Ga⁺beam lithography for nanoscale silicon reactive ion etching

Abstract

By using a dry etch chemistry which relies on the highly preferential etching of silicon, over that of gallium (Ga), we show resist-free fabrication of precision, high aspect ratio nanostructures and microstructures in silicon using a focused ion beam (FIB) and an inductively coupled plasma reactive ion etcher (ICP-RIE). Silicon etch masks are patterned via Ga(+) ion implantation in a FIB and then anisotropically etched in an ICP-RIE using fluorinated etch chemistries. We determine the critical areal density of the implanted Ga layer in silicon required to achieve a desired etch depth for both a Pseudo Bosch (SF(6)/C(4)F(8)) and cryogenic fluorine (SF(6)/O(2)) silicon etching. High fidelity nanoscale structures down to 30 nm and high aspect ratio structures of 17:1 are demonstrated. Since etch masks may be patterned on uneven surfaces, we utilize this lithography to create multilayer structures in silicon. The linear selectivity versus implanted Ga density enables grayscale lithography. Limits on the ultimate resolution and selectivity of Ga lithography are also discussed.

Maxwell Fisheye Lens as a Waveguide Crossing for Integrated Photonics

“…The precision of the final device is dependent on milling parameters, such as beam current, overlapping, pixel spacing, ion energy, exposure area, and dwell time 34 The diameters of these circular artifacts vary depending on the resulting gradient resolution 41,42 . By decreasing the beam size and current, the resolution increases.…”

Focused Ion Beam Lithography

“…Starting from an ion dose of 2· 10^15 cm¯² (Chekurov et al, 2009), a change in the reactive ion etcher (RIE) etch speed of Si inside doped areas is noticed for fluorine-based plasmas. Only recently it was discovered that by modulating the ion dose, the time the highly doped layer is able to withstand the etching can also be modulated (Henry et al, 2010). The dependence of the etch depth from the applied Ga dose may be employed as an effective way for 3D patterning.…”

Structural inhomogeneity in silicon-on-insulator probed with coherent X-ray diffraction

“…SOI based MOSFETs are considered to be one of the best alternatives to conventional bulk-silicon MOSFET technology, however, fabrication of SOI wafers is significantly more technologically challenging as the dimensions of the devices shrink dramatically. State-of-Art lithography-based fabrication techniques [1] are starting to be employed to overcome the possibility of strain arising from SOI fabrication [2].…”