JPH07225109A - Method for measuring positional deviation between superposed patterns - Google Patents

Abstract

PURPOSE:To provide a method for optically measure the positional deviation between two patterns superposed upon another at the time of manufacturing an integrated circuit by superposing semiconductor elements upon another. CONSTITUTION:When a first pattern and second pattern formed on a substrate in a superposing state respectively have slopes, the focal point of irradiating laser light 41 is controlled twice so that the intensity of reflected light from the substrate can become equal to that of reflected light from the first pattern and the intensity of reflected light from the first pattern can become equal to that of reflected light from the second pattern and the minimum-intensity positions of the intensity signals 43 and 44 of the two reflected light detected at their focal points are detected. Since the minimum-intensity positions respectively correspond to the centers of the slopes of the first and second patterns, the positional deviation between the two patterns is measured from the difference between the distances to the centers of the slopes. Therefore, the positional deviation can be measured with high accuracy regardless of the shape of the slopes and the reflectivity, surface roughness, and level difference of the members. In addition, this measuring method can be suitably used for in-line measurement of production lines, because the method does not require any complicated software.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for optically measuring mutual positional deviation of superposed patterns when superposing semiconductor elements to manufacture an integrated circuit.

[0002]

2. Description of the Related Art In the manufacture of ICs, various patterns are sequentially superposed to form a predetermined pattern. In the superposition of these patterns, the mutual positional relationship between the underlying pattern and the overlying pattern to be superposed is important, and it is necessary to measure the positional deviation of the superposed patterns. Generally, a test pattern is created to detect the positional deviation, and the positional deviation is managed by measuring the pattern, but with the recent high integration, the pattern positional deviation requires a measurement accuracy of about 0.05 μm. Has been done. A method using a light wave of an electron microscope, a laser or the like is often used for the measurement of the displacement. However, for the measurement in the production line, a method using a light wave that facilitates automatic measurement is advantageous. Therefore, a TV camera system that uses a white light source to magnify and detect a pattern has been used in the early days, but recently laser scanning microscopes (LSM) are often used because of the limited resolution of measurement. It has come to be used. The LSM is an optical device that irradiates and scans a laser beam focused on a minute spot on a pattern surface, detects a change in intensity of reflected light from the pattern, and obtains a pattern image. As for LSM, as a hardware, the contrast characteristics of image detection, high S / N ratio, high resolution, etc.
Although it has many features as compared with the TV camera method, an edge detection method that detects pattern edges with high accuracy is important when applied to the measurement of positional deviation of overlay patterns.

Generally, the positional deviation of the overlay pattern is measured by a test pattern provided at a specific place in the wafer. FIG. 2 shows an example of a test pattern for measuring displacement. (A) is a plan view and (b) is a cross-sectional view in the height direction. The test pattern is substantially square and is composed of two patterns having a constant step, and the materials forming the patterns are different. 20 substrate portion made of S _i O _2, 21 is the base pattern (first pattern) consisting of aluminum or polysilicon, 22 is a front cloth pattern made of a resist film (a second pattern). In this pattern, the edge positions Ax, Bx, Cx, Dx in the X direction and the edge position A in the Y direction shown in (a) are shown.
y, By, Cy, Dy are determined, and the difference between the distances between the edges of the base pattern 21 and the top pattern 22 (for example, Ax-Bx) is determined.
And Cx-Dx)), the pattern position deviation is measured.
In the case of an IC, the cross-sectional shape of the pattern is not ideal vertical, and as shown in (b), the base pattern 21 and the upper ground pattern 22 each have slope portions 23 and 24 having a constant width. .

In order to measure the positional deviation of the pattern having such a slope portion, it is important to determine the lower surface edge positions 212 and 214 of the base pattern 21 and the lower surface edge positions 222 and 224 of the upper ground pattern 22. come. For example, the distance Ax-Bx between the edges is determined by the lower edge positions 212, 2 and 2.
It is the distance between 22. When the overlapping pattern is irradiated with the laser beam, the slopes 23 and 24 scatter the irradiated laser beam, the substrate 20, and the underlying pattern 2.
1. The flat portion of the upper pattern 22 serves as a reflector, and the intensity of reflected light varies depending on the slope shape (width), the step of each pattern, the reflectance, the surface roughness, and the intensity distribution of the irradiation laser light and the focus setting position. Change. In the case of a fine pattern such as an IC, the slope width is about 0.1 to 0.2 μm, but as the beam diameter of the irradiation laser light becomes smaller, the slope shape greatly affects the intensity change of the reflected light. . Therefore, the slope shape is an important factor in determining the edge position.

A conventional edge detection method will be described with reference to FIG. 3 which shows a reflected light intensity signal waveform obtained when a laser beam having a minute spot is scanned on the pattern surface by the above-mentioned LSM. Here, when the reflectances of the substrate 20, the base pattern 21, and the upper pattern 22 are r1, r2, and r3, r1 <r
2, the relationship of r2> r3, and the steps h1 and h2 of the base pattern 21 and the upper pattern 22 are assumed to be larger than the focal depth h0 of the irradiation laser light. For example, when the focal position of the irradiation laser light is set on the flat portion of the base pattern 21, the reflected light intensity signal waveform 31 has an intensity level of 32 when the laser light is applied to the substrate 20, and the vicinity of the slope portion 23. Then, the intensity of reflected light decreases due to scattering, and reaches the minimum intensity 33 in a certain irradiation state. When the upper surface of the base pattern 21 is irradiated, the intensity of the reflected light increases and the intensity level 34 becomes constant. Further, if the slope 24 of the upper ground pattern 22 is irradiated, the intensity decreases again and the extreme intensity 3
5, the intensity level becomes 36 at the flat portion. In such intensity signal 31, intensity level 32 and minimum intensity 3
Strengths 322 and 32 that are intermediate strength (50% strength) of 3
4 is determined and binarization processing is performed, and the scanning position serving as the cross point is set to the edge position 21 of the pattern shown in FIG.
It is defined as 2,214. In addition, strength 34 and minimum strength 35
Intermediate strengths 342 and 344 of the above are determined, and binarization processing is performed to define the edge positions 222 and 224 of the upper ground pattern 22. As described above, conventionally, the slice level is provided for the reflected light intensity, the edge position is determined by the binarization method, and the pattern position deviation is measured from the distance scanned between the edges.

[0006]

The shape and intensity level of the reflected light intensity signal waveform from the pattern are such that the reflectance, surface roughness and level difference between the substrate 20 and the patterns 21 and 22, and the shape of the slope portions 23 and 24. Change according to. Of these various factors, the width of the slopes 23 and 24 has the greatest effect on the reflected light intensity signal. It is slope 23,2
Since 4 is a scatterer, the intensity of the reflected light is greatly reduced. Therefore, the intensity of the reflected light is greatly reduced as the spot diameter of the irradiation laser beam becomes smaller or the slope width becomes wider. Therefore, in the conventional method of binarizing the reflected light intensity, the intermediate intensity position changes greatly depending on the slope width, so the pattern edge position detected by the binarization method does not match the original edge position and is accurate. There is a problem that it is not possible to detect a different edge position. Further, in the setting of the intermediate intensity when performing the binarization process, the intensity of the reflected light also varies depending on the variation of the surface roughness and the reflectance of the flat portion of the pattern, and thus the variation of the measured edge position becomes large. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a new measuring method for measuring a pattern position deviation with high accuracy without being affected by the slope width, the surface roughness of a member, and the fluctuation of reflectance. .

[0007]

In order to solve the above problems, the present invention takes the following methods. There is a first pattern having a sloped portion formed on a substrate and a second pattern having a sloped portion formed on the first pattern,
When measuring the positional deviation between the first pattern and the second pattern, the first focus control of the irradiation laser light is performed at a position where the reflected light intensity from the substrate and the first pattern are equal, and the focus position The first scanning of the irradiating laser light is performed to create a first reflected light intensity signal, and the second irradiating laser light is placed at a position where the reflected light intensities from the first pattern and the second pattern are equal. The focus control of, the second scanning of the irradiation laser light at the focus position to create a second reflected light intensity signal, the minimum intensity position for each of the first and second reflected light intensity signal The first pattern and the second pattern are detected by detecting the position of the central portion of the slope of the first pattern and the second pattern, and detecting the position of the central portion of the slope of the first pattern and the second pattern. To measure the positional deviation of the pattern .

[0008]

When the two superposed patterns each have a step and a slope, the first and second patterns are arranged so that the reflected light intensity from the substrate and the underlying pattern and the reflected light intensity from the underlying pattern and the top pattern are equal. The focus position control of the second irradiation laser light is performed. If the laser light is scanned on the pattern surface under this irradiation condition, the maximum intensity of the laser light having a Gaussian intensity distribution will be the maximum at the scanning position where the central part of the slope is irradiated, and the light scattering from the slope will be maximized. Light intensity is minimized. Therefore, the center position of the slope of the pattern can be determined from the minimum intensity position of the reflected light intensity signal. The slope center position of the ground pattern is determined by scanning the laser beam by the first focus control, and the slope center position of the upper ground pattern is determined by the scan by the second focus control. Thus obtained 4
The pattern position shift is measured from the change in the distance between the center positions of the two slopes. The center position of the slope thus determined does not depend on the reflectance, surface roughness, slope width, etc. of the members forming the pattern. Therefore, the present invention accurately measures the positional deviation of the superposed pattern by detecting the central position of the slope instead of detecting the lower edge position of the pattern having the slope.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a pattern position deviation measuring method of the present invention. Reference numeral 10 denotes a laser light source, which is composed of, for example, a semiconductor laser, a He-Ne laser, or the like, and emits laser light 100 having linearly polarized light. Reference numeral 11 denotes a polarization beam splitter (PBS) that performs optical path conversion when detecting reflected light. The laser light transmitted through the PBS 11 enters a first beam scanner 12 that scans the laser light in the X-axis direction and a second beam scanner 13 that scans the laser light in the Y-axis direction. The scanning of the first beam scanner 12 is controlled by a driving signal from the first scanning driver 120, and the scanning of the second beam scanner 13 is controlled by a driving signal from the second scanning driver 130. 1
Reference numeral 10 denotes an objective lens, which collects a laser beam 105 scanned in a two-dimensional plane into a minute spot and irradiates it onto the surface of a fine pattern 14 whose position shift is measured. The pattern 14 has the configuration shown in FIG. The reflected light from the pattern 14 again passes through the first and second beam scanners 12 and 13, is reflected by the PBS 11, and is detected by the light receiver 115 via the condenser lens 140. The reflected light 145 is always incident on a fixed position of the light receiver 115 regardless of which position on the surface of the pattern 14 is scanned by the irradiation laser light, so that detection at the scanning fixed point position becomes possible. Therefore, if a slit having a constant width is attached to the surface of the light receiver 115 and the intensity of a part of the range including the central portion of the intensity distribution of the reflected light is detected, a confocal laser scanning microscope is constructed. With this configuration,
The in-plane resolution can be increased as compared with the non-confocal type detection in which the entire reflected light intensity is detected, and the detection accuracy of the slope center position is improved.

Reference numeral 15 denotes a focus control unit for the irradiation laser beam, which performs focus position control twice in the case of a superposition pattern.
In the first focus control, focus control is performed at a height position such that the intensity of reflected light from the substrate portion 20 of the pattern 14 and the intensity of reflected light from the base pattern (first pattern) 21 become equal. In the second focus control, the focus control is performed at a height position where the intensity of reflected light from the underlying pattern 21 and the intensity of reflected light from the upper pattern (second pattern) 22 are equal. This focus control is performed via the Z stage 150 that moves the pattern 14 in the optical axis direction (Z direction). Reference numeral 16 denotes a first reflected light intensity signal generation unit, which irradiates the surface of the pattern 14 with the first focus-controlled laser light to perform the first scanning, and the reflected light intensity detected at each point of the scanning. The data is stored in a memory circuit and a first reflected light intensity signal corresponding to one scanning cycle is created. Reference numeral 17 denotes a second reflected light intensity signal generation unit, which irradiates the surface of the pattern 14 with the second focus-controlled laser light to perform the second scanning, and the reflected light intensity detected at each point of the scanning. The data is stored in the memory circuit and a second reflected light intensity signal corresponding to one scanning cycle is created. A first minimum intensity position detection unit 165 detects a scanning position where the intensity of the first reflected light intensity signal is minimum. A second minimum intensity position detector 175 detects a scanning position where the intensity of the second reflected light intensity signal is minimum. Since the scanning position with the minimum intensity corresponds to the center of the slope 14 of the pattern 14, the center of the slope 23 of the base pattern 21 in the first scan and the center of the slope 24 of the upper pattern 22 in the second scan. To be detected. Reference numeral 18 denotes a pattern position deviation detection unit, which is a base pattern 2
The pattern position shift is determined from the difference in the distance between the center position of the slope 1 and the center position of the upper ground pattern 22.

Measurement of the pattern positional deviation requires measurement in the X and Y directions. Therefore, if the above-described measurement is performed in each of the X and Y directions, the center position of the slope in the X and Y directions is determined, so that the two-dimensional positional deviation can be measured. As described above, the pattern misalignment measuring method according to the present invention can measure the pattern misalignment with high accuracy by stably detecting the center position of the slope without directly detecting the lower edge position of the pattern. Is possible.

Next, the principle of slope center position detection by the method of the present invention will be described. FIG. 4A shows an example of detecting the center position of the slope of the base pattern 21, and shows a state in which the center of the slope is irradiated with laser light. In the case of an IC, there is a step difference of about 0.5 to 1 μm between the substrate 20 and the base pattern 21, and
The reflectances r1 and r2 of the respective members are different from each other. In this example, the step h1 is equal to or larger than the depth of focus of the irradiation laser light, and the reflectance is r1 <
Assume r2. An irradiation laser beam 41 has a Gaussian distribution. When setting the focus position of the irradiation laser beam 41 for such a pattern, it is necessary to set the focus position according to the reflectance difference and the step. In the present invention, it is necessary to set the focal position so that the reflected light intensities from the substrate 20 and the base pattern 21 are equal to each other.
In this example, the focus is set at a position where the height from the substrate 20 is d. This is the first focus control. When the irradiation laser beam 41 is scanned at this focus position, the intensity maximum part 41
In the case of a deflected state in which 0 is radiated to the central portion of the slope, the intensity of scattered light from the region 42 surrounded by the diagonal line becomes maximum. In addition, a region 422 other than the region 42 irradiated on the substrate 20 and a region 424 irradiated on the flat portion of the base pattern 21.
The reflected light intensity from is equal. Therefore, the reflected light intensity detected by the light receiver 115 is minimized at this deflection position.
The same applies to the case of the base pattern 21 and the upper ground pattern 22. Therefore, the central position of the slope can be detected from the minimum intensity position of the reflected light intensity.

FIG. 4B shows an example of the reflected light intensity signal waveform obtained when the focus position is set as described above. The vertical axis represents the reflected light intensity, and the horizontal axis represents the scanning position (distance) of the irradiation beam.
A waveform 43 is a first reflected light intensity signal detected in the first scan, and a waveform 44 is a second reflected light intensity signal detected in the second scan. In the waveform 43, the intensity V1 is the reflected light intensity from the flat portion of the substrate 20 and the underlying pattern 21, and the intensity V2 is the reflected light intensity from the flat portion of the upper ground pattern 22. In this example, it is assumed that the reflectance of the upper pattern 22 is smaller than that of the underlying pattern 21. In the first focus control, the irradiation laser light has a large focus shift with respect to the upper ground pattern 22, so that the reduction of the reflected light intensity is generally large. The waveform 43 has the minimum intensity at the scanning positions 431 and 433 and the minimum intensity at the scanning positions 435 and 437, but at the scanning positions 431 and 433, the irradiation laser beam 41 is applied to the central portion of the slope of the base pattern 21.
However, at the scanning positions 435 and 437, the upper ground pattern 2
It does not come to the center of the slope of No.2. That is, even if the scattered light intensity from the slope of the upper ground pattern 22 is maximized, the reflected light intensity from the area irradiated to the flat portion of the underlying pattern 21 is the reflected light from the flat portion of the upper ground pattern 22. This is because the strength is larger than the strength, so that the strength does not become the minimum strength as a whole. In this way, by detecting the minimum intensity positions 431 and 433 of the reflected light intensity signal 43 detected in the first scan, the slope center position of the base pattern 21 can be determined.

In the waveform 44, the intensity V3 is the intensity of reflected light from the substrate 20, and the intensity V4 is the intensity of reflected light from the flat portions of the underlying pattern 21 and the upper pattern 22. In the second focus control, the irradiation laser light has a large focus shift with respect to the substrate 20, and thus the reflected light intensity decreases. In the waveform 44, the minimum intensity is obtained at the scanning positions 441 and 443, and the scanning position 4
A minimum strength is obtained at 45 and 447. Here, the scanning position 44
Reference numerals 1 and 443 represent a state in which the irradiation laser beam 41 is applied to the central portion of the slope of the upper ground pattern 22. However, the scanning positions 445 and 447 do not reach the center position of the slope of the underlying pattern 21 as described above. In this way
By detecting the minimum intensity positions 441 and 443 of the reflected light intensity signal 44 detected in the second scanning, the slope center position of the upper ground pattern 22 is determined. At the slope center positions 431 and 433 of the ground pattern 21 and the slope center positions 441 and 443 of the upper ground pattern 22 detected by the above-described two scans, the slope center positions 431 and 44 are detected.
1, and the pattern position shift is detected by comparing the difference in distance between 433 and 443.

Since the most important factor that determines the measurement accuracy of the center position of the slope described above is the scanning accuracy of the irradiation laser beam, a highly accurate two-dimensional scanning optical device is required for measuring the pattern positional deviation. An acousto-optic deflecting element (hereinafter abbreviated as AOD) is often used as a beam scanner with high scanning accuracy. Therefore, a two-dimensional scanning optical device can be constructed using two AODs. However, this configuration has a drawback that the optical system becomes complicated. Therefore, when an AOD is used for the first beam scanner 12 that scans in the X-axis direction, the second beam scanner 13 that scans in the Y-axis direction serves as a right-angle prism having apex angles of 30 ° and 60 °. The scanning optical apparatus can be simplified by using a PZT-moving deflecting prism in which regular triangular prisms having an apex angle of 60 ° are superposed. The structure of a two-dimensional scanning optical system combining these two scanners is disclosed in Japanese Patent Laid-Open Nos. 63-221377 and 63-278032 by the present inventor.
The details are omitted in the specification of the present application. In this scanning optical system, for example, 4 in both the X and Y directions.
When the scanning distance is set to about 0 μm, if the driving signal of each scanning element is divided into 1/4000 and the laser light is scanned stepwise, the scanning resolution becomes 0.01 μm. Therefore, it is possible to detect the center position of the slope with an accuracy of 0.01 μm. In the present invention, an example in which each pattern has a sloped portion has been described. However, even when the pattern has a vertical cross section, the minimum intensity position obtained by the focus-controlled scanning also coincides with the pattern edge position. Therefore, the method of the present invention can be applied even in the case of a vertical pattern.

[0016]

As described above, the present invention utilizes the light scattering effect of the slope of the fine pattern, and the focus position control of the irradiation laser light is performed twice, whereby the center position of the slope of each of the ground pattern and the upper ground pattern is controlled. Are detected independently. Therefore, it is possible to perform highly reliable measurement without being affected by the reflectance, step, surface roughness, slope width, etc. of the members forming the pattern. Furthermore, since only the minimum intensity position of the reflected light intensity signal is detected, simple software is sufficient, high-speed measurement is possible, and it is suitable for in-line measurement on the production line.

[Brief description of drawings]

FIG. 1 is a system block diagram illustrating a pattern position shift measuring method of the present invention.

FIG. 2 is a diagram illustrating an example of the shape of a superposition pattern applied to the present invention, in which (a) is a plan view of the pattern,
(B) is a sectional view.

FIG. 3 shows an example of a reflected light intensity signal waveform obtained by a conventional method.
It is a figure explaining the pattern edge detection method by a value-izing method.

4A and 4B are diagrams illustrating a method of detecting the center position of a slope according to the present invention. FIG. 4A is an example in which a laser beam is applied to the center of the slope, and FIG. 4B is an example of a reflected light intensity signal waveform.

[Explanation of symbols]

 10 Laser Light Source 12 First Beam Scanner 13 Second Beam Scanner 15 Focus Control Section 16 First Reflected Light Intensity Signal Creating Section 17 Second Reflected Light Intensity Signal Creating Section 18 Pattern Misalignment Detection Section 20 Pattern Substrate 21 Base pattern 22 Top pattern 41 Irradiated laser light 165 First minimum intensity position detector 175 Second minimum intensity position detector

Claims (1)

[Claims] 1. A first pattern having a sloped portion formed on a substrate and a second pattern having a sloped portion formed on the first pattern are scanned by laser light to obtain the first and the second patterns. In the method of measuring the positional deviation of the overlay pattern for measuring the positional deviation of the two patterns, the first focus control of the irradiation laser light is performed at a position where the reflected light intensities from the substrate and the first pattern are equal, and the focus is The first scanning of the irradiation laser light is performed at a position to create a first reflected light intensity signal, and the first portion of the irradiation laser light is arranged at a position where the reflected light intensity from the first pattern and the second pattern become equal. The second focus control is performed, the second scanning of the irradiation laser light is performed at the focus position to create the second reflected light intensity signal, and the minimum intensity position for each of the first and second reflected light intensity signals. To detect the first The position of the turn and the center of the slope of the second pattern is detected, and the positional deviation between the first pattern and the second pattern is measured from the difference in the position of the center of the slope of the first pattern and the second pattern. A method for measuring the positional deviation of an overlay pattern, which comprises: