JP2013089691A - Defect correction method and manufacturing method of reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect correction method and a manufacturing method of a reflective mask capable of ensuring correct understanding of the impact of a phase defect on a transfer pattern.SOLUTION: The defect correction method of a reflective mask having a substrate, a multilayer film formed on the substrate, an absorption layer patterned on the multilayer film, and a phase defect of the multilayer film includes: an observation step for observing the phase defect with EUV light and acquiring information about the phase defect including an inclination thereof for the thickness direction of the multilayer film from an optical image; and a correction step for correcting the phase defect on the basis of the information about the phase defect.

Description

  The present invention relates to a reflective mask used in extreme ultraviolet (EUV) lithography.

  In recent years, with the miniaturization of semiconductor devices, EUV lithography, which is an exposure technique using extreme ultraviolet rays (hereinafter sometimes referred to as EUV), is promising in the semiconductor industry. As a mask used in this EUV lithography, a reflective mask in which a multilayer film is formed on a substrate and an absorption layer is formed in a pattern on the multilayer film has been proposed (see, for example, Patent Document 1).

In the manufacturing process of the reflective mask, after the pattern is formed by etching the absorption layer, the pattern defect is usually inspected, and if a defect is found, the defect is corrected.
Here, the place where the pattern of the absorption layer is excessively formed or foreign matter is attached is called a black defect. Similar to defect correction of conventional photomasks, black defects can be corrected with a high degree of accuracy by removing excess absorption layer patterns and foreign matter using local etching techniques such as focused ion beams and electron beams. Is possible.

In the case of a reflective mask, there are defects called so-called phase defects in which the structure of the multilayer film is disturbed in addition to the black defects. Phase defects are caused by fine particles and pits existing on the surface of the substrate. During the mask blank manufacturing process, irregularities due to the fine particles and pits are propagated during the formation of the multilayer film, and the structure of the multilayer film is disturbed. Become. Similarly, a phase defect also occurs when fine particles are involved in the multilayer film during the process of forming the multilayer film. Since the direction in which the exposure light is reflected is disturbed due to the disorder of the structure of the multilayer film, the light intensity in the region where the phase defect exists is lower than the light intensity in the normal mask pattern.
Since the phase defect exists in the multilayer film, it is very difficult to directly correct like the black defect, and it is recognized that it is difficult to correct the phase defect. On the other hand, it is not realistic to obtain a reflective mask having no phase defect.

  Therefore, the surface shape of the multilayer film is observed with an atomic force microscope (hereinafter sometimes referred to as AFM), the shape of the phase defect is specified, and the pattern of the absorption layer around the phase defect is processed. Thus, a technique for correcting a decrease in light intensity due to a phase defect has been proposed (for example, see Patent Document 2).

JP 2002-319542 A Japanese translation of PCT publication No. 2002-532738

  Conventionally, in the phase defect model, for example, when a convex portion exists on the surface of the substrate, the phase defect 11 maintains the concavo-convex shape by the convex portion 10 on the surface of the substrate 2 as illustrated in FIG. The model that is formed in the vertical direction is used. When estimating the influence of the phase defect on the transfer pattern, the surface shape of the multilayer film is observed with an AFM, and the size of the phase defect is determined using a model in which the phase defect is formed in a direction perpendicular to the substrate surface. The three-dimensional shape such as height or depth is specified, and the influence on the transfer pattern is evaluated by inputting the three-dimensional shape of the phase defect to the simulator.

However, the inventors' research has revealed that phase defects are not necessarily formed in a direction perpendicular to the substrate surface.
Since the projection image of the mask pattern is affected by the disturbance of the structure inside the multilayer film, the phase defect 11 formed in the direction perpendicular to the surface of the substrate 2 as illustrated in FIG. The influence of the mask pattern on the projected image is different from that of the phase defect 11 formed in a non-perpendicular direction with respect to the surface of the substrate 2.

  In AFM, only the surface shape of the multilayer film is observed, and phase defects existing inside the multilayer film cannot be observed. Therefore, the influence of the phase defect on the transfer pattern cannot be accurately evaluated, and the phase defect cannot be corrected with high accuracy.

  Further, as long as a phase defect model formed in a direction perpendicular to the substrate surface is used, it is difficult to accurately grasp the influence of the phase defect on the transfer pattern.

  The present invention has been made in view of the above circumstances, and has as its main object to provide a reflection mask defect correcting method and a manufacturing method capable of accurately grasping the influence of a phase defect on a transfer pattern. To do.

  To achieve the above object, the present invention includes a substrate, a multilayer film formed on the substrate, an absorption layer formed in a pattern on the multilayer film, and a phase defect of the multilayer film. A method for correcting a defect of a reflective mask, wherein the phase defect is observed with EUV light, and an observation step of acquiring information on the phase defect including an inclination of the phase defect with respect to a thickness direction of the multilayer film from an optical image; And a correction step of correcting the phase defect based on the information on the phase defect.

  In the present invention, since phase defects are observed with EUV light having a very short wavelength, phase defects existing in the multilayer film can be observed with high sensitivity, and the inclination of the phase defect with respect to the thickness direction of the multilayer film is specified. Therefore, it is possible to accurately grasp the influence of the phase defect on the transfer pattern. Therefore, the phase defect can be corrected with high accuracy.

  In the above invention, it is preferable to use an optical system equivalent to the exposure optical system as the image forming means using the EUV light in the observation step. This is because the optical image obtained in the observation step can be made substantially equivalent to the projected image when the mask pattern is transferred, and the influence of the phase defect on the transfer pattern can be estimated more accurately.

  Moreover, in this invention, it is preferable to process the said absorption layer based on the information of the said phase defect in the said correction process. This is because the method of processing the absorbent layer is a relatively simple method.

  Furthermore, in the present invention, it is preferable that the wavelength of the EUV light in the observation step is in the range of 10 nm to 15 nm. This is because the wavelength of the EUV light is preferably the same wavelength as the exposure light used for transferring the mask pattern.

  According to another aspect of the present invention, there is provided a method of manufacturing a reflective mask, comprising a phase defect correcting step of correcting a phase defect of the reflective mask by performing the above-described defect correcting method of the reflective mask.

  In the present invention, since the above-described defect correction method for the reflective mask is performed, the phase defect can be corrected with high accuracy and the yield can be improved.

  In the present invention, there is an effect that it is possible to accurately grasp the influence of the phase defect on the transfer pattern.

It is a schematic sectional drawing which shows an example of the reflective mask in this invention. It is a schematic plan view which shows an example of the reflective mask in this invention. It is a schematic diagram which shows an example of the observation process in the defect correction method of the reflective mask of this invention. It is a schematic diagram which shows an example of the correction process in the defect correction method of the reflective mask of this invention. It is a schematic diagram which shows an example of the correction process in the defect correction method of the reflective mask of this invention. It is a schematic diagram which shows the other example of the correction process in the defect correction method of the reflection type mask of this invention. 3 is a projection view of a reflective mask in Embodiment 1. FIG. 6 is a model of a phase defect of a reflective mask in Comparative Example 1. 6 is a schematic diagram showing correction of a phase defect of a reflective mask in Comparative Example 1. FIG. 6 is a projection view of a reflective mask in Comparative Example 1. FIG.

  Hereinafter, the defect correction method and manufacturing method of the reflective mask of the present invention will be described in detail.

A. Reflection Mask Defect Correction Method First, the reflection mask defect correction method of the present invention will be described.
The reflection mask defect correcting method of the present invention includes a substrate, a multilayer film formed on the substrate, an absorption layer formed in a pattern on the multilayer film, and a phase defect of the multilayer film. A method for correcting a defect of a reflective mask, wherein the phase defect is observed with EUV light, and an observation step of acquiring information on the phase defect including an inclination of the phase defect with respect to a thickness direction of the multilayer film from an optical image; And a correction step of correcting the phase defect based on the information on the phase defect.

The reflection mask defect correcting method of the present invention will be described with reference to the drawings.
1 is a schematic cross-sectional view showing an example of the reflective mask of the present invention, FIG. 2 is a schematic plan view showing an example of the reflective mask of the present invention, and FIG. 1 is a cross-sectional view taken along line AA of FIG. It is.
As illustrated in FIGS. 1 and 2, the reflective mask 1 includes a substrate 2, a multilayer film 3 formed on the substrate 2, a capping layer 4 formed on the multilayer film 3, and a capping layer 4. And the phase defect 11 in which the structure of the multilayer film 3 is disturbed. The phase defect 11 is formed in a non-perpendicular direction with respect to the surface of the substrate 2, that is, inclined with respect to the thickness direction d of the multilayer film 3. Therefore, only a part of the phase defect 11 is visible on the surface of the multilayer film 3.

  FIG. 3 is a schematic view showing an example of an observation step in the defect correction method for a reflective mask according to the present invention. In the reflection mask defect correcting method of the present invention, first, as illustrated in FIG. 3, the region where the phase defect 11 exists in the multilayer film 3 is irradiated with EUV light 15 to form an image of the reflected light. Observe phase defects. Information on phase defects such as the phase defect size, height or depth, position, and the inclination of the phase defect with respect to the thickness direction of the multilayer film is acquired by the change in the light intensity of the optical image.

  When observing a phase defect with an AFM as in the prior art, only the surface shape of the multilayer film is observed, and the phase defect existing inside the multilayer film cannot be observed. It is also possible to observe phase defects with ultraviolet rays in the wavelength range of about 488 nm to 193 nm, but only the surface layer of the multilayer film can be observed, and phase defects existing below the surface layer of the multilayer film are observed. I can't do it. Therefore, it is difficult to specify the inclination of the phase defect with respect to the thickness direction of the multilayer film. On the other hand, when observing phase defects with EUV light, the wavelength of EUV light is very short, so it is possible to observe even the deep part of the multilayer film, and the phase defects existing inside the multilayer film are highly sensitive. The phase defect can be observed directly. Therefore, it is possible to specify the inclination of the phase defect with respect to the thickness direction of the multilayer film. Therefore, it is possible to accurately grasp the influence of the phase defect on the transfer pattern.

  Further, since EUV light is light used for transferring a mask pattern, an optical image obtained in the observation process is appropriately projected by transferring the mask pattern by appropriately selecting EUV light irradiation conditions. Therefore, it is possible to more accurately estimate the influence of the phase defect on the transfer pattern.

  FIGS. 4A to 4B are process diagrams showing an example of a correction process in the defect correction method for a reflective mask according to the present invention. FIG. 5 shows an example of a correction process in the defect correction method for a reflection mask according to the present invention. FIG. 4B is a cross-sectional view taken along line B-B in FIG. 5. In the reflection mask defect correcting method of the present invention, next, as illustrated in FIGS. 4A to 4B and FIG. 5, the light intensity of the phase defect 11 is determined based on the information of the phase defect 11. In order to correct the decrease, the absorption layer 5 located around the phase defect 11 is processed.

  In the present invention, it is possible to accurately grasp the influence of the phase defect on the transfer pattern as described above, so that the processing region of the absorption layer can be specified accurately, and the phase defect is corrected with high accuracy. It becomes possible.

  Hereinafter, each process and the reflective mask in the reflective mask defect correcting method of the present invention will be described.

1. Observation Step The observation step in the present invention is a step of observing the phase defect with EUV light and acquiring information on the phase defect including the inclination of the phase defect with respect to the thickness direction of the multilayer film from the optical image.

  The EUV light that is the inspection light is not particularly limited as long as the phase defect can be observed, but the wavelength of the EUV light is preferably the same as the exposure light used for transferring the mask pattern, Specifically, it is preferably in the range of 10 nm to 15 nm, and more preferably in the range of 13.5 ± 0.5 nm. The center wavelength is preferably 13.5 nm.

  Further, the optical system for irradiating EUV light is not particularly limited as long as a phase defect can be observed. For example, an optical system capable of adjusting EUV light irradiation conditions such as the incident angle, wavelength, and resolution of EUV light. An optical system equivalent to the exposure optical system used for transferring the system and the mask pattern can be used. In the case of an optical system capable of adjusting the irradiation conditions of EUV light, the phase defects existing in the multilayer film can be observed all over by changing the irradiation conditions and observing the phase defects. On the other hand, in the case of an optical system equivalent to the exposure optical system, it is possible to accurately observe the influence of a phase defect that needs to be corrected.

  Especially, it is preferable that the optical system which irradiates EUV light is an optical system equivalent to an exposure optical system. This is because the influence of the phase defect that needs to be corrected can be observed accurately as described above. In addition, the optical image obtained in the observation process can be made substantially equivalent to the projected image when the mask pattern is transferred, and the influence of the phase defect on the transfer pattern can be estimated more accurately.

  As an apparatus for observing phase defects with EUV light, for example, an EUV microscope can be used.

The phase defect information acquired in the observation process is information obtained from an optical image obtained by irradiating the multilayer film with EUV light to form reflected light, and the inclination of the phase defect with respect to the thickness direction of the multilayer film. In addition to the inclination of the phase defect with respect to the thickness direction of the multilayer film, for example, the size, height or depth, position, etc. of the phase defect can be mentioned.
The inclination of the phase defect with respect to the thickness direction of the multilayer film refers to the structure of the multilayer film from the unevenness of the substrate surface or the substrate surface or foreign matter in the multilayer film toward the multilayer film surface with respect to the thickness direction of the multilayer film. The inclination in the direction in which the turbulence is propagated.
The size of the phase defect means the size in plan view.
The height of the phase defect means the height of the convex portion when the phase defect is a convex defect. For example, in FIG. 3, the height of the phase defect 11 is indicated by h. Moreover, the depth of a phase defect means the depth of a recessed part in case a phase defect is a concave defect.

  When observing the phase defect, in addition to observing the phase defect with EUV light, the phase defect may be observed with AFM. It is possible to accurately determine whether the phase defect is a convex defect or a concave defect, and it is possible to specify the size, height, depth, etc. of the phase defect present on the multilayer film surface. This is because it is possible to acquire the information in detail.

2. Correction Step The correction step in the present invention is a step of correcting a phase defect based on phase defect information.

  As a method for correcting a phase defect, a general method for correcting a phase defect can be applied. For example, a method for processing an absorption layer, a region where a phase defect exists in a multilayer film, and a normal multilayer film The method of replacement is mentioned.

  4A and 4B are process diagrams showing an example of a method of processing the absorption layer, and FIG. 4B is a cross-sectional view taken along line BB in FIG. In the method of processing the absorbing layer, although not shown in the drawing, the processing region of the absorbing layer is specified in order to correct the decrease in light intensity due to the phase defect based on the phase defect information. As illustrated in (a) to (b) and FIG. 5, the processed region of the absorption layer 5 is removed.

  When specifying the processing region of the absorption layer, it may be observed by AFM. This is because it is possible to accurately determine whether the phase defect is a convex defect or a concave defect, and to specify the shape of the phase defect, and to specify the positional relationship between the phase defect and the pattern of the absorption layer. .

  The method for removing the processing region of the absorbing layer is not particularly limited as long as it can locally remove the processing region of the absorbing layer, and a general method for processing the absorbing layer should be applied. Can do. For example, a method of etching by irradiating the absorption layer with an energy beam, a method of cutting the absorption layer with a probe of a scanning probe microscope, and the like can be mentioned.

In the method of irradiating the absorption layer with the energy beam, the energy beam is not particularly limited as long as only the processing region of the absorption layer can be locally etched, but a focused ion beam or an electron beam is preferably used. It is done. This is because advanced microfabrication is possible and it is possible to cope with the processing region of a fine absorption layer.
In this case, the energy beam may be irradiated while supplying the assist gas to the absorption layer. This is because the absorption layer can be etched better than when only the energy beam is used. In the case of a focused ion beam, an assist gas may or may not be used. On the other hand, in the case of an electron beam, an assist gas is required.
The assist gas is not particularly limited as long as it is a gas that can etch the absorption layer, and examples thereof include XeF ₂ , iodine, SF ₆ , CF ₄ , and NO _x .

  In the case of the method of scraping the absorption layer with the probe of a scanning probe microscope, the probe of the scanning probe microscope is not particularly limited, and a commonly used probe can be used. Examples thereof include a diamond probe.

  6A to 6C are process diagrams showing an example of a method of removing a region where a phase defect exists in a multilayer film and replacing it with a normal multilayer film. In this method, first, as illustrated in FIGS. 6A to 6B, based on the information of the phase defect 11, the region where the phase defect 11 of the multilayer film 3 exists is removed in a predetermined shape, As illustrated in FIG. 6C, a normal multilayer film 3a cut into an equivalent shape is replaced.

  The method of removing the region where the phase defect of the multilayer film exists is not particularly limited as long as the multilayer film can be locally removed, and a general multilayer film processing method is applied. be able to. For example, a method of etching by irradiating the multilayer film with an energy beam, a method of cutting the multilayer film with a probe of a scanning probe microscope, and the like can be mentioned.

In the method of irradiating the multilayer film with the energy beam, the energy beam is not particularly limited as long as it can locally etch only the region where the phase defect of the multilayer film exists. A beam is preferably used. This is because high-level microfabrication is possible and it is possible to deal with a fine region.
In this case, the energy beam may be irradiated while supplying the assist gas to the multilayer film.

  Further, in the case of a method of scraping a multilayer film with a probe of a scanning probe microscope, the probe of the scanning probe microscope is not particularly limited, and a commonly used probe can be used. .

  When removing the region where the phase defect of the multilayer film is present, it is preferable to remove the multilayer film so that the height of the replaced multilayer film matches the peripheral multilayer film when the normal multilayer film is replaced. . In order to make the depth for removing the multilayer film appropriate, it is preferable to confirm the processing amount and the removal depth at the time of processing the multilayer film. This is because the progress of processing in the depth direction of the multilayer film may vary depending on the processing device, the material of the multilayer film, and the like, and there is a possibility of an error between the set processing amount and the actual processing amount. .

In order to remove the multilayer film so that the replaced multilayer film and the peripheral multilayer film have the same height, it is preferable to process the bottom of the portion where the multilayer film has been removed. At this time, the bottom of the portion from which the multilayer film is removed may be processed to be flat, or the bottom of the portion from which the multilayer film is removed may be processed to form a reference depth surface. Good.
When forming a surface having a reference depth at the bottom of the portion where the multilayer film has been removed, for example, processing is performed until the substrate is exposed while changing the removal depth of the multilayer film in the plane direction, and the multilayer is exposed. By grasping the processing amount of the film and removing the multilayer film with the processing amount, a surface having a reference depth can be formed. At this time, if at least three points have the reference depth, a surface having the reference depth can be formed. Further, portions other than the reference depth surface may be removed deeper than the reference depth. If at least three points become the reference depth, the depth of the bottom of the portion from which the multilayer film has been removed is determined. Therefore, portions other than at least the three reference depths may be scraped off. As illustrated in FIG. 6A, in the region where the phase defect 11 of the multilayer film 3 is present, the thickness is different from that of the normal multilayer film 3, so that it is difficult to accurately confirm the processing amount and the removal depth. However, since it can be removed deeper than the reference depth as illustrated in FIG. 6B, the phase defect can be completely removed.
Also, when processing so that the bottom of the portion where the multilayer film is removed is flat, the multilayer film is removed so that the substrate is exposed, and then the exposed substrate surface is processed to be flat. Good.

  In addition, when removing the region where the phase defect of the multilayer film is present, since the absorption layer is formed in a pattern on the multilayer film, the multilayer film replaced under the absorption layer and the peripheral multilayer film The multilayer film may be removed so that the boundary is located. As a result, the influence of the boundary between the replaced multilayer film and the peripheral multilayer film on the pattern transfer can be eliminated. In this case, when removing the multilayer film, a part of the absorption layer is also removed and replaced with a normal multilayer film, and then the absorption layer is formed again. A boundary with the membrane can be placed. In addition, after removing a part of the multilayer film and the absorption layer, replacing the multilayer film with the absorption layer formed in a pattern on the multilayer film, the multilayer film replaced under the absorption layer and the peripheral multilayer film A boundary can also be placed.

  In addition, by using DFM (Design for Manufacturing) technology, the boundary between the replaced multilayer film and the peripheral multilayer film is appropriately arranged so that the boundary between the replaced multilayer film and the peripheral multilayer film does not affect pattern transfer. You can also choose.

  After removing the region where the phase defect of the multilayer film is present and replacing it with a normal multilayer film, for example, the normal multilayer film is cut out and processed so that the bottom of the cut-out multilayer film becomes flat. It is possible to use a method of installing at a place where the water is removed.

When cutting out the multilayer film, it may be cut out from a reflective mask having a phase defect, or may be cut out from another mask blank or a reflective mask.
In addition, in order to place the boundary between the replaced multilayer film and the peripheral multilayer film below the absorption layer, a structure in which the absorption layer is formed in a pattern on the multilayer film may be cut out.

  As a method for cutting out the multilayer film and a method for processing the bottom of the cut-out multilayer film, for example, a focused ion beam can be used.

  When installing a normal multilayer film where the multilayer film has been removed, replace it so that the boundary between the replaced multilayer film and the surrounding multilayer film has a small gap so as not to affect pattern transfer. The alignment is preferably performed so that the multilayer film and the peripheral multilayer film have the same height.

  JP, 2010-34129, A can be referred to for a method of removing a region where a phase defect exists in a multilayer film and replacing it with a normal multilayer film.

  Among them, as a method for correcting the phase defect, a method of processing the absorption layer is preferable because it is a simple method.

3. Reflective mask The reflective mask in the present invention has a substrate, a multilayer film formed on the substrate, an absorption layer formed in a pattern on the multilayer film, and a phase defect of the multilayer film It is.
Hereinafter, each configuration in the reflective mask will be described.

(1) Phase defect In the present invention, a phase defect is a defect caused by the disorder of the structure of the multilayer film, and includes irregularities on the surface of the substrate, foreign matter adhering to the substrate, and entangled in the multilayer film when the multilayer film is formed. It is caused by a foreign material. This phase defect is a defect that a mask blank used for manufacturing a reflective mask has.

  The present invention is effective in correcting relatively small phase defects. As the magnitude of the phase defect, specifically, the full width at half maximum is preferably 100 nm or less, and more preferably in the range of 10 nm to 90 nm. Further, the height or depth of the phase defect is specifically preferably 10 nm or less, and more preferably in the range of 0.1 nm to 2 nm.

(2) Multilayer film The multilayer film in the present invention is formed on a substrate and reflects EUV light which is exposure light in EUV lithography using the reflective mask of the present invention.

  As a material for the multilayer film, a material generally used for a multilayer film of a reflective mask can be used, and among them, a material having an extremely high reflectance with respect to EUV light is preferably used. This is because the contrast can be increased when the reflective mask is used. For example, a Mo / Si periodic multilayer film is usually used as the multilayer film that reflects EUV light. In addition, as a multilayer film having a high reflectance in a specific wavelength range, for example, a Ru / Si periodic multilayer film, a Mo / Be periodic multilayer film, a Mo compound / Si compound periodic multilayer film, and a Si / Nb period A multilayer film, a periodic multilayer film of Si / Mo / Ru, a periodic multilayer film of Si / Mo / Ru / Mo, a periodic multilayer film of Si / Ru / Mo / Ru, and the like can also be used.

  The thickness of each layer constituting the multilayer film and the number of stacked layers are different depending on the material to be used and are appropriately adjusted. For example, as the Mo / Si periodic multilayer film, a multilayer film in which a Mo film and a Si film having a thickness of about several nm are stacked by 40 to 60 layers can be used.

The thickness of the multilayer film can be, for example, about 280 nm to 420 nm.
As a method for forming the multilayer film, for example, an ion beam sputtering method, a magnetron sputtering method, or the like is used.

(3) Absorbing layer The absorbing layer in the present invention is formed in a pattern on the multilayer film, and absorbs EUV light in EUV lithography using the reflective mask of the present invention.

  The material of the absorption layer is not particularly limited as long as it can absorb EUV light. For example, Ta, TaN, Ta as a main component, Cr, Cr as a main component, N, O, A material containing at least one component selected from C is used. Furthermore, TaSi, TaSiN, TaGe, TaGeN, WN, TiN, etc. can be used.

As a method for forming the absorption layer, for example, a magnetron sputtering method, an ion beam sputtering method, a CVD method, a vapor deposition method, or the like is used.
As a method for forming the absorption layer in a pattern, a photolithography method is usually used. Specifically, an absorption layer is formed on a substrate on which a multilayer film is formed, a resist layer is formed on the absorption layer, the resist layer is patterned, and the absorption layer is etched using the resist pattern as a mask to remain. The resist pattern is removed to form an absorption layer in a pattern. As the photolithography method, a general method can be used.

(4) Capping layer In the present invention, a capping layer may be formed between the multilayer film and the absorption layer. The capping layer is provided to prevent oxidation of the multilayer film and to protect the reflective mask during cleaning. By forming the capping layer, when the outermost surface of the multilayer film is a Si film or a Mo film, the Si film or the Mo film can be prevented from being oxidized. If the Si film or the Mo film is oxidized, the reflectance of the multilayer film may be reduced.
In the present invention, when a buffer layer described later is formed on the multilayer film, the capping layer and the buffer layer are usually stacked in this order on the multilayer film.

The material for the capping layer is not particularly limited as long as it exhibits the above functions, and examples thereof include Si and Ru.
Moreover, as thickness of a capping layer, it can be set as about 2 nm-15 nm, for example.
Examples of the method for forming the capping layer include a sputtering method.

(5) Buffer layer In this invention, the buffer layer may be formed between the multilayer film and the absorption layer. The buffer layer is provided to prevent damage to the lower multilayer film. By forming the buffer layer, it is possible to prevent the underlying multilayer film from being damaged when the absorption layer is subjected to pattern etching by a method such as dry etching.

As the material of the buffer layer, any material having high etching resistance may be used, and a material having a different etching characteristic from that of the absorption layer, that is, a material having a high etching selectivity with the absorption layer is usually used. The etching selectivity of the buffer layer and the absorption layer is preferably 5 or more, more preferably 10 or more, and still more preferably 20 or more. Furthermore, the material for the buffer layer is preferably a material having low stress and excellent smoothness. In particular, the smoothness of the buffer layer is preferably 0.3 nmRms or less. From such a viewpoint, it is preferable that the material of the buffer layer has a microcrystalline or amorphous structure.
Examples of such a buffer layer material include SiO ₂ , Al ₂ O ₃ , Cr, and CrN.

Further, the thickness of the buffer layer can be, for example, about 2 nm to 25 nm.
Examples of the method for forming the buffer layer include a magnetron sputtering method and an ion beam sputtering method. When using Cr, it is preferable to deposit Cr on the multilayer film in an Ar gas atmosphere using a Cr target by an RF magnetron sputtering method.

  When the buffer layer is formed on the multilayer film, the exposed buffer layer may be peeled after the patterning of the absorption layer. As a method for peeling the buffer layer, a general method for peeling the buffer layer can be used, and examples thereof include dry etching.

(6) Substrate As the substrate used in the present invention, a substrate generally used for a reflective mask substrate can be used, and for example, a glass substrate or a metal substrate can be used. Among these, a glass substrate is preferably used. A glass substrate is particularly suitable as a substrate for a reflective mask because good smoothness and flatness can be obtained. Examples of the material of the glass substrate include quartz glass, amorphous glass having a low thermal expansion coefficient (for example, SiO ₂ —TiO ₂ glass), crystallized glass on which β quartz solid solution is precipitated, and the like. Examples of the material for the metal substrate include silicon and Fe-Ni-based invar alloys. In addition, about the amorphous glass which has a low thermal expansion coefficient, Unexamined-Japanese-Patent No. 2010-135732 can be referred.

The substrate preferably has a smoothness of 0.2 nmRms or less and a flatness of 100 nm or less in order to obtain a high reflectance and transfer accuracy of a reflective mask. In addition, unit Rms which shows smoothness is a root mean square roughness, and can be measured using an atomic force microscope. The flatness is a value indicating the warpage (deformation amount) of the surface indicated by TIR (Total Indicated Reading). This value is the difference in height between the highest position on 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. Is the absolute value of. The smoothness is smoothness in a 10 μm square area, and the flatness is flatness in a 142 mm square area.
Moreover, as thickness of a board | substrate, it can be set as about 6 mm-7 mm, for example.

(7) Conductive film In the present invention, a conductive film may be formed on the surface of the substrate opposite to the surface on which the multilayer film and the absorption layer are formed. The conductive film is provided to attract the reflective mask to the electrostatic chuck of the exposure apparatus. By having such a conductive film, the reflective mask can be easily and firmly fixed to the exposure apparatus during exposure, and the pattern transfer accuracy and manufacturing efficiency can be improved.

The material of the conductive film is not particularly limited as long as it is generally used for the conductive film of the reflective mask. For example, a metal or a metal compound such as Cr or CrN showing conductivity is used.
In addition, the thickness of the conductive film can be, for example, about 30 nm to 150 nm.

  Examples of the method for forming the conductive film include a sputtering method. In the case where the conductive film is formed in a pattern, a sputtering method, a photolithography method, or the like through a mask can be used as the formation method.

B. Next, a method for manufacturing a reflective mask according to the present invention will be described.
The reflective mask manufacturing method of the present invention includes a phase defect correcting step of correcting a phase defect of the reflective mask by performing the above-described reflective mask defect correcting method.

  In the present invention, since the above-described defect correction method for the reflective mask is performed, the phase defect can be corrected with high accuracy. Further, even when a mask blank having a phase defect is used or when a phase defect is detected after manufacturing a reflective mask, the phase defect can be corrected and the yield can be improved.

The reflective mask manufacturing method of the present invention includes a reflective mask manufacturing process for manufacturing a reflective mask and a phase defect correcting process.
In the reflective mask manufacturing process, the method of forming each layer constituting the reflective mask has been described in the above section “A. Reflective Mask Defect Correction Method 3. Reflective Mask”. Description is omitted.
Further, in the phase defect correction step, the defect correction method for the reflective mask has been described in detail in the above section “A. Reflection Mask Defect Correction Method”, and thus the description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  The following examples illustrate the present invention in more detail.

[Example 1]
The effect of the present invention was verified in detail by simulation. The simulator used was EM-Suite made by Panoramic Technology. The simulation was carried out using the actual reflective mask structure and the optical system of the EUV exposure apparatus as a model, and the effect was verified by calculating a projection image when the mask pattern was transferred by the exposure apparatus.

  As shown in FIGS. 1 and 2, the reflective mask has a multilayer film 3 composed of 40 pairs of molybdenum and silicon (film thickness 2.8 nm / 4.2 nm) on a substrate 2 made of silicon oxide, A ruthenium capping layer 4 (film thickness of 2.5 nm) was sequentially laminated, and a line-and-space pattern absorption layer 5 (film thickness of 66 nm) having a line width of 225 nm was formed on the capping layer 4. Furthermore, the so-called phase defect 11 (half-value width 100 nm, height 3 nm) in which the multilayer structure of the multilayer film 3 is disturbed is arranged in a space portion where no absorption layer is formed. The phase defect 11 is formed in a non-perpendicular direction with respect to the surface of the substrate 2 and is inclined with respect to the thickness direction of the multilayer film.

  The transfer conditions were set in the optical system of an EUV exposure apparatus SFET (Small Field Exposure Tool) manufactured by Canon Inc., and NA = 0.3 and σ = 0.3 / 0.7 (inner / outer). The transfer dimension was calculated from the projected image when the mask pattern was transferred by the exposure apparatus.

The phase defect is observed using an EUV microscope, and information on the phase defect including the inclination of the phase defect with respect to the thickness direction of the multilayer film is obtained from the optical image. Based on the information on the phase defect, the phase defect transfer pattern is obtained. Estimated the impact. Then, the absorption layer 5 was processed as illustrated in FIGS. 4A to 4B and FIG. 5 so as to reduce the influence of the phase defect on the transfer pattern.
As shown in FIG. 7, the projection image 20 to which the mask pattern is transferred by the exposure apparatus has a dark portion 21 and a bright portion 22, and a projection image equivalent to the normal pattern is obtained at the corrected portion, and the corrected portion is transferred. The dimension was a line width of 45 nm.

[Comparative Example 1]
The reflective mask and transfer conditions were the same as in Example 1.

The surface shape of the multilayer film was observed with an atomic force microscope, and the shape of the phase defect was specified using a model of the phase defect 11 formed in the direction perpendicular to the surface of the substrate 2 as shown in FIG. Based on the shape of the phase defect, the absorption layer 5 is processed as illustrated in FIG. 9 so as to reduce the influence of the phase defect on the transfer pattern.
As shown in FIG. 10, the projection image 20 to which the mask pattern is transferred by the exposure apparatus has a dark portion 21 and a bright portion 22, and the phase defect is formed in a non-perpendicular direction with respect to the substrate surface. The affected convex part 23 was confirmed. At this time, as for the transfer size, the normal space portion had a line width of 45 nm, while the portion where the convex portion 23 was formed had a width of 15 nm.

DESCRIPTION OF SYMBOLS 1 ... Reflective mask 2 ... Substrate 3 ... Multilayer film 4 ... Capping layer 5 ... Absorbing layer 10 ... Convex part 11 ... Phase defect 15 ... EUV light d ... Thickness direction of multilayer film

Claims (5)

A reflection mask defect correction method comprising a substrate, a multilayer film formed on the substrate, an absorption layer formed in a pattern on the multilayer film, and a phase defect of the multilayer film,
An observation step of observing the phase defect with EUV light and obtaining information on the phase defect including an inclination of the phase defect with respect to a thickness direction of the multilayer film from an optical image;
And a correction step of correcting the phase defect based on the information on the phase defect.   2. The reflection mask defect correcting method according to claim 1, wherein an optical system equivalent to an exposure optical system is used as the image forming means using the EUV light in the observation step.   3. The defect correction method for a reflective mask according to claim 1, wherein, in the correction step, the absorption layer is processed based on information on the phase defect.   The defect correction method for a reflective mask according to any one of claims 1 to 3, wherein the wavelength of the EUV light in the observation step is in a range of 10 nm to 15 nm.   A reflection mask having a phase defect correction step of correcting a phase defect of the reflection mask by performing the defect correction method of the reflection mask according to any one of claims 1 to 4. Production method.

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