Method for fabricating a self-aligned T-gate metal semiconductor field effect transistor

A method for fabricating a metal semiconductor field effect transistor, comprising the steps of

• defining an N channel over a GaAs substrate with a photo-resist film and ion implanting Si to form the channel using the photo-resist film;
• removing the photo-resist film;
• sequentially forming a first insulation layer at a first temperature and a second insulation layer at a second temperature over the surface of the substrate, said first temperature being higher than said second temperature;
• coating a photo-resist film on the second insulation layer and patterning it to form a gate pattern;
• etching the first and second insulation layers using the gate pattern of the photo-resist pattern as a mask to expose the substrate;
• removing the gate pattern of the photo-resist film;
• forming a refractory metal over the surface of the first and second insulation layer and the exposed channel region;
• etching the refractory metal, thereby dividing it into two parts, of which one is formed on the channel region and the other is formed on the second insulation layer;
• selectively etching the first and second insulation layers to lift-off the refractory metal over the first and second insulation layers to lift-off the refractory metal over the first and second insulation layers, thereby forming a gate of a T-shape at the channel region;
• coating a photo-resist film and patterning it to form a channel pattern of the photo-resist film;
• ion implanting Si into the substrate using the gate and the channel pattern of the photo-resist film to form a self-aligned high concentration ion implantation region;
• removing the channel pattern of the photo-resist film;
• forming a third insulation layer for preventing As of the substrate from evaporating over all the surfaces of the substrate;
• carrying out a rapid thermal annealing for activation;
• removing the third insulation layer;
• and
• forming an ohmic electrode using a lift-off process.