Patent ID: 8649016

Claim:
A system for directly measuring the depth of a high aspect ratio etched feature on a wafer having an etched surface and a non-etched surface, said system comprising: a) a reflectometer that is positioned to face the non-etched surface of the wafer, wherein said reflectometer having means for producing a focused incident light of multiple optical frequencies that is applied to the non-etched surface of the wafer, and means for receiving and processing a reflected light that is also applied from the non-etched surface of the wafer, wherein said reflectometer produces an output signal representative of the intensity of Fabry Perot interference fringes in the reflected light for each of the multiple optical frequencies, b) an analog-to-digital converter (ADC) that converts the output signal to a corresponding digital data signal, c) a computer having means for processing the digital data signal and to display the depth of the high aspect ratio etched feature of the wafer.