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Optical spot geometric parameter determination using calibration targets

Optical spot geometric parameter determination using calibration targets description/claims

This application is a continuation application of co-pending U.S. patent application Ser. No. 11/828,666 filed on Jul. 26, 2007, which is hereby incorporated by reference.

1. Technical Field

The present disclosure relates in general to a processing system, and more particularly to determining a geometric parameter of an optical spot of a light beam of an optical metrology tool used in the processing system.

2. Background Art

Utilization of optical metrology in semiconductor manufacturing has grown significantly over the past several years. The technology provides capabilities to conduct measurements of a wide variety of critical device parameters, including, e.g., critical dimensions, depths and sidewall angles. Benefits of optical metrology include non-contact measurement capability that can be performed very quickly.

For optical metrology tools to yield reliable measurements, it is necessary that the tools produce well defined light beams, and collect the optical response for analysis, as designed. The size of the optical spot of the produced light beam, which is defined as the area illuminated by the incident light beam, can have a large impact on the measurement values. As a consequence, for example, the sizes of the optical spots of optical metrology tools affects the matching performance of the optical metrology tools.

An optical spot can initially appear to be symmetric. An optical spot may have an area (usually referred to as an “effective spot”) inside the optical spot, which provides most, e.g., 99%, of the information content. An effective spot is very sensitive to the small change in the area it illuminates. Usually, an effective spot comprises a small portion of a total optical spot. For example, the entire optical spot may illuminate an area of 1600 square microns, while the most sensitive area of the optical spot (i.e., the effective spot) may be a 100 square micron area. If the optical spot is symmetric, the effective spot will be located in the center of the optical spot. If the optical spot is not symmetric, then the effective spot will be located off the center of the optical spot. Whether an optical spot of an optical metrology tool is symmetric and the level of symmetry impact the measurement result and thus the matching of the optical metrology tools.

Conventional approaches to optical metrology do not have a satisfactory solution to characterize a geometric parameter of an optical spot and or or a level of symmetry of the optical spot.

A first aspect of the disclosure is directed to a method for determining a geometric parameter of an optical spot of a light beam, the method comprising: providing a calibration target, the calibration target including a systematic variation in a parameter; measuring the calibration target with respect to the systematic variation using the light beam to obtain a plurality of measurements; and analyzing the measurements and the systematic variation to determine the geometric parameter of the optical spot.

A second aspect of the disclosure is directed to a system for determining a geometric parameter of an optical spot of a light beam, the method comprising: means for controlling a calibration target, the calibration target including a systematic variation in a parameter; means for measuring the calibration target with respect to the systematic variation using the light beam to obtain a plurality of measurements; and means for analyzing the measurements and the systematic variation to determine the geometric parameter of the optical spot.

A third aspect of the disclosure is directed to a calibration target for measuring a size of an optical spot of a light beam, the calibration target comprising: a first portion, a dimension of which in a first axis systematically decreases along a second axis; a second portion; and a third portion; wherein the second portion and the third portion extend along opposite sides of the first portion and are separated by the first portion in the first axis, and include a material of different optical response than that of the first portion.

A fourth aspect of the disclosure is directed to a calibration target for measuring a level of symmetry of an optical spot of a light beam, the calibration target comprising: a gradient in a parameter along an axis of the calibration target, the gradient being a function of the axis, and including one of: a continuous gradient from one end of the calibration target to another end thereof in the axis; or a switch point in a given point of the calibration target in the axis between two sub-gradients, one of the two sub-gradients being an ascending gradient and the other being a descending gradient.

Other aspects and features of the present disclosure, as defined solely by the claims, will become apparent to those ordinarily skilled in the art upon review of the following non-limited detailed description of the disclosure in conjunction with the accompanying figures.

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