JP2016190762A - Manufacturing apparatus for aluminum nitride single crystal - Google Patents

Abstract

The present invention provides a production apparatus capable of effectively suppressing sublimation from the outer peripheral portion of a seed substrate and producing an aluminum nitride single crystal having good crystallinity. In an aluminum nitride manufacturing apparatus 1, a crucible 11 having an opening at an upper portion thereof and containing a raw material 12 at an inner bottom portion thereof, a lid body 13 installed above the opening portion, A seed substrate 14 disposed on the lower surface side so as to face the raw material 12, a seed substrate 14 disposed at a lower portion of the seed substrate 14, and in contact with at least a part of an outer peripheral portion of the seed substrate 14. A seed substrate holding member 15a having a through-opening 15A smaller than the outer diameter of the seed substrate 14. The seed substrate 14 is held by the seed substrate holding member 15a, and at least a part of the side surface is a metal film 14a. Covered with. [Selection] Figure 1

Description

  The present invention relates to an apparatus for producing an aluminum nitride (AlN) single crystal.

Aluminum nitride semiconductors are expected as deep ultraviolet laser diodes and high-efficiency, high-frequency electronic devices. As a substrate for growing this semiconductor, an aluminum nitride single crystal is optimal, and therefore, an aluminum nitride single crystal is being developed.
A characteristic of the aluminum nitride single crystal is that it has a very high thermal conductivity of 290 Wm ⁻¹ K ⁻¹ , which is very advantageous for diffusing heat generated during device operation.

  The aluminum nitride single crystal is produced by the flux method for the solution method, the metal-organic vapor phase epitaxy (MOVPE) for the vapor phase method, the hydride vapor deposition method (Hydride Vapor Phase Epitaxy, HVPE). ) And sublimation methods. Among these, the sublimation method is a powerful method for producing a bulk crystal because the growth rate is generally high. This sublimation method is a method of producing a single crystal by sublimating aluminum nitride as a raw material and recondensing it in a temperature region lower than the sublimation temperature.

Conventional growth of aluminum nitride single crystals by the sublimation method conventionally uses a crucible made of a high-temperature material that can be used at 2000 ° C. or higher, such as graphite or metal carbide, as a growth furnace.
In the crystal growth method using this crucible, the seed substrate is generally bonded and held to the lower surface of the crucible lid using an adhesive. For the bonding of the seed substrate, it is possible to use a commercially available high temperature adhesive mainly composed of a resin, an inorganic compound ceramic material, or a graphite material. However, commercially available high-temperature adhesives have a weak adhesive force on crucibles made of graphite, metal carbide, etc., and it may be difficult to fix and hold the seed substrate without peeling off at all. Therefore, even if the seed substrate falls off from the inner wall of the crucible during crystal growth or is partially fixed, crystal defects often occur from the part where peeling occurs, and a high-quality aluminum nitride single crystal is obtained. There was no case.
In addition, when there is a difference in thermal expansion coefficient between the seed substrate and the adhesive, and between the adhesive and the crucible, the seed substrate is attached to the inner wall of the crucible during high temperature crystal growth near 2000 ° C. or during temperature rise before the start of growth. In some cases, the crystal growth could not be performed in a state where the seed substrate was adhered and held on the inner wall of the crucible, such as being peeled off. Further, even if the seed substrate is fixed to the inner wall of the crucible by the adhesive during crystal growth, the seed substrate is greatly distorted due to the above-described difference in thermal expansion coefficient, and the crystallinity of the grown crystal deteriorates due to the influence.

In order to solve the problem, there is known a method capable of suppressing the separation of the seed substrate from the inner wall of the crucible during crystal growth, and producing an aluminum nitride single crystal having good crystallinity. (For example, refer to Patent Document 1). An apparatus for producing aluminum nitride described in Patent Document 1 is shown in FIG.
The aluminum nitride manufacturing apparatus 101 shown in FIG. 3 has an opening at the top, a crucible 111 for storing the raw material 112 at the inner bottom, a lid 113 installed above the opening, A seed substrate 114 arranged on the lower surface side so as to face the raw material 112, and on the lower side of the seed substrate 114, installed on the periphery 111a of the opening of the crucible 111 so as to cover the opening of the crucible 111; A seed substrate holding member 115a that is in contact with at least a part of the outer periphery of the seed substrate 114 and has a through-opening 115A that is smaller than the outer diameter of the seed substrate 114 and smaller than the opening of the crucible 111 at the center. 114 is held by a seed substrate holding member 115a.
Further, as shown in FIG. 4, the seed substrate 114 is separated from the external space of the crucible 111 by installing a ring-shaped seed substrate protection member 115 b between the lid 113 and the seed substrate holding member 115 a, A method for effectively suppressing sublimation from the outer periphery of the seed substrate 114 is also disclosed.

Japanese Patent No. 5517123

  However, even if the seed substrate is separated from the external space of the crucible by installing the seed substrate protection member, there is a gap space between the seed substrate and the seed substrate protection member, so sublimation from the outer periphery of the seed substrate. Is not completely suppressed.

  Therefore, the problem to be solved by the present invention is to provide a production apparatus that can effectively suppress sublimation from the outer peripheral portion of the seed substrate and can produce a good crystalline aluminum nitride single crystal. .

  The apparatus for producing aluminum nitride according to the present invention has an opening at the top, a crucible for storing the raw material at the inner bottom, a lid installed above the opening, and the raw material on the lower surface side of the lid A seed substrate disposed so as to face the seed substrate, and a through-opening disposed at a lower portion of the seed substrate and in contact with at least a part of an outer peripheral portion of the seed substrate and having a smaller central diameter than the outer diameter of the seed substrate The seed substrate is held by the seed substrate holding member, and at least a part of the side surface is covered with a metal film. Here, the metal film includes not only a single metal film but also a metal carbide or metal nitride film.

  According to the aluminum nitride manufacturing apparatus according to the present invention, the crucible having an opening at the top and storing the raw material at the inner bottom, a lid installed above the opening, and a lower surface side of the lid A seed substrate disposed so as to face the raw material, and disposed at a lower portion of the seed substrate, and is in contact with at least a part of an outer peripheral portion of the seed substrate, and has a central portion smaller than an outer diameter of the seed substrate. A seed substrate holding member having a through-opening, and the seed substrate is held by the seed substrate holding member, and at least a part of the side surface is covered with a metal film, whereby an outer peripheral portion of the seed substrate Sublimation from can be effectively suppressed.

  In the apparatus for producing an aluminum nitride single crystal according to the present invention, it is desirable that the seed substrate is further covered with a metal film at least a part of the back surface on the lid side.

  In the aluminum nitride single crystal manufacturing apparatus according to the present invention, it is desirable that the side surface of the seed substrate is a tapered inclined surface whose diameter decreases as it goes upward.

  In the apparatus for producing an aluminum nitride single crystal of the present invention, the metal film is selected from the group consisting of molybdenum, tungsten, tantalum, molybdenum carbide, zirconium carbide, tungsten carbide, tantalum carbide, molybdenum nitride, zirconium nitride, tungsten nitride, and tantalum nitride. It is desirable to be formed from at least one selected.

  ADVANTAGE OF THE INVENTION According to this invention, the sublimation from the outer peripheral part of a seed substrate can be suppressed effectively, and a favorable crystalline aluminum nitride single crystal can be manufactured.

It is a schematic block diagram which shows typically an example of the manufacturing apparatus of the aluminum nitride single crystal which concerns on embodiment of this invention. It is a cross-sectional schematic diagram explaining the processing procedure of the seed substrate of the manufacturing apparatus of the aluminum nitride single crystal which concerns on embodiment of this invention. It is a schematic block diagram which shows typically an example of the manufacturing apparatus of the conventional aluminum nitride single crystal. It is a cross-sectional schematic diagram explaining the seed substrate holding member of the manufacturing apparatus of the conventional aluminum nitride single crystal.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram schematically showing an example of an aluminum nitride single crystal manufacturing apparatus according to an embodiment of the present invention. The aluminum nitride single crystal manufacturing apparatus 1 of the present embodiment is an apparatus for growing an aluminum nitride single crystal by sublimating and recrystallizing aluminum nitride on a seed substrate by a sublimation method.

  An apparatus 1 for producing an aluminum nitride single crystal according to this embodiment includes a crucible 11 having an opening at the top, a lid 13 provided above the opening, and a seed substrate holding member provided below the lid 13. 15a and a seed substrate 14 for crystal growth held by the lid 13 and the seed substrate holding member 15a (in the example shown in FIG. 1, sandwiched between the upper surface of the seed substrate holding member 15a and the lower surface of the lid 13). And a ring-shaped seed substrate protection member 15b held by a lid 13 and a seed substrate holding member 15a so as to surround the seed substrate 14. The seed substrate 14 is, for example, a plate-like or disc-like silicon carbide single crystal, aluminum nitride single crystal, aluminum nitride / silicon carbide single crystal (an aluminum nitride single crystal film having a thickness of about 200 to 500 μm on the silicon carbide single crystal. Single crystal). In the present embodiment, the seed substrate 14 is entirely covered with the metal film 14a. Furthermore, the seed substrate 14 is also covered with a metal film having the same component as the metal film covering the side surface of the entire back surface on the lid 13 side. Note that either or both of the side surface and the back surface of the seed substrate 14 may be covered with a metal film. Further, in the present embodiment, the side surface of the seed substrate 14 has a tapered inclined surface whose diameter gradually decreases upward, but it may not be inclined. The seed substrate protection member 15b has a through opening larger than the outer diameter of the seed substrate 14, and the seed substrate 14 is provided in the through opening.

  The entire crystal growth space 17 composed of the crucible 11 and the lid 13 is disposed in a space formed by the graphite outer crucible 18 and the graphite outer lid 19 placed on the upper surface of the outer crucible 18. The outer crucible 18 and the crucible 11 are fixed in the crystal growth furnace 10 by fixing means (not shown). A raw material 12 such as aluminum nitride powder is stored in the inner bottom of the crucible 11, and a portion of the seed substrate 14 that does not contact the seed substrate holding member 15 a faces the raw material 12.

  A plurality of heating means 21 for heating the outer crucible 18, the crucible 11, the raw material 12, and the seed substrate 14 disposed in the crystal growth furnace 10 are provided along the outer periphery of the crystal growth furnace 10. . The heating means 21 is not particularly limited, and conventionally known ones such as high frequency induction heating (high frequency coil), resistance heating and infrared heating can be used. The heating temperature can be controlled by adjusting the heating means 21 while measuring the surface temperature of the outer crucible 18 with a radiation thermometer (not shown).

  A gas introducing portion 22 connected to a gas supply device such as nitrogen gas is formed in the ceiling portion of the crystal growth furnace 10. In addition, a decompression device such as a vacuum pump is connected to the bottom of the crystal growth furnace 10 via a pressure control valve (not shown), and a gas discharge unit 23 capable of discharging nitrogen gas or the like is formed. By operating the gas introduction part 22 and the gas discharge part 23, the crystal growth furnace 10, the inside of the outer crucible 18 and the crystal growth space 17 in the crucible 11 can be adjusted to a predetermined gas pressure. Here, the outer lid body 19 is placed or fitted on the upper part of the opening of the outer crucible 18 and has a semi-sealing structure in which nitrogen gas can easily enter and exit. Similarly, the lid 13, the seed substrate holding member 15 a, and the seed substrate protection member 15 b are placed or fitted on the upper part of the opening of the crucible 11, and are semi-sealed so that nitrogen gas can easily enter and exit. It is a space. By introducing a process gas such as nitrogen gas from the gas introduction part 22, nitrogen gas or the like flows into the internal space formed by the outer crucible 18 and the outer lid 19 and the crystal growth space 17 in the crucible 11. It is possible.

The crucible 11, the lid 13, the metal film 14a, the seed substrate holding member 15a, and the seed substrate protection member 15b are made of graphite, boron nitride, aluminum nitride, gallium nitride, silicon carbide, silicon nitride, molybdenum, tungsten, tantalum, molybdenum carbide, It is made of at least one selected from the group consisting of zirconium carbide, tungsten carbide, tantalum carbide, molybdenum nitride, zirconium nitride, tungsten nitride and tantalum nitride. Since these materials have thermal resistance at a high temperature of about 2000 ° C. during crystal growth of the aluminum nitride single crystal, the crucible 11, the lid 13, the metal film 14a, the seed substrate holding member 15a, and the seed substrate protection member 15b. This material is preferable.
A raw material 12 such as aluminum nitride powder is directly stored in the inner bottom portion of the crucible 11, and a seed substrate 14 is installed between the lid 13 and the seed substrate holding member 15a, which is suitable for bulk crystal growth. Exposure to aluminum nitride sublimation gas. Therefore, the materials constituting the crucible 11, the lid 13, the metal film 14a, the seed substrate holding member 15a, and the seed substrate protection member 15b are limited to those that are not subject to corrosion by the sublimation gas of aluminum nitride. In addition, in order to prevent contamination of aluminum nitride single crystal 16 (contamination due to solid solution) from the materials constituting these crucible 11, lid 13, metal film 14a, seed substrate holding member 15a and seed substrate protection member 15b. It is desirable to use a single metal or a nitride or carbide thereof that is significantly different from the ionic radius of aluminum. Therefore, among the materials described above as materials for the crucible 11, the lid 13, the metal film 14a, the seed substrate holding member 15a, and the seed substrate protection member 15b, molybdenum, tungsten, tantalum, molybdenum carbide, zirconium carbide, tungsten carbide, tantalum carbide. More preferably, it is formed of at least one selected from the group consisting of molybdenum nitride, zirconium nitride, tungsten nitride and tantalum nitride.
Note that an oxide cannot be used because the released oxygen forms an aluminum oxynitride (AlON) layer in the aluminum nitride single crystal and inhibits crystal growth of the aluminum nitride.

The seed substrate holding member 15a is installed on the peripheral edge 11a of the opening of the crucible 11 so as to cover the opening of the crucible 11, on which the seed substrate 14 and the seed substrate protection member 15b are placed, and further thereon A lid 13 is installed. That is, the seed substrate holding member 15a is disposed at the lower portion of the seed substrate 14 and is in contact with at least a part of the outer peripheral portion of the seed substrate 14 and has a through opening 15A smaller than the outer diameter of the seed substrate 14 at the center. It has a hollow disk shape.
The vicinity of the inner peripheral portion of the through-opening 15A of the seed substrate holding member 15a is installed in contact with the outer peripheral portion of the seed substrate 14, and the seed substrate 14 is formed between the lower surface of the lid 13 and the upper surface of the seed substrate holding member 15a. It is held between and held. Therefore, the seed substrate 14 is disposed on the lower surface of the lid 13 so as to face the raw material 12 without being fixed to the lid 13 with an adhesive or the like as in a conventional manufacturing apparatus. The seed substrate protection member 15b has a through opening larger than the outer diameter of the seed substrate 14, the seed substrate 14 is provided in the through opening, and at least a part of the side surface of the seed substrate 14 is a metal film 14a. Since it is covered, sublimation from the outer periphery of the seed substrate 14 can be effectively suppressed. If all the side surfaces of the seed substrate 14 and at least a part or all of the back surface on the lid 13 side are covered with the metal film having the same component as the metal film covering the side surfaces, sublimation can be suppressed more reliably. At the time of manufacturing the aluminum nitride single crystal, the raw material 12 is sublimated and decomposed and vaporized by heating, and is deposited on the seed substrate 14 exposed in the through-opening 15A of the seed substrate holding member 15a, so that the aluminum nitride single crystal 16 grows. To do.

Unlike the conventional manufacturing apparatus, the aluminum nitride single crystal manufacturing apparatus 1 of the present embodiment has at least a part of the side surface covered with the metal film 14a. Can be effectively suppressed. Thereby, the sublimation from the outer peripheral part of the seed board | substrate 14 can be suppressed effectively, and a favorable crystalline aluminum nitride single crystal can be manufactured.
In addition, since the seed substrate 14 is held by the seed substrate holding member 15a, the seed substrate 14 can be held without being bonded to the lid body 13, and therefore the seed substrate 14 is freely expanded regardless of the difference in thermal expansion coefficient. It is possible to produce an aluminum nitride single crystal having good crystallinity while preventing peeling and dropping off.

Next, an aluminum nitride single crystal manufacturing method using the aluminum nitride single crystal manufacturing apparatus 1 of the present embodiment will be described.
First, processing for covering the side surface and back surface (the lid body 13 side) of the seed substrate with a metal film is performed.
FIG. 2 is a schematic cross-sectional view for explaining the processing procedure of the seed substrate of the aluminum nitride single crystal manufacturing apparatus according to the embodiment of the present invention. 2A to 2C, the side surface and the back surface of the seed substrate are covered with the metal film. In FIG. 2A, a seed substrate having a crystal growth surface CMP (Chemical Mechanical Polishing) is prepared. Next, in FIG. 2B, side processing is performed using a beveling device to form a truncated cone shape. Then, after removing the lubricant used in the side processing in FIG. 2C by ultrasonic cleaning in an organic solvent such as acetone, the side surface and the back surface of the seed substrate are coated with a metal film by coating from the back surface side. Cover with. The coating method should just be able to cover with the dense metal film 14a, such as CVD (chemical vapor deposition) method and PVD (physical vapor deposition) method. If necessary after coating, heat treatment is performed to ensure the denseness of the metal film and the adhesion to the seed substrate. Through the above procedure, the seed substrate 14 whose side and back surfaces are covered with the metal film 14a is obtained.
The reason for making the truncated cone shape in FIG. 2B is that the side surface and the back surface of the seed substrate are formed by one coating by making the side surface of the seed substrate into a tapered inclined surface whose diameter gradually decreases upward. Is to be covered with a metal film. However, if only the side surface of the seed substrate is covered with a metal film, there is no need to form a truncated cone.

  Next, returning to FIG. 1, the raw material 12 such as aluminum nitride powder is set on the bottom of the crucible 11, and the seed substrate 14 and the seed substrate protection member 15 b are held by the seed substrate holding member 15 a and installed on the lower surface side of the lid 13. (In the example shown in FIG. 1, after the seed substrate 14 and the seed substrate protection member 15 b are nipped between the seed substrate holding member 15 a and the lid 13), the crystal growth space 17 in the crucible 11 and the outside The internal space formed by the crucible 18 and the outer lid 19 is put in a semi-sealed state.

  Further, a vacuum pump (not shown) is operated to remove the atmosphere inside the crystal growth furnace 10 from the gas discharge unit 23, and the pressure inside the crystal growth furnace 10 is reduced. Subsequently, nitrogen gas is introduced from the gas introduction unit 22 into the crystal growth furnace 10. Thereby, the growth of the aluminum nitride single crystal is performed in a high purity nitrogen gas atmosphere.

And the outer crucible 18 and the outer cover body 19 are heated with the heating means 21, and the temperature of the outer crucible 18 and the outer cover body 19 is measured with a radiation thermometer (not shown) to control these temperatures. During the growth of the aluminum nitride single crystal, the temperature of the outer crucible 18 is constantly controlled at 1700 to 2300 ° C. During aluminum nitride single crystal growth, the temperature at the lower end of the outer crucible 18 (raw material side temperature) is set to be higher than the temperature of the outer lid 19 (crystal growth side temperature).
Crystal growth is started by depressurizing the crystal growth furnace 10 after heating to the above-mentioned set temperature, and is performed by maintaining a constant pressure at 100 to 600 torr.

Further, during the heating, the nitrogen gas in the crystal growth furnace 10 is discharged from the gas discharge unit 23 while the nitrogen gas is supplied into the crystal growth furnace 10 from the gas introduction unit 22, thereby the crystal growth furnace 10. Adjust the nitrogen gas pressure and flow rate inside.
The raw material 12 is sublimated and decomposed and vaporized by heating, and grows on the seed substrate 14 exposed in the through-opening 15A of the seed substrate holding member 15a in a nitrogen gas atmosphere, so that the aluminum nitride single crystal 16 is formed on the seed substrate 14. And grow.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to a following example.
(Example)
An aluminum nitride single crystal was grown on the seed substrate 14 with the manufacturing apparatus 1 shown in FIG. As the seed substrate 14, a disk-shaped aluminum nitride single crystal (diameter 38 mm, thickness 1 mm) is used, side processing is performed so that the back surface has a diameter of 36 mm, and coating is performed from the back side using a high-frequency sputtering apparatus belonging to the PVD method. Then, the side and back surfaces of the seed substrate were covered with a tantalum carbide metal film. Note that the orientation and polarity of the crystal growth plane were (0001) Al plane and (000-1) N plane. A 1 mm-thick disk-shaped member was used as the seed substrate holding member 15a, and a through-opening having a diameter of 30 mm was provided at the center to form a ring-shaped member. The crucible 11, the lid 13, the seed substrate holding member 15a, and the seed substrate protecting member 15b were made of tungsten. After installing the crucible in the growth apparatus, the dry pump and the turbo molecular pump (not shown) are sequentially operated to remove the atmosphere in the crystal growth furnace 10 and the pressure in the crystal growth furnace 10 is set to 5 × 10. ^The pressure was reduced to ^-6 torr. Thereafter, nitrogen gas was introduced into the apparatus and the pressure was increased to 700 torr. Next, after the temperature of the crucible was raised to about 2200 ° C., the pressure inside the crystal growth furnace 10 was reduced to 100 to 600 torr to start aluminum nitride single crystal growth. When 200 hours passed from the start of the growth, the pressure in the crystal growth furnace 10 was increased to 700 torr with nitrogen gas, and then the seed substrate 14 and the raw material temperature were cooled to room temperature, thereby terminating the crystal growth. The obtained aluminum nitride single crystal had a diameter of 30 mm and a thickness of 10 mm.

(Comparative example)
An aluminum nitride single crystal was grown under the same conditions as described above using a seed substrate that was not processed with a metal film. As a result, an aluminum nitride single crystal having a diameter of 30 mm and a thickness of 9 mm was obtained. Moreover, the diameter of the seed substrate was reduced to 20 mm.

  Each aluminum nitride single crystal obtained in the examples and comparative examples was cut into a 1 mm thick plate in the vertical and horizontal directions with respect to the growth direction, and a sample for evaluation was prepared. The sample for evaluation was polished to a mirror surface with a flat surface, and damage due to cutting was removed from the surface as much as possible. As an evaluation method, crystallinity was analyzed by an X-ray topography method using an X-ray Lang camera. As a result, the sample for evaluation obtained in the example showed almost uniform crystallinity within the disk surface. On the other hand, the sample for evaluation obtained in the comparative example had many crystal defects in the outer peripheral portion, and the influence of sublimation from the outer peripheral portion of the seed substrate was expressed. As a result, the evaluation sample obtained in the example can use the entire surface of 30 mm in diameter, but the evaluation sample obtained in the comparative example can use only the portion of 20 mm in diameter included in the diameter of 30 mm.

DESCRIPTION OF SYMBOLS 1,101 ... Manufacturing apparatus 10 ... Crystal growth furnace 11, 111 ... Crucible 11a, 111a ... Perimeter 12, 112 ... Raw material 13, 113 ... Cover body 14, 114 ... Seed substrate 14a ... Metal film 15a, 115a ... Seed substrate holding Member 15A, 115A ... Through-opening 15b, 115b ... Seed substrate protection member 16 ... Aluminum nitride single crystal 17 ... Crystal growth space 18 ... Outer crucible 19 ... Outer lid 21 ... Heating means 22 ... Gas introduction part 23 ... Gas discharge part

Claims (4)

A crucible having an opening at the top and containing the raw material at the inner bottom;
A lid installed above the opening;
A seed substrate disposed on the lower surface side of the lid so as to face the raw material;
A seed substrate holding member disposed at a lower portion of the seed substrate and in contact with at least a part of an outer peripheral portion of the seed substrate, and having a through opening smaller than an outer diameter of the seed substrate at a central portion thereof,
The said seed substrate is hold | maintained by the said seed substrate holding member, At least one part of the side surface is covered with the metal film, The manufacturing apparatus of the aluminum nitride single crystal characterized by the above-mentioned.   2. The apparatus for producing an aluminum nitride single crystal according to claim 1, wherein the seed substrate is further covered with a metal film at least a part of the back surface on the lid side.   3. The apparatus for producing an aluminum nitride single crystal according to claim 1, wherein the side surface of the seed substrate is a tapered inclined surface whose diameter decreases as it goes upward.   The metal film is formed of at least one selected from the group consisting of molybdenum, tungsten, tantalum, molybdenum carbide, zirconium carbide, tungsten carbide, tantalum carbide, molybdenum nitride, zirconium nitride, tungsten nitride, and tantalum nitride. The apparatus for producing an aluminum nitride single crystal according to any one of claims 1 to 3.

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