Plastic properties of thin films on substrates as measured by submicron indentation hardness and substrate curvature tec
- PDF / 568,172 Bytes
- 7 Pages / 594 x 810 pts Page_size
- 7 Downloads / 217 Views
D. S. Gardner Integrated Circuits Laboratory, Stanford University, Stanford, California 94305
W. D. Nix Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (Received 8 August 1986; accepted 10 November 1986) Substrate curvature and submicron indentation measurements have been used recently to study plastic deformation in thin films on substrates. In the present work both of these techniques have been employed to study the strength of aluminum and tungsten thin films on silicon substrates. In the case of aluminum films on silicon substrates, the film strength is found to increase with decreasing thickness. Grain size variations with film thickness do not account for the variations in strength. Wafer curvature measurements give strengths higher than those predicted from hardness measurements suggesting the substrate plays a role in strengthening the film. The observed strengthening effect with decreased thickness may be due to image forces on dislocations in the film due to the elastically stiffer silicon substrate. For sputtered tungsten films, where the substrate is less stiff than the film, the film strength decreases with decreasing film thickness.
I. INTRODUCTION Interest in the mechanical properties of thin films has been accelerating recently due in a large part to concern over the reliability of metallizations used for integrated circuit interconnections. Knowledge of the mechanical strength of the materials used for these interconnections is important to an understanding of the failure mechanisms and to obtaining the appropriate solutions. Two common techniques used in the study of thin-film mechanical properties are substrate bending techniques1"6 for detecting stresses in thin films and submicron indentation techniques.7"10 This paper describes the application of both methods to the determination of the strength of two materials used for metallizations: aluminum and tungsten. II. EXPERIMENTAL A. Thin-film preparation Aluminum and tungsten thin films were deposited onto (100) oriented 10-20/nil cm/>-type silicon wafers by magnetron sputtering at room temperature. In the case of aluminum, 100 nm of a thermal oxide was grown on the wafers in wet oxygen prior to thin-film deposition. The SiO2 layer was grown to prevent epitaxial growth of the aluminum on silicon and to prevent dissolution of the silicon substrate in the aluminum during heating. Aluminum films 210, 260, 420, 590, and 1090 J. Mater. Res. 1 (6), Nov/Dec 1986 http://journals.cambridge.org
nm thick were deposited onto the oxidized silicon wafers using an aluminum target with a purity of 99.999%. These film thickness were determined by weighing the wafers before and after deposition. Tungsten films 70, 110, 160, 220, and 450 nm thick were deposited using a 99.95% pure tungsten target. For these films, the film thicknesses were determined by profilometer measurements on etched steps in the films. The deposition equipment used was a Balzers BAS 450 magnetron sputtering system. This system has an oil-free
Data Loading...
