JP2004069317A - Size measuring instrument and size measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a size measuring instrument and a size measuring method for simply and accurately measuring a minute measuring object. <P>SOLUTION: Domains below a threshold 25 of light intensity distribution signals obtained from an image of the measuring object are cut off based on the previously set threshold 25, leaving intact only portions with steep inclination of the distribution signals or regions facilitating the detection of an edge of the measuring object. The size of the measuring object can be measured accurately. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dimension measuring apparatus, and more particularly, to an optical dimension measuring apparatus for measuring a dimension of an object from reflected light of light applied to the object.
[0002]
[Prior art]
For example, when measuring the recording track width of a magnetic recording head, an optical dimension measuring device is used. Such an optical dimension measuring device can easily prepare a measurement sample as compared with a scanning electron microscope (SEM), an atomic force microscope (AFM), or the like, and can easily measure an object to be measured. For example, JP-A-2001-264024 describes an optical dimension measuring device. In such an optical dimension measuring device, light is emitted from a light source to an object to be measured. Then, the edge-to-edge dimension of the measured object is calculated based on the light intensity distribution signal of the reflected light from the measured object. Thus, the dimensions of the object to be measured are measured.
[0003]
[Problems to be solved by the invention]
In an optical dimension measuring device, the minimum dimension of an object to be measured depends on the wavelength of a light source to be irradiated. In other words, the use of light having a shorter wavelength as a light source enables a finer measurement of the DUT. For example, in an optical dimension measuring apparatus using ultraviolet light (λ = 365 nm) as a light source, a numerical aperture N.D. Assuming that A = 0.95, the dimension measurement limit was up to about 235 nm.
[0004]
FIG. 12 shows a graph in the case where measurement is performed by a conventional method using a UV microscope. The measurement conditions were numerical aperture N. A was set to 0.95, and the wavelength of the light source was set to 365 μm. As a comparison, an ideal line in which the measured value by the SEM and the measured value by the UV microscope were set to the same value was shown. According to FIG. 12, it was confirmed that when the measurement sample width became smaller than 0.3 μm, the measured value by the UV microscope gradually began to deviate from the actual measurement sample width. It has been found that when the diameter is smaller than 0.1 μm, the value measured by the UV microscope does not change even if the actual measurement sample width becomes smaller. Therefore, even if the UV-SEM correlation curve is obtained as it is, accurate measurement cannot be performed in a portion where the deviation from the SEM becomes large. In order to accurately measure a minute sample with a UV microscope, it is necessary to bring the measured value with the UV microscope closer to an ideal line as indicated by an arrow in the figure.
[0005]
In order to easily and accurately measure the width of a recording track that is becoming increasingly finer in recent years, a measuring apparatus that can accurately measure a fine object to be measured using an easily available light source such as ultraviolet light is desired. Was.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a dimension measuring apparatus and a dimension measuring method capable of easily and accurately measuring a fine measurement object.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to a first aspect, there is provided means for receiving reflected light of light emitted from a light source to an object to be measured and generating a light intensity distribution signal of the object to be measured. Out of the light intensity distribution signal, a means for generating a correction signal by cutting a region equal to or less than a predetermined threshold, and a means for calculating the size of the device under test based on the correction signal. A dimension measuring device is provided.
[0008]
According to such a dimension measuring apparatus, even a dimension measuring apparatus using visible light or near-ultraviolet light as a light source can accurately measure a fine object to be measured, which has been difficult to measure conventionally. .
[0009]
Such a light source may be one that emits light having a wavelength of 365 nm or less. If near-ultraviolet light is used as the light source, the dimension measuring device can be configured at low cost.
[0010]
In the second invention, a step of receiving reflected light of light emitted from the light source onto the object to be measured and generating a light intensity distribution signal of the object to be measured; There is provided a dimension measuring method including a step of generating a correction signal by cutting an area equal to or less than a prescribed threshold value, and a step of calculating a dimension of an object to be measured based on the correction signal.
[0011]
According to such a dimension measuring method, even a dimension measuring apparatus using a light source having a long wavelength, such as visible light or near ultraviolet light, can accurately measure a fine object to be measured, which has been difficult to measure conventionally. Becomes possible.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a dimension measuring device according to one embodiment of the present invention. The dimension measuring apparatus 10 includes a stage 12 on which a workpiece 11 such as a head slider is mounted on a surface. The stage 12 is enabled in the XY directions by a stage driver 23.
[0013]
A half mirror 14 is provided above the stage 12. The half mirror 14 reflects the light emitted from the light source 15 toward the stage 12. The light source 15 emits near-ultraviolet light of, for example, 365 nm. Light emitted from the light source 15 passes through the optical filter 20 and travels to the half mirror 14.
[0014]
An imaging lens 16 and a solid-state imaging device (CCD) 17 are provided above the half mirror 14. A solid-state imaging device (CCD) is a device that decomposes an image formed on the surface, that is, an optical signal into vertical and horizontal grid-like pixels and converts the optical signal into an electric signal for each pixel. In this experiment, a solid-state image pickup device of NTSC specification having pixels of 480 × 512 dots is used. The imaging lens 16 condenses the light emitted from the light source 15 and reflected by the stage 12 and the DUT 11 to form an image on the CCD 17. The CCD 17 photoelectrically converts the incident light. Then, an image signal of the device under test 11 is output. An A / D converter 18 is connected to the CCD 17. The A / D converter 18 performs A / D conversion of the image signal output from the CCD 17 and inputs the image signal to a computer 19 as a light intensity distribution signal of the device under test 11.
[0015]
The dimension measuring device 10 includes a computer 19. Such a computer 19 may be, for example, a personal computer. A RAM 21, a ROM 22, a monitor device 24, and a stage driver 23 are connected to the computer 19. The RAM 21 stores data when processing the input light intensity distribution signal. The ROM 22 stores threshold setting information described later. The monitor device 24 displays a dimension measurement result and the like. The stage driver 24 controls the movement of the stage 23.
[0016]
The operation of the dimension measuring device 10 having the above configuration will be described in detail. Now, assume a case where the width W1 of the minute object to be measured 11 shown in FIG. 2 is measured. As shown in FIG. 1, the device under test 11 is placed at a predetermined position on the stage 12. Near ultraviolet rays are emitted from the light source 15 toward the DUT 11. Light from the light source is reflected on the stage 12 as reflected light. The reflected light including the image of the device under test 11 is converged by the condenser lens 16 via the half mirror 14. An image of the DUT 11 is formed on the light receiving surface of the CCD 17.
[0017]
The CCD 17 photoelectrically converts the received reflected light including the image of the DUT 11 and outputs the reflected light to the A / D converter 18 as an image signal of the DUT 11. The A / D converter 18 performs A / D conversion on the input image signal, and inputs the image signal to a computer 19 as a light intensity distribution signal of the device under test 11. The computer 19 temporarily stores the input light intensity distribution signal of the device under test 11 in the RAM 21.
[0018]
FIG. 3 shows a measurement example of the input light intensity distribution signal. Ten different sized samples were measured. According to FIG. 3, when the size of the object to be measured is 1.0 μm, 0.7 μm, and 0.5 μm, the light intensity of the peak does not decrease, but when it is smaller than 0.5 μm, the flat portion at the peak disappears. It can be seen that the light intensity profile of the measured object decreases. Focusing on such a light intensity profile, as the size of the device under test decreases, the change in the upper part of the light intensity profile curve is larger than that in the lower part.
[0019]
In the present invention, attention has been paid to the characteristics of the light intensity profile curve of such a minute object to be measured. That is, only the upper region where the change of the light intensity profile curve is large is taken out and the measured value is calculated. For this purpose, first, as shown in FIG. 3, a threshold 25 is set in the light intensity profile of the device under test. For example, assume a situation in which a measurement sample of 0.3 μm is measured using a UV microscope, which cannot be accurately measured by a conventional measurement method. The light intensity distribution signal of the DUT 11 of 0.3 μm has a gentle slope on both sides. The light intensity distribution signal in such a form cannot accurately detect the edge of the DUT 11 as it is.
[0020]
The computer 19 reads the threshold setting information from the ROM 22. As shown in FIG. 4, the threshold may be set above the gently inclined portions on both sides of the light intensity distribution signal. The threshold value 25 may be set to, for example, 30 to 40%. Such a threshold value is a ratio of the light intensity on the basis of the light intensity when measuring a uniform solid film having no shading as 100%.
[0021]
Now, it is assumed that the threshold value 25 is set to 35%. As shown in FIG. 5, the computer 19 cuts an area below the threshold 25 of the light intensity distribution signal based on the set threshold 25. The light intensity distribution signal has only a steep portion, that is, only a region where the edge of the DUT 11 is easily detected. The correction signal corrected on the basis of the threshold value 25 is subjected to a first-order differentiation by a computer 19 by taking a difference between adjacent pixels.
[0022]
As shown in FIG. 6, the first-order differentiated correction signal accurately represents both edges of the device under test 11 because the region below the threshold 25 has been cut in advance. The calculator 19 calculates the distance between the two vertices X1 and X2 of the first-differentiated correction signal. Thus, the fine width W1 of the DUT 11 is accurately measured based on the distance between X1 and X2.
[0023]
As described above in detail, according to the present invention, even in the case of an optical dimension measuring device using visible light or ultraviolet light as a light source, an object to be measured having a minute dimension of about 0.1 to 0.3 μm can be measured. It becomes possible to measure. In addition, by cutting a part of the light intensity distribution signal obtained from the image of the device under test based on the threshold value, even if the device under test has a fine size close to the wavelength of the light source, the edge can be accurately detected. It is possible to detect and measure the dimensions.
[0024]
The present applicant has verified the correlation between the dimension measurement according to the present invention and the dimension measurement by the SEM. For verification, three types of materials 1 to 3 were prepared. A large number of measurement samples having different dimensions were prepared from the respective materials in the range of 0.15 to 0.6 μm in increments of 0.05 μm. Ultraviolet light was employed as the measurement light source. The threshold was set at 40%. FIG. 7 shows a correlation graph in which the measured values of the sample measured by the present invention are shown on the vertical axis and the measured values by SEM are shown on the horizontal axis.
[0025]
On the other hand, a comparative example was prepared for verification. A measurement sample similar to the measurement according to the present invention shown in FIG. 7 was prepared. Ultraviolet light was employed as the measurement light source. The light intensity distribution signal of the measurement sample was used for measurement as it was without cutting a part. FIG. 8 shows a correlation graph in which the measured value of the sample measured by the conventional method is shown on the vertical axis and the measured value by SEM is shown on the horizontal axis.
[0026]
According to the measurement results shown in FIG. 7, the fine sample of 0.15 to 0.6 μm dimensioned according to the present invention had a strong correlation with the dimension measurement result by SEM. It has been confirmed that a minute object to be measured close to the wavelength of the light source can be accurately measured according to the present invention. On the other hand, in the comparative example shown in FIG. 8, when the measurement sample became 0.4 μm or less, the correlation decreased. In the conventional method, a minute object to be measured close to the wavelength of the light source could not be measured accurately.
[0027]
The present applicant has verified the dispersion of these measurements based on the results of FIGS. 7 and 8 described above. For the verification, a measurement sample similar to the verification shown in FIGS. 7 and 8 was prepared. These samples were repeatedly measured 25 times by the measurement according to the present invention and the measurement according to the conventional method. FIG. 9 shows the measurement results according to the present invention. FIG. 10 shows a measurement result obtained by a conventional method.
[0028]
According to the measurement results shown in FIG. 9, the variation in the measurement is kept low even in the range of 0.15 to 0.3 μm. It was confirmed that the reliability was sufficiently ensured even in the measurement of a minute object to be measured. On the other hand, in the comparative example shown in FIG. 10, when the thickness is 0.3 μm or less, a large variation appears in the measurement results. It has been found that sufficient reliability is not ensured when measuring a minute object to be measured.
[0029]
Furthermore, the present applicant has verified the setting of the optimum threshold value in the measurement method of the present invention. In the verification, a large number of measurement samples having different dimensions were prepared in the range of 0.1 to 0.45 μm in increments of 0.05 μm. Using these many measurement samples, the thresholds were set to 0%, 30%, 40%, 45%, and 50%, and the light intensity distribution signals of the measurement samples were cut at the above-described thresholds, respectively, and then the dimensions were measured. . Thus, FIG. 11 shows a graph in which the measured values of the sample measured by the present invention are shown on the vertical axis, the measured values by SEM are shown on the horizontal axis, and the average value at each threshold value is represented by a line.
[0030]
According to the measurement results shown in FIG. 11, it has been confirmed that the threshold for cutting the light intensity distribution signal of the device under test may be set to 30 to 40%, which is close to the ideal value indicated by the thick line. It has been found that if the threshold value is set to 30 to 40%, accurate measurement of dimensions can be performed by the present invention even for a fine object to be measured having a size of 0.1 to 0.2 μm.
[0031]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a dimension measuring apparatus and a dimension measuring method capable of simply and accurately measuring a minute object to be measured. For the measurement of such a minute object to be measured, a UV microscope or the like, which can be easily measured, can be used.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a dimension measuring apparatus according to the present invention.
FIG. 2 is an explanatory view showing a sample for dimension measurement.
FIG. 3 is an explanatory diagram showing a light intensity distribution signal of an object to be measured in dimension measurement.
FIG. 4 is an explanatory diagram illustrating threshold setting in dimension measurement.
FIG. 5 is an explanatory diagram showing a light intensity distribution signal cut at a threshold.
FIG. 6 is an explanatory diagram illustrating a correction signal obtained by differentiating a light intensity distribution signal.
FIG. 7 is a correlation graph measured according to the present invention.
FIG. 8 is a correlation graph measured by a conventional method.
FIG. 9 is a graph verifying measurement variations according to the present invention.
FIG. 10 is a graph verifying a variation in measurement by a conventional method.
FIG. 11 is a graph showing the measurement of an optimum threshold setting according to the present invention.
FIG. 12 is a graph showing a comparison between an actually measured value and an ideal value measured by a conventional method using a UV microscope.
[Explanation of symbols]
Reference Signs List 10 Dimension measuring device 11 DUT 15 Light source 19 Computer 25 Threshold

Claims (5)

Means for receiving the reflected light of the light emitted from the light source onto the object to be measured and generating a light intensity distribution signal of the object to be measured; And a means for calculating a dimension of the DUT based on the correction signal. The dimension measuring device according to claim 1, wherein the means for calculating the dimension of the measured object includes at least a first derivative. The dimension measuring device according to claim 1, wherein the light source emits light having a wavelength of 365 nm or less. A step of receiving reflected light of light emitted from the light source onto the object to be measured, and generating a light intensity distribution signal of the object to be measured; And a step of generating a correction signal by cutting the target, and a step of calculating a dimension of the DUT based on the correction signal. The method according to claim 4, wherein the step of calculating the dimension of the device under test includes a step of performing at least a first derivative.

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