Hafnium silicate and nitrided hafnium silicate as gate dielectric candidates for SiGe-based CMOS technology

Transcription

1 Hafnium silicate and nitrided hafnium silicate as gate dielectric candidates for SiGe-based CMOS technology Swarna Addepalli, Prasanna Sivasubramani, Hongguo Zhang, Mohamed El-Bouanani, Moon J. Kim, Bruce E. Gnade and Robert M. Wallace Department of Materials Science University of North Texas AVS International Symposium Denver

2 Outline Motivation Strained epitaxial Si x Ge 1-x /Si High-κ oxides/si x Ge 1-x Experimental Hf-silicate/Si x Ge 1-x Nitrided Hf-silicate/Si x Ge 1-x Physical characterization Electrical characterization Interface stability Summary Acknowledgements

3 Strained epitaxial Si 1-x Ge x /Si Si 1-x Ge x Si 1-x Ge x /Si Si Lattice constants of Si and Ge differ by 4.17% at room temperature Lattice mismatch (between Si 1-x Ge x and Si) Ge concentration dependent. Deposition of Si 1-x Ge x on Si compressively strained, pseudomorphic layers Strain-induced changes in electronic properties enhanced hole mobility for Si 1-x Ge x /Si high-speed devices high processing temperatures cause relaxation of the strained interface J. F. A. Nijs, Advanced Silicon & Semiconducting Silicon- Alloy Based Materials & Devices, Institute of Physics Publishing Ltd. (1994)

4 High-κ oxides/si 1-x Ge x /Si Hafnium silicate, Nitrided hafnium silicate: High-κ dielectrics Thermodynamically stable in contact with Si Oxide of Si 1-x Ge x is a poor dielectric GeO 2 readily reduced to elemental Ge! reduced leakage current (film physically thicker than SiO 2 ) ultra thin SiO 2 exhibits excessive leakage current Capacitance of gate stack enhanced κ, crystallization temperature: Hf concentration dependent Deposition of a high-κ material in direct contact with Si 1-x Ge x Si capping layer used for SiO 2 growth degrades ultimate mobility Possibility of eliminating Si capping layer

5 PVD: Hf-silicate/Si x Ge 1-x Si Si x Ge 1-x Methanol+0.5% HF cleaned Si 1-x Ge x Sputter deposition from hafnium silicide target, room temperature Si Hafnium silicide Si 1-x Ge x UV-O 3 oxidation (400 Torr O 2, room temperature) Pt Si Al Hafnium silicate Si x Ge 1-x Post metallization anneal (Forming gas) Post-oxidation annealing (N 2 ) Capacitors: Pt evaporation (shadow mask) Al contact Si Bonding, composition: XPS Hafnium silicate Si 1-x Ge x Electrical characterization UV-O 3 oxidation at room temperature preserves pseudomorphic nature of the Si x Ge 1-x /Si interface

6 Deposition tool + UV lamp Plas ma sputtering syste m Q uartz la mp heater (in situ annealing) (Pt, Al) Base pressure 10-9 Torr

7 Hf-silicate/Si 1-x Ge x : XPS analysis Hf4f Hf-O-Si Hf-Si Si2p SiO 2 Si-O-Hf Si 0 Intensity (arb. units) Hf-O 15 Binding energy (ev) as deposited Hf-silicide (6 min., 25W) min. UV-O Intensity (arb. units) Binding energy (ev) UV-ozone oxide/si UV-ozone oxide /Si 1-x Ge x 60 min. UV-O 3 as deposited Hf-silicide (6 min., 25W) Hf 4f, Si 2p spectra consistent with silicate formation Composition of Hf-silicate from XPS: Hf (~ 12%), Si (~12%), O (~76%) G. D. Wilk, R. M. Wallace, J. Appl. Phys., 87, 484 (2000) D. Niu, R. W. Ashcraft, G. N. Parsons, Appl. Phys. Lett., 80, 3575 (2002)

8 Hf-silicate/Si 1-x Ge x : Interface characterization UV-ozone oxidation of Si 1-x Ge x at room temperature produces a mixture of silicon and germanium oxides Intensity (arb. units) clean Ge Ge2p IMFP: nm Sensitive to Ge oxidation Ge (Auger) Ge(L 3 MM) Ge3s Ge3p Overlap with Hf5p Ge3d Binding energy (ev) A. Agarwal, J. K. Patterson, J. E. Greene, A. Rockett, Applied Physics Letters, 68, 518 (1993)

9 Changes in Ge(L 3 MM) spectra Ge-O vs. Si-O formation easily detected 400 Ge (L 3 MM) Ge(ox) Ge 0 Germanium 70 Ge (L 3 MM) Ge(ox) Ge 0 Si 1-x Ge x Intensity (arb. units) GeO x /Ge Intensity (arb. units) UV-O 3 oxide (60min.) /Si 1-x Ge x clean Ge Kinetic energy (ev) clean Si 1-x Ge x Kinetic energy (ev) A. P. Pijpers, L. Lefferts, Applied Catalysis A: General, 185, 29 (1999)

10 UVO 3 oxidation time study 100 Ge(L 3 MM) Ge(ox) Ge Si2p Si +4 Si min min. Intensity min. 30 min. Intensity min. 30min min. UVO 3 15 min. UVO as deposited Hf-silicide (2 min.) as deposited Hf-silicide (2 min.) Kinetic energy (ev) Binding energy (ev) Interfacial layer growth obvious for t=45 minutes of UVO 3 oxidation Hf4f spectra indicate complete conversion of hafnium silicide to silicate Si2p spectra indicates interfacial SiOx formation for t=45 min

11 UV-O 3 oxidation of Hf-silicide HR-TEM result consistent with XPS: no detectible interfacial layer HR-TEM result consistent with XPS: no detectible interfacial layer Pt Hf-silicate 3 nm 1 nm Si x Ge 1-x HR-TEM sample preparation: (1) Sputter deposition of Hf-silicide on MeOH/HF cleaned Si 1-x Ge x for 2 min. at 25W power at room temperature (2) UVO 3 oxidation for 20 minutes (400 Torr O 2, room temperature). (3) E-beam evaporation of Pt cap (70 nm thick)

12 Hf-silicate/Si x Ge 1-x : Electrical characterization Pt/Hf-silicate (3 nm)/si x Ge 1-x (unannealed) Pt/Hf-silicate (3nm)/Si 0.75 Ge 0.25 Capacitance density (µf/cm 2 ) Pt/Hf-silicate (3nm)/Si 0.75 Ge 0.25 Capacitor area = 8 x 10-5 cm 2 Frequency = 100 khz Current density (A/cm 2 ) 1e+1 Capacitor area = 8x10-5 cm 2 Capacitor area = 3x10-4 cm 2 1e+0 1e-1 1e-2 1e-3 1e-4 1e-5 1e V g (Volts) 1e V g (Volts) Stretch-out High leakage Appropriate annealing conditions required

13 Hf-silicate/Si x Ge 1-x : Electrical characterization Effects of POA at different temperatures in N 2 Hf-silicate thickness = 3 nm Capacitance density (µf/cm 2 ) Pt/Hf-silicate (3nm)/Si 0.75 Ge 0.25 Capacitor area = 8x10-5 cm 2 frequency = 100 khz POA (N 2, 350 o C, 30m) POA (N 2, 350 o C, 1h) POA (N 2, 450 o C, 30m) POA (N 2, 450 o C, 1h) unannealed Current density (A/cm 2 ) 1e+0 capacitor area = 8 x 10-5 cm 2 1e-1 1e-2 1e-3 1e-4 POA (N 2, 350 o C, 30m) 1e-5 POA (N 2, 350 o C, 1h) POA (N 2, 450 o C, 30m) 1e-6 POA (N 2, 450 o C, 1h) 1e V g (Volts) V g (Volts) Stretch-out of C-V curves reduced after annealing at 350 o C Capacitance density increases as annealing temperature is increased to 350 o C. Under higher annealing conditions, interfacial layer growth occurs. κ = Current density at +1V = 10-3 A/cm 2

14 Hf-silicate/Si x Ge 1-x : Electrical characterization Effects of Post-metallization annealing in forming gas Current density (A/cm 2 ) 1e+0 1e-1 1e-2 1e-3 1e-4 1e-5 1e-6 capacitor area = 8x10-5 cm 2 N 2 (POA) N 2 (POA) + N 2 /H 2 (PMA) Capacitance density (µf/cm 2 ) Pt/Hf-silicate (3nm)/Si 0.75 Ge 0.25 Capacitor area = 8x10-5 cm 2 frequency = 100 khz 1e V g (Volts) Vg (Volts) Leakage current increased by at least 1 order of magnitude C-V curves indicate the presence of charge traps

15 Hf-silicate silicate-si x Ge 1-x interface Effects of annealing in forming gas Ge2p GeO 2 Ge 0 Possible reduction of GeO 2 to Ge: GeO 2 + 2H 2 Ge + 2H 2 O Intensity after forming gas anneal (450 o C, 30m) before forming gas anneal Elemental Ge formation reported for Si x Ge 1-x O 2 /Si x Ge 1-x either upon aging or annealing in NH 3 or vacuum. Hf-silicate/Si x Ge 1-x interface not stable Binding energy (ev) (1) W. S. Liu, J. S. Chen, M. A. Nicolet, V. Arbet-Engels, K. L. Wang, Journal of Applied Physics, 72, 4444 (1992) and, Applied Physics Letters, 62, 3321 (1993) (2) W. S. Liu, M. A. Nicolet, H. H. Park, B. H. Koak, J. -W. Lee, Journal of Applied Physics, 78, 2631 (1995)

16 Interface stability Ge-H Ge-N bond more stable than Ge-O bond Nitride film acts as a diffusion barrier to oxygen Incorporating N into the film might enhance Hf-silicate-Si x Ge 1-x interface stability AES intensity ratios for thin oxynitride films on Ge & Si vs. annealing T (1) K. Prabhakaran, T. Ogino, Surface Science, 387, L1068 (1997) (2) T. Angot, P. Louis, Physical Review B, 61, 11 (2000) (3) J-H.Ku, R. J. Nemanich, Journal of Applied Physics, 80, 4715 (1996)

17 HfSi x O y N z /Si x Ge 1-x Si Si 1-x Ge x Methanol+0.5% HF cleaned Si 1-x Ge x Ar+N 2 sputtering of hafnium silicide target, room temperature HfSi(O)N Si Si 1-x Ge x UV-O 3 oxidation, 400 Torr O 2, Room temperature Pt Si Al HfSi x O y N z Si 1-x Ge x Capacitors: Pt evaporation (shadow mask) Al backside contact Si HfSi x O y N z Si 1-x Ge x Electrical characterization Chemical etch profiling + XPS of oxidized films show interfacial Si-N & Ge-N

18 HfSi x O y N z /Si x Ge 1-x : Electrical characterization 2.5 Ar:N 2 ratio = 1:1 Ar:N 2 ratio = 10:1 Hf-silicate (no N 2 ) Pt/HfSi x O y N z (3 nm)/si x Ge 1-x (unannealed) 1e+3 1e+2 Capacitance density (µf/cm 2 ) capacitor area = 8x10-5 cm 2 frequency = 100 khz V g (Volts) Current density (A/cm 2 ) 1e+1 1e+0 1e-1 1e-2 1e-3 1e-4 Ar:N 2 ratio = 1:1 1e-5 Ar:N 2 ratio = 10:1 1e-6 capacitor area = 8x10-5 cm 2 1e V g (Volts) Ar: N 2 ratio Postoxidation annealing κ J at +1 V (A/cm 2 ) 1:1 None :1 None Electrical results for unannealed HfSi x O y N z better than Hf-silicate Interface stability to be tested by annealing in N 2 /H 2 Hf-silicate (no N 2 ) none

19 Summary Sputter deposition of Hf-silicide at room temperature on to clean Si x Ge 1-x + UV-O 3 oxidation Preserve pseudomorphic nature of the Si x Ge 1-x /Si interface Electrical properties of Hf-silicate films improved by N 2 anneal at 350 C Electrical properties of Hf-silicate/Si x Ge 1-x degrade after forming gas anneal Possible explanation: reduction of GeO 2 in the Si x Ge 1-x O 2 interfacial layer Incorporation of nitrogen in hafnium silicate might enhance interface stability

20 Acknowledgements University of North Texas Dr. Prakaipetch Punchaipetch Mr. Gaurang Pant Mr. Chun Yao Mr. Junjiang (Jason) Liu (TAMS student) Dr. David Strivay (Visiting scientist- 2001) Ms. Danni Su Financial Support DARPA (SPAWAR Grant no. N ) Texas Advanced Technology Program Texas Instruments Dr. Manuel Quevedo-Lopez