Papers

AVS1996 Session TF+VM-MoM: Microstructure Development

Monday, October 14, 1996 8:20 AM in Room 107B

Monday Morning

Start	Invited?	Item
8:20 AM		TF+VM-MoM-1 Microstructural Development in Cubic Boron Nitride Films D. Medlin, P. Mirkarimi, G. Cardinale, K. McCarty (Sandia National Laboratories) Cubic boron nitride (cBN) is an sp\super 3\-bonded material with many properties and applications that are similar to diamond. Although cBN can be synthesized in bulk form at high temperature and pressure, synthesis in thin film form has required the simultaneous bombardment of the growing film with a high flux of energetic ions. In this presentation, the state of our present understanding of the phase and microstructural evolution of cubic boron nitride thin films under energetic particle bombardment will be reviewed and discussed. cBN films grow with a unique, layered microstructure in which sp\super 2\-bonded graphitic boron nitride initially forms near the substrate interface, and nucleation and growth of the sp\super 3\-bonded cubic phase occurs further up in the film. Both the graphitic and cubic layers exhibit strong preferential crystallographic orientations: the graphitic layer possesses a strong in-plane (0002) orientation, whereas the cBN possesses an in-plane {111} orientation. This preferential orientation is consistent with an alignment between the cBN {111} planes and the basal planes of the layer of highly oriented graphitic boron nitride that forms in the initial stages of film growth. This relationship provides insight into the mechanisms controlling the initial nucleation of cBN and subsequent microstructural evolution of the films. This work is supported by the U. S. Department of Energy under contract DE- AC04-94AL85000 and in part by OBES-DMS
9:00 AM		TF+VM-MoM-3 Growth Mechanism and Structural Studies of Sputtered PbTiO/sub 3/ Thin Films Epitaxially Grown on Miscut (001) SrTiO/sub 3/ K. Wasa (Research Institute of Innovative Technology for the Earth, Japan); Y. Haneda (Research Institute of Innovative Technology for the Earth) The surface of the sputtered PbTiO/sub 3/ thin films, 5-200 nm in thickness, epitaxially grown on miscut (001) SrTiO/sub 3/ substrates with a miscut angle of 1.7 degrees comprised a periodic striped pattdrn which was reflected in the initial surfacs structure of the substrates (1). The electron microscopic analysis suggests that the film growth is governed by a step-flow model which corresponds to a Frank-van der Merwe mode. The surface was extremely smooth with surface roughness less than 3 nm for a film thickness of 200 nm. The sputtered films showed homogoneous microstructure with three dimensional epitaxy. The deposition on miscut substrates will realize the growth of perfect single crystal perovskite thins films having full in-plane alignment together with a continuous film through a large area. (1) T. Satoh, K. Wasa. K. Tabata, H. Adachi, Y. Ichikawa and K. Setsune, JVST A13, 1022 (1995).
9:20 AM		TF+VM-MoM-4 Texture Development and Surface Morphology of Polycrystalline Al Films Deposited by Magnetron Sputtering on Epitaxial W(001) and Ti\sub x\W\sub 1-x\(001) Underlayers L. Madsen (Link\um o\ping University, Sweden and University of Illinois, Urbana); D. Bergstrom, J. Chun, J. Greene (University of Illinois, Urbana); L. Hultman, J. Sundgren (Link\um o\ping University, Sweden) Controlling metallization film texture and surface morphology are essential for the reliable operation of ultra-high density microelectronic device structures where epitaxy or near-epitaxy will be demanded. Here, model systems consisting of thin Al films on epitaxial W and Ti\sub x\W\sub 1-x\ buffer layers were used to investigate texture and surface morphological evolution. The 140nm thick 001-oriented W-based buffer layers were grown on MgO (001) substrates by ultra-high vacuum magnetron sputtering at Ts=600 C. The W films were grown in Ar discharges, while Xe was used for the Ti\sub x\W\sub 1-x\ films to prevent Ti loss due to resputtering by energetic backscattered neutrals. Without breaking vacuum, Al films with a nominal thickness of 190nm were grown at Ts=40-350 C. Texture, microstructure, and surface morphology were determined by a combination of XRD pole figure analyses, AFM, SEM and TEM. The Al layers were twinned and exhibited a four-fold symmetry. The four-fold symmetric tilt boundary arises due to a coherent relaxation of strain at the Al/W interface by deformation along Al 111 slip planes. This mechanism is similar to that observed in a number of metal on metal systems. The texture varied with Ts evolving from a mixture of textures at low temperatures (a distorted 001 and 110 texture, best described as combination of 106 and 441), to a dominant 001 texture at high temperatures. The fine grained columns of the Al films were found to become increasingly faceted at higher growth temperatures. At Ts =350 C pronounced 111 facets developed as expected when growing an fcc metal at relatively high homologous temperatures on substrates with a high lattice mismatch.
9:40 AM		TF+VM-MoM-5 Studies on Growth Texture in Fe and FeTaN using Under Layers V. Inturi, J. Barnard (University of Alabama) Fe and FeTaN films grown on several under layers (Cr, Cu, Hf, Ta, Ti, and Ag) were investigated for their (110) growth texture. XRD scans were used to understand the structure and growth texture of these films. A well textured (110) FeTaN film has been found to have very good soft magnetic properties, i.e., low coercivity, low magnetostriction, and high initial permeability, and hence, the objective of this work is to make FeTaN films which exhibit strong (110) growth texture. A remarkable improvement in (110) growth texture has been noticed in Fe and FeTaN films when these are grown on well textured Ti (0002) under layers. (111) textured Ag also has beneficial effects but the other base layers mentioned have little effect on the enhancement of (110) growth texture in FeTaN films. In fact, Cr under layers (not well textured themselves) have a negative effect, i.e., they reduce the (110) texture in FeTaN films. The poor lattice matching of (110) FeTaN to (0002) Ti suggests that the enhancement of (110) growth texture in FeTaN films on the Ti under layer is not a result of 'local' epitaxy but is governed by energy considerations which favor close-packed planes parallel to close- packed planes. This phenomenon has been explained by the well known Nishiyama-Wassermann type orientation relationships.
10:00 AM		TF+VM-MoM-6 Nucleation and Growth of Aluminum Films on Sapphire (0001) K. McCarty, D. Medlin, R. Hwang, S. Guthrie, N. Moody, M. Baskes (Sandia National Laboratories) We are studying aluminum films on a-alumina as a model system for film/substrate effects in electronics packaging. In particular, we are investigating the relationship between growth and mechanical properties of aluminum films grown on sapphire (0001) surfaces by evaporation. The film structure is characterized in situ by low-energy electron diffraction and ex situ by high-resolution and conventional transmission electron microscopy (TEM). We find that the films are polycrystalline yet epitaxial with the substrate. All the aluminum grains have their close-packed planes (i.e., their (111) planes) parallel to the substrate (i.e., the sapphire's close-packed oxygen plane). However, three different rotational variants are found. The dominate variant has the close-packed directions of the film and substrate aligned. The two minor variants are rotated about 11 degrees and 30 degrees from the dominant orientation. Geometrical arguments show that the 11 degree and 30 degree variants on average minimize the misfit between the two lattices. Consistently, semi-empirical, atomistic calculations show only small energy differences between different three rotational variants. We investigate how the different variants nucleate and grow by examining non-continuous films using TEM and ex-situ atomic force microscopy. The film's work of adhesion is measured by micro-scratch testing. We will discuss how different microstructures prepared by altering the substrate's surface and the growth temperature affect film adhesion. This work was performed under U.S. DOE contract DE-AC04-94AL85000.
10:20 AM		TF+VM-MoM-7 Tayloring of Titanium and Boron Nitride Films by Energy Controlled Plasma Beam Processes H. Oechsner, F. Weber, M. Haag (University of Kaiserslautern, Germany) Low energy plasma beam sources which have been developed within the last few years provide extremely useful tools for the production of thin films with well controlled structural and chemical properties. By co-extraction of ions and electrons from a low pressure plasma excited in an arbitrary gas or gas mixture such instruments supply with broad monoenergetic, completely charge compensated ion beams with energies from a few 10 eV up to some keV, and energy independent current densities of a few mA cm\super -2\. Such sources have been already successfully employed for the deposition of extremely hard a- C:H and diamond films, and are in the present studies applied for tayloring the structural properties of titanium and boron nitride films. For that purpose Ti and B were sputter injected into the source plasma operated in nitrogen or an argon-nitrogen mixture. The film stoichiometry can be controlled by the ratio of the Ti/N or B/N fluxes to the substrate. For stoichiometric TiN the film structure switched from a completely anisotropic crystallite orientation to a pure (111)- texture within a narrow interval of the plasma beam energy at 90 - 130 eV. Simultaneously the film stress changed from the tensile to the compressive regime. The maximum stress around 8 GPa coincided with a Vickers hardness of 30 PGa. An even sharper influence of the energy input during film growth was observed for BN. While at plasma beam energies around 35 eV purely hexagonal films (hbN) are formed, the fraction of the cubic phase cBN increased steeply with increasing ion energy, and pure cBN is achieved at 75 eV. With increasing energy the peak-shaped curve for the cBN content drops steeply within a few eV to reach again the hBN-region. Since the half width energy of the plasma beam ions is only 4-5 eV, the formation of the pure cBN-phase has to be ascribed to an extremely sharp ion energy dependence which seems to be not established with other deposition techniques yielding in general maximum cBN fractions around 80%.
10:40 AM		TF+VM-MoM-8 Mass Spectroscopic Analyses of the Pathways for "Reactive" Species Incorporation during Reactive Magnetron Sputtering J. Abelson (University of Illinois, Urbana-Champaign) Reactive magnetron sputtering is a core industrial technology for depositing metallic, dielectric and semiconducting compounds. The experimental conditions which produce a desired film stoichiometry can usually be associated with variations in the reactive gas consumption, sputter target voltage, and other macroscopic observables. Yet we generally do not know the microscopic pathways by which the "reactive" species -- which is injected as a stable gas molecule -- becomes a component of the film. We developed the "double modulation" mass spectroscopy (DMMS) technique to directly analyze the identity and energy distribution of ionic and neutral species reaching the film surface from a magnetron sputtering source. Here we utilize DMMS, combined with particle transport simulations and ion flux measurements, to analyze the reactive incorporation mechanisms in three contrasting cases. For TiN growth from a Ti target in (Ar + N\sub 2\), the dissociative chemisorption of N\sub 2\ on Ti leads to compound formation both on the target and film surfaces, and the critical flow of N\sub 2\ is just that required to react with all sputtered Ti. For SiC growth from a Si target in (Ar + CH\sub 4\), the target surface becomes partially carburized, and the C sputtered from the target surface largely accounts for the C content in the film. For a-Si:H growth from a Si target in (Ar + H\sub 2\), reflection of H\sub 2\\super +\ ions from the target surface leads to a large flux of fast (~ 100 eV) neutral H which implant ~ 50 \Ao\ into the film surface. We discuss the implications of these mechanisms for film uniformity, microstructure, and process scale-up.
11:20 AM		TF+VM-MoM-10 The Effect of Oblique Sputtering on Microstructural Modifications of ZnO Thin Films Y. Lee, S. Kim (Seoul National University, Korea); Y. Kim (Kyonggi University, Korea); H. Kim (Seoul National University, Korea) Sputtering is one of the most popular deposition methods due to their versatility and reproducibility. And oblique sputtering is generally used to control structural properties of the sputtered films. However, during sputtering a growing film surface can be modified unintentionally by bombardment of high energetic particles including reflected argon ions from the target, negative ions emitted from the target surface, and ion accelerated from the plasma. Therefore, understanding of the effects of oblique sputtering on film growth behavior is essential to control the properties of films. In this study, we investigated the structural modifications of rf magnetron sputtered ZnO thin films on glass substrate with increasing an oblique angle of substrate. The film surface morphology and a in-plane crystallographic structure were singnificantly modified with a oblique angle of substrate because of a difference of energy distribution of incoming species. Using pure argon, symmertic and round etch pits were developed on the film surface at an incident angle of 0\super o\. With increasing an incident angle, the symmetric etch pits changed to aymmetric ones and irregular pyramids, ridge and ledge structures were developed. And c-axis preferred orientation was significantly reduced with an incident angle. While using argon and oxygen mixture, elongated large grains were developed in the matrix of fine columnar texture with increasing an incident angle. Above an incident angle of 45\super o\, elongated large grains were alinged normal to the incoming direction and covered the film surface resulting that the intensity of (101) diffraction peak increased while that of (002) decreased. These singnificant modifications with an oblique angle might be mainly caused by the energetic bombardment on the film surface during sputtering. Such high energetic particles bombardment changed significantly the resistivity of the film as well as the compositional change. We also investigated an in-plane film orientation by x-ray pole figures and transmission electron microscope.
11:40 AM		TF+VM-MoM-11 Ti\sub 1-x\Al\sub x\N-CrN Multi-layer PVD Films Deposited by a Reactive Unbalanced Magnetron Sputtering Technique L. Donohue, I. Smith, W. M\um u\nz (Sheffield Hallam University, United Kingdom); I. Petrov, J. Greene (University of Illinois, Urbana) During the last decade, the use of highly oxidation resistant, metastable, Ti\sub 1-x\Al\sub x\N coatings grown by reactive magnetron sputtering has significantly increased. This paper reports on the microstructure and microchemistry of polycrystalline Ti\sub 1-x\Al\sub x\N-CrN multi-layer coatings. The films were deposited on austenitic stainless steel and M2 high speed steel substrates by unbalanced magnetron sputter deposition and have been investigated using cross-sectional transmission electron microscopy with energy dispersive X-ray micro-analysis, Bragg-Brentano geometry X-ray diffraction, Rutherford backscattering spectrometry, Knoop microhardness, surface roughness and adhesion testing. The growth experiments were conducted in a deposition system in which the substrates are continuously rotated past one Cr and three Ti\sub 0.5\Al\sub 0.5\ cathodes, each capable of being operated independently in either unbalanced magnetron sputter or steered arc evaporation mode. In all cases the adhesion of the coating was enhanced by means of a steered cathodic arc metal ion etch pre-coa ting step followed by the deposition of an unbalanced magnetron sputtered Ti\sub 1-x\Al\sub x\N buffer layer. Deposition parameters varied during the experiments included Cr cathode power and substrate rotation velocity which led to variation in the multi-layer period from 2-5nm and the average Cr fraction from 0-30%. The Ti\sub 1-x\Al\sub x\N-CrN films exhibited <111> preferred orientation and a three zone architecture comprised of a metal-ion etched coating/substrate interface, a single phase B1-NaCl structure Ti\sub 1-x\Al\sub x\N buffer layer exhibiting competitive columnar growth, and the lamella multi-layer region which reproduces the columnar growth through local epitaxy on individual columns. Examination of the mechanical properties revealed that the multi-layers showed a maximum hardness, with equi-layer thickness and a period of \~\3.5nm, above 3000H\sub k0.025\ and average surface roughness of R\sub a\0.04\mu\m.