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Conference presentation

Data · June 2013

CITATIONS READS

50

4 authors, including: Some of the authors of this publication are also working on these related projects: CHALLENGE: 3C-SiCHetero-epitaxiALLy grown on silicon compliancE substrates and new 3C-SiC substrates for sustaiNable wide-band-Gap powEr devices View project WINSiC4AP, in the frame of ECSEL Calls 2016-1 call View project Andrea Severino STMicroelectronics

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• C. Locke

University of South Florida

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IMM

High Quality Cubic Silicon Carbide (3C-SiC) for MOS Applications

• A. Severino, F. La Via

IMM-CNR, sezione di Catania, Stradale Primosole 50, 95121, Catania, Italy

• C. Locke, S.E. Saddow

University of South Florida, EE Dept., 4202 E. Fowler Ave., 33625, Tampa, FL, USA

IMM

• Motivations for Silicon Carbide
• Material Properties and Application Fields
• 3C-SiC advantages and limitations
• 3C-SiC heteroepitaxy
• Growth process from thin to thick 3C-SiC films
• Defects in 3C-SiC
• On-axis vs Off-axis 3C-SiC films
• Towards MOS - Preliminary observation at nanoscale
• Conclusions and perspectives

Outline

IMM

Motivations for SiC

HIGH POWER APPLICATIONS RF APPLICATIONS

High EB Low on-state resistance High Eg Low ni Low leakage current High κ High thermal capability High νSAT High working frequencies

IMM

SiC advantages and drawbacks

Advantages

ü Well-established CVD growth technique ü Easy implementation of Si technology ü Chance to use SiO2 as stable gate oxide ü Ability to grow p-type and n-type material ü 3C-SiC growth on low-cost large-area Si substrates

Drawbacks

ü Anisotropy of important electrical properties in hexagonal SiC (4H, 6H-SiC) ü Limited wafer size in hexagonal SiC ü Elevated costs required to grow high- quality single crystal material

IMM

The 3C-SiC Polytype

Thermodynamically stable at lower temperature

• growth at reduced temperatures on large area Si substrates

Good electrical properties

• narrower bandgap energy (2.3 eV)
• lower density of traps at SiC/SiO2 interface
• higher electron channel mobility
• higher stability under electrical stress

Good mechanical properties

• high Young modulus (400-700 GPa) for high frequency MEMS
• stable for high working temperatures (~650 °C)

Lack of a bulk as substrate for 3C-SiC homoepitaxy Generation of stress and defects in 3C-SiC heteroepitaxy

• electrically active crystallographic defects (STACKING FAULTS)
• wafer bow

IMM

High electron mobility for MOSFET realization

Electron mobilities of monocrystalline bulk 6H-SiC and 3C-SiC thin films deposited on Si (100) off-axis towards (011)

‘Comparison of 6H-SiC, 3C-SiC and Si for Power Devices’ M. Bhatnagar, B.J. Baliga, IEEE Trans. On

• Electr. Dev. 40 (3), 645 (1993)

‘Fabrication of high performance 3C-SiC vertical MOSFETs’,

• H. Nagasawa et al., Phys. Stat. Sol. b, 245, No. 7, 1272 (2008)

IMM

The Main Limitation: Stacking Faults

STACKING FAULTS AFFECT STRONGLY THE LEAKAGE CURRENT OF P-N JUNCTION

IMM

• Horizontal HW/CW CVD Reactors
• Multi-step Chemical Vapor Deposition Process
• Various Chemistries
• Several Si orientations – Off-axis surfaces
• Modified/Compliant substrates

Growth Process

Epitaxial Reactor MF2 Sited in USF Tampa

IMM

Growth of thin films – The ‘Carbonization Step’

The initial stage of growth (buffer layer) depends on the experimental conditions

Pressure and Temperature affect: Ø Nucleation density Ø Nucleation regime Ø Interface morphology Ø Surface morphology Ø Defect generation Ø Stress nature in the system

400 Torr 760 Torr

IMM

10 20 30 40 50 500 1000 1500 2000 2500 3000 3500 4000

(200) 3C-SiC FWHM (arcsec)

3C-SiC film thickness (µm)

Growth of thick films – Defects in 3C-SiC

20% lattice mismatch between aSi and aSiC generates several crystallographic defects

XRD Rocking Curve FWHMs on surface diffraction plane

Low-defect density Better film quality High-defect density Worst film quality

Cross-section TEM of a thick 3C-SiC film

• Very high-density of crystallographic defects close

to the interface

• Better 3C-SiC quality by increasing film thickness

(narrower Rocking Curve FWHM)

• E. Polychroniadis et al., Journal of Crystal Growth 263, 68 (2004).
• A. Severino et al., Thin Solid Films, 518, S165 (2010).

IMM

Growth of thick films – The growth rate

IN ORDER TO REALIZE 3C-SiC SUITABLE FOR ELECTRONIC DEVICES OR SENSORS DEFECT DENSITY MUST BE REDUCED AND CRYSTAL QUALITY IMPROVED

Allowed by reducing the growth rate

DEFECTS, SUCH AS MICRO-TWINS, REDUCE THEIR DENSITY AT LOWER GR

IMM

Growth of on-axis thick films – Stacking Faults

Saturated regime attributed to annihilation/generation mechanism of SF?

Tending to saturation

IMM

Growth of thick films – 3C-SiC film morphology

ANTI-PHASE BOUNDARIES IN ON-AXIS FILMS MICRO-STEPS DETECTED ON BOTH FILMS STEP-BUNCHING RELATED MACRO STEPS ON OFF-AXIS FILMS ANISOTROPIC DISTRIBUTION OF STACKING FAULTS ON OFF-AXIS FILMS

IMM

Growth of thick films – Stacking Faults

LOWER STACKING FAULT LINEAR DENSITY WITH HIGHLY ANISOTROPIC DISTRIBUTION OF STACKING FAULTS IN OFF-AXIS FILMS

IMM

Growth of thick films – Stacking Fault Density

FWHM of (004) 3C-SiC Rocking Curve // [1-10] Linear Density

• f SF// [1-11]

FWHM of (004) 3C-SiC Rocking Curve // [110] Linear Density

• f SF// [111]

ON AXIS 3C-SIC FILM 349 arcsec 6.5 x 103 cm-1 380 arcsec 8 x 103 cm-1 OFF-AXIS 3C-SIC FILM 329 arcsec 6.5 x 103 cm-1 298 arcsec 2 x 103 cm-1

IMM

Oxidation of 3C-SiC films – Effect of Defects

MAIN CRYSTALLOGRAPHIC DEFECTS AFFECT THE OXIDE UNIFORMITY AND INTERFACE

ANTI-PHASE BOUNDARIES CAN BE ELIMINATED BY OFF-AXIS FILM GROWTH MICRO-TWINS ARE VANISHING FOR SUFFICIENT 3C-SIC THICKNESS STACKING FAULTS STILL SURVIVE

IMM

Electrical Characterization at Nanoscale

PRELIMINARY RESULTS

5 nm SiO2 uniform layer was thermally grown on 10 µm 3C-SiC films (on and off-axis) by RTP Oxidation in N2-O2 ambient at 1050°C followed by a RTA annealing at 800°C in pure Ar

NO EFFECT RELATED TO STACKING FAULTS OBSERVED

LARGE SIGNAL VARIATION AT STEP IN SCM MAP DUE TO LARGER CONTACT AREA OF THE TIP OR TO A LOCAL ENHANCEMENT OF THE ELECTRIC FIELD OVER THE STEPS

IMM

Experimental Flat-Band Voltage

PRELIMINARY RESULTS

LOW HYSTERESIS OBSERVED à à GOOD OXIDE PERFORMANCE NEGATIVE VFB SHIFT à à POSITIVELY CHARGED C-CLUSTER AND DANGLING BONDS HIGHER EXPERIMENTAL VFB SHIFT IN ON AXIS MATERIAL

IMM

Summary

• Silicon Carbide: excellent material properties but…
• 3C-SiC heteroepitaxy on large area Si substrates
• CVD growth process – from thin to thick 3C-SiC film growth
• Buffer layer formation
• The growth rate and film thickness on 3C-SiC film quality
• SFs show a saturation for thick film growth
• Influence of substrate orientation on SFs and morphology
• Influence of defects on oxidation morphology
• Preliminary electrical characteristic of MOS at nanoscale

IMM

Acknowledgements

• Dr. Andrea Canino for SEM analysis
• Mr. Corrado Bongiorno for TEM analysis
• Dr. Filippo Giannazzo for AFM and SCM analysis
• Dr. Patrick Fiorenza for AFM and SCM analysis

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