JP2014229652A - Reflective mask blank and reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask having a light-shielding frame 11 in which an image field (circuit pattern part) 10 is conducting with the outer peripheral part of a mask, without causing a defect due to charge (charge up), and reflection of EUV and DUV is removed from a mask region corresponding to the boundary region of a chip subjected to multiple exposure in a semiconductor substrate.SOLUTION: A reflective mask blank includes a substrate 1, a transparent conductive layer 6 formed on the substrate 1, a multilayer reflection layer 2 formed on the transparent conductive layer 6 and reflecting the exposure light, a protective layer 3 formed on the multilayer reflection layer 2 and protecting the multilayer reflection layer 2, an absorption layer 4 formed on the protective layer 3 and absorbing the exposure light, and a back conductive layer 5 formed on the surface of the substrate 1 opposite from the multilayer reflection layer 2. A light-shielding frame, i.e., a region of low reflectivity of the EUV light from where the absorption layer, the protective layer, and the multilayer reflection layer are removed, is provided in the peripheral part.

Description

  The present invention relates to a reflective mask and a method for manufacturing the same, and more particularly to a reflective mask used in a semiconductor manufacturing apparatus using EUV lithography using extreme ultraviolet (hereinafter referred to as “EUV”) as a light source. And a method of manufacturing a reflective mask.

(Description of EUV lithography)
In recent years, with the miniaturization of semiconductor devices, the demand for miniaturization of photolithography technology is increasing. As for lithography exposure, EUV lithography using EUV near the wavelength of 13.5 nm as a light source, which has a shorter wavelength than the conventional exposure using ArF excimer laser light having a wavelength of 193 nm, has been proposed. Since EUV lithography has a short light source wavelength and very high light absorption, it needs to be performed in a vacuum. In the EUV wavelength region, the refractive index of most substances is slightly smaller than 1. For this reason, the EUV lithography cannot use a transmission type refractive optical system which has been used conventionally, and becomes a reflection optical system. Accordingly, the photomask used as the original plate must be a reflective mask because a conventional transmissive mask cannot be used. (Hereinafter, in the present specification, a reflective mask used for EUV lithography may be referred to as an EUV mask or an EUV reflective mask).

(Description of EUV mask and blank structure)
A reflective mask blank, which is the basis of such a reflective mask, is a multilayer reflective layer (Mo and Si with a period of about 7 nm, 40 periods on a low thermal expansion substrate and having a high reflectance with respect to the exposure light source wavelength). Above = all 80 layers or more are formed), a protective layer of a multilayer reflective layer (Ru or the like is about 2.5 nm), and an absorption layer of the exposure light source wavelength are formed in order, and further on the back surface of the substrate A back surface conductive layer for an electrostatic chuck in the exposure machine is formed. There is also an EUV mask having a structure having a protective layer of a multilayer reflective layer and a buffer layer between the absorption layers. When processing from a reflective mask blank to a reflective mask, the absorption layer is partially removed by EB (electron beam) lithography and etching technology, and in the case of a structure having a buffer layer, this is also removed and absorbed. A circuit pattern including a portion and a reflection portion is formed. The light image reflected by the reflection type mask thus manufactured is transferred onto the semiconductor substrate via the reflection optical system.

(Explanation of the film thickness and reflectance of the absorption layer of the EUV mask)
In an exposure method using a reflective optical system, irradiation is performed at an incident angle (usually 6 degrees) inclined by a predetermined angle from the vertical direction with respect to the mask surface. Therefore, when the absorption layer is thick, a shadow of the pattern itself is generated. Therefore, since the reflection intensity in the shadowed portion is smaller than that in the non-shadowed portion, the contrast is lowered, and the transferred pattern is blurred in the edge portion and deviated from the design dimension. This is called shadowing (projection effect) and is one of the fundamental problems of the reflective mask.

In order to prevent such blurring of the pattern edge portion and deviation from the design dimension, it is effective to reduce the thickness of the absorption layer and reduce the height of the pattern, but when the thickness of the absorption layer becomes thin Since the attenuation amount of the exposure light in the absorption layer is reduced and the light shielding property is insufficient, the transfer contrast is lowered and the accuracy of the transfer pattern is lowered. That is, if the absorption layer is too thin, the contrast necessary for maintaining the accuracy of the transfer pattern cannot be obtained. From the viewpoint of shadowing and the exposure light absorptance of the absorbing layer, it is a problem whether the absorbing layer is too thick or too thin, so it is currently between 50 and 90 nm, and EUV light (extremely The reflectance at the absorbing layer (ultraviolet light) is about 0.5 to 3%.

(Explanation of multiple exposure of adjacent chips)
On the other hand, when a transfer circuit pattern is formed on a semiconductor substrate using a reflective mask, chips having a plurality of circuit patterns are formed on one semiconductor substrate. There may be a region where the outer periphery of the chip overlaps between adjacent chips. This is because the chips are arranged at a high density in order to improve productivity so as to increase as many chips as possible per semiconductor substrate (wafer). In this case, the region where the outer peripheral portions overlap is exposed (multiple exposure) a plurality of times (up to four times). The chip outer peripheral portion of this transfer pattern is also the outer peripheral portion on the mask, and is usually the absorption layer portion. However, as described above, since the reflectance of the EUV light on the absorption layer is about 0.5 to 3%, there is a problem that the outer peripheral portion of the chip is exposed by multiple exposure. Furthermore, although the EUV light source has a light spectrum in the range of 5 to 15 nm and has a peak of its emission spectrum, particularly at 13.5 nm (hereinafter, the EUV light source is referred to as light having a wavelength of 5 to 15 nm or 13.5 nm band), It is known that light in the near infrared region is emitted from vacuum ultraviolet rays other than the 13.5 nm band called out-of-band (Out of Band). This out-of-band is unnecessary and is unnecessary light to be removed by a filter or the like because the resist applied to the semiconductor substrate is exposed. However, since the absorption layer using tantalum (Ta) also reflects light in the vacuum ultraviolet to far ultraviolet region, as described above, a light amount that cannot be ignored is integrated in the semiconductor wiring portion near the boundary region of adjacent chips, and the wiring pattern is integrated. A problem occurs that affects the dimensions. For this reason, it has become necessary to provide a region (hereinafter referred to as a light-shielding frame) having a higher light-shielding property of EUV light than a normal absorption layer on the chip outer periphery on the mask.

  In order to solve such a problem, by reducing the reflectance of the multilayer reflective layer by forming a groove dug from the absorption layer of the reflective mask to the multilayer reflective layer, the light shielding property with respect to the wavelength of the exposure light source is reduced. A reflective mask provided with a high light-shielding frame has been proposed (see, for example, Patent Document 1).

  A schematic plan view of a reflective mask 100 without a light shielding frame is shown in FIG. 1A, and a schematic cross-sectional view is shown in FIG. On the other hand, FIG. 1B shows a schematic plan view of a reflective mask 101 having a light shielding frame 11 dug up to the multilayer reflective layer, and FIG. In FIG. 1B, a light shielding frame 11 is formed so as to surround the image field (circuit pattern portion) 10.

JP 2009-212220 A

  However, in the light shielding frame 11 in which the absorption layer 4 and the multilayer reflective layer 2 are simply dug, the image field (circuit pattern portion) 10 inside the light shielding frame 11 and the outside of the light shielding frame are electrically floating. Is not connected. When this mask is used in an EUV exposure machine, photoelectrons are emitted from metal materials (mainly Ta, Mo, Si, etc.) used for the EUV mask due to the photoelectric effect of EUV light (extreme ultraviolet light), and are electrically positive. Is charged (charged up). This causes a problem that foreign matter in the exposure machine is attached and transfer defects are induced. In addition, even in length measurement SEM and electron beam inspection machines that use electron beams during the mask manufacturing process, negative charge is generated when an electron beam is irradiated, increasing the noise component and enabling accurate measurement and electron beam inspection. The problem of not being possible arises.

  In Patent Document 1, as a countermeasure against such charging at the time of exposure, a structure in which several layers (including at least Mo having conductivity) of the lowermost layer of the multilayer reflective layer 2 are left, or Ta or the base layer of the multilayer reflective layer 2 is used. A structure in which one metal conductive layer containing Cr is provided in advance has been proposed.

  However, in the method of leaving the lowermost layers of the multilayer reflective layer 2, the etching rate when the multilayer reflective layer 2 is dug by dry etching or wet etching is not uniform in the mask plane, so the number of layers to be retained is uniform. It is difficult to process.

  Even if it can be processed, leaving several layers of the multilayer reflective layer 2 in the region of the light shielding frame 11 originally intended to reduce the reflectance of the EUV light to zero as much as possible is more effective than the absorbing layer 4 to reflect the EUV light. It is likely to lead to the opposite effect of increasing the rate. For example, the reflectance when Mo / Si remains for two cycles is an EUV light reflectance of about 1.8% in calculation, and is 0.3% or less, which is said to be an index of the light shielding frame 11 of the EUV mask. Far surpasses.

  In addition, in the measure by the structure in which one metal conductive layer containing Ta or Cr is previously provided on the base of the multilayer reflective layer 2, the charge-up can be suppressed, but the out-of-band included in the exposure light source wavelength of EUV sography Further, the metal layer of Ta, Cr, etc. has a high reflectivity, which causes another problem of an increase in out-of-band reflectivity.

  Except for the above problems when forming a light-shielding band, known EUV blanks are considered to be reduced in charge (charge-up) during electron beam writing in an image field by the multilayer reflective layer 2 and the absorption layer 4. As the standards required by the development of the system become stricter, it is necessary to aim to reduce the minor impacts. For this reason, the presence of a conductive layer is important as a structure in which the influence of charging is further reduced.

  The present invention has been made in view of the above-described problems. The image field (circuit pattern portion) 10 and the outer peripheral portion of the mask can be electrically connected to each other, so that defects caused by charging (charge-up) are not caused. It is an object of the present invention to provide a reflective mask having a light shielding frame 11 that removes reflection of EUV and DUV (Deep Ultra Violet) from a mask region corresponding to a boundary region of a multiple-exposed chip.

In order to solve the above problem, the invention of claim 1 of the present invention is:
A reflective mask blank used in lithography with light having a wavelength of 5 to 15 nm as exposure light,
A substrate,
A transparent conductive layer formed on the substrate;
A multilayer reflective layer for reflecting exposure light formed on the transparent conductive layer;
A protective layer for protecting the multilayer reflective layer formed on the multilayer reflective layer;
An absorbing layer for absorbing exposure light formed on the protective layer;
A reflective mask blank having a back conductive layer formed on a surface opposite to the multilayer reflective layer of the substrate.

The invention according to claim 2
A light shielding frame which is a region having a low reflectance of EUV light from which the absorbing layer, the protective layer, and the multilayer reflective layer are removed is provided in a peripheral portion, and the transparent conductive layer includes an inner side and an outer side of the light shielding frame. And the light shielding frame has a low reflectance with respect to out-of-band light (light in a vacuum ultraviolet ray to near infrared region other than the 13.5 nm band) included in exposure light. The reflective mask blank according to Item 1 is used.

The invention described in claim 3
The transparent conductive layer is any one selected from the group of transparent conductive materials of ITO (indium tin oxide), zinc oxide, tin oxide, and molybdenum silicide (MoSi) oxides, nitrides, and oxynitrides. Or a reflective mask blank according to claim 1, wherein the reflective mask blank is formed to include a plurality of them.

The invention according to claim 4
The sheet resistance of the said transparent conductive layer is 30 ohms / sq or less, It is set as the reflective mask blank in any one of Claims 1-3 characterized by the above-mentioned.

The invention according to claim 5
A reflective mask used in lithography with light having a wavelength of 5 to 15 nm as exposure light,
A substrate,
A transparent conductive layer formed on the substrate;
A multilayer reflective layer for reflecting exposure light formed on the transparent conductive layer;
A protective layer for protecting the multilayer reflective layer formed on the multilayer reflective layer;
An absorbing layer that absorbs exposure light having a circuit pattern formed on the protective layer;
A back surface conductive layer formed on a surface opposite to the multilayer reflective layer of the substrate,
A light shielding frame which is a region having a low reflectance of EUV light from which the absorbing layer, the protective layer, and the multilayer reflective layer are removed is provided in a peripheral portion, and the transparent conductive layer includes an inner side and an outer side of the light shielding frame. Is characterized in that the light-shielding frame has a low reflectance with respect to out-of-band light (light in the vacuum ultraviolet to near infrared region other than the 13.5 nm band) included in the exposure light. It is a type mask.

The invention described in claim 6
The transparent conductive layer is any one selected from the group of transparent conductive materials of ITO (indium tin oxide), zinc oxide, tin oxide, and molybdenum silicide (MoSi) oxides, nitrides, and oxynitrides. The reflective mask according to claim 5, wherein the reflective mask is formed to include a plurality of them.

The invention described in claim 7
7. The reflective mask according to claim 1, wherein the transparent conductive layer has a sheet resistance of 30 Ω / sq or less.

  In the EUV mask on which the digging-type light shielding frame 11 for removing the multilayer reflective layer 2 is formed, the image field (circuit pattern portion) 10 inside the light shielding frame 11 and the outside of the light shielding frame 11 can be electrically connected. Charging can be prevented at the time of measurement by a length measuring SEM using a line, at the time of inspection of a circuit pattern portion by an electron beam inspection machine, and at the time of EUV exposure by EUV lithography. The transparent conductive layer provided for electrical conduction causes out-of-band surface reflectance reduction and absorption in the light shielding frame region, and once passes through the transparent conductive layer and the substrate, is reflected from the back surface conductive layer 5 and returns again. Since the incoming light component is also attenuated by the transparent conductive layer, the out-of-band can be reduced as compared with the known light shielding frame 11 without the transparent conductive layer. Further, the presence of the transparent conductive layer 6 having a small electric resistance effectively acts at the time of drawing an electron beam in the image field, and helps to reduce charging (charge-up). For this reason, it is possible to provide a high quality mask and to reduce the adhesion of foreign matters to the EUV mask during EUV exposure in EUV lithography, so that a high quality wafer transfer pattern can be obtained. .

FIG. 6 is a schematic plan view of a reflective mask (a) having no light shielding frame and a reflective mask (b) having a light shielding frame, as an example of a conventional reflective mask. FIG. 6 is a schematic cross-sectional view of a reflective mask (a) having no light shielding frame and a reflective mask (b) having a light shielding frame, as an example of a conventional reflective mask. 1 is a schematic cross-sectional view of a reflective mask blank (a), a schematic plan view (b) and a schematic cross-sectional view (c) of a reflective mask after a light shielding frame is formed, as an example of an EUV reflective mask blank having a transparent conductive layer according to the present invention. ). The process flow which shows an example of the manufacturing process of the reflective mask which has the light-shielding frame by this invention. The schematic sectional drawing which shows a part of example of the manufacturing process of the EUV reflective mask which has the light-shielding frame by this invention. The schematic sectional drawing which shows the other part of an example of the manufacturing process of the EUV reflective mask which has the light-shielding frame by this invention.

(Configuration and layout of the reflective mask of the present invention)
Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

  First, the structure of the reflective mask of the present invention will be described. 3A is a reflective mask blank (reflective mask blank), FIG. 3B is a reflective mask, and FIG. 3C is a schematic cross-section cut along the broken line AA ′ in FIG. 3B. FIG. More specifically, a blank for a mask used for exposure using EUV light and a reflective mask using the same. The wavelength of this EUV light is 13.5 nm, for example. On one surface of the substrate 1, a transparent conductive layer 6, a multilayer reflective layer 2, a protective layer 3, and an absorption layer 4 are laminated in this order. A buffer layer may be formed between the protective layer 3 and the absorption layer 4. The buffer layer is a layer provided so as not to damage the underlying protective layer 3 when the image field 10 of the absorption layer 4 is corrected. A back conductive layer 5 is formed on the opposite side of the substrate 1 from the multilayer reflective layer 2 to complete the reflective mask blank of FIG. The transparent conductive layer 6 is formed using a known CVD, sputtering method, ion plating method, or vacuum deposition method. The multilayer reflective layer 2, the protective layer 3, the absorption layer 4, and the back surface conductive layer 5 are formed using a known sputtering method.

  This will be described more specifically.

The reflective mask blank 102 is used in lithography using light having a wavelength of 5 to 15 nm as exposure light. The substrate 1 is made of a material containing quartz (SiO ₂ ) as a main component and titanium oxide (TiO ₂ ). The transparent conductive layer 6 is formed on the substrate 1. It is formed of a transparent conductive layer made of ITO (indium tin oxide), zinc oxide, tin oxide, molybdenum silicide (MoSi) oxide, nitride, oxynitride or the like. The multilayer reflective layer 2 is a layer that is formed on the transparent conductive layer 6 and reflects exposure light. The multilayer reflective layer 2 is formed with a multilayer structure formed by stacking a plurality of layers in which a layer made of molybdenum (Mo) and a layer made of silicon (Si) are stacked. The protective layer 3 is formed on the multilayer reflective layer 2 and protects the multilayer reflective layer 2. The protective layer 3 has a single-layer structure or a stacked structure, and is formed of a material containing either ruthenium (Ru) or silicon (Si). When the protective layer 3 has a laminated structure, the uppermost layer of the protective layer 3 is made of any of ruthenium (Ru) oxide, nitride, oxynitride, silicon (Si) oxide, nitride, oxynitride. It is made of a material that contains it. The absorption layer 4 is formed on the protective layer 3 and absorbs exposure light. The back surface conductive layer 5 is formed on the surface of the substrate 1 opposite to the multilayer reflective layer 2. The back surface conductive layer 5 is formed of a material containing any one of chromium (Cr) and tantalum (Ta), or an oxide, nitride, or oxynitride thereof.

The manufacturing method of this mask is shown in FIG. 4, FIG. 5, and FIG. FIG. 4 shows the process, and FIGS. 5 and 6 show sectional views of the processed state. The blanks shown in FIG. 3A described above are prepared (step “start” in the figure), and the image field (circuit pattern) 10 and the light shielding frame 11 are formed on the absorption layer 4 in the following steps. A chemical amplification system or non-chemical amplification system resist 9 that reacts with an electron beam is applied (step S1), a predetermined image field (circuit pattern portion) 10 is drawn, and then developed (S2) with an alkaline solution or the like. To form an image field. Etching with gas plasma using fluorine-based gas or chlorine-based gas (S3) using the formed resist 9 pattern as a mask, and unnecessary resist 9 pattern is ashed with oxygen plasma or oxidized chemical solution such as sulfuric acid or ozone water. Dissolve by removal with an organic solvent. Thereafter, if necessary, cleaning treatment using ultrapure water, organic alkaline chemicals, surfactants, etc. in which acid / alkali chemicals, ozone gas, hydrogen gas, etc. are dissolved, and spin drying using centrifugal force (S4) are performed. Thus, the image field (circuit pattern portion) 10 was formed.

  Next, a light shielding frame 11 is formed around the image field (circuit pattern portion) 10 so as to surround the image field 10. A resist 29 that reacts to ultraviolet rays or electron beams is applied to the mask formed in step S4 (S5). Next, the light shielding frame 11 is exposed or drawn with an electron beam or ultraviolet light, and development (S6), etching (S7), resist removal, washing, and drying (S8) are performed as described above to complete the light shielding frame 11. In the etching step (S7), first, the protective layer 3 is removed using fluorine-based gas plasma, and the multilayer reflective film 2 is subjected to a method of alternately using fluorine-based gas plasma or chlorine gas-based plasma in the same manner as the protective layer 3.

  The reflective mask 103 with the new structure light-shielding frame is completed through the above steps.

  In other words, in the reflective mask 103, the image field (circuit pattern portion) 10 is formed by selectively removing the absorption layer 4, and the image field (circuit pattern portion) excluding the image field (circuit pattern portion) 10 is formed. A frame-shaped light-shielding frame region 11 in which the absorption layer 4, the protective layer 3, and the multilayer reflective layer 2 are selectively removed is formed in a portion around 10. Therefore, the transparent conductive layer 6 is provided in the frame-shaped light shielding frame region 11. According to the present invention, in an EUV mask in which a digging-type light shielding frame 11 for removing the multilayer reflective layer 2 is formed, an image field (circuit pattern portion) 10 inside the light shielding frame 11 and an outer side 12 of the light shielding frame 11 Since continuity can be obtained, charging can be prevented during measurement by a length measuring SEM using an electron beam, pattern inspection by an electron beam inspection machine, and EUV exposure by EUV lithography. Due to the transparent conductive layer provided for the purpose of conduction, out-of-band surface reflectance reduction and attenuation occur in the light shielding frame region 11, and the transparent conductive layer and the substrate are once transmitted and reflected from the back surface conductive layer 5 and again. Since the returning light component is also attenuated by the transparent conductive layer, the out-of-band can be reduced as compared with the known light shielding frame 11 without the transparent conductive layer. This also makes it possible to avoid exposure of the resist applied on the semiconductor substrate.

(Details of Configuration of Reflective Mask of the Present Invention: Explanation of Charging Status)
The resistance value of the surface of the EUV mask material varies depending on the specific conductivity and film thickness of the material used (Ta, Ru, Mo, Si), and the film formation state (porous, surface oxidation degree, etc.) of the material.

  In addition to the physical properties of the EUV mask material, there is a change in the charging state depending on the use environment such as measurement by a length measuring SEM using an electron beam, pattern inspection by an electron beam inspection machine, EUV exposure in EUV lithography, etc. .

In the measurement by the length measuring SEM using the electron beam and the pattern inspection by the electron beam inspection machine, it is expected that the problem of charging (charge-up) is large when a condition with a large irradiation electron dose is assumed.
In EUV exposure in EUV lithography, the kinetic energy of electrons emitted by the photoelectric effect is expressed by the following formula (1).

Since the wavelength of the EUV light to be irradiated is constant (13.5 nm), the kinetic energy is constant. However, when the intensity (light quantity) of the EUV light increases, the amount of emitted electrons also increases. The problem of (charge-up) increases.
The transparent conductive layer introduced this time has an effect on these problems, and can lead to the production of a more accurate mask.

  P in the formula (1) is called a work function, and is the minimum work amount (energy) necessary for ejecting electrons from the material, and has a value specific to the material.

eV = hμ-P (1)
<Left side>
eV: Kinetic energy of emitted electrons e: Charge of electrons V: Potential difference when energy of electrons is converted into potential difference <right side>
hμ: energy of incident light h: Planck's constant μ: frequency of light = 1 / λ (λ: wavelength = 13.5 nm for EUV)
P: Work function of blank material

(Details of the configuration of the reflective mask of the present invention: transparent conductive layer)
The transparent conductive layer 6 in FIG. 3A uses a transparent conductive layer that has low reflectivity with respect to EUV light, low reflectivity with respect to out-of-band, and high conductivity. As the transparent conductive layer, for example, an indium-tin oxide alloy (ITO), zinc oxide, tin oxide, antimony oxide, molybdenum silicide (MoSi) oxide, nitride or oxynitride, tantalum or other thin films or a plurality of these are included. A transparent conductive layer can be used, and an additive is doped to obtain a desired conductivity. Further, although the transparent conductive layer is described as a single layer, these transparent conductive layers may be formed in multiple layers. Besides these, there is no problem as long as it is a transparent conductive layer that can obtain conductivity without reflecting EUV light. The conductivity of the transparent conductive layer is a sheet resistance of 20000Ω / Sq or less, which may cause problems when processing a mask blank, and has a conductivity that can prevent charging when observed with an SEM. Since it is good, it has a sheet resistance equivalent to that of a known transparent conductive layer such as ITO, and is particularly preferably a transparent conductive layer having a sheet resistance of 30 Ω / Sq or less. The thickness of the transparent conductive layer is not particularly limited, but a thickness of 100 nm or more is preferable. It is necessary to have a selection ratio when digging the multilayer reflective layer 2. The thickness of the transparent conductive layer 6 is advantageous even when considering conductivity, out-of-band absorption and attenuation, surface flatness of the transparent conductive layer 6, resistance to chemicals, adhesion between layers, and the like. . Therefore, the thickness of the transparent conductive layer 6 is limited if the EUV reflectance on the surface of the transparent conductive layer 6 is lower than that of the known light-shielding frame 11 and no foreign matter that causes defects in the reflective mask is generated. Not. Further, when the reflective mask is cleaned, if the transparent conductive layer such as ITO is weakly resistant to chemicals used for cleaning, the protective layer of the transparent conductive layer 6 is made transparent if the EUV reflectance is not improved. You may comprise between the layer 6 and the multilayer reflective layer 2. FIG. As the protective layer, for example, a material having acid resistance such as silicon oxide, silicon nitride, polysilicon, or the like, or the transparent conductive layer 6 in the lower layer and within the range not in an insulating state with the upper multilayer reflective layer In addition, DLC (diamond-like carbon), SiC, or the like can be used as a single layer as the protective layer, or can be used after doping to improve conductivity.

(Details of the configuration of the reflective mask of the present invention: multilayer reflective layer, protective layer, buffer layer)
The multilayer reflective layer 2 in FIG. 3A is designed to achieve a reflectance of about 60% with respect to EUV light, and is a laminated film in which 40-50 pairs of Mo and Si are alternately laminated. The uppermost protective layer 3 is made of Ru (ruthenium) having a thickness of 2 to 3 nm or Si having a thickness of about 10 nm. The layer adjacent to the Ru layer is a Si layer.
The reason why Mo or Si is used in the multilayer reflective layer 2 is that the absorption (extinction coefficient) with respect to EUV light is small and the difference in refractive index between Mo and Si between EUV light is large, so that the interface between Si and Mo. This is because the reflectance at can be increased.
When the protective layer 3 is Ru, it plays a role as a protective layer against an etching stopper in processing the absorption layer 4 and a chemical solution during mask cleaning. When the protective layer 3 is Si, there may be a buffer layer between the absorption layer 4 and the protective layer 3. The buffer layer is provided to protect the Si layer, which is the uppermost layer of the multilayer reflective layer 2 adjacent to the bottom of the buffer layer, during etching or pattern modification of the absorption layer 4, and a chromium (Cr) nitrogen compound ( CrN).

(Details of the configuration of the reflective mask of the present invention: absorption layer)
The absorption layer 4 in FIG. 3A is made of a nitrogen compound (TaN) of tantalum (Ta) having a high absorption rate with respect to EUV. As other materials, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), and oxides thereof (TaBON, TaSiO, TaO) may be used.

  The absorption layer 4 in FIG. 3A may be an absorption layer having a two-layer structure in which an upper layer is provided with a low reflection layer having an antireflection function with respect to ultraviolet light having a wavelength of 190 to 260 nm. The low reflection layer is for increasing the contrast and improving the inspection property with respect to the inspection wavelength of the mask defect inspection machine.

(Details of the configuration of the reflective mask of the present invention: back surface conductive layer)
Although the back surface conductive layer 5 in FIG. 3A is generally made of chromium nitride (CrN), it is sufficient that the conductivity is higher than the electrostatic chuck can be used. Any material can be used.

  Although FIG. 3A shows the configuration having the back surface conductive layer 5, a reflective mask blank and a reflective mask that do not have the back surface conductive layer 5 may be used.

(Details of the configuration of the reflective mask of the present invention: digging a multilayer reflective layer)
A method for forming the light shielding frame 11 of the reflective mask of the present invention will be described.

A resist in which the periphery of the image field 10 is opened by photolithography or electron beam lithography with respect to an EUV mask having a pattern formed in the image field (circuit pattern portion) 10 or an EUV mask blank to be formed later. Form a pattern.
Next, the absorption layer 4 and the protective layer 3 in the opening of the resist pattern are removed by dry etching using a fluorine-based or chlorine-based gas (or both).
Next, the multilayer reflective layer 2 is penetrated and removed by dry etching using a fluorine-based gas and / or chlorine-based gas, or wet etching using an alkaline solution or an acidic solution.

When penetrating / removing the multilayer reflective layer 2 by dry etching, the fluorine-based gas and / or the chlorine-based gas is used for both Mo and Si, which are the materials of the multilayer reflective layer 2. It is for having. Examples of the fluorine-based gas used at this time include CF ₄ , C ₂ F ₆ , C ₄ F ₈ , C ₅ F ₈ , CHF ₃ , SF ₆ , ClF ₃ , Cl ₂ , and HCl.

For the etching solution when penetrating and removing the multilayer reflective layer 2 by wet etching,
It is necessary to be suitable for etching Mo and Si that are materials of the multilayer reflective layer 2. For example, as the alkaline solution, TMAH (tetramethylammonium hydroxide), KOH (potassium hydroxide), EDP (ethylenediamine pyrocatechol) and the like are suitable. A mixed solution of nitric acid and phosphoric acid is suitable as the acidic solution, but hydrofluoric acid, sulfuric acid, and acetic acid may be added thereto.

  When conducting dry or wet etching or cleaning the mask, if there is a concern about the erosion or corrosion of the transparent conductive layer 6, a protective layer may be provided between the transparent conductive layer 6 and the multilayer reflective layer 2. Good. As the structure of the protective layer, for example, a material having acidity such as silicon oxide, silicon nitride, polysilicon, or the like, or a transparent conductive layer 6 in the lower layer, and a range that does not become an insulating state with the upper multilayer reflective layer 2 If so, DLC (diamond-like carbon), SiC, or the like is used as a single layer as the protective layer. Alternatively, doping can be performed to further improve conductivity.

  The pattern formation in the image field 10 of the reflective mask may be performed before or after the formation of the light shielding frame 11 (conduction portion 13).

  As described above, the light shielding frame 11 from which the absorption layer 4, the protective layer 3, and the multilayer reflective layer 2 are removed so that the image field 10 of the reflective mask is defined, the lower layer of the light shielding frame 11 is electrically connected. By forming the transparent conductive layer 6 having the same characteristics, a reflective mask 103 is obtained in which charging (charge-up) in the image field is prevented and the out-of-band reflectance is reduced.

EXAMPLES Hereinafter, the manufacturing method of the reflective mask of this invention is demonstrated in detail by an Example.
The reflective mask blank 102 shown in FIG.
The reflective mask blank 102 was formed of ITO (indium tin oxide) as a transparent conductive layer 6 on the substrate 1 with a film thickness of 200 nm using a sputtering method. The sheet resistance of the formed transparent conductive layer 6 was 20 Ω / Sq or less. On the formed transparent conductive layer 6, there are 40 pairs of Mo and Si multilayer reflective layers 2 designed to have a reflectivity of about 64% with respect to EUV light having a wavelength of 13.5 nm. A protective layer 3 of 5 nm thick Ru and an absorption layer 4 made of tantalum silicide (TaSi) 70 nm thick are sequentially formed thereon.

  A positive chemically amplified resist 9 (FEP171: manufactured by FUJIFILM Electronics Materials) is applied to the reflective mask blank 102 with a film thickness of 300 nm (FIG. 5 (S1)), and an electron beam drawing machine (JBX9000: Japan). After drawing by an electronic company, development was performed at 110 ° C .; 10 minutes PEB (PoSt ExpoSure Bake) and a spray developing machine (SFG3000: manufactured by Sigma Meltech) to form a resist pattern on the resist portion (FIG. 5 (S2 )).

Next, the absorption layer 4 is removed by etching with CF ₄ plasma and Cl ₂ plasma using a dry etching apparatus (VLR700 series: Unaxis) (FIG. 5 (S3)), and then the resist is removed and cleaned. A reflective mask having the evaluation pattern shown in 5 (S4) was produced.
As the evaluation pattern, a chip of a 1: 1 line & space pattern having a dimension of 200 nm was arranged in the center of the mask with six faces. The size of the pattern region was 10 cm × 10 cm. Here, the interval of the scribe lines between the chips was 5 mm.

Next, a light shielding frame 11 was formed around the image field (pattern region) 10 of the reflective mask having the above-described evaluation pattern.
An i-line resist 29 is applied to a reflective mask (FIG. 5 (S4)) with a film thickness of 1000 nm (FIG. 5 (S5)), and drawing and development are performed there by a laser drawing machine (ALTA3000: manufactured by Applied Materials). As a result, a resist pattern was formed by removing a region that later becomes the light shielding frame 11 (FIG. 5 (S6)).
At this time, the opening width of the resist pattern was 3 mm, and the resist pattern was arranged at a distance of 3 μm from the pattern edge of the circuit pattern region of 10 cm × 10 cm in the center of the mask.

Next, using a dry etching apparatus (VLR700 series: manufactured by Unaxis), CHF3 plasma (pressure in the dry etching apparatus 50 mTorr, ICP (inductively coupled plasma) power 500 W, RIE (reactive ion etching) power 2000 W, CHF ₃ : flow rate The absorption layer 4 and the multilayer reflective layer 2 in the opening of the resist are penetrated and removed by vertical dry etching (20 Sccm, treatment time 6 minutes, which are the same in the following notation) (FIG. 5 ( S7)) Finally, the resist was removed and washed with a sulfuric acid-based stripping solution and ammonia hydrogen peroxide solution to remove the remaining resist by dry etching and wet etching (FIG. 5 (S8)).

  FIGS. 3B and 3C show the reflective mask 103 manufactured according to this example.

  The width of the light shielding frame 11 in the reflective mask 103 is 3 mm, and the width of the scribe line is 5 mm.

  In the manufacturing process (shading frame forming process) of the reflective mask 103 in this embodiment, the manufactured reflective mask and the reflective mask 101 having a conventional structure as a comparative sample are manufactured, and both masks are measured by a length measuring SEM. Measurements were performed.

  In the mask of the comparative sample that does not have the transparent conductive layer 6, the SEM image drift phenomenon due to charge-up occurred in the image field, which hinders measurement inside the light shielding frame 11. Then, no charge-up occurred and measurement was possible without problems. In addition, EUV and DUV reflections could be removed from the mask region corresponding to the boundary region of the chip that was subjected to multiple exposure on the semiconductor substrate.

  The present invention is useful for a reflective mask or the like.

DESCRIPTION OF SYMBOLS 1 Low thermal expansion board 2 Multilayer reflective layer 3 Protective layer 4 Absorbing layer 5 Back surface conductive layer 6 Transparent conductive layer 9 Resist 10 Image field (circuit pattern part)
11 light shielding frame 12 light shielding frame outer side 29 resist 100 reflective mask (no light shielding frame)
101 Reflective mask (with shading frame)
102 Reflective mask blank 103 according to the invention 103 Reflective mask according to the invention

Claims (7)

A reflective mask blank used in lithography with light having a wavelength of 5 to 15 nm as exposure light,
A substrate,
A transparent conductive layer formed on the substrate;
A multilayer reflective layer for reflecting exposure light formed on the transparent conductive layer;
A protective layer for protecting the multilayer reflective layer formed on the multilayer reflective layer;
An absorbing layer for absorbing exposure light formed on the protective layer;
A reflective mask blank, comprising: a back conductive layer formed on a surface opposite to the multilayer reflective layer of the substrate.   A light shielding frame which is a region having a low reflectance of EUV light from which the absorbing layer, the protective layer, and the multilayer reflective layer are removed is provided in a peripheral portion, and the transparent conductive layer includes an inner side and an outer side of the light shielding frame. And the light shielding frame has a low reflectance with respect to out-of-band light (light in a vacuum ultraviolet ray to near infrared region other than the 13.5 nm band) included in exposure light. Item 2. A reflective mask blank according to Item 1.   The transparent conductive layer is any one selected from the group of transparent conductive materials of ITO (indium tin oxide), zinc oxide, tin oxide, and molybdenum silicide (MoSi) oxides, nitrides, and oxynitrides. The reflective mask blank according to claim 1, wherein the reflective mask blank is formed by including a plurality of the masks.   The reflective mask blank according to claim 1, wherein the transparent conductive layer has a sheet resistance of 30 Ω / sq or less. A reflective mask used in lithography with light having a wavelength of 5 to 15 nm as exposure light,
A substrate,
A transparent conductive layer formed on the substrate;
A multilayer reflective layer for reflecting exposure light formed on the transparent conductive layer;
A protective layer for protecting the multilayer reflective layer formed on the multilayer reflective layer;
An absorbing layer that absorbs exposure light having a circuit pattern formed on the protective layer;
A back surface conductive layer formed on a surface opposite to the multilayer reflective layer of the substrate,
A light shielding frame which is a region having a low reflectance of EUV light from which the absorbing layer, the protective layer, and the multilayer reflective layer are removed is provided in a peripheral portion, and the transparent conductive layer includes an inner side and an outer side of the light shielding frame. Is characterized in that the light-shielding frame has a low reflectance with respect to out-of-band light (light in the vacuum ultraviolet to near infrared region other than the 13.5 nm band) included in the exposure light. Type mask.   The transparent conductive layer is any one selected from the group of transparent conductive materials of ITO (indium tin oxide), zinc oxide, tin oxide, and molybdenum silicide (MoSi) oxides, nitrides, and oxynitrides. 6. The reflective mask according to claim 5, wherein the reflective mask is formed to include a plurality of them.   The reflective mask according to claim 5 or 6, wherein a sheet resistance of the transparent conductive layer is 30 Ω / sq or less.

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