S. Shingubara

Self-organization of a porous alumina nanohole array using a sulfuric/oxalic acid mixture as electrolyte

The possibility of fabricating a highly regular nanohole array using different acid mixtures for the anodic oxidation of aluminum was investigated. The regularity of a nanohole array formed using a 1:1 sulfuric/oxalic acid mixture was quantified. Excellent regularity was obtained at around an anode voltage of 32 to 36 V. Cell pitch of the nanohole array at 36 V was 73 nm, which falls between those obtained using sulfuric acid (65 nm at 28 V) and oxalic acid (95 nm at 40 V). The present results strongly suggest that the pitch of the regular nanohole array can be varied by changing the ratio of the different acids.

Two-dimensional nanowire array formation on Si substrate using self-organized nanoholes of anodically oxidized aluminum

Abstract A highly ordered two-dimensional array of 48 nm Cu wires was successfully fabricated on Si substrate by the usage of anodic oxidation of aluminum (Al) for the first time. Anodic oxidation was carried out for Al sputtered film on Si substrate covered by a thin thermally oxidized SiO2 film, which was very effective to protect Si substrate from anodic oxidation. A highly ordered array of nanoholes was formed by the two steps Al anodic oxidation, and finally Cu was deposited by electroless plating in nanoholes which aspect ratio was 2.5. The present method suggests possibility of a large area two-dimensional array of quantum dots or wires on semiconductor substrate, which are considered to be a key technology for future ULSIs operated by single electron tunneling phenomena.

Electroless Plating of Copper on Metal-Nitride Diffusion Barriers Initiated by Displacement Plating

Copper is deposited on TaN and WN barrier layers by electroless plating without the need for activation preprocessing when substrates are (i) pretreated by wet chemical etching to remove surface oxides, and (ii) immersed in an electroless Cu plating solution containing glyoxylic acid as a reducing agent. Electrical potential measurements indicate that the redox potentials of TaN and WN in the plating solution are lower than that of copper, driving displacement plating of Cu in the initial stage of deposition. The adhesion between electroless-plated Cu and the TaN barrier layer after annealing is 0.11 kgf/cm as determined by a peeling test, which is sufficient for reliability during chemical mechanical polishing. A damascene Cu interconnect was successfully fabricated without delamination and exhibited an electrical resistivity of 2.2 μΩ cm after annealing for a 0.42 μm wide interconnect track. These results indicate that the proposed electroless process is suitable for the formation of a Cu seed layer prior to electrodeposition for the fabrication of ultralarge scale integrated interconnects.

Al dot hexagonal array formation using anodic oxidation and selective etching

Fabrication of nanoscale dot array are intensively required for realizing ultimately dense memory devices as well as quantum devices based on single-electron phenomena. However, there is an inherent problem for patterning time when pattern size shrinks below a few tens of nm, by lithographic methods based on beam technology. Patterning methods using self-organization phenomena provide alternative approach for realization of ordered array of nanostructure in relatively short time with a significant cost reduction. Al anodic oxidation has a high capability for realizing an extremely highly ordered array of nano-hole, so that there have been several attempts to realize nanowire arrays. The present study investigates formation of nano-dot array on semiconductor substrate using Al anodic oxidation.

Fabrication of nano holes array on Si substrate using anodically oxidized aluminum etching mask

The present study aims at the pattern transfer of nano hole array of alumina to Si semiconductor single crystalline substrates for wide applications to micro-electronics. The authors have succeeded in nano holes array fabrication on Si with diameter much smaller than that of the porous alumina nano holes etching mask. The etching process combined with sputtering and redeposition effect was very effective to reduce the transferred hole array from 60 to 13 nm. The present method is very promising for fabrication of room temperature operated quantum dot devices.

In Situ Observation of Thermal Stress in Nano-Size Thin Aluminum Films

In-situ observation of thermal stress in thin films deposited on a silicon substrate was made by synchrotron radiations. The specimens prepared in this experiment were nano-size thin aluminum films with SiO2 passivation. The thickness of the films was 10 nm, 20 nm and 50 nm. Residual stress in the as-deposited state was tensile. Compressive stress was developed in the heating cycle up to 300 oC and tensile stresses developed in the cooling cycle. The thermal stresses in the 50 nm film showed non-linear behavior in the first heating cycle from the room temperature to 300 oC. However, they linearly behaved in the first cooling cycle and the second thermal cycle. On the other hand, the thermal stresses in the 10 nm film behaved almost linearly without any hysteresis in the first and the second thermal cycles. The mechanism of thermal stress behavior of thin films is discussed.

Formation of Al Nanodot Array by the Combination of Nano-Indentation and Anodic Oxidation

The control of nanoholes formed by anodic oxidation of aluminum (Al) was investigated using AFM nano-indentation on Al film prior to the anodic oxidation. It is well known that ordered trigonal nanohole arrays are formed under certain voltage conditions of anodic oxidation of Al. We succeeded in forming both tetragonal and trigonal arrays of alumina nanoholes on a SiO 2 /Si- substrate by using nano-indentation on the surface of sputtered pure Al film. The ordered array of nanoholes was obtained at indentation intervals that were close to the nearest neighbor distance of nanoholes in the self-organization condition. Furthermore, we fabricated tetragonal and hexagonal Al nanodot arrays by the selective removal of porous alumina film.

Fabrication of ultra high density ferromagnetic column arrays by porous alumina template for magnetic recording media

In this paper, we succeeded in the fabrication of Co columns that had perpendicular anisotropy with density of 800 Gbit/inch/sup 2/. The proposed method for realizing the high-density magnetic recording media is suitable for obtaining perpendicular anisotropy, since the anisotropy can be controlled by changing the aspect ratio of the magnetic columns. For realizing ferromagnetic column array with higher recording density, filling of ferromagnetic materials in the porous alumina nanoholes formed at anodic voltages lower than 10 V is essential, and further study is in progress.

Formation of aluminum nano-dot array by the use of nano-indentation and anodic oxidation

Nanohole tetragonal and trigonal arrays as well as Al dot tetragonal and hexagonal arrays were successfully formed on Si substrates by the use of AFM nano-indentation and anodic oxidation. The ordered array of nanoholes could be obtained only at an indenting interval that depended on the anodic voltage. An Al dot hexagonal array with the nearest neighbor distance of 34 nm was formed. For further shrinkage of the Al dots, reduction of the indenting interval at an adequate anodic voltage would be necessary.

A large-scaled 2D array of alkanethiol-encapsulated gold particles fabricated using Langmuir-Blodgett technique

Assembly of metal nano-particles in ordered two-dimensional (2D) or three-dimensional (3D) arrays is believed capable of providing new materials not only for electronic engineering but also for basic studies, therefor has attracted a lot of research attention. In our previous work, an approach to fabrication of 2D array of alkanethiol-encapsulated gold particles was developed utilizing a self-organized process. However it is hard to fabricate a large-scaled perfect monolayer and well-controlled multilayer structures using this method. For this reason, in the present work, Langmuir-Blodgett (LB) technique was used to fabricate a large-scaled monolayer of nanoscaled gold particles. Comparing to other reports about LB films of gold particles, we got a much larger, higher-ordered 2D nanostructure.