SUPERLAYER RESIDUAL STRESS EFFECT ON THE INDENTATION ADHESION MEASUREMENTS Alex A. Volinsky, Neville R. Moody* and William W. Gerberich University of Minnesota, Dept. of Chemical Engineering and Materials Science, Minneapolis, MN 55455, volinsky@cems.umn.edu * Sandia National Laboratories, Livermore, CA 94550 ABSTRACT The practical work of adhesion has been measured in thin aluminum films as a function of film thickness and residual stress. These films were sputter deposited onto thermally oxidized silicon wafers followed by sputter deposition of a one micron thick W superlayer. The superlayer deposition parameters were controlled to produce either a compressive residual stress of 1 GPa or a tensile residual stress of 100 MPa. Nanoindentation testing was then used to induce delamination and a mechanics based model for circular blister formation was used to determine practical works of adhesion. The resulting measured works of adhesion for all films between 100 nm and 1 μm thick was 30 J/m 2 regardless of superlayer stress. However, films with the compressively stressed superlayers produced larger blisters than films with tensile stressed superlayers. In addition, these films were susceptible to radial cracking producing a high variability in average adhesion values. INTRODUCTION Several researchers have used nanoindentation to examine the effect of residual stress on the modulus and hardness of bulk materials and of thin films [1-4]. It has also been used to study adhesion of thin metallic and ceramic films where residual stresses drive delamination and failure. However, little work has been done using this technique to study adhesion of ductile thin films. These films cannot store enough strain energy or transmit forces of sufficient strength to the film-substrate interface for crack initiation and propagation. Recent work shows that deposition of a highly stressed superlayer onto thin ductile copper films can provide the stresses required for delamination during indentation testing [7, 9, 10]. Based on this work, we have employed nanoindentation in a study of compressive and tensile residual stresses created during sputter deposition of tungsten superlayers on the adhesion of thin ductile aluminum films. EXPERIMENT All thin film processing was conducted in a Class 10 clean room environment. Silicon <100> wafers (100 mm in diameter, 0.5 mm thick) were thermally oxidized at 1100 °C in steam to grow 3 μm of SiO 2 . Oxide thickness was measured with a Nanoscope Ellipsometer. Al films from 40 nm to 3.2 μm thick were then deposited onto the oxidized substrates in a Perkin-Elmer DC Magnetron sputtering apparatus. The base pressure of the system was 1 μTorr, and the Ar flow was 10 sccm, which corresponded to 6 mTorr Ar pressure. For Al films from 500 nm to 3.2 μm thick, 5000 Watts of power was applied to the target (Al-2% Si, w/o); for thinner films the sputtering power was reduced to 1000 Watts. Substrate table rotation was used to achieve uniform film thickness and structure. The maximum temperature during film deposition reached 100 °C for the longest deposition run of 3 μm Al, after which the system was cooled for one hour without breaking vacuum. Film thickness was measured using a DEKTAK surface profiler. Using the wafer curvature technique and Stoney’s equation [11], residual stresses measured were Mater. Res. Soc. Proc. Vol. 594, Fall 99 Symp. V: Thin Films -Stresses and Mechanical Properties VIII