JP2021067787A - Reflection type photomask and reflection type photomask blank - Google Patents

Abstract

To provide a reflection type photomask that alleviates degradation in transfer characteristics on a wafer by out-of-band light, specifically, an increase in LER (line edge roughness) of a resist pattern on a wafer or an unresolved pattern, and a reflection type photomask blank for producing the reflection type photomask.SOLUTION: The reflection type photomask comprises a high reflection part and a low reflection part for exposure light, in which the high reflection part is composed of a multilayer film with an overlaying protective film formed on a substrate, the low reflection part is formed by removing the protective film and the multilayer film, and an average of a phase difference at wavelengths of 180 nm, 240 nm and 300 nm between reflected light from the high reflection part and reflected light from the low reflection part is 160 to 200 degrees.SELECTED DRAWING: Figure 1

Description

The present invention relates to a reflective photomask and a reflective photomask blank, and in particular, uses EUV lithography using EUV having a wavelength near 13.5 nm as a light source, and a reflective photomask in which a multilayer film portion is dug into a low reflective portion. And the reflective photomask blank.

In recent years, with the miniaturization of semiconductor devices, EUV lithography using EUV having a wavelength near 13.5 nm as a light source has been developed. EUV lithography needs to be performed in vacuum because the light source wavelength is short and the light absorption is very high. Further, in the EUV wavelength region, the refractive index of most substances is slightly smaller than 1, so that a conventionally used transmissive refractive optics system can be used in EUV lithography. Instead, it is necessary to use a reflective optical system. Therefore, the photomask used as the original plate of EUV lithography cannot be a conventional transmissive mask, and therefore needs to be a reflective mask.

A typical layer structure of such a reflective photo mask (hereinafter referred to as an EUV mask) is a multilayer structure exhibiting high reflectance with respect to the exposure light source wavelength on a low thermal expansion substrate (hereinafter, appropriately simply referred to as a substrate). A film and a protective film (also called a capping film) for protecting the surface of the multilayer film are formed, and an absorption film that absorbs the exposure light source wavelength is formed on the upper layer thereof, and a circuit pattern is formed on the absorption film. Is formed.

Further, on the back surface of the substrate, a back surface conductive film made of CrN or the like for electrostatically chucking the EUV mask in the exposure machine is formed. In addition, there is also an EUV mask having a structure having a buffer film (etching stopper film when etching the absorbing film) between the protective film and the absorbing film to suppress damage to the base when the absorbing film is etched. is there.

In the case of the above EUV mask structure, in the patterning of the absorption film, after performing resist patterning by electron beam drawing, the absorption film is partially removed by dry etching technology to form a low reflection portion of EUV light by the absorption film. , The absorption film is removed to form a circuit pattern consisting of a highly reflective portion where the protective film and the multilayer film are exposed. In the case of a structure having a buffer membrane, the buffer membrane is also removed in the same manner. The light image reflected by the EUV mask thus produced is transferred onto the semiconductor substrate via the catadioptric system.

The multilayer film used for the EUV mask blank for making the current standard EUV mask is Si (silicon) and Mo (molybdenum) with a film thickness of about 4.2 nm and a film thickness of about 2.8 nm, respectively. It is composed of alternating film thicknesses, and is conventionally composed of 40 to 50 pairs (= about 80 to 100 layers) in total. Further, usually, the uppermost film of the multilayer film is Si, which has higher chemical stability than Mo.

Si and Mo are used because their absorption (extinction coefficient) to EUV light is small and the difference in refractive index between Si and Mo in EUV light is large, so that the reflectance at the interface between Si and Mo can be increased. .. In such a multilayer film, a part of the EUV light is reflected at the first interface, but the remaining unreflected and transmitted EUV light is reflected at the next interface, and then at the next interface, and so on 40 times ( There is a chance of reflection (in the case of 40 pairs). The sum of them is the reflectance of EUV light from the multilayer film. The EUV reflectance of EUV mask blanks sold by blank manufacturers is approximately 60 to 65%.

The protective film and the buffer film play a role as a film for preventing damage to the multilayer film in the dry etching step, the mask pattern correction step, and the mask cleaning step when manufacturing the mask. Ruthenium (Ru), which is said to have high cleaning resistance and etching resistance, is used as the protective film of the current standard EUV mask blank, and CrN is used as the buffer film (for example, Patent Document 1). ).

Since the EUV mask is a reflective mask as described above, it is generally necessary to make the EUV light obliquely incident on the mask surface at an angle of incidence of about 6 degrees. In that case, when the EUV light is reflected by the circuit pattern on the EUV mask, the height of the absorbing film becomes a shadow depending on the direction of the reflected light, a phenomenon that the wafer is not irradiated (so-called projection effect) occurs, and the transfer contrast becomes high. It has been pointed out that it will decrease. Therefore, in order to suppress the projection effect, a method of reducing the thickness of the absorbing film on which the circuit pattern is formed to reduce the projection effect has been studied, but the projection effect cannot be completely eliminated.

As another measure against the projection effect, an EUV mask having a structure different from that of the above EUV mask has also been proposed. This is a circuit pattern formed by etching the multilayer film on the low thermal expansion substrate. The multilayer film part is the same as the high reflection part of EUV light, but the absorption film is the low reflection part. Instead, the portion from which the multilayer film is removed is used as a low-reflection portion of EUV light (for example, Patent Document 2 and Non-Patent Document 1). With this type of EUV mask (hereinafter referred to as the digging type EUV mask), the high reflection part is the upper part of the pattern, so the projection effect does not occur, and the transfer contrast may be higher than that of the conventional EUV mask. Expected.

By the way, as the EUV light source of the EUV lithography apparatus, plasma light generated by irradiating _{a liquid metal (usually tin) dropped in a vacuum with a CO 2 pulse laser is used.} This plasma light includes not only EUV light (usually a wavelength of 13.5 nm) required for EUV lithography, but also vacuum ultraviolet rays (VUV; about 200 nm or less), deep ultraviolet rays (DUV; about 300 nm or less), and ultraviolet rays (UV; about 300 nm). In many cases, light in a wavelength band over 400 nm), near infrared rays (around 800 nm), and further in the infrared region (1000 nm or more) is also emitted. These wavelength bands are generally referred to as Out of Band. As described above, in EUV lithography, light having an out-of-band wavelength accompanying EUV light (hereinafter referred to as “OOB light”) also reaches the EUV mask through the mirror of the lithography apparatus.

In the case of the digging-type EUV mask, the EUV light is reflected by the high-reflection portion where the multilayer film is left, and is not reflected by the low-reflection portion where the multilayer film is removed. On the other hand, in OOB light, relatively high reflected light is generated in the portion where the multilayer film is left (usually, the outermost surface is a protective film Ru or Si), but even on the surface of the low thermal expansion substrate from which the multilayer film is removed, 5 to 20 About% of reflected light is generated.

FIG. 10 is a characteristic diagram illustrating the results of measuring the spectral reflectances of the high-reflection portion and the low-reflection portion of a normal digging-type EUV mask in the wavelength range of 100 to 200 nm. The highly reflective portion made of a Si / Mo40 pair multilayer film having a Ru protective film on the outermost surface has a reflectance of light having a wavelength of 100 nm of 15% or more, and the reflectance increases as the wavelength becomes longer. On the other hand, the low thermal expansion substrate having the conductive film CrN (here, 200 nm thick) on the back surface has a particularly high reflectance of about 17% near a wavelength of 120 nm and maintains a reflectance of 5% or more even at a wavelength of 200 nm.

As described above, since the OOB light has a reflectance of 5% or more even on the surface of the low thermal expansion substrate, the EUV resist on the wafer is exposed to the EUV resist by the OOB light, multiple exposures occur in the boundary region between the chips, and the amount of light that cannot be ignored is integrated. This causes deterioration of the transfer characteristics on the wafer. Specifically, an increase in LER (line edge roughness) of the resist pattern on the wafer and unresolution are caused.

In particular, regarding which wavelength region of OOB light is a problem, the resist for EUV lithography was originally developed based on the resist for lithography of KrF light (wavelength 248 nm) and ArF light (wavelength 193 nm). Therefore, OOB light in the wavelength range of 100 to 400 nm if broadly estimated, and 180 to 260 nm if more limited, becomes a problem.

Looking at the technique for solving the above-mentioned problem of OOB light, Patent Document 3 discloses one technique. This forms a microstructure pattern on the back surface of the low thermal expansion substrate opposite to the multilayer reflective film, whereby the OOB light incident on the low thermal expansion substrate reaches the back surface of the glass substrate and then conducts the back surface. It suppresses reflection by the film.

However, in order to verify the technique described in Patent Document 3, the inventors of the present application investigated the component of the OOB light reflected by the low reflection portion and irradiated to the wafer, and found that the light was reflected on the front surface of the substrate. It turns out that the light is more dominant than the light reflected on the back of the substrate. That is, in order to reduce the reflectance of the OOB light incident on the light-shielding region, it is not enough to suppress the reflected light reflected on the back surface of the substrate, but also suppress the influence of the reflected light on the front surface (front surface) of the substrate. There is a need to.

In Non-Patent Document 2, in order to reduce OOB light, a material for coating a mirror mounted on an optical system of a reflection lithography system and an SPF (Spectral Purity Filter) as a light source are studied, but EUV light There is a concern that the strength of the light source will decrease, and there is a problem that the system becomes complicated.

Japanese Unexamined Patent Publication No. 2003-249434 Japanese Unexamined Patent Publication No. 2009-212220 Japanese Unexamined Patent Publication No. 2013-074195

Proceedings of SPIE Vol. 8880, 88802M-6, 2013 Proceedings of SPIE Vol. 7273, 72731W-1, 2009

The present invention has been made in view of the above problems, and in lithography using a reflective photomask, particularly EUV lithography, deterioration of transfer characteristics on a wafer due to OOB light, specifically, a resist pattern on a wafer. It is an object of the present invention to provide a digging-type reflective photomask that alleviates an increase in LER and unresolution, and a reflective photomask blank for producing the same.

In order to solve the above problems, the reflective photomask of the present invention is a reflective photomask including a high-reflection portion and a low-reflection portion of exposure light.
The highly reflective portion is composed of a multilayer film formed on a substrate and having a protective film as an upper layer.
The low reflection portion is formed by removing the protective film and the multilayer film.
The average value of the phase difference between the reflected light from the high reflection portion and the reflected light from the low reflection portion at wavelengths of 180 nm, 240 nm, and 300 nm is 160 to 200 degrees.

In the reflective photomask of the present invention, the average value of the phase difference between the reflected light from the high reflecting portion and the reflected light from the low reflecting portion at wavelengths of 120 nm, 180 nm, 240 nm, 300 nm and 360 nm is 160 to It is preferably 200 degrees.

In the reflective photomask of the present invention, the protective film can also serve as a hard mask layer for dry etching.

In the reflective photomask of the present invention, the low-reflection portion may consist of a portion in which the substrate is dug, in addition to a portion from which the protective film and the multilayer film have been removed.

In the reflective photomask of the present invention, the multilayer film is a multilayer film in which Si and Mo are alternately laminated as a pair, and the number of layers may be 39 pairs or less.

The reflective photomask blank of the present invention is a reflective photomask blank for producing the reflective photomask of the present invention.
The phase difference is a phase difference between the reflected light from the high reflection portion and the reflected light from the low reflection portion when it is assumed that the low reflection portion is formed.

According to the present invention, in lithography using a reflective photomask, particularly EUV lithography, deterioration of transfer characteristics on a wafer due to OOB light, specifically, an increase in LER of a resist pattern on a wafer and unresolution. A mitigating digging reflective photomask and a reflective photomask blank for making it can be provided. As a result, it becomes possible to manufacture high quality semiconductor devices.

It is a schematic cross-sectional view which shows the 1st Embodiment of the digging type EUV mask of this invention. It is a schematic cross-sectional view which shows the modification of the 1st Embodiment of the digging type EUV mask of this invention. It is a schematic cross-sectional view which shows the 2nd Embodiment of the digging type EUV mask of this invention. It is a schematic cross-sectional view which shows the modification of the 2nd Embodiment of the digging type EUV mask of this invention. It is a schematic cross-sectional view which shows the 1st Embodiment of the digging type EUV mask blank of this invention. It is a schematic cross-sectional view which shows the 2nd Embodiment of the digging type EUV mask blank of this invention. It is a characteristic diagram which shows the result of having calculated the reflectance of the high reflectance part of the light of each wavelength, which concerns on 1st Embodiment of the digging type EUV mask, in comparison with the reflectance of a low reflectance part. It is a characteristic diagram which shows the result of having calculated the phase difference of the high reflectance part and the low reflectance part of the light of each wavelength which concerns on 1st Embodiment of the digging type EUV mask. It is a characteristic diagram which shows the result of having calculated the average value of the phase difference of the high reflectance part and the low reflectance part of the light of a plurality of wavelengths which concerns on 1st Embodiment of the digging type EUV mask. It is a characteristic diagram which illustrates the result of having measured the spectral reflectance of the high reflection part and the low reflection part of a normal digging type EUV mask.

Hereinafter, the reflective photomask and the reflective photomask blank according to the embodiment of the present invention will be described with reference to the drawings. The same components are designated by the same reference numerals unless there is a reason for convenience. In each drawing, the thickness and ratio of the components may be exaggerated for ease of viewing, and the number of components may also be reduced. Further, the present invention is not limited to the following embodiments as they are, and can be embodied by appropriate combinations and modifications as long as the gist is not deviated.

In the present application, the EUV mask and the EUV mask blank will be described as examples of the reflective photomask and the reflective photomask blank.

FIG. 1 is a schematic cross-sectional view showing a first embodiment 100 of the digging-type EUV mask of the present invention. The first embodiment 100 is a reflection type photomask including a high reflection portion 10 of exposure light (not shown) and a low reflection portion 20, and the high reflection portion 10 is formed on a substrate 1. It is composed of a multilayer film 2 having a protective film 3 as an upper layer, and the protective film 3 and the multilayer film 2 are removed from the low reflection portion 20. Moreover, the average value of the phase difference between the reflected light from the high reflecting portion 10 (not shown) and the reflected light from the low reflecting portion 20 (not shown) at wavelengths of 180 nm, 240 nm, and 300 nm is 160 to 200 degrees. It is characterized by that.

FIG. 2 is a schematic cross-sectional view showing a modified example 100a of the first embodiment of the digging-type EUV mask of the present invention. Comparing the modified example 100a of the first embodiment with the first embodiment 100 of FIG. 1, the low reflection portion 20a is not only the portion from which the protective film 3a and the multilayer film 2a are removed, but also the substrate 1 is dug. The only difference is that it also includes the spilled part 5.

FIG. 3 is a schematic cross-sectional view showing a second embodiment 200 of the digging-type EUV mask of the present invention. Comparing the second embodiment 200 with the first embodiment 100 of FIG. 1, the protective film 3 in the first embodiment 100 of FIG. 1 includes a protective film and a hard mask layer for dry etching the multilayer film 12. The only difference is that it is replaced by a dual-purpose film 7 that also serves as.

FIG. 4 is a schematic cross-sectional view showing a modified example 200a of the second embodiment of the digging-type EUV mask of the present invention. Comparing the modified example 200a of the second embodiment with the second embodiment 200 of FIG. 3, the low reflection portion 40a is not only the portion where the combined film 7a and the multilayer film 12a are removed, but also the substrate 1 is dug out. The only difference is that it also includes the sown portion 15.

As described above, in the embodiment of the digging-type EUV mask of the present invention, there are a plurality of OB lights in a specific wavelength range of the reflected light from the high-reflecting portion and the reflected light from the low-reflecting portion. It is characterized in that the average value of the phase difference of light having a wavelength is 160 to 200 degrees.

The plurality of wavelengths of the OOB light in a specific wavelength range are 180 nm, 240 nm, and 300 nm, and further, 120 nm, 180 nm, 240 nm, 300 nm, and 360 nm provide better transfer characteristics on the wafer. Preferred to obtain.

In order to explain the process leading to the above-mentioned phase difference condition definition, first, the number of pairs of multilayer films is changed, and the structure is structurally the same as the EUV mask of the first embodiment of the present invention. An example will be described in which a mask (hereinafter, simply referred to as the EUV mask of the first embodiment) is prepared, transferred by EUV exposure, and the line edge roughness and resolution of the transfer pattern on the wafer are evaluated.

On the surface of the low thermal expansion substrate, a multilayer film having a periodic thickness of 7.0 nm, which is a pair of Si (thickness 4.2 nm) and Mo (thickness 2.8 nm), is formed in pairs from 9 pairs to 40 pairs. , 32 types were prepared. A protective film made of Ru was formed on the multilayer film of each sample at 2 nm, and SiO ₂ was formed on the multilayer film with a film thickness of 10 nm as a hard mask for dry etching the multilayer film. A conductive film made of CrN is formed on the back surface of the substrate with a film thickness of 100 nm, and 32 types of E are formed.
A UV mask blank was prepared. The film formation of these materials was carried out by a DC sputtering method using a sputtering device.

Next, a positive electron beam resist (SEBP9012: Shin-Etsu Chemical Industry Co., Ltd.) was applied to 32 types of mask blanks having different numbers of layers of multilayer films prepared as described above to a thickness of 35 nm, and an electron beam drawing machine was used. (JBX3030: manufactured by JEOL Ltd.) draws a 1: 1 line & space pattern of 64 nm in dimensions on the mask, and spray develops for 90 seconds with an alkaline developer of TMAH aqueous solution (concentration 2.38%) (SFG3000). : Sigma Meltec Co., Ltd.) was performed to form a resist pattern.

Next, using the resist pattern as an etching mask, a SiO ₂ hard mask was dry-etched with a fluorine-based plasma (conditions; CF ₄ flow rate 40 sccm, pressure 5 mTorr, ICP power 200 W, RIE power 50 W, 120 seconds). Then, an oxygen plasma; by (Condition _{O 2} flow rate 50 sccm, pressure 5 mTorr, ICP power 100W, RIE power 50 W, 30 sec), was dry-etched Ru protective layer.

Next, the multilayer film is dry-etched and removed with chlorine-based plasma (conditions; Cl ₂ flow rate 50 _{sccm, O 2} flow rate 2 sccm, He flow rate 100 sccm, pressure 3 mTorr, ICP power 250 W, RIE power 20 W) until the substrate is exposed. did. This etching time was shortened as the number of pairs of multilayer films was smaller. _{Then, the unnecessary SiO 2} hard mask was removed by a fluorine-based plasma (conditions; CF ₄ flow rate 40 sccm, pressure 5 mTorr, ICP power 200 W, RIE power 50 W, 30 seconds). Finally, SPM (hydrogen peroxide solution) cleaning and megasonic cleaning were performed to prepare 32 types of digging-type EUV masks.

Next, the dimensions of the mask pattern produced by the above procedure were measured with a secondary electron scanning microscope (SEM) type pattern dimension measuring device (LWM9045: manufactured by Advantest). It was confirmed that a 1: 1 line & space pattern having a size of 64 nm was formed.

Next, the height difference between the high-reflection part (the part with the multilayer film) and the low-reflection part (the part with the multilayer film) is measured by an atomic force microscope (AFM) for all 32 samples having different number of film formation pairs of the multilayer film. As a result, it was confirmed that the value was 65 nm to 282 nm, which was obtained by adding 2 nm of the Ru protective film to the period of 7 nm × 9 pairs to the period of 7 nm × 40 pairs.

Next, using an EUV exposure apparatus (NXE3300B: manufactured by ASML), the digging-type EUV mask pattern produced above is reduced and transferred by 1/4 on a semiconductor wafer coated with a positive chemical amplification resist for EUV. did. The exposure amount at this time was 30 mJ / cm ² . At this time, since the reflectance of the EUV light reflecting portion is lower as the number of pairs of multilayer films is smaller, the exposure amount reaching the wafer is adjusted to 30 mJ / cm ² by adjusting the exposure time longer. .. As a result, the average line width of the transfer pattern for each sample was 16 nm, which was 1/4 times 64 nm.

[Evaluation method]
The line edge roughness (LER) of the transferred resist pattern and the resolution due to the presence or absence of disconnection or bridge are evaluated by a secondary electron scanning microscope (SEM) type pattern dimensional measuring device (LWM9045: manufactured by Advantest). It was.

[Evaluation results]
The results of the above measurements and evaluations are shown in Table 1. The numerical value of LER is a numerical value of 3σ.

As can be seen from the results in Table 1, when the number of pairs of the multilayer film is 12 to 14 pairs, 19 to 22 pairs, and 29 to 31 pairs, the good result that the LER of the wafer pattern is 2.2 nm or less is obtained. It turned out to appear periodically. Further, it was confirmed that when the LER was 2.6 nm or more, the wafer pattern was broken or bridged.

It is known that if the LER is 2.2 nm or less, the electrical characteristics on the semiconductor device of the logic 7 nm generation are not deteriorated, but if it is larger than 2.2 nm, the electrical characteristics are deteriorated.

[Verification by simulation]
Hereinafter, an example in which the reflectance and the phase difference of the OOB light are calculated by simulation and the conditions included in the reflective photomask of the present invention are examined in comparison with the results of the above examples will be described.

Generally, the optical characteristics (transmittance, reflectance, phase difference) of a thin film are determined by the optical constants (refractive index: n, extinction coefficient: k) between the substrate and the thin film, the film thickness of the thin film, and the wavelength of incident light. For example, it is uniquely determined and can be calculated by optical theory. The same applies to the multilayer film (for details, refer to, for example, Applied Physics Engineering Selection 3, Sadafumi Yoshida "Thin Film", Baifukan Co., Ltd., 1990).

Table 2 shows the optical constants for each wavelength of each material used in the calculation. _{Quartz (SiO 2} ), which has a similar composition, is used as a substitute for the low thermal expansion substrate. The numerical values in Table 2 are [Non-Patent Documents: I.I. P. It is a value collected from Kaminow, Handbook of Optical Constants of Solids I, II, III]. The optical constant of CrN at a wavelength of 120 nm is unknown and is not shown in Table 2. _{This is because the extinction coefficient of SiO 2} is large at a wavelength of 120 nm, light is absorbed by a thick (usually 6 mm or more) substrate, and CrN, which is a back surface conductive film, does not affect the reflected light.

FIG. 7 shows the multi-layered reflectance of the high reflectance portion of light having (a) a wavelength of 120 nm, (b) a wavelength of 240 nm, and (c) a wavelength of 360 nm in the first embodiment (FIG. 1) of the digging-type EUV mask. It is a characteristic figure which shows the result of having calculated with the number of pairs (1-40) of membranes as the horizontal axis. For comparison, the reflectance of the low reflectance part (which is a constant value because there is no multilayer film) is shown at the same time.

As can be seen from FIG. 7, at any wavelength, the reflectance of the high reflectance portion is saturated with the number of pairs of about 4 pairs or more, and becomes a substantially constant value. However, as a feature, at a wavelength of 120 nm (FIG. 7 (a)), the low reflection portion consisting of _{only the substrate (here, SiO 2} ) and the CrN back surface conductive film reflects more than the high reflection portion composed of the multilayer film and the protective film. The rate will be high. This is because, as described above, _{the extinction coefficient of SiO 2} is large at a wavelength of 120 nm, resulting in metallic optical characteristics. Therefore, it is presumed that the light having a wavelength near 120 nm has a greater influence on the resolution of the transfer pattern on the wafer than the light having a longer wavelength. However, it does not reflect the periodic change in resolution with respect to the number of pairs as seen in the experimental results in Table 1.

FIG. 8 shows the phase difference between the high reflectance portion and the low reflectance portion of light having (a) a wavelength of 120 nm, (b) a wavelength of 240 nm, and (c) a wavelength of 360 nm in the first embodiment of the digging-type EUV mask. It is a characteristic figure which shows the result of calculation with the number of pairs (1-40) of a multilayer film as the horizontal axis. In the figure, it seems that the flight is from 360 (deg = degree) to 0 (deg), but this means that the results calculated in 1-pair units are connected by a solid line, and the phase is 360 (deg) = 0. This is due to the fact that it is (deg), and is actually continuous from 360 (deg) to 0 (deg).

As can be seen from FIG. 8, the phase difference changes periodically from 0 (deg) to 360 (deg) depending on the number of pairs of multilayer films. The period becomes longer as the wavelength of light becomes longer, and the number of pairs having a phase difference of 180 degrees differs depending on the wavelength.

If the phase difference between the high reflectance part and the low reflectance part is 180 (deg), high reflection is also high in OOB light as in a mask having a halftone effect at EUV wavelength (for example, Japanese Patent Application Laid-Open No. 7-114173). It is considered that the reflected light at the boundary between the rate part and the low reflectance part overlaps and attenuates in the inverted phase, and the line edge roughness and resolution of the transfer pattern on the wafer are improved. The number of pairs having a phase difference of 180 degrees differs depending on the wavelength.

Therefore, considering the results of the examples, it is considered that the halftone effect in the OOB light at the boundary between the high reflectance portion and the low reflectance portion of the EUV mask is expressed by synthesizing a plurality of wavelength components.

FIG. 9 is a characteristic diagram showing the result of calculating the average value of the phase differences between the high reflectance portion and the low reflectance portion of light having a plurality of wavelengths according to the first embodiment of the digging-type EUV mask. In FIG. 9A, the phase differences of light having three wavelengths at equal intervals of 180 nm, 240 nm, and 300 nm are averaged, and in FIG. 9B, light having five wavelengths including 120 nm and 360 nm is averaged. The result of averaging the phase differences is shown.

According to FIG. 9A, the phase difference is close to 180 deg near the number of pairs 13, 21, and 30, which is almost the same as the number of pairs when the evaluation result (Table 1) is good in the example. I understand. Further, according to FIG. 9 (b) using 5 wavelengths, the phase difference is closer to 180 deg in the vicinity of the number of pairs 13, 21 and 30 than in FIG. 9 (a), and the evaluation result in the example (Table 1). It can be seen that the number of pairs is close to that when was good.

For comparison, FIG. 9 (c) is different from the examples and FIGS. 9 (a) and 9 (b) in that the CrN back surface conductive film is 20 nm and the phase difference at 5 wavelengths is the same as in FIG. 9 (b). It shows the averaged result. Again, the phase difference is within the range of approximately 160 to 200 deg, and even if the CrN film thickness is changed, the deterioration of the transfer characteristics on the wafer due to OOB light is suppressed as long as the EUV mask satisfies the conditions specified in the present invention. Therefore, it is considered that the increase in LER of the resist pattern on the wafer and the unresolution are alleviated.

As can be seen from the results of the examples and the simulation, in the digging-type EUV mask of the present invention, the number of laminated multilayer films, which was 40 to 50 pairs in the past, can be reduced to 39 pairs or less. That is, in the above example, good transfer characteristics can be obtained even when the number of pairs is about 13, 21, or 30. The fact that the number of multilayer films laminated can be reduced has the effect of reducing the manufacturing cost of the EUV mask blank and the EUV mask.

The first embodiment of the digging-type EUV mask has been described above as an example, but the average value of the phase difference between the reflected light from the high reflection portion and the reflected light from the low reflection portion at the specified wavelength is 160. It may be ~ 200 degrees. That is, the protective film may be the digging-type EUV mask of the second embodiment, which is a film that also serves as the protective film and the hard mask layer, and the low reflection portion is added to the portion where the protective film and the multilayer film are removed. It may be a modification of the first embodiment and the second embodiment including the portion where the substrate is dug.

The material of the multilayer film is not limited to Mo and Si, and any material composition and periodic film thickness suitable for producing high reflection with respect to the exposure light may be used. In order to obtain high reflection, it is good to combine materials with a large difference in refractive index. In the case of EUV exposure, for example, low refractive index materials include Ru, Mo, Rh, etc., and high refractive index materials include Si, There are Be, Al, etc.

The protective film is not limited to Ru. It suffices if it has irradiation resistance at the time of exposure and can be appropriately selected, but it is desirable that the material has high transparency to exposure light. In the case of EUV exposure, Si, Zr, Y, Be, Ti and the like are effective other than Ru.

The hard mask is not limited to _{SiO 2.} The hard mask may be sufficiently resistant to the etching gas used for etching the multilayer film, and may be appropriately selected depending on the gas used. For example, TaBO, TaO, SiON, SiN, CrN, Ru, Al ₂ O _{3 and the} like are also effective.

FIG. 5 is a schematic cross-sectional view showing the first embodiment 100b of the digging-type EUV mask blank of the present invention, and FIG. 6 is a schematic cross-sectional view showing the second embodiment 200b of the digging-type EUV mask blank of the present invention. It is a figure. In the first embodiment 100b, the protective film 6b is formed on the multilayer film 2b, and in the second embodiment 200b, a combined film 7b is formed instead of the protective film 6b.

In the digging-type EUV mask blank of the present invention, the reflected light from the high reflection portion including the multilayer film and the reflection from the low reflection portion when it is assumed that the portion including the multilayer film is removed to form the low reflection portion. The average value of the phase difference with light at wavelengths of 180 nm, 240 nm, 300 nm, or wavelengths of 120 nm, 180 nm, 240 nm, 300 nm, and 360 nm is 160 to 200 degrees.
It is characterized by that.

The present invention is not limited to EUV masks and EUV mask blanks, and can be applied to reflective photomasks and reflective photomask blanks in which deterioration of transfer characteristics due to OOB light is a problem.

100 ... First embodiment of the digging type EUM mask of the present invention 100a ... Modified example of the first embodiment of the digging type EUM mask of the present invention 100b ... Digging type EUV mask of the present invention First Embodiment 200 of the blank ... Second embodiment 200a of the digging type EUM mask of the present invention ... Modification 200b of the second embodiment of the digging type EUM mask of the present invention ... The present invention Second embodiment of the digging type EUV mask blank 10, 10a, 30, 30a ... High reflection part 20, 20a, 40, 40a ... Low reflection part 1 ... Low thermal expansion substrate 2, 2a, 12, 12a ... Multilayer film (after masking)
2b, 12b ・ ・ ・ ・ ・ ・ ・ ・ Multilayer film (when blank)
3, 3a ・ ・ ・ ・ ・ ・ ・ ・ Protective film (after masking)
3b ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Protective film (when blank)
4 ... Backside conductive film 5, 15 ... Digging part of low thermal expansion substrate 6b ... Hard mask layer 7, 7a ... Combined film (after masking)
7b ・ ・ ・ ・ ・ Combined film (when blank)

Claims (6)

A reflective photomask comprising a high-reflecting portion having a high reflectance with respect to exposure light and a low-reflecting portion having a low reflectance.
The highly reflective portion is composed of a multilayer film formed on a substrate and having a protective film as an upper layer.
The low reflection portion is formed by removing the protective film and the multilayer film.
The average value of the phase difference between the reflected light from the high reflection portion and the reflected light from the low reflection portion at wavelengths of 180 nm, 240 nm, and 300 nm is 160 to 200 degrees.
A reflective photomask that features this. The average value of the phase difference between the reflected light from the high reflection portion and the reflected light from the low reflection portion at wavelengths of 120 nm, 180 nm, 240 nm, 300 nm and 360 nm is 160 to 200 degrees.
The reflective photomask according to claim 1. The protective film also serves as a hard mask layer for dry etching.
The reflective photomask according to claim 1 or 2. The low-reflection portion includes a portion in which the protective film and the multilayer film have been removed, and a portion in which the substrate is dug.
The reflective photomask according to any one of claims 1 to 3. The multilayer film is a multilayer film in which Si and Mo are alternately laminated as a pair, and the number of layers is 39 pairs or less.
The reflective photomask according to any one of claims 1 to 4, wherein the reflective photomask is characterized in that. A reflective photomask blank for producing the reflective photomask according to any one of claims 1 to 5.
The phase difference is the phase difference between the reflected light from the high reflection portion and the reflected light from the low reflection portion when it is assumed that the low reflection portion is formed.
A reflective photomask blank.

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