1997 TMS Annual Meeting: Monday Session

EVOLUTION AND ADVANCED CHARACTERIZATION OF THIN FILM MICROSTRUCTURES: Session II: Stress and Mechanical Properties

Session Chairs: E.H. Chason, Sandia National Laboratories, Albuquerque, NM 87185-1415; R.C. Cammarata, Surface and Interface Science Branch, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375

SURFACE AND INTERFACE STRESS EFFECTS ON THIN FILM GROWTH: R.C. Cammarata, Surface and Interface Science Branch, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375

Associated with any solid surface is a surface stress. It is an intrinsic thermodynamic quantity that represents the reversible work per unit area needed to elastically stretch the surface. In materials where there is a large surface area to volume ratio, such as thin films, surface stresses can have a major influence on the growth and structure. In the case of a solid-solid interface, there are two interface stresses that represent the work needed to stretch the two phases on either side of the interface. Simple models for surface and interface stresses will be presented. These will then be used to analyze thin film epitaxial growth as well as intrinsic stress generation in nonepitaxial films. It will be shown that surface and interface stresses play a central role in determining the critical thickness for epitaxy, and can lead to significant intrinsic stresses in nonepitaxial films, especially during the early stages of growth.

2:40 pm INVITED

STRESS MONITORING DURING THIN FILM GROWTH: Jerrold A. Floro, Eric Chason, Sandia National Labs, P.O. Box 5800, Albuquerque, NM 87185-1415

Thin films are typically deposited under severe kinetic constraints, resulting in highly non-equilibrium microstructures. These films often exhibit stress levels far in excess of the bulk yield strength. The origin and evolution of the film stress during deposition is, in most cases, poorly understood. We have developed a technique for real-time measurement of film stress during deposition--the Multi-beam Optical Stress Sensor (MOSS). MOSS is a technique for determination of stress through measurement of the substrate curvature. It has the virtues of low sensitivity to ambient vibration, simplicity of setup, and ease of use. We will describe the technique, and demonstrate its use for the particular case of SiGe heteroepitaxial growth on Si. We first discuss the elastic/plastic behavior of SiGe, and then focus on the surface segregation of Ge during SiGe growth. The latter topic, while somewhat specialized, is well-suited to demonstrate the interpretation of MOSS data, and to highlight both the strengths and limitations of the technique.

3:20 pm

ELASTIC MODULUS MEASUREMENT OF THIN FILM USING A DYNAMIC METHOD: Y. Kim, Department of Metallurgical Engineering, Chonnam National University, Kwangju, 500-757, Korea

The effect of external medium (air in this study) and specimen damping was estimated for the elastic modulus measurement using the sonic resonance method. A two-layer composite model was developed and applied for measuring the elastic modulus of thin film that is generally difficult to measure. The Ti coated Si wafer composites were produced using magnetron sputtering and used to test the developed model.

3:40 pm BREAK

4:00 pm INVITED

EPITAXY AND STRESS IN METAL THIN FILM COMPOUNDS AND MULTILAYERS: B.M. Clemens, T.C. Hufnagel, V. Ramaswamy, M.C. Kautzky, C.T. Wang, Department of Materials Science and Engineering, Stanford University, Stanford, CA 93405-2205

Epitaxial growth can be used to control and help understand thin film properties. We use sputter deposition to grow a variety of epitaxial thin film structures, including compounds and multilayers. The large stresses observed in these materials can have a large effect on properties. Using in-situ stress measurements and x-ray diffraction we study the stress evolution during growth and relate this behavior to thin film structure and properties. For Fe on Cu (001), we find that Fe is fcc up to a thickness of 10-12 monolayers, whereupon bcc Fe is observed in first the Pitsch and then the Bain orientations. The fcc Fe shows some relaxation of the misfit from the Cu, as do the Pitsch orientation bcc, which is in tension, and the Bain orientation bcc, which is in compression. In the giant magnetostrictive compound TbFe2, we have used epitaxy and differential thermal contraction to control the stress and hence the orientation of magnetization. This understanding and and control can lead to improved device performance.

4:40 pm

THE MECHANICAL BEHAVIOR OF PZT THIN FILMS DEPOSITED BY A SOL-GEL TECHNIQUE: D.F. Bahr, J.S. Wright, L.F. Francis, N.R. Moody*, W.W. Gerberich; Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, *Sandia National Laboratories, Livermore, CA 94550

Lead-zirconate-titanate (PZT) thin films are used in microelectromechanical systems (MEMS) as piezoelectric components. Both the mechanical and electrical properties of the PZT layer must be known in order to understand the piezoelectic response of the PZT for use as either a sensor or actuator. These properties are controlled by the composition and structure of the PZT film and its interface. Variations in PZT film structure and morphology are caused by changing solution processing conditions. PZT films have been deposited to thicknesses between 400 and 600 nm onto a multilayered electrode structure of platinum, titanium, titanium dioxide and silicon oxide. Nanoindentation has been used to characterize the effects of grain size and structure on the mechanical properties of the PZT films. The effects of the substrate and the multilayered electrode are accounted for to determine the modulus and hardness of the PZT films.

5:00 pm

ADHESION OF CVD TiN ON 316L SURGICAL STAINLESS STEEL OBTAINED IN A MASS TRANSFER REGIME: M.H. Staia, School of Metallurgy and Materials Science, Universidad Central de Venezuela, Apartado 49141, Caracas 1042-A, Venezuela; C. Julia Schmutz, Swiss Centre for Electronics and Microtechnology Incorporated, P.O. Box 41, Neuchatel, Switzerland

An investigation has been undertaken to study the adhesion of TiN coatings deposited by using CVD process at 900°C on surgical stainless steel. The microscratch test method (CSEM) was employed to evaluate the coating adhesion. Three scratches were performed at progressive load under the test conditions. Observation of the surface damages by means of an optical microscope permitted to determine the critical load. No acoustic emission detections or frictional force fluctuations could be correlated with the optical observations. In this investigation, the critical load corresponds to the regular occurrence of delamination. Scanning electron microscopy provided the essential and detailed information about the mode of failure of the coatings along the scratch channel. It was found that the coatings presented high plastic deformation and cohesive fracture at values lower than the critical load, Lc.