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

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

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°

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.

Water Marks on Patterned Wafer

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

Wetting on Low-k dielectric Film Lowest Contact Angle on Low-k Surface CA @ 5s CA @ 10s CA @ 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

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

Removal of Surface Conditioner (Low-k Dielectric Surface) Contact Angle of Water Process CA @ 5s CA @10s CA @ 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

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

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)

Molar Absorptivity of Surfactant Ar T = e C P ArT= Integrated absorbance of a transmission spectrum in the range of 3000-2800 cm-1 C= Concentration of surfactant solution [M] P= Transmission cell path length

Surfactant Absorption

Surfactant Adsorption Density Surface Conditioner A Surface Conditioner E

Surface Desorption

Foam Generation Test foam glass frit Mass Flow Controller N2 Supply

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 ~ ~

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 3.5 0.87 USG* 2.6 0.85 Coral™ “A” 0.91 0.15 Defect Results  Normalized (Result / Baseline) *Un-doped Silicon Glass “Coral” is a trade mark of Novellus Systems, Inc.

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.

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