JPH0340934B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to an apparatus for projecting and exposing a mask pattern of an integrated circuit onto a semiconductor substrate.

[Conventional technology]

Large-scale integrated circuit (LSI) patterns are getting smaller and smaller every year, and reduction projection exposure equipment is becoming popular as a circuit pattern printing device that satisfies the demands for miniaturization and has high productivity.
In these conventionally used devices, the number of times (for example, 10
The reticle pattern of 1.2 times) is reduced and projected by a projection lens, and the area that is printed in one exposure is smaller than a square with a diagonal length of 14 mm on the wafer. Therefore, in order to print a pattern on the entire surface of a wafer with a diameter of about 125 mm, a so-called step-and-repeat method is used, in which the wafer is placed on a stage, moved a certain distance, and exposed repeatedly. In LSI manufacturing, patterns of several layers or more are sequentially formed on a wafer, but unless the overlay error of the patterns between different layers is kept below a certain value, the conductive or insulating state between the layers will not be as intended. It becomes impossible to perform the functions of the LSI. For example, for a circuit with a minimum line width of 1 μm, only an overlay error of about 0.2 μm is allowed at most. Among the causes of this overlay error, those caused by the exposure apparatus are (1) projection magnification error and projection distortion, and (2) relative positional deviation between the projected image and the wafer. The distortion caused by (1) above is the distortion aberration of the projection lens. 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 lens if the light beam on the reticle side of the projection lens is not telecentric. In some cases, the projection optical system can be made smaller by relatively shifting its internal components (optical members such as lenses) in the optical axis direction. Therefore, the distance between the reticle and the projection lens, the relative position of the components inside the projection lens, etc. must remain unchanged after adjustment.
The error due to cause (1) is constant and can be said to be a systematic error.

This systematic error (1) can be maintained stably and small over a long period of time by adjusting the equipment so that it is below a certain value while measuring the value. It must be made as small as possible during the adjustment during manufacturing of the device. Conventionally, error measurement in (1) is carried out by printing the image of a so-called test reticle, which has mark patterns drawn at multiple predetermined positions, onto a photoresist on a wafer, and then using the photoresist image of the printed marks. This was done by measuring the coordinates of the mark on the reticle and comparing the measured coordinates with the mark coordinates on the reticle. However, this method requires time and effort to expose and develop a test reticle pattern on the wafer, and also requires the use of expensive measuring equipment to measure the resist image of the mark. There is a problem.

On the other hand, the error caused by cause (2) includes many random error factors, including alignment errors in the horizontal direction (along the wafer surface) between the projected image and the wafer, and alignment errors between the projected image and the wafer. Alignment error in the vertical direction (direction of the optical axis of the projection lens),
It is broadly classified into so-called defocus.

Regarding defocus, no matter how good the performance of the projection lens is, it will extremely deteriorate the resist image of the reticle pattern that is finally printed, so extremely high-precision correction, or focus adjustment, is required. be. Generally, this type of projection exposure equipment has a gap sensor that detects changes in the height position (position in the projection optical axis direction) of the wafer surface, and uses this sensor to always maintain a constant distance between the wafer surface and the projection lens. A servo-controlled automatic focusing mechanism is provided.

As this gap sensor, an air micro type, an oblique incidence projection type, etc. are known.

[Problem to be solved by the invention]

However, this focusing method only detects how much the height position of the wafer surface deviates from a fixed position, and it cannot directly determine whether or not the projected image plane of the reticle pattern matches the wafer surface. It doesn't mean it's being detected.

Therefore, after systematically adjusting the error in (1) below a certain value, that is, adjusting the distance between the reticle and the main plane of the projection lens, or adjusting the position of the lens components inside the projection lens, it is necessary to Since the absolute position of the image plane in the optical axis direction changes, the drawback is that focusing based on the gap sensor is no longer reliable.

SUMMARY OF THE INVENTION An object of the present invention is to solve this drawback and provide a projection exposure apparatus that reliably maintains focus reliability.

[Means to solve problems]

In order to achieve this objective, in the present invention, a part of a projected image of a reticle (mask) pattern is received on a stage means on which a substrate such as a wafer is placed and which moves up and down in the optical axis direction for focusing. image plane position detection means 8, 9, 21, including photoelectric detection units 8, 9;
20, the image plane position detecting means is used to detect the height position of the projection image plane conjugate with the reticle, and at the detected height position, the focus adjustment mechanism using the gap sensor determines that the focus is in focus. The focus adjustment mechanism is configured to be calibrated so that the focus adjustment mechanism is calibrated.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a projection exposure apparatus to which an embodiment of the present invention is applied.

Illumination light from an exposure illumination light source 1 is once converged by a first condenser lens 2 and then reaches a second condenser lens 3. In the optical path, a shutter 4 for blocking and passing the illumination light is provided at a position where the light is converged. The light flux passing through the second condenser lens 3 illuminates a test reticle 5 (hereinafter simply referred to as reticle 5) serving as a mask. Light-transmissive marks M ₁₁ to _{M 16} are drawn on the lower surface of the reticle 5 at a plurality of predetermined positions. The light beam l ₁ that has passed through the marks M ₁₁ to _{M 16} on the reticle 5 is incident on the projection lens 6 as an imaging optical system. This projection lens 6 is an optical system in which the reticle 5 side, that is, the object side, is non-telecentric and the image side is telecentric. The light beam l ₁ is focused by the projection lens 6 and emerges as a light beam l ₂ . Note that the distance between the lower surface of the reticle 5 and the principal plane 6a of the projection lens 6 is L. The light beam l ₂ is then imaged onto a minute aperture 8 provided on a two-dimensionally movable stage 7. Furthermore, the light passing through the minute aperture 8 is transferred to the stage 7.
It is photoelectrically converted by the photoelectric detector 9 provided in the. Also, stage 7 is usually used for semiconductor wafer 10.
The wafer is placed on the wafer and moved in two dimensions.
0 is placed on a wafer holder 11 that moves two-dimensionally together with the stage 7. The wafer holder 11 is provided so as to be able to minutely rotate and move up and down relative to the stage 7. This wafer holder 11 moves up and down so that the projected image of the projection lens 6 is formed on the surface of the wafer 10, that is, so that focusing can be performed. Further, the aperture surface on which the minute aperture 8 is provided is determined to approximately match the height of the surface of the wafer 10, and this aperture surface and the photoelectric detector 9 move up and down together as the wafer holder 11 moves up and down. It is set up to do so. For this focusing, a gap sensor 12 is provided to measure the distance between the projection lens 6 and the surface of the wafer 10 (or the aperture surface of the minute aperture 8). Automatic focus adjustment is possible by the gap sensor 12 and the vertical movement of the wafer holder 11, and when printing a circuit pattern on the wafer 10, the height of the surface of the wafer 10 is detected and a projected image with always high contrast is obtained. can be transcribed.

On the other hand, the position of the stage 7 is determined by using a laser interferometer 13 to measure the distance to a reflecting mirror 14 fixed to the stage 7 using a laser beam.

Although FIG. 1 only shows the x-axis direction in the horizontal direction in the paper, the laser interferometer and the reflecting mirror are also shown in the y-axis direction perpendicular to the x-axis (perpendicular to the paper), which forms the plane of movement of the stage 7. is provided. Coordinate values of the stage 7 relative to a predetermined origin are sequentially measured by these laser interferometers.

Note that the intersection of the two measurement axes formed by the respective laser beams of the laser interferometer in the x-axis and y-axis directions is determined to coincide with the optical axis of the projection lens 6.

Further, the reticle holder 15 holds the reticle 5 and is movable two-dimensionally, and is driven and controlled by a reticle alignment control system, which will be described later, to position the reticle 5.

Now, FIG. 2 is a plan view of the reticle 5 shown in FIG. 1. The reticle 5 is constructed by depositing a chromium layer or a low-reflection chromium layer over the entire bottom surface of a glass substrate, as shown by the shaded area in the figure. In the chromium layer, cross marks as marks M through which light passes are formed in a 6×6 square matrix. The center position of these cross marks is approximately in the coordinate system O-XY on the reticle 5.
It shall be measured in advance by another measuring device with an error of 0.1 μm or less. The center positions of the cross marks are determined to be line symmetrical with respect to the coordinate axes X and Y, respectively, and point symmetrical 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 designated as M ₁₁ , M ₁₂ , ...M ₁₆ , and the marks in the row below are designated as M ₂₁ , M ₂₂ , ...M ₂₆ . To be determined sequentially. Therefore, the cross mark on the reticle 5 is generally specified by Mij (where i, j are 1 to 6), and the center position of the cross mark is specified by Pij (where i, j are 1 to 6) corresponding to Mij. ).

Further, FIG. 3 is a plan view of a light shielding member forming a minute opening 8 provided in the stage 7, and a cross-sectional view taken along the line A-A. The minute opening 8 is obtained by depositing a chromium layer 21 on a glass plate 20 to a thickness of about 0.1 μm, and forming two slit openings 8a and 8b in a portion of the chromium layer 21. The thickness of this chromium layer 21 is sufficiently thinner than the depth of focus (several μm) of the projection lens 6. Now, the extending directions of the slit openings 8a and 8b are determined to be perpendicular to each other, and are also determined to coincide with the moving direction xy of the stage 7, respectively. still,
Slit opening 8a elongated along the y-axis direction
is used to detect the x-direction position of the projected image of the projected cross mark Mij, and the slit opening 8b extending thinly along the x-axis direction is used to detect the position of the projected cross mark Mij in the x direction.
It is used to detect the position of the projected image of Mij in the y direction.

Further, the width of the slit openings 8a, 8b is set smaller than the width of the straight line portion of the projected image of the cross mark Mij. This will be explained in detail later.

Of course, the light receiving surface of the photoelectric detector 9 is located below this glass plate 20, and these glass plates 20,
The chromium layer 21, the minute apertures 8a and 8b, and the photoelectric detector 9 constitute the image plane position detection means of the present invention.

Incidentally, the gap sensor 12 described above can detect the surface of the chromium layer 21.

Next, a control system for controlling the apparatus shown in FIG. 1 will be explained based on the block diagram in FIG. 4. The entire device is equipped with a microcomputer (hereinafter simply referred to as CPU) 30 including memory etc. so that it can be controlled by programs and perform various arithmetic processing.
It is centrally controlled by. The CPU 30 exchanges various information with surrounding detection units, measurement units, or drive units via an interface 31 (hereinafter referred to as IF 31).

Now, the shutter drive unit 32 opens and closes the shutter 4 according to instructions from the CPU 30.
Reticle alignment control system 33 (hereinafter R-
ALG 33) is used to move and align 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 this R-ALG33 is not necessarily necessary in the embodiment of the present invention,
The following R-
ALG33 shall be used.

On the other hand, in order to measure the coordinates of the stage 7, the stage 7 is read by the laser interferometer 13 described above.
The x-direction position information of the stage 7 and the y-direction position information of the stage 7 read by the laser interferometer 34 are both sent to the CPU 30 via the IF 31. Also,
In order to move the stage 7 two-dimensionally, an x-axis drive unit 35 (hereinafter referred to as X-axis) drives the stage 7 in the x direction.
ACT35) and a y-axis drive unit 36 (hereinafter referred to as Y-ACT36) that drives the stage 7 in the y direction are provided to operate according to instructions from the CPU 30.

Additionally, a θ-axis rotation drive unit 37 (hereinafter θ-
ACT37) and a Z-axis drive unit 38 (hereinafter referred to as Z-ACT38) for vertically moving the wafer holder 11, photoelectric detector 9, and glass plate 20, and operates according to instructions from the CPU 30. .
And focus detection section 39 (hereinafter referred to as AFD 39)
inputs the signal from the gap sensor 12 shown in FIG. It is output to the CPU 30 via the CPU 30. The gap sensor 12, AFD 39, CPU 30, etc. constitute the focus adjustment means of the present invention.

Further, a terminal device 40 such as a monitor CRT or a printer for displaying measurement results, operating conditions, etc. is also connected to the CPU 30 via the IF 31.

In addition to the various control systems mentioned above, the actual exposure apparatus also includes a wafer alignment control system for positioning the wafer 10 in the x and y movement directions of the stage 7, but this is not directly related to the present invention. Explanation will be omitted.

Next, the calibration operation of the focus adjustment system using the above-mentioned exposure apparatus will be explained, but before that, the measurement operation of various optical characteristics of the projection lens 6 will be explained.

First, the reticle 5 set in the apparatus is positioned using the R-ALG 33. At this time, the optical axis of the projection lens 6 is set to the coordinate system O- on the reticle 5.
Align it so that it passes through the XY origin O. Furthermore, the X and Y axes of the coordinate system O-XY are the x of stage 7,
The position of the reticle 5 is determined so that it is parallel to the y movement direction, that is, the measurement axes x and y of the laser interferometers 13 and 34, respectively (including when they coincide). As a result, the extension directions of the two orthogonal straight line parts of the cross mark Mij are respectively x and y of the stage 7.
Matches the direction of movement.

Next, the stage 7 is moved by the X-ACT 35 and the Y-ACT 36, and the opening surface of the minute aperture 8, that is, the height of the surface of the chromium layer 21 in FIG. 3 is detected by the gap sensor 12 and the AFD 39. Based on the information, the Z-ACT 38 is driven so that the image plane of the projection lens 6 and the surface of the chromium layer 21 match, that is, so that the distance between the projection lens 6 and the chromium layer 21 becomes a constant value.

Next, the shutter drive section 32 drives the shutter 4.
is opened, the reticle 5 is illuminated, and the image of the cross mark Mij is projected onto the chrome layer 21. Then, the X
-Activate ACT35 and Y-ACT36 to move the stage 7. At that time, the slit openings 8a, 8
If, for example, the coordinate values of the laser interferometers 13 and 14 are determined when b is located on the optical axis of the projection lens 6, the approximate position of the image of each cross mark Mij can be obtained using the coordinate values as the reference position. Can be easily specified.

At this time, the size of the image of the projected cross mark Mij and the slit apertures 8a, 8 as the minute apertures 8 are determined.
The relationship with the size of b is as shown in Figure 5. That is, of the image of the cross mark Mij, a straight line portion extending in the y direction is defined as a slit image L _x , and a straight line portion extending in the x direction perpendicular to the slit image L _x is defined as a slit image _Ly . Then, the center of _the width D of each slit image L _x , Ly is set as the center line CL _x , CL _y respectively, and the center line
Let the intersection of CL _x and CL _y , that is, the center of the image of the cross mark Mij, be the center CP. In addition, the chromium layer 21
The width of the inner slit openings 8a and 8b is d, and the length is h.
It is determined that d<D<h.

Now, 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 L Outputs photoelectric signal I.
In FIG. 6a, 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 L _x . Therefore, the photoelectric signal I is set at a predetermined reference level.
The laser interferometer 13 measures the positions x ₁ and x ₂ of the stage 7 when the photoelectric signal I matches the reference level Ir in comparison with the reference level Ir. The measured value is
The position is taken into the CPU 30, and the two positions are averaged to find the position _x0 . That is, the CPU 30 determines the position x ₀ of the stage 7 determined by the calculation of (x ₁ +x ₂ )/2 as the projected position of the center line CL _x of the slit image L _x .

On the other hand, regarding the slit image _Ly , the stage 7 is moved in the y direction from the position shown in FIG _. Center line of L _y
Find it as the projected position of CL _y .

As a result, the coordinate values of stage 7 (x ₀ , y ₀ )
is measured as the projected position of the center CP of the image of the cross mark Mij, and is stored in the CPU 30.

Similarly, the images of other cross marks are measured, and the measured values are sequentially stored in correspondence with the position Pij of the cross mark Mij on the reticle 5.

In addition, the slit openings 8a, 8b and the cross mark Mij
The reason for setting the size of the image of d<D<h is that the slit opening 8
If a scans the slit image L _x together,
This is to enable position detection even if the slit opening 8a scans the slit image _Lx and the slit opening 8b scans the slit image _Lx at the same time.

For example, when the stage 7 is scanned in the x direction from a state where the slit aperture 8a intersects the slit image _Ly , the photoelectric signal of the photoelectric detector 9 is constant in the scanned portion of the slit image _Ly , as shown in FIG. 6b. This becomes a signal with an offset Iof and a maximum value Ip. The size of this offset Iof is the width d of the slit opening 8a.
and the width D of the slit image _Ly , and the maximum value Ip is proportional to the area determined by the width d and length h of the slit opening 8a.

To find the position x ₀ of the center line CL _x of the slit image L _x by comparing such a signal with the reference level Ir,
It must be Ir>Iof. Therefore, the width D of the slit image _Ly and the length h of the slit opening 8a are set so that D<h to satisfy this condition. Furthermore, the reason why the width d of the slit openings 8a and 8b is made smaller than the width D of the slit images L _x and _Ly is to make the rise and fall of the photoelectric signal more rapid, so that d<D stipulated in Making the rise and fall of the signal abrupt is advantageous for image contrast detection, which will be described later. Note that the relationship between the width d and D is not limited to d<D, and even if d=D, there is no substantial effect on photoelectric detection/position detection, and as in the above example, the center position of the image of the cross mark Mij is required.

Next, the CPU 30 calculates optical characteristics such as the projection magnification and distortion amount of the projection lens 6 based on the measured projection position of the image of each cross mark Mij and the position Pij.

Furthermore, if the projected position of the image of each cross mark Mij measured as the position of the stage 7 is Tij, Pij is expressed by coordinate values (Xij, Yij), and Tij is expressed by coordinate values (xij, yij). . Therefore, as an example of a formula for calculating the projection magnification N, the following formula is used.

In this equation (1), X _i1 and x _i1 are the positions in the X direction on the reticle 5 of the cross marks M ₁₁ , M ₂₁ , M ₃₁ , ...M ₆₁ forming the leftmost row in FIG. , and the projection position of the cross mark in the x direction, respectively. And, X _i6 and x _i6 are the positions in the X direction of the cross marks M ₁₆ , M ₂₆ , ...M ₆₆ forming the rightmost row on the reticle 5 in FIG. 2, and the positions of the six cross marks in the x direction. and the projection position, respectively. Furthermore, in equation (1), Y _1j and y _1j are the positions in the Y direction on the reticle 5 of the cross marks M ₁₁ , M ₁₂ , ...M ₁₆ forming the top row in FIG. 2, and the positions of the six marks. , and Y _6j and y _6j respectively represent the Y-direction positions of the cross marks M ₆₁ , M ₆₂ ,...M ₆₆ forming the bottom row, and the y-direction projection positions of those six marks. and respectively.

Furthermore, if the projection magnification to be set at the time of manufacturing or adjusting the projection lens 6 is No, then the coordinate error (αij, βij) including the distortion of the image of the projected cross mark is αij = xij − Xij・No βij=yij−Yij・No. However, at this time, it is assumed that the origin O of the coordinate system of the reticle 5 and the origin of the coordinate system of the projected image of the reticle 5 (that is, the origin of the coordinate values of the stage 7) are matched by appropriate calculation. This error (αij, βij) represents the amount of projection distortion. The calculated results are displayed on the terminal device 40.

Although the projection magnification and the projection distortion can be obtained as described above, equation (1) is just an example, and depending on the definition of the magnification, a calculation formula according to the definition may be used. For example, cross marks M ₁₁ , M ₁₆ ,
It is also possible to use only the four corner marks of M ₆₁ and M ₆₆ . If the calculated projection magnification exceeds the allowable amount, readjust the distance L between the reticle 5 and the main plane 6a of the projection lens 6 shown in FIG. Readjust the distance between the (lenses). Then, the magnification is measured again using the above method, and the adjustment and measurement of the projection lens 6 are repeated until the magnification error becomes an allowable value. Furthermore, when measuring the magnification error, the distortion aberration of the projection optical system is also measured to confirm that the aberration is tolerable. 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.

By using the method described above, the time and effort of exposing and developing a test reticle pattern and measuring the resist image using other measuring equipment can be omitted, and projection exposure equipment is usually used. By simply installing a photoelectric detector 9 for detecting a mark image on the movable stage, the projection lens 6 can be easily adjusted.
can measure and adjust the optical properties of In addition, not only when manufacturing exposure equipment, but also when replacing the projection lens 6 with a projection lens with a different reduction ratio at an LSI manufacturing site, no other special measuring equipment is required, so the optical Another advantage is that adjustments to optimize the characteristics can be made extremely efficiently.

In the above embodiment, the optical characteristics were calculated by the CPU 30 built into the exposure apparatus.
A similar 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 using another calculator based on the information on the detected position.

In the above explanation, the image formation position is the chromium layer 21.
The case where the surface coincides with the aperture surface was described. The apparatus shown in FIGS. 1 and 4 is equipped with a gap sensor 12, so if the gap sensor 12 has been accurately adjusted in advance to avoid detection errors, use this to correct the focus error with respect to the aperture plane. The AFD 39 can detect and focus.

However, in a configuration that uses a gap sensor to perform automatic focus detection, when manufacturing the device,
When replacing the projection lens or adjusting the optical elements inside the projection lens, the detection signal of the AFD39 is
In general, there is an offset for focus detection, and relying only on the gap sensor makes it impossible to accurately match the imaging plane of the projected image with the aperture plane. Of course, gap sensor 12
Focusing on the wafer 10 using the AFD 39 also has an offset.

Therefore, as an embodiment of the present invention, a photoelectric detector 9
The following describes the operation of detecting the focus from the contrast of the mark image projected using the AFD 39 and calibrating the AFD 39.

In this case, the wafer vertical movement mechanism Z-ACT
By using the fact that the micro aperture 8 and the photoelectric detector 9 are simultaneously moved up and down by the micro aperture 38, the micro aperture 8 is moved by a distance that divides the length of the focal depth of the projection lens 6 into several equal parts.
The operation of moving the stage 7 vertically, scanning the stage 7, 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 image intensity distribution is minimized is determined. Actually, the intensity distribution of the projected image of the cross mark on the reticle 5 is examined. Figure 7 shows when stage 7 is moved.
It shows the magnitude of a signal obtained by photoelectrically exchanging the image of the mark transmitted through the minute aperture 8, with the vertical axis representing the signal magnitude and the horizontal axis representing the position of the stage 7 in the x direction. If the aperture surface (chromium layer 21) on which the slit aperture 8a is formed is close to the image surface, and the waveform of the photoelectric signal _I1 is obtained as shown in FIG.
When the aperture plane and the image plane are further apart from each other than in this state, the waveform width becomes wider and becomes like signal _I2 . Therefore,
The best focus can be found by measuring the amount of waveform spread or the slope of the waveform shoulders (rising, falling) and finding the state where the amount of waveform spread is minimum or the slope of the waveform shoulder is maximum. condition is found. An example of a specific method will be explained below. As shown in Figure 7, 2
Two reference levels r ₁ and r ₂ are established. Reference level r ₁ ,
The magnitude of r ₂ is set to be a constant ratio to the maximum value of the photoelectric signal. Then, stage 7 is scanned to find the point where signal I ₁ matches these levels r ₁ and r ₂
p ₁ and p ₂ are detected, and the amount of waveform spread e ₁ is measured from the distance in the x direction between the p ₁ point and the p ₂ point. The distance in the x direction is calculated by the CPU 30 using a laser interferometer 13 that measures the stage position. Similarly, the positions of points p ₃ and p ₄ where the signal I ₂ matches the levels r ₁ and r ₂ are detected, and the amount of spread e ₂ of the waveform is measured. FIG. 8 is a graph in which the horizontal axis represents the vertical position Z of the aperture surface due to the Z-ACT 38, and the vertical axis represents the spread amount e of the waveform of the photoelectric signal. A certain amount, e.g. 0.5μ, in the vertical direction of the opening surface (chromium layer 21)
When the stage is moved by m and then stopped, the stage is scanned, and the amount of spread of the waveform shown in FIG. 7 is measured, the amount of spread e for the position Z is stored in the memory of the CPU 30 as the data shown in FIG. Ru. In the figure, the amount of expansion e ₀ indicates the position Z ₀ where the aperture plane exactly coincides with the image plane conjugate to the reticle pattern surface, and at positions Z ₁ and Z ₂ deviated from there, the amount of expansion is as shown in Figure 7. As explained, e ₁ and e ₂ increase successively. To actually focus, measure and memorize the amount of spread e at positions Z ₂ , Z ₁ , Z ₀ , etc., and then adjust Z- to return to position Z ₀ where the amount of spread is minimum. ACT38
This is done by driving the .

By the method exemplified above, the projection image forming surface of the projection lens 6 and the aperture surface of the minute aperture 8 (chromium layer 21)
can be matched. In this method, the contrast of the projected image itself is detected by a photoelectric detector 9 installed on the stage 7.
The S/N ratio of the signal is high, and the absolute focal position can be detected accurately. Next, while maintaining the height of the aperture surface (chromium layer 21) when the contrast of the projected image is maximized, the surface of the chromium layer 21 is detected using the gap sensor 12 shown in FIG. The detection signal indicates the in-focus state,
For example, calibrate with IF31, CPU30, etc. so that it becomes 0V. Once the detection offset is canceled through this calibration, regardless of whether the projection lens 6 is adjusted or replaced, a clear pattern will always be produced on the wafer 10 by focusing using the gap sensor 12 and AFD 39. can be transcribed into

As described above, in this embodiment, the reticle 5 shown in FIG.
The in-focus position can be checked by contrast detection at various positions within the effective exposure area of the projection lens 6 using the plurality of cross marks. Surface curvature), depth of focus distribution, etc. can be measured immediately. Therefore, the inclination of the optical axis of the projection lens 6 with respect to the movement plane (xy coordinate system) of the stage 7 can also be confirmed by the measurement data.

Furthermore, in the above embodiment, the mark on the reticle 5 is not limited to the cross mark;
It may also be a mark formed in an L-shape 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.

Although the minute openings 8 are also two slit openings 8a and 8b, they may be integrated into an L-shaped minute opening. In this case as well, the relationship between the sizes of the L-shaped slit opening and the projected image of the cross mark is preferably set to d<D<h, as described above.

Furthermore, if the reticle holder 15 shown in FIG. 1 is made movable up and down in the optical axis direction of the projection lens 6, the projection lens 6 does not need to be moved up and down when adjusting the magnification, which simplifies the mechanical configuration. becomes. In this case, as a matter of course, the best imaging plane (reticle conjugate plane) of the projection lens 6 also moves up and down.
Calibrate the focusing system AFD39 etc. in the same way.

As described above, according to the image plane position detection means of this embodiment,
The projection magnification and projection distortion of the projection optical system can be measured quickly and accurately, which is not only useful for adjustment during the manufacturing of exposure equipment, but also allows for partial replacement of the projection optical system.
Projection magnification and projection distortion can be measured quickly and easily even when performing measurements at the location where LSIs are manufactured.
There is an advantage that adjustment at the time of replacement can be completed quickly.

Furthermore, if you are concerned about projection performance, such as after transporting the exposure equipment or accidentally giving it a strong impact, you can easily check the projection performance using the image plane position detection means. .

Furthermore, this embodiment can not only be applied during manufacturing, service, or maintenance as described above, but also can be included as part of the normal operation of the exposure apparatus when it is desired to finely adjust the projection magnification by a predetermined amount. . For example, when the pattern of the nth layer is formed and the pattern of the (n+1)th layer is exposed,
When the entire wafer is stretched uniformly, the projection magnification can be easily measured using the photoelectric detector 9 of this embodiment, so it is easy to check after making small changes to the interval L in FIG. 1 of the embodiment. This can be dealt with by realizing an exposure apparatus with variable magnification and measurable projection magnification. According to such an exposure apparatus, the projection magnification can be changed in accordance with the expansion and contraction of the entire wafer. That is, if the wafer is stretched by k times, the projection magnification can be increased from the original value N times to kN times. To do this, it is necessary to make sure that the measured magnification is the desired amount.
It is sufficient to provide a driving means for relatively moving the projection lens 6 and reticle 5 in the optical axis direction based on a command from the CPU 30.

A device with a variable projection magnification that can be set accurately is not only effective when dealing with wafer expansion and contraction as described above, but also with other exposure devices, such as those with a soft X-ray radiation source. It is also effective to use an X-ray exposure apparatus that performs proximity exposure at a finite distance apart and a projection exposure apparatus in combination for manufacturing one device.

In other words, a circuit pattern on a certain layer is formed using an exposure device such as an X-ray exposure device in which the magnification between the pattern dimension on a mask and the pattern dimension printed on a wafer differs by a minute amount with respect to an integer value. When printing circuit patterns on a wafer and printing circuit patterns on other layers using an optical projection exposure device, the magnification relationship between the two at the time of manufacturing the mask or reticle used should be a perfect integer multiple or an integer fraction.
Even if it is doubled, it can be easily handled by adjusting the magnification on the projection exposure apparatus side, which has the advantage of making it easier to manufacture masks or reticles.

〔Effect of the invention〕

As described above, according to the present invention, the focus adjustment means detects the height position of the substrate (wafer) surface independently of the projection optical system and moves the stage means up and down so that the height position is at a constant position. Since it is calibrated to match the substrate to the projection image plane (mask conjugate plane), even if the exposure operation is performed after adjusting the magnification of the projection optical system, adjusting the image distortion, etc., the mask can be placed on the substrate with extremely clear contrast. An image of the pattern is formed.

In other words, the optical characteristics of the projection optical system itself or the projection conditions (such as the distance between the mask and the projection optical system) can be freely adjusted to create the best overlapping state, and pattern exposure can always be performed with the best resolution. , significant effects such as improved yield in semiconductor device manufacturing can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a projection exposure apparatus according to an embodiment of the present invention, FIG. 2 is a plan view showing a test reticle used for measuring optical characteristics, and FIG. A plan view of a light shielding member for forming an aperture, FIG. 4 is a block diagram showing the control system of the exposure device, and FIG. Figure 6 is a diagram showing the relationship, and Figure 6 is a diagram showing the light intensity distribution when the projected image of the mark is photoelectrically detected.
7 and 8 are diagrams for explaining focus detection using a minute aperture and a photoelectric detector. [Explanation of symbols of main parts], 5...Reticle,
6... Projection lens, 7... Stage, 8... Minute aperture, 9... Photoelectric detector, 12... Gap sensor, 30... CPU, 13, 34... Laser interferometer.

Claims (1)

[Scope of Claims] 1. A projection optical system for forming an image of a pattern formed on a mask onto a photosensitive substrate; an apparatus for exposing an image of the pattern onto the photosensitive substrate after performing focusing by moving the stage means in the optical axis direction, the apparatus comprising: a stage means for moving in the optical axis direction; has a sensor for detecting a change in the position of the surface of the photosensitive substrate in the optical axis direction, and the stage means is configured to maintain a substantially constant distance between the photosensitive substrate and the projection optical system according to the detection result of the sensor. a focus adjusting means for controlling movement in the optical axis direction of the stage means; having a surface that is provided on a part of the stage means and can be detected by the focus adjusting means, and having a photoelectric detection section on a part of the surface; and image plane position detection for detecting the position of the image forming plane of the projection optical system in the optical axis direction by receiving a part of the pattern image of the mask projected by the projection optical system by the photoelectric detection unit. A projection exposure apparatus comprising means for calibrating the focus adjusting means based on a detection result of the image plane position detecting means. 2. The image plane position detection means includes a light shielding member that is arranged substantially parallel to the photosensitive substrate and has a slit-shaped micro-aperture formed in a part thereof, and a light-shielding member that detects the micro-aperture among the light forming the pattern image. A photoelectric detector that receives the transmitted light, and a photoelectric signal from the photoelectric detector,
Claim 1, further comprising a control system that evaluates the stage means while moving it in the optical axis direction to identify a position in the optical axis direction where the contrast of the pattern image is the best. The device described. 3 The surface of the light shielding member is set at the position in the optical axis direction where the contrast of the pattern image is the best by the image plane position detection means and the stage means, and the surface of the light shielding member is set at the focal point. 3. The apparatus according to claim 2, wherein when detected by a sensor of the adjustment means, the detected offset is corrected so that the focus adjustment means indicates a focused state. 4. The projection optical system includes an optical element movable in the optical axis direction, a plurality of mark patterns are formed on the mask at positions spaced apart by a predetermined interval, and a micro-aperture of the image plane position detection means and a photoelectric By detecting the positional relationship of each projected image of the plurality of mark patterns with a detector, the magnification error and distortion aberration of the projection optical system are determined, and based on the results, the optical system of the projection optical system is determined. 3. The apparatus according to claim 2, wherein the focus adjustment means is calibrated after the magnification error and distortion are adjusted by moving the element.