JP2019139085A - Reflective photomask blank and reflective photomask - Google Patents

Abstract

To provide a reflective photomask blank and a reflective photomask capable of achieving improvement in transfer performance to a semiconductor substrate and cleaning resistance.SOLUTION: A reflective photomask blank 1 includes: a substrate 11; a reflection layer 13 which is formed on the substrate 11 and reflects incident light; and an absorption layer 15 which has an indium oxide film 15a having a single-layer structure and having a film thickness of 18 nm or more and 45 nm or less, is laminated on the reflection layer 13, and absorbs incident light.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reflective photomask blank and a reflective photomask.

  In the manufacturing process of semiconductor devices, with the miniaturization of semiconductor devices, there is an increasing demand for miniaturization of photolithography technology. In photolithography, the minimum resolution dimension of the transfer pattern greatly depends on the wavelength of the exposure light source, and the minimum resolution dimension can be reduced as the wavelength is shorter. For this reason, in the semiconductor device manufacturing process, a conventional exposure light source using ArF excimer laser light having a wavelength of 193 nm is being replaced with an exposure light source in the extreme ultraviolet (EUV) region having a wavelength of 13.5 nm.

  Most substances have a high light absorption for light in the EUV region. For this reason, a photomask for EUV exposure (EUV photomask) is a reflective photomask, unlike a conventional transmissive photomask (see, for example, Patent Document 1). In Patent Document 1, in a reflective exposure mask used for EUV lithography, a multilayer film in which two or more kinds of material layers are periodically stacked is formed on a base substrate, and a metal film containing nitride is formed on the multilayer film. Forming a mask pattern comprising a laminated structure of a metal nitride film and a metal film.

  In addition, since EUV lithography cannot use a refractive optical system that utilizes light transmission as described above, the optical system member of the exposure machine is not a lens but a reflection type (mirror). For this reason, deflection using a transmissive beam splitter is impossible. Therefore, there is a problem that the incident light and the reflected light on the EUV photomask cannot be designed on the same axis. Normally, in EUV lithography, the EUV light is incident with the optical axis inclined by 6 degrees from the vertical direction of the EUV photomask, and minus 6 A technique is adopted in which reflected light reflected at an angle of degrees is guided to a semiconductor substrate.

JP 2001-237174 A

  Thus, since EUV lithography inclines the optical axis, a problem called a projection effect occurs in which EUV light incident on the EUV photomask becomes a shadow of the mask pattern (absorbing layer pattern) of the EUV photomask. This projection effect is a fundamental problem of EUV lithography that tilts the optical axis.

  In the present EUV photomask blank, an absorption layer having a film thickness of 60 to 90 nm containing tantalum (Ta) as a main component is used. When exposure is performed using an EUV photomask manufactured from such an EUV photomask blank, depending on the relationship between the incident direction and the orientation of the mask pattern, a decrease in contrast is caused at the edge portion that becomes the shadow of the mask pattern. It is. In particular, when the pattern size on the semiconductor substrate is a fine pattern of 20 nm or less, when this decrease in contrast is caused, the transfer pattern is poorly resolved, the line edge roughness is increased, and the line width cannot be formed to a desired size. This causes problems such as transfer performance.

  Moreover, the EUV photomask is repeatedly used after being cleaned before and after use. For this reason, the EUV photomask needs to have durability (cleaning resistance) against cleaning so that transfer performance is not deteriorated by this cleaning.

  Accordingly, an object of the present invention is to provide a reflective photomask blank and a reflective photomask that can improve the transfer performance to a semiconductor substrate and the cleaning resistance.

  In order to achieve the above object, a reflective photomask blank according to one embodiment of the present invention has a substrate, a reflective layer that is formed over the substrate and reflects incident light, and a single-layer structure or a stacked structure. It has an indium oxide film with a film thickness of 18 nm or more and 45 nm or less, and is provided with an absorption layer that is stacked on the reflective layer and absorbs incident light.

  The film thickness of the indium oxide film may be 18 nm or more and 33 nm or less.

  The indium oxide film may be a film having an atomic ratio of oxygen to indium of 0.5 to 1.5.

  The indium oxide film may include a compound material that occupies an atomic ratio of 80% or more with indium and oxygen.

  When the intensity of reflected light from the reflective layer is Rm, the intensity of reflected light from the absorbing layer is Ra, and the optical density based on the reflective layer and the absorbing layer is OD, the optical density is “OD = -Log (Ra / Rm) "and the value may be 1 or more.

  The reflective layer may include a multilayer reflective film and a capping film formed on the multilayer reflective film.

  In order to achieve the above object, a reflective photomask according to one embodiment of the present invention includes a substrate, a reflective layer that is formed over the substrate and reflects incident light, and has a single-layer structure or a stacked structure. And an indium oxide film having a film thickness of 18 nm to 45 nm and having a predetermined pattern formed thereon, and an absorption layer that is stacked on the reflective layer and absorbs incident light.

  According to one embodiment of the present invention, it is possible to improve transfer performance to a semiconductor substrate and cleaning resistance.

It is a schematic sectional drawing which shows the structure of the reflection type photomask blank by one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the reflection type photomask by one Embodiment of this invention. It is a figure explaining the reflective photomask blank and reflective photomask by one Embodiment of this invention, Comprising: It is a graph which shows the optical constant of each metal material in the wavelength of EUV light. It is a graph which shows the simulation result of the reflectance in EUV light of the reflective photomask blank by one Embodiment of this invention. It is a graph which shows the simulation result of OD value in the wavelength of EUV light of the reflection type photomask blank by one Embodiment of this invention. It is a graph which shows the simulation result of the HV bias value which is one of the lithography characteristics of the reflective photomask by one Embodiment of this invention. It is a graph which shows the simulation result of the HV bias value in each OD value of the reflection type photomask by one Embodiment of this invention. It is a graph which shows the simulation result of the pattern contrast in the film thickness of the reflection type photomask by one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the reflection type photomask blank by the Example of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the reflection type photomask by the Example of one Embodiment of this invention. It is a schematic sectional drawing which shows the manufacturing process of the reflection type photomask by the Example of one Embodiment of this invention.

  Hereinafter, a reflective photomask blank and a reflective photomask according to an embodiment of the present invention will be described with reference to the drawings. The reflective photomask blank and the reflective photomask according to this embodiment are used in lithography using extreme ultraviolet (EUV) in a semiconductor manufacturing process. The effectiveness of using the layer containing indium (In) and oxygen (O) proposed in the present invention for the absorption layer will be described based on the characteristics of the layer containing In and O.

(Schematic configuration of a reflective photomask blank and a reflective photomask according to an embodiment of the present invention)
A reflective photomask blank 1 according to an embodiment of the present invention is a photomask blank for forming a reflective photomask that reflects EUV light and irradiates the transfer sample with the reflected light.
As shown in FIG. 1, the reflective photomask blank 1 according to the present embodiment includes a substrate 11 and a reflective layer 13 that is formed on the substrate 11 and reflects incident light. The reflective photomask blank 1 has an indium oxide (InO) film 15a having a single layer structure and a film thickness of 18 nm to 45 nm and is laminated on the reflective layer 13 to absorb incident light. 15 is provided. In this embodiment, the indium oxide film 15a provided on the absorption layer 15 has a single layer structure, but may have a stacked structure in which a plurality of indium oxide films are stacked. In this case, the plurality of stacked indium oxide films may have different atomic ratios of oxygen (O) to indium (In).

  The reflective layer 13 includes a multilayer reflective film 13a and a capping film 13b formed on the multilayer reflective film 13a. The multilayer reflective film 13a has a plurality of laminated films 131 in which, for example, a silicon (Si) film and a molybdenum (Mo) film are laminated. The plurality of stacked films 131 are stacked on each other. The multilayer reflective film 13a is laminated with several tens of pairs (for example, 40 pairs), but in FIG. 1 and FIG. 2 described later, the laminated film 131 is illustrated with three pairs of multilayer reflective films 13a for easy understanding. ing. The capping film 13b functions as a protective film for protecting the multilayer reflective film 13a. The capping film 13b is made of, for example, ruthenium (Ru).

  The reflective photomask according to one embodiment of the present invention has an absorption layer pattern (predetermined for forming a pattern to be transferred onto a semiconductor substrate or a semiconductor wafer (not shown) on the absorption layer 15 of the reflective photomask blank 1. Example of pattern) 151 is formed by processing. Therefore, as shown in FIG. 2, the reflective photomask 2 includes a substrate 11 and a reflective layer 13 that is formed on the substrate 11 and reflects incident light. The reflective photomask 2 has an indium oxide (InO) film 15a having a single layer structure and a film thickness of 18 nm to 45 nm and having an absorption layer pattern 151 formed thereon, and is laminated on the reflective layer 13. An absorption layer 15 that absorbs incident light is provided. In the present embodiment, the indium oxide film 15a provided on the absorption layer 15 of the reflective photomask 2 has a single layer structure, but has a stacked structure in which a plurality of indium oxide films are stacked. Also good. In this case, the plurality of stacked indium oxide films may have different atomic ratios of oxygen (O) to indium (In). The reflective layer 13 provided on the reflective photomask 2 has the same configuration as the reflective layer 13 provided on the reflective photomask blank 1 shown in FIG.

(Explanation of light absorption of absorption layer)
The absorption layer is a layer that absorbs EUV light applied to the reflective photomask after an absorption layer pattern, which is a predetermined exposure transfer pattern, is formed by dry etching. The absorbing layer needs to be formed thin in order to reduce the projection effect that is a problem. Conventionally, Ta (tantalum), which is generally used as a material for forming the absorption layer provided in the reflection type photomask blank and the reflection type photomask, is not sufficiently absorbed by EUV light when formed simply thinly. The reflectivity in the region becomes higher. For this reason, in order to achieve the thinning of the absorption layer and the light absorption of EUV light at the same time, a material having higher light absorption with respect to EUV light than the existing absorption layer material is required.

(Explanation of drawbacks of superabsorbent materials)
FIG. 3 is a graph showing optical constants of each metal material at the wavelength of EUV light. The horizontal axis in FIG. 3 indicates the refractive index n, and the vertical axis indicates the extinction coefficient k. As shown in FIG. 3, materials having a high extinction coefficient k include silver (Ag), nickel (Ni), tin (Sn), tellurium (Te), indium (In), and the like. The extinction coefficient of these metal materials is in the range of 0.07 to 0.08, which is about twice as large as the extinction coefficient of Ta, which is a conventional material for forming the absorption layer, of 0.041. For this reason, the absorption layer formed of these metal materials can have high light absorption. However, these metal materials have a problem that elemental halides have low volatility and dry etching properties are poor. For this reason, even if a reflection type photomask blank having an absorption layer formed of these metal materials is manufactured, the absorption layer pattern cannot be patterned on the absorption layer, and as a result, the reflection type photomask blank is made a reflection type. There arises a problem that the photomask cannot be processed. Alternatively, since the melting points of these metal materials are low, there is a problem that the reflective photomask cannot be used with heat at the time of manufacturing the reflective photomask or EUV exposure, resulting in poor practical photomask.

(Description of InO film of the present invention)
In order to avoid the above-described drawbacks, the reflective photomask blank of the present invention and the absorption layer of the reflective photomask have an InO film that is an oxide of indium. In In alone, the melting point is around 157 ° C., which is lower than the temperature of heat at the time of manufacturing a reflective photomask or EUV exposure, and there is a problem in thermal stability and cleaning resistance. On the other hand, the melting point of the InO film can be 800 ° C. or higher. As a result, the InO film has sufficient resistance to heat during the production of a reflective photomask or during EUV exposure. Furthermore, since the InO film is chemically stable due to the chemical bond between In and O, the InO film has sufficient resistance to acidic cleaning solutions and alkaline cleaning solutions used at the time of manufacturing a reflective photomask and before and after use. .

In addition, while the InO film is chemically stable, dry etching using a chlorine-based gas is possible, so that the reflective photomask blank can be processed into a reflective photomask. This is because the volatility of InCl ₃ , which is a compound of In and chlorine (Cl), is higher than that of the superabsorbent material other than In shown in FIG.

(Explanation of the atomic ratio (O / In ratio) of oxygen to indium in the InO film of the present invention)
The InO film of the absorption layer provided in the reflective photomask blank and the reflective photomask according to an embodiment of the present invention has an oxygen atomic ratio (O / In ratio) of 0.5 to 1.5. It is a film. InO has an optical constant (extinction coefficient, refractive index) for EUV light that is almost the same as that of In alone when the O / In ratio is 0.5 to 1.5. Can be maintained. On the other hand, when the O / In ratio is less than 0.5, the cleaning resistance deteriorates. Further, as will be described in Examples described later, it was confirmed that an InO film having an O / In ratio exceeding 1.5 could not be formed.

  Actually, a plurality of InO film samples in which the oxygen content was changed in the range of O / In ratio of 0.5 or more and 1.5 or less were measured, and the optical constant at the EUV light wavelength (13.5 nm) was measured. In both cases, the refractive index n was in the range of 0.920 to 0.930, and the extinction coefficient k was in the range of 0.067 to 0.070. The ranges of these values of the refractive index n and the extinction coefficient k include values of In alone (refractive index n is 0.93 and extinction coefficient k is 0.07) shown in FIG. Therefore, it can be seen that the optical constant of InO hardly changes from that of In alone when the O / In ratio is 0.5 or more and 1.5 or less.

(Comparison of reflectance, OD and film thickness between InO film and Ta film)
FIG. 4 is a graph comparing the absorption layer having the InO film and the absorption layer having the conventional Ta film with respect to the EUV light reflectance at the wavelength of the EUV light. The horizontal axis in FIG. 4 indicates the film thickness (nm) of the absorption layer, and the vertical axis indicates the EUV light reflectance (%). FIG. 5 is a graph comparing an absorption layer having an InO film and an absorption layer having a Ta film with respect to an optical density (OD) value indicating the basic performance of the mask. The horizontal axis in FIG. 5 indicates the film thickness (nm) of the absorption layer, and the vertical axis indicates the OD value. The EUV light reflectance and OD value are calculated based on the optical constant of the InO film (refractive index n is 0.923, extinction coefficient k is 0.068).

The OD value is a contrast (intensity ratio of reflected light) between the EUV light reflected by the absorbing layer and the EUV light reflected by the reflecting layer, and is derived by the following equation (1). In Expression (1), the reflected light intensity of the EUV light reflected by the reflective layer region is represented by “Rm”, the reflected light intensity of the EUV light reflected by the absorbing layer region is represented by “Ra”, and the OD value. Is represented by “OD”.
OD = -log (Ra / Rm) (1)

  In general, a higher OD value is better for a reflective photomask blank and a reflective photomask. The EUV light reflectance shown in FIG. 4 and the OD value shown in FIG. 5 are respectively a capping layer (protective layer) made of Ru having a thickness of 2.5 nm below the absorption layer, and a pair of Si and Mo below it. A reflective photo film in which a plurality of (eg, 40 pairs) multi-layer films are laminated, a flat synthetic quartz substrate underneath, and a backside conductive layer made of chromium nitride (CrN) on the back side of the synthetic quartz substrate It is calculated using the optical constant (refractive index, extinction coefficient) and film thickness of each layer for the mask blank. That is, the OD value is calculated based on the configuration in which the back surface conductive layer is provided on the back surface of the substrate 11 of each of the reflective photomask blank 1 shown in FIG. 1 and the reflective photomask 2 shown in FIG. However, the material and film thickness of the reflective photomask blank and reflective photomask of the present invention are not limited to the materials and film thicknesses of the multilayer reflective layer, capping layer, back surface conductive layer, and substrate.

  As can be seen from FIG. 4, when the InO film has the same film thickness as the Ta film, the EUV light reflectance can be reduced to half or less. In addition, the InO film can be reduced to half or less of the thickness when the reflectance is the same as that of the Ta film. Thus, the InO film is effective as a component constituting the high absorption layer at the wavelength of EUV light.

  As can be seen from FIG. 5, in order to obtain an OD value of 1 or more, the Ta film needs to have a thickness of at least 40 nm, whereas the InO film may have a thickness of about 18 nm. Thus, it can be seen that the InO film is effective as a component that can reduce the entire thickness of the absorption layer as compared with the Ta film from the viewpoint of the OD value.

  In order to obtain an OD value of 2 or more, the Ta film needs to have a thickness of at least 70 nm, whereas the InO film may have a thickness of 33 nm. Thus, it can be seen that the InO film is effective as a component that can reduce the entire thickness of the absorption layer as compared with the Ta film even at an OD value of 2 or more. In a conventional absorption layer, a Ta film having a thickness of about 70 nm (OD value is 2) is typically used.

  Thus, by using the InO film for the absorption layer, the absorption layer can be made thin while maintaining the OD value indicating the basic performance of the reflection type photomask blank and the reflection type photomask.

(Comparison of HV bias of Ta film and InO film)
Next, in order to evaluate the influence of the projection effect, how the HV bias value changes when the film thickness is changed in each of the Ta film and the InO film was compared by simulation. FIG. 6 is a graph showing a simulation result of the HV bias value. The horizontal axis in FIG. 6 indicates the film thickness (nm) of the absorption layer provided in the reflective photomask, and the vertical axis indicates the HV bias value (nm).

  The HV bias value is a line width difference of the transfer pattern depending on the orientation of the mask pattern, that is, a difference between the line width in the horizontal (Horizontal: H) direction and the line width in the vertical (Vertical: V) direction. The line width in the H direction indicates the line width of a linear pattern orthogonal to the surface formed by incident light and reflected light (hereinafter sometimes referred to as “incident surface”), and the line width in the V direction is The line width of the parallel linear pattern is shown. That is, the line width in the H direction is the length in the direction parallel to the incident surface, and the line width in the V direction is the length in the direction orthogonal to the incident surface.

  The line width in the H direction is affected by the projection effect, which causes a decrease in contrast at the edge portion of the transfer pattern and a decrease in the line width in the H direction. The pattern affected by the projection effect has a line width after transfer smaller than a desired line width. On the other hand, the line width in the V direction is hardly affected by the projection effect. Therefore, a line width difference (HV bias) occurs between the line width of the transfer pattern in the direction perpendicular to the incident surface and the line width of the transfer pattern in the direction parallel to the incident surface.

  The pattern used in this simulation is a mask pattern designed to have a size of LS of 16 nm on the semiconductor substrate (the ratio of the line to the space is 1: 1). In EUV lithography, since it is usually a reduction projection exposure of 1/4, the absorption layer pattern formed on the absorption layer of the EUV photomask (that is, the reflection type photomask) is in a direction parallel to and perpendicular to the incident surface. Both are LS patterns with a pattern size of 64 nm. As shown in FIG. 6, it can be seen that the HV bias value of the transfer pattern formed on the semiconductor substrate increases as the film thickness increases, regardless of whether it is an absorption layer composed of a Ta film or an InO film. .

  Here, when the HV bias values of the Ta film (film thickness 70 nm) and the InO film (film thickness 33 nm) with an OD value of 2 were compared, as shown in FIG. Although it is very large as 10.5 nm, the InO film can be significantly reduced to 5.0 nm and is improved. Further, even when comparing the Ta film (film thickness 40 nm) and InO film (film thickness 18 nm) with an OD value of 1, the HV bias value is 3.2 nm for the Ta film and 2.2 nm for the InO film. It has been reduced and improved. Thus, it can be seen that in the reflective photomask blank and reflective photomask of the present invention, the influence of the projection effect (HV bias) can be greatly reduced by using InO as the material for forming the absorption layer.

(Comparison of NILS in Ta film and InO film (explanation of film thickness range of InO film))
The influence of the projection effect also appears in a pattern contrast called NILS (Normalized Image Log Slope). NILS is a characteristic value indicating the slope of the bright part and the dark part obtained from the light intensity distribution of the transfer pattern. The larger the NILS value, the better the pattern transferability. FIG. 8 shows the result of NILS evaluation by calculation using the optical constants of the respective absorption layer materials of Ta and InO. The horizontal axis of FIG. 8 shows the film thickness (nm) of the absorption layer, and the vertical axis shows NILS. In FIG. 8, “InO—X” indicates NILS in the X direction (line width direction in the V direction) of the transfer pattern in the InO film, and “InO—Y” indicates the Y direction (in the H direction in the transfer pattern in the InO film). "Ta-X" indicates the NILS in the X direction of the transfer pattern in the Ta film, and "Ta-Y" indicates the NILS in the Y direction of the transfer pattern in the Ta film.

  As shown in FIG. 8, the NILS of the Ta film (film thickness 70 nm) having an OD value of 2 is 1.5 in the X direction (line width direction in the V direction) and the Y direction (line width in the H direction). ) Is 0.2. Thus, the NILS in the Y direction corresponding to the direction of the line width in the H direction affected by the projection effect is greatly deteriorated.

  Such a large difference in pattern contrast (NILS) between the X direction and the Y direction causes a large HV bias value of the Ta film as described above. On the other hand, in an InO film (film thickness of 33 nm) having an OD value of 2, the NILS in the X direction is 1.5 and the NILS in the Y direction is 0.7. In this manner, the InO film has a significantly improved NILS in the Y direction compared to the Ta film, so that the pattern transfer property is improved and the HV bias value is also reduced.

A decrease in NILS (pattern contrast) in the Y direction not only affects the HV bias, but also increases the line edge roughness of the transfer pattern, and in the worst case, causes a serious problem that the image cannot be resolved.
As shown in FIG. 8, if the thickness of the InO film is 18 nm or more and 33 nm or less, the NILS in the Y direction can be set to a relatively high value including the maximum value. The NILS in the Y direction in the InO film having a film thickness of 18 nm or more and 33 nm or less is equal to or greater than the NILS in the Y direction in the Ta film in the whole range of the film thickness in the simulated range of 14 to 70 nm. Further, an InO film having a film thickness of greater than 33 nm and less than or equal to 45 nm can have a higher NILS in the Y direction than a 70 nm thick Ta film having an OD value of 2.

[Reflective Photomask Blank and Reflective Photomask According to this Embodiment]
The reflective photomask blank and reflective photomask of one embodiment of the present invention include an InO film having a film thickness of 18 nm or more and 33 nm or less (a range expressed as “OD = 1 to 2” in FIG. 8). You may have an absorption layer. Accordingly, the reflective photomask blank and the reflective photomask according to the present embodiment are compared with the reflective photomask blank and the reflective photomask having an absorption layer that does not include an InO film having a film thickness of 18 nm to 33 nm. Since the influence of the projection effect can be reduced, the NILS in the Y direction can be increased.

  Further, the reflective photomask blank and the reflective photomask having the absorption layer including the InO film of 18 nm to 33 nm are compared with the reflective photomask blank and the reflective photomask having the absorption layer including the Ta film, The effect of the projection effect can be greatly improved.

(Explanation that the compound material forming the InO film may contain 80% or more of In and O)
The InO film included in the reflective photomask blank and the absorption layer of the reflective photomask according to the present embodiment is a film containing a compound material that occupies an atomic ratio of 80% or more between indium (In) and oxygen (O). Yes, the rest may be mixed with other materials. This is because, when the ratio of indium and oxygen in the InO film is less than 80%, the EUV light absorbability of the InO film decreases. On the other hand, if the ratio of indium and oxygen in the InO film is 80% or more, the decrease in the EUV light absorption property of the InO film is negligible. Thereby, the InO film containing a compound material that occupies 80% or more of the atomic ratio of indium (In) and oxygen (O) can prevent a decrease in performance as an absorption layer of the EUV photomask.

  Materials other than indium and oxygen include metals such as silicon (Si), tin (Sn), tellurium (Te), tantalum (Ta), platinum (Pt), chromium (Cr), ruthenium (Ru), nitrogen and carbon A light element such as may be mixed in the InO film depending on the purpose of the reflective photomask blank and the reflective photomask. For example, by putting Sn into the InO film, the InO film can have conductivity while ensuring transparency. For this reason, inspecting performance can be improved in mask pattern inspection using deep ultraviolet (DUV) light having a wavelength of 190 to 260 nm. Alternatively, when nitrogen or carbon is mixed in the InO film, the etching speed during dry etching of the InO film can be increased. In the reflective photomask blank and the reflective photomask according to the present embodiment, the material mixed in the InO film other than indium and oxygen is not particularly limited.

(Explanation that OD value is 1 or more)
The reflective photomask blank and the reflective photomask according to an embodiment of the present invention may have an OD value defined by the above-described formula (1) of 1 or more. When an exposure simulation was performed with an InO film (thickness less than 18 nm) with an OD value of less than 1, it was found that the contrast between the absorption layer and the multilayer reflective layer was insufficient, and it was difficult to form a transfer pattern on a semiconductor substrate or semiconductor wafer. did. Therefore, even if the pattern can be formed, the line edge roughness is assumed to be deteriorated. The same was found for the Ta film.

  As described above, according to the reflective photomask blank and the reflective photomask according to the embodiment of the present invention, the projection effect is influenced by having the absorption layer including the InO film having a film thickness of 18 nm to 33 nm. Can be reduced. In addition, the reflective photomask blank and the reflective photomask according to the present embodiment can obtain a high NILS in the Y direction of the transfer pattern as compared with the conventional product having the absorption layer made of the Ta film. Therefore, it is possible to improve the resolution of the transfer pattern and reduce the line edge roughness. In the reflective photomask blank and reflective photomask according to the present embodiment, since NILS in the X direction and the Y direction are close to each other, the HV bias value can be reduced and a transfer pattern faithful to the mask pattern can be obtained.

  Hereinafter, a reflective photomask blank and a reflective photomask according to examples of one embodiment of the present invention will be described with reference to FIGS. 9 to 11 and Tables 1 and 2. FIG. Table 1 is a table showing the mask characteristics of each sample blank of the reflection type photomask blank and the lithography characteristics of each sample mask of the reflection type photomask according to this example and the comparative example. Table 2 is a table showing the mask characteristics of each sample blank of the reflection type photomask blank and the lithography characteristics of each sample mask of the reflection type photomask when the thickness of the indium oxide film is changed. . “NILS-X” shown in Tables 1 and 2 indicates NILS in the X direction, and “NILS-Y” indicates NILS in the Y direction. In addition, “OK” described in the “Resolution” column of Tables 1 and 2 indicates that the transfer pattern has been resolved. Furthermore, “-” described in the “LER” column of Tables 1 and 2 indicates that the line edge roughness could not be measured.

(Description of reflective photomask blank production)
As shown in FIG. 9, for example, 40 pairs (total film thickness is 280 nm) of a laminated film 131 including silicon (Si) and molybdenum (Mo) as a pair on a substrate 11 having a low thermal expansion characteristic such as synthetic quartz. A multilayer reflective film 13a formed by stacking is formed. In FIG. 9, for easy understanding, the multilayer reflective film 13 a is illustrated as three pairs of laminated films 131. Next, a capping film 13b made of ruthenium (Ru) was formed on the multilayer reflective film 13a so as to have a film thickness of 2.5 nm. As a result, the reflective layer 13 having the multilayer reflective film 13a and the capping film 13b is formed on the substrate 11. An indium oxide film was formed on the capping film 13b to form the absorption layer 15 having the indium oxide film 15a, and the reflective photomask blank 3 was produced. A plurality of reflective photomask blanks 3 were prepared as sample blanks. A sputtering apparatus was used to form each film on the substrate 11. The oxygen content in the indium oxide film 15a was controlled by the amount of oxygen introduced into the chamber during sputtering. The oxygen amount was controlled by the reactive sputtering method when forming the indium oxide film 15a. The film thickness of each sample was measured by a transmission electron microscope, and the O / In ratio was measured by XPS (X-ray photoelectron spectroscopy) and confirmed.

As a result of confirming the composition of the absorption layer 15, each sample blank of the reflective photomask blank 3 has an O / In ratio in the range of 0 to 1.5, and has an O / In ratio greater than 1.5. The indium oxide film 15a could not be formed. Here, confirm the film formation rate for samples with O / In ratios of 0, 0.5, 1.0 and 1.5, and calculate the film thickness so that the OD value of each sample is 2 or 1. To form a film. The thickness of the sample blank of the reflection type photomask blank 3 with the target values of the produced ODs of 2 and 1 is 33 nm in the case of the indium oxide film 15a having an O / In ratio of 0 (that is, a film of indium alone (In film)). a 17 nm, O / an in ratio is indium film 15a _{(InO 0.5} layer) in 33nm and 18nm oxide of 0.5, an indium oxide film 15a (InO ₁ film) O / an in ratio of 1, and 33nm It was confirmed that the indium oxide film 15a (InO _1.5 film) having an O / In ratio of 1.5 was 33 nm and 18 nm. Further, as shown in FIG. 9, a back surface conductive layer 31 made of chromium nitride (CrN) was formed on the back surface of the substrate 11 with a film thickness of 100 nm.

(Reflectance measurement and OD calculation)
With respect to the In film and InO film having the above O / In ratio, the reflectance Rm of the reflective layer 13 region and the reflectance Ra of the absorbing layer 15 region were measured with a reflectance measuring device using EUV light. As a result of calculating the OD value, which is a mask characteristic, from the measurement results, as shown in Table 1, it is found that all sample blanks of the reflective photomask blank 3 can be manufactured with OD values of 2 and 1. It was. Also from this, if the film composition has an O / In ratio in the range of 0.5 to 1.5, the absorption layer 15 having the indium oxide film 15a is the same film as the absorption layer having an indium film of indium alone. It can be seen that the mask characteristics (EUV reflectance and OD value calculated from this EUV reflectance) equivalent to the thickness can be obtained.

(Sample blank containing Ta film as a comparative example in the absorption layer)
As a comparative example, a sample blank of a reflective photomask blank was prepared in the same manner as the reflective photomask blank 3 for a Ta film that is an existing film used in a conventional product. In order to achieve an OD value of 2 or 1, the Ta film was formed with a film thickness of 70 nm and 40 nm. As a result of measuring a sample blank of a reflective photomask blank in which the Ta film was formed with this film thickness using a reflectance measuring apparatus using EUV light, it was confirmed that the OD values were 2 and 1 as intended. .

(Reflective photomask production)
As shown in FIG. 10, the reflective photomask 4 according to the example of one embodiment of the present invention has a configuration in which an absorbent layer pattern 151 is formed on the absorbent layer 15 of the reflective photomask blank 3 shown in FIG. doing.

  Here, a manufacturing method of the reflective photomask 4 will be described with reference to FIGS. As shown in FIG. 11, a positive chemically amplified resist R15a (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) is applied to a thickness of 120 nm on the absorption layer 15 provided in the reflective photomask blank 3 produced as described above. To do. Next, a predetermined pattern is drawn on the positive chemically amplified resist R15a by an electron beam drawing machine (JBX3030: manufactured by JEOL Ltd.). Thereafter, the positive chemically amplified resist R15a is subjected to PEB treatment at 110 ° C. for 10 minutes, and then spray development (SFG3000: manufactured by Sigma Meltech Co., Ltd.). Thus, as shown in FIG. 11A, a resist mask R15 having a resist pattern R151 having the same shape as the absorption layer pattern 151 (see FIG. 10) was formed.

  Next, by using the resist mask R15 as an etching mask, the indium oxide film 15a is patterned by dry etching mainly using a fluorine-based gas or a chlorine-based gas, and as shown in FIG. An absorption layer pattern 151 was formed on the substrate. Next, the resist mask R15 was peeled off to produce a reflective photomask 4 (see FIG. 10) according to this example. In this embodiment, the absorption layer pattern 151 formed on the absorption layer 15 has a shape of 64 nm LS (line and space) on the reflective photomask 4. The reflective photomask 4 was prepared for the indium oxide film 15a having O / In ratios of 0, 0.5, 1.0, and 1.5 and OD values of 1 and 2, respectively. Furthermore, the same shape as the absorption layer pattern 151 formed on the reflective photomask 4 by the same method as that of the reflective photomask 4 is applied to the reflective photomask including the absorption layer having the Ta film as the comparative example. The absorption layer pattern was formed on an absorption layer having a Ta film, and a sample mask of a reflective photomask as a comparative example was produced.

(Wafer exposure evaluation)
Next, using the sample mask of the reflection type photomask 4 according to the present example produced by the above procedure, a semiconductor wafer coated with a positive chemically amplified resist for EUV using an EUV light exposure apparatus (NXE3300B: manufactured by ASML) ( The pattern is transferred and exposed by the reflected light reflected by the sample mask of the reflective photomask 4 on the upper surface (not shown), a transfer pattern is formed on the resist, and the transfer pattern is observed, the line width is measured, and the line is measured by an electron beam dimension measuring machine. Edge roughness (LER) measurement was performed. Line edge roughness is a backlash of the side surface of the transfer pattern. The measurement result of the line edge roughness is shown in the “LER” column of Table 1.

(HV bias)
The lithography characteristics were confirmed from the resist pattern formed on the semiconductor wafer. As shown in the “lithographic characteristics” column of Table 1, in this example, the confirmed lithography characteristics are the above-described line edge roughness, HV bias, and resolution. The dimension in the X direction of the transfer pattern and the dimension in the Y direction of the transfer pattern affected by the projection effect were measured, and the difference in these dimensions was calculated to confirm the HV bias value. As a result, as shown in Table 1, a reduction effect of the projection effect due to the thinning was observed. Specifically, when the OD value is 2, the HV bias value is 4.7 nm at a film thickness of 33 nm for an In film, 4.9 nm at a film thickness of 33 nm for InO _0.5 , and a film thickness of 33 nm for an InO ₁ film. 5.0 nm, and the InO _1.5 film has a thickness of 33 nm and 5.0 nm. The HV bias value when the absorption layer having the In film and the InO film is provided is greatly improved as compared with 11.1 nm at the 70 nm film thickness of the HV bias value when the absorption layer having the Ta film as a comparative example is provided. I confirmed that Further, as shown in Table 1, when the OD value is 1, the In film has a 17 nm film thickness of 2.1 nm, the InO _0.5 film has an 18 nm film thickness of 2.2 nm, and the InO ₁ film has an 18 nm film thickness of 2 nm. In the case of .2 nm and InO _1.5 film, 18 nm film thickness was 2.2 nm, and the existing Ta film 40 nm film thickness was better than 3.5 nm.

(Line edge roughness)
The line edge roughness (LER) of the transfer pattern was confirmed. As shown in Table 1, the line edge roughness of the transfer pattern formed with a reflective photomask having a Ta film thickness of 70 nm could not be measured due to unresolved. The transfer pattern formed with a reflective photomask having a Ta film thickness of 40 nm had a line edge roughness of 4.2 nm. In the reflective photomask 4, it was confirmed that the line edge roughness of the transfer pattern was as good as 3.9 nm or less regardless of the film thicknesses of the In film and InO film.

(Washing resistance)
After the wafer transfer evaluation, the resistance of the reflective photomask 4 to sulfuric acid / water washing was evaluated. The In film was dissolved by sulfuric acid / hydrogen peroxide, and the absorption layer pattern 151 disappeared. Thereby, it was confirmed that the reflection type photomask provided with the absorption layer having the In film has no cleaning resistance. In the reflection type photomask 4 provided with the absorption layer having the InO film, the absorption layer pattern remained without any problem in the washing with sulfuric acid / hydrogen peroxide regardless of the O / In ratio. From the above, it was confirmed that indium oxide was stable as film characteristics and improved in cleaning resistance.

(About the range of film thickness of 18 to 33 nm of the indium oxide film constituting the absorption layer)
When the thickness of the indium oxide film constituting the absorption layer is in the range of 18 nm to 33 nm, the line edge roughness and the NILS in the Y direction are excellent, and the HV bias at the same OD value is improved. Here, the same level of the OD value means a range of ± 0.2 with respect to a predetermined OD value (1 or 2 in this example). Specifically, as shown in Table 1, when the thickness of the indium oxide film constituting the absorption layer is in the range of 18 nm to 33 nm, the line edge roughness is 3.7 nm or 3.8 nm and the NILS in the Y direction is 0. .7 to 0.9. Thus, when the film thickness of the indium oxide film is within this range, both the line edge roughness and the YLS NILS values are better than the Ta film. When the thickness of the indium oxide film constituting the absorption layer is in the range of 18 nm to 33 nm and the OD value is the same level as 1, the HV bias is 2.2 nm and the OD value is 1.1. The HV bias of the Ta film is improved from 3.5 nm. Further, when the thickness of the indium oxide film constituting the absorption layer is in the range of 18 nm to 33 nm and the OD value is the same level as 2, the HV bias is 4.9 or 5.0 nm, and the OD value However, the HV bias of the Ta film of 1.8 is improved from 11.1 nm.

(Evaluation of indium oxide film thickness)
In order to evaluate the film thickness of the indium oxide film included in the absorption layer 15, the reflective photomask blank 3 in which the film thickness of the indium oxide film having an O / In ratio of 1.5 is changed in the range of 12 nm to 50 nm, and A reflective photomask 4 was prepared and evaluated for lithography characteristics and cleaning resistance. Table 2 shows the evaluation results.

  As shown in Table 2, when the film thickness of the indium oxide film is in the range of 19 nm to 45 nm, the HV bias value of the transfer pattern formed on the resist of the semiconductor wafer can be suppressed to the range of 2.4 m to 8.0 nm. It was. Further, when the film thickness of the indium oxide film is in the range of 19 nm to 45 nm, the transfer pattern formed on the resist of the semiconductor wafer is not unresolved, and the line edge roughness is in the range of 3.7 nm to 4.1 nm. It was suppressed.

  On the other hand, when the film thickness of the indium oxide film is in the range of 12 nm to 15 nm, the HV bias value of the transfer pattern formed on the resist of the semiconductor wafer is suppressed to a range of 1.3 nm to 2.0 nm. The line edge roughness is in the range of 4.2 nm to 4.3 nm and tends to deteriorate. Further, when the film thickness of the indium oxide film is in the range of 48 nm to 50 nm, the transfer pattern formed on the resist of the semiconductor wafer becomes unresolved, and the line edge roughness cannot be measured.

  Further, after the wafer transfer evaluation, the resistance of the reflective photomask 4 to the sulfuric acid / water cleaning was evaluated. The absorption layer pattern formed on the absorption layer having an indium oxide film having a thickness in the range of 12 nm to 50 nm was not lost by the sulfuric acid / hydrogen peroxide cleaning. Therefore, it was confirmed that the reflective photomask provided with an absorption layer having an indium oxide film having a thickness of 12 nm to 50 nm has cleaning resistance.

  From the above evaluation results, the film thickness of the indium oxide film constituting the absorption layer may be 45 nm or less, and together with the evaluation results shown in Table 1, the range of the film thickness of the indium oxide film constituting the absorption layer is 18 nm or more and 45 nm or less may be sufficient. A reflective photomask blank and a reflective photomask having an absorption layer having an indium oxide film with a thickness in the range of 18 nm or more and 45 nm or less improve transfer performance to a semiconductor substrate or semiconductor wafer and cleaning resistance. Can do.

  As described above, according to the reflective photomask blank and the reflective photomask according to the embodiment of the present invention, it is possible to suppress the influence of the projection effect, which is a principle problem of EUV lithography. For this reason, the reflective photomask blank and the reflective photomask according to the present embodiment greatly improve the transfer characteristics for forming an exposure pattern on the semiconductor substrate, that is, lithography characteristics (HV bias, resolution, line edge roughness). At the same time, mask processability and cleaning resistance can be improved. As described above, the present invention is extremely effective in the reflection type photomask blank and the photomask.

1, 3 Reflective photomask blanks 2, 4 Reflective photomask 11 Substrate 13 Reflective layer 13a Multilayer reflective film 13b Capping film 15 Absorbing layer 15a Indium oxide film 31 Back surface conductive layer 131 Laminated film 151 Absorbing layer pattern R15 Resist mask R15a Positive Type chemically amplified resist R151 resist pattern

Claims (7)

A substrate,
A reflective layer formed on the substrate and reflecting incident light;
A reflection type comprising: an indium oxide film having a single layer structure or a laminated structure and a film thickness of 18 nm to 45 nm; and an absorption layer which is laminated on the reflection layer and absorbs incident light Photomask blank. The reflective photomask blank according to claim 1, wherein the indium oxide film has a thickness of 18 nm to 33 nm. 3. The reflective photomask blank according to claim 1, wherein the indium oxide film is a film having an atomic ratio of oxygen to indium of 0.5 or more and 1.5 or less. 4. The reflective photomask blank according to claim 1, wherein the indium oxide film includes a compound material that occupies an atomic ratio of 80% or more with indium and oxygen. 5. When the intensity of the reflected light from the reflective layer is Rm, the intensity of the reflected light from the absorbing layer is Ra, and the optical density based on the reflective layer and the absorbing layer is OD, the optical density is expressed by the following equation: The reflective photomask blank according to any one of claims 1 to 4, wherein the reflective photomask blank is defined by (1) and has a value of 1 or more.
OD = -log (Ra / Rm) (1) The reflective photomask blank according to any one of claims 1 to 5, wherein the reflective layer includes a multilayer reflective film and a capping film formed on the multilayer reflective film. A substrate,
A reflective layer formed on the substrate and reflecting incident light;
An indium oxide film having a single layer structure or a laminated structure and a film thickness of 18 nm or more and 45 nm or less and having a predetermined pattern formed thereon, and an absorption layer which is laminated on the reflective layer and absorbs incident light. A reflection-type photomask comprising:

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