Cryogenic Etching of High Aspect Ratio 400-nm Pitch Silicon Gratings

Abstract

The cryogenic process and Bosch process are two widely used processes for reactive ion etching of high aspect ratio silicon structures. This paper focuses on the cryogenic deep etching of 400 nm pitch silicon gratings with various etching mask materials including polymer, Cr, SiO2 and Cr-on-polymer. The undercut is found to be the key factor limiting the achievable aspect ratio for the direct hard masks of Cr and SiO2, while the etch selectivity responds to the limitation of the polymer mask. The Cr-on-polymer mask provides the same high selectivity as Cr and reduces the excessive undercut introduced by direct hard masks. By optimizing the etching parameters, we etched a 400 nm pitch grating to ≈ 10.6 μm depth, corresponding to an aspect ratio of ≈ 53.

Analysis of optical emission spectroscopy data during silicon etching in SF6/O2/Ar plasma

“…Recently, many studies have performed plasma diagnostics using in situ sensors [20][21][22]. Although various approaches with cryogenic temperatures and sidewall passivation have been utilized [23,24], achieving anisotropic HAR etching is still a major challenge. In order to overcome this hurdle, research has been conducted with various approaches until recently.…”

Analysis of a silicon comb structure using an inverse Talbot–Lau neutron grating interferometer

“…The details of silicon comb structures of periods, heights, and duty cycles are provided in the nominal section of Table 3 . All silicon comb structures were fabricated using cryogenic and Bosch processes 27 , 28 and had a fabricated area of 20 mm × 20 mm on a 102 mm diameter silicon wafer. For a silicon density of 2.32 g/cm 3 , the difference between the neutron scattering length densities of silicon and air at a neutron wavelength of 4.4 Å is = 206.5 μm −2 .…”

Nanomechanical Traceable Metrology of Vertically Aligned Silicon and Germanium Nanowires by Nanoindentation

“…At a temperature of −85 °C, an etching depth of around 2.4 μm was attained, while utilization of lower temperatures (i.e., −105 °C and −120 °C) caused not only crystal-plane-dependent etching, but also a reduction of the etch rate (Figure 2d-f). One can control the etch depth by controlling the chamber pressure, since at higher chamber pressure the kinetic energy of the ion flux is reduced [9]. As a result, a gradual reduction of etch rate (i.e., 188 nm/min, 132 nm/min, and 68 nm/min) was apparent at increasing chamber pressure (i.e., 0.1, 1.0, and 2.0 Pa) (Figure 2g-i).…”