SiC device ohmic contact preparation method and SiC device

Abstract

The invention provides a SiC device ohmic contact preparation method and a SiC device, and the preparation method comprises the following steps: providing an n-type SiC substrate, and depositing a Ni film layer on the surface, forming ohmic contact, of the n-type SiC substrate; annealing the Ni film layer by using laser pulse to form a NiSi film layer; removing the NiSi film layer by adopting a wet etching process; and depositing a conductive metal layer. Compared with the prior art, the preparation method of the SiC device ohmic contact has the advantages that the Ni film layer is deposited firstly, then the laser pulse annealing process is performed, so that the density of carbon vacancies in the SiC substrate is greatly increased, and the downward bending amplitude of an energy band of the SiC of a contact interface is increased, so that the width of a conductive metal layer and a SiC barrier is greatly reduced; according to the method, the electron tunneling probability is greatly increased, the ohmic contact resistivity is reduced, meanwhile, the adhesion of the conductive metal layer on the back face is improved by removing the NiSi film layer, and the reliability of ohmic contact on the back face of the n-type SiC power device is improved.

Description

Technical Field

[0001] The present invention relates to the technical field related to semiconductor device preparation, and in particular to a method for preparing an ohmic contact of a SiC device and a SiC device. Background Art

[0002] Compared with silicon, silicon carbide (SiC) has a wider bandgap, higher thermal conductivity, higher breakdown voltage, higher carrier saturation drift velocity, and extremely low intrinsic carriers under isothermal conditions, making it suitable for working under higher voltage, high current and high temperature conditions. With all its excellent properties, silicon carbide wafers have great value and great potential in various fields.

[0003] In order to increase the drain-source voltage and reduce the on-state resistance of SiC power devices, the design of power devices generally adopts a vertical structure, making the gate-source cell structure on the surface of the wafer, and depositing metal on the back of the wafer to form the drain. The back metal and semiconductor contact are required to form an ohmic contact to reduce the on-resistance and have good adhesion to ensure the reliability of the package.

[0004] In order to ensure that the front process of the silicon carbide wafer is not affected, the current ohmic contact on the back of the n-type SiC power device wafer is usually made by first using magnetron sputtering to deposit a Ni metal film on the back of the wafer, and then using laser pulses for rapid thermal annealing to form a NiSi alloy, of which the NiSi alloy is considered to be the key to forming an ohmic contact. Although the ohmic contact resistivity formed by the above method can reach 10 -6 Ω·cm 2 However, the proportion of carbon in the NiSi alloy will increase with the increase of laser energy. To a certain extent, a carbon layer will be formed in the NiSi. This carbon layer cannot be completely removed by surface treatment process. The presence of the carbon layer in the NiSi alloy will reduce the adhesion of the back metal and affect the reliability of the back metal. If the laser energy is reduced, although the formation of the carbon layer in the NiSi alloy can be avoided, the ohmic contact resistivity will be greatly increased, and even no ohmic contact will be formed. In summary, the laser annealing energy needs to be kept sufficient and stable to ensure the reliability of the ohmic contact of the back metal of the SiC power device.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those skilled in the art. Summary of the invention

[0006] In view of the problems in the prior art, the purpose of the present invention is to provide a method for preparing an ohmic contact of a SiC device and a SiC device. The preparation method greatly increases the density of carbon vacancies in the SiC substrate, reduces the width of the conductive metal layer and the SiC barrier, reduces the resistivity of the ohmic contact, and improves the adhesion of the back conductive metal layer, thereby improving the reliability of the back ohmic contact of the n-type SiC power device.

[0007] A first aspect of the present invention provides a method for preparing an ohmic contact of a SiC device, the method comprising the following steps:

[0008] Providing an n-type SiC substrate, and depositing a Ni film layer on a surface of the n-type SiC substrate forming an ohmic contact;

[0009] Annealing the Ni film layer using laser pulses to form a NiSi film layer;

[0010] The NiSi film layer is removed by wet etching process;

[0011] A conductive metal layer is deposited.

[0012] According to the first aspect of the present invention, the energy density of the laser pulse is 3.0-7.0 J / cm 2 .

[0013] According to the first aspect of the present invention, the pulse width of the laser pulse is 20-120ns.

[0014] According to the first aspect of the present invention, the Ni film layer is deposited by a sputtering deposition process; and or the conductive metal layer is deposited by a sputtering deposition process.

[0015] According to the first aspect of the present invention, the thickness of the Ni film layer is 80-100 nm.

[0016] According to the first aspect of the present invention, the conductive metal layer is a TiNiAg film layer.

[0017] According to a first aspect of the present invention, the step of depositing a conductive metal layer comprises:

[0018] Depositing a Ti layer, a Ni layer and an Ag layer respectively;

[0019] The Ti layer, the Ni layer, and the Ag layer are heat-treated.

[0020] According to the first aspect of the present invention, the thickness of the Ti layer, the thickness of the Ni layer, and the thickness of the Ag layer are 100±20 nm, 400±50 nm, and 1000±100 nm, respectively.

[0021] According to the first aspect of the present invention, the doping concentration of the n-type SiC substrate is greater than or equal to 1×1019 cm -3 .

[0022] A second aspect of the present invention provides a SiC device, comprising an n-type SiC substrate, wherein one surface of the SiC substrate is provided with an ohmic contact obtained by using the method for preparing the ohmic contact of the SiC device.

[0023] Compared with the prior art, the preparation method of the SiC device ohmic contact of the present invention greatly increases the density of carbon vacancies in the SiC substrate by first depositing a Ni film layer and then performing a laser pulse annealing process, and increases the downward bending amplitude of the energy band of the SiC at the contact interface, thereby greatly reducing the width of the conductive metal layer and the SiC barrier, greatly increasing the probability of electron tunneling, and reducing the ohmic contact resistivity. At the same time, by removing the NiSi film layer, the adhesion of the back conductive metal layer is improved, thereby improving the reliability of the back ohmic contact of the n-type SiC power device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present application, and together with the specification, are used to explain the principles of the present application. By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more apparent. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings without creative work. In addition, the drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same figure numbers in the figures represent the same or similar parts, and their repeated descriptions will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0025] Figure 1 A flow chart of a method for preparing an ohmic contact of a SiC device according to an embodiment of the present invention;

[0026] Figures 2 to 5 It is a schematic structural diagram corresponding to each step of a method for preparing an ohmic contact of a SiC device according to an embodiment of the present invention;

[0027] Figure 6 Elemental distribution map of ohmic contacts obtained for existing processes; and

[0028] Figure 7 This is an element distribution diagram of an ohmic contact obtained by a method for preparing an ohmic contact for a SiC device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in the present invention. The present invention can also be implemented or applied through other different specific embodiments, and the details in the present invention can also be modified or changed according to different viewpoints and application systems without departing from the spirit of the present invention. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0030] The following is a detailed description of the embodiments of the present invention with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. The present invention can be embodied in many different forms and is not limited to the embodiments described herein.

[0031] In the representation of the present invention, the reference terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics represented in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials or characteristics represented may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples represented in the present invention and the features of different embodiments or examples, unless they are contradictory.

[0032] In order to clearly describe the present invention, components not related to the description are omitted, and the same reference numerals are given to the same or similar components throughout the specification.

[0033] Throughout the specification, when a device is said to be "connected" to another device, this includes not only the case of "direct connection" but also the case of "indirect connection" by placing other elements therebetween. In addition, when a device is said to "include" a certain component, unless otherwise stated, it does not exclude other components, but means that other components may be included.

[0034] When a device is said to be "on" another device, it may be directly on the other device, but there may also be other devices between it. In contrast, when a device is said to be "directly" on another device, there are no other devices between it.

[0035] Although the terms first, second, etc. are used to represent various elements in some examples, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, the first interface and the second interface, etc. are represented. Moreover, as used in this article, the singular forms "one", "one" and "the" are intended to also include plural forms, unless there is an opposite indication in the context. It should be further understood that the terms "comprising" and "including" indicate the existence of features, steps, operations, elements, components, projects, kinds, and / or groups, but do not exclude the existence, occurrence or addition of one or more other features, steps, operations, elements, components, projects, kinds, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean any one or any combination. Therefore, "A, B or C" or "A, B and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B and C". Only when the combination of elements, functions, steps or operations is inherently mutually exclusive in some way, will there be an exception to this definition.

[0036] The technical terms used herein are only used to refer to specific embodiments and are not intended to limit the present invention. The singular form used herein also includes the plural form as long as the sentence does not clearly indicate the opposite meaning. The meaning of "including" used in the specification is to specify specific characteristics, regions, integers, steps, operations, elements and / or components, and does not exclude the existence or addition of other characteristics, regions, integers, steps, operations, elements and / or components.

[0037] Although not defined differently, all terms, including technical and scientific terms used herein, have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with the content of relevant technical literature and current disclosures, and unless defined, shall not be overly interpreted as ideal or very formal meanings.

[0038] In order to overcome the above technical problems, the present invention provides a method for preparing an ohmic contact of a SiC device and a SiC device, the preparation method comprising the following steps: providing an n-type SiC substrate, depositing a Ni film layer on the surface of the n-type SiC substrate on which an ohmic contact is formed; annealing the Ni film layer using laser pulses to form a NiSi film layer; removing the NiSi film layer using a wet etching process; and depositing a conductive metal layer.

[0039] Compared with the prior art, the method for preparing the ohmic contact of the SiC device of the present invention significantly increases the density of carbon vacancies in the SiC substrate by first depositing a Ni film layer and then performing a laser pulse annealing process, and increases the downward bending amplitude of the energy band of the SiC at the contact interface, thereby significantly reducing the width of the conductive metal layer and the SiC barrier, significantly increasing the probability of electron tunneling, and reducing the ohmic contact resistivity. At the same time, by removing the NiSi film layer, the adhesion of the back conductive metal layer is improved, thereby improving the reliability of the back ohmic contact of the n-type SiC power device.

[0040] The following further describes the method for preparing the ohmic contact of the SiC device and the SiC device of the present invention in conjunction with the accompanying drawings and specific embodiments. It can be understood that the various specific embodiments are not intended to limit the protection scope of the present invention.

[0041] Figure 1 The present invention is a flowchart of a method for preparing an ohmic contact of a SiC device according to an embodiment of the present invention. Specifically, the preparation method comprises the following steps:

[0042] Step S100: providing an n-type SiC substrate 10, and depositing a Ni film layer 20 on the surface of the n-type SiC substrate 10 where an ohmic contact is formed. Figure 2 .

[0043] Silicon carbide is a material with a variety of crystal structures. The differences between polymorphs affect the electrical, thermal and mechanical properties of the material. The crystal form of SiC can be determined according to the type of device. Here, the n-type SiC substrate can be a 6H-SiC, 4H-SiC substrate, etc. For SiC materials, N-type impurity doping ions include nitrogen ions (N + ), phosphorus ion (P + ), arsenic ions (As + ) and antimony ions (Sb + ) etc. The conductivity of the SiC substrate itself can be controlled by controlling the concentration of doped ions. Generally, in order to form an ohmic contact, the SiC substrate forming the ohmic contact needs to be heavily doped. Preferably, the doping concentration of the n-type SiC substrate 10 is greater than or equal to 1×10 19 cm -3 .

[0044] In step S100, the Ni film layer 20 can be deposited by a sputtering deposition process; the sputtering deposition process refers to bombarding the target surface with charged energy particles in a vacuum chamber, knocking out atoms and other particles in the target through particle momentum transfer, and causing them to precipitate on the substrate to form a thin film. The sputtering deposition process has the advantages of being able to achieve large-area rapid deposition, good bonding between the deposited film layer and the substrate, controllable film layer thickness, and high film layer density. In this application, the thickness of the Ni film layer can be accurately controlled by the sputtering deposition process. The thickness of the Ni film layer directly affects the thickness of the NiSi film layer formed during the subsequent laser pulse annealing process, and accordingly, affects the density of C vacancies in the SiC substrate. Preferably, the thickness of the Ni film layer is between 80-120nm, such as 80nm, 90nm, 100nm, 105nm or 120nm.

[0045] After the Ni film layer 2 is deposited on the surface of the n-type SiC substrate 10, step S200 is performed: the Ni film layer 20 is annealed by laser pulses to form a NiSi film layer 20. Figure 3 .

[0046] The laser pulse annealing process mainly uses a high-energy-density laser beam to irradiate the surface of the annealing material, thereby causing the temperature of the irradiated area to suddenly rise, achieving the annealing effect. The advantage of laser pulse annealing is that it can selectively anneal the substrate locally. In this application, the area where the ohmic contact needs to be formed can be selected as the annealing area, and because the heating time of the annealing area is very short, the impurities in other non-radiation areas are almost not diffused, so that the electrical parameters in other areas of the SiC substrate are basically unaffected. At the same time, the temperature of the radiated surface can be controlled by selecting parameters such as the energy density and pulse width of the laser pulse.

[0047] Ni silicide is formed during the annealing process of the Ni film and the SiC substrate, and different annealing temperatures result in different compositions of the obtained Ni silicide. The chemical reaction formula is as follows:

[0048]

[0049] Preferably, the purpose of S200 of the present invention is to increase the concentration of C vacancies. As can be seen from the above formula, the laser pulse annealing temperature of this step is preferably greater than 1000°C, such as the annealing temperature can be between 1000°C and 1350°C. Accordingly, the energy density of the laser pulse is between 3.0-7.0 J / cm 2 The pulse width of the laser pulse is 20-120 ns. In an embodiment, the energy density of the laser pulse is 3.0 J / cm 2 , 4.0J / cm 2 , 5.0J / cm 2 、6.0J / cm 2, 7.0J / cm 2 wait.

[0050] Then, step S300 is performed: the NiSi film layer is removed by a wet etching process. In this step, the SiC substrate of step S200 can be first cleaned by an RCA cleaning process, and then the NiSi film layer on the surface of the SiC substrate can be removed by using a SPIN-E solution (HF / HNO3 / H2SO4 / H2O2 mixed solution). It should be noted that while the NiSi film layer is removed in step S300, the carbon layer in the NiSi film layer is also removed. Unlike the SiC substrate 10 of step S100, the SiC substrate 10' ( Figure 4 )'s surface C vacancies concentration is increased by steps S200 and S300.

[0051] In some embodiments, after removing the NiSi film layer on the surface of the SiC substrate, the Asher treatment is used to further clean the surface of the SiC substrate. The Asher treatment can further remove the carbon remaining on the surface of the SiC substrate after wet etching the NiSi film layer, further improving the cleanliness of the surface of the SiC substrate, thereby effectively improving the adhesion between the substrate and the conductive metal layer, thereby improving the ohmic contact reliability.

[0052] Step S400: depositing a conductive metal layer 30, see Figure 5 The conductive metal layer 30 may be deposited by a sputtering deposition process. The conductive metal layer 30 may be made of a material selected from, but not limited to, Al, Al / Cu, Al / Si / Cu, Ti, TiNi, TiNiAg, TiNiAu, CrNiAg, CrNiAu, or a combination of Al, Al / Cu, Al / Si / Cu and the above metals.

[0053] In one embodiment, the conductive metal layer 30 is a TiNiAg film layer. In this case, the step of depositing the conductive metal layer in step S400 includes:

[0054] Step S410: depositing a Ti layer, a Ni layer and an Ag layer respectively; the thickness of the Ti layer, the thickness of the Ni layer and the thickness of the Ag layer are 100±20nm, 400±50nm and 1000±100nm respectively, such as the thickness of the TiNiAg film layer is 100 / 400 / 1000nm. And

[0055] Step S420: heat-treating the Ti layer, the Ni layer and the Ag layer. The temperature of the heat-treating may be between 700° C. and 1000° C., and the time may be between 0.5 min and 10 min.

[0056] Figure 6 and Figure 7The element distribution diagrams of the ohmic contact obtained by the existing process and the ohmic contact obtained by the method for preparing the ohmic contact of the SiC device according to one embodiment of the present invention are respectively shown. The element distribution diagram is obtained by TEM mapping, that is, scanning each point in a transmission electron microscope, and then drawing the energy spectrum diagram obtained at each point according to specific element peaks. It can be seen that the ohmic contact obtained by the existing process has an obvious carbon layer near the surface of the NiSi alloy layer. The presence of the carbon layer will reduce the adhesion between the TiNiAg metal and the NiSi alloy, and it is very easy to cause the back metal electrode to fall off during device packaging. However, no carbon layer is found in the element distribution diagram of the ohmic contact obtained by the method for preparing the ohmic contact of the SiC device according to the present invention. It can be seen that the preparation method of the present invention eliminates the carbon layer in the original process, thereby ensuring the adhesion of the back metal electrode, thereby improving the reliability of the ohmic contact of the back metal electrode of the SiC device.

[0057] The present invention also provides a SiC device, which can have a metal oxide field effect transistor (MOSFET) structure and a bipolar transistor (BJT) structure. Specifically, the SiC device includes at least an n-type SiC substrate, one side surface of the SiC substrate is prepared with a plurality of device structures, and the other side surface is prepared with an ohmic contact, and the ohmic contact is obtained by the preparation method of the ohmic contact of the SiC device. Since the density of carbon vacancies in the n-type SiC substrate is greatly increased, the downward bending amplitude of the SiC energy band at the contact interface is increased, and the width of the back metal and SiC barrier is greatly reduced, thereby greatly increasing the probability of electron tunneling and reducing the ohmic contact resistivity. At the same time, since the NiSi film layer and the carbon layer in the film layer are removed from the ohmic contact in the present invention, the problem of reduced adhesion of the back metal electrode caused by the presence of the carbon layer is avoided, and the reliability of the n-type SiC device is greatly improved.

[0058] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

[0059] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for preparing an ohmic contact of a SiC device, characterized in that: The preparation method comprises the following steps: Providing an n-type SiC substrate, and depositing a Ni film layer on a surface of the n-type SiC substrate forming an ohmic contact; Annealing the Ni film layer using laser pulses to form a NiSi film layer; The NiSi film layer is removed by wet etching process; A conductive metal layer is deposited.

2. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: The energy density of the laser pulse is 3.0-7.0 J / cm 2 .

3. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: The pulse width of the laser pulse is 20-100ns.

4. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: Depositing the Ni film layer using a sputtering deposition process; and / or The conductive metal layer is deposited by a sputtering deposition process.

5. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: The thickness of the Ni film layer is 80-120 nm.

6. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: The conductive metal layer is a TiNiAg film layer.

7. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: The step of depositing a conductive metal layer comprises: Depositing a Ti layer, a Ni layer and an Ag layer respectively; The Ti layer, the Ni layer, and the Ag layer are heat-treated.

8. The method for preparing an ohmic contact of a SiC device according to claim 6, characterized in that: The thickness of the Ti layer, the thickness of the Ni layer, and the thickness of the Ag layer are 100±20 nm, 400±50 nm, and 1000±100 nm, respectively.

9. The method for preparing an ohmic contact of a SiC device according to claim 1, characterized in that: The doping concentration of the n-type SiC substrate is greater than or equal to 1×10 19 cm -3 .

10. A SiC device, characterized in that: The SiC device comprises an n-type SiC substrate, and an ohmic contact obtained by the method for preparing an ohmic contact of a SiC device according to any one of claims 1 to 9 is provided on one surface of the SiC substrate.

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