Improvement of high aspect ratio Si etching by optimized oxygen plasma irradiation inserted DRIE

Abstract

This paper describes an advanced Si-deep etching process achieving a high aspect ratio with excellent verticality by the improvement of the O 2 plasma source condition in the oxygen plasma irradiation inserted deep reactive ion etching (OP-DRIE) process that we have developed. The conventional DRIE process which we call the Bosch process has a trade-off relation between the high aspect ratio and verticality in the trench profile. Our developed process technique, repeating the conventional DRIE and the O 2 plasma irradiation process alternately, can achieve the vertical trench profile with a higher aspect ratio than that of the conventional DRIE process. In order to maximize an advantage of the developed process, a thickness of the SiO 2 layer formed by irradiation of O 2 plasma should be large enough as a protection layer. However, because of insufficient SiO 2 thickness formed by O 2 plasma, the aspect ratio has been limited in previous work. Furthermore, mask material (SiO 2 ) erosion which is another limitation factor of the aspect ratio is increased by the insertion of O 2 plasma irradiation. In this paper, we have investigated optimum O 2 plasma source conditions that allow an increase in SiO 2 thickness with a high oxidation rate, and at the same time, with less mask erosion on the top of the wafer. We have clarified the effects of frequency and pulsed/CW modes of the plasma source on the effectiveness in SiO 2 formation. From the obtained oxygen plasma source condition, we achieved the etched Si trench having an aspect ratio of over 70 with excellent verticality (uniform trench width).

Sacrificial structures for deep reactive ion etching of high-aspect ratio kinoform silicon x-ray lenses

“…Although not pursued in the current study, profile control with further precision may be possible by fine tuning the etch parameters and consulting the relevant literature. [54][55][56][57][58][59] Figures 4(a) and 4(b) show etched large square fields (p ¼ 5 lm, s ¼ 7 lm) before and after removal of the sacrificial structures, respectively. The sacrificial structures partially collapsed during the wafer cleaning and SiO 2 etching after DRIE, but were completely removed from the wafer surface and structures.…”

Plasma chemical etching of high-aspect-ratio silicon micro- and nanostructures

“…Strictly vertical trenches with AR > 73 could be obtained, when their sidewalls were passivated by oxidation in an oxygen-containing plasma [21]. It should be noted that even though the high-and ultrahigh-aspect-ratio silicon etching was performed in a Bosch process, the etching rate was fairly low (less than 2 µm/min) in view of aperture limitations.…”

“…Therewith, the etching rate can reach 50 µm/min. The third group includes the etching processes forming structures with an ultrahigh aspect ratio (АR > 25) [20,21]. The development of technologies on the basis of these processes is restrained by the fact that a different DOI: 10.1134/S10703632150540424 negative effects distorting the profile of the resulting structures are still to be overcome [22,23].…”

Micro‐/Nanopillars for Micro‐ and Nanotechnologies Using Inductively Coupled Plasmas

“…Micro‐ and nanotechnologies are widely used in industry and applied science and often exploit silicon as a substrate material. Dry etching is one of the preferred pattern transfer methods because it allows wide parameter tunability, allowing the optimization of the etched profile and thus yielding high aspect ratio structures and straight sidewalls . On the contrary, the profile is usually not tunable for wet etching, providing curved profiles and modest aspect ratios.…”

“…Dry etching is one of the preferred pattern transfer methods because it allows wide parameter tunability, allowing the optimization of the etched profile and thus yielding high aspect ratio structures and straight sidewalls. [1][2][3][4][5][6] On the contrary, the profile is usually not tunable for wet etching, providing curved profiles and modest aspect ratios. Due to its reliability and versatility, the inductively coupled plasma (ICP) reactor is widely used nowadays for mass production and low-cost anisotropic silicon etching.…”