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矽鍺技術SiGe Technology

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smif 矽鍺技術課程

• 雙極元件是矽基元件中，速度最快，電流驅動力最強的一族。而矽鍺元件則是雙極元件中最令人著目的新興技術。本課程中將指導學生SiGe元件的製作技術，帶溝工程，SiGe/Si HBT，MODFET之元件設計及用於光電元件之考量。

• Introduction• SiGe basic physical and mechanical properties• Synthesis methods• Characterization of SiGealloy• Integration issue in IC process• New trend in SiGe

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教科書:E. Kasper, “Properties of strained and relaxed silicon germanium”IEE publication, 2000

成績評量方式: midterm 40%, final report 50% final exam 10% 歡迎電子/電機/物理相關科系研究生選修，將視同學程度,調整授課深、廣度。█上課地點：教學411 █上課時間：5-FGH

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smif Outline

1. Introduction

2. SiGe basic physical and mechanical properties

3. Synthesis methods

4. Characterization of SiGe alloy

5. Integration issue in IC process

6. New trend in SiGe

7. Conclusions

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1. Introduction

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smif SiGe lattice and band gap

aSi: 0.543 nmaGe: 0.5646 nm

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smif Applications of SiGe alloy

• Increases the speed of bipolar transistors, allowing SiGe to move into 3-

GHz wireless, high-speed data communications and other traditional GaAs applications and in 20-GHz applications like optical fiber, DBS,

home-RF, WLAN and 'last mile' data connections.

• Because SiGe circuits can be fabricated on existing (slightly modified) process lines, they should cost little more than conventional bipolar.

• SiGe BiCMOS for telecommunication

• Strained Si and Ge in MOSFET

• For the compound market, the ratio of SiGe increase from 16% to 38% (From Solid State Technology, July 2002, p.52.)

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Strained and relaxed SiGe

Pseudomorphic

Strained

Relaxed

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smif SiGe alloy phase diagram

Ge melting point

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smif Mechanical property of SiGe

Ge concentration

Lattice constant of SiGe

Vegard’s law

aSiGe = (1-x)*aSi+ x* aGe-0.0272*x*(1- x)

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smif Strain relaxation mechanism

Misfit dislocation

Surface roughness (wavy)

Growth temperature effect

Ge concentration

Growthtemperature

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smif Electronic band of SiGe

EC

EvRelaxed Si Relaxed Si

RelaxedSiGe

StrainedSiGe

Relaxed SiGeStrained Si

Ec

Ev

3

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smif Carrier mobility in SiGe

Electron mobility in SiGe

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II. Synthesis methods

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smif Synthesis methods for SiGe

• Molecular beam epitaxy (MBE)

• Chemical vapor deposition (CVD)

• Liquid phase epitaxy (LPE)

• Solid phase epitaxy (SPE)

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smif MBE system

MBE system

REED spectrumIncluding GSMBE and SSMBE

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smif CVD methods for SiGe

• APCVD

• LPCVD

• RTCVD

• LEPECVD

• UHVCVD

• UHV-LPCVD

The main difference:Pressure and temperature

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smif Epitaxy requirement

• Precursor gas purity (need purifier)

• Growth environment (residual O2 and H2O

ppm)

• Surface conditions (free of contaminations)

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smif Surface cleaning methods

• High temperature H2 baking

SiO2(s) + H2(V) -> 2SiO (v) + H2O (v)

• High temperature desorption

SiO2(s) + Si (s) -> 2 SiO (v)

• Ion gun sputtering

• H2 plasma treatment

• HF dip ( H-passivation)

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smif H2O partial pressure vs. temperature

Form SiO2

Epitaxy region

G. Ghidini and F. W. Smith, J. ElectrocChem. Soc. 131 (1984), 2924

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smif SiGe epitaxial mechanism in CVDGates et al. (1990) proposed

2SiH4 + 4 Si - > 2H (s) + 2SiH3 (s)

2SiH3 (s) + 2Si - > 2H (s) + 2SiH2 (s)

2SiH2 (s) -> 2SiH (s) + H2 (g)

2 SiH (s) - > Si (s) + H2 (g) + 2-

B. Cunningham et al. (1991) suggested Ge

2GeH4 + 4 - > 2H (s) + 2GeH3 (s)

2GeH3 (s) + 2 - > 2H (s) + 2GeH2 (s)

2GeH2 (s) -> 2GeH (s) + H2 (g)

2 GeH (s) - > Ge (s) + H2 (g) + 2-

From Appl. Phys. Lett 59, (1991)3574

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From J. Electrochem. Soc. 142 (1995) 2458

1. High temperature2. Native oxide impede the epitaxial growth

H desorption

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smif LPCVD or UHV-LPCVD

Kinetic mechanism

S. M. Jang et al. propose

x/(1-x) = m×PGeH4/PSiH4

Here:x : the concentration of Ge

PX: x gas partial pressure

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RTCVD Module•Derived from field-proven stand-alone epitaxy system

•Blanket and selective Si andSiGe epitaxy processes

•Polycrystalline Si and SiGe(in-situ) doped for gate electrodes

•Silicon-nitride for advanced gate dielectrics and other applications •Oxidation and nitridation ofsilicon or silicon-oxide surfaces

•Rapid thermal annealing (RTA)

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•High deposition rate

•In situ plasma cleaning, remove the surface contamination

•Growth rate is independent on the temperature

Key point: low energy plasmaavoid damage;reduce the thermal budget

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smif Hot wall UHVCVD

A: pump system

B: furnace

C: reactor tube

D: loader chamber

E: air clean module

F: pump system of loader

G: gas box

RCA 1

RCA2

HF dip

Evac. in loader

Epitaxial growth

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SiGe epitaxy growth using SiH4 and GeH4

H coverage vs. SiH4 flux and temperatureGrowth rate vs. concentration and temperature

From J. Appl. Phys. 69, (1991) 3729

Defects in Si epitaxy

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smif Ge concentration and growth rate

0 2 4 6 8 10 1 20

5

1 0

1 5

2 0

Pe

rce

nt G

e in

so

lid

Percent Ge in gas

From Appl. Phys. Lett. 48, (1988) 2555

0 5 10 15 200

1

2

3

4

5

6

7

8

Gro

wth

rat

e (n

m)

Percent Ge in soild

HF dip pretreatment

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smif Dopant v s. flow rate

P dopant vs. flow rate N dopant vs. flow rate

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smif Hydrogen effect in SiGe epitaxial growth

1. Maintain the Si/Ge interface abruptness

2. Suppress the intermixing of Si/Ge

3. Prevent the roughness

4. Prevent the segregation of Ge

Without H

With H

From Appl. Phys. Lett. 64, (1994) 52

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3. Characterization of SiGe alloy

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smif Non-destructive methods

• Double crystal X-ray diffraction (DCD)

• Triple axis X-ray or High resolution diffraction

• Photoluminescence

• Raman spectroscopy

• Optical microscopy

• Atomic force microscopy

• Ellipsometry

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smif Destructive methods

• Transmission electron microscopy (TEM)

• Scanning electron microscopy

• Auger electron spectroscopy (AES)

• Second ion mass spectroscopy (SIMS)

• Rutherford back scattering (RBS)

• Defect etching by Nomarski optical microscopy

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smif Electrical characterization

• Capacity-Voltage

• Current-Voltage

• Admittance; Spacer charge method

• Deep level transient spectroscopy

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smif High resolution x-ray diffraction

High resolution DCD

7

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smif Simulation of DCD x-ray results

Amend model

Experimental data

Structure model

Simulation

Curve fitting

- 2 0 0 0 -1500 -1000 -500 0 5001

10

100

1000

10000

100000

(004)

arcsecond

Inte

nsit

y (C

PS

)

Pendellösung fringes

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smif Photoluminescence

From Appl. Phys. Lett.73 (1995) 2488

To obtain the band edge

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smif Defects etch of SiGe

Etching solution:

HF + HAC + CrO3

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smif Raman spectroscopy

Raman spectra of strained Si

• Raman parameters: frequency, intensity, bandwidth, polarisation behaviour.

• Use Raman parameters to characterise lattice dynamics, composition, stress, impurities and free carriers in semiconductor materials.

• Other advantages

– non-destructive and non-invasive

– can operate either as a macro -probe or con-focal microprobe.

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smif Ellipsometry

From Appl. Phys. Lett. 67 (1995)3402

nSiGe(x,λ)=nSi(λ)+(1.16– 0.26 λ)x2

Refraction index vs wavelength

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4. Integration issue in IC process

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• SiGe HBT high ft and fmax PNP device; lower power consumption than Si bipolar; monolithic integration with Si CMOS device (Bicmos)

• SiGe : C HBTC impedes B diffusion; higher ft and fmax PNP device than SiGe; lower power consumption than SiGe HBT

• ApplicationsCommunications related to BICMOS Ics; RF small signal amplifiers;RF power amplifier; High data rate transfer

The motivations for SiGe and SiGe: C HBT

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smif Carbon suppress boron out-diffusion

C suppress the diffusion of B

The relation between C anddopant

B: retardationP: retardationAs: enhancementSb: enhancement

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smif C suppress interstitials

Cs + I àCI

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smif Substitutional carbon incorporation rate

• Suppress B diffusion• Enhance thermal stability

How to increase the Cs concentration• Low growth temperature• High growth rate• High process gas pressure

Cs

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smif Oxidation problems

oxidationWhen Ge < 50 %

SiGe

Substrate

Substrate

SiGe

Ge precipitation

SiGe

Substrate

Substrate

SiGe

oxidationWhen Ge > 50 %

Oxide

From: Appl. Phys. Lett.59, (1991)1200

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smif Strained Si in conventional MOSFET

From K. Rim, IEEE ED 47 (2000) 1406

9

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smif The challenge of strained Si

• Short channel effect

• Junction capacitance

• Minimizing the threading dislocation

• Process integration with keep the strained

field

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smif Fabrication of virtual substrate

• Ion implantation of H and He• Grade concentration of buffer layer• Grade super-lattice of buffer layer• Short periods super-lattice• Oxide compliant substrate• Low temperature Si compliant substrate

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smif Graded SiGe buffer layer

Disadvantage:1. Time consuming2. Cross-hatch3. Lithography

Critical thick of strained Si on SiGe

20 nmStrained Si

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Graded concentration XTEM and cross-hatch

Growth at 600 °C

Growth at800 °C

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smif Surface pit and cusp during SiGe

Surface pit in Si60Ge40

From Appl. Phys. Lett. 66 (1995)34

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smif Graded Super-lattice buffers

SiGe x = 5 %Si

SiGe x = 10 %

SiGe x = 15 %

SiGe x= 18 %Si 50 A

SiGe x= 20 %

Si 50 A

Si

Si sub

×3

200 A

200 A

200 A

200 A

50 A

50 A

5000 ACap Si

10

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smif Short period Ge/Si buffer

The structure of short periods

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smif Low temperature compliant substrate

Low temperature Si

Without low temperature epitaxy

Low temperature SiGe

LT SiGe

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smif SiGe on insulator (SGOI) (I)

From Appl. Phys. Lett. 80, (2002)3560IEEE, ED 22, (2001)92

SG on Al2O3

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smif SiGe on insulator (SGOI) (II)

Si70Ge30

Smart cut

Si cap

Si substrate

From J. Appl. Phys. 91(2002)9716,

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smif Thin relaxed SiGe on insulator

BOX

Strained Si

SiGe

Si

Si must be less than 50 nm

Limitation of SiGe and Si buffer

Si

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SIMOX in SGOI

From T. Mizuno et al., IEEE ED 48, (2001) 1612

AES for SIMOX

Oxide block

SiO2 as a diffusion barrier

11

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Toshiba SGOI approach

Scheme of SGOI by Ge condensation

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Mesa structure of SGOI

Enhance relaxation

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5. New trends in SiGe

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smif Selective SiGe growth (I)

1. Create raised source and drain

2. Simplify the process flow

3. Shrinkage the active region width

Method for reactive gas chemistry

1. . Cl based gas

2. Alternated cycles

3. Atomic hydrogen

4. Dichlorosilane (SiH2Cl2) à It is the possible solution.

5. SiH4 based precursor

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smif Selective growth (II)

IEEE ED, 49 (2002) 739Without loading effect

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smif Elevated source and drain

Facet effect

•Reduce parasitic series resistance•Shallow contacting junctions to

minimize short channel effects.

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smif The problem of SiGe: C and SiC

• The lattice mismatich (52 % for Si and C)

• The low solid solubility of C in Si and Ge

• The disruption of epitaxy due to C

• β-SiC precipitate

• Without stable GeC phase

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smif SiGe : C alloy formation

Carbon Gas : SiH3CH3

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smif Strain Ge channel

Ge channel on Si30Ge70

Test structure

Enhanced hole mobility

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smif Optical Electron IC application (I)

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smif OEIC (II)RTO

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smif SiGe nano-structure

1. Quantum well

2. Quantum dots

3. Quantum wires

Due to the hertroepitaxy

13

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smif Quantum well applications

SiGe quantum well photo-diodeQW RTD

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smif Ge quantum dots (QDs) application

Stack Ge/Si bi-layerFrom Phys. Rev. B 61 (1998) 13721Ge QDs on Si substrate

For optical communication

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smif Micro-cooler application

From Appl. Phys. Lett. 78, (2001) 1581

XTEM of Si/SiGeC multi-quantum well

The device structure

The cooling effects

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smif Nano-structure on virtual substrate

Quantum well on VS

Critical thickness on Si0.5 Ge0.5

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6. Conclusions

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smif Conclusions

The advantages of Si/SiGe or SiGe:C

1. Expand the mature Si process

2. Provide an extra boost in performance of Si CMOS

3. Integrate optical and read out circuit on a chip

14

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smif References

• Physics World 13(2),D.J. Paul, pp27-32 (February 2000)

• E. Kasper, ed., Properties of Strained and Relaxed Silicon Germanium, EMIS Datareviews Series No. 12, London: IEE, INSPEC, 1995.

• B. S. Meyerson, Proceedings of the IEEE 80, 1592 (1992).

• D.L. Harame et al. IEEE ED 46, 455-482 (1995)

• D.L. Harame et al. IEEE ED 46, 455-482 (1995)

• D.L. Harame et al. IEEE ED 48, 2555 (2001)

• R. People, IEEE QE 22(9), 1696 (1986)

• D. L. Schroder, Semiconductor mater and device characterization

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smif 感謝

‧明新科技大學陳邦旭教授提供講義資料