JPH05267120A - Projection exposure device - Google Patents

Abstract

PURPOSE:To provide a projection exposure device, which can resolve even a fine periodic pattern having high space frequency excellently and in which the load of an imagery optical system is also reduced. CONSTITUTION:A second photo-mask 2 is lit up by an illumination optical system arranged to an upper section, and a pattern formed to the second photo- mask 2 is imaged onto a first photo-mask 1 through a second imagery optical system 14, and further imaged onto a wafer 5 through a first imagery optical system. A pattern shaped to the first photo-mask 1 is imaged onto the wafer 5 through the first imagery optical system 3. Accordingly, the patterns of the first photo-mask 1 and the second photo-mask 2 are synthesized, and a pattern having frequency higher than the space frequency of the first and second photo- masks 1, 2 is formed onto the wafer 5.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A conventional projection exposure apparatus of this type has a structure as shown in FIG. In the figure, a photomask 10
1 is held horizontally so as to be substantially orthogonal to the optical axis of an illumination optical system (not shown), and is transmitted and illuminated by exposure light having a predetermined wavelength emitted from the illumination optical system. The photomask 101 which has been generally used conventionally has a structure in which a light-shielding pattern made of metal such as chrome is formed on a transparent substrate, and when it is transmitted and illuminated, diffracted light corresponding to the pattern shape is generated. .. These diffracted lights are collected on the image plane again by the image forming optical system 103, whereby the pattern image of the photomask 101 is transferred onto the surface of the wafer 105 held so as to match the image plane.

[0003]

In the conventional projection exposure apparatus as described above, the pattern on the photomask is basically similar to the pattern to be transferred onto the wafer, that is, the imaging optical system. Both must be the same except for the image forming magnification and the deformation due to the diffraction effect of light of the image forming optical system. In the phase shift masks that have been researched and developed in recent years (those in which a phase shift member that changes the phase of light is added to a predetermined portion of the transparent portion), an auxiliary pattern that is not transferred onto the wafer is placed on the photomask. Alternatively, a technique has been proposed in which a pattern is formed only by the phase shift member and the edge portion of the phase shift member is transferred onto the wafer as a dark line, but in the conventional general projection exposure technique, the pattern on the wafer is The patterns on the photomask are basically similar, and there are the following problems associated with this.

First, when a periodic pattern and an isolated pattern are present in the same photomask, the resolution conditions of both must be satisfied at the same time, so that the pattern size, exposure amount, etc. It was a big constraint on various conditions. In general, even if the dimensions of the pattern itself are the same, the resolution of the isolated pattern is better than that of the periodic pattern. This is because the periodic pattern generates diffracted light with discrete diffraction angles, while the isolated pattern generates continuous diffracted light. Therefore, the pattern rules (rules such as the minimum pattern width) had to be adjusted to the periodic pattern. Further, since the optimum exposure amount differs between the periodic pattern and the isolated pattern, when both coexist, the margin regarding the exposure amount becomes small.

Secondly, in the case of a periodic pattern, the spatial frequency becomes higher as the pattern size becomes smaller, so that there is a problem that projection exposure cannot be performed for a periodic pattern having a frequency above a limit frequency determined from optical theory.

The present invention has been made in view of the above circumstances, and provides a projection exposure apparatus capable of satisfactorily resolving a fine periodic pattern having a high spatial frequency and reducing the load on the imaging optical system. The purpose is.

[0007]

A projection exposure apparatus according to claim 1 is a projection exposure apparatus equipped with a projection optical system for projecting a pattern on a photomask onto a photosensitive substrate. A first image forming optical system as the projection optical system for forming an image of the pattern of the first photomask on the photosensitive substrate, and an image forming the pattern of the second photomask on the first photomask. A second imaging optical system, wherein the first and second imaging optical systems include the first and second imaging optical systems.
The numerical aperture on the substrate side by the combination system of the imaging optical systems and the numerical aperture on the substrate side of the first imaging optical system are configured to be equal to each other, and the numerical aperture is set via the first imaging optical system. The first photomask pattern is projected onto the photosensitive substrate, and the second photomask pattern is transferred via the second imaging optical system, the first photomask, and the first imaging optical system. The image is projected on the photosensitive substrate.

According to a second aspect of the projection exposure apparatus, the maximum spatial frequency of the pattern image formed on the photosensitive substrate by the first and second imaging optical systems is F0, and the pattern of the first photomask is When the highest spatial frequency is F1 and the highest spatial frequency of the pattern of the second photomask is F2, F1 ≦ F0, F2 ≦ F0 (where F1 and F2 are converted to the spatial frequency on the photosensitive substrate). Is satisfied.

The first and second photomasks used in the projection exposure apparatus according to the third aspect have a polarizing member that converts the polarization state of light into a predetermined state.

[0010]

In the present invention, the pattern conventionally formed on one photomask is decomposed into a plurality of photomasks so that the spatial frequency included in the pattern becomes low, and the pattern of the decomposed photomasks is decomposed. Is simultaneously projected and exposed.

In order to carry out the present invention using a general photomask conventionally used (a photomask consisting of a transparent portion and a light-shielding portion), the transmittance distribution of a plurality of photomasks projected and exposed at one time The pattern may be decomposed so that the product coincides with the light intensity distribution to be exposed on the photosensitive substrate (wafer). For the sake of simplicity, a plurality of photomasks will be described as two, and the transmittance is 1 or 0 depending on the location in the conventional photomask. When two photomasks are superimposed and projected, the result is as shown in Table 1.

[0012]

Further, in the present invention, a photomask (hereinafter referred to as a polarization photomask) in which a polarizing member for converting a polarization state of light into a predetermined state is added to a transparent portion is used,
It is also possible to reduce the spatial frequency of the pattern formed on the mask.

This polarization photomask was previously proposed by the present inventor (Japanese Patent Application No. 3-167381,
Japanese Patent Application No. 3-167383) will be briefly described here.
Conventional photomasks project and expose a desired pattern using information on the amplitude or phase of light, but polarization photomasks use the third information, which is the polarization state, to increase the resolution. is there. Specifically, the photomask proposed in Japanese Patent Application No. 3-167381 has a transparent member provided with a polarizing member that transmits only the light whose electric vector oscillates in a direction parallel to the sides of the pattern. Thus, it is possible to align the vibration directions of the diffracted light generated in the pattern, enhance the interference effect, and improve the image contrast. Further, the photomask proposed in Japanese Patent Application No. 3-167383 has polarization states that are mutually orthogonal to the transparent portion (1. two linearly polarized light whose vibration directions are orthogonal to each other; 2. right-handed circularly polarized light and leftly polarized light). Rotating circularly polarized light 3. Elliptical polarized light whose major axes are orthogonal to each other and whose rotational directions are opposite.
By providing at least two kinds of polarizing members for converting into, the basic period of the pattern can be increased (spatial frequency is lowered) and the resolution can be improved.

Now, in the case of superposed projection using a polarized photomask, the superposed results of the respective photomasks are as shown in Table 2. In Table 2, the notations of P and S are used to indicate the polarization state, but this is not limited to P and S in linearly polarized light, and they are in the orthogonal state.
It shows two polarization states. In addition, in the result of superposition, the light portion was marked as 1 and the dark portion was marked as 0.

[0016]

As shown in Tables 1 and 2, in the case of a conventional photomask composed of a transparent portion and a light shielding portion, two photomasks are combined by AND product in logic, and a polarization photomask In this case, two photomasks are combined by NAND product.

In the present invention, as described above, the pattern conventionally formed on one photomask is decomposed into a plurality of photomasks, and the spatial frequency of each photomask is lowered. Then, an imaging optical system is provided for each photomask and a plurality of photomasks are superimposed and projected to form a target pattern on the photosensitive substrate. The decrease in the spatial frequency of each photomask means that the diffraction angle of the diffracted light becomes smaller accordingly, and fine patterns can be resolved even in an imaging optical system whose numerical aperture is not so large. If an imaging optical system with the same numerical aperture is used,
It is possible to resolve a pattern having a higher frequency than before, that is, a finer pattern.

[0019]

1 is a schematic diagram of a projection exposure apparatus according to an embodiment of the present invention. As shown in FIG. 1, the imaging optical system (projection optical system) includes the first imaging optical system 3 in order from the substrate 5 side.
And the second image forming optical system 4 are arranged in series, and the first photomask 1 is arranged at a position conjugate with the substrate 5 with respect to the first image forming optical system 3. Imaging optical system 4
The second photomask 2 is arranged at a position conjugate with the first photomask 1.

The second photomask 2 is illuminated by an illumination optical system (not shown) arranged above, and the pattern formed on the second photomask 2 passes through the second imaging optical system 4 to produce a first photomask. An image is formed on the mask 1, and further formed on the wafer 5 via the first photomask 1 and the first image forming optical system 3. The pattern formed on the first photomask 1 is imaged on the wafer 5 via the first imaging optical system 3.
That is, the first photomask 1 and the second photomask 2 are superimposed and projected, and the first and second photomasks 1,
A composite image of the two patterns is formed on the wafer 5.

Here, the numerical aperture of the first imaging optical system 3 and the second imaging optical system 4 on the substrate side (image side) and the substrate side of the first imaging optical system 3 (image side). The first and second image forming optical systems are configured so that the numerical apertures of are equal. In other words, the numerical aperture on the substrate side (image side) of the first imaging optical system 3 is NA.
_If the numerical aperture on the first photomask side (image side) of the second imaging optical system 4 is NA ₂ and the absolute value of the magnification of the first imaging optical system 3 is M ₁ , then The second imaging optical system has an NA
₂ / M ₁ = NA ₁ is satisfied.

Now, the patterns arranged on the first photomask 1 and the second photomask 2 will be described with reference to FIGS. 3 and 4. First, FIG. 3 shows a case where a conventional photomask including a transparent portion and a light shielding portion is used. here,
As an example, assume a periodic line-and-space pattern (a pattern in which a light-shielding portion and a transparent portion are repeated). FIG. 3A shows the intensity distribution of a target pattern to be transferred onto the surface of the wafer 5, and the basic period of this pattern (bright part with intensity 1 to dark part with intensity 0) is shown by P _A.

To form the pattern shown in FIG. 3A using the apparatus of this embodiment, the first photomask 1 and the second photomask 2 are formed as shown in FIGS. 3B and 3C. It suffices to arrange a pattern of various transmittance distributions. That is, as can be seen from Table 1 above, a portion where both the first photomask 1 and the second photomask 2 are transparent portions is a bright portion on the wafer 5, and if either one is a light shielding portion, the wafer is a wafer. Since it becomes a dark part on the line 5, the part corresponding to the dark part of the line-and-space pattern may be made to be a light shielding part alternately in the first photomask 1 and the first photomask 2. At this time, the basic periods of the patterns in FIGS. 3B and 3C are P _B and P _C (periods converted on the wafer surface in consideration of the magnifications of the first and second imaging optical systems. As is clear from the figure, P _A <P _B , P _A <P _C
(P _B = P _C = 2 × P _{A in} the example of FIG. 3). Discussing this in terms of spatial frequency, if the spatial frequency is expressed as F, the spatial frequency is the reciprocal of the period, so that F _A > F
_B, and F _A> F _C.

That is, by using the apparatus of this embodiment, an image containing a fundamental frequency higher than the fundamental frequencies contained in the first and second photomasks 1 and 2 is formed on the wafer surface. Can be done. Or, in other words, the patterns of FIGS. 3B and 3C are (A)
Since it is closer to the state of the isolated pattern compared to the pattern of, the true isolated pattern (even if it is not decomposed,
Even when patterns that are originally isolated) are mixed, the imaging performance equivalent to that of the isolated pattern can be achieved. As described in the action section, the larger the fundamental period (the smaller the spatial frequency) is, the smaller the diffraction angle of the diffracted light generated by the photomask becomes.
Even if the numerical apertures of the image forming optical systems 3 and 4 are the same as those of the conventional apparatus, the resolving power is improved as compared with the conventional apparatus.

Next, the case of using a polarization photomask will be described with reference to FIG. FIG. 4A shows the intensity distribution of the target pattern to be transferred onto the surface of the wafer 5,
(B) and (C) show schematic arrangements of patterns to be arranged on the first and second photomasks 1 and 2, respectively. As in the case of FIG. 3, the basic period of the target pattern of (A) is P _A , and the basic periods of the patterns of (B) and (C) are P _B and P _C.

In the case of a polarization photomask, as shown in Table 2, if two orthogonal polarization states are P and S,
The polarization states of the light transmitted through the corresponding portions of the patterns of the first and second photomasks 1 and 2 are the same (PP or S
-S), the composite pattern on the wafer 5 becomes a bright part, and when the polarization state is different, it becomes a dark part. Thus, the line and the period P _A as shown in FIG. 4 (A)
In order to form a space pattern, in the first and second photomass 1 and 2, the illumination light is equal to the period P _A of the pattern having the pattern width (A) considered on the wafer 5 and the illumination light is in the polarization state of P. Polarizing part for converting to (shown as P in the figure)
And a pattern in which a polarization portion (shown as S in the figure) for converting the illumination light into the polarization state of S and having a width of P _A which is also considered on the wafer is alternately repeated, and both patterns are P
_{It is} enough to shift by _A / 2.

Also in this case, as in the case of FIG. 3, P _A <
Since P _B and P _A <P _C , F _A > F _B and F _A > F _C are expressed in spatial frequency. This means that the fundamental spatial frequency when the second photomask 2 is imaged via the second image forming optical system 4 and the first image forming optical system 3 is F _B , and the first photomask forms the first image forming image. the fundamental spatial frequency when imaged via the optical system 3 as F _C, it fundamental spatial frequency F _a synthetic pattern to be formed on the wafer 5 which has become higher than F _B, F _C Means

That is, as compared with the conventional method (FIG. 2), the spatial frequency propagating in the imaging optical system can be lowered, so that it is higher if the numerical aperture and exposure wavelength of the imaging optical system are the same as in the conventional method. The resolution performance can be expected. Furthermore, if a polarization photomask is used as shown in FIG.
Since the width itself of the polarization pattern formed on the photomask of (1) can be made larger than the width of the light shielding pattern when the pattern (A) is projected and exposed by the conventional apparatus (2 in the example of the figure).
That is, the pattern formation is facilitated and the yield is improved.

Now, in the case of using a polarization photomask, in the patterns of FIGS. 4B and 4C, P
It is preferable that the polarization directions of the polarized light passing through the portion S and the polarized light passing through the portion S are inclined by 45 degrees with respect to the sides of the pattern, as indicated by arrows in the figure. This is due to the following reasons. Linearly polarized light has a TE (transverse electric)
) The polarization state and the vibration direction of the magnetic vector are perpendicular to the incident surface, that is, the vibration direction of the electric vector is in the incident surface.
There is an M (transverse magnetic) polarization state, and the light applied to the photomask has an average state of TE polarization and TM polarization. Suppose that the TE polarized light (see FIG.
A polarizing member that transmits an electric vector vibrates in a direction parallel to the side of the pattern of FIG.
If a polarizing member that transmits only the electric vector (vibration) is provided in the arrangement direction of the pattern, the following problem occurs.

That is, when the photomask is transmitted and illuminated,
Diffracted light of each order is generated from the photomask, and light with different diffracted orders reaches the image plane through different optical paths in the incident plane. Since the vibration directions of the batteries are always aligned with the direction perpendicular to the incident surface, the interference effect of the diffracted lights is maximized. On the other hand, in the case of TM polarized light, the vibration direction of the electric vector of the diffracted light of different orders corresponding to the difference in the diffraction angle is deviated, and the interference effect between the diffracted lights decreases.

Therefore, in the image plane, the light intensity of the portion corresponding to the portion through which TE polarized light is transmitted (the portion S in both the first and first photomasks) is high, and the portion through which TM polarized light is transmitted (compared with that) In both the first and second photomasks, the light intensity of the portion corresponding to the portion P) becomes low, and the brightness of the bright portion differs within the series of line and space patterns. In the present embodiment, in order to avoid such a difference in brightness, the vibration direction of the light transmitted by the polarization parts P and S is inclined by 45 degrees with respect to the sides of the pattern, and the pattern image is bright. In the section, a light intensity intermediate between the TE polarized light and the TM polarized light is obtained.

When the light intensity of the bright part of the pattern image does not have to be uniform, the vibration directions themselves are particularly limited as long as the vibration directions of the polarized light from the P and S parts are orthogonal to each other. It goes without saying that it is not a thing. Although only two types of polarizing members are used in the example of FIG. 4, the number of polarizing members used in the polarization photomask may be three or more. It is needless to say that a polarizing member suitable for each pattern is used at a position where the arrangement direction of the pattern is different, or three or more kinds of polarizing members may be used in a series of patterns.

Further, in the above embodiment, the target pattern was decomposed into two photomasks and projection exposure was performed using two image forming optical systems, but the target pattern is formed by the same principle. It is also possible to disassemble into three or more photomasks and perform projection exposure with three or more imaging optical systems. Furthermore, in the above embodiment, the imaging optical system is a refraction system and the photomask is a transmission type. However, the scope of application of the present invention is not limited to this example, and the imaging optical system is The same applies when a reflective system is used or when a reflective photomask is used.

[0034]

As described above, according to the present invention, the target pattern to be transferred onto the photosensitive substrate is decomposed into a plurality of photomasks, and each of them is simultaneously projected and exposed through the imaging optical system. The spatial frequency of the pattern formed on the mask can be lowered, and the load on each imaging optical system can be reduced. In other words, even if the numerical aperture of the imaging optical system is the same as the conventional one, it is possible to resolve a pattern having a higher frequency than the conventional one, that is, a finer pattern.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram of a conventional projection exposure apparatus.

3A is a diagram showing an intensity distribution of a target pattern image, and FIGS. 3B and 3C are diagrams showing transmittance distributions of patterns formed on the first and second photomasks.

FIG. 4A is a diagram showing an intensity distribution of a target pattern image, and FIGS. 4B and 4C are schematic diagrams of polarization patterns formed on the first and second photomasks.

[Explanation of symbols]

1 ... 1st photomask, 2 ... 2nd photomask, 3
... 1st imaging optical system, 4 ... 2nd imaging optical system, 5 ... Photosensitive substrate (wafer).

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 7352-4M 311 W

Claims (3)

[Claims] 1. A projection exposure apparatus including a projection optical system for projecting a pattern on a photomask onto a photosensitive substrate, wherein the projection optical system forms an image of the pattern of the first photomask on the photosensitive substrate. And a second image forming optical system for forming an image of the pattern of the second photomask on the first photomask. The first and second image forming optical systems include: , A numerical aperture on the substrate side by a combined system of the first and second imaging optical systems and a numerical aperture on the substrate side of the first imaging optical system are equal to each other, The pattern of the first photomask is projected onto the photosensitive substrate via an optical system, and
A projection exposure apparatus, which projects the pattern of the second photomask onto the photosensitive substrate via the imaging optical system, the first photomask, and the first imaging optical system. 2. The highest spatial frequency of the pattern image formed on the photosensitive substrate by the first and second imaging optical systems is F0, the highest spatial frequency of the pattern of the first photomask is F1, and When the highest spatial frequency of the pattern of the first photomask is F2, F1 ≦ F0 and F2 ≦ F0 (where F1 and F2 are converted into the spatial frequency on the photosensitive substrate) are satisfied. The projection exposure apparatus according to claim 1. 3. The projection exposure apparatus according to claim 1, wherein the first and second photomasks each include a polarization member that converts a polarization state of light into a predetermined state.