The Effects of Process Parameters during the Deposition of SiNx using

PECVD

Presented by John Nice and Joyce PalmerGeorgia Institute of TechnologyNNIN RETs Summer 2006

Objective

Evaluate the effect of process parameter changes for the deposition of Silicon Nitride (SiNx) using Plasma Enhanced Chemical Vapor Deposition (PECVD)

– Utilized the Plasma Therm, Unaxis and STS PECVD systems

– Changed the standard settings for gas flow rate, pressure, temperature and power

– Determined the effect of process changes on deposition rate, uniformity, and index of refraction.

Methodology

Ten minute cleaning process performed before process runs.

One minute seasoning run performed for each recipe prior to deposition.

Typical process run time of ten minutes unless otherwise noted.

Ten minute cleaning process run between consecutive depositions.

Two hour standard cleaning process run at conclusion of testing session.

Analysis of Films

Woollam Ellipsometer: Thin nitride 5-point scan recipe used. Film thickness, index of refraction (n) @ λ=633nm, and uniformity compared.

Plas-Mos Ellipsometer: Film thickness and index (n) @ λ=633nm compared

Nanospec Refractometer: Thin nitride recipe used. Film thickness compared.

Tencor P-15 Profilometer-FC: Thin nitride recipe used. Stress measurements compared.

Plasma Therm PECVD

Plasma Therm PECVD

Changed gas flow rates for SiH4 and NH3. Changed pressure up and down 100 mTorr. Changed temperature from 200-325°C in

25°C increments. Deposited films for 10 minutes except for

deposition rate analysis experiment.

Standard Recipe Used for the Plasma Therm PECVD (Stdnit.prc)

2% SiH4/N2 200 sccm

NH3 5 sccm

N2 900 sccm Temperature 250 °C Pressure 900 mTorr Power 30 Watt

SiH4 Changes for Plasma Therm

Varied Silane gas flow rate from 180 sccm to 220 sccm.

– NH3 5 sccm

– N2 900 sccm

– Temperature 250°C– Pressure 900 mTorr– Power 30 Watt

Woollam Ellipsometer Analysis for Deposition

Deposition of SiN film in 10 minutes vs. Silane Changes on Plasma Therm PECVD on Woollam

1195

1220

1245

1270

1295

1320

1345

1370

1395

175 180 185 190 195 200 205 210 215 220 225

SiH4 Gas Flow Rates (sccm)

De

po

sit

ion

in 1

0 m

inu

tes

(Ǻ

)

Woollam Ellipsometer Analysis for Index of Refraction

Index of refraction vs. SiH4 Flow rate on Plasma Therm PECVD measured with Woollam

1.86

1.87

1.88

1.89

1.9

1.91

1.92

180 190 200 210 220

SiH4 Gas Flow Rate (sccm)

Ind

ex o

f R

efra

ctio

n @

63

3nm

Woollam Ellipsometer for Uniformity for Silane Changes on Plasma Therm PECVD

Uniformity of SiN Film vs. Silane Gas Flow Rate on Plasma Therm PECVD

0

1

2

3

4

5

175 180 185 190 195 200 205 210 215 220 225

SiH4 Gas Flow Rates (sccm)

Un

ifo

rmit

y %

Film Deposition Comparison for NH3 as Measured on both Woollam and Plas-Mos Ellipsometers and Nanospec

Comparison of Deposition of SiN film in 10 minutes vs. Ammonia Gas Flow Rate on Plasma Therm PECVD

700

900

1100

1300

1500

1700

1900

3 3.5 4 4.5 5 5.5 6 6.5 7

NH3 Gas Flow Rates(sccm)

De

po

sit

ion

in 1

0 m

inu

tes

(Ǻ

)

Deposition on Plas-Mos

Deposition on Woollam

Nanospec

NH3 Changes for Plasma Therm

Changed gas flow rate from 3-7 sccm in 0.5 sccm increments

– 2% SiH4/N2 200 sccm

– N2 900 sccm

– Temperature 250°C– Pressure 900 mTorr– Power 30 Watt

Film Deposition Analysis Measured on Woollam Ellipsometer for NH3 Changes

Deposition of SiN film in 10 minutes vs. Ammonia Gas Flow Rate on Plasma Therm PECVD measured on Woollam

1200

1300

1400

1500

1600

1700

1800

2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

NH3 Gas Flow Rates (sccm)

De

po

sit

ion

in

10

m

inu

tes

(Ǻ

)

Film Deposition Analysis Measured on Plas-Mos for NH3 Changes

Deposition of SiN film in 10 minutes vs. Ammonia Gas Flow Rate on Plasma Therm PECVD measured on Plas-Mos

1200

1250

1300

1350

1400

1450

1500

3 3.5 4 4.5 5 5.5 6 6.5 7

NH3 Gas Flow Rates (sccm)

Dep

osi

tio

n in

10

min

ute

s (Ǻ

)

Film Deposition Analysis Measured on Nanospec Refractometer for NH3 Changes

Nanospec Analysis for NH3 Film Deposition for Plasma-Therm PECVD

700

900

1100

1300

1500

1700

3 4 5 6 7

NH3 Gas Flow Rate (sccm)

Dep

ost

ion

in

10

min

ute

s (Ǻ

)

The Plas-Mos Ellipsometer and the Woollam Ellipsometer each can measure the film thickness and the index of refraction. The data from the Woollam is generally preferred, since the Woollam determines its values from a large range of wavelengths and measures at multiple points on the wafer. The Plas-Mos and the Nanospec only measure at one point. The Plas-Mos uses only one frequency of light.

Choices of Metrology Tools

Index of Refraction Analysis for NH3 Changes Measured on Woollam

Index of Refraction at 633nm of SiN Film vs Ammonia Gas Flow Rate measured on

Woollam

1.8

1.85

1.9

1.95

2

3 3.5 4 4.5 5 5.5 6 6.5 7

NH3 Gas Flow Rates (sccm)

Ind

ex o

f R

efra

ctio

n @

63

3nm

Uniformity for NH3 Changes on Woollam

Uniformity of SiN Film vs Ammonia Gas Flow Rate measured on Woollam

00.20.40.60.8

11.2

3 3.5 4 4.5 5 5.5 6 6.5 7

NH3 Gas Flow Rates (sccm)

Un

ifo

rmit

y %

Pressure Changes on Plasma Therm PECVD

The following pressures were tested: 900 mTorr, 1000 mTorr, and 800 mTorr

– 2% SiH4/N2 200 sccm

– NH3 5 sccm

– N2 900 sccm

– Temperature 250°C– Power 30 Watt

Woollam Analysis for Film Deposition for Pressure Change

Deposition of SiN Film in 10 minutes vs. Pressure on Woollam

0

200

400

600

800

1000

1200

1400

1600

0 200 400 600 800 1000 1200

Pressure (mTorr)

De

po

sit

ion

in

10

min

ute

s (

Ǻ)

Woollam Analysis for Index of Refraction for Pressure Changes

Index of refraction @ 633nm vs. Pressure on Woollam

1.8

1.85

1.9

1.95

2

0 200 400 600 800 1000 1200

Pressure (mTorr)

Ind

ex o

f R

efra

ctio

n @

633

nm

Uniformity for Pressure Changes on Woollam

Uniformity vs. Pressure on Woollam

0

0.2

0.4

0.6

0.8

1

0 200 400 600 800 1000 1200

Pressure (mTorr)

Un

ifo

rmit

y %

Temperature Changes on Plasma Therm PECVD

Temperature was changed between 200°C and around 325°C in 25°C increments.

– 2% SiH4/N2 200 sccm – NH3 5 sccm– N2 900 sccm– Pressure 900 mTorr– Power 30 Watt

Woollam Analysis for Film Deposition for Temperature Changes

Deposition after 10 minutes vs. Temperature on Plasma Therm PECVD

1250

1300

1350

1400

1450

1500

150 200 250 300 350

Temperature (°C)

Dep

osi

tio

n a

fter

10

min

ute

s (Ǻ

)

Woollam Analysis for Index of Refraction for Temperature Changes

Index of refraction @ 633nm vs. Temperature on Plasma Therm PECVD

1.87

1.875

1.88

1.885

1.89

1.895

1.9

1.905

150 200 250 300 350

Temperature (°C)

Ind

ex o

f re

frac

tio

n @

633

nm

Woollam Analysis of Uniformity for Temperature Changes

Uniformity vs. Temperature on Plasma Therm PECVD

0

0.2

0.4

0.6

0.8

1

1.2

150 200 250 300 350

Temperature (°C)

Un

ifo

rmit

y %

Unaxis PECVD

Standard Recipe For Unaxis PECVD (stdnit.prc)

5% SiH4/He 200 sccm

NH3 8 sccm He 560 sccm N2 150 sccm Temperature 250°C Pressure 1100 mTorr Power 50 watt

SiH4 Gas Flow Rate Changes

The following gas flow rates in sccm for Silane were tested: 220, 215, 210,205, 200, 195, 190, 185, 180

– NH3 8 sccm

– He 560 sccm– N2 150 sccm

– Temperature 250°C– Pressure 1100 mTorr– Power 50 watt

Woollam Analysis for Film Deposition for Silane Changes

Deposition after 10 minutes vs. Silane flow rate on the Unaxis PECVD

800

850

900

950

1000

175 180 185 190 195 200 205 210 215 220 225

Silane Gas Flow Rates (sccm)

Depo

sitio

n af

ter 1

0 m

inut

es (Ǻ

)

Woollam Analysis for Index of Refraction for Silane Changes

Index of refraction at 633nm vs. Silane flow rate on the Unaxis PECVD

1.9

1.92

1.94

1.96

1.98

2

175 180 185 190 195 200 205 210 215 220 225

Silane Gas Flow Rates (sccm)

Inde

x of

Ref

ract

ion

Woollam Uniformity Analysis for Silane Changes

Uniformity vs. Silane flow rate on the Unaxis PECVD

0

1

2

3

4

5

175 180 185 190 195 200 205 210 215 220 225

Silane Gas Flow Rates (sccm)

Unifo

rmity

(%)

Tencor P-15 Profilometer Stress Analysis for Silane Changes

Average Tensile Stress vs Silane Flow Rate on the Unaxis

0

10

20

30

40

50

60

70

80

170 180 190 200 210 220 230

Silane Flow Rate (sccm)

Avg

. T

ensi

le S

tres

s (M

Pa)

NH3 Changes for Unaxis PECVD

The following NH3 gas flow rates in sccm were tested: 10, 9.5, 9, 8, 7, 6

– 5% SiH4/He 200 sccm

– He 560 sccm– N2 150 sccm

– Temperature 250°C– Pressure 1100 mTorr– Power 50 watt

Woollam Analysis for Film Deposition for NH3 Change

Deposition after 10 minutes by changing Ammonia flow rate on the Unaxis PECVD

800825850875900925950975

1000

5 6 7 8 9 10 11

Ammonia Gas Flow Rates (sccm)

Dep

osi

tio

n a

fter

10

min

ute

s (Ǻ

)

Woollam Analysis for Index n @633nm for Ammonia Change

Index of refraction at 633nm vs. Ammonia flow rate on the Unaxis PECVD

1.9

1.95

2

2.05

2.1

5 6 7 8 9 10 11

Ammonia Gas Flow Rates (sccm)

Ind

ex

of

Re

fra

cti

on

@

63

3n

m

Woollam Uniformity Analysis for Ammonia Change

Uniformity vs. Ammonia flow rate on the Unaxis PECVD

0

1

2

3

4

5

5 6 7 8 9 10 11

Ammonia Gas Flow Rates (sccm)

Un

ifo

rmit

y (%

)

Tencor P-15 Profilometer Analysis for Ammonia Change

Average Stress vs. Ammonia Flow Rate on the Unaxis

0

50

100

150

200

250

300

350

400

0 5 10 15

NH3 Flow Rate (sccm)

Avg

. S

tres

s (M

Pa)

Tensile Stress

Compressive Stress

Pressure Changes on Unaxis PECVD

The following pressures were tested in mTorr: 1200, 1100, 900, 800

– 5% SiH4/He 200 sccm– NH3 8 sccm– He 560 sccm– N2 150 sccm– Temperature 250°C– Power 50 watt

Woollam Analysis for Film Deposition for Pressure Change

Deposition after 10 minutes by changing Pressure on the Unaxis PECVD

700725750775800825850875900

700 800 900 1000 1100 1200 1300

Pressure (mTorr)

Dep

osi

tio

n a

fter

10

min

ute

s (Ǻ

)

Woollam Analysis for Index n@633nm for Pressure Change

Index of refraction at 633nm vs. Pressure on the Unaxis PECVD

1.9

1.92

1.94

1.96

1.98

2

700 800 900 1000 1100 1200 1300

Pressure (mTorr)

Ind

ex o

f R

efra

ctio

n

Uniformity Analysis for Pressure Change

Uniformity vs. Pressure on the Unaxis PECVD

0

1

2

3

4

5

700 800 900 1000 1100 1200 1300

Pressure (mTorr)

Un

ifo

rmit

y (%

)

STS PECVD

Low Frequency Standard Thin Nitride Recipe Used(lfsin.set)

2% SiH4/N2 2000 sccm

NH3 20 sccm Temperature 300°C Pressure 550 mTorr Power 60 watts

SiH4 Gas Flow Changes for STS PECVD

The following SiH4 gas flow changes in sccm were tested: 2200, 2150, 2100, 2050, 1950, 1900, 1850, 1800,

– NH3 20 sccm

– Temperature 300°C– Pressure 550 mTorr– Power 60 watts

Woollam Analysis for Film Deposition for Silane Changes

Deposition after 10 minutes by changing Silane flow rate on the STS PECVD

300032503500375040004250450047505000

1700 1800 1900 2000 2100 2200 2300

Silane Gas Flow Rates (sccm)

Depo

sitio

n af

ter 1

0 m

inut

es (Ǻ

)

Woollam Analysis for Index n@633nm for Silane Changes

Index of refraction at 633nm vs. Silane flow rate on the STS PECVD

1.8

1.84

1.88

1.92

1.96

2

1700 1800 1900 2000 2100 2200 2300

Silane Gas Flow Rates (sccm)

Ind

ex o

f R

efra

ctio

n

@ 6

33 n

m

Uniformity Analysis for Silane Changes

Uniformity vs. Silane flow rate on the STS PECVD

0

1

2

3

4

5

6

1700 1800 1900 2000 2100 2200 2300

Silane Gas Flow Rates (sccm)

Un

ifo

rmit

y (%

)

Tencor P-15 Profilometer Stress Analysis for Silane Changes

Compressive Stress vs. Silane Flow Rate on the STS

0

100

200

300

400

500

600

700

800

900

1700 1800 1900 2000 2100 2200 2300

Silane Flow Rate (sccm)

Co

mp

ress

ive

Str

ess

(MP

a)

Conclusions

As the silane flow rate increased, we saw an increase in the deposition rate and the index of refraction. Uniformity was generally constant.

As the ammonia flow rate increased, the deposition rate decreased on the Plasma-Therm, but was unchanged on the Unaxis. The index of refraction decreased as ammonia flow rate increased on both PECVDs. Uniformity was generally constant

Conclusions

As the pressure of the chamber increases, the deposition rate increases. The film becomes more porous. The index of refraction decreased as pressure increased on the Plasma-Therm. The uniformity was better as the pressure decreased on the Plasma-Therm. The results for the Unaxis were inconclusive for all cases.

Conclusions

As temperature increased, the deposition rate decreased, the index of refraction increased, and the uniformity improved.

The cleaning process is very important for getting consistent results. If process parameters are changed by a large amount, rather than in small steps, the results can be skewed. Longer cleaning is indicated for more consistent results.

Mentors

Dr. Nancy Healy Dr. Kevin Martin Janet Cobb-Sullivan Steven Parente