Abstract:

Gallium Nitride (GaN) is a promising material for back-end-of-line (BEOL) access transistors in monolithic 3D integration. However, traditional metalorganic chemical vapor deposition (MOCVD) growth methods for GaN require high temperatures that exceed the BEOL thermal budget of 450 °C. At reduced growth temperatures, crystal quality and electrical properties often degrade, resulting in a decline in overall device performance. Overcoming these obstacles necessitates the development of innovative growth strategies, supported by advanced X-ray-based characterization techniques, to achieve the desired material properties for successful BEOL integration. 

In this study, we employed X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to systematically investigate the degradation mechanisms of low-temperature-grown GaN, with a focus on temperature-dependent stoichiometry and crystallinity. Through process optimization, we achieved improved electrical properties that align with the target structural and compositional characteristics. Furthermore, we demonstrated the growth of amorphous GaN (a-GaN) at BEOL-compatible temperatures, resulting in significantly enhanced Hall mobility. Comprehensive material characterization confirmed the amorphous nature of the material through XRD, while angle-resolved XPS identified unique lateral compositional variations. 
To further explore the device-level potential of a-GaN, we examined metal/a-GaN interfaces using XPS. Detailed compositional analyses provided insights into interface chemistry, while XPS valence band maximum (VBM) spectra offered direct measurements of interface band alignment.