Al(2)O(3) atomic layer deposition (ALD) growth with Al(CH(3))(3) (trimethylaluminum (TMA)) and H(2)O as the reactants was examined at the relatively low temperature of 125 degrees C using quartz crystal microbalance (QCM) measurements. The total Al(2)O(3) ALD mass gain per cycle (MGPC) and MGPCs during the individual TMA and H(2)O reactions were measured versus TMA and H(2)O exposures. The Al(2)O(3) MGPC increased with increasing H(2)O and TMA exposures at fixed TMA and H(2)O exposures, respectively. However, the TMA and H(2)O reactions were not completely self-limiting. The slower surface reaction kinetics at lower temperature may require very long exposures for the reactions to reach completion. The Al(2)O(3) MGPCs increased quickly versus H(2)O exposure and slowly reached limiting values that were only weakly dependent on the TMA doses. Small TMA exposures were also sufficient for the Al(2)O(3) MGPCs to reach different limiting values for different H(2)O doses. The TMA MGPCs increased for higher TMA exposures at all H(2)O exposures. In contrast, the H(2)O MGPCs decreased for higher TMA exposures at all H(2)O exposures. This decrease may occur from more dehydroxylation at larger hydroxyl coverages after the H(2)O exposures. The hydroxyl coverage after the H(2)O exposure was dependent only on the H(2)O exposure. The Al(2)O(3) MGPC was also linearly dependent on the hydroxyl coverage after the H(2)O dose. Both the observed hydroxyl coverage versus H(2)O exposure and the Al(2)O(3) ALD growth versus H(2)O and TMA exposures were fit using modified Langmuir adsorption isotherm expressions where the pressures are replaced with exposures. These results should be useful for understanding low-temperature Al(2)O(3) ALD, which is important for coating organic, polymeric, and biological substrates.
Microfabricated test patterns are used to measure the orientation-dependent rates of KOH/silicon etching of 180 surfaces in the Si [110] zone. The concentration and temperature dependence of the reaction is quantified, and a pronounced kinetic isotope effect is observed for all orientations. Although the kinetics of the KOH etching of silicon are complicated, the magnitude of the kinetic isotope effect, the morphology of the macrosteps on vicinal Si(111) surfaces, the pronounced hydrophobicity and H-termination of the etched surfaces are all consistent with a chemical mechanism that is rate-limited by cleavage of a Si-H bond by OH -. There is no evidence of a gross change in chemical mechanism with surface orientation. Silicon surfaces in the [110] zone can be divided into four regions of similar reactivity: vicinal Si(100), vicinal Si(110), and two types of vicinal Si(111) surfaces. Within each region, all surfaces display remarkably similar chemical kinetics. These regions are separated by morphological transitions of unknown origin. The orientations of the morphological transitions are temperature dependent, which implies that they are not associated with surface structural transitions, such as reconstructions. The etch rate of vicinal Si(111) surfaces is well fit by a simple step flow model; however, etching-induced step bunching is also observed. The observed kinetics are inconsistent with existing theoretical models of step bunching. Low miscut vicinal Si(110) surfaces have very isotropic etch rates, which are attributed to etching induced faceting. The macroscopic etch rate displays markedly non-Arrhenius behavior (the etch anisotropy actually increases with temperature!), and the concentration dependence cannot be fit by a simple empirical rate law. These phenomena are attributed to the multisite nature of the etching reaction.
W ∕ Al 2 O 3 multilayers were fabricated using W and Al2O3 atomic layer deposition (ALD) to produce x-ray mirrors. The x-ray reflectivity from an optimized W∕Al2O3 multilayer was 96.5%±0.5% for the first-order Bragg peak at λ=1.54Å. The ultrahigh x-ray reflectivity is attributed to the precise bilayer thicknesses and ultrasmooth interfaces obtained from ALD film growth. The self-limiting ALD surface chemistry prevents randomness during film growth and produces conformal deposition with correlated roughness that enhances the x-ray reflectivity.
Today, the smallest feature on the best microprocessor in commercial production is 150 nm. In contrast, the distance between binding sites on a human antibody is 10 nm-our smallest devices are 15 times larger than Nature's! Although impressive strides are being made in the microelectronics industry, nanofabrication at the 10 nm length scale
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