JP3466488B2 - Photo mask - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used when forming a fine pattern on a semiconductor device.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, a mask used for transferring a pattern to a resist is Kr.
When using ultraviolet light (DUV) such as F or ArF, a chrome / quartz mask is used, and when using X-ray, Au /
Si (or W / SiC) or the like is used. DU
In the V mask, a material (chrome) that shields light is formed on a material (quartz) that has a property of transmitting light, and the resist is patterned to have a desired shape. Normally, the shape of the mask is the same as or similar to the shape of the pattern formed on the resist.

Further, when the pattern of the semiconductor element has a size less than the resolution limit of the exposure wavelength, phenomena such as rounded corners of the right-angled pattern (other lines are shortened, pattern thinning, etc.) are remarkable. Become. As a method of preventing the deterioration of the pattern, there is a method of using an auxiliary pattern or making a cutout portion in the pattern. This technique is a method of obtaining a desired resist transfer pattern by partially deforming the shape of the mask in anticipation of pattern deterioration.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 58-200238, a pattern of a square or rectangular pattern is provided at right angles to four corners by providing an auxiliary pattern having a size equal to or smaller than a resolution limit and not transferring a resist alone. The curl of the corner is suppressed. In addition, JP-A-4
According to Japanese Patent Laid-Open No. 161956, if the corner of the pattern is 0 to 180 degrees, the corner of the mask is smaller than the corner of the pattern to be formed.
If the angle is 80 to 360 degrees, a method of applying correction so that the corner of the corner of the mask is larger than the corner of the pattern to be formed is used.

On the other hand, there is a technique of using a phase shifter in order to improve the resolution when the pattern of the semiconductor element is about the resolution limit of the exposure wavelength or less. In the phase shift technology, a part that is normally transmitted and a part that is in the opposite phase (the phase is shifted by 180 °) are formed in the opening, and at the boundary, the optical amplitudes interfere with each other and cancel each other. Get the resolution.

A typical example of the phase shift technique is a Levenson type phase shifter. This technique inverts the phase of one of the two light-transmitting portions sandwiching the light-shielding portion to obtain a high resolution (for example, Japanese Patent Laid-Open No. 62-50).
No. 811, etc.). Further, as a technique of using the phase shifter as an auxiliary pattern, for example, Japanese Patent Application Laid-Open No. 3-8934.
In Japanese Patent Laid-Open No. 6-26, there is proposed a technique of using a phase shifter whose resolution is less than or equal to the resolution limit of the projection optical system used for the outermost pattern of the linear light-transmitting portion group which is present in proximity to a plurality. As a technique to which the technique of both the auxiliary pattern and the phase shifter is applied, there is, for example, a technique of obtaining a desired rectangular pattern (JP-A-4-05656).

Now, a mask without correction is shown in FIG.
FIG. 8B shows the result obtained by simulation of the light intensity contour map of the positive resist pattern transferred when the mask of FIG. 8A is used. The conditions of the projection optical system are: exposure wavelength: 248 [nm] (KrF excimer laser), NA: 0.6, coherent factor σ:
0.45, 1/5 reduction projection system, line width 0.18 [μ
m] was used. The following simulation uses the same optical condition as this.

As shown in FIG. 8B, in the line corner portion of the light shielding portion 1, the light intensity is strengthened by the light diffraction effect on the outer side 1a, so that the resist pattern transferred to the resist is inside the line corner portion. Curl toward. Further, in the inner side 1b, similarly, due to the diffraction effect of light, since it does not have a sufficient light intensity to expose the resist in the region which is originally the light transmitting part 1, the inner side 1b is also rounded toward the inside of the line corner part.

On the other hand, in the conventional method, correction is performed by deforming the mask shape. FIG. 9 shows an embodiment of the conventional method for correcting the mask shape of FIG. FIG. 9A shows an example of the shape of the mask. The shape of the light-shielding portion 1 of the mask is such that an auxiliary, for example, a key-shaped pattern 3 is provided outside the corner portion of the line and a cutout portion 5 is provided inside. Is being transformed. FIG. 9 (b) shows the result obtained by simulation of the contour map of the light intensity transferred to the resist. It can be seen that the rounding at the line corner portion is suppressed as compared with FIG. 8B.

[0010]

However, in the conventional method, there is a problem that the mask shape becomes complicated in order to carry out the correction, especially when a fine pattern is supplementarily provided outside the corner portion.

In the present invention, both the features that the aperture has a light-shielding property when the size is equal to or less than the resolution limit of the exposure wavelength and the phase shifter has an effect of improving the resolution at the same time. In addition, a phase shifter is provided as an auxiliary pattern at the mask corner so that it can be effectively used. As a result, firstly, it is possible to obtain a sharper transfer pattern while obtaining the same effect as the conventional method, and secondly, it is possible to obtain the effect of the conventional level (or more) with a simple shape.

[0012]

According to a first aspect of the present invention, in a photomask used for forming a fine pattern of a semiconductor element, a pattern at a corner portion of the mask is prevented from being rounded at a corner portion of the mask. an auxiliary phase shifter of the following size resolution limit of the projection optical system the mass
The photomask is characterized in that it is provided at a position not protruding from the corner portion .

According to a second aspect of the present invention, a mask corner is provided.
Prevents the inner pattern from being rounded inside the part
The cutout according to claim 1, wherein the cutout is provided.
Is a photo mask of.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.

[Embodiment 1] FIG. 1A shows an example of the shape of a photomask according to an embodiment of the present invention.

In this embodiment, in order to solve the above-mentioned problems,
The auxiliary phase shifter 4 having a minute opening is provided at a position not protruding from the mask corner portion in the mask corner portion . In order to prevent the inner pattern from being rounded inside the line corner portion, the notch 5 is provided in the light shielding portion of the mask as in the conventional method. Figure 1 (b) shows
The result of having obtained the contour map of the light intensity transferred to the resist by simulation is shown. It can be seen that the rounding at the mask corner portion is suppressed as compared with FIG. 8B.

Also, in the above, the aperture phase shifter 4
The transmitted light that has passed through is in a phase opposite to that of the transmitted light of the light transmitting unit 2. If the size of the phase shifter 4 is appropriately selected so as to be equal to or smaller than the resolution limit of the projection optical system,
It is not possible to transmit all the projection light, and it is possible to have the function as the light shielding unit 1 rather than the light transmitting unit 2. Therefore, the pattern is not cut in the portion where the phase shifter 4 which is the opening in FIG. 1A is provided. Further, the transmitted light that has passed through the phase shifter 4 to such an extent that the resist is not exposed has an antiphase relationship with the transmitted light that has passed through the transparent portion (2) of the mask.
Therefore, since the transmitted lights interfere with each other at the boundary, the gradient of the light intensity becomes steep and the resolution is improved.

The above effect is shown in FIG. In FIG. 2, the mask is not changed (FIG. 8 (a) AA ′), the conventional method (FIG. 9 (b)).
BB ′) and a graph plotting the light intensities in the present example (FIG. 1 (a) CC ′). Graph X shows no change in the mask, graph Y shows the conventional light intensity, graph Z shows the respective light intensities of this embodiment, and the hatched line shows the position of the desired transfer pattern. FIG. 2 directly shows the effect of this embodiment. That is, since the phase shifter 4 in this embodiment has a light-shielding property, the phase shifter 4 has the same effect as the conventional method using the auxiliary pattern (see reference numeral 3 in FIG. 9), and the effect of the phase shifter reduces the gradient of the light intensity. It is steep. Although the KrF excimer laser is assumed as the exposure light source in the simulation, the same effect can be obtained by using an ArF excimer laser or another light source having a different exposure wavelength.

Further, the shape of the mask pattern according to the conventional method shown in FIG. 9A and the shape of the mask pattern in this embodiment shown in FIG. 1A are compared. In the conventional method, a step due to the auxiliary pattern 3 is formed on the outer side 1a of the line corner portion, but in the present embodiment, the step is not formed on the outer side 1a of the line corner portion, and the mask shape can be simply formed.
In the case of a minute and complicated mask pattern, even if it is a normal pattern, it may be erroneously detected as a contaminant or a pseudo defect during the mask inspection, which is a problem. According to this embodiment, since the mask shape can be simplified, it is possible to reduce erroneous measurement during mask inspection.

The above-mentioned pattern shown in FIG. 1A shows a characteristic pattern of the present invention.
The same applies to the pattern shown in ( c ).

[Reference Example 1] FIG. 3A shows a phase shifter 4 having the same shape as the corner portion, that is, a simple rectangular phase shifter 4 arranged and formed in the mask corner portion. In Figure 4,
Graph X: No change in mask (Fig. 8 (a) AA '),
Graph Y: Conventional method (FIG. 9 (b) BB ′), Graph Z:
A plot of the light intensity in this example (FIG. 3A) is shown . Since the phase shifter 4 shown in FIG. 3A has a rectangular shape and is larger in size than others, not only can the mask be simplified, but there is an advantage that the influence of contaminants can be reduced when the mask is formed.

Reference Example 2 FIG. 3B shows a conventional method (see FIG. 9).
The structure is similar to that of (a), except that the auxiliary pattern 3 on the outer side 1a is replaced by the phase shifter 4. In FIG. 5, there is no change in the mask (FIG. 8 (a) A-
A ′), the conventional method (FIG. 9 (b) BB ′), this embodiment (FIG. 3)
Graph X plotting the light intensity in (b)),
Y and Z are shown. As shown in FIG. 5, even in the pattern example shown in FIG. 3B, the gradient of the light intensity is steeper than that of the conventional method due to the effect of the phase shifter, and the light wraparound is small even though the auxiliary pattern has the same size. You can see that Therefore, it is possible to more effectively serve as the auxiliary pattern as compared with the conventional method.

[Embodiment 2] FIG. 3C considers a case where the correction amount of the outer portion of the mask corner portion is too large, and the phase shifter 4 is arranged and formed at a position not protruding from the mask corner portion. It was done. In FIG. 6, the mask is not changed (FIG. 8 (a) AA ′) and the conventional method (FIG. 9) is used.
(B) BB ') and graphs X, Y, and Z in which the light intensities in this example (FIG. 3C) are plotted are shown. Figure 3
In FIG. 3C, the correction amount is smaller than that in FIG. 3B, but since the gradient of the light intensity is steep, a sharp transfer effect can be obtained as in the pattern example of FIG. 3B.

Reference Example 3 In FIG. 3D, as is apparent from comparison with the pattern example of FIG. 1A, the mask corner portion has a dimension larger than the vertical line width.
A slightly larger phase shifter 4 is arranged and formed. In the case of such a shape, since the phase shifter has a large size, the light intensity becomes large in the pattern. In this case, the light intensity in the pattern can be weakened by setting the transmittance of the phase shifter 4 to 1.0 or less. In FIG. 7, the mask is unchanged (FIG. 8 (a) AA ′), and the conventional method (FIG. 9) is used.
(B) BB ′) and graphs X, Y, and Z (1, 2) in which the light intensities in this example (FIG. 3D) are plotted are shown. Z1 is the simulation result when the transmittance of the phase shifter 4 is 1.0 and Z2 is 0.5 in the pattern of FIG. 3D. The transmittance is 1.
Since the light intensity in the pattern is suppressed as compared with the case of 0, the resist is hard to be exposed in the pattern, and the disconnection of the pattern is less likely to occur. It is needless to say that both of them can obtain a sharper pattern than the conventional method because the gradient of the light intensity is steep as shown in FIG.

[0025] In FIG. 3, to prevent the inner pattern of the mask corners of the photomask rounded, cut arranged in the light shielding part 2 or the corner portion of the mask corners, formed was a phase shifter 4 The notch 5 is provided.

The above, illustrated, or has been omitted, the shape of a photomask satisfying the above-mentioned effects, the sequence of the phase shifter, in addition to the shape example if formed Figs. 1 (a) and 3 (c) Various things are possible.

[0027]

As described above, according to the photomask of the present invention , when the pattern is transferred to the resist in the manufacturing process of the semiconductor device, the corner portion of the line pattern is rounded. As compared with the conventional improved method using the auxiliary pattern, a sharp transferred image can be obtained, and the mask pattern having a simple structure can prevent the deterioration of the transferred pattern shape and obtain a pattern close to a desired one.

Further , in the conventional method, outside the line corner portion.
Although the step by the auxiliary pattern is formed, it engaged with the present invention
According to the photo mask, a step is formed outside the line corner.
And the mask shape can be simply formed.
Therefore, it is possible to reduce erroneous measurement at the time of mask inspection.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram for explaining the characteristics of FIG.

FIG. 3 is a diagram illustrating a reference example and another shape example of the present invention.

FIG. 4 is a diagram for explaining the characteristics of FIG.

FIG. 5 is a diagram for explaining the characteristics of FIG. 3 (b).

FIG. 6 is a diagram for explaining the characteristic of FIG.

FIG. 7 is a diagram for explaining the characteristic of FIG.

FIG. 8 is a diagram illustrating a conventional example in which the mask shape is not changed.

FIG. 9 is a diagram for explaining a conventional example in which a mask shape is improved.

[Explanation of symbols]

1 light shield 2 Translucent part 4 phase shifter 5 notches

Claims (2)

(57) [Claims] 1. A photomask used for forming a fine pattern of a semiconductor element, which prevents the pattern at the mask corner from being rounded at the mask corner, and has an auxiliary size smaller than the resolution limit of the projection optical system. Up phase shifter
A photomask, characterized in that it is provided at a position not protruding from the mask corner portion . 2. A putter on the inside of the mask corner portion.
With cutouts to prevent rounding
The photomask according to claim 1, wherein the photomask is a photomask.