JP2018045133A - Reflection type photomask and reflection type photomask blank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type photomask having fine absorption film pattern formed and therefor capable of reducing projection effects even when high absorptive material is used as an absorption film in a reflection type photomask having a substrate, a multilayer reflection layer, a protection film and the absorption film, and a reflection type photomask blank for manufacturing the same.SOLUTION: There are provided a reflection type photomask and a reflection type photomask blank in which an absorption film consists of a two layer structure of a first absorption film and a second absorption film, both of the first absorption film and the second absorption film have extinction coefficient to extreme-ultraviolet ray with wavelength of 13.5 nm of 0.05 or more, one of the first absorption film and the second absorption film is easy to be etched to a chlorine-based gas and hardly being etched to a fluorine-based gas, and another is easy to be etched to the fluorine-based gas and hardly being etched to the chlorine-based gas.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a reflective photomask used in lithography using extreme ultraviolet (EUV) as exposure light, and a reflective photomask blank for producing the same.

  In the manufacturing process of semiconductor devices, with the miniaturization of semiconductor devices, there is an increasing demand for miniaturization of photolithography technology. Already, lithography is being replaced by conventional exposure using ArF excimer laser light having a wavelength of 193 nm to exposure using light in the EUV region having a wavelength of around 13.5 nm.

  Since most substances have high light absorptivity with respect to light in the EUV region, a photomask for EUV exposure (EUV mask) is a reflective photomask, unlike a conventional transmissive photomask. . For example, in Patent Document 1, a reflective layer made of a multilayer film in which a silicon (Si) film and a molybdenum (Mo) film are alternately laminated on a glass substrate is formed, and a protective film for protecting the reflective layer thereon A structure is disclosed in which a circuit pattern (absorbing film pattern) is formed of an absorbing film containing tantalum (Ta) as a main component via a (Capping film).

  Similarly, in an optical system using EUV light, a refractive optical system cannot be used, and deflection using a transmissive beam splitter is impossible. Therefore, the optical system of the exposure machine is also a reflection type. Therefore, in the EUV mask, the incident light and the reflected light on the mask cannot be designed on the same axis, and the reflected light of the light incident on the mask with the optical axis tilted about 6 degrees is guided to the semiconductor substrate (wafer) and applied onto the wafer. A method of exposing the photosensitive resin thus formed is employed.

  As described above, in the EUV exposure, the optical axis is inclined. Therefore, when the light is reflected by the mask, a part of the absorption film pattern becomes a shadow depending on the incident direction of the light to the mask, and the original on the wafer. It is known that a phenomenon (projection effect) in which a circuit pattern different from a design pattern is formed occurs. That is, the projection effect causes line width error and pattern position shift on the wafer depending on the line width, direction, pitch, etc. of the absorption film pattern, and deteriorates the transfer quality. The effect of the projection effect becomes more prominent as the pattern line width becomes finer.

Therefore, in order to reduce the projection effect, the thickness of the absorption film is reduced to reduce the height of the absorption film pattern, and as a material that can be thinned, a highly absorbing material for EUV light is used as the absorption film. (For example, Patent Document 2).

JP 2009-088166 A Japanese Patent No. 5609865

For the patterning of the light shielding film in the transmission type photomask, dry etching is generally used with the progress of miniaturization, and the dry etching is also applied to the patterning of the absorption film in the EUV mask. However, in general, a high-absorbency material that can reduce the thickness of the absorption film of the EUV mask is a material having a low dry etching rate, and therefore, it is necessary to increase the thickness of the resist serving as an etching mask. There is a problem that it is difficult to form a fine absorption film pattern due to the above.

  The present invention has been made to solve the above-described problems. The object of the present invention is to provide a fine absorption film pattern even when a high-absorption material is used as an absorption film of an EUV mask. Therefore, it is an object of the present invention to provide a reflective photomask that can reduce the projection effect, and a reflective photomask blank for producing the same.

In order to solve the above problem, the invention described in claim 1 is a reflective photomask including a substrate, a multilayer reflective layer, a protective film, and an absorption film,
The absorption film has a two-layer structure of a first absorption film and a second absorption film,
Each of the first absorption film and the second absorption film has an extinction coefficient of 0.05 or more with respect to extreme ultraviolet light having a wavelength of 13.5 nm,
One of the first absorption film and the second absorption film is a material that is easily etched with respect to a chlorine-based gas and difficult to be etched with respect to a fluorine-based gas, and the other is easily etched with respect to a fluorine-based gas. This is a reflective photomask characterized in that it is a material that is difficult to be etched by a chlorine-based gas.

  The invention according to claim 2 is that at least one of the first absorption film and the second absorption film is selected from the group consisting of Sn and oxides, nitrides, and oxynitrides thereof. And at least one atom selected from the group consisting of Te and their oxides, nitrides, and oxynitrides, and a molecule as a main component. The reflection type photomask according to Item 1 is obtained.

The invention according to claim 3 is a reflective photomask blank comprising a substrate, a multilayer reflective layer, a protective film, an absorption film,
The absorption film has a two-layer structure of a first absorption film and a second absorption film,
Each of the first absorption film and the second absorption film has an extinction coefficient of 0.05 or more with respect to extreme ultraviolet light having a wavelength of 13.5 nm,
One of the first absorption film and the second absorption film is a material that is easily etched with respect to a chlorine-based gas and difficult to be etched with respect to a fluorine-based gas, and the other is easily etched with respect to a fluorine-based gas. This is a reflective photomask blank characterized by being a material that is difficult to be etched with respect to a chlorine-based gas.

  According to a fourth aspect of the present invention, at least one of the first absorption film and the second absorption film is selected from the group consisting of Sn and oxides, nitrides, and oxynitrides thereof. And at least one atom selected from the group consisting of Te and their oxides, nitrides, and oxynitrides, and a molecule as a main component. The reflective photomask blank according to Item 3 is used.

  According to the reflection type photomask of the present invention and the reflection type photomask blank for producing the same, the absorption film is a two-layer absorption film made of a high absorption material having different dry etching characteristics. The film thickness can be used, and a fine superabsorbent film pattern can be formed. As a result, it is possible to reduce the projection effect, and it is possible to reduce line width errors and pattern positional deviations on the wafer.

It is a schematic cross section which shows the structure which concerns on embodiment of the reflective photomask blank for producing the reflective photomask of this invention. It is a schematic cross section for demonstrating the structure which concerns on embodiment of the reflective photomask of this invention, and a reflectance. It is a schematic cross section for demonstrating the manufacturing process of the reflection type photomask of this invention. It is a characteristic view which shows the example of calculation of the optical characteristic of the reflection type photomask of this invention. It is a characteristic view which shows another calculation example of the optical characteristic of the reflection type photomask of this invention.

  Hereinafter, a reflective photomask according to an embodiment of the present invention and a reflective photomask blank for producing the same will be described in detail. In addition, the same code | symbol is attached | subjected about the same component unless there is a reason for convenience, and the overlapping description is abbreviate | omitted. Also, in the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner, and the dimensional ratios of the respective constituent elements are not the same as the actual ones.

  FIG. 1 is a schematic cross-sectional view showing a structure according to an embodiment of a reflective photomask blank 10 for producing a reflective photomask of the present invention. A reflective photomask blank 10 of the present invention is a reflective photomask blank including a substrate 1, a multilayer reflective layer 2, a protective film 3, a first absorption film 4, and a second absorption film 5. As another form, a buffer film (not shown) serving as an etching stop layer of the first absorption film 4 and serving as a buffer at the time of correcting the absorption film pattern defect is provided between the protective film 3 and the first absorption film 4. There is a form to prepare.

Not only EUV exposure but also optical characteristics required for a photomask for realizing transfer by projection exposure are firstly mask contrast. In a normal transmission mask, the mask contrast is evaluated by the following equation (1), where T _{0 is} the transmittance through the transparent substrate portion and T is the transmittance through the pattern portion including the light shielding film.
OD = −log (T / T ₀ ) (1)
Here, OD is called optical density and represents the degree of light shielding property of the light shielding film.

Also in the EUV mask, the mask contrast can be evaluated in the same manner, where R _{0 is} the reflectance of the high reflection portion composed of the multilayer reflective layer 2 and the protective film 3, and R is the reflectance from the low reflection portion including the absorption film (see FIG. 2), as in the case of the transmission type mask, the evaluation is made by the following equation (2).
OD = −log (R / R ₀ ) (2)
In order to perform good EUV transfer, although depending on exposure conditions and patterns, the OD is usually preferably 2.0 to 3.0. As can be seen from Equation (2), the OD increases as the reflectance R decreases. In order to reduce the reflectance R, an absorption film having a high absorbability for EUV light, that is, a large extinction coefficient may be used. In other words, if the OD value is the same, the absorption film can be made thinner as the high absorption film having a larger extinction coefficient is used.

  In the reflective photomask blank 10 of the present invention, the first absorption film 4 and the second absorption film 5 both have an extinction coefficient of 0.05 or more for EUV light having a wavelength of 13.5 nm. Conventional absorption films, as represented by Ta, have an extinction coefficient of 0.04 or less for EUV light having a wavelength of 13.5 nm. Since both the first absorption film and the second absorption film of the reflective photomask blank of the present invention are 0.05 or more, the absorptivity is high and even if the total film thickness is two layers, It can be made thinner than the film thickness. Therefore, it is possible to reduce the projection effect by the absorption film pattern when the reflective photomask 20 (see FIG. 2) is used.

The reflective photomask blank 10 of the present invention further includes one of the first absorption film 4 and the second absorption film 5 that is easily etched with respect to the chlorine-based gas and less easily etched with respect to the fluorine-based gas, and the other is fluorine. It has a characteristic that it is easy to be etched with respect to a system gas and is difficult to be etched with respect to a chlorine-based gas. As a result, when the first absorption film 4 is etched, the pattern of the second absorption film 5 on the upper layer can function as an etching mask. Therefore, the resist pattern on the second absorption film 5 only needs to function as an etching mask when the second absorption film 5 is mainly etched. Therefore, a conventional reflective photomask manufacturing process using a high-absorbency material is used. The resist film thickness can be made thinner than that. As a result, it is possible to reduce the difficulty of forming a fine absorption film pattern made of a highly absorbent material.

  Generally, in dry etching, the introduced gas collides with electrons in the plasma, and active radicals and reactive ions dissociated into various forms are generated to cause etching, but low-boiling volatile products are formed on the etching surface. The easier it is to etch, the index is the boiling point and vapor pressure of the reaction product due to the material to be etched and the introduced gas. That is, the lower the boiling point of the reaction product is, the more vaporized, the higher the vapor pressure, and the easier it is to exhaust.

  In the etching of the absorption film of the reflection type photomask, as a measure of the above “easy to be etched” and “not easily etched”, for example, when etching is easily performed with a chlorine-based gas, at least one kind of chloride generated by etching is used. If the boiling point of the product is 150 ° C. or less and it is difficult to etch with respect to chlorine-based gas, the stoichiometric form of the chloride generated by etching may have a boiling point of 300 ° C. or more as a guide. it can. The same applies to the fluorine-based gas.

  Which of the first absorption film 4 and the second absorption film 5 is a material that is easily etched with respect to a chlorine-based gas and the other is a material that is easily etched with respect to a fluorine-based gas depends on the protective film 3 to be used. What is necessary is just to determine by which gas (when using a buffer film) a buffer film is easily etched. That is, when the protective film 3 (or buffer film) is easily etched with a fluorine-based gas, the first absorption film 4 is a material that is easily etched with respect to a chlorine-based gas, and the second absorption film 5 is a fluorine-based gas. On the other hand, when the material is easily etched and the protective film 3 (or the buffer film) is easily etched by the chlorine-based gas, the opposite structure may be adopted.

  FIG. 3 shows a manufacturing process of the reflective photomask 20 using the reflective photomask blank 10 of the present invention. In FIG. 3A, a multilayer reflective layer 2 is formed on a flat low thermal expansion substrate 1, a protective film 3 for protecting the multilayer reflective layer 2 is formed thereon, and a first absorption film is further formed thereon. 4 shows a form in which a resist 6 for electron beam drawing or laser drawing is formed on a reflective photomask blank 10 of the present invention on which 4 and a second absorption film 5 are formed.

  Next, pattern drawing is performed with an electron beam or a laser, and development is performed to form a resist pattern 6a (FIG. 3B). Then, the resist pattern 6a is used as an etching mask to form a second pattern with a fluorine-based gas (or chlorine-based gas). The second absorption film 5 is etched to form a second absorption film pattern 5a (FIG. 3C). At this time, the resist pattern 6a is reduced according to the etching selection ratio with the second absorption film 5 to become a resist pattern 6b.

Subsequently, the first absorbing film pattern 4a is formed by etching the first absorbing film 4 with a chlorine-based gas (or fluorine-based gas) using the resist pattern 6b and the second absorbing film pattern 5a that have been reduced in thickness as an etching mask. To do. The resist pattern 6b disappears during this process, but after the disappearance of the resist pattern 6b, the second absorption film pattern 5a functions as an etching mask. At this time, the film thickness of the second absorption film pattern 5a is reduced according to the etching selection ratio with the first absorption film 4, but the film reduction amount is measured in advance by experiments, and the amount of the film reduction amount is the same. If the second absorption film 5 is formed thick, the thickness of the second absorption film pattern 5a required finally is obtained. Similarly, when the line width of the second absorption film pattern 5a is narrowed during the etching of the first absorption film 4 and the first absorption film pattern 4a is thinner than a predetermined line width, the amount of thinning is experimentally determined in advance. Is measured, and the line width of the drawing pattern is increased accordingly.

  In this way, the reflective photomask 20 of the present invention can be manufactured (FIG. 3D). In the conventional reflective photomask manufacturing process, a resist pattern peeling process is required after the absorption film is etched. However, in the reflective photomask 20 manufacturing process of the present invention, the resist pattern disappears during the process. Therefore, one of the features is that no peeling process is required.

  As the first absorption film and the second absorption film used in the reflection type photomask and the reflection type photomask blank of the present invention, the EUV light absorptivity (extinction coefficient), dry etching characteristics, cost, etc. are comprehensive. From one point of view, one of the main components is at least one atom and molecule selected from the group consisting of Sn and their oxides, nitrides, and oxynitrides, and the other is Te and their oxides and nitrides. It is preferable that at least one atom and molecule selected from the group consisting of oxynitrides are the main constituent elements. Here, the “main constituent element” means that the sum of the number of atoms constituting these atoms and molecules is 90% or more of the total number of atoms.

  Here, in addition to the simple metals Sn and Te, their oxides, nitrides, and oxynitrides are candidates. Usually, oxides, nitrides, and oxynitrides are more photoactive than single metals. This is because the resistance to the cleaning liquid necessary for the mask is improved. On the other hand, since the dry etching rate is lowered, in the case of oxides, nitrides, and oxynitrides, oxides, nitrides, and oxynitrides containing more metal than the stoichiometric ratio are preferable. As can be seen from the comparison of optical constants of Sn and SnO at the EUV wavelength (13.5 nm) in Table 1 described later, the extinction of the high absorption region is achieved by becoming an oxide, nitride, or oxynitride. The coefficient does not change much more than in the case of a single unit.

Table 1 shows optical constants (refractive index: n, extinction coefficient: k) of various materials at EUV wavelength (13.5 nm). The numerical values in Table 1 summarize the values found in various literatures and websites. Based on the numerical values in Table 1, as an embodiment of the reflective photomask of the present invention, the result of calculating the OD value when one of the first absorption film and the second absorption film is Sn and the other is Te Are shown in FIGS. In these calculations, the protective film is calculated as a Ru film having a thickness of 2.5 nm, and the multilayer reflective layer is calculated as 40 pairs of multilayer films of Si and Mo.

  FIG. 4A shows the total thickness of the first and second absorption films, where the second absorption film is Te (film thickness 10 nm) and the first absorption film is Sn (film thickness 0 to 50 nm). It is the result of calculating the OD value with the horizontal axis by the optical thin film theory. FIG. 4B shows a total film of the first and second absorption films, where the second absorption film is Te (film thickness 20 nm) and the first absorption film is Sn (film thickness 0 to 40 nm). It is the result of calculating the OD value when the thickness is on the horizontal axis.

  Similarly, in FIG. 5A, the second absorption film is Sn (film thickness 10 nm), the first absorption film is Te (film thickness 0 to 50 nm), and the total of the first and second absorption films is shown. It is the result of calculating the OD value when the film thickness is on the horizontal axis. FIG. 5B shows a total film of the first and second absorption films, where the second absorption film is Sn (film thickness 20 nm) and the first absorption film is Te (film thickness 0 to 40 nm). It is the result of calculating the OD value when the thickness is on the horizontal axis.

  As can be seen from FIGS. 4 and 5, in order to obtain OD = 2.0 to 3.0, the total film thickness of the first and second absorption films may be about 25 nm to 40 nm. When a conventional Ta film is used, at least about 60 nm thickness is required to obtain OD = 2.0. Therefore, the structure of the two-layer absorption film of the present invention is effective as a high absorption film capable of reducing the film thickness. I understand.

As described above, generally, the ease of dry etching can be estimated by comparing the boiling points of the reaction product by the material to be etched and the introduced gas. Table 2 shows the boiling points of typical fluorides and chlorides of Te, Sn, and Ru, Si, and Al, which are conventional protective film candidates, suitable as the absorption film material of the reflective photomask of the present invention. The numerical values in Table 2 summarize values found in various documents (CRC Handbook of Chemistry and Physics, 78th Edition, etc.) and websites.

  As can be seen from Table 2, Te is a fluorine-based gas and Sn is a chlorine-based gas. It is desirable that the protective film is difficult to be etched, and Ru is less likely to be etched with respect to both a fluorine-based gas and a chlorine-based gas, but is more difficult to be etched with a chlorine-based gas. Si is relatively easily etched with both fluorine-based gas and chlorine-based gas, but etching with chlorine-based gas is more difficult. Also, Al is less likely to be etched with a fluorine-based gas than with a chlorine-based gas.

From the above results, when Ru is used as a protective film, it is preferable that the first absorption film (lower layer) is Sn that is easily etched with a chlorine-based gas, and the second absorption film (upper layer) is Te. The first absorption film may be Te and the second absorption film may be Sn. When Si is used as the protective film, it is preferable that the first absorption film is Sn which is easily etched with a chlorine-based gas, and the second absorption film is Te. When Al or Al ₂ O ₃ is used as the protective film, it is preferable that the first absorption film is Te which is easily etched with a fluorine-based gas, and the second absorption film is Sn.

  With the structure of the two-layer absorption film as described above, in the reflection type photomask and reflection type photomask blank of the present invention, the second absorption film functions as an etching mask when the first absorption film is etched. Therefore, even with a high absorption material, a thinner resist film thickness can be used than before, and a fine absorption film pattern can be easily formed. As a result, the projection effect due to the highly absorbent film pattern can be reduced more effectively.

  The present invention is not limited to the above-described embodiments as they are, and can be modified and embodied without departing from the gist of the present invention. Various inventions can be envisaged by appropriate application of the matters shown in the specification. For example, a third absorption film that is difficult to be etched by either chlorine-based gas or fluorine-based gas and is easily etched by another gas type is introduced to form a high-absorption film having a three-layer structure.

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Multilayer reflective layer 3 ... Protective film 4 ... 1st absorption film 4a ... 1st absorption film pattern 5 ... 2nd absorption Film 5a ... second absorption film pattern 6 ... resist 6a ... resist pattern 6b ... reduced resist pattern 10 ... reflective photomask blank 20 ... reflective photomask I .... Incident light R, _R0 ... Reflected light

Claims (4)

A reflective photomask comprising a substrate, a multilayer reflective layer, a protective film, an absorption film,
The absorption film has a two-layer structure of a first absorption film and a second absorption film,
Each of the first absorption film and the second absorption film has an extinction coefficient of 0.05 or more with respect to extreme ultraviolet light having a wavelength of 13.5 nm,
One of the first absorption film and the second absorption film is a material that is easily etched with respect to a chlorine-based gas and difficult to be etched with respect to a fluorine-based gas, and the other is easily etched with respect to a fluorine-based gas. A reflective photomask characterized in that it is a material that is not easily etched by chlorine-based gas. One of the first absorption film and the second absorption film is mainly composed of at least one atom and molecule selected from the group consisting of Sn and oxides, nitrides, and oxynitrides thereof, 2. The reflective photomask according to claim 1, wherein the other is composed mainly of at least one atom and molecule selected from the group consisting of Te and oxides, nitrides, and oxynitrides thereof. . A reflective photomask blank comprising a substrate, a multilayer reflective layer, a protective film, an absorption film,
The absorption film has a two-layer structure of a first absorption film and a second absorption film,
Each of the first absorption film and the second absorption film has an extinction coefficient of 0.05 or more with respect to extreme ultraviolet light having a wavelength of 13.5 nm,
One of the first absorption film and the second absorption film is a material that is easily etched with respect to a chlorine-based gas and difficult to be etched with respect to a fluorine-based gas, and the other is easily etched with respect to a fluorine-based gas. A reflective photomask blank characterized in that it is a material that is difficult to be etched against a chlorine-based gas. One of the first absorption film and the second absorption film is mainly composed of at least one atom and molecule selected from the group consisting of Sn and oxides, nitrides, and oxynitrides thereof, 4. The reflective photomask according to claim 3, wherein the other is composed mainly of at least one atom and molecule selected from the group consisting of Te and oxides, nitrides, and oxynitrides thereof. blank.

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