Customizable Surface Chemistry Models for Chemical Vapor Deposition in Ansys Fluent

Hello, today I would like to demonstrate how to set up a CVD model in Ansys Fluent. This model is largely based on a tutorial from the Ansys Fluent page.

So, the model, as shown here, is basically a model where we have an inlet velocity gas, gas velocity inlet at the top containing a mixture of gases, and an outlet at the bottom, and the reactions happen on the surface of the disk that you see here inside of the domain, basically.

So, basically, the first step to ensure that this works properly is we have to define the species model. We have to enable volumetric and mole surface reactions. And then apply the right mixture material, which we have to define as well.

So, for this, basically, I had to set up a number of species, including solid species like Gallium Arsenic, as well as the site species for AS and GA. So, basically, if I open up here, you can actually see the setup where we have the selected species that are participating in the gas phase.

The second reaction, likewise, we have TMGA reacting with a site species, forming a solid species, another site species, and CH3 radicals. And we also have Arrhenius rates specified for this reaction. So, basically, we have two reactions.

In the setup, the mechanism is set to basically a wall surface with a specified site density. For this case, we used 1e- 8. We can also define the initial site coverage, so basically, for each site species, how much are they occupying.

So, here we set a fraction of 0 for the GA and 0 for the AS site species. So, we also have to define the properties of the mixture and the properties of each species participating in the mixture.

So, we have here Ash3, and here are the properties that we've defined, with kinetic theory being used for thermoconductivity and viscosity, as well as diffusivity.

The basics of the setup, there's a lot of things that we need to enter for each separate species, but once that is defined, we can hopefully utilize the model.

Once we have all the mixture defined, all the reactions defined, which is the key part for this model, we can specify the boundary conditions as well. So, here I specify the velocity inlet, and I'm using an input variable for my velocity inlet.

Velocity inlet with a specified temperature, as well as the species. I've specified also a mass fraction for the two gaseous species entering the domain. Hydrogen is my last species here, so it's not shown.

And basically, we also have an outlet, which is just an outlet pressure, and we also have a backflow species mass fraction.

Based on some testing, the walls have specified temperatures, some of them at least, and basically, we have a temperature specified for wall 1 here, and I can show what wall 1 is. Wall 1 is right at the entrance where the gas entered the domain. Wall 4 is our disk; I can show that here.

Wall 4 is where the reactions are supposed to happen. To make sure that the reactions happen at wall 4, we have to specify a reaction, link the reaction mechanism, mechanism 1, and we've also specified a wall temperature for that surface.

Another important thing is this disk is moving at a certain angular speed, so we specified an angular speed as an input parameter as well, with a rotation axis direction on the z-axis, basically. So, it's a rotational motion that we defined as a moving wall.

So, if I go into the bottom here, we can visualize what the input parameters are. So, my angular velocity for this simulation is 80 radians per second. My Ash mass fraction and TMGA mass fraction are 0.4 and 0. 15. And velocity inlet for the gas is 0.01, and the wall temperature is 1023 Kelvin.

I've already run the simulation, so we can visualize some of the results. Here you can see the deposition rate of AS. So, basically, what we have is a higher deposition rate at the center, and it kind of fades away as you move towards the edges.

We can also visualize the same for GA, so very similar profile here. We can visualize the temperature profile. So, the temperature profile here on a cross-section of the domain, basically of the cylindrical domain.

Using this plugin, we can see it with high temperature and also look at high-temperature spacing. We could include a user-defined function, for example, if you want to specify a different kinetics for reaction. We can do that by basically hooking up a UDF to my case file, to my simulation.

So, compiling a UDF and then linking that, and that would basically control the rate of my reactions. So, I can actually have a UDF that controls the rates for the two reactions here.

So, that allows us a lot of flexibility if you want to use a more complex kinetics with more detailed chemistry and physics involved. Another way to customize a simulation is by using PyFluent.

PyFluent allows you to basically automate a lot of the processes involved in setting up a simulation, running a simulation, and conducting parametric studies.

This is an example of a Python script using Ansys products that we could use to deploy parametric studies using the same model that I've shown before. Post-processing, basically generating some of the contour plots of the disk for the GA deposition rate.

We can also generate data files as well if you want to do more post-processing within the Python environment. So, there's a lot of flexibility, a lot of things that could be done here. This is just a sample code showing some of these capabilities.

Afterwards, you can save your case and data file separately, and if you need to ever re-run again, you can basically use this as a starting point. So, this is basically it. Please contact us at https://ozeninc.com/contact for more information.