JP6915280B2 - Reflective photomask and reflective photomask blank - Google Patents

Description

The present invention relates to a semiconductor manufacturing technique, and more particularly to a reflective photomask used in lithography using extreme ultraviolet (EUV) as exposure light, and a reflective photomask blank for producing the same.

In the semiconductor device manufacturing process, the demand for miniaturization of photolithography technology is increasing with the miniaturization of semiconductor devices. Already, lithography exposure is replacing the conventional exposure using ArF excimer laser light having a wavelength of 193 nm with the exposure using light in the EUV region having a wavelength around 13.5 nm.

Since most substances have high light absorption to the light in the EUV region, the photomask for EUV exposure (EUV mask) is different from the conventional transmissive mask, and is a reflective photo that reflects EUV light. Use a mask. For example, in Patent Document 1, a reflective layer composed of a multilayer film in which a silicon (Si) film and a molybdenum (Mo) film are alternately laminated on a glass substrate is formed, and a protective film for protecting the reflective layer is formed on the reflective layer. A structure is disclosed in which a semiconductor circuit pattern (absorption film pattern) is formed by an absorption film containing tantalum (Ta) as a main component via a (Capping film).

Similarly, in an optical system using EUV light, a refracting optical system as in the case of ultraviolet exposure cannot be used, and deflection using a transmissive beam splitter is not possible, so that the optical system of the exposure machine also reflects. It becomes a mold.
Therefore, in an exposure optical system using an EUV mask, the incident light and the reflected light on the mask cannot be designed coaxially, and the reflected light of the light incident on the mask is transferred to the semiconductor substrate (wafer) by tilting the optical axis by about 6 degrees. A method of guiding and exposing the photosensitive resin coated on the wafer is adopted.

As described above, since the optical axis is tilted in EUV exposure, when reflected by the mask, a part of the absorption film pattern becomes a shadow depending on the direction of light incident on the mask, which is the original effect on the wafer. It is known that a phenomenon (projection effect) in which a circuit pattern different from the design pattern is formed occurs. Due to this projection effect, a line width error and a pattern misalignment occur on the wafer depending on the line width, orientation, pitch, etc. of the absorption film pattern, and the transfer quality is deteriorated. The effect of this projection effect becomes more pronounced as the pattern line width becomes finer.

Therefore, in order to reduce the projection effect, the film thickness of the absorption film is thinned to reduce the height of the absorption film pattern, and as a material that can be thinned, a highly absorbent material for EUV light is proposed as the absorption film. (For example, Patent Document 2). The film thickness of the absorption film generally used at present is 60 nm to 70 nm.

Furthermore, it has been proposed that by utilizing the principle of phase shift, the absorption film can be made thinner by giving the absorbing film a phase difference of 180 degrees while maintaining the contrast (for example, Patent Document 3). According to this document, the phase shift effect is obtained by utilizing the reflected light and the phase difference that cannot be completely absorbed from the absorption film due to the thinning.

However, in these methods, the film thickness that can be achieved with a phase difference of 180 degrees changes depending on the material, and the reflectance changes depending on the material. Therefore, in order to obtain the desired reflectance, select from the materials each time. There is a problem that it is necessary to re-optimize the process design and processing conditions each time.

Japanese Unexamined Patent Publication No. 2009-88166 Japanese Patent No. 5609865 International Publication 2011/004850

Therefore, in view of these problems, the subject of the present invention is that the thin film can be formed, and the desired phase difference and reflectance can be obtained by using the same material without particularly changing the process design of the photomask. It is an object of the present invention to provide a reflective photomask and a reflective photomask blank.

In order to solve the above problem, the invention according to claim 1 is
A reflective photomask in which a multilayer reflective layer, a protective film, and an absorption film layer pattern are provided in this order on a substrate, wherein the absorption film layer pattern is a first absorption film pattern and a second absorption film pattern from the side far from the substrate. It consists of a two-layer film structure with an absorption film pattern.
The first absorption film pattern is a high absorption material having an extinction coefficient of 0.06 or more at a wavelength of 13.5 nm, and the second absorption film pattern has an extinction coefficient of 0.02 at a wavelength of 13.5 nm. It is the following low absorption material and
The absorption film layer pattern is characterized in that the phase difference at a wavelength of 13.5 nm is 160 degrees to 200 degrees and the reflectance is 1% to 40% .
In the first absorption film pattern and the second absorption film pattern, at least one atom or molecule in which one of the absorption film patterns is selected from the group consisting of Sn and its oxides, nitrides and oxynitrides. Is the main component, and the other absorption film pattern is mainly composed of at least one atom or molecule selected from the group consisting of Mo and its oxides, nitrides, and oxynitrides. It is a type photo mask.

Further, the invention according to claim 2 is
A reflective photomask blank having a multilayer reflective layer, a protective film, and an absorbing film layer on the substrate in this order.
The absorption film layer has a two-layer film structure of a first absorption film and a second absorption film from the side far from the substrate.
The first absorption film is a high-absorption material having an extinction coefficient of 0.06 or more at a wavelength of 13.5 nm, and the second absorption film has an extinction coefficient of 0.02 or less at a wavelength of 13.5 nm. The first absorption film layer is a low-absorption material and has a phase difference of 160 ° C to 200 ° C and a reflectance of 1% to 40% at a wavelength of 13.5 nm. The film and the second absorption film are mainly composed of at least one atom or molecule selected from the group consisting of Sn and their oxides, nitrides, and oxynitrides, and the other absorption film is the main component. It is a reflective photomask blank characterized in that the absorption film is mainly composed of at least one atom or molecule selected from the group consisting of Mo and its oxides, nitrides and oxynitrides. ..

According to the reflective photomask of the present invention and the reflective photomask blank for producing the same, the absorbent film is a two-layer absorbent film of a high absorption material and a low absorption material, so that the film thickness ratio of the two layers is used. By changing the above, it is possible to make a thin film, and it is possible to manufacture a reflective photomask having a desired phase difference and reflectance and a reflective photomask blank without particularly changing the material. As a result, it is possible to reduce the projection effect due to the effects of high contrast and thin film due to phase shift and reflectance, and it is possible to reduce line width error and pattern misalignment on the transferred wafer pattern. It becomes.

It is a schematic cross-sectional view which shows the layer structure which concerns on embodiment of the reflective photomask blank of this invention. It is a schematic cross-sectional view for demonstrating the layer structure and the reflection state of EUV light which concerns on embodiment of the reflection type photomask of this invention. (a) to (d) are schematic cross-sectional views for explaining a mask manufacturing process according to the embodiment of the reflective photomask of the present invention. It is a figure for demonstrating the relationship between the SnO film ratio at a phase difference of 180 degrees, the reflectance, and the total film thickness of an absorption film layer which concerns on embodiment of the reflective photomask of this invention.

Hereinafter, the reflective photomask blank according to the embodiment of the present invention and the reflective photomask using the same will be described in detail. The same components are given the same sign unless there is a reason for convenience, and duplicate explanations will be omitted. Further, in the drawings used in the following description, in order to make the features easy to understand, the featured portions may be enlarged and shown, and the dimensional ratio of each component is not the same as the actual one.

FIG. 1 is a schematic cross-sectional view showing a structure according to an embodiment of the reflective photomask blank 10 of the present invention.
The reflective photomask blank 10 of the present invention is formed by laminating a multilayer reflective layer 2, a protective film 3, a second absorbing film 4, and a first absorbing film 5 on a substrate 1 in this order. Here, the second absorption film 4 and the first absorption film 5 are collectively referred to as an absorption film layer 6.

The reflective photomask blank of the present invention is not limited to the above embodiment. For example, as another embodiment, a buffer film (not shown) is provided between the protective film 3 and the second absorbing film 4. Can be done. This buffer film is a film that serves as an etching stop layer for the second absorption film 4 and serves as a buffer when correcting an absorption film pattern defect.

In the reflective photomask blank 10 of the present invention, the extinction coefficient of the first absorption film 5 with respect to EUV light having a wavelength of 13.5 nm is 0.06 or more, and the extinction coefficient of the second absorption film 4 is 0. It is 0.02 or less. That is, the first absorption film 5 is made of a high absorption material, and the second absorption film 4 is made of a low absorption material.

The absorption film of the conventional reflective photomask blank has an extinction coefficient of 0.04 or less with respect to EUV light having a wavelength of 13.5 nm, as typified by Ta. On the other hand, since the first absorption film of the reflective photomask blank of the present invention is 0.06 or more, it has high absorbency, and therefore, the film thickness of the conventional absorption film can be made thinner than 70 nm.

Therefore, it is possible to reduce the projection effect due to the absorption film pattern when the reflective photomask 20 as shown in FIG. 2 is used. FIG. 2 shows the layer structure and the state of EUV light incident and reflected according to the embodiment of the reflective photomask of the present invention. In FIG. 2, a pattern is formed like the absorption film layer pattern 16 composed of the first absorption film pattern 15 and the second absorption film pattern 14, and the incident light I incident on the pattern opening is the protective film 3. The incident light I incident on the absorption layer 16 is reflected like the reflected light R, and is reflected by the multilayer reflection layer 2 like the reflected light R0.

The reflective photomask blank 10 of the present invention further controls the film thickness ratio of the first absorption film 5 and the second absorption film 4, thereby making the absorption film layer 6 desired at a phase difference of 160 ° C to 200 ° C. It has the property that the reflectance can be adjusted within the range of 1% to 40%. Such a desired reflectance can be obtained by optical calculation using the film thickness, the refractive index, and the extinction coefficient of each film. In these calculations, the wavelength of EUV light is set to 13.5 nm.

Further, even when a desired circuit pattern is formed using the reflective photomask of the present invention, it is possible to easily obtain a desired reflectance suitable for the pattern type, size, and pitch only by adjusting the film thickness ratio. can. As a result, high contrast can be obtained during exposure, and the projection effect can be reduced.

FIG. 3 shows a manufacturing process of the reflective photomask 20 using the reflective photomask blank 10 of the present invention by the lithography technique.
In FIG. 3A, a multilayer reflective layer 2 is formed on a flat low thermal expansion substrate 1, a protective film 3 for protecting the multilayer reflective layer 2 is formed on the film, and a second absorption film is formed on the film. It shows a form in which a resist 7 for electron beam drawing or laser drawing is coated on a reflective photomask blank 10 in which a film 4 and a first absorbing film 5 are formed in this order.

Next, as shown in FIG. 3 (b), a pattern is drawn by an electron beam or a laser and developed to form a resist pattern 7a, and then the resist pattern 7a is etched as shown in FIG. 3 (c). The first absorption film 5 is dry-etched with a chlorine-based gas (or bromine-based, iodine-based, or fluorine-based gas) to form the first absorption film pattern 5a. At this time, the resist pattern 7a is reduced in size according to the etching selectivity with the first absorbing film 5, and becomes the resist pattern 7b.

Subsequently, as shown in FIG. 3D, the second absorption film 4 is made of a fluorine-based gas (or chlorine-based gas), using the resist pattern 6b with reduced film and the first absorption film pattern 5a as an etching mask. Is dry-etched to form a second absorption film pattern 4a. Even if the resist pattern 6b disappears during this process, the first absorbing film pattern 5a functions as an etching mask after the resist pattern 6b disappears.

At this time, in the first absorption film pattern 5a, the film is reduced according to the etching selectivity with the second absorption film 4, but the amount of film loss is measured in advance by an experiment, and the amount of film loss is increased by the amount of the film loss. The absorption film 5 of 1 may be formed thickly. If the line width of the first absorption film pattern 5a finally required becomes narrower and the second absorption film pattern 4a becomes thinner than the planned line width, the amount of thinning is measured in advance by an experiment, and the amount of thinning is measured accordingly. Only the line width of the drawing pattern should be increased.

In this way, the reflective photomask 20 of the present invention can be produced.

The materials of the first absorption film and the second absorption film used in the reflective photomask of the present invention and the reflective photomask blank include EUV light absorption (extinction coefficient), dry etching characteristics, cost, and the like. From a comprehensive point of view, one has at least one atom and molecule selected from the group consisting of Sn and their oxides, nitrides and oxynitrides as the main constituents, and the other is Mo and their oxides. , At least one atom selected from the group consisting of nitrides and oxynitrides, and molecules are preferably the main constituents. Here, the "main component" means that the sum of these atoms and the number of atoms forming the molecule is 90% or more of the total number of atoms.

Next, an example examined for optimizing the reflective photomask blank of the present invention is shown.

First, Table 1 shows the optical constants (refractive index: n, extinction coefficient: k) of various materials at the EUV wavelength (13.5 nm).

Based on the numerical values in Table 1, as an example of the reflective photomask blank of the present invention, the first and first absorption films at a phase difference of 180 degrees when the first absorption film is SnO and the second absorption film is Mo. FIG. 4 shows the results of calculating the EUV reflectance and the total film thickness of the absorption film layer with the ratio of the SnO film to the total film thickness of the absorption film of 2 as the horizontal axis.
In these calculations, the protective film is a Ru film having a thickness of 2.5 nm, and the multilayer reflective layer is a 40-pair multilayer film made of Si and Mo.

From FIG. 4, in the first absorption film, that is, the SnO film which is a high absorption material, by changing the ratio of the SnO film thickness to the total film thickness, the high reflectance is 37.5% and the low reflectance is 3.1%. It was found that the reflectance can be adjusted in a wide range and the desired reflectance can be obtained.
At this time, the film thickness of the absorption film layer is 44 to 45 nm, which is thinner than that of the conventional absorption film having a film thickness of 60 to 70 nm.

As described above, in the reflective photomask blank of the present invention, if the structure of the two-layer absorbing film is as described above, it is desired only by adjusting the film thickness ratio of the first absorbing film and the second absorbing film. It is possible to obtain the reflectance of the above, and further, it is possible to make the film thinner than the conventional film thickness.

For example, a high reflectance is expected to reduce the projection effect, and a low reflectance is expected to result in high contrast. As a result, by selecting the optimum structure according to the pattern type, dimensions, and pitch of the desired circuit pattern, characteristics such as reduction of the projection effect and high contrast can be obtained, and line width error and line width error can be obtained on the transferred wafer. It is possible to reduce the misalignment of the pattern.

1 ... Substrate 2 ... Multilayer reflective layer 3 ... Protective film 4 ... Second absorption film 4a ... Second absorption film pattern 5 ... First absorption Film 5a ... First absorption film pattern 6 ... Absorption film layer 7 ... Resist 7a ... Resist pattern 7b ... Reduced film resist pattern 10 ... Reflective photomask blank 14 ... Second absorption film pattern 15 ... First absorption film pattern 16 ... Absorption film layer pattern 20 ... Reflective photomask I ... Incident light R ... Reflected light in the absorption layer R0: Reflected light in the multilayer reflective layer + protective layer

Claims (2)

A reflective photomask in which a multilayer reflective layer, a protective film, and an absorption film layer pattern are provided in this order on a substrate, wherein the absorption film layer pattern is a first absorption film pattern and a second absorption film pattern from the side far from the substrate. It consists of a two-layer film structure with an absorption film pattern.
The first absorption film pattern is a high absorption material having an extinction coefficient of 0.06 or more at a wavelength of 13.5 nm, and the second absorption film pattern has an extinction coefficient of 0.02 at a wavelength of 13.5 nm. It is the following low absorption material and
The absorption film layer pattern is characterized in that the phase difference at a wavelength of 13.5 nm is 160 degrees to 200 degrees and the reflectance is 1% to 40%, and the first absorption film pattern and the second absorption film pattern are characterized. In the absorption film pattern, one of the absorption film patterns is mainly composed of at least one atom or molecule selected from the group consisting of Sn and their oxides, nitrides, and oxynitrides, and the other absorption film pattern. Is a reflective photomask characterized in that the main component is at least one atom or molecule selected from the group consisting of Mo and its oxides, nitrides and oxynitrides. A reflective photomask blank having a multilayer reflective layer, a protective film, and an absorbing film layer on the substrate in this order.
The absorption film layer has a two-layer film structure of a first absorption film and a second absorption film from the side far from the substrate.
The first absorption film is a high absorption material having an extinction coefficient of 0.06 or more at a wavelength of 13.5 nm, and the second absorption film has an extinction coefficient of 0.02 or less at a wavelength of 13.5 nm. It is a low absorption material and
The absorption film layer is characterized in that the phase difference at a wavelength of 13.5 nm is 160 ° C. to 200 ° C. and the reflectance is 1% to 40%. , One of the absorption films is mainly composed of at least one atom or molecule selected from the group consisting of Sn and their oxides, nitrides and oxynitrides, and the other absorption film is Mo and their oxidation. A reflective photomask blank comprising at least one atom or molecule selected from the group consisting of substances, nitrides, and oxynitrides as a main component.

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