Threshold vol. variation by implant addition to the channel

[Brittoo]

Hello all

This is in reference to the statement : "The threshold vol. of a nmos FET can be increased by doping the channel with p-type impurities."[/b]

The channel is formed along the gate poly length.This poly also acts as a mask for S/D implantation.So, when/how is this implantation done in the channel region ?

Regards
Brittoo

 

[erikl]

Re: Threshold vol. variation by implant addition to the chan

when/how is this implantation done in the channel region ?

A special (additional) (Boron) p-implant - either on the full non-n-well area, or using an extra selection mask for the concerned transistors before the poly deposition.

 

[Brittoo]

Re: Threshold vol. variation by implant addition to the chan

Hi erikl

when/how is this implantation done in the channel region ?

A special (additional) (Boron) p-implant - either on the full non-n-well area, or using an extra selection mask for the concerned transistors before the poly deposition.

Thanks for your reply.Is there any paper/book that could give more information concerning this matter ?


Regards
Brittoo

 

[erikl]

Re: Threshold vol. variation by implant addition to the chan

Thanks for your reply.Is there any paper/book that could give more information concerning this matter ?
Brittoo

Hi Brittoo,
I got this from a technical documentation of our fab, and this is company confidential of course, sorry!
It concerns additional process options: Low leakage needs high Vth; additional VTN & VTP masks are necessary in this case.
There are also contrary low Vth process options available, in order to create special low Vth or even so-called native fets (Vth≈0). Vth lowering is achieved with counter-doping. All these process options need 1 or 2 additional masks with the associated lithography step, low voltage low dose ion implantation and concluding oxide deposition.
Cheers, erikl

 

[dick_freebird]

Re: Threshold vol. variation by implant addition to the chan

Channel implant is your N-well, P-well (depending on
process construction, whether you have one, the other
or both). Not self-aligned. May be supplemented for
additional "flavors".

My primary process has 8 kinds of FET, N and P with
depletion mode, intrinsic, low and high VT each. The
combination of gate poly doping and epi doping makes
it possible to do this with I think only 5 explicit implant
shots.