Porous films in microelectronics

• For decreasing the capacitance of interconnection isolators in integrated circuits:
  • Decrease of RC time delay (increase of operating frequency)
  • Decrease of power consumption
• For further decreasing the dielectric constant, the material has to be porous
  • This implies additional reliability questions, eg.:
    • Cracking / adsorption loss (need to stay on the substrate for long)
    • Mechanical strength (need to survive chemical-mechanical polishing, CMP)
      • Typical Young modulus of SiO2 is 70 GPa (for dense SiOCH: <15 GPa, for porous SiOCH: <10 GPa)
    • Moisture absorption (need to be hydrophobic, in order to remain a good insulator)
  • Dielectric constant depend on porosity, eg. for porous SiOCH*:
    • ULK (ultra low-k): k ≈ 2.5 , with porosity ≈ 20% and pore size ≈ 3-4 nm
    • ELK (extreme low-k): k ≈ 2.3, with porosity ≈ 30% and pore size ≈ 5-6 nm
• Characterization of porous dielectric layers is necessary to ensure reliable layer fabrication