Atomic force microscopy (AFM) makes it possible to directly detect morphological changes on the surface of a zeolite that are due to dissolution when the crystal is immersed in either an alkaline (0.1 N NaOH) or acidic (0.2 N H2SO4) aqueous solution at room temperature. The AFM images revealed for the first time that for heulandite (a natural zeolite crystal) (i) NaOH attacked the uppermost layer of aluminosilicate of the (100) surface, leaving isolated or agglomerated islands, (ii) similarly, H2SO4 attacked the (010) surface, forming pits, and (iii) step retreat did not occur for either solution. This unique dissolution pattern, in which the aluminosilicate layers of heulandite dissolve from terraces layer-by-layer, results from the characteristic pore structure of heulandite. This microscopic-level analysis should prove vital in the further development of new zeolite structures, which are critical to the activity of this important class of materials.

No abstract

The influence of humidity on the dielectric constant and leakage current of self-assembled porous silica films which have two-dimensional hexagonal periodic porous structures was investigated quantitatively by proposing a new water adsorption model. The amount of H 2 O adsorption was calculated by the modified Rayleigh model, where H 2 O molecules are assumed to be adsorbed on the inner surface of cylindrical porous silica structures and form a dispersal concentric double-layer dielectric cylinder system. The amount of H 2 O calculated by the proposed model was consistent with the measured dielectric constant and thermogravimetry data. It suggests that inner-surface coverage of the cylindrical porous silica wall with a hydrophobic group is the most effective way to suppress water adsorption. Hexamethyldisilazane as a surface coverage molecule was introduced to the periodic cylindrical porous silica film and the leakage current was suppressed by a factor of 1/100 even below 0.5% relative humidity, resulting in the improvement of time-dependent dielectric breakdown lifetime by a factor of 30.Scaling of interconnects in ultralarge-scale integrated circuits ͑ULSI͒ has caused the increase of signal delay time due to the increase of interconnect resistance ͑R͒ and its parasitic capacitance ͑C͒, 1 while the transistor scaling is still effective to reduce the gate delay time. 2 For a 1-mm-long interconnect line fabricated on a Si chip, the RC delay time becomes a few hundred picoseconds, which is approximately 10 times larger than that of a metal oxide semiconductor field effect transistor ͑MOSFET͒. The RC delay time increases with decreasing the thickness and width of the metal interconnect as well as the spacing. In order to overcome this problem, copper and low-k interlayer dielectrics have been introduced. The interlayer dielectric films with the dielectric constants k ഛ 2.0 are required for future ULSI beyond 45 nm technology node. From the material point of view, various porous films have been developed to lower the dielectric constants. 3 However, the porous low-k films absorb moisture, resulting in the degradation of the film properties. To avoid this problem, a hexamethyldisilazane ͑HMDS͒ treatment has been commonly used to make the film hydrophobic.In this study, the influence of water adsorption on the dielectric constant and leakage current in the porous silica films 4 are investigated quantitatively, and the effect of HMDS treatment is discussed.Experimental p-Type Si substrates were cleaned in an RCA solution ͑NH 4 OH:H 2 O 2 :H 2 O = 36:720:1680͒ and dipped into a 0.5% HF solution. They were oxidized in O 2 ambient at 900°C to form 5 nm thick SiO 2 .A precursor solution for porous silica films was prepared by adding a surfactant, which was a PEO ͑polyethylene oxide͒-PPO ͑poly-propylene oxide͒-PEO triblock copolymer and an acidic silica sol derived from tetraethyl orthosilicate ͑TEOS͒ in ethanol diluted with water. The precursor solution was spin-coated on a Si substrate to form a homogeneous thin layer. Af...

No abstract

Plasma-induced damages of porous silica films during plasma processes were investigated by using a plasma beam irradiation apparatus. We used the porous silica films incorporated with methyl groups to achieve high hydrophobicity. The carbon (methyl group) reductions in the film as an index of the level of damages induced by Ar, He, O2, H2, and N2 plasma irradiations were examined by x-ray photoelectron spectroscopy and secondary ion mass spectroscopy. The damage due to Ar and He plasma bombardment increased with an increase in the ion dosage, although it was not strongly affected by the ion energy in the range higher than 130eV. Furthermore, it was found that the damage near the film surface was influenced more by metastable He atoms than by metastable Ar atoms. Both O ions and O atoms caused severe damage. N atoms did not affect the decrease of carbon content but reacted with carbon to form CN bonds. H atoms decreased carbon content slightly, but the amount of decrease was saturated by the further irradiation of H atoms.

No abstract

Organic nanolayers attract much attention for the isolation and adhesion promotion of the Cu line and insulator in Cu interconnection of microelectronic devices. This paper proposes a strategy for selective formation of adhesion nanolayer on the insulator surface with etching it on Cu surface by Cu-oxide-assisted pyrolysis. After deposition of a uniform polyelectrolyte layer on both SiO2 and Cu surfaces, heat treatment at 350 °C in ambient nitrogen was applied. Then, a larger thickness decrease was observed on the polyelectrolyte layer on Cu when compared to that on SiO2. According to the TDS and XPS analysis, the polyelectrolyte layer was relatively stable on SiO2 up to the intrinsic decomposition temperature of the material, but on the Cu surface it decomposed to volatile small molecules at a lower temperature due to Cu2O-assisted oxidization. This substrate dependent selective pyrolysis was examined for 100 nm width Cu lines and SiO2 spaces, and then a patterned polyelectrolyte layer on the SiO2 surface was obtained with a single nanometer scale edge resolution.

No abstract