Novel development of a slurry-based spray coating technology to create a high temperature and corrosion resistant tantalum carbide protection coating for semiconductor material manufacturing and processing

Internally funded project


Start date : 01.09.2021


Project details

Short description

Das Forschungsprojekt wird im Rahmen eines LEB-Promotionsvorhabens in Zusammenarbeit mit dem Fraunhofer Institut für Integrierte Systeme und Bauelementetechnologie (IISB) bearbeitet.

Scientific Abstract

The rapidly expanding SiC market requires the installation of large production capacities for the manufacture of SiC crystals and SiC devices. This is also associated with a large demand for graphite components, which are subject to a great deal of wear during the growth processes of the SiC crystals and epitaxial layers. The introduction of high temperature and corrosion resistant protective coatings based on tantalum carbide (TaC) can help to save resources, deescalate supply shortage and reduce costs. In addition, protective TaC coatings could help improve process stability and thus material quality and yield. This thesis presents the development of an alternative slurry-based spray coating approach which has the advantage over all sorts of different coating technology routes like thermal spraying, electro deposition, carbonization, sol-gel method, sputtering and especially compare to conventional chemical vapour deposition (CVD). With our technology approach it is possible to coat components of any size and geometry, to adjust the coating properties over a wide range, such as thickness, density, composition, and even to repair a component in defective areas after it has been used in application.

The slurry-based spray coating technology starts with manufacturing a stable suspension, proceeds with creating a homogeneous spray coated layer on top of the graphite substrate with hardly any structural defects like lunkers, etc. and ends with a sintering process to generate the functional TaC coating with distinctive structural and mechanical properties.

In general, there are three main requirements to the coating as a protective layer itself which should be fulfilled. First, the coating should be homogenous and smooth so there are no weak points for a concentrated assault of reactive gases. Second, a strongly adherent coating is necessary for protection over a certain amount of time, especially in a harsh high temperature environment. Finally, to protect the components to its full extent the coating has to be crack-free, thick, and less porous, to act as a functional separation layer.

Using the right mixture of selected ingredients, including fine powder with a distinct particle size distribution, water, a dispersing agent, a binding agent and a defoamer, it is possible to create a defect-free spray coating layer on graphite with a perfectly homogenous particle distribution. Due to a fundamental and systematic investigation using graphite materials with different properties, especially open pore morphology, it was possible to identify graphites with surface pore structures which can be coated smooth and homogeneously without any depressions. By using the coating procedure repeatedly, this alternative approach, compared to conventional CVD process, can create thick coatings up to 300µm with hardly to no effort. But thicker coatings tend to delaminate easier if the surface bonding is not sufficient. For that reason, the bonding strength and wear resistance of the coating was tested for different coating thicknesses by a standardized pull-off test and scratch test setup. Another important parameter is the difference in thermal expansion coefficient between the TaC coating and the graphite component which should be as small as possible to avoid cracks, that could also lead in delamination and eventual failure under application environments. The sintering conditions defines the porosity of the coating and is also evaluated.

To finally evaluate the performance of the coating under real application conditions, small pieces of graphite were coated all around and were put in a reactor chamber to test them under industrial physical vapour transport (PVT) SiC growing conditions. It is demonstrated that the coating on specific selected graphite materials including the right coating properties can withstand the harsh high temperature growing conditions and is also suitable for use in SiC epitaxy. In addition to basic investigations, results on real components as used in the PVT and epitaxy process will also be presented. Results on the variation of process times in the PVT process and the repeated use of coated components are done.

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