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About P+ rppoly and N+ rnpoly...Plz reply

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omsi

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p+ implant + poly + resistance

Hi ,
I have a doubt regarding the formation of rppoly and rnpoly resistors.
For instance,the rppoly is formed with nwell,p impant and the poly.Here is my doubt.
Since we need only poly resistance why we put that poly in P or N implants?
why cant we form that poly resistor on substrate only?How poly resistance will change when we put it in P and N implants as there is no electrical connection with poly fron these implants?

Please give some answers.

Thanks in Advance,
Omsi.
 

resistor poly n+ p+ poly type noise

It is an implant layer... not a diffusion layer... implant layer is a mask layer. its not a physical layer on the dye. where as a diffusion layer is a physical layer. Thus the question of connectivity between an implant layer and any other layer does not arise at all...
The implant is for the poly itself.. the polysilicon is itself implanted with n or p type dopants. rppoly has higher sheet res than rnpoly bcos of the p-doping done...

hope this helps..

PS: i am a designer.. fab guys plz correct me if my understanding is wrong...
 

    O

    omsi

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implant layer

Thanks Srieda,
Why we need implantation for poly resistor?
 

n+ poly resistor

Because the sheet resistance of undoped poly is very high. It require N/P implant to adjust the resistance to usable range.
 

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    omsi

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rnpoly resistance

poly resistors inherently give high resistances. I think by doping them, we can have slight control over the resistivity... i am not sure...
also, by doping p, one can achieve a negative temp co-efficient for the resistor.

all these are valid only for non-silicided resistors only...
 

    O

    omsi

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p+ poly resistor connection

Hi all,What's the usage of nwell here?
 

    O

    omsi

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Nwell is used to differentiate the substrate from resistor formation region.
If no Nwell ,active region forms on the substrate and acts as transistor.
 

Hi,

If a poly resistor which is used for CDM ESD protection is placed in Nwell, will the nwell gets in snapback mode?
 

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