JP4346656B2 - Reflective mask blank and reflective mask - Google Patents

Description

  The present invention relates to a reflective mask blank for exposure and a reflective mask used for semiconductor pattern transfer and the like.

In recent years, with the miniaturization of semiconductor devices, EUV lithography, which is an exposure technique using EUV (Extreme Ultra Violet) light, is promising in the semiconductor industry. Here, EUV light refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, and specifically refers to light having a wavelength of about 0.2 to 100 nm. As a mask used in the EUV lithography, an exposure reflective mask described in Japanese Patent Application Laid-Open No. 8-213303 has been proposed.

  In such a reflective mask, a multilayer reflective film that reflects light is formed on a substrate, an intermediate layer is formed on the multilayer reflective film, and an absorption film that absorbs light is formed in a pattern on the intermediate layer. It is a thing. The light incident on the reflective mask in the exposure machine is absorbed by a portion having the absorption film, and the image reflected by the multilayer reflection film without the absorption film is transferred onto the wafer through the reflection optical system. Here, the intermediate layer is formed in order to protect the multilayer reflective film when forming the pattern of the absorption film using dry etching or the like in the mask manufacturing process, and is easy to obtain and handle. From this point, SiO2 film or the like is generally used.

  In a reflective mask having a structure having such an intermediate layer, if the intermediate layer remains on the reflective region of the mask when the mask is used, the reflectance in the reflective region is lowered. After pattern formation, a method of removing the intermediate layer remaining on the reflective region according to the absorption film pattern is employed.

  However, when the intermediate layer remaining on the reflection region is removed as described above, there are the following problems. In a reflective mask in which an intermediate layer is formed of a material composed of a SiO2 film, the SiO2 film, which is an intermediate layer, is usually removed by wet etching using HF or the like. There is a possibility that pattern peeling occurs.

On the other hand, a method of removing the intermediate layer by dry etching is also conceivable. However, when dry etching is used, the multilayer reflective film is inevitably exposed to etching for a certain time. As a result, micro-etching and surface roughness of the multilayer reflective film surface occur, causing fluctuations in reflectance and in-plane reflectance non-uniformity. Japanese Patent Application Laid-Open No. 8-213303 describes that the intermediate layer has a two-layer structure, and a thin carbon layer of about 10 nm on the multilayer reflective film side is etched with oxygen plasma. The intermediate layer cannot be completely removed without causing any damage to the reflective film.

  On the other hand, if the intermediate layer is not removed and the intermediate layer is left on the multilayer reflective film, the multilayer reflective film will not be damaged, and the multilayer reflective film can be protected even when the mask is used. No intermediate material has been known so far with little incursion and a sufficient etch selectivity with the layer to be etched.

The present invention has been devised in order to solve the above-mentioned problems, and by adopting a specific material for the intermediate layer, it is possible to minimize a decrease in reflectivity and to eliminate the need for removing the intermediate layer, and to perform multilayer reflection. The purpose is to prevent damage to the film. Another object of the present invention is to obtain a reflective mask and a reflective mask blank for manufacturing the same, by preventing damage to the multilayer reflective film, thereby preventing deterioration of transfer accuracy due to a decrease in reflectance or uneven reflection. To do.

The present inventors have found that the above object can be achieved by using a material containing at least one element selected from Cr, Ru, and Rh and Si as an intermediate layer.
Therefore, the first invention is
A substrate, a multilayer reflection film that reflects the exposure light, and an absorption film that selectively absorbs the exposure light, and is formed between the multilayer reflection film and the absorption film. A reflective mask blank for exposure in which an intermediate layer resistant to an etching environment is formed,
A reflective mask blank for exposure, wherein the material of the intermediate layer is formed of a material containing at least one element selected from Cr, Ru, and Rh and Si.
The second invention is
An etching environment of the absorption film between the previous multilayer reflection film and the absorption film, comprising a substrate, a multilayer reflection film reflecting the exposure light, and an absorption film absorbing the exposure light, which are sequentially formed on the substrate A reflective mask blank for exposure formed with an intermediate layer resistant to
The intermediate layer includes a plurality of layers, and a material of a layer located adjacent to the multilayer reflective film among the plurality of layers includes at least one element selected from Cr, Ru, Rh, and Si. It is a reflective mask blank for exposure characterized by being formed with material.
The third invention is
The intermediate layer is positioned adjacent to the multilayer reflective film, and is formed of a material including at least one element selected from Cr, Ru, and Rh and Si, and the absorption film The reflective mask blank for exposure according to the second invention, characterized in that it comprises a second intermediate layer located adjacent to the second intermediate layer.
The fourth invention is
The reflective mask blank for exposure according to the third invention, wherein the material of the second intermediate layer is a material containing Ta as a main metal component.
The fifth invention
The reflective mask blank for exposure according to the second to fourth inventions, wherein the absorption film is a material containing Cr as a main metal component.
The sixth invention is
The multilayer reflective film is formed by alternately laminating a first material layer having a relatively large refractive index at a wavelength of the exposure light and a second material layer having a relatively small refractive index,
The reflective mask blank for exposure according to any one of the first to fifth inventions, wherein a layer adjacent to the intermediate layer among the layers of the multilayer reflective film is formed of a first material.
The seventh invention
A reflective mask for exposure, wherein a pattern is formed on the absorption film of the reflective mask blank for exposure of the first to sixth inventions.

  ADVANTAGE OF THE INVENTION According to this invention, the reflection type mask blank for manufacturing the reflective mask for exposure which suppresses the fall of the reflectance by an intermediate | middle layer and can form a highly accurate pattern is obtained.

  Embodiments of the reflective mask blank and the reflective mask according to the present invention will be described below. As an embodiment of the present invention, the first embodiment in which the intermediate layer has a single-layer structure and the second embodiment in which the intermediate layer has a plurality of layers will be described separately.

(First embodiment)
The reflective mask blank according to the first embodiment of the present invention has a multilayer reflective film formed on a substrate, and contains at least one element selected from Cr, Ru, Rh and Si on the multilayer reflective film. An absorption film is formed on the intermediate layer made of the material and the intermediate layer. The reflective mask blank of the present invention can be manufactured by sequentially forming a multilayer reflective film, an intermediate layer, and an absorption film on a substrate by a film forming method such as a sputtering method.

(Middle layer)
The intermediate layer of the present invention has a function of protecting the multilayer reflective film as an etching stop layer when a transfer pattern is formed on the absorption film. The material is formed of a material containing at least one element selected from Cr, Ru, and Rh and Si. Cr, Ru, and Rh are excellent in smoothness and have a good etching selectivity with a material mainly composed of Ta, which is preferably used as the material of the absorption film, but the exposure light transmittance is relatively low. By adding Si to such Cr, Ru, and Rh, the transmittance of exposure light can be improved. Therefore, by using a material containing at least one element selected from Cr, Ru, and Rh and Si for the intermediate layer, even when the intermediate layer is left in the reflective region of the mask, the decrease in reflectance is minimized. It is done. Therefore, damage to the multilayer reflective film that occurs when the intermediate layer is removed can be prevented.

Si and at least one element selected from Cr, Ru and Rh used as the intermediate layer material of the present invention
Examples of the material containing Cr include a material containing Cr and Si, a material containing Ru and Si, and a material containing Rh and Si. Next, a preferable composition ratio of these materials will be described. In the case of a material containing Cr and Si, the Si ratio is preferably 5 to 50 at%. The reason is that as Si increases, the transmittance of exposure light improves, but the etching selectivity with the absorbing film tends to decrease.

One advantage of using a material containing Cr and Si as an intermediate layer is the reuse of a substrate with a multilayer reflective film. That is, if a defect occurs in the pattern of the absorption film and the intermediate film and cannot be corrected, only the substrate with the multilayer reflective film can be easily reused. For example, a part or all of the intermediate layer is dissolved by wet etching using Cr etchant (cerium ammonium nitrate + perchloric acid + pure water), and the intermediate layer and the absorption film are removed together from the multilayer reflective film. be able to. By doing so, the multilayer reflective film-coated substrate can be reused without damaging the multilayer reflective film. In this case, an increase in the Si ratio tends to make it difficult to dissolve in the Cr etchant. Therefore, when reproducing a substrate with a multilayer reflective film, the Si ratio is preferably 5 to 30 at%.

The intermediate layer containing Ru and Si preferably has a Si ratio of 5 to 50 at%. Similarly, the intermediate layer containing Rh and Si preferably has a Si ratio of 5 to 50 at%. In either case, the transmittance increases as Si increases, but the etching selectivity tends to decrease. The intermediate layer containing at least one element of Cr, Ru, Rh and Si contains at least one element selected from N, O, C for film modification in addition to Cr, Ru, Rh, and Si. May be. These elements can be contained up to about 20 at%. For example, a material containing Cr, Si, and N, a material containing Cr, Si, and O, a material containing Cr, Si, N, and O can be used. By adding N or O, resistance to oxidation is improved, so that it is possible to improve the stability over time.

The intermediate layer can be formed by a sputtering method such as DC sputtering, RF sputtering, or ion beam sputtering. As the thickness of the intermediate layer increases, the reflectance of the mask decreases. It is better to make it thin. From such a viewpoint, the intermediate layer is formed to a thickness of about 1 to 10 nm. More preferably, the thickness is 1 to 5 nm.

Moreover, since the film thickness of the intermediate layer can be reduced by increasing the etching selection ratio between the intermediate layer and the absorption film, the absorption of light in the intermediate layer can be reduced and the reflectance can be improved. it can. From such a viewpoint, it is preferable to select the material of the absorption film so that the etching selectivity between the intermediate layer and the absorption film is 5 or more, preferably 10 or more, and more preferably 20 or more.
In order to prevent a decrease in reflectance, the light transmittance in the intermediate layer is preferably 98% or more.

  In addition to having resistance to mask cleaning liquid and environmental resistance, other preferable properties as the intermediate layer material are preferably low stress and smoothness of 0.3 nmRms or less. From such a viewpoint, the material forming the intermediate layer preferably has a microcrystalline or amorphous structure.

(Multilayer reflective film)
Next, the multilayer reflective film of the present invention has a structure in which substances having different refractive indexes are periodically laminated to reflect light of a specific wavelength. For example, for exposure light having a wavelength of about 13 nm, a multilayer reflective film in which Mo and Si are alternately stacked for about 40 cycles is usually used. In the case of the Mo / Si reflective multilayer film, the layer having a relatively high refractive index is Mo, and the layer having a relatively low refractive index (refractive index closer to 1) is Si. Usually, a layer having a relatively high refractive index is an element having a relatively large atomic number (hereinafter referred to as heavy element) or a compound containing a heavy element, and a layer having a relatively small refractive index is an element having a relatively small atomic number. (Hereinafter referred to as a light element) or a compound containing a light element.

What is necessary is just to select the material which forms a multilayer reflective film suitably according to the wavelength of the light to be used. Examples of other multilayer reflective films used in the EUV light region include Ru / Si periodic multilayer reflective films, Mo / Be periodic multilayer reflective films, Mo compound / Si compound periodic multilayer reflective films, and Si / Nb periodic multilayer reflective films. Si / Mo / Ru periodic multilayer reflective film, Si / Mo / Ru / Mo periodic multilayer reflective film, and Si / Ru / Mo / Ru multilayer reflective film.

  The multilayer reflective film can be formed on the substrate by, for example, DC magnetron sputtering. In the case of a Mo / Si multilayer reflective film, the Si target and the Mo target may be alternately used in an Ar gas atmosphere to be stacked for 30 to 60 cycles, preferably 40 cycles, and finally a Si film may be formed. As another film forming method, an IBD (ion beam deposition) method or the like can be used.

  Generally, among the layers forming a multilayer reflective film, a heavy element layer having a relatively high refractive index, such as Mo, is likely to change with time in optical properties due to oxidation. Layer) is the uppermost layer of the multilayer reflective film. However, according to the present invention, since the high reflectance can be maintained without removing the intermediate layer in the reflective region of the mask (the region where the absorber pattern is not formed), the upper part of the multilayer reflective film is covered with the intermediate layer even when the mask is used. be able to. For this reason, among the layers forming the multilayer reflective film, a layer having a relatively large refractive index (heavy element layer), for example, Mo, Ru, Rh, W, NiCr, etc. can do.

In general, if the layer having a relatively high refractive index is the top layer, the reflectance of the multilayer reflective film itself is improved compared to the case where the layer having a relatively low refractive index is the top layer. By setting the layer having a large refractive index as the uppermost layer, the reflectance of the multilayer reflective film itself can be improved. When the multilayer reflective film has a periodic structure of two or more elements or compounds, the layer having the highest refractive index may be the top layer.

(Absorption film)
As the material of the absorption film of the present invention, a material having a high light absorptivity and a sufficiently large etching selectivity with respect to the intermediate layer is selected. As the material of the absorption film to be combined with the intermediate layer made of a material containing Si and at least one element of Cr, Rh, and Ru of the present invention, a material containing Ta as a main metal component is preferable. By using a material containing Ta as the main metal component for the absorption film, the etching selectivity between the intermediate layer and the absorption film can be increased (10 or more), and the film thickness of the intermediate layer can be reduced. It is possible to further suppress a decrease in reflectance due to the absorption of light.

  Here, the material having Ta as a main metal element means that the metal having the largest composition ratio among the metal elements in the component is Ta. The material having Ta as a main metal element used for the intermediate layer of the present invention is usually a metal or an alloy. Further, those having an amorphous or microcrystalline structure are preferable from the viewpoint of smoothness and flatness. By forming such a film structure, a smoothness of 0.2 nmRms or less can be obtained. A material having Ta as a main metal element has a feature that the internal stress can be easily controlled.

Materials containing Ta as a main metal element include materials containing Ta and B, materials containing Ta and N, materials containing Ta, B and O, materials containing Ta and Si, and materials containing Ta, Si and N , Ta and Ge containing material, Ta
And a material containing Ge and N can be used. By adding B, Si, Ge or the like to Ta, an amorphous material can be easily obtained and the smoothness can be improved. In addition, when N or O is added to Ta, resistance to oxidation is improved, so that an effect of improving stability over time can be obtained.

As a material preferable as a material containing Ta as a main metal component, for example, a material containing Ta and B can be given. In the case of this material, the ratio of Ta to B is the atomic ratio, and Ta / B is 8.5 / 1.5 to 7
. By selecting 5 / 2.5, a microcrystalline or amorphous structure can be obtained. In particular, Ta4B containing 25% B can easily be made into an amorphous structure, so that good smoothness and flatness can be obtained. The absorption coefficient of Ta4B for light with a wavelength of 13.4 nm is 0.0.
38.

A material containing Ta, B, and N is also a preferable material. In the case of this material, N is 5 to 30 at%, and when the remaining component is 100, if it is selected so that B is 10 to 30 at%, an amorphous structure or a microcrystal can be easily obtained. A typical example is an amorphous structure material in which Ta is the main component, B is 15 at%, and N is 10 at%. In this material, the absorption coefficient for exposure light with a wavelength of 13.4 nm is 0.036. is there. Moreover, oxidation resistance improves with the contained N.

  The absorption film containing Ta as a main metal element is preferably formed by sputtering. When formed by the sputtering method, the internal stress can be easily controlled by changing the power to be applied to the sputtering target and the input gas pressure. In addition, since it can be formed at a low temperature of about room temperature, the influence of heat on the multilayer reflective film and the like can be reduced.

When forming a film containing Ta and B, generally, a target containing tantalum and boron is used as a sputtering target, or a tantalum target is used, and a gas containing boron atoms (eg, diborane) is mixed into the sputtering gas. The film is formed by reactive sputtering. The control of the film stress in the case of the Ta4B film can be realized by selecting the film formation condition to a predetermined value. First, a correlation between the film stress and the power applied to the target is obtained in advance by experiments or the like.

  When the correlation is obtained in this way, it can be seen that the internal stress becomes compressed by increasing the power applied to the target, and the internal stress becomes tensile when the power applied is lowered. By utilizing this correlation, the film stress can be controlled to a desired value. The input power can be controlled very precisely, and by setting the input power accurately, the internal stress of the resulting film can be reduced to almost zero. It is possible to prevent a decrease in pattern position accuracy due to the stress of the film.

The absorption film may be formed to a thickness that can sufficiently absorb the exposure light, but is usually about 70 nm. In addition to materials other than Ta as a main component, W, Ti, TiN, or the like can be used as the absorption film of the present embodiment.

(substrate)
The substrate of the present invention has a range of 0 ± 1.0 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.3 × 10 ⁻⁷ / ° C. in order to prevent pattern distortion due to heat during exposure. Those having a low thermal expansion coefficient within the range are preferred. As a material having a low thermal expansion coefficient in this range, any of amorphous glass, ceramic, and metal can be used. For example, SiO 2 —TiO 2 glass or quartz glass can be used for amorphous glass, and crystallized glass on which β quartz solid solution is precipitated can be used for crystallized glass. As the metal, an Invar alloy (Fe—Ni alloy) or the like can be used.

The substrate is preferably a substrate having high smoothness and flatness in order to obtain high reflectance and transfer accuracy. In particular, it preferably has a smoothness of 0.2 nmRms or less (smoothness in a 10 μm square area) and a flatness of 100 nm or less (flatness in a 142 mm square area).
The substrate preferably has high rigidity in order to prevent deformation of the film formed thereon due to film stress. In particular, those having a high Young's modulus of 65 GPa or more are preferable.

In the present invention, the unit Rms indicating smoothness is the root mean square roughness, and can be measured with an atomic force microscope. Further, the flatness in the present invention is a value indicating the surface warpage (deformation amount) indicated by TIR (total indicated reading). This is the difference in height between the highest position of the substrate surface above the focal plane and the lowest position below the focal plane when the plane defined by the least square method based on the substrate surface is the focal plane. Absolute value. The configuration and manufacturing method of the reflective mask blank according to the first embodiment of the present invention are as described above.

(Reflective mask manufacturing method)
Next, a reflective mask according to the first embodiment of the present invention will be described. The reflective mask of the present invention can be manufactured by forming a pattern on the absorption film of the reflective mask blank described above.

  For pattern formation on the absorption film, an EB resist layer is formed on the reflective mask blank, a resist pattern is formed by EB drawing, and the absorption film is etched by a method such as dry etching using this pattern as a mask. When the absorption film is a material containing Ta as a main metal component, the pattern can be formed by dry etching using chlorine with the intermediate layer as a protective layer of the multilayer reflective film. After forming the pattern of the absorption film, the resist layer remaining on the pattern of the absorption film is removed to obtain the reflective mask of the present invention.

As described above, in the reflective mask of the present invention, by using a material containing at least one element selected from Cr, Ru, Rh and Si as the intermediate layer, the transmittance of the exposure light in the intermediate layer is increased. Therefore, it is not necessary to remove the intermediate layer. Therefore, it is possible to obtain a reflective mask that does not damage the reflective multilayer film at all and can perform highly accurate pattern transfer.

(Second Embodiment)
Next, a reflective mask blank and a reflective mask according to the second embodiment of the present invention will be described. In the second embodiment of the present invention, as described above, the intermediate layer is formed of two layers of the first intermediate layer adjacent to the multilayer reflective film side and the second intermediate layer positioned on the absorption film side. This is the main difference from the first embodiment. Since the substrate and the multilayer reflective film are the same as those described in the first embodiment, description thereof will be omitted.

First, a first intermediate layer is formed on a multilayer reflective film formed on a substrate. First of this embodiment
As the material for the intermediate layer, a material containing at least one element selected from Cr, Ru, and Rh and Si similar to that described in the first embodiment is used. The same applies to the film forming method and the like. The first intermediate layer functions as an etching stop layer when removing the second intermediate layer formed on the absorption film side.

  As will be described later, since the first intermediate layer is not removed during the mask manufacturing and remains on the multilayer reflective film, sufficient etching is performed when the second intermediate layer is etched in order to prevent a decrease in reflectance. It is preferable to form it as thin as possible within a range in which the stop function can be secured. In view of this, the first intermediate layer is formed to a thickness of about 1 to 5 nm, preferably about 2 nm. In order to prevent a decrease in reflectance, the light transmittance of the first intermediate layer is preferably 98% or more.

Next, a second intermediate layer is formed on the first intermediate layer. The second intermediate layer functions as an etching stop layer when forming a pattern on the absorption film. After the pattern is formed on the absorption film, the second intermediate layer is removed by etching using the first intermediate layer as an etching stop layer. Therefore, when selecting the second intermediate layer, a material having a high etching selectivity with respect to the absorption film and a high etching selectivity with the first intermediate layer is selected. The etching selectivity between the second intermediate layer and the absorption film and the first intermediate layer is both 5 or more, preferably 10 or more, and more preferably 20 or more.

A material preferable as the second intermediate layer is a material containing Ta as a main metal component in view of the etching selectivity with respect to the first intermediate layer. As a material containing Ta as a main metal component, a material similar to the material that can be used as the absorption film in the first embodiment can be used as the second intermediate layer. The film forming method is the same. In addition to materials other than Ta as the main component, W, Ti, TiN, WN, etc. can be used as the second intermediate layer.

The film thickness of the second intermediate layer may be formed in a range that can ensure an etching stop function at the time of pattern formation and correction of the absorption film, but is usually formed to be about 30 to 70 nm. A preferred combination of the first intermediate layer and the second intermediate layer is a first combination containing Cr and Si in terms of etching selectivity and smoothness.
An intermediate layer and a second intermediate layer containing Ta, B, and N.

Next, an absorption film that absorbs exposure light is formed on the second intermediate layer. In selecting the absorption film, a material having a high light absorption coefficient and a high etching selection ratio with the second intermediate layer is selected. The etching selectivity between the absorption film and the second intermediate layer is preferably 5 or more, preferably 10 or more, more preferably 20 or more.

As such a material, a material containing Cr as a main metal component is preferably used for the absorption film. Examples of materials containing Cr as a main metal component include materials containing at least one element selected from Cr and N, O, and C in addition to Cr alone. For example, Cr _1-X N _X (preferably 0.05 ≦ X ≦ 0.5), Cr _1-X O _X (preferably 0.05 ≦ X ≦ 0.6) Cr _1-X C _X (preferably 0.05 ≦ X ≦ 0.4) Cr _{1 -XY} N _X C _Y (preferably 0.05 ≤ X ≤ 0.45, 0.01 ≤ Y ≤ 0.3) Cr _1-XYZ N _X O _Y C _Z (preferably 0.05 ≤ X ≤ 0.40, 0.02 ≤ Y ≤ 0.3, 0.01 ≤ Z ≤ 0.2).

The absorption film can be formed by a sputtering method such as a DC magnetron sputtering method. The absorption film may be formed to a thickness that can sufficiently absorb exposure light in the absorption pattern region. Usually about 50 nm is formed. In addition to the material containing Cr as a main metal component, a film containing Ru, a film containing Rh, a film containing Ti, or the like can be used as the absorption film of the present embodiment. Is selected in consideration of the etching selectivity. Thus, the reflective mask blank of the second embodiment of the present invention is obtained by forming the absorption film on the second intermediate layer.

In this example, the intermediate layer has two layers. However, if the layer adjacent to the multilayer reflective film is a layer made of a material containing Cr, Ru, Rh, and Si, the intermediate layer has three or more layers. May be. that time,
For the absorption film, a material having a high light absorption coefficient and a high etching selectivity with respect to the uppermost layer of the intermediate layer is appropriately selected.

Next, a reflective mask according to the second embodiment of the present invention will be described. The reflection type mask of the present invention can be manufactured by forming a pattern on the absorption film of the reflection type mask blank as in the first embodiment. In the second embodiment, the second intermediate layer is further formed. Are removed according to the pattern of the absorbing film.

The transfer pattern is formed on the absorption film by forming an EB resist layer on the reflective mask blank described above, forming a resist pattern by EB drawing, and etching the absorption film by a method such as dry etching using this pattern as a mask. To do. When the absorption film is made of a material containing Cr as a main metal component, the second intermediate layer can be used as an etching stop layer to form a pattern by, for example, dry etching using chlorine and oxygen.

After forming the transfer pattern of the absorption film, the second intermediate layer in the reflective region of the mask (the portion without the absorption film pattern) is selectively removed according to the pattern of the absorption film. As a result, the absorption film pattern is formed on the second intermediate layer pattern. However, the absorption action may be performed by the absorption film alone or by the cooperation of the absorption film and the second intermediate layer. Note that when the second intermediate layer is etched, the first intermediate layer serves as an etching stopper to protect the multilayer reflective film, so that damage to the multilayer reflective film can be prevented. When the second intermediate layer is a material containing Ta as a main metal component, the second intermediate layer can be removed by dry etching using chlorine. Thereafter, the resist layer remaining on the absorption film pattern is removed to obtain a reflective mask according to the second embodiment of the present invention.

  As described above, the intermediate layer is divided into a plurality of layers, and the functions are separated into a layer adjacent to the absorption film side having the etching stop function of the absorption film and a layer adjacent to the multilayer reflection film side having the protective function of the multilayer reflection film. Finally, if only the layer adjacent to the multilayer reflective film is left on the multilayer reflective film, the intermediate layer finally left on the multilayer reflective film is thinner than when the intermediate layer is a single layer. Therefore, it is possible to obtain a reflective mask that hardly causes a decrease in reflectivity and does not damage the multilayer reflective film.

  Any of the above-described reflective masks and reflective mask blanks of the present invention is suitable when the above-mentioned EUV light (wavelength of about 0.2 to 100 nm) is used as exposure light, but it is suitable for light of other wavelengths. Also, it can be used as appropriate.

  Examples and application examples of the present invention will be described below with reference to FIGS. 1 and 3 are sectional views of a reflective mask blank according to an embodiment of the present invention, FIGS. 2 and 4 are sectional views of a reflective mask according to the present embodiment, and FIG. 5 is a reflective type according to an embodiment of the present invention. It is a figure which shows the exposure method which uses a mask.

(Example 1)
FIG. 1 shows a reflective mask blank 10 of the first embodiment. The substrate 1 is a SiO2-TiO2-based glass substrate (outer shape 6 inch square, thickness 6.3 mm). This substrate has a thermal expansion coefficient of 0.2 × 10 ⁻⁷ / ° C. and a Young's modulus of 67 GPa. The glass substrate was formed by mechanical polishing to have a smooth surface of 0.2 nmRms or less and a flatness of 100 nm or less.

In this embodiment, the multilayer reflective film 2 formed on the substrate 1 is a Mo / Si periodic multilayer reflective film in order to form a multilayer reflective film suitable for an exposure light wavelength band of 13 to 14 nm. The multilayer reflective film 2 was formed by alternately laminating Mo and Si on the substrate by DC magnetron sputtering. First, using a Si target, a Si film was formed to 4.2 nm at an Ar gas pressure of 0.1 Pa, and then using a Mo target, a Mo film was formed to a 2.8 nm film at an Ar gas pressure of 0.1 Pa. After 40 cycles, an Si film was finally formed to 4 nm. The total film thickness is 234 nm. With respect to this multilayer reflective film, the reflectivity at an incident angle of 2 degrees of light of 13.4 nm was 65%.

The intermediate layer 3 formed on the multilayer reflective film 2 is made of CrSi. The film thickness is 5nm
It is. The Cr content was 80 at%, and the Si content was 20 at%. The intermediate layer 3 was formed by a DC magnetron sputtering method using a CrSi target and using Ar as a sputtering gas. The film formation conditions were a sputtering gas pressure of 0.1 Pa and a power input to the target of 1 kW. It was confirmed by X-ray diffraction that the crystal state of the formed intermediate layer 3 was a microcrystal.

The absorption film 4 formed on the intermediate layer 3 is made of Ta4B. The film thickness was 50 nm. This absorption film 4 was formed by a DC magnetron sputtering method using a Ta4B sintered body target. Prior to film formation, the set value of the film stress of the absorption film was determined. In the case of this example, since the combined stress of the film other than the absorption film and the substrate when used as a mask by experiment is almost zero, the film stress was controlled so that the film stress of the absorption film was also almost zero. In the control method, the relationship between the film stress and the power applied to the target was obtained in advance, and the power applied to the target at which the film stress was substantially zero was determined (2 kW). The other film forming conditions were Ar gas as a sputtering gas and a sputtering gas pressure of 0.2 Pa. The absorption film 4 formed under such film formation conditions had almost the same composition ratio as the target, and the crystal state was amorphous. As described above, the reflective mask blank of this example shown in FIG. 1 was obtained.

  Next, a method for manufacturing the reflective mask 20 shown in FIG. 2 from the above-described reflective mask blank will be described. First, a resist for electron beam irradiation was applied on the absorption film 4 of the reflective mask blank 10, drawn with an electron beam and developed to form a resist pattern.

Using this resist pattern as a mask, the absorption film 4 is dry etched using chlorine,
The absorption film pattern 4a was formed. The dry etching conditions were a gas pressure of 0.1 Pa, a substrate temperature of 20 ° C., and an RF bias of 100 W. The CrSi film as the intermediate layer 3 was exposed to the etching gas by overetching, but the decrease in film thickness was about 1 nm, and substantially remained.

Next, the resist pattern remaining on the absorption film pattern 4a was removed with hot sulfuric acid at 100 ° C., thereby obtaining a reflective mask 20 having a structure shown in FIG. A 16 Gbit-DRAM pattern having a design rule of 0.07 μm could be formed as designed on the reflective mask 20 thus manufactured.

  Using this reflective mask 20, the reflectance was measured with EUV light having a wavelength of 13.4nm and an incident angle of 2 degrees. The reflectance was 63%, and the reflectance of the multilayer reflective film itself without the intermediate layer 3 was calculated. In comparison, the decrease in reflectance was as small as 2%.

Next, with reference to FIG. 5, a method of transferring a pattern by EUV light to the resist-coated semiconductor substrate 34 using the reflective mask 20 will be described. A pattern transfer apparatus 50 equipped with a reflective mask is roughly composed of a laser plasma X-ray source 31, a reflective mask 20, a reduction optical system 33, and the like. The reduction optical system 33 used an X-ray reflection mirror. By the reduction optical system 33, the pattern reflected by the reflective mask 20 is usually reduced to about 1/4. The exposure wavelength is 1
Since a wavelength band of 3 to 14 nm is used, the optical path was set in advance so as to be in a vacuum.

In this state, EUV light obtained from the laser plasma X-ray source 31 is incident on the reflective mask 20, and the light reflected here is transferred onto the Si wafer 34 through the reduction optical system 33.
The light incident on the reflective mask 20 is absorbed by the absorption film and is not reflected in the portion having the pattern of the absorption film, while the light incident on the portion without the absorption film is reflected by the multilayer reflection film. In this way, an image formed by the light reflected from the reflective mask 20 enters the reduction optical system 33. The exposure light that has passed through the reduction optical system 33 exposes the transfer pattern on the resist layer on the Si wafer 34. Then, a resist pattern was formed by developing the exposed resist. As a result of pattern transfer onto the semiconductor substrate as described above, it was confirmed that the accuracy of the reflective mask was 16 nm or less, which is the required accuracy of the 70 nm design rule.

(Comparative Example 1)
In this comparative example, a reflective mask was formed in the same manner as in Example 1 except that a Cr film was formed as an intermediate layer instead of the CrSi film. The Cr film was formed using a Cr target, Ar gas as a sputtering gas, and a Cr film having a thickness of 5 nm by DC magnetron sputtering. A reflective mask was manufactured in the same manner as in Example 1, and the reflectance was measured with EUV light having a wavelength of 13.4 nm and an incident angle of 2 degrees. The reflectance was 58%, and the multilayer reflective film itself without an intermediate layer Compared to the reflectance, the decrease in reflectance was as large as 7%.

(Example 2)
FIG. 3 shows a reflective mask blank 30 according to the second embodiment. The reflective mask blank 30 of this embodiment shown in FIG. 3 has a two-layer structure in which the intermediate layer is composed of a first intermediate layer 23 located on the multilayer reflective film side and a second intermediate layer 24 located on the absorption film side. This is the main difference from the first embodiment. The substrate 1 and the multilayer reflective film 2 in this embodiment are the same as those in the first embodiment.

First, a first intermediate layer 23 made of CrSi shown in FIG. 3 was formed on the multilayer reflective film 2 formed on the substrate 1 by using the same method as in Example 1. However, the film thickness was 2 nm. Cr is 80at%
, Si is 20 at%. Next, as the second intermediate layer 24 formed on the first intermediate layer 23, a film made of Ta4B was formed to a thickness of 30 nm. The second intermediate layer 24 was formed by a DC magnetron sputtering method using a Ta4B sintered body target. The film formation conditions were the same as the formation of the absorption film of Example 1. The obtained film had almost the same Ta4B composition ratio as the target, and the crystal state was amorphous.

Next, an absorption film 25 made of a material containing N and O in Cr was formed on the second intermediate layer 24 to a thickness of 70 nm. This absorption film 4 was formed by DC magnetron sputtering. The film formation conditions were as follows: a Cr target was used, and a gas in which 20% of N ₂ and O ₂ were added to Ar was used as a sputtering gas.
The sputtering gas pressure was 0.25 Pa, and the input power to the target was 1 kW. In the formed absorption film 25, the atomic ratio of Cr, N, and O was 70:15:15. In this way, the reflective mask blank of this example shown in FIG. 3 was obtained.

Next, a method of manufacturing the reflective mask 40 having the structure shown in FIG. 4 using the reflective mask blank 30 described above will be described. This reflective mask 40 has a design rule of 0.07 μm.
It has a pattern for 16Gbit-DRAM.

  The reflective mask 40 of this embodiment has a two-layer structure in which an intermediate layer is a first intermediate layer located on the reflective multilayer film 2 side and a second intermediate layer located on the absorption film 25 side. The second intermediate layer pattern 24a is also formed on the layer according to the absorption film pattern 25a.

First, a resist for electron beam irradiation was applied on the absorption film 25 of the reflective mask blank 30, and the resist pattern was formed by drawing and developing with an electron beam. Using this resist pattern as a mask, the absorption film 25 was dry etched using chlorine + oxygen gas to form an absorption film pattern 25a.

Next, the first intermediate layer 23 is used as an etching stop layer of the multilayer reflective film, and the absorption film pattern 25a.
The second intermediate layer 24 in the region where the film is not formed is removed by etching according to the absorption film pattern 25a to form a second intermediate layer pattern 24a. Since the second intermediate layer 24 is formed of a Ta4B film, dry etching using chlorine was used to remove the second intermediate layer 24. The thickness of the first intermediate layer 24 is slightly reduced by over-etching when the second intermediate layer 25 is removed, and becomes substantially 4 nm.

Next, the resist pattern remaining on the absorption film pattern 25a is removed with hot sulfuric acid at 100 ° C.,
As a result, the reflective mask 40 of this example shown in FIG. 4 was obtained. Using this reflective mask 40, the reflectance was measured with EUV light having a wavelength of 13.4 nm and an incident angle of 2 degrees. The reflectance was 64%, which was compared with the reflectance of the multilayer reflective film itself without an intermediate layer. Then, the decrease in reflectance was 1%. As described above, in this example, the intermediate layer has a two-layer structure, and the intermediate layer remaining on the multilayer reflective film can be thinned by removing other than the intermediate layer located on the multilayer reflective film side. The drop in was very small.

  Moreover, when the pattern transfer onto the Si wafer was performed using the transfer apparatus shown in FIG. 5 as in Example 1 using the reflection mask 40 of the present invention, the accuracy of the reflection mask of the present invention was as follows. It was confirmed that the required accuracy of the 70nm design rule was 16nm or less.

(Application examples)
In this example, a method of recycling the reflective mask created in the above embodiment will be described. Such recycling is necessary when a defect occurs in the mask pattern. In order to reuse the substrate with the multilayer reflective film not related to the pattern defect, the defect pattern is removed. In order to recycle the reflective masks 20 and 40 produced in Example 1 and Example 2 described above, the intermediate layer and the absorption film formed above the multilayer reflective film 2 are removed.

Specifically, in order to remove each layer of the intermediate layer and the absorption film formed on the multilayer reflective film 2,
The reflective masks 20 and 40 prepared in Example 1 and Example 2 were immersed in a Cr stripping solution (secondary ammonium nitrate + perchloric acid + pure water). Immersion conditions were 20 minutes at room temperature. By immersing the reflective mask in the Cr stripping solution, the CrSi layer, which is an intermediate layer formed on the multilayer reflective film 2, is stripped from the multilayer reflective film, whereby the intermediate layer formed on the multilayer reflective film and The absorbing film was separated from the multilayer reflective film. As described above, in this example, the intermediate layer and the absorption film were removed without damaging the surface of the multilayer reflective film, and a substrate with a multilayer reflective film was obtained. A new intermediate layer and absorption film can be formed and reused on this multilayer reflective film-coated substrate.

(Example 3)
The reflective mask of Example 3 is different from the reflective mask of Example 2 in that Mo is formed instead of the uppermost Si layer of the multilayer reflective film. Other configurations were the same as in Example 2 to manufacture a reflective mask blank and a reflective mask in which the same intermediate layer as in FIGS. 3 and 4 had a two-layer structure. At the time when the multilayer reflective film was formed on the substrate, the reflectance at an incident angle of 2 degrees of 13.4 nm exposure light was measured with respect to this multilayer reflective film. The reflectance was 67% and the uppermost layer was a Si layer. It was 2% higher than when there was.

Next, when the reflectance was measured with EUV light having a wavelength of 13.4 nm and an incident angle of 2 degrees with respect to the reflective mask of this example, the reflectance was 65%, and the multilayer reflective film when the intermediate layer was not formed Compared to the reflectance, the decrease in reflectance was as small as 2%. In the reflective mask of this example, since the multilayer reflective film itself has a high reflectance, a higher reflectance was obtained as compared with Example 2. Further, when pattern transfer onto the semiconductor substrate shown in FIG. 5 was performed in the same manner as in Example 2, the exposure characteristics were sufficient, and the accuracy of the reflective mask was as required by the 70 nm design rule. It was confirmed that it was 16 nm or less.

1 is a cross-sectional view showing a structure of a reflective mask blank according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the reflective mask concerning Example 1 (1st Embodiment) of this invention. It is sectional drawing which shows the structure of the reflective mask blank concerning Example 2 (2nd Embodiment) of this invention. It is sectional drawing which shows the structure of the reflective mask concerning the form of Example 2 (2nd Embodiment) of this invention. It is a schematic diagram of the method of transferring the pattern on a semiconductor substrate using a reflective mask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Multi-layered reflective film 10, 30 Reflective mask blank 20, 40 Reflective mask 23 First intermediate layer 24 Second intermediate layer 24a Second intermediate layer pattern 3 Intermediate layers 4, 25 Absorbing film 4a, 25a Absorbing film pattern 31 Laser plasma X-ray source 33 Reduction optical system 34 Si wafer 50 Pattern transfer device

Claims (7)

A substrate, a multilayer reflective film for reflecting are formed on the substrate exposure light, an absorption film that selectively absorbs the exposure light is formed on the multilayer reflective film, and the multilayer reflective film and the absorber film It is made an intermediate layer having a resistance is formed on the etching environment of the absorbing film between, EUV light as exposure light is applied
A reflective mask blank used in lithography ,
The material of the intermediate layer viewed including the Cr, Ru, and at least one element and Si selected from Rh, the content ratio of Si is a material which is 5~50at%, thickness is formed on the 1 nm to 10 nm,
The reflective mask blank is characterized in that the absorption film is made of a material containing Ta as a main metal component . 2. The intermediate layer according to claim 1, wherein the transmittance for EUV light is 98% or more.
The reflective mask blank as described. A substrate, a multilayer reflective film for reflecting are formed on the substrate exposure light, an absorption film that selectively absorbs the exposure light is formed on the multilayer reflective film, and the multilayer reflective film and the absorber film It is made an intermediate layer having a resistance is formed on the etching environment of the absorbing film between, EUV light as exposure light is applied
A reflective mask blank used in lithography ,
The intermediate layer includes a first intermediate layer located adjacent to the multilayer reflective film and a second intermediate layer located adjacent to the absorption film,
The first intermediate layer, Cr, looking contains at least one element and Si Ru, selected from Rh, using a material containing ratio is 5～50At% of Si, thickness is formed on 1nm~5nm ,
The reflective mask blank is characterized in that the absorption film is made of a material containing Ta as a main metal component . The first intermediate layer has a transmittance for EUV light of 98% or more.
3. A reflective mask blank according to 3. A substrate, a multilayer reflective film that is formed on the substrate and reflects exposure light, an absorption film that is formed on the multilayer reflective film and selectively absorbs the exposure light, and the multilayer reflective film and the absorption film An EUV light is applied to the exposure light.
A reflective mask blank used in lithography,
The intermediate layer is located adjacent to the multilayer reflective film, includes at least one element selected from Cr, Ru, and Rh and Si, and uses a material having a Si content ratio of 5 to 50 at%. A first intermediate layer having a thickness of 1 nm to 5 nm;
A second intermediate layer located adjacent to the absorption film and formed of a material having Ta as a main metal component ;
4. The reflective mask blank according to claim 3, wherein the absorption film is made of a material containing Cr as a main metal component . The multilayer reflective film is formed by alternately laminating a first material layer having a relatively large refractive index and a second material layer having a relatively small refractive index at the wavelength of the exposure light. The reflective mask blank according to claim 1, wherein a layer adjacent to the intermediate layer among the layers forming the multilayer reflective film is formed of the first material. . Reflective mask, characterized in that the formation of the transfer pattern on the absorber layer of the reflective mask blank according to any one of claims 1 to 6.

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