Thin film transistor

Thin film field effect transistors are disclosed having direct or near direct contact of the source and drain electrodes to the channel region. Inverted gate (Fig. 3d) and non-inverted gate (Fig. 4e) types are fabricated by forming metallic source and drain electrodes (54′, 56′; 78, 80) within a layer of semiconductor material (46; 68) in contact with the channel region. The electrodes are formed by converting monocrystalline, polycrystalline or amorphous silicon regions to a refractory metal such as tungsten by using a non-self-­limiting metal hexafluoride reduction process. The tungsten conversion process is isotropic and provides self-alignment of the source and drain electrodes with the gate in the non-inverted gate TFT. The process is low temperature, allowing the use of amorphous silicon as the semiconductor material. The transistors are especially useful for formation on large glass sub­strates for fabricating large flat panel displays.