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Nov 2001

Volume 19, Issue 6, pp. 2007-2934

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Investigation of molecular beam epitaxial NdF3/Si(111) heterostructures by atomic force microscopy and x-ray diffractometry

J. M. Ko, S. D. Durbin, T. Fukuda, and K. Inaba

J. Vac. Sci. Technol. B 19, 2007 (2001); http://dx.doi.org/10.1116/1.1409388 (6 pages)

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NdF3 layers were grown on Si(111) substrates at 400, 550, and 700 °C by molecular beam epitaxy. The surface morphology observations by atomic force microscopy indicated that the NdF3 layers on Si(111) substrates grew as islands associated with screw dislocations, which coalesced less densely at higher growth temperatures. The layers grown at higher temperatures were more susceptible to formation of microcracks due to larger mismatch of the thermal expansion coefficient. The orientational relationship between NdF3 layers and Si(111) substrates was confirmed to be NdF3(0002)〈11−20〉‖Si(111)〈1−10〉 by x-ray diffraction measurement. As a function of growth temperature and layer thickness, the crystallinity of resulting layers in terms of full width at half maximum values was investigated. In particular, for NdF3 layers grown at a high temperature of 700 °C, lattice relaxation and crystallinity degradation with layer thickening were found. © 2001 American Vacuum Society.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness

Polymer pattern formation on SiO2 surfaces using surface monolayer initiated polymerization

Xiaohua Chen, Laren M. Tolbert, Clifford L. Henderson, Dennis W. Hess, and Jurgen Ruhe

J. Vac. Sci. Technol. B 19, 2013 (2001); http://dx.doi.org/10.1116/1.1409391 (7 pages) | Cited 4 times

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The use of surface monolayer initiated polymerization, in which initiators are chemically bound to a surface, can generate robust barrier polymers for pattern formation in silicon by reactive ion etching. The combination of poly(vinylarenes) and a new surface initiator based upon a phenylazo initiator provides excellent etch resistance and superior performance. © 2001 American Vacuum Society.
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82.35.Gh Polymers on surfaces; adhesion
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Deep plasma etching of piezoelectric PZT with SF6

M. Bale and R. E. Palmer

J. Vac. Sci. Technol. B 19, 2020 (2001); http://dx.doi.org/10.1116/1.1409392 (6 pages) | Cited 6 times

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Reactive ion etching with sulfur hexafluoride (SF6) gas has been employed to create deep structures in bulk samples of the piezoelectric material lead zirconate titanate, Pb(Zr,Ti)O3 (PZT). SF6 is chosen for compatibility with dry etching of silicon with a possibility for production of hybrid silicon-piezoelectric devices. Thick photoresist layers have been used to pattern PZT to a depth of 2 μm at a rate of 120 nm min−1. The use of more durable nickel masks, formed by electroplating through the thick resist, leads to structures greater than 100 μm in height, with an average sidewall angle of ∼72°. The profile of the deep PZT structures is seen to depend on etch duration and the spacing of structures, attributed to the redeposition of mask and etch products, respectively. The addition of nitrogen and argon to the SF6 plasma is shown to produce small improvements in the profiles. By combining gas addition with heating of the substrate PZT etch rates up to 200 nm min−1 have been obtained. © 2001 American Vacuum Society.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Materials aspects, electrical performance, and scalability of Ni silicide towards sub-0.13 μm technologies

Anne Lauwers, An Steegen, Muriel de Potter, Richard Lindsay, Alessandra Satta, Hugo Bender, and K. Maex

J. Vac. Sci. Technol. B 19, 2026 (2001); http://dx.doi.org/10.1116/1.1409389 (12 pages) | Cited 54 times

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Ni-silicide phase formation with and without a Ti capping layer was studied by sheet resistance, x-ray diffraction and transmission electron microscopy. Ni monosilicide is found to be the stable phase in a temperature range from 400 to 600 °C. At lower temperatures the Ni2Si phase is found to be present. For temperatures higher than 700 °C NiSi is converted into NiSi2. Pyramidal NiSi2 precipitates were found to grow epitaxially along the Si〈111〉 planes for annealing temperatures as low as 310 °C. The epitaxial NiSi2 grains were found to disappear when the annealing temperature is increased. Stress buildup during Ni silicidation was measured in situ and could be correlated to the formation of the different Ni-silicide phases. The stress induced by Ni-monosilicide formation compares favorably to the stress induced by Co disilicide and Ti disilicide. The average silicon consumption required to obtain a certain sheet resistance was found to be 35% lower for Ni monosilicide compared for Co disilicide. It was found that a two-step process is needed to obtain complete conversion to the preferred Ni-monosilicide phase without lateral silicide growth. The sheet resistance of Ni-silicided narrow poly-Si and active area lines was found to be low, even when Ni silicide was formed without a Ti cap. No degradation of the Ni silicide on the narrow poly-Si lines was observed when the silicidation temperature was increased to 600 °C. The reverse bias leakage of shallow Ni-silicided and Co-silicided square diodes was compared for varying junction depths and varying silicide thicknesses. For similar junction depth and similar sheet resistance, a lower reverse bias leakage current was obtained for a Ni-silicided junction compared to its Co-silicided counterpart. This may be attributed to the reduced Si consumption of Ni monosilicide compared to Co disilicide. © 2001 American Vacuum Society.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
68.60.Bs Mechanical and acoustical properties
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Reduced brightness of the ZrO/W Schottky electron emitter

A. H. V. van Veen, C. W. Hagen, J. E. Barth, and P. Kruit

J. Vac. Sci. Technol. B 19, 2038 (2001); http://dx.doi.org/10.1116/1.1409390 (7 pages) | Cited 18 times

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The reduced brightness for a 〈100〉 ZrO/W Schottky electron emitter with a tip radius of 0.8 μm has been measured. The maximum reduced brightness measured was 2×108 A/(m2 sr V). The measurements of the reduced brightness are compared with the extended Schottky theory and the theory on stochastic Coulomb interactions. At high angular current densities the reduced brightness is limited by statistical Coulomb interactions in the gun lens region. The limits to the maximum reduced brightness in an ideal configuration are explored and found to be 2×109 A/(m2 sr V) for a 0.2 μm tip and a current limiting aperture in the extractor electrode. © 2001 American Vacuum Society.
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79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions

Experimental conditions for a highly ordered monolayer of gold nanoparticles fabricated by the Langmuir–Blodgett method

Shujuan Huang, Gen Tsutsui, Hiroyuki Sakaue, Shoso Shingubara, and Takayuki Takahagi

J. Vac. Sci. Technol. B 19, 2045 (2001); http://dx.doi.org/10.1116/1.1410943 (5 pages) | Cited 21 times

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A highly ordered monolayer film of alkanethiol-encapsulated gold nanoparticles was fabricated on a silicon substrate by using the Langmuir–Blodgett (LB) method. The effects on the particle order, of the particle concentration and the type of solvent of the LB spreading suspension of encapsulated gold particles, were studied. We found that a low particle concentration of 0.06–0.3 mg/mL in chloroform is optimal for the fabrication of high quality gold particle monolayers. Since the proposed method is not restricted to gold particles, it is believed to be a practical process for fabricating quantum dot structures of various particle sizes and compositions. © 2001 American Vacuum Society.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
82.70.Kj Emulsions and suspensions
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Modification of polycarbonate and polypropylene surfaces by argon ion cluster beams

H. Biederman, D. Slavinska, H. Boldyreva, H. Lehmberg, G. Takaoka, J. Matsuo, H. Kinpara, and J. Zemek

J. Vac. Sci. Technol. B 19, 2050 (2001); http://dx.doi.org/10.1116/1.1410944 (7 pages) | Cited 7 times

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Impacts of energetic argon ion clusters on surfaces of inorganic solids have shown modification of the respective surface properties. Polymeric samples such as (PC) polycarbonate and (PP) polypropylene were irradiated by argon ion clusters (average size of 3000 atoms) accelerated to 10 and 20 keV at doses ranging from 109 to 1014 cluster/cm2. The irradiated surfaces were investigated by surfometer (profilometer), atomic force microscope, contact angle measurements and x-photoelectron spectroscopy. Measurements using these techniques show that the smoothing effect and the postirradiation oxidation of the surface take place. The direct evidence was obtained in case of PP that the irradiation dose 1011 cluster/cm2 produces the smoothest surface as measured by surfometer. In the case of PC the same conclusion is suggested indirectly. © 2001 American Vacuum Society.
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81.65.Ps Polishing, grinding, surface finishing
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.80.Jh Ion radiation effects
61.82.Pv Polymers, organic compounds
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
68.03.Cd Surface tension and related phenomena
79.60.Fr Polymers; organic compounds
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Valence band alignment and work function of heteroepitaxial nanocrystals on GaAs(001)

S. Heun, Y. Watanabe, B. Ressel, Th. Schmidt, and K. C. Prince

J. Vac. Sci. Technol. B 19, 2057 (2001); http://dx.doi.org/10.1116/1.1410942 (6 pages) | Cited 2 times

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The differences in valence band structure and work function between heteroepitaxial nanocrystals and the surrounding substrate were measured with a spectroscopic photoemission and low energy electron microscope which allows laterally resolved photoemission spectroscopy. The nanocrystals were obtained by depositing nominally 2 and 4 monolayers (ML) of InAs on a Se-terminated GaAs(001) surface. The samples showed differences in the valence band edge energy and work function both between nanocrystals and substrate as well as between 2 and 4 ML. We suggest that Se termination of the nanocrystals is the reason for these differences. © 2001 American Vacuum Society.
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73.22.Dj Single particle states
79.60.Jv Interfaces; heterostructures; nanostructures
73.30.+y Surface double layers, Schottky barriers, and work functions

Chemical composition, morphology, and deep level electronic states of GaN (0001) (1×1) surfaces prepared by indium decapping

A. P. Young, L. J. Brillson, Y. Naoi, and C. W. Tu

J. Vac. Sci. Technol. B 19, 2063 (2001); http://dx.doi.org/10.1116/1.1412656 (4 pages) | Cited 1 time

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Ordered GaN (0001) (1×1) surfaces are prepared after removal from the growth chamber via thermal desorption of a thin In cap layer at 650 °C in combination with one thermal flash of Ga metal to reduce residual O and C contamination. Auger electron spectroscopy (AES) and low energy electron-excited nanoscale luminescence (LEEN) spectroscopy results show that In can prevent contamination during atmospheric exposure if it can cover the surface uniformly. LEEN spectra of the ordered surface show that the In capping layer is desorbed from the GaN without reacting to produce InxGa1−xN or diffusing into the GaN to produce new localized states. Subsequent atomic force microscopy (AFM) measurements reveal an atomically smooth film plus Ga droplets residual to the flash annealing. These results suggest that In decapping may be useful in obtaining clean, LEED-ordered GaN surfaces after transport in air with a minimum of UHV treatment. © 2001 American Vacuum Society.
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68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.43.Vx Thermal desorption
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
78.60.Hk Cathodoluminescence, ionoluminescence
79.20.Fv Electron impact: Auger emission

Improvement of the SiO2/Si interface characteristics by two-step deposition with intermediate plasma treatment using O2/He gas

Chung Yi, Hyo Uk Kim, Shi Woo Rhee, Sang Ho Oh, and Chan-Gyung Park

J. Vac. Sci. Technol. B 19, 2067 (2001); http://dx.doi.org/10.1116/1.1412657 (6 pages) | Cited 1 time

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We studied two-step deposition with an O2/He intermediate plasma treatment to improve the SiO2/Si interface characteristics. Using this method, we can minimize the plasma damage on the Si surface and improve the interface characteristics such as intermediate oxidation states, interface trap density Dit, and Vfb shift. The interface characteristics were improved with the intermediate plasma treatment after a 6 nm first oxide deposition. The number of Si atoms (NSiOx) in the suboxide region, compared with the sample without plasma treatment, was decreased 14.7% and a sixfold ring structure became dominant. Interface trap density was decreased from 1.65×1011/eV cm2 to 6.87×1010/eV cm2 by the oxygen incorporation in the transition region. The moderate oxygen incorporation near the SiO2/Si interface reduced the Vfb shift due to the decrease of the fixed oxide charge. © 2001 American Vacuum Society.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.Ct Interface structure and roughness
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Lp Transmission electron microscopy (TEM)

In situ submicron patterning with silicon nitride evaporation masks

U. Purbach and A. de Lozanne

J. Vac. Sci. Technol. B 19, 2073 (2001); http://dx.doi.org/10.1116/1.1412658 (4 pages) | Cited 1 time

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We describe a technique for ultra-high-vacuum compatible deposition of structures on flat substrates. This technique allows one to form micrometer and even submicron-sized structures on a flat surface with minimal contamination. It also has the advantage of producing a smooth edge profile similar to those achieved using a two-layered resist.© 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz Deposition technology
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Dv Composition, segregation; defects and impurities

Parameter extraction for 193 nm chemically amplified resist from refractive index change

Young-Soo Sohn, Hye-Keun Oh, and Ilsin An

J. Vac. Sci. Technol. B 19, 2077 (2001); http://dx.doi.org/10.1116/1.1414016 (5 pages) | Cited 2 times

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Some of the important areas to be improved for lithography simulation are: obtaining correct exposure parameters and determining the change of refractive index. It is known that the real and imaginary refractive indices are changed during exposure. We obtained these refractive index changes during exposure for 193 nm chemically amplified resists. The variations of the transmittance as well as the resist thickness were measured during ArF excimer laser exposure. We found that the refractive index change is directly related to the concentration of the photo acid generator and deprotected resin. It is important to know the exact values of acid concentration from the exposure parameters since a small difference in acid concentration magnifies the variation in the amplified deprotection during postexposure bake. We developed and used a method to extract Dill ABC exposure parameters for 193 nm chemically amplified resist from the refractive index change upon exposure. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Characterization of reactive ion etch lag scaling

D. Keil and E. Anderson

J. Vac. Sci. Technol. B 19, 2082 (2001); http://dx.doi.org/10.1116/1.1414116 (7 pages) | Cited 17 times

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Recent advances in ultralarge-scale integration have typically depended on reductions in etched feature size. This has motivated efforts to find etch processes that will precisely etch increasingly smaller features while retaining the ability to etch larger features. As feature sizes push below 0.25 μm, reactive ion etch (RIE) lag control becomes increasingly important. Knowing how RIE lag scales with feature size for a given process aids in determining if that process must be discarded and a new one developed. In those situations where a process cannot be discarded, an understanding of RIE lag scaling aids in predicting fabrication difficulties for a given device design. Using a minimal set of initial assumptions, it is shown that a relationship can be derived which relates etch rate to the time development of the feature aspect ratio. It is then shown that this relationship can be used to derive an expression for the etch depth as a function of time and feature size. The assumptions made are justified by phenomenological observation rather than by an assumed mechanism. This approach enhances the generality of the results obtained, thus making them useful for a variety of practical etch engineering applications. © 2001 American Vacuum Society.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Initial surface reactions between Cl2 molecules and the GaAs (001) 2×4 surface

Yu Tanaka and Masashi Ozeki

J. Vac. Sci. Technol. B 19, 2089 (2001); http://dx.doi.org/10.1116/1.1414118 (6 pages) | Cited 2 times

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Initial reactions for Cl2 molecules at the GaAs(001)-(2×4) surface have been investigated by using a supersonic molecular-beam scattering technique. Results with a high corrugation GaAs(001)-(2×4) surface indicate a complex, dynamical behavior of Cl2 molecules interacting with the surface. A fine chemisorption probability measurement at an incident translational energy of 0.12 eV suggests an extremely fast dissociative chemisorption process with an initial probability of ∼93%. Angular distributions measured for scattered Cl2 molecules at 0.06, 0.12, and 1.45 eV strongly indicate three channels of behavior: inelastic direct scattering, trapping/desorption, and multiple scattering. In particular, the multiple scattering channel arises from the corrugation of the surface. © 2001 American Vacuum Society.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.05.Ea III-V semiconductors
68.49.Df Molecule scattering from surfaces (energy transfer, resonances, trapping)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies
68.35.B- Structure of clean surfaces (and surface reconstruction)

Study of the surface reactivity of optical fibers under aging conditions by flexural resonance

Johann Mertens, Eric Finot, Eric Bourillot, Arnaud Fabre, and Jean Pierre Goudonnet

J. Vac. Sci. Technol. B 19, 2095 (2001); http://dx.doi.org/10.1116/1.1414113 (9 pages) | Cited 1 time

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This article reports an original technique for measuring the flexural resonance response of optical fibers of around 1 mm in length considered as atomic force microscope cantilevers. This technique was found particularly suitable for precisely investigating the effect of aging of optical fibers due to external factors such as temperature, action of hydrogen, or ionic aggressive solutions. Compared to the corresponding atomic force microscopy images, the measurement of the resonance frequency shift leads to the determination of two factors characteristic of the surface reactivity of the fiber: first, the decrease in frequency that can be considered in terms of mass loading, and second both the frequency increase and the loss in Q factor resulting from the variation of the Young modulus and the internal friction of the fiber. © 2001 American Vacuum Society.
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42.81.Cn Fiber testing and measurement of fiber parameters
46.80.+j Measurement methods and techniques in continuum mechanics of solids
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Gy Mechanical properties; surface strains
62.20.D- Elasticity
07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)

Global pattern density effects on aluminum alloy etching for sub-0.25 μm technology logic devices

Kye Hyun Baek, Kil Ho Kim, Chung Ho Hwang, and Dae Hoon Lee

J. Vac. Sci. Technol. B 19, 2104 (2001); http://dx.doi.org/10.1116/1.1414114 (4 pages)

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Global pattern density effects on aluminum alloy etching were quantitatively analyzed for sub-0.25 μm technology logic devices. We found that etching the metal layer with one pattern density while applying the plasma activation parameters optimized for the other pattern density often results in inferior performance, even if the minimum design rules of both layers are the same. Additional studies show that the aluminum etch rate has an almost linear relationship to the pattern density of the etched metal layer when all the activation parameters are fixed. This evokes the necessity that the plasma activation parameters be optimized properly with the pattern density of each metal layer as well as with the minimum design rule. We speculate that these pattern density effects are caused by the variation of etching environment that is solely determined by effective etchants density and their effective residence time. Thus it may be possible to alleviate the global pattern density effects by controlling the plasma activation parameters in such a way that these two effective values are independent of the pattern density. Based on the aforementioned speculation we controlled total pressure and feed gas flow rate and were able to achieve stable etching performance independent of the global pattern density. © 2001 American Vacuum Society.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
84.30.Sk Pulse and digital circuits
82.40.Np Temporal and spatial patterns in surface reactions

Investigation of fluorine in dry ultrathin silicon oxides

G. Vereecke, E. Röhr, R. J. Carter, T. Conard, H. De Witte, and M. M. Heyns

J. Vac. Sci. Technol. B 19, 2108 (2001); http://dx.doi.org/10.1116/1.1414050 (6 pages)

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The origins of fluorine in dry ultrathin silicon oxides (<1 nm) were investigated as the incorporation of fluorine in these layers may improve their reliability and interface quality. Oxides were grown at room temperature (RT) by UV/O2 in an integrated tool combining vapor HF surface preparation and oxide growth in a single chamber. The chemical composition and thickness of the layers were characterized by x-ray photoelectron spectroscopy. It is shown that incorporation of fluorine in these oxides originated mainly from the contamination of the tool (dead spaces and surface adsorption) and from the fluorine left at the wafer surface by the in situ HF process. The levels of these sources of fluorine were about two orders of magnitude higher than from a wet HF dip. No evidence was found for the existence of subsurface fluorine [Kasi et al., Appl. Phys. Lett. 58, 2975 (1991)] as oxides grown in a separate noncontaminated cell (UV/O2, 1 atm O2, RT to 200 °C) did not show any significant increase in fluorine content as a function of oxide thickness. Hence the amount of fluorine incorporated into oxides grown in cluster tools under similar conditions will depend not only on the method selected for surface preparation but also on whether surface preparation and oxidation are performed in the same chamber or not. The possible benefits of determined fluorine levels are discussed. © 2001 American Vacuum Society.
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81.65.Mq Oxidation
68.55.Nq Composition and phase identification
68.35.Dv Composition, segregation; defects and impurities
79.60.Dp Adsorbed layers and thin films

Investigation of the bonding strength and interface current of p-Si/n-GaAs wafers bonded by surface activated bonding at room temperature

M. M. R. Howlader, T. Watanabe, and T. Suga

J. Vac. Sci. Technol. B 19, 2114 (2001); http://dx.doi.org/10.1116/1.1414115 (5 pages) | Cited 8 times

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Equivalent bulk strength of the interface between p-Si/n-GaAs bonded through the surface activated bonding (SAB) method is found. The interface current was extensively investigated. Nonideal behavior of the pn junction current is found to be due to the tunneling current between the conduction band and valence band across the transition region associated with band gap states. Interface current decreases with increasing sputtering time and energy and vice versa. Irradiation time and energy dependent behavior indicates that the accumulation of radiation induced defects associated with the doping controls the interface current of p-Si/n-GaAs. Moreover, strong impact of the exposure to an ultrahigh vacuum atmosphere of the activated surfaces on the interface current of p-Si/p-Si is found. Finally it can be suggested that a laser diode can be fabricated by the bonding between p-Si and n-GaAs through the SAB method, because of the achievement of equivalent bulk strength of the interface. © 2001 American Vacuum Society.
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68.35.Np Adhesion
81.05.Cy Elemental semiconductors
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
42.55.Px Semiconductor lasers; laser diodes

Metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors on GaAs with InxGa1−xP graded buffer

K. Yuan, K. Radhakrishnan, H. Q. Zheng, and G. I. Ng

J. Vac. Sci. Technol. B 19, 2119 (2001); http://dx.doi.org/10.1116/1.1415516 (4 pages) | Cited 1 time

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A new metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistor (HEMT) structure was grown on a GaAs substrate with a InxGa1−xP graded buffer layer by solid-source molecular beam epitaxy. The In0.53Ga0.47As channel layer was grown on the InGaP buffer layer directly without an InAlAs buffer as in the conventional design. High-resolution x-ray diffraction reveals that the whole layer structure is nearly fully relaxed. Hall measurement showed that this new layer design exhibits higher electron mobility and carrier concentration as well as lower light sensitivity compared to the reference sample with the conventional design. The promising device performance demonstrates the potential of using this metamorphic HEMT device in high speed and high frequency applications. © 2001 American Vacuum Society.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

In situ measurement of aspect ratio dependent etch rates of polysilicon in an inductively coupled fluorine plasma

Th. Lill, M. Grimbergen, and D. Mui

J. Vac. Sci. Technol. B 19, 2123 (2001); http://dx.doi.org/10.1116/1.1415514 (6 pages) | Cited 10 times

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The etch rate of polysilicon in high aspect ratio structures has been studied in an inductively coupled fluorine based plasma (pure SF6). The change of the silicon etch rate with increasing aspect ratio [aspect ratio dependent etch rate or reactive ion etching (RIE) lag] has been measured in situ by interferometry. The experimental structures as well as the process conditions were chosen such that (i) the interaction of neutral fluorine atoms with the silicon surface determines the etch rate, (ii) the ion energy is minimized, (iii) the mass transport of neutrals is in a molecular flow (Knudsen) regime, and (iv) the interaction of the etch species with the sidewalls can be neglected. Under these conditions, the experimental findings indicate that the RIE lag effect is reduced for higher pressures and lower cathode temperatures, i.e., for higher fluorine atom coverages of the silicon surface. This is in agreement with the Knudsen transport model by Coburn and Winters [W. Coburn and H. F. Winters, Appl. Phys. Lett. 55, 2730 (1989)]. Probabilities for the reaction of fluorine atoms with the silicon surface between 0.03 and 0.11 can be derived when fitting the experimental data with this model. The findings reported in this work are of relevance for the formation of deep trench storage capacitors and polysilicon plugs. In particular, we show that we can control RIE lag and etch rate independently for the given process conditions. © 2001 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.05.Cy Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
07.60.Ly Interferometers

Ion-assisted etching of W film by an Ar+ beam in XeF2 with the addition of H2, N2, or O2

Hideo Ichinose

J. Vac. Sci. Technol. B 19, 2129 (2001); http://dx.doi.org/10.1116/1.1415518 (4 pages) | Cited 1 time

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W etching is carried out by an Ar+ beam in XeF2 with the addition of H2, N2 or O2. The energy of the beam is 400 eV and the current is 0.2 μA. The spontaneous etching rate in XeF2 with the addition of N2 or O2 decreases by about 0.6 times compared with that in XeF2 (2×10−6 Torr), for which the total pressure of the mixed gas is 2×10−5 Torr. The nitrogen or oxygen atoms attached on the W surface disturb the attachment between W and fluoride atoms. The ion-assisted etching rate increases by about 1.5 times in XeF2 by adding N2 or O2 compared with that in XeF2 (2×10−6 Torr), for which the total pressure of the mixed gas is 2×10−5 Torr. It is speculated that the addition of N2 or O2 gas to fluorinated gas acts upon the surface reaction to suppress the sidewall etching rate when the mask patterned W gate line is plasma etched by the same kind of gas mixture. The mixing layer is thought to be formed by W and nitrogen or by an oxygen atom by ion-assisted etching. The W–W bond in the mixing layer is thought to be weaker than that in W film both physically and chemically, which makes the etching increase. The thickness of the mixing layer is estimated to be about 10 Å. But the spontaneous ion-assisted etching rate did not change in the case of H2 addition. © 2001 American Vacuum Society.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
61.82.Bg Metals and alloys
85.40.Hp Lithography, masks and pattern transfer

Etching technique for ruthenium with a high etch rate and high selectivity using ozone gas

M. Nakahara, S. Tsunekawa, K. Watanabe, T. Arai, T. Yunogami, and K. Kuroki

J. Vac. Sci. Technol. B 19, 2133 (2001); http://dx.doi.org/10.1116/1.1415517 (4 pages) | Cited 8 times

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We have studied the characteristics of ruthenium etching reactions and the etch selectivity of Ru to photoresist in ozone gas. The Ru was etched at a maximum etch rate of 950 nm/min at between 100 and 150  °C by the formation of a volatile product, RuO4. However, the etch rate decreased at temperatures above 150 °C, since the formation of RuO2 on the Ru surface hindered the etching reaction. A comparison between the etching reaction of Ru and that of photoresist revealed that Ru was etched predominantly by ozone, whereas the photoresist was etched predominantly by atomic oxygen. This difference in etching behavior enables us to control the etch selectivity between Ru and photoresist. Below 150 °C, the Ru/photoresist selectivity was higher than 40 due to a small amount of atomic oxygen. Conversely, above 300 °C, the selectivity of photoresist/Ru was higher than 40 due to RuO2 formation. Therefore, a high degree of selectivity was achieved by manipulating the temperature. © 2001 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Bx Metals, semimetals, and alloys
79.60.Dp Adsorbed layers and thin films
68.43.Vx Thermal desorption

Ultrathin zirconium oxide films as alternative gate dielectrics

J. P. Chang, Y-S. Lin, S. Berger, A. Kepten, R. Bloom, and S. Levy

J. Vac. Sci. Technol. B 19, 2137 (2001); http://dx.doi.org/10.1116/1.1415513 (7 pages) | Cited 36 times

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ZrO2 films were deposited on Si(100) wafers by the rapid thermal chemical vapor deposition process using a zirconium (IV) t-butoxide Zr(OC4H9)4 precursor and oxygen. Interfacial zirconium silicate formation was observed by high resolution transmission electron microscopy and medium energy ion scattering. The intermixing of the interface can be suppressed by forming a thin silicon nitride layer on the silicon substrate prior to ZrO2 deposition. The dielectric constant of ZrO2 achieved in this work is 15–18 with very small capacitance–voltage hysteresis, ideal for metal–oxide–semiconductor field effect transistor (MOSFET) application. The NMOSFET device has good turn-on characteristics, however, the transconductance is lower than expected due to the incomplete removal of zirconium silicate at the source and drain contacts and poses integration challenges to use ZrO2 as the gate dielectric material. © 2001 American Vacuum Society.
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85.30.Tv Field effect devices
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Ion-implanted photoresist removal using water/carbon dioxide mixtures at elevated temperature and pressure

K. L. Chavez, G. L. Bakker, and D. W. Hess

J. Vac. Sci. Technol. B 19, 2144 (2001); http://dx.doi.org/10.1116/1.1415519 (5 pages) | Cited 3 times

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The ability of water and water/1% carbon dioxide mixtures to remove ion-implanted photoresist from silicon substrates was investigated. Photoresist with implant levels up to 2×1015/cm2 of boron and phosphorus were stripped effectively at a temperature of 165 °C and a pressure of 58.6 bar (850 psi) by both water and water/carbon dioxide. Removal of photoresist at low implant levels (2×1012/cm2) proceeded rapidly, while samples at higher dose levels (>2×1015/cm2) had a thin carbonized layer at the photoresist surface that inhibited the removal rate. Removal of this carbonized layer required approximately 2 min for water/carbon dioxide and approximately 8 min for water, while complete removal of the remaining photoresist film took less than 30 min for both fluids. Patterned, arsenic-implanted (1×1016/cm2) photoresist layers were removed by water/carbon dioxide at 200 °C, 850 psi, 3 ml/min flow rate, and 30 min exposure. Under all conditions investigated, water/carbon dioxide proved more effective than pure water at removing ion-implanted photoresist. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ry Impurity doping, diffusion and ion implantation technology

Interplay of current crowding and current self-quenching effects in planar cold cathodes

Y. Modukuru and M. Cahay

J. Vac. Sci. Technol. B 19, 2149 (2001); http://dx.doi.org/10.1116/1.1415515 (6 pages) | Cited 2 times

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In planar cold cathodes making use of semimetallic thin films to achieve low or negative electron affinity, the effects of dc current crowding can be affected by the trapping of electrons being reflected towards the cathode as a result of space-charge effects in the vacuum gap between cathode and anode. A self-consistent solution of the interplay between current crowding and space-charge effects can lead to a nonmonotonic lateral distribution of the anode current density depending on the width of the emission window. This behavior is in sharp contrast with the monotonic decrease of the anode current density from the edges towards the center of the emission window when space-charge effects in the vacuum region are neglected. © 2001 American Vacuum Society.
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85.45.Bz Vacuum microelectronic device characterization, design, and modeling
77.22.Jp Dielectric breakdown and space-charge effects
79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters

Processing and characterization of ultralow-dielectric constant organosilicate

Shu Yang, Janice C.-H. Pai, Chien-Shing Pai, Gary Dabbagh, Omkaram Nalamasu, Elsa Reichmanis, Joko Seputro, and Yaw S. Obeng

J. Vac. Sci. Technol. B 19, 2155 (2001); http://dx.doi.org/10.1116/1.1417542 (7 pages) | Cited 9 times

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A class of nanoporous organosilicate has been developed that can reach an ultralow-dielectric constant (k⩽2). In this approach a series of triblock polymers, poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-b-PEO), are used as sacrificial materials in silicon based spin-on matrices, poly(methylsilsesquioxane) (MSQ) to generate pores when heated above 400 °C. To improve the electrical and mechanical properties, different parameters, such as temperatures, heating rates, polymer molecular weights, copolymer compositions, and the molecular weight of MSQ prepolymers, were studied. Heating temperatures and ramping rates have no large effect on dielectric constants and dielectric breakdown strength. However, at a higher temperature, 500 °C, the mechanical properties are found stronger than those from 400 °C. A higher molecular weight of MSQ prepolymer will also lead to higher mechanical properties of the final porous MSQ, while no temperature effect is observed. Block copolymers with different molecular weights and compositions give similar dielectric constants depending on the polymer loading in MSQ and no substantial change in the dielectric strength of the films with different compositions. © 2001 American Vacuum Society.
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81.05.Rm Porous materials; granular materials
77.84.Jd Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects

Patterning nonflat substrates with a low pressure, room temperature, imprint lithography process

Matthew Colburn, Annette Grot, Byung Jin Choi, Marie Amistoso, Todd Bailey, S. V. Sreenivasan, John G. Ekerdt, and C. Grant Willson

J. Vac. Sci. Technol. B 19, 2162 (2001); http://dx.doi.org/10.1116/1.1417543 (11 pages) | Cited 24 times

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Step and flash imprint lithography (SFIL) is a technique that has the potential to replace photolithography for patterning resist with sub-100 nm features. SFIL is a low cost, high throughput alternative to conventional photolithography for high-resolution patterning. It is a molding process in which the topography of a template defines the patterns created on a substrate. The ultimate resolution of replication by imprint lithography is unknown but, to date, it has only been limited by the size of the structures that can be created on the template. It is entirely possible to faithfully replicate structures with minimum features of a few hundred angströms. SFIL utilizes a low-viscosity, photosensitive silylated solution that exhibits high etch contrast with respect to organic films in O2 reactive ion etching. In this article we describe the SFIL process, the development of a multilayer etch scheme that produces 6:1 aspect ratio features with 60 nm linewidths, a method for patterning high-aspect-ratio features over topography, and a metal lift-off process. A micropolarizer array consisting of orthogonal 100 nm titanium lines and spaces fabricated using this metal lift-off technique is reported. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
81.65.Cf Surface cleaning, etching, patterning

Deep reactive ion etching of silicon carbide

S. Tanaka, K. Rajanna, T. Abe, and M. Esashi

J. Vac. Sci. Technol. B 19, 2173 (2001); http://dx.doi.org/10.1116/1.1418401 (4 pages) | Cited 14 times

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In this article, we describe more than 100-μm-deep reactive ion etching (RIE) of silicon carbide (SiC) in oxygen-added sulfur hexafluoride (SF6) plasma. We used a homemade magnetically enhanced, inductively coupled plasma reactive ion etcher (ME-ICP-RIE) and electroplated nickel masks. First, 5 h etching experiments using etching gases with 0%, 5%, 10% and 20% oxygen were performed by supplying rf power of 150 and 130 W to an ICP antenna and a sample stage, respectively. They demonstrated a maximum etch rate of 0.45 μm/min and residue-free etching in the case of 5% oxygen addition. Observation of the cross sections of etched samples using a scanning electron microscope confirmed a microloading effect, which is reduction of the etched depth with a decrease in the mask opening width. Next, a 7 h etching experiment using an etching gas with 5% oxygen was performed by increasing the rf power to the sample stage to 150 W. This yielded an etched depth of 216 μm. © 2001 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.05.Hd Other semiconductors

Optical and structural studies in InGaN quantum well structure laser diodes

Shigefusa F. Chichibu, Takashi Azuhata, Mutsumi Sugiyama, Toshio Kitamura, Yuuki Ishida, Hajime Okumura, Hisayuki Nakanishi, Takayuki Sota, and Takashi Mukai

J. Vac. Sci. Technol. B 19, 2177 (2001); http://dx.doi.org/10.1116/1.1418404 (7 pages) | Cited 25 times

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An InGaN multiple-quantum-well laser diode wafer that lased at around 400 nm was shown to have the InN mole fraction, x, of only 6% in the wells. Nanometer-probe compositional analysis showed that the fluctuation of x was as small as 1% or less, which is the resolution limit. However, the wells exhibited a Stokes-like shift (SS) of 49 meV at 300 K, which was approximately 65% of the luminescence linewidth, and effective localization depth, E0, was estimated to be 35 meV at 300 K. Since the effective electric field due to polarization in the wells was estimated to be as small as 300 kV/cm, SS was considered to originate from effective band-gap inhomogeneity. Because the well thickness fluctuation was insufficient to reproduce SS or E0 and bulk cubic In0.02Ga0.98N that does not suffer any polarization field or thickness fluctuation effect exhibited a SS of 140 meV at 77 K, the exciton localization is considered to be an intrinsic phenomenon in InGaN, which is due to the large band-gap bowing and In clustering in InGaN material. The spontaneous emission from the InGaN wells was thus assigned as being due to the recombination of excitons localized at the exponential tail-type potential minima in the density of states. The upper bound of the lateral localization size has been estimated to be 50 nm. Such shallow and low density localized states are leveled by injecting high density carriers under the lasing conditions. © 2001 American Vacuum Society.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Organic polymeric coatings deposited by plasma enhanced chemical vapor deposition

Ram W. Sabnis, Mario Cazeca, William L. DiMenna, Mary J. Spencer, Douglas J. Guerrero, and Min-Shyan Sheu

J. Vac. Sci. Technol. B 19, 2184 (2001); http://dx.doi.org/10.1116/1.1418402 (6 pages) | Cited 3 times

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A process of depositing thin organic polymeric coatings on electronic substrates by plasma enhanced chemical vapor deposition (PECVD) has been developed. We have designed halogenated compounds with PECVD reactive functionality attached to optically active moieties. Compounds have been screened selectively to lower the dielectric constant and enhance plasma polymerization efficiency. The chemical, optical, and mechanical properties of the deposited films such as film uniformity, film defectivity, film solubility, resist compatibility, conformality, adhesion to semiconductor substrates, refractive index, optical density, and photolithographic behavior have been studied. Plasma polymerized materials exhibit high sensitivity, excellent resolution, and good process latitude. PECVD provides a completely dry deposition process for wafer coating. The coatings possess high optical density at 193 nm. © 2001 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.Gh Polymers on surfaces; adhesion

Electromigration performance of AlCu/Ti and AlCu/Ti/TiN/Ti metallization

Kazuyoshi Kamoshida

J. Vac. Sci. Technol. B 19, 2190 (2001); http://dx.doi.org/10.1116/1.1418400 (5 pages)

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The electromigration (EM) lifetimes of top-TiN/Ti/Al-0.5%Cu/Ti-bottom and top-TiN/Ti/Al-0.5%Cu/Ti/TiN/Ti-bottom stacked structures were investigated using five-level Al-alloy interconnections with tungsten-filled vias. TiN/Ti/AlCu /Ti stacked structures had an EM lifetime ten times longer than TiN/Ti/AlCu/Ti/TiN/Ti ones. This longer EM lifetime is probably due to the small grain-boundary diffusivities for the bamboo microstructure. In the TiN/Ti/AlCu/Ti structure, a localized Al3Ti intermetallic compound layer was formed by the reaction between Al and Ti at the AlCu/Ti interface. On the other hand, in the TiN/Ti/AlCu/Ti/TiN/Ti structures, an almost uniform Al3Ti intermetallic compound layer was formed at the AlCu/Ti interface. In the initial nucleation process in Al, the Al grain growth increased on Ti/SiO2 compared with Ti/TiN/Ti/SiO2 according to atomic force microscopy observation. Using the optimum Ti thickness (10 nm) made it possible to form long-EM-lifetime multilevel interconnections without using many metal stacked structures. © 2001 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Focus latitude enhancement of symmetrical phase mask design for deep submicron contact hole patterning

Shuo-Yen Chou, Jen-Chung Lou, Li-Jui Chen, Lin-Hung Shiu, Ru-Gun Liu, Chien-Ming Wang, and Tsai-Sheng Gau

J. Vac. Sci. Technol. B 19, 2195 (2001); http://dx.doi.org/10.1116/1.1418398 (11 pages) | Cited 2 times

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The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask (PSM) with symmetrical assist features improves the depth of focus (DOF) by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole imaging fails the mask pattern transfer, which limits the application of the phase-shifting method to pattern pitch greater than mathλ/NA. A tiny amount of spherical aberration results in prominent asymmetrical defocus behavior because the wave deformation in the projection lens shifts the distribution of constructive and destructive interference patterns to opposite defocus directions. The printing characteristics of 0.17 μm contact using an 18% transmission, rim-type attenuated phase-shifting mask are investigated to corroborate our analysis of defocus behavior. The dependence of depth of focus on pattern duty is stressed to elucidate the difference in mechanisms of focus latitude improvements for a sparse hole and periodic dense hole. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.25.Hz Interference
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
42.15.Fr Aberrations

Optical, electrical, and structural characteristics of yttrium oxide films deposited on plasma etched silicon substrates

J. J. Araiza, M. A. Aguilar-Frutis, and C. Falcony

J. Vac. Sci. Technol. B 19, 2206 (2001); http://dx.doi.org/10.1116/1.1418399 (6 pages) | Cited 6 times

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Yttrium oxide thin films were deposited on Si(100) substrates using the rf-sputtering technique at low power density and low temperatures (up to 300 °C). Previous to deposition, the substrates were plasma etched during different lengths of time. The characteristics of these films and the effect of surface etching on the substrate were studied by ellipsometry, x-ray diffraction at grazing angle, atomic force microscopy, and x-ray energy dispersive spectroscopy (EDS). The deposited films were polycrystalline, presenting cubic and/or monoclinic phases. The deposition rate, refractive index, surface roughness, and degree of crystallinity were strongly dependent on etching time of the substrate, especially for low deposition temperatures. The electrical characterization of the films incorporated in a metal–oxide–semiconductor structure showed a good dielectric constant value (up to 11), surface states densities as low as 6.7×1011 cm−2 eV−1 at midgap and breakdown strength in the range of 1.16–4.84 MV/cm. EDS measurements on these films showed a higher oxygen content than expected for Y2O3 stoichiometry. © 2001 American Vacuum Society.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
73.20.At Surface states, band structure, electron density of states
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
77.22.Jp Dielectric breakdown and space-charge effects

Photoemission study of energy-band alignments and gap-state density distributions for high-k gate dielectrics

Seiichi Miyazaki

J. Vac. Sci. Technol. B 19, 2212 (2001); http://dx.doi.org/10.1116/1.1418405 (5 pages) | Cited 114 times

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The determination of the energy band gaps of thin-gate insulators has been demonstrated from the onsets of the energy-loss spectra of O 1s (or N 1s) photoelectrons. The valence-band lineups of thin high-dielectric-constant (high-k) dielectrics such as Ta2O5, Al2O3, and ZrO2 formed on metals and Si(100) have also been determined by measuring the energy difference between the valence-band density-of-states curves. The energy band diagrams for metal/high-k dielectrics/Si(100) systems have been derived explicitly from considering the measured band gaps, valence-band lineups, electron affinities, and metal work functions in the systems. It is also demonstrated that total photoelectron yield spectroscopy can be used to quantify the energy distributions of both the defect states in high-k gate dielectrics and at the dielectric/Si(100) interfaces over the entire Si band gap without gate formation. © 2001 American Vacuum Society.
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79.60.Jv Interfaces; heterostructures; nanostructures
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.20.Ps Other inorganic compounds
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.60.Dp Adsorbed layers and thin films
73.20.At Surface states, band structure, electron density of states
77.55.-g Dielectric thin films
73.30.+y Surface double layers, Schottky barriers, and work functions

Photoluminescence characterization of Si-based nanostructured films produced by pulsed laser ablation

A. V. Kabashin, M. Meunier, and R. Leonelli

J. Vac. Sci. Technol. B 19, 2217 (2001); http://dx.doi.org/10.1116/1.1420494 (6 pages) | Cited 14 times

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Photoluminescence (PL) properties of nanostructured Si-based films produced by pulsed laser ablation in a residual gas are studied. Two types of PL signals have been identified. Signals of the first type are sensitive to the ablation conditions with the PL peak position depending on the gas pressure during the deposition. Signals of the second type with PL peaks around 1.6–1.7 and 2.2– 2.3 eV are almost independent of the ablation conditions and are mainly determined by the presence of oxygen-related complexes in the film composition. These complexes can be formed through a prolonged natural oxidation or thermal annealing of the films, or through the direct laser ablation in the presence of oxygen. Possible mechanisms of PL signals are discussed. © 2001 American Vacuum Society.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
81.15.Fg Pulsed laser ablation deposition
81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Etch mechanisms of low dielectric constant polymers in high density plasmas: Impact of charging effects on profile distortion during the etching process

D. Fuard, O. Joubert, L. Vallier, M. Assous, P. Berruyer, and R. Blanc

J. Vac. Sci. Technol. B 19, 2223 (2001); http://dx.doi.org/10.1116/1.1420492 (8 pages) | Cited 14 times

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We have studied the etching of very high aspect ratio contact holes in hydrocarbon materials SiLK™, potential dielectric candidates for the next generation of interconnections. During the etch process, slight deformation of the etch profiles such as bowing are observed. Experiments described in this article suggest that bowing originates from the deflection of ions on the sidewalls of the polymer, generating some etching. The mechanisms leading to the ion deflection on the sidewalls are presented and discussed. This study also shows how the process can be tuned to minimize the bow formation. © 2001 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
85.40.Ls Metallization, contacts, interconnects; device isolation
77.84.Jd Polymers; organic compounds
52.77.Bn Etching and cleaning
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Etching characteristics and plasma-induced damage of high-k Ba0.5Sr0.5TiO3 thin-film capacitors

D. S. Wuu, C. C. Lin, R. H. Horng, F. C. Liao, and Y. H. Liu

J. Vac. Sci. Technol. B 19, 2231 (2001); http://dx.doi.org/10.1116/1.1420205 (6 pages) | Cited 7 times

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The inductively coupled plasma (ICP) etching behavior of Ba0.5Sr0.5TiO3 (BST) thin films has been characterized with Cl2/Ar gas mixtures by varying the process parameters such as chamber pressure, ICP power, and substrate bias rf power. The etching characteristics of BST were investigated in terms of etch rate, etch profile, surface residue, and electrical properties. The results obtained can be further interpreted by the plasma properties (ion flux and dc bias) in situ measured by a Langmuir probe. Quantitative analysis of the plasma-induced damage in the Pt/BST/Pt capacitor was attempted to discuss the mechanism of leakage current density and dielectric constant with various substrate bias rf power and ICP power levels. Finally, optimization of the etch parameters for fabricating BST capacitors was performed to minimize the plasma-induced damage. The optimum condition appears to be under a 30% Cl2/(Cl2+Ar) gas mixture, ICP power of 800 W, substrate bias rf power of 100 W, and chamber pressure of 0.67 Pa. Furthermore, it is found that the damage samples can be effectively recovered after annealing at 600 °C in oxygen ambient. The result can be confirmed by the x-ray diffraction data, which indicates that an improvement of BST crystalline quality after annealing occurs. This makes the leakage current density of the Pt/BST/Pt capacitor decrease to 3×10−7 A/cm2 under an applied voltage of 1.5 V, while its dielectric constant can recover from 150 to 180. © 2001 American Vacuum Society.
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84.32.Tt Capacitors
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Structural and optical properties of ternary Cs–Pb–Cl nanoaggregates in thin films

F. Somma, P. Aloe, S. Lo Mastro, S. Santucci, C. Giampaolo, M. Nikl, K. Nitsch, P. Fabeni, and G. P. Pazzi

J. Vac. Sci. Technol. B 19, 2237 (2001); http://dx.doi.org/10.1116/1.1421542 (3 pages) | Cited 4 times

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Ternary nanophases of CsPbCl3 and Cs4PbCl6 were evidenced in co-evaporated CsCl–PbCl2 thin films using x-ray diffraction spectroscopy. A morphological study by atomic force microscopy revealed the granular nature of the films consisting of the grains of about 150 nm size. The optical properties of CsPbCl3 and Cs4PbCl6 nanostructures were determined. CsPbCl3 is a wide gap semiconductor with direct band transitions and a pronounced Wannier free exciton emission round 418 nm at 5 K with a very small Stokes shift. Cs4PbCl6 is characterized by the auto-localized exciton emission around 365 nm. In both cases, the optical features are closely similar to the bulk ternary crystals which were reported earlier. © 2001 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Ps Atomic force microscopy (AFM)
78.40.Fy Semiconductors
78.55.Hx Other solid inorganic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Scaling considerations for high performance 25 nm metal–oxide–semiconductor field effect transistors

Samar Saha

J. Vac. Sci. Technol. B 19, 2240 (2001); http://dx.doi.org/10.1116/1.1420207 (7 pages) | Cited 4 times

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This article presents a systematic simulation-based study on scaling gate oxide thickness and the source–drain extension junction depth to achieve high performance 25 nm metal–oxide–semiconductor field effect transistor devices for low power operation. In order to obtain the target 25 nm devices, complementary metal–oxide–semiconductor (CMOS) technologies were designed by scaling source–drain extension junction depths to 14, 20, and 26 nm and the corresponding gate lengths to 40, 50, and 60 nm, respectively. Each technology was separately optimized for each value of the equivalent gate oxide thickness 1, 1.5, and 2 nm to achieve the target value of off-state leakage current of about 10 nA/μm for 25 nm devices. The simulation results show that for a low voltage operation of 25 nm devices with a fixed off-state leakage current, the magnitude of threshold voltage, subthreshold slope, and the drain-induced barrier lowering is too high while the magnitude of drive current is too low for gate oxide thickness ⩾1.5 nm. However, the variation in the magnitude of threshold voltage, subthreshold slope, drain-induced barrier lowering, and the drive current for the similar devices is insignificant within the range of source–drain extension junction depth between 14 and 26 nm. It is also found that the increase in the gate delay is ⩾12% for 25 nm devices with the source–drain extension junction depth ⩾20 nm compared to the similar devices with a source–drain extension junction depth of about 14 nm. This article demonstrates that the continuous scaling of gate oxide thickness below 1.5 nm and the source–drain extension junction depth below 20 nm is essential for achieving high performance CMOS technologies with 25 nm nominal devices for low power application. © 2001 American Vacuum Society.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
81.16.-c Methods of micro- and nanofabrication and processing

Characteristic features of new electron-multiplying channels in a field emission display

Whikun Yi, Taewon Jeong, Sunghwan Jin, SeGi Yu, Jeonghee Lee, Jungna Heo, Jibeom Yoo, and J. M. Kim

J. Vac. Sci. Technol. B 19, 2247 (2001); http://dx.doi.org/10.1116/1.1420206 (5 pages)

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We have developed a microchannel plate (MCP) to increase the efficiency of a field emission display (FED) by introducing new materials and process technologies. A substrate was constructed with alumina, and channel walls of pore arrays of the MCP were deposited with thin films using electroless plating and sol-gel process. The resulting MCP has been evaluated with a high input current source from a continuous electron beam and from Spindt-type field emitters. Some features of the MCP were also characterized in terms of brightness, anode current, input and output pulse, and focused luminescent spot, in a FED. With the MCP between the cathode and the anode of a FED, the brightness and anode current increased four- to fivefold due to electron multiplication through an array of pores in the device. In addition, the fabricated microchannel plate was found to prevent spreading of electrons emitted from the cathode tips, thus improving both display resolution and picture quality. © 2001 American Vacuum Society.
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85.45.Fd Field emission displays (FEDs)
79.70.+q Field emission, ionization, evaporation, and desorption
41.85.Ew Particle beam profile, beam intensity

X-ray photoemission spectroscopy study of silicidation of Ti on BF2+-implanted polysilicon

H. N. Chua, K. L. Pey, W. H. Lai, J. W. Chai, J. S. Pan, D. H. C. Chua, and S. Y. Siah

J. Vac. Sci. Technol. B 19, 2252 (2001); http://dx.doi.org/10.1116/1.1421565 (6 pages) | Cited 1 time

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Evaluation of fluorine-related species during Ti silicidation on BF2+-implanted polycrystalline silicon (polySi) under different temperatures has been studied using x-ray photoemission spectroscopy (XPS). The silicidation was carried out under sequential anneals from 500 to 700 °C with an interval of 50 °C in an ultrahigh vacuum (UHV) within the XPS chamber. The binding energy and peak intensity for Si 2p, Ti 2p, F 1s, O 1s, B 1s, and C 1s XPS peaks have been measured in the same XPS chamber immediately after the silicidation anneal without breaking the vacuum. The results show that fluorine from the BF2+ implantation is dissociated to form a mixture of SiFx (1⩽x⩽4) and TiFx (x=3,4) -like gaseous species at/near the TiSi2/polySi interface upon silicidation anneal. This can be characterized by the approximately 1.2 eV per Si–F bond chemical shift of the Si 2p core level, and the peak position for Ti 2p core levels with the resolved peaks at 465.1 eV corresponding to the Ti–F bond. The F 1s peaks further confirm the presence of SiFx and TiFx species. As the silicidation proceeds to higher temperatures, the intensity of these reaction species decreases due to their out-diffusion from the thin TiSi2 layer. These findings correlate well with the previously reported results on the void formation in sub-quarter-micron BF2+-implanted Ti-salicided polySi lines [H. N. Chua et al., J. Appl. Phys. 87, 8401 (2000)]. © 2001 American Vacuum Society.
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61.72.uf Ge and Si
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Scanning probe microscopy of domains and domain walls in sol–gel PbTiO3 thin films

Xiaofeng Chen, Weiguang Zhu, Weiguo Liu, and Zhihong Wang

J. Vac. Sci. Technol. B 19, 2258 (2001); http://dx.doi.org/10.1116/1.1421569 (4 pages) | Cited 4 times

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We report results on ferroelectric domain and domain-wall observation in sol–gel PbTiO3 thin films using scanning probe microscopy. By taking the phase and amplitude image of the local domain piezovibration separately, more information is given to interpret the domain contrast owing to the a domain and different crystallographic orientations. Particularly, the a–c and c–c domain walls appear as a transition region and a dark region in the amplitude image, respectively, and the corresponding thickness is estimated to be 70 and 8 nm. A torsion vibration model is proposed to describe the tip vibration at the c–c domain wall, which results in the dark contrast correspondingly. © 2001 American Vacuum Society.
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77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.37.-d Microscopy of surfaces, interfaces, and thin films

Automated Xe adsorption technique to measure small Brunauer–Emmett–Teller surface area of several square centimeters

Hiroshi Yanazawa, Ryoichi Furukawa, Satoshi Yamamoto, Isao Suzuki, and Kazuhisa Miura

J. Vac. Sci. Technol. B 19, 2262 (2001); http://dx.doi.org/10.1116/1.1421564 (6 pages) | Cited 1 time

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An automated Xe adsorption apparatus has been developed that enables the measurement of a Brunauer–Emmett–Teller (BET) surface area of several cm2 with a repeatability of 4% (standard deviation). The apparatus is equipped with a differential type capacitance manometer, each hand of which is connected to a sample and reference adsorption cell having a symmetrical design, that is the temperature-compensated volumetric system which was reported by one of the authors [I. Suzuki, Rev. Sci. Instrum. 53, 1061 (1982); ibid., 66, 5070 (1995); ibid., 68, 4531 (1998)]. All procedures for measuring gas adsorption are computer controlled, and the coolant meniscus height is also computer controlled to keep the adsorption cell volume constant. A specially polished Si crystal rod was adopted as the standard sample. The BET surface area of the standard sample was measured by both the original temperature-compensated system and the newly developed automated system. Obtained results are fully consistent. We propose the adsorption cross section of Xe to be 0.25 nm2 based on our measurements. In addition, we demonstrate a series of experimental results which show a quantitative correlation between the capacitance and surface microroughness of a capacitor with rugged surface electrode. © 2001 American Vacuum Society.
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82.80.-d Chemical analysis and related physical methods of analysis
68.43.Mn Adsorption kinetics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.07.Mp Transducers
07.05.Bx Computer systems: hardware, operating systems, computer languages, and utilities

Carrier mobilities and process stability of strained Si n- and p-MOSFETs on SiGe virtual substrates

M. T. Currie, C. W. Leitz, T. A. Langdo, G. Taraschi, E. A. Fitzgerald, and D. A. Antoniadis

J. Vac. Sci. Technol. B 19, 2268 (2001); http://dx.doi.org/10.1116/1.1421554 (12 pages) | Cited 106 times

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Surface channel strained Si metal–oxide–semiconductor field-effect transistors (MOSFETs) are a leading contender for future high performance complementary metal–oxide–semiconductor (CMOS) applications. The carrier mobility enhancement of these devices is studied as a function of channel strain, and the saturation behavior for n- and p-channel devices is compared. Carrier mobility enhancements of up to 1.8 and 1.6 are achieved for n- and p-channel devices, respectively. The process stability of strained Si MOSFETs is also studied, and carrier mobility enhancement is shown to be robust after well implantation and virtual substrate planarization steps. The effects of high-temperature implant activation anneals are also studied. While no misfit dislocation introduction or strain relaxation is observed in these devices, increased interface state densities or alloy scattering due to Ge interdiffusion are shown to decrease mobility enhancements. Channel thickness effects are also examined for strained Si n-MOSFETs. Loss of carrier confinement severely limits the mobility of devices with the thinnest channels. Overall, surface channel strained Si MOSFETs are found to exhibit large carrier mobility enhancements over coprocessed bulk Si devices. This, combined with the high process stability exhibited by these devices, makes them superb candidates for future CMOS applications. © 2001 American Vacuum Society.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.65.Ps Polishing, grinding, surface finishing
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing
68.60.Bs Mechanical and acoustical properties

Growth and characterization of Fe(100)/InAs(100) hybrid structures

Hiroshi Ohno, Kanji Yoh, Toshihiro Doi, Agus Subagyo, Kazuhisa Sueoka, and Koichi Mukasa

J. Vac. Sci. Technol. B 19, 2280 (2001); http://dx.doi.org/10.1116/1.1421563 (4 pages) | Cited 6 times

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We report on the growth of planar/patterned Fe thin films on InAs(100) substrates and their subsequent characterization using reflection high-energy electron diffraction, low-energy electron diffraction, superconducting quantum interference device, and four-terminal contact resistance measurements. Epitaxial growth of body-centered-cubic Fe crystal on InAs(100) was verified for growth temperatures of 23 °C and 175 °C. A patterned Fe wire array showed clear uniaxial shape anisotropy with the easy axis along the wire direction. Its coercive force was found to depend on the growth temperature and the width of the Fe wires. Four-terminal contact resistance measurement of Fe/n-InAs revealed that Fe forms decent ohmic contact to the InAs substrate with a resistivity of the order of 10−6 Ω cm2. Samples grown at room temperature showed equally decent or even better magnetic and electrical characteristics than those obtained by higher temperature growth. These results indicate that the Fe/InAs hybrid structures have definite potential for spin-related semiconductor devices with practical process sequences. © 2001 American Vacuum Society.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
73.40.Ns Metal-nonmetal contacts
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
73.40.Cg Contact resistance, contact potential
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Structure analysis of Ba2In2O5 and related compounds by electron microscopy

M. Mitome, M. Okamoto, Y. Bando, and H. Yamamura

J. Vac. Sci. Technol. B 19, 2284 (2001); http://dx.doi.org/10.1116/1.1421566 (5 pages) | Cited 5 times

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Crystal structures of Ba2In2O5: (Ba1−xLax)2In2O5+x (x=0.1, 0.2, 0.3, and 0.5), and Ba2(In1−xGax)2O5 (x=0.1, 0.2 and 0.5) are analyzed by transmission electron microscopy and electron diffraction. Ba2In2O5 has an orthorhombic brownmillerite structure and belongs to space group Ibm2. (Ba1−xLax)2In2O5+x has a tetragonal brownmillerite structure while Ba2(In1−xGax)2O5 has an orthorhombic brownmillerite structure. These compounds consist of small domains that are at 90° orientation to each other. The domain size gets small with increasing La or Ga content. The oxygen vacancies are distributed randomly in the compounds with high La or Ga content, and consequently, the structure approximates as a cubic perovskite structure.© 2001 American Vacuum Society.
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61.66.Fn Inorganic compounds
61.72.J- Point defects and defect clusters

Characteristics of sputtered Ti1−xAlxN films for storage node electrode barriers

Dae-Gyu Park, Tae-Ho Cha, Sang-Hyeob Lee, In-Seok Yeo, Jin Won Park, and Sam-Dong Kim

J. Vac. Sci. Technol. B 19, 2289 (2001); http://dx.doi.org/10.1116/1.1421567 (6 pages) | Cited 8 times

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We report on the characteristics of sputter-deposited Ti1−xAlxN (TiAlN) thin films for storage node electrode barriers of Pt/(BaSr)TiO3(BST)/Pt metal–insulator–metal (MIM) capacitors with a comparative study of TiN films. The substrate temperature (Ts) was found to be one of the key factors affecting the properties of TiAlN thin films, i.e., the resistivity of TiAlN is ∼350 μΩ cm for high Ts deposition (∼450 °C) and ∼1100 μΩ cm for low Ts (∼100 °C). The lower resistivity of TiAlN films deposited at high Ts (450 °C) is attributed to the (200) texture with larger grain size and smaller oxygen concentration compared to those prepared at low Ts. The electrical characteristics of Pt/BST/Pt MIM capacitors on TiAlN were superior to those on the TiN barrier in terms of smaller equivalent oxide thickness (tox), lower tangent δ, and lower leakage current. Better oxidation resistance of TiAlN over TiN appears to be responsible for the better electrical results, especially with the (111) or (200) texture. We also discuss a BST bulge and local thinning due to the Pt deformation on TiAlN over an anneal of 600 °C in O2, resulting in leakage current degradation of the BST MIM capacitor. © 2001 American Vacuum Society.
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84.32.Tt Capacitors
66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.Cd Deposition by sputtering
85.30.Tv Field effect devices

Three-dimensional carrier concentration profiles and ionization energy plots for low-temperature GaAs

N. C. Halder, V. Krishnan, and Bradley Baker

J. Vac. Sci. Technol. B 19, 2295 (2001); http://dx.doi.org/10.1116/1.1421568 (4 pages) | Cited 1 time

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We have investigated the carrier concentration profiles in molecular-beam epitaxy-grown, Si-implanted, low-temperature (LT) GaAs. The samples were grown at 300 °C and the Schottky diodes were fabricated using Au contacts. The capacitance voltage measurements were made in the temperature range 100–350 K at an interval of 2 K. From the field-effect transient spectroscopy experiments, data were collected for the peak positions and peak energy of the trap levels. The effective carrier concentration increased with temperature showing a saturation around 350 °C. The ionization energy of the carriers indicated a linear relationship. The overall results indicate that the carrier concentration in three-dimensional mapping is a reliable indicator of the sample quality and of the Schottky diode characteristics. Additionally, one should be specific about the temperature and the reverse bias voltage before selecting the value of the carrier concentration when determining the deep trap concentration in semiconductors, specifically, in LT GaAs. © 2001 American Vacuum Society.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
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Nanostructure patterns written in polycarbonate by a bent optical fiber probe

Sy-Hann Chen and Yung-Fu Chen

J. Vac. Sci. Technol. B 19, 2299 (2001); http://dx.doi.org/10.1116/1.1421555 (2 pages) | Cited 1 time

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An atomic force microscope operated in tapping mode using a homemade bent optical fiber probe was used to pattern nanometer-scale features. Trenches of different dimensions were written on polycarbonate that was pre-exposed to an excimer laser. Lines with widths varying from 260 to 600 nm and depths ranging from 30 to 120 nm have been made. The present technique as a complementary tool to other lithographic processes has been demonstrated to be potentially suitable for low-cost and high-precision applications. © 2001 American Vacuum Society.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
07.79.Lh Atomic force microscopes
42.81.Wg Other fiber-optical devices
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Electron-beam CARL resist development for 70 nm direct write

O. Kirch, K. Elian, and G. Falk

J. Vac. Sci. Technol. B 19, 2301 (2001); http://dx.doi.org/10.1116/1.1418403 (3 pages)

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Because of the need of 70 nm structures in the near future, electron-beam (e-beam) lithography as a means for high resolution lithography is discussed mostly for mask or ASIC fabrication but also for the application in standard lithography. Besides the improvement of new e-beam writing concepts including software and hardware enhancement, the development of new resists and processes is a main objective for a high throughput production. To understand the principal reactions that occur during the patterning process we decided to carry out basic examinations based on chemical amplification of resist lines (CARL) [W.-D. Domke et al., Microlithogr. World 42, 2 (1999)] resist materials. The first step was to look at the interaction between the polymer and e-beam. Polymers consisting of chemically identical monomers were synthesized in different molecular ratios and processed as resists without other additives. Detailed investigations of the resists included e-beam patterning with a JEOL JSM-840A/nanobeam pattern generator. The next step was to examine the CAR reaction, i.e., the interaction of the polymer/photoacid generator matrix with the e-beam electrons. Perfluorinated alkysulfonates as PAGs were focused. These compounds generate very strong acids through irradiation. They can be compared, e.g., by their different acid strength, different vapor pressure of the resulting acid, and by their different molecular size. These parameters strongly affect the acid diffusion and consequently the resist resolution as far as the line edge roughness. Within this current article the first complete resist mixtures have been evaluated under process conditions. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Reduction in surface roughness during secondary ion mass spectrometry depth profiling with an ion-milling method

Z. X. Jiang, S. Backer, S. Chen, J. Lerma, T. Guenther, J. J. Lee, and D. Sieloff

J. Vac. Sci. Technol. B 19, 2304 (2001); http://dx.doi.org/10.1116/1.1421553 (3 pages) | Cited 3 times

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Depth resolution for secondary ion mass spectrometry (SIMS) profiling of poly Si/SiO2/Si gate stacks is often hindered by roughness of poly Si surfaces. In order to maintain the high depth resolving power of low-energy SIMS for the gate stacks, an ion-milling method was developed to smoothen and thin poly Si films by O2+ beam bombardment at normal incidence. The ion milling has led to a remarkable smoothening in the sputtered area: the rms roughness in poly Si was reduced from 4.5 to 0.6 nm, after removal of 120 nm poly Si by 5 keV O2+ bombardment at normal incidence. SIMS profile analyses with the ion milling provided detailed in-depth distributions of As and Si in a gate stack, showing vividly the pile up of As at the poly Si/SiO2 interface and the difference in the beam-induced diffusion of As in Si and SiO2. © 2001 American Vacuum Society.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.Dv Composition, segregation; defects and impurities
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back to top PLENARY SESSION

From nanometers to gigaparsecs: The role of nanostructures in unraveling the mysteries of the cosmos

Mark L. Schattenburg

J. Vac. Sci. Technol. B 19, 2319 (2001); http://dx.doi.org/10.1116/1.1418410 (10 pages) | Cited 5 times

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High launch costs and the extreme distance to astrophysical objects place a premium on astrophysical instrumentation with the highest attainable sensitivity and resolution at the lowest possible weight and cost. Many interesting and useful optical phenomena occur when the size and placement accuracy of features are comparable to, or smaller than, the wavelength of light. These considerations have compelled us to develop a variety of nanotechnoligies that have now been utilized in space physics instrumentation on nine missions. These include 200- and 400-nm-period membrane-supported transmission gratings for high-resolution spectroscopy of astrophysical x-ray sources, mesh-supported transmission gratings for solar extreme ultraviolet (EUV) monitoring, and UV nanofilters with 45 nm slots that are key components of atom cameras observing Earth’s magnetosphere. This article will describe instruments on space missions where we have applied nanotechnology. One application is the NASA Chandra Observatory x-ray telescope, for which we manufactured a large quantity of transmission gratings for high-resolution spectroscopy. Chandra is now returning a torrent of high-quality x-ray images and spectra from such interesting objects as supernova remnants, the accretion disks around black holes and neutron stars, stellar coronae, galaxy cluster cooling flows, and other x-ray-emitting objects up to gigaparsecs distant. [A short astronomy lesson: As Earth orbits Sol, nearby stars in the sky appear to wobble due to parallax. At a distance of one parsec (a “parallax-second”), the diameter of Earth’s orbit (∼1.5×1011 m) subtends one arcsecond, so a parsec is around 3.3 light years, or 3.1×1016 m. For reference, the nearest star is around a parsec away, our Milky Way galaxy is a few kiloparsecs across, nearby galaxies are megaparsecs away, and the known universe is measured in gigaparsecs (1025 m).] Another application is the atom “camera” on the NASA Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft that studies Earth’s magnetosphere, the belt of plasma around the Earth formed by swept-up ions from the Solar wind trapped in the bottle of Earth’s magnetic field. The camera images the magnetosphere in the “light” of neutral atoms, rather than photons, emitted from the plasma due to charge exchange processes. We developed nanofilters, consisting of 500-nm-thick gold foils with 45-nm-wide slots, that are designed to block unwanted deep-UV and EUV photons which would otherwise overwhelm the detector with a million-to-one noise-to-signal ratio, thus allowing the camera to detect the weak atom fluxes. IMAGE is now sending back spectacular atom movies of the magnetosphere revealing a wealth of new information about this complex and dynamic environment. Finally, I describe work in our laboratory aimed at developing microtechnology for the shaping and assembly of glass microsheet optics to few-nanometer accuracy. We believe these new x-ray optics will spawn a new generation of diffraction-limited x-ray telescopes with massive collecting areas and resolution approaching 0.1 microarcsecond (∼1 picoradian). These new telescopes may enable the direct imaging of the massive black holes believed to lurk at the center of most galaxies. © 2001 American Vacuum Society.
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95.55.Ka X- and γ-ray telescopes and instrumentation
94.80.+g Instrumentation for space plasma physics, ionosphere, and magnetosphere
95.55.Ev Solar instruments
81.07.-b Nanoscale materials and structures: fabrication and characterization
07.85.Nc X-ray and γ-ray spectrometers
41.50.+h X-ray beams and x-ray optics
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Low-k1 optical lithography for 100 nm logic technology and beyond

Anthony Yen, Shinn-Sheng Yu, Jeng-Horng Chen, Chun-Kuang Chen, Tsai-Sheng Gau, and Burn Jeng Lin

J. Vac. Sci. Technol. B 19, 2329 (2001); http://dx.doi.org/10.1116/1.1412894 (6 pages) | Cited 4 times

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In this article, we present 193 nm lithography at a k1 factor of 0.37–0.40 and discuss several topics important to 100 nm logic such as optical proximity correction (OPC), control of critical dimension (CD) variation, and lowering of the mask error factor (MEF). In OPC, the best correction results can be achieved by developing accurate models and using reasonable segmentation rules. The technique of variable-dose exposures is demonstrated as a means to reduce interfield CD variation once the cause is known and can be characterized. A more than 30% reduction in CD variation is realized for variation caused by temperature nonuniformity in hot plates. The concept of two dimensional (2D) MEF is introduced to describe situations at feature ends. Higher numerical aperture or more effectively, quadrupole illumination, can be used to lower 1D and 2D MEFs. We also explore the technique of dipole illumination, which may be a candidate for taking optical lithography to k1<0.35. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
84.30.Sk Pulse and digital circuits

Image metrology and system controls for scanning beam interference lithography

Carl G. Chen, Paul T. Konkola, Ralf K. Heilmann, G. S. Pati, and Mark L. Schattenburg

J. Vac. Sci. Technol. B 19, 2335 (2001); http://dx.doi.org/10.1116/1.1409379 (7 pages) | Cited 12 times

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We are developing scanning beam interference lithography (SBIL) for writing and reading large gratings with nanometer level distortion. Our distortion goals require fringe locking to a moving substrate with subnanometer spatial phase error while measuring and controlling the fringe period to approximately one part per million. In this article, we describe the SBIL optical system design along with some major subsystems. The design incorporates measurements and controls of the parameters that limit the accuracy of our system. We describe in detail a novel image metrology scheme, which uses interferometry to measure in situ both the period and the phase of the grating image formed by the interference of two laser beams. For a grating period of approximately 2 μm, experiments demonstrate a period measurement repeatability of three parts per ten thousand, one sigma. Phase measurement indicates a slow fringe drift at 0.25 mrad/s. Both the repeatability error and the phase drift are expected to improve by about three orders of magnitude after several improvements including the installation of an environmental enclosure and thermally stable metrology frames. © 2001 American Vacuum Society.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
42.79.Dj Gratings

Digital heterodyne interference fringe control system

Ralf K. Heilmann, Paul T. Konkola, Carl G. Chen, G. S. Pati, and Mark L. Schattenburg

J. Vac. Sci. Technol. B 19, 2342 (2001); http://dx.doi.org/10.1116/1.1410096 (5 pages) | Cited 12 times

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In traditional interference lithography, interference fringes are typically phase locked to a stationary substrate using analog homodyne photodiode signals that are fed back to control a phase-shifting device such as an electro-optic modulator or a piezoelectrically transduced mirror. Commercially available fringe-locking systems based on this approach often achieve stability of the interference fringes to within a small fraction of the fringe period p (typically ±p/20 peak-to-peak). We describe the performance of a heterodyne fringe control system utilizing acousto-optic phase shifters and digital controls that is designed to satisfy the much more stringent fringe control requirements for scanning beam interference lithography. We demonstrate locking to ±p/100, and expect further significant improvements. This versatile system can also be used to lock the phase of moving fringes in almost arbitrary fashion at fringe velocities up to 2.5×107 periods/s and to measure the phase of gratings. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
42.79.Jq Acousto-optical devices
07.05.Dz Control systems

Method for reducing hyperbolic phase in interference lithography

Michael E. Walsh and Henry I. Smith

J. Vac. Sci. Technol. B 19, 2347 (2001); http://dx.doi.org/10.1116/1.1421558 (6 pages) | Cited 7 times

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A new method is proposed for correcting nonlinear spatial phase in gratings produced with spherical beam interference lithography. We suggest that a concave exposure surface can be used to compensate for the variations in interference angle and fringe inclination which lead to hyperbolic phase progression on a flat exposure plane. Experiments are shown using a spherical concave exposure surface that demonstrate the validity of the method. © 2001 American Vacuum Society.
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42.79.Dj Gratings
42.25.Hz Interference
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
42.30.Ms Speckle and moiré patterns

Immersion lithography at 157 nm

M. Switkes and M. Rothschild

J. Vac. Sci. Technol. B 19, 2353 (2001); http://dx.doi.org/10.1116/1.1412895 (4 pages) | Cited 43 times

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We present a preliminary study on the feasibility of immersion lithography at 157 nm for patterning below 70 nm. This technology can enable an enhancement in resolution of ∼40% without radical changes in lasers, optics, or resist technology. We have identified a class of commercially available liquids, perfluoropolyethers, which are good candidates for use as immersion liquids. They are transparent (α≈10−3 μm−1 base 10), optically clean, chemically inert, and compatible with at least some current resist materials and with the semiconductor manufacturing environment. We have also constructed a high-resolution lensless interference immersion lithography system, preserving much of the design of a previous nonimmersion interference system. With this immersion interference tool, we have patterned resist with 30 nm dense features. © 2001 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Feasibility of utilizing hexamethyldisiloxane film as a bottom antireflective coating for 157 nm lithography

C. H. Lin and L. A. Wang

J. Vac. Sci. Technol. B 19, 2357 (2001); http://dx.doi.org/10.1116/1.1417549 (5 pages) | Cited 1 time

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The feasibility of utilizing a bottom antireflective coating (BARC) layer composed of hexamethyldisiloxane (HMDSO) film for 157 nm lithography is studied. The vaporized liquid HMDSO is used as a coating material in a conventional electron cyclotron resonance-plasma enhanced chemical vapor deposition process. The required optical constants of suitable HMDSO films can easily be tuned by adjusting the gas flow rate ratio of O2 to HMDSO. The swing effect is experimentally shown to be reduced significantly on Si substrates by applying either a single layer BARC or a bilayer BARC. Additionally, the bilayer BARC is shown by simulation to be capable of providing larger thickness-controlled tolerances than a single layer BARC. © 2001 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Hp Lithography, masks and pattern transfer
42.79.Wc Optical coatings
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Demonstration of two-photon lithography

Ch. J. Schwarz, A. V. V. Nampoothiri, J. C. Jasapara, W. Rudolph, and S. R. J. Brueck

J. Vac. Sci. Technol. B 19, 2362 (2001); http://dx.doi.org/10.1116/1.1418409 (4 pages) | Cited 2 times

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Show Abstract
Two-photon exposure is demonstrated using ∼12 fs duration pulses at a center wavelength of 800 nm and a standard I-line photoresist. Using direct-writing with a focused Gaussian beam, developed resist features as small as 300 nm, compared with the ∼1 μm focal spot diameter, have been achieved. The experiments reveal substantial differences (∼104) in the two-photon absorption coefficient for multiple pulse trains (100 MHz) and for single pulses. A simple model involving photoexcitation of an intermediate conformation of the photoactive compound and relaxation back to the ground state can explain this observation. The resolution enhancement of √ resulting from the two-photon absorption is demonstrated by writing two lines as close as possible to each other with both one- and two-photon absorption mechanisms. © 2001 American Vacuum Society.
Show PACS
85.40.Hp Lithography, masks and pattern transfer