Rakesh Sohal

Under the Supervisionof

Prof. Dr. Dieter Schmeißer

Chemical Vapour Deposition of 3C-SiC

Lehrstuhl für Angewandte Physik - SensorikBrandenburgische Technische Universität Cottbus, Germany

• Introduction•Motivation: Why SiC /3C-SiC?•Chemical Vapour Deposition•CVD of 3C-SiC

• ExperimentalSubstrate CleaningCarbonization & Growth

• ResultsXPS FTIR XRD

• Conclusions• Future Directions

Outline

•First Germanium then Silicon•Bang gap larger than Ge•Stable & high quality SiO2 can be grown•Larger intrinsic resistivity•Economically cheap

Ge Si III-V, II-VI Silicon Carbide

Silicon is so great, why do we need anything else ?

Introduction - Semiconductors

•Good Mechanical Properties•Wide Band Gap ( 2.2 - 3.3 eV)•High Thermal Conductivity 3.2 W cm-1K-1 for 3C-SiC•High Breakdown electric field•High Saturation electron drift velocity•High forward current density

SiC have Distinguished properties

•IV-IV Compound•Discovered in 1824 by Berzelius•Initially used for Grinding and Cutting•SiC realized to be high (temperature/power/frequency)semiconductor at early stage of Si development•Problem of Single Crystal Growth•1955-Lely Solved the problem - Modified Lely Process•Heteroepitaxial Growth on Silicon Wafers

POLYTYPISM

Silicon Carbide - An Introduction

•Polymorphism- Same compound & different Crystal structure•One dimensional polymorphism is termed POLYTYPISM

ABCBABCB

ABABABAB

Stacking Order in SiC Polytypes

3C-SiC 2H-SiC 4H-SiC

Polytypism in SiC

ABCABCABC

4H SiC

- C

- Si

Zinc Blend

SiC - Crystal Structures

3C-SiC

Hexagonal Close Packed

5.43 4.36 3.07 3.08

2.23

SiC Comparison with others

CFM

OF

0

200

400

Si GaAs 6H-SiC 4H-SiC

EEB

CFOMSi

BS

20

2

0

•Johnson‘s figure of merit•Keyes‘s figure of merit•Baliga‘s figure of merit

Combined Figure of Merit (CFOM)

Material functions well beyond the limits• high temperature• high power • high radiation conditions • Chemically harsh environments

Applications • high voltage switching for energy saving in electric power distribution• sensors and controls for cleaner burning• components for more fuel efficient jet aircraft and car engines• more powerful microwave electronics for radar and • communications higher operating voltages and wide operating temperature ranges.

SiC Materials Technology

• Wide band gap semiconductor

• Excellent mechanical, chemical, and physical properties

• SiC is a good candidate for high power electronic devices and MEMS/NEMS.

• Gas sensors in high temperature environment

Motivation

•Acheson Process - reduction of quartz sand, pure Cin electric discharge oven•Van-Arkel Process - thermal decomposition of precursors on hot graphite•Lely Process•LPE•MBE•Chemical Vapour Deposition

SiC Production

Chemical Constituents react in vapour phase near or on heated substrate to form thin films or powder

Chemical Vapour Deposition

Widely used to fabricate Semiconductor Devices

CVD Types - APCVD, LPCVD, PECVD and MOCVD

Substrate

CVD Essentials

ReactorPrecursor

Activation Energy

Gas phase products

Solid products(Thin films or Powders)

CVD Essentials

• Precursor vapourization and transport to reactor

•Diffusion of precursor molecules across boundary layer

•Decomposition of precursor molecules and incorporation into solid film

•Recombination of molecular byproducts and desorption in Gas phase

Fundamental CVD Steps

•Reactor geometry •Process parametersFlow rates, temperature, pressure and time•Chemical reactions•Transport phenomena - mass/heat transport•Kinetics & Thermodynamics

So, CVD technique combines several scientific and engineering disciplines

Film - Quality Control

103/T

Gro

wth

rat

eA

B

A. Mass transport or diffusion limitedB. Reaction rate limited

Temperature role in CVD

•Epitaxial growth ?•Considerable factors for epitaxial growth(i) thermal & lattice mismatch(ii) deposition temperature(iii) rate of deposition(iv) surface contamination and defects

20% lattice and 8% thermal expansion coefficient mismatch between Si and 3C-SiC

3C-SiC epitaxial growth by CVD

Japan

Nagaoka University of TechnologyTriod Plasma CVD using dimethylsilane, substrate heating by same method, in-situ RHEED analysis, observed the temperature when growth starts

Hoya CorporationStudied the effect of alternate supply of gases, growth on undulated substrates, could deposite 200µm thick layer in 5hrs.

SiC CVD working Groups

Effect of Undulated surface

Korea

Korea Research Institute of Chemical Technology

LP-MOCVD using single precursor, 750-970°C, deposited polycrystalline layers, Also studied the effect of different heating ramp rate > 1.5°C/s gives polycrystalline, <1.5°C/s gives single crystalline layers.

SiC CVD working Groups (contd.)

USA

Nishino @ Lewis Research CentreAPCVD using silane+propane or HMDS, Studied the effect of H2 poor ambient using Ar, Studied the effect of using Coated & uncoated graphite susceptor, Introduced buffer layer to minimize effect of lattice mismatch, Deposited of full wafer and studied the uniformity on different positions

Y. Gao @ Kansas State UniversityStudied the effect of adding HCL Gas - Improved crystallinity and stoichiometry, and eliminates Oxygen content.HCL eliminates Si nucleation, HCL allows the adsorbed species more time

SiC CVD working Groups (contd.)

Germany

TU - BraunschweigCVD with UV stimulation alongwith heating, Also done some patterning of grown layers

Angewandte Physik - Sensorik @ BTU CottbusStudied Buffer layer formation with LPCVD using acetelene & Trichlorosilane

SiC CVD working Groups (contd.)

CVD of 3C-SiC @

Angewandte Physik - SensorikBTU Cottbus

To Rotary pump

PC for MFCs control during carbonization and growth

Reaction chamber

Tubing to TCSilane cylinder

MFC for TCS

Pyrometer

Low pressure guage head

MFC for Hydrogen

MFC for Acetelene

High pressure guageTurbo Pump

CVD System

Substrate holder Electrodes

SubstrateHolding clips

Window for loading

Temperature range

400°C to 1200°C

Substrate Holder

Experimental

•Substrate Cleaning - cleaned in HF for 2min then rinsed in DI

water

•Carbonization & Growth

Gas flow rate (sccm) Pressure (mbar)

Temperature (°C)

Time (min.)

Carbonization

GROWTH

8 X 10-1 1000 - 1200 3

1.4 1000 - 1200 10 - 30

CVD Process Parameters

TCS Ac. H2

0 5 50

50525

Results - FTIR Spectra after Carbonization

600 700 800 900 1000

1200 °C

1100 °C

1000 °C900 °C

600 °C800 °C

Tran

smis

sion

(a.u

)

Wave number (cm-1)

795cm-1

Optimum temperature: 1200>Tc >1000

Results - FTIR peak width after Carbonization

1000 1050 1100 1150 1200

46

48

50

52

54

56

58

60

62

64

66

position (796.40)

position (804.17)

position (804.17)Pe

ak w

idth

Carbonization temperature (°C)

Peak width vs Carbonization Temperature

Note: Carbonization at higher temperature results peaks at higher values

Results - FTIR Spectra after 10 min. Growth

500 600 700 800 900 1000 1100

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

794

795

798

796

Gr1100°C

Gr1200°C

Gr1000°C

Tran

smitt

ance

(%)

Wavenumber

Different Growth temperature with Carbonization temp. 1000°C

500 600 700 800 900 1000 1100

0

20

40

60

80

100

120 794

796

794

795

Gr-1200°C

Gr-1000°C

Gr-1100°C

Tran

smitt

ance

(%)

Wavenumber

Different Growth temperatures with Carbonization temp. 1100°C

Note: All peaks position is around 795cm-1 which corresponds to SiC.Growth at lower temperature shifts the peak position to higher value.

Effect of Substrate Temperature

Results - FTIR Spectra after 10 min. Growth

500 600 700 800 900 1000 1100

0

20

40

60

80

100794

796

798

C-1100°C

C-1000°C

Tran

smitt

ance

(%)

Wavenumber

Diff. Carbonization temp with Growth temperature 1000°C

500 600 700 800 900 1000 11000

20

40

60

80

100

120

140

794

794

794

C-1100°C

C-1000°C

Tran

smitt

ance

(%)

Wavenumber

Diff. Carbonization temp with growth temp 1100°C

500 600 700 800 900 1000 1100

0

20

40

60

80

100

120

140

794

795

794

C-1000°C

C-1100°C

Tran

smitt

ance

(%)

Wavenumber

Diff. Carbonization temperatures with growth temp.1200°C

Results - FTIR peak width & Area

Carbonization

Growth

1000°C 1100°C

1000°C 88 1231100°C 42 381200°C 129 32

Carbonization

Growth

1000°C 1100°C

1000°C 9693 152871100°C 5450 34621200°C 13638 4367

WIDTH AREA

Notes: 1. Both width and area are very large2. Suitable for our CVD System

Results - FTIR peak width Vs. Growth temperature

1000 1050 1100 1150 120020

40

60

80

100

120

140

C-1000°C

C-1100°C

Pea

k w

idth

Growth temperature (°C)

C. Serre et al Sensors and Actuators 169-173, 74(1999)Note: Obtained FWHM is below 42 cm-1

Results - FTIR Spectra after 30 min. Growth

500 600 700 800 900 1000 1100

10

20

30

40

50

60

70

80

90

100

110

120Width

798

65

94

65 1111a

1111b

1111c

Tran

smitt

ance

(%)

Wavenumber

500 600 700 800 900 1000 1100

0

20

40

60

80

100

120 Width

796

92

46

119 1112a

1112b

1112c

Tran

smitt

ance

(%)

Wavenumber

500 600 700 800 900 1000 1100

40

50

60

70

80

90

100

110

120

130

140

Width

802

50

77

65

1011c

1011b

1011a

Tran

smitt

ance

(%)

Wavenumber Note: •Peak positions are consistent for same growth

parameters•Carbonization at 1000°C results higher peak

position.•Carbonization at 1100°C and growth at 1200°C

results less strained layers•Peak intensities are higher as compared to that of

layers grown for 10 minutes •Sample 1112b was the uniform layer and its ftir

peak is also very intence and symmetric.

Results - FTIR peak intensity Vs. Growth time

0 5 10 15 20 25 30

0

20

40

60

80

100

1200°C

1100°C

Pea

k in

tens

ity

Growth time (min.)

Peak intensity is higher by 25% for 30min. Grown layer Thicker layer

Results - XRD pattern after Carbonization

20 30 40 50 60101

102

103

104

XRD -2 scan

SiC 200

Si 200

In

tens

ity [c

ps]

TwoTheta [degree]

SiC01 SiC02

Results - XRD pattern after 30 min. Growth

20 30 40 50 60 70

10

100

1000

10000

100000

Si (111)25.52

27.1

Si (111)28.46

59.8

Si (222)58.74

3C-SiC (111)35.58In

tens

ity

2 theta (degrees)

Carbonization temp. 1000°CGrowth temp. 1100°C

Probably due to 3C-SiC (220)

Results - XRD pattern after 30 min. Growth

20 30 40 50 60 70

10

100

1000

10000

100000

Inte

nstiy

2 theta (degrees)

20 30 40 50 60 70

10

100

1000

10000

100000

Inte

nsity

2 Theta (degrees)

20 30 40 50 60 70

10

100

1000

10000

100000

25.52

27.1

28.4628.26

59.8

58.74

35.58Inte

nsity

2 theta (degrees)

1011

1112

1111

Note:•Layers are probably polycrystalline 3C-SiC•Peak intensity increases with Carb. temp.•Peak intensiy/crystallinity increases with Growth temp.

Conclusions

•Films were analysed by XPS, FTIR and XRD•Substrate temperature was optimized forcarbonization and growth•Epitaxial less strained film was grown on Si(111) substrates

Future Directions .. ..

•Growth on Si (100) substrates for longertime•Growth on undulated Si substrates•SiO2 growth on SiC surface by heatingin ambient air•Electrical contacts (Schottky or Ohmic) suitable for gas sensors

Dankeschön !