Metal-Oxide-Metal (MOM) capacitors and GaN-based High Electron Mobility Transistors (HEMTs) devices for integrated circuits: a reliability study

In the present thesis, Metal-Oxide-Metal (MOM) based on silicon (Si) substrates and high electron mobility transistors (HEMTs) devices based on Gallium Nitride (GaN), both provided by STMicroelectronics S.r.l., underwent to a systematic reliability investigation through, respectively, thermal characterization and micro-Raman spectroscopy. In the first case, the aim was to establish a reliable and efficient alternative approach to detect any non-functional MOM-based devices, evaluating the thermal emission. Such technique allows to overcome the limits arising from the conventional electrical tests that are not able to detect some non-functional devices thus constituting a reliability risk. In particular, ad-hoc devices, known as test pattern, characterized by at least 4-times larger MOM area with respect to the “standard” BCD8 device, were utilized to enhance the probability to intercept reliability issue and hence their correct functionality. The obtained results revealed, as a general trend, a close correlation with the preliminary analyses performed through both visual inspection and current-voltage (I-V) analysis, proving that the technique is reliable and quick in the detection of non-functional MOM capacitors. In the case of HEMTs GaN-based device, two different micro-Raman investigations were undertaken. The first was mainly focused on the evaluation of the internal stresses occurring in GaN crystals, starting from the analysis of the frequency shifts exhibited by specific spectral features, upon the application of an external mechanical perturbation by means of home-made three-point assembly. The second investigation was aimed at quantify the packaging impact on the residual stress along the GaN and GaN/Si interfaces, by analysing the frequency shifts induced by the device packaging on specific spectral components. It is worth of note that the device packaging, although its application typically provides non-negligible residual stresses which can, in principle, originate reliability failures, possesses several key functions in protecting the device core from the external environment. As main results, a high-frequency shift of the E2(high) frequency centre in the case of packaged sample was observed, indicating a compressive stress closely to the package. It is worth of note that the results reported in this thesis appear crucial not only for ensuring better performance and reliability in MOM and HEMTs-based devices and technology, but also could provide, in principle, useful notions to be implemented in large-scale semiconductor industrial processes.