JPH05275306A - Aligner and aligning method - Google Patents

Abstract

PURPOSE:To make it possible to prevent positional shift of a projected image even if a light transmissive member having different optical path length is inserted into the objective face side of a projection optical system. CONSTITUTION:Sum of the optical path lengths of light transmissive members 2b, 31, inserted between a projection optical system 4 and a photomask 1, is set constant at all times wherein the projection optical system 4 is set to focus the projection image of a mask pattern 1b on the photomask 1 onto a body 6 to be exposed. Consequently, when a cover glass of different thickness is inserted between the projection optical system 4 and the photomask 1, positional shift of focus image of the mask pattern 1b due to fluctuation of the thickness of the cover glass 2b can be eliminated without adjusting the optical system 4 through combination of the cover glass 2b and another light transmissive which compensates the fluctuation of thickness and making constant the sum of the optical path lengths.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method and exposure apparatus for transferring a fine pattern onto a semiconductor wafer or the like having a resist film formed thereon using a photomask.

[0002]

2. Description of the Related Art For example, when an IC or the like is manufactured, an exposure for transferring a circuit pattern is performed on a silicon wafer or the like on which a resist is formed. In this exposure, a projected image of a mask pattern of a photomask is used. A method of forming an image on the object to be exposed by a projection optical system is used.

In this exposure method, if foreign matter such as dust adheres directly to the mask pattern of the photomask, the dust pattern may also be exposed and the yield of products may be deteriorated. Therefore, mask protection for preventing this occurs. The body is used.

In this mask protector, one opening of a frame is covered with a light-transmissive member, and the other opening not covered with the light-transmissive member is provided with a mask pattern of a photomask. The end portion of the frame body is adhered to the photomask toward the main surface, whereby the mask pattern of the photomask is arranged in the closed space formed by the mask protector and the photomask, and the dust is removed. This is to prevent foreign matters such as the above from directly adhering to the mask pattern. As the mask protector, an organic film was used for the translucent member,
A so-called pellicle is generally used, but one using a glass plate (cover glass) as a translucent member is also known (for example, JP-A-59-191039, US Pat. No. 406381).
(See No. 2). The mask protector using this glass plate is used in place of the pellicle in such a case because wrinkles are generated in the pellicle and a flat film cannot be formed, especially in the case of a large photomask. Also in the case of, since it is more durable than the pellicle and is relatively easy to handle, it is used when these points are important.

[0005]

By the way, in the case of the above-mentioned pellicle, since the film thickness is about 0.9 to 3 μm, even if the refractive index is set to about 1.5, the pellicle has a thickness of about 1 μm. Even if the fine pattern with high resolution is interposed in the optical path of the optical system for exposing, the deviation of the image forming position due to the presence or absence of the pellicle does not pose a problem.

However, in the case of the mask protector using the above-mentioned glass plate, the thickness of the glass plate is about 1 to several mm, so that the deviation of the image forming position due to the presence or absence of this glass plate poses a problem. I found out. That is, for example, when a projected image of a mask pattern is formed on an object to be exposed by a unit-magnification projection optical system, if a mask protector using a quartz glass plate with a thickness of 1 mm is attached to the photomask, the mask protector is protected. Approximately 0.3m compared to when the body is not attached
It was also found that the image forming position of m also deviated. Therefore, in such a case, it is necessary to readjust the object plane position and the image plane position of the unit-magnification projection optical system to match the image formation position. But,
The optical system itself has a highly precise and complicated mechanism, and the automatic attachment / detachment of masks and wafers is performed on the object plane and image plane of the optical system.
Since the transport mechanism and the like are arranged, it is extremely difficult to accurately change the object plane position and the image plane position of the optical system in a short time.

In particular, in the case of performing high-resolution exposure, if a thick glass plate of a mask protector is inserted on the object side of the unit-magnification optical system as described above, image formation by this is assumed. Even if the positional deviation is readjusted, there is an optical path difference in the projection light passing through the glass plate, which causes a problem of spherical aberration.

The present invention has been made under the background described above, and a first object thereof is to project without adjusting the projection optical system even if a translucent member is inserted on the object side. It is to provide a method capable of preventing the image forming position shift.
The purpose of is to prevent deviation of the image formation position of the projected image and spherical aberration without adjusting the projection optical system even if a translucent member is inserted on the object side when using a unit-magnification projection optical system. A third object is to provide an exposure apparatus that implements these methods.

[0009]

In order to solve the above-mentioned problems, according to the present invention, (1) exposure is performed by forming a projected image of a mask pattern of a photomask on a body to be exposed by a projection optical system. In the exposure method, the sum of the optical path lengths of the translucent members inserted between the projection optical system and the photomask is always constant, and in this case, the projection optical system is the mask pattern of the photomask. A configuration characterized in that the projection image is set to be formed on the exposed object,
Further, as an aspect of the method of configuration 1, (2) in the exposure method according to configuration 1, the maximum optical path of the translucent members that may be inserted between the projection optical system and the photomask. Assuming that a thing having a length is inserted between them, in this case, the projection optical system is set so as to form a projected image of the mask pattern of the photomask on the exposed object, When the light-transmissive member inserted between the projection optical system and the photomask at the time of exposure is less than the assumed maximum optical path length, an optical path length having an optical path length that compensates for the insufficient optical path length. A configuration in which the correction translucent member is inserted between the projection optical system and the photomask, and as a mode in the case where the projection optical system used is a unit magnification optical system, 3) In the exposure method according to configuration 1, the projection is performed. In the case where an equal-magnification projection optical system is used as the optical system, and a translucent member is inserted between the photomask and the projection optical system, a translucent member having the same optical path length as this translucent member is inserted. An optical member is inserted between the unit-magnification projection optical system and the object to be exposed. Further, (4) Configuration 2 is provided as an apparatus for performing the method of Configuration 2. An exposure apparatus for carrying out the exposure method, a light source, an illumination optical system for condensing light emitted from the light source, a photomask arranged in a condensing part of the illumination optical system, and the photomask. And a projection optical system for forming a projected image of the mask pattern on the exposed object,
As the projection optical system, the one having the maximum optical path length among the translucent members that may be inserted between the photomask and the projection optical system is inserted when the translucent member is inserted between them. A light-transmissive member inserted between the photomask and the projection optical system at the time of exposure is used by using a photomask that is set so as to form a projected image of the mask pattern of the photomask on the exposed object. An optical path length correction device that inserts an optical path length correcting translucent member having an optical path length that compensates for the shortest optical path length when it does not reach the assumed maximum optical path length between the projection optical system and the photomask. Further, as an apparatus for carrying out the exposure method of Structure 3, (5) is an exposure apparatus for carrying out the exposure method of Structure 3, wherein a light source and light emitted from this light source are collected. A condenser device that emits light and this condenser A photomask disposed in the condensing part of the device, and a unity-magnification projection optical system for forming a unity-magnification projected image of the mask pattern of the photomask on the exposed object,
When a translucent member is inserted between the photomask and the projection optical system, a translucent member having the same optical path length as the translucent member is provided between the unity-magnification projection optical system and the exposed object. And an optical path length correction device to be inserted into.

[0010]

According to the above configuration 1, the sum of the optical path lengths of the translucent members inserted between the projection optical system and the photomask is always constant, and in this case, the projection optical system is Since the projection image of the mask pattern of the photomask is set to form an image on the object to be exposed, for example, a transparent member such as a cover glass having various thicknesses between the projection optical system and the photomask. When inserting, the other transparent members are combined so as to secure the fluctuation of the thickness of the cover glass and have a constant optical path length, and insert these between the projection optical system and the photomask. By doing so, it is possible to prevent the displacement of the image forming position of the mask pattern due to the variation of the thickness of the cover glass without adjusting the projection optical system.

Further, according to the configuration 2, it is possible to cope with a variation in the thickness of the cover glass or the like within a necessary range.

According to the configuration 3, when the unit-magnification projection optical system is used as the projection optical system, the translucency inserted between the photomask and the unit-magnification projection exposure apparatus (on the object side). Since the translucent member having the same optical path length as the member is inserted between the unit-size projection exposure apparatus and the object to be exposed (image surface side), the translucent member is inserted on the object side. The influence due to is canceled out by the translucent member inserted on the image plane side. As a result, it is possible to effectively prevent the deviation of the image forming position and the occurrence of spherical aberration.

Further, according to the constitutions 4 and 5, it is possible to obtain an apparatus for carrying out the exposure method of the constitutions 2 and 3.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view showing the arrangement of an exposure apparatus for carrying out an exposure method according to an embodiment of the present invention. An embodiment of the present invention will be described in detail below with reference to FIG. In this embodiment, a projection exposure apparatus of equal size is used as the projection exposure apparatus, and a translucent member having the same optical path length as the translucent member inserted on the object side is inserted on the image side. This is an example of the case where the image forming position shift and the spherical aberration due to the insertion of the transparent member such as the cover glass are prevented.

In FIG. 1, reference numeral 1 is a photomask, reference numeral 1a is a glass substrate, reference numeral 1b is a mask pattern, reference numeral 2 is a mask protector, reference numeral 2a is a frame, reference numeral 2b is a cover glass, and reference numeral 31 is the object side. Optical path length correction plate, reference numeral 4 is a projection optical system, reference numeral 51 is an image surface side optical path length correction plate, reference numeral 6 is an exposed object, reference numeral 6a is an exposure surface (image forming surface), reference numeral 7 is a light source, and reference numeral 8 is a condenser. A lens, reference numeral 30 is an object surface side optical path length correction device, and reference numeral 50 is an image surface side optical path length correction device. The cover glass 2b, the object-side optical path length correction plate 31 and the image-side optical path length correction plate 51 constitute the translucent member in the present invention.

In FIG. 1, this apparatus performs exposure by forming a projected image of a mask pattern 1b of a photomask 1 on an exposure surface 6a of an object 6 to be exposed by a projection optical system 4.

The photomask 1 is a 6 × 6 inch square quartz glass substrate 1a having a thickness of 0.15 inch, and one main surface of the quartz glass substrate 1a.
That is, the mask pattern 1b formed of a light-shielding film such as a chromium film is formed on the lower side surface in the drawing.

The mask pattern 1b of this photomask 1
A mask protector 2 is attached to the surface on which is formed.
The mask protector 2 is formed by covering one opening (lower opening in the drawing) of a frame 2a formed of aluminum or the like in a cylindrical shape with a cover glass 2b and not covered with the cover glass 2b. The other opening is directed to the main surface of the photomask 1 on which the mask pattern 1b is formed, and the end portion of the frame body 2a is bonded to the photomask, whereby the mask pattern 1b of the photomask 1 becomes the mask protector 2. The photomask 1 is arranged in a closed space formed by the glass substrate 1a of the photomask 1 so that foreign matters such as dust are not directly attached to the mask pattern 1b. The cover glass 2b is a quartz plate having a thickness t ₁ = 0.1 inch (refractive index n =
1.4585).

On the front side of the cover glass 2b, that is, on the lower side in the figure, an object side optical path length correcting plate 31 attached to an object side optical path length correcting device 30 is arranged. The object-side optical path length correction device 30 is one in which a plurality of object-side optical path length correction plates are attached to the rotation shaft 33a of the rotation drive device 33, and by rotating the rotation shaft 33a,
An object side optical path length correction plate having a desired optical path length is arranged on the front side of the cover glass 2b. In the figure, only two of the object-side optical path length correction plates 31 and 32 of the plurality of object-side optical path length correction plates attached to the object-side optical path length correction device 30 are shown. The object-side optical path length correction plates (31, 32) are made of the same quartz plate as the cover glass 2b. The thickness t _{2 of the} object-side optical path length correction plate 31 is 0.1 inch. Further, the thickness t ₄ of the object side optical path length correction plate 32 is set to be equal to or larger than the thickness of the thickest cover glass among the cover glasses used. The object side optical path length correction plate 32 is inserted into the object side when the cover glass 2b is inside. As described below,
In the projection optical system 4, the focus position and the like are adjusted with the light-transmissive member having this thickness inserted on the object side.

On the other hand, the condenser lens 8, the light source 7 and the reflecting mirror 71 are sequentially arranged on the side opposite to the side where the mask protector 2 of the photomask 1 is attached, that is, on the upper side in the figure. Thereby, the light L emitted from the light source 7
₀ is condensed by the condenser lens 8 and enters the photomask 1, passes through the mask pattern 1b, and is projected onto the projection light L.
₁ becomes cover glass 2b and object side optical path length correction plate 3
It passes through 1 and enters the projection optical system 4. The light source 7 may be, for example, an i-line with a wavelength of 365 nm or a wavelength of 248 nm.
A lamp or the like capable of emitting the KrF line is used.

The projection optical system 4 is an equal-magnification projection optical system that receives the projection light L ₁ and forms a projection image of the mask pattern 1b on the exposure surface 6a of the exposure target 6 at the same magnification. In addition,
Actually, there are many examples that consist of reflective optics, but in the figure,
It is shown schematically.

An image plane side optical path length correcting plate 51 attached to an image plane side optical path length correcting device 50 is arranged between the projection optical system 4 and the exposed body 6. The image plane side optical path length correction device 50 includes the rotation shaft 5 of the rotation drive device 53.
3a has a plurality of image plane side optical path length correction plates attached,
By rotating the rotating shaft 53a, an image plane side optical path length correction plate having a desired optical path length is inserted between the projection optical system 4 and the exposed body 6. In the figure, two image plane side optical path length correction plates 5 out of the plurality of image plane side optical path length correction plates attached to the image plane side optical path length correction device 50 are shown.
Only 1,52 are shown. The image-side optical path length correction plates (51, 52) are also made of the same quartz plate as the cover glass 2b. The thickness of the image-side optical path length correction plate 51 is 0.
It is 20 inches. The image plane side optical path length correction plate 51 does not need to be changed unless the total optical path length of the translucent member inserted on the object side is changed. In this embodiment, when the optical path length on the object plane side is changed and the projection optical system is readjusted, this can be immediately dealt with on the image plane side.

The focus position of the projection optical system is adjusted in advance on both the object side and the image side in consideration of the focus position variation (about 2.0 mm) due to the inserted cover glass 2b or the like.

The exposed body 6 is a wafer having a diameter of 6 inches whose surface is coated with a resist, is placed on a stage 61 whose position can be adjusted, and is exposed on the exposure surface 6a at the image forming position of the projected image of the mask pattern 1b. Can be matched.

In the method of this embodiment, when the thickness of the cover glass 2b is t ₁ and the thickness of the object plane side optical path length correction plate 31 is t ₂ , the image plane side optical path length correction is performed. Board 5
The thickness t ₃ of ₁ is set so that t ₃ = t ₁ + t ₂ is always established. Such a setting is easily realized by appropriately selecting and combining the respective correction plates in the object-side optical path length correction device 30 and the image-side optical path length correction device 50 according to the thickness of the cover glass 2b. be able to. Although the materials of the translucent members are all the same in one embodiment, when they are different, the respective thicknesses are set so that the following equation is satisfied.

{N ₃ −1) / n ₃ } · t ₂ = {n ₁ −1) / n ₁ } · t ₁ + {n ₂ −1) / n ₂ } · t ₂ , where n ₁ ; cover The refractive index n ₂ of the glass ₂ b; the refractive index n _{3 of the} object-side optical path length correction plate 31; the refractive index of the image-side optical path length correction plate 51.

According to this, when the photomask 1 is replaced, even if the thickness of the cover glass 2b of the mask protector 2 attached to the photomask 1 is different from that before replacement, the object side is always present. Since a light-transmissive member having the same optical path length as that of the light-transmissive member inserted in is inserted on the image surface side, the influence of the insertion of the light-transmissive member on the object side is changed to the image surface side. It can be offset by the inserted translucent member. As a result, it is possible to effectively prevent the deviation of the image forming position and the occurrence of spherical aberration.

In the above-described embodiment, the thickness of the optical path length compensating plate inserted on the image plane side is made variable so that a large number of combinations are possible, but it is not always necessary to do so. no, if as the sum of the thickness t ₂ of the thickness t ₁ and the object surface side optical path length correction plate 31 of the cover glass 2b is always constant, the image plane-side optical path length correction plate inserted on the image surface side It suffices to use 51 having the same constant thickness as this, and it is not necessary to replace it.

When the cover glass 2b, the object plane side optical path length correcting plate 31 and the image plane side optical path length correcting plate 51 having different refractive indexes are used, the optical path is taken into consideration in consideration of the refractive index difference between them. The length is calculated, and the sum of the optical path lengths of the cover glass 2b and the object plane side optical path length correction plate 31 is calculated as the image plane side optical path length correction plate 51.
The optical path length should be equal to.

Further, in the above-described embodiment, when a projection optical system of equal magnification is used as the projection optical system, a translucent member is also inserted on the image plane side to prevent the deviation of the image forming position. Although an example of the case in which the spherical aberration can be prevented from occurring is also given. However, in the case where the spherical aberration is not a problem, the translucent member to be inserted on the image plane side can be omitted by the following. it can.

That is, it is assumed that a translucent member having a maximum optical path length among translucent members that may be inserted on the object side is inserted between them, and in this case, the projection optical system is The projection image of the mask pattern is set so as to form an image on the object to be exposed. When the translucent member inserted on the object side during exposure is less than the maximum optical path length assumed above, an optical path length correction plate having an optical path length that compensates for the shortage of the optical path length is used. Insert on the face side. As a result, even if the thickness of the cover glass changes, the image forming position can be maintained so as not to shift. In this case, the projection optical system does not necessarily have to be the same-magnification projection optical system, and may be a reduction projection optical system.

[0032]

As described above in detail, according to the present invention, the sum of the optical path lengths of the translucent members inserted between the projection optical system and the photomask is always constant. Since the projection optical system is set so as to form a projected image of the mask pattern of the photomask on the exposed object, for example, a cover glass having various thicknesses between the projection optical system and the photomask, etc. When inserting a translucent member, another translucent member that guarantees the variation of the thickness of the cover glass and keeps the sum of the optical path lengths constant is combined with them to form the projection optical system and the photomask. By inserting the mask pattern between and, it is possible to prevent the displacement of the image forming position of the mask pattern due to the variation of the thickness of the cover glass without adjusting the projection optical system.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an apparatus for carrying out an exposure method according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Photomask, 1a ... Glass substrate, 1b ... Mask pattern, 2 ... Mask protector, 2a ... Frame body, 2b ... Cover glass, 3 ... Object side optical path length correction plate, 4 ... Projection optical system, 5
... Image plane side optical path length correction plate, 6 ... Exposed body, 6a ... Exposure surface (imaging surface), 7 ... Light source, 8 ... Condenser lens, 30 ... Object plane side optical path length correction device, 50 ... Image plane side optical path It is a length correction device

Claims (5)

[Claims] 1. An exposure method in which a projection image of a mask pattern of a photomask is formed on a body to be exposed by a projection optical system to perform exposure, and a light-transmitting light inserted between the projection optical system and the photomask. The sum of the optical path lengths of the flexible members is always constant, and in this case, the projection optical system is set so as to form a projected image of the mask pattern of the photomask on the exposed object. Exposure method. 2. The exposure method according to claim 1, wherein among the translucent members that may be inserted between the projection optical system and the photomask, those having the maximum optical path length are those. Assuming that the projection optical system is inserted in between, the projection optical system is set so as to form a projected image of the mask pattern of the photomask on the exposed object, and the projection optical system is set at the time of exposure. When the translucent member inserted between the system and the photomask is less than the assumed maximum optical path length, an optical path length correcting translucent member having an optical path length that compensates for the insufficient optical path length is used. By inserting it between the projection optical system and the photomask, the sum of the optical path lengths of the translucent members inserted between the projection optical system and the photomask is made constant. Exposure method. 3. The exposure method according to claim 1, wherein a transmissive member is inserted between the photomask and the projection optical system when a unit-magnification projection optical system is used as the projection optical system. At this time, a light-transmitting member having the same optical path length as the light-transmitting member is inserted between the unit-magnification projection optical system and the object to be exposed. 4. An exposure apparatus for carrying out the exposure method according to claim 2, wherein a light source, an illumination optical system for condensing light emitted from the light source, and a converging section of the illumination optical system. A photomask arranged and a projection optical system for forming a projection image of a mask pattern of the photomask on an object to be exposed, wherein the projection optical system is provided between the photomask and the projection optical system. When a member having the maximum optical path length among the translucent members that may be inserted into the photomask is inserted between them, a projected image of the mask pattern of the photomask is formed on the exposed object. When the light-transmissive member inserted between the photomask and the projection optical system at the time of exposure is less than the assumed maximum optical path length during exposure, the insufficient optical path For optical path length correction with an optical path length that compensates for the length An exposure apparatus comprising an optical path length correction device that inserts a transparent member between the projection optical system and a photomask. 5. An exposure apparatus for carrying out the exposure method according to claim 3, wherein the light source, a condenser device for condensing the light emitted from the light source, and a condenser portion of the condenser device are arranged. And a photomask, a unity-magnification projection optical system for forming a unity-magnification projection image of the mask pattern of the photomask on an object to be exposed, and the photomask and the unit-magnification projection optical system. It is assumed that a transparent member having the maximum optical path length is inserted between these, and it is inserted between the photomask and the unit-magnification projection optical system at the time of exposure. When the translucent member is less than the assumed maximum optical path length, an optical path length correcting translucent member having an optical path length that compensates for the insufficient optical path length is provided between the photomask and the equal-magnification projection optical system. Insert it in between and always throw it at the same size as the photo mask. A first optical path length correction device that keeps the sum of the optical path lengths of the light transmissive members inserted between the optical system and the optical system, and a transmissive member inserted between the photomask and the equal-magnification optical system. An exposure apparatus having a second optical path length correction device for inserting a translucent member having an optical path length equal to the sum of the optical path lengths of the optical members between the unit-magnification projection optical system and the object to be exposed.