Intrinsic correlation between mobility reduction by remote Coulomb scattering (RCS) and threshold voltage shift (ΔV t ), both of which are induced by interface dipole modulation at high-k/SiO 2 interface, is investigated. Three types of dipole modulation are examined; Al addition, La addition, and changing quality of interfacial SiO 2 layer. Extrinsic scattering components due to increases of interface state and surface roughness are extracted and separated. It is found that RCS due to interface dipole modulation by Al addition increases with increasing ΔV t , while that by La addition is constant, independent of ΔV t . Inevitability of additional scattering for ΔV t is discussed based on two different models for dipole formation mechanisms.
IntroductionAggressive MOSFET device scaling requires a metal gate (MG)/high-k insulator (HK) gate stack [1] . Achieving suitable threshold voltage (V t ) for CMOS is one of the biggest issues for introduction of MG/HK stack, especially in production by gate-first process. Recently, the presence of energy offset at the high-k/SiO 2 interface is evidenced [2][3][4] , which is attributed to interfacial dipole layer. V t control technique by modulation of the interface dipole with adding atoms has been developed for CMOS integration. La [2,[5][6][7][8] and Al [3,4,9] are widely known to be effective for lowering V t of nMOS and pMOS, respectively. V t shift (ΔV t ) of several hundred mV due to interface dipole modulation corresponds to formation of charges (negative and positive) of larger than 10 13 cm -2 at the high-k/interfacial layer (IL) interface, which may affect channel mobility (μ) by remote Coulomb scattering (RCS) mechanism [10] . From observation of strong correlation between μ reduction and ΔV t , Ota et.al. [11] proposed a model that interface dipole scattering governs μ of high-k MOSFET. According to this model, tradeoff relation between μ reduction and ΔV t is inevitable. However, there are several reports showing an unaffected μ for V t shifted device [7,8] . It is of great importance to clarify intrinsic correlation between μ reduction and ΔV t after correcting μ reduction by extrinsic effects depending on processes.In this paper, we systematically investigate quantitative correlation between μ reduction and ΔV t . Three types of V t shifts are examined; Al addition, La addition, and changing quality of IL. Extrinsic scattering components by increases of interface state and surface roughness are experimentally
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