JPH08288201A - Method and apparatus for alignment applied to proximity exposure - Google Patents

Abstract

PURPOSE: To perform an alignment operation with high accuracy without lowering a throughput by a method wherein a mask mark and a wafer mark are observed from the vertical direction with reference to the face of a mask and the alignment operation is formed. CONSTITUTION: The relative position of a mask mark and a wafer mark which are observed by a vertical detection by an image detection device 31 is detected. Then, a wafer-mask movement means 51 is driven so as to obtain a relative positional relationship as a target, and an alignment operation in an in-plane direction is performed. Then, when the alignment operation by the vertical detection is completed, a control device 50 stores the position of an image observed by an image detection device 41 in an oblique direction. Then, a semitransparent mirror 2 is pulled into the side of an objective lens tube 1 as as to be retreated from an exposure area. After its retreat, the image detection device 31 cannot observe an image by the vertical detection. Even when the image detection device 41 retreats the semitransparent mirror 2, it can observe an image by an oblique detection in the same manner as before its retreat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus, and more particularly to an alignment apparatus 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,
A chromatic aberration 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. Since the chromatic aberration double focus method can set the optical resolution of the lens to be high in principle, the absolute alignment accuracy can be improved.

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 during exposure, it causes a decrease in alignment accuracy during exposure.

In the oblique detection method, the optical system is arranged so that the optical axis is inclined with respect to the mask surface, so that the exposure light can be arranged so as not to be blocked. 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 positional deviation during exposure without lowering throughput.

[0006]

In the oblique detection method, the alignment mark and the mask mark are observed obliquely to form an image, and thus the absolute accuracy of alignment is deteriorated due to image distortion. Further, since the optical axis of the illumination light and the optical axis of the detection light do not coincide with each other, it is impossible to perform the fall telecentric illumination. If the illumination optical axis deviates from the ideal optical axis, the image changes and it becomes difficult to perform accurate alignment.

An object of the present invention is to provide an alignment method and an alignment apparatus which can perform highly accurate alignment without lowering the throughput.

[0008]

According to one aspect of the present invention, a wafer having an exposure surface on which first and second wafer marks for alignment are formed, and the first and second wafer marks A step of arranging an exposure mask having first and second mask marks for aligning each other with a gap so that the exposure surface faces the exposure mask; and a normal line of the exposure surface. From the direction, observing the first wafer mark and the first mask mark,
A step of aligning the wafer and the exposure mask in the exposure surface, and observing the second wafer mark and the second mask mark from an oblique direction with respect to the exposure surface, and observing both marks The step of storing the position of the wafer mark, the step of stopping the observation from the normal direction of the exposure surface, the step of observing the second wafer mark and the second mask mark from the oblique direction, and the wafer mark and the mask. And a step of maintaining the position of the mark so as not to shift from the position stored in the step of storing the position.

The first and second wafer marks may be one mark, and the first and second mask marks may be one mark. According to another aspect of the invention,
A gap is formed between a wafer having an exposure surface on which a wafer mark for alignment is formed and an exposure mask on which a mask mark for aligning with the wafer mark is formed so that the exposure surface faces the exposure mask. And a step of arranging with the optical system having an optical axis in an oblique direction with respect to the exposure surface, and forming a point on the focusing surface of the wafer mark and the mask mark on the imaging surface, In the image plane, measuring the distance between two points obtained by vertically projecting the image point of the wafer mark and the image point of the mask mark onto an incident plane including the oblique optical axis; There is provided an alignment method including a step of changing a gap width between the exposure surface and the mask so that a gap between two points matches a target gap.

According to another aspect of the present invention, a wafer holding means for holding a wafer having an exposure surface on which a wafer mark for alignment is formed, and a mask on which a mask mark for aligning with the wafer mark is formed. A mask holding means for holding an exposure mask having a surface and arranging the exposure mask on the exposure surface with a gap, and changing the relative position in the plane of the wafer and the exposure mask. In-plane direction moving means for moving at least one of the wafer holding means and the mask holding means, an optical system having an oblique optical axis obliquely intersecting the exposure surface, and arranged on the oblique optical axis, along the oblique optical axis. Optical axis splitting / combining means for transmitting a part of the traveling light beam and reflecting a part thereof, and the optical axis of the reflected light beam becomes a vertical optical axis perpendicular to the exposure surface; Means, alignment apparatus having an optical axis dividing and synthesizing means moving mechanism for moving in a direction having a component in the linear direction at least the oblique axis and the vertical projection to the exposure surface is provided.

According to another aspect of the present invention, further, the light reflected from the exposure surface and the mask surface and propagating along the vertical optical axis is reflected by the optical axis splitting / combining means, and then the optical system is turned on. The first in-plane moving means for detecting the image formed through the first in-plane moving means based on the relative positional relationship between the images of the wafer mark and the mask mark detected by the first image detecting means. There is provided an alignment apparatus having a control unit that controls and aligns a wafer and an exposure mask in an in-plane direction.

According to another aspect of the present invention, the light reflected from the exposure surface and the mask surface and propagating along the oblique optical axis passes through the optical axis dividing / combining means and then passes through the optical system. Second image detecting means for detecting an image formed by the image forming means, and vertical moving means for moving the wafer holding means and the mask holding means so that the gap width between the wafer and the exposure mask changes. And the control means is the second
An alignment apparatus is provided which controls the vertical movement means based on the relative positional relationship between the images of the wafer mark and the mask mark detected by the image detection means to change the gap width between the wafer and the exposure mask.

According to another aspect of the present invention, the control means has a storage means for storing a positional relationship between the image of the wafer mark and the image of the mask mark detected by the first detection means. An alignment apparatus for controlling the in-plane direction moving means is provided so that the positional relationship between the images of the wafer mark and the mask mark detected by the second detecting means maintains the positional relationship stored in the storage means.

[0014]

[Operation] By observing and aligning the mask mark and the wafer mark from the direction perpendicular to the mask surface,
Highly accurate alignment can be performed.

When alignment marks such as mask marks and wafer marks are observed from an oblique direction, it is difficult to perform highly accurate alignment, but it is possible to detect relative displacement during observation with high precision. is there. Observation from an oblique direction is possible without disposing the optical system directly above the alignment mark. Since the optical system does not block the exposure light, the alignment mark can be observed even during the exposure period. By observing the alignment mark from the oblique direction during the exposure period and controlling the positions of the mask and the wafer so that relative displacement does not occur,
It is possible to prevent positional deviation during the exposure period.

When the alignment mark is observed from an oblique direction, it is focused on a plane perpendicular to the observation optical axis, so that only a part of the mark is focused. The distance between the focused image points of the two marks is proportional to the distance between the mask surface and the wafer surface. Therefore, the distance between the mask surface and the wafer surface can be detected by observing the alignment mark from an oblique direction and measuring the distance between the image points.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A shows the tip of an optical system of an alignment apparatus according to an embodiment of the present invention. The front end portion of the optical system includes an objective lens barrel 1, a half mirror 2, and a linear actuator 3. The mask surface 4 on which the mask pattern is formed and the wafer surface 5 to be exposed are held in parallel with a gap. Mask marks 6 and 7 are formed on the mask surface 4, and wafer marks 8 and 9 are formed on the wafer surface 5.

The optical axis BA1 of the objective lens barrel 1 is
It is arranged so as to be oblique to the mask surface 4 and the wafer surface 5. FIG. 1A shows the case where the angle formed by the normal line direction of the wafer surface 5 and the optical axis BA1 is 50 °.

The half mirror 2 is arranged so that a part of the light beam propagating along the optical axis BA1 is reflected and the optical axis BA2 of the reflected light is perpendicular to the wafer surface 5. The mask mark 6 and the wafer mark 8 are arranged in the observation range of the vertical optical axis BA2, and the mask mark 7 and the wafer mark 9 are arranged in the observation range of the oblique optical axis BA1.

A linear actuator 3 is attached to the side surface of the front end of the objective lens barrel 1, and the half mirror 2
Are held on the optical axis BA1. The linear actuator 3 can move the half mirror 2 in parallel along the optical axis BA1.

The linear actuator 3 is a half mirror 2.
When the lens is extended forward from the tip of the objective lens barrel 1, the tip of the half mirror 2 enters the exposure area EA. In this state, the mask mark 6 and the wafer mark 8 can be observed, but if the exposure is performed as it is, the exposure light is blocked. When the linear actuator 3 pulls the half mirror 2 toward the objective lens barrel 1, the half mirror 2 is retracted to the outside of the exposure area EA as shown by the broken line in the figure.
By retracting the half mirror 2 out of the exposure area,
It is possible to perform exposure without blocking the exposure light.

FIG. 1B shows the mask surface 4 and the wafer surface 5.
The mask marks 6 and 7 and the wafer mark 8 formed on the
9 shows a plan view of FIG. The wafer marks 8 and 9 are both spaced by the distance W.
And includes two straight line portions arranged parallel to each other. Corresponding straight line portions of wafer marks 8 and 9 are arranged on a straight line with a distance L. Mask marks 6 and 7 are
Both of them include a straight line portion and are arranged in line with each other with a distance L therebetween.

At the time of alignment, the mask marks 6 and 7
And, the straight lines of the wafer marks 8 and 9 are arranged so as to be parallel to the straight line obtained by vertically projecting the oblique optical axis BA1 onto the wafer surface 5. The mask marks 6 and 7 are the wafer marks 8 and
It is positioned so that it lies midway between the two straight portions of 9.

FIG. 2A is a schematic view showing the entire alignment apparatus including the tip of the optical system shown in FIG. 1A. The alignment apparatus includes an optical system tip portion 10, an illumination optical system 20, two detection optical systems 30, 40, a control means 50, and a wafer mask moving means 51.

The illumination optical system 20 includes two light sources 21, 2
2, a dichroic mirror 23, an optical fiber 24, a lens 25, a mirror 26, and a half mirror 27. The light sources 21 and 22 emit illumination light having different wavelengths. The dichroic mirror 23 includes the light sources 21, 2
The illumination lights radiated from 2 are combined and enter the optical fiber 24. The illumination light emitted from the optical fiber 24 is converged by the lens 25, reflected by the mirror 26, and the half mirror 2
7 is introduced on the oblique optical axis BA1.

The illumination light introduced on the oblique optical axis BA1 is reflected by the half mirror 2 and is irradiated vertically on the mask surface 4 and the wafer surface 5. It should be noted that oblique illumination light is emitted from a light source (not shown) from the opposite direction to the reflected light that has passed through the half mirror 2 and is reflected by the mask surface 4 and the wafer surface 5.

The optical system 30 comprises a relay lens 32 and an image detecting device 31. The optical system 40 includes a half mirror 44, a mirror 43, a relay lens 42, and an image detecting device 4.
It consists of 1.

The reflected light reflected from the mask surface 4 and the wafer surface 5 and propagating along the oblique optical axis BA1 and the vertical optical axis BA2 is combined by the half mirror 2 and propagates along the oblique optical axis BA1. The combined reflected light is split by the half mirror 44, and one reflected light is converged by the relay lens 32 to form an image on the light receiving surface of the image detection device 31. The other reflected light is reflected by the mirror 43, is converged by the relay lens 42, and forms an image on the light receiving surface of the image detection device 41.

An optical sensor 1 is provided on the light receiving surface of the image detecting device 31.
The vertical reflection image formed on the light receiving surface is converted into an electric signal. An optical sensor is two-dimensionally arranged on the light receiving surface of the image detecting device 41, and converts the oblique reflection image formed on the light receiving surface into an electric signal.

The control device 50 processes the electric signals from the image detection devices 31, 41 and calculates the distance between the mask mark and the wafer mark. The calculated distance is compared with the previously stored target distance, and a control signal is sent to the wafer mask moving means 51 so that the distance between the marks approaches the target distance.

The wafer mask moving means 51 comprises the control means 5
Based on a control signal from 0, the wafer or mask is moved relatively. The movement direction is the biaxial direction in the mask plane, the in-plane rotation direction, and the direction perpendicular to the mask plane.

Next, the optical path of the optical system of the alignment apparatus shown in FIG. 2 will be described. First, suppose light of a single wavelength. FIG. 3A shows the tip of the optical system of the alignment apparatus, focusing on the optical axis. Mask surface 4 and wafer surface 5
However, they are arranged in parallel at a distance δ. Mask surface 4
The oblique optical axis BA1 is arranged so as to form an angle of 50 ° with the normal line direction. A vertical optical axis BA2 divided from the oblique optical axis BA1 by the half mirror 2 intersects the mask surface 4 perpendicularly.

Points P ₁ and P ₂ respectively represent an intersection between the vertical optical axis BA2 and the mask surface 4 and an intersection between the vertical optical axis BA2 and the wafer surface 5, and a point Q ₁ represents the oblique optical axis BA1 and the mask surface 4. The intersection, point O, represents the intersection of the oblique optical axis BA1 and the vertical optical axis BA2.

The distance between the mask surface 4 and the wafer surface 5 is 27 μ.
Consider a case where m and the length of the line segment OP ₁ are 3.45 mm.
The length of the line segment P ₁ Q ₁ is about 4.11 mm. Therefore,
The distance L between the mask marks 6 and 7 shown in FIG. 1B may be about 4.11 mm.

The length of the line segment OQ ₁ is about 5.37 mm. The reflected light from the point Q ₁ on the oblique optical axis BA1 and the vertical optical axis B
The optical path difference of the reflected light from the point P ₁ on A 2 is OQ ₁ −OP
_Since it is _1, it is about 1.92 mm. When imaging the P _1, Q ₁ these points in the lens, the point Q ₁ is, imaged at a position closer to the lens than the point P _1. Objective lens magnification is 1
When the magnification is 0 times, the distance between the image forming point of the point P _{1 and} the image forming point of the point Q ₁ is about 108.6 mm.

By arranging the light receiving elements at the image forming point of the point P _{1 and} the image forming point of the point Q ₁ , respectively, a mask mark in the observation area of the vertical optical axis BA2 and a mask mark in the observation area of the oblique optical axis BA1. Can be observed respectively.

FIG. 3B shows the tip portion 10 of the optical system and the detection optical systems 30 and 40 focusing on the optical axis. The reflected lights reflected at the points P ₁ and Q ₁ are combined by the half mirror 2 to form one light beam, which propagates along the oblique optical axis BA1.
The combined light flux is converged by the objective lens 10a and split by the half mirror 44. Both the light flux transmitted through the half mirror 44 and the light flux reflected by the half mirror 44 include the reflected light from the point P ₁ and the point Q ₁ .

The light flux transmitted through the half mirror 44 is converged again by the relay lens 32. By disposing the light receiving surface of the image detecting device 31 at the image forming point of the point P ₁ , the image detecting device 31 can observe the mask mark within the observation range of the vertical optical axis BA2. Observing the mask mark from the optical axis perpendicular to the mask surface is called vertical detection.

The light beam reflected by the half mirror 44 is reflected by the mirror 43 and is converged again by the relay lens 42.
By disposing the light receiving surface of the image detecting device 41 at the image forming point of the point Q ₁ , the image detecting device 41 can observe the mask mark in the observation range on the oblique optical axis BA1. in this way,
Observing a mask mark through an optical axis that is oblique to the mask surface is called oblique detection.

It should be noted that on the light receiving surface of the image detecting device 31, the point Q ₁
The light flux reflected by the light is also incident, and the light flux reflected by the point P ₁ is also incident on the light receiving surface of the image detecting device 41. However, since the in-focus position of these light rays is far from the light receiving surface, flare or the like occurs. There is no adverse effect on the observation of the image.

In FIG. 3A, the light irradiating the mask surface 4 and the wafer surface 5 along the vertical optical axis BA2 has two different wavelengths λ ₁ and λ ₂ (λ ₁ <, as described in FIG. λ
₂ ) Contains the light. Light reflected by the points P ₁ and P _2, connecting the two images at different positions by the chromatic aberration of the optical system.

The image of the reflected light of the wavelength λ ₂ at _one of the points P _{1 and} the image of the reflected light of the other wavelength λ _{1 at} the point P ₂ are both formed on the light receiving surface of the image detector 31. By adjusting the chromatic aberration, the mask mark and the wafer mark can be accurately focused and observed simultaneously by the image detection device 31.

Next, with reference to FIG. 4, the state of image formation of the mask mark and the wafer mark observed obliquely will be described. FIG. 4A shows a cross section of the mask surface 4 and the wafer surface 5 near the oblique optical axis BA1. Mask surface 4 and wafer surface 5
A mask mark 7 and a wafer mark 9 which are linear are formed on the respective sides in the lateral direction of the drawing.

Consider the case where the focus is at the position of the point Q ₂ on the wafer mark 9. The wafer mark 9 is shown in FIG.
Since it has two straight line portions arranged in parallel as shown in (B), the positions of both points Q ₂ of the two straight line portions are in focus. At this time, on the mask mark 7, the position of the intersection Q ₁ with the virtual plane passing through the point Q ₂ and perpendicular to the optical axis BA ₁ is focused.

FIG. 4B shows a state of an image formed on the light receiving surface of the image detecting device 41 shown in FIG. 3B. Points Q ₁ , Q
Reference numeral ₂ denotes the image points of points Q ₁ and Q ₂ in FIG. 4 (A), respectively. An imaginary plane (incident surface) including the oblique optical axis BA1 and perpendicular to the wafer surface intersects with a vertical intersection line perpendicular to the paper surface in FIG. Although the mask mark and the wafer mark also extend above and below the points Q ₁ and Q _2, the image is blurred because they are out of focus.

The mark spacing c shown in FIG. 4B is a virtual plane (incident surface) that includes the oblique optical axis BA1 and is perpendicular to the wafer surface.
Is the distance between the two projected points when the points Q ₁ and Q ₂ are vertically projected on the. The mark spacing c corresponds to the spacing between the mask surface 4 and the wafer surface 5 as described later. Points Q ₁ and Q
The relative position in the horizontal direction in FIG. ₂ corresponds to the relative position in the direction perpendicular to the paper surface of the mask surface 4 and the wafer surface 5 in FIG.

Next, the interval δ between the mask surface 4 and the wafer surface 5
The detection method of will be described. Wafer surface 5 is the wafer surface
When moved to the position of 5 ', the focus point Q of the wafer mark 9
₂Point Q₂Move to ‘ Therefore, the smell in FIG.
Image point Q₂Moves to the top of the figure and the mark spacing c also decreases
I do.

In FIG. 4A, when the length of the line segment Q ₁ Q ₂ is represented by L (Q ₁ Q ₂ ), the relationship of δ = L (Q ₁ Q ₂ ) × sin (θ) is established. . Here, θ is an angle formed by the oblique optical axis BA1 and the normal line direction of the wafer surface 5. L (Q ₁ Q ₂ ) is
Since it can be calculated from the mark distance c in FIG. 4A based on the magnification of the optical system, the distance δ between the mask surface 4 and the wafer surface 5 can be obtained by measuring the mark distance c.

The right side of the image plane in FIG. 4B shows the vertical luminance distribution in the image plane. By performing processing such as similarity pattern matching on the luminance distribution (page 4, lower left column, line 14 to page 7, upper left column, line 3 of Japanese Patent Laid-Open No. 2-91502), a resolution of about 10 nm is obtained. L (Q ₁ Q ₂ ) can be measured. When the angle θ is 50 °, L (Q ₁ Q ₂ ) varies by 1.3 μm when the interval δ varies by ₁ μm. Therefore, the interval δ can be detected with sufficient accuracy.

Next, a method of performing alignment using the alignment apparatus shown in FIG. 2 will be described. First, the half mirror 2 is extended forward from the tip of the objective lens barrel 1, and the mask marks 6 and 7 and the wafer marks 8 and 9 shown in FIG. As described above, the mask mark 6
And the wafer mark 8 are observed by vertical detection, and at the same time, the mask mark 7 and the wafer mark 9 are observed by oblique detection. In the image detection device 41, an image as shown in FIG. 4 (B) is observed. The control device 50 shown in FIG. 2 measures the mark interval c by, for example, the similarity pattern matching described above,
The interval δ is calculated.

The calculated interval δ is compared with the previously stored target interval, and the interval δ matches the target interval.
A control signal is sent to the wafer mask moving means 51. The wafer mask moving means 51 moves the wafer or the mask based on the control signal and sets the interval δ to a desired interval.

Next, the mask mark 6 and the wafer mark 8 (FIG. 1) observed by the image detection device 31 by vertical detection.
The relative position of (A)) is detected. The wafer mask moving means 51 is driven to perform the in-plane alignment so that the target relative positional relationship is achieved. That is, alignment is performed by vertical detection. Actually, three sets of alignment devices shown in FIGS. 1 and 2 are provided, and each alignment device performs alignment. In this way, the alignment in the biaxial direction in the mask plane and the in-plane rotation direction can be performed.

When the alignment by the vertical detection is completed, the control device 50 stores the position of the image observed by the image detection device 41 by the oblique detection. Next, the half mirror 2 is pulled toward the objective lens barrel 1 side and retracted from the exposure area. After the evacuation, the image detection device 31 cannot observe the image by the vertical detection. Even if the half mirror 2 is retracted, the image detecting device 41 can observe the image by the oblique detection as before the retracting.

Exposure is performed after the half mirror 2 is retracted. The control device 50 monitors the position of the oblique detection image obtained by the image detection device 41 from the time when the half mirror 2 is retracted until the end of the exposure. From the controller 50 to the wafer mask moving means 51 so as to maintain the position of the oblique detection image at the time when the alignment is completed by the vertical detection.
A control signal is sent to.

In the above-mentioned alignment method, first, the position is aligned by the vertical detection, and the aligned positional relationship is maintained by the diagonal detection. It is difficult to ensure high positional accuracy in the alignment by the oblique detection due to the influence of astigmatism of the lens. Further, since the mask mark and the wafer mark are formed by providing unevenness on the mask surface and the wafer surface, the size and position of the shadow also change when the optical axis of the illumination light changes. The change in the size and position of the shadow causes a registration error.

On the other hand, in the case of the vertical detection, the influence of the astigmatism of the lens is small, and the fluctuation of the illumination optical axis is changed by using the epi-illumination telecentric illumination in which the observation optical axis and the illumination optical axis are matched. Can be prevented. Therefore,
Vertical detection enables highly accurate alignment.

Further, it is difficult to secure sufficient positional accuracy only by performing positional control of the wafer and the mask using, for example, a laser interferometer during the exposure period after performing the absolute positional alignment. It is difficult to detect the absolute position with high accuracy by the position adjustment by the oblique detection, but the position deviation during observation can be detected with sufficiently high accuracy. In addition, if the optical axis of the illumination light is fixed from the completion of alignment by vertical detection until the end of exposure, shadows do not change, so the positional relationship can be maintained with high accuracy. is there.

In the above alignment method, since absolute position alignment is first performed by vertical detection, it is possible to perform position alignment with high accuracy. Since the relative positional relationship is maintained by the oblique detection during the exposure period, it is possible to perform the exposure in a highly accurately aligned state.

In addition, since it is sufficient to retract the half mirror between the vertical detection and the exposure, it is not necessary to retract the entire detection optical system, so that quick exposure can be performed and the reduction in throughput can be suppressed. can do.

Next, the conditions required for the illumination light for oblique detection will be described. FIG. 5 shows the positional relationship between the detection optical axis and the illumination optical axis. As described above, since it is only necessary to detect the relative positional relationship with high accuracy in the oblique detection, the constraint condition for the illumination optical axis for the oblique detection is loose. That is, the specularly reflected light from the mask surface and the wafer surface may enter the objective lens. Assuming that the numerical aperture of the objective lens is NA, the illumination optical axis has an aperture angle of sin around the optical axis BA3 that is symmetrical with respect to the normal direction of the mask surface 4 within the plane including the detection optical axis BA1.
It is only necessary to be within the cone CN of ^-1 (NA).

FIG. 6 shows an example of arrangement of wafer marks.
Unit exposure areas 60 are arranged in a matrix on the wafer surface with a scribe line 61 interposed therebetween. Wafer mark 62 for alignment of exposure area 60 in the center of the figure
A, 62B, and 62C are arranged on the scribe line surrounding the exposure area 60. Each wafer mark includes two pairs of straight line portions 8 and 9, for example, as shown in FIG.

The wafer marks 62A and 62B are for alignment in the vertical direction of the drawing and the in-plane rotation direction of the wafer, and the wafer mark 62C is for alignment in the horizontal direction of the drawing.
It is necessary to arrange a wafer mark for vertical detection and a wafer mark for oblique detection at a predetermined interval on a wafer that is symmetrical in position alignment in the alignment method according to the present embodiment. Therefore, it is preferable to arrange the wafer mark on the scribe line as shown in FIG. The exposure area 60 is an area in which a circuit pattern or the like is formed, and the areas actually exposed are the wafer marks 62A to 6A.
It is a region including 2C.

Next, the result of the confirmation experiment for understanding the influence of the half mirror 2 shown in FIG. 1 (A) will be described. Figure 7
Indicates the optical system used in the confirmation experiment. A plane parallel glass 71 and a wafer 72 are arranged on the optical axis of the lens 70. The pattern formed on the surface of the wafer 72 was observed through the plane-parallel glass 71 to measure the decrease in resolution and contrast.

As the plane-parallel glass 71, a thickness of 0.33 mm (manufactured by Nippon Filcon Co., Ltd.) and a thickness of 1 mm (manufactured by Nikon Co., Ltd.), which conform to the JIS standard for transmission observation, are used.
Experiments were carried out on two types. The numerical aperture NA of the objective lens is 0.4, and the total magnification of the optical system is 100 times. The step difference of the pattern formed on the wafer surface is about 1 μm.

In this confirmation experiment, it was possible to confirm the influence of the thickness of the plane-parallel glass on the spherical aberration. When the pattern on the wafer surface was observed through the plane-parallel glass, no decrease in resolution and contrast was observed when the glass thickness was 0.33 mm and 1 mm. From this, when the numerical aperture of the objective lens is 0.4, it is considered that there is no practical problem if the thickness of the half mirror is 1 mm or less.

The linear actuator 3 shown in FIG. 1 (A)
For example, those commercially available under the trade name of Pico Table from NOK F-Tech Co., Ltd. can be used. The stroke of this linear actuator is 5 mm /
10 mm, loading mass 0.3 kg, running parallelism 5 μm
Is.

The alignment apparatus can be applied to ordinary visible light exposure, ultraviolet light exposure, and X-ray exposure. In particular, it is effective for X-ray exposure in which reduction exposure is difficult. Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0068]

As described above, according to the present invention,
The vertical detection enables highly accurate alignment of the wafer and the mask. Further, it is possible to prevent the positional deviation during the exposure period by the oblique detection. Further, it is possible to suppress a decrease in throughput due to withdrawal from the exposure area of the optical system.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a tip portion of an optical system of an alignment apparatus according to an embodiment of the present invention, and a plan view showing an arrangement of mask marks and wafer marks.

FIG. 2 is a schematic perspective view of an entire alignment apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an optical axis of a tip portion of the optical system shown in FIG. 1 and a diagram showing an optical system of the alignment apparatus shown in FIG.

4A and 4B are a cross-sectional view of an alignment portion and a plan view of an image plane for explaining a state of an image by oblique detection.

FIG. 5 is a diagram for explaining an optical axis of illumination light for oblique detection.

FIG. 6 is a plan view for explaining the arrangement of exposure areas and wafer marks on the wafer surface.

FIG. 7 is a diagram showing an optical system of a confirmation experiment for grasping the influence of the half mirror.

[Explanation of symbols]

 1 Objective lens barrel 2, 27, 44 Half mirror 3 Linear actuator 4 Mask surface 5 Wafer surface 6, 7 Mask mark 8, 9 Wafer mark 10 Optical system tip part 20 Illumination optical system 21, 22 Light source 23 Dichroic mirror 24 Light Fiber 25 Lens 26, 43 Mirror 30, 40 Detection optical system 31, 41 Image detection device 32, 42 Relay lens 50 Control device 51 Wafer mask moving means 60 Exposure area 61 Scribe line 62A to 62C Wafer mark 70 Lens 71 Parallel plane glass 72 wafers

Claims (11)

[Claims] 1. A wafer having an exposure surface on which first and second wafer marks for alignment are formed, and first and second wafers for aligning with the first and second wafer marks, respectively. Arranging an exposure mask on which a mask mark is formed with a gap so that the exposure surface faces the exposure mask; and, from the normal direction of the exposure surface, the first wafer mark and the first wafer mark. Observing the first mask mark and aligning the wafer and the exposure mask in the exposure surface, and the second wafer mark and the second mask from an oblique direction with respect to the exposure surface. Observing the marks and storing the positions of both marks; stopping the observation from the normal direction of the exposure surface; and from the oblique direction, the second wafer mark and the second wafer mark. Mask mark The observed alignment method comprising the steps of: the position of the wafer mark and the mask mark is maintained so as not deviated from the position stored in the step of storing the position. 2. The first and second wafer marks are one mark, and the first and second mask marks are one.
The alignment method according to claim 1, which is one mark. 3. A wafer having an exposure surface on which a wafer mark for alignment is formed, and an exposure mask on which a mask mark for aligning with the wafer mark is formed, the exposure surface being the exposure mask. A step of arranging with a gap so as to face each other, and an optical system having an optical axis in an oblique direction with respect to the exposure surface,
Forming an image of a point on the focusing surface of the wafer mark and the mask mark on an image forming surface; and forming an image forming point of the wafer mark and an image forming point of the mask mark on the image forming surface. Measuring a distance between two points vertically projected onto an incident surface including an oblique optical axis; and a gap between the exposure surface and the mask so that the distance between the two points matches a target distance. And a step of changing the width. 4. A wafer holding means for holding a wafer having an exposure surface on which alignment wafer marks are formed, and an exposure mask having a mask surface on which mask marks for aligning with the wafer marks are formed. Then, the mask holding means for arranging the exposure mask on the exposure surface with a gap therebetween, and the wafer holding means and the mask holding means for changing the relative position in the plane of the wafer and the exposure mask. An in-plane moving means for moving at least one of the means, an optical system having an oblique optical axis that obliquely intersects the exposure surface, and a part of the light flux arranged on the oblique optical axis and traveling along the oblique axis. At least one of: an optical axis splitting / combining means for transmitting a part of the light beam, reflecting a part thereof, and an optical axis of the reflected light flux being a vertical optical axis perpendicular to the exposure surface; Alignment apparatus having an optical axis dividing and synthesizing means moving mechanism for moving the oblique axis in a direction having a linear direction of ingredients vertically projected to the exposure surface. 5. The optical system has an objective lens, and the optical-axis division / combination means moving mechanism translates the optical-axis division / combination means along the oblique optical axis in the image-forming light flux of the objective lens. The alignment apparatus according to claim 4, wherein the alignment apparatus is provided. 6. The alignment apparatus according to claim 4, wherein the optical axis division / combination means is a half mirror. 7. The light reflected from the exposure surface and the mask surface and propagating along the vertical optical axis is reflected by the optical axis dividing / combining means,
A first image detecting means for detecting an image formed through the optical system; and the in-plane based on the relative positional relationship between the images of the wafer mark and the mask mark detected by the first image detecting means. The control means for controlling the direction moving means to align the wafer and the exposure mask in the in-plane direction.
6. The alignment device according to any one of 6. 8. The light reflected by the exposure surface and the mask surface and propagating along the oblique optical axis is transmitted through the optical axis dividing / combining means, and then an image formed through the optical system is detected. Second image detecting means, and vertical moving means for moving the wafer holding means and the mask holding means so that the gap width between the wafer and the exposure mask changes, and the control means comprises: 8. The gap width between the wafer and the exposure mask is changed by controlling the vertical moving means based on the relative positional relationship between the images of the wafer mark and the mask mark detected by the second image detecting means. The alignment device according to any one of the above. 9. The control means has a storage means for storing the positional relationship between the images of the wafer mark and the mask mark detected by the first detection means, and is detected by the second detection means. 9. The alignment apparatus according to claim 4, wherein the in-plane direction moving means is controlled so that the positional relationship between the images of the wafer mark and the mask mark is maintained in the positional relationship stored in the storage means. 10. The alignment apparatus according to claim 4, wherein the optical axis division combining means moving mechanism moves the optical axis division combining means in parallel with the oblique optical axis. 11. Further, it is arranged on the oblique optical axis on the side opposite to the exposure mask with the optical axis dividing / combining means interposed therebetween,
An optical axis splitting means for splitting an optical axis is provided, and one of the first and second image detecting means is arranged on the oblique optical axis, and the other is a light split by the optical axis splitting means. The alignment device according to claim 4, wherein the alignment device is arranged on an axis.