The Study of Plasma-Enhanced Silicon NitrideDeposition Using SiH4/NH3/N2 Mixture

Ladthai Thaiyotin

Sompong Charoenkit, Win Bunjongpru, Charndet Hruanan and Itti Rittaporn

Thai Microelectronic Center (TMEC)

National Electronics and Computor Technology Center (NECTEC)

Out line

- Introduction

- Experiment

- Result

- Conclusion

IntroductionPlasma Enhanced Chemical Vapor Deposition (PECVD)

- IC and MEMs Passivation Layer

Low processing temperature, Good step coverage, good passivationfor both moisture and sodium ions.

- Process Gas

SiH4+N2 ----> Less controllable

SiH4+NH3 ----> More Hydrogen content

SiH4 + NH3 + N2The Study of Plasma-Enhanced Silicon NitrideDeposition Using SiH4/NH3/N2 Mixture

Experiment

PECVD

Model: P5000 Mark II by AMAT

Figture 1. PECVD picture

Figture 2. PECVD Schematic

Table 1. Deposition parameters

SiH4 150-250NH3 25-100N2 1500-4500

2-5 300-600300-450250-400

Gas flow(sccm)

Total pressure(torr)

Spacing(mils)

RF power(watt)

Subs. temp.( oc )

SiH4+NH3, SiH4+N2, SiH4+NH3+N2

- Etch rate

- Si-N ratio (Refractive index)

- Stress

Comparision:

Substrate temperature (OC)

800

850

900

950

1000

Substrate temperature (c)

Dep

ositi

on ra

te (n

m/m

in)

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Uni

form

ity (%

)

250 300 350 400

Dep. rate

Unif.

500

600

700

800

900

1000

1100

300 350 400 450RF power (watts)

Dep

ositi

on ra

te (n

m/m

in)

0.75

0.80

0.85

0.90

0.95

1.00U

nifo

rmity

(%)

Dep. rate

Unif.

RF Power (watt)

Results

-500-450-400-350-300-250-200-150-100-50

0

Substrate temperature (C)

Stre

ss (M

Pa)

1.7

1.8

1.9

2.0

2.1

2.2

2.3

Ref

ract

ive

inde

x

250 300 350 400

Index

Stress

Tensile

-400

-300

-200

0

100

200

300

RF power (watts)

Stre

ss (M

Pa)

2.0

2.1

2.2

2.3

2.4

2.5

Ref

ract

ive

inde

x

300 350 400 450

-100 Index

Stress

Tensile

930

935

940

945

950

955

960

300 400 500 600Spacing (mils)

Dep

ositi

on ra

te (n

m/m

in)

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Uni

form

ity (%

)Dep. rate

Unif.

Spacing (mils)

Total pressure (torr)

700

750

800

850

900

950

1000

Total pressure (torr)

Dep

ositi

on ra

te (n

m/m

in)

00.5

1.01.52.0

2 .53.03.5

4.04.5

Uni

form

ity (%

)

2 3 4 5

Dep. rate

Unif.

-200

-150

-100

-

0

50

100

300 400 500 600Spacing (mils)

Stre

ss (M

Pa)

Ref

ract

ive

inde

x

-50

2.00

2.05

2.10

2.15

2.20

2.25.

2.30

Index

Stress

Tensile

-450-400-350-300-250-200-150-100-50

0

2 3 4 5Total pressure (torr)

Stre

ss (M

Pa)

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

Inde

x

Index

Stress

Compressive

910

920

930

940

950

960

970

980

990D

epos

ition

rate

(nm

/min

)

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Uni

form

ity (%

)

100 150 200 250SiH4 (sccm)

Unif.

Dep. rate

SiH4 (sccm)

500

600

700

800

900

1000

1100

Dep

ositi

on ra

te (n

m/m

in)

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Uni

form

ity (%

)

NH3 (sccm)25 50 75 100

Dep. rate

Unif.

NH3 (sccm)

-500

-300

-100

100

300

500

25 50 75 100

Stre

ss (M

pa)

2.0

2.1

2.2

2.3

2.4

2.5

Ref

ract

ive

inde

x

NH3 (sccm)

Tensile

Index

Stress

-250

-200

-150

-100

0

50

100

150

Stre

ss (M

pa)

1.50

1.65

1.85

1.95

2.10

2.25

2.40

2.55

Ref

ract

ive

inde

x

SiH4 (sccm)

-50

100 250200150

tensile

Index

Stress

820

840

860

880

900

920

940

960

Dep

ositi

on ra

te (n

m/m

in)

0

1

2

3

4

5

6

Uni

form

ity (

%)

N2 (sccm)1500 2500 3500 4500

Dep. rate

Unif.

N2 (sccm)

- 300

-200

-100

0

100

200

1500 2500 3500 4500N2 (sccm)

Stre

ss (M

pa)

Ref

ract

ive

inde

x

Compressive

Index

Stress

2. 10

2. 15

2. 20

2. 25

2. 30

Table 1. Silicon nitride trendsummary.

N2 (sccm)

NH3 (sccm)

SiH4 (sccm)

Total pressure (torr)

Spacing (mils)

RF power (watt)

Substrate temp (oC)

Refractive indexCompressive stressUniformityDeposition rateIncrease item

Figture 3. Silicon nitride film

Table 3 Etch rate, Si/N ratio and stress of nitride films depositionusing different gas mixture.

125118236Stress (Mpa)

313747Si/N ratio

320287637Etch rate (nm/min)

SiH4/NH3/N2SiH4/N2SiH4/NH3Gas mixture

PECVD silicon nitride deposition using SiH4+NH3+N2

Good uniformity

- Increase substrate temp, total pressure

- Decrease spacing and RF power

Refractive index (2.0-2.1) obtained by

- Increase RF power, total pressure

Reactive gas ratio

Good uniformity, increase N2

Refractive index (2.0-2.1) obtained by

- increase NH3 and N2

Conclusion

LowLowHighStress (Mpa)

Nitrogen rich(2.0 - 2.2)

Nitrogen rich(index 1.9 - 2.1)

Silicon richSi/N ratio

MiddleLowHigh porocityEtch rate (nm/min)

SiH4/NH3/N2SiH4/N2SiH4/NH3Gas mixture

SiH4+N2 less controllable

SiH4+NH3 High Hidrogen

SiH4+N2+NH3 Optimum