Tomomi Goto

New Process for Si Nanopyramid Array (NPA) Fabrication by Ion-Beam Irradiation and Wet Etching.

It has been found that the rate of Si etching by hydrazine (N2H4H2O) is drastically retarded by ion-beam exposure. By utilizing this new phenomenon, a simple process of fabricating nanopyramid arrays (NPAs) on a Si surface is proposed. Two-dimensional arrays of dots and lines are written directly on a Si substrate with 60 keV Si, P and BF2 ion beams at doses of 1013–1015 cm-2. Subsequently, the Si substrate is dipped in hydrazine solution, where unexposed regions are selectively etched by hydrazine. Using this simple process, 130 nm convex NPAs with 200 nm pitch and 40 nm concave NPAs with 150 nm pitch can be fabricated easily. It is shown that the electrical property of the apex of the pyramid can be controlled by dopant ion irradiation. The cause of the retarded etch rate of ion-beam-exposed Si by hydrazine is comprehensively discussed.

Simple nanostructuring on silicon surface by means of focused beam patterning and wet etching

Abstract Two simple and easy processes have been demonstrated to fabricate two-dimensional (2-D) nanostructure array on Si surfaces by using only focused beam patterning and wet etching. First, we took advantage of the enhanced etch rate (ER) of electron-beam-exposed SiO2 in HF based solution. A 30-nm thick oxide layer was shot with 30-keV focused-electron beam with spot doses ranging from 20 to 140 pC/dot. After development of SiO2 layer in 1% HF solution, the Si substrate was etched by hydrazine (N2H4H2O) to form pyramidal etch-pits. By using this process, 50-nm concave nanopyramid array (NPA) with 100-nm period can be fabricated successfully. Second, we utilized the newly found retarded ER of ion-beam-exposed Si in hydrazine. 2-D arrays of dots were written directly on the Si substrate with 60-keV Si focused-ion beam (FIB) with a dose of 5×1014 ions/cm2. The Si substrate was then dipped in hydrazine solution, where the unexposed region was selectively etched by hydrazine. By using this process, 100-nm convex NPA with 200-nm period can be fabricated easily. The performance of the proposed processes is compared in terms of pattern size, throughput and process diversity.

Fabrication of adenosine triphosphate-molecule recognition chip by means of bioluminous enzyme luciferase

We have succeeded in detecting the adenosine triphosphate (ATP) concentration in a solution quantitatively using an ATP-molecule recognition chip. The ATP-molecule recognition chip is composed of a silicon photodiode on which bioluminous enzyme luciferase is immobilized. When the chip was immersed in an ATP-containing solution, the luciferase emitted light and the photoinduced current detected by the photodiode was in proportion to the ATP concentration. We found that the photoinduced current fits the Michaelis-Menten plot. These results indicate that the luciferase is successfully immobilized on the silicon chip without losing the bioluminous activity and that the proposed device enables us to detect the ATP concentration in a solution by measuring the photoinduced current.

Novel Process for High-Density Buried Nanopyramid Array Fabrication by Means of Dopant Ion Implantation and Wet Etching

A simple and high-throughput process to fabricate a high-density buried nanopyramid array (BNPA) on a Si surface has been developed by means of dopant ion implantation and wet etching. In this process, the combination of two interesting etching phenomena was utilized to form the BNPA. One is the enhanced etching of ion-exposed SiO2 in HF. The other is the newly found retarded etching of ion-exposed Si in hydrazine (N2H4). A p-type Si(100) substrate with 27-nm-thick SiO2 was exposed to 50-keV phosphorus ions with a dotted pattern. Then, the ion-exposed SiO2 was selectively etched away by dipping in HF. Finally, the BNPA was formed under the patterned SiO2 layer by dipping in hydrazine. By using this simple process, the BNPA with 250 nm pitch was successfully fabricated. The electrical property of the fabricated nanopyramid was also investigated using scanning Maxwell-stress microscopy (SMM).

High-Density Nanoetchpit-Array Fabrication on Si Surface Using Ultrathin SiO2 Mask

Nanoetchpit arrays (NEPAs) with a density of 1.56 T(1012)pit/in2 were artificially fabricated on Si surfaces. The key to the success of high-density-NEPA fabrication is through utilization of ultrathin SiO2 layer as an Si etching mask and N2H4 (hydrazine) solution as an Si etchant. The NEPAs were fabricated in only three steps: (1) focused electron-beam (EB) irradiation onto SiO2 mask, (2) SiO2 mask development using an HF-based solution, and (3) Si etching using hydrazine. The enhanced etching phenomenon of EB-exposed SiO2 in an HF-based solution was applied to pattern the SiO2 mask. Thin SiO2 layers with a thickness of 8 nm at the initial stage (4 nm after the development) were used as Si etching mask to suppress both spreading of the EB-exposed region by the forward scattering of the electrons and lateral extension of the SiO2 etching region during the development. Si substrates were etched through 4-nm-thick SiO2 mask by dipping in a hydrazine solution with an extremely high etching selectivity for Si/SiO2. By using this simple process, 8-nm-diameter NEPAs with a 20 nm pitch were successfully arranged on Si surfaces.

Simple fabrication of high density concave nanopyramid array (NPA)on Si surface

A simple process to fabricate two-dimensional (2-D) concave nanopyramid array (NPA) with nanometer period on Si surface has been developed by using electron beam (EB) irradiation and wet etching. The enhanced etch rate (ER) of EB-exposed SiO 2 in HF-based solution has been utilized. Mask oxide layers with the thicknesses of 11-30 nm were shot with 30-keV focused EB at spot doses ranging from 20 to 140 pC/dot. EB-exposed SiO 2 layers were selectively etched by dipping in 1% HF or buffered HF (BHF). The Si substrates were then dipped in anisotropic etchant hydrazine (N 2 H 4 .H 2 O) to form concave NPAs, where patterned SiO 2 layers were used as etch mask. By using this simple process, 50-nm period concave NPA with the size of 20 nm was fabricated successfully.