JP2006047571A - Phase shift mask and exposure method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase shift mask for forming a fine line pattern at a relatively low cost and to provide an exposure method using the mask. <P>SOLUTION: The mask pattern 10 is used for exposing a line pattern in a photolithographic process. The mask pattern 10 is divided into two areas: a center area extended along the center line; and a peripheral area 12 with a constant width W surrounding the center area. The center area is further divided into a plurality of square unit areas 11 arranged in adjacent to each other along the center line, wherein a first phase shifter portion 21 to invert the phase of light is formed in the center of each unit area 11 in such a manner that the phase shifter portion 21 is laid axisymmetric around the center point of each unit area 11 and has 50% area of each unit area 11. A second phase shifter portion 22 to invert the phase of light is formed all over the peripheral area 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a phase shift mask for exposing a fine line pattern in a photolithography process when a circuit pattern such as a TFT is formed on a transparent insulating substrate such as a glass substrate or a plastic substrate, and to use the same. Related to the exposure method.

  In order to improve the performance of the TFT, it has been studied to miniaturize the TFT. In order to make a TFT fine and manufacture, it is necessary to increase the resolution of an exposure apparatus used there. The resolution of the exposure apparatus for TFT is currently about 1.5 μm or 3 μm. Attempting to increase the resolution further reduces the depth of focus. For example, when the resolution exceeds about 0.8 μm, the depth of focus becomes shallower than the glass thickness deviation (about 9 μm / 100 mm □) of the glass on which the TFT is formed, and a desired resist pattern cannot be formed. . For example, the width of the line becomes thick, and adjacent lines stick to each other.

  In the field of LSI, with the miniaturization of semiconductor elements, an exposure method (phase shift method) using a phase shift mask has been adopted for the purpose of improving resolution and depth of focus in an exposure process. However, the phase shift method still has the following problems as described in, for example, “Ultra-fine processing technology” (Ohm Co., pp. 29-41).

  That is, by adopting the phase shift method, the resolution and depth of focus at the time of exposure can be improved. In that case, there is no problem with an infinitely long line and space pattern, but there is a problem with an actual mask pattern. That is, in the actual mask pattern, since the pattern length is finite, as shown in FIG. 12, when exposed using the mask pattern in which the light shielding film 61 and the phase shifter 62 are arranged, as shown in FIG. Lines 64 that are not originally required are generated in the resist pattern 63 after development.

  As methods for preventing the generation of such unnecessary lines, the following methods have been proposed so far. One of them is to prevent the generation of unnecessary lines as shown in FIG. 14 by changing the phase in multiple stages at the periphery of the phase shifter 62 as shown in FIG.

  Another method is to remove the latent image of unnecessary lines before development, which is caused by using the phase shift mask (FIG. 11) as described above, by performing double exposure. That is, after performing the first exposure using the mask pattern in which the light shielding film 61 and the phase shifter 62 are arranged as shown by the broken line in FIG. 15, the solid line in FIG. The second exposure is performed using a mask pattern in which an opening 65 is provided in the light shielding film so that the exposure light strikes the latent image as shown. By removing the latent image by double exposure in this way, it is possible to prevent generation of unnecessary lines in the resist pattern after development.

  Although solutions like these are known, the former method increases the number of steps when manufacturing a phase shift mask, leading to an increase in the manufacturing cost of the mask, and the latter method increases the number of masks. There is a problem that the throughput of the exposure process is reduced.

  Further, Optical Microlithography 16 (Part Two), pp. In order to prevent the generation of unnecessary lines as described above, the following auxiliary pattern (referred to as “rim”) is proposed in 979-985. That is, as shown in FIG. 16, an auxiliary pattern 72 (width W) for shifting the phase of light by 180 ° is provided around a mask pattern 71 (width Q) made of a Cr thin film. However, when this method is employed, there is a problem that two etching steps of etching of the Cr thin film and etching of the quartz substrate are required when manufacturing the mask.

  The 51st Applied Physics-related Joint Lecture Proceedings No. 2, p. 929, 28a-ZG-3 describes a technique for creating a desired light intensity distribution on the irradiated surface using a “duty modulation element”. Here, the duty modulation element is an optical phase modulation element in which fine uneven patterns (phase shifters) for shifting the phase of light by 180 ° are distributed on a quartz substrate. By changing the ratio of the area occupied by the concavo-convex pattern (referred to as “duty ratio”) regularly within the quartz substrate surface, various light intensity distributions can be created on the irradiated surface.

However, this document does not particularly describe the use of such a duty modulation element in the resist exposure process and the resolution and depth of focus in that case.
"Ultra fine processing technology" published by Ohm, pp. 29-41 Optical Microlithography 16 (Part Two), pp. 979-985 Proceedings of the 51st Joint Conference on Applied Physics 2, p. 929, 28a-ZG-3

  The present invention has been made in view of the above-described problems of the exposure method using the conventional phase shift mask. The object of the present invention is to provide a TFT on a transparent insulating substrate such as a glass substrate or a plastic substrate. It is an object of the present invention to provide a phase shift mask capable of exposing a fine line pattern at a relatively low cost and an exposure method using the same.

The phase shift mask of the present invention is
A phase shift mask used in a photolithography process in forming a circuit pattern on a transparent insulating substrate,
The band-shaped mask pattern for exposing the line pattern is divided into two regions, a central region extending on the center line and a peripheral region surrounding the central region with a certain width, and the central region is further Divided into a plurality of square unit areas arranged adjacent to each other on the center line,
In the center of each unit region, a first phase shifter that inverts the phase of light is axisymmetric with respect to the center point of each unit region and occupies 50% ± 10% of the area of each unit region Each formed,
A second phase shifter portion for inverting the phase of light is formed in the entire peripheral region.

  In the phase shift mask of the present invention, a strip-shaped mask pattern for exposing a line pattern is configured by arranging the first and second phase shifter portions under the above conditions. According to the phase shift mask of the present invention, by using only the arrangement pattern of the phase shifter portion without using a light shielding film such as a Cr thin film, the line patterns are made to interfere with each other on the exposure surface. Can be exposed. Note that the target value of the ratio of the area occupied by the first phase shifter portion in the unit region is 50% at which the maximum light shielding effect is obtained by light interference, but the processing accuracy limit of the phase shifter portion and Considering the tolerance, a sufficient light-shielding effect can be realized if it is about 50% ± 10%.

  According to the phase shift mask of the present invention, since the interference of light is used based on the principle of the phase shift method, the resolution and the depth of focus at the time of exposure are excellent. In addition, since the mask pattern for exposing the line pattern can be made only by processing the phase shifter portion without using the light shielding film, the manufacturing process of the mask for exposure can be simplified. .

  Preferably, the width of the peripheral region is 20% ± 7.6% of the width of the mask pattern, that is, 12.4% or more and 27.6% or less. By setting the width of the peripheral area within this range, a high resolution is ensured.

  The first phase shifter portion and the second phase shifter portion are formed by processing a concave portion or a convex portion on the surface of the substrate of the phase shift mask. At this time, the target value of the phase difference of the phase shifter portion is 180 degrees at which the maximum light shielding effect can be obtained by light interference. However, in consideration of the limit of processing accuracy of the phase shifter portion and its tolerance, 180 degrees ± If it is about 10%, a sufficient light shielding effect can be realized.

Here, when exposure is performed using the phase shift mask according to the present invention, as in the case of using the conventional phase shift mask, the numerical aperture NA and the coherence factor σ are appropriately set to be high. Resolution and depth of focus can be achieved. The coherence factor σ is defined by NA _i / NA (where NA _i is the numerical aperture of the illumination system and NA is the numerical aperture of the projection lens system). Further, the optimum value of the above values (NA, σ) can be found by calculating a light intensity distribution by performing simulation calculation.

  When exposure is performed using the phase shift mask according to the present invention, the appropriate value of the numerical aperture NA is about 6/7 of NA when a conventional mask of only a Cr thin film is used, and the coherence factor σ The appropriate value of is about the same as the case where a conventional mask of only a Cr thin film is used.

  For example, using a phase shift mask according to the present invention, i-line (wavelength: 365 nm) is used as an exposure light source in a 1 × projection exposure, and a chemically amplified resist is used as a resist, and the line is 0.5 μm wide. When exposing equally spaced line and space patterns, the preferred range of numerical aperture NA is 0.3 ± 0.01, and the preferred range of coherence factor σ is 0.75 or more and 0.85 or less.

  Similarly, when exposing an equally spaced line and space pattern consisting of 0.8 μm wide lines, the preferred numerical aperture NA is 0.185 ± 0.015 and the preferred coherence factor σ is It is 0.75 or more and 0.85 or less.

  By using the phase shift mask of the present invention, a deep depth of focus can be obtained as compared with the case of using a mask of only a light shielding film such as a conventional Cr thin film. In particular, in a thin film transistor manufacturing process, exposure is performed on the surface of a glass substrate having a relatively large plate thickness deviation, so that a deep depth of focus is required. Therefore, the phase shift mask according to the present invention is particularly useful as a means for realizing miniaturization of a thin film transistor.

  In addition, according to the phase shift mask of the present invention, a mask pattern for exposing a line pattern can be formed only by processing the phase shifter portion without using a light shielding film. The manufacturing cost can be reduced.

  In addition, according to the phase shift mask of the present invention, a deeper depth of focus can be obtained by using a projection lens system having a smaller numerical aperture than in the case of using a conventional mask of only a light shielding film. This facilitates the design and manufacture of the projection lens system.

  FIG. 1 shows an example of a mask pattern in a phase shift mask according to the present invention. Here, FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the center line c in FIG.

  This is a belt-like mask pattern used for exposing a line pattern in a photolithography process. The mask pattern 10 is formed on a transparent mask substrate 9 (for example, a glass substrate or a quartz glass substrate). The mask pattern 10 is first divided into two regions: a central region extending on the center line and a peripheral region 12 surrounding the central region with a certain width W. The central region is further divided into a plurality of square unit regions 11 arranged adjacent to each other on the central line. In the center of each unit region 11, a first phase shifter portion 21 that shifts the phase of light by 180 ° is axisymmetric with respect to the center point of each unit region 11 and 50% of the area of each unit region 11. Each is formed to occupy. In this example, the planar shape of the first phase shifter portion 21 is also a square shape. A second phase shifter portion 22 that shifts the phase of light by 180 ° is also formed in the entire peripheral region 12.

  The mask pattern 10 is, for example, an equidistant line-and-space pattern composed of lines having a width of about 0.5 μm to 0.8 μm in the case of the same magnification projection exposure.

The depth d of the first and second phase shifter portions 21 and 22 is given by the following equation, where λ is the wavelength of the exposure light source and n is the refractive index of the mask substrate 9 on which the phase shifter portion is formed:
d = λ / 2 (n−1)
That is, the depth d of the first and second phase shifters 21 and 22 is about 400 nm when the exposure light source is i-line (wavelength 365 nm) and the mask substrate 9 is quartz glass (n = 1.46). .

  For example, when a line pattern having a width of 0.5 μm is exposed by equal magnification projection, the width L of the mask pattern 10 is also 0.5 μm. At this time, the width W of the peripheral region 12 is appropriately about L / 5, that is, about 0.1 μm. Therefore, the length S of one side of each unit region 11 is about 3L / 5.

  Note that a preferable range of the width W of the peripheral region 12 will be described later using simulation calculation results.

  In the example shown in FIG. 1B, the first and second phase shifter portions 21 and 22 are formed by processing grooves (concave portions). However, as shown in FIG. Grooves may be processed in regions other than the first and second phase shifter portions 21 and 22, and the first and second phase shifter portions 21 and 22 may be convex portions.

  FIG. 3 shows another example of the mask pattern in the phase shift mask according to the present invention. Here, FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along the center line c in FIG.

  In this example, as shown in FIG. 3A, the planar shape of the first phase shifter portion 21 is circular. Other shapes and dimensions, that is, the width L of the mask pattern 10, the width W of the peripheral region 12, and the length S of one side of each unit region 11 are the same as the example shown in FIG. .

  In the example shown in FIG. 3B, the first and second phase shifter portions 21 and 22 are formed by processing grooves (concave portions). As shown, grooves may be processed in regions other than the first and second phase shifter portions 21 and 22, and the first and second phase shifter portions 21 and 22 may be convex portions.

  In the case of 1 × projection exposure, if circuit patterns such as TFT gate electrodes, gate wirings, and source / drain wirings are formed using the mask pattern shown in FIG. 1A or FIG. Is thinner than 1 μm, for example, a deep depth of focus can be obtained even when the thickness is 0.5 to 0.8 μm.

  In the above embodiment, the first and second phase shifters 21 and 22 are stepped by etching the glass substrate. However, the phase difference between the patterns, for example, 180 degrees may be given. A transparent thin film may be deposited on the surface, and the thin film may be etched to form patterns as shown in FIGS. For example, the first and second phase shifter portions 21 and 22 are formed by applying a glass film, and the first and second phase shifter portions 21 and 22 are formed by sputtering the SiO2 film. And a method of forming the first and second phase shifters 21 and 22 by forming a SiO2 film by a CVD method.

  Next, a method for performing exposure using the phase shift mask according to the present invention will be described.

  FIG. 5 shows an outline of an optical system when performing exposure using the phase shift mask based on the present invention.

In the figure, 51 is a phase shift mask, 52 is a glass substrate coated with a photoresist, 53 is an illumination system, 54 is a projection lens system, 55 is an NA stop, 56 is a pupil plane, 57 is an exposure light source, and 58 is An integrator 59 represents a condenser lens. The exposure light source 57 is, for example, a mercury lamp having a wavelength of 365 nm. The illumination optical system 53 includes, for example, an integrator 58 and a condenser lens 59. The integrator 58 is an optical system that collects light from the light source 57 and makes it uniform. The condenser lens 59 is an optical system that illuminates the phase shift mask 51 with uniform light. The exposure light is focused on the phase shift mask 51 by the illumination system 53. The exposure light that has passed through the phase shift mask 51 passes through the projection lens system 54 and the NA stop 55 disposed in the middle thereof, and is again focused on the surface of the glass substrate 52 to be exposed.

In this figure, the numerical aperture NA (generally meaning the numerical aperture of the projection lens system 54) is defined as “sin θ”, and the numerical aperture NA _i of the illumination system 53 is defined as “sin φ”. Further, the coherence factor σ is defined by “NA _i / NA”.

  When exposure is performed using the phase shift mask according to the present invention, as in the case of using the conventional phase shift mask, by setting the numerical aperture NA and the coherence factor σ appropriately, high resolution and deep A depth of focus can be realized. In addition, the optimum values of the above values (NA, σ) can be found by performing a simulation calculation to obtain the light intensity distribution on the exposed surface and its vicinity. Furthermore, although the optimum values of the above values (NA, σ) vary slightly depending on the type of resist, here, a chemically amplified resist is used.

  FIG. 6 shows a result obtained by simulation calculation of the depth of focus when exposure is performed using the phase shift mask according to the present invention. However, this calculation is based on the case where the mask pattern shown in FIG. 1 is used and a 0.5 μm line and space pattern is projected at the same magnification and a chemically amplified resist is used as the resist. is there. The width L of the mask pattern 10 is set to 0.5 μm, the width W of the peripheral region 12 is changed at three levels to be 0.05 μm, 0.1 μm, and 0.15 μm, and the numerical aperture NA is 0.27 to 0. The depth of focus for each case was determined by varying between .33. Note that the value of the coherence factor σ is constant at 0.8.

  As can be seen from FIG. 6, the maximum value of the depth of focus appears when the width W = 0.1 μm and NA = 0.3, and the value is ± 2.3 μm. In the figure, the point indicated by the symbol C is the maximum value of the depth of focus in the case of a conventional mask with only a Cr thin film. In the case of the conventional mask of only a Cr thin film, the maximum value appears when NA = 0.35, and the value is about ± 1.6 μm. It was also found that a relatively large depth of focus of about 2 μm can be obtained between NA = 0.29 and 0.31.

  For further comparison, FIG. 7 shows the result of the simulation calculation of the depth of focus when the exposure is performed using the phase shift mask (Cr thin film with an auxiliary pattern added) shown in FIG. Show. This calculation is also performed when a 0.5 μm line and space pattern is projected at the same magnification, and a chemically amplified resist is used as the resist. The width L of the mask pattern 10 and the peripheral region 12 The values of the width W, the numerical aperture NA, and the coherence factor σ are the same as those shown in FIG.

  As can be seen from FIG. 7, in this case as well, the maximum value of the depth of focus appears when the width W is 0.1 μm and NA = 0.3, and the value is ± 2.3 μm. That is, it can be seen that by using the phase shift mask according to the present invention, the same depth of focus as that of the phase shift mask in which the auxiliary pattern is added to the Cr thin film can be realized.

  FIG. 8 shows the result of the simulation calculation for the relationship between the coherence factor σ and the depth of focus when exposure is performed using the phase shift mask according to the present invention. However, this calculation is also performed when the mask pattern shown in FIG. 1 is used and a 0.5 μm line-and-space pattern is projected at the same magnification and a chemically amplified resist is used as the resist. The width L of the mask pattern 10 is 0.5 μm, and the width W of the peripheral region 12 is 0.1 μm. In this calculation, the numerical aperture NA was set to 0.3, and the value of the coherence factor σ was changed between 0.6 and 0.9, and the depth of focus for each case was obtained.

  As can be seen from FIG. 8, when the coherence factor σ is 0.75 or more, the depth of focus is 2 μm or more, and good results are obtained. The upper limit of the coherence factor σ is about 0.85. The reason is that if the coherence factor σ exceeds 0.85, it becomes difficult to design and manufacture the illumination system of the exposure apparatus.

  FIG. 9 shows a 0.8 μm line-and-space pattern isotope projection exposure using a phase shift mask according to the present invention, and the depth of focus when a chemically amplified resist is used as a resist by simulation calculation. The obtained result is shown. However, this calculation is performed when exposure is performed using a mask pattern similar to that shown in FIG. 1, and the width L of the mask pattern 10 is 0.8 μm. The width W of the peripheral region 12 is changed at three levels to 0.20 μm, 0.16 μm, and 0.1 μm, and the numerical aperture NA is changed between 0.17 and 0.2. Depth of focus was determined. The value of the coherence factor σ was constant at 0.8.

  As can be seen from FIG. 9, the maximum value of the depth of focus appears when the width W is 0.16 μm and NA = 0.18, and the value is ± 7.3 μm. Moreover, a large depth of focus of 6.5 μm or more was obtained between NA = 0.17 and 0.19. In the figure, the point indicated by the symbol D is the maximum value of the depth of focus in the case of a conventional mask made of only a Cr thin film. In the case of the conventional mask of only a Cr thin film, the maximum value appears when NA = 0.21, and the value is about ± 5 μm.

  FIG. 10 shows a coherence factor σ and focus when a 0.8 μm line-and-space pattern is projected at the same magnification using a phase shift mask according to the present invention and a chemically amplified resist is used as the resist. The result of having obtained the relationship of depth by simulation calculation is shown. However, this calculation is also performed when exposure is performed using a mask pattern similar to that shown in FIG. 1, and the width L of the mask pattern 10 is set to 0.8 μm and the width W of the peripheral region 12 is set. Were changed at three levels of 0.1 μm, 0.16 μm and 0.20 μm. In this calculation, the numerical aperture NA was set to 0.18, and the coherence factor σ was changed between 0.6 and 0.9, and the depth of focus for each case was obtained.

  As can be seen from FIG. 10, when the coherence factor σ is 0.75 or more, the depth of focus is 6 μm or more, and good results are obtained. Note that the upper limit of the coherence factor σ is about 0.85 for the reason mentioned above.

  From the results shown in FIGS. 6, 8, 9 and 10, if the width W of the peripheral region 12 is within the range of 20% ± 7.6% of the width L of the mask pattern, a large depth of focus can be obtained. I understand that.

It is a figure which shows an example of the mask pattern in the phase shift mask based on this invention, Comprising: (a) is a top view, (b) is sectional drawing along a centerline. Sectional drawing which shows the other example of the mask pattern in the phase shift mask based on this invention. It is a figure which shows the other example of the mask pattern in the phase shift mask based on this invention, Comprising: (a) is a top view, (b) is sectional drawing along a centerline. Sectional drawing which shows the other example of the mask pattern in the phase shift mask based on this invention. The figure which shows the outline | summary of the optical system at the time of performing exposure using the phase shift mask based on this invention. Using the phase shift mask according to the present invention, a 0.5 μm line-and-space pattern is projected at the same magnification, and the relationship between the numerical aperture NA and the depth of focus when a chemically amplified resist is used as a resist is simulated. The figure which shows the result calculated | required by calculation. For comparison, a phase shift mask (FIG. 16) in which an auxiliary pattern is added to a Cr thin film is used to perform projection with the same magnification, and the relationship between the numerical aperture NA and the depth of focus when a chemically amplified resist is used as a resist. The figure which shows the result calculated | required by simulation calculation. Using the phase shift mask according to the present invention, 0.5 μm line-and-space pattern equal magnification projection exposure is performed, and the relationship between the coherence factor σ and the depth of focus when a chemically amplified resist is used as a resist, The figure which shows the result calculated | required by simulation calculation. Using the phase shift mask according to the present invention, a 0.8 μm line-and-space pattern is projected at the same magnification, and the relationship between the numerical aperture NA and the depth of focus when a chemically amplified resist is used as a resist is simulated. The figure which shows the result calculated | required by calculation. Using the phase shift mask according to the present invention, 0.8 × m line-and-space pattern equal magnification projection exposure is performed, and the relationship between the coherence factor σ and the depth of focus when a chemically amplified resist is used as a resist, The figure which shows the result calculated | required by simulation calculation. It is a figure which shows an example of the conventional one-stage type phase shift mask, Comprising: (a) is a top view, (b) is sectional drawing along the AA. The figure explaining the resist pattern formed when it exposes using the phase shift mask shown in FIG. The top view which shows an example of the conventional multistage type phase shift mask. FIG. 14 is a diagram illustrating a resist pattern formed when exposure is performed using the phase shift mask illustrated in FIG. 13. The figure which shows an example of the mask pattern used when performing double exposure in order to remove the latent image of an unnecessary line, The figure which shows an example of the phase shift mask in which the auxiliary pattern which consists of phase shifters was provided around the mask pattern comprised by Cr thin film.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Mask pattern, 11 ... Unit area | region, 12 ... Peripheral area | region, 21 ... 1st phase shifter part, 22 ... 2nd phase shifter part, 51 ... Phase shift mask 52 ... Glass substrate, 53 ... Illumination system, 54 ... Projection lens system, 55 ... NA stop, 56 ... Pupil plane, 57 ... Exposure light source, 58 ... Integrator, 59 ... condenser lens, 61 ... light shielding film, 62 ... phase shifter, 63 ... resist pattern, 64 ... unnecessary line, 65 ... opening, 71 ... mask pattern, 72: Auxiliary pattern.

Claims (5)

A phase shift mask used in a photolithography process in forming a circuit pattern on a transparent insulating substrate,
The band-shaped mask pattern for exposing the line pattern is divided into two regions, a central region extending on the center line and a peripheral region surrounding the central region with a certain width, and the central region is further Divided into a plurality of square unit areas arranged adjacent to each other on the center line,
In the center of each unit region, a first phase shifter that inverts the phase of light is axisymmetric with respect to the center point of each unit region and occupies 50% ± 10% of the area of each unit region Each formed,
A phase shift mask characterized in that a second phase shifter portion for inverting the phase of light is formed in the entire peripheral region.   2. The phase shift mask according to claim 1, wherein the width of the peripheral region is 20% ± 7.6% of the width of the mask pattern.   2. The phase shift mask according to claim 1, wherein the first phase shifter portion and the second phase shifter portion are either concave portions or convex portions having a phase difference of 180 ° ± 10%. An exposure method using the phase shift mask according to claim 1 and exposing an equidistant line and space pattern composed of 0.5 μm wide lines by equal magnification projection exposure using i-line as an exposure light source. And
An exposure method using a phase shift mask, wherein the numerical aperture NA is 0.3 ± 0.01 and the coherence factor σ is 0.75 or more and 0.85 or less. An exposure method that uses the phase shift mask according to claim 1 and uses i-line as an exposure light source and exposes an equidistant line and space pattern composed of 0.8 μm wide lines by equal magnification projection exposure. And
An exposure method using a phase shift mask, wherein a numerical aperture NA is 0.185 ± 0.015, and a coherence factor σ is 0.75 or more and 0.85 or less.

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