JPH05267122A - Projection exposure device - Google Patents

Abstract

PURPOSE:To provide a projection exposure device, from which an image having the deep depth of focus and a high contrast is obtained. CONSTITUTION:A light source 1 shifted from the optical axis of an illumination optical system 5 is mounted movably in a plane orthogonal to the optical axis AX, and light from the eccentric light source 1 is projected obliquely to a photo- mask 2. +primary light D+1 in diffracted light from the photo-mask 2 is diffracted outside a projection optical system (a pre-stage optical system 6 and a post-stage optical system 8), and zero-order light D0 and -primary light D-1 are projected to a projection optical system. A filter 7, where the ratio of amplitude transmittance at the positions of the passage of zero-order light D0 and -primary light D-1 reaches approximately 2/pi:1, is disposed onto the pupil plane of the projection optical system, and moved synchronized with the eccentric light source 1. Accordingly, the pattern of the photo-mask 2 is imaged by two luminous flux having equal amplitude and symmetric to the optical axis AX.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for projecting and exposing a pattern of a photomask (also called a reticle) on a wafer coated with a photoresist when manufacturing an integrated circuit such as an LSI. Is.

[0002]

2. Description of the Related Art FIG. 2 is a conceptual diagram for explaining the structure of a conventional projection exposure apparatus. In this type of conventional device, a substantial surface light source 101 is formed at the stop position of the illumination optical system, and the photomask 102 is formed by the light flux from the surface light source 101.
Is illuminated. As a result, diffracted light is generated from the pattern formation surface of the photomask 102. The diffracted light is condensed again on the photosensitive substrate 104 by the projection optical system (not shown), but the high-order diffracted light having a large diffraction angle is blocked by the aperture stop 103 of the projection optical system. Here, assuming that the pattern is a line-and-space pattern (that is, the amplitude of the secondary light is zero), and the diffracted light of the third order or higher is shielded, the pattern of the photomask 102 is the 0th order light D. ₀ , ±
The photosensitive substrate 104 is formed by the three light beams of the primary lights D ₊₁ and D _-1.
Imaged above.

Further, in FIG. 2, the case where a normal photomask consisting of a transparent portion and a light shielding portion is used is explained, but a so-called phase shift mask in which a phase member for changing the phase of transmitted light is provided at a specific position of the transparent portion. May be used. This method using a phase shift mask can obtain a high-contrast image due to the interference effect of light, but has a drawback that it is difficult to manufacture and inspect the mask.

Further, in recent years, the technique of performing projection exposure using the surface light source of FIG. 2 as an annular light source has been attracting attention. Imaging by a projection exposure apparatus that employs this annular light source will be described with reference to FIG. Here, the same pattern is formed on the photomask 102 of FIGS.
The diffraction angle of the next light is assumed to be approximately the same θ. In the figure,
Reference numeral 111 is a donut-shaped annular light source that shields the central portion of a conventional surface light source, and the light flux from this annular light source 111 is oblique to the photomask 102, specifically, the optical axis AX.
Is incident from a direction that forms an angle of approximately θ / 2 with respect to. Therefore, in the case of FIG. 3, the 0th-order light D from the photomask 102
₀ travels in a direction that forms an angle of approximately θ / 2 with respect to the optical axis AX, and the ± first-order lights D ₊₁ and D ₋₁ travel in a direction that forms an angle of θ with respect to the 0th-order light D ₀ . That is, in FIG. 3, the + 1st order light is the optical axis A.
Since it has a large inclination angle of approximately (θ + θ / 2) with respect to X, it travels outside the aperture of the aperture stop 103, and the 0th-order light D
Only two light fluxes of _0th and −1st order light pass through the aperture stop 103 and form a pattern image on the photosensitive substrate 104.

Here, comparing the image formations of FIGS. 2 and 3,
First, in the case of FIG. 3, since the two light fluxes involved in image formation are symmetrical with respect to the optical axis AX, the phase difference between the two light fluxes is the same even if the position of the photosensitive substrate 104 in the optical axis AX direction is changed, and The depth is very large. On the other hand, in the case of FIG. 2, the optical axis AX
Since the phase difference between the 0th-order light and the 1st-order light changes depending on the position in the direction, the depth of focus is shallower than in the case of FIG. Thus, it can be said that the projection exposure by the annular illumination is very advantageous in terms of the depth of focus.

The ring illumination method is introduced, for example, in Nikkei Microdevices November 1991 issue P73-77, Nikkei Microdevices January 1992 issue P79-80, Nikkei Microdevice February 1992 issues P66-67. Has been done.

[0007]

However, the conventionally proposed projection exposure apparatus using annular illumination has the following problems. Consider the case where the ₊ 1st-order light D ₊₁ is diffracted out of the entrance pupil of the projection optical system and imaged by two light fluxes of the 0th-order light D ₀ and the -1st-order light D _-1 , as described above. This 2
The image formation by the light flux is very advantageous in terms of the depth of focus as described above, but since the 0th-order light and the 1st-order light have different amplitudes (described later in detail), sufficient contrast cannot be obtained. The image contrast is as follows when compared with the case where a phase shift mask is used. Here, assuming a line-and-space pattern, if a phase member is provided in every other transmission part and the phase of the transmitted light is shifted by π (or λ / 2: where λ is the wavelength), the 0th-order light is canceled. Then, the images are formed with two light beams of ± first-order light. Therefore, a deep depth of focus can be obtained by using the phase shift mask. Further, in this case, since ± 1st order lights having the same amplitude participate in the image formation, theoretically, 100% contrast can be obtained. On the other hand, in the case of the annular illumination shown in FIG. 3, the contrast of the image is reduced by the difference between the amplitudes of the 0th order light and the 1st order light.

The present invention has been made in view of the above points, and an object of the present invention is to provide a projection exposure apparatus capable of obtaining an image having a deep depth of focus and a high contrast.

[0009]

A projection exposure apparatus according to the present invention comprises an illumination optical system for illuminating a photomask and a projection optical system for transferring a pattern on the photomask onto a photosensitive substrate. In order to achieve the above object, the illumination optical system is provided with a light source eccentric from the optical axis of the illumination optical system, the light source being movably provided in a plane orthogonal to the optical axis of the projection optical system. An eccentric light source forming unit is provided, and a filter having a predetermined transmittance distribution with respect to the diffracted light generated by the illumination light from the eccentric light source forming unit passing through the photomask is provided in the pupil plane of the projection optical system. The filter is movably provided and the filter is moved in synchronization with the movement of the eccentric light source forming means.

[0010]

The operation of the present invention will be described below. First, consider the image formation in the conventional example shown in FIG. Here, a grid line-and-space pattern is assumed as the pattern of the photomask 102. As previously mentioned,
Of the diffracted light generated from the photomask 102, the 0th-order light D ₀ and the −1st-order light D ₋₁ enter the entrance pupil of the projection optical system, and +1
It is assumed that the next light D ₊₁ goes out of the entrance pupil. In this case, the amplitudes of the 0th-order light and the 1st-order light are given by the Fourier spectrum of the object pattern. When the n-th order light spectrum and a _n,
a _n is given by Equation 1. In Equation 1, P is the period of the grating and Δ is the width of the bright portion.

[0011]

[Equation 1]

Assuming now that Δ / P = 1/2 (the width of the dark portion is the same as the width of the bright portion), then a ₀ = 1/2 and a ± ₁ = 1 / π. Therefore, the image intensity distribution I (x) is given by Expression 2.

[0013]

[Equation 2]

From equation 2, the light intensity in the dark part and the light intensity in the bright part are respectively expressed by I
_{When min} and I _max are set, the contrast (I _max −I
_min ) / (I _max + I _min ) is 4π / (4 + π ² ) =
It becomes 0.906. That is, the image contrast is about 90.
It will be 6%. In the present invention, a filter having a predetermined transmittance distribution with respect to the diffracted light from the photomask is arranged on the pupil plane of the projection optical system, and the amplitudes of the 0th-order light and the 1st-order light are made substantially equal to each other. It improves the contrast.

Specifically, assuming that the amplitude transmittance of the filter in the portion through which the 0th order light passes is 2 / π (≈0.637) and the amplitude transmittance of the filter in the portion through which the 1st order light passes is 1. Equation 2 above has been rewritten as Equation 3 to give a theoretical 10
It is understood that 0% contrast is achieved.

[0016]

[Equation 3]

Now, in the present invention, the light source which is decentered from the optical axis of the illumination optical system is provided so as to be movable in a plane orthogonal to the optical axis of the projection optical system without using the annular light source as the light source. The reason why the filter arranged on the pupil plane is moved in synchronization with the eccentric light source will be described. First, when the light source is an annular light source, the diffracted light generated by the light from the position indicated by the black circle in FIG. 3 proceeds in the direction as shown in the figure, but is generated by the light from another position of the annular zone. The diffracted light travels in a direction different from that in FIG. That is, since the positions of the 0th-order light and the 1st-order light that pass through the pupil plane of the projection optical system change depending on from which direction the illumination light enters, when the 0th-order light and the 1st-order light are illuminated simultaneously from different directions, It is difficult to individually control the amplitude transmittance of light. In other words,
If the photomask is irradiated from one direction, the 0th-order light and the 1st-order light pass through predetermined positions on the pupil plane of the projection optical system, so the amplitude transmittance ratio of this portion is set to 2 / π: 1. Then, it is possible to equalize the amplitudes of the 0th-order light and the 1st-order light reaching the photosensitive substrate.

At this time, if only a pattern in a specific arrangement direction is projected, even if the eccentric light source and the filter are fixed at positions corresponding to the pattern, the 0th-order light and the -1st-order light ( Alternatively, an image can be formed by two light fluxes (or + 1st order light). However, when the arrangement direction of the pattern is changed, the image formation as shown in FIG. 3 is not realized by the illumination from the same position, and in some cases, only the 0th-order light enters the entrance pupil of the projection optical system. Can also be removed. In the present invention, in order to avoid such an inconvenience and to realize a deep depth of focus and high contrast regardless of the pattern arrangement direction, the eccentric light source can be moved, and the filter is moved in synchronization with the light source.

The eccentric light source and the filter do not have to be moved so as to draw a circle, but may be moved in any plane within a plane orthogonal to the optical axis of the projection optical system. The movement of the eccentric light source and the filter may be continuous or intermittent. Furthermore, the light source may emit light continuously or may emit light discretely only at a specific position.

[0020]

FIG. 1 is a schematic configuration diagram for explaining a projection exposure apparatus according to an embodiment of the present invention. The light source 1 is located at a position decentered from the optical axis AX of the illumination optical system 5, and is movable in a plane orthogonal to the optical axis AX. It goes without saying that the eccentric light source 1 does not need to have the light emitting device itself at the position shown in the figure, and may be, for example, the exit end of an optical fiber.
In the present embodiment, the eccentric light source 1 is rotated by a driving unit (not shown) so as to draw a circle with a predetermined radius r centered on the optical axis AX.

The photomask 2 is an optical axis AX of the illumination optical system 5.
The projection optical system (pre-stage optical system 6 and post-stage optical system 8) is disposed below the photomask 2 so as to be orthogonal to the photomask 2. On the pupil plane (incident pupil plane) of this projection optical system, a filter 7 having a predetermined transmittance distribution (described later) for diffracted light from the photomask 2 is rotatably arranged around the optical axis AX. The light source image of the eccentric light source 1 is formed here. That is, the eccentric light source 1 and the filter 7 are conjugated with each other. A wafer (photosensitive substrate) 4 is held on the image forming surface of the post-stage optical system 8.

In the projection exposure apparatus as described above, the light from the eccentric light source 1 is obliquely incident on the photomask 2 via the illumination optical system 5. As described above, the eccentric light source 1 is configured to be rotatable about the optical axis AX,
Due to the rotational movement of the eccentric light source 1, the photomask 2 is scanned with the incident illumination light along the side surface of the cone. A pattern to be transferred onto the wafer 4 is formed on the photomask 2, and diffracted light corresponding to the pattern is generated from the photomask 2. For the sake of explanation, assuming that the diffraction angle of the first-order light is θ ₁ , if the radius r of the rotational movement of the eccentric light source 1 is set so that the inclination angle of the illumination light is approximately θ _1/2 , Light D
_{The 0} and −1st order light D ₋₁ is approximately θ _{1/2 with} respect to the optical axis AX,
The + _1st order light D ₊₁ is approximately (θ ₁ + θ ₁ /
Proceed in the direction of 2). That is, as shown in FIG. 1, the + 1st-order light having a large tilt angle is diffracted to the outside of the entrance pupil of the pre-stage optical system 6, and the 0th-order light and the -1st-order light are symmetrical with respect to the optical axis AX. To form a diffraction image on the pupil plane of the projection optical system. In the figure, for the sake of explanation, the + 1st-order light is diffracted to the outside of the projection optical system entrance pupil, and the -1st-order light enters the projection optical system entrance pupil, but the reverse case is also considered. It goes without saying that it will be done.

The filter 7 is rotatably arranged on the pupil plane as described above, and the 0th order light D ₀ and the + 1st order light D _{+1 are provided.}
The difference in the transmittance depending on the location is provided so that the amplitude transmittance ratio of the passage portion of is about 2 / π: 1. In this embodiment, the filter 7 is an eccentric light source 1 driven by a driving means (not shown).
It is rotated in synchronism with the rotational movement of the zero-order light D _0,
And the amplitude transmittance of the primary light D ₋₁ is always constant. The 0th-order light D ₀ and the 1st-order light D _{−1 that} have passed through the filter 7 are equal amplitude 2
It becomes a light flux and forms an image on the photosensitive substrate 4 through the rear optical system 8 of the projection optical system. That is, if projection exposure is performed with the apparatus of FIG. 1, the pattern of the photomask 2 is imaged with two light fluxes of equal amplitude and symmetrical with respect to the optical axis AX.
Images with a very deep depth of focus and high contrast can be obtained.

The reason why the eccentric light source 1 is rotated in the above embodiment is as follows. First, it is for realizing a deep depth of focus and improvement of contrast regardless of the orientation of the pattern on the photomask 2. Secondly, by rotating the eccentric light source 1, a substantial telecentricity on the wafer 4 side is secured. The telecentricity is ensured without rotating the eccentric light source 1 in the example shown in FIG. It is preferable to rotate the light source 1 so that the dimension of the transferred pattern does not change even when it is displaced from the image plane.

However, when the pattern of the photomask 2 is limited to some extent, the eccentric light source 1 does not necessarily have to rotate. For example, in the case where most of the line-and-space patterns parallel to the sides of the photomask 2 are almost the same as the four sides of the photomask 2, in order to prevent only 0th-order light from entering the projection optical system. You may make it light-emit only in four places corresponding to the center. In this case, it is not necessary to rotate the light source 1, and the light source 1 may be moved in any order to the four places to emit light.

Further, the filter 7 has a 0th-order light and a 1st-order light.
If it is possible to make the above-mentioned portion having the amplitude transmittance ratio of 2 / π: 1 follow the passing position of the next light, it is not always necessary to perform the rotational movement. The shape of the filter is not limited to the disk shape.

Since the diffraction angle θ ₁ shown in FIG. 1 varies depending on the size of the pattern of interest, in order to ensure the symmetry of the two light beams involved in the image formation with respect to the optical axis, the diffraction angle θ ₁ should be changed according to the pattern. Distance r from the optical axis of the eccentric light source 1
It is desirable to change (the radius of gyration in the case of this embodiment). Even when the eccentric light source 1 is rotated around the optical axis AX as in this embodiment, if the radial position is also variable, the incident direction of the illumination light can be easily optimized according to the pattern.

[0028]

As described above, according to the present invention, the eccentric light source is movably provided in the plane orthogonal to the optical axis of the projection optical system, and a predetermined transmittance distribution is obtained for the diffracted light from the photomask. It has a filter that can be moved in the pupil plane of the projection optical system and moves the filter in synchronization with the movement of the eccentric light source, so it is possible to achieve a high-contrast image while maintaining a very large depth of focus. Is.

[Brief description of drawings]

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

FIG. 2 is a conceptual diagram for explaining a conventional general projection exposure apparatus.

FIG. 3 is a conceptual diagram for explaining a conventional projection exposure apparatus using ring illumination.

[Explanation of symbols]

1 ... Decentered light source, 2 ... Photomask, 4 ... Wafer, 5 ... Illumination optical system, 6 ... Pre-stage optical system of projection optical system, 7 ... Filter, 8 ... Post-stage optical system of projection optical system.

Claims (1)

[Claims] 1. An illumination optical system for illuminating a photomask,
In a projection exposure apparatus including a projection optical system that transfers a pattern on the photomask onto a photosensitive substrate, the illumination optical system is movably provided in a plane orthogonal to an optical axis of the projection optical system, An eccentric light source forming unit that forms a light source eccentric from the optical axis of the illumination optical system is provided, and the illumination light from the eccentric light source forming unit has a predetermined transmittance with respect to diffracted light generated by passing through the photomask. A projection exposure apparatus, wherein a filter having a distribution is provided so as to be movable in a pupil plane of the projection optical system, and the filter is moved in synchronization with the movement of the eccentric light source forming means.