Fabrication of silicon molds with multi-level, non-planar, micro- and nano-scale features

Abstract

A method for single-step fabrication of arbitrary, complex, three-dimensional (3D) silicon structures from the nano- to millimeter-scale at multiple levels on non-planar, curved, or domed surfaces is reported. The fabrication is based on focused or masked ion beam irradiation of p-type silicon followed by electrochemical anodization. The process allows fabrication of a wide range of surface features at multiple heights and with arbitrary orientations by varying the irradiated feature width, ion type, energy fluence, and subsequent anodization conditions. The technology has achieved depth resolution of 10 nm as step heights and is capable of creating lateral features down to 7 nm at high aspect ratios of up to 40, with surface roughness down to 1 nm scaled up to full wafer areas. The single-step ability has seamlessly interfaced a network of complex, integrated micro- to nano-structures in 3D orientations with no alignment required. The final template has been converted to a master copy for nano-imprinting lithography of 3D fluidic structures and optical components.

Unconventional micro-/nanofabrication technologies for hybrid-scale lab-on-a-chip

“…However, fabrication of the nanoscale convex parts of a hybrid-scale mold is limited because the processes are complex, expensive, and time-consuming (e.g., direct writing methods). 40,49 To overcome these weaknesses, various alternative methods have been developed for nanoscale convex mold fabrication, such as ion beam irradiation on silicon followed by electrochemical anodization, 50 a gold sidewall transfer process with subsequent silicon etching, 46,47 duplication of a polymer mold or use of a replica from a silicon master mold, 42,51 and the nanoimprint method itself. 45 The pre-patterned nanoscale mold is integrated with the corresponding microscale parts by precise alignment, which produces a hybrid-scale mold.…”

Sidewall patterning—a new wafer-scale method for accurate patterning of vertical silicon structures

“…The ultimate technologies for obtaining similar control over all three dimensions of structures probably come from the field of 3D printing/writing, in which material is deposited or modified only at the exact position where it is desired. Some of these techniques reach the micrometer or even nanometer scale [1][2][3][4][5][6][7], especially two-photon polymerization laser writing. Many complex structures can be realized with this technique, as long as every voxel is attached to another voxel or the substrate.…”

Nanoscale lithography of LaAlO3/SrTiO3wires using silicon stencil masks

“…Proton and helium ion energies of greater than 20 keV are above the Bragg peak of nuclear energy loss [35,36], so their maximum rate of defect generation lies beneath the surface, close to their end-of-range depth, where the defect density is typically 10 to 20 times greater than it is close to the surface. These depleted regions remain as crystalline regions [37][38][39][40][41][42][43][44][45][46] and do not undergo porous silicon formation during subsequent electrochemical anodization. This process has been developed for a variety of applications in 3D silicon machining, silicon photonics, microelectromechanical systems, and photonic lattices, as reviewed in [42].…”