Novel high-k materials Can we nominate candidates for the 22 and the 16 nm nodes? Olof Engstrom Chalmers University of Technology Paul Hurley Tyndall National Institute Octavian Buiu University of Liverpool Max Lemme AMO

Outline Why high-k? Essential properties needed Why are rare-earth oxides interesting? Comparison between different candidates Finalists?

Bulk MOS: Oxide voltage vs gate voltage Oxide thickness= 10 [Å] k Silicon doping: cm -3 Oxide voltage [V] Gate voltage [v] M S qsqs EFEF V O

The k-value should be ”lagom” Mohapatra et al, IEEE Trans. Electron. Dev. 49, 826 (2002) F For L g = 70 nm SiO 2 k = 10 k = 25 k = 50

Essential properties EcEc EvEv k-values Energy offsets  E c and  E v Reactivity with silicon Hygroscopicity Structural stability Interface states Charge carrier traps

Metals of interest

Polarizability and k-value Clausius-Mosotti D. G. Schlom et al, Thin films and heterostructures for oxide electronics, (Springer, 2005), p. 31

Energy offset vs. k-value Borders for the 22 nm LSTP bulk node: A/cm 2 EOT=0.6 nm V ox = 1V (Target) Requires k  E ≈ 70 eV O. Engström, B. Raeissi, S. Hall, O. Buiu, M.C. Lemme, H.D.B. Gottlob, P.K. Hurley, K. Cherkaoui, SSE, 51, 622 (2007) LaLuO 3

Reactivity Lu 2 O 3 (ALD) Scham et al Topics in Appl. Phys. Vol. 106, p. 153 (Springer, 2007) La 2 O 3 (evap) Kim et al SSE 49, 825 (2005) Gd 2 O 3 (MBE) Czernohorsky et al APL 88, (2006) 550 C 950 C As grown

Reactivity Si + MO M + SiO 2 MSi + SiO 2 M + MSiO  G 1000C For Si + O  G 1000C < 0  G 1000C SiO 2 D. G. Schlom et al, Thin films and heterostructures for oxide electronics, (Springer, 2005), p. 31

Hygroscopicity K.Kakushima, K.Tsutsui, S-I. Ohmi, P.Ahmet V.R. Rao and H. Iwai in Rare earth oxide thin films ( Springer, 2007), p. 345 water + oxidehydroxide

Structural stability APL, 89, (2006) Example: LaLuO 3

Leakage Gd 2 O 3 [2], HfO 2 [1], ZrO 2 [1] HfGdO [3] Lu 2 O 3 [4] with epitaxial Lu 2 O 3 - silicate IL) [1] H. Iwai et al, Proc. IEDM, 2002 [2] H.D.B. Gottlob et al, IEEE Electron Dev. Lett. 27, 814 (2006) [3] S. Govindarajan et al, APL 91, (2007) [4] P. Darmawan et al, APL 91, (2007) [5] A. Ogawa et al Microel. Eng. 84, 1861 (2007) Leakage current [A/cm 2 ] EOT [nm] HfO 2 and ZrO 2 3 La 2 O 3 [1] HfO 2 [5] (with HfSiO IL)

Experimental C = f (V,freq.) Gd 2 O 3 ALD Gd 2 O 3 MBE B.Raeissi, J.Piscator, O.Engström, S.Hall, O.Buiu, M.C.Lemme, H.D.B.Gottlob, P.Hurley, K.Cerkaoui and H.J.Osten, Proc. ESSDERC, 2007, p 287 HfO 2 React. sputt.

LaSiO x /Si interface LaSiO x E-beam evap. LaSiO x P.K.Hurley, K.Cherkaoui, E.O’Connor, M.C.Lemme, H. D.B. Gottlob, M.Schmidt, S.Hall, Y.Lu, O.Buiu, B.Raeissi, J. Piscator and O.Engstrom, J. Electrochem. Soc., in press

D it for HfO 2, Gd 2 O 3 and LaSiO x P.K.Hurleya, K.Cherkaoui, E.O’Connor, M.C.Lemme, H. D.B. Gottlob, M.Schmidt, S.Hall, Y.Lu, O.Buiu, B.Raeissi, J. Piscator and O.Engstrom, J. Electrochem. Soc., in press

Final solution: The Nominees Nominees Too low k  E c,v Wild cards Exists only in Andromeda

Finalists Pr 2 O 3 La 2 O 3 Gd 2 O 3 LaLuO 3 HfO 2 ZrO 2 k x DE c k x DE v Low ReactivityHigh LowHigh Hygroscop.LowHigh Low Struct. stab.Low High Low

Conclusion there is a lot more work to do! Lantanum based oxides seem worth a bid but fortunately for academic people

Theoretical C=f(V,freq.) C-V D it = f(  G n ) log  n = f(  G n ) C [F] Gate voltage [V]  G n [eV] D it [m -2 eV -1 ]  n [m 2 ]

The concept of polarization F = V/d P/(3    F loc = F + P/(3    P = (1/V m )  c F loc    c [A 3 ]

Large  means sloppier material + -  spring constant/mass) 1/2 Si High-k oxide LO-phonon Remote phonon scattering Fischetti et al, PRB 90, 4587 (2001)