JP2013074134A - Reflective mask blank, reflective mask, electrostatic chuck and exposure apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask blank capable of suppressing the reduction of flatness at the time attraction using an electrostatic chuck of an EUV exposure apparatus.SOLUTION: A reflective mask blank comprises: an EUV reflection layer 13 for reflecting EUV light; an EUV absorption layer 14 formed on the EUV reflection layer 13; a substrate 12 for supporting the EUV absorption layer 14 via the EUV reflection layer 13; a first conductive film 10 formed on the rear face of the substrate 12 which is on the opposite side to the EUV reflection layer 13; and a second conductive film 11, formed on each lateral face of the substrate 12, which is not brought into electrical conduction with the first conductive film 10. The first conductive film 10 is electrostatically attracted to a rear-side electrostatic attraction surface of an electrostatic chuck, while the second conductive film 11 is electrostatically attracted to a lateral-side electrostatic attraction surface of the electrostatic chuck.

Description

  The present invention relates to a reflective mask blank and a reflective mask used in lithography using EUV (extreme ultraviolet) light. The present invention also relates to an electrostatic chuck and an exposure apparatus that hold the reflective mask by suction.

  In semiconductor manufacturing technology, the increase in speed and capacity of semiconductor devices is largely due to advances in miniaturization technology. Among the miniaturization techniques, in particular, the progress of lithography technology for forming a pattern plays a central role. Recently, higher integration of semiconductor devices is further demanded, and it is difficult to deal with lithography techniques using conventional KrF excimer lasers and ArF excimer lasers under a design rule of 100 nm or less. Therefore, as a lithography technique that can handle such design rules, an EUV lithography technique using extreme ultraviolet light (EUV; Extreme UV), which has the same image forming principle as conventional optical lithography and has a wavelength shorter by one digit or more, is proposed. Has been. In such EUV lithography technology, it has been studied to fix the reflective mask so that EUV light having a wavelength in the vicinity of 13.5 nm can be reflected from the reflective mask from below.

  EUV exposure is used in a state where the reflective pattern surface of the reflective mask faces downward and the back surface is adsorbed by an electrostatic chuck. However, the flatness of the reflective mask can be kept high by bending due to the weight of the reflective mask. Can not. Further, the flatness of the reflective mask may be reduced by the deflection of the electrostatic chuck due to its own weight. The flatness deterioration of the reflective mask is a serious problem due to the fact that EUV light during EUV exposure is obliquely incident, leading to pattern shift during exposure. Therefore, a method has been proposed in which the electrostatic chuck is processed into a concave shape in advance so that the flatness is maintained when the reflective mask is attracted to the electrostatic chuck (see Patent Document 1).

JP 2005-191515 A

  However, in this method, since the reflective mask is actually adsorbed during the processing of the electrostatic chuck, the flatness thereof is measured, and the processing is repeated until a desired flatness is obtained. Furthermore, it is necessary to process the electrostatic chuck for each reflective mask, and it is difficult to control the flatness only by the shape of the electrostatic chuck. In order to avoid such a problem, it is important to control the mask flatness during exposure.

  The present invention has been made by paying attention to the above-described problems, and a first object thereof is a reflective mask blank and a reflective mask that can suppress a decrease in flatness during electrostatic chuck adsorption of an EUV exposure apparatus. Is to provide. A second object of the present invention is to provide an electrostatic chuck capable of suppressing a reduction in flatness of a reflective mask during EUV exposure. A third object of the present invention is to provide an exposure apparatus that can accurately perform EUV exposure using a reflective mask.

  In order to solve the above-described problem, a first aspect of the present invention is an EUV reflection layer that reflects EUV light, an EUV absorption layer formed on the EUV reflection layer, and the EUV reflection layer through the EUV reflection layer. A reflective mask blank including a substrate that supports an EUV absorption layer, wherein a first conductive film is formed on a back surface of the substrate opposite to the EUV reflective layer, and the first conductive film is electrically connected to the first conductive film. A second conductive film that is not electrically conductive is formed on each side surface of the substrate.

In a second aspect of the present invention, each side surface of the substrate is located at a position where the second conductive film is lower than the interface between the EUV reflective layer and the substrate and higher than the interface between the substrate and the first conductive film. It is characterized by being formed.
A third aspect of the present invention is characterized in that the first conductive film is formed on the back surface of the substrate with a width smaller than the length of one side of the substrate.

In a fourth aspect of the present invention, the second conductive film is formed so that a conductive film non-formation region is formed with a width of 0.5 mm or more between the four corners of the substrate and the second conductive film. It is formed on each side surface of the substrate.
According to a fifth aspect of the present invention, the second conductive film is divided into a plurality of regions and formed on each side surface of the substrate.
A sixth aspect of the present invention is a reflective mask produced from the reflective mask blank of any one of the first to fifth aspects.

According to a seventh aspect of the present invention, there is provided an electrostatic chuck that holds the reflective mask of the sixth aspect by attracting and holding the surface of the EUV reflective layer of the reflective mask facing down, with the first conductive film interposed therebetween. A backside electrostatic attracting surface for electrostatically attracting the backside of the substrate and four side surface side electrostatic attracting surfaces for electrostatically attracting the side surface of the substrate through the second conductive film are provided. .
An eighth aspect of the present invention is an exposure apparatus including the electrostatic chuck according to the seventh aspect.

  According to the present invention, the labor and cost of processing the shape of the electrostatic chuck in advance are eliminated, and the flatness of the substrate at the time of exposure can be controlled with high accuracy. In the conventional electrostatic chuck, the flatness is controlled only on the back side of the substrate, but the force pulling the outer periphery of the substrate acts by adsorbing from the side surface of the substrate, which is more accurate than the conventional electrostatic chuck structure. Since the flatness can be controlled, the exposure accuracy is improved. In addition, since the flatness of the substrate is controlled in the suction state at the time of actual exposure, the effect is higher than the improvement of the flatness of the substrate alone.

It is a figure which shows the side surface of the reflective mask blank which concerns on the 1st Embodiment of this invention. It is a figure which shows the side surface and lower surface of the reflective mask blank which concerns on the 2nd Embodiment of this invention. It is a figure which shows the upper surface and side surface of the reflective mask blank which concern on the 3rd Embodiment of this invention. It is a figure which shows the upper surface and side surface of the reflective mask blank which concern on the 4th Embodiment of this invention. It is a top view which shows one Embodiment of the electrostatic chuck which concerns on this invention. It is a figure which shows the AA cross section of FIG. It is a figure which shows the BB cross section of FIG. It is a figure which shows the reflection type mask and electrostatic chuck which were produced by attracting and holding the board | substrate of a reflection type mask blank with the electrostatic chuck of FIG. It is sectional drawing which shows other embodiment of the electrostatic chuck which concerns on this invention. It is a figure which shows the reflection type mask and electrostatic chuck which were produced by attracting and holding the board | substrate of a reflection type mask blank with the electrostatic chuck of FIG.

First, a reflective mask blank according to the present invention will be described with reference to FIGS.
As shown in FIGS. 1 to 4, the reflective mask blank of the present invention includes an EUV reflective layer 13 that reflects EUV light having a wavelength of 13.5 nm ± 5 nm, and an EUV formed on the EUV reflective layer 13. An absorption layer 14 and a substrate 12 that supports the EUV absorption layer 14 via the EUV reflection layer 13 are provided. A first conductive film 10 is formed on the back surface of the substrate 12 opposite to the EUV reflective layer 13, and a second conductive film 11 is formed on each side surface of the substrate 12.

The substrate 12 used in the reflective mask blank of the present invention preferably has a low thermal expansion coefficient (specifically, the thermal expansion coefficient at 20 ° C. is preferably 0 ± 0.1 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.05 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.03 × 10 ⁻⁷ / ° C.), smoothness, flatness, and photomask cleaning after mask blank or pattern formation The thing excellent in the tolerance to the washing | cleaning liquid used for etc. is preferable. Specifically, glass having a low thermal expansion coefficient, such as SiO ₂ —TiO ₂ glass, is used, but is not limited thereto. For example, a substrate made of crystallized glass, quartz glass, silicon, metal, or the like on which β quartz solid solution is deposited can be used. The substrate 12 has a smooth surface with a surface roughness (rms) of 0.15 nm or less, preferably 0.12 nm or less, and a flatness of 100 nm or less, preferably 80 nm or less. A reflective mask is desirable because high reflectivity and transfer accuracy can be obtained. The size, thickness, etc. of the substrate 12 are appropriately determined according to the design value of the mask.

  The EUV reflective layer 13 is not particularly limited as long as it has desired characteristics as a reflective layer of a reflective mask blank. Here, the characteristic particularly required for the EUV reflection layer 13 is a film having a high EUV light reflectance. Specifically, when the surface of the reflective layer is irradiated with light in the wavelength region of EUV light, the maximum value of light reflectance at a wavelength of 13.5 nm ± 5 nm is preferably 60% or more, and 65% or more. It is more preferable.

As the EUV reflection layer 13 satisfying the above characteristics, there is a Si / Mo multilayer film in which 40-50 pairs of Si films and Mo films are alternately laminated. The reason why Mo or Si is used is that the absorption (extinction coefficient) with respect to EUV light is small and the difference in refractive index between Mo and Si EUV light is large. This is because it can be high.
The material of the EUV absorption layer 14 formed on the EUV reflection layer 13 by a method such as sputtering is selected from Ta, TaN, Ta as a main component, Cr, Cr as a main component, N, O, C. A material containing at least one component is used. As other materials, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), and oxides thereof (TaBON, TaSiO, TaO) may be used.

Although not shown, a capping layer formed by depositing Si or Ru by a method such as sputtering is used as an EUV reflective layer 13 and an EUV absorption layer in order to prevent oxidation of the EUV reflective layer 13 and protect it during mask cleaning. 14 may be formed.
Further, an intermediate layer (not shown) serving as an etching stopper layer when the EUV absorption layer 14 is dry-etched may be formed between the EUV reflection layer 13 and the EUV absorption layer 14. Examples of the material for the intermediate layer include Cr, Al, Ru, Ta, and nitrides thereof, and SiO ₂ , Si ₃ N ₄ , Al ₂ O _{3, and the} like. The thickness of the intermediate layer is preferably 10 to 60 nm.

The first conductive film 10 and the second conductive film 11 are used for chucking and holding the substrate 12 with an electrostatic chuck. The conductive films 10 and 11 are made of a material such as Cr or CrN that exhibits conductivity. Mention may be made of metal or metal compound thin films in the range of about 80 to 150 nm.
The conductive films 10 and 11 are preferably a highly conductive conductive film or a dielectric film that generates dielectric polarization when an electric field is applied. Specifically, a film having a volume resistivity of 100 Ω · cm or less is preferable. The sheet resistance of the conductive films 10 and 11 is preferably 100 Ω / square (ohm / square) or less from the viewpoint that the dielectric breakdown of the EUV reflective layer 13 does not occur.

The electrostatic chuck layer of the electrostatic chuck that attracts the reflective mask produced from the reflective mask blank of the present invention is not particularly limited as long as it satisfies the sheet resistance value of the conductive film, but Cr, Ni, Ti , Ta, Mo, Si and W are preferably one or more metal materials selected from the group consisting of W, and Cr is particularly preferable for the following reasons.
The content of the metal material in the chuck layer is preferably 10 to 70 atomic percent (atomic percent) in terms of the chuck layer capability. Since Cr has a high electric conductivity, it is convenient to make the sheet resistance of the conductive films 10 and 11 100Ω / □ (ohm / square) or less. In addition, the conductive film made of Cr is excellent in adhesion to the substrate 12.

The surface hardness of the conductive films 10 and 11 is preferably high. This is to prevent particles from being generated by rubbing between the electrostatic chuck and the conductive films 10 and 11 when the substrate 12 is chucked by the electrostatic chuck.
The film thickness of the conductive films 10 and 11 is preferably 10 to 500 nm. If the film thickness of the conductive films 10 and 11 is less than 10 nm, the adsorption effect may be insufficient when fixed to the conductive film.

The second conductive film 11 formed on the side surface of the substrate 12 is formed by sputtering so that a portion where the conductive film 11 is not formed is covered with a shielding plate so as to be formed only in a desired region.
If the conductive film 11 formed on the side surface of the substrate 12 is electrically connected to the EUV reflective layer 13 or the like, the charge charged in the first conductive film 10 formed on the back surface of the substrate 12 is also transferred to the EUV reflective layer side. As a result, the substrate surface on which films such as the EUV reflection layer 13, the intermediate layer, and the EUV absorption layer 14 are formed is charged.

When the substrate surface is charged, the following problems occur.
Particles in the chamber formed by sputtering are usually positively or negatively charged, so if the substrate surface is charged as described above, some particles are negatively (or positively) charged on the substrate. As a result, the number of defects in the film may increase. In addition, when the EUV reflective layer is a multilayer film, conduction may occur even after the first layer in the EUV reflective layer is formed. As a result of being charged immediately after the first layer is formed, During the formation of all the films constituting the multilayer film, particles are attracted, and as a result, there is a possibility of causing a wide range of defects in the reflective layer.

  Furthermore, a pattern was formed by drawing a fine circuit pattern on the resist film on the reflective mask blank using an electron beam or laser light, and patterning an absorption layer on the reflective mask blank by plasma etching. In each process such as an exposure process in which a pattern is reduced and transferred to a resist film on a Si wafer using a reflective mask, the reflective mask blank and the reflective mask are chucked and held by an electrostatic chuck. For this reason, the EUV reflective layer 13 and the EUV absorption layer 14 formed on the substrate surface are also charged, and the formed pattern may be damaged such as dielectric breakdown.

From the above, the second conductive film 11 formed on the side surface of the substrate 12 is formed so as not to be electrically connected to the film surface of the reflective mask blank.
The state of no conduction means that in the case of a reflective mask blank, the resistance value between the EUV reflective layer 13 and the first conductive film 10 is 1 MΩ or more, particularly 5 MΩ or more, 10 MΩ or more, and further measurement. It is preferable that the resistance value is as high as possible.

  1 to 4, in any case, the first conductive film 10 on the back side of the substrate and the second conductive film 11 on the side surface of the substrate are formed in a positional relationship without conduction. As a result, the electrodes of each electrostatic chuck can output different voltages, and the adsorption force can be changed between the back surface and the side surface of the substrate 12. The second conductive film 11 is formed at a lower height than the EUV reflective layer 13 and is not electrically connected to the EUV reflective layer 13.

  In the reflective mask blank shown in FIG. 1, the second conductive film 11 is lower than the interface between the EUV reflective layer 13 and the substrate 12 and higher than the interface between the substrate 12 and the first conductive film 10. By being formed on the side surface, each second conductive film 11 is electrically insulated from the EUV reflective layer 13 and the first conductive film 10. In this case, the second conductive films 11 formed on the side surfaces of the substrate 12 may be electrically connected to each other. When the second conductive films are electrically connected, the four electrostatic chucks that attract the substrate side surfaces are The same voltage output is controlled, and the same adsorption force acts on the four sides of the outer periphery of the substrate.

  In the reflective mask blank shown in FIG. 2, the first conductive film 10 has a width smaller than the length of one side of the substrate 12 in order to avoid electrical conduction between the first conductive film 10 and the second conductive film 11. It is formed on the back side. At this time, even if the second conductive film 11 is formed at the same height as the interface between the substrate 12 and the first conductive film 10, conduction can be avoided because the first conductive film 10 is smaller than the outer shape of the substrate. .

  In the reflective mask blank shown in FIG. 3, the conductive film non-forming region is 0.5 mm or more between the four corners of the substrate 12 and the second conductive film 11 in order to avoid electrical conduction between the second conductive films. The second conductive film 11 is formed on each side surface of the substrate 12 so as to have a width of 1 mm. Furthermore, since each voltage can be controlled independently by separately providing power supplies connected to the electrodes of the electrostatic chucks on the four sides, it is possible to control the flatness and distortion of the reflective mask blank with high accuracy. .

  FIG. 4 shows a reflective mask blank in which the second conductive film 11 is divided into a plurality of regions and formed on each side surface of the substrate 12. In the reflective mask blank shown in FIG. 4, it can be arranged so that the pins of the holding chuck for substrate transport and process processing are in contact with the portion where the second conductive film 11 on the side surface of the substrate is not formed, Generation of particles due to rubbing with the pins of the holding chuck can be prevented.

Next, the electrostatic chuck according to the present invention will be described with reference to FIGS.
As an electrostatic chuck, (1) the substrate 12 is attracted and held by a Coulomb force generated between the substrate 12 and (2) the substrate 12 is attracted and held by a Johnson Labek force generated at a contact interface with the substrate 12. (3) Non-uniform electrolysis is generated on the substrate surface, and the substrate 12 is adsorbed and held by a gradient force generated between the substrate 12 and the substrate 12.

In the case of a reflective mask blank having a conductive film, the adsorption action of the electrostatic chuck is due to the Coulomb force and the Johnson-Rahbek force. The Coulomb force depends on the dielectric constant of the material forming the dielectric layer, and the Johnson-Rahbek force depends on the volume resistivity of the material forming the dielectric layer. Specifically, the adsorption force when the volume resistivity of the dielectric layer is greater than 10 ¹⁵ Ω · cm is governed by the Coulomb force, and the Johnson-Rahbek force decreases as the volume resistivity of the dielectric layer decreases. It is known that when the volume resistivity value of the dielectric layer is less than 10 ¹² Ω · cm, the attractive force is governed by the Johnson-Rahbek force, which provides a larger attractive force than the Coulomb force. However, if the volume resistivity value of the dielectric layer is less than 10 ⁸ Ω · cm, the amount of leakage current increases and adversely affects the substrate held on the attracting surface, so that the dielectric layer is 10 ⁸ to 10 ¹² Ω. -It is made of a material having a volume resistivity of cm.

  As described above, the electrostatic force depends on the specific resistance value of the dielectric layer, and in the case of the intermediate resistance, both the Coulomb force and the Johnson Rabeck force act. The Coulomb force here is an attracting force that creates a substantially uniform electric field in the thickness direction of the dielectric by giving a potential difference between the electrode and the conductive attractant, and the electrostatic chuck dielectric Includes Johnson Rahbek force generated by lowering resistance.

  On the other hand, when the reflective mask blank does not have a conductive film, it is the same as the case where the object to be attracted is electrically insulating, and an electrostatic chuck that is mainly attracted by a gradient force is used. In order to adsorb and hold a glass substrate with a gradient force, it is necessary to improve the gradient force by densifying the electrodes. Specifically, the distance between the electrodes is narrowed, and the distance from the electrodes to the object to be adsorbed is shortened.

There are two configurations of electrodes built in the electrostatic chuck: a monopolar type and a bipolar type.
The monopolar type is used in the etching, CVD, PVD, and ashing process apparatuses that are plasma processes, and the bipolar type does not require the presence or absence of plasma to perform the adsorption operation. It is also frequently used in charged particle and light exposure processes.
In general, in the case of a unipolar type, it is necessary to take a ground in order to avoid the dielectric breakdown of the object to be adsorbed. On the other hand, in the case of the bipolar type, it is not necessary to ground the back surface of the substrate and the side conductive film.

Depending on the configuration of the electrodes, the substrate may be attracted by a gradient force that generates a non-uniform electric field on the surface of the electrostatic chuck. Specifically, the gradient force acts on the object to be adsorbed by forming electrodes that form a positive and negative pair in a fine pattern having a pattern interval of several millimeters or less and forming an electrode near the surface of the dielectric layer.
Materials that make up the chucking surface of the electrostatic chuck include inorganic materials such as sintered ceramics such as alumina, silicon carbide, and aluminum nitride, or ceramic coating in which alumina or alumina is mixed with titanium oxide, polyimide resin, fluorine resin, etc. Various materials are used up to organic materials. And since the material which comprises this adsorption | suction surface acts also as a dielectric material in an electrostatic chuck, the electrical characteristics, such as a resistance value and a dielectric constant, have big influence on the performance of an electrostatic chuck.

  A bipolar electrode is used as the electrode on the back side of the substrate. For example, in the electrostatic chuck shown in FIG. 5, the back surface side electrostatic adsorption surface 25 for electrostatically adsorbing the back surface (the surface on which the first conductive film 10 is formed) of the substrate 12 is disposed in the center, and this back surface side. A plus-side electrode 22 and a minus-side electrode 23 are formed on the electrostatic chucking surface 25 in a parallel pattern and arranged in a comb-teeth shape. The two electrodes 22 and 23 are formed on the back surface side electrostatic attracting surface 25 with the same area ratio and the area ratio of the electrode occupied with respect to the back side electrostatic attracting surface 25 being 60 to 90% or more. The electrodes 22 and 23 are connected to a positive power source (+ V2 volts) and a negative power source (−V2 volts), respectively, and the back surface side electrostatic attracting surface 25 is supported by the stage 20 as a base.

  Further, in the electrostatic chuck shown in FIG. 5, the electrodes on the side surface side electrostatic attracting surfaces 24, 30, 40, 50 for attracting the side surface of the substrate 12 are as shown in FIGS. 6 and 7. A monopolar electrode 21 is used. The electrodes 21 formed on the side surface electrostatic attracting surfaces 24, 30, 40 and 50 are grounded from the electrode side opposite to the electrostatic chuck in order to avoid insulation breakdown on the substrate surface side. Then, as shown in FIG. 8, in a state where the reflective mask 100 is adsorbed, a ground wire is taken from the vicinity of the end on the substrate surface side.

  As shown in FIG. 5, the electrodes 21 formed on the electrostatic chucking surfaces 24, 30, 40, 50 on the side surface of the electrostatic chuck are connected to power sources V3, V4, V5, V6, respectively, and different voltages are applied to the respective electrodes. By applying to the electrode 21, the adsorption force can be changed on the four sides of the substrate 12. At this time, as shown in FIG. 3, the second conductive film is formed so that the conductive film non-forming region is formed with a width of 0.5 mm or more between the four corners of the substrate 12 and the second conductive film 11. It is preferable to form the film 11 on each side surface of the substrate 12 because electrical conduction between the conductive films does not occur between the side surfaces of the substrate 12.

  By connecting each electrode 21 of the side surface side electrostatic attracting surfaces 24, 30, 40, 50 to the power source on the plus side or the minus side, the second conductive film 11 has a charge opposite to that on the electrode side, As a result, an attractive force is generated between the electrodes 21 on the side surface electrostatic attracting surfaces 24, 30, 40, and 50 and the second conductive film 11 on the side surface of the substrate.

  Like the electrostatic chuck shown in FIG. 9, each electrode 21 of the side surface side electrostatic adsorption surfaces 24, 30, 40, 50 that adsorb the side surface of the substrate 12 may be a bipolar type, and the electrode 21 is a bipolar type. This eliminates the need for grounding. In this case, as shown in FIG. 10, the two electrodes 21 are formed on the side surface electrostatic attracting surfaces 24, 30, 40, and 50 so as to have almost the same area as the second conductive film 11 on the side surface of the substrate. The adsorption force of the electrostatic chuck to the side surface of the substrate can be increased. Further, by forming the two electrodes 21 on the side surface side electrostatic attracting surfaces 24, 30, 40, 50 at a distance of 0.5 mm or more, discharge breakdown can be avoided.

In general, the bipolar type has a smaller adsorbing force than the monopolar type, and therefore it is necessary to increase the applied voltage as compared with the case of the monopolar type. In addition, the electrodes are arranged in a comb-like dense parallel pattern, the width between the electrodes is narrowed, and the distance between the conductive film on the back surface of the substrate and the electrodes is shortened, so that a nonuniform electric field is generated on the surface of the electrostatic chuck. It is generated and the electrostatic adsorption force due to the gradient force acts.
In addition, this invention is not limited to said embodiment.

Hereinafter, embodiments of the present invention will be described more specifically with reference to examples.
(Production of reflective mask blanks)
As a substrate for the reflective mask blank, a low expansion SiO ₂ —TiO ₂ glass substrate having an outer diameter of 6 inches square and a thickness of 6.3 mm was used. Next, after mechanically polishing the surface of the glass substrate until the surface roughness becomes 0.2 nmRms or less and the flatness becomes 30 nm, an EUV reflection layer, an etching stopper layer, and an EUV absorption layer are sequentially formed on the surface of the glass substrate by sputtering. Formed. In this process, the flatness of the convex shape was emphasized, and finally a reflective mask blank having a flatness of 50 nm and a reflective film surface having a convex shape was obtained.

(Production of reflective mask)
Next, using a reflective mask blank, a reflective mask having a desired pattern was produced by the following method.
First, an EB resist was applied on the reflective mask blank, dried, and subjected to EB drawing, a PEB process, and a development process to form a resist pattern. Using this resist pattern as a mask, the EUV absorption layer was dry etched using chlorine to form an EUV absorption pattern. Thereafter, the resist pattern remaining on the EUV absorption pattern is removed, and the intermediate layer composed of the underlying CrN film is removed by etching using a mixed gas of chlorine and oxygen using the EUV absorption pattern as a mask, and the reflective type A mask was prepared.

Next, in order to perform EUV exposure using a reflective mask, as shown in FIG. 8, the reflective film surface of the reflective mask 100 faces downward, and the reflective mask 100 is attracted by the electrostatic chuck shown in FIG. Retained. In this state, EUV exposure was performed. At this time, the reflective film surface of the reflective mask 100 held by suction on the electrostatic chuck was grounded to prevent charging of the reflective film surface.
In such EUV exposure, distortion due to the electrostatic chuck and the substrate's own weight is applied to the reflective mask 100, so that it is important to control the flatness during exposure. The deterioration of the flatness of the reflective mask leads to a pattern shift at the time of exposure due to the property of oblique incidence of EUV light during EUV exposure, which is a major problem. Therefore, the reflective mask was actually electrostatically chucked on the stage of the exposure apparatus. In the state, it is important to reduce the flatness.

The flatness of the reflective mask surface side was measured while the reflective mask 100 was attracted and held by the back surface side electrostatic attracting surface 25 provided on the stage 20 in the exposure apparatus. At this time, the reflective mask had a convex flatness of 100 nm. The side electrostatic attracting surfaces 24, 30, 40, and 50 were retracted at positions that did not contact the substrate side without applying voltage.
Next, after moving the side surface electrostatic attracting surfaces 24, 30, 40, 50 to positions where they can be attracted, based on the measured flatness, the back side electrostatic attracting surface is set so that the flatness becomes a desired value. 25 and the applied voltages to the side surface electrostatic attracting surfaces 24, 30, 40, and 50 were individually controlled. As a result, the flatness was improved to 30 nm, and a desired flatness was obtained.

That is, the flatness of the mask substrate is measured with the electrostatic chuck in the EUV exposure apparatus holding only the back side of the substrate by suction, and the side surface of the substrate is divided so that the flatness becomes more appropriate from the measurement result. In addition, the electrostatic chuck can be individually controlled to adjust the flatness distortion to a value suitable for exposure. Deterioration of the surface flatness due to the formation of the reflection pattern and surface flatness deterioration during electrostatic chucking can be suppressed, and it is possible to contribute to improvement of exposure accuracy such as EUV exposure.
When applying a voltage to each electrode on the side surface of the substrate after adsorbing the back surface of the substrate, it is not necessary to apply a voltage to each electrode on the side surface of the substrate at the same time. May be adjusted.

  DESCRIPTION OF SYMBOLS 10 ... 1st electrically conductive film, 11 ... 2nd electrically conductive film, 12 ... Board | substrate, 13 ... EUV reflection layer, 14 ... EUV absorption layer, 20 ... Stage, 21, 22, 23 ... Electrode, 25 ... Back surface side electrostatic adsorption surface 24, 30, 40, 50... Side surface electrostatic adsorption surface, 100.

Claims (8)

A reflective mask blank comprising an EUV reflection layer that reflects EUV light, an EUV absorption layer formed on the EUV reflection layer, and a substrate that supports the EUV absorption layer via the EUV reflection layer. And
A first conductive film is formed on the back surface of the substrate opposite to the EUV reflective layer, and a second conductive film that is not electrically connected to the first conductive film is formed on each side surface of the substrate. A reflective mask blank characterized by that.   The second conductive film is formed on each side surface of the substrate at a position lower than an interface between the EUV reflective layer and the substrate and higher than an interface between the substrate and the first conductive film. The reflective mask blank according to claim 1.   The reflective mask blank according to claim 1, wherein the first conductive film is formed on the back surface of the substrate with a width smaller than the length of one side of the substrate.   The second conductive film is formed on each side of the substrate such that a conductive film non-formation region is formed with a width of 0.5 mm or more between the four corners of the substrate and the second conductive film. The reflective mask blank according to claim 1, wherein the reflective mask blank is provided.   The reflective mask blank according to any one of claims 1 to 4, wherein the second conductive film is divided into a plurality of regions and formed on each side surface of the substrate.   A reflective mask produced from the reflective mask blank according to claim 1.   An electrostatic chuck that holds the reflective mask according to claim 6 by holding the EUV reflective layer surface of the reflective mask facing down, and electrostatically chucks the back surface of the substrate through the first conductive film. An electrostatic chuck comprising: a back surface side electrostatic adsorption surface; and four side surface side electrostatic adsorption surfaces that electrostatically adsorb the side surface of the substrate through the second conductive film.   An exposure apparatus comprising the electrostatic chuck according to claim 7.

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