JP3084761B2 - Exposure method and mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a circuit pattern of a semiconductor or the like, and more particularly to a mask used in a lithography process, a projection exposure method using the mask, and an exposure apparatus.

[0002]

2. Description of the Related Art In forming a circuit pattern of a semiconductor or the like,
In the case of the current miniaturized LSI, an original (mask, reticle) including a light-shielding portion and a transmissive portion that is magnified 5 to 10 times that of an actual pattern is formed on a semiconductor substrate (mask or reticle) using a reduction projection exposure apparatus. An image is formed on a photosensitive film (resist) applied on the surface of a wafer or the like, and a method of exposing the image is used.

Conventionally, a circuit pattern to be transferred has been drawn on a reticle to be used at a magnification of a projection type exposure apparatus, so that the circuit pattern is transferred to a desired size on a wafer. Is done. Conventionally, in an apparatus of this type, as shown in FIG. 15, an illumination light beam L10 is projected near a pupil plane (Fourier transform plane) of an illumination optical system.
The reticle (mask) R is illuminated as a light beam L11 passing through a circular area centered on the optical axis of the illumination optical system by the substantially circular aperture stop 100 arranged substantially conjugate with the pupil ep of L. Here, a solid line representing a light beam represents a principal ray of light emitted from one point.

At this time, the ratio between the numerical aperture of the illumination optical system and the numerical aperture on the reticle side of the projection optical system PL, that is, the so-called σ value is determined by the
It is determined by 0, and the value is generally about 0.3 to 0.6. The illumination light L11 is diffracted by the pattern PP patterned on the reticle R. From the pattern PP, the 0th-order diffracted light D ₀ , the + 1st-order diffracted light Dr, and the −1st-order diffracted light Dl
Occurs. The respective diffracted lights are condensed by the projection optical system PL and generate interference fringes on the wafer (sample substrate) W. This interference fringe is an image of the pattern PP.

At this time, the 0th-order diffracted light D ₀ and the ± 1st-order diffracted light D
The angle θ formed by r and Dl is determined by sin θ = λ / P (λ: exposure wavelength, P: pattern pitch). When the pattern pitch becomes finer, sin θ becomes larger, and when sin θ becomes larger than the reticle-side numerical aperture (NA _R ) of the projection optical system, the ± first-order diffracted lights Dr and Dl cannot enter the projection optical system PL.

At this time, only the zero-order diffraction D ₀ reaches the wafer W, and no interference fringes occur. That is, when sinθ> NA _R , an image of the pattern PP cannot be obtained, and the pattern P
P cannot be transferred onto the wafer W. As described above, in the conventional exposure apparatus, sin θ = λ
The pitch P at which / P ≒ NA _R is obtained by the following equation: P ≒ λ / NA _R (1) This pitch P is the minimum pitch on the reticle of a pattern that can be transferred onto the wafer W.

Therefore, the minimum pattern width is about 0.5 × λ / NA _R which is half of this, but in actuality, about 0.6 × λ / NA _R is the minimum pattern width due to the depth of focus. Has become. If this is converted to the image plane (wafer W) side of the projection optical meter, 0.6 × λ / NA _W (where NA _W is the numerical aperture on the wafer side of the projection optical system, NA _W = B · NA _R , and B is the projection Optical system).

Hereinafter, this value is called the resolution limit of the projection optical system. In order to transfer a pattern finer than the resolution limit of the projection optical system itself, a method of increasing the resolution by changing the reticle pattern itself has been proposed. This is a method called phase shift, in which a so-called phase shifter film is formed on the reticle, where the phase of the transmitted light is shifted by π from the other parts, and the interference effect of the transmitted light between the phase shifter part and the other parts The resolution and the depth of focus are enhanced by using (especially the offset effect).

[0009]

In a conventional projection type exposure apparatus, the fineness (size) of a circuit pattern that can be transferred onto a wafer is such that the exposure wavelength is λ and the numerical aperture on the wafer side of the projection optical system is NA _W. The limit was about 0.6 × λ / NA _W. This is due to the diffraction phenomenon that occurs because the light is a wave. Therefore, if the exposure wavelength is made shorter, the resolution is improved in principle.

However, when the wavelength is shorter than 200 nm, there are many problems that there is no suitable optical material that transmits the wavelength and that absorption by air occurs. The numerical aperture NA _W is now already in the technical limitations, no more larger the NA is the situation can not be expected. Although the exposure using the phase shift method can improve the resolution and increase the depth of focus, the reticle with a phase shifter used in the phase shift method has a complicated manufacturing process and therefore has a high defect rate. In addition, the manufacturing cost is extremely high. Further, there are many problems such as an inspection method and a correction method not yet established, and many problems remain for practical use.

In the current LSI manufacturing process, film formation,
Usually, the cycle of photolithography (circuit pattern transfer) and etching is repeated about 20 times. The thickness of each film is about 0.05 μm to 1 μm. Therefore, as the process proceeds, a step of about several μm is formed on the wafer. A projection exposure method is required.

On the other hand, as one method for increasing the depth of focus, a multi-focus exposure method is also known. In the depth increasing method by this exposure method, a normal exposure method is particularly applied to a pattern which exists alone (a pattern having a size other than the pattern with respect to the pattern size of about 1: 3 or more, hereinafter abbreviated as an isolated pattern). Although a larger practical depth of focus can be obtained as compared with, it is impossible in principle to improve the resolution.

The present invention has been made in view of such a situation, and uses the same reticle (mask) comprising a light-shielding portion and a transmissive portion as before, and provides an exposure method capable of obtaining high resolution and a deep depth of focus. It is intended to provide a device.

[0014]

According to the present invention, a mask (R) is irradiated with illumination light through an illumination optical system, and a projection optical system (P) is illuminated.
L) to expose the photosensitive substrate (W) with illumination light. In the first exposure method according to the present invention, the plurality of different patterns (PA, PB) include at least one periodic pattern (PA) and a part of the periodic pattern (PA ₂ ) on the photosensitive substrate. ) Is irradiated with illumination light to each of the plurality of patterns so as to overlap with another pattern (PB) having a different shape, and the photosensitive substrate is subjected to multiple exposure. In this system, the light amount distribution of the illumination light on a predetermined plane (pupil plane), which is substantially in a Fourier transform relationship with the pattern plane of the mask, is increased outside the central portion. Therefore, a fine pattern to be formed on the photosensitive substrate can be transferred with high resolution and a large depth of focus. In addition,
It is desirable to define the light quantity distribution of the illumination light in a local area decentered from the optical axis on a predetermined surface in the illumination optical system or in an annular area. In the second exposure method according to the present invention, in order to form a fine pattern (PA ₂ ) on the photosensitive substrate, dummy patterns (PA ₁ , PA ₁ ,
The first pattern (PA) provided with PA ₃ ) is irradiated with illumination light to expose the photosensitive substrate, and the predetermined area on the photosensitive substrate where a dummy pattern transfer image is formed is irradiated with illumination light. . Therefore, the size and shape of the fine pattern can be accurately defined on the photosensitive substrate,
The transfer image of the dummy pattern is not formed.
In addition, in order to prevent irradiation of the illumination light to the region where the fine pattern is formed on the photosensitive substrate, it is possible to irradiate the predetermined pattern with the illumination light by overlapping the second pattern (PB) on the fine pattern on the photosensitive substrate. desirable.

Further, the present invention relates to a mask used for multiple exposure of a photosensitive substrate for forming a fine pattern (such as an isolated pattern) on a photosensitive substrate (W) via a projection optical system (PL). is there. In the first mask according to the present invention, a periodic first pattern (PA) including a fine pattern in a part thereof and a second pattern (PB) superimposed on a part of the first pattern on the photosensitive substrate. Are formed, and at the time of multiple exposure of the photosensitive substrate using the first and second patterns, the second pattern is superimposed on a part of the first pattern. Further, the second mask according to the present invention is different from the first pattern (PA) in which the dummy patterns (PA ₁ , PA ₃ ) are provided in the vicinity of the fine pattern (PA ₂ ) in a shape different from the first pattern, and A second pattern (PB) to be superimposed on the fine pattern is formed on the photosensitive substrate. For this reason, the size and shape of the fine pattern can both be accurately defined on the photosensitive substrate, and the mask does not need to be replaced during multiple exposure using the first and second patterns, thereby improving the throughput of the exposure apparatus. It is possible to aim at.

In the projection exposure apparatus to which the present invention is applied, the light amount distribution of the illumination light can be changed on a predetermined plane (pupil plane) in the illumination optical system which becomes a Fourier transform plane of the pattern surface of the mask. In particular, the light amount distribution on a predetermined surface is enhanced outside the optical axis of the illumination optical system, that is, in a local region centered on at least one point other than the optical axis on the predetermined surface, or on a predetermined surface. It is preferable to be able to adopt an illumination method that increases the intensity within an annular zone centered on the optical axis. Thereby, by applying the illumination method to the periodic first pattern used in the multiple exposure or the first pattern having the dummy pattern in the present invention, the first pattern can be further improved on the photosensitive substrate with higher resolution. In addition, the image can be transferred with a large depth of focus, and the transfer accuracy of a fine pattern to be formed on the photosensitive substrate, for example, the fidelity of a dimension (such as a line width) and a shape can be improved. When the mask according to the present invention is used, when exposing a photosensitive film formed on the surface of a substrate to be exposed (a semiconductor wafer or the like) to a plurality of sub-exposures (to perform multiple exposure of the photosensitive substrate),
In each of the plurality of sub-exposures, the relative positional relationship between the mask (reticle) and the photosensitive substrate is made different in a plane perpendicular to the optical axis of the projection optical system. At this time, the relative positional relationship between the mask and the photosensitive substrate was such that at least one region on the photosensitive substrate was subjected to overlapping exposure of different patterns on the mask in all of the plurality of sub-exposures.

It is assumed that at least two of the plurality of patterns to be superposed and exposed consist of a group of patterns arranged substantially periodically, and that the periods or directions of the periodic patterns are different from each other. You may make it do. Further, the group of patterns forming the periodic pattern is finer than about the resolution limit of the projection optical system, and the other patterns are composed of patterns or pattern groups about twice or more as large as the resolution limit. Is desirable. Further, in each of the plurality of sub-exposures, the relative positional relationship between the mask and the photosensitive substrate (such as a semiconductor wafer) is changed by moving the stage holding the photosensitive substrate with respect to the optical axis of the projection optical system. It may be a thing.

[0018]

In a plane in an illumination optical system having a relationship between a reticle pattern and a Fourier transform used in the present invention, one or more illumination light beams for illuminating the reticle are centered at one or more points other than the optical axis. Using a projection exposure apparatus focused on an area can increase the resolution and depth of focus, especially for periodic reticle patterns.

Hereinafter, this principle will be described with reference to the drawings. In a conventional projection exposure apparatus, exposure light incident on a reticle from above at various angles of incidence is used indiscriminately, and 0th order, ± 1st order, ± 2th order generated in a reticle pattern is used.
Next, each of the diffracted lights transmitted through the projection optical system almost indefinitely to form an image on the wafer. On the other hand, in the projection exposure apparatus according to the present invention, as shown in FIG. 16, the optical axis AX of the illumination optical system is set in a plane having a relationship between the illumination light L10 and the reticle pattern surface in the illumination optical system in a substantially Fourier transform relationship. A light shielding plate 100 ′ having a transmission portion other than the central portion through which the light passes does not pass on the optical axis of the illumination optical system, that is, any two light beams obliquely incident on the reticle pattern at a specific direction and at an angle. L12, L13, or 2n light beams (n is a natural number) are formed to illuminate the reticle pattern PP. The reticle pattern PP usually includes many patterns having a periodic structure in which light transmitting portions and light shielding portions are repeatedly formed at a predetermined pitch. Then, the 0th-order diffracted light and ± 1st-order diffracted light generated by the reticle pattern PP are imaged on the wafer W via the projection optical system PL.

That is, by irradiating two or 2n luminous fluxes in a predetermined direction and at an angle to the pattern PP according to the fineness of the reticle pattern PP, optimal 0th-order diffracted light and ± 1st-order light are generated. This makes it possible to form a pattern that could not be resolved sufficiently in the past on the wafer W with a high contrast and a large depth of focus. Here, the light beam L1 incident on the reticle R
Reference numerals L13 and L13 are converted into two luminous fluxes having chief rays that are incident symmetrically with respect to the optical axis AX of the projection optical system PL at a predetermined angle に よ っ て by the above-described light shielding plate 100 ′. Again, the solid line representing the luminous flux represents the chief ray of the light emitted from one point. First, the illumination light L1 based on FIG.
2 will be described. The illumination light L12 is diffracted by the reticle pattern PP and is diffracted by the 0th order light D ₀ , +1.
A first-order diffracted light Dr and a first-order diffracted light Dl are generated. However, since the illumination light L12 is incident on the reticle pattern PP at an angle に 対 し て with respect to the optical axis AX of the projection optical system PL, the zero-order diffracted light D ₀ is also at an angle ψ with respect to the optical axis AX of the projection optical system PL. Proceed only in the inclined direction. Here, the projection optical system PL is a two-sided telecentric system.

Accordingly, the + 1st-order light Dr travels in the direction of θ _P + ψ with respect to the optical axis AX, and the −1st-order diffracted light Dl receives the optical axis AX.
Proceeds in the direction of θ _m −ψ. At this time, θ _P , θ
_m is sin (θ _P + ψ) -sinψ = λ / P (2) sin (θ _m + ψ) -sinψ = λ / P (3)

It is assumed that both the + 1st-order diffracted light Dr and the -1st-order diffracted light Dl are incident on the projection optical system PL. When the diffraction angle increases with the miniaturization of the reticle pattern PP, the + 1st-order diffracted light Dr that first travels in the direction of θ _P + ψ cannot pass through the projection optical system PL (sin (θ _P + ψ)).
> NA _R ). However, since the illumination light L12 is incident obliquely with respect to the optical axis AX, even the diffraction angle at this time is -1.
The next-order diffracted light Dl can pass through the projection optical system PL (s
in (θ _m + ψ) <NA _R ).

Accordingly, interference fringes are generated on the wafer W by two light beams of the _0th-order diffracted light D0 and the -1st-order diffracted light Dl. This interference fringe is an image of the reticle pattern PP. When the reticle pattern PP is 1: 1 line and space, about 90%
%, And the pattern PP can be patterned on the wafer W having the surface coated with the resist. The resolution limit at this time is when sin (θ _m + ψ) = NA _R (4), and therefore, NA _R + sinψ = λ / PP = λ / (NA _R + sinψ) (5) Is the pitch of the minimum transferable pattern on the reticle.

Assuming that sinψ is about 0.5 × NA _R , the minimum pitch of the pattern on the reticle that can be transferred is P = λ / (NA _R + 0.5NA _R ) = 2λ / 3NA _R (6) ). On the other hand, as shown in FIG. 15, in the case of a conventional exposure apparatus in which the illumination light is a light beam passing through a circular area centered on the optical axis AX of the projection optical system PL, the resolution limit is expressed by the equation (1). As described above, P ≒ λ / NA _R was satisfied. Therefore, a higher resolution than the conventional exposure apparatus can be realized.

Considering the illumination light L13 similarly,
Primary light Dr₁Is θ with respect to the optical axis AX. _P1Proceed in the direction of -ψ
-1st order diffracted light Dl₁Is θ with respect to the optical axis AX._m1+ Ψ
Proceed in the direction. D₀₁Represents the zero-order diffracted light. this
When θ_P1, Θ_m1Are sin (θ_m1+ Ψ) −sinψ = λ / P (7) sin (θ_P1−ψ) + sinψ = λ / P (8), and the resolution limit is sin (θ_P1−ψ) = NA_RWhen
It is.

Therefore, similarly to the case of the illumination light L12, the pattern pitch shown in the equation (5) is the minimum pitch of a transferable pattern. By using both the illumination lights L12 and L13, the center of gravity of the light quantity is not deviated with respect to the optical axis of the projection optical system. Next, the exposure light is incident on the reticle pattern in a specific incident direction and an incident angle, and an imaging pattern is formed on the wafer using the 0th-order diffracted light and the 1st-order diffracted light, thereby increasing the depth of focus. The reason will be explained.

When the wafer coincides with the focal position of the projection optical system, each diffracted light that leaves one point on the reticle and reaches one point on the wafer passes through any part of the projection optical system. All have the same optical path length. For this reason, even when the zero-order diffracted light penetrates substantially the center of the pupil plane of the projection optical system as in the related art, the optical path lengths of the zero-order diffracted light and the other diffracted lights are equal, and the mutual wavefront aberration is zero. However, when the wafer does not match the focal position of the projection optical system (when defocusing occurs), the optical path length of the high-order diffracted light obliquely incident is focused on the 0th-order diffracted light passing near the optical axis. The distance is short in front (away from the projection optical system) and long behind the focal point (approaching to the projection optical system), and the difference depends on the difference in the incident angle. Therefore, the 0th-order, 1st-order,... Diffracted lights mutually form wavefront aberrations, and blur the imaging pattern before and after the focal position. This wavefront aberration ΔW
Is expressed by the following equation: ΔW = 1/2 × (NA) ² Δf Δf: Defocus amount NA: Value representing the distance from the center on the pupil plane by the numerical aperture. For the penetrating zero-order diffracted light (ΔW = 0), the radius r ₁ ([N
In 1st-order diffracted light that passes through the a unit) of A], will have a wavefront aberration of _{ΔW = 1/2 × r 1} 2 Δf, are resolution before and after the focal position, i.e. the depth of focus decreases.

On the other hand, in the case of the projection type exposure apparatus used in the present invention, as shown in FIG. 16, for example, when two light beams are incident on the reticle pattern PP at an incident angle of θ _m = 2０, will pass through the position where the equal distance from the approximate center in order diffracted light D ₀ and the first order on diffraction light Dl transgressions pupil plane ep (both the radius r _2), 0-order diffracted light D ₀ and 1 wavefront aberration of the diffracted light Dl Are equal, ΔW = １ ／ × r ₂
² Δf, the aberration of the first-order diffracted light with respect to the zero-order diffracted light becomes zero, and blurring due to defocus is eliminated within a certain range. Therefore, the depth of focus is larger than that of the conventional device.

As described above, the projection type exposure apparatus used in the present invention can increase the resolution and the depth of focus, especially for a periodic pattern. In the present invention, a plurality of different patterns on the reticle are overlaid and exposed on the same portion on the wafer to form one circuit pattern. Therefore, a pattern formed on a substrate to be exposed, such as a semiconductor wafer, is a composite image of a plurality of reticle patterns. If the plurality of reticle patterns are “0” (substantially light-shielded portion) and “1” (substantially transmissive portion) in accordance with the transmittance of this composite image, the logical sum of these reticle patterns is obtained. Is formed as That is, only the portion where all the reticle patterns are “0” (substantially light-shielded portion) is in a different state from the other portions. If the photosensitive film (photoresist) to be used is a positive type (light-irradiated portion is removed), only the portion where the reticle pattern to be superimposed becomes “0” remains, and the resist is removed in other portions. A so-called isolated line pattern or isolated island pattern is formed.

If the photoresist used is a negative type (light-irradiated portions remain), a so-called isolated space pattern or an isolated hole pattern is formed. At this time, of the plurality of reticle patterns to be superimposed,
At least one is a pattern having a substantially periodic arrangement, and the illumination optical system of the projection type exposure apparatus to be used includes:
As described above, it is assumed that the resolution and the depth of focus have been adjusted to the maximum with respect to the pattern having the substantially periodic arrangement. Of the circuit patterns to be formed by superposition, the most important one is a pattern consisting of a periodic array or a combination of a plurality of patterns consisting of a periodic array. The depth can be increased.

Alternatively, even if the same projection optical system is used, the characteristic that the depth of focus becomes deeper for a pattern having a larger line width is utilized. If the resolution limit is about twice or more than the resolution limit of the system, the depth of focus of the projected image can be made sufficiently large for all the reticle patterns to be superimposed.

[0032]

FIG. 1 shows an embodiment of a projection type exposure apparatus used in the present invention. Illumination light (i-line or g-line) emitted from a mercury lamp 1 is condensed at a second focal point by an elliptical mirror 2. Is done. A shutter 3 for blocking and releasing illumination light is disposed at the second focal point, and is driven by a motor 4. The illumination light that has passed through the shutter 3 is converted into a substantially parallel light beam by a relay lens (collimator lens) 5 and enters a fly-eye lens 6. Each light beam from the exit end secondary light source formed on the respective (group of point light sources images) of each element lenses of the fly's eye lens 6 is condensed by the relay lens 7, is reflected by the mirror M _1, The light is superimposed on the incident portion 8A of the light splitter 8. Therefore, the intensity distribution of the illumination light beam is almost uniform at the position of the incident portion 8A. In FIG. 1, the fly-eye lens 6
Only the luminous flux from one point light source on the optical axis among the point light source images appearing on the exit side of FIG. Now, the light splitter 8
Divides the illumination light from the incident part 8A into a plurality of emission parts 8B and 8C with almost equal intensity. The respective cross-sectional areas of the emitting portions 8B and 8C are assumed to be equal, and the center point thereof is decentered from the optical axis AX by a predetermined amount. The detailed structure of the light splitter 8 will be described later. Note that the emission units 8B and 8C are arranged in a plane 9 conjugate to the exit pupil ep (or entrance pupil) of the projection lens PL, that is, in a Fourier transform plane, in order to perform projection exposure by Koehler illumination.

The divergent light beam emitted from one point on the emission portions 8B and 8C is converted into a substantially parallel light beam by a first relay lens (collimator lens) 10 to form a reticle blind ARB.
Is illuminated with uniform illuminance. For simplicity, FIG. 1 shows only the traveling state of the luminous flux diverging from one point on the emission units 8B and 8C. The reticle blind ARB limits the illumination area on the reticle R by arbitrarily adjusting the four edge positions by the driving unit 11. In the case of FIG. 1, a plurality of parallel light beams (corresponding to the number of the emission portions 8B, 8C,...) That are basically symmetrically inclined with respect to the optical axis AX are applied to the illumination light beam passing through the rectangular opening determined by the reticle blind ARB. Only the light beam is included, and there is no parallel light beam traveling parallel to the optical axis AX. These parallel light beam is converged by the second relay lens 12, it is reflected by the mirror M _2, together incidence angle again enters the main condenser lens 13 irradiates the reticle R is different from a plurality of parallel light beams.
At this time, the pattern surface of the reticle R (the surface facing the projection lens PL) is a reticle blind AR with respect to the combined system of the main condenser lens 13 and the second relay lens 12.
Since it is conjugate with B, a rectangular aperture image of the reticle blind ARB is projected on the reticle R.

The illumination light passing through the transparent portion of the reticle R is projected onto the wafer W via the projection lens PL, and a pattern image of the reticle R is formed on the photoresist layer. Here, the broken line shown in the optical path from the reticle blind ARB to the wafer W in FIG. 1 is a light ray meaning a pupil conjugate. As described above, in the present embodiment, the reticle R is illuminated with at least two beams that are symmetrically inclined, thereby improving the resolving power and the depth of focus even in a normal reticle pattern configuration. The light splitter 8 is newly provided to achieve the function.

Here, the detailed behavior of the illumination light beam will be described with reference to FIG. FIG. 2 shows the light splitter 8 in FIG.
3 schematically shows a system from the two emission units 8B and 8C to the reticle R, and particularly shows how an illumination light beam advances on the emission unit 8B side. First, it is assumed that the center of the emission end of the emission part 8B is eccentric by ΔH from the optical axis AX. The solid lines show how each of the light beams generated from the points P ₁ and P ₂ at both ends of the exit end advances to the reticle R. Dashed lines L ₁ and L ₂ shown in the optical path in FIG. 2 represent one light beam of the light flux from points P ₁ and P ₂ , respectively, and are assumed to be parallel to the optical axis AX in the pupil space. As is clear from FIG. 2, the points P ₁ and P ₂ are imaged as points P ₁ ′ and P ₂ ′ on the plane EP ′ in the pupil space between the second relay lens 12 and the main condenser lens 13. . Therefore, the plane EP ′ is conjugate to the plane 9 and is also a Fourier transform plane. Now, the light beam from the point P ₁ (point P ₁ ′) becomes a substantially parallel light beam on the reticle R and irradiates a certain area, and the light beam from the point P ₂ (point P ₂ ′) also becomes a substantially parallel light beam. To illuminate a certain area. At this time, the incident angles of the two parallel light beams reaching the reticle R are shifted by an angle Δθ. This angle Δ
θ is determined depending on the deviation between the points P ₁ and P _{2 in} the plane 9, that is, the size (or cross-sectional area) of the emission section 8B as an effective light source. If it becomes infinitely small, the angle Δθ also becomes infinitely small. However, in practice, the light source image formed at the exit end of the exit section 8B has a practically large size (however, sufficiently smaller than the pupil diameter), and it is difficult to completely reduce the angle Δθ to zero. It is not necessary to make it completely zero. In addition, the injection unit 8B
2 has a two-dimensional size, the angle Δθ exists in a direction perpendicular to the paper surface in addition to the direction in the paper surface in FIG. 2. Then, as described above with reference to FIG. 16, the center line of the light beam from the emission part 8B is inclined by an angle に 対 し て with respect to the optical axis AX, and in relation to the deviation amount ΔH, ΔH = m · sinψ (where m is a constant). In addition, as an example, the behavior of the illumination light beam from another emission unit 8C symmetrically arranged with respect to the optical axis AX is such that the light beam from the emission unit 8B is turned around the optical axis AX.

Referring again to FIG. 1, the structure of the apparatus will be described. Wafer stage WST moves two-dimensionally
It is placed on top and driven by the motor 20. The coordinate position of wafer stage WST is sequentially monitored by an interferometer 21 using a laser beam for the relative distance between a movable mirror on stage WST and a fixed mirror attached to the lower end of projection lens PL.

On the other hand, the reticle R is also mounted on a reticle stage RST that finely moves in two dimensions, and is driven by a motor (not shown) or the like. The alignment of the reticle R with respect to the optical axis AX is performed by a reticle alignment system 22, and the direct alignment (die-by-die alignment) between the reticle R and the wafer W is performed by TTR (through-the-die).
(Reticle) This is performed by the alignment system 23. Further, the alignment of the wafer W alone is performed by a TTL (through-the-lens) detecting a mark on the wafer W via the projection lens PL.
The lens) alignment system 24 or projection lens P
OFF-AXIS for detecting a mark on the wafer W without passing through the projection lens PL at a position close to the visual field of L
This is performed by an (off-axis) alignment system 25. Alignment signals from the respective alignment systems 22, 23, 24, and 25 are collectively processed by the control device 30, and the wafer stage WST or the reticle stage RS
Used for precise positioning of T. This control device 30
A motor 4 for opening and closing the shutter 3, a motor (not shown) for adjusting the positions of the emission sections 8B and 8C of the light splitter 8, a driving section 11 for the reticle blind ARB, and a motor 20 for driving the wafer stage WST. Control is also performed. FIG.
Although not shown, a photometric element for detecting the amount of illumination (exposure) to the reticle R is provided at an appropriate position in the optical path of the illumination system from the mercury lamp 1 to the main condenser lens 13. Shutter 3 by combining with
Is performed with an appropriate exposure amount.

Next, referring to FIG. 3 and FIG.
Will be described in detail. FIG. 3 shows the light splitter 8 viewed from the side, and FIG. 4 is a view of FIG. 3 viewed from the direction of the optical axis AX. The light beam from the incident part 8A is divided into four by the optical fiber 80, and each of the four
B, 8C, 8D, and 8E. Four injection units 8B,
Each of 8C, 8D, and 8E is a pupil image range 9 on the pupil conjugate plane 9.
A variable length support rods 81B, 81C, 8
1D, supported by 81E. The four support rods 81B to 81E are movable members 82B, 82C, 82D, and 82E that can move in the circumferential direction along the annular guide 83.
Are combined with each other. The four support rods 81B to 81E are
The emission units 8B to 8E are moved in the radial direction with respect to the optical axis AX. These support rods 81B to 81E and movable member 82B
Are driven by a motor. In addition, the incident part 8
The bracket for holding the optical fiber A is configured to be freely rotatable about the optical axis AX,
The stress of the optical fiber 80 caused by the rotation of B to 8E is reduced.

In the apparatus used in this embodiment, four injection units 8B to 8E are provided. However, the number is not limited to four, but may be two (one in principle) or more. I just need. In the present embodiment, the illumination light beam is divided by the optical fiber. However, another member such as a diffraction grating or a polygon prism may be used. Further, another fly-eye lens may be added to the reticle R side from the light splitter 8. At this time, the fly-eye lens may be a single fly-eye lens or may be composed of a plurality of fly-eye lens groups.

Although the projection lens PL is a refraction system here, it may be a reflection system or a catadioptric system. The projection magnification may be arbitrary, but it is desirable to use a reduction system for exposing and transferring a fine pattern. Further, although a mercury lamp is used as a light source, another light source such as a bright line lamp or a laser light source may be used.

Next, an example of the principle of a reticle pattern used in the method according to the present invention and an exposure method will be described with reference to FIG. FIG. 5 shows a typical pattern example for forming an isolated line pattern (when using a positive resist) or an isolated space pattern (when using a negative resist) by the method according to the present invention. First, as shown in FIG. 5A, one pattern PA to be overlap-exposed is, for example, three light-shielding line patterns PA ₁ , PA ₂ ,
PA ₃ in line and space (duty 1: 1)
Keep it. Then, the reticle R is positioned so that the optical axis AX passes through a specific point on the pattern PA (reticle), and the first exposure is performed on the resist layer on the wafer W. In this FIG. 5 (A), the isolated line pattern to be formed on the wafer W originally a light-shielding pattern PA _2.
The apparatus shown in FIG. 1 is extremely effective in projecting a pattern PA having periodicity as shown in FIG. As described above, the apparatus shown in FIG. 1 uses a plurality of emission units 8B to 8B in the illumination optical system in accordance with the periodicity of the pattern on the reticle R.
In order to optimize the position of 8E, even if the pattern PA is miniaturized, the contrast is high (that is, the resolution is high),
There is a feature that the depth of focus becomes deep. If the original isolated line pattern PA ₂ to be formed on the wafer W
Only be provided on the reticle R, be performed projection exposure in the apparatus of FIG. 1, only by the line pattern PA ₂ for ± 1-order diffraction component hardly occurs, it can not be expected sufficiently resolved. That is, the line patterns PA ₁ and PA _{3 on} both sides shown in FIG. 5A act as dummy patterns for providing the pattern PA with periodicity as a whole.

The exposure amount (dose amount) to the resist layer at the time of the first exposure in FIG. 5A is, for example, the minimum exposure amount Eth (or the reduction in film thickness) at which the resist layer is completely removed during development. It is set to be larger than the minimum exposure amount Ec) to be started. FIG. 6A shows the distribution (similar to the intensity distribution) IA of the exposure amount given to the positive resist layer by the first exposure in the sectional direction. FIG. 6 (A)
The vertical axis indicates the exposure amount, and the horizontal axis indicates the position of the pattern PA in the periodic direction.

Here, specific numerical examples will be given. now,
The line width of the line pattern PA ₂ to be formed on the wafer W 0.3 [mu] m (pitch 0.6 .mu.m), 365 nm wavelength λ of the exposure illumination light (i line), and the reduction ratio of the projection lens PL 1/5 Then, from the theoretical expression of the diffraction angle, the incident angle の of the light beam generated from one emission part in the illumination optical system and illuminating the reticle R is expressed by the following expression as described with reference to FIG. sin2ψ = λ / 5 · P = 0.365 × 10 ⁻⁶ /(5×0.6×10 ⁻⁶ ) ≒ 0.122 Accordingly, the incident angle に な る is about 3.5 °.

Next, as shown in FIG. 5B, the other pattern PB to be overlaid and exposed is arranged in place of the pattern PA, and the second exposure is performed at the same position on the wafer W. In this case, the width Db of the pattern PB, is defined greater than the narrow and the line width of the line pattern PA ₂ than distance Da of the both sides of the previous pattern PA line patterns PA ₁ and PA _3. That is, the pattern PB is defined shape as shields only the image of the line pattern PA ₂ formed as a latent image on the wafer W, and all the peripheral transmissive portion, the size. Therefore, in the case of the pattern shape as shown in FIG. 5, the width Db of the pattern PB is set in the range of 0.5P <Db <1.5P from the pitch P of the line pattern PA. As shown in FIG. 6B, the exposure dose distribution given to the resist layer only by this pattern PB is IB
Becomes Here, also at the time of the second exposure, it is assumed that the resist layer is given an exposure amount larger than the minimum exposure amount Eth. When the double exposure is performed on the wafer W in this manner, the distribution IA of FIG. 6A and the distribution I of FIG.
The light quantity distribution IS combined with B is given as shown in FIG. As apparent from FIG. 6C, the image of the synthesized light amount distribution IS (referred to as a synthesized image) is either a periodic pattern PA or a non-periodic (isolated) pattern PB. In this case, only the light shielding portion (line pattern PA ₂ ) is sufficiently dark, and all other portions are brighter than the minimum exposure amount Eth. Therefore, in the case of a positive resist, as shown in FIG. 6D, a portion having a minimum exposure amount (threshold value) Eth or less by development becomes an isolated line pattern Pr in which the remaining film is left. It is clear that this isolated line pattern Pr corresponds to a line pattern PA ₂ in FIG. 5 (A).

In the above embodiment, the periodic pattern PA
Can be increased to about 1.5 to 2 times the resolution of the conventional exposure method.
So that only an isolated pattern is left from the transfer image (latent image) of
Since double exposure is performed with another pattern PB, the resist pattern finally formed on the wafer W becomes an extremely fine isolated pattern. As described above, the width Db of the non-periodic pattern PB is preferably about two to three times the width (pitch / 2) of one line pattern of the periodic pattern PA.
One line pattern (PA ₂ ) of the periodic pattern PA
Is 1/2 to 1 / 1.5 of the conventional resolution,
The width of the non-periodic pattern PB is about twice the resolution limit of the related art, and a sufficient depth of focus can be obtained for the projection of the pattern PB.

In the case of a positive resist, the relationship between the exposure amount and the remaining film thickness is as shown in FIG. 17A. In the case of a negative resist, as shown in FIG. Is completely determined, and the minimum exposure Eth at which the resist completely remains is determined. For this reason,
When the exposure shown in FIGS. 5A and 5B is performed using a negative resist, it is possible to form an isolated space pattern that is 1.5 to 2 times as fine as the conventional one.

FIGS. 7 and 8 show examples of reticle patterns for forming an isolated island pattern (when a positive resist is used) and an isolated hole pattern (when a negative resist is used). FIG. 7A shows a total of nine fine light-shielding patterns PAn in three columns on the left and right and three rows on the upper and lower sides which are smaller than about the resolution limit (0.6 × λ / NA _R ) of the projection optical system. A light shielding pattern PAs finer than the light shielding pattern PAn is arranged between the light shielding patterns PAn. The 7 of the periodic pattern of (A), the resist pattern to be formed on the wafer W actually is the center of the light-shielding pattern PA _2.

On the other hand, FIG. 7B shows the light shielding pattern P
This represents a light-shielding pattern PB that is about 2-2.5 times larger in both the vertical direction and the horizontal direction than An. Here, each of the nine light-shielding patterns PAn is a square, and the space width in the horizontal direction and the vertical direction is equal to the width of the pattern PAn. Further Dax spacing of the light-shielding pattern PAn sandwiching the center of the light-shielding pattern PA ₂ in the left and right, when Day spacing of the light-shielding pattern PAn sandwiching the light-shielding pattern PA ₂ in the vertical, in the lateral direction of the light-shielding pattern PB shown in FIG. 7 (B) The width Dbx is Dbx <Dax, and the vertical width Dby is Dby <Day.

As in the case of FIG. 6, the projected image of the periodic pattern shown in FIG. 7A is also exposed with a higher resolution and a deeper depth of focus than the conventional one because of its periodicity. On the other hand, since the projection image of the pattern PB in FIG. 7B also has a sufficient size, it is also exposed with a large depth of focus. Therefore, an isolated island pattern PS5 formed by a composite image by double exposure (when using a positive resist)
Is formed with a sufficient depth of focus as shown in FIG. This periodic pattern PAn
If, superposition of the pattern PB is a light-shielding pattern PA ₂ in the center of the nine light-shielding pattern, and that multiple exposure by aligning each reticle R and the wafer W so that the center of the pattern PB coincides I do. The reason why the resist remains only in the portion (PA ₂ ) where both the periodic pattern PAn and the non-periodic pattern PB are the light-shielding portions is the same as in the example shown in FIG.

The four corners of the non-periodic pattern PB are arranged so as to coincide with the smaller periodic pattern PAs by superposition. For this reason, when any of a plurality of reticle patterns are superimposed, each of them becomes a light shielding portion,
The periodic pattern PAs is sufficiently smaller than the resolution limit, and does not provide a sufficient light-shielding effect on the projected image on the wafer W. As a result, a resist pattern is not formed at a matching portion between the periodic pattern PAs and the non-periodic pattern PB. The periodic pattern PAs is an auxiliary pattern (corner emphasis) for making the shape of the isolated island pattern PS5 to be formed closer to a square. Therefore, the formation of the isolated island pattern PS5 can be performed without the periodic pattern PAs. It is possible.

FIG. 8 (A) shows line and space patterns PA ₁ , PA ₂ ,
Indicates PA _3, FIG. 8 (B) is a line-and-space pattern PB _1, PB ₂ with periodicity in the vertical direction in the drawing,
Shows the PB _3. Both shaded portions of these two patterns represent light-shielding portions. These two periodic patterns PA,
Each of the PBs is a periodic pattern, so that the high resolution and the large depth of focus, which are features of the present invention, can be obtained in exposure of any pattern. A composite image (resist image) obtained by superposing and exposing the two patterns PA and PB is an isolated island pattern P shown in FIG.
It becomes S6. Here, assuming that the interval between the left and right line patterns PA ₁ and PA ₃ of the periodic pattern PA is Dax, and the lengths of the three line patterns PA ₁ , PA ₂ and PA ₃ are both Day, the other periodic pattern PA The distance Dby between the line patterns PB ₁ and PB ₃ above and below PB is Dby>
Day, and three line patterns PB ₁ , PB
Length Dbx of _2, PB ₃ is set to Dbx <Dax. Then, the resist pattern to be formed on the wafer W is a square portion which can be by the intersection of the line pattern PA ₂ and PB _2. In this overlay exposure,
Multiple exposure is performed such that the center of the periodic pattern PA and the center of the periodic pattern PB coincide at the same point on the wafer W. In addition, only three images are required as a resist image.
Line pattern P at the center of book light-shielding line pattern
Since only the intersection of A ₂ and PB ₂ , the length (long side dimension) of each line and space should be more than three times the width (short side dimension) so that the light-shielding sections do not overlap in other areas. It should be short. Alternatively, the length of each line-and-space pattern is made longer, and for the unnecessary overlapping of the light-shielding portions, a pattern equivalent to the pattern PB of FIG. May be removed (unnecessary light shielding portions are exposed by this). This will be described in detail later as an example.

The example of forming an isolated island pattern has been described above with reference to FIGS. 7 and 8, but it is assumed that a positive resist is used. If a negative resist is used, an isolated hole pattern can be formed by the same method. In addition, in FIGS. 6, 7 and 8 described above, three line patterns or three rows and three columns of dot patterns are given as examples of the periodic pattern.
The number of lines or dots constituting the periodic pattern is not limited to this, and may be any number such as 5 or 7 or 5 rows and 5 columns. Further, the line width ratio (duty) between the light-transmitting portion and the light-shielding portion of the periodic pattern is not limited to 1: 1 and may be arbitrary. However, when the line width of the light-shielding portion was increased by about 20% with respect to the line width of the light-transmitting portion, it was found that better results could be obtained experimentally.

The periodicity of the periodic pattern does not need to be so strict. For example, a pattern forming a periodic pattern, that is, two lines at both ends in the case of three lines may be thinner than the pattern at the center. As described above, the embodiments of various patterns to be subjected to overlay exposure (multiple exposure) according to the present invention have been described. However, the embodiments are applied to the actual positional relationship of each reticle pattern on the reticle and the overlay method. This will be described with reference to FIGS. 9 and 10. FIG. 9 is a pattern layout diagram of a reticle R in which both the pattern PA and the pattern PB shown in FIGS. 5, 7, and 8 are drawn together. The reticle R is used for forming a contact hole during an IC manufacturing process. In FIG. 9, the pattern formation region of the reticle R is surrounded by a light-shielding band SB, and a mark RM for reticle alignment is provided outside thereof.
₁ and RM ₂ are formed. In the pattern area, a pattern PA represented by black square dots and a pattern PB represented by white square dots are regularly arranged in the X and Y directions. The periphery of these patterns PA and PB are all light transmitting portions. In this reticle, it is assumed that an isolated hole (contact hole) pattern is formed by performing overlay exposure of two patterns PA and PB on a negative resist. In a memory IC, generally, unit memory cells are regularly (periodically) arranged to form a memory cell group. Therefore, contact holes corresponding to each memory cell are also periodically arranged. Also in FIG. 9, pattern PA and pattern PB
Are arranged such that the pitch in the X direction is Px and the pitch in the Y direction is Py, and the pattern PB is
It is formed at a position (Px / 2, Py / 2) apart from the pattern PA.

Using such a reticle R, first, a first exposure is performed on the wafer W at an appropriate exposure amount Eth or more. Therefore, each pattern P
A light amount corresponding to A and PB is exposed. Subsequently, the relative position of the reticle R and the wafer W in the X and Y directions is moved by (Px / 2, Py / 2) (dimension on the reticle) by the wafer stage WST or the reticle stage RST, and then the appropriate exposure is performed. The second exposure is performed with the amount Eth or more. In the case of FIG. 9, it is moved to the upper right. This movement is performed by the motor 2 for driving the wafer stage WST in the case of the apparatus shown in FIG.
0, the interferometer 21, and the controller 30.

As described above, the pattern PA and the pattern P
Since the distance to B was (Px / 2, Py / 2),
By the first and second exposures, the pattern PA and the pattern PB are overlaid and exposed on the wafer W. Note that there are four relative movement directions in which the pattern PA and the pattern PB are precisely overlapped on the wafer W, as is apparent from the reticle pattern arrangement in FIG. That is, the reticle R or the wafer W can be moved in any one of diagonally upper right, diagonally upper left, diagonally lower right, and diagonally lower left in the plane of FIG. In which direction the relative movement is performed can be set arbitrarily. In the case of the pattern arrangement shown in FIG. 9, of the pattern PA (black square) located at the outermost periphery in the pattern formation region, the row aligned with one side in the Y direction and X
Each pattern PA existing in a row aligned with one side in the direction is not exposed twice with the pattern PB, and remains as a film. Since the remaining pattern is incomplete as a contact hole pattern, it is preferable that the remaining pattern is not formed as a resist image. Therefore, it is preferable to provide a margin (transparent portion) having a width of about Px or Py between the arrangement of the outermost patterns PA in FIG. 9 and the light-shielding band SB. By doing so, the margin is double-exposed to the latent image of the outermost pattern PA, and the formation of an unnecessary remaining pattern can be prevented.

As described above, when the negative resist is used, the resist pattern P shown in FIG.
Contact holes such as S5 or the resist pattern PS6 in FIG. 8C have a pitch Px / 2 in the X and Y directions.
M, Py / 2M (where 1 / M is the projection magnification). Although such a contact hole pattern has a periodicity, since each hole pattern is discretely arranged, it can be considered as an isolated pattern, and the exposure apparatus shown in FIG. Even if a reticle pattern for forming a hole is set and exposed, sufficient resolution cannot be obtained.

FIG. 10 shows a state of double exposure when the reticle pattern of FIG. 9 is composed of the pattern PA and the pattern PB shown in FIG. Pattern PA having periodicity in X direction and pattern P having periodicity in Y direction
By the double exposure with B, a resist pattern PS6 serving as a contact hole is formed. In the figure, patterns PA and PB indicated by broken lines are obtained by the first exposure, and patterns PA and PB indicated by solid lines are obtained by the second exposure.

FIG. 11 is an embodiment showing another positional relationship of a reticle pattern to be subjected to multiple exposure. In this embodiment,
It is assumed that the reticle R and the wafer W are shifted twice, and the overlap exposure is performed three times. As shown in FIG. 8 or FIG. 10, the periodic pattern PA in which diffracted light is likely to be generated,
When PB is used, each pattern P
The number of line and space repetitions of A and PB is preferably as large as possible. So three patterns PA, PB, P
C is formed on the same reticle. The pattern PA is formed in the shape of a diffraction grating having a periodicity in the X direction and a duty of about 1: 1 and has five light-shielding line patterns (shaded portions). The pattern PB is formed in the form of a diffraction grating having a periodicity in the Y direction and a duty of about 1: 1 and has five light-shielding line patterns (hatched portions). Here, the center of the pattern PA and the center of the pattern PB are ΔY in the Y direction.
And the center of the third pattern PC is the pattern P
A square light-shielding portion (hatched portion) formed in the X direction by a distance ΔX from the center of B. The area AB around the pattern PC is substantially equal to the shape and area when the two patterns PA and PB are overlapped. The periphery of each of the patterns PA, PB, and PC is a transparent portion. In forming the contact hole pattern, a square overlapping portion is used by superimposing the light blocking line pattern at the center of the pattern PA and the light blocking line pattern at the center of the pattern PB. Pattern PC is composed of patterns PA and PB
This is for erasing unnecessary overlapping portions (latent images) caused by the superposition of the images.

After performing a first exposure on a wafer using such a reticle, the first exposure position is
The second exposure is performed by shifting the relative positions of the reticle R and the wafer W in the respective in-plane directions by (0, + ΔY) on the reticle. Then, from the first exposure position, the relative positions of the reticle R and the wafer W in the respective in-plane directions are set on the reticle by (−ΔX,
The third exposure is performed by shifting by −ΔY).

FIG. 12 shows the state of latent images PA ′ and PB ′ formed on the negative resist when the pattern PA and the pattern PB in FIG. 11 are overlaid and exposed. In FIG. 12, broken lines represent the edges of the latent image of each pattern, and a plurality of isolated areas painted black represent unexposed portions that were not exposed at all by the two overlapping exposures.
Of the plurality of isolated areas, the central square pattern P
S8 remains unexposed even after the third overlapping exposure with the pattern PC, and other unexposed isolated areas located around the pattern PS8 are formed by the transparent portion (area AB) around the pattern PC. Fully exposed. Therefore, only the square pattern PS8 is finally formed on the wafer W. In the case of a negative resist, a portion of the pattern PS8 is removed by development, and the peripheral resist is almost completely left, so that a contact hole pattern is formed in the same manner as described with reference to FIG. .

FIG. 13 shows an example in which a plurality of one set of pattern arrangements shown in FIG. 11 are regularly formed on the reticle R to form a contact hole pattern.
In FIG. 13, the pattern PA in FIG. 11 is represented by a circle, the pattern PB is represented by a square, and the pattern PC is represented by a triangle. Using such a reticle R, similarly, the relative position with respect to the wafer W is shifted twice, and when the overlay exposure is performed three times, the pitch of the resist of the wafer W in the X direction becomes Δ
A contact hole pattern group having a pitch of ΔY in the X and Y directions is formed.

In FIG. 11 or FIG. 13, the pattern formed in the reticle is three, PA, PB, and PC, but the number is not limited to this, and two patterns are used.
Four or more patterns may be formed, and two or four overlapping exposures may be performed. Also, the patterns PA, P
A pattern group such as B and PC may be regarded as one block, and a plurality of blocks may exist.

As shown in FIGS. 5, 7, and 11, when only an isolated hole pattern is formed by overlapping exposure, the first exposure, the second exposure, or the third exposure is used. The irradiation light amount (exposure amount) may be the same twice or three times, and it is rather preferable that the irradiation light amount differs for each exposure. For example, when exposing a periodic pattern (PA, PB), the irradiation light amount may be larger than when exposing a non-periodic pattern (PC). In the exposure apparatus shown in FIG. 1, the control of the irradiation amount is performed by the control device 30, the shutter 3, and an irradiation amount meter (not shown). Control device 3
0 recognizes that the currently performed exposure is the upper n-th exposure, obtains the irradiation light amount in accordance with the output signal from the above-described dosimeter, and stops the exposure when it reaches the target value. Is sent to the drive motor 4 of the shutter 3. As shown in FIGS. 9, 10, and 13, when a plurality of pairs of patterns PA and PB (or PC) are regularly provided on the same reticle, the first exposure and the second exposure are performed. Alternatively, it is desirable that the irradiation light amount in the third exposure be the same.

When the relative position between the reticle and the wafer is to be moved by the method described in each of the above embodiments, in the apparatus shown in FIG. Moved during the second exposure, or between the second and third exposures. Or,
As another method, the stage RST holding the reticle R may move, or both stages may move.
However, most of the actual projection type exposure apparatuses already have a wafer stage that moves two-dimensionally, and perform step-and-repeat or step-and-scan exposure by using the wafer stage. The method of moving based on the measured coordinate values by 21 can be realized most easily even in a conventional apparatus.

FIG. 14 is a view showing almost the entire surface of a reticle used in the exposure method according to the present invention. The reticle pattern area (pattern formation) is inscribed in the effective area circle 91 of the projection lens PL shown in FIG. 14, that is, in an area in which various performances such as resolution, distortion, and uniformity of illuminance of the projection optical system are well guaranteed. Area) 92 is present. In the conventional exposure method, it is possible to draw a circuit pattern on the entire area of the reticle pattern area 92 and to expose and transfer the circuit pattern onto the wafer W. However, in the present invention, as shown in FIGS. 9 and 10, for example, the relative positional relationship between the reticle and the wafer differs between the first exposure and the second exposure. In FIG. 14, the area used for the first exposure is within a broken line 93, and the area used for the second exposure is within a two-dot chain line 94.

Therefore, the area (shaded area) used for both the first and second exposures becomes an effective reticle pattern area when the present invention is used, which is smaller than the conventional one. However, for example, in a current step-and-repeat type projection exposure apparatus, the size (X ₀ , Y
₀ ) is around 100 mm (dimension on the reticle), and the relative displacement between the first exposure and the second exposure (Px / 2, Py / 2) shown in FIGS. Is approximately equal to the memory cell size,
It is around 0 μm (ΔX, ΔY in FIG. 14).

Therefore, the conventional reticle effective area 10
In the present invention, (100,000-2 × 10) μm × (10,000 μm × 100,000 μm).
000-2 × 10) μm. The ratio of this value is
1: 0.9996, and thus the reticle pattern effective area reduced by the present invention is only about 0.04% of the area in the conventional case.

FIG. 14 shows a step-and-repeat type projection exposure apparatus in which the effective area of the projection optical system is circular, but other projection type exposure apparatuses, for example, a step-and-scan type exposure apparatus. The same applies to an exposure apparatus, and the area of the reticle pattern area that is reduced is still very small. In each of the above embodiments, when the apparatus shown in FIG. 1 is used, as one of the methods for shifting the relative position between the reticle R and the wafer W by (ΔX, ΔY), the mark detection center in each of the alignment systems 22 to 25 is used. (Tilt of parallel flat glass) or electrically offset the reticle R with respect to the offset mark detection center.
The reticle stage RST or the wafer stage WST may be servo-controlled so as to drive the mark or the mark on the wafer W. Furthermore, in the description so far, one of the reticle R and the wafer W is shifted by (ΔX, ΔY), but both the reticle R and the wafer W may be shifted in the opposite direction or the same direction. . In an apparatus that performs mirror image projection using a unit-magnification projection optical system, it does not make sense to shift the reticle and the wafer by the same distance in the opposite direction with respect to the optical axis. A similar shift is possible by moving the wafer. In the case of a reduction projection optical system (mirror image projection), when the projection magnification is 1 / M, it is meaningless to shift the wafer movement amount in the reverse direction by 1 / M with respect to the reticle movement amount. In the case of a shift method (including movement in the same direction) using other movement amount ratios, the same position shift is possible. In the case of reduced projection, the reticle R
Even when the projection optical system and the wafer W are kept stationary on the apparatus and only the projection optical system is moved in parallel in a direction perpendicular to the optical axis AX, the relative position between the projection image and the wafer can be similarly shifted.

[0069]

As described above, according to the present invention, one periodic pattern and another pattern provided at different positions in one master (mask) are overlaid and exposed, and a special pattern is formed. By using a projection type exposure apparatus having an illumination optical system, it becomes possible to expose and transfer a fine pattern, particularly a fine isolated pattern, which has conventionally been difficult to realize.

Further, according to the present invention, since a plurality of patterns to be subjected to multiple exposure are formed on one mask instead of being formed on separate masks, the throughput is correspondingly high. At the same time, the manufacturing cost of the mask is reduced. In addition, since a plurality of patterns to be superimposed are located at close positions in the same mask, the amount of misalignment due to mask manufacturing errors can be extremely reduced. Further, since there is a pattern to be superimposed on the same mask, no superposition error due to the alignment error occurs.

The mask used in the present invention is a normal mask having only information on transmittance, and has an advantage that it is not necessary to provide a phase shifter. In the above embodiment, the projection type exposure apparatus used is one in which the light quantity distribution of the illuminating light beam is concentrated in a local area having a center at a position decentered from the optical axis on the pupil plane in the illumination optical system as described above. However, as a modification, an exposure apparatus having an annular light quantity distribution on the pupil plane (or a Fourier transform plane in the illumination optical system) can be used. in this case,
The outer diameter of the annular light quantity distribution is preferably about 0.6 to 0.8 corresponding to the σ value, and the inner diameter is preferably about 0.3 to 0.6 corresponding to the σ value.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a projection exposure apparatus used in the present invention;

2 is an optical path diagram schematically showing an illumination system of the apparatus of FIG.

FIG. 3 is a side view showing a configuration of a light splitter;

FIG. 4 is a front view showing the configuration of a light splitter;

FIG. 5 is a perspective view illustrating the principle and operation of an exposure method according to the present invention;

FIG. 6 is a view for explaining a light amount distribution at the time of pattern exposure obtained by the exposure method of FIG. 5;

FIG. 7 is a diagram illustrating a combination of reticle patterns according to another embodiment of the present invention;

FIG. 8 is a diagram illustrating a combination of reticle patterns according to another embodiment of the present invention;

FIG. 9 is a pattern layout diagram of a reticle provided with the reticle pattern shown in FIG. 8;

FIG. 10 is a view showing a mode of multiple exposure when the reticle of FIG. 9 is used;

FIG. 11 is a diagram showing an arrangement of a reticle pattern according to another embodiment of the present invention;

FIG. 12 is a diagram showing a state when the reticle pattern of FIG. 11 is subjected to multiple exposure;

FIG. 13 is a view showing an example in which the reticle pattern of FIG. 11 is arranged on an actual reticle;

FIG. 14 is a view for explaining a pattern effective area on a reticle using the present invention;

FIG. 15 is a diagram illustrating a configuration and an exposure state of a conventional projection exposure apparatus;

FIG. 16 is a view for explaining the principle of an exposure apparatus used in the present invention,

FIG. 17 is a graph showing the relationship between the amount of exposure to a resist layer and the remaining film thickness.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 3 ... Shutter, 8 ... Light splitter, 8B-8E
... Ejection unit, 9 ... Fourier transform surface, 20 ... Motor, 21 ...
Interferometer, 30: control device, R: reticle, W: wafer,
PL: Projection optical system, RST: Reticle stage, WST
... wafer stage, PA ... first periodic pattern, PB
... second pattern, PC ... third pattern

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7/20

Claims (50)

(57) [Claims] 1. A irradiates illumination light to the mask through an illumination optical system, a method of exposing a photosensitive substrate with the illumination light via the projection optical system, the plurality of different patterns with each other at least one periodic pattern The periodic pattern on the photosensitive substrate.
So that another pattern with a different shape overlaps a part of the
To, as well as multiple exposure the photosensitive substrate by irradiating each of the plurality of patterns the illumination light, during the transfer of the periodic pattern, substantially the Fourier transform with respect to the pattern surface of the mask in the illuminating optical system An exposure method characterized in that the light amount distribution of the illumination light on a predetermined surface, which satisfies the following relationship, is increased outside the central portion. 2. The exposure method according to claim 1, wherein said plurality of patterns have different shapes, and a specific portion where said plurality of patterns overlap is a fine pattern to be formed on said photosensitive substrate. 3. The exposure method according to claim 2, wherein the plurality of patterns have different shapes or sizes from the fine patterns. 4. The exposure method according to claim 2, wherein the fine pattern is an isolated pattern. 5. The periodic pattern according to claim 1, wherein a dummy pattern is formed near a fine pattern to be formed on the photosensitive substrate. Exposure method. 6. The exposure method according to claim 5, wherein the dummy pattern is formed at both ends of the fine pattern. 7. The fine pattern is an isolated pattern,
The exposure method according to claim 5, wherein the dummy pattern has substantially the same shape and size as the fine pattern. 8. The exposure method according to claim 5, wherein a distance between the dummy pattern and the fine pattern is substantially equal to a size of the fine pattern. 9. The periodic pattern according to claim 1, wherein a line width of the light shielding portion is larger than a line width of the transmission portion.
The exposure method according to any one of the above. 10. The periodic pattern includes a fine pattern to be formed on the photosensitive substrate as one element pattern, one of the plurality of patterns being larger than the fine pattern, The exposure method according to any one of claims 1 to 4, wherein the pattern is overlapped with the fine pattern in the periodic pattern. 11. The size of the one pattern in the arrangement direction of the periodic pattern is about two to three times the size of the one element pattern constituting the periodic pattern in the arrangement direction. The exposure method according to claim 10, wherein 12. The fine pattern is sandwiched between the two element patterns in the periodic pattern, and the one pattern has a size in the arrangement direction of the periodic pattern that is equal to the two element patterns. 11. The exposure method according to claim 10, wherein the distance is smaller than the distance. 13. The exposure method according to claim 1, wherein the periodic pattern includes the fine pattern in which an auxiliary pattern is formed close to the periodic pattern. 14. The exposure method according to claim 1, wherein the plurality of patterns include two periodic patterns having different periods or directions from each other. 15. The exposure method according to claim 14, wherein the two periodic patterns are overlapped on the photosensitive substrate so that their arrangement directions cross each other. 16. The exposure method according to claim 15, wherein the arrangement directions of the two periodic patterns are substantially orthogonal. 17. The device according to claim 15, wherein each of the two periodic patterns is formed by partially overlapping element patterns sandwiched between two element patterns.
7. The exposure method according to 6. 18. One of said two periodic patterns is:
The size of the two periodic patterns in the other array direction is the size of the two element patterns arranged with the element pattern overlapped with the one periodic pattern in the other periodic pattern. 18. The exposure method according to claim 17, wherein the distance is smaller than the interval. 19. The exposure method according to claim 2, wherein the illumination light is applied to an unexposed portion where the plurality of patterns overlap except for the specific portion which becomes the fine pattern. 20. When irradiating the unexposed portion with the illumination light, one of the plurality of patterns is superimposed on the specific portion to prevent the illumination light from reaching the specific portion. The exposure method according to claim 19, wherein 21. The exposure method according to claim 19, wherein the fine pattern is formed by partially overlapping two periodic patterns having different periods or directions. 22. Illumination light distributed outside the central portion on the predetermined surface illuminates the mask while being inclined with respect to the optical axis of the illumination optical system by an angle corresponding to the fineness of the periodic pattern. The exposure method according to any one of claims 1 to 21, wherein the exposure is performed. 23. The 0th-order diffracted light and other diffracted light generated from the periodic pattern by the irradiation of the illumination light have their optical axes on a Fourier transform plane with respect to the pattern plane of the mask in the projection optical system. 23. The exposure method according to claim 22, wherein the light passes through a position that is substantially equidistant from. 24. The exposure method according to claim 22, wherein illumination light traveling substantially along the optical axis of the illumination optical system is prevented from entering the mask. 25. The illumination light according to claim 1, wherein a light amount distribution on the predetermined surface is enhanced in a local region decentered from an optical axis of the illumination optical system. Exposure method according to 1. 26. The exposure method according to claim 25, wherein the light quantity distribution is increased in each of a plurality of local regions having substantially equal distances from the optical axis of the illumination optical system. 27. A zero-order diffracted light and another diffracted light generated from the periodic pattern by irradiation of a light flux emitted from the local area are formed on a Fourier transform plane with respect to the mask pattern in the projection optical system. 26. The position of the local area on the predetermined surface is adjusted so as to pass through a position substantially equidistant from the optical axis.
Or the exposure method according to 26. 28. The exposure method according to claim 23, wherein the other diffracted light is one of ± first-order diffracted lights. 29. A first diffracted light generated from the periodic pattern by irradiation of a first light beam emitted from a first local area of the plurality of local areas, and a second local area different from the first local area. The second diffracted light having a different order from the first diffracted light, which is generated from the periodic pattern by the irradiation of the second light flux emitted from the region, passes through the first optical path in the projection optical system and is exposed to the light. The exposure method according to claim 26, wherein the light is irradiated onto the substrate. 30. A third diffracted light having an order different from that of the first diffracted light, which is generated from the periodic pattern by the irradiation of the first light flux, and a third diffracted light generated by the irradiation of the second light flux from the periodic pattern. The fourth diffracted light having a different order from the second diffracted light is irradiated on the photosensitive substrate through a second optical path different from the first optical path in the projection optical system. Item 30. An exposure method according to Item 29. 31. The apparatus according to claim 30, wherein the first and second optical paths have substantially the same distance from the optical axis on a Fourier transform plane with respect to the mask pattern in the projection optical system. Exposure method. 32. The exposure method according to claim 30, wherein the first and fourth diffracted lights are zero-order diffracted lights. 33. The exposure method according to claim 32, wherein the second and third diffracted lights are first-order diffracted lights. 34. The exposure method according to claim 25, wherein the light quantity distribution is increased in each of a pair of local regions arranged along the direction in which the periodic patterns are arranged. 35. The exposure method according to claim 1, wherein a light amount distribution of the illumination light on the predetermined surface is increased in a substantially annular specific region. 36. An outer diameter of the specific area is determined so that a ratio of a numerical aperture of illumination light emitted from the specific area to a numerical aperture of the projection optical system is about 0.6 to 0.8. The exposure method according to claim 35, wherein: 37. An inner diameter of the specific area is determined so that a ratio of a numerical aperture of illumination light emitted from the specific area to a numerical aperture of the projection optical system is about 0.3 to 0.6. The exposure method according to claim 35 or 36, characterized in that: 38. The plurality of patterns are formed on the same mask, and the relative positional relationship between the mask and the photosensitive substrate is adjusted so that the plurality of patterns are overlapped on the photosensitive substrate during the multiple exposure. The exposure method according to claim 1, wherein: 39. A method of irradiating a mask with illumination light through an illumination optical system and exposing a photosensitive substrate with the illumination light through a projection optical system, wherein the fine pattern is formed on the photosensitive substrate. A first pattern having a dummy pattern provided in the vicinity of the pattern is irradiated with the illumination light to expose the photosensitive substrate, and the illumination light is applied to a predetermined area where a transfer image of the dummy pattern is formed on the photosensitive substrate. An exposure method characterized by irradiating. 40. When irradiating the predetermined area with the illumination light,
40. The exposure method according to claim 39, wherein a second pattern is superimposed on the fine pattern in order to prevent irradiation of the illumination light on a region where the fine pattern is formed on the photosensitive substrate. 41. The illumination light applied to the first pattern has a light amount distribution on a predetermined surface which is substantially Fourier-transformed with respect to a pattern surface of the mask in the illumination optical system. 41. The exposure method according to claim 39, wherein the temperature is also increased outside of the area. 42. The exposure method according to claim 41, wherein the light quantity distribution is enhanced in an annular area on the predetermined surface or in a local area decentered from the optical axis of the illumination optical system. 43. The exposure method according to claim 35, wherein the fine pattern is an isolated pattern. 44. A mask used for multiple exposure of the photosensitive substrate for forming a fine pattern on the photosensitive substrate via a projection optical system, the mask comprising a periodic pattern including the fine pattern in a part thereof. A first pattern and a second pattern superposed on a part of the first pattern are formed on the photosensitive substrate, and the first pattern is formed by multiple exposure of the photosensitive substrate using the first and second patterns. A mask, wherein the second pattern is superimposed on a part of the pattern. 45. The method according to claim 45, wherein the second pattern is overlapped so as to include one of a plurality of element patterns constituting the first pattern, and the one element pattern is formed as the fine pattern. 45. The mask according to claim 44. 46. The device according to claim 45, wherein each of the plurality of element patterns is the same as the fine pattern.
The mask according to 1. 47. The apparatus according to claim 47, wherein the second pattern is overlapped with one of a plurality of element patterns constituting the first pattern so as to intersect, and the intersection is formed as the fine pattern. 44. The mask according to 44. 48. The mask according to claim 47, wherein said second pattern is a periodic pattern, and one element pattern other than both ends overlaps a part of said first pattern. 49. A mask used for multiple exposure of the photosensitive substrate for forming a fine pattern on the photosensitive substrate via a projection optical system, wherein a mask provided with a dummy pattern near the fine pattern is provided. 1
A mask, wherein a pattern and a second pattern having a shape different from the first pattern are formed, and the second pattern is superimposed on the fine pattern on the photosensitive substrate. 50. The mask according to claim 49, wherein said dummy pattern is formed at both ends of said fine pattern.