Characterisation of an RF-excited broad beam ion source with CHF3-O2 gas mixture

Broad-beam ion source with extraction switched on and ion beam directed at the entrance aperture of a mass spectrometer (ESMS) during a measurement.

The ever-increasing demands on high-precision optical elements require a deeper understanding of the manufacturing process itself. Ion beam etching is one of the most promising methods when it comes to creating surfaces with very low roughness in the sub-nm range and precisely transferring functional structures. Ion beam processing is already the method of choice for the highest precision requirements, e.g. for trimming the layer thickness of acoustic bulk or surface acoustic wave filters, the final shape correction of telescope mirrors or the production of highly efficient pulse compression gratings. The large number of adjustable process parameters such as process gas, ion energy or ion incidence angle results in a finely tunable process for realising the desired surface properties. By using reactive gases, for example, the selectivity (ratio of the etch rate of the substrate material to the etch rate of the mask material) can be adjusted over a wider range, a key parameter that characterises the type of structure transfer to the substrate. In addition, large surfaces to be processed require long process times and thus detailed knowledge of the ion beam source performance. The simplest and most direct way here is to measure the ion beam composition and ion energy distribution. These ion beam properties in turn depend heavily on the plasma excitation method used in the ion beam source.

In order to gain a detailed understanding of the etching process with an RF-excited broad beam ion source, studies to quantify the ion beam composition with a gas mixture of CHF3 and O2 were carried out for the first time in the IOM's "Ion beam assisted patterning and smoothing" working group. These studies form the basis for the description of the ion energy distributions and the ion beam composition for a selected set of process parameters, also for future investigations. This also opens up the possibility of improving the comparability and reproducibility of corresponding technologies and production systems.

The results of the investigations were recently published in the following paper:

Erik Rohkamm, Daniel Spemann, Frank Scholze, Frank Frost
Characterization of an RF-excited broad beam ion source operated with a mixture of CHF3 and O2
J. Appl. Phys. 135, 223303 (2024)

Further link: Unveiling the Power of Hiden EQP in RF-Excited Broad-Beam Ion Source Characterisation - Hiden Analytical