[SOLVED] DRC issue in AMS 0.35 µm HV

Hello all,

I have 2 DRC errors that i do not understand in my layout. I am actually routing a very simple inverter but using a HV NMOS, with a protective diode on the bulk. And since the layout of this transistor do not looks like the one we have usually when we use a common HV MOS, i am a bit confused.

Here are the 2 messages i do not understand:

"DNR002: Utmost structures within DNTUB must be closed NTAP rings in SNTUB"

"SNR005: RPTUB shape in DNTUB is totally outside sntub ring Each RPTUB shape inside DNTUB must be fully enclosed with SNTUB"

Many thanks for your help and time.

K4R1 said:

"DNR002: Utmost structures within DNTUB must be closed NTAP rings in SNTUB"

Click to expand...

All structures within DNTUB (deep n-well) must be enclosed by NTAP (n+) rings in SNTUB (shallow n-well)

K4R1 said:

"SNR005: RPTUB shape in DNTUB is totally outside sntub ring Each RPTUB shape inside DNTUB must be fully enclosed with SNTUB"

Click to expand...

RPTUB (p-well) shape found in DNTUB (deep n-well) which is totally outside sntub (shallow n-well) ring. Each RPTUB shape inside DNTUB must be fully enclosed with SNTUB.

See this cross-section:

Many thanks for the reply.

Actually, does it mean that i have to draw a PD_N via around the transistor and draw a SNTUB around it ? What are the layers used to draw the NTAP ?

Thanks for your time.

K4R1 said:

... does it mean that i have to draw a PD_N via around the transistor and draw a SNTUB around it ? What are the layers used to draw the NTAP ?

Click to expand...

I don't know the layer names of the AMS 0.35 µm HV process, sorry. Yes, it means that you have to draw an n-well (SNTUB) ring around it, with an n+ tap contact ring within it, contacting it by vias to metal_1 and your highest VDD. See my explanation and the figure above.

Ok, i got it ! Actually, here is how i solved the problem: Draw a "ndiff_rptub" guard ring around the transistor with the automated ring creator in Layout XL. Solved my issue !

Many thanks for the help !

By the way, i was wondering ,what is the physical explanation for having a RPTUB ring outside a DNTUB ? Why is an HV MOS not like a regular MOS in 0.35 µm ??!

K4R1 said:

... what is the physical explanation for having a RPTUB ring outside a DNTUB ? Why is an HV MOS not like a regular MOS ... ??!

Click to expand...

This is a guard ring, well appropriate to catch and feed straying holes to GND. This is to prevent thyristor action between the HV nMOS and a (possibly) nearby pMOS in the substrate.

HV MOS transistors operate with higher electric fields than regular (LV) transistors, thus creating larger space-charge regions and leakages, by this more straying charge carriers which could trigger thyristor action, i.e. latch-up.

Re Hello,

I have an other question related to the layout of an isolated MOS. Actually, i am trying to route the two transistor circled in red and connect the diode linked on the bulk. But i do not understand which part of the blk connection i am supposed to connect to my high voltage so the diode can be biased ? I am trying to connect the green squared bulk connection to the metal 2 but it does not seems to be working...

Many thanks for your help.

see below in the picture to understand what i mean:



- - - Updated - - -

Ohhhh... actually i solved it, my problem was that i putted two transistors with two different bias voltage on each bulk... Remember this rule of thumb for those in my case: one rptub ring = one voltage on the bulk inside !!

K4R1 said:

one rptub ring = one voltage on the bulk inside !!

Click to expand...

Of course! Thank you for your feedback!