High electron mobility transistor and method for forming the same

A high electron mobility transistor (HEMT) structure, comprising:

• a gate electrode disposed on a substrate;
• source/drain electrodes disposed on the substrate at opposite sides of the gate electrode;
• metal pillars disposed on the source/drain electrodes;
• a first dielectric layer surrounding a bottom portion of the gate electrode and bottom portions of the metal pillars;
• and
• a first metal layer disposed on the first dielectric layer,
• wherein the first metal layer covers top surfaces and top portion of sidewalls of the metal pillars.

A method for forming a high electron mobility transistor (HEMT) structure, comprising:

• forming a gate electrode on a compound semiconductor substrate;
• forming a source electrode and a drain electrode on the compound semiconductor substrate at opposite sides of the gate electrode;
• forming a first metal pillar and a second metal pillar on the source electrode and the drain electrode respectively;
• forming a dielectric layer on the compound semiconductor substrate to cover the gate electrode, the first metal pillar, and the second metal pillar;
• thinning the dielectric layer to expose a top of the gate electrode, a top of the first metal pillar, and a top of the second metal pillar, wherein a bottom of the gate electrode, a bottom of the first metal pillar, and a bottom of the second metal pillar are surrounded by a remaining portion of the dielectric layer;
• forming a metal layer on the remaining portion of the dielectric layer, wherein the metal layer straddles the top of the gate electrode, the top of the first metal pillar, and the top of the second metal pillar.