NL2029666B1

NL2029666B1 - MANUFACTURING METHOD OF SILICON CARBIDE (SiC) SINGLE CRYSTAL

Info

Publication number: NL2029666B1
Application number: NL2029666A
Authority: NL
Inventors: Yao Heng; Yu Yonghao; Yao Tai
Original assignee: Nanjing Hongtaijing Intelligent Equipment Tech Co Ltd
Priority date: 2021-11-08
Filing date: 2021-11-08
Publication date: 2023-06-05

Abstract

The invention discloses a manufacturing method of a silicon carbide (SiC) single crystal, and belongs to the technical field of manufacturing of semiconductor materials. A manufacturing method of a SiC single crystal includes the following steps of: Sl, cleaning a crucible with a composite crucible cover and performing empty burning on the crucible; SZ, placing high-purity SiC micro-powder at a bottom of the cooled crucible, and heating the crucible to 1,7000C to 2,4OOOC by a composite heater under a positive pressure of a protective gas, and S3, maintaining a temperature of a system in S3, and cooling to a room temperature to obtain the SiC single crystal. A seed crystal used in the present disclosure is a part of the composite crucible cover, so that disturbance caused by independently arranging the seed crystal (substrate) to a temperature field in the crucible is prevented. The composite heater arranged in the present disclosure can adjust a temperature field in which the crucible is located by adjusting a position of a movable graphite ring, thus better controlling a growing process of the SiC single crystal.

Description

MANUFACTURING METHOD OF SILICON CARBIDE (SiC) SINGLE

CRYSTAL

TECHNICAL FIELD

[01] The present disclosure relates to the technical field of manufacturing of semiconductor materials, in particular to a manufacturing method of a silicon carbide (SiC) single crystal.

BACKGROUND ART

[02] With continuous innovation of semiconductor technologies, the third generation of semiconductor materials represented by SiC has gradually become the core support of the new generation of information technologies. With various excellent performances such as a forbidden bandwidth, a high breakdown electric field, a high thermal conductivity, a high electron saturation drift rate, a high chemical stability and a high radiation resistance, a SiC single crystal has become a preferred material for high- temperature-resisting, high-frequency, radiative and large-power semiconductor devices.

[03] At present, a SiC single crystal is mainly manufactured by a thermal sublimation method, a liquid phase epitaxy method and a chemical vapor deposition method. Where, as a mature manufacturing method, the thermal sublimation method has gone through three development stages since its creation: an Acheson method, a Lely method and a physical vapor transport (PVT) method. When the thermal sublimation method is used to grow a SiC single crystal, simple equipment is required, and the operation is easy to control.

[04] In a PVT method, the most influential factors on properties of a SiC single crystal include: a purity of raw material SiC powder, selection of a substrate, a matching degree between a seed crystal and the SiC single crystal, and control on a temperature field in a manufacturing process.

[05] In a PVT crystal growing furnace, temperature distribution has a significant influence on growth of a SiC crystal. For example, under a reasonable temperature distribution, technological parameters such as a growing temperature and a growing pressure also have a significant influence on the growth of the crystal. However, during use of a commonly used heater, a temperature gradient inside a crucible cannot be adjusted effectively, therefore a manufactured SiC single crystal usually has a defect concentration exceeding the standard.

SUMMARY

[06] The present disclosure aims to solve at least one of the above technical problems existing in the prior art. Therefore, the present disclosure provides a manufacturing method of a SiC single crystal, which can more accurately control a temperature field in a growing process of the SiC single crystal.

[07] According to one aspect, the present disclosure provides a manufacturing method of a SiC single crystal, which includes the following steps of:

[08] SI, cleaning a crucible with a composite crucible cover and performing empty burning on the crucible;

[09] S2, placing high-purity SiC micro-powder at a bottom of the cooled crucible, and heating the crucible to 1,700°C to 2,400°C by a composite heater under a positive pressure of a protective gas; and

[10] S3, maintaining a temperature of a system in S3, and cooling to a room temperature to obtain a SiC single crystal, where

[11] the high-purity SiC micro-powder has a purity higher than or equal to 99.9999%.

[12] A preferred embodiment of the present disclosure has at least the following beneficial effects:

[13] (1) A seed crystal used in the present disclosure is a part of the composite crucible cover, thus avoiding disturbance caused by independently arranging the seed crystal (substrate) to a temperature field in the crucible.

[14] (2) By the composite heater arranged in the present disclosure, the temperature field in the crucible can be adjusted by adjusting a position of a movable graphite ring, thus better controlling a growing process of the SiC single crystal.

[15] (3) The composite heater provided by the present disclosure can also be used as a heater for growing other single crystal materials by a physical vapor transport method, and has a wide application range.

[16] In some embodiments of the present disclosure, in step S1, the composite crucible cover includes a graphite layer, a high-purity silicon layer and a seed crystal layer which are sequentially arranged.

[17] In some embodiments of the present disclosure, the high-purity silicon layer has a thickness of 180um to 2004m.

[18] In some embodiments of the present disclosure, the high-purity silicon layer has a purity higher than or equal to 99.9999%.

[19] In some embodiments of the present disclosure, the seed crystal layer is made from SiC with a carbon concentration which increases gradiently from the high-purity silicon layer.

[20] In some embodiments of the present disclosure, the seed crystal layer is made from SiC.

[21] In some embodiments of the present disclosure, in the SC, 0<x<1, and Oy.

[22] A surface, close to one side of the high-purity silicon layer, seed crystal layer has the x close to 1 and the y close to 0, therefore there is almost no lattice mismatch between the seed crystal layer and the high-purity silicon layer, and the grown seed crystal layer has a low defect content.

[23] A surface, away from one side of the high-purity silicon layer, of the seed crystal layer has the x close to 1 and the y close to 1, that is, the seed crystal layer has a composition close to a stoichiometric ratio of SiC, and has a good lattice matching degree with SiC which is to grow on the surface of the seed crystal layer. In this way, a high-quality SiC single crystal can grow.

[24] In some embodiments of the present disclosure, in step S1, a manufacturing method of the composite crucible cover includes: growing the seed crystal layer on the high-purity silicon layer by a metal-organic chemical vapor deposition (MOCVD) method, and bonding a surface, away from one side of the seed crystal layer, of the high- purity silicon layer with the graphite layer.

[25] In some embodiments of the present disclosure, in step S1, the cleaning includes the following steps of:

[26] Sla, wiping inner and outer surfaces of a crucible body and the composite crucible cover with alcohol cotton balls; and

[27] S1b, performing ultrasonic treatment on the crucible body and the composite crucible cover with deionized water, absolute ethanol, acetone and deionized water for 10 min to 20 min respectively.

[28] In some embodiments of the present disclosure, in step S1, after the cleaning is completed, there is no dust or oil stain on surfaces of the crucible body and the composite crucible cover, but there will be residual moisture.

[29] In some embodiments of the present disclosure, in step S1, the empty burning treatment includes the following steps of:

[30] Sic, placing the crucible cleaned in step S1b in a growing furnace as required, and lowering a vacuum degree of the growing furnace to be less than or equal to 10” Pa; and

[31] S1d, introducing a protective gas (at least one of an inert gas and nitrogen with a purity higher than or equal to 99.999%) into the growing furnace obtained in step Slc until a pressure of the growing furnace is 6x10* Pa to 1x10° Pa, performing empty burning at 1800°C to 2200°C for 3 h to 5 h, and naturally cooling the growing furnace to a room temperature.

[32] By the empty burning treatment, a solvent remained in cleaning can be removed.

[33] By the empty burning treatment, residual impurity elements on a surface of the crucible (including the crucible body and the composite crucible cover) as well as surfaces of accessory devices such as thermal insulation cotton and a heater can be removed, and a growing environment of the SiC single crystal can be purified.

[34] In some embodiments of the present disclosure, in step S2, the composite heater includes a cylindrical heater and a movable graphite ring which is located between the cylindrical heater and the crucible.

[35] By movement, the movable graphite ring can adjust a temperature gradient in the crucible. For example, at the beginning of a reaction, in order to accelerate evaporation of SiC micro-powder, the movable graphite ring can be placed at a bottom of the crucible to increase an evaporation temperature; and during the reaction, in order to lower the temperature gradient in the crucible to control a crystal growing process of the SiC single crystal, the movable graphite ring can be moved towards the composite crucible cover.

[36] In some embodiments of the present disclosure, the manufacturing method further includes a step of lowering a pressure of a vacuum chamber to be smaller than or equal to 4x 107! Pa before step S2.

[37] The pressure of the vacuum chamber 1s lowered to be smaller than or equal to 4-107 Pa to remove an impurity gas in a reaction system.

[38] In some embodiments of the present disclosure, in step S2, the protective gas has a positive pressure ranging from 6x10* Pa to 1x10 Pa.

[39] In some embodiments of the present disclosure, in step S2, the protective gas has a positive pressure about 1+ 10° Pa.

[40] In some embodiments of the present invention, in step S3, the positive pressure of the protective gas during temperature maintaining is from 6x10* Pa to 8x10* Pa.

[41] In some embodiments of the present disclosure, during the temperature 5 maintaining in step S3, the pressure is 8x 10* Pa at the beginning 10 min to 40 min and is 6x10" Pa at other times.

[42] In some embodiments of the present disclosure, during the cooling in step S3, the protective gas has a positive pressure of 9x10% Pa to 1.1+10° Pa.

[43] In some embodiments of the present disclosure, during the cooling in step S3, the protective gas has a positive pressure about 1.1x10° Pa.

[44] In some embodiments of the present disclosure, the cooling in step S3 includes the steps of: cooling to a temperature lower than or equal to1,600°C at a velocity of 15°C/min to 25°C/min, and naturally cooling to a room temperature.

[45] In some embodiments of the present disclosure, the protective gas 1s at least one of an inert gas and nitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

[46] The present disclosure is further described below with reference to accompanying drawings and embodiments, where

[47] FIG. 1 is a structural schematic diagram of a composite crucible cover used in an embodiment 1 of the present disclosure;

[48] FIG. 2 is a schematic top view of a composite heater used in the embodiment 1 of the present disclosure; and

[49] FIG. 3 is a sectional schematic diagram of the composite heater used in the embodiment 1 of the present disclosure.

[50] Reference Numerals:

[51] 100, graphite layer; 200; composite binder; 300, high-purity silicon layer; 400, seed crystal layer; 500, cylindrical heater; and 600, movable graphite ring.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[52] The embodiments of the present disclosure are described below in detail.

Examples of the embodiments are shown in the accompanying drawings. The same or similar numerals represent the same or similar elements or elements having the same or similar functions throughout the specification. The embodiments described below with reference to the accompanying drawings are exemplary, and are merely intended to explain the present disclosure but should not be construed as a limitation to the present disclosure.

[83] In the description of the present disclosure, it should be understood that, in orientation description, orientation or position relationships indicated by terms such as "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inside" and "outside" are orientation or position relationships as shown in the drawings. These terms are merely intended to facilitate and simplify the description of the present disclosure, rather than to indicate or imply that the mentioned device or components must have a specific orientation or must be constructed and operated in a specific orientation. Therefore, these terms should not be understood as a limitation to the present disclosure. [S4] Inthe description of the present disclosure, "several" means a number larger than 1, while "a plurality of” means a number larger than 2; "larger than", "smaller than", “over” and the like are construed as not including the number, and "above", "below", “within” and the like are construed as including the number. The "first" and "second" in the description are merely intended to distinguish technical features, and cannot be construed as indicating or implying a relative importance or implicitly indicating a number of indicated technical features or implicitly indicating a sequence relationship of the indicated technical features.

[55] In the description of the present disclosure, unless otherwise explicitly defined, the words such as "arrange", "install" and "connect" should be understood in a broad sense, and those skilled in the technical field can reasonably determine the specific meanings of the above words in the present disclosure in combination with specific contents of the technical solutions.

[56] In the description of the present disclosure, the description with reference to the terms “one embodiment”, "some embodiments", "exemplary embodiments", "examples", or "specific examples" means that specific features, structures, materials or characteristics described in combination with the embodiments or examples are included in at least one embodiment or example of the present disclosure. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[57] Example 1

[58] In this example, a SiC was manufactured through a specific process including the following steps of:

[59] SI, a crucible with a composite crucible cover was cleaned and subjected to empty burning;

[60] Sla, inner and outer surfaces of a crucible body and the composite crucible cover were wiped with alcohol cotton balls;

[61] Slb, the crucible body and the composite crucible cover were subjected to ultrasonic treatment with deionized water, absolute ethanol, acetone and deionized water for 20 min respectively;

[62] Sic, the crucible cleaned in step S1b was arranged in a growing furnace as required, and a vacuum degree of the growing furnace was lowered to be less than or equal to 107 Pa; and

[63] Sld, a protective gas (nitrogen, with a purity higher than or equal to 99.999%) was introduced into the growing furnace obtained in step Slc until a pressure of the growing furnace was 6x10* Pa, empty burning was performed at 1800°C for 3 h at a heating velocity of 30°C/min, and the growing furnace was naturally cooled to a room temperature;

[64] S2, high-purity SiC micro-powder was placed at a bottom of the cooled crucible, the crucible was vacuumized until a pressure reached 10% Pa, nitrogen (with a purity higher than or equal to 99.999%) was introduced until the pressure reached 1=105 Pa, and afterwards the crucible was heated to 2,350°C at a velocity of 30°C/min, where a movable graphite ring was positioned at a bottom of a cylindrical heater in a heating process; and

[65] S3, under a nitrogen pressure of 8x10* Pa, after a temperature of a system in step S3 was maintained for 20 min, a pressure of the system was lowered to 6x10* Pa, the movable graphite ring was moved 30 mm towards a top of the crucible, and a reaction was maintained, thus obtaining a SiC single crystal with a growing height of 2.2 mm.

[66] As shown in FIG. 1, a structure of the composite crucible cover used in this example includes a graphite layer 100, a composite binder 200, a high-purity silicon layer 300 and a seed crystal layer 400 which are sequentially stacked.

[67] As shown in FIG. 2 and FIG. 3, a structure of a composite heater used in this example includes a cylindrical heater 500 and a movable graphite ring 600 nested in the cylindrical heater 500.

[68] Comparative Example 1

[69] In this comparative example, a SiC crystal is manufactured in a specific process different from that of the example 1 as follows:

[70] (1) A position of the graphite ring is not moved in step S3.

[71] Comparative Example 2

[72] In this example, a SiC crystal is manufactured in a specific process different from that of the example 1 as follows:

[73] (1) The crucible cover used in step SI is an ordinary crucible cover; meanwhile, a structure including a high-purity silicon layer 300 and a seed crystal layer 400 is arranged at a position 10 mm away from the crucible cover; and the seed crystal layer 400 faces the high-purity SiC micro-powder, namely faces a bottom of the crucible.

[74] Test Example

[75] In this test example, defect degrees of the SiC single crystals manufactured in the examples and the comparative examples are tested. Where,

[76] a density of a penetrating dislocation density was observed with an optical microscope. Results are shown in Table 1.

[77] Table 1 Penetration Dislocation Density of SiC Single Crystals Obtained in

Examples and Comparative Examples

Examples Example | Comparative Comparative

Te es

Penetration screw type | 92 450 430 poet tr

Penetration blade type | 3500 28000 26500 we

[78] The results in Table 1 show that a growing temperature gradient of the SiC single crystal in the crucible is adjusted by using the composite heater; and in addition, the composite crucible cover used has the function of a seed crystal, which also reduces influences caused by independently arranging a seed crystal (Comparative Example 2) on a temperature field in the crucible. Therefore, the obtained SiC single crystal has a lower penetrating dislocation density.

[79] The embodiments of the present disclosure are described above in detail with reference to the accompanying drawings, but the present disclosure is not limited to the above embodiments.

Within the scope of knowledge possessed by those of ordinary skill in the technical field, various changes can also be made without departing from the purpose of the present disclosure.

In addition, the embodiments in the present disclosure and features in the embodiments may be combined with each other in a non-conflicting situation.

Claims

Conclusions

A process for manufacturing a single crystal of silicon carbide (SiC), comprising the steps of: S1, cleaning a crucible with a composite crucible cover, and performing a blank firing on the crucible; S2, placing a micropowder of high-purity SiC on the bottom of the cooled crucible, and heating the crucible to 1,700 °C — 2,400 °C by a composite heater under a positive pressure of a shielding gas; and S3, maintaining a temperature of a system in S3, and cooling to a room temperature to obtain the single crystal of SiC, the micropowder of high purity SiC having a purity greater than or equal to 99.9999% .

The manufacturing method according to claim 1, wherein in step S1, the composite crucible cover includes a graphite layer, a high-purity silicon layer, and a seed crystal layer arranged sequentially.

The manufacturing method according to claim 2, wherein the seed crystal layer is made of SiC having a carbon concentration gradually increasing from the high purity silicon layer.

The manufacturing method of claim 1, wherein in step S2, the composite heater comprises a cylindrical heater and a movable graphite ring located between the cylindrical heater and the crucible.

The manufacturing method according to claim 1, wherein the manufacturing method before step S2 further comprises a step of lowering a pressure of a vacuum chamber to be less than or equal to 4x10™* Pa.

The manufacturing process according to claim 1, wherein in step S2 the shielding gas has a positive pressure ranging from 6x10* Pa - 1x10° Pa.

The manufacturing method according to claim 1, wherein the protective gas has a positive pressure of 6x10% Pa - 8x10% Pa in a temperature maintenance process in step S3.

The manufacturing method according to claim 1, wherein the shielding gas has a positive pressure of 9x10* Pa - 1.1x10° Pa in a cooling process in step S3.

The manufacturing process according to claim 1, wherein in step S3 cooling cooling to a temperature of less than or equal to 1600°C at a rate of 15°C/min - 25°C/min and natural cooling to room temperature includes.

The manufacturing method of claim 1, wherein the shielding gas is at least one of an inert gas and nitrogen.