L. Gładyszewski

Stress development during evaporation of Cu and Ag on Silicon

This work presents results of stress measurements during deposition of thin silver and copper films on 100 µm Si substrate. The stress in thin films has been determined by means of an optical system for the measurement of samples curvature. This system was applied in situ in a high vacuum deposition system. For Ag films the stress occurring during deposition goes from a low compressive value to tensile for thickness less than 30 nm and to compressive above this. For Cu films we observe tensile stress for thickness less 20 nm and above 50 nm. The same general trend of stress evolution with thickness is present in all cases at initial stage. There is the same growth mode for Cu and Ag because of the similar shapes of stress curves for thickness lower than 30 nm The behavior of stress evolution was explained by island nucleation and growth, island coalescence and continuous film growth. The difference in the stress evolution above 30 nm is caused by the fact that silver may be less sensitive than copper to adsorption of impurities. Adsorbed contamination inhibits compressive stress increase generated by grain boundary and defects remaining in the film.

Alkali migration and desorption energies on polycrystalline tungsten at low coverages

Abstract This work concerns research on fluctuations (noises) of the ion thermoemission currents of five alkali metals emitted from the tungsten surface. These noises are generated as a result of adsorbate density fluctuations. Adsorbate density fluctuations cause random changes of the work function, which influence the intensity of the emitted ion current. The methods used made it possible to determine the ion desorption energy and the surface diffusion energy for Li, Na, K, Rb and Cs.

Stress development during thin film growth and its modification under ion irradiation

The paper presents the results of average stress measurements during deposition of thin copper and silver films and during ion irradiation of molybdenum thin films. Deposition chamber and ion implanter were equipped with the same optical systems for radius of curvature measurement (scanning technique). The average stress in the 92 nm total thick Cu/Ag/Cu/Ag system on 100 μm Si substrate during deposition at room temperature is reported. Deposition process was intermitted after each material. The non-continuous changes of the stress are interpreted as differences in temperature of the sample in different deposition stages. High residual stresses up to 3 GPa were evidenced in the Mo thin films deposited on Si substrate with RF sputtering. During ion implantation with Kr and Ar ions stress relaxation effect of Mo thin films was observed. Kr ion irradiation of the silicon substrate without a film was additionally performed. After the irradiation (total dose 1.4 x 10 15 ions/cm 2 ), the implanted region of the silicon wafer was under compressive stress. A stress maximum was evidenced for a dose of 1 x 10 14 ions/cm 2 .

Power spectra and autocorrelation functions for surface diffusion of lithium on tungsten

The surface ionization of lithium on polycrystalline tungsten and ionic thermal desorption are studied by a method based on the Li+ ion current noise arising from the fluctuation of the work function as a result of random fluctuations of the Li adsorbate density. The activation energy for surface diffusion and energy of desorption for Li atoms have been determined by measuring the time correlation function of the local ion thermoemission current fluctuations.

Thermoemission of Eu+ ions and its fluctuations

Abstract The surface ionization of europium on tungsten has been studied using a single filament ion source in a 90° magnetic mass spectrometer. The influence of temperature on the ion current was measured between 1100 and 2800 K. Additionally, the ion current noises arising from the fluctuations of the work function as a result of random fluctuations of the adsorbate density on the ion emitter surface has been investigated. The spectral density functions and their temperature dependence are discussed in terms of the surface diffusion noise model at adsorption-desorption equilibrium. The density probability function seems to be Gaussian and its skewness Sk and kurtosis Ex were: Sk ∼ 0, Ex ∼ 3.

Thermoemission of Ce+ ions and its fluctuations

The surface ionization of cerium on tungsten and its fluctuatins (noises) have been studied using a single filament ion source in a 90° magnetic mass spectrometer. The statistical behaviour of the spectral density and autocorrelation functions for Ce+ ion thermoemission noise were investigated by means of a special stochastic analyser. These noises are generated as a result of adsorbate density fluctuations. The method used made it possible to determine the atom desorption and migration energy for cerium from tungsten.

Charge transfer activation energy for alkali atoms on Re and Ta

Ion and atom desorption energies for five alkali metals on Re and Ta were determined using the ion thermal emission noise method. The activation energies for the charge transfer process in the adsorbed state were calculated using a special energetic balance equation, which describes the surface ionization and thermal desorption effect.Energies for desorption of Li, Na, K, Rb and Cs from Re and Ta surfaces were determined by measuring the time autocorrelation function of the ion thermoemission current fluctuations.

Mass spectrometric study of ion thermoemission noise

Abstract The statistical behaviour of the amplitude probability density and spectral density functions for K+ and Cs+ ion thermoemission noise were investigated by means of a mass spectrometer and a special electronic system. To describe the probability density function, the first four central moments were used. It is more convenient to use the dimensionless parameters skewness and kurtosis instead of μ3 and μ4 moments. These values are defined by Sk = μ3 / σ3 and Ex = μ4 / σ4. For relatively low temperatures (T > 1300 K) the probability density appears Gaussian. For T > 1300 K, large values of kurtosis were observed, which is typical for non-stationary processes. The spectral densities may always be represented by the Lorentzian function: S = S0/1 + (ωτ)2.

Surface diffusion investigated by ion current noise method

The surface diffusion for two magnesium isotopes on polycrystalline tungsten and ionic thermal desorption are studied by a method based on the ion current noise arising from the fluctuation of the work function as a result of random fluctuations of the magnesium adsorbate density. The activation energy for surface diffusion for magnesium isotopes have been determined by measuring the spectral density functions and their parameters.