Wafer-level sensor structure for measurements of the ion energy distribution function and the ion angle distribution function in low-pressure plasmas
The investigation of a novel function principle for the simultaneous measurement of the ion energy distribution function and the ion angle distribution function on a substrate surface in low-pressure plasmas is the main objective of the intended project. In contrast to all known principles, the sensor offers the possibility to measure solid angle resolved. The measurement spot can be aligned to each position on the plasma sheath and ions will be detected, which were emitted from this region unexceptionally. The spot size are adjustable by the constructive setting of the sensor structure. With an overall thickness of 2.5 mm, the sensor represents a miniaturization of at least factor 2 in comparison to common analyzers. To achieve a deeper understanding of the new principle and its properties, a combined analysis strategy consisting of experimental work and corresponding simulations is another objective. With the simulations, the distribution functions will be calculated with to respect to the geometries of the available test reactors. These results are important to check the correctness of the measurement results. Partly the simulations will be used to dimension the sensor structure. In dependence on the pressure inside the test reactors, particle-in-cell- as well as fluid- and hybrid-simulations are intended. The novel function principle bases on a silicon plate, which is moveable mounted on four silicon springs. With four piezoelectric actuators, the plate is tiltable in each direction of the solid angle. With a perforation inside the plate in the shape of cylindrical holes with small diameters, a defined acceptance angle for impacting ions can be achieved. The symmetry axis of the perforation is displaceable on each position on the plasma sheath. With a metallization on top of the plate, the energy distribution of the impacting ions is analyzable by the formation of a directional retarding field on the adjusted solid angle with a variable voltage. The realization of the sensor on wafer level is planned. This includes the operation of a micro-electro-mechanical-system inside a plasma. To characterize the influence of the sensor itself on the measured distribution functions, the establishing of a special simulation code is another objective of the project. This code offers the possibility to retrace the trajectories of ions through the analyzer in dependence of inside generated electrical fields by solving the Newton-equation of motion and the Lorentz-equation of force. Therefore the three dimensional replication of the sensor by a corresponding model is necessary. The practical use of the sensor in three different plasma chambers as well as the analysis of the influence of different parameters, e.g. chamber pressure and source power, on the distribution functions finalizes the intended project.