JPH08167550A - Position detecting device - Google Patents

Abstract

PURPOSE: To conduct a focussing operation in a stable and highly precise manner by preventing the effect of the pattern of a mask when the focussing operation is conducted using the image in the prescribed visual field of observation on the detection mark. CONSTITUTION: The projection image 7 of a focalizing mark is projected on the wafer mark 48 of the object of detection, and the width HAF of non- measurement direction T of the projection image 7 is set integral multiples of the pitch PT of the wafer mark 48 in the non-measurement direction T. The image 7A of the above mentioned projection image 7 is image-picked up by an image pickup element, and the amount of deviation of the focussing point of the wafer mark 48 is computed on the basis of barycentric position of the integral signal ΣVAF obtained by integrating the image pickup signal in non-measurement direction T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus system for automatically bringing a substrate under test into a focused state when detecting the position of a periodic alignment mark on the substrate under test such as a semiconductor wafer. The present invention relates to a position detection device with a function, and is particularly suitable for application to an alignment system mounted on an exposure device, a microscope for observing periodic alignment marks on a substrate to be inspected, or the like.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device, a liquid crystal display device, or the like, a stepper or the like is used to print a pattern of a reticle as a mask on each shot area on a wafer (or glass plate, etc.) coated with a photosensitive material. Exposure apparatus is used. In such an exposure apparatus, in order to maintain the overlay accuracy between layers when forming a multi-layer circuit pattern on a wafer within a predetermined allowable range, alignment positions attached to each shot area on the wafer are aligned. An alignment device is provided for detecting the position of the mark (wafer mark) for use and accurately aligning the corresponding shot area with the exposure position based on the detection result.

However, since the surface of the wafer has unevenness due to warpage during manufacturing or through various processes, the alignment apparatus has conventionally been used to detect the height of a wafer mark to be detected. A focus detection device is provided to detect whether or not it matches the focus of the objective lens,
The wafer mark is focused by the autofocus method based on the detection result.

In the conventional focusing point detecting device, as disclosed in, for example, Japanese Patent Laid-Open No. 63-90825, an image of a focusing mark is projected on a mark to be detected. FIG. 12 is an explanatory diagram of the detection principle of the conventional focus detection device. In FIG. 12A, the mark 52 to be detected is a dark portion 52a and a bright portion at a predetermined pitch in the X direction which is the position measurement direction. It is assumed that the marks 52b and 52b are alternately arranged. In this case, first, the position of the mark 52 is roughly adjusted by pre-alignment, and then the mark 5
A projected image 53 of the focusing mark is projected on the image.
The projected image 53 of the focusing mark has an S direction intersecting with the X direction at a predetermined angle (this is referred to as a “measurement direction” of the focusing mark), and a T direction (non-measurement direction) perpendicular to this measuring direction S. Is a rectangular bright pattern having sides parallel to, and the reflected light from the projected image 53 is condensed by, for example, a detection optical system whose telecentricity is lost, and the projected image 53 is formed.
Image is re-formed on the image sensor. The projected image 53 of the focusing mark is used to set the observation field of view of the mark 52, and the re-formed image is the image of the mark 52 inside the projected image 53.

Then, an image pickup signal V _AF obtained by scanning the re-formed image in a direction corresponding to the measurement direction S (also referred to as the measurement direction S) on the image pickup element is set in the measurement direction S. Integration is performed in the vertical non-measurement direction to obtain an integrated signal ΣV _AF as shown in FIG. In this case, the barycentric position of the integrated signal ΣV _{AF in} the measurement direction S is obtained as the reference position S1 in advance in a state where the mark 52 matches the focal point of the objective lens for detection, and the integrated signal ΣV _AF is Focusing is performed by adjusting the height of the mark 52 so that it becomes the reference position S1.

[0006]

However, in the conventional technique as described above, the mark to be measured is shown in FIG.
In the case of the mark 52 having a light-dark pattern as shown in (a), if the position of the projected image 53 of the focusing mark shifts, the waveform of the integration signal ΣV _AF changes, and accurate focusing is performed. There was the inconvenience that it could not be done.

That is, in FIG. 13A, the position 54 is the projected image 53 of the focusing mark in FIG. 12A.
Position, and the projected image 53 is almost -X from the position 54.
Direction, then the re-formed image is captured and integrated signal Σ
When V _AF is obtained, a waveform as shown in FIG. 13B is obtained. Since the waveform of FIG. 13B is significantly different from the waveform of FIG. 12B, the position of the center of gravity of the waveform of FIG. 13B deviates from the reference position S1. Therefore, the integrated signal ΣV _AF
When focusing is performed based on the deviation of the barycentric position from the reference position S1, there is an inconvenience that defocus (focus error) occurs.

In particular, in recent years, for example, with the miniaturization of semiconductor integrated circuits, the alignment accuracy has become higher. Therefore, in order to keep the alignment accuracy within the required accuracy, the focus at the time of detecting the position of the alignment mark. It is desired to make the deviation smaller than before. In view of such a point, the present invention eliminates the influence of the mark pattern when performing focusing using an image in a predetermined observation visual field on a mark to be detected, and stably and highly accurately. An object of the present invention is to provide a position detection device that can perform focusing.

[0009]

A position detecting apparatus according to the present invention is provided with a substrate (4) to be tested as shown in FIGS. 1 to 3, for example.
4) Position detection illumination systems (1 to 6) that irradiate the first light flux (L2) on the alignment marks (48) formed on the above in a predetermined direction (X direction) with a predetermined pitch, and their positions. Photoelectric detection means (10) for receiving the first light flux (L2) returned from the alignment mark, and focus detection illumination system (1) for irradiating the alignment mark with the second light flux (L3).
1, 12, 3 to 6) and the second light flux (L3) returned from the alignment mark (48) to form an image of the alignment mark (48) for focus detection ( 6,
5, 8, 14, 15), an image pickup means (16) for picking up an image of the alignment mark (48) formed by the focus detection light receiving system, and an image pickup signal of the image pickup means for processing the image pickup signal. The image pickup signal processing means (17) for detecting the degree of focus of the alignment mark and the height adjusting means (45) for adjusting the height of the substrate under test (44) are provided. In the apparatus for detecting the position of the alignment mark (48) based on the detection signal of the photoelectric detection means (10) after maximizing the focus degree of the alignment mark (48) via the (16) Positioning mark (4
Imaging signal processing means (1) of the observation field (7) of the image of (8)
The field-of-view limiting means (7) for limiting the width _HAF in the direction T perpendicular to the measurement direction S to an integer multiple of the pitch P _T in the direction T perpendicular to the measurement direction S of the image of the alignment mark (48) ( 13; 17).

In this case, an example of the field-of-view limiting means is arranged on a plane substantially conjugate with the surface of the substrate (44) to be tested in the focus detecting illumination system or the focus detecting light receiving system. A field stop (13). Another example of the visual field limiting means is an imaging signal selecting means (17) for extracting an imaging signal in the observation visual field from the imaging signal of the imaging means (16).
Is.

In this case, for example, as shown in FIG. 8, the position detecting illumination system and the focus detecting illumination system are constituted by an integrated illumination system (1, 2, 4 to 6). The striped pattern (32) formed at a predetermined pitch in the measurement direction S by the imaging signal processing means (17) may be arranged on a surface substantially conjugate with the arrangement surface of the substrate (44) to be tested. .

[0012]

According to the present invention, as shown in FIG.
The alignment mark (48) to be measured is compared to
For example, the dark part (48a) and the bright part (48b) can be separated by a predetermined distance in the X direction.
If the marks are arranged in the
Width H in the non-measurement direction T perpendicular to the measuring direction S_AFBut alignment
Pitch P of marking mark (48) in non-measurement direction T _TOrder of
It is set to several times (1 time in FIG. 3A). Therefore,
An image in the observation visual field (7) of the image pickup device (16),
When the image pickup signal is integrated in the non-measurement direction T, it is shown in FIG.
Integrated signal ΣV_AFIs obtained.

Further, as shown in FIG. 4 (b), even if the observation visual field (7) moves in parallel on the alignment mark (48), the obtained integrated signal ΣV _AF is as shown in FIG. 4 (b). To Figure 3
It is similar to (c). That is, the obtained waveform of the integrated signal ΣV _AF is stable regardless of the position of the observation field of view (7), the influence of the pattern of the alignment mark (48) is eliminated, and accurate focusing is performed.

When the observation field (7) on the alignment mark (48) is electrically limited by selecting the image pickup signal of the image pickup means (16), as shown in FIG. The position detecting illumination system and the focus detecting illumination system are constituted by an integrated illumination system (1, 2, 4 to 6), and substantially the arrangement surface of the substrate (44) to be inspected in the illumination system. Stripe patterns (32) formed at a predetermined pitch in the measurement direction S may be arranged on the conjugate plane. In this case, for focusing, for example, the position of the re-formed image of the image of the striped pattern (32) may be set to a predetermined reference position. Further, as shown in FIG. 9, for example, as for the width H _WMX of the position detection field of view (34X) of the alignment pattern (48) in the non-measurement direction (Y direction), the image of the striped pattern (32) is obtained. The effect of the image of the striped pattern (32) is removed by setting the integer of the pitch of (32A) in the Y direction and integrating the obtained image in the Y direction.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the position detecting device according to the present invention will be described below with reference to the drawings. [First Embodiment] The first embodiment will be described with reference to FIGS. In this embodiment, the present invention is applied to an off-axis type alignment system of a projection exposure apparatus for manufacturing semiconductor devices. FIG. 1 shows a main part of the projection exposure apparatus of this example. In FIG. 1, the reticle 41 held on a reticle stage 42 is exposed under an illumination light L1 for exposure from an illumination optical system (not shown). An image of the pattern through the projection optical system 43 is projected and exposed on each shot area of the wafer 44. Here, the Z axis is taken parallel to the optical axis of the projection optical system 43, the X axis is taken parallel to the paper surface of FIG. 1 in the plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the paper surface of FIG.

The wafer 44 is held on a Z stage 45 which positions the wafer 44 in the Z direction.
Are placed on an XY stage 46 that positions the wafer 44 in a direction parallel to the X axis (X direction) and in the Y direction. Each shot area of the wafer 44 is positioned based on the wafer mark attached to each shot area. Figure 2 (a)
2A shows a certain shot area 47 on the wafer 44. In FIG. 2A, an X-axis wafer mark 48 formed of an uneven pattern arranged adjacent to the shot area 47 at a predetermined pitch in the X direction, and Wafer marks 49 for the Y-axis are formed of a concavo-convex pattern arranged in the Y-direction at a predetermined pitch. In this example, the wafer mark 4 for the X axis is used.
8 is the detection target.

Returning to FIG. 1, an off-axis imaging system alignment system 50 is arranged in the lateral direction of the projection optical system 43. The imaging system alignment system is FIA
It is also called a (Field Image Alignment) type alignment system. In the alignment system 50, the illumination light L2 emitted from the light source 1 such as a halogen lamp for position detection is converted into a substantially parallel light flux by the lens system 2 and reaches the beam splitter 3. The illumination light L2 that has passed through the beam splitter 3 is once condensed by the lens system 4 and reaches the half mirror 5, and the light flux reflected by the half mirror 5 is for the X axis on the wafer 44 via the objective lens system 6. The area including the wafer mark 48 is illuminated. Under the illumination light L2, the surface of the wafer 44 has a substantially Fourier transform relationship with the surface on which the light source 1 is arranged.
Illumination of the illumination light L2 is almost Koehler illumination.

The illumination light L2 reflected from the wafer 44 is
The light beam condensed by the objective lens system 6 returns to the half mirror 5, the light beam passing through the half mirror 5 reaches the beam splitter 8, and the light beam passing through the beam splitter 8 passes through the imaging lens system 9 to form a two-dimensional CCD or the like. An image of the wafer mark 48 is formed on the image pickup surface of the image pickup device 10 for position detection.

FIG. 2B shows an image pickup surface 10a of the image pickup device 10.
2B, the image pickup surface 10a is shown in FIG.
An image 48A of the wafer mark 48 is formed in the center of the image. In this case, the imaging surface 10a of FIG. 2B corresponding to the measurement direction (X direction) of the wafer mark 48 on the wafer 44.
An image of the wafer mark 48 with the measurement direction above as the X direction
Index marks 19A and 19B are formed on both sides of A in the X direction. The index marks 19A and 19B can be omitted when the pixel of the image sensor 10 is used as a reference.
Then, an image is converted into an image pickup signal along the scanning line 20 parallel to the X direction on the image pickup surface 10a, and the obtained image pickup signal is processed, whereby the wafer mark 48 with the index marks 19A and 19B as a reference is formed. The position in the X direction is detected.

Next, an in-focus point detection system for carrying out autofocus by the alignment system 50 will be described. First, a light source for focus detection (hereinafter referred to as “AF light source”) 11
The illumination light L3 from illuminates the AF pattern plate 13 via the condenser lens 12, and the AF pattern plate 13
The illumination light L3 that has passed through the rectangular aperture pattern reaches the beam splitter 3. A light emitting diode, a semiconductor laser, or the like can be used as the AF light source 11, but a halogen lamp or the like may be used as the AF light source 11.

Illumination light L reflected by the beam splitter
3 reaches the half mirror 5 through the lens system 4, and the light flux reflected by the half mirror 5 passes through the objective lens system 6 and forms the opening pattern in the AF pattern plate 13 on the wafer mark 48 of the wafer 44. An image, that is, a projected image 7 of the focusing mark is formed. That is, under the illumination light L3, A
The arranging surface of the F pattern plate 13 and the surface of the wafer 44 are almost conjugate with each other, and an observation visual field for focus detection of the wafer mark 48 is set by the projected image 7 of the focusing mark.

The illumination light L3 reflected from the projection image 7 of the focusing mark returns to the half mirror 5 via the objective lens system 6, and the illumination light L3 transmitted through the half mirror 5 reaches the beam splitter 8. Then, the illumination light L3 reflected by the beam splitter 8 passes through the side surface of the pupil limiting plate 14 covering the half surface in a predetermined direction from the optical axis (referred to as “measurement direction S”), and then the imaging lens system. 2 through 15
An image of the pattern in the projected image 7 of the focusing mark is formed on the image pickup surface of the image pickup device 16 for detecting the focus point, which is composed of a two-dimensional CCD or the like. In the focused state, the surface of the wafer 44 and the image pickup surface of the image pickup device 16 are conjugate under the illumination light L3,
The arrangement surface of the pupil limiting plate 14 has a Fourier transform relationship with the surface of the wafer 44. Due to the pupil limiting plate 14, the telecentricity of the image forming optical system from the wafer 44 to the image pickup device 16 is deteriorated. Therefore, when the wafer 44 deviates from the focal point in the + Z direction or the −Z direction, the image pickup device 1
The position of the image of the projected image 7 of the focusing mark on 6 is laterally displaced in the measurement direction S. In this example, this is used to detect the in-focus point.

The image pickup signal V _AF from the image pickup device 16 is supplied to the signal processing device 17, and the signal processing device 17 integrates the image pickup signal to obtain the defocus amount of the wafer mark 48 based on the integrated signal ΣV _AF ( The focus degree) is calculated, and this defocus amount is output to the stage control system 18. Stage control system 1
In 8, the Z stage 45 is driven in the Z direction by the amount of defocus. As a result, the wafer mark 48 is focused by the autofocus method.

Next, the operation for detecting the in-focus point in this example will be described in detail with reference to FIGS. 3 and 4. FIG. 3 (a)
3 is an enlarged plan view of the wafer mark 48 in FIG. 1. In FIG. 3A, the projection image 7 of the focusing mark is formed on the wafer mark 48. If the direction in FIG. 3A corresponding to the measurement direction S determined by the pupil limiting plate 14 in FIG. 1 is also the measurement direction S and the direction perpendicular to the measurement direction S is the non-measurement direction T, the projected image 7 is measured. It is a rectangle having sides parallel to the direction S and the non-measurement direction T, respectively. The measurement direction S intersects the X direction, which is the measurement direction of the wafer mark 48, counterclockwise at an angle θ, and the angle θ is, for example, about 45 °. The wafer mark 48 is formed by periodically forming convex portions 48a and concave portions 48b extending in the Y direction at the pitch P _WM in the X direction. As an example, the convex portion 48a has a small reflectance and the concave portion 48b is small. Is assumed to have a high reflectance.

In this case, the pitch P _T of the arrangement of the wafer marks 48 in the non-measurement direction _T is P _WM / sin θ. In this example, the width _HAF of the projected image 7 of the focusing mark in the non-measurement direction T is set to an integral multiple of the pitch P _T of the wafer mark 48 in the non-measurement direction T. That is, the relationship of the following expression (1) is established by using an integer n of 1 or more. In the example of FIG. 3A, the width H _AF is 1 times the pitch P _T (n =
It is set to 1).

H _AF = n · P _T (1) However, the width of the projected image 7 of the focusing mark in the measuring direction S is arbitrary, and for example, the projected image 7 of the focusing mark 7
May be divided in the measurement direction S into a plurality of patterns. FIG. 3B shows an observation image of the image sensor 16 for focus detection of FIG. 1 corresponding to FIG.
In (b), an image 7A of the projected image 7 of the focusing mark is formed at the center of the image pickup surface 16a of the image pickup device 16,
In the image 7A, a dark stripe image 48aA corresponding to the convex portion of the wafer mark 48 and a light stripe image 48bA corresponding to the concave portion.
Is imaged for one cycle in the non-measurement direction T. In the image pickup device 16 in this state, along parallel scan lines 21 in the measurement direction S and outputs an image pickup signal V _AF converts sequentially photoelectrically image, the imaging signal V _AF in the signal processing device 17 in the non-measurement direction T Is integrated (added), the integrated signal ΣV _AF shown by the solid rectangular curve 22A in FIG. 3C is obtained.

At this time, in FIG. 1, under the illumination light L2 for position detection, the wafer mark 48 is on a plane conjugate with the image pickup surface of the image pickup device 10 for position detection, that is, the wafer mark 48 is The center of gravity S1 in the measurement direction S of the integrated signal ΣV _AF in FIG. 3C is obtained and stored as the reference position in the state where the objective lens system 6 is in the focal point under the illumination light L2. The reference position S1 is, for example, the image pickup element 16
It is calculated based on the pixels at the ends of the. After that, when actually performing focusing, when the position (focal position) of the wafer mark 48 in the Z direction in FIG. 1 shifts vertically from the focused point (under the illumination light L2) with respect to the objective lens system 6, Since the telecentricity is lost on the image pickup device 16 for detection, the position of the image of the projected image 7 of the focusing mark shifts back and forth along the measurement direction S. That is, the obtained integrated signal ΣV _AF is the dashed-line curves 22B and 22 in FIG.
As shown by C, since it shifts back and forth along the measurement direction S, focusing is performed by driving the Z stage 45 so that the center of gravity of the integrated signal ΣV _AF becomes the reference position S1.

At this time, since the precision of the pre-alignment is not so high, the position of the wafer mark 48 in FIG. 1 may be displaced, for example, in the -X direction. When such a positional deviation occurs, as shown in FIG. 4A, the position of the projected image 7 of the focusing mark on the wafer mark 48 is changed from the position 23 in FIG. Mark 4
8 shifts in the + X direction. However, the width of the projection image 7 of the focusing mark in the non-measurement direction T is
Since it is an integral multiple of the pitch of the wafer mark 48 in the non-measurement direction T, an integrated signal Σ obtained by integrating the image pickup signal
The center-of-gravity position of V _AF does not deviate from the reference position S1 as shown by the curve 22D in FIG. Therefore, focusing can be performed with high accuracy without being affected by the pattern of the wafer mark 48 and the reflectance distribution.

Incidentally, in FIG. 3A, the reflectances of the convex portions 48a and the concave portions 48b of the wafer mark 48 are different,
Focusing can also be performed with high accuracy on wafer marks having the same reflectivity between the convex portion 48a and the concave portion 48b. Further, even when the wafer mark to be detected is a mark having no unevenness and only different reflectance distributions, focusing can be performed with high accuracy in the same manner.

The shape of the wafer mark attached to each shot area on the wafer 44 (pitch in the measuring direction, etc.)
May vary depending on the process. Therefore, in FIG. 1, as the AF pattern plate 13, a plurality of pattern plates each having an opening pattern satisfying the condition of the expression (1) for the wafer mark to be detected are prepared.
The pattern plates may be mechanically replaced according to the wafer mark to be detected.

Further, the AF pattern plate 13 is not a fixed type, but is composed of a plurality of movable blades driven by a mechanical driving mechanism, and these are set so as to satisfy the formula (1) according to the wafer mark to be detected. You may adjust the expansion-contraction amount of a movable blade. Further, the AF pattern plate 13 is made of a member such as a liquid crystal panel that can electrically form the transparent portion in an arbitrary shape, and after recognizing the shape of the mark to be measured, the formula (1) is satisfied. The shape of the transmission part, that is, the shape of the observation visual field on the measured mark may be set.

Further, the observation field of view is not limited by the projected image 7 of the focusing mark on the wafer mark 48, but on the image pickup surface 16a (see FIG. 3B) of the image pickup device 16 for detecting the focus position. The image capturing area may be limited according to the condition of the expression (1). For this purpose, a frame memory is provided in the signal processing device 17, the image pickup signal V _AF from the image pickup device 16 is stored in this frame, and then the address corresponding to the capture area set in accordance with the condition of the equation (1). It suffices to read the image pickup signal inside. In this case as well, if the measured mark is known in advance, the detection area may be fixed,
Further, after the shape of the mark to be measured is recognized, the read area may be arbitrarily limited.

[Second Embodiment] In the second embodiment, the AF pattern plate 13 of FIG. 1 is replaced with two other members in the first embodiment to increase the signal intensity for focus detection. Is. FIG. 5 shows an essential part of the second embodiment. In FIG. 5, between the condenser lens 12 and the beam splitter 3, an AF pattern plate 26 made of a light transmissive substrate and an AF field stop 24 are arranged in this order. Are arranged. In this case, under the illumination light L3 for focus detection, as shown in FIG.
AF field stop 2 on a surface almost conjugate to the surface of the wafer 44 of
4 is arranged, and the AF pattern plate 26 is arranged at a position defocused by ΔZ in the optical axis direction from the AF field stop 24.

An aperture 24a having the same shape as the aperture pattern in the AF pattern plate 13 shown in FIG. 1 is formed in the AF field stop 24. Thus, an uneven phase grating is formed at a predetermined pitch Q. The other configuration is similar to that of FIG. 1, and therefore its description is omitted. In the present embodiment, the defocus amount ΔZ of the AF pattern plate 13 as the phase object is set to a different amount depending on the shape of the wafer mark to be measured, the illumination condition, etc., but the defocus amount ΔZ. Is
The lens system 4 at least on the AF field stop 24.
And the depth of focus δ _AF of the relay lens system including the objective lens system 6 must be made larger.

The intensity distribution curve 27A of FIG. 6A shows the wafer mark 48 of FIG. 1 when the defocus amount ΔZ is 0.
_6A shows the light intensity distribution I _AF of the projected image of the aperture 24a of the AF field stop 24, and the horizontal axis of FIG. 6A is for focus detection on the wafer 44 corresponding to the measurement direction S of FIG. Measuring direction S
Indicates. When the projection magnification of the relay lens system including the lens system 4 and the objective lens system 6 on the wafer 44 is β, the pitch of the intensity distribution curve 27A in the measurement direction S is β ·
The intensity distribution curve 27A is Q / 2.
It is almost the same as the light intensity distribution obtained in the embodiment of FIG. 1 except that there is a sharp drop in every Q / 2.

On the other hand, when the absolute value of the defocus amount ΔZ is made larger than at least the depth of focus δ _AF of the relay lens system, the light of the projected image of the aperture 24a of the AF field stop 24 on the wafer mark 48 is projected. The intensity distribution I _AF is shown in FIG.
As shown by the intensity distribution curve 27B in (b), the measurement direction S
To the sine wave of pitch β · Q. Therefore,
When the image is picked up by the image pickup device 16 of FIG. 1, the SN ratio of the obtained image pickup signal V _AF is partially improved. Therefore, for example, even when the maximum level of the obtained image pickup signal V _AF is buried in the noise level in the state of FIG.
In the state of (b), since the level of the image pickup signal V _AF partially becomes higher than the noise level, focus detection becomes possible.
Further, as a method of processing the image pickup signal V _AF , for example, FIG.
6B may be regarded as a multi-mark, and the average value of the positions of the respective peaks of the integrated values of the imaging signal V _{AF in} the non-measurement direction corresponding to FIG. 6B may be set to the reference position that is obtained in advance. This improves the SN ratio at the time of focus detection.

[Third Embodiment] In the third embodiment, the beam splitters 3 and 8 shown in FIG. 1 are used in order to prevent the light amount of the illumination light from decreasing and to prevent the two kinds of illumination light L2 and L3 from overlapping. Instead of each dichroic mirror 29
And 30 are used. FIG. 7 shows the alignment system of the third embodiment. In FIG. 7, in which parts corresponding to those in FIG. 1 are designated by the same reference numerals, the illumination light L2 from the light source 1 for position detection is the lens system 2 Through dichroic mirror 2
After being reflected at 9, it reaches the lens system 4. On the other hand, the illumination light L3 from the AF light source 11 for focus detection is condensed by the condenser lens 12 on the AF pattern plate 13,
The illumination light L3 that has passed through the aperture pattern of the AF pattern plate 13 passes through the cylindrical lens 28, then passes through the dichroic mirror 29, and reaches the lens system 4. The illumination lights L2 and L3 that have passed through the lens system 4 reach the wafer mark 48 on the wafer 44 via the half mirror 5 and the objective lens system 6 in a superimposed manner, and the illumination light L3 becomes the wafer mark 4
A projected image 7 of the focusing mark is formed on 8.

The illumination lights L2 and L3 reflected by the wafer mark 48 enter the dichroic mirror 30 through the objective lens system 6 and the half mirror 5, and the illumination light L2 reflected by the dichroic mirror 30 is combined. The illumination light L3 that forms the image of the wafer mark 48 on the image sensor 10 via the image lens system 9 and is transmitted through the dichroic mirror 30 is transmitted to the image sensor 16 via the pupil limiting plate 14 and the imaging lens system 15. An image of the projected image 7 of the focusing mark is formed. The dichroic mirrors 29 and 30 of this example are
It has wavelength selectivity that reflects the illumination light L2 for position detection and transmits the illumination light L3 for focus detection. Other configurations are the same as those in FIG.

In this embodiment as well, focusing is performed based on the image pickup signal of the image pickup device 16 as in the first embodiment. Furthermore,
Only the illumination light L2 is incident on the image sensor 10,
Since only the illumination light L3 is incident on 6, the position detection and the focus detection are performed with a high SN ratio, and there is no light amount loss of the illumination lights L2 and L3 at the dichroic mirrors 29 and 30, so that the illumination efficiency is the first. It is almost four times that of the first embodiment.

However, in the embodiment of FIG. 7, the illumination light L3 for focusing is transmitted through the dichroic mirror 29, and the AF pattern plate 13 for limiting the observation field of view for focusing is provided on the light source side. Therefore, as it is, the projection image 7 of the focusing mark on the wafer 44 is blurred due to a large astigmatism, and the condition of the expression (1) cannot be satisfied. Therefore, in this example, in the illumination system for focusing,
The cylindrical lens 28 is arranged so as to cancel the astigmatism due to the dichroic mirror 29, and the wafer 44
The projected image 7 of the upper focusing mark is a clear image that satisfies the condition of Expression (1).

[Fourth Embodiment] In the fourth embodiment, the light source for position detection (for alignment) and the light source for focus detection are made a common light source such as a halogen lamp. Figure 8 (a)
8A shows the alignment system of the fourth embodiment, and in FIG. 8A in which parts corresponding to those in FIG. 1 are assigned the same reference numerals, the illumination light L2 from the light source 1 composed of a halogen lamp is shown.
Illuminates the AF pattern plate 31 through the collimator lens 2. As shown in FIG. 8B, the striped pattern 32 is formed on the AF pattern plate 31 at a predetermined pitch in the measurement direction S with a duty ratio in which a dark portion is narrower than a bright portion. The illumination light L2 that has passed through the AF pattern plate 31 passes through the lens system 4, the half mirror 5, and the objective lens system 6 onto the wafer mark 48 of the wafer 44 to form the striped pattern 3
2 image, that is, the projected image 32A of the focusing mark (see FIG. 9).
).

The illumination light L2 reflected by the wafer 44 reaches the beam splitter 8 via the objective lens system 6 and the half mirror 5, and the light beam reflected by the beam splitter 8 is reflected by the pupil limiting plate 14 and the imaging lens. A projected image 32A of the focusing mark on the image pickup surface of the image pickup device 16 through the system 15.
Forming an image of. Further, the light beam that has passed through the beam splitter 8 is split into two by the half mirror 5A after passing through the imaging lens 9, and the split light beams are respectively placed on the X-axis image pickup device 10X and the Y-axis image pickup device 10Y. The image of the mark 48 is formed. In addition, the image pickup devices 10X and 10Y
The images formed on 16 and 16 are in common that the image of the wafer mark 48 and the image of the projected image 32A of the focusing mark are superimposed.

FIG. 9 shows an illumination field (illumination field) 33 on the wafer mark 48 of this example. As shown in FIG. 9, the wafer mark 48 has a pattern of concavities and convexities formed in the X direction at a pitch P _WM. And the projected image 32A of the focusing mark
Is a light-dark pattern arranged at a pitch P _AF in the measurement direction S that intersects the X direction clockwise at 45 °. The detection area of the X-axis image pickup device 10X of FIG. 8 is an area conjugate with the detection area 34X of the width H _{WMX in} the Y direction of FIG. 9, and the detection area of the image pickup device 16 of FIG. detection region 34S of the non-measurement direction width H _AF perpendicular to the measurement direction S in FIG. 9
This is a region conjugate with. In this example, their widths H _AF and H
_WMX is set so as to substantially satisfy the following _expressions for the pitches P _WM and P _AF , respectively. However, n and n ′ are each an integer of 1 or more.

H _AF = n · P _WM · 2 ^1/2 (2) H _WMX = n ′ · P _AF · 2 ^1/2 (3) In other words, this is the detection area 34X for position detection (alignment). Width H _WMX in the non-measurement direction (Y direction) of
Was set to an integer multiple of the pitch of the projected image 32A of the focus mark alignment in the Y direction, the wafer mark width H _AF of non-measurement direction of the detection region 34S of the focus detection in the non-measurement direction 4
It means that it is set to an integral multiple of the pitch of 8. That is,
The condition of the expression (2) is the same as the condition of the expression (1).

The image pickup signal V _AF output from the image pickup device 16 of the present example becomes drop portions 32B to 32F at a predetermined pitch along the measurement direction S as shown in FIG. It becomes the flat portion 48B. Actually, the signal of the portion corresponding to the boundary portion of the unevenness of the wafer mark 48 also drops, but since the equation (2) is substantially established, the drop is caused by integrating the imaging signal V _AF in the non-measurement direction. Offset.
Therefore, in FIG. 9, the projected image 32 of the focusing mark is shown.
Even if the wafer mark 48 is laterally displaced with respect to A, the obtained image pickup signal V _AF maintains the state of FIG. Therefore, FIG. 10A is regarded as, for example, a multi-pattern image, and the average value of the positions of the recesses 32B to 32F in the measurement direction S is obtained. Then, the focus shift amount is obtained by obtaining the shift amount of this average value from the reference position S2 obtained in advance in the in-focus state.

On the other hand, as shown in FIG. 10B, the image pickup signal V _WMX output from the image pickup device 10X for position detection has a _drop portion 4 at a predetermined pitch along the X direction which is the measurement direction.
It becomes 8C. These recesses 48C correspond to the boundaries of the unevenness of the wafer mark 48. Actually, the signal of the portion corresponding to the dark portion of the projected image 32A of the focusing mark also falls, but since the equation (3) is substantially established, the drop is caused by the imaging signal V _WMX in the non-measurement direction (Y direction). (Direction corresponding to) is offset by integration. Therefore, even if the projected image 32A of the focusing mark and the wafer mark 48 are laterally displaced in FIG. 9, the obtained image pickup signal V _WMX maintains the state of FIG. 10B. Therefore, for example, in FIG.
By _obtaining the average value of the position in the X direction of the drop portion 48C of the image pickup signal V _WMX of 0 (b), and _obtaining the deviation amount of this average value from the reference position X2 corresponding to the optical axis of the objective lens system 6. , The amount of displacement of the wafer mark 48 in the X direction is obtained.

In this example, as shown in FIG. 9, the duty ratio of the projected image 32A of the focusing mark is set so that the dark portion becomes narrow, so that the illumination light amount of the wafer mark 48 increases and the position detection. There is an advantage that the level of the image pickup signal V _WMX for video is high. Further, because of such a duty ratio, the width H of the detection area 34X for position detection in the Y direction is H.
_{Even if the WMX} deviates from the condition of expression (3) to some _extent , Fig. 10 (b)
As described above, there is an advantage that the apparent illuminance distribution obtained as the image pickup signal V _{WM X} has a small influence.

Further, in this example, since the halogen lamp having a wider wavelength range than the light emitting diode is used as the light source 1 for illumination, the image pickup signal V _AF for _autofocus is applied on the wafer 44. It is less likely to be adversely affected by thin film interference due to the photoresist, and erroneous detection of the in-focus point can be prevented. Further, since a dedicated illumination system for focus detection is unnecessary, the optical system can be simplified and the manufacturing cost can be expected to be reduced. The position of the Y-axis wafer mark 49 shown in FIG. 2A is detected by processing the image pickup signal of the Y-axis image pickup device 10Y shown in FIG. The autofocus at this time is performed by the image pickup signal V
It is done based on _AF .

[Fifth Embodiment] In the fifth embodiment, the present invention is applied to a mechanism for autofocusing when observing a periodic mark with a differential interference microscope. 11, which is used to describe the fifth embodiment, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 11 shows the differential interference microscope of the fifth embodiment. In FIG. 11, the illumination light L2 from the light source 1 for position detection passes through the collimator lens 2, the polarizer 35A, and the phase plate 36, and the beam splitter. Up to 3. Then, after being emitted from the AF light source 11 for focus detection, the illumination light L3 that has passed through the condenser lens 12 and the AF pattern plate 13 is combined with the illumination light L2 by the beam splitter 3, and this combined light is used in the lens system. 4, a half mirror 5, a double image prism 37, and an objective lens system 6 irradiate a wafer mark 48 on a wafer 44 to form a projected image 7 of a focusing mark on the wafer mark 48. Wafer 44
Are mounted on a sample table 51 which positions the sample in the optical axis direction of the objective lens system 6. Then, the reflected light from the wafer 44 reaches the beam splitter 8 via the objective lens system 6, the compound image prism 37, and the half mirror 5, and the light flux transmitted through the beam splitter 8 forms the imaging lens system 9
An image of the wafer mark 48 is formed on the image sensor 10 via the analyzer 35B. Other configurations are the same as those in FIG.

Further, also in this example, as in FIG. 3A, the width of the projected image 7 of the focusing mark in the non-measurement direction T is set to an integral multiple of the pitch of the wafer mark 48 in the non-measurement direction T. Set. As a result, the integral obtained by integrating the image sensor from the image sensor 16 for focus detection does not depend on the direction of polarization separation of the compound image prism 37, the direction of the polarizer 35A or the analyzer 35B, or the phase difference of the phase plate 36. The signal is shown in Figure 3.
The waveform becomes stable as shown in (c). This is the phase plate 3
The same applies to an optical system that does not use 6 or the analyzer 35B, or an optical system in which the compound image prism 37 is placed only in the detection optical system (between the beam splitter and the image sensor 10).

In the above embodiment, the position of the mark to be inspected is detected by the imaging method (FIA method), but in addition to that, the mark to be inspected is irradiated with a coherent laser beam from two directions, and the detected mark is irradiated. Even when using a so-called heterodyne interference type alignment system that detects the position of the test mark based on the phase of the heterodyne beam returned from the test mark, the present invention can be applied to perform stable autofocus. it can.

The present invention is not limited to the above embodiment,
Of course, various configurations can be adopted without departing from the scope of the present invention.

[0054]

According to the present invention, the width of the alignment mark image in the non-measuring direction of the alignment mark image is limited only by the visual field limiting means, and the alignment mark pattern (reflectance Focusing can be performed stably and highly accurately by eliminating the influence of (including distribution). Therefore, even if the position of the alignment mark is displaced, there is an advantage that the focus can be accurately performed, and the position of the alignment mark can always be detected with high accuracy.

If the field limiting means is a field stop arranged on a plane conjugate with the surface of the substrate to be inspected in the focus detection illumination system or the focus detection light receiving system, the light flux for focus detection is used. Can be prevented from being irradiated to unnecessary areas. Further, when the field-of-view limiting unit is an image-capturing signal selecting unit that extracts an image-capturing signal in the observation visual field from the image-capturing signal of the image-capturing unit, the observation visual field can be electrically set arbitrarily,
The mechanical portion is simplified and the shape of the alignment mark can be easily changed.

Next, the position detecting illumination system and the focus detecting illumination system are constituted by an integrated illumination system, and the illumination system or the focus detecting light receiving system is provided with a plane conjugate with the arrangement surface of the substrate to be inspected. When arranging the striped patterns formed at a predetermined pitch in the measurement direction by the image pickup signal processing means, the optical system is simplified.
Furthermore, position detection and focus detection can be performed separately by the striped pattern.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a projection exposure apparatus to which a first embodiment of a position detection apparatus according to the present invention is applied.

2A is an enlarged plan view showing a wafer mark provided in a shot area on the wafer of FIG. 1, and FIG. 2B shows an image of the wafer mark 48 on an image pickup surface of the image pickup device 10 of FIG. It is an enlarged image.

FIG. 3 is an explanatory diagram when focusing is performed in the first embodiment.

FIG. 4 is an explanatory diagram showing a case where the position of the wafer mark is displaced in the first embodiment.

FIG. 5 is a perspective view showing a main part of a second embodiment of the present invention.

FIG. 6 is a diagram showing a light intensity distribution on a wafer in a second example.

FIG. 7 is a configuration diagram showing an alignment system according to a third embodiment of the present invention.

8A is a configuration diagram showing an alignment system according to a fourth embodiment of the present invention, and FIG. 8B is an enlarged view showing a striped pattern on the AF pattern plate 31 in FIG. 8A. .

FIG. 9 is an enlarged plan view showing a projected image of a focusing mark on a wafer mark in the fourth embodiment.

10A is a waveform diagram showing an image pickup signal V _AF for focus detection obtained in the fourth embodiment, and FIG. 10B is a waveform diagram showing an image pickup signal V _WMX obtained in the fourth embodiment. It is a figure.

FIG. 11 is a configuration diagram showing a differential interference microscope according to a fifth embodiment of the present invention.

FIG. 12 is a diagram illustrating the principle of a conventional focus detection method.

13 is an explanatory diagram showing a state in which the mark 52 is displaced from the state of FIG.

[Explanation of symbols]

 1 Light source for position detection 3,8 Beam splitter 5 Half mirror 6 Objective lens system 7 Projected image of focusing mark 11 AF light source 13 AF pattern plate 14 Pupil limiting plate 10 Image sensor 16 for position detection 16 For focus detection Image pickup device 17 Signal processing device 18 Stage control system 24 Field stop 25 AF pattern plate 28 Cylindrical lens 29, 30 Dichroic mirror 31 AF pattern plate 44 Wafer 45 Z stage 48 Wafer mark

Claims (4)

[Claims] 1. A position detection illumination system for irradiating a first light flux to a positioning mark formed on a substrate to be tested at a predetermined pitch in a predetermined direction, and the first mark returned from the positioning mark. Photoelectric detection means for receiving the second light flux, a focus detection illumination system for irradiating the alignment mark with a second light flux, and a second light flux returned from the alignment mark for condensing A light receiving system for focus detection that forms an image of the alignment mark, an image capturing unit that captures an image of the alignment mark formed by the light receiving system for focus detection, and an image capturing signal of the image capturing unit. Image pickup signal processing means for detecting the focus degree of the alignment mark, and height adjusting means for adjusting the height of the substrate to be inspected are provided, and the position adjusting means is used for the alignment. To maximize the focus of the mark After that, in a device for detecting the position of the alignment mark based on the detection signal of the photoelectric detection means, a measurement direction of the observation field of view of the image of the alignment mark by the imaging means by the imaging signal processing means The position detecting device is provided with a visual field limiting means for limiting a width in a direction perpendicular to the direction to an integral multiple of a pitch of the image of the alignment mark in a direction perpendicular to the measuring direction. 2. The field-of-view limiting means is a field stop disposed on a surface substantially conjugate with the surface of the substrate to be inspected in the focus detection illumination system or the focus detection light receiving system. The position detecting device according to claim 1, wherein: 3. The position detecting device according to claim 1, wherein the field-of-view limiting unit is an image-capturing signal selecting unit that extracts an image-capturing signal within the observation visual field from an image-capturing signal of the image-capturing unit. 4. The position detecting illumination system and the focus detecting illumination system are configured as an integrated illumination system, and the imaging is performed on a plane substantially conjugate with a surface on which the substrate to be tested is arranged in the illumination system. The position detecting device according to claim 2 or 3, wherein striped patterns formed at a predetermined pitch are arranged in a measurement direction by the signal processing means.