KR20210010243A - Manufacturing method of single crystal - Google Patents

Abstract

A single crystal manufacturing method according to an embodiment of the present invention includes the steps of: forming a protective film on a seed crystal growth surface provided at a lower end of a seed axis; moving the seed axis so that the seed crystal on which the protective film is formed is located on a molten solution inside a crucible; heating the crucible in a state in which a raw material containing silicon and a metal solvent are put in the crucible; and performing a crystal growth process in which the molten solution and the seed crystal meet, wherein the melting point of the material forming the protective film is 2100°C or higher.

Description

Manufacturing method of single crystal {MANUFACTURING METHOD OF SINGLE CRYSTAL}

The present invention relates to a method for producing a single crystal, and more specifically, to prevent damage to the seed crystal. It relates to a single crystal manufacturing method.

Silicon carbide (SiC) single crystal has excellent mechanical strength such as abrasion resistance, heat resistance, and corrosion resistance, so it is widely used as a component material for semiconductors, electronics, automobiles, and machinery.

Silicon carbide single crystal manufacturing methods include the Acheson method in which carbon and silica are reacted in a high-temperature electric furnace of 2000 degrees Celsius or higher, chemical vapor deposition method, sublimation method in which silicon carbide is sublimated at a high temperature of 2000 degrees Celsius or higher as a raw material to grow a single crystal There is a melt method using a crystal pulling method.

However, the Acheson method is very difficult to obtain a high-purity silicon carbide single crystal, and the chemical vapor deposition method has a problem that the thickness is limited to a thin film level. The sublimation method is also generally performed at a high temperature of 2400 degrees Celsius or higher, and has a limit in terms of production cost due to the high possibility of various defects such as micropipes and lamination defects. Research on the melt method is continuing.

The silicon carbide melt method is a method of extracting solid single crystals from liquid raw materials containing silicon and carbon contained in a crucible. Among them, a silicon carbide melt method using the Top Seeded Solution Growth (TSSG) method is widely known, and it is a method of growing a silicon carbide crystal by contacting a silicon carbide seed crystal with the upper surface of the melt.

1 is a view showing a seed and a seed holder inside a conventional crucible.

Referring to FIG. 1, in the related art, the seed 30 is bonded to the seed holder 35 in the form of a disk inside the crucible 10, and the seed shaft 40 connected to the pulling shaft 50 is lowered to lower the seed 30. ) And the melt 40 can be brought into contact with each other to grow a single crystal. At this time, surface contamination and deformation of the seed 30 due to evaporation and condensation of the melt 50 occurred.

In other words, in order to use the TSSG method, it is necessary to contact silicon carbide seed crystals with a high-temperature molten solution in which raw materials and solvents are dissolved, and evaporation of the liquid melt occurs during heating. At this time, condensation occurs when the evaporated raw material moves to the upper portion of the melt in gaseous and liquid phases and encounters a seed surface with a relatively low temperature. If this state persists for a long time, silicon carbide may be melted by the condensed raw material and then condensed again to form a seed and other polycrystalline silicon carbide. Polycrystalline types of silicon carbide having different properties may be deposited by these defects.

An object to be solved by the present invention is to provide a single crystal manufacturing method that suppresses damage to seed crystals and generation of polycrystalline silicon carbide due to evaporation of raw materials.

However, the problems to be solved by the embodiments of the present invention are not limited to the above-described problems and may be variously expanded within the scope of the technical idea included in the present invention.

A method of manufacturing a single crystal according to an embodiment of the present invention includes forming a protective film on a seed crystal growth surface provided at a lower end of the seed shaft, moving the seed shaft so that the seed crystal on which the protective film is formed is located on the melt inside the crucible, In a state in which a raw material including silicon and a metal solvent are put in the crucible, heating the crucible, and performing a crystal growth process when the melt and the seed crystal meet, and the material forming the protective layer The melting point is over 2100 degrees Celsius.

The single crystal manufacturing method may further include the step of lowering the seed axis so that the protective layer meets the melt and the protective layer is removed.

The step of removing the protective film may include dissolving the protective film in the melt and mixing it with the melt.

The protective layer may be formed on one surface of the seed crystal facing the melt or on one surface and side surfaces of the seed crystal.

The protective layer may completely cover the seed crystal growth surface.

The protective layer may be formed of a material soluble in the melt.

The protective layer may include a transition metal.

The protective layer may include at least one of Mo, Ta, W, and Nb.

The melting point of the material forming the protective layer may be 2400 degrees Celsius or higher.

The thickness of the protective layer may be 1 micrometer or less.

The thickness of the protective layer may be 0.4 micrometer or less.

According to embodiments, by forming a silicon carbide seed crystal protective film, it is possible to prevent condensation generated by evaporation of the melt from affecting the seed crystal. Thereafter, when the seed crystal touches the melt, the protective film is dissolved in the melt and mixed with the melt, so that the surface of the seed crystal is completely protected and the crystal growth process can be started without surface change.

1 is a view showing a seed and a seed holder inside a conventional crucible.
2 is a schematic diagram of a single crystal growing apparatus for explaining a method of manufacturing a single crystal according to an exemplary embodiment of the present invention.
3 is a graph showing the degree of incorporation into silicon carbide.
4 is a view for explaining the protection of the seed surface by the protective film according to an embodiment of the present invention.
5 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective film according to an embodiment of the present invention is formed of Mo.
6 is a graph showing a phase balance diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of Mo.
7 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective layer according to an embodiment of the present invention is formed of Nb.
8 is a graph showing a phase equilibrium diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of Nb.
9 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective film according to an embodiment of the present invention is formed of Ta.
10 is a graph showing a phase equilibrium diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of Ta.
11 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective layer according to an embodiment of the present invention is formed of W.
12 is a graph showing a phase equilibrium diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of W.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

In order to clearly describe the present invention, parts irrelevant to the description have been omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, so the present invention is not necessarily limited to the illustrated bar. In the drawings, the thicknesses are enlarged to clearly express various layers and regions. And in the drawings, for convenience of description, the thickness of some layers and regions is exaggerated.

In addition, when a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only "directly over" another part, but also a case where another part is in the middle . Conversely, when one part is "directly above" another part, it means that there is no other part in the middle. In addition, to say "on" or "on" the reference part means that it is located above or below the reference part, and means that it is located "above" or "on" in the direction opposite to gravity. no.

In addition, throughout the 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.

2 is a schematic diagram of a single crystal growing apparatus for explaining a method of manufacturing a single crystal according to an exemplary embodiment of the present invention.

Referring to FIG. 2, a single crystal growing apparatus according to an embodiment of the present invention is a single crystal growing apparatus using a melt method, and a chamber (not shown), a crucible 100 disposed inside the chamber, and a height of the crucible 100 A pulling shaft 500 that may extend along a direction, a seed shaft 400 connected to the pulling shaft 500, and a seed holder 350 positioned at an end of the seed shaft 400. A seed crystal 300 is attached to the seed holder 300, and further includes a protective layer 250 positioned on a growth surface of the seed crystal 300.

The crucible 100 may have a container shape with an open upper side. However, the present invention is not limited thereto and may be in any form for forming a silicon carbide single crystal. In the crucible 100, a molten raw material injected for growth of silicon carbide may be charged and accommodated.

When the crucible 100 is heated, the melt 200 contained in the crucible 100 changes into a melt 200 containing carbon (C) and silicon (Si), and the crucible 100 is continuously heated to When 200 becomes a supersaturated state, a silicon carbide single crystal may be grown on the seed crystal 300 in contact with the melt 200.

The pulling shaft 500 serves to inject the seed crystal 300 into the melt 200 contained in the crucible 100. The pulling shaft 500 is connected to the seed shaft 400, and a seed holder 350 is formed at the end of the seed shaft 400 to connect the silicon carbide seed crystal 300 to the top and bottom of the pulling shaft 500. The seed crystal 300 may be moved into the crucible 100 through movement. The pulling shaft 500 has a cylindrical shape extending along the height direction of the crucible 100, but is not limited thereto. The seed shaft 400 may use a ceramic sintered body to secure stability in a region where high-temperature metal melting occurs.

Although not shown, the heat insulating portion may be disposed on the outer circumferential surface of the crucible 100 and serves to block heat emitted from the crucible 100. That is, the heat insulating part may function to maintain the temperature inside the crucible 100 as a single crystal growth temperature.

Although not shown, it may further include a heating unit disposed outside the heat insulating unit to heat the crucible 100. The heating unit may be an induction coil. In this case, by heating the crucible 100 by passing a current through the induction coil, the melt 200 charged in the crucible 100 may be heated.

The method of manufacturing a single crystal according to an embodiment of the present invention includes forming a protective film 250 on a growth surface of the seed crystal 300 provided at the bottom of the seed shaft 400 by using the single crystal growing apparatus, and the protective film 250 The step of moving the seed shaft 400 so that the formed seed crystal 300 is located above the melt 200 inside the crucible 100, in a state in which the raw material containing silicon and the metal solvent are put in the crucible 100, the crucible It includes heating (100), and performing a crystal growth process when the melt 200 and the seed crystal 300 meet. In this case, the protective layer 250 may be removed in a step in which the melt 200 and the seed crystal 300 meet and perform a crystal growth process. To this end, the seed shaft 400 is lowered so that the protective film 250 meets the melt 200 so that the substance forming the protective film 250 is dissolved in the melt 200, and the dissolved protective film 250 material is the melt 200 Can be mixed with.

The protective film 250 according to the present embodiment includes damage to the seed crystal 300 due to evaporation of the raw material contained in the melt 200 and polycrystalline type until the melt 200 and the seed crystal 300 after heating contact each other. It is possible to suppress the formation of silicon carbide. In other words, when the melt 200 is heated to a high temperature state, a part of the melt 200 is evaporated. When the raw material evaporated on the surface of the seed crystal by evaporation hits the seed crystal 300 and condenses, the seed crystal 300 is formed. Can be dissolved. However, in this embodiment, this phenomenon may be prevented by the protective layer 250. As shown in FIG. 2, the protective film 250 according to the present embodiment may be formed on one surface of the seed crystal 300 facing the melt 200, or may be formed on one surface and a side surface of the seed crystal 300. In this case, the protective layer 250 may completely cover the growth surface of the seed crystal 300.

Hereinafter, a shape in which contamination occurs before contact between the melt and the seed crystal will be described in more detail.

When the melt 200 is heated to a high temperature state, the raw material in the melt is evaporated to dissolve the seed crystals and re-solidify to form small protrusions of a polycrystalline type different from the silicon carbide single crystal that must be originally formed. Due to these protrusions, the surface roughness of the seed crystal growth surface may be very large, which may prevent uniform crystal growth from occurring.

Referring again to FIG. 2, the melting point of the material forming the protective layer 250 according to the present embodiment may be approximately 2100 degrees Celsius or higher. When the raw materials contained in the crucible 100 and the melt 200 are heated by a heating unit such as a work coil, the temperature of the seed crystal 300 also increases. Until the seed crystal 300 and the melt 200 contact, the protective film 250 must not melt and become a liquid or be separated from the seed crystal 300. If the protective layer 250 is melted, the surface of the seed crystal 300 may be melted because the liquid has more reactivity than the solid. In addition, when the passivation layer 250 is melted, a bumpy surface is generated due to the agglomeration of the passivation layer 250, and the seed crystal is exposed, and the evaporation material meets the seed crystal, which may negatively affect crystal growth. Therefore, the melting point of the material forming the protective layer 250 according to the present embodiment should be approximately 2100 degrees Celsius or higher. Examples of the composition of the material forming the melt 200 may include Si ₅₆ Cr ₄₀ Al ₄ and Si ₇₄ Ti ₂₃ Al ₃ . When Si-Cr-Al is used, crystal growth mainly proceeds at a temperature of approximately 1900 degrees Celsius, and in the composition of Si-Ti, crystal growth proceeds at a temperature of approximately 1800 degrees Celsius. In addition, in the composition of Si-Cr-Al, crystal growth may proceed at approximately 2050 degrees Celsius.

The passivation layer 250 according to the present embodiment may be formed of a transition metal. Since the passivation layer 250 formed of the transition metal is hardly incorporated into the seed crystal 300 made of silicon carbide, electrical characteristics may not be affected. As a comparative example, if a protective film is formed using a metal oxide such as SiO ₂ , bubbles may be caused in the melt when melting, but the protective film 250 according to the present embodiment is not formed using a metal oxide. Since it is made of a transition metal, this problem can be avoided.

3 is a graph showing the degree to which a metal component is incorporated into silicon carbide. 3 is a Material Science Forum Vol. 897, pp 32-35, referring to FIG. 3, as a result of SIMS (secondary ion mass spectroscopy) analysis, the concentration of transition metals in the silicon carbide crystal is very small except for Ti, V, Cr, and Hf. Or, most appear to have an unmeasurable concentration. Accordingly, it is preferable that the passivation layer 250 according to the present exemplary embodiment include at least one of Mo, Ta, W, and Nb among transition metals.

The materials forming the protective layer 250 may be a material that is dissolved in the melt 200. In order to remove the protective film 250 prior to the step of performing the crystal growth process when the melt 200 and the seed crystal 300 meet, for example, the seed shaft 400 is lowered so that the protective film 250 is combined with the melt 200 The material that meets and forms the protective layer 250 is dissolved.

Referring to Table 1 below, molybdenum, tantalum, tungsten and niobium are approximately 2400 degrees Celsius or higher as examples of preferred materials for forming the protective layer 250 according to the present embodiment. Therefore, it is preferable that the melting point of the material forming the protective layer 250 according to the present embodiment is approximately 2400 degrees Celsius or higher.

Melting point(℃) Molybdenum (Mo) 2623 Tantalum (Ta) 3017 Tungsten (W) 2422 Niobium (Nb) 2477

When the condensate generated by the evaporation of the melt 200 is condensed on the surface of the protective film 250, the metal forming the protective film 250 may be melted. At this time, the reaction with the condensed silicon should not be fast. In this regard, referring to Table 2 below, when the evaporation of Si condenses at 1900 degrees Celsius and is deposited on the surface of the seed crystal, the protective film may melt, and the weight ratio at that time is shown, and when interpreting this, durability against Si is Mo> It has the same order as W>Nb>Ta.

~ 1900℃ Metal(g) Si(g) Molybdenum (Mo) 31.89 68.11 Tantalum (Ta) 58.84 41.16 Tungsten (W) 54.04 55.96 Niobium (Nb) 54.93 45.07

Hereinafter, a phenomenon in which the protective film according to the present embodiment prevents a seed crystal surface defect will be described in detail with reference to FIG. 4. 4 is a view for explaining the protection of the seed surface by the protective film according to an embodiment of the present invention.

Referring to FIG. 4, when the protective film 250 is formed in the step where the melt 200 is heated to evaporate raw materials, Si condensation is blocked by the protective film 250 and affects the seed crystal 300. Can be prevented.

Looking at the following Tables 3 and 4, when heated to 1900 degrees Celsius for 4 hours using the metal density value and the durability (g ratio) for Si forming the protective film 250 according to the embodiment of the present invention, Si In order to find out the conditions (durability) for withstanding against, the volume of the protective film 250 was calculated and the required height was calculated. Accordingly, it is preferable that the required thickness of the protective layer 250 is approximately 1 micrometer or less. More preferably, it may be 0.4 micrometer or less, and more preferably, it may be 0.2 micrometer or less.

(g/cm3) density Si 2.33 Mo 10.28 Nb 8.57 W 19.25 Ta 16.69

Height (micrometers) Mo 0.174 Nb 0.542 W 0.191 Ta 0.326

As a comparative example, instead of forming the protective film 250 as in the present embodiment, the seed crystal surface may be melted using a melt and a smooth surface may be formed. Subsequently, by performing a crystal growth process, crystal growth may occur without defects. However, according to this method, since the thickness of the grown silicon carbide crystal is reduced, there is a disadvantage in the process.

5 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective film according to an embodiment of the present invention is formed of Mo. 6 is a graph showing a phase balance diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of Mo.

7 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective layer according to an embodiment of the present invention is formed of Nb. 8 is a graph showing a phase equilibrium diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of Nb.

9 is a graph showing a phase equilibrium diagram showing reactivity with SiC when a protective film according to an embodiment of the present invention is formed of Ta. 10 is a graph showing a phase equilibrium diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of Ta.

11 is a graph showing a phase balance diagram showing reactivity with SiC when a protective film according to an embodiment of the present invention is formed of W. 12 is a graph showing a phase equilibrium diagram showing reactivity with Si when a protective film according to an embodiment of the present invention is formed of W.

The passivation layer 250 according to the present embodiment should have low reactivity with the SiC seed, and thus it is preferable that the liquid region is not large. This is because the liquid region is more reactive than the solid state. Referring to FIGS. 5, 7, 9, and 11, as a result of comparing the size of the liquid region in the phase equilibrium of the material forming the protective layer 250 according to the present embodiment, the degree of reactivity of Mo>Nb>Ta>W You can check. Compared to Mo, Nb has a smaller liquid region, Ta is smaller than Nb, and W has no liquid region, so the reactivity is the lowest.

6, 8, 10, and 12, when drawing a horizontal line corresponding to temperature, there is a part that meets according to the mass fraction, and when the protective film meets the Si melt, the part occupied by the metal in the mass fraction is As the number increases, it can be quickly dissolved in a small amount of Si, so the durability against Si is weak. For example, referring to FIG. 6, when Si is 1.0 and Mo is 0, it can be seen that Mo is in a liquid state, but when Si is 0.68 and Mo is 0.32, it is not in a liquid state. Referring to FIG. 8, when Si is 1.0 and Nb is 0, it is in a liquid state, but the mass fraction of Nb gradually increases so that Si is 0.45, and it is in a liquid state only when Nb becomes 0.55, and the mass fraction of Nb is It can be seen that it is in a solid state until Si becomes 0 and Nb becomes 1.0. At this time, the ratio of Si and metal is as shown in Table 2 above.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of rights of

100: crucible
200: melt
250: shield
300: seed crystal
350: seed holder
400: seed axis
500: pulling shaft

Claims (11)

Forming a protective film on the seed crystal growth surface provided at the bottom of the seed axis,
Moving the seed shaft so that the seed crystal on which the protective film is formed is located on the melt inside the crucible,
Heating the crucible in a state in which a raw material containing silicon and a metal solvent are put in the crucible, and
Including the step of performing a crystal growth process when the melt and the seed crystal meet,
The melting point of the material forming the protective layer is 2100 degrees Celsius or higher, a single crystal manufacturing method. In claim 1,
The method of manufacturing a single crystal further comprising the step of removing the protective film by lowering the seed axis so that the protective film meets the melt. In paragraph 2,
The step of removing the protective film includes the step of dissolving the protective film in the melt and mixing it with the melt. In claim 1,
The protective film is a single crystal manufacturing method that is formed on one surface of the seed crystal facing the melt or on one surface and side surfaces of the seed crystal. In claim 4,
The protective film completely covers the seed crystal growth surface. In claim 1,
The protective layer is a single crystal manufacturing method formed of a material soluble in the melt. In claim 1,
The protective layer is a single crystal manufacturing method comprising a transition metal. In clause 7,
The protective layer is a single crystal manufacturing method comprising at least one of Mo, Ta, W, and Nb. In claim 1,
The melting point of the material forming the protective layer is 2400 degrees Celsius or higher. In claim 1,
The thickness of the protective film is a single crystal manufacturing method of 1 micrometer or less. In claim 10,
The thickness of the protective layer is 0.4 micrometers or less, a single crystal manufacturing method.

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