Papers by Keyword: ALD

Abstract: The effect of surface treatments prior to the deposition of Al₂O₃ is performed on 4H-SiC MOS capacitors and MOSFETs. 40 nm of Al₂O₃ were deposited on 4H-SiC using atomic layer deposition (ALD) as a gate dielectric. Different surface treatments were used to investigate the capacitance-voltage and current-voltage characteristics on MOS capacitors and MOSFETs respectively, including the important parameters such as interface state density, flat band voltage, threshold voltage and field-effect mobility. Forming gas annealing and rapid oxidation processes were found to be effective in reducing the interface state density and results in high field-effect mobility with peak field-effect mobility of 130 cm²Vs^-1. The experimental results obtained manifest that the surface treatment prior to Al₂O₃ deposition is critical to producing high performance of 4H-SiC MOSFETs.

Abstract: The SiO₂/SiC interface quality has a significant effect on the performance of 4H-SiC MOS devices. The introduction of nitrogen to the SiO₂/SiC interface is a well-known method for reducing the interface state density (D_it). In this study, we introduced nitrogen to the SiO₂/SiC interface by forming SiN_x films using atomic layer deposition (ALD) and thus improved the interface quality. O₂ annealing with a SiN_x interface layer of optimal thickness enhanced the field effect mobility.

Abstract: Charge trapping at 4H-SiC/dielectric interfaces in 4H-SiC MOS capacitors has been investigated using constant capacitance deep level transient spectroscopy (CCDLTS). The experiments were focused on further understanding of the following aspects related to 4H-SiC/SiO₂ interfaces: (i) Origin of near interface oxide traps (NITs), (ii) Effect of interfacial impurity/passivation methods and (iii) Characterization of near-interface oxide traps for different SiC wafer orientations. For the (0001) Si-face 4H-SiC/ SiO₂ interface, two types of NITs are typically detected by CCDLTS, named ‘O1’ and ‘O2’ traps with emission activation energies of about 0.15±0.05 eV and 0.39±0.1 eV respectively below the 4H-SiC conduction band. Based on comparison with previous ab initio calculations, the physical identities of these defects have been suggested to be carbon dimers substituted for O dimers (‘O1’) and interstitial silicon atoms (‘O2’) in the near interfacial SiO₂ respectively. In this work, it is shown for the first time that such traps are not observed for 4H-SiC/ Al₂O₃ interfaces, proving that these traps are inherent to the near-interfacial SiO₂. In addition, the summary of CCDLTS results for Si-face with different interface trap passivation methods are included in this study. Finally, a comparison is presented for NO annealed (0001) Si-face, (11-20) a-face and (000-1) C-face interfaces that highlight the difference of CCDLTS signatures for the different crystal faces.

Abstract: The article presents the results of research on tribological properties and corrosion resistance of hybrid and individual coatings embedded with the ALD (Atomic Layer Deposition) and PVD (Physical Vapour Deposition) technique on aluminum alloy substrates. Al-Si-Cu alloys coated with hybrid ALD+PVD coatings show significantly higher abrasion resistance compared to uncoated samples. In particular, the TiO₂+WC hybrid coating has the highest abrasion resistance. The highest resistance to corrosion is demonstrated by the sample with the TiO₂ type ALD coating. As a result of coating, the surface roughness of the tested samples increases, which is related to the occurrence of morphological heterogeneity in the form of solidified drops.The innovative approach of combining several technologies, while simultaneously selecting proper materials and parameters can significantly affect the future and functionality of products obtained. The technique of combining the hybrid coating technology still requires a lot of researches, the results of which can change the meaning and use of new innovative products. Keyword: PVD, ALD, hybrid coatings, TEM, corrosion resistance,

Abstract: This paper presents application examples of atomic layer deposition method (ALD) adopted for production of multifunctional thin films for various usage such as passive, antireflection and transparent conductive films. First part of this paper introduces the mechanism of ALD process, in the rest of it, aluminum oxide (as passive and antireflection) and zinc oxide (as antireflection and transparent conductive) ALD thin films are presented. In the literature one can find reports on the use of the Al₂O₃ layer as passivating and ZnO layers as a transparent conductive oxide in diodes, polymeric and dye sensitized solar cells. In this article, the ALD layers were tested for their use in silicon solar cells, using their good electrical and optical properties. For examination of prepared thin films characteristics, following research methods were used: scanning electron microscope, atomic force microscope, X-ray diffractometer, ellipsometer, UV/VIS spectrometer and resistance measurements. By depositing a layer thickness of about 80 nm, the short-circuit current on the surface of the solar cell was increased three times while reducing the reflection of light. In turn, by changing the deposition temperature of the ZnO thin film, you can control its electrical properties while maintaining high transparency. The obtained results showed that the ALD method provide the ability to produce a high quality multifunctional thin films with the required properties.

Abstract: In this framework, an investigation of biomorphous composite materials was performed. The application of a natural reinforcement allows to obtain biomorphous composite materials. Pine wood samples were subjected to the pyrolysis process in order to obtain carbon char. The samples were subjected to Atomic Layer Deposition and the sol-gel coating process in order to obtain a titanium oxide and titanium carbide coating, respectively. Ti-gel carbon char samples were subjected to ceramisation. Pure carbon char coated with TiO and TiC was infiltrated with an Al alloy. The investigations of the obtained composite materials were performed using light microscopy, transmission and scanning electron microscopy for microstructure determination. Raman spectroscopy and X-ray analysis were performed, along with hardness and tribological tests. Crystallites were detected after infiltration of the porous samples with an Al alloy, which were up to several microns in size, depending on the selected coating. As a result of the investigation on coating samples, a significantly smaller presence of Al carbides was found. An increase of hardness and wear resistance of biomorphous composite materials containing the carbides phase was confirmed. The TiO₂ coating prevents the occurrence of a reaction during the infiltration process and the formation of Al carbides.

Abstract: This study reports the electrical characteristics and reliability of the atomic layer deposited SiO₂ on the 4H-SiC substrate. By controlling the thickness of SiO₂ in each ALD cycle, improved device properties like mobility and gate leakage were obtained as compared to the single deposition. Moreover, the optimized process dramatically reduces the threshold voltage shift under positive and negative bias stresses. This improvement can be attributed to the effective removal of unreacted metal-organic precursors, active traps, and broken bonds in the ALD SiO₂ dielectrics as well as reduction in interface state density at SiC/SiO₂ interface.

Abstract: This paper reports on the effect of forming gas annealing on the C-V characteristics and stability of Al2O3/SiC MOS capacitors deposited by atomic layer deposition, (ALD). C-V and I-V measurements were performed to assess the quality of the Al2O3 layer and the Al2O3/SiC interface. In comparison to as-deposited sample, the post oxide annealing (POA) in forming gas at high temperatures has improved the stability of C-V characteristic and the properties at the interface of Al2O3/SiC capacitors. However, the oxide capacitance and oxide breakdown electric field degrade with increased annealing temperature. The results provide indications to improve the performance of Al2O3/SiCcapacitors 4H-SiC devices by optimizing the annealing temperature.

Abstract: 3-Dimensional 4H-SiC metal-oxide-semiconductor capacitors have been fabricated to determine the effect of the sidewall on the characteristics of 3-Dimentional gate structures. Al2O3 deposited by Atomic Layer Deposition (ALD) was used as the gate dielectric layer on the trench structure. The 3-D MOS capacitors exhibit increasing accumulation capacitance with excellent linearity as the sidewall area increases, indicating that ALD results in a highly conformal dielectric film. The capacitance – voltage characteristics also show evidence of a second flatband voltage, located at a higher bias than that seen for purely planar devices on the same sample. We also observe that the oxide capacitance of planar and 3-D MOS capacitors increases with temperature. Finally, we have found that the 3-D MOS capacitor has a weaker temperature dependence of flatband voltage in comparison to the conventional planar MOS capacitor due to the incorporation of the (1120) plane in the sidewall.

Abstract: The computational prediction of the surface adsorption in atomic layer deposition of gallium oxide by using trimethylgallium (TMG) is investigated. One dimer of Si (100)(2×1) is used as the substrate. The hydroxyl radicals are used to produce the absorption sites for the TMG adsorbed surface as OH–Si–Si–OH surface species. Two sites adsorption of the TMG on the surface are predicted. The geometry, vibrational frequency, and free energy of –OH adsorption sites and TMG adsorption are calculated by Gaussian 09 package by using standard B3LYP method. The results showed that TMG is possible to adsorb on silicon dimer with two sites adsorption. The geometry and vibrational frequencies are also reported in this paper.