Nickel Electrodeposition

Advanced Process Control Of Nickel Electrodeposition for Packaging in Semiconductor Industry

Authored by Eugene Shalyt, Jingjing Wang, Vishal Parekh, Michael MacEwan
Presented at the ElectroChemical Society’s 226th Biannual meeting in Cancun, Mexico, 2014.

ECI Technology, Totowa, NJ 07512, USA

Outline

• Use of Nickel Electrodeposition in Packaging
• Components of electrolyte and their function
• Metrology approaches and field validation with specific focus on
  • Surfactant
  • Leached Photoresist
  • Sulfur-Bearing Additive and/or Breakdown Product
  • Nickel
• Conclusions

Use of Ni Electrodeposition

Nickel is not used as a final layer. It is used as a diffusion barrier between Cu and other final layers: Sn and it’s alloys, Pd, and Au.

Barrier Properties of Ni Electrodeposit

Components of Electrolyte

Root Cause of Pitting

Pitting Remediation

• Reduce amount of H₂ bubbles
  • maintaining pH > 4 to reduce partial current of H₂ formulation
    however Ni(OH)₂ formation can occur above pH 4.5
• Reduce lifetime of bubbles
  • Intense agitation
  • Use of surfactant/wetter to lower surface tension

Effect of Surfactant on Voltammogram

Suppression vs. Wetter Property

There is no link. Chemical can have both properties, none, or only one.

Measurement of Surfactant by Surface Tension

• Response is not linear
• Matrix and temperature dependent
• Surface tension results cannot be used for precise measurements

Measurement of Surfactant by Titration

R- SO₃^–Na⁺ + R₄NCl^–  –> RSO₃NR₄ + NaCl

Measurement of Leached Photoresist

Field Data on Accumulation of PR

Effect of PR on Voltammogram

Effect of S Compound

S Compound

Source:

• Added on purpose (Saccharine derivative)
• Sulfamate breakdown product

Monitoring of S Compound

• HPLC
• Polarography
• Stress Measurement
• Cyclic Voltammetry
• Spectroscopy (new)

Monitoring of S Component

Field Data for S Component

Monitoring of Ni

• Complexometric titration
  • Slow, high cost of ownership
• Spectroscopy
  • Realtime, non-reagent, low cost of ownership

UV-Vis Spectra of Ni Solutions

Ni @ 66 g/l
matrix components are varied within process range

Majority of spectral range is highly selective to Ni and free of interferences

Monitoring of Other Components

Conclusions

• Comprehensive suite of automated analytical methods have been developed to meet the challenges of modern semiconductor applications:
• Nickel
• Boric
• Anode Activator (Cl, Br)
• pH
• Surfactant
• Leached Photoresist
• Sulfur-Bearing Additive and/or Breakdown Product