Silicon carbide device and preparation method thereof

Abstract

The invention discloses a silicon carbide device and a preparation method thereof. According to the invention, diamond is used as a substrate, a silicon carbide substrate is bonded on the surface of the diamond, an epitaxial layer is grown on the basis, and a silicon carbide power device is manufactured on the epitaxial layer; after the wafer front face process step is completed, a groove extending to the position, close to the bonded silicon carbide substrate, inside the diamond substrate is formed in the diamond substrate part through the silicon through hole process technology, the groove is filled with copper or tungsten, redundant filling metal outside the groove is ground away, back face metal growth is carried out subsequently, and the back face process is completed. Diamond is used for replacing silicon carbide to serve as a supporting substrate, the heat conductivity of the device can be improved, and the heat dissipation efficiency of the device is improved; the silicon through hole technology is mature and simple, copper and tungsten filled in the groove serve as materials with low resistance and good heat conduction performance, heat can be effectively conducted out under the condition that normal operation of the device can be guaranteed, and the problem that the silicon carbide device is poor in short circuit endurance capacity is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a silicon carbide device and a preparation method thereof. Background Art

[0002] Silicon carbide (SiC) materials have begun to attract attention and research due to their superior physical properties. Compared with traditional Si devices, SiC devices have the characteristics of high voltage, fast frequency, and working voltage resistance. However, silicon carbide devices have the problem of poor short-circuit tolerance. At present, after the industry processes the wafer (Wafer) through the back thinning process, the thickness of the SiC substrate layer is still much higher than the thickness of the epitaxial layer (EPI). The epitaxial layer as the N drift region has a low concentration and high heat generation. Although SiC has a higher thermal conductivity than Si, the excessively high current density and thick substrate still make it impossible for the chip of the SiC device to dissipate heat quickly and effectively.

[0003] By comparing the short-circuit reliability of silicon carbide MOSFET and silicon IGBT at 1200V, the short-circuit tolerance of silicon carbide MOSFET is only about 3 microseconds (μs), which is far behind silicon IGBT devices (≥10 microseconds). Therefore, it is necessary to improve the heat dissipation efficiency of SiC devices while ensuring the normal operation of the devices to solve the problem of poor short-circuit tolerance of SiC devices. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a silicon carbide device and a preparation method thereof, which can effectively conduct heat while ensuring the normal operation of the device and solve the problem of poor short-circuit tolerance of SiC devices.

[0005] To solve the above problems, an embodiment of the present invention provides a method for preparing a silicon carbide device, the method comprising the following steps: providing a diamond substrate, the diamond substrate having a relative front side and a back side; providing a silicon carbide substrate, and bonding the front side of the diamond substrate to the silicon carbide substrate; forming an epitaxial layer on a side of the silicon carbide substrate away from the diamond substrate, and forming a device structure in the epitaxial layer; using silicon through via technology to form at least one groove extending into the diamond substrate on the back side of the diamond substrate; forming a metal heat dissipation structure in the groove; and forming a back metal layer covering the back side of the diamond substrate and all the metal heat dissipation structures.

[0006] In some embodiments, the silicon carbide substrate is an N-type 4H-SiC substrate, and the thickness of the N-type 4H-SiC substrate ranges from 1 micron to 2 microns.

[0007] In some embodiments, the groove does not expose the silicon carbide substrate.

[0008] In some embodiments, the depth of the groove is less than the thickness of the diamond substrate, and the depth of the groove is greater than half the thickness of the diamond substrate.

[0009] In some embodiments, the step of using through silicon via technology to form at least one groove on the back side of the diamond substrate extending into the diamond substrate specifically includes: forming a plurality of the grooves, the plurality of the grooves extending in a direction perpendicular to the back side of the diamond substrate and uniformly distributed in a direction parallel to the back side of the diamond substrate.

[0010] In some embodiments, the step of forming a metal heat dissipation structure in the groove specifically includes: depositing a first metal material to form a first metal material layer that fills the groove and covers the back side of the diamond substrate; removing the first metal material layer outside the groove, and the remaining first metal material layer in the groove forms the metal heat dissipation structure.

[0011] In some embodiments, the step of removing the first metal material layer outside the groove specifically includes: using a chemical mechanical polishing process to polish and remove the first metal material layer outside the groove.

[0012] In some embodiments, the step of forming a back metal layer covering the back side of the diamond substrate and all the metal heat dissipation structures specifically includes: performing a metal sputtering process to form a second metal material layer as the back metal layer.

[0013] In some embodiments, the material of the metal heat dissipation structure is metal copper or metal tungsten, and the material of the back metal layer is selected from titanium, nickel, silver or alloys thereof.

[0014] In order to solve the above problem, an embodiment of the present invention further provides a silicon carbide device, wherein the silicon carbide device is manufactured by the method for manufacturing the silicon carbide device described in the present invention.

[0015] The above technical scheme uses diamond as a substrate to bond a silicon carbide substrate on its surface, grows an epitaxial layer on this basis, and then makes a silicon carbide power device on the epitaxial layer, that is, bonding first and then making the device, to complete the wafer front process; after completing the wafer front process steps, the through silicon via process technology is used to open a groove extending to the inside of the diamond substrate close to the bonded silicon carbide substrate on the diamond substrate part of the back of the wafer, fill the groove with copper or tungsten, and grind off the excess filling metal outside the groove on the back of the wafer, and then grow the back metal to complete the back process. Using diamond to replace silicon carbide as a supporting substrate can improve the thermal conductivity of the device and improve the heat dissipation efficiency of the device; the through silicon via process is mature and simple, and the copper and tungsten filled in the groove are materials with low resistance and good thermal conductivity, which can effectively conduct heat and reduce the probability of wafer damage. It can effectively conduct heat while ensuring the normal operation of the device, solving the problem of poor short-circuit tolerance of silicon carbide devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 A schematic diagram of the steps of a method for preparing a silicon carbide device provided in one embodiment of the present invention;

[0018] Figure 2 A schematic diagram of a device structure of a diamond substrate provided in one embodiment of the present invention;

[0019] Figure 3 A schematic diagram of a device structure after bonding provided by an embodiment of the present invention;

[0020] Figure 4 A schematic diagram of a device structure after forming an epitaxial layer according to an embodiment of the present invention;

[0021] Figure 5 A schematic diagram of a device structure after a groove is formed according to an embodiment of the present invention;

[0022] Figure 6A to Figure 6B A schematic diagram of a device structure after a metal heat dissipation structure is formed according to an embodiment of the present invention;

[0023] Figure 7 A schematic diagram of a device structure after a back metal layer is formed according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0025] An embodiment of the present invention provides a method for preparing a silicon carbide device.

[0026] Please also read Figure 1 to Figure 7 ,in, Figure 1 A schematic diagram of the steps of a method for preparing a silicon carbide device provided in one embodiment of the present invention; Figure 2 A schematic diagram of a device structure of a diamond substrate provided in one embodiment of the present invention; Figure 3 A schematic diagram of a device structure after bonding provided by an embodiment of the present invention; Figure 4 A schematic diagram of a device structure after forming an epitaxial layer according to an embodiment of the present invention; Figure 5 A schematic diagram of a device structure after a groove is formed according to an embodiment of the present invention; Figure 6A to Figure 6B A schematic diagram of a device structure after a metal heat dissipation structure is formed according to an embodiment of the present invention; Figure 7 A schematic diagram of a device structure after a back metal layer is formed according to an embodiment of the present invention.

[0027] like Figure 1 As shown, the method for preparing the silicon carbide device described in this embodiment includes the following steps: S1, providing a diamond substrate, wherein the diamond substrate has a front side and a back side opposite to each other; S2, providing a silicon carbide substrate, and bonding the front side of the diamond substrate to the silicon carbide substrate; S3, forming an epitaxial layer on a side of the silicon carbide substrate away from the diamond substrate, and forming a device structure in the epitaxial layer;

[0028] S4, forming at least one groove extending into the diamond substrate on the back side of the diamond substrate using through silicon via technology; S5, forming a metal heat dissipation structure in the groove; and S6, forming a back metal layer covering the back side of the diamond substrate and all the metal heat dissipation structures.

[0029] Please refer to step S1 and Figure 2 , a diamond substrate 21 is provided, wherein the diamond substrate 21 has a front side 211 and a back side 210 opposite to each other.

[0030] In this embodiment, the diamond substrate 21 is used to support the SiC power device above it after bonding. Different types of diamond have different thermal conductivities at different temperatures; at 20°C, II aThe thermal conductivity of 4H-SiC is about 4.9W / (cm·K), while the thermal conductivity of diamond is 120W / (cm·K). Using diamond instead of SiC as a supporting substrate can improve the thermal conductivity of the device and improve the heat dissipation efficiency of the device.

[0031] Please refer to step S2 and Figure 3 , provide a silicon carbide substrate 31, and bond the front surface 211 of the diamond substrate 21 to the silicon carbide substrate 31. The bonding technology can refer to the prior art and will not be described here.

[0032] According to different resistivities, 4H-SiC substrates can be divided into conductive type and semi-insulating type. Conductive SiC substrates have low resistivity and are mainly used to manufacture power devices such as MOSFET and IGBT. According to different doping elements, conductive SiC substrates can be divided into N-type and P-type. In this embodiment, the silicon carbide substrate 31 is an N-type 4H-SiC substrate. Specifically, the thickness of the N-type 4H-SiC substrate ranges from 1 micron to 2 microns. The thickness of the N-type 4H-SiC substrate can be, for example: 1 micron, 1.2 microns, 1.3 microns, 1.4 microns, 1.5 microns, 1.6 microns, 1.7 microns, 1.8 microns, 1.9 microns, 2 microns, etc.

[0033] Please refer to step S3 and Figure 4 , an epitaxial layer 41 is formed on the side of the silicon carbide substrate 31 away from the diamond substrate 21, and device structures 491 and 492 are formed in the epitaxial layer 41. That is, in this embodiment, bonding is performed first and then device formation is performed, thereby completing the wafer front side process steps.

[0034] In this embodiment, the epitaxial layer 41 is a thin film layer having substantially the same crystal structure and electrical properties as the N-type 4H-SiC substrate, which is epitaxially grown (EPI) on an N-type 4H-SiC substrate. The device structures 491 and 492 formed in the epitaxial layer 41 can be corresponding SiC power devices. The epitaxial layer 41 can be grown by a chemical vapor deposition (CVD) method. CVD technology is mainly a method of generating a thin film by chemically reacting one or more gas phase compounds or single substances containing thin film elements on the surface of a substrate. Homogeneous epitaxial growth is performed on an N-type 4H-SiC substrate using CVD equipment, and the epitaxial layer has a high growth rate, improved thickness non-uniformity and doping concentration non-uniformity, and the surface of the grown epitaxial layer is smooth and the growth defect density is low, which has a good guiding role in the development of the current silicon carbide epitaxial industry and the domestic substitution of semiconductor equipment.

[0035] Please refer to step S4 and Figure 5, at least one groove 50 extending into the diamond substrate 21 is formed on the back side 210 of the diamond substrate 21 by using the through silicon via technology. That is, after completing the wafer front side process step, this embodiment forms a groove in the diamond substrate on the back side of the wafer by using the through silicon via (TSV) process technology. Specifically, the groove 50 extends to the position inside the diamond substrate 21 close to the silicon carbide substrate 31.

[0036] In some embodiments, after completing the wafer front process steps, the wafer can be flipped over to perform a through silicon via process on the diamond substrate 21. Through Silicon Via (TSV) technology is to make vertical openings between chips and wafers by etching or laser, and then fill the holes with conductive materials such as copper, tungsten, and polysilicon. Compared with the inductively coupled plasma etching (ICP) method that uses gas glow discharge to generate plasma and realizes the pattern transfer process from the photoresist mask to the chip surface through the dual effects of chemistry and physics, the through silicon via technology used in this embodiment is mature, simple, and low-cost.

[0037] In this embodiment, the groove 50 does not expose the silicon carbide substrate 31. That is, the groove 50 extends to a position inside the diamond substrate 21 close to the silicon carbide substrate 31, and the bottom of the groove 50 is located inside the diamond substrate 21 and does not expose the silicon carbide substrate 31, thereby avoiding affecting the silicon carbide substrate 31, the epitaxial layer 41, and the device structure in the epitaxial layer 41, and ensuring that the device can operate normally.

[0038] In some embodiments, the depth H2 of the groove 50 is less than the thickness H1 of the diamond substrate 21, so that the groove 50 does not expose the epitaxial layer 41. Further, the depth H2 of the groove 50 is greater than half of the thickness H1 of the diamond substrate 21. That is, H1>H2>H1 / 2. By deepening the groove depth as much as possible without exposing the silicon carbide substrate, the heat dissipation area of ​​the subsequently formed metal heat dissipation structure can be increased as much as possible, thereby effectively conducting heat, solving the problem of poor short-circuit tolerance of silicon carbide devices, and avoiding affecting the silicon carbide substrate 31, the epitaxial layer 41, and the device structure in the epitaxial layer 41, thereby ensuring that the device can operate normally.

[0039] In this embodiment, the step of forming at least one groove 50 extending into the diamond substrate 21 on the back side 210 of the diamond substrate 21 using the through silicon via technology specifically includes: forming a plurality of the grooves 50, the plurality of the grooves 50 extending in a direction perpendicular to the back side 210 of the diamond substrate 21 and uniformly distributed in a direction parallel to the back side 210 of the diamond substrate 21. Specifically, the density of the grooves 50 in the diamond substrate 21 is determined according to actual process requirements.

[0040] Please refer to step S5 and Figure 6B , a metal heat dissipation structure 61 is formed in the groove 50 .

[0041] In this embodiment, the step of forming the metal heat dissipation structure 61 in the groove 50 specifically includes: (1) depositing a first metal material to form a first metal material layer 610 that fills the groove 50 and covers the back side 210 of the diamond substrate 21, such as Fig. 6A (2) removing the first metal material layer 610 outside the groove 50, and the remaining first metal material layer 610 in the groove 50 forms the metal heat dissipation structure 61, as shown Figure 6B shown.

[0042] Continuing with the above embodiment, the step of removing the first metal material layer 610 outside the groove 50 specifically includes: using a chemical mechanical polishing process (CMP) to polish and remove the first metal material layer 610 outside the groove 50. By using the chemical mechanical polishing process, the exposed surface of the formed metal heat dissipation structure 61 can be made a smooth surface, and the exposed surface of the metal heat dissipation structure 61 is flush with the back side 210 of the diamond substrate 21, which is conducive to the subsequent formation of the back side metal layer.

[0043] In some embodiments, the thickness of the metal heat dissipation structure 61 is less than the thickness of the diamond substrate 21 , and the thickness of the metal heat dissipation structure 61 is greater than half of the thickness of the diamond substrate 21 .

[0044] In this embodiment, the material of the metal heat dissipation structure 61 is metal copper or metal tungsten. By filling the groove 50 on the back side 210 of the diamond substrate 21 with copper and tungsten materials with low resistance and good thermal conductivity, the heat dissipation of the diamond substrate 21 is enhanced, the heat can be effectively conducted out, the thermal resistance of the device is reduced, and thus the heat dissipation performance of the device is improved, and the probability of wafer damage is reduced.

[0045] Please refer to step S6 and Figure 7 , forming a back metal layer 71 covering the back side 210 of the diamond substrate 21 and all the metal heat dissipation structures 61 .

[0046] In this embodiment, the step of forming a back metal layer 71 covering the back side 210 of the diamond substrate 21 and all the metal heat dissipation structures 61 specifically includes: performing a metal sputtering process to form a second metal material layer as the back metal layer 71, and flipping the wafer again after the process is completed.

[0047] In some embodiments, the material of the back metal layer 71 is selected from titanium, nickel, silver or alloys thereof. Specifically, magnetron sputtering technology can be used to sputter and deposit metal Ti / Ni / Ag on the back side 210 of the diamond substrate 21 to form the back metal layer 71 .

[0048] Based on the same inventive concept, an embodiment of the present invention provides a silicon carbide device, which is prepared by adopting the above-mentioned method for preparing the silicon carbide device of the present invention.

[0049] Please also read Figure 1 to Figure 7 The silicon carbide device described in this embodiment includes: a diamond substrate 21, a silicon carbide substrate 31 bonded to the diamond substrate 21, an epitaxial layer 41, device structures 491 and 492 formed in the epitaxial layer 41, at least one groove 50 formed on the back side of the diamond substrate 21, a metal heat dissipation structure 61 filled in the groove 50, and a back metal layer 71 formed on the back side of the diamond substrate 21.

[0050] Specifically, the diamond substrate 21 has a front side 211 and a back side 210 opposite to each other, the silicon carbide substrate 31 is bonded to the front side 211 of the diamond substrate 21, the epitaxial layer 41 is formed on a side of the silicon carbide substrate 31 away from the diamond substrate 21, and device structures 491 and 492 are formed in the epitaxial layer 41. That is, in this embodiment, bonding is performed first and then devices are made, thereby completing the wafer front side process steps.

[0051] Specifically, the groove 50 is formed by through silicon via technology and extends from the back side 210 of the diamond substrate 21 to the inside of the diamond substrate 21. The exposed surface of the metal heat dissipation structure 61 is a smooth surface, and the exposed surface of the metal heat dissipation structure 61 is flush with the back side 210 of the diamond substrate 21. The back metal layer 71 covers the back side 210 of the diamond substrate 21 and all the metal heat dissipation structures 61.

[0052] In this embodiment, the silicon carbide substrate 31 is an N-type 4H-SiC substrate. Specifically, the thickness of the N-type 4H-SiC substrate ranges from 1 micron to 2 microns. The thickness of the N-type 4H-SiC substrate can be, for example, 1 micron, 1.2 microns, 1.3 microns, 1.4 microns, 1.5 microns, 1.6 microns, 1.7 microns, 1.8 microns, 1.9 microns, 2 microns, etc. The epitaxial layer 41 is a thin film layer epitaxially grown on an N-type 4H-SiC substrate and having substantially the same crystal structure and electrical properties as the N-type 4H-SiC substrate. The device structures 491 and 492 formed in the epitaxial layer 41 can be corresponding SiC power devices.

[0053] In some embodiments, the thickness of the metal heat dissipation structure 61 is less than the thickness of the diamond substrate 21, so that the metal heat dissipation structure 61 does not contact the epitaxial layer 41. Further, the thickness of the metal heat dissipation structure 61 is greater than half the thickness of the diamond substrate 21. By deepening the groove depth as much as possible without exposing the epitaxial layer, the heat dissipation area of ​​the formed metal heat dissipation structure can be increased as much as possible, so as to effectively conduct heat, solve the problem of poor short-circuit tolerance of silicon carbide devices, and avoid affecting the silicon carbide substrate 31, the epitaxial layer 41 and the device structure in the epitaxial layer 41, so as to ensure the normal operation of the device.

[0054] The above embodiments use diamond as a substrate to bond a silicon carbide substrate on its surface, grow an epitaxial layer on this basis, and then make a silicon carbide power device on the epitaxial layer, that is, bonding first and then making the device, to complete the wafer front process; after completing the wafer front process steps, a groove extending to the inside of the diamond substrate close to the bonded silicon carbide substrate is opened on the diamond substrate part of the back of the wafer using the silicon through hole process technology, and copper or tungsten is filled in the groove, and the excess filling metal outside the groove on the back of the wafer is removed, and then the back metal is grown to complete the back process. Using diamond to replace silicon carbide as a supporting substrate can improve the thermal conductivity of the device and improve the heat dissipation efficiency of the device; the silicon through hole process is mature and simple, and the copper and tungsten filled in the groove are materials with low resistance and good thermal conductivity, which can effectively conduct heat and reduce the probability of wafer damage. It can effectively conduct heat while ensuring that the device can operate normally, solving the problem of poor short-circuit tolerance of silicon carbide devices.

[0055] It should be noted that the terms "including" and "having" and their variations involved in the document of the present invention are intended to cover non-exclusive inclusions. The terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence, unless the context clearly indicates, and it should be understood that the data used in this way can be interchanged under appropriate circumstances. The term "one or more" depends at least in part on the context, and can be used to describe features, structures or characteristics in a singular sense, or can be used to describe features, structures or combinations of features in a plural sense. The term "based on" can be understood as not necessarily intended to express a set of exclusive factors, but can alternatively, also at least in part depending on the context, allow the presence of other factors that are not necessarily explicitly described. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. In addition, in the above description, the description of well-known components and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. In the above embodiments, each embodiment focuses on the differences from other embodiments, and the same / similar parts between the embodiments can be referred to each other.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a silicon carbide device, characterized in that: The method comprises the following steps: Providing a diamond substrate, the diamond substrate having a front side and a back side opposite to each other; Providing a silicon carbide substrate, and bonding the front side of the diamond substrate to the silicon carbide substrate; forming an epitaxial layer on a side of the silicon carbide substrate away from the diamond substrate, and forming a device structure in the epitaxial layer; At least one groove extending into the diamond substrate is formed on the back side of the diamond substrate by using through silicon via technology; forming a metal heat dissipation structure in the groove; as well as A back metal layer is formed to cover the back side of the diamond substrate and all the metal heat dissipation structures.

2. The method according to claim 1, characterized in that The silicon carbide substrate is an N-type 4H-SiC substrate, and the thickness of the N-type 4H-SiC substrate ranges from 1 micron to 2 microns.

3. The method according to claim 1, characterized in that The groove does not expose the silicon carbide substrate.

4. The method according to claim 1, characterized in that The depth of the groove is smaller than the thickness of the diamond substrate, and the depth of the groove is greater than half of the thickness of the diamond substrate.

5. The method according to claim 1, characterized in that The step of forming at least one groove extending into the diamond substrate on the back side of the diamond substrate by using the through silicon via technology specifically includes: A plurality of the grooves are formed, and the plurality of the grooves extend in a direction perpendicular to the back surface of the diamond substrate and are evenly distributed in a direction parallel to the back surface of the diamond substrate.

6. The method according to claim 1, characterized in that The step of forming a metal heat dissipation structure in the groove specifically includes: Depositing a first metal material to form a first metal material layer that fills the groove and covers the back side of the diamond substrate; The first metal material layer outside the groove is removed, and the remaining first metal material layer in the groove forms the metal heat dissipation structure.

7. The method according to claim 6, characterized in that The step of removing the first metal material layer outside the groove specifically includes: The first metal material layer outside the groove is removed by a chemical mechanical polishing process.

8. The method according to claim 1, characterized in that The step of forming a back metal layer covering the back side of the diamond substrate and all the metal heat dissipation structures specifically includes: A metal sputtering process is performed to form a second metal material layer as the back metal layer.

9. The method according to claim 1, characterized in that: The material of the metal heat dissipation structure is metal copper or metal tungsten, and the material of the back metal layer is selected from titanium, nickel, silver or alloys thereof.

10. A silicon carbide device, characterized in that: The silicon carbide device is prepared by the method for preparing a silicon carbide device according to any one of claims 1 to 9.

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