1. Title
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
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group

2. Recommendations for future work
Title
Outline
Introduction
organic removal from low-k by He/H2-DSP* ash
detection of porogen residues by UV spectroscopic ellipsometry
Experimental
Results
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
Conclusions
Recommendations for future work
*DSP – downstream plasma
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group

3. Organic material embedded in low-k matrix is removed by He/H2-DSP without Si-CH3 group breakage1
Photresist
removal with
“zero damage”
residue
removal
TOFSIMS shows carbon removal, but it does not come from Si-CH3, as FTIR shows
1A. M. Urbanowicz, et al., in 25th Advanced Metallization Conference, San Diego, CA, 2008
2A. M. Urbanowicz, et al., in Electrochemical and Solid State Letters, 12(8), 2009
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

4. UV ellipsometry is very sensitive to presence of porogen in low-k films
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)
SiOC:H
matrix
P. Marsik, A. Urbanowicz et al., AMC 2008 proc., p (2009)
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

5. Experiment Spin-on PECVD PECVD Spin-on UV curing: Ash: 20 – 700 s
Porogen
residue removal
Ash: 20 – 700 s
porogen
Porogen residue
Spin-on
Spin-on
Organic
removal?
Silica
nanoparticles
UV curing
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

6. He/H2-DSP removes organic content from all films
Title
He/H2-DSP removes organic content from all films
Pristine films properties
Spectroscopic ellipsometry
Film
UV-source
Open
porosity k
CVD 2.5 B2
>200 nm
24 %
2.5 E2
~172 nm
CVD 2.3 Ea
32 %
2.3 Eb
34 % B3
36 %
SOG 2.3 N
32%
Before
Porogen
residue
content
After
Observations:
PECVD with k~2.3 contains
more porogen residues
Spin-on contains minimal amount of organics N
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group

7. Depth of porogen residue removal decreases logarithmically with time
Title
Depth of porogen residue removal decreases logarithmically with time
UV-spectroscopic ellipsometry
Mass balance on
300 mm wafers
To fit logartimic functions (Eddy’s paper). Animations -> trasform to logaritmic scale.
Observation:
Depth of porogen residue removal increases with film porosity
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group

8. Depth of porogen residue removal decreases logarithmically with time
Title
Depth of porogen residue removal decreases logarithmically with time
UV-spectrocopic ellipsometry
Mass balance on
300 mm wafers
To fit logartimic functions (Eddy’s paper). Animations -> trasform to logaritmic scale.
Observation:
Depth of porgen residue removal increases with film porosity
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group

9. Overash results in k-value reduction, but..
Hg-probe
Observation
SOG and CVD 2.5: Longer times cause k-value increase
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

10. k-value increase for longer over-ash times can be explained by minor polar group incorporation
N2-purged FTIR
Observation
FTIR shows minor polar groups incorporation for all treated films
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

11. Final k-value is determined by 2 competing phenomena: density reduction and polar group incorporation
Debye’s equation
Polar groups
incorporation
Density reduction
Mass balance on
300 mm wafers
FTIR
k  k
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

12. CVD 2.3 show the highest k-value reduction accopanied by mechanical properties degradation
Nano-indentation
Hg-probe
Observations:
No mechanical properties reduction for CVD 2.5 and SOG 2.3 film while sinficant mechanical properties degradation for CVD 2.3
The highest k-value reduction for CVD 2.3
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

13. 3 effects of He/H2-DSP overash due to porogen residue/organics removal and silianol incoroporation
Nano indentation and Hg-probe I II
Ref
I – k and YM ~ const
CVD 2.5 (T<100 s)
II - k and YM ~ const
CVD 2.5 (T>100 s) and SOG 2.3)
III - k and YM 
CVD 2.3
Ref
Ref
Ref
III
Ref
Ref
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

14. Title
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
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group

15. Title
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
Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France
FirstName LastName – Activity / Group