JPH0817720A - Projection exposure device - Google Patents

Abstract

(57) [Summary] [Object] To construct a reflection type reduction projection exposure apparatus and to provide a projection optical system which can be used even in a short wavelength region where a transmission refraction lens cannot be used. A projection exposure apparatus that exposes a pattern of the mask onto a photosensitive substrate through a projection optical system by irradiating a light beam from a light source means on the mask, wherein the projection optical system has a curved reflecting surface. Including a plurality of reflecting members having at least one diffractive optical element. The diffractive optical element is formed on the reflecting surface of a reflecting member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type projection exposure apparatus used for projecting a predetermined pattern formed on a mask onto a photosensitive substrate.

[0002]

2. Description of the Related Art Conventionally, a so-called lithographic process involving transfer exposure of a predetermined pattern has been applied to a manufacturing process of a semiconductor device such as an IC or an LSI, a liquid crystal device similar thereto, a member having a fine pattern such as a thin film direct head. Has been done. Here, a step of exposing and projecting this pattern from a mask having a predetermined circuit pattern or the like onto a photosensitive substrate such as a silicon wafer via a projection optical system is performed.

Further, as the degree of integration of semiconductor elements increases and the miniaturization of patterns progresses, a reduction magnification is generally used as the magnification of the projection system of this type of apparatus.
The reason for this is that if the same size is used, the pattern on the photomask must be formed with the same size as the pattern to be projected, which makes it difficult to form the photomask. Further, it is expected that it will be difficult to manage defects and dust on the photomask.

The projection optical system of the projection exposure apparatus used for the transfer exposure of such a pattern is required to have a high resolution, but since the resolution of the optical system is related to the wavelength of the light flux used, this type of The wavelength of the light flux used in the optical system is becoming shorter. Looking at the history of shorter wavelengths up to today, the g-line (λ = 43
6 nm), i-line (λ = 365 nm), Kr
An exposure apparatus using a −F excimer laser (λ = 248 nm) is becoming commercially available.
And Ar-F excimer laser (λ = 193 nm)
An exposure apparatus using is used.

By the way, in a so-called semiconductor integrated circuit,
With the recent shift from conventional ICs and LSIs to VLSIs, ULSIs, and the like, higher integration is progressing, and the required resolution (resolution) is also becoming higher. For this reason, a projection type optical system is used, but there is a need to cope with the demand for higher integration by means such as using a light flux having a shorter wavelength than in the past. Utilization of ₂ lasers (157 μm) and X-rays has been studied.

However, a conventional projection optical system using a refracting lens has a problem that sufficient imaging characteristics cannot be obtained due to a problem such as transmittance, and a conventional optical element or a correction means alone causes a short wavelength. The reality is that we cannot fully meet the demand for higher integration. In addition, although a projection optical system using only a reflecting member has been put into practical use, it is extremely difficult to construct a reduction type projection optical system effective for transferring a fine pattern because of the problem of the reflection characteristics of a spherical mirror, etc. There was a problem that the system could not be constructed.

As described above, in the flow of technological development for the purpose of reducing the wavelength and shortening the wavelength (increasing the resolution), what kind of projection optical system (or projection exposure apparatus)
Let's take a quick look at what has happened so far.

As a form of an optical system that has been used for a long time and up to the present, the most commonly used form is a refractive optical system. This refraction optical system is
It is used in an ep-and-Repeat System (so-called stepper type projection exposure apparatus), and a plurality of refracting members are arranged on the optical axis to achieve reduction magnification and to correct various imaging aberrations. Is. Here, the refraction member is a so-called lens configured by a curved surface that is rotationally symmetrical about the optical axis.

On the other hand, as a conventional projection optical system which does not use a refracting member, a reflection optical system composed of only a reflection surface can be considered most easily. It is known that magnification can be realized. An example thereof is known as a so-called Offner optical system, and its specific configuration is described in JP-B-57-
No. 51083. However, a reduction-magnification projection optical system composed of only a reflecting surface has not yet been found.

[0010]

In the prior art as described above, a refraction member was indispensable in the optical system constituting the projection optical system, but in the short wavelength region, the glass material as the refraction member is transmitted. It is well known that the rate is extremely poor.

Specifically, since a general optical glass cannot be used in the range of the wavelength of the Kr-F excimer laser (λ = 248 nm) to the wavelength of the Ar-F excimer laser (λ = 193 nm). The refracting member in the optical system is made of a special glass material such as quartz or fluorite glass.

If a glass material or the like having a poor transmittance in the wavelength range is used for the refraction member, the amount of transmitted light is reduced, the performance of the exposure apparatus is deteriorated, and not only the throughput of the exposure operation is deteriorated, but also the transmission work. Since the amount of light that is not absorbed is absorbed by the glass material that constitutes the refraction member, the serious problem is that the entire optical system suffers from performance deterioration due to problems such as thermal deformation and refractive index change due to heat generated here. To be

In view of the extension of the trend of shortening the wavelength, therefore, considering a reduction projection exposure apparatus, the ArF excimer laser (λ
= 193 nm) is the limit for shortening the wavelength, and a further reduction in wavelength, for example, a reduction projection exposure apparatus using a F ₂ laser (λ = 157 nm) as a light source cannot be configured.

On the other hand, it is impossible to construct a reduction type optical system capable of performing accurate exposure and transfer of a pattern only by the reflection optical system, because it is impossible with the conventional technique due to the limit of the reflection characteristic only. Although the one using it has been realized, the refracting member (in which the transmitted optical path is long) is large, and the light flux of short wavelength cannot be used.

[0015] For example, an exposure apparatus that is issued by SVGL, Inc. under the trade name of Micrascan is a Step-and-Scan System.
In this device, a catadioptric optical system is used as the projection optical system. In this catadioptric optical system, a plurality of reflecting surfaces and a plurality of refracting members are used.

The present invention has been made in view of the above problems, and constructs a reduction type projection optical system that can be used even in a short wavelength region where a general refracting member cannot be used. However, it is an object of the present invention to provide a reduction type projection exposure apparatus having the optical system.

[0017]

In order to achieve the above object,
In the invention described in claim 1 of the present application, in the projection exposure apparatus, which exposes the pattern of the mask onto the photosensitive substrate through the projection optical system by irradiating the mask with the light flux from the light source means, the projection optical system comprises: A projection exposure apparatus including a plurality of reflecting members having curved reflecting surfaces and at least one diffractive optical element.

According to a second aspect of the invention, in the projection exposure apparatus according to the first aspect, the diffractive optical element is
It is characterized in that it is formed on the reflecting surface of the reflecting member.

According to a third aspect of the invention, in the projection exposure apparatus according to the first or second aspect, at least two of the plurality of reflecting members are located at positions where the respective centers of curvature of the reflecting surfaces are different from each other. It is arranged so that
A feature is that a reduction optical system is configured as the entire projection optical system.

[0020]

Since the present invention is configured as described above, the projection optical system is constituted by the reflecting member and the diffractive optical element. Therefore, in addition to the deflecting action of the optical path by the reflecting member, the deflection of the optical path by the diffractive element is performed. By combining the actions, a predetermined pattern is projected (transferred).

Here, the diffractive optical element is an optical element that deflects the optical path by utilizing the diffracting action of light, and has recently been attracting attention as an optical element used in a projection exposure apparatus of this type. According to this diffractive optical element, it is possible to arbitrarily deflect the optical path of a light flux having a short wavelength.

Further, since it exhibits a wavelength-deflection characteristic different from that of a so-called refraction lens, new aberration correction means or the like by combining with a refraction lens is drawing attention, but it can also be applied to correction of reflection characteristics. However, it became clear in the study of the present inventors.

As the diffractive optical element, for example, a Fresnel zone plate or the like is well known, but a general Fresnel zone plate has a structure in which a concentric light shielding member is provided on a light transmissive substrate, Generally, the light beam is condensed at a predetermined position by utilizing the diffraction effect of the light beam from the transmission region.

The structure of the diffractive optical element including the zone plate is not limited to the structure of the transmitting portion and the light shielding portion as described above, but may be one in which regions having different transmission characteristics (refractive index, transmission distance, etc.) are provided stepwise. It is known that the substrate is provided with a portion having different transmission characteristics due to the refractive index distribution. The former representative is a so-called binary optical element (BOE), and the latter representative is a so-called hologram optical element (HOE).

In the BOE, a stepwise surface shape is formed on the light transmissive member (may be formed on the surface of the reflective member) by using a lithography process, and the transmission distance is partially made different to diffract. Fig. 2 shows a configuration that produces the action and has the action and effect of the Fresnel zone plate.
For example. BOE has an advantage that a fine arbitrary pattern can be constructed with high accuracy and freely from its manufacturing method.
Its field of application is of particular interest. (Photo industry, 19
(March 1994, p. 94)

According to these sophisticated diffractive optical elements such as BOE, the diffracted light to be generated is not only the one which has the well-known well-known focusing function, but also any light wavefront is converted into a desired light wavefront. By doing so, it is possible to generate a free diffraction action such as having a light diverging function and combining a light focusing function and a light beam separating function.

Furthermore, BOE is thin and lightweight, easy to mass-produce, easy to manufacture and high in diffractive action, high in light utilization rate, and capable of deflecting an optical path even in a light beam in the deep ultraviolet region. Therefore, the application of the projection optical system as an optical member has been studied.

By the way, the behavior of the diffractive optical element is as follows.
W. C. Sweatt's paper (J. Opt. Soc. A.
m. vol. 69, No. 3, p. 486 (197)
According to 9)), it is equivalent to a refractive lens having an infinitely small thickness and an infinite refractive index.

Therefore, in the projection optical system of the reduction type with the reduction magnification, the role of the refracting member is assigned to the diffractive optical element, so that the projection optical system of the reduction magnification is realized only by the reflecting surface and the diffractive optical element. It becomes possible to do it.

In the present invention, since the reduction type projection optical system is composed of the reflection member and the diffractive optical element, reduction is achieved even in a short wavelength region where a general transmission type refraction member cannot be used. A mold type projection exposure apparatus can be realized.

Here, there are the following restrictions on the structure of the reflection type reduction projection exposure apparatus according to the present invention. First of all, the diffractive optical element has a dispersion according to the wavelength width of the light used. This is because the diffraction angle varies depending on the wavelength. Therefore, speaking in the paraxial region, it is desirable for the diffractive optical element to have a power (or diffraction angle) close to zero (focal length, infinity).

However, this does not mean that the diffractive optical element is equivalent to a parallel plate. Since the diffractive optical element can easily and arbitrarily deflect the optical path in other parts even if the power is formed to be zero in the paraxial region, it is easy to construct a diffractive optical element that has the same effect as an arbitrary aspherical surface. You can do it.

Secondly, considering the dispersion characteristics of such a diffractive optical element, it is preferable that the wavelength range of the light beam used is small, and a light source for producing such a light beam has a small wavelength width. It will be appreciated that one is suitable. Therefore, a laser is desirable as the light source.

Thirdly, as described above, since the diffractive optical element is equivalent to infinite refractive index, its contribution to the Petzval sum is zero. Therefore, the Petzval sum must be corrected only by the optical member excluding the diffractive optical element, preferably by the reflecting member, as the entire optical system. Therefore, both the convex surface and the concave surface must be used as the curved reflecting surface of each of the plurality of reflecting members.

That is, taking these into consideration, a Petzval sum is corrected by using a light source having a narrow oscillation wavelength band (a laser having a short wavelength or the like) and combining a plurality of reflecting members having convex and concave reflecting surfaces. As long as this is done, an optical system designed to have a desired magnification is constructed, and at the same time, the diffractive optical element partially deflects aberrations and reflected deflected light that cause distortion in the projected image, By designing to deflect the optical path so that an accurate projected image can be obtained, a reflection type reduction projection optical system and a projection exposure apparatus using the same can be constructed.

If the diffractive optical element has a diffraction pattern constructed on a thin light transmissive substrate such as BOE, it may be arranged as a transmissive member in the optical path of the projection optical system. The decrease in the amount of transmitted light at 10 is not a problem. It is also possible to construct a reflective diffractive optical element by constructing a diffraction pattern on a reflective substrate. Therefore, by providing the reflection type diffractive optical element on the optical path of the projection optical system, it is possible to construct a projection optical system in which there is no problem in reducing the amount of light due to the transmission of the optical member.

In the second aspect of the invention, the diffractive optical element is formed on the curved reflecting surface of the reflecting member. In other words, the diffractive optical element and the reflecting member are integrally formed. There is an advantage that the number of members constituting the projection optical system is reduced.

Such an integrated reflection diffractive optical element is
It can be constructed by forming a diffraction pattern on the surface of the reflecting mirror. For example, it can be easily manufactured by a method such as applying a manufacturing process such as BOE on the reflecting surface to form a laminated pattern of light transmitting members.

Further, in the invention described in claim 3, since at least two of the plurality of reflecting members are arranged such that the respective centers of curvature of the reflecting surfaces are different from each other, these are provided. The projected image is magnified by the reflecting action of the reflecting member. That is, the zooming action of the projection optical system in the present invention may be performed by the curved reflecting action of the reflecting member or the diffractive deflection action of the diffractive optical element, but at least if the centers of curvature of the reflecting members are the same. There is no scaling effect between the two, and the magnification becomes equal.

As in the present invention, by making the centers of curvature of the reflecting members different, the projected image is magnified by the reflection and deflection action between them. However, since the projection image is distorted only by the reflection of such a curved surface, the diffractive optical element is provided with a deflecting action for correcting the optical path so as to cancel the distortion of the projection image.

[0041]

The present invention will be described in more detail with reference to the following examples. FIG. 1 shows a main part of a projection optical apparatus according to an embodiment of the present invention. A photomask 1 is transmissively illuminated by exposure light emitted from an illumination optical system (not shown) and coated with a photoresist. The image of the predetermined pattern of the photomask 1 is formed on the photosensitive substrate 2 made of a wafer. Here, as the light source means Ar-
An F laser (λ = 193 nm) is used.

The light flux that has passed through the photomask 1 is reflected by a reflecting mirror 11 having a concave curved reflecting surface, guided to a reflecting mirror 12 having a convex curved reflecting surface, and further reflected here to have a concave curved surface. It is guided to the reflecting mirror 13 having a reflecting surface. The light beam reflected by the reflecting mirror 13 is transmitted through the diffractive optical element 21.
The light path is partially deflected and guided to a diffractive reflecting mirror 14 having a concave curved reflecting surface and a diffractive pattern 22 formed on the reflecting surface, where it is reflected and diffracted to form a mask on the photosensitive substrate 2. The image of the pattern No. 1 is reduced and scaled and projected.
The positions of the centers of curvature of these reflecting surfaces are arranged so that they do not all coincide.

Here, the diffractive optical element 21 is a diffractive optical element having a diffraction pattern made of, for example, a transmissive member formed on a quartz glass substrate. The quartz glass substrate itself may be etched to form a diffraction pattern.

Although the diffractive optical element 21 is of a transmissive type, the substrate itself can be constructed with a very thin one according to a manufacturing method such as so-called BOE. Differently, the transmittance (decrease in the amount of transmitted light) and the heat (absorption of light) are hardly problems. It is also possible that the diffractive optical element 21 has a diffraction pattern provided on a flat reflecting member, and the optical path is bent here to form an optical system. In this case, the projection optical system is used without using a transmissive element. Can be built.

On the other hand, the diffractive reflecting mirror 14 is also a kind of diffractive optical element in which a diffractive pattern having a laminated structure of a transmissive member or a reflective member is formed on the surface of the reflective mirror. As described above, the diffractive optical element such as BOE can form the diffraction pattern not only on the flat surface but also on the curved surface, and can be formed not only on the transmitting member but also on the reflecting surface.

Next, the basic magnification of the projection optical system of this embodiment is basically determined only by the reflecting surface (reflecting mirrors 11, 12, 13 and the diffractive reflecting mirror 14). That is, a projection optical system with a reduced magnification composed of only reflecting surfaces is constructed by the reflection (deflection) action of three concave curved surfaces and one convex curved surface.

As a reduction trend, it is said that 1/4 to 1/5 times is appropriate as the current trend. Further, it is preferable that the image formation relationship between the photomask surface and the photosensitive substrate is performed in the annular slit region, and the photomask and the photosensitive substrate are scanned along the reduced imaging magnification ratio. . Further, the diffractive optical element (21, 2)
2) has the effect of an aspherical surface in terms of the so-called analogy of the refracting action on the refracting surface, and has the function of correcting the aberration of the variable power optical system configured by the reflecting mirror as described above. .

That is, since the basic magnification of the projection optical system is determined by the reflecting surface other than the diffractive optical element, the diffractive optical element is configured to contribute to aberration correction. Here, the aberrations include spherical aberration, coma aberration, astigmatism, field curvature, distortion aberration, etc. When a plurality of diffractive optical elements are used, the aberration to be corrected is determined by the arrangement configuration.

For example, when it is arranged near the pupil plane of the whole view, the effect of aberration correction is large in the order of spherical aberration, coma, astigmatism, field curvature, and distortion. In the case of being arranged near the image plane (including the intermediate image), on the contrary, the effect of aberration correction is large in the order of distortion, field curvature, astigmatism, coma and spherical aberration.

In the embodiment shown in FIG. 1, since an intermediate image is formed near the diffractive optical element 21, the diffractive optical element 2
1, the distortion correction, the field curvature, and the astigmatism are mainly corrected, and the diffractive optical element 22 located near the pupil surface mainly corrects the spherical aberration, the coma, and the astigmatism.

Therefore, in this embodiment, an exposure apparatus using the reflection type reduction projection optical system can be constructed as described above, and the projected image reproduces a fine pattern without distortion. In addition, the basic design is based on an even shorter wavelength (F ₂ laser (λ = 15
It is also possible to construct an exposure apparatus in accordance with (7 nm) and the like), and transfer exposure of a fine pattern with higher accuracy than ever can be performed.

In this embodiment, two diffractive optical elements are arranged at the positions shown in FIG. 1. However, this is determined by the aberration correction caused by the arrangement of the reflecting mirrors in this embodiment. However, the present invention is not limited to this. Even with the same arrangement of reflecting mirrors, different numbers of diffractive optical elements having different configurations may be provided at different positions.

The arrangement of the reflecting surfaces is not limited to the arrangement shown in FIG. Depending on the configuration of the optical system designed according to the required magnification, etc., in any number,
It can be arranged at any position. In any case, various configurations may be designed by combining a reflecting mirror and a diffractive optical element within a range not departing from the gist of the present invention so that an accurate projected image can be obtained at an appropriate magnification.

[0054]

As described above, according to the present invention,
Since the reflection type reduction projection optical system can be easily constructed by using the diffractive optical element, there is an advantage that the range of application as the projection optical device is widened.

In particular, a variable-magnification (reduction type) projection optical system can be realized mainly by a reflecting member without using a transmissive-refractive member, which has heretofore been impossible. Therefore, transfer exposure in a short wavelength region becomes possible. That is, it is possible to realize a reduction projection optical system that can be used even in a short wavelength region where it is generally considered that a refraction member cannot be used. Needless to say, shortening the wavelength of the used light flux means improving the resolution of the projection optical system, so that it is possible to perform highly precise transfer exposure of a fine pattern using a light flux in the short wavelength range. .

Furthermore, the present invention can be applied not only as a projection exposure apparatus equipped with a reduction projection optical system used in so-called photolithography but also as an exposure apparatus in so-called X-ray lithography. That is, X-rays are also a type of electromagnetic wave, and the reflection on the reflecting member follows Snell's law (incident angle = reflection angle), and the diffraction phenomenon in the diffractive optical element is recognized as in light. Therefore, by applying the present invention, it is also possible to construct a projection optical system of equal magnification or variable magnification using X-rays.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram showing a main configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a schematic configuration of an example of a binary optical element (diffractive optical element).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1: Photomask 2: Photosensitive substrate 11, 13: Concave reflecting mirror 12: Convex reflecting mirror 14: Diffractive reflecting mirror 21: Transmissive diffractive optical element 22: Reflective diffractive optical element (provided on the reflective mirror Diffraction pattern)

Claims (3)

[Claims] 1. A projection exposure apparatus that exposes the pattern of the mask onto a photosensitive substrate through a projection optical system by irradiating the mask with a light beam from a light source means, wherein the projection optical system is a reflection on a curved surface. A projection exposure apparatus comprising a plurality of reflecting members each having a surface and at least one diffractive optical element. 2. The projection exposure apparatus according to claim 1, wherein the diffractive optical element is formed on a reflecting surface of the reflecting member. 3. At least two of the plurality of reflecting members are arranged such that the respective centers of curvature of their reflecting surfaces are different from each other, and constitute a reduction optical system as a whole of the projection optical system. The projection exposure apparatus according to claim 1 or 2, wherein