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Silicon dioxide in mosfets for gate insulation

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chaithanyateja9

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why only sio2 is used as a gate oxide for insulation in MOSFET? why not other insulating materials used?
 

erikl

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Re: silicon dioxide in mosfets for gate insulation

Why SiO2 became so popular:

- ease of growth (oxidation of Si)
- very high quality of oxide (good for low leakage, high reliability, etc.)
- very high quality of Si-SiO2 interface (low defect density) - important for carrier transport in inversion layer

But starting from ~90nm technology, nitrogen was added to SiO2 (nitridation - using various processes), to prevent boron penetration from the doped gate (or pMOSFETs) to the channel, and to somewhat increase the dielectric constant.
Then, high-K dielectrics (usually on top of a very thin SiO2 - for interface quality purpose) were introduced, to increase physical thickness and to reduce tunneling thropugh gate dielectric.
 

crutschow

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Re: silicon dioxide in mosfets for gate insulation

It was very fortuitous that silicon produces an oxide with such good physical and dielectric characteristics.
It's what made planar processing and large integrated circuits initially possible.

For example, germanium does not produce such a good oxide, thus it is not possible to make germanium circuits with a similar simple process.
 

dick_freebird

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Re: silicon dioxide in mosfets for gate insulation

Your premise / question is not true.

HfO2 and other "high K dielectrics" have been used,
whether or not they continue to be I don't know.

Si3N4 and SONOS dielectrics have been used for MOS
nonvolatile memories since the '80s.

SiO2 was used because it's a "freebie" (grows naturally
on native silicon, can be grown faster and thicker in
high temp oxygen-rich or steam environments). Of
course there's a "secret sauce" to getting defectivity
down and reliability up, cost effectively.
 

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