JP2000105451A - Photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deformation of a pattern at a mask corner part at the time of transferring the pattern in a photomask used when the minute pattern of a semiconductor element is formed. SOLUTION: In the photomask used when the minute pattern of the semiconductor element is formed, an auxiliary phase shifter 4 which prevents the pattern at the mask corner part from being rounded and has size smaller than resolution limit of a projection optical system is provided at the mask corner part. Thereby a transferring pattern of more sharpness can be obtained while obtaining a similar effect as by a conventional method to enable obtaining similar effect as in a conventional one (or more effect than in the conventional one) by a simple form.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for forming a fine pattern of 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.
A chromium / quartz mask is used when ultraviolet light (DUV) such as F or ArF is used, and an Au / quartz mask is used when X-rays are used.
Si (or W / SiC) or the like is used. DU
In the V mask, a material (chrome) for shielding light is formed on a material (quartz) having a property of transmitting light, and the resist is patterned so as to have a desired shape. Usually, the shape of the mask is the same or similar to the shape of the pattern formed on the resist.

Further, when the pattern of the semiconductor element has a size smaller than the resolution limit of the exposure wavelength, phenomena such as the corner portion of the right-angled pattern becoming round (other lines become shorter, the pattern becomes thinner, etc.) become remarkable. Become. As a method of preventing the deterioration of the pattern, there is a method of using an auxiliary pattern or a method of forming a notch in the pattern. This technique is a method of obtaining a desired resist transfer pattern by partially deforming the shape of a mask in anticipation of pattern deterioration.

For example, in Japanese Patent Application Laid-Open No. 58-200338, an auxiliary pattern which is smaller than the resolution limit and which does not transfer a resist alone is provided at a right angle of the four corners of a square or rectangular pattern. The rounded corners are suppressed. In addition, Japanese Unexamined Patent Application Publication No.
According to Japanese Patent Application Laid-Open No. 161956, when the corner of the pattern is 0 to 180 degrees, the corner of the corner of the mask is made smaller than the corner of the pattern to be formed.
When the angle is 80 to 360 degrees, a method is used in which correction is performed so that the corner of the corner of the mask is made larger than the corner of the pattern to be formed.

On the other hand, there is a technique using a phase shifter 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 technique, a portion having a phase opposite to that of a normally transmitted portion (a phase is shifted by 180 °) is formed in an aperture, and at the boundary, the light amplitudes interfere with each other and cancel each other out, thereby achieving a high level. Get the resolution.

A typical example of the phase shift technique is a Levenson type phase shifter. According to this technique, a high resolution is obtained by inverting the phase of one of the two light-transmitting portions sandwiching a light-shielding portion therebetween (for example, see Japanese Patent Application Laid-Open No. Sho 62-50).
No. 811). Further, as a technique of using a phase shifter as an auxiliary pattern, for example, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 6-26204 proposes a technique using a phase shifter that is equal to or less than the resolution limit of a projection optical system used for the outermost pattern of a plurality of linear light-transmitting portions existing in close proximity to each other. As a technique to which both the auxiliary pattern and the phase shifter are applied, for example, there is a technique for obtaining a desired rectangular pattern (JP-A-4-05656).

FIG. 8A shows a mask that is not corrected.
FIG. 8B shows the result of a simulation of a contour map of the light intensity of the positive resist pattern transferred when the mask shown in FIG. 8A is used. The conditions of the projection optical system are as follows: exposure wavelength: 248 [nm] (KrF excimer laser), NA: 0.6, coherent factor σ:
0.45, 1/5 reduction projection system, line line width 0.18 [μ
m] was used. In the following simulations, the same optical conditions are used.

As shown in FIG. 8 (b), at the line corners of the light-shielding portion 1, the light intensity is increased on the outer side 1a due to the diffraction effect of light, so that the resist pattern transferred to the resist is on the inner side of the line corners. Curl towards. Similarly, in the inner side 1b, since the light intensity is not sufficient to expose the resist in the region that originally becomes the light transmitting portion 1 due to the light diffraction effect, the light is also rounded toward the inside of the line corner portion.

On the other hand, in the conventional method, correction is performed by deforming the mask shape. FIG. 9 shows an embodiment of correction by the conventional method for the mask shape of FIG. FIG. 9A shows an example of the shape of the mask, in which a supplementary, for example, key-shaped pattern 3 is provided outside the corner of the line, and a cutout 5 is provided inside the mask. Is deformed. FIG. 9B shows a result of a contour map of the light intensity transferred to the resist obtained by simulation. It can be seen that the rounding at the line corner is suppressed as compared with FIG.

[0010]

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

According to the present invention, both the features of having a light-shielding property even when the size of the aperture is smaller than the resolution limit of the exposure wavelength, and that the phase shifter has the function of improving the resolution are simultaneously obtained. A phase shifter is provided as an auxiliary pattern at a mask corner so as to be used effectively. 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 an effect of a conventional shape (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. A photomask comprising an auxiliary phase shifter having a size smaller than the resolution limit of the projection optical system.

According to a second aspect of the present invention, in the photomask according to the first aspect, the phase shifter is disposed and formed outside a corner portion of the mask.

According to a third aspect of the present invention, in the photomask according to the first aspect, the phase shifter is arranged and formed in a rectangular shape at a corner of the mask.

According to a fourth aspect of the present invention, the phase shifter is formed at a mask corner portion to be larger than the corner portion shape, and the transmittance of the phase shifter is 1 or less. 3. The photomask according to 3.

According to a fifth aspect of the present invention, a notch is provided inside the corner of the mask to prevent the inner pattern from being rounded. Photomask.

[0017]

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

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

In this embodiment, in order to solve the above-mentioned problem,
An auxiliary phase shifter 4 with a minute opening is provided at the mask corner. It is the same as the conventional method to provide the notch 5 in the light-shielding portion of the mask in order to prevent the inner pattern from being rounded inside the line corner portion. FIG.
(B) shows the result of a contour map of the light intensity transferred to the resist obtained by simulation. FIG. 8B
It can be seen that the rounding at the mask corner is suppressed as compared with FIG.

In the above, the phase shifter 4 having the aperture
The transmitted light transmitted through the light-transmitting portion 2 has an opposite phase to the transmitted light of the light transmitting portion 2. If the size of the phase shifter 4 is appropriately selected to be smaller than the resolution limit of the projection optical system,
It is not possible to transmit all of 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 at the portion where the phase shifter 4 which is the opening in FIG. 1A is provided. Further, the transmitted light transmitted through the phase shifter 4 to such an extent that the resist is not exposed has an opposite phase relationship to the transmitted light transmitted through the light transmitting portion (2) of the mask.
Therefore, at the boundary, transmitted light interferes with each other, so that the gradient of light intensity becomes steep, which leads to improvement in resolution.

The above effect is shown in FIG. FIG. 2 shows no change in the mask (FIG. 8A, AA '), and the conventional method (FIG. 9B).
BB ′) and a graph in which the light intensity in the present example (FIG. 1A, CC ′) is plotted. The graph X shows no change in the mask, the graph Y shows the conventional method, the graph Z shows the light intensity of this embodiment, and the oblique lines show the positions of the desired transfer patterns. FIG. 2 simply shows the effect of this embodiment. That is, since the phase shifter 4 in the present embodiment has a light shielding property, it has the same effect as the conventional method using the auxiliary pattern (see reference numeral 3 in FIG. 9), and the gradient of the light intensity is reduced by the effect of the phase shifter. It is steep.
In the simulation, a KrF excimer laser was assumed as an exposure light source, but 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 will be compared. In the conventional method, a step due to the auxiliary pattern 3 is formed on the outside 1a of the line corner, but in this embodiment, no step occurs on the outside 1a of the line corner, and the mask shape can be simply formed.
In the case of a fine and complicated mask pattern, even if it is a normal pattern, it may be erroneously detected as a contaminant or a pseudo defect at the time of mask inspection. According to the present embodiment, since the mask shape can be simplified, erroneous measurement at the time of mask inspection can be reduced.

The pattern shown in FIG. 1A shows a characteristic pattern of the present invention, and FIG.
The same applies to the patterns shown in (a) to (d).

FIG. 3A shows a phase shifter 4 having a shape as it is, that is, a simple rectangular shape, arranged and formed in a mask corner portion. In FIG. 4, graph X: no change in mask (FIG. 8 (A) AA ′), graph Y: conventional method (FIG. 9 (b) BB ′), graph Z: this embodiment (FIG. The figure which plotted the light intensity in a)) is shown.
As is clear from FIG. 4, the same effect as in the embodiment of FIG. 1 is obtained, and the phase shifter 4 shown in FIG.
Since the shape is rectangular and the size is larger than others, there is an advantage that not only the mask can be simplified, but also the influence of contaminants at the time of forming the mask can be reduced.

Although the pattern is not as simple as the conventional method, if it is desired to sufficiently improve the resolution as compared with the conventional method and if the shape of the transfer pattern can be made close to the desired pattern, a mask pattern is required. Is not simple, but pattern examples as shown in FIGS. 3B to 3D are also preferable.

FIG. 3B is similar in structure to the conventional method (see FIG. 9A), except that the auxiliary pattern 3 on the outer side 1a is replaced by the phase shifter 4. In FIG.
Graph X, in which the light intensity was plotted without changing the mask (FIG. 8 (a) AA ′), the conventional method (FIG. 9 (b) BB ′), and the present example (FIG. 3 (b)). Y and Z are shown. FIG.
Accordingly, 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 wraparound of light is reduced even though the auxiliary pattern has the same size. You can see that there is. For this reason, a role as an auxiliary pattern can be provided more effectively than in the conventional method.

FIG. 3C shows a case in which the correction amount of the outer portion of the mask corner is too large, and the phase shifters 4 are arranged and formed at positions not protruding from the mask corner. In FIG. 6, the mask is not changed (FIG. 8A, AA ′), and the conventional method (FIG.
B ′) and graphs X, Y, and Z plotting the light intensity in the present example (FIG. 3C). In FIG. 3C,
Although the correction amount is smaller than that in FIG. 3B, a sharp transfer effect can be obtained similarly to the pattern example in FIG. 3B because the gradient of the light intensity is steep.

FIG. 3 (d) shows that the mask corners are vertical, as is apparent from comparison with the pattern example of FIG. 1 (a).
A slightly larger phase shifter 4 having a size larger than the horizontal line width is arranged and formed. In such a shape, the phase shifter is large in size, so that the light intensity in the pattern increases. In this case, the light intensity in the pattern can be reduced by setting the transmittance of the phase shifter 4 to 1.0 or less. In FIG. 7, the mask is not changed (FIG. 8A, AA '), and the conventional method (FIG.
B ′) and graphs X, Y, and Z (1, 2) plotting the light intensity in the present example (FIG. 3D). Z1 is the pattern of FIG.
0 and Z2 are simulation results when the transmittance of the in-phase shifter 4 is set to 0.5. Since the light intensity in the pattern is suppressed as compared with the case where the transmittance is 1.0, the resist is not easily exposed in the pattern, and the disconnection of the pattern is less likely to occur. In both cases, as shown in FIG. 7, since the gradient of the light intensity is steep, it is needless to say that a sharper pattern can be obtained as compared with the conventional method.

In FIG. 3, in order to prevent the pattern pattern inside the mask corner portion of the photomask from being rounded, a notch is formed in the light-shielding portion 2 at the mask corner portion or the phase shifter arranged and formed at the corner portion. 4
Is provided.

Although not shown or described above, FIG. 1 (a) and FIGS. 3 (a) to 3 (d) show the photomask shape and the phase shifter arrangement and formation which satisfy the above-mentioned effects.
Various shapes other than the above shape examples are possible.

[0031]

As described above, according to the mask according to the present invention, the conventional auxiliary pattern is used to solve the problem that the corners of the line pattern are rounded when the pattern is transferred to the resist in the manufacturing process of the semiconductor device. A sharper transfer image can be obtained as compared with the improved method to be used, and the transfer pattern shape can be prevented from deteriorating with a mask pattern having a simple structure, and a pattern close to a desired one can be obtained.

[Brief description of the 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 another example of the shape 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 characteristics of FIG. 3 (c).

FIG. 7 is a diagram for explaining the characteristics 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]

 DESCRIPTION OF SYMBOLS 1 Shield part 2 Translucent part 4 Phase shifter 5 Notch

Claims (5)

[Claims] In a photomask used for forming a fine pattern of a semiconductor element, an auxiliary mask having a size equal to or smaller than the resolution limit of a projection optical system is provided at a mask corner to prevent the pattern of the mask corner from being rounded. A photomask comprising a phase shifter. 2. The photomask according to claim 1, wherein the phase shifter is arranged and formed outside a corner of the mask. 3. The photomask according to claim 1, wherein the phase shifter is arranged and formed in a rectangular shape at a corner of the mask. 4. The photomask according to claim 3, wherein the phase shifter is formed at a corner of the mask to be larger than a corner shape, and the transmittance of the phase shifter is 1 or less. 5. The photomask according to claim 1, further comprising a notch inside the corner of the mask to prevent the inner pattern from being rounded.