JP2000012434A - Aligner, exposure system and exposing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a superposing accurary, when a superposing exposure is made while varying an illuminating iris by an exposure device having a variable illuminating iris. SOLUTION: When a superposing exposure of a wafer 25 on which a projecting pattern of a standard layer is formed is made, a control circuit 40 reads parameters on adjusting values at a relative position alignment of a reticle stage 18 and a wafer stage 18 and on adjusting values of projecting multiples of a optical profecting system 23, out from an outer memory device 44 according to an aperture form selected from a variable illuminating iris provided on a turret plate 7. The parameters are predefined as a superposing error caused by the variations in a strain value which is generated on a projecting pattern image of a reticle 16 projected on each layer to be reduced by varying the kind of the illumination iris, when a superposing exposure between defferent layers on the wafer 25 is made. The control circuit 40 adjusts the relative position between the reticle stage 18 and the wafer stage 27 and a projecting multiples of the optical projecting system 23, based upon the parameters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus, an exposure system, and an exposure method. The present invention relates to an exposure apparatus, an exposure system, and an exposure method capable of obtaining alignment accuracy.

[0002]

2. Description of the Related Art In an optical lithography process for manufacturing semiconductor devices such as LSIs, imaging devices such as CCDs, liquid crystal display devices, or semiconductor devices such as thin film magnetic heads, masks or reticles (hereinafter referred to as reticles) are used. As for the exposure apparatus for exposing the pattern of the original onto a photosensitive substrate such as a wafer, a higher-precision one is required as the degree of integration of the above-mentioned elements increases.

With this type of exposure apparatus, with the miniaturization and high integration of patterns on a mask to be exposed, it is possible to further improve the overlay accuracy when performing overlay exposure between different layers on a substrate. It has been demanded.

On the other hand, with the above-mentioned high integration of elements, a projection optical system mounted on an exposure apparatus is also required to have a high resolution. To respond to this, high NA of the projection optical system
Many studies have been made on shortening of the wavelength of illumination light used for exposure and exposure. Further, there is known a technique of inserting a deformed illumination stop into an optical path of an illumination optical system that irradiates a substrate with illumination light for exposure in order to increase the resolution and depth of focus of a projection optical system. The deformed illumination diaphragm is mounted on a turret plate (hereinafter, referred to as a turret plate) having a plurality of shapes prepared according to a required resolution. By rotating the turret plate, it is possible to insert an illumination stop having a desired opening shape into the optical path of the illumination optical system.

[0005]

However, as described above, if the aperture shape of the illumination stop inserted into the optical path of the illumination optical system is changed, distortion generated in the circuit pattern formed on the substrate by the projection optical system will occur. Change. Hereinafter, a change in distortion generated in the circuit pattern due to a change in the aperture shape of the illumination diaphragm is referred to as a difference between diaphragms. As the degree of integration of circuit patterns increases, higher overlay accuracy has been required, and the above-described aperture difference has sometimes become a problem when trying to obtain a desired overlay accuracy. .

Further, when a plurality of overlapping exposures are performed on one substrate in the above-described photolithography process, a so-called mix-and-match system using an exposure system having a plurality of exposure apparatuses in accordance with the exposure process is used. There is a method called. In the mix-and-match method, in addition to the difference between the apertures described above, a difference occurs in a distortion generated in a circuit pattern formed on a substrate due to a difference in a projection optical system incorporated in each exposure apparatus. . Hereinafter, a change in distortion generated in a circuit pattern due to a difference in an exposure apparatus used for exposure is referred to as a difference between apparatuses. Due to the difference between the apparatuses, the deterioration of the overlay accuracy at the time of the overlay exposure by the mix-and-match method sometimes makes it difficult to miniaturize the circuit pattern formed on the substrate.

SUMMARY OF THE INVENTION It is an object of the present invention to suppress a decrease in overlay accuracy of circuit patterns formed on different layers due to the above-described aperture difference and apparatus difference, thereby achieving a more accurate overlay exposure. An exposure apparatus, an exposure system, and an exposure method capable of performing the above-described operations.

[0008]

FIG. 1 shows an embodiment of the present invention.
The present invention will be described with reference to FIG. (1) According to the first aspect of the present invention, the aperture shape of the illumination stop provided in the optical path of the illumination optical system can be changed in accordance with the pattern of the mask 16 projected on the layer formed on the substrate 25. Illumination aperture opening shape changing means 7 and 8;
The present invention is applied to an exposure apparatus having position adjusting means 18 or 27 for adjusting the relative position between the mask 16 and the substrate 25. The amount of distortion generated in the pattern image of the mask 16 projected on the different layer changes due to the change of the aperture shape of the illumination stop when the overlay exposure is performed between the different layers on the substrate 25. The object described above is achieved by providing the position adjustment amount output means 40 for outputting a position adjustment amount for reducing the resulting overlay error of the pattern images by the position adjustment means 18 or 27. (2) The invention according to claim 2 is a position adjustment amount storage means 4 for storing the position adjustment amount corresponding to the opening shape of the illumination stop.
4 is further provided. (3) According to the third aspect of the present invention, the aperture shape of the illumination stop provided in the optical path of the illumination optical system can be changed in accordance with the pattern of the mask 16 projected on the layer formed on the substrate 25. Illumination aperture opening shape changing means 7 and 8;
Exposure comprising position adjusting means 18 or 27 for adjusting the relative position between the mask 16 and the substrate 25, and projection magnification adjusting means 41 capable of adjusting the projection magnification of the pattern image of the mask 16 projected on the substrate 25. Substrate 2 having a plurality of devices
The present invention is applied to an exposure system in which a plurality of exposure apparatuses are mixed when performing overlay exposure between different layers on the fifth layer.
When overlay exposure is performed between different layers on the substrate 25, distortion caused in a pattern image of the mask 16 projected on different layers is caused by using different exposure apparatuses or illumination apertures having different opening shapes. An adjustment amount for outputting an adjustment amount for reducing at least one of the position adjustment by the position adjustment unit 18 or 27 and the magnification adjustment by the projection magnification adjustment unit 41 to reduce the overlay error caused by the change. It has output means 40. (4) The invention according to claim 4 further comprises an adjustment amount storage means 44 for storing the adjustment amount corresponding to the opening shape of the illumination stop and each of the exposure apparatuses constituting the plurality of exposure apparatus groups. is there. (5) According to the fifth aspect of the invention, the aperture shape of the illumination stop arranged in the optical path of the illumination optical system can be changed in accordance with the pattern of the mask 16 projected on the layer formed on the substrate 25. Illumination aperture opening shape changing means 7 and 8;
The present invention is applied to an exposure method of an exposure apparatus having position adjusting means 18 or 27 for adjusting a relative position between the mask 16 and the substrate 25. Further, the distortion caused in the pattern image of the mask 16 projected on the different layer changes due to the change of the opening shape of the illumination stop when performing the overlay exposure between different layers on the substrate 25. The position adjusting means 1
It is reduced by adjusting the position at 8 or 27. (6) According to the invention described in claim 6, the opening shape of the illumination stop arranged in the optical path of the illumination optical system can be changed corresponding to the pattern of the mask 16 projected on the layer formed on the substrate 25. Illumination aperture opening shape changing means 7 and 8;
Exposure comprising position adjusting means 18 or 27 for adjusting the relative position between the mask 16 and the substrate 25, and projection magnification adjusting means 41 capable of adjusting the projection magnification of the pattern image of the mask 16 projected on the substrate 25. Substrate 2 having a plurality of devices
The method is applied to an exposure method of an exposure system in which a plurality of exposure apparatuses are mixed when performing overlay exposure between different layers on 5. When overlay exposure is performed between different layers on the substrate 25, the distortion generated in the pattern image of the mask 16 projected on the different layers changes due to the use of illumination apertures having different opening shapes. The superposition error caused by the position adjustment means 18 or 27
And the magnification adjustment by the projection magnification adjustment means 41.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easy to understand. However, the present invention is not limited to this.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the configuration of the exposure apparatus to which the present invention is applied, the illumination aperture, the aperture difference measuring method, the apparatus difference measuring method, and the aperture difference when performing the overlay exposure, How to correct the difference will be described.

FIG. 1 shows a schematic configuration of a scanning exposure type exposure apparatus according to the present invention. The light source 1 oscillates in response to a trigger pulse sent from the light source control circuit 45 and emits pulsed light. The light source control circuit 45 controls the light source 1 according to a command from a main controller (control circuit) 40 that controls the entire exposure apparatus. As the light source 1, for example, 19
An ArF excimer laser light source that oscillates pulse light having an output wavelength of 3 nm is used. Laser light emitted from the light source 1 as a substantially parallel light beam is guided to a light transmission window 3 on the main body side of the exposure apparatus via a shutter 2. Shutter 2
For example, the illumination light path is closed during replacement of the wafer or reticle, whereby the light source 1 self-oscillates to stabilize (adjust) the beam characteristics including at least one of the center wavelength, the wavelength width, and the intensity of the pulsed light.

The main body of the exposure apparatus is a chamber 10
0, and is controlled so that the temperature inside the chamber 100 is kept constant. The laser beam that has passed through the light transmission window 3 is shaped into a laser beam having a predetermined cross-sectional shape by a beam shaping optical system 4, and a plurality of ND filters provided on a turret plate TP having different transmittances (light reduction ratios) from one another. (ND1 in FIG. 1), is reflected by the reflection mirror 5, and is guided to a fly-eye lens 6 as an optical integrator. The fly-eye lens 6 is formed by bundling a large number of lens elements, and on the exit surface side of this lens element, a large number of light source images (secondary light sources) corresponding to the number of lens elements constituting the lens element are provided. It is formed.

In this embodiment, the turret plate TP is 6
ND filters ND1 to ND6 (ND1 in FIG. 1,
(Only ND2 is shown), and the turret plate TP is rotated by the motor MT1, so that the six ND filters can be interchangeably arranged in the illumination optical system.

Instead of the turret plate TP shown in FIG. 1, for example, two plates each having a plurality of slits are arranged to face each other, and the two plates are relatively moved in the slit arrangement direction so that the pulse The light intensity may be adjusted.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 7-142354, in the present embodiment, the reticle 16 and the wafer 25 are moved synchronously by the reticle stage 18 and the wafer stage 27 described later. While exposing the wafer 25 with the image of the pattern
The mirror 5 is rotated (vibrated) by the motor MT2.
Accordingly, during scanning exposure, interference fringes such as speckles move within the illumination area on the reticle 16 defined by the variable field stop 12, and the integrated light quantity distribution of the pulse light on the wafer 25 becomes substantially uniform. . At this time, reticle 1
6. Move the interference pattern at least once while a point on 6 traverses the illumination area along the scanning direction. Also,
It is preferable to vibrate the reflection mirror 5 so that the interference fringes move in the scanning direction and in the direction perpendicular to the scanning direction in the illumination area. When the interference fringes are moved along the scanning direction of the reticle 16 within the illumination area,
Considering the distance that the reticle 16 moves during the pulse emission,
The swing angle of the reflection mirror 5 between the pulse emission, that is, the movement amount of the interference fringe is determined so that the positional relationship between the one point and the interference fringe changes while the one point on the reticle 16 crosses the illumination area. I do.

Although one fly-eye lens 6 is provided in the present embodiment, a second fly-eye lens 6 is provided between the reflection mirror 5 and the turret plate TP as disclosed in, for example, Japanese Patent Application Laid-Open No. 1-259533. A fly-eye lens as an optical integrator may be provided, and an internal reflection type rod-shaped optical member may be used as the optical integrator instead of the fly-eye lens.

At positions where a number of secondary light sources formed by the fly-eye lens 6 are formed, a plurality of aperture stops 7 having at least one of different shapes and sizes from each other.
A turret plate 7 on which a to 7f are formed is provided. The aperture stops 7a to 7f will be described later. The turret plate 7 is driven to rotate by a motor 8, and one aperture stop is selected according to the pattern of the reticle 16 to be transferred onto the wafer 25 and inserted into the optical path of the illumination optical system. The turret plate 7 and the motor 8 constitute an illumination aperture opening shape changing device.

Light beams from a number of secondary light sources formed by the fly-eye lens 6 pass through an aperture stop of the turret plate 7 and are split into two light paths by a beam splitter 9, and the reflected light is converted into an integrator sensor (photoelectric detection). Vessel) 10
And the illuminance (intensity) of the illumination light is detected. A signal corresponding to the detected illuminance is input to the control circuit 40. On the other hand, the transmitted light passes through a relay lens 11, a variable field stop 12 defining an aperture, and a relay lens
After being reflected by the lens, the light is condensed by a condenser optical system 15 composed of a plurality of refractive optical elements such as lenses. Thereby, the illumination area on the reticle 16 defined by the opening of the variable field stop 12 is illuminated almost uniformly in a superimposed manner.
Then, an image of the circuit pattern on the reticle 16 is formed on the wafer 25 by the projection optical system 23, the resist applied on the wafer 25 is exposed, and the circuit pattern image is transferred onto the wafer 25.

With respect to the illumination area on the reticle 16 defined by the variable field stop 12, during the exposure operation, the width of the reticle 16 in the scanning direction is smaller than the pattern area size, and the width in the direction perpendicular to the scanning direction is smaller. It is wider than the pattern area size. This illumination area is centered on the optical axis AX of the projection optical system 23 and is located along its diameter within the circular image field of the projection optical system 23.

The shape and size of the rectangular aperture of the variable field stop 12 can be changed in addition to the above-described exposure operation. In other words, the shape and size of the rectangular aperture of the variable field stop can be changed by moving at least one blade constituting the variable field stop 12 by the motor MT3. This variable field stop 12
It is also used when measuring the difference between the apertures described later.

The projection optical system 23 of this embodiment is entirely composed of optical elements such as refractive lenses, and an aperture stop Ep is arranged at the position of the pupil (entrance pupil) of the projection optical system 23.
The aperture stop Ep may have a mechanism capable of changing its size so as to change the numerical aperture of the projection optical system. In this case, the aperture stop Ep in the projection optical system and the illumination stop in the illumination optical system may be used. 7a to 7f are arranged at optically conjugate positions. The projection optical system 23 is fixed to a vibration isolation table 24.

The reticle 16 is held and fixed to a reticle stage 18 by a reticle holder 17. The reticle stage 18 is provided on the base 22 so as to move two-dimensionally along a plane orthogonal to the plane of FIG. A mirror 21 is provided on the reticle holder 17, and laser light from the laser interferometer 20 is reflected by the mirror 21 and enters the laser interferometer 20, and the position of the reticle stage 18 is measured by the laser interferometer 20. The position information is input to the control circuit 40. Based on the position information, the control circuit 40 drives the reticle stage driving motor 19 to control the position of the reticle 16, the speed of the reticle 16 during scanning exposure, and the like. I have. Also, the reticle holder 17
Is configured to be rotatable relative to the reticle stage 18 about an axis parallel to the optical axis AX of the projection optical system 23 by a rotation mechanism (not shown).

The wafer 25 is held and fixed on a wafer stage 27 by a wafer holder 26. Wafer stage 27
Is provided so as to move two-dimensionally along a plane orthogonal to the paper surface of FIG. A mirror 31 is provided on the wafer stage 27, and laser light from the laser interferometer 30 is reflected by the mirror 31 and enters the laser interferometer 30,
The position of wafer stage 27 is measured by laser interferometer 30. The position information is input to the control circuit 40. Based on the position information, the control circuit 40 drives the wafer stage driving motor 29 to control the position of the wafer 25, the speed of the wafer 25 during scanning, and the like. An illuminance sensor (photoelectric detector) 28 is provided on the wafer stage 27, and detects the illuminance of exposure light applied to the wafer 25. The detection signal of the illuminance sensor 28 is input to the control circuit 40.

In the exposure apparatus shown in FIG.
The pressure adjuster 41 is provided for controlling the pressure of the air gap between the plurality of lenses constituting the above and finely adjusting the projection magnification of the projection optical system 23. The pressure regulator 41 and the projection optical system 23 communicate with each other through a conduit 43. The control circuit 40 issues a pressure control signal to the pressure adjuster 41 to adjust the projection magnification of the projection optical system to a desired value. The detailed structure of the pressure regulator 41 is described in Japanese Patent Application Laid-Open No. 60-2861.
3 or JP-A-60-78454, and a description thereof will be omitted.

As a method of adjusting the projection magnification of the projection optical system 23, a method disclosed in Japanese Patent Application Laid-Open No. 4-134813 is used instead of the method of adjusting the pressure in the air gap between the lenses as described above. Alternatively, some lens elements constituting the projection optical system 23 may be mechanically moved.

An off-axis field image alignment unit (hereinafter referred to as an off-axis FIA unit) 42 fixed to the projection optical system 23 will be described. When overlay exposure is performed on the same wafer, when a circuit pattern or the like of a reference layer is formed on the wafer 25, the outer peripheral portion of the circuit pattern serves as an index of alignment for overlay exposure of subsequent layers. An alignment mark is formed at the same time. Off-axis FIA unit 42
Is a microscope provided with an epi-illumination device, and its field-of-view image is captured by an imaging device. This field image will be described with reference to FIG.

FIG. 2 shows an off-axis FIA unit 42.
1 shows a field-of-view image captured by an image pickup device such as a CCD incorporated in a camera. Indices 41a to 41 in the visual field image
d is shown, and an enlarged image AM ′ of the alignment mark formed on the reference layer of the wafer 25 is captured in a region surrounded by the indices 41a to 41d. The control circuit 40 includes an off-axis FIA unit 42
The relative distance between the enlarged image AM 'of the alignment mark and the indices 41a to 41d is obtained by image processing based on the signal input from the CPU, and the position of the alignment mark is determined. The alignment marks are provided outside two adjacent sides (for example, an upper side and a left side) of a rectangular circuit pattern formed on the reference layer. The control circuit 40
Based on the position detection results of these alignment marks,
The center position of the circuit pattern formed on the reference layer is calculated and the wafer stage 27 and the reticle stage 18 are calculated.
Are driven to perform alignment, and are subjected to overlay exposure.

The exposure apparatus to which the present invention is applied is configured as described above. In the following description, the Z axis is taken along the optical axis direction of the projection optical system 23 as shown in FIG. Further, in the plane orthogonal to the Z axis, the X axis is taken along the direction of the paper of FIG. 1, and the Y axis is taken along the direction perpendicular to the plane of the drawing. The directions along these X, Y, and Z axes are defined as an X direction, a Y direction,
The description will be made with the Z direction and the rotation direction about the Z axis as the θZ direction. The external storage device 4 connected to the control circuit 40
4 will be described later.

-Illumination stop- A turret 7 for changing the opening shape of the illumination stop (ie, the shape and size of the secondary light source) in the exposure apparatus will be described with reference to FIG. In the turret plate 7,
Conventional Aperture (hereinafter “Conventional”) 7
a, medium σ stop (hereinafter, medium σ) 7b, small σ stop (hereinafter, small σ) 7c, 輪 annular zone stop (hereinafter, 輪 annular zone) 7d,
It has six aperture stops: a 2/3 annular aperture (hereinafter, 2/3 annular zone) 7e and a quadrupole aperture (hereinafter, quadrupole) 7f.
The aperture stops 7a to 7f are provided for the purpose of improving the resolution of the reticle image formed on the reticle 25 and the depth of focus of the projection optical system 23 as described in the related art. 1/2 zone 7d, 2/3 zone 7e,
The hatched portion of the quadrupole 7f is shielded from light, and so-called oblique illumination (tilt illumination) can be performed by using these apertures.

Here, regarding the above-mentioned medium σ7b and small σ7c, the meaning of σ will be described. As shown in FIG. 1, the illumination optics determined by the principal ray Ri parallel to the optical axis AX from the outermost periphery (outermost diameter) of the illumination stop inserted into the optical path of the illumination optical system on the turret plate 7. The numerical aperture of the system is N
Ai (= sin θi), an opening on the illumination optical system side of the projection optical system 23 determined by a principal ray Ro parallel to the optical axis AX from the outermost edge (outermost diameter) of the aperture stop Ep of the projection optical system 23 When the number is NAo (= sin θo), the σ value as the coherence factor is defined by the following equation.

Σ = NAi / NAo

The aperture stop Ep arranged at the position of the pupil (entrance pupil) of the projection optical system 23 and the illumination stop on the turret plate 7 of the illumination optical system are at optically conjugate positions. Since the image of the illumination stop (the image of the secondary light source) is formed on the pupil, the maximum coherence factor is obtained when the diameter of the image of the illumination stop is D7 and the diameter of the aperture stop Ep of the projection optical system 23 is D23. Can be defined by the following equation.

## EQU2 ## σ = D7 / D23

Generally, the σ value of the exposure apparatus in the photolithography process is set to be in the range of 0.3 to 0.8. Depending on the magnitude of this σ, it is called medium σ or small σ. As described above, the present embodiment has a medium σ7b and a small σ7c.

-Measurement of Difference Between Apertures- Here, the significance of the measurement of the difference between apertures will be described again. 1
When performing overlapping exposure using a single exposure apparatus to form a circuit pattern including a plurality of layers, the distortion generated in the projection pattern changes as the aperture shape of the illumination stop is changed. The aperture difference measurement is performed for the purpose of minimizing the overlay error caused by the change of the distortion, but not for minimizing the distortion itself. This aperture difference measurement may be performed at the final adjustment step of the step of assembling the exposure apparatus, when installing the exposure apparatus at a customer's factory, or at the time of regular maintenance after the start of operation of the exposure apparatus. Is also good.

In the following, two types of measuring methods will be described as the method of measuring the difference between the apertures. That is, a method using an optical interference type coordinate measuring machine as the first aperture difference measurement method will be described, and an alignment system of an exposure apparatus such as an off-axis FIA unit 42 will be used as the second aperture difference measurement method. The method will be described.

-Method of measuring aperture difference using light wave interference type coordinate measuring machine-Before describing the method of measuring the difference of apertures, the light wave interference type coordinate measuring machine will be briefly described. This light wave interference type coordinate measuring machine includes a precision XY stage system capable of reading position coordinates with a laser interferometer, and a pattern edge detection system detecting an edge position of a pattern formed on a mask or the like as an object to be measured. And a line width / coordinate measuring device having: In the following description, the light wave interference type coordinate measuring machine is simply called “coordinate measuring machine”.
Called. The measurement of the difference between the apertures using a coordinate measuring machine is generally performed in the following procedure. That is, the pattern image of the test reticle is projected on the wafer. Is subjected to processing such as development and etching. The position coordinates of the test pattern formed on the wafer are read using a coordinate measuring machine, and the distortion of the pattern is measured. The above steps (1) to (4) are repeated while changing the shape of the aperture stop formed in the turret plate, and the difference between the stops is obtained.

FIG. 4 is a diagram schematically showing a test reticle 16A used for measuring the difference between the apertures and the difference between the devices using a coordinate measuring machine (the difference between the devices will be described later). The test reticle 16A is provided with 16 cross-shaped patterns A1 to D4 arranged in a grid, and these 16 patterns constitute a test pattern. The number of cross-shaped patterns constituting the test pattern is increased or decreased as necessary. Also,
The cross-shaped pattern shape and the arrangement method can also be changed as needed. Although FIG. 4 shows a positive reticle pattern, in this case, the resist applied to the wafer may be a positive resist. vice versa,
When the reticle pattern shown in FIG. 4 is a negative type, the resist applied to the wafer may be a negative type.

In measuring the difference between the apertures, one test reticle 16A shown in FIG. 4 and six test wafers used for each of the six types of aperture stops 7a to 7f are prepared. This test wafer is an unexposed one coated with a resist in advance.

First, the turret plate 7 of the exposure apparatus shown in FIG.
Is driven, and the conventional 7a is selected as the aperture stop shape. Subsequently, the test reticle 16A described above is placed on the reticle holder 17 of the exposure apparatus, and reticle alignment is performed. Then, the wafer 25 is placed on the wafer holder 26, and wafer alignment is performed. Thereafter, exposure and movement of the wafer stage 27 are repeatedly performed.

By performing the processing such as development and etching after the above procedure, the test wafer TW
As shown in (a), n projection pattern images Pa11 ′,
Pa12 ′,..., Pa1n ′ are formed. The reason why n projection pattern images are formed is to increase the number of samples and improve the accuracy of distortion measurement described later. FIG.
In (a), each projection pattern image Pa11 ′, Pa1
The details of 2 ′,..., Pa1n ′ are not shown.

Referring to FIG. 5B showing details of the projection pattern image Pa11 ', a method of measuring distortion using a coordinate measuring machine will be described. In the projection pattern image Pa11 ', images A1' to D4 'of cross-shaped patterns A1 to D4 provided on the test reticle 16A shown in FIG. 4 are formed (hereinafter simply referred to as "pattern images A1' to D4 '"). "). The formation positions of these pattern images A1 'to D4' are the "ideal positions" due to the distortion, that is, the positions where the images are formed without any distortion (the position of the grid formed by the two-dot chain line in FIG. 5B). (The intersection position corresponds to the “ideal position”). This shift amount, for example, XA1 and YA1 in the case of the pattern image A1 'is measured by a coordinate measuring machine. This will be described below.

After placing the test wafer TW on the coordinate measuring machine, the design coordinate value and the feed pitch δ with respect to the reference position of the test wafer TW are input to the coordinate measuring machine. That is,
The “ideal position” of the pattern image is input to the coordinate measuring machine. The coordinate measuring machine measures the amount of deviation in the X and Y directions from the “ideal position” of the pattern images A1 ′ to D4 ′ based on the input design coordinate values and the feed pitch. To explain this, the coordinate measuring machine repeats step movement / stop of the XY stage with high accuracy based on the input design coordinate values and feed pitch. Each time the XY stage stops, the pattern edge detection system calculates the amount of displacement of the pattern images A1 'to D4'. Hereinafter, similarly, the amount of displacement is measured for each of the pattern images of the projection pattern images Pa12 ′ to Pa1n ′, and the average value of the measurement results is obtained.

In the example shown in FIG. 5B, the amount of displacement of the pattern images A1 'to D4' in the X direction is constant. This is because the exposure apparatus according to the present embodiment is a scanning exposure type exposure apparatus. That is, the distortion in the X direction, that is, the scanning direction is averaged to be a constant amount by the scanning exposure. On the other hand, the averaging effect by the scanning exposure also acts in the non-scanning direction, for example, the pattern images A1 'to A1'
The displacement amount in the Y direction in 4 ′ is constant. However, the pattern images A1 'to A4', B1 'to B4', C1 'to C
4 'and D1' to D4 'do not always become equal when comparing the Y direction displacement amounts. On the other hand, when exposure is performed by an exposure apparatus of a one-time exposure system (a so-called stepper), the pattern images A1 'to D4'
In the X direction and the Y direction vary.
In the present embodiment, an example in which the present invention is applied to a scanning exposure type exposure apparatus will be described.
The batch exposure method can be applied to any type of exposure apparatus.

As described above, the distortion is not always symmetric with respect to the optical axis Ax of the projection optical system 23 (FIG. 1). Therefore, in order to improve the overlay accuracy when overlay exposure is performed using different aperture stops, when performing alignment between the reticle 16 and the wafer 25, shifting in the X and Y directions, rotation in the Zθ direction, Alternatively, it is effective to perform relative position correction by a combination of these. When the difference in distortion caused by using different aperture stops includes an axially symmetric component, adjusting the projection magnification in addition to the above-described relative position correction is also effective.

Next, a method of measuring the difference between the apertures using the coordinate measuring machine will be described. The procedure of the above-described exposure, development / etching, and measurement of the amount of displacement of the pattern image is repeatedly performed by sequentially changing the aperture shape of the illumination stop to the conventional 7a, the medium σ7b,. The table shown in FIG. 8 is obtained by repeating the above procedure. The table in FIG. 8 will be described after the description of the method of measuring the difference between diaphragms using the alignment system of the exposure apparatus.

An aperture difference measuring method using an alignment system of an exposure apparatus; an aperture difference measurement using an alignment system of an exposure apparatus
The procedure is roughly as follows. That is, the pattern image of the test reticle is projected on the wafer. Is exposed without overlapping the reference pattern without developing the wafer. Is subjected to processing such as development and etching. The relative position coordinates of the test pattern with respect to the reference pattern position are measured using an alignment system, based on the pattern of the test reticle formed on the wafer having undergone the above processing and the reference pattern. The above steps (1) to (4) are repeated while changing the shape of the aperture stop formed in the turret plate, and the difference between the stops is obtained.

FIG. 6 is a diagram schematically showing a test reticle 16B used for measuring a difference between apertures using an alignment system. The test reticle 16B has 16 rectangular frame-shaped patterns P1 to S4 arranged in a grid.
Are provided. The test reticle 16B is also provided with a rectangular point pattern P (hereinafter, referred to as a "point pattern P") at the center thereof. A test pattern is composed of these 16 rectangular frame-shaped patterns P1 to S4 and the dot pattern P. The number of rectangular frame-shaped patterns constituting the test pattern is increased or decreased as necessary. The shape and arrangement of the rectangular frame pattern and the shape of the dot pattern P can also be changed as necessary. Although a positive reticle pattern is shown in FIG. 6 for the sake of illustration, a negative pattern in which the pattern of FIG.

In measuring the difference between the apertures, one test reticle 16B shown in FIG. 6 and six test wafers used for each of the six types of aperture stops 7a to 7f are prepared. This test wafer is an unexposed one coated with a resist in advance.

First, the turret plate 7 of the exposure apparatus shown in FIG.
Is driven, and the conventional 7a is selected as the aperture stop shape. Subsequently, the test reticle 16B described above is placed on the reticle holder 17 of the exposure apparatus, and reticle alignment is performed. Then, the wafer 25 is placed on the wafer holder 26, and wafer alignment is performed. Thereafter, the opening width of the reticle blind 12 (FIG. 1) in the non-scanning direction is fully opened, and scanning exposure is performed. Thereby, test reticle 1
The rectangular frame-shaped patterns P1 to S4 and the dot-shaped pattern P formed on 6B are projected onto a wafer and exposed. Hereinafter, this is referred to as first exposure.

By the above first exposure, 16 wafers are left on the wafer.
The latent images of the rectangular frame-shaped patterns P1 to S4 and the dot pattern P are formed. Subsequently, the latent image is exposed so as to overlap the reference pattern. The exposure of the reference pattern is performed as follows.

First, the reticle blind 12 of the exposure apparatus is narrowed down so that only the dot pattern P of the test reticle 16B is exposed. Subsequently, the wafer stage 27
Is moved 16 times in the X and Y directions at a movement pitch δ, and the operation of exposing the image of the dot pattern P is repeated 16 times. Thereby, a latent image of the reference pattern in which the images of the dot pattern P are arranged in a 4 × 4 grid pattern is formed. In other words, on the assumption that there is almost no distortion in the projected image on the optical axis Ax of the projection optical system 23, the reference pattern is printed on the wafer using the dot pattern P located at the center of the test reticle 16B. Hereinafter, this is referred to as a second exposure.
Thereafter, the first exposure and the second exposure described above are alternately repeated while moving the wafer stage 27 by a predetermined amount.

The reference pattern will be further described. Assuming that the 16 latent images of the rectangular frame-shaped patterns P1 to S4 described above are formed in an “ideal system” without distortion, the latent image of the dot-shaped pattern P has 16 rectangular frames. It is formed so as to be located at the center of each of the latent image patterns. In other words, after performing a process such as development and etching on the wafer that has been subjected to a series of exposures as described above, the image of the dot pattern P and the image of the dot pattern P are squarely surrounded as described later. By measuring the distance in the X and Y directions from the images of the formed rectangular frame-shaped patterns P1 to S4, the amount of positional deviation can be obtained.

The rectangular frame-shaped patterns P1 to P1 described above
The procedure of printing the image and the reference pattern in S4 on the wafer was performed by alternately repeating the first exposure and the second exposure. On the other hand, first, only the first exposure is repeatedly performed to form a plurality of rectangular frame-shaped patterns P1 to S4 on the wafer.
, And then only the second exposure is repeated to form a reference pattern.

The procedure of the first exposure and the second exposure described above is repeated, and thereafter, processes such as development and etching are performed, so that n test pattern images are formed on the test wafer TW as shown in FIG. Pa21 ', Pa22', ...
Pa2n 'is formed. In FIG. 7A,
Each projected pattern image Pa21 ', Pa22', ..., Pa2
The details of n 'are not shown.

Referring to FIG. 7B showing details of the projection pattern image Pa21 ', a method of measuring distortion using an alignment system will be described. Projection pattern image Pa21 '
Are formed with images P1 ′ to S4 ′ of rectangular frame-shaped patterns P1 to S4 provided on the test reticle 16B shown in FIG. 6 (hereinafter, these are simply referred to as “pattern images P1 ′ to S4”).
4 '"). These pattern images P1 'to S4'
The center position of the “ideal position” (FIG. 7B)
(The position of the intersection of the grid formed by the two-dot chain lines corresponds to the "ideal position"). This shift amount,
For example, in the case of the pattern image P1 ', XP1 and YP1 are measured by the alignment system. Hereinafter, an example in which the off-axis FIA unit 42 (FIG. 1) is used as an alignment system will be described.

After the test wafer TW that has been subjected to the above-described processing such as development and etching is placed on the exposure apparatus, the wafer stage 27 is moved to change the pattern image P1 ′ to the off-axis FI.
It is located within the field of view of the imaging device incorporated in the A unit 42. Then, the positional deviation amounts XP1 and YP1 in the X and Y directions between the center position of the image P 'of the dot pattern P and the center position of the image P1' of the rectangular frame-shaped pattern P1 are obtained by image processing. Similarly, the remaining rectangular frame-shaped patterns P2 to S4
For the images P2 'to S4', the amount of positional deviation is determined while the wafer stage 27 is moved stepwise in the X and Y directions. Hereinafter, the pattern images Pa22 ′ to P22 shown in FIG.
Similarly, for a2n ', the amount of displacement is measured, and the average value of the measurement results is obtained. Regarding the above-described procedure of the first exposure, the second exposure, the development / etching, and the measurement of the displacement amount of the pattern image, the opening shape of the illumination stop is sequentially changed to the conventional 7a, the medium σ7b,. Repeat.

FIG. 8 shows a method of calculating the overlay error minimization parameter. FIG. 8 shows the results of measuring the amount of displacement of the pattern images A1 'to D4' shown in FIG. Are summarized for each opening shape. For example, the measurement results of the X and Y direction displacement amounts of the pattern images A1 'to D4' generated when the exposure is performed using the conventional 7a are shown as XA1a, YA1a to XD4a, and YD4a in the vertical direction of the table. The subscripts of the displacement amounts X and Y will be described. The first two characters following X or Y are the pattern image A.
1 ′ to D4 ′ indicate which cross pattern is related to the positional shift amount, and the last character is the positional shift amount when any of the aperture shapes 7a to 7f of the illumination aperture is used. Is shown. Then, regarding the last character, a is a conventional 7a, and b is a medium σ7.
b, c is the small σ7c, d is the 1/2 annular zone 7d, and e is 2
/ 3 zone 7e, and f indicates the amount of displacement when the quadrupole 7f is used.

The results of measuring the amount of displacement (distortion) of the pattern images P1 'to S4' shown in FIG. 7B using the off-axis FIA unit 42 can be summarized in the same manner as shown in FIG. . For the sake of simplicity, a table summarizing distortion measurement results using the off-axis FIA unit 42 is not shown here. Hereinafter, a method of calculating the overlay error minimization parameter will be described with reference to FIG.

As described above, when overlay exposure is performed using illumination apertures having different aperture shapes, an overlay error occurs due to the difference between the apertures described above. In the present embodiment, reticle 1 is used as a parameter for minimizing the overlay error (hereinafter, referred to as “overlay error minimization parameter”).
The relative shift amounts x, y, and zθ in the X, Y, and Zθ directions between the wafer 6 and the wafer 25 and the projection magnification adjustment amount m of the projection optical system 23 are used.

The overlay error minimizing parameter is:
For example, after forming a pattern on a reference layer using the conventional 7a, overlay exposure is performed on the pattern of the reference layer using the quadrupole 7f;
This is different from the case where the overlay exposure is performed using the medium σ7b. The opening shape of the illumination stop used when forming a pattern on each layer differs from time to time, depending on the degree of integration of the pattern formed on each layer. Thereby, X, Y, Z between the reticle 16 and the wafer 25 necessary for minimizing an overlay error can be obtained.
The relative shift amount in the θ direction and the projection magnification adjustment amount of the projection optical system 23 also differ from time to time. The overlay error minimization parameter is used when obtaining the relative shift amount and the projection magnification adjustment amount.

The superposition error minimization parameter x,
In determining y, zθ, and m, for example, the following method is used.

(A) RMS minimization method This relates to the projection position of each cross pattern A1 to D4.
Find the square root of the sum of squares of the difference between the ideal position and the measured value,
In this method, convergence calculation is performed while changing each of the overlay error minimizing parameters x, y, zθ, and m so that this value is minimized. Then, x, y, zθ, and m when the square root of the above sum of squares takes the minimum (minimum) value
Is used as the overlay error minimization parameter. (B) Maximum displacement reduction method This relates to the projection positions of the cross patterns A1 to D4,
Iterative calculation is performed so that the maximum value among the deviation amounts between the ideal position and the actually measured values (for example, XA1a to XD4a and YA1a to YD4a in FIG. 8) becomes smaller, and the respective overlay error minimization parameters x, y, This is a method for obtaining zθ and m. For example, assuming that the shift amount at the cross pattern position of A1 is the maximum in the initial state of the calculation, provisional values of the overlay error minimizing parameters x, y, zθ, and m are determined so as to reduce the maximum shift amount. . Then, the displacement amount at another cross pattern position becomes the maximum value next. On the other hand, the maximum deviation amount is reduced while the temporary value of each overlay error minimizing parameter is appropriately changed. In this case, the calculation should be terminated when the maximum deviation amount becomes small in accordance with the required overlay accuracy, and whether the provisional value at this time should be used as a parameter for overlay error minimization may be determined in advance.

The overlay error minimizing parameters determined as described above are not necessarily x, y, zθ,
It is not necessary to use four of m, and in some cases only x, y, x, y, and zθ, or any combination of these four overlay error minimization parameters May be used. In the scanning exposure type exposure apparatus, a parameter for adjusting a speed ratio between the scanning speed of the reticle stage 18 and the scanning speed of the wafer stage 27 may be added to the above-described overlay error minimizing parameter. It is also possible to use another adjustment amount, for example, an amount of mechanically moving an element of the lens constituting the projection optical system 23, as one of the overlay error minimization parameters.

-Measurement of Inter-Device Difference and Calculation of Overlay Error Minimization Parameter- The significance of the inter-device difference measurement will now be described. In the case of performing a so-called mix-and-match, that is, when forming a pattern composed of a plurality of layers on one substrate by using a plurality of exposure apparatuses, the aperture shape of the illumination diaphragm and the exposure apparatus need to be changed. Therefore, the distortion of the projection pattern also changes. The inter-device difference measurement is performed for the purpose of minimizing the overlay error caused by the change in the distortion of the projection pattern. Hereinafter, a case where mix and match is performed using two exposure apparatuses of the first and second units will be described as an example.

In the mix-and-match method, the same type of exposure apparatus may be used as the first and second units, or the first unit may be a scanning exposure type exposure unit and the second unit may be a batch exposure type exposure unit. In some cases, different types and different types of exposure apparatuses are used in combination.
At this time, it is needless to say that different types and different types of exposure apparatuses are used in combination as the first and second units, even if the same type of exposure apparatus is used and the same type of illumination aperture opening shape is used. Even if they are used, the distortion, projection magnification, etc. are not always the same.
This is because even if the projection optical systems have the same design, their optical performances do not always match due to manufacturing variations and the like.

Therefore, in measuring the difference between the apparatuses and calculating the overlay error minimization parameter, the following procedure is roughly performed. That is, first, the difference between the apertures is measured for each of the first and second units, and the measurement results of are calculated as shown in FIG. 8 to obtain the overlay error minimization parameters of the first and second units.

The inter-apparatus difference measurement and the calculation of the overlay error minimization parameter may be performed when the exposure apparatus is installed in a customer's factory, or may be performed during regular maintenance after the exposure apparatus starts operating. Is also good.

As described above, the method using the coordinate measuring machine and the method using the alignment system of the exposure apparatus have been described as methods for measuring the difference between the apertures generated in one exposure apparatus. On the other hand, it is desirable to use a coordinate measuring machine when measuring the difference between the devices. This is due to the difference in the characteristics of each exposure apparatus, such as the orthogonality of the X and Y movement directions of the wafer stage 27 of each exposure apparatus. This is because an error may occur. Hereinafter, this will be described.

When the aperture difference is measured by using the alignment system, the pattern formed on the wafer by the first exposure is replaced with the reference pattern serving as an index for the aperture difference measurement by the second exposure as described above. Form. At this time, the reference pattern is formed by repeating exposure while stepwise driving the wafer stage 27 in the X direction and the Y direction. Therefore, if there is an error in the orthogonality of the wafer stage in the X and Y driving directions, the arrangement of the reference patterns formed on the wafer will be distorted, and an error will occur in the measurement result of the displacement. However, when the difference between the apertures is measured by one exposure apparatus, this error is constant regardless of the aperture shape of any illumination aperture. Therefore, when calculating the overlay error minimizing parameter, this error is canceled out, so that no problem occurs. However, when performing mix and match, there may be individual differences in the errors of the first and second units. Therefore, when trying to perform high-accuracy overlay exposure by mix-and-match, the above-mentioned error is added to the measurement result of the difference between the apparatuses,
This can reduce the overlay accuracy. For the above reasons, it is preferable to use a coordinate measuring machine when measuring the difference between the devices.

(1) Overlay Exposure Using One Exposure Apparatus- A method of performing overlay exposure with high precision using the overlay error minimization parameter obtained as described above is shown in FIGS. It will be described with reference to FIG.

FIG. 9 is a diagram showing only the control circuit 40 and the external storage device 44 of the exposure apparatus shown in FIG.
In the external storage device 44, a superposition error minimization parameter is recorded corresponding to the aperture shape of the illumination stop used at the time of exposure.

In the following, a case where the circuit pattern of the reference layer is exposed with the medium σ 7b (FIG. 3) and the circuit pattern of the second layer is subsequently exposed with the 輪 ring zone 7d is executed by the control circuit 40. The procedure to be performed will be described.

(Reference Layer Exposure Procedure Performed Using Medium σ7b) In response to a control signal being sent from the control circuit 40 to a reticle loader (not shown), the reticle loader executes a reticle on which a circuit pattern for the reference layer is drawn. 16 is placed on the reticle holder 17. In response to a control signal being sent from the control circuit 40 to a wafer loader (not shown), the wafer loader places the unexposed wafer 25 on the wafer holder 26. The control circuit 40 performs reticle alignment. The control circuit 40 sets the illumination stop to medium σ7b.
At this time, the control circuit 40 stores information on the aperture shape of the illumination stop used for the reference layer exposure in the internal memory or the external storage device 44. In the exposure of the reference layer, alignment adjustment and projection magnification adjustment based on the overlay error minimizing parameter are not performed. That is, processing is performed with all of these parameters set to 0. The control circuit 40 alternately repeats the scanning exposure and the step movement of the wafer stage 27, and sequentially projects the circuit pattern drawn on the reticle 16 onto the wafer 25. By the way, an alignment mark is drawn on the reticle 16 together with the circuit pattern, and a projection image of the above-mentioned alignment mark is formed on the wafer 25 together with a projection image of the circuit pattern as a latent image. When exposure of the entire region on the wafer 25 is completed, the control circuit 40 issues a control signal to the wafer loader. In response to this, the wafer loader unloads the wafer 25, for which the exposure of the reference layer has been completed, from the wafer holder 26. In addition, this wafer 25 is developed, etched,
Doping, resist stripping, resist recoating, and the like are performed.

(Exposure Procedure of Second Layer Using 1/2 Ring Zone 7d) In response to a control signal being sent from the control circuit 40 to a reticle loader (not shown), the reticle loader uses a circuit for the second layer. The reticle 16 on which the pattern is drawn is placed on the reticle holder 17. In response to a control signal being sent from the control circuit 40 to a wafer loader (not shown), the wafer loader places the wafer 25 on which the circuit pattern of the reference layer has been formed and the resist has been re-coated on the wafer holder 26. The control circuit 40 performs reticle alignment. The control circuit 40 sets the illumination aperture to the 1/2 annular zone 7d. The control circuit 40 reads, from the external storage device 44, information on the aperture shape (in this case, medium σ7b) of the illumination stop stored in the exposure procedure of the reference layer. The control circuit 40 reads from the external storage device 44 the overlay error minimization parameter (in this case,
_{x b, y b, zθ b} , the m _b. This is referred to as a reference layer parameter. ) And overlay error minimization parameters (in this case, x _d , y _d , zθ _d , and m _d ) corresponding to the type of illumination stop used for the exposure of the second layer. ) Is read. The control circuit 40 calculates the difference between the above-described parameter of the second layer and the parameter of the reference layer. This is the amount of alignment correction and the amount of magnification adjustment during the alignment described below. The third layer, the fourth layer
Control circuit 4 when performing overlay exposure with layers, etc.
0 is the parameter of the layer for performing the overlay exposure (the parameter of the third layer, the parameter of the fourth layer,
…) And the parameter of the reference layer. The control circuit 40 detects an alignment mark position formed together with the circuit pattern of the reference layer on the wafer 25 by the off-axis FIA unit 42, and performs wafer alignment based on the detection result. At this time, the control circuit 40 determines X, Y, θ based on the alignment correction amount and the magnification adjustment amount obtained in the above-described procedure.
The alignment in the Z direction is corrected, and a control signal is issued to the pressure adjuster 41 to adjust the projection magnification of the projection optical system 23. The control circuit 40 alternately repeats the scanning exposure and the step movement of the wafer stage 27, and sequentially superposes the circuit pattern drawn on the reticle 16 on the circuit pattern formed on the reference layer of the wafer 25 and performs exposure.
Then, when the exposure on all the regions on the wafer 25 is completed,
A control signal is issued from the control circuit 40 to the wafer loader. In response to this, the wafer loader unloads the wafer 25 on which the exposure of the second layer has been completed from the wafer holder 26.

As described above, the exposure apparatus of the present embodiment performs the correction of the wafer alignment and the adjustment of the projection magnification based on the overlay error minimization parameter corresponding to the aperture shape of the illumination stop used for the projection exposure. Do. This can reduce the overlay error of the pattern image due to the change in the amount of distortion generated in the projection pattern image due to the difference in the aperture shape of the illumination diaphragm, so that the overlay exposure can be performed with higher accuracy. it can.

Referring to FIGS. 1 and 10, an example in which overlay exposure is performed using an exposure system having a plurality of exposure apparatuses will be described. In the following description, in order to avoid complication,
A description will be given of an example in which overlay exposure is performed using an exposure system having two exposure apparatuses of the first and second units.

FIG. 10 shows a state in which two exposure apparatuses including the first apparatus having the control circuit 40A and the second apparatus having the control circuit 40B are connected to the host computer 200 to constitute an exposure system. The host computer 200 is connected to an external storage device 244 that stores the overlay error minimization parameters for the first and second units. The host computer 200 manages an exposure process when performing a mix-and-match using the first and second units. The operator or the host computer 200 manages which variable illumination stop of which exposure apparatus is used when exposing the circuit pattern of the reference layer of the wafer 25.

In the following, the first unit (the illumination aperture is a quadrupole 7f)
The following describes an example in which the circuit pattern of the reference layer is exposed using (No.) and then the circuit pattern of the second layer is exposed using the second device (the illumination aperture uses the conventional 7a).

(Reference Layer Exposure Procedure Performed in Unit 1 Using Quadrupole 7f) Upon receiving a reference layer exposure start command issued from the host computer 200, the control circuit 40A issues a control signal to a reticle loader (not shown). In response, the reticle loader places the reticle 16 on which the circuit pattern for the reference layer is drawn on the reticle holder 17 of the first machine. In response to a control signal being sent from the control circuit 40A to a wafer loader (not shown), the wafer loader places the unexposed wafer 25 on the wafer holder 26 of the first machine. The control circuit 40A performs reticle alignment. Based on an instruction from the host computer 200, the control circuit 40A sets the illumination stop to the quadrupole 7f. At this time, the host computer 200 stores information on the exposure device (in this case, the first device) used for the reference layer exposure and the aperture shape of the illumination stop (in this case, the quadrupole 7f) in the internal memory or the external storage device 244. I do.
The exposure of the reference layer without adjusting the alignment or adjusting the projection magnification based on the overlay error minimizing parameter is the same as the case where the overlay exposure is performed by one exposure apparatus. The control circuit 40A controls the scanning exposure and the wafer stage 27.
Are alternately repeated, and the circuit pattern and the alignment mark drawn on the reticle 16 are
5 is projected sequentially. As a result, a projected image of the alignment mark is formed as a latent image on the wafer 25 together with the projected image of the circuit pattern. When the exposure of the entire region on the wafer 25 is completed, the control circuit 40A issues a control signal to the wafer loader. In response to this, the wafer loader unloads the wafer 25, for which the exposure of the reference layer has been completed, from the wafer holder 26. At this time, the control circuit 40A notifies the host computer 200 of the completion of the reference layer exposure operation. The wafer 25 is subjected to processing such as development, etching, doping, resist stripping, and resist re-coating in another process.

The following description will proceed with the assumption that the host computer 200 manages which exposure apparatus has used which aperture shape of the exposure apparatus when exposing the reference layer on the wafer 25 having undergone the above-described steps.

(Second Layer Exposure Procedure Performed by Unit 2 Using Conventional 7a) Upon receiving a second layer exposure start command issued from the host computer 200, the control circuit 40B sends a control signal to a reticle loader (not shown). Emit. In response, the reticle loader places the reticle 16 on which the circuit pattern for the second layer is drawn on the reticle holder 17 of the second machine. In response to a control signal being sent from the control circuit 40B to a wafer loader (not shown), the wafer loader places the wafer 25 on which the circuit pattern of the reference layer has been formed and the resist has been re-coated on the wafer holder 26 of the second machine. The control circuit 40B performs reticle alignment. The control circuit 40B adjusts the illumination aperture to a conventional 7
Set to a. In accordance with the wafer 25 placed on the wafer holder 26 in the above procedure, the overlay error minimization parameters (in this case, x _f 1, x _f 1, y _f 1, zθ _f 1,
m _f 1 This is referred to as a reference layer parameter. A), error minimization parameter overlay corresponding to the type of aperture illumination is used during the exposure of the second layer (in this case, x _a 2, y _a 2, a z [theta] _a 2, m _a 2. This second (Referred to as a layer parameter) is output from the host computer 200 to the control circuit 40B. The control circuit 40B calculates the difference between the parameter of the second layer and the parameter of the reference layer. This is the amount of alignment correction and the amount of magnification adjustment during wafer alignment described below. The control circuit 40B detects the position of the alignment mark formed together with the circuit pattern of the reference layer on the wafer 25 by the off-axis FIA unit 42, and performs wafer alignment based on the detection result. At this time, the control circuit 40B calculates X, Y, and X based on the alignment correction amount and the magnification adjustment amount obtained in the above procedure.
The alignment in the θZ direction is corrected, and a control signal is issued to the pressure adjuster 41 to adjust the projection magnification of the projection optical system 23. The control circuit 40B controls the scanning exposure and the wafer stage 27.
Are alternately repeated, and the circuit pattern drawn on the reticle 16 is sequentially overlaid on the circuit pattern formed on the reference layer of the wafer 25, and exposure is performed. When the exposure of the entire area on the wafer 25 is completed, the control circuit 40B issues a control signal to the wafer loader. In response to this, the wafer loader unloads the wafer 25 on which the exposure of the second layer has been completed from the wafer holder 26.

As described above, when the overlay exposure is performed using the exposure system including a plurality of exposure apparatuses, the overlay error is minimized based on the overlay apparatus used in the projection exposure and the overlay error minimization parameter corresponding to the aperture shape of the illumination stop. Correction of wafer alignment and adjustment of projection magnification. As a result, it is possible to reduce an overlay error caused by a difference between devices or a difference between apertures.

In the correspondence between the above-described embodiment and the claims, the wafer 25 is a substrate, the reticle 16 is a mask, the turret plate 7 and the motor 8 are illumination aperture opening shape changing means, the reticle stage 18 and the wafer. The stage 27 constitutes position adjusting means, the control circuits 40, 40A and 40B constitute position adjusting amount output means, the pressure adjuster 41 constitutes projection magnification adjusting means, and the external storage devices 44 and 244 constitute position adjusting amount storing means. I do.

[0083]

As described above, according to the first aspect of the present invention, the relative position between the mask and the substrate is determined based on the position adjustment amount output from the position adjustment amount output means. When performing overlay exposure between different layers on the substrate, changing the aperture shape of the illumination stop changes the amount of distortion that occurs in the pattern image of the mask projected on each layer. Therefore, it is possible to reduce the overlay error generated between the pattern images projected on the respective layers due to this. Therefore, it is possible to perform higher-accuracy overlay exposure with higher accuracy. (2) According to the second aspect of the present invention, the position adjustment amount storage means for storing the position adjustment amount corresponding to the shape of the opening of the illumination stop allows the position to be adjusted each time the opening shape of the illumination stop is changed. There is no need to input the amount, and the workability of overlay exposure is excellent. (3) According to the third or sixth aspect of the present invention, a pattern image of a mask is projected on each layer as different exposure apparatuses or illumination apertures having different aperture shapes are used in the overlay exposure. Can be reduced by adjusting at least one of the relative position adjustment between the mask and the substrate and the projection magnification. Therefore, even when overlay exposure is performed using an exposure system having a plurality of exposure devices, overlay exposure with higher accuracy can be performed. (4) According to the invention as set forth in claim 4, when performing overlapping exposure by a plurality of exposure devices, the adjustment amount storage means for storing the adjustment shape corresponding to the opening shape of the illumination stop used and the exposure device. With this configuration, it is not necessary to input a position adjustment amount every time the exposure device or the aperture shape of the illumination stop is changed, and the workability of the overlay exposure is excellent.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an exposure apparatus.

FIG. 2 is a diagram illustrating a visual field image captured by an imaging device of an off-axis field alignment unit.

FIG. 3 is a diagram illustrating an illumination stop.

FIG. 4 is a view for explaining a test reticle used when measuring a difference between apertures or a difference between devices with a light wave interference type coordinate measuring machine.

5A and 5B are diagrams illustrating an example of a projection pattern formed on a wafer, wherein FIG. 5A illustrates a state in which a plurality of projection patterns are formed on a wafer, and FIG. The enlarged one of a plurality of projection patterns is shown.

FIG. 6 is a view for explaining a test reticle used when measuring a difference between apertures by an alignment system of the exposure apparatus.

7A and 7B are diagrams illustrating another example of a projection pattern formed on a wafer, wherein FIG. 7A illustrates a state in which a plurality of projection patterns are formed on a wafer, and FIG. 1 shows an enlarged one of a plurality of projection patterns to be performed.

FIG. 8 is a view for explaining a state in which the measurement results of the aperture difference are summarized in a list.

FIG. 9 is a view for explaining a data structure of a superposition error minimization parameter stored in an external storage device.

FIG. 10 illustrates a schematic configuration of an exposure system that performs mix-and-match and a data structure of a superposition error minimization parameter stored in an external storage device connected to a host computer that controls the exposure system. FIG.

[Explanation of symbols]

 Reference Signs List 7 turret plate 7a to 7f illumination stop 16 reticle 16A, 16B test reticle 18 reticle stage 23 projection optical system 25 wafer 27 wafer stage 40, 40A, 40B control circuit 41 pressure regulator 42 off-axis FIA unit 44, 244 external storage device 200 Host computer TW Test wafer

Claims (6)

[Claims] An illumination aperture opening shape changing unit configured to change an aperture shape of an illumination aperture provided in an optical path of an illumination optical system in accordance with a pattern of a mask projected on a layer formed on a substrate; In an exposure apparatus having position adjustment means for adjusting a relative position between the mask and the substrate, with changing the shape of the opening when performing overlapping exposure between different layers on the substrate, A position adjustment amount output for outputting a position adjustment amount for reducing the overlay error of the pattern image caused by a change in a distortion amount generated in the pattern image of the mask projected on a different layer by the position adjusting means. Exposure apparatus characterized by having means. 2. The exposure apparatus according to claim 1, further comprising a position adjustment amount storage unit that stores the position adjustment amount corresponding to an opening shape of the illumination stop. 3. An illumination stop opening shape changing means capable of changing an opening shape of an illumination stop provided in an optical path of an illumination optical system in accordance with a pattern of a mask projected onto a layer formed on a substrate; There are provided a plurality of exposure apparatuses each including a position adjusting unit for adjusting a relative position between the mask and the substrate, and a projection magnification adjusting unit capable of adjusting a projection magnification of a pattern image of the mask projected on the substrate. In an exposure system in which the plurality of exposure apparatuses are mixed when performing overlay exposure between different layers on the substrate, when performing overlay exposure between different layers on the substrate, different exposure apparatuses or A superposition resulting from a change in distortion occurring in a pattern image of the mask projected on the different layer with the use of illumination apertures having different aperture shapes. Exposure comprising adjusting amount output means for outputting an adjusting amount for reducing at least one of the position adjustment by the position adjusting means and the magnification adjustment by the projection magnification adjusting means. system. 4. The exposure system according to claim 3, further comprising: an adjustment amount storage unit configured to store the adjustment amount in correspondence with an opening shape of the illumination stop and each of the plurality of exposure apparatuses constituting the plurality of exposure apparatus groups. An exposure system further comprising: 5. An illumination stop aperture shape changing means capable of changing an aperture shape of an illumination stop arranged in an optical path of an illumination optical system in accordance with a pattern of a mask projected on a layer formed on a substrate; In an exposure method of an exposure apparatus having a position adjusting unit for adjusting a relative position between the mask and the substrate, the opening shape is changed when performing overlay exposure between different layers on the substrate. Accordingly, a superposition error of the pattern image caused by a change in distortion generated in the pattern image of the mask projected on the different layer is reduced by adjusting the position by the position adjusting unit. Exposure method. 6. An illumination stop opening shape changing means capable of changing an opening shape of an illumination stop provided in an optical path of an illumination optical system in accordance with a mask pattern projected on a layer formed on a substrate; There are provided a plurality of exposure apparatuses each including a position adjusting unit for adjusting a relative position between the mask and the substrate, and a projection magnification adjusting unit capable of adjusting a projection magnification of a pattern image of the mask projected on the substrate. In the exposure method of an exposure system in which the plurality of exposure apparatuses are mixed when performing overlay exposure between different layers on the substrate, different overlay overlay exposure is performed between different layers on the substrate. With the use of the aperture-shaped illumination stop, the overlay error caused by the change in the distortion generated in the pattern image of the mask projected on the different layer, Among magnification adjustment by the position adjustment and the projection magnification adjusting means according to the serial position adjusting means, an exposure method characterized by reducing at least one.