The mechanism of selective corrugation removal by KOH anisotropic wet etching

Abstract

The mechanism of selective corrugation removal by anisotropic wet etching-which reduces a periodic corrugation, called 'scalloping', formed on the sidewalls of microstructures by the Bosch process in deep reactive-ion etching (D-RIE)-was investigated. In particular, the corrugation-removal mechanism was analyzed by using the etching rate distribution pattern, and two equations for predicting the corrugation-removal time by the etching were derived. A Si{1 0 0} wafer was first etched by D-RIE at a depth of 29.4 μm (60 cycles) to form the corrugation on the sidewall surface. The height and pitch of the corrugation were 196 and 494 nm, respectively. Selective removal of the corrugation by using 50% KOH (40 • C) was experimentally tried. The corrugation formed on Si{1 0 0} sidewall surfaces was gradually reduced in size as the etching progressed, and it was completely removed after 5 min of etching. Similarly, the corrugation formed on a Si{1 1 0} sidewall surface was also selectively removed by KOH etching (etching time: 3 min). The roughness value of the sidewall surface was reduced from 17.6 nm to a few nanometers by the etching. These results confirm that the corrugation-removal mechanism using anisotropic wet etching can be explained in terms of the distribution pattern of etching rate.

Through wafer via holes manufacturing by variable isotropy Deep RIE process for RF applications

“…Figure 5a present a SEM photo after reducing the wall roughness by selective wet etching (TMAH 25%, 74°C, 10 min) using Shikida's solution (Shikida et al 2010) and seed layer deposition (Cr/Au, 5/150 nm); in this case, due to the walls roughness, deposited layers are not continuous on the bottom part of the TWV's. On the other two samples a good coverage all over the walls can be seen (Figs.…”

“…For small wall angles, roughness could affect the quality of barrier and seed layers deposition. To reduce roughness, selective scalloping removal (by using the method described by Shikida et al (2010), consisting in a short wet etching) or different anisotropic etching recipes providing smaller roughness can be used. Also, isotropic etching processes can be important to reduce the roughness, having a polishing effect over the surfaces, if there is enough space and high angles are allowed.…”

Bio-Inspired Wide-Angle Broad-Spectrum Cylindrical Lens Based on Reflections from Micro-Mirror Array on a Cylindrical Elastomeric Membrane

“…Prior to the actual transfer-printing step (Figure 2g), a couple of process optimizations had to be performed to guarantee that (1) sidewalls of each micro-mirror were smoothened to serve as perfect reflectors to focus light without undesirable aberrations and distortions in the images due to scattering; and (2) large-area surface coverage of the micro-mirror array on the cylindrical polymeric membrane to maximize the FOV of the device. First, the sidewall scalloping induced by the DRIE process was removed by a 45% potassium hydroxide (KOH, Fisher Scientific, Waltham, MA, USA) wet-etching process at 40 °C for 5 min [20]. Second, the BOX layer was selectively undercut by a 6:1 buffered oxide etch (BOE, Fisher Scientific) to a level that all micro-mirrors were just slightly adhered to the underlying substrate and were ready to be transferred onto the elastomeric membrane.…”

Effect of low temperature and concentration KOH etching on high aspect ratio silicon structures

“…Recently, Shikida et al have studied a high concentration (50% wt.) and relatively high temperature (40 °C) DRIE sidewalls etching [12]. These solutions ensure a good smoothing of the (100) crystallographic plane but the surface of the (110) is rougher.…”