Methods of forming microelectronic device wafers include fabricating a plurality of semiconductor dies at an active side of a semiconductor wafer, depositing a mask on the semiconductor wafer, removing a central portion of the mask and the semiconductor wafer, and etching. The semiconductor wafer has an outer perimeter edge and a backside that is spaced from the active side by a first thickness. The mask is deposited on the backside of the semiconductor wafer and has a face that is spaced from the backside by a mask thickness. The thinned portion has a thinned surface that is spaced from the active side by a second thickness that is less than the first thickness, and the thinned surface is etched.