JP7023703B2 - Step measurement method and step measurement device - Google Patents

Description

The present invention relates to a step measuring method and a step measuring device, and more particularly to a step measuring method and a step measuring device for a sample containing a transparent film.

Examples of the method of measuring the step on the surface of the sample in a non-contact and non-destructive manner include a method using a confocal optical system and a method using an interferometer. For example, in step measurement using a cofocal optical system, the position of the objective lens with respect to the sample is changed along the optical axis direction of the objective lens. In this case, the step on the surface is measured from the difference in the position where the brightness of the reflected light reflected by the sample is the peak.

Japanese Unexamined Patent Publication No. 2015-087197 Japanese Unexamined Patent Publication No. 2005-266584 JP-A-2007-199511 Japanese Unexamined Patent Publication No. 2010-075997 Japanese Unexamined Patent Publication No. 2012-098692 Japanese Unexamined Patent Publication No. 2002-039721

In the process of manufacturing electronic devices such as compound semiconductor lasers, thin film transistors for displays, and three-dimensional structures such as MEMS (Micro Electrical Mechanical Systems), an opaque metal film is formed on a substrate on which a transparent or translucent insulating film is formed. May be formed.

FIG. 1 is a cross-sectional view illustrating a sample 140 in which a metal film 143 is formed on a transparent insulating film 142 formed on a substrate 141. As shown in FIG. 1, the insulating film 142 of the sample 140 includes a plurality of layers 142a to 142d made of a transparent film. The metal film 143 of the sample 140 is an opaque film, for example, a patterned electrode. A step is formed on the surface of the sample 140. Specifically, a step is formed in which the upper surface of the metal film 143 is the upper stage and the upper surface of the insulating film 142 is the lower stage.

As shown in FIG. 1, when the transparent insulating film 142 that transmits visible light is exposed on the surface of the sample 140, the illumination light passes through the insulating film 142 and is also reflected on the lower surface of the insulating film 142. Therefore, the reflected light reflected by the sample 140 by the illumination light includes the reflected light reflected on the upper surface of the insulating film 142 and the reflected light reflected on the lower surface of the insulating film 142. When the transparent film is a multilayer film, the reflected light reflected by the sample 140 also includes the reflected light reflected at the interface between the layers 142a to 142d.

Therefore, the Z position where the brightness of the reflected light shows a peak is a position deviated from the position showing the upper surface of the insulating film 142. Therefore, in such a case, it is not possible to accurately measure the step between the upper surface of the metal film 143 of the sample 140 and the upper surface of the insulating film 142.

FIG. 2 is a cross-sectional view illustrating a sample 140a in which transparent insulating films 142 having different film thicknesses are formed on an uneven substrate 141. As shown in FIG. 2, one insulating film 142 includes four layers 142a to 142d, and the other insulating film 142 includes two layers 142e and 142f. As described above, when the film thicknesses of one transparent insulating film 142 and the other transparent insulating film 142 are different, the difference in film thickness does not necessarily mean a step on the surface. For example, when the surface of the substrate 141 is uneven, the difference in film thickness between the upper surface of one transparent insulating film 142 and the upper surface of the other transparent insulating film 142 is the difference in film thickness and the substrate 141. Includes unevenness and unevenness.

When measuring such a step, the position where the brightness of the reflected light shows a peak is a position deviated from the position showing the upper surface of the insulating film 142. Therefore, even in such a case, it is not possible to accurately measure the step between the upper surface of one transparent insulating film 142 and the upper surface of the other transparent insulating film 142.

The present invention has been made to solve such a problem, and provides a step measuring method and a step measuring device capable of accurately measuring a step on the surface of a sample containing a transparent film.

The step measuring method according to the present invention is a step measuring method for measuring a step on the surface of a sample including a portion where a transparent film is exposed, and is the sample along the optical axis direction of an objective lens of a cofocal optical system. When the position of the objective lens is changed with respect to the sample, the step of measuring the pseudo step on the surface of the sample and the transparency from the difference in the position showing the peak of the brightness of the reflected light reflected by the sample. Optical calculation using the step of measuring the film thickness of the transparent film, the step of determining the Z-dependent function indicating the relationship between the brightness and the position, and the film thickness and the refractive index of the transparent film. The step of introducing the Z-dependent Frenel coefficient of the product of the Z-dependent function at the interface position and the Frenel coefficient of the transparent film at the interface position, and the Z-dependent Frenel coefficient synthesized at each of the interface positions. It is provided with a step of determining a shift amount from the position where the reflectance calculated from the square of the absolute value of is showing a peak in the optical axis direction, and a step of deriving a step from the pseudo step and the shift amount. With such a configuration, the step on the surface of the sample including the transparent film can be measured with high accuracy.

Further, in the step of measuring the film thickness, the sample is irradiated with the illumination light of the first wavelength and the illumination light of the second wavelength through the cofocal optical system, and the reflected light reflected by the sample is irradiated. Is detected via the cofocal optical system, a first image by the light of the first wavelength and a second image by the light of the second wavelength are acquired, and the film thickness of the transparent film is calculated. In order to obtain the measurement data of the reflectance for the first wavelength and the second wavelength, respectively, based on the first image and the second image, the relationship between the wavelength and the reflectance is the transparent film. The thickness of the transparent film is approximately calculated from the measurement data with reference to the calculation data shown for each thickness.

Further, the step of measuring the film thickness is the brightness of the reflected light reflected by the sample when the position of the objective lens is changed with respect to the sample along the optical axis direction of the objective lens. , The calculated IZ curve which measures the IZ curve showing the relationship with the position and plots the reflectance simulated using the Z-dependent Fresnel coefficient in the case of a plurality of the assumed film thicknesses of the transparent film. Is prepared, and the calculated IZ curve is fitted to the measured IZ curve to calculate the film thickness of the transparent film.

In the step of determining the Z-dependent function, the square root of the Lorentz function is used as the Z-dependent function.

Further, the step of introducing the Z-dependent Frenel coefficient is a step of calculating the optical film thickness of the transparent film using the film thickness and the refractive index of the transparent film, and the step of using the optical film thickness. A step of calculating the optical interface position of the transparent film is included.

Further, the transparent film is a multilayer film in which a plurality of transparent layers are laminated.

The step measuring device according to the present invention is a step measuring device that measures a step on the surface of a sample including a portion where a transparent film is exposed, and is a light detector that detects reflected light reflected by the sample. A cofocal optical system having an objective lens and guiding the illumination light to the sample and guiding the reflected light from the sample to the light detector, and the sample along the optical axis direction of the objective lens. The processing unit includes a processing unit that changes the position of the objective lens with respect to the sample, and the processing unit is pseudo on the surface of the sample because of the difference in the position showing the peak of the brightness of the reflected light reflected by the sample. The step is measured, the film thickness of the transparent film is measured, a Z-dependent function indicating the relationship between the brightness and the position is determined, and the film thickness and the refractive index of the transparent film are used. The Z-dependent Frenel coefficient obtained by introducing the Z-dependent Frenel coefficient of the product of the calculated Z-dependent function at the optical interface position and the Frenel coefficient of the transparent film at the interface position was introduced, and the Z-dependent Frenel was synthesized at each of the interface positions. The reflectance calculated from the square of the absolute value of the coefficient determines the shift amount from the position showing the peak in the optical axis direction, and derives the step from the pseudo step and the shift amount. With such a configuration, the step on the surface of the sample including the transparent film can be measured with high accuracy.

Further, when measuring the film thickness of the transparent film, the processing unit irradiates the sample with the illumination light of the first wavelength and the illumination light of the second wavelength by switching through the cofocal optical system. Then, the reflected light reflected by the sample is detected via the cofocal optical system, and a first image by the light of the first wavelength and a second image by the light of the second wavelength are acquired. In order to calculate the film thickness of the transparent film, the measurement data of the reflectance for the first wavelength and the second wavelength is obtained based on the first image and the second image, respectively, and the wavelength and the reflectance are obtained. The relationship is calculated by approximating the film thickness of the transparent film from the measurement data with reference to the calculation data shown for each film thickness of the transparent film.

Further, when the processing unit changes the position of the objective lens with respect to the sample along the optical axis direction of the objective lens when measuring the film thickness, the illumination light is reflected by the sample. The IZ curve showing the relationship between the brightness of the reflected light and the position is measured, and the reflectance simulated using the Z-dependent Frenel coefficient in the case of a plurality of the film thicknesses assumed for the transparent film is obtained. A plotted calculated IZ curve is prepared, and the calculated IZ curve is fitted to the measured IZ curve to calculate the film thickness of the transparent film.

The Z-dependent function is the square root of the Lorentz function.

Further, when calculating the Z-dependent Frenel coefficient, the processing unit calculates the optical film thickness of the transparent film by using the film thickness and the refractive index of the transparent film, and calculates the optical film thickness of the transparent film. The thickness is used to calculate the optical interface position of the transparent film.

Further, the transparent film is a multilayer film in which a plurality of transparent layers are laminated.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a step measuring method and a step measuring device capable of accurately measuring a step on the surface of a sample containing a transparent film.

It is sectional drawing which illustrates the sample which the metal film was formed on the transparent insulating film formed on the substrate. It is sectional drawing which illustrates the sample which the transparent insulating film of different film thickness was formed on the substrate with unevenness. It is a figure which illustrated the structure of the step measuring apparatus 1 which concerns on embodiment. It is a flowchart which illustrates the step measurement method which concerns on embodiment. It is sectional drawing which illustrates the sample which the step on the surface is measured by the step measuring method which concerns on embodiment. It is a flowchart which illustrates the film thickness measurement of the step measuring method which concerns on embodiment. It is a graph exemplifying the IZ curve which concerns on embodiment, the horizontal axis shows the position in the Z direction, and the vertical axis shows the brightness of standardized reflected light. It is a figure which illustrated the introduction of the Z-dependent Fresnel coefficient of the step measurement method which concerns on embodiment. It is a flowchart illustrating the introduction of the Z-dependent Fresnel coefficient of the step measurement method which concerns on embodiment. It is a figure which illustrated the optical film thickness in the introduction of the Z-dependent Fresnel coefficient of the step measuring method which concerns on embodiment. It is a figure which illustrated the optical interface position in the introduction of the Z-dependent Fresnel coefficient of the step measuring method which concerns on embodiment. It is a figure exemplifying the Fresnel coefficient in the introduction of the Z-dependent Fresnel coefficient of the step measurement method which concerns on embodiment. It is a figure exemplifying the Z-dependent Fresnel coefficient in the introduction of the Z-dependent Fresnel coefficient of the step measurement method which concerns on embodiment. It is a flowchart which illustrates the determination of the shift amount of the step measurement method which concerns on embodiment. It is a figure which illustrated the synthesis of the Z-dependent Fresnel coefficient of the step measurement method which concerns on embodiment. It is a figure which exemplifies the absolute reflectance calculated from the square of the absolute value of the combined extended Fresnel coefficient of the step measuring method which concerns on embodiment. It is sectional drawing which illustrates the sample of Example 1 which concerns on Embodiment. It is a graph exemplifying the IZ curve of Example 1 which concerns on embodiment, the horizontal axis shows the position in the Z direction, the vertical axis (left) shows the luminance, and the vertical axis (right) shows the frennel of each interface. Shows the absolute value of the coefficient. It is sectional drawing which illustrates the sample of Example 2 which concerns on Embodiment. It is a graph exemplifying the IZ curve of Example 2 which concerns on embodiment, the horizontal axis shows the position in the Z direction, the vertical axis (left) shows the luminance, and the vertical axis (right) shows the frennel of each interface. Shows the absolute value of the coefficient. It is sectional drawing which illustrates the sample of Example 3 which concerns on Embodiment. It is a graph exemplifying the IZ curve of Example 3 which concerns on embodiment, the horizontal axis shows the position in the Z direction, the vertical axis (left) shows the luminance, and the vertical axis (right) shows the frennel of each interface. Shows the absolute value of the coefficient. It is sectional drawing which illustrates the sample of Example 4 which concerns on Embodiment. It is a graph exemplifying the IZ curve of Example 4 which concerns on embodiment, the horizontal axis shows the position in the Z direction, the vertical axis (left) shows the luminance, and the vertical axis (right) shows the frennel of each interface. Shows the absolute value of the coefficient. It is a graph exemplifying the IZ curve of Example 5 which concerns on embodiment, the horizontal axis shows the position in the Z direction, the vertical axis (left) shows the luminance, and the vertical axis (right) shows the frennel of each interface. Shows the absolute value of the coefficient. It is explanatory drawing for deriving the average incident angle factor which concerns on embodiment. It is explanatory drawing for deriving the average phase difference which concerns on embodiment. It is a figure which exemplifies the relationship between the step measuring method and the film thickness measuring method which concerns on the modification of embodiment, and an NA objective lens. It is explanatory drawing which illustrates the film thickness measurement in the step measurement method which concerns on the modification of embodiment.

Hereinafter, a specific configuration of the present embodiment will be described with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, those with the same reference numerals indicate substantially the same contents.

(Embodiment)
The step measuring device and the step measuring method according to the embodiment will be described. First, the configuration of the step measuring device will be described. After that, a step measuring method using a step measuring device will be described.
(Step measuring device)

The configuration of the step measuring device 1 according to the present embodiment will be described. FIG. 3 is a diagram illustrating the configuration of the step measuring device 1 according to the embodiment. As shown in FIG. 3, the step measuring device 1 according to the present embodiment includes a light source 11, an interference filter 12, lenses 13a, 13b, 13c, a slit 14, a beam splitter 15, a vibration mirror 16, an objective lens 17, and a stage 18. It includes a photodetector 19 and a processing unit 30. The light source 11 and the interference filter 12 constitute a light source unit 10. The lenses 13a, 13b, 13c, the slit 14, the beam splitter 15, the vibration mirror 16, and the objective lens 17 constitute the cofocal optical system 20. The sample 40 is placed on the stage 18. The step measuring device 1 is a device for measuring the step on the surface of the sample 40 including the portion where the transparent film is exposed. The transparent film means a film that transmits at least a part of illumination light having a predetermined wavelength.

The light source 11 is, for example, a xenon lamp having a wide continuous spectrum in the ultraviolet to infrared region (185 nm to 2000 nm). The xenon lamp is useful for making a qualitative judgment because a natural interference color distribution can be observed when capturing a color review image other than a single wavelength image. Further, the light source 11 may generate white light including a plurality of emission lines in a continuous spectrum such as a mercury xenon lamp. The light source 11 is not limited to a xenon lamp, but may be a white diode, a white laser, or the like. It is preferable that the wavelength of the light source 11 can be selected. The light source 11 is not limited to visible light as long as it can be detected by the photodetector 19.

The light emitted from the light source 11 may pass through the interference filter 12 and be converted into light having a specific wavelength. The interference filter 12 is, for example, a plurality of bandpass filters that selectively transmit light having a specific wavelength. As a result, a plurality of single wavelength illumination lights are selectively transmitted. For example, as the wavelength of the illumination light, 405 nm, 436 nm, 546 nm, 578 nm, which are wavelengths corresponding to the emission line of the mercury xenon lamp, and 486 nm, 514 nm, 633 nm, which are not the emission lines of the mercury xenon lamp, can be selected. When using a mercury xenon lamp, it is also possible to select light having a wavelength other than the wavelength corresponding to the emission line with a filter. Since the intensity of light other than the wavelength of the emission line is small, it can be balanced by widening the half width of the interference filter. The wavelength may be switched continuously or intermittently, and for example, 5 to 7 wavelengths may be selected between 400 nm and 650 nm. As described above, the step measuring device 1 includes a light source unit 10 capable of switching at least the illumination light having the first wavelength and the illumination light having the second wavelength.

A laser light source that emits a single-wavelength laser beam may be used as the light source 11, and a wavelength conversion element may be provided. For example, by generating a second harmonic, wavelength conversion of single-wavelength light incident on a wavelength conversion element can be performed. It is also possible to use a tunable wavelength laser as the light source 11. Further, a plurality of laser light sources that emit laser light having different wavelengths may be provided, and light having a desired wavelength may be selected from the plurality of laser light sources.

The confocal optical system 20 has an objective lens 17 and guides the illumination light from the light source unit 10 to the sample 40 and guides the reflected light from the sample 40 to the photodetector 19. The single-wavelength illumination light that has passed through the interference filter 12 passes through the lens 13a and is incident on the slit 14. The illumination light is shaped into a line, for example, through the slit 14. Then, the illumination light is incident on the beam splitter 15. The beam splitter 15 transmits a part of the illumination light. For example, approximately half of the illumination light passes through the beam splitter 15.

After that, the light traveling to the right in FIG. 3 is incident on the vibration mirror 16. For example, the vibration mirror 16 scans the illumination light shaped into a line in the X direction on the sample 40 in the Y direction. As a result, the surface of the sample 40 can be scanned in the XY direction. As the vibration mirror 16, for example, a galvano mirror, a polygon mirror, or the like can be used.

The illumination light reflected downward by the vibration mirror 16 is collected by the objective lens 17 and irradiated to the sample 40. The optical axis direction of the objective lens 17 may be the Z-axis direction. The sample 40 is placed on the stage 18. Then, the reflected light from the sample 40 passes through the objective lens 17 again, is reflected again by the vibration mirror 16, and is incident on the beam splitter 15. After that, about half of the incident light is reflected by the beam splitter 15 and incident on the lens 13c. The lens 13c forms an image of synthetic light on the light receiving surface of the photodetector 19. The light transmitted through the lens 13c is received by the photodetector 19.

In this embodiment, the photodetector 19 is a CCD line sensor that captures a confocal image of the sample 40. The illumination light transmitted from the light source 11 through the slit 14 is reflected by the sample 40 and detected by the CCD line sensor. A slit confocal image is captured by scanning on the sample 40 with the vibration mirror 16. In this way, the photodetector 19 detects the reflected light reflected by the illumination light on the sample 40 and acquires an image in a predetermined region of the sample 40. If the method of the confocal optical system is used, the scanning method and the like may be different, and the slit and the photodetector suitable for the method can be appropriately used. For example, a vibration mirror for scanning in the X direction and the Y direction may be used, or an AOD which is an acoustic optical element may be used in the X direction.

The stage 18 has a Z-axis drive motor (not shown), and the sample 40 can be moved in the vertical direction of FIG. The stage 18 is controlled so that the sample surface comes to the focal position by moving in the Z-axis direction. Instead of moving the stage 18 in the Z direction, the objective lens 17 can be moved to adjust the focal position.

In the confocal optical system 20, it is conceivable that the focal position changes when the observation wavelength is changed, and the change in luminance is expected due to this. This is to measure the deviation of the focal position of each wavelength in advance and store it in the PC, and when switching wavelengths, automatically fine-tune the Z position of the sample 40 or the objective lens 17 by the deviation. You can cancel with. Alternatively, omnifocal images may be produced by Z-scan at each wavelength. The wavelength dependence of the observation optical system itself can be corrected by calculation by measuring in advance a sample having a known reflection spectrum, such as silicon or quartz glass.

The processing unit 30 changes the position of the objective lens 17 with respect to the sample 40. For example, the processing unit 30 moves the stage 18 in the Z-axis direction to perform a Z scan. The processing unit 30 may move the objective lens 17 in the Z-axis direction for Z-scanning.

In the present invention, the reflectance is measured while switching the illumination wavelength using a confocal microscope. The processing unit 30 measures the reflectance from the images obtained by the respective photodetectors 19 when the illumination light having a plurality of different wavelengths is irradiated. Then, the film thickness of the thin film formed on the substrate is calculated. That is, in order to calculate the film thickness of the thin film, the processing unit 30 uses an image (first image) with illumination light of a certain wavelength (first wavelength) and an image (second wavelength) with illumination light having a different wavelength (second wavelength). Based on the second image), the measurement data of the reflectance for each wavelength is obtained. Then, the processing unit 30 approximates the film thickness of the thin film from the measurement data by referring to the calculation data in which the relationship between the wavelength and the reflectance is shown for each film thickness of the thin film.

(Step measurement method)
Next, a step measuring method using the step measuring device 1 will be described. In the step measuring method of the present embodiment, the step on the surface of the sample 40 is measured. FIG. 4 is a flowchart illustrating an example of a step measuring method according to an embodiment. As shown in FIG. 4, the step measurement method of the present embodiment includes measurement of pseudo step (step S11), measurement of film thickness (step S12), determination of IZ curve and Z-dependent function (step S13), and Z dependence. It is divided into steps of introducing the Fresnel coefficient (step S14), determining the shift amount (step S15), and calculating the correction step (step S16). Hereinafter, they will be described in sequence.

(Measurement of pseudo step: Step S11)
As shown in step S11 of FIG. 4, the pseudo step on the surface of the sample 40 is measured. First, the sample 40 will be described. FIG. 5 is a cross-sectional view illustrating the sample 40 in which the step on the surface is measured by the step measuring method according to the embodiment.

As shown in FIG. 5, the sample 40 includes a substrate 41, a transparent film 42, and an opaque film 43. The substrate 41 is, for example, a glass substrate, a silicon substrate, or the like. The substrate 41 is not limited to a glass substrate, a silicon substrate, or the like.

The transparent film 42 is formed on the substrate 41. The transparent film 42 refers to a film that transmits at least a part of illumination light having a predetermined wavelength. The transparent film 42 may be a multilayer film in which a plurality of transparent layers LY1 to 42d are laminated. Each layer LY1 to 42d of the multilayer film contains a transparent film 42.

The opaque film 43 is, for example, a metal film. The opaque film 43 is formed on the transparent film 42. The opaque film 43 is partially formed on the transparent film 42. Therefore, the surface of the sample 40 includes a portion where the transparent film 42 is exposed. As described above, in the step measuring method of the present embodiment, the step on the surface of the sample 40 including the exposed portion of the transparent film 42 is measured. That is, the length in the stacking direction between the upper surface of one film constituting the step and the upper surface of the other film is measured. Specifically, the length of the upper surface of the opaque film 43 and the upper surface of the transparent film 42 in the stacking direction is measured.

Here, for the convenience of explaining the step measurement method, an XYZ orthogonal coordinate axis system is introduced. The stacking direction of the transparent film 42 of the sample 40 is the Z-axis direction, the direction from the substrate 41 to the surface is the + Z-axis direction, and the opposite direction is the −Z-axis direction. The direction along the edge of the opaque film 43 in the plane orthogonal to the Z-axis direction is defined as the Y-axis direction. The direction orthogonal to the Y-axis direction in the plane orthogonal to the Z-axis direction is defined as the X-axis direction. The optical axis of the objective lens 17 is along the Z-axis direction.

Most of the reflected light reflected on the upper surface of the opaque film 43 is reflected on the upper surface of the opaque film 43. Therefore, when the position of the objective lens 17 with respect to the sample 40 is changed along the optical axis direction of the objective lens 17, the position showing the maximum brightness of the reflected light is the position showing the upper surface of the opaque film 43. As described above, the opaque film 43 is a film in which most of the reflected light is reflected light on the upper surface, and the position showing the maximum brightness of the reflected light is the position showing the upper surface.

On the other hand, in the portion where the transparent film 42 is exposed, the illumination light passes through the transparent film 42. Therefore, the reflected light includes the reflected light reflected on the surface of the transparent film 42 and the reflected light reflected on the lower surface of the transparent film 42 and the interface between the layers LY1 to 42d. Therefore, the Z position indicating the maximum brightness of the reflected light from the transparent film 42 is measured deviating from the position indicating the upper surface of the actual transparent film 42.

Then, the step between the upper surface of the opaque film 43 and the upper surface of the transparent film 42 includes a deviation in the actual step. The step measured by deviating from the actual step is called a pseudo step ha. The deviation between the actual step h0 and the pseudo step ha is called the shift amount Zd. Therefore, the shift amount Zd is the peak position of the brightness of the reflected light when the position in the Z direction with respect to the actual outermost surface of the transparent film 42 is set to 0.

As described above, in the measurement of the pseudo step ha, when the Z position of the objective lens 17 with respect to the sample 40 is changed along the optical axis direction of the objective lens 17 of the confocal optical system 20, the illumination light is the sample 40. The pseudo step ha on the surface of the sample 40 is measured from the difference in the position showing the peak of the brightness of the reflected light reflected in. Specifically, the processing unit 30 changes the position of the objective lens 17 with respect to the sample 40 along the optical axis direction of the objective lens 17 to perform Z scanning. Then, the processing unit 30 measures the pseudo step ha on the surface of the sample 40 from the difference in the position where the illumination light shows the peak of the brightness of the reflected light reflected by the sample 40. The measurement conditions are a single wavelength using a relatively high NA lens, the wavelength is, for example, 546 [nm], and the NA of the objective lens 17 is 0.9.

(Measurement of film thickness: step S12)
Next, as shown in step S12 of FIG. 4, the film thickness of the transparent film 42 of the sample 40 is measured. The film thickness of the transparent film 42 is, for example, the method disclosed in Patent Document 1 and is obtained from a omnifocal image using illumination light having 6 wavelengths. The method for measuring the film thickness of the transparent film 42 of the sample 40 is not limited to the method disclosed in Patent Document 1.

FIG. 6 is a flowchart illustrating the film thickness measurement of the step measuring method according to the embodiment. As shown in step S21 of FIG. 6, when measuring the film thickness of the transparent film 42, the processing unit 30 gives the sample 40 the illumination light of the first wavelength and the second wavelength via the confocal optical system 20. It irradiates by switching with the illumination light of. Next, as shown in step S22, the reflected light reflected by the sample 40 is detected via the confocal optical system 20, and the first image by the light of the first wavelength and the second image by the light of the second wavelength are detected. Get the image and. Next, as shown in step S23, in order to calculate the film thickness of the transparent film 42, the measurement data of the reflectances for the first wavelength and the second wavelength are obtained based on the first image and the second image, respectively. Ask. Next, as shown in step S24, the film thickness of the thin film is approximately calculated from the measurement data with reference to the calculation data in which the relationship between the wavelength and the reflectance is shown for each film thickness of the thin film.

If the film thickness of the transparent film 42 of the sample 40 is known, the value of the film thickness may be used. The objective lens 17 may be a high NA objective lens 17 used for measuring the pseudo step ha, or a low NA objective lens different from the objective lens 17 used for measuring the pseudo step ha.

(Determination of IZ curve and Z-dependent function: step S13)
Next, as shown in step S13 of FIG. 4, the IZ curve and the Z-dependent function are determined. The IZ curve is a curve showing the relationship between the brightness I of the reflected light from the sample 40 and the position in the optical axis direction. The IZ curve and the Z-dependent function are determined, for example, for the member that reflects on the outermost surface. For example, when determining the IZ curve, the Lorentz function shown in the following equation (1) is used as the IZ curve.

The processing unit 30 optimizes the parameters A, B, and C in the equation (1) and fits them to the measured values to determine the IZ curve showing the relationship between the luminance I and the position. For example, the Lorentz function is determined as an IZ curve showing the relationship between the brightness and the position in the optical axis direction. The brightness is normalized by the following equation (2). Further, as the IZ curve showing the relationship between the luminance and the position in the optical axis direction, for example, a Gaussian function may be used instead of the Lorentz function, or any function capable of reproducing the measured value may be used. Further, a reference table that can reproduce the measured values may be used.

Next, as shown in the following equation (3), the square root of the IZ curve is defined as a Z-dependent function. In this way, the Z-dependent function is determined.

FIG. 7 is a graph illustrating the IZ curve and the Z-dependent function according to the embodiment. The horizontal axis indicates the position in the Z-axis direction, that is, the position of the objective lens 17 in the optical axis direction, and the vertical axis is standardized. Indicates the brightness of the reflected light. On the horizontal axis, the position where the luminance I peaks is defined as Z = 0. The vertical axis indicates the brightness I of the reflected light. In FIG. 7, f (Z) showing the IZ curve is, for example, a Lorentz function. F (Z) indicates a Z-dependent function.

(Introduction of Z-dependent Fresnel coefficient: step S14)
Next, as shown in step S14 of FIG. 4, the Z-dependent Fresnel coefficient is introduced. FIG. 8 is a diagram illustrating the introduction of the Z-dependent Fresnel coefficient of the step measurement method according to the embodiment. The Z-dependent Frenel coefficient is the product of the Z-dependent function at the optical interface position calculated using the film thickness and refractive index of the transparent film 42 and the Frenel coefficient of the transparent film 42 at the optical interface position. say.

The outline of the introduction of the Z-dependent Fresnel coefficient will be described with reference to FIG. First, using the physical film thickness t _j (j = 1 to 4) and the complex refractive index N _j (j = 1 to 4) of the transparent film 42, the optical film thickness _dj (j) of the transparent film 42 is used. = 1 to 4) are calculated. As shown in FIG. 8, the complex refractive index N ₀ of air, the complex refractive index N ₁ of the layer LY 1 of the transparent film 42, the complex refractive index N ₂ of the layer LY 2, the complex refractive index N ₃ of the layer LY 3, and the layer LY 4. The complex refractive index N ₄ and the complex refractive index _NS of the substrate 41 are as follows (4) to (9). Note that n ₀ , n ₁ , etc. are refractive indexes, k ₁ , k ₂ and the like are extinction coefficients, and i is an imaginary unit.

Further, in the layers LY1 to LY4, when the physical film thickness t _j (j is 1 to 4) of each layer LY is used, the optical film thickness _dj (j is 1 to 4) of each layer LY is as follows (j is 1 to 4). 10) Equation.

Further, using the optical film thickness _dj , the optical interface positions _{pj and j + 1} (j is 1 to 4) of the transparent film 42 are calculated. The optical interface positions pj and _{j + 1} (j are 1 to 4) at the interface of each layer LY and the interface between the layer LY4 and the substrate 41 are given by the following equation (11). Here, the interface (0, 1) is the upper surface of the transparent film 42, that is, the upper surface of the layer LY1. The interface (1, 2) is the interface between the layer LY1 and the layer LY2. The interface (2, 3) is the interface between the layer LY2 and the layer LY3. The interface (3, 4) is the interface between the layer LY3 and the layer LY4. The interface (4, 5) is the interface between the layer LY4 and the substrate 41.

The Z-dependent Frenel coefficient is calculated from the product of the Z-dependent function of the amplitude at the optical interface positions p _{j and j + 1} calculated in this way and the Frenel coefficient of the transparent film 42 at the optical interface positions p _{j and j + 1} . Introduce.

Next, the details of the introduction of the Z-dependent Fresnel coefficient will be described. FIG. 9 is a flowchart illustrating the introduction of the Z-dependent Fresnel coefficient of the step measurement method according to the embodiment. FIG. 10 is a diagram illustrating an optical film thickness in the introduction of the Z-dependent Fresnel coefficient of the step measuring method according to the embodiment. FIG. 11 is a diagram illustrating the optical interface position in the introduction of the Z-dependent Fresnel coefficient of the step measuring method according to the embodiment. FIG. 12 is a diagram illustrating the Fresnel coefficient in the introduction of the Z-dependent Fresnel coefficient of the step measuring method according to the embodiment. FIG. 13 is a diagram illustrating the Z-dependent Fresnel coefficient in the introduction of the Z-dependent Fresnel coefficient of the step measuring method according to the embodiment.

As shown in step S31 of FIG. 9, the optical film thickness _dj of the transparent film 42 is calculated using the physical film thickness and the refractive index of the transparent film 42. As shown in FIG. ₁₀ , the optical film thicknesses d1 to dL of the layers LY1 to _LYL are the following equations (12) to (15). Equation (14) is a generalized equation.

Here, assuming that the incident angle at the interface (j-1, j) is θ _j-1 , and the refraction angle is θ _j , the incident angle factor β _j and the incident angle average <β _j > are obtained by the following equation (16) and It becomes equation (17). The incident angle factor β _j and the incident angle average <β j> will be described later, but the incident angle average <β j> indicates the average of the incident angles 0 [radian] to NA with respect to the NA of the objective lens 17. ..

Next, as shown in step S32 of FIG. 9, the optical interface positions _{pj and j + 1} are calculated using the optical film thickness _dj . The optical interface positions _{pj and j + 1} are interface positions in consideration of the change in film thickness due to refraction. As shown in FIG. 11, the upper surface p0, 1, of the transparent film 42, that is, the optical interface position p0, ₁ of the layer LY1 is p0, ₁ = ₀ as shown in the following equation (18). be. Therefore, it is the same surface as the actual upper surface. Optical interface positions p1, ₂ between layer LY1 and layer LY2, optical interface positions p2, ₃ between layer LY2 and layer LY3, optical interface positions pj _{, j + 1} , layer LYL between layer LYj and layer LYj + 1. The optical interface positions p _{L and S} between the substrate 41 and the substrate 41 are given by the following equations (19) to (22).

Next, as shown in step S33 of FIG. 9, the Fresnel coefficient is calculated. As shown in FIG. 12, the upper surface p0, ₁ of the transparent film 42, that is, the Fresnel coefficient r0, ₁ on the upper surface p0, 1 of the layer _LY1 is as shown in the following equation (23). Fresnel coefficient r1, ₂ at the optical interface position p1, ₂ between the layer LY1 and the layer LY2, Fresnel coefficient r2, ₃ at the optical interface position p2, ₃ between the layer LY2 and the layer LY3, and the layer LYj and the layer. The optical interface positions p _j with LYj + 1, the Fresnel coefficients r _{j, j + 1} at j + 1, the optical interface positions p _L between the layer LYL and the substrate 41, and the Fresnel coefficients r _{L, S at S} are as follows (24) to ( 27) Equation.

Next, as shown in step S34 of FIG. 9, the Z-dependent Fresnel coefficient is introduced from the product of the Fresnel coefficient at the optical interface position and the Z-dependent function at the optical interface position. As shown in FIG. 13, the Z-dependent Fresnel coefficients r0, ₁ (Z) at the upper surface p0, 1, that is, the optical interface position _p0 , 1 of the layer _LY1 of the transparent film 42 are as follows (28). It becomes like an expression. Z-dependent Fresnel coefficient r1 and ₂ (Z) at the optical interface position p1 and ₂ between the layer LY1 and the layer LY2, and Z-dependent Fresnel coefficient r2 at the optical interface position p2 and ₃ between the layer LY2 and the layer _LY3 . _3, (Z), the optical interface position p _j between the layer 42j and the layer 42j + 1, the Z-dependent Fresnel coefficients r _{j, j + 1} (Z) at j + 1, and the optical interface position p _{L, S} between the layer LYL and the substrate 41. The Z-dependent Fresnel coefficients r _{L and S} (Z) are given by the following equations (29) to (27).

In this way, the complex Fresnel coefficient r at each optical interface position is calculated and once separated into the absolute value | r | of the Fresnel coefficient and the phase term e (iΦ). Then, the Z-dependent function F (Z) is introduced into the absolute value term. The phase term is left as it is. In this way, a new Z-dependent Fresnel coefficient r (Z) is defined with respect to the conventional Fresnel coefficient r.

(Determination of shift amount: step S15)
Next, as shown in step S15 of FIG. 4, the shift amount is determined. In the processing unit 30, the reflectance calculated from the square of the absolute value of the synthetic Z-dependent Fresnel coefficient _r'0 , 1 (Z) of the entire structure obtained by synthesizing all the Z-dependent Fresnel coefficients at each optical interface position is the optical axis. The shift amount is determined from the position showing the peak in the axial direction.

FIG. 14 is a flowchart illustrating determination of the shift amount of the step measuring method according to the embodiment. In order to determine the shift amount, first, as shown in step S41 of FIG. 14, the synthetic Fresnel coefficient is calculated. FIG. 15 is a diagram illustrating the synthesis of the Z-dependent Fresnel coefficient of the step measurement method according to the embodiment. As shown in FIG. 15, the Z-dependent Fresnel coefficients _r'0 , ₁ (Z) at the upper surface p0, 1, that is, the optical interface position p0, ₁ of the layer LY1 of the transparent film 42 are as follows (33). ), It is synthesized by using the Z-dependent Fresnel coefficients _r'1 , ₂ of the optical interface positions p1 and 2 of the lower layer. The Z-dependent Fresnel coefficients r'1, ₂ (Z) at the optical interface positions p1 and ₂ between the layer LY1 and the layer LY2 are the optical interface positions _p'2 of the lower layer as shown in the following equation (34). ₃ is used for synthesis. Hereinafter, the Fresnel coefficients r'j and _{j + 1} (Z) at the optical interface positions pj and _j + 1 between the layer LYj and the layer LYj + 1 use the lower layer r'j + 1 and _{j + 2} as shown in the following equation (35). It will be synthesized. The Z-dependent Fresnel coefficients r'L and S (Z) at the optical interface positions p _{L and S} between the layer LYL and the substrate 41 are r _{L and S} (Z) as shown in the following equation (36). .. In this way, the Z-dependent Fresnel coefficients are synthesized in order from the bottom layer substrate 41 to the outermost surface. This makes it possible to calculate the Z-dependent Fresnel coefficient of the structure of the entire transparent film 42.

Here, _Δj is the following equation (37).

δ _j and γ _j are the following equations (38) and (39).

< _Αjn > and _<αjk ^> are the following equations ⁽ 40) and (41), which are the angular averages of the terms depending on the incident angle in the phase difference and the absorption coefficient. Will be described later.

Next, as shown in step S42 of FIG. 14, the square of the absolute value of the synthetic Fresnel coefficient is calculated, and the absolute reflectance is calculated. FIG. 16 is a diagram illustrating an absolute reflectance calculated from the square of the absolute value of the synthesized synthetic Fresnel coefficient of the step measuring method according to the embodiment. As shown in FIG. 16, the absolute reflectance is calculated by the square of the absolute value of the synthetic Fresnel coefficient of all layers. The IZ curve can be obtained by calculating the Z dependence of the reflectance of the entire structure. That is, the electric field amplitude (Fresnel coefficient) at each interface is synthesized, and the reflectance is calculated from the square of the absolute value of the synthesized combined Fresnel coefficient. The shift amount Zd can be obtained from the difference between the position pmax at which the luminance I has the maximum value Imax and the optical interface positions p0 and ₁ . In this way, as shown in step S43 of FIG. 14, the shift amount Zd is determined.

(Calculation of correction step: step S16)
Next, as shown in step S16 of FIG. 4, the correction step h ₀ is calculated. For example, the processing unit 30 derives an actual step from the pseudo step ha and the shift amount Zd. Specifically, as shown in the equation (42), the processing unit 30 adds the shift amount Zd to the pseudo step ha.

In this way, the step h ₀ on the surface of the sample 40 can be measured.

Next, Examples 1 to 5 to which this embodiment is specifically applied will be described. Examples 1 to 3 show a calculation example of the shift amount Zd when the material (refractive index) and the thickness of each layer LY in the transparent film 42 are given. In Examples 4 and 5, a comparison with the corrected step h ₀ when a known step is given is shown.

(Example 1)
First, the first embodiment of the present embodiment will be described. FIG. 17 is a cross-sectional view illustrating the sample 40a of Example 1 according to the embodiment. FIG. 18 is a graph illustrating the IZ curve of the first embodiment according to the embodiment, in which the horizontal axis indicates the position in the Z direction, the vertical axis (left) indicates the luminance, and the vertical axis (right) indicates the brightness. The absolute value of the Fresnel coefficient at each interface is shown.

As shown in FIG. 17, in the sample 40 of Example 1, the transparent film 42 formed on the glass substrate 41 is, from above, a layer LY1 containing a silicon nitride film, a layer LY2 containing a silicon oxide film, and silicon nitride. It has a layer LY3 including a film and a layer LY4 including a silicon oxide film. The thicknesses of layer LY1, layer LY2, layer LY3 and layer LY4 are 300 [nm], 300 [nm], 100 [nm] and 100 [nm], respectively. A metal layer containing aluminum is formed on the transparent film 42 as an opaque film 43.

As the condition of Example 1, a value of 546 [nm] is used as the optical constant. The refractive indexes of air, silicon oxide, silicon nitride, and glass are 1,1.4600979, 2.0313239, and 1.5187272, respectively. The extinction coefficient k is 0 for all materials. Approximated by the Lorentz function as an IZ curve, the parameters A, B and C are 1, pi _{, j + 1} and 0.55, respectively. As the measurement parameters, the NA of the objective lens is 0.9, and the wavelength of the illumination light is 546 [nm].

As shown in FIG. 18, the position where the reflectance calculated from the square of the absolute value of the synthesized Z-dependent Fresnel coefficient shows a peak in the optical axis direction is shifted from the position on the upper surface of the transparent film 42. The shift amount Zd is −0.17 [μm].

(Example 2)
Next, Example 2 will be described. FIG. 19 is a cross-sectional view illustrating the sample 40b of Example 2 according to the embodiment. FIG. 20 is a graph illustrating the IZ curve of the second embodiment according to the embodiment, in which the horizontal axis indicates the position in the Z direction, the vertical axis (left) indicates the brightness, and the vertical axis (right) indicates the brightness. The absolute value of the Fresnel coefficient at each interface is shown.

As shown in FIG. 19, in the sample 40 of Example 2, the transparent film 42 formed on the glass substrate 41 is, from above, a layer LY1 containing a silicon oxide film, a layer LY2 containing a silicon nitride film, and silicon oxide. It has a layer LY3 including a film and a layer LY4 including a silicon nitride film. The thicknesses of layer LY1, layer LY2, layer LY3 and layer LY4 are 300 [nm], 300 [nm], 100 [nm] and 100 [nm], respectively. A metal layer containing aluminum is formed on the transparent film 42 as an opaque film 43. The conditions of Example 2 are the same as those of Example 1. As shown in FIG. 20, the shift amount Zd is −0.48 [μm].

(Example 3)
Next, Example 3 will be described. FIG. 21 is a cross-sectional view illustrating the sample 40c of Example 3 according to the embodiment. FIG. 22 is a graph illustrating the IZ curve of Example 3 according to the embodiment, in which the horizontal axis indicates the position in the Z direction, the vertical axis (left) indicates the brightness, and the vertical axis (right) indicates the brightness. The absolute value of the Fresnel coefficient at each interface is shown.

As shown in FIG. 21, in the sample 40 of Example 3, the transparent film 42 formed on the glass substrate 41 is, from above, a layer LY1 containing a silicon nitride film, a layer LY2 containing a silicon oxide film, and a layer LY2. It has a layer LY3 including a silicon nitride film. The thicknesses of the layer LY1, the layer LY2, and the layer LY3 are 300 [nm], 400 [nm], and 100 [nm], respectively. A metal layer containing aluminum is formed on the transparent film 42 as an opaque film 43. The conditions of Example 3 are the same as those of Example 1. As shown in FIG. 22, the shift amount Zd is +0.02 [μm].

(Example 4)
Next, Example 4 will be described. FIG. 23 is a cross-sectional view illustrating the sample 40d of Example 4 according to the embodiment. FIG. 24 is a graph illustrating the IZ curve of Example 4 according to the embodiment, in which the horizontal axis indicates the position in the Z direction, the vertical axis (left) indicates the brightness, and the vertical axis (right) indicates the brightness. The absolute value of the Fresnel coefficient at each interface is shown.

As shown in FIG. 23, in the sample 40 of Example 4, the transparent film 42 formed on the silicon substrate 41 has a layer LY1 including a silicon oxide film. The result of measuring the thickness of the layer LY1, that is, the actual step, by another method is 395 [nm]. The pseudo step ha actually measured by the confocal optical system 20 of the present embodiment is 0.226 [μm]. The calculation result of the shift amount is −0.18 [μm]. Therefore, the step derived from the pseudo step ha and the shift amount Zd is 0.406 [μm]. The difference between this value and the actual step of 395 [μm] is +0.011 [μm], which is a good agreement. In this embodiment, since the upper stage of the step shifts by Zd and the lower stage does not shift, h0 = ha-Zd. Therefore, h0 = 0.226- (−0.18) = 0.406.

(Example 5)
Next, Example 5 will be described. FIG. 25 is a graph illustrating the IZ curve of Example 5 according to the embodiment, where the horizontal axis indicates the position in the Z direction, the vertical axis (left) indicates the luminance, and the vertical axis (right) indicates the brightness. The absolute value of the Fresnel coefficient at each interface is shown.

The configuration of the sample of Example 5 has the layer LY1 containing the silicon oxide film on the silicon substrate 41 as in the sample of Example 4. The result of measuring the thickness of the layer LY1, that is, the actual step by another method, is 993 [nm], unlike the fourth embodiment. The pseudo step ha actually measured by the confocal optical system 20 of the present embodiment is 0.457 [μm]. The calculation result of the shift amount Zd is −0.53 [μm]. Therefore, the step derived from the pseudo step ha and the shift amount Zd is 0.987 [μm]. The difference between this value and the actual step of 993 [μm] is +0.006 [μm], which is a good agreement. Similar to the above, since the upper stage of the step shifts by Zd and the lower stage does not shift, h0 = ha-Zd. Therefore, h0 = 0.457- (−0.53) = 0.987.

(Calculation of <β _j >)
Next, the above-mentioned calculation of <β _j >, the calculation of <α _j ⁿ >, and the calculation of <α _j ^k > will be described. First, equation (17) for β _j is derived. FIG. 26 is an explanatory diagram for deriving the average incident angle factor according to the embodiment. As shown in FIG. 26, the incident angle is θ _j-1 , and the refraction angle is θ _j . The refractive index of the layer having the physical film thickness t _j is n _j , and the refractive indexes of the upper and lower layers of the layer are n _j-1 and n _{j + 1} . The numerical aperture of the objective lens is NA. Then, the following equations (43) and (44) are established.

Therefore, equation (17) is derived as follows. Since the angle of incidence on the interface includes 0 to θ _j-1 ^m , β _j can be an angular average <β _j > as shown in the following equation (40).

(Calculation of <α _j ⁿ >)
Next, the calculation of <α _j ⁿ > will be described. FIG. 27 is an explanatory diagram for deriving the average phase difference according to the embodiment. As shown in FIG. 27, the optical distance of the upper surface reflection of the layer and the optical distance of the lower surface reflection of the layer are the following equations (46) and (47).

Then, the phase difference due to the optical path difference between the upper surface and the lower surface of the film due to the incident angle becomes the following equations (48) and (49).

The terms depending on the incident angle can be angle-averaged and used as the average phase difference as shown in the following equation (50).

(Calculation of <α _j ^k >)
Next, the calculation of <α _j ^k > will be described. As shown in FIG. 27, the following equation (51) holds.

入射角による層内を通過する行路長による吸収は、以下の（５２）式になる。

Absorption by the path length passing through the layer due to the incident angle is given by the following equation (52).

The terms depending on the angle of incidence can be angle-averaged and used as average absorption as shown in Eq. (53).

Next, the effect of this embodiment will be described.
In the present embodiment, the pseudo step ha on the surface of the sample 40 including the transparent film 42 measured by the confocal optical system 20 can be corrected by the shift amount Zd calculated using the Z-dependent Frenel coefficient. As a result, the level difference on the surface of the sample 40 including the transparent film 42 can be measured with high accuracy.

Z dependence is introduced into the amplitude reflection from each interface of the multilayer film structure. Thereby, the position of the maximum brightness in the Z direction can be predicted in consideration of the multiple reflection and the interference effect inside the multilayer film. Therefore, the shift amount Zd between the pseudo step ha and the actual step h ₀ can be calculated accurately, and the step h ₀ can be measured accurately.

The Z-dependent Fresnel coefficient includes a Z-dependent function that indicates the relationship between the luminance and the position in the Z direction. Therefore, it can be made dependent on the position in the Z direction, and the shift amount Zd can be calculated.

To measure the film thickness of the transparent film 42, a method obtained from an omnifocal image using illumination light of 6 wavelengths is used. This makes it possible to measure the film thickness with high accuracy. In the film thickness measuring method used in this embodiment, a film sufficiently thin with respect to the depth of focus is preferable. Then, it is preferable to measure the pseudo step with an objective lens having a high NA and to measure the film thickness with an objective lens having a low NA.

The Lorentz function is used as the IZ curve. The square root of the Lorentz function is used as the Z-dependent function. Therefore, the measured IZ curve can be fitted well.

(Modification example)
Next, a film thickness measuring method will be described as a modification of the present embodiment. FIG. 28 is a diagram illustrating the relationship between the step measuring method and the film thickness measuring method according to the modified example of the embodiment and the NA of the objective lens. FIG. 29 is an explanatory diagram illustrating the film thickness measurement according to the modified example of the embodiment.

As shown in FIG. 28, the step measuring method of the embodiment is based on the principle of the confocal optical system, and uses an objective lens having a relatively high NA. Thereby, the pseudo step on the surface of the sample 40 including the multilayer film in which the transparent film is laminated in multiple layers is measured. Then, the step can be measured using the shift amount calculated from the Z-dependent Fresnel coefficient.

On the other hand, the film thickness measurement is based on the principle of reflection spectroscopy, and a high NA objective lens or a low NA objective lens may be used. In the film thickness measurement, the reflectance can be calculated, and in the case of an objective lens having a high NA, the Fresnel coefficient can be improved to measure the film thickness.

As shown in FIG. 29, the first method for analyzing the film thickness uses an actual step as known information, a pseudo step as a measured value, and a shift amount as a reference value. Then, the shift amount is calculated using the film thickness as a parameter, and the film thickness is determined so that the shift amounts match. As described above, in the first method, the film thickness can be measured from the actual step and the pseudo step by using the method opposite to the step measurement of the embodiment.

The second method for analyzing the film thickness uses an IZ curve obtained by XZ cross-sectional measurement as a measured value and an IZ curve as a reference value. Then, the film thickness is determined so that the measured IZ curve matches the IZ curve obtained in advance.

XZ cross-section measurement is one of the measurement modes of the confocal microscope. In this measurement, the luminance data in the X direction of the screen is Z-scanned, the horizontal axis is in the X direction, and the vertical axis is in the Z direction, and the luminance is expressed in gray scale on the screen. A plot of the Z coordinate and the luminance I for any point X is an actually measured IZ curve. The film thickness can be calculated by fitting the simulated calculated IZ curve to the measured measured IZ curve.

In the measured IZ curve, the position in the Z direction is a relative value, so that the slide amount in the Z direction may be used as a parameter at the time of fitting. Further, the luminance I may be multiplied by a coefficient so that the shapes of the IZ curves match in a similar shape. If the measured measured IZ curve and the simulated calculated IZ curve have similar figures, the measured film structure and film thickness are the film structure and film thickness used in the simulation.

As described above, in the second method, when measuring the film thickness, the IZ curve showing the relationship between the brightness of the reflected light and the position in the optical axis direction is measured, and a plurality of film thicknesses assumed for the transparent film are obtained. Prepare a simulated reflectance IZ curve using the Z-dependent Frenel coefficient in the case of, and fit the calculated IZ curve to the measured IZ curve with the film thickness as a parameter to determine the thickness of the transparent film. Can be calculated.

In the third method of analyzing the film thickness, the reflectance of the reflected light from the illumination light having six wavelengths is used as the measured value, and the reflectance is used as the reference value. Then, by using the film thickness as a parameter and calculating the maximum luminance corresponding to the peak Z of the IZ curve calculated from the Z-dependent Fresnel coefficient as the reflectance, the film thickness can be measured by the curve fit method.

In the fourth method of analyzing the film thickness, the reflectance of the pseudo step and the reflected light from the illumination light having 6 wavelengths is used as the measured value, and the reflectance is used as the reference value. Then, the pseudo step and the film thickness are collectively measured with the same objective lens.

Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications that do not impair the purpose and advantages thereof, and is not limited by the above embodiments.

1 Step measuring device 10 Light source 11 Light source 12 Interference filter 13a, 13b, 13c Lens 14 Slit 15 Beam splitter 16 Vibration mirror 17 Objective lens 18 Stage 19 Optical detector 20 Confocal optical system 30 Processing unit 40 Sample 41 Substrate 42 Transparent Films 42a, 42b, 42c, 42d Layer 43 Opaque film 140, 140a Sample 141 Substrate 142 Insulation film 142a, 142b, 142c, 142d, 142e, 142f Layer 143 Metal film h0 Step ha Pseudo step I Brightness Zd Shift amount

Claims (10)

It is a step measurement method that measures the step on the surface of a sample including the exposed part of the transparent film.
The transparent film is a multilayer film in which a plurality of transparent layers are laminated.
When the position of the objective lens with respect to the sample is changed along the optical axis direction of the objective lens of the confocal optical system, the difference in the position showing the peak of the brightness of the reflected light reflected by the sample. From the step of measuring the pseudo step on the surface of the sample,
The step of measuring the film thickness of the transparent film and
A step of determining a Z-dependent function indicating the relationship between the luminance and the position,
The Z-dependent Fresnel coefficient of the product of the Z-dependent function at the optical interface position calculated using the film thickness and the refractive index of the transparent film and the Fresnel coefficient of the transparent film at the interface position. Steps to introduce and
Synthesis of the entire structure by synthesizing all the Z-dependent Fresnel coefficients at each of the interface positions The reflectance calculated from the square of the absolute value of the Z-dependent Fresnel coefficient shows the shift amount from the position showing a peak in the optical axis direction. Steps to decide and
The step of deriving the step from the pseudo step and the shift amount, and
Step measurement method with. The step of measuring the film thickness is
The sample is irradiated with the illumination light of the first wavelength and the illumination light of the second wavelength by switching through the confocal optical system.
The reflected light reflected by the sample is detected via the cofocal optical system, and a first image by the light of the first wavelength and a second image by the light of the second wavelength are acquired.
In order to calculate the film thickness of the transparent film, the measurement data of the reflectance for the first wavelength and the second wavelength are obtained based on the first image and the second image, respectively.
The relationship between the wavelength and the reflectance is calculated by approximating the film thickness of the transparent film from the measurement data with reference to the calculation data shown for each film thickness of the transparent film.
The step measuring method according to claim 1. The step of measuring the film thickness is
An IZ curve showing the relationship between the brightness of the reflected light reflected by the sample and the position when the position of the objective lens with respect to the sample is changed along the optical axis direction of the objective lens. Measure and
Prepare a calculated IZ curve that plots the reflectance simulated using the Z-dependent Fresnel coefficients for the plurality of film thicknesses assumed for the transparent film.
The calculated IZ curve is fitted to the measured IZ curve to calculate the film thickness of the transparent film.
The step measuring method according to claim 1. In the step of determining the Z-dependent function,
The square root of the Lorentz function is used as the Z-dependent function.
The step measuring method according to any one of claims 1 to 3. The step of introducing the Z-dependent Fresnel coefficient is
A step of calculating the optical film thickness of the transparent film using the film thickness and the refractive index of the transparent film, and
The step of calculating the optical interface position of the transparent film using the optical film thickness, and
including,
The step measuring method according to any one of claims 1 to 4. It is a step measuring device that measures the step on the surface of a sample including the exposed part of the transparent film.
The transparent film is a multilayer film in which a plurality of transparent layers are laminated.
A photodetector that detects the reflected light reflected by the sample as the illumination light,
A confocal optical system having an objective lens and guiding the illumination light to the sample and guiding the reflected light from the sample to the photodetector.
A processing unit that changes the position of the objective lens with respect to the sample along the optical axis direction of the objective lens.
Equipped with
The processing unit
A pseudo step on the surface of the sample is measured from the difference in the position where the illumination light shows the peak of the brightness of the reflected light reflected by the sample.
Measure the film thickness of the transparent film and
A Z-dependent function indicating the relationship between the luminance and the position is determined.
The Z-dependent Fresnel coefficient of the product of the Z-dependent function at the optical interface position calculated using the film thickness and the refractive index of the transparent film and the Fresnel coefficient of the transparent film at the interface position. Introduced,
Synthesis of the entire structure by synthesizing all the Z-dependent Fresnel coefficients at each of the interface positions The reflectance calculated from the square of the absolute value of the Z-dependent Fresnel coefficient shows the shift amount from the position showing a peak in the optical axis direction. Decide and
A step is derived from the pseudo step and the shift amount.
Step measuring device. The processing unit is used when measuring the film thickness of the transparent film.
The sample is irradiated with the illumination light of the first wavelength and the illumination light of the second wavelength by switching through the confocal optical system.
The reflected light reflected by the sample is detected via the cofocal optical system, and a first image by the light of the first wavelength and a second image by the light of the second wavelength are acquired.
In order to calculate the film thickness of the transparent film, the measurement data of the reflectance for the first wavelength and the second wavelength are obtained based on the first image and the second image, respectively.
The relationship between the wavelength and the reflectance is calculated by approximating the film thickness of the transparent film from the measurement data with reference to the calculation data shown for each film thickness of the transparent film.
The step measuring device according to claim 6 . The processing unit is used when measuring the film thickness.
An IZ curve showing the relationship between the brightness of the reflected light reflected by the sample and the position when the position of the objective lens with respect to the sample is changed along the optical axis direction of the objective lens. Measure and
Prepare a calculated IZ curve that plots the reflectance simulated using the Z-dependent Fresnel coefficients for the plurality of film thicknesses assumed for the transparent film.
The calculated IZ curve is fitted to the measured IZ curve to calculate the film thickness of the transparent film.
The step measuring device according to claim 6 . The Z-dependent function is the square root of the Lorentz function.
The step measuring device according to any one of claims 6 to 8 . The processing unit calculates the Z-dependent Fresnel coefficient.
Using the film thickness and the refractive index of the transparent film, the optical film thickness of the transparent film is calculated.
Using the optical film thickness, the optical interface position of the transparent film is calculated.
The step measuring device according to any one of claims 6 to 9 .

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