UHV cluster tool for deposition of phase change materials, dielectrics, and metals

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In the newly established collaborative research center (CRC) 1459 “Intelligent Matter” at the University of Münster, physicists, chemists, biologists, and computer scientists investigate matter that responds and adapts to stimuli and shows memory capabilities. Besides switching molecules and soft matter also solid-state materials are explored. Here, so-called phase-change materials (PCMs) are of particular importance. PCMs usually contain germanium, antimony, tellurium, and often additional chemical elements. Those alloys exhibit a pronounced contrast in their electrical and optical properties between their amorphous and crystalline states. As optically or electrically induced transitions between these states can be extremely fast, i.e. completed within nanoseconds, PCMs are excellent candidates for emerging memories applicable in electronic and photonic hardware. However, their integration in devices is challenging. PCMs must be deposited under clean conditions because contamination with foreign species significantly alters their properties. In addition, thin films of PCM once deposited must be protected by a dielectric capping layer to prevent oxidation and to provide mechanical support during operation. Dielectrics are also required in the mentioned research projects for integrated photonic components and as passivation. Ideally, the deposited dielectric layers exhibit optimal properties such as low optical loss, low strain, high density, and mechanical robustness. Compared to magnetron sputtering, ion beam deposition allows deposition at lower pressures with independent tuning of process parameters like ion energy and flux. The method is therefore widely used for high-quality optical coatings and an ideal technique for the described applications. Metals are required for device electrodes, electrical waveguides, contact pads, and marker structures for electron-beam lithography. In electrical phase change devices, high-melting metals such as platinum and especially tungsten are useful, because they are resistant against mixing with the PCM. For electron-beam evaporation of tungsten, high power and cooling of the chamber walls is necessary. A UHV cluster tool with dedicated deposition chambers for phase-change materials, dielectrics, and metals, each with the most suitable deposition technique, will allow the combination of materials for a variety of purposes without compromising the cleanliness of the processes and the according outcome. As this deposition system will be operated in the framework of the Muenster Nanofabrication Facility (MNF), it will be available to a large number of users within the CRC 1459 “Intelligent Matter” and beyond.