JP3309920B2 - Exposure method and projection exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, in manufacturing a semiconductor device or a liquid crystal display device in a photolithography process, and projects a photomask pattern onto a photosensitive substrate via a projection optical system. The present invention relates to an exposure apparatus.

[0002]

2. Description of the Related Art An illumination optical system for illuminating a pattern of a photomask or a reticle (hereinafter, collectively referred to as a "photomask") with exposure light when a semiconductor element or a liquid crystal display element is manufactured by a photolithography process. A projection exposure apparatus having a projection optical system for projecting and exposing the pattern on a substrate such as a wafer or a glass substrate coated with a photosensitive material is used. That is, the conventional projection exposure apparatus has a configuration in which one photomask is arranged under an illumination optical system, and the pattern of the photomask is projected on a photosensitive substrate.

Recently, as LSIs and the like are further integrated, there is a demand for a projection exposure apparatus to further increase the resolving power. As understood from elementary optics, in order to increase the resolution of a pattern to be exposed, a numerical aperture (NA) of a projection optical system must be increased to a large NA, or a shorter wavelength using shorter wavelength light as exposure light. A method of increasing the wavelength is known, and conventionally, measures have been taken to increase the NA and shorten the wavelength of the exposure light. In addition, some other techniques have been proposed to enhance this type of optical performance.

One of such new techniques is to use a phase shift mask as disclosed in Japanese Patent Publication No. Sho 62-50811, for example. There are various modifications of the phase shift mask, but basically, the optical imaging performance is improved by changing the phase of some of the illumination light entering the opening on the photomask surface with a phase shifter. It is to let.

[0005]

However, there is a limit to increasing the numerical aperture of the projection optical system, and at the present time, when the wavelength of the exposure light is shortened, it is suitable as a lens system constituting the projection optical system. There are inconveniences such as a small number of types of glass materials. In addition, when a phase shift mask is used, there is an inconvenience that it is more difficult to manufacture a photomask than when a conventional photomask is used. In view of the above, the present invention provides an exposure method capable of improving the resolution of a pattern to be exposed similarly to a case where a phase shift mask is used even when a conventional photomask is used , and such an exposure method.
It is an object of the present invention to provide a projection exposure apparatus capable of performing an optical method .

[0006]

According to the first projection exposure apparatus of the present invention, as shown in FIG. 1, for example, an illumination optical system (1) for illuminating a mask (4) on which a pattern for transfer is formed with illumination light. , and 2), in a projection exposure apparatus having a projection optical system (5) for projecting an image of a pattern for the transfer on the photosensitive substrate (6), together with the illumination light is irradiated, for its transfer pattern An auxiliary mask (3) having a pattern similar to that of (1) is provided , and the mask (4) is illuminated with diffracted light emitted from the auxiliary mask (3).

In this case, the pattern forming surface (4a) of the mask (4) and the pattern forming surface (3a) of the auxiliary mask (3).
Is preferably set between 1 μm and 100 μm. Further, as shown in FIG. 5, for example, it is desirable to integrate the mask (4) and the auxiliary mask (3). Next, a second projection exposure apparatus according to the present invention is a projection exposure apparatus having an illumination optical system for irradiating a mask with illumination light and a projection optical system for projecting an image of a pattern of the mask onto a photosensitive substrate. Includes a diffractive optical element that receives the illumination light and generates a diffracted light that becomes a spherical wave near the edge of the transmitting part of the pattern, or a diffracted light that has a different phase between the center and the edge of the transmitting part. Illuminate the mask with the diffracted light. A third projection exposure apparatus according to the present invention is a projection exposure apparatus having an illumination optical system that irradiates illumination light onto a mask and a projection optical system that projects an image of a pattern of the mask onto a photosensitive substrate. Each other within a predetermined area on the mask where the illumination light is irradiated
It is arranged corresponding to various mask patterns respectively formed on different regions , and the pattern shapes correspond to the various mask patterns.
Different patterns depending on the mask pattern
Having a pattern plate on which patterns are formed , and various masks thereof
Put each of the patterns on the pattern board
Diffracted light emitted from the pattern corresponding to each turn
And individually illuminate. Next, the exposure method according to the present invention includes irradiating a mask having a pattern for transfer with illumination light, and exposing a photosensitive substrate with the illumination light through the mask. Diffracted light that becomes a spherical wave near the edge of the transmitting portion, or diffracted light having different phases at the center and the edge of the transmitting portion, and illuminates the mask with the diffracted light.

[0008]

The principle of the present invention will be described with reference to a specific example shown in FIG. FIG. 3 shows a photomask 4 and an auxiliary photomask 3 as an example of the mask (4) and the auxiliary mask (3) in the present invention. An opening 7 is formed on the photomask 4 and An opening 8 having a width smaller than that of the opening 7 is formed. However, the width of the opening 8 may be the same as or wider than the opening 7. In this case, it is assumed that the auxiliary photomask 3 is vertically irradiated with exposure light 9 composed of a plane wave from an illumination optical system (not shown).
At this time, diffracted light (diffraction wave) is emitted from the opening 8 of the auxiliary photomask 3. According to the teaching of Huygens' principle, secondary spherical waves are generated from each point of the opening 8 of the auxiliary photomask 3 and their "envelopes" form a diffracted wavefront.

In this case, as shown in FIG. 3, the exposure light 10 for illuminating the opening 7 of the photomask 4 is not a plane wave but a spherical wave near the edge of the opening 7. Further, since the shape of each opening of the auxiliary photomask 3 above each opening of the photomask 4 is changed corresponding to each opening of the photomask 4, it is arranged in one photomask 4. Exposure light for illuminating various patterns is converted into a spherical wave near the edge. Therefore, the resolution is improved by substantially the same operation as when the phase shift mask is used as the photomask 4.

The operation of the present invention will be described more specifically. In FIG. 3, assuming that the opening 8 of the auxiliary photomask 3 is sufficiently small, the exposure light 10 as a diffracted wave can be regarded as a substantially spherical wave. If the distance between the auxiliary photomask 3 and the photomask 4 is z and the distance from the center of the opening 7 of the photomask 4 in the horizontal direction is x, the amplitude の of the exposure light 10 composed of a spherical wave is It can be represented by an equation.

１ = exp ｛ik (z ² + x ² ) ^1/2 ｝ / (z ² + x ² ) ^1/2

Here, k is a wave number, and k = 2π / λ (λ:
Wavelength). Here, if z≫x, the amplitude ψ can be approximated as follows.

[Number 2] ψ ≒ {exp (ikz) / z} · exp {ikx 2 / (2z)} αexp {ikx 2 / (2z)} This is the same as what is known as Fresnel diffraction at the optical is there.

Referring to FIG. 4, the behavior of the diffracted wave having the amplitude ψ will be examined based on (Equation 2). 4A shows the opening 7 of the photomask 4, and FIGS. 4B and 4C show the real part and the phase of the amplitude の of (Equation 2) at the position x on the opening 7, respectively. From FIG. 4, it can be seen that the phase of the diffracted wave as the exposure light is inverted between the central portion and the peripheral portion of the opening 7 of the photomask 4. That is, it can be seen that ReＲｅ> 0 at the center of the opening 7 but Reψ <0 at the periphery (edge) of the opening 7 assuming that Re indicates a real part.

FIG. 4 (c) shows how the phase of the amplitude と 共 に changes with the position x.
From (c), the phase is changed to non-linear in the opening 7, and the phase is π (180
°) You can see the degree has changed. Such a change in phase is almost equivalent to what is known as an “edge-emphasized phase shift mask” from the viewpoint of a change in the phase of exposure light on the opening of the photomask. This means that, according to the present invention, a wavefront having a phase distribution equivalent to the case where a phase shift mask is used is emitted from the photomask 4 without using a phase shift mask. Therefore,
As in the case where the phase shift mask is used, the resolution of the projected image can be improved.

The pattern forming surface (4) of the mask (4)
When the distance between a) and the pattern forming surface (3a) of the auxiliary mask (3) is set between 1 μm and 100 μm,
The pattern forming surface (4a) of the mask (4) is arranged in a region where the diffracted wave emitted from the pattern forming surface (3a) of the auxiliary mask (3) is substantially Fresnel diffraction. Therefore, a wavefront close to the case where the phase shift mask is used is emitted from the mask (4). If the interval is too large, a diffracted wave from a certain pattern of the auxiliary mask (3) illuminates a wide area of the mask (4), and the imaging characteristics may be deteriorated. Further, when the mask (4) and the auxiliary mask (3) are integrated, the setting work of the mask (4) and the auxiliary mask (3) is speeded up.

[0015]

1 and 2 show an embodiment of the present invention .
This will be described with reference to FIG. FIG. 1 shows a projection exposure apparatus of the present embodiment. In FIG. 1, reference numeral 1 denotes a light source device including a light source and an optical integrator. The exposure light IL emitted from the light source device 1 illuminates the auxiliary photomask 3 with uniform illuminance via the condenser lens system 2. In this example, the principal ray of the exposure light IL is almost perpendicularly incident on the auxiliary photomask 3. The photomask 4 is arranged in proximity to the pattern forming surface 3a on the lower surface of the auxiliary photomask 3 and projected on the upper surface of the photomask 4, that is, a surface (hereinafter, referred to as a "pattern forming surface") 4a facing the auxiliary photomask 3. A circuit pattern for exposure is formed. Further, a pattern similar to the circuit pattern on the photomask 4 is formed on the pattern formation surface 3a of the auxiliary photomask 3 (details will be described later).

The exposure light IL is diffracted by the pattern formed on the pattern forming surface 3a on the lower surface of the auxiliary photomask 3, and the diffracted wave illuminates the pattern on the pattern forming surface 4a of the photomask 4. The pattern formed on the photomask 4 is projected through a projection optical system 5 onto a wafer 6 coated with a photoresist. FIG. 2 (a)
5B and 5B show patterns of the photomask 4 and the auxiliary photomask 3 of the present example, respectively. On the pattern formation surface of the photomask 4, various opening patterns 7-
1, 7-2,..., 7-7 are formed. Also, on the pattern forming surface of the auxiliary photomask 3, opening patterns 8-1, 8-2,..., 8-7 smaller than the respective opening patterns on the photomask 4 are formed between the light shielding films.

Specifically, the opening pattern on the auxiliary photomask 3 corresponding to the slit-shaped opening pattern 7-1 on the photomask 4 is a slit-shaped opening pattern 8-1, but the opening pattern 8-1 is Although it is narrower by 2d1 and 2d2 than the opening pattern 7-1 in the width direction and the longitudinal direction, respectively, the reduction amount d1 in the width direction and the reduction amount d2 in the longitudinal direction are different. Further, the reduction amounts d1 and d2 are different from each other in that the phase of the exposure light composed of the diffracted wave emitted from the aperture pattern 8-1 is smaller than the aperture pattern 7 of the photomask 4.
-1 is set so as to be different by about 180 degrees between the center part and the edge part. Similarly, other opening patterns 8-
2, .DELTA. Also represent the opening pattern 7- of the photomask 4.
The phase of the exposure light is 180 at the center and the edge of 2,.
The opening patterns 7-2, パ タ ー ン are set to be smaller than the opening patterns 7-2, ‥‥.

FIG. 3 shows a relationship between a typical opening (opening pattern) 8 of the auxiliary photomask 3 and a typical opening 7 of the photomask 4. As shown in FIG. The opening 8 is illuminated with exposure light 9 substantially consisting of a plane wave. The exposure light 10 diffracted by the opening 8 and having a spherical wave shape at the edge illuminates the opening 7 of the photomask 4, and the exposure light 10 at the center and the edge of the opening 7.
Are approximately 180 ° different. Accordingly, the exposure light emitted from the opening pattern of the photomask 4 of the present embodiment undergoes a phase change similar to that of the edge emphasizing phase shift mask, and as a result, the imaging performance can be improved.

In FIG. 1, the auxiliary photomask 3
The distance between the pattern forming surface 3a and the pattern forming surface 4a of the photomask 4 is desirably set to about 1 μm to 100 μm. If the interval is too small, the diffracted wave emitted from the opening pattern of the auxiliary photomask 3 does not have a spherical wave shape, and there is substantially no point in using two photomasks. If the interval is excessively large, the diffracted wave from one opening pattern of the auxiliary photomask 3 spreads over a wide area on the photomask 4, and the resolution of another opening pattern may be deteriorated. Thus, the auxiliary photomask 3 and the photomask 4
In the case where a normal photomask composed of a chromium-deposited portion and a transmissive portion is used as the auxiliary photomask 3 and the photomask 4, respectively, the chromium-deposited surfaces are opposed to each other as shown in FIG. It is desirable to arrange. In such an arrangement, the photomask 4
Since the glass surface 4b side enters the image forming system, it is desirable that the glass surface 4b is polished with high precision and that the spherical aberration correction for the glass thickness is performed by the projection optical system 5.

The phase shift of the exposure light between the central portion and the edge portion of the opening pattern of the photomask 4 may be a predetermined value other than 180 ° in some cases. The phase difference is determined by the resolution of the pattern image finally projected on the wafer 6. In other words, it is only necessary that the phase difference of the exposure light between the central part and the edge part of the opening pattern of the photomask 4 be a predetermined value. Therefore, as shown in FIG. In addition to the case where the opening pattern of the auxiliary photomask 3 is smaller than that of the opening pattern of the photomask 4, the opening pattern of the auxiliary photomask 3 may have the same size as the opening pattern of the photomask 4. Further, the opening pattern of the auxiliary photomask 3 may be larger than the opening pattern of the photomask 4 in some cases.

Further, as shown in FIG. 5, the auxiliary photomask 3 and the photomask 4 may be integrally formed. That is, in FIG. 5, the auxiliary photomask 3 and the photomask 4 are fixed via the spacers 11A and 11B, and the light shielding film 12 having an opening pattern is formed on the surface of the photomask 4 on the side of the spacers 11A and 11B. A light-shielding film 13 having an opening pattern is also formed on the surface of the auxiliary photomask 3 on the side of the spacers 11A and 11B. In this case, the spacers 11A and 11B that define the distance between the auxiliary photomask 3 and the photomask 4 are provided not only in the peripheral part but also in the peripheral part.
It can also be arranged in a large light shielding area in the photomask 4. When the auxiliary photomask 3 and the photomask 4 are integrally formed as shown in FIG. 5, it is necessary to align the photomask and the auxiliary photomask when exchanging the photomask in the exposure step. And the time of the exposure step can be shortened.

In the above-described embodiment, in order to emphasize that a phase shift mask is not required, both the auxiliary photomask 3 and the photomask 4 use, for example, a conventional chromium vapor deposition mask having a light shielding portion and a transmission portion. ing. However, the present invention is not limited to this, and it is also possible to use a conventional chromium deposition mask for one of the auxiliary photomask 3 or the photomask 4 and use a mask using only a phase shifter for the other.

FIG. 6 shows an example in which a mask using only a phase shifter is used as the auxiliary photomask 3. In FIG.
An opening pattern is formed as a region between 2-2 and ‥‥. In the regions on the auxiliary photomask 3 facing the light shielding films 12-1, 12-2,..., The phase shifters 13-1, 13- for shifting the phase of the exposure light by a predetermined amount (for example, 180 °) are provided. 2, ‥‥ are formed. In this case, the exposure lights IL1 and IL2 incident on the central portion and the edge portion of the opening pattern of the photomask 4 differ in phase by a predetermined amount, so that a wavefront equivalent to the case where one phase shift mask is used is obtained. .

Therefore, even when a mask using only a phase shifter is used as the auxiliary photomask 3, an improvement in optical imaging performance can be expected. Further, in the case of the conventional phase shift mask, it is difficult to manufacture because a light-shielding pattern and a phase shifter pattern are mixed in one photomask, whereas in the example of FIG. Since the mask on which the pattern is formed is separated from the mask on which the pattern of the phase shifter is formed, there is an advantage that the manufacturing is easy.

It should be noted that the present invention is not limited to the above-described embodiment, but can take various configurations without departing from the spirit of the present invention.

[0026]

According to the present invention, for example , each pattern on the mask is illuminated by the diffracted light from the corresponding pattern on the auxiliary mask disposed directly above the mask, and the center and the edge of each pattern on the mask are illuminated. Since the phase difference of the illumination light can be set to a predetermined value between the first and second portions, the advantage that the resolution of the pattern to be exposed can be improved even when a conventional photomask is used as in the case of using a phase shift mask. is there.

When the distance between the pattern forming surface of the mask and the pattern forming surface of the auxiliary mask is set between 1 μm and 100 μm, it is possible to obtain an imaging characteristic close to that of using a phase shift mask. . Further, when the mask and the auxiliary mask are integrated, the work efficiency at the time of mask replacement is improved.

[Brief description of the drawings]

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

2A is a plan view showing a pattern of the photomask 4 shown in FIG. 1, and FIG. 2B is a plan view showing a pattern of an auxiliary photomask 3 shown in FIG.

FIG. 3 is an enlarged cross-sectional view of a main part showing a state in which a photomask 4 is illuminated with diffracted light from an auxiliary photomask 3 in FIG.

4A is an enlarged cross-sectional view of an opening of the photomask 4 in FIG. 3, FIG. 4B is a characteristic diagram showing the amplitude of exposure light at a certain point on the opening, and FIG. FIG. 7 is a characteristic diagram showing a phase at a certain point on an opening.

FIG. 5 is a side view showing an example in which an auxiliary photomask and a photomask are integrated.

FIG. 6 is a side view showing another example of the auxiliary photomask.

[Explanation of symbols]

 Reference Signs List 1 light source device 2 condenser lens system 3 auxiliary photomask 4 photomask 5 projection optical system 6 wafer 7-1, 7-2, opening pattern 8-1, 8-2, opening pattern 11A, 11B spacer 13- 1,13-2 Phase shifter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/30 515F

Claims (5)

(57) [Claims] To 1. A mask pattern is formed for transfer
In a projection exposure apparatus having an illumination optical system that emits illumination light and a projection optical system that projects an image of the transfer pattern onto a photosensitive substrate, the illumination light is emitted, and the transfer pattern Provide an auxiliary mask with a similar or identical pattern
For example, a projection exposure apparatus characterized by illuminating the mask with the diffracted light emitted from the auxiliary mask. 2. The method according to claim 1, wherein the distance between the pattern forming surface of the mask and the pattern forming surface of the auxiliary mask is 1 μm to 100 μm.
2. The projection exposure apparatus according to claim 1, wherein the distance is set between m. 3. A projection exposure apparatus comprising: an illumination optical system that irradiates illumination light onto a mask; and a projection optical system that projects an image of a pattern of the mask onto a photosensitive substrate. A diffractive optical element that generates diffracted light that becomes a spherical wave near the edge of the transmitting portion of the pattern, or diffracted light that has different phases at the center and the edge of the transmitting portion, illuminates the mask with the diffracted light And a projection exposure apparatus. 4. A projection exposure apparatus comprising: an illumination optical system for irradiating a mask with illumination light; and a projection optical system for projecting an image of a pattern of the mask on a photosensitive substrate, wherein the illumination light on the mask is irradiated with the illumination light. each other in the predetermined region to be
It arranged corresponding to the various mask path <br/> turn respectively formed on different regions in the stomach, and the pattern shape pairs
Various different types depending on the corresponding mask pattern
A pattern plate having a pattern formed thereon , each of the various mask patterns being placed on the pattern plate;
From the pattern corresponding to each of the mask patterns
A projection exposure apparatus characterized in that the emitted diffraction light is individually illuminated. 5. A method of irradiating a mask having a pattern for transfer with illumination light and exposing a photosensitive substrate with the illumination light through the mask, comprising: an edge portion of a transmission portion of the pattern from the illumination light. An exposure method comprising: generating diffracted light that becomes a spherical wave in the vicinity, or diffracted light having different phases at a central portion and an edge portion of the transmitting portion, and illuminating the mask with the diffracted light.