T-Gate Fabrication

T-Gate Fabrication

T-shaped gates improve high electron mobility transistors (HEMTs) performance. T-gate structures are usually fabricated in high electron mobility heterostructures like InGaAs. Sub 50nm gate length result in reduced capacitance, high electron mobility, and ultra high RF characteristics. Tri-layer resist structures with a PMGI layer (aqueous developer) in between two PMMA layers (solvent developer) are being used for precise control of the T-gate shape to optimize device electrical properties.

LOR & PMGI: Benefits/Attributes

  • Sacrificial layer to assist in fabrication of higher gate stem heights
  • Excellent adhesion to III-V substrates
  • Suitable for multi-layer processing
  • Suitable for use as a protective separation layer between incompatible layers
  • Allows gate head and gate foot to be written separately for improved resolution
  • Can be used in a resist stack with low intermixing

PMMA: Benefits/Attributes

  • Positive tone; E-beam imageable
  • Wide range of film thicknesses
  • Excellent adhesion to most substrates

Definition of Gate Stem

Pattern Transfer to SiN

E-beam Litho. On Gate Stem

Final Trip Gate
Courtesy of Seoul Nat University