Wafer shape thickness and trench measurement

A method for simultaneously measuring the thickness of individual wafer layers, including a direct method for measuring the depth of etched features, and the distance to a first wafer surface, wherein said method comprises the following steps:

• a) acquire a test object comprising a wafer,
• b) place the wafer on a wafer chuck so that the wafer completes a measurement leg of an interferometer,
• c) record a spectrum of the received light from the interferometer,
• d) evaluate the periodicities in the recorded spectrum, allowing for dispersion, if necessary, and transforming the spectrum to time delay domain,
• e) determine signal peaks in time delay domain,
• f) assign one time delay peak to indicate the path length difference between the measurement leg and a reference leg of the interferometer,
• g) assign the other time delay peaks to the various wafer thickness layers, including an etch depth layer according to the direct method for etch depth measurement, and
• h) convert the time delay to distance or thickness.