JPH0961986A - Phase shift exposure mask and exposure method using phase shift exposure mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase shift exposure mask and an exposure method using the phase shift exposure mask by which a practical bottleneck such as decrease in the depth of focus is not caused but its performance can be enough made use of. SOLUTION: A light-shielding film 2 is formed on a transparent substrate 1 such as quartz to form a semi light-shielding part 3 and a light-transmitting part 4. Moreover, this structure is formed in such a manner that the phase of transmitted light through the semi light-shielding part 3 is different from the phase of the light through the light-transmitting part 4. A diffraction pattern 5 to diffract transmitted light is formed on the opposite surface of the substrate to the surface where the light-shielding film 2 is formed. By using the phase shift exposure mask having this structure, exposure light P is made to irradiate through the exposure diffraction pattern 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift mask and an exposure method using the phase shift mask. INDUSTRIAL APPLICABILITY The present invention can be used, for example, as an exposure mask that performs exposure by transmitting exposure light and an exposure method using the same. INDUSTRIAL APPLICABILITY The present invention can be used for exposure in various fields, for example, pattern exposure when forming an electronic material (semiconductor device or the like).

[0002]

2. Description of the Related Art Conventionally, there is known a so-called phase shift mask technique for exposing a portion having a different phase (generally 180 ° phase inversion) for transmitting light to perform exposure with good resolution. There is.

By the way, it is difficult to arrange not only the phase shift mask but also the exposure pattern in order to form the exposed pattern to some extent or more because it is affected by the proximity effect. For example, if a 1: 1 so-called hole pattern is to be formed, a portion having a high light intensity appears in the central portion between the exposure patterns due to the proximity effect, and the resist film is reduced. This cannot be avoided even by using the phase shift method. Rather, the proximity effect becomes more severe, and the sub-peak intensity specific to the phase shift method is enhanced by the interference effect. Therefore, for example, when it is used for exposure of a photoresist, the film thickness of the resist is also reduced, so that it is more difficult to arrange the patterns closer to each other than in the conventional method.

For example, a phase shift mask having a light transmitting portion and a semi-shielding portion (referred to as a halftone portion) is known. This type is called a halftone type phase shift mask. This kind of phase shift mask
Usually, it is composed of an opening that forms a light transmitting portion and a semi-shielding portion that has a slight light transmittance.
A phase shift portion (referred to as a shifter) made of a phase shift material is provided so as to give a phase difference of 0 °. In this way, the resolution is improved by the interference effect of light having different phases, and the transmittance of portions other than the opening is suppressed to, for example, several to several tens%, so that the resolution of this portion or the reduction of the resist film is prevented.

The halftone type phase shift mask exhibits excellent characteristics in improving resolution, depth of focus, etc., as compared with a normal mask. However, when the patterns become dense,
It is particularly remarkable in the halftone type phase shift method. 2
The intensity of the next peak (called side lobe) is emphasized by the proximity effect and is resolved to form an unnecessary pattern. Therefore, the performance of the halftone phase shift mask is significantly limited, especially when it includes a dense pattern.

For example, in the conventional halftone type phase shift mask, when two or more patterns come close to each other, a portion where the light intensity exceeds the resolution limit appears due to interference of diffracted light. That is, the structure of a conventional general halftone type phase shift mask is shown in FIG. 7 (planar) and FIGS. 8 (a) and 8 (b) (cross section). (Quartz substrate) Semi-light-shielding film (halftone film) 2 made of Cr thin film or the like formed on the entire surface of the quartz substrate 2
And a semi-light-shielding portion 3 formed with a halftone and a light-transmitting portion 4a, 4b having neither a halftone semi-transmissive portion nor a shifter, and a dugout is formed for phase shift (see FIG. a)) or the semi-light-shielding film 2 is formed with an appropriate thickness (FIG. 8B). In this structure, a high-strength portion is formed due to the proximity effect as described above. That is, as shown in FIG. 9, a peak (sub-peak 4C), which is preferably not present, occurs between the light peaks 4A and 4B, which are the light distributions from the light transmitting portions 4a and 4b. This is a major obstacle to the practical application of the halftone phase shift mask. This problem is a problem that occurs in any case when the exposure patterns (light transmitting portions) are arranged close to each other.

FIG. 9 shows the simulation result by TREPTON, and the conditions are NA: 0.45, δ:
0.5 KrF excimer laser light source (λ = 248 nm)
To be used. The parameter of the halftone mask is the transmissivity 10 of the halftone part which is the semi-shielding part 11.
%, The size of the openings forming the light transmitting portions 4a and 4b is 0.37 μm on the wafer, which is based on the assumption that a 0.3 μm hole pattern is formed. Distance between holes is 1.0 between centers
μm (all sizes are on the wafer).

Therefore, there is a demand for a phase shift mask technique that solves the problem of the proximity effect.

As one of means for solving the restriction based on the above problem, a method of exposing in combination with a so-called modified light source such as oblique incidence or annular illumination has been proposed (1994).
Autumn Meeting of Applied Physics 20p-ZP-1,20p-
ZP-2 “Study by combination of halftone method and annular illumination method (1)” “Same (2)” (Onodera et al.).

[0010]

By using the above method, the secondary peak intensity in a dense pattern is weakened and a practical pattern transfer mask performance in a dense pattern can be obtained. However, in such a modified light source, the light in the portion effective for the phase shift action is weakened. For example, with annular illumination, the light at the center of the exposure light source, which is effective for the phase shift method, is cut, so the depth of focus is significantly reduced in isolated patterns, and overall performance is better than when combined with normal illumination. No big improvement can be expected. This will be described with reference to FIG.

That is, FIG. 10 shows the results obtained by simulation and shows the problems of the conventional method. In the graph of FIG. 10A, the biased holes (0.28, 0.3
0, 0.32, 0.34, 0.36 and 0.38 μm)
When a hole pattern of 0.3 μm is formed on the resist by using
It shows the depth of focus (DOF) for forming a hole of 0.30 μm when the μm hole is used. In each case, the relationship between the light transmittance (%) and the depth of focus (μm) is shown. The depth of focus of the isolated pattern shown by the broken line I is close to 3 μm, but it drops considerably in the two holes shown by the broken line II, and 1.6 in the dense pattern shown by the broken line III.
It drops to about μm. Further, FIG. 2B shows the same data as to the combination of the half tone phase shift method and the annular illumination. In the case of annular illumination, since there is no central light, the depth of focus cannot be obtained with an isolated pattern as indicated by I ′, and the limit is 1.6 μm.

Therefore, in practice, in combination with ordinary lighting,
The mask bias is increased to suppress the exposure amount and the secondary peak intensity is suppressed. For example, when forming a 0.30 μm hole, 0.36 μm is used instead of a 0.30 μm (5 times on the mask. The same applies below) mask pattern. However, in this case, the depth of focus is lowered by applying a large bias. Therefore, it does not meet the basic requirements.

For this reason, the halftone phase shift method cannot be used under the condition that the performance can be sufficiently exhibited, while having a great potential.

The present invention solves the above-mentioned problems of the prior art and makes it possible to make full use of its performance without causing a practical bottleneck such as a decrease in depth of focus, and a phase shift exposure mask. It is an object to provide an exposure method using a mask.

[0015]

The phase shift exposure mask of the present invention and the exposure method using the phase shift exposure mask are
The above-mentioned object is achieved by adopting the following configuration.

The phase shift mask according to the present invention has a structure in which a light-shielding film is formed on a transparent substrate and has a semi-shielding portion and a light-transmitting portion, and the semi-shielding portion and the light-transmitting portion have different phases. A phase shift exposure mask, wherein a pattern for diffusing exposure light is formed on a surface opposite to a surface on which a light-shielding film is formed, in a phase shift mask which is configured to transmit transmitted light.

In this case, the light shielding film forms a portion having a high pattern density and a portion having a low pattern density, and the diffraction pattern is selectively formed in a portion having a high pattern density among these pattern forming portions. Can be configured.

Further, the light transmittance of a portion of the surface on which the diffraction pattern is formed, excluding the formed diffraction pattern, may be lower than that of the portion on which the diffraction pattern is formed. This makes it possible to adjust the transmitted light intensity of the portion excluding the diffraction pattern to the same level as the transmitted light intensity of the portion provided with the diffraction pattern.

In the exposure method according to the present invention, a light-shielding film is formed on a transparent substrate to have a semi-light-shielding portion and a light-transmitting portion, and the semi-light-shielding portion and the light-transmitting portion have different phases. Using a phase shift exposure mask having a pattern for transmitting the transmitted light and diffracting the transmitted light on the surface opposite to the surface on which the light shielding film is formed, irradiating the exposure light from the transmitted light diffraction pattern side It is an exposure method characterized by performing exposure.

In this case, the light-shielding film forms a portion having a high pattern density and a portion having a low pattern density, and the diffraction pattern is selectively formed in a portion having a high pattern density among these pattern forming portions. Can be configured.

Further, in this case, the light transmittance of a portion of the surface on which the diffraction pattern is formed, excluding the formed diffraction pattern, is made lower than that of the portion on which the diffraction pattern is formed, and a portion on which the diffraction pattern is provided. It is possible to adopt a configuration in which the exposure mask is adjusted to have the same intensity as the transmitted light intensity and the exposure light is irradiated from the exposure light diffraction pattern side to perform the exposure.

[0022]

According to the present invention, it is possible to form a pattern for diffracting the exposure light on the side opposite to the surface on which the light-shielding film is formed, and irradiate the exposure light through the pattern to perform the phase shift exposure. Therefore, the influence of the secondary peak is attenuated by this pattern due to the pattern, and as a result, the halftone phase shift mask can be used under the condition where the performance can be maximized without considering the influence of the secondary peak. become able to. Further, according to the present invention, the secondary peak can be efficiently suppressed, and as a result, the effect of the halftone phase shift method can be sufficiently exerted even when an isolated pattern and a dense pattern are mixed. Can be configured to.

The concept of providing a grid pattern between the mask and the light source is described in Jpn. J. Appl.
Phys. Vol. 32 (1993) pp. 5903-
5908 "Lithographic Graphic Perform
ance Enhancement Using Du
mmy Diffraction Mask "Hyun
g Joon Yoo, et. disclosed in al.
This normally forms a grid pattern between the mask and the light source to give the same effect as the modified light source. However, this method does not solve the problem of the halftone phase shift mask.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail by describing specific examples of the present invention. However, needless to say, the present invention is not limited by the following examples.

Example 1 This example embodies the present invention with respect to an exposure mask technique used in a manufacturing process of a miniaturized and integrated semiconductor device. Please refer to FIG. 1 and FIG.

The phase shift exposure mask of this embodiment is shown in FIG.
As shown in FIG. 3, a light-shielding film 2 is formed on one surface of a transparent substrate 1 (here, a quartz substrate. Here, “transparent” means that it is transparent to the exposure light used). Part 3
And a light transmitting portion 4, and the semi-shielding portion 3
Means that the transmitted light is transmitted with a phase different from that of the light transmitting portion 4, and a diffraction pattern 5 for diffracting the exposure light is formed on the surface opposite to the surface on which the light shielding film 2 is formed. (See also FIG. 2. In FIG. 2, a diffraction pattern forming portion having a diffraction pattern formed by reference numeral 5A is shown).

In the exposure method of this embodiment, the phase shift exposure mask configured as described above is used to perform exposure by irradiating the exposure light P from the exposure light diffraction pattern 5 side. That is,
As shown in FIG. 2, a light source is arranged above the drawing (diffraction pattern 5 side) to irradiate the exposure light P to perform exposure.

This embodiment will be described in more detail.
First, as shown in FIGS. 1 and 2, the surface opposite to the surface on which the light shielding film 2 of the halftone phase shift mask is formed (referred to as the back surface).
A pattern 5 having a zigzag pattern (checkered pattern) capable of diffracting the exposure light is formed on. As a result, the same effect as in the case of combining with the modified illumination can be obtained in the portion through the diffraction pattern 5. This is because the diffraction pattern 5 causes the exposure light from the light source to be obliquely incident. Therefore, the secondary peak intensity is reduced here and the depth of focus can be extended. As a result, it is possible to perform exposure that fully exhibits the performance of the halftone phase shift method.

Embodiment 2 In this embodiment, as shown in FIG. 3, the diffraction pattern 5 is
Of the pattern portions 2A and 2B formed by the light shielding film 2, the pattern portion 2A having a high pattern density is selectively formed. In FIG. 3, a portion forming the diffraction pattern 5 is indicated by reference numeral 5A.

For example, as shown in FIG. 4, the diffraction pattern forming portion 5A (FIG. 4A) is replaced with the dense portion 2A (FIG. 4) of the light-shielding film (halftone) pattern on the pattern forming side.
(B)).

In the exposure method of this embodiment, the phase shift exposure mask configured as described above is used to perform exposure by irradiating exposure light from the exposure light diffraction pattern 5 side. That is, as shown in FIG. 5, the upper part of the figure (diffraction pattern forming portion 5A
A light source is disposed on the side) to irradiate the exposure light to perform the exposure.

In the present embodiment, a lattice-shaped pattern 5 capable of diffracting exposure light is formed on the back surface of the halftone phase shift mask. At this time, the pattern is selectively formed in a dense portion. By forming it, the same effect as in the case of combining with the modified illumination can be obtained in this portion. This is because the diffraction pattern 5 causes the exposure light from the light source to be obliquely incident. Therefore, the secondary peak intensity is reduced here and the depth of focus can be extended. On the other hand, in the portion where the pattern is relatively rough (the portion indicated by reference numeral 2B in FIG. 4B), since the exposure light does not pass through the diffraction pattern 5, it is eventually exposed by normal illumination, and the depth of focus decreases. Does not happen. Therefore, it is possible to perform exposure that fully exhibits the performance of the halftone phase shift method.

Embodiment 3 In this embodiment, when a plurality of line-shaped patterns are formed by a light shielding film and a halftone pattern is formed in a line and space pattern, as shown in FIG. The diffraction pattern 5 is provided so as to extend in parallel with the pattern. The effect of making the exposure light obliquely incident on the halftone pattern is excellently achieved.

Example 4 In this example, on the surface of the mask on the side where the diffraction pattern 5 is provided, the light transmittance of the portion excluding the formed pattern 5 (ie, reference numeral 4 in FIG. 1). The light transmittance of the portion is reduced so that the transmitted light intensity of the portion provided with the diffraction pattern 5 is adjusted to the same level.

That is, when the method of the present invention is used, the light intensity tends to decrease at the portion where the diffraction pattern 5 (grating) is formed. Since the size of a dense pattern changes as compared to an isolated pattern due to the proximity effect, it may be necessary to reduce the exposure light transmittance except for the portion where the grating is formed. Therefore, the present embodiment adjusts the light transmittance in such a case. That is, in this case, a method may be employed in which a resist pattern is used as a mask in the portion where the grid pattern is formed by EB direct drawing, a predetermined amount of a material such as chromium that reduces the transmittance is sputtered, and a film is formed by lift-off. Alternatively, instead of sputtering, Ga ⁺ ions were implanted to reduce the transmittance, thereby reducing the light transmittance of that portion and adjusting the overall light transmittance. This configuration,
It can be applied to any of the first to third embodiments.

[0036]

As described above, according to the present invention, there is provided a phase shift exposure mask and a phase shift exposure mask which can fully utilize their performance without causing a practical bottleneck such as a decrease in depth of focus. The exposure method used could be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a phase shift exposure mask of Example 1.

FIG. 2 is a configuration diagram showing an exposure method of the first embodiment.

FIG. 3 is a sectional view showing a structure of a phase shift exposure mask of Example 2.

FIG. 4 is a plan view showing a configuration of a phase shift exposure mask of Example 2.

FIG. 5 is a configuration diagram illustrating an exposure method according to a second embodiment.

FIG. 6 is a plan view showing a configuration of a phase shift exposure mask of Example 3.

FIG. 7 is a plan view showing a configuration of a conventional phase shift exposure mask.

FIG. 8 is a sectional view showing a configuration of a conventional phase shift exposure mask.

FIG. 9 is a diagram showing a problem of the conventional technique.

FIG. 10 is a diagram showing a problem of the conventional technique and a diagram showing a simulation result.

[Explanation of symbols]

 1 Transparent substrate (quartz substrate) 2 Light-shielding film 3 Anti-light-shielding part 4 Light-transmitting part 5 Diffraction pattern 5A Diffraction pattern forming part 2A Light-shielding film pattern dense part 2B Light-shielding film pattern sparse part

Claims (6)

[Claims] 1. A structure in which a light-shielding film is formed on a transparent substrate to include a semi-light-shielding portion and a light-transmitting portion, and the semi-light-shielding portion and the light-transmitting portion have different phases to transmit transmitted light. In the phase shift mask of 1), a pattern for diffracting the exposure light is formed on the surface opposite to the surface on which the light shielding film is formed. 2. A portion having a high pattern density and a portion having a low pattern density are formed by the light shielding film, and the diffraction pattern is selectively formed in a portion having a high pattern density among these pattern forming portions. The phase shift exposure mask according to claim 1, wherein 3. The light transmittance of a portion of the surface on which the diffraction pattern is formed, excluding the diffraction pattern, is lower than that of the portion on which the diffraction pattern is formed.
The phase shift exposure mask described in [4]. 4. A light-shielding film is formed on a transparent substrate to provide a semi-light-shielding portion and a light-transmitting portion, and the semi-light-shielding portion and the light-transmitting portion have different phases to transmit transmitted light, Further, a phase shift exposure mask is used in which a pattern for diffracting transmitted light is formed on the surface opposite to the surface on which the light-shielding film is formed, and the exposure light is irradiated from the side of the transmitted light diffraction pattern to perform exposure. Exposure method. 5. A portion having a high pattern density and a portion having a low pattern density are formed by the light shielding film, and the diffraction pattern is selectively formed in a portion having a high pattern density among these pattern forming portions. The exposure method according to claim 4, wherein exposure is performed by irradiating exposure light from the side of the transmitted light diffraction pattern using an exposure mask. 6. The light transmittance of a portion of the surface on which the diffraction pattern is formed, excluding the diffraction pattern, is made lower than that of the portion on which the diffraction pattern is formed, and is equal to the high transmission intensity of the portion on which the diffraction pattern is formed. Using an exposure mask adjusted to a degree,
The exposure method according to claim 4, wherein exposure is performed by irradiating the exposure light from the exposure light diffraction pattern side.