3D Width Effect Simulation

mos2ex04.in : 3D Width Effect Simulation

Requires: SSuprem 4/DevEdit 3D/Device 3D
Minimum Versions: Athena 5.22.1.R, Atlas 5.22.1.R

This example demonstrates Id/Vgs simulation of a narrow N-channel MOS structure in three dimensions.

In this example a 2D width cross-section of a MOS transistor is constructed using SSuprem 4. The structure is then passed to DevEdit 3D for extending to 3D. Then the structure is interfaced to Atlas for electrical testing. The input file consists of the following main portions:

  • Process simulation of field oxide bird's beak in Athena
  • Interface of the 2D structure from Athena to DevEdit 3D
  • Structure editing to create 3D MOSFET
  • Interface of the 3D structure from DevEdit 3D to Atlas
  • Simulation of the Id/Vgs characteristic in Atlas
  • Extraction of Vt and sub-threshold leakage parameters

The first stage of the input file simulates width cross section on an NMOS device. The process sequence is for a LOCOS oxidation with a mask edge at X=0.0um. A channel stop implant is performed before the oxidation. Following the mask removal, a gate oxide is grown. Then a channel implant is done before poly deposition.

The gate and substrate electrodes are defined at the end of the process sequence. Only these two electrodes are present in this 2D section. The source and drain will be added in DevEdit 3D.

DevEdit 3D is used convert the 2D Athena result to a 2D structure. Each region from the 2D structure is given an extent in the Z direction. This example will be a 0.5 micron long transistor. Thus the polysilicon region extends only from 0.3 to 0.8 microns. The basic procedure in DevEdit 3D is:

  • Modify existing region extent in Z direction (eg. polysilicon)
  • Add new aluminum regions for source and drain contacts. Specify these as electrode regions.
  • Add N+ arsenic doping for source and drain. Be sure the Z extent of the doping includes a 0.1 micron spacer away from the gate edge. Specify y-rolloff (junction depth) and x and z rolloffs (lateral spread).
  • Define base level mesh (0.2x0.2 microns) and mesh the structure in X and Y.
  • Use REFINE to add mesh points in the channel region
  • Use the z.plane statement to control the mesh in the Z direction. The Z direction mesh is made up of planes XY mesh leading to prismatic mesh elements.

To generate DevEdit 3D syntax for a given set of structure editing and mesh operation, it is often best to do these same operations in the graphical mode of DevEdit 3D. DevEdit 3D allows users to save the commands used in the graphical mode to a command file. It is this command file that is used as the basis for the batch-mode DevEdit 3D used in this example.

The Atlas simulation begins by reading in the structure from DevEdit 3D. DeckBuild provides an automatic interface between DevEdit 3D and Atlas so that the structure produced by DevEdit 3D is transferred to Atlas without having to indicate the mesh statement in Atlas

The contact statement is used to set a work function on the polysilicon gate. The models statement is used to select a set of physical models for this simulation. In this case, these models are SRH recombination, the CVT mobility model, and one carrier model (carriers=1)

The drain voltage is set to 0.1V, and gate voltage is ramped. The IV data is saved to a log file. This file is used as input to the EXTRACT routines for threshold voltage and sub-threshold leakage. This file can also be plotted in TonyPlot. The save statement saves a 3D solution file. This can be plotted in TonyPlot 3D to see 3D distributions of potential and carriers.

To load and run this example, select the Load example button in DeckBuild. This will copy input file and any support files to your current working directory. Select the run button to execute the example.