Why Do (110) Silicon Wafers Form Perpendicular Trenches with (111)?

[Lenei]

Regarding the anisotropic etching of the (110) silicon wafer, why will the (110) oriented wafers form perpendicular trenches with the (111)?

 

[Hyo X]

Regarding the anisotropic etching of the (110) silicon wafer, why will the (110) oriented wafers form perpendicular trenches with the (111)?

If the etching is truly anisotropic, the walls of the etched features should be perpendicular to the surface of the wafer.