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.