Zenglin Wang

Bottom-Up Fill for Submicrometer Copper Via Holes of ULSIs by Electroless Plating

In this report, the hole-filling characteristics upon addition of SPS were evaluated in detail by cross-sectional scanning electron microscopy ~SEM!, and the effects of SPS concentration on bottom-up fill ability, and fundamental film properties such as contaminant level, crystal texture, and surface morphology were investigated. Experimental ICB-Pd layers with a thickness of 1 or 2 nm were deposited on the surface of three types of TaN/SiO2 /Si substrates, hole patterns ~diameter, 0.31-1.0 mm; depth, 1.5 mm! for investigating filling viahole; trench patterns ~length, 100 mm; width, 0.21-100 mm; depth, 0.3 mm! for electrical resistivity measurement; and blankets for measurement of the deposition rate of electroless plating with SPS concentration. The thickness of the Pd layer was determined by a quartz microbalance placed on the substrate surface. Prior to electroless copper plating, all substrates were cleaned by ultrasonication in acetone at room temperature for 10 min. The composition of the electroless copper plating solution was CuSO4 i 5H2O ~6.6 g/L! ,C 10H16N2O8 ~EDTA; 70.0 g/L!, glyoxylic acid ~18.0 g/L! as a reducing agent, 2,28-dipyridine ~0.04 g/L! as stabilizer, polyethylene glycol ~4000 MW, 0.5 g/L! as the surface activator. The pH of the plating bath was adjusted to approximately 12.5 using tetramethylammonium hydroxide ~TMAH! and the bath temperature was maintained at 70°C. The interfacial structure and morphology of samples were characterized by field-emission scanning electron microscopy~FE-SEM! and field-emission transmission electron microscopy~FE-TEM! .A ll SEM and TEM samples were prepared by focused ion beam ~FIB!. To protect the surface of the Cu film for etching during FIB cutting, a fine film of epoxy resin was coated on the surface of Cu by spin

Effects of Li content on the phase structure and electrical properties of lead-free (K0.46−x∕2Na0.54−x∕2Lix)(Nb0.76Ta0.20Sb0.04)O3 ceramics

Lead-free (K0.46−x∕2Na0.54−x∕2Lix)(Nb0.76Ta0.20Sb0.04)O3 piezoelectric ceramics were prepared by the conventional solid state sintering method without cold-isostatic pressing process. The x-ray diffraction and Raman scattering results show that the phase structure of the ceramics undergoes a transition from pseudocubic to tetragonal phase with increasing x from 0 to 0.10. Significantly enhanced electrical properties (d33=259pC∕N, kp=0.42, er=1653, and tan δ=0.027) were obtained in the ceramics with x=0.04 near the morphotropic phase boundary, and only the tetragonal-cubic phase transition was observed above the room temperature in the er-T curve. The temperature stability of the ceramics with x=0.04 was also investigated.

Phase transitional behavior, microstructure, and electrical properties in Ta-modified [(K0.458Na0.542)0.96Li0.04] NbO3 lead-free piezoelectric ceramics

Lead-free [(K0.458Na0.542)0.96Li0.04] (Nb1−xTax)O3 ceramics were prepared by ordinary sintering technique. The effects of Ta content on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics were investigated. X-ray diffraction results indicate that the phase structure undergoes a transition from orthorhombic to tetragonal phase with the increase in x. The small and large peaks observed in the Raman spectra can all be attributed to the internal modes of the NbO6 octahedron, and both ν5 and ν1 modes slightly shift to lower frequency numbers by increasing x. Ta substitution for Nb leads to the disappearance of the abnormal grain growth behavior, inhibits the grain growth, and improves the density of the ceramics. Increasing x leads to the different variations of dielectric constants before and after poling and makes the ceramics more relaxorlike. The proper substitution of Ta shifts the polymorphic phase transition (at To-...

Adhesion improvement of electroless copper to a polyimide film substrate by combining surface microroughening and imide ring cleavage

In order to enhance the adhesion strength of copper metal film to a polyimide (PI) film substrate, a method combining surface microroughness formation and imide ring cleavage was investigated. The results showed that imide rings were cleaved with a KOH treatment while carboxyl and amide groups were formed on the surface of the PI film. The surface micro-roughness did not change with the KOH treatment, and the adhesion strength of the copper metal film to the PI film was slightly improved to 30 g/mm, which could be attributed to the interaction of both carboxyl and amide groups with the copper atoms. When the PI films were successively treated with an alkaline permanganate and a KOH solution, many recesses were formed on the surface in an alkaline permanganate solution, and the size and depth of the recesses increased with alkaline permanganate treatment time. The results of the AFM measurements showed that the average roughness (R) increased from 3.54 to 10.23 nm after combined treatment with alkaline permanganate and KOH solutions. The adhesion strength of the copper metal film to the PI film reached 150 g/mm, which was five times greater than that achieved with the KOH treatment only.

Suppression of native oxide growth in sputtered TaN films and its application to Cu electroless plating

Electroless plated copper can be deposited on a TaN surface initiated by displacement plating when the surface oxide layer is removed by wet chemical etching. For application to ultra-large-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, TaN films with various N/Ta atomic ratios were fabricated by reactive sputtering and native oxide growth on the surface was investigated by x-ray photoelectron spectroscopy, high resolution Rutherford backscattering spectrometry, and x-ray diffraction (XRD). It was found that when the N/Ta atomic ratio in the film was lower than 1.2, surface oxidation of the TaN film advanced with time. When the ratio was higher than 1.2, oxidation of the TaN film stopped at 1 ML. The XRD spectra indicated that when the N/Ta atomic ratio was between 0.82 and 1.25, face-centered-cubic TaN films were formed and the resistivity increased with an incr...

Phase coexistence and high electrical properties in (KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 piezoelectric ceramics

(KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O–Nb–O stretching vibration v1 and a triply degenerate symmetric O–Nb–O bending vibration v5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v5 and v1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition (at To-t) is shifted to near room temperature by ...

Electroless Plating of Copper on Metal-Nitride Diffusion Barriers Initiated by Displacement Plating

Copper is deposited on TaN and WN barrier layers by electroless plating without the need for activation preprocessing when substrates are (i) pretreated by wet chemical etching to remove surface oxides, and (ii) immersed in an electroless Cu plating solution containing glyoxylic acid as a reducing agent. Electrical potential measurements indicate that the redox potentials of TaN and WN in the plating solution are lower than that of copper, driving displacement plating of Cu in the initial stage of deposition. The adhesion between electroless-plated Cu and the TaN barrier layer after annealing is 0.11 kgf/cm as determined by a peeling test, which is sufficient for reliability during chemical mechanical polishing. A damascene Cu interconnect was successfully fabricated without delamination and exhibited an electrical resistivity of 2.2 μΩ cm after annealing for a 0.42 μm wide interconnect track. These results indicate that the proposed electroless process is suitable for the formation of a Cu seed layer prior to electrodeposition for the fabrication of ultralarge scale integrated interconnects.

Wurtzite-to-tetragonal structure phase transformation and size effect in ZnO nanorods

The deformation of [0001]-oriented ZnO nanorods with hexagonal cross sections under uniaxial tensile loading is analyzed through molecular statistical thermodynamics (MST) simulations. The focus is on the size dependence of mechanical behavior in ZnO nanorods with diameters ranging from 1.95 to 17.5 nm. An irreversible phase transformation from the wurtzite (P6(3)mc space group) structure to a tetragonal structure (P4(2)/mnm space group) occurs during the tensile loading process. Youngs modulus before the transformation demonstrates a size dependence consistent with what is observed in experiments. A stronger size dependence of response is seen after the transformation and is attributed to the polycrystalline nature of the transformed structure. A comparison of the MST and molecular dynamics (MD) methods shows that MST is 60 times faster than MD and yields results consistent with the results of MD.

Influence of Surface Oxide of Sputtered TaN on Displacement Plating of Cu

Copper can be deposited on TaN by displacement electroless plating when a surface oxide layer is removed by wet chemical etching. For application to ultralarge-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, we investigated surface oxidation of sputtered TaN films kept in air atmosphere by X-ray photoelectron spectroscopy (XPS) analysis. TaN films were sputtered in a mixture of Ar and N2 gases, where Ar partial pressure was kept constant at 3.0 mTorr and N2 partial pressure was varied. When N2 partial pressure was lower than 0.5 mTorr, surface oxidation of the TaN films advanced with time. However, when N2 partial pressure was higher than this value, oxidation of TaN film stopped at one monolayer. We confirmed that the redox potentials of TaN films formed with N2 partial pressures higher than 0.5 mTorr are lower than that of Cu, which suggests that displacement plating of Cu is possible on TaN films with thickness smaller than 10 nm.

Adhesion Improvement of ABS Resin to Electroless Copper by H2SO4–MnO2 Colloid with Ultrasound-Assisted Treatment

The adhesion strength between electroless copper and acrylonitrile-butadiene-styrene (ABS) resin can be improved significantly by an environmentally friendly etching system containing H2SO4–MnO2 colloid as a replacement for conventional chromic acid etching solutions. In this paper, the effects of the H2SO4 concentration and ultrasound-assisted treatment (UAT) on the surface roughness and adhesion strength were investigated. When the H2SO4 concentration was 11.8∼12.7 M, good etching was obtained. With UAT, many uniform cavities formed on the ABS surface with the average surface roughness (R a) and maximum roughness (R max) of ABS substrates decreasing from 386 and 397 nm to 278 and 285 nm, respectively, which were much lower than that etched by CrO3–H2SO4 colloid (420 and 510 nm, respectively). The average adhesion strength increased from 1.29 to 1.39 kN/m, which was close to that obtained with chromic acid etching treatment (1.42 kN/m). The surface contact angle measurement indicated that the density of the polar groups on the ABS surface increased with increasing time of UAT. The results indicated that surface etching with UAT not only improved the uniformity of cavities, but also enhanced the oxidation rate of ABS resin, which in turn resulted in greater adhesion strength and a lower surface roughness.