Influence of the noise driving force on the diffusion of copper in aluminium thin films

The diffusion of copper in thin polycrystalline aluminium films subjected to current stressing at 140 C was studied. Experimental aluminium stripes were doped with copper in a limited (source) region and the movement of copper away from this region was investigated by electron probe microanalyser. Samples were stressed both by dc and by superimposed dc and noise current. The dc density (5×10⁵ A/cm²) was equal to that of the effective (r.m.s.) value of superimposed current. The frequency range of the noise signal with the Gaussian distribution of amplitudes was 5 Hz to 20 kHz. Under the described conditions copper diffused due to the concentration gradient as well as the electromigration driving force. The diffusion coefficients of copper at both current stressings were obtained by fitting the measured concentration profiles to those calculated theoretically. The results yield that the diffusion becomes enhanced when the noise is applied. The values of thermal grain boundary-assisted diffusion coefficient obtained in six independent measurements with dc loading vary betweenD _Tb=8×10^–13 cm²/s and 25×10^–13 cm²/s. The corresponding values of total diffusion coefficient (i.e. the sum of the thermal and noise induced component) areD _b=(20÷83)×10^–13 cm²/s. The noise-induced enhancement of the diffusion was predicted theoretically. Thus, the present results confirm the previous theoretical calculations.The authors wish to thank Dr. V. Bezák for stimulating discussions.     

Electrical and optical properties of electron-irradiated ZnGeP2

Conclusions and summary The following conclusions are drawn from the reported study:The electrophysical properties of ZnGeP₂ crystals and their optical transparency in the range hG are attributable to the presence of a density-dominant (10¹⁷–10¹⁹ cm^–3) deep [E_v+(0.5–0.6) eV] growth defect associated predominantly with Zn vacancy clusters.Irradiation by high-energy electrons induces a shift of the Fermi level in the direction of E_G/2 and increases the resistivity of ZnGeP₂ to values of approximately 10¹² ·cm at 300 K. Irradiation with high-energy electrons is an effective technique for the optical bleaching of p-ZnGeP₂. The reversible modification of the optical absorption spectra of p-ZnGeP₂ in connection with irradiation and subsequent annealing indicates that the absorption step in the vicinity of h 0.6 eV is not attributable to light absorption by germanium inclusions, but to optical transition from the valence band to the growth-defect level E_v+(0.5–0.6) eV.Enhancement of the optical transmissivity of p-ZnGeP₂ in the range hG can be achieved in two wayss 1) as the result of a decrease in the density of centers with the level E_v+0.6 eV by variation of the growth conditions or subsequent annealing; 2) by shifting the Fermi level above the energy position E_v+0.6 eV through the irradiation-induced injection of compensating donor centers.The injection of radiation defects is an effective technique for controlling the electrical and optical parameters of the compound ZnGeP₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 122–130, August, 1986.     

Diffusion of silicon in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained film structure (B ₊ films) have been examined as diffusion barriers, preventing the silicon diffusion in silicon devices. The silicon diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) after annealing at temperatures up to 900° C, in view of application of high-temperature processes. The diffusivity from 400 to 900° C: D (m² s^–1)=2.5×10^–18 exp[–31 kJ/mol/(RT)] in B ₀ layers and D (m² s^–1)=3×10^–19 exp[–26 kJ/mol/(RT) in B ₊ TiN layers. The diffusivities determined correspond to grain boundary diffusion, the difference being due to the different microstructure. The very low diffusivity of silicon in B ₊ TiN layer makes it an excellent high-temperature barrier preventing silicon diffusion.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

Aluminium diffusion in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained (B ₊ films) film structures, respectively, have been examined as diffusion barriers for preventing aluminium diffusion. The aluminium diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) at temperatures up to 550° C. The diffusivity from 300° C to 550° C is: D[m²s^–1]=3×10^–18 exp[–30/(RT)] in B ₀ layers and D[m²s^–1]=1.4×10^–16 exp[–48/(RT)] in B ₊ TiN layers. The activation-energy values determined indicate a grain boundary diffusion mechanism. The difference between the diffusion values is determined implicitly by the microstructure of the layers. Thus, the porous B ₀ layers contain a considerable amount of oxygen absorbed in the intercolumnar voids and distributed throughout the film thickness. As found by AES depth profiling, this oxygen supply allows the formation of Al₂O₃ during annealing the latter preventing the subsequent diffusion of the aluminium atoms.     

Investigation of the electrical and photoelectric properties of manganese-doped gallium arsenide as a material for photoresistive detectors

An investigation was made into the electrical and photoelectric properties of gallium arsenide with an initial electron density 5×10¹⁵–4×10¹⁷ cm^–3 doped with Mn in different thermodynamic diffusion regimes characterized by diffusion temperatures of 900 and 1000°C and arsenic vapor pressure 10^–2 and 10^–3 atm. The ionization energy and defect concentration were determined by a computer analysis of the equilibrium hole density determined from the Hall effect. Centers with ionization energy 0.08–0.10 eV were found, their concentration varying from 2×10¹⁹ to 2×10²⁰ cm^–3 depending on the diffusion temperature and the doping level of the original crystals. Data obtained by investigating the stationary intrinsic photoconductivity were used to determine a hole lifetime of t_p 10^–9 sec. The photoconductivity spectra were investigated in the range 0.5–2 eV at 77°K, and defects with ionization energy E_v + 0.6 eV were found in all samples. The impurity photoconductivity at wavelength 10.6 m was investigated. It was shown that GaAsMn can be used as a material for impurity photoresistors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 15–19, March, 1981.     

The behavior of copper impurity in CdSnAs2

Single crystals of n-type CdSnAs₂ with a carrier concentration of 2 ·10¹⁷–4 ·10¹⁸ cm^–3 and mobility (3 to 6) · 10³ cm²/V ·sec were copper doped by diffusion saturation at temperatures from 400 to 570C. As a result of the study of the electrical properties of the doped crystals it was established that the copper in CdSnAs₂ is a fast-diffusing acceptor impurity. The solubility of Cu depends primarily on the donor-center concentration and has clearly a retrograde character. Low-temperature heat treatment (over the 200–400C range) of the Cu-doped specimens results in an increase in the acceptor concentration. The form of the log R(10³/T) curve indicates the existence of acceptor centers with an ionization energy of 0.05 eV in the Cu-doped CdSnAs₂ specimens.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 39–44, July, 1973.     

Laser-fluorescence diagnostics for condensation in laser-ablated copper plasmas

We are investigating the thermodynamic conditions under which condensation occurs in laser ablated copper plasma plumes. The plasma is created by XeCl excimer laser ablation (308 nm, 300 mJ/pulse) at power densities from 500–1000 MW/cm² into backing pressures of helium in the range 0–50 torr. We use laser-induced fluorescence (LIF) to probe velocity and relative density of both atomic copper and the copper dimer molecule, Cu₂, which is formed during condensation onset. At low pressure (10 mtorr), the atomic Cu velocity peaks at approximately 2×10⁶ cm/s. Copper dimer time-of-flight data suggest that condensation onset occurs after the Cu atoms have slowed very significantly. Excitation scans of the Cu₂A-X (0,0) and (1,1) bands yield a rotational and vibrational temperature in the neighborhood of 300 K for all conditions studied. Such low temperatures support the theory that Cu₂ is formed under thermally and translationally cold conditions. Direct laser beam absorption is used to determine the number density of atomic copper. Typical densities attained with 5 torr of helium backing gas are 6–8×10¹³ cm^–3. Rayleigh scattering from particulate is easily observable under conditions favorable to particulate production.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

Energy-band structure of semiconductors having the chalcopyrite lattice II. MgSiP2, ZnGeP2, ZnSiAs2, and CdSiP2

The pseudopotential method is used to calculate the band structure of MgSiP₂, ZnGeP₂, ZnSiAs₂, and CdSiP₂. The valence band of these compounds is shown to consist of several allowed subbands separated by energy gaps. There are two levels at the top of the valence band, slightly separated in ZnGeP₂ and ZnSiAs₂ and well-separated in MgSiP₂ and CdSiP₂ — in which there is significant tetragonal compression of the lattice. The effective electron masses at the bottom of the conduction band turn out to be anisotropic, with m/m 7–10.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 95–100, June, 1970.     

Lattice dynamics of ZnGeP2 and AgGaS2 in a tensor-charge model

A tensor-charge model is developed for the lattice dynamics of the ternary compounds A²B⁴C ₂ ⁵ and A¹B³C ₂ ⁶ . The long-wavelength phonon frequencies are calculated for ZnGeP₂ and AgGaS₂ crystals. The tensor-charge parameters are determined by comparing the theoretical and experimental values of the infrared intensities of active frequencies. In the crystal ZnGeP₂, the tensor charges of the zinc and phosphorus are found to be close to the isotropic charges of the point-ion model, while the tensor charge of germanium is very different from the point-ion charge. In the AgGaS₂ crystal, the tensor charges of all the atoms differ appreciably from the point-ion charges. The results are discussed from the point of view of the chemical bond.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 40–44, September, 1980.     

Preparation and properties of epitaxial ZnGeP2 films

Thermodynamic analysis has been applied to the vapor over a ZnGeP₂ crystal when the chlorine source is provided by ZnCl₂. ZnGeP₂ film growth has been examined and the electrophysical and photoluminescence parameters have been measured. All these autoepitaxial films have the chalcopyrite structure, while those parameters are determined by the defects and the substrate orientation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 74–78, April, 1988.We are indebted to L. G. Lavrent'eva for interest, to A. I. Gribenyukov and T. E. Tkachenko for assistance in growing the single crystal; and to F. Kim for the microprobe analysis.     

Reaction of Cu and Cl2 stimulated by synchrotron radiation

Light-induced reactions of poly-Cu with Cl₂ and the formation of CuCl _x films were studied in the spectral range of 105–400 nm by using synchrotron radiation. The efficiencies of the reactions with Cl₂ pressures between 10^–5 and 10^–2 mbar were determined from the height distributions of spatial structures in the CuCl _x films. The heights typically range from 10 to 10⁴ nm. An efficiency of about 10⁷ CuCl _x molecules per dissociated Cl₂ molecule is observed at high Cl₂ exposures. At low Cl₂ pressures CuCl _x formes anisotropically in the irradiated area. The efficiency is determined by light-induced surface processes supporting the build up of CuCl _x in the long wavelength range and competing processes at short wavelengths which reduce the efficiency.     

Mechanisms of loss formation in nonlinear optical crystals ZnGeP2 in the terahertz frequency range

Physical mechanisms of formation of radiation losses in the terahertz range in ZnGeP₂ crystals have been experimentally studied in the wave number range of 5–350 cm^?1 at temperatures of 10–300 K. The dominant contribution of two-phonon difference processes to the loss formation in the given frequency range has been shown.     

Volume and grain boundary diffusion of implanted 113Sn in aluminium

Volume and grain boundary diffusion of ¹¹³Sn in aluminium was investigated with the radiotracer method. The implantation technique was used for tracer deposition to avoid problems of tracer hold-up caused by the oxide layer always present on aluminium. The diffusion penetration was chosen large enough to permit serial sectioning of samples with the aid of a microtome.The temperature dependence of the volume diffusivity was determined as D(T)=4.54×10^–5×exp[–(114.5±1.2)kJmol^–1/RT] m ² s ^–1. This confirms previous measurements from our group which already showed that Sn is the fastest foreign metal diffusor so far investigated in aluminium.Grain boundary diffusion of ¹¹³Sn in Al polycrystals was measured in the type-B kinetic regime. The grain boundary diffusion product P=sD _gb (s=segregation factor, =grain boundary width, D _gb=grain boundary diffusivity) was found to be strongly affected by the impurity content of aluminium. For Al polycrystals of 99.9992% nominal purity we obtained P _5N(T)=1.08×10^–8exp [–(96.9±7.5) kJ mol^–1/RT] m³ s^–1 and for less pure Al polycrystals of 99.99% nominal purity P _4N(T)=3.0×10^–10 exp [–(90.1±4.2) kJ mol^–1/RT] m³ s^–1 was determined. The grain boundary diffusion product in the purer material is more than one order of magnitude higher than in the less pure material. Very likely this is an effect of co-segregation of non-diffusant impurities into the grain boundaries.     

Behavior of copper in gallium arsenide with a high concentration of tellurium

The photoelectric properties of gallium arsenide with a high concentration of tellurium (n=2· 10¹⁸ cm^–3) alloyed with copper are investigated for different conditions of diffusion. From the photoconductivity spectrum, the position of the impurity centers with an ionization energy of (E_v+0.6) eV is determined, the concentration of which depends on the vapor pressure of arsenic. The lifetime of the holes in the material studied is determined. Its magnitude and temperature dependence is explained by the presence of certain recombination channels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 11–15, September, 1979.     

Ion-beam induced mixing in Al-Ni

Ion beam induced mixing of Al-Ni has been studied using N ₂ ⁺ and Ar⁺ bombardment. High dose (4×10¹⁷ ions cm^–2) nitrogen bombardment was found to cause blister formation with no unambiguous evidence of mixing. However, using argon ions at elevated substrate temperatures (400–450 °C) led to extensive mixing of 2000 Å Al layers on Ni. The mixing mechanism is considered to be point defect mediated radiation enhanced diffusion with a possible contribution from cascade mixing and interfacial oxide layer breakdown during the initial stages of treatment.     

Electronic structure of high-temperature superconductors II. La-Ba-Cu-O systems

Electronic structure of La_2–x Ba _x CuO₄ superconductors has been studied. Model systems La₁₀CuO ₂₂ ^–12 , La₁₀cuO ₁₄ ⁺⁴ and La_gBaCuO ₁₄ ⁺³ with various Ba positions have been investigated using the quasirelativistic INDO molecular orbital method. The oxidation state of copper atoms corresponds to Cu(II). The influence of Ba/La substitution on copper atoms is much lower than on their oxygen ligands sphere.     

Characteristic diffusion constants of cadmium in silicon

This investigation was devoted to experimental determination and analysis of curves describing the diffusive distribution of cadmium in silicon at different levels of prealloying of the silicon with phosphorus and different temperatures of isothermal diffusion, with allowance for the characteristic exponential relation between the pre-exponent D₀ and the activation energy Q. Numerical values of D_k and Q₀ were found. They are equal to 4·10^–8 cm² · sec^–1 and 0.22 eV, respectively.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 65–68, November, 1984.