Bao Zhu

High-performance ultralow dielectric constant carbon-bridged mesoporous organosilica films for advanced interconnects

Mesoporous organosilica (MO) films are prepared using precursor 1,2-bis(triethoxysilyl)ethane (BTEE) and porogen template poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (P123). The effects of annealing temperature, P123/BTEE molar ratio, and moisture adsorption on the characteristics of the MO films are investigated. It is indicated that MO films prepared at a P123/BTEE molar ratio of 0.016 display the lowest dielectric constant (κ) of 1.80, a small dissipation factor of 0.0068 at 100 kHz, an extremely low leakage current density of 2.01 × 10−9 A cm−2 at 0.5 MV cm−1, a modulus (E) of 6.27 GPa, and a hardness (H) of 0.58 GPa. Following moisture adsorption, the κ value increases by ∼12%. However, ultraviolet treatment significantly reduces the extent of increase of the κ value to 4%. The films maintain an ultralow κ value of ∼2.0 and a very low leakage current density of 1.7 × 10−9 A cm−2 at 0.5 MV cm−1. Following annealing at 500 °C, the superior performance of the MO films is demonstrated by their κ value of ∼1.92, leakage current density of 7.08 × 10−9 at 0.5 MV cm−1, and improved E of ∼9.1 GPa and H of ∼0.8 GPa. Such MO films are very promising for advanced interlevel insulators.

Three-dimensional AlZnO/Al2O3/AlZnO nanocapacitor arrays on Si substrate for energy storage

High density three-dimensional AZO/Al2O3/AZO nanocapacitor arrays have been fabricated for energy storage applications. Using atomic layer deposition technique, the stack of AZO/Al2O3/AZO has been grown in the porous anodic alumina template which is directly formed on the Si substrate. The fabricated capacitor shows a high capacitance density of 15.3 fF/μm2 at 100 kHz, which is nearly 2.5 times over the planar capacitor under identical conditions in theory. Further, the charge-discharge characteristics of the capacitor are characterized, indicating that the resistance-capacitance time constants are equal to 300 ns for the charging and discharging processes, and have no dependence on the voltage supply. This reflects good power characteristics of the electrostatic capacitor.

Full ALD Al 2 O 3 /ZrO 2 /SiO 2 /ZrO 2 /Al 2 O 3 Stacks for High-Performance MIM Capacitors

Metal-insulator-metal (MIM) capacitors with full atomic-layer-deposition Al₂O₃/ZrO₂/SiO₂/ZrO₂/Al₂O₃ stacks were explored for the first time. As the incorporated SiO₂ film thickness increased from 0 to 3 nm, the quadratic and linear voltage coefficients of capacitance (α and β) of the MIM capacitors reduced significantly from positive values to negative ones. For the stack with 3-nm SiO₂ film, a capacitance density of 7.40 fF/μm², α of -121 ppm/V², and β of -116 ppm/V were achieved, together with very low leakage current densities of 3.08 × 10^-8 A/cm² at 5 V at room temperature (RT) and 5.89 × 10^-8 A/cm² at 3.3 V at 125 °C, high breakdown field of 6.05 MV/cm, and high operating voltage of 6.3 V for a 10-year lifetime at RT. Thus, this type of stacks is a very promising candidate for next generation radio frequency and analog/mixed-signal integrated circuits.

Voltage linearity modulation and polarity dependent conduction in metal-insulator-metal capacitors with atomic-layer-deposited Al2O3/ZrO2/SiO2 nano-stacks

Excellent voltage linearity of metal-insulator-metal (MIM) capacitors is highly required for next generation radio frequency integration circuits. In this work, employing atomic layer deposition technique, we demonstrated how the voltage linearity of MIM capacitors was modulated by adding different thickness of SiO2 layer to the nano-stack of Al2O3/ZrO2. It was found that the quadratic voltage coefficient of capacitance (α) can be effectively reduced from 1279 to −75 ppm/V2 with increasing the thickness of SiO2 from zero to 4 nm, which is more powerful than increasing the thickness of ZrO2 in the Al2O3/ZrO2 stack. This is attributed to counteraction between the positive α for Al2O3/ZrO2 and the negative one for SiO2 in the MIM capacitors with Al2O3/ZrO2/SiO2 stacks. Interestingly, voltage-polarity dependent conduction behaviors in the MIM capacitors were observed. For electron bottom-injection, the addition of SiO2 obviously suppressed the leakage current; however, it abnormally increased the leakage curr...

Formation of Cylindrical Nanoholes in Heavily Doped P-Type Si(100) Substrate via Pt Nanoparticles-Assisted Chemical Etching

Metal assisted chemical etching of heavily doped p-type Si(100) wafer was investigated in a solution containing HF and hydrogen peroxide using Pt nanoparticles as catalyst. The Pt nanoparticles were formed on Si(100) substrate by magnetron sputtering and post-deposition annealing. In a solution containing low concentration HF, formation of cylindrical nanoholes are unstable in the early stage of the etching process. After that, nanoholes with diameters ranging from 40 to 50 nm are stably formed in silicon substrate and the calculated growing rate is 60 nm/min. Instead, in a solution containing high concentration HF, cylindrical nanoholes with a diameter of about 10 nm can be stably produced in silicon substrate all the time and the growing rate is increased to as fast as 160 nm/min. In both cases, no Pt nanoparticles are observed at the bottom of the nanoholes. Finally, the underlying mechanisms of the aforementioned phenomena are also discussed.

Atomic layer deposition of amorphous Ni-Ta-N films for Cu diffusion barrier

Novel Ni-doped TaN (Ni-Ta-N) films are deposited by remote plasma-enhanced atomic layer deposition (ALD) with pentakis(dimethylamino)tantalum, nickelocene, and NH3 precursors for Cu diffusion barriers. Various Ni-Ta-N films with different compositions are achieved by changing the deposition cycles (n) of Ni sublayer while fixing the deposition cycles of TaN sublayer at 2. As n increases from 1 to 6, the root-mean-square roughness of the deposited film increases from 0.150 to 0.527 nm, and the resistivity decreases from 0.18 to 1.1 × 10−2 Ω cm. After annealing at 400 °C for 30 min in the forming gas (N2/H2), these films still maintain an amorphous texture and demonstrate a negligible reduction of resistivity and a weak increase of density. Subsequently, the barrier effects of the Ni-Ta-N films with different compositions are compared against Cu diffusion after annealing. The results reveal that the Ni-Ta-N films with n ≤ 4 exhibit barrier effects comparable with the ALD TaN film even after annealing at 550...

Band alignment of In2O3/β-Ga2O3 interface determined by X-ray photoelectron spectroscopy

The energy band alignment of the atomic-layer-deposited In2O3/β-Ga2O3 ( 2 ¯ 01) interface is evaluated by X-ray photoelectron spectroscopy. The X-ray diffraction pattern reveals that the In2O3 film grown at 160 °C is amorphous, while it becomes polycrystalline at a higher deposition temperature of 200 °C. The bandgaps, determined by reflection electron energy loss spectroscopy, are 4.65, 3.85, and 3.47 eV for β-Ga2O3, polycrystalline In2O3, and amorphous In2O3, respectively. Both amorphous and polycrystalline In2O3/β-Ga2O3 interfaces have Type I alignment. The conduction and valence band offsets at the polycrystalline (amorphous) In2O3/β-Ga2O3 interface are 0.35 and 0.45 eV (0.39 and 0.79 eV), respectively. These observations suggest that polycrystalline In2O3 as an intermediate semiconductor layer is beneficial to the barrier reduction of metal/Ga2O3 contact.The energy band alignment of the atomic-layer-deposited In2O3/β-Ga2O3 ( 2 ¯ 01) interface is evaluated by X-ray photoelectron spectroscopy. The X-ray diffraction pattern reveals that the In2O3 film grown at 160 °C is amorphous, while it becomes polycrystalline at a higher deposition temperature of 200 °C. The bandgaps, determined by reflection electron energy loss spectroscopy, are 4.65, 3.85, and 3.47 eV for β-Ga2O3, polycrystalline In2O3, and amorphous In2O3, respectively. Both amorphous and polycrystalline In2O3/β-Ga2O3 interfaces have Type I alignment. The conduction and valence band offsets at the polycrystalline (amorphous) In2O3/β-Ga2O3 interface are 0.35 and 0.45 eV (0.39 and 0.79 eV), respectively. These observations suggest that polycrystalline In2O3 as an intermediate semiconductor layer is beneficial to the barrier reduction of metal/Ga2O3 contact.

Morphological and optical properties of silicon nanoholes produced by Pt-nanoparticles assisted chemical etching

Silicon nanoholes have been fabricated in heavily doped P-type single-crystalline silicon via Pt-nanoparticles assisted chemical etching. The morphologies of silicon nanoholes are modulated by varying etching time and HF concentration, respectively. Vertical aligned cylindrical nanoholes are observed in all fabricated films. As the etching time increase, the diameter of silicon nanoholes stays the same and the depth and roughness increase, though. The reflection spectrum indicates that these silicon nanoholes have great antireflection property and reflectivity as low as 2.5 % is obtained. When the HF concentration is raised, the depth of silicon nanoholes has a maximum and the diameter and roughness decrease. The reflection spectrum shows apparent interference fringes when the HF concentration is very high.

Au Nanowires Encapsulated in Carbon Nanotubes: Structure, Melting and Mechanical Properties

Classical molecular dynamics simulation was used to investigate the structure, melting and mechanical properties of Au nanowires encapsulated in single-walled carbon nanotubes (SWCNT). A possibility of synthesizing controlled Au nanowires was firstly studied by encapsulating small clusters into CNTs with suitable diameters. The nanowires with multi-shell structure of cylindrical symmetry are predicted as a consequence of spontaneous and confined coalescence of gold clusters. The investigation of melting temperature and behavior of a gold nanowire with multi-shells in a carbon nanotube (CNT) showed that the melting temperature of the enclosed Au nanowire is lower than its bulk counterpart and higher than that observed for free-standing ones. Different from the melting behavior of freestanding Au nanowires, the melting of Au nanowires enclosed in CNTs with tube diameters (D) in the range of 1.08 nm < D < 2.09 nm investigated here was found to initiate from the center layers. Finally, the deformation behavior of the gold-filled single-walled carbon nanotube was simulated under axial compression. The results show that the buckling strength of the Au-filled carbon nanotube is increased compared with that of a hollow tube, and is similar to the case of filling with gases or fullerenes. The interactions between filling elements and the carbon wall help restrain the collapse of the tube. With Au-filling, the filled tube experiences an elastic-inelastic transition, somewhat like the behavior of metals, which is different from the cases when it is filled with gases or fullerenes, particularly for low filling density.