JPH1074696A - Projection type aligner and projection exposing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase reproducibility of measurement by a method wherein positions of an optical element are adjusted based on projection magnification, calculating means for calculating values corresponding to distortion aberration and calculated values. SOLUTION: A plurality of marks Mij formed in a mask are illuminated with exposed lights, and a surface of a reference plate provided in a part of a stage 7 coincides substantially with an image surface of a projection optical system 6 by a specific focusing means 12. Each of projection images of the plurality of marks Mij is sequentially projected to a surface of the reference plate by irradiation of exposed lights, and the projection positions are respectively detected. Based on the projection positions of the plurality of marks detected and an arrangement relationship of the marks Mij on the mask, optical performance of a projection optical system 6 is measured, and exposure of a substrate 10 is made based on the measurement results. Thereby, errors of projection images traceable to projection magnification and distortion aberration are measured with excellent reproducibility and the adjustment is simply made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for 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. Therefore, if the distance between the reticle and the projection lens and the relative position of the optical element inside the projection lens do not change, the error caused by the factor (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.

[0005]

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 continue to be mounted on the stage of the exposure apparatus, but must be replaced without fail. 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.

An object of the present invention is to solve these problems and to provide a projection exposure apparatus capable of adjusting the 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 apparatus capable of performing measurement with good accuracy and moving and adjusting some optical elements in a projection optical system.

[0009]

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 apparatus provided with position measuring means (laser interferometers 13 and 34) for measuring the coordinate position of the stage (7).

In the present invention, marks (M _ij ) formed at a plurality of positions (P _ij , or X _ij , Y _ij ) predetermined as a pattern of the mask (reticle 5) are projected optically. Mark position measuring means (T _ij , or x _ij , y _ij ) to be sequentially projected into the image plane via the system (6) in cooperation with the position measuring means (13, 34) A minute aperture 8, a photoelectric detector 9, a CPU 30);
The positional relationship (position P) of each mark (M _ij ) on the mask (R)
_ij ) and a value (N, or α _ij , β _ij ) corresponding to the projection magnification by the projection optical system (6) or distortion based on the measured position (T _ij ) of each mark. Means (CPU 30) and means for adjusting the position of some optical elements (such as lenses) constituting the projection optical system (6) based on the calculated values are provided.

[0011]

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.

[0012]

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.
The plurality of predetermined positions on the lower surface of the reticle 5, the light transmission of the mark M ₁₁ ~M ₁₆ is depicted. The light beam LB ₁ that has passed through the mark M ₁₁ ~M ₁₆ of the reticle 5 is incident on the 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 LB ₁ is focused by a projection lens 6, and emits a light beam LB _2. Note that the distance between the lower surface of the reticle 5 and the main plane 6a of the projection lens 6 is L. Then, the light beam LB ₂ is focused on the minute aperture 8 provided in the two-dimensional movable stage 7. 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 normally carries a semiconductor wafer 10 and moves two-dimensionally. The wafer 10 is placed on a wafer holder 11 that moves two-dimensionally with the stage 7. The wafer holder 11 is the stage 7
It is provided so as to be able to perform minute rotation and vertical movement with respect to. The wafer holder 11 is moved up and down so that a projection image of the projection lens 6 is formed on the surface of the wafer 10, that is, so that focusing can be performed. 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, the projection lens 6 and the surface of the wafer 10 (or the opening surface of the minute opening 8)
Is provided with a gap sensor 12 for measuring an interval with the gap. Automatic focus adjustment is possible by the vertical movement of the gap sensor 12 and the wafer holder 11, and the wafer 10
When printing the upper circuit pattern, the height of the surface of the wafer 10 is detected, and a projection image with high contrast can always be transferred.

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, the marks in the top row of the reticle 5 are denoted by M ₁₁ ,
M ₁₂ ,..., M _16, and the mark in the lower row is M ₂₁ ,
M _22, determined sequentially so as to ···· M _26. Therefore, a cross mark on the reticle 5 is generally M _ij (where, i, j is 1 to 6) shall be identified by, its central position of the cross mark P _ij (except in response to M _ij, i, j is 1 to 6).

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 of the projected image of the cross mark M _ij in the x direction, and the slit opening 8b elongated along the x axis direction detects the position of the projected image of the cross mark M _ij in the y direction. Used for 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 M _ij . 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 driving 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 driving section 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 M _ij 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 chrome 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. The cross mark M _ij image and the slit opening 8a, the positional relationship between 8b is, for example, as is shown in FIG. 5, by operating the X-ACT35, Y-ACT36 moves the stage 7. 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 M _ij 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 M _ij and the slit openings 8 a and 8
The relationship with the size of b is as shown in FIG. That is, in the image of the cross mark M _ij , 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 M _ij 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 moved to the position 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 x ₁ and x of the stage 7 when the photoelectric signal I and the reference level Ir match.
₂ is measured by the laser interferometer 13. The measured value is taken into CPU 30, and averaging the two positions to determine the position x _0. That is, the CPU 30 (x ₁
The position x ₀ of the stage 7 obtained by the calculation of + x ₂ ) / 2 is obtained as the projected coordinate position of the center line CLx of the slit Lx.

On the other hand, for the slit image Ly,
The stage 7 is moved from the position of FIG.
Scans the aperture 8b to determine the y direction of the stage 7 from the light intensity distribution.
Direction position y₀Is the projection center of the center line CLy of the slit image Ly.
Obtain as a reference position. Thus, the coordinates of the stage 7
Value (x₀, Y₀) Is the cross mark M_ijOf the center CP of the image
Is measured and stored in the CPU 30. Likewise
Measurement of the image of the other cross mark.
Cross mark M_ijPosition P on reticle 5 _ijCompatible with
And sequentially store them.

The reason why the sizes of the slit openings 8a and 8b and the image of the cross mark _Mij are set to d <D <h is that when the projection position in the x direction is detected, the slit opening 8a This is to enable position detection even when both Lx and the slit image Ly are scanned, or when the slit opening 8a scans the slit image Lx and the slit opening 8b simultaneously scans the slit image Lx. is there.

For example, when the slit opening 8a has the slit image L
When the stage 7 from the state crosses the x scanning in the x direction, as in the photoelectric signal of the photoelectric detector 9 FIG. 6 (b), the maximum value Ip having a constant offset I _of the scanning portion of the slit image Ly 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.

[0028] Such signal is compared with a reference level Ir, to determine the position x ₀ of the center line CLx of the slit image Lx, it must be Ir> I _of. 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, and the cross mark M _ij is used as in the above embodiment.
Of the image is determined.

Next, the CPU 30 calculates the projected position of the image of each cross mark M _ij and the position P _ij based on the measured position.
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 M _ij measured as the position of the stage 7 is T _ij , P _ij is a coordinate value (X _ij , Y
_ij ), and T _ij is represented by coordinate values (x _ij , y _ij ). Therefore, the following equation 1 is used as an example of an equation for calculating the projection magnification N.

[0030]

(Equation 1)

Equation 1 is calculated by the CPU 30, and the magnification N is, as is apparent from the form of 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, X _i1 and x _i1 are _calculated as shown in FIG.
Cross marks M ₁₁ , M ₂₁ , M ₃₁ , forming the middle and left end rows
, M _{61 on} the reticle 5 in the X direction, and the projected positions of the six cross marks in the x direction. X _i6 and x _i6 are the positions of the cross marks M ₁₆ , M ₂₆ ,..., M ₆₆ forming the rightmost line in FIG. 2 in the X direction on the reticle 5, and the cross marks of the six cross marks. and the projection position in the x direction. Further, in Equation 1, Y _1j and y _1j
Are the cross marks M ₁₁ , M ₁₂ ,...
M ₁₆ represents the position of the reticle 5 on the reticle 5 in the Y direction, and the projection positions of the six cross marks in the y direction.
Y _6j and y _6j are cross marks M ₆₁ in the bottom row in FIG. 2,
M _62, each represents ..., the position in the Y direction on the reticle 5 in M _66, and the projection position in the y direction of the six cross mark.

When the projection magnification to be set is N ₀ when the projection lens 6 is manufactured or adjusted, an error (α _{ij) in} each coordinate axis direction on coordinates including distortion of the projected image of the cross mark is set. , Β _ij ) represent the 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 M ₁₁ , M ₁₆ , M ₆₁ and M ₆₆ 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 device 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.
However, the same applies to a case where the terminal device 40 displays only the detected position of the projected image of each cross mark M _ij , and then performs a predetermined calculation in another computer based on the information of the detected position. The effect 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.

A 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 passing 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. If the opening plane and the image plane with a slit opening 8a is approaching, if the waveform of the photoelectric signal I ₁ is obtained as shown in FIG. 7, when the opening plane and the image plane away than this state wider range of waveforms, so that the signal I _2. 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 r ₁ and r ₂ are provided. The magnitudes of the reference levels r ₁ and r ₂ are set to have a fixed ratio with respect to the maximum value of the photoelectric signal. Then, the stage 7 is scanned to detect points p ₁ and p ₂ where the signal I ₁ coincides with these levels r ₁ and r _2, and the spread amount of the waveform is determined from the distance between the points p ₁ and p _{2 in} the x direction. to measure the e _1. 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 p ₃ and p ₄ where the signal I ₂ coincides with the levels r ₁ and r ₂ are detected, and the spread amount e _{2 of the} waveform is detected.
Is measured.

FIG. 8 is a graph in which the horizontal axis indicates the vertical position Z of the opening plane by the Z-ACT 38, and the vertical axis indicates the spread e of the photoelectric signal waveform. 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 e ₀ is a position Z ₀ at which the aperture plane coincides with the image plane.
At the positions Z ₁ and Z ₂ deviated therefrom, the spread amounts are e ₁ and e ₂ as described in FIG. In order to actually focus, the spread amount e is sequentially measured and stored at the positions Z ₂ , Z ₁ ,..., Z ₀ ,. as returns to the position Z _0, performed by driving the Z-ACT 38.

According to 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 like 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.

Further, 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.

[0044]

As described above, according to the present invention, it is possible to obtain a projection exposure apparatus capable of adjusting the projection performance with high reproducibility, and in particular, to reproduce a projection image error caused by a 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. Further, by examining the focus position at various positions in the effective exposure area of the projection optical system, even the curvature of the image forming surface in the exposure area can be measured accurately and with good reproducibility.

[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 9, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Projection type exposure apparatus and projection exposure method

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

In the projection exposure apparatus according to the present invention, a reference plate (20) provided on a part of the stage (7) and having a predetermined light receiving portion (8) formed on a surface thereof; A) a photoelectric detector (9) for outputting a photoelectric signal in accordance with the intensity of the light received in the step (b), and focusing for making the surface of the reference plate (20) substantially coincide with the image plane of the projection optical system (6). Means (12) and a mark (M) formed at each of a plurality of predetermined positions (P _ij or X _ij , Y _ij ) as a mask pattern.
_ij ) is projected through the projection optical system (6) under exposure light, and focusing means (1) is formed.
The projection image of the plurality of marks is received by the light receiving section (8) of the reference plate (20) by making the reference plate surface substantially coincide with the image plane of the projection optical system (6) using 2). Mark (M
_ij ) is measured based on the photoelectric signal from the photoelectric detecting means (9) and the measurement value from the position measuring means (13, 34), and a mark position measuring means (30) on the mask. An arithmetic unit (30) for calculating the optical performance of the projection optical system (6) based on the arrangement relationship of each mark and each position where each mark is projected is provided. In a further projection exposure method of the present invention illuminates the plurality of marks formed on the mask (M _{i j)} with an exposure light, provided in a part of the stage (7) using a predetermined focusing means (12) The surface of the reference plate (20) thus obtained is made substantially coincident with the image plane of the projection optical system (6), and the respective projected images of the plurality of marks (M _ij ) by the irradiation of the exposure light are sequentially placed on the surface of the reference plate (20). The projection position of each of the plurality of marks (M _ij ) is detected by projection, and the projection optical system (6) is controlled based on the detected positions of the plurality of marks and the positional relationship of the plurality of marks on the mask. The optical performance was measured, and the substrate (10) was exposed based on the measurement result.

Claims (4)

[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. In a projection exposure apparatus having a stage for two-dimensionally moving in a plane and position measuring means for measuring a coordinate position of the stage, a mark formed at each of a plurality of positions predetermined as the mask pattern Mark position measuring means for sequentially measuring each position to be projected into the image plane via the projection optical system in cooperation with the position measuring means; and the arrangement relationship of each mark on the mask and the mark Calculating means for calculating a value related to the projection magnification or distortion based on each of the measurement positions measured by the position measuring means; and performing the projection based on the value calculated by the calculating means. Projection exposure apparatus characterized by comprising a means for adjusting the positions of some of the optical elements constituting the academic system. 2. A plate provided on a part of the stage, wherein a reference mark having a shape superimposable on a projected image of a mark of the mask is formed on the stage,
A stage driving unit that moves the stage so that the reference mark sequentially overlaps with each projection image of the plurality of marks on the mask, and a stage driving unit that moves each of the projection images of the plurality of marks with the reference mark. The apparatus according to claim 1, further comprising: a storage unit that sequentially stores the position of the stage based on a measurement value of the position measurement unit. 3. The plate is formed of a transparent member having a light-shielding layer formed on a surface thereof and a part of the light-shielding layer made transparent in the shape of the reference mark, and the mark position measuring means is projected by the projection optical system. The apparatus according to claim 2, further comprising a photoelectric detector that receives the image of the mask mark formed through the transparent member. 4. A projection optical system for forming an image of a pattern formed on a mask in a predetermined image plane, and a sensitive substrate is held so as to substantially coincide with the image plane. A stage that moves two-dimensionally in a plane; a unit that moves the sensitive substrate up and down on the stage for focusing the sensitive substrate; and a position measurement unit that measures a coordinate position of the stage. In the projection type exposure apparatus, when marks formed at a plurality of positions predetermined as a pattern of the mask are projected on the image plane side via the projection optical system, the images of the plurality of marks are A mark focus position detecting means for sequentially detecting a focus position in cooperation with the vertical movement means; and an arrangement relationship of each mark on the mask and each focus position detected by the mark focus position detection means. Based on, projection exposure apparatus characterized by comprising a means for measuring the curvature of the image plane of the projection optical system.