Accurate Spice Netlist Extraction in Stellar Using New Substrate Partition Feature

Introduction

By default STELLAR calculates the capacitances between interconnect lines and the whole substrate. In certain conditions it may lead to some inaccuracies. For example STELLAR may calculate the capacitance of a poly line over an active area but this capacitance is already present in the spice compact model (Cox). Another example is that the substrate of a MOSFET transistor is usually connected to Vdd or Gnd depending on its polarity. So we may need to separate the Vdd areas from the grounded substrate. The aim of the substrate partition feature is to divide the substrate in different regions to calculate or not capacitances between interconnect lines and these different substrate regions. For example, we do not want to calculate the capacitance between a line over the substrate region shown in Figure 1.

STELLAR GUI

Techno file: layer setup
We will explain here how to define the mask layers shown in Figure 1. The NWELL, PACT, NACT regions are defined in the original gds file (Figure 2).