JP3223932B2 - Semiconductor device manufacturing method, and position detecting apparatus and exposure apparatus used in the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device of a projection exposure apparatus used for manufacturing, for example, a semiconductor device or the like, and more particularly, to a position detecting mark position on a photosensitive substrate via a projection optical system. It is suitable for use in detecting.

[0002]

2. Description of the Related Art When a semiconductor device or the like is manufactured using photolithography technology, a circuit pattern image formed on an original plate to be projected (hereinafter referred to as a "reticle") is exposed to a photoresist on a wafer through a projection optical system. A projection exposure apparatus for transferring to a layer is used. Generally, semiconductor elements are formed by superimposing a large number of circuit patterns on a wafer. Therefore, when a circuit pattern of a second layer or later is transferred onto a wafer in a projection exposure apparatus, the semiconductor element is formed on a front layer on the wafer. It is necessary to accurately perform relative alignment (alignment) between the circuit pattern thus formed and the reticle to be projected.

In order to perform such alignment, alignment marks (wafer marks) for alignment are formed on a wafer together with a circuit pattern, and alignment marks (reticle marks) for alignment are also formed on a reticle. ing. Then, by setting the relative positional relationship between the wafer mark and the reticle mark to a predetermined relationship, the alignment between the wafer and the reticle is performed.
In order to perform such positioning, an apparatus for detecting the position of a wafer mark on a wafer is first required.

As a conventional position detecting apparatus for a wafer mark, a through-the-lens (TT) for detecting a wafer mark through a projection optical system using predetermined alignment light is used.
L) and a through-the-reticle (TTR) type detection device for detecting a wafer mark via a reticle are known. At this time, since the projection optical system of the projection exposure apparatus is well corrected for aberration only with respect to the wavelength of the exposure light, when the alignment light has a different wavelength from the exposure light, various aberrations occur in the projection optical system. Would.

However, when the alignment light has the same wavelength as the exposure light, the photoresist layer applied on the wafer absorbs the alignment light and is exposed, and the reflected light from the wafer mark decreases, and There is a problem that the SN ratio of the detection signal at the time of mark detection is reduced. For this reason, as this type of position detecting device,
For example, as disclosed in Japanese Patent Application Laid-Open No. 1-227431, an alignment light having a wavelength different from that of exposure light is used to correct chromatic aberration (axial chromatic aberration) in the optical axis direction. Gazette, Tokuhei 2-3544
As disclosed in Japanese Unexamined Patent Application Publication No. 7-1995, there has been proposed an apparatus having an optical system for correcting astigmatism and coma in alignment light that is monochromatic light.

[0006]

In the prior art as described above, the position of a wafer mark on a wafer to be detected is generally off-axis of the projection optical system at the time of alignment. In order to observe an image of a mark with a projection optical system having chromatic aberration, monochromatic light has been used as alignment light.

However, if monochromatic light is used as the alignment light, interference occurs between the reflected light from the photoresist applied on the wafer and the reflected light from the surface of the wafer, making it impossible to detect the position of the wafer mark. Alternatively, the position of the wafer mark may be erroneously detected. That is, in general, the wafer mark is formed as an uneven pattern on the wafer, and the distribution of the thickness of the photoresist applied thereon is unavoidably asymmetric, and thus the thin film is formed by thin film interference. Interference fringes are also asymmetric. Therefore, the detection signal obtained from the interference fringes is also asymmetric and complicated, which causes inconvenience such that a wafer mark cannot be detected or a detection error increases.

Further, even when the photoresist is unevenly coated on the wafer, the formed interference fringes are asymmetric and complicated, which hinders the position detection of the wafer mark. On the other hand, if light having a certain wavelength bandwidth is used as alignment light in order to reduce the influence of the thin film interference by the photoresist layer, a considerable amount of light will be generated in the projection optical system due to the wavelength difference within the wavelength band of the alignment light. Chromatic aberration occurs, and the image of the wafer mark is blurred.

In particular, it is important to provide a wafer mark on the wafer in a sagittal direction (a direction orthogonal to a plane including the optical axis of the projection optical system on the wafer) in a meridional direction (an optical axis of the projection optical system on the wafer). (In-plane direction), it is important to improve the alignment accuracy. However, the presence of chromatic aberration of magnification (lateral chromatic aberration) in chromatic aberration greatly hinders position detection in the meridional direction.

Here, the problem of lateral chromatic aberration in the wavelength band of the alignment light will be described with reference to FIGS. In general, when an off-axis alignment mark is observed in the meridional direction via a projection optical system with alignment light having a certain wavelength band, FIG.
As shown in (1), lateral displacement of the wafer mark occurs. Assuming that the reference wavelength of the alignment light is the center wavelength λ ₀ , FIG.
In (a), the detection signal of the image of the wafer mark at the reference wavelength λ ₀ is a solid curve 14A, and the detection signal of the image of the wafer mark at the minimum wavelength λ ₋ in the wavelength band of the alignment light is a dotted curve 14B. , The detection signal of the image of the wafer mark at the maximum wavelength λ _{+ is shown} by a dashed line curve 14C.

On the other hand, the wafer mark is detected as a composite image of the images at the respective wavelengths. If the reflected light intensity from the wafer mark at each wavelength is substantially the same as in the case of FIG. As shown in FIG. 8B, a detection signal whose waveform 15 is symmetric with respect to the center 16 is obtained as a composite image of. However, when the wafer mark is covered with a thin film such as a photoresist, the intensity of the reflected light may change due to slight coating unevenness.

FIG. 9 shows the relationship between the thickness t of the photoresist and the intensity I of the reflected light at each wavelength. In FIG. 9, curves 17A, 17B and 17C respectively indicate the reference wavelength λ in the wavelength band of the alignment light. ₀ , the change in the intensity I of the reflected light with respect to the minimum wavelength λ ₋ and the maximum wavelength λ ₊ . That is, the intensity I of the reflected light periodically changes with respect to the film thickness t with a wavelength-dependent period, and a slight change in the film thickness t causes a large difference in the reflection intensity at each wavelength.

For example, in FIG. 9, when the thickness of the photoresist is t ₁ , the intensity I of the reflected light is I (λ ₊ )>
I (λ 0)> I (λ ₋ ), and as shown in FIG. 10A, the image intensity at the maximum wavelength λ ₊ (represented by the curve 18C) increases, and the image intensity at the minimum wavelength λ ₋ (the curve 18B). As a result, the wafer mark is observed as an image having an asymmetric combined intensity as represented by a curve 19 shown in FIG. 10B, and the center 20 of the image intensity is different from the center 16 in the case of FIG. It will be shifted by Δx.

That is, when a certain wavelength width is given to the alignment light in order to reduce the influence of light interference, a problem of chromatic aberration of magnification newly arises, and the shape of the composite image of the image of each wavelength is changed to a photoresist. Changes due to slight coating unevenness of the film thickness. As a result, an error occurs in the result of detecting the position of the wafer mark. Further, the chromatic aberration of the projection optical system includes axial chromatic aberration (longitudinal chromatic aberration), and when this axial chromatic aberration exists, if the alignment light has a certain wavelength bandwidth, the detection surface of the detecting element Above, the image of the wafer mark may be blurred, and the accuracy of detecting the position of the wafer mark may be reduced.

In view of the above, the present invention detects an image of an alignment mark on a photosensitive substrate via a projection optical system having chromatic aberration of magnification and axial chromatic aberration, and aligns the mask with the photosensitive substrate. When performing the alignment, even if the alignment mark is covered with a thin film, the position of the alignment mark on the photosensitive substrate can be detected with high accuracy without being affected by the thin film interference. With the goal.

[0016]

According to the position detecting device of the present invention, for example, as shown in FIG.
Illuminate the pattern on the mask (R) on the substrate (W)
When transferring the mark (W) onto the substrate (W), the mark (W) on the substrate (W) is detected by an apparatus for detecting the position of the mark (WM) on the substrate (W).
M), the position detecting light from the mark (WM) is condensed with an illumination optical system (1, 2, 6 to 10) for illuminating position detecting light in a predetermined wavelength range different from the exposure light. Projection to image
An image is formed by the optical system (1) and the projection optical system (1).
An imaging optical system (2, 4) for re-imaging the image formed to form an image of the mark (WM), and detecting means (5) for detecting an image of the mark (WM). .

The position detection light from the mark (WM) passes through the projection optical system (1), so that the projection optical system (1)
In order to convert the magnification chromatic aberration and the axial chromatic aberration generated in the above into the axial chromatic aberration for the imaging optical system (2, 4), the imaging optical system (2, 4) The optical axis of (4) is arranged obliquely, a correction optical system (2) for correcting the converted axial chromatic aberration is provided in the imaging optical system (2, 4), and a reference wavelength of the position detection light is provided. Plane (R1) conjugate with the plane of formation of the mark (WM) on the substrate (W)
In contrast, the detection surface of the detection means (5) is connected to the imaging optical system (2, 2).
4) is arranged in a tilt relationship.

In this case, the imaging optical system (2, 4)
An objective lens (2) for condensing position detection light from the mark (WM) and an imaging lens (4) for forming an image of the mark (WM) by the position detection light passing through the objective lens (2). Then, the objective lens (2) may be used as the correction optical system. Further, the exposure apparatus according to the present invention provides the position detection according to the present invention.
And an exposure optical system for illuminating the mask.
It is. Next, a method for manufacturing a semiconductor device according to the present invention
Mark on the substrate to be exposed
Lighting process to illuminate the position detection light, and the
An imaging process of forming a mark image by condensing position detection light
And a detecting step of detecting the mark image, and the mark image
The chromatic aberration of magnification and axial chromatic aberration that occur when detecting
Conversion process to convert to upper chromatic aberration and conversion in the conversion process
Correction process to correct the axial chromatic aberration,
Pattern on the mask and transfer the pattern on the mask onto the substrate
And a transfer step.

[0019]

According to the present invention, on-axis (longitudinal) chromatic aberration and magnification (lateral) chromatic aberration generated in the projection optical system (1) are as follows:
When the area to be observed by the position detecting optical system is narrow, the amount is almost the same over the entire observation visual field. The amount of chromatic aberration of magnification generated in the projection optical system (1) changes almost linearly with respect to the wavelength in the wavelength range of the position detection light. Therefore, the reference wavelength of the position detection light is the center wavelength λ ₀ in the wavelength range, the minimum wavelength in the wavelength range is λ ₋ , and the maximum wavelength is λ
_{If +} , any one of the marks (WM) by the position detection light reflected from the marks (WM) on the substrate (W) in FIG.
Image of the point, as shown in FIG. 2, the surface R1 _- distributed in A ₊ point point _A~ surface point A~ surface R1 ₊ above on R1 above. Then, due to the chromatic aberration of magnification, these points A ₋ , A and A ₊
Is inclined with respect to the optical axis of the projection optical system (1).

Therefore, in the present invention, as shown in FIG.
The optical axis of the detection optical system (2, 4) as the imaging optical system is set parallel to a straight line passing through the points A ₋ , A and A ₊ . This means that the chromatic aberration of magnification of the projection optical system (1) with respect to the wavelength range of the position detection light has been converted into axial chromatic aberration. Next, the chromatic aberration is corrected only by correcting the axial chromatic aberration by the correction optical system (2) of the detection optical systems (2, 4).

However, since the optical axes of the detection optical systems (2, 4) are inclined, as shown in FIG. 3, under the light of the reference wavelength λ ₀ in the position detection light, the substrate (W) Mark above (W
The plane R1 conjugate to M) and the optical axis of the detection optical system (2, 4) are inclined. Therefore, the surface R1 and the detection surface of the detection means (5) are arranged in a substantially tilt relationship with respect to the detection optical system (2, 4). Thus, the detection means (5) can observe a clear image without chromatic aberration of the mark (WM).

As shown in FIG. 4, the surface R1 (object surface) intersects the object side main plane of the detection optical system (2, 4) at an angle θ, and the detection surface (1) of the detection means (5). Assuming that the image plane) intersects the image-side principal plane of the detection optical system (2, 4) at an angle α, the magnification of the detection optical system (2, 4) is β. In this case, if the tilt relationship is established, the angle α of the detection surface is determined by the Scheimpflug condition (ie, tan α = β · tan θ).

However, under a normal tilt relationship, the magnification differs depending on the image height, so that the detection optical system (2, 4) shown in FIG.
Preferably have a telecentric optical arrangement on both sides. Thereby, the magnification in the direction perpendicular to the image plane becomes β. However, even in this case, the magnification γ along the image plane is (β ⁴ · si
n ² θ + β ² · cos ² θ) ^1/2 . Furthermore, as shown in FIG. 1, for example, the detection optical system (2, 4)
An objective lens (2) for condensing the position detection light from M) and an imaging lens (4) for forming an image of the mark (WM) by the position detection light passing through the objective lens (2); When the objective lens (2) is a correction optical system for correcting axial chromatic aberration, the configuration of the detection optical system (2, 4) is simplified.

[0024]

1 to 6 show a first embodiment of the present invention .
This will be described with reference to FIG. FIG. 1 shows a main part of a projection exposure apparatus in which the position detecting device of the present embodiment is incorporated. In FIG. 1, exposure light from an exposure optical system (not shown) has a transfer circuit pattern formed thereon. Illuminate the reticle R uniformly,
A circuit pattern image of the reticle R is projected and transferred onto the wafer W via the projection optical system 1 under the exposure light.
That is, the pattern forming surface of the reticle R and the exposure surface of the wafer W are conjugated with respect to the projection optical system 1.

On the other hand, a position detecting device for detecting the position of a wafer mark WM as an alignment mark formed near each shot area on the wafer W is disposed above the reticle R. The relative position between each shot area on the wafer W and the reticle R is determined by the position detecting device and a position detecting device (not shown) for detecting the position of a reticle mark (not shown) as an alignment mark on the reticle R. An alignment system for performing accurate alignment is configured. In this case, the position of the reticle mark on the reticle R may be simultaneously detected by the position detection device of the present example for detecting the position of the wafer mark WM. That is, the alignment system of the present embodiment is a so-called TTR (through-the-reticle) system that can simultaneously detect a reticle mark and a wafer mark WM.

Hereinafter, the wafer mark WM on the wafer W will be described.
The configuration of the position detecting device of the present example for detecting the position of the position will be described. In FIG. 1, a light source 10 is a light source for alignment light of the present embodiment, and the light source 10 emits light of a certain wavelength width, for example, a white light source, a halogen lamp,
Light emitting diodes or multi-wavelength laser light sources can be used. A light beam having a certain wavelength band emitted from the light source 10 is converted into a parallel light beam by the collimator lens 9, and then the wavelength band is narrowed by the dichroic filter 8 that passes only a light beam in a predetermined wavelength band. . That is,
The light beam that has passed through the dichroic filter 8 is alignment light having a wavelength different from that of the exposure light and having a predetermined wavelength range.

The alignment light narrowed in this way is focused by the condenser lens 7 and enters the half mirror 6, and the alignment light reflected by the half mirror 6 is
The light is converted into a parallel light beam through the objective lens 2. The alignment light thus converted into a parallel light beam illuminates the wafer mark WM on the wafer W via the reticle R and the projection optical system 1. At this time, the light source 10, the collimator lens 9, the dichroic filter 8, the condenser lens 7, the half mirror 6, and the objective lens 2 constitute an illumination optical system of the position detecting device.

In this embodiment, the reference wavelength in the wavelength range of the alignment light emitted from the illumination optical system is set to the center wavelength λ ₀ in the wavelength range. In FIG. 1, the imaging light flux under the reference wavelength λ ₀ is shown by a solid line, and as shown in FIG.
The reflected light of the reference wavelength λ ₀ from the wafer mark WM on the wafer W illuminated by the illumination optical system is transmitted to the projection optical system 1.
Then, via the reticle R, the image of the wafer mark WM is formed on the surface R1 separated upward from the reticle R by ΔL, that is, the surface R1 shifted by the axial chromatic aberration of the projection optical system 1.
Therefore, the surface R1 is conjugate with the exposure surface of the wafer W with respect to the projection optical system 1 under the light of the reference wavelength λ ₀ .

Assuming that the minimum wavelength in the wavelength range of the alignment light is λ ₋ and the maximum wavelength is λ ₊ , the surface conjugate with the exposure surface of the wafer W under the light of the minimum wavelength λ ₋ is a surface R1 ₋ , The plane conjugate with the exposure plane of the wafer W under the light of the maximum wavelength λ ₊ is the plane R
1 ₊ Surface R1 _- and the optical axis direction between ΔL1 surface R1 ₊ and the projection optical system 1 is a axial chromatic aberration (longitudinal chromatic aberration) amount by the projection optical system 1 with respect to the alignment light. Also,
Under the light of the reference wavelength λ ₀ , let Y be the image height of an image point on the plane R 1 conjugate with the wafer mark WM with respect to the projection optical system 1.

Then, the minimum wavelength λ of the alignment light
_- the position of the defocused image of the wafer mark WM on the surface R1 to light, the surface R with respect to the maximum wavelength lambda ₊ light
The distance between the position of the defocused image of the wafer mark WM on the surface 1 and the direction along the surface R1 is ΔY. This interval ΔY is the amount of lateral chromatic aberration (lateral chromatic aberration) of the alignment light by the projection optical system 1.

In this case, in this embodiment, a detection optical system is constituted by the objective lens 2, the half mirror 6, the cylindrical lens 3, and the imaging lens 4 arranged in order above the reticle R. surface R1 - blurred image of the wafer mark WM distributed to _~ face R1 ₊ is, by the detection optical system is re-imaged as sharp image on the detection surface of the detection element 5 consisting of two-dimensional CCD or the like. The optical axis of the detecting optical system, intersects at a predetermined crossing angle to the optical axis AX0 of the projection optical system 1, the wafer W with respect to a reference wavelength lambda ₀
The surface R1 conjugate to the exposure surface of
The detection optical system satisfies the tilt image formation relationship.

Hereinafter, the configurations of the detection optical system and the detection element 5 of this embodiment will be described in detail. Therefore, first, the surface R1
The chromatic aberration of the projection optical system 1 when the image height of the wafer mark WM is Y is described below. FIG.
FIG. 6 shows the axial (vertical) chromatic aberration of the projection optical system 1 based on the wavelength λ _{e of the} exposure light. FIG. 6 shows the projection optical system 1 based on the reference wavelength λ ₀ of the alignment light. 2 shows lateral (horizontal) chromatic aberration. In FIG. 5, since the projection optical system 1 is aberration-corrected only for the wavelength λ _e of the exposure light, the image forming position of the reference light λ ₀ of the alignment light is compared with the image forming position of the exposure light λ _e. Are shifted by ΔL in the optical axis direction. The minimum wavelength lambda relative imaging position of the reference wavelength lambda _{0 -} imaging position of the ΔL1 downwards _- shifted, an imaging position of the maximum wavelength lambda ₊ relative imaging position of the reference wavelength lambda ₀ Above ΔL1 ₊ . Width ΔL1 _- and width Δ
The sum with L1 ₊ is the axial chromatic aberration amount ΔL1 in FIG.

In FIG. 6, the image forming position at the maximum wavelength λ ₊ is shifted from the image forming position at the reference wavelength λ ₀ of the alignment light by ΔY ₊ in a plane orthogonal to the optical axis, and the minimum wavelength λ ₋ ΔY by the imaging position in the opposite direction to the case of the maximum wavelength lambda _+, with respect to an imaging position of the reference wavelength lambda _{0 -}
Just shift. The sum of the width ΔY ₋ and the width ΔY ₊ is the chromatic aberration of magnification ΔY in FIG.

[0034] FIG. 2, the surface R1 in Figure 1 _- shows an enlarged-surface R1 ₊ of the wafer mark WM imaging area 100 of the image of,
In FIG. 2, an image of an arbitrary point of the wafer mark on the wafer W in FIG. 1 is formed on the surface R1 _{− with} respect to the alignment light having the minimum wavelength λ ₋ , the reference wavelength λ _0, and the maximum wavelength λ _+.
A point above A _-, distributed in A ₊ a point A and a surface R1 ₊ on a point on the surface R1. And, by the axial chromatic aberration and the chromatic aberration of magnification,
These points A _-, a straight line passing through the points A and A ₊ is inclined with respect to the optical axis of the projection optical system (1). Eg, point A _- Each deviation amount in the lateral direction and the longitudinal direction between the point A [Delta] Y _- and .DELTA.L1 _- a. Accordingly, the inclination angle of the straight line passing through the points A ₋ , A and A ₊ with respect to the optical axis of the projection optical system 1 is substantially Δ
Y _- / .DELTA.L1 _- represented by.

FIG. 3 shows the detection optical system and the detection element 5 shown in FIG.
3 is an enlarged view of the detection unit 200 including FIG.
Of the half mirror 6 is omitted. In this example, as shown in FIG. 3, the optical axis AX1 of the detection optical system including the objective lens 2, the cylindrical lens 3, and the imaging lens 4 is set to a point A.
_- , Set parallel to a straight line passing through point A and point A ₊ . As a result, the axial chromatic aberration and the lateral chromatic aberration of the projection optical system 1 with respect to the wavelength range of the alignment light are converted into only the axial chromatic aberration.

[0036] In this example then, the longitudinal chromatic aberration distribution point A~ _point A~ point A ₊ is corrected by the objective lens 2, the astigmatism caused by the projection optical system 1, perpendicular to the plane of FIG. 3 The light flux passing through the cylindrical lens 3 passes through the imaging lens 4 to form a clear image of the wafer mark WM on the detection surface of the detection element 5 through the imaging lens 4.

Specifically, the structure of the objective lens 2 for correcting longitudinal chromatic aberration will be described. In FIG. 3, the principal plane of the objective lens 2 at the reference wavelength λ ₀ is H. Then, the main plane H ₊ at the maximum wavelength lambda ₊ light, relative to the main plane ^{_{H {(ΔL1 +) 2 +}} (ΔY +) 2} shifted upward by ^1/2, the minimum wavelength lambda _- in the light principal plane H _-, a main plane ^{_{H {(ΔL1 -) 2 +}} (ΔY -) 2} was designed by ^1/2 so as to shift downward, Note and the reference wavelength lambda _0, the maximum wavelength lambda ₊ and The focal length of the objective lens 2 with respect to the light having the minimum wavelength λ- is made equal. Further, as already described, the optical axis AX1 of the objective lens 2, ₊ point A, point A and point A _- are arranged to coincide with the straight line passing through the three points. With this configuration, axial chromatic aberration and lateral chromatic aberration caused by the projection optical system 1 are corrected by the axial chromatic aberration of the objective lens 2.

However, in FIG. 3, since the optical axis AX1 of the objective lens 2 is inclined, a plane conjugate with the exposure plane of the wafer W with respect to the reference wavelength λ _{0 with} respect to the plane 11 perpendicular to the optical axis of the objective lens 2. R1 is inclined by the angle θ. Therefore, in order to clearly form the image of the wafer mark WM on the surface R1 on the detection surface of the detection element 5, the surface 12 conjugate with the surface 11 with respect to the objective lens 2, the cylindrical lens 3, and the imaging lens 4 is formed. On the other hand, the detection surface of the detection element 5 is set at an angle θ ′.
It is necessary to arrange the detection surface and the surface R1 so as to satisfy the tilt image forming relationship.

In order to satisfy the tilt image formation relationship, the detection surface of the detection element 5 may be inclined with respect to the surface 12 at an angle which satisfies the condition of Scheimpflug. Thus, the image of the wafer mark WM is clearly formed on the detection surface. FIG. 4 shows a simplified version of FIG. 3. In FIG. 4, the focal lengths of the objective lens 2 and the imaging lens 4 are denoted by f ₁ and f ₂ , respectively.
The imaging optical system composed of the imaging optical systems 2 and 4. Since the cylindrical lens 3 in FIG. 3 is provided to remove astigmatism, it is omitted here. The conditions for Scheimpflug include the distance from the intersection of the extension of the surface R1 (object surface) and the object-side principal plane of the imaging optical systems 2 and 4 to the optical axis, and the detection surface (image surface) of the detection element 5 Are the same as the distance from the intersection of the extension line of with the image-side principal planes of the imaging optical systems 2 and 4 to the optical axis.
Therefore, for the sake of simplicity, assuming that the object-side main plane is equal to the image-side main plane, the extension of the surface R1 and the extension of the detection surface of the detection element 5 are defined by the imaging optical system 2 under the condition of Scheimpflug. , 4 intersect on the main plane.

The angle between the principal plane and the surface R1 is θ,
Assuming that the angle between the principal plane and the detection surface of the detection element 5 is α and the projection magnification of the imaging optical systems 2 and 4 from the object plane to the image plane is β, the angle α is determined by the following equation. tan α = β · tan θ (1) However, simply establishing a tilt image-forming relationship generally results in a different magnification depending on the image height Y ′. Therefore, as shown in FIG. 4, a stop 13 is arranged near the main plane of the imaging optical systems 2 and 4, and the imaging optical systems 2 and 4 are arranged so as to be telecentric on both sides. This allows
The magnification in the direction perpendicular to the plane of FIG. 4 is constant at β. However, even in this case, the magnification γ along the image plane is as follows.

Γ = (β ⁴ · sin ² θ + β ² · cos ² θ) ^1/2 (2) Accordingly, on the detection surface of the detection element 5, the aspect ratio of the image of the wafer mark WM is The aspect ratio of the wafer WM itself is different. By storing such a difference in magnification in advance, the position of the wafer mark WM can be accurately detected. Further, the aspect ratio of the wafer mark WM on the wafer W is previously determined by the magnification β
The adjustment may be made in consideration of the magnification γ. And
The position of the image of the wafer mark formed on the detection surface is
For example, the position of the wafer mark WM on the wafer W is detected by comparing with the position of the fixed index mark.

As described above, according to this embodiment, the objective lens 2
By converting the axial chromatic aberration and the chromatic aberration of magnification generated in the projection optical system 1 into axial chromatic aberration, the objective lens 2 corrects the axial chromatic aberration. Then, by inclining the optical axis of the objective lens 2, the imaging surface R1 of the image of the wafer mark WM at the reference wavelength and the detection surface of the detection element 5 are set in a tilt relationship, and Prevents blurring of the image. Therefore, the chromatic aberration generated in the projection optical system 1 can be corrected with a simple configuration by using light in a predetermined wavelength range in which thin film interference with the photoresist applied on the wafer W is unlikely to occur as alignment light. .

In FIG. 1, the cylindrical lens 3 corrects astigmatism by matching the meridional image and the sagittal image. Instead of the cylindrical lens 3, for example, a parallel flat plate is inclined. It may be arranged.

Next, a second embodiment of the present invention will be described with reference to FIG. This example is TTL (through the lens)
The present invention is applied to an alignment system of a system.
In FIG. 7, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 7 shows a main part of a projection exposure apparatus in which the position detecting device of the present embodiment is incorporated. In FIG. 7, exposure light from an exposure optical system (not shown)
The reticle R on which the transfer circuit pattern is formed is uniformly illuminated, and a circuit pattern image of the reticle R is projected and transferred onto the wafer W via the projection optical system 1 under the exposure light.

A position detecting device for detecting the position of a wafer mark WM formed in the vicinity of each shot area on the wafer W is arranged on the side of the projection optical system 1.
In this embodiment, a light beam having a certain wavelength band emitted from a light source 10 is converted into a parallel light beam by a collimator lens 9, and the wavelength band is narrowed by a dichroic filter 8.

The alignment light narrowed in this way is focused by the condenser lens 7 and enters the half mirror 6, and the alignment light reflected by the half mirror 6 is
The light is converted into a parallel light beam through the objective lens 2. After the collimated alignment light is reflected by the mirror 21, it illuminates the wafer mark WM on the wafer W via the reticle R and the projection optical system 1.

Then, the reflected light of the reference wavelength λ ₀ from the wafer mark WM on the wafer W thus illuminated is separated from the mirror 21 by the predetermined distance to the side via the projection optical system 1 and the mirror 21. An image of the wafer mark WM is formed on the surface R1. Further, the surface conjugate with the exposure surface of the wafer W under the light of the minimum wavelength λ ₋ in the wavelength range of the alignment light is conjugate with the surface R1 ₋ and the exposure surface of the wafer W under the light of the maximum wavelength λ _+. The surface becomes surface R1 ₊ . Surface R1 _- and the optical axis direction between ΔL1 surface R1 ₊ and the projection optical system 1 is a axial chromatic aberration (longitudinal chromatic aberration) amount by the projection optical system 1 with respect to the alignment light.

Then, the minimum wavelength λ of the alignment light
_- the position of the defocused image of the wafer mark WM on the surface R1 to light, the surface R with respect to the maximum wavelength lambda ₊ light
The distance between the position of the defocused image of the wafer mark WM on the surface 1 and the direction along the surface R1 is ΔY. This interval ΔY is the amount of lateral chromatic aberration (lateral chromatic aberration) of the alignment light by the projection optical system 1.

The image-forming light beam having the aberrations mixed as described above is focused on the detection surface of the detection element 5 by the objective lens 2, the half mirror 6, the cylindrical lens 3 and the imaging lens 4, and the wafer mark WM is placed on the detection surface. Is formed. Also in this example, the optical axis of the objective lens 2 is inclined so as to convert the lateral chromatic aberration and the axial chromatic aberration by the projection optical system 1 into the axial chromatic aberration, and the axial chromatic aberration after the conversion is corrected by the objective lens 2. . Further, the surface R1 and the detection surface of the detection element 5 are arranged so as to satisfy a tilt relationship with respect to an imaging optical system including the objective lens 2 to the imaging lens 4.

In the example shown in FIG.
A diaphragm for making the imaging optical system telecentric on both sides may be arranged between the imaging lens 4 and the imaging lens 4. In the above embodiment, the alignment light in the predetermined wavelength range is used, but the alignment light may be either continuous spectrum light or polychromatic light composed of a plurality of monochromatic lights having different wavelengths.

As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0052]

According to the present invention, when a mark on a substrate such as a wafer is illuminated with light in a predetermined wavelength range or polychromatic light composed of a plurality of lights having different wavelengths from each other and observed through a projection optical system. In addition, on-axis chromatic aberration and lateral chromatic aberration generated in the projection optical system are corrected by the tilt of the optical axis and the correction optical system, and the influence of the tilt of the optical axis is corrected by using a tilt optical arrangement.
Therefore, there is an advantage that a good image can be formed with a simple configuration and the influence of interference by a thin film on a substrate can be reduced.

The imaging optical system has an objective lens for condensing position detection light from the mark and an imaging lens for forming an image of the mark by the position detection light passing through the objective lens. When the objective lens is the correction optical system, the configuration of the optical system is simplified.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a main part of a projection exposure apparatus in which a position detection device according to a first embodiment of the present invention is incorporated.

FIG. 2 is an image forming area 100 of an image of a wafer mark WM in FIG. 1;
FIG.

FIG. 3 is an enlarged view showing a detection unit 200 including the detection optical system and the detection element 5 of FIG.

FIG. 4 is a diagram that is supplied to explain the optical arrangement of the tilt and the arrangement when the optical arrangement is configured as a double-sided telecentric system.

FIG. 5 is a diagram illustrating an example of a change in axial chromatic aberration (longitudinal chromatic aberration) of a projection optical system at a certain image height with wavelength.

FIG. 6 is a diagram illustrating an example of a change in chromatic aberration of magnification (lateral chromatic aberration) of a projection optical system at a certain image height depending on a wavelength.

FIG. 7 is a schematic configuration diagram showing a main part of a projection exposure apparatus in which a second embodiment of the present invention is incorporated.

8A is a diagram illustrating an example of an image for each wavelength, and FIG. 8B is a diagram illustrating a composite image thereof.

FIG. 9 is a diagram showing a change in the intensity of reflected light for each wavelength when the thickness of a photoresist changes.

FIG. 10A illustrates another example of an image for each wavelength.
(B) is a diagram showing the composite image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Projection optical system 2 Objective lens 3 Cylindrical lens 4 Imaging lens 5 Detection element 6 Half mirror 7 Condensing lens 8 Dichroic filter 9 Collimator lens 10 Light source

Claims (4)

(57) [Claims] 1. An apparatus for irradiating an exposure light onto a mask and detecting a position of a mark on the substrate when transferring a pattern on the mask onto the substrate , comprising: An illumination optical system for illuminating position detection light in a predetermined wavelength range different from light, and a projection system for condensing the position detection light from the mark to form an image.
The image formed by the shadow optical system and the projection optical system is re-formed.
An imaging optical system for forming the mark image by image, and detection means for detecting the mark image, on the position detection light from the mark is the projection optical system by through the projection optical system to convert the axial chromatic aberration and a lateral chromatic aberration and longitudinal chromatic aberration occurring Te with respect to the imaging optical system, tilting the optical axis of the imaging <br/> optical system with respect to the optical axis of the projection optical system The image forming optical system is provided with a correction optical system for correcting the converted axial chromatic aberration, and conjugate with the mark forming surface on the substrate with respect to light having a reference wavelength of the position detection light. A position detecting device, wherein a detecting surface of the detecting means is arranged in a tilted relationship with respect to the image forming optical system with respect to a simple surface. Wherein said imaging optical system, an objective lens for condensing the position detection light from the mark, and an imaging lens for forming an image of the mark by the position detection light through an objective lens The position detecting device according to claim 1, wherein the objective lens is the correction optical system. 3. The position detecting device according to claim 1 or 2,
An exposure apparatus comprising: an exposure optical system that illuminates the mask. 4. An illuminating step of illuminating a mark on a substrate to be exposed with position detection light in a predetermined wavelength range, and forming an image of the mark by condensing the position detection light from the mark. Step, a detecting step of detecting the mark image, a converting step of converting the chromatic aberration of magnification and axial chromatic aberration generated when detecting the mark image into axial chromatic aberration, and an axis converted in the converting step. A method for manufacturing a semiconductor device, comprising: a correction step of correcting upper chromatic aberration; and a transfer step of irradiating exposure light onto a mask and transferring a pattern on the mask onto a substrate.