JP3353124B2 - Phase shift photomask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift photomask used as an original in a reduction projection exposure apparatus.

[0002]

2. Description of the Related Art Conventionally, formation of a fine pattern in a solid-state device such as a VLSI has been mainly performed by a reduced exposure projection method. The above method uses a projection optical system to reduce and form light transmitted through a photomask on which an enlarged wiring pattern is drawn on a resist-coated substrate,
This is for transferring the pattern.

In recent years, as the density of patterns has increased,
A phase shift photomask has been proposed because the interval between patterns becomes smaller, becomes closer to the wavelength of the light source, and lowers the resolution and contrast of the projected image, as disclosed in Japanese Patent Application Laid-Open No. 62-67514. It has been proposed to provide a second opening pattern in a peripheral portion of the pattern to further increase the resolution.

However, in an actual semiconductor manufacturing process, 1 to 1
Although it is necessary to transfer a fine pattern over the entire area of the wafer surface having a step of 2 μm, when a pattern is formed simultaneously at different focus positions with a conventional phase shift photomask, large variations occur in the transferred dimensions. There was a problem that occurred.

[0005]

SUMMARY OF THE INVENTION The present invention provides a phase shift photomask for forming a fine pattern with high dimensional accuracy even at different focus positions as described above.

[0006]

According to the present invention, a light-shielding film 2 made of chrome or the like is provided on a transparent substrate 1 made of quartz or the like.
An opening pattern 4a in which the light shielding film 2 is partially removed;
The first opening pattern 4a is adjacent to the first opening pattern 4a.
And a second opening pattern 4b having a fine width provided in a ring shape and continuously opening so as to surround the first opening pattern 4a and the second opening pattern 4b. This is a phase shift photomask in which a light-shielding film 2c is formed so as to limit transmitted light at the four corners of the second opening pattern 4b in a phase shift photomask provided with the phase shifter layer 3 on one side.

The first opening pattern 4a is generally rectangular, and the second opening pattern 4b is formed in the shape of a rectangular frame close to the first opening pattern 4a. The light-shielding films at the four corners of the portion are left. The degree of adjacency and the line width of the second opening pattern 4b may be within a range in which the second opening pattern 4b is not independently resolved on the wafer, and the light shielding film 2c at the four corners and the second opening pattern may be used. The boundary with the second opening pattern (4b) is formed so as to be approximately 45 ° with respect to one side of the frame as shown in FIG. 1 or at the corner of the second opening pattern (4b) as shown in FIG. It is characterized in that it is formed by an arc-shaped curve projecting outside the photomask connecting two sides.

That is, the adjacent second opening pattern 4b is formed in a ring shape so as to surround the periphery of the first opening pattern 4a, and the light-shielding film at the four corners is formed so that the second opening pattern 4b is resolved and has no adverse effect. 2c, and a phase shifter layer 3 for providing a phase difference of 180 ° to one of the first opening pattern 4a and the second opening pattern 4b is provided.

[0009]

The second opening pattern 4b provided around the first opening pattern 4a is formed in a ring shape so as to leave the light-shielding film 2c at the four corners, and the phase shifter layer 3 providing a phase difference of 180 ° is formed. The depth of focus is increased without resolving the second opening pattern 4b, and the pattern can be transferred with almost the same size regardless of the focus position.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings in comparison with the prior art. (Embodiment 1) FIG. 1 is a plan view for explaining an example of the phase shift photomask of the present invention, in which the boundary between the light shielding film 2c and the second opening pattern 4b at four corners is one side of the opening pattern 4b. Is formed at an angle of approximately 45 ° with respect to. FIG. 3 is a plan view illustrating an example of a conventional phase shift photomask in which the adjacent second opening pattern 4b is non-circular (not annular). FIG. 4 is a plan view illustrating the conventional adjacent second opening pattern 4b. FIG. 2 is a plan view illustrating an example of an annular phase shift photomask. FIG. 5 is a cross-sectional view taken along the line XX of FIG. 1 and, at the same time, a cross-sectional view taken along the line XX of FIGS. 3 and 4. Reference numerals 1 are a transparent substrate, 2 is a light-shielding film, 3 is a phase shifter layer, 4a is a first opening pattern, 4b is a second opening pattern, and in each case, the phase shifter layer 3 is a second opening pattern. Is formed to completely cover the opening pattern 4b. FIG. 6 corresponds to FIGS.
Depth of focus of a stepper at the time of wafer transfer to each phase shift photomask (hereinafter referred to as DOF: Dep)
It is called th Of Pocus. FIG. 4 is an explanatory view illustrating the relationship between the dimensional change on the wafer and the dimensional change.

In this embodiment, a stepper having a wavelength λ = 365 nm, a lens numerical aperture NA = 0.5, and a partially coherent σ = 0.4 is used. In the conventional non-annular (non-annular) phase shift photomask in which the adjacent second opening pattern 4b shown in FIG. O. At the relative light intensity where the dimension on the wafer is 0.4 μm when F = 0, the D.F. O.
When F was changed to 0.4, 0.8, and 1.2 μm, the size tended to decrease. On the other hand, in the case of the phase shift photomask in which the adjacent second opening pattern 4b shown in FIGS. 1 and 4 is annular, the dimension on the wafer is 0.4 μm.
At a relative light intensity of O. F to 0.4, 0.
When it was changed to 8, 1.2 μm, the size tended to increase.

By the way, assuming that the margin (permissible limit) for the dimensional accuracy is 10% of 0.04 μm, in the phase shift photomask of FIG. 1 and FIG. O. Even if F = 1.2 μm, it is within the margin for dimensional accuracy, whereas in the case of a phase shift photomask in which the adjacent second opening pattern 4b in FIG. O. F = 0.
Only up to about 9 μm is allowed.

On the other hand, the phase shift photomask shown in FIG. 4 has a high light intensity at the four corners of the adjacent annular second opening pattern 4b and a relative light intensity at which the dimension on the wafer is 0.4 μm. Whereas the portions corresponding to the four corners are resolved and adversely affect the transfer pattern, the phase shift photomask of the present invention in FIG.
By adjusting the area through which light passes in the shape of c, the four corners of the second opening pattern are resolved and the transfer pattern is not adversely affected, and the focus is equal to or greater than that of the conventional phase shift photomask. Can have a depth. FIG. 7 shows FIG.
FIG. 5 is a diagram comparing light intensities at the time of pattern transfer in cross sections of the phase shift photomasks of FIG. In the phase shift photomask of the present invention shown in FIG.
It can be seen that the light intensity at the four corners of the opening pattern is kept low. (Embodiment 2) FIG. 2 is a plan view for explaining another embodiment of the present invention.
The boundary with b is formed by a curve connecting two sides of the corner of the second opening pattern 4b. This phase shift photomask was able to obtain the same effect as the phase shift photomask of FIG. 1 described above.

As described above, according to this embodiment, the phase shift photomask in which the adjacent second opening pattern 4b is formed in a ring shape so as to leave the light-shielding film 2c at the four corners and the phase shifter layer 3 is provided, It is possible to form a pattern with a small dimensional difference even at different focus positions without resolving the two opening patterns 4b.

[0015]

As described above, in the phase shift photomask of the present invention, it is possible to form a pattern having a small dimensional difference even at different focus positions.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an example of a phase shift photomask of the present invention.

FIG. 2 is a plan view illustrating another embodiment of the phase shift photomask of the present invention.

FIG. 3 is a plan view illustrating an example of a conventional phase shift photomask in which adjacent second opening patterns 4b are non-circular (not circular).

FIG. 4 is a plan view illustrating an example of a conventional phase shift photomask in which adjacent second opening patterns 4b are annular.

FIG. 5 is a sectional view taken along line XX of FIG. 1;

FIG. 6 shows the D.D. of each phase shift photomask of FIGS. 1, 3 and 4; O. It is explanatory drawing which illustrates the relationship between F and the dimensional change on a wafer.

FIG. 7 is a graph showing Y- of each phase shift photomask of FIGS. 1 and 4;
It is the figure which compared the light intensity at the time of pattern transfer in the cross section by Y arrow.

[Explanation of symbols]

 Reference Signs List 1 transparent substrate 2 light-shielding film 2c light-shielding film at four corners 3 phase shifter layer 4 opening pattern 4a first opening pattern 4b second opening pattern

Claims (3)

(57) [Claims] 1. A rectangular or rectangular first opening pattern (4) in which a light shielding film (2) on a transparent substrate (1) is partially removed.
a), the first opening pattern (4a) is adjacent to the first opening pattern (4a) , and is annular and continuous so as to surround the first opening pattern (4a).
A second opening pattern (4b) having a fine width provided so as to open the opening, and one of the first opening pattern (4a) and the second opening pattern (4b) is provided with a phase shifter layer (4). In the phase shift photomask provided with 3), the second
The light-shielding film (2c) is formed so as to remain at the four corners of the opening pattern (4b), and the fine width of the second opening pattern is such that the second opening pattern is formed on the wafer. A phase shift photomask characterized by being in a range that cannot be resolved alone. 2. The boundary between the light-shielding film (2c) at the four corners and the second opening pattern (4b) is formed so as to be approximately 45 ° with respect to one side of the second opening pattern (4b). The phase shift photomask according to claim 1, wherein 3. A boundary between the light-shielding film (2c) at the four corners and the second opening pattern (4b) is defined by the second opening pattern (4).
2. The phase shift photomask according to claim 1, wherein the phase shift photomask is formed by an arc-shaped curve projecting outward from the photomask, connecting the two sides of the corner of b).