Support for Diffusion Layers During Extraction

Some manufacturing processes define diffusion shapes that must be explicitly implanted by n-type or p-type implant shapes to get their own type. If the implant is p-type, the diffusion shape is considered to be p-type. If the implant is n-type, the diffusion shape is considered to be n-type.

Other processes derive the implant type from the definition of the diffusion layer, “ndiff” or “pdiff”, in the technology file. This is the case when an explicit implant does not exist. The connectivity extractor supports both types of diffusion layers.

The connectivity extractor does not modify the connectivity of implant shapes.

Analog processes typically feature a single diffusion layer and two or more layers for implants. The extractor recognizes shapes on layers with function diff as unimplanted diffusion: they need an explicit ‘n’ or ‘p’ implant shape to connect to the appropriate pwell or nwell.
The functions table for such a process might include the following definitions.
```
functions(
;( layer          function         [maskNumber])
;( -----          --------         ------------)
 ( pwell          "pwell"          10          )
 ( nwell          "nwell"          20          )
 ( diff           "diff"           30          )
 ( poly           "poly"           40          )
 ( pimp           "pplus"          50          )
 ( nimp           "nplus"          60          )
);functions
```
Only diff diffusion is defined, so there are also pimp and nimp layers defined explicitly for the implants. A shape on diff must overlap with a shape on pimp to connect to a shape on pwell or with a shape on nimp to connect to a shape on nwell. The connectivity stack is derived as follows:
```
metal -> cut -> (diff & nplus) -> nwell or ntype substrate
```
```
metal -> cut -> (diff & pplus) -> pwell or ptype substrate
```

Manufacturing processes used in digital design often define separate layers for n and p diffusion. A shape on these layers is considered to have an implicit implant whose type is derived from the layer function.
Here, the functions table might include the following definitions.

functions(
;( layer          function         [maskNumber])
;( -----          --------         ------------)
 ( lv_nwell       "nwell"          10          )
 ( hv_nwell       "nwell"          20          )
 ( hv_pwell       "pwell"          30          )
 ( ndiff          "ndiff"          40          )
 ( ndiff_hv       "ndiff"          50          )
 ( pdiff          "pdiff"          60          )
 ( odiff_hv       "pdiff"          70          )
 ( poly           "poly"           80          )
);functions

There are no layers defined for implants, the extractor differentiates between p-type and n-type implants based on whether the function is pdiff or ndiff. An ndiff shape connects to shapes that have the nwell function; a pdiff shape connects to shapes that have the pwell or substrate function.
The connectivity stack is derived as follows:

metal -> cut -> ndiff -> nwell or ntype substrate

Metal -> cut -> pdiff -> pwell or ptype substrate

Some processes have a single active diffusion layer, such as “ndiff”, which is used to connect to both types of wells and substrates. These processes also have a single implant, such as “pimp”, which takes priority over the diffusion type.
The functions table for such a process might include the following definitions:
```
functions(
;( layer          function         [maskNumber])
;( -----          --------         ------------)
 ( M1             "metal"          10          )
 ( CO             "cut"            20          )
 ( NOD            "ndiff"          30          )
 ( PP             "pplus"          40          )
 ( NW             "nwell"          50          )
 ( PW             "pwell"          60          )
 );functions
```
Both, a diffusion layer, ndiff, and an implant layer, pimp, are defined. An ndiff shape connects to shapes that have the nwell function. An ndiff shape when overlapped by a pimp shape connects to shapes that have the pwell function.
The connectivity stack is derived as follows:
```
metal -> cut -> ndiff -> nwell or ntype substrate
```
```
metal -> cut -> (ndiff & pplus) -> pwell or ptype substrate
```

Virtuoso Layout Suite XL: Connectivity Driven Editing User Guide
Product Version IC23.1, November 2023