JPH06250377A - Exposure method and photomask used in the same - Google Patents

Abstract

PURPOSE:To expose a bright isolated pattern such as a contact hole with sufficient depth of focus. CONSTITUTION:A light shielding film 12 with an opening 12a is formed on a transparent, substrate 11 and a phase member 15 with conical inclination is fixed on the opening 12a in the resulting photomask. A bright region of nondiffracted beams is formed between points A1 and B1 by illumination light passing through the phase member 15. A photosensitive substrate 16 is disposed in a region A3-B3 conjugated with the projected optical system 18 of the bright region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method for printing a pattern of a photomask as an original plate on a photosensitive substrate when, for example, manufacturing a semiconductor device or a liquid crystal display device by using a photolithography technique, and an exposure method therefor. The present invention relates to a photomask used in an exposure method.

[0002]

2. Description of the Related Art For example, when a semiconductor device or a liquid crystal display device is manufactured by using a photolithography technique, a pattern of a photomask or reticle (hereinafter referred to as "photomask") is exposed through a projection optical system. 2. Description of the Related Art A projection exposure apparatus that exposes a material coated substrate (wafer, glass plate, or the like) is used. As a photomask for such a projection exposure apparatus, conventionally, a photomask in which a pattern is formed on a transparent substrate with a light shielding film has been generally used.

FIG. 4A shows a photomask made of a conventional light-shielding film. In FIG. 4A, a light-shielding film 12 such as a chromium film is formed on a transparent substrate 11 such as a glass substrate. The opening 12a formed in 12 corresponds to the bright pattern. Recently, as the pattern of semiconductor elements and the like becomes finer, the projection exposure apparatus is required to have improved resolution. The projection optical system, the illumination optical system, and the photomask have been improved in order to enhance the resolution, but a so-called phase shift mask has been attracting attention as a photomask for enhancing the resolution.
Various variations have been proposed for the phase shift mask. Now, assuming that the pattern to be transferred on the photosensitive substrate is an isolated bright pattern, an example of a phase shift mask for such an isolated pattern is shown in FIGS. 4B and 4C.
Shown in.

FIG. 4B shows a phase shift mask called “auxiliary pattern type”. In FIG. 4B, an auxiliary opening 12b is formed around the opening 12a of the light shielding film 12 on the transparent substrate 11. Is formed, and the phase member 13 is formed on the opening 12b. On the other hand, FIG. 4C shows a photomask called “edge-enhanced type” or the like. In FIG. 4C, the edge portion of the opening 12 a of the light shielding film 12 on the transparent substrate 11 is covered. The phase member 14 having an opening is formed in the.

In both of the phase shift masks of FIGS. 4B and 4C, the phase member 13 or 14 covers a part of the transmissive portion formed by the opening 12b or 12a, and the phase member 13 is formed.
Alternatively, the phase of the light passing through 14 is changed by π as compared with the light passing through the opening without passing through the phase member. That is, when the refractive index of the phase members 13 and 14 is n, the thickness is d, the wavelength of the exposure light is λ, and k is an integer, the thickness d is set to satisfy the following equation. There is.

[0006]

(N-1) d = (k + 1/2) λ It has been confirmed that the resolution of the pattern is improved by using such a conventional phase shift mask.

[0007]

Generally, when the pattern to be transferred is miniaturized, the numerical aperture of the projection optical system increases accordingly, and as the numerical aperture increases,
The depth of focus, which is the range in which good image formation is performed, becomes shallow.
This is the same even when the phase shift mask is used, and there is a disadvantage that the depth of focus is not always sufficient even if the resolution is increased by using the phase shift mask.
Further, as the exposure apparatus, a contact type or proximity type exposure apparatus that does not use a projection optical system is also used. However, in such an exposure apparatus, especially when a pattern to be transferred is miniaturized, the transfer of the pattern may occur. It will be difficult.

However, it has been known that, for a periodic pattern such as a line-and-space pattern having a predetermined pitch, the so-called modified light source method can improve the resolution and secure the depth of focus. However, there is currently no effective method for ensuring the depth of focus for isolated patterns such as contact holes. In view of the above point, the present invention has an object to provide an exposure method capable of exposing a bright isolated pattern such as a contact hole with a sufficient depth of focus. Furthermore, the present invention aims to provide a photomask used in such an exposure method.

[0009]

In the first exposure method according to the present invention, for example, as shown in FIG. 2, a pattern of transmissive portions (12a) arranged between light shielding members (12) is formed. The photomask is illuminated, and the image of the pattern on the photomask is projected through the projection optical system (18) onto the substrate (1
6) In the method of exposing on the photomask, a phase member (15) having a cone-shaped inclination is arranged on the transmissive part (12a) on the photomask, and projected by the illumination light that has passed through the phase member (15). The substrate (16) is arranged in regions (A3 to B3) that are conjugate with the projection optical system (18) with respect to regions (A1 to B1) of the bright part formed in the optical axis direction of the optical system (18). It is the one.

Further, in the second exposure method of the present invention, as shown in FIG. 1, for example, a photomask on which a pattern made up of transmissive portions (12a) arranged between light shielding members (12) is formed is illuminated. Then, in the method of exposing the pattern on the photomask onto the substrate (16), a phase member (15) having a cone-shaped inclination is arranged on the transmissive portion (12a) on the photomask, The substrate (16) is arranged in the bright area (A1 to B1) formed in the thickness direction of the photomask by the illumination light that has passed through the member (15).

Further, the photomask of the present invention has a predetermined opening (1) on a transparent substrate (11) as shown in FIG.
2a) is provided to dispose the light shielding member (12), and the phase member (15) having a cone-shaped inclination is provided so as to cover a part or the whole of the transmission part (12a) surrounded by the light shielding member (12). It is arranged.

[0012]

According to the first exposure apparatus of the present invention, since the conical-shaped phase member (15) is arranged in the transmissive portion (12a) of the pattern on the photomask, the conical-shaped phase member (15) is formed. The light transmitted through the phase member (15) forms a non-diffraction beam (described later), which is transmitted through the projection optical system (18) to the substrate (1
6) Image the pattern of the photomask on top. Here, a non-diffraction beam does not spread when propagating in space,
That is, it is a light beam that travels without being diffracted, and its existence is described in the following document “J. Durnin,“ Exact solutions for non
-diffracting beams.I.The scalar theory, "J.Opt.So
c. Am.A4, 651-654 (1987) ”.

Further, the non-diffracted beam is formed on the exit side of the conical lens by making a light beam incident vertically from the bottom side of the conical lens to the bottom surface of the conical lens, for example. Herman et al, “Production and uses
of diffractionless beams, ", J.Opt.Soc.Am.A8,932-94
2 (1991) ”. That is, the present invention is such that the non-diffracted beam, which has been clarified in the above literature, is formed in the opening (transmission portion) of the photomask. As a result, a light beam that does not spread is formed in the optical axis direction of the projection optical system (18) in the region (A1 to B1) behind the opening (12a) of the photomask. Since a beam-like bright object elongated in the optical axis direction is imaged on the substrate (16) via the projection optical system (18), the depth of focus as an optical imaging performance is increased. .

According to the second exposure method, the cone-shaped phase member (1) that covers the transmissive portion (12a) of the photomask is used.
The non-diffracted light beam that has passed through 5) forms an image equivalent to an elongated bright object in a predetermined range of areas (A1 to B1) behind the transmission section (12a). Therefore, the board (1
By arranging 6), exposure is performed with a deep depth of focus in the proximity method.

The photomask of the present invention is used in the above-mentioned exposure method.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a photomask of this embodiment,
In FIG. 1, a light shielding film 12 such as a chromium film formed on a transparent substrate 11 such as a glass substrate (downward in FIG. 1).
A circular opening 12a is formed in a part of the
A phase member 15 in the shape of a convex cone (cone or pyramid) is attached so as to cover 2a.

In FIG. 1, when the illumination light 101, 102, 103 enters the opening 12a of the transparent substrate 11 from above, since the phase member 13 has a pyramidal shape, the illumination light 101-
103 is refracted by the phase member 15 and refracted light 104, 10
5,106,107. Here, considering the behavior of light in a region of height Δ1 between points A1 and B1 in FIG. 1, the amplitude of light on a line segment C1 indicated by a broken line between points A1 and B1. Is represented everywhere by the combination of the plane waves formed by the refracted lights 104 and 105 and the plane waves formed by the refracted lights 106 and 107. Therefore, it can be considered that the light intensity on the line segment C1 is constant. The above is a qualitative description of the non-diffracted beam, but detailed wave-optical analysis is disclosed in the above-mentioned document.

A portion having a constant light intensity is formed in the area between the point A1 and the point B1 on the exit side of the photomask in this manner. Therefore, for example, by disposing the photosensitive substrate 16 in this portion, it becomes deep. The isolated pattern of the photomask can be exposed on the photosensitive substrate 16 at the depth of focus. Furthermore, even if an image in the vicinity of the line segment C1 is formed on a photosensitive substrate via a projection optical system (not shown), a uniform light intensity distribution can be realized in a certain range in the optical axis direction on the image plane side.

FIG. 2 shows a case in which the projection optical system 18 is arranged in such a manner. In FIG. 2, a kind of bright image is formed in the area between points A1 and B1 by the non-diffracted beam passing through the phase member 15. Is formed. The image between the points A1 and B1 is formed in the area between the points A3 and B3 via the projection optical system 18. That is, the height Δ between the points A3 and B3
A bright image due to the non-diffracted beam is also formed in the area 3 and an image with an increased depth of focus can be realized.
Therefore, in the area between the points A3 and B3, the photosensitive substrate 1
By arranging 6, a high resolution and a deep depth of focus can be obtained.

Next, a second embodiment of the present invention will be described. FIG. 3 shows a photomask of the second embodiment. In FIG. 3, an opening is formed in a part of a light shielding member 12 such as a chrome film formed on a transparent substrate 11 (downward in FIG. 3). 12a is formed, and a concave cone-shaped phase member 17 is provided so as to cover the opening 12a. When the illumination light 101, 102, 103 enters the opening 12a from above in FIG. 3, since the phase member 17 has a concave cone shape, the illumination light is refracted by the phase member 17 to be refracted light 108, 10.
It becomes 9,110,111. In the case of a concave cone, a virtual image of the non-diffracted beam is formed at a position where the refracted lights 108 to 111 extend in the direction opposite to the traveling direction.

That is, when the projection optical system is used, when viewed from the projection optical system side, the refracted lights 108 to 111 are equivalent to the light from the non-diffracted beam of the virtual image between the points A2 and B2. . When these refracted lights 108 to 111 form an image on the photosensitive substrate side via the projection optical system, a non-diffracted beam is also formed on the photosensitive substrate side, and an image with an increased depth of focus is realized. This is similar to the case of the first embodiment shown in FIGS.

In order to form a non-diffracted beam in both the first and second embodiments, the cone-shaped phase member 15 or 1
It can be said that light is preferably incident vertically on the bottom surface of No. 7 and that the numerical aperture (NA) of the illumination optical system is smaller. Further, in the above embodiments, it is essential that the shape of the phase members 15 and 17 is a cone, and the cone may be a cone or a pyramid. Further, in the above-described embodiment, the phase members 15 and 17 are placed on the opening 12a, but the transparent substrate 11 is etched into a convex or concave cone shape in the opening 12a to form a phase. Member 15,
An effect equivalent to 17 may be provided.

Further, by arranging the phase member having the convex cone shape as in the first embodiment, the non-diffracted beam is formed below the photomask, so that the focus is substantially focused even in the proximity exposure. The depth is increased, and exposure can be performed with a deep depth of focus. It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0024]

According to the first exposure method of the present invention, of the patterns on the photomask, a non-diffracted beam of a real image or a virtual image corresponding to a bright pattern (transmission part) isolated in a dark background. Can be formed,
By forming an image on the substrate side via the projection optical system, there is an advantage that an image with an increased depth of focus can be realized.

Further, as can be estimated from FIG. 2, it is possible to obtain an effect similar to that of the present invention by providing a ring-shaped aperture filter for blocking the central portion on the pupil plane 19 of the projection optical system 18. (See, for example, Japanese Patent Laid-Open No. 61-91662),
The present invention does not reach the following points. That is, the loss of the light amount in the filter in the pupil portion becomes large. Image formation by the non-diffracted beam and normal image formation cannot be realized in the same filter. In other words, the exposure of the pupil filter must be taken in and out, and separate exposure shots must be taken. It can be said that these opposite effects are irreversible and are advantages of the present invention.

Further, as a side effect of the present invention, as shown in FIGS. 1 and 3, the non-diffraction beam region is located below the photomask depending on whether the phase member has a convex shape or a concave shape. Or it changes to the upper part. This means that if there is a step structure on the substrate due to the process, the depth of focus range can be changed for each pattern in the photomask example in accordance with the step structure. As described above, according to the present invention, not only the depth of focus for one isolated pattern can be increased, but also the total depth of focus can be increased in accordance with the step structure on the substrate.

According to the second exposure method of the present invention,
Since the non-diffracted beam is formed below the photomask by arranging the convex phase member having the shape of a cone in the transmission part, the pattern of the photomask can be exposed on the substrate by proximity exposure. Further, according to the photomask of the present invention, the above-mentioned exposure method can be implemented.

[Brief description of drawings]

FIG. 1 is an end view along a cross section of a photomask according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing an arrangement when a projection optical system is used in the first example.

FIG. 3 is an end view along a cross section of a photomask according to a second embodiment of the present invention.

FIG. 4A is an end view along a cross section showing a conventional ordinary photomask, and FIGS. 4B and 4C are end views along a cross section showing a conventional phase shift mask, respectively.

[Explanation of symbols]

 11 Transparent Substrate 12 Light-shielding Films 15 and 17 Cone-Shaped Phase Member 16 Photosensitive Substrate 18 Projection Optical System 19 Projection Optical System Pupillary

Claims (3)

[Claims] 1. A method of illuminating a photomask on which a pattern made up of transmissive portions arranged between light shielding members is formed, and exposing an image of the pattern on the photomask onto a substrate through a projection optical system. An area of a bright part formed in the optical axis direction of the projection optical system by arranging a phase member having a cone-shaped inclination on the transmission part on the photomask and illuminating light passing through the phase member. On the other hand, the exposure method is characterized in that the substrate is arranged in a region conjugate with the projection optical system. 2. A method of illuminating a photomask on which a pattern made up of transmissive portions arranged between light shielding members is formed and exposing the pattern on the photomask onto a substrate, wherein the transmissive light on the photomask is used. A phase member having a cone-shaped inclination is arranged on the portion, and the substrate is arranged in a region of a bright portion formed in the thickness direction of the photomask by the illumination light passing through the phase member. Exposure method. 3. A light shielding member is arranged on a transparent substrate with a predetermined opening, and a phase member having a cone-shaped inclination is arranged so as to cover a part or the whole of a transmission part surrounded by the light shielding member. A photomask characterized by the above.