Patent ID: 7684039

Claim:
A method for conducting near infrared measurements of a substrate having an amorphous carbon layer formed thereon, the method comprising: providing at least one overlay target formed as part of a substrate having a topography that includes an amorphous carbon layer formed on the substrate; producing an illumination beam with near infrared (NIR) radiation; filtering the illumination beam so that the filtered beam consists of a near infrared (NIR) illumination beam; directing the NIR illumination beam onto a portion of the surface such that some of the NIR radiation passes through the amorphous carbon layer to impinge on material under the amorphous carbon layer to generate an output signal that includes NIR radiation, where the output signal that includes NIR radiation passes from the material under the amorphous carbon layer back through the amorphous carbon layer; chromatically correcting the NIR radiation of the output signal; detecting the chromatically corrected NIR radiation of the output signal, where detected chromatically corrected NIR radiation is configured to indicate at least one overlay metrology measurement of the at least one overlay target formed as part of the substrate having an amorphous carbon layer formed thereon; and processing the detected chromatically corrected output signal to obtain metrology measurements of the substrate.