JP5703841B2 - Reflective mask - Google Patents

Description

  The present invention relates to a reflective mask and an exposure apparatus, and more specifically, a reflection film and an absorption film are formed on a film formation surface of a glass substrate, and the reflection is held by contacting the back surface with respect to the film formation surface. The present invention relates to a mold mask and an exposure apparatus cleaning method.

  2. Description of the Related Art Conventionally, in the semiconductor industry, a photolithography method using visible light or ultraviolet light has been used as a technique for transferring a fine pattern necessary for forming an integrated circuit on a Si (silicon) substrate or the like. Semiconductor integrated circuits are being miniaturized and highly integrated in order to improve performance and productivity, and also with regard to lithography technology for forming circuit patterns, technological development for forming finer patterns with high precision Is underway.

  Along with this, the light source of the exposure apparatus used for pattern formation has been shortened, and extreme ultraviolet light (Extreme Ultra Violet light; hereinafter referred to as “EUV light”) having a wavelength of 13.5 nanometers (nm). ) And pattern transfer processes have been developed.

  Since EUV light is easily absorbed by all substances including air and has a refractive index close to 1, a conventional refractive optical system such as photolithography using visible light or ultraviolet light cannot be used. Therefore, in a lithography apparatus using EUV light as a light source (hereinafter referred to as “EUV exposure apparatus”), a reflective optical system, that is, a reflective photomask (hereinafter referred to as “EUV mask”) in a vacuum environment. .) And a mirror.

  As shown in FIG. 4, a conventional EUV exposure apparatus mainly includes an EUV light source, an illumination optical system, a mask stage, a projection (imaging) optical system, and a wafer (sensitive substrate) stage coated with EUV photosensitive resin (resist). Composed of etc. In FIG. 4, 1 is an EUV light source, 2 to 11 are mirrors, 12 'is an EUV mask, 13 is a mask stage, 14 is a wafer, 15 is a wafer stage, and 16 is a housing. Since EUV light is absorbed and attenuated by the atmosphere, all of its optical paths are maintained at a predetermined degree of vacuum.

  In the case of an EUV mask original (mask blanks), as shown in FIG. 3, a reflective layer that reflects EUV light and an absorbing layer that absorbs EUV light are arranged in this order on a substrate (usually a low thermal expansion glass substrate) 103. It has the structure formed by. The reflective layer is composed of two different layers (high refractive layer and low refractive layer) to give reflectivity to EUV light, and several tens of layers whose thickness is designed to match the phase of the light reflected at the interface A multilayer reflective film 102 made of is used. For the absorption film 101, a material having a high absorption coefficient for EUV light, specifically, a material mainly composed of, for example, chromium (Cr) or tantalum (Ta) is used. In addition, a conductive film 104 having a higher dielectric constant and conductivity than the base material 103 is formed on the back surface of the base material 103.

  The manufactured EUV mask 12 ′ is loaded into the EUV exposure apparatus shown in FIG. 4, and the exposure apparatus is a reflection optical system and an optical system that receives light having an angle of about 6 degrees with respect to the mask. Therefore, if the pattern forming surface of the EUV mask 12 ′ is displaced in the thickness direction, that is, the vertical direction, there is a problem that the image forming position on the wafer 14 is shifted.

  Further, the EUV light that has not been reflected on the EUV mask 12 'is absorbed by the EUV mask 12' and is converted into heat, so that there is a problem of image position displacement due to thermal expansion of the mask. In order to solve the above two problems, the EUV mask original (blanks) is required to have a low thermal expansion substrate having very high flatness.

  At the same time, in order to correct the deflection of the entire mask due to the stress of the film formed on the base material 103, the mask stage 13 of the EUV exposure apparatus placed in a vacuum environment is an ordinary photolithographic exposure apparatus. Similarly, it is located at the counter electrode of the wafer stage 15 and the entire back surface of the mask is adsorbed by an electrostatic chuck made of a material such as ceramic or quartz, and the entire weight of the mask is supported by the electrostatic chuck. Is uniformly defined by the shape of the electrostatic chuck surface.

  Since the glass substrate constituting the base material 103 has a low dielectric constant and electrical conductivity, it is necessary to apply a high voltage to obtain a sufficient chucking force, and there is a risk of causing dielectric breakdown. In order to solve such problems, a film (conductive film 104) of a material having a higher dielectric constant and higher conductivity than that of a glass substrate is usually formed on the side opposite to the pattern formation surface, and the EUV mask 12 ' Increasing the chucking force is performed.

  As the conductive film 104 formed for the purpose of increasing the chucking force of the base material 103, a film mainly composed of Cr is mainly employed. The conductive material has a dielectric constant that is not comparable to an insulator such as glass.

  As described above, the EUV mask 12 ′ is subjected to a very strong adsorption force between the electrostatic chuck and the conductive film 104 formed on the back surface of the substrate 103. For this reason, it has been confirmed by a number of experiments that substances having high rigidity are bonded to each other, and foreign matter bites into and adheres to the back surface conductive film 104 of the EUV mask 12 'to be adsorbed.

  The adhered foreign matter is an inorganic substance in which a part of the chuck constituent material or the conductive film is peeled off by a strong chucking force in addition to the substance adhering to either surface of the electrostatic chuck and the conductive film. In many cases, the EUV mask 12 'cannot be completely removed not only by cleaning chemicals but also by cleaning with physical force such as scrub cleaning.

  Even if cleaning is performed, the foreign matter adhered to the back surface of the EUV mask 12 'causes residual microscopic warpage of the mask surface when it is chucked again on the mask stage 13 of the EUV exposure apparatus, There is a problem that transfer accuracy deteriorates. In addition, by repeatedly sucking the EUV mask 12 ', there is a concern about deterioration of the electrostatic chuck surface, and the flatness of the chuck itself may change.

  In order to solve such a problem, a method of removing foreign substances by slightly removing the back surface conductive film of the EUV mask with an etching solution has been proposed (for example, see Patent Document 1). In addition, as a method for removing foreign matter adhering to the inside of the exposure apparatus, a method for removing foreign matter attached to a mirror placed on the optical path of EUV light has been proposed (for example, see Patent Document 2).

JP 2010-286632 A Japanese Patent No. 4539335

  However, Patent Document 1 can remove only the foreign matter adhered to the back surface conductive film, and does not consider the foreign matter attached to the electrostatic chuck side or the deterioration of the electrostatic chuck caused by repeated attachment and detachment. In addition, Patent Document 2 is also intended to remove foreign matters attached to the mirror surface in the EUV exposure apparatus, and does not consider foreign matters attached on the electrostatic chuck.

  In order to solve the above-described problems of the prior art, the present invention suppresses foreign matter adhering to the surface of the conductive film as a result of the suction holding by the electrostatic chuck, and easily removes the attached foreign matter. An object of the present invention is to provide a method for suppressing deterioration of the material.

According to a first aspect of the present invention, there is provided a reflective mask comprising: a base material; a multilayer reflective layer formed on a surface of the substrate and reflecting a high refractive layer and a low refractive layer that reflects extreme ultraviolet light; and the multilayer reflective layer. comprising an absorbent layer for absorbing EUV light formed on the layer, and formed on the lower surface of the substrate conductive layer, uniformly applied on the lower surface of the conductive film, silicon as an element, fluorine, metal A protective coating composed of an organic polymer containing no element is further provided, and the protective coating is configured to be removable by means without applying physical external force.

  By using the reflective mask and the exposure apparatus of the present invention, it is possible to suppress the generation of inorganic foreign matters that have occurred on the back surface of the EUV mask and the electrostatic chuck surface that are repeatedly attached and detached. Also, it can be easily removed in the process of removing the protective film.

  Thereby, it is possible to suppress the fine warpage of the mask surface caused by the inorganic foreign matter, and the transfer accuracy of the mask can be improved. Further, by applying the present invention to a mask and a mask stage that have already deteriorated on the surface of the electrostatic chuck and the back of the mask due to attachment / detachment or the like, a protective film having a buffering action against foreign matters is formed on the mask surface. In order to suppress warpage, the transfer accuracy of the mask can be increased.

It is sectional drawing which shows an example of the structure of the reflection type mask which concerns on the Example of this invention. It is a figure which shows an example of a structure of the reflection type mask exposure apparatus which concerns on the Example of this invention. It is sectional drawing which shows an example of the structure of the conventional reflective mask. It is a figure which shows an example of a structure of the conventional reflection type mask exposure apparatus.

Hereinafter, a mask and an exposure apparatus of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an EUV mask 12 according to an embodiment of the present invention. In the EUV mask 12 which is a reflection type mask, the EUV light absorbed at the time of exposure is changed into thermal energy. Therefore, the base material 103 is not a synthetic quartz used in a normal photomask, but a low thermal expansion glass doped with TiO _2. Etc. are used. On the base material 103, a multilayer reflective film 102 that reflects EUV light, which is highly transmissive to EUV light and in which high refractive index layers and low refractive index layers are alternately stacked, is formed. An example is a Si / Mo multilayer film in which silicon (Si) films and molybdenum (Mo) films are alternately stacked.

  As a constituent material of the absorption film 101 formed on the multilayer reflective film 102, a material having a high absorption coefficient for EUV light is selected, and specifically, it is often composed of Ta and its nitride. Further, another functional film may be formed between the multilayer reflective film 102 and the absorption film 101 or on the absorption film 101.

  As an example, a protective (capping) film (not shown) may be formed on the multilayer reflective film 102 in order to prevent oxidation of the surface of the multilayer reflective film 102, and ruthenium (Ru) is used as a main raw material. It is comprised from an alloy, Si, etc. In addition, in order to increase the contrast at the time of mask pattern inspection, a low reflection layer (not shown) having a low reflectance with respect to the inspection light wavelength used for mask pattern inspection may be formed on the absorption film 101.

  A conductive film 104 having a higher dielectric constant and conductivity than the base material 103 is formed on the back surface of the base material 103. As an example, a film mainly composed of Cr is often used. In the present invention, the EUV mask 12 is characterized in that a protective coating 105 having carbon atoms as a basic skeleton is uniformly applied to the opposite side of the pattern surface.

  There are various coating methods such as die coating and slit coating, but the spin coating method is desirable as a means for uniformly coating the protective film 105 on one side. Examples of the type of the protective coating 105 include organic polymers that do not contain silicon, fluorine, and metal elements, such as polyolefins, acrylic resins such as PMMA, polyvinyl alcohol, and polyvinyl acetate.

  These protective coatings 105 do not generate non-volatile substances such as silicon oxide, fluoropolymers, and hardly soluble metal oxides during the decomposition reaction represented by the oxidation reaction, and do not adhere to the surface. The protective film 105 can be easily removed with cleaning solutions using various acid and alkaline chemicals used for cleaning the mask.

  The EUV mask 12 on which the protective film 105 is thus formed is adsorbed to the mask stage 13 of the EUV exposure apparatus shown in FIG. In FIG. 2, 1 is an EUV light source, 2 to 11 are mirrors, 12 is an EUV mask, 13 is a mask stage (mask holding unit), 14 is a wafer, 15 is a wafer stage, 16 is a housing, 17 is a light source for cleaning, Reference numeral 18 denotes an energy beam irradiated from the cleaning light source 17, and 19 denotes a cylinder filled with a gas or chemical for cleaning the EUV mask 12. Reference numeral 20 denotes a valve for controlling the opening and closing of the cylinder 19. Further, a vacuum pump (not shown) is provided in the housing 16 for discharging the gas generated during the cleaning of the EUV mask 12 to the outside of the EUV exposure apparatus. Since EUV light is absorbed and attenuated by the atmosphere, all of its optical paths are maintained at a predetermined degree of vacuum.

  The mask stage 13 adsorbs the conductive film 104 on the back surface of the EUV mask through the protective film 105 by electrostatic force. When the protective film 105 is present, not only the distance between the chuck and the conductive film 104 is changed, but also the medium filling the electrostatic chuck and the conductive film 104 is changed. The organic polymer exemplified above has a dielectric constant that is about the same as that of the glass as the base material 103 and about 2 to 3 times that of the vacuum. For this reason, it is necessary to adjust the attracting force appropriately by adjusting the voltage value applied to the electrostatic chuck.

  In this way, the conductive film 104 on the back surface of the EUV mask and the mask stage 13 provided with the electrostatic chuck come into contact with each other through the protective film 105 made of an organic substance, and foreign matter is directly adhered to the back surface conductive film 104. Can be prevented. After the exposure, in the mask cleaning process for removing the carbon compound adhered to the surface of the EUV mask 12, the protective film 105 on the back surface of the mask can be removed by using an acid or alkaline chemical solution.

  Further, the foreign matter adhered to the back surface of the EUV mask is removed from the back surface conductive film 104 at the same time as the protective film 105 is removed in the mask cleaning process. By forming the protective film 105 again on the back surface of the EUV mask that has been cleaned, the film that protects the back surface can be regenerated any number of times.

  Further, when the EUV mask 12 on which the protective coating 105 is formed is detached from the mask stage 13, it is considered that a part of the protective coating 105 adheres and remains on the mask stage 13 side. The mask stage 13 is irradiated with an energy beam having high reactivity and decomposability to the protective film 105 represented by ultraviolet rays, and in combination, either oxygen (oxygen atom) or hydrogen (hydrogen atom), Alternatively, an organic substance remaining on the mask stage 13 is removed by providing the exposure apparatus with a mechanism for introducing a gas including both into the vicinity of the mask stage 13.

  Specifically, the protective film 105 attached to the mask stage 13 is decomposed by the action of the energy beam 18 irradiated from the cleaning light source 17 to be decomposed by the action of the introduced energy beam, and the molecular weight is reduced. The introduced gas is decomposed to generate oxygen and hydrogen radicals. The oxygen and hydrogen radicals react with the protective film 105 attached to the mask stage 13 to change into gaseous substances such as carbon dioxide and methane, and EUV exposure is performed from a vacuum pump (not shown) incorporated in the housing 16. By being discharged out of the apparatus, the organic matter on the mask stage 13 is decomposed and discharged.

In FIG. 2, the unit that generates the energy beam 18 is introduced into the EUV exposure apparatus and irradiated. However, a mechanism for introducing the energy beam outside the apparatus is provided, and the scope of the present invention is not exceeded. Deformation and modification are possible.
The description of the scope of the claims at the beginning of the application is added below.
[C1] A base material, a multilayer reflective layer formed on the surface of the substrate and reflecting a high refractive layer and a low refractive layer for reflecting extreme ultraviolet light, and an extreme ultraviolet light formed on the multilayer reflective layer. A reflective mask comprising: an absorbing layer for absorbing; a conductive film formed on a lower surface of the substrate; and a protective film uniformly applied to the lower surface of the conductive film.
[C2] The reflective mask according to [C1], wherein the protective film is formed of an organic polymer that does not include silicon, fluorine, and a metal element as constituent elements.
[C3] The reflective mask according to [C1] or [C2], wherein the protective film is configured to be removable by means that does not apply physical external force.
[C4] An exposure apparatus that holds the reflective mask according to any one of [C1] to [C3] by a mask holding unit, and exposes and transfers a pattern formed on the reflective mask onto a sensitive substrate. ,
The exposure apparatus according to claim 1, wherein the mask holding unit is in contact with the reflective mask through a protective film.
[C5] The exposure apparatus according to [C4], further comprising means for irradiating the reflective mask held by the mask holding unit with an energy beam.
[C6] The exposure apparatus according to [C4] or [C5], comprising a mechanism for introducing a substance composed of one or both of oxygen atoms and hydrogen atoms in the vicinity of the mask holding portion. An exposure apparatus characterized by the above.

  DESCRIPTION OF SYMBOLS 1 ... Light source, 2-11 ... Mirror, 12, 12 '... EUV mask, 13 ... Mask stage, 14 ... Wafer, 15 ... Wafer stage, 16 ... Housing | casing, 17 ... Light source for washing | cleaning, 18 ... Energy beam, 19 ... Cylinder, 20 ... valve, 101 ... absorption film, 102 ... multilayer reflective film, 103 ... substrate, 104 ... conductive film, 105 ... protective coating.

Claims (1)

A base material, a multilayer reflective layer formed on the surface of the substrate and reflecting a high refractive layer and a low refractive layer that reflects extreme ultraviolet light, and an absorption formed on the multilayer reflective layer to absorb extreme ultraviolet light comprising layer and a conductive a film formed on the lower surface of the substrate,
A protective coating that is uniformly applied to the lower surface of the conductive film and is composed of an organic polymer that does not contain silicon, fluorine, and metal elements as constituent elements ,
The reflective mask according to claim 1, wherein the protective coating is configured to be removable by means without applying physical external force in a mask cleaning process using a chemical solution .

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