Mechanism of k-value Reduction of PECVD Low-k Films Treated with He/H2

Ash Plasma

A.M. Urbanowicz, M. Cremel, K. Vanstreels, D. Shamiryan, S. De Gendt, M.R. Baklanov

1Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

2

Outline

Introduction organic removal from low-k by He/H2-DSP* ash

detection of porogen residues by UV spectroscopic ellipsometry

ExperimentalResults

depth of porogen residue removal for different low-k’s

mechanism of k-value reduction by He/H2-DSP*

effect of porogen residue removal on mechanical properties

ConclusionsRecommendations for future work

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

*DSP – downstream plasma

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France3

Organic material embedded in low-k matrix is removed by He/H2-DSP without Si-CH3 group breakage

He/H2 plasma at 280 oC

UV

Porogenresidue removal

Low-k Low-k Low-k

Porogenresidue

Photresistremoval with “zero damage”

1A. M. Urbanowicz, et al., in 25th Advanced Metallization Conference, San Diego, CA, 2008

residue removal

2A. M. Urbanowicz, et al., in Electrochemical and Solid State Letters, 12(8), 2009

1

0 200 400 600 800 1000 1200 1400 16001

10

100

1000

1300 1280 1260 12400.000

0.005

0.010

0.015

0.020

0.025

0.030

C17 ref. C19 35s C21 140s C23 700s

Abs

orba

nce

Wavenumber cm -1

Si-CH3

700 s He/H2

140 s He/H2

Ref. (EB)

Car

bon

inte

nsity

, a.u

.Sputtering time, a.u.

35 s He/H2

FTIR

TOFSIMS shows carbon removal, but it does not come from Si-CH3, as FTIR shows

4

UV ellipsometry is very sensitive to presence of porogen in low-k films

P. Marsik, A. Urbanowicz et al., AMC 2008 proc., p. 543-549 (2009)

SiOC:H matrix has silmilar optical properties to SiO2

Porogen residue (a-C) contains sp2 orbitals (C=C) which have transtion band ~4.5 eV (275 nm)

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

SiOC:Hmatrix

5

Experiment

UV curing:

Ash: 20 – 700 s

porogenPorogen residue

Gas inlet

Plasma area

Reactive species

Grid : electrical neutralization

Wafer at 280 C

HH

H

He/ H2

Porogenresidue removal

Silica nanoparticles UV curing

Organicremoval?

Spin-on

PECVD

PECVD

Spin-on

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

900 750 600 450 300 150

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

B2

Eb

Ea

ext

inct

ion c

oeffi

cien

t

Wavelenght [nm]

B3

Porogenresiduecontent

He/H2-DSP removes organic content from all films

N

Film UV-source Open porosity

k

CVD 2.5B2 >200 nm 24 % 2.5E2 ~172 nm 24 % 2.5CVD 2.3Ea ~172 nm 32 % 2.3Eb >200 nm 34 % 2.3B3 >200 nm 36 % 2.3SOG 2.3N >200 nm 32% 2.3

Before

After

Observations:PECVD with k~2.3 containsmore porogen residuesSpin-on contains minimal amount of organics

Spectroscopic ellipsometryPristine films properties

6Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

7

Depth of porogen residue removal decreases logarithmically with time

0 100 200 300 400 500 600 700 800

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 N

He/H2-DSP treatment time [s]

Ma

ss lo

ss [

mg

]0 100 200 300 400 500 600 700 800

0

20

40

60

80

100

120

140

160

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 N

Mo

dyf

ica

tion

De

pth

[n

m]

He/H2-DSP treatment time [s]

Mass balance on 300 mm wafers

UV-spectroscopic ellipsometry

Observation: Depth of porogen residue removal increases with film

porosity

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

8

10 100 1000

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 N

He/H2-DSP treatment time [s]

Mas

s lo

ss [m

g]10 100 1000

0

20

40

60

80

100

120

140

160

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 N

Mod

yfic

atio

n D

epth

[nm

]

He/H2-DSP treatment time [s]

Mass balance on 300 mm wafers

UV-spectrocopic ellipsometry

Observation:Depth of porgen residue removal increases with film porosity

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

Depth of porogen residue removal decreases logarithmically with time

9

Overash results in k-value reduction, but..

0 100 200 300 400 500 600 700 8001.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7k-

valu

e

He/H2-DSP treatment time [s]

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3N

ObservationSOG and CVD 2.5: Longer times cause k-value increase

Hg-probe

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

k-value increase for longer over-ash times can be explained by minor polar group incorporation

10

3900 3800 3700 3600 3500 3400 3300 3200 3100-0.005

0.000

0.005

0.010

0.015

0.020

Ab

sorb

an

ce,

a.u

.

Wavenumber, cm-1

B2 700 s He/H2-DSP

Si-OH + H2O

N2-purged FTIR1

1

3900

3100

( )k cm

i

k cm

A A k dk

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

ObservationFTIR shows minor polar groups incorporation for all treated films

0 100 200 300 400 500 600 700 800

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

CVD 2.5 B2 E2

SOG 2.3 N

CVD 2.3 Eb Ea B3

Inte

gra

ted

OH

ab

sorb

an

ceHe/H

2-DSP treatment time [s]

0 100 200 300 400 500 600 700 800

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

CVD 2.5 B2 E2

SOG 2.3 N

CVD 2.3 Eb Ea B3

Inte

grat

ed O

H a

bsor

banc

e

He/H2-DSP treatment time [s]

0 100 200 300 400 500 600 700 800

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 N

He/H2-DSP treatment time [s]

Ma

ss lo

ss [

mg

]

11

Final k-value is determined by 2 competing phenomena: density reduction and polar group incorporation

kk

kT

pN

k

k o

o 33

4

2

1 2

Density reduction

Polar groups incorporation

Mass balance on 300 mm wafers

FTIR

Debye’s equation

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

12

CVD 2.3 show the highest k-value reduction accopanied by mechanical properties degradation

0 100 200 300 400 500 600 700 800

2.53.03.54.04.55.05.56.06.57.07.58.08.5

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 NE

last

ic M

od

ulu

s [

GP

a]

He/H2-DSP treatment time [s]

Hg-probeNano-indentation

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

0 100 200 300 400 500 600 700 8001.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

k-va

lue

He/H2-DSP treatment time [s]

CVD 2.5 B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3N

Observations:No mechanical properties reduction for CVD 2.5 and SOG 2.3 film while sinficant mechanical properties degradation for CVD 2.3The highest k-value reduction for CVD 2.3

13

1.8 2.0 2.2 2.4 2.6 2.82

3

4

5

6

7

8

9CVD 2.5

B2 E2

CVD 2.3 Ea Eb B3

SOG 2.3 N

You

ng's

Mod

ulus

(G

Pa)

k-value

3 effects of He/H2-DSP overash due to porogen

residue/organics removal and silianol incoroporation

Nano indentation and Hg-probe

Ref

Ref

Ref

Ref

Ref

I II

III

I – k and YM ~ constCVD 2.5 (T<100 s)II - k and YM ~ constCVD 2.5 (T>100 s) and SOG 2.3)III - k and YM CVD 2.3

Ref

Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

Conclusions

Mechanism of k-value reduction of PECVD low-k’s exposed at He/H2-DSP ash is a superposition of two competing phenomena:

porogen residue removal results in k-value reduction

minor silanol group incorporation results in k-value increase

Reduction of k-value by removing porogen residue is beneficial (T<100 s)for PECVD with k=2.5 since no degradation of their mechanical properties is observed

Depth of porogen removal decreases logarithmically with time. Can be as high as:

~70 nm for PECVD (k=2.5) with 25% open porosity

~160 nm for PECVD (k=2.3) with >32 % open porosity

14Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

Future plans

Effect of He/H2-DSP ash modification on subsequent damascene processing steps:

chemical or physical-chemical cleaning

barrier deposition

Fabrication of porogen-residue-free PECVD films by porogen removal by He/H2-DSP before UV curing step

15Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France