JP3048895B2 - Position detection method applied to proximity exposure - Google Patents

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 at the time of 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 of 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 the alignment mark obliquely.

As a focusing method used in the vertical detection method,
The chromatic double focus method is known. The chromatic aberration bifocal method observes a mask mark formed on a mask and an alignment mark formed on a wafer with light of different wavelengths,
This is a method of forming an image on the same plane using 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 in 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 a moving time for evacuation is required, the throughput is reduced. 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, the absolute accuracy of position detection is reduced due to image distortion.
In the oblique detection method reported so far, the observation optical axis and the illumination optical axis are separated and arranged at opposing positions, so that the positional relationship between the two optical axes is easily shifted. If the positional relationship between the two optical axes is slightly shifted, 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 high-accuracy alignment without lowering the 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 are provided. Disposing an exposure mask on which a mask mark for alignment is formed with a gap therebetween so that the exposure surface faces the exposure mask; and irradiating the wafer mark and the mask mark with illumination light, And, the image by the scattered light from the edge of the mask mark, simultaneously imaged on the light receiving surface using an optical system having an observation optical axis oblique to the exposure surface, observing the formed image, Detecting a 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 illuminating light is irradiated from a direction in which specularly reflected light from the wafer mark and the mask mark does not enter the optical system. A detection method is provided.

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 an edge of a wafer mark at a focal point of the optical system; The image of the scattered light, the step of measuring the distance between two images perpendicularly projected on the incident surface including the optical axis of the optical system, based on the distance measured in the step of measuring the distance, Determining a distance between an exposure surface and the exposure mask.

[0011]

Generally, when the illumination optical axis and the observation optical axis are coaxial 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 usually returns in the direction of the observation optical axis. Therefore, the images of these marks cannot be observed. Here, the regular reflection refers to a reflection such that when a parallel light beam is incident, the reflected light also becomes a parallel light beam, and the incident angle and the reflection angle become equal. If an edge for scattering incident light is provided on the wafer mark and the mask mark, an image can be formed by a light flux in 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.

The image formed on the light receiving surface of the observation optical system is only the scattered light from the edges of the wafer mark and the mask mark at the focal point. The distance between the two images obtained by vertically projecting the images of the scattered light from the edges of the wafer mark and the mask mark at the in-focus position onto the incident surface is determined by dividing the edge at the in-focus position on the wafer mark and the mask mark by the incident surface. Corresponds to the distance between the points projected vertically to. The distance between the exposure surface and the mask surface can be determined from the distance between the points at which the edges at the focal points on the wafer mark and the mask mark are vertically projected onto the incident surface.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an edge scattered light observed in an embodiment of the present invention will be described with reference to FIG.

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

Consider a case where the wafer surface 1 is observed with an optical system including an objective lens 5 having an optical axis coaxial with the incident optical axis. Since the light regularly reflected on the upper surface of the convex portion 2 does not enter the objective lens 5, an image cannot be formed by the regular reflection light from the wafer mark. On the other hand, since the scattered light from the edge is emitted in all directions, a part of the scattered light is
Incident on. Therefore, the 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 the scattered light from the edge.

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

The wafer / mask holder 10 comprises a wafer holder 15, a mask holder 16, and a driving 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 certain gap is formed between the exposure surface of the wafer 11 and the mask 12. On the exposure surface of the wafer 11,
A 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 have edges formed to 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 driving mechanism 17 can relatively move the wafer holder 15 and the mask holder 16. When the x-axis is taken in the horizontal direction of the drawing, the y-axis is taken in a direction perpendicular to the paper surface, and the z-axis is taken in the normal direction of the exposure surface, the wafer 11 and the mask 12 are relatively in the x, y, z, and it is movable about a rotating direction of the z-axis (theta _{z-direction).} It is also possible to rotate in rotation directions (θ _x and θ _y directions) around the x axis and the y axis.

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. Illumination light emitted from the light source 24 is reflected by the half mirror 23 to form a light flux along the optical axis 25, and is obliquely incident on the exposure surface through the lens 22. The light source 24 is disposed at the focal point on the image side of the lens 22, and the illumination light emitted from the light source 24 is collimated by the lens 22 into a parallel light beam. In addition, 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 forms an image on the light receiving surface of the image detecting device 21. Thus, the illumination by the optical system 20 is coaxial epi-telecentric illumination.

The image detecting device 21 photoelectrically converts the image 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 control device 30 processes the image signal input from the image detection device 21 to detect a relative position between 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 a 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 parallel to 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 as 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 a chain line A1-A1 in FIG. 2B. Illumination light incident on the wafer mark 13 and the mask mark 14 is scattered at 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 lens 2
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 an image due to 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 reflecting 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 a 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.

When 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 the scattered light from the edge is equivalent to observing the linear image intensity distribution of the lens. The left figure in FIG.
3A illustrates a shape of an image formed on a light receiving surface of the image detection device 21. FIG. Let x be the direction of the line of intersection between the incident surface including the observation optical axis and the light receiving surface.
Assuming that the direction orthogonal to the x-axis in the light-receiving surface is the y-axis, 1
The image by the two edges has a linear shape parallel to the y-axis.
Therefore, the image of each mark is a linear image parallel to the y-axis, x
The shape becomes three 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. Also, since the observation optical axis is oblique to the exposure surface, the image 14A of the mask mark
And the wafer mark image 13A are detected at different positions in the x-axis direction.

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

For example, when it is desired to position the mask mark such that the mask mark is located at the center of the pair of wafer marks in the y-axis direction, one of the wafer and the mask is positioned relative to the other such that y1 and y2 are equal. It is only necessary to move it. Thus, alignment can be performed in the y-axis direction in FIG. FIG.
By arranging three sets of alignment marks and an optical system as shown in FIGS. 3A and 3B, the x-axis, the y-axis, and 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 formed 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 is referred to as an “imaging plane”.

Of the respective edges of the wafer mark and the mask mark, scattered light from the edge on the image plane is focused on the light receiving surface, but scattered light from the edge not on the image plane is focused. The focus defocuses as it moves away from the image plane without being scorched. Therefore, the image of the scattered light from the edge closest to the image plane among the edges of each mark becomes the sharpest, and the image becomes blurred as the distance from the edge in the x-axis direction increases.

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 substantially equal to the distance between the point at which the focal point of the wafer mark and the focal point of the mask mark are vertically projected on the incident surface.

FIG. 2D is a sectional view of the wafer surface 11 and the mask surface 12 on the incident surface in the vicinity of the imaging surface. The point Q ₂ is a point on the line of intersection between the wafer surface 11 and the imaging surface, the point Q ₁
Is a point on the line of intersection between the mask surface 12 and the image-receiving 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 the angle between the normal direction of the wafer surface 11 and the optical axis 25. Therefore, by determining the length of the line segment Q ₁ Q ₂ by measuring the distance x ₁ in FIG. 2 (C), the can know the interval [delta]. In order to know the interval δ more accurately, it is preferable to accurately measure the distance x ₁ . For this purpose, it is better that the focal depth of the lens is 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 driving mechanism 17 as described above, the wafer surface 1 is controlled.
Set the distance between 1 and mask surface 12 to a desired distance
Can be.

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

Observations were made on a wafer in which the wafer mark having the shape shown in FIG. 3A was formed of resist, polysilicon, or aluminum, and on a mask in which the mask mark having the shape shown in FIG. 3A was formed. . FIG. 3 (B)
2E to 2E show each wafer or mask.
(A) shows a part of a cross section taken along dashed-dotted line B2-B2.

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

FIG. 3C shows a wafer on which a wafer mark is formed with polysilicon. An SiO ₂ film 51 is formed on the surface of a silicon substrate 50, and a wafer mark 52 is formed of polysilicon 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 thickness of the SiO ₂ film 51 is 102.6 nm, and the thickness of the wafer mark 52 is 19
8.6 nm, and the thickness of the resist film 53 is 1.8 μm. If this substrate is considered as a substrate in the course of the MOSFET manufacturing process, 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 on which a wafer mark is formed with aluminum. An SiO ₂ film 61 is formed on the surface of a 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 thickness of the wafer mark 62 is 523 nm, and the thickness of the resist film 63 is 1.8 μm. Note that a silicon film for preventing reflection is formed on the surface of the wafer mark 62.

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

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

FIG. 3 (F) is a sketched micrograph of the wafer (FIG. 3 (C)) on which a wafer mark is formed with polysilicon. About two-thirds of the image from the top, two edge scattered light images clearly appear. The images of the 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 focused area. No optical interference was observed between the mask and the wafer. 3B, FIG. 3D, and FIG. 3E, a clear image could be detected similarly to the wafer of FIG. 3C.

FIG. 3G shows an image observed by 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 interval between the scanning lines is 15 μm. That is, the interval between the scanning lines of only the even-numbered fields is 30 μm. FIG.
As shown in (G), three images in the center of the figure clearly appear, and the upper and lower images are blurred. For other samples, clear images 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 in FIG. 3 (G). 4A to 4F show signal waveforms of the 120th to 125th scanning lines of 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 substantially the center in the horizontal direction of the image in FIG.

As shown in FIGS. 4B to 4E, 1
In the 21st to 124th four scanning lines, a rectangular peak appears at the center. This peak corresponds to the image due to the edge scattered light. The negative peaks on both sides of the central peak are horizontal synchronizing signals of the video signal.

For the fourth and fifth images from the top in FIG. 3 (G), the same waveform as the signal waveform corresponding to the third image could be obtained. 5 for the fourth image, 5
For the second image, peaks were detected in four scan lines. That is, peaks were detected on a total of 13 scanning lines for the three clearly appearing images in FIG.

Considering the scanning lines of the odd field, peaks are detected in a total of 26 scanning lines. Since the interval between the scanning lines is 15 μm and the optical magnification is 100 times, the detection of the signal waveform of the scanning line at which the peak appears is 26 [lines] × 15 [μm / lines] ÷ 100 on the observation object surface.
= 3.9 [μm] is equivalent to detecting a mark in a 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 dual focus method. In order to expand the detectable range, the arrangement pitch of the rectangular patterns in FIG.

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

According to the embodiment of the present invention, by observing the wafer mark and the mask mark from an oblique direction, the alignment can be performed in the longitudinal direction of the edge. Since it is not necessary to dispose the optical system within the exposure range, when exposing the wafer after the alignment, the position can always be detected even during the exposure. In addition, since the illumination optical axis and the observation optical axis are coaxial, a stable image can be obtained without any axial deviation.

Further, since the telecentric illumination is used, a change in the image of the edge scattered light when the edge moves within the range of the depth of focus can be suppressed. The regular reflection light of the illumination 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 applied on the exposure surface or the like, the position can be stably detected without being affected by the interference. In addition, since incoherent illumination light is used, there is no light interference at the gap between the wafer surface and the mask surface. In addition, even if coherent light is used, edge scattered light can be observed.

In the observation experiments shown in FIGS. 3 and 4, the angle between the observation optical axis and the normal to the exposed surface was set to 30 degrees.
Even when the angle was changed in the range of degrees to 45 degrees, a clear image due to 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. As described above, any positional relationship may be used as long as specular reflection light of the illumination light does not enter the observation optical system. For example, the angle between two line images perpendicularly projecting the illumination optical axis and the observation optical axis onto the exposure surface is 9
The positional relationship may be smaller than 0 degrees.

FIG. 5A shows that the angle between two line images perpendicularly projecting the illumination optical axis and the observation optical axis onto the exposure surface is 90 degrees.
FIG. 4 is a schematic plan view showing a positional relationship between a positioning mark, an illumination optical system, and an observation optical system when the positional relationship is smaller than the degree. Exposure area EA in the x-axis direction of the positioning marks M _x, y-axis direction positioning marks M _y1 and M _y2 are arranged. Note that FIG.
In FIG. 2, the wafer mark and the mask mark are collectively represented as one mark.

[0067] three marks M _x, by M _y1 and M _y2,
x-axis direction, it is possible to perform the y-axis direction, and the alignment of the rotational direction (theta _z-direction) in the xy plane. The mark M _x is irradiated with illumination light from the illumination optical system L _x , and the mark M _x
Edge scattered light is observed by the observation optical system D _x from. Angle alpha _x constituting the optical axis of the illumination optical system L _x and the optical axis of the observation optical system D _x mutually two line images were vertically projected to the exposure surface
There can be arranged on one side smaller than 90 degrees, the the observation optical system D _x an illumination optical system L _x together with respect to 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 each other, and only the angle between both optical axes and the Z axis may be different.

FIG. 5B shows an alignment mark in the case of the conventional method in which the exposure surface is irradiated with illumination light from an oblique direction, and specular reflection light from the mark is observed to perform alignment.
FIG. 2 is a schematic plan view illustrating a positional relationship between an illumination optical system and an observation optical system. Figure 5 mark M _x if and for alignment in the same manner as the exposure area EA of (A), M _y1 and M _y2 are arranged.

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 symmetrically with respect to the normal to the exposure surface. For example, the illumination light is irradiated from the illumination optical system L _x which is above the figure mark M _x, observing the specular reflection light by the detection optical system D _x which is arranged at the bottom of FIG. Therefore, it is necessary to arrange the illumination optical system and the observation optical system at positions facing each other with the exposure area interposed therebetween. Further, in order to prevent the displacement of the relative positions of the illumination optical axis and the observation optical axis, it is preferable to mount the illumination optical system L _x and a detection optical system D _x into one fixed 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 . The mounting detection optical system D _y1 and the illumination optical system L _y1 to the fixing member F _y1, preferred to attach the detection optical system D _y2 and the illumination optical system L _y2 to the fixing member F _y2. For this reason, the arrangement of the optical system around the exposure area EA is complicated, and the size of the apparatus is also increased.

On the other hand, in the case of the positioning device shown in FIG. 5A, the illumination optical system and the observation optical system can be arranged on one side with respect to the exposure area EA as described above. The arrangement of the optical system is simplified. Therefore, the size of the apparatus can be reduced, and the optical axis can be easily adjusted.

The present invention has been described in connection with the preferred 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 from an oblique direction, the position can be detected with high accuracy. When exposing the wafer after the alignment, it is not necessary to dispose an optical system in the exposure range, so that the position can be always detected even during the exposure period. Therefore, high-precision exposure can be performed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a wafer mark for describing a state of reflection and edge scattering from the wafer mark.

FIG. 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 diagram showing an image due to edge scattered light from the wafer mark and the mask mark and a light intensity distribution in the image plane, and FIG. 2D is a cross-sectional view of the wafer plane and the mask plane in the vicinity of the imaging plane.

FIG. 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 a mask on which a mask mark is formed. FIG. 3F is a view in which an edge scattered light from the wafer mark shown in FIG. 3
FIG. 3 is a diagram in which an image obtained by observing edge scattered light from a wafer mark shown in FIG.

FIG. 4 is a diagram showing signal waveforms for each scanning line of a photograph taken by the television camera in FIG. 3 (G).

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Wafer surface 2 Convex part 3, 4 Illumination light 5 Objective lens 10 Wafer / mask holder 11 Wafer 12 Mask 13 Wafer mark 14 Mask mark 15 Wafer holder 16 Mask holder 17 Drive mechanism 20 Optical system 21 Image detector 22 Lens Reference Signs List 23 Half mirror 24 Light source 25 Optical axis 30 Controller 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)

(57) [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 having an alignment mask mark having an edge for scattering incident light formed thereon. Is disposed with a gap so that the exposure surface faces the exposure mask, and irradiating the wafer mark and the mask mark with illumination light,
The image by the scattered light from the edge of the wafer mark and the mask mark is simultaneously formed on the light receiving surface using an optical system having an observation optical axis oblique to the exposure surface, and the formed image is observed. Detecting the relative position between the wafer and the exposure mask. 2. The position detection method according to claim 1, wherein the illumination light is applied from a direction in which specular reflection light from the wafer mark and the mask mark does not enter the optical system. 3. In the step of detecting the relative position,
A line image of the optical axis of the illumination light vertically projected onto the exposure surface,
3. The position detecting method according to claim 2, wherein an angle between the observation optical axis and a line image perpendicularly projected on the exposure surface is smaller than 90 degrees. 4. The position detecting method according to claim 3, wherein an optical axis of the illumination light and an optical axis of the observation light are common. 5. The position detecting method according to claim 4, wherein the illumination light is collimated light. 6. In the step of detecting the relative position,
The position detecting method according to claim 1, wherein a relative position between the wafer and the exposure mask in a longitudinal direction of the edge is detected. 7. The step of detecting the relative position includes: an image of scattered light from an edge of a wafer mark at a focal point of the optical system; and an image of scattered light from an edge of a mask mark at a focal point of the optical system. A step of measuring the distance between two images perpendicularly projected on the incident surface including the optical axis of the optical system, and the exposure surface and the light based on the distance measured in the step of measuring the distance. 7. The method according to claim 1, further comprising: determining an interval between the exposure mask and the exposure mask.