ICMCTF2000 Session F4: Microstructural, Microanalytical and Imaging Characterizaiton

Medium Energy Ion Scattering Spectroscopy (MEIS) can analyze the composition and structure of ultrathin films down to 10nm with atomic layer depth resolution. In this paper, applications of MEIS to understand the surface modifications due to low energy ion bombardment and interfaces of ultrathin films will be reviewed.

Surface damages and composition changes due to energetic ion-surface interactions were studied with MEIS for Si(001), Ta₂O₅, WSi₂and Pt(111) to understand the effect of ion beam bombardment on the distortion of original composition and profiles in sputter depth profiling as well as on the growth of thin films.@MEIS could be successfully applied for detailed analysis of the composition and structure of the ultrathin film interfaces such as nm SiO₂gate oxide on Si(100), nm Co on Pt(100), nm Ge on Si(100) to study the initial stage of ultrathin epitaxial film growth. The composition and structural depth profiles of nm thin S! iO₂on Si(100) grown by thermal and ion beam oxidation methods were analyzed with MEIS. MEIS could directly observe strained Si lattices and its distribution in the Si(001)-SiO₂interface. The interface strain was relaxed by annealing in N₂O. The H surfactant effects on the epitaxial growth of 1-10 Ge layers on Si(100) beyond the critical thickness of 3 monolayer were investigated with clear observation of the change of the morphology and the strain of the Ge over layer. It could be also observed clearly that there is no interface mixing between nm Co ultratin films on Pt(111) at room temperature but above 400°C, Co atoms diffuse into the substitutional Pt sites with vertical compressive strain. The ultimate single atomic layer depth resolution was realized for Cu₃Au(100) with 100 keV N⁺ions.

Finally, what can be d one with in-situ MEIS to understand and control the thin film growth will be discussed.

Ceramic nanocrystalline particles of Si-C-N embedded in an amorphous matrix of Si were obtained using chemical vapor deposition induced by modulated RF plasmas. This technology has been extensively used for producing ceramic Si-based nanoparticles with unique characteristics including spherical morphology and controlled ultrafine particle size distribution (2-100 nm) and composition (SiC_xN_y, 0 < x,y < 1). For the present study, a low density of crystalline nanoparticles were incorporated into an amorphous Si film during its growth, and then the films were annealed at low temperature, with the approach to create hybrid structures that have improved thermomechanical properties. In this system, the crystalline nanoparticles act as seeds for crystallization of the immediate interfaces surrounding the particles.

The phase structure, microstructure and morphology of the hybrid films were examined by transmission electron microscopy and selected area electron diffraction, which revealed that nanoparticles of SiCN were distributed within the amorphous Si matrix. The hardness, Young's modulus and fracture toughness were measured by the nanoindentation technique, and the wear properties were evaluated using a improved pin-on-disc system. These results showed that the mechanical properties of the films were notable affected by the presence of the nanoparticles there within.

Potential applications of these films include the production of tough, hard and optically transparent coatings, corrosion and high temperature resistant coatings; as well as inorganic membranes, buffer layers for heterogeneous coatings, and coatings with anisotropic properties.

Ti films were deposited onto 25x20 mm glass substrates using vacuum arc deposition under the following conditions: arc current of 170 A, residual gas pressure of ~10-4 Torr, coating duration of 10 s, and a coating rate of 3-4.5 nm/s. A voltage of U= 0-100 V d. c. was applied between 25x5 mm silver paint electrodes, separated by 20 mm, on the exposed surface. The films were examined by atomic force microscopy (AFM), X-ray photo-electron spectroscopy (XPS), grazing incidence x-ray diffractometry (GIXRD) and grazing incidence x-ray reflectometry (GIXR).

Three-dimensional AFM showed that the surface of films deposited with applied voltage consisted of quasi-periodic rows of titanium "hills" separated by "valleys", and that the rows were orientated parallel to the direction of the electric field which was applied during deposition The surface structure was more regular and finer at U=20V than at U=0 and 40V. Two-dimensional AFM showed that the film surface grown with U=0 contained separated columns while the film grown at U=20 V was more homogeneous and denser. The film surface grown at U= 40 V had structural elements of the two former samples. The film resistances were 60, 38 and 50 Ω at U=0, 20 and 40 V, respectively.

After deposition, the samples were annealed at 450° in air for 19 hours. XPS showed that upper layer of annealed samples was composed of TiO₂. AFM showed that the profile of the titanium oxide layer produced during annealing was mainly like the profile of the titanium layers grown at U=0 and 40 V, while the oxide layer on the titanium layer grown at U=20 V was more homogeneous. The size of the titanium oxide grains increased with U. It was 0.2, 0.3 and 0.6 µm at 0, 20 and 40 V, respectively. GIXR before and after annealing indicated that the maximum film thickness and minimum roughness of all interfaces (air-titanium oxide, titanium oxide-titanium and titanium-glass substrate) were obtained at U = 20 V

TiN is only used as wear protective and decorative coatings in various applications. These coatings are deposited by standard industrial methods such as CVD and PVD , including the magnetron method or its modifications (for example, the PMD method). Depending on the method used and on the deposition regime the coatings have different microstructure (size and morphology of grains, their orientation, dislocation structure, residual stress and so on). The mechanical properties (wear resistance, microhardness, fatigue limit) of a TiN coating depend in many respects on its microstructure.

The results of comparative TEM investigations of the microstructure of thin TiN coatings deposited by classical CVD and PVD as well as the PMD method are presented. A combined method of electrolyte polishing and ion milling was used to prepare thin foils. The microstructure was studies in sections parallel to the coating surface. The grain size was estimated on the dark field images. The amplitude of the residual stress field was determined using the bend extinction contours on the bright field images of TiN coating.

It is found that the TiN coatings deposited by PVD, CVD and PMD methods have different grain microstructures and residual stresses. The CVD coatings have the equiaxial microcrystal structure with very low level of the local residual stress. The mean grain size is 0.5µm. The PVD coating has a non-equilibrium submicron grain structure with high level of the local residual stress. The stress amplitude is equal to 0.15E, where E is Young's modulus. The mean grain size is 0.15µm in the section parallel to coating surface. The PMD coating structure is highly non-equilibrium nanocrystal. There is a very high level of residual stress equal to 0.45E. The mean grain size is 0.05µm.

Correlation between TiN coating microstructure and mechanical surface properties is discussed.