<p>Challenges with integrating high-κ gate dielectric,retrograde Si<sub>1-x</sub>Ge<sub>x</sub>channel and silicided contacts in future CMOStechnologies are investigated experimentally and theoreticallyin this thesis. ρMOSFETs with either Si or strained Si<sub>1-x</sub>Gex surface-channel and different high-κgate dielectric are examined. Si<sub>1-x</sub>Gex ρMOSFETs with an Al<sub>2</sub>O<sub>3</sub>/HfAlO<sub>x</sub>/Al<sub>2</sub>O<sub>3</sub>nano-laminate gate dielectric prepared by means ofAtomic Layer Deposition (ALD) exhibit a great-than-30% increasein current drive and peak transconductance compared toreference Si ρMOSFETs with the same gate dielectric. Apoor high-κ/Si interface leading to carrier mobilitydegradation has often been reported in the literature, but thisdoes not seem to be the case for our Si ρMOSFETs whoseeffective mobility coincides with the universal hole mobilitycurve for Si. For the Si<sub>1-x</sub>Ge<sub>x</sub>ρMOSFETs, however, a high density ofinterface states giving riseto reduced carrier mobility isobserved. A method to extract the correct mobility in thepresence of high-density traps is presented. Coulomb scatteringfrom the charged traps or trapped charges at the interface isfound to play a dominant role in the observed mobilitydegradation in the Si<sub>1-x</sub>Ge<sub>x</sub>ρMOSFETs.</p><p>Studying contacts with metal silicides constitutes a majorpart of this thesis. With the conventional device fabrication,the Si<sub>1-x</sub>Ge<sub>x</sub>incorporated for channel applications inevitablyextends to the source-drain areas. Measurement and modelingshow that the presence of Ge in the source/drain areaspositively affects the contact resistivity in such a way thatit is decreased by an order of magnitude for the contact of TiWto p-type Si<sub>1-x</sub>Ge<sub>x</sub>/Si when the Ge content is increased from 0 to 30at. %. Modeling and extraction of contact resistivity are firstcarried out for the traditional TiSi<sub>2</sub>-Si contact but with an emphasis on the influenceof a Nb interlayer for the silicide formation. Atwo-dimensional numerical model is employed to account foreffects due to current crowding. For more advanced contacts toultra-shallow junctions, Ni-based metallization scheme is used.NiSi<sub>1-x</sub>Gex is found to form on selectively grown p-typeSi<sub>1-x</sub>Ge<sub>x</sub>used as low-resistivity source/drain. Since theformed NiSi1-xGex with a specific resistivity of 20 mWcmreplaces a significant fraction of the shallow junction, athree-dimensional numerical model is employed in order to takethe complex interface geometry and morphology into account. Thelowest contact resistivity obtained for our NiSi<sub>1-x</sub>Ge<sub>x</sub>/p-type Si<sub>1-x</sub>Ge<sub>x</sub>contacts is 5´10<sup>-8</sup>Ωcm<sup>2</sup>, which satisfies the requirement for the 45-nmtechnology node in 2010.</p><p>When the Si<sub>1-x</sub>Ge<sub>x</sub>channel is incorporated in a MOSFET, it usuallyforms a retrograde channel with an undoped surface region on amoderately doped substrate. Charge sheet models are used tostudy the effects of a Si retrograde channel on surfacepotential, drain current, intrinsic charges and intrinsiccapacitances. Closed-form solutions are found for an abruptretrograde channel and results implicative for circuitdesigners are obtained. The model can be extended to include aSi<sub>1-x</sub>Ge<sub>x</sub>retrograde channel. Although the analytical modeldeveloped in this thesis is one-dimensional for long-channeltransistors with the retrograde channel profile varying alongthe depth of the transistor, it should also be applicable forshort-channel transistors provided that the short channeleffects are perfectly controlled.</p><p><b>Key Words:</b>MOSFET, SiGe, high-k dielectric, metal gate,mobility, charge sheet model, retrograde channel structure,intrinsic charge, intrinsic capacitance, contactresistivity.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:kth-3720 |
| Date | January 2004 |
| Creators | Persson, Stefan |
| Publisher | KTH, Microelectronics and Information Technology, IMIT, Kista : Mikroelektronik och informationsteknik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Trita-EKT, 1650-8599 ; 2004:2 |
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