Abstract: In high frequency circuits, the switching speed of devices is often limited by the series resistance and capacitance across the input terminals. To reduce the resistance and capacitance, the cross-section of input electrodes is made into a T-shape or inverted L-shape through lithography. The prior art method for the formation of cavities for T-gate or inverted L-gate is achieved through several steps using multiple photomasks. Often, two or even three different photoresists with different sensitivity are required. In one embodiment of the present invention, an optical lithography method for the formation of T-gate or inverted L-gate structures using only one photomask is disclosed. In another embodiment, the structure for the T-gate or inverted L-gate is formed using the same type of photoresist material.

Abstract: The prior art method for the formation of T-gate or inverted L-gate is achieved through several lift-off processes and requires at least two different photoresists and hence two different developers. In one embodiment of the present invention, an etching method for the formation of the source, the drain and the T-gate or inverted L-gate of a compound semiconductor HEMT device is disclosed. In such a method, only one type of photoresist and developer are needed. In one other embodiment, a fabrication process for a HEMT device is disclosed to have the stem of the T-gate or the inverted L-gate defined by a dielectric cavity and its mechanical strength enhanced by a dielectric layer. In another embodiment, a fabrication process for a HEMT device is disclosed to have the stems of the source and the drain defined by dielectric cavities and their mechanical strength enhanced by a dielectric layer.