Impact of growth conditions on stress and quality of aluminum nitride (AlN) thin buffer layers

Abstract

In this study, we report about an analysis of the crystal quality and stress conditions of aluminum nitride (AlN) buffer layers by changing several process conditions during the growth at a metal‐organic chemical vapor deposition (MOCVD) reactor. A two‐steps process has been implemented for AlN growth on Si, consisting of a low‐temperature AlN (LT‐AlN) nucleation step followed by a high‐temperature AlN (HT‐AlN) growth step. An improvement of the crystal quality has been observed for lower V/III ratio used in the LT‐AlN step. Growth temperature of HT‐AlN was also examined showing a weak variation of AlN growth rates. Crystal quality and residual stress conditions as a function of the AlN layer thickness were studied. X‐ray diffraction (XRD) rocking curves and Raman spectroscopy suggest a better crystal quality when AlN thickness is increased, due to enlargement of islands and reduction of extended defects. After a certain thickness, namely 300 nm, slip lines occurs in epitaxial layers leading to reduction of the residual biaxial stress perpendicular to growth direction. Electrical measurements have been carried out with a critical electric field of 2.1 MV cm−1 achieved.