JP5193715B2 - Multi-tone photomask - Google Patents

Description

The present invention relates to a multi-tone photomask using a semi-transparent film, and more particularly to preventing a decrease in contrast (light intensity ratio) at a boundary portion between a light-shielding portion and a semi-transparent portion.

Since multi-tone photomasks can form resist patterns with different film thicknesses by one exposure, they are attracting attention because of various advantages such as a reduction in the number of mask processes (see Patent Documents 1 to 3, etc.).

JP 2002-196474 A JP 2007-233350 A JP 2008-058943 A

The conventional multi-tone photomask has a problem in that, when projection exposure is performed using an exposure apparatus, the resolution limit of the projection optical system of the exposure apparatus is exceeded, so that contrast does not occur. This phenomenon occurs mainly at the boundary between the light shielding portion and the semi-transparent portion. For this reason, as a method for improving the resolution of the exposure apparatus, various methods such as shortening the exposure wavelength and changing the numerical aperture of the projection optical system have been proposed. Even with this method, it is difficult to improve resolution. In the case of a so-called top half type multi-tone photomask having a structure in which a semi-transmissive film is formed on the pattern of the light-shielding film, the exposure light is scattered by the step of the semi-transmissive film on the edge of the light-shielding film. The problem of making it happen is also being solved.

For example, FIGS. 3A and 3B show a conventional so-called top half type multi-tone photomask 101. As shown in these drawings, the conventional multi-tone photomask includes a light-shielding portion A, a semi-transparent portion B, and a translucent portion C, and the pattern of the light-shielding film 111 constituting the light-shielding portion is the semi-transparent film 112. As is clear from the cross-sectional view shown in FIG. 3B, the light shielding part of the pattern of the light shielding film 111 and the boundary part (edge part) of the pattern of the semi-transparent film 112 are A step S of the semi-transparent film 112 formed when the semi-transparent film 112 covers the pattern of the light shielding film 111 is formed.

FIG. 3C shows a cross section of a resist pattern completed by irradiating the multi-tone photomask 101 shown in FIG. 3B with exposure light I from an exposure apparatus (not shown), and then developing and the like. Shape. A resist pattern 305 having a film thickness changed according to an exposure site is formed on the exposure target substrate 300, but the resist film thickness in the semi-translucent portion is thick and uneven at both ends, and the light shielding portion It can be seen that the resist film thickness changes gently at the boundary with the semi-transparent part. It can be seen that this is a shape far from the ideal resist pattern shape R indicated by the broken line in the figure.

FIG. 4 shows how the exposure light I is scattered at the step S. As shown in this figure, at the step S, the film thickness is locally larger than the film thickness of the adjacent semi-transparent film 112, and the surface shape is a gently curved cross section. For this reason, the exposure light passing through the step S cannot travel straight and is scattered in various directions.

As a result, the shape of the resist pattern corresponding to the projection-exposed semi-transparent portion becomes gentle at the portion corresponding to the step S, and the contrast (light intensity ratio) is lowered, so that the change in gradation is caused. It becomes difficult to discriminate and the process margin of the process is insufficient.

The present invention has been made in view of the above-described problems. The film thickness of the semi-transparent film in the semi-transparent part is made constant, and the gradation change at the boundary between the semi-transparent film and the light-shielding film is made. The technical problem is to increase the process margin of the process by making it steep.

The multi-tone photomask according to the present invention is a top half-type multi-tone photomask for forming a resist pattern on an exposure target substrate on which a resist film is formed by irradiating exposure light from an exposure apparatus. Te, and a light transmitting portion for transmitting the exposing light and semi-light-transmitting portion which transmits a part of the exposure light comprising light shielding portions and the thin film for blocking the exposure light of a thin film on a transparent substrate, said transparent Subtracting an increase in exposure amount due to having the transmission part and having a transmission part set below the resolution limit of the exposure apparatus where the substrate is exposed at the boundary between the light shielding part and the semi- transmission part. The translucency of the semi-translucent portion is adjusted to be small .

When a resist pattern is formed using a multi-tone photomask having the above structure, the contrast between the light-shielding part and the semi-translucent part (light intensity ratio) is improved, so that the gradation change is discriminated. It becomes easy and the process margin of a process can be enlarged.

In particular, it is preferable that the transmissive portion is provided at a boundary portion between the light shielding portion and the semi-transmissive portion, and the interval between the transmissive portions is set to be equal to or less than a resolution limit of the exposure apparatus.

The interval between the transmission parts is not particularly limited as long as it is less than the resolution limit of the exposure apparatus, but when the resolution is about 2 μm, it is preferably set in the range of 0.5 μm to 1.5 μm.

The first multi-tone photomask manufacturing method according to the present invention includes a step of forming a light-shielding film on a transparent substrate, and a first photoresist film on the light-shielding film to form exposure light from an exposure apparatus. A first pattern forming step of forming a light-shielding film pattern by irradiating and developing, a step of forming a semi-transparent film so as to cover the pattern of the light-shielding film, and a first step on the semi-transparent film. A second pattern forming step of forming a pattern of a semi-translucent film by forming a photoresist film of 2 and irradiating and developing exposure light from an exposure apparatus;
In the second pattern forming step, a transmission part is formed in a step portion of the semi-transparent film formed at a boundary part between the light shielding film and the semi-transparent film.

This shows a basic manufacturing procedure when a multi-tone photomask according to the present invention is manufactured from the beginning. In this way, by forming the transmission part when forming the pattern of the semi-transparent film, it is possible to manufacture a multi-tone photomask including the transmission part without increasing the number of processes in view of the conventional manufacturing process. it can.

In addition, by irradiating exposure light from an exposure apparatus, it is used to form a resist pattern on an exposure target substrate on which a resist film is formed,
For a multi-tone mask including a light-shielding part that blocks the exposure light on a transparent substrate, a semi-transparent part that transmits part of the exposure light, and a translucent part that transmits the exposure light,
You may comprise so that the transmission part with the space | interval below the resolution limit of the said exposure apparatus may be formed in the boundary part of the said light-shielding part and the said semi-transparent part.

In this manner, a transmission part can be provided afterwards for a multi-tone photomask that is not provided with a transmission part that has already been completed by a conventional manufacturing method. This method is effective when the process margin is insufficient with the multi-tone photomask obtained by the conventional manufacturing method.

In the multi-tone photomask according to the present invention, since the transmission part is provided between the light shielding part and the semi-transparent part, when the resist pattern is formed using this photomask, the light shielding part and the semi-transparent part are provided. Since the contrast (light intensity ratio) with respect to is improved, a change in gradation can be easily discriminated, and the process margin of the process can be increased.

(First embodiment)
FIG. 1A is a plan view showing a part of the pattern of the multi-tone photomask according to the first embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line X2-X2 shown in FIG. As shown in these drawings, the multi-tone photomask 1 has a light shielding film pattern 11 formed on the surface of a transparent substrate 10 and a semi-transparent film pattern 12 formed thereon.

This multi-tone photomask 1 is provided with a light-shielding portion A, a semi-transparent portion B, and a translucent portion C on a transparent substrate 10 so that an intermediate intensity can be obtained by changing the intensity of exposure light by one exposure. It can express gradation.

The light shielding portion A is configured by a portion where the pattern of the light shielding film 11 is formed, and this includes a portion where the semi-transparent film 12 is laminated on the light shielding film. The semi-translucent portion B is constituted by a portion where 12 patterns of the semi-translucent film are formed, and this includes a transmissive region provided at an end portion of the semi-transparent film. The light transmitting portion C is a portion other than the light shielding portion and the semi-light transmitting portion in the exposure pattern forming region, and is a portion where a film that greatly changes the transmittance is not formed on the transparent substrate 10.

  The transmissive part 20 is provided between the semi-transmissive part B and the light-shielding part A and is a transmissive area having a predetermined interval. The transparent substrate is exposed in the transmissive part 20, but the distance d between the transmissive parts 20. Is set below the resolution limit of the exposure apparatus. For this reason, even if exposure light is irradiated, the pattern of the transmission part is not transferred onto the photoresist.

When the transmissive part 20 is provided in the semi-translucent part B, the amount of exposure light passing through the semi-transparent part increases, so it is preferable to set the transmissivity of the semi-transparent film to be small. Specifically, the film thickness of the semi-transparent film is set to be larger than that in the case where the transmission part is not provided, or the composition of the semi-transparent film is adjusted, and metal atoms (for example, chromium or the like) constituting the semi-transparent film are adjusted. ) To increase the composition ratio. In this way, it is possible to adjust so that the overall light amount does not change when the exposure is performed by subtracting the increase in the light amount by the transmission unit 20.

As described above, the distance d between the transmissive portions 20 needs to be selected in consideration of both the size of the semi-transmissive portion, particularly the distance between the opposing light shielding portions and the resolution of the exposure apparatus. For example, when the interval between the semi-transparent portions (distance between the light shielding portions facing each other) is 4 μm and the resolution of the exposure apparatus is about 2 μm, according to the results of various experiments, the interval between the transmissive portions is about 0.1 mm. A range of 5 to 1.5 μm has been found to be preferred.

FIG. 1C is a cross-sectional view of a resist pattern completed by irradiating the multi-tone photomask 1 shown in FIG. 1B with exposure light I from an exposure apparatus (not shown), and then developing and the like. Shape. A resist pattern 35 having a film thickness changed according to an exposure site is formed on the substrate 30 to be exposed, but the resist film thickness in the semi-transparent part is uniform, and the boundary part between the light-shielding part and the semi-translucent part Then, it can be seen that the resist film thickness changes sharply.

That is, according to the multi-tone photomask according to the first embodiment of the present invention, it approaches the ideal resist pattern shape R indicated by the broken line in the figure, and the contrast at the boundary between the light shielding portion and the semi-transparent portion. The process margin can be increased by increasing the light intensity ratio.

(Second Embodiment)
Fig.2 (a)-FIG.2 (c) have shown the variation of the shape of a permeation | transmission part. FIG. 2A shows a case where a region sandwiched between two light-shielding films configured in an L shape is a semi-transparent part, and constitutes a semi-transparent part with the light-shielding film 11a constituting the light-shielding part. A transmission part 20a is provided at the boundary with the semi-transparent film 12a. FIG. 2B shows a case where a region sandwiched between two light-shielding films configured in an I-shape is a semi-transparent part, and constitutes a semi-transparent part with the light-shielding film 11b constituting the light-shielding part. A transmission part 20b is provided at the boundary with the semi-transparent film 12b. FIG. 2C shows a case where a region inside the light shielding film formed in a hole shape such as a regular polyhedron (including a circle) becomes a semi-translucent portion, and the light shielding film 11c constituting the light shielding portion and the semi-transparent portion. A transmission part 20c is provided at the boundary with the semi-transparent film 12c constituting the light part.

In any case, by providing the transmissive portions 20a to 20c, the change in the resist film thickness at the boundary between the light shielding portion and the semi-transparent portion after the formation of the photoresist pattern becomes steep, and the process margin of the process increases. did.

(Other embodiments)
In the first and second embodiments, an embodiment using a multi-tone photomask having a so-called “top half type” structure in which a light-shielding film pattern is formed and then a semi-transparent film is formed will be described. However, the present invention can also be applied to a multi-tone mask having a structure called “bottom half type” in which a semi-transparent film is provided below a light-shielding film.

As is well known, the bottom half-type multi-tone photomask is composed of an upper light shielding film and a lower semitransparent film with respect to a mask blank in which a semitransparent film and a light shielding film are laminated in this order on a transparent substrate. Can be obtained by sequentially patterning, but can be easily manufactured by forming the pattern of the transmission part during the pattern forming process of the semi-translucent film. As described above, in the bottom half type multi-tone photomask, the step S as shown in FIG. 3 is unlikely to occur, but even in such a case, by providing the transmission part, the film of the semi-transmission film in the semi-transmission part is provided. It is possible to increase the process margin of the process by making the thickness constant and making the change of gradation at the boundary between the semi-transparent film and the light shielding film steep.

Also, if the process margin is insufficient even with a multi-tone photomask that has already been completed by the conventional manufacturing method, laser zapping is applied to necessary parts such as the boundary between the semi-translucent part and the light-shielding part. And a transmission part may be provided later.

The multi-tone photomask according to the present invention has a great industrial applicability as it increases the process margin in the resist pattern forming process.

FIG. 1A is a plan view showing a part of the pattern of the multi-tone photomask according to the first embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line X2-X2 shown in FIG. FIG. 1C is a cross-sectional view of a resist pattern completed by irradiating the multi-tone photomask 1 shown in FIG. 1B with exposure light I from an exposure apparatus (not shown), and then developing and the like. Shape. Fig.2 (a)-FIG.2 (c) have shown the variation of the shape of a permeation | transmission part. FIG. 2A shows a case where a region sandwiched between two light shielding films configured in an L shape is a semi-transparent portion, and FIG. 2B shows two light shielding films configured in an I shape. 2 (c) shows a case where a region inside a light shielding film configured in a hole shape such as a regular polyhedron (including a circle) becomes a semi-translucent portion. It is. FIG. 3A is a plan view showing a part of a pattern of a conventional multi-tone photomask. FIG. 3B is a cross-sectional view taken along line X1-X1 shown in FIG. FIG. 3C shows a cross section of a resist pattern completed by irradiating the multi-tone photomask 101 shown in FIG. 3B with exposure light I from an exposure apparatus (not shown), and then developing and the like. Shape. FIG. 4 shows how exposure light is scattered at the step S of the semi-transparent film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multi-gradation photomask 10 Transparent substrate 11, 111 Light-shielding film 12, 112 Semi-transparent film 20 Transmission part 30, 300 Exposure target substrate 35, 305 Resist pattern A Light-shielding part B Translucent part C Semi-translucent part R Ideal Resist pattern shape

Claims (4)

A top half-type multi-tone photomask for forming a resist pattern on an exposure target substrate on which a resist film is formed by irradiating exposure light from an exposure apparatus, the exposure comprising a thin film on a transparent substrate A resolution limit of the exposure apparatus in which the transparent substrate is exposed, including a light-shielding portion that blocks light, a semi-transparent portion that transmits a part of the exposure light composed of a thin film, and a translucent portion that transmits the exposure light The translucent part set below is provided at the boundary between the light-shielding part and the semi-translucent part, and the transmittance of the semi-translucent part is reduced by subtracting the increase in exposure amount due to the transmissive part. Multi-tone photomask adjusted to. 2. The multi-tone photomask according to claim 1, wherein a film thickness of the film constituting the semi-transmissive portion is large so that the semi-transmissive portion has a smaller transmittance than that in the case where the semi-transmissive portion is not provided. 2. The multi-tone photomask according to claim 1, wherein a composition ratio of a film constituting the semi-transmissive portion is adjusted so that the semi-transmissive portion has a transmittance smaller than that of the case where the semi-transmissive portion is not provided. 4. The multi-tone photomask according to claim 1, wherein the transmissive portion has a distance d in a range of 0.5 μm to 1.5 μm.

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