JP4900656B2 - Reflective mask blank, reflective photomask, and reflective photomask manufacturing method - Google Patents

Description

  The present invention relates to a reflective photomask used in a semiconductor device manufacturing method using a photolithographic method using light having a wavelength in the soft X-ray region, particularly extreme ultraviolet light, that is, EUV (Extreme Ultraviolet) light, and a manufacturing method thereof, In addition, the present invention relates to a reflective photomask blank used therefor.

With the recent high integration of semiconductor elements, the miniaturization of pattern transfer onto a Si substrate by photolithography is accelerating.
And since the shortening of the wavelength of the light source in the photolithography method using the conventional lamp light source (wavelength 365 nm) and excimer laser light source (wavelength 248 nm, 193 nm) has approached the resolution limit, particularly fine processing of 65 nm or less is performed. It has become an urgent task to establish a new photolithography method that enables this.

  Recently, so-called immersion exposure technology has been developed to fill a space between a projection lens of an exposure apparatus and a substrate with a liquid such as water. By using a medium having a refractive index larger than that of air, an effect equivalent to shortening the wavelength is obtained. With this technique, it is said that it is extremely difficult to transfer a pattern smaller than 50 nm, although the conventional wavelength of 193 nm is expected to reach about 65 nm.

Therefore, in recent years, an EUV lithography method using EUV light (wavelength 13.5 nm) having a wavelength of 10 to 15 nm, which is one digit or more shorter than these ultraviolet lasers, as a light source has been developed.
In this EUV lithography method, since the refractive index of a substance in the EUV light wavelength region is slightly smaller than 1, a refractive optical system used in a conventional light source cannot be used, and exposure by a reflective optical system is not possible. Used. In addition, since most substances have high light absorption in the EUV wavelength region, a reflective photomask is used as a pattern transfer photomask instead of an existing transmissive photomask. As described above, in the EUV lithography method, the optical system and the photomask used for the exposure are remarkably different from the conventional exposure technique.

In this reflective photomask for EUV lithography, a mirror (reflecting mirror) having a high reflectance at the exposure wavelength is provided on a flat substrate using a material having a very low thermal expansion coefficient such as SiO2 doped with titanium. Further, a light absorption layer made of a substance having particularly high absorbability with respect to EUV light is formed thereon by pattern processing according to a desired exposure pattern.
A mirror (reflecting mirror) for EUV light is composed of a multilayer reflective film made of a combination of materials having greatly different refractive indexes. In the reflection type photomask, the exposure pattern of the exposure pattern is determined by the contrast of the EUV reflectance between the absorption region where the multilayer reflection film surface is covered with the light absorption layer pattern and the reflection region where the multilayer reflection film surface is exposed without the light absorption layer. Perform pattern transfer.

Also, the inspection of the pattern formed on the light absorption layer is usually performed by making DUV (far ultraviolet) light having a wavelength of about 190 nm to 260 nm incident on the mask surface, detecting the reflected light, and using the reflectance contrast. Done.
Specifically, before patterning of the light absorption layer, the buffer layer surface arbitrarily provided immediately below the light absorption layer as a protective layer of the multilayer reflective film becomes a reflection region, and the absorption region consisting of the patterned light absorption layer surface First, a first-stage inspection is performed to determine whether or not the light absorption layer is patterned as designed. In this case, a portion (black defect) where the light absorption layer that should be etched is not etched and remains on the buffer layer, or a part of the light absorption layer that should be left on the buffer layer without being etched is etched. Detected spot (white defect).
Note that the buffer layer is formed for the purpose of preventing the reflectance from decreasing due to damage to the multilayer film when the light absorption layer is processed by dry etching and when pattern defects of the light absorption layer are corrected. The This buffer layer is required to have high resistance to dry etching of the light absorption layer, high resistance in the correction process, and little damage to the light absorption layer when removing unnecessary buffer films. (For example, see Patent Document 1).

  After correcting the defects detected in the first stage inspection, the buffer layer is further removed to expose the surface of the multilayer reflective film immediately below the buffer layer, and then the second stage for the pattern formed in the light absorption layer. The final inspection is performed using the contrast of the reflectance between the absorption region formed of the light absorption layer surface and the reflection region formed of the multilayer reflective film surface. In some cases, it may not be necessary to remove the buffer layer. However, if there is a coating film for the buffer layer on the surface of the multilayer reflective film, the reflectance of the multilayer reflective film tends to be lowered. Often done.

In the inspection of the light absorption layer pattern by the DUV inspection light in the first stage and the second stage described above, the surface of the buffer layer from which the light absorption layer has been removed and the light remaining without removing the light absorption layer, respectively. This is performed using the contrast of the DUV light reflectivity between the absorption layer surface and the multilayer film reflection surface from which the buffer layer has been removed and the light absorption layer surface. Therefore, in order to further improve the inspection sensitivity, the DUV inspection is performed on the buffer layer surface and the light absorption layer surface in the first stage inspection, and on the multilayer reflective film surface and the light absorption layer surface in the second stage inspection. It is desirable that the difference in reflectance at wavelengths is large.
In response to such demands, a multilayer light absorption layer in which a chromium or tantalum oxide or nitride is provided on a light absorption layer in the same manner as a transmission type low reflection chromium mask blank conventionally used. (For example, refer to Patent Document 2).
Note that, as the outermost surface layer of the multilayer reflective film, a layer may be specially provided for the purpose of reducing the change in reflectance over time, and is referred to as a capping layer. In this case, the surface of the reflective multilayer film can be read as the surface of the capping layer.
JP-A-7-333829 JP 2004-39884 A

  However, in the prior art in which a chromium or tantalum oxide or nitride is provided on the light absorption layer to form a multilayer light absorption layer, the reflectivity of the chromium or tantalum oxide or nitride can be lowered in the DUV inspection light. However, since the absorption by EUV light is smaller than that of single chromium or tantalum, there is a problem that the thickness of the absorption layer must be increased to 80 nm or more.

Hereinafter, the relationship between light absorption and film thickness will be described.
First, the light absorption of each material can be expressed by the optical constant of the material. In the EUV or X-ray wavelength region, the refractive index is almost slightly smaller than 1, so (1- δ) + iβ (i is an imaginary unit) and is generally expressed. Β in the imaginary part is called an extinction coefficient, and the larger β is, the more light is absorbed.

For example, in the case where 40 pairs of alternating multilayer films of Mo and Si are formed on a quartz glass substrate, chromium nitride is 10 nm as a buffer layer, and a two-layer structure of tantalum silicide and tantalum silicide oxide films is used as a light absorption film, Assuming optical constants, the reflectance at a wavelength of 13.5 nm can be calculated as follows.
FIG. 16 assumes that the light absorption film uses a lower absorption film of tantalum silicide and an upper absorption film of tantalum oxide, the optical constant for a wavelength of 13.5 nm is 1-0.022 + 0.035i, and 13 of tantalum oxide. When the optical constant for .5 nm is 1-0.050 + 0.025i and the film thickness of the upper light absorption film is 18 nm, the relationship between the film thickness of the lower absorption film and the reflectance at 13.5 nm is shown. is there.
FIG. 16 also shows a calculated value when, for example, a value of β is 0.057, assuming a material having a larger β than tantalum oxide. When β is 0.027, there is a thickness at which the reflectance becomes the smallest when the thickness of the lower absorption film is 70 to 90 nm. On the other hand, when β is a large value of 0.057, it is clear from FIG. 16 that the film thickness of the lower absorption film having the smallest reflectance becomes small.
For this reason, a material having a larger β value has been demanded as a material for the upper light absorption film.

  Further, since exposure by a reflective optical system is used at the EUV wavelength, the light incident on the mask is not perpendicular to the substrate but is incident at an incident angle of, for example, 5 to 6 degrees. Due to this influence, for example, the aerial image is likely to be asymmetric or an XY direction difference is likely to occur. For this reason, it is desired to make the thickness of the light absorption layer as thin as possible.

The present invention was obtained in view of the above circumstances, and not only the EUV light reflectance at the time of transfer of the exposure pattern, but also the DUV light reflectance in the pattern inspection of the light absorption layer is sufficiently low, and the reflective region An object of the present invention is to provide a reflective photomask having a light absorption layer capable of obtaining a sufficient contrast, having a highly accurate mask pattern transfer, and a high inspection sensitivity.
In addition, the present invention provides not only the EUV light reflectance at the time of mask pattern transfer, but also the DUV light reflectance at the pattern inspection of the light absorbing layer is sufficiently low, and a light absorbing layer capable of obtaining a sufficient contrast with respect to the reflective region. It is an object of the present invention to provide a reflective photomask blank that can process a reflective photomask having high accuracy, mask pattern transfer, and high inspection sensitivity.
Furthermore, the present invention provides a light absorbing layer in which not only the EUV light reflectance at the time of mask pattern transfer but also the DUV light reflectance in the pattern inspection of the light absorbing layer is sufficiently low, and sufficient contrast can be obtained for the reflective region It is an object of the present invention to provide a reflective photomask having high accuracy, high-accuracy mask pattern transfer and high inspection sensitivity, and a reflective photomask manufacturing method capable of processing the same.

In order to achieve the above object, a reflective photomask blank of the present invention has a substrate, a multilayer reflective film provided on the substrate, and a light absorption layer provided on the multilayer reflective film, The light absorption layer is formed by laminating a second light absorption film on the first light absorption film, and the first light absorption film is selected from the group consisting of tantalum, oxygen, nitrogen, carbon, and silicon. The second light absorption film is a film containing indium and oxygen , and the light absorption layer has a reflectivity with respect to extreme ultraviolet (EUV) light of 0. The light absorption layer is less than 6%, has a reflectivity for deep ultraviolet (DUV) light of less than 10%, and has a thickness of 20 to 100 nm .
Moreover, the reflection type photomask of the present invention includes a light absorption layer of a reflection type photomask blank having a substrate, a multilayer reflection film provided on the substrate, and a light absorption layer provided on the multilayer reflection film. A patterned reflective photomask,
The light absorption layer is formed by laminating a second light absorption film on the first light absorption film, and the first light absorption film is selected from the group consisting of tantalum, oxygen, nitrogen, carbon, and silicon. The second light absorption film is a film containing indium and oxygen , and the light absorption layer has a reflectivity with respect to extreme ultraviolet (EUV) light of 0. It is less than 6%, has a reflectivity for deep ultraviolet (DUV) light of less than 10%, and the light absorption layer has a thickness of 20 to 100 nm .
Further, the manufacturing method of the present invention pattern-processes a light absorption layer of a reflective photomask blank having a substrate, a multilayer reflection film provided on the substrate, and a light absorption layer provided on the multilayer reflection film. A method of manufacturing a reflective photomask , comprising: forming a first light-absorbing film containing tantalum and at least one element selected from the group consisting of oxygen, nitrogen, carbon, and silicon; By forming a second light absorption film containing indium and oxygen on the light absorption film, the light absorption layer has a reflectivity with respect to extreme ultraviolet (EUV) light of less than 0.6%. A step of forming a light absorbing layer having a reflectivity with respect to deep ultraviolet (DUV) light of less than 10% and a thickness of 20 to 100 nm, and forming a resist layer on the light absorbing layer, exposing and developing By the predetermined pattern The step of partially removing the resist layer according to the pattern and exposing a part of the light absorption layer, and dry etching the light absorption layer through the resist layer, thereby patterning the light absorption layer And a step of processing.

According to the present invention, by providing the light absorbing layer used in the reflective photomask blank and the reflective photomask with a film containing indium, not only during pattern transfer exposure by EUV light exposure but also by DUV light. Even at the time of pattern inspection, a good reflection contrast is obtained with respect to the reflection region, and the pattern transfer accuracy and defect inspection sensitivity of the reflective photomask are improved. Further, by performing EUV light exposure using this reflective photomask, a semiconductor device can be manufactured with a fine pattern with high accuracy.
The light absorption layer is formed by sequentially laminating a layer containing at least one element selected from the group consisting of tantalum, oxygen, nitrogen, carbon, and silicon, and a layer containing indium and oxygen. It is preferable. Further, a capping layer or a buffer layer may be provided on the multilayer reflective film. In that case, the light absorption layer is formed on the capping layer or the buffer layer.

  A reflective photomask blank according to an embodiment of the present invention includes a substrate, a multilayer reflective film provided on the substrate, and a light absorbing layer provided on the multilayer reflective film. Have a structure in which a film containing one or more elements selected from the group consisting of tantalum, oxygen, nitrogen, carbon, and silicon, and a film containing indium and oxygen are stacked. The reflective photomask blank is a product before processing the reflective photomask, and the light absorption layer of the reflective photomask blank is not subjected to pattern processing according to the exposure pattern to be transferred. is there.

FIG. 1 is a schematic sectional view showing a configuration example of a reflective photomask blank according to an embodiment of the present invention, and FIG. 2 is a configuration example of a reflective photomask created using the reflective photomask blank shown in FIG. It is a schematic sectional drawing which shows.
As shown in FIG. 1, the reflective photomask blank 10 of this embodiment has a structure in which a multilayer reflective film 2, a buffer layer 3, and upper and lower light absorption films 4, 5 are sequentially laminated on a substrate 1. The buffer layer 3 can be arbitrarily provided. In addition, the multilayer reflective film 2 is actually multilayered, but is simply shown as a single layer in the figure.

The reflective photomask of this example has the same configuration as the reflective photomask blank except that the light absorption layer is patterned.
That is, as shown in FIG. 2, the reflective photomask 20 of this example is provided with patterned light absorption films 4 a and 5 a instead of the light absorption films 4 and 5, and the buffer layer 3. 1 has the same structure as that shown in FIG. 1 except that a patterned buffer layer 3a is provided instead. In this reflection type photomask 20, the light absorption films 4 a and 5 a are partially removed by this pattern processing, and a portion where a part of the surface of the multilayer reflection film 2 is exposed is the reflection region B, and the light remaining without being removed. The surface of the absorption layer 5a constitutes the absorption region A.

  According to the present embodiment, the light absorption layer used has the light absorption film containing indium, whereby the absorption coefficient of the light absorption layer can be increased. Thereby, the film thickness of a light absorption layer can be made thin. And if the film thickness of a light absorption layer becomes thin, a pattern can be formed with sufficient dimensional accuracy. Further, by laminating a film containing indium and oxygen, and a film containing at least one element selected from the group consisting of tantalum, oxygen, nitrogen, carbon, and silicon, in the DUV wavelength region. The reflectance can be lowered. Since the reflectance in the DUV wavelength region can be reduced, the reflection contrast with the reflection region is increased, and the defect inspection sensitivity is increased.

  The reflective photomask manufacturing method of the present embodiment is an example of a method for obtaining the reflective photomask 20 using the reflective photomask blank 10, and the light of the reflective photomask blank is used. A resist layer is formed on the absorption layer, exposed and developed to remove part of the resist layer in accordance with a predetermined pattern and expose a part of the light absorption layer, and through the resist layer A step of patterning the light absorption layer by dry etching the light absorption layer.

3 to 14 are diagrams for explaining an example of the manufacturing process of the reflective photomask of the present embodiment.
First, in FIG. 3, the substrate is preferably a material having a small thermal expansion coefficient and good flatness and a small surface roughness. For example, as shown in FIG. 3, the surface of the substrate is polished by polishing SiO2-TiO2 flatly. A glass substrate 1 is prepared.
Next, in FIG. 4, 40 cycles of Mo film 2.8 nm and Si film 4.2 nm are alternately laminated on the substrate 1 by DC magnetron sputtering or ion beam sputtering, and as shown in FIG. A multilayer reflective film 2 having a maximum reflectance with respect to an exposure wavelength of 5 nm can be produced. Moreover, the effect of protecting the multilayer film against surface oxidation can be obtained by setting the thickness of the outermost Si film to about 11 nm. Although this multilayer reflective film 2 is a multilayer film, it is shown as a single layer in the figure for simplicity.
Thereafter, as shown in FIG. 5, a buffer layer of, eg, chromium nitride is formed to a thickness of 10 nm, for example.

Further, as shown in FIG. 6, tantalum silicide is deposited on the buffer layer 3 as the lower light absorption film 4, for example, 60 nm.
Then, as shown in FIG. 7, for example, indium oxide is formed to a thickness of, for example, 15 nm on the lower absorption film 4 by sputtering to form the upper light absorption film 5. Thereafter, the light absorption film 5 is patterned by an electron beam lithography technique, for example.
First, as shown in FIG. 8, an electron beam exposure resist coating solution is applied on the upper light absorption film 5 and baked to form the electron beam exposure resist layer 6.

Next, a desired pattern is drawn on the resist layer 6 by an electron beam drawing apparatus, and developed with a developer such as a 2.38 wt% tetramethylammonium hydroxide aqueous solution, for example, as shown in FIG. A resist pattern 6a serving as a mask for etching the absorption film 5 is formed.
For example, when indium oxide is used for the upper light absorption film, the resist pattern is transferred to the upper light absorption film 5 by performing dry etching using a gas containing a component having a methyl group, such as methane or methanol. As shown in FIG. 10, the upper layer light absorption pattern 5a can be formed. In addition, when the concentration of the compound having a methyl group is high, a polymerization reaction occurs in a region where no etching reaction occurs, and the inside of the etching processing apparatus is contaminated. Therefore, the conditions are diluted with a gas such as hydrogen. Is preferred.
In addition, when dry etching with methane-based gas is performed, the etching of the upper light absorption film proceeds, and the etching rate rapidly decreases when reaching the lower layer containing tantalum. This is because tantalum and methane do not produce volatile reactive organisms.

Next, after the etching of the upper light absorption film, the remaining resist is removed with a stripper containing N-methylpyrrolidone as a main component, for example. Note that the resist layer may be left until etching of the lower-layer absorption film to be performed later.
Thus, only the upper layer of the light absorption layer after the resist is peeled is patterned. Even in this state, pattern inspection using the DUV wavelength is possible, and correction processing can be performed as necessary.

Next, dry etching of the lower absorption film is performed using the patterned upper light absorption film as an etching mask. The film containing tantalum can be etched using either chlorine or a compound gas containing chlorine, or a gas containing fluorine such as CF 4.
Further, the upper light absorption film used as an etching mask is hardly etched when the substrate is not heated by plasma using chlorine-based or fluorine-based gas. This is because the vapor pressure of indium chloride and fluoride is very low at room temperature. From this, the pattern of the upper light absorption film can be processed to the lower layer with almost no loss of dimensional accuracy.

Further, when the etching of the lower absorption film proceeds and reaches the underlying buffer layer, the etching rate becomes very small. For example, when a layer mainly composed of chromium is used for the buffer layer, chromium is hardly etched with a fluorine-based gas, and chromyl chloride, a volatile product, is produced when oxygen is not present even with a chlorine-based gas. do not do. In this way, the pattern 4a of the lower layer light absorption film is obtained as shown in FIG. FIG. 11 shows a case where the resist is not removed before the etching process of the lower light absorption film.
If the resist pattern 6a is not removed before the lower light absorption film is etched, the resist pattern 6a may be removed at this stage using, for example, a stripper containing N-methylpyrrolidone as a main component. it can.

After the etching of the lower absorption film and the peeling of the resist pattern are completed, as shown in FIG. 12, the surface of the light absorption region is an upper absorption film and the surface of the reflection region is a buffer film. In this state, as shown in FIG. 13, pattern inspection using light having a DUV wavelength can be performed, and the pattern can be corrected as necessary.
After the inspection and correction of the light absorption layer pattern, the buffer layer can be dry etched using plasma containing chlorine and oxygen gas, for example, when chromium is the main component. Note that the upper layer light absorption film containing indium and oxygen is very difficult to be etched with respect to chlorine-based and fluorine-based plasmas, so that the pattern dimension variation due to the etching of the buffer layer is extremely small. Then, after the etching of the buffer layer is completed, a final inspection and correction as necessary are performed to obtain a reflective photomask having a configuration similar to that of FIG.

  As the multilayer reflective film used in this embodiment, a film in which materials having different refractive indexes are laminated in multiple layers can be used in order to have a high reflectance at the wavelength of EUV light. When EUV light having a wavelength of around 13.5 nm is used, a combination of a Mo layer and a Si layer can be used. In order to obtain a high reflectance, it is desirable that the refractive index changes sharply at the interface between the layers. The uppermost layer of the multilayer film can theoretically have a higher reflectance than the Mo layer, but since the oxide film formed on the surface is unstable, Si can be formed in the uppermost layer. In order to protect the multilayer film from surface oxidation, the outermost Si layer may have a slightly larger film thickness.

The light absorption layer used in this embodiment has at least two light absorption films.
The light absorption layer used here refers to a layer that is patterned on a mask and forms a region with low light intensity in an exposure process. As the light absorbing film, a material having a high ability to absorb light having an EUV wavelength can be used. The absorption capability is determined by the optical constant at the wavelength of light used for exposure.
In this embodiment, at least one of the light absorption films used contains indium and oxygen.
Thus, when the light absorption film contains indium, the extinction coefficient (imaginary part of the optical constant) of the film is increased, and there is an advantage that a film having a smaller film thickness and a large absorption can be obtained.

  When the light absorption film is formed of indium alone, the melting point of indium is very low, so that the process for forming the mask pattern is not sufficiently resistant. For this reason, the light absorption layer of this embodiment contains indium and oxygen, and is very chemically stable as compared with indium alone. In addition to indium and oxygen, at least one component of tin or zinc can be added. Since these elements have different valences from indium, they can impart conductivity to the light-absorbing film, and have an effect of reducing charging of the mask substrate surface during electron beam exposure. Since a volatile product is obtained by plasma using a gas containing a methyl group as in the case of indium, there is an advantage that dry etching is easily performed. Tin and zinc also have the ability to absorb EUV light comparable to indium, and there is an advantage that the reduction of the extinction coefficient is suppressed by the addition of different elements.

Moreover, it is preferable that the light absorption film used in this embodiment has a reflectance with respect to EUV light of less than 0.6%. The lower the reflectance, the better the contrast and the better the mask image can be obtained. If it exceeds 0.6%, the contrast becomes insufficient, and the resolution tends to be adversely affected in the exposure process.
Moreover, it is preferable that the reflectance with respect to DUV light is less than 10%. The lower the reflectivity, the greater the contrast at the time of inspection, which tends to be advantageous for detection of minute defects. If the reflectance exceeds 10%, the contrast is lowered and the detection limit of defects is lowered. Tend.
The film thickness of the light absorption layer is preferably 20 to 100 nm. When the film thickness is within this range, a pattern with better dimensional controllability can be formed. If it is less than 20 nm, the EUV light reflectance tends not to be sufficiently low, and if it exceeds 100 nm, the amount of dimensional variation during pattern formation tends to be large, making it difficult to obtain an accurate pattern. When used as a mask for exposure, the influence of shadows caused by oblique incidence tends to increase.

Further, the light absorption film used in this example is selected from the group consisting of tantalum, oxygen, nitrogen, carbon, and silicon, in addition to the film containing indium and oxygen (hereinafter referred to as I layer). A light-absorbing film (hereinafter referred to as a T layer) containing at least one element.
Here, it is preferable that the I layer has a high transparency at the inspection wavelength in the DUV region, and the T layer has a high reflectance at the same wavelength. This is because the interference between the light reflected on the surface of the I layer and the light reflected on the interface between the I layer and the T layer is increased, and the antireflection effect is enhanced. In order to increase the transparency of the I layer, indium must be sufficiently oxidized, and the oxygen content is preferably 50 to 70 at%.

  Further, in order to make the T layer a metallic film having a high reflectance of DUV light, the Ta content is preferably 50 at% or more. When a single Ta film is used, crystal grains tend to grow at the time of film formation, and there is a tendency that the roughness of the pattern increases, the fluctuation of stress is large, and the pattern position accuracy decreases. Addition of nitrogen, carbon, or silicon has an effect of suppressing the growth of such crystal grains. These components also have an advantage that a volatile reaction product is generated when the T layer is processed by dry etching, so that a good pattern shape can be obtained and an etching residue is hardly generated.

In this embodiment, a buffer layer can be further provided between the light absorption layer and the multilayer reflective film. The buffer layer has a high resistance to etching of the lower light absorption layer, a high resistance in the correction process, and a material that causes little damage to the light absorption layer when the buffer film is removed after the correction process can be used. . Further, after dry etching of the light absorption layer, the portion where the buffer film is exposed on the surface can have a higher contrast at the time of inspection when the reflectance is higher.
As the material of the buffer film, chromium, chromium oxide, nitride, carbide and mixture thereof, tantalum, tantalum nitride, carbide, silicide and mixture thereof, zirconium, zirconium oxide, nitride, silicide and mixture thereof A mixture, silicon oxide, carbon, etc. can be mentioned.
If this embodiment is used, pattern transfer with high accuracy is possible in EUV lithography in the method for manufacturing a semiconductor device, so that a semiconductor device having a miniaturized pattern can be manufactured.

Hereinafter, the present embodiment will be described in more detail using specific numerical examples.
First, a synthetic quartz glass substrate having a size of 6 inches × 6 inches × 0.25 inches was prepared as the substrate 1 shown in FIG.
Next, in FIG. 4, a Mo layer having a film thickness of 2.8 nm in a substrate temperature of 25 ° C. and an argon atmosphere, using Mo and Si targets alternately using a magnetron sputtering apparatus, and 4 A multilayer reflection film 2 was formed by laminating 40 periods each including a Si layer having a thickness of .2 nm. The uppermost layer of the multilayer reflective film 2 was Si, and the film thickness was 11 nm. The multilayer reflective film 2 had a light reflectance of 56% at a wavelength of 257 nm.

Next, in FIG. 5, a buffer made of chromium nitride is formed on the multilayer reflective film 12 using a magnetron sputtering apparatus with chromium as a target, a substrate temperature of 25 ° C., and a argon and nitrogen flow rate ratio of 10: 3. Layer 13 was deposited to 10 nm.
Thereafter, in FIG. 6, a lower light absorption film having a thickness of 56 nm was formed on the buffer layer by DC magnetron sputtering using tantalum and silicon as targets.

Further, by forming a 17 nm upper light absorption film made of indium oxide by magnetron sputtering in an argon and oxygen gas atmosphere using indium oxide as a target, a reflective mask blank 30 for EUV light is formed as shown in FIG. Obtained. The estimated value of the extinction coefficient β of this indium oxide film at 13.5 nm was 0.060.
When the reflectance in the ultraviolet wavelength region was measured at an incident angle of 10 degrees in this state, the result shown in FIG. 15 was obtained, which was a sufficiently low value of about 5% in the ultraviolet wavelength region used for inspection. I confirmed.

The mask blank 30 is spin-coated with an electron beam resist FEP171 (manufactured by FUJIFILM Electronics Materials) to a thickness of 300 nm, baked on a hot plate at 110 ° C. for 10 minutes, and a resist layer as shown in FIG. 16 was formed.
Next, in FIG. 9, a pattern was drawn with a dose of 10 μC / cm 2 using an electron beam drawing apparatus. The drawn blank was baked on a hot plate at 110 ° C. for 10 minutes, developed with a 2.38 wt% tetramethylammonium hydroxide aqueous solution for 90 seconds, rinsed with pure water, and spin-dried to obtain a resist pattern 16a. .

Subsequently, in FIG. 10, using the resist pattern as an etching mask, the upper light absorption film 5 was etched by reactive ion etching using methane and hydrogen gas to obtain an upper absorption film pattern 5a.
Subsequently, in FIG. 11, by using the resist pattern 6a and the upper light absorption film pattern 5a as an etching mask, the lower absorption film pattern 4a was obtained by reactive ion etching using CF4 gas.

Further, in FIG. 12, after performing plasma ashing in an oxygen gas atmosphere, the resist and the residue generated by the dry etching reaction were removed by immersing in a stripper containing N-methylpyrrolidone as a main component.
The reflectance of the inspection light having a wavelength of 257 nm in the portion protected by the resist pattern 6a was 6%. Further, the reflectance of the surface of the buffer layer made of chromium nitride exposed by etching was 52%. From this difference in reflectance, it was confirmed that the pattern could be inspected.

After confirming the formed pattern, the exposed portion of the buffer film is removed by dry etching using chlorine and oxygen gas to obtain a reflective EUV photomask according to this example as shown in FIG. It was.
The reflectivity at 257 nm of the surface of the reflective multilayer film exposed after etching was 62%, and the reflectivity of the light absorption pattern portion was 6%, and it was confirmed that the final pattern inspection could be performed based on the difference in reflectivity. At this time, the reflectance of the light absorption pattern portion at 13.5 nm was less than 0.1%, which was good.

Next, a comparative example (Comparative Example 1) of Example 1 as described above will be described.
First, a reflective EUV photomask was formed in the same manner as in Example 1 except that a lower light absorption film made of tantalum and silicon and an upper light absorption film made of tantalum, silicon and oxygen were used as the light absorption film. However, in order to obtain a reflectance equivalent to the reflectance at a wavelength of 13.5 nm when the lower light absorption film made of indium oxide is used, the thickness of the lower absorption film made of tantalum and silicon is set to 78 nm, and the upper light absorption is achieved. It was found that the film thickness needs to be 21 nm. Therefore, it is necessary to make the thickness of the light absorption layer of the above-described embodiment about 20 nm or more larger.

  The reflective photomask for EUV light according to the present embodiment is preferably used for forming a fine pattern using a resist for EUV light in manufacturing processes of various semiconductor elements, semiconductor devices, electronic circuit devices and the like. Can do.

It is a schematic sectional drawing showing the structural example of the reflection type photomask blank concerning the Example of this invention. It is a schematic sectional drawing showing the structural example of the reflection type photomask concerning the Example of this invention. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic sectional drawing for demonstrating an example of the manufacturing process of the reflection type photomask shown in FIG. It is a schematic diagram showing the reflectance of the ultraviolet wavelength range of the Example of the reflection type photomask blank shown in FIG. It is a schematic diagram for demonstrating an example of the relationship between the film thickness of a lower layer absorption film, and the reflectance in a wavelength of 13.5 nm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... EUV reflective multilayer film, 3 ... Buffer film, 4 ... Lower layer absorption film, 4a ... Lower layer absorption film pattern, 5 ... Upper layer absorption film, 5a ... Upper layer absorption film pattern, 6 ... resist film, 6a ... resist pattern.

Claims (6)

A substrate, a multilayer reflective film provided on the substrate, and a light absorption layer provided on the multilayer reflective film,
The light absorption layer is formed by laminating a second light absorption film on the first light absorption film,
The first light absorption film is a film containing tantalum and at least one element selected from the group consisting of oxygen, nitrogen, carbon, and silicon,
The second light absorption film is a film containing indium and oxygen ,
The light absorbing layer has a reflectance of less than 0.6% for extreme ultraviolet (EUV) light and a reflectance of less than 10% for deep ultraviolet (DUV) light;
The light absorbing layer has a thickness of 20 to 100 nm.
A reflective photomask blank characterized by that. The light absorbing layer is chromium and nitrogen, oxygen, reflective photo according to claim 1, characterized in that it is laminated on a layer containing at least one element selected from the group consisting of carbon Mask blank. A reflection type photomask in which a light absorption layer of a reflection type photomask blank having a substrate, a multilayer reflection film provided on the substrate, and a light absorption layer provided on the multilayer reflection film is patterned. And
The light absorption layer is formed by laminating a second light absorption film on the first light absorption film,
The first light absorption film is a film containing tantalum and at least one element selected from the group consisting of oxygen, nitrogen, carbon, and silicon,
The second light absorption film is a film containing indium and oxygen ,
The light absorbing layer has a reflectance of less than 0.6% for extreme ultraviolet (EUV) light and a reflectance of less than 10% for deep ultraviolet (DUV) light;
The light absorbing layer has a thickness of 20 to 100 nm.
A reflective photomask characterized by that. 4. The reflection type photo according to claim 3 , wherein the light absorption layer is laminated on a layer containing chromium and at least one element selected from the group consisting of nitrogen, oxygen, and carbon. mask. A reflective photomask manufacturing method for patterning a light absorbing layer of a reflective photomask blank having a substrate, a multilayer reflective film provided on the substrate, and a light absorbing layer provided on the multilayer reflective film Because
Forming a first light-absorbing film containing tantalum and at least one element selected from the group consisting of oxygen, nitrogen, carbon, and silicon; and indium and oxygen on the first light-absorbing film; By forming the second light absorption film to be laminated, the light absorption layer has a reflectance of less than 0.6% for extreme ultraviolet (EUV) light and a reflectance of 10 for deep ultraviolet (DUV) light. Forming a light absorption layer having a thickness of less than 20% and a thickness of 20 to 100 nm ;
Forming a resist layer on the light absorbing layer, exposing and developing, partially removing the resist layer according to a predetermined pattern to expose a part of the light absorbing layer;
And a step of patterning the light absorption layer by dry-etching the light absorption layer through the resist layer. 6. The reflection type photo according to claim 5 , wherein the light absorption layer is laminated on a layer containing chromium and at least one element selected from the group consisting of nitrogen, oxygen, and carbon. Mask manufacturing method.

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