JP2017191285A - Reflection type photomask - Google Patents

Abstract

An object of the present invention is to suppress the reflectance of a light shielding region with respect to out-of-band light. The substrate includes a substrate, a multilayer reflective layer that is formed on the substrate and reflects exposure light, and an absorption layer that is formed on the multilayer reflective layer and absorbs exposure light. A circuit pattern 10 is formed on the absorption layer 14, and a multilayer reflective layer 12 and a light shielding region 20 where the absorption layer 14 is removed and the substrate 11 is exposed are formed outside the region where the circuit pattern 10 is formed. Is done. On the surface of the portion of the light shielding region 20 where the substrate 11 is exposed, a low refractive index layer 30 having a refractive index with respect to out-of-band light of 100 nm to 300 nm emitted from the light source is lower than the refractive index of the substrate 11 is formed. The In the low refractive index layer 30, the refractive index on the substrate 11 side is larger than the refractive index on the surface side. [Selection] Figure 1

Description

  The present invention relates to a reflective photomask for lithography (including a reflective photomask blank).

In the manufacturing process of a semiconductor device, with the miniaturization of a semiconductor device, the demand for miniaturization in the photolithography technology is increasing. The exposure light for photolithography around 2000 was mainly 193 nm ArF excimer laser light. At present, the application of light mainly in the wavelength region of 15 nm or less (hereinafter referred to as “EUV light”) called EUV (Extreme Ultra Violet) light, particularly EUV light of 13.5 nm is being promoted.
Since EUV light is very easily absorbed by most substances, a photomask that uses EUV light for exposure (hereinafter referred to as “EUV mask”) is different from a conventional transmissive photomask in that it reflects light. Type photomask. In the EUV mask, for example, a multilayer reflective layer in which a molybdenum (Mo) layer and a silicon (Si) layer are alternately laminated on a glass substrate is formed, and a light absorption layer mainly composed of tantalum (Ta) is formed thereon. And a circuit pattern is formed on the light absorption layer.

In lithography using a reflective EUV mask, the incident angle of EUV light to the EUV mask is generally set to about 6 degrees, and the reflected EUV light is guided to a wafer that is an object to be exposed and applied onto the wafer. A resist having photosensitivity to EUV light is exposed.
Here, when the incident optical axis of the EUV light incident on the EUV mask is inclined as described above, when the EUV light is reflected by the circuit pattern on the EUV mask, depending on the direction of the reflected light, a part of the light absorption layer It has been pointed out that a phenomenon (so-called projection effect) that does not radiate on the wafer occurs. Therefore, in order to suppress the projection effect, a method is used in which the thickness of the light absorption layer on which the circuit pattern is formed is reduced to reduce the influence of the shadow.

  However, if the light absorption layer is simply made thin, the amount of light attenuation that is necessary in the light absorption layer is insufficient. Therefore, the reflected light of the EUV light emitted to the resist on the wafer increases more than necessary, and the circuit pattern There is a concern that the formation accuracy deteriorates. In addition, in actual exposure work, chips are often applied to a single wafer, so there is a particular concern that the exposure amount of the resist in the boundary region between adjacent chips increases. That is, multiple exposure that affects circuit pattern formation accuracy occurs in the boundary region between chips, and this multiple exposure causes a reduction in quality and throughput of chips obtained in subsequent processes. Therefore, when making the light absorption layer thin in this way, there is a method of removing all of the multilayer reflective layer in addition to the light absorption layer in the EUV mask and forming a groove dug up to the surface of the glass substrate. (See Patent Document 1). This is intended to suppress the multiple exposure in the boundary region between adjacent chips by suppressing the reflection of the EUV light in the light shielding region by using the groove as a light shielding region having a high light shielding property with respect to the wavelength of the EUV light. .

  However, from a light source that generates EUV light, not only light in the EUV region near 13.5 nm, but also vacuum ultraviolet light (VUV; about 200 nm or less), deep ultraviolet light (DUV; about 300 nm or less), ultraviolet light (UV; about 400 nm). In the following, light in a wavelength band extending in the near infrared (about 800 nm) and further in the infrared region (1000 nm or more) is often emitted. This wavelength band is generally called out-of-band. As described above, light having an out-of-band wavelength (hereinafter referred to as “out-of-band light”) is incident on the EUV mask along with the EUV light. And in the light shielding area | region of the conventional EUV mask mentioned above, although the light shielding property of EUV light is comparatively high, the light shielding property of out-of-band light is comparatively low. For this reason, in the light shielding region, the reflection of EUV light out of the light emitted from the light source can be suppressed, but a part of the out-of-band light is reflected on the light shielding region and emitted onto the wafer. In addition, there is a problem that multiple exposure as described above occurs in the boundary region between chips. Since the resist for EUV lithography used on the wafer was originally developed based on a resist for lithography of KrF light (wavelength 248 nm) or ArF light (wavelength 193 nm), it is particularly out of the wavelength region of 100 to 400 nm. High sensitivity to band light (hereinafter abbreviated as OOB light).

  As a technique for solving such a problem, there is a technique described in Patent Document 2. This is because a fine structure pattern is formed on the back surface of the glass substrate opposite to the multilayer reflective layer, so that the OOB light incident on the light shielding region reaches the back surface of the glass substrate from a vacuum, and then the back surface conductive film. It suppresses that it reflects by.

JP 2009-212220 A JP 2013-074195 A

However, in order to verify the technique described in Patent Document 2, the present inventors examined the component of OOB light reflected from the light shielding region and emitted to the wafer. It was found to be dominant over the light reflected on the back side of the substrate. Therefore, in order to reduce the reflectance of the OOB light incident on the light shielding region, it is not sufficient to suppress the reflected light reflected on the back surface of the substrate, and it is necessary to suppress the reflected light on the surface of the substrate. I came to a conclusion.
The subject of this invention is suppressing the reflectance of the light-shielding area | region with respect to out-of-band light.

  A reflective photomask according to one embodiment of the present invention includes a substrate, a multilayer reflective layer that is formed over the substrate and reflects exposure light, and an absorption layer that is formed over the multilayer reflective layer and absorbs exposure light. A reflective photomask used for lithography using exposure light having a wavelength of 5 nm or more and 15 nm or less, wherein a circuit pattern is formed in the absorption layer, and outside the region where the circuit pattern is formed, The multilayer reflective layer and the light-blocking region where the substrate is exposed by removing the absorption layer are formed, and the refractive index with respect to the out-of-band light of 100 nm to 300 nm emitted from the light source on the surface of the portion of the light-blocking region where the substrate is exposed However, a low refractive index layer lower than the refractive index of the substrate is provided, and the refractive index on the back surface side of the low refractive index layer is larger than the refractive index on the front surface side.

  According to the present invention, since the reflection of out-of-band light in the light-shielding region can be suppressed more than before in the reflective photomask in which the light-shielding region is formed, the EUV can be used when the chip is applied to the wafer in multiple faces. Multiple exposure in the boundary region between chips due to not only light but also out-of-band light can be effectively suppressed. Then, a highly accurate and high quality circuit pattern can be transferred to the wafer.

It is a block diagram of a reflective photomask. It is a figure which shows a low-refractive-index layer. It is a figure which shows the manufacturing process until formation of a circuit pattern. It is a figure which shows the manufacturing process until formation of a light shielding area | region. It is a figure which shows the manufacturing process until formation of a low refractive index layer. It is a figure which shows the measurement result of a reflectance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each drawing is schematic and may be different from the actual one. Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the configuration is not specified as follows. That is, the technical idea of the present invention can be variously modified within the technical scope described in the claims.

<Embodiment>
(Description of EUV mask film structure)
FIG. 1 is a configuration diagram of a reflective photomask.
In the figure, (a) is a top view of the reflective photomask 101, and (b) is a cross-sectional view taken along line AA 'of (a).
The reflective photomask 101 is for EUV lithography that uses exposure light of light having a wavelength of 5 nm or more and 15 nm or less, in particular, EUV light of 13.5 nm, and the film structure thereof includes a multilayer reflective layer 12 and a protective layer 13 on a substrate 11. The absorbing layer 14 is formed in order, and the back surface conductive film 15 is provided on the back surface of the substrate 11.

Examples of the material of the substrate 11 include a material containing quartz (SiO ₂ ) as a main component and titanium oxide (TiO ₂ ). In addition, when the lithography technique and the etching technique are used as the processing technique, it is desirable to use quartz glass as the material of the substrate 11. In the present embodiment, extremely low thermal expansion glass using quartz (SiO ₂ ) (Corning Inc., refractive index: 1.801 to 1.4892) is used.

  The multilayer reflective layer 12 is a film that reflects EUV light, and is made of a material that has a small absorption (extinction coefficient) with respect to the EUV light and a large refractive index difference in the EUV light between the laminated films. The multilayer reflective layer 12 is, for example, a molybdenum (Mo) layer having a thickness of 2 to 3 nm and silicon (Si) having a thickness of 4 to 5 nm, which is designed to achieve a reflectivity of about 72% theoretically for EUV light. 40) 50 layers are alternately stacked. Molybdenum (Mo) and silicon (Si) have low absorption (extinction coefficient) with respect to EUV light and a large difference in refractive index with respect to EUV light, so that the reflectance at these interfaces can be made high.

The protective layer 13 needs to be a material having resistance to washing against acids and alkalis. For example, ruthenium (Ru) having a thickness of 2 to 3 nm or silicon (Si) having a thickness of about 10 nm can be used.
When the protective layer 13 is made of ruthenium (Ru), the protective layer 13 plays a role as a stopper layer in the processing of the absorption layer 14 or a protective layer against a chemical solution in mask cleaning. The uppermost layer of the multilayer reflective layer 12 located under the protective layer 13 made of ruthenium (Ru) is a Si layer.

When the protective layer 13 is made of silicon (Si), a buffer layer (not shown) may be provided between the absorption layer 14 and the protective layer 13. In that case, the buffer layer is provided to protect the silicon (Si) layer located under the buffer layer during etching or pattern correction of the absorption layer 14, and may be composed of, for example, chromium nitrogen compound (CrN). it can.
The protective layer 13 may have a single layer structure or a laminated structure. When the protective layer 13 has a laminated structure, the uppermost layer of the protective layer 13 is ruthenium (Ru), ruthenium oxide, nitride, oxynitride, silicon (Si), silicon oxide, nitride, acid. It is made of a material containing any of nitrides.

  The absorption layer 14 is a film that absorbs EUV light, and may have a single-layer structure or a two-layer structure. When the absorption layer 14 has a single-layer structure, the absorption layer 14 is formed of a material containing, for example, any one of tantalum (Ta), tantalum oxide, nitride, and oxynitride that has a high absorption rate for EUV light. The Specifically, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), and oxides thereof (TaBON, TaSiO, TaO) can be used. When the absorption layer 14 has a two-layer structure, a low reflection layer (not shown) having an antireflection function with respect to ultraviolet light having a wavelength of 190 to 260 nm may be provided as an upper layer.

As the low reflection layer, for example, a material containing any of tantalum (Ta) oxide, nitride, oxynitride, silicon (Si) oxide, nitride, and oxynitride can be used. The low reflection layer is for increasing the contrast and improving the inspection property with respect to the inspection wavelength of the mask defect inspection machine. The film thickness of the absorption layer 14 is 50 to 70 nm.
The back surface conductive film 15 only needs to have conductivity, for example, any metal of chromium (Cr) and tantalum (Ta), or an oxide, nitride, or oxynitride thereof, or is conductive. It is formed of a material including other metal materials. Specifically, CrN is often used. The film thickness of the back surface conductive film 15 is 20 to 400 nm.
The multilayer reflective layer 12, the protective layer 13, the absorption layer 14, and the back conductive film 15 can be formed using a sputtering method or the like.

(Description of light shielding area of EUV mask)
As shown in FIG. 1, the reflective photomask 101 has a light shielding region 20 disposed so as to surround the circuit pattern 10. The width of the light shielding area 20 is usually about 2 mm to 5 mm, depending on the structure of the EUV exposure machine (exposure area is set accuracy) and the interval of chip arrangement when the semiconductor manufacturer exposes the wafer. In the present embodiment, the width of the light shielding region 20 is not limited. This is because a sufficient effect can be obtained if the width is at least the necessary width.

In the light shielding region 20, the absorption layer 14, the protective layer 13, and the multilayer reflective layer 12 are completely removed. The OOB light having a wavelength of 100 nm to 300 nm formed on the substrate 11 is formed on the bottom surface of the light shielding region 20. A low refractive index layer 30 exhibiting a low refractive index. In this way, the multilayer reflective layer 12 responsible for EUV light reflection is completely removed, so that a light shielding performance against the EUV light is obtained, and the EUV light is not reflected only by the substrate 11.
However, since the reflection of the OOB light cannot be suppressed only by removing the multilayer reflective layer 12, the low refractive index layer 30 is provided for the purpose of suppressing it.

When the refractive indexes of the first medium and the second medium having different refractive indexes are n1 and n2, respectively, the reflectance R can be generally expressed as shown in the formula (1) from the Fresnel equation.
R = ((n2-n1) / (n2 + n1)) ² (1)
When the first medium is vacuum, since n1 = 1.0, the smaller the value of n2, the smaller the reflectance. Since the extremely low thermal expansion glass using quartz (SiO ₂ ) used as the substrate 11 has n2 = 1.5, the refractive index of the low refractive index layer 30 is specifically 1.0 or more. It is desirable that it is 1.5 or less.

  Further, by providing the low refractive index layer 30 whose refractive index changes stepwise, reflection of OOB light emitted from the plasma light source along with EUV light can be more efficiently suppressed. The surface of the low refractive index layer 30 shows the refractive index closest to the refractive index n1 = 1.0 in a vacuum, and gradually increases in the depth direction from there. On the substrate 11 side of the layer 30, by making the refractive index close to the refractive index n2 = 1.5 of the substrate 11, an effect of hardly reflecting the OOB light is brought about.

As the film thickness of the low refractive index layer 30 effective for low reflection with respect to out-of-band light with a wavelength of 100 nm to 300 nm, it is desirable that the film has a film thickness equal to or greater than the wavelength, and the refractive index gradually changes therein. . However, if the film thickness is 10 nm, a certain effect can be obtained.
As a method for changing the refractive index of the low refractive index layer 30 in a stepwise manner, for example, the following can be cited.
Method 1: Method of including a material having a low refractive index and changing the content Method 2: Method of stacking a large number of materials having a low refractive index Method 3: Method of changing density

As a specific method of Method 1, there is a method in which a metal material is used as a sputtering target and the flow rate of oxygen or nitrogen introduced into the chamber is gradually changed during film formation. Alternatively, if a multi-source sputtering apparatus is used, simultaneous film formation using a plurality of targets is possible, so that the target ratio can be gradually changed during film formation. Similarly in CVD (Chemical Vapor Deposition), a method of gradually changing the gas flow rate, or a film to be contained in the film by CVD or the like, and then heat-treating in a diffusion furnace, the direction in the film It is also possible to form a film (low refractive index layer) whose concentration (content) changes stepwise.
As a specific method of Method 2, there is a method of forming a film a plurality of times using sputtering or CVD under slightly different film forming conditions. In the case of sputtering, the target may be replaced each time.
These methods 1 and 2 can be realized by various film forming methods, and the film forming method is not limited in this embodiment.

  As a specific method of Method 3, the film density is changed stepwise by changing the introduction amount of an inert gas (Ar, N 2, etc.) or changing the degree of vacuum during film formation such as sputtering. A method is mentioned. Alternatively, the low refractive index layer 30 can be formed on the surface of the substrate 11 by performing ion implantation treatment of an inert gas on the surface of the substrate 11 instead of forming a film. Particularly in this case, the difference in refractive index becomes gentle at the interface between the refractive index of the substrate 11 (about 1.5) and the surface modified by ion implantation (= low refractive index layer). Low reflection effect. The density of the low refractive index layer 30 is desirably in the range of 59% to 100% with respect to the true density of the substrate 11. Further, the low refractive index layer 30 may have a porous structure having holes.

Thus, although the example of the method of forming the low-refractive-index layer 30 was demonstrated, it is not limited to this, The essence is the low-refractive index from which the refractive index changes to the surface of the board | substrate 11 in steps. The layer 30 is provided.
The material used for the low refractive index layer 30 is aluminum (Al), silver (Ag), copper (Cu), rhodium (Rh), titanium (Ti) that exhibits a low refractive index with respect to OOB light having a wavelength of 100 nm to 300 nm. ), Platinum (Pt), cobalt (Co), copper aluminum (AlCu), or magnesium fluoride (MgF ₂ ).

FIG. 2 is a diagram showing a low refractive index layer.
(A) in the figure is a flat surface with no irregularities on the surface shape of the low refractive index layer 30, and (b) is an irregular surface surface. As described above, the surface shape of the low refractive index layer 30 is not limited, and reflection of OOB light can be suppressed even when it is a flat surface. However, since there is an uneven pattern or the like, further suppression of reflection can be expected. Therefore, a pattern may be formed as shown in (b). Further, the low refractive index layer 30 may be previously installed on the surface of the mask blank substrate 11. Furthermore, the low refractive index layer 30 may have a porous structure having holes.

When there is no low refractive index layer 30 on the surface of the substrate 11, the reflectance of OOB light is about 5 to 20%. However, by forming the low refractive index layer 30, the reflectance of OOB light is up to 4% or less. Can be reduced. Further, the reflectance with respect to EUV light is equivalent (almost zero) as compared with the case where the low refractive index layer 30 is not provided.
As described above, a reflective photomask having a light-shielding region with low reflectivity with respect to OOB light can be obtained.

Hereinafter, Example 1 in which the reflective photomask 101 is manufactured and the reflectance with respect to OOB light is evaluated will be described. Here, a method (Method 2) in which a large number of low refractive index materials are stacked will be described.
(Description of EUV blank used)
Here, on the substrate 11, 40 pairs of multilayer reflective layers 12 of Mo layer and Si layer designed to have a reflectance of about 64% with respect to EUV light having a wavelength of 13.5 nm are formed thereon. A protective layer 13 having a thickness of 2.5 nm and an absorbing layer 14 made of TaSi having a thickness of 70 nm are sequentially formed thereon. A back conductive film 15 is formed on the back surface of the substrate 11.

(EUV mask manufacturing process)
FIG. 3 is a diagram showing a manufacturing process up to formation of a circuit pattern.
(A) in the figure is a reflective photomask blank, (b) is after resist coating, (c) is after drawing, (d) is after development, and (e) is after dry etching. (F) is after resist removal / cleaning and drying.
In order to form a circuit pattern on the reflective photomask blank, first, a resist 21 (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) made of a positive chemically amplified resist is formed on the surface of the reflective photomask blank (FIG. 3A). The film was applied to a film thickness of 150 nm (FIG. 3B). Next, an electron beam drawing machine (JBX3040: manufactured by JEOL Ltd.) is used to produce a 1: 1 line & space pattern with a line width of 100 nm in an area of 10 cm × 10 cm at the center of the mask. After drawing (FIG. 3 (c)), PEB was performed at 110 ° C. for 10 minutes, followed by spray development (SFG3000: manufactured by Sigma Meltech) to form a resist pattern (FIG. 3 (d)).
Next, the absorption layer 14 was etched with CF ₄ plasma and Cl ₂ plasma using a dry etching apparatus (FIG. 3E). Thereafter, the remaining resist pattern was peeled, washed, and dried to produce a reflective photomask having the circuit pattern 10 in the absorption layer 14 (FIG. 3F).

(Light-shielding region manufacturing process)
FIG. 4 is a diagram illustrating a manufacturing process up to formation of a light shielding region.
(A) in the figure is after resist coating, (b) is after drawing, (c) is after development, (d) is after dry etching, (e) is resist stripping / cleaning, After drying.
A resist 22 made of an i-line resist is applied to the pattern surface of a reflective photomask with a circuit pattern to a thickness of 500 nm (FIG. 4A), and an i-line drawing machine (ALTA3000: manufactured by Applied Materials) is applied there. Then, a light shielding region was drawn (FIG. 4B) and developed (FIG. 4C). As a result, a resist pattern was formed in which a portion to be a light shielding region later was opened on the absorption layer 14. At this time, the opening width of the resist pattern was 5 mm, and the resist pattern was drawn and formed so that the distance from the end of the opening to the end of the circuit pattern previously spread in the 10 cm × 10 cm region was 3 μm.

Thereafter, the absorption layer 14, the protective layer 13, and the multilayer reflective layer 12 in the openings of the resist pattern are selectively removed by vertical dry etching using CHF ₃ plasma under the following conditions (FIG. 4D )), A reflective photomask with a circuit pattern having a conventional light-shielding region was produced by stripping, washing, and drying the remaining resist (FIG. 4E).
Pressure in dry etching equipment: 4 mTorr
ICP (inductively coupled plasma) power: 350 W
RIE (reactive ion etching) power: 200W
CHF ₃ flow rate: 20 sccm
Processing time: 6 minutes

(Production process of low refractive index layer)
FIG. 5 is a diagram illustrating a manufacturing process up to formation of a low refractive index layer.
(A) in the figure is after resist application, (b) is after drawing, (c) is after development, (d) is after the first film formation of the low refractive index layer, ( e) is after the second film formation of the low refractive index layer, and (f) is after the resist is peeled, washed and dried.
First, a resist 23 made of an i-line resist is applied to the entire mask surface with a film thickness of 200 nm (FIG. 5A). Further, an i-line drawing machine is used to draw on the resist 23 on the light shielding region 20 (FIG. 5B). By developing this, a portion other than the light shielding region 20 is covered with the resist 23 (FIG. 5C). On the mask in this state, MgF ₂ is formed over the entire surface with a film thickness of 10 nm as a material 30a for the first layer of the low refractive index layer 30 using a sputtering apparatus (FIG. 5D). Further, Co is formed on the entire surface with a film thickness of 10 nm as the second layer material 30b (FIG. 5E). Thereafter, by removing the resist 23, the excess low refractive index layer 30 formed on the surface of the resist 23 is also removed at the same time. Therefore, the reflective type in which the low refractive index layer 30 is formed only on the surface of the light shielding region 20 A photomask 101 is manufactured (FIG. 5F).

(Confirmation of OOB light reflectivity)
About both the conventional reflective photomask with a circuit pattern having a light-shielding region and the reflective photomask of the present invention having the low refractive index layer 30 on the surface of the substrate 11 in the light-shielding region 20 produced in the procedure of Example 1. As a result of measuring the spectral reflectance of OOB light having a wavelength of 100 to 300 nm, the reflectance of the light-shielding region having the low refractive index layer on the substrate surface is reduced by about 60% compared to the case without the low refractive index layer. I was able to confirm.
FIG. 6 is a diagram illustrating a measurement result of reflectance.

As Example 2, also in the case where a low refractive index material was contained in the substrate 11 (Method 1), a reflection type photomask was prepared, and the reflectance measurement of OOB light was performed. The production procedure and production conditions of the reflective photomask are the same as those in Example 1 until the process for producing the conventional light-shielding region.
The method of forming the low refractive index layer 30 is different from the method 2 in that it is not a method of laminating on the surface of the substrate 11, but a refractive index change is given by implanting another material directly into the substrate 11 using ion implantation.

First, a reflective mask in the state shown in FIG. 4E is manufactured by the same method as the manufacturing process of the conventional light shielding region 20. The substrate 11 is exposed at the bottom of the light shielding region 20, and Rh ions are implanted into the substrate 11 using an ion implantation apparatus to form the low refractive index layer 30. The Rh content of the low refractive index layer 30 was highest on the surface of the substrate 11 and tended to decrease in the depth direction.
(Confirmation of OOB light reflectivity)
About both a reflection type photomask with a circuit pattern having a conventional light shielding region 20 and a reflection type photomask having a low refractive index layer 30 on the surface of the substrate 11 in the light shielding region 20 produced in the procedure of Example 2. As a result of performing the spectral reflectance measurement of the OOB light having a wavelength of 100 to 300 nm, the reflectance of the light shielding region 20 having the low refractive index layer 30 on the surface of the substrate 11 is compared with the case where the low refractive index layer 30 is not provided. It was confirmed that the reduction was about 50%.

As Example 3, also in the case where the density of the low refractive index layer 30 on the surface of the substrate 11 was changed (Method 3), a reflection type photomask was prepared and the reflectance measurement of OOB light was performed. The production procedure and production conditions of the reflective photomask are the same as those in Example 1 until the process for producing the conventional light-shielding region.
Next, the same process was performed until the portion other than the light shielding region 20 was covered with the resist 23 (FIG. 5C).

As a method for forming the low refractive index layer 30 on the surface of the substrate 11 in the light shielding region 20, plasma CVD film formation was used, and a SiO 2 material was formed on the surface of the substrate 11. At this time, Ar, which is an inert gas, was introduced and a negative voltage was applied to the substrate 11 side to perform ion-assisted film formation in which film formation was performed while Ar ions were incident on the substrate 11. At this time, by gradually changing the voltage applied to the substrate 11 side, a film in which the SiO2 film density gradually changed was formed.
(Confirmation of OOB light reflectivity)
A reflection type photomask having a circuit pattern having a conventional light shielding region 20 and a low refractive index layer 30 having a changed film density on the surface of the substrate 11 of the light shielding region 20 produced in this embodiment. As a result of performing spectral reflectance measurement of OOB light having a wavelength of 100 to 300 nm for both of the photomasks, the reflectance of the light shielding region 20 having the low refractive index layer 30 on the surface of the substrate 11 is not the low refractive index layer 30. Compared to the case, it was confirmed that it was reduced by about 56%.

  Although the present invention has been described with reference to a limited number of embodiments, the scope of rights is not limited thereto, and modifications of the embodiments based on the above disclosure are obvious to those skilled in the art.

DESCRIPTION OF SYMBOLS 101 Reflective photomask 11 Substrate 12 Multilayer reflective layer 13 Protective layer 14 Absorbing layer 15 Back surface conductive film 10 Circuit pattern 20 Light shielding region 30 Low refractive index layer 21 Resist 22 Resist 23 Resist

Claims (8)

A substrate,
A multilayer reflective layer formed on the substrate and reflecting exposure light;
An absorption layer formed on the multilayer reflective layer and absorbing the exposure light,
A reflective photomask used in lithography using exposure light having a wavelength of 5 nm to 15 nm,
A circuit pattern is formed on the absorption layer,
Outside the region where the circuit pattern is formed, a light shielding region where the multilayer reflective layer and the absorbing layer are removed and the substrate is exposed is formed,
On the surface of the portion where the substrate is exposed in the light shielding region, a low refractive index layer having a refractive index with respect to out-of-band light of 100 nm or more and 300 nm or less emitted from a light source is lower than the refractive index of the substrate,
The reflective photomask according to claim 1, wherein the low refractive index layer has a refractive index on the back side larger than that on the front side.   2. The reflective photomask according to claim 1, wherein a refractive index of the low refractive index layer is in a range of 1.0 to 1.5.   The reflective photomask according to claim 1, wherein the low refractive index layer has a multilayer structure of two or more layers. The low refractive index layer includes aluminum (Al), silver (Ag), copper (Cu), rhodium (Rh), titanium (Ti), platinum (Pt), cobalt (Co), copper aluminum (AlCu), and fluorine. among the magnesium reduction (MgF _2), the reflection type photomask according to any one of claims 1 to 3, characterized in that a material containing at least one.   The reflective photomask according to any one of claims 1 to 3, wherein the low refractive index layer contains a material having a refractive index different from that of the substrate. The material contained in the low refractive index layer is aluminum (Al), silver (Ag), copper (Cu), rhodium (Rh), titanium (Ti), platinum (Pt), cobalt (Co), copper aluminum ( The reflective photomask according to claim 5, wherein the reflective photomask is at least one of AlCu) and magnesium fluoride (MgF ₂ ).   The reflective photomask according to claim 1, wherein a density of the low refractive index layer is in a range of 59% to 100% with respect to a true density of the substrate. .   The reflective photomask according to claim 7, wherein the low refractive index layer has a porous structure having holes.

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