Preparation and properties of high dose nitrogen implanted epitaxially grown gadolinium oxide on silicon

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Electrical property improvements of high-k gate oxide by in situ nitrogen incorporation during atomic layer deposition

Atomic layer deposition (ALD) process for oxynitrides of high-k gate dielectrics employing NH4OH as a single source for reactants, water and NH3, was studied. By this method, nitrogen was incorporated up to 1-3 at. % for ALD Al2O3 and Ta2O5 films from metal organic precursors. A comparative study with water based ALD showed that the electrical properties were improved. The leakage current of oxide films from NH4OH based ALD had been reduced and, more importantly, the dielectric strength was found to be enhanced by more than two orders of magnitude from a time dependent dielectric breakdown measurement. (c) 2007 American Institute of Physics.X119sciescopu

Atomic scale nitrogen depth profile control during plasma enhanced atomic layer deposition of high k dielectrics

Nitrogen incorporation produces several benefits in the performance of high k gate oxides. However, since too much nitrogen incorporation at the interface of gate dielectric can result in device degradation, the atomic scale control of nitrogen depth profile is desirable. In this study, the authors have improved electrical properties and interface properties by depth profile control of in situ nitrogen incorporation during plasma enhanced atomic layer deposition. The best electrical properties in terms of hysteresis, equivalent oxide thickness, and interface states were obtained when the nitrogen is incorporated in the middle of the thin film, which has not been achievable by other techniques.open111719sciescopu

HfO2 as gate dielectric on Si and Ge substrate

Hafnium oxide HfO2 has been considered as an alternative to silicon dioxide SiO2 in future nano-scale complementary metal-oxide-semiconductor (CMOS) devices since it provides the required capacitance at the reduced device size because of its high dielectric constant. HfO2 films are currently deposited by various techniques. Many of them require high temperature annealing that can impact device performance and reliability. In this research, electrical characteristics of capacitors with HfO2 as gate dielectric deposited by standard thermal evaporation and e-beam evaporation on Si and Ge substrates were investigated. The dielectric constant of HfO2 deposited by thermal evaporation on Si is in the range of 18-25. Al/HfO2/Si MOS capacitors annealed at 450°C show low hysteresis, leakage current density and bulk oxide charges. Interface state density and low temperature charge trapping behavior of these structures were also investigated. Degradation in surface carrier mobility has been reported in Si field-effect-transistors with HfO2 as gate dielectric. To explore the possibility of alleviating this problem we have used germanium (Ge) substrate as this semiconductor has higher carrier mobility than Si. Devices fabricated by depositing HfO2 directly on Ge by standard thermal evaporation were found to be too leaky and show significant hysteresis and large shift in flatband voltage. This deterioration in electrical performance is mainly due to the formation of unstable interfacial layer of GeO2 during the HfO2 deposition. To minimize this effect, Ge surface was treated with the beam of atomic nitrogen prior to the dielectric deposition. The effect of surface nitridation, on interface as well as on bulk oxide, trap energy levels were investigated using low temperature C-V measurements. They revealed additional defect levels in the nitrided devices indicating diffusion of nitrogen from interface into the bulk oxide. Impact of surface nitridation on the reliability of Ge/HfO2/Al MOS capacitors has been investigated by application of constant voltage stress at different voltage levels for various time periods. It was observed that deeper trap levels in nitrided devices, found from low frequency and low temperature measurements, trap the charge carrier immediately after stress but with time these carriers detrap and create more traps inside the bulk oxide resulting in further devices deterioration. It is inferred that though nitrogen is effective in reducing interfacial layer growth it incorporates more defects at interface as well as in bulk oxide. Therefore, it is important to look into alternative methods of surface passivation to limit the growth of GeO2 at the interface

Improved performance for OTFT with HfTiO2 as gate dielectric by N2O annealing

OTFTs with HfTiO 2 as gate dielectric have been successfully fabricated. The devices show small threshold voltage and subthreshold slope, and thus are suitable for low-voltage and low-power applications. This work also finds that OTFT with gate dielectric annealed in N 2O has larger dielectric constant, smaller threshold voltage, smaller subthreshold slope and larger on/off ratio than the N 2-annealed sample. This demonstrates that the N 2O annealing is an important surface treatment for preparing a high-quality insulator/organic interface. © 2007 IEEE.published_or_final_versio

Plasma Enhanced Chemical Vapor Deposition of Silicon Nitride and Oxynitride Films Using Disilane as Silicon Source.

Process characterization details along with the electrical properties of plasma enhanced chemical vapor deposited silicon nitride and oxynitride films are reported, for the first time, using disilane as the silicon source. Two regimes of deposition, namely excess-disilane regime and excess-ammonia regime, were observed for deposition of silicon nitride films using disilane, ammonia and helium. Films deposited under process conditions falling at the boundary of these two regimes had deposition rates that were mostly dependent on rf power and gas flow ratio resulting in highly repeatable film qualities. Silicon nitride films deposited on Si wafers at 250°C and post-metallization annealed in N2 ambient at 420°C exhibited fixed effective interface charge density of ∼3 x 1011 cm-2 and minimum interface state density of 2--3 x 1011cm -2 eV-1. The net bulk and interface charge density, charge trap density, interface trap density in the midbandgap region, and leakage current through the films were all lower for films that received a post-metallization anneal in both N2 and forming gas ambients compared to the values for films annealed in either N2 or forming gas ambients alone. All films exhibited higher instability due to hole trapping under negative gate bias stressing than due to electron trapping under positive gate bias stressing. Silicon oxynitride films were deposited by introducing N2O gas into the disilane/ammonia/helium gas system. Films deposited using higher N2O flow rates exhibited higher net effective fixed interface charge densities. The charge trapping in the films decreased with increasing N 2O flow rates employed in deposition except at the highest N2O flow rate investigated. In general, a turn-around behavior was observed in the trend for several electrical properties of the oxynitride films with increasing N2O flow rates. All the oxynitride films examined exhibited fewer occurrences of extrinsic breakdown compared to silicon nitride films, indicating reduction of pinhole density in the oxynitride films. Reviewing the overall properties of these films, it was deduced that the silicon oxynitride films deposited using NH3 to N2O flow rate of 20 in the present system would be the most practical choice for their use as gate dielectric films in thin film transistor applications