JPH06130646A - Pattern formation and mask - Google Patents

Abstract

PURPOSE:To provide the pattern formation which can improve contrast while a subpeak is suppressed small in the transfer technology which uses a phase shift mask with a fine pattern of a super LSI, etc. CONSTITUTION:The pattern formation in which patterns which are arrayed at least in one direction are transferred by using a phase shift mask includes a process wherein exposure is performed by using a phase shift mask whose main hole 1 and phase shifters 2 and 3 on it are reduced size in the array direction of the patterns on the basis of a desired pattern as compared with those in other directions and a process wherein development is carried out at such a level that the light of interference between the phase shifter 2 and 3 is not developed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure technique, and more particularly to a transfer technique using a phase shift mask having a fine pattern such as VLSI.

In order to improve resolution in photolithography, a phase shift mask that actively utilizes interference of light waves to form a pattern has attracted attention.

[0003]

2. Description of the Related Art In photolithography, the resolution of a lens depends on the wavelength of light used. Even if an attempt is made to transfer a small pattern, the light spreads outside the pattern due to diffraction, and the size that can be resolved is limited.

The phase shift mask is a technique for improving resolution by using lights having different phases. For example, a phase shifter for generating light of opposite phase is provided around the main hole corresponding to the hole pattern to be transferred so as to compensate the diffracted light of the light transmitted through the hole pattern. The light arriving from the main hole and the light arriving from the phase shifter have different phases (for example, opposite phases), and the light intensity decreases. In this way, by using the phase shift mask, a resolution that has been impossible in the past has been obtained.

FIG. 2 shows an example of a conventional phase shift mask. FIG. 2A shows a phase shift mask in which a square main hole 51 of phase π is formed in the central portion, a phase shifter 52 of phase “0” is formed around it, and the periphery thereof is covered with a light shielding portion of Cr. Indicates. This phase shifter has a simple shape and is easy to manufacture.

The phase shifter only needs to be able to compensate the diffracted light from the main hole, and does not have to be in contact with the main hole. In FIG. 2B, four phase shifters 53 having the same length as the sides of the main hole 51 are arranged along each side of the square main hole 51 of phase π and at a predetermined distance from the main hole 51. The configuration is shown. Around the main hole 51 and the phase shifter 53 is a light shielding film such as Cr. The periphery of the main hole and the phase shifter face each other with almost the same length, and the corner resolution is also high.

In the case of transferring a repetitive pattern of minute patterns in a VLSI or the like, if a phase shifter is provided around each pattern, a sub-peak may occur between desired patterns. It is considered that the sub-peaks are generated because the lights reaching from the phase shifter are strengthened each other.
Therefore, when the sub-peak occurs, the width of the phase shifter is reduced to prevent the sub-peak from occurring.

[0008]

When the optimum phase shifter is provided, the effect itself of the phase shifter is reduced and the contrast is sufficiently improved if the width of the phase shifter is narrowed when a sub-peak occurs. It gets harder. Therefore, the effect of the phase shifter cannot be sufficiently exerted to suppress the sub-peak.

An object of the present invention is to provide a pattern forming method capable of improving the contrast while keeping the sub-peak small.

[0010]

A pattern forming method of the present invention is a pattern forming method for transferring a pattern arranged side by side in at least one direction using a phase shift mask, when a desired pattern is used as a reference, A step of exposing using a phase shift mask in which the size of the main hole on the phase shift mask is reduced in the direction in which the patterns are arranged in comparison with other directions, and a step of developing at a level where the interference light of the phase shifters does not develop Including and

[0011]

When transferring patterns arranged side by side in at least one direction, the size of the main hole in the arrangement direction is reduced to obtain a light intensity distribution with a small sub-peak on the image plane and improved contrast. be able to.

[0012]

1 shows one unit of a mask according to an embodiment of the present invention. FIG. 1A shows a mask for transferring a pattern such as a contact hole having substantially the same vertical and horizontal lengths.

A rectangular main hole 1 having a phase π whose horizontal side is set longer than the vertical side surrounds a phase shifter 2 having a phase “0” whose horizontal side is also set longer than the vertical side. . The phase shifter 2 has a rectangular outer shape. Further, the width of the phase shifter is set such that the upper and lower parts which are long in the horizontal direction are narrower than the left and right parts which are long in the vertical direction. A light shielding film 5 covers the periphery of the phase shifter 2. Such unit masks are assumed to be repeatedly arranged in the vertical direction. In addition, it may be arranged two-dimensionally in the horizontal direction as well as in the vertical direction.

FIG. 1 (B) shows the same main hole 1 as shown in FIG. 1 (A) around the main hole 1 with a predetermined distance from the main hole 1.
Four phase shifters 3 are arranged. Phase shifter 3
Has a width that is narrower in the top and bottom that is longer in the horizontal direction than in the left and right that is long in the vertical direction. A region other than the main hole 1 and the phase shifter 3 is covered with the light shielding film 5.

It is premised that the unit masks are also arranged in the vertical direction in the same manner as the unit mask shown in FIG.
In addition, the two-dimensional array may be arranged in the horizontal direction as well as in the vertical direction. In this case, it is assumed that the vertical pitch is shorter than the horizontal pitch.

As described above, when the patterns are continuously arranged, when the distances between the patterns are close to each other, at least the main hole is reduced in a direction closer to each other.
It is even more effective to reduce the width of the phase shifter along with the main hole.

FIG. 3A shows an optical system for transferring the pattern on the mask. The light emitted from the light source 11 is condensed by the condenser lens 12 and illuminates the mask (reticle) 14 via the diaphragm 13. The light passing through the mask 14 is imaged on the projection surface 17 by the projection lens 16. When transferring to a photoresist layer or the like, the photoresist layer is a layer having undulations and thickness. Therefore, not only the light intensity distribution on the projection surface 17 but also the light intensity distribution on the defocus surface 18 defocused from the projection surface 17 becomes a problem.

FIG. 3B shows an example of a device pattern to be formed on a resist layer or the like on a semiconductor substrate. In the illustrated device pattern, basic patterns 22 including contact holes 21 are arranged side by side in the vertical and horizontal directions. The size of the basic pattern 22 is a rectangle whose horizontal length is longer than its vertical length. Basic pattern 22
When the contact holes 21 are arranged in the central portion, the distance between the adjacent contact holes 21 is long in the horizontal direction and short in the vertical direction. In such a case, the resolution in the vertical direction becomes a particular problem.

Hereinafter, the case where the unit mask according to the embodiment of the present invention is used as the mask 14 will be described in comparison with the case where the unit mask according to the conventional technique is used. FIG. 4 shows an example of a unit mask according to an embodiment of the present invention. 4A shows a plan view of the mask, and FIG. 4B shows a light intensity distribution on the projection surface.

In FIG. 4A, in terms of the size on the image plane, the main hole 1 is a rectangle having a horizontal length of 0.8 μm and a vertical length of 0.46 μm, and the phase shifter 2 surrounds the rectangle. Surrounding. The width of the phase shifter depends on its direction. The width of the phase shifter that is long in the horizontal direction is 0.14 μm, and the width of the phase shifter that is long in the vertical direction is 0.22 μm. The outer periphery of the phase shifter 2 is a rectangle of 1.24 μm in the horizontal direction and 0.74 μm in the vertical direction. A light shielding film 5 of Cr or the like covers the periphery of the phase shifter 2.

FIG. 4B shows the light intensity distribution obtained when the unit mask shown in FIG. 4A is projected alone onto the projection surface. The optical system has a numerical aperture NA = 0.5 and a wavelength W of light.
L = 0.365 μm, coherency factor S = 0.3
Shall have.

The pattern on the projection plane obtained by the unit mask is 2.0 μm in each of the vertical direction and the horizontal direction.
Suppose A light intensity distribution that is long in the horizontal direction is obtained on the projection surface according to the shape of the unit mask that is long in the horizontal direction. However, looking at the light intensity distribution in the central part, it can be seen that the shape has changed from a horizontally long shape to a substantially isotropic shape.

FIG. 5 shows an example of a unit mask according to the prior art. FIG. 5A is a plan view of the unit mask.
(B) shows the light intensity distribution obtained on the projection surface. Figure 5
In (A), a square main hole 51 is formed in the central portion, and the periphery thereof is surrounded by a phase shifter 52. The outer periphery of the phase shifter 52 is also square. The outside of the phase shifter 52 is covered with a light shielding film 55 such as Cr. This unit mask corresponds to a dimension of 2.0 μm × 2.0 μm on the image plane.

FIG. 5B shows a light intensity distribution obtained on the projection surface. A four-fold symmetrical light intensity distribution is obtained on the projection surface, depending on the four-fold symmetrical configuration of the mask. The light intensity distribution in the center is almost circular.

Comparing the light intensity distributions of FIGS. 4B and 5B, it can be seen that the unit mask according to the conventional technique is superior in order to obtain a single contact hole. However, the situation changes when such unit masks are continuously arranged in the horizontal and vertical directions.

Hereinafter, in order to obtain a device pattern as shown in FIG. 3 (B), a unit mask has a lateral pitch of 2.0 μm.
A case in which they are arranged at m and a vertical pitch of 1.0 μm will be described. FIG. 6 shows a light intensity distribution on the projection surface obtained when the unit masks shown in FIG. 4A are arranged at a horizontal pitch of 2.0 μm and a vertical pitch of 1.0 μm. The dimensions of each part of the mask and the parameters of the optical system are as described above. It can be seen that each contact hole is decomposed and the light intensity distribution is low between the contact holes.

FIG. 7 is a graph in which the light intensity distribution of FIG. 6 is plotted along the X and Y directions. FIG. 7 (A)
The X-direction light intensity distribution shown in (1) shows a high light intensity at the contact hole portion and a low peak corresponding to the phase shifter at the side portion thereof. When the main peak is about 1.2, the sub peak is about 0.2. With this level of strength,
It is easy to develop only the Maypeak without developing the subpeak.

In the light intensity distribution in the Y direction shown in FIG. 7B, peaks with a high light intensity distribution appear at a pitch of 1.0 μm, and one subpeak appears in the middle of each peak. That is, one subpeak is formed by the two phase shifters. When the height of the main peak is 1.2, the height of the sub peak is about 0.15, which is sufficiently low.

FIG. 8 shows the light intensity distribution on the projection plane when the unit mask according to the example of the conventional technique shown in FIG. 5 is used. It can be seen that the light intensity distribution in each contact hole portion is flattened in the lateral direction as compared with the case where the unit mask is used alone, and a considerably high sub-peak is formed between the contact holes.

FIG. 9 is a graph in which the light intensity distribution of FIG. 8 is plotted in the X and Y directions through the center of the contact hole. The light intensity distribution in the X direction shown in FIG. 9 (A) has a lower sub-peak height than the light intensity distribution of the example shown in FIG. 7 (A) and shows excellent performance. However,
A new peak is generated between the sub-peaks corresponding to the phase shifter.

The light intensity distribution in the Y direction shown in FIG. 9B is
It shows that a single, fairly high sub-peak occurs between the main peaks. The intensity of the main peak is about 1.15
Then, the intensity of the sub-peak is about 0.5 or more. In practice, it is difficult to develop only the main peak without developing such sub-peaks, and it can be seen that such a mask is not practical.

As described above, in the semiconductor device or the like, the light intensity distribution is important not only on the projection surface but also on the defocus surface. 10 and 11 show the light intensity distributions on the 0.5 μm defocus surface according to the example of the embodiment.

It can be seen from the plan view of FIG. 10 that substantially the same resolution and contrast are obtained as compared with the plan view of FIG. When this is observed in more detail in FIG. 11, it can be seen that the light intensity distribution of the main peak is slightly reduced, but the light intensity distribution of the sub peak is also reduced, and the contrast is almost the same. This is almost the same in the light intensity distribution in the Y direction shown in FIG.

12 and 13 show an example of the prior art.
7 shows a light intensity distribution on a 0.5 μm defocused surface. Similar to the light intensity distributions on the projection plane shown in FIGS. 8 and 9, a high resolution is obtained in the X direction, but the intensity of the sub-peak becomes high in the Y-direction, and it is not possible to develop after removing the sub-peak. It is practically difficult.

14 and 15 show the light intensity distribution on the 1.0 μm defocus surface when the unit mask according to the example of the embodiment shown in FIG. 4 is used. The light intensity distribution of the main peak is reduced, but the contrast is maintained almost the same. Although a new peak is observed between the sub-peaks, the light intensity distribution is small, which is not a practical problem.

FIGS. 16 and 17 show the light intensity distribution on the 1.0 μm defocus surface when the mask according to the prior art example shown in FIG. 5 is used. It is observed from FIG. 16 that the light intensity distribution in the low illuminance region is considerably deformed. Further, the light intensity distributions in the X direction and the Y direction shown in FIG. 17 show that the sub-peaks are rather reduced.
However, the Y-direction sub-peak intensity shown in FIG. 17B cannot be said to be sufficiently low.

FIG. 18 shows a unit mask according to another embodiment of the present invention. In FIG. 18A, the phase shifters 2 having different widths are formed around the square main hole 1a. The width of the inter-pattern phase shifter in the vertical direction is narrowed on the assumption that they are densely arranged in the vertical direction. By narrowing the width of the phase shifter 2 in the direction in which the repetition pitch is short, the resolution in the direction in which the repetition pitch is short is improved.

In FIG. 18B, a phase shifter 3 is arranged around the square main hole 1a and apart from the main hole. The length of the phase shifter is equal to the side length of the main hole. The width of the phase shifter 3 is narrowed in the vertical direction on the assumption that the phase shifter 3 is arranged at a short repetition pitch.

Light intensity distributions obtained when the unit masks shown in FIG. 18A are arranged at a repeating pitch of 2.0 μm in the X direction and 1.0 μm in the Y direction are shown in FIGS. 18C and 18D. Since the pitch is long in the X direction, a sufficiently high contrast is obtained. In the Y direction, the sub-peak is considerably developed, but it can be seen that it is considerably improved as compared with the light intensity distribution shown in FIG. 9 (B).

Although the case where the width of the phase shifter is changed depending on the direction has been described, it is also possible to change the size of the main hole depending on the direction and keep the width of the phase shifter isotropic. When the device pattern has different sizes in the X and Y directions, the size of the main hole or / and the phase shifter formed on the mask may be changed from a proportional value in accordance with the repeating pitch.

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 changes, improvements, combinations and the like can be made.

[0042]

As described above, according to the present invention,
It is possible to suppress the occurrence of subpeaks due to interference between the phase shifters.

[Brief description of drawings]

FIG. 1 is a plan view showing the shape of a unit mask according to an embodiment of the present invention.

FIG. 2 is a plan view showing a shape of a unit mask according to a conventional technique.

FIG. 3 shows an exposure system for performing transfer. 3A is a schematic diagram showing an optical system, and FIG. 3B is a schematic plan view showing a device pattern.

FIG. 4 shows an example of a unit mask according to an embodiment of the present invention.
FIG. 4A is a plan view showing the configuration, and FIG. 4B is a contour diagram showing the light intensity distribution on the projection surface.

FIG. 5 shows an example of a unit mask according to a conventional technique. Figure 5
5A is a plan view showing the configuration, and FIG. 5B is a contour diagram showing the light intensity distribution on the projection surface.

FIG. 6 is a contour diagram showing a light intensity distribution on a projection surface according to an example of the present invention.

7 is a graph plotting the light intensity distributions in the X and Y directions of the light intensity distribution shown in FIG.

FIG. 8 is a contour diagram showing a light intensity distribution on a projection surface according to an example of a conventional technique.

9 is a graph in which the light intensity distributions in the X direction and the Y direction of the light intensity distribution of FIG. 8 are plotted.

FIG. 10 is a contour diagram showing a light intensity distribution on a 0.5 μm defocus surface according to an example of the present invention.

11 is a graph plotting the light intensity distributions along the X and Y directions of the light intensity distribution of FIG.

FIG. 12 is a contour diagram showing a light intensity distribution on a 0.5 μm defocus surface according to an example of a conventional technique.

13 is a graph in which the light intensity distributions along the X direction and the Y direction of the light intensity distribution of FIG. 12 are plotted.

FIG. 14 is a contour diagram showing a light intensity distribution on a 1.0 μm defocus surface according to an example of an example.

15 is a graph plotting the light intensity distributions along the X and Y directions of the light intensity distribution of FIG.

FIG. 16 is a contour diagram showing a light intensity distribution on a 1.0 μm defocus surface according to an example of a conventional technique.

17 is a graph plotting the light intensity distributions along the X and Y directions of the light intensity distribution of FIG.

FIG. 18 shows another embodiment of the present invention. FIG. 18 (A),
18B is a plan view showing a mask configuration of another embodiment, and FIGS. 18C and 18D are X-direction and Y-direction obtained on the projection surface by the set of unit masks of FIG. 18A. It is a graph of the light intensity distribution along.

[Explanation of symbols]

 1 Main Hall 2, 3 Phase Shifter 5 Light-shielding Film 11 Light Source 12 Condenser Lens 13 Aperture 14 Mask 16 Projection Lens 17 Projection Surface 18 Defocus Surface

Claims (8)

[Claims] 1. At least 1 using a phase shift mask
In a pattern forming method for transferring patterns arranged side by side, when the desired pattern is used as a reference, the size of the main hole (1) on the phase shift mask is compared with other directions in the direction in which the patterns are arranged. Pattern forming method including a step of exposing using a phase shift mask that has been reduced in size, and a step of developing at a level where the interference light of the phase shifters (2, 3) are not developed. 2. At least 1 using a phase shift mask
In a pattern forming method of transferring patterns arranged side by side, when the desired pattern is used as a reference, the width of the phase shifter (2, 3) on the phase shift mask is set in the direction in which the patterns are arranged and in the other direction. A pattern forming method including a step of exposing by using a phase shift mask which is reduced in comparison, and a step of developing at a level where the interference light of the phase shifters (2, 3) are not developed. 3. The pattern is distributed on a two-dimensional plane,
3. The pattern forming method according to claim 1, wherein the reduction is set smaller as the distance between the patterns is shorter. 4. A pattern forming method for forming a two-dimensional distributed hole pattern, wherein a repeating pitch in the X direction is longer than a repeating pitch in the Y direction, and a phase is set with respect to a ratio of a dimension of the desired hole in the X direction to a dimension of the Y direction. A pattern forming method including a step of performing exposure using a phase shift mask in which a dimension of a main hole on a shift mask in an X direction is set to be larger than a dimension in a Y direction. 5. A pattern forming method for forming a two-dimensional distribution hole pattern, wherein a repeating pitch in the X direction is longer than a repeating pitch in the Y direction, in a phase shifter formed on a side portion of the main hole in the Y direction and long in the X direction. A pattern forming method including a step of performing exposure using a phase shift mask whose width is set to a side portion of the main hole in the X direction and set to be narrower than the width of a phase shifter long in the Y direction. 6. The pattern forming method according to claim 4, wherein each hole of the hole pattern has an X direction length and a Y direction length that are substantially equal to each other. 7. A phase shift mask for transferring a two-dimensional distribution hole pattern, wherein a repeating pitch in the X direction is longer than a repeating pitch in the Y direction, the ratio of the dimension in the Y direction to the dimension in the X direction of a desired hole. On the other hand, the phase shift mask in which the dimension in the Y direction is smaller than the dimension in the X direction of the main hole on the phase shift mask. 8. A phase shift mask for transferring a two-dimensional distribution hole pattern, wherein a repeating pitch in the X direction is longer than a repeating pitch in the Y direction, the mask being formed on a side portion of the main hole in the Y direction and extending in the X direction. A phase shift mask in which the width of the long phase shifter is formed on the side of the main hole in the X direction and is set narrower than the width of the long phase shifter in the Y direction.