Fabrication of complex curved three-dimensional silicon microstructures using ion irradiation

Abstract

We have developed a process to fabricate arbitrary-shaped, three-dimensional microstructures in 0.4 cm p-type silicon using focused high-energy proton beam irradiation, followed by electrochemical anodization. This has enabled us to produce free-standing complex microstructures such as arrays or long wires, grids, wheels, vertically stacked wires and wires which can be controllably bent upward and downward in the vertical plane. The two most important factors which determine the wire cross-section dimensions and depth are the irradiation ion fluence and energy. We can controllably vary the width of wires from 1 to 5 μm by varying the fluence of 1 MeV protons and the depth of wires from 2 to 15 μm by varying the proton energy. By using a combination of multiple energy proton irradiation over a range of 200-1000 keV, and gray-scale masks, different ion penetration depths and multilevel free-standing three-dimensional silicon structures can be obtained in a single etch step.

Fabrication of 3D photonic components on bulk crystalline silicon

“…There is no detectable light transmitted through the waveguides in this row, partly because their size is small, less than one tenth of the size of the other two layer waveguides, the surface roughness is high (~10 nm) and ion induced defects present from the irradiation process act as scattering centers. We have previously studied the effect of high temperature oxidation on reducing propagation losses in 2D waveguides fabricated using this process [12], following the work described in [14,15]. After oxidation at around 1000°C for three hours we find that the surface roughness may be significantly reduced to around 1 nm.…”

“…Thus, by varying the ion energy and using low fluences within an irradiated volume, it is possible to directly fabricate 3D microstructures on silicon comprising unetched end-of-range regions. See [15,16] for an account of our work in 3D microfabrication using direct writing with a focused proton beam. However, this direct writing approach is not appropriate for upscaling to large volume production of 3D photonic components, so we have developed a facility [17] in which a high beam current of about 1 μA is used to uniformly irradiate large sample areas.…”

Fabrication of porous silicon based tunable distributed Bragg reflectors by anodic etching of irradiated silicon

“…The resistivity change induced by gamma irradiation is more prominent as compared to that induced by single energy ion irradiation of equivalent fluence. These changes can reduce the flow rate of electric holes through the irradiated regions during anodic etching [21][22][23][24]. Hence, it results in the change in structural and optical properties of the pSi layers.…”

Enhanced electrochemical etching of ion irradiated silicon by localized amorphization

“…For high ion energies of hundreds of keV, well-above the Bragg peak, the maximum defect density is a few micrometers beneath the wafer surface, above this lies a zone where the defect density is fairly uniform. Exclusion of hole current flow from the end-of-range peak of high defect density was demonstrated 11 and the resultant buried silicon wires used to fabricate a variety of 3D micro-and nano-scale structures with applications in a variety of fields [12][13][14][15] . However, for low ion energies, such as 30 keV helium, experimental results do not agree with simulations; instead a dip is observed at the center of high fluence irradiated lines.…”