M. Wittmer

Electrical characteristics of TiN contacts to N silicon

We have performed a detailed investigation of TiN contacts on n‐type silicon. The barrier height was found to be 0.49±0.01 V and the contact resistivity on 0.001‐Ω cm substrates below 10−4 Ω cm2. The TiN layers were produced by reactive sputtering. The resistivity of the layers depends on the partial pressure of N2 in the N2+Ar sputtering gas mixture. A minimum of 55 μΩ cm was obtained, which is below the resistivity of pure Ti films. Finally, we have developed two etching solutions which allow patterning of TiN layers using conventional photolithography techniques.

Dynamics of laser‐induced formation of palladium silicide

The formation of palladium silicide by laser irradiation of a thin Pd film evaporated on single‐crystal silicon has been studied. We used 18‐ns pulses from a Q‐switched Nd : YAG laser to induce the reaction. The process of laser‐induced silicide formation takes place through interdiffusion of the molten elements, followed by thermal quenching. A diffusion constant of 4×10−4 cm2/s was estimated. The reacted layer was found to consist of a mixture of different metal‐silicon compounds.

A study of silicide formation by laser irradiation

We have studied the formation of palladium‐silicide and platinum‐silicide by laser irradiation of a thin metal film evaporated on single‐crystal silicon. The laser‐induced silicide layers are very smooth and uniform as found by SEM analysis. The thickness of the reacted metal film has been measured as a function of applied laser fluence. X‐ray diffractometry showed that the reacted layers are a mixture of different metal‐silicon compounds. This fact is explained by describing the process through which silicides are formed by laser irradiation.

Interference effects on the surface of Nd:YAG‐laser‐reacted Pd‐silicide

The generation of silicides by laser irradiation of Pd‐coated Si wafers is often associated with circular ripple patterns formed in the irradiated area. These surface modulations are explained by inhomogeneous reaction of Pd with Si due to interference effects in the incident laser beam.

Laser produced amorphous phases in NbSi and VSi thin films

Abstract The binary systems NbSi and VSi are investigated by laser induced melting and quenching of vapor deposited thin films. Glassy phases of various compositions are produced. The established compositional glass forming ranges support that the equilibrium compounds Nb4Si is stable only at high temperature. Thermal decomposition of the amorphous NbSi films proceeds via several intermediate stages. In particular, the AuCu3-type configuration of Nb3Si was found to be formed. In addition, amorphous NbSi films around 20 at.% si show the formation of an undentified metastable compounds upon post-irradiation annealing. Amorphous VSi films proved to be stable up to at least 500°C. Above this temperature they decompose directly into their respective equilibrium phases.

Laser induced reaction of magnesium with silicon

Abstract We have studied the formation of magnesium silicide by irradiation with high power pulses from a Q-switched Nd: YAG laser. X-ray analysis showed that the silicide contains the compound Mg 2 Si. The microstructure of the silicide is composed of poly-crystallites of Si and Mg 2 Si. The observed compound Mg 2 Si is identical to the only phase which is found in a binary Mg + Si reaction performed under thermodynamic equilibrium. These results are compared with the composition and structure of other laser induced metal silicides.

STRUCTURE OF LASER-PRODUCED SILICIDE LAYERS

The occurrence of solidification instabilities is demonstrated in laser reacted films of Pd-Si, Pt-Si and W-Si. The conditions for such instabilities are discussed.

The thermal stability of laser‐produced silicide layers

We have studied the thermal stability of laser‐reacted Pd and Pt silicides upon post‐irradiation annealing in a vacuum furnace. It was found from both Rutherford backscattering and x‐ray analysis that thermal annealing at temperatures between 400 and 800 °C for 15 h causes Si to diffuse out of the silicide layer and to grow epitaxially on the single‐crystal substrate. Hereby, a single silicide phase tends to form at the expense of the other phases present. The reported compositional changes do not occur during standard heat treatment cycles used in semiconductor device fabrication.

Laser Quenched Metal-Silicon Alloys

Q-Switch laser pulses are used to convert vapor-deposited metal-Si thin films into the amorphous state by a melting, mixing and quenching process. Experimental findings obtained with the metals Au, Pt, Pd, V and Nb are presented and compared with results from a numerical simulation of the laser induced melting and quenching process.

Medium power diodes with contacts formed by laser irradiation

Abstract The electrical characteristics of Nd: YAG laser-reacted silicide contacts to medium power diodes are shown to be equivalent to contacts made by standard technologies. The energy necessary for contact formation can be minimized by proper choice of the initial surface roughness of the samples.