Process Tutorial

FLOOPS is the subset of FLOOXS that deals with process modeling of electronic devices. This page serves as an introduction to the commands and concepts used by FLOODS to model electronic device fabrication. The goal of process modeling is to use physics informed models to predict how different process parameters change the structure of electronic devices .

Process Steps

Each step in the device fabrication process is modeled by a FLOOPS command that uses the LevelSet method to compute the structure. Once the structure is computed a new mesh is generated and another process step can be applied to the mesh. Each command will be explained and an example will be given.

Base Layer and Gas

In order to preform any device fabrication we need to start with a base layer. This base layer can be a silicon wafer, oxide, or some other material that thin films can be processed on. To begin modeling another material called Gas is needed. Gas is a region of the mesh that allows FLOOPS to keep track of some region outside the base layer. To create these two materials run the following commands:

   line x loc=-1.5 spac=0.1 tag=GasTop 
   line x loc=0.0  spac=0.1 tag=Top
   line x loc=1.0  spac=0.1 tag=Bottom
    
   line y loc=-2.0 spac=0.1 tag=Left
   line y loc=2.0  spac=0.1 tag=Right
   
   region Gas     xlo=GasTop xhi=Top    ylo=Left yhi=Right
   region Silicon xlo=Top    xhi=Bottom ylo=Left yhi=Right
   init
   
   window row=1 col=2 width=800 height=800
   plot2d grid gas

The line commands define spatial locations that need to be in increasing order in each xyz dimension. The region command creates a box region of the specified material in the line tags. Init generates the mesh based on the specified regions. To plot the grid we use the window command to open up a window with 2 plot columns of with 800 pixels and height 800 pixels. The two columns will be useful later. To actually plot the grid the 'plot2d grid gas' command plots the grid and the gas. You should get the following result:

Deposit

The next step we are going to deposit an oxide isotopically. The deposit command has the following options:

   deposit -help

Result of above command:

   Deposit
   Length Scale Default is microns which can be changed with the option command
   Name            Type     Default               Information
   mater           Switch                        material specification
   rate            Float    1.000000e-01         isotropic deposition rate default length scale/min
   time            Float    1.000000e+00         isotropic deposition time min
   spacing         Float    1.000000e-02         spacing in the level set mesh
   grid            Int      1                    grid steps in the deposition
   tolerance       Float    1.000000e-02         grid accruacy tolerance in default length scale
   plot.surface    Boolean  0                    plot the surface step by step

From the list of these options we see that to deposit a material we only need to specify the material name. However, we probably want to specify the rate and time to match our exact process. For this example we will run the following command after our Base Layer and Gas example.

   deposit oxide time= 4.0 spacing= 2.0e-2
   plot2d grid gas

This deposits an oxide that is about 400nm thick. The spacing command is something you can play around with. It is a command that defines the spacing of the LevelSet grid and has the following tradeoff, making it larger decreases computation time but makes the computation less accurate. The results of this deposition: