Why first NMOS device was fabricatd nearly a decade after PMOS fabrication?

[amit.31]

Hi all

What took so long that first NMOS device was fabricated after nearly a decade of PMOS fabrication?
Since it just need to reverse the source and substrate region.

 

[D.A.(Tony)Stewart]

Your assumptions are incorrect and do not reflect the complexity of process fabrication steps. THe initial fab processes did not work with n-ch depletion mode very well. They could only make p-ch dep. mode then when enhancement mode was possible, as I recall by replacing diffusion & thermal oxidation with ion implant and CVD deposition.


This shows some history.

**broken link removed**