N. Croitoru

Reactive-sputter-deposited TiN films on glass substrates

Abstract Sputter-deposited TiN thin films on glass substrate were investigated by X-ray diffraction analysis. The lattice parameter determined on the basis of (200) and (220) peaks is smaller than that determined on the basis of (111) peaks. A decrease in lattice parameter with increasing temperature was observed on annealing. The films exhibited preferred orientation. The tendency towards a specific preferred orientation is discussed on the basis of strain and surface energies. At low substrate temperatures and/or at small film thicknesses surface energy controls growth and a (100) preferred orientation is expected. At large film thicknesses and at high substrate temperatures the strain energy predominates and the (111) orientation is expected.

Characterization of hollow fibers for the transmission of infrared radiation.

Plastic hollow fibers were made from plastic tubes covered on the internal wall with a metal layer (a-type) or a metal layer and dielectric layer on top of it (b-type). The CO(2) laser energy transmission through the hollow fiber was measured as a function of the radius of curvature and the coupling lens (focal length at a constant fiber length). The yield of the transmission decreased in subtle curvatures (radius of curvature up to 100 cm) and remained almost constant as the curvature became sharper (down to radius of curvature of 13 cm). For the a-type fibers, the characteristics of attenuation depended on the focal length of the coupling lenses. The energy distribution at the output was measured and mapped. The experimental results showed that the maximum of the energy distribution is asymetrically positioned relative to the center and closer to the internal wall at a smaller bending radius. This was predicted in our previous theoretical calculation. The value of transmitted power attenuation was up to 1.4 dB/m. Maximum power at the output was 30 W, for a fiber of 50-cm length and a cross-sectional diameter of 1.9 mm. These types of hollow fiber have already been used in surgical experiments on dogs.

Study of HfO2 films prepared by ion-assisted deposition using a gridless end-hall ion source

HfO2 thin films were deposited using e-beam gun evaporation with ion assisted deposition (IAD) of low energy oxygen ions (40–100 eV) from an end-Hall ion source. A comparison was made using Hf and HfO2 starting materials. The index of refraction was measured as a function of the ion source voltage and compared to results without IAD. Application to high power laser mirrors was verified by measurements of laser damage thresholds at 1.06 μm.

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.

Linear electro‐optic effect in sputtered polycrystalline LiNbO3 films

Light guiding and modulation was demonstrated in sputtered LiNbO3 films deposited on glass substrates. We report on films’ exceptionally low attenuation (<2 dB/cm) and the highest electro‐optical coefficient reported so far for this kind of film (1.34×10−12 m/V).

Lattice distortion in thin films of IVB metal (Ti, Zr, Hr) nitrides

Abstract Nitride films of IVB metals (titanium, zirconium and hafnium) exhibit non-conventional lattice distortion which is displayed in the expansion of the lattice parameter calculated from the (111) diffraction peak. It is commonly assumed that this phenomenon may be explained in terms of rhombohedral distortion of the cubic lattice. However, our experimental data do not agree with the shift and broadening of the peak that are characteristic of rhombohedral distortion. We propose an alternative model for the observed expansion which is based on selective trapping of interstitial atoms in various crystallographic planes. It is shown that entrapment of interstitial atoms in the (111) plane is favorable, in comparison with the (100) plane. Entrapped atoms cause hydrostatic lattice expansion which varies with the different orientations of the grains. Non-uniform lattice expansion seems to be the main source of intrinsic microstrains and macrostrains usually observed in thin sputtered films.

Properties of TiO2 films prepared by ion-assisted deposition using a gridless end-Hall ion source

Abstract TiO 2 thin films were deposited using electron-beam gun evaporation with ion-assisted deposition (IAD) of low energy oxygen ions from an end-Hall ion source. The index of refraction and stress were measured as a function of the ion source voltage and current and were compared with results without IAD. The index of refraction increased with the increase of the ion gun voltage. The stress changed from compressive to tensile with the voltage increase, resulting in a better performance than conventional thermal evaporation. Atomic force microscopy was used to study the microstructure of the films. Quantitative roughness measurements of the surface showed that the roughness of the IAD films was smaller than that of layers without IAD.

Plastic hollow fibers as a selective infrared radiation transmitting medium

Plastic hollow waveguides (used as fibers) for infrared (IR) transmission were made from plastic tubes covered, on the internal wall, with a metal layer (Ag) and growing a dielectric thin (AgI) overlayer by direct iodination on it. The existence of several absorption lines at given wavelengths in the middle infrared (mid‐IR) region is predicted theoretically and measured experimentally. From the wavelengths of absorption lines the thickness of the AgI film has been computed. The average thickness of the AgI in the hollow waveguide increased with the iodination time and with the concentration of the iodine solution. The crystal size of the AgI was increased with the increase of the AgI thickness. By controlling the iodination process it was possible to make waveguides which can be employed as filters for various wavelengths of the transmitted mid‐IR radiation.

Amorphous diamond-like carbon films—a hard anti-reflecting coating for silicon solar cells

Abstract Amorphous diamond-line carbon (a:DLC) films are suitable for use as a protective layer and/or anti-reflecting coating for silicon solar cells. Microhardness tests show a high hardness of about 4700 kg mm−2. Optical measurements in the visible light on a silicon solar cell without anti-reflecting coating where a:DLC was deposited as an anti-reflecting (AR) coating, show a significant reduction in the reflection of the light of about 25–45% as compared with the reflection from the solar cell before deposition of the a:DLC film. The current-voltage (I–V) characteristics of solar cells without an anti-reflecting coating and with a:DLC as the AR coating layer show an improvement in the short circuit current (from 107 mA to 116 mA) and in the efficiency of the cell by 1% (from 8% to 9%). I–V characteristics of a solar cell with AR coating and deposited a:DLC (400Athickness) over that film as a protective coating, show a slight reduction of the short circuit current (from 168 mA to 145 mA), and the efficiency of the solar cell decreases (16% to 14%). However, the microhardness was significantly increased.