FIG. 4 shows the substrate W bonded to the carrier substrate CW, with the second surface 10 b uppermost. [0055] As shown in FIG. 5, the wafer W is ground to a desired thickness, T, e.g. of about 70 ??m, and the upper surface 10 b??? finished as required for the devices to be formed on it. [0056] To locally etch through the first substrate to reveal the reversed markers 1-8, the second surface 10 b