KR102242438B1 - Seed attachment method - Google Patents

Abstract

An embodiment is a method of attaching a seed crystal, comprising the steps of: (1) attaching a protective film to one surface of the seed crystal on which the ingot is grown; (2) coating an adhesive composition on the other surface of the seed crystal; (3) a first curing step of heat-treating the seed crystal; (4) removing the protective film; (5) a second hardening step of heat-treating the seed crystal; And (6) by including the step of attaching the seed crystal to the seed crystal holder, it is possible to improve the growth stability and quality during the growth of the SiC single crystal ingot.

Description

Seed crystal attachment method {SEED ATTACHMENT METHOD}

The embodiment relates to a method for attaching a seed crystal capable of improving growth stability and quality during growth of a SiC single crystal ingot.

Silicon carbide (SiC) is excellent in heat resistance and mechanical strength, has strong properties against radiation, and has the advantage of being able to produce even large-diameter substrates, so active research is being conducted as a substrate for next-generation power semiconductor devices. In particular, single crystal silicon carbide (single crystal SiC) has a large energy band gap, and a maximum break field voltage and thermal conductivity are superior to that of silicon (Si). In addition, the carrier mobility of single crystal silicon carbide is comparable to that of silicon, and the electron saturation drift rate and breakdown pressure are also high. Therefore, single crystal hydrocarbons are expected to be applied to semiconductor devices requiring high power, high efficiency, high breakdown voltage, and large capacity.

In order to grow SiC single crystal ingots, an adhesive has been generally applied to one side of the seed crystal and attached to the seed crystal holder. However, as described above, when the adhesive is applied to one side of the seed crystal, the other surface of the seed crystal, that is, the other surface of the seed crystal on which the ingot is grown, may be contaminated due to an excessive amount of application or a rotational force generated during coating. For this reason, there is a problem that the quality is deteriorated during the growth of the SiC single crystal ingot.

For example, Korean Patent Registration No. 1101983 discloses a seed crystal attached to one surface of a graphite thin plate by an adhesive and a seed crystal holder attached to the other surface of the graphite thin plate by an adhesive, which is between the seed crystal and the seed crystal holder. Discontinuous defects can be effectively prevented, but it is difficult to prevent one side of the seed crystal on which the ingot is grown from being contaminated.

Korean Registered Patent No. 1101983

Accordingly, the embodiment is to provide a seed crystal attachment method capable of improving growth stability and quality when growing a SiC single crystal ingot by effectively preventing one surface of the seed crystal on which the ingot is grown from being contaminated.

A seed crystal attachment method according to an embodiment includes the steps of: (1) attaching a protective film to one surface of the seed crystal on which the ingot is grown; (2) coating an adhesive composition on the other surface of the seed crystal; (3) a first curing step of heat-treating the seed crystal; (4) removing the protective film; (5) a second hardening step of heat-treating the seed crystal; And (6) attaching the seed crystal to the seed crystal holder.

The method of attaching the seed crystal according to the embodiment effectively prevents contamination of one surface of the seed crystal on which the ingot is grown, thereby improving growth stability and quality when growing a SiC single crystal ingot.

1 is a schematic diagram of a seed crystal attachment method according to an embodiment.
2 shows an image of the surface on which the ingot of the seed crystal of the embodiment is grown.
3 shows an image of a surface on which an ingot of a seed crystal of a comparative example is grown.
Figure 4 shows a surface image of the SiC single crystal ingot of the embodiment.
5 shows a UV image of the SiC single crystal ingot of the embodiment.
6 shows a surface image of a seed crystal after growth of the SiC single crystal ingot of Example is completed.

Hereinafter, the invention will be described in detail through embodiments. The implementation is not limited to the content disclosed below, and may be modified in various forms unless the gist of the invention is changed.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

All numbers and expressions indicating amounts of components, reaction conditions, and the like described herein are to be understood as being modified by the term "about" in all cases unless otherwise specified.

A seed crystal attachment method according to an embodiment includes the steps of: (1) attaching a protective film to one surface of the seed crystal on which the ingot is grown; (2) coating an adhesive composition on the other surface of the seed crystal; (3) a first curing step of heat-treating the seed crystal; (4) removing the protective film; (5) a second hardening step of heat-treating the seed crystal; And (6) attaching the seed crystal to the seed crystal holder.

1 is a schematic diagram of a seed crystal attachment method according to an embodiment. Specifically, (1) a protective film 200 is attached to one surface of the seed crystal 100 on which the ingot is grown, and (2) a coating layer 300 is formed by coating an adhesive composition on the other surface of the seed crystal 100 After that, (3) undergoing a first curing step of heat-treating the seed crystal 100, (4) removing the protective film 200, (5) a second curing of heat treating the seed crystal 100 After passing through the step, (6) the step of attaching the seed crystal 100 to the seed crystal holder 400 is shown.

In the present specification, one surface of the seed crystal refers to a surface on which a single crystal ingot is grown, and the other surface of the seed crystal refers to a surface attached to the seed crystal holder.

Step (1)

The step (1) is a step of attaching a protective film to one surface of the seed crystal on which the ingot is grown.

The seed crystal may be a seed crystal having various crystal structures, such as 4H-SiC, 6H-SiC, 3C-SiC, or 15R-SiC, depending on the type of crystal to be grown.

The seed crystal may be subjected to a cleaning step before coating. A silicon dioxide oxide film formed by reacting silicon with oxygen may be formed on the surface of the seed crystal, and this oxide film is preferably removed by cleaning in advance because the seed crystal may be separated or defects may be generated when a single crystal ingot is grown in a subsequent process. The cleaning may be performed using acetone, alcohol, distilled water, an acid solution, etc., may be performed by ultrasonic treatment or immersion, or the like, and may be performed once or twice or more.

According to one embodiment, the protective film includes at least one selected from the group consisting of polyethylene terephthalate-based resins, polyimide-based resins, polypropylene-based resins, and polyamide-based resins. For example, a resin having a glass transition temperature of 70°C or higher, 70°C to 350°C, 80°C to 350°C, 75°C to 330°C, or 80°C to 310°C may be included. Since the protective film contains a resin that satisfies the glass transition temperature range, it has excellent heat resistance and does not change shape even after passing through the first curing step of step (3), so that the quality of the seed crystal can be prevented from deteriorating.

According to one embodiment, the thickness of the protective film may be 50 μm to 500 μm. For example, 70 µm to 500 µm, 80 µm to 450 µm, 90 µm to 400 µm, 100 µm to 400 µm, 100 µm to 350 µm, 100 µm to 300 µm, 100 µm to 250 µm, 100 µm to 200 Μm or 100 µm to 150 µm.

According to one embodiment, the cross-sectional area of the protective film may be equal to or greater than the cross-sectional area of the seed crystal. Specifically, the protective film may be attached to cover all of the surface of the seed crystal. The protective film may be attached using an adhesive, or may be attached by pressure and heat treatment.

According to one embodiment, the peeling force of the protective film in step (1) may be 100 to 500 gf/inch. For example, the peeling force of the protective film in step (1) may be 100 to 400 gf/inch, 150 to 350 gf/inch, or 200 to 300 gf/inch.

According to one embodiment, the protective film may further include a filler.

The filler may be a carbon-based filler, a metallic filler, or a composite filler thereof. For example, the filler is impression graphite, earth graphite, expanded graphite, carbon black, carbon nanotubes, graphene, tantalum (Ta), tungsten (W), rhenium (Re), molybdenum (Mo), hafnium (Hf) , It may contain components such as tantalum carbide (TaC) and tungsten carbide (WC). The filler may prevent excessive shrinkage in the step of heat-treating the adhesive composition to prevent cracks from being formed.

By attaching a protective film to one surface of the seed crystal on which the ingot is grown, it is possible to effectively prevent contamination of the surface of the seed crystal on which the ingot is grown, thereby improving the growth stability and quality when growing the SiC single crystal ingot.

Step (2)

The step (2) is a step of coating an adhesive composition on the other surface of the seed crystal.

According to one embodiment, the adhesive composition may include a thermosetting resin and a carbon-based material.

According to one embodiment, the thermosetting resin is one selected from the group consisting of polyamic acid resin, phenol resin, polyacrylonitrile resin, pitch resin, polyvinyl chloride resin, polyacrylic acid resin, furan resin, and epoxy resin. It may include more than one.

According to one embodiment, the carbon-based material may be carbon black, graphite, or a combination thereof.

According to one embodiment, based on the total weight of the adhesive composition, the thermosetting resin may be included in an amount of 70 to 90% by weight, and the carbon-based material may be included in an amount of 20 to 35% by weight.

For example, based on the total weight of the adhesive composition, the thermosetting resin may be 75 to 90% by weight, 80 to 90% by weight, or 80 to 85% by weight. When the above range is satisfied, there is an advantageous effect in improving adhesion of the adhesive layer composition, as well as maintaining viscosity and thickness stability during application.

In addition, based on the total weight of the adhesive composition, the carbon-based material may be 20 to 35% by weight, 20 to 30% by weight, or 20 to 25% by weight. When the above range is satisfied, it is possible to effectively prevent the occurrence of shrinkage and cracks, and to promote carbonization or graphitization in a subsequent heat treatment.

Accordingly, the adhesive composition may further include a solvent such as ethanol, methanol, acetone, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Specifically, the solvent may be ethanol, but is not limited thereto. In this case, the solid content of the liquid composition may be 10% by weight to 90% by weight, or 20% by weight to 50% by weight.

In addition, the adhesive composition may further include additives such as a wetting and dispersing agent and an antifoaming agent.

In the step (3), the adhesive composition may be coated by applying the adhesive composition to the other surface of the seed crystal. For example, a conventional coating method such as spin coating or taping may be used, but is not limited thereto.

When the adhesive composition is coated on the other surface of the seed crystal, contamination of one surface of the seed crystal may be prevented by the protective film. In particular, the seed crystal may be easily contaminated during processes such as spin coating, and the protective film protects one side of the seed crystal to prevent contamination, from which it prevents defects caused by seed crystal contamination during ingot growth. can do.

Step (3)

The step (3) is a first curing step of heat-treating the seed crystal.

According to one embodiment, the first curing step is a step of heat treatment at 50° C. to 200° C. for 30 minutes to 1 hour. For example, the first curing step may be heat-treated at 70°C to 200°C, 70°C to 180°C or 80°C to 150°C for 30 minutes to 50 minutes, 30 minutes to 45 minutes, or 30 minutes to 40 minutes. have.

When it is within the above range, the solvent components contained in the adhesive composition can be effectively opportunityed, and defects such as bubble generation, cracks, and cracks can be prevented.

Step (4)

The step (4) is a step of removing the protective film. Specifically, it is a step of removing the protective film attached to one surface of the heat-treated protective film.

According to one embodiment, the residual adhesion rate of the protective film in step (4) may be 90% or more. For example, the residual adhesion rate of the protective film in step (4) may be 92% or more, 93% or more, or 95% or more. In addition, the peeling force of the protective film in step (4) may be 5.0 gf/inch or less. For example, the peeling force of the protective film in step (4) may be 4.5 gf/inch or less or 4.0 gf/inch or less. Specifically, the protective film that has undergone the first curing step has an increased residual adhesion, so that it is easy to remove the protective film from the other surface of the seed crystal. The peeling force is based on when each evaluation tape is laminated and peeled at a peeling angle of 180° and a speed of 12 inches per minute after 30 minutes at room temperature.

Step (5)

The step (5) is a second curing step of heat-treating the seed crystal.

According to one embodiment, the second curing step is a step of heat-treating at 200°C to 350°C for 30 minutes to 1 hour. For example, the first curing step may be heat-treated at 200°C to 330°C, 200°C to 300°C, or 220°C to 300°C for 30 minutes to 50 minutes, 30 minutes to 45 minutes, or 30 minutes to 40 minutes. have.

In the second curing step, by heat-treating the seed crystal once more after the protective film is removed, the solvent is effectively vaporized to minimize defects such as bubble generation, cracks, and cracks.

Step (6)

The step (6) is a step of attaching the seed crystal to the seed crystal holder.

According to one embodiment, prior to the step (6), an adhesive coating layer may be additionally formed on the cured coating layer of the seed crystal.

For example, the adhesive coating layer may include a binder resin such as a phenol resin or a polyacrylonitrile resin, and may further include a filler illustrated above as needed. The adhesive coating layer may be formed by a spin coating method, a bar coating method, a knife coating method, a brush coating method, or the like.

According to one embodiment, step (6) may include patterning a lower surface of the seed crystal holder. For example, patterning may be performed using a grinding grinder, but is not limited thereto.

In the present specification, the lower surface of the seed crystal holder refers to a surface on which the seed crystal holder and the adhesive layer are attached.

Specifically, by patterning the lower surface of the seed crystal holder, when the SiC single crystal ingot is grown, the generation of bubbles generated on the adhesion surface between the adhesive layer and the seed crystal holder can be suppressed, so that the seed crystal is prevented from separating during the growth of the SiC single crystal ingot. Can be prevented.

According to one embodiment, the patterned seed crystal holder may have a surface roughness (Ra) of 0.5 mm to 3 mm, preferably 1.5 mm to 2 mm.

According to an embodiment, after step (6), drying, curing, and carbonization or graphitization of the seed crystal may be further included.

According to one embodiment, the drying may be performed at a temperature range of 30°C to 350°C, and the curing may be performed at a temperature range of 100°C to 400°C. Specifically, by satisfying the drying and curing conditions, there is an advantageous effect in forming a solid protective layer as well as forming an adhesive layer formed on the protective layer.

For example, the drying may be performed for 1 hour to 5 hours at a temperature range of 50°C to 350°C or 50°C to 300°C. In addition, the curing may be performed for 1 to 10 hours at a temperature range of 100°C to 400°C or 150°C to 400°C.

According to one embodiment, the carbonization or graphitization may be performed at a temperature of 200°C to 2,500°C and a pressure condition of 1 torr to 1,500 torr. Specifically, by satisfying the carbonization or graphitization conditions, it is possible to increase the growth stability of the SiC single crystal ingot, thus improving the quality of the SiC single crystal ingot, as well as controlling polymorphism.

For example, the carbonization or graphitization may be performed at a temperature of 1,500°C to 2,500°C, 2,000°C to 2,500°C, or 2,000 to 2,200°C and a pressure condition of 500 torr to 1,000 torr or 500 torr to 800 torr. In addition, the carbonization or graphitization may be performed for 1 hour to 10 hours, 2 hours to 5 hours, or 1 hour to 5 hours, but is not limited thereto.

According to one embodiment, the carbonization or graphitization may be performed at a temperature increase rate of 0.5°C/min to 5°C/min and a temperature condition of 500°C or higher or 600°C or higher. For example, it may be carried out by raising the temperature to a temperature of 500°C to 1,000°C, maintaining the temperature, heating for 1 to 5 hours, and then cooling at a rate of 0.5°C/min to 5°C/min.

According to another embodiment, the carbonization or graphitization may be performed at a temperature increase rate of 1° C./min to 5° C./min and a temperature condition of 1,500° C. or more or 2,000° C. or more. For example, the temperature is raised to a temperature of 1,500° C. to 2,500° C. or 2,000° C. to 2,500° C., maintained at the temperature, heated for 1 to 5 hours, and then at a rate of 1° C./min to 5° C./min. It can be done by cooling.

According to one embodiment, the carbonization or graphitization means heat treatment in an inert atmosphere. The inert atmosphere may be a nitrogen atmosphere or an argon atmosphere, but is not limited thereto.

The above will be described in more detail by the following examples. However, the following examples are for illustrative purposes only, and the scope of the examples is not limited thereto.

[Example]

A PET film (manufactured by SKC) having a thickness of about 100 μm was attached as a protective film on one side of the seed crystal on which the ingot was grown.

A liquid phenol resin (KC-5536, Kangnam Chemical) as a thermosetting resin and an impression graphite (purity 80 to 99%, D50, 2.5 μm) as a carbon-based material were mixed in a weight ratio of 7:3, and wetting compared to 100 parts by weight of the mixture After further mixing 3 parts by weight of a dispersant and an antifoaming agent, it was dispersed to obtain an adhesive composition. The adhesive composition was spin-coated on the other surface of the seed crystal to obtain a coating film having a thickness of 0.5 mm. The coated seed crystal was cured at 100° C. for 40 minutes. After removing the protective film from one side of the coated seed crystal, it was cured at 250° C. for 40 minutes.

The coating layer of the seed crystal and the seed crystal holder were attached. The attached seed crystal holder and the seed crystal were put into a heater and heated at a rate of 1° C./min to reach 600° C., followed by heat treatment for 2 hours to carbonize or graphite. Then, it was cooled at a rate of 1° C./min.

After mounting the seed crystal holder to which the seed crystal was attached to the inner upper part of the graphite crucible, SiC powder was charged to the lower part of the crucible. The crucible was surrounded by a heat insulating member and placed in a reaction chamber equipped with a heating coil. After making the inside of the crucible in a vacuum state, argon gas was slowly injected. In addition, the temperature in the crucible was raised to 2,400° C., and the pressure was raised to 700 torr. Thereafter, the pressure was gradually lowered to reach 30 torr, and a SiC single crystal ingot was grown in seed crystals for 50 hours under the above conditions to prepare a SiC single crystal ingot.

[Comparative Example]

A SiC single crystal ingot was manufactured in the same manner as in the above example, except that the protective film was not attached to one side of the seed crystal in which the ingot was grown.

[Evaluation Example 1: Image of the shape of the growth surface of seed crystal]

Images were evaluated using an optical microscope on one side of the seed crystal on which the ingots prepared in the above Examples and Comparative Examples were grown.

FIG. 2 shows an image of the surface on which the ingot of the seed crystal of the Example is grown, and FIG. 3 shows an image of the surface on which the ingot of the seed crystal of the Comparative Example is grown.

As shown in FIG. 2, one surface of the seed crystal on which the ingot manufactured according to the embodiment is grown is not contaminated and thus impurities or foreign substances are not visible and is clean, whereas, as shown in FIG. 3, the ingot manufactured according to the comparative example is grown. One side of the seed crystal was contaminated and impurities and foreign substances were observed.

[Evaluation Example 2: Evaluation of the surface image of the ingot]

With respect to the SiC single crystal ingot prepared in the above example, the surface image was evaluated with the naked eye using an optical microscope.

Figure 4 shows a surface image of the SiC single crystal ingot of the embodiment.

As shown in FIG. 4, in the SiC single crystal ingot manufactured according to the embodiment, one surface of the seed crystal on which the ingot is grown is not contaminated, so that the ingot grows stably, and impurities or foreign substances are not found on the surface.

[Evaluation Example 3: UV image evaluation]

With respect to the SiC single crystal ingot prepared in the above example, the UV image was evaluated through visual inspection using UV lamp irradiation.

5 shows a UV image of the SiC single crystal ingot of the embodiment.

As shown in FIG. 5, it can be seen that the desired 4H is uniformly formed in the SiC single crystal ingot manufactured according to the embodiment.

[Evaluation Example 4: Evaluation of the surface image of seed crystal]

In the above example, the surface image of the seed crystal after the growth of the SiC single crystal ingot was completed was evaluated with the naked eye using an optical microscope.

6 shows a surface image of a seed crystal after growth of the SiC single crystal ingot of Example is completed.

As shown in FIG. 6, the seed crystal grown in the SiC single crystal ingot manufactured according to the Example did not have any defects or the like found on the surface. That is, when growing the SiC single crystal ingot, one surface of the seed crystal on which the ingot is grown is not contaminated, and thus it can be seen that the ingot has grown stably.

100: seed crystal
200: protective film
300: coating layer
400: seed crystal holder

Claims (11)

(1) attaching a protective film to one surface of the seed crystal on which the ingot is grown;
(2) coating an adhesive composition on the other surface of the seed crystal;
(3) a first curing step of heat-treating the seed crystal;
(4) removing the protective film;
(5) a second hardening step of heat-treating the seed crystal; And
(6) attaching the seed crystal to the seed crystal holder,
The peeling force of the protective film in the step (1) is 100 to 500 gf/inch,
In the step (4), the peeling force of the protective film is 5.0 gf/inch or less, and the residual adhesion rate is 90% or more. The method of claim 1,
The protective film comprises at least one selected from the group consisting of polyethylene terephthalate-based resin, polyimide-based resin, polypropylene-based resin, and polyamide-based resin. The method of claim 2,
The protective film includes a filler, seed crystal attachment method. The method of claim 1,
The adhesive composition comprises a thermosetting resin and a carbon-based material, the method of attaching seed crystals. The method of claim 4,
Seeds wherein the thermosetting resin comprises at least one selected from the group consisting of polyamic acid resin, phenol resin, polyacrylonitrile resin, pitch resin, polyvinyl chloride resin, polyacrylic acid resin, furan resin and epoxy resin How to attach a tablet. The method of claim 4,
The carbon-based material is carbon black, graphite, or a combination thereof, the method of attaching seed crystals. The method of claim 1,
The first curing step is heat-treated at 50°C to 200°C for 30 minutes to 1 hour, and the second curing step is heat-treated at 200°C to 350°C for 30 minutes to 1 hour. delete The method of claim 1,
Prior to the step (6), further forming an adhesive coating layer on the cured coating layer of the seed crystal, seed crystal attaching method. The method of claim 1,
After the step (6), further comprising the step of drying, curing, and carbonization or graphitization of the seed crystal. The method of claim 10,
The drying is carried out in a temperature range of 30 ℃ to 350 ℃,
The curing is performed at a temperature range of 100°C to 400°C,
The carbonization or graphitization is carried out at a temperature of 200 ℃ to 2,500 ℃ and pressure conditions of 1 torr to 1,500 torr, seed crystal attachment method.

Images