1. Surface Treatment Solutions for Low-k Dielectrics
Peng Zhang, Brenda Ross, Bridget Horvath, John A. Marsella, Gary Johnson
Air Products and Chemicals
Daniel Koos, Frank Huang, Marie Mitchel
Novellus Systems

2. Outline
Surface Treatment Solutions in Post-CMP Cleans for Low-k Dielectrics
Contact Angle Studies
ATR-FTIR Results
Foam Data
Defect Performance
Conclusions

3. Surfactants in Semiconductor Cleaning Process
Hydrophobic substrate surfaces
Organic materials, low-k
Smaller features
Substrate
193nm Resist
Low-k dielectrics
Hydrophobic Si
Contact angle of water
>60°
~70°
> 80°

4. Post-CMP Cleans Challenge for Hydrophobic Low-k Dielectrics
Hydrophobic surface are seen to de-wet during transfer from the polisher to the cleaner.
Additional de-wetting can occur during the rinse / dry process.
De-wetting leads to increase particle counts and associated water marks.

5. Water Marks on Patterned Wafer

6. Surface Conditioners in Post-CMP Cleans
Reduce defects by wetting the surface in the wafer transfer and rinse/dry process
Have Superior wetting under dynamic conditions
Can be easily removed from substrate surface
Low foaming

7. Wetting on Low-k dielectric Film
Lowest Contact Angle on Low-k Surface 5s
10s
20s
Surface Conditioner A
27.6
23.6
<20
Surface Conditioner B
53.2 53
52.5
Surface Conditioner C
48.7
48.1
47.5
Surface Conditioner D
57.4
54.2
53.7
Surface Conditioner E
42.8
41.8
37.3

8. Wetting on Low-k Surface
Surface Conditioner A
45 degrees set as acceptable contact angle to wet wafer.

9. Removal of Surface Conditioner (Low-k Dielectric Surface)
Contact Angle of Water
Process 5s
20s
Blank + DI
73.2
73.1
72.8
SC A + DI
72.5
71.5
71.3
SC B + DI
70.2
69.8
SC C + DI
70.9
70.4
70.1
SC D + DI
69.5
SC E + DI
67.7
67.3
66.9

10. ATR FTIR Technique on Si Crystal
Solution flow
IR Beam
Solution flow
Flow Cell

11. Adsorption Density Calculation
A/N = bulk contribution + surface contribution
= e Cs de + e (2de/dp) G
A: Absorbance of surfactant molecules
N: number of internal reflections
e: molecular absorptivity
Cs: bulk concentration
de:effective depth
dp: penetration depth of the evanescent wave
G: adsorption density of surfactant (moles/cm2)

12. Molar Absorptivity of Surfactant
Ar T = e C P
ArT= Integrated absorbance of a transmission spectrum in the range of cm-1
C= Concentration of surfactant solution [M]
P= Transmission cell path length

13. Surfactant Absorption

14. Surfactant Adsorption Density
Surface Conditioner A Surface Conditioner E

15. Surface Desorption

16. Foam Generation Test
foam
glass
frit
Mass Flow
Controller
N2 Supply

17. Foam Dissipation Test Foam Height Fluorosurfactant
Surface Conditioner A
Initial Height
2.5 cm
2.1 cm
20 sec
0 cm
1 min
1.4 cm
2 min
1.3 cm
3 min
1.2 cm ~ ~

18. Post-CMP Clean Performance (Surface Conditioner A)
Processing
Polish
Transfer
Clean
Rinse/Dry
Polish Plus Clean Defect Results
2% Solutions
Film Comparison SC A Cu
USG*
Coral™ “A”
Defect Results
 Normalized (Result / Baseline)
*Un-doped Silicon Glass
“Coral” is a trade mark of Novellus Systems, Inc.

19. Conclusions
Surface conditioners can be used effectively to wet hydrophobic low-k surface.
They can also be easily removed from the hydrophobic surface without impact on the bulk film properties.
Superior defect performance was obtained in post-CMP cleans.

20. Acknowledgement University of Arizona
A. Marcia Almanza-Workman, Srini Raghavan