1. 2.Local Electric Property 5.Composition and Structure
Studies on Local Electrical Properties and Annealing Behaviors of High-κ Er2O3 Films Haiyue Zhang, Wei Wang, Ting Ji, Zuimin Jiang State Key Laboratory of Surface Physics, Fudan University, Shanghai , PRC.
1. Introduction
Thermally grown silicon dioxide has been used as a gate dielectric in MOSFETs ever since the first working transistor was created in The progress in microelectronics over the last decades is based on the high quality of SiO2 and its interface with silicon. However, gate oxide thickness has to be scaled down aggressively towards sub-1nm within the next decade. The unacceptably high tunneling currents through such thin films present a fundamental scaling limit for SiO2. Therefore, alternative materials with a higher permittivity (high-k) are currently investigated as replacements for SiO2. Unfortunately, most of these amorphous materials are not sufficiently stable….
One possible solution to these problems is the use of rare earth metal oxide. Recently, it was demonstrated that Erbium Oxide (Er2O3) films have excellent dielectric properties and possess sufficient processing stability. Additionally, nanometer-scale electrical and topographical Conductive Atomic Force Microscopy (CAFM) measurements were performed directly on the Er2O3 surface in an attempt to explain the observed macroscopic behavior.
3. Annealing in O2
4. Annealing in N2
2.Local Electric Property
FIG.3 Three high dots were selected and marked, namely O1, O2 and O3.
FIG.7 Three high dots were selected and marked, namely N1, N2 and N3.
FIG.1 Topography and electrical current map of Er2O3 surface measured by CAFM. High dots on topography map were corresponded with leaky dots on current map.
FIG.4 Topography and electrical current map as grown(a), after annealing at the temperature of 400℃ in Oxygen ambient for 15min(b), 30min(c) and 45min(d) .
FIG.8 Topography and electrical current map after annealing at the temperature of 400℃ in Nitrogen ambient for 15min(a), 30min(b), 45min(c) and 60min(d).
FIG.5 I-V measurements in the point-contact mode performed on marked dots.
FIG.9 I-V measurements in the point-contact mode performed on marked dots.
FIG.2 Three consecutive scans on a certain area with bias of -3.0V (above) and -6.0V (below) respectively. Neither on topography or on electrical current map obvious change were observed.
FIG.6 Diameters, heights and leaky voltage(Tunneling current reaches 100pA) of the three marked dots.
FIG.10 Diameters, heights and leaky voltage(Tunneling current reaches 100pA) of the three marked dots.
5.Composition and Structure
Oxygen %
As grown
9.7%
16.5%
2.4%
4.2%
Anneal in O2
12.1%
12.3%
12.6%
8.3%
Anneal in N2
18.2%
19.6%
3.8%
5.2%
The grain boundaries in polycrystalline materials are known to be more conductive as there exist a large number of defects. This difference could be a possible interpretation of the various electrical behaviors for either high dots or plane area, as shown in FIG.12
In FIG.11, the four colors were the SAES result of the surface of the high dots, the surface of plane area (green), the inside of the high dots (blue) and the inside of the plane area (black).
FIG.11 SAES results of Er2O3 as grown (a), anneal in O2 (b) and anneal in N2 (c)
FIG. 12 Cross-sectional HRTEM image of Er2O3 film as grown
6.Conclusion
The local electric property and effect of thermal annealing on the electrical properties of thin Er2O3 film grown on Ge substrate was studied by Conductive Atomic Force Microscopy (CAFM). It is observed in situ that the leaky dots on current map always relates to morphologically high dots. Such leaky dots perform improvement in their electrical properties, namely as the reduction of the leaky current and the enhancement of the band gap, after annealed in O2. However, the samples annealed in N2 showed a different behavior. The result from SAES demonstrated a lack of oxygen in the film especially the leaky point. Such lack could be complemented via a thermal anneal in Oxygen ambient, but not in Nitrogen ambient.