JPH11126747A - Projection aligning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection aligning method which can adjust a projection performance with a high reproducibility. SOLUTION: Marks Mij are formed at a predetermined plurality of positions on a reticule 5 projected, and positions Tij of the marks Mij projected in an image plane through a projection lens 6 are sequentially measured with use of a laser interferometer, a fine opening 8 and a photoelectric detector 9 provided in a stage 7. Values (N, αij, βij)(where αij and βij are errors in coordinate axis directions) corresponding to a projection magnification N of the lens 6 and distortion aberration are calculated on the basis of a positional relationship (positions Pij) of the marks on the reticle 5 and the measured positions Tij of the marks. And the positions of the optical elements (lenses) as part of the lens 6 are adjusted on the basis of the calculated values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of projecting and exposing a mask (reticle) pattern of an integrated circuit or the like on a sensitive substrate such as a semiconductor substrate with a predetermined imaging performance.

[0002]

2. Description of the Related Art Although miniaturization of large-scale integrated circuit (LSI) patterns has been progressing year by year, a reduced projection type exposure apparatus has spread as a circuit pattern printing apparatus which satisfies the demand for miniaturization and has high productivity. I have. In these apparatuses conventionally used, a reticle pattern several times (for example, 10 times) a pattern to be printed on a silicon wafer or the like (hereinafter, referred to as a wafer) coated with a photosensitive agent is reduced by a projection lens. What is projected and printed in one exposure is an area on the wafer that is smaller than a 14 mm diagonal square. Therefore, the diameter 125
In order to print a pattern on the entire surface of a wafer of about mm, a so-called step-and-repeat method is adopted, in which the wafer is placed on a stage, moved a fixed distance, and repeatedly performs exposure.

In the manufacture of LSI, several or more layers of patterns are sequentially formed on a wafer. However, unless the overlay error of patterns between different layers is kept below a certain value, the conductive or insulating state between the layers can be reduced. Is not intended, and the function of the LSI cannot be achieved. For example, for a circuit having a minimum line width of 1 μm, at most 0.2
Only a total overlay error of about μm is allowed. Among the causes of the overlay error, those caused by the exposure apparatus are (1) a projection magnification error and a projection distortion, and (2) a relative displacement between a projection image and a wafer. The distortion caused by the above (1) is distortion of the projection optical system. On the other hand, the magnification error can be reduced by changing the distance between the reticle and the principal point (principal plane) of the projection optical system when the reticle-side light beam of the projection optical system is not telecentric. The components (optical members such as lenses) inside the projection optical system can be made smaller by relatively displacing them in the optical axis direction.

Accordingly, the distance between the reticle and the projection lens,
If the relative position of the optical element inside the projection lens does not change, the error due to the cause (1) is constant and can be said to be a systematic error. On the other hand, the error caused by the factor (2) includes many factors of a random error, and is a main cause that the overlay error varies every time alignment (positioning) is performed.

Now, a systematic error (1)
By adjusting the apparatus so that it is less than or equal to a certain value while measuring the value, it is possible to maintain a small value stably over a long period of time. Must be kept. Conventionally, the measurement of the error in (1) has been performed by printing an image of a reticle having a pattern of marks at a plurality of predetermined positions, a so-called test reticle, on a photoresist on a wafer, and a resist image of the baked mark. Was measured by comparing the measured coordinates with the mark coordinates on the reticle.

[0006]

However, according to the conventional method, it takes time and effort to expose a test reticle pattern on a wafer and develop it, and to measure the position of a resist image of a mark. However, there is a disadvantage that an expensive measuring device must be used to perform the measurement. This disadvantage becomes extremely noticeable when, for example, it is necessary to repeat the measurement after measuring the magnification error, distortion and the like, adjusting the exposure apparatus based on the measurement results, and the like.

Further, in the conventional method, since it is necessary to exclusively detect the resist image of the mark, there is a problem that a detection error depending on the optical characteristics of the resist image is essentially unavoidable. Therefore, when adjusting the projection performance of the exposure apparatus to the expected one, there is no guarantee that the drive-in accuracy will always increase in proportion to the number of repetitions of the work (measurement) of printing the mark image on the reticle and the adjustment work. Did not.

Further, in the printing operation of the image of the reticle mark performed before and after the adjustment operation of the exposure apparatus, the wafer does not always remain on the stage of the exposure apparatus, but must be replaced. The mounting state of the wafer (for example, the flatness of the wafer surface) may slightly change between the previous printing operation and the post-adjustment printing operation, thereby increasing the dispersion of the measurement results. Therefore, there is a problem that high reproducibility cannot be obtained even if the projection performance of the exposure apparatus is adjusted to a desired state.

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems and to provide a projection exposure apparatus capable of adjusting projection performance with high reproducibility, and in particular, to reproduce errors in a projected image caused by projection magnification and distortion. It is an object of the present invention to obtain a projection exposure method in which measurement is performed with good accuracy and a part of optical elements in a projection optical system is moved and adjusted.

[0010]

According to the present invention, there is provided a projection optical system (projection lens 6) for projecting a pattern formed on a mask (reticle 5) within a predetermined image plane, and a sensitive substrate (wafer 10). (7) that is held substantially coincident with the image plane and is moved two-dimensionally in a plane parallel to the image plane.
The present invention relates to an improvement in a projection exposure method using position measuring means (laser interferometers 13 and 34) for measuring the coordinate position of the stage (7).

In the present invention, the mark (Mij) formed at each of a plurality of predetermined positions (Pij or Xij, Yij) as the pattern of the mask (reticle 5) is projected by the projection optical system (6). (Tij, or xij, yij) projected onto the image plane via the measuring device (13, 34), and sequentially measured using, for example, the minute aperture 8, the photoelectric detector 9, and the like. A projection optical system (6) based on the arrangement relationship (position Pij) of each mark (Mij) on the mask (R) and the measured position (Tij) of each mark.
(N, N) corresponding to the projection magnification and distortion of the projected image
Or αij, βij), and based on the calculated values, some optical elements constituting the projection optical system (6) so that each of the projection magnification and the distortion does not exceed a predetermined allowable range. (Lens etc.) position is adjusted.

[0012]

According to the present invention, the projected image positions of a plurality of marks on a mask (reticle) are measured in a moving coordinate system of a stage (7) defined by a laser interferometer as position measuring means. Therefore, the reference for position measurement is unified to high-resolution position measuring means such as a laser interferometer, and the reproducibility of measurement is improved. In adjusting the projection performance, since some optical elements in the projection optical system are moved, it is possible to appropriately correct both the magnification error and the distortion of the projected image.

[0013]

FIG. 1 is a schematic view of a projection type exposure apparatus according to an embodiment of the present invention. After the illumination light from the illumination light source 1 for exposure is once converged by the first condenser lens 2,
It reaches the second condenser lens 3. A shutter 4 for blocking and passing the illumination light is provided at a position where the light is converged in the optical path. The light beam having passed through the second condenser lens 3 illuminates a test reticle 5 (hereinafter simply referred to as a reticle 5) as a mask.
Light transmissive marks M11 to M16 are drawn on the lower surface of the reticle 5 at a plurality of predetermined positions. The light beam LB1 transmitted through the marks M11 to M16 of the reticle 5 enters a projection lens 6 as a projection optical system. In this embodiment, the projection lens 6 is a non-telecentric optical system on the reticle 5 side, that is, the object side, and a telecentric optical system on the image side. The light beam LB1 is converged by the projection lens 6 and emitted as a light beam LB2. Note that the distance between the lower surface of the reticle 5 and the main plane 6a of the projection lens 6 is L. The light beam LB2 is imaged on a minute aperture 8 provided on a stage 7 which can move two-dimensionally. Further, the light passing through the minute aperture 8 is photoelectrically converted by a photoelectric detector 9 provided on the stage 7.

The stage 7 is usually a semiconductor wafer 1
The wafer 10 is mounted on a wafer holder 11 that moves two-dimensionally together with the stage 7. The wafer holder 11 is provided so as to be capable of minute rotation and vertical movement with respect to the stage 7. The wafer holder 11 holds the projection image of the projection lens 6 on the wafer 1.
It moves up and down so as to form an image on the surface of 0, that is, to achieve focusing. The opening surface in which the minute opening 8 is provided is determined so as to substantially coincide with the height of the surface of the wafer 10, and the opening surface and the photoelectric detector 9 move up and down integrally with the up and down movement of the wafer holder 11. It is provided to be. For this focusing, a gap sensor 12 for measuring the distance between the projection lens 6 and the surface of the wafer 10 (or the opening surface of the minute opening 8) is provided. Automatic focus adjustment can be performed by the vertical movement of the gap sensor 12 and the wafer holder 11. When printing a circuit pattern on the wafer 10, the height of the surface of the wafer 10 is detected, and a projection image with high contrast is always transferred. it can.

On the other hand, the position of the stage 7 is
According to 3, the distance to the reflecting mirror 14 fixed to the stage 7 is obtained by measuring using a laser beam. Although FIG. 1 shows only the x-axis direction in the horizontal direction on the paper surface, the laser interferometer and the reflecting mirror are similarly used for the y-axis direction perpendicular to the x-axis (perpendicular to the paper surface) forming the moving plane of the stage 7. Is provided. With these laser interferometers, coordinate values for a predetermined origin of the stage 7 are sequentially measured. The intersection of the extension lines of the two measurement axes formed by the laser beams of the laser interferometer in the x-axis and y-axis directions is determined so as to coincide with the optical axis of the projection lens 6. The reticle holder 15 can move two-dimensionally while holding the reticle 5, and is driven and controlled by a reticle alignment control system described later to position the reticle 5.

FIG. 2 is a plan view of the reticle 5 shown in FIG. The reticle 5 is formed by depositing a chromium layer or a low-reflection chromium layer on the entire lower surface of the glass substrate as shown by hatching in the figure. A cross mark as mark M through which light passes is 6 × 6 on the chrome layer.
Are formed in a square matrix. It is assumed that the center positions of these cross marks have been measured by another measuring device in advance with an error of about 0.1 μm or less in the coordinate system O-XY on the reticle 5. Further, the center positions of the cross mark are determined so as to be line-symmetric with respect to the coordinate axes X and Y, and point-symmetric with respect to the origin O which is the center of the reticle 5. In order to identify these cross marks, marks on the top row of the reticle 5 are denoted by M11,
M12,... M16, and the marks in the lower row are M21, M2.
2,... M26 in order. Therefore, the cross mark on the reticle 5 is generally Mij (where i and j are 1).
6), and the center position of the cross mark is Pij (where i and j are 1 to 6) corresponding to Mij.

FIG. 3 is a plan view of a light-shielding member for forming a minute opening 8 provided in the stage 7, and a cross-sectional view taken along the line AA of FIG. The fine openings 8 are formed by depositing a chromium layer 21 on a glass plate 20 to a thickness of about 0.1 μm, and forming two slit openings 8 a and 8 b in a part thereof. The thickness of the chrome layer 21 is determined by the depth of focus of the projection lens 6 (several μ).
m) is much thinner. Now, the extending directions of the slit openings 8a and 8b are determined so as to be orthogonal to each other, and are determined so as to coincide with the moving directions xy of the stage 7, respectively. Note that the slit opening 8 is elongated along the y-axis direction.
a is used to detect the position in the x direction of the projected image of the cross mark Mij, and the slit opening 8b elongated along the x axis direction is used to detect the position of the projected image of the cross mark Mij in the y direction. used. Further, the slit openings 8a, 8
The width of b is set to be smaller than the width of the linear portion of the projected image of the cross mark Mij. This will be described later in detail. Of course, the light receiving surface of the photoelectric detector 9 is located below the glass plate 20.

Next, a control system for controlling the apparatus shown in FIG. 1 will be described with reference to the block diagram of FIG. The entire apparatus is generally controlled by a microcomputer (hereinafter simply referred to as a CPU) 30 including a memory or the like so that control by a program and various arithmetic processing can be performed.
The CPU 30 is an interface (hereinafter, referred to as IF) 3
1, various types of information are exchanged with a peripheral detecting unit, measuring unit, or driving unit.

Now, the shutter drive unit 32 has a CPU 30
, The shutter 4 is opened and closed, and a reticle alignment control system 33 (hereinafter, R-ALG33)
) Is to move the reticle holder 15 so that the reticle 5 is at a predetermined position with respect to the optical axis of the projection lens 6. Although the R-ALG 33 is not always necessary in the embodiment of the present invention, the positioning of the reticle 5 can be performed more accurately and at a higher speed than by manual visual operation using the alignment mark on the reticle 5. In this apparatus, an R-ALG 33 is provided below.

On the other hand, in order to measure the coordinates of the stage 7, the stage 7 read by the laser interferometer 13 is used.
, And the position information in the y direction of the stage 7 read by the laser interferometer 34 are sent to the CPU 30 via the IF 31. Further, in order to move the stage 7 two-dimensionally, the stage 7 is driven in the x direction.
An axis drive unit 35 (hereinafter, referred to as X-ACT 35) and a y-axis drive unit 36 (hereinafter, Y-ACT 35) that drives the stage 7 in the y-direction.
ACT 36) is provided to operate according to a command from the CPU 30.

Further, a θ-axis rotation drive unit 37 (hereinafter referred to as θ-axis) for minutely rotating the wafer holder 11 on the stage 7.
ACT 37), and a z-axis drive unit 38 for vertically moving the wafer holder 11, the photoelectric detector 9, and the glass plate 20.
(Hereinafter, Z-ACT 38), and operates according to a command from the CPU 30. Then, the focus detection unit 39 (hereinafter, referred to as AFD 39) receives a signal from the gap sensor 12 shown in FIG. 1 and inputs the signal from the surface of the wafer 10 (or the opening surface of the minute opening 8) and the focal position of the projection lens 6. The shift information is output to the CPU 30 via the IF 31.

Further, a terminal device 40 such as a monitor CRT or a printer for displaying the measurement result and the operation state is also connected to the CPU 30 via the IF 31. The actual exposure apparatus includes a wafer alignment control system for positioning the wafer 10 in the xy movement directions of the stage 7 in addition to the various control systems described above.
The description is omitted because it is not directly related to the present invention.

Next, the operation of measuring various characteristics of a projected image by the projection lens 6 of the exposure apparatus will be described. First, the reticle 5 set in the apparatus is placed in the R-ALG33.
Position using. At this time, the alignment is performed so that the optical axis of the projection lens 6 passes through the origin O of the coordinate system O-XY on the reticle 5. Further, the X and Y axes of the coordinate system O-XY correspond to the x and y movement directions of the stage 7, that is, the laser interferometer 1
The position of the reticle 5 is determined so as to be parallel (including coincidence) with each of the measurement axes x and y of 3 and 34 respectively. As a result, the extending directions of the two orthogonal linear portions of the cross mark Mij coincide with the xy moving directions of the stage 7, respectively.

Next, the stage 7 is moved by the X-ACT 35 and the Y-ACT 36, and the height of the opening surface of the minute opening 8, that is, the surface of the chromium layer 21 in FIG. 3 is detected by the gap sensor 12 and the AFD 39. Based on the detection information, the Z-ACT 38 is driven such that the image plane of the projection lens 6 and the surface of the chrome layer 21 match. Next, the shutter 4 is opened by the shutter drive unit 32 to illuminate the reticle 5, and an image of the cross mark Mij is projected on the chrome layer 21. Then, the X-ACT 35 and the Y-ACT 36 are operated to move the stage 7 so that the positional relationship between the image of the cross mark Mij and each of the slit openings 8a and 8b is, for example, as shown in FIG. At that time, the slit opening 8a,
If the coordinate values of the laser interferometers 13 and 34 when the position 8b is located on the optical axis of the projection lens 6 are determined, for example,
The rough position of the image of each cross mark Mij can be easily specified using the coordinate value as a reference position.

At this time, the size of the projected image of the cross mark Mij and the slit openings 8a and 8
The relationship with the size of b is as shown in FIG. That is, in the image of the cross mark Mij, a linear portion extending in the y direction is defined as a slit image Lx, and a linear portion extending in the x direction so as to be orthogonal to the slit image Lx is defined as a slit image Ly. And
The center of the width D of each slit image Lx, Ly is set to the center line CL.
x, CLy, and the intersection of the center lines CLx and CLy, that is, the center of the image of the cross mark Mij is set as the center CP. Further, when the width of the slit openings 8a and 8b in the chromium layer 21 is d and the length is h, d <D <h.

When the stage 7 is moved at a constant speed in the x direction from the position shown in FIG. 5 and the slit image Lx is scanned by the slit opening 8a, the photoelectric detector 9 is turned on as shown in FIG.
The photoelectric signal I as shown in FIG. FIG. 6 (a)
The horizontal axis represents the position of the stage 7 in the x direction, and the vertical axis represents the magnitude of the photoelectric signal I, which is equivalent to the light intensity distribution in the width direction of the slit image Lx. Then, the photoelectric signal I is compared with a predetermined reference level Ir, and the positions x1 and x2 of the stage 7 when the photoelectric signal I and the reference level Ir match.
Is measured by the laser interferometer 13. The measured value is taken into the CPU 30, and the two positions are averaged,
Find the position x0. That is, the CPU 30 calculates (x1 + x
2) The position x0 of the stage 7 obtained by the calculation of / 2
As the projected coordinate position of the center line CLx of the slit image Lx.

On the other hand, for the slit image Ly,
The stage 7 is moved in the y direction from the position shown in FIG. 5, the slit opening 8b is scanned, and the position y0 of the stage 7 in the y direction is determined as the projected coordinate position of the center line CLy of the slit image Ly from the light intensity distribution. Thus, the coordinate values (x0, y0) of the stage 7 are measured as the projection position of the center CP of the image of the cross mark Mij, and stored in the CPU 30. Similarly, measurement is performed on the images of the other cross marks, and the measured values are sequentially stored in correspondence with the positions Pij of the cross marks Mij on the reticle 5.

The reason why the size of the slit openings 8a and 8b and the image of the cross mark Mij is set to d <D <h is that when the projection position in the x direction is detected, the slit image 8x And the slit image Ly are scanned together, or even when the slit opening 8a scans the slit image Lx and at the same time the slit opening 8b scans the slit image Lx, the position can be detected. .

For example, when the slit opening 8a has the slit image L
When the stage 7 is scanned in the x-direction from the state where it intersects with x, the photoelectric signal of the photoelectric detector 9 has a maximum value Ip having a certain offset Iof in the scanning portion of the slit image Ly as shown in FIG. Signal. The size of the offset Iof is determined by the width d of the slit opening 8a and the width D of the slit image Ly.
The maximum value Ip is proportional to the area determined by the width d and the length h of the slit opening 8a.

In order to determine the position x0 of the center line CLx of the slit image Lx by comparing such a signal with the reference level Ir, Ir> Iof must be satisfied. Therefore, the width D of the slit image Ly and the length h of the slit opening 8a are set to satisfy D <h in order to satisfy this condition. Further, with respect to the width D of the slit images Lx, Ly, the slit openings 8a, 8
The reason why the width d of b is reduced is to make the rising and falling of the photoelectric signal steep, so that d <D. Note that the relationship between the widths d and D is not limited to d <D. Even if d = D, there is no substantial effect on photoelectric detection and position detection.
Of the image is determined.

Next, the CPU 30 determines the projected position and the position Pij of the image of each cross mark Mij measured above.
Calculate optical performance such as magnification error and distortion amount of the projected image. still,
Assuming that the projected position of the image of each cross mark Mij measured as the position of the stage 7 is Tij, Pij is a coordinate value (Xij, Y
ij), and Tij is represented by coordinate values (xij, yij). Therefore, the following equation 1 is used as an example of an equation for calculating the projection magnification N.

[0032]

(Equation 1)

This equation 1 is calculated by the CPU 30, and the magnification N is, as is clear from the form of the equation 1, the sum of the value of the magnification in the x direction and the value of the magnification in the y direction being 1
/ 2. In equation 1, Xi1 and xi1 are calculated as shown in FIG.
Cross marks M11, M21, M31, forming the middle and leftmost lines
, M61 on the reticle 5 in the X direction, and the projected positions of the six cross marks in the x direction. Xi6 and xi6 are the positions in the X direction of the cross marks M16, M26,..., M66 forming the rightmost row in FIG. 2 on the reticle 5, and the projection positions of the six cross marks in the x direction. And represent respectively. Further, in Equation 1, Y1j and y1j
Are the cross marks M11, M12,...
M16 represents the position of the M16 on the reticle 5 in the Y direction, and the projection positions of the six cross marks in the y direction.
Y6j and y6j are the cross marks M61 and M6 in the bottom row in FIG.
,..., M66 on the reticle 5 in the Y direction, and the projection positions of the six cross marks in the y direction.

When the projection magnification to be set at the time of manufacture or adjustment of the projection lens 6 is N0, errors (αij, βij) in the respective coordinate axis directions on the coordinates including the distortion of the projected image of the cross mark. ) Represents projection distortion. The calculated results are displayed by the terminal device 40.
As described above, the projection magnification and the projection distortion can be obtained. However, Equation 1 is merely an example, and depending on the definition of the magnification, a calculation formula according to the definition may be used. For example, only the four corner marks of the cross marks M11, M16, M61 and M66 may be used. Then, if the calculated projection magnification exceeds the allowable amount, the distance L between the reticle 5 and the main plane 6a of the projection lens 6 shown in FIG.
Alternatively, the distance between the optical components (lenses) constituting the projection lens 6 is readjusted to change the focal length. Then, the magnification is measured again by the above method, and the adjustment and measurement of the projection lens 6 are repeated until the magnification error becomes an allowable value. Also, when measuring the magnification error, the distortion of the projection optical system is also measured, and it is confirmed that the aberration is also acceptable. If the distortion exceeds the allowable amount, the position of the optical element inside the projection lens 6 is adjusted, or the optical element is replaced with another one.

As described above, according to the present embodiment, the labor and labor of exposing and developing the pattern of the test reticle and measuring the resist image with another measuring instrument as in the prior art can be omitted. The optical characteristics of the projection lens 6 can be measured extremely simply by providing a photoelectric detector 9 for detecting a mark image on a moving stage normally provided in a projection type exposure apparatus. In addition, not only when manufacturing the exposure apparatus, but also when exchanging the projection lens 6 with a projection lens having a different reduction ratio at the LSI manufacturing site, no special measuring equipment is required. There is also an advantage that the adjustment for optimizing the characteristics can be performed very efficiently. In the above embodiment, the calculation of the optical characteristics is performed by the CPU 3 incorporated in the exposure apparatus.
The same effect can be obtained by displaying only the detected position of the projected image of each cross mark Mij on the terminal device 40 and then performing a predetermined calculation by another computer based on the information of the detected position. Is obtained.

As described above, the present embodiment has described the case where the image forming position coincides with the surface of the chromium layer 21, that is, the opening surface. In the present embodiment, since the gap sensor 12 shown in FIG. 1 is attached, if the gap sensor 12 is adjusted so as not to have a detection error, this is used, and the focus error with respect to the aperture surface is determined by the AFD 39. Detection and focusing can be performed. However, in the configuration in which the automatic focus detection is performed using the gap sensor, the detection signal of the AFD 39 generally has an offset with respect to the focus detection when the device is manufactured or when the projection lens is exchanged, and the gap is determined. If only the sensor is used, it is not possible to exactly match the imaging plane of the projection image with the aperture plane.

The case where the focus is detected from the contrast of the projected mark image using the photoelectric detector 9 will be described. In this case, the wafer vertical movement mechanism Z-AC
By utilizing the fact that the minute aperture 8 and the photoelectric detector 9 are moved up and down at the same time by T38, the minute aperture 8 is moved up and down by a distance that divides the length of the focal depth of the projection lens 6 into several parts. The operation of scanning the stage 7 in the xy directions and measuring the intensity distribution of the image is repeated. Then, a focus state in which the width of the rise or fall in the intensity distribution of the image is minimized is determined. In practice, the intensity distribution of the projected image of the cross mark on the reticle 5 is examined.

FIG. 7 shows the magnitude of the signal obtained by photoelectrically converting the image of the mark transmitted through the minute aperture 8 when the stage 7 is moved. The vertical axis represents the magnitude of the signal, and the horizontal axis represents the stage 7. In the x direction. Assuming that the waveform of the photoelectric signal I1 is obtained as shown in FIG. 7 when the aperture surface having the slit opening 8a and the image surface are close to each other, if the aperture surface and the image surface are farther than this state, the waveform Becomes wider, and becomes like the signal I2. Therefore, the amount of spread of the waveform, or the slope of the shoulder of the waveform is measured, and if the amount of spread of the waveform is minimized, or if the slope of the shoulder of the waveform is maximized,
The best focus condition is found. An example of a specific method will be described below.

As shown in FIG. 7, two reference levels r1
, R2. The magnitude of the reference levels r1 and r2 is
The ratio is set to a fixed ratio with respect to the maximum value of the photoelectric signal. Then, the stage 7 is scanned to detect points p1 and p2 where the signal I1 coincides with these levels r1 and r2.
From the distance in the x direction between points p1 and p2, the spread e1 of the waveform
Is measured. The measurement of the distance in the x direction is performed by the CPU 30 using the laser interferometer 13 for measuring the stage position. Similarly, the positions of points p3 and p4 where the signal I2 coincides with the levels r1 and r2 are detected to measure the spread e2 of the waveform.

FIG. 8 is a graph in which the horizontal axis indicates the vertical position Z of the opening surface by the Z-ACT 38 and the vertical axis indicates the spread e of the waveform of the photoelectric signal. When the aperture surface is moved in the vertical direction by a predetermined amount, for example, 0.5 μm and stopped, and the stage is scanned to measure the spread amount of the waveform shown in FIG. e is stored as such data. In the figure, the spread amount e0 is the position Z0 at which the aperture plane coincides with the image plane.
At the positions Z1 and Z2 deviated therefrom, the spread amounts are e1 and e2 as described with reference to FIG. To actually focus, the spread amount e is measured and stored in order at the positions Z2, Z1,..., Z0,. The operation is performed by driving the Z-ACT 38 so as to return.

By the method exemplified above, the projection lens 6
And the aperture plane of the minute aperture 8 can be matched, so that the coordinates of the image can be measured in the focused state. As described above, in this embodiment, the contrast of the projected image itself is detected by the photoelectric detector 9 provided on the stage 7, so that the S / N ratio of the signal is high, and it is possible to accurately detect the focus position. Become. Therefore, the height of the opening surface when the contrast of the projected image is maximized is detected by the gap sensor 12 in FIG. 1 so that the detection signal of the AFD 39 becomes a signal indicating the in-focus state, for example, 0V. If calibration is performed, that is, if the detection offset is canceled, the projection lens 6
Regardless of the adjustment or replacement, a clear pattern can always be transferred onto the wafer 10. Further, the projection lens 6 is formed by using a plurality of cross marks of the reticle 5 shown in FIG.
By examining the in-focus position at various positions in the effective exposure area, it is possible to immediately measure the minute unevenness distribution on the imaging surface in the exposure area, that is, the curvature of the image plane, the depth of focus distribution, and the like. Therefore, the inclination of the optical axis with respect to the movement plane (xy coordinate system) of the stage 7 of the projection lens 6 can be confirmed from the measurement data.

In the above embodiment, the mark on the reticle 5 is not limited to a cross mark, but may be an L-shaped mark such as the slit openings 8a and 8b. The arrangement of the marks is not limited to a square matrix, and a plurality of marks may be arranged radially from the center of the reticle 5. Further, although the minute opening 8 is also the two slit openings 8a and 8b, they may be integrated into an L-shaped minute opening. Also in this case, the relationship between the size of the L-shaped slit opening and the projected image of the cross mark is preferably set to d <D <h as described above.

Also, if the reticle holder 15 shown in FIG. 1 can be moved up and down in the optical axis direction of the projection lens 6, the projection lens 6 will not be moved up and down when adjusting the magnification.
The mechanical configuration is simplified. As described above, according to the present invention, the projection magnification and distortion of the projection optical system can be measured quickly and accurately, and with good reproducibility, which is useful not only for adjustment at the time of manufacturing an exposure apparatus, but also for improving projection performance. LS adjustment
Since the projection magnification and the projection distortion can be measured quickly and easily even at the site where I is manufactured, there is an advantage that the adjustment at the LSI manufacturing site can be completed quickly. Further, when there is a concern about the projection performance, such as after transporting the exposure apparatus, or after giving a strong impact to the exposure apparatus by mistake, the present invention can easily confirm the projection performance.

The present invention can be applied not only at the time of manufacturing, service or maintenance as described above,
When it is desired to finely adjust the projection magnification by a predetermined amount, it can be included in a part of the normal operation of the exposure apparatus. For example, (n +
1) According to the present invention, when the pattern of the layer is overlapped and the entire wafer is stretched uniformly, the change in the projection magnification can be easily measured according to the present invention. Confirmation after the change can be easily performed, and an exposure apparatus capable of changing the magnification and measuring the projection magnification can be realized and dealt with. According to such an exposure apparatus, the projection magnification may be changed in accordance with expansion and contraction of the entire wafer. That is, if the wafer is extended by k times, the projection magnification may be increased from the original value N times to kN times. For this purpose, the distance between the projection lens 6 and the reticle 5 or the distance between the optical components forming the projection lens 6 in the optical axis direction is relatively controlled by a command from the CPU 30 so that the measured magnification becomes a desired amount. What is necessary is just to provide the drive means to move.

An apparatus in which the projection magnification is variable and which can be accurately set is not only effective for coping with expansion and contraction of a wafer as described above, but also has another exposure apparatus, for example, a soft X-ray radiation source, An X-ray exposure apparatus and a projection-type exposure apparatus that perform proximity exposure at a finite distance from the radiation source
It is also effective when used for manufacturing two devices. That is, the pattern size on the mask like an X-ray exposure apparatus,
By using an exposure apparatus in which the magnification between the pattern size to be printed on the wafer and the magnification is slightly different from the integer value, the circuit pattern of one layer is printed on the wafer, and the circuit pattern of the other layer is an optical projection type. When printing with an exposure apparatus, even if the magnification relationship between the mask and the reticle to be used is made to be an integral multiple or a fraction of an integral number when producing the mask or reticle to be used, the magnification can be easily adjusted on the projection exposure apparatus side. This has the advantage that the fabrication of the mask or reticle is facilitated.

[0046]

As described above, according to the present invention, it is possible to obtain a projection exposure method capable of adjusting projection performance with high reproducibility, and particularly to reproduce a projection image error caused by projection magnification and distortion. It is possible to easily perform the measurement and, for example, move some optical elements in the projection optical system to easily perform the adjustment.

[Brief description of the drawings]

FIG. 1 is a schematic view of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 shows a test used for measuring the optical performance of the projection optical system.
FIG. 3 is a plan view showing a reticle.

FIG. 3 is a plan view of a light shielding member for forming a minute opening provided on a stage of the projection exposure apparatus.

FIG. 4 is a block diagram showing a control system of the projection exposure apparatus.

FIG. 5 is a diagram showing the relationship between the size of a projected image and the size of a minute aperture when a mark on a reticle is projected.

FIG. 6 is a diagram showing a light intensity distribution when a projected image of a mark is photoelectrically detected.

FIG. 7 is a diagram illustrating focus detection using a minute aperture and a photoelectric detector.

FIG. 8 is a view for explaining focus detection using a minute aperture and a photoelectric detector.

[Explanation of symbols]

 Reference Signs List 5 reticle 6 Projection lens 7 Stage 8 Micro aperture 9 Photoelectric detector 10 Wafer 30 CPU 13, 34 Laser interferometer

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[Procedure amendment]

[Submission date] September 17, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems and to provide a projection exposure method capable of adjusting projection performance with high reproducibility, and particularly to reproduce a projection image error caused by a projection magnification and distortion. It is an object of the present invention to obtain a method capable of performing measurement and adjustment with good performance.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

[0010]

SUMMARY OF THE INVENTION The present invention relates to an improvement in a projection exposure method using a projection optical system (projection lens 6) for projecting a pattern formed on a mask (reticle 5) into a predetermined image plane. Things.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

In the present invention, a plurality of positions (Pij or Xi) determined in advance as a mask pattern are used.
j, Yij), each mark (Mij) formed on the image plane via the projection optical system (6).
Or xij, yij) are measured using, for example, the minute aperture 8, the photoelectric detector 9, or the like, and the arrangement relationship (position Pij) of each mark (Mij) on the mask and the measured position (Tij) of each mark are measured.
ij), the values (N or αij, β) related to the projection magnification and distortion of the projection image projected by the projection optical system (6).
ij), and based on the calculated values, some optical elements (such as lenses) constituting the projection optical system (6) so that each of the projection magnification and the distortion does not exceed a predetermined allowable range. The position of was adjusted.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

[0012]

In the present invention, the positions of a plurality of marks on a mask are measured to calculate values relating to a magnification error and a distortion of the projected image, and one of the values in the projection optical system is calculated based on the calculated values. Since the optical elements of the unit are moved, it is possible to correct both the magnification error and the distortion of the projected image accurately and easily.

Claims (3)

[Claims] 1. A projection optical system for forming an image of a pattern formed on a mask in a predetermined image plane, a sensitive substrate being held substantially coincident with the image plane, and a projection optical system being substantially parallel to the image plane. A projection exposure method for transferring a pattern formed on the mask to the sensitive substrate by using a stage that moves two-dimensionally in a plane and a position measurement unit that measures a coordinate position of the stage. Measuring, in cooperation with the position measuring means, sequentially the respective positions at which the marks formed at a plurality of predetermined positions are projected on the image plane via the projection optical system; Calculating means for calculating a value related to the projection magnification and distortion of a projection image by the projection optical system based on the arrangement relationship of each mark and the measured positions measured; And adjusting the positions of some of the optical elements constituting the projection optical system so that each of the projection magnification and the distortion does not exceed a predetermined allowable range based on the obtained values. . 2. The method according to claim 1, wherein measuring the positions where the images of the plurality of marks are projected includes a reference mark having a predetermined shape that can be superimposed on the image of the mark provided on a part of the stage; The stage is moved so that each image sequentially overlaps, and the position of the stage when each of the images of the plurality of marks is aligned with the reference mark is sequentially determined based on the measurement value of the position measurement unit. 2. The method according to claim 1, wherein the method is performed by storing. 3. The reference mark has a transparent portion having the predetermined shape, and an image of the mark projected by the projection optical system is detected by a photoelectric detector via the transparent portion having the predetermined shape. 3. The method according to claim 2, wherein: