JPS63177123A - Projection exposing device - Google Patents

Abstract

PURPOSE:To increase the effective depth of focus of an exposure optical system regardless of the flattening of a substrate by putting plural images which have conjugation planes of a pattern at different positions in the direction of an optical axis at the same position on the substrate and projecting the composite image on the substrate for exposure. CONSTITUTION:Light which is emitted by a light source 1 and passed through an illumination optical system 2 and a reticle 3 is split by a half-mirror 11 in two directions. One of the split light beams is incident on a projection lens 6 through a mirror 12, a mirror 13, and a half-mirror 14 to form an image of the mask pattern on the reticle 3 at a position 9 nearby the surface 8 of the substrate on a substrate stage 7. The other light beam is incident on a projection lens 6 through an auxiliary optical system 4 for image position correction, an auxiliary optical system 5 for magnification correction, and the half-mirror 14 to form an image of the pattern at a position 10 nearby the surface 8 of the substrate. At this time, the image formation position 9 and image formation position 10 do not match with each other in general because of the effect of the optical path difference between the two optical paths to be put together. Consequently, the light intensity contrast of the image can be maintained over a wider range in the optical-axis direction and the effective depth of focus increases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection exposure apparatus suitable for forming fine patterns of, for example, semiconductor devices, magnetic bubble mesori devices, superconducting elements, and the like.

[Prior Art] As is well known, the projection exposure method is widely used to form various fine patterns for semiconductor devices, magnetic bubble memory devices, and the like. Projection exposure methods, especially reduction projection exposure methods, are useful for forming extremely fine patterns, but in conventional projection exposure methods, the focus tolerance of the exposure optical system strongly depends on the numerical aperture of the projection lens and the exposure wavelength. was. The depth of focus of a projection lens is inversely proportional to the square of its numerical aperture and proportional to the exposure wavelength, so if you increase the numerical aperture or shorten the exposure wavelength to improve resolution, The depth of focus becomes shallow. For this reason, it is becoming increasingly difficult to deal with obstacles caused by image plane distortion of the projection lens and irregularities on the surface of the substrate. Problems caused by steps caused by relatively fine patterns have been dealt with by smoothing using a well-known multilayer resist method.

However, even if this method is used, it is not possible to completely flatten the level difference caused by the large-area pattern, and it is inevitable that imaging defects will occur above or below the level difference.

Regarding the multilayer resist method, for example, please refer to the journal
of Vacuum Science and Technology,
Bee 1 (4), (1983) pp. 1235-1
240 pages (J, Vac, Sci.

technol, B l (1983) p p
235-1240) and others.

Furthermore, various types of reduction projection exposure apparatuses are known, such as Semiconductor World (Se
m1conductor World), 198
It is shown in the July 2004 issue, pages 110-114.

[Problems to be solved by the invention] As semiconductor integrated circuits have become more highly integrated in recent years, patterns have become finer, while the unevenness of the substrate surface has increased significantly.
Responses to these are required.

When a projection exposure method is used to form a pattern, the exposure optical system needs to have a larger depth of focus in order to cope with an increase in uneven steps. However, in order to improve the resolution, it is necessary to increase the numerical aperture of the projection lens as described above, so the depth of focus is conversely becoming shallow. Furthermore, because the image plane is not completely flat due to image plane distortion of the projection lens, it has become difficult to ensure a depth of focus corresponding to the unevenness of the surface over the entire exposure area.

With the multilayer resist method, it is not possible to completely flatten the unevenness of a large-area pattern, and even if complete flattening is achieved, the mask pattern may be distorted due to the field distortion of the lens and the overall inclination of the substrate. The image plane does not coincide with the substrate surface, making it difficult to deal with the above problem.

An object of the present invention is to provide a new device that can increase the effective depth of focus of an exposure optical system without relying on flattening the substrate, and to reduce the increase in unevenness of the substrate and the field distortion of the lens. The objective is to cope with the decrease in focus latitude due to tilting, the increase in the numerical aperture of the projection lens, and the shortening of the wavelength of exposure light.

[Means for Solving the Problems] According to the study of the present invention, the effective depth of focus of the exposure optical system is determined by It has been revealed that the amount increases by superimposing images.

The above images are superimposed by combining the lights that have passed through a plurality of optical paths, each having a different imaging plane near the surface of the substrate on which the mask pattern is to be projected and exposed, in front of the projection lens with their optical axes aligned. This is done by entering the reflected light into a projection lens and projecting it.

[Function] In order for the pattern to be well resolved on the resist layer above and below the uneven steps on the substrate surface over the entire exposed area, it is determined by the image plane distortion of the projection lens, the flatness of the substrate, and the height of the uneven steps on the substrate surface. It is preferable that a light intensity contrast of a certain level or higher is maintained within a certain range in the optical axis direction. On the other hand, in the projection exposure method, the light intensity contrast for forming a pattern on the resist layer has a sufficient value to faithfully reflect the mask pattern near the imaging plane of the mask pattern (so-called depth of focus). (within the range), and the contrast decreases rapidly as you move away from it. Therefore, when the depth of focus becomes shallow, it becomes impossible to maintain the necessary contrast within a range that requires light intensity contrast above a certain level, resulting in poor resolution.

Therefore, a plurality of images of the same pattern having imaging planes at different positions on the optical axis where a light intensity contrast of a certain level or higher is required are superimposed. Figure 3 a)-C
) are the light intensity distributions of the image formed at the position Z = +1.5 pm on the optical axis, the image formed at Z = -1.5 μm, and the image obtained by combining the above two machine numbers. The calculation results are shown for several positions in the optical axis direction to illustrate the principle of the present invention. The pattern is assumed to be a 0.5 μm hole pattern.1 As a result of synthesis, a light intensity distribution effective for pattern formation is realized over a wider range in the optical axis direction than the light intensity above and below a single imaging plane. has been done. As can be seen from FIG. 3, the light intensity approaches O as the distance from the image plane increases. Therefore, as a result of superposition, only the light intensity effective for pattern formation remains. This property may be characteristic of isolated exposed areas in light shielding areas such as hole pattern returns.

In more general patterns such as line and space, the light intensity distribution uniformly approaches a certain level as you move away from the image plane, thus.

By superimposing this uniform light intensity distribution on the light intensity distribution effective for pattern formation, the contrast of the light intensity is reduced. However, in this case as well, the effective depth of focus is
increase

Figure 4 shows the relationship between the position in the optical axis direction and the calculated value of the light intensity contrast of 0.7 μm line and space.
In FIG. 4, which is shown for each case of light synthesis using a point as an imaging point, the origin of the position in the optical axis direction is a single imaging point and the center point of two imaging points. As shown in Figure 4, although the absolute value of the light intensity contrast generally decreases due to the combination of light having different imaging points compared to the case of a single imaging point, the contrast above a certain level is maintained over a wider area. It can be seen that it is maintained. Further, by setting the distance between the two image forming points to an appropriate value, a constant light intensity contrast can be obtained within a certain range in the optical axis direction. The effective depth of focus increase rate by this method is determined by the lower limit of the light intensity contrast that can be resolved by the materials and processes used, such as the resist, developer, and contrast enhancement material. According to FIG. 4, the increase rate of the effective depth of focus by using this method is 45% when the lower limit of the light intensity contrast is 0.5, assuming that the distance between the two imaging points is 3.5 μm. On the other hand, when the lower limit of the light intensity contrast is 0.4, it becomes about 70%.

Furthermore, if the lower limit is 0.3, the effective depth of focus is 150 by superimposing three lights with different imaging planes.
% contrast of 60.3 can be sufficiently resolved by using CEL, and contrast of 0.5 can be resolved by using a resist with γ of 2.5 or more such as TSMR8800 manufactured by Tokyo Ohka Co., Ltd. It is sufficiently resolvable.

For isolated exposed areas in light-shielding areas such as hole patterns, there is almost no decrease in contrast due to one overlapping, so by increasing the number of image forming planes to be set, the effective depth of focus can be virtually unlimited. can be increased.

This projection exposure apparatus combines images of the same or the same type of mask pattern that have passed through a plurality of different optical paths, and then projects and exposes the images at the same position on the same substrate at the same time. At this time, the images that have passed through a plurality of different optical paths are formed at different positions in the optical axis direction due to the difference in the optical path length of each optical path or the difference in the structure of the optical system in each optical path.

Therefore, according to the present apparatus, exposure can be performed using a composite image of a plurality of images formed at different positions on the same optical axis. That is, this apparatus realizes a multiple imaging exposure function. As described above, this function allows the light intensity contrast of the image to be maintained over a wider range in the optical axis direction, increasing the effective depth of focus.

[Example] Example 1 An embodiment of the present invention will be described below with reference to FIG.

This device uses light source 1. Illumination optical system 2. It is equipped with a projection optical system 15, a substrate stage 7, and other various components necessary for a normal projection exposure apparatus. The projection optical system 15 includes two half mirrors 11, 14° and two mirrors 12, 13 . Auxiliary optical system for image formation position correction 49 Auxiliary optical system for magnification correction 5.
It includes a projection lens 6. These components are arranged as shown in FIG.

Light emitted from a light source 1, passed through an illumination optical system 2, and a reticle 3 is split into two directions by a half mirror 11. One of the divided lights is mirrored 12. The light enters the projection lens 6 through the mirror 13 and the half mirror 14, and then the substrate stage 7.
The mask pattern on the reticle 3 is imaged at a position 9 near the surface 8 of the upper substrate. The other light split by the half mirror 11 is sent to the auxiliary optical system 49 for correcting the imaging position and the auxiliary optical system 5 for magnification correction. The light enters the projection lens 6 via the half mirror 14, and forms an image of the pattern at a position 10 near the substrate surface 8.

Auxiliary optical system for image formation position correction 4. Or, due to the effect of the optical path difference between the two optical paths divided by the half mirror 11 and combined by the half mirror 14, the image forming position 9 and the image forming position v110 generally do not coincide. Therefore, with this apparatus, it is possible to perform exposure using a so-called multiple imaging exposure method in which a plurality of images having imaging planes at different positions on the same optical axis are superimposed and exposed.

The imaging position 10 can be set at any position within a range determined by changing the conditions of the auxiliary optical system 4 for correcting the imaging position. Further, by driving the substrate stage 7 in the optical axis direction, the relative position of the imaging position 9 with respect to the substrate surface 8 can be changed. Therefore, the imaging position 8. and 1
0 relative to the substrate surface can be set arbitrarily. The auxiliary optical system for correcting the imaging position may be provided in both of the two optical paths divided by the half mirror 11. Also, mirror 1
In the case where the imaging position 9 is changed by changing the optical path length of the optical path through the mirror by changing the position of 2.13, etc., the auxiliary optical system 4 for correcting the imaging position may be omitted.

In this case, the positions of the two imaging points 9 or 10 are set by adjusting the optical path lengths of the two optical paths.

Due to the effects of the auxiliary optical system 4 for correcting the imaging position and the optical path difference, the magnifications of the images that have passed through the two optical paths are generally not equal at each imaging position. Therefore, the auxiliary optical system 5 for magnification correction was provided at the position shown in FIG. The magnification correction auxiliary optical system 5 may be provided on the mask side of the imaging position correction auxiliary optical system 4. Also, the auxiliary optical system for magnification correction is the same as the auxiliary optical system for image formation position correction.
can be provided in both of the two optical paths. Further, when the imaging position is set by the optical path difference, an auxiliary optical system for magnification correction may be provided regardless of whether or not there is an auxiliary optical system for correcting the imaging position. If a change in magnification due to a change in the imaging position does not adversely affect pattern formation, the auxiliary optical system for magnification correction can be omitted.

In this embodiment, the optical path is divided into two, but a half mirror may be further added to divide the optical path into three or more parts, and the light passing through each part may be imaged at different positions in the optical axis direction. Increasing the number of imaging planes further increased the effective depth of focus of the optical system.

The amount of light passing through different optical paths is determined by the reflectance and transmittance of the half mirror, the reflectance of the mirror, the auxiliary optical system inserted into each optical path, and the like. In multiple imaging exposure, it is generally desirable that the exposure amount for each imaging point be approximately equal. Therefore, in this case, the reflectance and transmittance of the half mirrors 11 and 14 are set to be approximately equal to the number of optical paths divided into one. The number of divided optical paths is 3
Even in the case of more than one half mirror, the reflectance and transmittance of each half mirror must be adjusted so that the ratio of the amount of light that passes through each optical path and is reflected on the projection lens becomes equal.

In FIG. 1, each optical system is shown with a minimum lens configuration, but in actual equipment, it is assembled from more complex optical elements.

Using this apparatus, a hole pattern or a line and space pattern having a size of about 0.5 μm was projected onto a substrate having irregularities of various heights on the surface and developed. With conventional apparatuses that perform exposure using a single imaging plane, it has been impossible to resolve these patterns over the entire exposed area even when there are no uneven steps on the substrate surface. However, the width of the projection lens of this device is 1.5μ.
The substrate used in the experiment has a slope of 1 μm in width within the exposure area.

However, by equipping the apparatus shown in this embodiment with the same projection lens as the conventional apparatus described above, and using the same substrate, setting the imaging points at two points 3 μm apart from each other and performing multiple imaging exposure, Even when a probe with a height of 2 μm was present on the substrate surface, a pattern of 0.5 μm or less could be formed above and below the step.

The steepness of the pattern cross section depended on the type and size of the mask pattern, the material and process of the resist used, etc.

Generally, in the case of line-and-space patterns, the steepness of the cross-section of the resist pattern is somewhat reduced when multiple imaging exposure method is used, so CEL method, high-gamma resist process, etc. were used in combination.

However, in the case of contact holes, no deterioration of the pattern shape was observed even when the multiple imaging exposure method was applied.

Example 2 A second embodiment of the present invention will be described using FIG. 2.

This apparatus includes two sub-optical systems 100a and 100b, an image-synthesizing optical system 111. It consists of a projection lens 106° and other various components necessary for a normal projection exposure apparatus. The two sub-optical systems 100a and 100b are light sources 101a and 10, respectively.
1b, illumination optical system LO2a, 102b, exposure shutter 107a.

107b, reticles 103a and 103b, auxiliary optical systems for image formation position correction 104a and 104b, and auxiliary optical systems for magnification correction 105a and 105b. The optical system for image synthesis includes a mirror 112. Consists of 113 half mirrors. These components are arranged as shown in FIG.

The light emitted from the light source 101a is transmitted to the illumination optical system 102a, the exposure shutter 107a, and the reticle 103a.

Auxiliary optical system for image formation position correction 104a, auxiliary optical system for magnification correction 105a, mirror 112. and half mirror 113
The light then enters the projection lens 106.

The pattern on the reticle 103a is imaged at a position [109] near the substrate surface 108. On the other hand, the light emitted from the light source 101b includes an illumination optical system 102b, an exposure shutter 107b, a reticle 103b, an auxiliary optical system 104b for correcting the imaging position,
The light enters the projection lens 106 through the magnification correction auxiliary optical system 105b and the half mirror 113, and forms an image of the pattern on the reticle 103b at a position 110 near the substrate surface 108.

Imaging position 1 of the pattern on the reticles 103a, 103b
09 and 110 are respectively auxiliary optical systems 104a for correcting the imaging position.
, 104b, and the two ministries generally do not agree.

Additional, 1. Position adjustment of each imaging position does not depend on the auxiliary optical system for imaging position correction, but by moving the reticles 103a, 103b in the optical axis direction, etc., and changing the optical path length of the auxiliary optical systems 100a, 100b. You can do it by letting them do it.

In this case, the auxiliary optical system for correcting the imaging position may be omitted.

Auxiliary optical systems 105a and 105b for magnification correction are used for the reticle 103a at each imaging position 109 and 110 as in the first embodiment.
, 103b is adjusted so that the magnification of the pattern becomes the specified value. The arrangement of the auxiliary optical system for magnification correction is not limited to the position shown in FIG. 2, and as in the first embodiment, it can be omitted if unnecessary.

The number of sub-optical systems is limited to two as shown in this embodiment, but may be three or more.

By increasing the number of sub-optical systems, the number of imaging planes near the substrate surface can be increased. By increasing the number of imaging planes, the depth of focus of the optical system was further increased.

The contribution of each sub-optical system to exposure can be arbitrarily set by adjusting the reflectance and transmittance of the half mirror 113, the open time of the exposure shutters 107a and 107b, etc.

Using the apparatus shown in this example, the experiment shown in Example 1 was conducted and similar effects were confirmed.

[Effects of the Invention] As is clear from the above description, according to the present invention, the effective depth of focus in the projection exposure method can be increased, so that the numerical aperture of the projection lens can be increased, the wavelength of the exposure light can be shortened, It is possible to cope with the image plane distortion of the projection lens, the inclination of the mounting plate surface, and the increase in uneven steps. When the present invention is combined with a high contrast resist process such as the CEL method,
The effective depth of focus of a submicron pattern can be increased by about 70 to 100% when the number of set imaging planes is two, and by about 150 to 200% when the number of set imaging planes is three, compared to the conventional method.

As a result, even if there is a height difference of 2 μm or more on the substrate surface, for example, it is possible to apply 0.5 μm to the entire exposed area without making any special improvements to the image plane distortion of the lens, the inclination of the substrate, etc.
Patterns smaller than m can be resolved.

Conventionally, it was virtually impossible to apply optical lithography to the production of LSIs with a line width of 0.5 μm due to the lack of depth of focus, but by adopting the present invention,
It has become possible to do this with a yield of 80% or more.

In addition, excimer lasers have recently been used as light sources for optical lithography.
is attracting attention, but when this is used, the exposure wavelength becomes even shorter and the focus latitude decreases further. Therefore, the present invention is very effective as a technology for utilizing excimer lasers.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention. FIG. 2 is a configuration diagram of an embodiment of the present invention. FIG. 3 is a conceptual diagram showing the principle of the present invention. FIG. 4 is a curve diagram showing the effects of the present invention. 1...Light source, 2...Illumination optical system, 3.
... Reticle, 4... Auxiliary optical system for image formation position correction, 5... Auxiliary optical system for magnification correction, 6.
...Projection lens, 7...Substrate stage,
8... Substrate surface, 9... First imaging point,
10...Second imaging point, 11.14...
Half mirror, 12, 13...Mirror, 15.
...Projection optical system. (Figure 2) 110a, 100b - sub-optical system, 10
1a, 101b-light source, 102a, 102b... illumination optical system, 103a
, 103b...Reticle, 104a, 104b
...... Auxiliary optical system for image formation position correction, 105a, 1
05b...Auxiliary optical system for magnification correction, 106
...Projection lens, 107a, 107b...
...Exposure shutter, 108...Substrate surface, 1
09...First imaging point, 110...Second
Image forming point, 111... Optical system for merging, 112.
...Mirror, 113...Half mirror-0
10th Taku 4 Axial front body 1 [anchor]

Claims (1)

[Claims] 1. In an apparatus for projecting and exposing a mask pattern onto a substrate, a plurality of images each having a conjugate plane of the pattern at different positions in the optical axis direction at the same position on the substrate are synthesized, A projection exposure apparatus having a multiple imaging exposure function for projecting exposure onto the substrate. 2. The projection exposure apparatus according to claim 1, characterized in that the number of the masks is one, and the mask has a plurality of different optical paths. 3. The projection exposure apparatus according to claim 1, wherein there are two or more masks, and each of the masks has a different optical path.