JP2006237192A - Method of manufacturing reflection type mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a reflection type mask which can make thin a chrome buffer film to be formed between a multilayered reflection film and an absorber film, by improving the etching controllability and in-plane uniformity of the tantalum absorber film of a multilayered structure. <P>SOLUTION: The reflection type mask comprises a substrate 11, the multilayered reflection film 12 which reflects the exposure light, and the absorber film 16 which absorbs the exposure light. The absorber film 16 has a two-layer structure which consists of an exposure light absorber layer 14 consisting of an EUV light absorber as a lower layer, and a low reflectivity layer 15 consisting of an absorber of the test light to be used for testing a mask pattern as an upper layer. Both the upper and lower layers are formed of a material, mainly of tantalum (Ta). In a process of dry-etching the absorber film 16, an etching gas containing fluorine (F) is used and the ratio of etch rate of the layers constituting the absorber film 16 is between 0.1 and 10. The buffer film 13 containing chrome which is formed between the multilayered reflection film 12, and the absorber film 16 has a thickness of 2-10 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a reflective mask for exposure used for manufacturing a semiconductor device.

In recent years, in the semiconductor industry, with the miniaturization of semiconductor devices, EUV lithography, which is an exposure technique using extreme ultraviolet (hereinafter referred to as EUV) light, is promising. Here, EUV light refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, and specifically, light having a wavelength of about 0.2 to 100 nm. As a mask used in this EUV lithography, for example, an exposure reflective mask described in Patent Document 1 below has been proposed.
In such a reflective mask, a multilayer reflective film that reflects exposure light is formed on a substrate, and an absorber film that absorbs exposure light is formed in a pattern on the multilayer reflective film. Light incident on the reflective mask mounted on the exposure machine (pattern transfer device) is absorbed in a part where the absorber film is present, and light reflected by the multilayer reflective film is transmitted through the reflective optical system in a part where the absorber film is not present. Transferred onto a semiconductor substrate.

Further, in Patent Document 2 below, in order to improve the inspection accuracy of a mask pattern, an exposure light absorber layer composed of an absorber of exposure light in a short wavelength region such as EUV light is used as a lower layer for inspection of a mask pattern. There has been proposed a reflective mask including an absorber film having at least a two-layer structure with a low reflectance layer formed of an inspection light absorber to be used as an upper layer.
As the multilayer reflective film, for example, a film in which EUV light of 13 to 14 nm is reflected, and a film in which Mo and Si having a thickness of several nm are alternately stacked for about 40 to 60 cycles are known. In order to increase the reflectivity, it is desirable to use a Mo film having a large refractive index as the uppermost layer. However, Mo is easily oxidized when it is exposed to the atmosphere, and as a result, the reflectivity is reduced. For example, a Si film is provided as the uppermost layer as a protective film for the purpose.
Patent Document 2 below discloses a reflective mask in which a buffer film is formed between the multilayer reflective film and the absorber film pattern in order to prevent damage to the multilayer reflective film surface during etching of the absorber film. Is also described.

Japanese Patent Publication No. 7-27198 International Publication No. 03/085709 Pamphlet

The reflective mask is manufactured as follows.
First, a reflective mask blank in which a multilayer reflective film and an absorber film are formed in this order on a substrate is prepared. A resist layer is formed on the absorber film of the reflective mask blank, and pattern drawing and development are performed to form a predetermined resist pattern.
Next, using the resist pattern as a mask, the absorber film is etched to form an absorber film pattern. When the buffer film is provided between the multilayer reflective film and the absorber film, the exposed buffer film is usually removed by etching according to the absorber film pattern after the above-described absorber film pattern is formed. Then, the surface of the multilayer reflective film that becomes the reflective region of the mask is exposed. By providing the buffer film, damage to the multilayer reflective film at the time of pattern correction as well as at the time of pattern formation of the absorber film described above is prevented, so that pattern formation and pattern correction of the absorber film are easy. This is preferable.
A reflective mask is completed as described above.

By the way, as the absorber film in the reflective mask, it has a function of absorbing exposure light such as EUV light, and tantalum (Ta) alone or a material mainly composed of Ta is preferably used. As the buffer film, when the absorber film is a tantalum material, a material containing chromium (Cr) having a different etching characteristic from that of the absorber film is preferably used.
The film thickness of the conventional chromium-based buffer film was about 20 to 50 nm from the viewpoint of preventing damage to the multilayer reflective film during pattern formation or pattern correction of the absorber film. Since a chromium-based buffer film having such a thickness, for example, a chromium nitride (CrN) film, is removed in accordance with the absorber film pattern, the periphery of the pattern tends to remain as a residue when etching by dry etching. However, there is a problem of affecting the transferred image. If the buffer film is over-etched to completely remove this residue, the longer the over-etching time, the greater the damage to the lower multilayer reflective film, and the lower the reflectivity. Therefore, it is necessary to reduce the thickness of the buffer film so that the residue does not remain as much as possible, and even if the residue remains as it is, it does not affect the transferred image.

  However, when the thickness of the buffer film is reduced, the function of preventing damage to the multilayer reflective film during pattern formation or pattern correction of the absorber film is impaired. For example, when a focused ion beam (FIB) is used to correct the absorber film pattern, if the buffer film is thin, the multilayer reflective film is damaged by ion implantation. Therefore, when considering the function of the buffer film, it is desirable that the buffer film is thicker, and it is difficult to achieve the above-described thinning.

In addition, as described in Patent Document 2, the absorber film has an exposure light absorber layer composed of an absorber of exposure light in a short wavelength region such as EUV light as a lower layer, and is used for mask pattern inspection. In the case of a laminated structure having a low reflectivity layer composed of an inspection light absorber as an upper layer, for example, on a TaBN layer that is an EUV light absorber, the purpose is to reduce the reflection of inspection light having a wavelength of 257 nm From the viewpoint of etching control, it is desirable that the etching rate of the upper layer and the lower layer is as close as possible, that is, the ratio of the etching rate of the upper layer to the lower layer is close to 1. . However, a chlorine-based gas is generally used for dry etching of a conventional single-layer Ta-based absorber film, and when the above-described laminated absorber film is dry-etched using this chlorine-based gas, The etching rate of the TaBN layer with respect to the TaBO layer is extremely large (the etching rate of the TaBN layer is about 20 times larger than the etching rate of the TaBO layer), and the etching control is very difficult. There arises a problem that the variation is large. Furthermore, when chlorine-based gas is used, the etching rate of the TaBO layer, which is a part of the absorber film, is small, so it is necessary to set the substrate bias as an etching parameter to a high bias condition, and when the absorber film is over-etched Also, damage to the buffer film is increased. Therefore, from this point of view, it is desirable that the buffer film is thicker.
In this case, a method of dry etching by selecting an optimum etching gas for each layer of the absorber film is also conceivable, but there is a problem that the manufacturing process becomes complicated and the productivity is deteriorated.

As described above, the buffer film is preferably thin from the viewpoint of eliminating the influence on the transferred image due to the residue at the time of etching, but the absorber film, particularly when the absorber film having a multilayer structure is etched or From the viewpoint of preventing damage to the multilayer reflective film at the time of correcting the absorber film pattern, it is desirable that the film thickness be thicker, and therefore, in the conventional reflective mask manufacturing process, one must be sacrificed. It was.
In view of this, the object of the present invention is to manufacture a reflective mask that improves the etching controllability and in-plane uniformity (pattern line width, degree of damage to the buffer film, etc.) of the laminated tantalum absorber film. It is to provide a method, and secondly, to provide a method for manufacturing a reflective mask capable of thinning a chromium-based buffer film provided between a multilayer reflective film and an absorber film.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1) A reflective mask blank having a substrate, a multilayer reflective film that reflects exposure light formed on the substrate, and an absorber film that absorbs exposure light formed on the multilayer reflective film is prepared. And forming a resist pattern on the absorber film to form an absorber film pattern to be a transfer pattern for the transfer object, and etching the absorber film using the resist pattern as a mask. A method of manufacturing a reflective mask having a film pattern forming step, wherein the absorber film is formed with an exposure light absorber layer composed of an absorber of exposure light in a short wavelength region including an extreme ultraviolet region as a lower layer, and a mask pattern Consisting of at least two layers with a low-reflectance layer composed of an inspection light absorber used for the inspection as an upper layer, and both the upper layer and the lower layer are made of a material mainly composed of tantalum (Ta), In the step of etching the absorber film, the same dry etching gas is used, and the etching rate ratio of each layer constituting the absorber film is in the range of 0.1 to 10, wherein the reflective mask is manufactured. Is the method.

  According to Configuration 1, the absorber film is an inspection light absorber used for mask pattern inspection, with the exposure light absorber layer formed of an absorber of exposure light in a short wavelength region including the extreme ultraviolet region as a lower layer. The upper layer and the lower layer are made of a material mainly composed of tantalum (Ta), and the absorber film having such a laminated structure is formed with the same etching gas. The etching controllability of the laminated tantalum-based absorber film is improved when the etching rate ratio of each layer constituting the absorber film is in the range of 0.1 to 10 when dry etching is performed using Therefore, the in-plane uniformity such as the pattern line width and the degree of damage to the buffer film can be improved.

(Structure 2) The reflective mask manufacturing method according to Structure 1, wherein the absorber film is dry-etched using a gas containing fluorine (F).
As in Configuration 2, when the tantalum-based absorber film having the laminated configuration is dry-etched using a gas containing fluorine (F), the etching rate ratio of each layer constituting the absorber film is in a preferable range as in Configuration 1. It can control to become.

(Configuration 3) A reflective mask blank having a substrate, a multilayer reflective film that reflects exposure light formed on the substrate, and an absorber film that absorbs exposure light formed on the multilayer reflective film is prepared. And forming a resist pattern on the absorber film to form an absorber film pattern to be a transfer pattern for the transfer object, and etching the absorber film using the resist pattern as a mask. A method of manufacturing a reflective mask having a film pattern forming step, wherein the absorber film is formed with an exposure light absorber layer composed of an absorber of exposure light in a short wavelength region including an extreme ultraviolet region as a lower layer, and a mask pattern It consists of at least two layers with a low reflectivity layer composed of an inspection light absorber used for the inspection, and one of the upper or lower layers is tantalum (Ta), boron (B), and oxygen (O). The other of the upper layer or the lower layer is made of a material containing tantalum (Ta), boron (B), and nitrogen (N), and the absorber film is formed using a gas containing fluorine (F). A reflective mask manufacturing method characterized by dry etching.

  According to Configuration 3, the absorber film is an inspection light absorber used for mask pattern inspection, with the exposure light absorber layer formed of an absorber of exposure light in a short wavelength region including the extreme ultraviolet region as a lower layer. The upper layer or the lower layer is made of a material containing tantalum (Ta), boron (B), and oxygen (O), and the upper layer or the lower layer is composed of at least two layers. The other is made of a material containing tantalum (Ta), boron (B) and nitrogen (N), and dry-etching the absorber film having such a laminated structure using a gas containing fluorine (F). The etching rate ratio of each layer constituting the absorber film can be controlled within a preferable range, and the etching controllability of the laminated tantalum-based absorber film, the pattern line width, the degree of damage to the buffer film, etc. Inner average It is possible to improve the sex.

(Structure 4) According to any one of Structures 1 to 3, further comprising a step of correcting a defect existing in the absorber film pattern by bringing an electron beam or a needle-like member into contact with the defect. It is a manufacturing method of a reflective mask.
As in Configuration 4, in the reflective mask manufacturing method of the present invention, a defect in the absorber film pattern formed in the absorber film pattern forming step is brought into contact with an electron beam or a needle-like member. It is preferable to include the step of correcting by the above because damage to the multilayer reflective film at the time of correction can be reduced.
(Structure 5) Any one of Structures 1 to 4, wherein a buffer film containing chromium (Cr) having etching characteristics different from those of the absorber film is provided between the multilayer reflective film and the absorber film. It is a manufacturing method of the reflective mask described in 1.
When the buffer film containing chromium (Cr) having etching characteristics different from those of the absorber film is provided between the multilayer reflective film and the absorber film as in the configuration 5, when the pattern of the absorber film is formed, and the pattern Since damage to the multilayer reflective film due to etching during correction is prevented, pattern formation and pattern correction of the absorber film are facilitated, which is preferable. In addition, since the buffer film made of a chromium-based material has high smoothness and the surface of the absorber film formed thereon has high smoothness, pattern blur can be reduced.

(Structure 6) The reflective mask manufacturing method according to Structure 5, wherein the buffer film has a thickness of 2 nm to 10 nm.
In the present invention, when a buffer film containing chromium (Cr) is provided between the multilayer reflective film and the absorber film, damage to the buffer film due to etching during pattern formation of the absorber film and pattern correction is small. The buffer film can be made as thin as 2 to 10 nm. Since the buffer film can be thinned, when removing the buffer film by etching according to the absorber film pattern, it is possible to prevent the residue from remaining as much as possible, and to prevent the transfer image from being affected even if it remains as a residue. it can. In addition, when the buffer film is thinned so that a decrease in reflectance can be suppressed without being removed in a pattern as described above, the buffer film removal step can be omitted. That is, even if the thickness of the buffer film is reduced, it is possible to obtain a reflective mask that can suppress a decrease in the reflectance of the multilayer reflective film during the reflective mask manufacturing process and can perform good pattern transfer.

According to the reflective mask manufacturing method of the present invention, the etching controllability and in-plane uniformity (pattern line width, degree of damage to the buffer film, etc.) of the laminated tantalum absorber film can be improved. Thus, it is possible to prevent damage to the multilayer reflective film during the reflective mask manufacturing process, to suppress a decrease in the reflectance of the multilayer reflective film, and to obtain a reflective mask that can perform good pattern transfer.
In addition, according to the reflective mask manufacturing method of the present invention, the chromium-based buffer film provided between the multilayer reflective film and the absorber film can be thinned, so that a decrease in reflectance of the multilayer reflective film can be suppressed. Thus, a reflective mask that can perform good pattern transfer can be obtained.

Hereinafter, the present invention will be described in detail by embodiments.
FIG. 1 is a cross-sectional view of a reflective mask blank used in the method for producing a reflective mask of the present invention, and FIG. 2 is a cross-sectional view of a reflective mask obtained by the present invention. FIG. 3 is a sectional view showing a schematic process according to the reflective mask manufacturing method of the present invention.
The reflective mask blank used in the reflective mask manufacturing method of the present invention is configured as shown in FIG. That is, on the substrate 11, in order, a multilayer reflective film 12 that reflects exposure light in a short wavelength region including the EUV region, a buffer film 13 that protects the multilayer reflective film 12 during mask pattern formation and mask pattern correction, and EUV An absorber film 16 that absorbs exposure light in a short wavelength region including a region is formed. In this embodiment, the lower layer of the absorber film 16 is an exposure light absorber layer 14 in a short wavelength region including an EUV region. 1 is a reflective mask blank 1 having a two-layer structure in which an upper layer is a low reflection layer 15 for inspection light used for inspection of a mask pattern.

Further, as shown in FIG. 2, the reflective mask 2 obtained by the present invention includes the absorber film 16 (that is, the low reflective layer 15 and the exposure light absorber layer 14) in the reflective mask blank 1 as described above. The buffer film 13 is formed in a pattern.
The reflective mask including the absorber film having the laminated structure described above functions as a layer that absorbs exposure light and a layer that has a low reflectance with respect to the mask pattern inspection wavelength. By separating and laminating, a sufficient contrast at the time of mask pattern inspection is obtained.
The reflective mask obtained by the present invention is used for lithography using light in a short wavelength region including an EUV light region in order to enable transfer of a finer pattern exceeding the transfer limit by the conventional photolithography method. , Which can be used as a reflective mask for EUV exposure light.

Next, the structure of each layer of the reflective mask blank 1 used in the present invention will be described.
As the substrate 11, a glass substrate can be preferably used. A glass substrate has good smoothness and flatness, and is particularly suitable as a mask substrate. Examples of the glass substrate material include amorphous glass having a low thermal expansion coefficient (for example, SiO ₂ —TiO ₂ glass), quartz glass, crystallized glass on which β quartz solid solution is deposited, and the like. The substrate preferably has a smooth surface of 0.2 nmRms or less and a flatness of 100 nm or less in order to obtain high reflectivity and transfer accuracy. In the present invention, the unit Rms indicating smoothness is the root mean square roughness, and can be measured with an atomic force microscope. Further, the flatness in the present invention is a value indicating the surface warpage (deformation amount) indicated by TIR (total indicated reading). This is the difference in height between the highest position of the substrate surface above the focal plane and the lowest position below the focal plane when the plane defined by the least square method based on the substrate surface is the focal plane. Absolute value. Smoothness is indicated by smoothness in a 10 μm square area, and flatness is indicated by flatness in a 142 mm square area.

  The multilayer reflective film 12 is made of a material that reflects exposure light in a short wavelength region including the EUV region, but it should be understood that the multilayer reflective film 12 is made of a material that has a very high reflectivity for light in the short wavelength region such as EUV light. Is particularly preferable since it can increase the contrast when used as a reflective mask. For example, as a multilayer reflective film of EUV light that is a soft X-ray region of about 12 to 14 nm, a periodic laminated film in which thin films of silicon (Si) and molybdenum (Mo) are alternately laminated is representative. Usually, these thin films (thickness of about several nm) are repeatedly laminated for 40 to 60 periods (number of layers) to form a multilayer reflective film. Examples of other multilayer reflective films used in the EUV light region include Ru / Si periodic multilayer reflective films, Mo / Be periodic multilayer reflective films, Mo compound / Si compound periodic multilayer reflective films, and Si / Nb periodic multilayer reflective films. Examples thereof include a film, a Si / Mo / Ru periodic multilayer reflective film, a Si / Mo / Ru / Mo periodic multilayer reflective film, and a Si / Ru / Mo / Ru periodic multilayer reflective film. The multilayer reflective film is formed using, for example, an ion beam sputtering method or a magnetron sputtering method.

The buffer film 13 is provided for the purpose of protecting the lower multilayer reflective film 12 from being damaged by etching when the mask pattern is formed on the absorber film 16 as described above. Therefore, as the material of the buffer film 13, a material having an etching characteristic different from that of the absorber film 16, that is, a material having a high etching selectivity with the absorber film 16 is selected. The etching selectivity between the buffer film and the absorber film is 5 or more, preferably 10 or more, more preferably 20 or more. Furthermore, a material having low stress and excellent smoothness is preferable, and in particular, it has a smoothness of 0.3 nmRms or less. From such a viewpoint, it is preferable that the material for forming the buffer film has a microcrystalline or amorphous structure.
In the present invention, the material of the absorber film 16 is a material containing tantalum (Ta). When a Ta-based material is used as the material of the absorber film, it is preferable to use a material containing chromium (Cr) as the buffer film. For example, Cr alone or a material in which at least one element of nitrogen, oxygen, and carbon is added to Cr can be used. Specifically, chromium nitride (CrN) or the like is used.

  It is desirable that the buffer film 13 be as thin as possible. This is because, as described above, when the buffer film is removed by etching according to the absorber film pattern, as much residue as possible remains, and even if it remains as a residue, the transferred image can be prevented from being affected. Because. In addition, when the buffer film is thin, the buffer film removal step can be omitted if the reduction in reflectance can be suppressed without removing it in a pattern as described above. Further, as apparent from FIG. 2, when the thickness of the buffer film 13 is large, the difference in height between the surface of the multilayer reflective film 12 and the surface of the absorber film 16 becomes large, and the incident is about 5 degrees. This is because the edge portion of the mask pattern is blurred due to the relationship of the optical path of the EUV exposure having a corner. In the present invention, the thickness of the buffer film 13 is preferably in the range of 2 nm to 10 nm. The buffer film 13 can be formed using a known film forming method such as a magnetron sputtering method or an ion beam sputtering method.

Conventionally, when the thickness of the buffer film is as thin as 2 to 10 nm, damage to the multilayer reflective film at the time of forming the absorber film pattern and correcting the pattern could not be suppressed. When the reflective mask manufacturing method is applied, damage to the multilayer reflective film can be sufficiently prevented even with a buffer film having a thickness of 2 to 10 nm.
In addition, the buffer film 13 may be provided as necessary. However, in the present invention, by having the buffer film, damage to the multilayer reflective film during the formation of the absorber film pattern and the pattern correction can be reliably suppressed. In addition, since the thickness of the buffer film can be reduced and problems due to the increased thickness do not occur, it is preferable to provide the buffer film.

As described above, the absorber film 16 has a lower layer made of an absorber layer 14 for exposure light in a short wavelength region including the EUV region, and an upper layer made of a low reflection layer 15 for inspection light used for mask pattern inspection. In this way, the absorber film 16 has a laminated structure in which functions are separated into an absorption layer for exposure light and a low reflection layer for inspection light.
The lower exposure light absorber layer 14 is made of a material that absorbs light in a short wavelength region such as EUV. As such a material, a material containing tantalum (Ta) is used in the present invention. For example, it is preferable to use tantalum alone or an alloy containing tantalum, or a material containing nitrogen and / or oxygen. Specifically, tantalum (Ta), tantalum nitride (TaN), tantalum oxide (TaO), tantalum silicon alloy (TaSi), tantalum silicon alloy nitride (TaSiN), tantalum boron alloy (TaB), tantalum Examples thereof include nitrides of boron alloys (TaBN), tantalum germanium alloys (TaGe), and nitrides of tantalum germanium alloys (TaGeN).

Further, the minimum required characteristics of the upper inspection light low reflection layer 15 are low reflection with respect to the mask pattern inspection wavelength, pattern formation is possible, and the buffer film 13 is removed by etching. It is not etched at this time (there is an etching selection ratio with the buffer film). Furthermore, it is more preferable to have an EUV light absorption function because the total film thickness of the absorber film 16 can be reduced.
For mask pattern inspection, deep ultraviolet (Deep Ultra Violet) light of about 190 to 260 nm is usually used, for example, light having a wavelength of about 257 nm or 193 nm. For example, nitrides, oxides, nitride oxides of materials constituting the above-described exposure light absorber layer 14, or materials further containing silicon or the like can be used.

  Specific examples of the material of the low reflective layer 15 include oxides, nitrides, oxynitrides of tantalum (Ta), oxides of nitrides of tantalum (Ta) and boron, nitrides, oxynitrides, tantalum ( Examples thereof include oxides, nitrides, oxynitrides of alloys of Ta) and silicon, oxides, nitrides, oxynitrides of alloys of tantalum (Ta), silicon, and boron. For example, tantalum oxide (TaO), tantalum nitride (TaN), tantalum oxynitride (TaNO), tantalum boron alloy oxide (TaBO), tantalum boron alloy nitride (TaBN), tantalum boron alloy oxynitride (TaBNO), tantalum silicon alloy oxide (TaSiO), tantalum silicon alloy nitride (TaSiN), tantalum silicon alloy oxynitride (TaSiON), tantalum silicon boron alloy oxide (TaSiBO), tantalum silicon boron Alloy nitride (TaSiBN), tantalum silicon boron alloy oxynitride (TaSiBNO), tantalum germanium alloy nitride (TaGeN), tantalum germanium alloy oxide (TaGeO), tantalum germanium alloy oxynitride (TaGeNO) ,tantalum Nitride luma um silicon alloy (TaGeSiN), oxides of tantalum germanium silicon alloy (TaGeSiO), oxynitride of tantalum germanium silicon alloy (TaGeSiNO), and the like.

In addition, with nitride and oxide, the effect of lowering the reflectivity tends to be greater with oxide, and therefore, the material of at least tantalum and oxygen is particularly preferable as the material for the low reflection layer.
In order to make the surface of the absorber film 16 smooth, the low reflection layer is preferably an amorphous film. For example, in the case of Ta, it can be amorphized by appropriately containing B.
For example, when the low reflective layer is a tantalum boron alloy oxide (TaBO), O is 30 to 70 at%, more preferably 40 to 60 at%. If the amount of O is small, low reflection characteristics cannot be obtained. Conversely, if the amount of O is large, the insulating property becomes high and charge-up occurs due to electron beam irradiation.

  By the way, the combination of materials in the lower exposure light absorber layer 14 and the upper low reflection layer 15 will be described. The metal contained in the exposure light absorber layer 14 is also preferably included in the low reflection layer 15. Specifically, the exposure light absorber layer is made of a material containing tantalum, for example, Ta single substance, TaN, TaB, TaBN, TaBO, TaBNO or the like, and the low reflection layer contains tantalum and nitrogen or oxygen. One kind of material can be used among the materials to be included, such as TaO, TaBO, TaBNO, TaNO, TaSiO, TaSiON, and the like. In this way, by using the same metal as the exposure light absorber layer in the low reflection layer, the low reflection layer has a function of absorbing EUV light to some extent because it includes a metal having an EUV light absorption function. There is an advantage that the light absorber layer and the low reflection layer can be formed in the same film formation chamber.

A smaller overall film thickness of the absorber film 16 composed of the lower exposure light absorber layer 14 and the upper inspection light low reflection layer 15 is basically preferable because the etching time can be shortened. Further, if the thickness of the entire absorber film 16 is large, the difference in height between the surface of the multilayer reflective film 12 and the surface of the absorber film 16 becomes large, as in the case where the film thickness of the buffer film 13 is large. Sometimes the edge of the mask pattern is blurred.
Therefore, the total film thickness of the absorber film 16 is 100 nm or less, preferably 70 to 90 nm.
In the absorber layer 16, it is desirable that the thickness of the upper low reflection layer 15 is smaller than the thickness of the lower exposure light absorber layer 14. If the thickness of the upper low reflection layer 15 is too thick, the EUV light absorption characteristics of the entire absorber film 16 may be deteriorated. Therefore, the film thickness of the upper low reflection layer 15 is preferably about 5 to 30 nm, and the film thickness of the lower exposure light absorber layer 14 is preferably about 30 to 60 nm. The exposure light absorber layer 14 and the inspection light absorber layer 15 can also be formed by using a well-known film formation method such as a magnetron sputtering method, an ion beam sputtering method, other CVD methods, and vapor deposition methods.
Note that an intermediate region in which the composition continuously changes from the lower layer composition to the upper layer composition may be provided between the lower layer and the upper layer of the absorber film 16. This intermediate region is a transition region in which elements contained in the lower layer and elements contained in the upper layer are mixed.

Next, with reference to FIG. 3, the manufacturing method of the reflective mask of this invention is demonstrated.
FIG. 1A shows the configuration of the reflective mask blank 1 used in the present invention. The configuration has already been described above. The reflective mask blank 1 is formed by laminating a multilayer reflective film 12, a buffer film 13, an exposure light absorber layer 14, and an inspection light low reflective layer 15 in this order on a substrate 11.

Next, the absorber film 16 composed of the exposure light absorber layer 14 which is an EUV light absorber and the inspection light low reflection layer 15 is processed to form a predetermined absorber film pattern (patterning step, FIG. b)). Usually, an electron beam drawing resist is applied to the surface of the absorber film 16, a predetermined resist pattern is formed through drawing and development, and then the absorber film is etched.
In the present embodiment, the absorber film 16 is composed of a laminated structure of an exposure light absorber layer 14 constituted by an EUV light absorber and a low reflection layer 15 constituted by an inspection light absorber of a mask pattern. It consists of the material which has a tantalum (Ta) as a main component. In the step of etching the absorber film 16, when dry etching is performed using the same etching gas, the etching rate ratio of each layer constituting the absorber film 16 may be in the range of 0.1 to 10. It is a feature. Thereby, the etching controllability of the laminated tantalum-based absorber film can be improved, and therefore the in-plane uniformity such as the pattern line width and the degree of damage to the buffer film can be improved.

In the present invention, it is most preferable to use a gas containing fluorine (F) as an etching gas when the absorber film 16 having the above-described laminated structure is dry-etched. When the tantalum-based absorber film 16 having the laminated structure is dry-etched using a gas containing fluorine (F), the etching rate ratio of each layer constituting the absorber film 16 can be controlled to be within the above-described preferable range. Because you can.
Examples of the gas containing fluorine (F) include CF ₄ , CHF ₃ , C ₂ F ₆ , C ₃ F ₆ , C ₄ F ₆ , C ₄ F ₈ , CH ₂ F ₂ , CH ₃ F, and C ₃ F. ₈ , SF ₆ , F and the like. Although such a fluorine-containing gas may be used alone, two or more kinds of mixed gases selected from the above-mentioned fluorine gas, a rare gas such as argon (Ar), or a chlorine (Cl ₂ ) gas is mixed. May be used.

Either one of the exposure light absorber layer 14 and the low reflection layer 15 constituting the absorber film 16 is made of a material containing tantalum (Ta), boron (B), and oxygen (O), and the other is tantalum ( When the absorber film 16 is dry-etched using a gas containing fluorine in the case where the absorber film 16 is made of a material containing Ta), boron (B), and nitrogen (N), the etching rate ratio of each layer constituting the absorber film 16 Can be controlled to be in the range of 0.15 to 5.0, the present invention is particularly suitable.
According to the present invention, the etching rate ratio of each layer constituting the absorber film 16 is in the range of 0.1 to 10 by dry etching the laminated tantalum absorber film using, for example, a gas containing fluorine. As a result, the etching controllability of the absorber film 16 can be improved, and damage to the lower layer when the absorber film 16 is etched can be minimized. That is, when a chromium-based buffer film is provided between the absorber film and the multilayer reflective film, the etching selectivity between the absorber film and the buffer film can be increased, so the thickness of the buffer film must be very thin. I can do it.
After the absorber film 16 is etched as described above, the remaining resist pattern is removed by a method such as oxygen ashing.

Next, at this stage, it is inspected whether the absorber film pattern is formed as designed. As a result of this pattern inspection, for example, as shown in FIG. 3B, a pinhole defect (also referred to as a white defect) 21 due to adhesion of foreign matter to the resist layer at the time of forming the absorber film pattern, and an insufficient etching defect ( If there is a black defect 22), the necessary correction is made. The pinhole defect 21 is repaired by depositing the carbon film 23 on the pinhole by, for example, a focused ion beam (FIB) assisted deposition method. In addition, the etching deficiency defect 22 is corrected by removing the remaining portion 22a by etching using electron beam (EB) irradiation or by bringing the needle-like member into contact with the remaining portion 22a and physically removing the remaining portion 22a. By doing so, a removed portion (pattern by correction) 25 of the absorber film 16 having a two-layer structure is obtained.
Thus, according to the modification of the absorber film pattern using the electron beam or the needle-like member, the damage to the lower layer at the time of the modification can be minimized as compared with the pattern modification by the conventional FIB irradiation, for example. It is preferable to provide a chromium-based buffer film between the absorber film and the multilayer reflective film because the buffer film is less damaged and therefore the buffer film can be made very thin.

  Next, with the absorber film 16 having the above pattern formed as a mask, the chromium-based buffer film 13 exposed in the portion from which the absorber film 16 has been removed (becomes a reflective region of the mask) is removed by, for example, dry etching. (Buffer film removal step). In the case of a chromium-based buffer film, for example, dry etching can be performed using a mixed gas of chlorine and oxygen. According to the present invention, as described above, since the damage to the buffer film 13 due to etching at the time of pattern formation of the absorber film 16 and pattern correction is small, the film thickness of the buffer film 13 is reduced to, for example, 2 nm to 10 nm. can do. Since the buffer film 13 can be thinned in this way, when the buffer film 13 is removed by etching according to the absorber film pattern, the transfer image is affected so as not to leave as much residue as possible. It is possible to make it not to give. In addition, when the buffer film is thinned and the reduction in reflectance can be suppressed without removing depending on the film thickness, the buffer film removal step can be omitted.

Thus, the reflective mask 2 is completed by forming the pattern 26 of the absorber film 16 and the buffer film 13 (see FIG. 4D).
When the thus produced reflective mask 2 is exposed to EUV light 31, it is absorbed in a portion of the mask surface where the absorber film 16 is present, and is exposed in a portion where the other absorber film 16 and buffer film 13 are removed. When the EUV light 31 is reflected by the reflective film 12 (see FIG. 5E), it can be used as a reflective mask for lithography using EUV light.

Hereinafter, the embodiment of the present invention will be described more specifically with reference to examples.
Example 1
The substrate to be used is a SiO ₂ —TiO ₂ glass substrate (6 inch square, thickness 6.3 mm). This substrate has a thermal expansion coefficient of 0.2 × 10 ⁻⁷ / ° C. and a Young's modulus of 67 GPa. This glass substrate was formed by mechanical polishing to have a smooth surface of 0.2 nmRms or less and a flatness of 100 nm or less.
As the multilayer reflective film formed on the substrate, a Mo film / Si film periodic multilayer reflective film was employed in order to obtain a multilayer reflective film suitable for an exposure light wavelength band of 13 to 14 nm. That is, the multilayer reflective film was formed by alternately stacking on the substrate by ion beam sputtering using a Mo target and a Si target. The Si film was 4.2 nm, the Mo film was 2.8 nm, and this was taken as one period, and then 40 periods were stacked. Finally, a Si film was formed as a protective film to a thickness of 3.5 nm. When the reflectivity of this multilayer reflective film was measured with 13.5 nm EUV light at an incident angle of 6.0 degrees, the reflectivity was 63.5%.

Next, a buffer film was formed on the multilayer reflective film of the substrate with the multilayer reflective film obtained as described above. As the buffer film, a chromium nitride film was formed to a thickness of 10 nm. Using a chromium (Cr) target, a film was formed by a DC magnetron sputtering method using a mixed gas of argon (Ar) and nitrogen (N ₂ ) as a sputtering gas. In the formed CrNx film, nitrogen (N) was 10 at% (x = 0.1).

Next, a material containing Ta, B, and N was formed to a thickness of 65 nm as an exposure light absorber layer under the absorber film on the buffer film. That is, using a target containing Ta and B, 10% by volume of nitrogen (N ₂ ) was added to argon (Ar), and a film was formed by DC magnetron sputtering. The composition ratio of the formed TaBN film was Ta at 80 at%, B at 10 at%, and N at 10 at%.
A material containing Ta, B, and O was formed to a thickness of 15 nm as a low reflection layer on the exposure light absorber layer. That is, using a target containing Ta and B, 30% by volume of oxygen (O ₂ ) was added to argon (Ar), and a film was formed by DC magnetron sputtering. The composition ratio of the formed TaBO film was Ta at 40 at%, B at 10 at%, and O at 50 at%. The exposure light absorber layer and the low reflection layer were continuously formed by using the same target in the same film forming chamber and switching the gas type halfway.
As described above, a reflective mask blank used in this example was produced.

Next, using this reflective mask blank, a reflective mask for EUV exposure having a pattern for 16 Gbit-DRAM with a design rule of 0.07 μm was produced as follows.
First, an electron beam drawing resist layer (3000 mm) was formed on the reflective mask blank, and a predetermined resist pattern was formed by electron beam drawing and development.
Using this resist pattern as a mask, the laminated absorber film was dry etched using an ICP (Inductively Coupled Plasma) type dry etching apparatus to form an absorber film pattern serving as a transfer pattern on the absorber film. At this time, a mixed gas of CHF ₃ gas and Ar gas is used as an etching gas, and the flow rate ratio of CHF ₃ gas and Ar gas, gas pressure at the time of dry etching, ICP power, and bias are appropriately adjusted to form an absorber film. Dry etching was performed. When the absorber film is dry-etched, the etching rate of the TaBO layer is 141 分 / min, the etching rate of the TaBN layer is 68 Å / min, and the etching rate ratio of the TaBO layer to the TaBN layer (TaBO layer etching rate / TaBN layer) The etching rate was 2.07. The etching selectivity of the absorber film to the resist layer was 0.57, and the etching selectivity of the absorber film to the buffer film was 40 or more. When the film thickness of the CrN buffer film after etching the absorber film was examined, no film loss was observed.

  After removing the remaining resist pattern by oxygen ashing and washing, the formed absorber film pattern was inspected by a mask inspection machine using light having a wavelength of 257 nm. As a result, an under-etching defect (black defect) was confirmed. Therefore, the absorber film pattern was corrected based on the inspection result. That is, the black defect portion was irradiated with an electron beam to remove the remaining portion. In addition, when atomic force microscope (AFM) and cross-sectional TEM observation were performed about the state of the CrN buffer film after correction, the film thickness of the buffer film at the corrected portion disappeared by about 1 to 2 nm.

Then, chlorine gas mixture of (Cl ₂₎ and oxygen (O ₂₎ (mixing ratio of chlorine (Cl ₂₎ and oxygen (O ₂₎ (flow rate ratio) is 8: 2) using a reflective area on the (absorption The buffer film in the portion without the body film pattern) was removed by dry etching according to the pattern of the absorber film, and the multilayer reflective film was exposed to obtain a reflective mask.
When the final confirmation inspection of the obtained reflective mask was performed using the mask inspection machine, it was confirmed that a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm could be formed as designed. Further, the reflectance of EUV light in the reflective region was 63.5%, which was the same as the reflectance measured with the multilayer reflective film-coated substrate.

Next, using the obtained reflective mask of this example, exposure transfer was performed by a pattern transfer apparatus using EUV light onto the semiconductor substrate shown in FIG.
A pattern transfer apparatus 50 equipped with a reflective mask is roughly composed of a laser plasma X-ray source 32, a reduction optical system 33 and the like. The reduction optical system 33 uses an X-ray reflection mirror. By the reduction optical system 33, the pattern reflected by the reflective mask 20 is usually reduced to about ¼. Since the wavelength band of 13 to 14 nm is used as the exposure wavelength, it was set in advance so that the optical path was in vacuum.
In this state, the EUV light obtained from the laser plasma X-ray source 32 is incident on the reflective mask 20, and the light reflected here passes through the reduction optical system 33 on the silicon wafer (semiconductor substrate with resist layer) 34. Transcribed to.
When pattern transfer onto the semiconductor substrate was performed as described above, it was confirmed that the accuracy of the reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

(Example 2)
This example is the same as Example 1 except that the type of etching gas used during dry etching of the absorber film and other etching conditions are adjusted as appropriate, and the etching rate ratio of the TaBO layer to the TaBN layer is changed. A reflective mask was prepared.
That is, the absorber film pattern was formed using a reflective mask blank produced in the same manner as in Example 1. In this example, when the absorber film was dry-etched, the etching rate of the TaBO layer was 141 Å / min, the etching rate of the TaBN layer was 1410 Å / min, and the etching rate ratio of the TaBO layer to the TaBN layer was 0.1 Met. The etching selectivity of the absorber film to the resist layer was 2.17, and the etching selectivity of the absorber film to the buffer film was 40 or more. When the film thickness of the CrN buffer film after etching the absorber film was examined, no film loss was observed.

In addition, pattern inspection and pattern correction after the formation of the absorber film pattern were performed in the same manner as in Example 1. The removal of the CrN buffer film was also performed in the same manner as in Example 1.
When the final confirmation inspection of the obtained reflective mask was performed, it was confirmed that a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm could be formed as designed. Moreover, the reflectance of EUV light in the reflective region was the same as the reflectance of the multilayer reflective film surface measured in the reflective mask blank manufacturing process.
Furthermore, when pattern transfer onto the semiconductor substrate was performed using the apparatus shown in FIG. 4, it was confirmed that the accuracy of the reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

(Example 3)
This example is the same as Example 1 except that the type of etching gas used during dry etching of the absorber film and other etching conditions are adjusted as appropriate, and the etching rate ratio of the TaBO layer to the TaBN layer is changed. A reflective mask was prepared.
That is, the absorber film pattern was formed using a reflective mask blank produced in the same manner as in Example 1. In this example, when the absorber film was dry-etched, the etching rate of the TaBO layer was 349 Å / min, the etching rate of the TaBN layer was 35 Å / min, and the etching rate ratio of the TaBO layer to the TaBN layer was 10. It was. The etching selectivity of the absorber film to the resist layer was 0.87, and the etching selectivity of the absorber film to the buffer film was 40 or more. When the film thickness of the CrN buffer film after etching the absorber film was examined, no film loss was observed.

In addition, pattern inspection and pattern correction after the formation of the absorber film pattern were performed in the same manner as in Example 1. The removal of the CrN buffer film was also performed in the same manner as in Example 1.
When the final confirmation inspection of the obtained reflective mask was performed, it was confirmed that a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm could be formed as designed. Moreover, the reflectance of EUV light in the reflective region was the same as the reflectance of the multilayer reflective film surface measured in the reflective mask blank manufacturing process.
Furthermore, when pattern transfer onto the semiconductor substrate was performed using the apparatus shown in FIG. 4, it was confirmed that the accuracy of the reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

Example 4
In this embodiment, the pattern correction (black defect correction) after the absorber film pattern formation in the first embodiment is physically removed by bringing the needle-like member into contact with the black defect portion (residual portion). A reflective mask was produced in the same manner as in Example 1 except that the absorber film pattern was corrected.
When AFM and cross-sectional TEM observation was performed on the state of the modified CrN buffer film, the film thickness of the buffer film at the corrected portion disappeared by about 1 nm.
When the final confirmation inspection of the obtained reflective mask was performed, it was confirmed that a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm could be formed as designed. Moreover, the reflectance of EUV light in the reflective region was the same as the reflectance of the multilayer reflective film surface measured in the reflective mask blank manufacturing process.
Furthermore, when pattern transfer onto the semiconductor substrate was performed using the apparatus shown in FIG. 4, it was confirmed that the accuracy of the reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

(Comparative example)
A reflective mask blank was produced in the same manner as in Example 1 except that the CrN buffer film was formed to a thickness of 20 nm. The reflectivity of EUV light on the surface of the multilayer reflective film was 63.5%.
Using this reflective mask blank, an absorber film pattern was formed using an ICP (Inductively Coupled Plasma) type dry etching apparatus. In this comparative example, chlorine gas was used as the etching gas at this time, and the absorber film was dry etched by appropriately adjusting the chlorine gas flow rate, gas pressure during dry etching, ICP power, and bias. When the absorber film was dry etched, the etching rate of the TaBO layer was 41 Å / min, the etching rate of the TaBN layer was 905 Å / min, and the etching rate ratio of the TaBO layer to the TaBN layer was 0.05. The etching selectivity of the absorber film to the resist layer was 0.58, and the etching selectivity of the absorber film to the buffer film was 0.5. In addition, when AFM and cross-sectional TEM observation were performed about the state of the CrN buffer film after etching of the absorber film, a film loss of about 10 nm was confirmed.

Next, pattern inspection after absorber film pattern formation was performed using a mask inspection machine, and based on the results, residual portions of black defects were removed by FIB-excited gas-assisted etching. Damaged portions (specifically, portions removed by FIB irradiation and portions where FIB ions entered) were formed on the surface of the buffer film due to the energy generated by.
Next, in the same manner as in Example 1, the buffer film on the reflective region (the portion without the absorber film pattern) is mixed according to the pattern of the absorber film using a mixed gas of chlorine (Cl ₂ ) and oxygen (O ₂ ). The multilayer reflective film was exposed by removing by dry etching to obtain a reflective mask.

When the final reflective inspection of the obtained reflective mask was performed using the mask inspection machine, a pattern for 16 Gbit-DRAM with a design rule of 0.07 μm was formed temporarily, but the in-plane variation was large. It was. This is considered to be because the etching controllability is poor because the etching rate ratio between the TaBN layer and the TaBO layer constituting the absorber film is large in this comparative example. Further, the reflectance of EUV light in the reflective region was 61.5%, which was lower than the reflectance measured with the multilayer reflective film-coated substrate. The reason why the reflectivity was lower than when the multilayer reflective film was formed was that the CrN buffer film was formed to a thickness of 20 nm at the time of manufacturing the reflective mask, but the absorber film pattern formation and pattern correction were still performed. It is considered that the damage to the buffer film was so great that the damage to the multilayer reflective film surface could not be prevented.
Furthermore, the pattern was transferred onto the semiconductor substrate using the apparatus shown in FIG. 4, but the resolution was lowered. The reason for this is that when the buffer film in the reflective region is removed by dry etching, the film thickness is large, so that the peripheral part of the removed part remains as a residue and affects the transferred image. The difference in height between the surface of the multilayer reflective film and the absorber film is large due to the thick part, causing the problem that the edge part of the mask pattern blurs during exposure, and the reflectivity of the reflective area has decreased. It is done.

It is sectional drawing of the reflective mask blank used for the manufacturing method of the reflective mask of this invention. It is sectional drawing of the reflection type mask obtained by this invention. It is sectional drawing which shows the schematic process which concerns on the manufacturing method of the reflection type mask of this invention. It is a figure which shows schematic structure of the pattern transfer apparatus carrying a reflection type mask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reflective mask blanks 2 and 20 Reflective mask 11 Substrate 12 Multilayer reflective film 13 Buffer film 14 Exposure light absorber layer 15 Low reflective layer 16 Absorber film 50 Pattern transfer device

Claims (6)

A reflective mask blank having a substrate, a multilayer reflective film that reflects exposure light formed on the substrate, and an absorber film that absorbs exposure light formed on the multilayer reflective film is prepared, and the absorption Forming a resist pattern on the body film to form an absorber film pattern to be a transfer pattern for the transfer object, and etching the absorber film using the resist pattern as a mask; A reflective mask manufacturing method comprising:
Low reflectivity in which the absorber film is composed of an exposure light absorber layer composed of an absorber of exposure light in a short wavelength range including the extreme ultraviolet region, and an inspection light absorber used for mask pattern inspection. The upper layer and the lower layer are both made of a material mainly composed of tantalum (Ta).
In the step of etching the absorber film, the same dry etching gas is used, and the etching rate ratio of each layer constituting the absorber film is in the range of 0.1 to 10, wherein the reflective mask is manufactured. Method.   The method of manufacturing a reflective mask according to claim 1, wherein the absorber film is dry-etched using a gas containing fluorine (F). A reflective mask blank having a substrate, a multilayer reflective film that reflects exposure light formed on the substrate, and an absorber film that absorbs exposure light formed on the multilayer reflective film is prepared, and the absorption Forming a resist pattern on the body film to form an absorber film pattern to be a transfer pattern for the transfer object, and etching the absorber film using the resist pattern as a mask; A reflective mask manufacturing method comprising:
Low reflectivity in which the absorber film is composed of an exposure light absorber layer composed of an absorber of exposure light in a short wavelength range including the extreme ultraviolet region, and an inspection light absorber used for mask pattern inspection. The upper layer or the lower layer is made of a material containing tantalum (Ta), boron (B), and oxygen (O), and the other of the upper layer or the lower layer is made of tantalum ( A method of manufacturing a reflective mask, comprising a material containing Ta), boron (B), and nitrogen (N), and dry-etching the absorber film using a gas containing fluorine (F).   4. The reflective mask according to claim 1, further comprising a step of correcting a defect present in the absorber film pattern by bringing an electron beam or a needle-like member into contact with the defect. Manufacturing method.   5. The buffer film containing chromium (Cr) having etching characteristics different from those of the absorber film is provided between the multilayer reflective film and the absorber film. 6. Method for manufacturing a reflective mask.   6. The method of manufacturing a reflective mask according to claim 5, wherein the buffer film has a thickness of 2 nm to 10 nm.

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