Periodic patterns and technique to control misalignment between two layers

Abstract

A method and system to measure misalignment error between two overlying or interlaced periodic structures are proposed. The overlying or interlaced periodic structures are illuminated by incident radiation, and the diffracted radiation of the incident radiation by the overlying or interlaced periodic structures are detected to provide an output signal. The misalignment between the overlying or interlaced periodic structures may then be determined from the output signal.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates in general to metrology systems for measuring periodic structures such as overlay targets, and, in particular, to a metrology system employing diffracted light for detecting misalignment of such structures. [0002] Overlay error measurement requires specially designed marks to be strategically placed at various locations, normally in the scribe line area between dies, on the wafers for each process. The alignment of the two overlay targets from two consecutive processes is measured for a number of locations on the wafer, and the overlay error map across the wafer is analyzed to provide feedback for the alignment control of lithography steppers. [0003] A key process control parameter in the manufacturing of integrated circuits is the measurement of overlay target alignment between successive layers on a semiconductor wafer. If the two overlay targets are misaligned relative to each other, then the electronic devices fabricated w...

AI Technical Summary

Benefits of technology

[0007] An advantage of the target is the use of the same diffraction system and the same target to measure critical dimension and overlay misregistration. Another advantage of the measurement of misregistration of the target is that it is free from optical asymmetries usually associated with imaging.

[0010] In one embodiment, a neutral polarization angle, defined as an incident polarization angle where the differential intensity is equal to zero for all overlay misregistrations, is determined. The slope of differential intensity as a function of incident polarization angle is highly linear when plotted against the overlay misregistration. This linear behavior reduces the number of parameters that need to be determined and decreases the polarization scanning needed. Thus, the method of detecting misalignment is faster when using the slope measurement technique.

Problems solved by technology

If the two overlay targets are misaligned relative to each other, then the electronic devices fabricated will malfunction, and the semiconductor wafer will need to be reworked or discarded.

The accuracy of the optical microscope is limited by the accuracy of the line profiles in the target, by aberrations in the illumination and imaging optics and by the image sampling in the camera.

Such methods are complex and they require full imaging optics.

These techniques suffer from a number of drawbacks.

First, the grabbed target image is highly sensitive to the optical quality of the system, which is never ideal.

The optical quality of the system may produce errors in the calculation of the overlay misregistration.

Second, optical imaging has a fundamental limit on resolution, which affects the accuracy of the measurement.

Third, an optical microscope is a relatively bulky system.

It is difficult to integrate an optical microscope into another system, such as the end of the track of a lithographic stepper system.

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