ECE1398 L5 - Silicon On Insulator.pdf

SOI

  • silicon on insulator - addition of insulator on-top of silicon
  • goal is to reduce parasitic cap

Considerations

  • SiO2 doesn't have perfect crystalline structure making growing Si above difficult
  • Floating bulk

Processing Techs

  • Fully depleted body except for inverted channel region with the use of thinner Si layer

  • Partially depleted devices leads to floating body and kink in dc IV chars due to Vth variation

  • ways to improve PD

    • LDD
    • body ties
    • germanium implant

  • ways to improve FD

    • near-fully depleted operation
    • doping based on constant dose
    • raised SD regions

SOI Wafers

  • SIMOX

    • Implant oxygen to location under surface
    • High temp annealing to regen crystalline quality of top Si layer and form oxide layer
    • Polish

  • simox has non standard equipment and needs very high temps

  • Wafer Bonding

    • One wafer with oxide layer on top and bond with Van der walls forces
    • more annealing improves bond strength
    • thin one substrate
    • use RIE with etch stop for thin film

Smart Cut

  • Bond wafers, and cut one to reclaim silicon
  • uses standard equipment
  • Steps
    • oxide one, implant other. Implant one has cavities at end of Rp
    • Bond wafers
    • Cut with thermal activation, cuts at cavities
    • Anneal and polish

Advantages

  • offers instant power and performance uplift with elimination of capacitance and body effect