JPH06101427B2 - Exposure equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for semiconductor wafers, etc., and more particularly, it moves a wafer, etc. two-dimensionally with respect to a transfer image by a mask, such as a step-and-repeat method. And exposure apparatus.

(Background of the Invention) Of these types of apparatuses, the one currently operating mainly is called a reduction projection type exposure apparatus. This is to project and transfer a circuit pattern, a mark or the like formed on a reticle onto a wafer via a projection lens. In the case of an apparatus for exposing a wafer, it is necessary to accurately superimpose the circuit pattern already formed on the wafer and the projected image of the reticle pattern. For this superposition, many devices are equipped with a through-the-lens (TTL) type alignment optical system that detects the position of the alignment mark formed for each exposure shot on the wafer through the projection lens. By-die alignment is possible. This method uses an ON-Axis that allows you to see both the alignment mark on the reticle and the alignment mark on the wafer at the same time.
There are two methods, the TTL alignment method and the OFF-Axis TTL alignment method that only sees the alignment marks on the wafer. In either case, the illumination light for scanning or the scanning beam has a single wavelength (He-Ne laser, He -Specific oscillation wavelength spectrum of Cd laser or g of mercury discharge lamp
Line, i-line, etc.). However, if a photoresist layer is coated on the wafer surface and the wafer base is a polysilicon layer or the like, the polysilicon layer transmits light with a high refractive index, so the photoresist coating state and the polysilicon layer The alignment light undergoes interference or scattering depending on the formation state of the. For this reason, there is a drawback that the optical information (regular reflection light, edge scattered light, etc.) from the alignment mark is modulated, and accurate position detection is often difficult.

Therefore, when detecting a mark on a wafer through a projection lens, the same mark is irradiated with a plurality of spectra having different wavelengths as alignment illumination light, and the photoelectric signals when illuminated with each spectrum are compared. It is known that the position of the alignment mark is detected by reducing the influence of interference or the like. However, in this case, since the projection lens is designed by adjusting the chromatic aberration with respect to the wavelength spectrum for exposure, if other wavelength spectra are used, the imaging position (conjugate relationship) on the wafer side or reticle side due to chromatic aberration. Is coming off. For this reason, the configuration of the alignment optical system was unavoidably complicated.

On the other hand, it is also known to provide a non-TTL alignment optical system that detects only a mark on a wafer without passing through a projection lens. In this case, since the alignment optical system is fixed to the outside of the projection lens, it is not necessary to consider the optical characteristics such as chromatic aberration of the projection lens when selecting the illumination method, and a high degree of freedom can be obtained (the optimum method is Can be adopted).

However, TTL alignment optical system,
Even with a non-TTL alignment optical system, the position of the wafer stage when detecting the marks attached to the shot area on the wafer and the position of the wafer stage when exposing the shot area are relatively far apart. If
Alternatively, if the direction of mark position detection or position error detection by the alignment optical system does not satisfy the Abbe condition, there is a problem that high-precision overlay cannot be achieved due to the influence of yawing (micro rotation) of the wafer stage. there were.

(Object of the Invention) The present invention solves the above problems and is caused by yawing of the stage when the substrate to be exposed is moved on the stage so that a mark on the substrate to be exposed such as a wafer is detected by the alignment optical system. It is possible to provide an exposure apparatus capable of preventing deterioration of alignment accuracy due to an error in a detected mark position detection result and superimposing a shot area on a substrate to be exposed and a projected image (pattern image of a reticle) with high accuracy. To aim.

(Outline of the Invention) The present invention is a projection optical system (projection lens 2) for projecting an original image pattern formed on a mask (reticle R) onto a substrate (wafer W) to be exposed, and a wafer W on a coordinate system XY. It is applied to an exposure apparatus provided with a moving stage (1) for two-dimensionally moving. In the present invention, the detection center (P ₂ ) is set at a position displaced from the projection center point (P ₁ ) of the projection lens 2 by the distance L in the X direction or the Y direction, and the shot area (SA ) Alignment mark (Mx, M
y, Mθ) position or alignment detection means (20; 20x, 20y) for detecting the alignment error of the mark,
When the alignment detecting means detects at least the mark position and the alignment error, a yawing measuring means (differential interference) that detects a value (sin θ ₀ ) corresponding to a minute rotation amount on the coordinate system XY of the moving stage (1). 12 or 16)
And the moving stage (1) is moved so that the projected image of the projection lens 2 and the shot area (SA) to be exposed on the wafer W are aligned (superposed) based on the detected mark position or alignment error. The yaw measuring means (differential interferometer 12 or 16) detected (sin θ
₀ ) and the distance L to correct the moving position of the moving stage (1) (correction of L · sin θ ₀ minutes by calculation) is provided.

(Embodiment) FIG. 1 is a perspective view showing a schematic configuration of an exposure apparatus according to an embodiment of the present invention. In FIG. 1, a wafer W to be exposed is placed on a stage 1 that moves two-dimensionally in the X and Y directions. The movement of the stage 1 is controlled by the step-and-repeat method so that a projection image of the circuit pattern Pr of the reticle R by the projection lens 2 is exposed on the photosensitive layer on the wafer W. The reticle stage 3 is arranged so that the optical axis AX of the projection lens 2 passes through the center point of the circuit pattern Pr.
Held in. The reticle stage 3 can be finely moved in the X direction, the Y direction, and the rotation direction (hereinafter referred to as the θ direction). Further, the reticle R is provided with three alignment marks SX, SY, Sθ at positions where it can be projected by the projection lens 2. The projected images of these marks SX, SY, Sθ are SX ′, SY ′, S
It is indicated by θ '. Further, the intersection point with the projection image plane of the optical axis AX is P ₁
Then, the mark images SX ′, SY ′, Sθ ′ are located as a line pattern radially extending from the point P ₁ . The marks SX, SY, Sθ on the reticle R are mainly used for alignment of the reticle R with respect to the apparatus (reticle alignment), alignment with marks formed for each shot area on the wafer W, and baseline measurement described later. Sometimes used. Therefore, although not shown in FIG. 1, it is turned on above the reticle R.
A microscope for Axis alignment is installed to detect each mark SX, SY, Sθ.

By the way, the position of the stage 1 in the X direction is measured by the laser interferometer 4, and the position in the Y direction is measured by the laser interferometer 5. The measurement axis of the laser interferometer 4, that is, the laser beam BX is vertically incident on the moving mirror 6 on the stage 1,
The measurement axis of the laser interferometer 5, that is, the laser beam BY is vertically incident on the moving mirror 7 on the stage 1.

The laser beam BX is parallel to the X axis of the coordinate system XY, and the laser beam BY is parallel to the Y axis of the coordinate system XY. The two beams BX and BY define the moving coordinate system of the stage 1. Furthermore, the plane containing the center lines of the two beams BX and BY coincides with the image plane of the projection lens 2, and the intersection of the center lines is P ₁
Matches Further, in this embodiment, since the moving stroke of the stage 1 is larger than that of the conventional stepper, the yawing of the stage 1 is detected to correct the relative minute rotation error between the projected image in the coordinate system XY and the wafer W. Therefore, a so-called differential interferometer is provided. In Figure 1, a moving mirror
A differential interferometer is provided for each of 6 and 7, but only one of them may be provided. A laser beam BL ₁ from a laser light source (not shown) is split by a beam splitter 10 as an interferometer, one of which is a beam B ₁ which is vertically incident on a moving mirror 7 and the other is a beam B which is reflected by a mirror 11. It becomes ₂ and is vertically incident on the movable mirror 7. The beams B ₁ and B ₂ are determined so as to be separated by a certain distance in the X direction, and the reflected light of the beam B _{1 by} the moving mirror 7 and the reflected light of the beam B _{2 by} the moving mirror 7 are combined by the beam splitter 10. It is incident on the receiver 12. The receiver 12 detects the tilt of the reflecting surface of the moving mirror 7 between the beams B ₁ and B ₂ with respect to the X axis. Originally, the reflecting surface of the movable mirror 7 is formed in a highly accurate plane so that the stage 1 does not move in the Y direction at the position of the measurement axis when the stage 1 moves only in the X direction. However, since the running of stage 1 can cause yawing in the order of submicron,
The moving mirror 7 is detected as tilted in the XY plane between the beams B ₁ and B ₂ .

Similarly, with respect to the movable mirror 6, a differential interferometer including a beam splitter 14 for splitting the laser beam BL ₂ into two, a mirror 15 and a receiver 16 is provided, and the movable mirror 6 uses the beams B ₃ and B ₄ as measurement axes. The displacement difference in the Y direction at that point of 6 is detected. Thereby, the yawing amount of the stage 1 is detected.

In the present embodiment, the alignment optical system 20 is provided at a distance L from the projection lens 2 in order to perform the alignment for each shot by the OFF-Axis method. That is, the optical lx (center of detection) of the alignment optical system 20 and the optical axis AX of the projection lens 2 are separated by a distance L. Optical axis lx
Let P ₂ be the point of intersection with the projected image forming plane, P ₂ is determined so as to coincide with the measurement axis of the laser interferometer 5. This is not essential in the present invention, but it is important for minimizing the Abbe error at the time of detecting the position of the alignment mark formed on the wafer W. Although only one alignment optical system 20 is shown in FIG. 1, two or more alignment optical systems may be provided depending on the detection direction of the alignment mark. That is, the X-direction mark and the Y-direction mark associated with one exposure shot area on the wafer W may be detected separately. What is important in the embodiment is that the alignment optical system 20 can detect the marks of all the shot areas to be exposed on the wafer W, and all the shot areas are aligned with the projection image by the projection lens 2. This is to increase the movement stroke of the stage 1. Specifically, the movement stroke is set to a value equal to or larger than the value determined by the sum of the diameter of the wafer W and the constant distance L. Therefore, the lengths of the movable mirrors 6 and 7 are also determined corresponding to the movement strokes.

The positions Wa, Wb, Wc of the wafer W shown by the phantom lines in FIG.
Shows a case where a point P ₂ is made to coincide with each corner point when a square inscribed in the circular wafer W is defined, and the actual stroke of the stage 1 is larger than that shown in the figure. By the way, when the OFF-Axis type alignment optical system 20 is provided in this way, the distance between the points P ₁ and P ₂ (baseline amount)
Therefore, the fiducial mark FM is provided on the stage 1. The reference mark FM is detected by either the alignment optical system 20 or a TTL or ON-Axis type alignment system (reticle alignment system or the like) (not shown) that detects the marks SX, SY, Sθ of the reticle R. At this time, since the TTL-type alignment-type illumination light passes through the projection lens 2, light having an exposure wavelength is preferable.

FIG. 2 is an optical layout diagram showing a specific configuration of the alignment optical system 20. Here, a case where only the X-direction alignment mark Mx on the wafer W is detected will be described.
The light guide 200 guides and emits light for illuminating the mark Mx on the wafer W from a light source (a tungsten lamp, a mercury discharge lamp, or a laser) not shown. When a tungsten lamp is used as the light source, the wavelength of the emitted light has a continuous spectrum. When using a laser light source,
Select one that has several oscillation spectra in the wavelength range of 600 nm to 800 nm. The light from the light guide 200 passes through the relay optical systems 201a and 201b, the filter 202, and the lens 203, is reflected by the half mirror 204, and enters the objective lens 205. Here, the filter 202 is, for example, 530 nm so as not to expose the photoresist FR applied on the wafer W to light.
It is set to cut a shorter wavelength range. Therefore, the light that illuminates the wafer W through the objective lens 205 is 530 nm.
It has a continuous spectrum or a plurality of spectra in a longer wavelength range. The short wavelength of 530 nm or less is cut off as the illumination light because it is assumed that OFPR800 (trade name) is used as a positive photoresist.
Further, the illumination light emitted from the objective lens 205 becomes uniform parallel light parallel to the optical axis lx and irradiates the wafer W. Further, the wavelength band of the illumination light is preferably about 200 nm.

Now, the reflected light (regularly reflected light, scattered light, diffracted light, etc.) generated from the surface of the wafer W enters the imaging lens 206 via the objective lens 205 and the half mirror 204, and is an index plate made of glass or the like. An image is formed on the lower surface of 207. On the index plate 207, index marks 208 are formed of chrome or the like so as to sandwich the magnified image of the mark Mx on the wafer W or the magnified image of the reference mark FM.

Here, a so-called telecentric objective optical system is constituted by both the objective lens 205 and the imaging lens 206, and the wafer W
The chief ray is parallel to the optical axis lx on both the side and the index plate 207 side. The half mirror 204 is obliquely installed at the pupil position of this telecentric objective optical system. The image of the mark Mx (or mark FM) formed on the index plate 207 and the index mark 208 are formed on the image pickup surface 210a of the image pickup tube 210 via the telecentric magnifying optical system by the image forming lenses 209a and 209b. To be imaged. At the pupil position of this telecentric magnifying optical system, a spatial filter 211 for cutting specularly reflected light is removably arranged. When this spatial filter 211 exists in the optical path, the mark M on the wafer W
A dark field image of x (or the reference mark FM) is captured, and a bright field image is captured when the spatial filter 211 is not in the optical path. In FIG. 2, a field stop for defining an illumination area on the wafer W is appropriately provided in the illumination optical system from the light guide 200 to the imaging lens 203.

FIG. 3 shows the image signal from the image pickup tube 210 as a cathode ray tube (CRT).
It is a figure which shows an example of how each mark looks when it is displayed in FIG. An image Mx ′ of the mark Mx is provided between the index marks 208a and 208b.
When the wafer W is positioned so that
It is assumed that the center position x ₃ of the image Mx ′ is displaced in the X direction by Δx with respect to the center position x _{c of the} 208a and 208b in the X direction.
This deviation amount Δx is a so-called alignment error, which is a minute amount of ± 1 μm or less on the wafer W after the global alignment of the wafer W. Center position x _c is mark 20
Determined as the midpoint between the center x ₂ center x ₁ and mark 208b of 8a. When such a mark is positioned within the predetermined scanning area 210b, the image signal by the scanning line SL has a waveform as shown in FIG. Here, the case of bright field detection without the spatial filter 211 will be illustrated. In FIG. 4, the vertical axis represents the magnitude (level) I of the image signal, and the horizontal axis represents the position (X). In the case of the present embodiment, as is apparent from the configuration of FIG. 2, the index plate 207 is illuminated by the reflected light from the wafer W (or the plate on which the reference mark FM is formed), and therefore the position x ₁ , x ₂ , the level I becomes the bottom because of the marks 208a and 208b. For mark Mx, scan line SL
Light scattering occurs at the two step edges extending in the direction orthogonal to the direction, so that it becomes the bottom at the positions E ₁ and E ₂ .
Since the position x ₃ is detected as the midpoint between the positions E ₁ and E ₂ , and the position x _c is detected as the midpoint between the positions x ₁ and x ₂ , the alignment error Δx is represented by the equation (1).

At this time, since the absolute position of the stage 1 in the X direction is detected by the laser interferometer 4 with a resolution of, for example, about 0.02 μm, alignment can be achieved by moving the stage 1 in the X direction by −Δx from the current position. Will be done. Also, a linear pattern of the reference mark FM extending in the Y direction can be detected in the same manner as the mark Mx on the wafer W.

By the way, according to the alignment sensor configured as shown in FIG. 2, since the illumination light on the wafer W does not have a single wavelength spectrum, the interference effect and the scattering phenomenon are reduced. Therefore,
These conventional phenomena will be described with reference to FIGS. FIG. 5 shows the cross-sectional shape of the LOCOS structure mark. Here, 150 is silicon (Si), 151 is polysilicon (poly Si), 152 is silicon oxide (SiO ₂ ), and a photoresist FR is applied thereon. Generally, the photoresist FR, the silicon oxide 152, and the polysilicon 151 are light-transmissive, and therefore, when irradiated with light of a single wavelength λ ₀ ,
Reflected light on the surface of photoresist FR, silicon oxide 150
The reflected light on the surface of, the reflected light on the surface of the polysilicon 151, and the reflected light on the silicon 150 interfere with each other to generate so-called interference fringes. This interference fringe is remarkable on the waveform of the image signal.
Reduce the S / N ratio. It as shown in FIG. 6 for example, a number of bottom B ₁ that is similar to the bottom E _1, E ₂ in addition to the bottom E _1, E ₂ generated by the step edges of the _{mark, B 2, B 3, B} 4 …
This is because the superposition occurs. Although it is not so difficult to automatically recognize the positions of the bottoms E ₁ and E ₂ accurately from such a signal waveform, it is possible to avoid the problem that false detection easily occurs as the time becomes extremely long. There wasn't.

FIG. 7 shows the convex mark portion 156 on the surface of the aluminum (Al) layer 155.
In this case, aluminum particles 153 are randomly formed on the surface of the aluminum layer to form a rough surface. Then, a photoresist FR is applied on such an aluminum layer 155. When the light of the single wavelength λ ₀ irradiates the mark portion 156, remarkable scattered light is generated not only from the step edges but also from the particles 153. Therefore, in the case of bright-field detection, the image signal has a large waveform distortion as shown in FIG.
The N ratio also decreases. That is, the bottoms E ₁ and E ₂ corresponding to the edge position of the main body are not sharp, and many bottoms due to the background occur. Such a signal waveform is also difficult to process, and of the conventional alignment apparatuses that use light of a single waveform, it is inferior to the alignment accuracy of only the resist pattern on silicon (Si).

However, as in the embodiment of the present invention, the wavelength of the illumination light has a bandwidth, or by irradiating a plurality of wavelength spectra at the same time, the interference effect and the scattering phenomenon are reduced, and the distortion and S / N of the signal waveform are reduced. The ratio can be significantly improved.

Next, the overall operation of this embodiment will be described. First, the reticle R is placed on the reticle stage 3 as shown in FIG. 1, and then the reticle alignment system is used to mark.
The reticle stage 3 is positioned so that the reticle R comes to a predetermined position with respect to the optical axis (exposure center) AX by detecting SX, SY, Sθ and the like. Next, a wafer W as shown in FIG.
Is pre-aligned and then placed at a predetermined position on the wafer stage 1. At this time, a shot area including a circuit pattern and various marks for alignment is formed on the wafer W.
It is assumed that the SA has already been formed. Shot area SA
Are arranged in a matrix according to the arrangement coordinates (orthogonal system) on the wafer W. In this state, the wafer W
The above array coordinate system and the laser interference system 4,5 of the wafer stage 1.
The accuracy of pre-alignment corresponds to the measurement coordinate system defined by, and is at most about ± 30 μm. Therefore, marks WGy, WGθ, and WGx for global alignment formed at specific positions on the wafer W are provided, for example, in Japanese Patent Laid-Open No. 56-102823.
It is detected by an alignment microscope as disclosed in Japanese Patent Publication No. Since the position of the detection center of this alignment microscope is accurately measured in the measurement coordinate system of the wafer stage 1, the alignment coordinate system of the shot area SA and the measurement coordinate of the wafer stage 1 are detected by detecting the marks WGy, WGθ, and WGx. The system is associated with an accuracy within ± 1 μm. At this time, if the θ table that rotates only the wafer W by a minute amount is incorporated on the wafer stage 1, the mark
The rotation error of the wafer W is obtained by detecting the WGy and the mark WGθ without changing the position of the wafer stage 1 in the Y direction, and the θ table is rotated so that the error is corrected. This completes the global alignment of the wafer W.

Next, the wafer stage 1 is moved by a simulated step-and-repeat method, and each shot area on the wafer W is moved.
Each-shot alignment associated with SA (hereinafter ESA
Mark Mx, My, Mθ for
Detect with. In this case, two alignment optical systems 20 are separately provided for the X-direction alignment and the Y-direction alignment, and when the X-direction mark detection point and the Y-direction mark detection point are largely separated, Only for the alignment mark Mx in the direction, for each shot area SA,
The position is sequentially detected and stored. That is, the detection center P ₂ of the alignment optical system 20 for the X-direction alignment sequentially substantially coincides with the mark Mx (as shown in FIG.
The wafer stage 1 is stepped so as to be sandwiched between 8a and 208b), and the current position of the stepped wafer stage 1 is corrected by the alignment error Δx and the position is sequentially stored as the shot address value Xs ′. However, at this time, when the optical system 20 for X-direction alignment is apart from the center P _{1 in the} Y-direction by the distance L as shown in FIG. 1, the wafer stage 1 is detected when the mark Mx in the X-direction is detected. By yawing in the X direction of Abbe
Errors can occur. This Abbe error ΔXab is expressed by equation (2).

_{ΔXab = L · Sinθ 0 ...... (} 2) where theta ₀ is yawing amount measured by the receiver 12 or 16 of the differential interferometer. Therefore, since the measurement position of the mark Mx at the point P ₁ has an error of ΔXab, the true shot address value Xs in the X direction is expressed by the equation (3).

Xs = Xs ′ + ΔXab (3) Next, the position of the alignment mark My or Mθ in the Y direction is sequentially detected by the optical system 20 for Y direction alignment. In this case, the optical system 20 for Y-direction alignment is a line passing through the point P ₁ and parallel to the X-axis (that is, the measurement axis in the X-direction).
When the detection center point is located above and is separated from the point P ₁ by L in the X direction, the Abbe error ΔYab may occur due to yawing of the wafer stage 1 in the Y direction. Therefore mark M
Letting Ys' be the shot address value in the Y direction due to the laser interference 5 when y is detected, the true shot address value Ys in the Y direction is expressed by equation (4).

Ys = Ys ′ + ΔYab = Ys ′ + L · Sin θ ₀ (4) Then, at the time of actual exposure, the wafer stage is moved to a position corrected by the distance L with respect to the stored true shot address coordinate value (Xs, Ys). 1 may be sequentially stepped. If it is determined that the shot address values for all the shot areas SA on the wafer W before exposure are not preferable in terms of throughput, only the shot areas SA at several discrete spots on the wafer W are obtained. A method of obtaining a true shot address value of all shot areas SA (so-called block alignment or zone alignment) may be used by obtaining a shot address value for, and using the value as a correction amount of the shot position defined at the time of global alignment.

By the way, in the above embodiment, the arrangement of the two separate alignment optical systems 20 regulates the case as shown in FIG. In this case, the optical system 20x for the X-direction alignment and the optical system 20y for the Y-direction alignment are both L apart from the point P _1, so an Abbe error occurs in both the mark position measurement in the X-direction and the Y-direction. One shot address coordinate value (Xs, Y
Correction of ΔXab and ΔYab was required for both Xs and Ys to determine s).

Therefore, as shown in FIG. 11, if the optical system 20x for X-direction alignment is arranged on the measurement axis BX and the optical system 20y for Y-direction alignment is arranged on the measurement axis BY, mark positions in both directions can be set. Abbe error does not theoretically occur during detection. Therefore, Xs = Ys 'and Ys = Ys' are set, and the measurement process is simplified, and there are no elements that are unstable in accuracy. However, the same applies to the case of FIG. 10, but X
If the direction and the Y direction are composed of separate alignment optical systems, the wafer stage 1 must have a large movement stroke in both the X direction and the Y direction. This means that the precision of both reflecting surfaces of 7 must be highly accurate over a long dimension, which makes it difficult to manufacture.

Therefore, the objective lens 205 of the alignment optical system 20 is shared to form a biaxial alignment optical system in the X and Y directions. Specifically, in FIG. 2, for example, the imaging lens 20
A half mirror is provided between 6 and the index plate 207 to divide the reflected light from the wafer W into two, and for one of the two reflected light beams, the index plate for the X direction, the lenses 209a and 209b, and the image pickup. A tube is provided, and a Y-direction indicator plate and a lens 20 are provided for the other side.
9a and 209b and the image pickup tube are provided. And this 2
The axis alignment optical system 20 is arranged so that the detection center is located on the measurement axis BY as shown in FIG. 12, for example. At this time, no Abbe error occurs in the mark position detection in the Y direction (measurement axis BY direction), but in the X direction (measurement axis BX direction)
Abbe error occurs in the mark position detection. Therefore, when the distance between the point P ₁ and the center of the alignment optical system 20 is L, the true shot address value is expressed by the equations (5) and (6).

Xs = Xs ′ + L · sin θ ₀ (5) Ys = Ys ′ (6) With such a structure, when the diameter of the wafer W is D, the movement stroke of the wafer stage 1 in the Y direction is L + D or more. It is understood that the moving stroke in the X direction may be D or more. That is, only the length of the moving mirror 6 in the Y direction needs to be L + D or more, and the length of the moving mirror 7 in the X direction may be D or more. Since the wafer W is mounted on the stage 1, the wafer mounting surface is set to the projection lens 2
Also, a stroke for pulling the alignment optical system 20 from directly below and positioning it at the loading position is required.

Further, as shown in FIG. 12, the mark S on the reticle R is
The distance between the projected position of each image SY 'and Sθ' of Y and Sθ and the center position of the alignment optical system 20 in the X direction and the Y direction, that is, the so-called baseline amount is L by design, but the alignment error of the reticle R. In consideration of the above, the laser interferometers 4 and 5 fluctuate to the extent that they can be detected with the resolution (0.02 μm). Therefore, the wafer stage 1 is positioned so that the reference mark FM and the mark SY (or Sθ) on the wafer stage 1 are accurately overlapped and detected by the alignment system of the TTL / ON-Axis method. The position y ₁ in the Y direction of is stored. Next, the wafer stage 1 is positioned so that the reference mark FM is detected by the alignment optical system 20, and the position y ₂ of the wafer stage 1 in the Y direction at that time is stored. Then, y ₁ −y ₂ is calculated and stored as the baseline amount. This value is obtained with accuracy determined by the resolution of the laser interferometer. Of course, in the X direction as well, the shift between the mark SX and the alignment optical system 20 in the X direction may be detected, and the shift amount may be used as the baseline amount in the X direction. At this time, the image SX ′ of the mark SX is also the alignment optical system.
The X-direction detection center of 20 is also displaced from the measurement axis BX, so an Abbe error may occur, which can be easily corrected based on the yawing amount θ ₀ obtained by the differential interferometer.

Further, as shown in FIG. 9, when the marks My and Mθ are located at rotationally symmetrical positions with respect to the center CC of the shot area SA, the marks My and M can be adjusted by the alignment optical system 20 (or 20y).
By obtaining the position of θ in the Y direction and calculating the difference, a minute rotation error within the array coordinate meter (or the coordinate system of the wafer stage 1) of the shot area SA itself is also obtained.
Therefore, the wafer W is rotated by the θ table by that amount so that the minute rotation error (so-called chip rotation) is corrected during exposure, or the reticle stage 3 is provided with a minute rotation mechanism and the reticle R is rotated for each exposure shot. If corrected, the overlay accuracy is further improved.

Furthermore, the marks Mx, My, Mθ of the ESA method on the wafer W are T
Reticle R using TL / ON-Axis alignment system
It is more preferable that the arrangement is such that the marks (SX, SY, Sθ) above can be observed (detected) at the same time. This is because it is possible to immediately check whether or not the result of alignment performed by the alignment optical system 20 is accurate.

In addition to the detection method using the image pickup tube as the alignment optical system 20, a laser beam having several wavelength spectra that does not expose the photoresist to light is made into spot light on the wafer W and is subjected to relative scanning (scanning of laser spot or wafer stage). The same effect can be obtained even with the moving method. In the method of scanning the laser spot itself, a reference index mark is required in the alignment optical system, and the mark on the wafer W is scanned with the same laser spot light together with this index mark. Further, in the system in which the laser spot is slightly vibrated to synchronously detect the photoelectric signal corresponding to the reflected light from the mark, the vibration center is the detection center of the alignment optical system 20. In addition, the wafer stage 1 is scanned without moving the laser spot at all, and photoelectric signals corresponding to the reflected light (scattered light, diffracted light, etc.) from the mark are sampled by the measurement pulse signals from the laser interferometers 4 and 5. Then, the center of the laser spot itself in the scanning direction is the detection center.

As shown in FIG. 13, the configuration of the differential interferometer is such that when the two laser beams B ₃ and B ₄ are positioned with the laser beam (measurement axis) BX interposed therebetween, the Y of the movable mirror 6 required. The direction length is minimized.

As described above, according to the present invention, it is possible to accurately align the original image pattern image of the mask with the shot area of the exposed substrate by correcting the influence of yawing caused by the movement of the moving stage at the time of detecting the mark. . Especially when the alignment detecting means for detecting the mark position is provided out of the Abbe condition, if the movable stage is positioned at a desired point based only on the mark measurement position by the alignment detecting means, it may be affected by yawing of the stage. Although the alignment accuracy will definitely deteriorate, according to the present invention, the yawing amount is measured when detecting the mark in the shot area or when detecting the reference mark on the stage, and the position is measured at the time of overlay exposure. Since the correction is made when the determination or the baseline amount is determined, there is almost no accuracy deterioration.

According to the embodiment of the present invention, the off-axis (OFF-A
Since the stroke of the moving stage is increased so that each shot shot alignment can be performed by the xis) method, it is possible to provide an optimal alignment optical system that matches the surface condition of the substrate to be exposed. Therefore, it is less susceptible to the interference of the photoresist and the scattering of the mark underlayer condition, which enables highly accurate mark detection. Furthermore, according to the embodiment, the alignment optical system is a part of the projection optical system,
Or, since all of them are not used at all, there is no need to be limited to the NA (numerical aperture) on the wafer side of the projection optical system,
Can be made bigger. For example, it is possible to set the NA to about 0.95 on the objective side of the alignment optical system. When the NA is increased as described above, not only the effect of the interference of the imaging light rays is further reduced, but also high resolution is obtained. Therefore, since the resolution of the edge of the mark is increased, the S / N ratio of the alignment signal (image signal, photoelectric signal) is also increased, and there is an advantage that the detection accuracy is improved. Further, since the objective lens having a high NA has a small depth of focus and the bottom and top of the mark can be separated and focused, for example, alignment corresponding to only the bottom of the mark can be performed.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of a projection type exposure apparatus according to an embodiment of the present invention, FIG. 2 is an optical layout diagram of an alignment optical system for off-axis type, die-by-die alignment, and FIG. FIG. 4 is a diagram showing a state of detecting an alignment error using an alignment mark, FIG. 4 is a wavemeter diagram of an alignment signal, FIG. 5 is a sectional view of a wafer for explaining an interference effect, and FIG. 6 is a case of FIG. Waveform diagram of alignment signal, FIG. 7 is a cross-sectional view of the wafer for explaining the scattering phenomenon, and FIG.
FIG. 9 is a waveform diagram of the alignment signal in the case of FIG. 7, FIG. 9 is a plan view showing the shot arrangement and mark arrangement on the wafer,
FIG. 10 is a plan view showing the arrangement of the alignment optical system, and FIG.
The figure is a plan view showing another arrangement of the alignment optical system,
The figure is a plan view showing another alignment optical system arrangement,
FIG. 13 is a plan view showing another configuration of the differential interferometer. (Explanation of symbols of main parts) R ... Reticle, W ... Wafer 1 ... Wafer stage, 2 ... Projection lens 4,5 ... Laser interferometer 6,7 ... Moving mirror 20 ... Alignment optical system

Claims (8)

[Claims] 1. A projection optical system for projecting an original image pattern formed on a mask onto an exposed substrate, and a two-dimensional movement of the exposed substrate on a predetermined coordinate system XY with respect to a projection area of the projection optical system. An exposure apparatus that sequentially exposes each of a plurality of different shot areas on the substrate to be exposed with a projection image of the original image pattern, in the X direction or from the center of the projection area of the projection optical system. An alignment detection unit having a detection center set at a position displaced by a distance L in the direction, and detecting the position of an alignment mark formed accompanying the shot area on the substrate to be exposed or the alignment error of the mark; Yawing measuring means for detecting a value according to a minute rotation amount of the moving stage on the coordinate system XY when the mark is detected by the alignment detecting means; When the moving stage is moved so that the projection area and the shot area to be exposed are aligned on the basis of the mark position detected by the element detecting means or the alignment error, the value detected by the yawing measuring means and the value An exposure apparatus comprising means for correcting the moving position of the moving stage based on the distance L. 2. The yawing measuring means projects a beam from the Y direction to each of different positions on a first reflecting mirror extending in the X direction on the moving stage, and receives reflected light of each beam. The first differential interferometer for detecting a change in a minute rotation amount of the first reflecting mirror within the coordinate system XY by including the first differential interferometer according to claim 1. apparatus. 3. The yawing measuring means projects a beam from the X direction to different positions on a second reflecting mirror extending in the Y direction on the moving stage, and receives reflected light of each beam. The second differential interferometer for detecting a change in a minute rotation amount of the second reflecting mirror in the coordinate system XY by including the second differential interferometer. apparatus. 4. The alignment detecting means irradiates a non-photosensitive irradiation light to a local portion including a mark on the substrate to be exposed, and telecentrically forms an image of the local area on a predetermined image plane. The apparatus according to claim 1, further comprising: a telecentric objective optical system that forms an image, and an image pickup device that picks up an image of the mark formed through the objective optical system. 5. The non-photosensitive irradiation light is continuous or plural in a wavelength range of at least about 200 nm so that an interference action generated between a resist on the substrate to be exposed and a base thereof is reduced. Device according to claim 4, characterized in that it has a spectral distribution of the book. 6. The alignment detecting means includes a telecentric objective optical system that telecentrically forms an enlarged image of a local portion including a mark on the substrate to be exposed, and a top portion and a bottom portion of the mark are separated. 2. The apparatus according to claim 1, wherein a numerical aperture on the exposed substrate side of the telecentric objective optical system is set to be large in order to reduce the depth of focus to such an extent that focusing can be achieved. 7. Prior to the exposure of a projected image onto the substrate to be exposed, the alignment detecting means attaches to a plurality of discrete shot regions among all the shot regions on the substrate to be exposed. The apparatus according to claim 1, wherein the moving stage is moved so as to sequentially detect the alignment marks. 8. A projection optical system for projecting an original image pattern formed on a mask onto a substrate to be exposed, and the substrate to be exposed is two-dimensionally moved on a predetermined coordinate system XY with respect to a projection area of the projection optical system. A first alignment detection for detecting a projection position of the mask stage formed outside the original image pattern on the mask by the projection optical system using a reference mark fixed on the movement stage. And a detection center is set at a position deviated from the center of the projection area of the projection optical system by a certain distance in the X direction or the Y direction, and is attached to the shot area on the substrate to be exposed. Board mark,
Alternatively, a position of the reference mark of the moving stage, or a second alignment detecting means for detecting an alignment error of the mark; a first position where the reference mark is arranged at a projection position of the mask mark of the mask, When the moving stage moves to a second position where the reference mark is detected by the second alignment detecting means, a value corresponding to a minute rotation of the moving stage on the coordinate system XY is detected. Yawing measuring means; when determining the baseline amount between the center position of the mask determined by the arrangement of the mask mark and the detection center of the second alignment detecting means, the mask mark is drawn from the center of the projection area. Distance to the projection position, or distance from the center of the projection area to the detection center of the second alignment detection means An exposure apparatus comprising: a separation and a means for correcting an Abbe error amount according to the value detected by the yawing measurement means.