Inorganic multilayer systems
... from optics to semiconductors
Metallic multilayer systems are used in a variety of ways. They are an integral part of many optical components (for example, lenses, filters, etc.), but are also used as heat protection layers, for the improvement of electrical contacts, as complex layer systems in semiconductors, or for the enhancement of the appearance of plastics. The use of analytical techniques can be very useful, in development as well as in quality assurance, as the following example shows:
Failure of laser mirrors
Trace impurities with major effects
After a short period of operation, the quality of a dielectric laser mirror had fallen below the manufacturer's specification. Initial examinations (e.g., WLI) of the mirror surface provided no indication of the cause of the failure. Therefore, contamination of the glass substrate or impurities of the metal oxide films deposited thereon was presumed to be a source of error. In addition, several potentially error-causing substances (such as polishes, organic contaminants, surfactants, etc.) were identified in the production, so that a screening of the layer structure by ToF-SIMS depth profiling seemed worthwhile. ToF-SIMS is an ideal method for viewing damaged components due to the sensitive, parallel detection of all elements. The ToF-SIMS depth profile of the laser mirror shows that the basic layer structure of the optical component (layer thickness, quality of the boundary layers) meets the specifications.
Only after a closer examination of the trace element composition of the individual layers, it was possible to detect increased intensities of Mg and Al in the first Hafnium oxide layer. Further analysis revealed that these elemental enrichments were due to residues from the polish used to process the glass substrate. This remained on the glass surface due to incomplete cleaning.