JP2005045138A - Method of forming resin film, and method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize curing of a resin film at a low temperature in a short time by irradiating the resin film with a light having a suitable wavelength. <P>SOLUTION: A method for forming the resin film includes a step of forming the resin film 12 having a triple bond of carbons and double bond of carbons, then cutting only the triple bond of the carbons except the double bond of the carbons of the resin film 12 by irradiating with the light, and curing the resin film 12 by crosslinking. The resin film 12 is made of a film formed by coating with a polyarylether resin. The method also includes a step of curing the resin film 12 by cutting only the triple bond of the carbons except the double bond of the carbons of the resin film 12 by irradiating the resin film 12 with a light having a wavelength of 190 nm or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a resin film that can be easily cured at a low temperature, and a method for manufacturing a semiconductor device in which an interlayer insulating film is formed using the method for forming a resin film.

  In recent years, with the high integration of semiconductor devices, the processing dimensions of wiring required for circuit formation have been continually miniaturized, and the number of wirings has been increasing. In addition to high integration, low power consumption and high-speed operation are required.

  The increase in wiring resistance and wiring capacity caused by the miniaturization of wiring and the reduction in wiring pitch leads to deterioration of the operation speed and increase of power consumption of the semiconductor device. Therefore, in order to meet the demands for high integration, low power consumption, and high-speed operation, multilayer wiring using copper with low electrical resistance as the wiring material and low dielectric constant film as the interlayer insulating film is indispensable. become.

  Therefore, instead of the silicon oxide film formed by the chemical vapor deposition (CVD) method or the spin-on coating method that is widely used as an insulating film material for the inter-wiring insulating film and the interlayer insulating film, an oxide containing fluorine is used. The use of low dielectric constant materials such as silicon films, silicon oxide films containing carbon, hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), polyaryl ether resins, and fluororesins has been studied. ing. Hereinafter, an insulating film formed of these low dielectric constant materials is referred to as a low dielectric constant insulating film (Low-k film). In particular, examples of the coating film of the polyaryl ether resin applied in the present invention include SiLK (TM) of Dow Chemical Company, FLARE (TM) of Honeywell Company, GX-III (TM), and the like. .

  However, it is known that, among the low dielectric constant insulating films, for example, a coating type polyarylether resin-based material does not sufficiently cure unless heat treatment is performed at a high temperature of 400 ° C. or more for 60 minutes or more. In addition, when this coating type polyaryl ether resin material is used for an interlayer insulating film and copper having a low electrical resistance is applied as a wiring material, it is known that thermal budget becomes a problem by applying a heat treatment at 400 ° C. It has been. For example, as a problem caused by this thermal budget, it is known that reliability deteriorates due to the occurrence of migration, diffusion and peeling of copper due to an interlayer insulating film or copper thermal stress fluctuation.

  Further, a technique is known in which a spin-on polymer film is used as a low dielectric constant insulating film and is cured by exposing it to an electron beam (see, for example, Patent Document 1).

  However, it is difficult to control the penetration depth of the electron beam by the technique of curing the spin-on polymer film by electron beam exposure. When the low dielectric constant insulating film is laminated, the upper low dielectric constant insulating film is not formed. The electron beam irradiated for curing may be exposed to the electron beam a plurality of times by reaching the lower dielectric constant insulating film. In this way, the low dielectric constant insulating film exposed to the electron beam more than necessary becomes a brittle film because the bonds are broken. Further, when the electron beam reaches the transistor and capacitor portions, charges are accumulated in the insulating film portion, and the insulating film is destroyed. Furthermore, since the basic skeleton portion of the spin-on polymer film is broken by the electron beam and an unexpected bond is generated, there arises a problem that, for example, the film shrinks or the moisture resistance deteriorates.

Special table 2000-511006 gazette

  The problem to be solved is that a resin film having a carbon double bond and a carbon triple bond, such as a polyaryl ether resin, has a carbon triple bond in a state in which the carbon double bond remains. In order to cure by cutting and crosslinking reaction, heat treatment at 400 ° C. or higher is required. In addition, when such high-temperature heat treatment is performed, it is difficult to apply the resin film to an insulating film of a wiring using copper that has a thermal budget problem.

  According to the method of forming a resin film of the present invention, after a resin film having a carbon triple bond and a carbon double bond is formed, the carbon double bond of the resin film is left by light irradiation to leave a carbon triple bond. The most important feature is that the resin film is cured by cutting only the bonds. In particular, the resin film is a film formed by applying a polyaryl ether resin, and by irradiating the resin film with light having a wavelength of 190 nm or less, carbon double bonds of the resin film are left, Only the triple bond is cut and the resin film is cured.

  According to the method of manufacturing a semiconductor device of the present invention, after an insulating film used between wirings or between wiring layers of a semiconductor device is formed of a resin film having a carbon triple bond and a carbon double bond, the resin film is irradiated by light irradiation. The most important feature is that the resin film is cured by cutting only the carbon triple bond while leaving the carbon double bond. In particular, the resin film is a film formed by applying a polyaryl ether resin, and by irradiating the resin film with light having a wavelength of 190 nm or less, carbon double bonds of the resin film are left, Only the triple bond is cut and the resin film is cured.

  In the resin film forming method of the present invention, since the resin film is cured by light irradiation, the resin film can be cured at a low processing temperature of less than 400 ° C., particularly 200 ° C. or less, in a short time. There is an advantage that the present invention can be applied to a method for forming an inter-wiring insulating film and an inter-wiring insulating film having a wiring structure using copper wiring without causing a budget problem.

  In the method of manufacturing a semiconductor device of the present invention, since the resin film is cured by light irradiation, the resin film can be cured at a low temperature of less than 400 ° C., particularly 200 ° C. or less, and in a short time, so there is a problem of thermal budget. There is an advantage that the present invention can be applied to a method for forming an inter-wiring insulating film and an inter-wiring insulating film having a wiring structure using copper wiring in a semiconductor device.

  The purpose of forming a resin film to be used for an insulating film having a wiring structure using copper wiring is realized without causing a thermal budget problem by curing the resin film by light irradiation.

  An embodiment according to a method for forming a resin film of the present invention will be described with reference to a manufacturing process sectional view shown in FIG. In this embodiment, as an example, a method for forming a polyarylether-based resin film as a resin having a carbon triple bond and a carbon double bond will be described.

  As shown in (1) of FIG. 1, a coating type polyaryl ether resin having a carbon triple bond and a carbon double bond is applied on a substrate 11 by a normal coating method to form a resin film. 12 is formed. As this coating type polyarylether resin, for example, commercially available products such as SiLK of Dow Chemical Company, FLARE of Honeywell Company, GX-III, and the like can be used.

  Next, as shown in FIG. 1B, the resin film 12 is irradiated with light hν. As this light hν, light having a wavelength of 100 nm to 190 nm is used. For example, a light source having an emission wavelength of 190 nm or less, preferably 140 nm or more and 160 nm or less is used. Since the light hν is light having a wavelength of 190 nm or less, only the carbon triple bond is cut without breaking the carbon double bond. The reason is that the double bond of carbon is cut by irradiation with light having a wavelength of 197 nm or more, and in order to avoid this, the wavelength is set to 190 nm or less. On the other hand, the bond energy of the triple bond of carbon is 791 J / mol, and the wavelength most easily absorbed by this bond energy is 150 nm. Further, if the wavelength is too short like an electron beam or an X-ray, the coupling is unnecessarily cut as described in the prior art, which is not preferable. Therefore, the wavelength of light applied to the resin film 12 is set to 100 nm or more. In addition, since the wavelength at which the triple bond of carbon is cut is 150 nm, it is effective to use a light source that oscillates a wavelength close to that wavelength. Therefore, the emission wavelength of the light source is set to 140 nm or more and 160 nm or less.

  In this way, the resin film 12 is cured by cutting off only the carbon triple bond leaving the carbon double bond of the resin film 12 by the light irradiation. At that time, it is preferable to heat the substrate 11 at a temperature not higher than the thermal decomposition temperature of the resin film 12. By heating the substrate 11, the curing time of the resin film 12 is shortened. The heating temperature is set to be equal to or lower than the thermal decomposition temperature of the resin film 12. However, when the resin film 12 is used for an insulating film of a copper wiring, for example, a temperature that does not cause a thermal budget such as copper migration, For example, it shall be 200 degrees C or less. Since the curing time of the resin film 12 varies depending on the heating temperature of the substrate 11, the heating temperature and the light irradiation time are appropriately selected. As a result, the resin film 12 is cured at a lower temperature and in a shorter time than conventional. In this way, a low dielectric constant insulating film made of the resin film 12 is formed.

  Further, in the method for forming a resin film according to the present invention, even if light irradiation is performed excessively, the double bond of carbon is not cut, so that the resin film bonding that occurs when an electron beam is used is used. Is not divided into a brittle film. In addition, there is no problem that a new unexpected bond is generated due to the breakage of the bond and the film shrinks or the moisture resistance is deteriorated.

  A first embodiment of the method for manufacturing a semiconductor device of the present invention will be described with reference to the process chart shown in FIG.

  As shown in FIG. 1A, a resin film 12 of polyaryl ether resin is formed on the substrate 11 by a coating method. Here, as an example, a polyaryl ether resin called SiLK was used.

Thereafter, as shown in FIG. 1 (2), the resin film 12 formed on the substrate 11 is irradiated with light hν having a wavelength of 190 nm or less to cut the double bond of carbon in the resin film 12. The resin film 12 was hardened by cutting the triple bond of carbon and causing a crosslinking reaction. For the light hν, for example, a fluorine (F ₂ ) laser beam having an oscillation wavelength of 157 nm was used. The irradiation time of the light L was 15 minutes, and the substrate temperature was 23 ° C. (room temperature).

  A second embodiment of the method for manufacturing a semiconductor device according to the present invention will be described with reference to the process chart shown in FIG. The second embodiment is a case where the substrate 11 is heated and the light irradiation time is shortened as compared with the first embodiment.

  As shown in FIG. 1A, a resin film 12 of polyaryl ether resin is formed on the substrate 11 by a coating method. Here, as an example, a polyaryl ether resin called SiLK was used.

Thereafter, as shown in FIG. 1 (2), the resin film 12 formed on the substrate 11 is irradiated with light hν having a wavelength of 190 nm or less to cut the double bond of carbon in the resin film 12. The resin film 12 was hardened by cutting the triple bond of carbon and causing a crosslinking reaction. For the light hν, for example, a fluorine (F ₂ ) laser beam having an oscillation wavelength of 157 nm was used. The irradiation time of the light hν was 5 minutes, and the substrate temperature was 150 ° C.

  Next, as a comparative example, a conventional resin film curing treatment (treatment temperature: 400 ° C., treatment time: 60 minutes) is performed on the substrate 11 on which the resin film 12 of polyaryl ether resin (SiLK) is formed. It was.

  And the Fourier-transform infrared spectral absorption spectrum of the resin film hardened | cured by the said Example 1, Example 2, and the comparative example was investigated. The result is shown in FIG. In FIG. 2, the vertical axis indicates the intensity of absorbed light, and the horizontal axis indicates the wave number of infrared rays. As shown in FIG. 2, it was found that all of Examples 1, 2 and Comparative Examples had similar absorption spectra. Therefore, it was confirmed that by using the method for forming a resin film of the present invention, the resin film can be cured at a low temperature and in a short time without any difference from a resin film subjected to a conventional curing process.

  As described above, in the method for forming the resin film according to Example 1 and Example 2, if the light irradiation is performed at room temperature, the treatment is performed for 15 minutes, or if the light irradiation is performed by heating the substrate 11 to 150 ° C., the process is 5 minutes. It's all you need. That is, since the resin film 12 is cured at a low temperature in a short time, the thermal budget generated by applying a heat treatment at a high temperature of 60 minutes at 400 ° C. like the conventional resin film curing process. It does not cause a problem.

The present inventor repeated various studies and experiments in order to achieve the curing treatment of the polyaryl ether-based resin film at a low temperature and in a short time, and obtained the following conclusions. By irradiating the polyaryl ether resin film with fluorine (F ₂ ) laser light (wavelength 157 nm), the carbon triple bond, which is a reactive group of the polyaryl ether resin, is selectively cut to form a double bond. As a result, it was found that crosslinking could proceed. For example, in the case of a coating film of a polyaryl ether resin (SiLK) having a chemical structure as shown in FIG. 3 (1), by irradiating a wavelength (157 nm) corresponding to the binding energy of this carbon triple bond, As shown in FIG. 3 (2), it was found that the carbon triple bond can be selectively cleaved and crosslinked.

  Hereinafter, an example of the details will be described with reference to an explanatory diagram of the curing reaction of the resin film shown in FIG. The resin film 12 is cured by the same reaction in both the resin film forming method of Example 1 and the resin film forming method of Example 2.

  As shown in FIG. 3A, a polyaryl ether resin (for example, SiLK) generally has a structure represented by chemical formula (1). That is, a divalent group Ar having a triple bond of carbon and having a phenyl group Ph bonded to one bond of the triple bond of carbon is derived from an aromatic hydrocarbon. The benzene ring is bonded to the benzene ring via the divalent group Ar derived from the other aromatic hydrocarbon, and the benzene ring is bonded to the benzene ring in the same manner as described above. A group consisting of n groups having a triple bond of carbon via a divalent group Ar derived from a group hydrocarbon, and having a phenyl group Ph bonded to one bond of the triple bond carbon. A phenyl group Ph is bonded to a bond to which a divalent group Ar derived from each aromatic hydrocarbon of each benzene ring is not bonded.

Next, as shown in FIG. 3B, the fluorine (F ₂ ) laser beam hν having an oscillation wavelength of 157 nm is irradiated onto the resin film 12 made of the polyaryl ether resin having the above structure. By irradiation with this light hν, the triple bond of carbon is cut and a crosslinking reaction occurs. At this time, the carbon double bond remains without being broken. As a result, the structure shown in chemical formula (2) is obtained. That is, it has a double bond of carbon, a divalent group Ar derived from an aromatic hydrocarbon is bonded to one bond of the carbon having the double bond, and one of the carbons having the double bond A phenyl group Ph is bonded to a bond, and the remaining two bonds of the carbon having the double bond are bonded to another carbon bond having a double bond.

As described above, even when the polyarylether resin is irradiated with fluorine (F ₂ ) laser light (wavelength 157 nm), the carbon double bond is not broken, so that the curing treatment does not proceed excessively. This is because the absorption energy is low because the bond energy of the carbon double bond is on the shorter wavelength side than the wavelength of the fluorine (F ₂ ) laser beam.

  Further, as described in the second embodiment, the resin film 12 is cured at a higher speed by heating the substrate 11 together with light irradiation at a temperature that does not cause a problem of thermal budget such as copper migration. Processing can proceed. As a matter of course, the upper limit of the temperature is not more than the thermal decomposition temperature of the resin film 12 and not more than a temperature at which the problem of thermal budget does not occur. For example, when a polyaryl ether resin film is used for an interlayer insulating film of a copper wiring, a problem of thermal budget such as copper migration may occur when the temperature exceeds 200 ° C. Therefore, the temperature at which the substrate 11 is heated Was, for example, 200 ° C. or lower. In addition, although a minimum becomes room temperature or more, when taking out the effect of heating, 150 degreeC or more heating is required.

  In each of Examples 1 and 2 described above, the fluorine laser beam having an oscillation wavelength of 157 nm was used. The wavelength for curing the polyarylether-based resin film 12 applied to the substrate 11 was 100 nm to 190 nm. The light is not limited to fluorine laser light.

  The method for curing an insulating film according to the present invention contains a carbon triple bond as in a coating type polyaryl ether resin film, and is crosslinked when the carbon triple bond is cut to form a carbon double bond. As long as it is formed in a laminated structure having an interlayer insulating film that progresses in curing, the composition can be applied without restriction. In particular, in a method for manufacturing a semiconductor device, it is effective to apply a polyaryl ether resin-based low dielectric constant coating film as a treatment for curing at a low temperature.

  Next, an embodiment according to a method for manufacturing a semiconductor device of the present invention will be described with reference to manufacturing process cross-sectional views shown in FIGS. In this embodiment, as an example, a method for manufacturing a semiconductor device in which a multilayer wiring is formed using a resin having a carbon triple bond and a carbon double bond will be described. Here, as an example, a case where a polyaryl ether resin is used as a resin having a carbon triple bond and a carbon double bond will be described.

  As shown in FIG. 4 (1), an insulating film 22 is formed on the substrate 21, and a wiring groove 23 is formed in the insulating film 22. In the wiring groove 23, a copper first wiring 25 having a groove wiring structure is formed through a barrier metal layer 24 that prevents diffusion of copper, intrusion of oxygen and moisture, and the like. A barrier metal layer 26 is formed on the first wiring 25 to prevent copper diffusion, oxygen and moisture intrusion, and the like. A resin first resin film 31 having a carbon triple bond and a carbon double bond as a low dielectric constant insulating film is formed on the insulating film 22 on which the first wiring 25 is formed by a coating method. Form a film. As the first resin film 31, a polyaryl ether resin film can be used. As a polyaryl ether resin, SiLK, FLARE, GX-III, etc. as described above can be used as an example. Next, the first resin film 31 is cured by light irradiation.

Thereafter, as described in the method for forming the resin film, light having a wavelength for breaking the triple bond of carbon without breaking the double bond of carbon and causing the crosslinking reaction to proceed, for example, a wavelength of 100 nm to 190 nm is used. 1 Resin film 31 is irradiated. Here, as an example, fluorine (F ₂ ) laser light (wavelength = 157 nm) was used. For example, when the substrate temperature is room temperature, the irradiation time is 15 minutes, and when the substrate temperature is 150 ° C., the irradiation time is 5 minutes. The irradiation time is appropriately changed depending on the substrate temperature so that the first resin film 31 is cured.

  Next, as shown in FIG. 4B, an insulating film 32 having etching selectivity with the first resin film 31 is formed on the first resin film 31. The insulating film 32 is formed of, for example, a low dielectric constant silicon oxide insulating film having a dielectric constant of 3.5 or less. Thereafter, a resist mask (not shown) for forming a connection hole is formed on the insulating film 32 by a normal resist coating and lithography technique, and then an opening is formed in the insulating film 32 by an etching technique using this resist mask. 33 is formed. Thereafter, the resist mask is selectively removed with respect to the base.

  Next, as shown in FIG. 5 (3), a second resin film 34 of a resin having a carbon triple bond and a carbon double bond as a low dielectric constant insulating film on the insulating film 32 by a coating method. Is deposited. As the second resin film 34, a polyaryl ether resin film can be used, and the same material as that used for the first resin film 31 can be used. Next, the second resin film 34 is cured by light irradiation.

  That is, as described in the method for forming the resin film, light having a wavelength for breaking the carbon triple bond without breaking the carbon double bond and causing the crosslinking reaction to proceed, for example, a wavelength of 100 nm or more and 190 nm or less. 2 The resin film 34 is irradiated. Here, as an example, fluorine laser light (wavelength = 157 nm) was used. For example, when the substrate temperature is room temperature, the irradiation time is 15 minutes, and when the substrate temperature is 150 ° C., the irradiation time is 5 minutes. The irradiation time can be appropriately changed depending on the substrate temperature so that the second resin film 34 is cured.

  Next, as shown in FIG. 5D, a mask forming film 35 having etching selectivity with the second resin film 34 is formed on the second resin film 34. The mask formation film 35 is formed of an inorganic film such as silicon oxide or silicon nitride. Thereafter, a resist mask (not shown) for forming a wiring groove is formed on the mask forming film 35 by ordinary resist coating and lithography techniques, and then the mask forming film 35 is formed by an etching technique using this resist mask. Opening 36 is formed.

  Then, as shown in FIG. 6 (5), a wiring groove 37 is formed in the second resin film 34 using the mask forming film 35 as an etching mask. Further, a connection hole 38 is formed in the first resin film 31 using the insulating film 32 as an etching mask. Note that the resist mask may be removed when the wiring trench 37 and the connection hole 38 are formed. Further, the insulating film 32 at the bottom of the wiring trench 37 may be removed.

  Next, as shown in FIG. 6 (6), a barrier metal layer 39 that prevents diffusion of copper, intrusion of oxygen, moisture, and the like is formed on the inner surfaces of the connection hole 38 and the wiring groove 37 by a normal groove wiring formation technique. Form. This barrier metal layer 39 is also formed on the mask formation film 35. Then, after forming a copper seed layer (not shown), the connection hole 38 and the wiring groove 37 are filled with copper by copper plating. At this time, copper is deposited on the second resin film 34 together with the barrier metal layer 39 via the mask formation film 35. Next, excess copper and the barrier metal layer on the second resin film 34 are removed by a chemical mechanical polishing (CMP) method, and the inside of the connection hole 38 and the wiring groove 37 is interposed via the barrier metal layer 39. The second wiring 40 and the connection part 41 made of copper are formed. In this CMP, the mask forming film 35 serves as a polishing stopper. Thereafter, a barrier metal layer (not shown) is formed on the second wiring 40. Thereafter, the mask forming film 35 having a relatively high dielectric constant may be removed.

  In the above manufacturing method, the barrier metal layer formed on the upper surface of each of the first wiring 25 and the second wiring 40 can be formed of, for example, a cobalt tungsten phosphorus (Co—WP) film, or silicon nitride It can also be formed of a nitride film such as a film. Alternatively, a silicon carbide film can be used. Further, copper or a copper alloy can be used as the main material of the copper wiring.

  In the method of manufacturing a semiconductor device, even after the copper wiring that is feared to be migrated by heat is formed, the low dielectric constant resin films (the first resin film 31 and the second resin film 34) can be formed. become able to. For this reason, it becomes possible to form an inter-wiring insulating film and an inter-wiring interlayer insulating film with a resin film made of a polyaryl ether resin for the purpose of reducing the inter-wiring capacitance and the inter-wiring interlayer capacitance. As a result, the signal delay of the wiring is improved, and the signal can be propagated at a higher speed than before. The inter-wiring insulating film refers to an insulating film coupled between wirings in the same layer, and refers to an insulating film between wirings in layers different from the wiring interlayer insulating film.

  The method for forming a resin film and the method for manufacturing a semiconductor device according to the present invention include a resin film having a carbon triple bond and a carbon double bond, for example, a coating film such as a polyaryl ether resin at a temperature of 200 ° C. or lower. It is most suitable for applications that require curing at a low temperature and in a short time, and can be applied to any manufacturing method that requires such a method.

It is manufacturing process sectional drawing which shows embodiment which concerns on the formation method of the resin film of this invention. It is a Fourier-transform infrared spectral absorption spectrum figure of the resin film hardened | cured by Example 1, Example 2, and the comparative example. It is explanatory drawing of hardening reaction of a polyaryl ether resin film. It is manufacturing process sectional drawing which shows embodiment which concerns on the manufacturing method of the semiconductor device of this invention. It is manufacturing process sectional drawing which shows embodiment which concerns on the manufacturing method of the semiconductor device of this invention. It is manufacturing process sectional drawing which shows embodiment which concerns on the manufacturing method of the semiconductor device of this invention.

Explanation of symbols

  12 ... resin film, hν ... light

Claims (8)

After forming a resin film having a carbon triple bond and a carbon double bond,
The resin film is formed by curing the resin film by cutting only the carbon triple bond while leaving the carbon double bond of the resin film by light irradiation. The resin film is a film formed by applying a polyaryl ether resin,
2. The resin film is cured by irradiating the resin film with light having a wavelength of 190 nm or less, leaving only a carbon triple bond in the resin film and cutting only a carbon triple bond. The resin film formation method of description. The method for forming a resin film according to claim 1, wherein the resin film is heated at a temperature equal to or lower than a thermal decomposition temperature of the resin film when the resin film is cured. The method for forming a resin film according to claim 2, wherein a light source having an emission wavelength of 140 nm to 160 nm is used for the light irradiation. After forming the insulating film used between the wirings of the semiconductor device or between the wiring layers with a resin film having a carbon triple bond and a carbon double bond,
A method of manufacturing a semiconductor device, comprising: curing the resin film by cutting only a carbon triple bond while leaving a carbon double bond in the resin film by light irradiation. The resin film is composed of a polyaryl ether resin-based coating film,
6. The resin film is cured by irradiating the polyaryl ether resin-based coating film with light having a wavelength of 190 nm or less, leaving only the triple bonds leaving the double bonds. Manufacturing method of the semiconductor device. The method for manufacturing a semiconductor device according to claim 5, wherein the resin film is heated at a temperature of 200 ° C. or lower when the resin film is cured. The method of manufacturing a semiconductor device according to claim 6, wherein a light source having an emission wavelength of 140 nm to 160 nm is used for the light irradiation.

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