question about technology layers

[diemilio]

Hello everyone.

most of the tech files I have work with have a N well layer, an N+ diffusion layer, P+ diffusion layer, POLY layers and METAL layers. So, for instance, if you wanted to create a NMOS you just had to place the POLY diffusion over the N+ diffusion (since the substrate was the working space). Now I'm working with a tech file which, not only has PPLUS and NPLUS layer, but it also has a layer called DIFF. I some examples I have seen, to create a NMOS you have to place not only the POLY over the NPLUS layer, but also you have to include the DIFF (see attached pic)!!

I don't understand why!! Is this related to some kind of fabrication procedure???

Thanks for your help,

diemilio

 

[CK815]

Hi diemilio,

DIFF is Field Oxide (FOX). So where ever you draw DIFF, there WON'T be any FOX growth. Please let me know if you need further explanation!

Regards,

C.

 

[diemilio]

Hi diemilio,

DIFF is Field Oxide (FOX). So where ever you draw DIFF, there WON'T be any FOX growth. Please let me know if you need further explanation!

Regards,

C.

Wow!! I didn't know that. I thought that Oxide was grown in larger areas (or as big as) than PPLUS or NPLUS diffusions. Why is the FOX area here smaller than the diffusion implants???

Thanks for your repply,

diemilio

 

[Hughes]

DIFF area (active area) is formed prior to the N+ and P+ implants. If DIFF is in same size with NPLUS / PPLUS, then some of active area may not be doped by N+ / P+ due to misalignment in the lithography process.

 

[huojinsi]

Actually,the DIFF layer is active layer generally named, only the name is not same!

 

[diemilio]

OK... I finally understood what you all where trying to say. The diff layer is the portion where there won't be any FOX so that the P and N diffusions can be implanted, right??

That makes sense to me

Thanks everyone for your help.