Vacuum Deposition Chamber

Problem raised by Galileo Vacuum System spa

Coordinating teachers of the problem:

Riccardo Ricci (Università degli Studi di Firenze)

Miguel Ángel Herrero (Universidad Complutense de Madrid)

Exposition of the problem:

Physical Vacuum Deposition (PVD) is industrially used for the generation of a coating on substrates of different materials.

In the particular case we have to deal with, the coating is a constituted by a sandwich of Aluminium and a polymeric film (HMDSO) upon a substrate of polycarbonate. The final product of the industrial process is the reflecting part of projectors for automotive.

The deposition of the final coating is achieved in three steps:

1. Within a cylindrical metallic chamber, the atmosphere is brought to a very low pressure

2. Within the chambers, aluminium is vaporised by means of the Joule Effect. In this way, the Aluminium covers up the surface of the substrates located within the chamber.

3. A monomer flows through nozzles at relatively high pressure. In the plasma atmosphere, generated by the strong electric field, the monomer polymerise on the substrate, covering up the surface. In this way a thin (~ 10 nm) film of HMDSO is made to protect the surface of the projectors.

At the end of the process, the chamber is opened and the projectors are ready to be assembled.

The scope of the model and simulations, should be to suggest new and better setting of the chamber and electrodes, such as shape, position and size of the electrodes, and optimised process parameters (such as pressure and voltage applied to the electrodes), in order to have a mostly uniform energy and charge density, a uniform potential, a uniform distribution of current lines and so on, so to reduce the possible inhomogeneities in the final coating.

Clearly, the real situation would not allow for the resulting model to be actually solved. However, as the aim of the model is to analyse the distribution of potential and charged particles within the chamber, one can drastically reduce the complexity by making some simple assumptions.

The activity we propose is to start the construction of the model under some simplifying assumptions like stationary field, plasma at equilibrium and simple boundary conditions and develop analytical and numerical descriptions.

Scheme of the work to be done:

1) Set the physical model

2) Discuss the appropriate simplifications

3) Solve numerically the simplified model

4) Draw consequences from the numerical results