Chemical factors for chemical–mechanical and electrochemical–mechanical planarization of silver examined using potentiodynamic and impedance measurements

Ag may eventually replace Cu (like Cu has replaced Al) in sub-micron interconnects used for integrated circuits. Fabrication of such Ag lines would typically involve damascene structures patterned by chemical–mechanical planarization (CMP). Our present work focuses on certain chemical aspects of CMP of Ag in alkaline polishing slurries. Specifically, we study the oxidation and dissolution reactions of Ag that are relevant for CMP of this metal in KOH (pH 10) solutions, and we investigate the role of O₂ in these reactions. The surface reactions are probed with Fourier transform electrochemical impedance spectroscopy in combination with potentiodynamic measurements. The reaction steps are discussed in terms of circuit models, and the possibility of incorporating electro-activated reactions in CMP through electrochemical–mechanical planarization (ECMP) of Ag is briefly discussed.     

Role of iodate ions in chemical mechanical and electrochemical mechanical planarization of Ta investigated using time-resolved impedance spectroscopy

Chemical mechanical planarization (CMP) is currently used in the processing of Cu/Ta interconnect structures. Electrochemical mechanical planarization (ECMP) is an emerging extension of CMP that can potentially allow low down-pressure planarization of newer interconnect structures containing easily breakable porous dielectrics. In both CMP and ECMP of Ta, it is necessary to chemically (or electrochemically) form a “soft” surface film that can be easily removed by minimum mechanical abrasion. Alkaline KIO₃ solutions appear to serve this purpose in CMP of Ta and, as we show in this work, may also be utilized in ECMP of Ta. Using time-resolved impedance spectroscopy we study here the relevant surface reactions of IO₃⁻ that lead to a structurally weak surface film of soluble hextantalate [(Ta₆O₁₉)⁸⁻] embedded in (native or electro-generated) Ta₂O₅ on Ta. Catalytic reduction of IO₃⁻ on Ta₂O₅ enhances the local pH at the oxidized surface and promotes the conversion of Ta₂O₅ to (Ta₆O₁₉)⁸⁻. The chemical role of iodate ions in material removal through these reactions is similar to that of hydrogen peroxide in CMP of Ta in alkaline media.     

Effect of glycine and hydrogen peroxide on chemical-mechanical planarization of copper

Chemical-mechanical planarization (CMP) of copper is a vital process to produce sub-micron range and multilevel metallization to meet the demands of the current interconnect technology. The present investigation was focussed to understand the oxidation, dissolution and modification of Cu surface using hydrogen peroxide as oxidizer and glycine as inhibitor during Cu-CMP employing electrochemistry as well as dynamic and static removal rate measurements. Surface modification of copper was investigated in detail using X-ray photoelectron spectroscopy to understand the interaction of Cu-H₂O₂-glycine complex formation during CMP. Atomic force microscopy was employed to reveal any change in surface morphology during the CMP process. In the presence of 0.1 M glycine, copper removal rate was found to be high in the solution containing 2.5% H₂O₂ at pH 4 because of Cu²⁺-glycine complexation reaction. In the absence of glycine, the removal rate of copper decreased with increasing H₂O₂ concentration due to the formation of a less soluble copper oxide film. The present investigation helped understanding the mechanism of Cu surface alteration in presence of oxidizers and glycine for formulation of highly effective CMP-slurry.     

Magnetic and electrical properties of new inorganic complex based materials derived from bis(1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolato)metalate(II) ions

Magnetic and electrical properties of a series of new inorganic complex based materials [n-Pr₄N]₂[Pb(ecda)₂], [Et₄N]₄[Hg₂(ecda)₄] and M[M′(ecda)₂] (M=Co(II), Ni(II), Cu(II), Cd(II) or Pb(II); M′=Hg(II) or Pb(II); ecda²⁻=1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate) have been investigated using molecular spectroscopic (IR, Raman, EPR, electronic and mass) and conducting properties. Complete quenching of paramagnetism indicates strong Cu–Cu interaction in the layered polymeric array of Cu[Hg(ecda)₂] and Cu[Pb(ecda)₂] in the solid state. The ¹H NMR spectrum of Ni[Pb(ecda)₂] in DMSO-d₆ gives narrow unshifted peaks due to diamagnetic, square-planar geometry around Ni(II) and shows absence of some octahedral units (μ_eff=1.49 BM) present in the solid state of this product. While the peak broadening indicates paramagnetic nature and absence of dominant Cu–Cu interaction in solution for Cu[Hg(ecda)₂] and Cu[Pb(ecda)₂]. The temperature dependent (305–373 K) compressed pellet conductivity together with activation energy (0.36–1.23 eV), show semiconducting behaviour of some of the bimetallic derivatives.     

Electrical properties of complex bimetallic salts [M(N–N)3]2+[Cu(MNT)2]2− and heterobimetallic AgI–CuII/HgII–CuII bis(maleonitriledithiolato) bridged coordination polymers

This paper presents the solid-state electrical conductance properties of a series of complex bimetallic salts of the form [M(N–N)₃][Cu(MNT)₂] (M=Fe(II), Co(II), Ni(II), or Cd(II); N–N=1,10-phenanthroline (phen) or ethylenediamine (en); MNT²⁻=maleonitriledithiolate) and bridged heterobimetallic complexes Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] that have been prepared by treatment of complex salt Na₂[Cu(MNT)₂] (generated in situ) with one equivalent of cationic complexes [M(N–N)₃]X₂ or Hg(CH₃COO)₂ and two-equivalent of AgNO₃ in aqueous–methanol mixture and characterised by relevant spectroscopies (IR, EPR, UV-Visible) as well as by powder XRD spectra. Solution conductivity measurements in 10⁻³ M DMSO solution revealed 1:1 electrolytic behaviour of the bimetallic salts. Diamagnetism together with powder EPR spectra for Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] show strong antiferromagnetic interaction between two adjacent copper(II) centers at room temperature. Majority of the complexes exhibited compressed pellet σ_rt in 8.19×10⁻¹¹ to 5.37×10⁻⁷ S cm⁻¹ range and show semiconductivity over the 303–383 K temperature range. Conductivity of both coordination polymers are appreciably higher compared to the bimetallic salts. For the salts [Co(phen)₃][Cu(MNT)₂], [Ni(phen)₃][Cu(MNT)₂] and bridged complexes Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] the conductivity remarkably increases, i.e., 10² to 10³ order of magnitude at elevated temperature showing some sort of phase transformation producing S⋯S intermolecular contact.     

Substitutions in vanadate garnets

Following the original synthesis of Durif of NaCa₂Cu₂V₃O₁₂ and later synthesis by Bayer of NaCa₂M⁺⁺V₃O₁₂ and Ca₃LiM⁺⁺V₃O₁₂, where M was Mg, Co, Ni, Cu or Zn, forty-one variations were prepared as phase-pure garnets. The general formulae of the garnets attempted were [A₂⁺⁺B⁺] M₂⁺⁺V₃O₁₂ (Type I) and A₃⁺ [B⁺M⁺⁺]V₃O₁₂ (Type II), where A⁺⁺ = Mg, Sr, Pb, Cd or Ba, M⁺⁺ = Mg, Co, Ni, Cu or Zn and B⁺ = Li, Ag, K or Rb.     

Behavior of Microamounts of <Superscript>22</Superscript>Na, <Superscript>85</Superscript>Sr, <Superscript>137</Superscript>Cs,and <Superscript>152</Superscript>Eu in Sorption and Coprecipitation on Mixed Potassium Neodymium Ferrocyanide from Solutions

Sorption of ⁸⁵Sr, ¹³⁷Cs, ²²Na, and ¹⁵²Eu on solid mixed potassium neodymium ferrocyanide KNd[Fe(CN)₆]·4H₂O from neutral, acidic, and alkaline media and also coprecipitation of these radionuclides with KNd[Fe(CN)₆]·4H₂O in its formation from a homogeneous solution were studied. It was found that ⁸⁵Sr and ²²Na do not noticeably coprecipitate with solid KNd[Fe(CN)₆]·4H₂O and are not sorbed by this substance. In aqueous medium, depending on the cesium concentration in solution, from 80 to 98% of ¹³⁷Cs coprecipitates with solid KNd[Fe(CN)₆]·4H₂O. In this case, the distribution coefficient K_d depends on both the cesium concentration in solution and solution pH. Within 30 min of contact of the solid and liquid phases, the degree of recovery of ¹³⁷Cs from aqueous solution with KNd[Fe(CN)₆]·4H₂O is approximately 95.0% of the initial amount. ¹⁵²Eu coprecipitates with solid KNd[Fe(CN)₆]·4H₂O during its formation from a homogeneous solution to 98–99.9%. The degree of recovery of ¹⁵²Eu from aqueous solution with KNd[Fe(CN)₆]·4H₂O precipitate within 60 min of contact of the solid and liquid phases is 70.3% of the initial amount.     

Thinning of CIGS solar cells: Part I: Chemical processing in acidic bromine solutions

CIGSe absorber was etched in HBr/Br₂/H₂O to prepare defined thicknesses of CIGSe between 2.7 and 0.5 μm. We established a reproducible method of reducing the absorber thickness via chemical etching. We determine the dissolution kinetics rate of CIGSe using trace analysis by graphite furnace atomic absorption spectrometry of Ga and Cu. The roughness of the etching surface decreases during the first 500 nm of the etching to a steady state value of the root-mean-square roughness near 50 nm. X-ray photoelectron spectroscopy analyses demonstrate an etching process occurring with a constant chemical composition of the treated surface acidic bromine solutions provide a controlled chemical thinning process resulting in an almost flat surface and a very low superficial Se⁰ enrichment.     

Temperature cycling effects between Sn/Pb solder and electroless copper plated AIN substrate

Thermal cycling effects on Sn/Pb solder and electroless Cu-plated AIN substrates are investigated. X-ray diffraction patterns reveal the existence of Cu₂O for the electroless Cu-plated AIN after thermal cycling in an environmental chamber. Moisture in the chamber results in the oxidation of electroless plated Cu and fracture takes place at the Cu₂O/Cu interface. The oxidation of Cu is also confirmed by Auger depth profile and electrical sheet resistance measurement. For the solder/Cu/AIN system, fracture occurs at the Cu/solder interface. No intermetallic compounds between solder and Cu are found after thermal cycling. Stress resulting from the thermal expansion mismatch is the major cause of loss of adhesion     

Chemical etching of InP (1 0 0) wafer based on a volcanic mineral water

We have successfully demonstrated that a solution of spa water [Tamagawa Spa water (TaSW):H₂O₂ = 1:1] etches InP (1 0 0) wafer. The TaSW is a colorless acidic liquid of pH ∼1.1. It contains a considerable amount of positive ions, such as H⁺, Al³⁺, and Ca²⁺. The Cl⁻, HSO₄²⁻, and SO₄²⁻ ions are the main anions. The TaSW-etchant system provides shiny flat surfaces on the etched bottoms. The spa-etchant system has reproducible etching rates and does not erode photoresist masks. The etching kinetics is reaction-rate limited. The spa-etchant system is also found to etch GaAs (1 0 0) wafer, but the etched surface is considerably roughened.     

Surface planarization and masked ion-beam structuring of YBa2Cu3O7 thin films

Surface planarization and masked ion-beam structuring (MIBS) of high-T_c superconducting (HTS) YBa₂Cu₃O_7-δ (YBCO) thin films grown by pulsed-laser deposition (PLD) method is reported. Chemical-mechanical polishing, plasma etching, and oxygen annealing of YBCO films strongly reduce the particulate density (~ 10^-2 ×) and surface roughness (~ 10^-1 ×) of as-grown PLD layers. The resistivity, critical temperature T_c ≈ 90 K and critical current density J_c (77 K) > 1 MA/cm² of films are not deteriorated by the planarization procedure. The YBCO films are modified and patterned by irradiation with He⁺ ions of 75 keV energy. Superconducting tracks patterned by MIBS without removal of HTS material and, for comparison, by wet-chemical etching show same T_c and J_c(T) values. Different micro- and nano-patterns are produced in parallel on planarized films. The size of irradiated pattern depends on the mask employed for beam shaping and features smaller than 70 nm are achieved.     

Effect of Pb2+ and Cu2+ as a codopant on the structure,morphology and conductivity of nanostructured polyaniline

Polyaniline (PANI) has been successively synthesized in aqueous diethylene glycol solution medium by chemical oxidative polymerization of aniline using ammonium peroxidisulfate [(NH₄)₂S₂O₈] as an oxidant in an aqueous solution of 0.5 M acetic acid (CH₃COOH) as a dopant. Polyaniline–lead (PANI–Pb) and polyaniline–copper (PANI–Cu) nanocomposites have been chemically prepared for the first time by oxidative polymerization of aniline in aqueous diethylene glycol/acetic acidic medium. The synthesized PANI and nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR). Conductivity measurements of the polymer and nanocomposites were performed using the four-probe technique. Morphology changes of the composites were investigated by scanning electron microscopy (SEM). PANI nanotubes were formed without added codopant, but when Pb(CH₃COO)₂ or Cu(CH₃COO)₂ was added as a codopant, the morphology of PANI obviously changed. The PANI–Cu and PANI–Pb nanocomposites exhibit higher conductivity than the PANI homopolymer, but the conductivity of the composites slightly decreased on increasing the metal concentrations.     

Spectroscopic characterization of tungstated zirconia prepared by equilibrium adsorption from hydrogen peroxide solutions of tungsten(VI) precursors

Two series of WO _x /ZrO₂ samples are prepared by equilibrium adsorption from H₂O₂ solutions at pH 1.8 containing two different precursor anions, [W₂O₃(O₂)₄(H₂O)₂]²⁻ and [H₂W₁₂O₄₀]⁶⁻. The starting material is amorphous zirconium oxyhydroxide. The maximum W densities obtained are larger than that reported in the literature for systems synthesized by the same method using aqueous non-peroxide solutions. In the case of the metatungstate precursor, this increase is attributed to the generation of additional anchoring sites by interaction between the amorphous support and H₂O₂. The high uptake achieved when the peroxo complex is used as a precursor is a result of both the ZrO _x (OH)_4-2x –H₂O₂ interaction and low nuclearity of the adsorbing anion. The materials are characterized by XRD, DR–UV–vis, Micro-Raman and FT-IR spectroscopy. The surface acidities of samples with identical W loading prepared by equilibrium adsorption from the [H₂W₁₂O₄₀]⁶⁻–H₂O₂ system and by impregnation with aqueous solution of ammonium metatungstate are investigated by FT-IR spectroscopy of CO adsorbed at 80 K.     

Formation mechanism of NaNbO<Subscript>3</Subscript> powders during hydrothermal synthesis

Hydrothermal synthesis of NaNbO₃ fine powders was investigated, and the formation mechanism was revealed. The lowest temperature to form NaNbO₃ powders was about 140 °C. An intermediate hexaniobate, Na₈Nb₆O₁₉·13H₂O, was formed first before the precursors were eventually converted to the perovskite phase. The step of dissolving Nb₂O₅ powders in OH⁻ solution and forming Nb₆O₁₉ ⁸⁻ ion was very important to the synthesis of NaNbO₃. For [OH⁻] = 3.0 M, Nb₂O₅ had the highest yield. There was another dissolvable sodium niobate in the hydrothermal system, which was stable when [OH⁻] = 1.2 M. The reaction mechanism was in situ transformation. The reaction speed first increased then decreased with [OH⁻]. High [OH⁻] is not always favorable in preparing perovskite NaNbO₃, and there is an optimum [OH⁻].     

Formation and mechanism of silicon nanostructures by Ni-assisted etching

Instead of noble metal like Pt, Au and Ag, cheap Ni nanoparticles (Ni NPs) were used to fabricate silicon nanostructures. Ni was found to be etched off during the etching process, while forming silicon nanostructures with very low reflectance of 1.59 % from 400 to 900 nm. The formation mechanism of silicon nanostructures by Ni-assisted etching was presented from the point of view of the low electronegativity of Ni. The Ni NPs were found being etched off during the assisted etching process, which implies that the transfer rate of electrons from Si to Ni is slower than that from Ni to O^? in the case of using Ni as assisted metal. The reason of sparser and deeper silicon nanostructures etched in lower H₂O₂ concentration solution is that the Ni NPs can be lasted for longer time in the etching solution with lower H₂O₂ concentration so that more silicon atoms will be oxidized and then removed for those under Ni NPs due to the hole transfer and those where uncovered by Ni NPs due to the hole diffusion.     

Lithium insertion into manganese spinels

Lithium has been inserted chemically and electrochemically into Mn₃O₄ and Li[Mn₂]O₄ at room temperature. From X-ray diffraction, it is shown that the [Mn₂]O₄ subarray of the A[B₂]X₄ spinels remains unperturbed and that the electrons compensating for the Li⁺-ion charge reduce Mn³⁺ to Mn²⁺ in Mn₃O₄ and Mn⁴⁺ to Mn³⁺ in Li[Mn₂]O₄. In Li_xMn₃O₄, the tetragonal distortion due to a cooperative Jahn-Teller distortion by octahedral-site Mn³⁺ ions decreases with x from $\text{c}\text{a}\text{= 1.157}$ for x = 0 to $\text{c}\text{a}\text{= 1.054}$ for x = 1. The system Li_1+x[Mn₂]O₄, is cubic at x = 0 and tetragonal ($\text{c}\text{a}\text{= 1.161}$) at x = 1.2. Electrochemical data reveal a two-phase region in the Li_1+xMn₂O₄ system and a maximum x_m = 1.25. X-ray diffraction confirms the coexistence of a cubic and a tetragonal phase in the compositional range 0.1 ≤ x ≤ 0.8. The X-ray data also show that the inserted Li⁺ ions occupy the interstitial octahedral positions of the spinel structure. However, in Li_xMn₃O₄ the tetrahedral-site Mn²⁺ions are displaced from the A positions to the interstitial octahedral positions, as in Li_xFe₃O₄, whereas the tetrahedral-site Li⁺ ions in Li[Mn₂]O₄ remain on the A sites.     

Electrochemical extraction of lithium from LiMn2O4

Lithium has been removed electrochemically at 15 μA/cm² from LiMn₂O₄ (spinel) to yield single phase Li_1?xMn₂O₄ for 0 < × ? 0.60. The electrochemical curve suggests that beyond x = 0.60 an electrochemical process other than lithium extraction occurs. Powder X-ray-diffraction spectra indicate that during the extraction process the [Mn₂]O₄ framework of the spinel structure remains intact. Previous results have shown that 1.2 Li⁺ ions can also be inserted into LiMn₂O₄, which suggests that lithium may be cycled in and out of the [Mn₂]O₄ framework of the spinel structure over a wide range of x, at least from Li_0.4Mn₂O₄ to Li₂Mn₂O₄. Discussion of the mechanism of formation of λ-MnO₂ in an acidic environment is extended.     

Reaction of ozone with Np(V) and Np(IV) in carbonate solutions

A spectrophotometric study showed that ozone in concentrated carbonate solutions forms complexes with CO ₃ ^2? ions, which inhibits the ozone decomposition. Free ozone oxidizes Np(V) at high rate. The bound ozone reacts with Np(V) at moderate rate. Np(IV) reacts with O₃ slowly, with Np(VI) formed in NaHCO₃ solution and only Np(V) formed in Na₂CO₃ solution.     

Bandgap Tunable Oxynitride LaNb2O7–xNx Nanosheets

Bandgap tunable lanthanum niobium oxynitride [LaNb₂O_7-xN_x]^(1+x)− nanosheet is prepared by the delamination of a Ruddlesden−Popper phase perovskite oxynitride via ion−exchange and two−step intercalation processes. The lanthanum niobium oxynitride nanosheets have a homogeneous thickness of 1.6 nm and exhibit a variety of chromatic colors depending on the nitridation temperature of the parent-layered oxynitride. The bandgap energy of the nanosheets is determined by ultraviolet photoemission spectroscopy, Mott–Schottky, and photoelectrochemical measurements and is found to be tunable in the range of 2.03–2.63 eV. Furthermore, the oxide/oxynitride superlattice structures are fabricated by face−to−face stacking of 2D crystals using oxynitride [LaNb₂O_7-xN_x]^(1+x)− and oxide [Ca₂Nb₃O₁₀]⁻ nanosheets as building blocks. Moreover, the superlattices-like restacked oxynitride/oxide nanosheets hybrid exhibits unique proton conductivity and dielectric properties strongly influenced by the oxynitride nanosheets and enhanced photocatalytic activity under visible light irradiation.     

Effects of radical-distribution control on etching-profile uniformity in dielectric etching

Uniformity control of etching profile and etching rate across a wafer during damascene etching was investigated using a UHF-ECR etching apparatus with a dual-zone gas-injection system. Uniform etching rate was obtained under various conditions by controlling magnetic field distribution. It was found that etching profile could be controlled without affecting etching-rate uniformity by changing the ratio of inner- to outer-nitrogen-gas flow rate above the wafer. The effect of feed-gas control on radical distribution was evaluated by simulation and measurement of the radical distribution, which showed that controlling the gas-mixing ratio changed the distribution of the nitrogen-to-CF_x ratio. With SiOC via hole etching, nanometer-level bottom-CD uniformity at high etching-rate uniformity was obtained.