Alexandra Inberg

Electroless Silver and Silver with Tungsten Thin Films for Microelectronics and Microelectromechanical System Applications

In this study we present the results of electroless deposition of silver (Ag) and silver tungsten [Ag(W)] layers on Si, intended for application in microelectronics and microelectromechanical systems (MEMS) technology. Silver has excellent resistivity but its thin-film properties and its vulnerability to corrosion may cause a problem. In this work we present a novel Ag(W) type of layer that has improved thin-film properties, such as resistivity and surface roughness, and can serve as both barrier layer and capping layer for corrosion protection of the Ag thin films. The thin-film composition was studied as a function of the deposition parameters. We found the presence of tungsten, up to 3.1 atom %, and oxygen, up to 8 atom %, in addition to the silver atoms. We also studied the thin-film morphology using atomic force microscopy and scanning tunneling microscopy imaging of the surface after each process step. Finally, we discuss the possible mechanisms for the deposition of Ag(W ).

Electroless processes for micro- and nanoelectronics

Abstract Electroless deposition of metals has many applications in micro- and nanotechnologies. Currently, electroless Cu, Co, Ni, Ag and their alloys are used as materials for interconnects and packaging applications for ultralarge-scale integration (ULSI) as well as for microelectro-mechanical systems (MEMS). Electroless methods offer high-quality ultrathin films that are compatible with high-resolution patterns such as sub-100 nm interconnects, contacts and via contacts for ULSI and in high aspect ratio structures for MEMS. In this paper, we present an overview of electroless methods for microtechnologies applications. We also present Cu, Ag, and Co alloys that are designed to improve performance and reliability of the pure metals. Next, we present new concepts of electroless deposition methods that will be useful for nanotechnologies. We explore the possibility to use electroless methods that can be combined with self-assembly of organic compounds such as proteins to form metallic interconnect network. Silver deposition on organic substrates is described as a novel approach to produce high-quality Ag coating on features with 1–10 nm critical dimensions.

Spectroscopy in the gas phase with GaAs/AlGaAs quantum-cascade lasers.

We demonstrate what we believe is the first application of the recently developed electrically pumped GaAs/AlGaAs quantum-cascade lasers in a spectroscopic gas-sensing system by use of hollow waveguides. Laser light with an emission maximum at 10.009 microm is used to investigate the mid-infrared absorption of ethene at atmospheric pressure. We used a 434-mm-long silver-coated silica hollow waveguide as a sensing element, which served as a gas absorption cell. Different mixtures of helium and ethene with known concentrations are flushed through the waveguide while the laser radiation that passes through the waveguide is analyzed with a Fourier-transform infrared spectrometer. The experimentally obtained discrete ethene spectrum agrees well with the calculated spectrum. A detection threshold of 250 parts per million is achieved with the current setup.

Electroless-deposited Ag-W films for microelectronics applications

Abstract Thin Ag–W films, with a tungsten concentration of up to 3.2 at.% and a thickness in the range 20–300 nm, were directly deposited on Si(100) substrate by the electroless (auto-catalytic) method. The deposition characteristics and the thin film electrical and physical properties were studied as a function of the bath composition. The role of tungsten in the silver matrix was studied via measurements of the film microhardness and thermal stability as a function of the thin film composition. Ag–W films thicker than 200 nm had a shiny appearance with good reflectivity and their specific electrical resistivity was 2 μΩ cm. The specific resistivity of films increased with decreasing thickness. Exposure of electroless silver films to air at 200°C for a few h causes them to tarnish severely and their sheet resistance to significantly increase, while similar Ag–W films were not affected under the same conditions. Therefore, we assume that silver–tungsten films can be used for applications that require reliable conducting thin films, such as packaging and interconnects for microelectronics.

Flexible waveguides for Er-YAG laser radiation delivery

Flexible plastic waveguides (FPW) were devised for the delivery of Er-YAG laser radiation. The FPW characteristics were studied under various conditions. In vitro studies were carried out to explore the drilling procedure on extracted teeth and the FPW-tissue mutual effects. The results which were obtained proved that the FPW as a delivery device might be a substitute hand applicator for the pneumatic turbine for drilling in teeth.<<ETX>>

Characterization of the Initial Growth Stages of Electroless Ag(W) Films Deposited on Si(100)

Scanning tunneling microscopy (STM). high resolution scanning electron microscopy, and transmission electron microscopy (TEM) have been used to study the film evolution at the initial stage of deposition and the structure of electrolessly deposited silver films that contain tungsten [Ag(W)] on single crystal silicon (100). We present the surface covering process at the initial stage of electroless deposition. The surface reconstruction in this case takes place at room temperature. The state and position of the tungsten was also investigated; TEM measurements indicate that NaWO 3 is present in the film. STM images of the Ag(W) film growth show a spiral feature that may reveal a dominant electrochemical driving force during the crystal growth. The presence of well-resolved steps in the deposition process and its electrochemical nature were demonstrated by fast immersion chronovoltametry. This method was also applied to follow the changes in the surface energy, which were caused by the surface pretreatment processes and the deposition process itself.

Characterization of a mid-infrared hollow waveguide gas cell for the analysis of carbon monoxide and nitric oxide.

Infrared spectroscopy is commonly applied to the analysis of small gas-phase molecules. One of the limitations of using Fourier transform infrared (FT-IR) spectroscopy for these applications is the time response of long path length gas cells. Hollow waveguides (HW) that transmit in the mid-infrared spectral range have higher optical efficiencies compared to long path length cells due to smaller cell volumes. This study characterizes a silver coated, 2 mm inner diameter HW for the analysis of carbon monoxide (CO) and nitric oxide (NO) and compares the performance to a 3 m gas cell and traditional gas analyzers. The HW was found to have a CO response time less than the NDIR analyzer and approximately one-tenth of the response time on the FT-IR system equipped with a 3 m gas cell. The utility of the increased response time was demonstrated by measuring CO concentrations in sidestream cigarette smoke at the same temporal resolution as an NDIR analyzer. A 10 to 60% increase in sensitivity using various frequencies for both CO and NO was observed using the HW compared to the 3 m multipass gas cell. However, cost savings for gas-sensing applications can be achieved on a per analyte basis by using FT-IR spectroscopy, especially in combination with a HW gas-sensing module, which is significantly less expensive than a multipass gas cell.

Electroless deposition of novel Ag-W thin films

The seedless electroless deposition of silver-tungsten (Ag-W) thin films on silicon dioxide substrate was performed using wet palladium activation from ammonia-acetate and benzoate solutions. Introducing tungsten in the plating bath catalyzes the deposition for benzoic acid solution and decreases the deposition rate for ammonia-acetate solution. The tungsten content in the deposit was 0-1.0 at%, mainly in WOx form. It was found that the electrical, optical, and mechanical properties of the Ag-W films depends on the W content in the deposit. The optimal Ag-W thin films that were deposited from either the ammonia-acetate or benzoate bath demonstrate good adhesion to the substrate, high brightness, and do not corrode at temperatures up to 350 °C in air. Sub-100 nm thick Ag-W deposits have demonstrated resistivity of about 4 µΩ cm after vacuum annealing at 350 °C for 1 h. Finally, we present the film microstructure characterization and discuss the possibility of using Ag-W thin films for advanced microelectronics metallization.

Novel Highly Conductive Silver-Tungsten Thin Films Electroless Deposited from Benzoate Solution for Microelectronic Applications

In this study we present the results of electroless deposition of silver-tungsten (Ag-W) films on SiO 2 , suitable for applications in microelectronics and ultralarge-scale integration technology. The thin-film composition and resistivity was studied as a function of the bath formulation. The optimal parameters (temperature, pH) and composition of aqueous solution for the deposition of Ag-W thin films with minimum resistivity were defined. It was shown that elevated temperature of the deposition bath results in impairment of solution stability and causes the Ag-W film resistivity to increase. Thin-film morphology was studied using scanning electron microscopy and optical microscopy. Ag-W electrical properties as a function of film deposition rate, composition, and structure were discussed. Novel Ag-W layers with improved properties, such as electrical resistivity and surface coverage, are presented in this work. The highest concentration of tungsten in Ag-W deposits was ∼2.1 atom % with oxygen concentration about 4 atom %. Resistivity of 150 nm thick Ag-W films reaches a value of ∼4 μΩ cm, and it is ∼6 μΩ cm for layers thinner than 60 nm. These films can be applied as both barrier and capping layers for corrosion protection of Ag. The possibility of reducing Ag-W film resistivity using vacuum annealing is demonstrated.

Electrical resistivity of thin electroless Ag-W films for metallization

It is shown that optimization of the electroless deposition and the use of vacuum annealing yield dramatic decrease in the resistivity and its scatter in 100- and 50-nm silver-tungsten (Ag-W) films. Physical processes, which control the resistivity drop during low-temperature annealing and the residue resistivity in the annealed films are discussed.