High quality MIM capacitors with improved capacitance density, low leakage currents and linear C(V) behaviour are the object of active research, with potential applications in CMOS, BICMOS and bipolar technologies as filters, analog to digital converters and related radio-frequency operating devices. Several high-k materials (Ta2O5, HfO2, Y2O3, Al2O3-HfTiO, HfON-SiO2) have been put on trial as possible candidates for SiO2 substitution which is required by the aggressive downscaling of electronic devices. Among those, HfO2- based materials seem to offer promising properties, combining a high chemical stability with Si and a high k value. However, HfO2 shows a strong ability to favour charge defects such as oxygen vacancies, which in turn affect the intrinsic properties of devices such as threshold voltage or leakage currents. These oxygen vacancies are actually thought to accumulate in the vicinity of the electrode, thus forming an oxidized interfacial layer and inducing a significant voltage linearity degradation of MIM capacitors.
In this work, it will be shown that this oxide layer thickness can be strongly minimized by using appropriate bottom electrode material. Indeed, high work function materials can efficiently prevent oxygen vacancies charge stocking on their surface. Several MIM devices have been prepared based on HfO2, Al2O3 and SrTiO3 as dielectric materials, and TiN, WSi2.7 and Pt as bottom electrode material. All these devices have been fully characterized in terms of materials properties and electrical behaviour. These results have been analysed and show that a reduced dielectric thickness is preferred to achieve high capacitance density, but is also responsible for voltage linearity degradation. High work function electrode material can help improve this degraded linear behaviour, thanks to the formation of a reduced interfacial oxygen trap layer thickness. Leakage currents seem to be deeply correlated with the morphological state of the dielectric material, an amorphous state being obviously more efficient to prevent current pathways through grain boundaries.
All these results will be presented in detail and discussed with regards to different models proposed in the literature to account for these data.