Microstructural studies by transmission electron microscopy of the formation of ultrathin PtSi layers with novel silicid
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Microstructural studies by transmission electron microscopy of the formation of ultrathin PtSi layers with novel silicidation processes S. Jin,a) H. Bender, and R. A. Donaton IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
K. Maex IMEC, Kapeldreef 75, B-3001 Leuven, Belgium and INSYS, Katholieke Universiteit Leuven, Belgium (Received 18 February 1998; accepted 26 January 1999)
Ultrathin and uniform Pt-silicide layers are prepared by electron beam evaporation on a heated silicon substrate and by magnetron sputtering at room temperature followed by rapid thermal annealing (RTP) and selective etching, respectively. In the electron-beam deposited samples, continuous Pt-silicide layers of 6–8 nm thickness are formed after thermal annealing. The interfaces between the silicide layers and the silicon substrate are not atomically flat. In the case of the sputtered Pt, continuous PtSi layers down to 3 nm thick can be produced by using two-step (low-high temperature) and modified two-step (selective etch and high-temperature anneal) RTP silicidation processes. In one-step (high-temperature) processed samples, PtSi is the dominant phase; meanwhile, a small fraction of Pt12 Si5 phase is inhomogeneously distributed in the case of thicker PtSi layers. In the two-step RTP processed samples, a PtyPt2 SiyPtSiySi layered structure is formed after the first RTP step. The first anneal step is found to be crucial for the roughness and epitaxy of the final PtSi layer. The best Schottky barrier heights are found to be 0.249 eV for the 3 nm PtSiyp-Si(100) Schottky diodes. The e-beam and the sputtered PtSi layers follow different epitaxial growth models.
I. INTRODUCTION
Thin silicide films are becoming more important with the increasing packing density of integrated circuits (IC).1,2 Platinum silicide is a candidate for applications in making both ohmic and Schottky barrier contacts to MOS and bipolar devices. Since platinum silicide has a relatively high work function, the most attractive application is to form Schottky barrier junctions with p-type silicon for applications in infrared detectors. Up to now, several Pt-silicide phases have been reported.3 Pt-monosilicide (PtSi) has many advantages over the other Pt-silicides due to its low resistance (30 mV cm)4 and Schottky barrier height (SBH) of 0.23 eV to p-type silicon.5 Moreover, it is the stable phase when in contact with Si. For a detector, the noise level ultimately determines the sensitivity of the device, while lateral potential variations generated by a spatially inhomogeneous SBH at the metal/semiconductor interface determine the noise power density.6 Furthermore, the silicide layer has to be thin, with thickness in the range of 2 to 8 nm for good infrared detection. Therefore, the tight control of the PtSi layer uniformity and thickness has become very important for the optimal detector behavior. a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 6, Jun 1999
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