Metal recess depth measurements by capacitor test structure

A testing apparatus, comprising:

• a dielectric layer in the wafer;
• a metal layer in the dielectric layer and vertically under a top surface thereof;
• and
• a first region and a second region formed laterally adjacent to each other,
• wherein the first region comprises the dielectric layer, and the metal layer, wherein the second region comprises the dielectric layer, the metal layer, and a first metal pad and a second metal pad that are laterally separated from each other by a portion of the dielectric layer, vertically extend into the dielectric layer from the top surface and are in contact with the metal layer, wherein the testing apparatus is configured to work with probe pads to perform a measuring of metal recess depths into the wafer, and wherein the probe pads are positioned vertically over the test structure.

A method of measuring a metal pad recess depth, comprising:

• receiving a test structure comprising a first region and a second region adjacent to each other in a wafer, wherein the first region comprises a dielectric layer and a metal layer, and wherein the second region comprises the dielectric layer, the metal layer, and a first metal pad and a second metal pad that laterally separated from each other, vertically extend into the dielectric layer, and contact the metal layer;
• placing probe pads vertically adjacent to the test structure, wherein the probe pads comprise a first probe pad and a second probe pad vertically over the first region, and a third probe pad and a fourth probe pad vertically aligned with the first metal pad and the second metal pad in the second region, respectively;
• and
• calculating a recess depth of the first metal pad and the second metal pad from a top surface of the dielectric layer into the wafer as a function of capacitance values between the probe pads and the test structure.