CN119121384A

CN119121384A - A high-quality silicon carbide substrate and a preparation method thereof and a semiconductor device

Info

Publication number: CN119121384A
Application number: CN202411279470.6A
Authority: CN
Inventors: 高超; 石志强; 杨晓俐; 潘亚妮; 高宇晗; 方帅; 彭红宇
Original assignee: Shandong Tianyue Advanced Technology Co Ltd
Current assignee: Shandong Tianyue Advanced Technology Co Ltd
Priority date: 2023-09-28
Filing date: 2024-05-13
Publication date: 2024-12-13
Also published as: CN118147740A; CN116988158A; CN118147740B

Abstract

The present invention provides a high-quality silicon carbide substrate, a preparation method thereof and a semiconductor device, and relates to the technical field of silicon carbide wafers. The preparation method of the crystal includes a crystal stable growth stage, and the growth process conditions of the crystal stable growth stage include the following steps: S1: There is a limiting edge near the crystal growth edge, and the distance between the limiting edge and the crystal growth edge is not more than 5mm, and a negative radial temperature gradient of ‑5°C/mm‑‑0.1°C/mm is set within the range of the limiting edge and the crystal growth edge; a continuous positive temperature gradient of ≤3°C/cm is set from the limiting edge to the center of the crystal; S2: A seed crystal larger than the diameter of the target silicon carbide crystal is used for crystal growth, and the seed crystal diameter is at least 5mm larger than the target crystal and substrate diameter, and a high-quality silicon carbide substrate is obtained after processing the target crystal. The silicon carbide substrate of the present invention has high quality uniformity and significantly improves the reliability of the device.

Description

High-quality silicon carbide substrate, preparation method thereof and semiconductor device

The application discloses a high-quality silicon carbide substrate, a preparation method thereof and a semiconductor device, which are applied separately under the application number CN202410586417.4, the application date of the original application is 2024, 05, 13, the priority date of the original application is 2023, 09 and 28.

Technical Field

The invention relates to the technical field of silicon carbide wafers, in particular to a high-quality silicon carbide substrate, a preparation method thereof and a semiconductor device.

Background

At present, silicon carbide crystals have two major problems, namely 1, quality problem, influence on yield, performance and reliability of silicon carbide device ends, and 2, cost problem, influence on application of silicon carbide in terminals. The loss of material and device yield caused by material quality is also a main reason for high cost and difficult application of silicon carbide crystals at present.

Furthermore, the quality problems of the silicon carbide substrate include two types, namely the dominant quality problems such as material quality and yield caused by defect problems, which can be well reflected in substrate material indexes, and the quality problems such as material yield and device performance reliability caused by quality consistency problems, which are often difficult to reflect in substrate material indexes, so that the reliability of subsequent devices is more risky.

Specifically, in the conductive silicon carbide crystal, the problem of consistency is mainly characterized in that on one hand, defects are distributed, defect aggregation can cause macroscopic black spots on a silicon carbide substrate, so that the defects such as light transmittance and dislocation density fluctuation are large, and although the crystallization defects in the current silicon carbide crystal are greatly improved, the problems of unstable defect control, uneven distribution and low overall defect density and high local density still exist. These local defect concentrations result in reduced device yields, reduced performance in certain areas. On the other hand, the quality distribution, such as resistivity distribution, is that the lower the low on-resistance characteristic of the power device is, the better the material resistivity is, but the excessively wide electrical property distribution can cause the device performance to be too large, the lower the resistivity of a specific area, such as a growth characteristic surface, can cause the generation of defects of dislocation, stacking fault and the like in the area, can also cause the problem that the stacking fault is expanded in the subsequent use process of the device, and seriously threatens the reliability problem of the device.

At present, a conventional physical vapor transport method (PVT for short) is used for preparing SiC crystals and substrates, and the "facet" refers to a growth characteristic surface, and the growth characteristic surface is an inherent attribute when the SiC crystals are prepared by a sublimation method. The growth characteristic surface is commonly called as a 'facet', 'growth facet', 'characteristic growth surface' and the like in the field, defects are concentrated in the area due to the existence of the growth characteristic surface, and elements are induced to be accumulated and increased at the growth characteristic surface in the element doping process, so that the doping is uneven, the resistivity is higher at the growth characteristic surface than in other areas, the carrier uniformity of the whole substrate is poor, and the large-scale use of the silicon carbide substrate is limited. In addition, the growth feature in the present invention does not refer to a growth interface.

Improving quality and reducing cost are targets for continuous development of silicon carbide crystal materials. Particularly, in the current stage of rapidly stepping into large-scale production and application in the silicon carbide industry, the stability, consistency and reliability of the performance of the silicon carbide material play a vital role in the industrial development.

Disclosure of Invention

In order to solve the problems, the first aspect of the invention provides a high-quality silicon carbide substrate which is conductive and does not contain any one or more than two of a growth characteristic surface, a high doping region and a defect aggregation region in the whole area, wherein the silicon carbide substrate is prepared by adopting a PVT method.

The growth characteristic surface is an inherent attribute of the SiC crystal prepared by the PVT method, and the high-quality silicon carbide substrate can change the movement trend of the growth characteristic surface when the PVT method grows, so that the growth characteristic surface moves towards the edge of the crystal and is fixed within a range of 5mm away from the edge of the crystal, and the edge is cut when the crystal is actually used, so that the silicon carbide substrate without the growth characteristic surface can be obtained along with the processing of cutting, grinding, polishing and the like of the crystal.

The defects in the original substrate are dense in the region due to the existence of the growth characteristic surface, and elements are induced to gather and increase in the growth characteristic surface in the element doping process, so that the doping is uneven, the resistivity is higher than that of other regions in the growth characteristic surface, the light transmission uniformity of the whole substrate is poor, and the large-scale use of the silicon carbide substrate is limited.

The high-quality silicon carbide substrate has no growth characteristic surface, and the whole substrate is uniformly distributed in the radial direction and the axial direction, so that the generation and aggregation of defects can be fundamentally restrained, element aggregation in the doping process is avoided, element uniform doping is realized, the doping uniformity, the resistivity uniformity and the light transmittance uniformity of the substrate are improved, and therefore, the device produced by adopting the silicon carbide substrate has good self performance and good consistency of mass production, and is beneficial to industrialized popularization and use.

Optionally, the silicon carbide substrate is doped with N-type elements, the doping concentration of the N-type elements is more than 1e ¹⁸cm^-3, and the property of the silicon carbide substrate in the whole area range meets any one or two of the following conditions;

a. The difference of the in-plane resistivity is not higher than 2.0mΩ·cm;

b. the difference in light transmittance is not higher than 3%.

Optionally, the in-plane resistivity difference is not higher than 1.0mΩ·cm.

Optionally, the doping concentration is 2e ¹⁸～7e¹⁸cm^-3, and the in-plane resistivity difference is 0.62-0.86 mΩ·cm.

Optionally, the light transmittance difference is 0.5% -1.6%.

Optionally, the doping of the N-type element is N ₂ doping, the in-plane resistivity difference is 0.62-0.86 mΩ & cm, and the light transmittance difference is 0.5% -1.6%.

The in-plane resistivity difference is "in-plane resistivity maximum value-in-plane resistivity minimum value", and the light transmittance difference is "light transmittance maximum value-light transmittance minimum value".

The doping concentration of the N-type element is larger than 1e ¹⁸cm^-3, which belongs to medium-high nitrogen doping, and for the person skilled in the art, the higher the doping concentration is, the more uneven the doping is, so that the larger the difference value of the in-plane resistivity is, the application fixes the growth characteristic surface on the edge of the crystal in the process of controlling the movement trend of the growth characteristic surface, thereby improving the doping uniformity in the doping process and ensuring that the light transmittance of the substrate is more uniform.

The light transmittance is related to the doping concentration and uniformity in the crystal, and the difference of the light transmittance of the silicon carbide substrate is not higher than 3 percent, so that the light transmittance of the silicon carbide substrate is uniform, thereby being beneficial to improving the quality of the photoetching process at the downstream device end and further improving the device performance.

Optionally, the silicon carbide substrate TDV is less than 200cm ^-2.

Optionally, the silicon carbide substrate TDV is less than 100cm ^-2.

Preferably, the silicon carbide substrate TDV is less than 10cm ^-2.

The Total Density Variation (TDV) is defined as dividing a plurality of square grids with specific areas in the substrate, such as n square grids with the areas of 1mm x1mm,2mm x2mm,5mm x5mm and 10mm x10mm, and The Edge Dislocation (TED) or screw dislocation (TSD) in the square grids has the densities of d1, d2, d3.. TDV is the difference dmax-dmin between the TED or TSD density maximum and the TED or TSD density minimum.

The silicon carbide substrate eliminates the growth characteristic surface, so that the TED and TSD are distributed more uniformly, the TDV value is lower, the dislocation distribution representing the whole substrate is more uniform, and the problems of low overall defect density and high local density existing in the existing substrate are solved.

When the substrate is used for preparing a power electronic device, the device can be ensured to have excellent electrical performance and reliability in the process of producing the device due to the characteristics of low in-plane resistivity difference and low light transmittance difference.

Alternatively, the silicon carbide substrate has a size of 4 inches, 6 inches, 8 inches, or 10 inches.

The second aspect of the present invention provides a method for producing a high-quality silicon carbide substrate obtained by subjecting a crystal to at least a dicing step, the method comprising a crystal-stable growth stage, the growth process conditions of the crystal-stable growth stage comprising the steps of:

s1, a limiting edge exists near the crystal growth edge, the distance between the limiting edge and the crystal growth edge is not more than 5mm, and a negative radial temperature gradient of-5 ℃ to-0.1 ℃ per mm is arranged in the range between the limiting edge and the crystal growth edge;

s2, crystal growth is carried out by using a seed crystal with the diameter larger than that of the target grown silicon carbide crystal, the diameter of the seed crystal is at least 5mm larger than that of the target crystal and that of the substrate, and the high-quality silicon carbide substrate is obtained after the target crystal is processed.

Optionally, the defined edge is no more than 3mm from the crystal growth edge.

Optionally, in step S1, a negative radial temperature gradient of-5 ℃ to-0.1 ℃ per mm is set in a range of less than 5mm from the crystal growth edge, and a continuous positive temperature gradient is set in a range of more than 5mm from the crystal growth edge, wherein the continuous positive temperature gradient value is less than or equal to 3 ℃ per cm.

Optionally, in step S1, a negative radial temperature gradient of-3 ℃ per mm to-1 ℃ per mm is set within less than 5mm from the crystal growth edge.

The radial temperature gradient is calculated as the ratio of the difference (T2-T1) between the temperature T1 at a point closer to the center of the wafer body and the temperature T2 at a point farther from the center of the wafer body to the distance d between the two points in the direction of radiating outwards in the radial direction with the center of the wafer body as the origin, and the positive (forward) temperature gradient DeltaT= (T2-T1)/d, whereas the negative temperature gradient DeltaT= (T1-T2)/d.

The preparation method adopted at this time can drive the growth characteristic to move towards the edge of the crystal and fix the growth characteristic within the range of 5mm of the edge of the crystal under the arrangement of the step S1 so as to obtain the high-quality silicon carbide substrate. However, it will be understood by those skilled in the art that the movement trend of the growth feature may be controlled in other ways to obtain the silicon carbide substrate of the present application, and thus the present application is merely illustrative of the method of preparing a high quality silicon carbide substrate prepared this time, and other methods of controlling the movement trend of the growth feature are not within the scope of the present application.

The radial temperature gradient of crystal growth in step S1 may be set by means of conventional techniques in the art, such as adjusting parameters such as temperature or pressure in the growth chamber or thickness of the insulating layer material. The discontinuous temperature gradient arrangement can be realized by carrying out structural improvement in the crystal growth chamber and optimizing the temperature distribution of a crystal growth interface, thereby realizing the controllable adjustment of the temperature gradient, such as placing a material with lower heat conductivity than a central area at the edge of the crystal growth chamber, reducing the heat dissipation of the edge, thereby realizing the temperature distribution jump at the crystal growth interface, otherwise, the reverse temperature gradient distribution can be arranged, such as placing a material with higher heat conductivity at the edge of the crystal growth or reducing the thickness of an edge heat preservation layer, and the like, and in addition, different thermal field structures or novel materials can be arranged in the growth chamber to adjust the temperature distribution, such as arranging TaC coating materials coated with high reflectivity on a graphite ring at the edge of the crystal growth, so that the heat radiation in the growth chamber is concentrated towards the edge of the crystal growth, thereby realizing the temperature gradient jump. Through the technical means which are more common in the industry, the scheme configuration can be carried out according to the actual requirements so as to achieve the purpose of adjusting the temperature gradient in the crystal growth chamber.

Alternatively, during the crystal growth stabilization phase, the temperature in the growth chamber is first raised to above 2200 ℃ at a rate of 10-50 ℃ per minute while the pressure in the growth chamber is reduced to 1-100mbar, after which the crystal growth is carried out for more than 50 hours at the settings of steps S1 and S2.

Alternatively, during the crystal growth stabilization phase, the temperature in the growth chamber is first raised to above 2200 ℃ at a rate of 10-30 ℃ per minute while the pressure is reduced to 5-50mbar, after which the crystal growth is carried out for more than 50 hours at the setting of steps S1 and S2.

In the invention, a PVT method is adopted to prepare silicon carbide crystals, isostatic pressing graphite is adopted as a raw material of a growth chamber (crucible) for crystal growth, and SiC powder is adopted as a raw material for crystal growth. In order to ensure excellent and stable electrical properties of the silicon carbide, the invention preferably adopts silicon carbide synthetic powder with certain purity, the total impurity content of the silicon carbide powder is not higher than 1E ¹⁹cm^-3, and more preferably, the total impurity content of the silicon carbide powder is not higher than 1E ¹⁷cm^-3.

In the invention, when silicon carbide crystal grows, siC powder is filled into a cavity of a graphite crucible, siC seed crystals are placed at the top of the growth cavity, the crucible is sealed, the crucible is placed in a thermal insulation material prepared from graphite soft felt or hard felt to wrap, and then the crucible is moved into a cavity of crystal growth equipment to carry out crystal growth.

Optionally, the method further comprises a crystal nucleation stage before the crystal stable growth stage, and the growth process conditions of the crystal nucleation stage comprise the following steps:

After the growth chamber of the crystal is sealed, vacuumizing the growth chamber to below 10 ^-3 Pa, stabilizing for a period of time in a vacuum stage, starting to introduce inert gas, gradually raising the pressure in the growth chamber to 100-1000mbar, keeping constant, and simultaneously introducing nitrogen into the chamber at a rate of 1ml/min-100 ml/min.

Optionally, the temperature in the growth chamber is gradually increased from room temperature to 1600-2100 ℃ and then is constant while the pressure in the growth chamber is increased in the crystal nucleation stage, and the crystal growth stage is performed after the temperature is maintained for 5-50h at constant temperature and constant pressure.

Optionally, the temperature in the growth chamber in the crystal nucleation stage is constant at 1800-2100 ℃, the pressure in the growth chamber is constant at 300-800mbar, and the crystal growth stage is performed after the constant temperature and constant pressure are maintained for 30-50 h.

In the crystal nucleation stage, silicon carbide powder sublimates to form crystal nucleus, and in the crystal stable growth stage, the silicon carbide powder can fully sublimate and is transferred to a seed crystal for stable growth, and finally the silicon carbide crystal is obtained, and the diameter of the seed crystal in the step S2 is at least 5mm larger than that of a target crystal and a substrate, so that the prepared SiC crystal has edge machining allowance, and the edge is cut to obtain the high-quality silicon carbide crystal. For example, the seed crystal diameter is 160mm, the substrate diameter is 150mm or the seed crystal diameter is 210mm, and the substrate diameter is 200mm, so that the smooth preparation of the large-size silicon carbide substrate can be ensured, and the quality of the prepared silicon carbide substrate can be improved.

A third aspect of the present invention provides a semiconductor device comprising the silicon carbide substrate described above.

Compared with the prior art, the invention has at least one of the following beneficial effects:

(1) The silicon carbide substrate prepared by the method does not contain a growth characteristic surface, the resistivity difference in the whole area range is not higher than 2.0mΩ & cm, and the light transmittance difference is not higher than 3%, so that the silicon carbide substrate has high uniformity, and the semiconductor device prepared by using the silicon carbide substrate has higher yield, performance and reliability.

(2) The TDV of the silicon carbide substrate prepared by the method is smaller than 200cm ^-2 in the whole area range, the problems of low overall defect density and high local density in the existing substrate are solved, and the defects of dislocation, stacking fault and the like are hardly generated, so that the method is more suitable for being popularized and used in a large range.

(3) According to the preparation method, the movement trend of the growth characteristic surface can be controlled by regulating and controlling the step S1 in the growth of the crystal, the movement trend is locked within the range of 5mm of the edge area of the crystal, and then the target silicon carbide substrate can be obtained after the crystal is subjected to cutting, grinding, polishing and other processing.

(4) The silicon carbide substrate prepared by the method has high electrical uniformity (such as resistivity uniformity), high light transmittance uniformity and high defect distribution uniformity, and when the substrate is cut and used for preparing a semiconductor device, the effective area utilization rate can be improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation on the invention. In the drawings:

FIG. 1 illustrates an exemplary embodiment of a schematic structure of a silicon carbide substrate having macroscopic growth features;

FIG. 2 illustrates an exemplary embodiment of a growth process schematic of the growth feature of the present application;

FIG. 3 illustrates one exemplary embodiment of a schematic view of the crystal structure of silicon carbide of the present application;

FIG. 4 shows a light transmittance test method graph;

FIG. 5 shows a graph of resistivity mapping for a silicon carbide substrate of example 1 of the present application;

FIG. 6 is a graph showing resistivity mapping of a silicon carbide substrate in accordance with example 2 of the present application;

FIG. 7 shows a graph of resistivity mapping for a silicon carbide substrate in accordance with example 3 of the present application;

FIG. 8 shows a graph of resistivity mapping for a silicon carbide substrate in accordance with example 4 of the present application;

FIG. 9 shows a graph of resistivity mapping of a silicon carbide substrate of comparative example 1 of the present application;

FIG. 10 shows a graph of resistivity mapping of a silicon carbide substrate of comparative example 1 of the present application;

FIG. 11 shows a graph of resistivity mapping of a silicon carbide substrate of comparative example 1 of the present application;

FIG. 12 is a graph showing the resistivity mapping of a silicon carbide substrate of comparative example 1 of the present application;

FIG. 13 is a graph showing the transmittance of a silicon carbide substrate of example 2 of the present application versus a silicon carbide substrate of comparative example 1;

FIG. 14 is a graph showing the transmittance change of a silicon carbide substrate according to example 3 of the present application;

Fig. 15 shows a schematic view of the structure of a silicon carbide substrate without growth features of the present application.

Detailed Description

In order to more clearly illustrate the general inventive concept, a detailed description is given below by way of example with reference to the accompanying drawings.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

At present, the existing silicon carbide substrate has the defects of dislocation, stacking fault and the like in the area and the problems of stacking fault expansion and the like in the subsequent use process of the device due to the fact that the growth characteristic surface exists and the resistivity at the growth characteristic surface is too low, so that the resistivity distribution is uneven in the whole area of the silicon carbide substrate, the light transmittance distribution is uneven and the carrier concentration change rate is uneven. In order to solve the problems, the invention provides a high-quality silicon carbide substrate, wherein a growth characteristic surface which is visible to naked eyes is not formed in the whole area of the silicon carbide substrate, and the resistivity, doping concentration, light transmittance and carrier concentration of the silicon carbide substrate are highly uniform in the whole area of the silicon carbide substrate.

In the process of preparing the silicon carbide substrate in the following embodiments 1 to 6, the growth characteristic surface can be locked at the edge of the silicon carbide crystal, and the silicon carbide substrate without the growth characteristic surface can be obtained along with the cutting of the edge of the crystal, and the defect number of the silicon carbide substrate per se is reduced and cannot be aggregated due to the disappearance of the inherent structural attribute of the growth characteristic surface, meanwhile, the aggregation of elements in doping can be avoided, namely, the existence of a high doping area is avoided, so that the doping uniformity, the light transmission uniformity and the resistivity uniformity of the silicon carbide substrate without the structure of the growth characteristic surface are all mentioned.

Example 1

The embodiment relates to a preparation method of a 6-inch high-quality silicon carbide substrate, which specifically comprises the following steps:

(1) Nucleation stage of crystals

And (3) loading silicon carbide powder and seed crystals into a crucible, sealing a growth chamber, vacuumizing the growth chamber to below 10 ^-3 Pa through a mechanical pump and a vacuum pump, starting to introduce inert gas after the vacuum stage is stable for a period of time, gradually raising the pressure in the growth chamber to 100mbar, and simultaneously introducing nitrogen into the chamber at a speed of 100 ml/min. While the pressure in the growth chamber is increased in the crystal nucleation stage, the temperature in the furnace is gradually increased from room temperature to 1600 ℃ through power setting and maintained for 50h.

(2) Crystal stable growth stage

After the crystal nucleation phase has ended, the temperature is raised to 2200℃at a rate of 20℃per minute, while the pressure in the growth chamber is reduced to 50mbar and maintained for 50 hours by regulating the pressure controller. Specific:

s1, setting negative radial temperature gradient-0.1 ℃ per mm within a range of less than 5mm from the crystal growth edge and setting continuous positive temperature gradient within a range of more than 5mm from the crystal growth edge, wherein the continuous positive temperature gradient is 1 ℃ per cm;

S2, using a seed crystal with the diameter larger than the target silicon carbide crystal to grow, wherein the diameter of the seed crystal is 5mm larger than that of the target crystal. And cutting, grinding, polishing and the like the target crystal obtained by growth to obtain the target silicon carbide substrate.

Example 2

(1) Nucleation stage of crystals

And (3) loading silicon carbide powder and seed crystals into a crucible, sealing a growth chamber, vacuumizing the growth chamber to below 10 ^-3 Pa through a mechanical pump and a vacuum pump, starting to introduce inert gas after the vacuum stage is stable for a period of time, gradually raising the pressure in the growth chamber to 300mbar, and simultaneously introducing nitrogen into the chamber at a speed of 40 ml/min. While the pressure in the growth chamber in the crystal nucleation stage is raised, the temperature in the furnace is gradually raised to 1800 ℃ from room temperature through power setting and maintained for 30 hours.

(2) Crystal stable growth stage

After the crystal nucleation phase has ended, the temperature is raised to 2400℃at a rate of 30℃per minute, while the pressure in the growth chamber is reduced to 10mbar and maintained for 70h by regulating the pressure controller. Specific:

s1, setting negative radial temperature gradient-5 ℃ per mm within a range of less than 4.5mm from the crystal growth edge and setting continuous positive temperature gradient within a range of more than 4.5mm from the crystal growth edge by taking the crystal growth edge as a boundary, wherein the continuous positive temperature gradient is 1 ℃ per cm;

S2, using a seed crystal with the diameter larger than the target silicon carbide crystal to grow, wherein the diameter of the seed crystal is 6mm larger than that of the target crystal. And cutting, grinding, polishing and the like the target crystal obtained by growth to obtain the target silicon carbide substrate.

Example 3

(1) Nucleation stage of crystals

And (3) loading silicon carbide powder and seed crystals into a crucible, sealing a growth chamber, vacuumizing the growth chamber to below 10 ^-3 Pa through a mechanical pump and a vacuum pump, starting to introduce inert gas after the vacuum stage is stable for a period of time, gradually raising the pressure in the growth chamber to 500mbar, and simultaneously introducing nitrogen into the chamber at a speed of 40 ml/min. While the pressure in the growth chamber was raised during the crystal nucleation stage, the temperature in the furnace was gradually raised from room temperature to 2100 ℃ by power setting and maintained for 50h.

(2) Crystal stable growth stage

After the crystal nucleation phase has ended, the temperature is raised to 2500℃at a rate of 10℃per minute, while the pressure in the growth chamber is reduced to 20mbar and maintained for 70h by regulating the pressure controller. Specific:

S1, setting negative radial temperature gradient-3 ℃ per mm within a range of less than 3.5mm from the crystal growth edge and setting continuous positive temperature gradient within a range of more than 3.5mm from the crystal growth edge by taking the crystal growth edge as a boundary, wherein the continuous positive temperature gradient is 3 ℃ per cm;

Example 4

(1) Nucleation stage of crystals

And (3) loading silicon carbide powder and seed crystals into a crucible, sealing a growth chamber, vacuumizing the growth chamber to below 10 ^-3 Pa through a mechanical pump and a vacuum pump, starting to introduce inert gas after the vacuum stage is stable for a period of time, gradually raising the pressure in the growth chamber to 300mbar, introducing nitrogen into the chamber at 30ml/min, and doping P. While the pressure in the growth chamber is increased in the crystal nucleation stage, the temperature in the furnace is gradually increased from room temperature to 2000 ℃ through power setting and maintained for 50h.

(2) Crystal stable growth stage

After the crystal nucleation phase has ended, the temperature is raised to 2600℃at a rate of 40℃per minute, while the pressure in the growth chamber is reduced to 20mbar and maintained for 80 hours by regulating the pressure controller. Specific:

s1, setting negative radial temperature gradient-4 ℃ per mm within a range of less than 3mm from the crystal growth edge and setting continuous positive temperature gradient within a range of more than 3mm from the crystal growth edge, wherein the continuous positive temperature gradient is 0.5 ℃ per cm;

S2, using a seed crystal with the diameter larger than the target silicon carbide crystal to grow, wherein the diameter of the seed crystal is 8mm larger than that of the target crystal. And cutting, grinding, polishing and the like the target crystal obtained by growth to obtain the target silicon carbide substrate.

Example 5

The difference between this example and example 2 is that in step S1, a negative radial temperature gradient of-1 ℃ per mm is set in a range of less than 4.5mm from the crystal growth edge, and this example produces an 8-inch silicon carbide substrate, and the remaining steps are the same as in example 2.

Example 6

The difference between this example and example 2 is that in step S1, a continuous positive temperature gradient is set in a range of more than 4.5mm from the crystal growth edge, the continuous positive temperature gradient being 3℃/cm, and the remaining steps are the same as in example 2.

Comparative example 1

This comparative example differs from example 2 in that in step S1, a continuous positive temperature gradient is set from the center to the edge of the crystal, the continuous positive temperature gradient being 3℃/cm, and the remaining steps are the same as example 2.

Comparative example 2

This comparative example differs from example 2 in that in step S1, a negative radial temperature gradient of-6 ℃ per mm is set in a range of less than 4.5mm from the crystal growth edge, and this example produces an 8-inch silicon carbide substrate, and the remaining steps are the same as example 2.

The PVT crystal growth method is adopted in the marketed examples and comparative examples to prepare silicon carbide crystals, and silicon carbide substrates obtained by the same edge cutting (5 mm cutting), radial cutting, grinding and polishing procedures are adopted in the examples and comparative examples, and the performance of the obtained silicon carbide substrate samples is tested, and the results are shown in Table 1, and the specific test method is as follows:

the resistivity adopts Semilab WT-2000 low-resistance tester, 73 points uniformly and symmetrically distributed in the silicon carbide substrate slice are taken for testing, and the mapping graph is adopted to represent the resistivity distribution condition of the substrate slice.

The light transmittance was measured using a haze meter CS-700, using a test method as shown in FIG. 4, at several points along the diameter of the substrate sheet through the center and growth feature area.

Table 1 silicon carbide substrate Performance test table

The discontinuous temperature gradient distribution is arranged in the radial direction of the crystal growth surface, so that the crystal edge has enough transverse growth driving force, and the continuous expanding growth capacity of the crystal edge is ensured. The crystals of the examples and comparative examples were subjected to conventional identical edge cutting, radial cutting, grinding, polishing processes without changing the quality of the substrate. It can thus be seen from the data of table 1 that the preparation method of the present application can control the movement trend of the growth feature surface, locking it at the crystal edge, with reference to fig. 2, and with reference to fig. 3, the growth feature surface at the crystal edge can be removed along with the cutting of the crystal edge, so that the substrates of examples 1 to 6 have no growth feature surface, whereas neither the existing forward temperature gradient of comparative example 1 nor the temperature gradient of edge-6 ℃ per mm of comparative example 2 can move the growth feature surface toward and fix it at the edge.

The silicon carbide substrates of comparative example 1 and comparative example 2 each contained macroscopic growth features, the structure of which is shown in fig. 1, and it can be seen that the silicon carbide substrates without growth features do not contain "birthmark" like black spots over the entire area. The silicon carbide substrates prepared in examples 1-6 all contained no macroscopic growth features, and the structure is shown in FIG. 15. As can be seen from the above examples and comparative examples and FIGS. 1 and 15, the silicon carbide substrate without growth feature surface was obtained by the preparation method of the present application, and as can be seen from the other parameters disclosed in Table 1, the difference in-plane resistivity of the silicon carbide substrate was not more than 2.0mΩ & cm, the difference in light transmittance was not more than 3%, and TDV was less than 200cm ^-2, which represents that the overall performance of the silicon carbide substrate was improved, while the difference in resistivity in the silicon carbide substrate with growth feature surface in comparative examples 1 and 2 was more than 5mΩ & cm, the difference in light transmittance was more than 10%, and TDV was more than 400cm ^-2, which represents that the overall performance of the silicon carbide substrate was poor.

Fig. 5 shows a resistivity mapping graph of a silicon carbide substrate according to the present application of example 1, fig. 6 shows a resistivity mapping graph of a silicon carbide substrate according to the present application of example 2, fig. 7 shows a resistivity mapping graph of a silicon carbide substrate according to the present application of example 3, fig. 8 shows a resistivity mapping graph of a silicon carbide substrate according to the present application of example 4, referring to fig. 5 to 8, the abscissa indicates a diameter of the silicon carbide substrate, a center point of the silicon carbide substrate is a point of coordinates 00, a test area of equipment in the mapping graph is (-60 mm,60 mm), the ordinate indicates a resistivity, and a color change indicates a resistivity distribution, it can be seen that the resistivity distribution in the silicon carbide substrate of the present application is uniform, there is no abnormal low resistance region, a difference in the resistivity plane is <3mΩ·cm, and preferably, a difference in the resistivity plane is <1mΩ·cm.

Fig. 9, 10, 11 and 12 show resistivity mapping graphs of comparative example 1 of the present application, respectively, and the inventors conducted 4 sets of repeated experiments on comparative example 1, and as shown in reference to fig. 9, 10, 11 and 12, the center point of the silicon carbide substrate is the point of coordinates 00, the abscissa represents the area (-60 mm,60 mm) of the test silicon carbide substrate, and the ordinate represents the resistivity, and it can be seen that there is a significant low resistance anomaly region on the resistivity distribution due to the presence of the growth characteristic surface, and the difference in the resistivity plane is generally >5mΩ·cm.

FIG. 13 is a graph showing the transmittance of the silicon carbide substrate of example 2 according to the present application compared with that of the silicon carbide substrate of comparative example 1, wherein in FIG. 13, the abscissa represents the number of test points and the ordinate represents the transmittance, the circle curve is a graph of the transmittance of the silicon carbide substrate of example 2, and the square curve is a graph of the transmittance of the silicon carbide substrate of comparative example 1. As can be seen from fig. 13, the visible light transmittance of comparative example 1 suddenly drops in the growth feature surface region, because the doping concentration and carrier concentration of the growth feature surface region are much higher than those of the other regions, resulting in absorption of the visible light partial band. The silicon carbide substrate prepared in the embodiment 2 of the application eliminates the problems of overhigh doping concentration and carrier concentration at the growth characteristic surface, so that the impurity and carrier concentration in the substrate surface are uniformly distributed, and the uniformity and consistency of the transmittance in the visible light surface are greatly improved.

Fig. 14 shows a graph of transmittance change of a silicon carbide substrate according to example 3 of the present application, the abscissa represents different test coordinate points of the silicon carbide substrate, and the ordinate represents transmittance, and it can be seen from fig. 14 that in-plane transmittance distribution is uniform.

The application eliminates the growth characteristic surface, greatly improves the uniformity of resistivity and light transmittance in the substrate, does not have the aggregation of the defects such as wrappage or dislocation, microtubules and the like at the growth characteristic surface of the substrate, greatly improves the quality and yield of the substrate, and greatly improves the performance and reliability of the substrate in the subsequent device process and use process.

According to the analysis, the silicon carbide substrate prepared in examples 1-6 breaks through the conventional continuous forward radial temperature distribution design, creatively designs a negative radial temperature gradient at the crystal growth edge, drives the growth characteristic surface to change the movement trend, locks the growth characteristic surface at the crystal edge area, combines with a seed crystal with a diameter at least 5mm greater than the target diameter, finally fixes the growth characteristic surface within a range of 5mm from the crystal edge, and then cuts, grinds, polishes and the crystal to obtain the silicon carbide substrate without the growth characteristic surface.

Since the elimination of the growth characteristic surface is completed in the crystal growth stage, the subsequent substrate processing process will not affect the electrical properties, so the substrate processing mode is not particularly limited in the invention, and the routine operation is performed by those skilled in the art. The growth scheme is simple and easy to realize, and can ensure stress and defect control in a continuous and smaller temperature gradient of the central region of the crystal. Through the innovation, the growth characteristic surface can be fixed at the edge position of the crystal and removed in the subsequent crystal processing process, so that the whole crystal rod and the substrate processed therewith are free of the growth characteristic surface, the purpose of eliminating a defect aggregation area is achieved, and the end yield and the reliability of the device are ensured.

However, the method of preparing a silicon carbide substrate without a growth feature of the present application includes, but is not limited to, this. Those skilled in the art can also prepare the silicon carbide substrate in other ways capable of controlling the characteristic growth surface, and thus the preparation methods disclosed in the present application are only exemplary and do not limit the performance of the silicon carbide substrate itself, and those skilled in the art can also study new preparation methods by using existing technical reserves and creative efforts to obtain the silicon carbide substrate of the present application, and other preparation methods are not in the scope of the present application, and no study is conducted for this purpose.

The foregoing is merely exemplary of the present invention and is not intended to limit the present invention. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are to be included in the scope of the claims of the present invention.

Claims

1. The preparation method of the high-quality silicon carbide substrate is characterized in that the preparation method of the crystal comprises a crystal stable growth stage, and the growth process conditions of the crystal stable growth stage comprise the following steps:

2. The method of claim 1, wherein the defined edge is no more than 3mm from the crystal growth edge.

3. The method according to claim 1, wherein in the step S1, a negative radial temperature gradient of-5 ℃ per mm to-0.1 ℃ per mm is set within a range of less than 5mm from the crystal growth edge, and a continuous positive temperature gradient of not more than 3 ℃ per cm is set within a range of more than 5mm from the crystal growth edge.

4. A method according to claim 3, wherein in step S1 a negative radial temperature gradient of-3 ℃ per mm-1 ℃ per mm is set in a range of less than 5mm from the crystal growth edge.

5. The preparation method according to claim 1, wherein in the crystal growth stabilizing stage, the temperature in the growth chamber is raised to 2200 ℃ or higher at a rate of 10 to 50 ℃ per minute while the pressure in the growth chamber is reduced to 1 to 100mbar, and then the crystal growth is performed for 50 hours or more under the settings of steps S1 and S2.

6. The preparation method according to claim 5, wherein in the crystal growth stabilizing stage, the temperature in the growth chamber is raised to 2200 ℃ or higher at a rate of 10 to 30 ℃ per minute while the pressure is reduced to 5 to 50mbar, and then the crystal growth is performed for 50 hours or more with the settings of steps S1 and S2.

7. The method of any one of claims 1-6, further comprising a crystal nucleation stage prior to the crystal stable growth stage, wherein the growth process conditions of the crystal nucleation stage comprise the steps of:

8. The method according to claim 7, wherein the temperature in the growth chamber is raised from room temperature to 1600 to 2100 ℃ gradually while the pressure in the growth chamber is raised in the crystal nucleation stage, the temperature is kept constant, and the crystal growth stage is performed after the temperature is kept at constant temperature and constant pressure for 5 to 50 hours.

9. A high-quality silicon carbide substrate, characterized in that the high-quality silicon carbide substrate is conductive and does not contain any one or more of a growth characteristic surface, a high doping region and a defect aggregation region in the whole area.

10. A semiconductor device, characterized in that, the semiconductor device comprising the high quality silicon carbide substrate of claim 9.