Optimized CMP of ULK Dielectrics

Optimized CMP of ULK Dielectrics Taek-Soo Kim Markus Ong Reinhold H. Dauskardt (dauskardt@stanford.edu) Collaborations: Tatsuya Yaman and Tomohisa Konno JSR Micro, Inc. Research supported by the SRC, DOE and the Microelectronics Industry.

Reliable Processing of Interconnect Structures Applied CMP down force Si ULK CMP Slurry Applied CMP shear load σ f P cracking delamination abrasive Via Low-k nano-scale defect PAD 0.1 μm Process yield and reliability determined by the evolution of defect thermomechanical reliability of low k films soft/ductile buffer layers silicon device CMP and package contact stresses effect of metal density and aspect ratio cracking depends on flux composition

Road Map for Optimized CMP of ULK Dielectrics Threshold of G, G TH (J/m 2 ) 2.2 2.0 C 12 1.8 1.6 C 10 C 18 1.4 Gemini 1.2 0 20 40 60 80 100 Number of EO, n Defect Evolution CMP Damage Damage ~ v k Increase k ~ D Diffusion Coefficient, D (m 2 s -1 ) G ~ a b th D M ~ 10-12 10-13 Diffusion C 10 C 12 Gemini D 10 2 10 3 Molecular Weight, M (g mol -1 ) Optimized CMP ~ RR M α ~ D c M d RR G β Removal Rate (RR) RR of LKD 10 4 10 3 10 2 th C 12 C 8 10 1 10 0 10 1 10 2 Number of EO, n

Outline Cracking Involving Chemically Active Solutions fracture of ULK materials slurry chemistry effects on damage evolution Diffusion of Chemically Active Solutions diffusion of aqueous solutions effects of nonionic surfactants Correlations with CMP Removal Rate role of surfactants removal, diffusion and defect evolution rates Summary

Crack Driving Force and Subcritical Cracking Applied CMP down force P elastic-plastic contact σ f Si ULK CMP Slurry PAD Applied CMP shear load σ f P cracking delamination abrasive damage initiated by abrasive or pad asperity total Crack Driving Force G = G + G + G G G film contact film 2 Zσ f hf = E f contact CMP 2 P = χ elastic-plastic 3 E a contact f film stress G CMP = fn( shear, pressure) In the absence of chemically active environmental species, crack propagates if G G J m total total c c 2 ( / ) In the presence of chemically active species during CMP, crack propagates if G < G J m 2 ( / ) CMP slurry accelerates defect evolution

DTS Company Automated Crack Velocity Testing Vapor environment Port for vapor injection Liquid environment adhesive/cohesive crack P o Load, P Crack Length, a Thermocouple Delaminator System, DTS Company Load Relaxation Crack Growth Technique dp/dt da/dt Time (s) System and support available from: DTS Company, Menlo Park, CA (contact: dauskardt@stanford.edu) Solution container compliance analysis fracture path cap liner Low k OSG Crack Growth Velocity, da/dt (m/s) 10-8 10-9 10-10 ph 4.5 3%H 2 O 2 Accelerated Cracking In low k OSG aqueous ph 11 1 2 aqueous ph 3 threshold crucial for reliability Applied Strain Energy Release Rate, G (J/m 2 )

Dielectric Cracking in Non-Buffered Solutions Crack growth rates are accelerated with increasing ph (increasing hydroxide ion concentration) Crack Propagation Rate, da/dt (m/s) 10-8 10-9 10-10 OH - mediated reaction ph 14.4 Transport of OH - ph 11 ph 5.8 30ºC Polymeric Cap Porous MSSQ 1.2 1.4 1.6 1.8 2 2.2 2.4 Applied Strain Energy Release Rate, G(J/m 2 ) E. Guyer and R. H. Dauskardt (JMR) - 2005 crack tip reaction Si O Si + nh 2 O 2(Si OH) Si O Si + noh _ Si OH + Si O _ bulk solution dominated by [OH] l crack velocity a o stagnant boundary layer Issues: model predictions reaction order what is crack tip [OH]?

Decelerated Crack Growth by Crack Tip Blunting Crack Growth Rate, da/dt (m/s) 10-8 10-9 10-10 Electrolytes in DI water w/o surfactants ph 10 (NH 4 OH) ph 7 ph 10 (NaOH) ph 10 (KOH) 50%RH 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Applied Strain Energy Release Rate, G (J/m 2 ) Alkali metal ions in solution result in crack tip blunting by dissolution of silica Silica gel dissolution in aqueous alkali metal hydroxides Wijnen, 1989

C m Effects on Crack Growth Behavior (in ph 10 KOH) Alkali metal ion + EO Complexation C m Metal ion Nonionic surfactant Polyoxyethylene Alkyl Ethers EO of Polyoxyethylene Alkyl Ether Carbon Oxygen Okada (1993) The EO chain locked by the cation, stabilzed by two electron-rich oxygen atoms, decreases mobility Crack Growth Rate, da/dt (m/s) 10-8 10-9 10-10 C 18 E 10 KOH ph10 + 0.1wt% surfactant NH 4 OH KOH C 18 E 20 C 18 E 100 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Applied Strain Energy Release Rate, G (J/m 2 ) Crack tip blunting effects suppressed by shielding of potassium ion. Also, complexation reduces hydrogen bonding sites G bridging (see later)

Extensive Damage during CMP 45 s CMP Crack growth rates ~ m/s during gross delamination observed in CMP experiment Crack Growth Rate, da/dt (m/s) 10-3 NH 4 OH DI Water Citric Acid TMAH H 2 O 2 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Applied Strain Energy Release Rate, G (J/m 2 ) NH 4 OH DI water Citric acid TMAH H 2 O 2 Ave. Crack Velocity, da/dt (m/s) 10-3 DI water H 2 O 2 NH 4 OH citric acid TMAH 40 45 50 55 60 65 70 75 80 85 90 Area fraction of Delamination

Reduced Damage and High Yield in CMP low crack growth rates critical for growth of nano-scale flaws dominated by threshold behavior in v-g curves Crack growth rates <10-10 m/s (below threshold) necessary to achieve reliable integration Crack Growth Rate, da/dt (m/s) 10-3 NH 4 OH DI Water Citric Acid TMAH H 2 O 2 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Applied Strain Energy Release Rate, G (J/m 2 ) threshold crucial for reliability Synergistic effects of CMP slurry chemistry and stress on defect evolution/crack growth are unknown!

Crack Growth Rate, da/dt (m/s) 10-8 10-9 10-10 Defect and Damage Evolution during CMP 0.1 wt% surfactant ph 7 slurry surfactant effects C 10 C 12 E 4 E 6 E 9 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Applied Strain Energy Release Rate, G (J/m 2 ) Crack Growth Rate, da/dt (m/s) Crack Crack Propagation Growth Rate, Rate, da/dt (m/s) 10-8 10-9 10-10 crack copper 250Å TaN ph 11 ESC-797 Crack Growth Rate, da/dt (m/s) 10-8 10-9 10-10 0.1 wt% surfactant ph 7 E 4 E 7 E 23 E 50 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 cleaning solutions CVD-CDO BD I ph 11 Buffered Applied Strain Energy Release Rate, G (J/m 2 ) Test at 30 o C ph 1.5 Kanto MO2 accelerated cracking 0.5 1 1.5 2 2.5 3 Applied Strain Energy Release Rate, G(J/m 2 ) pad slurry low k layer silicon Mode I crack initiation and propagation P elastic-plastic contact σ f damage created by slurry particle or pad asperity

Technique developed by: Shaw, et.al. (2004) Worsley, et.al. (2004) Watch solutions diffuse into porous films change in RI Diffusion of Solutions into Films ph 11 buffered solutions SiN x Porous MSSQ Silicon 1.5 hours 20 hours 44 hours Diffusion Distance, x (μm) 150 100 50 ph 11 solutions Concentrated Buffer Regular Buffer Weak Buffer Non-Buffer 0 0 200 400 600 800 1000 Square Root Time, t 0.5 (sec 0.5 ) ν = 1.3 10-9 m/s 50μm ν = 4.9 10-10 m/s 50μm ν = 3.8 10-10 m/s 50μm Guyer, Patz and Dauskardt (JMR) - 2006

Surfactant Enhanced Diffusion Mechanism Diffusion Coefficient, D (m 2 s -1 ) 10-12 10-13 10-14 10-15 0.1wt% solution C m Dimeric Surfynol -1.96-1.85 10 2 10 3 10 4 Molecular Weight (g mol -1 ) Diffusion Coefficient, D (m 2 s -1 ) 10-12 10-13 100 wt% surfactant C 10 C 12-1.31-1.25 Dimeric Surfynol -0.14 10 2 10 3 Molecular Weight (g mol -1 ) D ~ M α D diff const M mol. Weight α const Real surfactant diffusion, not a surface phenomena Increase in k-value after direct CMP versus HLB of surfactant (Kondo et. al., IITC, 2007) Hydrophilic-Lipophilic Balance (HLB)

Increase of Carbon Content by Surfactant Diffusion Ar ion etching (2 mm x 2 mm) XPS scan (0.1 mm x 0.1 mm) Side view SiN x Nanoporous ULK Silicon 200 nm 500 nm (1) (2) (3) Atom % C 10 E 9 pure surfactant in liquid phase (1) (2) (3) O 27.97 42.88 47.82 Top view C Si 41.30 30.73 23.84 33.28 22.27 29.90 0.5 mm 0.5 mm ph7 NH 4 OH DI water + 0.1wt% C 10 E 9 nanoporous ULK surfactant molecule internal surface chemistry diffusion Carbon % 45 40 35 30 25 Diffusion distance C 10 E 9 pure surfactant 20 C 10 E 9 surfactant solution 0 1 2 3 4 x (mm) O C Si (1) 36.63 35.80 27.57 (2) 45.76 21.61 32.63 (3) 46.01 21.15 32.84

Mechanism Likely Related to Polymer Reptation D ~ M α α = 2 polymer reptation theory -2 Data for poly(butadiene) Experimentally, 2.3 D ~ M Jones, Soft Condensed Matter, p. 92 Diffusion Coefficient, D (m 2 s -1 ) 10-12 10-13 10-14 Dimeric Surfynol 10-15 10 2 10 3 C m -1.96 Molecular Weight (g mol -1 ) nanoporous ULK -1.85 diffusion Dynamic tube by polymer entanglement surfactant molecule internal surface chemistry Static tube by Interconnected nanopores

Surfactant Molecules to Probe Internal Pore Surface Chemistry Intensity, I Monochromatic Xe excimer λ= 172 nm E = 7.2 ev 100 200 300 400 Wavelength, λ Rapid increase in absorption UV curing reduces pore interconnectivity. Broadband suppresses solvent diffusion better than monochromatic. Low absorption Diffusion Distance, x (mm) 5.0 4.0 3.0 2.0 1.0 0.0 Broadband 500 Solvent: Dodecane (C 12 ) Surfactant: Nonionic C 12 E 4 No UV Monochromatic Broadband 0 100 200 300 400 500 600 700 Square Root Time, t 1/2 (sec 1/2 ) OH Hydrophobic interaction OH CH 3 Diffusion Distance, x (mm) CH 3 1.0 0.8 0.6 0.4 0.2 CH 3 OH Hydrophobic Hydrophilic Hydrophilic interaction OH CH CH CH 3 3 OH 3 pore surface C 12 E 4 No UV Broadband Monochromatic 0.0 0 400 800 1200 1600 2000 Square Root Time, t 1/2 (sec 1/2 )

CMP Removal and Defect Evolution Rates Crack Growth Rate, da/dt (m/s) Crack Growth Rate, da/dt (m/s) 10-8 10-9 10-10 10-8 10-9 10-10 0.1 wt% surfactant ph 7 C 10 E 4 E 6 E 9 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Applied Strain Energy Release Rate, G (J/m 2 ) 0.1 wt% surfactant ph 10 NH 4 OH E E 6 E 9 4 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Applied Strain Energy Release Rate, G (J/m 2 ) Crack Growth Rate, da/dt (m/s) Crack Growth Rate, da/dt (m/s) 10-8 10-9 10-10 0.1 wt% surfactant C 12 ph 7 E 4 E 7 E 23 E 50 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 10-8 10-9 10-10 Applied Strain Energy Release Rate, G (J/m 2 ) 0.1 wt% surfactant ph 10 NH 4 OH E 50 E 23 E 4 E 7 30 o C 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Applied Strain Energy Release Rate, G (J/m 2 ) RR of LKD 1200 1000 800 600 400 200 Removal Rate (RR) C 8 C 12 0 0 10 20 30 40 50 EO Length, n Removal Rate inversely related to G TH

CMP Removal and Defect Evolution Rates Removal Rates, RR 1200 1000 800 600 400 200 # of C = 8 # of C = 12 0 0 10 20 30 40 50 EO Length, n Log-Log plot RR of LKD 10 4 10 3 10 2 C 12 C 8 10 1 10 0 10 1 10 2 Number of EO, n This is the only RR data we have. RR is inversely proportional to G TH. Threshold of G, G TH (J/m 2 ) 2.2 2.0 1.8 1.6 1.4 C 10 C 12 RR ~ G β Gemini 1.2 0 20 40 60 Number of EO, n th

CMP Removal Rates and Diffusion Removal Rates, RR 1200 1000 800 600 400 200 # of C = 8 # of C = 12 0 0 10 20 30 40 50 EO Length, n Log-Log plot Removal Rate, RR 10 4 10 3 10 2 C 12 C 8 10 1 10 0 10 1 10 2 Number of EO, n This is the only RR data we have. RR is inversely proportional to D. Diffusion Coefficient, D (m 2 s -1 ) 10-12 10-13 C 12 C 10 Gemini RR 10 2 10 3 Molecular Weight, M (g mol -1 ) ~ D c M d