bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent Progress of Low Temperature Poly Si TFT Technology
Authors: Yoneda Kiyoshi
Published: April 2011

Since being introduced to the production line in 1996, replacing the first generation a-Si TFT line, low-temperature poly-Si production technology aimed at manufacturing small and medium size LCD products has improved steadily corresponding to customers' requirements for rapid growth of the DVC and DSC markets. In the future, this production technology must progress to actual industry technology levels in order to cope with production applied not only to large size displays, which have a major market share in the present display market, but also to a large glass substrate, which effectively cuts the cost of products, although improvement of production yield and productivity in terms of pursuing cost reduction must be proceeded.

This paper has described existing problems of inherent low-temperature poly-Si TFT processes and their relating additional processes in present production methods. We have also discussed updating production technologies. To cope with production for a large size display, it is necessary to establish fabrication technology of higher performance TFTs with electron mobility larger than 200cm2/V s. We believe that one key technology is to fabricate a large-scale and highly-uniform recrystallized poly-Si film with smooth surface morphology as well as precisely-controlled grain size in production. To cope with production using a large glass substrate, it is essential to develop ELA equipment with laser power greater than 200W.
Grain Engineering Approaches for High-Performance Polysilicon Thin-Film Transistor Fabrication
Authors: Giust G. K. , Sigmon T. W.
Published: April 2011

Using an approach we call “grain engineering,” we discuss several techniques to control grain growth during excimer laser annealing, to create low-defect density polysilicon films. By adjusting of laser parameters, for example, we obtain polysilicon films with grain sizes of more than 9 µm, without substrate heating. These high-quality films are used in the fabrication of low-temperature unhydrogenated polysilicon thin-film transistors (TFT's) yielding mobilities of > 260 cm2/Vs and on/off current ratios > 107. We investigate the laser recrystallization of “prepatterned” films as another technique of grain engineering. We find the performance of TFT's fabricated in active areas that are prepatterned before laser recrystallization is dramatically improved compared to those TFT's fabricated from the laser recrystallization of blanket polysilicon films. A novel “recessed” structure is also examined as a new grain engineering tool. By depositing a blanket silicon film on a patterned oxide layer on a heat sink, the heat flow through the continuous silicon film may be controlled during laser recrystallization to simultaneously produce adjacent regions of remarkably different grain microstructure.
Electrical Test Sites for AMLCD-TFT Array Process Characterization
Authors: Colgan E.G. , Polastre R.J. , Takeichi M. , Wisnieff R. L.
Published: April 2011

Electrical test structures provide a method of rapid and low cost end-of-process metrology for both materials properties and specific process information. We have demonstrated the use of electrical test structures for monitoring key process parameters such as line width, edge taper width, layer-to-layer alignment, and data metal coverage over topography. These results are compared with those from traditional metrology methods and in all cases, the correlation was good, demonstrating that electrical test structures have sufficient accuracy for process control applications. For the structures used, the line width, edge taper width, and layer-to-layer alignment electrical measurements have uncertainties of less than 0.1 micron. A novel capacitance method was used for layer-to-layer alignment measurements and a combination of resistive and capacitive line width measurements were used to electrically determine the gate metal taper width. The test structures are all compatible with typical thin film transistor array processing.
Variation of the Photoelectric Threshold of Boron Doped Diamond Films
Authors: Akwani I.A. , Sosa E.D. , Bernhard J. , Lim S.C. , Stallcup R.E. , Perez J.M. , Golden D.E.
Published: April 2011

Boron doped polycrystalline diamond films grown on p-type single-crystal Si substrates using chemical vapor deposition with a gas mixture of hydrogen, methane and diborane were characterized with scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Raman spectroscopy and photoelectric current measurements. The energy distributions are not sensitive to boron doping for diborane concentrations from 0 to 4.75 ppm, although the boron doping modifies the surface morphology and the photoemission intensity. The photoemission intensity is high where the microcrystalline content is highest (at diborane concentrations of 2.91 and 4.75 ppm. The photoelectric threshold is found to be at 4.38 eV, in agreement with earlier measurements. The present results are characteristic of valence band emission at 4.38, 4.63, 4.92, 5.12 and 5.30 eV for incident photons between 4.87 and 5.63 eV.
The Effect of Aspect Ratio and SP2/SP3 Content on the Field Emission Properties of Carbon Films Grown by N2-Spiked PECVD
Authors: Tong William M. , Pan Lawrence S. , Felter Thomas E. , Anders Simone , Cossy-Favre Aline , Stammler Thomas
Published: April 2011

We have deposited carbon films from mixtures of methane and N2 using Plasma Enhanced Chemical Vapor Deposition. By changing the percentage of N2 in the feed gas, we were able to produce films that have various aspect ratios and sp2/sp3 contents. The film with the highest field emission contains spears of aspect ratio of 10:1. We also found that in our sp3-rich films, higher sp2 content enhanced field emission. This is ascribed to improved charge transport to the field emission sites.
Comparison of Lateral Field Emitter Characteristics for Titanium Silicide, Poly-Si, and Single Crystal Si Tip
Authors: Lim Moo-Sup , Park Cheol-Min , Han Min-Koo , Choi Yearn-Ik
Published: April 2011

We have fabricated poly-Si, Si, and Ti-silicide field emitter arrays employing in-situ vacuum encapsulated lateral field emitter structures and investigated the field emission characteristics such as turn-on voltage, emission current density, and the stability of emission current. Although poly-Si and Si emitter have almost identical turn-on voltages, Si emitter has a sharper turn-on than poly-Si emitter due to its uniform surface. The current densities of poly-Si, and Si emtter are 0.47, 0.43 μA/tip respectively at anode to cathode voltage of 90 V. The turn-on voltage and current density of Ti-silicide emitter are about 31 V, and 1.81 μA/tip at VAK of 90 V. The data of the normalized current fluctuations indicate that Ti-silicide emitter has the most stable current.

Our experiment shows that Ti-silicide is most promising among these three materials due to its low work function, uniform surface, and the stable characteristics.
Electron Emission Properties of Diamond and III-V Nitrides
Authors: Nemanich R. J. , Baumann P.K. , Benjamin M.J. , English S.L. , Hartman J.D. , Sowers A.T. , Ward B.L. , Yang P.C.
Published: April 2011

Wide bandgap semiconductors such as diamond and the III-V nitrides of GaN and AIN exhibit small or even negative electron affinities. Recent results have shown that surface treatments will modify the electron affinity of diamond to cause a negative electron affinity (NEA). Results are presented which correlate the field emission from single crystal p-type (boron doped) diamond with the electron affinity of the surfaces. The field emission is explored for nitrogen doped polycrystalline films. The threshold for field emission is significantly higher than from p-type diamond, and in fact, most surfaces are severely damaged during the emission measurement. High resolution photo-electron emission microscopy (PEEM) and field emission electron microscopy (FEEM) are employed to determine the relation of the emission to the surface morphology. PEEM results presented for diamond indicate relatively uniform emission with increased intensity at protruding crystallite edges. Results are presented for cold cathodes fabricated from epitaxial nitrides grown on 6H-SiC.
Simultaneous Field Emission and Photoemission Characterization of N-Doped CVD Diamond
Authors: Matsuda Ryuichi , Okano Ken , Pate Bradford B.
Published: April 2011

The kinetic energy and spatial distribution of field electron emission from nitrogen (urea) doped, chemical vapor deposited (CVD) diamond films have been examined with simultaneous field emission and photoemission. A linear Fowler-Nordheim characteristic was measured over a wide range of currents. The field emission electrons originate from distinct areas of the flat sample. The dominant origin of field emission is due to electrons tunneling from near the valence band maximum. A time dependent fluctuation in the kinetic energy and spatial distribution of the emission is observed when the applied electric field (and hence emission current density) is increased well above the emission threshold.
Electron Emission from Gated Diamond Emitter Array
Authors: Ha Seung -Chul , Kang Dae-Hwan , Kim Byung-Sung , Min Seok-Hong , Kim Ki-Bum
Published: April 2011

A novel processing sequence for the formation of gated diamond field emitter arrays (triode system) is proposed and the feasibility is tested by investigating the field emission property. The processing scheme is based on the selective deposition of diamond using the well established nucleation enhanced process on silicon substrate, so called bias enhanced nucleation (BEN). Selective deposition of diamond using the same process was also demonstrated on titanium nitride (TIN) electrode layer. Our preliminary results show that the diamond field emitter is turned on at around 97 V/μm with the current level of about several μA.
Mechanism of Field Emission in Diamond and Diamondlike Carbon
Authors: Robertson J
Published: April 2011

It is shown that the facile electron field emission from diamond and diamond-like carbon occurs because surface groups such as C-H can produce large changes in electron affinity, so that electric fields from the anode can be focused towards unhydrogenated surface areas of high affinity, the fields ending on negative charges in an underlying depletion layer. The resulting downwards band bending creates very large fields which cause Fowler-Nordheim emission, while not exceeding the breakdown field, which is the highest for any solid.
Characterization of Spin -on Glasses by Microindentation.
Authors: Simonyi Eva E. , Lee K.-W. , Cook Robert F. , Liniger Eric G. , Speidell James
Published: April 2011

Spin-on glasses are candidates in the microelectronics industry as low dielectric constant insulating layers. Spin-on glasses are very brittle materials. This paper discusses measurement problems as relevant to the characterization of a brittle material by the indentation technique. As for all polymeric materials curing temperature is the most important preparation parameter. There is a correlation between hardness, Young's modulus, the onset of cracking with curing temperature. This dependence on curing temperature is also expressed by the change in Si-H bond density as shown by FTIR data. Life expectancy or aging characteristics were also investigated for these features. As an example results on silsesquioxane spin -on glasses are presented.
Thermal stability and structural evolution of low-K Fluorinated amorphous carbon during thermal annealing
Authors: Yang Hongning , Tweet Douglas J. , Ma Yanjun , Nguyen Tue , Evans David R. , Hsu S.-T.
Published: April 2011

Highly crosslinked a-F:C films can undergo a significant change after thermal annealing, where the film expands by ∼3%, the density reduces by ∼10% and the internal stress changes from compressive to tensile. The loss of fluorine concentration and the reduction of CF. are accompanied by the transition of (C-C, sp3) to (C=C, sp2) groups. After annealing, the dielectric constant is reduced and the leakage current increases slightly. Most importantly, these changes occur only at the initial stage of annealing. After the initial annealing, the a-F:C film tends to be thermally stable and retains reasonably good electrical properties as a low-k interlayer dielectric. The profound impact of these results on Cu/a-F:C integration will be briefly discussed.
Polymerization of C-Si Films on Metal Substrates: Potential Adhesion/Diffusion Barriers for Microelectronics
Authors: Chen Li , Kelber J. A.
Published: April 2011

Carbon-Silicon polymeric films have been formed by electron beam bombardment (500eV) of molecularly adsorbed vinyl silane precursors under ultra-high vacuum (UHV) conditions. Temperature programmed desorption (TPD) studies show that polymerization is occurring via the vinyl groups, while Auger spectra show that the polymerized films have compositions very similar to the starting precursors; vinyltrichlorosilane (VTCS) or vinyltrimethylsilane(VTMS). VTCSderived films ˜ 100 Å thick show no reaction with Cu substrates and no diffusion of Cu until temperatures greater than 700 K, while Cu deposited on VTMS films on Al substrates show no diffusion prior to Al reaction/decomposition at 600 K. Auger and TPD studies also show that fluorocarbon precursors, such as perfluorobenzene can be incorporated into the films by e-beaminduced reactions, a first step in the controlled growth of adherent polymer films on unreactive substrates such as Cu.
Time-Dependent Reliability Of The Interface Between A-C:F And Inorganic Dielectrics
Authors: Endo Kazuhiko , Shinoda Keisuke , Tatsumi Toni , Matsubara Yoshihisa , Iguchi Manabu , Horiuchi Tadahiko
Published: April 2011

We have investigated the time dependent reliability of a-C:F films, and found that SiO 2 or SiN cover layers on a-C:F films peeled off partially after about a week when the a-C:F film was grown from C4F8. and annealed in N2 or grown from C4F8+CH4. The interfaces between a-C:F and SiN have a mixing layer indicating a radical reaction at the interface. An a-C:F film grown from C4F8+CH4 has greater water-absorption than a film grown from C4F8 Thus, hydrolysis and radical formation after annealing may cause degradation of the interface. We found that hydrogen annealing effectively decreases the dielectric constant and suppresses such time-dependent degradation.
Templating Nanopores Into Poly(MethylSilsesquioxane): New Lowdielectric Coatings Suitable for MicroElectronic Applications
Authors: Remenar Julius F. , Hawker Craig J. , Hedrick James L. , Kim Sung Mog , Miller Robert D. , Nguyen Cattien , Trollsås Mikael , Yoon Do Y.
Published: April 2011

Thin films of nanoporous poly(methylsilsesquioxane) have been prepared from organic/inorganic polymer hybrids. Low molecular weight 6-arm star poly(caprolactone)s are incorporated into partially pre-condensed methylsilsesquioxane resin. Upon heating, the glass resin cross-links around the organic polymer templates. Thermal decomposition of the orgainc polymer produces nanoporous thin films which show tunable dielectric constants as low as 1.9 and exhibit properties suitable for use in interconnect devices. Experimental data including porosity, morphology, and dielectric constants are presented.
Pulsed Plasma Synthesis of Low Dielectric Constant Materials
Authors: Han Licheng M. , Timmons Richard B. , Lee Wei W.
Published: April 2011

The utility of a variable duty cycle, pulsed plasma polymerization technique to produce low dielectric constant materials (k < 2.3) is described. The molecular compositions (and thus the dielectric constants) of the plasma polymers are controllable via changes in the plasma duty cycles employed during synthesis, all other reaction variables being held constant. In the present study, this compositional controllability under pulsed conditions is illustrated with two fluoroaromatic monomers. The dielectric constants of the films decrease as the plasma duty cycles employed during polymerization are decreased. Although the as deposited films exhibit relatively poor thermal stability, it was discovered that post-plasma annealing of the films, particularly at 400 °C under N2, provides dramatic improvements in the thermal stability of these materials. Most importantly, this enhanced thermal stability is achieved with relatively minor changes in the dielectric properties of these materials. In fact, synthesis of high thermal stability films having k < 2.0 is demonstrated in this work using the perfluoroaromatic monomer perfluoroallyl benzene.
Fabrication and Characterization of Spin-On Silica Xerogel Films
Authors: Nitta S. , Jain A. , Pisupatti V. , Gill W. N. , Wayner P. C. , Plawsky J. L.
Published: April 2011

Xerogel films of high porosity were fabricated using an ambient pressure technique. The same porosity can be obtained with different microstructures by varying the aging time of the films. The dielectric constant of these films as a function of porosity at 1 MHz follows correlations originally developed for bulk aerogels. Diffusion of copper is orders of magnitude faster in these xerogels than in the corresponding thermal oxide. An activation energy of 0.9 eV was estimated based on a convective diffusion model.
Non-Micropipe Dislocations in 4H-SiC Devices: Electrical Properties and Device Technology Implications
Authors: Neudeck P. G. , Huang W. , Dudley M. , Fazi C.
Published: April 2011

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vectors > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per cm 2, nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has been previously shown that diodes containing elementary screw dislocations exhibit a 5% to 35% reduction in breakdown voltage, higher pre-breakdown reverse leakage current, softer reverse breakdown I-V knee, and concentrated microplasmic breakdown current filaments when measured under DC testing conditions. This paper details the impact of elementary screw dislocations on the experimentally observed reverse-breakdown pulse-failure characteristics of low-voltage (< 250 V) small-area (< 5 × 10-4 cm2) 4H-SiC p+n diodes. The presence of elementary screw dislocations did not significantly affect the failure properties of these diodes when subjected to non-adiabatic breakdown-bias pulsewidths ranging from 0.1 μs to 20 μs in duration. Diodes with and without elementary screw dislocations exhibited positive temperature coefficient of breakdown voltage and high junction failure power densities well above the failure power densities exhibited by highly reliable silicon power rectifiers. This preliminary result, based on measurements from one wafer of SiC diodes, suggests that highly reliable low-voltage SiC rectifiers may be attainable despite the presence of elementary screw dislocations.
Cathodoluminescence Deep Level Spectroscopy of Etched and In-Situ Annealed 6H-SiC
Authors: Young A. P. , Aptowitz K. , Brillson L. J.
Published: April 2011

Through variable-energy electron beam excitation (0.5 keV-2.0 keV), we observe depth dependent differences in the cathodoluminescence spectra of 6H-SiC (0001) Si-terminated surfaces. The etched SiC exhibits three deep level defects in the near-surface region, including a defect peak observed at 0.92 eV, known to be associated with vanadium. In-situ annealing produces a dramatic relative decrease in the luminescence from vanadium impurities near the surface after annealing to 500 °C, and then the subsequent re-emergence of vanadium in the nearsurface regime after annealing to 810 °C. This temperature-dependent redistribution suggests either diffusion or segregation of vanadium from the bulk up toward the near-surface region.
Piezoelectric Quantization in GaInN thin Films and Multiple Quantum Well Structures
Authors: Wetzel Christian , Takeuchi Tetsuya , Amano Hiroshi , Akasaki Isamu
Published: April 2011

Details of the electronic bandstructure in pseudomorphic Gal-xInxN/GaN single heterostructures (0 < x < 0.22) are studied. In photocarrier modulated reflectance strong modulation of the density of states (Franz-Keldysh oscillations) is found due to a piezoelectric field of about 0.6 MV/cm in the strained layer. No excitons are expected to form in the presence of this field. Studying the composition dependence we determine a piezoelectric coefficient ∂|P|/∂εzz = 0.46 C/m2 and extrapolate a spontaneous polarization in GaN |Peq| = 3.9 mC/m2. Photoreflection indicates the presence of localized tail states 50 – 100 meV below the bandgap which are well explained by the Franz-Keldysh effect involving k non-conserving transitions in the large electric field. Luminescence is found to originate in these electric field induced states. The derived bandgap energies can be approximated by an interpolation yielding bowing parameters b = 2.6 eV (photoreflection) and b = 3.2 eV (luminescence) for pseudomorphic films with 0.07 ≤ x ≤ 0. 22. These findings may affect interpretation of device performance.
Semiconducting Molybdenum Pyrochlores for high Temperature Applications
Authors: Ponnambalam V. , Varadaraju U. V.
Published: April 2011

The solid solutions (Y1-xYbx)2Mo2O7 were prepared and the systematic changes in the electrical resistivity (ρ=l/σ), thermopower (S) and power factor (S2σ) have been studied in the temperature range 300–900 K. The lattice parameters ‘a’ and ‘c’ are smaller for higher Yb3+ content phases due to smaller Yb3+ radius and a small tetragonality is observed for all the phases. Semiconducting behaviour is seen for all compositions with systematic increase in activation energy with increasing Yb content. All compositions show negative thermopower indicating electrons are the majority charge carriers in the temperature range of measurements. The calculated power factor values S2σ increase with increasing temperature in the low temperature region and a maximum power factor of ∼0.76×10−7 Wcm−1K−2 is observed at 650K.
CVD Diamond as Dielectric Material for Capacitor Applications
Authors: Heidger S. , Fries-Carr S. , Weimer J. , Jordan B. , Wu R.
Published: April 2011

Diamond films synthesized using Microwave Plasma Chemical Vapor Deposition (MWCVD) were evaluated for use as dielectric material for high power and high temperature capacitors. The effect that the deposition parameters and annealing have on the frequency and temperature stability of the electronic properties was investigated. Dielectric constants ranging between 8.0 and 4.2 and resistivities between 1× 108 ohm-cm and 5×1014 ohm-cm were obtained. Diamond produced using less than 6.6% methane had very stable dielectric constants over the frequency range of 100 Hz to IMHz, and the loss tangent was less than 0.01. Adding oxygen to the precursor gas increased the dielectric constant and lowered the loss tangent of CVD diamond, but the resistivity was also lowered. As the temperature increased to 300°C, the dielectric constant and loss tangent increased. However, when diamond was annealed to 700°C, there was less than a 5% change in the dielectric constant from 23°C to 300°C.
Optical Characteristics Of Mocvd-Grown Ingan/Gan Multiple Quantum Wells Investigated By Excitation Energy Dependent Pl And Ple Spectroscopy
Authors: Cho Yong-Hoon , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: April 2011

We have systematically studied the optical properties of InGaN/GaN multiple quantum wells (MQWs) at 10 K under different excitation conditions using photoluminescence (PL) and PL excitation (PLE) spectroscopy. The MQWs were grown on 1.8-μm-thick GaN on c-plane sapphire films by metal-organic chemical vapor deposition. Structures consist of 12 MQWs with 3-nm-thick In0.2Ga0.8N wells, 4.5-nm-thick GaN barriers, and a 100-nm-thick A10.07Ga0.93N capping layer. We found that the PL emission consists of a strong main peak at 2.80 eV and a much weaker and broader secondary peak at ˜ 2.25 eV. We observed that both the peak position and the spectral width of the main peak vary with the excitation energy. The PL peak blueshifts and narrows when the excitation energies are varied from 3.81 eV (above the bandgap of the AlGaN capping layer) to 2.99 eV (below the bandgap of the GaN barrier layers). The intensity ratio of the main peak to the secondary peak also varied with excitation energy. The PLE studies, combined with the excitation dependent PL emission studies, reveal that the two observed emission peaks originate from different layers of the MQWs. In addition, we found that the InGaN-related spontaneous emission processes are strongly affected by different carrier generation conditions with further complications associated with compositional fluctuations and possible carrier localization. The differences in the observed emission processes under varying excitation conditions can be explained by considering the transfer of carriers between the different layers of the MQW structures.
Thermally Stable Schottky Contacts TO n-GaN
Authors: Venugopalan H. S. , Mohney S. E.
Published: April 2011

The barrier heights of Ni/Ga/Ni and Re Schottky contacts to n-GaN were investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The elemental Ni contacts were also investigated for comparison. The Ni/Ga/Ni and Re diodes were stable on short term annealing up to 700 °C. It was also shown that the Ni/Ga/Ni (84 at% Ni, 16 at% Ga) diodes were more stable than Ni diodes. This work provides the first demonstration of Schottky diodes to n-GaN that are stable upon annealing at 700 °C.
Calculation of Unstable Mixing Region In Wurtzite InGaN
Authors: Takayama Toru , Ueda Tetsuzo , Ishida Masahiro , Yuri Masaaki , Itoh Kunio , Baba Takaaki , Harris James S.
Published: April 2011

The InGaN ternary system, which is useful for blue and green light emitting or laser diodes, is studied with respect to an unstable mixing region in the phase field. The unstable region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The interaction parameters of InGaN obtained by our analysis for the wurtzite and zinc-blende structures are 7.81 kcal/mol and 6.63 kcal/mol, respectively. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN and zinc-blende InGaN are found to be 1967 K and 1668 K, respectively. This suggests that, at a typical growth temperature of 800°C, a wide unstable mixing region exists in both wurtzite and zinc-blende structures. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.
Examination of the Silicon – Silicon Carbide Interface by Ultraviolet Photoemission Spectroscopy
Authors: Koitzscht C. , O'Brient M. , Johri D. , Stoltzt A. , Nemanicht R.
Published: April 2011

Photoemission spectroscopy (UPS) was used to investigate the interface properties of deposited silicon on hexagonal 6H-silicon carbide. SiC cleaned in Si flux from a molecular beam epitaxy (MBE) system was used for this study. All processes were accomplished in an ultra high vacuum integrated system that allowed all cleaning, deposition, and analysis to be completed without exposure to ambient atmosphere. Thicknesses of sub- to multiple monolayers were deposited and the valence band structure was investigated. The valence band maximum (VBM) was observed to shift for Si depositions greater than 1 monolayer. The VBM offset was determined to be 2.4eV for a layer of 60Å Si on SiC. Furthermore, the prominent surface state feature of the silicon carbide (0001)si surface is reduced after Si deposition. The results are discussed in terms of the electronic properties of the Si – SiC interface.
Site-Selective Photoluminescence Spectroscopy of Er-Implanted Wurtzite Gan Under Various Annealing Conditions
Authors: Kim S. , Rhee S. J. , Li X. , Coleman J. J. , Bishop S. G.
Published: April 2011

The ˜1540 nm 4I13/2 → 4I15/2 emissions of Er3+ in Er-implanted GaN annealed at temperatures in the 400 to 1000 °C range were investigated to gain a better understanding of the formation and dissociation processes of the various Er3+ sites and the recovery of damage caused by the implantation with increasing annealing temperature (TA). The monotonic increase in the intensity of the broad defect photoluminescence (PL) bands with increasing TA proves that these are stable radiative recombination centers introduced by the implantation and annealing process. These centers cannot be attributed to implantation-induced damage that is removed by postimplantation annealing. Selective wavelength pumping of PL spectra at 6 K reveals the existence of at least nine different Er3+ sites in this Er-implanted semiconductor. Most of these Er3+ PL centers are attributed to complexes of Er atoms with defects and impurities which are thermally activated at different TA. Only one of the nine observed Er3+ PL centers can be pumped by direct 4f absorption and this indicates that it is the highest concentration Er3+ center and it represents most of the optically active Er3+ in the implanted sample. The fact that this Er3+ center cannot be strongly pumped by above-gap light or broad band below-gap absorption indicates that it is an isolated center, i.e. not complexed with defects or impurities. This 4f-pumped PL spectrum appears at annealing temperatures as low as 400°C, and although its intensity increases monotonically with increasing TA, the wavelengths and linewidths of its characteristic peaks are unaltered. The observation of this high quality Er3+ PL spectrum at low annealing temperatures illustrates that the crystalline structure of GaN is not rendered amorphous by the ion implantation. The increase of the PL intensities of the various Er3+ sites with increasing TA is due to the removal of competing nonradiative channels with annealing.
In Situ Characterization of Ain Films Grown on Silicon by MOCVD
Authors: Serra A. D. , Richardson H. H.
Published: April 2011

Films of AIN were grown on Si under vacuum pressure at 900°C and examined ex situ with infrared reflectance spectroscopy and microscopy, scanning electron microscopy, x-ray diffraction and rutherford backscattering spectroscopy. Collection of IR emission spectra for in situ characterization was successful and used to identify growth parameters during film growth.
Doping of GaN by Ion Implantation: Does it Work?
Authors: Suvkhanov A. , Hunn J. , Wu W. , Thomson D. , Price K. , Parikh N. , Irene E. , Davis R. F. , Krasnobaev L.
Published: April 2011

Epitaxially grown GaN by metal organic chemical vapor deposition (MOCVD) on SiC were implanted with 100 keV Si+ (for n-type) and 80 keV Mg+ (for p-type) with various fluences from 1×1012 to 7×1015 ions/cm2 at liquid nitrogen temperature (LT), room temperature (RT), and 700 °C (HT). High temperature (1200 °C and 1500 °C) annealing was carried out after capping the GaN with epitaxial AIN by MOCVD to study damage recovery. Samples were capped by a layer of AIN in order to protect the GaN surface during annealing. Effects of implant temperature, damage and dopant activation are critically studied to evaluate a role of ion implantation in doping of GaN. The damage was studied by Rutherford Backscattering/Channeling, spectroscopic ellipsometry and photoluminescence. Results show dependence of radiation damage level on temperature of the substrate during implantation: implantations at elevated temperatures up to 550 °C decrease the lattice disorder; “hot implants” above 550 °C can not be useful in doping of GaN due to nitrogen loss from the surface. SE measurements have indicated very high sensitivity to the implantation damage. PL measurements at LT of 80 keV Mg+ (5×1014 cm-2) implanted and annealed GaN showed two peaks : one ∼100 meV and another ∼140 meV away from the band edge.
Relaxation Of Non-Equilibrium Hydrogen Distributions In a-Si:H
Authors: Adriaenssens Guy J. , Zhiang Qing
Published: April 2011

It is shown that a reduction of the three-level energy diagram proposed by Van de Walle (Phys. Rev. B 53, 11292, 1996) to describe the relaxation of non-equilibrium hydrogen distributions, to just the interstitial transport level and a distribution of traps, allows an essentially equivalent formulation of the hydrogen relaxation kinetics. The modified formulation offers the possibility of accounting for dispersive diffusion while preserving the essential multiple retrapping aspect of the original proposal.
Concentration of Hydrogen in Titanium Measured by Neutron Incoherent Scattering
Authors: Chen-Mayer H. H. , Mildner D. F. R. , Lamaze G. P. , Lindstrom R. M. , Paul R. L. , Kvardakov V. V. , Richards W. J.
Published: April 2011

Mass fractions of hydrogen in titanium matrices have been measured using neutron incoherent scattering (NIS) and compared with results from prompt gamma activation analysis (PGAA). Qualitatively, NIS is a more efficient technique than PGAA which involves neutron absorption, and the former may be suitable for on-line analysis. However, for NIS the scattering contribution comes from both the hydrogen and the matrix, whereas prompt gamma emission has minimal matrix effect. To isolate the signal due to hydrogen scattering, a set of polypropylene films is used to simulate the increasing amount of hydrogen, and the scattered intensity is monitored. From this response, an unknown amount of the hydrogen can be deduced empirically. We have further attempted a first principle calculation of the intensity of the scattered signal from the experimental systems, and have obtained good agreement between calculation and the measurements. The study can be used as a reference for future applications of the scattering method to other hydrogen-in-metal systems.
Standards for Hydrogen in Titanium Alloy
Authors: Lindstrom R. M. , Paul R. L.
Published: April 2011

Mass-fraction standards of dilute hydrogen in titanium alloy are prepared by direct reaction of the elements, and verified by cold-neutron prompt-gamma activation analysis. The procedure is applied to the production and characterization of Standard Reference Materials.
Hydrogen Cycling-induced Phase Segregation in AB 5-Type Intermietallics
Authors: Mordkovich V. Z.
Published: April 2011

A study of hydrogen cycling-induced phase segregation in AB5-type intermetallics is presented. Influence of temperature for the alloy compositions Yni4AI, LaNi5, Ce0.5La0.5Ni5 and Ce0.7La0.3Ni5 is shown. Morphology of the nanostructured particles formed is studied and discussed.
Hydrogen-Enhanced SCC of 304 Austenitic Stainless Steel in MgCl2
Authors: Gao K. W. , Qiao L-J. , Luo J. L.
Published: April 2011

SCC of 304 stainless steel(ss) in boiling MgCl2at 416K was performed to investigated the effect of hydrogen during test. Results showed that the existence of hydrogen enhanced the susceptibility of SCC of 304ss. The fractography of specimen charged with hydrogen contained more intergranular than that of uncharged ones, and for the both specimens charged or uncharged with hydrogen, SCC initiated and propagated along { 111 } plane.
Hydrogen On Semiconductor Surfaces
Authors: Schaefer J. A. , Balster T. , Polyakov V. , Rossow U. , Sloboshanin S. , Starke U. , Tautz F. S.
Published: April 2011

We review structural and electronic aspects of the reaction of hydrogen with semiconductor surfaces. Among others, we address the Si(100), GexSi1-x(100), GaAs(100), InP(100), SiC(100), SiC(0001) and SiC(0001) surfaces. It is demonstrated that high resolution electron energy loss spectroscopy (HREELS) in conjunction with a number of other surface sensitive techniques like low energy electron diffraction (LEED) and photoelectron spectroscopy (XPS/UPS) can yield important information about the surface atomic structure, the effects of hydrogen passivation and etching and on electronic properties of the surfaces.
Formation of Hydrogen-Related Traps in Electron-Irradiated N-type Silicon by Wet Chemical Etching
Authors: Tokuda Yutaka , Shimada Hitoshi
Published: April 2011

Interaction of hydrogen atoms and vacancy-related defects in 10 MeV electron-irradiated n-type silicon has been studied by deep-level transient spectroscopy. Hydrogen has been incorporated into electron-irradiated n-type silicon by wet chemical etching. The reduction of the concentration of the vacancy-oxygen pair and divacancy occurs by the incorporation of hydrogen, while the formation of the NHI electron trap (Ec – 0.31 eV) is observed. Further decrease of the concentration of the vacancy-oxygen pair and further increase of the concentration of the NH1 trap are observed upon subsequent below-band-gap light illumination. It is suggested that the trap NHI is tentatively ascribed to the vacancy-oxygen pair which is partly saturated with hydrogen.
Dose-Dependent “Activation Energy” For Blistering Phenomenon In Hydrogen-Implanted Silicon
Authors: Bedell S. W. , Lanford W. A.
Published: April 2011

Silicon samples were implanted with 100 keV hydrogen at doses ranging from 4.9 to 9.9 × 1016 H/cm2. The samples were then annealed in an argon atmosphere using a special furnace mounted on a microscope stage. The time required to observe the onset of Si blistering was then measured as a function of temperature for the various hydrogen doses. An Arrhenius plot of the time-temperature data was made and an “activation energy” was calculated for each dose. The measured activation energies range from 2.6 to 1.1 eV corresponding to 4.9 to 9.9 × 1016 H/cm2, respectively. A qualitative explanation of the dose dependence is given in terms of a stressinduced lowering of the Si-Si bond energy. The hydrogen distribution as a function of annealing temperature was monitored using the 1H(15N,αγ)12C nuclear reaction. The results from the hydrogen profiling indicate that the hydrogen profile flattens at 500°C and concentrates at 550 °C.
Hydrogen Structures in Heavily Hydrogenated Crystalline and Amorphous Silicon
Authors: Jackson W. B. , Franz A. , Chabal Y. , Weldon M. K. , Jin H.-C. , Abelson J. R.
Published: April 2011

The hydrogen binding energy distribution and IR spectra of hydrogen platelets in c-Si have been measured and compared to H in other forms of silicon including hydrogenated polycrystalline and amorphous Si. The binding distribution for platelet containing samples, determined using H evolution, exhibits two peaks: a bulk peak at 1.8–1.9 eV below the transport barrier, and a second possibly surface related peak 1.8–1.9 eV below the surface evolution barrier. The bulk peak grows at 250C and is consistent with calculated energies for platelet structures. The same two evolution peaks are found in hydrogenated polycrystalline Si and amorphous silicon. The IR spectra for heavily hydrogenated c-Si are dominated by the stretching modes at 2076 and 2128 cm-1. Most surprisingly there appears to be a strong mode at 856 cm-1 which is associated with a deformation mode of SiH3. Even more surprising, this SiH3 856 cm-1 mode remains until 550 C indicating that the SiH3 containing structures are rather stable.
Crystallographic Texture and Phase Formation in Blanket TifriN/AICu Films
Authors: DeHaven P. W. , Clevenger L. A. , Schnabe R. F. , Weber S. J. , Iggulden R. C. , Rodbell K. P.
Published: April 2011

Interconnection metallization uses film stacks, often composed of thin (<10 nm) Ti, TiN, or Ti/TiN underlayer(s) with a thick (200–1000 nm) Al-alloy film deposited on top. The texture or preferred orientation in such film stacks has important implications for both processing and reliability. Earlier studies' have demonstrated the importance of the underlayers on Al texture; however, to date no systematic work has been done on the effect of processing conditions on underlayer texture. This study examines the effect of deposition parameters on the underlayer texture development as well as the effect of this underlayer texture on subsequently deposited Al-alloy films. Fiber plots were obtained for Ti <002> and <101> and Al <111> reflections for a series of 20 nm Ti/ 10 nm TiN/400 nm AlCu films using both a conventional Siemens D500 diffractometer with a pole figure attachment and a Siemens HI-STAR Area Detector system using Cu radiation from a rotating anode source. Because of overlap between the Al <111> and Ti <101> reflections, the Al was removed with a subtractive etch. In this way both the Al and underlayer film textures could be quantified. It was found that the Ti and Al-alloy film textures vary depending on the deposition temperature, deposition method and final film thickness. For example, an increase in the substrate temperature from 300° to 500°C caused the Ti film texture to change from <002> to <101>. Additionally, switching the TiN deposition process from physical vapor deposition (PVD) sputtering to chemical vapor deposition (CVD) in a Ti/TiN/AlCu film stack caused a degradation in the AlCu <111 > texture.
Imaging Spatial Variations in Resistance Along Interconnects
Authors: Wen Qingzhe , Clarke David R.
Published: April 2011

A non-destructive, non-contact method is described for imaging resistance variations along electrical conductors such as interconnects. In its basic implementation, an intensity modulated laser beam is scanned over the circuit carrying a d.c. current and the voltage induced in the circuit at the modulation frequency is used to vary the intensity of a synchronously scanned display. Resistance variations, such as caused by defects, produce variations in the image thereby identifying their spatial location. The voltage signal depends on a number of parameters including the temperature coefficient of resistivity of the conductor, the power of the incident laser, the absorption coefficient of the conductor and the rate of thermal diffusion to the surroundings. One advantage of the method is that it is possible to produce images of conductors below the surface. Whilst there is a degradation in contrast when imaging sub-surface features, it is still possible to identify and distinguish, for instance, tungsten vias and aluminum interconnects passivated by several microns of dielectric, as well as electromigration-induced damage. Under certain circumstances, other features in the immediate vicinity of the conductors, such as remanent photoresist and decohered interfaces, can also be imaged.
Improved Thermal Stability of Ultrathin CoSi2 Layers by Oxygen Annealing
Authors: Tung R. T. , Ohmi S.
Published: April 2011

The thermal stability of thin CoSi2 layers is demonstrated to improve with the use of oxygen-containing annealing ambients. Layer agglomeration in epitaxial and polycrystalline CoSi2 layers grown on single crystal Si and polycrystalline CoSi2 layers grown on α-Si was retarded by oxygen annealing. A thin SiO2 layer grown during oxygen anneals which curbs surface diffusion and reduces the rates of kinetic processes is thought to be the primary reason for the improvement in CoSi2 thermal stability.
Nanopatterning of Thin Cobaltdisilicide Layers by Local Oxidation
Authors: Klinkhammer F. , Kappius L. , Antons A. , Dolle M. , Trinkaus H. , Mesters St. , Bochem H.-P. , Mantl S. , Heinig K.-H.
Published: April 2011

Local oxidation of thin cobaltdisilicide layers (10–30 nm) allows patterning with distances between silicide pads as small as 70 nm. The epitaxial silicide layers were grown by molecular beam allotaxy (MBA) on Si(100) substrates. They were characterized by TEM, RBS and sheet resistance measurements showing good crystal quality and excellent thermal stability up to 1200°C. Similar to the well established technology for local oxidation of silicon (LOCOS), the silicide layer was caped by 20 nm SiO2 followed by 300 nm of Si3N4. The nitride was patterned by optical lithography and dry etching. During dry oxidation at temperatures ranging from 900°C to 1000°C SiO2 is formed on the unprotected areas of the silicide. The Co atoms diffuse from the SiO2/CoSi2 interface to the CoSi2/Si interface to form CoSi2. Near the edges of the nitride mask the silicide layer thins and finally separates. Two metallic pads electrically separated by Si and SiO2 with a gap of 70 nm were produced this way. Monte Carlo simulations of the process revealed that the reason for the separation is stress dependent diffusion due to the stress induced by the nitride mask. The stress dependence of the separation process was experimentally verified using different nitride thicknesses. SEM and TEM studies showed perfect lateral patterning. This patterning process could be used in the fabrication of MOSFET's with ultrashort gatelengths.
IS Selective CVD an Improvement for the Titanium Silicide Process in Sub-Quarter Micron Technology? A Phase Formation Study Using X-ray Diffraction
Authors: Roy Ronnen , Cabral Cryil , Lavoie Christian , Jordan-Sweet Jean , Viswanathan R. , Ozturk Mehmet , Fang Hua , Swenberg Johanes , Achutharaman Raman
Published: April 2011

The C54 phase formation process of titanium silicide was studied after selective chemical vapor despostion (CVD) onto very small silicon structures, to ascertain the efficacy of CVD to form low resistance contacts in sub-quarter micron technology. Because the selective CVD process forms silicide on any exposed silicon in a CMOS device, the process was studied on both polysilicon and Si (100) chips. The structures consisted of arrays of about 106 identical lines, 0.1 2.0 μm in width, depending on the chip. The CVD process employed TiCl4 and SiH4 for the most part as process gases and the depostion temperature ranged from 730–825°C. X-ray diffraction (XRD) was used to document the amount of C54 phase present after deposition. In some cases samples were annealed after deposition and the phase transformation behavior studied by in-situ XRD. The latter technique employed a synchrotron radiation source providng for rapid XRD spectra collection, so that the C49-C54 phase transformation could be examined with great precision in real time during rapid thermal annealing. The results of CVD depositions were compared to titanium silicide formed by sputter deposition of Ti on identical silicon chips, followed by a typical salicide protocol. Although the phase formation is affected by both film thickness and substrate temperature during CVD, the general result is that the C54 formation is more facile using the CVD process, especially for the smallest line dimensions. The findings are discussed with respect to nucleation processes occurring during growth and post-deposition thermal processing.
Formation of Tisi2 Thin Films from Chemical Vapor Deposition Using TiI4
Authors: Rhee HwaSung , Jang TaeWoong , Baek JongTae , Ahn ByungTae
Published: April 2011

The formation of TiSi2 films by chemical vapor deposition was investigated for the application as a contact plug material because of its low resistivity, low contact resistance with n+ and p+ Si, and good chemical stability with Si. TiI4 and SiH4 were used as source gases. Since TiI4 is thermodynamically less stable than TiCl4, the deposition temperature of TiSi2 with TiI4 precursor could be lower than that of TiSi2 from TiCl4 precursor. TiSi2 thin films with C49 phase were formed at 650°C on Si (100) wafer, while a Ti5Si3 phase was formed at 650°C on SiO2 substrate. The resistivity of the C49 phase films was 210 μΩ-cm. The C49 phase was completely transformed into a C54 phase above 800°C annealing in an N2 atmosphere and the resistivity reduced to 34 μΩ-cm. We were able to deposit TiSi2 films at lower temperature using TiI4 precursor, compared to TiCl4 precursor. The Cl and HCI byproducts originated from TiCl4 can be excluded using TiI4 precursor.