E. A. Kneer

Electrochemistry of Chemical Vapor Deposited Tungsten Films with Relevance to Chemical Mechanical Polishing

The electrochemical behavior of chemically vapor deposited tungsten films in solutions of interest to tungsten chemical mechanical polishing has been investigated using dc potentiodynamic polarization, linear polarization, and Tafel methods. It was found that in the absence of an oxidizer, the tungsten surface was passivated most effectively at acidic pH values. At pH 2 or 4, a WO{sub 2}/WO{sub 3} duplex oxide layer of less than 50 A thickness was detected over the tungsten layer by X-ray photoelectron spectroscopy. The oxide layer formed at pH 2 was much thicker, and had better passivity compared to the oxide formed at pH 4. Addition of H{sub 2}O{sub 2} at pH 2 or 4 resulted in a dramatic increase in tungsten dissolution.

Electrochemical Measurements during the Chemical Mechanical Polishing of Tungsten Thin Films

A polishing tool and a potentiostat were used to simultaneously polish and measure the direct current (dc) open-circuit potential and anodic polarization behavior of chemical vapor deposited tungsten films in the presence of various oxidants. Of the different oxidants tested at pH 1.5 or pH 4.4, (NH 4 ) 6 Mo 7 O 24 formed the most protective passive layer on tungsten. Even in the presence of the most aggressive oxidant, Fe(NO 3 ) 3 , the dissolution rates of chemical vapor deposited tungsten were approximately 3 nm/min during abrasion, which is a very small fraction of typical removal rates reported for chemical mechanical polishing of tungsten. This indicates that electrochemical oxidation followed by abrasive removal of the oxidation product and dissolution may not be the primary mechanism for tungsten removal. Atomic force microscopy scans of polis ed tungsten films indicate that corrosion assisted fracture may be an important removal mechanism for tungsten during chemical mechanical polishing.

A Comparative Electrochemical Study of Copper Deposition onto Silicon from Dilute and Buffered Hydrofluoric Acids

An electrochemical direct current polarization method was used to investigate characteristics of copper deposition onto silicon from dilute and buffered hydrofluoric acid solutions. The corrosion current density and corrosion potential of silicon were not very sensitive to the Cu 2+ concentration, up to 1000 parts per billion, in buffered hydrofluoric acid. However, the extent of copper deposition, as measured by total reflection X-ray fluorescence, increased as the Cu 2+ concentration in solution increased. In dilute hydrofluoric acid, Cu 3+ addition had a significant and systematic effect on the corrosion potential and corrosion current density of silicon. However, in both types of solution, the cathodic current calculated from the measured copper deposition was found to be only a small fraction of the corrosion current (less than 1%). This indicates that the primary cathodic reaction is not copper ion reduction but hydrogen ion reduction. Illumination affected the electrochemical behavior of both p- and n-type silicon in Cu 2+ spiked dilute hydrofluoric acid, but only that of p-type silicon in buffered hydrofluoric acid.

Electrochemical Impedance Spectroscopy of Copper Deposition on Silicon from Dilute Hydrofluoric Acid Solutions

Electrochemical impedance spectroscopy was used to probe the mechanism of copper deposition on silicon from dilute hydrofluoric acid solutions. Reaction parameters such as polarization resistance and space-charge capacitance were evaluated using an equivalent circuit model. The electrochemical impedance technique was found to be sensitive to parts per billion levels of Cu 2+ ion in dilute hydrofluoric acid solutions. An inductive loop appeared in Nyquist plots only when Cu 2+ ions were present in hydrofluoric acid solutions. Both the polarization resistance and inductance decreased significantly as the solution Cu 2+ concentration increased. Addition of a nonionic surfactant to hydrofluoric acid solutions significantly altered impedance characteristics of the silicon/solution interface. Total reflection X-ray fluorescence results showed that illumination enhanced deposition of copper on silicon nearly an order of magnitude.

Effect of top metallization on the fatigue and retention properties of sol-gel pzt thin films

Abstract Fatigue and retention problems pose significant hurdles towards successful implementation of ferroelectric (FE) memory. The PZT-substrate or PZT-electrode interface is well known to affect the FE properties and specifically the fatigue behaviour. Bottom electrode (or the substrate) is typically a noble metal such as Pt or Au. Pt-PZT-Pt capacitors exhibited fatigue resistance up to 108 - 109 cycles while RuO2, La0.5Sr0.5CoO3 and YBa2Cu3O7 electrodes yielded fatigue-free devices up to 1011 - 1012 cycles. In an early study which compared the fatigue behaviour of bulk PLZT ceramics with various metal electrodes, it was found that In offered the best fatigue performance (up to 109 cycles). These films were fired to 700C to achieve single-phase FE perovskite films. Monolithic capacitors were obtained by depositing top electrodes of Ag, Al, Bi, Cr, Cu, Mg, Ni, Pb, Pd, Pt, Sn, V and Zn. Work function difference alone did not fully explain the dependence of the observed electrical properties and fatigue b...

Evolution of surface relief during firing of PZT thin films

Abstract A controlled test of platinum bottom electrode preparation has been performed. Different types of Ti or TiOx layers have been used to promote adhesion of the platinum electrode. This paper correlates the surface roughness of these electrodes with electrical properties that result.

Compositional tailoring of the dielectric and ferroelectric properties of sol-gel derived PLZT thin films

Abstract PZT films, especially PZT 53/47 films, have been intensively explored for a wide range of applications. A broad range of dopants can be incorporated fairly easily into PZT using sol-gel techniques, resulting in compositional tailoring of material properties. One important dopant is La, forming PLZT compositions which have a larger range of dielectric and ferroelectric properties than the PZT materials. To date, PLZT films have received less attention in electrical applications than PZT films in spite of the wider range of film properties achieveable with the former. A series of sol-gel derived PLZT films was prepared on platinized Si wafers. Selected compositions were prepared covering the entire PLZT phase diagram, namely PLZT x/y/z with y/z = 20/80, 53/47 and 65/35 and x = 0, 2, 4, 6, 8, 10 and 12; and × = 7.5 with y/z = 0/100, 20/80, 65/35, 53/47, 35/65, 80/20 and 0/100. The films were spincoated on platinized Si wafers and fired to 650 – 700 C to convert them into single phase perovskite film...

Investigation of surface roughness and hillock formation on platinized substrates used for Pt/PZT/Pt capacitor fabrication

Abstract Hillock formation on Pt bottom electrode surfaces has been investigated for 〈111〉 Si and sapphire substrates. This paper correlates the electrical performance of Pt/PZT/Pt structured capacitors with the observed surface roughness and/or hillock presence on the Pt bottom electrode.

Effect of Zr/Ti stoichiometry ratio on the ferroelectric properties of sol-gel derived PZT films

A series of sol-gel-derived PZT (lead zirconate titanate) films with Zr:Ti ratios of 100:0, 94:6, 80:20, 65:35, 53:47, 35:65, 20:80, and 0:100 was prepared on platinized Si wafers. The precursor chemistries were based on lead acetate and Zr/Ti alkoxides containing the appropriate amounts of cations in the required stoichiometries. Excess PbO was incorporated to compensate for PbO loss during processing. Films were fired to 700 degrees C where they were all single-phase perovskite as determined by XRD (X-ray diffraction). Microlithography was performed to obtain Pt-PZT-Pt monolithic capacitors with 130- mu m by 130- mu m electrode pads. The ferroelectric properties on these pads were measured along with the leakage characteristics. The dielectric and ferroelectric properties of the PZT films were found to be highly dependent on composition and processing conditions.<<ETX>>

Influence of Ti interfacial layers on the electrical and microstructural properties of SOL-gel prepared PZT films

Abstract Sol-gel derived lead zirconate titanate (PZT) thin films were deposited onto monolithic Pt bottom electrodes which used Ti interlayers for Pt adhesion on thermally oxidized 〈111〉 Si. The rf-sputter deposited Pt/Ti films were annealed at 400° – 600°C for 15 minutes. Atomic Force Microscopy (AFM) was used to analyze the Pt surface features. Transmission Electron Microscopy (TEM), transmission electron diffraction, scanning transmission electron microscopy (STEM), and scanning electron microscopy (SEM) were used to investigate the microstructure of PZT films crystallized onto these electrodes. RT-66A testing was conducted to evaluate the electrode performance of the Pt/PZT/Pt structure devices. It was found that the lower temperature bottom electrode anneal created a more dense, smaller grained nucleated PZT film.