JP6949522B2 - A method for manufacturing a substrate for a mask blank, a method for manufacturing a mask blank, and a method for manufacturing a transfer mask. - Google Patents

Description

The present invention relates to a method for producing a mask blank substrate, a method for producing a mask blank using the mask blank substrate, and a method for producing a transfer mask using the mask blank. In particular, the present invention relates to a method for manufacturing a mask blank substrate having few defects, a method for manufacturing a mask blank, and a method for manufacturing a transfer mask.

The presence of defects on the mask blank substrate, the mask blank, and the transfer mask causes transfer defects during wafer exposure using the transfer mask. Therefore, in recent years, further reduction of defects has been required for mask blank substrates, mask blanks, and transfer masks.

The mask blank is manufactured by performing a step of forming a thin film for pattern formation on the main surface of a glass substrate by a sputtering method or the like (thin film forming step). Generally, the main surface of the substrate is cleaned before the thin film forming step. In this substrate cleaning, generally, cleaning is performed with a cleaning liquid having an action of etching the surface of the substrate.

In Patent Document 1, an etching solution is injected into the first main surface of a mask blank substrate having two main surfaces, a first surface and a second main surface, and the first main surface is covered with the etching solution. A method for manufacturing a mask blank substrate including a step of wet etching (wet etching step) is described. Patent Document 1 describes that an aqueous solution of a strongly alkaline compound having a pH of 10 or more is used as the etching solution used in the wet etching step.

Japanese Unexamined Patent Publication No. 2015-184523

Generally, when removing foreign substances adhering to the main surface of a mask blank substrate, scrub cleaning or ultrasonic cleaning is performed. Scrub cleaning is cleaning that removes foreign substances adhering to the main surface of the substrate by bringing the cleaning brush into contact with the main surface of the substrate while applying the cleaning liquid. Further, ultrasonic cleaning is cleaning that removes foreign substances adhering to the main surface of the substrate by applying a cleaning liquid to which ultrasonic waves are applied to the surface of the substrate. In the case of scrub cleaning, there is a problem that foreign matter removed from the main surface of the substrate easily adheres to the cleaning brush and reattaches to the main surface of the substrate.

In the case of ultrasonic cleaning, relatively large foreign substances (for example, equivalent to 100 nm or more in diameter) can be washed away from the main surface of the substrate by the flow of the cleaning liquid to which ultrasonic waves are applied. However, it is difficult to wash away relatively small foreign matter (for example, less than 100 nm) from the main surface of the substrate. This problem is difficult to solve because the flow velocity of the liquid drops significantly in the vicinity of the main surface of the substrate due to the relationship between the liquid and the viscosity.

On the other hand, when manufacturing a mask blank substrate, a wet etching step as disclosed in Patent Document 1 may be performed. In the wet etching step, a cleaning liquid having an etching action on a mask blank substrate such as a glass substrate is used, and the surface of the mask blank substrate is wet-etched to remove foreign substances adhering to the surface. In the case of cleaning by this wet etching, foreign matter is removed together with the surface layer of the substrate, so that the above-mentioned relatively small foreign matter can also be removed from the main surface of the substrate.

In this wet etching step, in addition to dissolving and removing foreign substances with a cleaning liquid having an etching action, foreign substances are removed together with the surface layer by dissolving the surface layer of the substrate. Since the wet etching is an etching having a large tendency to be isotropic, the wet etching proceeds so as to wrap around the surface layer of the substrate directly under the foreign matter. Then, as the contact area between the main surface of the substrate and the foreign matter gradually decreases, the adhesive force of the foreign matter decreases, and eventually the foreign matter floats in the cleaning liquid and is removed from the main surface of the substrate. By this action, even a foreign substance having a component having low solubility in the etching solution can be removed.

However, even if the foreign matter has a relatively high solubility in the cleaning solution, if the size of the foreign matter is large, it takes time for the foreign matter to dissolve. In the case of a foreign substance having a low solubility in a cleaning solution and a large size, the adhesion force of the foreign substance to the main surface is weakened and the time until the foreign substance floats in the etching solution becomes significantly longer. In these cases, the foreign matter acts as a mask during the wet etching process, and an etching step due to the foreign matter may occur on the surface of the substrate. Such an etching step may have an adverse effect on the mask blank and the transfer mask as a convex defect.

Therefore, an object of the present invention is to obtain a mask blank substrate, a mask blank, and a transfer mask with reduced convex defects. Specifically, an object of the present invention is to obtain a method for manufacturing a mask blank substrate, which reduces the occurrence of etching steps caused by foreign matter adhering to the surface of a glass substrate which is a raw material for a mask blank substrate. ..

In the process of manufacturing the mask blank substrate, the present inventors perform cleaning for removing foreign substances on the surface of the mask blank substrate (wet etching step) a plurality of times, particularly twice using different cleaning liquids. The present invention has been made by finding that it is possible to obtain a method for manufacturing a mask blank substrate, which can remove a large amount of foreign matter and reduce the occurrence of etching steps caused by the foreign matter.

In order to solve the above problems, the present invention has the following configurations. That is, the present invention comprises a method for manufacturing a mask blank substrate, which has the following configurations 1 to 6, a method for producing a mask blank, which has the following configuration 7, and the following configuration 8. It is a method for manufacturing a transfer mask, which is characterized in that it is present.

(Structure 1)
Configuration 1 of the present invention is a method for producing a mask blank substrate manufactured from a glass substrate having two main surfaces, wherein the pH is greater than 9 and less than 11, and a cleaning liquid containing no chelating agent is used. The first cleaning step of cleaning one main surface of the glass substrate and the second cleaning of covering the one main surface of the glass substrate with an etching solution having a pH of 11 or more and containing a chelating agent and performing wet etching. It is a method for manufacturing a substrate for a mask blank, which comprises a process.

According to the configuration 1 of the present invention, a mask blank substrate with reduced convex defects can be obtained. Specifically, according to the configuration 1 of the present invention, it is possible to obtain a method for manufacturing a mask blank substrate in which the occurrence of etching steps due to foreign matter is reduced.

(Structure 2)
The mask blank according to the first aspect of the present invention is the mask blank according to the first aspect, wherein the etching solution used in the second cleaning step is supplied to the one main surface of the glass substrate at a temperature higher than room temperature. This is a method for manufacturing a substrate.

In the method for manufacturing a substrate for a mask blank of the present invention, the etching solution used in the second cleaning step is supplied to one main surface of the glass substrate at a temperature higher than room temperature, so that the mask in the second cleaning step is used. The etching rate of the blank substrate can be increased. Thereby, foreign matter on the surface of the mask blank substrate can be removed more effectively.

(Structure 3)
Configuration 3 of the present invention is characterized in that the etching solution used in the second cleaning step contains one or more alkaline agents selected from sodium hydroxide, potassium hydroxide, and tetramethylammonium. Alternatively, it is the method for manufacturing a substrate for mask blank of 2.

According to the configuration 3 of the present invention, the pH of the second cleaning step can be easily set to a predetermined value by containing a predetermined alkaline agent in the etching solution used in the second cleaning step. In addition, the etching rate for the glass substrate can be increased.

(Structure 4)
Configuration 4 of the present invention is a method for producing a mask blank substrate according to any one of configurations 1 to 3, wherein the cleaning liquid used in the first cleaning step contains a surfactant.

According to the configuration 4 of the present invention, since the cleaning liquid used in the first cleaning step contains a surfactant, foreign substances can be more reliably removed in the first cleaning step.

(Structure 5)
In the configuration 5 of the present invention, in the first cleaning step, the cleaning liquid to which ultrasonic waves having a frequency of 2.0 MHz or more and 5.0 MHz or less are applied from the cleaning nozzle while rotating the glass substrate is applied to the glass substrate. This is a method for manufacturing a mask blank substrate according to any one of the configurations 1 to 4, wherein the glass blank is supplied so as to hit one of the main surfaces.

According to the configuration 5 of the present invention, by applying ultrasonic waves having a predetermined frequency to the cleaning liquid in the first cleaning step, foreign matter can be removed more effectively in the first cleaning step.

(Structure 6)
In the configuration 6 of the present invention, in the second cleaning step, the etching solution is supplied only on the one main surface, and wet etching is performed while swinging the etching solution on the one main surface. This is a method for manufacturing a mask blank substrate according to any one of the features 1 to 5.

According to the configuration 6 of the present invention, the foreign matter on the surface of the mask blank substrate in the second cleaning step can be removed more effectively by shaking the etching solution. As a result, it is possible to more effectively prevent the occurrence of etching steps caused by foreign matter.

(Structure 7)
In the configuration 7 of the present invention, a thin film for forming a transfer pattern is formed on the one main surface of the mask blank substrate obtained by the method for manufacturing a mask blank substrate according to any one of configurations 1 to 6. This is a method for manufacturing a mask blank.

According to the configuration 7 of the present invention, it is possible to obtain a mask blank in which the occurrence of etching steps (convex defects) caused by foreign matter is reduced.

(Structure 8)
The configuration 8 of the present invention is a method for producing a transfer mask, which comprises patterning the thin film of the mask blank obtained by the method for producing a mask blank according to the configuration 7 to form a transfer pattern.

According to the configuration 8 of the present invention, it is possible to obtain a transfer mask in which the occurrence of etching steps (convex defects) caused by foreign matter is reduced.

According to the present invention, it is possible to provide a mask blank substrate, a mask blank, and a transfer mask with reduced convex defects. Specifically, according to the present invention, it is possible to provide a method for manufacturing a mask blank substrate, which reduces the occurrence of etching steps caused by foreign matter adhering to the surface of a glass substrate which is a raw material of the mask blank substrate. can.

It is a schematic diagram which shows an example of the cleaning apparatus which can be used in the 1st cleaning step of the manufacturing method of the substrate for a mask blank of this invention. FIG. 5 is a schematic plan view showing an example of a cleaning device (wet etching device) that can be used in the second cleaning step of the method for manufacturing a substrate for a mask blank of the present invention. FIG. Is a schematic view of the lower surface. It is sectional drawing which shows an example of the cleaning apparatus (wet etching apparatus) which can be used in the 2nd cleaning step of the manufacturing method of the substrate for a mask blank of this invention. It is a flowchart which shows an example of the 2nd cleaning process of the manufacturing method of the substrate for a mask blank of this invention. It is a figure which shows the zeta potential _{of SiO 2 and the} like when the pH is changed.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. It should be noted that the following embodiments are embodiments for embodying the present invention, and do not limit the present invention to the scope thereof.

An embodiment of the present invention is a method for manufacturing a mask blank substrate manufactured from a glass substrate having two main surfaces. The method for manufacturing a substrate for a mask blank includes a first cleaning step and a second cleaning step. By including the predetermined first cleaning step and the second cleaning step in the method for manufacturing the mask blank substrate, it is possible to reduce the occurrence of etching steps caused by foreign matter in the mask blank substrate. As a result, a mask blank substrate with reduced convex defects can be obtained.

(Material for mask blank substrate)
The glass substrate used for manufacturing the mask blank substrate is not particularly limited as long as it has translucency with respect to the exposure wavelength used. In the present invention, a synthetic quartz glass substrate and various other glass substrates (for example, soda lime glass, aluminosilicate glass, etc.) can be used. Among them, the synthetic quartz glass substrate has a high transmittance even for short wavelength ultraviolet rays such as ArF excimer laser (wavelength 193 nm), and therefore is a glass for a binary mask blank used for forming a high-definition transfer pattern. It is suitable as a substrate or a glass substrate for a phase shift mask blank.

Further, as the glass substrate used for the mask blank substrate, low thermal expansion glass used for a reflective mask using EUV (Extreme Ultra Violet) light as exposure light can be used. Examples of low thermal expansion glass used for the reflection type mask, for example, _SiO 2 -TiO ₂ type glass having the characteristics of low thermal expansion (binary _(SiO 2 -TiO ₂₎ and ternary _(SiO 2 -TiO ₂ -SnO ₂ ))), for example, so-called multi-component glass such as _{SiO 2-} Al ₂ O _3- Li _{2 O-based crystallized glass can be used.}

(Polishing process and pre-cleaning process)
In the process of manufacturing a substrate for a mask blank, after the process of polishing the glass substrate, particles existing on the main surface of the glass substrate (for example, foreign substances such as abrasive grains adhering to the surface of the glass substrate) are removed. A pre-cleaning step is carried out.

The mask blank substrate (glass substrate) has two opposing main surfaces. These two opposing main surfaces are referred to as a first main surface (also referred to as "front main surface") and a second main surface (also referred to as "back main surface"). A thin film for forming a transfer pattern is formed on the first main surface (front main surface).

In the polishing process of the glass substrate, the polishing pad is brought into contact with the main surface of the glass substrate, a polishing liquid containing polishing abrasive grains is supplied to the surface of the glass substrate, and the glass substrate and the polishing pad are relatively moved. Polish the main surface of the glass substrate. For example, the glass substrate is pressed against the polishing platen to which the polishing pad is attached, and the polishing platen and the glass substrate are relatively moved (that is, the polishing pad and the glass substrate) while supplying the polishing liquid containing the polishing abrasive grains. Is relatively moved) to polish the main surface of the glass substrate. As the polishing abrasive grains, colloidal silica is preferably used at least in the finish polishing of the precision polishing step because good smoothness and flatness of the glass substrate can be obtained. For this polishing step, for example, a planetary gear type double-sided polishing device can be used.

After the completion of ultra-precision polishing, cleaning (pre-cleaning step) is performed to remove colloidal silica abrasive grains. Specifically, after brush cleaning the main surface and end faces of the glass substrate, spin cleaning with pure water is performed. Instead of brush cleaning, it is possible to perform dip cleaning by immersing a mask blank substrate, which is a glass substrate, in a liquid bath of an aqueous hydrofluoric acid solution, and / or cleaning with a detergent containing a surfactant. can.

After the pre-cleaning step, an inspection step for inspecting defects such as adhesion of foreign matter on the surface of the mask blank substrate can be included.

(1st cleaning step)
The method for producing a mask blank substrate of the present invention includes a first cleaning step. The first cleaning step comprises cleaning one main surface of the glass substrate with a cleaning solution having a pH greater than 9 and less than 11 and containing no chelating agent. The main purpose of this first cleaning step is to remove foreign substances having a relatively large size (for example, equivalent to 100 nm or more in diameter) among the foreign substances adhering to one main surface of the glass substrate. .. As the cleaning liquid used in the first cleaning step, a liquid having a relatively small etching action on the glass substrate or which does not substantially etch the glass substrate is used. One main surface is preferably the first main surface (front main surface). Hereinafter, cleaning of the first main surface will be described as an example.

_{When a material containing SiO 2} such as synthetic quartz is used as the glass substrate for manufacturing the mask blank substrate, the surface (including the first main surface) to which the cleaning liquid of the substrate comes into contact is due to the alkaline cleaning liquid. The zeta potential of each surface) becomes negative. Further, as the pH rises, the negative value of the zeta potential on the surface with which the cleaning liquid of the substrate comes into contact tends to increase. FIG. 5 shows, as an example, the zeta potentials _{of SiO 2} , Si, Si ₃ N ₄ , and Al ₂ O _{3 when the pH of the aqueous solution is changed.} As is clear from FIG. 5, in any of the materials, the zeta potential tends to increase in the negative direction as the pH increases. Generally, in the region from acidic to about pH 8, the zeta potential shows various values depending on the material. On the other hand, in the region of pH 9 or higher, the zeta potential becomes negative regardless of the material. For example, silica fine particles are negative in the neutral region and have the same polarity as the glass substrate. Therefore, once the foreign matter is detached from the glass substrate, it can be estimated that reattachment to the glass substrate is unlikely to occur. On the other hand, the alumina fine particles are positively charged near neutrality, and even if they are once removed, they tend to reattach to the negatively charged glass substrate. However, when the pH is raised to 9 or more, the zeta potential of a material that is easily charged positively such as alumina also becomes negative, and it becomes difficult to reattach to the surface of the glass substrate. Therefore, since the cleaning liquid is alkaline at a predetermined pH, the particles of the negatively charged foreign matter receive a repulsive force from the surface of the glass substrate due to the negative zeta potential on the surface of the glass substrate. As a result, it is possible to prevent foreign matter from adhering to the surface of the glass substrate.

The cleaning liquid used in the first cleaning step has a pH of more than 9 and less than 11, and is alkaline. Therefore, from the above, the zeta potentials of both the surface of the glass substrate (each surface including the first main surface) and the foreign matter become negative. That is, since the cleaning liquid in the first cleaning step is alkaline at a predetermined pH, foreign matter can be removed from the first main surface of the glass substrate by the electric repulsive force. Further, the removed foreign matter can be prevented from reattaching to the first main surface of the glass substrate. Therefore, in the first cleaning step, it can be said that foreign matter having a relatively large size can be effectively removed from the glass substrate and reattachment to the glass substrate can be prevented.

Further, the cleaning liquid used in the first cleaning step does not contain a chelating agent. As will be described later, when the cleaning liquid is alkaline and contains a chelating agent, the etching rate of the cleaning liquid for wet etching on the glass substrate increases. Since the cleaning liquid used in the first cleaning step does not contain a chelating agent, the etching rate of the cleaning liquid used in the first cleaning step for wet etching on the glass substrate is small. Therefore, in the first cleaning step, it can be said that the possibility of an etching step caused by foreign matter adhering to the first main surface of the glass substrate is extremely low.

Since the cleaning liquid used in the first cleaning step contains an alkaline agent, it is an aqueous solution having a pH in a predetermined range. The alkaline agent contained in the cleaning liquid can be used without limitation as long as the cleaning liquid can have a predetermined pH. Examples of the alkaline agent contained in the cleaning liquid used in the first cleaning step include hydroxides of alkali metals. As the alkali metal hydroxide, for example, sodium hydroxide (NaOH) and potassium hydroxide (KOH) can be preferably used from the viewpoint of easy availability and handling. It is also possible to use an organic alkaline agent such as TMAH (tetramethylammonium hydroxide).

The cleaning liquid used in the first cleaning step preferably contains a surfactant. Since the cleaning liquid used in the first cleaning step contains a surfactant, the surface tension of the cleaning liquid is lowered and the permeation of the cleaning liquid between the substrate and the foreign matter is promoted. , Can be done more reliably.

As the surfactant that can be contained in the cleaning liquid in the first cleaning step, a commercially available surfactant can be used without limitation. From the viewpoint of more effectively removing foreign substances, the surfactant contained in the cleaning liquid used in the first cleaning step is preferably selected from an anionic surfactant and a nonionic surfactant.

The temperature of the cleaning liquid used in the first cleaning step is preferably 5 to 35 ° C. (20 ± 15 ° C.), more preferably 22 to 30 ° C. In addition, in this specification, 5 to 35 degreeC (20 ± 15 degreeC) is also referred to as "normal temperature".

In the method for manufacturing a mask blank substrate of the present invention, in the first cleaning step, while rotating the glass substrate, a cleaning liquid to which ultrasonic waves having a frequency of 2.0 MHz or more and 5.0 MHz or less is applied from the cleaning nozzle is applied to the glass substrate. It is preferable to supply it so as to hit one of the main surfaces. By applying ultrasonic waves having a predetermined frequency to the cleaning liquid in the first cleaning step, foreign matter can be removed more effectively in the first cleaning step.

When ultrasonic waves are applied to the cleaning liquid for cleaning the glass substrate, latent scratches may occur inside the glass substrate. By setting the frequency of the ultrasonic waves applied to the cleaning liquid within a predetermined range, it is possible to suppress the occurrence of latent scratches inside the glass substrate. Specifically, the inside of the glass substrate (particularly the substrate) is cleaned by applying a cleaning liquid to which an ultrasonic wave having a frequency of 2.0 MHz or higher is applied toward the first main surface of the glass substrate to clean the surface of the glass substrate. It is possible to suppress the occurrence of latent scratches on the surface layer of the main surface). Further, it is preferable to apply a cleaning liquid to which an ultrasonic wave of 2.5 MHz or more is applied because the occurrence of latent scratches can be suppressed more reliably. Whether or not a latent scratch has occurred inside the substrate can be confirmed by, for example, making the latent scratches manifest with an alkaline chemical solution or the like.

Further, by applying a cleaning method of applying a cleaning liquid to which ultrasonic waves are applied to clean the first main surface of the glass substrate, even if the cleaning liquid is to which ultrasonic waves higher than a predetermined frequency are applied, the cleaning liquid is applied. Particles existing on the main surface of the substrate can be reliably eliminated. In the present invention, it is desirable that the upper limit of the frequency of the ultrasonic wave applied to the cleaning liquid is 5.0 MHz or less. If the frequency of the ultrasonic waves applied to the cleaning liquid is higher than 5.0 MHz, the particle removal rate of the first main surface of the substrate after cleaning, particularly the removal rate of relatively large particles having a particle size of 200 nm or more may decrease. .. It is desirable that the upper limit of the frequency of the ultrasonic waves applied to the cleaning liquid is 4.0 MHz or less, preferably 3.5 MHz or less because the removal rate of relatively large particles can be further improved.

From the above, the ultrasonic wave applied to the cleaning liquid in the first cleaning step is preferably an ultrasonic wave having a frequency of 2.5 MHz or more and 4.0 MHz or less, more preferably 2.5 MHz or more and 3.5 MHz or less. Is desirable.

FIG. 1 is a configuration diagram showing an example of a cleaning device that can be used in the first cleaning step.

The cleaning device 310 shown in FIG. 1 is a single-wafer cleaning device, and includes a spin chuck 311 for holding the substrate 301 and an ultrasonic cleaning nozzle 314 provided at the tip of the arm 315. The spin chuck 311 is rotatably provided by an electric motor 312. Further, the ultrasonic cleaning nozzle 314 applies ultrasonic waves to the cleaning liquid supplied from the cleaning liquid supply device 316. The cleaning liquid to which the ultrasonic waves are applied is directly applied to the first main surface of the substrate 301 from above and supplied. At the time of cleaning, the ultrasonic cleaning nozzle 314 is configured to move (swing) from the center to the end face of the substrate 301 by the arm 315 while rotating the substrate 301 at a predetermined rotation speed. Further, the periphery of the spin chuck 311 is covered with a cleaning cup 313 to prevent the cleaning liquid from scattering.

When the above cleaning device is used, when the ultrasonic cleaning nozzle 314 is moved (swinged) by the rotation of the arm 315, the rotation of the arm 315 is a repetitive rotation within a predetermined angle range, for example, a range of ± 15 degrees. It is preferable to exercise.

When the above cleaning device is used, it is desirable that the rotation speed of the substrate and the moving speed of the ultrasonic cleaning nozzle at the time of cleaning are appropriately set so that the entire substrate 301 is uniformly cleaned. The flow rate of the cleaning liquid applied to the first main surface of the substrate 301 varies slightly depending on the number of rotations of the substrate during cleaning and the moving speed of the ultrasonic cleaning nozzle, but is generally about 1.0 to 5.0 liters / minute. It is preferable, and particularly preferably about 1.0 to 3.0 liters / minute.

Further, regarding the shape of the tip of the ultrasonic cleaning nozzle 314 in the cleaning device, for example, a circular shape or a rectangular shape (slit shape or the like) can be arbitrarily used.

As described above, even when the cleaning method using the cleaning liquid to which ultrasonic waves are applied is applied at the time of cleaning the glass substrate in the first cleaning step, the cleaning liquid to which the ultrasonic waves of a predetermined frequency is applied is applied to the substrate. 1 By applying the glass substrate to the main surface for cleaning, there is no risk of latent scratches occurring inside the glass substrate, and particles existing on the main surface of the substrate can be reliably eliminated.

In the above description, the cleaning device that can be used in the first cleaning step has been described with reference to FIG. 1, but the present invention is not limited to this. In the first cleaning step, a cleaning device as shown in FIGS. 2 and 3 that can be used in the second cleaning step described later may be used.

(Second cleaning process)
The method for producing a mask blank substrate of the present invention includes a second cleaning step. The second cleaning step includes performing wet etching by covering one main surface of the glass substrate with an etching solution having a pH of 11 or more and containing a chelating agent. The main purpose of this second cleaning step is to remove foreign substances having a minute size (for example, less than 100 nm in diameter) among the foreign substances adhering to one main surface of the glass substrate. One main surface is preferably the first main surface (front main surface). Hereinafter, cleaning of the first main surface will be described as an example.

By performing a second cleaning step of wet etching the first main surface of the substrate from which foreign substances have been removed by the first cleaning step with a cleaning liquid having a pH of 11 or more and containing a chelating agent, the substrate is further subjected to a second cleaning step. It is possible to lift off minute foreign matter adhering to the first main surface of the above.

The cleaning liquid used in the second cleaning step is an aqueous solution containing an alkaline agent and a chelating agent. The present inventors have found that the etching rate of a glass substrate increases when a cleaning solution having a high pH (11 or more) and containing a chelating agent is used. When such a cleaning liquid having a high etching rate is used as the cleaning liquid in the first cleaning step described above, a relatively large foreign matter acts as an etching mask, causing a difference in the amount of in-plane etching on the first main surface of the substrate. This may result in the formation of new convex defects on the surface. Therefore, in the first cleaning step, an alkaline cleaning solution containing no chelating agent is used to reliably remove foreign substances having a relatively large size. On the other hand, after removing the foreign matter in the first cleaning step, it is possible to remove minute foreign matter that could not be removed in the first cleaning step by cleaning with an alkaline cleaning solution containing a chelating agent as the second cleaning step. can. Further, since the above-mentioned first cleaning step can remove foreign matter having a relatively large size and prevent the foreign matter from reattaching during the first cleaning step, the etching rate is high in the second cleaning step. Even when used as a cleaning liquid (an aqueous solution containing an alkaline agent and a chelating agent), it is possible to suppress the occurrence of an etching step caused by foreign matter adhering to the first main surface of the glass substrate.

The cleaning liquid used in the second cleaning step is an aqueous solution of an alkaline compound having a pH of 11 or more. The pH of the aqueous solution of the alkaline compound is more preferably 12 or more, and particularly preferably 13 or more. As described above, the aqueous solution of the alkaline compound makes the zeta potential of the surface of the glass substrate (each surface including the first main surface) negative. Therefore, the foreign matter having the same negative zeta potential repels each other with the first main surface of the glass substrate, so that the reattachment of the foreign matter can be prevented. Therefore, it is advantageous for the cleaning liquid to have a predetermined pH in terms of the ability to remove foreign substances.

Since the cleaning liquid used in the second cleaning step contains an alkaline agent (alkaline compound), it is an aqueous solution having a pH in a predetermined range. As the type of alkaline compound, either an inorganic alkaline compound or an organic alkaline compound can be used. Since the cleaning liquid used in the second cleaning step has a high etching rate with respect to the glass substrate as described above, the cleaning liquid used in the second cleaning step may be referred to as an “etching liquid”.

Examples of the inorganic alkaline compound include alkali metal hydroxides (KOH, NaOH, LiOH, RbOH, and CsOH). Among them, Na ions (Na ⁺⁾ and K ions ^{(K +)} is silicate ions liberated from the glass substrate _(SiO ^{3 2-like)} and can stably coexist. Therefore, a KOH aqueous solution in which these ions are dissociated and a NaOH aqueous solution are preferable in that the etching reaction can proceed stably.

An aqueous solution of an organic alkaline compound can also be used as an etching solution. In the case of an organic alkaline compound, the pH of the etching solution is 11 or more, preferably 13 to 14.

When an organic alkaline compound is used as a solute in an etching solution, a quaternary ammonium hydroxide can be used. Specific examples include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), and the like, which are available. Tetraalkylammonium hydroxide can be preferably used because of its ease of use.

Further, as another example of the quaternary ammonium hydroxide, those having an alkoxy group can be mentioned. Specific examples thereof include trimethylhydroxyethylammonium hydroxide, methyltri (hydroxyethyl) ammonium hydroxide, tetra (hydroxyethyl) ammonium hydroxide, and benzyltrimethylammonium hydroxide (BTMAH).

Of the organic alkaline substances, weakly basic compounds such as tertiary alkylamines and ammonia have poor ability to etch glass, so it is appropriate to use them alone as an etchant for wet etching. Not. When ammonia is used as a component of the etching solution, ammonia is adsorbed on the surface of the glass substrate and reacts with the component of the cleaning solution (for example, sulfate ion) used in the subsequent cleaning step to produce the product (for example, ammonium sulfate). Is not preferable because it may precipitate and cause haze.

In the method for producing a substrate for a mask blank of the present invention, the cleaning liquid (etching liquid) used in the second cleaning step contains one or more alkaline agents selected from sodium hydroxide, potassium hydroxide, and tetramethylammonium. However, it is particularly preferable. Since the etching solution used in the second cleaning step contains a predetermined alkaline agent, the pH of the second cleaning step can be easily set to a predetermined value.

A known chelating agent can be used as the chelating agent contained in the cleaning liquid (etching liquid) used in the second cleaning step. As the chelating agent, for example, one selected from EDTA (edetic acid), HEDP (etidronic acid) and the like can be preferably used. The amount of the chelating agent added is preferably 0.1 wt% or more.

Since the concentration of the etching solution ^{depends on the concentration of hydroxy ions (OH −} ) that contribute to the etching reaction, it may be adjusted to a concentration within the above pH range. For example, when a strong alkaline compound such as KOH or NaOH having a large dissociation constant is used, it is preferable to use a compound having an alkaline concentration of 0.01 mol / L or more. It is preferably 0.1 mol / L or more, and particularly preferably 1 mol / L or more. In the case of an etching solution with poor solute volatility such as NaOH or KOH, the rinsing time after etching may become longer, so the sum of the concentrations of the inorganic alkaline components should be adjusted to 3 mol / L or less. Is preferable. When an etching solution containing only an inorganic alkaline component is used, the pH is 11 or more, and the preferable pH is 13 to 14.

In the method for producing a mask blank substrate of the present invention, it is preferable that the etching solution used in the second cleaning step is supplied to one main surface of the glass substrate at a temperature higher than room temperature. In the present specification, as described above, the normal temperature means 20 ± 15 ° C., that is, 5 to 35 ° C. By supplying the etching solution used in the second cleaning step to one main surface of the glass substrate at a temperature higher than room temperature, the etching rate of the mask blank substrate in the second cleaning step can be increased. Thereby, foreign matter on the surface of the mask blank substrate can be removed more effectively.

The supply temperature of the wet etching solution is higher than normal temperature, preferably 40 ° C. or higher, and particularly preferably 60 ° C. or higher. When an inorganic alkaline compound having no volatility is used as a solute, the temperature of the etching solution is preferably 95 ° C. or lower. As the distance from the etching solution supply point increases, the solute concentrates due to the volatilization of water as a solvent, which may cause a concentration distribution of the etching solution. It is preferably 80 ° C. or lower.

The wet etching solution has at least one etchant, and the boiling point of the etchant is preferably higher than the temperature of the etching solution described above. Since the boiling point of the etchant is higher than the supply temperature of the etching solution, the solubility does not decrease due to the temperature rise and the concentration does not decrease due to the volatilization of the solute, which is preferable in that the etching solution is stabilized. For example, when an inorganic strong alkaline component such as an alkali metal hydroxide is used as an etchant, the wet etching solution is heated to a high temperature (steam pressure) because it has a high boiling point and very low volatility (vapor pressure) in an environment of 100 ° C. or lower. As described above, even if it is basically used at 95 ° C. or lower), it is unlikely that the concentration will decrease due to the volatility of the solute.

When an organic alkaline compound is used as an etchant, four methyl groups of the quaternary ammonium hydroxide are substituents, and tetramethylammonium hydroxide (TMAH), which has a low molecular weight and a low boiling point, has a boiling point of 130 ° C. or higher. Therefore, even if a wet etching solution containing a typical quaternary ammonium hydroxide as an etchant is used at a high temperature, the concentration does not easily decrease due to volatilization.

Examples of the wet etching method in the second cleaning step include a wet etching method, a spin etching method, and a spray etching method in which an etching solution is supplied to the surface to be etched, and these can be performed individually or in combination. .. Of these, wet etching and spin etching, which are performed by supplying an etching solution to the surface to be etched, are effective, and a method in which both are combined is preferable. By spin rotation during spin etching, the mask blank substrate can be quickly moistened with an etching solution, and after wetting, the etching solution can be subsequently supplied to the substrate surface to perform wet etching. By doing so, it is possible to prevent variations in the etching progress due to differences in the contact time with the etching solution, and to avoid the risk of cross contamination. Further, by supplying an etching solution to the surface of the substrate and performing wet etching, the amount of the etching solution used can be reduced.

Further, by making the temperature of the first main surface of the substrate uniform and appropriately supplying the etching solution to the first main surface of the substrate, the liquid film of the etching solution on the first main surface of the substrate can have substantially the same thickness. For example, the etching reaction can be carried out uniformly. When wet etching is performed by supplying an etching solution to the first main surface of the substrate, the etching solution can be statically applied to the entire surface of the first main surface of the substrate to be processed before etching.

In the second cleaning step, in order to make the in-plane distribution of the temperature of the glass substrate more uniform, for example, as described in Patent Document 1 (Japanese Unexamined Patent Publication No. 2015-184523), with the main surface to which the etching solution is supplied. A liquid such as pure water whose temperature has been adjusted to a temperature higher than normal temperature can be supplied to the opposing main surface side. As a result, the in-plane distribution of the temperature of the glass substrate is suppressed. The reaction rate of the etching reaction differs depending on the contact temperature between the etching solution and the glass substrate, but the strength of the etching reaction can be made uniform by suppressing the in-plane distribution of the glass substrate temperature.

As the cleaning device that can be used in the second cleaning step, a cleaning device (etching device) as shown in FIGS. 2 and 3 shown in Patent Document 1 can be used, but the cleaning device is not limited thereto. In the second cleaning step, a cleaning device as shown in FIG. 1 described in the above-mentioned first cleaning step may be used.

In the second cleaning step, it is preferable to supply the etching solution only on one main surface and perform wet etching while swinging the etching solution on one main surface. As used herein, the term "swing" refers to a repetitive rotational motion within a predetermined angle range, for example, a range of ± 30 degrees (preferably a range of ± 15 degrees). By swinging the etching solution, foreign matter on the first main surface of the mask blank substrate in the second cleaning step can be removed more effectively. As a result, it is possible to more effectively prevent the occurrence of etching steps caused by foreign matter.

In the second cleaning step, as in the case of the first cleaning step, an etching solution to which ultrasonic waves having a frequency of 2.0 MHz or more and 5.0 MHz or less is applied from the etching solution supply nozzle is applied to one main surface of the glass substrate. Can be supplied so as to hit.

(Rinse cleaning process)
After the etching by the second cleaning step, a rinsing cleaning step for removing the etching solution remaining on the mask blank substrate is performed. Since the main purpose of the rinsing cleaning step is to remove the etching solution, at least pure water cleaning may be performed. An example of a cleaning method in the rinse cleaning step is a spin cleaning method. Preferably, by supplying a cleaning liquid (ultrasonic cleaning liquid) to which ultrasonic waves are applied or warm water of about 40 ° C. to 60 ° C. on the mask blank substrate, the alkaline component adsorbed on the surface of the mask blank substrate is efficiently removed. can do. Moreover, it can be performed particularly effectively by performing spin cleaning and ultrasonic cleaning liquid or the above-mentioned hot water in combination. The second cleaning step and the cleaning after the second cleaning (rinse cleaning step) are preferably repeated a plurality of times, for example, 3 to 5 times in succession.

As described above, the mask blank substrate can be manufactured.

(Manufacturing of mask blank)
The present invention is a method for manufacturing a mask blank, which comprises forming a thin film for forming a transfer pattern on one main surface of the mask blank substrate obtained by the above-mentioned method for manufacturing a mask blank substrate. be. According to the present invention, it is possible to obtain a mask blank in which the occurrence of etching steps (convex defects) caused by foreign matter is reduced.

A thin film is formed on the mask blank substrate after the above cleaning step, and a light-shielding film used for the binary mask blank, a light transflective film for a halftone phase shift mask blank, or a multilayer reflective film for a reflective mask. And an additional functional film are formed depending on the type of the mask blank substrate and the use of the transfer mask.

(1) Binary Mask Blank A binary mask blank is manufactured by forming a thin film containing a light-shielding film on a synthetic quartz glass substrate that has been treated up to the wet etching step. The light-shielding film (thin film for transfer pattern) is a material containing a simple substance of a transition metal selected from chromium, tantalum, ruthenium, tungsten, titanium, hafnium, molybdenum, nickel, vanadium, zirconium, niobium, palladium, rhodium and the like, or a compound thereof. Can be formed with. For example, the light-shielding film can be formed of chromium or a chromium compound containing one or more elements selected from elements such as oxygen, nitrogen, and carbon in chromium. Further, for example, the light-shielding film can be formed of a tantalum compound containing one or more elements selected from elements such as oxygen, nitrogen, and boron in tantalum.

On the other hand, the light-shielding film can be formed of a material containing a transition metal and silicon. For example, the light-shielding film can be formed of a transition metal silicide compound containing one or more elements selected from oxygen and nitrogen in the transition metal and silicon. As the transition metal, molybdenum, tantalum, tungsten, titanium, hafnium, nickel, vanadium, zirconium, niobium, palladium, ruthenium, rhodium, chromium and the like can be applied. On the other hand, the light-shielding film can be formed of a material containing silicon. For example, the light-shielding film can be formed of a silicon compound obtained by adding one or more elements selected from oxygen and nitrogen to silicon.

Such a binary mask blank has a light-shielding film having a two-layer structure of a light-shielding layer and a front surface antireflection layer, or a three-layer structure in which a back surface antireflection layer is further added between the light-shielding layer and a glass substrate. .. Further, the composition gradient film may have a composition in which the composition of the light-shielding film in the film thickness direction is continuously or stepwise different.

(2) Phase shift mask blank The phase shift mask blank is in the form of having a light semitransmissive film (thin film for transfer pattern) on a synthetic quartz glass substrate treated up to the wet etching step, and the light semitransmissive film. A halftone type phase shift mask is produced, which is a type in which a shifter portion is provided by patterning.

In such a phase shift mask, in order to prevent a pattern defect of the transferred glass substrate due to the light semitransmissive film pattern formed in the transfer region based on the light transmitted through the light semitransparent film, the light semitransmissive film is formed on the glass substrate. There is a form having a light-shielding film (light-shielding band) on the light-shielding film. In addition to the halftone type phase shift mask blank, there are mask blanks for the Levenson type phase shift mask and the enhancer type phase shift mask, which are the glass substrate digging type in which the glass substrate is dug by etching or the like to provide a shifter portion. Can be mentioned.

The light semitransmissive film of the halftone type phase shift mask blank transmits light of an intensity that does not substantially contribute to exposure (for example, 1% to 30%, preferably 1% to 20% with respect to the exposure wavelength). Those having a predetermined phase difference (for example, 150 degrees to 200 degrees). A light semi-transmissive portion in which the light semi-transmissive film is patterned and a light transmissive portion that transmits light having an intensity that substantially contributes to exposure, in which the light semi-transmissive film is not formed, transmit the light semi-transmissive portion. The phase of light is substantially inverted with respect to the phase of light transmitted through the light transmitting portion. Therefore, the light that has passed near the boundary between the light transmissive portion and the light transmissive portion and wraps around the other region due to the diffraction phenomenon cancels each other out. As a result, the contrast, that is, the resolution of the boundary portion can be improved by setting the light intensity at the boundary portion to almost zero.

Examples of the light semi-transmissive film include a material composed of a material containing a transition metal and silicon, and the transition metal and silicon containing one or more elements selected from oxygen, nitrogen and carbon. As the transition metal, molybdenum, tantalum, tungsten, titanium, hafnium, nickel, vanadium, zirconium, niobium, palladium, ruthenium, rhodium, chromium and the like can be applied.

Further, in the case of a form having a light-shielding film on the light-transmissive film, since the material of the light-transmissive film contains a transition metal and silicon, the light-shielding film material has etching selectivity with respect to the light-transmissive film. It is preferable to have (having etching resistance). The light-shielding film is particularly preferably composed of chromium or a chromium compound obtained by adding elements such as oxygen, nitrogen, and carbon to chromium.

Since the Levenson type phase shift mask is manufactured from a mask blank having the same structure as the binary type mask blank, the structure of the pattern forming thin film is the same as that of the light shielding film of the binary type mask blank. The light semitransmissive film of the mask blank for the enhancer type phase shift mask transmits light of an intensity that does not substantially contribute to exposure (for example, 1% to 30% with respect to the exposure wavelength), but transmits it. A film having a small phase difference generated in the exposure light (for example, a phase difference of 30 degrees or less, preferably 0 degrees). In this respect, the light semitransmissive film of the mask blank for the enhancer type phase shift mask is different from the light semitransmissive film of the halftone type phase shift mask blank. The material of this light semi-transmissive film contains the same elements as the light semi-transmissive film of the halftone type phase shift mask blank, but the composition ratio and film thickness of each element are predetermined with a predetermined transmittance with respect to the exposure light. It is adjusted so that the phase difference is small.

Further, in order to reduce the film thickness of the resist film to form a fine pattern, an etching mask film may be provided on the light-shielding film. The etching mask film preferably has etching selectivity (having etching resistance) with respect to etching of the light-shielding film. At this time, the mask blank may be produced with the etching mask film left on the light-shielding film by providing the etching mask film with an antireflection function.

When the light-shielding film is formed of the above-mentioned chromium compound, the etching mask film is made of a silicon compound in which elements such as oxygen, nitrogen, and carbon are contained in silicon, which is a material having etching selectivity for the light-shielding film. It is preferable to use the same material. When the light-shielding film is made of the above-mentioned transition metal silicide compound, tantalum compound, or silicon compound, the etching mask film is made of chromium or chromium, which is a material having etching selectivity for these light-shielding films. It is preferably composed of a material made of a chromium compound containing elements such as oxygen, nitrogen and carbon.

In the case of a multi-gradation mask blank having a laminated structure of the semi-transmissive film and the light-shielding film, the material of the semi-transmissive film is the same element as the light semi-transmissive film of the halftone type phase shift mask blank. In addition, metal simple substances such as chromium, tantalum, titanium, and aluminum, alloys thereof, or materials containing compounds thereof are also included. The composition ratio and film thickness of each element are adjusted so as to have a predetermined transmittance with respect to the exposure light. As the material of the light-shielding film, the light-shielding film of the binary mask blank can be applied. Further, the composition and film thickness of the light-shielding film material can be adjusted so as to have a predetermined light-shielding performance (optical density) in the laminated structure of the light-shielding film and the semi-transmissive film.

Further, in the above-mentioned various thin films, an etching stopper film having etching resistance to the light-shielding film or the light-transmissive film may be provided between the glass substrate and the light-shielding film, or between the light-transmissive film and the light-shielding film. good. The etching stopper film may be a material capable of simultaneously peeling off the etching mask film when etching the etching stopper film.

(3) Reflective Mask Blank In the case of the reflective mask blank, low thermal expansion glass (for example, SiO _2- TiO ₂ glass) that has been subjected to the wet etching step is used as the mask blank substrate. The thin film of the reflective mask has a structure in which a multilayer reflective film that reflects exposure light is formed on a glass substrate, and an absorber film (thin film for transfer pattern) that absorbs exposure light is formed in a pattern on the multilayer reflective film. Has.

The multilayer reflective film is formed by alternately laminating high refractive index layers and low refractive index layers.

Examples of the multilayer reflective film include a Mo / Si periodic laminated film in which Mo films and Si films are alternately laminated for about 40 cycles, a Ru / Si periodic multilayer film, a Mo / Be periodic multilayer film, and a Mo compound / Si compound periodic multilayer film. , Si / Nb periodic multilayer film, Si / Mo / Ru periodic multilayer film, Si / Mo / Ru / Mo periodic multilayer film, Si / Ru / Mo / Ru periodic multilayer film and the like. The material can be appropriately selected depending on the exposure wavelength. Further, the absorber film has a function of absorbing exposure light such as EUV light, and for example, tantalum (Ta) alone or a material containing Ta as a main component can be preferably used.

(Manufacturing of transfer mask)
The present invention is a method for producing a transfer mask, which comprises patterning a thin film of a mask blank obtained by the above-mentioned method for producing a mask blank to form a transfer pattern. According to the present invention, it is possible to obtain a transfer mask in which the occurrence of etching steps (convex defects) caused by foreign matter is reduced.

The method for producing a transfer mask of the present invention includes a step of forming a transfer pattern on a thin film of the mask blank produced by the above-mentioned method for producing a mask blank. Hereinafter, a process of manufacturing a transfer mask from a mask blank will be described. The mask blank used here is the halftone type phase shift mask blank described in (2) above. This phase shift mask blank has a structure in which a translucent film (thin film for forming a transfer pattern) and a light-shielding film are sequentially laminated on a translucent substrate. Further, the method for manufacturing this transfer mask (phase shift mask) is an example, and it is possible to manufacture the mask even if some procedures are changed.

First, a resist film is formed on the light-shielding film of the phase shift mask blank by a spin coating method. For this resist film, a chemically amplified resist for electron beam exposure drawing is preferably used. Next, the transfer pattern to be formed on the light transflective film is exposed and drawn on the resist film with an electron beam, and a predetermined process such as development is performed to form a resist pattern having the transfer pattern. Subsequently, dry etching is performed on the light-shielding film using the resist pattern as a mask to form a transfer pattern to be formed on the light-transmitting film on the light-shielding film. After dry etching, the resist pattern is removed. Next, the light semi-transmissive film is dry-etched using a light-shielding film having a transfer pattern as a mask to form a transfer pattern on the light semi-transmissive film. Subsequently, the resist film is formed again, a pattern to be formed on the light-shielding film (a pattern such as a light-shielding band) is exposed and drawn with an electron beam, and a predetermined process such as development is performed to form a resist pattern. The light-shielding film is dry-etched using a resist pattern having a pattern such as a light-shielding band as a mask to form a pattern such as a light-shielding band on the light-shielding film. Then, a predetermined cleaning treatment or the like is performed to complete a transfer mask (phase shift mask).

Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples.

(Experiments 1-6)
In Experiments 1 to 6, the glass substrate was etched with a predetermined cleaning liquid (etching liquid), and the etching rate was measured.

(Preparation and polishing process of glass substrate)
The glass substrate used is a synthetic quartz glass substrate (size 152.4 mm × 152.4 mm, thickness 6.35 mm). The end face of this synthetic quartz glass substrate was chamfered and ground, and the glass substrate that had been roughly polished and precision polished with a polishing solution containing cerium oxide abrasive grains was set in the carrier of the double-sided polishing device, and the following was set. Polishing (ultra-precision polishing) was performed under the conditions.
Polishing pad: Soft polisher (suede type)
Abrasive liquid: Colloidal silica abrasive grains (average particle size 100 nm) + water Processing pressure: 50 to 100 g / cm ²
Processing time: 60 minutes After the ultra-precision polishing was completed, colloidal silica abrasive grains were removed, and the main surface and end faces of the glass substrate were brush-cleaned.

(Evaluation of etching rate of glass substrate)
The etching rate when wet etching was performed on the synthetic quartz glass substrate prepared as described above with the cleaning liquids (etching liquids) of Experiments 1 to 6 was measured. The etching rate was measured by immersing the glass substrate in a cleaning liquid for 72 hours with a part of the glass substrate masked, cleaning the glass substrate, and then measuring the size of the step generated by the etching. Table 1 shows the composition and etching rate of the etching solutions of Experiments 1 to 6. In Table 1, "TMAH" is tetramethylammonium hydroxide and "EDTA" is edetic acid.

As is clear from Table 1, the pH is in the range of more than 9 and less than 11, and the etching rate when the cleaning solutions of Experiments 1 to 3 containing no chelating agent are used is 0.02 nm / hour or less, and the pH is It can be seen that the pH is 11 or more and is considerably smaller than that of the cleaning solution containing the chelating agent. Therefore, if the cleaning solutions of Experiments 1 to 3 are used, the etching rate for the glass substrate can be reduced, so that the foreign matter can be removed without the occurrence of the etching step caused by the foreign matter. Therefore, it can be said that the cleaning solutions of Experiments 1 to 3 are suitable as the cleaning solution used in the first cleaning step.

On the other hand, as is clear from Table 1, in the case of the cleaning liquids of Experiments 4 to 6 containing a chelating agent, the pH is 11 or more, and the etching rate for the glass substrate is 0.05 nm / hour or more. It can be seen that it is relatively large. Therefore, if the cleaning solutions of Experiments 4 to 6 are used as the cleaning solution used in the second cleaning step, the etching rate for the glass substrate can be increased, so that minute foreign substances that could not be removed in the first cleaning step can be removed. Can be done. Therefore, it can be said that the cleaning liquids of the cleaning liquids of Experiments 4 to 6 are suitable as the cleaning liquid used in the second cleaning step.

(Example 1)
As Example 1, the first cleaning step was performed under the conditions of Experiment 3 and the second cleaning step was performed under the conditions of Experiment 6 to produce a mask blank substrate.

Ten glass substrates were prepared in the same procedure as in Experiments 1 to 6 above, and ultra-precision polishing was performed. After the completion of ultra-precision polishing, the glass substrate was immersed in hydrofluoric acid for cleaning to remove colloidal silica abrasive grains. Next, scrub cleaning was performed on the main surface and end faces of the glass substrate, spin cleaning with pure water, and spin drying were performed. After spin drying, a defect inspection device (M6640 manufactured by Lasertec Co., Ltd.) with a sensitivity of 60 nm using a laser interference confocal optical system was used on the main surface (first main surface) on the side where the thin film of 10 glass substrates was formed. Defect inspection was performed. As a result, an average of 49 convex defects having a size equivalent to 100 nm or more were detected on 10 glass substrates, and an average of 1269 convex defects having a size smaller than 100 nm were detected.

Next, as a first cleaning step, ultrasonic cleaning was performed on the first main surface of 10 glass substrates using the cleaning solution of Experiment 3 using the cleaning device shown in FIG. Specifically, ultrasonic waves having a frequency of 2.0 MHz were applied. Further, the flow rate of the cleaning liquid to which the ultrasonic waves flowing down from the ultrasonic cleaning nozzle toward the first main surface of the substrate was applied was adjusted to 1.5 liters / minute. The number of rotations of the substrate during cleaning and the moving speed of the cleaning nozzle were appropriately set.

The substrate was washed for 5 minutes under the above conditions. The first main surface of the glass substrate after the first cleaning step was inspected for defects using the above-mentioned defect inspection apparatus (M6640 manufactured by Lasertec Co., Ltd.). As a result, no convex defects having a size equivalent to 100 nm or more were detected on the 10 glass substrates, but 153 convex defects having a size smaller than 100 nm were detected on average.

Next, the second cleaning step was carried out on the first main surface of the ten glass substrates on which the above-mentioned first cleaning step was carried out. As the cleaning liquid (wet etching liquid), the cleaning liquid of Experiment 6 above was used. The etching solution was supplied at 1 L / min. 2 and 3 show a schematic view of the cleaning device used in the second cleaning step.

The alkaline etching in the second cleaning step includes spin etching in which the etching solution heated to 60 ° C. is supplied to the front main surface 101 of the glass substrate 100 which is spin-rotated, and spin etching in which the supply of the etching solution is stopped and the etching solution is stopped on the glass substrate 100. Wet etching performed by the liquid film of the etching solution formed in the above was continuously performed.

FIG. 4 shows the flow of the second cleaning step (including the rinsing cleaning step). First, the glass substrate 100 subjected to the first cleaning step is fixed by the holding member 28 of the wet etching apparatus 1 (step S1). Next, the distance between the back side main surface (second main surface) 102 of the glass substrate 100 and the stage 12 is adjusted to be 1 mm (step S2). Pure water at 60 ° C. is supplied from the hole 18 of the stage 12 toward the back side main surface 102, and as shown in FIG. 3, a liquid film flow of warm pure water 202 is formed between the back side main surface 102 and the stage 12 (step). S3). At the same time, the nozzle 37 is moved onto the glass substrate 100 by the rotation mechanism 36, and the glass substrate is spin-rotated (step S4). After that, warm pure water at 60 ° C. is supplied from the nozzle 37 to the front main surface (first main surface) 101 of the glass substrate to sufficiently warm the substrate (step S5).

After that, the position is adjusted by using the rotation mechanism and the expansion / contraction mechanism so that the tip of the nozzle 34 faces the center of the front main surface 101 of the glass substrate. At this time, the position of the nozzle 37 is adjusted in a timely manner so that the nozzle 37 and the arm 35 do not interfere (contact) with the nozzle 34 and the arm 32. Then, the turntable (stage 12) is rotated (10 rpm), the warm pure water from the nozzle 37 is stopped, and the alkaline etching solution is supplied from the nozzle 34 to the front main surface 101 of the glass substrate (step S6). Next, the rotation speed of the turntable is reduced to stand still, spin etching is completed (step S7), and the supply of the alkaline etching solution is stopped (step S8).

Then, while continuing to supply warm pure water to the back side main surface 102, wet etching was performed with a liquid film of the etching solution formed on the front side main surface 101 of the glass substrate (step S9). Next, a rinsing cleaning step was performed in which pure water was supplied onto the front main surface 101 of the glass substrate 100 and the etching solution on the front main surface 101 was replaced with warm pure water (step S10). During this period, a liquid film flow of pure water was continuously formed on the back side main surface 102 side. Warm pure water was supplied from the nozzle 37 and the nozzle 42 to the front main surface 101. The temperature of the warm pure water used for cleaning was initially set to 60 ° C, and set to 40 ° C at the timing when complete replacement with the alkaline etching solution was completed. The nozzle 42 is provided with an ultrasonic oscillator, and the pure water supplied from the nozzle 42 is ultrasonic wave applied water. By using the ultrasonic wave-applied water, foreign substances and chemical components lifted off from the front main surface 101 can be efficiently removed. The ultrasonic wave applied water was supplied onto the glass substrate 100 at 1 L / min from the nozzle 42.

When the cleaning step is completed, the process returns to the step of starting the spin rotation of the substrate (step S4) (the supply of warm pure water to the back side main surface 102 remains continuous). This step S4 to step S10 is repeated three times. Then, when the final cleaning step was completed, the glass substrate 100 was spin-dried.

The second cleaning step was performed on 10 glass substrates as described above to produce a mask blank substrate. Each mask blank substrate was inspected for defects with the above-mentioned defect inspection device (M6640 manufactured by Lasertec Co., Ltd.). No convex defects with a size of 100 nm or more were detected on the 10 glass substrates, and only 3 convex defects with a size of less than 100 nm were detected on average.

As a result, the 10 glass substrates produced by the method of Example 1 were able to achieve a high level of foreign matter removal in all regions of the surface subjected to the etching treatment before and after etching.

Further, when a magnified image was confirmed by the magnified image display function of the defect inspection device for each place where a convex defect having a size equivalent to 100 nm or more was detected in the defect inspection of the glass substrate before the first cleaning step, any glass was found. No etching step was observed at the relevant part of the substrate due to foreign matter adhering to the main surface of the glass substrate.

(Comparative Example 1)
As Comparative Example 1, a mask blank substrate was produced in the same manner as in Example 1 except that the first cleaning step was performed under the conditions of Experiment 5 and the second cleaning step was performed under the conditions of Experiment 6.

Defect inspection was performed on the main surface (first main surface) of the 10 glass substrates before the first cleaning step on the side where the thin film was formed, using the above-mentioned defect inspection apparatus (M6640 manufactured by Lasertec Co., Ltd.). As a result, 42 convex defects having a size equivalent to 100 nm or more were detected on average, and 1124 convex defects having a size smaller than 100 nm were detected on average in the 10 glass substrates of Comparative Example 1.

Next, the first cleaning step was performed on the 10 glass substrates of Comparative Example 1. The first main surface of the glass substrate after the first cleaning step was inspected for defects using the above-mentioned defect inspection apparatus (M6640 manufactured by Lasertec Co., Ltd.). As a result, an average of 8 convex defects having a size equivalent to 100 nm or more were detected on 10 glass substrates, and an average of 123 convex defects having a size smaller than 100 nm were detected.

Further, the second cleaning step was performed on the 10 glass substrates of Comparative Example 1. The first main surface of the glass substrate after the second cleaning step was inspected for defects using the above-mentioned defect inspection apparatus (M6640 manufactured by Lasertec Co., Ltd.). As a result, eight convex defects having a size equivalent to 100 nm or more were detected on an average of 10 glass substrates, but only two convex defects having a size smaller than 100 nm were detected on average.

As a result, it was found that the 10 glass substrates produced by the method of Comparative Example 1 could not remove the convex defects having a size equivalent to 100 nm or more. When the magnified image was confirmed by the magnified image display function of the defect inspection device for each of the places where the convex defect having a size equivalent to 100 nm or more was detected, an etching step was observed in each of the corresponding parts of the glass substrate.

(Manufacturing of halftone type phase shift mask blank)
A halftone type phase shift mask blank was manufactured using the mask blank substrate manufactured by the method for manufacturing a mask blank substrate of Example 1.

First, a semitransmissive film made of nitrided molybdenum and silicon was formed on the first main surface of the mask blank substrate. Specifically, a mixing target of molybdenum (Mo) and silicon (Si) (Mo: Si = 10 mol%: 90 mol%) is used, _{and a mixture of argon (Ar), nitrogen (N 2} ) and helium (He) is used. In a gas atmosphere (gas flow ratio Ar: N ₂ : He = 5: 49: 46), the gas pressure is 0.3 Pa, the power of the DC power supply is 3.0 kW, and molybdenum, silicon and molybdenum, silicon and A MoSiN film made of nitrogen was formed with a film thickness of 69 nm. Next, the glass substrate on which the MoSiN film was formed was heat-treated using a heating furnace in the air at a heating temperature of 450 ° C. and a heating time of 1 hour. The MoSiN film had a transmittance of 6.16% and a phase difference of 184.4 degrees under ArF excimer laser exposure light.

The following light-shielding film was formed on the light semi-transmissive film. Specifically, a chromium (Cr) target is used as the sputtering target, _{and a mixed gas atmosphere of argon (Ar), carbon dioxide (CO 2} ), nitrogen (N ₂ ) and helium (He) (gas pressure 0.2 Pa, Gas flow ratio Ar: CO ₂ : N ₂ : He = 20: 35: 10: 30), the power of the DC power supply is 1.7 kW, and a CrOCN layer with a film thickness of 30 nm is formed by reactive sputtering (DC sputtering). Filmed. Subsequently, a mixed gas atmosphere of argon (Ar) and nitrogen (N ₂ ) (gas pressure 0.1 Pa, gas flow rate ratio Ar: N ₂ = 25: 5) was set, the power of the DC power supply was set to 1.7 kW, and the reaction was carried out. A CrN layer having a film thickness of 4 nm was formed by sex sputtering (DC sputtering). Finally, a mixed gas atmosphere of argon (Ar), carbon dioxide (CO ₂ ), nitrogen (N ₂ ) and helium (He) (gas pressure 0.2 Pa, gas flow ratio Ar: CO ₂ : N ₂ : He = 20:35:5:30), the power of the DC power supply is 1.7 kW, a CrOCN layer with a thickness of 14 nm is formed by reactive sputtering (DC sputtering), and a three-layer laminated structure with a total thickness of 48 nm is formed. A chromium-based light-shielding film was formed.

This light-shielding film has a laminated structure with the light semi-transmissive film, and the optical density (OD) is adjusted to be 3.0 at a wavelength of 193 nm of ArF excimer laser exposure light. The surface reflectance of the light-shielding film with respect to the wavelength of the exposure light was 20%.

(Manufacturing of halftone type phase shift mask)
First, a chemically amplified positive resist film for electron beam writing (PRL009 manufactured by Fuji Film Electronics Materials Co., Ltd.) was formed on the mask blank as a resist film. The resist film was formed by rotary coating using a spinner (rotary coating device). After applying the resist film, a predetermined heat-drying treatment was performed. The film thickness of the resist film was 150 nm.
Next, a desired pattern was drawn on the resist film formed on the mask blank using an electron beam drawing apparatus, and then developed with a predetermined developer to form a resist pattern.

Next, the light-shielding film was etched using the resist pattern as a mask. A mixed gas of _{Cl 2} and O ₂ was used as the dry etching gas. Subsequently, the light semi-transmissive film (MoSiN film) was etched to form a light semi-transmissive film pattern. A mixed gas of _{SF 6} and He was used as the dry etching gas.

Next, the remaining resist pattern is peeled off, the same resist film as above is formed on the entire surface again, drawing is performed to form a light-shielding band on the outer peripheral portion of the mask, and after drawing, the resist film is developed to resist. Formed a pattern. Using this resist pattern as a mask, the light-shielding film other than the light-shielding zone region was removed by etching.

Next, the remaining resist pattern was peeled off to obtain a phase shift mask.

In the phase shift mask obtained as described above using the mask blank substrate of Example 1, a fine pattern having a 45 nm half pitch was formed with good pattern accuracy.

(Manufacturing of binary mask blank)
A binary mask blank was manufactured as follows using the glass substrate obtained by the method for manufacturing a mask blank substrate of the example. A MoSiN film (light-shielding layer) and a MoSiN film (surface antireflection layer) were formed as light-shielding films on the first main surface of the glass substrate of the above embodiment, respectively. Using a mixed target of Mo and Si (Mo: Si = 13 at%: 87 at%), in _{a mixed gas atmosphere of Ar and N 2} , a MoSiN film composed of molybdenum, silicon, and nitrogen (membrane composition ratio: Mo: 9. 9 at%, Si: 66.1 at%, N: 24.0 at%) was formed with a film thickness of 47 nm.

Next, using a target of Mo: Si = 13 at%: 87 at%, a MoSiN film composed of molybdenum, silicon, and nitrogen was formed with a film thickness of 13 nm in a mixed gas atmosphere of _{Ar and N 2.} The total film thickness of the light-shielding film was 60 nm.

The optical density (OD) of the light-shielding film (light-shielding layer + surface antireflection layer) was 3.0 at a wavelength of 193 nm of ArF excimer laser exposure light.

Next, the following Cr-based etching mask film was formed on the MoSi-based light-shielding film. Specifically, a CrN film (film) having a film thickness of 5 nm is used by reactive sputtering (DC sputtering) in a mixed gas atmosphere of _{argon (Ar) and nitrogen (N 2} ) using a chromium (Cr) target as the sputtering target. Composition ratio: Cr: 75.3 at%, N: 24.7 at%) was formed into a film. The Rutherford backscattering analysis method was used for the elemental analysis of each layer of the light-shielding film and the Cr-based etching mask film.

(Manufacturing of binary mask for transfer)
A binary mask for transfer was manufactured using the above binary mask blank.

First, a chemically amplified positive resist film for electron beam writing (PRL009 manufactured by Fuji Film Electronics Materials Co., Ltd.) was formed on the mask blank as a resist film. The resist film was formed by rotary coating using a spinner (rotary coating device). After applying the resist film, a predetermined heat-drying treatment was performed. The film thickness of the resist film was 100 nm.

Next, a desired pattern was drawn on the resist film formed on the mask blank using an electron beam drawing apparatus, and then developed with a predetermined developer to form a resist pattern.

Next, the etching mask film was etched using the resist pattern as a mask. A mixed gas of _{Cl 2} and O ₂ was used as the dry etching gas. Subsequently, using the pattern formed on the etching mask film as a mask, the MoSi-based light-shielding film (MoSiN / MoSiN) was etched to form a light-shielding film pattern. As the dry etching gas, _{a mixed gas of SF 6} and He was used.

Next, the remaining resist pattern was peeled off, and the etching mask film pattern was further removed by etching.

In the MoSi-based binary mask obtained as described above using the mask blank substrate of Example 1, a fine pattern having a 32 nm half pitch was formed with good pattern accuracy.

1 Wet etching device 10 Fluid forming means 12 Stage 14 Pillar 18 Hole 20 Glass substrate holding mechanism 28 Holding member 32 Arm 33 Rotating mechanism 34 Nozzle 35 Arm 36 Rotating mechanism 37 Nozzle 40 Arm 41 Rotating mechanism 42 Nozzle 100 Glass substrate (mask) Blank substrate)
101 Main surface on the front side of the glass substrate (first main surface)
102 Main surface on the back side of the glass substrate (second main surface)
201 Wet etching liquid 202 Warm pure water (liquid adjusted to a temperature higher than normal temperature)
301 Substrate 310 Cleaning device 311 Spin chuck 312 Electric motor 313 Cleaning cup 314 Ultrasonic cleaning nozzle 315 Arm 316 Cleaning liquid supply device

Claims (8)

A method for manufacturing a mask blank substrate, which is manufactured from a glass substrate having two main surfaces.
A first cleaning step of cleaning one main surface of the glass substrate with a cleaning solution having a pH greater than 9 and less than 11 and containing no chelating agent.
A second cleaning in which the glass substrate cleaned by the first cleaning step is wet-etched by covering the one main surface of the glass substrate with an etching solution having a pH of 11 or more and containing a chelating agent. A method for manufacturing a substrate for a mask blank, which comprises a process. The method for manufacturing a mask blank substrate according to claim 1, wherein the etching solution used in the second cleaning step is supplied to the one main surface of the glass substrate at a temperature higher than room temperature. The mask according to claim 1 or 2, wherein the etching solution used in the second cleaning step contains one or more alkaline agents selected from sodium hydroxide, potassium hydroxide, and tetramethylammonium. A method for manufacturing a blank substrate. The method for producing a mask blank substrate according to any one of claims 1 to 3, wherein the cleaning liquid used in the first cleaning step contains a surfactant. In the first cleaning step, while rotating the glass substrate, the cleaning liquid to which ultrasonic waves having a frequency of 2.0 MHz or more and 5.0 MHz or less is applied from the cleaning nozzle hits the one main surface of the glass substrate. The method for manufacturing a mask blank substrate according to any one of claims 1 to 4, wherein the mask blank substrate is supplied to. The second cleaning step is characterized in that the etching solution is supplied only on the one main surface, and wet etching is performed while swinging the etching solution on the one main surface. 5. The method for manufacturing a mask blank substrate according to any one of 5. A thin film for forming a transfer pattern is formed on one of the main surfaces of the mask blank substrate obtained by the method for manufacturing a mask blank substrate according to any one of claims 1 to 6. Manufacturing method of mask blank. A method for producing a transfer mask, which comprises patterning the thin film of the mask blank obtained by the method for producing a mask blank according to claim 7 to form a transfer pattern.

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