JPS6026343A - Projection exposing device - Google Patents

Abstract

PURPOSE:To enable detection of positions on an image formed plane by relatively moving a photoelectric detector and the optical image of fine line elements through an optical system in a plane perpendicular to the optical axis, and generating, in plural times, photoelectric signals obtained when the optical image and a slit are aligned. CONSTITUTION:A luminous flux past the second condenser lens 3 illuminates a reticle 5 as a mask. Plural light transmitting marks M11a-M13a are described on the underside of the reticle 5. The luminous flux l1 past the mask falls on a projection lens 6 as an image forming optical system. The flux l1 is converged through the lens 6 and the flux l2 is emitted and focused on a slit plate 8 having plural fine openings movable 2-dimensionally. A photoelectric signal good in S/N can be obtained and exact focused positions can be precisely measured in a short time by relatively scanning with a photoelectric detecting means having plural fine openings.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an exposure apparatus capable of measuring the optical characteristics of an imaging optical system, and more particularly, to an exposure apparatus that projects and exposes a mask pattern of an integrated circuit onto a semiconductor substrate. The present invention relates to a projection exposure apparatus that is capable of measuring characteristics of a projection optical system, such as the inclination of an image plane and the 4I curve.

(Background of the Invention) The miniaturization of large-scale integrated circuit (LSI) patterns is progressing year by year, and reduction projection exposure equipment has become popular as a device for printing circuit patterns that satisfies the demands for miniaturization and has high productivity. I've been doing it.

In these devices that have been used in the past, a reticle pattern that is several times (for example, 10 times) the size of the pattern to be printed onto a silicon wafer (hereinafter referred to as Ueno) is reduced and projected by a projection lens, and is printed once. What is printed by this exposure is an area smaller than a square with a diagonal length of 14 mm on the sea urchin. 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, several layers or more of patterns are sequentially formed on the surface of the sea urchin, 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 is no longer something to do,
It becomes impossible to perform the functions of the LSI. For example, 1μ
For a circuit with a minimum line width of m, an overlay error of about 0.2 μm is allowed at most. Among the causes of this overlay error, those caused by the exposure device are (1
) Projection magnification error, projection distortion, curvature and tilt of the image plane, and (2
) is the relative positional shift between the projected image and the sea urchin. the above(
The cause of distortion in 1) is the distortion aberration of the projection optical system. On the other hand, if the light beam on the reticle side of the projection optical system is not telecentric, the magnification error can be reduced by changing the distance between the reticle and the principal point (principal plane) of the projection optical system. In the case of a rack, components inside the projection optical system (optical members such as lenses)
can be made smaller by relatively shifting the position in the optical axis direction. Therefore, unless the distance between the reticle and the projection lens and the relative positions of the components inside the projection lens change, the error caused by cause (1) is constant and can be said to be a systematic error. On the other hand, errors due to cause (2) include many random error factors, and alignment (
This is the main cause of variation in overlay errors each time alignment is performed.

Now, the error in (1), which is a systematic error, is
If you adjust the equipment so that the value is below a certain value while measuring it, you can maintain a stable small value over a long period of time. I have to keep it. From before (
Among the errors in 1), the measurement of the curvature and inclination of the image plane is caused by measuring the image of a reticle with mark patterns drawn at multiple predetermined positions, a so-called test reticle, by slightly increasing the distance between the wafer and the projection lens. This was done by burning the photoresist on the Ueno film while changing the marks, measuring the resolution and coordinates of the printed mark's resist image, and adjusting the resolution and projection distortion. However, this method requires time and effort to expose the test reticle pattern on the wafer and develop it, and also requires the use of a scanning electron microscope or the like to measure the resist image of the mark. There was a drawback that it was not possible. In addition, in recent years, a photoelectric detector with a slit has been installed on the stage, and by scanning the edges of the projected pattern image and examining the rise of the photoelectric signal, the optical axis that provides the image with the best contrast has been developed. A method of detecting the position of the direction and finding the image forming plane of the projection optical system is disclosed in an earlier application by the applicant, Japanese Patent Application No. 57-20485.
It is disclosed in No. 6. However, the method disclosed herein cannot necessarily be said to be able to detect the imaging plane with high precision. In other words, if the slit width of the photoelectric detector is made approximately equal to the minimum line width that can be resolved by the projection optical system, it should be possible to detect the contrast of the pattern image with high precision. ,
This has the disadvantage that the S/C ratio of the photoelectric signal is lowered, making highly accurate detection impossible.

(Objective of the Invention) An object of the present invention is to solve these drawbacks and provide a projection exposure apparatus that can easily and accurately detect the position of an imaging plane, field curvature, inclination, etc.

(Summary of the invention → The present invention arranges a plurality of slits in a photoelectric detector with slits, and also arranges a plurality of microline elements on a mask imaged by an imaging optical system.Then, the photoelectric detection When the light image of the micro wire element and the optical image formed by the imaging optical system of the micro wire element are moved relative to each other in a plane perpendicular to the optical axis, and the optical image of the micro wire element and the slit (micro aperture) of the photoelectric detector are aligned. The photoelectric signal obtained at The technical point is to do so.

(Embodiment) 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 illumination light is provided at a position where the light is converged. The light beam 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 are placed on the lower surface of the reticle 5 at a plurality of predetermined positions.
11 to MI3 are depicted. Here, only three marks are shown schematically. Marks M, -M on this reticle 5
, 3 enters a projection lens 6 as an imaging optical system whose optical characteristics are to be measured. 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 11 is focused by the projection lens 6 and becomes a light beam 12.
and ejects. Note that the distance between the lower surface of the reticle 5 and the principal plane 6a of the projection lens 6 is L. i, te, luminous flux β
2 is imaged onto a slit plate 8 having a minute slit opening provided on a two-dimensionally movable stage 7. Furthermore, the light passing through the slit plate 8 is photoelectrically converted by a photoelectric detector 9 provided on the stage 7. This slit plate 8
and the photoelectric detector 9 constitute a photoelectric detection means. Further, the stage 7 usually carries a semiconductor wafer 10 thereon and moves two-dimensionally, and the wafer 10 is placed on Lh of a wafer holder which moves two-dimensionally together with the stage 7. , will be done.

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 1
It moves up and down so that the projected image of the lld projection lens 6 is formed on the surface of the wafer 100, that is, so that focusing can be performed. Further, the slit opening surface of the slit plate 8 is set to almost match the height of the surface of the wafer 2, and the slit plate 8 and the photoelectric detector 9 are integrated with each other as the wafer holder 11 moves. It is installed so that it can move up and down.

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 opening surface of the slit plate 8). Automatic focus adjustment is possible using the gap sensor 12 and the vertical movement of the wafer holder 11. When printing a circuit pattern on the wafer 10, the height of the surface of the wafer 100 is detected and a projected image with high contrast is always transferred. can.

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 left-right direction in the paper, it is perpendicular to the X-axis that forms the movement plane of the stage 7 (
Similarly, a laser interferometer and a reflecting mirror are provided in the y-axis direction (perpendicular to the plane of the paper).

These laser interferometers successively measure the coordinate values of the stage 7 with respect to a predetermined origin.

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
It is movable dimensionally and can be driven and controlled by a reticle alignment control system, which will be described later, to position the reticle 5. Incidentally, the projection lens 6 is fixed by a holding means 16 formed integrally with the stage 70 base.

Now, FIG. 2 is a plan view of the reticle 5 shown in FIG. 1. The reticle 5 is made by forming a chrome layer or a low-reflection chrome layer as a light shielding part on the entire lower surface (the surface facing the projection lens 6) of a transparent substrate such as glass, and then peeling off the chrome layer at the part that will become the mark M to transmit light. It is a gendered thing. As shown in Fig. 2, the orthogonal coordinate system X whose origin is the center 0 of the reticle 5
When Y is determined, nine marks M11 to M33 are provided in a 3×3 square matrix according to this coordinate system XY. Each of the marks M11 to M33 consists of a collection of three minute slits extending in the X direction and the Y direction.

For example, Mark M1! mark M11a in which three minute slits extending in the Y direction are arranged in the X direction, and mark MI in which three minute slits extending in the X direction are arranged in the Y direction.
B). Other eight marks M12, M, 3
, M2. , M22, M2S, MB, ,
MB2. The same applies to M2S. still,
As shown in Fig. 2) 7-ri M +za + Mz2
a + Ma2a o center o minute slit is coordinate system X
Located on the YOY axis, mark 8% + b + M,,,,
b, The small slit in the center of M23b is on the X axis.

The positions of these nine marks MII-M33 have been accurately measured in advance with a resolution of 061 μm using a precision position measuring device.

Note that the nine marks M, , -M, , will be generally referred to as marks Mij (where i and j are 1 to 3) below.

On the other hand, FIG. 3 shows a plan view of the rib i/plate 8, and FIG. 4 shows a sectional view taken along the line A--A in FIG. Slit plate 8i
A chromium layer 21 serving as a light-shielding portion is deposited on the entire upper surface of the -J glass plate 20 to a thickness of about 0.1 μm, and then the portion that will become the slit opening is removed by etching or the like to make it transparent. As shown in FIG. 3, the slit plate 8 is formed with three minute slit openings 8a extending in the y direction and three minute slit openings C1B extending in the X direction. The width of each slit in the slit opening F'sa and sb is the projection l.
It is set to be approximately equal to the minimum line width that can be resolved by lenses UK, for example, 1μ+1.

Note that the X direction and the X direction of the slit plate 8 are determined to be the same as the moving coordinate system of the stage 7 31 . and,
The slit opening 8a is necessary to detect the projected image of the mark M i j B, and the slit 1) old ZJ 81) p;
The projection image of one mask Mijb is detected. The light receiving surface of the photoelectric detector 9 shown in FIG. 1 is located on the F side of the glass plate 20 of the slit plate 8.

(Next, the control system for controlling the device shown in Figure 1 is
This will be explained based on the block diagram shown in FIG.

The entire device is equipped with a microcomputer (including memory, etc.) to enable program control and various arithmetic processing.
It is centrally controlled by a CPU (hereinafter referred to as CPU) 30. The CPU 30 exchanges various information with surrounding detection sections, measurement sections, or drive sections via an interface 31 (hereinafter referred to as IF 51).

Now, the image soter drive unit 32 opens and closes the shutter 4 in response to instructions from the CPU 3Q, and the reticle alignment control system 33 (hereinafter referred to as R-ALG 33) adjusts the reticle 5 to a predetermined position with respect to the optical axis of the projection lens 6. The reticle boulder 15 is moved and aligned so that the reticle boulder 15 is aligned. Although the R-ALG33 is not necessarily required in the embodiment of the present invention, the reticle 5
The following R-ALG 33 is provided in this apparatus because the positioning can be performed more accurately and faster than by visual manual operation using alignment marks on the reticle 5.

On the other hand, in order to measure the coordinates of the stage 7, the positional information of the stage 7 in the X direction read by the laser interferometer 13 and the positional information of the stage 7 in the X direction read by the laser interferometer 34 are Both CPU via 11F'31
Sent to 30. Also, in order to move the stage 7 two-dimensionally, an X-axis drive section 35 that drives the stage 7 in the X direction is provided.
(hereinafter referred to as X-ACT 35) and a y-axis drive unit 36 (hereinafter referred to as Y-ACT 36) that drives the stage 7 in the X direction are provided to operate according to instructions from the CPU 30. These stage 7, X-ACT35, Y
- The ACT 36 constitutes a first moving means. - The θ-axis rotation drive unit 37 (hereinafter referred to as θ-ACT 37) for slightly rotating the wafer holder 11 on the stage 7
, wafer holder 11, photoelectric detector 9, and slit plate 8
In order to vertically move the C
It operates according to instructions from PU30. Then, the focus detection section 39 (hereinafter referred to as AFD 39) inputs the signal from the gap sensor 12 shown in FIG. The focal position shift information is sent to the CP via the IF51.
Output to U'30.

In addition, a terminal device 40 such as a monitor CRT or a printer for displaying measurement results, operating status, etc.
It is connected to the CPU 30 via F51.

In addition to the various control systems mentioned above, an 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.

Finally, FIG. 6 is a circuit block diagram showing an example of a circuit for detecting the position of the imaging plane included in the IF 31.

In FIG. 6, the same parts as in FIG. 5 are given the same reference numerals.

Up/down pulses SP (hereinafter simply referred to as pulses SP) generated from the laser interferometer 13 for each unit of movement of the stage 7 in the X direction are sent to a counter 10 for position measurement in the X direction.
Enter 0 and it will be counted. Although not shown, similar pulses are also generated from the laser interferometer 34, and these pulses are similarly counted by a counter.

Now, the count value of the counter 100 is read into the CPU 30 as position information Dx of the stage 7 in the X direction.Meanwhile, the photoelectric signal of the photoelectric detector 9 is amplified by the amplifier 101, and then the signal S circuit:
+o2 (hereinafter referred to as S/H1o2) is done manually. S/
)f102 is for ±sampling the signal S in response to the pulse SP of the laser interferometer 13, and the sampled signal S is converted into digital data in synchronization with the generation timing of the pulse SP. (hereinafter referred to as ADC 103) is manually operated. The ADC 103 outputs the digital value of the signal S as information Df to C1) U knee IQ.

Further, the sensor 104 detects the amount of drive of the Z-ACT 38, thereby controlling the slit plate 8 and the wafer holder 1.
1's vertical movement position, that is, X y , and the position in two directions perpendicular to the IF plane are detected, and the detected value t is input to an analog-digital converter 105 (hereinafter referred to as ADCI05). ADC105 is a digitally converted slit plate 8
, C with the position of the wafer holder 11 in the Z direction as information DZ.
Output to PU30.

In addition, C1) 030 has a memory circuit 106 (hereinafter referred to as RAM 106) that can store various information, calculated values, etc.
is connected.

In addition, the above amplifier 101, S/H102, ADCI Q
3. The sensor 104, ADC 105, and CPU 30 constitute means for detecting the image plane position of the projection optical system.

Next, the operation of measuring the optical characteristics of the projection lens 6 using the exposure apparatus described above will be explained.

First, R-AL the reticle 5 set in the device.
Position using G33. At this time, the projection lens 6 is aligned so that its optical axis passes through the origin 0 of the coordinate system XY on the reticle 5. Roughly speaking, the X and Y axes of the coordinate system XY are the X and Y movement directions of the stage 7, that is, the laser interferometer 13.3
The position of the reticle 5 is determined so that it is parallel to each of the measurement axes X + y (including cases in which they coincide).

Thereafter, the CPU 30 starts measurement according to the flowchart shown in FIG.

Step 200 First, the CPU 30 reads the position information from the laser interferometers 13 and 14, and
The stage 7 is moved by driving. Part 1. Then, position the slit plate 8 so that it is directly below the gap sensor 12. After that, gap sensor = 12 and AFD
39 detects the two height positions of the surface of the slit plate 8, and the CPU 30 drives the Z-ACT 38 so that the imaging plane of the projection lens 6 and the surface of the slit plate 8 coincide. As described above, the slit plate 8 is focused on the imaging plane of the projection lens 6. Then, the shutter drive unit 32 opens the shutter 4 to move the reticle 5 to the illumination 1.
2. Project the image of mark Mij.

Next, the stage 7 is moved to position the projected image Mij' of the mercury MiJ on the slit plate 8.

At this time, the relationship between the projected image Mi) and the slit plate 8 is determined as shown in FIG.

In FIG. 8, the projected image M of the mark M2□ in the center of the reticle 5
22a', M22b' and slit openings sa, sb
The positional relationship is shown.

Here, the slit opening I 8a+8b and the size and shape of the projected image Mi3 will be described in detail.

The slit opening 8a is composed of three slit openings 8al + 8a2 + 8a3 having the same shape and having a width W and are regularly arranged at a period d. Slit opening 8b
Similarly, there are three slit openings 8b+ with a width W.

It consists of 8b2 and 8b3 arranged regularly with a period d.

Furthermore, the projected image M22a' is also a slit-shaped image L with a width of approximately W.
xl, Lx2, and Lx3 are lined up at a period of d, and the projected image M22b' is similarly shaped like slit-shaped images "Vl+"I2+''i3 with a width of approximately W are lined up at a period of d. There is.

The width W of the slit is set equal to the line width value of the resolution limit of the projection lens 6, for example, 1μ, and the period d is twice W. Here, d does not necessarily have to be twice W, but (
It is desirable that dw) be closer to the line width value of the resolution limit, since this increases the sensitivity of measurement of the imaging plane of the projection lens 6, that is, focus detection. In addition, the number of slits in each of the slit openings 8a + 8b does not necessarily have to be three.
Although it is preferable to have a larger number because the S/N ratio improves due to the increase in the optical signal and the measurement accuracy increases, here, in order to simplify the explanation, only three are used. In addition, the slit openings 8aI, 8
a2゜8aa does not have to be the same width, but the image Lx
I.

and slit opening 8a1, image Lx2 and slit opening IT]8
a2, the width of the image Lx3 and the slit opening 8a3 need to be approximately the same.

Next, the stage 7 is moved in the X direction from the position shown in FIG. 8 to form images LX 1 + LX 2 + LX 3
A signal obtained by the photoelectric detector 9 when scanned by the slit apertures 8all 8a2 + 8aa will be explained. Figure 9(a)'(b) is (d I-rX
3 + LX 2 + LX 3 shows the light intensity distribution in the X direction of The intensity distribution is shown [7]. In the focused state, each intensity distribution of the images LX I, IjX 2 + 1iK3 is Ix, l rX2 + rX3,
The rising and falling parts are sharp, and the bottom parts (minimum values) of the distributions Ix1, Ix2, and Ix3 are clearly separated in the X direction as well.

On the other hand, since the images Lx1, Lx2, and Lx3 are set to the width of the resolution limit of the projection lens 6, if even the slightest deviation of focus occurs, the distribution Ixl will change as shown in FIG. 9(b).

The rising and falling parts of Ix2 and Ix3 become gentle, and the bottom parts are not separated but are continuous. Note that these distributions Ix1. Beak position xi of Ix2 and Ix3
I X2 + x3 are images Lxl, Lx2, respectively
It is clear that it represents the projection position of Lx3 in the X direction.

Now, the projected image M22a' of such a light intensity distribution is scanned in the X direction with the slit opening 8a. Then, the signal S from the photoelectric detector 9 has five peaks Pl as shown in FIG.
-P[l appears. In FIG. 10, a signal Sa indicated by a solid line indicates an in-focus state, and a signal sb indicated by a broken line indicates an out-of-focus state.

In this signal S, the peak Pl is caused by the overlap of only the slit opening 8a3 and the image Lxl, and the peak P2 is caused by the overlap of the slit opening 8a3 and the image Lx2, and the overlap of the slit opening 8a2 and the image Lx1. The peak P3 is the slit opening 8al to 8aa, respectively, and the image Lxl
- This is caused by overlapping with Lx2.

Now, returning to the explanation of FIG. 7, when scanning the stage 7 in the X direction from the position of FIG. 8, the CPU 30&j position information D
x is read and the scanning start position of the stage 7 in FIG. 8 is memorized. Then, information Df of the sampled signal S is sequentially sent to the CPU in response to the pulse SP generated with scanning.
30 (or not), the data is stored in the RAM 106 address by address.

At this time, the pulse SP is sent to the RAM via CPtJao.
It is used for updating and accessing address 106.

Step 202 Next, the CPU 3o examines the fc information Df stored in the RAMI 06, and finds the position xO of the peak P3, which is the largest among the peaks P and -P5. Since the scanning start position of the d1 stage 7 is known, it can be easily calculated by calculating the number of samples (the number of pulses SP) from the start position until the peak P3 appears.

Step 203 Now, when the position XQ of the maximum peak P3 is reached, the stage 7 is set to the scanning start position again, and then the Z-AC
The slit plate 8 is moved downward in two directions (in the direction away from the projection lens 6) by T38. Note that the amount of downward positional shift is determined by the focal depth of the projection lens 6 (for example, 5 doors).
It is destined to go inside.

The operation of actually precisely measuring the position of the imaging plane of the projection lens 6 starts from the following steps.

In this step 204, the slit plate 8 is moved in the Z direction by ΔZ(
Is the depth of focus increased by a fraction of the value (for example, 05 μm)? b Repeat m times (judge whether it is .

Next, the positions of the slit plate 8 in two directions are memorized.

This is done by the CPU 3Q storing the information Dz of the ADC 105.

Next, stage 7 is scanned, and as in step 201,
The sampled information Df is sequentially stored in one processor 4106.

Step 207 Next, the CPU 30 calculates the magnitude of the variable W1 component all of the central peak waveform P3 in the signal S based on the stored information Df. For example, as shown in FIG. 10, the difference al between the maximum value of a peak waveform P3 such as g sb and the minimum value of the bottoms on both sides of the peak waveform P3 is calculated and stored.

Then, the X-ACT 35 is driven to reset the i+f and digit shift to the scanning start position.

Next, the slit plate 8 is raised by ΔZ using the Z-ACT 38. Thereafter, the process is repeated again from step 204. As a result, the modulation component an is detected every time the slit plate 8 rises by ΔZ, and when m times are completed in step 204, the process proceeds to the next step 210.

Step 210 Now, the relationship between the modulation component an determined in this way and the position of the slit plate 8 in the Z direction is as shown in FIG. Therefore, the CPU 3Q detects the position Z5 where the modulation component an is maximum and stores information Dz corresponding to the position z5.

Step 211 Now, through each of the above steps, the focal position of the projected image M22a' of the mark M22 has been measured.

Next, measurements are performed on the other marks M i j a in exactly the same manner. If measurement has been completed for all marks, the measurement operation ends, but if there are marks that have not been measured yet, the process proceeds to the next step 212.

Step 212 Here, the stage 7 is moved so that the slit openings ga and 8b are positioned as shown in FIG. 8 with respect to the projected image of the mark that has not yet been measured.

Thereafter, similar measurements are repeated from step 201.

In the above manner, the local position of the number of image forming surfaces of the projection lens 6 in the Z direction has been measured. Further, although the above operation was performed for the marks M i and ia , the stage 7 is subsequently moved in the Z direction so as to scan the projected images Mi and ib' of the mark Mijb with the slit opening 8b, and the projected image Mijb' Measure the position 1a of the image plane of 0 mark MijO projected image Mi ja/, Mi jb']Z
If the positions in the directions are Zija and Zijb, then the position 1Zi
ja and Zijb, the state of the projection surface of the projection lens 6, that is, the inclination and curvature of the imaging surface can be determined.

Of course, since the positions of the projected images Mija' and Mijb' are determined from the position of the stage 7 where the signal S from the photoelectric detector 9 is maximum (for example, the position Xo as shown in FIG. 10), the projection area of the projection lens 6 A map of the inclination, curvature, etc. of the imaging plane can be created based on the coordinate values of the projected image Mij' therein.

Furthermore, information regarding astigmatism can also be extracted based on the position information Zija and Zijb. However, when measuring astigmatism, the slit of the mark Mij located other than the center O of the reticle 5 as shown in FIG. The direction of growth,
It is better to use marks in two directions, one in the radial direction from the center O and one in the perpendicular direction.

Figure 12 Deke mark MIIIM131M311M33
Each slit is provided at an angle of 45° or 135° with respect to each axis XY of the coordinate system XY of the reticle 5.

Therefore, when using such a reticle 5, the slit plate 8 is opened as shown in FIG.
In addition to b, 45° or 135° with respect to the coordinate system xy
The slit openings 8c and 8d are provided so that the direction of the slit is inclined by the same amount. And mark M in Fig. 12.
, M, 3. M3. , M33, by scanning the slit apertures 8 c + 8 d, the same measurement as in the previous embodiment can be performed.

In the above embodiment of the present invention, the position of the stage 7 was measured using a laser interferometer 13.34.
This is to accurately detect the projection position of the mark Mij on the reticle 5. Therefore, when simply detecting the position of the image plane of the projection lens 6 in the Z direction, a position measuring device such as the laser interference H[ is not necessarily required.

Furthermore, although the number of slits in -=t-ri Mi ja and Aii jb was made to match the number of slits in each of the slit openings 8a and 8b of the slit plate 8, it is not necessary to do so.
As long as a photoelectric signal can be extracted with a good S/N ratio, it is no problem to combine the slits on the projection image side and the slits on the slit plate 8 in any number.

Furthermore, each slit of the marr Mij and the slit openings 8a l 8b of the slit plate 8 were provided at a constant pitch,
They may be provided at random pitches. That is, mark Mi
Projected image M i j ' of j and slit opening 1'' 8a or 8
When b is aligned accurately, each slit image of the projected image Mij' and each slit of slit opening c'+Ba, 8b overlap one to one, and if the alignment shifts even slightly, they overlap each other. A random pitch may be used such that the number of slits that fit together rapidly decreases.

Now, the slit plate 8 actually has slits open [-18a,
In addition to 8b, marks are provided for setting the reference position of the stage 7 and calibrating the alignment optical system. 14th
The figure is a plan view of the slit plate 8. In FIG. 14, a slit opening Ba extends parallel to each of the xyOy axes and the X axis of the coordinate system determined to match the movement coordinate system of the stage 7.

8b is provided in the same manner as in the previous embodiment. moreover,
A single slit 8e18f extending in the y- and and is provided. Also, mark 81
slit opening 8a, sleeve) 8e l lattice pattern 8
The mark 8j indicates the center of the slit opening Bb, the slit 8f, and the lattice pattern 8h in the X direction.

Above, slit opening 8 a + 8 b s slit 8
e.

8f, grid pattern 8g, 8h and mark 8t.

The chromium layer on the surface of the slit plate 8 is removed by etching or the like, so that both of the plates 8j and 8j become optically transparent.

Here, I will explain how to use the Slima I/board 8 1f45f.

The slit openings 8a and 8b are used to measure the height position of the image plane of the projection lens 6, as described in the previous embodiment.゛ma/kosuri month-8e, 8f is reticle 5
and a so-called TTL alignment optical system (hereinafter referred to as step monitor optical system) that directly observes the overlapping state of the mark on the reticle 5 and the mark on the wafer 10- through the projection lens 6. It is used for calibrating the optical system and positioning each optical system when inserting and removing it into the projection optical path. The slits 8e and 8f are imaged by a television camera or the like via a reticle alignment optical system or a step monitor optical system, and automatic position detection is performed based on the image signal. Therefore, the slits 8e and 8f are designed in consideration of the image resolution of the television camera.
The width and length are determined to be appropriate for the imaging condition.

Furthermore, the grid patterns 8g and 8h are determined to be the same as the wafer fist alignment marks provided on the wafer 1°. Generally, as the manufacturing process progresses, irregularities are formed on the wafer surface due to circuit patterns. Therefore, it is convenient for alignment to provide marks having a shape different from those of the circuit patterns. That is, in the exposure apparatus shown in FIG.
- When an alignment microscope is installed and the wafer is aligned using this microscope, so-called off-axis wafer alignment is performed, when calibrating by measuring the distance and position between the optical axes of multiple wafer alignment microscopes. , the diffracted light from the grating patterns 8g and 8h may be detected.

Therefore, the slit plate 8 shown in FIG. 14 is used to detect the height position of the image plane, and also serves as a reference mark for setting the reference of the alignment optical system of the exposure device or a mark for determining the reference position of the stage 7. It is also used as.

Now, since the inclination of the image plane can be accurately determined by the slit openings 8a + 8h, a so-called leveling mechanism is used to correct the inclination of the transfer area on the wafer each time a pattern is exposed by step-and-repeat. In an exposure apparatus incorporating a
It becomes possible to perform leveling so that the image plane and the wafer plane coincide. In this case, the entire surface of one transfer area,
In an exposure apparatus equipped with a high-resolution projection lens that always exposes a circuit pattern that is in focus and has a small depth of focus, there is an advantage that the yield of semiconductor device manufacturing can be significantly improved.

Furthermore, when the position of the image plane coincides with the slit opening 8, the slit plate 8 is detected by the gear sensor 12.
If the height position information is calibrated to indicate that the image is in focus, there is an advantage that the detection center of the gap sensor 12 can be prevented from being deviated due to long-term trits or the like.

In the above embodiment, each slit image of the mark Mij and the slit openings 8a and 8b of the slit plate 8 were located parallel to each other, and the stage 7 was scanned in a direction perpendicular to the extending direction of the slits. As shown in FIG. 15, a scanning trajectory l may be determined such that projection images Mija' and Mijb', which are orthogonal to each other, intersect at 45 degrees, and this scanning trajectory 11KG may scan the slit openings 8a and 8b. In this case as well, the slit openings 8a and 8b intersect at rrs9t9, and with respect to the scanning trajectory l, they are determined to intersect with each other at 45.

Then, the projected image Mija' is detected 1 at the slit opening 8a.
The projected image Mijb' is detected by the slit opening 8b.

Furthermore, in order to separate and detect the projection images Mija' and Mijb', the projection images Mija' and Mi
jb' and the distance D2 between the slit openings 8a and 8b are set to be different. In this case, the scanning trajectory l
When shifts in the direction perpendicular to its scanning direction, the interval increases,
also changes, but even if there is a change, the interval 5 and D
It is desirable that the numbers 2 and 2 do not match.

If such a slit group is used for positioning, etc., it is sufficient that the interval D1 coincides with the interval D2 within the range of change of the interval D1 due to the shift of the scanning trajectory l. At that time, the intersection C2 of the slit openings 8a and 81) in the extending direction and the intersection C1 of the projected images Mija' and Mijb' in the extending direction
When the stage is moved so that they match, the photoelectric detector 9
The photoelectric signal of is maximum. Therefore, alignment or position detection can be performed by detecting the maximum value.

Further, in each embodiment, the slit plate 8 and the photoelectric detector 9 are scanned by moving the stage 7 as the Fi first moving means. A similar effect can be obtained even if the projected image Mij' of the mark Mij is moved relative to (. a, Mi
The number of slits M in each slit of j b is made sufficiently larger than the number of slits in the slit openings 8a and 8b, and when the slit openings B'a and Bb scan the projected images of the marks Mija and Mijb, the slit plate is simultaneously The positions of the photoelectric detector 8 and the photoelectric detector 9 in the Z direction may be changed. At this time, the signal S has a modulated waveform as shown in FIG. 16, for example.

In FIG. 16, the horizontal axis represents, for example, the scanning position of the slit plate 8 and the photoelectric detector 9 in the X direction, and the vertical axis represents the magnitude of the signal S. This modulation waveform is from +txs to x6''!
, while the slit opening 8a is scanned by the slit opening 8a.
This is obtained when the Z-ACT 38 is driven so that a moves in the optical axis direction perpendicular to the imaging plane of the projection lens 6.

Still, each peak in the modulation waveform appears when the slit opening 8a and the slit-shaped projected image of the mark Mija are aligned.

Between positions xB and X00, the envelope ES of the modulated waveform reaches its maximum value at position XQ.

Therefore, if we calculate the position information Dz of the slit plate 8 in the Z direction when the envelope Es becomes maximum, the projection lens 6
image plane can be detected. In this case, specifically, in the circuit shown in FIG. 6, an AC amplifier that inputs the signal S from the amplifier 101 is provided, extracts only the AC component from the modulated waveform shown in FIG. By rectifying and smoothing the waves, a signal corresponding to the envelope E, that is, a signal equivalent to the waveform shown in FIG. 11, is obtained. Transfer the sono signal to S/H102, AI) C103 and send it to CPU3Q as digital data and t, -c.
All you have to do is to insert J2. In this case, since the stage 7 only needs to be scanned once, there is an advantage that the position 1d of the imaging plane of the projection lens 6 can be detected extremely quickly and with high precision.

Further, in each embodiment of the present invention, the reticle 5 has been considered as a so-called dedicated reticle for testing, but it is noted that there are marks Mi
, i may be provided.

Roughly speaking, when a mark M1j is provided on a normal reticle, it can also be used as a mark for positioning the reticle with respect to the exposure device a or for aligning the reticle and the wafer.

(Effects of the Invention) As described above, in the present invention, a mark in which a plurality of minute line elements are aligned is imaged by an imaging optical system, and the projected image is relatively scanned by a photoelectric detection means having a plurality of minute apertures. As a result, a photoelectric signal with an extremely good SIN ratio can be obtained, and
Even if the minute line elements or minute apertures are partially irregular, the overall S/N ratio of the optical telegraph obtained will hardly decrease, and the exact imaging position can be precisely measured in a short time. . Therefore, there is an advantage that the inclination and curvature of the imaging plane of the projection optical system can be automatically measured with good reproducibility.

Furthermore, since the position of the imaging plane can be detected accurately using the photoelectric detection means, it is possible to automate the calibration of the automatic focus detection system by detecting the distance between the imaging optical system and the exposure target. .

[Brief explanation of drawings]

FIG. 1 is a schematic overall configuration diagram of a reduction projection type exposure apparatus according to an embodiment of the present invention, FIG. 2 is a plan view of a reticle (mask), FIG. 3 is a plan view of a slit plate, and FIG. 4 is a plan view of a reticle (mask). Fig. 3 is a cross-sectional view taken along the line A-A of the slit plate, Fig. 5 is a block diagram of the control system that controls the exposure apparatus shown in Fig. 1, and Fig. 6 is a reticle using a photoelectric detector and a laser interferometer. 7 is a circuit block diagram for measuring the projected position of the mark and the position of the image plane; FIG. 7 is a flowchart diagram for measuring the position of the image plane;
Fig. 8 is a plan view showing the positional relationship between the projected image of the mark on the reticle and the slit opening of the slit plate, Fig. 9(a),
(t)) is a diagram showing the light intensity distribution of the projected image of the mark on the reticle, Figure 10 is a waveform diagram of the photoelectric signal generated when the projected image of the mark and the slit plate are moved relative to each other, and Figure 11 is the projected image. Fig. 12 shows how the position of the image plane of the lens is detected, and shows the relationship between the position of the photoelectric detector in the optical axis direction and the magnitude of the modulation component of the photoelectric signal. Fig. 12 shows another embodiment of the reticle. A plan view, FIGS. 13 and 14 are plan views showing other embodiments of the slit plate, FIG. 15 is a view showing another positional relationship between the projected image of the mark and the slit plate, and FIG. 16 is a plan view showing other embodiments of the slit plate. FIG. 3 is a waveform diagram showing a modulation waveform of a photoelectric signal obtained in an example. [Explanation of symbols of main parts] 1... Illumination light source, 6... Projection lens,
8... Slit plate, 9... Photoelectric detector 1
3.34...Laser interferometer, 38...Z-axis drive section, 100...Counter 102...Sample/hold circuit, 103°...Analog-digital converter, 30・・・・・・・・・Microcomputer, Ml, ~M33・・・Mark, 8 a + 8 b・° Slit opening Applicant Nippon Kogaku Co., Ltd. Agent Takao Watanabe O・1 Figure □γ 20 N Sai 4 diagram Kai = Shi = = Shikizai q Sen 710 Figure Sai 1? Figure off 1. Tf, figure 14 figure 15 figure-D2-1

Claims (1)

[Claims] an illumination means for illuminating a mask in which a plurality of minute line elements are arranged; an imaging optical system for forming an image of the mask; and an array of optical images of the minute line elements formed by the imaging optical system. a photoelectric detector having a plurality of microscopic apertures that are arranged in substantially the same direction as the microscopic line element and can be aligned with each optical image of the microline elements, and outputs a photoelectric signal according to the light that has passed through the microscopic apertures; a first moving means for relatively moving the microscopic aperture of the photoelectric detector and the optical image of the microline element in a plane substantially perpendicular to the optical axis of the imaging optical system; the imaging optical system and the photoelectric detection; a second moving means for moving the imaging optical system or the microscopic aperture so as to change the distance from the microscopic aperture of the device;
The photoelectric signal obtained when each optical image of the minute line element and each minute aperture of the photoelectric detector are aligned by the moving means is generated a plurality of times by changing the interval by the second moving means. A projection exposure apparatus comprising: position detection means for detecting the position of the imaging surface of the imaging optical system based on a photoelectric signal.