JP6728748B2 - Reflective photomask - Google Patents

Description

The present invention relates to a reflective photomask for lithography.

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

Since EUV light has a property of being easily absorbed by most substances, a photomask used for EUV exposure (hereinafter referred to as “EUV mask”) is different from a conventional transmissive photomask in that it is of a reflective type. It becomes a photo mask. In the EUV mask, for example, a multilayer reflective film in which molybdenum (Mo) layers and silicon (Si) layers are alternately laminated is formed on a glass substrate, and a light absorbing material mainly containing tantalum (Ta) is generally formed thereon. A film is formed, and a circuit pattern is formed on the light absorption film.

In lithography using an EUV mask, generally, the incident angle of the EUV light to the EUV mask is tilted by about 6 degrees, the reflected EUV light is guided to a wafer as an exposure target, and the EUV light applied on the wafer. The resist having photosensitivity is exposed.

When the incident angle of the EUV light incident on the EUV mask is inclined as described above, when the EUV light is reflected by the circuit pattern on the EUV mask, a part of the circuit pattern formed by the light absorption film may be formed depending on the direction of the reflected light. It is known that a phenomenon occurs in which a shadow is generated and the wafer is not irradiated (so-called projection effect). 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, when the light absorption film is made thin, the amount of light attenuation 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 is increased. Is a concern. In addition, in an actual exposure process, since chips are often attached to one wafer in many ways, it is particularly concerned that the exposure amount to the resist in the boundary region between adjacent chips is increased. That is, multiple exposure occurs in the boundary region between chips, which affects the formation accuracy of the circuit pattern, resulting in deterioration of the quality of chips obtained in the subsequent process and deterioration of throughput.

Therefore, when thinning the light absorbing film as described above, all the light absorbing film and the multilayer reflective film in the outer peripheral portion that surrounds the circuit pattern of the photomask, which is the boundary region between adjacent chips on the wafer, are removed. There is a method of forming a groove that is dug up to the surface of a glass substrate (see Patent Document 1). This is to make the above-described groove a light-shielding region having a high light-shielding property with respect to the wavelength of EUV light and suppress the reflection of EUV light to suppress multiple exposure in the boundary region between adjacent chips.

However, from a light source that generates EUV light, not only light in the EUV region around 13.5 nm, but also vacuum ultraviolet light (VUV; approximately 200 nm or less), deep ultraviolet light (DUV; approximately 300 nm or less), ultraviolet light (UV; approximately 400 nm) The following), near-infrared light (around 800 nm), and light in a wavelength band extending over an infrared region (1000 nm or more) are also 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. Therefore, in the light-shielding area, the reflection of EUV light among the light emitted from the light source can be almost suppressed, but a part of the OOB light is reflected by the light-shielding area and irradiated onto the wafer. Then, there is a problem that the above-described multiple exposure occurs in the boundary area between the chips. Since the resist for EUV lithography used on the wafer is originally developed based on the resist for lithography of KrF light (wavelength 248 nm) or ArF light (wavelength 193 nm), OOB light in the wavelength region of 100 to 400 nm is especially used. The photosensitivity is high.

Therefore, looking at a technique for solving such a problem, there is a technique described in Patent Document 2. This is because a fine-structured pattern is formed on the back surface of the glass substrate opposite to the multilayer reflection film, whereby the OOB light incident on the light-shielding area reaches the back surface of the glass substrate and then the back surface conductive film is formed. 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 the OOB light reflected on the light-shielded region and applied to the wafer, and found that the light reflected on the front (front) surface of the substrate Was found to be more dominant than the light reflected on the backside of the substrate. Therefore, in order to reduce the reflectance of the OOB light that has entered the light-shielded region, it is not enough to suppress the reflected light reflected on the back surface of the substrate, and it is necessary to suppress the reflected light on the front surface of the substrate. Came to.

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

In order to solve the above-mentioned problems, the invention according to claim 1 is a reflection type photomask including a substrate, a multilayer reflection film, and an absorption film,
The surface of the photomask is divided into a plurality of areas including a circuit pattern area and a light shielding area outside the circuit pattern area,
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-shielded region, the substrate surface has an uneven structure,
The average reflectance for incident light having a wavelength of 200 to 400 nm in the light-shielding region is 4% or less,
The concavo-convex structure has a line & space pattern, a dot pattern, and a hole pattern in a plan view.
Including at least one pattern selected from the group consisting of
The at least one type of pattern included in the concavo-convex structure has at least 1 in plan view.
Has a kind of periodic structure,
At least one period of the periodic structure is the at least one type included in the uneven structure.
If the type of pattern is a line & space pattern, it is 20 nm to 3000 nm.
When the at least one type of pattern included in the uneven structure is a dot pattern or a hole pattern, it is 20 nm to 4000 nm,
The depth of the concavo-convex structure is 57 nm or more when the at least one type pattern included in the concavo-convex structure is a line & space pattern, and the at least one type pattern included in the concavo-convex structure is a dot pattern or A reflective photomask having a hole pattern of 42 nm or more.

In the invention according to claim 2, the period of the periodic structure is at least two types of 20 nm to 500 nm and 500 nm to 3000 nm when the at least one type of pattern included in the uneven structure is a line & space pattern. 2. When the at least one kind of pattern included in the concavo-convex structure is a dot pattern or a hole pattern, it includes at least two kinds of cycles of 20 nm to 500 nm and 500 nm to 4000 nm. The reflective photomask described in 1.

In the invention according to claim 3 , the cross-sectional shape of the concavo-convex structure is a rectangular shape or an inclined shape.
The reflective photomask according to claim 1 or 2, wherein the reflective photomask is provided.

In the invention according to claim 4, the inclined shape is a trapezoidal shape, a pyramid shape, or an inverted pyramid.
Shape, hemisphere, parabola, cone, inverted hemisphere, sine curve, hyperbola
The reflective photomask according to claim 3, wherein the reflective photomask includes at least one selected shape .

According to the present invention, in the reflection-type photomask in which the light-shielding region is formed, the reflection of out-of-band light in the light-shielding region can be suppressed more than ever before, so when the chips are mounted on the wafer in multiple planes, It is possible to effectively suppress not only the EUV light but also the multiple exposure in the boundary region between the chips due to the out-of-band light. Then, a highly accurate and high quality circuit pattern can be transferred onto the wafer.

The schematic (a) top view (b) sectional drawing of the reflection type photomask which concerns on this invention. (A) A schematic plan view of a reflective photomask according to the present invention (b) to (j) is a schematic plan view showing an example of a pattern of a concavo-convex structure in a light shielding region. (A)-(h) Schematic sectional drawing which showed the example of the uneven|corrugated structure of the light shielding area of the reflection type photomask which concerns on this invention. Manufacturing process of reflective photomasks of Examples and Comparative Examples (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 peeling, washing and drying. Manufacturing process of reflective photomasks of Examples and Comparative Examples (up to formation of light-shielding regions) (a) After resist application (b) After drawing (c) After development (d) After dry etching (e) Stripping and cleaning of resist・After drying. Manufacturing process of the reflective photomask of the embodiment (up to formation of the concavo-convex structure in the light-shielding area) (a) After resist application (b) After drawing (c) After development (d) After dry etching (e) Resist peeling/cleaning After drying. 5 is an atomic force microscope image of the concavo-convex structure of the light-shielding region of Example 1 (an example of a line & space pattern having a period of 1 μm). The measurement result (line & space pattern) of the spectral reflectance of the OOB light of the light-shielding area of Example 1 and the comparative example. Atomic force microscope image of the concavo-convex structure of the light shielding region of Example 2 (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 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 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 of Example 3 (dot array pattern of high aspect ratio) and Comparative Example. 8 is a relationship between the resist dimension variation amount (variation amount with respect to the chip center portion) and the OOB light reflectance at the chip corner portion (quadruple exposure portion) in the exposure evaluation of Example 1 and the comparative example.

Embodiments of the present invention will be described below with reference to the drawings. In addition, the same reference numerals are given to the same components unless there is a reason for convenience, and duplicated description will be omitted. In addition, in the drawings used in the following description, in order to make the features easy to understand, the characteristic portions may be illustrated in an enlarged manner, and the dimensional ratios of the respective components may not be the same as the actual ones. ..
First, constituent elements that characterize the reflective photomask of the present invention will be described.

(Overall Structure of 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 used for EUV lithography in which light having a wavelength of 5 to 15 nm, particularly EUV light of 13.5 nm is used as exposure light, and its film structure has a multilayer reflective film 12 on a substrate 11 and a protective film. The film 13 and the absorption film 14 are sequentially formed, and a back surface conductive film 15 is provided on the back surface of the substrate 11. Further, the reflective photomask of the present invention is provided with the light shielding region 20 having the concavo-convex structure 30 so as to surround the circuit pattern region 10.

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

(Light-shielding area 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 reflection film 12 are completely removed, the substrate 11 is exposed at the bottom surface of the light-shielding region, and the uneven structure 30 is formed on the surface thereof. As described above, the multilayer reflection film 12 that is responsible for the reflection of EUV light is completely removed, so that the light shielding property against EUV light is obtained. The substrate 11 alone does not reflect EUV light.

Further, the concavo-convex 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 exerts a function of suppressing excessive exposure of the resist on the wafer. ing. When the substrate surface does not have the concavo-convex structure 30, the reflectance of OOB light is about 5 to 20%, but when the concavo-convex structure is formed, the average reflectance of the OOB light at 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 sectional shape.

FIG. 2 shows an example of the uneven structure 30 in 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 in FIG. 2A. The concavo-convex structure 30 preferably includes at least one type of pattern selected from the group consisting of line & space patterns, dot patterns, and hole patterns in a plan view. This is because these patterns can have periodicity. In the present invention, the directions of the patterns are irrelevant as shown in FIGS. 2(b) and 2(e), and the shape of holes or dots in plan view is a perfect circle, a square, a triangle, or those shapes are slightly dull. A certain effect can be obtained with any of the patterns.

It is preferable that the at least one type of pattern has at least one type of periodic structure and is densely arranged in a plan view. When 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 having a period substantially equal to or less than the wavelength of OOB light, a cone-shaped structure (hereinafter referred to as a moth-eye structure) in which the line width gradually changes in cross-section and the refractive index gradually changes from the substrate surface in the depth direction. By calling it, the effect of confining light on the surface of the substrate (lowering the reflection) 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 if it has a rectangular shape in a sectional view, the diffraction phenomenon of reflected light appears and regular reflection (0th order diffracted light) decreases. The number of diffracted lights other than the 0th, 2nd,... Since the light that reaches the wafer is only specular reflection, the effect of reducing the OOB light with which the wafer is irradiated is brought about. As described above, the reflection type photomask of the present invention can be realized by the low reflection effect due to the moth-eye structure and the effect of reducing the regular reflection component due to the diffraction phenomenon.

The fact that the low reflection effect of the OOB light having the period of 20 to 4000 nm and the wavelength of 100 to 400 nm is high is the result obtained by the experiment, and in what kind of period the pattern is specifically formed is , Semiconductor manufacturers using EUV lithography can make arbitrary choices. This is because the EUV resist used for EUV lithography is different for each company, and depending on the resist used, the wavelength band having high photosensitivity in OOB light also differs.

Even if only one kind of cycle of the above-mentioned concavo-convex structure is obtained, the effect can be sufficiently obtained, but there may be two or more kinds of cycle as shown in FIG. First, the reason why the effect is obtained even with one cycle 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. This is to bring. As for the diffraction phenomenon, for example, when OOB light hits a concavo-convex structure having a certain period, the angle of reflection of the first-order or second-order diffracted light differs depending on the respective wavelengths contained in the OOB light. The diffraction phenomenon of reflected light itself is surely exhibited. Therefore, the fact that the specular reflection component decreases and the diffracted light of the first order or the second order increases is a phenomenon that can be said for a wide wavelength region of the OOB light.

In addition, since there are two or more types of periods of the concavo-convex structure, in OOB light, particularly when there are a plurality of wavelengths for which the reflectance is desired to be reduced, it is possible to select an effective period for each of the plurality of wavelengths. it can. Alternatively, it is also possible to use two or more types of periods in order to strongly exhibit both the low reflection effect and the diffraction phenomenon due to the moth-eye structure. In particular, a concave-convex structure having two types of periods, one period of 20 to 500 nm and one period of 500 to 4000 nm, can sufficiently reduce the reflectance.

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 due to the above-mentioned moth-eye structure and to reduce the regular reflection component due to the diffraction phenomenon, the depth D of the uneven structure is basically better as it is deep, but the effect can be obtained even if it is relatively shallow. It turned out by experiment. The depth D of the concavo-convex structure of the present invention is preferably 25 nm or more in order to obtain a certain effect in reducing the reflectance. In order to obtain a sufficient effect, the thickness is preferably 50 nm or more.

The 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. Rectangle (a), trapezoid (b), pyramid (c), inverted pyramid (d), hemisphere (e), parabola (f), cone (c), inverted hemisphere (g), It is preferable to include at least one kind of cross-sectional shape selected from the group consisting of a sine curve shape (not shown) and a hyperbola shape (not shown). Further, as shown in FIGS. 3A, 3B, 3D, and 3H in which the pattern period P in FIG. 3G is changed, the convex portions of the concavo-convex structure may be flat. On the contrary, the concave portion of the concavo-convex structure may be flat.

The uneven structure having various cross-sectional shapes as described above includes dry etching after heat-flowing the resist, dry etching conditions for obtaining an isotropic cross-sectional shape, multi-stage dry etching, variable dry etching that continuously changes the conditions, and wet etching. It can be formed by a method such as combined use with etching.

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

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

Regarding the order of forming the concavo-convex structure, in the above embodiment, an example in which the concavo-convex structure is formed after forming the conventional light-shielding region has been shown, but the invention is not limited to this. For example, at the same time as or before forming a circuit pattern in the exposure area, a concavo-convex structure is formed in a part of the absorption film which will be a light shielding area later, and etching for forming the light shielding area (absorption film, protective film, multilayer A method of forming the uneven structure of the substrate by transferring the uneven structure of the absorbing 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.

As the material of the substrate 11, a material having characteristics suitable for processing for forming a fine uneven structure on the surface of the substrate 11 in the light shielding region is desirable. For example, a material containing quartz (SiO ₂ ) as a main component and titanium oxide (TiO ₂ ) may 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 is made of a material that has a small absorption (extinction coefficient) for EUV light and a large difference in refractive index between the stacked films with EUV light. The multilayer reflective film 12 is designed to theoretically achieve a reflectance of about 72% with respect to EUV light having a wavelength of 13.5 nm, 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 laminated. Since molybdenum (Mo) and silicon (Si) have a small absorption (extinction coefficient) for EUV light and a large difference in refractive index for EUV light, they can be configured to have a high reflectance at their interface.

The protective film 13 needs to be a material that has resistance to cleaning with acid or alkali, and 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 processing the absorption film 14 and a protective film against a chemical solution in mask cleaning. The uppermost layer of the multilayer reflective film 12 located below 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 that case, the buffer layer is provided to protect the protective film 13 when the absorbing film 14 is etched or the pattern is modified, and can be made of, for example, a nitrogen compound of chromium (CrN). Further, 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 of a material containing any of the above.

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 tantalum (Ta) having a high absorptivity for EUV light and any one of its oxide, nitride, and oxynitride. Is formed. Specifically, tantalum (Ta), tantalum boron nitride (TaBN), tantalum silicon (TaSi), and oxides thereof (TaO, TaBON, TaSiO) can be used. The thickness of the absorption film 14 is usually 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 with respect to ultraviolet light having a wavelength of 190 to 260 nm for inspection. For the low-reflection layer, for example, a material containing any one of tantalum (Ta) oxide, nitride, oxynitride, silicon (Si) oxide, nitride, and oxynitride can be used. The low reflective layer is for increasing the contrast and improving the inspectability with respect to the inspection wavelength of the mask defect inspection machine.

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

The multilayer reflective film 12, the protective film 13, the absorbing film 14, and the back surface conductive film described above can be formed by 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 each of the above embodiments, and may be a single layer as long as the required high reflection is obtained. Further, the reflective photomask according to the present invention may have a structure 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 according to the manufacturing process, and the results of measuring the reflectance with respect to OOB light will be described.

<Example 1>
(Used reflective photomask blank)
FIG. 4A shows the used reflective photomask blank. For the reflective photomask blank, a 40-layered multilayer reflective film 12 of a Mo layer and a Si layer, which is designed to have a reflectance of about 64% with respect to EUV light having a wavelength of 13.5 nm, is formed on a substrate 11. However, a protective film 13 made of Ru 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. The conductive film 15 is also formed on the back surface. As the substrate 11, extremely low thermal expansion glass (manufactured by Corning, refractive index 1.4801-1.892) using quartz (SiO ₂ ) is used.

[Fabrication structure mask manufacturing process]
(Up to 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 FUJIFILM Electronic Materials) is formed on the surface of the reflective photomask blank (FIG. 4A). Was applied to a film thickness of 150 nm (FIG. 4(b)). Next, an electron beam drawing machine (JBX3040: manufactured by JEOL Ltd.) was used to draw a 1:1 line and space pattern with a line width of 100 nm in a 10 cm×10 cm area at the center of the mask (FIG. 4C). PEB was performed at 10° C. for 10 minutes, and further spray development (SFG3000: manufactured by Sigma Meltec) was performed to form a resist pattern ((FIG. 4(d))).

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

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

After that, 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 under the following conditions using CHF ₃ plasma (FIG. 5D). The remaining resist was peeled off, washed, and dried to produce a reflection type photomask having a light shielding region 20 (FIG. 5(e)).
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: 350W
RIE (Reactive Ion Etching) power: 200W
Processing time: 6 minutes

As described above, the steps up to this point are similar to those of the conventional reflective photomask.

(Formation of uneven structure)
Next, a negative chemically amplified resist (resist 23) (FEN271: manufactured by FUJIFILM Electronic Materials) was applied to the entire surface of the reflective photomask including the light-shielding region in a thickness of 400 nm (FIG. 6A). ). Then, the entire surface other than the light-shielding area is drawn, and three types of 1:1 line & 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 area (see FIG. 6). (B)) It did. Then, the line & space pattern of the resist 23 was formed in the light-shielded region by PEB and spray development (SFG3000: manufactured by Sigma-Meltech) at 110° C. for 10 minutes (FIG. 6C).

Then, the surface of the substrate 11 is etched by CF ₄ plasma in a treatment time of 60 seconds using a dry etching apparatus (FIG. 6(d)), and then the remaining resist is peeled off, washed and dried to form a light-shielded region. A reflective photomask of the present invention having an uneven structure 30 on the substrate surface was prepared (FIG. 6(e)).

<Comparative example>
By the same material, the same device, and the same process steps as the steps up to the formation of the light-shielding region (FIG. 5E) in the manufacturing process of the reflective photomask according to the first embodiment of the present invention, the process shown in FIG. A conventional reflective photomask having the form

(Atomic force microscope measurement)
Of the concavo-convex structure of the reflective photomask of the present invention produced in Example 1, the cross-sectional shape and the pattern depth of the 1 μm line & space pattern were measured with an atomic force microscope. The observed image at this time is shown in FIG. The cross-sectional shape of the pattern was a rectangle as shown in FIG. 3A, although the bottom of the recess had a slight roundness, and the depth D was 57 nm.

(Measurement of reflectance of OOB light)
Spectral reflectance measurement of OOB light having a wavelength of 200 to 400 nm was performed on both the reflective photomask having an uneven structure in the light-shielding region of Example 1 and the reflective photomask of Comparative Example manufactured as described above. The results are shown in Fig. 8. As described above, the reflectance of the light-shielding region of Example 1 having the uneven structure of lines and spaces on the substrate surface is reduced to about 1/2 to 1/4 as compared with the comparative example having no uneven structure. I was able to confirm.

<Example 2>
As a second embodiment, the case where the concavo-convex structure formed in the light-shielding region of the present invention has a dot array pattern of a period of 280 nm (0.28 μm), 1000 nm (1 μm), 3000 nm (3 μm), and a hole array pattern will be described. A mask was made. The manufacturing procedure and manufacturing conditions of the reflective photomask are the same as those of the first embodiment except that the drawing area for manufacturing the dot array pattern and the hole array pattern is changed.

(Atomic force microscope measurement)
The produced concavo-convex structure (dot array pattern and hole array pattern) was observed with an atomic force microscope, and the pattern depth was measured. In each case, the depth was about 42 nm. Observation images at this time are shown in FIGS. 9(a) and 9(b).

(Measurement of reflectance of OOB light)
The results of measuring the spectral reflectance of OOB light having a wavelength of 200 to 400 nm for the reflective photomask of Example 2 are shown in FIG. 10 (dot array pattern) and FIG. 11 (hole array pattern). As described above, even when the dot array pattern or the hole array pattern is formed on the substrate surface, the reflectance of the light shielding region is reduced to about 1/2 to 1/4 as compared with the comparative example having no uneven structure. I was able to confirm that

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

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

In Example 3, since the concavo-convex structure has a high aspect ratio and the depth cannot be measured by the atomic force microscope, a plurality of similar samples are prepared, cut, and the cross section is observed by the 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 a half of the period 280 nm). The dot array pattern of Example 280 having a period of 280 nm had a depth of 42 nm, and thus has an aspect ratio of 0.3.

(Measurement of reflectance of OOB light)
The spectral reflectance of OOB light having a wavelength of 200 to 400 nm was measured for the reflective photomask of Example 3 having the dot array pattern having a high aspect ratio (deep unevenness) in the light-shielding region, which was manufactured as described above. Results are shown in FIG. As a result, it was confirmed that it was significantly reduced to about 1/10 to 1/20 as compared with the comparative example having no uneven structure. It is considered that the confinement efficiency of light is increased due to the pattern width narrower than the wavelength (cycle 280 nm×1/2) and the pattern depth deeper than the wavelength.

(Exposure evaluation)
Next, using the reflection type photomask of the present invention (three types having a period of 3 μm, 1 μm and 280 nm) of the present invention prepared in Example 1 and the reflection type photomask of the comparative example having no concavo-convex structure, on the wafer with an EUV exposure machine. The chips were exposed to light on four sides to evaluate the exposure, and the dimensional variation of the resist was examined at the corners (quadruple exposure parts) of the overlapping chips. In the case of four-sided mounting, in addition to the exposure for forming a pattern of itself on the corner portion of the chip, an extra three times of multiple exposure (three times of irradiation from the OOB light reflected from the light-shielded area) causes four-fold exposure. There are corners where the receiving and dimensional fluctuations are most likely to occur. As the exposure device, NXE3300 manufactured by ASML was used, and the exposure conditions were normal illumination and a dose amount of 30 mJ/cm ² . Table 1 shows the average reflectance of OOB light having a wavelength of 200 to 300 nm and the amount of dimensional variation with respect to the chip center portion of the chip corner portion subjected to quadruple exposure in each sample at this time.

From the results of Table 1, in the reflective photomask of the present invention, the average reflectance of OOB light is 2.8% as compared with the reflective photomask of the comparative example in which the average reflectance of OOB light is 5.2%. , 2.0%, 1.6%, all three types were able to reduce the dimensional variation in the corners. A graph plotting the relationship between the average reflectance of OOB light and the amount of dimensional variation is shown in FIG. As described above, it was confirmed that the smaller the reflectance of OOB light, the less the variation of the resist pattern size at the chip corner portion on the wafer, the more uniform the resist pattern was formed, and the higher the accuracy of forming the circuit pattern.

101 Reflective Photomask 11 Substrate 12 Multilayer Reflective Film 13 Protective Film 14 Absorption Film 15 Backside Conductive Film 10 Circuit Pattern 20 Light-shielding Area 30 Concavo-convex Structures 21, 22, 23 Resist

Claims (4)

A reflection type photomask comprising a substrate, a multilayer reflection film, and an absorption film,
The surface of the photomask is divided into a plurality of areas including a circuit pattern area and a light shielding area outside the circuit pattern area,
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-shielded region, the substrate surface has an uneven structure,
The average reflectance for incident light having a wavelength of 200 to 400 nm in the light-shielding region is 4% or less,
The concavo-convex structure has a line & space pattern, a dot pattern, and a hole pattern in a plan view.
Including at least one pattern selected from the group consisting of
The at least one type of pattern included in the concavo-convex structure has at least 1 in plan view.
Have different types of periodic structures,
At least one period of the periodic structure is the at least one type included in the uneven structure.
If the type of pattern is a line & space pattern, it is 20 nm to 3000 nm.
When the at least one type of pattern included in the uneven structure is a dot pattern or a hole pattern, it is 20 nm to 4000 nm,
The depth of the concavo-convex structure is 57 nm or more when the at least one type pattern included in the concavo-convex structure is a line & space pattern, and the at least one type pattern included in the concavo-convex structure is a dot pattern or A reflective photomask having a hole pattern of 42 nm or more. The period of the periodic structure is defined by the at least one type of pattern included in the concavo-convex structure.
20 nm to 500 nm and 500 nm to 3000 nm for in-and-space patterns
And at least one type of pattern included in the concavo-convex structure.
If the pattern is a dot pattern or a hole pattern, 20 nm to 500 nm,
2. At least two types of periods of 500 nm to 4000 nm are included.
The reflective photomask described in 1. The concavo-convex structure has a rectangular cross section or an inclined cross section.
The reflective photomask according to claim 1 or 2. The inclined shape is a trapezoid, a pyramid, an inverted pyramid, a hemisphere, a parabola, or a circle.
At least one selected from the group consisting of a cone, an inverted hemisphere, a sine curve, and a hyperbola.
The reflective photomask according to claim 3, wherein the reflective photomask has a shape of.