Gerhard Prechtl

GaN virtual prototyping: From traps modeling to system-level cascode optimization

The present paper focuses on the system-level optimization of GaN technology for high voltage applications. We will show that a key requirement for the future success of the GaN technology is the full system-optimization achieved by a simultaneous optimization of technology, packaging and applications. We will also show that Virtual Prototyping (VP) becomes, in GaN technology, a fundamental tool that allows not only to have a fundamental understanding of the device properties but more importantly it allows to strongly link device optimization, technology and system-level performance. In the present paper we will describe our view on the system-level optimization of high voltage GaN technology and present detailed simulations and comparison with experiments for both normally on isolated GaN transistors and cascoded GaN devices in real switching applications.

Improvement of chrome CDU by optimizing focus ring design

Uniform radical distribution in the etching plasma is essential to meet chrome critical dimension (CD) uniformity for future technology nodes on chrome masks. The Etec Systems Tetra photomask etch chamber utilizes an alumina focus ring in order to optimize the etch uniformity of the chrome mask by minimizing gas flow effects and shaping the radial distribution of the etching radicals over the mask surface. This paper describes a systematic investigation to optimize the current focus ring, in order to improve etch critical dimension uniformity. The focus ring (FR) optimization work was made possible by manufacturing a modular focus ring that allowed the geometry to be varied at different heights and diameters. The circular shape of the modular focus ring, along with the height and diameter combinations, has a large influence on the etch performance at the mask corners and edges. The underlying mechanism was investigated by modeling and simulation. Based on simulation results the focus ring geometry was varied and the optimum FR configuration was found. The critical dimension uniformity could be adjusted on uniformly patterned masks with different pattern loads to meet production specifications.

Thermal activation of PBTI-related stress and recovery processes in GaN MIS-HEMTs using on-wafer heaters

Threshold voltage instabilities are investigated in GaN-based metal-insulator-semiconductor (MIS) high-electron-mobility-transistors (HEMTs) with specially designed on-wafer heaters structures. The heaters are based on metal lines or 2-dimensional electron gas (2DEG) resistors and enable to choose the temperature during stress and recovery in the stress-recovery experiments independently. It allows to decouple thermal activation of capture (<; 0.9 eV) and emission (0.4-0.9 eV) processes at the dielectric/nitride interface, which is not possible in stress-recovery experiments performed at a common ambient temperature.