Silicon carbide two-stage annealing process and silicon carbide wafer

Abstract

The application belongs to the technical field of silicon carbide new materials, and particularly relates to a silicon carbide two-stage annealing process and a silicon carbide wafer. The annealing process comprises the following steps: S1: placing the washed and dried silicon carbide wafer on the graphite paper laid in the annealing furnace chamber; S2: performing vacuumizing treatment on the annealing furnace chamber until a preset pressure value is reached; S3: starting the temperature rising mode of the annealing furnace and simultaneously introducing nitrogen into the chamber, stopping the introduction of nitrogen when the temperature reaches 1550-1600 DEG C and starting the introduction of hydrogen into the chamber, continuing to raise the temperature until the temperature reaches 2000 DEG C, stopping heating and keeping the temperature for a period of time to anneal the silicon carbide wafer; S4: after the annealing is completed, opening the furnace door of the annealing furnace subjected to the temperature lowering and air treatment and taking out the silicon carbide wafer. Through the above process, the annealing of the silicon carbide wafer can be realized, the carbonization reaction on the surface of the silicon carbide wafer can be effectively inhibited, and the wafer after the annealing still has good quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of silicon carbide new material, and particularly relates to a two-stage annealing process of silicon carbide and a silicon carbide wafer. BACKGROUND

[0002] The silicon carbide is one of the third generation semiconductor materials which replaces the second generation semiconductor material silicon due to the excellent physical properties of the material itself, and can reduce energy loss. In addition to stable operation at high pressure, it is more resistant to high temperature and easy to realize miniaturization.

[0003] As one of the steps in the production process of the silicon carbide wafer, annealing can effectively reduce the internal stress of the silicon carbide wafer and is beneficial to subsequent processing. In the annealing process of the silicon carbide, etching occurs at the edge of the step, and at the same time, carbonization effect of silicon atom escape occurs in the non-edge area. Only when the temperature is low, the influence of the carbonization effect is lower compared with the etching rate of the edge step. When the temperature reaches a certain degree, the influence of the annealing treatment on the surface of the silicon carbide crystal is that the carbonization effect occupies a dominant position. At this time, a large number of atoms on the surface of the silicon carbide wafer, especially silicon atoms, escape, leaving a large number of carbon atoms on the surface of the silicon carbide wafer, forming a layer of graphite structure. Therefore, long-time high-temperature annealing will affect the surface structure of the silicon carbide wafer, which is a problem to be solved at present.

[0004] In order to solve the carbonization phenomenon at high temperature in the annealing process, people usually use ion implantation activation process, that is, grow a carbon film on the surface of the silicon carbide wafer to inhibit the escape of silicon, but this method will form carbon residues on the surface of the silicon carbide wafer which are difficult to remove, especially in the trench type silicon carbide device, the residual carbon is more difficult to remove.

[0005] In order to reduce the influence of carbon residues, some people use silane inhibition method to anneal the silicon carbide, that is, silane is introduced into the high-temperature furnace to inhibit the precipitation of silicon atoms in the silicon carbide. However, this method is difficult to control accurately because it needs to accurately control the pressure in the chamber. Therefore, it is not a good choice.

[0006] Some research groups also use aluminum nitride film to cover the surface of the silicon carbide to inhibit the escape of silicon, but when the temperature rises to above 1600 DEG C, the aluminum nitride will lose its effect due to the appearance of voids. SUMMARY

[0007] The present application aims to provide a two-stage annealing process of silicon carbide and a silicon carbide wafer to solve the problem that long-time high-temperature annealing will affect the surface structure of the silicon carbide wafer in the prior art.

[0008] The present application provides a two-stage annealing process of silicon carbide, which comprises the following steps:

[0009] S1: Place the cleaned and dried silicon carbide wafers on graphite paper laid flat inside the annealing furnace chamber;

[0010] S2: Vacuum the annealing furnace chamber until the preset pressure value is reached;

[0011] S3: Turn on the heating mode of the annealing furnace and simultaneously introduce nitrogen into its chamber. When the temperature reaches 1550-1600℃, stop introducing nitrogen and start introducing hydrogen into its chamber. Continue heating until the temperature reaches 2000℃, then stop heating and maintain the temperature for a period of time to anneal the silicon carbide wafer.

[0012] S4: After annealing, open the furnace door of the annealing furnace that has been cooled and ventilated, and remove the silicon carbide wafers.

[0013] The silicon carbide two-stage annealing process provided by this invention may also have the following additional technical features:

[0014] In one specific embodiment of the present invention, in step S1, the silicon carbide wafer is washed and dried using an acidic liquid or a mixture of acidic liquids.

[0015] In one specific embodiment of the present invention, in step S1, a plurality of washed and dried silicon carbide wafers are laid flat on the graphite paper in a completely non-overlapping manner.

[0016] In one specific embodiment of the present invention, in step S2, when the pressure inside the annealing furnace chamber is reduced to 0.5-0.8 Pa, the vacuuming can be stopped and the next operation can be carried out.

[0017] In one specific embodiment of the present invention, in step S3, the heating rate in the heating mode is 5-7℃ / s.

[0018] In one specific embodiment of the present invention, step S3, introducing nitrogen into the chamber includes: introducing nitrogen into the chamber at a small flow rate of 0.01-0.1 L / min for 1-2 min, and then introducing nitrogen into the chamber at a large flow rate of 1-5 L / min until the target temperature is reached.

[0019] In one specific embodiment of the present invention, step S3, introducing hydrogen gas into the chamber, includes introducing hydrogen gas into the chamber at a flow rate of 1-3 L / min.

[0020] In one specific embodiment of the present invention, in step S3, the temperature control holding time is 8-15 hours, and during the temperature control holding time, the gas pressure in the annealing furnace chamber is maintained at 420-470T.

[0021] In one specific embodiment of the present invention, step S4, cooling and ventilating the annealing furnace includes: turning off the heating mode of the annealing furnace, extracting all the gas in its chamber and introducing air, and opening the furnace door when the air pressure in the chamber reaches atmospheric pressure.

[0022] The present invention also provides a silicon carbide wafer, which is processed by the silicon carbide two-stage annealing process described in any one of the above-mentioned methods.

[0023] This invention addresses the impact of high temperatures on the surface of silicon carbide wafers through a two-stage annealing process. Specifically, during high-temperature annealing of silicon carbide, silicon and carbon atoms experience increased energy and enhanced molecular vibrations, leading to a significant amount of escape. The two-stage annealing process provided in this application divides the heating process into two stages based on temperature. In the first stage, before the temperature inside the chamber reaches the carbonization temperature, nitrogen gas is introduced into the chamber during heating. In the second stage, when the temperature reaches or exceeds the carbonization critical temperature, hydrogen gas is introduced into the chamber during heating. Because hydrogen gas possesses dangling bonds and has high energy, it etches a very stable structure on the wafer surface, thus protecting the surface morphology of the annealed wafer through the etching effect of hydrogen. Since hydrogen gas is relatively light and tends to float at the top of the chamber, this invention uses a nitrogen-first method to form a mixed gas, which drives the hydrogen gas to flow within the chamber, effectively ensuring the etching effect and suppressing the carbonization reaction. Meanwhile, nitrogen is relatively stable. In a confined space with high temperature and high pressure, an increase in nitrogen content means a decrease in the relative content of hydrogen, which is less stable, thus improving the safety of the entire annealing apparatus. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a flowchart of the two-stage annealing process for silicon carbide in this invention;

[0026] Figure 2 This is a schematic diagram of the microstructure of the processed surface of a silicon carbide wafer, in which... Figure 2 a is a schematic diagram of the microstructure of a surface processed after typical annealing. Figure 2 b is a schematic diagram of the microstructure of the surface processed after annealing according to the present invention. Detailed Implementation

[0027] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0028] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0029] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0030] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "over," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure is flipped, an element described as "below other elements or features" or "below other elements or features" would subsequently be oriented as "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0031] like Figure 1 As shown, the present invention provides a two-stage annealing process for silicon carbide. Specifically, the two-stage annealing process includes the following steps:

[0032] S1: Place the cleaned and dried silicon carbide wafers on graphite paper laid flat inside the annealing furnace chamber;

[0033] Specifically, the silicon carbide wafers are cleaned and dried using an acidic liquid or a mixture of acidic liquids. The cleaned and dried silicon carbide wafers can be annealed individually or in multiples simultaneously. When multiple wafers are annealed simultaneously, they are laid flat on the graphite paper without overlapping to prevent the overlapping parts from sticking together when the silicon carbide wafers are subjected to high temperature and high pressure conditions. This would not only make them difficult to separate but also affect the surface structure of the silicon carbide wafers.

[0034] S2: Vacuum the annealing furnace chamber until the preset pressure value is reached;

[0035] Specifically, a vacuum pump is used to evacuate the annealing furnace chamber. Vacuuming is stopped and the next step can proceed when the pressure inside the annealing furnace chamber reaches 0.5-0.8 Pa. Preferably, vacuuming is stopped when the pressure inside the annealing furnace chamber reaches 0.7 Pa.

[0036] S3: Turn on the heating mode of the annealing furnace and simultaneously introduce nitrogen into its chamber. When the temperature reaches 1550-1600℃, stop introducing nitrogen and start introducing hydrogen into its chamber. Continue heating until the temperature reaches 2000℃, then stop heating and maintain the temperature for a period of time to anneal the silicon carbide wafer.

[0037] Specifically, the heating rate in the heating mode is 5-7℃ / s;

[0038] The process of introducing nitrogen into the chamber includes: introducing nitrogen into the chamber at a low flow rate of 0.01-0.1 L / min for 1-2 min, and then introducing nitrogen into the chamber at a high flow rate of 1-5 L / min until the target temperature is reached;

[0039] Introducing hydrogen into the chamber includes: introducing hydrogen into the chamber at a flow rate of 1-3 L / min;

[0040] In addition, the temperature control holding time is 8-15 hours, and during the temperature control holding time, the gas pressure in the annealing furnace chamber is maintained at 420-470T. Preferably, the temperature control holding time is 10 hours, and the gas pressure in the annealing furnace chamber is maintained at 450T.

[0041] When nitrogen is introduced, a small flow rate followed by a large flow rate can be used to avoid blowing up the silicon carbide on the graphite paper and to further prevent the silicon carbide sheets from overlapping. In addition, nitrogen has good stability and will not react chemically with silicon carbide under high temperature and high pressure, thus it will not damage its surface structure.

[0042] The introduced hydrogen gas can undergo an etching reaction with the silicon carbide surface under high temperature and pressure, thereby suppressing the escape of silicon atoms under high temperature conditions and preventing carbonization of the silicon carbide surface. Furthermore, because hydrogen is relatively light, it tends to float at the top of the chamber. The nitrogen gas introduced first can form a mixture with the hydrogen, driving the hydrogen flow within the chamber and more effectively ensuring the etching effect. At the same time, nitrogen is relatively stable; in a confined space under high temperature and pressure, an increased nitrogen content means a relatively decreased content of less stable hydrogen, improving the safety of the entire annealing apparatus.

[0043] S4: After annealing, open the furnace door of the annealing furnace that has been cooled and ventilated, and remove the silicon carbide wafers.

[0044] Specifically, the cooling and ventilation process for the annealing furnace includes: turning off the heating mode of the annealing furnace, extracting all the gas in its chamber and introducing air, and opening the furnace door when the air pressure in the chamber reaches atmospheric pressure.

[0045] Furthermore, the present invention also provides a silicon carbide wafer, which is processed by the silicon carbide two-stage annealing process shown above.

[0046] Specifically, Figure 2 A schematic diagram of the microstructure of the processed surface of a silicon carbide wafer is shown, in which... Figure 2 a is a schematic diagram of the microstructure of a surface processed after typical annealing. Figure 2 b is a schematic diagram of the microstructure of the surface processed after annealing according to the present invention.

[0047]

[0048] Data results show that the sheets processed by the annealing process of this invention have better flatness, and some indicators such as curvature and warping are significantly reduced. In addition, it was found that the pass rate of the sheets was also improved in production, and the probability of chipping and breaking was reduced. This is because the annealing process of this invention reduces the occurrence of carbonization reaction on the surface of the sheets, with less carbon residue. The overall hardness of the sheets is increased, and pitting will not occur due to partial carbonization defects in subsequent processing, thus improving the processing quality of the sheets.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A two-stage annealing process for silicon carbide, characterized in that, Includes the following steps: S1: Place the cleaned and dried silicon carbide wafers on graphite paper laid flat inside the annealing furnace chamber; multiple cleaned and dried silicon carbide wafers are laid flat on the graphite paper in a completely non-overlapping manner. S2: Vacuum the annealing furnace chamber until the preset pressure value is reached; S3: Turn on the heating mode of the annealing furnace and simultaneously introduce nitrogen into its chamber. When the temperature reaches 1550-1600℃, stop introducing nitrogen and start introducing hydrogen into its chamber. Continue heating until the temperature reaches 2000℃, then stop heating and maintain the temperature for a period of time to anneal the silicon carbide wafer. S4: After annealing, open the furnace door of the annealing furnace that has been cooled and ventilated, and remove the silicon carbide wafers.

2. The silicon carbide two-stage annealing process according to claim 1, characterized in that, In step S1, the silicon carbide wafer is washed with an acidic liquid or a mixture of acidic liquids and then dried.

3. The silicon carbide two-stage annealing process according to claim 1, characterized in that, In step S2, when the pressure inside the annealing furnace chamber is reduced to 0.5-0.8 Pa, the vacuuming can be stopped and the next step can be carried out.

4. The silicon carbide two-stage annealing process according to claim 1, characterized in that, In step S3, the heating rate in the heating mode is 5-7℃ / s.

5. The two-stage annealing process for silicon carbide according to claim 1, characterized in that, In step S3, introducing nitrogen into the chamber includes: introducing nitrogen into the chamber at a small flow rate of 0.01-0.1 L / min for 1-2 min, and then introducing nitrogen into the chamber at a large flow rate of 1-5 L / min until the target temperature is reached.

6. The two-stage annealing process for silicon carbide according to claim 1, characterized in that, In step S3, introducing hydrogen gas into the chamber includes introducing hydrogen gas into the chamber at a flow rate of 1-3 L / min.

7. The two-stage annealing process for silicon carbide according to claim 1, characterized in that, In step S3, the temperature control holding time is 8-15 hours, and during the temperature control holding time, the gas pressure in the annealing furnace chamber is maintained at 420-470T.

8. The two-stage annealing process for silicon carbide according to claim 1, characterized in that, In step S4, the cooling and ventilation process for the annealing furnace includes: turning off the heating mode of the annealing furnace, extracting all the gas in its chamber and introducing air, and opening the furnace door when the air pressure in the chamber reaches atmospheric pressure.

9. A silicon carbide wafer, characterized in that, It is processed using the silicon carbide two-stage annealing process described in any one of claims 1-8.

Images