitude of the band offset.
A study of radiation damage in SiN and SiC mask membranes
Authors: Itoh Masamitsu , Hori Masaru , Komano Haruki , Mori Ichiro
Published: July 2002

Radiation damage in SiN and SiC films prepared by low-pressure chemical vapor deposition (LPCVD) is reported. A pattern placement error of 0.05 μm at the edge of the x-ray radiation area was introduced for SiN membranes by a radiation dose of 12 kJ/cm2. The electron spin resonance (ESR) signals with a g value of 2.004, which was attributed to the Si–N dangling bond, were observed. Both the error and the spin density increased with increasing radiation dose up to 12 kJ/cm2 and remained constant thereafter. The error was explained as the result of Si–N bond scission caused by x-ray radiation, leading to tensile stress relaxation in the radiated area. In the case of SiC films, a pattern placement error was less than a detection limit of 0.03 μm for a radiation dose of 10 kJ/cm2. ESR signals with a g value of 2.003, being attributed to the Si–C dangling bond, were observed. However, the spin density in this case did not change by radiation up to 20 kJ/cm2. It is inferred that the LPCVD SiC membrane is damage free to x-ray radiation.
The representative figure method for the proximity effect correction [III]
Authors: Abe Takayuki , Yamasaki Satoshi , Yoshikawa Ryoichi , Takigawa Tadahiro
Published: July 2002

The representative figure method for the proximity effect correction was proposed in the previous papers in order to eliminate the correction time dependence on the large-scale integrated (LSI) pattern density. In this report, a new calculation method for the proximity effect correction is proposed. The method uses both the representative figure method and the dose formula method. When the formula of Pavkovich is adopted as a dose formula, the total correction error for the proposed method is at most 4%. The intrinsic error of the representative figure method itself is at most 0.5%. The proposed method reduces the total calculation time to (1/28) compared with the conventional method, when the minimum feature size is 0.15 μm and the acceleration voltage is 50 kV. Here, the total calculation time includes (1) preparation time for representative rectangles and (2) shorter calculation time for the correction. Furthermore, the total time is found to become less than the data format conversion time, when the minimum feature size is <0.5 μm. The calculation time for the correction is found to be <1 h for any pattern density, when the newly proposed method and the 50 MIPS engineering workstation (EWS) are used. The problem of the proximity effect correction is reduced to an easier problem; i.e., how to reduce the calculation time for obtaining the areas and the center of gravity of the LSI patterns.
Growth and characterization of P-on-n HgCdTe liquid-phase epitaxy heterojunction material for 11–18 μm applications
Authors: Pultz G. N. , Norton Peter W. , Krueger E. Eric , Reine M. B.
Published: July 2002

The capability of growing long-wavelength infrared HgCdTe liquid-phase epitaxy P-on-n heterojunction films with state-of-the-art photodiode performance, with excellent thickness uniformity (±10%), and with excellent cutoff wavelength uniformity (e.g., 10.5±0.1 μm) across 2.5 cm×4.0 cm wafers has been demonstrated. In addition, we have extended the region of HgCdTe photodiode operation to wavelengths of 18–19 μm at 80 K. Both measured carrier lifetime and photodiode data show that the n-type HgCdTe base layers are of excellent quality, with 77 K carrier lifetimes at the calculated Auger-1 limit for film carrier concentrations above 4×1014 cm−3. The R0A products for large-area diodes (10−3 cm2 ) with cutoff wavelengths of 11–19 μm are consistent with n-side diffusion current calculated using the film Auger-1 lifetime. Smaller diodes of area 1×10−5 cm2 have typical R0A values of 12 Ω cm2 at 80 K for a 12.2 μm cutoff wavelength. Large area diodes with an 80 K cutoff wavelength of 18–19 μm have R0A products of 0.14 Ω cm2 at 80 K and 0.4 Ω cm2 at 70 K. Quantum efficiency values of 60% are observed with no antireflection coating (corresponding to 75% internal quantum efficiency) and the spectral response data are classical.
Optical and magneto-optic properties of HgTe/CdTe superlattices in the inverted-band semiconducting regime
Authors: Yang Z. , Yu Z. , Lansari Y. , Cook J. W. , Schetzina J. F.
Published: July 2002

Low temperature infrared transmission and far-infrared magneto-optic transmission experiments were completed for a series of HgTe/CdTe superlattices (SLs). The SLs studied were grown with layer thicknesses intentionally chosen to make the samples inverted-band semimetals or inverted-band semiconductors, a new regime of the HgTe/CdTe SL which only recently has been predicted by theory. Cyclotron resonance of electrons in the first conduction subband H1 was observed in the far-infrared magneto-transmission experiments. From these measurements electron effective masses were calculated. The optical transition from the second heavy hole subband H2 to the second conduction subband E2 was observed in the infrared transmission experiments. The H2–E2 transition energy was observed to decrease with increasing SL well width LZ. In addition, the electron effective mass was found to increase as LZ increases. Both of these observations indicate that all of the SL samples are, indeed, inverted-band SLs. This in turn implies that the valence band offset between HgTe and CdTe must be large, ∼400 meV at 4.5 K.
Novel x-ray mask distortion measurement technique employing holographic gratings and phase-shifting interferometry
Authors: Hansen M. E. , Chen H. T. H. , Chen G. , Engelstad R. L. , Cerrina F.
Published: July 2002

This article presents a new optical metrology technique that has been developed at CXrL to investigate potential distortions induced in x-ray masks during their fabrication, mounting, and x-ray irradiation. The technique employs a Zygo phase-shifting Fizeau interferometer to acquire the in-plane distortion (IPD) and out-of-plane distortion (OPD) present in the masks. The interferometer measures the OPD directly, while IPD measurements are obtained with the aid of holographic gratings that have been printed onto the masks. When positioned at the Littrow angle of the gratings, the interferometer can acquire a retrodiffracted wavefront that contains the IPD information. Subtraction of the pre- and postdistortion interferograms yields the induced distortions. Computer models to simulate x-ray mask distortions have been developed and implemented using ansys, a commercially available finite element analysis software package. Numerical results have shown excellent agreement with interferometric data. The authors believe that these new interferometric techniques and models should prove invaluable as metrologic and predictive tools for the measurement, characterization, and design of x-ray masks in the 0.25 μm regime.
Deposition and characterization of polysilicon films deposited by rapid thermal processing
Authors: Ren Xiaowei , Öztürk Mehmet C. , Wortman Jimmie J. , Zhang Bojun , Maher Dennis M. , Batchelor Dale
Published: July 2002

Low-pressure chemical vapor deposition (LPCVD) of polycrystalline silicon in a cold-wall, lamp-heated, rapid-thermal processor was investigated. Blanket polysilicon films were obtained by the pyrolysis of a 10% silane–argon gas mixture onto (100) Si wafers which were capped with a thermal SiO2 layer. The depositions were performed at a total pressure ranging from 1 to 5 Torr and in a temperature range from 575 to 850 °C. It was found that the deposition of films was controlled by a surface limited reaction at temperatures below ∼780 °C, and an activation energy of 39±2 kcal/mol was measured for this reaction. Above 780 °C, a decrease in activation energy was observed. To meet the throughput requirement of single wafer processing, deposition temperatures higher than 700 °C are needed. In this temperature range, deposition rates exceed 1000 Å/min as compared to 20–300 Å/min in conventional LPCVD furnaces. The structural characteristics of the films were assessed by ultraviolet surface reflectance, Raman spectroscopy, and transmission electron microscopy. The transition temperature from amorphous silicon to polycrystalline silicon occurs at ∼600 °C. Processing windows, which result in smooth films with a root-mean-square roughness of less than 100 Å, are defined. Polysilicon films (∼2500 Å in thickness) have a columnarlike grain structure, and the grains span distances as little as ∼100 Å near the SiO2 interface to ≥1000 Å as they approarch the upper surface. A correlation between average projected grain size and surface roughness is demonstrated. Oxygen levels were derived from secondary ion mass and Auger electron spectroscopic data. The oxygen content of the polysilicon films is estimated to be in the range of 3%–4%. We speculate that relatively high oxygen levels in the films may be responsible for smooth films at high temperatures. If this is true, it may be possible to obtain smooth polysilicon films at high deposition temperatures by adding measured amounts of oxygen to the gas stream.
Molecular-beam epitaxy of ZnS using an elemental S source
Authors: Cook J. W. , Eason D. B. , Vaudo R. P. , Schetzina J. F.
Published: July 2002

The successful growth of ZnS using elemental sources of Zn and S is reported. This wide band gap semiconductor is difficult to grow by molecular-beam epitaxy (MBE) using elemental sources because of the very high vapor pressure of S. As a consequence, a new type of effusion cell, designed for very low temperature operation, was developed. Techniques for the evaporation and containment of S in the MBE system are also described. ZnS films were deposited onto (100) GaP substrates, with and without ultraviolet radiation incident on the substrate during film growth. High quality epitaxy of semi-insulating ZnS was achieved at temperatures as low as 150 °C by means of photoassisted MBE. N-type ZnS:Cl films were also prepared using ZnCl2 as a solid dopant source. The electrical and optical properties of these epilayers are discussed.
Scanning tunneling optical spectroscopy of semiconductor thin films and quantum wells
Authors: Wessels B. W. , Qian L. Q.
Published: July 2002

The application of scanning tunneling optical spectroscopy to the study of semiconductor surfaces, heterojunctions, and quantum well structures is described. The technique offers the possibility of determining the local optical and electronic properties of surfaces as well as buried layers. In this study, the predominant mechanisms for the interaction between light and the tunnel junction were evaluated. Structures examined include silicon surfaces, InP/GaAs heterostructures, and InAsP/InP quantum wells.
HgCdTe double heterostructure diode lasers grown by molecular-beam epitaxy
Authors: Zucca R. , Zandian M. , Arias J. M. , Gil R. V.
Published: July 2002

While HgCdTe has been used extensively to fabricate high performance photodiodes and focal plane arrays, little has been done to apply this technology to light emitting devices. We recently succeeded in fabricating and operating the first HgCdTe diode laser. Here we discuss the early results in detail, and present new results on an expanded range of operation. The stripe-geometry double-heterostructure lasers were grown by molecular-beam epitaxy. Active layer thicknesses ranged between 0.9 and 1.4 μm, and the p+ and n+ confinement layers were in situ doped up to 1018 cm−3 with arsenic and indium, respectively. Three double heterostructures were grown, and they all produced working lasers. The devices were operated under pulsed current at temperatures between 40 and 90 K. At 77 K, the emission wavelengths were 2.9, 3.4, and 3.9 μm, and the lowest threshold current density measured was 521 A/cm2. Further characterization data including temperature dependence of the threshold currents, far field patterns, spectral analysis of longitudinal modes, and imaging of the laser emission in a near field configuration are discussed.
Novel on-axis interferometric alignment method with sub-10 nm precision
Authors: Moel A. , Moon E. E. , Frankel R. D. , Smith Henry I.
Published: July 2002

A novel on-axis interferometric alignment scheme, especially applicable to x-ray lithography, is described which combines the position sensitivity of interferometry and the robustness of imaging. It employs broadband illumination, and hence should be relatively immune to many of the effects that tend to corrupt alignment signals in conventional interferometric systems. In its initial demonstration a standard deviation (σ) of 6 nm was achieved in both X and Y. Ultimate limits are calculated to be below 1 nm. On an Apple Quadra 800 computer, the spatial-phase information that measures misalignment is fully analyzed in 200 ms.
Selectively dry gate recessed GaAs metal–semiconductor field-effect transistors, high electron mobility transistors, and monolithic microwave integrated circuits
Authors: Cameron N. I. , Ferguson S. , Taylor M. R. S. , Beaumont S. P. , Holland M. , Tronche C. , Soulard M. , Ladbrooke P. H.
Published: July 2002

The application of nanofabrication techniques such as molecular-beam epitaxy, electron-beam lithography, and selective reactive ion etching, to metal–semiconductor field-effect transistor (MESFET), high electron mobility transistor (HEMT), and monolithic microwave integrated circuit (MMIC) fabrication allows precise control of physical device parameters such as layer thickness, doping density, and gate length. Such well characterized, flexible, and accurate technologies allow high performance devices and circuits to be fabricated with predictable yield. The application of nanofabrication techniques to both low noise, 0.2 μm mushroom gate, GaAs/Al0.3Ga0.7As MESFETs and MMICs is demonstrated. The MESFETs have 0.75 dB noise figure and 11 dB associated gain at 12 GHz; while the MMICs have ‘‘right-first-time’’ performance with more than 15 dB gain at 44 GHz. It is also shown that these techniques are applicable to pseudomorphic HEMTs and predicted that the use of nanofabrication in general and selective reactive ion etching in particular, will be essential to the implementation of MMICs working at frequencies of 100 GHz and beyond.
Photoluminescence properties of strained molecular-beam epitaxy Si1−xGex/Si multiquantum wells
Authors: Noël J.-P. , Rowell N. L. , Houghton D. C. , Wang A. , Perovic D. D.
Published: July 2002

Si1−xGex/Si multiquantum well (MQW) structures grown by molecular-beam epitaxy exhibit a broad, intense photoluminescence (PL) peak ∼120 meV below the band gap energy and/or phonon-resolved, near-band gap PL, depending on the MQW strain and the growth conditions.The origins of these two PL types have been identified. For MQWs with thin alloy layers (≤40–100 Å), the SiGe PL at 2 K is dominated by boron bound–exciton annihilation, which yields phonon-resolved transitions. For thicker layers, the PL is dominated by a broad, intense peak due to exciton recombination at small (≤∼15 Å) interstitial-type platelets that occur in densities up to ∼109 cm−2/QW. Etching experiments revealed that within a given MQW the platelet density is lowest in the first grown well and progressively increases in subsequent wells with increasing strain energy density, indicating that platelet formation is strictly a morphological phenomenon.
Growth of GaxIn1−xP/Ga0.5In0.5P multiple-quantum wires by strain induced lateral layer ordering process
Authors: Chen A. C. , Moy A. M. , Pearah P. J. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

A GaxIn1−xP/Ga0.51In0.49P multiple-quantum-wire heterostructure was formed in situ through a strain induced lateral layer ordering process occurring spontaneously when (GaP)2/(InP)2 short period superlattices were grown on (100)-oriented on-axis GaAs substrates. Cross-sectional transmission electron microscopy estimated average quantum wire cross sections of ∼50 Å×100 Å leading to a high linear density of ∼100 wires/μm. The existence of the multiple-quantum wires is also supported by the strong anisotropy for two orthogonal polarizations in polarized photoluminescence measurements.
Molecular-beam epitaxy flux transient monitoring and correction using in situ reflection mass spectrometry
Authors: Celii F. G. , Kao Y. C. , Beam E. A. , Duncan W. M. , Moise T. S.
Published: July 2002

The use of reflection mass spectrometry (REMS) for in situ monitoring of group III flux transients during molecular-beam epitaxial growth is reported. Normal shutter closure caused effusion cell heating which resulted in flux overshoots of up to 30%. The variation of the magnitude and time constant of the overshoot, as a function of group III material and shutter closed time, was determined for our Riber 2300 system. It was verified that the observed REMS transients corresponds to growth transients using photoluminescence and transmission electron microscopy analysis of GaAs/AlGaAs and InGaAs/InAlAs multiple quantum well (MQW) structures. Flux transient correction during GaAs/AlGaAs MQW growth was accomplished by ramping the temperature of the Ga effusion cell, based on our previous analysis of the transients.
Ion exposure characterization of a chemically amplified epoxy resist
Authors: Stumbo D. P. , Wolfe J. C.
Published: July 2002

The negative-tone proton exposure characteristics of a chemically amplified resist based on an epoxy resin (Shell SU-8) and an onium salt sensitizer (General Electric UVE-1014) are described. This resist was developed by IBM for UV, electrons, and x rays, for which it exhibits high contrast, good etch resistance, low minimum dose for exposure, excellent adhesion to a variety of substrates, and resolution of better than 0.1 μm. In the present work, the exposure properties of this resist were measured as a function of sensitizer concentration when exposed with 100 keV protons. The best contrast measured for 100 keV protons was 1.4, at a sensitizer concentration of 1 wt % and the corresponding minimum dose for exposure was 0.13 μC/cm2. Sub-0.1 μm resolution was also demonstrated using ion beam proximity printing. However, the resist develops as a porous mat for low ion doses, a phenomenon which can result in significant pattern edge roughness. It is suggested that this problem arises because the resist is sufficiently sensitive to register single ion tracks.
Carbon doping of InGaAs in solid-source molecular beam epitaxy using carbon tetrabromide
Authors: Hwang Wen-Yen , Miller D. L. , Chen Y. K. , Humphrey D. A.
Published: July 2002

Carbon tetrabromide was used to dope (In,Ga)As layers lattice matched to InP grown by solid-source molecular beam epitaxy. The maximum hole density depended on substrate temperature. A hole concentration as high as 7.5×1019 cm−3 was achieved at a substrate temperature of 450 °C with reduced As2 flux. Variations in arsenic flux intensity were found to have little effect on the doping density. Hole mobility was comparable to the mobility of Be-doped material grown in our MBE system and to the mobility of CCl4-doped material grown elsewhere. We observed a short-term doping memory effect which we attribute to desorption of CBr4 from growth chamber internal surfaces due to radiant heat from column III ovens. (In,Al)As/(In,Ga)As Npn heterojunction bipolar transistors fabricated using CBr4 doping for the (In,Ga)As base layer with p=2×1019 cm−3 exhibited a dc current gain of eight.
Realization of limited-area cathodes and their performance in an electron optical column
Authors: Maloney C. E. , Nakamura H. , Broers A. N. , Xia S. , Peters L.
Published: July 2002

Limited-area cathodes based upon impregnated dispenser cathode material have been investigated in an electron optical column at accelerating voltages of up to 30 kV. A peak axial brightness of about 6×105 A/cm2 sr was obtained at this voltage using a flat cathode. Brightness values greater by a factor of 10 were measured using a conical limited-area cathode with a tip radius of curvature of 0.075 mm. The latter measurements were affected by space–charge spreading in the beam.