JPH05142749A - Mask for exposure - Google Patents

Abstract

PURPOSE:To provide the exposure mask which is applied to an actual integrated circuit pattern to obtain effect and also displays maximum phase shift effect. CONSTITUTION:A transmission part is sectioned into four areas S0-S3, which are a 1st area, a 2nd area having a 90 deg. phase difference from the 1st area, a 3rd area having a 180 deg. phase difference from the 1st area, and a 4th area having a 270 deg. phase difference from the 1st area; when the out-of-phase areas are adjacent at the transmission part, the phase difference between those areas is 90 deg. and when the out-of-phase areas are adjacent to each other across a light shield part, the phase difference between those areas is 180 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure mask,
In particular, it relates to a phase shifter for a lithographic mask.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit, high integration and miniaturization are being pursued, and how to realize this by photolithography with high accuracy is a major issue. For example, when two patterns s1 and s2 are formed very close to each other on the transparent substrate 11 as shown in FIG. 5 (a), the light intensity of the pattern projected through this pattern is as shown in FIG. ), It becomes impossible to clearly distinguish and resolve the patterns s1 and s2. At this time, although the light transmitted through s1 and s2 has the same phase, there is a method for improving the resolution by shifting these phases.

This is called a phase shift method. In an exposure mask having a light-shielding region and a light-transmitting region, a transparent material is superposed on at least one of a pair of light-transmitting regions sandwiching the light-shielding region. This is a mask structure in which a phase difference is generated between the lights transmitted through the respective transmission regions so that these lights do not interfere with each other by interfering with each other in the regions that are originally the light shielding regions of the wafer (Japanese Patent Publication No. 62-59296). Bulletin). That is, this method is intended to improve the pattern accuracy by providing a phase inversion layer in the light transmitting region, removing the influence of light diffraction from the adjacent pattern.

FIG. 6 shows this principle. As shown in FIG. 6A, this mask is transparent as a phase shifter 13 formed between mask patterns 12 made of chromium (Cr) or chromium oxide (Cr ₂ O ₃ ) formed on a quartz substrate 11. Using a mask with a film formed, the phase of this part is inverted as shown in Fig. 6 (b) and the amplitude of the light cancels out the light of phase 0 ° and phase 180 ° at both ends of the transmission part, and the light intensity decreases. The contrast is improved (Fig. 6 (c)). As a result, the light intensity at both ends of the transmission part is almost zero.
Thus, as shown in FIG. 6 (d), the patterns formed on the wafer can be separated by the two transmissive portions.

Among the phase shift methods, there is a Levenson type phase shifter in which two adjacent light transmitting portions are alternately provided with a phase difference of 180 degrees. With this method, it is difficult to exert an effect when three or more patterns are adjacent to each other. That is, when the optical phase difference between the two patterns is 180 degrees, the other pattern has the same phase as one of the previous two patterns, and as a result, the patterns having a phase difference of 180 degrees are resolved, but the phase difference is 180 degrees. There is a problem in that 0-degree patterns are unresolved with each other. In order to solve this problem, it is necessary to consider the device design fundamentally, and it is quite difficult to put it into practical use immediately.

For example, as shown in FIG. 7, a region 13 having a phase difference of 180 degrees and a region 14 having a phase difference of 0 degrees.
When and are arranged with the light shield 15 interposed therebetween, the region 13 having a phase difference of 180 degrees is also in contact with the outer region which should be the transmission region.
There is a problem that light is not transmitted between 6 and 17, so a method of solving this problem is to add a region having a phase difference of 0 ° to 180 ° to the boundary region. Proposed. For example, on page 491 (Lecture No. 27p-ZG-4) of the 51st Annual Meeting of the Applied Physics Society of Japan in September 1990, the phase difference is 0 degree, 60 degree and 120 degree as shown in FIG. It has been reported to use 180 degrees, and p. 492 (Lecture No. 27p-
In ZG-6), a structure using a 90-degree sub-shifter 20 on the boundary between the phase shifter 19 and another transmission region on the mask substrate 18 is reported as shown in FIG. Or, on page 537 (Lecture No. 29p-ZC-7) of the proceedings of the 38th Joint Lecture of Applied Physics, March 1991, see Figure 1.
There is also a proposal as shown in 0. This is because a first phase shifter P1 having a phase difference of 90 degrees with the mask substrate P0 and a second phase shifter P2 having a phase difference of 270 degrees are alternately arranged, so that a pair of 180 degree phases are provided between adjacent patterns. This is to generate a relative phase difference.

In all of these reports, if the phase difference at the boundary between the shifter and other portions is 180 degrees, an unnecessary light-shielding area is formed there. Therefore, three types of areas having different phase differences are used. The phase difference is gradually changed to prevent such a phenomenon from occurring, and the effect is enhanced.

[0008]

As described above, the conventional technique using the phase difference between the pair of transmissive regions as described above in the two-dimensional arrangement makes it possible to perform simple repetitive arrangement in the following manner.
It has become possible to obtain good effects.

However, in the actual integrated circuit pattern, there are many patterns other than the simple repeating pattern.
Therefore, it has been found that there is a problem in application to a typical example of an actual integrated circuit pattern.

That is, for example, as shown in FIG. 9, the integrated circuit pattern forms a region having a pair of phase differences of 180 degrees with the light shield 21 sandwiched therebetween, and another pair of phase differences 180 having the light shield 23 sandwiched therebetween. Areas with degrees can be formed. However, the light shield 23 between the light shield 21 and the light shield 22 cannot form a pair of regions having a phase difference of 180 degrees with the light shield 23 interposed therebetween. This means that the above-described method is often not applicable to actual integrated circuit patterns.

The present invention has been made in view of the above-mentioned circumstances, and provides an exposure mask which can be applied to an actual integrated circuit pattern to obtain an effect and can maximize the phase shift effect. The purpose is to do.

[0012]

Therefore, in the exposure mask of the present invention, the transmissive portion is divided into four regions, and the regions have different phases of transmitted light.
A second area having a phase difference of 90 degrees with respect to the first area, a third area having a phase difference of 180 degrees with respect to the first area, and a 270 degree phase difference with respect to the first area. When a region having a different phase is adjacent in the transmissive part, including a fourth region having a phase difference, the phase difference between these regions is 90 degrees, and when a region having a different phase is adjacent with the light-shielding part interposed therebetween. The phase difference between these regions is 180 degrees.

[0013]

By dividing the transmission part into four regions in this way, the phase difference is 18 in all cases with the light-shielding part interposed therebetween.
Since it can be set to 0 degree, the phase of this portion is inverted as in the case shown in FIG. 6, and the light having the phase difference of 180 degrees at the both ends of the transmitting portion cancels each other out, and the light intensity decreases. The contrast is improved, and as a result, the light intensity at both ends of the transmissive part becomes almost 0. As shown in FIG.
The pattern formed on the wafer can be separated from the two transparent portions. In this way, the resolution is improved, and the pattern separability and accuracy can be improved.

That is, if the transmissive portion is divided so that the phase difference with the adjacent area is 180 degrees and the separated portions have a phase difference of 90 degrees or 270 degrees with each other, the separation portion will be separated. It does not become a shaded area.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a view showing the arrangement of phase shifters of a light shielding part and a light transmitting part in an exposure mask of a first embodiment of the present invention.

This exposure mask comprises a quartz substrate on which a light shield made of a Cr film pattern is formed.
A pattern portion is formed by the reference numerals 2 and 3. The light transmitting portion around the light shield portion has four phase shifter regions S1 to S4 (phase difference 0 °, 90 ° relative to a region where no phase shifter is formed) configured such that the light phase differs depending on the transmitting portion.
, 180 degrees, 270 degrees).

As is apparent from the drawing, in the phase shifter, when the regions of different phases are adjacent to each other in the light transmitting portion (phase shifter regions S0 and S1, phase shifter regions S1 and S2), the phase difference is 90 degrees. On the other hand, when the light shielding portion is sandwiched (phase shifter regions S1 and S3, phase shifter regions S0 and S2), the phase difference is 180 degrees.

When a pattern is formed by a stepper using this mask, the wavelength of the light source by the stepper used is 0.365 μm, the coherency σ of the illumination system is 0.3,
When the NA of the projection optical system is 0.5, a 0.25 μm pattern can be accurately formed on the positive resist. By the way, conventionally, only a pattern of 0.4 μm could be obtained. Also, the joint between the phase shifters, that is, the boundary between S0 and S1 and the boundary between S0 and S3, has a phase difference 90
Since it is set to 270 degrees or 270 degrees, it does not appear as a pattern.

The film thickness d of the shifter is d = (λ / 4)  (n-1) when the phase difference is 90 degrees, where n is the refractive index of the shifter material and λ is the exposure wavelength. When it is 180 degrees, d = (λ / 2) · (n−1), and when it is 270 degrees, d = (3λ / 4) · (n−1).

In manufacturing this exposure mask, a light-transmitting film to serve as a shifter is deposited on the entire substrate by a silicon oxide film by the CVD method, and is formed by lithography and etching so as to have the thickness of each phase shifter. You can do it like this.

The phase difference is not necessarily a strictly accurate value, but the same effect can be obtained even if there is some error.

Next, a second embodiment of the present invention will be described.

In this case, the pattern example is different, and as shown in FIG. 2, it is formed by four light-shielding band portions 4, 5, 6, 7 and light transmitting portions (S0 to S3). Also in this case, as in the case of the first embodiment, a region having a phase shifter with a phase difference of 0 or a region not provided with a phase shifter is S0, and 90 °, 1
The areas of 80 degrees and 270 degrees are represented by S1, S2, and S3, respectively.

When a pattern is formed by a stepper using this mask, the wavelength of the light source by the stepper used is 0.365 μm, the coherency σ of the illumination system is 0.3,
When the NA of the projection optical system is 0.5, a 0.25 μm pattern can be accurately formed on the positive resist.

In the above embodiment, the case where the positive resist is used has been described, but it goes without saying that the present invention is also applicable to the case where the negative resist is used. As another embodiment, a negative resist pattern is shown in FIGS. Also in this case, as in the above-described embodiment, the region with the phase shifter with the phase difference of 0 or the region without the phase shifter is set to S0 in (b), and the regions of 90 degrees, 180 degrees, and 270 degrees are S1, S2, and S3, respectively. It is divided into

[0027]

As described above, according to the present invention, by dividing the transmissive portion into four regions, the phase difference can be 180 degrees with the light-shielding portion sandwiched in any case. Therefore, the resolution can be improved, and the pattern separability and accuracy can be improved.

[0028]

[Brief description of drawings]

[0029]

FIG. 1 is a diagram showing an example of pattern arrangement of an exposure mask according to a first embodiment of the present invention.

[0030]

FIG. 2 is a diagram showing an example of pattern arrangement of an exposure mask according to a second embodiment of the present invention.

[0031]

FIG. 3 is a diagram showing an example of pattern arrangement of an exposure mask according to another embodiment of the present invention.

[0032]

FIG. 4 is a diagram showing an example of pattern arrangement of an exposure mask according to another embodiment of the present invention.

[0033]

FIG. 5 is a diagram showing a resolution principle of an ordinary exposure mask.

[0034]

FIG. 6 is a diagram showing a resolution principle of a conventional phase shift mask.

[0035]

FIG. 7 is a diagram showing an example of inconvenience caused by a conventional phase shift mask.

[0036]

FIG. 8 is a diagram showing a conventional phase shifter.

[0037]

FIG. 9 is a diagram showing a conventional phase shifter.

[0038]

FIG. 10 is a diagram showing a conventional phase shifter.

[0039]

[Explanation of symbols]

 1 to 7 light-shielding band 11 quartz substrate 12 light-shielding film 13 phase shifter

Claims (1)

[Claims] 1. An exposure mask for transferring a pattern, which includes a transmissive part and a light-shielding part, and divides the transmissive part into four regions configured to have different phases of transmitted light, and the transmissive part includes: A first region; a second region having a phase difference of 90 degrees with respect to the first region;
A third region having a phase difference of 180 degrees with respect to the region of
A fourth region having a phase difference of 270 degrees with respect to the first region, and when regions of different phases are adjacent in the transmission part, the phase difference of these regions is 90 degrees, and the light shielding part is When regions of different phases are adjacent to each other with a phase difference between them, the phase difference between these regions is 1
An exposure mask, which is configured to be 80 degrees.