CN209890759U - Seed crystal support - Google Patents

Abstract

The application provides a seed crystal holds in palm, holds in the palm the central zone of basement through at the seed crystal and is equipped with the heat-conducting layer to the thermal conductivity of heat-conducting layer is greater than the thermal conductivity that the basement was held in the palm to the seed crystal. When SiC seed crystals are bonded on the seed crystal support for single crystal growth, the heat conductivity of the heat conducting layer in the central area of the seed crystal support is larger than that of the base of the graphite seed crystal support, so that the surface temperature of the seed crystals corresponding to the central area is lower than that of other areas of the seed crystals, the concentration of corresponding growth components is high, the supersaturation degree is large, when the supersaturation reaches the critical supersaturation degree, nucleation is started, the temperature of other areas of the surface of the seed crystals is relatively higher, the critical supersaturation degree cannot be reached, and spontaneous nucleation cannot be realized. Thus, the silicon carbide single crystal can be grown slowly centering on the crystal nuclei formed in the central region, and the advantage of the central crystal nuclei is established, thereby obtaining the silicon carbide single crystal. The application utilizes the heat conduction layer to modulate the surface temperature field of the seed crystal, reduces the nucleation number and improves the quality of the SiC crystal.

Description

Seed crystal support

Technical Field

The application relates to the technical field of silicon carbide crystal preparation, in particular to a seed crystal support.

Background

Silicon carbide (SiC), which is a third-generation wide bandgap semiconductor material developed after Si and GaAs, has excellent physicochemical characteristics such as a large forbidden band width, a high critical breakdown field strength, a high thermal conductivity, and a good chemical stability, and therefore, the SiC single crystal material and device industry has become a strategic industry in the high-tech field, and the research of SiC devices has risen worldwide. The large-size SiC wafer can effectively improve the preparation efficiency of the SiC device, greatly reduce the cost of the SiC device and is more beneficial to the popularization of the practicability of the silicon carbide single crystal. For example, the widespread implementation of 150mm diameter SiC substrates and future 200mm, 250mm substrates can impart significant cost reductions to SiC-based semiconductor devices.

At present, the most mature and effective method for growing large-size bulk SiC single crystals is a Physical Vapor Transport (PVT) method, and the basic principle is that SiC polycrystalline powder is heated to a certain temperature or above, gas phase components of the SiC polycrystalline powder after high-temperature sublimation are subjected to material Transport under the action of concentration gradient, and finally, recrystallization is performed on the surface of a silicon carbide seed crystal with lower temperature to grow SiC single crystals. During the growth of SiC single crystal, the temperature field control and optimization are the key points for growing high-quality crystal, for example, the shape evolution of crystal growth interface and the diameter change of single crystal area are all related to the temperature field of crystal growth. Further, a near-planar and slightly convex growth interface is generally considered to be most conducive to high crystal quality, since convex or concave growth interfaces cause step coalescence, stacking faults, polytype inclusions, and other defects at the growth interface. Moreover, for SiC single crystal growth, only one nucleation growth center is most reasonable, so that the step can be pushed to the edge and is not blocked, and stable growth can be carried out. However, there is often a multi-nuclear competition phenomenon during the initial stage of crystal growth, which results in the generation of a large number of defects, such as small corners, when one growth center annihilates another or two growth centers meetGrain boundaries, micropipes, dislocations, and polytype inclusions. The reason for the multi-core competition is that the temperature distribution on the surface of the seed crystal is not uniform, so that the growth components (Si and Si) on the surface of the seed crystal are generated₂C、SiC₂Etc.) the supersaturation distribution is uneven, corresponding to low temperature, the concentration of the growth components is high, the supersaturation is large, and in addition, a large number of dislocation outcrop points are arranged on the surface of the seed crystal, so that spontaneous nucleation is easy to generate a large number of growth centers.

In conclusion, for the growth of large-size SiC single crystals (the diameter is larger than 100mm), the requirement on the uniformity of the temperature field on the surface of the seed crystal is extremely high due to the fact that the area of the seed crystal is greatly increased. However, in the actual crystal growth process, the absolute uniformity of the temperature field in the area of the large-size seed crystal is difficult to ensure, and when a plurality of local low-temperature points exist in the temperature field on the surface of the seed crystal in the initial growth stage and the supersaturation degree reaches the critical value required by nucleation at the positions, the multi-core phenomenon is generated, and the crystal quality is deteriorated. Therefore, in order to inhibit the spontaneous nucleation growth phenomenon, establish the initial central facet nucleation center advantage and ensure the single growth center growth of the single crystal, a large radial temperature gradient is required to be introduced, which is inconsistent with the near-flat micro-convex temperature field required by the growth of the high-quality silicon carbide single crystal, and for the growth of the large-size single crystal, the large radial temperature gradient can introduce considerable internal stress into the single crystal, introduce a large amount of defects such as dislocation, stacking fault and the like into the crystal, and even directly cause the direct cracking of the single crystal.

SUMMERY OF THE UTILITY MODEL

The embodiment of the utility model provides a seed crystal holds in palm to solve the problem of the multinuclear phenomenon among the prior art in the single crystal growth.

According to the utility model discloses an aspect provides a seed crystal holds in palm, and this seed crystal holds in palm the seed crystal support basement including the graphite material, wherein:

a heat conduction layer is arranged in the central area of one side, used for bonding seed crystals, of the seed crystal support substrate, and the seed crystals are bonded to the heat conduction layer and the seed crystal support substrate around the heat conduction layer through an adhesive;

the heat conduction layer has a thermal conductivity greater than that of the seed holder base.

Optionally, the area of the heat conducting layer accounts for 5% -10% of the total area of the seed crystal holder base.

Optionally, the heat conducting layer is a heat conducting thin film structure arranged on the surface of the seed holder substrate, and the heat conducting thin film comprises a single-layer thin film structure or a multi-layer thin film structure.

Optionally, a groove is formed in a central region of one side of the seed crystal support substrate, which is used for adhering the seed crystal, and the heat conduction layer is filled in the groove.

Optionally, a central region of the seed holder base is provided with a through hole, and the heat conduction layer is filled in the through hole.

Optionally, the surface of the heat conducting layer and the surface of the seed holder base are at the same level.

Optionally, the material used for the heat conducting layer comprises a refractory metal, a carbide of a refractory metal, a nitride of a refractory metal or a polycrystalline silicon carbide.

According to the second aspect of the embodiment of the utility model, still provide another kind of seed crystal and hold in the palm, this seed crystal holds in the palm the basement including the seed crystal of graphite material, wherein:

the heat conducting layer is arranged in the central area of the back surface of the seed crystal support base, and the front surface of the seed crystal support base is used for bonding seed crystals through an adhesive;

the heat conduction layer has a thermal conductivity greater than that of the seed holder base.

Optionally, the area of the heat conducting layer accounts for 5% -10% of the total area of the seed crystal holder base.

It can be seen from the above-mentioned embodiment that, the seed crystal support that this embodiment provided, through being equipped with the heat-conducting layer in the central zone of seed crystal support base, when holding the SiC seed crystal and carrying out single crystal growth on the seed crystal support, because the heat conductivity of the heat-conducting layer of seed crystal support central zone is bigger than graphite seed crystal support base, consequently, the seed crystal surface temperature that corresponds this central zone compares other regional temperatures of seed crystal low, and then it is high to correspond growth component concentration, the degree of supersaturation is big, when its supersaturation reaches critical supersaturation, begin nucleation promptly, and other regions of seed crystal surface are because the temperature is relatively higher, the degree of supersaturation is little, still can not reach critical supersaturation, can. Thus, the silicon carbide single crystal can be obtained by slowly growing the crystal nuclei formed in the central region as the center, establishing the central crystal nucleus dominance, and then rapidly growing the silicon carbide single crystal by changing the conditions. Utilize above-mentioned seed crystal to hold in the palm the heat-conducting layer modulation seed crystal surface temperature field in base central zone, can make the SiC single crystal under the radial temperature gradient condition that is close to zero, preferentially form the crystal nucleus at the seed crystal center, consequently, not only reduced nucleation quantity but also avoided big radial temperature gradient to introduce the problem of big internal stress inside the single crystal, improved SiC crystal quality.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive labor.

Fig. 1 is a schematic diagram of a basic structure of a seed crystal holder provided in an embodiment of the present application;

FIG. 2 is a schematic view of the upper surface structure of the seed holder in FIG. 1;

FIG. 3 is a schematic view of the seed holder of FIG. 1 after being bonded with a silicon carbide seed crystal;

FIG. 4 is a schematic diagram of a basic structure of another seed holder provided in the embodiments of the present application;

FIG. 5 is a schematic diagram of a basic structure of another seed holder provided in the embodiments of the present application;

FIG. 6 is a schematic diagram of another seed holder with a silicon carbide seed crystal bonded thereto according to an embodiment of the present disclosure;

fig. 7 is a schematic flow chart of a method for growing a silicon carbide single crystal according to an embodiment of the present application.

Detailed Description

In order to make the technical solutions in the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts shall belong to the protection scope of the present invention.

Aiming at the problem that in the prior art, a multi-core competition phenomenon exists in the initial growth stage of a silicon carbide single crystal, so that a large number of defects are generated in the crystal, and particularly a large-size SiC single crystal is grown (the diameter is larger than 100 mm). However, in order to inhibit multi-core competition, the large radial temperature gradient growth method adopted at present can introduce a large amount of defects such as dislocation, stacking fault and the like into the single crystal due to considerable internal stress in the single crystal, and even directly cause the problem of direct cracking of the single crystal. This example provides a seed holder that produces high quality large diameter SiC crystals by controlling the nucleation process and the number of nucleation on the seed surface.

Example one

Fig. 1 is a schematic diagram of a basic structure of a seed holder according to an embodiment of the present disclosure. Fig. 2 is a schematic view of the upper surface structure of the seed holder in fig. 1. As shown in fig. 1 and 2, the seed holder includes a seed holder base 10 made of graphite, wherein a heat conduction layer 20 is disposed in a central region of one side of the seed holder base 10 for bonding the seed, specifically, the heat conduction layer 20 is a heat conduction thin film structure disposed on the surface of the seed holder base 10, and the heat conduction thin film includes a single-layer thin film structure or a multi-layer thin film structure. Meanwhile, the heat conducting layer 20 and the seed-holder base 10 are required to have a certain thermal conductivity difference, and the thermal conductivity of the material of the heat conducting layer 20 is larger than that of the seed-holder base 10.

The heat conducting layer 20 may be made of high melting point metal, carbide of high melting point metal, nitride of high melting point metal, or polycrystalline silicon carbide. The refractory metal described in this embodiment may include high-melting-point metals such as tungsten, tantalum, niobium, iridium, and titanium. In the fabrication, the heat conductive layer 20 may be formed on the upper surface of the seed-holder base 10 by a film formation method such as sputtering or vapor deposition. Also, when the heat conductive layer 20 has a multilayer film structure, the films may be made of the same or different materials.

Further, the area of the heat conducting layer 20 accounts for 5% to 10% of the total area of the seed holder base 10, for example, the diameter thereof may be 20mm, preferably 10mm, more preferably 5mm or 2 mm. Since this example requires SiC nucleation in the central region corresponding to the heat conducting layer 20, theoretically, the smaller the area of this region, the smaller the number of nucleation, and the easier it is to establish the advantage of a single nucleus, therefore, this example verifies according to experiments that the lower limit of the area of the heat conducting layer 20 in the total area of the seed-holder substrate 10 is set to 5%. However, if the area of the central region is too small, the central crystal nucleus dominance is not easily established, and therefore, the lower limit of the area of the heat conductive layer 20 to the total area of the seed-crystal-holder substrate 10 is 5% according to experimental verification.

FIG. 3 is a schematic view of the structure of the seed holder of FIG. 1 after the silicon carbide seed crystal is bonded thereto. In use, as shown in fig. 3, the seed crystal 40 is adhered to the heat conductive layer 20 and the seed holder base 10 around the heat conductive layer by the adhesive 30. Then, the seed crystal holder with the seed crystal bonded thereto is put into a SiC single crystal growth furnace to perform bulk growth of a SiC single crystal on the seed crystal 40 by physical vapor transport.

Specifically, when the SiC seed crystal 40 is bonded to the seed holder for SiC crystal growth, the heat conducting layer 20 in the central region of the seed holder has a certain thermal conductivity difference with the graphite material around the seed holder, and the material thermal conductivity is large and the heat dissipation is fast. Therefore, in certain temperature and pressure range, the central area of the surface of the seed crystal is lower in temperature than other areas of the seed crystal, the corresponding growth component concentration is high, the supersaturation degree is large, when the supersaturation concentration reaches the critical supersaturation degree, nucleation is started, and the other areas of the surface of the seed crystal cannot perform spontaneous nucleation due to the fact that the temperature is relatively higher, the supersaturation degree is small and the critical supersaturation degree is not reached. It should be noted that the temperature range should exactly fall within the temperature window in which the 4H or 6H crystal forms are stable, so as to ensure that the central nucleation is the required crystal form nucleation, and no other heterogeneous phase nucleation generates multi-type inclusions. After the central area of the surface of the seed crystal is nucleated once, under the growth condition, slow growth is carried out, and the step formed by the nucleation center at the center of the seed crystal is gradually expanded outwards until the step is expanded to the edge of the large-diameter seed crystal, so that the central nucleus advantage is established, wherein the growth rate can be controlled to be below 100 mu m/h, preferably below 50 mu m/h, and more preferably below 30 mu m/h. And finally, increasing the temperature, reducing the pressure and increasing the growth rate to grow the crystal thick, and finishing the growth when the thickness of the crystal reaches a preset value. Wherein the growth rate may be 300 μm/h, 500 μm/h, or even 1 mm/h.

The seed crystal support provided by the embodiment utilizes the central region material to have higher heat conductivity than the surrounding region, so as to modulate the temperature field of the surface of the seed crystal, and further in the crystal growth process, so that the SiC crystal can be under the condition of nearly zero radial temperature gradient (such as the temperature field of nearly flat and slightly convex), the crystal nucleus is preferentially formed at the seed crystal center and the formation density of the crystal nucleus is low, and the optimal condition is that only a single crystal nucleus is formed, thereby avoiding a large number of defects of small-angle crystal boundaries, micro-tubes, dislocation, multi-type inclusions and the like generated when a plurality of growth centers meet or annihilate in the prior art, and further avoiding the problem that large internal stress is introduced into the single crystal by large radial temperature gradient, thereby obtaining the high-quality large-size silicon carbide single crystal.

The seed crystal holder provided by the embodiment can be suitable for manufacturing single crystals of 4H, 6H and 15R crystal forms and also suitable for n-type and semi-insulating single crystals. The diameter of the seed crystal support in the embodiment can be 100mm, 125mm, 150mm, 200mm or 250mm, and even larger-sized silicon carbide single crystals, and the advantages are more obvious when the size of the single crystal is larger.

Example two

The larger the surface area of the heat conducting layer 20 on the seed holder base 10 is, the more obvious the temperature field regulation effect on the seed crystal surface is, but the larger the area is, the number of nucleation in the area is increased. Therefore, the embodiment also provides another seed holder on the basis of the first embodiment.

Fig. 4 is a schematic diagram of a basic structure of another seed holder provided in the embodiments of the present application. As shown in fig. 4, the seed holder provided in this example includes a seed holder base 10, and a central region of one side of the seed holder base 10 for adhering the seed crystal is provided with a groove in which the heat conductive layer 20 is filled. Meanwhile, the heat conducting layer 20 and the seed-holder base 10 are required to have a certain thermal conductivity difference, and the thermal conductivity of the material of the heat conducting layer 20 is larger than that of the seed-holder base 10.

Furthermore, in order to ensure the nucleation quantity and quality, the area of the heat conduction layer 20 accounts for 5% -10% of the total area of the seed crystal holder base 10.

In this embodiment, the heat conduction layer 20 is embedded in the seed crystal holder substrate 10, so that on one hand, the surface area of the heat conduction layer 20 can be increased, and on the other hand, the thickness of the seed crystal holder substrate 10 corresponding to the region can be thinned, the heat conduction effect is increased, and further, the temperature field on the surface of the seed crystal can be better.

Further, in order to facilitate the adhesion of the seed crystal to the seed crystal holder and prevent the air layer problem at the interface between the heat conduction layer 20 and the seed crystal holder substrate 10 in the surrounding area due to poor filling of the adhesive, the present embodiment is to design the surface of the heat conduction layer 20 and the surface of the seed crystal holder substrate 10 to be in the same horizontal plane, that is, the surface of the whole seed crystal holder is a flat surface.

EXAMPLE III

In the above embodiment, the heat conducting layer 20, mainly the crystal support substrate and the binder around the heat conducting layer, radiate heat through heat conduction, so as to achieve the purpose of adjusting and controlling the temperature field, and in order to make the heat conducting layer 20 have a more direct heat radiation effect, the temperature difference between the central position of the surface of the seed crystal is larger than that between other regions of the seed crystal. This embodiment provides another seed holder on the basis of the first and second embodiments.

Fig. 5 is a schematic diagram of a basic structure of another seed holder provided in the embodiments of the present application. As shown in fig. 5, the seed holder provided in this example includes a seed holder base 10, and a through hole is opened in a central region of the seed holder base 10, and the heat conductive layer 20 is filled in the through hole. Meanwhile, the heat conducting layer 20 and the seed-holder base 10 are required to have a certain thermal conductivity difference, and the thermal conductivity of the material of the heat conducting layer 20 is larger than that of the seed-holder base 10.

Furthermore, in order to ensure the nucleation quantity and quality, the area of the heat conduction layer 20 accounts for 5% -10% of the total area of the seed crystal holder base 10. In addition, in order to facilitate the attachment of the seed crystal to the seed holder, the present embodiment is designed such that the surface of the heat conducting layer 20 and the surface of the seed holder base 10 are at the same level, i.e., the entire surface of the seed holder is a flat surface.

In this embodiment, the heat conduction layer 20 is disposed in the through hole formed on the seed holder base 10, and the back surface thereof not in contact with the seed crystal can directly perform convection heat dissipation with the surrounding air, and thus, a more direct heat dissipation effect can be obtained.

Example four

The above embodiments all have the heat conduction layer 20 disposed on the front surface of the seed holder base 10 for adhering the seed crystal, but it is also possible to design the heat conduction layer on the back surface.

Fig. 5 is a schematic diagram of a basic structure of another seed holder provided in the embodiments of the present application. As shown in fig. 5, the seed holder provided in this example includes a seed holder base 10, a heat conductive layer 20 is provided in a central region of a back surface of the seed holder base 10, and a front surface of the seed holder base 10 is used for bonding the seed by an adhesive. Meanwhile, the heat conducting layer 20 and the seed holder base 10 have a certain thermal conductivity difference, and the thermal conductivity of the material of the heat conducting layer 20 is larger than that of the seed holder base 10.

Thus, the central region of the seed crystal holder base 10 can be lower in temperature than other regions through the heat conduction layer 20, and the central region of the surface of the seed crystal is lower in temperature than other regions of the seed crystal, so that the effect of temperature field regulation is achieved.

Of course, a groove may be dug on the back of the seed holder base 10, and the heat conduction layer 20 may be filled in the groove.

Further, with the seed crystal holder provided in the above embodiment, the present example also provides a silicon carbide single crystal growth method. Fig. 7 is a schematic flow chart of a method for growing a silicon carbide single crystal according to an embodiment of the present application. As shown in fig. 7, the method specifically includes the following steps:

step S110: and adhering the seed crystal to the seed crystal holder by using the seed crystal through an adhesive.

The seed crystal support comprises a seed crystal support base made of graphite, and a heat conducting layer is arranged in the central area of the seed crystal support base, wherein the heat conductivity of the material of the heat conducting layer is larger than that of the seed crystal support base.

Step S120: and (4) putting the seed crystal holder adhered with the seed crystal into a growth furnace, and vacuumizing.

Step S130: the growth temperature is controlled to be 2000-2100 ℃, the temperature field is a nearly flat slightly convex temperature field, the area of the seed crystal provided with the heat conduction layer is nucleated, and the step formed by the nucleation center of the seed crystal is gradually expanded outwards until the step is expanded to the edge of the seed crystal.

Wherein, the growth pressure can be 200mbar, the growth temperature field is a nearly flat slightly convex temperature field by designing heat preservation, the center of the seed crystal is controlled to carry out nucleation, the seed crystal grows at a slow speed for 10-20h, the step formed by the nucleation center at the center of the seed crystal gradually expands outwards until the step expands to the edge of the large-diameter seed crystal, and the advantage of the center nucleus is established.

Furthermore, before the step, the surface of the seed crystal can be etched to remove the stress damage layer.

Step S140: and (4) heating and reducing the pressure to grow the silicon carbide single crystal to be thick until the thickness of the silicon carbide single crystal is the preset thickness.

By utilizing the steps, the density of nucleation growth centers on the surface of the large-size seed crystal is greatly reduced under a temperature field which is nearly flat and slightly convex, the reduction of the density of the growth centers means the reduction of the defect density, a large number of defects such as small-angle crystal boundaries, micro-tubes, dislocation, multi-type inclusions and the like generated when a plurality of growth centers meet or annihilate are avoided, the improvement of the crystal quality is facilitated, and the high-quality large-size silicon carbide single crystal can be obtained.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for apparatus or system embodiments, since they are substantially similar to method embodiments, they are described in relative terms, as long as they are described in partial descriptions of method embodiments. The above-described embodiments of the apparatus and system are merely illustrative, and the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

The above is only a specific embodiment of the present invention, and it should be noted that, for those skilled in the art, a plurality of improvements and decorations can be made without departing from the principle of the present invention, and these improvements and decorations should also be regarded as the protection scope of the present invention.

Claims (9)

1. A seed crystal support is characterized by comprising a seed crystal support base made of graphite, wherein:

a heat conduction layer is arranged in the central area of one side, used for bonding seed crystals, of the seed crystal support substrate, and the seed crystals are bonded to the heat conduction layer and the seed crystal support substrate around the heat conduction layer through an adhesive;

the heat conduction layer has a thermal conductivity greater than that of the seed holder base.

2. A seed holder as set forth in claim 1, wherein the area of the heat conducting layer is 5-10% of the total area of the base of the seed holder.

3. The seed holder as claimed in claim 1, wherein the heat conducting layer is a heat conducting thin film structure provided on the substrate surface of the seed holder, and the heat conducting thin film comprises a single-layer thin film structure or a multi-layer thin film structure.

4. A seed holder as set forth in claim 1, wherein a central region of a side of the base of the seed holder for adhering the seed crystal is provided with a groove, and the heat conductive layer is filled in the groove.

5. A seed holder as set forth in claim 1, wherein a central region of the base of the seed holder is provided with a through hole, and the heat conductive layer is filled in the through hole.

6. A seed holder as claimed in claim 4 or 5, wherein the surface of the heat conducting layer is at the same level as the surface of the seed holder base.

7. A seed holder as claimed in claim 1, wherein the material used for the heat conducting layer comprises a refractory metal, a carbide of a refractory metal, a nitride of a refractory metal or a polycrystalline silicon carbide.

8. A seed crystal support is characterized by comprising a seed crystal support base made of graphite, wherein:

the heat conducting layer is arranged in the central area of the back surface of the seed crystal support base, and the front surface of the seed crystal support base is used for bonding seed crystals through an adhesive;

the heat conduction layer has a thermal conductivity greater than that of the seed holder base.

9. A seed holder as set forth in claim 8, wherein the area of the heat conducting layer is 5-10% of the total area of the base of the seed holder.

Images