JP2009160681A - Manufacturing method of mask blanking substrate, manufacturing method of substrate with multilayer reflective film, and manufacturing method of reflective mask blank as well as manufacturing method of reflective mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mask blanking substrate capable of reducing fine surface defects on a substrate surface, and having high smoothness and reduced variation in surface roughness among substrates and within a substrate plane, a reflective mask blank with high reflectance and reduced variation in reflectance among the substrates and within the substrate plane, and a reflective mask free from transfer pattern defects caused by the fine surface defects and the variation in the reflectance among the substrates and within the substrate plane. <P>SOLUTION: A manufacturing method includes a polishing step of supplying a polishing liquid containing polishing abrasive grains onto a surface of a glass substrate and polishing the surface of the glass substrate by relatively moving the glass substrate and a polishing pad, wherein the polishing abrasive grain is colloidal silica and the polishing liquid with pH ranging 1-5 and a negative (minus) sign of zeta-potential is used. A multilayer reflective film 2 and an absorber film 4 are formed on the obtained mask blanking substrate 1 to make the reflective mask blank 10, and the absorber film 4 in the reflective mask blank 10 is patterned to form an absorber pattern to make the reflective mask 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a mask blank substrate, a method for manufacturing a substrate with a multilayer reflective film using the substrate, a method for manufacturing a reflective mask blank, and a method for manufacturing a reflective mask. It relates to a manufacturing method.

The demand for surface smoothness and surface defects of a glass substrate for mask blanks is becoming more and more severe year by year due to the recent increase in density and accuracy of VLSI devices. Here, as a precision polishing method for reducing the surface roughness of a conventional glass substrate for mask blank, for example, there is one described in Patent Document 1 (Japanese Patent Laid-Open No. 64-40267). In this precision polishing method, polishing is performed using an abrasive mainly composed of cerium oxide, and then finish polishing is performed using colloidal silica.
Patent Document 2 below (Japanese Patent Laid-Open No. 2006-35413) includes a polishing slurry containing colloidal silica having an average primary particle size of 50 nm or less and adjusted to have a pH in the range of 0.5 to 4. A method of using and polishing a glass substrate surface is disclosed.

JP-A 64-40267 JP 2006-35413 A

  According to the study of the present inventor, it has been found that even if the technique described in the above-mentioned prior art document is used, it does not satisfy a high level condition for surface smoothness and surface defects demanded in recent years. That is, on the surface of the glass substrate obtained by the polishing method listed in the prior art, a convex protrusion having a height of about several nm to several tens of nm and a size of about several tens of nm to 2,000 nm, and a depth of several It was found that concave defects having a size of about nm to 200 nm and a size of about several tens of nm to 500 nm were formed. This is a defect inspection device developed to confirm the demand for high-level surface defect freeness that has recently been demanded for minute convex protrusions and concave defects that cannot be confirmed by conventional visual inspection. This was the first time I could confirm. Such surface defects are formed because the pH value (hydrogen ion concentration) of the polishing liquid during polishing changes, and the zeta potential of the polishing abrasive fluctuates accordingly. This is thought to be due to the deterioration of sex. That is, the abrasive grains dispersed in the polishing liquid have a zeta potential, but when the zeta potential is close to 0 (zero) mV, the abrasive grains are likely to aggregate, and the polishing abrasive grains in the polishing liquid tend to aggregate. Dispersibility deteriorates. In the case of standard colloidal silica that can be used as abrasive grains, the zeta potential can be either + (plus) or-(minus) depending on the pH value (for example, the zeta potential is + in the acidic range where the pH is 5 or less). (Plus), the zeta potential is-(minus) in an alkaline region where the pH is 8 or more), and may approach zero in the process.

  For example, when a reflective mask blank in which a multilayer reflective film and an absorber film are formed on a glass substrate in which such minute convex protrusions and concave defects are formed on the substrate surface, and a reflective mask are produced, These surface defects cause transfer pattern defects. In other words, if a convex or concave defect exists in the vicinity of the pattern on the mask surface, a phase change caused by the defect occurs in the reflected light. This change in phase causes the positional accuracy and contrast of the transferred pattern to deteriorate. In particular, when short-wavelength light such as extreme ultraviolet (Extreme Ultra Violet, hereinafter EUV) light having a wavelength of about 0.2 to 100 nm is used as exposure light, the phase change is very large with respect to fine irregularities on the mask surface. Therefore, the influence on the transferred image is increased. For example, when the height of the convex protrusion is 5 nm, the exposure wavelength is 13.5 nm and the phase change exceeds 20 degrees. As a result, the CD error is poor and cannot be ignored. In the case of a reflective mask blank, as a reflective film for exposure light on a substrate, for example, in the case of an alternating laminated film of Si and Mo, a multilayer film in which a thin film of about several nm is laminated at least 80 layers (40 cycles) or more is used. Therefore, even if the defect on the substrate surface is a minute defect that does not cause a problem, the formation of the multilayer reflection film results in the formation of a multilayer reflection film surface in which the uneven shape of the substrate surface is increased.

  Further, when the zeta potential of the abrasive grains is changed during polishing and the dispersibility of the abrasive grains is deteriorated, there is a problem that the polishing speed is changed and the surface roughness varies between substrates. Variations in the surface roughness of the substrate cause variations in the reflectance of the exposure light in the multilayer reflective film formed on the substrate, so variations in the surface roughness between the substrates are reflected between the substrates in the reflective mask. This causes variation and further transfer pattern defects. Further, not only between the substrates but also the variation in the surface roughness within the substrate surface occurs, which causes the variation in the reflectance within the substrate surface in the reflective mask, and further causes the transfer pattern defect.

As described above, the requirements for the surface smoothness and surface defects of the mask blank substrate (particularly, the reflective mask blank substrate for EUV exposure) are very strict, and the conventional polishing as described in the above-mentioned prior art documents. Even if the processing method is applied and the state of the polishing liquid is optimized at the beginning, the pH value of the polishing liquid and the zeta potential of the abrasive grains change during the polishing process, and the dispersibility of the abrasive grains is unstable. Therefore, it is actually very difficult to stably obtain a highly smooth and defect-free substrate surface that satisfies the above requirements.

Accordingly, the present invention provides a mask blank substrate manufacturing method that reduces minute surface defects on the substrate surface, is highly smooth, and reduces variations in surface roughness between substrates and in the substrate surface. One purpose.
In addition, the present invention provides a method for manufacturing a substrate with a multilayer reflective film, in which minute surface defects on the substrate surface are reduced, and in addition, the reflectance variation between substrates and in the substrate surface is reduced, and a reflective mask blank. It is a second object to provide a manufacturing method.
Furthermore, the present invention provides a method for manufacturing a reflective mask free from phase defects and pattern defects caused by minute surface defects on the substrate surface, or transfer pattern defects caused by reflectance variations between substrates and in the substrate surface. This is the third purpose.

As a result of intensive studies to solve the above-described problems, the present inventors have found that during the polishing process in order to satisfy the high level requirements for surface smoothness and surface defects required for recent mask blank substrates. With the recognition that it is necessary to suppress fluctuations in the state of the polishing liquid, the present invention having the following configuration has been completed.

(Configuration 1) A polishing pad is brought into contact with the surface of the glass substrate, a polishing liquid containing abrasive grains is supplied to the surface of the glass substrate, and the glass substrate and the polishing pad are moved relative to each other to form the glass substrate. A method for producing a glass substrate for a mask blank having a polishing step of polishing the surface of the substrate, wherein the polishing abrasive grains are colloidal silica, and the pH of the polishing liquid is in the range of 1 to 5, and the sign of zeta potential A method for producing a mask blank substrate, wherein a polishing liquid having a (polarity) of-(minus) is used.
As in Configuration 1, the abrasive grains contained in the polishing liquid used in the polishing step are colloidal silica, the pH of the polishing liquid is in the range of 1 to 5, and the sign (polarity) of the zeta potential is − (minus). ), The sign (polarity) of the zeta potential of the polishing liquid containing colloidal silica abrasive grains is − (minus) in the acidic range where the pH of the polishing liquid is in the range of 1 to 5. Therefore, colloidal silica abrasive grains dispersed in the polishing liquid do not agglomerate and maintain a good dispersibility, and the state of the polishing liquid is stable, so that minute surface defects on the substrate surface are reduced and high A mask blank substrate is obtained which is smooth and reduces variations in surface roughness between substrates and within the substrate surface.

(Structure 2) The mask blank substrate according to claim 1, wherein the polishing liquid has a zeta potential fluctuation within a range of -30 mV to 0 (zero) in a pH range of 1 to 5. Manufacturing method.
In particular, as shown in Configuration 2, by using a polishing liquid having a small change in zeta potential such that the change in zeta potential in the range of pH 1 to 5 is in the range of −30 mV to 0 (zero). Further, even when used for a long time, the abrasive grains do not aggregate and the polishing liquid is kept in a stable state, so that the effect of the invention of Configuration 1 is further exhibited.
(Structure 3) The cleaning liquid for use in the mask blank according to Structure 1 or 2, wherein a cleaning liquid having a zeta potential sign (polarity) of-(minus) is used as a cleaning liquid used in the cleaning process after the polishing process. A method for manufacturing a substrate.
And like the structure 3, it is preferable to use the washing | cleaning liquid whose code | symbol (polarity) of zeta potential is-(minus) as a washing | cleaning liquid used by the washing | cleaning process after the said grinding | polishing process. This makes it possible to reliably remove the abrasive grains remaining on the substrate surface by washing without using a highly acidic or alkaline cleaning solution, and to prevent the occurrence of convex defects due to the adhesion of the abrasive grains. it can.

(Structure 4) The mask blank substrate according to any one of Structures 1 to 3, wherein the substrate is a multi-component glass substrate.
Further, as in Configuration 4, the present invention is suitable when the mask blank substrate is a multi-component glass substrate. The multi-component glass substrate can improve the polishing speed when an acidic polishing liquid is used.
(Structure 5) The mask blank substrate according to Structure 1 or 2, wherein the substrate is a glass substrate containing SiO ₂ and TiO ₂ .
And, when the mask blank substrate is a glass substrate containing SiO ₂ and TiO ₂ that is frequently used for a reflective mask blank for EUV exposure, as in Configuration 5, surface defects are reduced and high smoothness is achieved. The resulting invention is particularly suitable.

(Structure 6) A method for producing a substrate with a multilayer reflective film, comprising: forming a multilayer reflective film that reflects exposure light on the surface of the mask blank substrate according to any one of Structures 1 to 5.
As in Configuration 6, by forming a multilayer reflective film that reflects exposure light on the surface of the mask blank substrate, minute surface defects on the surface of the substrate are reduced, and between the substrates and with high reflectivity. A substrate with a multilayer reflective film with reduced reflectance variation in the substrate surface can be obtained.
(Structure 7) A method for producing a reflective mask blank, wherein an absorber film for preventing reflection of exposure light is formed on the multilayer reflective film in the substrate with a multilayer reflective film described in Structure 6.
Further, as in Configuration 7, by forming an absorber film that prevents reflection of exposure light on the multilayer reflective film in the substrate with the multilayer reflective film, minute surface defects on the substrate surface can be reduced and high A reflection type mask blank in which the reflectance variation between the substrates and in the substrate surface is reduced by the reflectance is obtained.

(Structure 8) A method for manufacturing a reflective mask, comprising forming an absorber pattern by patterning the absorber film in a reflective mask blank obtained by the method for manufacturing a reflective mask blank according to Structure 7. .
Moreover, according to the reflection type mask obtained by patterning the absorber film in the reflection type mask blank and forming the absorber pattern as in the configuration 8, the substrate surface is transferred during pattern transfer onto the semiconductor substrate. It is possible to prevent the occurrence of phase defects and pattern defects caused by minute surface defects, or transfer pattern defects caused by variations in reflectance between substrates and in the substrate surface.

ADVANTAGE OF THE INVENTION According to this invention, the board | substrate for mask blanks which reduced the surface defect on the surface of a board | substrate, and was highly smooth and reduced the dispersion | variation in the surface roughness between board | substrates and in a board | substrate surface can be provided.
In addition, according to the present invention, the mask blank substrate according to the present invention is used to reduce a minute surface defect on the substrate surface, and with high reflectivity, a multi-layer with reduced reflectivity variation between substrates and in the substrate surface. A substrate with a reflective film and a reflective mask blank can be provided.
Further, according to the present invention, using the reflective mask blank according to the present invention, transfer caused by phase defects and pattern defects caused by minute surface defects on the substrate surface, or reflectance variations between substrates and in the substrate surface. A reflective mask free of pattern defects can be provided.

Hereinafter, a method for manufacturing a mask blank substrate according to the best mode for carrying out the present invention, a method for manufacturing a substrate with a multilayer reflective film using the mask blank substrate, a method for manufacturing a reflective mask blank, and this A manufacturing method of the reflective mask using the reflective mask blank will be described in detail.

In the method for manufacturing a mask blank substrate according to the present invention, a polishing pad is brought into contact with the surface of a glass substrate, a polishing liquid containing abrasive grains is supplied to the surface of the glass substrate, and the glass substrate and the polishing pad are combined. A method for producing a glass substrate for a mask blank having a polishing step of polishing the surface of the glass substrate by relatively moving, wherein the abrasive grains are colloidal silica, and the pH of the polishing liquid is 1-5. A polishing liquid having a zeta potential sign (polarity) of-(minus) is used.

  Thus, the abrasive grains contained in the polishing liquid used in the polishing step are colloidal silica, the pH of the polishing liquid is in the range of 1 to 5, and the sign (polarity) of the zeta potential is − (minus). By using the polishing liquid, the polishing liquid containing colloidal silica abrasive grains has a zeta potential sign (polarity) of-(minus) in the acidic range where the pH of the polishing liquid is in the range of 1 to 5. Colloidal silica abrasive grains dispersed in the liquid do not aggregate and can maintain a good dispersibility. Therefore, since the state of the polishing liquid is always stable during polishing, by performing polishing using such a stable polishing liquid, it is possible to reduce minute surface defects on the surface of the substrate, and it is highly smooth, A mask blank substrate with reduced variations in surface roughness between substrates and in the substrate surface can be obtained. In addition, when a multilayer reflective film that reflects exposure light, for example, is formed on such a mask blank substrate, high reflectance can be obtained, and variation in reflectance between substrates and in the substrate surface can be reduced. .

The mask blank substrate is preferably a glass substrate because good smoothness and flatness can be obtained by polishing. The material of the glass substrate is not particularly limited. Examples of the material of the glass substrate include synthetic quartz glass, borosilicate glass, aluminosilicate glass, aluminoborosilicate glass, soda lime glass, alkali-free glass, crystallized glass, and low thermal expansion glass (for example, SiO ₂ —TiO ₂ type). Glass).
The present invention is suitable when the mask blank substrate is a multi-component glass substrate. In the case of a multi-component glass substrate, the polishing speed can be improved particularly when an acidic polishing liquid is used. In particular, when the mask blank substrate is a glass substrate containing SiO ₂ and TiO ₂ frequently used for a reflective mask blank for EUV exposure, for example, the present invention can reduce surface defects and obtain a highly smooth substrate. Is particularly preferred.

In the polishing step, for example, a mask blank substrate (glass substrate) is pressed against a polishing surface plate to which a polishing pad is adhered, and the polishing surface plate and the substrate are relatively moved while supplying a polishing liquid containing polishing abrasive grains. The surface of the substrate is polished by moving the substrate (that is, relatively moving the polishing pad and the substrate). In this polishing step, a planetary gear type double-side polishing apparatus described later can be used. The polishing may be either double-side polishing or single-side polishing.

In the present invention, as the polishing liquid, a polishing liquid in which the pH of the polishing liquid is in the range of 1 to 5 and the sign (polarity) of the zeta potential is − (minus) is used. Colloidal silica abrasive dispersed in the polishing liquid when the sign (polarity) of the zeta potential of the polishing liquid containing colloidal silica abrasive grains is-(minus) in the acidic range where the pH of the polishing liquid is in the range of 1 to 5. The grains do not aggregate, and the dispersibility of the colloidal silica abrasive grains in the polishing liquid is good and a stable state can be maintained.
In the present invention, the polishing liquid is particularly preferably a polishing liquid in which the fluctuation of the zeta potential in the range of pH 1 to 5 is in the range of −30 mV to 0 (zero). By using a polishing liquid with little fluctuation in zeta potential in such an acidic range of pH 1 to 5, the polishing liquid does not aggregate even if used for a long time, and the polishing liquid remains stable. Therefore, the effect by this invention can be exhibited further.

In the present invention, the polishing liquid has an acidic range with a pH in the range of 1 to 5. In the case of a glass substrate (especially a multicomponent glass substrate), the polishing speed can be improved by an acidic polishing liquid. As described above, in order to obtain a polishing liquid in an acidic region having a pH of 1 to 5, it is preferable to adjust the pH to a range of 1 to 5 by including, for example, an inorganic acid in the polishing liquid.
Although it does not necessarily limit as said inorganic acid, For example, hydrochloric acid, a sulfuric acid, nitric acid, phosphoric acid, boric acid. Phosphonic acid. Examples include phosphinic acid, and among these, at least one selected from hydrochloric acid, sulfuric acid, and phosphoric acid is particularly preferable. This is because when these hydrochloric acid, sulfuric acid, and phosphoric acid are used, excessive erosion of the substrate surface particularly in a multi-component glass substrate can be suppressed, and surface roughness of the substrate can be prevented.
The content of the inorganic acid may be an appropriate content for adjusting the pH of the polishing liquid to an acidic range of 1 to 5.

In addition, in the course of the polishing process, ions contained in the glass substrate are eluted into the polishing liquid, and the pH of the polishing liquid may fluctuate, affecting the polishing speed, the zeta potential of the abrasive grains, etc. In the present invention, in order to keep the pH of the polishing liquid during polishing in the range of 1 to 5 as much as possible, it is preferable to contain an organic acid in addition to the inorganic acid. Examples of organic acids that can be preferably used in the present invention for such purposes include tartaric acid, maleic acid, malonic acid and the like.
The content of the organic acid varies depending on the type of inorganic acid used, the content, and the pH value of the polishing liquid, so it cannot be said unconditionally, but is generally in the range of about 0.1 wt% to 0.4 wt%. It is preferable to do. Preferably, the organic acid content is 0.2 wt% to 0.3 wt%.

In the present invention, colloidal silica is preferably used as the abrasive grains from the viewpoint of obtaining good smoothness and flatness of the glass substrate. In the present invention, a polishing liquid in which the pH of the polishing liquid is in the range of 1 to 5 and the zeta potential sign (polarity) is − (minus) is used, but the zeta potential sign (polarity) of the polishing liquid is Since it is mainly determined by the sign (polarity) of the zeta potential of the colloidal silica in the polishing liquid, in the present invention, the colloidal whose zeta potential sign (polarity) is-(minus) in the pH range of 1 to 5. Silica is preferably used. That is, in the acidic range where the pH of the polishing liquid is in the range of 1 to 5, the sign (polarity) of the zeta potential of the colloidal silica abrasive grains is − (minus), so that the abrasive grains dispersed in the polishing liquid aggregate. This is because the dispersibility can be kept in a good state without doing so. Thus, when the colloidal silica abrasive grains have a zeta potential sign (polarity) of-(minus) in the pH range of 1 to 5, nonionic (nonionic) colloidal silica, anionic colloidal silica, cation Any of colloidal silica may be used. The colloidal silica abrasive grains have a zeta potential sign (polarity) of-(minus) in the pH range of 1-5, and the zeta potential fluctuation in the pH range of 1-5 is -30 mV- It is particularly preferable that it is within the range of 0 (zero). In this way, by using colloidal silica abrasive grains with little fluctuation in zeta potential in the pH range of 1 to 5, the abrasive grains do not aggregate even if used for a long time, and the state of the polishing liquid is stabilized. Can keep.
The conditions such as the formulation and temperature of the polishing liquid containing polishing abrasive grains, the material of the polishing pad, the processing pressure, and the polishing time are appropriately set so as to obtain desired smoothness.

After the substrate surface is mirror-polished so that predetermined smoothness can be obtained by the polishing step, a step of performing local processing on the substrate surface may be performed as necessary.
For example, as a mask blank substrate for EUV exposure, a glass substrate having a low thermal expansion (for example, a SiO ₂ —TiO ₂ substrate or the like) is usually used in order to suppress distortion of a transfer pattern due to heat during exposure. In the case of a mask blank substrate for EUV exposure, high flatness is required in addition to high smoothness in order to prevent pattern distortion and displacement during pattern transfer. Therefore, after the polishing process, local processing mainly for the purpose of increasing the flatness may be performed. In this method, the surface shape of the substrate surface after the polishing process is measured, the convex portion is specified, and the convex portion is locally processed under processing conditions corresponding to the height (convexity) of the convex portion. The local processing can be performed by, for example, plasma etching, ion beam (gas cluster ion beam, etc.) or the like. However, a work-affected layer may be generated by such local processing, and in this case, short-time polishing for the purpose of removing the work-affected layer may be performed as necessary after the local processing.

In addition, after the polishing step (or the polishing step and the local processing step) is performed, the substrate surface is washed to remove abrasive grains adhering to the substrate surface. As the cleaning liquid used in the cleaning process after the polishing process, it is preferable to use a cleaning liquid having a zeta potential sign (polarity) of-(minus). As a result, the polishing abrasive grains remaining on the substrate surface can be reliably removed by cleaning without using a strong acidic or alkaline cleaning liquid that tends to cause roughening of the substrate surface after cleaning. The occurrence of convex defects can be prevented, and the substrate surface form obtained by the polishing step or the like can be maintained well after cleaning.
As described above, a mask blank substrate can be obtained in which minute surface defects on the substrate surface are reduced, and the surface roughness is highly smooth and reduced in surface roughness between substrates and in the substrate surface.

Next, the production of a substrate with a multilayer reflective film using a mask blank substrate according to the present invention, a reflective mask blank, and a reflective mask using them will be described.
By forming a multilayer reflective film that reflects exposure light on the surface of the mask blank substrate obtained according to the present invention, minute surface defects on the surface of the multilayer reflective film are reduced, and the reflectance between the substrates and A substrate with a multilayer reflective film with reduced reflectance variation in the substrate surface can be obtained.
In addition, by forming an absorber film that prevents reflection of exposure light on the multilayer reflective film in the substrate with the multilayer reflective film, minute surface defects on the surface of the multilayer reflective film are reduced, and high reflectivity is achieved. Thus, a reflective mask blank with reduced reflectance variation between substrates and within the substrate surface can be obtained.

The production of a substrate with a multilayer reflective film and a reflective mask blank according to the present invention, and the production of a reflective mask using them include (1) a substrate preparation step, and (2) film formation of a multilayer reflective film on the substrate. (3) Buffer film (intermediate layer) film forming process, (4) Exposure light absorber film forming process, (5) Resist coating process, (6) Drawing process, (7) Etching process It consists of a process. Hereinafter, a description will be given with reference to FIG.

(1) A substrate preparation step. The substrate 1 preferably has a low coefficient of thermal expansion, and is excellent in smoothness, flatness, and resistance to a cleaning solution used for cleaning a mask, etc., and glass having a low coefficient of thermal expansion, for example, SiO ₂ —TiO ₂ type Although glass etc. are used, it is not limited to this, Crystallized glass, quartz glass, silicon | silicone, a metal, etc. board | substrate which precipitated (beta) quartz solid solution can also be used. As an example of the metal substrate, an Invar alloy (Fe—Ni alloy) or the like can be used. By using the mask blank substrate of the present invention as the substrate 1, a reflective mask blank having high reflectivity and reduced reflectance variation between substrates and in the substrate surface can be obtained.

(2) Step of forming a multilayer reflective film on the substrate (see FIG. 1A). As the multilayer reflective film 2, an alternating laminated film made of Mo and Si is frequently used. As a material capable of obtaining a high reflectance in a specific wavelength range, Ru / Si, Mo / Be, Mo compound / Si compound, An Si / Nb periodic multilayer film, an Si / Mo / Ru periodic multilayer film, an Si / Mo / Ru / Mo periodic multilayer film, an Si / Ru / Mo / Ru periodic multilayer film, or the like may be used. However, the optimum film thickness varies depending on the material. In the case of a multilayer film composed of Mo and Si, a Si film is first formed in an Ar gas atmosphere using a Si target by a DC magnetron sputtering method, and then a Mo film is used in an Ar gas atmosphere using a Mo target. Is formed as a single cycle, and 30 to 60 cycles, preferably 40 cycles, are stacked, and finally a Si film is formed. By this step, a substrate with a multilayer reflective film is obtained.

(3) A film forming process of the buffer film (intermediate layer) (see FIG. 1A). CrN is often used as the material of the buffer film 3 (which has a function as an etching stopper for the multilayer reflective film at the time of patterning by etching of the absorber film), but depending on the conditions for etching the absorber film 4, etching resistance SiO ₂ or the like may be used as a highly material. When CrN is used, it is preferable to form a CrN film on the multilayer reflective film 2 using a Cr target by a DC magnetron sputtering method in a mixed gas atmosphere of Ar and nitrogen.

(4) Step of forming the exposure light absorber film (see FIG. 1A). As a material of the absorber film 4 for exposure light such as EUV light, a material containing Ta as a main component, a material containing Ta as a main component and containing at least B, an amorphous structure material containing Ta as a main component, and Ta as a main component And an amorphous structure material containing at least B (for example, an amorphous structure material containing about 25% of B represented by Ta ₄ B), a material containing Ta, B, and N (for example, B containing Ta as a main component and B Material having an amorphous structure containing about 15% of N and about 10% of N). Furthermore, in order to reduce the reflectance at the wavelength of the inspection light (usually DUV light) used for mask inspection, it is common to increase the contrast of mask inspection by forming an oxide layer on the absorber film. is there. For example, a material containing Cr as a main component and containing at least one component selected from N, O, and C (for example, a material in which O and C are added to CrN and CrN) is preferable. However, the present invention is not limited to this, and TaSi, TaSiN, TaGe, TaGeN, WN, Cr, TiN, and the like can be used.

The absorber film 4 may be a single layer or a laminated structure. In an example in which a TaB compound thin film is used as the material of the absorber film 4, a TaB film is first formed in an Ar gas atmosphere using a TaB target by a DC magnetron sputtering method, and subsequently in an atmosphere of Ar and oxygen gas, For example, it is preferable to form a TaBO film.
Through the above steps, the reflective mask blank 10 (see FIG. 1A) is obtained.

(5) Resist application process. A reflective mask can be manufactured by forming a pattern on the absorber film 4 of the obtained reflective mask blank 10. An EB resist is applied to the mask blank obtained in step (4) and baked.

(6) Drawing process. A predetermined pattern is drawn on the mask blank coated with the EB resist by using, for example, an EB drawing apparatus and developed to form a resist pattern 5a (see FIG. 1B).

(7) Etching process. Using the resist pattern 5a as a mask, the absorber film 4 is dry-etched, for example, to form the absorber pattern 4a (see FIG. 1B). Then, the resist pattern remaining on the absorber pattern is removed with, for example, hot concentrated sulfuric acid (see FIG. 1C). Further, the underlying buffer film 3 is removed by, for example, dry etching along the absorber pattern 4a. Through this step, the reflective mask 20 is obtained (see FIG. 1D).
If the damage to the multilayer reflective film is small depending on the material of the absorber film 4 and the etching conditions, the buffer film 3 may be omitted. The reflective mask blank referred to in the present invention may have a configuration in which a resist film is formed on the above-described absorber film.

According to the reflective mask obtained by patterning the absorber film in the reflective mask blank obtained by the present invention to form the absorber pattern, a minute surface defect on the substrate surface during pattern transfer onto the semiconductor substrate It is possible to prevent the occurrence of a transfer pattern defect due to a phase defect or a pattern defect due to the above, or a reflectance variation between substrates or in the substrate surface.

  In the above description, the mask blank substrate according to the present invention is applied to a multilayer reflective film-coated substrate and a reflective mask blank. However, the present invention is not limited to this. Is also suitable. The substrate for a phase shift mask blank is also required to have extremely strict requirements for smoothness and surface defects. According to the present invention, high smoothness and reduction of minute defects can be realized, which are caused by minute surface defects. Since a change in phase difference can be suppressed, it is also suitable for a glass substrate for a phase shift mask blank.

Hereinafter, based on an Example, this invention is demonstrated more concretely. In the following example, a reflective mask blank glass substrate for EUV exposure (hereinafter also simply referred to as a glass substrate) will be described as an example of the mask blank substrate.
First, a planetary gear type double-side polishing apparatus used in the polishing process in the following embodiments will be described with reference to FIG.

The planetary gear type double-side polishing apparatus meshes with the sun gear 12, the internal gear 13 arranged concentrically on the outer side thereof, the sun gear 12 and the internal gear 13, and the sun gear 12 and the internal gear 13. A carrier 14 that revolves and rotates in response to rotation, and an upper surface plate 15 and a lower surface plate 16 that can hold a work piece (glass substrate 1) held by the carrier 14 to which a polishing pad 17 is attached; A polishing liquid supply unit (not shown) for supplying a polishing liquid is provided between the upper surface plate 15 and the lower surface plate 16.
At the time of polishing, the workpiece to be polished held by the carrier 14 is sandwiched between the upper surface plate 15 and the lower surface plate 16, and the polishing liquid is provided between the polishing pad 17 of the upper and lower surface plates 15, 16 and the workpiece to be polished. As the sun gear 12 and the internal gear 13 rotate, the upper and lower surfaces of the workpiece are polished while the carrier 14 revolves and rotates.

The following Examples 1 and 2 are specific examples of a method for producing a mask blank glass substrate.
Example 1
The glass substrate that has been subjected to the chamfering and grinding of the end face of the SiO ₂ —TiO ₂ -based low thermal expansion glass substrate (152.4 mm × 152.4 mm) and the rough polishing with the polishing liquid containing cerium oxide abrasive grains is described above. And was polished (precise polishing) under the following polishing conditions.
Polishing pad: Soft polisher (suede type)
Polishing liquid: acidic aqueous solution (pH: 1 to 5) containing anionic colloidal silica abrasive grains (average particle diameter 100 nm)
Processing pressure: 50 to 100 g / cm ²
Processing time: 60 minutes

  In addition, hydrochloric acid and tartaric acid were added to the said polishing liquid, and it adjusted beforehand so that pH might become the range of 1-5. The anionic colloidal silica abrasive grains had a zeta potential of −30 mV to −10 mV in the pH range of 1 to 5. The sign (polarity) of the zeta potential in the pH range of 1 to 5 of the polishing liquid containing the colloidal silica abrasive grains is − (minus), and the fluctuation of the zeta potential in the range of pH 1 to 5 is −30 mV to 0 (zero). It was in the range.

  After the precision polishing, the surface shape of the glass substrate was measured with an optical interference type flatness measuring device. As a result, the flatness of the substrate was 0.2 μm (convex shape). From the obtained surface shape measurement results, the shape was adjusted with a gas cluster ion beam so that the flatness of the glass substrate was the flatness required for the glass substrate for a reflective mask blank for EUV exposure. After adjusting the shape with the cluster ion beam, the flatness of the glass substrate surface was measured and found to be as good as 0.05 μm.

In this way, in order to remove abrasive grains adhering to the glass substrate after precision polishing, the glass substrate is subjected to an alkaline cleaning liquid (NaOH: 5 wt% concentration) in which the sign (polarity) of the zeta potential is − (minus). Was immersed in a cleaning tank containing ultrasonic waves (applied with ultrasonic waves) and washed for 10 minutes.
A plurality of batches of the above-described precision polishing and the like were performed to produce 100 glass substrates (glass substrates for reflective mask blanks for EUV exposure).

The surface roughness of the main surface of the 100 glass substrates thus obtained was very good at root mean square roughness (RMS) of 0.13 nm or less. In addition, the variation in surface roughness (RMS) between the substrates and in the surface of each of the 100 glass substrates thus obtained is within 0.5 to 1.0%, and the variation in surface roughness is extremely high. It was small. The surface roughness was calculated based on data obtained by measurement with an atomic force microscope (AFM).
Further, when the main surface of the obtained glass substrate was examined for minute convex and concave surface defects using a defect inspection apparatus using a laser interference confocal optical system, the number of minute surface defects generated was 0. It was 02 pieces / cm ² .

(Example 2)
In Example 1 described above, the polishing liquid used in the precision polishing step was an acidic aqueous solution (pH: 1 to 5) containing anionic colloidal silica abrasive grains (average particle diameter 100 nm). To the polishing liquid used in this example, sulfuric acid and tartaric acid were added, and the pH was adjusted in advance to be in the range of 1-5. The colloidal silica abrasive grains had a zeta potential of -5 mV to -10 mV in the pH range of 1-5. The sign (polarity) of the zeta potential in the pH range of 1 to 5 of the polishing liquid containing the colloidal silica abrasive grains is − (minus), and the fluctuation of the zeta potential in the range of pH 1 to 5 is −30 mV to 0 (zero). It was in the range.
In this example, except that the polishing liquid having the above composition was used, precision polishing, shape adjustment, and cleaning were performed in the same manner as in Example 1 to obtain a glass substrate (glass substrate for reflective mask blanks for EUV exposure). 100 sheets were produced.

The surface roughness of the main surface of the 100 glass substrates thus obtained was very good at root mean square roughness (RMS) of 0.13 nm or less. In addition, the variation in surface roughness (RMS) between the substrates and in the surface of each of the 100 glass substrates thus obtained is within 0.9 to 1.4%, and the variation in surface roughness is extremely high. It was small.
Further, when the main surface of the obtained glass substrate was examined for minute convex and concave surface defects using a defect inspection apparatus using a laser interference confocal optical system, the number of minute surface defects generated was 0. The number was 08 / cm ² .
Also in this example, it was found that a glass substrate having high smoothness, small variation in surface roughness, and extremely few micro surface defects can be obtained.

(Comparative Example 1)
In Example 1 described above, the polishing liquid used in the precision polishing step was an acidic aqueous solution (pH: 1 to 5) containing cationic colloidal silica abrasive grains (average particle diameter 100 nm). To the polishing liquid used in this comparative example, sulfuric acid was added to adjust the pH in the range of 1 to 5 in advance. Note that tartaric acid was not added to the polishing liquid. During the polishing process, the pH value of the polishing liquid gradually increased with the progress of the polishing process, and could not be maintained within the above range. Further, the cationic colloidal silica abrasive grains take a value of + (plus) in the range of pH 1 to 5, but take a value of-(minus) when the pH becomes 6 or more.
Thus, in this comparative example, except that the polishing liquid having the above composition was used, precision polishing, shape adjustment, and cleaning were performed in the same manner as in Example 1 to obtain a glass substrate (glass substrate for reflective mask blanks for EUV exposure). ) 100 sheets were produced.

When the main surface of the 100 glass substrates thus obtained was examined for minute convex and concave surface defects using a defect inspection apparatus using a laser interference confocal optical system, the number of minute surface defects generated was 2 a .8 pieces / cm ^2, it was found that the microscopic surface defect occurs very much.
Further, the surface roughness of the main surface of the 100 glass substrates thus obtained was all the root mean square roughness (RMS) of 0.15 nm or less. The variation in the surface roughness (RMS) in the substrate surface was larger than that in the above-described example, and the variation in the surface roughness was large.

The large number of minute surface defects and the large variation in surface roughness are caused by fluctuations in the zeta potential of the abrasive grains during polishing (for example, approaching zero), resulting in agglomeration and the like. It is considered that this is because the state of the polishing liquid during the polishing process was unstable due to the deterioration of the dispersibility of the abrasive grains.

(Example 3)
Mo and Si were laminated as the multilayer reflective film 2 on one main surface of the reflective mask blank glass substrate for EUV exposure obtained in Example 1 described above. By DC magnetron sputtering, an Si film is first formed with an Ar gas of 0.1 Pa using a Si target, and then a Mo film is formed with an Ar gas pressure of 0.1 Pa. A film was formed, and this was defined as one period. After 40 periods were laminated, a Si film was finally formed to a thickness of 11 nm. Thus, a substrate with a multilayer reflective film was produced. The reflectance of the multilayer reflective film with respect to exposure light having a wavelength of 13.5 nm was 65%, and a high reflectance was obtained. Further, the variation in reflectance within the substrate surface was within ± 0.5%, which was very small. Furthermore, the variation in the reflectance between the substrates in 100 substrates with multilayer reflection films produced in the same manner was also very small.

Next, a buffer film 3 composed of a CrN film is formed on the multilayer reflective film 2 by a DC magnetron sputtering method using a Cr target and using a mixed gas obtained by adding 20% nitrogen to Ar gas as a sputtering gas. The film was formed to a thickness of 10 nm.

Finally, on the buffer film 3 composed of the CrN film, a film containing Ta, B, and N (Ta: B: N = 70: 15: 15 (atom (Number ratio)) was deposited by DC magnetron sputtering to a thickness of 68 nm. Thus, a reflective mask blank 10 was produced.

Next, using this reflective mask blank, a reflective mask having a design rule of 32 nm half pitch (DRAM) (minimum line width is 128 nm) was produced by the following method.
First, an EB resist was applied on the reflective mask blank 10 and dried, and a resist pattern was formed by EB drawing.
Using this resist pattern as a mask, the absorber film 4 made of TaBN was dry-etched using chlorine to form an absorber pattern. Thereafter, the resist pattern remaining on the absorber pattern is removed, and the buffer film 3 composed of the underlying CrN film is removed by dry etching using a mixed gas of chlorine and oxygen using the absorber pattern as a mask. A reflective mask was prepared.

Using the produced reflective mask, pattern transfer onto a semiconductor substrate was performed by a pattern transfer apparatus (exposure apparatus) shown in FIG. As shown in FIG. 2, EUV light (soft X-rays) obtained from a laser plasma X-ray source 31 is incident on the reflective mask 20, and the light reflected here passes through a reduction optical system 32, for example, a Si wafer substrate 33. Transfer on top.

An X-ray reflecting mirror can be used as the reduction optical system 32. The pattern reflected by the reflective mask 20 by the reduction optical system is usually reduced to about ¼. For example, the transfer of the pattern to the Si wafer substrate 33 can be performed by exposing the pattern to a resist film formed on the Si substrate 3 and developing the pattern. When a wavelength band of 13 to 14 nm is used as the exposure wavelength, transfer is usually performed so that the optical path is in a vacuum.
As a result of performing pattern transfer onto the semiconductor substrate by the pattern transfer apparatus shown in FIG. 2 using the reflective mask obtained in this embodiment, there is no phase defect or pattern defect and high accuracy. It was confirmed that a fine pattern could be formed.

(Comparative Example 2)
On the main surface of the reflective mask blank glass substrate for EUV exposure obtained in Comparative Example 1, the multilayer reflective film 2, the buffer film 3, and the absorber film 4 are sequentially formed in the same manner as in Example 3. A reflective mask blank was prepared by coating.
The reflectance of the multilayer reflective film with respect to exposure light having a wavelength of 13.5 nm was 62%, which was lower than that in Example 3. Further, the variation in reflectance within the substrate surface was ± 1%, which was larger than that of Example 3. Furthermore, the variation in the reflectance between the substrates in 100 substrates with multilayer reflection films produced in the same manner was also larger than that in Example 3. In addition, surface defects due to minute surface defects on the glass substrate surface were observed on the surface of the multilayer reflective film.
Next, using this reflective mask blank, a reflective mask was fabricated in the same manner as in Example 3.

As a result of performing pattern transfer onto the semiconductor substrate by the pattern transfer apparatus shown in FIG. 2 using the reflective mask obtained in this comparative example, phase defects and pattern defects are generated, and further transfer is performed. The pattern accuracy of the image was also poor. This is because, in this comparative example, the occurrence of surface defects on the surface of the multilayer reflective film due to the presence of minute surface defects on the surface of the glass substrate and variations in surface roughness between and within the substrate surface, the reflectance This is probably due to the large variation.

It is typical sectional drawing which shows the manufacturing process of a reflection type mask. It is a block diagram of a pattern transfer apparatus (exposure apparatus). It is sectional drawing which shows schematic structure of the double-side polish apparatus of the planetary gear system used in a grinding | polishing process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Multilayer reflective film 3 Buffer film 4 Absorber film 10 Reflective mask blank 12 Sun gear 13 Internal gear 14 Carrier 15 Upper surface plate 16 Lower surface plate 17 Polishing pad 20 Reflective mask 50 Pattern transfer apparatus

Claims (8)

A polishing pad is brought into contact with the surface of the glass substrate, a polishing liquid containing abrasive grains is supplied to the surface of the glass substrate, and the surface of the glass substrate is polished by relatively moving the glass substrate and the polishing pad. A method of manufacturing a mask blank glass substrate having a polishing step to perform,
The mask is characterized in that the polishing abrasive is colloidal silica, and the polishing solution has a pH of 1 to 5 and a polishing solution having a zeta potential sign (polarity) of-(minus). A method for manufacturing a blank substrate.   2. The method of manufacturing a mask blank substrate according to claim 1, wherein the polishing liquid has a zeta potential fluctuation in a range of pH of 1 to 5 in a range of −30 mV to 0 (zero).   The mask blank substrate according to claim 1 or 2, wherein a cleaning liquid having a zeta potential sign (polarity) of-(minus) is used as a cleaning liquid used in the cleaning step after the polishing step. Method.   The method for producing a mask blank substrate according to any one of claims 1 to 3, wherein the substrate is a multi-component glass substrate. The method for manufacturing a mask blank substrate according to claim 4, wherein the substrate is a glass substrate containing SiO ₂ and TiO ₂ .   A multilayer reflective film for reflecting exposure light is formed on the surface of a mask blank substrate obtained by the method for producing a mask blank substrate according to any one of claims 1 to 5. A method for manufacturing a substrate with a substrate.   A method for producing a reflective mask blank, comprising: forming an absorber film for preventing reflection of exposure light on the multilayer reflective film in the substrate with a multilayer reflective film according to claim 6. A method for manufacturing a reflective mask, comprising forming an absorber pattern by patterning the absorber film in a reflective mask blank obtained by the method for manufacturing a reflective mask blank according to claim 7.

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