Why is the resistance of Poly much higher than that of diffusion?

[cmos_dude]

Why is it that the resistance of Poly is much higher than that of diffusion inspite of the fact that poly is much more highly doped than diffusion ??

--Cmos_Dude

 

[n1cm0c]

Re: Resistance values

If I recall correctly, it's because polysilicon is doped silicon , just not a continuous crystal, but several crystalline solids (the POLY comes from the SEVERAL), like rice grains. The fact that the material is GRAINY reduces the conductivity (carrier lifetime, scattering, and All That Jazz). Doped diffusion is crystalline silicon, where carriers propagate on a semi-infinite nearly perfect lattice.

Added after 10 minutes:

I couldn't have said it better than this,

The electrical properties of a polysilicon resistor are significantly affected by properties of crystal grains, such as grain diameter and crystallinity, which constitutes the resistor. For instance, the electrical resistance of a polysilicon layer is significantly varied by the decrease in the number of conductive carriers due to unbalanced distribution of dopant impurities in a grain boundary, and the decrease of carrier mobility due to grain boundary diffusion. Accordingly, it is important to keep the grain boundary density present in an electrically conductive region to be uniform as much as possible in order to fabricate a resistor made of polysilicon and having stage electrical properties. In other words, it is important to arrange the number of crystal grains present in polysilicon resistors to be identical to one another. However, since the number of crystal grains has always a statistical dispersion, the dispersion in the number of crystal grains is increased with the absolute number of crystal grains being decreased.


but then, to have all that in my dynamic memory, i'd have to refresh often!

hope this helps!

 

[leo_o2]

Resistance values

However, it is not case I met.
In most of process I used, highly doped poly1 resistor has a lower square resistance than diffusion resistors.
For example, highly doped poly1 resistor
is 18ohm/sq and N+ diffusion resistor is 66ohm/sq and P+ diffusion resistor is 171ohm/sq.

 

[yibinhsieh]

Re: Resistance values

In deep submicron process (maybe 0.18um or lower), the resistance of poly and diffusion are almost the same. You can refer the following example:

For UXC 0.13um process:

N+/ P+ poly salicide: 10ohms/square
N+/P+ diffision salicide: 10ohms/square.

But for non-salicide resistor,
N+ ploy: 150 ohms/square
P+ poly: 230 ohms/square
N+ diff: 100 ohms/square
P+ diff: 150 ohms/square

But I think they can be adusted.

Therefore, generally poly resistance is higher than diffusion resistor.
But it also can be cumtomized.

Yibin.

 

[ch1k0]

Re: Resistance values

below 0.5um poly layer is not only poly-crystal. to reduce RC delay poly has silicide on top. that make poly less resistance than diffusion. poly resistors have silicide BLOCK layer, to except resistor from silicide.

 

[lladnar23]

Resistance values

Also, your diffused resistors may be thicker than the poly resistors depending upon the junction depth of your process...

 

[flysnows]

Re: Resistance values

In deep submicron process (maybe 0.18um or lower), the resistance of poly and diffusion are almost the same. You can refer the following example:

For UXC 0.13um process:

N+/ P+ poly salicide: 10ohms/square
N+/P+ diffision salicide: 10ohms/square.

But for non-salicide resistor,
N+ ploy: 150 ohms/square
P+ poly: 230 ohms/square
N+ diff: 100 ohms/square
P+ diff: 150 ohms/square

Yibin.

my question is: silicide is usually used to increase the sheet resistance , why in UXC 0.13um process the sheet resistance of non-silicide poly is higher than that of silicide poly?

 

[castrader]

Re: Resistance values

no quenstion there!
Rsq for sab is higher than salicide Rsq !
silicide is used to decrease Rsq! for good contact!


my question is: silicide is usually used to increase the sheet resistance , why in UXC 0.13um process the sheet resistance of non-silicide poly is higher than that of silicide poly?[/quote]

 

[Alan_Nesta]

Resistance values

agree!
maybe flysnows misunderstand salicide and sab layer.

 

[n1cm0c]

Re: Resistance values

salicide is SELF-ALIGNED silicide...

silicide is used to *decrease* the sheet resistance of tracks/wires in diffusion and poly-si . Silicide block mask is used to prevent the siliciding step, and then you'll get higher sheet resistances with the underlying material...

 

[forkschgrad]

Re: Resistance values

some books say salicide is the same with silicide but with the discussion they're not. pls differentiate the two. tnx.

 

[ch1k0]

Re: Resistance values

salicide, silicide , difference explain,

https://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/9153/29056/01309496.pdf

or

https://www.freepatentsonline.com/20040097060.html

or

**broken link removed**

google is friend!