Apparatus and methods for detecting overlay errors using scatterometry

A method for determining overlay error between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, the method comprising:

• providing targets A, B, C, and D that each include a portion of the first and second structures,
• wherein the target A is designed to have an offset Xa between its first and second structures' portions,
• wherein the target B is designed to have an offset Xb between its first and second structures' portions,
• wherein the target C is designed to have an offset Xc between its first and second structures' portions,
• wherein the target D is designed to have an offset Xd between its first and second structures' portions,
• wherein each of the offsets Xa, Xb, Xc, and Xd is different from zero, Xa is an opposite sign and differs from Xb, and Xc is an opposite sign and differs from Xd;
• illuminating the targets A, B, C, and D with electromagnetic radiation to obtain spectra SA, SB, SC, and SD from targets A, B, C, and D, respectively;
• and
• determining and storing any overlay error between the first structures and the second structures using a scatterometry technique based on the obtained spectra SA, SB, SC, and SD, and without using calibration or modeling data to determine any overlay error,
• wherein obtaining the spectra SA, SB, SC, and SD comprises acquiring radiation from the targets A, B, C, and D using an imaging spectroscopic ellipsometer, and
• wherein an illumination and imaging NA's of the imaging spectroscopic ellipsometer are chosen to optimize the performance of the instrument on scattering structures by ensuring that only the zeroth diffraction order is collected.

A system for determining overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, comprising:

• a scatterometry module for illuminating plurality of targets A, B, C and D with electromagnetic radiation to obtain spectra SA, SB, SC, and SD from the targets A, B, C, and D, respectively;
• and
• a processor operable for determining any overlay error between the first structures and the second structures using a scatterometry technique based on the obtained spectra SA, SB, SC, and SD,
• wherein the targets A, B, C and D each include a portion of the first and second structures,
• wherein the target A is designed to have an offset Xa between its first and second structures' portions,
• wherein the target B is designed to have an offset Xb between its first and second structures' portions,
• wherein the target C is designed to have an offset Xc between its first and second structures' portions,
• wherein the target D is designed to have an offset Xd between its first and second structures' portions,
• wherein each of the offsets Xa, Xb, Xc and Xd is different from zero, Xa is an opposite sign and differs from Xb, and Xc is an opposite sign and differs from Xd,
• wherein the scatterometry module is an optical apparatus in the form of (i) a spectroscopic normal incidence polarized differential reflectometer and an oblique incidence spectroscopic ellipsometer or (ii) a spectroscopic near-normal incidence polarized differential reflectometer and an oblique incidence spectroscopic ellipsometer.