Harvard University Huazhi Li, Ralph Pugh and Deo Shenai Rohm and Haas Company North Andover, MA Roy G. Gordon, Jean-Sébastien Lehn, Yiqun Liu, Kyoung H. Kim, Zhengwen Li and Michael Coulter Harvard University Cambridge, MA New Precursors for ALD of High-k Dielectrics Harvard University Volatile Precursors for Lutetium Oxide ALD of La2O3 and LaAlO3 Volatile Precursors for Lanthanum Oxide Stable, amorphous high-k dielectrics => LaLuO3 has the best properties ALD HfO2 from stable Hf amidinate precursors Outline Harvard University Hf alkylamide precursors decompose too quickly at 350 oC Deposition T ~ 350 oC needed for HfAlOx with ALD Al2O3 Thermal decomposition destroys uniformity and conformality Thermal decomposition of organic precursors adds C to films Carbon impurity in films increases leakage High-k HfO2 or ZrO2 with very low electrical leakage needed Why More Stable Hf and Zr Precursors? N H3C Hf N N CH3 CH3 N N N N CH3 CH3 H CH3 CH3 H TG data for Hf(Me2-fmd)4 Harvard University => Sufficient volatility and thermal stability for ALD Temperature (oC) 187 oC Negligible residue after TG H N H3C H Hafnium tetrakis(N,N’-dimethylformamidinate) Remaining mass (%) Hf N N CH3 CH3 N N N N CH3 CH3 R CH3 CH3 R <20 CH2CH3 CH2CH2CH3 bmd 171 80 amd pmd CH3 H 246 251 221 Melting TG T½ oC Point, oC fmd 141 187 Harvard University R = CH2CH2CH3 (propyl) is a liquid Hf precursor 20 oC R = H is the most volatile; liquid in bubbler > 141 oC Solid at 20 oC, soluble for use in direct liquid injection N H 3C R N H3C R R Hafnium Amidinates 0 20 40 60 80 100 % of complex remaining 120 0 4 6 Time (h) 8 Harvard University 2 10 12 Zr(NMe2)4 Zr(NEt2)4 Hf(NMe2)4 Hf(NMeEt)4 14 Hf and Zr amides completely decomposed in a few hours at 200 oC: 0 20 40 60 80 100 120 0 200 600 Time (h) 400 800 Hf(Me2-pmd)4 Hf(MEM)4 Zr(MMM)4 Zr(Me2-amd)4 Hf(MMM)4 Hf(Me2-amd)4 1000 No decomposition of Hf or Zr amidinates during 1000 hours at 200 oC: Precursors dissolved in mesitylene-d12, heated, and NMR spectra taken periodically Thermal Stability of Hf and Zr Precursors % of complex remaining % of complex remaining 0 20 40 80 Time (h) 60 100 120 Zr(Me2-amd)4 Hf(MMM)4 Hf(Me2-amd)4 Zr(MMM)4 140 120 0 20 40 60 80 100 0 50 100 200 Time (h) 150 250 300 Harvard University 350 Zr(Me2-amd)4 Hf(MMM)4 Hf(Me2-amd)4 Zr(MMM)4 Decomposition after ~200 hours at 280 oC => Hf and Zr amidinates much more stable than amides 0 20 40 60 80 100 120 No decomposition during 140 hours at 250 oC Thermal Stability of Hf and Zr Amidinates % of complex remaining Harvard University => High evaporation rates from thermally stable liquids Highest rate with Hf tetrakis(N,N’-dimethylformamidinate) Vaporization Rates of Hafnium Amidinates Harvard University Breakdown field ~6 MV/cm Dielectric constant >16 Electrical Properties (non-optimized) ALD “window” ~150 to ~400 oC ALD with H2O self-limiting at ~0.1 nm per cycle Typical bubbler temperatures 100-150 oC (mp 141 oC) ALD Conditions ALD of HfO2 from Amidinate Precursors 3.9 8 12 18 20 22 22 32 Conduction Valence band offset band offset 3.5 4.4 2.8 4.9 1.5 3.4 1.9 3.2 2.0 2.6 2.0 2.5 2.0 2.5 2.1 2.1 Harvard University => LaLuO3 has the best properties! SiO2 Al2O3 HfSiO4 LaAlO3 La2Hf2O7 GdScO3 DyScO3 LaLuO3 k Stable Amorphous High-k Dielectrics Stays amorphous and doesn’t form alloys with Si or Ge Sharp interface with Si, and no low-k interlayer Harvard University helping to achieve low leakage currents Both band offsets w.r.t Si are large (2.1 eV), after respective S/D activation anneals High dielectric constant (k~32) for amorphous phase Advantages of LaLuO3 as high-k dielectric N R1 N N Ln R1 N N N R2 R2 R3 Harvard University The choices of Rn affect the volatility, reactivity and stability. R3 can be an alkyl group or hydrogen The R1 and R2 are alkyl groups: isopropyl, tert-butyl, ethyl, etc. R3 R 2 R1 R3 Amidinate Precursors for Lanthanides N La N N N CH N N N C CH3 H3 C H3C H3 C N C N N C CH3 CH3 CH3 CH3 CH3 N La CH3 C N N Harvard University => Vaporization temperature increases with molecular mass N HC N H C H3 C N C La CH3 C N N Thermogravimetric Analysis of Lanthanum Amidinates Harvard University => La(iPr2-fmd)3 is most volatile La compound known, 60 mTorr at 100 oC N HC N N La H C N N N CH La(iPrCp)3 Vapor Pressures of Lanthanum Precursors Harvard University Precursors: H2O and N HC N N La H C N N N CH => negligible delay in nucleation on SiH => 0.16 nm per cycle tris(N,N’-diisopropylformamidinato)lanthanum (iPr2-fmd)3La ALD of La2O3 Harvard University 90 oC 110 oC 120 oC N HC N N La H C N N N CH Growth even at bubbler temperature <100 oC => ALD saturation at 0.08 nm per La cycle Bubbler temperature 90 to 120 oC Substrate temperature 300 oC tris(N,N’-diisopropylformamidinato)lanthanum (iPr2-fmd)3La 100 oC Precursors: Me3Al, H2O and Growth per La Cycle for ALD LaAlO3 Harvard University Precursors: Me3Al, H2O and N HC N N La H C N N N CH => 2 x as many Al atoms as La atoms per dose => Composition control by changing ratio of precursor doses Growth conditions: Bubbler temperature 120 oC Substrate temperature 300 oC tris(N,N’-diisopropylformamidinato)lanthanum (iPr2-fmd)3La Composition of ALD LaxAl1-xO3/2 Harvard University Details of the infrared spectra were given in a paper this morning by J. Kwon, M. Dai, E. Langereis, Y. Chabal, K.-H. Kim and R. G. Gordon. => Completely uniform surface coverage by La amidinate La amidinate reacts with nearly all the Si-H bonds in only 3 cycles Hf alkylamide only reacts with half of the Si-H bonds on the surface even after many cycles Precursor Reactivity with SiH Surface by IR Harvard University => Uniform nucleation and thickness => Sharp interfaces with silicon without interlayers TEMs of ALD LaAlO3 and GdScO3 Harvard University => negligible carbon contamination from solvent Low leakage current similar to films made from a bubbler. Vapor source: a solution of the La precursor (mp 194 oC) vaporized with an MKS MDD system Leakage Current through ALD La2O3 N Lu N N C CH3 Harvard University => Sufficient volatility and thermal stability for ALD Evaporation with negligible residue H3C N C CH3 C N N Thermal Gravimetric Analysis of Lutetium tris(N,N’-diisopropylacetamidinate) N Lu N N N CH H3C N C N Lu N CH3 C N N N C CH3 N C N N C CH3 CH3 CH3 CH3 CH3 N Lu CH3 C N N Harvard University => Lu amidinates are slightly more volatile than La amidinates N HC N H C H3C H3C H3C Thermal Gravimetric Analyses of Lanthanum and Lutetium Amidinates Harvard University ALD experiments and film characterization are underway. . . . ALD of Lu2O3 and LaLuO3 Harvard University Current work on ALD of LaAlO3, Lu2O3 and LaLuO3 La and Lu amidinates are volatile ALD precursors LaLuO3 is a very promising high-k dielectric Hf amidinates are suitable as ALD precursors Hf amidinates are more stable than Hf amides Conclusions Harvard University Supported in part by the US National Science Foundation Infrared data from Jinhee Kwon, Min Dai, Erik Langereis, Leszek Wielunski and Yves J. Chabal, Rutgers University MDD liquid delivery system supplied by MKS Instruments, Inc. Amidinate precursors supplied by Rohm and Haas Company Acknowledgements
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