Theoretical investigation of Pt monosilicide and several germanides: electronic structure, surface energetics, and work
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0980-II05-43
Theoretical Investigation of Pt Monosilicide and Several Germanides: Electronic Structure, Surface Energetics, and Work Functions. Manish K. Niranjan, Leonard Kleinman, and Alexander A. Demkov The University of Texas, Austin, TX, 78712
ABSTRACT We present a theoretical study of the electronic structure, surface energies and work functions of orthorhombic Pt monosilicide and germanides of Pt, Ni, Y and Hf within the framework of density functional theory (DFT). Our calculated bulk structures are within 1-2% of reported experimental values. Calculated work functsions for the (001) surfaces of PtSi, NiGe and PtGe are 5.12, 4.57 and 4.83 eV, respectively, suggesting that these metals and their alloys can be used as self-aligned contacts to p-type silicon and germanium. Work functions for Y and Hf germanides range from 2.4 to 4.3 eV making them a possible n-type contact material. In addition, we also report an ab-initio calculation of the Schottky-barrier height at the Si(001)/PtSi(001) interface. The p-type Schottky barrier height of 0.28 eV is found in good agreement with predictions of a simple metal induced gap states (MIGS) theory and available experiment. This low barrier suggests PtSi as a low contact resistance junction metal for silicon CMOS technology. We identify the growth conditions necessary to stabilize this orientation.
INTRODUCTION As scaling of traditional silicon based technology reaches its physical limit, a germanium channel field effect transistor (FET) is generating a lot of interest [1]. The germanium channel metal oxide semiconductor FET (MOSFET) offers high mobility of both carriers (electrons and holes) resulting in higher overdrive current, enhanced transconductance, and higher cutoff frequencies as compared with a Si transistor. To fully exploit transport properties of germanium, a low resistance contact technology needs to be developed based on metal germanides, much in the same way that self aligned metal silicides are used in a standard complementary metal oxide semiconductor (CMOS) process today [2-4]. Metal silicides are used to form ohmic contacts with source, drain, and gate silicon because of their low resistivity, low contact resistance to Si, reasonable thermal stability, and excellent process compatibility with Si technology. Over the past two decades, silicides of Ti, Co and Ni have been successively used in integrated circuit manufacturing. In the deep submicron regime NiSi is now succeeding CoSi2 [5]. However, NiSi suffers from the low thermal stability [5], and both CoSi2 and NiSi exhibit relatively large (0.50.6 eV) Schottky barriers to Si contributing to large contact resistance. At present, this contact resistance amounts to a quarter of the total parasitic resistance [5], and will clearly only rise as scaling continues. Thus, it is desirable to identify new metals or alloys with a lower Schottky barrier to n- and p- type Si for use in NMOS and PMOS, respectively [6]. Adding Pt to NiSi significantly enhances the NiSi thermal stability. PtSi is attractive in i
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