Need of Epitaxial layer in cmos fabrication

[the moon is back]

Hi everyone,

I need to know that whats the significant of epitaxial layer in cmos ic fabrication.
why cant the ic is directly manufactured on the P-substrate?
If done so, what are the effects?
Is formation of epitaxial layer on the P-substrate is necessary?

Kindly provide some use full information.

Thanks & Regards

 

[dick_freebird]

The use of the epitaxial layer is not so much about the
device quality (bulk P- would do as well, for explicit
FET qualities) but the abnormal - latchup especially.
Epi is how you get a high resistivity device layer on a
heavily doped handle, that does a better job of shunting
parasitic BJTs and much eases latchup prevention.