JP2009092840A - Photomask and photomask blank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-reflective photomask which essentially consists of aluminum, has high light-shielding property and excellent pattern processability, exhibits a low reflectance at an exposure wavelength, is relatively gradual in reflectance variation in a wavelength range from 200 to 400 nm, and is suitable for lithographic techniques aiming to a half pitch of 45 nm and beyond (smaller) on a wafer, and to provide a photomask blank. <P>SOLUTION: The photomask blank has a thin film of a single layer or two or more layers formed on a transparent substrate, and is characterized in that: the outermost surface layer of the thin film of a single layer or two or more layers comprises an aluminum compound and metal aluminum added to the aluminum compound; and the rate of content of the metal aluminum is ≤60 atomic%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photomask used for manufacturing high-density integrated circuits such as LSI and VLSI, and a photomask blank for manufacturing the photomask. In particular, the present invention uses a high NA exposure apparatus and is substantially the same as the exposure wavelength. The present invention relates to a low reflection type photomask and a photomask blank used in advanced lithography technology in which a mask pattern of a certain size is transferred onto a wafer and the half pitch of the pattern on the wafer is 45 nm or more.

  Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by repeating a so-called lithography process using a photomask (hereinafter also referred to as a mask). The photomask substrate before patterning is known as photomask blanks (hereinafter also referred to as blanks), and binary photomask blanks have been put into practical use with a transparent substrate and a light shielding film composed mainly of chromium (Cr). ing. In order to realize a highly accurate semiconductor integrated circuit, photomask blanks are required to have low defects, film composition / film structure for improving etching controllability, low stress, and low reflectivity for exposure wavelength. . In order to satisfy these requirements, various film compositions, layer structures, and film formation methods have been proposed and put into practical use in photomask blanks mainly composed of chromium (for example, see Patent Documents 1 to 3). ).

  However, the specifications required for photomasks are becoming stricter year by year. For example, according to the ITRS roadmap 2006 update, the CD uniformity and linearity of masks required for DRAM 65 nm half pitch are 3 nm and 10 nm, respectively. The review from the mask material has been reviewed (see Non-Patent Document 1).

  As a mask material other than chromium, an aluminum (Al) compound is not as common as chromium, but is one of mask materials that have been studied for a long time. A photomask material using an aluminum compound such as aluminum nitride (AlN) as an intermediate layer in order to improve the adhesion between a transparent substrate typified by synthetic quartz and a chromium-based light-shielding film has been proposed (Patent Document 4,). (See Patent Document 5). In addition, since aluminum compounds have high transparency in the ultraviolet region, they have been proposed as phase shift mask materials including mixing with silicon compounds (see Patent Document 6) or phase shift mask materials by mixing with chromium compounds (patents). Reference 7). The aluminum-based material applied to the conventional photomask blank described in the above-mentioned literature is mainly used as a semi-transmissive film using the high light transmittance of an aluminum compound.

  On the other hand, metallic aluminum itself has a large absorption even at a short wavelength after the ultraviolet region, and is suitable as a light shielding material at an exposure wavelength of an ArF laser (193 nm) or a KrF laser (248 nm). In addition, since it is classified as a light element, the influence of backscattering at the time of resist drawing using a high acceleration electron beam drawing machine is small, and it can be said that the material is suitable for electron beam drawing. Since it can be dry-etched with oxygen-free chlorine-based gas on the processed surface, compared with chromium-based materials, resist thinning is effective for increasing resist resolution, loading effect is reduced, and mask dimensions from resist dimensions are reduced. The shift amount can be reduced. In addition, since fluorine gas is not substantially dry etched, each layer can be selectively processed when combined with a phase shift mask material that is dry etched with a fluorine gas such as molybdenum silicide oxynitride film. It has the advantage that it can be improved.

However, aluminum-based materials are conventionally used such as SPM (sulfuric acid / hydrogen peroxide, a mixture of sulfuric acid and hydrogen peroxide) or SC-1 (ammonia hydrogen peroxide, a mixture of ammonia and hydrogen peroxide). The acid and alkali mask cleaning solutions are extremely weak and inferior in practicality. On the other hand, as the exposure wavelength is shortened and energy is increased, residual ions such as sulfate ion or ammonium ion on the mask during mask cleaning grows during exposure, and it has become clear that wafer transfer is adversely affected. Therefore, improvement of the cleaning method itself is urgently needed. As a means of suppressing residual ions on the mask while maintaining the cleaning capability, ozone water cleaning is effective and put into practical use instead of SPM cleaning, and aluminum-based materials have excellent resistance to ozone water cleaning. Have Therefore, it has been expected that the problem of poor chemical resistance during conventional cleaning with aluminum-based materials can be avoided or reduced by changing the cleaning method.
JP-A 61-272746 JP-A-4-9847 JP 2006-146152 A Japanese Patent No. 1547203 JP 62-35361 A JP 2002-62638 A JP-A-8-272074 International Technology Roadmap For Semiconductors 2006 Update, Lithography, p. 9. Semiconductor Technology Roadmap Technical Committee (2006)

  However, when a metal aluminum thin film is used as a light shielding film for a mask, multiple reflections of exposure light occur due to the extremely high reflectance of the surface of the aluminum thin film when transferring the mask pattern to the wafer, reducing the resolution of the wafer transfer image. There was a problem that. Therefore, in order to use an aluminum-based compound as a light-shielding film, a photomask (hereinafter referred to as a low-reflection type photomask) having a low-reflection-type light-shielding film in which the light-shielding film surface has a low reflectance at the exposure wavelength (for example, a reflectance of 20% or less) Called a mask).

The inventor of the present invention targets KrF and ArF excimer laser steppers, and in particular, an exposure wavelength of 193 nm of an ArF excimer laser as a main target, and is a light-shielding photo-type mainly composed of aluminum (Al) in order to maintain light shielding properties. When trying to reduce the reflection of the mask, due to the remarkably low refractive index (0.26) of aluminum, silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O) It has been found that even when a conventional general antireflection film such as ₃ ) is laminated on an aluminum thin film, the reflectance cannot be reduced to 20% or less in the exposure wavelength region.

  In addition, when aluminum nitride (AlN) is used as an antireflection film, the reflectance near 193 nm can be reduced to 20% or less by optimizing the film thickness, but on the other hand, it is reflected in the wavelength region of 200 to 400 nm. Since the rate changes abruptly, there is a problem that it becomes difficult to control the reflectance in the wavelength range of 200 to 400 nm, which may be used in inspection / measurement, and this hinders inspection / measurement.

  Therefore, the present invention has been made in view of the above problems. That is, the object of the present invention is to have aluminum as a main component, high light-shielding property, excellent pattern processability, low reflectance at the exposure wavelength, and relatively low reflectance fluctuation in the wavelength range of 200 to 400 nm. To provide a low-reflection photomask and a photomask blank that are gentle and suitable for lithography technology with a half pitch of 45 nm or more on a wafer.

  In order to solve the above problems, a photomask blank according to the invention of claim 1 is a photomask blank in which a single-layer thin film or two or more thin films are formed on a transparent substrate. The outermost surface layer of two or more thin films is composed of an aluminum compound and metallic aluminum added to the aluminum compound, and the content of the metallic aluminum is 60 atomic% or less.

  A photomask blank according to the invention of claim 2 is the photomask blank of claim 1, wherein the aluminum compound is aluminum nitride, aluminum oxide, or aluminum oxynitride.

  A photomask blank according to a third aspect of the present invention is the photomask blank according to the first or second aspect, wherein the single-layer thin film or the thin film of two or more layers has a film thickness of 200 nm at an exposure wavelength of 193 nm or 248 nm. In the following cases, the optical density is 3 or more, and the surface reflectance is 20% or less.

  The photomask according to the invention of claim 4 is a photomask obtained by patterning a single-layer thin film or two or more thin films on a transparent substrate, wherein the outermost surface layer of the single-layer thin film or the two or more thin-films is It is composed of an aluminum compound and metallic aluminum added to the aluminum compound, and the content of the metallic aluminum is 60 atomic% or less.

  A photomask according to a fifth aspect of the present invention is the photomask according to the fourth aspect, wherein the aluminum compound is aluminum nitride, aluminum oxide, or aluminum oxynitride.

  A photomask according to a sixth aspect of the present invention is the photomask according to the fourth or fifth aspect, wherein the single-layer thin film or the two or more thin films have a film thickness of 200 nm or less at an exposure wavelength of 193 nm or 248 nm. The optical density at that time is 3 or more, and the surface reflectance is 20% or less.

  According to the photomask blank of the present invention, by adding 60 atomic% or less of metal aluminum to a thin film made of an aluminum compound to form a low reflection film, the light-shielding film having a remarkably small refractive index like aluminum is used. In addition, it is possible to reduce the reflection. As a result, this method also improves the light-shielding property of the low-reflection film from ultraviolet to visible light, and also has the effect of moderately changing the reflectance in the ultraviolet to visible light region. In addition, since the outermost surface layer is maintained to be an aluminum-based material, excellent characteristics in the drawing, etching, and cleaning processes unique to the aluminum-based material are maintained. In addition, by controlling the amount of aluminum added, the light-shielding property is maintained even in a single-layer structure, making it possible to reduce the thickness of the resist effectively for increasing the resolution of the resist. Thus, a high-precision photomask with reduced loading effect during dry etching and reduced shift of the mask dimension from the resist dimension can be obtained.

  According to the photomask of the present invention, the mask pattern has a high light shielding property, the reflectance at the exposure wavelength is kept low, a high resolution wafer transfer image is obtained, and the mask pattern at the inspection / measurement wavelength is obtained. Since the reflectance is relatively gentle, stable pattern inspection / measurement is possible. Further, it is possible to obtain a high-resolution single-layer low-reflection photomask that is non-chromium and excellent in CD uniformity.

  Hereinafter, a low reflection type photomask and a photomask blank according to an embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a photomask blank (FIG. 1A) made of a low-reflection type light-shielding film having a single-layer structure according to the present embodiment and a photomask according to the present embodiment manufactured using the same (FIG. 1B). It is a cross-sectional schematic diagram which shows an example. As shown in FIG. 1A, the photomask blank of this embodiment includes a transparent substrate 11 and a low-reflection type single-layer light-shielding film 12 provided thereon. The light-shielding film 12 includes an aluminum compound, It is comprised with the metal aluminum added to this aluminum compound, and the content rate of metal aluminum shall be 60 atomic% (it is hereafter described also as atm%) or less.

  In the present embodiment, as the transparent substrate 11, optically polished synthetic quartz glass, fluorite, calcium fluoride, or the like that transmits the exposure light with high transmittance can be used. A synthetic quartz glass which is stable and has a high transmittance for exposure light having a short wavelength is more preferable.

In the present embodiment, the aluminum compound constituting the light shielding film 12 is preferably aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), or aluminum oxynitride (AlON). The light shielding film 12 is made of aluminum (Al) as a target, Ar / N ₂ gas when an aluminum nitride film is formed as a sputtering gas, Ar / O ₂ gas or aluminum oxide when an aluminum oxide film is formed. In the case of forming aluminum nitride, Ar / N ₂ / O ₂ can be used, and it can be formed by a normal film forming method such as sputtering.

  The low reflection type light shielding film 12 of the present embodiment has a single layer structure, and since metal aluminum exists on the surface of the thin film, the resistance of the blank surface can be reduced, and a resist pattern is formed using an electron beam drawing machine. In addition, charge-up during drawing can be suppressed, and pattern accuracy can be improved.

  The low reflection type light shielding film 12 of the present embodiment is a light shielding film having a single layer structure and can be etched with an oxygen-free chlorine-based gas without requiring oxygen gas during dry etching. The amount of reduction can be reduced, and as a result, a fine resist pattern can be formed by thinning the resist, and accordingly, a fine light-shielding film pattern can be formed. Since the light shielding film 12 is etched with a chlorine-free oxygen-containing gas, when the transparent substrate 11 is made of synthetic quartz, the synthetic quartz is not etched, and as shown in FIG. A low reflection type photomask having the reflection type light shielding film pattern 13 can be obtained.

  In the photomask according to the present embodiment, the light shielding film pattern 13 maintains a high light shielding property with an optical density (OD) of about 3 at the exposure wavelength by setting the content of metal aluminum added to the aluminum compound to 60 atm% or less. The film shows a low reflectance with respect to the exposure wavelength, and can be preferably 20% or less, and a mask image having a high contrast can be transferred onto the wafer. Furthermore, the reflectance fluctuation in the wavelength range of 200 to 400 nm, which may be used for inspection / measurement, becomes relatively gradual. For example, stable inspection / measurement is possible in inspection / measurement at wavelengths of 257 nm and 365 nm. .

(Second Embodiment)
FIG. 2 shows an example of a photomask blank (FIG. 2A) made of a light-shielding film having a two-layer structure according to this embodiment and a photomask of the present invention manufactured using the same (FIG. 2B). It is a cross-sectional schematic diagram. As shown in FIG. 2A, in the photomask blank of this embodiment, a light-shielding film 22 and a low-reflection film 23 are sequentially laminated on a transparent substrate 21, and the low-reflection film 23 serving as the outermost surface layer is aluminum. It consists of a compound and metallic aluminum added to the aluminum compound, and the content of metallic aluminum is 60 atomic% or less.

  In the present embodiment, the transparent substrate 21 is made of the same material as that of the first embodiment, and optically polished synthetic quartz glass, fluorite, calcium fluoride, or the like can be used. Synthetic quartz glass having a high light transmittance is more preferable.

  In the present embodiment, the light shielding film 22 is not limited to aluminum (Al), and other metal films having high light shielding properties such as titanium (Ti), tantalum (Ta), zirconium (Zr), etc. may be used. However, the same kind of aluminum (Al) as that of the low reflection film 23 can be formed and patterned with the same apparatus, which is more preferable. Hereinafter, the case where aluminum (Al) is used as the light shielding film 23 will be described. The light shielding film 22 can be formed by a normal film forming method such as a sputtering method using aluminum as a target.

In the present embodiment, the aluminum compound constituting the low-reflection film 23 serving as the outermost surface layer is preferably aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), or aluminum oxynitride (AlON). These aluminum compounds By adding metallic aluminum to the film, a low reflection film can be obtained. The low reflection film 23 is formed of aluminum (Al) as a target, Ar / N ₂ gas when an aluminum nitride film is formed as a sputtering gas, and Ar / O ₂ gas when an aluminum oxide film is formed. In the case of forming aluminum nitride, Ar / N ₂ / O ₂ can be used, and it can be formed by a normal film forming method such as sputtering.

  The blank of this embodiment has a two-layer structure, and since metal aluminum is present in the low-reflection film 23 of the outermost surface layer, the resistance of the blank surface can be reduced, and a resist pattern is formed using an electron beam drawing machine Thus, charge-up during drawing can be suppressed and pattern accuracy can be improved.

  In addition, in the photomask blank having a plurality of layers as shown in FIG. 2, when the light shielding film 22 is made of an aluminum material, the light shielding film 22 can be dry-etched with a chlorine-based gas simultaneously with the low reflection film 23, which is unique to the aluminum material. The drawing, etching, and cleaning characteristics can be maintained. On the other hand, when the light shielding film 22 is a material that is not substantially etched with a chlorine-based gas and can be etched with a fluorine-based gas or an oxygen-containing chlorine-based gas, the light-shielding film 22 is etched using the low reflection film 23 as an etching mask. It is also possible. Although the case of the two-layer structure has been described with reference to FIG. 2, the present invention can be applied by forming the outermost surface layer as a low reflection film made of an aluminum compound containing 60 atomic% or less of metal aluminum even in the case of three or more layers. can do.

The photomask according to the present embodiment has a low reflectivity with respect to the exposure wavelength while maintaining a light shielding property of about an optical density (OD) of 3 by setting the content of metal aluminum added to the aluminum compound to 60 atm% or less. And preferably 20% or less, and a mask image with high contrast can be transferred onto the wafer. Further, since the low reflection film pattern 25 constituting the mask image contains metallic aluminum and has a light shielding property in the ultraviolet to visible light region, it has an effect of making the reflectance spectrum gentle in this wavelength region. The reflectance fluctuation in the 200 to 400 nm wavelength region that may be used in the above becomes relatively moderate. For example, in the inspection and measurement at wavelengths of 257 nm and 365 nm, stable inspection and measurement are possible.
In the following, the embodiment will be described in more detail.

Tables 1 and 2 show the Al content (Al / (AlN + Al) of a metal aluminum (Al) -containing aluminum nitride film formed by reactive sputtering using a parallel plate DC magnetron sputtering apparatus with aluminum as a target. ) And optical constants of wavelengths 193 nm and film types in which the Al content (Al / (AlO + Al)) of the aluminum oxide film containing metal aluminum is changed. Note that the composition ratio of aluminum nitride and aluminum oxide formed by sputtering is not necessarily stoichiometric, and the present invention has the same effect on nitrides and oxides having other composition ratios. Obviously, in the following description of the present invention, aluminum nitride is described as AlN, and aluminum oxide as AlO.

The film formation conditions of each film type shown in Table 1 and Table 2 are as follows: pressure: 9 mTorr, cathode power: 1.5 kW. When forming Al-containing AlN, Ar / N ₂ gas and Al-containing AlO are formed. In this case, Ar / O ₂ gas is used, and the gas flow rate is appropriately adjusted. The composition ratio of Al, AlN, and AlO in the formed film is obtained from spectral analysis of Al2p photoelectron binding energy using an X-ray photoelectron spectrometer (XPS: Xray Photoelectron Spectroscopy, Quantum 2000 manufactured by ULVAC-PHI). Was obtained by measurement of an ellipsometer (VUV-VASE manufactured by JA Woollam).

  Next, various kinds of photomask blanks were prepared by sputtering the film types obtained in Tables 1 and 2 on an optically polished 6-inch square and 0.25-inch thick transparent synthetic quartz substrate. Film formation was optimized so that the optical density (OD) at an exposure wavelength of 193 nm or 248 nm was approximately 3, and blanks having film thicknesses and reflectivities shown in Tables 3 to 10 were obtained. In Tables 3 to 10, the optical density was measured with MCPD 3000 manufactured by Otsuka Electronics Co., Ltd., and the reflectance was measured with MCPD 7000 manufactured by Otsuka Electronics Co., Ltd., and the film thickness of the light shielding film was the light shielding on the portion where the resist was coated on the substrate before film formation. The film was removed by stripping the resist after film formation to form a step, and measurement was performed using an AFM apparatus (L-trace manufactured by SII Nano Technology). 3 to 10 are graphs of the results shown in Tables 3 to 10.

In the present invention, as a photomask blank composed of a single layer thin film or two or more layers, the film thickness when the surface reflectance at the exposure wavelength is 20% or less and the optical density (OD) is approximately 3 is 200 nm or less. Was selected as the preferred film type. This is because if the surface reflectance at the exposure wavelength exceeds 20%, multiple reflections of exposure light occur, which may reduce the resolution of the wafer transfer image. If the optical density (OD) is less than 3, there is a risk of fogging of the resist due to overlapping exposure during stepper exposure, and if the thickness of the thin film exceeds 200 nm, it becomes difficult to form a fine pattern. It is.
Each example will be described below based on the chart.

Example 1
<Addition of metal Al to AlN film (single layer): exposure wavelength 193 nm>
As blanks for an exposure wavelength of 193 nm, metal Al was added to the AlN film (single layer) based on the results obtained in Table 1, and blanks of film types a to f shown in Table 3 were obtained. With a single layer (film type f in Table 3) consisting of only an AlN film, sufficient light shielding properties were not obtained with a film thickness of 200 nm or less, which is a practical level, but as shown in film types c to e in Table 3, AlN When metal Al was added to the film in a range of about 20 to 60 atm%, even an AlN film single layer was able to obtain a light-shielding property at a practical film thickness, and the reflectance at a wavelength of 193 nm could be reduced to 20% or less. FIG. 3 is a graph of the results shown in Table 3. As shown in FIG. 3, the reflectivity at wavelengths of 193 nm, 248 nm, and 365 nm increases as the Al content increases and the Al content increases in the AlN film. Change is slow.

  In the case of this example, as described above, the surface reflectance at the exposure wavelength is 20% or less, the film thickness is 200 nm or less when the optical density (OD) is approximately 3, and the change in reflectance at a wavelength of 200 to 400 nm is achieved. Was selected, and film types c, d, and e in Table 3 were selected as blanks. In addition, when the sheet resistance of the photomask blank created with the film type c was measured, it was 100Ω / □.

  Next, an electron beam resist ZEP520A manufactured by Nippon Zeon Co., Ltd. is applied to the selected blanks with a film thickness of 100 nm. After pre-baking, pattern exposure is performed using an electron beam drawing apparatus, and development is performed using ZEN-N50 manufactured by Nippon Zeon. A resist pattern having a desired shape was formed.

Next, using the resist pattern as a mask, the light shielding film exposed from the resist pattern was dry-etched and patterned by a dry etching apparatus. The blank of the film type c has high conductivity, does not cause a problem of charge-up at the time of drawing, and high-precision pattern drawing is easy. Since dry etching was performed with oxygen-free chlorine-based gas, the light-shielding film etching rate was three times faster than the resist etching rate, and the light-shielding film could be patterned without any problem with a resist film thickness of 100 nm. Finally, the resist is removed by ashing with O ₂ plasma, and ArF having a fine low-reflective light-shielding film pattern having a good cross-sectional shape with the single-layer structure of the first embodiment according to the film types c to e in Table 3 A low-reflection photomask for excimer laser was obtained.

(Example 2)
<Addition of metal Al to AlN film (single layer): exposure wavelength 248 nm>
In the same manner as in Example 1, as a blank for an exposure wavelength of 248 nm, metal Al was added to an AlN film (single layer), and blanks of film types a to f shown in Table 4 were obtained. FIG. 4 is a graph of the results shown in Table 4. In Table 4, when the reflectance at a wavelength of 248 nm is 20% or less, the film types d and e are film types d and e, but the film type e is not suitable as a practical film thickness.

  In the case of this example, the film thickness is 200 nm or less when the surface reflectance at the exposure wavelength is 20% or less, the optical density (OD) is approximately 3, and the change in reflectance at a wavelength of 200 to 400 nm is gentle. As a seed, the film type d in Table 4 in which 40 atm% of metal Al was added to the AlN film was selected as a suitable blank.

  Next, in the same manner as in Example 1, the blanks of film type d shown in Table 4 are patterned, and the single-layer structure of the first embodiment has a fine low-reflection type light-shielding film pattern with a good cross-sectional shape. A low reflection type photomask for a KrF excimer laser was obtained.

(Example 3)
<Addition of metal Al to AlO film (single layer): exposure wavelength 193 nm>
As blanks for an exposure wavelength of 193 nm, metal Al was added to the AlO film (single layer) based on the results obtained in Table 2, and blanks of film types a and g to k shown in Table 5 were obtained. In Table 5, the film type i and j have a reflectivity of 20% or less at a wavelength of 193 nm, but the film type j is not suitable as a practical film thickness. A graph of the results in Table 5 is shown in FIG.

  In the case of this example, the film thickness is 200 nm or less when the surface reflectance at the exposure wavelength is 20% or less, the optical density (OD) is approximately 3, and the change in reflectance at a wavelength of 200 to 400 nm is gentle. As a seed, film type i in Table 5 in which 40 atm% of metal Al was added to the AlO film was selected as a suitable blank.

  Next, in the same manner as in Example 1, the blanks of film type i in Table 5 were patterned, and the single-layer structure of the first embodiment had a fine low-reflection type light-shielding film pattern with a good cross-sectional shape. A low reflection type photomask for ArF excimer laser was obtained.

Example 4
<Addition of metal Al to AlO film (single layer): exposure wavelength 248 nm>
In the same manner as in Example 3, as a blank for an exposure wavelength of 248 nm, metal Al was added to an AlO film (single layer), and blanks of film types a and g to k shown in Table 6 were obtained. A graph of the results in Table 6 is shown in FIG. In Table 6, when the reflectance at a wavelength of 248 nm is 20% or less, the film types i and j are film types i and j, but the film type j is not suitable as a practical film thickness.

  In the case of this example, the film thickness is 200 nm or less when the surface reflectance at the exposure wavelength is 20% or less, the optical density (OD) is approximately 3, and the change in reflectance at a wavelength of 200 to 400 nm is gentle. As a seed, the film type i in Table 6 in which 40 atm% of metal Al was added to the AlO film was selected as a suitable blank.

  Next, in the same manner as in Example 1, the blanks of film type i in Table 6 are patterned, and the single-layer structure of the first embodiment has a fine low-reflection type light-shielding film pattern with a good cross-sectional shape. A low reflection type photomask for a KrF excimer laser was obtained.

(Example 5)
<Addition of metal Al to AlN low reflection film on Al light shielding film: exposure wavelength 193 nm>
Using the parallel plate type DC magnetron sputtering apparatus, an Al film is formed as a light shielding film on a synthetic quartz substrate, and then the film types a to f obtained in Table 1 are used as low reflection films on the Al film. Film formation was performed to create a two-layer photomask blank, and the film thickness and reflectance of each blank shown in Table 7 were obtained. FIG. 7 is a graph of the results in Table 7. The film thickness of each blanks shown in Table 7 is optimized so that the reflectance at a wavelength of 193 nm is minimized while aiming at an optical density (OD) 3 of a wavelength of 193 nm. The first film thickness is an Al film, The second layer is an AlN film to which Al is added.

  In the case of the present example, as described above, as a film type having a surface reflectance at an exposure wavelength of 20% or less and an optical density (OD) of about 3, the film type is 200 nm or less. , D, e, and f, but as shown in FIG. 7, the reflectivity of the film type f (AlN low reflection film not containing metal Al) changes rapidly in the wavelength range of 200 to 400 nm. As in the previous period, it will interfere with inspection and measurement. Therefore, film types c, d, and e in Table 7 were selected as blanks.

  As shown in Table 7, the photomask blanks (film types c to e in Table 7) in which metal Al is added to the AlN low-reflection film on the Al light-shielding film in an amount of 60 atm% or less has a reflectance of 193 nm at a wavelength of 20% or less. As the metal Al was added, the reflectance change at wavelengths of 193 nm, 248 nm, and 365 nm became gradual, and stable inspection and measurement became possible.

Next, an electron beam resist was applied on each of the selected blanks, and pattern exposure was performed with an electron beam drawing apparatus to form a resist pattern having a desired shape. Next, using the resist pattern as a mask, dry etching was performed in the order of the metal Al-added AlN low-reflection film exposed from the resist pattern and then the Al film in a dry etching apparatus, followed by patterning. Since both the low reflection film and the light-shielding film are made of Al, etching can be performed sequentially with a chlorine-based gas. Finally, the resist is removed by ashing with O ₂ plasma, and the low-reflection film for ArF excimer laser having the fine pattern in the two-layer structure of the light-shielding film and the low-reflection film of the second embodiment according to the film types c to e in Table 7 is used. A reflective photomask was obtained.

(Example 6)
<Addition of metal Al to AlN low reflection film on Al light shielding film: exposure wavelength 248 nm>
In the same manner as in Example 5, as a blank for an exposure wavelength of 248 nm, an Al film was formed as a light shielding film, and then the film types a to f obtained in Table 1 were formed on the above Al film as a low reflection film. Then, a photomask blank having a two-layer structure was prepared, and the film thickness and reflectance of each blank shown in Table 8 were obtained. FIG. 8 is a graph of the results in Table 8.

  In Table 8, the film thickness when the reflectance at a wavelength of 248 nm is 20% or less and the optical density (OD) is approximately 3 is 200 nm or less, and the change in reflectance at a wavelength of 200 to 400 nm is a gradual change. The film types d and e in Table 8 were selected, and in this example, the film types d and e were selected as suitable as blanks.

  Next, in the same manner as in Example 5, the blanks of film types d and e in Table 8 are patterned, and a KrF excimer laser having a fine pattern with a two-layer structure of the light-shielding film and the low-reflection film of the second embodiment A low reflection type photomask was obtained.

(Example 7)
<Metal Al is added to the AlO low reflection film on the Al film: exposure wavelength 193 nm>
As a blank for an exposure wavelength of 193 nm, an Al film and film types a and g to k obtained in Table 2 were formed in this order as a low reflection layer on a synthetic quartz substrate to prepare a photomask blank. In addition, the film thickness of each layer was optimized so that the reflectance at a wavelength of 193 nm would be a minimum value while aiming at an optical density (OD) 3 of a wavelength of 193 nm, and the results shown in Table 9 were obtained. FIG. 9 is a graph of Table 9.

  As shown in Table 9, the aluminum oxide (AlO) low reflection film alone (film type k in Table 9) has a reflectance of 54% at a wavelength of 193 nm even when the film thickness of the low reflection film is optimized. In photomask blanks (film types h to j in Table 9) to which about 20 to 60% of aluminum (Al) is added, the reflectance at a wavelength of 193 nm can be made 20% or less, and the wavelength of 193 nm is increased as the metallic aluminum is added. The change in reflectance at 248 nm and 365 nm was moderate.

  In the case of this example, as described above, the surface reflectance at the exposure wavelength is 20% or less, the film thickness is 200 nm or less when the optical density (OD) is approximately 3, and the change in reflectance at a wavelength of 200 to 400 nm is achieved. Was selected, and the film types h, i, and j in Table 9 were selected as blanks.

  Next, a blank of the film types h, i, and j in Table 8 is patterned, and a low-reflection photomask for ArF excimer laser having a fine pattern with a two-layer structure of a light-shielding film and a low-reflection film of the second embodiment Got.

(Example 8)
<Metal Al is added to the AlO low reflection film on the Al film: exposure wavelength 248 nm>
In the same manner as in Example 7, as a blank for an exposure wavelength of 248 nm, an Al film was formed as a light shielding film, and then the film type obtained in Table 2 was formed as a low reflection film on the above Al film. A photomask blank having a layer structure was prepared, and the film thickness and reflectance of each blank shown in Table 10 were obtained. FIG. 10 is a graph of the results in Table 10.

  In Table 10, as a film type in which the reflectance at a wavelength of 248 nm is 20% or less, the film thickness is 200 nm or less when the optical density (OD) is approximately 3, and the change in reflectance at a wavelength of 200 to 400 nm is gradual. The film types i and j in Table 10 were selected, and in this example, the film types i and j were selected as blanks.

  Next, the blanks of film types i and j in Table 10 are patterned to obtain a KrF excimer laser low-reflection photomask having a fine pattern with a two-layer structure of a light-shielding film and a low-reflection film of the second embodiment. It was.

  In the above embodiment, the case where the aluminum compound constituting the blank and the mask is aluminum nitride or aluminum oxide has been described. However, in the present invention, the same effect can be obtained even when the aluminum compound is aluminum oxynitride. It is what By adding 60 atomic% or less of metal aluminum to the aluminum oxynitride thin film, a low reflection film can be obtained, and excellent characteristics in the drawing, etching, and cleaning processes unique to the aluminum-based material are maintained. In addition, by controlling the amount of aluminum added, the light-shielding property is maintained even in a single layer structure, the influence of backscattering during electron beam drawing is small, and a highly accurate fine resist pattern can be formed, and the loading effect during dry etching is reduced. Thus, a highly accurate photomask in which the shift amount of the mask dimension from the resist dimension is reduced can be obtained.

1 is a schematic cross-sectional view showing an example of a photomask blank (FIG. 1A) made of a low-reflection type light-shielding film having a single-layer structure of the present invention (FIG. 1A) and a photomask of the present invention manufactured using the same (FIG. 1B). FIG. It is a cross-sectional schematic diagram which shows an example of the photomask blank (FIG.2 (a)) which consists of a light shielding film of the 2 layer structure of this invention, and the photomask (FIG.2 (b)) of this invention manufactured using it. . It is a reflectance spectrum when Al is added to an AlN film having a single layer structure of the present invention in the case of an exposure wavelength of 193 nm. It is a reflectance spectrum when Al is added to an AlN film having a single layer structure of the present invention in the case of an exposure wavelength of 248 nm. It is a reflectance spectrum when Al is added to an AlO film having a single layer structure of the present invention in the case of an exposure wavelength of 193 nm. It is a reflectance spectrum when Al is added to an AlO film having a single layer structure of the present invention in the case of an exposure wavelength of 248 nm. It is a reflectance spectrum when Al is added to the low-reflection film AlN film on Al of the two-layer structure of the present invention when the exposure wavelength is 193 nm. It is a reflectance spectrum when Al is added to the low reflection film AlN film on Al of the two-layer structure of the present invention when the exposure wavelength is 248 nm. It is a reflectance spectrum when Al is added to the low reflection film AlO film on the Al of the two-layer structure of the present invention when the exposure wavelength is 193 nm. It is a reflectance spectrum when Al is added to the low reflection film AlO film on the Al of the two-layer structure of the present invention when the exposure wavelength is 248 nm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 21 Transparent substrate 12 Low reflection type light shielding film 13 Low reflection type light shielding film pattern 22 Light shielding film 23 Low reflection film 24 Light shielding film pattern 25 Low reflection film pattern Qz Quartz substrate

Claims (6)

In photomask blanks in which a single-layer thin film or two or more thin films are formed on a transparent substrate,
The outermost surface layer of the single-layer thin film or the two or more thin films is composed of an aluminum compound and metallic aluminum added to the aluminum compound, and the content ratio of the metallic aluminum is 60 atomic% or less. Photomask blanks to be used.   The photomask blank according to claim 1, wherein the aluminum compound is aluminum nitride, aluminum oxide, or aluminum oxynitride.   The single layer thin film or the two or more thin films have an optical density of 3 or more and a surface reflectance of 20% or less when the film thickness is 200 nm or less at an exposure wavelength of 193 nm or 248 nm. Item 3. The photomask blank according to item 1 or item 2. In a photomask patterned with a single layer thin film or two or more layers on a transparent substrate,
The outermost surface layer of the single-layer thin film or the two or more thin films is composed of an aluminum compound and metallic aluminum added to the aluminum compound, and the content ratio of the metallic aluminum is 60 atomic% or less. Photo mask to be used.   The photomask according to claim 4, wherein the aluminum compound is aluminum nitride, aluminum oxide, or aluminum oxynitride.   The single layer thin film or the two or more thin films have an optical density of 3 or more and a surface reflectance of 20% or less when the film thickness is 200 nm or less at an exposure wavelength of 193 nm or 248 nm. Item 6. The photomask according to item 4 or item 5.