Correlation between the nanoscale electrical and morphological properties of crystallized hafnium oxide-based metal oxide semiconductor structures

Abstract

The relationship between electrical and structural characteristics of polycrystalline HfO2 films has been investigated by conductive atomic force microscopy under ultrahigh vacuum conditions. The results demonstrate that highly conductive and breakdown (BD) sites are concentrated mainly at the grain boundaries (GBs). Higher conductivity at the GBs is found to be related to their intrinsic electrical properties, while the positions of the electrical stress-induced BD sites correlate to the local thinning of the dielectric. The results indicate that variations in the local characteristics of the high-k film caused by its crystallization may have a strong impact on the electrical characteristics of high-k dielectric stacks.

Resistive switching in hafnium dioxide layers: Local phenomenon at grain boundaries

“…In no one of all collected images, a perfect granular structure, which is characteristic of the polycrystalline samples, can be observed. This is consistent with the previous reports 13,14 showing that the grains in polycrystalline samples can be distinguished in topographic maps only when the annealing temperature is sufficiently high. However, an increase in RMS points to the anneal-induced phase modification, which a)…”

“…1(f)) a perfect granular structure was not observed. 13,14 In this scan, since no bias has been applied, no leaky spots were observed in the current map (Fig. 3(a)).…”

“…1(e)), the granular structure is not as clear as in sample C. Accordingly, the topography (GB)-current correlation is more difficult to identify (although some depressions are seen on the surface, as indicated by the arrows and blue dashed line in Fig. 1(b), 14,18 suggesting a lower level of crystallization, because the film smaller thickness (compared to sample C) impedes grain growth. 19,20 In any case, the differences in the CAFM maps (Figs.…”

“…1(f)) are associated with a significant thickness reduction, suggesting that these locations correspond to grain boundaries (GBs), which were shown to form depressed regions on the dielectric surface. 14,16 However, it should be emphasized that leakage at GBs is not higher there only because of lower thickness but also due to a high oxygen vacancy concentration. 17 In the current image of sample B ( Fig.…”

Conductive-AFM topography and current maps simulator for the study of polycrystalline high-k dielectrics

“…In this context, C-AFM has been demonstrated to be a very powerful technique to evaluate the topographic and electrical properties of high-k dielectrics at the nanoscale. 4,5 In particular, this technique was successfully used in several studies to evaluate the impact of polycrystallization. [5][6][7] One of the most relevant conclusions of these works was that, in polycrystalline HfO 2 layers, the gate leakage current mainly flows through grain boundaries (GBs).…”