CN111379026A

CN111379026A - Seed crystal processing method and device

Info

Publication number: CN111379026A
Application number: CN201911161732.8A
Authority: CN
Inventors: 匡怡君
Original assignee: Shanghai Lianxing Business Consulting Center
Current assignee: Shanghai Lianxing Business Consulting Center
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2020-07-07

Abstract

The invention provides a seed crystal processing method and a device, wherein a groove is arranged at the center of a disc-shaped graphite disc for fixing the seed crystal, the lower surface (non-growth surface) of the seed crystal is tightly attached to a porous groove of the graphite disc, raw materials are sublimated by adopting a PVT method, sublimed gas passes through the porous groove, and then a thin compact silicon carbide layer is grown between the lower surface (non-growth surface) of the seed crystal and the graphite disc by adjusting the temperature, the pressure and the processing time, so that the function of bonding the seed crystal and the graphite disc is achieved. The seed crystal processing method and the seed crystal processing device provided by the invention can be used for processing seed crystals in batches.

Description

Seed crystal processing method and device

Technical Field

The invention relates to a silicon carbide wafer processing technology, in particular to a seed crystal processing method and a seed crystal processing device.

Background

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

At present, the growth technology of silicon carbide single crystal at home and abroad is a physical vapor transport method (PVT). Namely, the silicon carbide raw material is sublimated at high temperature, and the generated gas-phase components are transported to the surface where the seed crystal grows to be recrystallized.

The connection between the seed crystal and the graphite cover is generally realized by the solidification and sintering of carbon adhesive and carbon-containing organic matter: firstly, after manual uniform gluing is carried out on the seed crystal bonding position on the lower surface of graphite, preburning graphite paper is pasted on the gluing position of a graphite cover, compacting is carried out, manual uniform gluing is carried out again on the pasted graphite paper, the back surface of the seed crystal growth is pasted on the glued graphite paper, and solidification and connection are carried out through a heavy object or a pneumatic compaction sintering method after compacting. During sintering, the glue shrinks and carbonizes, and the generated gases are combined together to form a cavity. Because the lower surface of the graphite cover is heated unevenly in the sintering process, and the time for carbonizing the glue is short, the time for curing the glue is not uniform. If the glue at the edge is cured firstly and the glue at the center is cured later, the gas discharge path generated by the glue at the edge part is short, and the gas discharge path generated by the glue at the center part is long, so that the bubbles generated at the center part cannot be discharged in time, and large-area cavities between the seed crystals and the graphite can be caused. In the growth process of the seed crystal with the large-area cavity, heated bubbles in the cavity expand at high temperature to a certain extent, so that the seed crystal and the graphite cover fall off to cause growth failure. Even though the removed glue is uniform, the glue shrinks and releases air bubbles all the time during the carbonization process until the glue shrinks to a carbonization and solidification state. In the process, the contracted glue causes the graphite and the seed crystal to be in point contact or connected into blocks by small-area glue after the glue is carbonized. In the early stage of crystal growth, the small holes on the back of the seed crystal can cause the uneven temperature field on the surface of the crystal growth, so that an irregular growth surface type is generated, and the temperature difference around the small holes can cause the evaporation of the back of the crystal to generate the phenomenon of back corrosion.

In order to eliminate the influence caused by the holes in the crystal growth process, CN106757321A discloses a seed crystal treatment method, in which two dense graphite layers are obtained on the back of the seed crystal by a one-step method, the graphite layers can be kept stable at high temperature, the occurrence of sublimation on the back of the seed crystal can be inhibited, and the defect of a planar hexagonal cavity caused by sublimation on the back in the crystal growth process is eliminated. However, the method cannot ensure that the growth surface of the seed crystal is not influenced by the treatment process, the treatment process is low in efficiency, and batch seed crystal treatment cannot be realized.

Disclosure of Invention

In order to solve the defects that the artificial adhesion of the seed crystal is not uniform and bubbles are easy to generate to cause the falling of the seed crystal, the invention aims to provide a seed crystal processing method and a seed crystal processing device, which are used as a pretreatment step for manufacturing a silicon carbide wafer by a PVT sublimation method, namely, the technical scheme is to adhere the seed crystal to a graphite disk and ensure that the growth surface of the seed crystal is not influenced, so that the graphite disk with the seed crystal can be directly applied to the subsequent crystal growth process.

In the subsequent crystal growth process of the silicon carbide, the graphite disk is inverted at the bottom of the crucible cover, so that the seed crystal and the graphite disk are required to be completely bonded and cannot fall off. After the crystal growth process is finished, the seed crystal and the graphite disk are cut and separated, so that the silicon carbide film protrusion on the lower surface (non-growth surface) of the seed crystal does not influence the final silicon carbide wafer finished product.

The invention provides a seed crystal processing method and a seed crystal processing device, which aim to effectively avoid bubbles from being generated between a seed crystal and a graphite disk and ensure the close connection of the seed crystal and the graphite disk.

In order to achieve the purpose, the invention adopts a technical scheme that: a method of processing a seed crystal, the method comprising: graphite paper is adhered to the growth surface of the seed crystal through graphite glue, and the graphite paper covers the whole upper surface (growth surface) of the seed crystal so as to prevent the surface of the seed crystal from evaporating and the surface of the seed crystal from inducing nucleation due to the deposition of silicon carbide components in the atmosphere during the seed crystal treatment process. Meanwhile, the heat insulation effect of the graphite paper can cause the temperature of the lower surface of the seed crystal to be lower than that of the surrounding graphite heating piece, so that the nucleation of silicon carbide on the lower surface of the seed crystal is facilitated;

attaching the lower surface (non-growth surface) of the seed crystal to a graphite disc;

fixing the graphite disc in a support frame, and putting the support frame into the crucible at the upper side;

and treating the crucible at high temperature and introducing treatment gas to sublimate the raw material at the bottom of the crucible, wherein the raw material is preferably a mixture of carbon powder and silicon powder, and the introduction flow rate, the treatment pressure and the high-temperature treatment time of the treatment gas are adjusted simultaneously until the seed crystal is bonded with the graphite disk. The introduction of the processing gas generates airflow in the crucible, and a layer of compact silicon carbide layer grows on the lower surface (non-growth surface) of the seed crystal at the porous part of the graphite disk under the action of the airflow, so that the seed crystal and the porous graphite disk are tightly combined together to play a role in seed crystal bonding. Wherein the raw material is selected from a mixture of compounds or gases containing a silicon source and a carbon source, preferably with a particle size of 50-500 microns.

Wherein, the treatment gas is preferably argon gas and methane, the flow rate of the argon gas is 1-500sccm, the flow rate of the methane is 1-100sccm, and the pressure of the treatment gas is 1-600 torr.

Wherein the high temperature treatment comprises treatment at 1600-2100 ℃ for 8-20 hours.

In order to achieve the above object, the present invention further provides a seed crystal processing apparatus, which comprises a graphite disk, a crucible and a support frame, wherein the graphite disk has a plurality of regularly arranged through holes, the support frame comprises a support frame wall and a main body part, the main body part comprises a support arm, a bracket and a central hollow hole from outside to inside, and the support frame can be fixed on the upper side inside the crucible.

The graphite disk comprises a disk edge and a groove, the graphite disk is of an outer structure and an inner structure, the through holes are located in the groove, the through holes can be in the shapes of patterns in any shapes and hole intervals in any sizes, and the premise is that a silicon carbide atmosphere in the bottom space can be transmitted through the through holes to form a compact silicon carbide layer on the growth back of the seed crystal to be bonded with the graphite disk, and the graphite disk is preferably arranged in a circular ring regular distribution manner or in a parallel regular distribution manner.

The groove can be any groove with the size of the seed crystal, and the premise is that the groove has a certain depth, so that the problem of bonding dislocation caused by the fact that the seed crystal slides in the bonding process is solved. The depth of the groove is not higher than the height of the seed crystal, the inner diameter of the groove is 0.1-0.2mm larger than the outer diameter of the seed crystal, so that the seed crystal can freely move in the groove to a certain extent without large-area sliding, the adhesion of the seed crystal bonded silicon carbide layer and the graphite disk is ensured, and the stress in the seed crystal is not greatly increased due to the adhesion of the seed crystal.

The shape of the bracket of the support frame is matched with the shape of the edge of the graphite disc.

The diameter of the central hole is the same as that of the groove of the graphite disc, and the diameter of the support frame bracket is the same as that of the graphite disc, so that when the graphite disc is placed on the support frame, the edge of the graphite disc is matched with the support frame bracket, and the groove of the graphite disc is matched with the central hole of the support frame.

Wherein, the hole diameter of the through holes is preferably 0.1-2mm, and the hole spacing is preferably 0.1-2 mm.

Wherein, the interval between the support arm is at least 10 mm.

And a circle of through holes are formed between the surface of the support frame and the inner wall of the support frame by 1-23.5 mm and are used for silicon source gas circulation. The hole diameter of the through holes is preferably 0.1-2mm, and the hole spacing is preferably 0.1-2 mm.

The support frame is formed by combining two semicircular components, so that the multilayer graphite disk can be conveniently taken and placed.

Effects of the invention

Compared with the prior art, the invention has the advantages that:

(1) according to the method and the device provided by the invention, the seed crystals are fixed on the grooves on the upper surface of the graphite disc, the bottom surface of the graphite disc is provided with the plurality of through holes, and the through holes are required to be uniformly distributed on the graphite disc, so that the firm bonding of the seed crystals and the graphite disc is ensured, and the defect that the seed crystals fall off due to the fact that the seed crystals are not uniformly bonded manually and bubbles are easily generated is overcome.

(2) According to the method and the device provided by the invention, the supporting frame with the multiple layers of supporting arms is arranged in the crucible, and each layer of supporting arm can be independently used for processing one seed crystal, so that the mass seed crystal bonding is realized, and the cost advantage is greatly saved for realizing industrialization quantification of subsequent crystals.

Drawings

FIG. 1: the crucible structure provided by the embodiment of the invention is schematic.

FIG. 2: the embodiment of the invention provides a structural schematic diagram of a support frame.

FIG. 3: the front view of the graphite disc provided by the embodiment of the invention.

FIG. 4: the embodiment of the invention provides a front view of a seed crystal adhered with graphite paper and placed on a graphite disk.

FIG. 5: the embodiment of the invention provides a schematic structural diagram of a graphite disk.

FIG. 6: the embodiment of the invention provides a top view of a graphite disk with circular through holes arranged in parallel.

FIG. 7: the embodiment of the invention provides a top view of a graphite disk with rectangular through holes arranged in parallel.

FIG. 8: the embodiment of the invention provides a top view of a graphite disk with hexagonal through holes arranged in parallel.

FIG. 9: the embodiment of the invention provides a top view of a graphite disk with concentric circular through holes.

FIG. 10: the embodiment of the invention provides a top view of a graphite disk with concentric rectangular through holes.

FIG. 11: the embodiment of the invention provides a top view of a graphite disk with hexagonal through holes arranged in concentric circles.

FIG. 12: the crucible provided by the embodiment of the invention is placed in a front view of the support frame.

FIG. 13: the crucible provided by the embodiment of the invention is placed in a supporting frame, but is not placed in a graphite disc.

FIG. 14: the graphite disc provided by the embodiment of the invention is in a position relation graph with a crucible and a support frame in the processing process. Wherein, a graphite disc is arranged on the first layer of the supporting frame, and a seed crystal is also arranged on the graphite disc.

FIG. 15: the contrast graph of the microtube density of the crystal after the growth of the bonded seed crystal and the seed crystal bonded by glue is adopted.

Description of reference numerals: (1) the crucible is characterized in that the crucible is a disc edge, (2) the crucible is a groove, (3) the crucible is a through hole, (4) the crucible cover, (5) the support frame wall, (6) the bracket, (7) the support arm, (8) the through hole on the support arm, (9) the central hollow hole, (10) the crucible outer wall, and (11) the raw material at the bottom of the crucible.

Detailed Description

The present invention will now be described in further detail with reference to the accompanying drawings, but the following embodiments do not limit the present invention.

Examples 1 to 4:

the seed crystal adopts 4 inches of seed crystal with the diameter of 100mm and the thickness of 0.5mm, graphite glue is evenly smeared on the upper surface (growing surface) of the seed crystal, and then the seed crystal which is smeared with the graphite paper with the diameter of 100mm and the thickness of 0.02mm is tightly attached to the seed crystal, so that the graphite paper completely covers the upper surface of the seed crystal. After the graphite paper and the seed crystal are compacted, the residual glue on the side surface of the seed crystal is cleaned. The seed crystal stuck with the graphite paper is placed in the groove (2) of the graphite disk, wherein the lower surface (non-growth surface) of the seed crystal is attached to the graphite disk, as shown in figure 4. The diameter of the graphite disc is 110mm, the thickness of the graphite disc is 2mm, multiple holes (3) which are regularly arranged in a circular ring shape are formed in the groove (2) of the graphite disc, the diameter of each hole is 1mm, the distance between every two holes is 1mm, the holes are arranged according to a concentric circle equidistant method, and as shown in figure 9, the depth of the groove is 0.3 mm. The graphite discs are placed in the central hollow (9) of the support frame as shown in figures 13 and 14. The diameter of the central hollow hole is 100mm, the diameter of the bracket (6) is 110mm, the thickness of the bracket is 0.5mm, and the shape of the bracket is matched with that of the disc edge (1) of the graphite disc. A plurality of circles of holes (8) with the diameter of 1mm are arranged on the supporting arm (7) of the supporting frame 1mm away from the supporting frame wall (5), the diameter of each hole is 1mm, and the distance between the holes is 1mm, as shown in figure 13. The support arm thickness of support frame is 2mm, and support frame wall (5) thickness is 4mm, and the support frame is inside to include nine support arms, and as shown in fig. 2, the interval between the support arm is 10mm, and the total height of support frame is 118mm, and the external diameter 190 mm. The supports are placed on the upper inner side of the crucible with the support walls (5) resting just above the protrusions on the inner wall of the crucible as shown in figures 12 and 14. The crucible has the outer diameter of 206mm, the total height of 230mm, the bottom thickness of 12mm, the inner bottom height of 100mm and the upper bottom height of 118mm, and the wall thickness of 8 mm. The bottom center of the crucible is provided with a small temperature measuring hole with the diameter of 10mm and the depth of 7 mm. As shown in figures 1, 12 and 14, the crucible cover is T-shaped, the diameter of the upper surface of the crucible cover is 206mm, the thickness of the crucible cover is 5mm, the center of the crucible cover is provided with a small temperature measuring hole, the diameter of the hole is 10mm, and the depth of the hole is 10 mm. The diameter of the lower boss of the crucible cover is 190mm, and the height of the column is 10 mm.

Before treatment, a mixture of silicon powder and carbon powder with a particle size of about 200 microns is loaded in advance at the bottom of the crucible as a raw material (11), wherein the silicon powder and the carbon powder are mixed with a silicon carbide raw material according to a molar ratio of 1: 1.2, the height of the raw material is 40mm, and the raw material weighs about 500g, as shown in FIG. 14. Secondly, the support frame with the seed crystal is placed in the crucible, and the crucible cover is covered. Carrying out high-temperature treatment on the crucible in a specific device, wherein the crucible reaches the treatment temperature in about 3 hours, the temperature of the upper bottom is controlled to be 1800 ℃ under the monitoring of upper and lower temperature measurement, the temperature of the lower part is 2021 ℃ through the adjustment of a coil, the temperature difference between the upper part and the lower part is 221 ℃, and the average value of the temperature gradient is 1 ℃/mm; argon gas was introduced at a flow rate of 100sccm and methane at a flow rate of 2sccm at the same time as the start of heating, and the gas pressure in the treatment chamber was controlled to be stabilized at 10Torr for 30 minutes, the argon gas and methane were mixed at a molar ratio of 50: 1, and the pressure of the high-temperature treatment was kept constant at 10 Torr. And (3) after the high-temperature treatment is finished, closing the methane, continuously filling argon, keeping the flow rate unchanged, reducing the heating power to 0 within about 6 hours, and then closing the argon. After cooling, taking out the seed crystal.

According to the method and the device, 4 embodiments are arranged, high-temperature treatment is carried out for 8 hours, 12 hours, 16 hours and 20 hours respectively, after cooling, the seed crystal is taken out, and the seed crystal is bonded with the graphite disk. The weight change of the seed crystal and the graphite disk is numbered from top to bottom in sequence as follows: upper 1-upper 3, middle 1-middle 3, lower 1-lower 3, three segments. The weight changes before and after 4 experiments are respectively shown in tables 1-4:

sequence of tablets

Upper

1

Upper 2

Upper 3

In 1

In 2

Middle 3

Lower 1

Lower 2

Lower 3

Weight gain

0.41g

0.43g

0.44g

0.46g

0.48g

0.50g

0.51g

0.56g

0.58g

TABLE 1

TABLE 2

Sequence of tablets

Upper

1

Upper 2

Upper 3

In 1

In 2

Middle 3

Lower 1

Lower 2

Lower 3

Weight gain

2.24g

2.26g

2.28g

2.29g

2.30g

2.32g

2.33g

2.35g

2.38g

TABLE 3

Sequence of tablets

Upper

1

Upper 2

Upper 3

In 1

In 2

Middle 3

Lower 1

Lower 2

Lower 3

Weight gain

3.65g

3.68g

3.69g

3.71g

3.72g

3.73g

3.75g

3.76g

TABLE 4

Example 5:

in accordance with the above-described method and apparatus, embodiments are provided in which the plurality of apertures are arranged in parallel, as shown in FIGS. 6-8. The porous shape is circular, rectangular and hexagonal, three holes are respectively arranged, and the holes are uniformly placed in the upper, middle and lower three sections of areas of the support frame, for example, the circular holes are placed in the upper 1, the middle 1 and the lower 1; placing the rectangle into the upper part 2, the middle part 2 and the lower part 2; the hexagon is placed in the upper 3, middle 3 and lower 3. High temperature treatment for 12hr, cooling and taking out seed crystal, and adhering the seed crystal and graphite disc together. The weight change of the seed crystal and the graphite disk is numbered from top to bottom in sequence as follows: upper 1-upper 3, middle 1-middle 3, lower 1-lower 3, three segments. The weight changes before and after the experiment are respectively shown in table 5:

sequence of tablets

Upper

1

Upper 2

Upper 3

In 1

In 2

Middle 3

Lower 1

Lower 2

Lower 3

Weight gain

0.98g

1.02g

1.04g

1.05g

1.07g

1.08g

1.09g

1.11g

1.13g

TABLE 5

Example 6:

embodiments of the method and apparatus described above, wherein the plurality of holes are arranged in concentric circular arrays, are shown in fig. 9-11. The porous shape is circular, rectangular and hexagonal, three holes are respectively arranged, and the holes are uniformly placed in the upper, middle and lower three sections of areas of the support frame, for example, the circular holes are placed in the upper 1, the middle 1 and the lower 1; placing the rectangle into the upper part 2, the middle part 2 and the lower part 2; the hexagon is placed in the upper 3, middle 3 and lower 3. High temperature treatment for 12hr, cooling and taking out seed crystal, and adhering the seed crystal and graphite disc together. The weight change of the seed crystal and the graphite disk is numbered from top to bottom in sequence as follows: upper 1-upper 3, middle 1-middle 3, lower 1-lower 3, three segments. The weight changes before and after the experiment are respectively shown in table 6:

sequence of tablets

Upper

1

Upper 2

Upper 3

In 1

In 2

Middle 3

Lower 1

Lower 2

Lower 3

Weight gain

1.03

1.04g

1.05g

1.06g

1.08g

1.09g

1.10g

1.11g

1.14g

TABLE 6

The above examples 1-6 all ensure that the seed crystal is firmly bonded with the graphite disk and are used in the subsequent PVT method.

In the subsequent growth, 12 pieces of the bonded seed crystals are selected from the bonded seed crystals of the invention, 3 pieces of the bonded seed crystals are randomly selected respectively after 8 hours, 12 hours, 16 hours and 20 hours of treatment, and then the same seed crystals are bonded with glue for 12 pieces of the seed crystals respectively (2 pieces of the bonded seed crystals fail to be bonded in the process of sintering the glue, and the seed crystals slide and are bonded in the process of sintering 1 piece of the seed crystals.)

24 sets of experiments were performed with every 3 sets of bonded seed crystals of the present invention crossed with the glue bonded seed crystals. The experimental gluing seed crystals are sequenced in a sequence of 0-1, 0-2..0-12, and the seed crystals of the invention are sequenced at the beginning of the time of high-temperature treatment, 8-1, 8-2, 8-3. From the experimental effect, the success rate of the seed crystal adhesion by using the seed crystal of the invention reaches 100 percent, and the success rate of the seed crystal adhesion by using the glue is 80 percent. The parameters of the single crystal growth are counted by average micropipe density, the micropipe density of the crystal grown by the bonded seed crystal is controlled to be below 30, particularly the time of processing for 12 hours is preferred, and the micropipe density is 10/cm². And the density of the seed crystal microtubes which are adhered is more than 100.

The method and the device for bonding the seed crystal provided by the invention are described in detail, the principle and the implementation mode of the invention are explained by applying a specific example, and the description of the implementation is only used for helping to understand the method and the core idea of the invention; while the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A method of processing a seed crystal, the method comprising:

adhering graphite paper to the growth surface of the seed crystal through graphite glue, wherein the graphite paper covers the whole upper surface of the seed crystal;

attaching the lower surface of the seed crystal to a graphite disc;

and treating the crucible at a high temperature, introducing treatment gas to sublimate the raw material at the bottom of the crucible, and simultaneously adjusting the introduction flow rate and the treatment pressure of the treatment gas until the back of the seed crystal is bonded with the graphite disk.

2. The method of claim 1, wherein the feedstock is a mixture of compounds or gases containing a silicon source and a carbon source, and wherein the feedstock has a particle size of between 50 and 500 microns.

3. The method of claim 2, wherein the process gas is argon and methane, the argon is introduced at a flow rate of 1 to 500 seem, the methane is introduced at a flow rate of 1 to 10 seem, and the process pressure is between 1 to 600 torr.

4. The method as claimed in any one of claims 1 to 3, wherein the high temperature treatment comprises a treatment at 1600 ℃ and 2100 ℃ for 8 to 20 hours.

5. The device for processing the seed crystal is characterized by comprising a graphite disc, a crucible and a support frame, wherein the graphite disc is provided with a plurality of through holes which are regularly arranged, the support frame at least comprises a support frame wall and a main body part, and the main body part comprises a support arm, a bracket and a central hollow hole from outside to inside.

6. The apparatus of claim 5, wherein the graphite disk comprises at least a disk edge and a groove, wherein the plurality of through holes are located in the groove, and the through holes are circular or polygonal and are regularly distributed in a circular ring shape or regularly distributed in a parallel shape.

7. The apparatus as claimed in claim 6, wherein the depth of the groove is not higher than the height of the seed crystal, and the inner diameter of the groove is 0.1-0.2mm larger than the outer diameter of the seed crystal.

8. The apparatus of claim 7, wherein the shape of the cradle of the support frame conforms to the shape of the disc edge of the graphite disc; the diameter of the central hole of the support frame is the same as that of the groove of the graphite disk, and the diameter of the bracket is the same as that of the graphite disk.

9. The device of any of claims 5-8, wherein the support arm is multilayered.

10. Device as claimed in claim 9, characterized in that the support arm is provided with a ring of through-holes at a distance from the inner edge of the support frame wall for gas circulation.