1. CMP-MIC 2006 Modeling Wafer Surface Damage Caused During CMP Terry A. Ring ◊, Paul Feeney, Jaishankar Kasthurirangan, Shoutian Li, David Boldridge, James Dirksen ◊ Chemical Engineering Department 50 S. Central Campus Drive, MEB3290 University of Utah Salt Lake City, UT 84112 www.che.utah.edu/~ring Cabot Microelectronics Corporation and 870 Commons Drive Aurora, IL 60504

2. CMP-MIC 2006 Overview Description of Surface Damage –Fracture Mechanics Description of Surface Damage Experiments Description of Surface Damage Model –Two Simultaneous Population Balances Under Wafer Impurity Particles Surface Damage Comparison of Model with Experiments Conclusions

3. CMP-MIC 2006 Surface Damage Indenter = Hard Impurity Particle Indenter Forced Into Surface Indenter Dragged Across Surface Plastic Deformation (Plow) Brittle Fracture gives Flakes

4. CMP-MIC 2006 Surface Damage ILD (PETEOS) Failure by Brittle Fracture

5. CMP-MIC 2006 Surface Damage Copper Plastic Deformation

6. CMP-MIC 2006 Surface Damage Copper Plastic Deformation D p =1-2 micron

7. CMP-MIC 2006 Experiments Copper CMP –Copper Slurry Fumed SiO 2 Abrasive –Same Copper Slurry With 0.07% wgt 1.1  m  -Al 2 O 3 particles ILD CMP –Copper Slurry Fumed SiO 2 Abrasive –Same Copper Slurry With 0.07% wgt 1.1  m  -Al 2 O 3 particles 100 mm Blanket Wafers, 60 s polishing on a Logitech CDP polisher (Logitech Ltd., Glasgow, UK) with an A110 pad with CMC standard concentric grooving (30 mils x 10 mils x 80 mils)

8. CMP-MIC 2006 Experimental Results – Candela Instruments PETEOS –Explosion of Brittle Fractures Copper –Explosion of Surface Damage Plow Lines Rolling Indenter

9. CMP-MIC 2006 Depth of Defects AFM of Copper Surface Damage δ ave =9.6 nm δ ave =1.7 nm ?

10. CMP-MIC 2006 Model Equations-1 1) Surface Damage type=i; surface material=j, Population No./cm 2 Population Balance of Surface Damage Removal Generation Uncovery s  s=  /  i Impurity Particles

11. CMP-MIC 2006 Surface Damage Results Evolution of the Initial Size Distribution of Scratches with time, RR o =-400 nm/s, UR=0, PR=0. Time Total Number density of Scratches

12. CMP-MIC 2006 Add 0.2% Impurity Particles RR o =-400 nm/s, UR= 0, PR = - 0.002*0.2*RR o. 20% of RR is mechanical 0.2% Impurity Particles Time

13. CMP-MIC 2006 Add Impurity Particles 2% impurity particles 0.2% impurity particles 0% impurity particles PR = (% I Particles) RR o (Fraction Mechanical Removal) RR o = -400 nm/s

14. CMP-MIC 2006 Uncover of Pores with Scratch Production Total Number of Scratches as a Function of Polishing Time, RR o = -400 nm/s, UR= -RR o commencing at 5 s and continuing until the 4,000 nm pores are uncovered, PR = - 0.02*0.2*RR o. w/o uncovery w uncovery s  s=  /  i s Pore

15. CMP-MIC 2006 Surface Damage Model Conclusions Dynamic Population Balance Model of Scratches has been developed –With simple models for RR, PR and UR –Results are Expected Starting with a large population of surface scratches –Low PR results in decreased number of scratches –High PR results in increased number of scratches Uncover of pores is a temporal problem

16. CMP-MIC 2006 Model Equations-2 2) Impurity Particle Population No./mL Under Wafer Impurity Particle Population Balance Dissolution InflowOutflow ProductionRemoval by Grooves

17. CMP-MIC 2006 Impurity Particles Production Rate (ILD only) Removal Rate in Grooves The collision frequency, α c, varies from 10 -3 to 10 4 Hz The particle removal frequency, β, β values ranging from 14 Hz to 440 Hz. Impurity Particle Rotation Particle Mass Transfer

18. CMP-MIC 2006 Size of scratch debris particles (red line) versus the size of the indenter causing the damage to the wafer surface (ILD). 12 Evans, A.G. and Marshall, D.B. Fundamentals of Friction and Wear of Materials, (ASM: 1980), p. 441 s α(s) 1/8 Results Pointed Particle with 1/10 th radius of curvature Flake n=1

19. CMP-MIC 2006 Flow in Grooves Velocity Vectors for Flow of Slurry in Groove, V rel = 1 m/s Particle Trajectories for Flow of Slurry in Groove, V rel = 1 m/s

20. CMP-MIC 2006 Solution for Impurity Particles Impurity Particle Population Balance Separation of Variables Solve for functions individually Initial Condition

21. CMP-MIC 2006 Solution for Impurity Particles Cases – Impurity Particle Equation –with particle dissolution –with particle generation –with particle removal Flow Types –Wafer Center – Dead (Stagnant) Zone Batch –Wafer Periphery Well mixed Plug flow

22. CMP-MIC 2006 Impurity Particles - Stagnant Zone Analytical Solutions Stagnant Zone – dissolution + generation, n=0 Stagnant Zone – dissolution + generation Stagnant Zone – dissolution + generation + Groove removal

23. CMP-MIC 2006 Stagnant Zone – dissolution Plot of impurity particle population with time for the conditions, n = 0, α c = 10 -4 Hz, s c = 500 nm, D = 30 nm/s, N o =1/mL, s o =10 3 nm. η I_o (s) is given by the red solid line, the population η I (s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot- dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd. Impurity Particles

24. CMP-MIC 2006 Stagnant Zone – dissolution + generation Plot of impurity particle population with time for the conditions, n = 2, α c = 10 -2 Hz and 10 -4 Hz, s c =500 nm, D = 30 nm/s, N o =1/mL, s o =10 3 nm. η I_o (s) is given by the red solid line, the population η I (s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd. Impurity Particles α c = 0.0001 Hzα c = 0.01 Hz

25. CMP-MIC 2006 Stagnant Zone – dissolution + generation + groove removal Plot of groove enhanced impurity particle population with time for the conditions, β = 1 Hz (A) and 10 Hz (B), d 50 = 1000 nm, n = 2, α c = 10 -4 Hz, s c =500nm, D = 30 nm/s, N o =1/mL, s o =10 3 nm. η I_o (s) is given by the red solid line, the population η I (s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd.  =1 Hz  =10 Hz α c = 0.00001 Hz

26. CMP-MIC 2006 Conclusions-Impurity Particle Model When Impurity Particle Production Rate is Dominant –Explosion of Impurity Particles When Impurity Particle Removal Rate is Dominant –Decreasing Population of Under Wafer Impurity Particles

27. CMP-MIC 2006 Apply to Several Types of Surface Damage ILD –Brittle Fracture Copper –Plastic Plow –Rolling Indenter One Equation for Each type of Surface Damage

28. CMP-MIC 2006 Surface Damage Coupled to Impurity Population Balance Removal Generation Uncovery Surface Damage type=i; surface material=j, s s=  /  i 

29. CMP-MIC 2006 Scratch Depth κ κ δ δ s s Particle Pressed into Pad Asperity by Wafer Surface

30. CMP-MIC 2006 Rate of Surface Damage F D is the fraction of particle collisions with the wafer surface that cause surface damage. K.P_RC (s) is the particle collision rate with wafer surface due to particle rotation. K.P_MT (s) is the particle collision rate with wafer surface due to particle mass transfer. ILD Surface Damage (i=1) Surface Damage Mechanism (j) k ij (s = δ/κ i )κiκi Comment Brittle Fracture Scratching F D K.P_MT (s)0.1Only valid for impurity particles above a certain size Chatter Surface Damage F D K.P_RC (s)(1-(s/δ gap )) >0.1Impurity particles must be larger than the gap between wafer and pad Copper Surface Damage (i=2) Surface Damage Mechanism (j) k ij (s = δ/κ i )κiκi Comment Plastic plow surface deformation (line scratches) F D K.P_MT (s)0.54Only valid for impurity particles between certain sizes, the size associated with the elastic limit and the plastic yield point Rolling Indenter Particle Surface Damage F D K.P_RC (s)(s/δ gap )0.54Impurity particles must be larger on one axis than the gap between wafer and pad

31. CMP-MIC 2006 Stagnant Zone w/o Grooves Stagnant Zone for Pad Without Grooves

32. CMP-MIC 2006 Stagnant Zone w Grooves

33. CMP-MIC 2006 Peripheral (CSTR) w/o Grooves

34. CMP-MIC 2006 Peripheral (CSTR) w Groove

35. CMP-MIC 2006 Model Comparison Measure the number, types and location of surface defects on a wafer polished under a given set of CMP operating conditions –Standard Slurry –Spiked with Impurity Particles

36. CMP-MIC 2006 Conclusions Surface Damage Mechanisms –Copper Plastic Deformation Line Scratch & Rolling Indenter –ILDBrittle Fracture Chatter Scratch & Brittle Fracture Model Gives Size Distribution of Defects as it Changes with Polish Time Slightly More Scratching in Stagnant Zone (Wafer Center) When there is an excess of debris production compared to debris removal by either washout or removal in the pad grooves, the impurity particles will build up and cause surface damage

37. CMP-MIC 2006 Extra Slides

38. CMP-MIC 2006 Die Yield N = No. metal layers n = No. metal CMP )perations m = No. ILD CMP Operations o = No. Barrier CMP Operations P i = Probability of die failure due to CMP

39. CMP-MIC 2006 Surface Damage at Wafer Rim Scratching in Wafer Rim Production Rate (BSG only) Impurity Particle Rotation Across Gap x = R w - r

40. CMP-MIC 2006 Wafer Rim has more Surface Damage RimCenter

41. CMP-MIC 2006 Model Equations Impurity Particle Population No./mL Under Wafer Impurity Particle Population Balance Surface Damage type=i; surface material=j, Population No./cm 2 Population Balance of Surface Damage Dissolution InflowOutflow ProductionRemoval by Grooves Removal Generation Uncovery s  s=  /  i

42. CMP-MIC 2006 Increase Generation Rate Stagnant Zone – dissolution + generation + groove removal Plot of groove enhanced impurity particle population with time for the conditions, β = 1 Hz (A) and 10 Hz (B), d 50 = 1000 nm, n = 2, α c = 10 -2 Hz, s c =500nm, D = 30 nm/s, N o =1/mL, s o =10 3 nm. η I_o (s) is given by the red solid line, the population η I (s,t) is given by all the other lines with the dotted blue line for t = 0.1 τ, the dashed green line for t = 2 τ, the dot-dash magenta line for t = 4 τ, the dotted cyan line for t = 6 τ, the dotted brown line for t = 8 τ, the dashed black line for t = 10 τ, the dot-dash red line for t = 12 τ and the solid blue line for t = 14 τ where τ = 10 s. Scratch Debris Batch-2.mcd.  =1 Hz  =10 Hz α c = 0.01 Hz