Dimethyl Gold Hexafluoroacetylacetonate Research Articles

Microstructure of gold grown by ion-induced deposition

Ion-induced deposition is a process of film growth where adsorbed gas (usually organometallic) molecules are decomposed on the surface by ion impact leaving a deposit behind. This process is used in focused ion beam repair of microelectronic devices and masks. The deposited films are usually mixtures of metal and carbon. We have studied the microstructure of ion deposited gold by transmission electron microscopy. The gas used was dimethylgold hexafluoroacetylacetonate. The film is found to be made up of segregated gold and carbon. The gold can either be in the form of grains (isolated, approximately spherical islands 20–50 nm in diameter), in the form of columns of comparable diameter perpendicular to the surface, or in the form of a normal polycrystalline structure. Higher temperature growth (80–100 °C) or slower growth rate favors the polycrystalline films, while faster growth or growth at room temperature tends to produce granular films with a high carbon content. The incorporation of carbon may be related to the inability of the reaction products to escape from the surface.

Laser direct writing of gold to repair defective lines in thin-film metallizations

Laser chemical vapour deposition (LCVD) with dimethylgold hexafluoroacetylacetonate was used to repair defective lines in thin-film metallizations on alumina ceramic and polyimide. A process is described to deposit gold on polyimide and various substrates. Different patterns were deposited. Resistivities on polyimide have been achieved which are lower than 4.7 μΩ·cm, which is twice the value of bulk gold. Bond strengths of 10 N/mm 2 were measured on polyimide. With this method contacts have been produced to thin-film gold metallizations. Contact resistances have been measured in the range of 5–10 mΩ.

Materials Issues In X-Ray Mask Repair by Focused Ion Beams

AbstractIn x-ray mask repair high Z absorber features, such as gold or tungsten, must be removed or added. The main challenges are the small lateral dimensions (0.25 μm and below) and the thickness of the absorbers (˜ 0.5 μm) The focused ion beam appears to be the best tool developed to meet this challenge. Unwanted features are removed by ion milling while missing absorber is reconstructed using ion induced deposition from a locally piped-in precursor gas. The high aspect ratio of the features complicates both of these processes. Milling away 0.5 μm thick absorber can lead to redeposition of the sputtered material on neighboring features. The crystal grains of the absorber mill at different rates depending on orientation which results in nonuniform features. A possible alternative which only works with W absorber is to use ion assisted etching. In ion induced deposition a precursor gas such as dimethylgold hexafluoro acetylacetonate is provided by a capillary tube aimed at the region scanned by the ion beam. The incident Ga+ ions, usually at energies in the 25–100 keV range, dissociate the adsorbed precursor molecules leaving a deposit of gold mixed with carbon. The carbon content can approach 50 atomic % resulting in an x-ray attenuation which is about one half of that of pure gold. A number of unexplored materials science issues are associated with mask repair including: the reduction of the carbon content, redeposition both from milling and from induced deposition, milling as a function of crystal orientation and energy, and deposition of high aspect features. The technology is well enough developed so that mask repair of 0.25 μm features can be considered. However, a better understanding of the materials science aspects of x-ray mask repair will help to advance the state-of-the-art.

Surface Morphology and Line Fill Properties of Gold Grown by Organometallic Chemical Vapor Deposition

Dimethyl gold hexafluoroacetylacetonate, (DMAu(hfac)) was used to grow gold films by thermal decomposition. We found that surface morphology and line fill properties greatly depend on the substrate temperature and reactor pressure. Under optimum growth conditions, we have obtained gold films with flat surfaces and fine line fillings. We propose a growth model to explain the variation in surface morphology at various growth temperatures and reactor pressures.

Focused ion beam induced deposition and ion milling as a function of angle of ion incidence

In the repair of integrated circuits, and x-ray masks focused ion beam induced deposition, and ion milling often have to be performed over quite nonplanar topography. Thus, the milling and the deposition as a function of the angle of ion incidence are important. The milling yield of Si, SiO2, Au, and W versus angle of incidence using 25 keV Ga+ ions has been measured. In qualitative agreement with simulations, the yield rises with angle and then falls as grazing incidence is approached. Deposition yield versus angle was measured using dimethylgold hexafluoro-acetylacetonate and W(CO)6 as the precursor gases. The measurements were carried out using cylindrical quartz fibers 30–50 μm in diameter which automatically provide angles of incidence from 0° to 90° or on planar surfaces at various angles. Rippling of the deposited material is observed at angles of incidence greater than 50°.

Time-resolved reflectance studies of surface melting during laser-assisted deposition with a modulated laser source

Time-resolved reflectance measurements have been used to study the time evolution of the surface reflectance during deposition of gold from dimethylgold hexafluoroacetylacetonate with both modulated and unmodulated laser light. The observed change in reflectivity found during deposition with a modulated laser source is due to surface melting or sintering of the gold deposit. The change in reflectance observed upon undergoing a transition from a rough to a smooth surface is theoretically calculated for a surface with a random distribution of facet shapes and sizes. The observed changes in reflectance are consistent with the rough polycrystalline surface layer becoming smooth in a transient molten state. An impulsive temperature rise due to a rapid exothermic reaction taking place at the leading edge of the laser pulse has been estimated theoretically and is consistent with the observed time-dependent data.

The role of the ion-solid interaction in ion-beam-induced deposition of gold

Gold films were deposited on quartz-crystal microbalances by decomposing C7H7F6O2Au (dimethyl gold hexafluoroacetylacetonate) with 2–10-keV Xe+, Kr+, Ar+, Ne+, or He+ ion beams. The number of molecules decomposed per incident ion (i.e., the total decomposition yield) was determined as a function of ion mass and energy. The total decomposition yield increases with increasing ion mass and ion energy, and is approximately proportional to the nuclear stopping power. A binary collision model and a thermal spike model are developed that relate the energy deposited by the ion, at the substrate surface, to the total number of molecules decomposed. Both models predict total decomposition yields that are in reasonable agreement with the experimental measurements; however, the variation of total yield with changes in ion mass and energy are best described by the binary collision model. The success of both models demonstrates that the energy deposited into the substrate surface through the ion-solid interaction is responsible for the decomposition of adsorbed molecules.

UV desorption and photochemistry of dimethylgold hexafluoroacetylacetonate adsorbed on a quartz substrate

The photodesorption and photodecomposition pathways of dimethylgold hexafluoroacetylacetonate, DMG (hfac), adsorbed on a cooled quartz substrate is reported for 222-nm KrCl excimer laser radiation. The time-of-flight (TOF) of neutral photoproducts, desorbed from the surface of the gold film formed during the experiment, were analyzed under collisionless conditions by a differentially-pumped mass spectrometer. Extensive dissociation of adsorbed DMG (hfac) into DMG and the hfac ligand was observed. The ligand was found to recombine with a CH3 radical on the surface. Translational energy distributions for the detected species were obtained by deconvoluting the TOF curves into a self-consistent set of Maxwell-Boltzmann distributions for the desorbed parent molecule, laser-induced decomposition products, and surface recombination reaction products. The implications of these results for the mechanistic details of the low-pressure, laser-assisted organometallic deposition of DMG(hfac) are discussed.

Spontaneous decomposition of dimethyl gold hexafluoroacetylacetonate on ion bombarded surfaces

Aluminum and gold coated quartz crystal oscillators were bombarded by 7 keV Ga+ and then exposed to fairly low pressures (∼1 mTorr) of dimethyl gold hexafluoroacetylacetonate [denoted Me2Au(hfac) ] at room temperature for several hours. While unirradiated crystals exhibit a mass increase corresponding to approximately one monolayer of Me2Au(hfac), irradiated crystals accumulate significantly more mass. Typically, the accumulated mass on the irradiated surfaces corresponds to a film of gold several hundred angstroms thick. Thus, simple condensation of the organometallic molecules cannot explain the large mass increase. Rather it suggests that spontaneous decomposition of the Me2Au(hfac) is occurring on the irradiated surface. X-ray photoelectron spectroscopy indicates that the deposited mass is essentially pure gold. Rutherford backscattering spectroscopy indicates that as many as 20 Au atoms are deposited for each implanted Ga atom. Surfaces irradiated with Au ions show much less mass accumulation, but some growth still occurs. These results indicate that two processes contribute to film growth during ion induced deposition: ion decomposition plus the spontaneous decomposition described here.

Surface melting of metal deposits during laser-induced chemical vapor deposition with a modulated continuous-wave laser

Thermal laser-induced chemical vapor deposition of gold crystals on alumina substrates has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when the laser source is modulated. Time-resolved reflectance measurements have been used to study the time evolution of the surface reflectance during growth with both modulated and unmodulated laser light. These experiments suggest that the surface melting observed with a modulated laser source is primarily due to the heat released by the exothermic decomposition of reactant adsorbed on the surface during the time that the laser intensity is off.

Mechanism of ion beam induced deposition of gold

Gold films were deposited on quartz crystal microbalances (QCM) by decomposing C7H7F6O2Au [dimethyl gold hexafluoroacetylacetonate, or DMG(hfac)] with a 5 keV argon ion beam. A model for ion beam induced deposition is presented which relates the net deposition yield to the gas adsorption, the decomposition cross section, and the sputtering yield. The deposition rate was measured in situ as a function of ion current, gas pressure, and substrate temperature using the QCM. The deposition yield (mass deposited per incident ion) increased with increasing gas pressure and decreasing substrate temperature. The QCM was also used to measure the adsorption of DMG(hfac). The results demonstrated that the variation in deposition yield with temperature and pressure was proportional to the number of DMG(hfac) molecules adsorbed per cm2. Based on the observed correlation between deposition yield and adsorption, a decomposition cross section for 5 keV argon ions of 2×10−13 cm2 was estimated.

The role of gas adsorption in ion-beam-induced deposition of gold

Gold films were deposited on quartz crystal microbalances (QCM) by decomposing C7H7F6O2Au [dimethyl gold hexafluoroacetylacetonate, or DMG(hfac)] with a 5-keV argon-ion beam. A model for ion-beam-induced deposition is presented which relates the net deposition yield to the gas adsorption, the decomposition cross section, and the sputtering yield. The deposition rate was measured in situ as a function of ion current, gas pressure, and substrate temperature using the QCM. The deposition yield (mass deposited per incident ion) increased with increasing gas pressure and decreasing substrate temperature. The QCM was also used to measure the adsorption of DMG(hfac). The results demonstrated that the variation in deposition yield with temperature and pressure was proportional to the number of DMG(hfac) molecules adsorbed per cm2. Based on the observed correlation between deposition yield and adsorption, a decomposition cross section for 5-keV argon ions of 2×10−13 cm2 was estimated.

Focused ion beam fabrication of submicron gold structures

Because of their ability to both mill and deposit material with submicron resolution, focused ion beams are now used to repair photolithography masks and are of increasing technological interest in the repair of x-ray lithography masks and in integrated circuit restructuring. With the latter two applications in mind, we have fabricated milled and deposited Au features with linewidths of ≤0.1 μm using a 40 keV Ga focused ion beam. In addition, we present the results of a study parameterizing focused ion beam induced Au deposition under conditions of practical interest. Milling is accomplished by simple physical sputtering. Examples of milled microfeatures include a grating with a 210 nm period milled through a 5000 Å thick evaporated Au film. Deposition is accomplished by ion bombarding a SiO2 substrate on which a precursor gas, dimethyl gold hexafluoro acetylacetonate, is continuously being adsorbed. Examples of deposited Au features include a 3×3 μm patch 1-μm-thick with steep sidewalls. The deposition rate was measured at room temperature as a function of ion and precursor flux, and a simple model of the process is fitted to the data. Ion beam induced deposition efficiency is shown to depend critically on the time averaged beam current density and only weakly on the precursor flux. The maximum achievable growth rate is shown to be ∼10 Å/s. Deposited Au films contain 30–60 at. % carbon and have conductivities 200–600 times less than that of bulk Au. Those films formed using lower organometallic pressures or higher ion beam current densities are characterized by greater purity with more continuous microstructure.

I n s i t u measurement of ion-beam-induced deposition of gold

An experimental system for measuring ion-beam-induced deposition yield is described. Gold films were deposited on quartz-crystal microbalances (QCM) by decomposing dimethyl gold hexafluoroacetylacetonate molecules (C7H7F6O2Au) with a 5-keV argon-ion beam. The QCMs provide an in situ measurement of the deposition rate as a function of ion dose, dose rate, gas pressure, and substrate temperature. The deposition yield, or mass deposited per incident ion, is shown to increase with increasing pressure and decreasing temperature. The yield is independent of the ion dose rate, which implies that the deposition process is not due to macroscopic heating. The deposition yield is shown to depend on the sputter yield of the substrate. The density of the deposited films was determined to be about 10 g/cm3, which is about half the density of bulk gold (19.3 g/cm3). The difference in density is due to carbon contamination in the deposited films.

A diffusive transport relaxation technique for studying laser-induced chemical vapor deposition reactions at high pressures

A diffusive transport relaxation technique has been developed to study the chemical processes occurring during laser-induced chemical vapor deposition. The technique is based on modulation of the laser light intensity which results in a modulation of the surface reaction rate. This perturbation of the reaction rate produces transients in the gas-phase reactant and product concentrations for the case of gas-phase transport-limited deposition. Product species can be differentiated from species formed from the reactant during ionization and fragmentation due to the phase-sensitive nature of the detection scheme. The system response is examined theoretically by describing the response of the surface reaction rate to the modulated laser light and then examining the response of the gas-phase reactant and product concentrations to the modulated surface reaction. The technique was used to identify the gaseous products formed during laser-induced deposition of gold using dimethyl gold hexafluoroacetylacetonate.

Focused Ion Beam Induced Deposition

AbstractFocused ion beam induced deposition is already in use commercially for the repair of clear defects in photomasks, where missing absorber is added. Research is being carried out to extend this technique to the repair of x-ray lithography masks and to the restructuring and repair of integrated circuits, particularly in the prototype phase. In this technique a local gas ambient is created, for example, by aiming a small nozzle at the surface. The gas molecules are thought to adsorb on the surface and to be broken up by the scanned focused ion beam. A deposit is formed with linewidth equal to the beam diameter which can be below 0.1 Ό m. At small beam diameters and low currents (50–100 pA) the time to deposit 1Όm3 is in the vicinity of 10–20 sec. If the gas is a hydrocarbon, the deposit is largely carbon, which is useful for photomask repair. On the other hand, if the gas is a metal halide or a metal organic, the deposit is metallic. The deposits have substantial concentrations of impurities due to the atoms in the organometallic, to the ion species used, or to the ambient in the vacuum chamber. Thus the resistivities of the "metal" films deposited typically range from 150 to 1000 ΌΏcm which is usable for some repairs. (Pure metals have resistivities in the range 2.5 to 12 pQcm.) We have deposited gold from dimethyl gold hexafluoro acetylacetonate and have achieved linewidths down to 0.1 Όm, patches of 1 Όm thickness with steep side walls and in some cases, resistivities approaching the bulk value. Other workers have reported deposits of Al, W, Ta, and Cr. We will review previous work in the field and present some of our own current results.

Time-Resolved Studies of Surface Melting During Laser-Induced Chemical Vapor Deposition with Laser Intensity Modulation

ABSTRACTThermal laser-induced chemical vapor deposition of gold deposits has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when laser source is modulated. Time-resolved reflectance measurements have been used to study the surface reflectance during growth with modulated and unmodulated laser source. The reflectance measurements indicated that surface melting does not occur under unmodulated cw irradiation at equivalent laser intensities. Variation in the modulation duty cycle indicates that there is a minimum laser-off cycle time length required for surface melting to be observed. Evidence is presented which suggests that surface melting is due to the heat released by the exothermic decomposition of reactant adsorbed during the time that the laser intensity is off.

In-Situ Measurement of Ion Beam Induced Deposition of Gold

Abstractmechanistic model of the ion beam induced deposition (IBID) process is proposed, and an experimental system for measuring IBID is described. In IBID, the kinetic energy of the incident ion is deposited in the substrate surface resulting in the ejection of atoms (sputtering), and the decomposition of adsorbed molecules. Net deposition occurs when the number of atoms added through decomposition exceeds the number removed by sputtering.Gold films were deposited by decomposing dimethyl gold hexafluoroacetylacetonate (C7H7F6O2Au) molecules with a 5 keV argon ion beam. The beam current density was 5 μA/cm2. These films were deposited on quartz crystal microbalances (QCM). The QCM's provide an in-situ measurement of the deposition rate as a function of ion dose, dose rate, gas pressure, and substrate temperature. The mass of the depositing film increases with increasing ion dose. The deposition yield, or mass deposited per incident ion, is independent of the power input of the ion beam and therefore, the decomposition is not due to macroscopic heating. The deposition yield is shown to depend on the sputter yield of the substrate. The yield increases with increasing gas pressure and decreasing substrate temperature. This increase is proportional to the adsorption of the organometallic gas.

The Microstructure of Gold Films Written by Focused Ion Beam Induced Deposition

ABSTRACTFocused ion beam induced deposition of gold microfeatures is accomplished by 40 keV Ga+ bombardment of a substrate on which dimethyl gold hexafluoro acetylacetonate is continuously adsorbed. Under optimum conditions, deposition rates exceeding 11 Å/s have been achieved as well as high aspect ratio features, linewidths of approximately 0.1.μm, and resistivities of 500—1500 μΩcm. The microstructure, composition, and yield of the deposits have been examined as a function of various process parameters. Improved film growth and purity are observed in deposits made with lower organometallic pressures or higher current densities.

Modulated laser beam relaxation spectrometry of laser-induced chemical vapor deposition

The surface chemical reactions occurring during the laser-assisted deposition of gold from dimethyl gold hexafluoroacetylacetonate were studied using a photothermal modulation technique. A modulated argon ion laser was used to heat an area roughly 1 mm in diameter on an alumina substrate. Products of the photothermal reaction along with reactants were sampled through a 150×150 μm orifice located at the center of the deposit and were then introduced directly into a quadrupole mass filter. An inert buffer gas was required to confine changes in the reactant and product concentrations to the region surrounding the sampling orifice. Since the reactant concentration at the surface decreased when the laser was turned on while the product concentration at the surface increased when the laser was turned on, modulating the surface reaction rate by modulating the argon ion laser beam and employing phase-sensitive detection allowed the identification of reaction products. The behavior of the system was described qualitatively using a theory for coupled reactant transport to the deposit surface and surface chemical reaction.