Thermal Stability and Internal Stress for Strongly (111) Oriented Cu Films
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Thermal Stability and Internal Stress for Strongly (111) Oriented Cu Films Sinji Takayama , Makato Oikawa and Tokuji Himuro Dept. of Systems and Control, Hosei University, 3-7-2, Kajino-cho, Koganei, Tokyo, 184-8584, Japan ABSTRACT Internal stresses and thermal stability of strongly (111) oriented Cu thin films, which are one of promising interconnect materials in advanced ULSI devices, have been studied comparing with those of non-oriented Cu films. Their internal stresses parallel to a film surface were measured by a conventional X-ray diffraction technique (d-spacing vs. sin2ψ method), while the strain distribution with depth by a grazing incidence X-ray scattering (GIXS) methods. Large stress relaxation in strongly (111) oriented Cu films takes place at 200℃ without showing any significant grain growth and formation of thermal defects like hillocks. The residual internal stresses of highly oriented (111) Cu films increase almost linearly throughout the thickness up to the substrates. The feature of stress distribution in film depth does not change on annealing. The changes of the residual stresses at each depth are nearly the same as stresses parallel to film surface measured. INTRODUCTION Copper films are the most promising interconnect materials in advanced ULSI devices. They show lower resistivity, higher reliability against electromigration (EM), and better mechanical properties. It was reported that Cu (111) textured films showed much longer electromigration lifetime and thermal stabilities than Cu (200) textured films [1]. Thus, the formation of highly (111) oriented Cu films is one of keys to improve not only EM resistance, but also thermal stability for the application of interconnect lines in advanced ULSI devices. Strongly oriented (111) Cu films have recently been successfully made by using novel high-energy ion plating method (URT-IP) developed by Sumitomo Heavy Industries, Ltd. In this report, to characterize these films, we investigate the change of the structures and internal stresses on annealing by using both conventional X-ray diffraction and grazing incidence X-ray scattering (GIXS) methods. Particularly, internal stress distributions in film depth and their thermal changes were revealed by GIXS method. EXPERIMENTS Strongly (111) oriented Cu films were deposited on a Tan(25nm)/SiO2(800nm)/Si(100) substrates by using a novel high-energy ion plating apparatus (URT-IP). The non-oriented (111) texture Cu films are also made for comparison on the same above substrates by utilizing a conventional DC magnetron spattering apparatus. These Cu films were annealed isochronally in a vacuum of less than 10-4 MPa at various temperatures for 30 min. Structure and internal stresses in a film were analyzed by conventional X-ray diffraction technique (out of plain
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scattering) and/or grazing incidence X-ray scattering (GIXS) methods (in-plain scattering), respectively, using Rigaku Rint 2500. The latter technique allow us to obtain the information perpendicular to the sample surfaces utilizin
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