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Electroless Ni Plating

To replace Al evaporation

Hacker Fab

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Metalization

Metal thin films on chip surface

Forms electrical connections and wires

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Hacker Fab

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Electroless Plating vs Thermal Evaporation

Electroless Plating:

  • Atmospheric pressure
  • $55
  • Plating in ~10 minutes

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Al Evaporation:

  • High Vacuum
  • $15,000
  • Several hours with pump down

Hacker Fab

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Nickelex & Electroless Plating

Similar to electroplating, but driven by reaction:

Ni2+(complex) + H2 = Ni (s) + 2H+

H2PO2– + H2O = H2OPO3– + H2

Reaction is very sensitive to the surface

Faster on conducting surfaces

Temperature range: 90-98°C

Deposition rate: 40 nm/min at ~90°C

Hacker Fab

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Sintering & Oxidation

Sintering:

  • High temperatures, increases mobility
  • Creates more uniform material

Oxidation:

  • High temp, Ni reacting with O2 in air
  • Increases resistance and thickness

Before: 60 nm, 59 Ω

After: 120 nm, 135 Ω

Before

After

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Selective Plating & Ni-Si interface

Selective plating can pattern chips (8.5 μm)

Measure the resistance of Ni-Si interface

Intercept - Contact Resistance Slope - Sheet Resistance/Width

Ohmic Contact

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Ni

Glass - 700B

Ni

700B

Si

Doped Si

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Contact (Ω*cm2)

Sheet (Ω/sq)

Ni-Si

12*10-4

1.87

Al-Si

7.3*10-4

43.1

Hacker Fab

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Sensitization & AuCl3

AuCl3 acts as a catalyst for the plating

✅Plating on SOG and photoresist

❌Plating too fast:

  • Poor adhesion
  • Flaking of Ni

❌Overall inconsistent thickness:

  • Spin coated didn’t help

❔Impact on electrical properties

Hacker Fab

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Selectively plated transistor

Selectively plate Ni into contact holes of transistor

Transistor behavior with low gate leakage

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Hacker Fab

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Reliability and next steps

Ni plating was not consistent enough

  • 1 of 50+ transistors worked across 3 chips
  • Damage photoresist while plating
  • Flaking and oxidation of Ni

Future Work:

  • Prevent resist damage and improve plating on glass
  • Improve AuCl3 sensitization and Ni etching
  • Use alternative chemisity for plating

Hacker Fab

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Questions

Hacker Fab

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Nickel Etchant TFG

  • For electroless plated Ni
    • From Transene (Nickelex provider)
  • 50 Å/second at 40°C
    • Double with every 10°C
    • Max temp: 80°C
  • Compatibility:
    • Etch: Al, C, Co, Ni, Mg
    • Slight Etch: Fe
    • No etch: Al2O3, Au, Cr, Cu, GaAs, MgO, Nb, Si, Glass, Alumina, Nitride, HDPE, PP, Teflon, PFA, PVC

Hacker Fab

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Nickel Etching

✅Ni was etched

❌Much slower than expect

  • Expected: 6 min at 50°C
  • Actual: 30+ min at ~70°C

❌Etching of photoresist

❌ AuCl slows etching

❔Glass hard mask

30 sec

10 min

2 min

30+ min

Hacker Fab

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Hacker Fab

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