bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-phase liquid phase epitaxy of In0.53Ga0.47As on InP
Authors: Chen Mu-Kuen , Lin Hao-Hsiung
Published: July 2002

The growth of the In0.53Ga0.47As epilayer on InP by two-phase liquid phase epitaxy is investigated. To saturate the In melt before growth, an overweight GaAs wafer is chosen as solid source and put on top of the melt. By adjusting the weight of In, epilayers with a lattice mismatch Δa⊥/a below 2×10−4 are obtained. It is found that the quantity of InAs source required is more than that used in single-phase growth and the growth rate is smaller in two-phase growth. The result is explained using the phase diagram and the theoretical calculation. The growth rate, lattice-mismatch data, and photoluminescence spectra of the epilayers are also presented.
Molecular beam epitaxial growth and properties of Si-doped GaAs/AlGaAs quantum wells
Authors: Asom M. T. , Livescu G. , Swaminathan V. , Geva M. , Luther L.
Published: July 2002

We report on molecular beam epitaxial growth of Si doped, single and multiple quantum well structures. We have examined the effects of growth parameters such as substrate temperature, group V/III ratio, and intentional and unintentional impurities, on the electrical and optical properties of the quantum wells structures. Capacitance–voltage and secondary ion mass spectrometry analysis of the structures reveal that the net density of electrically active carriers in the wells is controlled by the number of acceptor states in the AlGaAs barrier. We have assigned the source of the acceptor state to the presence of oxygen in the AlGaAs barrier. We observe that the strength of the intersubband optical absorption from the quantum wells increases linearly with the Si-doping in the well. Photoluminescence measurements indicate that for a given substrate temperature, a lower V/III ratio results in higher quality quantum well.
Characteristic Zeeman patterns in novel graded gap II–VI quantum well structures
Authors: Hagston W. E. , Weston S. J. , O’Neill M. , Stirner T. , Harrison P. , Hogg J. H. C. , Ashenford D. E. , Lunn B.
Published: July 2002

Novel methods of growing graded gap structures are described. In order to provide a check that the structures are indeed graded in the correct manner, magnetic ions in the structure have been employed. The good agreement between the predicted and observed Zeeman splitting of the corresponding light- and heavy-hole exciton transitions, together with the magnetic field dependence of the Zeeman splittings and intensity of a forbidden heavy-hole exciton transition, is taken as direct evidence that graded gap structures having the correct composition have indeed been fabricated.
Novel integration of a group IV electron-beam deposition capability with a III–V molecular beam epitaxy system*
Authors: Lee H. P. , Szalkowski F. J. , Sato D. L. , Liu X. , Ranalli E. , George T.
Published: July 2002

A novel way of integrating epitaxial Si and carbon (C) doping capabilities within an existing solid-source III–V molecular beam epitaxy system by means of electron-beam evaporation is reported. By significantly increasing the Si evaporation rate over conventional effusion cells, this technique offers a practical way of growing high Si content (III–V)–Si alloys and superlattices. The use of GaAs–Si alloys with adjustable lattice constants for GaAs on Si growth with improved crystalline quality over previous methods is also demonstrated. Both uniform layer and delta-doped C in GaAs (p-type concentration up to the mid 1019/cm3 range) are demonstrated with carrier mobility comparable to other doping sources. These extended capabilities should find wide applications ranging from material synthesis to III–V devices and technology.
Quantum-confined Stark shift observed by electroluminescence and circularpolarized luminescence excitation spectroscopy in GaAs/AlGaAs coupled quantum wells
Authors: Kato Y. , Takahashi Y. , Fukatsu S. , Shiraki Y. , Ito R.
Published: July 2002

The quantum-confined Stark effect in electroluminescence (EL) spectra was observed using Al0.3Ga0.7As/GaAs symmetric coupled quantum-well (CQW) structures. The Stark shift of the transition between the ground electron state and heavy-hole state was found to be symmetrical with regard to the flatband bias for EL and for photoluminescence (PL), in which the electric field was applied in reverse direction. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was also employed to clarify the origins of optical transitions. Six transitions between electrons and light and heavy holes in the CQWs were clearly identified by PL and by polarization of CPPLE measurement.
Ordered and randomly disordered AlAs/GaAs short-period superlattices
Authors: Arent D. J. , Alonso R. , Horner G. , Bode M. , Olson J. M. , Yin X. , DeLong M. C. , SpringThorpe A. J. , Majeed A.
Published: July 2002

Unique optical signatures of different atomic arrangements of Al0.5Ga0.5As, deposited by molecular-beam epitaxy and having nominally identical average composition, have been observed in steady-state photoluminescence and photoluminescence excitation spectroscopies. Compared to the observations from a random pseudobinary alloy and a (AlAs)2(GaAs)2 ordered superlattice, intense photoluminescence emission is observed from disordered (AlAs)n(GaAs)4−n superlattices where n is randomly chosen from the sets 0≤n≤4 or 1≤n≤3. The photoluminescence peak energies of the randomly ordered superlattices are red-shifted by 100–400 meV from the emission energy of the pseudobinary alloy, suggesting that a significant density of localized or band tail states exists at energies lower than the band gap, which are confirmed by photoluminescence excitation spectroscopy. We also measure greatly increased photoluminescence intensity from the randomly ordered superlattices at high temperatures indicating that these materials may be suitable for optoelectronic applications in previously unattainable energy regions.
Application of a dry turbo vacuum pump to semiconductor manufacturing processes
Authors: Nagaoka T. , Mase M.
Published: July 2002

Recently it has become common to use dry vacuum pumps in semiconductor manufacturing processes. One problem with this application, however, is that etching by-products (e.g., aluminum trichloride, AlCl3) often deposit in the pumps. We have therefore studied these deposition processes and techniques to prevent deposits from forming. Our results indicate that the gas passage temperature must be kept above the sublimation temperature of the substance passing through the pump (e.g., AlCl3) to prevent deposits from forming. To accomplish this, we modified the cooling jacket construction and changed the coolant from water to oil. The modified cooling jacket resulted in more uniform temperatures than with the previous cooling jacket. Considering AlCl3, the gas passage temperature was raised by about 50 °C in order to keep the gas above the sublimation temperature of AlCl3. The modified pump was operated with a test semiconductor apparatus. A small amount of deposit was found after one year of equivalent running time, but it was not enough to interfere with proper operation of the pump. The same pump was also successfully demonstrated with a silicon nitride chemical vapor deposition process.
Comparative study of cross-sectional scanning tunneling microscopy/spectroscopy on III–V hetero- and homostructures: Ultrahigh vacuum-cleaved versus sulfide passivated
Authors: Smith A. R. , Gwo S. , Sadra K. , Shih Y. C. , Streetman B. G. , Shih C. K.
Published: July 2002

A comparative study of surfaces prepared by sulfide passivation and by UHV cleaving using cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) is performed. Test samples used include both GaAs/(AlGa)As heterojunctions and GaAs pn junctions. Sulfide- passivated heterojunction surfaces allow much useful electronic information to be deduced from the tunneling spectroscopy since the tip-induced band bending problem is solved. Atomic resolution across UHV-cleaved heterojunctions allows a direct measurement of the asymmetrical interfacial roughness which agrees very well with the value deduced from tunneling spectroscopy on the sulfide-passivated surface. In the case of the UHV-cleaved pn junction surface, the tip-induced band bending effect is seen to manifest itself as a spatial shift in the conductivity profile within the depletion region. Sulfide-passivated pn junctions show a topographic profile which correlates very well with the secondary ion mass spectrometry profile, indicating that this technique is a potentially powerful dopant profiling method. Each type of prepared surface possesses its own advantages and disadvantages which are discussed. In particular, we address the manifestation of the tip-induced band bending effect in the tunneling spectroscopy.
Measurements of potentials and sheath formation in plasma immersion ion implantation
Authors: Collins G. A. , Tendys J.
Published: July 2002

Collecting and emitting probes have been used to explore the distribution of potentials and the dynamic behavior of the cathodic sheath in the rf glow discharge plasmas used for plasma immersion ion implantation (PI3). On application of a negative voltage pulse, the sheath expands rapidly but comes to a steady-state position within a few microseconds. The potential distribution then remains stable as long as there is sufficient plasma outside the sheath region to replace the ions lost to the cathode. The various dc potentials in the plasma that arise from rectification of the rf fields are also important. At power levels up to 500 W, the plasma potential is several hundred volts above the average dc potential of the antenna. The magnitude of this voltage difference depends on the antenna geometry, its insulation from the plasma and the dc potential that can exist between it and the chamber walls. The floating potential of a typical PI3 target can vary from 50 to 300 V below the plasma potential but in all cases the difference is sufficient to ensure that there is a sheath and presheath structure around the target before the application of the high voltage pulse.
Activation, stabilization degradation, and lifetime predictions of refractory thin films emitters operated in cold cathode magnetrons*
Authors: Kopylov M. F.
Published: July 2002

Qualitative physical and chemical analysis of cold cathode magnetrons, field emitter activation process, and emission stabilization is described. The field emitter materials being presented are super thin films of Ta, Nb, W and their alloys and secondary electron emitters being presented by different kinds of emission active materials. Degradation processes of cold cathode magnetrons with field electron excitation are studied. Criteria for predicting of long (≳10 000 h) life, including individual life predictions are defined. Parameters of the lowest voltage state-of-the-art cold cathode magnetron with 7.5 and 5 kW pulse output power in 3 cm wavelength range are tabulated.
Diffusion on an elliptical field emission cathode*
Authors: Eremchenko D. V. , Makhov V. I.
Published: July 2002

The stability limit for curvature of a charged elliptical surface is found beyond the Dyke et al. approximation.
Elimination of long-term calibration drift in molecular beam epitaxy by cooling the source flange
Authors: Larkins E. C. , Thaden H. , Betsche H. , Eichin G. , Ralston J. D.
Published: July 2002

Drifts in the growth rate calibration with time constants of the order of hours are observed during molecular beam epitaxy growth, adversely influencing the calibration stability and reproducibility. The principal cause of these drifts was found to be high, time-dependent source flange temperatures (≳40 °C) at the thermocouple feedthroughs. The installation of water-cooled blocks on the furnace flanges eliminated this long-term drift and improved the calibration reproducibility by a factor of 3. In addition, these cooling blocks significantly reduced the ion-pump current in the growth chamber, presumably due to reduced outgassing of the source flange.
Damage behavior of silicon by MeV Ge+ irradiation under tilted angle
Authors: Wang Ke-Ming , Shi Bo-Rong , Ma Shi-Jie , Liu Xiang-Dong , Zhai Hong-Ying , Xu Tian-Bin , Zhu Pei-Ran , Zhao Qing-Tai
Published: July 2002

The damage behavior of Si induced by MeV Ge+ under tilted angle has been studied. In order to investigate the effect of implanted energy and angle on the damage distribution, the energies were varied from 1 to 2 MeV and the angles were varied from 7° to 60°. The experimental damage distribution is extracted based on the procedure by Feldman and Rodgers [L. E. Feldman and J. W. Rodgers, J. Appl. Phys. 41, 3776 (1970)] using the multiple-scattering model. The experimental data obtained are compared with the TRIM’90 code. The results show that the lateral damage spread can not be neglected; the shape and the depth of damage distribution are well described by the TRIM’90 code under tilted angle irradiation for Si(100).
Scanning tunneling microscopy of liquid crystals, perylene-tetracarboxylic-dianhydride, and phthalocyanine
Authors: Freund J. , Probst O. , Grafström S. , Dey S. , Kowalski J. , Neumann R. , Wörtge M. , Putlitz G. zu
Published: July 2002

Scanning tunneling microscopy measurements conducted on pure liquid crystals and liquid crystals in combination with the dyes perylene-tetracarboxylic-dianhydride (PTCDA) and phthalocyanine (Pc), all adsorbed on highly oriented pyrolytic graphite (HOPG), are being reported on. The liquid crystal octylcyanobiphenyl (8CB) was used as a solvent for the dyes, allowing the preparation of ordered dye layers in a very simple way. A combination of vapor deposition of PTCDA and liquid deposition of 8CB provided films, where 8CB and PTCDA are embedded in each other on a small length scale. The samples were prepared in two different ways yielding either 8CB islands within a PTCDA monolayer or PTCDA islands surrounded by 8CB. The Pc films on HOPG exhibit a hexagonal molecular lattice that could be related to the lattice of the graphite substrate and for which a structural model is proposed. For dodekylcyanobiphenyl (12CB) on HOPG the ordering in unit cells containing 10 rather than 8 molecules is reported for the first time.
Friction force microscopy on clean surfaces of NaCl, NaF, and AgBr
Authors: Howald L. , Lüthi R. , Meyer E. , Gerth G. , Haefke H. , Overney R. , Güntherodt H.-J.
Published: July 2002

With a bidirectional atomic force microscope, measurements are performed on insulating surfaces of ionic crystals, such as NaF, NaCl, and AgBr. Atomic-scale friction is observed on surfaces, and is being prepared and studied in ultrahigh vacuum, where contaminants can be excluded. Comparative measurements show the favorable frictional properties of NaCl.
Fabrication of ultrafine anisotropic SiO2 mask by the combination of electron beam lithography and SF6 reactive ion beam etching using aluminum lift-off technique
Authors: Nishibe Tohru
Published: July 2002

We propose a new process for fabrication of an ultrafine anisotropic SiO2 mask, successfully combining electron beam (EB) lithography and SF6 reactive ion beam etching using an Al lift-off. SiO2 etching had a high selectivity of 50 over Al with an SF6 pressure of 0.9 mTorr and an ion energy of 300 V, because formation of AlF3 near the surface prevented the etching of Al. EB patterns were precisely transferred to the SiO2 mask with a vertical wall. Using this process, lines with widths of 70 nm and dot arrays composed of columns with diameters of 70 nm were realized.
Flexible-diaphragm force microscope
Authors: Rice Paul , Moreland John
Published: July 2002

A flexible polyimide diaphragm was used in place of the usual cantilever for atomic force microscopy. Images of hard disk surface features are presented demonstrating the practicality of the method.
Strained layer epitaxy: How do capping layers and oppositely strained intermediate layers enhance the critical thickness?
Authors: Lefebvre I. , Priester C. , Lannoo M. , Hollinger G.
Published: July 2002

Within a valence force field framework, we calculate the critical thickness of a film that is lattice mismatched to the substrate on which it is epitaxially deposited. A capping layer that is lattice matched to the substrate is known to enhance the critical thickness. We calculate the efficiency of the capping layer as a function of its thickness. We also demonstrate that this efficiency can be improved by using a capping layer that is not lattice matched to the substrate. When the capping layer is undesirable, another way of enhancing the critical thickness is to use an oppositely strained intermediate (OSI) layer between the substrate and the film. To maximize efficiency, the OSI layer lattice constant should be larger (respectively, smaller) than that of the substrate if the film is in tension (respectively, compression). We demonstrate that a single OSI layer has no significant effect on the critical thickness. A microscopic description of the strain on all of system is provided, and the mechanism of strain compensation is explained.
Gate oxide degradation during polysilicon etching in a parallel-plate plasma-type etcher
Authors: Lee Dong-Duk , Kim Jeong-Ho , Shin Ki-Soo , Park Hae-Sung , Choi Soo-Han
Published: July 2002

Gate oxide degradation by transient surge current has been tested during polysilicon etching in a parallel-plate plasma-type etcher. To reduce the transient surge current, rf power is removed gradually at a rate of 50 W/s after 50% overetch. Breakdown voltage distribution measured at a metal–oxide–semiconductor capacitor array structure with gate edges is improved considerably by the ramping down of rf power. This clearly indicates that the transient surge current can cause charge damage to some extent even in a plasma-type etcher. Gate oxide recovery during the interpolyoxide deposition is also discussed.
Fabrication of sub-100 nm GaAs columns by reactive ion etching using Au islands as etching mask
Authors: Ahopelto J. , Airaksinen V.-M. , Sirén E. , Niemi H. E.-M.
Published: July 2002

A new method for fabrication of reactive ion etching masks for nanoscale GaAs columns is proposed. The mask consists of sub-100 nm Au islands formed by in situ heating a thin gold film on the substrate surface. The resulting areal density of the Au islands can exceed 1010 cm−2. The islands show good resistance against etching, making the method suitable for fabrication of nanoscale structures with very high aspect ratios. This is demonstrated by etching over 1 μm high GaAs and AlGaAs/GaAs columns with widths below 100 nm.
Design of a high voltage electron gun for lithography applications
Authors: Petric Paul F.
Published: July 2002

A development project was undertaken at IBM to meet the needs of production e-beam lithography at increased beam energies up to 100 kV. The project was divided into two separate development efforts. The first part, which is the topic of this article, dealt with the gun vacuum and its overall design. The second half dealt with the high voltage design. This article describes the design of the overall gun and its vacuum system and the initial results of testing as they pertain to the vacuum system of the gun and its operation with the integral ion pump design.
Distortion analysis of stencil masks with stress-relief structures
Authors: Wolfe John C. , Chalupka A. , Löschner H. , Stengl G. , Vonach H. , Shimkunas A. R. , Mauger P. E.
Published: July 2002

We present an exact solution to an axially symmetric continuum model of distortion in stencil masks. A correction procedure is studied where the pattern displacement vectors are calculated from a linear approximation to the pattern distribution function. For practical mask patterns this can reduce distortion to near the levels needed for very large scale integration. Additional gains can be achieved by using a ring of perforations around the integrated circuit field to reduce stress. Corrected distortion figures below 20 nm on a 60 mm mask seem possible.
High accuracy thickness measurements by means of backscattering electron metrology
Authors: Baciocchi M. , Di Fabrizio E. , Gentili M. , Grella L. , Maggiora R. , Mastrogiacomo L. , Peschiaroli D.
Published: July 2002

A novel technique based on backscattered electrons (BEs) for accurate determination of thickness (Z metrology) of thin metal films with electron-beam (e-beam) machines is presented. The algorithm, based on phenomenological considerations accounting for the basic electron–material interactions in both the sample and the substrate, results in a relationship between the electron detector counts and the actual height of the samples, having the shape of a saturating exponential of the type 1−e−(h/h0), and identifies the associated uncertainties. The algorithm has been tested on Au electroplated features on bulk Si substrates, having thicknesses ranging from 50 to 480 nm, previously measured with conventional techniques such as profilometry and scanning electron microscopy. The e-beam system used in this study is a lithography machine used in metrology mode at 40 kV, a Leica EBMF 10 cs/120, by which BEs were collected through its standard channel plate electron detector. The e-beam scan results are transformed into thicknesses’ measurements by means of the proposed algorithm. Au features were also tested on 100-nm-thick silicon nitride membranes, and the feasibility of the algorithm was pointed out. Achievable errors for both Si bulk and silicon nitride membrane substrates range from about 30% for thin markers to about 10% for thicker ones, making it possible, for thick samples, to exploit the algorithm for measuring thicknesses of phase-working devices.
Spectroscopic ellipsometric monitoring of electron cyclotron resonance plasma etching of GaAs and AlGaAs
Authors: Snyder P. G. , Ianno N. J. , Wigert B. , Pittal S. , Johs B. , Woollam J. A.
Published: July 2002

In situ real time spectroscopic ellipsometry measurements were made during electron cyclotron resonance plasma etching of radio frequency biased GaAs and AlGaAs samples. Gas mixtures used were CH4/H2/Ar, pure H2, and pure Ar. Ellipsometry provided information about damage to the surface region and AlGaAs epilayer thickness. For the methane mixture GaAs etch, damage appeared in the form of redshifted and broadened E1 and E1+Δ1 critical point features in a surface layer several tens of nm thick. The damage layer began forming within a few seconds after the start of etching, and stabilized within 1 min. Hydrogen etching caused a thicker damage layer with greater redshifting and broadening, while argon caused relatively little damage. Possible mechanisms for the redshifting are discussed. During etching of an AlGaAs/GaAs heterostructure with the methane mixture, the same redshifting and broadening effects were seen in the AlGaAs critical point structure. The AlGaAs thickness was determined from the real time data, from which an etch rate of about 20 nm/min was derived.
Flux masking and thickness uniformity in molecular beam epitaxy
Authors: Sadra K. , Lin Chih-Hsiang , Meese J. M.
Published: July 2002

We suggest that properly designed masks altering the rotation-integrated flux arriving at the substrate may be used to improve thickness uniformity in a variety of crystal growth techniques. As an illustration, we calculate the dimensions of the mask required to produce a perfectly uniform flux for a single group-III species in single- and multiple-wafer III–V molecular beam epitaxy. Estimates of the detrimental role of errors in mask machining and position are provided and schemes for correcting flux nonuniformities for multiple sources are suggested. Our results imply that flux masking can lead to significant uniformity improvements for growth on single or multiple wafers.
Analysis of InP etched surfaces using metalorganic chemical vapor deposition regrown quantum well structures
Authors: Yu D. G. , Keller B. P. , Holmes A. L. , Hu E. L. , DenBaars S. P.
Published: July 2002

We have studied a wide variety of wet and dry etching methods for InP substrates and subsequent surface treatments in preparation for regrowth. To evaluate these processes, a multiple quantum well heterostructure consisting of InGaAs quantum wells of varying widths was regrown on these etched surfaces by metalorganic chemical vapor deposition. This heterostructure was chosen so that we could use low temperature photoluminescence to determine etch damage propagation from the surface. We have found that the photoluminescence intensity of regrown quantum wells close to CH4/H2/Ar reactive-ion-etched surfaces is greater than for quantum wells grown the same distance from wet etched surfaces. This technique provides isolation of the characteristics of the etch and clean-up procedure.
Scanning tunneling microscopy investigation of Co cluster growth and induced surface morphology changes on highly oriented pyrolitic graphite
Authors: Xu H. , Ng K. Y. S.
Published: July 2002

Co nucleation and growth on graphite were studied by scanning tunneling microscopy. Co atoms were found to adsorb preferentially on the B sites. Two- and three-dimensional Co clusters were observed, distributed uniformly on the graphite surface. The internal structure of the Co cluster is quite disordered. Cluster evolution on the surface was observed in sequential images, suggesting that atom dissociation and incorporation may be one of the mechanisms for cluster migration. Co cluster-induced superstructures were observed to localize around the clusters on the surface. The patterns of some superstructures reflect graphite’s threefold symmetry. Thermal annealing of the sample resulted in Co-promoted etching of the graphite surface.
Charges and defects in SiO2/Si systems after exposure to microwave plasmas
Authors: Chau T. T. , Chan K. W. , Kao K. C.
Published: July 2002

SiO2/Si systems with the SiO2 films produced by plasma-enhanced chemical vapor deposition (PECVD) usually have a high density of interface traps (Dit) as compared to those with the SiO2 films grown thermally because in the former the systems have been subjected to plasma radiation. To simulate the radiation effects due to microwave plasmas during the deposition of SiO2 films by PECVD, we used high-quality thermally grown SiO2 films to form SiO2/Si systems and studied the changes of the behavior of such systems after being exposed to microwave plasmas at various device temperatures. The results show that for SiO2/Si systems without metallic electrodes, the density of electron-trapped charges, Qot, in the SiO2 bulk and Dit are higher after plasma radiation. For SiO2/Si systems with aluminum electrodes on the oxide and the Si surfaces, the effects of plasma radiation on the values of Qot and Dit are less, indicating that aluminum electrodes act as protective layers partly screening the plasma radiation, but the penetration of vacuum ultraviolet light from the plasma to the SiO2 bulk produces electrons and holes in SiO2 bulk, which react with oxygen vacancies in the SiO–Si (nonbridging) bonds forming positive trapped charge in the SiO2 bulk and at the SiO2/Si interface. The value of Dit increases with increasing SiO2 film thickness and decreases as the device temperature is increased from 25 to 200 °C during radiation. A further increase in device temperature beyond 200 °C leads to a reverse trend, implying that the defect generation and annihilation processes take place simultaneously during plasma radiation. Annealing in a forming gas at 400 °C removes most of the radiation-induced defects. It should be noted that under a PECVD situation the radiation damage could be much worse particularly at the beginning of the PECVD process whereas the SiO2 film is still very thin.
Metrology of subwavelength photoresist gratings using optical scatterometry
Authors: Raymond Christopher J. , Murnane Michael R. , Sohail S. , Naqvi H. , McNeil John R.
Published: July 2002

The widths and overall profiles of dielectric grating lines can be determined by measuring the intensity of diffracted laser light from the sample over a specified range of incident beam angles. This technique, known as 2-Θ scatterometry, is able to accurately and precisely measure photoresist structures in the subhalf micron regime. Moreover, a 2-Θ scatterometer is capable of making measurements in a rapid and nondestructive manner. To test this technique we measured five identically processed wafers with nominal 0.5 μm line/0.5 μm space grating patterns. Each wafer comprised gratings in a Shipley 89131 negative photoresist exposed in a matrix of incremental exposure doses and focus settings. The scatterometry results were consistent with cross-sectional and top-down scanning electron microscopy (SEM) measurements of the same structures. The average deviation of 11 scatterometer linewidth measurements from top-down SEM measurements, over a broad exposure range, is 14.5 nm. In addition, the repeatability (1σ) of the 2-Θ scatterometer is shown to be excellent: 0.5 nm for consecutive measurements and 0.8 nm for day-to-day measurements.
Fabrication of InGaAs/InP avalanche photodiodes by reactive ion etching using CH4/H2 gases
Authors: Park Chan-Yong , Yoo Ji-Beom , Park Chongdae , Hyun Kyung-Sook , Oh Dae-Kon , Lee Yong Hee , Lee Choochon , Park Hyung-Moo
Published: July 2002

In this article, the first successful application of CH4/H2 reactive ion etching (RIE) techniques to the fabrication of an InGaAs/InP avalanche photodiode (APD) with very low dark current is reported. A partial charge sheet layer in the device periphery prepared by the CH4/H2 RIE was used for the fine control of electric field. On the top of the dry-etched partial charge sheet layer and charge plate layer, an n−-InP multiplication layer was grown by metalorganic chemical vapor deposition. Very low dark current less than 1 nA at 90% of breakdown voltage was obtained, indicating the minimal RIE-induced damages. The CH4/H2 RIE was shown to be applicable to devices operating under high electric field, such as APD’s.
Nanometer-scale modifications of gold surfaces by scanning tunneling microscope
Authors: Ohi A. , Mizutani W. , Tokumoto H.
Published: July 2002

The modification of gold surfaces with scanning tunneling microscopy in ultrahigh vacuum was investigated. At a tunneling resistance higher than 1 GΩ, a hole was created by applying a negative voltage pulse to a gold tip, and a mound by a positive one. The existence of a critical field together with the polarity dependence suggests that a mechanism of the modification would be the field evaporation of positive Au ions. On the other hand, at a low resistance, a mound adjacent to a hole was often created by the negative pulse and the current kept flowing even after the voltage pulse. These results indicate that the formation of a mound in the case of negative pulses is a result of necking after the massive transfer of gold from the surface to the tip apex. The size of the hole created by applying the negative pulse with the threshold voltage decreased as the initial tunneling resistance decreased.
Effects of resist thickness and thin-film interference in I-line and deep ultraviolet optical lithography
Authors: Xiao Jiabei , Garofalo Joseph , Cirelli Raymond , Vaidya Sheila
Published: July 2002

As the resolution of optical lithography reaches 0.35 μm and below, linewidth can no longer be predicted by aerial image alone. Accordingly, we incorporate thin-film interference within the resist/substrate stack and postexposure bake diffusion effects in our latent image formation model. The impact of resist thickness and antireflective coatings on optical proximity effect and process latitude has been examined. Taking various optical effects into account, our simulation matches the experimental data very well. Using the enhanced simulation tool, we have studied the practical process window and possible enhancement techniques.
Role of etch pattern fidelity in the printing of optical proximity corrected photomasks
Authors: Kornblit A. , DeMarco J. J. , Garofalo J. , Mixon D. A. , Novembre A. E. , Vaidya S. , Kook T.
Published: July 2002

Optical proximity effect correction has been proven to improve critical dimension control, increase overlay margins, and, when used with phase-shifting masks and/or modified illumination and mask-plane nonprinting assist features, also extend resolution and increase depth of focus of current generation lithographic exposure technology. While the potential enhancements afforded by such schemes are enticing, their successful implementation is imposing demands on mask fabrication, inspection, and repair which surpass the state of the art in industry today. This article focuses on the influence of the mask pattern fidelity on the ensuing wafer lithographic performance. Both wet and dry etch techniques were applied to an ensemble of proximity-corrected test patterns using standard binary chrome-on-glass test masks. The chrome was wet etched with polybutene sulfone as the masking resist using an optimized zero-bias process. For comparison, the same test structures delineated with a silicon containing resist were also reactive ion etched with Cl2/O2/N2 chemistry, developed to retain submicron pattern fidelity, and anisotropic absorber wall profile. Comparative wet and dry-etched mask and resulting wafer metrology results are presented for 5× i-line and 4× deep ultraviolet exposures.
Use of positive and negative chemically amplified resists in electron-beam direct-write lithography
Authors: Tritchkov Alexander , Jonckheere Rik , Van den hove Luc
Published: July 2002

This article describes the performance of available deep-ultraviolet (UV) resists for electron-beam direct-write lithography applications. Shipley XP9402, JSR KRF-K2G, and JSR KRF-L7 positive resists were evaluated for dark-field layers and Shipley XP90166 negative resist for clear-field layers. We investigate in detail the resolution capability, sensitivity, exposure latitudes and proximity, and postexposure delay (PED) time stability for isolated and dense features, as well as for contact holes. The influence of baking conditions on resolution and stability will be described. PED time effect in air and vacuum is measured for features with dimensions down to 0.2 μm. No linewidth variations are observed down to 200 nm feature size with XP9402 for delay time of 1 h in air if the postexposure bake (PEB) is done at low pressure in He ambience. Feature sizes down to 0.25 μm are kept within ±10% of the coded size, for a PED in air of 90 min if the PEB is done using a conventional hot plate in air. A process for printing 0.2 μm contact holes is established. Resolution down to 0.15 μm for dense, 0.12 μm for isolated features, and 0.2 μm for contact holes is obtained with KRF-K2G for PED of 11/2 h in air using a top coating. PED stability of more than 2 h and resolution down to 0.2 μm for contact holes is obtained with KRF-L7 without applying a top coating. For clear-field layers we focus on a negative tone process. Resolution and process latitude issues using reduced resist thickness will be described. With 560-nm-thick XP90166, resist lines smaller than 0.2 μm are resolved over polytopography with better than 25% exposure latitude. Further reducing the resist thickness to 500 nm, poly-Si gates with size down to 0.15 μm are defined on the shift register of a 0.25 μm random logic complementary metal–oxide–semiconductor deep-UV design.
Reaction modeling of chemically amplified resists for ArF excimer laser lithography
Authors: Ohfuji T. , Nakano K. , Maeda K. , Hasegawa E.
Published: July 2002

The deprotection and dissolution reactions for the ArF chemically amplified resist, consisting of a new alicyclic terpolymer with tricyclodecanyl groups and new alkylsulfonium salts are analyzed quantitatively. The deprotection of the tetrahydropyranyl groups is analyzed by Fourier transform infrared measurement, and this analysis shows that the order of acid reaction (1.4) and acid lifetime (1000 s) are the same as in other KrF resist systems. Furthermore, this analysis of dissolution behavior demonstrated that the new polymer has a dissolution rate ratio more than 1000 and a slope similar to that of the conventional novolac resist. These characteristics indicate that the performance of this new terpolymer system is satisfactory for use in lithography.
In situ monitoring of GaAs etched with a Cl2/Ar discharge in an electron cyclotron resonance source
Authors: Kahaian D. J. , Thomas S. , Pang S. W.
Published: July 2002

Quadrupole mass spectrometry (QMS) has been used as an in situ diagnostic for GaAs etching with a Cl2/Ar plasma generated by an electron cyclotron resonance source. Partial pressure from reactive species and volatile etch products down to 10−10 Torr can be detected. AsCl+x (x=1–3) products have been detected from 6×6 mm2 GaAs samples. The 145AsCl+2 signal is generally the strongest. For an increase of microwave power from 50 to 400 W, the GaAs etch rate increased from 151 to 263 nm/min and the 145AsCl+2 partial pressure increased from 0.6×10−8 to 2.8×10−8 Torr. The effects of changing source distance, rf power, and pressure were also studied and the changes in etch rate can be correlated to the mass spectrometric intensities of AsCl+x. QMS has been used to monitor the etching of surface oxide on GaAs for different dc biases on the sample. It is found that the oxide etch time is a function of ion energy. For a self-induced dc bias of −100 V, the 145AsCl+2 signal remained at 1.4×10−9 Torr for the first 15 s of etching. After the oxide was removed the signal increased to 5.5×10−9 Torr. O2 and N2 were added to determine the effects of residual gases in the plasma system. Adding 2.5% O2 in the Cl2/Ar discharge caused significant reduction in the etch rate from 171 to 43 nm/min and the 145AsCl+2 intensity was reduced from 8.0×10−9 Torr down to the noise level. For complete substitution of N2 for Ar the etch rate only dropped by 1/3 and the partial pressure of the etch products showed a similar decrease. O2 was added during an etch to determine the sensitivity of the mass spectrometer to changes in plasma conditions. The decrease in the 145AsCl+2 signal intensity follows the increase in the 16O+2 signal intensity with less than 2 s delay.
Polycrystalline tungsten and iridium probe tip preparation with a Ga+ focused ion beam
Authors: Hopkins L. C. , Griffith J. E. , Harriott L. R. , Vasile M. J.
Published: July 2002

We have used a Ga+ focused ion beam (FIB) milling technique to produce sharp scanning-probe microscope tips. The FIB procedure employs a roughly 0.2-μm-diam 20 keV Ga ion beam vector scanned in an annular pattern across the apex of an electrochemically etched wire. This method usually produces exceptionally sharp conical tips, but occasionally it generates a nearly cylindrical spike at the apex. In this paper, we show examples of the spikes, and we discuss possible mechanisms by which they are produced.
Damage characterization of ion beam exposed metal–oxide–semiconductor varactor cells by charge to breakdown measurements
Authors: Brünger W. H. , Buchmann L.-M. , Naumann F. , Friedrich D. , Finkelstein W. , Mohondro R.
Published: July 2002

Damage in thin (10 nm) oxide layers of metal–oxide–semiconductor varactor cells caused by exposures with ions, electrons, and x rays has been electrically characterized by constant-current stress time-dependent dielectric breakdown and capacitance-voltage measurements. The time-dependent dielectric breakdown investigations show measurable damage if the ions (H+; 74 keV) are allowed to penetrate the resist (300 nm PMMA) and the poly-Si layer (250 nm) to reach the oxide. This is not the case if the ions (H+2; 74 keV) are stopped inside the poly-Si layer by use of a thicker (450 nm) resist. Also for electrons and x rays the exposure with lithographic doses did not change the time-dependent dielectric breakdown curves. The capacitance-voltage measurements demonstrate that electrons and x rays which do penetrate the gate oxide cause a flatband voltage shift of nearly 400 mV. This shift could not be observed if the H+2 ions were stopped in the poly-Si buffer layer. Ions seem to create no secondary effects like x-ray generation which reach beyond the penetration depth. The measurements were performed in the unannealed state to detect all possible damage effects including those which can be removed by annealing.
Interaction of vinyltrimethylsilane with the Si(111)-(7×7) surface
Authors: Andersohn L. , Kochanski G. P. , Norman J. A. T. , Hinch B. J.
Published: July 2002

Vinyltrimethylsilane (vtms) serves as a ligand in the precursor molecule Cu(I)(vtms)(hfac) used in copper chemical vapor deposition. Investigations of the interaction of vtms with the Si(111)-(7×7) surface utilizing scanning tunneling microscopy, Auger electron spectroscopy, and thermal desorption spectroscopy (TDS) are reported. The adsorption is found to be highly site sensitive with an initial sticking coefficient most probably in excess of 0.03. With the exception of hydrogen, TDS spectra do not display vtms or any other desorbing species. Heating of the vtms covered surface to ≊530 °C leads to the formation of three-dimensional clusters which remain stable in shape and size up to temperatures as high as 1100 °C. We believe the observed clusters consist of carbon and/or SiC. In addition, the observation of (5×5) reconstructed areas between the clusters suggests the deposition of silicon during the annealing process. This indicates that vtms undergoes thermal decomposition on a silicon surface. This is in significant contrast to the observed behavior on metal and insulating surfaces. Consequently we cannot expect contaminant-free interfaces between the Si(111) substrate and copper films grown from the Cu(I)(vtms)(hfac) precursor.
Study of the function of fluorine anions in development-free vapor photolithography
Authors: Lu Jianping , Hong Xiaoyin , Liu Dan , Wang Peiqing , Chen Yongqi
Published: July 2002

Development-free vapor photolithography (DFVP) is a unique all-dry pattern transfer technique, which is based on the reaction of SiO2 with HF vapor under a polymer film in the presence of accelerators at a temperature above 100 °C. This article investigates the function of fluorine anions in DFVP. We found that the etching rate was affected not only by the concentration of fluorine anions formed with the help of accelerators, but also by the activity of fluorine anions. Based on this proposal, a novel and more effective accelerator was found. Now, it has been successfully applied to the power electronic device manufacture.
High rate and highly selective anisotropic etching for WSix/poly-Si using electron cyclotron resonance plasma
Authors: Nojiri Kazuo , Tsunokuni Kazuyuki , Yamazaki Kazuo
Published: July 2002

High rate and highly selective anisotropic etching for tungsten polycide (WSix/poly-Si) has been developed by fully utilizing such advantages of the electron cyclotron resonance plasma etcher, as high plasma density and independent control of ion energy and plasma density. Highly anisotropic etching with a WSix/poly-Si etch rate of 400 nm/min and a poly-Si/SiO2 selectivity of 50 was realized by adding O2 to Cl2 and reducing the ion energy. O2 addition increases the WSix etch rate and reduces the SiO2 etch rate, keeping the poly-Si etch rate nearly constant. This leads to the same etch rate for WSix and poly-Si, and a higher selectivity for poly-Si/SiO2. The decrease in the SiO2 etch rate was found to be mainly caused by a deposition of SiOx on the surface. The role of the O2 was found to be not only increasing the WSix etch rate and the poly-Si/SiO2 selectivity but forming a sidewall protection film to achieve an anisotropic etching.
Heterostructure interface characterization using scanning tunneling microscope excited time-resolved luminescence
Authors: Horn J. , Vogt A. , Aller I. , Hartnagel H. L. , Stehle M.
Published: July 2002

We present time-resolved luminescence measurements from n+n−n+-GaAs homostructures and from an AlGaAs/GaAs heterostructure using a scanning tunneling microscope for excitation. From the transient decay of the luminescence intensity, the minority carrier lifetime in the semiconductor can be determined. The longest lifetime measured is 200 ns for a GaAs homostructure. We also demonstrate that the presented technique can be used for the study of recombination at heterointerfaces.
Generation mechanism of distortion aberration in a symmetric magnetic doublet for an electron beam projection system
Authors: Nakasuji Mamoru , Shimizu Hiroyasu
Published: July 2002

Radial and azimuthal distortion aberrations are increasingly a function of the image side lens bore radius in the range from 1.25 to 5 times as large as the maximum image field radius. This phenomenon is inconsistent with our previous understanding. An assumption is made that these large distortions for the large bore radii come from the influence of the magnetic field of one on the other, thereby destroying the symmetry. This assumption is confirmed from the following simulation. When these distortions are calculated for the ideal case where the magnetic fields are calculated in the condition without the other lens, they are decreased to around 1/10 of those for the case where the magnetic fields are calculated in the real condition with the lenses in proximity. When the object–image distance is 800 mm and the bore radii of lens 1 are 100 and 20 mm, the residual radial and azimuthal distortions are 1.5 and 0.7 nm, the beam blur is smaller than 45 nm for the beam semiangle from 0.05 to 0.7 mrad, where the main-field and subfield sizes in the image plane are 20 mm and 250 μm, respectively, the beam energy is 100 keV, and the space charge effects are neglected.
Surface morphologies for Br-etched Si(100)-2×1: Kinetics of pit growth and step retreat
Authors: Williams F. J. , Aldao C. M. , Weaver J. H.
Published: July 2002

Temperature-dependent surface morphologies of Si(100) resulting from Br etching at 700 and 800 K have been studied using scanning tunneling microscopy. Quantitative analysis of linear pit distributions allows us to interpret the mechanisms involved in surface pattern formation. We show that linear chains growing at 800 K on 450-Å-wide terraces are in quasi-steady-state conditions in that their lengths follow the most probable Flory–Schulz distribution. Results obtained under equivalent conditions at 700 K, however, demonstrate that this distribution is not reached. The difference reflects the rate of step retreat relative to the rate of pit growth. At 700 K, pits that develop on terraces are erased before their length distributions reach quasi-steady-state values even though the overall morphology does not change. The surface morphologies that are reached at long times can then be understood by considering the temporal evolution of linear chains on terraces where quasi-steady-state conditions are not fulfilled.
Reactive ion etching of sloped sidewalls for surface emitting structures using a shadow mask technique
Authors: Jacobs B. , Zengerle R.
Published: July 2002

A novel, very simple technique for the direct adjustment of the slope of facets in a reactive ion etching process is presented. The etching process is performed by screening the sample partially with an aluminum shadow mask, which is located inside the dark space of the plasma. The sidewall angle of etched lines, defined by a pattern mask on the sample, depends strongly on the distance between the shadow mask and the sample. The investigations are carried out with a methane-hydrogen plasma. The angle of inclination of the sidewalls can be varied in a controllable manner by more than 45°. This technique is well suited to fabricate 90° reflectors, which are necessary for three-dimensional optical interconnects with planar waveguide structures. To analyze the optical quality of the etched mirror plane, the beam transformation was investigated by reflectivity measurements using a single aluminum-evaporated mirror structure, which is illuminated by a focused laser beam at a wavelength of 633 nm.