S. Y. Son

Low temperature nitrogen incorporation method for enhanced electrical properties in hafnia based gate dielectrics

A low temperature method (∼400°C) for nitrogen incorporation in hafnia based dielectrics has been developed for future gate dielectric applications. Hf metal films were deposited on Si substrates in ammonia ambient and were subsequently oxidized under ultraviolet illumination. Using this method, an interfacial layer comprising Hf–Si–O–N bonding was formed at the hafnia-Si interface, which led to a substantial enhancement in the overall dielectric properties of the film. An equivalent oxide thickness of 11.5A and leakage current densities lower than 10−4A∕cm2 at a gate bias of −1V were achieved by this approach.

Strain induced changes in gate leakage current and dielectric constant of nitrided Hf-silicate metal oxide semiconductor capacitors

Uniaxial-mechanical-stress altered gate leakage current and dielectric constant of silicon metal-oxide-semiconductor (MOS) devices with nitrided Hf-silicate (HfSiON) dielectric are measured as a function of uniaxial stress applied using four-point wafer bending along the [110] direction. The gate leakage current and dielectric constant are found to increase by ∼2% per 100MPa of tensile and compressive stresses. A decrease in hole trap activation energy in hafnium oxide-based dielectric is used to explain the mechanical stress altered gate leakage. It is proposed that the HfSiON dielectric constant increase results from band gap narrowing caused by strain induced N p band splitting.

Fabrication of compositional graded Si1−xGex layers by using thermal oxidation

Compositional graded and highly relaxed Si1−xGex layers have been fabricated by using thermal oxidation at high temperature. It was found that the behavior of Ge atoms during thermal oxidation was significantly dependent of the oxidation temperature. The Ge accumulation below the oxide occurred at 800 and 900 °C due to a large difference of the heat formation of GeO2 and SiO2. However, Si1−xGex layers oxidized in 1000 °C did not show any Ge accumulation because Ge diffusion efficiently occurred. The compositional graded Si1−xGex layers fabricated by thermal oxidation can be used as virtual substrates for the strained-Si and relaxed-SiGe applications.

An Evaluation of Ti-Based Metal Gate Electrodes on Hf-Silicate Dielectrics for Dual-Metal-Gate Applications

An evaluation of Ti-based gate metals (Ti, TiN, and TiB 2 ) on Hf-silicate gate dielectric prepared by atomic layer deposition has been reported. The effective metal work functions, calculated by taking an interface layer and interface charge into consideration, were 4.27, 4.56, and 5.08 eV for Ti, TiN, and TiB 2 , respectively. Regardless of gate electrodes, the conduction mechanism of the samples was fitted with the Poole-Frenkel model, which is related to oxygen vacancies in the film. A Ti gate electrode was found to be more favorable for n-channel metal oxide semiconductor (MOS) devices, and TiB 2 gate electrode can be used for p-channel MOS devices with Hf-silicate dielectrics.

An evaluation of thermal stability of TiB2 metal gate on Hf silicate for p-channel metal oxide semiconductor application

An evaluation of TiB2 gate metal on Hf-silicate dielectric prepared by atomic layer deposition method has been reported. The extracted effective metal work function for TiB2 gate was about 5.08eV. The work function showed almost identical values and the sharp interface between metal and dielectric was confirmed after postdeposition annealing at 1000°C. The work function lowering (4.91eV) at 1100°C was caused by metal-dielectric intermixing and oxygen vacancy formation. TiB2 gate electrode was found to be suitable for use in p-channel metal oxide semiconductor device.

Microlens Array Fabrication by Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) was used to shape hexagonally arranged 20 μm diam cone-shaped structures, prepared by wet etching of Coming 2496 glass, into microlenses. Edge rounding, which occurs during CMP due to a higher removal rate at the edges, was utilized for shaping of the microlenses. Microlenses with an H/D ratio of ∼ 1/10 and radius of curvature of 27.5 μm were obtained. CMP variables that affect the contact pressure and material removal rate are downpressure, linear velocity, slurry, and properties of the pad. These variables being external to substrate provide great flexibility and, hence, suitability of the process for a wide range of materials.

Study of interface degradation of Hf-silicate gate dielectrics during thermal nitridation process

An evaluation of the effect of nitridation temperature on interface layer (IL) quality of Hf-silicate gate dielectric prepared by the atomic layer deposition method has been reported. An increase in IL density and IL roughness was observed by x-ray reflectivity as the nitridation temperature was increased. X-ray photoelectron spectroscopy showed preferential interface reaction at the dielectric-Si interface at higher temperatures. The progressive increase in IL roughness finally led to degradation of the breakdown voltage, a shift in flat band voltage (∼0.54V), and deterioration of electron channel mobility by ∼20% in samples nitrided at 850°C.

High efficiency nitrogen incorporation technique using ultraviolet assisted low temperature process for hafnia gate dielectric

An evaluation of a low temperature process (∼350°C) for nitrogen incorporation in hafnia gate dielectric has been reported. This method is based on postdeposition nitridation under ultraviolet light illuminated NH3 ambience. X-ray photoelectron spectroscopy confirmed the amount of nitrogen incorporated by this process was comparable to that of high temperature (∼650°C) thermal nitridation (∼7%). Uniformity of nitrogen distribution in the film was analyzed by secondary ion mass spectroscopy. A capacitance density of ∼3.96μF∕cm2 with 9.4A equivalent oxide thickness and 10A thick interface layer were obtained by ultraviolet assisted nitridation process.