Study of Nitrogen-doped Crystalline High-K/Metal Gate Stacks Prepared by Remote Plasma Atomic Layer Deposition
Date Issued
2014
Date
2014
Author(s)
Huang, Jhih-Jie
Abstract
High-K dielectric zirconium oxide (ZrO2) was fabricated by the Remote Plasma Atomic Layer Deposition (RP-ALD) technique. In this thesis, the first part discusses the effect of nitridation on ZrO2 gate dielectrics. The crystalline ZrO2 high-K gate dielectrics treated with in-situ atomic layer doping of nitrogen using remote N2 and NH3 plasma were investigated, to suppress the capacitance equivalent thickness (CET), and leakage current density (Jg). The stress-induced leakage current (SILC) was reduced significantly as well. In addition, the interfacial states density (Dit) was also reduced by hydrogen passivation as a result of the remote NH3 plasma treatment. Next, the electrical characteristics of crystalline ZrO2 gate dielectrics with different nitrogen depth profiles were investigated, which were treated by the in-situ atomic layer doping of nitrogen and post-deposition nitridation processes, respectively, using remote NH3 plasma at a low treatment temperature of 250 oC. As compared with the in-situ atomic layer doping of nitrogen, the post-deposition nitrogen process leads to a lower capacitance equivalent thickness of 1.13 nm with a low leakage current density of 1.35×10-5 A/cm2. The enhanced capacitance density caused by the post-deposition nitrogen treatment was ascribed to the high nitrogen concentration at the top surface of gate dielectric, giving rise to the suppression of oxygen diffusion toward the interface and so a thinner interfacial layer. The result reveals that the nitrogen depth profile has significant impact on the electrical properties of the gate dielectrics in the advanced metal-oxide-semiconductor devices.
The other part discusses the effect of the bilayer structure based on the combination of ZrO2 and buffer layer Al2O3. The gate stack composed of crystalline ZrO2 high-K dielectrics and nitrided Al2O3 buffer layer was investigated to reduce the CET, Jg, and Dit. The Jg was suppressed by the insertion of the Al2O3 buffer layer between ZrO2 and Si. A suppressed Jg of 8.12×10-6 A/cm2 and Dit of 2.77×1011 cm-2eV-1 were achieved in the crystalline ZrO2/nitrided Al2O3 gate stack with a low CET of 1.2 nm. The gate stack was also optically probed through the photoluminescence from Si, revealing that the hydrogen passivation and depassivation effects caused by the remote NH3 plasma treatment are highly correlated with the Dit. Finally, the gate dielectric stack composed of crystalline ZrO2 and Al2O3 buffer layer treated with double nitridation was developed to reduce the CET, Jg, Dit, and enhance thermal stability as well. The Jg and Dit were suppressed by the insertion of the Al2O3 buffer layer treated with remote NH3 plasma nitridation. A further nitridation using remote N2 plasma on ZrO2 was carried out to reduce the CET and Jg. Accordingly, a low CET of 1.09 nm, Jg of 3.43×10-5 A/cm2, and Dit of 3.35×1011 cm-2eV-1 were achieved in the crystalline ZrO2/Al2O3 buffer gate stack treated with the double nitridation. The hysteresis was also minimized significantly by the post-deposition annealing at 800 oC, which is attributed to the enhanced thermal stability. The results indicate that the crystalline high-K dielectrics/buffer layer with double nitridation treatments is a promising gate stack structure beneficial to the sub-nanometer CET scaling in the future.
Subjects
高介電係數介電層
二氧化鋯
原位原子層摻雜
沉積後氮化處理
緩衝層
遠程電漿輔助原子層沉積技術
Type
thesis
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