crystalline sic on si technology: applications and...

Crystalline SiC on Si Technology: Applications and Perspectives

Francesca Iacopi, Li Wang, Glenn Walker, Leonie Hold,

Ben Cunning, Jisheng Han, Philip Tanner, Alan Iacopi, Sima Dimitrijev Queensland Micro- and Nanotechnology Centre,

Griffith University, Nathan 4111, Queensland, Australia

• Introduction: » WBG semiconductors and SiC on Si platform

• 3C-SiC on Si at Griffith

» Queensland Microtechnology Facility » EPI process and characteristics

• SiC application for MEMS

• SiC as intermediate layer for III-N and graphene on Si

• Summary

Queensland Micro and Nanotechnology Centre FI

Outline

Why SiC?

Queensland Micro and Nanotechnology Centre FI 3

SiC: wide bandgap, highly efficient in areas where Si is leaky (hi V, harsh environment)

Not supposed to replace, but to complement Si grow c-SiC on Silicon wafers

Ge 0.66eV

SiC (& other WBG) properties

1. Electronic: low leakage/high efficiency switches 2. Optoelectronic: emission/detection in the blue/UV 3. Mechanical: high E, SiC hi fracture strength 4. High chemical and T resistance (SiC, ZnO..) 5. Biocompatible and possible to functionalize (SiC)

6. Piezo-electrical: most wide-bandgap Note: best and most controlled properties when in c- form (polytypes)

“Green” applications: power electronics (energy), lighting (general, automotive, aerospace), micro –systems for remote

sensing and imaging (energy, environment, medical….)


• c-SiC grown as 3C (cubic poly-type) on Si (20% lattice mismatch)

• 3C-SiC on Si(111) hexagonal pattern matching 2H-GaN (3%

mismatch only!)

» good quality 3C-SiC on Si provide large platform opportunities 3C-SiC on Si for MEMS and NEMS III-N on Si (opto and power electronics)

Si Si (111) 3C-SiC

3C-SiC (111) 6H-SiC 2H-GaN 2H-AlN Sapphire Graphene

Band gap eV 1.12 (I) 1.12 (I) 2.4 (I) 2.4 (I) 3.4 3.47 (D) 6.28 (D) gapless

Lattice constant a Å 5.43 3.84 4.36 3.08 3.07 3.19 3.11 4.785 2.4

Lattice constant c Å 9.41 7.55 15.01 5.19 4.99 13

Thermal expansion coefficient (a) 10-6 K-1 2.6 2.6 3.28 3.2 5.59 5.27 6.6

Thermal conductivity W cm-1 K-1 1.3 3.6 1.3 2.85 0.25

3C-SiC on Silicon


Memory

Devices

and Circuits Power and High

Frequency

Devices

and Circuits

Optoelectronics

Solar cells

Sensors/actuators

for harsh

environments


Why c-SiC on Si? Low cost and integration!

3C-SiC on Si

Platform Technologies

Graphene on Si

technologies

Heterogeneous integration w

CMOS

Logic Devices and Circuits,

use mainstream packaging,

avoid LLO, use 3D/TSVs

Substrates for wide-band-gap semiconductors?

• SiC » device quality SiC/GaN epilayers » 4H and 6H polytypes » Only up to 4”, expensive (3” wafer ~$1000 » + $1500/epilayer) » 6” pgrm on hold (ie Cree) » Transparent, good thermal conductivity » Bulk machining available but non std


Sapphire (Al2O3)

» up to 6” (8”, 12”possible), less expensive than SiC

» Transparent

» worst thermal conductivity

» Insulating

» Mismatch, but epi III-V optimized on c-plane

Substrates for wide-band-gap semiconductors?


Silicon

» Inexpensive, electronic grade quality, large area (>300mm)

» Processing CMOS and bulk machining infrastructure available

» Non- transparent, low thermal conductivity

» Main issues: epitaxial relationship (III-V), lattice and thermal mismatch

Memory

Devices

and Circuits Power and High

Frequency

Devices

and Circuits

Optoelectronics

Solar cells

Sensors/actuators

for harsh

environments


Interest of 3C-SiC on Si: Low cost and integration

3C-SiC on Si

Platform Technologies

Graphene on Si

technologies

Heterogeneous integration w

CMOS

Logic Devices and Circuits,

use mainstream packaging,

avoid LLO, use 3D/TSVs


Interest of 3C-SiC on Si: Low cost and integration

CMOS –based

device

SiC –based

device

Heterogenous

Device/

Microsystem!

Through-

Silicon-

Vias (TSV)

SiC on Si TECHNOLOGY @ GRIFFITH


• LPCVD deposition demonstrated on large Si wafers (up to 8”, MkI) • Up to 300mm wafers (MkII, SPTS batch reactor 2012) • Optimised carbonisation steps robust barrier on Si • Low T growth (1000˚C) • Exceptional uniformity: 1.5% across 6” wafer • p and n –type doping:

» Unintentional n- type doping level ~E+18 cm-3

» n- type doping range E+17 – 5E+19 cm-3 » p-type doping range 3E+17 – 2E+19 cm-3

• Deposition and further processing in clean room environment


SiC on Si: Griffith technology

L.Wang et al., Thin Solid Films 2011

L.Wang et al, Journal of Crystal Growth, in press

Queensland Microtechnology Facility Unique facility in Australia, focus: c-SiC on silicon

CR Lithography Class 10

Ball room area Class 1000

wafer processing (6“/8”)

1.0µm lithography

Epitaxial SiC deposition on Si

Dielectric, poly and metal deposition

Plasma and wet etching


http://en.wikipedia.org/wiki/File:Tigris-Australia_location_Queensland.svg

SPTS Thermal Products Division

• Makes vertical furnaces and APCVD reactors

• Serving the MEMS, semiconductor, power, HB-LED and advanced packaging markets

• Over >2,000 systems installed in production

Griffith University - QMF

• Extensive research of SiC on silicon wafer processing capability

• Focused on developing commercial epitaxial 3C SiC on Si technology

• Targeted at LED, memory, MEMS, and power applications

SiC on Si JDA w SPTS

MkII: batch vertical furnace,

up to 300mm wafers

- Prototype @Griffith Q2 2012

- Volume production eq available

in 2013

Si substrate

Surface clean

Si substrate

SiC

Carbonization

Epitaxial growth

SiC

Si substrate


3C-SiC epitaxial sequence

within wafer uniformity +/- 1.5%

wafer-to-wafer uniformity +/-1.1%

best WWU in literature,

Note: no rotational stage

L.Wang et al., Thin Solid Films 2011


3C-SiC

Si (100)

stacking

faults

TEM – SiC on Si(100)

<100>

X-Ray Diffraction 1000nm 3C-SiC on Si(100)

Only 3C polytype detected.

Orientation same as Si substrate


FWHM=0.22o

FWHM=0.69o

X-Ray Diffraction 1000nm 3C-SiC on Si(111)

Only 3C polytype detected.

Orientation same as Si substrate.


FWHM=0.19o

FWHM=0.57o

3C-SiC FOR MEMS


• SiC: excellent mechanical properties, high T and chemical stability • SiC on Si: use Si micromachining techniques

• Sensors for harsh environments: capacitive, piezoresistive, resonant (high Q)

» Pressure

Ex.: SiC pressure sensor


SiC on Si for MEMS

D.J.Young et al, IEEE Sensors J, 2004

3C-SiC on Si(100) demonstrated

functioning up to 400˚C (capacitive)

V.Cimalla et al, J. Phys. D: Appl. Phys. 40 2007

• Harsh environments (T, P, acceleration and chemical resistance) • High f, high Q resonators, potentially better than a-SiN

» Clear advantage of c-SiC (also for burst strength/fatigue)

• Potential for bio-sensing:

» SiC is bio- and possibly hemo-compatible


SiC on Si resonant sensing

E (GPa) r (g/cm3)

a-Si3N4 200-270 3.1

c- 3C-SiC 400 3.2

a-SiC 100

1/Er=((1-ni2)/Ei)+((1-vs

2)/Es)

Nanoindentation of 3C-SiC/Si

Data courtesy of Dr.M.Martyniuk, UWA

recalculated Young’s modulus assuming n=0.2

E (SiC(100)) ~300GPa

E (SiC(111)) ~400GPa

H (3C-SiC) 25-40GPa



Stress engineering

Baseline on Si(100):

- ~ thermal stress only

(<400MPa tensile)

- Decrease vs thickness

Baseline on Si(111):

- higher tensile stress: contribution

from lattice mismatch

- slow trend vs with thickness

Residual stresses can be tuned in a large range...

• Wafer bow after removal of backside SiC deposition Queensland Micro and Nanotechnology Centre FI

Stress engineering


SiC on Si microfabrication

Cantilevers, other clamped beams:

Dry etch SiC and wet –release from Si substrate

Membranes:

Wet or dry etch Si from backside, wafer-level

<d>500mm-10mm


R.Steinmann et al, S&A 48, 1995

Diaphragm theory

both film properties and residual stresses are critical properties!

Membrane testing

1) 3D dynamic characterisation doppler vibrometer (UQ, Prof.H.Huang)

2) Bulging: tests elastic properties and strength of thin membranes

(Stanford U, Prof.R.Dauskardt)

• load-deflection behaviour

• burst resistance

• fatigue

• effects of residual stresses

• eigenfrequencies spectrum

• resonance Q factor

• effects of residual stresses


SiC as intermediate layer for GaN on Si

=> MEMS, Optoelectronics, etc…


• c-SiC grown as 3C (cubic poly-type) on Si (20% lattice mismatch)

• 3C-SiC on Si(111) hexagonal pattern matching 2H-GaN (3% mismatch

only!)

Si Si (111) 3C-SiC

3C-SiC (111) 6H-SiC 2H-GaN 2H-AlN Sapphire Graphene

Band gap eV 1.12 (I) 1.12 (I) 2.4 (I) 2.4 (I) 3.47 (D) 6.28 (D) gapless

Lattice constant a Å 5.43 3.84 4.36 3.08 3.07 3.19 3.11 4.785 2.4

Lattice constant c Å 9.41 7.55 15.01 5.19 4.99 13

2H-GaN lattice mismatch strain % 20% -3.4% 2.5% -14%

Thermal expansion coefficient (a) 10-6 K-1 2.6 2.6 3.28 3.2 5.59 5.27 6.6

2H-GaN thermal mismatch % 53% 41% 6% -18%

Thermal conductivity W cm-1 K-1 1.3 3.6 3.6 1.3 2.85 0.25

Wide-band-gap semiconductors on 3C-SiC on Silicon



SiC as buffer for III-N on Si

III-N on 3C-SiC

III-N on Si

III-N on 3C-SiC, RMS 0.227nm III-N on Si, RMS 0.416nm

Higher defect density

bunching of SFs can create

trenching in the AlN, filled by GaN

most SFs do not create defects

further than a few nm into AlN

Y.Abe et al, J.Cryst.Growth 318, 460-463, 2011

Y.Abe et al, J.J.Appl.Phys. 51, 035603, 2012

SiC as buffer for III-N on Si

Most SFs do

not propagate defects

AlN

3C-SiC(111)

Occasionally, trenching

Filled in by GaN

On Griffith samples Queensland Micro and Nanotechnology Centre FI

J.Han et al, ICSCRM 2010


Summary

1. 3C-SiC on Si @Griffith: low epi dep T, up to 200mm wafers, low stress,

excellent uniformity

2. 3C-SiC on Si: ideal platform for harsh environment, high f sensors

& resonators

1. Based on 3C-SiC, or III-N/SiC, or graphene/SiC

2. Available on large size Si wafer (8”, soon on 12”)

3. Cost efficient: use of large area Si, use Si infrastructure and

micromachining

3. Promising perspectives also in the optoelectronics and power

electronics areas by enabling high quality GaN on Si

(3C-SiC on Si devices not contemplated yet, electrically active defects need

to be controlled)

Acknowledgments

http://www.spts.com/

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