bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of silicon–hydrogen bond characteristics on the crystallization of hydrogenated amorphous silicon films prepared by plasma enhanced chemical vapor deposition
Authors: Kim Hae-Yeol , Choi Jae-Beom , Lee Jai-Young
Published: July 2002

The crystallization behavior of hydrogenated amorphous silicon (a-Si:H) films prepared by plasma enhanced chemical vapor deposition is investigated in view of the silicon–hydrogen (Si–Hn) bond characteristics. A-Si:H films deposited at various pressures (0.1–1.0 Torr) are annealed to polycrystalline silicon (poly-Si) films in a conventional vacuum furnace at 600 °C. The final grain size in the poly-Si films increases with the deposition pressure, up to 1.6 μm in the case of the films deposited at 1.0 Torr. The Si–Hn bond characteristics are analyzed by Fourier transform infrared spectroscopy and modified gas chromatography for hydrogen thermal evolution experiment. Finally, the Si–Hn bond characteristics are suggested to be an important factor affecting the crystallization behavior of a-Si:H films, which is also related to the film stress as well as the structural disorder in a-Si network.
Anisotropic plasma etching of polymers using a cryo-cooled resist mask
Authors: Schüppert B. , Brose E. , Petermann K. , Moosburger R.
Published: July 2002

An anisotropic etching process of a perfluorocyclobutene polymer that makes use of a spin-coated photoresist mask instead of a commonly used thin metal layer is reported. We demonstrate that such masking can be applied to advantage for anisotropic reactive ion etching of polymers if the wafer is cooled down to T=−50 °C. For the fabrication of integrated optical waveguides, the choice of an appropriate photoresist is very important if the edge roughness needs to be low in order to avoid optical scattering losses. For such applications, the Microresist Technology ma-P 1275 has been found to be very suitable.
Nonisomorphic ErF3 layers on Si(111) substrates grown by molecular beam epitaxy
Authors: Ko J. M. , Durbin S. D. , Fukuda T. , Inaba K.
Published: July 2002

ErF 3 layers were grown on Si(111) substrates at 400, 550, and 700 °C by molecular beam epitaxy. Reflection high-energy electron diffraction in situ and x-ray rocking curve analysis ex situ showed that at the high growth temperature of 700 °C, an ErF3 layer of the native orthorhombic structure could be grown conformably on the hexagonal atomic arrangement of the Si(111) substrate. The surface morphology and flatness of the resulting layers were studied by atomic force microscopy as a function of growth temperature and layer thickness. At higher temperatures, layers consist of highly perfect crystallites aligned with b axes normal to the substrate, and c axes along one of six symmetrically related 〈011̄〉 directions of the Si substrate.
Preparation and characterization of rf-sputtered SrTiO3 thin films
Authors: Radhakrishnan K. , Tan C. L. , Zheng H. Q. , Ng G. I.
Published: July 2002

Electrical and structural properties of strontium titanate (SrTiO3) thin films deposited on Si and GaAs substrates by a conventional radio frequency-magnetron sputtering technique at different oxygen (O2) partial pressures and substrate temperatures have been reported. Dielectric constant of the as-deposited samples increases with the substrate temperature as well as the O2 partial pressure. However, it shows a decreasing trend at higher O2 partial pressure values. When the samples were annealed for 1 h at temperatures above 500 °C the dielectric constant value of the SrTiO3 (STO) films increased by five times and a maximum value of 147 was obtained. The increase in the dielectric constant value is reflected in x-ray diffraction measurements with the development of high intensity lines corresponding to STO phase. The thickness dependence of the dielectric constant is also reported. Thin film STO capacitors fabricated with Pt as top and bottom electrodes showed low leakage current densities and a high breakdown voltage of 855 kV/cm suggesting the possibility of considering these capacitors for integration with devices.
Schottky barrier formation of Ag on GaAs(110)
Authors: Ludeke R. , Chiang T.-C. , Miller T.
Published: July 2002

Photoemission studies of Ag deposits on cleaved n- and p-type GaAs for coverages from ∼0.003 to 20 monolayers indicate clustered Ag growth and undetectable chemical interactions with the substrate. The position of the surface Fermi level changed throughout the deposit range. The data is inconsistent with most of the existing Schottky barrier models. The results are interpreted in terms of donor- and acceptorlike interface states which are characteristic of the clusters but modified by the screening at the interface. Values for the Schottky barrier of 0.89 eV on n-type and 0.35 eV on p-type material were obtained for the thickest coverage.
End-point detection and etch-rate measurement during reactive-ion etching using fluorescent polymer films
Authors: Kolodner Paul , Katzir A. , Hartsough Neal
Published: July 2002

We have developed a remote, optical method for real-time etch-rate measurement and extremely precise end-point detection during reactive-ion etching of photoresist films. The photoresist solution is doped with a fluorescent dye before spin coating, and the fluorescence from the resulting film is observed to decrease in time as the material is removed by etching. In this manner, we make a rapid, single-calibration etch-rate measurement and have determined the etch endpoint with a precision, in film thickness, of ±30 Å.
Performance results of an electron beam lithography machine and process by means of dc electrical test structures
Authors: Rissman Paul , Liu En-Den , Owen Geraint
Published: July 2002

Direct current electrical tests have been used to measure the performance of electron beam resists and an exposure system. Resist characterization is done by using electrical tests to measure the linewidth defined as a function of an incremental dose. The quality of different resists can be compared by means of δ, the slope of the normalized linewidth versus the logarithm of the incident dose curve. Data have been measured for three negative resists (PCMS 30, PCMS 200, and OEBR 100) and PMMA for two development conditions. Resistors fabricated from 60 nm chromium films, 300 nm polysilicon films, or 60 nm titanium films gave results within ±40 nm of one another for 500 nm lines. Without proximity effect correction, linewidth difference from design value is more than ±300 nm and the 0.5P μm lines were undefined for PMMA and the given development conditions, and 0.5P and 1.0P μm lines were undefined for PCMS 30 and the given exposure conditions. With proximity effect correction, all line sizes are within 100 nm of design value with the exception of 0.5P μm in PCMS 30. The beam diameter varies from an undeflected value of 350 nm to a maximum of 650 by 480 nm, without dynamic corrections, as calculated from measurements of 500 nm lines placed throughout the 5 mm field of view. Two-level alignment measured electrically in the center and four corners of the 5 mm field is within 100 nm, with standard deviations typically less than 60 nm at each location for each axis. Butting of exposure subfields, measured electrically, is within 80 nm; the one sigma standard deviation of this measurement is 42 and 82 nm for the x and y axes, respectively, but is less than 15 nm at a higher exposure frequency.
Effects of an order–disorder transition on surface deep levels in metastable (GaAs)1−x Ge2x
Authors: Bowen Marshall A. , Redfield Andrew C. , Froelich David V. , Newman Kathie E. , Allen Roland E. , Dow John D.
Published: July 2002

The major chemical trends in the energy levels of deep point defects at the (100) surfaces of (GaAs)1−x Ge2x alloys are elucidated. These levels are predicted to exhibit bifurcation as functions of alloy composition x (at xc ≂0.3) because of an order–disorder phase transition from a zincblende phase for xxc. Levels associated with distinct anion and cation sites of the zincblende structure coalesce into a single level of the diamond structure.
Simulation of backscattered electron signals for x-ray mask inspection
Authors: Rosenfield M. G. , Neureuther A. R. , Viswanathan R.
Published: July 2002

The successful use of an electron-beam lithography system for the inspection of x-ray masks requires an in depth understanding of the scattering properties of the defects. A new Monte Carlo computer program has been developed to simulate the backscattered electron signal from various types of two-dimensional gold-on-silicon structures. Simulation results for a variety of submicron patterns show excellent agreement with experimental backscattered electron signals from an annular silicon diode detector. It is found that the simulated energy signal, rather than the number signal, gives the best results. The program is used to optimize the placement of the annular detector by examining the take-off angle distributions from different structures. The optimum take-off angle range for this detector is found to be 30°–57.5° as opposed to the lower angle range favored for registration signals. It is also found through this investigation that small steps of gold on silicon will be the hardest defects to detect for this optimum take-off range.
In-lens deflection system with nonequisectored-type multipole electrostatic deflectors
Authors: Goto E. , Soma T. , Idesawa M. , Sasaki T. , Goto T. , Konno S. , Someya T. , Tanaka K. , Miyauchi S.
Published: July 2002

For the purpose of increasing throughput of electron beam lithography machines, an in-lens electrostatic deflection system, using 20 pole nonequisectored-type deflectors has been investigated with a view to extending scanning fields to as much as 10 mm squares. This type of deflector requires only two sets of driving voltages: ±X and ±Y. It has been confirmed with experiments that an in-lens deflection system using 20 pole nonequisectored-type deflectors can provide sufficiently good scanning properties in the wide scanning field up to 10 mm square.
Numerical considerations on multipole-type electrostatic deflectors
Authors: Idesawa M. , Soma T. , Goto E. , Sasaki T.
Published: July 2002

High performance electrostatic deflectors are required for wide angle and high precision deflection systems. Much work has been performed and reported regarding multipole-type deflectors without asymmetrical errors. Asymmetrical errors may deteriorate wide range deflection properties. Conventional small angle deflection theory cannot be applied to such a wide area and high precision deflection system. In this paper, geometrical errors in manufacturing are taken into account in evaluating nonequisectored-type multipole electrostatic deflectors. A contribution factor is introduced to evaluate wide range deflection properties. Deflection performance of manufactured deflectors can be evaluated easily by the proposed method from their geometrical dimension. Furthermore, pattern distortion of a shaped beam is investigated.
Computer simulation of high dose reactive-ion implants into silicon
Authors: Dobson R. M. , Arrowsmith R. P. , Hemment P. L. F.
Published: July 2002

A simple computer program has been developed to model the interaction of a high dose oxygen implant into a hot silicon target. By taking account of sputtering, lattice expansion, range modification, chemical change, and assuming that oxygen diffuses only in formed silicon dioxide, a good fit with experimentally measured oxygen profiles is obtained up to doses of ∼2×1018 ions/cm2 at 200 keV. A good fit to higher dose implants can be made if the sputtering coefficient is allowed to increase rapidly when damaged silicon is exposed at the surface.
A two-layer photoresist process for patterning high-reflectivity substrates
Authors: Ong E. , Baker R. M. , Hale L. P.
Published: July 2002

A two-layer photoresist process is reported where the lower layer is thick PMMA, a resist sensitive in the deep UV, and the top layer is thin RD2000N, a negative resist also sensitive in the deep UV. The thick PMMA serves to planarize substrate topography. The high absorptivity of RD2000N in the deep UV prevents transmission of light to the PMMA thus enabling its use in a bilayer scheme, and therefore also eliminates the problem of substrate reflectivity even for aluminum-coated substrates. In addition, interfacial problems which were commonly found in an all positive two-level photoresist process, were not observed in this scheme. The bilayer resist was used to pattern aluminum substrates having device topography. Excellent linewidth control was observed over steps, with no observable effect due to substrate reflectivity. In addition, due to the excellent resistance of RD2000N to chlorine plasmas, the entire bilayer resist structure is well preserved after aluminum etching. This bilayer scheme holds promise to solve the problems associated with substrate reflectivity and resist erosion which affect linewidth control during the aluminum patterning step in device fabrication. Future development of deep UV optics for the step and repeat projection printers could also take advantage of such a bilayer scheme to achieve submicron resolution capability.
The role of interfaces in ultrasmall semiconductor devices
Authors: Ferry D. K.
Published: July 2002

As semiconductor devices become smaller, the temporal and spatial scales become sufficiently short and the electric field sufficiently large that new physical constraints are reached in treating the transport of carriers within the devices. These devices are now controlled by strong size-related effects: coupling to the environment of contacts, interfaces/boundaries/surfaces, interconnects, and other devices. This is especially the case in MOSFET’s, where remote interface phonons and surface roughness scattering dominate the transport. In this talk, a general treatment of device–environment interaction will be discussed. Special cases for MOS transport and the specific role of interfaces will be treated.
Titanium silicide films prepared by reactive sputtering
Authors: Blom H.-O. , Berg S. , Ostling M. , Petersson C. S. , Deline V. , d’Heurle F. M.
Published: July 2002

Thin films of titanium silicides were deposited by means of reactive sputtering of titanium in an atmosphere of argon containing silane. The overall compositions of the films were determined by Rutherford backscattering which also indicates the presence of included argon. Hydrogen and oxygen were determined by other analytical techniques. The crystallization of the films during heat treatment was determined by x-ray diffraction which also allows the determination of the different phases present. Resistivities of about 20 μΩ cm observed in films annealed at 800 °C agree well with values previously reported for TiSi2 films prepared by other means. During heat treatment metal-rich layers deposited on silicon equilibrate with their substrate to form stoichiometric TiSi2, the rejection of silicon out of silicon-rich layers is greatly more difficult.
Cr on GaAs (110): The effect of electronegativity on the Schottky barrier height
Authors: Williams M. D. , Kendelewicz T. , List R. S. , Newman N. , McCants C. E. , Lindau I. , Spicer W. E.
Published: July 2002

Cr deposited in sequential steps on atomically clean GaAs(110) surfaces shows strong chemical reactivity at the interface with Cr-arsenide formation. Soft x-ray and ultraviolet photoemission spectroscopies have been employed to elucidate the room temperature chemistry and the Fermi level pinning behavior of this system. It was recently reported that the Pd/n-GaAs(110) system has a Schottky barrier height of ∼0.9 eV, is highly reactive, and is characterized by similar adatom arsenide formation. The distinction here is that Cr/n-GaAs(110) has a barrier height of ∼0.7 eV. Thus the Schottky barrier height appears to be independent of the nature of the reaction. An examination of the trends in the electronegativity (Pauling’s scale) shows a significant correlation to the Fermi level pinning. We found that low electronegativity (∼1.6) metals like Cr pin at the 0.7 eV level (below the conduction band minimum) which normally acts as an acceptor. The Fermi level of higher electronegativity (∼2.0) materials, e.g., Pd, Cu, Ag, and Au, is observed to pin at the 0.9 eV level which normally acts as a donor. This is exactly what one expects for charge transfer between the semiconductor and the metal using electronegativity as a basis. Further confirmation is found in the examination of changes in the ionization potential threshold of the Cr/GaAs system with metal deposition.
Topography-induced thickness variation anomalies for spin-coated thin films
Authors: White L. K. , Miszkowski N.
Published: July 2002

A low-pass frequency filter model for predicting thickness variations on complex topography is investigated for several spin-coated thin films. Frequency weighting parameters are presented for PMMA, HPR204, HPR206, OFPR800, MPR resist coatings and a spun-on glass coating (X-600). One weighting parameter a tends to be inversely proportional to the solution viscosity and indicates the conformality of the coating. The other parameter Pmin depends on the spun-on film thickness and the step height. Simulated coated topography contours are compared to experimental profilometer traces to demonstrate the validity of the modeling technique. Effects of topography orientation with respect to the wafer center are also examined. More uniform spun-on coatings on topography are obtained at lower spin speeds. PMMA and HPR206 coatings are compared. Simulations of two- and three-dimensional coated topography are presented to indicate coating thicknesses variations within complex arrays and at the edge of large arrays.
Growth of metal overlayers on semiconductor surfaces: A prototype study
Authors: Batra Inder P.
Published: July 2002

Widespread interest in the field of epitaxy has stimulated us to perform a first principles atomistic calculations dealing with the energetics of bicrystals. Using a self-consistent pseudopotential approach we have calculated total energy as a function of growth sequence of a metal on a semiconductor surface. The prototype system we study is the pseudomorphic growth of aluminum on an unreconstructed Ge(001). For Al(001)–Ge(001) in the epitaxial relationship (001) [100]Al∥(001) [110]Ge where the [100]Al axis has been rotated 45° with respect to the Ge[100] a small lattice mismatch might allow coherency. We present the results of total energy calculations starting from submonolayer coverages of Al to multilayer deposition of metal. Of the two possible symmetric sites (bridge and on top) where the overlayer can begin to grow, our calculation favors the bridge site. Upon increasing the overlayer thickness we found a striking change (∼35% increase) in the interplanar distance between the substrate and the overlayer. The absolute value of the interplanar distance increased from about 1.2 to about 1.7–1.8 Å. An important observation we wish to make is that the interplanar distance between two expitaxially grown systems rapidly tends to stabilize at the average interplanar separation of the constituents. Even though our calculations are for a specific system, we suggest that this might be more generally applicable. An experimental corroboration of this fact should be very valuable. We also present results for the unsupported aluminum film and show that its lattice constant is contracted by about 10% as compared to the bulk value. From this we are able to calculate a realistic value for the elastic energy contribution to the total energy. Some important implications of the thin film effect for the structural properties of the overgrowth are briefly discussed.
Investigation of MBE-grown (001) GaAs surfaces using low-dose SIMS
Authors: Croydon W. F. , Dowsett M. G. , King R. M. , Parker E. H. C.
Published: July 2002

A combined SIMS-MBE UHV system has been used for growth and subsequent analysis of differently reconstructed (001)GaAs surfaces. Some small, but significant, differences are found in SIMS spectra from the different surfaces, indicating that the (2×4)As stabilized surface commonly used for MBE growth may be more ‘‘bulklike’’ than other reconstructions. Spectra obtained after oxygen exposure indicate involvement of both Ga and As at the initial stages of oxidation, and the different surface reconstructions showed very similar response to oxygen exposure. These SIMS analyses do not indicate large differences in either the surface composition or chemistry of differently reconstructed surfaces.
Linewidth control with masked ion beam lithography using stencil masks
Authors: Randall J. N. , Bromley E. I. , Economou N. P.
Published: July 2002

Masked ion beam lithography (MIBL) is capable of high resolution (<50 nm) proximity printing with short exposure times (<1 s). In this letter we demonstrate the large process latitude and precise linewidth control possible with MIBL when stencil masks are employed. Features, 0.65 μm in dimension, exposed in polymethylmethacrylate (PMMA) show negligible linewidth variation (<50 nm) for a change in dose of over an order of magnitude. This linewidth control is a result of the high contrast of stencil masks, the low divergence of the ion beam, lack of diffraction, and small proximity effect of this technology. The linewidth control of MIBL is compared to the linewidth control of optical projection lithography and x-ray lithography.
A hydrogen field ion source with focusing optics
Authors: Lewis G. N. , Paik H. , Mioduszewski J. , Siegel B. M.
Published: July 2002

We have constructed a hydrogen field ionization ion source which includes focusing optics. Both the ion source and a three-electrode accelerating lens are cooled to cryogenic temperatures. The source and lens are designed to operate at 50 kV and the lens characteristics are optimized for an ionization voltage of 5 kV, such as would be used with ion milled emitters. This source and lens are part of a hydrogen ion beam lithography system currently under construction. The design of the source and lens, their operating characteristics, and the results and problems encountered in using them are presented.
Dry developed negative resist in synchrotron radiation lithography
Authors: Tsuda M. , Oikawa S. , Yabuta M. , Yokota A. , Nakane H. , Atoda N. , Hoh K.
Published: July 2002

The examination of synchrotron radiation (SR) lithography of a dry developable negative resist comprising poly(methylisopropenylketone) and 2,6-di (4′-azidobenzylidene)-4-methylcyclo hexanone-1 was carried out using the facilities of the storage ring of ETL-TERAS where the electron energy is 600 MeV, the storage current is 100 mA, the orbital radius is 2 m, and the distance from the source to the sample is 10 m. The results obtained were excellent, i.e., sharp-shaped and high aspect ratio resist patterns comparable to those of PMMA patterns in SR lithography were easily obtained in a single layer resist with the dry development and contact printing. In the proximity printing, sharp-shaped patterns were also obtained, but the resolution depends on the conditions of the imagewise exposure although the reproducibility is good. The sensitivities are 1380 mJ/cm2 (approximately equal to PMMA) and 1840 mJ/cm2 in saturation of remaining resist thickness for contact and proximity printings, respectively. The time required for the complete dry development of 4 μm thick resist coatings in an oxygen plasma is only 4 min which is remarkably shorter than the time required for the thick bottom layer in the trilevel process [53 min for 4 μm; Matsui and Endo, Microelectron. Eng. 1, 51 (1983)].
Study of solid phase and molecular beam epitaxial cobalt silicide films on Si〈111〉 using electron energy loss spectroscopy
Authors: de Fresart E. , Kao Y. C. , Wang K. L.
Published: July 2002

Very thin cobalt silicide films of several atomic compositions from Co to CoSi2 have been grown by thermal reaction of Co deposited at room temperature and by molecular beam epitaxy on Si〈111〉 substrates under ultrahigh vacuum conditions. They were analyzed by electron energy loss spectroscopy. Loss spectra characteristic of the Co-rich silicides, CoSi, and CoSi2 phases were found to be quite different, first by the energy of the bulk plasmons, around 22 eV for Co-rich silicides, 20.6 and 19.5±0.7 eV for CoSi and CoSi2, respectively, second by the interband and surface-state transitions. In the CoSi and CoSi2 spectra, two transitions were interpreted as related to the excitation of  bonding Co(3d)–Si(3p) and nonbonding Co(3d) electronic states. A transition at 1.7 eV obtained on CoSi2 grown both by the solid phase and molecular beam epitaxy techniques was found to be sensitive to the surface conditions and was attributed to a surface state. This result was correlated to the surface morphology and film crystallinity checked by scanning electron microscopy and electron channeling. Energy loss spectra were correlated to the alloy composition ratios obtained by Auger spectroscopy and Rutherford backscattering spectrometry.
Formation of TiN on Si and SiO2 by rapid processing using a large area electron beam
Authors: Sun Die-chi , Yu Zeng-qi , Li Fu-ming , Du Yuan-cheng , Wang Hai , Jiang Guo-bao
Published: July 2002

Rapid nitridation of Ti film evaporated on a Si and SiO2/Si wafer using a large area electron beam has been described. A predominant enhanced processing of an e-beam should be considered. The film structure of the sample processed by an e-beam has been characterized by Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) analysis, after rapid processing. Identification of the chemical composition of the film was performed with x-ray diffraction. The minimum sheet resistance of TiN was about 0.6 and 14.2 Ω/⧠ for Si and SiO2/Si substrate, respectively. A ratio of 0.96%±5% (N/Ti), the stoichiometric composition of the sample characterized by RBS, has been obtained.
Inverse photoemission from surface and interface states of III–V semiconductors
Authors: Drube W. , Himpsel F. J. , Ludeke R.
Published: July 2002

We have measured unoccupied surface and interface states on Ga- and In-derived III–V semiconductors with momentum-resolved inverse photoemission. The position of the surface states is found to be unrelated to the fundamental band gap. Instead, a connection with the gap of p-like states can be made. This finding is discussed in the context of theories of Fermi level pinning and band lineup, which use (virtual) gap states as a reference energy. Unoccupied metal-induced gap states are found for transition metals (Y, Ti, V, Mn, Pd) on GaAs(110) and InP(110). Their energy tracks the Fermi level pinning position, suggesting that these states are connected with the pinning process. A tentative assignment in terms of nonbonding metal d states is given.
Ion implantation and annealing properties of molecular-beam epitaxy grown GaAs-on-Si
Authors: Lee J. W. , Tran L. T. , Tsai H. L. , Shichijo H.
Published: July 2002

The material properties of ion-implanted and annealed GaAs-on-Si layers have been investigated in terms of surface morphology, wafer warpage, defect state, and device performance. For this work GaAs-on-Si layers were grown by molecular-beam epitaxy (MBE) with various growth conditions and several of them were ion-implanted and annealed. Morphologies and warpages were not changed after ion implantation and subsequent thermal annealing at 850 °C for 15 min, however, additional features were usually observed after 1-h annealing. The total defect densities were reduced by several orders of magnitude by the thermal annealing, and this reduction is independent of the growth history of GaAs-on-Si layer. To test the device compatibility of As-on-Si wafers, emitter-down AlGaAs/GaAs heterojunction bipolar transistor structures were grown on Si substrates and processed using ion implantation. A maximum current gain of 25, which was equal to a concurrently processed on GaAs-on-GaAs wafer, was achieved.
Computer programs for designing multipole electron and ion optical systems
Authors: Smith M. R. , Munro E.
Published: July 2002

New computer programs have been developed for designing multipole electron and ion beam systems. The charge density method is used to calculate the axial field distribution for electrostatic quadrupole and octopole lenses and deflectors, dipole deflectors, and rotated magnetic quadrupole lenses. The programs are described and some comparisons against analytic models are presented. An existing finite element program is used so that electrostatic round lenses may also be included in the analysis. An optical properties program uses a new compact aberration theory developed by the authors to calculate the first-order focusing and deflection properties, third-order geometrical and first-order chromatic aberrations, for any combination of the elements already mentioned. The desired focusing is obtained by using an iterative least squares routine to focus the round and quadrupole lenses. An analysis of crossed electrostatic and magnetic quadrupole lenses is presented showing how the first-order axial chromatic aberration coefficient can be reduced to less than 0.1 mm, making the size of the chromatic disk negligible.
Application of x-ray lithography for manufacturing a metal-oxide semiconductor field-effect transistor tetrode
Authors: Hersener J. , Piper E. , Wilhelm A. , Birkenstock G.
Published: July 2002

Using x-ray lithography the gate level of a MOSFET tetrode was fabricated in a ‘‘mix and match’’ technique. All the other levels were exposed with conventional 400 nm photolithography. As an x-ray source the synchrotron radiation of the Berlin electron storage ring (BESSY) was used. The employed x-ray mask is based on a stress compensated Si membrane, which consists of a simultaneously B- and Ge-doped epitaxial layer.
Cermet as an inorganic resist for ion lithography
Authors: Melngailis J. , Ehrlich D. J. , Pang S. W. , Randall J. N.
Published: July 2002

Al/O cermet has been found to act as a high-resolution resist for ion lithography. The change in chemical etching produced by the ions appears to be similar to that produced by excimer laser irradiation. Both a focused Ga-ion beam and collimated Ar ion or proton beams with stencil masks have been used for exposure. Cermet films 500 Å thick were e-beam evaporated in an atmosphere of O2 and were exposed to ion doses of 5×1014 to 1.6×1016 cm−2 at energies ranging from 800 eV to 75 keV. The etch rate in a phosphoric acid based, Al etch falls rapidly to about 1/2 of the rate for unexposed material after exposure to 70 keVAr+ ions with a dose of 1×1015 cm−2 and is near zero for doses above 8×1015 cm−2. The etch rate in BCl3 plasma is less sensitive to dose and decreases by 30% for a dose of 8×1015 cm−2. Although comparison of Auger analysis of exposed and unexposed cermet indicates that ion bombardment increases the concentration of Al bound in Al2O3 on the surface compared to Al in the metallic state, the mechanism of the ion induced etch resistance is at this point unclear. A film of SiO2 on Si was patterned using the exposed cermet as a mask to reactive ion etch in CHF3. Linewidths down to 0.1 μm were produced.
A hydraulic X–Y stage system for application in electron beam exposure systems
Authors: Nielsen R. J. , Bruning J. H. , Richman R. M. , Biddick C. J. , Giacchi J. , Kossyk G. J. W. , Bush D. R. , Barna S. J. , Alles D. S.
Published: July 2002

A hydraulic X–Y stage system for application in electron beam lithography machines is described. The X–Y table is supported on hydrostatic bearings and is driven hydraulically. This system operates in a vacuum and is used in the AT&T Bell Laboratories’ EBES4 electron beam exposure system. The X–Y stage system consists of a yoke assembly mounted on the end of a large hydraulic piston and cylinder assembly. The X–Y table is mounted on a movable carriage that rides on a smaller hydraulic piston fixed in the yoke assembly. Carriage motion in the yoke is orthogonal to the motion of the large hydraulic cylinder, providing X and Y motions, respectively. Both hydraulic axes use hydrostatic bearings to minimize sliding friction and to prevent undesired motion normal to the travel directions. The hydrostatic bearings, appropriately shaped, also prevent rotation. All sliding portions of the X–Y drive are enclosed with flexible metal bellows. The entire hydraulic system, including the pump, is sealed and evacuated to about 50 mTorr. The hydraulic fluid is a narrow distillate fraction of a perfluorinated polyether vacuum pump oil. The position of the X–Y table is measured to within (1)/(64) μm with a standard two-axis laser interferometer system. Stage velocity can be as high as 10 cm/s but is typically less than 5 cm/s during pattern writing. Oil temperature is actively controlled to keep the stage head temperature constant within 0.1 °C under all operating conditions. The position of each axis is independently controlled by a 16-bit microcomputer through an analog control board. The analog board drives a standard two-stage electrohydraulic servovalve that controls oil flow to and from the hydraulic actuator. The analog gains and offsets are set digitally. Position feedback and positioning strategies, including acceleration and velocity limits, are implemented in the microcomputer.
Automatic electron beam metrology system for development of very large-scale integrated devices
Authors: Matsuoka Genya , Ichihasi Mikio , Murakoshi Hisaya , Yamamoto Kenichi
Published: July 2002

A computer-controlled electron beam metrology system has been developed which is capable of measuring a large number of features automatically. The system also evaluates the distribution of critical dimensions (CD) on a wafer in order to promote submicron very large-scale integrated process technology. This system provides nondestructive measurement in a semiconductor production line by using a low voltage electron beam from a field emission gun. The system consists of a computer-controlled optical column, a precise X-Y stage controlled by a laser interferometer, high-accuracy electronic circuits and a control computer. The system places submicron patterns under the electron beam within a ±0.05 μm deviation and measures them step-by-step under the optimum beam conditions. Repeatability is 0.008 μm with a throughput of 100 features/h.
Prototype to production using the Hewlett–Packard quarter-micron electron beam system
Authors: Studebaker Lawrence G. , DeWitte Gordon J. , Bugely Faith L. , Riehl David H.
Published: July 2002

For the past year, one of Hewlett–Packard’s electron beam lithography systems has been in use at the Microwave Technology Division in Santa Rosa, California. Applications include surface acoustic wave (SAW), MESFET, MODFET, and GaAs IC development as well as photomask fabrication. The system presents some distinct advantages to the user in terms of linewidth, layer-to-layer alignment, turnaround time, yield, and repeatability. These advantages have reduced product development time by giving users freedom to explore device variations with rapid turnaround and high yield. After a brief description of the system, we present the system from the users’ point of view: day-to-day performance, process monitors, and ongoing applications work. The system has a spot size below 0.25 μm over a 2.496 mm2 field at a beam current of 200 nA. Beam placement accuracy is 0.1 μm over the field, with overlay accuracy of 0.125 μm for direct write. The system grid is 0.25 μm but can be varied continuously down to 0.1 μm. Linewidths of 0.25 μm in bilayer resist structures and 0.35 μm in single layer resists are routinely achieved by careful system and process control.
Very large scale integrated pattern registration improvement by photoablation of resist-covered alignment targets
Authors: Polasko Kenneth J. , Elliott David J. , Piwczyk Bernhard P.
Published: July 2002

A principal limitation for densely packed, submicrometer very large scale integrated circuits is reproducible registration accuracy. The resist covering the alignment targets is a major contributor to poor and nonreproducible alignment signals. Further, the availability of new imaging materials (contrast enhancing materials and multilayer resists systems) allows for submicrometer production resolution, but with the limitation that the alignment signal may be further degraded. This study presents data on registration improvement resulting from the removal of patterning material covering alignment targets. The patterning materials were removed by photoablation using an excimer laser system operating at 193 nm. The removal involves the illumination of the target area with 10–12 laser pulses of ∼17-ns duration. During the illumination the contrast enhancing material and resist disintegrate into largely molecular fragments that are scavenged by an air-bearing nozzle. Electrical probe measurements of polysilicon wafers processed with this technique displayed three-sigma registration variation of better than 850 Å.
Thermal nitridation of silicon dioxide films
Authors: Menéndez I. , Fernández M. , Sacedón J. L.
Published: July 2002

The breakdown and C–V characteristics of SiO2 films treated in either N2 or NH3 atmospheres at different temperatures have been investigated. The Auger electron spectroscopy profiles of the samples treated in a N2 atmosphere at 1200 °C indicate that the nitrogen is preferentially incorporated into the Si/SiO2 interface, thus increasing both the dielectric breakdown and the positive spatial charge associated with the interface. A similar increase of the dielectric breakdown is observed in the NH3 treated samples, although in this case the nitrogen is found across the whole oxide thickness.
New silicon-containing negative resists
Authors: Granger Diana D. , Miller Leroy J. , Lewis Margaret M.
Published: July 2002

Poly[γ-methacryloyloxypropyltris(trimethylsiloxy)silane], or PMOTSS, is an intrinsically negative resist with a sensitivity comparable to that of the polyhalostyrenes. Although the homopolymer is rubbery, copolymers of MOTSS and halostyrenes are hard solids and are excellent candidates for use as the top, imaging layer of a bilayer resist for electron beam and masked ion-beam lithography.
Plasma polymerized styrene: A negative resist
Authors: Fong F.-O. , Kuo Hong C. , Wolfe J. C. , Randall John N.
Published: July 2002

Preliminary studies of the use of plasma deposited styrene as a negative electron-beam resist for lithography in V grooves are reported. We show that reactor pressure and power strongly affect the exposure and mechanical properties of the resist. Contrast decreases, sensitivity increases, conformality improves, and swelling becomes more pronounced with increasing power or decreasing pressure. An optimized process has been developed for lithography in silicon V grooves. The contrast for that process is 2.3 and the sensitivity is 0.008 C/cm2.
A multiple exposure strategy for reducing butting errors in a raster-scanned electron-beam exposure system
Authors: Dameron David H. , Fu Chong-Cheng , Pease R. F. W.
Published: July 2002

As integrated circuit (IC) feature sizes shrink, correspondingly greater demands are put on the reticle writing systems for pattern placement accuracy. In raster-scanned electron-beam exposure systems such as MEBES which build up the pattern as a mosaic of stripes, quite small placement errors at the stripe boundaries can have serious consequences in terms of the electrical performance of the finished IC. The specifications of butting error for these exposure systems is typically 0.1 μm for a 0.25-μm address size. While this is in itself not a serious error for most features, it can be troublesome if it shows up as a linewidth error for a submicron gate electrode. Here we have demonstrated that this error can be substantially reduced by using multiple exposures or scans to build up the pattern data so that in each exposure the stripe boundary is offset within the pattern from the remainder of the exposures. Thus, for N exposures, only 1/N of the total dose at any one stripe boundary includes the placement error from stripe butting. Consequently, the butting error is significantly reduced in the exposed resist image. We have implemented this procedure using a novolak resist which is exposed with a scan or exposure count of 3; the reduction of the placement error by a factor better than 4 is demonstrated by metrology techniques.
Observation of Aharonov–Bohm effect in quasi-one-dimensional GaAs/AlGaAs rings
Authors: Mankiewich P. M. , Behringer R. E. , Howard R. E. , Chang A. M. , Chang T. Y. , Chelluri B. , Cunningham J. , Timp G.
Published: July 2002

Small structures in high-mobility semiconductor heterojunctions are expected to show a variety of quantum mechanical phenomena associated with electron interference. At low temperatures in the high-mobility two-dimensional electron gas at a GaAs/AlGaAs heterojunction, both the elastic and inelastic electron scattering lengths are several microns, making it possible to fabricate complete devices contained within these dimensions. In ring shaped devices we have observed periodic magnetoconductance oscillations (Aharonov–Bohm effect) caused by electron interference. The magnitude of this effect is as much as 10% of the total conductance, much larger than seen in previously studied metal systems. High-resolution electron (e)-beam lithography and reactive ion etching were used to fabricate rings of 1, 2, and 2.5 μm mean diameters with linewidths of 0.5 μm. The electrical channel width is smaller than the physical channel width because of edge depletion. Samples with conducting channels varying from about 0.6 to 0.2 μm have been made. The magnetoconductance of these rings oscillate with a period of hc/e (±2%) based on the mean diameter, as expected for a single electron interference effect. The Hall resistance of these samples show strong nonlocal effects, demonstrating that the channel acts as a phase preserving electron waveguide. These devices are an excellent test system for studying electron transport in the extreme quantum limit, and exploring the consequences of the limits of microfabrication.
New portable conformable masking excimer laser lithography using water-soluble contrast enhanced material
Authors: Endo M. , Sasago M , Hirai Y. , Ogawa K. , Ishihara T.
Published: July 2002

A new portable conformable masking (PCM) using excimer laser lithography has been developed. This method is characterized by the combination of poly(dimethylglutarimide) and the water-soluble contrast enhanced material developed here and the use of KrF excimer laser exposure. Using this lithography, we obtained good resist pattern profiles and submicron region resolution by a very simple process.
Fully scaled 0.5 μm metal–oxide semiconductor circuits by synchrotron x-ray lithography: Mask fabrication and characterization
Authors: Viswanathan R. , Acosta R. E. , Seeger D. , Voelker H. , Wilson A. , Babich I. , Maldonado J. , Warlaumont J. , Vladimirsky O. , Hohn F. , Crockatt D. , Fair R.
Published: July 2002

Several sets of x-ray masks for a metal–oxide semiconductor (MOS) device program were fabricated using boron-doped silicon as the membrane and gold as the absorber. The metrology of the mask sets was characterized. Mask-to-mask overlay error is <0.12 μm (3σ) including measurement error. Absorber induced distortion is not the dominating mask error. (Lack of better measurement systems and techniques preclude exact analysis of errors.) Quarter-micron patterns have been resolved using a multilayer resist system. Linewidth variations are <0.017 μm (1σ) across the entire membrane. The mask sets have been successfully used to fabricate fully scaled n-type MOS circuits.
High-resolution and high-fidelity x-ray mask structure employing embedded absorbers
Authors: Chou S. Y. , Maluf N. I. , Pease R. F. W.
Published: July 2002

Existing x-ray masks often suffer from a variety of problems. These include poor adhesion of small absorber features to the substrate, severe undercut in the etching of sub-half-micron absorber lines, distortion of absorbing features formed by plating through a resist stencil, distortion of the absorber due to metal migration and due to local stress, and mechanical damage due to handling. Here we describe an x-ray mask structure in which a high atomic number metal fills trenches etched into a single-crystal silicon mask membrane. Thus the problems mentioned earlier for conventional x-ray masks can be either effectively eliminated or greatly reduced. The trenches were formed in the silicon by a combination of ultrathin resist, high-resolution electron beam exposure, and novel etching techniques involving metal masking. The trenches were half-micron deep with a sidewall angle of 1.5° to the vertical, and the minimum trench width measured at the top of the trenches was 70 nm, which gives an aspect ratio of 7:1. The trenches were filled with tungsten by both selective and nonselective chemical vapor deposition, and back etching (if any) was performed using reactive ion etching. Scanning electron microscopy reveals that the tungsten features are faithful replicas of the vertically walled trenches. A one-dimensional stress model shows that for a finite absorber stress, the embedded mask can have zero in-plane distortion and an out-of-plane distortion that is much less than that in a conventional mask.
Highly sensitive thermally developable positive resist systems
Authors: Ito Hiroshi , Ueda Mitsuru , Schwalm Reinhold
Published: July 2002

Acid-catalyzed thermal depolymerization of polyphthalaldehyde derivatives has been utilized in the design of highly sensitive, thermally developable, positive resist systems incorporating two stages of chemical amplification. Poly(4-chlorophthalaldehyde) mixed with triphenylsulfonium hexafluoroantimonate can be thermally developed to the substrate simply by heating the resist after exposure to <1 mJ/cm2 of 254-nm radiation or 1 μC/cm2 of 18-keV electron beam radiation. The images obtained by postbaking at 160 °C do not exhibit any thermal flow. Poly(4-trimethylsilylphthalaldehyde) (PSPA) sensitized with triphenylsulfonium triflate exhibits a high deep UV sensitivity of <2 mJ/cm2 and a high electron beam sensitivity of 1 to 2 μC/cm2 (20 keV) when the thermal development is performed at 100–130 °C. The high contrast (γ=4.3) of the PSPA resist allows thermal imaging of submicrometer features, which can then be transferred to the bottom planarizing layer by oxygen reactive ion etching (RIE). The combination of the thermal development and oxygen RIE pattern transfer provides a new mode of all dry bilayer processes.
Measuring overlay errors and critical dimensions by correlating binarized Laplacian of Gaussian convolved images
Authors: Crossley P. A. , Nishihara H. K.
Published: July 2002

A technique is described for measuring alignment and critical dimensions, which is tolerant of noise, defects, and details of target image appearance. The targets are composed of small elements which can be at the minimum feature size of the photolithographic process. Grey-level images of the targets are bandpass filtered and hard clipped to produce binary patterns representing the clustering structure of the target elements while attenuating details of the individual elements. Correlation of these binary patterns allows extraction of alignment error and critical dimensions without the use of thresholds, stored templates, or edge detection.