ICMCTF2000 Session FP: F Poster

In the scratch test method, scratches are generated on the coated sample using a diamond indenter (usually a Rockwell C profile) which is drawn across the surface under either constant or progressively increasing load. The sample is displaced at constant speed and at a certain load damage occurs along the scratch path. This value of critical load, Lc, can be used to accurately characterise the adhesive strength of the coating-substrate system. With modern scratch testing instruments, the critical load can be determined by acoustic emission, optical microscopy, variation in penetration depth or variation in the tangential frictional force between tip and sample. However, it is difficult to express the adherence of a coating-substrate system in a quantitative way because the critical load depends on several parameters related to the testing conditions.

Experience in the scratch testing field has shown that various different radii of diamond indenter are often required in order to adequately characterise the adhesion of modern thin films and coatings. The constant reduction in thickness of coatings, as well as the increase in development of softer (polymeric) coatings has meant that a whole range of indenter geometries are needed to cover the scope of elastic and plastic properties measured by scratch testing. This paper considers the effect of intrinsic parameters such as scratching speed, loading rate and diamond indenter radius on the measured critical load for scratch tests performed on various different coating-substrate combinations (TiN, W, DLC, Al and Au). Results are presented which suggest definite correlations between critical load and indenter radius, and which should aid users in making the right choice of indenter for a given coating-substrate system.

The model of X-Ray fluorescence analysis at the total reflection of the excitating X-Ray beam (TXRF) is a fairly established technique for the quantity chemical diagnostic of surface layers with 2-5 nm thickness of polished targets today. There are the beautiful industrial TXRF spectrometers (for example, EXTRA II - Sèifert, RUGAKU-3700) but cost of it's equipment is very high. The present work describes of TXRF spectrometer modified by using of the slitless collimator for the primary X-Ray beam. The prime cost of our spectrometer is not over 20000$ at the excellent analytical characteristics and a simplicity of the using.

Standard TXRF spectrometer is complete by the monochromator for the forming of the excitating X-Ray beam with angle divergence near 0.001°. The primary X-Ray beam in our spectrometer is formed by the slitless collimator X-Ray radiation comprising two quartz polished plates intimate mated together. In a clearance between this plates the standing wave arises transported the beam on the distance near 100 mm without weakening. The beam divergence in output of the collimator is equal to double value of the total reflection critical angle for a quartz (2Θ_c~0.2°). Half of this beam is a source of X-Ray fluorescence excitation in the target studied. The X-Ray density on the surface layer of a target in our spectrometer is higher two orders in compared with a standard one.

It guarantees the reduction of the contamination detection levels for the TXRF spectrometer with slitless collimator no less then the order. The detection limits for the Fe group elements at the surface analysis of Si wafer are obtained better then 10¹⁰ atoms/cm² in measurements with the standard X-Ray tube (Mo, 2 kW) at the exposition time 600 sec.

In technological applications as etching or deposition of thin films, the energy balance of the substrate is affected by the plasma itself. Hence, the experimental determination of the energy influx towards the substrate is of great importance.

The total energy flux has been measured by means of a simple thermal probe. The procedure is based on the measurement of temporal slope of the substrate temperature during the plasma process. A substrate dummy of known heat capacity, which is thermally isolated is inserted into plasma at substrate position. The obtained heating curve and (after switching-off the plasma) the cooling curve are taken and their time derivatives at the same environmental temperature are calculated. By knowing the heat capacity of the sensor, the difference of the derivatives is a measure of the deposited power at the surface. By means of the dummy it is also possible to measure the substrate current simultaneously. In order to vary the contribution of the charge carriers to the energy influx, an additional substrate bias voltage can be realized, too. The presented thermal probe allows for sensitivities of about 10^-3 J/cm ²s and it can be simply used under typical plasma environments.

The procedure has been demonstrated for different applications were the probe has already been employed. Examples are a-C:H film deposition in a CH₄-ECR plasma and by magnetron sputtering of a graphite target in Ar/H₂, respectively, and the energy flux measurement in an RF plasma which is used for the modification of micro-disperse powder particles.

Ion beam sputtering from SiC targets assisted with an atomic nitrogen source were employed to deposit amorphous SiCN films in the presentstudy.  It was found that atomic nitrogen source significantly enhanced the incorporation of nitrogen in the SiCN films and promoted the formation of Si-N and C-N bonds, which lead to a higher hardness(H) and elastic modulus(E).  High nitrogen content (61%) amorphous SiCN films attain a hardness H around 20 GPa typical of inorganic ceramics, but have Young’s  modulus values E around 79 Gpa significantly lower  than ceramics.  The corresponding H/E ratios (~0.25) are relatively high and their values are more similar to that for hard polymers than to those for ceramics.  This compressive residual stress amorphous SiCN films have great potential to be applied to tribological application.  

The compressive stresses of amorphous SiCN films were found to increase with  the deposition temperature.  Post treatments such as rapid thermal annealing and laser irradiation were carried out to reduce residual stress.

Research has recently been focused on finding ways and means of forming SiO₂ of reasonable thickness (1000Å or more) at relatively low temperatures. A system of special interest is the Au-Si structure as it exhibits low temperature oxidation behavior when heated in an oxidizing atmosphere.

When an amorphous Si layer is introduced between the Au and Si(100) substrate to form a Au/Si(a)/Si(100) structure Si atoms from the amorphous layer diffused through the Au layer and oxidized on the surface. The introduction of the amorphous Si resulted in the lowering of the melting point of Au as well as the enhancement of oxidation for specific amorphous Si thicknesses.

Rutherford Backscattering Spectrometry (RBS) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDS) have been used to investigate the structures and oxidation mechanisms of the two systems.

Si_1-xGe_x/Si heterostructures are of great interest because of their potential application in heterojunction devices and formation of metal contacts on Si_1-xGe_x plays an essential role in the various devices utilizing Si_1-xGe_x/Si including heterojunction bipolar transistors (HBT), modulated doped field effect transistors, quantum well metal-oxide semiconductor field effect transistors, and photodetectors. In recent years, electrical properties of W schottky contacts on Si_1-xGe_x alloys formed by sputtering were measured¹. However, electrical properties such as schottky barrier height were strongly dependent upon the W deposition conditions such as pressure during sputtering.

In this study, we investigated the electrical properties of CVD-W/p-Si_1-xGe_x(x=0.17) schottky contacts in which W contacts are formed by chemical vapor deposition (CVD). Fully-strained 90 nm-thick p-type Si_1-xGes! ! ub x(x=0.17) epitaxial thin film with the boron concentration of 5x10¹⁷ cm^-3 was deposited on n-type Si(001) substrate at the substrate temperature of 650°C by low-pressure chemical vapor deposition (LPCVD) utilizing SiH₄, GeH₄, B₂H₆, and H₂ gases. W layers to Si_1-xGe_x(x=0.17) alloy were grown by low pressure chemical vapor deposition using the WF₆ precursor and H₂ as a carrier gas as a function of the growth temperature, T_s = 350 - 500^oC. W schottky contacts with various sizes from 0.2 mm² to 0.6 mm² were defined by photolithography and selective etching. Then, ohmic contacts on Si_1-xGe_x(x=0.17) were formed by Al sputtering using a shadow mask followed by the annealing at 400°C. Electrical properties of the CVD-W/Si_1-xGe_x(x=0.17) schottky diodes were characterized by the current-voltage (I-V) and capacitance-voltage (C-V) measurements. Th! ! e structural and chemical properties of CVD-W/Si_1-xGe_x(x=0.17) interfaces were analyzed by x-ray diffraction (XRD), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The correlation between electrical and structural properties of their interfaces will be discussed.

¹ F. Meyer, M.Mamor, and V.Aubry-Fortuna, et al., J.Electron.Mater.25,11 (1996)

Due to the numerous possible combinations of coating/substrate materials and configurations, the accurate computation of the yield initiation and the complex mode of plastic deformation in such systems can only be made possible by means of numerical methods.

In this study, the threshold loads corresponding to the initiation of plastic deformation in both the coating and substrate under normal contact with a deformable indenter are investigated using finite element methods. A wide range of practical values for the ratios of coating thickness to radius of indenter, t/a, coating to substrate elastic modulus E_c/E_s, and coating to substrate yield strength, Y_c/Y_s are analysed. This leads to an operational envelope for the coating and substrate materials subjected to similar indentation loading, within which the materials will deform elastically.

Layers of almost pure cubic boron nitride (c-BN) have been deposited in a hollow cathode arc evaporation device on silicon and on titanium nitride (TiN) coated tungsten carbide (WC) substrates. The internal stresses of 400-600 nm thin films deposited are in the order of 10 GPa. The layer growth and the annealing experiments are analyzed in situ by infrared reflection spectroscopy. The optical setup can be used either as infrared spectroscopic ellipsometer (IRSE) in a rotating analyzer configuration as well as polarized infrared reflection spectrometer (PIRRS). Spectra can be taken every 10 seconds. They are sensitive to determine the phase of the growing film due to different phonon absorption frequencies of hexagonal BN (h-BN) and c-BN and can also be used to determine the film thickness.

The annealing behavior of c-BN films was investigated in situ with PIRRS and IRSE on silicon and TiN coated WC substrates. The phonon frequency is correlated to stress in c-BN films. The frequency shift observed during annealing experiments is influenced by different processes:

a) frequency shift to lower values due to temperature dependence of phonon vibrations,

b) frequency shift by stress relaxation,

c) frequency shift induced by stress resulting from different thermal expansion coefficients of film and substrate.

The temperature dependence of phonon vibrations is an indicator for high temperature behavior of the elastic constants and the hardness of c-BN films. A relaxation of the stress in c-BN films should occur at a characteristic temperature and is followed by an irreversible frequency shift to lower values. By comparing spectra before and after annealing it is possible to specify the size of both effects. A frequency shift due to thermal stress was identified by comparing the spectra of films on different substrates.

The mechanism of formation of the films, deposited by magnetron reactive sputtering of W-30at%Ti alloy in Ar-N₂ mixture, was studied. The dependencies of the film composition, growth rate (V_g), structure and microhardness as like the gas phase composition during the sputtering, on the working gas composition, substrate bias and discharge current, were investigated.

The mass-spectrometry of the sputtered particles revealed the presence of TiN⁺ and WN⁺ ions. Relative concentrations of TiN⁺ /Ti⁺ and WN⁺ /W⁺ increased monotony with increasing of %N₂ in Ar-N₂ mixture and achieved TiN⁺ /Ti⁺ ~10% and WN⁺ /W⁺ ~30% at %N₂ =60%. Investigation of the composition of the films deposited in identical conditions showed the gradual decrease of the W and increase of N content in the film with increasing of %N₂ up to 60%. Simultaneously the Ti content in the film increased with increasing of %N₂ up to 20% and than decreased gradually. The dependence of the V_g) of the film on the %N₂ had the same trend as the Ti content in the film. The main feature of this dependence was that the V_g) increased as the N₂ was added in working gas and exceeded the V_g) of the film deposited in pure Ar. When the %N₂ in Ar-N₂ exceeded 20% the Vg started to decrease. Correlated decrease of Ti/W and N content in the film was observed with the increase of the substrate bias from -100 up to -200 V.

All these observations including the structure investigations, allowed to suggest the mechanism of formation of the composition and structure of reactively sputtered films, in which nitride molecules play much more significant role than it was considered earlier.