JP2017146547A - Reflection type photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce reflection ratio of an out of band light which includes in a light source of exposure light and reaches wafer which is an article to be exposed in a reflection type photomask having a light shielding area for reducing effects of multiple light exposure formed.SOLUTION: There is provided a reflection photomask having a substrate, a multilayer reflection film and an absorption film, a surface of the photomask is divided into a plurality areas including a circuit pattern area and a light shielding area in an outside of the circuit pattern area, the multilayer reflection film and the absorption film are laminated on the substrate in this order in the circuit pattern area, the absorption film consists a circuit pattern, the substrate surface has an uneven structure in the light shielding area and average reflection ratio to an incident light with wavelength of 100 to 400 nm is 4% or less in the light shielding area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reflective photomask for lithography.

  In the manufacturing process of a semiconductor device, with the miniaturization of a semiconductor device, the demand for miniaturization in the photolithography technology is increasing. In recent years, ArF excimer laser light having a wavelength of 193 nm has been mainly used as exposure light for photolithography. At present, application of light having a wavelength region of 15 nm or less (hereinafter referred to as “EUV light”) called EUV (Extreme Ultra Violet) light, particularly EUV light having a wavelength of 13.5 nm, is in progress.

  Since EUV light is very easily absorbed by most substances, a photomask used for EUV exposure (hereinafter referred to as “EUV mask”) is different from a conventional transmission type photomask, and is a reflective type. It becomes a photomask. An EUV mask is, for example, a multilayer reflective film in which a molybdenum (Mo) layer and a silicon (Si) layer are alternately laminated on a glass substrate, and a light absorption generally comprising tantalum (Ta) as a main component. A film is formed, and a circuit pattern is formed on the light absorption film.

  In lithography using an EUV mask, in general, the incident angle of EUV light to the EUV mask is tilted by about 6 degrees, and the reflected EUV light is guided to a wafer that is an object to be exposed, and applied to the wafer. A resist having photosensitivity is exposed.

  When the incident angle of the EUV light incident on the EUV mask is tilted as described above, when the EUV light is reflected by the circuit pattern on the EUV mask, depending on the direction of the reflected light, a part of the circuit pattern by the light absorption film may be It is known that a phenomenon (so-called projection effect) occurs in which a shadow is formed and the wafer is not irradiated. Therefore, in order to suppress the projection effect, a method is used in which the thickness of the light absorption film on which the circuit pattern is formed is reduced to reduce the influence of the shadow.

  However, if the light absorption film is made thin, the amount of attenuation of light originally required in the light absorption film is insufficient, so that the reflected light of the EUV light irradiated to the resist on the wafer increases more than necessary, and the circuit pattern formation accuracy There is concern about deterioration. In addition, in an actual exposure process, chips are often applied to a single wafer, so that there is a particular concern that the amount of exposure to the resist in the boundary region between adjacent chips increases. That is, multiple exposure occurs in the boundary region between chips, which affects the formation accuracy of the circuit pattern, resulting in a reduction in the quality and throughput of chips obtained in subsequent processes.

  Therefore, when thinning the light absorption film as described above, all of the light absorption film and multilayer reflection film on the outer periphery surrounding the circuit pattern of the photomask, which is a boundary region between adjacent chips on the wafer, are removed. There is a method of forming a groove dug up to the surface of a glass substrate (see Patent Document 1). This is intended to suppress the multiple exposure in the boundary region between adjacent chips by suppressing the reflection of the EUV light by using the groove described above as a light blocking region having a high light blocking property with respect to the wavelength of the EUV light.

However, from a light source that generates EUV light, not only light in the EUV region near 13.5 nm, but also vacuum ultraviolet light (VUV; about 200 nm or less), deep ultraviolet light (DUV; about 300 nm or less), ultraviolet light (UV; about 400 nm). In the following, light in a wavelength band extending in the near infrared (about 800 nm) and further in the infrared region (1000 nm or more) is often emitted. These wavelength bands are generally called out-of-band. In this way, light having an out-of-band wavelength (hereinafter referred to as “OOB light”) is incident on the EUV mask along with the EUV light.

  In the light shielding region of the conventional EUV mask described above, the light shielding property of EUV light is relatively high, but the light shielding property of out-of-band light is relatively low. For this reason, reflection of EUV light in the light emitted from the light source can be hardly suppressed in the light shielding region, but a part of the OOB light is reflected on the light shielding region and irradiated onto the wafer. In addition, there is a problem that multiple exposure as described above occurs in the boundary region between chips. Since the resist for EUV lithography used on the wafer is originally developed based on a resist for lithography of KrF light (wavelength 248 nm) or ArF light (wavelength 193 nm), OOB light particularly in the wavelength region of 100 to 400 nm. The photosensitivity is high.

  Then, when looking at the technique for solving such a problem, there is a technique described in Patent Document 2. This is because a fine pattern is formed on the back surface opposite to the multilayer reflective film of the glass substrate, whereby the OOB light incident on the light shielding region reaches the back surface of the glass substrate, and then the back surface conductive film. It suppresses reflection.

JP 2009-212220 A JP 2013-074195 A

  In order to verify the technique described in Patent Document 2, the present inventors examined the component of OOB light reflected on the light-shielding region and irradiated onto the wafer. As a result, the light reflected on the front (front) surface of the substrate was examined. Was found to be dominant over the light reflected from the backside of the substrate. Therefore, in order to reduce the reflectance of the OOB light incident on the light shielding region, it is not sufficient to suppress the reflected light reflected on the back surface of the substrate, and it is necessary to suppress the reflected light on the surface of the substrate. It came to.

  The present invention has been made in view of the above problems, and an object of the present invention is to be included in a light source of exposure light in a reflective photomask in which a light-shielding region for reducing the influence of multiple exposure is formed. It is an object of the present invention to provide a reflective photomask that can reduce the reflectance of out-of-band light that reaches a wafer, which is an object, as compared with the conventional case.

In order to solve the above-described problem, the invention described in claim 1 is a reflective photomask including a substrate, a multilayer reflective film, and an absorption film,
The surface of the photomask is divided into a plurality of regions including a circuit pattern region and a light shielding region outside the circuit pattern region;
In the circuit pattern region, the multilayer reflective film and the absorption film are laminated in this order on the substrate, and the absorption film constitutes a circuit pattern,
In the light shielding region, the substrate surface has an uneven structure,
The reflective photomask is characterized in that an average reflectance with respect to incident light having a wavelength of 100 to 400 nm in the light shielding region is 4% or less.

  The invention according to claim 2 is the reflective photomask according to claim 1, wherein the average reflectance is 2% or less.

  The invention according to claim 3 is characterized in that the concavo-convex structure includes at least one pattern selected from the group consisting of a line & space pattern, a dot pattern, and a hole pattern in plan view. Alternatively, the reflective photomask described in 2 is used.

  The reflective photomask according to claim 3, wherein the at least one pattern included in the concavo-convex structure has at least one periodic structure in plan view. It is what.

  The invention according to claim 5 is the reflective photomask according to claim 4, wherein at least one period of the periodic structure is 20 nm to 4000 nm.

  The invention according to claim 6 is the reflective photomask according to claim 5, wherein the period of the periodic structure includes at least two periods of 20 nm to 500 nm and 500 nm to 4000 nm. is there.

  The invention according to claim 7 is the reflective photomask according to any one of claims 1 to 6, wherein the depth of the concavo-convex structure is 25 nm or more.

  The invention according to claim 8 is the reflective photomask according to any one of claims 1 to 6, wherein the depth of the concavo-convex structure is 50 nm or more.

  The invention according to claim 9 is the reflective photomask according to any one of claims 1 to 8, wherein a cross-sectional shape of the concavo-convex structure is a rectangular shape or an inclined shape. Is.

  In the invention described in claim 10, the inclined shape is selected from the group consisting of trapezoidal shape, pyramid shape, inverted pyramid shape, hemispherical shape, parabolic shape, conical shape, inverted hemispherical shape, sine curve shape, and hyperbolic shape. The reflective photomask according to claim 9, further comprising at least one shape.

  According to the present invention, in the reflection type photomask in which the light shielding region is formed, the reflection of the out-of-band light in the light shielding region can be suppressed as compared with the conventional case. It is possible to effectively suppress multiple exposure not only in EUV light but also in the boundary region between chips due to out-of-band light. Then, a highly accurate and high quality circuit pattern can be transferred onto the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS (a) Top view (b) Sectional drawing of the reflection type photomask which concerns on this invention. (A) Schematic plan views of a reflective photomask according to the present invention (b) to (j) are schematic plan views showing an example of a pattern of concavo-convex structure in a light shielding region. (A)-(h) The schematic sectional drawing which showed the example of the uneven structure of the light-shielding area | region of the reflection type photomask which concerns on this invention. Example and Comparative Example Production Process of Reflective Photomask (Up to Circuit Pattern Formation) (a) Reflective Photomask Blank (b) After Resist Application (c) After Drawing (d) After Development (e) After Dry Etching (F) After resist removal / cleaning / drying. Production steps of reflective photomasks of Examples and Comparative Examples (until formation of light shielding region) (a) After resist application (b) After drawing (c) After development (d) After dry etching (e) Resist stripping and washing・ After drying. Production process of reflective photomask of example (until formation of uneven structure of light shielding region) (a) After resist application (b) After drawing (c) After development (d) After dry etching (e) Resist peeling / cleaning After drying. 2 is an atomic force microscope image of a concavo-convex structure in a light shielding region of Example 1 (an example of a line and space pattern with a period of 1 μm). The measurement result (line & space pattern) of the spectral reflectance of the OOB light of the light shielding area | region of Example 1 and a comparative example. (A) Dot array pattern (example with a period of 280 nm) (b) Hole array pattern (example with a period of 280 nm). The measurement result of the spectral reflectance of the OOB light of the light shielding area | region of Example 2 (dot array pattern) and a comparative example. The measurement result of the spectral reflectance of the OOB light of the light shielding area | region of Example 2 (hole array pattern) and a comparative example. The measurement result of the spectral reflectance of the OOB light of the light shielding area | region of Example 3 (high aspect ratio dot array pattern) and a comparative example. The relationship between the resist dimension variation | change_quantity (variation with respect to a chip | tip center part) in the chip | tip corner part (quad exposure part) in the exposure evaluation of Example 1 and a comparative example, and an OOB light reflectance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same component unless there is a reason for convenience, and the overlapping description is abbreviate | omitted. In addition, in the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner, and the dimensional ratios of the respective components are not always the same as the actual ones. .
First, components that characterize the reflective photomask of the present invention will be described.

(Whole structure of the reflective photomask of the present invention)
FIG. 1 is a schematic view of a reflective photomask 101 of the present invention. The reflective photomask 101 of the present invention is for EUV lithography that uses 5 to 15 nm wavelength light, particularly 13.5 nm EUV light as exposure light, and its film structure is a multilayer reflective film 12 on a substrate 11 and a protective film. A film 13 and an absorption film 14 are sequentially formed, and a back surface conductive film 15 is provided on the back surface of the substrate 11. Furthermore, the reflective photomask of the present invention includes a light shielding region 20 having a concavo-convex structure 30 so as to surround the circuit pattern region 10.

  The width of the light-shielding area 20 depends on the structure of the EUV exposure machine (exposure area setting accuracy) and the interval of chip arrangement when the semiconductor manufacturer exposes the wafer, but it is usually about 2 mm to 5 mm. In the present invention, the width of the light shielding region is not limited. This is because a sufficient effect can be obtained if the width is at least the necessary width.

(Light-shielding region of the reflective photomask of the present invention)
In the light shielding region 20, the absorption film 14, the protective film 13, and the multilayer reflective film 12 are completely removed. The substrate 11 is exposed on the bottom surface of the light shielding region, and the uneven structure 30 is formed on the surface thereof. Thus, the multilayer reflective film 12 responsible for EUV light reflection is completely removed, so that a light shielding property against EUV light is obtained. EUV light is not reflected by the substrate 11 alone.

  Furthermore, the uneven structure 30 in the light shielding region reduces the reflection of OOB light having a wavelength of 100 to 400 nm emitted from the plasma light source along with the EUV light, and expresses the function of suppressing excessive exposure to the resist on the wafer. ing. When there is no concavo-convex structure 30 on the substrate surface, the reflectance of OOB light is about 5 to 20%. However, if the concavo-convex structure is formed, the average reflectance of OOB light with a wavelength of 100 to 400 nm is reduced to 4% or less. 2% or less can be obtained by selecting a more effective pattern type, period, depth, and cross-sectional shape.

  FIG. 2 shows an example of the uneven structure 30 of the light shielding region. 2B to 2J are enlarged views of a part of the light shielding region of the reflective photomask of the present invention shown in FIG. The uneven structure 30 preferably includes at least one pattern selected from the group consisting of a line & space pattern, a dot pattern, and a hole pattern in plan view. This is because these patterns can have periodicity. In the present invention, the orientation of the pattern does not matter as in FIGS. 2B and 2E, and the shape of the hole or dot in plan view is also a perfect circle, square, triangle, or those shapes are slightly dull. A certain effect can be obtained with any of the patterns.

  The at least one type of pattern preferably has at least one type of periodic structure in plan view and is densely arranged. If the period is 20 to 4000 nm, reflection of OOB light having a wavelength of 100 to 400 nm can be effectively reduced. In a concavo-convex structure with a period substantially equal to or less than the wavelength of the OOB light, a cone-shaped structure (hereinafter referred to as a moth-eye structure) in which the line width gradually changes in cross-sectional view and the refractive index gradually changes in the depth direction from the substrate surface. In this case, the effect of confining light (reducing the reflection) on the substrate surface can be obtained. On the other hand, in the concavo-convex structure having a period substantially equal to or longer than the wavelength of the OOB light, even when it has a rectangular shape in cross-sectional view, a diffraction phenomenon of reflected light appears, regular reflection (0th order diffracted light) decreases, and 1 Second, second,... Diffracted light other than the 0th order increases. Since the light reaching the wafer is only specular reflection, it brings about an effect of reducing the OOB light irradiated to the wafer. Thus, the reflection type photomask of the present invention can be realized by the low reflection effect by the moth-eye structure and the effect of reducing the regular reflection component by the diffraction phenomenon.

  The fact that the low reflection effect of OOB light having a period of 20 to 4000 nm and a wavelength of 100 to 400 nm is high is a result obtained by an experiment, but in what period the pattern is specifically formed. The semiconductor manufacturer using EUV lithography can arbitrarily choose. This is because EUV resists used in EUV lithography are different in each company, and depending on the resist used, the wavelength band with high photosensitivity is different even in OOB light.

  The effect of the above-described concavo-convex structure can be sufficiently obtained even with one type, but for example, there may be two or more types as shown in FIG. First, the reason why the effect can be obtained even with one period is that the low reflection effect and the light diffraction phenomenon due to the moth-eye structure described above are not effective only for a single wavelength, but are effective for a relatively wide wavelength region. To bring. For example, regarding the diffraction phenomenon, when the OOB light hits a concavo-convex structure having a certain period, the reflection angle of the diffracted light such as the first order or the second order varies depending on the respective wavelengths included in the OOB light. The diffraction phenomenon of reflected light itself is surely manifested. Therefore, the specular reflection component decreases and the first-order and second-order diffracted light increases, which is a phenomenon that can be said for a wide wavelength region of OOB light.

  In addition, since there are two or more types of periods of the concavo-convex structure, when there are a plurality of wavelengths in the OOB light that are particularly desired to reduce the reflectance, it is possible to select an effective period for each of these wavelengths. it can. Alternatively, two or more types of cycles can be used in order to strongly develop both the low reflection effect and the diffraction phenomenon due to the moth-eye structure. In particular, a sufficient reflectance reduction effect can be obtained with a concavo-convex structure having two periods of one period of 20 to 500 nm and one period of 500 to 4000 nm.

  Next, the depth (height) D (see FIG. 3) of the concavo-convex structure in the light shielding region of the reflective photomask of the present invention will be described. In order to reduce the low reflection effect by the moth-eye structure and the regular reflection component by the diffraction phenomenon, the depth D of the concavo-convex structure is basically better as it is deeper, but the effect can be obtained even when it is relatively shallow. It became clear by experiment. The depth D of the concavo-convex structure of the present invention is preferably 25 nm or more so that a certain effect can be seen in reducing the reflectance. In order to obtain a sufficient effect, the thickness is desirably 50 nm or more.

  The cross-sectional shape of the concavo-convex structure of the reflective photomask of the present invention is a rectangular shape or an inclined shape. An example of the cross-sectional shape is shown in FIG. Rectangular shape (a), trapezoidal shape (b), pyramid shape (c), inverted pyramid shape (d), hemispherical shape (e), parabolic shape (f), conical shape (c), inverted hemispherical shape (g), It is preferable to include at least one cross-sectional shape selected from the group consisting of a sine curve shape (not shown) and a hyperbolic shape (not shown). Further, as shown in FIGS. 3A, 3B, and 3D and FIG. 3G in which the pattern period P is changed (h), the convex portions of the concavo-convex structure may be flat. Conversely, the concave portion of the concavo-convex structure may be a flat surface.

  The concavo-convex structure having various cross-sectional shapes as described above includes dry etching after heat-flowing the resist, dry etching conditions that provide an isotropic cross-sectional shape, multistage dry etching, variable dry etching that continuously changes conditions, wet It can be formed by a technique such as combined use with etching.

  The concavo-convex structure according to the present embodiment is formed on the entire exposed portion of the substrate in the light shielding region, but the concavo-convex structure according to the present invention is not limited to this, as long as reflection of out-of-band light can be suppressed. Further, it may be formed on a part of the exposed part of the substrate.

(Other matters according to the present invention)
In the above-described embodiment, the reflective photomask manufacturing method according to the present invention is formed by using lithography and dry etching to form the concavo-convex structure. However, the present invention is not limited to this embodiment. For example, a resist pattern formed by nanoimprint or a self-assembled monomolecular film may be used instead of lithography, and wet etching may be used instead of dry etching. Alternatively, a conventional light-shielding region may be formed, and the surface of the exposed substrate may be roughened by sandblasting or plasma treatment to form a concavo-convex structure.

  Regarding the order of forming the concavo-convex structure, in the above-described embodiment, the example in which the concavo-convex structure is formed after the conventional light-shielding region is formed is shown, but the present invention is not limited thereto. For example, a concave / convex structure is formed in the absorption film in a portion that will later become a light shielding region at the same time or before the formation of the circuit pattern in the exposure region, and etching for forming the light shielding region (absorption film, protective film, multilayer) A method of forming the concavo-convex structure of the substrate by transferring the concavo-convex structure of the absorption film to the surface of the underlying substrate by removing the reflective film may be used.

  Hereinafter, other elements constituting the reflective photomask of the present invention will be described.

The material of the substrate 11 is preferably a material having characteristics suitable for processing for forming a fine concavo-convex structure on the surface of the substrate 11 in the light shielding region. For example, a material containing quartz (SiO ₂ ) as a main component and titanium oxide (TiO ₂ ) can be used. When the lithography technique and the etching technique are used as the processing technique, it is desirable to use quartz glass as the material of the substrate 11.

  The multilayer reflective film 12 is a film that reflects EUV light, and a material that has a small absorption (extinction coefficient) with respect to the EUV light and that has a large refractive index difference in the EUV light between the stacked films is used. The multilayer reflective film 12 is designed so that, for example, a reflectance of about 72% can be theoretically achieved with respect to EUV light having a wavelength of 13.5 nm, and a molybdenum (Mo) layer having a thickness of 2 to 3 nm and a thickness of 4 to 5 nm. 40 to 50 pairs of silicon (Si) layers are alternately stacked. Molybdenum (Mo) and silicon (Si) have low absorption (extinction coefficient) with respect to EUV light and a large difference in refractive index with respect to EUV light, so that the reflectance at these interfaces can be made high.

  The protective film 13 needs to be a material having resistance to washing with an acid or an alkali. For example, ruthenium (Ru) having a thickness of 2 to 3 nm or silicon (Si) having a thickness of about 10 nm can be used. When the protective film 13 is made of ruthenium (Ru), the protective film 13 serves as a stopper layer in the processing of the absorption film 14 and serves as a protective film against a chemical solution in mask cleaning. The uppermost layer of the multilayer reflective film 12 located under the protective film 13 made of ruthenium (Ru) is a Si layer.

  When the protective film 13 is made of silicon (Si), a buffer layer (not shown) may be provided between the protective film 13 and the absorption film 14. In this case, the buffer layer is provided to protect the protective film 13 during etching of the absorption film 14 or pattern correction, and can be composed of, for example, a chromium nitrogen compound (CrN). The protective film 13 may have a single layer structure or a laminated structure. When the protective film 13 has a laminated structure, the uppermost layer of the protective film 13 is ruthenium (Ru) and its oxide, nitride, oxynitride, silicon (Si) and its oxide, nitride, and oxynitride. It is formed with the material containing any of these.

  The absorption film 14 is a film that absorbs EUV light, and may have a single-layer structure or a two-layer structure. When the absorption film 14 has a single layer structure, the absorption film 14 is generally made of a material containing, for example, tantalum (Ta) having a high absorption rate for EUV light and any of oxides, nitrides, and oxynitrides thereof. Formed. Specifically, tantalum (Ta), tantalum boron nitride (TaBN), tantalum silicon (TaSi), and oxides thereof (TaO, TaBON, TaSiO) can be used. The film thickness of the absorption film 14 is normally 50 to 70 nm.

  When the absorption film 14 has a two-layer structure, a low reflection layer (not shown) may be provided as an upper layer so as to have an antireflection function for ultraviolet light with a wavelength of 190 to 260 nm for inspection. As the low reflection layer, for example, a material containing any of tantalum (Ta) oxide, nitride, oxynitride, silicon (Si) oxide, nitride, and oxynitride can be used. 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.

  The back surface conductive film only needs to have conductivity, and is generally one of chromium (Cr) or tantalum (Ta) metal or oxide, nitride, oxynitride thereof, or is conductive. It is formed of a material including other metal materials. Specifically, CrN is often used. The film thickness of the back conductive film is 20 to 400 nm.

  The multilayer reflective film 12, the protective film 13, the absorption film 14, and the back surface conductive film described above can be formed using a sputtering method or the like.

  The reflective layer of the reflective photomask according to the present invention is not limited to the multilayer reflective film shown in the above embodiments, and may be a single layer as long as necessary high reflection can be obtained. In addition, the reflective photomask according to the present invention may have a configuration in which the back surface conductive film is not provided on the substrate.

  Hereinafter, examples of the reflective photomask of the present invention will be described in accordance with the manufacturing process, and the results of measuring the reflectance with respect to OOB light will be described.

<Example 1>
(Reflective photomask blank used)
FIG. 4A shows the used reflection type photomask blank. In the reflective photomask blank, 40 pairs of multilayer reflective films 12 of Mo layer and Si layer designed to have a reflectance of about 64% with respect to EUV light having a wavelength of 13.5 nm on the substrate 11. However, a Ru protective film 13 having a thickness of 2.5 nm is formed thereon, and an absorption film 14 made of TaSi having a thickness of 70 nm is further formed thereon. A conductive film 15 is also formed on the back surface. As the substrate 11, an extremely low thermal expansion glass using quartz (SiO ₂ ) (made by Corning, refractive index: 1.4801 to 1.4892) is used.

[Manufacturing process of uneven structure mask]
(Until circuit pattern formation)
In order to form a circuit pattern on the reflective photomask blank, first, a positive chemically amplified resist (resist 21) (SEBP9012: manufactured by Fuji Film Electronics Materials) is formed on the surface of the reflective photomask blank (FIG. 4A). Was applied to a film thickness of 150 nm (FIG. 4B). Next, a 1: 1 line & space pattern having a line width of 100 nm is drawn in an area of 10 cm × 10 cm in the center of the mask by an electron beam drawing machine (JBX3040: manufactured by JEOL) (FIG. 4C), and then 110 PEB was carried out at a temperature of 10 minutes, followed by spray development (SFG3000: manufactured by Sigma Meltech) to form a resist pattern ((FIG. 4 (d)).

Next, the absorption film 14 was etched by CF ₄ plasma and Cl ₂ plasma using a dry etching apparatus (FIG. 4E). Thereafter, the remaining resist pattern was peeled, washed, and dried to produce a reflective photomask having a circuit pattern on the absorption film 14 (FIG. 4F).

(Shading area formation)
Next, an i-line resist (resist 22) is applied to the pattern surface of the reflective photomask with a circuit pattern to a thickness of 500 nm (FIG. 5A), and an i-line drawing machine (ALTA3000: A portion to be a light-shielding region was drawn (Applied Materials Co., Ltd.) (FIG. 5 (b)) and developed (FIG. 5 (c)). As a result, a resist pattern in which a portion to be a light shielding region was opened on the absorption film 14 was formed. At this time, the opening width of the resist pattern was 5 mm, and the distance from the end of the opening to the end of the circuit pattern region previously formed in the 10 cm × 10 cm region was 3 μm.

Thereafter, the absorption film 14, the protective film 13, and the multilayer reflective film 12 in the resist pattern opening are selectively removed by vertical dry etching using CHF ₃ plasma under the following conditions (FIG. 5D), The remaining resist was peeled, washed, and dried to produce a reflective photomask having a light shielding region 20 (FIG. 5E).
The dry etching conditions are as follows.
CHF ₃ flow rate: 20 sccm
Pressure in dry etching equipment: 4 mTorr
ICP (inductively coupled plasma) power: 350 W
RIE (reactive ion etching) power: 200W
Processing time: 6 minutes

  The steps so far are the same as those of the conventional reflective photomask.

(Formation of uneven structure)
Next, a negative chemical amplification resist (resist 23) (FEN271: manufactured by FUJIFILM Electronics Materials Co., Ltd.) was applied to the entire surface of the reflective photomask including the light shielding region with a film thickness of 400 nm (FIG. 6A). ). Next, the entire surface other than the light shielding region is drawn, and three types of 1: 1 line and space patterns having a period of 280 nm (0.28 μm), 1000 nm (1 μm), and 3000 nm (3 μm) are drawn in the light shielding region (FIG. 6). (B)). Thereafter, the line and space pattern of the resist 23 was formed in the light shielding area by PEB and spray development (SFG3000: manufactured by Sigma Meltech) for 10 minutes at 110 ° C. (FIG. 6C).

Next, using a dry etching apparatus, the surface of the substrate 11 is etched with a CF ₄ plasma in a processing time of 60 seconds (FIG. 6D), and then the remaining resist is peeled off, washed and dried, and the light shielding region. A reflective photomask of the present invention having a concavo-convex structure 30 on the substrate surface was prepared (FIG. 6E).

<Comparative example>
The process up to the formation of the light-shielding region (FIG. 5E) in the manufacturing process of the reflective photomask of the first embodiment of the present invention described above is performed using the same material, the same apparatus, and the same process steps, as shown in FIG. A conventional reflective photomask of the form was prepared.

(Measurement by atomic force microscope)
Of the concavo-convex structure of the reflective photomask of the present invention produced in Example 1, the cross-sectional shape and pattern depth of the 1 μm line & space pattern were measured with an atomic force microscope. An observation image at this time is shown in FIG. The pattern cross-sectional shape was slightly round at the bottom of the recess, but was rectangular as shown in FIG. 3A, and the depth D was 57 nm.

(Measurement of OOB light reflectivity)
Spectral reflectivity measurement of OOB light having a wavelength of 200 to 400 nm was carried out for both the reflection type photomask having the concavo-convex structure in the light shielding region of Example 1 and the reflection type photomask of the comparative example, which were manufactured as described above. The results are shown in FIG. Thus, the reflectance of the light-shielding region of Example 1 having the line-and-space concavo-convex structure on the substrate surface is reduced to about ½ to ¼ compared to the comparative example without the concavo-convex structure. I was able to confirm.

<Example 2>
As Example 2, a reflection-type photo is formed when the uneven structure formed in the light-shielding region of the present invention is a dot array pattern having a period of 280 nm (0.28 μm), 1000 nm (1 μm), 3000 nm (3 μm), and a hole array pattern. A mask was prepared. The production procedure and production conditions of the reflective photomask are the same as those in Example 1 except that the drawing area for producing the dot array pattern and the hole array pattern is changed.

(Measurement by atomic force microscope)
When the produced uneven structure (dot array pattern and hole array pattern) was observed with an atomic force microscope and the pattern depth was measured, the depth was about 42 nm. The observation images at this time are shown in FIGS.

(Measurement of OOB light reflectivity)
FIG. 10 (dot array pattern) and FIG. 11 (hole array pattern) show the results of the spectral reflectance measurement of OOB light having a wavelength of 200 to 400 nm for the reflective photomask of Example 2. Thus, even when a dot array pattern or a hole array pattern is formed on the substrate surface, the reflectance of the light shielding region is reduced to about ½ to ¼ compared with the comparative example without the uneven structure. I was able to confirm.

<Example 3>
As Example 3, a reflective photomask in which the concavo-convex structure formed in the light-shielding region of the present invention has a higher aspect ratio than Examples 1 and 2 was produced. The concavo-convex structure was a dot array pattern having the same period of 280 nm (0.28 μm) as in Example 2.

The manufacturing procedure and manufacturing conditions of Example 3 are the same as those of the dot array pattern having a period of 280 nm in Example 2 until the step of forming the circuit pattern and the light shielding region (FIG. 5E). In the step of forming the concavo-convex structure of Example 3 (FIG. 6), the etching process time (FIG. 6D) of the surface of the substrate 11 by CF ₄ plasma was 600 seconds, which is 10 times that of Example 2. did.

  In Example 3, since the concavo-convex structure has a high aspect ratio and the depth cannot be measured with an atomic force microscope, a plurality of similar samples are produced, cut, and observed with a scanning electron microscope. When the depth (height) of the uneven structure of the dot array was confirmed, the depth was 411 nm. Therefore, the aspect ratio of the pattern was 2.9 (= the value obtained by dividing the depth 411 by 140, which is half the period of 280 nm). The dot array pattern having a period of 280 nm in Example 2 had a depth of 42 nm, and thus the aspect ratio was 0.3.

(Measurement of OOB light reflectivity)
Spectral reflectance measurement of OOB light having a wavelength of 200 to 400 nm was performed on the reflective photomask of Example 3 having a dot array pattern with a high aspect ratio (deep concavoconvex) in the light-shielding region produced as described above. The results are shown in FIG. As a result, compared with the comparative example without a concavo-convex structure, it was confirmed that it was significantly reduced to about 1/10 to 1/20. This is probably because the light confinement efficiency is increased by the pattern width narrower than the wavelength (period 280 nm × 1/2) and the pattern depth deeper than the wavelength.

(Exposure evaluation)
Next, using the reflective photomask of the present invention prepared in Example 1 (three types having a period of 3 μm, 1 μm, and 280 nm) and the reflective photomask of the comparative example having no concavo-convex structure, an EUV exposure machine is used on the wafer. Then, the exposure evaluation for attaching the four faces of the chip was performed, and the dimensional variation of the resist at the corner portion (four exposure portion) of each overlapping chip was examined. In the case of four-sided attachment, in addition to exposure for forming the pattern itself, the corner portion of the chip is subjected to four times of extra exposure by three times of multiple exposure (three times of irradiation from OOB light reflected from the light shielding region). Therefore, there is a corner portion where the dimensional variation is likely to be greatest. The exposure machine used was NXE3300 manufactured by ASML, and the exposure conditions were normal illumination and a dose of 30 mJ / cm ² . Table 1 shows the average reflectance of each sample at this time with respect to OOB light having a wavelength of 200 to 300 nm and the dimensional variation with respect to the chip center portion of the chip corner portion subjected to quadruple exposure.

  From the results shown in Table 1, the average reflectance of OOB light is 2.8% in the reflective photomask of the present invention compared to the reflective photomask of the comparative example in which the average reflectance of OOB light is 5.2%. In all three types, 2.0% and 1.6%, the dimensional variation of the corner portion could be reduced. A graph plotting the relationship between the average reflectance of the OOB light and the dimensional variation is shown in FIG. As described above, it was confirmed that the smaller the OOB light reflectance, the smaller the variation of the resist pattern dimension at the chip corner portion on the wafer, the more uniform resist pattern is formed, and the circuit pattern formation accuracy is improved.

DESCRIPTION OF SYMBOLS 101 Reflective photomask 11 Substrate 12 Multilayer reflective film 13 Protective film 14 Absorbing film 15 Back surface conductive film 10 Circuit pattern 20 Light-shielding region 30 Uneven structure 21, 22, 23 Resist

Claims (10)

A reflective photomask comprising a substrate, a multilayer reflective film, and an absorption film,
The surface of the photomask is divided into a plurality of regions including a circuit pattern region and a light shielding region outside the circuit pattern region;
In the circuit pattern region, the multilayer reflective film and the absorption film are laminated in this order on the substrate, and the absorption film constitutes a circuit pattern,
In the light shielding region, the substrate surface has an uneven structure,
A reflection type photomask having an average reflectance of 4% or less with respect to incident light having a wavelength of 100 to 400 nm in the light shielding region.   2. The reflective photomask according to claim 1, wherein the average reflectance is 2% or less.   The reflective photo according to claim 1, wherein the concavo-convex structure includes at least one pattern selected from the group consisting of a line & space pattern, a dot pattern, and a hole pattern in plan view. mask.   4. The reflective photomask according to claim 3, wherein the at least one pattern included in the concavo-convex structure has at least one type of periodic structure in a plan view.   The reflective photomask according to claim 4, wherein at least one period of the periodic structure is 20 nm to 4000 nm.   6. The reflective photomask according to claim 5, wherein the period of the periodic structure includes at least two kinds of periods of 20 nm to 500 nm and 500 nm to 4000 nm.   The reflective photomask according to any one of claims 1 to 6, wherein a depth of the concavo-convex structure is 25 nm or more.   The reflective photomask according to any one of claims 1 to 6, wherein a depth of the concavo-convex structure is 50 nm or more.   9. The reflective photomask according to claim 1, wherein a cross-sectional shape of the concavo-convex structure is a rectangular shape or an inclined shape.   The inclined shape includes at least one shape selected from the group consisting of trapezoidal shape, pyramid shape, inverted pyramid shape, hemispherical shape, parabolic shape, conical shape, inverted hemispherical shape, sine curve shape, and hyperbolic shape. The reflective photomask according to claim 9.