Atomic force microscope investigation of the thermal stability of thin TiSi 2 films
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Atomic force microscope investigation of the thermal stability of thin TiSi2 films Alberto V. Amorsolo, Jr.a) and Paul D. Funkenbusch Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627
Alan M. Kadin Department of Electrical Engineering, University of Rochester, Rochester, New York 14627 (Received 4 December 1996; accepted 14 October 1997)
The thermal stability of TiSi2 films on Si has been studied using the atomic force microscope (AFM). Changes in the surface roughness, film morphology, and sheet resistance were monitored during a series of rapid thermal annealing treatments. A linear increase of the root-mean-square (rms) roughness with time was observed during the early stages of degradation, in agreement with a surface diffusion model of thermal grooving, followed by an apparent saturation roughness that was attributed to the effective rupture of the film. I. INTRODUCTION
TiSi2 is one of the most useful silicides for silicon integrated circuit applications.1–4 This electronic material is used as a diffusion barrier to prevent Al spiking of shallow junctions while providing low contact resistance.5,6 In the self-aligned or salicide technology, TiSi2 is formed on exposed Si and poly-Si regions, to lower the sheet resistance and the junction contact resistances that are in series with the active device.5 As a result, there is significantly higher current drive capability and a much improved circuit performance. TiSi2 can also be utilized as low resistance interconnects between poly-Si emitter and base contacts in bipolar devices.7,8 All of these applications are made possible by the low resistivity of TiSi2 (the face-centered orthorhombic C54TiSi2 phase has the lowest among the refractory metal silicides2,7 ) and its other valuable properties such as good adhesion to Si,9 reliability of formation on both polyand single-crystal Si by thermal reaction,3,5 and thermal stability.7,10,11 The thermal stability of a silicide is its ability to resist thermal degradation when subjected to a prolonged heat treatment at high temperatures. A silicide such as TiSi2 must have sufficient thermal stability to withstand all the thermal processing that might be required, in addition to the annealing treatment needed to form it from the initial metallic film of Ti on Si. In particular, there are situations which require subsequent heat treatment, such as the formation of a polycide in which the silicide is formed prior to formation of the diffusion regions. In order to form the required junction by annealing, the silicide will have to be heated to a much higher temperature than required for a salicide process. Other a)
Present address: Department of Mining and Metallurgical Engineering, University of the Philippines, Diliman, Quezon City 1101, Philippines.
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J. Mater. Res., Vol. 13, No. 7, Jul 1998
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reasons for additional heat treatments include thermal oxidation, deposition of insulatin
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