GR-Mon-A10 - Improving the quality of PVT-grown AlN-crystals by utilizing a seed recovery process
1. GrowthGleb Lukin1, Roland Weingärtner1, Leon Schiller1, Jochen Friedrich1
1 Fraunhofer Institute for Integrated Systems and Device Technology IISB
Abstract text
Aluminum nitride (AlN) is a raising material for future high frequency and power electronics applications due to its high thermal conductivity of 3-4 W/cmK and its ultra-wide bandgap of 6.2 eV resulting in an extremely high critical electrical field and energy efficiency of AlN-based transistors. However, diameters of at least 100 mm are needed to arouse industrial interest in manufacturing electronic devices based on single crystal AlN-substrates. Strong efforts are being made to expand the diameter as effective as possible, but still many crystal generations are needed. This increases the probability that the crystal quality will degrade due to the successive incorporation of defects.
In this contribution we present a method of using seeds from minor quality crystals to grow crystals that are structurally of superior quality. This is achieved by combining a floating seed approach to grow AlN-crystals by physical vapor transport with a tailored seed preparation. The spatial defect distribution in terms of threading dislocations and basal plane dislocations obtained from X-ray topography measurements on seed wafers is compared to those on the grown AlN-crystals. It is shown that extended defects such as threading dislocation clusters or polycrystalline inclusions in the seed can be eliminated entirely. The corresponding regions of the grown crystals show a near-zero density of threading dislocations, especially of those with a screw component. However, a tendency to increased amounts of basal plane dislocations is observed. The consequences of such defect transformation for the structural quality of a subsequent crystal generation are presented.
Our results suggest an opportunity for seed recovery by the rapid growth of new, high-quality material after removal of defective portions of the seed. The method is very relevant in terms of being able to maintain very good structural quality even over a large amount of crystal generations.