Multifrequency Sputtering for the Deposition of Ceramic Layers

From fundamental understanding to predictive control

“Sputtering” refers to the atomization and subsequent deposition of a material using plasma. This is usually done in vacuum systems at about 1/100000 of atmospheric pressure. The material to be sputtered is called target (e.g. aluminum disk), the object on which the new layer grows is called substrate (e.g. silicon wafer). The target is sputtered by the plasma with the help of high-energy ions. The ablated particles then deposit on the substrate and form the new layer. By adding reactive gas, it is also possible to create more complex materials than just the target material (example: aluminum target and oxygen -> aluminum oxide layer).

In subproject C1, a novel reactor concept for reactive sputtering processes in the form of a large-area capacitively coupled multi-frequency discharge (MFCCP) is developed, characterized and optimized. The MFCCP is operated at three high frequencies: 13.56 MHz, 27.12 MHz and 60 MHz. By adjusting the phase between the two low-frequency voltage signals, the ion energy at the substrate as well as at the target is controlled independently of the ion flux. This should make it possible to selectively manipulate the properties of the deposited films.

For the development of a detailed understanding of reactive sputtering processes in the MFCCP, a synergistic combination of experimental diagnostics and simulations will be used. Existing plasma diagnostics will be combined in a targeted manner, allowing measurement of surface coefficients (secondary electron emission, sticking) under plasma conditions. Precise knowledge of the surface coefficients is important, as these can change massively during the sputtering process, thus altering the properties of the generated layers. In addition, the diagnostics used in C1 will be used to characterize other plasmas in other subprojects of the SFB (A3, C2).

Through its fundamental investigations with quantitative consideration of all important individual steps in the reactive sputtering process, the C1 project makes a significant contribution with regard to the final goal of the SFB, which is to replace the empirical approach predominantly used in industry with a well-founded understanding of the process in order to enable the deposition of coatings with precisely adjustable properties.