A cathode assembly for a physical vapor deposition (PVD) system includes a target holder and a thickness detector. The target holder is for holding a target, in which the target has a first major surface and a second major surface. The first major surface and the second major surface are respectively proximal and distal to the target holder. The thickness detector is disposed on the target holder. At least one portion of the first major surface is exposed to the thickness detector for allowing the thickness detector to detect the thickness of the target through the first major surface.