AVS1997 Session VM+TF-ThM: Microstructure Development

Thursday, October 23, 1997 8:20 AM in Room F

Thursday Morning

Start	Invited?	Item
8:20 AM		VM+TF-ThM-1 Microstructure in Epitaxial Aluminum Nitride Thin Films Grown on (0001) Aluminum Oxide D.L. Medlin, J.R. Heffelfinger, K.F. McCarty (Sandia National Laboratories) Understanding the character and origin of defect structures in aluminum nitride films is critical for improving the quality of the material. We are investigating the microstructure and initial stages of growth of aluminum nitride films deposited epitaxially by molecular beam epitaxy onto annealed (0001) Al₂O₃ substrates. An RF driven source for atomic nitrogen and an aluminum effusion cell were used to generate the deposition fluxes. Films were grown at substrate temperatures between 700 and 900 C and examined using conventional and high resolution transmission electron microscopy. Films were aligned with (0001)_AlN (0001)_Al2O3 and [11-20]_AlN [10- 10]_Al2O3. This orientation matches the close-packed directions in the two lattices despite a mismatch of 13.6%. The films possess a high density of planar defects, which are generally faceted on [11-20] type planes. The nature of these defects and their relationship to the growth process will be discussed. This work was performed under USDOE contract DE-AC04-94AL85000 and supported in part by the Office of Basic Energy Sciences, Division of Materials Sciences.
8:40 AM		VM+TF-ThM-2 Influence of N₂ and O₂ on Aluminum Film Microstructure Development During Sputter Deposition and Annealing J.E. Sanchez, Jr., J.L. Reynolds, C.J. Wauchope (University of Michigan); I. Hashim (Applied Materials); P. Besser, G. Morales (Advanced Micro Devices) Sputter deposited aluminum alloy thin films are used as the primary interconnects in advanced integrated circuit devices. Desirable microstructure evolution during processing leading to large grain sizes and optimum (111) Al crystallographic textures has been shown to increase manufacturing yields and the reliability of interconnect structures. This requires careful process control of the sputtering environment since gas impurities may limit optimum microstructure development in films and interconnects. We present the characterization of the effects of N₂, O₂ and target purity levels on microstructure development in sputtered multilayered 250Å Ti/8000Å Al-Cu/150Å Ti /950Å TiN films during processing. The grain size and crystallographic texture of as-deposited (at 350°) and annealed (at 430°) Al-Cu films were determined by plan view transmission electron microscopy and x-ray pole figure analysis, respectively. Incorporation of N and O in the Al-Cu films was determined by SIMS depth profiling. All films had a typical (111) fiber or near-(111) fiber texture as is common in sputtered Al films, with all films showing random in-plane orientations. In some of the as-deposited films, the (111) fiber texture was offset by approximately 5° from the film normal. The presence of O₂ had little effect on the volume fraction of (111) grains in the as-deposited films, and appeared to improve the (111) fiber texture of the annealed films. N₂ slightly degraded the texture of the as-deposited films and slightly improved the texture of the annealed films. For the same level of gas impurity, the nitrogen films had a much weaker (111) fiber texture than the oxygen impurity films. The grain sizes of all the films were between about 1µm and 1.5µm. Gas impurities appeared to have no effect on the as-deposited grain size, while increased O₂ levels decreased the annealed film grain size. N₂ incorporation did not show a clear effect on the grain size of the annealed films. In addition, degraded sputter target purity was shown to effect Al-Cu film microstructure roughly as much as the highest levels of gas impurities. The effects of O and N incorporation on film microstructure development during deposition and annealing and the implications for interconnect reliability will be discussed.
9:00 AM		VM+TF-ThM-3 Monolithic and Multilayer Cr/CrN, Cr/Cr₂N and Cr₂N/CrN Coatings on 52100 Steel M.L. Kuruppu, G. Negrea, I. Ivanov, S.L. Rohde (University of Nebraska, Lincoln) The purpose of this work is to study the role of ion bombardment during low-temperature sputter deposition of Cr-N based coatings and to examine the relative advantages and disadvantages of various coating architectures on the thin film/substrate systems. All the monolithic and multilayer structures were deposited using reactive magnetron sputtering in a mixed Ar/N₂ atmosphere at low temperature (200°C). The optimal point for deposition of stoichiometric CrN and Cr₂N coatings has been determined from analysis of the target state, and results are supported by in-situ spectroscopic ellipsometric measurement of the optical properties of the films during growth. Plasma probe studies were undertaken, to determine the salient atom and ion fluxes, as well as ion energies. Film/substrate couples have been characterized by X-ray, SEM, RBS, and TEM. The film properties have been evaluated by microhardness, scratch adhesion, and wear-testing. Many of the multilayer coatings gave microhardness values in excess of 3000 H_v, and in some cases resulted in better adhesion than individual (monolithic) films.
9:20 AM	Invited	VM+TF-ThM-4 Process Controlled Microstructural and Binding Properties of PVD and CVD Films H. Oechsner (Universität Kaiserslautern, Germany) An appropriate and accurate selection of the energy and momentum input during PVD and CVD processes gives access to a precise control of the microstructure and the binding configurations of thin films. Experimentally, such possibilities are readily provided by low energy plasma beam sources delivering precisely charge compensated monoenergetic ion beams of arbitrary composition and variable energy. When operated with molecular gases such sources can be applied for remote CVD processes with controllable concentrations of radicals. Energy or momentum input into growing films in well defined directions can be established with IBAD techniques. As corresponding examples controlled texture formation of plasma beam deposited TiN-films, the existence of a narrow window of the energy input for the production of the pure cubic phase of BN, and the deposition of CN films with experimental indications for the existence of the hypothetical Β-phase of C₃N₄ will be discussed. The possibility to switch between amorphous and crystalline phases with remote CVD is exemplified for hydrogenated Si and Ge films via a controlled variation of the dissociation degree of the source plasmas operated in pure SiH₄ or GeH₄. The utilization of the high flexibility of IBAD processes is discussed by a second group of examples: A variation of the energy input into the growing film is shown to result in a step-like transition of the grain size of TiN-films which is accompanied by a corresponding change of the mechanical properties and the texture of the films. Finally, uniformly tilted layer textures are shown to become established by changing the geometric relations between the incident neutral particle and ion beams with regard to the substrate plane in IBAD arrangements. Such findings are discussed on the basis of structure zone models for ion beam assisted deposition, and on an atomistic scale via bombardment induced collision effects.
10:00 AM		VM+TF-ThM-6 From Microcrystalline to Nanocrystalline Diamond Thin Films Grown by H₂/Ar/CH₄ Microwave Plasmas D. Zhou, D.M. Gruen, L.C. Qin, T.G. McCauley, A.R. Krauss (Argonne National Laboratory) The transition from microcrystalline to nanocrystalline diamond film grown in H₂/Ar/CH₄ microwave plasmas has been investigated. It is demonstrated that both surface morphology and growth phenomenon of the diamond films can be controlled by varying the ratio of H₂ to Ar in H₂/Ar/CH₄ microwave discharges. Cross-section and top-view secondary electron microscopy (SEM) characterization reveals that the diamond films prepared from H₂/Ar/CH₄ plasmaes with a high concentration of H₂ consist of facet microcrystalline diamond with a columnar growth phenomenon. Howevr, the films produced from the plasmas with a high concentration of Ar and a low concentration of H₂ consist of nanocrystalline diamond, and no columnar growth structure has been observed in these films. Transmission electron microscopy (TEM), selected area electron diffraction (SAED), and electron energy loss spectroscopy (EELS) confirm that the films, prepared by Ar/CH₄ microwave plasmas with either a very low concentration of H₂ or no H₂ addition, consist of a phase pure nanocrystalline diamond. X-ray diffraction (XRD) and Raman spectroscopy analyses further illustrate that the shapes of both diffraction peaks and Raman shifts of the as-grown films are affected heavily by the ratio of H₂ to Ar in the plasmas, suggesting a transition from microcrystalline diamond to nanocrystalline diamond. The surface roughness of the diamond films has been measured by atomic force microscopy (AFM). It reveals that for microcrystalline diamond films the thickness of the film strongly affects its surface roughness normally of micrometer scale, while the surface roughness of nanocrystalline diamond films is about 20 to 40 nanometers independent of the film thickness. Consequently, we demonstrate that the diamond films deposited from H₂/Ar/CH₄ plasmas can be changed from microcrystalline to nanocrystalline by varying the ratio of H₂ and Ar in the reactant gases. The significant transition starts at H₂/Ar in a value of 0.65, and the nanocrystalline diamond films are formed at a H₂/Ar ratio of 0.1. We propose that C₂ dimer, rather than hydrocarbons, appears to be the growth species for the nanocrystalline diamond films deposited from the Ar domain plasmas.
10:20 AM		VM+TF-ThM-7 Thickness-Dependent Crystallinity of Sputter Deposited Titania J.D. DeLoach, C.R. Aita (University of Wisconsin, Milwaukee) Titania (TiO₂) is a material with structural flexibility. Its polymorphs (rutile, anatase, brookite) have identical nearest neighbor Ti-O coordination but different long range order. As a consequence, stoichiometric thin titania films grown near room temperature are usually amorphous or contain a large amorphous component. An earlier study¹ of sputter deposited titania on fused silica showed that 1.7-2.3 kÅ-thick films consisted of an amorphous matrix embedded with rutile and anatase "seed" nanocrystallites. Low temperature (400°C) ex situ annealing caused partial amorphous-to-anatase crystallization. Here, we report a similar transformation occurring in situ during growth of thicker films. A Ti metal target and a pure O₂, 300 W rf-discharge were used to grow films 2.6 to 7.1 kÅ-thick. X-ray diffraction showed that all films contained rutile and anatase phases, but the thinnest films were poorly crystallized. The anatase content increased at the expense of the amorphous material, with increasing film thickness, whereas the rutile content remained constant. The results are discussed in terms of growth interface heating from: 1) particle bombardment, which supplies a constant heat flux, and 2) target blackbody radiation, which supplies an increasing heat flux with increasing deposition time due to the inability of the Ti target to efficiently dissipate heat through the water-cooled cathode. The above analysis is applicable to any target with low thermal conductivity. Supported by USARO Grant Nos. DAAH04-93-G-0238 and DAAH04-95-1-0242 and the Johnson Controls Foundation. ¹M.D. Wiggins, M. Nelson, and C.R. Aita, J. Vac. Sci. Technol., A14, 772 (1996).
10:40 AM		VM+TF-ThM-8 Development of Crystallography and Morphology of Sputter Deposited Vanadia on Smooth and Rough Surfaces B.K. Blackmon, C.R. Aita (University of Wisconsin, Milwaukee) Vanadia (V₂O₅) is a low melting point (690 °C), wide band gap semiconductor with a layered structure that gives rise to technologically usefull catalytic, intercalation, electrical, and optical behavior. Here, we study the effect of substrate morphology on vanadia film crystallography and morphology. From these results, we propose a path for vanadia film crystallization from the successive oxidation of hypercritical nuclei of lower oxides. The films were grown in a rf diode system, using a V target and 400 W, -1.6 kV, 10 mtorr discharges of Ar-O₂ mixtures or pure O₂. The substrates were <111>-cut Si wafers. Two surface finishes were studied: a) polished (26 nm out-of-plane roughness) and b) lapped (298 nm out-of-plane roughness, ~2.5 micron in-plane roughness). X-ray diffraction showed for that films on polished substrates, crystallography evolved from a preferred (110) orientation to a sole (010) orientation with increasing gas O₂ content. This growth pattern is consistent with oxidation of VO₂ and/or V₆O₁₃ nuclei at low gas O₂ content, whereas at high gas O₂ content. the critical nuclei are already V₂O₅. On lapped substrates, crystallography evolved from amorphous to preferred, but not sole, (010) orientation with increasing gas O₂. This growth pattern is consistent with shadowing due to surface roughness. On both polished and lapped substrates, film morphology roughened with increasing gas O₂ content, reflecting the changing nature of the critical nuclei from a high melting point (VO₂) to a low melting point (V₂O₅) compound. Supported by USARO Grant Nos. DAAH04-93-G-0238 and DAAH04-95-1-0242 and the Johnson Controls Foundation
11:00 AM		VM+TF-ThM-9 Material and Temperature Effects on Obliquely Deposited Film Microstructures J.P. Parks, K. Robbie, M.J. Brett, D. Vick, L.J. Friedrich, S.K. Dew (University of Alberta, Canada) The successful design of novel devices using deposition techniques such as GLAD (GLancing Angle Deposition) ¹ will require a thorough understanding of the role of material, substrate temperature and incident flux angle in determining film microstructure. A number of heuristic rules ²,³, based on empirical and geometric arguments, have been reasonably successful in predicting the columnar structure for low temperature and non-oblique (<60 degree) incidence, while including no temperature or material dependence. To address the limitations of these models, an experimental study relating the dependence of column orientation and structure to deposition angle and temperature for various materials in the highly oblique incidence regime (65-88 degree) has been undertaken. Materials with different melting temperatures (including Cr, Cu and Mn) and heated substrates were employed. This will provide large variance in diffusivity, which dominates column growth at highly oblique incidence, thus providing a large range of microstructure to evaluate. Experiment has shown that materials with low melting temperatures (and correspondingly high diffusivity) lead to a more oblique microstructure, in contradiction of expected behaviour. For instance, with 85 degree incidence, Cu (T_m = 1082 degrees C) had a column angle (measured from the substrate normal) of roughly 70 degrees , while Cr (T_m = 1890 degrees C) was oriented at 45 degrees. Detailed experimental results will be presented, and used to extend current theory and evaluate the microstructural models SIMBAD and GROFILMS ⁴. ¹K. Robbie and M. J. Brett, J. Vac. Sci. Tech. A 15(3), (1997). ²J. M. Nieuwenhuizen and H. B. Haanstra, Philips Tech. Rev. 27, 87 (1966). ³R. N. Tait, T. Smy, M. J. Brett, Thin Solid Films 226, 196 (1993). ⁴M. J. Brett, S. K. Dew, T. Smy, Thin Films 22, 1, (1996).
11:20 AM		VM+TF-ThM-10 Synthesis of Electron Beam Thermal Barrier Coatings Using Directed Vapor Deposition D.D. Hass, H.N.G. Wadley (University of Virginia) The efficiency of gas turbine engines would be dramatically improved if operating temperatures could be increased. Unfortunately, current superalloy systems utilized for the hot structural components of gas turbine engines already operate at greater than 90% of their melting temperature. Advancements in component cooling technology have traditionally been incorporated to increase operating temperatures. These approaches have now matured and the gas turbine engine community is seeking new means for achieving higher temperatures. One approach incorporates the insulative properties of thermal barrier coatings (TBC's) for the thermal protection of engine components at elevated temperature. State-of-the-art TBC's are multilayer systems consisting of an columnar yttria partially-stabilized zirconia (YSZ) top layer with low thermal conductivity and an underlying MCrAlY or aluminide bond coat designed to improve coating adherence and provide oxidation and hot corrosion resistance. Today's TBC deposition techniques result in either unreliable or costly coatings. Thus improved deposition techniques are required before TBC's coatings can fulfill their potential in gas turbine engines. Here, electron beam directed vapor deposition (EB-DVD) is explored. EB-DVD is an emerging new deposition technique which employs a supersonic helium jet in combination with low vacuum (10^-3 - 10 Torr) electron beam evaporation. Initial work on the deposition of YSZ using EB-DVD will be presented. These studies have centered on the effect of deposition conditions on the microstucture of YSZ coatings applied to superalloy substrates. Results indicate an ability to tailor YSZ coatings to obtain the desired columnar microstructure with controlled porosity and column thickness.