Effect of Pump Induced Particle Agglomeration On CMP of Ultra Low k Dielectrics Rajiv K. Singh, F.C. Chang and S. Tanawade, Gary Scheiffele Materials Science and Engineering Particle Science Engineering Center University of Florida, Gainesville FL
Outline Introduction and Challenges Objectives Experimental Design Results and Discussion Particle Oversize- Pump Variable Correlations Defectivity Measurements Correlation Defectivity- Oversize Conclusions
Back-end ITRS Roadmap 2005 2007 2010/2011 Technology Node (nm) 90 65 45 # of Metal levels 10 11 12 Average dielectric constant 3.1-3.6 2.7-3.0 2.3-2.6 Dishing Planarity (nm) 30 19 14 Min. defect particle size (nm) 50 32.5 22.5 Grand Challenges 45 nm/through 2010 Introduction of new materials to meet conductivity requirements Engineering manufacturable interconnect compatible with new materials and processes Summary of Issues Creates integration and material characterization challenges. Integration complexity, CMP damage, resist poisoning, dielectric constant degradation. More Complicated and Lower Defect Based CMP Processing
Particle Challenges in Cu/ULK CMP Integration of Ultra low K (ULK) Dielectrics Low Stress Polishing of fragile materials Process Simplification Easy Handling (High Stability) Enhanced Performance Reduced Defectivity >> Particle Size/Size Distribution and Oversize Affects CMP Performance
Polishing of Fragile materials Hardness of Low k materials Materials Silica Silicon-oxycarbide Porous SiLK (Dow Chemical) Porous Silica Dielectric constant (k) 4.1 3.3 2.2-2.7 1.9-2.2 Hardness (GPa) ~ 8 ~ 4 ~ 0.4 0.29 0.47 New materials are mechanically fragile and exhibit poor adhesion with substrate
Particle Size Distribution Effects Polishing Rate Concentration Defectivity Particle Size
Large Particle Defectivity Delamination δ δ 3 4 Papp = φ ( ) 2/3 2KE φ = Particle Size E = Young s Modulus P = Applied Load Scratches
Large Particle Settling Effects Increased Defectivity Due to Settling
Proposed Adoption of Low K Dielectrics for Various Editions of ITRS Roadmaps Dielectric Constant (Average) 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1999 ed. 2001 ed. 2003 ed. 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Year Technology Node (nm) OSG (2.5<k<2.8) OSG (2.2<k<2.4) Porous MSQ (2.2<k<2.4) Porous polymer (2.0<k<2.4) Ultra-low k (k<2.0) research required qualification/pre-production continuous Improvement OSG: organosilicate glass MSQ: Methyl sisesquioxane Push out in low k integration due to integration challenges 2004 90 2007 65 2010 45 2013 32
Pump Effects on CMP Slurries Pumps for Slurry Handling Can Significantly Affect Particle Characteristics Particle Size Distribution Oversize Particle Production Critical in Polishing of copper/low k dielectric ( more susceptible to scratches)
Pump Based Particle Agglomeration Pumps (Types) Bellows, Diaphragm, Centrifugal Typically bellows/diaphragm pumps are used have shown significant agglomeration in silica based slurries. (CT Associates) Agglomeration attributed to high shear stress in partial sample volumes. Magnetically levitated centrifugal pumps have shown considerable less agglomeration. (attributed to low shear rates/cavitation effect)
Objectives Role of Oversize Particles in Defectivity Generation in Low K/ ultra low k Polishing (most sensitive to oversize particles). Evaluation of Agglomeration-free pumping systems ( Centrifugal Pumps) for low k/ ultra low K polishing
Outline Introduction and Challenges Objectives Experimental Design Results and Discussion Particle Oversize- Pump Variable Correlations Defectivity Measurements Correlation Defectivity- Oversize Conclusions
Experimental Details Slurry Loop DI Water Pressure Gauge Air Supply Pump Dampener Flowmeter Out In Drain Particle Measurements Dynamic Light Scattering Average Particle Size Accusizer Optical Particle Counter Oversize Tail
Experimental Details CMP Polishing Systems IPEC 372 M 8 inch wafers Struers Table Top Polisher Wafers TEOS BD1 low k (k = 3.0), LKD 5109 (JSR) ULK ( k = 2.2) Slurries Planar Solutions Step II Slurry Cu 10 K Series Metrology Optical Scattering AFM : RMS and R max Optical Microscopy
Outline Introduction and Challenges Objectives Experimental Design Results and Discussion Particle Oversize- Pump Variable Correlations Defectivity Measurements Correlation Defectivity- Oversize Conclusions
Average Particle Size Vs Slurry turnovers particle size (µm) 0.25 0.2 0.15 0.1 0.05 Centrifugal Pump particle size (µm) 0.25 0.2 0.15 0.1 0.05 Bellows Pump 0 0 250 500 1000 0 0 250 500 1000 particle size (µm) 0.25 0.2 0.15 0.1 0.05 0 no. of turnovers Diaphragm Pump 0 250 500 1000 no. of turnovers no. of turnovers Average particle size remains constant for all pumps Independent of number of slurry turnovers
Oversize Distribution Bellows (12lit/min) Diaphragm (12lit/min) Centrifugal (12lit/min) Significant increase in particle tail in Bellows & Diaphragm pumps Insignificant change in particle tail in Centrifugal pump
12 10 Normalized Oversize Distribution Bellows Diaphragm Centrifugal C 500 /C 0 Turnovers 8 6 4 2 0 0 2 4 6 8 10 12 Particle Size (µm) Insignificant increase in oversize particles for centrifugal pump
Oversize Increase Vs Pump Speed 5 4.5 4 C1000/C0 turnovers 3.5 3 2.5 2 1.5 1 0.5 9 lit/min 12 lit/min 0 Centrifugal Diaphragm Bellows Centrifugal pump shows least oversize increase
Oversize Increase Vs Turnovers cum. con.(#/ml) 80000 70000 60000 50000 40000 30000 20000 10000 0 12 lit/min Centrifugal Diaphragm Bellows 250 turnover 500 turnover 1000 turnover cum. con.(#/ml) 9 lit/min 70000 60000 50000 250 turnover 40000 500 turnover 30000 1000 turnover 20000 10000 0 Centrifugal Diaphragm Bellows Centrifugal pump has least oversize increase in different turnovers and pump speeds
Pump vs Particle Size Distribution Average Size (no change) Concentration Oversize [significant change for positive displacement pumps] Particle Size
Outline Introduction and Challenges Objectives Experimental Design Results and Discussion Particle Oversize- Pump Variable Correlations Defectivity Measurements Correlation Defectivity- Oversize Conclusions
Diaphragm Pump (12 lit/min-1000 turnovers) Centrifugal Pump (12 lit/min-1000 turnovers) BD1 Wafer BD1 Wafer ULK Wafer ULK Wafer AFM AFM
Defectivity vs. Pump Speed scratch density (#/sq. mm) 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 BD1 wafer Centrifugal Diaphragm Bellows 9 lit/min 12 lit/min 9 lit/min Bellows 12 lit/min Bellows 1000 turnovers slurry from pump scratch density (#/sq. mm) 6 5 4 3 2 1 0 ULK wafer 9 lit/min 12 lit/min Centrifugal Diaphragm Bellows 1000 turnovers slurry from pump Increased defectivity with high pump speed 9 lit/min Bellows 12 lit/min Bellows Centrifugal pump has least defectivity
Scratch density (#/sq. mm) 4 3.5 3 2.5 2 1.5 1 0.5 0 Defectivity vs. Turnovers BD1 wafer Centrifugal Diaphragm 250 500 1000 Turnovers Centrifugal Diaphragm Scratch density (#/sq. mm) 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 ULK wafer 250 500 1000 Turnovers Centrifugal Diaphragm Increased defectivity with high turnovers for Diaphragm Centrifugal Diaphragm
RMS-Roughness vs. Pump types BD1 Wafer 0.25 0.2 Rms (nm) 0.15 0.1 0.05 9 liters/min 12 liters/min 0 Centrifugal-1000 turnover Diaphragm-1000 turnover Bellows-1000 turnover Least roughness observed in Centrifugal pump
R Max (nm) Surface Damage & Pump Speed 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 Centrifugal-1000 turnover Diaphragm-1000 turnover Bellows-1000 turnover 9 liters/min 12 liters/min AFM-Centrifugal 12 liters/min AFM-Diaphragm 12 liters/min AFM-Bellows 12 liters/min
Surface Roughness Vs number of Turnovers 0.25 0.2 BD1 Wafer-12 liters/min Rms (nm) 0.15 0.1 0.05 Centrifugal Diaphragm 0 250 turnover 1000 turnover AFM-Centrifugal AFM-Diaphragm AFM-Centrifugal AFM-Diaphragm 250 turnover 250 turnover 1000 turnover 1000 turnover
Oversize Distribution Bellows (12lit/min) Diaphragm (12lit/min) Centrifugal (12lit/min) Significant increase in particle tail in Bellows & Diaphragm pumps Insignificant change in particle tail in Centrifugal pump
Oversize increase Vs Defectivity scratch density (#/sq. mm) 7 6 5 4 3 2 1 0 Centrifugal Pump Conventional Pumps 1 1.5 2 2.5 3 3.5 Normalized oversize particles 2 RMS roughness (nm) 0.25 0.20 0.15 0.10 0.05 Centrifugal Pump Conventional Pumps 0.00 1 1.5 2 2.5 3 3.5 Normalized oversize particles 2 Excellent Correlation between oversize particle increase with RMS roughness and scratch density
Conclusions Bellows and diaphragm pumping systems result in significant agglomeration ( oversize particles) of low k slurries. The degree of agglomeration depends on slurry turnovers and pump speed. Centrifugal pumps based on magnetic levitation did not show appreciable particle agglomeration in low k slurries. Significant Increase in Defectivity (scratches, roughness, particle deposition) were observed in conventional pump processed slurries Least Defectivity observed for Centrifugal pump processed slurries Excellent Correlation between roughness/ defect density and the degree of agglomeration
Acknowledgements The authors would like to thank Levitronix for their financial support on this project. The authors also thank Christos Monovoukas for his technical input in this project.