Tai D. Nguyen

Effects of dc bias on the kinetics and electrical properties of silicon dioxide grown in an electron cyclotron resonance plasma

Thin (3–300‐nm) oxides were grown on single‐crystal silicon substrates at temperatures from 523 to 673 K in a low‐pressure electron cyclotron resonance (ECR) oxygen plasma. Oxides were grown under floating, anodic or cathodic bias conditions, although only the oxides grown under floating or anodic bias conditions are acceptable for use as gate dielectrics in metal‐oxide‐semiconductor technology. Oxide thickness uniformity as measured by ellipsometry decreased with increasing oxidation time for all bias conditions. Oxidation kinetics under anodic conditions can be explained by negatively charged atomic oxygen, O−, transport limited growth. Constant current anodizations yielded three regions of growth: (1) a concentration gradient dominated regime for oxides thinner than 10 nm, (2) a field dominated regime with ohmic charged oxidant transport for oxide thickness in the range of 10 nm to approximately 100 nm, and (3) a space‐charge limited regime for films thicker than approximately 100 nm. The relationship ...

Lpcvd Polycrystalline Silicon Thin Films: The Evolution of Structure, Texture and Stress

An investigation of undoped LPCVD polycrystalline silicon films deposited at temperatures ranging from 605 to 700 C and silane pressures from 300 to 550 mTorr revealed large variations in stress with processing conditions and a correlation between stress and texture. TEM and HRTEM analysis show that morphology differences also exist. At lower temperatures (≈605 C) and higher pressures (≈400 mTorr), the films appear to deposit in an amorphous state and crystallize during the deposition to form microstructures characterized by equi-axed grains, tensile residual stress, and a texture with {110} and {11/} (/=2 or 3) components. Higher temperatures (between 620 and 650 C) produce films that nucleate at the Si02 interface, creating a {110} oriented columnar microstructure. At 700 C, the grains are still columnar, but the dominant texture is {100}. Films deposited at temperatures greater than 620 C exhibit compressive stress, and some contain regions of hexagonal silicon. This paper proposes possible causes of the varying stresses, textures, and microstructures in the films.

High resolution electron microscopy study of as-prepared and annealed tungsten-carbon multilayers

A series of sputtered tungsten-carbon multilayer structures with periods ranging from 2 to 12 nm in the as-prepared state and after annealing at 500/degree/C for 4 hours has been studied with high resolution transmission electron microscopy. The evolution with annealing of the microstructure of these multilayers depends on their period. As-prepared structures appear predominantly amorphous from TEM imaging and diffraction. Annealing results in crystallization of the W-rich layers into WC in the larger period samples, and less complete or no crystallization in the smaller period samples. X-ray scattering reveals that annealing expands the period in a systematic way. The layers remain remarkably well-defined after annealing under these conditions. 12 refs., 4 figs., 1 tab.

Microstructure and Stability Comparison of Nanometer Period W/C, Wc/C, and Ru/C Multilayer Structures

Multilayer structures of W/C, WC/C, and Ru/C, of various periods were prepared and studied by high-resolution transmission electron microscopy. Comparison of the phases in the layered structures is made for as-prepared and annealed samples. Both as-prepared and annealed WC/C multilayers are predominantly amorphous, while the phases in the W/C depend on the periods. The 2 nm period W/C multilayer remains amorphous after annealing, and the longer periods recrystallize to form W{sub 2}C. The layered microstructures of W/C and WC/C are stable on annealing at all periods, while the amorphous Ru-rich layers in the 2 nm period Ru/C multilayer agglomerate upon annealing to form elemental hexagonal Ru crystallites. Larger period Ru/C multilayers show stable layered structures, and indicate hexagonal Ru in the Ru-rich layers. X-ray measurements show that the multilayer periods expand on annealing for all metal-carbon multilayers studied. 15 refs., 5 figs., 1 tab.

Intrinsic Stress and Microstructural Evolution in Sputtered Nanometer Single and Multilayered Films

The relationship of intrinsic stress and microstructural evolution in nanometer thick Mo and Si films, and Mo/Si multilayers deposited by magnetron sputtering at low working pressure (2.5 mTorr) is studied. The stress depends strongly on the microstructure which evolves with the film thickness. Transition from tensile to compressive films is observed in the metal films, in which nucleation and columnar grain growth occur. Deposition of layered Mo films by time-delayed sequential sputtering of thin layers results in smaller grains that do not extend through the film thickness, and in more tensile stress state than thick films of trie same thickness. The Si films are highly compressive at all thicknesses studied. The multilayers in this study show compressive stresses, with higher compressive stress at longer periods, and decreasing stress at shorter periods. The interface stress in amorphous Mo/Si multilayers is determined to be 1.1 J/m 2 . Comparison with values in other systems is made.

Stress, Microstructure, and Thermal Behavior in Mo/Si X-Ray Multilayers

The relationship between intrinsic stress and microstructural evolution in nanometer Mo/Si multilayers deposited by magnetron sputtering at low working pressure (2.5 mTorr) is studied. The stress depends strongly on the microstructure which evolves with the multilayer period. In-situ thermal stress measurements show stress relaxation is observed in Mo/Si multilayers after annealing at 300°C in nitrogen ambient, due to microstructural changes in the multilayers. Average stress exhibits changes after annealing at 500°C which correspond to increased interdiffusion between the layer materials and crystallization at the interfaces.

Stability of Ruthenium-Silica Bilayer Structures

The microstructural evolution of ruthenium-silicon dioxide bilayer structures upon annealing is studied using transmission electron microscopy. SiO 2 /Ru/SiO 2 structures, with thicknesses of 2/1/2 nm, 4/2/4 nm, 8/4/8 nm, and 20/10/20 nm, are formed by magnetron sputtering and annealed at 300 or 600°C. As-deposited films have grain sizes on the order of the Ru film thickness. After annealing at 600°C, significant grain growth is observed for all thicknesses, such that the final grain sizes are approximately 3 to 20x greater than the original film thickness. The largest increase in the average Ru grain size is observed for the 2 nm thick ruthenium film possibly due to the coalescence of Ru grains. The coalescence of the Ru particles in the 1 and 2 nm thick films results in the formation of lamellar Ru grains, which disrupts the contiguity of the Ru film. In all other cases, the increase in grain size is attributed to normal grain growth, but the formation of anomalous spherical grains is also observed.