Thegate oxide is thedielectric layer that separates thegate terminal of aMOSFET (metal–oxide–semiconductor field-effect transistor) from the underlying source and drain terminals as well as the conductive channel that connects source and drain when the transistor is turned on. Gate oxide is formed bythermal oxidation of the silicon of the channel to form a thin (5 - 200 nm) insulating layer ofsilicon dioxide. The insulating silicon dioxide layer is formed through a process of self-limiting oxidation, which is described by theDeal–Grove model. A conductive gate material is subsequently deposited over the gate oxide to form the transistor. The gate oxide serves as thedielectric layer so that the gate can sustain as high as 1 to 5 MV/cm transverseelectric field in order to strongly modulate theconductance of the channel.
Above the gate oxide is a thin electrode layer made of aconductor which can bealuminium, a highly dopedsilicon, arefractory metal such astungsten, asilicide (TiSi,MoSi2,TaSi orWSi2) or a sandwich of these layers. This gate electrode is often called "gate metal" or "gate conductor". The geometrical width of the gate conductor electrode (the direction transverse to current flow) is called the physical gate width. The physical gate width may be slightly different from the electrical channel width used to model the transistor as fringing electric fields can exert an influence on conductors that are not immediately below the gate.
The electrical properties of the gate oxide are critical to the formation of the conductive channel region below the gate. In NMOS-type devices, the zone beneath the gate oxide is a thin n-type inversion layer on the surface of thep-type semiconductor substrate. It is induced by the oxide electric field from the applied gatevoltage VG. This is known as the inversion channel. It is the conduction channel that allows theelectrons to flow from the source to the drain.[1]
Overstressing the gate oxide layer, a commonfailure mode of MOS devices, may lead to gate rupture or tostress induced leakage current.
During manufacturing byreactive-ion-etching the gate oxide may damaged byantenna effect.
The firstMOSFET (metal–oxide–semiconductor field-effect transistor, or MOS transistor) was invented by Egyptian engineerMohamed Atalla and Korean engineerDawon Kahng atBell Labs in 1959.[2] In 1960, Atalla and Kahngfabricated the first MOSFET with a gate oxide thickness of100 nm, along with agate length of20 μm.[3] In 1987,Bijan Davari led a research team at theIBM Thomas J. Watson Research Center that demonstrated the first MOSFET with a10 nm gate oxide thickness, usingtungsten gate technology.[4]