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Nov 2005

Volume 23, Issue 6, pp. 1487-1744

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When seeing is not believing: Oxygen on Ag(111), a simple adsorption system?

Angelos Michaelides, Karsten Reuter, and Matthias Scheffler

J. Vac. Sci. Technol. A 23, 1487 (2005); http://dx.doi.org/10.1116/1.2049302 (11 pages) | Cited 34 times

Online Publication Date: 14 October 2005

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A number of recent studies indicate that, under the oxygen rich conditions of oxidation catalysis, some transition metal catalysts may be covered by thin oxide overlayers. Moreover, it has been suggested that such “surface-oxide” layers are catalytically active, possibly more active than the pure metal surfaces as was traditionally assumed. This contemporary picture can be traced back to Ag catalysis, where over 30 years ago it was suggested that the top layer of Ag(111) reconstructed to an epitaxial Ag2O like overlayer upon exposure to oxygen [ Rovida et al., Surf. Sci. 43, 230 (1974) ]. Extensive experimental work, including scanning tunneling microscopy studies in which the oxide was apparently imaged with atomic resolution, as well as density-functional theory calculations, largely confirmed this interpretation. However, a review of published experimental data and new density-functional theory results presented here indicate that previous conclusions are significantly incomplete and that the structure of this original surface oxide must be reconsidered.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.47.De Metallic surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
01.30.Rr Surveys and tutorial papers; resource letters

Quest for high brightness, monochromatic noble gas ion sources

V. N. Tondare

J. Vac. Sci. Technol. A 23, 1498 (2005); http://dx.doi.org/10.1116/1.2101792 (11 pages) | Cited 31 times

Online Publication Date: 14 October 2005

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Focused ion beam (FIB) machines are key tools for state-of-the art sample preparation in electron microscopy, for characterization and repair in material sciences, for the semiconductor industry and for nanotechnology in general. Liquid-metal ion sources (LMIS) are widely used in FIB machines because they meet the minimum ion source requirements such as source brightness and reliability. However, in FIB machines, noble gas ion sources are favorable for sputtering, beam-induced etching and deposition, because the implanted ions do not change the electrical behavior of the substrate significantly. There are several efforts by various researchers to develop noble gas ion sources that can be used in FIB machines instead of LMIS. The gas ion sources could not meet the minimum ion source requirements. Therefore, LMIS are still a popular choice among FIB machine users. This review article takes a critical look at the reported efforts in the literature to develop noble gas ion sources for FIB machines.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Lg Ion sources: polarized
01.30.Rr Surveys and tutorial papers; resource letters
52.50.Dg Plasma sources
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Prediction of ultraviolet-induced damage during plasma processes in dielectric films using on-wafer monitoring techniques

Yasushi Ishikawa, Yuji Katoh, Mitsuru Okigawa, and Seiji Samukawa

J. Vac. Sci. Technol. A 23, 1509 (2005); http://dx.doi.org/10.1116/1.2049297 (4 pages) | Cited 7 times

Online Publication Date: 17 October 2005

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We measured electron-hole pairs generated in dielectric film using our developed on-wafer monitoring technique to detect electrical currents in the film during the plasma etching processes. The electron-hole pairs were generated by plasma induced ultraviolet (UV) photons, and the number of electron-hole pairs depends on the UV wavelength. In SiO2 film, UV light, which has a wavelength of less than 140 nm, generates electron-hole pairs, because the band gap energy of the film is 8.8 eV. On the other hand, in Si3N4 film, which has a band gap energy level of 5.0 eV, UV light below 250 nm induces the electron-hole pairs. Additionally, we evaluated the fluorocarbon gas plasma process that induces UV radiation damage using multilayer sensors that consisted of both SiO2 and Si3N4 stacked films. In these cases, electron-hole pair generation depended on the dielectric film structure. There were more electron-hole pairs generated in the SiO2 deposited on the Si3N4 film than in the Si3N4 deposited on the SiO2 film. As a result, our developed on-wafer monitoring sensor was able to predict electron-hole pair generation and the device characteristics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films

Reactive magnetron sputtering of hard Si–B–C–N films with a high-temperature oxidation resistance

Jaroslav Vlček, Štěpán Potocký, Jiří Čížek, Jiří Houška, Martin Kormunda, Petr Zeman, Vratislav Peřina, Josef Zemek, Yuichi Setsuhara, and Seiji Konuma

J. Vac. Sci. Technol. A 23, 1513 (2005); http://dx.doi.org/10.1116/1.2049298 (10 pages) | Cited 28 times

Online Publication Date: 17 October 2005

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Based on the results obtained for C–N and Si–C–N films, a systematic investigation of reactive magnetron sputtering of hard quaternary Si–B–C–N materials has been carried out. The Si–B–C–N films were deposited on p-type Si(100) substrates by dc magnetron co-sputtering using a single C–Si–B target (at a fixed 20% boron fraction in the target erosion area) in nitrogen-argon gas mixtures. Elemental compositions of the films, their surface bonding structure and mechanical properties, together with their oxidation resistance in air, were controlled by the Si fraction (5–75%) in the magnetron target erosion area, the Ar fraction (0–75%) in the gas mixture, the rf induced negative substrate bias voltage (from a floating potential to −500 V) and the substrate temperature (180–350 °C). The total pressure and the discharge current on the magnetron target were held constant at 0.5 Pa and 1 A, respectively. The energy and flux of ions bombarding the growing films were determined on the basis of the discharge characteristics measured for the rf discharge dominating in the deposition zone. Mass spectroscopy was used to show composition of the total ion fluxes onto the substrate and to explain differences between sputtering of carbon, silicon and boron from a composed target in nitrogen-argon discharges. The films, typically 1.0–2.4 μm thick, possessing a density around 2.4 g cm−3, were found to be amorphous in nanostructure with a very smooth surface (Ra ⩽ 0.8 nm) and good adhesion to substrates at a low compressive stress (1.0–1.6 GPa). They exhibited high hardness (up to 47 GPa) and elastic recovery (up to 88%), and extremely high oxidation resistance in air at elevated temperatures (up to a 1350 °C substrate limit).
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81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Np Adhesion
61.43.Er Other amorphous solids
81.65.Kn Corrosion protection
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.65.Mq Oxidation

Physical properties of high pressure reactively sputtered TiO2

E. San Andrés, M. Toledano-Luque, A. del Prado, M. A. Navacerrada, I. Mártil, G. González-Díaz, W. Bohne, J. Röhrich, and E. Strub

J. Vac. Sci. Technol. A 23, 1523 (2005); http://dx.doi.org/10.1116/1.2056554 (8 pages) | Cited 22 times

Online Publication Date: 17 October 2005

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We present a study of the physical properties of TiO2 thin films deposited at 200 °C on Si by high pressure reactive sputtering, a nonconventional deposition method. Just after deposition, the TiO2 films were in situ annealed in the deposition chamber at temperatures between 600 and 900 °C in O2 atmosphere. Morphological, compositional, structural and electrical characterization of the samples was performed by means of several techniques, including transmission electron microscopy, heavy-ion elastic recoil detection analysis, infrared spectroscopy, x-ray and electron diffraction and capacitance-voltage measurements. Microscopy images show that the TiO2 films are polycrystalline, and that a SiO2 film spontaneously grows at the TiO2/Si interface. The unannealed TiO2 films are oxygen rich, as shown by compositional measurements. By annealing this oxygen excess is released. For temperatures above 600 °C the TiO2 films are stoichiometric. Infrared spectroscopy and diffraction measurements show that as-deposited films are a mixture of anatase and rutile grains. During annealing there is a phase transformation, and at 900 °C the anatase phase disappears and only the rutile phase is found. The relative dielectric permittivity of the TiO2 film is calculated from capacitance-voltage measurements, and very high values in the 88–102 range are obtained.
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81.15.Cd Deposition by sputtering
62.50.-p High-pressure effects in solids and liquids
81.40.Gh Other heat and thermomechanical treatments
78.30.Hv Other nonmetallic inorganics
61.66.Bi Elemental solids
61.66.Dk Alloys
77.22.Ch Permittivity (dielectric function)
64.70.K- Solid-solid transitions
73.61.Ng Insulators

Experimental and numerical study of the optimal operation pressure within Crookes radiometer

Zhangde Lu

J. Vac. Sci. Technol. A 23, 1531 (2005); http://dx.doi.org/10.1116/1.2091198 (4 pages) | Cited 2 times

Online Publication Date: 17 October 2005

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The optimal operation pressure within Crookes radiometer is studied using experimental and direct simulation Monte Carlo (DSMC) method. The rotational rates of the rotor in the Crookes radiometer versus pressure are measured using a freely rotating rotor with two different dimensions, one is called a 20 mm rotor, which the side length of rotor blade is 20 mm, and the other is called a 10 mm one. The experiment results indicate that the optimal operation pressure varies with the side length of rotor blade and appears at 0.1 Pa and 3 Pa in the cases of 20 mm and 10 mm rotors, respectively. The pressure difference distributions of gas on the back and front surfaces of the rotor blades are simulated by DSMC method. It is indicated that the maximum pressure differences appear at 0.1–0.5 Pa in the case of the 20 mm rotor, and at 2–5 Pa in the case of the 10 mm rotor, respectively. The results are consistent with the experiment results. The velocity vector fields of gas within Crookes radiometer with the 20 mm rotor under four different pressures are also presented.
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07.60.Dq Photometers, radiometers, and colorimeters

Preparation of bead metal single crystals by electron beam heating

Bert Voigtländer, Udo Linke, H. Stollwerk, and J. Brona

J. Vac. Sci. Technol. A 23, 1535 (2005); http://dx.doi.org/10.1116/1.2101793 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2005

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For the fabrication of small metal bead crystals a gas flame is used to melt a wire forming a liquid droplet which solidifies upon cooling into a single crystal metal bead. Due to oxidation under ambient conditions bead crystals can be formed only from noble metals using this method. Here we describe a method how to fabricate bead crystals from a wide variety of metals and metal alloys (Cu, Mo, Ru, Rh, Pd, Ag, Ta, W, Re, Ir, Pt, Au, PtPd, Pd80Pt20, PtRh, AuAg, and PtIr) by electron beam heating under vacuum conditions. Narrow x-ray diffraction peaks confirm a high crystal quality of the bead crystals.
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81.05.Bx Metals, semimetals, and alloys
61.80.Fe Electron and positron radiation effects
61.82.Bg Metals and alloys
64.70.D- Solid-liquid transitions

Effect of blade-surface-roughness on the pumping performance of a turbomolecular pump

T. Sawada, M. Yabuki, W. Sugiyama, and M. Watanabe

J. Vac. Sci. Technol. A 23, 1538 (2005); http://dx.doi.org/10.1116/1.2101794 (7 pages) | Cited 1 time

Online Publication Date: 17 October 2005

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Turbomolecular pumps (TMPs) are widely used in the semiconductor and other thin film industries. Some semiconductor processes form corrosive gases such as HCl or HF as byproducts. The elements of a TMP are sometimes coated with ceramic (SiO2) film for the purpose of preventing corrosion of the TMP. The blades coated with SiO2 have relatively rough surfaces. The effect of the surface roughness of the blades on the pumping performance has been studied experimentally and theoretically. Experimental results for TMPs with two rotor disks and one stator disk show that the TMP coated with SiO2 film gives about 11% to 13% higher maximum-compression ratio than the noncoated TMP when the blade speed ratio is 0.47. The theory based on the conic peak/dimple-surface-roughness model that has been proposed by the authors explains the change in the compression ratio with the surface roughness shown in the experiment.
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07.30.Cy Vacuum pumps
89.20.Bb Industrial and technological research and development
81.65.Kn Corrosion protection
68.35.B- Structure of clean surfaces (and surface reconstruction)

Low-energy sputtering yields of tungsten and tantalum

R. P. Doerner

J. Vac. Sci. Technol. A 23, 1545 (2005); http://dx.doi.org/10.1116/1.2110385 (3 pages) | Cited 3 times

Online Publication Date: 17 October 2005

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The sputtering yields of tungsten and tantalum due to low-energy (30–125 eV) xenon ion bombardment in a plasma environment are measured both using weight loss and spectroscopic techniques. The yields of both tungsten and tantalum are practically identical and show a reduction of 3 when compared to the molybdenum yield at 125 eV and a reduction of a factor of 10 when compared to the molybdenum yield at 50 eV.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

High current pulsed electron beam treatment of AZ31 Mg alloy

Bo Gao, Shengzhi Hao, Jianxin Zou, Thierry Grosdidier, Limin Jiang, Jiyang Zhou, and Chuang Dong

J. Vac. Sci. Technol. A 23, 1548 (2005); http://dx.doi.org/10.1116/1.2049299 (6 pages) | Cited 20 times

Online Publication Date: 17 October 2005

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This paper reports, for the first time, an analysis of the effect of High Current Pulsed Electron Beam (HCPEB) on a Mg alloy. The AZ31 alloy was HCPEB treated in order to see the potential of this fairly recent technique in modifying its wear resistance. For the 2.5 J/cm2 beam energy density used in the present work, the evaporation mode was operative and led to the formation of a “wavy” surface and the absence of eruptive microcraters. The selective evaporation of Mg over Al led to an Al-rich melted surface layer and precipitation hardening from the over saturated solid solution. Due to the increase in hardness of the top surface layer, the friction coefficient values were lowered by more than 20% after the HCPEB treatments, and the wear resistance was drastically (by a factor of 6) improved. The microhardness of the HCPEB samples was also increased significantly down to a depth of about 500 μm, far exceeding the heat-affected zone (about 40 μm). This is due to the effect of the propagation of the shockwave associated with this HCPEB treatment.
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61.82.Bg Metals and alloys
61.80.Fe Electron and positron radiation effects
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.40.Pq Friction, lubrication, and wear
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Crystallization and chemical structures with annealing in ZrO2 gate insulators studied by photoemission spectroscopy and x-ray absorption spectroscopy

J. Okabayashi, S. Toyoda, H. Kumigashira, M. Oshima, K. Usuda, M. Niwa, and G. L. Liu

J. Vac. Sci. Technol. A 23, 1554 (2005); http://dx.doi.org/10.1116/1.2049300 (4 pages) | Cited 4 times

Online Publication Date: 20 October 2005

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We have performed photoemission spectroscopy and x-ray absorption spectroscopy (XAS) to investigate the chemical states and the crystallization from the amorphous structure by annealing of the ZrO2 gate insulators on Si. Angular-dependent core-level photoemission spectra revealed the chemical states including the interfacial layers. Annealing-temperature dependence in valence-band spectra and XAS revealed the relationship between crystallization and the changes in spectral line shapes although core-level photoemission spectra are not sensitive to the crystallization. Valence-band spectra are split into double peak structures and the line shapes of O K-edge x-ray absorption spectra become sharp by the annealing at 800 °C corresponding to the crystallization temperature of amorphous ZrO2 films. It suggests that the valence-band spectra and XAS can be utilized to characterize the crystallization features in the gate insulators.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.Dm X-ray absorption spectra
81.40.Gh Other heat and thermomechanical treatments
73.20.At Surface states, band structure, electron density of states

Modeling complex vapor-transport systems using Monte-Carlo techniques: Radioactive ion beam applications

Y. Zhang and G. D. Alton

J. Vac. Sci. Technol. A 23, 1558 (2005); http://dx.doi.org/10.1116/1.2056553 (10 pages) | Cited 1 time

Online Publication Date: 20 October 2005

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A Monte-Carlo code has been developed that can be used to optimally design vapor transport systems for isotope-separator-on-line-based radioactive ion beam facilities in lieu of costly iterative trial and error design methods. The code provides a powerful means for delineating diffusion-release and effusive-flow (molecular-flow) processes, in combination, the delay times of which are principal intensity limiters of short-lived radioactive species at such facilities. The code provides time dependent particle evacuation, average distance traveled per particle, and particle/wall interaction information during particle transit through a given vapor-transport system under molecular-flow conditions, independent of the chemistry between particles of interest and the materials of which the transport system are constructed. In addition, the code provides powerful graphical insight via particle trajectories that serve as strong assets in arriving at a final design by identifying regions within the transport system where hold-up times are problematical. In this article, we compare simulation and experimental measurement results for transport of noble gases through selected vapor-transport systems using both cosine and isotropic particle re-emission distributions about the normal to the surface following adsorption (isotropic re-emission distributions are found to be in close agreement with experimental measurements) and describe a concept vapor-transport system that reduces transport times over those of conventional systems by >two orders of magnitude.
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51.20.+d Viscosity, diffusion, and thermal conductivity
51.10.+y Kinetic and transport theory of gases
68.03.Fg Evaporation and condensation of liquids

Crystallization and segregation in vitreous rutile films annealed at high temperature

M. A. Omari, R. S. Sorbello, and C. R. Aita

J. Vac. Sci. Technol. A 23, 1568 (2005); http://dx.doi.org/10.1116/1.2091094 (7 pages) | Cited 8 times

Online Publication Date: 20 October 2005

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Vitreous titania films with rutile short-range order were sputter deposited on unheated fused silica substrates, sequentially annealed at 973 and 1273 K, and examined by Raman microscopy, scanning electron microscopy, and x-ray diffraction. A segregated microstructure developed after the 1273 K anneal. This microstructure consists of supermicron-size craters dispersed in a matrix of submicron rutile crystals. Ti–O short-range order in the craters is characteristic of a mixture of two high pressure phases, m-TiO2 (monoclinic P21/c space group) and α-TiO2 (tetragonal Pbcn space group). We calculated that a high average compressive stress parallel to the substrate must be accommodated in the films at 1273 K, caused by the difference in the thermal expansion coefficients of titania and fused silica. The formation of the segregated microstructure is modeled by considering two processes at work at 1273 K to lower a film’s internal energy: crystallization and nonuniform stress relief. The Gibbs–Thomson relation shows that small m-TiO2 crystallites are able to form directly from vitreous TiO2 at 1273 K. However, the preferred mechanism for forming α-TiO2 is likely to be by epitaxial growth at crystalline rutile twin boundaries (secondary crystallization). Both phases are denser than crystalline rutile and reduce the average thermal stress in the films.
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64.70.K- Solid-solid transitions
64.75.-g Phase equilibria
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
61.72.Mm Grain and twin boundaries
65.40.De Thermal expansion; thermomechanical effects
68.60.Bs Mechanical and acoustical properties
78.66.-w Optical properties of specific thin films
78.30.Hv Other nonmetallic inorganics
81.40.Gh Other heat and thermomechanical treatments

Diamond microstructures fabricated using silicon molds

M. C. Salvadori, D. R. Martins, R. D. Mansano, P. Verdonck, and I. G. Brown

J. Vac. Sci. Technol. A 23, 1575 (2005); http://dx.doi.org/10.1116/1.2091095 (4 pages) | Cited 2 times

Online Publication Date: 20 October 2005

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We have fabricated diamond microstructures using silicon molds into which microcrystalline diamond was deposited by plasma assisted chemical vapor deposition. Prior to diamond deposition the silicon molds were seeded with the diamond powder of two different grain sizes, math and 1 μm. Scanning electron microscopy and atomic force microscopy were used to view and characterize the resultant diamond microstructures. Analysis of the diamond replicas indicates better reproduction fidelity for the math μm diamond powder, and a surface roughness of 20 nm.
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81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
52.77.Dq Plasma-based ion implantation and deposition
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)

Morphology evolution on diamond surfaces during ion sputtering

T. M. Mayer, D. P. Adams, M. J. Vasile, and K. M. Archuleta

J. Vac. Sci. Technol. A 23, 1579 (2005); http://dx.doi.org/10.1116/1.2110386 (9 pages) | Cited 12 times

Online Publication Date: 20 October 2005

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We have conducted an extensive study of the evolution of surface morphology of single crystal diamond surfaces during sputtering by 20 keV Ga+ and Ga++H2O. We observe the formation of well-ordered ripples on the surface for angles of incidence between 40 and 70°. We have also measured sputter yields as a function of angle of incidence, and ripple wavelength and amplitude dependence on angle of incidence and ion fluence. Smooth surface morphology is observed for <40°, and a transition to a step-and-terrace structure is observed for >70°. The formation and evolution of well-ordered surface ripples is well characterized by the model of Bradley and Harper, where sputter-induced roughening is balanced by surface transport smoothing. Smoothing is consistent with an ion-induced viscous relaxation mechanism. Ripple amplitude saturates at high ion fluence, confirming the effect of nonlinear processes. Differences between Ga+ and Ga++H2O in ripple wavelength, amplitude, and time to saturation of amplitude are consistent with the increased sputter yield observed for Ga++H2O. For angle of incidence <40°, an ion bombardment-induced “atomic drift” mechanism for surface smoothing may be responsible for suppression of ripple formation. For Ga++H2O, we observe anomalous formation of very large amplitude and wavelength, poorly ordered surface ridges for angle of incidence near 40°. Finally, we observe that ripple initiation on smooth surfaces can take place by initial stochastic roughening followed by evolution of increasingly well-ordered ripples.
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61.80.Jh Ion radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

On the origin of a-type threading dislocations in GaN layers

Y. B. Kwon, J. H. Je, P. Ruterana, and G. Nouet

J. Vac. Sci. Technol. A 23, 1588 (2005); http://dx.doi.org/10.1116/1.2049301 (4 pages) | Cited 8 times

Online Publication Date: 24 October 2005

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The origin of threading dislocations (TDs) in GaN epitaxial layers grown on sapphire (0001) substrate is investigated using moiré fringes from plan-view transmission electron microscopy. The studied samples are nucleation layers deposited at 560 °C for times ranging from 20 s to 180 s. This initial stage growth gives rise to islands which are randomly rotated and relaxed with misfit dislocations. The islands that start to coalesce from 60 s growth time keep this random orientation and this leads to the bending of 60° misfit dislocations in the interface plane to form a-type TDs inside low angle boundaries.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Etching of high aspect ratio features in Si using SF6/O2/HBr and SF6/O2/Cl2 plasma

Sergi Gomez, Rodolfo Jun Belen, Mark Kiehlbauch, and Eray S. Aydil

J. Vac. Sci. Technol. A 23, 1592 (2005); http://dx.doi.org/10.1116/1.2049303 (6 pages) | Cited 7 times

Online Publication Date: 24 October 2005

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We have investigated the etching of high aspect ratio holes ( ∼ 4 μm deep, ∼ 0.2 μm diameter) in silicon using plasmas maintained in mixtures of SF6, O2, and HBr or Cl2 gases. The etching experiments were conducted in a low pressure (25 mTorr), high density, inductively coupled plasma etching reactor with a planar coil. Visualization of the profiles with scanning electron microscopy is used in conjunction with plasma diagnostics such as optical emission and mass spectroscopies to understand the key factors that control the feature profile shape and etch rate. HBr addition to SF6/O2 mixture reduces the F-to-O ratio, increases sidewall passivation and reduces mask undercut. Addition of Cl2 to SF6/O2 discharge also decreases the F-to-O ratio, but Cl-enhanced F chemical etching of silicon significantly increases the mask undercut and lateral etching. In both SF6/O2/HBr and SF6/O2/Cl2 mixtures, reduction of O2 flow rate and subsequent increase of the halogen-to-O ratio eventually results in significant lateral etching because of the lack of oxygen required to form a siliconoxyhalide passivating film on the sidewalls.
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52.77.Bn Etching and cleaning
81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
81.65.Rv Passivation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.30.-q Plasma dynamics and flow
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Silicon etch by fluorocarbon and argon plasmas in the presence of fluorocarbon films

Joseph J. Végh, David Humbird, and David B. Graves

J. Vac. Sci. Technol. A 23, 1598 (2005); http://dx.doi.org/10.1116/1.2049304 (7 pages) | Cited 15 times

Online Publication Date: 24 October 2005

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Molecular dynamics simulations have been conducted to study the mechanisms of silicon etch in the presence of fluorocarbon species (CF and C4F4), F atoms and Ar+ ions. The specific goal of the study was to find conditions in which steady Si etching occurs in the presence of a fluorocarbon (FC) film. Results indicate that if incident species are not properly chosen for the simulation, either steady etching is observed with no FC film present, or a FC film is present (often continuously growing in thickness) with no steady etching of the underlying film. With the proper set of incident species, C/F ratio, neutral/ion flux ratio, and ion energy, we observed steady Si etching in the presence of a steady FC film. We also observed that the thicker the FC film, the lower the etch yield. A sufficiently thick film results in no etching and a continuous deposition. Simulation results are in qualitative agreement with analogous experimental measurements. The key is to find FC species that will stick with a high probability, forming a relatively open and porous film. In addition, our results suggest that this film will fluctuate in thickness from impact to impact, resulting in better transport of incident F and SiFx species, to and from the underlying Si, respectively. Steady state etching appears unlikely if the overlying FC film has the hard, dense, cross-linked character of films deposited from energetic fluorocarbon species. The basic mechanisms of etching, and the composition and depth of the underlying layers appear to be largely unaffected by the presence of the FC film. We have found ion energy deposition at a range of depths to be crucially important in the creation and transport of etch products. Ion energy deposition, ion-induced mixing, and reaction promotion are the key processes in all of the ion-assisted processes simulated, including the present case of etching in the presence of FC film. The FC film retards etching by slowing the rate at which etchants (e.g., F) reach the underlying film and the rate at which etch products leave. If the film is sufficiently thick or dense, etching will cease.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
64.75.-g Phase equilibria
52.77.Bn Etching and cleaning

Ammonium chloride complex formation during downstream microwave ammonia plasma treatment of parylene-C

K. G. Pruden and S. P. Beaudoin

J. Vac. Sci. Technol. A 23, 1605 (2005); http://dx.doi.org/10.1116/1.2049305 (5 pages) | Cited 2 times

Online Publication Date: 24 October 2005

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In this work, parylene-C is exposed to the effluent from a microwave ammonia plasma with a goal of producing primary amine groups on the parylene-C. These amine groups are desired as sites for the attachment of various biomolecules that will influence the biocompatibility of the parylene-C. Ammonia plasma treatment is an effective approach for creating amine species on polymers. In this work, attenuated total reflectance infrared spectroscopy studies showed that no primary amine groups resulted from this treatment of parylene-C. Instead, reactive nitrogen-bearing radicals from the plasma appear to have been complexed by chlorine in the polymer. The formation of these complexes scavenged nitrogen-bearing radicals from the plasma and prevented the formation of nitrogenous species, such as the desired primary amines, on the parylene-C. These results are consistent with results of ammonia plasma treatment of other chlorinated polymers and suggest that alternative approaches are required to create nitrogen-bearing species on parylene-C.
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52.77.-j Plasma applications

Electron conditioning of technical aluminium surfaces: Effect on the secondary electron yield

F. Le Pimpec, R. E. Kirby, F. K. King, and M. Pivi

J. Vac. Sci. Technol. A 23, 1610 (2005); http://dx.doi.org/10.1116/1.2049306 (9 pages) | Cited 6 times

Online Publication Date: 24 October 2005

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The effect of electron conditioning on commercially available aluminium alloys 1100 and 6063 was investigated. Contrary to the assumption that electron conditioning, if performed long enough, can reduce and stabilize the secondary electron yield (SEY) to low values ( ⩽ 1.3, the value for many pure elements), the SEY of aluminium did not go lower than 1.8. In fact, it reincreased with continued electron exposure dose. The SEY was monitored as a function of electron dose and the surface chemistry was measured with x-ray photoelectron spectroscopy (XPS). The XPS carbon and aluminium core levels showed that the late increase in SEY is due to electron desorption of adsorbed gas, thereby exposing high-SEY Al2O3.©
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79.20.Hx Electron impact: secondary emission
68.49.Jk Electron scattering from surfaces
68.43.Mn Adsorption kinetics
79.70.+q Field emission, ionization, evaporation, and desorption

Hafnium diboride thin films by chemical vapor deposition from a single source precursor

Sreenivas Jayaraman, Yu Yang, Do Young Kim, Gregory S. Girolami, and John R. Abelson

J. Vac. Sci. Technol. A 23, 1619 (2005); http://dx.doi.org/10.1116/1.2049307 (7 pages) | Cited 14 times

Online Publication Date: 24 October 2005

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High quality, stoichiometric thin films of hafnium diboride are deposited by chemical vapor deposition from the precursor Hf[BH4]4 at deposition temperatures as low as 200 °C. An activation energy of 0.43 eV(41 kJ/mol) is obtained for the overall process as monitored by temperature programmed reaction studies. Films deposited at low temperatures (<500 °C) are structurally amorphous to x-ray diffraction; a 12 nm thick film is sufficient to prevent copper diffusion into silicon during a 600 °C anneal for 30 min. Films deposited above 500 °C are crystalline, but have a columnar microstructure with low density. All the films are metallic, but the low temperature amorphous films have the lowest resistivity ∼ 440 μΩ cm. The process is also highly conformal, e.g., a 65 nm wide trench with a 19:1 depth-width aspect ratio was coated uniformly.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
61.43.Dq Amorphous semiconductors, metals, and alloys
73.61.At Metal and metallic alloys

Dry-etch of As2S3 thin films for optical waveguide fabrication

Weitang Li, Yinlan Ruan, Barry Luther-Davies, Andrei Rode, and Rod Boswell

J. Vac. Sci. Technol. A 23, 1626 (2005); http://dx.doi.org/10.1116/1.2049308 (7 pages) | Cited 11 times

Online Publication Date: 24 October 2005

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Plasma etching to As2S3 thin films for optical waveguide fabrication has been studied using a helicon plasma etcher. The etching effects using the processing gases or gas mixtures of O2, Ar, and CF4 were compared. It was found that the O2 plasma had no chemical etching effect to the As2S3, but it could oxidize the surface of the As2S3. The Ar plasma provided a strong ion sputtering effect to the films. The CF4 plasma exhibited a too strong chemical etch to the As2S3, leading to serious undercutting and very rough sidewalls of the waveguides. Ar and O2 gases were compared as the additives to dilute the CF4 processing gas. The etch rate of the As2S3 was reduced dramatically from over 2000 nm/min to a few hundred nm/min when the pure CF4 gas was heavily diluted with 70% Ar or O2 gas. The undercutting and sidewall roughness of the etched waveguides were also decreased greatly when above dilution was made, which was associated with an enormous weakening of the isotropic chemical etch induced by neutral reactants in the plasma. In addition, the O2 showed a better dilution effect than the Ar in reducing the etch rate of the As2S3; and the O2/CF4 plasma also enabled a much lower erosion rate to Al mask layers than the Ar/CF4 plasma at similar plasma conditions. The As2S3 waveguides with near vertical and very smooth sidewalls were obtained using an optimized O2/CF4 plasma. Moreover, the etching behaviors and mechanisms were explained base on the etching results, and on the characteristics of the applied plasma diagnosed using Langmuir probe and optical spectroscopy techniques.
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52.77.Bn Etching and cleaning
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
85.40.Hp Lithography, masks and pattern transfer
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
81.65.Mq Oxidation
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.65.Cf Surface cleaning, etching, patterning

Low-temperature synthesis of gallium nitride thin films using electron cyclotron resonance plasma assisted pulsed laser deposition from a GaAs target

J. Sun, A. M. Wu, N. Xu, Z. F. Ying, X. K. Shen, Z. B. Dong, J. D. Wu, and L. Q. Shi

J. Vac. Sci. Technol. A 23, 1633 (2005); http://dx.doi.org/10.1116/1.2091093 (5 pages) | Cited 1 time

Online Publication Date: 24 October 2005

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Using reactive pulsed laser deposition assisted by electron cyclotron resonance (ECR) plasma, we have synthesized GaN thin films from a polycrystalline GaAs target at low temperatures. This was achieved by ablating the GaAs target in the reactive environment of a nitrogen plasma generated from ECR microwave discharge in pure nitrogen gas and depositing the films with concurrent bombardment by the low-energy nitrogen plasma stream. High-energy ion backscattering spectroscopy analysis shows that the synthesized films are gallium rich. Characterizations by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirm the presence of GaN bonds in the films. The recorded absorption spectrum also reveals GaN stretching mode characteristic of the hexagonal GaN phase. The synthesized GaN films are transparent in the visible region and have a band gap of 3.38 eV. Optical emission from the plume during film deposition reveals that the plume created by pulsed laser ablation of the GaAs target consists mainly of monoatomic atoms and ions of gallium and arsenic. Mechanisms responsible for the formation of GaN molecules and the growth of GaN films are also discussed.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
52.77.Dq Plasma-based ion implantation and deposition
76.40.+b Diamagnetic and cyclotron resonances
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.30.Fs III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds

Thermal reaction of polycrystalline SiC with XeF2

Morimichi Watanabe, Yukimasa Mori, Hiroaki Sakai, Takashi Iida, Shunsuke Koide, Eri Maeta, Kyoichi Sawabe, and Kosuke Shobatake

J. Vac. Sci. Technol. A 23, 1638 (2005); http://dx.doi.org/10.1116/1.2110387 (9 pages) | Cited 1 time

Online Publication Date: 24 October 2005

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Studies on the thermal reaction behavior of polycrystalline cubic silicon carbide (SiC) with effusive xenon difluoride (XeF2) have been carried out over the sample temperature (Ts) range from 300 to 900 K using molecular beam quadrupole mass spectrometry combined with a time-of-flight technique and ex situ surface analyses, i.e., x-ray photoelectron spectroscopy (XPS) and scanning Auger microscopy (SAM). Above Ts = 700 K, the reaction product desorbed from the SiC surface was identified as SiF4. The flux intensity of SiF4 increases monotonically as a function of Ts above 700 K. The flux intensity of XeF2 desorbed from the SiC surface decreases above Ts = 700 K, and at Ts = 900 K, approximately 10% of the incident XeF2 was found to be consumed by the thermal reaction. No ions at m/e = 31 (CF+), 50 (CF2+), and 69 (CF3+) to be ascribed to carbon fluoride species were detected under the present experimental conditions, and thus C atoms in SiC were found to remain as residue. From the XPS and SAM observations of the SiC samples exposed to XeF2 vapor at 1.8×10−4 Torr, we find that fluorination of a native oxide layer formed on the SiC surface takes place at Ts = 300 K. At Ts = 520 K, the native oxide layer was partially removed from the surface, and the presence of a reaction layer composed of partially fluorinated C atoms was observed. As Ts is increased above 520 K, the reaction layer becomes thicker. Above Ts = 700 K, a thick reaction layer mainly composed of C atoms is formed, while only the near-surface reaction layer is fluorinated. The fast desorption of SiF4 products reduces the Si concentration in the SiC surface and the residual C atoms having comprised the SiC lattice are left as the reaction layer.
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68.43.Mn Adsorption kinetics
82.80.Rt Time of flight mass spectrometry
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Thermal reaction of polycrystalline AlN with XeF2

Morimichi Watanabe, Yukimasa Mori, Takahiro Ishikawa, Hiroaki Sakai, Takashi Iida, Keijiro Akiyama, Shogo Narita, Kyoichi Sawabe, and Kosuke Shobatake

J. Vac. Sci. Technol. A 23, 1647 (2005); http://dx.doi.org/10.1116/1.2110395 (10 pages)

Online Publication Date: 24 October 2005

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Detailed studies on the thermal reaction behavior of polycrystalline aluminum nitride (AlN) with effusive xenon difluoride (XeF2) have been carried out over the sample temperature (Ts) range from 300 to 920 K using molecular beam mass spectrometry combined with a time-of-flight technique and ex situ surface analyses, i.e., X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy (SEM). The species desorbed from the AlN/XeF2 system were monitored using molecular beam mass spectrometry, as a function of sample temperature. Above Ts = 800 K, the desorbed reaction products were identified as N2 and AlF3, and their flux intensities increase monotonically as the sample temperature is increased. The flux intensity of XeF2 desorbed after physisorption to the AlN surface is found to decrease as Ts is raised above Ts = 800 K, and approximately one half of the incoming XeF2 is consumed by the thermal reaction at 920 K. The results of surface analyses show that the thermal reaction of AlN with XeF2 starts at approximately Ts = 700 K, forming a reaction layer composed of AlF3. The AlF3 layer becomes thick as Ts is increased from Ts = 700–800 K. Above Ts = 800 K, however, as a result of fast desorption of AlF3 and F atoms from the AlF3 layer, only partially fluorinated AlFx (x = 1 and/or 2) layers are formed and the bulk AlN is revealed again. The SEM photographs indicate that the surfaces exposed above Ts = 850 K are strongly etched but a slight change is observed at Ts ⩽ 800 K. On the basis of these results, three reaction stages are proposed for the AlN/XeF2 reaction depending on the sample temperature range: Stage 1 (300 ⩽ Ts<700 K); no reaction, stage 2 (700 ⩽ Ts<800 K); surface fluorination, and stage 3 (800 ⩽ Ts); etching. At stage 3, AlF3 formed on the surface starts to evaporate and fast etching proceeds, since the vapor pressure of AlF3 is high enough in this temperature range.
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68.43.Mn Adsorption kinetics
82.80.Rt Time of flight mass spectrometry
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Fv Electron impact: Auger emission
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.65.Cf Surface cleaning, etching, patterning

Effect of surface temperature on plasma-surface interactions in an inductively coupled modified gaseous electronics conference reactor

Baosuo Zhou, Eric A. Joseph, Sanket P. Sant, Yonghua Liu, Arun Radhakrishnan, Lawrence J. Overzet, and Matthew J. Goeckner

J. Vac. Sci. Technol. A 23, 1657 (2005); http://dx.doi.org/10.1116/1.2049309 (11 pages) | Cited 12 times

Online Publication Date: 25 October 2005

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The effect of wall temperature, from 50 to 200 °C, on gas phase chemistry and substrate etching rates has been studied in inductively coupled CF4 plasma under two distinctive initial wall conditions, namely “clean” and “seasoned.” During plasma etching, we found that the gas phase chemistry exhibits a weak dependence on the initial wall cleanliness when the wall is either cold (50 °C) or hot (200 °C). In the mid-temperature range, the wall cleanliness can strongly affect gas phase chemistry. The study of temperature dependence of the fluorocarbon film deposition on the substrate indicates that ion-assisted incorporation, direct ion incorporation and ion-assisted desorption are the major factors determining film growth and removal. Ion-assisted incorporation and desorption are surface-temperature-dependent, while direct ion incorporation is independent of the surface temperature.
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52.40.Hf Plasma-material interactions; boundary layer effects

Interplay of hydrogen and deposition temperature in optical properties of hot-wire deposited a‐Si:H Films: Ex situ spectroscopic ellipsometry studies

S. Gupta, B. R. Weiner, and G. Morell

J. Vac. Sci. Technol. A 23, 1668 (2005); http://dx.doi.org/10.1116/1.2056552 (8 pages) | Cited 4 times

Online Publication Date: 25 October 2005

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High-quality hydrogenated amorphous silicon (a‐Si:H) thin films were grown by hot-wire chemical vapor deposition on glass (Corning 7059) using silane with relatively high hydrogen albeit avoiding the formation of microcrystalline hydrogenated silicon. They were grown as a function of substrate temperature (TS) ranging from 50 to 515 °C resulting in the corresponding hydrogen concentration [CH] variation from 20.0 to 0.2 at. %. They are optically examined ex situ using spectroscopic phase modulated ellipsometry from near IR to near UV (i.e., 1.5–5.0 eV) obtaining pseudo-dielectric function (〈εr(E)〉,〈εi(E)〉) for investigating the role of hydrogen in network disorder. The raw ellipsometry data were modeled using Bruggeman effective medium theory and the dispersion relations for the amorphous semiconductors. A two-layer model consisting of a top surface roughness layer (dS) containing an effective medium mix of 50% a‐Si:H and 50% voids and a single “bulk” layer (dB) of 100% a‐Si:H was used to simulate the data reasonably well. We performed these simulations by nonlinear least-square regression analysis and it was possible to estimate the true dielectric function, energy band gap (Eg), film thickness (dSE), bulk void fraction, surface roughness layer (dS), and confidence limits (χ2). Moreover, it is shown that the Tauc–Lorentz model fits the ellipsometry data reasonably well and helps elucidating the layered structure of a‐Si:H thin films. We also compared the optical band gap determined using ellipsometry modeling and the Tauc gap. We discuss the variation of the deduced parameters in terms of role of TS (T role) or of hydrogen (H role) yielding possible physical meaning and found an agreement with the excitation dependent Raman spectroscopy results reported earlier [ S. Gupta, R. S. Katiyar, G. Morell, S. Z. Weisz, and J. Balberg, Appl. Phys. Lett. 75, 2803 (1999) ]. Atomic force microscopy was also used to validate the simulations. These analyses led to a correlation between the films’ microstructure (or network disorder) and their electronic properties for electronic device applications, in general and for photovoltaic applications, in particular.
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78.66.Db Elemental semiconductors and insulators
61.43.Dq Amorphous semiconductors, metals, and alloys
78.66.Jg Amorphous semiconductors; glasses
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Optical properties of La-based high-K dielectric films

E. Cicerrella, J. L. Freeouf, L. F. Edge, D. G. Schlom, T. Heeg, J. Schubert, and S. A. Chambers

J. Vac. Sci. Technol. A 23, 1676 (2005); http://dx.doi.org/10.1116/1.2056555 (5 pages) | Cited 17 times

Online Publication Date: 25 October 2005

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We have characterized thin films of LaScO3 and LaAlO3 which were grown by molecular beam deposition on Si substrates. Samples of LaScO3 were also grown by pulsed laser deposition on MgO substrates. Using transmission studies between 1.5 and 6 eV, we have established that low temperature deposition leads to a reduced band gap with respect to the bulk crystal. Furthermore, using spectroscopic ellipsometry from 5 to 9 eV we observe substantial differences in near-band gap absorption between thin and thicker films for both materials. We obtain a band gap of 5.84 eV for the thinner film of LaAlO3, whereas we find a band gap of 6.33 eV for the thicker film of LaAlO3. Similarly we find band gaps of 5.5 and 5.96 eV, respectively, for thin and thick films of LaScO3.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
71.20.-b Electron density of states and band structure of crystalline solids
78.66.-w Optical properties of specific thin films

Indium growth on Si(100)-2×1 by femtosecond pulsed laser deposition

M. A. Hafez, M. S. Hegazy, and H. E. Elsayed-Ali

J. Vac. Sci. Technol. A 23, 1681 (2005); http://dx.doi.org/10.1116/1.2073427 (6 pages) | Cited 1 time

Online Publication Date: 25 October 2005

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Indium was grown on Si(100)-2×1 at room temperature by femtosecond pulsed laser deposition. Reflection high-energy electron diffraction (RHEED) was performed in situ to study film morphology and in-plane lattice spacing. Indium was found to grow on Si(100)-2×1 by the Stranski–Krastanov mode. The initial two-dimensional In layer formed in the In-2×1 structure with a lattice constant of 3.65 Å. The full-width at half-maximum (FWHM) of the specular peak decreased during the growth, indicating an increase of the In islands size. Further In growth on the initial In-2×1 layer showed the formation of hexagonal, elongated, and hemispherical islands when examined ex situ by atomic force microscopy. The hexagonal islands were faceted and varied in size from ∼ 170 to  ∼ 400 nm, with an average height of 5 nm. The elongated islands showed preferential growth orientation and had a length and height of ∼ 200 and ∼ 60 nm, respectively.
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81.15.Fg Pulsed laser ablation deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)

Direct imprinting using soft mold and gas pressure for large area and curved surfaces

Jer-Haur Chang, Fang-Sung Cheng, Chi-Chung Chao, Yung-Chun Weng, Sen-Yeu Yang, and Lon A. Wang

J. Vac. Sci. Technol. A 23, 1687 (2005); http://dx.doi.org/10.1116/1.2073447 (4 pages) | Cited 17 times

Online Publication Date: 25 October 2005

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In this paper we report a simple and effective method that renders direct imprinting of sub-micron structures onto PMMA resist coated on large area and curved substrates using the PDMS mold on a closed chamber. Nitrogen gas was employed to generate a uniform pressure. The patterns of the soft mold could be replicated with high quality over an entire 12 in. resist-coated area. The process was further successfully applied to the imprinting of a curved substrate.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Etching characteristics of high-k dielectric HfO2 thin films in inductively coupled fluorocarbon plasmas

Kazuo Takahashi, Kouichi Ono, and Yuichi Setsuhara

J. Vac. Sci. Technol. A 23, 1691 (2005); http://dx.doi.org/10.1116/1.2073468 (7 pages) | Cited 7 times

Online Publication Date: 25 October 2005

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Inductively coupled fluorocarbon (CF4/Ar and C4F8/Ar) plasmas were used to etch HfO2, which is a promising high-dielectric-constant material for the gate of complementary metal-oxide-semiconductor devices. The etch rates of HfO2 in CF4/Ar plasmas exceeded those in C4F8/Ar plasmas. The tendency for etch rates to become higher in fluorine-rich (high F/C ratio) conditions indicates that HfO2 can be chemically etched by fluorine-containing species. In C4F8/Ar plasmas with a high Ar dilution ratio, the etch rate of HfO2 increased with increasing bias power. The etch rate of Si, however, decreasd with bias power, suggesting that the deposition of carbon-containing species increased with increasing the power and inhibited the etching of Si. The HfO2/Si selectivity monotonically increased with increasing power, then became more than 5 at the highest tested bias power. The carbon-containing species to inhibit etching of Si play an important role in enhancing the HfO2/Si selectivity in C4F8/Ar plasmas.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
52.77.Bn Etching and cleaning
81.05.Cy Elemental semiconductors
77.55.-g Dielectric thin films
81.65.Cf Surface cleaning, etching, patterning

In situ photovoltage measurements using femtosecond pump-probe photoelectron spectroscopy and its application to metal–HfO2–Si structures

Daeyoung Lim and Richard Haight

J. Vac. Sci. Technol. A 23, 1698 (2005); http://dx.doi.org/10.1116/1.2083909 (8 pages) | Cited 4 times

Online Publication Date: 25 October 2005

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We report in situ photovoltage measurements of metal-oxide-semiconductor (MOS) structures using femtosecond pump-probe photoelectron spectroscopy. This technique, which employs a single femtosecond laser, is a noncontact noninvasive measurement method for extracting the magnitude and direction of the band bending in Si substrates covered with high-k dielectric stacks and thin metal layers. We studied MOS structures consisting of thin metal layers of both high and low work functions deposited atop HfO2 grown on Si (100) substrates during various phases of processing. Excitation of the sample by a pulse of laser light flattens the bands of the Si substrate, which can be monitored as a rigid shift in the observed photoelectron spectrum. Particular attention is given to the potential effects of electron-hole recombination and metallic screening on the magnitude of the shift in the photoelectron spectra. We find that while as-deposited metals follow the metal-induced gap state model, thermal annealing of these structures drives the interface silicon Fermi energy to midgap. Charged oxygen-vacancy related defects at or near the HfO2/metal interface contribute significantly to the Fermi energy shift.
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72.40.+w Photoconduction and photovoltaic effects
78.47.-p Spectroscopy of solid state dynamics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Optical band gaps and composition dependence of hafnium–aluminate thin films grown by atomic layer chemical vapor deposition

N. V. Nguyen, S. Sayan, I. Levin, J. R. Ehrstein, I. J. R. Baumvol, C. Driemeier, C. Krug, L. Wielunski, P. Y. Hung, and Alain Diebold

J. Vac. Sci. Technol. A 23, 1706 (2005); http://dx.doi.org/10.1116/1.2091096 (8 pages) | Cited 30 times

Online Publication Date: 25 October 2005

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We report the optical properties of unannealed hafnium–aluminate (HfAlO) films grown by atomic layer chemical vapor deposition (ALCVD) and correlate them with the aluminum contents in the films. Vacuum ultraviolet spectroscopic ellipsometry (VUV-SE), high-resolution transmission electron microscopy (HRTEM), channeling Rutherford backscattering spectrometry (RBS), and resonant nuclear reaction analysis (NRA) were employed to characterize these films. In the analyses of ellipsometry data, a double Tauc–Lorentz dispersion produces a best fit to the experimental VUV-SE data. As a result, the determined complex pseudodielectric 〈ε〉 functions of the films clearly exhibit a dependency on the aluminum densities measured by RBS and NRA. We show that the optical fundamental band gap Eg shifts from 5.56±0.05 eV for HfO2 to 5.92±0.05 eV for HfAlO. The latter was grown by using an equal number of pulses of H2O/HfCl4 and H2O/TMA (trimethylaluminum) precursors in each deposition cycle for HfO2 and Al2O3, respectively. The shift of Eg to higher photon energies with increasing aluminum content indicates that intermixing of HfO2 and Al2O3 occurred during the ALCVD growth process. We found that Eg varies linearly with the mole fraction x of Al2O3 in the alloy (HfO2)x(Al2O3)1−x, but has a parabolic dependency with the aluminum density. We also observed a consistent decrease in the magnitudes of the real 〈ε1〉 and imaginary 〈ε2〉 part of 〈ε〉 of HfAlO films with respect to those of HfO2 as the Al density increased. The absence of the ≈ 5.7 eV peak in the 〈ε〉 spectrum, which was previously reported for polycrystalline HfO2 films, indicates that these films are amorphous as confirmed by their HRTEM images.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
78.40.Pg Disordered solids
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
77.22.Ch Permittivity (dielectric function)

Quantitative analysis of sputter processes in a small magnetron system

Ivo Knittel, Marc Gothe, and Uwe Hartmann

J. Vac. Sci. Technol. A 23, 1714 (2005); http://dx.doi.org/10.1116/1.2091197 (7 pages) | Cited 2 times

Online Publication Date: 25 October 2005

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Sputter deposition of titanium in argon from a small circular magnetron is characterized. The dependence of the deposition rate on pressure, power, and target–substrate distance has been measured. A framework for the application of the analytic approach by Keller and Simmons of ballistic and diffusive transport to simple three-dimensional sputter geometries is developed and applied. The sputter yield and the pressure–distance product are determined from the data set as the only fit parameters of the model. For the entire range of operation of the magnetron, the sputter process can be described in terms of the relatively simple approach.
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81.15.Cd Deposition by sputtering
73.23.Ad Ballistic transport

Application of a Matsumoto-Ohtsuka-type vacuum flange to beam ducts for future accelerators

Y. Suetsugu, M. Shirai, and M. Ohtsuka

J. Vac. Sci. Technol. A 23, 1721 (2005); http://dx.doi.org/10.1116/1.2101808 (7 pages) | Cited 2 times

Online Publication Date: 25 October 2005

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The Matsumoto-Ohtsuka (MO)-type vacuum flange, which can provide a gapless connection and a highly reliable electric contact between flanges, was studied experimentally for a possible application to beam ducts for high-current accelerators, where the apertures have a complicated structure, such as the combination of a beam channel and one or two flat rectangular antechambers. In spite of the complex aperture, test flanges showed a good vacuum-sealing property. Vacuum sealing was successfully achieved with a reasonable fastening torque (15–20 N m), and remained sealed after baking at 250 °C for 24 h. A twist between flanges of up to about 5 mrad was also manageable. A pseudoelastic structural analysis well reproduced the observed deformation of the flange. This analysis should be available for optimizing the flange structure. The MO-type vacuum flange was found to be promising for connecting flanges of the beam duct with a complicated aperture in future accelerators. The flange will also be available as a compact vacuum flange in cases where a complex aperture is required.
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07.30.Kf Vacuum chambers, auxiliary apparatus, and materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Technique for the production, preservation, and transportation of H atoms in metal chambers for processings

S. G. Ansari, Hironobu Umemoto, Takashi Morimoto, Koji Yoneyama, Atsushi Masuda, Hideki Matsumura, Manabu Ikemoto, and Keiji Ishibashi

J. Vac. Sci. Technol. A 23, 1728 (2005); http://dx.doi.org/10.1116/1.2101809 (4 pages) | Cited 10 times

Online Publication Date: 25 October 2005

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Three different coating materials for lowering the H-atom recombination probability on stainless-steel chamber walls were investigated and the results were compared. SiO2 films prepared by natural oxidation of perhydropolysilazane, polytetrafluoroethene (Teflon) films, and H3PO4 coated SiO2 films were used as coating materials. Among them, the SiO2 film was found to be the most useful for this purpose. The densities of H atoms produced by catalytic decomposition of H2 on heated tungsten surfaces were measured by a vacuum-ultraviolet laser absorption technique under various conditions. The H-atom density increased by one order of magnitude with SiO2 and Teflon coating, the former of which is easier to use and more economical. No further increase in H-atom density was observed when the chamber was coated with H3PO4. SiO2 films prepared from perhydropolysilazane were not etched by H atoms. Quadrupole mass spectrometric analysis showed that the production of either SiH4 or H2O is extremely minor. No surface etching was confirmed by x-ray photoelectron spectroscopy (XPS), either. Scanning electron microscopic (SEM) observations showed that the SiO2 films are not porous even after H-atom exposure. It is also suggested that cooling of the chamber walls is important to preserve the H-atom density.
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81.05.Bx Metals, semimetals, and alloys
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.Mq Oxidation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Tailored synthesis of TiC/a-C nanocomposite tribological coatings

D. Martínez-Martínez, C. López-Cartes, A. Justo, A. Fernández, J. C. Sánchez-López, A. García-Luis, M. Brizuela, and J. I. Oñate

J. Vac. Sci. Technol. A 23, 1732 (2005); http://dx.doi.org/10.1116/1.2101810 (5 pages) | Cited 13 times

Online Publication Date: 25 October 2005

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Composite coatings made of nanocrystalline TiC (nc-TiC) particles and amorphous carbon (a-C) have been prepared in a double magnetron sputtering system using graphite and titanium targets under Ar bombardment. Chemical composition and microstructure of coatings were studied by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and x-ray diffraction (XRD) for a set of samples prepared varying the ratio and intensity of power applied to each magnetron. Changes in coatings microstructure, from a quasipolycrystalline TiC to a nanocomposite formed by nanocrystals of TiC embedded in an amorphous matrix of carbon (nc-TiC/a-C), are observed depending on the synthesis conditions. Tribological and mechanical properties of coatings were tested using a pin-on-disk tribometer and an ultramicrohardness indenter, respectively. Coatings with moderate hardness (7–27 GPa), low friction (0.1–0.2), and low wear rates (k ∼ 10−7 mm3/N m) were obtained. A percentage between 15% and 30% of TiC is found as an optimum value to get a good compromise between good mechanical and tribological properties. Finally, a mapping of the mechanical and tribological properties of the nc-TiC/a-C system is presented for the synthesis conditions employed.
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81.07.Bc Nanocrystalline materials
81.05.Mh Cermets, ceramic and refractory composites
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
62.25.-g Mechanical properties of nanoscale systems
81.40.Pq Friction, lubrication, and wear
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
79.20.Uv Electron energy loss spectroscopy
82.80.-d Chemical analysis and related physical methods of analysis
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Use of glovebags for less hazardous working conditions during the maintenance operations on molecular-beam epitaxy systems

Michael M. Oye, J. Ahn, C. Cao, H. Chen, W. Fordyce, D. Gazula, S. Govindaraju, J. B. Hurst, S. Lipson, D. Lu, J. M. Reifsnider, O. Shchekin, R. Sidhu, X. Sun, D. G. Deppe, et al.

J. Vac. Sci. Technol. A 23, 1737 (2005); http://dx.doi.org/10.1116/1.2091119 (3 pages)

Online Publication Date: 25 October 2005

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06.60.Wa Laboratory safety procedures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Simple method for estimating and comparing x-ray damage rates

D. R. Baer, M. H. Engelhard, A. S. Lea, and L. V. Saraf

J. Vac. Sci. Technol. A 23, 1740 (2005); http://dx.doi.org/10.1116/1.2073387 (5 pages) | Cited 2 times

Online Publication Date: 25 October 2005

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In this note we describe an approach for estimating and comparing rates or thresholds for x-ray-induced specimen damage during surface analysis. The method uses a common reference material to compare x-ray damage rates reported in the literature and in publications to the rates of damage that may occur on a specific instrument. Although the method makes several assumptions that are only partially valid, results from a few damage datasets appear acceptably consistent when comparing estimates to a time for 10% damage or signal change.
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61.80.Cb X-ray effects
61.82.Pv Polymers, organic compounds
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