JPH0661115A - Gap detection and setting device - Google Patents

Abstract

PURPOSE:To provide a gap detection and setting device, which is highly precise but simple in construction, to be used in a proximity exposing operation. CONSTITUTION:The gap detection and setting device is composed of a mask 1, a projection optical system, with which the slit image of an S polarized light is projected to a substrate 2, and a light-receiving optical system with which the above-mentioned slit image is projected to a detection system. A gap is computed by detecting the interval between the mask 1 to be projected and the slit image of substrate 2 using a linear image sensor 11. The relation between the number of the pixels on the linear image sensor 11 and the gap is tabulated in advance, the number of pixels in the interval of the detected slit image and the number of pixels of the gap desired to be set are compared by a memory and computing part 15. The gap is set by driving a vertically moving mechanism 23 in such a manner that the difference of the above- mentioned comparison becomes zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a gap between a mask and a substrate in a proximity exposure method in which a mask and a substrate are brought close to each other and a mask pattern is transferred onto the substrate in a manufacturing process of electronic devices such as semiconductors and liquid crystal elements. And a gap detection setting device to be set.

[0002]

2. Description of the Related Art A proximity exposure method is an exposure method in which a mask and a wafer are opposed to each other with a minute gap and a mask pattern is transferred onto a substrate. As a method of detecting this minute gap, there are a method of indirectly obtaining it with an air micrometer, and a method of detecting it while directly facing it by applying an ultrasonic wave or an optical system.

As a method for detecting a gap by applying an optical system, a focus detection method for detecting each surface, a method for measuring a distance between a mask pattern and a projection pattern on a substrate,
There is a method of applying interference.

The focus detection method is a method in which the surface of the mask and the surface of the substrate are separately detected, and the gap is measured from the difference between the focal positions, which is an indirect detection method.

As an example of the method for measuring the distance between the mask pattern and the projection pattern on the substrate, Japanese Patent Laid-Open No. 61-2673 is available.
There is 21. This method provides a pattern on a mask, illuminates it obliquely, and projects its shadow on a substrate. By measuring the distance between the mask pattern and the pattern projected on the substrate with a linear image sensor,
Gaps can be detected.

A method of applying interference is disclosed in Japanese Patent Laid-Open No. Sho 64-64.
There is an example described in -47904. Laser light is incident as TM wave polarized light (P polarized light) at a Brewster's angle, and the laser light reflected from the mask back surface and the wafer front surface is caused to interfere with each other to measure the pitch of interference fringes and detect a gap.

[0007]

In the conventional gap detection method in the proximity exposure apparatus, the absolute value of the gap cannot be directly measured by the focus detection method as described above, and the accuracy of the mechanism for moving the focus position and The reliability is affected by the detection accuracy.

As a method of directly measuring the absolute value of the gap, in the method of projecting the mask pattern, it is necessary to provide a pattern of a predetermined shape on a predetermined position of the mask.

On the other hand, the method for detecting the pitch of the interference fringes is as follows:
From the relationship between the incident angle and the reflectance shown in FIG. 2, when light is incident on the upper surface of the mask with TM (P) polarization and the polarization angle ip ₁ (56.3 °), the reflectance becomes 0 and all the light is reflected within the mask. Proceed to. Light incident on the mask is refracted at an angle of 33.7 ° and travels, and when exiting from the mask into the air, the polarization angle ip
_{At 2} (33.7 °), the reflectance becomes 0, and all the light is not reflected on the lower surface of the mask but is transmitted and travels toward the wafer. That is, not all the incident light is reflected on the upper and lower surfaces of the mask but is reflected on the wafer, and the reflected light is transmitted through the lower and upper surfaces of the mask and emitted at the same angle as the incident angle. Therefore, in this method, two-beam interference due to reflected light from the lower surface of the mask and the upper surface of the wafer cannot occur.

In the proximity exposure apparatus, in order to detect the gap with high accuracy and in a short time, it is advantageous to measure the absolute value with the mask and the substrate facing each other. However, there are constraints on the mask and the processing method as described above.

It is an object of the present invention to detect a gap with a mask and a substrate facing each other with high precision and in a short time with a simple structure and control method, and to set a predetermined gap. It is to provide a gap detection and setting device.

[0012]

In order to achieve the above object, the present invention provides a mask and a substrate on which light has a limited cross-sectional shape in a state where a mask having a circuit pattern and a substrate are brought close to each other. An irradiation optical system consisting of a refraction system that obliquely irradiates and projects at a certain angle, and a refraction system that receives the irradiation light flux of the cross-sectional shape irradiated on the mask and the substrate at a reflection angle corresponding to the incident angle of the irradiation optical system. A light receiving optical system consisting of, a position detecting system consisting of a photoelectric conversion circuit and a detector for converting the light flux of the cross-sectional shape received by the light receiving optical system into an electric signal, and a mask and a substrate obtained by the position detecting system. A calculation unit that stores the position of the light flux and calculates the gap between the mask and the substrate from the difference between the positions, and a variable that moves either or both of the mask and the substrate according to the calculated gap value. The gap detection and setting and means.

Further, the irradiation optical system has a slit having a limited cross-sectional shape, the incident angle with respect to the mask and the substrate is set to 50 to 70 °, and the slit is formed by a refraction system near the mask pattern surface and the substrate surface. Project and image on.

Further, the slit image formed on the mask pattern surface and the substrate surface is set at an exit angle of 50 to 70 ° with respect to the mask and the substrate, and is formed on the position detection system by the refraction system. The interval of the slit image of is detected.

Further, the NA of the refracting system in the irradiation optical system and the light receiving optical system is calculated with the gap detection range as the depth of focus, and the slit width of the irradiation optical system is set to a value closer to the resolution limit than the NA.

Further, a linear image sensor is used as a detector of the position detection system, and the relationship between the interval between slit images projected and formed on the linear image sensor and the number of pixels of the linear image sensor is obtained, and the number of pixels is further determined. The relationship between the mask and the gap between the mask and the substrate is made into a table in advance so that the number of pixels for the gap to be set can be immediately obtained, and either or both of the mask and the substrate can be moved to reach the number of pixels. .

Further, in place of the slits, a pattern having the same shape as the slit width is provided, and the periphery thereof is made of a plate, so that in the linear image sensor, the interval between the portions where the light flux does not reach is obtained. Similarly, the gap is detected.

Also, the contrast of the image reflected by the mask and the substrate is increased by making it possible to switch the laser light to be emitted to S-polarized light or P-polarized light according to the refractive index of the mask and the substrate.

Further, a polarizing element is arranged in the optical path of the irradiation optical system and is rotated so that the light can be arbitrarily switched to S-polarized light or P-polarized light.

[0020]

FIG. 2 shows the reflectance when laser light is incident on the mask as S-polarized light. The refractive index of the mask is 1.
It is the case when it is set to 5. Here, for example, when the light is incident at 67 °, the intensity incident on the mask is 70%, and the intensity reflected on the surface is 30%. The light incident on the mask is 38
Go through the mask at °. Next, when going from the inside of the mask into the air, the intensity of the light transmitted through the mask and emitted is 70%, that is, 49% reaches the substrate. On the other hand, 30% is reflected on the lower surface of the mask.

Thus, with S-polarized light, for example, 50 to 70 °
When the light is incident on the mask at a certain level, there are light reflected on the lower surface of the mask and light reflected on the substrate surface, and the gap can be detected by detecting the difference between the light reflected from both surfaces.

FIG. 3 shows how the light flux travels and the light intensity when the mask and the substrate are brought close to each other. Here, the incident / emitted and reflected intensities are shown beside the arrow when the incident intensity on the mask is 1.

The irradiation optical system has a structure in which a rectangular slit is illuminated with laser light and the slit is imaged by a lens near the lower surface of the mask and the surface of the substrate. The light receiving optical system projects the image of the slit formed on the lower surface of the mask and the surface of the substrate on the detector by the lens. By doing so, stable detection can be performed without being affected even when the mask or the substrate is tilted. The detector uses a linear image sensor to detect the interval between the images of the slit projected on the mask and the substrate. The relationship between the gap between the image of the slit projected on the mask and the substrate in the linear image sensor and the gap between the mask and the substrate is tabulated in advance.

With the above structure, a slit image can be projected on the surfaces of the mask and the substrate facing each other, and the gap can be detected by detecting the interval between the slit images. Further, if the relationship between the gap between the slit images and the gap is obtained in advance, the difference between the gap and the gap to be set can be calculated, and the substrate can be moved up and down so that the difference becomes 0, whereby the predetermined gap can be obtained. Become.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the basic structure of an optical system according to an embodiment of the present invention. This embodiment shows a gap detection optical system in a proximity exposure apparatus which transfers a pattern of the mask 1 onto the substrate 2 by opening a minute gap between the mask 1 and the substrate 2. The gap detection optical system is a projection optical system 3 that projects light.
And a light receiving optical system 4 for receiving the light reflected by the mask 1 and the substrate 2 and a detection system 5 for detecting the light.

The projection optical system 3 uses a laser 6 as a light source, and comprises a collimator lens 7 for expanding and collimating the laser 6 light and a slit 8 for the mask 1 and a first lens 9 for projecting an image on the substrate 2. . In FIG. 1, an arrow A view shows a pattern (back surface) of the mask 1 and a slit image 8 ′ projected on the front surface of the substrate 2 through the mask 1.

The light receiving optical system 4 is composed of a second lens 10 for projecting an image of the slit image 8 ′ projected on the mask 1 and the substrate 2 onto the detection system 5. The detection system 5 is composed of a linear image sensor 11 and a photoelectric conversion circuit 13, but the cylindrical lens 12 has a narrow sensing portion.
The slit image 8'is compressed by the linear image sensor 11
The image is projected and imaged on the light receiving pixel row of.

FIG. 2 shows the relationship between the angle of incidence on the mask 1 and the reflectance. The mask 1 has a refractive index of 1.5. Here, the laser light is S-polarized and the incident angle is 67 °.
When irradiated with, the surface of the mask 1 is reflected 30% and 70%
Enters mask 1.

When this relationship is applied to the actual relationship between the mask 1 and the substrate 2, it becomes as shown in FIG. The surface of the mask 1 reflects 30%, and 70% enters the mask 1. The entering light is refracted at 38 ° and is 3 on the mask 1 pattern (back side).
0% is reflected, and 70% proceeds toward the surface of the substrate 2. The light reflected by the mask 1 pattern (rear surface) repeats reflection and transmission again on the upper surface of the mask 1, and the transmitted light emerges from the surface of the mask 1 at the same 67 ° with respect to the incident angle and the axis. On the other hand, the light traveling toward the surface of the substrate 2 is reflected on the substrate 2 and then reflected and transmitted again on the mask 1 pattern surface and the mask 1 upper surface. Here, the light emitted from the upper surface of the mask 1 is also 6
Has an angle of 7 °. It should be noted that the ratio of reflection and transmission at the boundary surface between the mask 1 and the substrate 2 when the incident intensity on the mask 1 is 1 is shown by a number in each optical path. The strength coming out from the back surface of the mask 1 is about 15%, and the strength coming out from the substrate surface is about 24%. Here, the gap can be obtained by measuring the distance between the image reflected from the back surface of the mask 1 and the image reflected from the surface of the substrate 2.

FIG. 4 shows a method of calculating the gap. When the slit is projected at the incident angle θ, the gap between the slit images 8 ′ on the surfaces of the mask 1 and the substrate 2 is represented by g / cos θ where the gap is g. When the magnification of the light-receiving optical system 4 to the detection system 5 is n, the linear image sensor 11 has n · g / cos θ. The slit image 8 ′ actually projected on the linear image sensor 11 is output by the photoelectric conversion circuit 13 as the contrast of the electric signal.

For example, when the incident angle is 67 °, the distance between the light emitted from the slit image 8 ′ projected on the mask 1 and the substrate 2 is 2.56 · n · g on the linear image sensor 11.
Becomes

FIG. 5 shows a means for obtaining the gap from the number of pixels of the linear image sensor 11. The linear image sensor 11 is an array of fine pixels, and the pixel pitch p is fixed. Therefore, the slit image 8 ′ projected on the linear image sensor 11 at an interval of n · g / cos θ can be represented by m · p obtained by multiplying the pixel pitch p by the number of pixels m (a). Here, the enlargement magnification n and the incident angle θ are determined by the specifications of the optical system, and the pixel pitch p is determined by the specifications of the linear image sensor 11. Therefore, if the number of pixels m is determined, the gap g is uniquely determined (b).

As described above, by preliminarily tabulating the relationship between the number of pixels of the linear image sensor 11 and the gap, the value of the gap can be calculated immediately from the obtained number of pixels.

Next, the NA of the first lens 9 used in the projection optical system 3 and the second lens 10 used in the light receiving optical system 4
The width of the slit 8 of the projection optical system 3 will be described with reference to FIGS. The slit 8 forms a slit image 8 ′ on the mask 1 pattern surface and the substrate 2 surface by the first lens. Slit image 8'on mask 1 pattern surface and substrate 2 surface
Is represented by g / cos θ. Here, when the maximum gap to be detected is G, the interval between the mask 1 pattern surface and the slit image 8 ′ on the substrate 2 surface is G / cos θ.
In this range, it is necessary that the slit image 8 ′ does not cause defocusing on the back surface of the mask 1 and the front surface of the substrate 2. Therefore, the NA of the first lens 9 at that time can be expressed by Equation 1.

[0036]

[Equation 1]

Further, the NA of the second lens 10 used in the light receiving optical system 4 may be obtained in the same manner as in the equation (1).

Next, the slit width W is inevitably determined when the NA is determined, and can be expressed by the equation (2).

[0039]

[Equation 2]

The slit width W obtained by the equation 2 represents the resolution limit of the first lens 9 and the second lens 10.
This is the slit image 8'on the linear image sensor 11.
Is photoelectrically converted and output as a contrast, but if the detection and setting gap is narrow, the slit images 8 ′ projected on the mask 1 and the substrate 2 may approach each other and overlap each other, and detection may not be possible. Therefore, the width of the slit 8 is also the first
This is because if the NA of the lens 9 and the second lens 10 is much larger than the resolution limit, the above-described phenomenon occurs, and it is preferable that the resolution is closer to the resolution limit.

A method for detecting and setting the gap will be described with reference to FIG. The mask 1 is fixed to the mask holder 21, and the substrate 2 is fixed to the substrate chuck 22. The substrate chuck 22 is mounted on the vertical movement mechanism 23. The linear image sensor 11 is connected to the storage / calculation unit 15 via the photoelectric conversion circuit 13 and the interface circuit 14, and is connected from the storage / calculation unit 15 to the drive circuit 24 of the vertical movement mechanism 23 via the interface circuit 14. There is. Further, the storage / calculation unit 15 stores data 16 which is a table of the relationship between the number of pixels of the linear image sensor 11 and the gap shown in FIG.

The order of setting the gap in the above configuration will be described with reference to the flowcharts shown in FIGS. 6 and 7. First, the mask 1 and the substrate 2 are set. The gap at this time is larger than the gap to be set. In this state, the linear image sensor 11 detects a waveform above a certain level. Two of these are extracted from the one with the largest output. Here, the slit image 8'of the mask 1 and the substrate 2
Which of the two is projected on which side of the linear image sensor 11 can be known from the configuration of the light receiving optical system 4. The reason why the two are extracted from the one with a large output is that the light intensity secondary-reflected from the pattern surface of the mask 1 and the surface of the substrate 2 is significantly smaller than the one with a primary reflection. Also, the reflected light from the upper surface of the mask 1 is 30
%, The gap is actually very narrow with respect to the thickness of the mask 1. Therefore, the specifications of the optical system and the linear image are set so that the reflected light from the surface of the mask 1 is out of the detection range of the linear image sensor 11. The specifications of the sensor 11 may be set.

Next, the pixel addresses A and B on the linear image sensor 11 are obtained from the two detected waveforms. This can be obtained by finding the center of the detected waveform and using it as the pixel address of the center. Here, since the relationship between the number of pixels and the gap is uniquely determined as shown in FIG. 5B, it is possible to know how far the number of pixels between A and B is by setting the gap. Therefore, if the vertical movement mechanism 23 of the substrate chuck 22 is driven while comparing with the set gap L, a predetermined gap can be set.

FIG. 8 shows an example of the configuration for applying the gap detection and setting method of the present invention to a proximity exposure apparatus. When the areas of the mask 1 and the substrate 2 are large and in order to set the gap with high accuracy, it is necessary to control the inclination of both surfaces. For that purpose, three gaps in the plane of the mask 1 and the substrate 2 may be detected and set. The gap detection system 30 shown in FIG. 1 is set at any three positions in the plane. The vertical movement mechanism 23 of the substrate chuck 22 is provided at three locations below the gap detection system 30 so that they can be independently driven. An exposure illumination system 31 is provided above the mask 1.
An alignment detection optical system (not shown) for aligning the pattern of the mask 1 and the pattern of the substrate 2 is provided. After the mask 1 and the substrate 2 are set in the above configuration, the gap detection and setting are performed on each of the three axes of the gap detection system.
By performing as shown in FIG. 7, it is possible to set the gap with high accuracy.

Although the structure described above is basic, as an applied modification, as shown in FIG. 9, the slit 8 shown in FIG. 1 is used.
Instead of, rectangular pattern 4 with opposite transmission and shielding
There is also a method of providing 0 on the glass surface. In this case, the linear image sensor 11 measures the interval of the part which is not exposed to light. The other detection and setting algorithms are the same as those in FIGS.

FIG. 10 shows the gap detection at the time of a minute gap. In the small gap, as shown in (a), the slit images reflected by the mask 1 and the substrate 2 have a short interval, so that their waveforms interfere with each other. For this reason mask 1
Also, it becomes difficult to detect the center positions A and B of the slit image reflected by the substrate 2, which may make the measurement impossible. Further, even if A and B can be detected, there is a high possibility that the slit image becomes asymmetrical, which causes a measurement error. As a countermeasure, this will be described with reference to the flowchart shown in FIG.
As shown in (b), the gap is such an amount that the slit images reflected by the mask 1 and the substrate 2 do not sufficiently interfere with each other. At this time, if the light is S-polarized light, the gap can be accurately detected in the slit images of the mask 1 and the substrate 2. The pixel A of the obtained slit image of the mask 1 is stored. Next, by setting the light to P-polarized light, the reflectance of the mask 1 is lowered as shown in (c), and the slit image of the mask 1 cannot be detected. Therefore, only the slit image reflected by the substrate 2 is formed, and the interference between the two slit images does not occur even in a minute gap. The actual gap amount can be accurately obtained by obtaining the interval between the mask pixel A previously obtained and B obtained by setting the P polarization.

FIG. 11 shows means for converting light into S-polarized light and P-polarized light. Polarizing element 50 in the optical path of projection optical system 3
Then, a polarization element drive mechanism 51 for rotating the polarization element 50 about the optical axis is arranged. For example, assuming that the polarizing element 50 is a ½λ plate and is set at a position for transmitting S-polarized light, the S-polarized light decreases as the polarizing element 50 is rotated about the optical axis. The polarized light increases, and when it is rotated by 45 °, it becomes all P-polarized light. still,
The detection and setting algorithm is the same as that shown in FIGS. By the method as described above, the gap can be accurately detected even in a minute gap area where the slit images of the mask 1 and the substrate 2 interfere with each other.

[0048]

According to the present invention, for example, in proximity exposure in which a mask and a substrate are set to have a minute gap and a mask pattern is transferred onto the substrate, the detection and setting of the gap between the mask and the substrate can be managed by an absolute value. High-precision setting is possible.

The fact that a highly accurate gap can be set has the effect that stable resolution performance can be realized in the proximity exposure apparatus over the entire surface of the substrate and the risk of yield reduction due to contact between the mask and the substrate can be reduced. Can be expected.

Further, since it is not necessary to provide a specific pattern on the mask or the substrate, there is an effect that there is no restriction to secure a special space in the mask design. This also means that the areas to be detected on the surface of the mask and the substrate are not limited, which has the effect of increasing the degree of freedom in the configuration of the exposure apparatus.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing an embodiment of a gap detection optical system for detecting a gap between a mask and a substrate according to the present invention.

FIG. 2 is a diagram showing a relationship between an incident angle of laser light and reflectance.

FIG. 3 is an explanatory diagram showing the states of reflection and transmission on the mask and substrate surfaces when the mask is irradiated with S-polarized laser light.

FIG. 4 is a configuration diagram of a gap detection system showing a gap calculation method.

5A and 5B are explanatory diagrams showing a relationship between a slit image interval projected on a linear image sensor and pixels, and a graph showing a relationship between the number of pixels and a gap of the linear image sensor.

FIG. 6 is a configuration diagram showing a detection and setting control system for detecting and setting a gap between a mask and a substrate.

FIG. 7 is a flowchart showing gap detection and setting in FIG.

8 is a perspective view showing an example in which the detection system of FIG. 6 is applied to a proximity exposure apparatus.

9 is a configuration diagram showing an applied modification of the gap detection system of FIG. 1. FIG.

FIG. 10 is an explanatory diagram of gap detection in a minute gap region.

11 is a configuration diagram showing a specific example of detection of a minute gap in FIG.

[Explanation of symbols]

1 ... Mask, 2 ... Substrate, 6 ... Laser, 8 ... Slit,
8 '... Slit image, 9 ... First lens, 10 ... Second lens, 11 ... Linear image sensor, 13 ... Photoelectric conversion circuit, 15 ... Memory operation unit, 16 ... Table, 23 ... Vertical movement mechanism, 30 ... Gap detection system.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Yoshida 292 Yoshida-cho, Totsuka-ku, Yokohama

Claims (8)

[Claims] 1. An irradiation comprising a refraction system in which light is made into a limited cross-sectional shape in a state where a mask on which a circuit pattern is formed and a substrate are brought close to each other and obliquely irradiates and projects on the mask and the substrate at a certain angle. An optical system, a light receiving optical system including a refracting system that receives the irradiation light flux of the cross-sectional shape irradiated on the mask and the substrate at a reflection angle corresponding to the incident angle of the irradiation optical system, and a cross section received by the light receiving optical system. A position detection system including a detector that converts a shaped light beam into an electric signal and a photoelectric conversion circuit, and the positions of the light beams from the mask and the substrate obtained by the position detection system are stored, and the mask and the substrate are determined from the difference between the positions. Of the gap and the displacement detecting means for moving the mask and / or the substrate according to the calculated value of the gap. . 2. The irradiation optical system has slits with a limited cross-sectional shape and has an incident angle of 50 with respect to a mask and a substrate.
2. The gap detection setting device according to claim 1, wherein the gap is set to about 70 [deg.], And the slit is projected and imaged near the mask pattern surface and the substrate surface by a refraction system. 3. The slit image formed on the mask pattern surface and the substrate surface is set at an emission angle of 50 to 70 ° with respect to the mask and the substrate, and is formed on a position detection system by a refraction system. 2. The gap detection setting device according to claim 1, wherein the gap between the slit images is detected. 4. The NA of the refracting system in the irradiation optical system and the light receiving optical system is calculated with the detection range of the gap as the depth of focus, and the slit width of the irradiation optical system is set to a value closer to the resolution limit than the NA. The gap detection setting device according to claim 2 or 3. 5. A linear image sensor is used as a detector of the position detection system, and a relationship between a gap between a slit image projected and imaged on the linear image sensor and a gap between a mask and a substrate is obtained in advance. The gap detection setting device according to claim 1. 6. The gap detection setting device according to claim 1, wherein a pattern having the same shape as the slit width is provided in place of the slit, and the periphery of the pattern is made of a plate. 7. The gap detection setting device according to claim 1, wherein the irradiation light can be switched between S-polarized light and P-polarized light according to the refractive indexes of the mask and the substrate. 8. A polarizing element is arranged in the optical path of the irradiation optical system,
8. The gap detection setting device according to claim 7, wherein the ratio of the S polarization component and the P polarization component of the light is changed by rotating this.