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The basic concepts of particle transfer at sputtering deposition process are summarized in this sheet.

When the particles are sputtered from the target, they have the kinetic energies of some to some ten's of electron volts. It is much larger than the thermal energy of ambient gases,

Sputtered particles then go some distance, collide with a gas atom and change direction, and go again. This stage is generally called as "Ballistic stage", because the energy of the particles are much higher than gases. In this stage, particles gradually lose their kinetic energy as they repeat the scattering with gas atoms.

Well, this process is strongly affected by the Mean Free Path of the particle, so gas pressure is very important.

The particles may reach the chamber wall during the ballistic stage, but they also may lose their initial kinetic energy completely in the chamber space. In the latter case, we cannot neglect the gas motion. It is called the thermalization of the particles. After that, the particle transfers diffusively.