JP4393164B2 - Photomask, manufacturing method thereof, and exposure method using the same - Google Patents

Description

The present invention relates to a structure of a photomask used in an optical lithography apparatus, a manufacturing method thereof, and an exposure method.

  Conventionally, in order to manufacture a semiconductor device such as an integrated circuit, a pattern is formed by a lithography method in which a pattern is transferred onto the surface of a silicon wafer using a photomask in which a pattern is formed of a light shielding film such as chromium on a quartz glass substrate. Is formed and the surface thereof is subjected to various treatments. That is, as shown in FIG. 10, a photomask 103 and a projection lens system 104 are arranged between a silicon wafer substrate 101 and an exposure light source 102, and formed on the photomask by light projected from the exposure light source. The pattern thus formed is transferred onto the silicon wafer substrate 101 via the lens system 104.

  A conventional photomask has a structure in which a light shielding film 32 is selectively formed on a transparent substrate 31, as shown in FIG. In the case of performing exposure by applying light having a wavelength of 157 nm or more, quartz glass is generally used as a transparent substrate material, and its size is 6 inch square and thickness is 0.25 inch. Further, as a material of the light shielding film 2, chromium (Cr) having an optical density of 3 or more (transmittance of 0.1% or less) is used, and the film thickness is set to 60 nm or more so that no pinhole defect is generated. Among various metal thin films, chromium is excellent in etching property, and the film thickness can be reduced to about 1/40 to 1/60 compared with gelatin conventionally used as a mask material, and the film strength is 30. The price is expensive because there is more than that, but it is currently the most widely used because one mask can be used for a long time. In addition to high-purity chromium particles (99.999%), chromium iodide is also used as a raw material for this chromium. The latter can provide a chromium film having a higher purity than the former, but is expensive. Since the chrome thin film has a metallic luster and reflects light well, if only the chrome film is deposited, multiple reflection occurs at the time of exposure transfer, resulting in poor transfer accuracy. As a countermeasure, a surface low-reflection chromium mask in which a chromium oxide film of about 30 nm is further formed on the chromium film as an antireflection film is widely used. The surface reflectance in the case of a chromium single layer is 50 to 60%, whereas the low reflection chromium mask has a reflectance of 5 to 10%.

In recent years, the exposure light wavelength used for lithography has become shorter in response to demands for higher density semiconductor devices, and the adoption of so-called F ₂ lines with a wavelength of 157 nm has been studied. In lithography using this F ₂ line, when a conventional photomask is applied and transferred to the photoresist using an exposure apparatus, a large amount of clear field area is caused by the influence of local flare caused by irregularities on the surface of the lens system. Due to the influence of scattered light, the line width of the transmission pattern near the clear field area becomes larger than the line width of the transmission pattern existing in the dark field area. As a result, the line width of the exposed pattern was reduced (Non-Patent Document 1).
As described above, when a wide clear field region and dark field region coexist in the mask pattern layout, there is a problem in that line width abnormality occurs.

Proceeding of SPIE vol. 4000 (2000)

The present invention has been made to solve this problem in photomasks, and can reduce the dimensional difference of patterns without depending on the density of the patterns on the photomask, and form a stable pattern. An object of the present invention is to realize a photomask that can be used, a manufacturing method thereof, and an exposure method using the photomask.

The first aspect of the present invention is a photomask having a translucent film formed on a transparent substrate and a light-shielding film formed on the translucent film and patterned,
The translucent film is patterned so as to exist in a region other than the region corresponding to the dark field region of the photomask, and not to exist in the opening region of the light shielding film in the dark field region , and the photomask The photomask is formed in an area corresponding to a clear field area .

In the first invention, the translucent film is selected from the group consisting of tantalum silicide (TaSi), zircon silicide (ZrSi), molybdenum silicide (MoSi), chromium fluoride (CrF), and silicon oxide (SiO ₂ ). Preferably, the light shielding film contains at least one selected from the group consisting of chromium (Cr) and chromium fluoride (CrF). Furthermore, the light shielding film is preferably a film having etching resistance when the semitransparent film is etched .

Furthermore, in the first aspect of the present invention, it is preferable that a space between patterns in the dark field region is less than 10 μm.

According to a second aspect of the present invention , a dark resist is formed in a region other than a portion corresponding to a clear field region of the first resist , and a step of applying a first resist to a blank mask having a translucent film formed on a transparent substrate. A step of patterning a portion corresponding to a field region, a step of etching a translucent film exposed by patterning of the first resist, a step of peeling and cleaning the first resist , and the first resist a step of forming a light shielding film on the transparent substrate and the translucent layer exposed by peeling and washing, and applying a second resist on the light shielding film, the said second resist a step of patterning the portion corresponding to the dark field region and the clear field region, before exposed by the patterning of the second resist Etching the light shielding film, a manufacturing method of a photomask, characterized in that it comprises at least the step of removing the second resist.

  In the second aspect of the present invention, the first and second resists are preferably electron beam resists.

In the second invention, the translucent film is selected from the group consisting of tantalum silicide (TaSi), zircon silicide (ZrSi), molybdenum silicide (MoSi), chromium fluoride (CrF), and silicon oxide (SiO ₂ ). In addition, the light shielding film may be at least one selected from the group consisting of chromium (Cr), chromium fluoride (CrF), and silicon oxide (SiO ₂ ). preferable. Furthermore, the light shielding film is preferably a film having etching resistance when the semitransparent film is etched .

In the second aspect of the present invention, the pattern spacing of the dark field region is preferably less than 10 μm.

According to a third aspect of the present invention, there is provided a photomask having a translucent film formed on a transparent substrate and a light-shielding film formed on the translucent film and patterned, wherein the photomask has a dark field region. The exposure method is characterized in that the semi-transparent film in the corresponding opening of the light-shielding film is removed, and exposure is performed with an F ₂ line using a photomask in which the semi-transparent film is formed in a clear field .

According to the invention of the photomask, the manufacturing method thereof, and the exposure method, it is possible to obtain a resist pattern that does not depend on the density of the photomask pattern and causes little pattern dimensional difference.

In order to study the local flare generated in the above-described prior art, the present inventors have studied by forming the mask pattern of FIG.
In the mask pattern for evaluating the influence of local flare in FIG. 4, a dark field region 42 using a line & space pattern is created in the 100 μm region, and the window width 44 is intentionally set to various values therein. A controlled clear field region 41 was created. In the clear field region 41, a line & space pattern 43 using a target line width is arranged. By measuring the line width of the line portion of the line & space pattern in the clear field area for each window width 44, it was examined how much the local flare has an influence.

FIG. 5 shows the results of examining the window width dependency of the line width using the local flare evaluation pattern. When the X axis is the window width of the clear field area and the Y axis is the line width of the in-window line & space pattern in the clear field area, the line width becomes smaller and stable as the window width increases. The window width 44 when the line width is saturated shows different values depending on the lens of the exposure apparatus.
In this way, it is clear that when a wide clear field region and a dark field region coexist in the mask pattern layout, line width abnormality occurs, and in order to solve this, the transmitted light of the clear field region The present invention has been completed by paying attention to the fact that the strength may be controlled.

Embodiments of the present invention will be described below.
(Photomask)
The photomask of the present invention will be described below. FIG. 1 is a cross-sectional view of a photomask of the present invention. In FIG. 1, reference numeral 11 denotes a transparent substrate formed of quartz glass or the like. A semi-transparent film 12 and a light-shielding film 13 are formed on the transparent substrate 11, and the semi-transparent film at a position corresponding to the opening 14 existing in the region corresponding to the dark field region 1B of the transparent substrate 11 is removed. On the other hand, a translucent film 12 is formed in the clear field region 1 </ b> A of the transparent substrate 11.

The operation principle of exposure using this photomask will be described below.
FIG. 6 is a diagram showing a cross-sectional structure (FIG. 6A), a light amplitude (FIG. 6B), and a light intensity (FIG. 6C) of the photomask of the present invention. FIG. 7 shows a cross-sectional structure of a conventional photomask (FIG. 7A), its light amplitude (FIG. 7B), and light intensity (FIG. 7C). Each light intensity distribution shows the light intensity 6A and 7A for determining the resist line width. That is, the region having the light intensity exceeding 6A and 7A has the intensity to expose the resist on the substrate to be processed such as a semiconductor substrate.

  As shown in FIG. 7, in the case of the conventional photomask, the scattered light of the transmitted light from the wide transmission region of the clear field region affects the light intensity distribution of the neighboring adjacent pattern. Then, as the pattern is closer to the clear transmission region in the clear field region, the light intensity distribution becomes gentler, and the influence of local flare that the light shielding region is reduced occurs. When the resist on the substrate to be processed is exposed using this photomask, the transmitted light of the portion 7B corresponding to the clear field region exposes the resist, so that the region exceeding the level 7A is exposed, and as a result, the positive resist is removed. When used, the area corresponding to 7C is opened, and it is clear that a dimensional difference is generated with respect to 7B which is the clear field area. Further, it is clear that the line width 7D is also narrowed for the pattern adjacent thereto due to the local flare of the clear field region 7B.

  On the other hand, when the photomask of the present invention is used, as shown in FIG. 6, since the transmittance of the wide transmission region of the clear field region is small, the light intensity of the transmitted light generated therefrom is small. Thus, the scattered light of the transmitted light is less likely to affect the light intensity distribution of the neighboring neighboring patterns. Even in a pattern close to a wide transmission region in the clear field region, the light intensity distribution hardly changes and the influence of local flare can be significantly reduced.

  As described above, by using the photomask of the present invention, the transmittance of the wide transmission region of the clear field region is reduced, the light intensity of the transmitted light generated therefrom is reduced, and the scattered light of the transmitted light is It is possible to make it difficult to influence the light intensity distribution of adjacent patterns. Even in a pattern close to a wide transmission region in the clear field region, the light intensity distribution hardly changes, and the influence of local flare can be significantly reduced. In addition, it is possible to significantly reduce the dimensional difference of the resist pattern between the clear field region and the dark field region caused by local flare.

In the present invention, the dark field region refers to a region where patterns are relatively dense in the region, while the clear field region refers to a region where patterns are relatively sparse. The line width narrowing of the pattern close to the clear field region of interest in the present invention is caused by so-called mid-range flare that occurs at a distance of about 10 μm, and the degree of density of the pattern is 10 μm as a boundary. It is preferable to evaluate. Therefore, the clear field region refers to a region where the line interval, that is, the space width is 10 μm or more, and the dark field region refers to a region where the line interval does not exceed 10 μm.
In the present invention, it is necessary to form the translucent film at the light shielding film opening in the clear field region having a line interval of 10 μm or more.

  On the other hand, in the so-called dark field region where the line spacing of the pattern is less than 10 μm, the light is transmitted through the mask when it is relatively unaffected by the above-mentioned midrange flare. Since the exposure amount itself is reduced, the tolerance of the light intensity for exposing the resist is lowered, which is not preferable because it causes a reduction in resolution. Therefore, it is necessary to form the translucent film only in the clear field region and not to form the translucent film in the dark field region.

ここで、λは光源の波長（ｎｍ）、ｎは半透明膜の屈折率である。また、ｉは整数（１，２，３・・・ｉ）である。
例えば、半透明膜タンタルシリサイドの場合は、λが１５７ｎｍのときに屈折率が、２．３であるので、ｔは次式のようになる。

In the present invention, the semi-transparent film has a light intensity sufficient to expose the resist on the substrate to be processed, that is, a transmittance enough to transmit light having the light intensity level 6A in FIG. It is necessary to be a material, and such a material is selected from the group consisting of tantalum silicide (TaSi), zircon silicide (ZrSi), molybdenum silicide (MoSi), chromium fluoride (CrF), and silicon oxide (SiO2). It is preferable that the material contains at least one selected. As the film thickness of this translucent film varies depending on the wavelength of light used, light intensity, and resist type, the optimum value cannot be determined unconditionally, but for the case where no translucent film exists, It is desirable to have a film thickness (t) that can have the same phase. t is expressed by the following equation.

Here, λ is the wavelength (nm) of the light source, and n is the refractive index of the translucent film. I is an integer (1, 2, 3... I).
For example, in the case of a semitransparent film tantalum silicide, the refractive index is 2.3 when λ is 157 nm, and therefore t is expressed by the following equation.

In the present invention, the light-shielding film needs to be a film that can block light having an exposure light wavelength, and specifically, chromium (Cr), chromium fluoride (CrF), silicon oxide (SiO ₂ ). At least one selected from the group consisting of: The light-shielding film material needs to remain when the semitransparent film is removed by etching, and therefore needs to have resistance to the etching material of the semitransparent film.

(Photomask manufacturing method)
Hereinafter, based on an Example, this invention is demonstrated in detail.
FIG. 2 is a diagram showing a manufacturing process of the halftone mask of the present invention. In the present embodiment, an electron beam resist is used as a resist used for patterning, but the present invention is not limited to this.

FIG. 2A is a diagram showing a cross-sectional structure of a mask blank applied to the present invention.
This mask blank is formed by, for example, forming a translucent film 22 on a transparent substrate 21 by sputtering, vacuum deposition, or the like, and further applying an electron beam resist 23 thereon.
The material of the transparent substrate 21 must have a high transmittance of 80% or more at the wavelength of the exposure light to be applied. For example, quartz having a transmittance of 85% or more at the wavelength of 157 nm or more of the exposure light. Glass is effective. The material of the semi-transparent film 22 is a transmittance that can completely remove the photoresist on the substrate to be processed when transferring the photoresist formed on the substrate to be processed such as a semiconductor substrate at the wavelength of the exposure light to be applied. Must have as low a transmittance as possible. As a material for the translucent film 22, tantalum silicide (TaSi), zircon silicide (ZrSi), molybdenum silicide (MoSi), chromium fluoride (CrF), and silicon oxide (SiO ₂ ) are effective.

Next, FIG. 2B is a diagram showing an electron beam drawing process.
In the electron beam drawing process, when the electron beam resist 23 is a positive resist, the region where the translucent film 22 is exposed is a region drawn by an electron beam. A necessary charge amount is set and an electron beam is irradiated.

FIG. 2C is a diagram showing an electron beam resist development process applied to the present invention.
By the electron beam drawing process and the developing process, the electron beam resist is patterned into a resist area and a non-resist area.
In the electron beam resist developing step, when a positive resist is applied as the electron beam resist 23, the electron beam resist 23 is dissolved in the developer and the translucent film is exposed in the region irradiated with the electron beam. In the region where the electron beam is not irradiated, the electron beam resist 23 is not dissolved in the developing solution, so that the electron beam resist pattern remains.

FIG. 2D is a diagram showing a semitransparent film etching process applied to the present invention.
When dry etching of the semitransparent film 22 is performed, a parallel plate type reactive ion etching (RIE) method is applied. For example, when the translucent film is molybdenum silicide, the etching gas is applied by controlling CF ₄ (tetrafluoromethane) and O ₂ (oxygen) at a flow rate ratio of 20: 1. At the time of etching, the etching selectivity with the synthetic quartz glass which is the transparent substrate 21 must be sufficient. The electron beam resist 23 functions as a protective film against etching, and only the semitransparent film in the region not covered with the electron beam resist is removed, and the transparent substrate 21 is partially exposed. When CF ₄ (tetrafluoromethane) and O ₂ (oxygen) are applied to dry etching of a molybdenum silicide (MoSi) film at a flow ratio of 20: 1, the electron beam resist 23 has sufficient dry etching resistance. .

FIG.2 (e) is a figure which shows the peeling process of the electron beam resist applied to this invention.
As the resist stripping solution, a mixed solution in which sulfuric acid and hydrogen peroxide solution are mixed at a ratio of 3: 1 is used. At this time, the peeling resistance between the exposed transparent substrate 21 and the semitransparent film 22 must be sufficient.

FIG. 2F is a diagram showing a light-shielding film forming process, an electron beam resist second coating process, and a second electron beam drawing process applied to the present invention.
In the process of forming the light shielding film 25, the light shielding film 25 is formed by sputtering, vacuum deposition, or the like. The material of the light shielding film 25 must have a low transmittance at the wavelength of the exposure light to be applied. For example, for light having a wavelength of 157 nm or more, chromium (Cr) having a transmittance of 0.5% or less is effective.
In the coating process of the second electron beam resist 26, the electron beam resist 26 must have excellent etching resistance when the light shielding film 25 is etched.
In the second electron beam drawing process, the region where the pattern of the light shielding film exists is not drawn. In the region where the transparent substrate is exposed, an amount of charge that can completely remove the resist is set, and the electron beam is irradiated.

FIG. 2G is a diagram showing a developing process of the second electron beam resist 26 applied to the present invention.
In the second development step, when a positive resist is applied as the electron beam resist 26, the electron beam resist 26 is dissolved in the developer in the region irradiated with the electron beam, and the light shielding film 25 is exposed. In the region where the electron beam is not irradiated, the electron beam resist 23 is not dissolved in the developing solution, so that the electron beam resist pattern remains.

FIG. 2H is a diagram showing a light shielding film etching process applied to the present invention.
When dry etching of the light shielding film 25 is performed, a parallel plate type reactive ion etching (RIE) method is applied. For example, when the light shielding film is chromium (Cr), the etching gas is controlled to CCl ₄ (tetrachloromethane) and O ₂ (oxygen) or CH ₂ Cl ₂ (dichloromethane) at a flow rate ratio of 1: 3. Apply. At the time of etching, the etching selectivity between the transparent substrate 21 and the halftone phase shift film 25 which is a light shielding film must be sufficient. Further, the electron beam resist 26 functions as a protective film against etching, and only the light shielding film in the region not covered with the electron beam resist is removed, and the transparent substrate 21 and the halftone phase shift film 25 are partially exposed. When applying CCl ₄ (tetrachloromethane) and O ₂ (oxygen) or CH ₂ Cl ₂ (dichloromethane) at a flow rate ratio of 1: 3 for dry etching of a chromium (Cr) film, an electron beam resist The dry etching resistance of 23 is sufficient.

FIG. 2 (i) is a diagram showing a second peeling step of the electron beam resist applied to the present invention.
As the resist stripping solution, a mixed solution in which sulfuric acid and hydrogen peroxide solution are mixed at a ratio of 3: 1 is used. At this time, the peeling resistance between the exposed transparent substrate 21 and the semitransparent film 22 must be sufficient.

Using the photomask produced by the above method, the photomask pattern was transferred using the F ₂ line by the photolithography apparatus shown in FIG.
As shown in FIG. 10, the exposure light emitted from the exposure light source 102 passes through the photomask 103 of the present invention, enters the exposure projection system lens 104, is converged inside the exposure projection system lens 104, and is processed. The photoresist on the wafer 101 is exposed.

FIG. 8 is a view showing a resist pattern after exposure and transfer using the photomask of the present invention. FIG. 9 is a view showing a resist pattern after exposure and transfer using a conventional photomask.
When a conventional photomask is applied and transferred to a photoresist using an exposure apparatus, the light intensity distribution in FIG. 7 is determined by the light intensity 7A for determining the resist line width. Such a resist pattern is obtained. In the case of the conventional photomask, the scattered light of the transmitted light from the wide transmission region of the clear field region affects the light intensity distribution of the neighboring pattern. This is because the pattern closer to the clear transmission region in the clear field region has a gentler light intensity distribution, and the influence of local flare that the light shielding region is reduced occurs. Therefore, a phenomenon occurs in which the line width of the line portion of the line & space pattern becomes smaller as the pattern 91d is closer to the clear transmission region of the clear field region (opening 92).

  However, when the photomask of the present invention is applied and transferred to the photoresist using an exposure apparatus, the resist line width is determined by the light intensity distribution 6A for determining the resist line width in the light intensity distribution of FIG. The resist pattern is as follows. In the case of the photomask of the present invention, since the transmittance of the wide transmission region of the clear field region (opening 82) is small, the light intensity of the transmitted light generated therefrom is reduced, and the scattered light of the transmitted light is This makes it difficult to influence the light intensity distribution of neighboring neighboring patterns. This is because even the pattern 81d close to the wide transmission region of the clear field region hardly changes the light intensity distribution, and the influence of local flare can be significantly reduced. Therefore, even in a pattern close to a wide transmission region in the clear field region, the phenomenon that the line width of the line portion of the line & space pattern becomes small does not easily occur.

  In this way, by using the photomask of the present invention, the transmittance of the wide transmission region of the clear field region is reduced, and further, the light intensity of the transmitted light generated therefrom is reduced, and the scattered light of the transmitted light is It is possible to realize an effect that it is difficult to affect the light intensity distribution of the adjacent patterns. Even in a pattern close to a wide transmission region in the clear field region, the light intensity distribution hardly changes, and the influence of local flare can be significantly reduced. And it becomes possible to implement | achieve significantly reducing the dimensional difference of the resist pattern of the clear field area | region and dark field area | region which generate | occur | produce due to a local flare.

It is a figure which shows the cross-section of the photomask of this invention. It is a figure which shows the manufacturing process of the photomask of this invention. It is a figure which shows the cross-sectional horizontal construction of the conventional photomask. It is a figure which shows the mask pattern for evaluating the influence by a local flare. It is a figure which shows the result of having evaluated the window width dependence of line | wire width. It is a figure which shows the cross-section of the photomask of this invention, its light amplitude, and light intensity. It is a figure which shows the cross-sectional fabrication of the conventional photomask, its light amplitude, and light intensity. It is a figure which shows the resist pattern after exposure transfer by the photomask of this invention. It is a figure which shows the resist pattern after exposure transfer by the conventional photomask. It is a figure which shows the optical lithography exposure technical concept.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 21, 31 ... Transparent substrate 12, 22 ... Semi-transparent film | membrane 13, 32 ... Light shielding film 14 ... Opening part 23 ... Electron beam resist 24 ... Electron beam 25 ... Light shielding film 26 ... 2nd electron beam resist 40 ... Photomask 41 ... Clear field region 42 ... Dark field region 43 ... Line 44 ... Clear field region window width 61, 71 ... Photomask 81, 91 ... Line 82, 92 ... Opening (space)
DESCRIPTION OF SYMBOLS 101 ... Wafer 102 ... Exposure light source 103 ... Photomask 104 ... Exposure projection system lens

Claims (12)

A photomask having a translucent film formed on a transparent substrate, and a light-shielding film formed on the translucent film and patterned,
The translucent film is patterned in a region other than the region corresponding to the dark field region of the photomask, patterned so as not to exist in the opening region of the light shielding film in the dark field region , and clearing the photomask A photomask formed in a region corresponding to a field region . The translucent film contains at least one selected from the group consisting of tantalum silicide (TaSi), zircon silicide (ZrSi), molybdenum silicide (MoSi), chromium fluoride (CrF), and silicon oxide (SiO ₂ ). The photomask according to claim 1, wherein the photomask is one.   3. The photomask according to claim 1, wherein the light-shielding film contains at least one selected from the group consisting of chromium (Cr) and chromium fluoride (CrF). The photomask according to claim 3, wherein the light shielding film is a film having etching resistance when the semitransparent film is etched .   5. The photomask according to claim 1, wherein a space interval of the pattern in the dark field region is less than 10 [mu] m. Applying a first resist to a blank mask in which a translucent film is formed on a transparent substrate;
Patterning a portion corresponding to a dark field region in a region other than a portion corresponding to a clear field region of the first resist ;
Etching the translucent film exposed by patterning the first resist ;
Removing and cleaning the first resist;
Forming a light shielding film on the transparent substrate and the semitransparent film exposed by peeling and cleaning the first resist ; and
Applying a second resist on the light shielding film;
Patterning portions corresponding to the dark field region and the clear field region in the second resist ;
Etching the light shielding film exposed by patterning the second resist;
A photomask manufacturing method comprising at least a step of removing the second resist.   7. The photomask manufacturing method according to claim 6, wherein the first and second resists are electron beam resists. The translucent film contains at least one selected from the group consisting of tantalum silicide (TaSi), zircon silicide (ZrSi), molybdenum silicide (MoSi), chromium fluoride (CrF), and silicon oxide (SiO ₂ ). 8. The method of manufacturing a photomask according to claim 6, wherein the photomask is a thing.   The said light shielding film contains at least 1 sort (s) chosen from the group which consists of chromium (Cr) and chromium fluoride (CrF), The Claim 6 thru | or 8 characterized by the above-mentioned. Photomask manufacturing method. The method for manufacturing a photomask according to claim 9, wherein the light shielding film is a film having etching resistance when the semitransparent film is etched .   The method of manufacturing a photomask according to any one of claims 6 to 10, wherein an interval between patterns in the dark field region is less than 10 µm. A photomask having a translucent film formed on a transparent substrate and a patterned light-shielding film formed on the translucent film, the opening of the light-shielding film corresponding to a dark field region of the photomask An exposure method characterized by exposing with an F2 line using a photomask in which the translucent film in the portion is removed and the translucent film is formed in a clear field .

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