U. Merkel

Influence of substrate quality on structural properties of AlGaN/GaN superlattices grown by molecular beam epitaxy

Short-period AlGaN/GaN superlattices were established as versatile test structures to investigate the structural properties of molecular beam epitaxy (MBE)-grown GaN and AlGaN layers and their dependence on the GaN substrate quality. X-ray diffractometry data of the investigated superlattices allow access to relevant structural parameters such as aluminum mole fraction and layer thicknesses. The occurrence of theoretically predicted intense high-order satellite peaks and pronounced interface fringes in the diffraction pattern reflects abrupt interfaces and perfect 2-dimensional growth resulting in smooth surfaces. The data unambiguously demonstrate that the structural quality of the MBE grown layers is limited by the structural properties of the GaN substrate.

Formation of regularly arranged large grain silicon islands by using embedded micro mirrors in the flash crystallization of amorphous silicon

The well-controlled formation of large silicon grains on predetermined positions is a key issue in order to produce single-grain thin film transistors on insulating substrates and thus to enable monolithic 3D integration. One way to achieve this is to artificially control the solidification of molten silicon during the flash crystallization of amorphous silicon. In this work, we present such an approach in which we used patterned metal layers below the amorphous silicon. The metal spots act as embedded micro mirrors and consequently introduce a lateral temperature gradient into the silicon film during flash crystallization. As a result, the grain growth from molten silicon is seeded from the predefined regions with the lowest temperature and thus the formation of large crystal silicon islands proceeds in a controlled manner. In the scope of this study, we evaluated a variety of different mirror patterns with respect to their suitability for this approach and observed that patterns of both circular and lin...

Investigations on Ru-Mn films as plateable Cu diffusion barriers

In this study Ru-Mn alloys are discussed in terms of some of the major questions that are typically associated with the development of new types of barriers. First, the Cu diffusion barrier performance after annealing at high temperatures and under subsequent bias temperature stress is investigated, on SiO2 and on low-k dielectrics. Second, the origin of the barrier performance - either a self forming barrier caused by segregation of an alloyed element, or the stuffing of grain boundaries - is investigated, since this is of importance with regard to an electromigration barrier at the bottom of a via. Third, Cu plating and Cu adhesion behavior are addressed, since they are also important with regard to electromigration, specifically along the side walls of trenches. Fourth, the blocking of oxygen diffusion is investigated. Furthermore, down-scaling of the Mn content to a lowest possible level is pursued in order to reduce line and via resistances.

Pseudo-vertical GaN-based trench gate metal oxide semiconductor field effect transistor

We report on the fabrication and characterisation of an enhancement mode n-channel pseudo-vertical GaN metal oxide semiconductor field effect transistor (MOSFET), which utilizes a high-k dielectric covered trench gate and a top side drain contact. The processing technology has been developed to be easily transferrable to a truly vertical MOSFET on GaN bulk material, as targeted for high-voltage power switching applications. Device functionality is demonstrated by linear transfer characteristic with a decent ON/OFF current ratio of 6 orders of magnitude and clear normally-off operation.

A Through Silicon Via concept for sensor applications

The use of Through Silicon Via (TSV) extends to different areas of electronics. Besides its utilization for logic and memory chips, a growing attention has been spent to sensor applications in the last years. Each application has its specific requirements which affect the whole processing scheme. Typically TSVs are generated by filling blind holes with copper and thinning the wafer afterwards, or by coating through holes with copper. Here we present an alternative concept which can be applied for biochemical sensors, so that a blind hole is created stopping on a SiO2 membrane. By this the need for a post wafer thinning is avoided.