JPH1172308A - Method and apparatus for measurement of height - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus in which height information is obtained even if a Z-movement step is made small. SOLUTION: The relative position of an objective lens 17 to a sample 19 is changed discretely in the direction of an optical axis by a Z-direction- movement control circuit 22. Then, an inflection point, i.e., the maximum value or a minimum value, in a change in an optical intensity detected by a photodetector 21 through a pinhole 20 at this time is detected. At this time, on the basis of the relative position of the objective lens 17 to the sample 19 as the inflection point, height information on the sample 19 is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a height measuring method and a height measuring apparatus for acquiring height information of a sample using confocal.

[0002]

2. Description of the Related Art For example, in a confocal scanning optical microscope, a sample is illuminated by a point light source in a point-like manner, and transmitted light or reflected light from the sample is focused on a pinhole. The surface information of the sample is obtained by detecting the intensity with a photodetector.

FIG. 8 is a schematic configuration diagram of a general confocal scanning optical microscope. The point light emitted from the point light source 1 is
After passing through the half mirror 2, the light is focused on the sample 4 by the aberration-corrected objective lens 3.

The light reflected on the illuminated surface of the sample 4 is condensed again by the objective lens 3 and is reflected by the half mirror 2.
The reflected light is cut off by the pinhole 5 arranged at the condensing position of the objective lens 3, and the reflected light from other than the converging point on the sample 4 is cut off. Is detected.

The illumination light condensed in a dot-like manner is raster-scanned over the entire surface of the sample 4, and the density information from the photodetector 6 is displayed on a monitor in correspondence with the raster scanning. , A two-dimensional image of the surface of the sample 4 is obtained.

When a two-dimensional image of the sample 4 is obtained with such a microscope, the surface of the sample 4 is not a flat surface but also has a surface which is shifted from the condensing position of the objective lens 3 as indicated by a symbol A, for example. I do.

The light reflected from the surface A does not converge on the pinhole 5 as indicated by the broken line in the microscope, and the light reflected from a position other than the converging position of the objective lens 3 The light is not cut by the hole 5 and detected by the photodetector 6.

In view of the above, in the above-mentioned microscope, the sample 4 located at the converging position of the objective lens 3, that is, the in-focus position.
Only the optical image of the surface can be measured with high accuracy. Assume that a sample 7 having three sample surfaces A, B, and C having different heights as shown in FIG. 9 is observed with a normal optical microscope.

When the sample 7 is focused on, for example, the sample surface A, the optical images of the other sample surfaces B and C fall in love. For this reason, it is impossible to observe a focused image on all the sample surfaces A, B, and C, that is, an optical image obtained when the sample surfaces A, B, and C are in focus.

On the other hand, in the confocal scanning optical microscope, after the focused images on the sample surfaces A, B, and C are stored, the focused images on the sample surfaces A, B, and C are optically added. As a result, in-focus pixels for all sample surfaces A, B, and C can be obtained. In practice, the maximum value of the brightness of the optical image generated from each of the sample surfaces A, B, and C may be added to each other.

The method of measuring the surface condition of a sample as described above is described in "THEORY AND PRACTI" in the literature.
CE OF SCANNING OPTICAL MI
CROSCOPY, "by Tony Wilson and Colin Sheppard, pages 126-130, published by ACADEMIC PRESS.

In this document, a technique for measuring the surface shape of a sample is described. That is, in a state where the focused light is irradiated to one point on the sample surface, the focused light is Z-scanned in the direction of the optical axis (Z direction), and a position (Z position) where the brightness becomes highest during the scanning is detected. And save.

Next, the focused light is moved in the X direction to irradiate the next point on the sample surface with the focused light, and the same Z-scan is performed at this point, and the luminance is maximized during this scanning. The position (Z position) is detected and stored.

As described above, it is repeated to move the focused light in the XY directions on the sample surface, irradiate the focused light at each point, and perform Z scanning at that point to detect the Z position at which the brightness becomes the highest. Thus, the surface shape of the sample is measured based on the luminance change.

The operation of measuring the height of a sample using a confocal scanning optical microscope will be specifically described. FIG. 10 shows a configuration diagram of the confocal scanning optical microscope. Microscope body 10
Is provided with a laser light source 11, and this laser light source 11
The scanning laser light emitted from the mirror is reflected by the mirror 12, passes through the half mirror 13, and enters the two-dimensional scanning mechanism 14.

The operation of the two-dimensional scanning mechanism 14 is controlled by the scanning control unit 15, and scans the incident scanning laser light on a two-dimensional plane (XY plane) using a galvanometer mirror or the like.

Below the two-dimensional scanning mechanism 14, a revolver 16 is provided, on which an objective lens 17 is mounted. And below this objective lens 17,
A stage 18 is provided.
9 are placed.

A photodetector 21 is arranged in the branching direction of the half mirror 13 via a pinhole 20.
The pinhole 20 is arranged at a position conjugate with the condensing position of the objective lens 17, and the photodetector 21 converts the light passing through the pinhole 20 into an electric signal corresponding to the light amount and outputs the electric signal. Is what you do.

The stage 18 includes a Z-direction movement control circuit 22
Is controlled to move up and down in the Z direction. The image processing unit 23 receives the electric signal output from the photodetector 21 and the count value of the number of times the stage 18 has been moved by the Z-direction movement control circuit 22 so that the amount of light detected by the photodetector 21 is maximum. It has a function of obtaining the in-focus position from the count value of the number of movements of the stage 18 indicating the value.

The image processing unit 23 includes a first image memory M ₁ and a second image memory M ₂ .
Largest in the image memory M _1, stored maximum value of the electric signal from the photodetector 21 obtained while the stage 180 moves, the second in the image memory M _2, electrical signals from the photodetector 21 is The count value of the number of movements of the stage 18 at the time of is stored.

The computer 24 includes the scanning control unit 1
5. Z-direction movement control circuit 22 and image processing unit 23
, And controls the measurement range, the amount of movement of the stage 18 within each measurement range, the image display, and the control of the microscope system.
And informs the observer.

The operation of the thus constructed microscope will be described with reference to the operation flowchart shown in FIG.
Here, the values stored in the first and second image memories M ₁ and M ₂ are M _a and M _b , respectively, and the count value of the number of movements of the stage 18 is k. Let the electrical signal to be taken be I _k . M _b ≠ k M _b is the value measured of k is initiated when I _k is maximum, at step S _1, the measurement initiating position stage 18 by a command from the computer 24 Z _o
It is set to, and the count value k of the number of times of movement of the stage 18 is cleared (k = 0) is, together with the first image memory M ₁ value M _a is cleared (= I _o), the second image memory the value stored in M ₂ M _b reset (M _b = 0)
Is done.

Next, the stage 18 is moved by ΔZ partial example above by controlling the Z-direction movement control circuit 22 in step S _2. The count value k ( _Mb ≠ k) of the number of movements of the stage 18 is counted up by “1”.

In this state, the scanning laser light emitted from the laser light source 11 is reflected by the mirror 12, passes through the half mirror 13, and enters the two-dimensional scanning mechanism 14. The two-dimensional scanning mechanism 14 scans the incident laser beam on the two-dimensional plane of the sample 19 using a galvanometer mirror or the like under the operation control of the scanning control unit 15.

Sample 1 when scanned on this two-dimensional plane
The laser light reflected from 9 is guided from the two-dimensional scanning mechanism 14 to the half mirror 13, reflected there, and incident on the photodetector 21 through the pinhole 20.

The photodetector 21 converts the light passing through the pinhole 20 into an electric signal corresponding to the amount of light and outputs the electric signal. Then, the computer 24, in step S _3, compares the electric signal I _k from the first value M _a stored in the image memory M ₁ current of the photodetector 21, the current of the photodetector 21 if the electrical signal I _k is greater than the value M _a from the first image memory M ₁ value M _a with rewriting the I _k proceeds to step S _4, the second image memory M ₂ value M Replace _b with k.

[0027] Incidentally, the smaller the electric signal I _k from the current of the photodetector 21 than the value M _a of the first image memory M _1, a first image memory M ₁ value M _a and the second image value M _b of the memory M ₂ is as it is.

As described above, the processing of steps S _{2 to} S ₄ is repeated a predetermined number of N times in the judgment of step S ₅ , so that the maximum value of the electric signal I _k output from the photodetector 21 becomes the first image. is stored as the value M _a memory M _1, the count value k of the number of times of movement of the stage 18 at the time is stored second image memory M _2.

In an actual confocal scanning optical microscope, a focused light is moved on an XY plane using a high-speed two-dimensional scanning mechanism such as a galvanometer or an AOD element.
The y-scan is performed to detect the luminance at each point of the sample 19, and the Z
While moving the position, and to shorten the measurement time of the whole of the sample 19 by comparing the magnitude of the electrical signal I _k at each point on the sample 19.

[0030]

However, in the case of the above-mentioned height measurement, the luminance value by the Z-scanning becomes, for example, each measurement data “○” shown in FIG. the relative position than continuously the value of the luminance on the change curve W ₁ of the luminance in the case of changing becomes maximum position Z _t, a position shifted Z _m from being stored as the Z position.

This shift is an error caused by discretely performing the Z scan, that is, an error caused by quantization of the Z scan. The shift amount is a maximum of 2 steps of the movement step Δz in the Z direction.
It will be a fraction. Since this shift amount is determined by the start position of the Z scan, it varies at every measurement, which causes deterioration of measurement reproducibility.

For example, when measuring the height between two points, an error of one half of the Z movement step is generated at each of these points, so that an error of the Z movement step Δz is generated as a whole. .

In order to reduce such an error, the Z movement step Δz may be reduced. However, in order to detect the position where the luminance is maximum, the photodetector 21 when driven one step in the Z direction is detected. output change must be greater than the electric noise and the first value of the luminance corresponding to one gradation of the image memory M _1.

Even if the Z-movement step Δz is reduced, the luminance value near the position where the light intensity becomes the maximum is equal to or less than the intensity corresponding to electric noise or one gradation of the first image memory M _1. If so, the magnitude of the original light intensity and the detected light intensity may not match, and the Z position at which the luminance value becomes maximum cannot be accurately detected.

That is, in the above method, the Z movement step Δz is determined by the amount of change in luminance near the position where the light intensity is maximum, the electrical noise, and the light intensity corresponding to one gradation of the first image memory M _1. In the vicinity of the position where the light intensity is maximum as shown in FIG. 12, since the change in luminance is small, the Z movement step Δz is necessarily smaller than a predetermined amount. Can not.

Therefore, in recent semiconductor processes, the measurement of the thickness of a pattern on a semiconductor wafer or the like requires 0.1 μm.
m and a reproducibility of 0.05μ
m or less, and the height measurement method described above and a microscope to which this method is applied cannot meet such requirements. Therefore, an object of the present invention is to provide a height measuring method and a height measuring method capable of accurately obtaining height information even when the Z movement step is reduced.

[0037]

According to a first aspect of the present invention, a sample is irradiated with light through an optical lens, and the light reflected from the sample is subjected to a minute aperture disposed at a position conjugate with the condensing position of the optical lens. Detecting the light intensity through the optical axis, and increasing the relative position between the optical lens and the sample, which is an inflection point in the change in the light intensity when the relative position between the optical lens and the sample is discretely changed in the optical axis direction. And acquiring the height information as height information.

According to the second aspect, the reflected light from the sample surface when the sample is irradiated with the light through the objective lens is incident on the photodetector through the minute aperture arranged at a position conjugate with the condensing position of the objective lens. Then, in a height measuring device that obtains height information between the optical lens and the sample based on the light intensity detected by the photodetector, the relative position between the objective lens and the sample is discretely changed in the optical axis direction. A moving mechanism; an inflection point detecting means for detecting an inflection point in a change in light intensity detected by the photodetector when the relative position between the objective lens and the sample is changed by the moving mechanism; And a height information obtaining means for obtaining the relative position between the objective lens and the sample as height information based on the inflection point detected by the output means.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The height measuring method according to the present invention includes a step of irradiating a sample with light through an optical lens, and detecting the light intensity of the light reflected from the sample through a minute aperture arranged at a position conjugate with the condensing position of the optical lens. And obtaining a relative position between the optical lens and the sample as an inflection point in a change in light intensity when the relative position between the optical lens and the sample is discretely changed in the optical axis direction as height information. It has.

FIG. 1 is a configuration diagram of a confocal scanning optical microscope to which the height measuring method is applied. It is to be noted that the same parts as those in FIG. A mirror 12 and a half mirror 1 are provided on the optical path of the scanning laser light emitted from the laser light source 11 provided in the microscope body 10.
A two-dimensional scanning mechanism 14 is arranged via the reference numeral 3.

The operation of the two-dimensional scanning mechanism 14 is controlled in response to the scanning control signal P ₁ output from the scanning control unit 15, and the two-dimensional scanning mechanism 14 converts the incident scanning laser light into a two-dimensional plane (XY plane) ) Has the function of scanning on.

Below the two-dimensional scanning mechanism 14, a revolver 16 to which an objective lens 17 is attached is provided. A stage 18 on which a sample 19 is placed is provided below the objective lens 17.

A photodetector 21 is arranged in the branching direction of the half mirror 13 via a pinhole 20.
The pinhole 20 is disposed at a position conjugate with the light condensing position of the objective lens 17 as described above.

The stage 18 has a Z-direction movement control circuit 22
Is driven and controlled in response to the Z control signal P ₂ output from
It has a function of moving up and down in the Z direction at every predetermined Z movement step Δz.

The image processing unit 30 receives the electric signal output from the photodetector 21, the count value of the number of times the stage 18 has been moved by the Z-direction movement control circuit 22, and has been detected by the photodetector 21. A function of acquiring the relative position between the objective lens 17 and the sample 19 as height information based on the inflection point in the change in the light intensity, for example, the count value k of the number of movements of the stage 18 at which the change in the light intensity is the largest. Have.

The image processing unit 30 includes a first image memory M ₁₀ , a second image memory M _11, and a third image memory M ₁₂ each of 512 pixels × 512 pixels × 8 bits (256 gradations). Is provided.

[0047] Among the above first image memory M _10, and the electric signal I _k-1 which is output from the photodetector 21 in the previous measurement point when moving the stage 18 for each Z moving step Δz time the maximum value of the difference between the electric signal I _k output from the photodetector 21 at the measurement point, i.e. the value I _k -I _k-1 indicating the maximum change in light intensity is stored.

[0048] Also, in the second image memory M _11, the electric signal I _k output from the optical detector 21 in the current measuring point
Is saved. Further, in the third image memory M ₁₂ of, I _k -
The count value k of the number of times of movement of the stage 18 at which I _k−1 becomes the maximum is stored.

The computer 31 issues commands to the scanning control unit 15, the Z-direction movement control circuit 22, and the image processing unit 30 in accordance with the operation flowchart shown in FIG. 2, and controls the measurement range. The movement amount of the stage 18 within each measurement range, the image display, the control of the microscope system, and the like are displayed on the monitor 25 to notify the observer.

Next, the operation of the optical microscope configured as described above will be described. The observer places the sample 19 on the stage 18
After being placed on the sample, the sample 1 is controlled by the computer 31.
9 is a laser beam for scanning a minute spot focused on XY
It is scanned on a plane.

That is, the scanning laser light emitted from the laser light source 11 is reflected by the mirror 12, passes through the half mirror 13, and enters the two-dimensional scanning mechanism 14. This 2
The dimensional scanning mechanism 14 performs raster scanning of the incident scanning laser light on a two-dimensional plane of the sample 19 using a galvanomirror or the like under the operation control of the scanning control unit 15.

At the same time, the stage 8 is moved stepwise in the Z direction under the drive control of the Z direction movement control circuit 22 to change the relative distance between the objective lens 17 and the sample 19. At this time, whether or not the sample 19 is in focus is determined by an observer watching the image displayed on the monitor 24.

Next, the observer sets each parameter related to the measurement operation. First, the measurement range L of the sample 19 and the stage 1 for starting the measurement by the computer 31
Position Z _o of 8 is set, after this, the movement amount in the Z direction per one stage 18 (Z-direction moving step) Delta] z
Is set.

In this Z-direction movement step Δz, the position of the sample 19 with respect to the converging position of the objective lens 17 is set to Z.
It is the amount of one movement when moving in the direction. Further, when the measurement range L and the Z-direction movement step Δz of the stage 18 once are set, the number of times N of movement of the stage 18 is determined according to the relationship L / Δz ≦ N (1).

The count value of the transfer times N of the stage 18 are stored on the third image memory M _12, the transfer times N of the stage 18, the gradation number of the third image memory M ₁₂ 2
Limited to 55 or less.

After the measurement range L, the amount of movement Δz and the number of movements N are set in this way, the measurement on the sample 19 is started. Here, the first to third image memory M ₁₀ ~M ₁₂ respectively M _a saved values in, M _b, and M _c, the count value of the number of times of movement of the stage 18 k, the light detector in this case the electric signal output from the 21 and I _k.

Next, the operation will be described with reference to the operation flowchart of the optical microscope shown in FIG. When the measurement is started, in step # 1, the stage 18 moves the Z-direction movement control circuit 2
The stage 18 is moved to the measurement start position Z _O by the drive of 2, and the count value k of the number of times the stage 18 moves is reset.

[0058] with the first image memory M value M _a stored in ₁₀ therewith is cleared, an electrical signal I _o output from the photodetector 21 shown in this case in FIG. 3, for example
There is stored in the second image memory M _11.

Next, in step # 2, the stage 18 moves in the Z direction by the Z direction movement step Δz by driving the Z direction movement control circuit 22, and the count value k of the number of movements of the stage 18 becomes “+1”. Is only counted up.

[0060] Subsequently, the image processing unit 30, stored in step # 3, this time enter the electric signal I _k output from the photodetector 21, on the electric signal I _k and the second image memory M ₁₁ the difference between the electric signal M _{b is, I k -M b (I k} -I k-1) ... (2) a determined, this first image memory M is stored in the ₁₀ and the value M _a (= 0).

As a result of this comparison, M _a <I _k −M _b (3) The relationship of the above equation (3) holds, and if I _k −M _b is larger than M _a , the image processing unit 30 proceeds to step # the value M _a stored in the first image memory M ₁₀ for moving to 4 save rewritten to I _k -M _b.

At the same time, the image processing unit 30
The value M _c of the image memory M _12, the stage at this time 18
Is rewritten and saved as the count value k of the number of times of movement. Save rewritten in step # 5 following the electrical signal I _k output the values M _b of the second image memory M ₁₁ from the photodetector 21.

As specifically shown in FIG. 3, for example, when the stage 18 is driven by the Z-direction movement control circuit 22, the count value of the number of times of movement of the stage 18 is changed from “k = 3” to “k = 4”.
In the case where the image processing unit 30 moves in the z position direction, the image processing unit 30 determines in step # 3 that the electric signal I ₄ output from the photodetector 21 at the current position of the stage 18 (k = 4). And the electric signal I ₄ and the second
From the previous electric signal M _b (= I ₃ ) at the position (k = 3) of the stage 18 stored in the image memory M ₁₁ , I ₄ −I ₃ ... (4). The maximum value of the previous value M _a (= I _{k + 1} −I _k ) stored in the one image memory M ₁₀ is compared with, for example, I ₃ −I ₂ in FIG.

As a result of this comparison, I ₄ -I ₃ becomes I ₃ -I ₂
Greater than, the image processing unit 30 stores rewrites the value M _a stored in the first image memory M ₁₀ of the process shifts to a step # 4 I ₃ -I ₂ to I ₄ -I ₃ .

[0065] At this time the third image memory M _12, the count value k of the number of times of movement of the stage 18 (= 4) is stored, in the second image memory M ₁₁ in step # 5 that follows is photodetector electrical signals I ₄ that is output from the 21 is stored.

As described above, the processing in steps # 2 to # 5 is repeated a predetermined number of N times by the determination in step # 6, so that the level change of the electric signal Ik output from the photodetector 21 is _obtained . maximum value, that is, the maximum value of the change in light intensity is stored in the first image memory M _10, the count value k of the number of times of movement of the stage 18 at that time is stored in the third image memory M ₁₂ of.

[0067] Figure 4 for variation curve W ₂ of the electric signal I _k output from the photodetector 21 when the user moves the stage 18 in the Z direction, the change of the electric signal _{I k (I k -I k-} 1)
That is, it is a diagram in which a differential value is taken.

From this figure, it can be seen that the change I _k -I of the electric signal I _k
The maximum value ΔI _ma and the minimum value ΔI _{mb of k−1} , that is, the differential value d
I _k / maximum value G ₁ of dx, the minimum value G ₂ in the Z-direction Z _a,
Found that appear to Z _b, changes in these electrical signals I _k I _k -I _k-1 of the maximum value [Delta] I _ma is stored as the value M _a of the first image memory M _10.

[0069] Here, in Sutebbu _{# 3 M a <I k -I} b
By performing the step # 4 when, the M _a stored maximum value [Delta] I _ma of I _k -I _k-1, by performing the step # 4 when M _a> I _k -I _b, the M _a is Minimum value ΔI of I _k −I _k−1
mb is saved.

[0070] In actual measurement, the change I _k of the electrical signal I _k
Only _one of the maximum values ΔI _ma and ΔI _mb of −I _k−1 needs to be detected. Here, in the confocal scanning optical microscope, the change in the light intensity when the relative position between the objective lens 17 and the sample 19 is continuously changed is described in, for example, the above-mentioned document “THEORY AND PRACTICE OF S”.
CANNING OPTICALMICROSCOP
Y ", theoretically, as described on page 126, and is expressed as follows.

I (Z) = [{sin (u / 2)} / (u / 2)] ² (5) u = 8πZ · sin ² (θ / 2) / λ NA = sin θ I is the light intensity, Z is the distance from the focal point, NA is the objective lens 1
The numerical aperture of 7, and λ is the wavelength of light.

If the reflectance and transmittance at each point of the sample 19 change, the light intensity I is multiplied by a factor in accordance with the reflectance and transmittance, and the brightness change curve W in FIG.
₂ but will be coefficients multiplied longitudinally, form themselves change curve W ₂ of the brightness does not change. Since the light intensity I becomes maximum when the differential coefficient of the light intensity I becomes “0”, the above equation (5) is differentiated by Z, and

[0073]

(Equation 1) Get.

In this equation (6), when u / 2 = 0,
That is, when Z = 0, dI / dZ = 0, and at this time, the luminance becomes maximum. On the other hand, since the change in light intensity dI / dZ becomes maximum when the differential coefficient of dI / dZ becomes “0”, the above equation (6) is further differentiated by Z, and

[0075]

(Equation 2) Get.

Therefore, when u / 2 = ± 1.303, d
² I / dZ ² = 0. Here, the sign “±”
Indicates whether the change in light intensity is positive or negative, and the sign of the sign indicates that the absolute value of the change in light intensity is equal. When the sign is "+", the change in light intensity is the maximum value, and when the sign is "-", the change in light intensity is the minimum value. That, Z _a, the maximum value [Delta] I _ma appearing in Z _b shown in FIG. 4, the minimum value [Delta] I _mb.

For example, NA = 0.95, λ = 488 nm
Then, the change of the light intensity becomes maximum when Z = ± 0.1.
47 μm. Therefore, in this case, a z-scan is performed at a certain point of the sample 19 to detect the Z position where the change in the light intensity is maximum, and 0.147 μm is added to the value. Is required.

Alternatively, the height of the sample 19 at that point can be obtained by detecting the Z position where the change in light intensity is minimum and subtracting 0.147 μm from the value. That is, NA =
0.95, when the lambda = 488 nm, the position Z _a shown in FIG. 4, by obtaining the position of the Z _b, these positions Z _a, the distance e _a from Z _b to the maximum value of the change curve W _a, e since _b is determined by the numerical aperture NA and the wavelength lambda, 0.1 at the position Z _a
The height of the sample 19 is obtained by adding the 47 [mu] m, also the height of the sample 19 is determined by subtracting the 0.147μm from the position Z _b.

[0079] Thus, the image processing unit 30, Z position changes of the light intensity becomes maximum or minimum, Z _a shown in FIG. 4, for example, upon detecting a Z _b, 0.147 to Z _a of this
μm is added to obtain the height of the sample 19 at that point, or 0.147 μm is subtracted from Z _b to obtain the sample 19 at that point.
Find the height of

Generally, for example, as shown in FIG. 9, the relative height (difference between the respective sample surfaces A, B, and C in the sample 19 (7) having three sample surfaces A, B, and C is shown. ) is to measure the respective sample surface a in such a case, B, each change curve for C is, for example, as W _a shown in FIG. 5 variation curve of the specimen surface a, W _b is the sample surface B change curve, W _c represents a change curve of the sample surface C.

The change curves W _a , W _b , W _c
Mounts a sample 19 (7) on a stage 18 and scans the entire sample 9 with a scanning laser beam by a two-dimensional scanning mechanism 14, and at this time, the laser beam reflected from the sample 19 (7) is The light intensity is detected by the photodetector 21 and the electric signal _Ik is input to the image processing unit 30, where the maximum value of the electric signal _Ik is sequentially detected. in each sample surface a, B, each change curve W to C _a, W _b, the position Z shown each maximum change in W _c
wa , Z _wb and Z _wc are determined.

Therefore, the image processing unit 30 determines that NA =
When 0.95 and λ = 488 nm, by adding 0.147 μm to each of these positions Z _wa , Z _wb , and Z _wc , the heights of the sample surfaces A, B, and C of the sample 19 (7) are adjusted. Then, the respective heights of the sample surfaces A, B, and C are compared to determine a difference between the relative heights of the sample surfaces A, B, and C.

[0083] The image processing unit 30, the respective change curves W _a, W _b, W each position showing the maximum change in _c Z _wa,
Without converting Z _wb , Z _wc to the height of each sample surface A, B, C,
Direct each position Z _wa, Z _wb, obtaining a difference between relative height of each sample surfaces A, B, C by comparing the Z _wc. For example,
This is because the difference Z _tb -Z _ta and Z _wb -Z _wa between the heights of the sample surfaces A and B are equal.

As described above, in the first embodiment, the relative position between the objective lens 17 and the sample 19 (7) is changed in the optical axis direction, and the light intensity detected by the photodetector 21 at this time is changed. Is detected, and the relative position between the objective lens 17 and the sample 19 (7) is determined from the position where the maximum or minimum is obtained. such noise and to a same extent as the light intensity difference corresponding to one gradation of the first image memory M ₁₀ can be reduced Z moving step, good heights quantization error less measurement reproducibility by Z moving step Can measure.

That is, the absolute value of the change in light intensity at the point where the change in light intensity is maximum or minimum is literally maximum on the change curve of light intensity (for example, the change curve W ₂ shown in FIG. 3). Thus, in this position, Z moving step Δz limit becomes 1 gradation at the same level of electrical noise and the first image memory M ₁₀ of the photodetector 21, the light at the position near the luminance is maximum Since the intensity change is naturally smaller than the Z-movement step Δz having the same relationship, the Z-movement step Δz can be reduced to reduce the error caused by the quantization of the z-movement.

Also, when measuring the relative height (difference) between each sample surface A, B, and C of the sample 19 (7) having three sample surfaces A, B, and C, these sample surfaces A , B, each change curve W _a for C, W _b, W each position Z _wa as the maximum change in _c, Z _wb, without converting the maximum a position of the light intensity from Z _wc, direct the position Z By comparing _wa , Z _wb , and Z _wc , it is possible to obtain the relative height (difference) between the sample surfaces A, B, and C, for example, the difference between the heights of the patterns on the semiconductor wafer.

Further, in comparison with the conventional microscope, only a simple change of adding one image memory is required. (2) Next, a second embodiment of the present invention will be described.
The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 6 is a configuration diagram of a confocal scanning optical microscope. A beam splitter 40 that splits the reflected light from the sample 19 into equal amounts is disposed in the branching direction of the half mirror 13 in the microscope main body 10.

A first photodetector 42 is arranged in one branch direction of the beam splitter 40 via a first pinhole 41 arranged at a position conjugate with the condensing position of the objective lens 17.

Further, in the other branching direction of the beam splitter 40, the second light is transmitted through a second pinhole 43 disposed at a position conjugate to the condensing position of the objective lens 17 and shifted from the position f. A detector 44 is arranged.

The position of the second pinhole 43 is different from the position f conjugate with the condensing position of the objective lens 17, that is, the position shifted by the distance corresponding to the minimum step of the z movement with respect to the first pinhole 41. Has become. That is, the second pinhole 43 is positioned at a position f conjugate with the converging position of the objective lens 17.
From a minimum of change in light intensity is limited by the amount of change in luminance in the vicinity of positions corresponding to the maximum, and the electrical noise or equivalent light intensity 1 gradation stored in the first image memory M ₁₀ of The optical system from the sample 19 to the pinhole 43 is placed at a position multiplied by the vertical magnification with respect to the Z movement step Δz.

The difference circuit 45 calculates the difference between the first electric signal output from the first photodetector 42 and the second electric signal output from the second photodetector 44, and calculates the difference signal. the has a function of sending to the first image memory M ₁₀ of the image processing unit 46.

The difference signal output from the difference circuit 45 is equivalent to the amount of change in light intensity when the relative position between the objective lens 17 and the sample 19 is moved in the Z direction by a distance corresponding to the smallest step. That is, as shown in FIG. 7, when the stage 18 is moved by the z movement step Δz, for example, it is equivalent to the difference I ₁₁ −I ₁₀ between the electric signals I ₁₁ and I ₁₀ .

The image processing unit 46 receives the difference signal output from the difference circuit 45 and the count value of the number of times the stage 18 has been moved by the Z-direction movement control circuit 22, and receives the difference signal output from the difference circuit 45. The relative position between the objective lens 17 and the sample 19 is acquired as height information based on the count value of the number of movements of the stage 18 at which the change in the maximum has been shown.

This image processing unit 46 has 5
12 pixels × 512 pixels × an 8-bit (256 gradations) the first image memory M ₁₀ and the third image memory M ₁₂ consisting of a maximum value of these difference signals in the first image memory M _10, i.e. Value M _a (= I _k) indicating the maximum change in light intensity
-I _k-1) is stored, and the change in light intensity in the third image memory M ₁₂ of which is intended to count value k of the number of times of movement of the stage 18 becomes maximum are stored.

Next, the operation of the microscope configured as described above will be described. The scanning laser light emitted from the laser light source 11 is reflected by the mirror 12, passes through the half mirror 13 and enters the two-dimensional scanning mechanism 14, and the two-dimensional scanning mechanism 14 performs a two-dimensional scanning of the sample 19. It is scanned on a plane.

At the same time, the stage 18 is moved stepwise in the Z direction under the drive control of the Z direction movement control circuit 22 to change the relative distance between the objective lens 17 and the sample 19. At this time, whether or not the sample 19 is in focus is determined by an observer watching the image displayed on the monitor 24.

Next, the observer sets the parameters related to the measurement operation, that is, the measurement range L of the sample 19 and the stage 18 where the measurement is started by the computer 31.
Position Z _o of the set, after which the movement amount Δz in the Z direction per stage 181 times is set.

When the measurement is started, the stage 1
8 is moved to the measurement start position Z _O by the driving of the Z-direction movement control circuit 22, and the count value k of the number of movements of the stage 18 is reset.

[0100] with the value M _a stored in the first image memory M ₁₀ together with this is clear, the differential signal output from the difference circuit 45 at this time is the first image memory M
Stored in ₁₀ .

Next, the stage 18 is moved in the Z direction by the movement amount Δz by driving the Z direction movement control circuit 22.
The count value k of the number of movements of the stage 18 is incremented by “+1”.

In this state, the reflected light from the sample 19 is 2
The light enters the beam splitter 40 from the dimensional scanning mechanism 14 via the half mirror 13, and is branched there in two directions, that is, the first pinhole 41 side and the second pinhole 43 side.

The light transmitted through the first pinhole 41 is incident on a first photodetector 42, which outputs a first electric signal I _k corresponding to the amount of incident light. Is output.

The light transmitted through the second pinhole 43 is incident on the second photodetector 44, and the second photodetector 44
Outputs a second electric signal I _k-1 corresponding to the amount of incident light.

The difference circuit 45 calculates a difference between the first electric signal I _k output from the first photodetector 42 and the second electric signal I _k-1 output from the second photodetector 44. I _k -I
The calculated _k-1, sends the differential signals I _k -I _k-1 in the first image memory M ₁₀ of the image processing unit 46.

That is, the difference signal I _k -I _{k -1} output from the difference circuit 45 is obtained by the objective lens 17 and the sample 19
Is equivalent to the amount of change in light intensity when the relative position is moved in the Z direction by a distance corresponding to the minimum step, for example, when the stage 18 is moved by the z movement step Δz as shown in FIG. and it has a differential I ₁₁ -I ₁₀ equivalent to the first and second electrical signals I ₁₁ and I _10.

The image processing unit 46 outputs the difference signal I _k −
I _k−1 and the value M _a stored in the first image memory M ₁₀
Compare with As a result of this comparison, M _a <I _k −I _k−1 (8) The relationship of the above equation (8) holds, and if I _k −I _k−1 is larger than M _a , the image processing unit 46 the value M _a stored in the first image memory M ₁₀ for storing rewrites the I _k -I _k-1.

[0108] At this time the third image memory M _12, the count value k of the number of times of movement of the stage 18 at this time is saved. By repeating the above process N times, the first photodetector 42 and the second photodetector 4
Each electrical signal I _k output from the 4 which the maximum value of the difference signal between I _k-1 is stored in the first image memory M ₁₀ as the value M _a, the count value of the number of times of movement of the stage 18 at that time k is stored in the third image memory M ₁₂ of.

Accordingly, as in the first embodiment, the image processing unit 46 has, for example, NA = 0.95 and λ = 0.95.
If a 488 nm, the position Z _a shown in FIG. 4, Z _b
It is possible to obtain the position, these positions Z _a, the distance e _a from Z _b to the maximum value of the change curve W _a, since e _b is determined by the numerical aperture NA and the wavelength lambda, 0.14 at the position Z _a
The height of the sample 19 is obtained by adding 7 μm.
Or it may also be determined height of the sample 19 by subtracting the 0.147μm from the position Z _b.

For example, as shown in FIG. 9, the relative height (difference) of each of the sample surfaces A, B, and C of the sample 199 (7) having three sample surfaces A, B, and C is measured. In this case, the image processing unit 46 determines that NA = 0.95 and λ = 4.
If a 88 nm, the positions Z _wa as shown in FIG. 5, Z
By adding 0.147 μm to _wb and Z _wc respectively, each height of each sample surface A, B and C of the sample 19 (7) is obtained, and each height of these sample surfaces A, B and C is compared. Then, the difference between the relative heights of the sample surfaces A, B, and C is obtained.

[0111] The image processing unit 46, the respective change curves W _a, W _b, W becomes maximum each position change of _c Z _wa,
Without converting Z _wb , Z _wc to the height of each sample surface A, B, C,
Direct each position Z _wa, Z _wb, obtaining a difference between relative height of each sample surfaces A, B, C by comparing the Z _wc.

As described above, in the second embodiment, the first photodetector 42 is disposed via the first pinhole 41 disposed at a position conjugate to the condensing position of the objective lens 17. And a second pinhole 4 arranged at a position shifted from a position f conjugate with the light condensing position of the objective lens 17.
3, a second photodetector 44 is disposed, and the first and second photodetectors 42 and 44 output the first and second photodetectors 44 respectively.
Since the maximum value of the difference signal of the electric signal is detected, it is equivalent to detecting the maximum value of the change of the light intensity as in the first embodiment, and the change of the light intensity is the first value.
And electrical noise of the second photodetectors 42 and 44 and the first
Image until the same extent as corresponding to the light intensity difference in one gradation of the memory M ₁₀ can be reduced Z moving step, it is good height measurement quantization error of less measurement reproducibility by Z moving step of.

Also, when measuring the relative height (difference) between the sample surfaces A, B, and C of the sample 19 (7) having three sample surfaces A, B, and C, each position Z is directly measured. _wa , Z _wb , Z _wc
Can be obtained to obtain the relative height (difference) between the sample surfaces A, B, and C, for example, the difference between the heights of the patterns on the semiconductor wafer.

Further, in terms of the configuration, even when compared with the conventional microscope, it is possible to cope with an image memory equivalent to that of the conventional microscope. In addition,
The present invention is not limited to the first and second embodiments, but may be modified as follows.

For example, when obtaining the height information of the three sample surfaces A, B, and C of the sample 7 shown in FIG.
Is coarsely moved to roughly position the objective lens 17 with respect to, for example, the sample surface C. Thereafter, the stage 18 is moved at each Z movement step Δz to acquire the height information of the sample surface C with high accuracy.

Next, the stage 18 is coarsely moved to roughly position the objective lens 17 with respect to the sample surface A, and thereafter, the stage 18 is moved at every Z movement step Δz to precisely move the sample surface A. Get height information.

Then, the stage 18 is coarsely moved to roughly position the objective lens 17 with respect to the sample surface B, and thereafter, the stage 18 is moved at every Z movement step Δz to precisely adjust the height of the sample surface B. Get information.

As described above, when the stage 18 is operated by combining the coarse movement and the Z movement step Δz, the stage 1
8 without being moved every Z movement step Δz,
Acquisition time of height information can be shortened.

Further, in the second embodiment, even when the step of z movement is set to a value larger than the minimum value, the output of the difference circuit 45 is the amount of change in luminance due to the z movement in the minimum step. Has been detected.

When the Z movement step is set to a value larger than the minimum value, the second pinhole 43 is moved from the position conjugate with the condensing position of the objective lens 17 according to the set Z movement step. If they are separated from each other, the amount of change in the light intensity output from the difference circuit 45 increases, and the effect of electrical noise is reduced, so that more accurate measurement can be performed.

In the second embodiment, the second
The pinhole 43 is arranged at a position apart from a position conjugate with the light-converging position of the objective lens 17 and at a position where the distance from the objective lens 17 is widened. On the contrary, the distance from the objective lens 17 is shortened. It may be arranged at a position. in this case,
The second photodetector 44 has a higher Z than the first photodetector 42.
The light intensity before the movement step Δz is detected.

[0122]

As described in detail above, according to the present invention, Z
Height information can be obtained by accurately detecting the position where the luminance value is maximum even if the moving step is reduced, that is, a change in the light intensity is caused by the electrical noise of the photodetector or the image memory.
It is possible to provide a height measuring method and a height measuring method which can reduce the Z movement step until the light intensity difference corresponding to the gradation becomes almost the same, has a small quantization error due to the Z movement step, and has good measurement reproducibility.

[Brief description of the drawings]

FIG. 1 shows a first example of a confocal scanning optical microscope according to the present invention.
FIG. 1 is a configuration diagram showing an embodiment.

FIG. 2 is an operation flowchart of the optical microscope.

FIG. 3 is a diagram for explaining an operation for detecting a maximum value of a change in light intensity.

FIG. 4 is a diagram showing a maximum value of a change in an electric signal when the stage is moved in a Z direction.

FIG. 5 is a diagram showing change curves for three sample surfaces.

FIG. 6 shows a second example of the confocal scanning optical microscope according to the present invention.
FIG. 1 is a configuration diagram showing an embodiment.

FIG. 7 is a view for explaining the operation of the difference circuit in the microscope.

FIG. 8 is a schematic configuration diagram of a general confocal scanning optical microscope.

FIG. 9 is an external view of a sample having three sample surfaces with different heights.

FIG. 10 is a configuration diagram of a conventional confocal scanning optical microscope.

FIG. 11 is an operation flowchart of the microscope.

FIG. 12 is a diagram illustrating an operation of detecting a maximum value of an electric signal output from a photodetector.

[Explanation of symbols]

Reference Signs List 10: microscope body, 11: laser light source, 14: two-dimensional scanning mechanism, 15: scanning control unit, 16: revolver, 17: objective lens, 18: stage, 19: sample, 20: pinhole, 21: photodetector , 22 ... Z direction movement control circuit, 25 ... monitor, 30 ... image processing unit, M ₁₀ ... first image memory, M ₁₁ ... second image memory, M ₁₂ ... third image memory, 31 ... computer, 40: Beam splitter 41: First pinhole 42: First photodetector 43: Second pinhole 44: Second photodetector 45: Difference circuit 46: Image processing unit

Claims (2)

[Claims] Irradiating a sample with light through an optical lens;
Detecting the light intensity of the light reflected from the sample through a small aperture disposed at a position conjugate to the light-converging position of the optical lens; and dispersing the relative position between the optical lens and the sample in the optical axis direction. Acquiring a relative position between the optical lens and the sample, which is an inflection point in the change of the light intensity when the light intensity is changed, as height information. 2. A light reflected from the sample surface when the sample is irradiated with light through an objective lens is incident on a photodetector through a minute aperture arranged at a position conjugate with a condensing position of the objective lens. In a height measurement device that obtains height information of the optical lens and the sample based on light intensity detected by a photodetector, a relative position between the objective lens and the sample is discretely changed in an optical axis direction. A moving mechanism that changes the relative position between the objective lens and the sample by the moving mechanism, and an inflection point detecting unit that detects an inflection point in a change in light intensity detected by the photodetector; Height information obtaining means for obtaining a relative position between the objective lens and the sample as height information based on the inflection point detected by the inflection point detecting means. Measurement Setting device.