JPH06333795A - Exposure method - Google Patents

Abstract

PURPOSE:To provide an exposure method capable of accurately and fast performing a multiplex exposure using a plurality of sheets of reticle. CONSTITUTION:In an aligning method of performing a multiplex alignment using a plurality of sheets of reticle 1, 2 and forming desired patterns on a wafer 70, a position of a wafer stage 72 of each shot on the wafer aligned in a preceding exposure sequence and a set position of the reticle 1 used in the preceding exposure sequence are stored. In a succeeding exposure sequence, with respect to the stored position of the wafer stage 72 of each shot, the difference between the set position of the preceding reticle 1 and the set position of the succeeding reticle 2 is algebraically added to obtain the position of the wafer stage 72, in which an alignment is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method used in a semiconductor manufacturing apparatus for exposing and transferring a pattern on an original plate such as a reticle or a mask onto a substrate such as a semiconductor wafer, for example, a stepper.

[0002]

2. Description of the Related Art The progress of semiconductor technology has been accelerating in recent years, and along with it, the progress of fine processing technology has been remarkable. In particular, the optical processing technology at the center of this is 1MDRA
We entered the sub-micron area with M as the boundary. What has been used so far as a means for improving the resolution is a method of fixing the wavelength and increasing the NA of the optical system. But recently, changing the exposure wavelength from g-line to i-line,
Attempts have also been made to expand the limits of light exposure methods in the area of ultra-high pressure mercury lamps.

Conventional approaches using g-line and i-line have also prompted advances in resist processes. It can be said that the optical lithography so far has progressed due to the combination of both the optical system and the process.

However, in general, the depth of focus of a stepper is N
It is known to be inversely proportional to the square of A, and submicronization at the same time presents a serious depth of focus problem. One of the methods that has come out to solve this is a method of using a shorter wavelength represented by an excimer laser. The short wavelength effect surely increases the depth of focus.

On the other hand, in addition to the trend of shortening the wavelength, a method using a phase shift film has appeared as a means for improving the resolution. This method is a method of forming a thin film on a part of a conventional reticle (mask) that gives a phase shift of 180 degrees from the other part, and a representative paper by IBM's Levenson et al. Is. The resolving power RP and the depth of focus DOF are generally expressed by the following equation: RP = k ₁ λ / NA DOF = k ₂ λ / NA ² . Where λ is the exposure wavelength. Usually 0.7 ~
It is known that the parameter k ₁ for which 0.8 is a practical range is significantly improved to about 0.35 by the spatial frequency modulation type phase shift method. This improvement in resolution is drastic and is drawing attention as it extends the limit of conventional optical lithography.

Various methods of phase shifting are known, and they are, for example, Nikkei Microdevice 1990.
Details on the papers by Mr. Fukuda et al. The most significant of these methods is the L, which they call in the paper as spatial frequency modulation.
It is said to be of the evenson type.

However, many problems still remain in order to put the spatial frequency modulation type phase shift reticle into practical use. For this reason, recently, a means for realizing the Levenson-type phase shift effect in the illumination system has been devised, and a representative example thereof is Japanese Patent Application Laid-Open No. 4-267515, which was previously filed by the applicant of the present application. it can. This method can produce the same effect as the Levenson type with an ordinary reticle without using a phase shift mask. The new lighting method presented in the above application is
This is a method called quadrupole illumination or modified illumination.

[0008]

However, this quadrupole illumination has a feature that the effect can basically be applied only to a repetitive pattern, like the phase shift mask. Therefore, it is difficult to apply to a contact hole process or the like, which is a problem due to a shallow depth of focus. The contact hole is a so-called isolated pattern in which a contact hole has a fine square or rectangular shape, and a pattern of a size corresponding to the length of the side of the square or rectangle does not exist around the contact hole. In this case, the diffraction pattern is not localized, and the advantages of the phase shift mask and the illumination system cannot be utilized.

Therefore, in consideration of application to an isolated pattern such as a contact hole, the development of an exposure apparatus using an excimer laser without such a restriction is being accelerated. Resists are the most obstacles in the excimer laser region, and although various negative resists have been developed, good positive resists have not yet been developed.

In the step of forming the contact hole pattern, a special exposure method is known in which the wafer is moved up and down in the focal direction to perform multiple exposure. However, this method is effective only for positive resists, and in actual application, the total contrast drops during image formation, which is a major problem in a system using an ultra-high pressure mercury lamp such as i-line. . Further, it cannot be applied to a negative type resist, which is a large negative factor against application to an isolated pattern which is the largest reason for performing excimer lithography.

By the way, in the method using the phase shift mask or the quadrupole illumination, there is known a method of obtaining a desired pattern as a result by superposing a plurality of patterns on a wafer for a pattern which is not good. There is.
As a typical example, after performing the previous exposure using the phase shift mask, the relative positional relationship between the reticle and the wafer is slightly shifted to perform the subsequent exposure, and as a result, unnecessary lines due to the phase shifter film are removed. Then, a desired pattern is formed on the wafer.

A typical example of the case where a plurality of patterns are overlapped for exposure as described above is a case where a plurality of reticles are used to overlap the patterns with each other. When a plurality of reticles can be used, preparing a dummy pattern can provide an image forming exposure method that can be widely applied to isolated patterns.

For example, as a first exposure, a reticle in which dummy repeated patterns are arranged around an isolated pattern is exposed by a modified illumination method such as quadrupole illumination, and as a subsequent exposure, a portion of the dummy pattern is exposed. Perform multiple exposure with a conventional illumination system using another reticle with a transmissive part,
By removing such a dummy pattern, it becomes possible to form the entire pattern.

Further, as a result of betting, the depth of the repetitive pattern, which is good at the modified illumination such as the quadrupole illumination, and the low frequency pattern possessed because the isolated pattern is isolated from the surroundings. It is possible to mix images and perform effective image formation with a large depth of focus as a whole.

However, the superposition of different patterns using a plurality of reticles results in an increase in wafer processing time. In particular, at the present time when the requirements for resolution and depth of focus are becoming strict, optical lithography is required to pursue cost performance in the same playing field as X-ray and EB exposure.

The present invention has been made in view of the above circumstances, and multiplex using a plurality of reticles so that good imaging performance can be exhibited even for an isolated pattern such as a contact hole. An object of the present invention is to provide an exposure method capable of performing exposure accurately and at high speed.

[0017]

In order to achieve the above-mentioned object, the present invention is an exposure method for forming a pattern on a wafer by performing multiple exposure using a plurality of reticles, in the previous exposure sequence. The wafer stage position of each shot on the exposed wafer and the set position of the reticle used in the previous exposure sequence are stored,
In the subsequent exposure sequence, the exposure is performed at the wafer stage position where the difference between the set position of the previous reticle and the set position of the subsequent reticle is algebraically added to the stored wafer stage position of each shot. There is.

In particular, when the reticle has different illumination states in the first and second exposure sequences, or when the illumination states are different, the illuminating state is changed when the reticle is replaced, and a plurality of reticles are used. This minimizes the time lost due to

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION To understand the concept of the present invention, first, the concept of pattern superposition using a plurality of reticles will be described.

Shown in FIG. 1 are two reticles 1 and 2 to be superposed on a wafer. The two reticles 1 and 2 are used as a pair, and after the wafer is exposed by the first reticle 1, the wafer is subjected to the second exposure by the second reticle 2 before being subjected to development.

The patterns to be exposed are various, such as a periodic pattern and an isolated pattern, but the exposure by a plurality of reticles is such a mixture of various patterns or an isolated pattern. This is effective when there are only non-repeating patterns. When there are only repetitive patterns, that is, patterns with periodicity, the quadrupole modified illumination method described above is sufficient.

Deformed illumination such as quadrupole illumination is excellent in depth of focus of repetitive patterns of fine high frequency, while it is relatively low frequency (specifically, k ₁ described above).
For a line width of 1.0 or more), there is a problem that the depth of focus decreases. In order to simplify the following explanation, quadrupole or modified illumination shows excellent characteristics when the k ₁ factor is 0.8 or less in a repetitive pattern, and the normal illumination method has excellent characteristics in a rough pattern with a k ₁ factor of 0.8 or more. I will proceed with the explanation. Although this assumption is rough, it shows a good correspondence in practice.

In the actual modified illumination, for example, in the case of quadrupole illumination, the value of 0.8 is slightly different depending on design parameters (for example, the distance from the center to each quadrupole and the shape of each quadrupole). However, a value of 0.8 is used here for convenience of explanation. Further, regarding the method of realizing various types of modified illumination such as quadrupole illumination and the parameters, the above-mentioned application by the present applicant can be referred to, and therefore the description thereof is omitted here.

In the two reticles used in this embodiment, the first reticle 1 has a periodic pattern, and the second reticle 2 overlaps at least the first reticle 1 so that the first reticle 1 has a periodic pattern. The pattern is arranged to eliminate the periodicity of. Since the integrated circuit pattern includes the cell portion and the peripheral circuit portion at the same time in the same reticle, it is generally formed by various complicated patterns. The patterns on the reticles 1 and 2 are not limited to patterns that are combined with each other. There is no. For example, a fine and periodic pattern exists on the reticle ₁ without being combined with the pattern on the reticle 2, and on the reticle 2, any pattern with a k ₁ factor of 0.8 or more is combined with the pattern on the reticle 1. You may exist independently without being.

When an integrated circuit pattern is formed only by one of the reticle 1 and the reticle 2 without being combined with each other, the reticle portion where the pattern is not formed is made of chrome because the resist used is negative. It is shaded by. Here, how the pattern of the reticle 1 and the pattern of the reticle 2 overlap with each other to form an isolated pattern will be described.

FIG. 2A shows a pattern on the first reticle used for forming a contact hole. At the position where the contact hole should be originally formed, 11e,
The patterns shown by 12e and 13e are arranged. With a normal reticle, only these three patterns are arranged, but in this embodiment, eight patterns 11a to 11i are provided around 11e and 12 patterns are provided around 12e.
8 patterns from a to 12i, and 8 patterns from 13a to 13i around 1e, respectively.
They are arranged so as to form a periodic matrix with 1e, 12e, and 13e at the center. In the case of a contact hole pattern, an isolated pattern is arranged and a sufficient distance can be secured between adjacent patterns, so that it is possible to add an additional pattern in this way.

The reticle 1 is provided with quadrupole illumination in order to utilize the periodicity. In the quadrupole illumination, a system characteristic is optimized for a pattern of a certain specific frequency, and a repeating pattern having a ratio of 1: 1 is advantageous as the pattern. Therefore, as for the line width for adding such an additional dummy pattern, a contact hole pattern size of 0.8 or less in terms of the k ₁ factor is advantageous, and a pattern of a size larger than that is preferable in view of the assumption for the above description. If so, a contact hole pattern may be formed on the reticle 2 in the same manner as the conventional method without adding an additional pattern or the like.

Generally speaking, the reticle 1 is characterized in that an additional pattern having the same thickness as the line width is periodically added to an isolated pattern having a small k ₁ factor. For example, if a 0.4 μm square hole pattern is formed on a wafer, the size of the additional pattern is also 0.4 μm square, and the distance between the centers of the patterns is 0.8 μm.

The pattern on the reticle 2 corresponding to this is shown in FIG. Reticle 1 and Reticle 2
When the coordinate axes based on the center of the pattern formed in each of the two are taken and the corresponding coordinates are compared, the center of the pattern 21 coincides with the center of the pattern 11e of the reticle 1, and the center of 22 corresponds to the center of 12e. , And the center of 23 coincides with 13e. However, the size of the corners of 21, 22, 23 is 2 of the size of 11e, 12e, 13e, respectively.
Has doubled. Since the lower limit of the k ₁ factor used in quadrupole illumination is considered to be around 0.5, it can be considered that the patterns 21 to 23 fall into a relatively coarse pattern classification.

The actual exposure procedure, which is the main subject of the present invention, will be described in detail later, but as a result, the reticle 1 is a quadrupole illumination,
Further, the reticle 2 is exposed not by the modified illumination method but by the usual illumination method. The normal illumination method here is an illumination method that has been generally applied in the past such that the effective light source formed on the pupil of the projection optical system has a uniform distribution or a Gaussian distribution. It has a certain intensity at the center of the and has a distribution that is symmetric about the optical axis of the projection optical system.

The pattern on the reticle 1 is transferred onto the wafer by the first exposure, and the second exposure is transferred onto the wafer by using the reticle 2. FIG. 3 shows how the images of the two reticles overlap at that time. As shown above, the two images overlap because the centers of the patterns 11e and 21 are aligned. The same applies to patterns 12 and below. When the two patterns are superposed in this way, only the portions 11e, 12e, and 13e are finally exposed to no light. The result is the pattern of FIG.

As a result of exposing a pattern having periodicity by quadrupole illumination, the patterns 11e to 13e are normally or isolated as isolated patterns by simply forming only 11e, 12e and 13e on the reticle as in the conventional case. The depth of focus is wider than when exposed with quadrupole illumination. Although the additional pattern that contributed to the increase in the depth of focus is resolved in the first exposure, light is given and erased in the second exposure. This is an advantage of the negative type resist.

Such double exposure is also advantageous in terms of transferring dust on the reticle. When a reticle such as a contact hole pattern, which is almost only a transparent portion, is exposed by using a negative resist, even if fine dust is attached, the dust is transferred as a defect. However, if the exposure is performed twice as in the present invention, the portion where the exposure light is blocked due to dust is also irradiated with the light in another exposure and the defect is corrected. If the cause of the defect is dust,
This is because the probability that dust will be deposited on the same location of two reticles only occurs with a negligible probability. In addition, the method of multiple exposure using the same reticle can
Known as "oting lithography".

FIG. 5 shows another example in which two reticles are used to form a non-repeating pattern. Figure 5
(A) is a pattern on the reticle 1 in which a repetitive pattern is formed and is exposed using quadrupole illumination. On the other hand, the pattern shown in FIG. 5B is a pattern on the reticle 2 which is not repeated or is coarsely repeated, and is exposed by using a normal illumination system.

As a result of performing the first exposure using the reticle 1 and the second exposure using the reticle 2,
FIG. 6 shows how two patterns are overlapped on a wafer. The resulting pattern is shown in FIG. 7, which is shielded by both patterns due to the characteristics of the negative resist, and the resist in the portion not exposed to light is removed,
The desired pattern is formed.

The patterns of FIG. 7 have different vertical lengths, and are not simple repeating patterns. In this embodiment, considering that the quadrupole illumination has a problem in the shape of the tip portion, the non-repeating pattern edges are arranged in the direction orthogonal to the extending pattern direction.
As a result, the shape of the tip of the pattern is affected by the illumination of the rough pattern in FIG. 5B, and the shape of the tip is significantly improved. By combining such fine repeating patterns and overlapping patterns, various patterns can be formed freely, and the advantages of quadrupole illumination for fine repeating patterns and the advantages of normal illumination for overlapping patterns. Can be combined.

Next, an apparatus for carrying out the present invention will be described. Since there are various precedents for realizing a fine quadrupole or modified illumination as described above, a system using an ultra-high pressure mercury lamp will be described here as a representative. The present invention is similarly applicable to steppers and the like that use the wavelength range of excimer laser light.

FIG. 8 shows an embodiment of the exposure apparatus. The light emitted from the extra-high pressure mercury lamp 51 in which the arc is arranged at the first focus position of the elliptical mirror 52 is reflected by the elliptical mirror 52,
The light is focused near the second focus position. 53 is a shutter, 5
Reference numeral 4 is a bending mirror that serves to bend the optical path, and when entering the optical path for quadrupole illumination, it passes through a quadrangular pyramid 55, a relay lens 56, and a wavelength selection filter 57 and enters an optical integrator 58.

Reference numeral 59 is a mechanical diaphragm for selecting only an integrator necessary for performing quadrupole illumination from the optical integrator 58, and quadrupole illumination is realized by passing through the diaphragm. Reference numeral 60 is a bending mirror, and 61 is a lens. An illuminance distribution adjusting member 62 is arranged if necessary to make the illuminance distribution on the wafer surface uniform.

On the other hand, since 56 'has a normal illumination structure, it can be exchanged with the quadrupole illumination system by switching the optical path in this embodiment. Specifically, the quadrangular pyramid 55 and the relay lens 56 are replaced with the relay lens 56 ′, and the diaphragm 59 is replaced with a normal diaphragm 59 ′. The reason why the relay lens is switched to 56 is to minimize the loss of light amount due to the illumination system. The illuminance unevenness adjusting member 62 ′ is replaced with 62 in order to correct the change in the illuminance unevenness on the wafer surface due to the switching of the illumination method. 62 and 62 ′ can be realized by combining a lens with partial absorption and a lens without absorption, or by coating with a thin film having absorption or reflection characteristics. 62 or 6
2'can be omitted if it is not necessary to correct uneven illuminance.

Reference numeral 63 denotes a half mirror, which is a half mirror 63.
The light reflected by is guided to the optical system 90 for detecting the integrated light amount and the detector 91. The light that has passed through the half mirror 63 reaches a mechanical blade 64 that performs masking. The position of the mechanical blade 64 is adjusted by a drive system (not shown) according to the size of the integrated circuit pattern portion of the reticle 1 to be exposed.

Reference numeral 65 is a mirror, 66 is a lens system, 67 is a mirror, and 68 is a lens system. The light from the extra-high pressure mercury lamp 51 illuminates the reticle 1 mounted on the reticle stage 85 via these members. .

Reference numeral 69 designates the pattern on the reticle on the wafer 7.
It is a projection optical system for projecting an image on 0. Reference numeral 87 denotes a lens controller which controls a subtle difference in projection optical system between quadrupole illumination and normal illumination, and changes in the projection optical system due to changes in atmospheric pressure, exposure state, temperature and the like. .

The wafer 70 is attracted to a wafer chuck 71, and the chuck 71 has a function of focusing and leveling in the optical axis direction of the projection optical system 69 together with a mirror 75 forming a part of a laser interferometer 76. It is mounted on the XY stage 72. Reference numeral 77 is a photoelectric detection unit mounted on the stage. Further, 73 is an off-axis alignment microscope which plays a role of performing alignment, and 74 and 74 'are paired and an off-axis type autofocus detection system for setting the position of the wafer 70 at a predetermined position with respect to the projection optical system. Is. The light projected from the light projecting system 74 is detected by the detecting system 74 '.

The reticle 1 is aligned with the reticle reference marks 81, 81 'held at a fixed position on the reticle stage 85. Marks for the reticle set are arranged on the reticle 1 at positions corresponding to the reference marks 81, 81 '. The mark for the reticle set is a predetermined mark for the apparatus and is also arranged on the reticle 2. At least two reticle set marks are provided on one reticle in order to enable two-dimensional alignment with the reticle reference mark.

The reticle reference marks 81 and 81 'can be arranged on the stage 72. In this embodiment, 2
A pair of set mark and reference mark provided at the location is LE
Illuminated by D80, 80 ', mirror prisms 82, 8
2 ', CCD camera 8 via imaging lenses 83, 83'
Imaged on 4, 84 '. After this, a processing system (not shown),
Also, the reticle 1 is aligned with the reference mark by the drive system.

On the other hand, the reticle 2 is a fork 86 for loading.
Waiting on After the first exposure using the reticle 1 is completed, the reticle 1 and the reticle 2 are exchanged by a transport exchange mechanism (not shown), and the reticle 2 is moved to the reticle reference marks 81 and 81 ′ on the reticle stage 85. Are aligned. Reference numeral 88 is a computer that controls the entire exposure apparatus.

These are the main hardware for carrying out the present invention. Next, how to expose two sheets according to the present invention will be described.

First, when the machine is started by a predetermined job, the reticle 1 is conveyed onto the reticle stage 85 according to an instruction from the computer 88, and the reticle set mark is used to perform alignment with the reticle reference marks 81 and 81 '. Be seen. The displacement amount between the reticle set mark and the reticle reference mark is detected by the CCD cameras 84 and 84 ', and the alignment is performed.

The minute residual when the alignment is performed is stored in the computer 88. At this time, the rotational component of the alignment error of the reticle 1 is adjusted until it becomes below a predetermined value. Here, the predetermined value is a value determined by the requirement of alignment accuracy called overlay, and for example, when it is desired to suppress the rotational component of the reticle to 2 ppm or less, it is desirable that the drive-in of the reticle 1 be 1 ppm or less. This is because by setting the reticle 2 used in the second exposure to be 1 ppm or less, the worst value of 2 ppm is guaranteed.

Since quadrupole illumination is performed on the reticle 1, a combination of 55, 56 and 62 for quadrupole illumination is set as the state of the illumination system, while the lens controller 87 is used.
Sets the projection optical system 69 in a state matching the quadrupole illumination. This completes the preparation for exposure using the reticle 1.

Next, the wafer 70 is set on the wafer chuck 71 by a wafer transfer system (not shown) and is adsorbed. Next, the detection for alignment with the wafer is XY
This is performed by moving the stage 72 in a predetermined procedure according to the pattern layout on the wafer and observing it using an off-axis alignment microscope 73. Based on the detected values, the coordinates for alignment that match the pattern layout of the wafer are obtained as the coordinate values at which the XY stage 72 should stop. Here, it is assumed that the baseline correction value of the off-axis microscope system is obtained in advance.

With the above, the alignment detecting operation for performing the exposure is completed. This procedure can be omitted when the exposure of the first layer called the first mask, that is, when no pattern is formed on the first wafer.
In the case of the first mask, since it is the first pattern formation, the exposure is performed based on the precision with the mechanical pre-alignment with the coordinate values determined in advance from the pattern layout.

Then, the apparatus enters the operation of exposure based on the instruction of the computer 88. The coordinates at which the XY stage 72 should move and stop during exposure are coordinates created based on the measurement values of the alignment microscope 73, which is an alignment optical system in the normal case where alignment is required. Yes, in the case of the first mask, the coordinate values are predetermined as described above. Based on this value, the stage is stopped, the shutter 53 in the illumination optical system is actuated to perform the exposure, and then the stage is moved to the next position and the predetermined operation of exposure is repeated to expose the entire surface of the wafer. Is done.

At this time, all the actual stop positions of the stage at the time of exposure at each exposure position are stored. Therefore, the positions at which the stage 72 stops for each exposure shot in the first exposure are all known amounts in the subsequent second exposure. With the above, the first using the reticle 1
The second exposure is completed.

Since the exposure using the reticle 1 is completed, the reticle 1 is removed from the reticle stage 85 by a transport system (not shown), and the reticle 2 is set on the reticle stage 85. The reticle 2 is aligned with the reticle reference marks 81 and 81 'by the reticle set mark provided on itself.

In order to prevent the reticle detection optical system from being out of focus even if the reticle thickness is different, the reticle is observed from the side where the pattern is formed in the system of FIG. Also at this time, the rotational component of the alignment error of the reticle 2 is driven in until it reaches a predetermined value, for example, 1 ppm or less. The reason why the rotation component is kept below the predetermined value is to prevent the wafer stage from rotating during the second exposure using the reticle 2.

If the mutual rotation components of the reticle 1 and the reticle 2 are kept below a desired value, it is not necessary to rotate the wafer chuck 71 at the time of the second exposure, and simple correction of translational components in the X and Y directions. Only need When rotation is involved, the occurrence of a translational component due to the position of the center of rotation cannot be ignored, and it is essential to newly perform alignment during the second exposure, and extra time is required. Of course, the wafer 70 is still attracted to the wafer chuck 71 until the entire exposure is completed.

In this way, the reticle 2 is set, and at the same time, the exposure and the illumination optical system are set in the normal illumination state, which is the illumination state of the reticle 2. By performing the setting simultaneously with the reticle exchange, the time demerit of exposing a plurality of sheets can be minimized. That is, the lens controller 87 resets the state of the projection optical system 69 to the parameter for normal illumination, and replaces 55, 56, 59, 62 on the illumination optical system side with 56 ′, 59 ′,
62 'is inserted in the optical path. This completes the preparation for exposing the reticle 2.

Then, the second exposure using the reticle 2 is started. When the reticle 1 is used, the position coordinates of the wafer to be exposed are already determined, and the wafer is still attracted to the wafer chuck 71 while the reticle 1 and the reticle 2 are exchanged. No alignment is required. Since it has been confirmed that the rotational component of the reticle alignment has already been driven in hardware, the only remaining translation component at the time of reticle alignment is left.

Since this translational component is known at the time of aligning the reticle, the correction of the residual amount is introduced and the coordinate value is corrected at the time of the second exposure. This correction may be performed by algebraically adding the set error of the reticle 2 to the coordinate value of each shot already made.

The correction of the translational component is easy because it does not involve the rotation of the wafer. The movement and exposure of the stage are repeated with the target value being the corrected value of the coordinates of the first exposure, and the second exposure is completed. When the exposure of all the shots is completed, the wafer 70 is released from the suction, is unloaded from the wafer chuck by a transfer system (not shown), and waits for the next wafer to be loaded. And the same reticle 1 again
When exposure is performed by the combination of the reticle 2 and the reticle 2, the reticle 1 is returned to the loading state described above.

Since the exposure order of the reticle 1 and the reticle 2 may be arbitrary, the reticle 1 and the reticle 2 are sequentially in the order of the first wafer, and the reticle 2 and the reticle 2 are in the order of the second wafer.
If the exposure order is alternated, such as reticle 1 in order, reticle 1 and reticle 2 in order for the third wafer, the number of times the reticle is set decreases, and efficient exposure can be performed.

The embodiment of the present invention shows the system using the ultra-high pressure mercury lamp shown in FIG. 1, but this is of course applicable to an exposure system using an excimer laser. Further, although the modified illumination technique has shown the quadrupole illumination system, a technique such as ring illumination can be applied to the illumination of the reticle 1.

Further, in the present embodiment, an example in which two reticles are combined to form a pattern is shown, but it is also possible to form the entire pattern by combining two or more reticles. For example, the quadrupole illumination method has directionality and is effective in increasing the depth of focus for a fine periodic pattern in the XY directions, but is ineffective for a pattern in the ± 45 ° directions. Therefore, rotating the direction of the quadrupole by 45 ° has the effect of increasing the depth of focus for fine periodic patterns in the ± 45 ° direction.

Therefore, using a reticle 3 having a pattern having a fine periodicity in the ± 45 ° direction, the quadrupole illumination system illuminates the reticle 1 and the effective light source is 45 °.
If pattern composition is performed using an illumination system that is rotated and arranged, pattern composition corresponding to various directions including isolated patterns can be performed. Needless to say, at this time, the projection optical system and the illumination system are also treated in accordance with the quadrupole illumination.

Although a normal reticle is used in this embodiment,
The present invention can be similarly applied to the phase shift mask. In the case of a phase shift mask, it is said that a small σ (coherence factor) is good, so that the illumination system and the like are switched according to the conditions of the reticle.

[0068]

As described above, when a plurality of reticles are used, modified illumination or normal illumination is selected in accordance with the characteristics of these reticles, and multiple exposure is performed on the wafer to form a pattern, so that the periodic It is possible to form an image with a large depth of focus, which has flexibility in a total sense including a characteristic pattern to an isolated pattern. Further, in this case, if the procedure of the present invention is followed, the alignment of the wafer only needs to be performed once, so that the time disadvantage of using a plurality of reticles is greatly reduced.

Further, the pattern synthesis by multiple exposure as in the present invention is particularly effective for a negative resist, and is a particularly effective method in excimer lithography in which the adoption of a chemically amplified negative resist is considered to be strong at present.

Further, according to the present invention, by suppressing the rotational component of the reticle set, it is possible to compensate for a time disadvantage caused by stacking a plurality of reticles. As a result, it is possible to realize extremely efficient fine pattern formation in terms of cost.

[Brief description of drawings]

FIG. 1 is a view showing reticles 1 and 2 used in the present invention.

FIG. 2 is a view showing a periodic pattern on the reticle 1 and a pattern on the reticle 2 corresponding to this pattern.

FIG. 3 is a diagram showing how the reticles in FIG. 2 overlap.

FIG. 4 is a diagram showing a pattern formed on a wafer by overlapping the reticles in FIG.

FIG. 5 is a diagram showing another example of the periodic pattern on the reticle 1 and a pattern on the reticle 2 corresponding to this pattern.

FIG. 6 is a diagram showing how the reticles in FIG. 5 overlap.

7 is a diagram showing a pattern formed on a wafer by overlapping the reticles in FIG.

FIG. 8 is a diagram showing an embodiment of an exposure apparatus to which the present invention is applied.

[Explanation of symbols]

 11, 12, 13 Periodic pattern on reticle 1, 22, 22, 23 Pattern on reticle 51 Ultra-high pressure mercury lamp 53 Shutter 55 Four-sided pyramid prism 56,56 'Relay lens 59,59' Effective light source selection member 62,62 ' Illuminance distribution adjusting member 69 Projection optical system 70 Wafer 71 Wafer chuck 72 Stage 73 Off-axis microscope 76 Laser interferometer 81,81 'Reticle reference mark 84,84' CCD 85 Reticle stage 86 Road hand 88 Computer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G03F 9/00 7316-2H 7352-4M H01L 21/30 311 C 7352-4M 311 L

Claims (3)

[Claims] 1. An exposure method for forming a pattern on a wafer by performing multiple exposure using a plurality of reticles,
The wafer stage position of each shot on the wafer exposed in the previous exposure sequence and the set position of the reticle used in the previous exposure sequence are stored, and the wafer stage position of each shot stored in the subsequent exposure sequence. On the other hand, the exposure method is characterized in that the exposure is performed at the wafer stage position where the difference between the set position of the previous reticle and the set position of the subsequent reticle is algebraically added. 2. The exposure method according to claim 1, wherein an illumination state on the reticle is different between the first and second exposure sequences. 3. The exposure method according to claim 2, wherein the illumination state is changed when the reticle is replaced.