Papers by Keyword: High-k Dielectrics

Abstract: We investigate the physical and electrical characteristics of the Al-doped or undoped HfO₂/SiO₂ gate stacks on 4H-SiC by testing MOSCAP chips fabricated in house. A clear reduction in accumulation capacitance (C_ox) with increasing chuck temperature from room temperature up to 523 K is observed, with Al-doping playing a key role and aligning with temperature-dependent Landau ferroelectric theory. Chips annealed at 1100°C in N₂ ambient show the highest C_ox decrease rates while maintaining functional MOS interfaces with acceptable flatband voltage, hysteresis, and Dit profiles. TCAD simulations on a double trench MOSFET model, based on the extracted data indicate improved electro-thermal performance, demonstrating that Al-doped HfO₂/SiO₂ gate stacks are a promising approach for enhancing 4H-SiC power devices.

Abstract: Silicon Carbide (SiC) based MOS devices are one of the promising devices for high temperature, high switching frequency and high power applications. In this paper, the static and dynamic characteristics of an asymmetric trench gate SiC IGBT with high-k dielectrics- HfO₂ and ZrO₂ are investigated. SiC IGBT with HfO₂ and ZrO₂ exhibited higher forward transconductance ratio and lower threshold voltage compared to conventionally used SiO₂. In addition, lower switching power losses have been observed in the case of high-k dielectrics due to reduced tail current duration.

Abstract: Charge-trapping memories such as SONOS and MONOS have attracted considerable attention as promising alternatives for next-generation flash memories due to dielectric layer’s scalability, process simplicity, power economy, operation versatility. Nevertheless, the continued miniaturization of the devices forces an application of high-k dielectrics. In this work high-k stacked dielectric structures based on the combination of Hf-based and SiN_x materials were fabricated. Their structural and electrical properties versus deposition conditions are studied by means of FTIR-ATR and high-resolution TEM techniques. All samples demonstrated smooth surface (roughness below 1 nm) and abrupt interfaces between the different stacked layers. No crystallization of Hf-based layers was observed after annealing at 800°C for 30 min, demonstrating their amorphous nature and phase stability upon annealing. Electrical characterization was carried out for all samples through capacitance-voltage (C-V) measurements of MIS capacitors. Uniform C-V characteristics were measured along the samples for all stacks. Besides, significant flat-band hysteresis due to charging of the stacks caused by carrier injection from the substrate was observed for the structures with pure HfO₂ layers.

Abstract: _{Subscript textSubscript text}Er₂O₃、Tm₂O₃ and Yb₂O₃ films were deposited on Si (100) and quartz substrates by radio frequency magnetron technique. The energy gaps of the films were measured by X-ray photoelectron spectroscopy (XPS) and optical methods. The energy gaps of Er₂O₃、Tm₂O₃ and Yb₂O₃ are found to be 6.3±0.1、5.8±0.1 and 7.1±0.1 eV by optical measurements. For XPS measurements, the energy gaps of the films are 6.2±0.2、6.0±0.2 and 6.9±0.2 eV, respectively. The results show that using XPS to measure the energy gap of rare earth metal oxide film is feasible in an allowable deviation.

Abstract: This paper aims to establish a new method to characterize the interface between 4H-SiC and passivating dielectric layers. The investigations are made on MOS test structures utilizing Al₂O₃ and SiO₂ dielectrics on 4H-SiC. These devices are then exposed to various fluences of Ar⁺ implantation and then measured by the new method utilizing optical free carrier absorption (FCA) technique to assess the interface traps. A program has been developed using MATLAB to extract surface recombination velocity (SRV) at the oxide/epi-layer interface from the optical data. Capacitance-voltage (CV) is done to extract the density of interface traps (D_it) and a comparison was made. It is observed that SiO₂ samples show a large rise of SRVs, from 0.5×10⁴ cm/s for a reference sample to 8×10⁴ cm/s for a fluence of 1×10^₁₂ cm^-2, whereas Al₂O₃ samples show more stable SRV, changing from 3×10⁴ cm/s for the un-irradiated reference sample to 6×10⁴ cm/s for a fluence of 1×10¹² cm^-2. A very similar trend is observed for D_it values extracted from CV measurements and it can therefore be concluded that the FCA method is a suitable technique for the interface characterization.

Abstract: High-k gate dielectrics and metal gate electrodes have become essential for emerging device technologies because they enable the continuous scaling down of devices while maintaining a high performance [. However, since they are composed of novel metallic elements that have never before been used in conventional processes, special care must be taken when handling these materials in the production line. In particular, cross-contamination that occurs due to transporting contamination via processed wafers can cause serious problems such as deterioration of device properties and yield loss [. The process of cleaning the backside and bevel of a wafer is now increasingly important for avoiding these problems. To date, there has been no detailed evaluation of contamination removal on various films performed for elements such as hafnium, which is one of the key elements in high-k/metal gate technologies. In this study, we evaluated hafnium contamination on three types of wafer surface after the cleaning process and investigated the cause of different residual amounts of hafnium contamination on the different wafers.

Abstract: With continual scaling of ICs, the thickness of gate oxide becomes thinner and thinner which affects the reliability of semiconductor device greatly. The mechanism of time-dependent dielectric breakdown (TDDB) was analyzed. Six mathematical models of TDDB which were divided according to the position of defects and the physical property of charged particles were discussed. Then the dielectric breakdown characteristic of high k dielectrics and the relationships between the breakdown electric field, field acceleration parameter and dielectric constant were analyzed in detail. Finally, the relationships and mathematical models were verified by experimental data which provided theoretical basis for the choosing and use of high k materials.

Abstract: The radiation hardness of Al2O3 as a dielectric for SiC surface passivation is studied and compared to SiO2 for potential application in radiation hard SiC devices. SiO2 is deposited on 4H-SiC by PECVD and post annealed in N2O, whereas Al2O3 is deposited by atomic layer deposition (ALD). The oxides are bombarded with Ar ions in an energy range to produce maximum damage near the oxide/SiC interface. Metal-insulator-semiconductor structures are prepared and their dielectric characteristics are analyzed using capacitance-voltage measurements. Additionally, the effect of the interface damage on surface recombination is studied using the optical free carrier absorption method for the same samples. The results indicate that the SiO2/SiC interface is significantly affected at 1×1011 cm-2 fluence of Ar ions, however, the dielectric properties of Al2O3/SiC interface remain unaffected even for ten times higher fluences. Similar observations are made for the surface recombination measurements.

Abstract: In this work we report on the structural and electrical properties of SiO₂/Si3N₄/HfO₂ memory stacks with emphasis upon the influence of Atomic Layer Deposition chemistry used for forming the HfO₂ blocking layer. Two HfO₂ precursor chemistries were employed, the tetrakis- (ethylmethylamino)hafnium (TEMAH) and the bis(methylcyclopentadienyl)methoxymethylhafnium (HfD-04). Ozone was used as the oxygen source. The structural characteristics of the stacks were examined by means of TEM and GIXRD. Comparative studies conducted with the use of platinum gated capacitors showed that the samples grown using TEMAH have an increased electron trapping ability in comparison to the HfD-04 ones. While the two structures exhibit similar Write/Erase and retention characteristics, The samples grown from TEMAH can sustain more repeated W/E cycles (> 3×10⁵ in the 10V/-11V, 10 ms regime) compared to the samples grown from HfD-04 (< 10⁴ W/E cycles). This difference in endurance characteristics is attributed mainly to the different deposition temperatures used with these two precursors and the nature of the interfacial layer they produce between the Si₃N₄ and the HfO₂ layers.

Abstract: Aluminum-based high-k dielectric materials have been studied for their potential use as passivation for SiC devices. Metal-insulator-semiconductor structures were prepared and their dielectric properties were analyzed using capacitance-voltage and current-voltage measurements. Atomic layer deposition was used for the deposition of dielectric layers consisting of AlN with or without a buffer layer of SiO2, and also a stack of alternating AlN and Al2O3 layers. It has been observed that AlN has a polycrystalline structure which provides leakage paths for the current through the grain boundaries. However, adding alternate amorphous layers of Al2O3 prevent this leakage and give better overall dielectric properties. It is also concluded that the breakdown of the dielectric starts from the degradation of the thin interfacial SiO2 layer.