JP5339085B2 - Reflective mask, manufacturing method thereof, and mask pattern inspection method - Google Patents

Description

  The present invention relates to a lithography mask and its manufacturing method in the manufacture of semiconductor devices and the like, and more particularly, to transfer a mask pattern onto a wafer using extreme ultraviolet light (Extreme Ultra Violet: hereinafter referred to as EUV). The present invention relates to a reflective mask for EUV exposure, a manufacturing method thereof, and a mask pattern inspection method.

  Along with the miniaturization of semiconductor devices, an exposure method of transferring a pattern onto a wafer using a photomask is currently being performed by an optical projection exposure apparatus using an ArF excimer laser. In these exposure methods using an optical projection exposure apparatus, the resolution limit will eventually be reached. Therefore, new pattern forming methods such as direct drawing using an electron beam drawing apparatus, imprint lithography, and EUV lithography have been proposed.

  Among these new lithography techniques, EUV exposure is a technique in which EUV light having a wavelength shorter than that of an excimer laser and having a wavelength of about 13.5 nm is used, and the exposure is usually reduced to about 1/4. It is regarded as the limit of wavelength conversion, and is attracting attention as a lithography technique for semiconductor devices. In EUV exposure, since a refractive optical system cannot be used due to a short wavelength, a reflective optical system is used, and a reflective mask is used as a mask. The reflective mask for EUV exposure is a mask in which a pattern is formed by providing at least a multilayer reflective film that reflects EUV light and an absorber layer that absorbs EUV light on the multilayer reflective film.

  In a conventional reflective mask for EUV exposure, after a mask pattern is formed on an absorber layer, it is inspected whether the pattern of the absorber layer is formed as designed without a defect. The defect inspection of the above pattern is usually obtained by the difference in reflectance between the surface of the absorber layer formed by irradiating the mask surface with light of 257 nm or 193 nm and reflecting the EUV light exposed by patterning. The pattern of the reflected image is inspected. In order to increase the difference in reflectance in the optical inspection described above, a low-reflection layer is usually provided on the absorber layer, and a proposal for increasing the contrast of the reflected image has been made (for example, Patent Documents). 1).

  FIG. 8 is a cross-sectional view showing an example of a conventional reflective mask for EUV exposure described in Patent Document 1. In FIG. The reflective mask 80 for EUV exposure shown in FIG. 8 has a reflective layer 82 that reflects EUV light in a multilayer structure on a substrate 81, and then prevents etching damage to the reflective layer 82 when forming a mask pattern. The buffer layer 83 is further provided with an absorber layer 86 that absorbs EUV light. The absorber layer 86 has an exposure light absorber layer 84 that absorbs EUV light as a lower layer for inspection of a mask pattern. It has a two-layer structure with a low reflection layer 85 made of an inspection light absorber used as an upper layer. In the reflective mask 80 described in Patent Document 1 shown in FIG. 8, in order to enable accurate and quick inspection of a mask pattern, an upper low-reflection layer 85 is made of chromium, manganese, and the like and elements thereof. And an oxide of at least one substance selected from an alloy containing benzene.

JP 2008-118143 A

  Along with the miniaturization of semiconductor element patterns, the inspection of defect of the pattern of the reflective mask is performed by the electron beam as well as the optical inspection. However, the structure of the conventional reflective mask provided with a low reflection layer having a low reflectance with respect to the inspection light described in Patent Document 1 is suitable for optical inspection, but is suitable for inspection with an electron beam. In pattern imaging with an electron beam, uneven charging of the surface of the low-reflection layer causes fluctuations in the contrast of the electron beam image and distortion of the image, contributing to deterioration in inspection sensitivity and instability. It was. On the other hand, the inspection with an electron beam raises the problem that the throughput is very slow, and there is a problem that an enormous amount of time is required to inspect the entire mask surface, which is not practical.

  Therefore, the present invention has been made in view of the above problems. That is, an object of the present invention is to provide a reflective mask suitable for both inspection using an electron beam having high resolution and optical inspection having high throughput, a manufacturing method thereof, and a mask pattern inspection method. It is.

  In order to solve the above-described problem, a reflective mask according to the invention of claim 1 includes a multilayer reflective film that reflects EUV light on one main surface of a substrate, and the EUV light on the multilayer reflective film. A reflective mask for EUV exposure having a transfer pattern formed by providing at least an absorber layer for absorption, wherein the transfer pattern formed on the absorber layer has the absorber layer as an uppermost layer And a pattern having a low reflection layer having a low reflectance with respect to the wavelength of light used for optical inspection of the pattern on the absorber layer, and the pattern having the low reflection layer as the uppermost layer. It is characterized by being.

  A reflective mask according to a second aspect of the present invention is the reflective mask according to the first aspect, wherein the pattern having the absorber layer as the uppermost layer is a critical pattern portion having strict dimensions and dimensional accuracy required for a circuit. The pattern having the low reflection layer as the uppermost layer is a non-critical pattern portion that does not require the same size and dimensional accuracy as the critical pattern portion.

  According to a third aspect of the present invention, there is provided a reflective mask manufacturing method comprising: a multilayer reflective film that reflects EUV light on one main surface of a substrate; and an absorber layer that absorbs the EUV light on the multilayer reflective film; A reflective mask for EUV exposure having at least a transfer pattern formed on the substrate, used for optical inspection of the multilayer reflective film, the absorber layer, and the pattern on the substrate A step of preparing a reflective mask blank in which a low-reflection layer having a low reflectance with respect to a wavelength of light is laminated in this order; a first resist pattern is formed on the low-reflection layer; and the first resist pattern is masked And a step of dry-etching the low reflection layer and the absorber layer to form an absorber layer pattern to be a transfer pattern and then peeling the first resist pattern; and the transfer pattern A second resist pattern is formed thereon, and using the second resist pattern as a mask, the low reflective layer in the critical pattern portion having strict dimensions and dimensional accuracy required on the circuit of the transfer pattern is dry-etched. And removing the second resist pattern after forming the pattern having the absorber layer as the uppermost layer, and the transfer pattern formed on the absorber layer has the absorber layer as the uppermost layer. It is formed by two types of patterns: a critical pattern portion that is an upper layer, and a non-critical pattern portion that does not require the same size and dimensional accuracy as the critical pattern portion, with the low reflection layer as the uppermost layer. It is.

  According to a fourth aspect of the present invention, there is provided a mask pattern inspection method comprising: a multilayer reflective film that reflects EUV light on at least one main surface of a substrate; and an absorber layer that absorbs the EUV light on the multilayer reflective film. A mask pattern inspection method for inspecting a defect of a reflective mask pattern for EUV exposure having a transfer pattern formed thereon, wherein the transfer pattern formed on the absorber layer includes the absorber layer. There are two types of patterns: a top layer pattern, and a low reflection layer having a low reflectance with respect to the wavelength of light used for optical inspection of the pattern on the absorber layer, and the low reflection layer as the top layer. The pattern having the absorber layer as the uppermost layer is a critical pattern portion having strict dimensions and dimensional accuracy required in the circuit, and the pattern having the lower reflective layer as the uppermost layer. Is a non-critical pattern portion that does not require the same size and dimensional accuracy as the critical pattern portion, and is characterized by performing electron beam inspection of the critical pattern portion and optical inspection of the non-critical pattern portion. .

  A mask pattern inspection method according to a fifth aspect of the present invention is the mask pattern inspection method according to the fourth aspect, wherein the reflective mask has a buffer layer, and the electron beam inspection of the critical pattern portion and the non-critical pattern portion. The optical inspection is performed after forming the two types of patterns on the absorber layer and before etching the buffer layer.

  According to the reflective mask of the present invention, the mask pattern is divided into a critical pattern portion and a non-critical pattern portion according to the required degree of dimensional and dimensional accuracy, and critical patterns with strict dimensional and dimensional accuracy required on the circuit are obtained. Reflective mask pattern for EUV exposure with high resolution while maintaining high throughput by inspecting parts with an electron beam and optically inspecting non-critical pattern parts that do not require dimensions and dimensional accuracy as high as critical pattern parts It becomes possible to inspect for defects. The reflection type mask of the present invention is a mask that improves the inspection accuracy and inspection speed of the mask pattern without causing any trouble in the pattern transferred by EUV exposure.

  According to the reflective mask manufacturing method of the present invention, the critical pattern portion is inspected with an electron beam by etching away the low reflective layer of the critical pattern portion of the reflective mask pattern, and other non-critical pattern portions. Can be inspected by optical inspection, enables high-throughput reflective mask inspection while maintaining high inspection sensitivity, and with a simple manufacturing process, a reflective mask suitable for optical inspection and electron beam inspection can be used. Manufacture is possible.

  According to the mask pattern inspection method of the present invention, using the reflective mask of the present invention, the pattern having the absorber layer as the uppermost layer is inspected by an electron beam, and the pattern having the low reflection layer as the uppermost layer is optically inspected. Therefore, it is possible to inspect pattern defects of the reflective mask for EUV exposure with high resolution while maintaining high throughput.

It is a cross-sectional schematic diagram which shows an example of embodiment in the reflective mask of this invention. It is a cross-sectional schematic diagram which shows the other example of embodiment in the reflective mask of this invention. It is a schematic plan view which shows an example of the pattern layout in the reflective mask of this invention. It is process cross-sectional schematic diagram which shows 1st Embodiment in the manufacturing method of the reflective mask of this invention. FIG. 5 is a process cross-sectional schematic diagram illustrating the first embodiment of the reflective mask manufacturing method of the present invention subsequent to FIG. 4; It is process cross-sectional schematic diagram which shows 2nd Embodiment in the manufacturing method of the reflective mask of this invention. FIG. 7 is a process cross-sectional schematic diagram illustrating a second embodiment of the reflective mask manufacturing method of the present invention subsequent to FIG. 6. It is a cross-sectional schematic diagram which shows the conventional reflective mask.

  Embodiments of a reflective mask for EUV exposure according to the present invention, a method for manufacturing the same, and a pattern inspection method for the reflective mask will be described below with reference to the drawings.

<Reflective mask>
First, the reflective mask of the present invention will be described. The reflective mask of the present invention is a transfer mask formed on at least one main surface of a substrate by providing at least a multilayer reflective film that reflects EUV light and an absorber layer that absorbs EUV light on the multilayer reflective film. A reflective mask for EUV exposure having a pattern for use, wherein the pattern formed on the absorber layer is a pattern having the absorber layer as the uppermost layer, and light used for optical inspection of the pattern on the absorber layer A low-reflection layer having a low reflectance with respect to the wavelength of the light-emitting layer is laminated, and the low-reflection layer is the uppermost layer.

  FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a reflective mask according to the present invention. As shown in FIG. 1, the reflective mask 10 includes a multilayer reflective film 12 that reflects EUV light on one main surface of a substrate 11, and an absorber layer 15 that absorbs EUV light on the multilayer reflective film 12. In order to prevent etching damage to the capping layer 13 that protects the reflective film on the multilayer reflective film 12, and then to the multilayer reflective film 12 when the mask pattern is formed. The buffer layer 14 is provided in order, and the absorber layer 15 that absorbs EUV light is formed thereon, and the pattern formed on the absorber layer 15 includes a pattern in which the absorber layer 15 is the uppermost layer and an absorption layer 15. Further, a low reflection layer 16 having a low reflectance with respect to the wavelength of light used for optical inspection of the pattern is further laminated on the body layer 15, and two types of patterns including a pattern having the low reflection layer 16 as the uppermost layer. It is more configuration. On the other main surface of the substrate 11, a conductive layer 17 is provided for an electrostatic chuck for mounting the reflective mask on an exposure apparatus or the like.

  FIG. 2 is a schematic cross-sectional view showing another example of the embodiment of the reflective mask of the present invention. As shown in FIG. 2, the reflective mask 20 has a structure without the buffer layer 14, and the other components are the same as those of the reflective mask 10 of FIG. 1, and the same reference numerals are used.

  In the reflective mask, the low reflective layer 16 is usually made of nitride (TaN) or oxide (TaO) such as tantalum, and has low conductivity, so it is charged unevenly by an electron beam from an electron beam microscope. This is likely to cause a change in contrast of the electron beam image and distortion of the image, leading to deterioration in inspection sensitivity and instability in electron beam inspection. Therefore, it is considered that a mask pattern structure in which the low reflection layer 16 is not provided on the uppermost layer is suitable for the electron beam inspection. Here, in the electron beam mask inspection apparatus used normally, this inventor has confirmed that the absorber layer is not damaged by the irradiated electron beam as described in the above cited reference 1.

  The defect of the mask pattern includes a defect called a so-called white defect in which an originally required pattern portion is lost and a defect called a so-called black defect in which an originally unnecessary portion remains. In the present invention, the above-described pattern defect inspection includes inspection of a dimensional defect whose pattern size does not fall within a specification value, a defect due to adhesion of a white defect, a black defect, and a foreign substance of the pattern.

  In the present invention, by using the reflective mask 10, the pattern having the absorber layer 15 as the uppermost layer is inspected with an electron beam, and the pattern having the low reflective layer 16 as the uppermost layer is optically inspected. It is possible to inspect the pattern of the reflective mask pattern for EUV exposure with high resolution while maintaining high throughput. The reflection type mask of the present invention is a mask that improves the inspection accuracy and inspection speed of the mask pattern without causing any trouble in the pattern transferred by EUV exposure.

  Further, in the reflective mask 10 of the present invention, the pattern having the absorber layer 15 as the uppermost layer is a critical pattern portion having strict dimensions and dimensional accuracy required in the circuit, and the low reflective layer is the uppermost layer. The pattern is a non-critical pattern portion that does not require the same size and dimensional accuracy as the critical pattern portion. In the present invention, the above dimensions and dimensional accuracy include the pattern CD (Critical Dimension) itself and its accuracy, as well as the pattern pitch itself and its accuracy.

  The critical pattern portion in the present invention will be described. Usually, 30 to 40 mask patterns are used to manufacture an LSI. These masks have critical layers with critical dimensions and dimensional accuracy, or have critical dimensions and dimensional accuracy, depending on the strictness of dimensional and dimensional accuracy required in the circuit of the pattern, pattern density, influence on device performance, etc. It is classified as a mask having a non-critical layer that is not so severe.

  Furthermore, even within a single mask, even a mask having a critical layer, not all regions are occupied by critical patterns, and there are critical patterns and non-critical patterns. Of the LSI mask patterns, parts with particularly high dimensional accuracy and high dimensional accuracy required for the circuit are called critical pattern parts, and parts other than critical pattern parts that do not require much dimensional and dimensional precision are included. This is called a non-critical pattern part. Examples of the critical pattern part include an FET gate pattern part, a contact pattern part, a wiring pattern part, and a pattern part having a short distance between adjacent patterns. Examples of the non-critical pattern part include a dummy pattern part and a CMP (Chemical Mechanical Polishing) pattern part. The critical pattern portion requires OPC (Optical Proximity Correction) with a large amount of data, and the non-critical pattern portion may be simplified OPC, simple graphic operation, or data itself.

  FIG. 3 is a schematic plan view showing an example of a pattern layout in the reflective mask of the present invention. The transfer pattern provided on the reflective mask 30 has a critical pattern portion 31 having the strictest dimension and dimensional accuracy required in the circuit, a pattern portion 32 in which a critical pattern and a rough pattern are mixed, a size and a critical pattern. It can be divided into four types of pattern portions, that is, a medium pattern portion 33 that does not require dimensional accuracy and a rough pattern portion 34 that does not have strict dimensional accuracy and dimensional accuracy. In the present invention, the critical pattern portion 31 and the critical pattern mixed portion 32 are combined as one critical pattern portion, the medium pattern portion 33 and the rough pattern portion 34 are combined as one non-critical pattern portion, and the above pattern The portion is divided into two types of pattern portions. The critical pattern portion is inspected with an electron beam, and the non-critical pattern portion is optically inspected. Whether a pattern is critical or non-critical can be determined by analyzing layout pattern data before OPC processing.

  As described above, in the reflective mask of the present invention, the pattern having the absorber layer as the uppermost layer is a critical pattern portion having strict dimensions and dimensional accuracy required in the circuit, and the pattern having the low reflective layer as the uppermost layer. Is a mask that is a non-critical pattern part that does not require the same size and dimensional accuracy as the critical pattern part, and the critical pattern part is subjected to electron beam inspection, and the non-critical pattern part is optically inspected. It is to inspect for defects.

  Using the reflective mask of the present invention, the mask pattern is divided into a critical pattern portion and a non-critical pattern portion according to the required degree of dimensional and dimensional accuracy, and the critical pattern portion with strict dimensional and dimensional accuracy required on the circuit. Inspects a reflective mask for EUV exposure with high resolution while maintaining high throughput by optically inspecting non-critical pattern portions that do not require dimensions and dimensional accuracy as high as critical pattern portions. It becomes possible.

  The reflective mask of this embodiment can be applied with the constituent material of the conventional reflective mask as it is, but will be described below.

(substrate)
The substrate 11 of the reflective mask 10 of the present invention has a low thermal expansion coefficient in order to maintain high pattern position accuracy, and has high smoothness and flatness in order to obtain high reflectivity and transfer accuracy. A glass substrate having excellent resistance to a cleaning solution used for cleaning in the manufacturing process is preferable. Glass substrate such as quartz glass, SiO ₂ —TiO ₂ low thermal expansion glass, crystallized glass on which β quartz solid solution is deposited, and silicon It can also be used. As the flatness of the mask blank, for example, 50 nm or less is required in the pattern region.

(Multilayer reflective film)
The multilayer reflective film 12 is made of a material that reflects EUV light used for EUV exposure with high reflectivity, and a multilayer film made of Mo and Si is frequently used. For example, Mo having a thickness of 2.74 nm and 4.11 nm are used. The reflective film which consists of a multilayer film which laminated | stacked 40 each of Si of this is mentioned. Other than that, as a material capable of obtaining a high reflectance in a specific wavelength range, Ru / Si, Mo / Be, Mo compound / Si compound, Si / Nb periodic multilayer film, Si / Mo / Ru periodic multilayer film, Si / Mo / Ru / Mo periodic multilayer film and Si / Ru / Mo / Ru periodic multilayer film can also be used. However, the optimum film thickness varies depending on the material. In the case of a multilayer film composed of Mo and Si, a Si film is first formed in an Ar gas atmosphere using a Si target by a DC magnetron sputtering method, and then a Mo film is used in an Ar gas atmosphere using a Mo target. Is formed as a cycle, and laminated for 30 to 60 cycles, preferably 40 cycles, to obtain a multilayer reflective film.

(Capping layer)
In order to increase the reflectivity of the multilayer reflective film 12, it is preferable to use Mo having a large refractive index as the uppermost layer. However, since Mo is easily oxidized in the atmosphere and the reflectivity is lowered, the Mo is prevented from being oxidized or mask washed. As a protective film for protecting Mo, Si or Ru may be formed by sputtering or the like, and the capping layer 13 may be provided. For example, Si is provided as a capping layer 13 on the uppermost layer of the multilayer reflective film 12 to a thickness of 11 nm. When ruthenium (Ru) is used as a capping layer, since Ru also has a function as a buffer layer, damage to the multilayer reflective film due to etching during pattern formation of the absorber layer and during pattern correction can be prevented. As shown in FIG. 2, a structure without a buffer layer can be obtained. The film thickness when Ru is used as a capping layer is preferably selected in the range of 0.5 nm to 5 nm.

(Buffer layer)
In order to prevent damage to the lower multilayer reflective film 12 when the absorber layer 15 that absorbs EUV light used for EUV exposure is subjected to pattern etching by a method such as dry etching, the multilayer reflective film 12 is usually used. And the absorber layer 15 are provided with a buffer layer 14. The buffer layer and the absorber layer preferably have different etching characteristics. Although CrN is frequently used as the material of the buffer layer 14, depending on the conditions for etching the absorber layer, Al ₂ O ₃ , Cr, SiO ₂ or the like may be used as a material having high etching resistance. In the case of using CrN, a CrN film having a thickness of about 5 nm to 15 nm is formed on the multilayer reflective film in a mixed gas atmosphere of Ar gas and nitrogen gas using a Cr target by RF magnetron sputtering. Is preferred.

(Absorber layer)
The material of the absorber layer 15 that forms a mask pattern and absorbs EUV light is selected from Ta, TaB, TaBN and other materials containing Ta as the main component, Cr, Cr as the main component, N, O, and C. A material containing at least one component is used in a thickness range of about 30 nm to 100 nm, and is formed by a sputtering method or the like.

(Low reflective layer)
For pattern inspection of the reflective mask, light having a wavelength of about 190 nm to 260 nm is usually used. For example, in order to increase the detection sensitivity at the time of mask pattern inspection using inspection light having a wavelength of 257 nm or 193 nm, the low reflection layer 16 having low reflection with respect to inspection light is provided on the absorber layer 15. Examples of the material of the low reflection layer 16 include tantalum nitride (TaN), oxide (TaO), oxynitride (TaNO), tantalum boron oxide (TaBO), and tantalum boron nitride (TaBN). The film thickness is about 5 nm to 30 nm and is formed by sputtering or the like. As described above, in the present invention, the low reflection layer 16 is provided on the absorber layer 15 in the non-critical pattern portion, but the low reflection layer 16 is not provided on the absorber layer 15 in the critical pattern portion. .

(Conductive layer)
As described above, the conductive layer 17 is provided for the electrostatic chuck of the EUV exposure mask, and the conductive layer 17 is provided with a thin film such as a metal or metal nitride exhibiting conductivity. For example, Cr, CrN, or the like is used by forming a film with a thickness of about 20 nm to 150 nm by a sputtering method or the like.
Next, the manufacturing method of the reflective mask of this invention is demonstrated.

<Manufacturing method of reflective mask>
The reflective mask manufacturing method of the present invention is formed by providing at least a multilayer reflective film that reflects EUV light and an absorber layer that absorbs EUV light on the multilayer reflective film on one main surface of the substrate. A method for manufacturing a reflective mask for EUV exposure having a transferred pattern, wherein a multilayer reflective film, an absorber layer, and a reflectance for a wavelength of light used for optical inspection of a pattern are low on a substrate A step of preparing a reflective mask blank in which a low reflective layer is laminated in this order, a first resist pattern is formed on the low reflective layer, and the low reflective layer and the absorber are formed using the first resist pattern as a mask. The layer is dry-etched to form an absorber layer pattern to be a transfer pattern, and then a step of peeling the first resist pattern, and forming a second resist pattern on the transfer pattern, Using the resist pattern 2 as a mask, the low-reflection layer of the critical pattern part with strict dimensions and dimensional accuracy required on the circuit of the transfer pattern is removed by dry etching to obtain a pattern with the absorber layer as the uppermost layer. And a step of peeling the second resist pattern, wherein the transfer pattern formed on the absorber layer has a critical pattern portion with the absorber layer as the uppermost layer and a critical pattern portion with the low reflection layer as the uppermost layer. It is characterized in that it is formed by two types of patterns including a non-critical pattern portion that does not require the same size and dimensional accuracy.

  According to the reflective mask manufacturing method of the present invention, the critical pattern portion is inspected with an electron beam by removing the low reflective layer of the critical pattern portion including the critical pattern mixed portion by etching in the above-described steps, By inspecting other non-critical pattern parts by optical inspection, inspection with high throughput is possible while maintaining high inspection sensitivity, and it is suitable for both optical inspection and electron beam inspection with a simple mask manufacturing process. A reflective mask can be manufactured.

  Hereinafter, an embodiment of a manufacturing method of a reflective mask for EUV exposure according to the present invention will be described with reference to the drawings. In the following drawings, the same reference numerals are used to indicate the same parts and materials as those in FIG. In addition, since each constituent material of the reflective mask in the manufacturing method of this invention is the same as the content described in said reflective mask, description is abbreviate | omitted.

(First embodiment)
FIG. 4 and subsequent FIG. 5 are process cross-sectional schematic views showing the first embodiment in the reflective mask manufacturing method of the present invention.

  First, a reflective mask blank 40 for EUV exposure is prepared (FIG. 4A). The reflective mask blank 40 has a pattern formed by providing at least a multilayer reflective film 12 that reflects EUV light on one main surface of the substrate 11 and an absorber layer 15a that absorbs EUV light on the multilayer reflective film 12. It is as a layer. In the reflective mask blank 40 shown in FIG. 4, a capping layer 13 and a buffer layer 14a are further provided in this order on the multilayer reflective film 12, and a low reflective layer 16a is provided on the absorber layer 15a. As described in the reflective mask, each layer constituting the blank is formed by sputtering or the like.

  Next, in order to pattern the absorber layer 15a, a first resist pattern 18 is formed (FIG. 4B), and the low reflection layer 16a and the absorber layer 15a are sequentially dry-etched and patterned for transfer. An absorber layer pattern (consisting of the low reflection layer 16 and the absorber layer 15) to be a pattern is formed, and the first resist pattern 18 is peeled off (FIG. 4C). It is preferable to perform defect inspection during the mask manufacturing process and defect correction accompanying the inspection at this stage. However, since the low reflection layer 16 is still provided on the absorber layer 15, when the conductivity of the low reflection layer 16 is low, in the present embodiment, it is described in the above [Problems to be solved by the invention]. As described above, the electron beam inspection during the mask manufacturing process is unsuitable, and the optical inspection is preferably applied.

  Next, the buffer layer 14a is dry-etched to produce a reflective mask 50 as shown in FIG. In the above step, the first resist pattern 18 may be peeled after the buffer layer 14 is formed.

  The reflective mask 50 includes at least a multilayer reflective film 12 that reflects EUV light on one main surface of the substrate 11, and an absorber layer 15 that absorbs EUV light on the multilayer reflective film 12 to provide a pattern forming layer. It is said. In the reflective mask 50 shown in FIG. 4D, a capping layer 13 and a buffer layer 14 are sequentially provided on the multilayer reflective film 12, and a low reflective layer 16 is provided on the absorber layer 15. I am doing.

Since the reflective mask 50 and its manufacturing method shown in FIG. 4D are known, details of the manufacturing method of FIG. 4 are omitted. The reflective mask 50 shown in FIG. 4 (d) can also perform defect inspection and defect correction accompanying inspection, but when the low reflective layer 16 has low conductivity, the electron beam inspection is inappropriate. Application of optical inspection is preferred.
Next, FIG. 5 shows a manufacturing method of the reflective mask of the present invention following FIG.

  As shown in FIG. 5A, the second resist layer 19a is applied and formed on the transfer pattern forming side of the substrate 11 using the reflective mask 50 described in FIG. Next, as shown in FIG. 5B, pattern exposure is performed so as to leave only the second resist pattern 19 on the non-critical pattern portion, and development is performed to expose the critical pattern portion.

  Next, as shown in FIG. 5C, with the second resist pattern 19 as a mask, the exposed low reflective layer 16 of the critical pattern portion is removed by dry etching, and the absorber layer 15 is used as the uppermost layer. Expose. Next, the second resist pattern 19 is peeled, and the pattern formed on the absorber layer 15 is divided into a critical pattern portion having the absorber layer 15 as the uppermost layer and a critical pattern portion having the low reflection layer 16 as the uppermost layer. The reflective mask 10 having two types of patterns, ie, a non-critical pattern that does not require the above-mentioned dimensions and dimensional accuracy, is formed (FIG. 5D). In the reflective mask 10 shown in FIG. 5D, the critical pattern portion having the absorber layer 15 as the uppermost layer is inspected with an electron beam having high resolution, and the non-critical pattern portion having the low reflection layer 16 as the uppermost layer. Can be inspected with light with high throughput. Furthermore, defects can be corrected as necessary.

  Various methods have been proposed for correcting defects. For example, a black defect is formed by transferring a defect image onto a wafer at the time of wafer exposure using a mask. In the present invention, various methods that have been conventionally used for correcting black defects on a photomask can be applied. For example, a gas assist etching method using an ion beam of a focused ion beam (FIB) mask correction apparatus, a gas assist etching method using an electron beam of an electron beam mask correction apparatus, or an atomic force microscope (AFM) A method of physically grinding defects using a probe is used.

  As described above, according to the reflective mask manufacturing method of the present embodiment, a reflective mask suitable for optical inspection and electron beam inspection can be manufactured with a simple manufacturing process. The critical pattern portion of the manufactured reflective mask is inspected with an electron beam, and the non-critical pattern portion is inspected with an optical inspection, thereby enabling inspection with high throughput while maintaining high inspection sensitivity.

(Second Embodiment)
FIG. 6 and subsequent FIG. 7 are process cross-sectional schematic views showing a second embodiment of the reflective mask manufacturing method of the present invention. The present embodiment enables electron beam inspection and optical inspection of a mask during mask manufacturing.

  As in the first embodiment, a reflective mask blank 40 for EUV exposure is prepared (FIG. 6A). The reflective mask blank 40 has a pattern formed by providing at least a multilayer reflective film 12 that reflects EUV light on one main surface of the substrate 11 and an absorber layer 15a that absorbs EUV light on the multilayer reflective film 12. It is as a layer. In the reflective mask blank 40 shown in FIG. 6, a capping layer 13 and a buffer layer 14a are sequentially provided on the multilayer reflective film 12, and a low reflective layer 16a is provided on the absorber layer 15a.

  Next, in order to pattern the absorber layer 15a, a first resist pattern 18 is formed (FIG. 6B), and the low reflection layer 16a and the absorber layer 15a are sequentially dry-etched and patterned for transfer. An absorber layer pattern composed of the low reflection layer 16 and the absorber layer 15 to be a pattern is formed, and the first resist pattern 18 is peeled off (FIG. 6C).

  Next, FIG. 7 shows a manufacturing method of the reflective mask of the present invention following FIG. As shown in FIG. 7A, a second resist layer 19a is applied and formed on the transfer pattern forming side of the substrate 11. Next, as shown in FIG. 7B, pattern exposure is performed so as to leave only the second resist pattern 19 on the non-critical pattern portion, and development is performed to expose the critical pattern portion.

  Next, as shown in FIG. 7C, by using the second resist pattern 19 as a mask, the exposed low reflective layer 16 of the critical pattern portion is removed by dry etching, and the absorber layer 15 is used as the uppermost layer. Expose.

  Next, the second resist pattern 19 is peeled, and the pattern formed on the absorber layer 15 is divided into a critical pattern portion having the absorber layer 15 as the uppermost layer and a critical pattern portion having the low reflection layer 16 as the uppermost layer. A substrate having two types of patterns, that is, a non-critical pattern that does not require the above-described dimensions and dimensional accuracy, is manufactured. At this stage, the buffer layer 14a is unprocessed (FIG. 7D).

  As described in the first embodiment, in the present invention, various methods that have been conventionally used for correcting black defects on a photomask can be applied. The reflective mask also functions to prevent damage to the underlying multilayer reflective film when the buffer layer is repaired with a defect. Therefore, it is preferable to perform the defect inspection during the mask manufacturing process and the defect correction based on the inspection result at the stage shown in FIG. In the present embodiment, the critical pattern portion having the absorber layer 15 as the uppermost layer is inspected with an electron beam having high resolution, and the non-critical pattern portion having the low reflection layer 16 as the uppermost layer is light having a high throughput. It is possible to inspect with.

  Next, the buffer layer 14a is dry-etched to produce the reflective mask 10 as shown in FIG. In the reflective mask 10 shown in FIG. 7E, the critical pattern portion having the absorber layer 15 as the uppermost layer is inspected with an electron beam having high resolution, and the non-critical pattern portion having the low reflection layer 16 as the uppermost layer. Can be inspected with light with high throughput. Further, when a defect is detected by pattern defect inspection of the manufactured mask, the defect can be corrected using the above-described defect correction method.

As described above, according to the reflective mask manufacturing method of the present embodiment, a reflective mask suitable for optical inspection and electron beam inspection can be manufactured with a simple manufacturing process. According to the present embodiment, not only the manufactured reflective mask but also during the mask manufacturing, the critical pattern portion can be inspected by the electron beam, and the non-critical pattern portion can be inspected by the optical inspection, and the high inspection sensitivity. High-throughput inspection is possible while maintaining
Next, the inspection method for the reflective mask of the present invention will be described.

<Inspection method of reflective mask>
The reflective mask inspection method of the present invention is formed by providing, on one main surface of a substrate, at least a multilayer reflective film that reflects EUV light and an absorber layer that absorbs EUV light on the multilayer reflective film. A mask pattern inspection method for inspecting a defect of a reflective mask pattern for EUV exposure having a transferred pattern, wherein the pattern formed on the absorber layer is a pattern having the absorber layer as the uppermost layer. A low reflection layer having a low reflectivity with respect to the wavelength of light used for optical inspection of the pattern is laminated on the absorber layer, and is composed of two types of patterns, the pattern having the low reflection layer as the uppermost layer, and the absorber The pattern with the top layer as the uppermost layer is a critical pattern part with strict dimensions and dimensional accuracy required on the circuit, and the pattern with the lower reflection layer as the uppermost layer has a dimension as large as the critical pattern part. A non-critical pattern portion which does not require fine dimensional accuracy, the critical pattern portion checks electron beam, is a non-critical pattern portion characterized in that optical inspection.

  Further, the mask pattern inspection method of the present invention can perform the above inspection method also in the course of mask manufacturing, and the reflective mask has a buffer layer and the absorber layer is the uppermost layer. The electron beam inspection of the critical pattern part and the optical inspection of the non-critical pattern part are performed after forming the two types of patterns with the low reflection layer as the uppermost layer and before the etching of the buffer layer. It is.

According to the mask pattern inspection method of the present invention, using the reflective mask of the present invention, the pattern having the absorber layer as the uppermost layer is inspected by an electron beam, and the pattern having the low reflection layer as the uppermost layer is optically inspected. Thus, it is possible to inspect pattern defects of a reflective mask for EUV exposure with high resolution while maintaining high throughput. As described above, in the present invention, pattern defect inspection includes inspection of defects such as dimensional defects, pattern defects, and foreign matters. The reflective mask inspection method of the present invention is an inspection method in which the pattern transferred by EUV exposure does not cause any trouble, and the mask pattern inspection accuracy and inspection speed can be improved.
Hereinafter, the present invention will be described in more detail by way of examples.

Example 1
On one main surface (front surface) of a 6-inch square (0.25-inch thick) synthetic quartz substrate that has been optically polished, a Si film using a Si target in an Ar gas atmosphere by DC magnetron sputtering. 4.2 nm, and then using a Mo target to form a 2.8 nm Mo film, stacking it for 40 periods, and finally forming a 11 nm Si film as a capping layer, A multilayer reflective film that reflects EUV light composed of a multilayer film of Mo and Si was formed. Next, a CrN film having a thickness of 10 nm was formed on the above capping layer in a mixed gas atmosphere of Ar and nitrogen using a Cr target by an RF magnetron sputtering method to form a buffer layer.

  Subsequently, a TaBN film is formed to a thickness of 80 nm in a mixed gas atmosphere of Ar and nitrogen using a target containing Ta and B by DC magnetron sputtering method on the CrN film, and absorbs EUV light. It was set as the absorber layer. Next, a TaBO film having a thickness of 10 nm was formed on the TaBN film by a DC magnetron sputtering method in a mixed gas atmosphere of Ar and oxygen to form a low reflection layer. Next, on the other main surface (back surface) of the synthetic quartz substrate, Cr was deposited to a thickness of 0.1 μm by RF sputtering to form a conductive layer, thereby obtaining a reflective mask blank for EUV exposure.

Next, using this EUV exposure mask blank, an EB resist was applied on the TaBO film low-reflection layer, and EB drawing was performed to form a first resist pattern. Next, the TaBO film low-reflection layer and the TaBN film absorber layer were dry-etched in the order of CF ₄ gas and Cl ₂ gas, respectively, and the first resist pattern was peeled off to form an absorber layer pattern. Subsequently, the CrN film buffer layer was dry-etched with a mixed gas of Cl ₂ and O ₂ to produce a reflective mask in which the uppermost layer of the pattern was a TaBO film low-reflection layer.

  Next, using the above-described reflective mask, a second resist layer is applied and formed on the transfer pattern forming side of the substrate, pattern exposure is performed so as to leave only the second resist pattern on the non-critical pattern portion, and development is performed. Then, the critical pattern portion was exposed. The distinction between the critical pattern part and the non-critical pattern part was made from the layout pattern data.

  Next, using the second resist pattern as a mask, the exposed TaBO film low reflection layer in the critical pattern portion was removed by dry etching, and the TaBN film absorber layer was exposed as the uppermost layer. Next, the second resist pattern is peeled off, and the pattern formed on the absorber layer is divided into a critical pattern portion having the TaBN film absorber layer as the uppermost layer and a critical pattern portion having the TaBO film low reflection layer as the uppermost layer. A reflective mask having two types of patterns, ie, a non-critical pattern that does not require the above dimensions and dimensional accuracy, was prepared.

  In the above-described reflective mask, the critical pattern portion having the TaBN film absorber layer as the uppermost layer is inspected for pattern defects by an electron beam inspection apparatus having high resolution, and the non-critical layer having the TaBO film low-reflection layer as the uppermost layer. The pattern portion can be inspected for pattern defects with a DUV inspection apparatus having a high throughput, and the mask pattern inspection accuracy and inspection speed have been improved.

(Example 2)
Using a reflective mask blank having the same configuration as that of Example 1, an EB resist was applied on the blank, and EB writing was performed to form a first resist pattern. Next, the TaBO film low-reflection layer and the TaBN film absorber layer were dry-etched in the order of CF ₄ gas and Cl ₂ gas, respectively, and the first resist pattern was peeled off to form an absorber layer pattern.

  Next, a second resist layer was applied and formed on the transfer pattern forming side of the substrate, pattern exposure was performed so as to leave only the second resist pattern on the non-critical pattern portion, and development was performed to expose the critical pattern portion.

Next, using the second resist pattern as a mask, the exposed TaBO film low reflection layer in the critical pattern portion was removed by dry etching with CF ₄ gas to expose the TaBN film absorber layer as the uppermost layer.
Next, the second resist pattern is peeled off, and the pattern formed on the absorber layer is divided into a critical pattern portion having the TaBN film absorber layer as the uppermost layer and a critical pattern portion having the TaBO film low reflection layer as the uppermost layer. The non-critical pattern that does not require the above-mentioned dimensions and dimensional accuracy, and the CrN film buffer layer was patterned to produce an unprocessed substrate.

Next, the defect inspection of the absorber layer pattern formed on the substrate was performed. The critical pattern portion having the TaBN film absorber layer as the uppermost layer was inspected with an electron beam having high resolution, and the non-critical pattern portion having the TaBO film low-reflection layer as the uppermost layer was inspected with light having a high throughput. The same apparatus as in Example 1 was used as the inspection apparatus. Since black defects estimated to be the residue of the absorber layer were detected by inspection, an electron beam mask repair device (MeRiT 65; manufactured by Carl Zeiss) was used to gas assist / etch the black defects using Cl ₂ as an assist gas. Removed and corrected. Since an unprocessed CrN film buffer layer is provided under the black defect, the multilayer reflective film was prevented from being damaged during defect correction.

Next, the buffer layer was patterned by dry etching with a mixed gas of Cl ₂ and O ₂ to produce a reflective mask. The produced reflective mask can be inspected with an electron beam for the critical pattern part with the TaBN film absorber layer as the uppermost layer, and can be inspected with a light for the non-critical pattern part with the TaBO film low reflection layer as the uppermost layer. Yes, the mask pattern inspection accuracy and inspection speed were improved.

10, 20 Reflective mask 11 Substrate 12 Multi-layer reflective film 13 Capping layer 14 Buffer layer 14a Buffer layer (before patterning)
15 Absorber layer 15a Absorber layer (before patterning)
16 Low reflective layer 16a Low reflective layer (before patterning)
17 Conductive layer 18 1st resist pattern 19a 2nd resist layer 19 2nd resist pattern 30 Pattern layout 31 Critical pattern part 32 Critical / rough pattern part 33 Medium pattern part 34 Rough pattern part 40 Reflective mask blanks 80 Reflective type Mask 81 Substrate 82 Reflection layer 83 Buffer layer 84 Exposure light absorber layer 85 Low reflection layer 86 Absorber layer

Claims (5)

For EUV exposure having a transfer pattern formed by providing at least a multilayer reflective film for reflecting EUV light and an absorber layer for absorbing EUV light on the multilayer reflective film on one main surface of the substrate A reflective mask of
The transfer pattern formed on the absorber layer includes a pattern having the absorber layer as an uppermost layer, and a low reflection layer having a low reflectance with respect to the wavelength of light used for optical inspection of the pattern on the absorber layer. A reflective mask characterized in that it is composed of two types of patterns, which are laminated and have the low reflective layer as the uppermost layer.   The pattern having the absorber layer as the uppermost layer is a critical pattern portion that has strict dimensions and dimensional accuracy required in the circuit, and the pattern having the low reflection layer as the uppermost layer has the same size and size as the critical pattern portion. The reflective mask according to claim 1, wherein the reflective mask is a non-critical pattern portion that does not require accuracy. For EUV exposure having a transfer pattern formed by providing at least a multilayer reflective film for reflecting EUV light and an absorber layer for absorbing EUV light on the multilayer reflective film on one main surface of the substrate A reflective mask manufacturing method of
Providing a reflective mask blank in which the multilayer reflective film, the absorber layer, and a low reflective layer having a low reflectance with respect to the wavelength of light used for pattern optical inspection are laminated in this order on the substrate; ,
A first resist pattern is formed on the low-reflection layer, and the low-reflection layer and the absorber layer are dry-etched using the first resist pattern as a mask to form an absorber layer pattern serving as a transfer pattern And then peeling off the first resist pattern;
Forming a second resist pattern on the transfer pattern, and using the second resist pattern as a mask, the low reflective layer in the critical pattern portion with strict dimensions and dimensional accuracy required on the circuit of the transfer pattern. Removing the second resist pattern after performing dry etching to form a pattern having the absorber layer as the uppermost layer,
The transfer pattern formed on the absorber layer includes a critical pattern portion having the absorber layer as the uppermost layer and a size and dimensional accuracy as low as the critical pattern portion having the low reflection layer as the uppermost layer. A method of manufacturing a reflective mask, characterized in that the reflective mask is formed by two types of patterns with a critical pattern portion. For EUV exposure having a transfer pattern formed by providing at least a multilayer reflective film for reflecting EUV light and an absorber layer for absorbing EUV light on the multilayer reflective film on one main surface of the substrate A mask pattern inspection method for inspecting defects of a reflective mask pattern,
The transfer pattern formed on the absorber layer includes a pattern having the absorber layer as an uppermost layer, and a low reflection layer having a low reflectance with respect to the wavelength of light used for optical inspection of the pattern on the absorber layer. It is composed of two types of patterns, a laminate and a pattern with the low reflective layer as the uppermost layer,
The pattern having the absorber layer as the uppermost layer is a critical pattern portion that has strict dimensions and dimensional accuracy required in the circuit, and the pattern having the low reflection layer as the uppermost layer has the same size and size as the critical pattern portion. It is a non-critical pattern part that does not require accuracy,
A mask pattern inspection method, wherein the critical pattern portion is subjected to electron beam inspection, and the non-critical pattern portion is optically inspected.   5. The mask pattern inspection method according to claim 4, wherein the reflective mask has a buffer layer, and the electron beam inspection of the critical pattern portion and the optical inspection of the non-critical pattern portion are performed on the absorber layer. A mask pattern inspection method, which is performed after the pattern is formed and before the etching of the buffer layer.

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