Surface Preparation of Aluminum Nitride for Metallization: Effect of Temperature on Surface Reactivity

The current aqueous cleaning step in the surface preparation of aluminum nitride (AlN) prior to metallization causes performance and reliability issues for the substrates used for microelectronic packaging due to surface reactions. These issues limit the use of AlN and its replacing of BeO, an environmentally hazardous material currently used. The aim of this investigation was to determine the effects of different solutions on the surface of AlN substrates under varying conditions at times up to 2419.2 ks (28 days). Concentration of the solutions, temperature, and immersion time were varied for the AlN samples in the solutions. Both elevated temperatures (50°C and 90°C) and low temperatures (5°C) were investigated.

Four general types of behavior were observed: minor changes in average surface roughness and microstructure, linear change in average surface roughness and pitted grains, nonlinear change in average surface roughness and product formation on AlN surface, and miscellaneous change in average surface roughness with surface product formation.

The surface roughening kinetics were very complex due to changes in both the reaction product morphology and reaction mechanism with temperature, solvent, and pH for a specific solvent. Minor changes in average surface roughness and microstructure were observed for HCl pH = 5, H₂ SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, deionized water and Alfred tap water at 5°C, HCl pH = 3 and oleic acid at 50°C and citric acid and oleic acid at 90°C. Linear changes in average surface roughness and pitted grains were observed for HCl pH = 2 and H₂SO₄ pH = 3 at 50°C and HCl pH = 2, H₂SO₄ pH = 3, and deionized water at 90°C. Non-linear change in average surface roughness and product formation on AlN surface was observed for HCl pH = 5, NaOH pH = 8 and Alfred tap water at 50°C and HCl pH = 5 and H₂SO₄ pH = 2 at 90°C. Miscellaneous changes in average surface roughness with surface product formation were observed for H₂SO₄ pH = 2, H₂SO₄ pH = 5, NaOH pH = 10, NaOH pH = 12, citric acid, Micro-90 and deionized water at 50°C and HCl pH = 3, H₂SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, Micro-90 and Alfred tap water at 90°C.     

Investigation of Iron-Fullerene Mixture Plasmas in ECR Discharge

Fullerene+iron (C₆₀+Fe) mixture plasmas were produced and studied in the ECR ion source of ATOMKI. The two main components of the plasma were obtained by different filament ovens. In this series of measurements we concentrated on the maximum ratio of C₅₈ (damaged fullerene) in the plasma. C₅₈ is less stable than C₆₀ and the probability to form new materials is higher. Using this method we produced molecules of mass M=752 both in single- and double-charged states with beam intensities of 8 · 10^-10A and 2 · 10^-10A, respectively. We identified this beam as a mixture of FeC₅₈, O₂C₆₀ and CO₂C₅₉, while the experiment did not give information on the exact location of the iron and oxygen in the carbon ball.     

Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70 and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92

The carbonylate anions [M(CO)₅]^- (M = Mn, Re), [Co(CO)₄]^-, [CpFe(CO)₂]^-, and [CpM(CO)₃]^- (M = Mo, W) react with C₇₀ via single electron transfer processes to give, respectively, the corresponding 17-electron, metal-centered radicals Co(CO)₄, M(CO)₅ (M = Mn, Re), CpFe(CO)₂, and CpM(CO)₃ (M = Mo, W) in addition to the radical anion C₇₀^-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO)₄ and M(CO)₅ (M = Mn, Re) combine with the C₇₀^- to form the new η²-C₇₀ complexes [Co(CO)₃(η²-C₇₀)]^- and [M(CO)₄(η²-C₇₀)]^-. However, the metal-centered radicals CpM(CO)₃ (M = Mo, W) require photolysis to react with C₇₀^- to form [CpM(CO)₂(η²-C₇₀)]^-, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO)₂ and C₇₀^-. The photochemical reaction of [Mn(CO)₅]^- with a mixture of higher fullerenes known to contain at least C₇₆, C₇₈, C₈₄, C₈₆, and C₉₀ resulted similarly in the formation of the higher fullerene complexes [Mn(CO)₄(η²-C_n)]^- (n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry.     

Chemical vapour deposition of praseodymium oxide films on silicon: influence of temperature and oxygen pressure

Metal-organic chemical vapour deposition (MOCVD) of various phases in PrO_x system has been studied in relation with deposition temperature (450–750 °C) and oxygen partial pressure (0.027–100 Pa or 0.2–750 mTorr). Depositions were carried out by pulsed liquid injection MOCVD using Pr(thd)₃ (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) precursor dissolved in toluene or monoglyme. By varying deposition temperature and oxygen partial pressure amorphous films or various crystalline PrO_x phases (Pr₂O₃, Pr₇O₁₂, Pr₆O₁₁) and their mixtures can be grown. The pure crystalline Pr₂O₃ phase grows only in a narrow range of partial oxygen pressure and temperature, while high oxygen pressure (40–100 Pa) always leads to the most stable Pr₆O₁₁ phase. The influence of annealing under vacuum at 750 °C on film phase composition was also studied. Near 90% step coverage conformity was achieved for PrO_x films on structured silicon substrates with aspect ratio 1:10. In air degradation of Pr₂O₃ films with transformation to Pr(OH)₃ was observed in contrast to Pr₆O₁₁ films.     

Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.     

Surface Preparation of Aluminum Nitride for Metallization

Currently, the surface preparation of aluminum nitride (AlN) substrates prior to metallization includes an aqueous cleaning step. Surface reactions that occur in this step cause performance and reliability issues with AlN substrates to be used in microelectronic packaging. There is a lack of published data on the reactivity of AlN substrates with common solvents. This study investigated the effects of different solvents on the surface corrosion of AlN substrates. The variables studied were pH, aqueous vs. organic solutions, prior surface condition, and time (up to 3.6 Ms or 42 days). The solvents tested were hydrochloric acid (HCl) with pH values ranging from 2 to 5, sulfuric acid (H₂SO₄) with pH values ranging from 2 to 5, sodium hydroxide (NaOH) with pH values ranging from 8 to 12, 1 M citric acid, oleic acid, Micro-90, methanol, ethanol, isopropanol, acetone, and deionized water. Three types of surface reaction behavior were observed in this study. The substrates either showed no reaction (HCl pH = 2, methanol, ethanol, isopropanol, acetone, citric acid, and oleic acid), slight corrosion without spalling (Micro-90, HCl pH = 3, H₂SO₄pH = 3), or they were severely corroded and spalled (HCl pH = 5, H₂SO₄pH = 5, all NaOH solutions, and deionized water).     

SPINNING FIBERS FROM POWDER SUSPENSIONS

Green ceramic fibers from Al₂O₃, Si₃N₄, Ce-ZrO₂, SiC, and other ceramics can be prepared by dry spinning of powder-loaded suspensions. The green fibers contain 54 to 64 vol. % ceramic powder in an ethyl methacrylate polymer base. Continuous fibers with an average diameter of 60 to 175 µm were spun at rates of 10 to 40 meters/minute. Spinnable dope compositions are defined for simple ternary powder + polymer + solvent systems, and are compared for several powders in MEK-based solvents. Spinnability is related to extrusion pressure, and drying conditions, and the shear rheological behavior of the dope. Fiber preparation by suspension dry spinning is compared with melt spinning of powder-loaded thermoplastics.     

Influence of a Weak Magnetic Field on Photoconductivity Spectrum of C60 Single Crystal

Comparative research of the excitation photoconductivity spectra (quantum light energy 2-5 eV) of C₆₀ single crystal in and out of magnetic field at the temperature T = 250-350 K has been carried. The spectral evolution at this temperature range is described. It is shown that the spectra changes abrupt at temperature T₁ ∼ 260 K and T₂ ∼ 315 K. An increase in the photoconductivity up to 15% was observed in the magnetic field (B = 0.4 T) within the photon energy range 2.5-4.5 eV. Local photoconductivity peak's appearances in the magnetic field have been proven that the charge transfer excitons take part in a photoconductivity.     

Electrochromic properties of nanocrystalline MoO3 thin films

Electrochromic MoO₃ thin films were prepared by a sol–gel spin-coating technique. The spin-coated films were initially amorphous; they were calcined, producing nanocrystalline MoO₃ thin films. The effects of annealing temperatures ranging from 100 °C to 500 °C were investigated. The electrochemical and electrochromic properties of the films were measured by cyclic voltammetry and by in-situ optical transmittance techniques in 1 M LiClO₄/propylene carbonate electrolyte. Experimental results showed that the transmittance of MoO₃ thin films heat-treated at 350 °C varied from 80% to 35% at λ = 550 nm (ΔT =  45%) and from 86% to 21% at λ ≥ 700 nm (ΔT =  65%) after coloration. Films heat-treated at 350 °C exhibited the best electrochromic properties in the present study.     

Some New Aspects of Chlorination of Fullerenes

The effect of the reagent ratio, reaction time and power of the reagent on the product composition in chlorination of [60]fullerene was studied. Chlorofullerenes C₆₀Cl₆, C₆₀Cl₈, C₆₀Cl₁₀, C₆₀Cl₁₂, C₆₀Cl₁₄, and C₆₀Cl₂₆ were synthesized and characterized by chemical analysis, FTIR, ¹³C NMR, and MALDI TOF mass spectrometry. The experimental data supported the coexistence of several isomers of C₆₀Cl_n (n = 8, 10, 12, 14, 26); the mixtures were not separated so far. Semiempirical calculations (AM1, PM3) were used to analyze the addition patterns and resulted in the most favorable structures of C₆₀Cl_8-26. Chlorination of C₇₀ under various conditions invariably yielded C₇₀Cl₁₀.     

Reaction Kinetics of C60 Fullerene Ozonation

It has been verified that the reaction between O₃ and C₆₀ follows the general second order reaction rate which is valid for all the reactions between ozone and unsaturated olefinic bonds: v = k[C=C][O₃]. The reaction rate constant k has been measured ≈(1.5 ± 0.3) × 10⁴ L mol^-1 s^-1. The value of this rate constant has the same order of magnitude of the rate constant measured for instance in the ozonation of 1,4-diphenylbutadiene.     

Thermolysis and Photolysis of C60 Diozonides

Ozonation of C₆₀ in o-xylene produced three C₆₀(O₃)₂ diozonides that were separated from one another and from two C₆₀(O₃)₃ triozonides by High Performance Liquid Chromatography (HPLC). Upon thermolysis at 10, 15, and 16.6°C, each of the diozonides dissociated sequentially, first to a C₆₀O(O₃) oxyozonide, then to a C₆₀O₂ diepoxide. The three diepoxides were stable in solution for at least 3 weeks. The mean lifetimes of the three diozonides were 52 ± 5, 62 ± 6, and 17.3 ± 1.8 min, respectively (all at 15°C). The mean lifetimes of the three oxyozonides were 69.7 ± 0.7 and 58 ± 6 min at 16.6°C, respectively and about 240 min at 10°C. Photolysis of the diozonides yielded two dioxidoannulenes with UV-Vis adsorption maxima at 333 and 332 nm, and what appeared to be an epoxide-oxidoannulene with UV-Vis adsorption maximum at 327 nm. These annulenes were observed to form dimers. We have synthesized and characterized six C₆₀O₂ dioxides, at least three and possibly four of which were hitherto unknown. We report the discovery of oxyozonides that form during the dissociation of diozonides.     

RE-ENTRAINMENT OF DUSTS FROM THE DUST LAYER ON THE THE DEPOSITED DUSTS IN THE CYCLONE DUST COLLECTORS

There were many papers concerning the experimental results of the collection efficiency, but up to this time there are a few papers concerning the experimental results of the re-entrainment or dispersion of the dust particles from the dust layer by the turbulent rotational air flow in the dust bunker for the cyclone dust collector. Then in this paper, the author described the experimental results of the re-entrainment of the test dust ( talc X_R50 = 8.O µm ) for the four kinds of the throat diameter D₃ = 50, 80, 100 and 150 mm. Especially it is very importance to take into consideration of flow rate Qb into the dust bunker which is a function of D₃ and cyclone diameter D₁ and the maximum tangential velocity Vet in the dust bunker which depends on D₁,D₃ and Qb.     

Reduction of film thickness for chemical solution deposited PbZr0.3Ti0.7O3 thin films revealing no size effects and maintaining high remanent polarization and low coercive field

Polycrystalline Pb(Zr_0.3,Ti_0.7)O₃ (PZT) thin films were prepared on platinized silicon wafers by chemical solution deposition (CSD) with thicknesses down to 30 nm. Electrical measurements with the superior ferroelectric properties of high remanent polarization (P_r) and low coercive field (E_c) will be presented for thicknesses down to 50 nm. In order to decrease the thickness of electrically dense PZT thin films by the CSD method experiments have been performed by using different degrees of dilutions of the precursor stock solutions, i.e. instead of diluting the PZT stock solution with 2-butoxyethanol in the standard ratio of 1:1 before the spin-on process, the dilution is increased stepwise to a ratio of 1:4. In addition the films have been annealed in nitrogen atmosphere instead of the typical oxygen atmosphere which has been shown to strongly improve a preferential (111) orientation of the PZT film [G. J. Norga, L. Fe, Mat. Res. Soc. Symp. Proc. Vol. 655, CC9.1.1 (2001)]. The approach of Norga et al. is confirmed and complemented by means of electrical hysteresis measurements.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).     

Traps identification in silicon nanocrystals memories by low noise technique

This work reports the extraction of oxide traps properties of n-metal–oxide–semiconductor field-effect transistors with W × L = 0.5 × 0.1 μm² using random telegraph signals (RTS) techniques. RTS study of nc-Si has been performed on thin tunnel oxides from 0.8 to 2.0 nm. RTS signals were two or more levels switching events observed on the drain current of transistors with and without nc-Si. The simple two levels RTS₁ noise was observed on samples without nc-Si. On transistors with nc-Si we distinguish two different RTSs (RTS₂ and RTS₃). RTS signal variations with temperature have shown that there's three slow interfacial traps located at E_c — 0.26 eV (trap1), E_c — 0.23 eV (trap2) and E_c — 0.2 eV (trap3). The spatial localization of traps 1, 2 and 3 from the Si–SiO₂ interface are determined using numerical simulations (x_Trap1 ≈ 0.6 nm, x_Trap2 ≈ 0.8 nm and x_Trap3 ≈ 0.4 nm). RTS noise observed on these devices is attributed to traps localized precisely at the interface thermal oxide/deposited control oxide. (RTS₁) noise is attributed to trap1 and (RTS₂, RTS₃) to traps 2 and 3. From RTS analysis in frequency domain, we extract the power spectrum density of the drain current noise (PSD). From these PSDs we have measured the cut-off frequencies of a single trap even at very low frequencies (for RTS₁ noise f_c = 5 Hz (trap1) and for RTS₂ noise f_c1 = 2 Hz (trap2), f_c2 = 130 Hz (trap3)). These results are in good agreement with those obtained by analysis in time domain and confirm the localization of each trap from the Si–SiO₂ interface.     

EFFECT OF PARTICLE SIZE DISTRIBUTION ON TRANSFER EFFICIENCY AND APPEARANCE IN POWDER COATINGS

Three powder samples of identical chemistry were taken from the same lot under different conditions: (1) relatively wide size distribution (Sample A) d₅₀ = 18.1μm, (2) narrow size distribution, d₅₀ = 22.4μm (Sample B), and (3) wide size distribution with more fines than Sample A, d₅₀ = 15.1μm (Sample C). Within this relatively minor variation of Particle Size Distribution (PSD) with respect to d₅₀, the appearance of the powder with minimum d₅₀ (15.1μm) was best. The results show two trends: (1) PSD with d₅₀ about 15μm can result in excellent appearance (GM Tension in the range of 18 to 19 on a scale of 0 to 20), and (2) the width of the distribution need not be narrow when d₉₀ is less than 40μm.

Polymer powders in this size range do not fluidize well without agitation, but when vibration was applied, all three samples had R values (fluidity) 200 or above, which is adequate for fluidization and transport. The maximum R value was obtained for Sample A, which had the widest size distribution. Thus, the fluidity tests agreed with the expected results.     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

Synthesis and Characterization of Bilayer Ferrofluids

The role of sodium dodecyle sulfate (SDS) adsorption as the second layer surfactant in a double layer surfactant ferrofluid is investigated. Preparation of the solid phase is based on the growth of the magnetic oxide by dehydration of a salt solution of FeCl₂ and FeCl₃ in an identical molar ratio. Particle size was determined through the magnetic measurements by VSM to be about 8-10 nm and by STEM to be about 12 nm. The data show that in a certain thermal interval, a local maximum appears in the magnetic oxide concentration which is a function of the stirring time and the SDS concentration. Increasing temperature causes surface oxidation which decreases the magnetization, similar to the behavior of monolayer ferrofluids. In addition, in the double layer systems, the intersolubility of the layers varies. This has a profound effect on the saturation magnetization.     

Influence of substrate on the pulsed laser deposition growth and microwave behaviour of KTa0.6Nb0.4O3 potassium tantalate niobate ferroelectric thin films

Thin films of potassium tantalate niobate KTa_0.6Nb_0.4O₃ (KTN) were grown by pulsed laser deposition on five different substrates suitable for microwave devices: (100)MgO, (100)LaAlO₃, (1–102)sapphire (R-plane), (0001)sapphire (C-plane) and alumina. The high volatility of potassium at the film growth temperature required the addition of an excess of potassium to the ablation target. For optimized deposition conditions, Rutherford backscattering showed that the KTN films had a 1: 1 atomic ratio for K:(Nb + Ta). As grown KTN thin films were single-phase, without any particular orientation on sintered alumina, whereas an epitaxial growth with the (100) orientation was achieved on (100)MgO and (100)LaAlO₃ with a mosaicity Δω_(100)KTN close to 0.7°–1.5° and  0.4°–0.9°, respectively, attesting a high crystalline quality. In contrast, growth of KTN on R-plane sapphire results in a texture with the (100) orientation and the presence of the (110) orientation as a secondary one. The room temperature measurements carried out on Au interdigited capacitors patterned on KTN coated (100) LaAlO₃ and sapphire led at 1 GHz to an agility ΔC / C  4.6% and  7.2%, respectively, for a moderate applied field of 15 kV cm^− 1. Stubs patterned on the same systems led to an agility ΔF_r / F_r of  2.2% and 4.2%, respectively, for F_r = 7 GHz and the same applied field.