JP5332741B2 - Reflective photomask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type photomask blank which has an absorption film reduced in thickness so as to reduce projection effect causing a phenomenon of deterioration in transfer precision due to EUV light, and is used for EUV photolithography, a reflection type photomask, and a method of manufacturing a semiconductor device. <P>SOLUTION: The reflection type photomask blank has a substrate, a multilayer reflection film formed on the substrate, and the absorption film formed above the multilayer reflection film, the absorption film being a thin film having a compound material containing tin (Sn) and oxygen (O). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a reflective photomask blank, a reflective photomask, and a semiconductor device manufacturing method.

  In recent years, an exposure method using extreme ultraviolet (hereinafter abbreviated as “EUV”) has been proposed. In EUV exposure, since the wavelength is short, the refractive index of the substance is almost the value of vacuum, and the difference in light absorption between the materials is also small. For this reason, in the EUV wavelength region, a conventional transmissive refractive optical system cannot be formed, and a reflective optical system is formed, and the mask is also a reflective mask. Conventional reflective photomasks that have been developed so far include a multilayer reflective film in which about 40 pairs of, for example, two layers of Mo and Si are stacked on a Si wafer or glass substrate, and capping that protects the multilayer reflective film. The film had a high reflection part, and a pattern of an absorption film and a buffer film was formed thereon as a low reflection part. The buffer film plays a role of reducing damage to the capping film and the multilayer reflective film when the absorption film is etched or when a defect is corrected by FIB (focused ion beam).

  In the reflection type photomask as described above, an absorption film that absorbs EUV light has a main function for forming a low reflection region. In order to ensure the contrast at the time of pattern defect inspection, the absorption film portion usually has a low reflectance with respect to deep ultraviolet (Deep Ultra Violet, hereinafter abbreviated as “DUV”) as defect inspection light. Designed. A method for reducing the reflectivity is to use an anti-reflection effect (hereinafter referred to as “AR”) using so-called thin film interference. Therefore, the absorption film is usually composed of two or more layers. A film transparent to DUV light is formed as an AR film on the upper layer.

  In addition, the lower absorption film portion excluding the upper absorption film (AR film) in the absorption film has the main function of absorbing EUV light in order to form a low reflection region for EUV light. Conventionally, a film mainly composed of Ta or Cr is used as the lower absorption film. Hereinafter, in principle, the upper absorption film is referred to as an AR film, and the lower absorption film is simply referred to as an absorption film.

The optical characteristic required for a photomask in realizing transfer exposure by projection exposure as well as EUV exposure is firstly mask contrast. In a normal transmission type mask, the mask contrast is evaluated by the following equation (1), where T is the transmitted light intensity transmitted through the transparent substrate portion and To is the transmitted light intensity transmitted through the pattern portion including the light shielding film.
OD = -log (To / T) (1)
Here, OD is called optical density and represents the degree of light shielding property of the light shielding film.

In the reflection type photomask, the mask contrast can be evaluated in the same manner, but since it is a reflection type photomask, the reflected light intensity from the high reflection part is Rm, and the reflected light intensity from the low reflection part including the absorption film is Ra. Then, it evaluates by the following (2) Formula similarly to a transmissive mask.
OD = -log (Ra / Rm) (2)
In order to perform good EUV transfer, OD needs to be at least 1.5 or more.

  Since EUV exposure is reflection exposure, the incident light is not vertical, but is incident on the reflective photomask from a slightly oblique direction (usually about 6 °) and becomes reflected light. In the reflection type photomask, it is the portions of the absorption film and the buffer film that are processed as a pattern. However, since EUV light is incident obliquely, a shadow of the pattern is generated. Accordingly, depending on the incident direction and the arrangement direction of the pattern, the transfer resist pattern formed on the wafer formed by the reflected light is displaced from the original position, and the pattern position accuracy is deteriorated. This is called a projecting effect and is a subject of EUV exposure.

  In order to reduce the projection effect, it is necessary to reduce the length of the shadow. For this purpose, the height of the pattern should be as small as possible. However, the thickness of the AR film is selected from the viewpoint of the antireflection property for the DUV light that is the inspection light, and the thickness of the buffer film is applied to the capping film or the multilayer reflective film in the patterning of the absorption film or the defect correction by FIB. It is selected from the necessary characteristics of damage reduction. Therefore, in order to reduce the height of the pattern, it is necessary to make the absorption film as thin as possible.

  In order to ensure mask contrast (OD> 1.5) even if the absorption film is thin, it is conceivable to use a material having a high absorbability for EUV light.

  More preferably, in order to reduce the height of the pattern, a buffer film having less EUV light absorption than the absorbing film is not used. As described above, the buffer film is for reducing damage to the capping film and the multilayer reflective film at the time of etching of the absorbing film and correcting the defect. By performing correction with an electron beam (EB) softer than FIB, the buffer film can be omitted.

  More preferably, in order to reduce the height of the pattern, an AR film having less EUV light absorption than the absorption film is not used. For this purpose, even if the absorption film itself does not use the AR film, it is necessary to have transparency with respect to the DUV light that is the inspection light, and therefore, it is necessary to make the absorption film portion have a low reflectance with respect to the DUV light.

  In addition, the photomask is not limited to a reflection type photomask, and the photomask is exposed to a cleaning solution using repeated acids, alkalis, etc. during its production process or transfer exposure period. Sufficient resistance to is required. In addition, the thin film to be patterned needs to have sufficient etching suitability (etch rate) so that a fine pattern can be formed.

  Furthermore, in forming a fine pattern such as a reflective photomask, in order to form an absorption film pattern with high line width accuracy and a good shape, the absorption film to be etched must have a small particle size and surface roughness. It is. Specifically, in terms of surface roughness, Rms needs about 0.5 nm or less.

  From the above, the reflective photomask has a high EUV light absorption property that achieves the required mask contrast (OD> 1.5) with the smallest possible pattern thickness, and at the same time is resistant to cleaning liquid. A fine absorption film that is high and easy to etch is desirable, but no suitable film material and configuration that satisfy these conditions have been proposed.

JP 2001-237174 A

The present invention is to provide a high EUV light absorbing layer has a relatively small thickness, and at the same time having both washing solution resistance, a reflection type photo mask that was selected by etching easily absorbing film materials.

The present invention also reflection type photomask which by performing transfer using a film reduced reflective photomask thickness of the absorbing layer, is relaxed the influence of the projection effect improves transfer performance such as resolution Is to provide

  In order to solve the above-mentioned problems and improve the transfer accuracy by EUV exposure, the present inventors have studied the type and characteristics of the absorbing film and the layer structure, and as a result, have come to make the present invention.

The invention according to claim 1 of the present invention includes a substrate, a high reflection portion formed on the substrate, and a patterned low reflection portion formed on the high reflection portion , and is patterned. Is a single-layer absorption film of 35 nm or more and 45 nm or less containing a compound material occupying a composition ratio of 90% or more with tin (Sn) and oxygen (O) , and the reflected light intensity from the high reflection portion is Rm. If the reflected light intensity from the low-reflection section and Ra including one in which OD defined by the following formula is a reflection type photo-mask, wherein at least two. .
OD = -log (Ra / Rm)

The invention according to claim 2 of the present invention is such that the low reflective portion is one or more selected from the group consisting of tantalum (Ta) and indium (In) in addition to tin (Sn) and oxygen (O). is obtained by a reflection type photo-mask according to claim 1, characterized in that a thin film having a compound material containing the element.

The invention according to claim 3 of the present invention is characterized in that the low reflection portion is a thin film containing indium (In) at a ratio of 0.05 to 0.1. This is

The invention according to claim 4 of the present invention, the low-reflection portion is obtained by a reflection type photo-mask according to claim 1, characterized in that the SnO film.

The invention according to claim 5 of the present invention is the reflective photomask according to claim 1 , wherein the low reflection portion is a SnO ₂ film .

The invention according to claim 6 of the present invention, highly reflective portion, and the multilayer reflective film, any one of claims 1 to 5, characterized in that it comprises a capping layer formed on the multilayer reflective film, the 1 The reflection type photomask described in the item .

The invention according to claim 7 of the present invention is characterized in that the low reflection part has a reflectance of 15% or less with respect to an ultraviolet ray having a wavelength of 190 nm to 260 nm, according to any one of claims 1 to 6 . This is a reflection type photomask.

The invention according to claim 8 of the present invention, the top of the low reflectivity portion is of claims 1 to 7 extinction coefficient for 260nm UV wavelength 190nm is equal to or consisting of a layer is 1.0 or less Among them, the reflection type photomask described in any one of the items is used.

  According to the present invention, the absorption film thickness is thinner than before, the EUV light absorption is high and the cleaning liquid resistance is high, and at the same time, etching is easy and the surface roughness is small, so that the processing accuracy and pattern position accuracy are improved. In addition, it is possible to provide a reflective photomask blank, a reflective photomask, and a semiconductor device manufacturing method in which the absorption film material and the layer configuration are selected.

  In addition, according to the present invention, by performing transfer using a reflective photomask with a reduced thickness of the absorption film, the influence of the projection effect is mitigated, and transfer performance such as resolution can be improved. According to the present invention, even if the film thickness is not changed, the exposure contrast is increased by increasing the absorption ability to EUV, so that the transfer performance can be improved. According to the present invention, when performing patterning by dry etching of the absorption film, the perpendicularity of the pattern can be improved by using a material that can obtain a stable resist selectivity.

It is a schematic sectional drawing which shows the reflection type photomask blank which concerns on the 1st Embodiment of this invention. It is a schematic sectional drawing which shows the reflection type photomask which concerns on the 1st Embodiment of this invention. (A) is a schematic sectional drawing which shows the structure of the reflective photomask which concerns on the 2nd Embodiment of this invention, (b) is the reflective photomask which concerns on the 3rd Embodiment of this invention. (C) is a schematic sectional view showing the structure of a reflective photomask according to the fourth embodiment of the present invention, and (d) is a fifth sectional view of the present invention. It is a schematic sectional drawing which shows the structure of the reflection type photomask which concerns on embodiment. It is a figure which displays the refractive index with respect to the light of wavelength 13.5nm vicinity of various materials, and an extinction coefficient. When Ta and SnO are made into an absorption film, it is the characteristic view which calculated OD value with respect to those film thicknesses. When Ta and SnO are made into an absorption film, it is the characteristic view which calculated OD value with respect to those film thicknesses. It is a table | surface which displays the refractive index and extinction coefficient of various materials for calculating the reflectance in 13.5 nm, 199 nm, and 257 nm based on the 2nd thru | or 5th embodiment of this invention. (A) And (b) is a characteristic view which shows the result of having calculated the reflectance with respect to the refractive index and extinction coefficient of absorption film material which concern on the reflective photomask of the 2nd Embodiment of this invention. It is a characteristic view which shows the result of having measured the spectral reflectance of the reflection type photomask which concerns on the 2nd Embodiment of this invention. It is a characteristic view which shows the result of having calculated the reflectance of the reflective photomask which concerns on the 2nd Embodiment of this invention with respect to SnO film thickness. (A)-(d) is a characteristic view which shows the result of having calculated the reflectance of the reflective photomask which concerns on the 3rd Embodiment of this invention with respect to SnO film thickness. (A) And (b) is a characteristic view which shows the result of having calculated the reflectance of the reflective photomask which concerns on the 4th Embodiment of this invention with respect to SiN film thickness. (A)-(d) is a characteristic view which shows the result of having calculated the reflectance of the reflective photomask which concerns on the 5th Embodiment of this invention with respect to SiN film thickness. It is a table | surface which displays the boiling point of the halide of various absorption film materials. (A)-(d) is a schematic sectional drawing which shows the manufacturing process of the reflective photomask which concerns on Example 1 of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. A duplicate description in the embodiment is omitted.

(First embodiment)
FIG. 1 is a schematic sectional view showing a reflective photomask blank 10 according to a first embodiment of the present invention. FIG. 2 is a schematic sectional view showing the reflective photomask 20 according to the first embodiment of the present invention. Here, the reflective photomask 20 according to the first embodiment of the present invention shown in FIG. 2 is the absorption film 4 of the reflective photomask blank 10 according to the first embodiment of the present invention shown in FIG. Is formed by patterning.

  As shown in FIG. 1, a reflective photomask blank 10 according to a first embodiment of the present invention includes a multilayer reflective film 2 on a substrate 1, a capping film 5 on the multilayer reflective film 2, and a capping film 5 on the multilayer reflective film 2. An absorption film 4 is provided. In addition, the absorption film 4 can be made into the structure of 2 layers which provided the low reflection layer for DUV inspection in the outermost surface, when the low reflection characteristic in a test | inspection wavelength is required. Although not shown here, a buffer film may be formed between the capping film 5 and the absorption film 4.

  As the substrate 1 according to the first embodiment of the present invention, a flat Si substrate, a synthetic quartz substrate, or the like can be used. Further, low thermal expansion glass to which titanium is added can be used, but the present invention is not limited to these as long as the material has a low coefficient of thermal expansion.

  The multilayer reflective film 2 according to the first embodiment of the present invention reflects EUV light (extreme ultraviolet light) that is exposure light, and is a multilayer reflective film 2 made of a combination of materials having significantly different refractive indexes with respect to EUV light. It is composed of For example, the multilayer reflective film 2 can be formed by repeatedly laminating a combination of Mo (molybdenum) and Si (silicon) or Mo (molybdenum) and Be (beryllium) for about 40 cycles.

  The buffer film (not shown) is formed of a material having resistance to dry etching performed when the absorption film 4 is formed, and etching that prevents damage to the multilayer reflective film 2 when the absorption film pattern 4a is etched. Although it functions as a stopper, it can be formed of CrN, Ru, or the like, but the present invention is not limited to these.

  The capping film 5 according to the first embodiment of the present invention can prevent a decrease in reflectance due to oxidation of the surface of the multilayer reflective film 2. Although not shown, a back conductive film can be formed on the surface of the substrate 1 where the multilayer reflective film 2 is not formed. The back conductive film is a film for fixing the reflective photomask 20 using the principle of an electrostatic chuck when the reflective photomask 20 is installed in an exposure machine.

  The absorption film 4 according to the first embodiment of the present invention absorbs irradiated EUV light when it is dry etched and formed into a predetermined exposure transfer pattern. That is, it can be selected from materials having high absorbability with respect to EUV light (described later).

  Furthermore, although the thickness of the absorption film 4 is an object of the present invention, it is required to reduce the film thickness while retaining a predetermined contrast characteristic with respect to EUV light. That is, since the reflectance of the multilayer reflective film 2 with respect to EUV light is designed to be maximum, conversely, for the absorption film 4, it is possible to increase the contrast by adopting a film having higher absorbability with respect to EUV light. It is required for this purpose. However, in order to achieve this simultaneously with the thinning of the absorption film 4, a material that has higher absorption with respect to EUV light than the material of the existing absorption film 4 is required.

  FIG. 4 shows the optical constant at the wavelength of EUV light, with the horizontal axis indicating the refractive index n and the vertical axis indicating the extinction coefficient k. In the reflective photomask blank 10 according to the first embodiment of the present invention, a material based on Sn and an extinction coefficient of 0.073 can be used as the thin film for the absorption film 4. However, the extinction coefficient of SnO is about 1.8 times larger than the extinction coefficient 0.041 of Ta, which is the mainstream base material of the conventional absorption film 4.

  FIG. 5 assumes a substrate on which a capping layer (not shown) made of Si and having a thickness of 11 nm is formed on a multilayer reflective film, and further an EUV in the case where an absorption film 4 (Ta and SnO) is formed thereon. It is the result of the simulation calculated | required about contrast (henceforth "OD". (Optical Density)).

  From FIG. 5, the difference in OD between SnO and Ta is small in the region where the absorption film 4 has a thickness of 80 nm or more, but SnO clearly secures OD in the thinner region. It turns out that it is advantageous at this point. Further, in EUV exposure transfer, an OD of at least about 2 is required, but in order to ensure this requirement stably, a film thickness of at least about 82 nm is required for Ta, whereas for SnO, It can be seen that the same EUV light contrast characteristics can be obtained with a film thickness of about 40 nm, which is a little less than half.

  The film thickness of the absorption film 4 is preferably 35 nm or more and 45 nm or less. If the thickness of the absorption film 4 is less than 35 nm, EUV light contrast characteristics cannot be obtained. Moreover, when the film thickness of the absorption film 4 is larger than 45 nm, transfer performance such as resolution is deteriorated.

  As described above, when SnO is used for the absorption film 4, the film thickness can be reduced to a little less than half while retaining the desired characteristics as compared with the case where the absorption film 4 is formed of a conventional Ta-based material. The profit obtained in terms of reducing the projection effect is great.

  When the absorption film 4 is formed of a thin film made of a compound material containing tantalum (Ta) in addition to tin (Sn) and oxygen (O), the ratio of tin (Sn) and oxygen (O) is set to 1. When an alloy containing 0.05 to 0.15 tantalum (Ta) is used, the extinction coefficient is about 0.065 to 0.073, and no significant decrease in the extinction coefficient is observed. There is almost no influence on the effect obtained in terms of the reduction of the projection effect.

  On the other hand, when the ratio of tin (Sn) and oxygen (O) is 1, the resist selectivity in dry etching of the absorption film 4 made of an alloy containing 0.05 to 0.15 of tantalum (Ta) is 1 .2, which is about 1.3 times higher than when the Ta ratio is 0.05 or less.

  Further, when the ratio of tin (Sn) and oxygen (O) is set to 1, an EUV in which indium (In) is included at a ratio of 0.05 to 0.1 is compared with the case where no indium is included. The absorption capacity for light is increased up to about 1.3 times.

  The reflective photomask 20 according to the first embodiment of the present invention has not only a reduced film thickness but also an EUV absorption capability by having a compound material containing Sn, O, Ta and In in the absorption film 4. By increasing the exposure contrast, the exposure contrast increases, the influence of the projection effect is reduced, and transfer performance such as resolution can be improved. In addition, when patterning the absorption film 4 by dry etching, the perpendicularity of the pattern can be improved by using a material having a stable resist selectivity.

  The semiconductor device manufacturing method using the reflective photomask 20 according to the first embodiment of the present invention selectively irradiates the extreme ultraviolet light reflected through the reflective photomask 20.

  Next, the reflected light reflected by the multilayer reflective film 2 of the reflective photomask 20 is exposed to an extreme ultraviolet light resist layer provided on the semiconductor substrate to form a pattern, and then the extreme ultraviolet light resist layer is formed. The pattern of the absorption film 4 of the reflective photomask 20 can be faithfully patterned on the reflective photomask 20 by transferring it to the semiconductor substrate.

  Next, second to fifth embodiments will be described. 2 and 3 are patterned into a positive type and a negative type by a resist used when patterning the absorption film 4. Note that description of materials overlapping those in the first embodiment will be omitted.

(Second Embodiment)
FIGS. 3A to 3D are schematic cross-sectional views showing the structures of reflective photomasks according to the second to fifth embodiments of the present invention. As shown in FIG. 3A, a reflective photomask 30 according to the second embodiment of the present invention includes a substrate 11, a multilayer reflective film 12 having high reflectivity formed on the substrate 11, A capping film 13 for protecting the multilayer reflective film 12 formed on the multilayer reflective film 12 and an absorption film pattern 15 having low reflectivity formed on the capping film 13 are provided. Here, in the present invention, a film containing Sn (tin) and oxygen (O) as main elements is used as an absorption film material for forming the absorption film pattern 15. Hereinafter, “main” means that tin and oxygen occupy a composition ratio of 90% or more. In the embodiment of the present invention, the multilayer reflection film 12 and the capping film 13 are high reflection portions.

  As the substrate 11 according to the second embodiment of the present invention, a silicon substrate or low thermal expansion glass to which titanium is added can be used, but any material may be used as long as it has a low coefficient of thermal expansion.

  As the multilayer reflective film 12 according to the second embodiment of the present invention, for example, a laminated body in which, for example, 40 pairs of Mo films and Si films are alternately formed can be used. The film thickness of each layer of the multilayer reflective film 12 is, for example, 2.8 nm for the Mo film and 4.2 nm for the Si film. As the capping film 13, for example, a Ru film, a Si film, or a SiN film can be used, but the present invention is not limited to these.

(Third embodiment)
Next, as shown in FIG. 3B, a reflective photomask 40 according to the third embodiment of the present invention includes a substrate 11 and a multilayer reflective film 12 having high reflectivity formed on the substrate 11. A capping film 13 protecting the multilayer reflective film 12 formed on the multilayer reflective film 12, a buffer film pattern 14 selectively formed on the capping film 13, and selectively formed on the buffer film pattern 14. And an absorption film pattern 15 having low reflectivity. Here, in the present invention, a film containing Sn and oxygen as main elements is used as an absorption film material for forming the absorption film pattern 15.

  The buffer film according to the third embodiment of the present invention is formed of a material having resistance to dry etching performed when the absorption film pattern 15 is formed, and more specifically, the absorption film pattern. 15 functions as an etching stopper to prevent damage to the capping film 13, and for example, a CrN film, a TaN film, a Ta film, a SiO film, or a SiN film can be used. However, it is not limited to these.

(Fourth embodiment)
A reflective photomask 50 according to the fourth embodiment of the present invention shown in FIG. 3C includes a substrate 11, a highly reflective multilayer reflective film 12 formed on the substrate 11, and multilayer reflection. A capping film 13 that protects the multilayer reflective film 12 formed on the film 12, an absorption film pattern 15 having low reflectivity that is selectively formed on the capping film 13, and selectively on the absorption film pattern 15. And an AR film pattern 16 having anti-reflection properties for DUV light. Here, in the present invention, a film containing Sn and oxygen as main elements is used as an absorption film material for forming the absorption film pattern 15.

  The antireflection property of the AR film pattern 16 according to the fourth embodiment of the present invention means that the AR effect on the DUV light is used by utilizing so-called thin film interference in order to enable defect inspection by the DUV light. is there. As the AR film material for forming the AR film pattern 16, for example, a SiO film or a SiN film can be used, but the present invention is not limited to these.

(Fifth embodiment)
A reflective photomask 60 according to the fifth embodiment of the present invention shown in FIG. 3D includes a substrate 11, a multilayer reflective film 12 having high reflectivity formed on the substrate 11, and multilayer reflection. A capping film 13 protecting the multilayer reflective film 12 formed on the film 12, a buffer film pattern 14 selectively formed on the capping film 13, and a low reflection selectively formed on the buffer film pattern 14. And an AR film pattern 16 having antireflection properties that is selectively formed on the absorption film pattern 15. Here, in the present invention, a film containing Sn and oxygen as main elements is used as an absorption film material for forming the absorption film pattern 15. As the AR film material for forming the AR film pattern 16, for example, a SiO film or a SiN film can be used, but the present invention is not limited to these. In the embodiment of the present invention, the buffer film pattern 14, the absorption film pattern 15, and the AR film pattern 16 are low reflection portions.

  In the second to fifth embodiments of the present invention, the reflectance of the patterned low reflection portion with respect to ultraviolet rays having a wavelength of 190 nm to 260 nm is 15% or less. More preferably, it is 10% or less. If the reflectance of the patterned low-reflection portion with respect to ultraviolet rays having a wavelength of 190 nm to 260 nm exceeds 15%, the absorption film pattern 15 cannot be reduced, and the defect inspection may be hindered.

  In the second to fifth embodiments of the present invention, the extinction coefficient with respect to ultraviolet light having a wavelength of 190 nm to 260 nm of the film mainly composed of Sn and oxygen constituting the patterned low reflection portion absorption film is set. 1.0 or less. More preferably, it is 0.7 or less. If the extinction coefficient with respect to ultraviolet rays with a wavelength of 190 nm to 260 nm of the film containing Sn and oxygen as main elements constituting the patterned low reflection portion absorption film exceeds 1.0, the absorption film pattern is reduced in reflection. Without being obtained, there is a possibility that the defect inspection may be hindered.

  Hereinafter, the characteristics of the absorption film having Sn and oxygen as main elements, as proposed in the present invention, regarding the effectiveness of the absorption film having Sn and oxygen as main elements and the effectiveness of the layer structure defined in the embodiment will be described. Based on

  As described above, in order to reduce the projection effect, it is necessary to reduce the film thickness of the pattern portion. For that purpose, it is effective to use an absorption film having a large absorbability with respect to EUV light. FIG. 4 is a plot of various literature values of the optical constants of each material at the EUV exposure wavelength (around 13.5 nm). The horizontal axis represents the refractive index: n, and the vertical axis represents the extinction coefficient: k. Here, from the viewpoint of optical theory, a film having a larger extinction coefficient has a higher absorbability for EUV light.

  As shown in Fig. 4, there are several films that have higher absorbency than Ta and Cr, which are conventionally used as the main absorption film materials. However, the acid / alkali cleaning solution resistance, suitability for dry etching, Materials that can clear all the fines are rare. Of the materials shown in FIG. 4, Sn is not preferable from the viewpoint of thermal stability because Sn is a simple substance and has a melting point of around 230 ° C., which is particularly low among metal materials.

However, when it is in the form of oxide as tin oxide (SnO ₂ ), the melting point is 1000 ° C. or more, the thermal expansion coefficient is about the same as that of a general metal oxide, and it is smaller and more stable than a general metal simple substance.

Therefore, when an SnO film is actually produced and the optical constant at the EUV wavelength (13.5 nm) is measured, the value shown in the following (3) is obtained. In the following (3), a value close to the SnO value shown in FIG. 4 was obtained.
Refractive index = 0.936 extinction coefficient = 0.0721 (3)

  Based on the result of (3), the OD at the EUV wavelength (13.5 nm) using the SnO absorption film is calculated and compared with a Ta film which is a conventional main absorption film, as shown in FIG. In this calculation, the SnO film or the Ta film is a single layer, and under these films, there are Ru capping films with a thickness of 2.5 nm, and there are 40 pairs of multilayer reflective films made of Si and Mo underneath. As calculated. As can be seen from FIG. 6, in order to obtain OD> 1.5, the Ta film needs to be about 47 nm thick, whereas the SnO film may be about 24 nm, which is effective as an absorption film that can reduce the film thickness. I know that there is. In addition, the optical constant in wavelength 13.5nm used for calculation of OD is shown in the 1st column of FIG.

  In the calculation of FIG. 6, the Ru capping film is used and the layer configuration without using the buffer film is calculated. However, when defect correction by FIB is performed, a normal buffer film is used. However, the buffer film is usually as thin as about 10 nm, and the EUV light absorption is about the same as or lower than Ta. For this reason, even in a configuration having a buffer film, the SnO film is still effective as an absorption film capable of reducing the absorption film thickness.

Next, when the optical constants of the SnO film at 199 nm and 257 nm, which are typical defect inspection wavelengths, were measured with an ellipsometer, the following values (4) and (5) were obtained.
199 nm: Refractive index = 1.87 extinction coefficient = 0.617 (4)
257 nm: Refractive index = 2.19 extinction coefficient = 0.341 (5)

  Here, as described above, on the multilayer reflective film (40 pairs of Si and Mo) on the structure having the Ru capping film with a thickness of 2.5 nm, the film (with a thickness of 24 nm obtained in FIG. 6) FIG. 8 shows the results of calculating the reflectance with respect to the inspection wavelength = 10% and the contour line of 5%, where X is the horizontal axis and the extinction coefficient is the vertical axis. . FIG. 8A shows the case where the wavelength is 199 nm, and FIG. 8B shows the case where the wavelength is 257 nm. In FIG. 8, the results obtained in the above (4) and (5) are plotted as shown in the figure. When X is SnO, the reflectance at 199 nm is about 10%, and the reflectance at 257 nm is 5%. It turns out that it becomes the following. In other words, it can be seen that with this structure, the SnO film has sufficiently low reflection at least around 24 nm without using the AR film, and the contrast at the inspection wavelength can be secured. The optical constants at wavelengths of 199 nm and 257 nm used for the calculation are shown in the second and third columns in FIG.

  FIG. 9 shows the spectral reflectance actually measured. In FIG. 9, before forming SnO, that is, when a Ru capping film having a thickness of 2.5 nm is formed on the multilayer reflective film (40 pairs of Si and Mo), SnO of 20 nm and 25 nm is then formed. The spectral reflectance at the stage of film formation is shown. As described above, after the SnO film is formed, the reflection is low at 199 nm and 257 nm, and it is understood that the inference based on the above calculation is appropriate.

  FIG. 10 shows the results of calculating the reflectivity at 199 nm and 257 nm with respect to the SnO film thickness when a Si capping film (11 nm thick) is used instead of the Ru capping film in FIG. Even in this case, it can be seen that the SnO film thickness is 20 nm to 25 nm and the reflection is sufficiently low without using the AR film, and the contrast at the inspection wavelength can be secured.

  Further, even when a buffer film is used to perform FIB correction, the SnO film can reduce reflection. FIG. 11 shows the reflectance calculated when a buffer film made of TaN or CrN is used between the SnO film and the Ru capping film. Thus, the reflection is low (approximately 15% or less) up to the SnO film thickness of about 30 nm, and it can be seen that the low reflection by the SnO film is effective. The optical constants such as TaN and CrN at wavelengths of 199 nm and 257 nm used for the calculation are shown in the second and third columns of FIG.

  Incidentally, although the optical constant of Sn, which is a single metal, is also plotted in FIG. 8, Sn is thus far away from the optical constant region where low reflection occurs. As the oxidation degree of Sn proceeds, the optical constant should move from the Sn plot point to the SnO plot point. That is, there are cases where the degree of oxidation is small, or in order to change the OD value even when the degree of oxidation is sufficient, it is desired to change the film thickness from the above-mentioned vicinity of 24 nm, or the SnO film is not desired to be the top layer for some reason Conceivable. In such a case, a separate AR film may be used on the SnO film.

  12 and 13 show the results of calculating the reflectance at 199 nm and 257 nm with respect to the SiN film thickness when the uppermost AR film is not a SnO absorption film but an SiN film. Thus, it can be seen that even if the SiN film is an AR film on the SnO film, the reflection is sufficiently low and the contrast at the inspection wavelength can be secured. 12 shows a case without a buffer film, and FIG. 13 shows a case with a buffer film.

  Next, as a dry etching gas for a thin film material, a fluorine-based or chlorine-based halogen gas is generally used. However, the ease of dry etching is known by comparing the boiling points of the halides of the dry etching material. be able to. That is, the lower the boiling point, the easier the etching product is gasified and exhausted. 14 summarizes the boiling points of Ta, Cr, which are conventional absorption film materials, and the Ru halide according to the embodiment of the present invention (for details, refer to CRC Handbook of Chemistry and Physics, 78th. Edition). reference). In this way, Ta can be dry-etched by fluorine or chlorine, Cr by chlorine + oxygen, and Sn by chlorine.

Further, a SnO film is formed on a quartz substrate by a sputtering method, and APM (NH ₃ : H ₂ O ₂ : H ₂ O = 1: 2: 20, room temperature), which is a general cleaning liquid, and SPM (H ₂ ). SO ₄ : H ₂ O ₂ = 3: 1, 100 ° C.) for 30 minutes, and the resistance of the SnO film to the cleaning solution was evaluated by the change in spectral transmittance. As a result, it was found that there was almost no change in spectral transmittance in both APM and SPM, and the SnO film was sufficiently resistant to cleaning liquid.

  Next, semiconductor device manufacturing methods using photomasks (reflection photomasks) according to second to fifth embodiments of the present invention will be described. In the semiconductor device manufacturing method using a photomask, for example, first, a photoresist layer is provided on a substrate on which a layer to be processed is formed, and then the reflection type photo according to the second to fifth embodiments of the present invention is used. The extreme ultraviolet light reflected through the mask is selectively irradiated.

  Next, unnecessary portions of the photoresist layer in the development process are removed, and an etching resist layer pattern is formed on the substrate. Then, the processed layer is etched using the etching resist layer pattern as a mask. Furthermore, by removing the pattern of the etching resist layer, a pattern faithful to the photomask pattern can be transferred onto the substrate.

  The present invention will be described below with reference to Examples 1 to 5.

  First, in Example 1, as shown in FIG. 15A, a reflective multilayer film 2 is formed on a substrate 1, a buffer film 3 is formed on the reflective multilayer film 2, and an absorption film 4 is formed on the buffer film 3. A reflective photomask blank 10 of the invention was produced.

  As the substrate 1, synthetic quartz having an outer shape of 6 inches (152.5 mm) square and a thickness of 0.25 inches (6.35 mm) polished to a flat surface was used. In addition, you may use for the quartz substrate 1 what comprises the chromium nitride (CrN) thin film for electrostatic chucks in the back surface. On the substrate 1, Mo and Si were alternately laminated by about 40 periods by DC magnetron sputtering to produce a reflective multilayer film 2 having a maximum reflectance with respect to EUV light in the wavelength region of 13 nm to 14 nm. At this time, the film thickness of one period composed of Mo and Si is 7 nm, of which the film thickness of Mo is 2.8 nm and Si is 4.2 nm, so that the uppermost layer of the multilayer reflective film 2 is Si. Finally, 7 nm of Si was deposited.

Next, a buffer film 3 made of Ru (ruthenium) is formed on the reflective multilayer film 2 with a film thickness of 4 nm, and further an SnO film is formed on the buffer film 3 to obtain an absorption film with a film thickness of 40 nm. 4 was produced. The SnO film as the absorption film 4 was formed by applying 300 W DC power to the Sn target at a gas pressure of 0.25 Pa in an Ar / O ₂ atmosphere. At this time, the surface roughness of the absorption film 4 after film formation was 0.21 nm rms, and the film had good surface smoothness. As described above, the reflective photomask blank 10 according to this example was produced.

  Next, as shown in FIG. 15B, a resist pattern is formed by a lithography process of EB (Electron Beam) drawing and development using a positive electron beam resist, manufactured by Fuji Film Arch, trade name “FEP-171”. 6a was formed.

Next, as shown in FIG. 15C, the SnO film (absorption film 4) was dry-etched using the resist pattern 6a as a mask to form the absorption film pattern 4a. For this dry etching, an ICP discharge type dry etching apparatus is used, and a bias power of 40 W and a source power in an atmosphere of a gas pressure of 5 mTorr (666.61 mPa) using a mixed gas of Cl ₂ gas 40 sccm and He gas 65 sccm. Performed at 200W. Further, the selection ratio with respect to the resist in the etching process of the absorption film 4 was about 0.95.

Further, as shown in FIG. 15C, the buffer film 3 made of Ru immediately below the absorption film 4 is dry-etched in a Cl ₂ / O ₂ mixed gas atmosphere to provide a buffer film having good sidewall anisotropy. 3 and the pattern of the absorption film 4 were obtained.

  Finally, as shown in FIG. 15D, the resist was peeled off to obtain a reflective photomask 20 of the present invention.

  In the reflection type photomask 20 of the present invention, the reflectance of the multilayer reflection film 2 and the absorption film 4 was determined by measurement using EUV light to be 2.2, and the conventional Ta-based absorption film Compared with the case where No. 4 is applied, the film thickness can be reduced without impairing the contrast characteristics.

  As described above, in the reflective photomask blank 10 and the reflective photomask 20 of the present invention, the absorbing film 4 is based on Sn, which has higher absorption than before, and employs thin films of O, Ta, and In. By doing so, it is understood that the film thickness can be reduced while improving the EUV contrast, which contributes to the reduction effect of the projection effect and the improvement of the pattern perpendicularity by the improvement of the resist selection ratio.

  As shown in FIG. 3D, first, 40 pairs of multilayer reflective films 12 made of Mo and Si were formed on the low thermal expansion glass substrate 11 by ion beam sputtering. The film thicknesses of the Mo and Si layers constituting the multilayer reflective film 12 were 2.8 nm and 4.2 nm, respectively. Further, a capping film 13 made of Si was formed to a thickness of 11 nm on the multilayer reflective film 12 by magnetron sputtering.

  Further, a buffer film 14 made of CrN was formed on the capping film 13 to a thickness of 10 nm by a magnetron sputtering method using CrN as a target and discharging Ar gas.

  Next, an absorption film 15 was formed on the buffer film 14 with a thickness of 20 nm by a magnetron sputtering method using SnO as a target and discharging Ar gas.

  Thereafter, a SiN film 16 as an AR film is formed with a thickness of 4 nm by a magnetron sputtering method using Si as a target and nitrogen added to Ar gas, to produce the reflective photomask 60 of the present invention. A reflective photomask blank was prepared.

  Thereafter, an electron beam resist was applied on the AR film 16, and a resist pattern was formed by an electron beam drawing method. Using this resist pattern as a mask, the AR film pattern 16 is formed by reactive ion etching with a fluorine-based gas, and then the absorption film 15 is patterned by reactive ion etching with a chlorine-based gas, and then with sulfuric acid and hydrogen peroxide solution. The electron beam resist was peeled off.

  Thereafter, after inspection of defects of the absorption film 15 and FIB correction were performed, the buffer film 14 made of CrN was peeled off by etching in which oxygen was added to chlorine gas. Thereafter, cleaning with ammonia and aqueous hydrogen peroxide was performed to produce a reflective photomask 60 of the present invention. After fabrication, the pattern portion was observed and measured with an electron microscope, but no deterioration in processing accuracy due to the particle size and surface roughness of the thin film was observed.

  As shown in FIG. 3C, first, 40 pairs of multilayer reflective films 12 made of Mo and Si were formed on the low thermal expansion glass substrate 11 by ion beam sputtering. The film thicknesses of the Mo and Si layers constituting the multilayer reflective film 12 were 2.8 nm and 4.2 nm, respectively. Further, a capping film 13 made of Ru with a thickness of 2.5 nm was formed on the multilayer reflective film 12 by magnetron sputtering.

  Next, on the capping film 13, a film having a thickness of 27 nm was formed as an absorption film 15 by a magnetron sputtering method using SnO as a target and discharging Ar gas.

  Thereafter, the SiN film 16 as an AR film is formed with a thickness of 4 nm by a magnetron sputtering method using Si as a target and nitrogen added to Ar gas, to produce the reflective photomask 50 of the present invention. A reflective photomask blank was prepared.

  Thereafter, an electron beam resist was applied on the AR film 16, and a resist pattern was formed by an electron beam drawing method. Using this resist pattern as a mask, the AR film pattern 16 is formed by reactive ion etching with a fluorine-based gas, and then the absorption film 15 is patterned by reactive ion etching with a chlorine-based gas, and then with sulfuric acid and hydrogen peroxide solution. The electron beam resist was peeled off.

  Thereafter, inspection of defects in the absorption film 15 and electron beam (EB) correction were performed. Thereafter, cleaning with ammonia and aqueous hydrogen peroxide was performed to produce the reflective photomask 50 of the present invention. After fabrication, the pattern portion was observed and measured with an electron microscope, but no deterioration in processing accuracy due to the particle size and surface roughness of the thin film was observed.

  As shown in FIG. 3B, first, 40 pairs of multilayer reflective films 12 made of Mo and Si were formed on the low thermal expansion glass substrate 11 by ion beam sputtering. The film thicknesses of the Mo and Si layers constituting the multilayer reflective film 12 were 2.8 nm and 4.2 nm, respectively. Further, a capping film 13 made of Si was formed to a thickness of 11 nm on the multilayer reflective film 12 by magnetron sputtering.

  Further, a buffer film 14 made of TaN was formed on the capping film 13 to a thickness of 10 nm by a magnetron sputtering method using Ta as a target and discharging a mixed gas obtained by adding nitrogen to Ar.

  Next, as the absorption film 15 on the buffer film 14, a film having a thickness of 20 nm is formed by a magnetron sputtering method using SnO as a target and discharging a mixed gas in which oxygen is added to Ar. A reflective photomask blank for producing the mask 40 was produced.

  Thereafter, an electron beam resist was applied on the absorption film 15, and a resist pattern was formed by an electron beam drawing method. Using this resist pattern as a mask, the absorption film 15 was patterned by reactive ion etching using a chlorine-based gas, and then the electron beam resist was stripped with sulfuric acid and hydrogen peroxide.

  Thereafter, after inspection of defects of the absorption film 15 and FIB correction were performed, the buffer film 14 made of TaN was peeled off by etching using a fluorine-based gas. At this time, since the etching rate of the SnO film by the fluorine-based gas was originally low and the etching was performed slowly with low power, the thickness reduction of the absorption film pattern 15 remained at 1 nm or less. Thereafter, cleaning with ammonia and aqueous hydrogen peroxide was performed to produce the reflective photomask 40 of the present invention. After fabrication, the pattern portion was observed and measured with an electron microscope, but no deterioration in processing accuracy due to the particle size and surface roughness of the thin film was observed.

  As shown in FIG. 3A, first, 40 pairs of multilayer reflective films 12 made of Mo and Si were formed on a low thermal expansion glass substrate 11 by an ion beam sputtering method. The film thicknesses of the Mo and Si layers constituting the multilayer reflective film 12 were 2.8 nm and 4.2 nm, respectively. Further, a capping film 13 made of Ru with a thickness of 2.5 nm was formed on the multilayer reflective film 12 by magnetron sputtering.

  Next, a film having a thickness of 24 nm is formed as an absorption film 15 on the capping film 13 by a magnetron sputtering method using SnO as a target and discharging a mixed gas in which oxygen is added to Ar. A reflective photomask blank for producing the photomask 30 was produced.

  Thereafter, an electron beam resist was applied on the absorption film 15, and a resist pattern was formed by an electron beam drawing method. Using this resist pattern as a mask, the absorption film 15 was patterned by reactive ion etching using a chlorine-based gas, and then the electron beam resist was stripped with sulfuric acid and hydrogen peroxide.

  Thereafter, inspection of defects in the absorption film 15 and electron beam (EB) correction were performed. Thereafter, cleaning with ammonia and aqueous hydrogen peroxide was performed to produce the reflective photomask 30 of the present invention. After fabrication, the pattern portion was observed and measured with an electron microscope, but no deterioration in processing accuracy due to the particle size and surface roughness of the thin film was observed.

  As described above in detail, by forming at least one layer of the absorption film 15 as the absorption film 15 containing Sn and oxygen as main elements, the EUV light absorbability is high and the cleaning liquid is thinner than the conventional film thickness. It is possible to provide a reflective photomask that has high resistance and is easy to etch, and thus has high processing accuracy and pattern position accuracy.

  The present invention is expected to be used in a wide range of fields where fine processing using EUV (Extreme Ultra Violet) light is required. In particular, it is expected to be used as a reflective photomask used for transferring an ultrafine circuit pattern using EUV light having a wavelength of about 10 nm to 15 nm in a manufacturing process of a semiconductor integrated circuit or the like.

DESCRIPTION OF SYMBOLS 1, 11 ... Substrate 2, 12 ... Multilayer reflection film 3 ... Buffer film 4 ... Absorption film 5, 13 ... Capping film 6a ... Resist pattern 3a, 14 ... Buffer film pattern 4a, 15 ... Absorption film pattern 16 ... AR film pattern 10 ... Reflective photomask blanks 20, 30, 40, 50, 60 ... Reflective photomask

Claims (8)

A substrate,
A highly reflective portion formed on the substrate;
A patterned low-reflection part formed on the high-reflection part,
The patterned low reflection portion is a single-layer absorption film of 35 nm or more and 45 nm or less containing a compound material occupying a composition ratio of 90% or more with tin (Sn) and oxygen (O) ,
A reflection type photomask characterized in that an OD defined by the following formula is at least 2 where Rm is a reflected light intensity from a high reflection portion and Ra is a reflected light intensity from a low reflection portion including an absorption film .
OD = -log (Ra / Rm) The low reflection portion is a thin film having a compound material containing one or more elements selected from the group consisting of tantalum (Ta) and indium (In) in addition to tin (Sn) and oxygen (O). The reflective photomask according to claim 1, wherein: The reflective photomask according to claim 1, wherein the low reflection portion is a thin film containing indium (In) at a ratio of 0.05 to 0.1. The reflective photomask according to claim 1, wherein the low reflection portion is a SnO film. The low reflection part is SnO. ₂ The reflective photomask according to claim 1, wherein the reflective photomask is a film. The high reflecting portion, and the multilayer reflective film, reflective photomask according to any one of claims 1 to 5, characterized in that it comprises a capping layer formed on the multilayer reflective film. The reflective photomask according to any one of claims 1 to 6, wherein the low-reflection portion has a reflectance of 15% or less with respect to ultraviolet rays having a wavelength of 190 nm to 260 nm. The top of the low reflectivity portion, the reflection type according to any one of claims 1 to 7 extinction coefficient for 260nm UV wavelength 190nm is equal to or consisting of a layer is 1.0 or less Photo mask.