Nuclear Reaction Profiling unraveling the incorporation of water in SiO 2 /SiC structures

Transcription

1 Nuclear Reaction Profiling unraveling the incorporation of water in SiO 2 /SiC structures Fernanda Chiarello Stedile, E. Pitthan, S. A. Corrêa, G. V. Soares, and C. Radtke Universidade Federal do Rio Grande do Sul: UFRGS Porto Alegre, Brazil HRDP 2016

2 Why SiC? Silicon Silicon carbide Bandgap Saturation drift velocity Mobility Thermal conductivity Breakdown el. field high temperature high voltage high power high frequency SiO 2 native oxide thermal oxidation

3 Water related problems in microelectronics humidity in a clean room fabrication facility is between 30 and 50% negative oxide charge buildup near the SiO 2 /Si interface increases in the interface state density already reported for SiO 2 /Si negative-bias-temperature instabilities attributed to water related species at the SiO 2 /Si interface

4 Challenges in SiC technology High interface states density (D it ) SiO 2 water vapor: D 2 O SiC Instabilities during operation

5 Water vapor incorporation in thermally grown SiO 2 /Si and SiO 2 /SiC: - Isotopically enriched gas - Nuclear reaction analyses thermal SiO 2 Silicon thermal SiO 2 4H-SiC (Si Face) G.V. Soares et al. Appl. Phys. Lett. 95 (2009) G.V. Soares et al. Electrochem. Solid-State Letters, 13 (2010) G95 S.A. Corrêa et al. NIMB 273 (2012) 139

6 SiO 2 thermal growth: 1100 C, 100 mbar dry natural 16 O 2 + vacuum annealing: 10-7 mbar, 700 C, 30 min

7 Water vapor (D 2 O) exposures: 1h, C, 10 mbar Válvula 1 Válvula 2 D2 O Líquido Vapor de Trabalho de D O 2 Válvula 1 Válvula 2 Vapor de D 2 O D2 O Líquido L N 2 Water partial pressure in air of 30% humidity at 25 C D 2 O O : natural abundance of 0.2% D : natural abundance of 0.015%

8 O quantification and profiling NRA NRP

9 D quantification D( 3 He,p) 4 He at 700 kev protons spectrum D( 3 He,p) 4 He 3 He + (< 700 kev) counts Channel sensitivity ~ 4.0 x D.cm -2 Accuracy: 10%

10 Areal density of O in Si dioxide films versus time of chemical dissolution in diluted HF-solution. Areal densities of deuterium in SiO 2 films on Si as a function of chemical etching time. The corresponding D profiles determined by differentiation are shown in the insets: (a) as-loaded with D 2 ; (b) loaded with D 2 and annealed in vacuum at 450 C for 30 min. I.J.R. Baumvol Surface Science Reports 36 (1999) 1

11 thermal SiO 2 SiC or Si O areal densities initial t ox = 7 nm SiO 2 /SiC SiO 2 /Si Oxygen areal density (at x cm -2 ) O D 2 O exposure temperature (ºC) O D 2 O exposure temperature (ºC) O(p, ) kev

12 thermal SiO 2 SiC or Si O and 16 O areal densities SiO 2 /SiC SiO 2 /Si Oxygen areal density (at x cm -2 ) O 16 O D 2 O exposure temperature (ºC) O 16 O D 2 O exposure temperature ( C) 16 O: c-rbs, He + at 2 MeV

13 thermal SiO 2 SiC or Si O and 16 O areal densities SiO 2 /SiC SiO 2 /Si Oxygen areal density (at x cm -2 ) O 16 O O + 16 O D 2 O exposure temperature ( C) O 16 O O + 16 O D 2 O exposure temperature ( C)

14 D profiles in Si 16 O 2 /SiC and in Si 16 O 2 /Si initial t ox = 6 nm T = 600ºC D concentration (10 20 at x cm -3 ) ºC Depth (nm) interface D concentration (10 20 at x cm -3 ) ºC interface Depth (nm) D( 3 He,p) 4 He at 700 kev

15 D profiles in Si 16 O 2 /SiC and in Si 16 O 2 /Si D concentration (10 20 at x cm -3 ) ºC 600ºC Depth (nm) D concentration (10 20 at x cm -3 ) ºC 600ºC Depth (nm) D( 3 He,p) 4 He at 700 kev

16 Samples preparation Si 16 O 2 6nm Si 16 O 2 10 nm Si 16 O 2 20 nm Si 16 O 2 50 nm 6H-SiC(0001) 6H-SiC(0001) 6H-SiC(0001) 6H-SiC(0001) 1. SiO 2 thermal growth: 1100 C, 100 mbar dry 16 O 2 2. Vacuum annealing: 700 C, 30 min 3. Water vapor (D 2 O) exposure: 1h, C, 10 mbar Si 16 O 2 6nm Si 16 O 2 10 nm Si 16 O 2 20 nm Si 16 O 2 50 nm Si(001) Si(001) Si(001) Si(001)

17 D incorpora on for oxide film thickness D areal density (10 13 at x cm -2 ) Si 16 O 2 /SiC Si 16 O 2 /Si 20 C Si 16 O 2 thickness (nm) D areal density (10 13 at x cm -2 ) C Si 16 O 2 thickness (nm) D areal density (10 13 at x cm -2 ) C Si 16 O 2 thickness (nm)

18 Alpha Yield (a.u.) Alpha Yield (a.u.) O excitation curves SiO 2 /SiC SiO 2 /Si Proton beam energy (kev) 20 C 1000 C Proton beam energy (kev) Proton beam energy (kev) Proton beam energy (kev)

19 O profiles SiO 2 /SiC SiO 20 C 2 /Si Depth (nm) Depth (nm) 1000 C Depth (nm) Depth (nm) O concentration (10 22 at x cm -3 ) O concentration (10 22 at x cm -3 )

20 Partial conclusions In SiC samples, in any exposure temperature, O from water is incorporated in all depths of the oxide films, mainly by isotopic exchange, reaching the SiO 2 /SiC interface, in contrast to SiO 2 /Si. In SiO 2 /SiC, D is transported and incorporated in the surface, bulk, and interface regions, whereas in SiO 2 /Si, it is observed only in near-surface regions of the oxide. In SiO 2 /SiC, the amount of incorporated D increases continuously with temperature and with initial oxide thickness, whileinsio 2 /Si there is no such dependence.

21 Influence of thermal conditions in the quality of the SiO 2 /SiC Longer oxidation times lead to higher D it and negative fixed charges SiO 2 x SiC x H. Watanabe et al. Appl. Phys. Lett. 99, (2011)

22 Influence of thermal conditions in the quality of the SiO 2 /SiC Longer oxidation times lead to higher D it and negative fixed charges SiO 2 x x SiC x H. Watanabe et al. Appl. Phys. Lett. 99, (2011)

23 Influence of thermal conditions in the quality of the SiO 2 /SiC Longer oxidation times lead to higher D it and negative fixed charges SiO 2 x x xx x SiC x x H. Watanabe et al. Appl. Phys. Lett. 99, (2011)

24 Alternative method to improve the SiO 2 /SiC interface quality Thermally grow a very thin and stoichiometric SiO 2 film to minimize the electrical degradation from the oxidation Deposition of a SiO 2 film to obtain a thicker film SiO 2 dep. SiC Thermal SiO 2 E. Pitthan et al. ECS Solid State Letters, 2 (2013) P8

25 Clean SiO 2 SiC x O y SiC X-ray Photoelectron Spectroscopy Intensity (a.u.) 0 min 5 min 10 min Si 2p photoelectron spectra at a take-off angle sensitive to the surface of Si-faced 4H-SiC samples thermally oxidized at 1100 C in 100 mbar of O 2 for different oxidation times, as indicated. 20 min Binding Energy (ev) E. Pitthan et al. ECS Solid State Letters, 2 (2013) P8

26 Samples dep. SiO 2 Silicon dep. SiO 2 4H-SiC (Si Face) dep. SiO 2 thermal SiO 2 4H-SiC (Si Face) thermal SiO 2 S.A. Corrêa et al. NIM B 332 (2014) H-SiC (Si Face)

27 Influence of substrate and of temperature in D 2 O vapor incorporation D areal density (10 13 at.cm -2 ) H-SiC Si remaining 20 nm D SiO ~ 90% 2 dep. Substrate HF D( 3 He,p) 4 He at 700 kev D 2 O exposure temperature ( C)

28 O profiles SiO 2 /SiC + 10 mbar D 2 O, 1h Counts (u.a.) O conc. (10 22 at.cm -3 ) Thickness (nm) 600 C ( thermal) 600 C (deposited) 800 C (deposited) Defects present in the surface region of the film thermally grown Larger O isotopic exchange in the bulk of the deposited film: larger concentration of defects? Proton energy (kev) E. Pitthan et al. Appl. Phys. Lett. 104 (2014)

29 O profiles SiO 2 /SiC + 10 mbar D 2 O, 1h Counts (u.a.) O conc. (10 22 át.cm -3 ) Espessura (nm) 600 C ( thermal) 600 C (deposited) 800 C (deposited) 16 O- O total isotopic exchange Similarly to the case of films thermally grown Proton energy (kev) E. Pitthan et al. Appl. Phys. Lett. 104 (2014)

30 Effect of oxidation prior to the deposition O 2 : 1h in 100 mbar of natural O 1100 C for 5 min D areal density (10 13 at.cm -2 ) as deposited SiO 2 film oxidation in O 2 + SiO 2 deposition D 2 O exposure temperature ( C) 20 nm dep. SiO 2 4H-SiC Si-face dep. SiO 2 thermal SiO 2 4H-SiC (Si Face)

31 Pre-deposition oxidation times D areal density (10 13 at.cm -2 ) h in O 2 + SiO 2 deposition 1 h in O 2 + SiO 2 deposition 5 min in O 2 + SiO 2 deposition D 2 O exposure temperature ( C) dep. SiO 2 thermal SiO 2 4H-SiC (Si Face)

32 D incorporation for different routes D areal density (10 13 at.cm -2 ) as deposited SiO 2 film thermally grown SiO 2 film 5 min in O 2 + SiO 2 deposition D 2 O exposure temperature ( C) E. Pitthan et al. Appl. Phys. Lett. 104 (2014) dep. SiO 2 4H-SiC (Si Face) thermal SiO 2 4H-SiC (Si Face) dep. SiO 2 thermal SiO 2 4H-SiC (Si Face)

33 Interaction of D 2 O with SiO 2 /SiC 5 min oxidation Oxidation in O 2 SiO 2 deposition + SiO 2 deposition Al Al Al Significant reduction in the negative effective charge in MOS capacitors after D 2 O exposure E. Pitthan et al. Appl. Phys. Lett. 104 (2014)

34 5 min oxidation + SiO 2 deposition X Ray Reflectivity (XRR) without interfacial layer with interfacial layer Intensidade Intensity (counts/s) (contagens/s) O 2 SiO SiO nm SiO 2 /SiC SiC (0001) SiC (0001) = 2.10 g/cm 3 = 2.75 g/cm 3 = 3.21 g/cm 3 0,2 0,4 0,6 0,8 1,0 1,2 1,4 ângulo Incident incidência angle ( ) (graus) E. Pitthan et al. Appl. Phys. Lett. 104 (2014)

35 @ 800 C without interfacial layer SiO 2 SiC (0001)

36 Partial Conclusions D incorporation in dep.sio 2 /SiC and dep.sio 2 /Si structures occurs mainly in the SiO 2 /semiconductor interface region Water vapor exposure at 800 C led to total isotopic exchange between O from water and 16 O present in the dep. SiO 2 film The thermal growth of SiO 2 prior to its deposition on SiC reduced the incorporation of D D incorporation increases with the oxidation time and exposure temperature for SiO 2 /SiC The incorporation of D depends on the route employed to obtain SiO 2 films on SiC

37 General Conclusions The route employed to obtain SiO 2 films on SiC has a great influence in the incorporation of O and of D from water vapor exposures Larger incorporation of D electrical defects larger amounts of Water vapor exposures led to the removal of the interfacial layer between the SiO 2 film and SiC reduced the effective negative charge in all tested structures High-Resolution Depth Profiling techniques were crucial to unravel these facts

38 Acknowledgements

39 Thank you!