JPH0567555A - Projection exposure method - Google Patents

Abstract

PURPOSE:To enhance the alignment accuracy of the title method by a method wherein a strain amount is detected from a separation distance between marks in a first drawing pattern and a second drawing pattern on a second mask is changed with reference to an optical axis so as to be approximated to the strain amount. CONSTITUTION:A strain amount epsilon in mask detection parts 25, 26 is detected in the following manner: a semiconductor wafer 7 is moved in the X-Y direction; positions of marks 11, 12 which have been formed on the semiconductor wafer 7 in a previous exposure operation are scanned by using the mask detection parts 25, 26 through a projection lens 6; and the positions of the marks 11, 12 are detected. The strain amount epsilon is computed by an operation part 24 from the detected positions of the marks 11, 12 and from reference positions of marks 11, 12, 13, 14; the movement amount in the Z-direction of mask-support- stand tilt control devices 4, 5 is computed; a mask support stand 2 is tilted on the basis of the movement amount; the angle of the normal line of a mask 1 to an optical axis is changed by 360 deg.. Thereby, it is possible to enhance the alignment accuracy of the title method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure method,
In particular, the present invention relates to a technique which is particularly effective when applied to a projection exposure method for transferring a drawing pattern of a mask onto a transfer target substrate.

[0002]

2. Description of the Related Art A projection exposure apparatus is used in a semiconductor wafer manufacturing process. This type of technique is described in, for example, Japanese Patent Laid-Open No. 63-164212.

As described in the above publication, in order to improve the overlay matching accuracy of the projection exposure apparatus, it is necessary to correct the magnification error of the projection optical system.

To correct the magnification error, for example, overlay marks are formed at four corners of a rectangular projection area,
Detecting this alignment mark at the next exposure, detecting the deviation between the detected alignment mark position and the position where the alignment mark originally should be (reference position), and correcting the magnification to match the detected displacement. It is done by.

[0005]

However, as a result of examining the above-mentioned prior art, the present inventor found the following problems.

In the manufacturing process of a semiconductor wafer, the semiconductor wafer is deformed non-uniformly due to stress during heat treatment, and warpage, extension, shrinkage, etc. occur. Regarding this kind of technology, for example, SP I E, No. 126
No. 4, Optical / Laser, Microlithography (1990), pages 54 and 55 (SPIE Vo
l. 1264 Optical / Laser Microlithography
(1990) PP54-55).

As described in the above-mentioned document, when the semiconductor wafer is deformed non-uniformly, the area exposed in the rectangular shape is distorted into a trapezoidal shape or the like. In this case, the conventional correction method described above has a problem in that only two alignment marks at the four corners of the projection area can be overlaid, and overlay matching accuracy is degraded.

An object of the present invention is, in a projection exposure method,
It is to provide a technique capable of improving overlay accuracy.

The above and other features of the invention and the description of the present invention will become apparent.

[0010]

The typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) In a projection exposure method of transferring a drawing pattern of a mask onto a substrate to be transferred along an optical axis, a first drawing pattern of a first mask in which a plurality of marks are formed at reference positions separated from each other. And the separation distance between the marks of the first drawing pattern transferred to the transfer substrate, and comparing the detected separation distance with the reference position distance. , A step of detecting the distortion amount of the first drawing pattern, and changing the second drawing pattern of the second mask or the transfer target substrate with respect to the optical axis by approximating the detected distortion amount to the transfer target substrate. And a step of forming a second drawing pattern of the second mask.

(2) The second drawing pattern of the second mask or the substrate to be transferred is slightly changed with respect to the optical axis.

[0013]

According to the above-mentioned means (1) or (2), the second pattern corresponding to the distortion amount of the drawing pattern of the first pattern is obtained.
By changing the second drawing pattern of the mask or the transfer substrate with respect to the optical axis, the intentionally distorted second drawing pattern is approximated to the first drawing pattern distorted by the distortion of the transfer substrate. Because they can be overlaid,
The overlay accuracy can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The components having the same function are designated by the same reference numerals, and repeated description will be omitted.

The configuration of the projection exposure apparatus of the embodiment of the present invention is as follows.
This will be described with reference to FIG. 2 (side view showing the outline of the reduction projection exposure apparatus of the embodiment of the present invention).

As shown in FIG. 2, the projection exposure apparatus of the present embodiment is a reduction projection exposure apparatus that reduces the drawing pattern formed on the mask 1 by the projection lens 6 and transfers it onto the semiconductor wafer 7. In FIG. 2, solid lines represent the light rays representing the conjugate relationship of the on-axis object points between the semiconductor wafer 7 and the mask 1 and the light rays of the mark detection light. The image forming system of the reduction projection exposure apparatus is telecentric only on the image side (semiconductor wafer 7 side) with respect to the projection lens 6, and is non-telecentric on the light source side (mask 1 side).

The mask 1 is placed on a mask support base 2. The mask support base 2 is tilted in the arrow direction of FIG. 2 by the mask support base tilt control devices 3 and 4 (5), so that the angle between the normal line of the mask 1 and the optical axis changes by a small angle. Mask support table tilt control device 3, 4
The control of (5) is performed by the calculation unit 24. The operation unit 24 is, for example, a logic circuit section and the CPU and a memory unit: is composed of (C entral P rocessing U nit central processing unit). In the memory unit of the arithmetic unit 24, the distance between the exposure regions (9), the area of the exposure region (9),
Data such as reference positions of alignment marks (11 ', 12', 13 ', 14') and the origin of the stage on which the semiconductor wafer 7 is placed are stored.

The semiconductor wafer 7 is mounted on the Z drive table 21. The Z drive base 21 is controlled by the Z drive base control unit 22. The movement of this Z drive base 21 is
It is monitored by the step error detector 23. The information monitored by the step error detector 23 is output to the calculation unit 24. The Z drive table 21 is arranged on the XY drive table 19. The XY drive base 19 is controlled by the XY drive base controller 20. The Z drive base controller 2
Each of the 2 and the XY drive base control unit 20 is controlled by the arithmetic unit 24. These Z drive bases 21, Z
A stage on which the semiconductor wafer 7 is placed is configured by each of the drive base controller 22, the step error detector 23, the XY drive base 19, and the XY drive base controller 20.

In the reduction projection exposure apparatus configured as described above, the step drive error detector 23 or the mark detectors 25 and 26 detect the distortion amount ε of the semiconductor wafer 7. The mark detectors 25 and 26 are, for example, CCs.
D, a photocoupler and the like are formed in a line sensor shape. The information detected by the mark detectors 25 and 26 is
It is output to the arithmetic unit 24. The mark detection unit 25,
When the strain amount ε is detected at 26, the semiconductor wafer 7 is moved in the XY direction by the XY drive table 19 so that the marks 11 formed on the semiconductor wafer 7 during the previous exposure, Position 12 (13, 14)
Through the projection lens 6, the mark detection units 25, 26
Scanning is performed and the positions of these marks 11, 12 (13, 14) are detected. The distortion amount ε is calculated by the calculation unit 24 from the positions of the detected marks 11, 12 (13, 14) and the reference positions of these marks 11, 12, 13, 14. Based on this distortion amount ε, the calculation unit 24 calculates the Z direction movement amount of the mask support table tilt control device 3, 4 (5). The arithmetic unit 24 controls the mask support table tilt control devices 3 and 4 (5) based on the calculated Z-direction movement amount to tilt the mask support table 2,
The angle between the normal line of the mask 1 and the optical axis is changed by 360 degrees. Next, the mask support table tilt control device 3, 4, 5
The configuration of FIG. 3 (a plan view of the main part of the mask support table part), FIG. 4 (a cross-sectional view of the main part of the mask support table tilt control device part) and FIG. The description will be made with reference to each of the main part sectional views shown).

As shown in FIG. 3, each of the mask support table tilt control devices 3, 4, 5 is provided with 3 and 4 at two adjacent corners of the mask support table 2, and one side which is conjugate to this. 5 is provided in the center. Therefore, the mask support 2
Will be supported at three points, and the rattling of the mask support base 3 can be minimized. For example, as shown in FIG. 4, each of the mask support tilt control devices 3, 4, and 5 mainly includes a support 25, a stepping motor 26, and a wedge-shaped moving member 28, respectively. The rotating shaft 27 of the stepping motor 26 has an external thread, and the external thread is fitted with the internal thread 29 of the wedge-shaped moving member 28. Therefore, the rotating shaft 27
Rotation causes the wedge-shaped moving member 28 to move on the support base 25, and as a result, the mask support base 2 moves in the Z direction. Further, as shown in FIG. 5, the mask support base 2 is provided on the support base 30 via the piezoelectric element 31, and the voltage applied to the piezoelectric element 26 is changed to move the mask support base 2 in the Z direction. You can also

Since the mask support table tilt control devices 3, 4, 5 thus constructed move the mask support table 2 independently in the Z direction, the angle formed by the optical axis and the mask support table 2, That is, the angle formed by the normal line of the mask 1 and the optical axis can be tilted by a minute angle with high precision. Also, mask 1
It is possible to accurately maintain the inclination of the normal line to the optical axis. Further, it is shown that when the mask 1 is tilted by the mask support tilt control devices 3, 4, 5 with the position of the projection lens 6 fixed, the distance between the projection lens 6 and the mask 1 is not uniform. ing. Here, since the mask 1 side of the projection lens 6 is non-telecentric, the transfer magnification varies depending on the position in the mask 1, and as a result, the projected image transferred onto the semiconductor wafer 7 is consciously changed. Can be distorted.

Further, the mask support table tilt control device 3, 4,
In the state of tilting the mask 1, the mask 5 can be moved in parallel with the optical axis. In this case, only the projection magnification can be changed without impairing the distortion shape (projection image distortion).

Next, the projection exposure method of this embodiment will be described with reference to FIG.
(Flowchart), FIG. 2, FIG. 6 (plan view of the semiconductor wafer), and FIG. 7 (plan view of an essential part showing the exposure region of FIG. 6 in an enlarged manner). 6 and 7, the strain of the semiconductor wafer 7 is shown larger than the actual strain amount in order to make the diagrams easy to see.

First, the semiconductor wafer 7 is placed on the Z drive table 21. At this time, the orientation flat of the semiconductor wafer 7 and the reference position of the Z drive table 21 are aligned <201>. After that, the back surface of the semiconductor wafer 7 is adsorbed and the semiconductor wafer 7 is fixed to the Z drive table 21.

Next, pre-alignment (preliminary alignment) of the semiconductor wafer 7 is performed <202>. At the time of this alignment, the positions of the marks 11, 12, 13, 14 formed on the semiconductor wafer 7 are detected, and the positions of the detected marks 11, 12, 13, 14 and the Z drive base 21 are detected. Align with the reference position to about ± 1 μm.

Next, the mask 1 and the projection lens 6 are aligned with each other <203>. In this alignment, the center of the mask 1 and the center of the projection lens 6 are aligned.

Next, the projection lens 6 and the semiconductor wafer 7 are aligned with each other <204>. In this alignment, the semiconductor wafer 7 is moved with respect to the projection lens 6 using the projection lens 6 as a reference. The accuracy at this time is about ± 0.1 μm. In this step, as shown in FIG. 6, the semiconductor wafer 7 is deformed from the shape 7 ′ at the previous exposure due to various stresses in the manufacturing process. As a result, the exposure area 9 is also distorted from the shape 9'of the previous exposure.

Here, as shown in FIG. 7, at the four corners of the exposure area 9, the marks 11, 12, 1 formed during the previous exposure are formed.
3, 14 are arranged. These marks 11, 12,
The positions of 13 and 14 are detected by the mark detection units 25 and 26, and the detected position information is output to the calculation unit 24 <205>. These marks 11, 12, 13,
14 is the position (11 ', 12', 13 ', formed in the previous process)
14 ') as a reference position, and the coordinates of the reference position are (X ₁ ', Y ₁ '), (X ₂ ', Y ₂ '), (X ₃ ', Y ₃ '),
(X ₄ ', Y ₄ '). The positions of the marks 11, 12, 13, 14 are changed from 11 ', 12', 13 ', 14', respectively, as the semiconductor wafer 7 is deformed from 7 '. As a result, the coordinates of the marks 11, 12, 13, 14 are (X ₁ , Y ₁ ), (X ₂ , Y ₂ ), (X ₃ , Y ₃ ), (X ₄ ,
It has changed to Y ₄ ). At this time, mark 11-12
, 13-14, 13-11, and 14-12, the respective strains are ε ₁ = (X ₁ −X ₁ ′ −X ₂ + X ₂ ′) / (X ₁ −X
₂ ), ε ₂ = (X ₃ −X ₃ ′ + X ₄ + X ₄ ′) / (X ₃ −X ₄ ),
ε ₃ = (Y ₁ −Y ₁ ′ −Y ₃ + Y ₃ ′) / (Y ₁ −Y ₃ ), ε ₄ =
_{(Y 2 -Y 2 '-Y 4} + Y 4') is calculated by / (Y ₂ -Y ₄₎ <
206>. The calculation of the strain ε is performed by the arithmetic unit 24.

To correct the calculated distortion, 11-1
The Z position of the mask 1 on the second side, the 13-14 side, the 13-11 side, and the 14-12 side may be individually changed, and the magnifications of the corresponding portions may be individually operated and corrected. However,
If the mask 1 is rigid and does not deform, it is impossible to change the Z position simultaneously and independently at these four positions. Therefore, the amount of movement of the mask support table tilt control devices 3, 4, 5 in the Z direction is calculated so that the correction is maximized as follows. For example, the mask support table tilt control device 3, 4,
5 of the magnification correction coefficient for the amount of movement in the Z direction is η (ppm /
μm), 11-12 side, 13-14 side, 13-
The Z-direction movement amounts of the mask corresponding to the strain amounts (ε ₁ , ε ₂ , ε ₃ , ε ₄ ) on the 11 side and 14-12 side are η ε ₁ , η ε ₂ ,
It is given by ηε ₃ and ηε ₄ . This value and mark 11,12,
Based on the coordinates of 13 and 14, the corrected surface of the mask 1 is fitted to the equation αX + βY + Z = γ representing the surface by the method of least squares, and the parameters α, β and γ are obtained. The calculation of this parameter is performed by the arithmetic unit 24.

Next, the mask support table tilt control device 3, 4, 5
Coordinates (X3, X3), (X4, Y) centered on the mask 1 of
4) and (X5, Y5) are substituted into the equation representing the surface to find the corresponding Z3, Z4 and Z5. For example, Z
4 = γ−αX4 + βY4. This Z3, Z4, Z5
Is the movement amount of the mask in the Z direction, and the calculation of the correction amount is completed.
207>. The calculation of the correction amount is performed by the arithmetic unit 24. Of course, by re-measurement, it is easy to make a closed loop for measuring and inspecting the amount of distortion after error correction.

Before exposure, the semiconductor wafer 7 is exposed to 10
After performing the alignment <202> of the exposure areas 9 at about a few places, the layout condition of the exposure areas 9 is grasped by the statistical processing, and the Z-direction movement amounts Z3, Z4 of the mask support table tilt control devices 3, 4, 5 are obtained. , Z5 may be calculated. The statistical processing,
The calculation of the Z-direction movement amount is performed by the arithmetic unit 24.

After the exposure process, the semiconductor wafer 7
The upper photoresist film is developed, and the developed marks 11, 12, 13, 14 of the photoresist film and the marks 11 ', 12', 13 ', 14' formed in the previous step (oxide film,
Distortion can also be detected by detecting a misalignment with a conductive film or the like). In this case,
Marks 11, 12, 13, 14 through the projection lens 6
Since it is not necessary to detect the position of, the types of light sources used in the optical system and the detection system can be used properly. For example, one can be a laser and the other can be an X-ray.

Next, the projection lens 6 and the surface of the semiconductor wafer 7 are focused. At this time, the semiconductor wafer 7
Is tilted by using each of the Z drive base 21 and the XY drive base 19 to focus. At the same time, the calculated Z
The mask supporting table tilting devices 3, 4, 5 are controlled based on the directional movement amounts Z3, Z4, Z5, the mask supporting table 2 is tilted, the angle between the normal line of the mask 1 and the optical axis is changed, and the projected image is displayed. Consciously distort <208>. These processes are performed under the control of the arithmetic unit 24.

Next, the drawing pattern of the mask 1 is exposed on the semiconductor wafer 7 <209>.

Through the above steps, the drawing pattern of the mask 1 can be transferred to one exposure area 9 of the semiconductor wafer 7. After that, the position of the exposure region 9 of the semiconductor wafer 7 is moved and the exposure is repeated. In this case,
The processing from 204> to <209> is repeated.

As described above, according to the exposure method of the present embodiment, the mask supporting table tilt control devices 3, 4, 5 are controlled individually by controlling the Z-direction movement amounts Z3, Z4, Z5. The angle between the normal line of 1 and the optical axis can be freely changed by 360 degrees. As a result, the drawing pattern of the mask 1 can be exposed by approximating the distortion of the exposure area 9, so that the exposure accuracy can be improved.

Further, the mask support table tilt control device 3, 4, 5
It is possible to continuously change the magnification within the lens field by individually controlling the Z-direction movement amounts Z3, Z4, and Z5.

The strains ε on the four sides of the exposure region 9 of the semiconductor wafer 7 are measured from the marks 11, 12, 13, 14 arranged at the four corners of the exposure region 9, respectively, and the strain amounts ε and From the coordinates of the reference positions of the marks 11 ′, 12 ′, 13 ′, 14 ′ already given, the coordinates of the mask support table tilt control devices 3, 4, 5 and the magnification correction coefficient η, the semiconductor wafer is calculated by the calculation unit 24. It is possible to calculate the Z-direction movement amounts Z3, Z4, Z5 of the mask support table tilt control devices 3, 4, 5 in order to distort the projected image in a shape similar to the distortion of the exposure area 9 of the c.

Further, since the overlay accuracy between the drawing patterns that are overlaid and exposed is improved, the reliability and the yield of the semiconductor device manufactured by the exposure method can be improved.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention.

For example, the marks 11, 12, 13, 14 are set to 4
The case of arranging in the corner has been described as an example, but it may be four sides or both four corners and four sides may be used together. Also,
Although the method of simultaneously detecting a plurality of marks by the plurality of detection units 25 and 26 has been described, the entire surface of the exposure region 9 can be collectively scanned by a single detection unit.

There are various kinds of operating methods of the image distortion adjusting means for intentionally distorting the projected image. For example, the relationship between the distance between the projection lens 6 and the mask 1 and the projection magnification is checked in advance, and the required distortion shape is calculated for the projection lens 6 by the mask support table tilt control devices 3, 4, 5 respectively. Convert to the magnification of the projected image at approximately the position. Next, the converted magnification,
By comparing the relationship between the distance between the projection lens 6 and the mask 1 and the projection magnification, it is possible to form a sequence in which the movement amounts of the mask support table tilt control devices 3, 4, 5 are adjusted.

Although an example in which the three points of the mask 7 are supported and the amount of movement of the three points in the Z direction is changed has been shown, the present invention performs TTL alignment at the four corners of the mask 1 to obtain a semiconductor wafer. The mask 1 can be tilted corresponding to the distortion of 7.

It is also possible to calculate the amount of distortion of the exposure region 9 and the amount of movement of the mask 1 in the Z direction from the alignment result of a plurality of already exposed exposure regions around the exposure region 9.

[0046]

The effects obtained by the representative ones of the inventions disclosed in this application will be briefly described as follows.

In the projection exposure method, overlay accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a flowchart of a projection exposure method of this embodiment.

FIG. 2 is a side view showing the outline of the reduction projection exposure apparatus of the embodiment of the present invention.

FIG. 3 is a plan view of a principal part of a mask support base portion of the reduction projection exposure apparatus.

FIG. 4 is a cross-sectional view of a main part of a mask support table tilt control device portion.

FIG. 5 is a sectional view of an essential part showing another example of the mask support table tilt control device portion.

FIG. 6 is a plan view of a semiconductor wafer.

FIG. 7 is a plan view of an essential part showing the exposure area of FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mask, 2 ... Mask support stand, 3,4,5, Mask support stand inclination control device, 6 ... Projection lens, 7 ... Semiconductor wafer
C, 9 ... Exposure area, 11, 12, 13, 14 ... Mark, 1
9 ... XY drive stand, 20 ... XY drive stand controller, 21 ...
Z drive base, 22 ... Z drive base control unit, 23 ... Step drive error detector, 24 ... Calculation unit, 25, 26 ... Mark detection unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinji Kuniyoshi 5-20-1 Kamimizuhoncho, Kodaira-shi, Tokyo Hitachi, Ltd. Musashi factory

Claims (2)

[Claims] 1. A projection exposure method for transferring a drawing pattern of a mask onto a transfer target substrate along an optical axis, wherein a plurality of marks are formed at reference positions separated from each other.
The step of transferring the first drawing pattern of the mask to the surface of the transfer substrate, the distance between the marks of the first drawing pattern transferred to the transfer substrate is detected, and the detected distance and the reference position And a distance between the first drawing pattern and the second drawing pattern of the second mask or the transferred substrate is changed with respect to the optical axis by approximating the detected distortion amount. And the second mask of the second mask is formed on the transferred substrate.
And a step of forming a drawing pattern. 2. The projection exposure method according to claim 1, wherein the second drawing pattern of the second mask or the transferred substrate is changed by a minute angle with respect to the optical axis.