NBTI and Spin Dependent Charge Pumping in 4H-SiC MOSFETs

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1 NBTI and Spin Dependent Charge Pumping in 4H-SiC MOSFETs Mark A. Anders, Patrick M. Lenahan, Pennsylvania State University Aivars Lelis, US Army Research Laboratory

2 Energy Deviations from the resonance condition provide useful information about the nature of specific defects Spin-Orbit Coupling: due to electron s orbital angular momentum about the nucleus E h g e H g H + m I A Electron-Nuclear Hyperfine Interaction: due to nearby nucleus with magnetic moment Magnetic Field At resonance, spin flips

3 In the data shown, the factor most responsible for deviations from hv=g e βh Bohr model: electron orbits nucleus; angular momentum n h (units of h). To an observer on the electron, it looks like the nucleus is orbiting the electron. The greater the nuclear charge and orbital angular momentum quantum number, the greater the spin orbit coupling. The orbiting nucleus looks like a current loop generating a magnetic field. This contribution is expressed in the g tensor.

4 Problem Conventional EPR has a sensitivity of about total paramagnetic defects It is also sensitive to ALL paramagnetic defects in a sample 1. We want to identify defects in transistors 2. We want to know what different defects do to device performance A main problem for electronic materials science is performing resonance inside fully processed transistors in integrated circuits EDMR provides sensitivity about 7 orders of magnitude higher than conventional EPR Solution: EDMR, spin dependent recombination (SDR), and spin dependent trap-assisted tunneling (SDT)

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7 What Are These Defects? Anticipated spectrum of the negatively charged silicon vacancy with the field parallel to the c-axis utilizing the hyperfine parameters of Isoya et al. J. Isoya, T. Umeda, N. Mizuochi, N. T. Son, E. Janzen, and T. Ohshima, Phys. Status Solidi B 245(7), 1298 (2008). 7

8 Silicon Vacancy Model Experimental Results 8

9 x5 Pre-stress x5 190 o C x5 Post-stress Hydrogen or Nitrogen related defect At interface, bulk, or possibly oxide Possible nitrogen related defect At interface or bulk

10 Utilizing VDMOSFET geometry, we probe bulk defects Biasing scheme: Strongly accumulate channel Forward bias drain/body diode Bulk recombination dominant current i N+ Source P+ N+ P Gate -V g Source P+ N+ Gate P accumulated channel N SiC Epi N+ SiC substrate Drain V d 10

11 150, or 250, or 360 MHz (low field) vs. ~9.5 GHz (X-band) Broadening due to g is field/frequency dependent Broadening due to hyperfine interactions is field/frequency independent (to first order) Simulated using easyspin 11

12 X-band Low field Previously, X-band measurements suggests broadening due to g or hyperfine EDMR measurements at low field reveal that broadening is at least partially due to hyperfine interactions 12

13 This technique is appropriate for levels around mid-gap. It does not, however, address traps near the band edges. We are interested in what s happening near the conduction band and valence band. Spin dependent charge pumping: a solution. 13

14 By utilizing a pulse wave at the gate voltage, we can explore more of the band gap with larger amplitude. 14

15 Gate Voltage G S oxide n+ n+ D Waveform Generator a a a b b c c i p semiconductor time (Vary b Voltage) (a) E F (b) E F (c) Flood interface with holes to recombine with interface trap electrons E F Fill Traps Allow time for traps above E F to empty

16 Enhanced sensitivity (2000x greater)

17 NO-annealed pmosfet Probing states throughout most of the bandgap shows a different line shape and broader center line compared to only mid-gap states 17

18 BAE SDCP The full bandgap spectra have g-values much lower than the mid-gap spectra in this sample Mid gap (BAE) spectra are mostly due to silicon vacancy 18

19 350 MHz ~9.5 GHz c-axis parallel to magnetic field c-axis parallel to magnetic field C-axis is parallel to magnetic field NO annealed nmosfet has broader shoulders than an nmosfet which did not receive an NO anneal Many abundant magnetic nuclei, likely nitrogen, would cause broadening 19

20 350 MHz ~9.5 GHz NO annealed nmosfet has a broader center line at both high and low fields Many abundant magnetic nuclei, likely nitrogen, would cause broadening 20

21 ~9.5 GHz The NO annealed device spectra is much broader than the non-no device spectra More evidence for Nitrogen hyperfine interactions 21

22 C dangling bond: g //c = g c = J. L. Cantin et al. If carbon dangling bonds largely contributed to the interface state density, we would observe a line at g //c = and g c = We do not. There are no carbon dangling bonds at the interface. 22

23 Non-NO nmosfet 23

24 Non-NO nmosfet Side peak amplitudes are reduced Defect responsible for side peaks are not near the conduction band edge 24

25 w/out NO nmosfet NO nmosfet Lower charge pumping frequencies probe further into the oxide Could provide a way to look a little into the gate oxide More work needs to be done to fully understand multi-frequency SDCP results 25

26 Low -field EDMR: GaN p-n diode The complex spectra is clearly due to hyperfine interactions 26

27 EDMR Amplitude vs Gate Bias EDMR amplitude of several different spectrum peaks Calculated recombination current 27