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Polycrystallization effects on the nanoscale electrical properties of high-k dielectrics.

Lanza M, Iglesias V, Porti M, Nafria M, Aymerich X - Nanoscale Res Lett (2011)

Bottom Line: In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties.The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept, Eng, Electrònica, Edifici Q, Campus UAB, 08193 Bellaterra, Spain. mario.lanza@uab.cat.

ABSTRACT
In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties. The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

No MeSH data available.


Related in: MedlinePlus

Topography (a, b, c) and current (d, e, f) maps obtained on a polycrystalline 5-nm-thick HfO2 sample in different environments: air (a, d), high-vacuum (b, e), and ultra-high-vacuum (UHV)--(c, f). In current images, white areas correspond to regions with a current above 0.2 pA, while the black areas show a current lower than the noise level.
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Figure 5: Topography (a, b, c) and current (d, e, f) maps obtained on a polycrystalline 5-nm-thick HfO2 sample in different environments: air (a, d), high-vacuum (b, e), and ultra-high-vacuum (UHV)--(c, f). In current images, white areas correspond to regions with a current above 0.2 pA, while the black areas show a current lower than the noise level.

Mentions: Toward the above aim, topographical and current images obtained on polycrystalline high-k dielectrics at different ambient conditions have been compared. Figure 5 shows topographical (first row) and current (second row) maps measured on a 5-nm-thick HfO2 layer grown on a Si substrate, obtained in air (a and d), high-vacuum (b and e, 1.2 × 10-6 mbar), and UHV (c and f, 10-9 mbar) [35]. In current images, the white areas correspond to the regions with a current above 0.2 pA, while the black areas show a current lower than the noise level. Note that as pressure decreases (and, therefore, the size of the water meniscus is reduced), topography images show a better-defined granular structure, which can be attributed to single (or a cluster of) nanocrystals (grain boundaries would correspond to the depressed regions [32]). Current maps show a similar behavior. While in UHV, a clear granular pattern can be observed [35] (which overlaps with that observed in the topographical image, indicating that current flows mainly through grain boundaries, as suggested in the sections "As-grown dielectrics" and "Stressed dielectrics"), in HV and, specially, in air, the granular structure is not so clearly distinguishable and a point-to-point correlation of the leakage spots with the position of the grain boundaries is not possible. If it is assumed that, in (d) and (e), the current is measured basically through GBs (conclusion that can be drawn from the analysis of images c and f), then the measured GB's width is much larger than that in (f). All these effects could be related, as demonstrated in [19], to the contact area increase because of the presence of the water meniscus. Therefore, the results clearly demonstrate that the AFM lateral resolution is very sensitive to the environment, a point that is extremely important when studying polycrystalline high-k dielectrics. Since the grain boundaries width is close to the limit of the AFM resolution, environmental conditions can be the determinant factors to precisely correlate the leakage spots position with the morphological structure of the high-k dielectric.


Polycrystallization effects on the nanoscale electrical properties of high-k dielectrics.

Lanza M, Iglesias V, Porti M, Nafria M, Aymerich X - Nanoscale Res Lett (2011)

Topography (a, b, c) and current (d, e, f) maps obtained on a polycrystalline 5-nm-thick HfO2 sample in different environments: air (a, d), high-vacuum (b, e), and ultra-high-vacuum (UHV)--(c, f). In current images, white areas correspond to regions with a current above 0.2 pA, while the black areas show a current lower than the noise level.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211152&req=5

Figure 5: Topography (a, b, c) and current (d, e, f) maps obtained on a polycrystalline 5-nm-thick HfO2 sample in different environments: air (a, d), high-vacuum (b, e), and ultra-high-vacuum (UHV)--(c, f). In current images, white areas correspond to regions with a current above 0.2 pA, while the black areas show a current lower than the noise level.
Mentions: Toward the above aim, topographical and current images obtained on polycrystalline high-k dielectrics at different ambient conditions have been compared. Figure 5 shows topographical (first row) and current (second row) maps measured on a 5-nm-thick HfO2 layer grown on a Si substrate, obtained in air (a and d), high-vacuum (b and e, 1.2 × 10-6 mbar), and UHV (c and f, 10-9 mbar) [35]. In current images, the white areas correspond to the regions with a current above 0.2 pA, while the black areas show a current lower than the noise level. Note that as pressure decreases (and, therefore, the size of the water meniscus is reduced), topography images show a better-defined granular structure, which can be attributed to single (or a cluster of) nanocrystals (grain boundaries would correspond to the depressed regions [32]). Current maps show a similar behavior. While in UHV, a clear granular pattern can be observed [35] (which overlaps with that observed in the topographical image, indicating that current flows mainly through grain boundaries, as suggested in the sections "As-grown dielectrics" and "Stressed dielectrics"), in HV and, specially, in air, the granular structure is not so clearly distinguishable and a point-to-point correlation of the leakage spots with the position of the grain boundaries is not possible. If it is assumed that, in (d) and (e), the current is measured basically through GBs (conclusion that can be drawn from the analysis of images c and f), then the measured GB's width is much larger than that in (f). All these effects could be related, as demonstrated in [19], to the contact area increase because of the presence of the water meniscus. Therefore, the results clearly demonstrate that the AFM lateral resolution is very sensitive to the environment, a point that is extremely important when studying polycrystalline high-k dielectrics. Since the grain boundaries width is close to the limit of the AFM resolution, environmental conditions can be the determinant factors to precisely correlate the leakage spots position with the morphological structure of the high-k dielectric.

Bottom Line: In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties.The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept, Eng, Electrònica, Edifici Q, Campus UAB, 08193 Bellaterra, Spain. mario.lanza@uab.cat.

ABSTRACT
In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties. The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

No MeSH data available.


Related in: MedlinePlus