JPH0927449A - Position detection method applicable to proximity exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an alignment with high precision without lowering a throughput by a method wherein a wafer having an exposure face formed with a wafer mark and an exposure mask having a mask mark are arranged so that an exposure face is opposed to the exposure mask, and a relative position is detected by scattered lights from an edge of the respective marks. SOLUTION: A wafer 11 is held on an upper face of a wafer holding pedestal 15 and a mask 12 is held on a lower face of the mask holding pedestal 16. The wafer 11 and the mask 12 are arranged at regular intervals between an exposure face of the wafer 11 and the mask 12. A wafer mark 13 is formed on the exposure face of the wafer 11 and a mask mark 14 is formed on a lower face of the mask 12, and an edge scattering incident lights is formed. Lights scattered by the edge of the wafer mark 13 and the mask mark 14 are incident on lens 22 and focused to form an image on a light receiving face of an image detector 21. The image is converted into image signals, which are input into a controller 30 to process the image signals, so that a relative position between the wafer mark 13 and the mask mark 14 is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting method during alignment, and more particularly to a position detecting method suitable for improving the throughput of proximity exposure.

[0002]

2. Description of the Related Art In an alignment apparatus combining a lens system and an image processing system, a vertical detection method and an oblique detection method are known as alignment methods for a wafer and a mask during alignment. The vertical detection method is a method of observing the alignment mark from a direction perpendicular to the mask surface, and the oblique detection method is a method of observing it obliquely.

As a focusing method used in the vertical detection method,
The chromatic double focus method is known. The chromatic aberration double focus method observes the mask mark formed on the mask and the alignment mark formed on the wafer with light of different wavelengths,
This is a method of forming an image on the same plane by utilizing chromatic aberration. In the chromatic aberration double focus method, since the optical resolution of the lens can be set high in principle, the absolute position detection accuracy can be increased.

On the other hand, in order to observe the alignment mark from the vertical direction, an optical system for observation enters the exposure area. If the exposure is performed as it is, the optical system blocks the exposure light. Therefore, it is necessary to retract the optical system from the exposure area during the exposure. Since the moving time for saving is required, the throughput decreases. Further, since the alignment mark cannot be observed at the time of exposure, the position cannot be detected. This causes a reduction in alignment accuracy during exposure.

In the oblique detection method, since the optical system is arranged so that the optical axis is oblique to the mask surface, it can be arranged so as not to block the exposure light. Therefore, it is not necessary to retract the optical system during exposure, and the alignment mark can be observed even during exposure. Therefore, it is possible to prevent the displacement during the exposure without lowering the throughput.

[0006]

In the oblique detection method, since the alignment mark and the mask mark are observed obliquely to form an image, image distortion reduces the absolute accuracy of position detection.
In the oblique detection methods that have been reported so far, since the observation optical axis and the illumination optical axis are separated and arranged at positions facing each other, the positional relationship between both optical axes is likely to shift. If the positional relationship between the two optical axes is slightly deviated, the image changes and it becomes difficult to perform accurate position detection.

An object of the present invention is to provide a position detecting method capable of performing highly accurate alignment without reducing throughput.

[0008]

According to one aspect of the present invention, a wafer having an exposure surface on which an alignment wafer mark having an edge for scattering incident light is formed, and a position having an edge for scattering incident light. A step of arranging an exposure mask on which a mask mark for alignment is formed with a gap so that the exposure surface faces the exposure mask; and irradiating the wafer mark and the mask mark with illumination light, And a step of observing scattered light from the edge of the mask mark to detect the relative position between the wafer and the exposure mask.

According to another aspect of the present invention, in the step of detecting the relative position, the scattered light is observed by an optical system having an observation optical axis oblique to the exposure surface, and the illumination light is the wafer. A position detection method is provided in which specularly reflected light from the mark and the mask mark is emitted from a direction in which the light does not enter the optical system.

According to another aspect of the present invention, there is provided a position detecting method in which the optical axis of the illumination light and the observation optical axis are common. According to another aspect of the present invention, the step of detecting the relative position includes an image of scattered light from the edge of the wafer mark at the in-focus position of the optical system and the edge of the mask mark at the in-focus position. Based on the distance measured in the step of measuring the distance between the two images obtained by vertically projecting the image of the scattered light on the incident surface including the optical axis of the optical system, the distance is measured based on the distance measured in the step of measuring the distance. And a step of determining a distance between the exposure surface and the exposure mask.

[0011]

In general, when the illumination optical axis and the observation optical axis are coaxial with each other and the optical axis is arranged obliquely with respect to the exposure surface, the regular reflection light from the wafer mark and the mask mark returns to the observation optical axis direction. Because of this, the images of these marks cannot be observed. Here, the regular reflection means a reflection in which reflected light becomes a parallel light flux when a parallel light flux is incident, and the incident angle and the reflection angle are equal. When an edge for scattering incident light is provided on the wafer mark and the mask mark, an image can be formed by a light beam within the aperture of the objective lens of the observation optical system out of the scattered light, so that the edge scattered light can be observed. .

Further, even if the illumination light is irradiated from a direction in which the specularly reflected light from the wafer mark and the mask mark does not enter the observation optical system and only the scattered light from the edge enters.
Edge scattered light can be observed.

Only the scattered light from the edges of the wafer mark and the mask mark at the in-focus position is imaged on the light receiving surface of the observation optical system. The distance between two images obtained by vertically projecting the images of scattered light from the edges of the wafer mark and the mask mark at the in-focus position on the incident surface is determined by the distance between the images at the in-focus positions on the wafer mark and the mask mark on the incident surface. Corresponds to the distance between the points projected perpendicular to. The distance between the exposure surface and the mask surface can be obtained from the distance between points obtained by vertically projecting the edge at the in-focus position on the wafer mark and the mask mark onto the incident surface.

[0014]

EXAMPLES First, the edge scattered light observed in the example of the present invention will be described with reference to FIG.

FIG. 1 is a perspective view of a wafer mark for alignment formed on the wafer surface. A convex portion 2 having a rectangular planar shape is formed on the wafer surface 1. Consider a coordinate system in which the x-axis and y-axis are parallel to the sides of this rectangle. When the illumination light having an incident surface perpendicular to the y-axis is obliquely incident on the wafer surface 1, the light 3 incident on the mirror surface area such as the upper surface of the convex portion 2 is specularly reflected, and the light 4 incident on the edge portion is scattered. . In the present specification, specular reflection means reflection such that when a parallel light flux is incident, the reflected light also becomes a parallel light flux and the incident angle and the reflection angle are equal.

Consider the case of observing the wafer surface 1 with an optical system including an objective lens 5 having an optical axis coaxial with the incident optical axis. Since the light specularly reflected by the upper surface of the convex portion 2 does not enter the objective lens 5, it is impossible to form an image by specularly reflected light from the wafer mark. On the other hand, since the scattered light from the edge is emitted in all directions, part of it is
Incident on. Therefore, scattered light can be observed from the same direction as the incident direction of the illumination light. In the embodiment of the present invention, the position of the wafer is detected by observing scattered light from the edge.

FIG. 2A is a schematic sectional view of the position detecting device according to the embodiment of the present invention. Position detection device is wafer /
The mask holding unit 10, the optical system 20, and the control device 30 are included.

The wafer / mask holder 10 is composed of a wafer holder 15, a mask holder 16 and a drive mechanism 17. At the time of alignment, the wafer 11 is held on the upper surface of the wafer holder 15 and the mask 12 is held on the lower surface of the mask holder 16. The wafer 11 and the mask 12 are arranged so that a constant gap is formed between the exposure surface of the wafer 11 and the mask 12. On the exposed surface of the wafer 11,
The wafer mark 13 for alignment is formed, and the mask 1
A mask mark 14 for alignment is formed on the lower surface (mask surface) of 4.

The wafer mark 13 and the mask mark 14 are formed with edges that scatter incident light. When light enters these marks, the incident light that strikes the edges is scattered, and the incident light that strikes other areas is specularly reflected.

The drive mechanism 17 can relatively move the wafer holder 15 and the mask holder 16. Taking the x-axis in the horizontal direction of the figure, the y-axis in the direction perpendicular to the paper surface, and the z-axis in the direction normal to the exposure surface, the wafer 11 and the mask 12 are relatively in the x-direction, the y-direction, the z-direction, and It is movable in the rotation direction around the z axis (θ _z direction). It is also possible to rotate in the rotation directions around the x-axis and the y-axis (θ _x and θ _y directions).

The optical system 20 includes an image detecting device 21 and a lens 2.
2, a half mirror 23, and a light source 24. The optical system 20 is arranged so that its optical axis 25 is oblique to the exposure surface. The illumination light emitted from the light source 24 is reflected by the half mirror 23 to be a light beam along the optical axis 25, and obliquely enters the exposure surface through the lens 22. The light source 24 is disposed at the image-side focal point of the lens 22, and the illumination light emitted from the light source 24 is collimated by the lens 22 to become a parallel light flux. The light source 24 can adjust the intensity of irradiation light.

Of the scattered light scattered at the edges of the wafer mark 13 and the mask mark 14, the light incident on the lens 22 is converged by the lens 22 and focused on the light receiving surface of the image detecting device 21. As described above, the illumination by the optical system 20 is a coaxial incident telecentric illumination.

The image detection device 21 photoelectrically converts the images of the wafer mark and the mask mark formed on the light receiving surface into an image signal. The image signal is input to the control device 30. The controller 30 processes the image signal input from the image detector 21 to detect the relative positions of the wafer mark 13 and the mask mark 14. Further, a control signal is sent to the driving mechanism 17 so that the wafer mark 13 and the mask mark 14 have a predetermined relative positional relationship. The drive mechanism 17 moves the wafer holder 15 or the mask holder 16 based on the control signal.

FIG. 2B is a plan view showing the relative positional relationship between the wafer mark 13 and the mask mark 14. One mark is formed by arranging three rectangular patterns having four sides arranged in parallel with the x-axis or the y-axis in the x-axis direction. Note that three or more rectangular patterns may be arranged as described later. The wafer mark 13 is formed in a pair, and the mask mark 14 is arranged between the pair of wafer marks 13.

The wafer mark 13 and the mask mark 14 in FIG. 2A show a cross section taken along one-dot chain line A1-A1 in FIG. 2B. The illumination light incident on the wafer mark 13 and the mask mark 14 is scattered by the edge protruding toward the optical axis of each rectangular pattern in FIG.
The light applied to the area other than the edge is specularly reflected, and the
No light is incident on 2. Therefore, only the scattered light from the edge can be detected by the image detection device 21.

Next, the nature of the image due to the edge scattered light will be described. The light intensity distribution I of an image by incoherent monochromatic light is

[0027]

[Equation 1]

## EQU1 ## Here, O (x, y) is the intensity distribution of the reflected light from the surface of the observation object, PSF (x, y) is the point spread function (point spread function) of the lens, and the integral is the integral over the entire surface of the observation object. Represent.

Focusing on one edge of each rectangular pattern in FIG. 2B, it can be considered that minute points that reflect light are arranged in parallel to the y-axis. It is assumed that the reflected light intensity distribution from this minute point is a Dirac delta function δ. In fact, the intensity distribution of the scattered light from a minute point could be approximated by a delta function. Assuming that the edge extends in the y-axis direction within a range in which the lens isoplanatism is established, O (x, y) = δ (x).

Equation (1) is

[0031]

[Equation 2]

It can be modified as follows. This I (x) is the line image intensity distribution (line spred function) of the lens,

[0033]

I (x) = LSF (x) (3) Here, LSF (x) represents the linear image intensity distribution of the lens.

If the illumination light has a continuous spectrum,

[0035]

(Equation 4)

## EQU2 ## Where λ is the wavelength of light, LS
Fλ is the line image intensity distribution of the wavelength λ, Δxλ is the lateral shift amount of the line image due to the chromatic aberration of the lens with respect to the light of the wavelength λ, and the integral is the integral over the entire wavelength region.

From equation (4), it can be seen that observing scattered light from the edge is equivalent to observing the line image intensity distribution of the lens. The left diagram of FIG.
The shape of the image formed on the light receiving surface of the image detection device 21 of (A) is shown. The direction of the line of intersection between the incident surface including the observation optical axis and the light receiving surface is x
If the y-axis is the direction perpendicular to the axis and the x-axis in the light-receiving surface, then 1
The image of one edge has a linear shape parallel to the y-axis.
Therefore, the image of each mark is a linear image parallel to the y-axis.
The shape is such that three pieces are arranged in the axial direction.

An image 14A formed by the edge scattered light of the mask mark 14 is formed between a pair of images 13A formed by the edge scattered light of the wafer mark 13. In addition, since the observation optical axis is oblique to the exposure surface, the mask mark image 14A
And the wafer mark image 13A are detected at different positions in the x-axis direction.

The right side of FIG. 2C shows a wafer mark image 1
3A and 3B and the image 14A of the mask mark show the light intensity distribution in the y-axis direction. The distance in the y-axis direction between the wafer mark image 13A and the mask mark image 14A is y1, and the distance in the y-axis direction between the other wafer mark image 13A and the mask mark image 14A is y2. By measuring y1 and y2, the relative positional relationship between the wafer mark 13 and the mask mark 14 in the y-axis direction in FIG. 2B can be known.

For example, when it is desired to position the mask mark in the center of the pair of wafer marks in the y-axis direction, one of the wafer and the mask is relatively positioned with respect to the other so that y1 and y2 are equal. Just move it. In this way, the alignment can be performed in the y-axis direction in FIG. FIG.
By arranging three sets of alignment marks and optical systems as shown in (A) and (B), the x-axis, the y-axis, and the θ _z
It can be aligned with respect to direction.

Next, a method for measuring the distance between the exposure surface and the mask surface will be described. The object point imaged on the light receiving surface of the image detection device 21 is on a plane perpendicular to the optical axis in the object space of the optical system 20. Hereinafter, this plane will be referred to as the "image plane".

Of the edges of the wafer mark and the mask mark, the scattered light from the edge on the imaged surface is focused on the light receiving surface, but the scattered light from the edge not on the imaged surface is focused. The focus is blurred as the distance from the image-forming surface increases without focusing. Therefore, the image of the scattered light from the edge of each mark that is closest to the image formation surface is the sharpest, and the image becomes blurred as the distance from the edge increases in the x-axis direction.

In FIG. 2C, the distance x ₁ represents the distance in the x-axis direction between the most in-focus points of the wafer mark image 13A and the mask mark image 14A. That is, the distance x ₁ is approximately equal to the distance between the points where the focal point of the wafer mark and the focal point of the mask mark are vertically projected on the incident surface.

FIG. 2D shows a cross-sectional view of the wafer surface 11 and the mask surface 12 on the incident surface near the image-formed surface. A point Q ₂ is a point on the line of intersection between the wafer surface 11 and the image formation surface, and a point Q ₁
Is a point on the line of intersection between the mask surface 12 and the image formation surface. The length of the line segment Q ₁ Q ₂ corresponds to the distance x ₁ in FIG.

When the length of the line segment Q ₁ Q ₂ is represented by L (Q ₁ Q ₂ ), the distance δ between the exposure surface 11 and the mask surface 12 is

[0046]

Δ = L (Q ₁ Q ₂ ) × sin (α) (5) Here, α is an angle formed by the normal line direction of the wafer surface 11 and the optical axis 25. Therefore, the distance δ can be known by measuring the distance x ₁ in FIG. 2C and determining the length of the line segment Q ₁ Q ₂ . In order to know the interval δ more accurately, it is preferable to accurately measure the distance x ₁ . For this purpose, the depth of focus of the lens should be shallow.

The control device 30 stores the distance x in advance.₁Target value
Memorized and measured distance x ₁Approaches the target value
By controlling the drive mechanism 17 so that the wafer surface 1
Setting the distance between 1 and the mask surface 12 to a desired distance
Can be.

Next, experimental results of observing scattered light from the wafer mark and the mask mark will be described. FIG.
(A) shows a plan view of a wafer mark and a mask mark to be observed. Rectangular patterns that are long in the horizontal direction in the figure are arranged in the vertical direction at a pitch of 4 μm. In practice, a vernier pattern for overlay accuracy evaluation was used.

Observation was performed on a wafer in which the wafer mark having the shape shown in FIG. 3A was formed of resist, polysilicon, or aluminum, and a mask in which the mask mark having the shape shown in FIG. 3A was formed. . FIG. 3 (B)
2A to 2E of FIG. 2 of each wafer or mask, respectively.
Part (A) of the cross section taken along one-dot chain line B2-B2 is shown.

FIG. 3B shows a wafer having a wafer mark formed with a resist. A resist pattern 41 is formed on the surface of the silicon substrate 40. The resist pattern 41 has a thickness of 1.8 μm.

FIG. 3C shows a wafer having a wafer mark formed of polysilicon. A SiO ₂ film 51 is formed on the surface of the silicon substrate 50, and a wafer mark 52 made of polysilicon is formed on the surface of the SiO ₂ film 51.
A resist film 53 is applied so as to cover the surface of the SiO ₂ film 51 and the wafer mark 52. The SiO ₂ film 51 has a thickness of 102.6 nm, and the wafer mark 52 has a thickness of 19
The thickness of the resist film 53 is 8.6 nm and 1.8 μm. Considering this substrate as a substrate in the process of manufacturing the MOSFET, the SiO ₂ film 51 corresponds to the gate insulating film, and the polysilicon wafer mark 52 corresponds to the gate electrode.

FIG. 3D shows a wafer having a wafer mark formed of aluminum. A SiO ₂ film 61 is formed on the surface of the silicon substrate 60, and a wafer mark 62 made of aluminum is formed on the SiO ₂ film 61. Si
A resist film 63 is applied so as to cover the surface of the O ₂ film 61 and the wafer mark 62. The wafer mark 62 has a thickness of 523 nm, and the resist film 63 has a thickness of 1.8 μm. A silicon film for antireflection is formed on the surface of the wafer mark 62.

FIG. 3E shows a mask on which mask marks are formed. A mask mark 71 made of tantalum is formed on the lower surface of the X-ray transparent film 70 made of SiN.
The X-ray transparent film 70 has a thickness of 2 μm, and the mask mark 71 has a thickness of 0.75 μm.

The samples shown in FIGS. 3 (B) to 3 (E) were observed with a metallographic microscope from a direction inclined 30 ° downward from the normal line direction of the exposure surface (paper surface) in FIG. 3 (A). When observing the wafer marks shown in FIGS. 3B to 3D, the wafer marks were observed through the X-ray transparent film of the X-ray exposure mask. The objective lens of the metal microscope used has a numerical aperture NA of 0.4, an imaging magnification of 100 times, the illumination light is white light from a halogen lamp, and the illumination method is coaxial incident telecentric illumination.

FIG. 3F is a sketch drawing of a micrograph of an observed wafer (FIG. 3C) having a wafer mark formed of polysilicon. The image of the two edge scattered lights clearly appears in a portion about 1/3 from the top of the image. The images of scattered light from the upper and lower edges are blurred because they are out of focus. Thus, a clear image could be detected in the in-focus area. No optical interference was observed between the mask and the wafer. With the wafers or masks of FIGS. 3B, 3D, and 3E, clear images could be detected as in the wafer of FIG. 3C.

FIG. 3G shows an image observed with a television camera having an optical magnification of 100 times and an electric magnification of 9.3 times. The horizontal scanning direction was set to be the horizontal direction in FIG. The spacing between scanning lines is 15 μm. That is, the spacing between the scanning lines in only the even fields is 30 μm. FIG.
As shown in (G), the three images in the center of the figure clearly appear, and the upper and lower images are blurred. As for the other samples, a clear image could be detected as in the case of the wafer in FIG.

FIG. 4 shows the signal waveform of the third clear image from the top of FIG. 4A to 4F show signal waveforms of the 120th to 125th scanning lines in the even field, respectively. The horizontal axis represents the horizontal scanning direction, and the vertical axis represents the light intensity. The center of the horizontal axis corresponds to the substantial center of the image in FIG.

As shown in FIGS. 4 (B) to 4 (E), 1
A rectangular peak appears in the center of the 21st to 124th scanning lines. This peak corresponds to the image by the edge scattered light. The negative peaks on both sides of the central peak are horizontal sync signals of the video signal.

With respect to the fourth and fifth images from the top of FIG. 3G, the same waveform as the signal waveform corresponding to the third image could be obtained. 5 for the fourth statue, 5
Peaks were detected at 4 scan lines for the second image. That is, peaks were detected in a total of 13 scanning lines for the three clearly appearing images in FIG.

Considering the scan lines in the odd fields, peaks are detected in a total of 26 scan lines. Since the interval between scanning lines is 15 μm and the optical magnification is 100 times, it is possible to detect the signal waveform of the scanning line where the peak appears on the observation object surface by 26 [lines] × 15 [μm / line] ÷ 100.
This is equivalent to detecting a mark in the range having a width of 3.9 [μm]. The size of this range is equivalent to the range that can be detected by position detection using the conventional chromatic aberration double focus method. Note that in order to expand the detectable range, the arrangement pitch of the rectangular patterns in FIG. 3A may be narrowed.

If a signal waveform having a clear peak can be obtained, the similarity pattern matching method disclosed in JP-A-2-91502, page 3, lower left column, line 11 to page 7, upper left column, line 3 can be used. It can be used to perform position detection.

According to the embodiment of the present invention, by observing the wafer mark and the mask mark obliquely, the alignment can be performed in the longitudinal direction of the edge. Since it is not necessary to arrange the optical system within the exposure range, when the wafer is exposed after the alignment, the position can be always detected during the exposure. Moreover, since the illumination optical axis and the observation optical axis are coaxial, there is no axis deviation and a stable image can always be obtained.

Further, since the telecentric illumination is used, it is possible to suppress the change in the image of the edge scattered light when the edge moves within the range of the depth of focus. Of the illumination light, the specular reflection light does not enter the observation optical system, and only the scattered light enters. Therefore, the S / N ratio of the image can be adjusted by adjusting the intensity of the illumination light. Since the edge scattered light does not interfere in the resist film or the like applied on the exposed surface, the position can be stably detected without being affected by the interference. Further, since the incoherent illumination light is used, there is no optical interference in the gap between the wafer surface and the mask surface. The edge scattered light can also be observed using coherent light.

In the observation experiment shown in FIGS. 3 and 4, the angle formed by the observation optical axis and the normal line of the exposure surface was set to 30 degrees.
Even when the angle was changed in the range of 45 degrees, a clear image due to the edge scattered light could be detected.

In the above embodiment, the case where the illumination optical axis and the observation optical axis are coaxial has been described, but the positional relationship between the illumination optical axis and the observation optical axis does not necessarily have to be coaxial. The positional relationship may be such that the specularly reflected light of the illumination light does not enter the observation optical system as described above. For example, the angle formed between two line images obtained by vertically projecting the illumination optical axis and the observation optical axis on the exposure surface is 9
The positional relationship may be smaller than 0 degree.

In FIG. 5A, an angle formed by two line images obtained by vertically projecting the illumination optical axis and the observation optical axis on the exposure surface is 90 degrees.
FIG. 6 is a schematic plan view showing a positional relationship among a positioning mark, an illumination optical system, and an observation optical system when the positional relationship is smaller than the degree. In the exposure area EA, alignment marks M _{x in} the x-axis direction and alignment marks M _y1 and M _{y2 in} the y-axis direction are arranged. Note that FIG. 5 (A)
, The wafer mark and the mask mark are collectively represented as one mark.

By the three marks M _x , M _y1 and M _y2 ,
Positioning can be performed in the x-axis direction, the y-axis direction, and the rotation direction (θ _z direction) in the xy plane. The mark M _x, illumination light is irradiated from the illumination optical system L _x, mark M _x
Edge scattered light from is observed by the observation optical system D _x . An angle α _x formed between two line images obtained by vertically projecting the optical axis of the illumination optical system L _{x and} the optical axis of the observation optical system D _x onto the exposure surface.
Is less than 90 degrees, both the observation optical system D _x and the illumination optical system L _x can be arranged on one side of the exposure area EA.

[0068] mark M _y1, M each of an illumination optical system for _y2 L _y1, L _y2 and observation optical system D _y1, D _y2 can also be arranged on one side of the same exposure area EA. In addition,
Images obtained by vertically projecting the illumination optical axis and the observation optical axis onto the exposure surface may overlap with each other so that only the angle between the optical axis and the Z axis is different.

FIG. 5B shows a mark for alignment in the case of the conventional method in which the exposure surface is obliquely illuminated with illumination light and regular reflection light from the mark is observed to perform alignment.
It is a schematic plan view which shows the positional relationship of an illumination optical system and an observation optical system. As in the case of FIG. 5A, alignment marks M _x , M _y1 and M _y2 are arranged in the exposure area EA.

In order to observe the specularly reflected light from the mark, it is necessary to arrange the illumination optical axis and the observation optical axis at positions symmetrical with respect to the normal line of the exposure surface. For example, the mark M _x is irradiated with illumination light from the illumination optical system L _x located above the drawing, and specular reflection light is observed by the detection optical system D _x located below the drawing. Therefore, it is necessary to arrange the illumination optical system and the observation optical system at positions facing each other across the exposure area. Further, in order to prevent the relative position of the illumination optical axis and the observation optical axis from shifting, it is preferable to attach the illumination optical system L _x and the detection optical system D _x to one fixing member F _x .

[0071] mark M _y1, each of the illumination optical system for M _y2 L _y1, L _y2 and detection optics D _y1, D _y2 also has to be disposed to face each other across the same exposure area . Further, it is preferable that the illumination optical system L _y1 and the detection optical system D _y1 are attached to the fixing member F _y1 , and the illumination optical system L _y2 and the detection optical system D _y2 are attached to the fixing member F _y2 . For this reason, the arrangement of the optical system around the exposure area EA becomes complicated, and the apparatus becomes large.

On the other hand, in the case of the alignment apparatus shown in FIG. 5A, the illumination optical system and the observation optical system can be arranged on one side of the exposure area EA as described above. , The arrangement of the optical system becomes simple. Therefore, the device can be downsized and the optical axis can be easily adjusted.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0074]

As described above, according to the present invention,
By observing the wafer mark and the mask mark obliquely, the position can be detected with high accuracy. When the wafer is exposed after performing the alignment, it is not necessary to dispose the optical system in the exposure range, and therefore the position can be always detected during the exposure period. Therefore, highly accurate exposure becomes possible.

[Brief description of drawings]

FIG. 1 is a perspective view of a wafer mark for explaining how reflection and edge scattering from the wafer mark occur.

2A is a schematic sectional view of a position detecting device used in an embodiment of the present invention, FIG. 2B is a plan view of a wafer mark and a mask mark, and FIG. FIG. 2D is a cross-sectional view of the wafer surface and the mask surface in the vicinity of the imaged surface, showing the image and the light intensity distribution in the image surface due to the edge scattered light from the wafer mark and the mask mark.

3A is a plan view of a wafer mark or a mask mark, FIGS. 3B to 3D are cross-sectional views of a wafer on which a wafer mark is formed, and FIG. 3F is a cross-sectional view of the mask on which a mask mark is formed, FIG. 3F is a sketch of a metal micrograph of edge scattered light from the wafer mark shown in FIG. 3A, and FIG. Three
It is the figure which sketched the image which observed the edge scattered light from the wafer mark shown to (A) with the television camera.

FIG. 4 is a diagram showing a signal waveform for each scanning line of a photograph taken by the television camera of FIG.

FIG. 5 is a plan view of an optical system and an exposure area for showing the arrangement of the optical system.

[Explanation of symbols]

1 Wafer Surface 2 Convex Part 3, 4 Illumination Light 5 Objective Lens 10 Wafer / Mask Holding Part 11 Wafer 12 Mask 13 Wafer Mark 14 Mask Mark 15 Wafer Holding Base 16 Mask Holding Base 17 Drive Mechanism 20 Optical System 21 Image Detection Device 22 Lens 23 Half Mirror 24 Light Source 25 Optical Axis 30 Control Device 40, 50, 60 Silicon Substrate 41, 52, 61 Wafer Mark 51 SiO ₂ Film 53, 62 Resist Film 70 X-Ray Transmission Film 71 Mask Mark

Claims (7)

[Claims] 1. A wafer having an exposure surface on which an alignment wafer mark having an edge for scattering incident light is formed, and an exposure mask on which an alignment mask mark having an edge for scattering incident light is formed. A step of arranging with a gap so that the exposure surface faces the exposure mask, and irradiating the wafer mark and the mask mark with illumination light,
And a step of observing scattered light from edges of the wafer mark and the mask mark to detect a relative position between the wafer and the exposure mask. 2. In the step of detecting the relative position,
The scattered light is observed by an optical system having an observation optical axis oblique to the exposure surface, and the illumination light is emitted from a direction in which specularly reflected light from the wafer mark and the mask mark does not enter the optical system. The position detection method according to claim 1. 3. In the step of detecting the relative position,
A line image obtained by vertically projecting the optical axis of the illumination light onto the exposure surface,
The position detecting method according to claim 2, wherein an angle formed by a line image obtained by vertically projecting the observation optical axis onto the exposure surface is smaller than 90 degrees. 4. The position detecting method according to claim 3, wherein the optical axis of the illumination light and the observation optical axis are common. 5. The position detecting method according to claim 4, wherein the illumination light is collimated light. 6. The method according to claim 1, wherein the step of detecting the relative position detects a relative position in the longitudinal direction of the edge.
The position detection method according to any one of 5 above. 7. The image of scattered light from the edge of the wafer mark at the in-focus position of the optical system and the image of scattered light from the edge of the mask mark at the in-focus position in the step of detecting the relative position. And a step of measuring a distance between two images vertically projected onto an incident surface including the optical axis of the optical system, and the exposure surface and the light source based on the distance measured in the step of measuring the distance. 7. The position detecting method according to claim 2, further comprising a step of obtaining a distance from the exposure mask.