Fabrication of 45° mirrors together with well-defined v-grooves using wet anisotropic etching of silicon

The most commonly used microstructure for passive fiber alignment is the ordinary v-groove, defined by {111} planes on a (100) silicon wafer. The plane at the end of the groove, having a 54.7° angle to the surface, can be used as a reflecting mirror. For single-mode fiber applications, a 45° mirror is advantageous together with high accuracy in the position of the fiber, i.e. a smooth mirror and good control of the groove geometry is needed. Two techniques are presented to form 45° mirrors along with well-defined grooves in silicon, using the wet anisotropic etchants EDP and KOH. These techniques are used: (1) to reveal {110} planes on (100) silicon and (2) to make {111} mirrors on wafers that are cut 9.7° off the [100] axis. On (100) silicon, EDP without pyrazine gave the best result. The best mirror and groove reproducibility was found on off-axis cut silicon, using 36 wt.% KOH, with isopropyl alcohol added