interface reaction kinetics

Transcription

1 Thermally oxidized SiO 2 formation on 4H-SiC substrate by considering the interface reaction kinetics Shun Nakatsubo, Tomonori Nishimura, Koji Kita, Kosuke Nagashio and Akira Toriumi Department of Materials Engineering The University of Tokyo Hongo, Tokyo , Japan This work was partly yp presented at SSDM 2011 (Nagoya). 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 1

2 Outline 1.Background and Objective 2. Sample Preparation 3. Experimental Results 4. Discussion 5. Conclusion 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 2

3 Effective WF vs. Vacuum WF Effectiv ve work fu unction (e V) Ge 0 4 Y Yb Sc Zr Ti ErLa Hf Al 5 S = 0.02 CNL 4.58eV Vacuum level n-type CB Ni Au CNL Pt VB Vacuumwork function m (ev) Effectiv ve work fu unction (e ev) Si 0 Vacuum level p-type n-type 4 CB Mg S=0.27 Y ErSc Zr Ti Ni CNL W Al 5 Au Pt VB Vacuum work function m (ev) 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 3

4 Interface Science of SiC Schottky Barrier B M S (S 1) 1 S B M 0 Ge Si SiC 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 4

5 Si Oxidation X 2 2 A t 2 A 4 B 2 Bt O 2 O 2 SiO 2 Si Si X B A t Deal Grove Model 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 5

6 Objective To demonstrate high quality SiO 2 /SiC interface in thermal oxidation i process of SiC SiO 2 SiC in O 2 SiC 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 6

7 Outline 1. Background and Objective 2.Sample Preparation 3. Experimental Results 4. Discussion 5. Conclusion 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 7

8 Kinetic Consideration of SiC Oxidation 1000 T ( C) B/ /A ratio (nm/h our) Si (Deal & Grove) Deal & Grove, JAP 36 (1965)3770. C-face Si-face T. Yamamoto et al., JJAP 47 (2008) /T (1/K) Because oxidation process is reaction limited, its rate is Si > C face SiC >> Si face SiC. 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 8

9 Kinetic Consideration of SiC Oxidation O 2 O 2 O 2 O 2 CO n SiO 2 SiO 2 SiO 2 CO n Si SiC Reaction SiC SiC No Reaction 1200ºC 800ºC 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 9

10 APL70 (1997) A uniform oxidation on nonplanar SiC by depositing Si prior to SiC oxidation Si 70 nm SiC Si Oxidation at 1050ºC in Wet O 2 Oxidation of deposited thick Si on SiC in high temperature also causes oxidation of SiC. 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 10

11 Sample Preparation Wafers Main process flow Si and C face 4H SiC Si deposition(~3 nm) 5~6 m epi layer Thermal oxidation / 800 C, dry O2 N dope ~1E16cm 3 5, 15, 50 min Back metallization i (Ni) PMA / 940 C, N2, 5 min HfO2 deposition(~10 nm) PDA / 500 C, 0.1% O2, 30 sec Au electrode Si HfO 2 SiO 2 4H-SiC NiSix 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 11

12 Why HfO 2? 1x x10-11 HfO 2 /SiO 2 /Si C (F) 6x x x kH khz 10 khz 100 khz 1 MHz V g (V) No frequency dispersion, nor hysteresis 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 12

13 Outline 1. Background and Objective 2. Sample Preparation 3.Experimental Results 4. Discussion 5. Conclusion 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 13

14 Si nessnmckthiosi2sicsi onc-faceonsi-facesic xidatnti(mcomparison between Si-face and C-face SiC - Oxidation Rate -1O 2 80Oxidizedat 800ºC )Oxidized at 800ºC SiO 2 6(0SiC SiC )Si C: nm OiomeinSi O: nm Just a monolayer SiO2 if any. Fig /1/30 IEEE EDS MQ WMNACT31 (TIT) 14

15 Comparison between Si-face and C-face SiC Bi di ti l C V Ch t i ti - Bi-directional C-V Characteristics - Si face C face4x10-75x10-71mhz3x10-74x10-71mhz2x10-73x10-7(f/cm2)100khz10khz1khz2x10-73x10(f/cm2)100khz10khz1khz01x10-72x10c01x10-7c vg(v) vg(v)dry oxidation at 800ºC for 50 min Ideal VFB Dry oxidation at 800ºC for 50 min On Si face, there are little frequency dependence and hysteresis, 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 15 and VFB is close to the ideal value.

16 Outline 1. Background and Objective 2. Sample Preparation 3. Experimental Results 4.Discussion 5. Conclusion 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 16

17 A big difference between Si-face and C-face SiC10This work8s(nm)onc-facesic6onsi-facesicthicknest. Yamamotoet al., JJAP 47 (2008) SiO2OxidationTime(min)T. Yamamoto et al., JJAP 47 (2008)7803. Although oxidation rate is significantly different, a same amount of C should be introduced into On Si face, no carbon will be introduced Into SiO2, because of negligible oxidation of Si face SiC. a given thickness of SiO 2. gg We can make a carbon free SiO 2 on Si face SiC 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 17 by low temperature oxidation of Si/SiC.

18 Conclusion and Future Outlook Good C V characteristics insic MOS capacitors have been demonstrated simply by oxidation in dry O 2 at 800ºC, on the basis of thermodynamic and kinetic consideration. High k dielectric films will be applicable for SiC gate stacks by using stable interfacial SiO 2 layer. SiC interface research is old but will be a hot topic. Si face is much better than C face due to a considerably lower oxidation rate in the present method. MOSFET fabrication and characterization will be the next challenge. 2012/1/30 IEEE EDS MQ WMNACT31 (TIT) 18