Effects of Alloying on Properties of NiSi for CMOS Applications
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Effects of Alloying on Properties of NiSi for CMOS Applications Mark van Dal1, Amal Akheyar2, Jorge A. Kittl3, Oxana Chamirian4, Muriel De Potter5, Caroline Demeurisse5, Anne Lauwers5 and Karen Maex4,5 1
Philips Research Leuven, Kapeldreef 75, B-3001 Leuven, Belgium Affiliate researcher at IMEC from Infineon 3 Affiliate researcher at IMEC from Texas Instruments 4 E.E. Department K.U. Leuven, Belgium 5 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
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ABSTRACT Effects of alloying Ni with Pt and Ta on silicide properties for CMOS technology have been studied. It was found that Pt is soluble in NiSi, which is in line with literature, whereas Ta segregates towards the surface during thermal treatment. Additionally, Ta retards NiSi formation at low temperature. Thermal stability of NiSi on Si is improved more efficiently by alloying Ni with Pt compared to Ta. Silicide/diffusion contact resistance is extracted using the Transmission Line Structure. In our experiments, contact resistivity appeared to be virtually unaffected with respect to the alloying element. Thermal stability on narrow poly Si structures was also improved when Ni was alloyed with Pt. Similar leakage currents for Ni and Ni(Pt) silicides on N+ and P+ junctions were obtained. The results presented in this work suggest that Pt is a better candidate as alloying element to improve NiSi thermal stability for CMOS processes than Ta. INTRODUCTION CMOS technology rapidly moves towards the 45 nm node, comprising devices with gate lengths decreasing to 25 nm and below and source/drain junction depths below 70 nm. Since scaling alone does not provide the improvements set by the ITRS Roadmap, the production of such small devices calls upon the integration of new material with superior properties. For instance, NiSi replaced CoSi2 (industry’s choice for previous nodes) due to the instability of CoSi2 on narrow poly gates [1]. One of the key issues for Ni silicide integration is its low thermal stability. It is well documented that thermal degradation of NiSi films can be reduced by adding an alloying element to Ni such as Ta [2], Pd [3] or Pt [3,4]. However, in order to integrate Ni alloys in future nodes, it is important to understand the impact of alloying on other silicide properties relevant to CMOS applications. In this work we will present results of a study on the effect of alloying Ni with Pt and Ta with respect to (1) the process window of silicidation, (2) morphological degradation of the thin Ni-based silicide film, (3) silicide/junction contact resistance extracted from transmission line measurements [5,6], (4) leakage on N- and P-type junctions, (5) linewidth effect and silicide thermal stability on narrow poly structures. EXPERIMENTAL DETAILS For the phase formation study, three blanket Si (100) wafers were used on which a film of Ni, Ni(10%Pt) or Ni(10%Ta) was co-sputtered. Prior to metal deposition, the Si wafers were
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cleaned in a 2% HF solution. RBS analysis of the deposited films showed that the actual thickness and content is as fol
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