KR101928439B1 - Optical measurement system and method for measuring critical dimension of nanostructure - Google Patents

Abstract

An optical measurement system for measuring a critical dimension (CD) of a sample having a nanostructured surface comprising a nanostructure formed on a plane, the optical measurement system comprising a microscope optical system, An image recording module for recording a defocus image in which the degree of defocus is nonuniform with respect to a plane; An optical design parameter control module for setting and outputting optical design parameters constituting the microscope optical system; An image calculation module receiving information on the parameters set by the control module and calculating an image of the nanostructured surface; And a comparison module for comparing the image recorded in the image recording module with the image calculated in the calculation module.

Description

Technical Field [0001] The present invention relates to an optical measuring system and a measuring method for a CD of a nanostructure,

This disclosure relates to measurement techniques, and more particularly, to a method of scanning a nanostructured object and measuring scattered light therefrom to measure geometric parameters for the nanostructure.

In recent years, there has been a tendency to reduce the critical dimension (CD) of structures fabricated in a microlithography technique developed for semiconductor chip fabrication. CD is the size of the nanostructure to be inspected, and its value is on the order of tens of nanometers. At present, the CD that can be implemented is about 30 nm, and it is expected to be reduced to about 20 nm in the near future.

For mass production of semiconductor structures with very small CDs, the accuracy and reliability of the measuring equipment, and the speed and cost of the measuring process are increased. In addition, existing measurement methods using SEM (scanning electron microscope) and AFM (atomic force microscope) are particularly effective when examining a chip having a well-known topology, It is very slow and expensive. For this kind of measurement, optical methods based on Ellipsometry [1] and scatterometry [2] techniques are being developed. In particular, the well-known optical critical dimension (OCD) method [3] has been used to identify semiconductor structures with CDs smaller than the Rayleigh limit.

Each of these optical analysis methods has its advantages and disadvantages.

In the OCD method, the degree of reflectance of the sub-wavelength structure with respect to the CD value, the wavelength of the incident light, and the incident angle is used. The first is to fix the wavelength of the incident light, to measure the dependence of the reflectance on the incident angle to the object through-angle scanning, the second to fix the incident angle, the wavelength scanning To measure the reflectance dependence on the wavelength of the through-wavelength scanning. In the second method, the spectrum of the incident and reflected irradiation is actually measured, and the dependence of the reflectance on the wavelength is calculated based on the spectrum of the incident and reflected light. The measured dependence is compared to the dependence calculated for the various CD values, and the best match of the measurement curve and the calculation curve is the CD value.

Although OCD technology is widely applied in the semiconductor manufacturing process, it is not possible to analyze an aperiodic structure, a structure with low periodicity, and a structure composed of one or more isolated objects.

Through-focus Scanning Optical Microscopy (TSOM) [4] based on the analysis of a defocused image of a recorded object using an optical microscope while scanning the object along the optical axis direction ] Can be used to analyze non-periodic and isolated objects.

In TSOM technology, a mechanical scanning system that moves an object through-focus with an accuracy of tens of nanometers is one of the basic ones, and at the same time is the most vulnerable in terms of the reliability of the module measuring the TSOM-plant . As the size of the object is reduced and the scanning step is reduced, the demand for the accuracy of the object positioning and the reduction of the scanning step is increased. In this situation, when there is vibration, the accuracy and reliability of the measurement is generally lowered.

This disclosure presents an optical measurement system and method for measuring CDs of nanostructures based on defocus image processing that does not use mechanical through focus scanning on the object being inspected.

An optical measurement system according to one type is an optical measurement system for measuring a critical dimension (CD) of a sample having a nanostructured surface including a nanostructure formed on a plane, the optical measurement system comprising a microscope optical system, An image recording module for recording a defocus image with respect to the nanostructured surface, the defocus image having a non-uniform degree of defocus; An optical design parameter control module for setting and outputting optical design parameters constituting the microscope optical system; An image calculation module receiving information on the parameters set by the control module and calculating an image of the nanostructured surface; And a comparison module for comparing the image recorded in the image recording module with the image calculated in the calculation module.

The sample may be arranged so that the normal of the nanostructured surface is inclined at a predetermined angle (?) With respect to the optical axis of the objective lens provided in the microscopic optical system.

α <θ <2α

Here, the α d ~ ² / λD, λ is the center wavelength of the light spectrum of the microscope optical system, D is a maximum character size of the nano-structure, d is the spatial resolution of the object lens provided in the microscope optical system.

The optical design parameter control module may be configured to measure and / or change the optical design parameters.

The microscope optical system may include a light source, a polarizer, an amplitude mask, a beam splitter, an objective lens, and an image sensor.

Wherein the optical design parameters include at least one of a frequency of an illumination spectrum illuminated in the light source, a polarization axis direction of the polarizer, an aperture size and / or shape and / or position of the amplitude mask, a numerical aperture of the objective lens, And an angle that is inclined with respect to the optical axis of the lens.

The band width of the illumination spectrum may be 100 nm or less, and the wavelength range may be 350 nm to 700 nm.

The amplitude mask may be disposed on a surface optically conjugate with the back focal plane of the objective lens.

The aperture size formed in the amplitude mask may satisfy the following condition.

0.1 < (NAill / NA) < 0.8

Here, NAill is the numerical aperture of the illumination, and NA is the numerical aperture of the objective lens.

The numerical aperture of the objective lens may have a value between 0.4 and 0.9.

The optical design parameter control module includes a spectrometer, an amplitude mask positioning system for setting the position of the amplitude mask, a CCD camera capable of measuring aperture size and shape of the amplitude mask, And a nanostructured surface positioning system capable of setting a tilted angle with respect to the normal of the lens.

The microscope optical system may use Kohler illumination.

The image calculation module may calculate an image using a Rigorous Coupled Waves Analysis (RCWA) method and a Finite-Difference Time-Domain (FDTD) method.

In addition, a measurement method according to one type is a method for measuring a critical dimension (CD) for a sample having a nanostructured surface of a nanostructure formed on a plane, Selecting an optical design parameter to set a microscope optical system for the optical system; Recording a defocus image on the nanostructured surface using the microscope optical system, the defocus image having a non-uniform degree of defocus; Computing an image of the nanostructured surface within a predetermined CD range according to the selected optical design parameters; And comparing the calculated image with the recorded image to determine an estimated value of the CD.

The step of determining the estimated value of the CD may use an optimization technique that calculates a CD value that minimizes the absolute value of the difference between the measured image and the computed image.

Alternatively, the step of determining the estimate of the CD may use a method of preforming a library of the computed images, and comparing the images from the library stepwise with the measured image.

Alternatively, the step of determining the estimated value of the CD may use a method of extracting a focus metric curve that depends on the degree of defocusing and the topology of the nanostructures, and comparing the computed image and the measured image, respectively .

According to the optical measurement system and method described above, one defocus image is measured on the nanostructured surface of the sample to be inspected and the CD value is estimated by comparing it with the calculated image. Since the one defocus image is an image having a different degree of defocus depending on the position, there is no need to mechanically scan the sample along the focal direction to obtain an image having a different degree of defocus, Stability, and accuracy.

According to the measurement system and method described above, it is possible to measure a CD having a nanostructure having an aperiodic structure as well as a periodic structure.

1 schematically shows an arrangement structure between a sample to be inspected and an objective lens for detecting a defocus image of a nanostructured surface in the optical measurement system and the measurement method according to the embodiment.
2 is a block diagram showing a schematic configuration of an optical measurement system according to an embodiment.
Figure 3 shows an exemplary optical arrangement of an image recording module that may be employed in an optical measurement system according to an embodiment.
Figure 4 is a flow chart outlining the steps of a measurement method according to an embodiment.
5A is an example of a measurement image of a nanostructured surface of a sample, which is a measurement image of a nanostructured surface on which a periodic grating having a period of 3 um and a height of a grating line of 100 nm is formed on a glass surface.
Figure 5b shows the focus metric curve extracted from the image of Figure 5a.
6 shows an example of a library configuration of an arithmetic image for comparison with a measured image. FIG. 6 shows three focus metric curves calculated with the grating line height as CD-10 nm? CD? CD + 10 nm.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of explanation.

FIG. 1 is a view showing an optical measurement system and a measuring method according to an embodiment of the present invention. In the optical measuring system and the measuring method according to the embodiment, in order to obtain a defocus image of a nanostructured surface NS, a sample 2 to be inspected is inclined with respect to the objective lens 1 The deployed structure is shown as an example.

Nanostructure refers to a structure in which at least one character size is smaller than the Rayleigh resolution limit, approximately tens of nanometers in size.

The optical measurement system and method according to the embodiment may register only one defocus image for the sample 2 to be inspected having the nanostructured surface NS and use the same Measure the CD.

Referring to FIG. 1, a sample 2 is disposed under the objective lens 1, and the sample 2 has a nanostructured surface NS formed by forming a nanostructure on a plane. The sample 2 is arranged below the objective lens 1 such that the normal line of the nanostructure surface NS and the optical axis of the objective lens 1 are inclined by?. According to this arrangement, on the nanostructured surface NS to be inspected, there is a region 4 clearly formed on the image sensor of the microscope optical system, that is, there is an optimal focus position, and also an image is unclearly formed, And areas 3 and 5 which are not the focus of the image pickup device 1. [ The degree of defocusing appears non-uniformly along the direction in which the sample 2 is inclined, that is, in the x direction. For example, the degree of defocusing varies linearly with the angle of view. Therefore, there is no need for mechanical through-focus scanning, which is generally used to obtain images with different defocus degrees, moving the sample in the direction through the focus of the objective lens 1. [

FIG. 2 is a block diagram showing a schematic configuration of an optical measurement system 100 according to an embodiment, and FIG. 3 is a block diagram of an exemplary image recording module 120 that may be employed in the optical measurement system 100 according to an embodiment. Optical arrangement.

The optical measurement system 100 includes a combination of equipment and software and includes an optical design parameter setting module 110, an image recording module 120, an image calculation module 130, and a comparison module 140.

The image recording module 120 is an optical module for recording an image of the nanostructured surface NS based on a microscopic optical system. The image recorded here is an image containing a complicated superposition of diffraction patterns from which an analysis for extracting an unknown CD can be made.

Referring to FIG. 3, the image recording module 120 constitutes a microscope optical system to obtain a defocus image of the nanostructured surface NS of the sample 2 to be inspected. The image recording module 120 may employ a microscopic optical system configuration using, for example, Kohler illumination operating in a bright field mode and includes a light source 8, a condenser lens 9, A polarizer 11, an amplitude mask 12, a beam splitter 14, an objective lens 1, and an image sensor 17.

The light source 8 provides illumination for obtaining an image of the sample 2. The sample 2 may be provided with an illumination spectrum consisting of light of a predetermined wavelength band and this illumination spectrum may be realized by the light source 8 or by the light source 8 and the color filter 10.

The beam splitter 14 branches the optical path such that the light from the light source 8 is directed to the sample 2 and the light reflected and scattered from the sample 2 is directed to the image sensor 17. The beam splitter 14 may be a polarizing beam splitter.

The amplitude mask 12 has openings of a predetermined shape and size and adjusts the size of the beam cross-section. The amplitude mask 12 may be disposed on a surface optically conjugate with the back focal plane 15 of the objective lens 1. [

A tube lens 16 may be disposed between the beam splitter 14 and the image sensor 17. A relay lens 13 may be disposed between the amplitude mask 12 and the beam splitter 14.

The image sensor 17 is an element for converting an optical image into an electric signal, and for example, a CCD (Charge Coupled Device) can be used.

Referring again to FIG. 2, the optical design parameter control module 110 sets the variables that constitute the optical system for recording an image for the nanostructured surface NS. For example, an optical scheme parameter constituting the optical system shown in Fig. 3 can be set and output. It is also possible to measure and / or change these optical design parameters.

The nanostructured surface (NS) image is recorded in the image recording module 120 according to the thus set optical scheme parameter. Also, to calculate the nanostructured surface (NS) image in the image computation module 130, the optical design parameters are sent to the image computation module 130.

The optical design parameters include variables related to the placement of the optical elements or the illumination conditions and may include, for example, the frequency of the illumination spectrum illuminated in the light source 8, the polarization axis direction of the polarizer 11, And / or the shape and / or position of the objective lens 1, the numerical aperture of the objective lens 1, and the angle at which the nanostructured surface NS is inclined relative to the optical axis 6 of the objective lens 1.

The optimal optical design parameters for the measurement of the nanostructured surface (NS) depend on the topology and CD value of the nanostructured surface (NS) and can be determined within the following range of variation.

The illumination spectrum may be a spectrum having a bandwidth of 100 nm or less at a wavelength range of 350 to 700 nm.

The amplitude mask 12 may be located on a surface that is optically conjugate to the back focal plane of the objective lens 1 and the aperture size of the amplitude mask 12 may be 0.1 <NAill / NA ) &Lt; 0.8. Here, NAill is the numerical aperture of the illumination, and NA is the numerical aperture of the objective lens 1.

The numerical aperture NA of the objective lens 1 can satisfy the condition of 0.4 < NA < 0.9.

An angle at which the normal 7 of the nano structure NS is inclined with respect to the optical axis 6 of the objective lens 1 can satisfy the condition of? <? <2 ?. Wherein an α ~ d ² / λD, λ is the center wavelength, d is the spatial resolution of the objective lens, D is the largest nanostructure character size of the illumination spectrum.

To this end, the optical design parameter control module 110 includes an amplitude mask positioning system for setting the positions of the spectrometer and the amplitude mask 12, a CCD camera (not shown) for measuring the aperture size and shape of the amplitude mask 12, And a nanostructured surface positioning system capable of setting an angle that the normal 7 of the nanostructured surface NS is inclined with respect to the optical axis 6 of the objective lens 1. [

The image operation module 120 receives the CD set in the above range and the parameters set in the optical design parameter control module 130 as an input, assuming that the unknown CD is changed within the known range CD1 < CD < CD2, . The image calculation module 130 can calculate an image using a Rigorous Coupled Waves Analysis (RCWA) method [5] and a Finite-Difference Time-Domain [FDTD] method.

The comparison module 140 compares the computed image with the measured image. This module, which compares the measured image to the computed image for the nanostructured surface (NS), is one of the most important modules in the measurement system. For comparison, the measured image in the image recording module 120 and the image calculated in the image calculation module 130 in consideration of the predetermined range of variation in the CD value are transmitted to be inputted to the comparison module 140. [ As a result of comparison, a best estimate of the measured CD value and / or a more narrowly tuned CD value variation range is derived.

The calculation in the image calculation module 130 and the comparison in the comparison module 140 continue to change the CD value until the calculated image and the measured image match. The CD value when the computed image matches the measured image is the best estimate for the measured CD value of the nanostructured surface (NS).

Figure 4 is a flow chart outlining the steps of a measurement method according to an embodiment.

First, an optical scheme parameter for setting a microscope optical system for image recording of a nanostructured surface is set (S201). The optical design parameters can be the variables described in the description of FIG. 2 and FIG.

A defocus image of the nanostructured surface is recorded using a microscope optical system configured according to the optical design parameters (S202). In order to record a defocus image, as shown in Fig. 1, a sample 2 having a nanostructured surface NS is arranged to be inclined with respect to the objective lens 1.

The image of the nanostructured surface is calculated in consideration of the set optical design parameters and the predetermined CD range (S203). The software module for computation is based on the solution of the exact Maxwell equations and can be implemented by a combination of the RCWA (Rigorous Coupled Waves Analysis) [5] and the Finite-Difference Time-Domain (FDTD) [6] . The input variables for the operation are the optical design parameters and the CD value variation range set to define the illumination and nanostructured surface recording conditions. In a practical semiconductor manufacturing process, the approximate range of CD value variation is well known and can be determined according to the opinion of the expert.

Next, the calculated image is compared with the measured image (S204). As a result of comparison, a best estimate of the measured CD value and / or a more narrowly tuned CD value variation range is derived. Several methods of digital image comparison that can be applied to software modules for comparison are known from the literature. For example, the comparison result may be a number indicating the degree to which the measured image matches the calculated image. The 'focus metric' variable [7], which is defined to analyze images of different degrees of defocusing, can be used, which will be described later in the description of Figures 5a, 5b and 6.

The matching degree between the calculated image and the measured image is determined within a given accuracy range (S205), and the CD value at which the matching is performed is output as the measured CD value. If no match is found, the CD change range is changed (S206), the image of the nanostructured surface is calculated (S203), and again the comparison with the measured image (S204) is repeated. Depending on the comparison of the measured and calculated images, a narrower range of CD value changes can be determined.

There are several ways to compare the measured image with the calculated image to select the CD value. For example, optimization techniques and computational techniques in image libraries can be used. When using optimization techniques, the best estimate of the CD value is obtained when the absolute value of the difference between the measured image and the calculated image is at a minimum. When using the library calculation technique, the measured image is compared step-by-step with previously calculated images on the assumption that the CD value varies within a known range.

5A is an example of a measurement image of a nanostructured surface of a sample, which is a measurement image of a nanostructured surface on which a periodic grating having a period of 3 um and a height of a grating line of 100 nm is formed on a glass surface. Figure 5b shows the focus metric curve extracted from the image of Figure 5a.

The focus metric variable may be a standard deviation calculated from a digital image representing the data array, such as the following equation, which characterizes the contrast of the image at a given degree of defocus. A variable M (I _{i , j} ) _, which depends on the topology of the object and the degree of defocusing _, is given corresponding to each defocus image I _{i , j} . This variable characterizes the image contrast, at a given degree of defocusing. In particular, this variable may be a standard deviation calculated from a digital image representing the data array.

(1)

(One)

는 이미지 내의 모든 픽셀에서의 평균 강도이고, N은 이미지 픽셀의 총 개수이다. Where M (I _{i , j} ) is the focus metric, I _{i , j} is the pixel intensity at the coordinates (i, j) in the image,

Is the average intensity at all pixels in the image, and N is the total number of image pixels.

A through-focus focus-metric curve M (h) passing through the focus can be obtained by calculating the focus metric of the image at each defocus position. Where h is the position of the object along the focus direction.

On the other hand, in the embodiment in which the nanostructured surface is arranged to be tilted with respect to the objective lens, the focus metric curve can be calculated along the inspection surface since the degree of defocusing changes along the direction in which the nanostructured surface is inclined. For this, a predetermined window must be defined. The size of the window should be small enough that the degree of defocusing can be regarded as a constant in this window. Next, this window is scanned along the nanostructured surface, and the focus metric is calculated at each window position. As a result of this image processing, a focus metric curve, M (x), is obtained. Here, x is a coordinate indicating the position of the window, that is, a coordinate along the direction in which the nanostructured surface is inclined.

In Fig. 5A, the arrow indicates the surface slope direction. The moire strip is easily identified along the arrow direction on the image, and the scanning window is visible at several locations on the image.

FIG. 5B shows a focus metric, M (x) graph, extracted in the image processing of FIG. 5A. The shape and all key features of this curve depend on the optical design parameters defining the conditions of the illumination and image recording, and the CD (height 100 nm) of the grating.

6 shows an example of a library configuration of an arithmetic image for comparison with a measured image. FIG. 6 shows three focus metric curves calculated with the grating line height as CD-10 nm? CD? CD + 10 nm.

It is easily observed that the focus metric curves M (x) are normalized to 1 and the shapes of the curves calculated for a grating with a height difference of 10 nm are similar to each other. The curves have three maximum points that are apparent. The measured and calculated focus metric curves can be compared by predetermined variables associated with the measured CD. In this case, the variable for comparing the focus metric curves extracted from the measurement and the calculation corresponds to the maximum value on the left side of the curve, and is a focus metric value satisfying the following condition.

M _{CD- 10 nm} <M _CD <M _{CD + 10 nm} .

When the focus metric curve (M _{CD *} ) and the calculated focus metric curve (M _CD ) extracted from the measured image are determined to be M _{CD *} = M _CD with the required accuracy, the CD value is calculated as the measured CD * value Can be assumed to be the best estimate.

The optical measurement system and method for measuring CD of a nanostructure according to the present invention have been described with reference to the embodiments shown in the drawings to facilitate understanding of the present invention. However, the present invention is not limited thereto. It will be understood that various modifications and equivalent embodiments are possible. Accordingly, the true scope of the present invention should be determined by the appended claims.

A list of references cited in the above description is as follows.

[1] "Handbook of ellipsometry" by Harland G. Tompkins, Eugene A. Irene;

[2] PETRE CATALINLOGOFATU et. al., Rom. Journ. Phys., Vol. 55, Nos. 3-4, P. 376-385, Bucharest, 2010;

[3] Ray J. Hoobler and Ebru Apak, Proceedings of SPIE Vol. 5256 23rd Annual BACUS Symposium on Photomask Technology;

[4] Attta, R., Silver, R.M., and Barnes, B.M., "Optical through-focus technique for differentiation in line width, line height, and sidewall angle for CD, overlay, and defect metrology applications," Proc. SPIE 6922OE-1-13, (2008);

[5] M. G. Moharam, Drew A. Pommet, and Eric B. Grann. J. Opt. Soc. Am. A, 12 (5): 1077 {1086}, May 1995;

[6] K. Umashankar, A. Taflove, "A Novel Method to Analyze Electromagnetic Scattering of Complex Objects", IEEE (1982);

[7] Attota, R., Silver R.M., and Potzick, J., "Optical illumination and critical dimension analysis using the through-focus focus metric", Proc. SPIE, 6289, p. 62890Q-1-10 (2006).

[8] Encyclopedia of physics and engineering. Microscopy. http://www.femto.com.ua/articles/part_1/2284.html.

100 ... optical measuring system 110 ... optical design parameter setting module
120 ... image recording module 130 ... image calculation module
140 ... Comparison module 1 ... objective lens
2 ... sample 8 ... light source
9 ... condenser lens 10 ... color filter
11 ... Polarizer 12 ... Amplitude Mask
13 ... relay lens 14 ... beam splitter
16 ... tube lens 17 ... image sensor

Claims (25)

1. An optical measurement system for measuring a critical dimension (CD) of a sample having a nanostructured surface including a nanostructure formed on a plane,
An image recording module that includes a microscope optical system and records, for the nanostructured surface, a defocus image in which the degree of defocus is uneven;
An optical design parameter control module for setting and outputting optical design parameters constituting the microscope optical system;
An image calculation module receiving information on the parameters set by the control module and calculating an image of the nanostructured surface;
And a comparison module for comparing the image recorded in the image recording module with the image calculated in the calculation module,
Wherein said sample is arranged such that a normal of said nanostructured surface is inclined at a predetermined angle (?) With respect to an optical axis of an objective lens provided in said microscope optical system,
Wherein the predetermined angle (?) Satisfies the following condition.
α <θ <2α
Here, α = d ² / λD, λ is the center wavelength of the light spectrum of the microscope optical system, D is a maximum character size of the nano-structure, d is the spatial resolution of the object lens provided in the microscope optical system. delete delete The method according to claim 1,
Wherein the optical design parameter control module is configured to be able to measure or change the optical design parameters. The method according to claim 1,
The microscope optical system
An optical measurement system comprising a light source, a polarizer, an amplitude mask, a beam splitter, an objective, and an image sensor. 6. The method of claim 5,
Wherein the optical design parameters include a frequency of an illumination spectrum irradiated from the light source, a polarization axis direction of the polarizer, an aperture size or shape or position of the amplitude mask, a numerical aperture of the objective lens, And an oblique angle with respect to the optical axis. The method according to claim 6,
Wherein the bandwidth of the illumination spectrum is 100 nm or less and the wavelength range is 350 nm to 700 nm. 6. The method of claim 5,
Wherein the amplitude mask is disposed on a surface optically conjugate with a back focal plane of the objective lens. 9. The method of claim 8,
Wherein the aperture size formed in the amplitude mask satisfies the following condition.
0.1 < (NAill / NA) < 0.8
Here, NAill is the numerical aperture of the illumination, and NA is the numerical aperture of the objective lens. 6. The method of claim 5,
Wherein the numerical aperture of the objective lens has a value between 0.4 and 0.9. 6. The method of claim 5,
The optical design parameter control module
Spectrometer and
An amplitude mask positioning system for setting the position of the amplitude mask;
A CCD camera capable of measuring the aperture size and shape of the amplitude mask,
And a nanostructured surface positioning system capable of setting an angle at which the normal of the nanostructured surface is tilted with respect to a normal of the objective lens. The method according to claim 1,
Wherein the microscope optical system uses Kohler illumination. The method according to claim 1,
Wherein the image computation module computes an image using a Rigorous Coupled Waves Analysis (RCWA) method and a Finite-Difference Time-Domain (FDTD) method. A method of measuring a critical dimension (CD) for a sample having a nanostructured surface of a nanostructure formed on a plane,
Selecting an optical design parameter to set a microscope optical system for image recording of the nanostructured surface;
Recording a defocus image on the nanostructured surface using the microscope optical system, the defocus image having a non-uniform degree of defocus;
Computing an image of the nanostructured surface within a predetermined CD range according to the selected optical design parameters;
And comparing the calculated image with the recorded image to determine an estimate of the CD,
Wherein said sample is arranged such that a normal of said nanostructured surface is inclined at a predetermined angle (?) With respect to an optical axis of an objective lens provided in said microscope optical system,
Wherein the predetermined angle (?) Satisfies the following condition.
α <θ <2α
Here, α = d ² / λD, λ is the center wavelength of the light spectrum of the microscope optical system, D is a maximum character size of the nano-structure, d is the spatial resolution of the object lens provided in the microscope optical system. delete delete 15. The method of claim 14,
The optical design parameters include at least one of the frequency of the illumination spectrum, the polarization axis direction of the polarizer, the aperture size or shape or position of the amplitude mask, the numerical aperture of the objective lens, and the angle at which the nanostructured surface is tilted with respect to the optical axis of the objective lens Included measuring methods. 18. The method of claim 17,
Wherein the band width of the illumination spectrum is 100 nm or less and the wavelength range is 350 nm to 700 nm. 18. The method of claim 17,
Wherein the aperture size formed in the amplitude mask satisfies the following condition.
0.1 < (NAill / NA) < 0.8
Here, NAill is the numerical aperture of the illumination, and NA is the numerical aperture of the objective lens. 18. The method of claim 17,
Wherein the numerical aperture of the objective lens has a value between 0.4 and 0.9. 15. The method of claim 14,
Using a bright field technique to record the defocus image. 15. The method of claim 14,
The step of computing the image of the nanostructured surface
A measurement method using a Rigorous Coupled Waves Analysis (RCWA) method and a Finite-Difference Time-Domain (FDTD) method. 15. The method of claim 14,
The step of determining an estimate of the CD
A measurement method using an optimization technique that calculates a CD value that minimizes the absolute value of the difference between the measured image and the computed image. 15. The method of claim 14,
The step of determining an estimate of the CD
Pre-forming a library of the computed images, and comparing the images from the library stepwise with the measured image. 15. The method of claim 14,
The step of determining an estimate of the CD
For each of the computed image and the measured image, a focus metric curve that depends on the degree of defocusing and the topology of the nanostructure is extracted and compared.

Images