Hafnium oxide (HfO 2 ) is one of the most promising high-k materials to replace SiO 2 as a gate dielectric. Here we report material and electrical characterization of atomic layer deposition ͑ALD͒ hafnium oxide and the correlations between the results. The HfO 2 films were deposited at 200, 300, or 370°C and annealed in a nitrogen ambient at 550, 800, and 900°C. Results indicate that deposition temperature controls both the material and the electrical properties. Materials and electrical properties of films deposited at 200°C are most affected by annealing conditions compared to films deposited at higher temperatures. These films are amorphous as deposited and become polycrystalline after 800°C anneals. Voids are observed after a 900°C anneal for the 200°C deposited films. The 200°C deposited films have charge trapping and high leakage current following anneals at 900°C. The 300°C deposited films have lower chlorine content and remain void-free following high-temperature anneals. These films show a thickness-dependent crystal structure. Annealing the films reduces leakage current by four orders of magnitude. Finally, films deposited at 370°C have the highest density, contain the least amount of impurities, and contain more of the monoclinic phase of HfO 2 than those deposited at 300 and 200°C. The best electrical performance was obtained for films deposited at 370°C.
Thin films of AlxGa1−xN (0.05 ≤ x ≤ 0.96) having smooth surfaces were deposited directly on both vicinal and on-axis 6H-SiC(0001) substrates. Cross-sectional TEM of Al0.13Ga0.87N revealed stacking faults near the SiC/Nitride alloy interface and numerous threading dislocations. EDX, AES and RBS were used to determine the compositions, which were paired with their respective CL near band-edge emission energies. A negative bowing parameter was determined. The CL emission energies were similar to the bandgap energies obtained by SE. FE-AES of the initial growth of Al0.2Ga0.8N revealed an aluminum rich layer near the interface. N-type (silicon) doping was achieved for AlxGa1−xN for 0.12 ≤ x ≤ 0.42. Al0.2Ga0.8N/GaN superlattices were fabricated with coherent interfaces. Additionally, HEMT structures using an AlN/GaN/AlN buffer structure were fabricated.
HfO 2 films deposited via tetrakis diethylamido hafnium ͑TDEAH͒ precursor using MOCVD ͑metal organic chemical vapor deposition͒ are presented. TDEAH is a promising precursor candidate for the deposition of high permittivity gate dielectrics. We report the impact of process and annealing conditions on the physical and electrical properties of the film. Deposition and annealing temperatures influence the microstructure, density, and impurity levels of TDEAH HfO 2 films. Spectroscopic ellipsometry shows that film microstructure manifests itself in the optical properties of the film, particularly in the presence of a band edge related feature at 5.8 eV. An impurity analysis using Auger electron spectroscopy, secondary ion mass spectroscopy, and Raman spectroscopy, indicates that carbon impurities from the precursor exist as clusters within the HfO 2 dielectric. The impact of deposition temperature and annealing temperature on the capacitance vs. voltage and current density vs. voltage characteristics of platinum gated capacitors is studied. Correlation of physical film properties with the capacitance and leakage behavior of the TDEAH HfO 2 films indicates that impurities, in the form of carbon clusters, and low HfO 2 film density are detrimental to the electrical performance of the gate dielectric.As the smallest feature size on a microprocessor approaches 50 nm, the primary dielectric layer in the field effect transistor, referred to as the gate dielectric or gate oxide, will thin to below 15 Å. Around this thickness, electrical leakage current through the dielectric becomes excessive and is expected to cause problems due to either high power dissipation or circuit reliability. 1 One solution to this problem is to replace SiO 2 dielectrics with higher permittivity dielectrics. A higher permittivity dielectric can be thicker and still achieve the same capacitance as a thinner SiO 2 dielectric. The starting point for identifying possible replacements for SiO 2 dielectrics is to evaluate their thermal stability in direct contact with silicon. Reactions between the high permittivity dielectric and the silicon substrate or electrode are undesirable. Extensive thermodynamic calculations have been performed by Hubbard and Schlom, 2 identifying numerous binary and ternary oxides that are candidate materials. Some of the binary oxides that are leading contenders for replacing SiO 2 include: ZrO 2 , HfO 2 , Y 2 O 3 , and Al 2 O 3 . In addition, there are numerous ternary ͑or mixed͒ oxides that have also been predicted, or experimentally determined, to be stable in contact with silicon.In general, the class IIIB and IVB oxides tend to be the most thermodynamically stable oxides for potential use in integrated circuit manufacturing. Doping the IIIB and IVB oxides with Al 2 O 3 or SiO 2 increases the crystallization temperature. Such amorphous dielectrics are desirable because grain boundaries enhance diffusion of dopants from the electrode to the substrate and possibly contribute to electrical leakage. On the other hand, doping...
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