In older CMOS processes silicon dioxide was used both for th

In older CMOS processes, silicon dioxide was used both for the gate dielectric as well as a final

passivation layer to protect the final fully fabricated device. Explain why the gate dielectric was typically formed by thermal oxidation, while the passivation layer was typically formed by plasma-enhanced chemical vapor deposition.

Solution

Thermal Oxidation is used to grow the silicon dioxide in larger quantity and is possible by thermal (dry) oxidation.

It is cheaper and size of the layer is not specific and we dont need the layer size to be specific because we rip this off in later stages using HydroFluoric acid.

Plasma Enhanced Chemical Vapour Deposition is a process of forming thin layers of SiO2 by exposing the silicon wafer to volatile precursors. This process gives high quality , high performance thin layers of Sio2 because it is controllable which gives the calculated thickness of Sio2 precisely..