A. Axelevitch

Hot-Probe method for evaluation of impurities concentration in semiconductors

Abstract Electrical, optical, and mechanical properties of thin films significantly differ from those of bulk materials. Therefore, characterization methods for evaluation of thin film properties became highly important. A novel approach to the well known “Hot-Probe” method is proposed and applied in our work. The conventional Hot Probe characterization method enables only the definition of a semiconductor type, P or N, by identifying the majority charged carriers. According to the new Hot Probe technique, one can measure and calculate the majority charged carriers concentration and its dynamic parameters. Feasibility proof of the upgraded Hot Probe method was done in Si and Ge bulk, and in thin film semiconductor samples.

Simulation and experimental investigation of optical transparency in gold island films

Localized surface plasmons-polaritons represent collective behavior of free electrons confined to metal particles. This effect may be used for enhancing efficiency of solar cells and for other opto-electronic applications. Plasmon resonance strongly affects optical properties of ultra-thin, island-like, metal films. In the present work, the Finite Difference Time Domain (FDTD) method is used to model transmittance spectra of thin gold island films grown on a glass substrate. The FDTD calculations were performed for island structure, corresponding to the Volmer-Weber model of thin film growth. The proposed simulation model is based on fitting of experimental data on nanostructure of ultra-thin gold films, reported in several independent studies, to the FDTD simulation setup. The results of FDTD modeling are then compared to the experimentally measured transmittance spectra of prepared thin gold films and found to be in a good agreement with experimental data.

Novel approach to sputtered tantalum film resistors with controlled pre-defined resistance

Abstract A controlled magnetron sputtering method to obtain precision thin-film tantalum resistors with preset resistance values, is presented. These tantalum film resistors consist of layers of pure tantalum atoms and tantalum oxides. The proposed sputtering method is based on a previous mathematical modeling developed by the authors. With this modeling, one can predict the final product performance as a function of its technological deposition parameters. Feasibility tests to obtain tantalum and tantalum oxide film resistors with a controlled range of resistances, were done on a dedicated sputtering set-up. As a reactive agent in the experimental tests, only residual gases were used. Using the proposed model, precision film resistors with repeatable properties, were achieved in direct relations to the sputtering process parameters. It was found that only two major independent parameters are influencing the resistivity of the tantalum films: (a) the argon pressure in the vacuum chamber; and (b) the sputtering high voltage given to the target. A threshold level of tantalum phase transition from metal to dielectric, was found. Around this threshold level all types of pre-defined resistance may be achieved. The resistance stability of the obtained films, following an annealing Vacuum Photothermal Processing (VPP) was studied as well. It was shown that the electrical properties of the obtained resistors following a VPP treatment were improved with a better resistance stability.

Integrated thin film heater-thermocouple systems

Abstract A novel system of integrated thin-film heater with an embedded thermocouple was developed. Thin-film metallic heaters are widely used today in various fields of electronics and microelectronics applications. The main goal of the heater is usually to maintain the temperature in the heated zone. A deterministic method to manufacture an in situ heater––thermocouple system, with a pre-determined heater resistance, to give a required heat power, was developed. In order to examine this novel method, thin-film heaters were made using layers of Al and NiCr alloys. The temperature of the thin-film heater was measured while heating by an embedded thin-film thermocouple, positioned in the vicinity of the heater. This thin-film thermocouple system consisted of Ni–Ag alloy. A precise control of the growing heater film, while deposition, became possible using a simultaneous measurement of the heater sample resistance.

GENERAL TECHNOLOGICAL MODELING METHOD FOR THE DESIGN OF TRANSPARENT CONDUCTIVE IN2O3 ELECTRODES

Highly conductive transparent indium oxide (In2O3) thin films were prepared by DC magnetron sputtering using pure indium oxide targets in a pure argon (Ar) atmosphere. A linear programming method for the design and optimization of the process was used. The physical model of the sputtering process was based on randomly selected sections of the parameter space. The processing model was optimized by the “steep rise” method, using the mathematical model gradient to obtain optimal parameters. The active independent factors of the sputtering process were Ar pressure during the process, substrate temperature, target voltage and deposition time. As a result of the optimization process, the transparent conductive indium oxide thin films had the following characteristics: Transmittance (T) was 90.7% at λ=550 nm on glass substrates with an uncoated external T=91.1% and resistivity of up to 0.043 Ω cm for a 250 nm film thickness. Thus, the linear model method for the design and optimization of this multiparameter phy...

Ring etching zones on magnetron sputtering targets

Abstract A practical and theoretical investigation into a method for estimating the forms and dimensions of etching zones on magnetron sputtering targets is presented. This estimation is based on detailed geometry considerations of the internal arrangement of the vacuum chamber and the sputtering parameters. It is proved theoretically and experimentally that etching zones on sputtering targets are in a ring shape and that their location and dimensions are independent on the target material or dimensions.

Solar Cells Efficiency Increase Using Thin Metal Island Films

Metal nanodimension structures have multiple applications in modern technology. Noncontinuous thin island metal films of several types of metals deposited on dielectric or semiconductor surface introduce a unique behavior. In response to light exposure in certain range, the metal islands present a resonant absorption of light accompanied with a collective behavior of free electrons in these islands. In this paper, we present one of the possible ways to increase the efficiency of solar cells with metal islands imbedded in a semiconductor junction. Rough calculation was performed for a silicon solar cell and showed an increase of 17.5% in the overall efficiency of the cell.

In situ evaluation of plane plasma

Low-pressure plane plasma discharge is a novel technique for thin film growth. It makes possible fine control of most of the sputtering parameters, as well as supporting a high growth rate. A low-pressure plane argon plasma was obtained in a triode sputtering system. The in situ non-static conditions of the plane plasma behaviour during sputtering were investigated. The electron temperature and ion concentration of the plane plasma were measured using a Langmuir probe technique. A further study was made of the reciprocal arrangement of the sputtering target and the reference ring electrode, which affects the process by causing re-sputtering or dry etching of the growing layers. All of the sputtering experiments were done using pure Ag targets. The sheet resistivity of the deposited silver films was measured using a four-point probe method.

Dislocations structure investigation in neutron irradiated silicon detectors using AFM and microhardness measurements

Abstract The structure, microhardness and deformation character for silicon detectors were investigated following a neutron irradiation, using optical and atomic force (AFM) microscopes. The results of these investigations have given an important contribution to the understanding of silicon damage process by neutron irradiation. It was shown that in the interval of neutron fluences 9.9×10 10 ≤ Φ ≤3.12×10 15 n/cm 2 , the shape of damage is accumulative (from small punctual to large defects). Abrupt changes of microstructure together with the electrical and mechanical properties [Bosetti M, Croitoru N, Furetta C, Pensotti S, Rancoita M, Rattaggi M, Redaelli M, Seidman A. Nucl Instr Methods B 1995;95:21; Croitoru N, Gambirasio A, Rancoita PG, Seidman A. Nucl Instr Methods B 1996;111:297; Croitoru N, Rancoita G, Rattaggi M, Rossi M, Seidman A. Nucl Instr Methods B 1996;114:120; Fretwurst N, Claussen N, Croitoru N, Papendick B, Pein U, Schatz H, Schultz T, Wunstorf R. Nucl Instr Methods A 1993;326:357; Croitoru N, Dahan R, Rancoita PG, Rattaggi M, Rossi G, Seidman A. Nucl Instr Methods B 1997;124:542], were found for Φ ≥10 14 n/cm 2 . Different kinds of defects (dislocations and interstitials) and their complexes appeared under neutron irradiation. For all fluences the regions (“White” — “W”) with a microhardness smaller than in nonirradiated silicon were observed. Microhardness is larger in the regions where the concentration of dislocation loops is high. The “W” regions have a small number of the dislocations loops, and single punctual defects were seen there using atomic force microscope. The dislocation loops are placed in specific (“Black” — “B”) regions, which increase in size with the increase of neutron fluence due to a process of vacancies and interstitials accumulation.

Investigation of Low-Pressure Plane Plasma Discharge

A low-pressure plane plasma discharge was obtained in a novel implementation of triode sputtering method. This plane plasma discharge is formed at a relatively low vapor pressure of 0.2-5 mTorr. Electron beam temperature and ion beam concentration distribution, as well as their dependence on argon pressure within the plasma, were experimentally studied, using the Langmuir probe technique. The influence of an external magnetic field on the ion beam concentration and electron beam temperature were studied too. As a result of these studies, sputtering of various materials was done using the novel plane plasma discharge method. This method enables the deposition of homogeneous thin film coatings. Analysis is done on Cu sputtered layers with plane plasma discharge.