JP2014130975A - Method of manufacturing substrate with multilayer reflection film, method of manufacturing reflective mask blank, and method of manufacturing reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a substrate with a multilayer reflection film which can satisfy three characteristics of high reflectance, high film thickness uniformity, and low surface roughness.SOLUTION: A multilayer reflection film is formed by laminating a plurality of periods of a lamination structure, where a high refractive index layer and a low refractive index layer are deposited in this order on a substrate, or a lamination structure, where a low refractive index layer and a high refractive index layer are laminated in this order, by using an ion beam sputtering method. The low refractive index layer is deposited by changing the deposition conditions so that, in the region of a low refractive index layer near the boundary to a high refractive index layer immediately above or below, the reflectance of multilayer reflective film is 65% or more than that of other regions, the in-plane variation of center wavelength is 0.04 nm or less, and the surface roughness of square mean root is 0.15 nm or less.

Description

  The present invention relates to a method for manufacturing a substrate with a multilayer reflective film, a method for manufacturing a reflective mask blank, and a method for manufacturing a reflective mask, which are original plates for manufacturing an exposure mask used in semiconductor device manufacturing and the like. is there.

With the further demand for higher density and higher precision of VLSI devices in recent years, 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 refers to 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 a reflective mask mounted on an exposure machine (pattern transfer device) is absorbed in a part where the absorber film is present, and a light image reflected by the multilayer reflective film is reflected in a part where there is no absorber film. And transferred onto the semiconductor substrate.

In order to achieve higher density and higher accuracy of semiconductor devices using such a reflective mask, the reflective region (surface of the multilayer reflective film) in the reflective mask is higher than the EUV light that is the exposure light. It is necessary to provide reflectivity.
The multilayer reflective film is a multilayer film in which elements having different refractive indexes are periodically laminated. Generally, a thin film of a heavy element or a compound thereof and a thin film of a light element or a compound thereof are alternately 40 to 40 A multilayer film laminated for about 60 cycles is used. For example, as a multilayer reflective film for EUV light having a wavelength of 13 to 14 nm, a Mo / Si periodic laminated film in which Mo films and Si films are alternately laminated for about 40 cycles is preferably used.

For example, in Patent Document 2, an angle formed between a normal line of a substrate and sputtered particles incident on the substrate is set to 35 degrees or more and 80 degrees by using an ion beam sputtering method for a multilayer reflective film made of a Mo / Si periodic laminated film. The following describes that the film is formed while being held.
Further, in Patent Document 3, for example, a Si layer, which is a high refractive index layer of a multilayer reflective film, is formed by direct incidence film formation so that sputtered particles are incident on the substrate surface in a substantially vertical direction. It is described that, for example, a Mo layer which is a low refractive index layer is formed by oblique incidence film formation in which sputtered particles are incident at an angle of 40 degrees to 80 degrees with respect to the normal direction of the substrate. Yes.

JP 2002-122981 A Japanese Patent No. 4858539 JP 2009-272317 A

  However, when the multilayer reflective film is formed under the film forming conditions for obtaining a high reflectance as disclosed in Patent Document 2 and Patent Document 3, the problem arises that the surface roughness of the multilayer reflective film deteriorates. . On the other hand, when a multilayer reflective film is formed under film-forming conditions that improve surface roughness mainly by direct-incidence film formation, the sputtered particles are incident at an angle close to the normal direction of the substrate. Since the kinetic energy in the direction is large and the diffusion layer between the Si layer and the Mo layer becomes large, there arises a problem that the exposure light reflectance of the multilayer reflective film decreases.

  In recent years, as optical specifications of reflective mask blanks used in generations after DRAM hp 20 nm, requirements regarding reflectance and variation in center wavelength (CW) have become stricter year by year. It is required to guarantee the quality of the mask blank using a sensitivity defect inspection apparatus. However, if the surface roughness of the multilayer reflective film is large, a large number of pseudo defects due to background noise are detected, and there is a problem that a highly accurate defect inspection cannot be performed.

  Therefore, in recent reflective mask blanks, not only is the reflectance high, but also the in-plane uniformity of the multilayer reflective film thickness that affects the variation in the center wavelength, and the multilayer reflective film has a low surface roughness. There is also a need to be. However, it has been difficult to satisfy all of the characteristics of high reflectivity, high in-plane uniformity, and low surface roughness under the conventional conditions for forming a multilayer reflective film.

Accordingly, an object of the present invention is, firstly, to provide a method for manufacturing a substrate with a high-quality multilayer reflective film that can satisfy all three characteristics of high reflectivity, high in-plane uniformity, and low surface roughness. Second, to provide a method for manufacturing a reflective mask blank using such a substrate with a multilayer reflective film, and a method for manufacturing a reflective mask.

The present inventor has completed the present invention as a result of intensive studies to solve the above problems.
That is, in order to solve the above problems, the present invention has the following configuration.
(Configuration 1)
A method of manufacturing a substrate with a multilayer reflective film comprising a multilayer reflective film that reflects exposure light comprising a multilayer film in which low refractive index layers and high refractive index layers are alternately laminated on a substrate, wherein the multilayer reflective film comprises: A laminated structure in which a high refractive index layer and a low refractive index layer are formed in this order on the substrate, or a laminated structure in which a low refractive index layer and a high refractive index layer are laminated in this order are laminated in a plurality of periods. The low refractive index layer has a reflectance of 65% or more, an in-plane variation of the center wavelength of 0.04 nm or less, and a surface roughness of 0.15 nm in terms of root mean square roughness. A multilayer characterized in that the film is formed by changing the film formation conditions in the vicinity of the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer, as described below. A method for manufacturing a substrate with a reflective film.

  As in Configuration 1, a single layer of a laminated structure in which a high refractive index layer and a low refractive index layer are formed in this order on the substrate, or a laminated structure in which a low refractive index layer and a high refractive index layer are laminated in this order. When the multilayer reflective film is formed by laminating a plurality of periods, the low refractive index layer has a reflectance of 65% or more, an in-plane variation of the center wavelength of 0.04 nm or less, and a surface roughness of square. In the region near the boundary with the high refractive index layer immediately below and just above the low refractive index layer, the average square root roughness is 0.15 nm or less. Film. In this way, the film formation conditions of the low-refractive index layer, which greatly depends on the surface state of the multilayer reflective film, are set to be highly reflective in the region near the boundary with the high-refractive index layer immediately below and immediately above the low-refractive index layer and other regions. By applying the film forming conditions that can realize the rate and high in-plane uniformity of the film thickness and the film forming conditions that can realize the low surface roughness other than the region near the boundary, The three characteristics of reflectivity, low in-plane variation of the center wavelength, and low surface roughness can be achieved at their respective best values.

(Configuration 2)
2. The method for manufacturing a substrate with a multilayer reflective film according to Configuration 1, wherein the multilayer reflective film is formed using an ion beam sputtering method.
The present invention is preferable since the effect of the present invention is more effectively exhibited when the multilayer reflective film is formed by using the ion beam sputtering method as in Configuration 2.

(Configuration 3)
3. The method for manufacturing a substrate with a multilayer reflective film according to Configuration 1 or 2, wherein the film formation condition of the low refractive index layer is an incident angle of sputtered particles with respect to a normal line of the main surface of the substrate.
As in the configuration 3, the effect of the present invention is preferably obtained by changing the incident angle of the sputtered particles with respect to the normal line of the main surface of the substrate as the film forming condition of the low refractive index layer.

(Configuration 4)
In the low refractive index layer, the incident angle of the sputtered particles with respect to the normal of the main surface of the substrate in the region near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer is other than in the region near the boundary. 4. The method for manufacturing a substrate with a multilayer reflective film according to Configuration 3, wherein sputtering film formation is performed under film formation conditions larger than an incident angle of sputtered particles with respect to a normal line of a main surface of the substrate.
As in Configuration 4, the film formation conditions of the low refractive index layer, which greatly depends on the surface state of the multilayer reflective film, are set in the region near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer. Low surface roughness except for the condition where the incident angle of the sputtered particles is relatively large with respect to the normal of the main surface of the substrate, which is a film forming condition that can realize reflectivity and in-plane uniformity with a high film thickness, and the region near the boundary. By applying the conditions under which the incident angle of the sputtered particles is relatively small with respect to the normal of the main surface of the substrate, which is a film forming condition that can realize a high degree of reflectance, the multilayer reflective film to be formed has a high reflectance and a low center wavelength The three characteristics of internal variation and low surface roughness can be made compatible at the respective best values.

(Configuration 5)
During the formation of the low refractive index layer, the incident angle of the sputtered particles with respect to the normal of the main surface of the substrate is 45 degrees or more in the region near the boundary with the low refractive index layer immediately below and immediately above the low refractive index layer. The method for producing a substrate with a multilayer reflective film according to Configuration 4, wherein the range is 55 ° or less, and the other region is 20 ° or more and 40 ° or less.
As in Configuration 5, when the low refractive index layer is formed, the incident angle of the sputtered particles with respect to the normal of the main surface of the substrate is set in the region near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer. Film forming conditions that can achieve high reflectivity and high in-plane uniformity in the region near the boundary by setting the range from 45 degrees to 55 degrees and in the other areas from 20 degrees to 40 degrees. In other areas, film formation conditions that can realize low surface roughness are applied, respectively, and the three types of reflection characteristics, that is, the high reflectance of the multilayer reflective film, the low in-plane variation of the center wavelength, and the low surface roughness. It is possible to achieve both characteristics at the best values.

(Configuration 6)
6. The method for manufacturing a multilayer reflective film-coated substrate according to any one of Structures 1 to 5, wherein a region in the vicinity of the boundary with the high refractive index layer is a region of 2 nm or less.
In order to obtain the effect of the present invention preferably, it is desirable that the region in the vicinity of the boundary with the high refractive index layer is a region of 2 nm or less as in the configuration 6.

(Configuration 7)
Manufacturing of a reflective mask blank, characterized in that an absorber film that absorbs exposure light is formed on the multilayer reflective film in the multilayer reflective film-coated substrate obtained by the manufacturing method according to any one of Structures 1 to 6. Method.
By manufacturing a reflective mask blank using a substrate with a multilayer reflective film that satisfies the three characteristics of high reflectivity, low in-plane variation of the center wavelength, and low surface roughness obtained by the present invention, high sensitivity defects A reflective mask blank having a high reflectance capable of assuring the quality of the mask blank can be obtained by defect inspection using an inspection apparatus.

(Configuration 8)
A method for manufacturing a reflective mask, comprising: patterning the absorber film in a reflective mask blank obtained by the manufacturing method according to Configuration 7.
By manufacturing a reflective mask using the reflective mask blank of the present invention capable of guaranteeing high quality, a high quality reflective mask with few defects can be obtained.

According to the present invention, all of the three characteristics of high reflectivity, low in-plane variation of the center wavelength, and low surface roughness are satisfied, and these characteristics are compatible with each other at the best value. A substrate with a multilayer reflective film can be obtained.
Further, according to the present invention, by using such a substrate with a multilayer reflective film, a reflective mask having a high reflectance that can guarantee the quality of a mask blank by defect inspection using a high-sensitivity defect inspection apparatus. A blank is obtained.
Furthermore, by manufacturing a reflective mask using such a reflective mask blank of the present invention, a high-quality reflective mask with few defects can be obtained.

It is sectional drawing which shows the layer structure of a board | substrate with a multilayer reflective film. It is sectional drawing which shows the layer structure of a reflection type mask blank. It is sectional drawing which shows the layer structure of a reflection type mask. It is sectional drawing which shows the detailed layer structure of a board | substrate with a multilayer reflective film. It is a schematic diagram which shows the structure of an ion beam sputtering apparatus.

Hereinafter, the present invention will be described in detail by embodiments.
[Substrate with multilayer reflective film]
First, the multilayer reflective film-coated substrate according to the present invention will be described.
FIG. 1 is a cross-sectional view showing a layer structure of a substrate with a multilayer reflective film according to the present invention. The multilayer reflective film has a multilayer reflective film 2 that reflects EUV light as exposure light on the substrate 1. The attached substrate 10 is shown.
In the case of EUV exposure, the substrate 1 is in the range of 0 ± 1.0 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.3 × 10 ⁻ in order to prevent pattern distortion due to heat during exposure. Those having a low thermal expansion coefficient in the range of ⁷ / ° C. are preferably used, and as a material having a low thermal expansion coefficient in this range, for example, SiO ₂ —TiO ₂ glass, multicomponent glass ceramics, or the like is used. I can do it.

The main surface of the substrate 1 on which the transfer pattern is formed is subjected to surface processing so as to have high flatness from the viewpoint of obtaining at least pattern transfer accuracy and position accuracy. For example, in the case of EUV exposure, the flatness is preferably 0.1 μm or less, particularly preferably 0.05 μm or less, in the region of the main surface 142 mm × 142 mm on the side where the transfer pattern of the substrate is formed. The main surface opposite to the side on which the transfer pattern is formed is a surface that is electrostatically chucked when being set in the exposure apparatus, and has a flatness of 1 μm or less, preferably 0.8 mm in a 142 mm × 142 mm region. 5 μm or less.
In the case of EUV exposure, the surface smoothness required for the substrate 1 is such that the surface roughness of the main surface on the side where the transfer pattern of the substrate is formed is 0.2 nm or less in terms of root mean square roughness (RMS). It is preferable that

The multilayer reflective film 2 is a multilayer film in which elements having different refractive indexes are periodically laminated, and generally, a thin film (low refractive index layer) of a heavy element or a compound thereof, which is a low refractive index material, A multilayer film in which thin films (high refractive index layers) of light elements which are high refractive index materials or compounds thereof are alternately stacked for about 40 to 60 cycles is used. The multilayer film may be formed by laminating a plurality of periods with a laminated structure in which a high refractive index layer and a low refractive index layer are laminated in this order from the substrate side. A plurality of layers may be stacked with a stacked structure sequentially stacked as one cycle. As the low refractive index material, an element selected from Mo, Ru, Rh, and Pt or an alloy thereof is used, and as the high refractive index material, Si or a Si compound is used. For example, as the multilayer reflective film for EUV light having a wavelength of 13 to 14 nm, a Mo / Si periodic laminated film in which Mo films and Si films are alternately laminated for about 40 to 60 periods is preferably used.

  The multilayer reflective film 2 can be formed by depositing each layer by ion beam sputtering. The present invention is suitable because the effects of the present invention are more effectively exhibited when a multilayer reflective film is formed using an ion beam sputtering method. In the case of the above-described Mo / Si periodic multilayer film, for example, by an ion beam sputtering method, a Si film having a thickness of about several nanometers is first formed using a Si target, and then a Mo film having a thickness of about several nanometers is formed using a Mo target. A film is formed, and this is set as one period, and after 40 to 60 periods are stacked, finally, a Si film is formed.

Here, an ion beam sputtering method that is preferably used as a method for forming the multilayer reflective film 2 of the present invention will be described.
FIG. 5 is a schematic diagram showing a configuration of an ion beam sputtering apparatus.
An ion beam sputtering apparatus 50 shown in FIG. 5 includes an ion beam generator 51, a target holder 53, a substrate stage 58, and the like. Two kinds of sputtering targets 54 and 55 are attached to the target holder 53. In the present invention, one of them is a high refractive index material target (for example, Si target), and the other is a low refractive index material target (Mo). Target). By rotation of the target holder 53, one of the high refractive material target and the low refractive index material target is directed to the film formation surface of the substrate 1. The substrate 1 is fixed on the substrate stage 58 by an electrostatic chuck or a mechanical chuck that mechanically holds the substrate, and is rotated in a predetermined direction by a driving device.

  In the ion beam sputtering apparatus 50 having such a configuration, the incident angle θ (specifically, the substrate) of the sputtered particles 56 generated when the ion beam 52 emitted from the ion beam generating apparatus 51 enters the sputtering target 54 (or 55). The position of the sputtering target 54 (or 55) is adjusted so that the incident angle of the sputtered particles with respect to the normal 57 of the main surface 1 is a predetermined angle, and the ion beam sputtering is performed while rotating the substrate 1. Thus, the multilayer reflective film 2 is formed.

The present invention provides a substrate with a multilayer reflective film comprising a multilayer reflective film that reflects exposure light comprising a multilayer film in which a low refractive index layer and a high refractive index layer are alternately laminated on the substrate, as in Configuration 1 above. The multilayer reflective film has a laminated structure in which a high refractive index layer and a low refractive index layer are formed in this order on the substrate, or a low refractive index layer and a high refractive index layer in this order. The low-refractive index layer has a reflectivity of 65% or more and an in-plane variation of the center wavelength (CW: Centroid Wavelength). Other regions in the vicinity of the boundary with the high refractive index layer immediately below and just above the low refractive index layer so that the surface roughness is 0.15 nm or less in terms of root mean square roughness of 0.04 nm or less. Is characterized by changing the film forming conditions to form a film.
Preferably, the low refractive index layer is formed so that the reflectance of the multilayer reflective film is 66% or more, the variation in center wavelength is 0.03 nm or less, and the surface roughness is 0.14 nm or less in terms of root mean square roughness. It is desirable to form a film by changing the film forming conditions in the region near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer.

FIG. 4 is a cross-sectional view showing a detailed layer structure of a substrate with a multilayer reflective film.
As shown in FIG. 4, a substrate 10 with a multilayer reflective film according to the present invention includes a multilayer reflective film 2 in which high refractive index layers 21 and low refractive index layers 22 are alternately laminated on a substrate 1. .

A characteristic of the present invention is that each of the low refractive index layers 22 changes the film formation conditions in the region 22a near the boundary with the high refractive index layer 21 immediately below and immediately above the low refractive index layer 22 from the other regions. To form a film.
Here, as the film forming condition of the low refractive index layer, it is preferable to select the incident angle θ of the sputtered particles with respect to the normal line of the main surface of the substrate 1. By changing the incident angle θ of the sputtered particles with respect to the normal of the main surface of the substrate as the film forming condition of the low refractive index layer, the effect of the present invention is preferably exhibited.

Specifically, at the time of forming each low refractive index layer 22, the incident angle θ of the sputtered particles with respect to the normal of the main surface of the substrate 1 is set to be different from that of the high refractive index layer 21 directly below and immediately above the low refractive index layer 22. In the boundary vicinity region 22a, a range of 45 degrees or more and 55 degrees or less is preferable. It is preferably 47 ° or more and 53 ° or less, particularly preferably (49 ° or more and 51 ° or less), and most preferably 50 °. When the incident angle of the sputtered particles is less than 45 degrees, the diffusion layer formed at the interface between the low refractive index layer and the high refractive index layer becomes large and the reflectance of the multilayer reflective film decreases. This is because the in-plane distribution of the film thickness is deteriorated, which is not preferable, and when it exceeds 55 degrees, the in-plane distribution of the film thickness of the low refractive index layer is deteriorated and the film formation rate is further decreased.
Moreover, it is preferable that the incident angle θ of the sputtered particles is in the range of 20 degrees to 40 degrees in the region other than the boundary vicinity region 22 a of the molybdenum layer 22. Especially preferably, it is the range of 25 degree | times or more and 35 degrees or less, Most preferably, it is 30 degree | times. If the incident angle of the sputtered particles is less than 20 degrees, the surface roughness of the low refractive index layer becomes large and the in-plane distribution of the film thickness of the low refractive index layer deteriorates. This is because the surface roughness of the refractive index layer increases and the in-plane distribution of the film thickness of the high refractive index layer deteriorates, which is not preferable.

  As described above, when each low refractive index layer 22 is formed, the incident angle θ of the sputtered particles with respect to the normal of the main surface of the substrate 1 is set to be equal to that of the high refractive index layer 21 directly below and immediately above the low refractive index layer 22. By setting the range in the vicinity of the boundary area 22a to 45 degrees or more and 55 degrees or less, and in the other areas in the range of 20 degrees or more and 40 degrees or less, the boundary vicinity area 22a has a high reflectivity and high in-plane uniformity. The film formation conditions that can realize the low reflectivity and the film formation conditions that can realize the low surface roughness in the other regions are applied, respectively. The three characteristics of surface roughness can be satisfied, and these three characteristics can be made compatible with each other at their best values.

In each low refractive index layer 22, the boundary vicinity region 22a with the high refractive index layer 21 is desirably a region of 2 nm or less in order to obtain the effect of the present invention. If the thickness is larger than 2 nm (thick), the diffusion layer formed by oblique incidence film formation of the low refractive index layer becomes unnecessarily thick, and the effect of reducing the surface roughness of the low refractive index layer becomes low, which is not preferable.

  On the other hand, in forming the high refractive index layer 21, the incident angle θ of the sputtered particles with respect to the normal of the main surface of the substrate 1 is preferably in the range of 25 degrees to 35 degrees, and most preferably over the entire layer. It is about 30 degrees, and the best film thickness in-plane distribution and low surface roughness can be realized.

  As described above, when the multilayer reflective film 2 is formed by laminating a plurality of periods in which the high refractive index layer 21 and the low refractive index layer 22 are formed in this order on the substrate 1 as a period, the low refractive index 2 The layer 22 changes the film formation condition, preferably the incident angle of the sputtered particles incident on the substrate, in the region 22a near the boundary with the high refractive index layer 21 immediately below and immediately above the low refractive index layer. For low refractive index layers whose film characteristics vary depending on the film formation conditions, film formation conditions that can achieve high reflectivity and high in-plane uniformity of the film thickness and low surface roughness can be realized. By applying the film forming conditions, it is possible to satisfy each of the best values of the three characteristics of the formed multilayer reflective film: high reflectivity, low in-plane variation of the center wavelength, and low surface roughness.

[Reflective mask blank]
The present invention also provides a method for manufacturing a reflective mask blank using a substrate with a multilayer reflective film manufactured by the above-described manufacturing method of the present invention.
FIG. 2 is a cross-sectional view showing the layer structure of the reflective mask blank. On the substrate 1, a multilayer reflective film 2 that reflects EUV light, a protective film (capping layer) 3 and a pattern for absorbing EUV light are formed. The reflective mask blank 20 in which the absorber film 4 is formed is shown. Although not shown, a back conductive film can be provided on the side of the substrate 1 opposite to the side where the multilayer reflective film or the like is formed.
The substrate with the multilayer reflective film in the state where the multilayer reflective film is formed on the substrate 1 is as described above, and the description thereof is omitted here.

Usually, the protective film 3 and the buffer film are provided between the multilayer reflective film 2 and the absorber film 4 for the purpose of protecting the multilayer reflective film 2 during patterning or pattern correction of the absorber film 4. As a material for the protective film 3, in addition to silicon, ruthenium or a ruthenium compound containing one or more elements of niobium, zirconium, and rhodium in ruthenium is used. As a material for the buffer film, a chromium-based material is mainly used. Used.
The protective film 3 and the buffer film are preferably formed by a sputtering method such as magnetron sputtering.
In the present invention, the substrate having the multilayer reflective film includes the protective film 3 formed on the multilayer reflective film 2. In the substrate with a multilayer reflective film on which the protective film 3 is formed, it is preferable that the reflectance is 62% or more, the in-plane variation of the center wavelength is 0.04 nm or less, and the surface roughness is root mean square roughness 0.15 nm or less. Particularly preferably, the reflectance is 63% or more, the variation in the center wavelength is 0.03 nm or less, and the surface roughness is 0.13 nm or less in terms of root mean square roughness.

The absorber film 4 has a function of absorbing exposure light such as EUV light. For example, tantalum (Ta) alone or a material mainly composed of Ta can be preferably used. The material mainly composed of Ta is usually an alloy of Ta. Such an absorber film preferably has an amorphous or microcrystalline structure in terms of smoothness and flatness.
As a material having Ta as a main component, a material containing Ta and B, a material containing Ta and N, a material containing Ta and B and further containing at least one of O and N, a material containing Ta and Si, Ta A material containing Si and N, a material containing Ta and Ge, a material containing Ta, Ge and N can be used. By adding B, Si, Ge or the like to Ta, an amorphous material can be easily obtained and the smoothness can be improved. Further, when N or O is added to Ta, resistance to oxidation is improved, so that an effect that stability with time can be improved is obtained.

Among these, as a particularly preferable material, for example, a material containing Ta and B (composition ratio Ta / B is in the range of 8.5 / 1.5 to 7.5 / 2.5), Ta, B and N are included. Materials (N is 5 to 30 atomic%, and B is 10 to 30 atomic% when the remaining components are 100). In the case of these materials, a microcrystalline or amorphous structure can be easily obtained, and good smoothness and flatness can be obtained.
Such an absorber film containing Ta alone or Ta as a main component is preferably formed by a sputtering method such as magnetron sputtering. For example, in the case of a TaBN film, a target containing tantalum and boron can be used and a film can be formed by a sputtering method using an argon gas to which nitrogen is added.

As the absorber film, materials other than materials mainly composed of Ta include materials such as WN, TiN, and Ti.
The thickness of the absorber film 4 may be a thickness that can sufficiently absorb, for example, EUV light as exposure light, but is usually about 30 to 100 nm. The absorber film 4 may have a laminated structure of a plurality of layers having different materials and compositions (for example, a laminated film of a TaBN film and a TaBO film).

Even in the case of a reflective mask that applies EUV light to exposure light, the inspection light used for pattern inspection is often light having a longer wavelength than EUV light having a wavelength of 193 nm, 257 nm, or the like. In order to deal with long-wavelength inspection light, it is necessary to reduce the surface reflection of the absorber film. In this case, the absorber film may have a structure in which an absorber layer mainly having a function of absorbing EUV light and a low reflection layer mainly having a function of reducing surface reflection with respect to inspection light are laminated from the substrate side. As the low reflection layer, when the absorber layer is a material mainly composed of Ta, a material containing O in Ta or TaB is suitable.
The reflective mask blank may be in a state where a resist film for forming a predetermined transfer pattern is formed on the absorber film.

According to the present invention, a reflective mask blank using a substrate with a multilayer reflective film that satisfies the three characteristics of high reflectivity, high in-plane uniformity, and low surface roughness obtained by the present invention described above. Thus, a reflective mask blank having a high reflectance capable of guaranteeing the quality of the mask blank by defect inspection using a high-sensitivity defect inspection apparatus is obtained.

[Reflective mask]
The present invention also provides a method for manufacturing a reflective mask using the reflective mask blank having the above-described configuration.
FIG. 3 is a cross-sectional view showing a layer structure of the reflective mask, and shows a reflective mask 30 including an absorber film pattern 4a in which the absorber film 4 in the reflective mask blank 20 of FIG. 2 is patterned.
As a method for patterning the absorber film 4 serving as a transfer pattern in the reflective mask blank, a photolithography method capable of performing high-definition patterning is most preferable.

By manufacturing a reflective mask using the reflective mask blank of the present invention that can guarantee the above-described high quality, a high-quality reflective mask with few defects can be obtained, particularly during pattern transfer by EUV exposure.

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 6.35 mm).
Then, the end surface of the glass substrate is chamfered and ground, and the glass substrate that has been subjected to rough polishing with a polishing liquid containing cerium oxide abrasive grains is set on the carrier of a double-side polishing apparatus, and the colloidal silica abrasive is used as the polishing liquid. Using an alkaline aqueous solution containing grains, precise polishing was performed under predetermined polishing conditions. After precision polishing, the glass substrate was washed.
As described above, an EUV reflective mask blank glass substrate was produced. The surface roughness of the main surface of the obtained glass substrate was as good as 0.150 nm or less in terms of root mean square roughness (RMS). Further, the flatness was as good as 50 nm or less in a measurement area of 142 mm × 142 mm.

Next, a multilayer reflective film was formed on the reflective mask blank glass substrate as follows. 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.

First, the Si target angle was adjusted so that the incident angle of sputtered particles with respect to the substrate main surface was 30 degrees, and a Si film was formed to 4.0 nm.
Subsequently, a Mo film was formed in the following three stages while changing the incident angle of the sputtered particles. First, in the first stage, the Mo target angle is adjusted so that the incident angle is 50 degrees, and 1 nm is formed. In the second stage, the Mo target angle is adjusted so that the incident angle is 30 degrees, and 1 nm is formed. In the third stage, the Mo target angle was adjusted so that the incident angle was 50 degrees, and 1 nm was formed to form a Mo film having a total thickness of 3.0 nm.

As described above, the Si film is formed to 4.0 nm and the Mo film is formed to 3.0 nm, and this is set as one period. After the incidence angle is set in the same manner as described above and 40 periods are stacked, the Si film is formed at an incident angle of 30 degrees. Was deposited to 4.2 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 66%.
Moreover, it was 0.03 nm as a result of measuring the in-plane dispersion | variation in the center wavelength (CW) of the multilayer reflective film surface. The in-plane variation of the center wavelength (CW) is obtained by measuring 81 points of the reflectance spectrum at equal intervals in the measurement area of 132 mm × 132 mm, and the maximum value of the center wavelength (CW) of the reflectance spectrum. And the minimum difference (MAX-MIN) was calculated. The measurement was performed using an EUV exposure measuring apparatus (a substrate with a multilayer reflective film provided with a protective film described later was also measured for variations in center wavelength (CW) by the same measurement method).
The surface roughness of the multilayer reflective film surface was as good as 0.130 nm in terms of root mean square roughness (RMS).

Next, a protective film (thickness 2.5 nm) made of RuNb was formed on the multilayer reflective film by a DC magnetron sputtering method.
When the reflectance of this protective film surface was measured with 13.5 nm EUV light at an incident angle of 6.0 degrees, the reflectance was 63%.
As described above, a multilayer reflective film-coated substrate provided with a protective film was produced.

As a result of measuring the in-plane variation of the center wavelength (CW) for the obtained substrate with a multilayer reflective film, it was 0.03 nm, which was the same as the measurement result on the surface of the multilayer reflective film.
Further, the surface roughness of the main surface of the obtained multilayer reflective film-coated substrate was as good as 0.13 nm in root mean square roughness (RMS), which was the same as the measurement result of the multilayer reflective film surface.
Moreover, the defect inspection of this multilayer reflective film-coated substrate was performed using a defect inspection machine using EUV light as inspection light. In the 132 mm × 132 mm defect inspection area, the signal intensity when one line scan was detected was detected, and the background level (BGL) was obtained. As a result, BGL was as good as 800. Therefore, since the pseudo defects in the defect inspection can be reduced, a good defect inspection can be performed.
As described above, according to the embodiment of the present invention, good results are obtained in any of EUV light reflectance, in-plane variation of the central wavelength, surface roughness, and BGL, and high reflectance and low central wavelength are obtained. Three characteristics of in-plane variation and low surface roughness can be achieved at the best values.

(Comparative Example 1)
In Example 1, each Si film was formed at an incident angle of 30 degrees, and each Mo film was also formed at 30 degrees (constant) without changing the incident angle in the middle. Similarly, a substrate with a multilayer reflective film was produced.
When the reflectance of the multilayer reflective film without the protective film was measured with 13.5 nm EUV light at an incident angle of 6.0 degrees, the reflectance was 64%. Moreover, when the reflectance was measured with respect to the surface of the protective film with the protective film attached thereto at an incident angle of 6.0 degrees with 13.5 nm EUV light, the reflectance was 60%.

As a result of measuring variations in the center wavelength (CW) for the multilayer reflective film surface and the substrate with the multilayer reflective film in the same manner as in Example 1, the surface of the multilayer reflective film and the substrate surface with the multilayer reflective film with the protective film attached Both were 0.05 nm.
Further, the surface roughness of the multilayer reflective film surface and the main surface of the substrate with the multilayer reflective film was as good as 0.120 nm in terms of root mean square roughness (RMS).
Moreover, the defect inspection of this multilayer reflective film-coated substrate was performed using a defect inspection machine using EUV light as inspection light in the same manner as in Example 1. As a result, the background level (BGL) was as good as 600.
As described above, according to this comparative example, although the results of surface roughness and BGL are good, the results of low EUV light reflectivity and large in-plane variation of the center wavelength are obtained, and high reflectivity, The three characteristics of low center surface wavelength variation and low surface roughness cannot be achieved at their best values.

(Comparative Example 2)
In Example 1, each Si film was formed at an incident angle of 30 degrees, and each Mo film was also formed at 50 degrees (constant) without changing the incident angle in the middle. Similarly, a substrate with a multilayer reflective film was produced.
When the reflectance of the multilayer reflective film without the protective film was measured with 13.5 nm EUV light at an incident angle of 6.0 degrees, the reflectance was 66%. Further, when the reflectance was measured with respect to the surface of the protective film with the protective film attached thereto at an incident angle of 6.0 degrees with 13.5 nm EUV light, the reflectance was 64%.

As a result of measuring variations in the center wavelength (CW) for the multilayer reflective film surface and the substrate with the multilayer reflective film in the same manner as in Example 1, the surface of the multilayer reflective film and the substrate surface with the multilayer reflective film with the protective film attached Both were 0.02 nm.
The surface roughness of the multilayer reflective film surface and the main surface of the substrate with the multilayer reflective film was as large as 0.170 nm in terms of root mean square roughness (RMS).
Moreover, as a result of performing defect inspection of this multilayer reflective film-coated substrate using a defect inspection machine using EUV light as inspection light in the same manner as in Example 1, the background level (BGL) was as large as 1200. Therefore, a large number of pseudo defects are detected, and good defect inspection cannot be performed.
As described above, even in this comparative example, although the results of variations in EUV light reflectance and center wavelength were good, the surface roughness and BGL were large, and a large number of pseudo defects were detected. As a result, the three characteristics of high reflectivity, center wavelength in-plane variation, and low surface roughness cannot be achieved at the respective best values.

(Example 2)
A laminated film of a TaBN film (film thickness of 56 nm) and a TaBO film (film thickness of 14 nm) was formed as an absorber film on the protective film of the substrate with a multilayer reflective film prepared in Example 1 by DC magnetron sputtering. .
Thus, a reflective mask blank was produced.

Next, using this reflective mask blank, a reflective mask for EUV exposure having a pattern of DRAM hp 20 nm generation in the semiconductor design rule was produced as follows.
First, a resist film for electron beam drawing was formed on the reflective mask blank, a predetermined pattern was drawn using an electron beam drawing machine, and after drawing, a resist pattern was formed by development.
Next, using this resist pattern as a mask, the TaBO film was dry-etched with fluorine-based gas (CF ₄ gas), and the TaBN film was dry-etched with chlorine-based gas (Cl ₂ gas) to form a transfer pattern on the absorber film.
Further, the resist pattern remaining on the absorber film pattern was removed with hot sulfuric acid to obtain a reflective mask.

When the final confirmation inspection of the obtained reflective mask was performed, it was confirmed that the DRAM hp 20 nm generation pattern in the semiconductor design rule was formed as designed.
Next, when pattern transfer by EUV light is performed on a semiconductor substrate using the obtained reflective mask of this embodiment, a semiconductor device of the semiconductor design rule DRAM hp 20 nm generation can be manufactured.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Multilayer reflective film 21 Si film 22 Mo film 3 Protective film 4 Absorber film 10 Multilayer reflective film-coated substrate 20 Reflective mask blank 30 Reflective mask 50 Ion beam sputtering apparatus 51 Ion beam generators 54 and 55 Sputtering target

Claims (8)

A method for producing a substrate with a multilayer reflective film comprising a multilayer reflective film that reflects exposure light comprising a multilayer film in which a low refractive index layer and a high refractive index layer are alternately laminated on a substrate,
The multi-layer reflective film has one cycle of a laminated structure in which a high refractive index layer and a low refractive index layer are formed in this order on the substrate, or a laminated structure in which a low refractive index layer and a high refractive index layer are laminated in this order. As a structure in which a plurality of periods are stacked,
The low refractive index layer has a reflectance of the multilayer reflective film of 65% or more, an in-plane variation of the center wavelength of 0.04 nm or less, and a surface roughness of root mean square roughness of 0.15 nm or less. Production of a substrate with a multilayer reflective film, characterized in that the film is formed by changing the film formation conditions in the area near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer Method.   The method for manufacturing a substrate with a multilayer reflective film according to claim 1, wherein the multilayer reflective film is formed using an ion beam sputtering method.   3. The method for manufacturing a substrate with a multilayer reflective film according to claim 1, wherein the film forming condition of the low refractive index layer is an incident angle of sputtered particles with respect to a normal of the main surface of the substrate.   In the low refractive index layer, the incident angle of the sputtered particles with respect to the normal of the main surface of the substrate in the region near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer is other than in the region near the boundary. 4. The method for manufacturing a substrate with a multilayer reflective film according to claim 3, wherein sputtering film formation is performed under film formation conditions larger than an incident angle of sputtered particles with respect to a normal line of the main surface of the substrate.   When forming the low refractive index layer, the incident angle of the sputtered particles with respect to the normal of the main surface of the substrate is 45 degrees or more in the region near the boundary with the high refractive index layer immediately below and immediately above the low refractive index layer. The method for producing a substrate with a multilayer reflective film according to claim 4, wherein the range is 55 ° or less, and in the other region, the range is 20 ° or more and 40 ° or less.   6. The method for manufacturing a substrate with a multilayer reflective film according to claim 1, wherein a region in the vicinity of the boundary with the high refractive index layer is a region of 2 nm or less.   A reflective mask blank comprising an absorber film that absorbs exposure light on the multilayer reflective film in the substrate with the multilayer reflective film obtained by the manufacturing method according to claim 1. Production method. A method for manufacturing a reflective mask, comprising patterning the absorber film in a reflective mask blank obtained by the manufacturing method according to claim 7.

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