STEPPER FOCUS CHARACTERIZATION USING DIFFRACTION FROM LATENT IMAGES

We present a novel technique for the rapid, nondestructive evaluation of the contrast of the latent image in photoresist. Measurements are m ade of the intensity of light diffracted from a grating pattern in exp osed, undeveloped photoresist, the so-called latent image. Optimum exp osure tool parameters such as exposure tool dose and focus can be dete rmined based on the intensity of light diffracted into specific orders . Employing the proposed technique, measurements can be made sufficien tly fast to allow rapid control of the exposure conditions, such as fo cus, which influences image contrast. The measurement can be made afte r an exposure, and corrections to focus for subsequent exposures may b e derived to compensate for changing optical or mechanical properties of the wafer. The technique may be used with a variety of photoresist materials on different substrates.