CN211471635U - Device for preparing single crystal - Google Patents

Abstract

The application discloses a device for preparing single crystal, and belongs to the field of semiconductor materials. The device for preparing the single crystal comprises a crucible, a heating coil group and a heat insulation structure, wherein the crucible forms a growth cavity, a seed crystal is arranged in the growth cavity, the heat insulation structure comprises an upper heat insulation structure, a temperature measuring hole is formed in a position corresponding to the seed crystal, the device further comprises an adjusting mechanism, the adjusting mechanism comprises a heat insulation ring group, the outer diameter of the heat insulation ring group is the same as the inner diameter of the temperature measuring hole, a through hole is formed in the center of the heat insulation ring group, the heat insulation ring group comprises a plurality of heat insulation rings with gradually decreased inner diameters, the adjusting mechanism can place the heat insulation rings with the inner diameters from large to small into the temperature measuring hole to reduce the opening area of the temperature measuring hole. The single crystal growing device can not only adjust the radial temperature gradient in the growing cavity for growing the single crystal; and the radial temperature gradient can be reduced, and simultaneously, a certain axial temperature gradient can be ensured, so that high-quality single crystals can be efficiently prepared.

Description

Device for preparing single crystal

Technical Field

The application relates to a device for preparing single crystal, belonging to the field of semiconductor material.

Background

Silicon carbide single crystal is one of the most important third-generation semiconductor materials, and is widely applied to the fields of power electronics, radio frequency devices, photoelectronic devices and the like because of the excellent properties of large forbidden bandwidth, high saturated electron mobility, strong breakdown field, high thermal conductivity and the like.

The main method for producing silicon carbide single crystals at present is the Physical Vapor Transport (PVT) method. In the process of preparing the crystal by the PVT method, a radial temperature gradient and an axial temperature gradient exist in a growth cavity for growing the crystal. In the stable growth stage of the crystal, the larger axial temperature gradient has a faster crystal growth speed, and the smaller radial temperature gradient can reduce the introduced stress and dislocation. However, it is difficult to achieve both a large axial temperature gradient and a small axial temperature gradient in actual production.

On the other hand, during the growth of a silicon carbide crystal, some variation in the radial temperature gradient is often required to improve the crystal quality. The crystal needs a certain radial temperature gradient in the initial growth stage to complete the transverse growth, and the larger radial temperature gradient in the initial growth stage can reduce the generation of voids to a certain extent. And the longitudinal growth of the crystal needs to be promoted at the later growth stage of the crystal, and a larger radial temperature gradient is not needed.

In general, in order to rapidly prepare high-quality and low-defect silicon carbide crystals, the radial temperature gradient at the initial growth stage of the crystals needs to be large, and the axial temperature gradient needs to be small; and the radial temperature gradient is small and the axial temperature gradient is large in the stable growth stage.

However, the PVT equipment for preparing silicon carbide at present generally uses induction coils with the same upper and lower diameters. On one hand, the existing heating mode of the induction coil is difficult to improve the axial temperature gradient of the growth cavity, the radial temperature gradient is not influenced, and the small radial temperature gradient is ensured; on the other hand, when the radial temperature gradient is reduced, the axial temperature gradient is also greatly reduced, and the growth rate cannot be ensured. In addition, the radial temperature gradient in the growth process of the silicon carbide crystal is difficult to regulate in a large range in the conventional equipment, and the change of the radial temperature gradient required in the growth of the silicon carbide crystal is difficult to realize.

Disclosure of Invention

In order to solve the above problems, there is provided a single crystal growing apparatus which can adjust a radial temperature gradient in a growth chamber where a single crystal is grown; and the radial temperature gradient can be reduced, and simultaneously, a certain axial temperature gradient can be ensured, so that high-quality and low-defect single crystals can be efficiently prepared.

According to one aspect of the application, a device for preparing single crystals is provided, which comprises a crucible, a heating coil group and a heat insulation structure, wherein the crucible forms a growth cavity, seed crystals are arranged in the growth cavity, the heat insulation structure comprises an upper heat insulation structure, a temperature measuring hole is formed in the position corresponding to the seed crystals, the device further comprises an adjusting mechanism, the adjusting mechanism comprises a heat insulation ring group, the outer diameter of the heat insulation ring group is the same as the inner diameter of the temperature measuring hole, a through hole is formed in the center of the heat insulation ring group, the heat insulation ring group comprises a plurality of heat insulation rings with gradually decreased inner diameters, and the adjusting mechanism can enable the heat insulation rings with gradually decreased inner diameters to be placed into the temperature measuring hole so as to reduce the opening area of the temperature measuring hole and further adjust the radial temperature gradient in the growth cavity. In the initial stage of single crystal growth, a large radial temperature gradient needs to be formed on a long crystal face, and a large-cross-section temperature measuring hole is needed; in the stable growth stage, the radial temperature gradient as small as possible needs to be formed on the long crystal face, and a temperature measuring hole with a small cross section is needed, so that a heat preservation ring is added in the temperature measuring hole to reduce the inner diameter of the temperature measuring hole. According to different requirements of the growth stage and the stable growth stage of the single crystal on the radial temperature gradient of the long crystal face in the growth cavity, the radial temperature gradient of the long crystal face is adjusted by adjusting the size of the temperature measuring hole.

Optionally, the heat preservation ring includes the brace table of the internal extension that heat preservation ring main part and heat preservation ring main part inner wall set up, the brace table sets up the bottom of heat preservation ring main part, the thickness of brace table is not more than 5 mm. Preferably, the support table has a thickness of 2 mm.

Optionally, the height of the heat retaining ring set is approximately the same as the thickness of the upper heat retaining structure.

Optionally, the proportion of the opening area of the temperature measuring hole to the area of the seed crystal is 2% -25%. Preferably, the proportion of the opening area of the temperature measuring hole in the area of the seed crystal is 7-15%.

Optionally, the ratio of the opening area of the central through hole of the heat-insulating ring group to the area of the seed crystal is 0.1% -10%. Preferably, the ratio of the opening area of the central through hole of the heat-preserving ring group to the area of the seed crystal is 0.5-2%.

Optionally, the adjusting mechanism further comprises an adjusting chamber and a first conveying mechanism;

the adjusting chamber is communicated with the temperature measuring hole, a quartz window is arranged in the adjusting chamber, and the quartz window is connected with the optical path of the temperature measuring hole so as to measure the temperature of the temperature measuring hole by using a non-contact temperature measuring meter arranged outside the quartz window;

and the first conveying mechanism conveys the heat-insulating ring group into the temperature measuring hole.

Optionally, the quartz window is arranged at the top of the adjusting chamber, and the quartz window is arranged opposite to the temperature measuring hole;

the heat-insulating ring group is arranged in the adjusting chamber and comprises a split heat-insulating ring group which is arranged in a split manner along the axial direction of the heat-insulating ring group;

the first conveying mechanism comprises an operation part arranged outside the adjusting chamber and a pushing part arranged inside the adjusting chamber; the inner diameter of the split heat-insulation ring is gradually increased along the direction from the pushing part to the temperature measuring hole; the control operation part drives the pushing part to push the split heat-insulation rings to sequentially enter the temperature measurement holes.

Preferably, the heat-insulating ring set comprises two split heat-insulating ring sets which are symmetrically arranged along the axial direction of the heat-insulating ring set, each split heat-insulating ring set is of a semicircular structure, and each first conveying mechanism comprises two pairs of first conveying mechanisms which are respectively arranged corresponding to the split heat-insulating ring sets.

As an implementation mode, the operation part comprises a handle, the pushing part comprises a pushing plate, the handle is connected with the pushing plate through a connecting rod, and the pushing plate is driven to push the split heat-insulation ring set to enter the temperature measuring hole by pushing the handle arranged outside the adjusting chamber.

As an implementation manner, the first conveying mechanism is configured as a manipulator, the operating portion includes a control panel, the pushing portion is a gripper, and the first conveying mechanism further includes a control system and a manipulator. And after the control panel is operated and the mechanical arm is moved to a target position through the control system, the gripper grabs the heat-insulating ring and then puts the heat-insulating ring into the temperature measuring hole, and the mechanical arm returns to the original position.

Optionally, the adjusting mechanism further comprises a buffer chamber, and the buffer chamber and the adjusting chamber are provided with a first valve;

the buffer chamber is connected with the gas path system and is provided with a heating element so as to control the temperature of the buffer chamber and the growth cavity to be the same as the ambient gas;

the first conveying mechanism is set as a mechanical arm, after the mechanical arm conveys the obtained heat-insulating ring to the buffer chamber, when the temperature of the heat-insulating ring is the same as that of the adjusting chamber, the first valve is opened, and the mechanical arm places the heat-insulating ring in the temperature measuring hole;

the quartz window is arranged on the side wall of the adjusting chamber, and a reflector is arranged in the adjusting chamber to connect the non-contact type temperature measurer with the light path of the temperature measuring hole.

The heating element is arranged in the adjusting chamber after the heat preservation ring with lower temperature is placed in the adjusting chamber, so that the temperature in the growth chamber is prevented from being greatly fluctuated. Preferably, the heating element is a graphite heater, and the heating element is arranged on the inner layer of the buffer chamber.

Optionally, the buffer chamber is further provided with a second valve, the heat-insulating ring group is placed into the buffer chamber after the second valve is opened, the buffer chamber is vacuumized and then filled with gas until the temperature of the buffer chamber is the same as that of the ambient gas in the adjusting chamber by using a vacuum pump, the temperature of the buffer chamber is increased to the temperature of the adjusting chamber by using the heating element, the first valve is opened, and the first conveying mechanism is controlled to place the heat-insulating ring into the temperature measuring hole.

Optionally, the buffer chamber is further provided with a second conveying mechanism, the reflective mirror is fixed to the second conveying mechanism, when the first conveying mechanism conveys the heat preservation ring into the adjustment chamber, the second conveying mechanism is adjusted to move the reflective mirror to a position where the first conveying mechanism is not affected in conveying the heat preservation ring, and after the heat preservation ring is conveyed, the second conveying mechanism is adjusted to reset the reflective mirror.

As an implementation mode, when the radial temperature gradient needs to be adjusted, the second valve is opened, the heat preservation ring is conveyed into the buffer chamber through the first conveying mechanism, the second valve is closed, and the buffer chamber is vacuumized and inflated to be close to the atmosphere in the growth cavity; after the steps are finished, the first valve is opened, the reflector for measuring the temperature is moved to the edge through the second conveying mechanism, and then the heat-insulating rings with different sizes are placed into the temperature measuring hole through the first conveying mechanism. Wherein, the rule for placing the heat preservation ring is as follows: the large-size heat preservation ring is firstly placed, and then the small-size heat preservation ring is placed, so that the size of the temperature measurement hole can be approximately and continuously changed.

Optionally, the growth chamber includes a raw material region for holding raw materials and a seed crystal growth region for setting seed crystals, the heating coil group is arranged around the side wall of the crucible, the heating coil group includes a first coil group arranged corresponding to the raw material region and a second coil group arranged corresponding to the seed crystal growth region, and the inner diameter of the second coil group increases along the direction from the raw materials to the seed crystals. Increasing the coil diameter from the region of the feedstock up, thereby reducing the temperature at the seed crystal, increases the axial temperature gradient compared to previous coil designs of constant diameter, but has less effect on the radial temperature gradient at the seed crystal. Although the reduction of the size of the temperature measuring hole can reduce the radial temperature gradient and the axial temperature gradient at the same time, the structure of the heating coil group enables a large axial temperature gradient to be arranged in the growth cavity, and the axial temperature gradient can still ensure the growth rate required by the growth of the single crystal.

Optionally, the inner diameters of the first coil groups are the same. In order to ensure that the temperature field in the raw material does not change greatly, the diameter of the coil is basically kept unchanged in the raw material area.

Optionally, the crucible and the heating coil group share a central axis, and the inner wall of the heating coil group at the same height is equidistant from the outer side wall of the crucible.

Preferably, the heating coil group is hollow cylindrical, and the crucible is cylindrical.

Optionally, the inner diameter of the second coil assembly is continuously increased, and an included angle between the side wall of the second coil assembly and the central axis of the crucible is 10-45 °. Preferably, the inner diameter of the second coil assembly is continuously increased, and an included angle between the side wall of the second coil assembly and the central axis of the crucible is 20-35 °.

According to still another aspect of the present application, there is provided a method for producing a silicon carbide single crystal, characterized in that it comprises any one of the above-described apparatuses for producing a single crystal, comprising the steps of:

1) assembling: assembling a crucible, a heat preservation structure and a heating coil;

2) removing impurities: controlling the pressure in the device to be more than 500mbar, and raising the temperature of the temperature measuring hole to 2000-2200 ℃;

3) at the initial stage of crystal growth: the pressure in the device is controlled to be reduced to 200mbar at the speed of 100 mbar/h-200 mbar/h and kept for 1h-2 h;

4) stabilizing the long crystal: reducing the pressure in the control device to 10-20mbar at the speed of 90-180 mbar/h, and simultaneously putting a heat preservation ring every 1-2 h according to the size sequence to ensure that the reduction rate of the area of the temperature measurement hole is 10-25%/h.

And 4) reducing the opening area of the temperature measuring hole in the stage of stabilizing the long crystal, thereby reducing the radial temperature gradient in the long crystal cavity formed by the crucible. Although the reduction of the size of the temperature measuring hole can reduce the radial temperature gradient and the axial temperature gradient at the same time, the structure of the heating coil group enables a large axial temperature gradient to be arranged in the growth cavity, and the axial temperature gradient can still ensure the growth rate required by the growth of the single crystal.

Preferably, the step 4) is started to reduce the opening area of the temperature measuring hole 5-15h, for example 10h, after the stable growth stage is started, so as to complete the lateral growth of the crystal and reduce the void defects in the crystal.

Optionally, the material of the heat insulation structure is selected from graphite heat insulation felt, the crucible is a graphite crucible, and the heating coil is a medium-frequency induction coil.

Preferably, the single crystal is selected from silicon carbide single crystal, the raw material of the silicon carbide single crystal is silicon carbide powder or silicon carbide polycrystal, and the seed crystal is silicon carbide seed crystal.

In this application, the ambient gas includes the pressure of the gas and the composition of the gas.

Benefits of the present application include, but are not limited to:

1. according to the device for preparing the single crystal, the radial temperature gradient in the growth cavity can be gradually adjusted by adjusting the size of the temperature measuring hole in the growth process of the single crystal, the condition that a larger radial temperature gradient is obtained at the initial growth stage of the single crystal is met, the radial temperature gradient as small as possible and a larger axial temperature gradient are obtained at the stable growth stage, and therefore the single crystal with high quality and low defect can be quickly prepared.

2. According to the device for preparing the single crystal, due to the arrangement mode of the heating coil group, the growth cavity can keep a certain axial temperature gradient when the radial temperature gradient is reduced, and the growth rate is ensured.

3. According to the device for preparing the single crystal, the inner diameter of the first coil group corresponding to the raw material area is unchanged, so that the heating uniformity of the raw material can be ensured; the inner diameter of the second coil group corresponding to the crystal growing region is increased, so that the axial temperature gradient from the surface of the raw material to the seed crystal can be increased, and the crystal growing rate is increased.

4. According to the apparatus for producing a single crystal of the present application, in producing a silicon carbide single crystal, not only can a silicon carbide single crystal be produced with high efficiency, but also the produced silicon carbide single crystal is high in quality and has few defects.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

fig. 1 is a schematic view of a crystal growth apparatus according to embodiment 1 of the present application.

Fig. 2 is an assembly view of the retainer ring assembly according to embodiment 1 of the present application.

Fig. 3 is a schematic view of a crystal growth apparatus according to embodiment 2 of the present application.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples.

In order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example in conjunction with the accompanying drawings.

So that the manner in which the above recited objects, features and advantages of the present application can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, however, the present application may be practiced in other ways than those described herein, and therefore the scope of the present application is not limited by the specific embodiments disclosed below.

In addition, in the description of the present application, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", and the like, indicate orientations and positional relationships based on those shown in the drawings, are only for convenience of description and simplicity of description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present application.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.

In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixed connections, removable connections, or integral parts; the connection can be mechanical connection, electrical connection or communication; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

In this application, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through intervening media. In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The apparatus for preparing a single crystal of the present application is applicable to any single crystal material for growing a single crystal by the PVT method, such as a silicon carbide single crystal, but is not limited thereto. The following examples illustrate an apparatus for producing a single crystal according to the present application, taking silicon carbide as an example.

Example 1

Referring to fig. 1 and 2, embodiments of the present application disclose an apparatus for preparing a single crystal. The device for preparing the single crystal comprises a crucible 2, a heating coil group and a heat insulation structure, wherein the crucible 2 forms a growth cavity, the growth cavity comprises a raw material area for containing raw materials 8 and a crystal growing area for arranging seed crystals 10, the heating coil group is arranged around the side wall of the crucible 2, the heat insulation structure comprises an upper heat insulation structure 62, a side heat insulation structure 64 and a bottom heat insulation structure 66, the seed crystals 10 are fixed on the inner side wall of a crucible 2 cover of the crucible 2, the upper heat insulation structure 62 is arranged above the crucible 2 cover, and temperature measurement holes 622 are formed in the positions, corresponding to the seed crystals 10, of the upper heat insulation structure; the crystal growth device further comprises an adjusting mechanism, and the adjusting mechanism can adjust the opening area of the temperature measuring hole 622 so as to adjust the radial temperature gradient in the growth cavity. The larger the opening area of the temperature measuring hole 622 is, the larger the radial temperature gradient in the growth cavity is, and the larger the axial temperature gradient is; the opening area of the temperature measuring hole 622 is adjusted to be reduced, and the radial temperature gradient in the growth cavity is reduced, and meanwhile, the axial temperature gradient is also reduced. The radial temperature gradient of the long crystal face in the growth cavity is regulated by regulating the size of the temperature measuring hole 622 according to the difference of the requirements on the radial temperature gradient of the long crystal face in the initial growth stage and the stable growth stage of the single crystal.

Preferably, the temperature measuring hole 622 is disposed at the center of the upper thermal insulation structure 62, and corresponds to the center of the seed crystal 10.

As an embodiment, the adjusting mechanism comprises a heat-insulating ring set, the outer diameter of the heat-insulating ring set is the same as the inner diameter of the temperature measuring hole 622, and a through hole is formed in the center of the heat-insulating ring set; the heat preservation ring group comprises a plurality of heat preservation rings 1222 with decreasing inner diameters, and the heat preservation rings 1222 with the inner diameters from large to small are sequentially placed into the temperature measurement hole 622 so as to reduce the inner diameter of the temperature measurement hole 622. A large radial temperature gradient needs to be formed on a long crystal face in the initial growth stage of the single crystal, and a temperature measuring hole 622 with a large opening area is needed; in the stable growth stage, the radial temperature gradient as small as possible needs to be formed on the long crystal face, and the temperature measuring hole 622 with a small opening area is needed, so that the heat preservation ring 1222 is added in the temperature measuring hole 622 to reduce the inner diameter of the temperature measuring hole 622.

To fixedly attach the thermal ring 1222, the thermal ring 1222 includes a thermal ring body 1224 and a support platform 1226, the support platform 1226 being disposed at the bottom of the thermal ring body 1224 and extending inwardly. The number and relative positional relationship of the support bases 1226 are not limited as long as the heat insulating ring main body 1224 fitted therein is supported. Preferably, 3 support platforms 1226 are uniformly provided per insulating ring body 1224. The thickness of the support 1226 is not more than 5 mm. Preferably, the thickness of the support 1226 is 2mm, and the thickness of the support 1226 is as thin as possible, so that the bottom surface of the thermal ring assembly tends to be as flat as possible.

Preferably, the height of the thermal ring set is approximately the same as the thickness of the upper thermal structure 62, so that the radial temperature of the crystal growth zone is uniform.

Optionally, the proportion of the opening area of the temperature measuring hole 622 to the area of the seed crystal 10 is 2-25%. Preferably, the ratio of the opening area of the temperature measuring hole 622 to the area of the seed crystal 10 is 7-15%. Optionally, the proportion of the opening area of the central through hole of the heat-insulating ring group in the area of the seed crystal 10 is 0.1-10%. Preferably, the proportion of the opening area of the central through hole of the heat-preserving ring group in the area of the seed crystal 10 is 0.5-2%. The opening area of the temperature measuring hole 622 influences the crystal growth rate at the initial stage of crystal growth, the area of the central through hole influences the crystal growth rate and the crystal growth quality at the stable crystal growth stage, and the crystal growth device is high in crystal growth rate and crystal growth quality.

The adjusting mechanism comprises a heat-preserving ring group, an adjusting chamber 124 and a first conveying mechanism 126; the first conveying mechanism 126 conveys the heat-insulating ring group into the temperature measuring hole 622; the adjusting chamber 124 is communicated with the temperature measuring hole 622, the adjusting chamber 124 is provided with a quartz window 1242, and the quartz window 1242 is optically connected with the temperature measuring hole 622 so as to measure the temperature of the temperature measuring hole 622 by using the non-contact type temperature detector 14 arranged outside the quartz window 1242. After the temperature of the temperature measuring hole 622 is reached to the target temperature, the thermal insulating rings 1222 are sequentially placed into the temperature measuring hole 622 from large to small at a specific time by the first conveying mechanism 126, so as to adjust the radial temperature gradient of the growth region.

In one embodiment, a quartz window 1242 is disposed on the top of the adjustment chamber 124, and the quartz window 1242 is disposed opposite to the temperature measuring hole 622; the heat-insulating ring group is arranged in the adjusting chamber 124 and comprises a split heat-insulating ring group 1228 which is arranged in a split manner along the axial direction of the heat-insulating ring group; the first transport mechanism 126 includes an operation portion 1262 provided outside the adjustment chamber 124 and a push portion 1264 provided inside the adjustment chamber 124; the inner diameter of the split heat-insulating ring arranged along the direction from the pushing part 1264 to the temperature measuring hole 622 increases progressively; the control operation part 1262 drives the pushing part 1264 to push the split heat-preserving rings to enter the temperature measuring hole 622 in sequence. The heat-insulating ring group is already placed in the adjusting chamber 124 before the reaction starts, the temperature of the heat-insulating ring group is close to that of the growth cavity, and the condition that the heat-insulating ring group influences the temperature of the growth cavity cannot occur.

In a preferred embodiment, the heat-insulating ring set includes two symmetrically-arranged split heat-insulating ring sets 1228 arranged in a split manner along an axial direction of the heat-insulating ring set, the split heat-insulating ring sets 1228 are semi-cylindrical structures, and the first conveying mechanism 126 includes two pairs of first conveying mechanisms 126 respectively arranged corresponding to the split heat-insulating ring sets 1228. The split heat-insulating ring group 1228 and the first conveying mechanism 126 are symmetrically arranged, and the split heat-insulating rings are sequentially pushed into the temperature measuring hole 622 from big to small respectively.

As an embodiment of the first conveying mechanism 126, the operating portion 1262 includes a handle, the pushing portion includes a pushing plate, the handle is connected to the pushing plate through a connecting rod, and the pushing plate is driven to push the split thermal insulation ring set 1228 to enter the temperature measuring hole 622 by pushing the handle disposed outside the adjusting chamber 124. The split thermal insulation ring set 1228 is placed in the adjustment chamber 124 in the order of arranging the inner diameters of the split thermal insulation rings from small to large in the direction from the pushing plate to the temperature measuring hole 622, and then the split thermal insulation ring with the large inner diameter firstly enters the temperature measuring hole 622 when pushed. The first conveying mechanism 126 has a simple structure, is convenient to operate, and can be operated manually or automatically.

In an embodiment, not shown, the first transport mechanism 126 is configured as a robot, the handling section 1262 comprises a control panel, the pushing section is a gripper, and the first transport mechanism 126 further comprises a control system and a robot arm. After the control panel is operated and the mechanical arm is moved to a target position through the control system, the gripper grabs the heat preservation ring 1222 and then places the heat preservation ring 1222 into the temperature measurement hole 622, and the mechanical arm returns to the original position. The heat preservation ring 1222 of this setting mode can be either an integral type or a split type, and the target position of this setting mode is accurate.

As an embodiment, the apparatus for preparing a single crystal includes a crucible 2, a heating coil group and a heat insulating structure, the crucible 2 forms a growth chamber, the growth chamber includes a raw material region for containing a raw material 8 and a seed crystal region for disposing a seed crystal 10, the heating coil group is disposed around a sidewall of the crucible 2, the heating coil group includes a first coil group 42 disposed corresponding to a height of the raw material region and a second coil group 44 disposed corresponding to a height of the seed crystal region, and an inner diameter of the second coil group 44 increases in a direction from the raw material 8 to the seed crystal 10. Increasing the coil diameter from the region up the feedstock 8, thereby reducing the temperature at the seed crystal 10, increases the axial temperature gradient within the growth chamber compared to previous coil designs of constant diameter, but has less effect on the radial temperature gradient at the seed crystal 10. The single crystal growing device can not only adjust the radial temperature gradient in the growing cavity for growing the single crystal; and the radial temperature gradient can be reduced, a certain axial temperature gradient can be ensured, and high-quality and low-defect single crystals can be efficiently prepared.

In one embodiment, the heating coil assembly is a medium frequency induction coil, and the heating coil assembly is formed by spirally winding a wire.

To ensure that the temperature field within the feedstock 8 does not change significantly, the coil diameter remains substantially constant over the feedstock area, the inner diameter of the first coil assembly 42 is the same, and the inner diameter of the second coil assembly 44 increases from above the surface of the feedstock 8.

In order to ensure that the temperature in the growth chamber is heated uniformly, the crucible 2 and the heating coil group share the same central axis, and the distance between the inner wall of the heating coil group at the same height and the outer side wall of the crucible 2 is equal.

As an embodiment, the cross-sectional area of the heating coil group is circular, and the crucible 2 is cylindrical, so that the heating in the growth chamber is uniform, the local carbonization of the raw material 8 does not occur, and the prepared silicon carbide single crystal has high quality and few defects.

Preferably, the inner diameter of the second coil assembly 44 is continuously increased, and the included angle between the side wall of the second coil assembly and the central axis of the crucible is 10-45 °. More preferably, the inner diameter of the second coil assembly 44 is continuously increased, and the included angle between the side wall of the second coil assembly and the central axis of the crucible is 20-35 °. The continuous increase of the internal diameter of second coil group 44 for the temperature of growing the crystalline region is at axial continuous variation, guarantees the temperature uniform change of growing the crystalline region, is favorable to the stability of thermal field, thereby makes the silicon carbide single crystal of high quality, low defect, the internal diameter growth rate of second coil group 44 is higher than this scope and can lead to seed crystal department temperature to hang down excessively, polytype defect easily appears, and crystal edge quality is relatively poor, the growth rate is less than this scope and then can't play the effect of increase axial temperature gradient.

Example 2

Referring to fig. 3, the present embodiment is different from the apparatus for manufacturing a single crystal of example 1 in that an adjustment mechanism is different, and the adjustment mechanism further includes a buffer chamber 128.

Specifically, the buffer chamber 128 is disposed above the adjustment chamber 124, and a first valve 1282 is disposed between the buffer chamber 128 and the adjustment chamber 124; the buffer chamber 128 is connected to the gas circuit system 1284 and a heating element 1286 is provided to control the temperature and ambient gas in the buffer chamber 128 and the growth chamber. The first conveying mechanism 126 is provided as a manipulator, after the manipulator conveys the obtained heat preservation ring 1222 to the buffer chamber 128, when the temperature of the heat preservation ring 1222 is the same as that of the adjustment chamber 124, the first valve 1282 is opened, and the manipulator places the heat preservation ring 1222 in the temperature measurement hole 622; the quartz window 1242 is arranged on the side wall of the adjusting chamber 124, and a reflector 1288 is arranged in the adjusting chamber 124 to optically connect the non-contact thermometer 14 with the temperature measuring hole 622. After the thermal insulation ring 1222 with a lower temperature is placed in the adjusting chamber 124, the heating element 1286 of the buffer chamber 128 is used for heating to avoid causing larger fluctuation of the temperature in the growth chamber, thereby ensuring the stability of the temperature of the growth chamber. Preferably, the heating element 1286 is a graphite heater, and the heating element 1286 is disposed on an inner layer of the buffer chamber 128.

In order to ensure the stability of the gas environment of the growth chamber, the buffer chamber 128 is further provided with a second valve 129, the heat-insulating ring 1222 is placed in the buffer chamber 128 after the second valve 129 is opened, the buffer chamber 128 is vacuumized and then flushed with gas to be the same as the ambient gas of the adjusting chamber 124 by using a vacuum pump, the temperature of the buffer chamber 128 is raised to be the same as the temperature of the adjusting chamber 124 by using a heating element 1286, the first valve 1282 is opened, and the first conveying mechanism 126 is controlled to place the heat-insulating ring 1222 in the temperature measuring hole 622. Preferably, the gas comprises an inert gas, such as helium and/or argon.

Preferably, the first valve 1282 is arranged at the top of the temperature measuring hole 622, the reflector 1288 is fixed at the top of the temperature measuring hole 622 at a position opposite to the quartz window 1242, in order to prevent the first conveying mechanism 126 from conveying the heat preservation ring 1222 to the temperature measuring hole 622 to touch the reflector 1288, the buffer chamber 128 is further provided with a second conveying mechanism 130, the reflector 1288 is fixed at the second conveying mechanism 130, when the first conveying mechanism 126 conveys the heat preservation ring 1222 into the adjusting chamber 124, the second conveying mechanism 130 is adjusted to move the reflector 1288 to a position which does not affect the first conveying mechanism 126 to convey the heat preservation ring 1222, and after the heat preservation ring 1222 is conveyed, the second conveying mechanism 130 is adjusted to reset the reflector 1288.

As a specific use embodiment, when the radial temperature gradient needs to be adjusted, the second valve 129 is opened, the heat-insulating ring 1222 is conveyed into the buffer chamber 128 through the first conveying mechanism 126, the second valve 129 is closed, and the buffer chamber 128 is vacuumized and inflated to be close to the atmosphere in the growth cavity; after the above steps are finished, the first valve 1282 is opened, the reflective mirror 1288 for measuring temperature is moved to the edge by the second conveying mechanism 130, and the thermal insulation rings 1222 of different sizes are placed into the temperature measuring hole 622 by the first conveying mechanism 126. Wherein, the rule for placing the heat preservation ring 1222 is as follows: the temperature measuring hole 622 can be changed approximately continuously by first enlarging the large-size heat-preserving ring 1222 and then enlarging the small-size heat-preserving ring 1222.

Example 3

The raw materials 8 in the examples of the present application were all purchased commercially, unless otherwise specified.

The analysis method in the examples of the present application is as follows:

1. the void test was carried out using a model BX51 microscope from OLYMPUS.

2. The surface type test of the silicon carbide single crystal substrate adopts a MicroProf @ TTV200 full-automatic surface type tester of FRT company.

Unless otherwise specified, the raw material 8 and the gas in the examples of the present application were commercially available, wherein the purity of the silicon carbide raw material 8 was 99.99%, and the purity of the high-purity inert gas (Ar or He) was more than 99.999%.

The growth of the silicon carbide single crystal is carried out using the crystal growth apparatus of any of the above embodiments, and the method for producing the silicon carbide single crystal includes the steps of:

1) assembling: placing silicon carbide powder at the bottom in a crucible 2, placing a silicon carbide seed crystal 10 on the inner side wall of a crucible 2 cover of the crucible 2, assembling the crucible 2, a heat preservation structure and a heating coil group, wherein the heat preservation structure is arranged around the crucible 2, the assembled heat preservation structure and the crucible 2 are placed in a crystal growth furnace, and the heating coil group is arranged around the outer side wall of the crystal growth furnace;

2) removing impurities: controlling the pressure of the high-purity inert gas in the crystal growing furnace to be more than 500mbar, and raising the temperature of the crystal growing furnace to 2000-2200 ℃ until the temperature of the temperature measuring hole 622 is controlled;

3) at the initial stage of crystal growth: vacuumizing the crystal growth furnace, reducing the pressure in the crystal growth furnace to 200mbar at a speed of 100-200 mbar/h, and keeping the pressure for 1-2 h;

4) stabilizing the long crystal: continuously vacuumizing, controlling the pressure in the crystal growing furnace to be reduced to 10-20mbar at the rate of 90-180 mbar/h, and simultaneously putting a heat preservation ring 1222 every 1-2 h according to the size sequence to ensure that the area reduction rate of the temperature measurement hole 622 is 10-25%;

wherein, the material of insulation construction is graphite heat preservation felt, and crucible 2 is graphite crucible 2, and the heating coil is medium frequency induction coil.

TABLE 1

The crystal edge polycrystallization conditions, surface shape quality, void defects, and crystal thickness of the prepared silicon carbide single crystal # 1-4 # and the comparative silicon carbide single crystal # D1-D4 # were measured for data of 6 inches, and the measurement results are shown in Table 2.

TABLE 2

Therefore, when the radial temperature gradient is too small in the initial stage due to too small outer diameter of the temperature measuring hole or the axial temperature gradient is too large due to too large included angle between the side wall of the second coil group and the central axis of the crucible, the edge polycrystalline defect is easy to occur. When the radial temperature gradient is too large due to too large aperture of the temperature measuring hole or the radial temperature gradient is too slow to reduce due to too low area reduction rate of the temperature measuring hole during growth, the crystal stress is too large, and the surface type data is poor. When the radial temperature gradient at the initial stage is too small due to the fact that the outer diameter of the temperature measuring hole is too small, cavity defects are prone to occurring. When the coil structure is improper, the axial temperature gradient is too large, or the temperature measuring hole area reduction rate is too fast, so that the temperature field change is unstable, and various defects are easy to occur. When the included angle between the side wall and the central axis of the crucible is increased, the crystal growth rate is accelerated, but when the inner diameter of the first coil group is continuously increased, the axial temperature gradient in the powder is too large, so that the atmosphere transmission is blocked, and the crystal growth rate is greatly reduced.

The above description is only an example of the present application, and the protection scope of the present application is not limited by these specific examples, but is defined by the claims of the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.

Claims (10)

1. A device for preparing single crystal comprises a crucible, a heating coil group and a heat preservation structure, wherein the crucible forms a growth cavity, a seed crystal is arranged in the growth cavity, the heat preservation structure comprises an upper heat preservation structure, a temperature measuring hole is arranged at a position corresponding to the seed crystal, and the device is characterized in that,

the device further comprises an adjusting mechanism, the adjusting mechanism comprises a heat-insulating ring set, the outer diameter of the heat-insulating ring set is the same as the inner diameter of the temperature measuring hole, a through hole is formed in the center of the heat-insulating ring set, the heat-insulating ring set comprises a plurality of heat-insulating rings with gradually decreasing inner diameters, and the adjusting mechanism can place the heat-insulating rings with the inner diameters from large to small into the temperature measuring hole so as to reduce the opening area of the temperature measuring hole and further adjust the radial temperature gradient in the growth cavity.

2. An apparatus for producing a single crystal according to claim 1, wherein the heat retaining ring includes a heat retaining ring main body and an inwardly extending support base provided on an inner wall of the heat retaining ring main body, the support base being provided on a bottom of the heat retaining ring main body, the support base having a thickness of not more than 5 mm.

3. The apparatus for producing a single crystal according to claim 1, wherein the adjusting mechanism further comprises an adjusting chamber and a first conveying mechanism;

the adjusting chamber is communicated with the temperature measuring hole, a quartz window is arranged in the adjusting chamber, the quartz window is connected with the light path of the temperature measuring hole, and a non-contact temperature measuring meter arranged outside the quartz window is used for measuring the temperature of the temperature measuring hole;

and the first conveying mechanism conveys the heat-insulating ring group into the temperature measuring hole.

4. The apparatus for producing a single crystal according to claim 3,

the quartz window is arranged at the top of the adjusting chamber and is opposite to the temperature measuring hole;

the heat-insulating ring group is arranged in the adjusting chamber and comprises a split heat-insulating ring group which is arranged in a split manner along the axial direction of the heat-insulating ring group;

the first conveying mechanism comprises an operation part arranged outside the adjusting chamber and a pushing part arranged inside the adjusting chamber; the inner diameter of the split heat-insulation ring is gradually increased along the directions of the pushing part and the temperature measuring hole; the control operation part drives the pushing part to push the split heat-insulation rings to sequentially enter the temperature measurement holes.

5. An apparatus for producing a single crystal according to claim 3, wherein the adjusting mechanism further comprises a buffer chamber, and a first valve is provided between the buffer chamber and the adjusting chamber;

the buffer chamber is connected with the gas path system and is provided with a heating element so as to control the temperature of the buffer chamber and the growth cavity to be the same as the ambient gas;

the first conveying mechanism is set as a mechanical arm, after the mechanical arm conveys the obtained heat-insulating ring to the buffer chamber, when the temperature of the heat-insulating ring is the same as that of the adjusting chamber, the first valve is opened, and the mechanical arm places the heat-insulating ring in the temperature measuring hole;

the quartz window is arranged on the side wall of the adjusting chamber, and a reflector is arranged in the adjusting chamber to connect the non-contact type temperature measurer with the light path of the temperature measuring hole.

6. The apparatus for preparing a single crystal according to any one of claims 1 to 5, wherein the heating coil group is disposed around a side wall of the crucible,

the heating coil group comprises a first coil group arranged corresponding to the raw material area and a second coil group arranged corresponding to the crystal growth area,

the inner diameter of the second coil assembly increases in a direction from the raw material to the seed crystal.

7. An apparatus for preparing a single crystal according to claim 6, wherein inner diameters of the first coil groups are the same.

8. The apparatus for preparing a single crystal according to claim 6, wherein the crucible and the heating coil group are concentric with each other, and an inner wall of the heating coil group is equidistant from an outer wall of the crucible.

9. An apparatus for preparing a single crystal according to claim 6, wherein the heating coil group has a hollow cylindrical shape and the crucible has a cylindrical shape.

10. An apparatus for preparing single crystal according to claim 6, wherein the inner diameter of the second coil group is continuously increased, and the side wall of the second coil group is inclined at an angle of 10-45 ° to the central axis of the crucible.

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