Controlled Stress Refractory Metallizations
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Controlled Stress Refractory Metallizations Ilan Golecki* and Margaret Eagan Honeywell International Inc. (formerly AlliedSignal Inc.), Corporate Advanced Materials and Devices Laboratory, 101 Columbia Road, Morristown, NJ 07962. * Phone (973) 455-4938; Fax (973) 455-4339; e-mail: [email protected] ABSTRACT Rhodium and iridium are highly electrically conductive refractory metals, which can be used as current-carrying thin-film metallizations. Their chemical inertness further enables their application at relatively high temperatures. However, due to the high elastic modulus of such metals, a residual tensile stress of 300 to 400 MPa is measured in evaporated thin films. We present novel results evidencing complete control over both the magnitude and the sign of the residual stress in such refractory thin films. The metallic layers are deposited by means of ion-beam-enhanced physical vapor deposition and both electrical resistivity and stress are controlled. Controlling the stress in this manner has enabled achieving thicker films and films with near-zero residual stress. INTRODUCTION AND MOTIVATION Rhodium and iridium have been shown to be attractive candidates for use in electronic metallizations1. These chemically inert, refractory elements crystallize in the face-centered cubic lattice and have relatively high intrinsic electrical conductivities. Both Rh and Ir have much higher Young’s moduli and tensile strengths, and lower thermal expansion coefficients compared to gold, which is a well established metallization material; see Table I. However, actual values of physical properties of materials, especially in thin film form, depend on the microstructures and purities, which are functions of the processing method and conditions. Previously1, we have demonstrated that the residual tensile stress and electrical resistivity of physically vapor deposited Rh and Ir thin films could be reduced significantly by appropriate choices of the deposition temperature and deposition rate. Here we present recent results evidencing that Rh and Ir thin films synthesized by ion-beam-enhanced physical vapor deposition can be obtained with essentially any desired value of tensile or compressive stress, including zero stress, while maintaining high electrical conductivity2,3. EXPERIMENTAL CONDITIONS Ir and Rh thin films have been deposited in high vacuum (baseline pressure in low 10-7 Torr range) on thin-chromium-coated (0.01-0.03 µm Cr), thermally-oxidized (~0.5 µm SiO2), fourinch diameter, (100) oriented, single-crystalline silicon substrates by means of electron-gun physical vapor deposition, without and with concurrent argon ion bombardment. The thermal oxide was present on both front and back of each substrate. The substrates were held face down on a planetary; each substrate rotated around its own axis as well as around the chamber axis (the latter at 2-12 rpm). The substrates were heated during deposition using quartz halogen lamps. A stationary thermocouple located in close proximity to the substrates was used to measure and
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