Possibilities of extension of 3D shapes by bulk micromachining of different Si (h k l) substrates

Abstract

Results on micromachining of Si substrates with untypical crystallographic orientations have been presented. The process was carried out in KOH and in KOH+IPA solutions with the use of specially designed mask patterns, adjusted individually to specific crystallographic orientations of etched substrate. Mask design and selection of Si substrates were followed by theoretical considerations. Grooves and holes with different inclination of sidewalls on differently oriented Si substrates have been obtained. They made the basis for developing two new seismic mass systems, fabricated on (1 1 0) and (1 1 2) Si wafers. The studies showed that the application of Si substrates with untypical crystallographic orientations gives new possibilities of extension of the 3D structure range fabricated by silicon anisotropic etching. Some design rules for the structures have been given.

A simple and robust model to explain convex corner undercutting in wet bulk micromachining

“…The proposed undercut model answers it on the basis of the fact that the tangent plane on the intersecting {111} planes (i.e. the convex corner) is {110} as shown in the Figure 2 and this plane exhibits high etch rate in pure KOH and TMAH solutions [7,10,11]. Since the convex corner lies on the {110} plane, the etch rate of the corner is much higher than the corresponding {111} planes forming the corner and therefore the phenomenon of undercutting is observed at the convex corners.…”

“…potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH), etc.) based silicon anisotropic etching is frequently used to make a wide range of microstructures in silicon wafers [1][2][3][4][5][6][7][8][9][10]. In this etching method, as shown in Figure 1, undercutting occurs at mask patterns containing the extruded (or convex) corners [11].…”

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

“…cantilever, diaphragm, cavity, etc.) [1][2][3][4][5]. It is a low cost technique and suitable for batch process.…”

A New Model for the Etching Characteristics of Corners Formed by Si<sub>{111}</sub> Planes on Si<sub>{110}</sub> Wafer Surface

“…Silicon micromachining is extensively performed using wet anisotropic etching for the fabrication of simple cavities to complex structures [1][2][3][4][5]. Moreover wet anisotropic etching is inevitable if the microstructures with slanted sidewalls are to be fabricated.…”

“…Two of the six {111} planes emerge at <110> direction, and are oriented at an angle of 35.3˚ to the {110} wafer surface, while the other four {111} planes appear at <112> directions and are vertical to the {110} surface. The appearance of vertical planes along <112> direction makes {110} silicon wafer an appropriate choice for the formation of deep trenches/ grooves with vertical sidewalls [4][5][6][7][8][9][10]. In both these types of wafers, prolonged etched patterns are generally bounded by {111} planes due to their slowest etch rate nature in all kinds of anisotropic etchants.…”