JPH0736174A - Optical mask - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to realize a light projection exposure having a resolution equal to or higher than that of a conventional phase shift mask or grazing incidence illumination. [Structure] Blocking exposure light In an optical mask in which a light-shielding portion and an opening for transmitting exposure light are formed, stripes formed of a conductive light-shielding material and having a pitch equal to or less than the wavelength of the exposure light are provided on the entire surface of the optical mask.
In an optical mask having a light-shielding portion that shields exposure light and an opening that transmits exposure light, a stripe formed of a conductive light-shielding material and having a pitch equal to or less than the wavelength of the exposure light is provided in the opening. Has been.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical mask used for projection exposure, and more particularly to an optical mask suitable for exposing a fine pattern.

[0002]

2. Description of the Related Art With the recent increase in speed and integration of semiconductor devices, finer pattern formation is required.
As photolithography using light, a phase shift mask and grazing incidence illumination are drawing attention in order to break through the limit of resolution.

Further, in order to overcome the limitation of photolithography using light and improve resolution, an X-ray exposure method using X-rays and an electron beam exposure method using an electron beam have been proposed and used. There is.

[0004]

In the X-ray exposure method, it is not easy to realize an optical system, and the apparatus tends to be large. Also,
The electron beam exposure method can achieve high resolution but low throughput.

An object of the present invention is to realize optical projection exposure having a resolution equal to or higher than that of a conventional phase shift mask or oblique incidence illumination.

[0006]

The optical mask of the present invention comprises:
In an optical mask having a light-shielding portion that shields exposure light and an opening that transmits exposure light, stripes made of a conductive light-shielding material and having a pitch shorter than the wavelength of the exposure light are provided on the entire surface of the optical mask. .

Another optical mask of the present invention is an optical mask in which a light-shielding portion that shields exposure light and an opening that transmits exposure light are formed, and the exposure light is made of a conductive light-shielding material only in the opening. Stripes with a pitch shorter than the wavelength of

Further, the openings have a shape elongated in one direction and are repeatedly arranged in another direction at right angles to the one direction, and the direction of the stripes is parallel to the other direction. preferable. Further, the repeatedly arranged openings may be provided with a member for shifting the phase of every other opening.

Further, the openings have a shape elongated in one direction and are repeatedly arranged in another direction perpendicular to the one direction, and the directions of the stripes provided in the adjacent openings are mutually opposite. It is preferable that they are orthogonal.

[0010]

By forming a stripe made of a conductive light-shielding material having a pitch shorter than the wavelength of exposure light on the optical mask, the transmitted light can be linearly polarized. for that reason,
It is not necessary to dispose a polarizing film between the exposure light source and the mask.

Further, when projecting and exposing a repetitive pattern having a shape elongated in one direction, the transmitted light is made to be linearly polarized light having a polarization axis parallel to the direction of the pattern, so that the transmitted light efficiently interferes with the image plane. Can be made.

When projecting and exposing a repetitive pattern having a shape elongated in one direction, the polarization axes of the transmitted lights passing through the adjacent patterns are made orthogonal to each other, so that the transmitted lights passing through the adjacent patterns on the image plane are Interference can be prevented. Therefore, the resolution can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before explaining the embodiments of the present invention, an exposure technique using the phase difference of a phase shift mask will be explained.

FIG. 6A schematically shows a phase shift mask. A light-shielding metal film 23 of chromium or the like is selectively formed on the surface of the transparent substrate 22 of quartz or the like to define the opening. A phase shifter 24 such as a SiO ₂ film is formed in one of the adjacent openings.

The thickness of the phase shifter 24 is selected so as to delay the phase of the light passing through the phase shifter with respect to the light passing through the opening without the phase shifter, and to cause a phase difference of, for example, a half wavelength.

Therefore, the light beam 21 passing through the adjacent apertures
Regarding a and 21b, the light 21a that has passed through the aperture without the phase shifter is the light 21b that has passed through the aperture with the phase shifter.
Half-wave phase is ahead of. Such waves having opposite phases cancel each other out when interference occurs and reduce the light intensity.

FIG. 6B schematically shows how the amplitude of light changes due to the interference of two types of light having such opposite phases. When the light having the amplitude shown by the curve a interferes with the light having the opposite phase amplitude shown by the curve b, the light amplitude shown by the curve c is obtained.
Here, in the area where the two light beams overlap, the phases of the light beams are opposite to each other, so that the amplitude decreases.

FIG. 6C shows the intensity distribution of the light having such interference. The light of opposite phase spread by diffraction overlaps in the middle skirt portion and reduces its amplitude. Therefore, the light intensity is also reduced. In this way, by interfering two light beams having a phase difference, it becomes possible to limit the distribution width of light expanded by diffraction.

FIG. 7 is a schematic diagram for explaining the function of the phase shift mask. Light rays 25 and 26 are incident on the mask, and one exits through the phase shifter. Outgoing ray 2
5c and 26c are one of them, for example, 26c is the other ray 2
It has a half-wavelength phase difference from 5c. The light having the opposite phase decreases in intensity according to the amplitude when interfering with each other.

To produce an image on the projection surface, 2
At least the -1st order diffracted lights 25a and 26a generated from the two light beams 25 and 26 and the 1st order diffracted lights 25b and 26b need to be interfered with each other on the projection surface.

Consider the direction in which the -1st-order diffracted light is generated with respect to the pitch p of the two light rays 25 and 26. Ray 26a
As shown on the right side of FIG. 6A, the optical path difference that has with respect to the light ray 25a is p · sin θ. The optical path difference is the same for the −1st order diffracted light.

If the pitch p is large, a large number of diffracted lights enter the projection lens, but as the pitch p decreases, the order of the light entering the projection lens decreases. Therefore, in order to obtain high resolution, the behavior of the 0th order light and the 1st order light is important.

In the phase shift mask, since the phase shifter is formed in one of the adjacent openings, the phase of the emitted light is shifted by π. Therefore, ± 1st-order diffracted light is generated in the direction in which p · sin θ becomes equal to the half wavelength. The angle θ of the first-order diffracted light increases as the pitch p decreases.

FIG. 7B schematically shows an image forming system using such a phase shift mask. The light from the light source irradiates the phase shift mask 32 through the condenser lens 31 for mask illumination. At this time, the central ray 3 of the light flux
4 is irradiated perpendicularly to the phase shift mask 32.

The light that has passed through the phase shift mask 32 becomes two light fluxes having opposite phases, and as described above, it goes straight to 0.
The next light 35 is canceled by the interference. If the light intensities of both light fluxes are almost equal, the light intensity almost disappears as a whole, and -1
The secondary light 36 and the primary light 37 are the main light rays. An image is formed by irradiating the projection surface with these two types of light rays 36 and 37 on the projection surface.

FIG. 8 is a schematic diagram for explaining the difference in image forming ability due to polarization. It is assumed that a line-and-space parallel pattern is formed on the mask. FIG. 8 (A)
[Fig. 6A] is a diagram for explaining imaging when polarized light parallel to the line-and-space pattern direction is used.

It is assumed that a line-and-space pattern is formed on the mask 7 in a direction perpendicular to the paper surface. It is assumed that linearly polarized light polarized in a direction perpendicular to the paper surface is vertically incident on the mask 7. That is, the polarization direction and the pattern direction are parallel.

After passing through the mask 7, the minus first-order diffracted light 15
The first-order diffracted light 16 is generated as shown in the figure, is condensed by the projection lens 8, and is incident on the exposure surface of the wafer 9 or the like. At this time, the polarization direction is always perpendicular to the paper surface,
The polarization directions of the −first-order diffracted light 15 and the first-order diffracted light 16 are the same. Therefore, the −1st-order diffracted light 15 and the 1st-order diffracted light 16 interfere with each other on the wafer 9 to form an image.

FIG. 8B shows the behavior of light when the direction of the line and space pattern and the polarization direction are vertical. It is assumed that the mask 7 has a line-and-space pattern in the direction perpendicular to the paper surface, as described with reference to FIG. It is assumed that linearly polarized light having a polarization direction in the plane of the paper is incident on the mask 7 from the vertical direction.

-1st-order diffracted light 1 generated by passing through the mask 7
The polarization directions of the fifth-order diffracted light 16 and the first-order diffracted light 16 are in the plane of the paper and are perpendicular to the traveling direction of the light. The polarization direction of the light condensed by the projection lens 8 and irradiated onto the wafer 9 is also perpendicular to the traveling direction of the light rays and exists in the plane of the paper as shown in the figure.

As is clear from the figure, the -1st order diffracted light 15
When the angle formed by and the first-order diffracted light 16 becomes large, the polarization directions cross each other, and the degree of interference between the −1st-order diffracted light 15 and the first-order diffracted light 16 is reduced.

If the -1st order diffracted light 15 and the 1st order diffracted light 16
If are orthogonal, no interference occurs. That is, these two lights do not form an image and become a noise component. According to the present invention, when the exposure light passes through the mask, as shown in FIG.
As in the case of (A), a technique of polarizing the exposure light in a direction parallel to the length direction of the line and space pattern is proposed. Further, as will be described later, a technique is proposed in which light transmitted through adjacent patterns is deflected so that the polarization axis directions thereof are orthogonal to each other.

FIG. 1 is a schematic diagram for explaining an exposure apparatus according to an embodiment of the present invention. The light source 1 is, for example, an ultra-high pressure mercury lamp. A reflecting mirror 2 is arranged above the light source 1 to reflect the light emitted to the upper side and direct it to the lower side.

A fly-eye lens 3 is arranged below the light source 1, and a mask 7 having a function of uniformly polarizing incident light is provided.
Irradiate on. A projection lens 8 is arranged below the mask 7 to focus incident light on the wafer 9.

The angle between the traveling direction of the light passing through the outermost side of the fly-eye lens 3 and the optical axis is θ ₁ , and the light axis when the light passing through the mask 7 passes through the outermost side of the projection lens 8. ₂ an angle theta, when light having passed through the outermost projection lens 8 goes on imaging surface, the angle between the traveling direction of the optical axis theta ₃
And

Here, σ = sin θ ₁ / sin θ ₂ and NA = sin θ ₃ . Note that σ is a coherence factor and NA is a numerical aperture.

FIG. 2A shows a sample pattern of the mask according to the embodiment. On the mask 7, line-and-space patterns having long space portions 12a in the Y direction of FIG. Parts other than the space 12a are covered with a light-shielding conductive film such as chromium.

Inside each space portion 12a of the line-and-space pattern, a second line-and-space pattern having a pitch of 0.1 μm in which space portions having a long shape in the X-direction are repeated in the Y-direction is further formed.

The pitch of the second line-and-space pattern is about the wavelength of the exposure light or less, and the line portion is made of a conductive film. Therefore, of the non-polarized light with which the space portion 12a is irradiated, the X-direction polarized component (P-polarized light) has its energy absorbed by the conductive film and cannot pass through the mask 7a. Therefore, the light transmitted through the mask 7a is only linearly polarized light (S polarized light) having a polarization axis in the Y direction.

In the space portion 12a of the line and space pattern having a pitch of 1 μm, every other phase shifter 1 is provided.
3 is provided. Each phase shifter 13 is formed by using a lift-off method on a SiO ₂ film deposited by a vacuum evaporation method. The film thickness of the phase shifter 13 is about 3880Å.

As a result, the phase of the light transmitted through the phase shifter 13 lags behind that of the light transmitted through the space 12a where the phase shifter is not provided by about 180 °. Therefore, as described with reference to FIG. 6, the skirts of the light beams which have been transmitted through the adjacent space parts and spread by diffraction are overlapped in opposite phases to reduce the amplitude. In this way, it is possible to limit the width of the distribution of light that is spread by diffraction.

At this time, the light transmitted through the mask 7 is linearly polarized light having a polarization axis in the Y direction. Therefore, as described with reference to FIG. 8, since there is no linearly polarized light having a polarization axis in the X direction which is a noise component, high resolution can be obtained.

FIG. 3 shows the calculation result of the contrast value in this embodiment. The horizontal axis represents the pitch of the line-and-space pattern imaged on the wafer in μm,
The vertical axis represents contrast. The optical conditions of the exposure system were an exposure wavelength of 365 nm, NA = 0.54, σ = 0.5, and a reduction rate of ⅕. The curves s1 and s2 respectively use S-polarized light, have a contrast when in focus, and 0.7.
The contrast when the focus is deviated by 5 μm is shown.

Curves p1 and p2 show the contrast when the P-polarized light is used and the contrast when the focus is deviated by 0.75 μm by using the mask 7b shown in FIG. 2B. Show.

In the mask 7b, the direction of the second line and space pattern of 0.1 μm pitch formed inside the space portion 12b of the first line and space pattern of 1 μm pitch is the first line and space pattern. The same point as the direction is that the mask 7a in FIG.
Different from Therefore, when the mask 7b is used, the transmitted light is only P-polarized light.

As is clear from FIG. 3, when the S polarized light is used, a higher contrast can be obtained than when the P polarized light is used. For example, when the pitch of the line and space pattern on the wafer is 0.2 μm, P
While the contrast was about 50% when polarized,
It improves up to 62% when S-polarized.

Next, another embodiment of the present invention will be described. FIG. 4A shows a mask 10 according to this embodiment.
A first line-and-space pattern having a pitch of 1.25 μm is formed by a light-shielding conductive film such as chromium.

The space portion is internally provided with a second line having a pitch of 0.1 μm in parallel with the first line-and-space pattern.
The space portions 12c provided with the line and space pattern and the space portions 12d provided with the second line and space pattern of 0.1 μm pitch are arranged alternately in the direction perpendicular to the space portions 12c. Accordingly, the light transmitted through the space portion 12c and the space portion 12c
The polarization axes of the light transmitted through d are orthogonal to each other.

FIG. 4B shows the amplitude on the image plane of the light transmitted through the two space portions 12c and 12d adjacent to each other. For example, the curves d and e are the space portion 12 respectively.
The amplitude of the light transmitted through d and 12c is shown. At this time, since the polarization axes of the respective lights are orthogonal to each other, no interference occurs. Therefore, the combined light intensity does not correspond to the sum of the amplitudes but is represented by the sum of the respective light intensities.

Curves f and g in FIG. 4C indicate the intensities of light corresponding to the curves d and e in FIG. 4B. A curve h shows the intensity of light obtained by combining these two lights. FIG. 4 (D) shows
A conventional mask is shown. Since the transmitted light in each space 13 of the line and space pattern is unpolarized light or light polarized in the same direction, each transmitted light causes interference. Figure 4
(E) shows the amplitude of the image plane of the light transmitted through the space portions 12e adjacent to each other. Since these two transmitted lights interfere with each other, the intensity of the combined light is proportional to the square of the sum of the amplitudes of the respective lights.

FIG. 4F shows the intensity of the combined light.
In this way, when the peak of the amplitude of the transmitted light overlaps with the valley of the skirt portion of the adjacent transmitted light, the intensity becomes weak and the contrast deteriorates.

In the light intensity distribution of this embodiment shown in FIG. 4 (C), compared to the conventional example shown in FIG. 4 (F), the parts with smaller amplitudes are not added in amplitude, and the intensity is proportional to the square. The addition of the light and the fact that the light with the positive amplitude and the light with the negative amplitude do not cancel each other even if they overlap each other can prevent the deterioration of the contrast.

FIG. 5 shows the results of contrast calculation in this example and the conventional example. The optical conditions of the exposure system are the same as in the above embodiment. The horizontal axis represents the pitch of the line-and-space pattern on the wafer image plane in μm, and the vertical axis represents the contrast.

A curve u shows the contrast of this embodiment when σ is 0.3, and a curve v shows the contrast of the conventional example when σ is 0.55. It can be seen that the contrast of this example is higher than that of the conventional example. For example, when the pitch of the line and space pattern is 0.25 μm,
While the contrast is about 20% in the conventional example, it is improved to about 62% in this embodiment.

In the above embodiment, the polarization axis direction of the transmitted light is
Although it is arranged to be parallel and at right angles to the direction of the first line and space pattern, it may be arranged in another direction. For example, the second line-and-space pattern may be formed so as to form an angle of 45 ° with the first line-and-space pattern, and the polarization axis directions of the lights passing through the space parts adjacent to each other may be orthogonal to each other. .

The first and second line-and-space patterns can be produced, for example, by patterning the same metal layer with one mask. Further, a member having a polarization effect may be provided not on the pattern surface of the mask but on the entire glass surface of the back surface.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0058]

As described above, according to the present invention,
A fine pattern can be formed without lowering the throughput, and a high-speed, highly integrated semiconductor device can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an exposure apparatus used in an embodiment of the present invention.

FIG. 2 is a plan view of a mask pattern according to an embodiment of the present invention.

FIG. 3 is a graph showing a calculation result of contrast according to an embodiment of the present invention.

4A is a plan view of a mask pattern according to another embodiment of the present invention and FIG. 4B is a graph showing the amplitude and intensity of light on an image plane.

FIG. 5 is a graph showing a calculation result of contrast according to another embodiment of the present invention.

FIG. 6 is a schematic diagram for explaining an exposure technique using a phase difference.

FIG. 7 is a schematic diagram for explaining a phase shift mask.

FIG. 8 is a schematic diagram for explaining a difference in image forming ability due to polarization.

[Explanation of symbols]

 1 Light source 2 Reflector 3 Fly-eye lens 7, 7a, 7b, 32 Mask 8, 33 Projection lens 9 Wafer 12a, 12b, 12c, 12d, 12e Space part 13, 24 Phase shifter 15, 25a, 26a, 36 -1 Next time Folding light 16, 25b, 26b, 37 1st-order diffracted light 21a, 21b, 25, 26 Light beam 22 Transparent substrate 23 Light-shielding metal film 25c, 26c, 35 0th-order diffracted light 31 Condenser lens 34 Central light beam

Claims (5)

[Claims] 1. An optical mask having a light-shielding portion that shields exposure light and an opening that allows exposure light to pass through, wherein the entire surface of the optical mask is made of a conductive light-shielding material, and the pitch is about the wavelength of the exposure light or less. An optical mask provided with stripes having. 2. An optical mask having a light-shielding portion for shielding exposure light and an opening for transmitting exposure light, wherein the opening is formed of a conductive light-shielding material and has a pitch of about a wavelength of the exposure light or less. An optical mask provided with stripes having. 3. The opening has a shape elongated in one direction and is repeatedly arranged in another direction at a right angle to the one direction, and the direction of the stripe is parallel to the other direction. The optical mask according to claim 1 or 2, which is characterized in that. 4. The opening has a shape elongated in one direction and is repeatedly arranged in another direction at a right angle to the one direction, and the alternatingly arranged openings are provided with alternating phases. A member for shifting is provided.
3. The optical mask according to any one of 3 above. 5. The openings have a shape elongated in one direction and are repeatedly arranged in another direction perpendicular to the one direction, and the directions of the stripes provided in the adjacent openings are mutually opposite. The optical mask according to claim 2, which are orthogonal to each other.