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Modeling The Deposit Thickness Distribution in Copper Electroplating of Semiconductor Wafer Interconnects

Modeling The Deposit Thickness Distribution in Copper Electroplating of Semiconductor Wafer Interconnects. Eugene Malyshev 1 , Uziel Landau 2 , and Sergey Chivilikhin 1 1 L-Chem, Inc Beachwood, OH 44122 and 2 Department of Chemical Engineering, Case Western Reserve University,

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Modeling The Deposit Thickness Distribution in Copper Electroplating of Semiconductor Wafer Interconnects

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  1. Modeling The Deposit Thickness Distribution in Copper Electroplating of Semiconductor Wafer Interconnects Eugene Malyshev 1, Uziel Landau 2, and Sergey Chivilikhin 1 1 L-Chem, Inc Beachwood, OH 44122 and 2 Department of Chemical Engineering, Case Western Reserve University, Cleveland OH 44106 AIChE Annual Meeting,San Fransisco, CA.

  2. Objectives • Analyze the effects of the different processparameters • Provide a convenient (for non-expert users) & comprehensive tool for: • Cell Design • Scale-up • Process Optimization

  3. Issues in Design • Deposit- • Deposit thickness uniformity (+/- ~3% across the • wafer) • Minimal edge exclusion (<5 mm) • Deposit texture/appearance • Good gap-fill • Extreme electrical/mechanical/chemical properties • Process- • Stable • Controllable • Scalable

  4. Parameters Analyzed • Cell Configuration (Dimensions, Edge gap, Shields) • Flow (Rotation and Convective Flow) • Seed Layer Thickness • Electrolyte Composition • Acid Concentration (Conductivity) • Reactant Concentration (Mass-Transport) • Additives (Kinetics/Polarization Curve) • Operating Parameters: Current/Voltage

  5. Cell “Generic” configuration Base Case: r = 100 mm, gap =10 mm i = 20 mA/cm2, K= 0.55 S/cm, seed thickness = 1000A rotation = 60 rpm impinging flow = 4 gpm 60 rpm WAFER HOLDER HOLDER WAFER GAP GAP 100 mm 10 mm 10 mm Seed thickness 150 mm Applied Voltage DISTRIBUTED FLOW = 4 gpm ANODE

  6. Flow effects Rotating Disk vs. Combined Flow Flow Map: Modified Design Flow Map: Base Case Base case Delta, cm Modified Levich eqn. r/R

  7. Numerical comparison with analytical model Model system: rotating disk, r = 7 mm, Cb = 0.28 mole/L, D = 6.7*10-6 cm2/s Cell-Design Delta, cm Levich eqn. Levich eqn. i lim, A/cm2 Cell-Design

  8. Effect of edge-gap Wafer r = 100 mm Simulated gaps: 5 mm, 10 mm, and 15 mm; Cb = 0.28 mole/L, D = 6.7*10-6; Impinging flow = 4 gpm 5 mm i lim, A/cm2 50 mm 100 mm 150 mm

  9. Resistive substrate effect HOLDER GAP HOLDER WAFER WAFER GAP 100 mm 10 mm 10 mm Seed thickness 150 mm Applied Voltage DISTRIBUTED FLOW = 4 gpm Seed thicknesses = 500, 1000 and 2000 Å. iaverage = 10 and 40 mA/cm2. Wafer r = 100 mm. Rotation = 60 rpm. Impinging flow = 4 gpm. Cb= 0.28 mol/L, k = 0.55 S/cm, D = 6.7*10—6cm2/s. ANODE 500 Å 1000 Å iaverage = 40 mA/cm2 2000 Å no seed resistance Current, A/cm2 500 Å iaverage = 10 mA/cm2 1000 Å no seed resistance 2000 Å

  10. 60 rpm WAFER HOLDER DISTRIBUTED FLOW = 4 gpm ANODE Gap Effect of edge-gap i = 20 mA/cm2 gap = variable seed = 1000 A Gap = 0 mm Gap = 10 mm Gap = 50 mm Deposit, [micron] Deposit, [micron] Deposit, [micron] 150 sec 150 sec 180 sec 1-3 time steps = 20 sec, 4-7 time steps = 30 sec

  11. Shield design 60 rpm 60 rpm 60 rpm HOLDER HOLDER HOLDER WAFER WAFER WAFER DISTRIBUTED FLOW = 4 gpm DISTRIBUTED FLOW = 4 gpm DISTRIBUTED FLOW = 4 gpm DISTRIBUTED FLOW = 4 gpm ANODE ANODE ANODE i, A/cm2 i, A/cm2 i, A/cm2 10% variation

  12. 200 mm wafer vs. 300 mm wafer 60 rpm Seed thickness = 1000 Å. Cb= 0.28 mol/L, k = 0.55 S/cm, D = 6.7*10—6cm2/s. WAFER HOLDER GAP 200 mm wafer 100 mm deposit(r/R=1) / deposit(r/R=0) =1.646 180 sec 10 mm 150 sec 120 sec 150 mm 90 sec Deposit, micron DISTRIBUTED FLOW = 4 gpm 60 sec 40 sec 20 sec r/R 300 mm wafer 150 mm 180 sec deposit(r/R=1)/deposit (r/R=0) =1.847 150 sec 10 mm 120 sec 90 sec 150 mm Deposit, micron 60 sec 40 sec DISTRIBUTED FLOW = 9 gpm 20 sec r/R

  13. 180 sec 150 sec 120 sec 90 sec 60 sec 40 sec 20 sec Electrolyte conductivity (pH) 200 mm wafer Deposit, [micron] Deposit, [micron] k = 0.55 S/cm k = 0.055 S/cm iaverage = 20 mA/cm2 seedth = 1000 A iaverage = 20 mA/cm2 seedth = 1000 A 180 sec 150 sec 120 sec 180 sec 90 sec 150 sec 120 sec 60 sec 90 sec 60 sec 40 sec 40 sec 20 sec 20 sec r/R r/R 300 mm wafer Deposit, [micron] Deposit, [micron] k = 0.55 S/cm k = 0.055 S/cm iaverage = 20 mA/cm2 seedth = 1000 A iaverage = 20 mA/cm2 seedth = 1000 A 180 sec 150 sec 120 sec 90 sec 60 sec 40 sec 20 sec r/R r/R Low acidity High (normal) acidity

  14. Additives effect Current density, [A/cm2] Pure copper sulfate (0.5 M, pH = 2, no additives ) With additives * r/R * - Plating from copper sulfate in the presence of 70 ppm Cl -, 50 ppm SPS and 200 ppm Polyethylene glycol [‘PEG’] - (molecular weight = 4000 )

  15. The effects of the various process parameters have been simulated The simulated results are in general agreement with observations. Some Specifics: A proper shield design at the wafer edge significantly enhances uniformity Electrode rotation has a larger effect than the convective flow (in the practiced range) Wafer plating (macroscopic scale) does not typically operate under mass transport control The edge-gap has a major effect on the flow and the current density near the wafer edge The resistive seed effect is noticed mostly at higher current densities (~40 mA/cm2) Scaling to 300 mm enhances the non-uniformity effects, unless compensating measures are taken,. Conclusions

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