Comparative electron diffraction analysis of strain relaxation in AlxGa1-xN materials in the microelectronics industry: 4D-STEM approach vs. TEM-based N-PED solution.

Owing to its high spatial resolution and its high sensitivity to chemical element detection, transmission electron microscopy (TEM) technique enables to address high-level materials characterization of advanced technologies in the microelectronics field. TEM instruments fitted with various techniques are well-suited for assessing the local structural and chemical order of specific details. Among these techniques, 4D-STEM is suitable to estimate the strain distribution of a large field of view. This study tends to discuss the viability of using two existing commercial solutions with a low-convergence angle 4D-STEM technique and TEM-based Nanobeam Precession Electron Diffraction (N-PED) methods for strain analysis in an industrial context. In such a framework, strain measurements intend to point out the extent of defects and thus reveal a trend of the stress field, rather than to precisely estimate the absolute values of the deformations. Strain distribution maps have been obtained for AlGaN/GaN HEMT devices using two transmission electron diffraction analysis methods. The performances of 4D-STEM and Nanobeam Precession Electron Diffraction (N-PED) solution for strain mapping have been compared for both a relatively thin (≈ 55 nm) and a thick (≈ 150 nm) TEM cross section specimen. The strain maps obtained with both methods have shown comparable results for a thin sample, with the ability to characterize the deformation induced by a 1 nm-thick layer of AlN spacer grown between the AlGaN barrier and GaN channel forming the 2DEG of the HEMT device. The results presented here also illustrate the limitation of both commercial solutions in the case of a thick sample.