JPH06196388A - Projection aligner - Google Patents

Abstract

PURPOSE:To prevent the image-formation performance with reference to an inclined pattern, especially the improvement degree of the depth of focus, of an aligner from being deteriorated by a method wherein, although many optimized parts are included in longitudinal and transverse patterns on a reticle as the light-source shape of a deformed light source, some optimum parts are also included in the inclined pattern. CONSTITUTION:The shape of a light-shielding plate 8 includes a surface light- source part which is effective in forming the image of slightly inclined patterns Ta, Tb, and the greater part of a central crossed light-shielding part shields a surface light-source part which is not suitable for not only a longitudinal pattern Pv and a groove pattern Pb but also the inclined patterns Ta, Tb. As a result, when the image of the inclined patterns Ta, Tb is formed, a resolution and a depth of focus which are remarkably higher than those by an ordinary illumination (a simply circular or polygonal surface light source using an optical axis AX as the center) in conventional cases can be obtained. Consequently, it is possible to prevent the image-formation performance with reference to the inclined patterns, especially the improvement degree of the depth of focus, of the aligner from being deteriorated.

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 used for exposing and transferring a fine pattern such as a semiconductor integrated circuit and a liquid crystal display element, and more particularly to a method for illuminating a mask (reticle) on which a pattern to be transferred is formed. The present invention relates to an exposure apparatus that has been devised.

[0002]

2. Description of the Related Art In a lithography process in which miniaturization progresses year by year, it is essential to introduce a practical projection exposure apparatus for manufacturing 64MD-RAM. In order to achieve the projection exposure transfer of such a fine pattern with sufficient accuracy, various measures have been conventionally proposed. Of which
Particularly, when the pattern to be transferred has a periodicity in a certain direction such as a line and space (hereinafter referred to as L & S), as a method for remarkably increasing the resolution and the depth of focus as compared with the conventional technique, Japanese Patent Laid-Open No. Hei 4 (1999) -1999. Super-resolution techniques such as Japanese Patent Laid-Open No. 108612 and Japanese Patent Laid-Open No. 4-225514 have been proposed.

This super-resolution technique is used for L & S for projection exposure.
Resolving a fine pattern that could not be resolved by conventional illumination methods with a sufficient depth of focus by making only the alignment characteristics of the illumination light on the mask substrate (reticle) on which the pattern is formed Is. The orientation characteristic of the illumination light is the distribution of the illumination light flux in the Fourier transform plane with respect to the reticle in the illumination optical system, that is, the distribution of the secondary light source image,
It is created by controlling according to the fineness (pitch etc.) of the L & S pattern of the reticle.

FIG. 1 is a perspective view showing a schematic configuration of an illumination optical system to which the technique disclosed in the above publication is applied. Here, the mercury lamp 1 is used as an illumination light source, and the light emitting point of the mercury lamp 1 is arranged at the first focal point of the elliptical mirror 2. The illumination light ILa reflected by the ellipsoidal mirror 2 is once converged at the second focal point 3 and then reflected by a mirror (not shown) to enter the collimator lens system 4. Generally, when the ellipsoidal mirror 2 and the mercury lamp 1 are combined as shown in FIG. 1, the illumination light ILa has a ring-shaped (donut-shaped) intensity distribution in its cross section. The illumination light ILa having the ring-shaped cross section is converted into a substantially parallel light flux by the collimator lens system 4 and reaches the light shielding plate 8 arranged on the Fourier transform surface in the illumination system. Four openings are provided on the light shielding plate 8 at positions equidistant from the optical axis AX, and fly-eye lenses 7A, 7B, 7C, and 7D are provided in each of the openings.
The incident surfaces of the fly-eye lenses 7A to 7D are
Both are located in the illumination light flux ILa having the annular cross section. In addition, on the exit side of each of the fly-eye lenses 7A to 7D,
The point light source image of the mercury lamp 1 is formed by the number of element lenses in the fly-eye lens. Therefore, secondary light source images (surface light sources) are formed on the exit surfaces of the fly-eye lenses 7A to 7D.

Illumination light from each of the fly-eye lenses 7A to 7D is formed on the pattern forming area PA of the reticle R by an inverse Fourier transform optical system 11 (hereinafter referred to as a condenser lens for convenience) including a condenser lens and the like. Irradiation is performed by superimposing them uniformly. When the reticle R is arranged so that the optical axis AX passes through the center of the pattern area PA of the reticle R and the center is the origin of the coordinate system XY, the L & S-shaped reticle pattern is often pitched in the X direction. And an L & S pattern (horizontal pattern) Ph having a pitch in the Y direction. That is, a pattern group having periodicity in two directions of the X direction and the Y direction is collectively formed in the pattern area PA.

If the illumination condition is optimized for the minimum pitch of the L & S patterns Pv and Ph in the X and Y directions, the decentering amount of each of the fly-eye lenses 7A to 7D from the optical axis AX. yα and xβ are determined in a unique relationship with the minimum pitch of the L & S pattern. For example L
The minimum pitch of the & S pattern Ph in the Y direction is Gy (μ
m), the wavelength of the illumination light ILa is λ (μm), the distance from the condenser lens 11 to the reticle R, that is, the focal length is f (mm), and the diffraction angle of the 1st-order diffracted light generated from the L & S pattern Ph (0th-order light Angle from 2θy (r
ad), the eccentricity amount yα in the Y direction of one fly-eye lens of interest is sin2θy = λ / Gy, yα = f
・ It is decided that sin θy is satisfied almost at the same time.

Further, when the minimum pitch of the L & S pattern Pv in the X direction is Gx (μm) and the diffraction angle of the first-order diffracted light generated from the L & S pattern Pv is 2θx (rad), one fly-eye lens of interest is selected. The eccentricity amount xβ in the X direction is determined so that sin2θx = λ / Gx and xβ = fsinθx are satisfied substantially at the same time. As described above, according to the conventional special illumination method (deformed light source), L & L on the reticle R is
Of the S patterns, a pattern P having a pitch in the X direction
For super-resolution projection of v, a pair of secondary light source images symmetrically decentered in the X direction on the Fourier transform plane (fly-eye lens 7A
And 7D, or the tilted illumination light from the fly-eye lenses 7B and 7C) contributes and has a pattern P having a pitch in the Y direction.
For super-resolution projection of h, a pair of secondary light source images symmetrically decentered in the Y direction on the Fourier transform plane (fly eye lens 7A
And 7B, or the tilted illumination light from the fly-eye lenses 7C and 7D) contributes.

In FIG. 1, the second focus 3 is provided with a rotary shutter or the like for controlling the start and interruption of the exposure, and the second focus 3 is formed on the exit surface side of each of the fly-eye lenses 7A to 7D. Of the fly-eye lenses 7A to 7D, and the respective incident surfaces of the fly-eye lenses 7A to 7D are conjugated to the pattern surface of the reticle R.

[0009]

In the above-mentioned conventional techniques, there is an effect of improving the resolution and the depth of focus only for a periodic pattern in a specific direction of a circuit original plate (reticle) to be transferred, for example, two orthogonal directions. . However, in other directions, especially in the above two orthogonal directions, respectively, 45
Regarding the pattern with periodicity in the rotated direction, there was a problem that the resolution and the depth of focus were lower than those of an exposure apparatus to which a normal illumination method was applied.

The present invention has been made in view of such a problem, and the resolution and depth of focus of a bidirectional pattern having a periodicity in each of the vertical and horizontal directions on the reticle, particularly in the vertical and horizontal directions parallel to the reticle outline, are significantly increased. It is an object of the present invention to provide a projection exposure apparatus capable of obtaining a higher resolution and a larger depth of focus than an ordinary apparatus even with respect to an oblique pattern (for example, rotated by 45 °) different in direction from the above while improving the above.

[0011]

According to the present invention, a two-dimensional shape of a light source image (surface light source) formed on a Fourier transform surface in an illumination optical system for mask illumination of a projection exposure apparatus,
In addition to the conventional shape, it is slightly deformed. Specifically, as shown in FIG. 2, of the surface light sources (here, the exit surface of the fly-eye lens 7) included in the substantially circular region C1, a ring outside the circle C2 having a predetermined radius from the origin. Do not shade the band at all. Then, inside the circle C2, cross-shaped light-shielding portions 8A extending in the X and Y directions from the origin are provided, and in each of the four quadrants defined by the X and Y coordinate axes,
The transmission part (light source surface) separated from each other was formed. The transmissive portions in the four quadrants contribute to super-resolution of a periodic pattern having pitches in the X and Y directions, as in the conventional case.

In the prior art, all the four tips of the cross-shaped light-shielding portion 8A were extended beyond the radius of the surface light source (the radius of the circle C1), but in the present invention, the four tips of the cross-shaped light-shielding portion 8 are provided. The area was made smaller than the radius of the surface light source, and the area light source was small outside the four tip portions. The setting of the orthogonal coordinate system XY in FIG. 2 is exactly the same as that of FIG. 1, and the origin of the coordinate system XY coincides with the optical axis AX of the illumination optical system or the projection optical system.
Further, in FIG. 2, EP represents the pupil plane of the projection optical system as seen in the exit plane of the fly-eye lens 7 as a two-dimensional light source image (surface light source).

Generally, in this type of projection exposure apparatus, a surface light source image (image of the exit surface of the fly-eye lens 7) is formed in the pupil plane (Fourier transform plane) of the projection optical system. Then, the ratio r of the radius r ₀ of the pupil EP of the projection optical system viewed on the Fourier transform surface in the illumination optical system and the radius r of the surface light source.
The value of / r ₀ is called the σ value. Therefore, in FIG. 2, if the radius of the circle C1 is about 0.7 to 0.8 in the σ value and the radius r ′ of the circle C2 is about 0.64r ₀ = 0.64r / σ, the values in the X and Y directions are The super-resolution effect can be sufficiently obtained even for a periodic pattern having a line width of 0.4 to 0.45 μm having a pitch in the direction rotated by 45 ° with respect to each of them. The setting conditions of the circles C1 and C2 and the dimensional conditions of the cross-shaped light shielding portion 8A shown in FIG. 2 will be described in detail in the following embodiments.

[0014]

In the present invention, the light source shape of the so-called modified light source includes many portions optimized for the vertical and horizontal patterns on the reticle, and is also the optimal portion for the oblique pattern (the cross-shaped light-shielding portion 8A in FIG. 2). Outside the tip)
I tried to include it slightly. For this reason, the resolution and depth of focus of the oblique pattern, which is worse than the conventional illumination in the conventional modified light source, can be improved as compared with the normal illumination. In addition, since the balance between the area (light intensity) of the light source optimized for vertical and horizontal patterns and the area (light intensity) of the light source optimized for diagonal patterns is optimized, the resolution when projecting vertical and horizontal patterns The improvement of the depth of focus and the depth of focus can be realized to the same extent as in the case of the conventional modified light source shape. When a ring-shaped surface light source unit (radius r ′ to r) is provided outside the cross-shaped light-shielding unit 8A as shown in FIG. 2, the periodicity directions of the oblique patterns are in the X and Y directions, respectively. Even if it is not necessarily 45 ° (or 135 °), the effect of the present invention can be obtained.

[0015]

FIG. 3 is a diagram showing the overall schematic construction of a projection exposure apparatus according to an embodiment of the present invention. The members in FIG. 3 having the same functions as those in FIG. 1 are designated by the same reference numerals. The illumination light ILa from the mercury lamp 1 is focused on the second focal point 3 by the elliptic mirror 2, and then enters the fly-eye lens 7 via the collimator lens system 4, the mirror 5 and the input side field lens 6. A rotary shutter 19A that rotates in one direction is arranged at the position of the second focus 3, and the shutter 19A is controlled by a drive unit (motor, drive circuit, etc.) 19B. Also, the illumination light I
When La enters the fly-eye lens 7, it has a ring-shaped intensity distribution as in the case of FIG. 1, but the shape of the light-shielding plate (diaphragm) 8 provided on the exit side of the fly-eye lens 7 is as shown in FIG. It is suitable for the case of making such a modified light source. However, when the light-shielding plate 8 is switched to the light-shielding plate 9 having a circular aperture stop similar to the conventional one to perform normal illumination, the illumination light I
The La zone intensity distribution of La is not very preferable. In particular, when the reticle R is the one to which the phase shift method is applied, the numerical aperture of the illumination light to the reticle R is a relatively small value (.sigma. Value is 0.
2 to 0.4)). In that case, only the illumination light from the element lens in the central portion of the fly-eye lens 7, that is, the light in the central portion of the annular light intensity distribution of the illumination light ILa is used for reticle illumination, which causes a decrease in illuminance. become.

Therefore, when switching to the normal illumination, a prism 30 as disclosed in USP 4,637,691 or the like is arranged in a replaceable manner between the collimator lens 4 and the field lens 6 so that the illumination light ILa has an annular shape. The intensity distribution of is preferably shaped into a circular distribution. On the exit side of the fly-eye lens 7, a light-shielding plate 8 for a modified light source and a light-shielding plate 9 for a normal light source as shown in FIG.
A let 10 is provided. The turret 10 is rotated at a predetermined angle by the drive unit 10A. Figure 3
Then, the light shielding plate 8 is positioned on the exit side of the fly-eye lens 7. In this way, the illumination light ILb that has passed through the transmission part of the light shielding plate 8 enters the condenser lens 11 via the output side field lens 13 and the mirror 12. The light from each of the point light sources of the selected plurality of element lenses in the fly-eye lens 7 is uniformly radiated by the condenser lens 11 so as to be superimposed on the pattern area of the reticle R. Illumination light ILa shown in FIG. 3 is representative of light from the point light source of one selected element lens.

Here, the relationship between the shape of the light-shielding portion of the light-shielding plate 8 and the arrangement of the element lenses of the fly-eye lens 7 is the same as that shown in FIG. 2, and in reality it is outside the circle C1 in FIG. Is also a light-shielding portion, and is formed by vapor-depositing a metal layer or the like on a transmission plate such as a quartz plate including the cross-shaped light-shielding portion 8A. The exit surface of the fly-eye lens 7 (or the surface of the light shielding plate 8) has an optical Fourier transform relationship with the pattern surface of the reticle R. Therefore, the light from the point light source formed by one element lens of the fly-eye lens 7 becomes a parallel light beam having an incident angle θ by the condenser lens 11 and obliquely illuminates the reticle R. At this time, the amount of eccentricity on the Fourier transform plane of one point light source (distance from the optical axis AX)
Is proportional to the sine of the incident angle θ. This incident angle θ has an appropriate value depending on the pitch of the periodic pattern on the reticle R. The method of determining the eccentricity amounts yα and xβ for the periodic patterns in the X and Y directions, respectively, is disclosed in Japanese Patent Application Laid-Open No. 4-225514, and the description thereof will be omitted here.

The reticle R is irradiated with the illumination light ILb.
Of the diffracted lights generated from the periodic pattern of the above specific pitch, the 0th-order diffracted light D ₀ and one 1st-order diffracted light D ₁ are symmetrically distributed in the pupil EP of the bilateral telecentric projection optical system PL. , Reach the wafer W. Therefore Reticle R
The periodic pattern of the above specific pitch is one 1st-order diffracted light D
_An image is formed on the wafer W as a bright and dark image created by the interference between the _1st and 0th order diffracted light D ₀ . Since the resist layer is coated on the surface of the wafer W, when the opening time of the shutter 19A is controlled to give an optimum exposure light amount suitable for the resist, a reduced image of the periodic pattern of the reticle R is formed on the resist layer. To be done.

The wafer W is placed on a stage WST which moves two-dimensionally in a plane perpendicular to the optical axis AX, and the stage WST drives a motor or the like based on the measurement result of the coordinate position by the laser interferometer 18A. It is driven by the unit 18B. The control unit 20 uses the wafer stage W
The ST, the shutter drive unit 19B, and the turret drive unit 10A are collectively controlled. In particular, the turret drive unit 10A can be automatically controlled by the registered name of the reticle R or manually controlled by an operator.

FIG. 4 is a plan view showing a concrete shape of the light shielding plate 8 according to the first embodiment, and FIG. 5 is a coordinate system X in FIG.
7 schematically shows the periodic pattern arrangement on the reticle R when viewed in the same coordinate system as Y. As shown in FIG. 5, on the reticle R, the direction X of each side of the outer shape of the reticle,
Periodic vertical pattern Pv parallel to Y (pitch is in X direction)
There are many horizontal patterns Ph (pitch is in the Y direction),
There is also a periodical oblique pattern Ta, Tb rotated by 45 ° (or 135 °) with respect to each of the X and Y directions, although the ratio is smaller than those. The structure of such a pattern is not limited to this embodiment, and is common in a reticle as a circuit original plate for a semiconductor device. The ratio of the vertical pattern Pv and the horizontal pattern Ph is high, and the ratio of the diagonal patterns Ta and Tb is high. Is generally low.

When the reticle R having these patterns is irradiated with the illumination light from the illumination optical system to which the shading plate 8 shown in FIG. 4 is applied, the reticle R is divided by the cross-shaped shading portion 8A having a width 2a and a length 2b. 4 fan-shaped transparent portions 81a, 8
Using 1b, 81c, and 81d as surface light sources, the resolution and depth of focus of the vertical pattern Pv and the horizontal pattern Ph on the reticle R at the time of projection are improved as in the conventional case. Here, the light-shielding plate 8 has a ring-shaped light-shielding portion 8B having an outer diameter _value r ₀ and an inner diameter r on the outermost periphery, and the cross-shaped light-shielding portion 8A from the origin (the point where the optical axis AX passes).
The length b to the tip of is set to have a relationship of r> b. In addition, the inner diameter edge of the annular light shielding portion 8B is a circle C1 in FIG.
And the outer diameter value r ₀ of the annular light-shielding portion 8B is the projection optical system P.
The effective maximum diameter of the pupil EP of L (that is, the maximum numerical aperture N.
A.), the ratio r / r ₀ between the inner diameter value r and the outer diameter value r ₀ of the annular light shielding portion 8B is nothing but the σ value of the coherence factor.

Further, in the light shielding plate 8 of FIG. 4, transparent portions 81e, 81f, 81 effective for forming an image of the oblique patterns Ta, Tb are provided at the respective tip portions of the cross-shaped light shielding portion 8A in the X and Y directions.
g, 81h are formed. In the conventional illumination method of this type, the four transparent portions 81e, 81f, 81g, 81
All h were used as a light shielding part. These four transparent parts 81e
Creating a light source image (surface light source) for each of the patterns 81h to 81h has a side effect of slightly degrading the resolution and the depth of focus when the vertical pattern Pv and the horizontal pattern Ph are projected. However, the fan-shaped transparent portion 81 effective for the vertical pattern Pv and the horizontal pattern Ph
a-81d compared to the individual area (or light quantity), 4
Since the area (or the light amount) of each of the two transparent portions 81e to 81h is sufficiently small, the projection performance for the vertical pattern Pv and the horizontal pattern Ph is not significantly impaired.

Here, the relationship among the respective values r (σ), a and b of the light shielding plate 8 is 0.1r / σ ≦ a ≦ 0.4r / σ and 0.4r / σ ≦ b
≦ 0.8 r / σ is set. When the value a becomes smaller than 0.1r / σ (that is, 0.1r ₀ ), the effect as a deformed light source disappears and there is no difference from normal illumination (a simple circular or polygonal surface light source centered on the optical axis AX). Further, when the value a becomes larger than 0.4r / σ (that is, 0.4r ₀ ), the center of gravity on the area of each of the four fan-shaped transparent portions 81a to 81d is formed at a position far away from the origin of the light shielding plate 8. Therefore, although the inclination angle of the illumination light can be optimized for the pattern Pv, Ph on the reticle R having a finer pitch, it can be optimized for the pattern having a coarser pitch. Will not be optimized, and it will be difficult to obtain the effect of increasing the depth of focus.

If the value b is smaller than 0.4r / σ, the area of the surface light source unsuitable for resolving the vertical pattern Pv and the horizontal pattern Ph, that is, the areas of the transparent portions 81e to 81h, increases, so that the vertical and horizontal patterns Pv, The depth of focus at the time of projecting Ph is remarkably reduced. Conversely, the value b is 0.8r / σ
When it becomes larger, the effect of improving the resolution and the depth of focus when projecting the oblique patterns Ta and Tb becomes weak.

Further, the shape of the light shielding plate 8 shown in FIG. 4 includes a surface light source portion which is effective for image formation of the oblique patterns Ta and Tb, and most of the central cross-shaped light shielding portion 8A. Not only the vertical pattern Pv and the horizontal pattern Ph, but also the inappropriate surface light source portion is shielded against the oblique patterns Ta and Tb. Therefore, even in the image formation of the oblique patterns Ta and Tb, it is possible to obtain a remarkably higher resolution and a greater depth of focus than the conventional normal illumination (a simple circular or polygonal surface light source centered on the optical axis AX).

FIG. 6 shows the shape of the shading plate 8 according to the second embodiment. The same parts as those of the shading plate 8 of FIG. 4 are designated by the same reference numerals. This embodiment is basically the same as the light shielding plate of FIG. 4, but is different in that a circular light shielding portion having a radius r _c (r _c > a) is provided at the center of the central cross-shaped light shielding portion 8A ′. When the central portion of the surface light source is shielded by the circular light-shielding portion in this manner, a light source portion that is particularly effective for image formation of the vertical pattern Pv and the horizontal pattern Ph, that is, four fan-shaped transparent portions 81a to 81a.
The area of each of 81d becomes smaller than that of the case of FIG. 4, and the ratio of the area of each of the light source portions, that is, the four transparent portions 81e to 81h, which are effective for forming the oblique patterns Ta and Tb relatively increases. Therefore, the diagonal patterns Ta, Tb
It is possible to further improve the resolution and the depth of focus at the time of image formation as compared with the case of FIG.

The portion newly shielded by the light shielding plate 8 in FIG. 6 is a position relatively close to the optical axis AX, and the pitch is slightly rough (for example, the line width on the wafer is 0.5 μm or more). Although there is an effect of improving the depth of focus when the vertical pattern Pv and the horizontal pattern Ph are imaged, there is not much effect of improving the resolution and the depth of focus for the vertical and horizontal patterns Pv and Ph having a finer pitch. Therefore, when the L & S pattern on the reticle R to be projected and exposed is limited to a pattern having a relatively fine pitch, and an oblique pattern having a similar pitch is included in a small amount but in a proper ratio, Vertical and horizontal patterns Pv, Ph using the light shielding plate 8 of FIG.
The overall image forming performance of is not particularly deteriorated as compared with the case where the light shielding plate 8 of FIG. 4 is used.

Here, the radius r2 of the circular light-shielding portion at the center of the light-shielding plate 8 in FIG. 6 is set to about 0.3r / σ ≦ r2 ≦ 0.4r / σ, and strictly speaking, the condition of a <r2 <b is also taken into consideration. To be done. Here, if the value of the radius r2 becomes smaller and eventually becomes a ≧ r2, there is no difference from the shape of the light-shielding plate 8 in FIG. 4, and therefore the depth-of-focus enlargement action during image formation of the oblique patterns Ta and Tb is slightly. Will decrease. On the contrary, when the value of the radius r2 is increased, the surface light source shape approaches the annular zone, so that the focal depth enlarging action at the time of image formation of the vertical and horizontal patterns Pv and Ph is reduced.

FIG. 7 shows the shape of the shading plate 8 according to the third embodiment, which is basically the same as the shape of the shading plate 8 of FIG. 4, but four inside the outer ring-shaped shading portion 8B. The difference is that minute shielding portions 8C and 8D having 90 ° corners are provided in a part of each of the fan-shaped transmitting portions 81a to 81d. These minute light-shielding portions 8C and 8D have edges parallel to the X-axis and the Y-axis, respectively, and are separated from the X-axis by a distance dy in the Y direction, and the parallel edges with the Y-axis are a distance dx from the Y-axis in the X direction. Just away. The minute light shields 8C and 8D are fan-shaped light shields 81a-8a.
In each of 1d, it is provided in the farthest part from the X-axis and the Y-axis respectively, and the illumination light flux from these light-shielding portions 8C and 8D has the smallest pitch as the vertical pattern Pv and the horizontal pattern Ph. Or, it has an alignment characteristic optimized for an oblique pattern with a fine pitch. For this reason,
As described above, when a vertical or horizontal pattern having the smallest pitch or a fine diagonal pattern is formed, a depth of focus expanding action can be obtained. However, the illumination light flux from the light-shielding portions 8C and 8D acts in the direction of decreasing the depth of focus rather than when forming an L & S pattern with a fineness of medium degree (for example, a line width of 0.4 to 0.5 μm). I will end up.

Therefore, the light-shielding plate 8 of FIG. 7 does not include a fine vertical / horizontal pattern in the minimum pitch that can theoretically be imaged by the modified light source system here, but is a coarser and finer L & S pattern of a medium degree. It can be said that it is suitable for projection exposure of a reticle R containing a. As is apparent from FIG. 7, the distances dx and dy of the edges of the minute light shielding portions 8C and 8D are
Is set to dx <r and dy <r here, and is further set to dx = dy if the pitches of the vertical pattern, the horizontal pattern, and the diagonal pattern on the reticle are approximately the same. Then, the fan-shaped transparent portions 81a to 81 in the light shielding plate 8 of FIG.
The positions of the respective area-wise center of gravity points (light quantity center of gravity points) of d are not so different from the center of gravity point positions when the minute light shielding portions 8C and 8D are not present. Further, when the distances dx and dy from the X and Y axes of the edges of the minute light shielding portions 8C and 8D are reduced, the fan-shaped transparent portions 81a to 81d are rectangular (or square).
Approaching.

In FIG. 8, the distances dx and dy from the X and Y axes of the edges of the minute light-shielding portions 8C and 8D are made relatively small, and the cross-shaped light-shielding portion 8A, the ring-shaped light-shielding portion 8B, and the minute light-shielding portion 8C. , 8D have respective cross-sectional shapes of the element lenses of the fly-eye lens 7 (here, square)
The shape of the light-shielding plate 8 in the case of matching with FIG. In the case of each of the light-shielding plates shown in FIGS. 4, 6, and 7, it is preferable that the edge of the light-shielding portion is matched with the sectional shape of the element lens. In FIG. 8, each of the four transparent portions 81e to 81h forming a light source portion effective when forming the oblique patterns Ta and Tb is
Two element lenses are located across the X and Y axes. The half value a of the width of the cross-shaped light shielding portion 8A is set to the size of one element lens, and the length b is set to the size of five element lenses. And the fan-shaped transparent portions 81a to 81d
In each of the above, a group of 4 × 4 element lenses from which one element lens at the outermost angle is removed is located. The portions corresponding to the minute light shielding portions 8C and 8D shield two element lenses, respectively. Further, in the case of the light shielding plate 8 in this figure, four fan-shaped transparent portions 81a
.About.81d and the transparent portions 81e to 81h are not connected to each other as in the above-described embodiments, but are independent from each other. Further, one element lens located at the innermost corner (corner closest to the origin) of each of the four fan-shaped transparent portions 81a to 81d is shielded, that is, 4 in the center portion.
It is also possible to add a square (or rectangular) light-shielding portion having the same size as the aggregate of the × 4 element lenses. By adding such a square light-shielding portion, the second light shielding portion shown in FIG.
It is possible to obtain the same operation and effect as the light shielding plate 8 of the above embodiment. In this case, the distances from the X-axis and the Y-axis of the edges of each side of the central quadrangular light-shielding portion are set in the same range as the radius C of the circular light-shielding portion in FIG.

Further, the fan-shaped transparent portions 81a to 81a shown in FIG.
The element lens groups of the fly-eye lens 7 located at 81d are all arranged symmetrically with respect to the X axis and the Y axis. By adopting such a symmetrical arrangement, there is no telecentric error in the projected image of the L & S pattern on the reticle (lateral displacement of the image when the wafer surface is slightly displaced from the best focus surface).

Here, referring to FIG. 9, when the light shielding plate 8 of FIGS. 4 and 6 to 8 is used, in the pupil plane EP of the image-forming light flux generated from the reticle R and incident on the projection optical system PL. The distribution of will be described. FIG. 9 is a view corresponding to FIG. 2, in which the light amount centroids 80A, 80 of the four fan-shaped light source units optimized for the vertical and horizontal patterns Pv, Ph having a predetermined pitch are shown.
B, 80C, 80D and their vertical and horizontal patterns Pv, Ph
Of the four light amount centroids optimized for the diagonal pattern Ta having the same pitch as
E and E are shown on the pupil plane EP. Each of the four center-of-gravity points 80A to 80D substantially coincides with the area centroid of each of the four fan-shaped transparent portions 81a to 81d in each example, and the centroid point 80E corresponds to the area centroid of the transparent portion 81e. It almost agrees with the point. First, four center of gravity points 80A-80D
Is optimized for the pitch of the target vertical and horizontal patterns, so that, for example, in the image formation light flux from the reticle R, 0 generated from the vertical and horizontal patterns by irradiation of the illumination light beam passing through the center of gravity 80A. Next light passes through the center of gravity 80A,
One of the ± 1st-order diffracted lights passes through the center-of-gravity points 80B and 80D which are located symmetrically to the X-axis and the Y-axis, respectively.

On the other hand, the ± first-order diffracted light ± Dx ₁ (the center of gravity of the diffracted light beam) generated from the vertical pattern Pv by the illumination light beam oriented so as to pass through the center of gravity 80E passes through the center of gravity 80E and is parallel to the X axis. However, since the position is outside the maximum diameter of the pupil plane EP as shown in FIG. 9, it does not affect the image formation of the vertical pattern Pv. However, one first-order diffracted light beam −Dy ₁ (the center of gravity of the diffracted light beam) generated from the lateral pattern Ph is distributed on the Y axis in the pupil EP, and therefore affects the image formation of the lateral pattern Ph. This first-order diffracted light
Since Dy ₁ is different from the ideal distribution position of the lateral pattern Ph by the modified illumination method, Dy ₁ is light that is not very preferable for imaging the lateral pattern Ph. However, the amount of illumination light that makes the center of gravity 80E is determined by the transparent portion 81e having a small area, and is much smaller than the amounts of illumination light of the other four centers of gravity 80A to 80D. For example, in the case of FIG. 8, the ratio is determined by the ratio of the number of element lenses of the fly-eye lens 7,
Therefore, the amount of undesired first-order diffracted light −Dy ₁ itself is remarkably small, and the imaging performance of the lateral pattern Ph is not significantly deteriorated in practical use.

Next, let us consider the distribution of the image forming light beam from the oblique pattern Ta (45 °). Here, the diffracted light generated from the oblique pattern Ta by the irradiation of the illumination light (transmissive portion of the fan-shaped transparent portion 81b) oriented so that the 0th-order light passes through the center of gravity 80B will be described as a representative. Assuming that the pitch of the diagonal pattern Ta is about the same as the pitch of the vertical and horizontal patterns Pv and Ph, the first-order diffracted light −Dt ₁ (the center of gravity of the diffracted light beam) from the diagonal pattern Ta has a radius around the center of gravity 80B. It is located on a circle of 2yα (or 2xβ) and on a line (135 °) connecting the centers of gravity 80B and 80B through the optical axis AX. This first-order diffracted light-Dt
₁ is not preferable for the image formation of the oblique pattern Ta, because the 45 ° line connecting the two barycentric points 80A and 80C does not have a symmetrical relationship with the 0th-order light beam passing through the barycentric point 80B. It's becoming light.

However, the oblique pattern T is formed at the center of gravity 80E.
Since the transparent portion 81e is provided on the light-shielding plate 8 so that the 0th-order light from a is positioned, the 1st-order diffracted light generated from the oblique pattern Ta by the illumination light from the transparent portion 81e-
Dt ₁ 'is on a circle having a radius 2yα (or 2xβ) centered on the center of gravity 80E and passing through the center of gravity 80E 13
It is located on the 5 ° line (parallel to the line connecting the centers of gravity 80B and 80D). The positional relationship between the center of gravity 80E and the first-order diffracted light −Dt ₁ ′ is substantially symmetrical with respect to the 45 ° line connecting the centers of gravity 80A and 80C (the central axis in the Fourier transform image of the oblique pattern Ta). There is. Therefore, the transparent portion 8
The illumination light from 1e becomes an effective component for forming an image of the oblique pattern Ta, and works in the direction of improving the resolution and the depth of focus of the oblique pattern Ta. In the case of FIG. 9, the first-order diffracted light −Dt from the oblique pattern Ta in which the center of gravity 80E is the 0th-order light.
₁ 'is located almost on the X axis, and that position is the light shield 8
Is closer to the center of gravity (80H) of the illumination light from the other transparent portion 81h for the oblique pattern. Like this one
The center of gravity 80 of the transparent portion 81h is located at the position of the next diffracted light −Dt ₁ ′.
The position of H means that the oblique pattern Ta is illuminated by two illumination light beams that are symmetrically inclined in the pitch direction.

From the above, assuming that the pitches of the vertical and horizontal patterns Pv and Ph and the oblique patterns Ta and Tb to be projected and exposed are the same on one reticle, the surface light source unit (for the oblique pattern) ( The light amount centroids of the transparent portions 81e to 81h) are ideally √ from the origin on the X axis and the Y axis.
It may be disposed (xβ ² + yα ²⁾ of the distance place. This relationship is an ideal condition, and even if the relationship deviates slightly (for example, about 20% to 30%) from reality, the effect of the present invention can be obtained to some extent.

FIG. 10 shows a partial structure of an illumination optical system according to a fourth embodiment of the present invention. Here, the fly-eye lens 7 shown in FIG. 3 is disclosed in Japanese Patent Publication No. 3-78607. Change to a two-lens fly-eye lens system. The illumination light ILa that has passed through the collimator lens 4 and the prism 30 in FIG. 3 enters the first-stage fly-eye lens 7E as shown in FIG. This fly eye lens 7
E is a bundle of four element lenses in the X and Y directions. The illumination light from each point light source image formed at the exit end of each element lens of the fly-eye lens 7E is
Through the lens system 25, the entire incident surface of the second-stage fly-eye lens 7F is superimposed and irradiated. The second-stage fly-eye lens 7F is a bundle of element lenses arranged in a 6 × 6 array, and a three-dimensional light source image (point light source) is formed in a space several mm away from the exit surface of each element lens. To be done.
In the case of this two-series fly-eye lens system, on the exit side of each element lens of the second-stage fly-eye lens 7F,
4 formed on the exit surface of the first-stage fly-eye lens 7E
Since 3 x 4 point light source images are formed, the 3D light source image is 1
It becomes a surface light source in which 6 × 36 point light sources are two-dimensionally assembled.

In the case of the present embodiment, the light shielding plate 8 shown in FIGS. 4 and 6 to 8 is located in the space where the three-dimensional light source image is formed on the exit side of the fly-eye lens 7F of the second stage. It is placed in the plane. FIG. 11 shows a three-dimensional light source image formed on the exit side of the fly-eye lens 7F and the light shielding portion 8A (8A ') of the light shielding plate 8,
8B shows an arrangement relationship with each edge of 8B. Figure 1
As shown in FIG. 1, on the exit side of one element lens of the fly-eye lens 7F, 4 × 4 point light sources SP are X,
They are arranged in the Y direction at substantially equal pitches. At this time, the outer edges of the cross-shaped light-shielding portion 8A (8A ') and the edges corresponding to the inner diameter circle C1 of the peripheral ring-shaped light-shielding portion 8B are all bent according to the pitch of the point light sources forming the three-dimensional light source image. It
That is, in the case of a single fly-eye lens system, it was necessary to define the edge of each light-shielding portion in accordance with the cross-sectional shape of the element lens of the fly-eye lens as shown in FIG. The fly-eye lens system does not have such a need. Moreover, since the number of point light sources forming a three-dimensional light source image is much larger than in the case of the single fly-eye lens system, the average illuminance distribution as a surface light source becomes extremely flat.

FIG. 12 shows the configuration of an illumination system according to the fifth embodiment of the present invention. Here, as disclosed in Japanese Patent Laid-Open No. 4-225514, XY on the Fourier transform plane in the illumination system. The vertical and horizontal pattern surface light sources located in each of the four quadrants in the coordinate system are composed of independent fly-eye lenses 70A, 70B, 70C, and 70D. Then, the illumination luminous flux having a ring-shaped distribution from the collimator lens 4 is divided into four luminous fluxes by the quadrangular pyramid prism 26, and the luminous fluxes are respectively incident on the four fly-eye lenses 70A to 70D. Also,
The surface light source for the oblique pattern is composed of the tip portions 70E, 70F, 70G, and 70H of the four optical fibers 90, and the other end (incident end) side of the four optical fibers 90 is bundled into one. A part of the illumination light branched after the shutter 19A is condensed at the incident end.

In this embodiment, since the system for producing the surface light source for the oblique pattern is independent of the system for producing the surface light source for the vertical and horizontal patterns, there is no oblique pattern on the reticle to be projected. Optical fiber 90
Insert another shutter or neutral density filter (ND filter) into the optical path on the incident end side of
It is possible to prohibit the emission of light or significantly reduce the amount of light. Furthermore, since the emission intensity of the tip portions 70E to 70H can be changed by adjusting the extinction rate of the ND filter, an optimum light amount is given according to the ratio of the diagonal pattern of the L & S pattern on the reticle R. be able to. Therefore, if the operator inputs the information regarding the ratio of the oblique pattern on the reticle R to the main control unit 20 in FIG.
It is also possible to automatically adjust the emission intensity of E to 70H to an optimum value (including zero) according to a predetermined table. Further, as shown in FIG. 12, since four fly-eye lenses 70A to 70D and four tip portions 70E to 70H are independently provided, each fly-eye lens is adjusted according to the pitch of the L & S pattern on the reticle R. The lens or the tip may be two-dimensionally or one-dimensionally movable in the XY plane. In that case, the pitches of the vertical and horizontal patterns and the diagonal pattern are almost the same, and the four fly-eye lenses 70 are used.
The light amount centroids of the surface light sources on the exit sides of A to 70D are X.
When the arrangement corresponding to the four corners of the square centered on the optical axis AX in the Y plane is taken, the four fly-eye lenses 70A to 7A are used.
The eccentric amount from the optical axis AX of the center of gravity of the light amount of 0D and the tip portion 7
It is advisable to move the light amount centroids of 0E to 70H in such a relationship that the eccentric amount from the optical axis of the gravity center point becomes substantially equal.

Note that in the configuration of FIG. 12, each of the four fly-eye lenses 70A to 70D may be a tandem fly-eye lens system as in FIG. 10, and each fly-eye lens 70A to 70D emits light. A diaphragm (light-shielding plate) may be separately provided on the side so that the size of each of the four surface light sources can be changed individually or in conjunction with each other.
By the way, in FIG. 12, fly-eye lenses 70A to 7A are provided.
No special light-shielding plate, etc. is provided between 0D, but when there is a large amount of stray light passing through the space between the fly-eye lenses that cannot be ignored, a simple light-shielding plate (cross shape)
Is desirable. Therefore, if the stray light component is sufficiently small, it is not necessary to provide a special light shielding plate. This can be similarly applied to the light shielding plate 8 shown in FIGS. 4 and 6 to 8, and the cross-shaped light shielding portions 8A and 8A.
This means that A ′, the ring-shaped light-shielding portion 8B, etc. do not have to be a complete light-shielding layer. For example, for each light shield on the light shield plate 8,
It may be composed of a dielectric thin film or the like having an extinction ratio of 90% or more at the wavelength of the illumination light for exposure (365 nm for i-line, 248 nm for KrF excimer laser).

Now, for the sake of explanation of the following simulation, examples of the diaphragm shapes of the conventional modified light sources that have been published so far are shown in FIGS. FIG. 13 is for a circular 4 light source having a center position (xβ, yα) optimized for a vertical pattern Pv having a specific pitch and a horizontal pattern Ph and an appropriate radius (a value of 0.1 to 0.3). It is an example of the light shielding plate. FIG. 14 shows a shading plate for a fan-shaped four light source, in which square openings are replaced by square openings in FIG. 13, and a part of the periphery of these four square openings is larger than a radius r corresponding to the σ value of the illumination optical system. Here is an example.

As an example, the vertical and horizontal L & S pattern using the light source shape shown in FIG. 14 and the oblique (45 ° or 135 °
(° direction) FIG. 15 shows a simulation result of the depth of focus DOF [μm] with respect to the line width size [μm] of the L & S pattern image obtained when the L & S pattern is projected. Here, the simulation conditions are that the wavelength λ is 0.365 [μm] for the i-line, and the numerical aperture NA on the wafer side of the projection optical system PL is 0.50 (0.
1), the inner diameter r of the ring-shaped light-shielding portion 8B of the light-shielding plate 8 is set to a value (r
/ R ₀ ) is 0.8 (σ value of an ordinary circular surface light source is also 0.
8), and the half-value a of the width of the cross-shaped light-shielding portion is set to 0.28 in terms of numerical aperture, that is, a = 0.28r / σ = 0.35r (a = 0 in normal illumination and no cross-shaped light-shielding portion is provided). ). Here, the value of the depth of focus (DOF) is from the range (full width) where the contrast of the 1: 1 line and space (L / S) pattern image is 60% or more, the thickness of the resist to be patterned is 1.2 μm, A constant value determined by the refractive index 1.7, which is a value obtained by subtracting 1.2 / 1.7≈0.706 [μm]. The characteristic DV1 of the simulation result represented by the two-dot chain line in FIG. 15 shows the depth of focus characteristics for the vertical and horizontal L & S patterns when the conventional light shielding plate of FIG. 14 is used, and the simulation characteristic DO1 of the broken line is the same. Diagonal (45 °, 135
°) Depicts the depth of focus characteristics for the L & S pattern. Figure 1
In the conventional modified light source shape as shown in FIG. 4, the depth of focus characteristic DO1 for the diagonal pattern is slightly inferior to the depth of focus characteristic DC for the diagonal pattern when using a normal circular surface light source simulated for comparison. still,
In the case of a normal circular light source shape, the depth of focus characteristic DC is obtained for any of vertical, horizontal, and diagonal patterns.

FIG. 16 shows a first embodiment (FIG. 4) of the present invention.
Simulation of depth of focus characteristics when using a light shield 8
Indicates the result. At this time, the cross-shaped light-shielding portion 8A in FIG.
Half width a is a = 0.28r₀= 0.35r
And half length b is b = 0.56r₀= 0.7r,
The exposure wavelengths λ, N.A. and σ were the same as those in FIG. This
Depth of focus in 1: 1 L & S pattern in the vertical and horizontal directions under
The characteristic DV2 corresponds to the conventional modified light source (FIG. 14) in FIG.
The characteristics are slightly inferior to DV1, but the diagonal L & S
Depth-of-focus characteristics DO2 for a turn is a normal circular surface light.
Depth of focus characteristics DC when using a source
Therefore, the effect of the present invention has been confirmed. In addition, vertical and horizontal putter
The depth of focus characteristics DV2 for
It does not impair the inherent ability of. In addition, this stain
In the simulation, the half-width a of the cross-shaped light-shielding part and the length
Half value b is a = 0.28r₀(Aperture of projection optical system
0.28 times the number N.A.), b = 0.56r₀(Numerical aperture N.
0.56 times A.), but these values are not
As mentioned above, the value a is 0.1r
₀(0.1 ・ N.A.) ≦ a ≦ 0.4r₀(0.4 ・ N.A.)
0.4r for the value b₀(0.4 ・ N.A.) ≦ b <
 0.8r₀If it is about (0.8N.A.), the effect of the present invention can be obtained.
You can However, the upper limit of value b is the value of radius r
On the other hand, it is necessary that b <r.

FIG. 17 shows a simulation result of the depth of focus characteristics when the light shielding plate 8 according to the second embodiment (FIG. 6) of the present invention is used. At this time, the shading plate 8 is a combination of a cross-shaped shading portion and a central circular shading portion as shown in FIG. 6, and the simulation condition is that the exposure wavelength λ is 0.365.
μm (i line), the numerical aperture NA of the projection optical system PL on the wafer side is 0.50, and the inner diameter r of the ring-shaped light shielding portion 8B on the outer periphery of the light shielding plate 8
Is 0.7 in terms of σ value (r / r ₀ ), the half width a of the cross-shaped light shielding portion is 0.28 r ₀ , and the half length b is 0.56 r ₀ .
The radius c of the central circular light-shielding portion was set to 0.46r ₀ .
As shown in the simulation result of FIG. 17, the depth of focus characteristic DO3 of the oblique L & S pattern is significantly improved as compared with the depth of focus characteristic DC of the conventional normal circular surface light source (σ = 0.7), and The depth of focus characteristics DV3 for the vertical and horizontal L & S patterns are also sufficiently large values.

In the simulation here, the value of the radius c of the central circular light-shielding portion was set to 0.46r / σ, but this is not limited to 0.46r / σ as in the half values a and b described above. , 0.3r / σ (0.3 · NA) <c <0.6r /
If it is about σ (0.6 · NA), the effect of the present invention can be sufficiently obtained. However, if the value of the radius c is too small, the shading plate 8 in FIG. 6 has the same shape as the shading plate in FIG. 4, so that the degree of improvement in the depth of focus for the diagonal pattern is slightly reduced. That is, the characteristic DO in FIG.
3 becomes like the characteristic DO2 in FIG. Further, if the value of the radius c is too large, it approaches annular illumination (described later), so in the depth-of-focus characteristic DV3 for the vertical and horizontal L & S patterns, the depth of focus as seen near the pattern size of 0.45 μm is particularly noticeable. There is no part that grows larger, which is also undesirable.

FIG. 18 shows a simulation result when the light shielding plate 8 according to the third embodiment (FIG. 7) of the present invention is used. The simulation conditions in this case are: the numerical aperture NA of the projection optical system is 0.50, the σ value (r / r ₀ ) which is the maximum radius of the surface light source is 0.8, each dimension of the cross shading portion 8A, and the half value a, The half value b is 0.28r ₀ and 0.56r ₀ , respectively, and the distance d to the peripheral minute light shields 8C and 8D is 0.64.
It was set to r ₀ . Comparing the simulation result of FIG. 18 with the simulation result shown in FIG. 16 described above, the depth of focus characteristics DO4 for the oblique pattern when the light shielding plate 8 of FIG. While the depth of focus characteristics DO2 when used (FIG. 16) or the depth of focus characteristics DO3 when the shading plate of FIG. 6 is used (FIG. 17) are improved to the same extent,
It can be seen that the depth of focus is improved as in the case of the depth-of-focus characteristic DV4 even for a pattern with a medium fineness of a line width of about 0.45 μm.

Incidentally, the minute light shielding portions 8C, 8 in the light shielding plate of FIG.
The value of the edge distance d of D is not limited to 0.64r ₀ , but may be in the range of 0.5r ₀ <d <0.8r ₀ . However, if the distance d is too small, the resolution with respect to the vertical and horizontal patterns will decrease, and if it is too large, the effect will not appear. Therefore, the light shielding plate 8 shown in FIG.
A central circular light-shielding portion as shown in FIG. 6 or a quadrangle light-shielding portion that further shields the vicinity of the optical axis may be added.

FIG. 19 shows a similar simulation result with annular illumination for comparison. At this time, the exposure wavelength λ is 0.365 μm, and 0.7.
Consider a circular surface light source having a radius corresponding to NA (σ = 0.7) and a central circular portion corresponding to a half radius (σ = 0.35) as a light shielding portion. According to the depth of focus characteristic DA for the L & S pattern obtained by such an annular illumination, the width of a rough pattern having a line (or space) width of 0.42 μm or more is approximately 1.5 μm.
A depth of focus of about m can be obtained. The depth of focus characteristic DC of the conventional circular surface light source is actually less than 1 μm.
However, considering the exposure time of the actual memory pattern,
In particular, a large depth of focus is required in the exposure step of the metal wiring layer, and for example, in 64M DRAM, a depth of focus of 2 μm or more is required for an L & S pattern having a line width of about 0.45 μm. Therefore, it is difficult to satisfy this requirement with the focal depth characteristic DA obtained by the annular illumination as shown in FIG. Further, even in the above-mentioned exposure process of the metal wiring layer, the depth of focus is especially required for the vertical and horizontal L & S patterns formed in the step (about 1 μm) portion, and therefore the modification as in the present invention. The light source shape is extremely effective.

In the embodiments, the light source is the mercury lamp and the i-line is used, but this may be another wavelength or a light source such as a laser. Also, under the conditions of the simulation, the numerical aperture NA of the projection optical system is set to 0.
5 and the maximum radius r of the surface light source created by the shading plate
Was set to 0.7 or 0.8 by the σ value, but numerical aperture NA,
The σ value is not limited to this. However, it is effective that the σ value is about 0.7 or more. Further, the outermost shape of the light source shape is limited by the circle (σ) defined by the inner diameter edge of the annular light shielding portion 8B of the light shielding plate 8,
The outermost shape may be defined by a quadrangle, a hexagon, or the like. Further, the shape of the light-shielding portion of the light-shielding plate 8 in each embodiment is the same (symmetrical) in the X and Y directions, but the shape may be different in the X and Y directions. That is, the dimension values a, b, and d of each light-shielding portion, or the value of the distance c from the center of each edge when a square light-shielding portion is provided in the center, are the X direction and the Y
The direction may be different.

In an actual illumination system, the light quantity distribution on the exit surface of the fly-eye lens is discrete according to the arrangement of the element lenses of the fly-eye lens, that is, a discrete set of point light sources. At this time, if the cross-sectional shape of each element lens is rectangular, the intervals of the discrete point light sources also differ in the X and Y directions. Therefore, in order to make effective illumination conditions (orientation characteristics of the illumination light to the reticle) in the X and Y directions, the dimension values a, b, c, and d of the light shielding portions are set to X,
It may be necessary to positively make the difference in the Y direction. In addition, in order to efficiently concentrate the illumination light and reduce the light amount loss with respect to each of the transmissive portions 81a to 81d and 81e to 81h of the light shielding plate 8 used in each embodiment of the present invention, they are provided in front of the light shielding plate 8. Condensing means (prism, mirror, fiber, etc.) for concentrating the illuminating light may be provided in the transmissive part.
Further, the light-shielding plate 8 of each embodiment is composed of the light-transmitting portion and the light-shielding portion, but a part or all of the light-shielding portion may be a semi-light-transmitting portion (desirably, the transmittance is 50% or less). Further, since the required depth of focus and the importance of the vertical and horizontal patterns and the diagonal pattern differ depending on the exposure process, a plurality of light-shielding plates 8 having a shape corresponding to them are provided in the turret 10 of FIG.
It is desirable to prepare it in advance and make it replaceable. In the simulation, the reticle used was a normal reticle composed of a light-shielding portion (chrome layer) and a light-transmitting portion. However, the present invention uses a so-called halftone phase shift (a transmittance of about 1 to 15% instead of the light-shielding portion). The effect of the present invention can be further enhanced by using it when projecting a reticle of a halftone transmissive portion (thin film is provided) which has a phase difference of π with light passing through the transmissive portion.

As is clear from the above simulation results, the line widths of the vertical and horizontal patterns Pv and Ph on the wafer are 0.4 to 0.5 which are used when the 64M-DRAM is manufactured.
When the thickness is about μm, the light shielding plate 8 shown in each of the embodiments works well for improving the depth of focus. Moreover, at the same time, the effect of improving the depth of focus is obtained for the oblique patterns Ta and Tb. However, when comparing the depths of focus in the same line width size between the vertical and horizontal patterns and the diagonal pattern, the depth of focus of the diagonal pattern is certainly not so large. However, when the pitch (line width size) of the diagonal pattern is about 1.2 to 1.5 times rougher than the pitch (line width size) of the vertical and horizontal patterns in one reticle, for example, as shown in FIG.
When the line width size is 0.42 μm in the characteristic DV3 for the vertical and horizontal patterns in FIG. 7, the line width in the characteristic DO3 for the diagonal pattern is 1.5 times (0.63 μm) the line width size of the diagonal pattern. With a size of 0.63 μm, a depth of focus of about 2 μm can be obtained.

By the way, as is clear from FIG. 9 described above, 4 optimized for the pitch of the target vertical and horizontal patterns.
The two light amount centroids (centroid of 0th order light) 80A-80D are
When located at each corner of the square in the pupil EP of the projection optical system PL, if the pitch of the diagonal pattern of interest is about 1.4 times the pitch of the vertical and horizontal patterns, it is supplementarily added for the diagonal pattern. The light amount centroid point 80E of the illumination light ideally coincides with the intersection of the line segment connecting the two centroid points 80A and 80B and the Y axis.

FIG. 20 shows a state in which the light amount centroids are arranged in an almost ideal relationship when the pitch relationship between the vertical and horizontal patterns and the diagonal pattern is about 1.4 times as described above. . In FIG. 20, zero-order light distributed in the pupil EP,
It is assumed that the first-order diffracted light has a predetermined size and spreads around each centroid. Originally, the shape (area) of the spread corresponds to the shape of the surface light source such as the transparent portions 81a to 81d and 81e to 81h of the light shielding plate 8, but it is simply represented here as a circle.

In the case of FIG. 20, an oblique pattern (45 °, 1
Four 0th-order lights (center of gravity 80A-8
0D) corresponding to the first-order diffracted light −Dt ₁
Pass through almost the center of. Also, the first-order diffracted light -Dt ₁ 'from an oblique pattern that passes through the center of gravity 80E as the 0th-order light.
Is the center of gravity 80H and 80F of the auxiliary light source for the diagonal pattern.
Pass each of the vicinity of, or the matched position. At the same time, the first-order diffracted light −Dy ₁ from the lateral pattern passing through the center of gravity 80E as the 0th order light is the center of gravity 80 of the auxiliary light source for the oblique pattern.
Pass the vicinity of G or the matched position.

Among the distributions of the 0th-order light and the 1st-order diffracted light, the components that reduce the effect of increasing the depth of focus with respect to the oblique pattern when the modified light source is used are the 4th-order diffracted lights appearing at the center of the pupil EP. It is Dt ₁ . Therefore, under such a condition, a neutral density filter (ND filter) may be arranged only in the central portion of the pupil EP of the projection optical system to appropriately attenuate the light amounts of the four first-order diffracted lights −Dt ₁ .

Note that the positional relationship between the circular areas for forming the four light quantity centroids 80A to 80D for the vertical and horizontal patterns and the small circular area for forming the four light quantity centroids 80E to 80H for the diagonal pattern in FIG. The shape is similar to the shape of the transparent portion of the light shielding plate 8 for the modified light source provided in the illumination system as it is. Therefore, as the light-shielding plate 8, the one in which the four large circular regions and the four small circular regions in FIG. 20 are made transparent can be used as it is.

[0059]

As described above, according to the present invention, it is possible to prevent the deterioration of the image forming performance, particularly the depth of focus improvement degree, for an oblique pattern, which has been a problem in the modified light source. Can obtain almost the same performance as the conventional modified light source.

[Brief description of drawings]

FIG. 1 is a perspective view of an illumination system having a modified light source that is the basis of the present invention.

FIG. 2 is a view showing a principle shape of a modified light source according to the present invention.

FIG. 3 is a diagram showing an overall configuration of a projection exposure apparatus as an embodiment of the present invention.

FIG. 4 is a view showing the shape of a light shielding plate for a modified light source according to the first embodiment.

FIG. 5 is a diagram showing an example of a periodic direction of an L & S pattern on a reticle.

FIG. 6 is a diagram showing the shape of a light shielding plate for a modified light source according to a second embodiment.

FIG. 7 is a diagram showing the shape of a light shielding plate for a modified light source according to a third embodiment.

FIG. 8 is a diagram showing an example of a positional relationship between the shape of the light shielding plate of FIG. 7 and a fly-eye lens.

FIG. 9 is a diagram schematically showing the luminous flux distribution on the pupil plane of the projection optical system when the modified light source shown in each example is used.

FIG. 10 is a diagram showing a partial configuration of an illumination system according to a fourth embodiment.

11 is a diagram showing the shape of a light shielding plate suitable for the illumination system of FIG.

FIG. 12 is a diagram showing a partial configuration of an illumination system according to a fifth embodiment.

FIG. 13 is a view showing the shape of a conventional light shielding plate for a modified light source.

FIG. 14 is a view showing a shape of a conventional light shielding plate for a modified light source.

15 is a graph showing a simulation result of depth of focus characteristics when the light shielding plate of FIG. 14 is used.

16 is a graph showing a simulation result of depth of focus characteristics when the light shielding plate of FIG. 4 is used.

FIG. 17 is a graph showing a simulation result of depth of focus characteristics when the light shielding plate of FIG. 6 is used.

FIG. 18 is a graph showing a simulation result of depth of focus characteristics when the light shielding plate of FIG. 7 is used.

FIG. 19 is a graph showing a simulation result of depth-of-focus characteristics when annular illumination is performed.

FIG. 20 is a diagram schematically showing the luminous flux distribution on the pupil plane of the projection optical system when the modified light source according to the present invention is used.

[Explanation of symbols]

1 ... Mercury lamp 7, 7A-7F, 70A-70D ... Fly-eye lens 70E-70H ... Optical fiber tip 8 ... Shading plate 11 ... Condenser lens R ... ..Reticle PL ... Projection optical system W ... Wafer

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G03F 7/20 521 7316-2H

Claims (8)

[Claims] 1. A projection exposure apparatus comprising: an illumination system for illuminating a mask on which a pattern to be projected is formed; and a projection optical system for projecting an image of the pattern onto a photosensitive substrate. An illumination optical system having a surface that is optically in a Fourier transform relationship with the pattern surface of the mask, and illumination light within a predetermined radius centered on the optical axis on the Fourier transform surface or on a surface in the vicinity thereof. And a light distribution setting unit that distributes the illumination light in a ring-shaped region having a predetermined width around the optical axis, and the center of the inside of the ring-shaped region. A projection exposure apparatus, characterized in that the illumination light is distributed in a plurality of discrete regions excluding parts. 2. A light source for irradiating a mask on which a pattern to be projected is formed with illumination light, and a surface having an optical Fourier transform relationship with the pattern surface of the mask are formed inside, The light from the pattern of the mask, which is illuminated by the illumination light from the illumination optical system and the illumination optical system in which the secondary light source of the light source is formed, is incident on the Fourier transform surface or a surface in the vicinity thereof, In a projection exposure apparatus including a projection optical system for image-forming and projecting an image on a photosensitive substrate, a first pattern shape in which patterns on the mask have periodicity in each of two directions orthogonal to each other, and the two directions And a second pattern shape having a periodicity in a direction intersecting with each other, and the proportion of the first pattern shape on the mask is larger than the proportion of the second pattern shape. In order to produce tilted illumination light corresponding to the direction of periodicity of the shape of the first pattern, the Fourier transform surface or a surface in the vicinity thereof is decentered from the optical axis of the illumination optical system by a predetermined amount and is symmetrical to each other. A first setting member that sets a first light source surface in each of the four regions located at, and the Fourier transform surface so as to create inclined illumination light corresponding to the direction of the periodicity of the second pattern shape, Alternatively, a second setting member that sets a second light source surface in each of four regions that are eccentric from the optical axis of the illumination optical system by a predetermined amount and are symmetrically located on the surface in the vicinity thereof is provided. The area of the light source surface is larger than the area of the second light source surface. 3. The first setting member and the second setting member are defined by a transmission part shape of a light shielding plate arranged on a Fourier transform surface of the illumination optical system or a surface in the vicinity thereof. The apparatus according to item 2. 4. The apparatus according to claim 3, wherein the illumination optical system includes a fly-eye lens that forms the light source surface, and the light-shielding plate is arranged on the exit surface side of the fly-eye lens. . 5. A first pattern shape having periodicity in two directions orthogonal to each other on a mask, and a second pattern shape having periodicity in the other directions are image-projected onto a photosensitive substrate. A projection optical system, a fly-eye lens that receives light from a light source to form a light source image having a size included in a circular area having a predetermined radius, and a light source image formed by the fly-eye lens is used as a pupil plane of the projection optical system. , Or a condensing optical system that forms an image in the center of a surface near the source and superimposes light from each point in the light source image on the mask, wherein the center of the light source image is the origin. When two coordinate axes corresponding to two directions orthogonal to each other among the periodicity directions of the pattern are set, the four quadrants defined by the two coordinate axes have substantially the same area. With a transparent part of 1 A light-shielding plate having second transmissive portions formed in substantially the same area at four positions on the two coordinate axes at positions substantially equidistant from the origin is disposed on the exit side of the fly-eye lens, The projection exposure apparatus is characterized in that the areas of the first transmissive portion and the second transmissive portion of the light shielding plate are different according to the importance of the first pattern shape and the second pattern shape. 6. A projection optical system for image-forming and projecting a pattern of a mask on a photosensitive substrate, and a surface of a predetermined shape on an optical Fourier transform surface with respect to the mask, or a surface in the vicinity thereof, upon incidence of light from a light source. In a projection exposure apparatus including a light source and an illumination optical system that uniformly irradiates light from the surface light source on the mask, an orthogonal coordinate system XY is defined with the center of the surface light source as an origin.
When the radius of a circle approximated to the outer shape of the surface light source is r and the coherence factor of the surface light source is a value, a coefficient a,
b is 0.1r / σ ≦ a ≦ 0.4r / σ, 0.4r /
σ ≦ b ≦ 0.8 r / σ, and −a ≦ X ≦ on the surface light source.
a, within the region of −b ≦ Y ≦ b and −a ≦ Y ≦ a, and −
A projection exposure apparatus comprising a light intensity distribution adjusting member for making the light intensity within the region of b ≦ X ≦ b smaller than that of other regions or substantially zero. 7. The light intensity distribution adjusting member has a coefficient c.
When 0.3r / σ ≦ c ≦ 0.6r / σ, on the surface light source, the light intensity in the region of X ² + Y ² ≦ c ² should be smaller than that of other regions, or should be almost zero. 7. A device according to claim 6, characterized in that 8. The illumination optical system is configured to form an image of the origin of the surface light source at the center of the pupil plane of the projection optical system,
When the radius at the surface on the light source of the effective pupil diameter of the projection optical system and r _0, the ratio r / r ₀ the radius r is σ value of the surface light source, and a 0.7 or higher Device according to any one of claims 6 or 7, characterized in that