JP5009590B2 - Mask blank manufacturing method and mask manufacturing method - Google Patents

Description

  The present invention provides a mask blank manufacturing method and a photomask having an antireflection film on a thin film surface for a transfer pattern, and having a reduced surface reflectance of the thin film with respect to a short wavelength region of about 190 to 300 nm (particularly near 250 nm). The present invention relates to a manufacturing method and a manufacturing method of a reflective mask.

  In general, in a manufacturing process of a semiconductor device, a fine pattern is formed using a photolithography method. In addition, a number of substrates called photomasks are usually used for forming this fine pattern. This photomask is generally provided with a light-shielding fine pattern made of a metal thin film or the like on a translucent glass substrate, and a photolithography method is also used in the production of this photomask.

  For manufacturing a photomask by photolithography, a photomask blank having a light-shielding film on a light-transmitting substrate such as a glass substrate is used. The production of a photomask using this photomask blank consists of an exposure process in which a desired pattern exposure is performed on a resist film formed on the photomask blank, and the resist film is developed in accordance with the desired pattern exposure to develop a resist pattern. A developing step for forming the light shielding film, an etching step for etching the light-shielding film along the resist pattern, and a step for peeling and removing the remaining resist pattern. In the above development process, the resist film formed on the photomask blank is subjected to a desired pattern exposure, and then a developer is supplied to dissolve a portion of the resist film soluble in the developer to form a resist pattern. To do. In the etching process, using this resist pattern as a mask, the exposed portion of the light-shielding film on which the resist pattern is not formed is dissolved by wet etching, for example, thereby forming a desired mask pattern on the translucent substrate. To do. Thus, a photomask is completed.

By the way, in order to miniaturize the pattern of a semiconductor device, in addition to miniaturization of a mask pattern formed on a photomask, it is necessary to shorten the wavelength of an exposure light source used in photolithography. As an exposure light source for manufacturing semiconductor devices, in recent years, the wavelength has been shortened from a KrF excimer laser (wavelength 248 nm) to an ArF excimer laser (wavelength 193 nm) and further to an F2 excimer laser (wavelength 157 nm).
Even if the mask pattern is miniaturized, if the exposure light is reflected on the surface of the light-shielding film pattern (mask pattern) when pattern transfer is performed using the photomask, the pattern transfer accuracy deteriorates due to the generation of stray light. Therefore, in order to prevent the occurrence of such stray light, an antireflection film made of a material such as CrO, CrON, CrCO, or CrCON is provided on the surface of the light shielding film in the photomask blank or photomask. (For example, refer to Patent Document 1).

JP 2001-305713 A

  In general, a light shielding film and an antireflection film in a conventional photomask blank are formed by a reactive sputtering method because a uniform film having a constant film thickness can be formed. Among the sputtering methods, the DC magnetron sputtering method using a DC (direct current) power source is usually preferably used because the mechanism is simple and the film forming speed is increased.

  When a photomask blank is produced by forming the light shielding film and the antireflection film by such reactive sputtering, first, for example, a Cr thin film or a Cr compound thin film containing Cr as a main component as a light shielding film on the substrate. After that, a thin film of Cr oxide (or Cr oxynitride, Cr oxycarbide, etc.) was formed as an antireflection film on the light shielding film by the same method. However, the formation of thin films such as Cr oxides by reactive sputtering is not stable due to the properties (high resistance, high stress) of thin films such as Cr oxides, making it difficult to form low defects. I was doing. If there are many defects in the light-shielding film that becomes a transfer pattern in the photomask blank, especially the antireflection film on the surface of the light-shielding film, pattern defects may occur during pattern inspection of photomasks made from photomask blanks. A problem that a defect is determined to occur in the defect inspection also occurs. In particular, such problems have become more prominent with the recent shortening of the wavelength of exposure light sources. Further, according to the research of the present inventors, it has been found that when the above-described antireflection film is formed by the conventional reactive sputtering method, the film density on the film surface is lowered, and the chemical resistance is deteriorated. It has also been found that a decrease in the film density of the upper layer portion of the film causes an increase in the amount of side etching during patterning by etching (particularly dry etching), resulting in a deterioration in CD accuracy.

  Further, EUV lithography using extreme ultraviolet (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. In the reflective mask used in this EUV lithography, a multilayer reflective film that reflects EUV light and an absorber film that absorbs EUV light are sequentially formed on a substrate, and a predetermined transfer pattern is formed on the absorber film. Yes. Such a reflective mask for EUV exposure is manufactured by sequentially forming a multilayer reflective film and an absorber film on a substrate and forming a transfer pattern on the absorber film. After the pattern is formed, it is inspected whether the pattern is formed as designed. Since this pattern inspection generally uses deep ultraviolet light having a wavelength of about 190 nm to 260 nm as inspection light, it is desirable to reduce the reflectance of the absorber film surface with respect to the inspection light in order to increase the contrast during the inspection. . For this purpose, it is conceivable to form a low reflection film for the inspection light on the absorber film. When such a low reflection film is formed by reactive sputtering in the same manner as the absorber film, the above-mentioned binary mask is used. Similar to the mask blank, problems such as difficulty in forming a low defect film and poor film chemical resistance occur.

  Accordingly, the present invention has been made to solve the conventional problems, and the object of the present invention is to firstly transfer a thin film (light-shielding film) for a transfer pattern having a reflectance adjustment film on the surface to a low defect. A mask blank and a photomask that can effectively reduce the surface reflectivity of the thin film in a short wavelength range of about 190 to 300 nm (especially around 250 nm) used as an exposure light source during pattern transfer and reduce defects. It is to provide a manufacturing method. Secondly, a transfer pattern thin film (absorber film) having a reflectance adjustment film on the surface can be formed with low defects, and deep UV light (especially 250 nm) of about 190 to 260 nm used for pattern inspection wavelengths. It is to provide a mask blank and a reflective mask manufacturing method that effectively reduce the surface reflectance of the thin film with respect to the vicinity. Thirdly, it is to provide a method for manufacturing a mask blank, a photomask, and a reflective mask with improved chemical resistance of the thin film and improved CD accuracy.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1) In a method of manufacturing a mask blank having a thin film for forming a transfer pattern on a substrate, after the thin film is formed on the substrate, ozone gas is allowed to act on the surface of the thin film to form a reflectance adjustment film. A method for manufacturing a mask blank, comprising: forming a mask blank.
(Structure 2) The mask blank manufacturing method according to Structure 1, wherein the concentration of the ozone gas is 80% by volume or more.
(Structure 3) The mask blank manufacturing method according to Structure 1 or 2, wherein a surface reflectance in a wavelength range of 190 to 300 nm of the reflectance adjusting film formed on the thin film surface is 20% or less.
(Structure 4) The method of manufacturing a mask blank according to any one of Structures 1 to 3, wherein the thin film is a light-shielding film made of a material containing chromium.
(Structure 5) The thin film formed on the multilayer reflective film by the manufacturing method according to any one of Structures 1 to 3, wherein a multilayer reflective film that reflects exposure light is formed on the substrate. A method of manufacturing a mask blank, comprising: forming a thin film as an absorber film that absorbs exposure light made of a material containing tantalum.
(Structure 6) A photomask manufacturing method comprising a step of patterning the thin film in a mask blank obtained by the manufacturing method according to any one of structures 1 to 4.
(Structure 7) A reflective mask manufacturing method comprising a step of patterning the thin film in a mask blank obtained by the manufacturing method according to Structure 5.

In the manufacturing method of a mask blank having a thin film for forming a transfer pattern on a substrate as in Configuration 1, after the thin film is formed on the substrate, ozone gas is allowed to act on the surface of the thin film to reflect the reflectance. By forming an adjustment film, a transfer pattern thin film (for example, a light-shielding film) having a reflectance adjustment film on the surface can be formed with low defects, so a short wavelength of about 190 to 300 nm used for an exposure light source during pattern transfer. A mask blank in which the surface reflectance of the thin film in the region (particularly near 250 nm) is effectively reduced and defects are reduced is obtained. There is no pattern defect of a mask manufactured from this mask blank, and good pattern accuracy can be obtained when pattern transfer onto a semiconductor substrate is performed using this mask. In addition, since the reflectance adjusting film can be formed without reducing the film density on the surface of the thin film, a thin film having good chemical resistance and good CD accuracy can be obtained.

As in Configuration 2, by setting the concentration of the ozone gas in Configuration 1 to a high concentration of 80% by volume or more, the surface reflectance in a short wavelength region (especially near 250 nm) of about 190 to 300 nm is low. A sufficiently reduced thin film (for example, 20% or less) can be formed.

Further, as in the configuration 3, the reflectance of the reflectance adjusting film formed on the surface of the thin film is 20% or less in the wavelength range of 190 to 300 nm. Even for an exposure light source that tends to have a wavelength, good pattern transfer accuracy can be obtained by preventing multiple reflections between the mask and the optical system. Moreover, in the reflective mask used for EUV lithography, the surface reflectance of the thin film (absorber film) with respect to deep UV light (particularly around 250 nm) of about 190 to 260 nm used for the pattern inspection wavelength is 20%. By reducing to the following, sufficient contrast with the inspection light can be obtained, and highly accurate pattern inspection can be performed.

In the mask blank for a binary mask in which the thin film is a light-shielding film made of a material containing chromium, the light-shielding film having a reflectance adjustment film on the surface can be formed with a low defect according to the present invention. it can.
Further, as in Configuration 5, a multilayer reflective film that reflects exposure light is formed on the substrate, and the multilayer reflective film is formed by the manufacturing method according to any one of Configurations 1 to 3. EUV exposure in which a low-defect absorber film having a reflectance adjustment film on the surface is formed by forming a thin film as an absorber film that absorbs exposure light made of a material containing tantalum. A reflective mask blank for use is obtained.

As in Configuration 6, the photomask manufacturing method includes a step of patterning the thin film in the mask blank obtained by the manufacturing method according to any one of Configurations 1 to 4, and is used as an exposure light source during pattern transfer. A photomask that reduces the surface reflectivity of the thin film in a short wavelength range of about 190 to 300 nm, has good pattern accuracy corresponding to pattern miniaturization, and has good chemical resistance and improved CD accuracy. Can be obtained.

In addition, as in Configuration 7, a reflective mask manufacturing method including a step of patterning the thin film in the mask blank obtained by the manufacturing method described in Configuration 5 provides sufficient contrast for inspection light used for pattern inspection. Highly accurate pattern inspection can be performed, and pattern transfer using EUV light as an exposure light source can provide good pattern transfer accuracy, and a reflective mask with improved chemical accuracy and improved CD accuracy can be obtained. it can.

According to the present invention, a transfer pattern thin film (light-shielding film) having a reflectance adjustment film on the surface can be formed with low defects, and a short wavelength region of about 190 to 300 nm (especially 250 nm) used as an exposure light source during pattern transfer. It is possible to provide a method for manufacturing a mask blank and a photomask that can effectively reduce the surface reflectance of the thin film in the vicinity) and reduce defects.
Further, according to the present invention, a transfer pattern thin film (absorber film) having a reflectance adjustment film on the surface can be formed with low defects, and deep UV light of about 190 to 260 nm used for a pattern inspection wavelength. It is possible to provide a method for manufacturing a mask blank and a reflective mask that can effectively reduce the surface reflectance of the thin film (particularly near 250 nm).
Moreover, according to this invention, the chemical resistance of the said thin film can be improved, and the manufacturing method of the mask blank and photomask which improved CD precision, and a reflective mask can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 is a sectional view showing a first embodiment of a mask blank obtained by the present invention.
The photomask blank 10 in FIG. 1 is in the form of a binary mask photomask blank having a light-shielding film 2 on a translucent substrate 1.
The photomask blank 10 is a mask blank corresponding to a photomask manufacturing method for patterning the light shielding film 2 by, for example, dry etching using a resist pattern formed on the light shielding film 2 as a mask.

Here, as the translucent substrate 1, a glass substrate is generally used. Since the glass substrate is excellent in flatness and smoothness, when pattern transfer onto a semiconductor substrate using a photomask is performed, highly accurate pattern transfer can be performed without causing distortion of the transfer pattern.

In the present invention, examples of the material for the light shielding film 2 include chromium alone and a material mainly composed of chromium. Examples of the material mainly containing chromium include a material containing chromium and at least one element such as nitrogen and carbon. The nitrogen content in the case where nitrogen is contained in the light shielding film 2 is not particularly limited, but for example, from the viewpoint of obtaining the effect of increasing the dry etching rate, a range of 20 to 80 atomic% is preferable. Further, the carbon content in the case where carbon is contained in the light shielding film 2 is not particularly limited, but for example, from the viewpoint of effectively reducing the reflectance in a short wavelength region of about 190 to 300 nm, 5 to 30 atoms. % Range is preferred.

  The method for forming the light-shielding film 2 is not particularly limited, but a sputtering film forming method is particularly preferable. The sputtering film formation method is suitable for the present invention because it can form a uniform film with a constant film thickness. When the light shielding film 2 is formed on the translucent substrate 1 by a sputtering film forming method, a chromium (Cr) target is used as a sputtering target, and sputtering gas introduced into the chamber is argon gas or helium gas. A mixture of an inert gas and a gas such as nitrogen, nitric oxide, or methane gas is used. When a sputtering gas in which nitrogen gas is mixed with an inert gas such as argon gas is used, a light-shielding film containing nitrogen in chromium can be formed, and nitrogen monoxide gas or nitrogen gas can be used as an inert gas such as argon gas. When a sputtering gas in which oxygen gas and oxygen gas are mixed is used, a light shielding film containing nitrogen and oxygen in chromium can be formed. When a sputtering gas in which methane gas is mixed with an inert gas such as argon gas is used, a light shielding film containing carbon in chromium can be formed.

  The film thickness of the light shielding film 2 is set so that the optical density with respect to the exposure light is, for example, 2.5 or more so that a predetermined light shielding property can be obtained. Specifically, the thickness of the light shielding film 2 is preferably 70 nm or less. The reason is that, in order to cope with the miniaturization of the pattern size to the submicron level in recent years, when the film thickness exceeds 70 nm, the resist film thickness as a mask layer when patterning the light shielding film 2 is reduced. This is because it may be impossible to form a fine pattern because it cannot be performed. The lower limit of the thickness of the light shielding film 2 can be reduced as long as a desired optical density is obtained.

In order to reduce the reflectance with respect to the exposure light, the light shielding film 2 forms a reflectance adjusting film on the surface thereof. In the present invention, ozone gas is allowed to act on the surface of the light-shielding film 2 by irradiating the surface of the light-shielding film 2 with ozone gas or exposing the substrate on which the light-shielding film 2 is formed to ozone gas. Then, a reflectance adjusting film made of an oxide film of a material constituting the light shielding film is formed. In this case, the concentration of ozone gas is preferably set to a high concentration of 80% by volume or more. By using such high-concentration ozone gas, a thin film with low defects and sufficiently reduced surface reflectance in a short wavelength region of about 190 to 300 nm (especially in the vicinity of 250 nm) (for example, 20% or less) is formed. be able to.

  In addition, there is no need to particularly limit the time (treatment time) for which ozone gas is applied, the ambient temperature, etc. However, for example, if the ambient temperature is high, the oxidation rate by ozone gas increases, so from the viewpoint of increasing productivity, the treatment time Is preferably in the range of, for example, about 5 to 60 minutes, and the ambient temperature is in the range of, for example, room temperature to about 300 ° C.

According to the present invention, the light shielding film for a transfer pattern having a reflectance adjusting film on the surface by forming ozone on the surface of the light shielding film formed on the substrate as described above to form the reflectance adjusting film. Can be formed with low defects. Therefore, the surface reflectance of the light shielding film in a short wavelength range of about 190 to 300 nm (especially around 250 nm) used as an exposure light source during pattern transfer can be effectively reduced to, for example, 20% or less, and the mask pattern is covered. When transferring to a transfer body, multiple reflections with the projection exposure surface can be suppressed, and deterioration in imaging characteristics can be suppressed. Furthermore, it is desirable to be able to reduce the reflectance with respect to a wavelength (for example, 257 nm) used for defect inspection of a photomask blank or photomask in order to detect defects with high accuracy. In addition, since a low-defective light-shielding film can be formed, the photomask produced from the mask blank according to the present invention has no pattern defect, and is good when pattern transfer onto a transfer substrate is performed using such a photomask. Pattern accuracy can be obtained. In addition, according to the present invention, since the reflectance adjusting film can be formed without reducing the film density on the surface of the light shielding film, a light shielding film with good chemical resistance and improved CD accuracy can be obtained.

Further, when the light shielding film 2 contains elements such as nitrogen and carbon in addition to chromium, the content thereof may be different in the depth direction, and may be a composition gradient film having a composition gradient stepwise or continuously. . In order to use such a light-shielding film as a composition gradient film, for example, a method of appropriately switching the type (composition) of the sputtering gas during the above-described sputtering film formation during film formation is suitable.

  Further, as shown in FIG. 2A, which will be described later, the photomask blank may have a form in which a resist film 3 is formed on the light shielding film 2 on which the reflectance adjustment film is formed. Absent. The film thickness of the resist film 3 is preferably as thin as possible in order to improve the pattern accuracy (CD accuracy) of the light shielding film. In the case of a so-called binary mask photomask blank as in this embodiment, specifically, the thickness of the resist film 3 is preferably 300 nm or less. The lower limit of the thickness of the resist film is set so that the resist film remains when the light shielding film is dry etched using the resist pattern as a mask. In order to obtain high resolution, the resist film 3 is preferably a chemically amplified resist having high resist sensitivity.

Next, a method for manufacturing a photomask using the photomask blank 10 shown in FIG. 1 will be described.
The photomask manufacturing method using the photomask blank 10 includes a step of patterning the light-shielding film 2 of the photomask blank 10. Specifically, for the resist film formed on the photomask blank 10, A step of performing desired pattern exposure (pattern drawing), a step of developing the resist film in accordance with the desired pattern exposure to form a resist pattern, a step of etching the light shielding film along the resist pattern, and a remaining resist And removing the pattern.

FIG. 2 is a cross-sectional view sequentially illustrating a photomask manufacturing process using the photomask blank 10.
FIG. 2A shows a state in which a resist film 3 is formed on the light shielding film 2 of the photomask blank 10 of FIG.
Next, FIG. 2B shows a step of performing desired pattern exposure (pattern drawing) on the resist film 3 formed on the photomask blank 10. Pattern exposure is performed using an electron beam drawing apparatus or the like.
Next, FIG. 2C shows a process of developing the resist film 3 in accordance with desired pattern exposure to form a resist pattern 3a.

Next, FIG. 2D shows a step of etching the light shielding film 2 along the resist pattern 3a. In the etching step, using the resist pattern 3a as a mask, the exposed portion of the light shielding film 2 where the resist pattern 3a is not formed is removed by dry etching, for example, and thereby a desired light shielding film pattern 2a (mask pattern) is formed. It is formed on the translucent substrate 1.
FIG. 2E shows a photomask 20 obtained by peeling off and removing the remaining resist pattern 3a.
As described above, a photomask manufactured from the mask blank according to the present invention is completed.

(Embodiment 2)
Hereinafter, an embodiment of a reflective mask blank and a reflective mask will be described as a second embodiment of the present invention.
FIG. 3 is a schematic sectional view showing a mask blank (reflection mask blank) according to the present invention and a process for manufacturing a reflection mask using the mask blank.
As shown in FIG. 3A, the reflective mask blank 30 of the present embodiment has a structure in which the multilayer reflective film 12, the buffer film 13, and the absorber film 14 are sequentially formed on the substrate 11. is doing.
First, each layer that forms the reflective mask blank 30 will be described.

The substrate 11 of the reflective mask blank has a low thermal expansion coefficient (in the range of 0 ± 1.0 × 10 ⁻⁷ / ° C., more preferably in the range of 0 ± 0.3 × 10 ⁻⁷ / ° C.). Those having excellent smoothness and flatness and resistance to the mask cleaning liquid are preferred, and glass having low thermal expansion, such as SiO ₂ —TiO ₂ glass, is used. In addition, crystallized glass on which β quartz solid solution is deposited, quartz glass, a substrate made of silicon, metal, or the like can also be used. Examples of metal substrates include Invar alloys (Fe—Ni alloys). The substrate 11 preferably has a smooth surface of 0.2 nmRms or less and a flatness of 100 nm or less in order to obtain high reflectivity and high transfer accuracy. The substrate 11 preferably has high rigidity in order to prevent deformation of the film formed thereon due to film stress. In particular, those having a high Young's modulus of 65 GPa or more are preferable.

  As the multilayer reflective film 12 in the reflective mask blank, a multilayer film in which elements having different refractive indexes are periodically stacked is used. In general, a multilayer film in which thin films of heavy elements or their compounds and thin films of light elements or their compounds are alternately stacked for about 40 to 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 and Si are alternately laminated for about 40 periods is preferably used. In addition, as a multilayer reflective film used in the EUV light region, Ru / Si periodic multilayer film, Mo / Be periodic multilayer film, Mo compound / Si compound periodic multilayer film, Si / Nb periodic multilayer film, Si / Mo / Examples include Ru periodic multilayer films, Si / Mo / Ru / Mo periodic multilayer films, and Si / Ru / Mo / Ru periodic multilayer films. The material may be appropriately selected depending on the exposure wavelength.

  The multilayer reflective film 12 can be formed by depositing each layer by a DC magnetron sputtering method, an ion beam deposition method, or the like. In the case of the Mo / Si periodic multilayer film described above, a Si film having a thickness of several nanometers is first formed in an Ar gas atmosphere using a Si target by a DC magnetron sputtering method, and then an Ar gas atmosphere is used using a Mo target. A Mo film having a thickness of several nanometers is formed, and this is taken as one cycle. After 40 to 60 cycles are stacked, a Si film is finally formed.

The buffer film 13 of the reflective mask blank 30 has a function of protecting the multilayer reflective film 12 when forming a pattern on the absorber film 14 and modifying the pattern. In the case where the absorber film 14 is made of a material mainly composed of tantalum (Ta), for example, a material containing chromium (Cr) is preferably used as the material of the buffer film 13. The buffer film 13 made of a material containing Cr has a large etching selection ratio of 20 or more with respect to the absorber film 14 containing Ta. Further, the material containing Cr can be removed with little damage to the multilayer reflective film 12 when the buffer film 13 is removed.

  As a material containing Cr used as the buffer film 13, a material containing at least one element selected from Cr and N, O, and C can be preferably used in addition to Cr alone. Examples thereof include chromium nitride (CrN), chromium oxide (CrO), chromium carbide (CrC), chromium oxynitride (CrNO), and carbon nitride nitride oxide (CrCNO).

  The buffer film 13 made of such a material containing Cr can be formed by a sputtering method such as a magnetron sputtering method. For example, in the case of the chromium nitride film described above, the film formation may be performed in a gas atmosphere using a Cr target and adding about 5 to 40% of nitrogen to argon. The thickness of the buffer film 13 is such that when the absorber pattern is corrected using a focused ion beam (hereinafter referred to as FIB), the buffer film is damaged. The thickness is preferably 30 to 50 nm so as not to affect the thickness 12, but when FIB is not used, the thickness can be reduced to 4 to 10 nm. The buffer film 13 may be provided as necessary, and the absorber film may be provided directly on the multilayer reflective film depending on the pattern formation / correction method, conditions, etc. of the absorber film.

The absorber film 14 in the reflective mask blank 30 has a function of absorbing, for example, EUV light that is exposure light.
Examples of the material of the absorber film 14 include materials containing tantalum as a main component, materials containing tantalum and boron, and materials containing at least one of oxygen and nitrogen in addition to these materials. Specifically, for example, tantalum nitride (TaN), tantalum boron alloy nitride (TaBN), tantalum boron alloy oxide (TaBO), tantalum boron alloy oxynitride (TaBNO), etc. Is mentioned.

Tantalum is an absorber layer material that has a large EUV light absorption coefficient, can be easily dry-etched with chlorine, and has excellent workability. Among these, tantalum boron alloy (TaB) has an advantage that it can be easily amorphized and a film excellent in smoothness can be obtained. Moreover, since it is excellent also in the controllability of the film stress, it is an absorber layer material that can be formed with high dimensional accuracy of the mask pattern.

The film structure of the absorber film 14 is preferably amorphous. A crystalline film is likely to undergo a change in stress over time. The thickness of the absorber film 14 may be any thickness that can sufficiently absorb EUV light as exposure light, but is usually about 30 to 100 nm.
The absorber film 14 can be formed by a sputtering method such as magnetron sputtering. For example, deposition can be performed by a sputtering method using a target containing tantalum and boron and using an argon gas to which oxygen or nitrogen is added.

In the present invention, a reflectance adjusting film is formed on the surface of the absorber film 14. That is, by causing ozone gas to act on the surface of the absorber film 14 by irradiating the surface of the absorber film 14 with ozone gas or exposing the mask blank in which the absorber film is formed on the substrate to ozone gas, A reflectance adjusting film made of an oxide film of a material constituting the absorber film is formed on the surface of the absorber film 14. Also in the present embodiment, in this case, the concentration of ozone gas is preferably set to a high concentration of 80% by volume or more. By using such high-concentration ozone gas, a thin film with low defects and sufficiently reduced surface reflectance in a short wavelength region of about 190 to 300 nm (especially in the vicinity of 250 nm) (for example, 20% or less) is formed. be able to.

  In the present embodiment also, there is no need to particularly limit the time (treatment time) during which ozone gas is applied, the atmospheric temperature, and the like. However, for example, if the atmospheric temperature is high, the oxidation rate by ozone gas increases, so the productivity is increased. From the viewpoint, it is preferable that the processing time is in the range of, for example, about 5 to 60 minutes, and the atmospheric temperature is in the range of, for example, room temperature to about 300 ° C.

According to the present invention, as described above, ozone gas is allowed to act on the surface of the absorber film to form the reflectance adjustment film, so that the absorber film for transfer patterns having the reflectance adjustment film on the surface can be reduced in defects. Can be formed. Therefore, the surface reflectance of the absorber film for deep UV light (especially around 250 nm) of about 190 to 260 nm used for the pattern inspection wavelength can be reduced to, for example, 20% or less, which is sufficient for inspection light. Contrast is obtained, which is desirable for detecting defects with high accuracy. In addition, since a low-defect absorber film can be formed, the reflective mask manufactured from the mask blank according to the present invention has no pattern defect, and pattern transfer onto the substrate to be transferred by EUV light can be performed using this reflective mask. When done, good pattern transfer accuracy is obtained. In addition, according to the present invention, since the reflectance adjustment film can be formed without reducing the film density on the surface of the absorber film, an absorber film with good chemical resistance and improved CD accuracy can be obtained. It is done.

The reflective mask blank 30 obtained by the present invention is configured as described above.
Next, a manufacturing process of the reflective mask using the reflective mask blank 30 will be described.
The reflective mask blank 30 (see FIG. 3A) obtained by the present invention is obtained by sequentially forming each layer of the multilayer reflective film 12, the buffer film 13, and the absorber film 14 on the substrate 11. The material and the forming method are as described above.

Next, an absorber pattern is formed on the absorber film 14 of the reflective mask blank 30. First, an electron beam resist is applied on the absorber film 14 and baked. Next, drawing is performed using an electron beam drawing machine, and this is developed to form a resist pattern 15a.
Using the formed resist pattern 15a as a mask, the absorber film 14 is subjected to, for example, dry etching to form the absorber pattern 14a (see FIG. 3B). The resist pattern 15a remaining on the absorber pattern 14a is removed (see FIG. 5C).

  Here, it is inspected whether the absorber pattern 14a is formed as designed. As described above, DUV light having a wavelength of about 190 nm to 260 nm is usually used for inspection, but a reflectance adjustment film that reduces the reflectance with respect to inspection light is formed on the surface of the absorber pattern 14a. Sufficient contrast can be obtained.

After the pattern inspection and the necessary correction are thus completed, the exposed buffer film 13 is removed according to the absorber pattern 14a, and the reflective mask 40 is manufactured (see FIG. 3D).
Finally, final confirmation inspection of the formed pattern is performed. Also in the case of this final confirmation inspection, the above-mentioned DUV light having a wavelength of about 190 nm to 260 nm is used. In the present invention, sufficient contrast can be obtained and high-precision inspection can be performed.

Hereinafter, the embodiment of the present invention will be described more specifically with reference to examples. In addition, a comparative example for the embodiment will be described.
Example 1
A light-shielding film was formed on a translucent substrate made of synthetic quartz glass whose main surface and end face were precisely polished, and a photomask blank for a binary mask was produced.
Reactive sputtering is performed on the substrate using an in-line sputtering apparatus, using a chromium target as a sputtering target, and in an atmosphere of a mixed gas of argon and nitrogen (Ar: 50% by volume, N ₂ : 50% by volume). Thus, a light shielding film was formed.

  Next, ozone gas was irradiated to the surface of the light shielding film formed as described above. The ozone gas concentration in this case was 80% by volume, the ambient temperature was 200 ° C., and the ozone gas irradiation time was 30 minutes.

  As a result of analyzing the formed light shielding film by Auger electron spectroscopy, oxygen is detected in addition to chromium and nitrogen on the very surface of the light shielding film, and an oxide film is formed on the surface of the light shielding film. It was confirmed. Further, the formed light shielding film had an optical density of 3.0. Further, the surface reflectance of this light-shielding film with respect to a KrF excimer laser (wavelength 248 nm) was as low as 19%. Furthermore, for the photomask defect inspection wavelength of 257 nm or 364 nm, the reflectances were 18% and 15%, respectively, and the reflectance was not a problem in the inspection.

Furthermore, as a result of measuring 10 defects of the light shielding film with a mask blank defect inspection apparatus (M1320: manufactured by Lasertec), the number of detected defects is an average of 3 or less per plate, and the light shielding film has a very low defect. Was found to be formed.
Thus, the photomask blank in which the light shielding film with a total film thickness of 70 nm was formed was obtained.

Next, using the obtained photomask blank, a photomask was produced according to the above-described process of FIG. That is, an electron beam resist (CAR-FEP171 manufactured by Fuji Film Electronics Materials), which is a chemically amplified resist, was spin-coated on the photomask blank 10 and subjected to a predetermined heat drying treatment.
Next, a desired pattern was drawn on the resist film formed on the photomask blank 10 using an electron beam drawing apparatus, and then developed with a predetermined developer to form a resist pattern 3a.

Next, the light shielding film 2 was dry-etched along the resist pattern 3a to form the light shielding film pattern 2a. As a dry etching gas, a mixed gas of Cl ₂ and O ₂ (Cl ₂ : O ₂ = 4: 1) was used.
The remaining resist pattern was peeled off to obtain a photomask 20. The obtained photomask 20 maintained a very low reflectance of, for example, 19% of the surface reflectance of the light shielding film pattern at an exposure wavelength of 248 nm. Further, since a light-shielding film having a low defect is formed, the mask pattern of the obtained photomask has no defect that causes a problem as a result of inspection. Further, in the above-described mask blank and photomask manufacturing processes, there was no film peeling of the light-shielding film or an increase in reflectance due to chemical cleaning, and there was no problem with the chemical resistance of the light-shielding film.

(Example 2)
On the same translucent substrate as in Example 1, a light-shielding film was formed as follows, and a photomask blank for a binary mask was produced.
Reactive sputtering is performed on the substrate using an in-line sputtering apparatus, using a chromium target as a sputtering target, and in a mixed gas atmosphere of argon and methane gas (Ar: 90% by volume, CH ₄ : 10% by volume). Thus, a light shielding film was formed.

  Next, ozone gas was irradiated to the surface of the light shielding film formed as described above. The ozone gas irradiation conditions in this case were the same as in Example 1, the ozone gas concentration was 80% by volume, the ambient temperature was 200 ° C., and the ozone gas irradiation time was 30 minutes.

  As a result of analyzing the formed light shielding film by Auger electron spectroscopy, oxygen is detected in addition to chromium and carbon on the very surface of the light shielding film, and an oxide film is formed on the surface of the light shielding film. It was confirmed. Further, the formed light shielding film had an optical density of 3.0. Further, the surface reflectance of this light-shielding film with respect to a KrF excimer laser (wavelength 248 nm) could be suppressed to a very low 15%. Further, for the photomask defect inspection wavelength of 257 nm or 364 nm, the reflectivity was 15% and 16%, respectively, and the reflectance was not problematic even in the inspection.

Furthermore, as a result of measuring 10 defects of the light shielding film with a mask blank defect inspection apparatus (M1320: manufactured by Lasertec Corporation), the number of detected defects is an average of 3 or less per plate, and the light shielding film has a very low defect. Was found to be formed.
Thus, a photomask blank having a light shielding film with a total film thickness of 65 nm was obtained.

  Next, a photomask was produced in the same manner as in Example 1 using the obtained photomask blank. The obtained photomask maintained a very low reflectance of, for example, 15% of the surface reflectance of the light shielding film pattern at an exposure wavelength of 248 nm. Further, since a light-shielding film having a low defect is formed, the mask pattern of the obtained photomask has no defect that causes a problem as a result of inspection. Further, in the above-described mask blank and photomask manufacturing processes, there was no peeling of the light-shielding film due to chemical cleaning and an increase in reflectance, and there was no problem with respect to the chemical resistance of the light-shielding film.

(Example 3)
First, a reflective mask blank 30 as shown in FIG. The substrate 11 to be used is a SiO ₂ —TiO ₂ glass substrate (outer shape 6 inch square, thickness 6.3 mm). The substrate 11 has a thermal expansion coefficient of 0.2 × 10 ⁻⁷ / ° C. and a Young's modulus of 67 GPa. This glass substrate was formed by mechanical polishing to have a smooth surface of 0.2 nmRms or less and a flatness of 100 nm or less.

  In this embodiment, the multilayer reflective film 12 formed on the substrate 11 is a Mo / Si periodic multilayer reflective film in order to form a multilayer reflective film suitable for an exposure light wavelength band of 13 to 14 nm. That is, the multilayer reflective film 12 was formed by alternately laminating Mo and Si on the substrate 11 by DC magnetron sputtering. First, using a Si target, a Si film having a thickness of 4.2 nm was formed at an Ar gas pressure of 0.1 Pa. Thereafter, using a Mo target, a Mo film having a thickness of 2.8 nm was formed at a Ar gas pressure of 0.1 Pa. As a cycle, 40 cycles were stacked, and finally a Si film was formed to 4 nm. The total film thickness is 284 nm. With respect to this multilayer reflective film 12, the reflectivity at an incident angle of 6 degrees of light of 13.5 nm was 65%. The surface roughness of the surface of the multilayer reflective film 12 was 0.12 nmRms. The reflectance of the surface of the multilayer reflective film 12 with respect to the inspection light having a wavelength of 257 nm was 60%.

The buffer film 13 formed on the multilayer reflective film 12 was made of chromium nitride. The film thickness is 50 nm. When this chromium nitride is expressed by Cr _1-X N _X , X = 0.1. This buffer film 13 was formed by a DC magnetron sputtering method using a Cr target and using a gas obtained by adding 10% of nitrogen to Ar as a sputtering gas.
The reflectance of the buffer film 13 surface with respect to light of 257 nm is 52%. The surface roughness of the buffer film 13 surface was 0.27 nmRms.

The absorber film 14 formed on the buffer film 13 is made of nitride of tantalum boron alloy (TaBN) with a film thickness of 50 nm. The absorber film 14 was formed by a DC magnetron sputtering method using a sintered body target containing Ta and B and using a gas obtained by adding 40% of nitrogen to Ar. The absorber film 14 deposited under such deposition conditions was amorphous.
Next, ozone gas was irradiated to the surface of the absorber film formed as described above. The ozone gas concentration in this case was 80% by volume, the ambient temperature was 200 ° C., and the ozone gas irradiation time was 30 minutes.

As a result of analyzing the formed absorber film by Auger electron spectroscopy, oxygen was detected on the very surface of the absorber film in addition to Ta, B and nitrogen, and an oxide film was formed on the surface of the absorber film. It was confirmed that it was formed. Further, the reflectivity of the absorber film surface with respect to light having a defect inspection wavelength of 257 nm was 10%, and could be kept very low.
Furthermore, as a result of measuring 10 defects of this absorber film with an EUVL mask blank defect inspection apparatus (M1350: manufactured by Lasertec Corporation), the number of detected defects is an average of 5 or less per plate, which is very low defect. It was found that an absorber film was formed. The surface roughness of the absorber film surface was 0.25 nmRms.

As described above, a reflective mask blank 30 of this example as shown in FIG.
Next, the above-described reflective mask 40 shown in FIG. 4D was produced from the reflective mask blank 30 described above. First, a resist for electron beam irradiation is applied on the absorber film 14 of the reflective mask blank 30, a pattern drawing for a 16 Gbit DRAM having a design rule of 0.07 μm is performed with an electron beam, and development is performed. 15a was formed.
Using this resist pattern 15a as a mask, the absorber film 14 was dry-etched using chlorine to form the absorber pattern 14a. The resist pattern 15a remaining on the absorber pattern 14a was removed with hot sulfuric acid at 100 ° C.
In this state, the absorber pattern 14a was inspected using inspection light having a wavelength of 257 nm. Sufficient contrast was obtained in the inspection.

Next, the buffer film 13 remaining on the reflective region (the portion without the absorber pattern 14a) was removed according to the absorber pattern 14a. The buffer film 13 was removed by dry etching using a mixed gas of chlorine and oxygen.
As described above, a reflective mask of this example was obtained.
The final confirmation inspection of the reflective mask thus obtained was performed. As the inspection light, light having a wavelength of 257 nm was used, and sufficient contrast was obtained even in the final confirmation inspection. Thus, it was confirmed by inspection that the reflective mask of this example was able to form a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm as designed. Moreover, in the manufacturing process of the above-mentioned mask blank and mask, there was no film peeling of the absorber film and an increase in reflectance due to chemical cleaning, and there was no problem with the chemical resistance of the absorber film.

Example 4
In the same manner as in Example 3, a multilayer reflective film 12 and a buffer film 13 were formed on the substrate 11.
Next, tantalum nitride (TaN) was formed to a thickness of 50 nm as the absorber film 14 on the buffer film 13. The absorber film 14 was formed by a DC magnetron sputtering method using a Ta target and using a gas obtained by adding 40% nitrogen to Ar.
Next, ozone gas was irradiated to the surface of the absorber film formed as described above. The ozone gas irradiation conditions in this case were the same as in Example 3. The ozone gas concentration was 80% by volume, the ambient temperature was 200 ° C., and the ozone gas irradiation time was 30 minutes.

As a result of analyzing the formed absorber film by Auger electron spectroscopy, oxygen is detected in addition to Ta and nitrogen on the very surface of the absorber film, and an oxide film is formed on the surface of the absorber film. Confirmed that. Further, the reflectivity of the absorber film surface with respect to light having a defect inspection wavelength of 257 nm could be suppressed to a very low value of 18%.
Furthermore, as a result of measuring 10 defects of this absorber film with an EUVL mask blank defect inspection apparatus (M1350: manufactured by Lasertec Corporation), the number of detected defects is an average of 5 or less per plate, which is very low defect. It was found that an absorber film was formed. The surface roughness of the absorber film surface was 0.25 nmRms.

As described above, a reflective mask blank of this example was obtained.
Next, as in Example 3, a reflective mask was produced from the obtained reflective mask blank.
When the final confirmation inspection of the produced reflective mask was performed, it was confirmed that the reflective mask of this example was able to form a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm as designed. Moreover, in the manufacturing process of the above-mentioned mask blank and mask, there was no film peeling of the absorber film and an increase in reflectance due to chemical cleaning, and there was no problem with the chemical resistance of the absorber film.

(Comparative example)
On the translucent substrate made of the same synthetic quartz glass as in Example 1, an in-line sputtering apparatus was used, a chromium target was used as the sputtering target, and a mixed gas of argon and carbon dioxide (Ar: 90% by volume, CO ₂ : 10% by volume, gas pressure: 0.3 Pascal) A light shielding layer was formed by performing reactive sputtering in an atmosphere. Subsequently, reactive sputtering is performed in an atmosphere of a mixed gas of argon, carbon dioxide, and nitrogen (Ar: 70% by volume, CO ₂ : 12% by volume, N ₂ : 18% by volume, gas pressure: 0.3 Pascal). An antireflection layer was formed. In this way, a photomask blank was obtained in which a light shielding film composed of a light shielding layer and an antireflection layer having a total film thickness of 100 nm was formed.
The light shielding film of this comparative example had an optical density of 3.0. Further, the surface reflectance of this light-shielding film at an exposure wavelength of 248 nm was 20%. Furthermore, as a result of measuring 10 defects of the light shielding film with a mask blank defect inspection apparatus (M1320: manufactured by Lasertec Corporation), the number of detected defects is 20 or more on average per plate, and the defects of the light shielding film are extremely high. I found many.

  Next, using the obtained photomask blank, a photomask was produced in the same manner as in Example 1 described above. As a result of the inspection, the obtained mask pattern of the photomask has many defects that are thought to be caused by the above-described defects of the light shielding film, and also includes defects that cause a malfunction of the semiconductor device. Further, in the above-described mask blank and photomask manufacturing processes, the reflectance due to chemical cleaning may increase, and there is a slight problem with the chemical resistance of the light shielding film. In addition, since the surface reflectance at the exposure wavelength of 248 nm of the light shielding film of this comparative example is 30%, which is higher than that of the above-described embodiment, when the mask pattern is transferred using a photomask, It is also conceivable that multiple reflections occur between them, and a desired pattern transfer cannot be performed.

  When an isolated line pattern of 200 nm was formed from the light-shielding film pattern in Examples 1 and 2, the absorber film pattern in Examples 3 and 4, and the light-shielding film pattern in the comparative example, a CD-SEM (Critical Dimension-Scanning Electron Microscope: length measurement) The CD accuracy obtained by measuring the pattern with a scanning electron microscope was 5 nm for Examples 1 to 4, but 15 nm for the comparative example. It can be seen that the CD accuracy of the mask in which the reflectance is adjusted by applying the ozone gas of the present invention is remarkably improved.

It is sectional drawing which shows one Embodiment of the photomask blank obtained by this invention. It is sectional drawing which shows the manufacturing process of the photomask using a photomask blank. It is sectional drawing which shows the manufacturing process of the reflective mask blank which concerns on the 2nd Embodiment of this invention, and a reflective mask using this mask blank.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Translucent substrate 2 Light-shielding film 3 Resist film 2a Light-shielding film pattern 3a Resist pattern 10, 30 Mask blank 11 Substrate 12 Multilayer reflective film 13 Buffer film 14 Absorber film 20 Photomask 40 Reflective mask

Claims (4)

In a method for manufacturing a mask blank having a thin film for forming a transfer pattern on a substrate,
After forming the thin film on the substrate, the surface of the thin film is irradiated with ozone gas to form an oxide film,
The concentration of the ozone gas is 80% by volume or more;
The atmospheric temperature when irradiating the ozone gas is from room temperature to 300 ° C.,
The thin film is a light-shielding film made of a material containing chromium , and the film thickness of the light-shielding film has an optical density of 2.5 or more and 70 nm or less with respect to exposure light. Method.   2. The method of manufacturing a mask blank according to claim 1, wherein the oxide film formed on the surface of the thin film has a surface reflectance of 20% or less in a wavelength range of 190 to 300 nm. Method for producing a mask blank according to claim 1 or 2, characterized in that the resist film is formed on the thin film. Method of manufacturing a mask comprising a step of patterning the thin film in the mask blank obtained by the method according to any one of claims 1 to 3.

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