Mobile Ion Effects on SiC MOS Bias- Temperature Instability Measurements

Transcription

1 14-15 Aug U.S. Army Research, Developmen and Engineering Command Mobile Ion Effecs on SiC MOS Bias- Temperaure Insabiliy Measuremens Daniel B. Habersa Neil Goldsman (UMD), and Aivars Lelis

2 14-15 Aug Ouline Overview of modeling approach Simulaion resuls Sweep ime (rae) Sress ime Temperaure Comparison wih experimenal daa Conclusion

3 14-15 Aug MODELING APPROACH

4 Surface Band Bending ψ s [V] Aug Mehod of Analysis Self-consisenly solve: Poisson equaion in semiconducor and oxide p d 2 ψ dx 2 = λ ψ Ion ranspor in oxide = 1 q dj p dx R p n J p = q pμ dψ dx Ion charge conservaion D dp dx p dx = p o x ox, Soluions of: ψ poenial n,p elecron and hole concenraion n A, n C anion and caion concenraion Exrac: ψ s = ψ-ψ b band bending V FB ={V GB ψ s =0} flaband V mid ={V GB ψ s = ψ b ) midgap V inv ={V GB ψ s = 2ψ b ) inversion V_inv V_mid V_FB Applied Bias V GB [V]

5 Mobiliy [cm 2 / V s] Transi Time [s] Mobiliy Models and Ion Transpor 1E-06 1E-08 1E-10 1E-12 1E-14 1E-16 1E-18 1E-20 Temperaure [ C] /T [ K -1 ] Na Li K Cu H 1E-6 1E-4 1E-2 1E0 1E2 1E4 1E6 1E8 500 Å SiO 2 3 MV/cm [1] G. Greeuw and J. F. Verwey, J. Appl. Phys., vol. 56, no. 8, pp , [2] M. W. Hillen, G. Greeuw, and J. F. Verweij, J. Appl. Phys., vol. 50, no. 7, pp , Jul [3] Y. Shacham Diamand, A. Dedhia, D. Hoffseer, and W. G. Oldham, J. Elecrochem. Soc., vol. 140, no. 8, pp , Aug [4] B. Tule, Phys. Rev. B, vol. 61, no. 7, pp , Feb Ions are assumed o freely move hrough he oxide, under he influence of local field (drif) and ion concenraions (diffusion) The gae conac and semiconducor inerface are boh impermeable o ions (charge conservaion) Daa comes from published experimens measuring mobiliy of ions in SiO 2, generally Arrhenius-like μ T = μ 0 exp E a k B T Mobiliy μ can be correlaed roughly wih ransi ime, he amoun of ime aken o drif across oxide hickness ox under an applied field E = ox μe Region of ineres (as defined by operaing condiions): 25 C 200 C μs 1,000 hrs ~15 V on gae 500 Å SiO 2 ypical 5

6 14-15 Aug Simulaion Scenarios V GB ΔV consan T V GB V GB consan T versus T SiC SiO 2 Goal: o mimic realisic sress-and-measure sequences while exploring impacs of various sequencing parameers sweep ime, sress ime, and emperaure.

7 14-15 Aug Simulaion Resuls SWEEP TIME (RATE)

8 14-15 Aug Mobiliy [cm 2 / V s] Transi Time [s] Sweep Rae Analysis V GB consan T 1E Temperaure [ C] E-6 1E-08 1E-4 1E-10 1E-2 Parameers Sweep ime varied Sress ime fixed, 0s Temperaure fixed, 150 C Srucure is 500Å SiO 2 on op of 4H:SiC, doping profile similar o ypical DMOSFET 1x10 12 cm -2 Na or K ions 1E-12 1E-14 1E-16 1E-18 1E /T [ K -1 ] Na K 1E0 1E2 1E4 1E6 1E8 500 Å SiO 2 3 MV/cm

9 semiconducor oxide Aug Raw Simulaion Daa (Typical Na ) V VGB ψ [V] SiC SiO 2 log n [m -3 ] x E [V/m] SiC SiO 2 log p [m -3 ] 3x10 8 0x10 8-3x SiC SiO SiC SiO 2 SiC SiO

10 Ion Displacemen Curren [(αc ox ) -1 ] Aug Deailed Movemen of Ions During Bias Ramp (Na ) 1 ~1 μs ~10 ms ~100 s 30 MV/s 3 kv/s 300 mv/s log p [m -3 ] ~1 μs Applied Bias V GB [V] ~10 ms ~100 s V GB log p [m -3 ] log p [m -3 ]

11 Surface Band Bending ψ s [V] Aug Surface Band Bending Applied Bias Relaionship (Na ) ~1 μs ~10 ms ~100 s 30 MV/s 3 kv/s 300 mv/s Vinv down Vinv up V GB Applied Bias V GB [V]

12 Slew Rae [V/s] Aug Sweep Time [s] Inversion Volage Versus Sweep Time, Na 1E-1 1E0 1E1 1E2 ~100 s Vinv up Vinv down 2E2 2E1 2E0 2E-1 1E3 1E4 1E5 ~10 ms 2E-2 2E-3 2E-4 V GB 1E6 1E7 1E ΔV inv =V down V up ~1 μs Applied Bias V GB [V] 2E-5 2E-6

13 ψ s Hyseresis (ΔV inv ) [V] Aug Inversion Hyseresis Versus Sweep Time 0 2E-6 2E-5 2E-4 Sweep Time [s] 2E-3 2E-2 2E-1 2E0 2E1 2E2 2E3 Na -0.5 K V GB E8 ulra-fas 1E6 fas 1E4 1E2 Slew Rae [V/s] True Ion Shif slow 1E0 1E-2

14 14-15 Aug Simulaion Resuls STRESS TIME

15 14-15 Aug Mobiliy [cm 2 / V s] Transi Time [s] Sress Time Analysis V GB consan T 1E Temperaure [ C] E-6 1E-08 1E-4 1E-10 1E-2 Parameers Sweep ime fixed, 2s Sress ime varied Temperaure fixed, 150 C Srucure is 500Å SiO 2 on op of 4H:SiC, doping profile similar o ypical DMOSFET 1x10 12 cm -2 Na or K ions 1E-12 1E-14 1E-16 1E-18 1E /T [ K -1 ] Na K 1E0 1E2 1E4 1E6 1E8 500 Å SiO 2 3 MV/cm

16 Sress Time [s] Aug Inversion Volage Versus Sress Time (K ) 1E4 1E3 Vinv down Vinv up 1E2 1E1 1E0 V GB 1E-1 1E-2 1E-3 K Transi Time (390 s) C μ=4.3x10-15 cm 2 /V s Applied Bias V GB [V]

17 ψ s Hyseresis (ΔV inv ) [V] Aug Inversion Volage Hyseresis Versus Sress Time Na K V GB -2 Na Transi Time (0.83 ms) C μ=2.0x10-9 cm 2 /V s True Ion Shif Sress Time [s]

18 14-15 Aug Simulaion Resuls TEMPERATURE

19 14-15 Aug Mobiliy [cm 2 / V s] Transi Time [s] Temperaure Analysis V GB versus T 1E Temperaure [ C] E-6 1E-08 1E-4 1E-10 1E-2 Parameers Sweep ime fixed, 2s Sress ime fixed, 1000s Temperaure varied Srucure is 500Å SiO 2 on op of 4H:SiC, doping profile similar o ypical DMOSFET 1x10 12 cm -2 Na or K ions 1E-12 1E-14 1E-16 1E-18 1E /T [ K -1 ] Na K 1E0 1E2 1E4 1E6 1E8 500 Å SiO 2 3 MV/cm

20 1000/T [ K -1 ] Aug Temperaure T [ K] Inversion Volage Versus Temperaure Na K ideal Vinv Vinv up Vinv down ideal Vinv Q/Cox ideal Vinv Vinv up Vinv down ideal Vinv Q/Cox Inversion Volage V inv [V] Inversion Volage V inv [V]

21 Inversion Volage Hyseresis ΔVinv [V] Aug Inversion Volage Hyseresis Versus Temperaure Temperaure [ C] Increasing sweep ime Increasing sweep ime K -1 Na True Ion Shif Increasing sress ime /T [ K-1]

22 14-15 Aug EXPERIMENTAL COMPARISON

23 Inversion Insabiliy ΔV inv [V] Aug Decrease in Insabiliy a 25 C Mobile Ions? "clean" "diry?" 0.2 K Na E1 1E2 1E3 1E4 Sress Time [s] Experimenal ΔV inv versus sress ime a 25 C Two samples from he same wafer clean shows ypical log-ime posiive insabiliy (charge rapping) diry shows a negaive insabiliy a longer imes (mobile ions?) ΔV inv a 25 C simulaed for 1x10 12 cm -2 Na and K, hen scaled o fi Neiher ion (nor heir combinaion) appears o adequaely explain ime dependence of he observed negaive insabiliy rend! Requires excessive amouns of K (>10 13 cm -2 ), no suppored by supplemenal daa

24 Inversion Insabiliy ΔV inv [V] Aug Inversion Insabiliy ΔV inv [V] Decrease in Insabiliy as T is increased Mobile Ions? Experimenal Simulaion K ΔV, 1E12 Na ΔV, 1E A B C D E Temperaure [ C] Temperaure [ C]

25 14-15 Aug Conclusions Parameer effecs Sweep ime Fas sweeps (<< ransi imes) freeze he ions in place Slow sweeps (>> ransi imes) ions follow he bias, couner charge rapping Med. sweeps (~ ransi ime) maximizes insabiliy Sress ime Only maers when sweep is <~ ransi ime Sauraes around scale of ransi ime Temperaure No direc effec, mosly modulaion of he mobiliy Effecs are subjec o he rules for boh sweep and sress ime Iniial comparisons of a free ion ranspor and ideal semiconducor model wih experimenal daa: Does no appear o explain room-emperaure sress ime dependence of some negaive insabiliies K -like ion can roughly mach emperaure-dependen insabiliy, hough low emperaure fi is poor Na could be presen, bu no definiive evidence eiher way so far Possible improvemens o his work include: Mechanisms oher han free ranspor (e.g., rapping, neural associaions, ec.) Including effecs from oher charge mechanisms such as inerface and oxide raps (shifs are no simply addiive) Presence of muliple ion species or oher mobile srucures Exend model o MOSFET srucure, calculae I D -V GS (poenial o incorporae ino UMD 2-D model) Invering he simulaion: wha mobiliy model & charge densiy are needed o reproduce experimenal daa? How abou a mobiliy specrum analysis similar o ha used in QMSA for Hall effec? Modeling assumed he bias ramp always sared wih ion charge a gae, whereas experimenal devices sar in indeerminae condiion and daa was measured sequenially (back-and-forh sress & measure does no reurn ions o iniial condiion) Device properies for he model could have been chosen incorrecly