Area junction capacitance NWELL/PSUB = 0.086 fF/um² for 0.6 um CMOS technology, which I use.
You may use diode NWELL/PSUB for simulation of this capacitance.
if you use MOSFETs,
CBD=Cj*(Bottom-Area)/(1-VBD/PB)^Mj + Cjsw*(Side-Round)/(1-VBD/PB)^Mjsw
CBS=Cj*(Bottom-Area)/(1-VBD/PB)^Mj + Cjsw*(Side-Round)/(1-VBD/PB)^Mjsw
* VBD = V(bulk-drain), VBS = V(bulk-source)
and if you use well,
CBB=Cj*(Bottom-Area) + Cjsw*(Side-Round)