Cluster Deposition
Deposition of clusters with variable kinetic energy (Energetic Cluster Impact ECI)
A.Häfele, J.Kraft, O.Rattunde, O. Rusu, W. Wolke and H.Haberland
A new process for thin film deposition (Energetic Cluster Impact, ECI) has been developed at the Freiburg Materials Research Center, FMF. Its basic idea is simple. The atoms do not hit the surface one after the other, as in all other deposition processes, but prior to the deposition the atoms are aggregated to clusters containing from several hundred up to ten thousand atoms. A large percentage of the clusters is electrically charged. These ionized clusters are accelerated and deposited with velocities of several kilometers per second onto a substrate. The resulting cluster impact can be compared with a snowball hitting a wall with very high velocity. Many clusters give rise to a compact thin film. Simulations show that on impact the temperature and the pressure rise to extreme values for a very short time. These extreme conditions lead to a good mixing of the impinging material with the substrate. Due to the high local temperature during the cluster impact, the substrate does not have to be heated. Mirror like and well adhering films are deposited, which do not show a columnar structure. Binary compounds like TiN, AlN, or Al2O3 can be deposited by introducing reactive gases into the deposition process at the point where the clusters are formed. In this way the chemical reaction takes place prior to the deposition and the compound clusters can be accelerated onto the substrate, as described above, at room temperature.