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

Abstract

O. (2015). Sacrificial structures for deep reactive ion etching of high-aspect ratio kinoform silicon x-ray lenses. Journal of Vacuum Science and Technology. Part B. Microelectronics and Nanometer Structures, 33(6), [062001]. DOI: 10.1116/1.4931622 Sacrificial structures for deep reactive ion etching of high-aspect ratio kinoform silicon x-ray lenses This article describes the realization of complex high-aspect ratio silicon structures with feature dimensions from 100 lm to 100 nm by deep reactive ion etching using the Bosch process. As the exact shape of the sidewall profiles can be crucial for the proper functioning of a device, the authors investigated how sacrificial structures in the form of guarding walls and pillars may be utilized to facilitate accurate control of the etch profile. Unlike other sacrificial structuring approaches, no silicon-on-insulator substrates or multiple lithography steps are required. In addition, the safe removal of the sacrificial structures was accomplished by thermal oxidation and subsequent selective wet etching. The effects of the dimensions and relative placement of sacrificial walls and pillars on the etching result were determined through systematic experiments. The authors applied this process for exact sidewall control in the manufacture of x-ray lenses that are very sensitive to sidewall shape nonuniformities. Compound kinoform lenses for focusing hard x-rays with structure heights of 200 lm were manufactured, and the lenses were tested in terms of their focusing ability and refracting qualities using synchrotron radiation at a photon energy of 17 keV. A 180 lm long line focus with a waist of 430 nm at a focal length of 215 mm was obtained.

Injection molded polymeric hard X-ray lenses

“…This variation must be reduced in the future, since it is significantly larger than the depth of focus (~1 mm [7]). A more accurate control of the sidewall profile can readily be achieved by means of a more extensive optimization of the etching process of the silicon master [23]. Although, in terms of economy, this will consume additional resources, it will be insignificant, not least because we expect that more than 1000 polymeric parts may be obtained from a single master [27].…”

“…DRIE was a critical process step in ensuring the near-90° sidewalls required to guarantee both lens uniformity and the successful release of the polymeric part from the mold. To this end, we utilized sacrificial structures, which facilitated accurate profile control [23]. Optical profilometry confirmed that the etched sidewalls were slightly positively tapered by 0.5°, which favored a successful release of the injection molded polymeric part.…”

Bulk Micromachining of Si by Annealing-Driven Magnetically Guided Metal-Assisted Chemical Etching

“…Si microstructures, such as pillar and hole arrays, can be prepared by photolithographically patterning photoresists (PRs) on surfaces and deep reactive-ion etching (DRIE). In particular, the Bosch process has been used to produce deep trenches during DRIE. , However, the DRIE process is expensive and passivation layers, such as C 4 H 8 , need to be coated along the side walls of the patterns to protect Si against lateral etching, which is undesirable for industrial applications. An alternative method of micromachining Si involves wet etching using an etchant such as TMAH (tetramethylammonium hydroxide) or a mixture solution of potassium hydroxide (KOH) and isopropyl alcohol (IPA), which enable the micromachining of bulk Si; however, etching directionality is highly restricted by the orientation of the Si crystal. , …”

Deep reactive ion etching of ‘grass-free’ widely-spaced periodic 2D arrays, using sacrificial structures

“…Anisotropic etching of silicon using deep reactive ion etching (DRIE) is among the key technologies for fabrication of microstructures for a wide range of applications [1,2,3]. DRIE processes are often based on the cyclic Bosch process [4].…”