METHOD FOR MEASURING DIMENSIONS AND OPTICAL SYSTEM USING THE SAME

Abstract

A method of measuring dimensions for an optical system to measure the critical dimension of a sample object according to this aspect of the present invention includes the steps of preparing a plurality of standard objects, selecting a predetermined focus metric algorithm, performing an analyzing process on each standard object to generate a plurality of focus metric distributions using the predetermined focus metric algorithm, analyzing the focus metric distributions to determine a target order, generating a reference relation, acquiring a measured characteristic value from the sample object, and determining the critical dimension of the sample object based on the measured characteristic value and the reference relation. Each standard object has a grating-shaped standard pattern with a predetermined pitch and line width. The focus metric algorithm is a gradient energy method, a Laplacian method, a standard deviation method, or a contrast method.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The objectives and advantages of the present invention will become apparent upon reading the following description and upon reference to the accompanying drawings.

FIG. 1 is a schematic view of an illustration of an optical system for measuring the dimension according to the prior art.

FIG. 2( a) and FIG. 2(b) are acquired images of the object at an on-focus position and an off-focus position.

FIG. 3 shows a graph illustration of the relation curve of the off-focus offset and the normalized focus measure obtained from the above-mentioned four focus algorithms according to one embodiment of the present invention.

FIG.4 is a top schematic view of a standard grating pattern with a rectangular shape of 25 μm according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view of the standard grating pattern according to one embodiment of the present invention.

FIG. 6 is a schematic view of an illustration of an optical system configuration for measuring the standard grating pattern according to the present invention.

FIG. 7 shows a graph illustration of the relation curve of the off-focus offset and the normalized focus measure calculated by the standard deviation method according to one embodiment of the present invention.

FIG. 8( a) and FIG. 8(b) show graph illustrations of the variation of the relation curve of the focus measure and the off-focus offset as the line width of the grating pattern varies according to one embodiment of the present invention.

FIG. 9( a) to FIG. 9(d) show graph illustrations of the relationship of the characteristic value and the critical dimension at different pitches according to one embodiment of the present invention.

FIG. 10 shows a graph illustration of the variation of the relation curve of the normalized focus measure and the off-focus offset as the line width of the grating pattern varies according to one embodiment of the present invention.

FIG. 11 shows a graph illustration of the relation curve of the normalized characteristic value and the critical dimension according to one embodiment of the present invention.

Claims

1. A method of measuring dimensions for an optical system to measure a critical dimension of a sample object, comprising: preparing a plurality of standard objects, each standard object having a grating-shaped standard pattern with a predetermined pitch and line width;selecting a predetermined focus metric algorithm;performing an analyzing process on each standard object, said step of performing an analyzing process comprising: moving the standard object to a plurality of predetermined positions with respect to an on-focus position of the optical system;capturing a plurality of images of the standard object on the predetermined positions using the optical system; andanalyzing the images using the predetermined focus metric algorithm to generate a plurality of distributions of focus metric values on the predetermined positions, each focus metric distribution having at least one extreme value;analyzing the focus metric distributions to determine target orders from the extreme value and a plurality of characteristic values corresponding to the target orders of the focus metric distributions;generating a reference relation correlating the characteristic values with the line widths of the standard objects;measuring the sample object to acquire a measured characteristic value; anddetermining the critical dimension of the sample object based on the measured characteristic value and the reference relation.

2. The method of measuring dimensions of claim 1, wherein the step of generating a reference relation comprises: generating a relation curve by a curve fitting process, said relation curve correlating characteristic values with the line widths of the standard objects.

3. The method of measuring dimensions of claim 1, wherein the step of generating a reference relation is comprised of a process of correlating the characteristic values with the pitches of the standard objects.

4. The method of measuring dimensions of claim 1, wherein the target order is a zero order peak, a positive first order peak, or a negative first order peak.

5. The method of measuring dimensions of claim 1, wherein the characteristic values are obtained by the focus metric algorithm, and correspond to peak values of the target orders.

6. The method of measuring dimensions of claim 1, wherein the characteristic values are obtained by the focus metric algorithm, and correspond to one of the predetermined positions in the target order.

7. The method of measuring dimensions of claim 1, wherein the predetermined positions use an on-focus position as a reference position.

8. The method of measuring dimensions of claim 1, wherein a target order is comprised of the steps of: normalizing the focus metric distribution based a zero order peak thereof, andselecting a peak or a valley other than the zero order peak as the target order.

9. The method of measuring dimensions of claim 8, wherein the characteristic values are obtained by the focus metric algorithm, and correspond to peak values of the target orders.

10. The method of measuring dimensions of claim 1, wherein the focus metric algorithm is a gradient energy method, a Laplacian method, a standard deviation method, or a contrast method.

11. A method of measuring dimensions for an optical system to measure a critical dimension of a sample object, comprising the steps of: using the optical system to capture a plurality of images from a plurality of objects, each object having a grating-shaped standard pattern with a predetermined pitch and a plurality of line widths;using an algorithm to analyze the images to generate a plurality of characteristic distributions corresponding to the line widths;determining characteristic values for the characteristic distributions to generate a relation curve of the characteristic values and the line widths;measuring the sample object to acquire a measured characteristic value; anddetermining a critical dimension of the sample object based on the measured characteristic value and the relation curve.

12. The method of measuring dimensions of claim 11, wherein the characteristic distributions are obtained by a focus metric algorithm.

13. The method of measuring dimensions of claim 11, wherein the algorithm is a gradient energy method, a Laplacian method, a standard deviation method, or a contrast method.

14. The method of measuring dimensions of claim 11, wherein each characteristic distribution is comprised of a plurality of peaks and valleys.

15. The method of measuring dimensions of claim 14, wherein the characteristic values for the characteristic distribution correspond to one of peaks or valleys.

16. The method of measuring dimensions of claim 14, wherein the characteristic values are the peaks or the valleys other than a zero order peak of the characteristic distributions after normalizing the characteristic distributions.

17. The method of measuring dimensions of claim 14, wherein the characteristic values for the characteristic distributions are peaks or valleys of the characteristic distributions before a normalizing process.

18. An optical system of measuring dimensions of a sample object, comprising: a database configured to store at least one characteristic relation curve of a pitch, the characteristic relation curve correlating a characteristic value with the pitch; anda measuring unit configured to acquire a measured characteristic value of the sample object,wherein a critical dimension of the sample object is determined based on the measured characteristic value and the characteristic relation curve.

19. The optical system of measuring dimensions of claim 18, wherein the characteristic value is an extreme value obtained by a focus metric algorithm.

20. The optical system of measuring dimensions of claim 18, wherein the characteristic value corresponds to one of peaks or valleys of the characteristic relation curve.