JP6713336B2 - Mask blank manufacturing method and transfer mask manufacturing method - Google Patents

Description

The present invention relates to a surface treatment method for a thin film made of a material containing silicon formed on a glass substrate, a method for manufacturing a mask blank, and a method for manufacturing a transfer mask.

In recent years, a mask blank using a thin film made of a material containing silicon (hereinafter, also referred to as a silicon-containing thin film) as a hard mask film has been widely used.
Since the silicon-containing thin film has excellent dry etching resistance to chlorine-based gas, it is a film suitable for dry-etching a chromium-based material film or the like used as a light-shielding film with chlorine-based gas, and has a thin film thickness. Also functions as an etching mask.

The surface of the silicon-containing thin film does not have sufficient mechanical adhesion to the resist film made of an organic compound having low polarity. Further, on the surface of the silicon-containing thin film, a developing solution or a rinsing solution easily penetrates into the interface between the silicon-containing thin film and the resist film during development. Therefore, the collapse of the resist pattern (peeling of the resist pattern) is likely to occur. Therefore, in the mask blank manufacturing process, a surface treatment for improving adhesion is performed on the silicon-containing thin film before forming the resist film on the silicon-containing thin film. A typical example of this surface treatment is HMDS (hexamethyldisilazane) treatment. The HMDS treatment is a surface treatment in which, for example, HMDS vaporized with nitrogen gas is brought into contact with a silicon-containing thin film to form a very thin hydrophobic surface layer on the surface of the silicon-containing thin film (for example, the following Patent Documents). 1).

JP, 2011-164598, A

With the progress of miniaturization of semiconductor devices, finer patterns are required on the transfer mask. For example, an SRAF (Sub-Resolution Assist Feature) having a line width of 40 nm or less has been provided on a transfer mask. Such a fine pattern is formed on a transfer mask by etching a silicon-containing thin film such as a hard mask film using the resist pattern formed by drawing and development as a mask. However, since the resist pattern is also fine, the adhesiveness is reduced accordingly. As a result, it has become difficult to sufficiently suppress the collapse of the resist pattern (peeling of the resist pattern) even if the surface modification treatment for improving the adhesion by HMDS is performed on the surface of the silicon-containing thin film. ..
The present invention provides a surface treatment method capable of forming a resist pattern with few defects on a silicon-containing thin film on a glass substrate by suppressing the collapse of the resist pattern. Further, the present invention provides a mask blank manufacturing method and a transfer mask manufacturing method suitable for manufacturing a transfer mask in which the resist pattern is prevented from collapsing and which has few defects.

The present inventors have made detailed studies on the collapse of the resist pattern that occurs when the resist pattern is formed on the silicon-containing thin film. As a result, it was found that the resist pattern formed on the silicon-containing thin film had a distribution in the in-plane distribution of the tendency of the resist pattern to collapse. Therefore, the resist pattern is formed by changing each condition such as coating conditions for forming a resist film on a silicon-containing thin film, drawing conditions for drawing a resist pattern on the resist film, and conditions for developing the resist film. As a result, it was not possible to obtain a clear correlation between the in-plane distribution of the tilt of the resist pattern and each condition.

As a result of further studies, the present inventors have found that there is a correlation between the surface state of the silicon-containing thin film, particularly the in-plane distribution of OH groups and the in-plane distribution of the collapse of the resist pattern. The HMDS treatment is a treatment in which a trimethylsilyl group having a hydrophobic property is bonded to an OH group on the silicon-containing thin film to make the surface of the film hydrophobic. If the uniformity of the in-plane distribution of OH groups on the silicon-containing thin film is low, the uniformity of the in-plane distribution of trimethylsilyl groups will also be low, and there will be a less hydrophobic part (hydrophilic part) than the surroundings in the surface. Then, the resist pattern is likely to collapse at that portion.

From the above results, the present inventors have made the in-plane distribution of OH groups present on the surface of the silicon-containing thin film uniform, so that when the resist pattern is formed on the silicon-containing thin film, the collapsed surface of the resist pattern. We have come to the conclusion that the uniformity of the inner distribution can be improved. Based on these examination results, the present invention has the following configurations in order to solve the above problems.

(Structure 1)
On the glass substrate, a step of preparing a glass substrate with a thin film provided with a thin film made of a material containing silicon,
An in-plane homogenization step of performing a treatment for increasing the uniformity of the in-plane distribution of OH groups existing on the surface of the thin film on the surface of the thin film;
And a step of subjecting the surface of the thin film after the in-plane homogenizing step to a surface treatment with a silane coupling agent.

(Configuration 2)
2. The surface treatment method according to Configuration 1, wherein the in-plane homogenization step includes a step of bringing an alkaline aqueous solution into contact with the surface of the thin film.

(Structure 3)
3. The surface treatment method according to Structure 1 or 2, wherein the in-plane homogenization step is a treatment for increasing the number of OH groups existing on the surface of the thin film.

(Structure 4)
4. The surface treatment method according to any one of configurations 1 to 3, wherein the silane coupling agent is hexamethyldisilazane.

(Structure 5)
The surface treatment method according to any one of configurations 1 to 4, wherein the thin film is made of a material containing silicon and oxygen.

(Structure 6)
On the glass substrate, a pattern forming thin film, and a hard mask film made of a material containing silicon, a step of preparing a mask blank provided in this order,
An in-plane homogenization step of performing a process for increasing the uniformity of the in-plane distribution of OH groups existing on the surface of the hard mask film on the surface of the hard mask film;
And a step of performing a surface treatment with a silane coupling agent on the surface of the hard mask film after the in-plane homogenizing step.

(Structure 7)
7. The method for manufacturing a mask blank according to Configuration 6, wherein the in-plane homogenizing step includes a step of bringing an alkaline aqueous solution into contact with the surface of the thin film.

(Structure 8)
8. The method for manufacturing a mask blank according to configuration 6 or 7, wherein the in-plane homogenization step is a treatment for increasing the number of OH groups existing on the surface of the hard mask film.

(Configuration 9)
9. The method for manufacturing a mask blank according to any one of configurations 6 to 8, wherein the silane coupling agent is hexamethyldisilazane.

(Configuration 10)
10. The method for manufacturing a mask blank according to any one of configurations 6 to 9, wherein the hard mask film is made of a material containing silicon and oxygen.

(Configuration 11)
11. The method of manufacturing a mask blank according to any one of Configurations 6 to 10, wherein the hard mask film has a thickness of 3 nm or more and 15 nm or less.

(Configuration 12)
12. The mask blank manufacturing method according to any one of configurations 6 to 11, wherein the pattern forming thin film is made of a material containing chromium.

(Configuration 13)
The pattern forming thin film is a light semitransmissive film made of a material containing silicon, and a light shielding film made of a material containing chromium is provided between the pattern forming thin film and the hard mask film. 12. The method for manufacturing a mask blank according to any one of Characteristic Configurations 6 to 11.

(Configuration 14)
14. The method of manufacturing a mask blank according to any one of configurations 6 to 13, further comprising the step of forming a resist film of an organic material in contact with the surface of the hard mask film after the surface treatment.

(Structure 15)
A method of manufacturing a transfer mask using the mask blank manufactured by the method of manufacturing a mask blank according to Structure 14,
A step of exposing and drawing a pattern to be formed on the pattern forming thin film on the resist film, and performing a developing process to form a pattern on the resist film;
And a step of forming a pattern on the hard mask film by dry etching using the resist film having the pattern as a mask.

In the method of the present invention, since the in-plane uniformity of the OH group on the silicon-containing thin film is enhanced by the in-plane homogenization step as described above, the surface treatment by the silane coupling agent that binds to the OH group is performed. In-plane uniformity is also enhanced. For this reason, it is difficult to generate a part where the number of silyl groups is small and the hydrophobicity is low on the silicon-containing thin film, so that the occurrence of the collapse of the resist pattern (peeling of the resist pattern) on the silicon-containing thin film is suppressed. It

Further, when a surface of the hard mask film is subjected to the surface treatment on a mask blank in which a pattern forming thin film and a hard mask film made of a material containing silicon are provided in this order on a glass substrate, Therefore, it is difficult to generate a part where the number of silyl groups is small and the hydrophobicity is low. Therefore, this mask blank is a mask blank in which the collapse of the resist pattern is suppressed.
Further, when a transfer mask is manufactured using this mask blank, it becomes possible to manufacture a transfer mask in which the occurrence of defects due to the collapse of the resist pattern is suppressed.

It is sectional drawing which shows the structure of the mask blank in the 1st Embodiment of this invention. It is a cross-sectional schematic diagram which shows the manufacturing process of the phase shift mask in the 1st Embodiment of this invention. It is a cross-sectional schematic diagram which shows the manufacturing process of the phase shift mask in the 1st Embodiment of this invention. It is a characteristic view which showed the effect of this invention by the in-plane ratio (in-plane distribution ratio) of the normalization secondary ion detection intensity of a center part and a peripheral part.

Hereinafter, embodiments of the present invention will be described.

[Manufacture of mask blanks and surface treatment]
The detailed configuration of the present invention will be described below with reference to the drawings. Here, as a surface treatment method on a silicon-containing thin film, an embodiment in which the present invention is applied to the production of a halftone type phase shift mask blank will be mainly described, and then a mask blank obtained by this production method will be described. A method of manufacturing a transfer mask (halftone type phase shift mask) using is explained. In addition, in each figure, the same components are denoted by the same reference numerals for description.

FIG. 1 is a schematic view of a cross-sectional structure for explaining the structure of the mask blank of the embodiment. Hereinafter, the method for manufacturing the mask blank of the embodiment will be described with reference to FIG.

First, as shown in FIG. 1A, a glass substrate 1 is prepared, and a light semi-transmissive film (phase shift film) 2, a light shielding film 3, and a hard mask film 4 made of a silicon-based material are provided on the glass substrate 1. Is performed in this order to form a film. Among these, the light semi-transmissive film 2 is formed with a fine pattern which is a transfer pattern when a transfer mask is manufactured from this mask blank. Further, in the hard mask film 4 and the light shielding film 3, a fine pattern to be formed on the light semi-transmissive film 2 is temporarily formed while the transfer mask is manufactured from this mask blank. Next, details of each component and the film forming procedure thereof will be described.

<Glass substrate 1>
The substrate 1 prepared here is a glass substrate made of a material containing silicon and oxygen.
When used as a mask blank for a phase shift mask or a binary mask, the glass substrate 1 is a material that is transparent to exposure light such as ArF excimer laser light (wavelength: about 193 nm) and is not easily deformed. Composed. As such a material, synthetic quartz glass is generally used, but in addition to this, aluminosilicate glass and soda lime glass can also be used. In particular, the synthetic quartz substrate has high transparency in a region of ArF excimer laser light or a wavelength shorter than that of ArF excimer laser light, and thus can be particularly suitably used for the mask blank of the present invention.
Further, in the case of a mask blank for a reflective mask, the glass substrate 1 is particularly preferably low thermal expansion glass (SiO ₂ —TiO ₂ glass or the like) whose thermal expansion due to heat generated during exposure is suppressed to a low level.

In the glass substrate 1 as described above, the end surface and the main surface are polished to have a predetermined surface roughness, and then subjected to a predetermined cleaning treatment and a drying treatment.

<Deposition of the light semi-transmissive film 2>
Next, the light semi-transmissive film 2 is formed on the main surface (first main surface) of the glass substrate 1 as described above by, for example, a sputtering method. The light semi-transmissive film 2 formed here is formed as a film containing silicon (Si), for example. It is preferable that the light semi-transmissive film 2 is made of a material containing nitrogen (N) in addition to silicon. Such a light semi-transmissive film 2 can be patterned by dry etching using a fluorine-based gas, and is sufficient for the light-shielding film 3 formed of a material containing chromium (Cr) described below. Patterning is possible with etching selectivity.

Further, the light semi-transmissive film 2 further contains at least one element selected from a semi-metal element, a non-metal element and a metal element as long as it is a material that can be dry-etched using a fluorine-based gas. May be.

One example of such a metalloid element is silicon, but is not limited to silicon. An example of the non-metal element is nitrogen (N), but other non-metal elements may be used, and examples thereof include oxygen (O), carbon (C), fluorine (F) and hydrogen (H). One or more elements selected may be mentioned. Examples of metal elements include molybdenum (Mo), tungsten (W), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), niobium (Nb), vanadium (V), cobalt. (Co), chromium (Cr), nickel (Ni), ruthenium (Ru), tin (Sn), boron (B), germanium (Ge) are mentioned. As the light semi-transmissive film 2 containing such an element, for example, a film made of MoSiN is exemplified.

Further, the light semi-transmissive film 2 has a refractive index n, an extinction coefficient k, and a film thickness d set so as to have a predetermined phase difference and a predetermined transmittance with respect to the exposure light. During the film formation, the composition of the film material and the film formation conditions are adjusted so that the refractive index n and the extinction coefficient k are obtained. The phase difference is, for example, 150° to 190°, and the transmittance is 1% to 30%.

The light semi-transmissive film 2 may be a single layer film or a multilayer film including a plurality of layers. The single-layer film has a characteristic that the manufacturing process is simplified, and the multilayer film has a characteristic that the adjustment range of the retardation and the transmittance is widened. Moreover, the light semi-transmissive film 2 may have a uniform composition or a composition having a distribution in the film thickness direction.

Further, in forming the light semi-transmissive film 2 by the sputtering method, a sputter target and a reactive gas containing the material forming the light semi-transmissive film 2 in a predetermined composition ratio are used, and further, argon ( Film formation is performed using an inert gas such as Ar), xenon (Xe), or helium (He).

After the light-semitransmissive film 2 is formed by the sputtering method, an annealing process at a predetermined heating temperature is performed as a post-treatment to adjust the film stress to a predetermined value. The heating temperature for annealing the light semi-transmissive film 2 is preferably 300° C. or higher, more preferably 350° C. or higher, and further preferably 400° C. or higher. By increasing the heating temperature of the annealing treatment, the denseness of the light semi-transmissive film 2 can be increased and the film stress can be reduced. The heating temperature of the annealing treatment for the light semi-transmissive film 2 is preferably 900° C. or lower, more preferably 700° C. or lower, and further preferably 600° C. or lower. If the heating temperature is too high, the physical properties of the glass substrate 1 heated together with the light semi-transmissive film 2 may be significantly changed, which is not preferable.

<Formation of light-shielding film 3>
Next, the light shielding film 3 is formed on the light semi-transmissive film 2 by, for example, a sputtering method. The light-shielding film 3 is a film made of a material containing chromium (Cr) and may be formed as a single layer, may be formed as a two-layer structure including a lower layer and an upper layer, and may be formed as a plurality of layers. You may form into a layer. When the light shielding film 3 is formed as a plurality of layers, it is preferable to change the content of chromium (Cr) and form each layer.

The light-shielding film 3 includes, in addition to chromium metal, one or more of chromium (Cr) selected from oxygen (O), nitrogen (N), carbon (C), boron (B), hydrogen (H), and fluorine (F). It may contain a material containing an element. Further, the light-shielding film 3 is selected from indium (In), tin (Sn), and molybdenum (Mo) for the purpose of suppressing the reduction of the etching rate of the entire film while maintaining the optical density (OD). It may also contain at least one or more metal elements.

Such a light-shielding film 3 can be patterned by dry etching using a chlorine-based gas containing oxygen. As described below, the hard mask film 4 formed of a material containing silicon (Si) has sufficient etching resistance against dry etching using this gas. Therefore, the material is a material that allows the light shielding film 3 to be patterned using the hard mask film 4 as a mask. The light semi-transmissive film 2 formed of a material containing silicon (Si) has sufficient etching resistance against dry etching using a chlorine-based gas containing oxygen. Therefore, the light-shielding film 3 can be etched or removed with almost no damage to the light-semitransmissive film 2.

The light-shielding film 3 as described above has a composition of materials and a film so that the shape accuracy in the dry etching is secured and the light-shielding film 3 has an optical density (OD) of a predetermined value or more with respect to the exposure light used in the exposure transfer process. Thickness is set. The light-shielding film 3 is required to have an optical density (OD) higher than 2.0 in a laminated structure with the light semi-transmissive film 2, and is preferably 2.8 or more, more preferably 3.0 or more. preferable.

In forming the light-shielding film 3 by the sputtering method, a target containing a constituent material of the light-shielding film 3 in a predetermined composition ratio and a reactive gas are used, and further, if necessary, argon (Ar), xenon (Xe), The film is formed using an inert gas such as helium (He).

<Deposition of hard mask film 4>
Then, the hard mask film 4 is formed on the light shielding film 3 by, for example, a sputtering method. The hard mask film 4 formed here is a film made of a material containing silicon (Si), and is thin enough to function as an etching mask until the dry etching for patterning the light shielding film 3 is completed. It is formed with a film thickness.

Such a hard mask film 4 contains, in addition to silicon (Si), one or more elements selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H). A film is formed using the material. In particular, a material containing oxygen (O) in addition to silicon (Si) is particularly preferable from the viewpoint that it has an excellent function as the hard mask film 4 and that the effect of the surface treatment of the present invention is enhanced. Specific examples of the material forming the hard mask film 4 include silicon oxide (SiO ₂ ), silicon oxynitride (SiON), silicon oxycarbide (SiOC), and silicon oxycarbonitride (SiOCN). Further, as a material containing no oxygen, silicon nitride (SiN) or the like can be given.

Such a silicon-containing material, particularly a material containing oxygen (O) in addition to silicon (Si) is easily dry-etched by a fluorine-based gas. Therefore, when this material is used for the hard mask film 4, The processing accuracy of the hard mask film 4 is improved, and it becomes possible to form a hard mask pattern with high accuracy.

Further, such a material containing silicon, particularly a material containing oxygen (O) in addition to silicon (Si) has sufficient etching resistance against dry etching using a chlorine-based gas containing oxygen. Therefore, even an ultrathin film having a thickness of 3 nm can be a sufficient etching mask when etching the light-shielding film 3 formed of a material containing chromium (Cr). Therefore, the thickness of the hard mask film 4 made of this material may be 3 nm or more. The film thickness of the hard mask film 4 is preferably 15 nm or less, more preferably 10 nm or less from the viewpoint of forming a fine pattern. When the film thickness of the hard mask film 4 is made thicker than these values, it is necessary to make the film thickness of the resist film for processing the hard mask film 4 too thick. This is because the pattern tends to collapse.

The hard mask film 4 may be formed by a sputtering method. There, a target containing a material forming the hard mask film 4 in a predetermined composition ratio is used, and an inert gas such as argon (Ar), xenon (Xe), or helium (He), oxygen (O), or the like is contained. A reactive gas is used if necessary.

<Surface treatment process>
The surface treatment step here is performed after an in-plane homogenization step for increasing the in-plane distribution uniformity of OH groups (silanol groups) bonded to silicon on the surface of the hard mask film (silicon-containing thin film) 4. It comprises a hydrophobic treatment step using a silane coupling agent.

The in-plane homogenization step of improving the in-plane distribution uniformity of the OH group includes a step of bringing the surface of the hard mask film 4 into contact with a strong alkaline aqueous solution. Here, as the strong alkaline aqueous solution, TMAH (TetraMethyl Ammonium Hydroxide) aqueous solution, TBAH (TetraButyl Ammonium Hydroxide) aqueous solution, ammonia water, ammonia hydrogen peroxide (aqueous solution consisting of ammonia water and hydrogen peroxide solution), KOH aqueous solution, NaOH aqueous solution, etc. Are listed.

Among them, the TMAH aqueous solution is used as a resist developing solution and the ammonia-hydrogen peroxide is used as a cleaning solution in the manufacturing process of the transfer mask, and the apparatus used is also used as the apparatus used for these treatments. Therefore, it can be preferably used. Here, when the TMAH aqueous solution is used, the concentration of the aqueous solution may be the same as that of the developing solution, that is, 2.38% by weight, and the treatment process may be the same as that of the developing treatment. Further, in the case of ammonia-hydrogen peroxide mixture, it may be the same as that used in the SC1 (Standard Clean 1) cleaning step used in cleaning for removing metal impurities.

When the hard mask film 4 made of a material containing silicon is treated with a strong alkali, as shown in FIG. 1A, an OH group is bonded to a dangling bond of silicon (Si) existing on the film surface. When an organic substance (contaminant) or the like is attached to the silicon on the film surface, a part of the organic substance (contaminant) is replaced with an OH group and bonded to silicon. As a result, the surface of the silicon-containing thin film is covered with OH groups (silanol groups) that are relatively uniformly and densely bonded to silicon, and the in-plane uniformity of distribution of OH groups is improved and the density of OH groups is also improved. .. Further, the strong alkali treatment reduces contamination on the hard mask film 4 and increases the number of OH groups reactive with the silane coupling agent. The unevenness is suppressed.

The region to be subjected to the in-plane uniformizing step for improving the in-plane distribution uniformity of the OH group is a region including at least a region defined as a quality area (transfer pattern forming region) on the surface of the hard mask film 4. Here, the quality area is defined as a mask blank product standard. For example, in the case of a mask blank of 6025 size (square with one side of about 152 mm), it is an inner region of a quadrangle of 132 mm×104 mm with the center of the main surface as a reference. However, in view of mask blank manufacturing management and mask blank management operation, the area where the in-plane homogenization step is performed is preferably an inner area of a quadrangle of 132 mm×132 mm with the center of the main surface as a reference, and 142 mm× The inner area of the quadrangle of 142 mm is more preferable, and the inner area of the quadrangle of 146 mm×146 mm is further preferable.

The uniformity of in-plane distribution of OH groups can be examined by time-of-flight secondary ion mass spectrometry (TOF-SIMS) (TOF-SIMS: Time-of-Flight Secondary Mass Spectroscopy). For example, the surface of the silicon-containing thin film (hard mask film 4) that has been subjected to the in-plane homogenization process is subjected to sufficient bromine (Br) modification treatment, and then bismuth ions (Bi ⁺ ) etc. are irradiated as the primary ion species. The uniformity of the in-plane distribution of OH groups can be investigated by comparing the in-plane distribution of the detected normalized secondary ion intensity derived from bromine. The normalized secondary ion intensity as referred to in the present specification is the total number of secondary ions emitted from the surface of the thin film, which is obtained by irradiating the predetermined region on the surface of the thin film with the primary ions. It is a numerical value calculated by dividing the number of ions (ions derived from bromine).

As a method of making the in-plane distribution of OH groups uniform, there is a method of improving the in-plane distribution uniformity of OH groups by annealing, in addition to the method using the strong alkaline aqueous solution. When a silicon-containing thin film is annealed at a temperature of 350° C. or higher and 900° C. or lower in the air or in an atmosphere purged with nitrogen gas, the amount of OH groups is reduced, but the surface condition is homogenized, The uniformity of the in-plane distribution is improved.

Next, the hard mask film (silicon-containing thin film) 4 after the in-plane homogenization step is subjected to a surface treatment using a silane coupling agent, and as shown in FIG. The OH group (silanol group) on the surface of the hard mask film 4 is modified with a chemical modifying group. Specific examples of the silane coupling agent include 1,1,3,3-tetramethyldisilazane, hexamethyldisilazane (HMDS), vinyltrimethylsilane, hexamethyldisilane, methylsilane, dimethylsilane, trimethylsilane, diethylsilane. , Propylsilane, phenylsilane, vinyltriethoxysilane, tetramethoxysilane, phenyltriethoxysilane, methyltriethoxysilane, octamethylcyclotetrasiloxane, and the like.

In the specific examples described above, HMDS is preferably used. HMDS is an amine compound having a trimethylsilyl group [—Si(CH ₃ ) ₃ ] and has an amino group that is a functional group capable of binding to the silanol group (—SiOH) on the surface of the hard mask film 4. In addition, it has a methyl group having excellent affinity with the resist film (bonding with the resist material by hydrophobic-hydrophobic interaction).

According to such a surface treatment using HMDS (HMDS surface treatment), the OH group bonded to silicon on the surface of the hard mask film 4 reacts with HMDS, and the OH group has a trimethylsilyl group [of the HMDS]. -Si _{(CH 3)} 3] it is attached as a chemically modifying group. As a result, the trimethylsilyl group is bonded to the surface of the hard mask film 4 that originally contains silicon. Therefore, the surface treatment of the hard mask film 4 can be performed with almost no change in film quality other than the degree of hydrophobicity. The ammonia generated by this reaction is promptly discharged to the outside as ammonia gas.

If the surface of the hard mask film 4 has a large number of OH groups, the amount of trimethylsilyl groups bonded to the surface of the hard mask film 4 also increases, and the surface of the hard mask film 4 also becomes more hydrophobic. Therefore, when a resist film is formed on the hard mask film 4 and the resist film is exposed and developed to form a resist pattern, a developer or a rinse is applied to the interface between the surface of the hard mask film 4 and the resist pattern. It becomes difficult for the liquid to enter, and the collapse of the resist pattern (peeling of the resist pattern) is suppressed.

The surface treatment with the silane coupling agent including the HMDS surface treatment may be either a gas phase treatment or a liquid phase treatment. For example, the silane-based coupling agent may be vaporized and introduced onto the surface of the hard mask film 4 for surface treatment, or the silane-based coupling agent may be used as a neat solution or mixed with a solvent such as acetone. The surface treatment may be performed by applying the mixed liquid onto the surface of the hard mask film 4.

In the surface treatment process using a silane coupling agent, such as HMDS surface treatment, silanol is controlled by controlling at least one of the treatment time, the supply flow rate of the silane coupling agent, and the treatment temperature. The amount of the chemically modified group bonded to the group can be adjusted.

<Formation of resist film>
Next, a resist film made of an organic material is formed on the surface of the hard mask film 4 which has been surface-treated by the bonding of the chemically modifying group (not shown). The formation of the resist film includes, for example, film formation of a resist material layer by a coating method such as a spin coating method and subsequent processing such as baking processing. The material of the resist film formed here is not particularly limited, but when forming a fine pattern, it is preferable to use a chemically amplified resist which is excellent in resolution. Further, both negative type and positive type resists can be applied. The resist made of an organic material has excellent adhesiveness to the surface-treated hard mask film 4, and resists the collapse of the resist pattern (peeling of the resist pattern). Further, since it is easy to secure an etching selection ratio when etching the hard mask film 4, and the hard mask film 4 can be easily removed without damaging the hard mask film 4 by ashing using a removing chemical solution or oxygen, the transfer mask Is preferred for producing

As described above, a mask blank in which the light semitransmissive film 2, the light shielding film 3, the hard mask film 4, and the resist film are laminated in this order on the glass substrate 1 is obtained. In the present invention, the resist film is not essential as the structure of the mask blank. That is, the resist film forming process is treated as one of the transfer mask manufacturing processes, and the light semi-transmissive film 2, the light shielding film 3, and the hard mask film are formed on the glass substrate 1 before the resist film is formed. It is also possible to handle a stack of 4 in this order as a mask blank.

[Method of manufacturing transfer mask]
2 and 3 are cross-sectional process diagrams for explaining a method for manufacturing the transfer mask (halftone type phase shift mask) of the embodiment, in which a mask blank surface-treated by the above method is used. Hereinafter, a method of manufacturing the transfer mask according to the present embodiment will be described with reference to FIGS. 2 and 3, the same components as those described with reference to FIG. 1 are designated by the same reference numerals, and overlapping description will be omitted.

<Formation of resist pattern>
First, a device pattern (circuit pattern), an alignment mark pattern, and the like are drawn, and then a baking process, a developing process, a rinsing process, and a spin drying process are performed on the resist film. By this process, the first resist pattern 5a is formed on the hard mask film 4 (see FIG. 2A). The first resist pattern 5a includes a large number of fine patterns such as a device pattern. However, since the surface of the hard mask film 4 is uniformly and sufficiently hydrophobized by the surface treatment, the resist pattern collapses (resist pattern). This is a good one in which pattern defects such as pattern peeling) are unlikely to occur.

<Patterning of hard mask film 4>
Next, as shown in FIG. 2B, the hard mask film 4 made of a material containing silicon is dry-etched using a fluorine-based gas using the first resist pattern 5a as an etching mask to form the hard mask pattern 4a. Form. Then, the first resist pattern 5a is removed. Here, the light-shielding film 3 may be dry-etched while the first resist pattern 5a is left without being removed.

<Patterning of the light semi-transmissive film 2 and the light shielding film 3>
Next, as shown in FIG. 2(c), the hard mask pattern 4a is used as an etching mask to shield light from a material containing chromium using a mixed gas of chlorine-based gas and oxygen gas (oxygen-containing chlorine-based gas). The film 3 is dry-etched to pattern the light-shielding film 3 to form the first light-shielding film pattern 3a.

After that, as shown in FIG. 3A, the light-semitransmissive film 2 formed of a material containing silicon is dry-etched by using a fluorine-based gas with the first light-shielding film pattern 3a as a mask. The semi-transmissive film 2 is patterned to form a light semi-transmissive film pattern 2a. In the dry etching of the light-semitransmissive film 2 formed of such a material containing silicon, the hard mask pattern 4a formed of a material containing silicon is also removed at the same time.

Next, a second resist pattern made of an organic material for forming a light-shielding band or the like is formed so as to cover the outer peripheral region of the glass substrate 1. The second resist pattern is not formed on the surface-treated hard mask film 4 which is hard to cause the resist pattern to collapse, but the light-shielding film 3 made of a material containing chromium is made of an organic resist. Since the second resist pattern is a pattern having a relatively large size such as a light-shielding band pattern, problems such as collapse of the resist pattern are unlikely to occur.

Then, using the second resist pattern as an etching mask, dry etching of the light shielding film 3 made of a material containing chromium is performed using a mixed gas of chlorine-based gas and oxygen gas. Then, the second resist pattern is removed to form a second light-shielding film pattern 3b having a light-shielding band or the like (see FIG. 3B). Thereafter, a predetermined process such as cleaning is performed to obtain the halftone type phase shift mask 30 which is a transfer mask.

[Effect of Embodiment]
According to the method of manufacturing a mask blank of the embodiment described above, an in-plane uniformizing step for increasing the in-plane distribution uniformity of OH groups on the surface of the hard mask film 4 made of a silicon-containing material, and after that step By the surface treatment including the hydrophobization treatment step using the silane coupling agent, the surface of the hard mask film 4 has high in-plane uniformity of hydrophobization and is appropriately hydrophobized. As a result, it is possible to manufacture a mask blank which has a high adhesiveness with the resist film and is less likely to cause collapse of the resist pattern when the resist film is exposed and developed to form a pattern.

Further, according to the manufacturing method of the transfer mask (halftone phase shift mask) described in the embodiment, the surface of the hard mask film 4 is subjected to the above-mentioned surface treatment, so that the surface of the hard mask film 4 is The first resist pattern 5a formed on the hard mask film 4 by being uniformly and moderately hydrophobized in the plane suppresses the collapse of the resist pattern and has few pattern defects. Therefore, it becomes possible to manufacture a transfer mask (halftone type phase shift mask) with few pattern defects.

In the above, the method for manufacturing a mask blank for a halftone type phase shift mask is illustrated as an embodiment of the method for manufacturing a mask blank. However, the manufacturing method of the mask blank of the present invention is a Levenson-type phase shift mask blank having a step of forming a resist film in contact with a hard mask film made of a material containing silicon, a mask blank for CPL (Chromeless Phase Lithography), It can be widely applied to a mask blank manufacturing method such as a binary mask blank, and similar effects can be obtained. Similarly, it can be widely applied to various methods of manufacturing transfer masks manufactured using these mask blanks, and similar effects can be obtained.

As such an example, for example, a binary type mask blank can be exemplified. When the present invention is applied to a method for manufacturing a binary mask blank, a light-shielding film made of, for example, a material containing chromium is formed on a glass substrate, and a hard mask film made of a material containing silicon is formed on the light shielding film. After forming the film, the surface treatment step may be performed on the surface of the hard mask film, and the same effect can be obtained.

Further, in the above, the case where the surface treatment is performed on a hard mask film made of a silicon-containing material is shown. However, the target of the surface treatment is not limited to the hard mask film, but a material containing silicon is used. It is also effective for thin films for other applications. The surface-treated silicon-containing thin film has high adhesion to the resist film, and as a result, it becomes possible to form a fine resist pattern on the thin film while suppressing the collapse of the resist pattern. ..

As such an example, for example, a binary type mask manufactured by directly forming a resist pattern on a light-shielding film made of a material containing silicon can be exemplified. In the manufacture of this binary mask, first, a light-shielding film made of a material containing silicon is formed on a glass substrate, and the surface treatment step is performed on the surface of the light-shielding film to prepare a mask blank. After that, a resist pattern is formed on the light-shielding film, and the light-shielding film pattern is formed by dry etching with a fluorine-based gas using the resist pattern as an etching mask. The binary mask manufactured in this way becomes a transfer mask with few pattern defects.

Hereinafter, the embodiment of the present invention will be described more specifically by way of examples.
(Example 1)
[Manufacture of mask blanks and surface treatment]
A glass substrate 1 made of synthetic quartz glass having a main surface dimension of about 152 mm×about 152 mm and a thickness of about 6.35 mm was prepared. The glass substrate 1 has its end face and main surface polished to a predetermined surface roughness or less (root mean square roughness Rq is 0.2 nm or less), and then subjected to a predetermined cleaning treatment and drying treatment. ..

Next, a light semi-transmissive film 2 (phase shift film) made of molybdenum, silicon and nitrogen was formed in a thickness of 69 nm in contact with the main surface of the glass substrate 1. Specifically, the glass substrate 1 is installed in a single-wafer DC sputtering apparatus, and a mixed sintering target of molybdenum (Mo) and silicon (Si) (Mo:Si=12:88 (atomic% ratio)) is set. Reactive sputtering using a mixed gas of argon (Ar), nitrogen (N ₂ ) and helium (He) (flow ratio Ar:N ₂ :He=8:72:100, pressure=0.2 Pa) as the sputtering gas. The light semi-transmissive film 2 was formed by (DC sputtering). The light semi-transmissive film (MoSiN film) formed under the same conditions on another glass substrate was analyzed by X-ray photoelectron spectroscopy (XPS), and the result was that the material composition ratio was Mo:Si:N=4. The ratio was 0.1:35.6:60.3 (atomic% ratio).

Next, the glass substrate 1 having the light semi-transmissive film 2 formed thereon was taken out from the sputtering apparatus, and the light semi-transmissive film 2 on the glass substrate 1 was heat-treated at 450° C. for 30 minutes in the atmosphere. The transmittance and the phase shift amount at the wavelength (193 nm) of the ArF excimer laser light were measured with respect to the light-semitransmissive film 2 after the heat treatment using a phase shift amount measuring device MPM193 (manufactured by Lasertec). Was 6.1% and the amount of phase shift was 177.3 degrees.

Next, the glass substrate 1 on which the light semi-transmissive film 2 is formed is put into the sputtering apparatus again, and a light shielding film having a laminated structure of a lower layer made of the CrOCN film and an upper layer made of the CrN film is placed on the light semi-transmissive film 2. 3 was formed. Specifically, using a target made of chromium, a mixed gas atmosphere of argon (Ar), carbon dioxide (CO ₂ ), nitrogen (N ₂ ) and helium (He) (flow ratio Ar:CO ₂ : N ₂ :He) is used. =20:24:22:30, pressure 0.3 Pa), a lower layer of the light shielding film 3 made of a CrOCN film having a thickness of 47 nm was formed on the light semitransmissive film 2 by performing reactive sputtering. Then, using the same chromium target, reactive sputtering is performed in a mixed gas atmosphere of Argon (Ar) and Nitrogen (N ₂ ) (flow ratio Ar:N ₂ =25:5, pressure 0.3 Pa). An upper layer of the light shielding film 3 made of a CrN film having a thickness of 5 nm was formed on the lower layer.

The composition of the CrOCN film as the lower layer of the formed light-shielding film 3 is Cr:O:C:N=49.2:23.8:13.0:14.0 (atomic% ratio), and the upper layer of CrN is CrN. The composition of the film was Cr:N=76.2:23.8 atomic% ratio). These compositions were measured by XPS.

The optical density (OD) of the laminated film including the light semi-transmissive film 2 and the light shielding film 3 was 3.0 or more (transmittance of 0.1% or less) at the wavelength of ArF excimer laser light (193 nm). Further, the transmittance at a wavelength of 880 nm (the wavelength of the detection light used for positioning the substrate mounted on the exposure apparatus) was 50% or less.

Next, the hard mask film 4 made of a SiON film was formed on the light shielding film 3. Specifically, using a silicon target, a mixed gas atmosphere of argon (Ar), nitric oxide (NO) and helium (He) (flow ratio Ar:NO:He=8:29:32, pressure 0.3 Pa). 2), the hard mask film 4 made of a SiON film having a thickness of 15 nm was formed on the light shielding film 3 by performing reactive sputtering. The composition of the formed SiON film was Si:O:N=37:44:19 (atomic% ratio). This composition was measured by XPS.

Then, TMAH (TetraMethyl Ammonium Hydroxide), which is a strong alkaline liquid, is dripped onto the hard mask film 4 as a surface treatment for enhancing the in-plane distribution uniformity of OH groups on the surface of the hard mask film 4, and a TMAH surface treatment for pouring the liquid. I went. Specifically, a 2.38 wt% TMAH aqueous solution was dropped onto the hard mask film 4 under the same conditions as when resist development was performed, and the puddle was poured thereon, and then rinsed with pure water.

This TMAH surface treatment improves the in-plane distribution uniformity of OH groups on the surface of the hard mask film 4. Next ion mass spectrometry (TOF-SIMS: Time-of-Flight Secondary Mass Spectroscopy) was performed and it investigated. Specifically, the SiON film that has been subjected to the TMAH surface treatment and the SiON film that has not been subjected to the TMAH surface treatment have their surfaces sufficiently modified with bromine (Br), and then the central portion (the center of the substrate is used as a reference). For the four corners of a quadrangle with a side of 10 mm: a total of four points) and the outer peripheral portion (four corners of a quadrangle with a side of 132 mm with respect to the center of the substrate: a total of four points), a standard derived from bromine by TOF-SIMS. The secondary ion intensity was measured. The measurement conditions in this TOF-SIMS are as follows.
Measuring device: TRIFT V nano TOF (made by ULVAC-PHI)
Primary ion species: Bi ⁺
Primary acceleration voltage: 30kV
Primary ion current: 1.0 nA
Primary ion irradiation area: Inside area of a square with one side of 650 μm Secondary ion measurement range: 0.5 to 3000 m/z

Then, for each of the SiON film subjected to the TMAH surface treatment and the SiON film not subjected to the TMAH surface treatment, a total of 8 points of the standardized secondary bromine derived from bromine measured at 4 points in the central part and 4 points in the outer peripheral part The minimum value I _min and the maximum value I _max were extracted from the ionic strengths. Further, the maximum value I _max is divided by the minimum value I _min of the normalized secondary ion intensity derived from bromine to obtain an in-plane distribution ratio (I _ratio =I _max /I) of the normalized secondary ion intensity derived from bromine. _min ) was calculated. The result is shown in FIG. In the case of the SiON film, the in-plane distribution ratio (I _ratio ) of the normalized secondary ion intensity derived from bromine was 2.45 when the TMAH surface treatment was not performed, whereas when the TMAH surface treatment was performed. Was 1.51, and the in-plane distribution ratio of the normalized secondary ion intensity was reduced by 0.94 by performing the TMAH surface treatment. This result means that the in-plane uniformity of the OH group on the surface of the SiON film was improved by the TMAH surface treatment, considering that the bromine (Br) modification is a modification for the OH group.

Then, the surface treatment using HMDS as a silane coupling agent was performed. Specifically, the glass substrate 1 on which the TMAH surface treatment has been performed on the hard mask film 4 made of a SiON film is placed in an HMDS surface treatment chamber and a decompressed state is introduced, and then HMDS in a gas phase is introduced into the surface treatment chamber. Then, the HMDS surface treatment was performed. The chemical modifying group in this case is a trimethylsilyl group [Si(CH ₃ ) ₃ ].

Next, the effect of performing both the TMAH surface treatment and the HMDS surface treatment was evaluated using the contact angle of water. A large contact angle with water means high hydrophobicity, and resist pattern collapse (resist pattern peeling) caused by infiltration of the developer or rinse solution into the interface of the film in contact with the resist pattern is suppressed. Means to be done. The water contact angle of the surface of the hard mask film 4 was measured using a fully automatic contact angle meter DM-701 (manufactured by Kyowa Interface Science Co., Ltd.) at room temperature of 23° C. The contact angle of the hard mask film 4 was measured at each measurement point (9 points×9 points) arranged at equal intervals in a grid shape with respect to an area inside a quadrangle having a side of 132 mm with respect to the center of the substrate. = 81 points in total).

As a result, the average value of the contact angles of water measured at the respective measurement points was 43.2° when the HMDS surface treatment was applied only to the hard mask film 4. In this case, it was confirmed that the measured value of the contact angle was locally below 40°. On the other hand, the case where two surface treatments, TMAH surface treatment and HMDS surface treatment, were performed on the hard mask film 4 was 52.8°. In this case, there was no measurement point where the measured value of the contact angle was locally lower than 40°.

By performing both the TMAH surface treatment and the HMDS surface treatment, the contact angle of the hard mask film 4 with respect to water was increased by 9.6°, and the hydrophobicity was increased. This is because the TMAH surface treatment increases the number of OH groups on the surface of the hard mask film 4 made of the SiON film, which is the binding destination of the silane coupling agent HMDS, so that the HMDS surface treatment alone causes It is considered that more trimethylsilyl groups were formed on the surface of the hard mask film 4. By performing the surface treatment with TMAH, the in-plane uniformity of OH groups is increased and the amount of OH groups is also increased, so that the surface of the hard mask film 4 has high in-plane uniformity and has sufficient hydrophobicity. Became.

After that, SLN-009+ (Fuji Film Electronics) which is a chemically amplified negative resist for electron beam writing is spin-coated on the upper surface of the hard mask film 4 which has been subjected to the two surface treatments of TMAH surface treatment and HMDS treatment. (Manufactured by Materials Co., Ltd.) was applied and a predetermined baking treatment was performed to form a resist film having a film thickness of 80 nm.
The mask blank of Example 1 was manufactured as described above.

[Manufacture of transfer mask]
Next, using this mask blank, a halftone phase shift mask was manufactured according to the manufacturing process shown in FIGS.
First, a predetermined device pattern was drawn on the resist film using an electron beam drawing machine, and then the resist film was developed to form a resist pattern 5a (see FIG. 2A). Here, the predetermined device pattern is a pattern (phase shift pattern) including a fine pattern (SRAF pattern having a line width of 40 nm or less) to be formed on the light semi-transmissive film 2. The resist pattern 5a formed on the hard mask film 4 was good in that no collapse of the resist pattern was observed.

Next, the hard mask film 4 was dry-etched using the resist pattern 5a as a mask to form a hard mask pattern 4a (see FIG. 2B). A fluorine-based gas (mixed gas of SF ₆ gas and He gas) was used as the dry etching gas. After removing the resist pattern 5a, the light-shielding film 3 including the upper and lower laminated films is continuously dry-etched using the hard mask pattern 4a as a mask to form a first light-shielding film pattern 3a (see FIG. See c)). As the dry etching gas, a mixed gas of Cl ₂ and O ₂ (Cl ₂ :O ₂ =8:1 (flow ratio)) was used.

Subsequently, the light-semitransmissive film 2 was dry-etched using the light-shielding film pattern 3a as a mask to form a light-semitransmissive film pattern 2a (phase shift pattern) (see FIG. 3A). A fluorine-based gas (mixed gas of SF ₆ gas and He gas) was used as the dry etching gas. In the etching process of the light semi-transmissive film 2, the hard mask pattern 4a exposed on the surface was removed.

Next, a resist film is formed on the substrate by a spin coating method, a predetermined pattern such as a light-shielding band pattern is drawn by using an electron beam drawing machine, and then developed to form a resist pattern (not shown). ). Here, PRL009 (manufactured by Fuji Film Electronics Materials Co., Ltd.), which is a chemically amplified positive resist for electron beam drawing, was used as the resist. Then, the exposed first light-shielding film pattern 3a is etched by using this resist pattern as a mask to remove the light-shielding film pattern 3a in the transfer pattern forming region, for example, to remove the periphery of the transfer pattern forming region. A second light-shielding film pattern 3b having a light-shielding band pattern was formed on the portion. As the dry etching gas in this case, a mixed gas of Cl ₂ and O ₂ (Cl ₂ :O ₂ =8:1 (flow rate ratio)) was used. Finally, the remaining resist pattern was removed, and a halftone type phase shift mask 30, which is a transfer mask, was manufactured (see FIG. 3B).

When the manufactured transfer mask 30 (halftone type phase shift mask) was inspected for defects, no defects due to the collapse of the resist pattern were observed, and it was confirmed that the transfer mask had few defects. Since there were few defects, the manufacturing yield of the transfer mask was high.

(Example 2)
In Example 2, the hard mask film 4 was formed of silicon oxide, and surface treatment of a silicon-containing thin film, manufacture of a mask blank, and manufacture of a transfer mask were performed. The procedure is the same as in Example 1 except for the film method. The points different from the first embodiment will be described below.

After forming the light-shielding film 3 in the same procedure as in Example 1, RF sputtering is performed using a target of silicon dioxide (SiO ₂ ) and argon (Ar) gas (pressure 0.03 Pa) as a sputtering gas. A hard mask film 4 made of a SiO ₂ film having a thickness of 12 nm was formed on the light shielding film 3. The composition of the formed SiO ₂ film was Si:O=35:65 (atomic ratio). This composition was measured by XPS.

Subsequently, the in-plane distribution ratio I _ratio of the normalized secondary ion intensity derived from bromine of the SiO ₂ film (hard mask film 4) was calculated by the same procedure as in Example 1. As a result, as shown in FIG. 4, the SiO ₂ film without TMAH surface treatment was 4.60, while the SiO ₂ film with TMAH surface treatment was 1.65. .. By performing the TMAH surface treatment, it was confirmed that the in-plane distribution ratio I _ratio of the normalized secondary ion strength was reduced by 2.95, and the in-plane uniformity of OH groups on the surface of the SiO ₂ film was improved.

When a resist pattern was formed on the hard mask film 4, no collapse of the resist pattern was observed. As a result, the manufactured transfer mask was a mask with few pattern defects.

(Comparative Example 1)
In Comparative Example 1, the surface treatment of the SiON hard mask film 4 was performed only by the HMDS surface treatment, and the mask blank and the transfer mask were manufactured. Other than that, that is, the TMAH surface treatment was not performed, there is no change from Example 1.
When a resist pattern was formed on the hard mask film 4 made of a SiON film, collapse of the resist pattern was observed in a part of the surface where the resist pattern was formed. As a result, the manufactured transfer mask has many pattern defects.
It is considered that this is because the in-plane uniformity of OH groups on the surface of the hard mask film 4 is low and the hydrophobicity of the surface is relatively small. As described in Example 1, if the TMAH surface treatment is not performed, the in-plane uniformity of OH groups of the hard mask film 4 is low, and the contact angle of water, which is an index of hydrophobicity, is low. ..

1... Glass substrate 2... Light semi-transmissive film (phase shift film)
2a... Light semi-transmissive film pattern (phase shift pattern)
3... Shading film 3a... 1st shading film pattern 3b... 2nd shading film pattern 4... Hard mask film 4a... Hard mask pattern 5a... Resist pattern 30... Halftone type phase shift mask

Claims (8)

On the glass substrate, a pattern forming thin film, and a hard mask film made of a material containing silicon, a step of preparing a mask blank provided in this order,
An in-plane homogenization step of performing a process for increasing the uniformity of the in-plane distribution of OH groups existing on the surface of the hard mask film on the surface of the hard mask film;
To the surface of the hard mask layer after the plane homogenizing step, possess and performing surface treatment with a silane coupling agent,
The hard mask film is a SiON film,
The in-plane homogenization step is a treatment for increasing the number of OH groups present on the surface of the hard mask film,
The in-plane homogenization step is performed without heat treatment after the hard mask film is formed on the glass substrate,
The in-plane homogenizing step is a step including a treatment of bringing an alkaline aqueous solution into contact with the surface of the pattern forming thin film, and the alkaline aqueous solution is dropped and puddle on the surface of the pattern forming thin film. A method of manufacturing a mask blank, comprising: The method for manufacturing a mask blank according to claim 1 , wherein the silane coupling agent is hexamethyldisilazane. The hard mask layer may mask blank manufacturing method according to any one of claims 1 or 2, characterized in that it consists of a material containing silicon and oxygen. The hard mask layer is, the production method of the mask blank as claimed in any one of 3, wherein the thickness is 3nm or more 15nm or less. The pattern forming thin film, the mask blank manufacturing method as claimed in any one of the 4, characterized in that it consists of a material containing chromium. The pattern forming thin film is a light semi-transmissive film made of a material containing silicon, and a light shielding film made of a material containing chromium is provided between the pattern forming thin film and the hard mask film. The method of manufacturing a mask blank according to claim 1, wherein the mask blank is manufactured. Method for producing a mask blank according to any one of claims 1 6, characterized in that it comprises a step of forming a resist film of an organic material in contact with the surface of the hard mask layer after performing the surface treatment .. A method of manufacturing a transfer mask using the mask blank manufactured by the method of manufacturing a mask blank according to claim 7 .
A step of exposing and drawing a pattern to be formed on the pattern forming thin film on the resist film, and performing a developing process to form a pattern on the resist film;
And a step of forming a pattern on the hard mask film by dry etching using the resist film having the pattern as a mask.

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