Schottky diode, its manufacturing method, and chip

Abstract

The present application provides a Schottky diode, comprising: a substrate; an epitaxial layer formed on the substrate; a Schottky metal layer formed on the epitaxial layer, wherein the metal composition in the Schottky metal layer continuously changes in a direction perpendicular to the Schottky metal layer from the interface with the epitaxial layer; and an electrode layer, comprising: an electrode layer formed on the Schottky metal layer, and a back electrode. The Schottky diode of the present application has a Schottky metal layer with a continuous composition change, which can avoid interface defects and has higher diode stability.

Description

Technical Field

[0001] This application generally relates to the field of electronic components, and specifically relates to a Schottky diode, a preparation method thereof, and a chip. Background Art

[0002] Silicon carbide materials have characteristics such as a large bandgap width, a high breakdown electric field strength, a large saturation drift velocity, and good thermal conductivity. These excellent physical properties make it an ideal material for manufacturing high-power, high-frequency, high-temperature, and radiation-resistant devices. Currently, silicon carbide materials have been used to prepare various power devices, such as Schottky diodes, junction barrier diodes, and field effect transistors, etc., with good performance and can partially replace current silicon devices.

[0003] The content in the background art section is only the technology known to the applicant and does not represent the prior art in this field. Summary of the Invention

[0004] This application provides a Schottky diode with a Schottky metal layer having a continuous composition change, which can avoid interface defects and the diode has higher stability.

[0005] According to one aspect of this application, the Schottky diode includes: a substrate; an epitaxial layer formed on the substrate; a Schottky metal layer formed on the epitaxial layer, wherein the metal composition in the Schottky metal layer continuously changes in a direction perpendicular to the Schottky metal layer from the interface with the epitaxial layer; an electrode layer, including: an electrode layer formed on the Schottky metal layer, and a back electrode.

[0006] According to some embodiments of this application, the thickness of the substrate is 300 - 500 microns.

[0007] According to some embodiments of this application, the thickness of the epitaxial layer is 3 - 15 microns.

[0008] According to some embodiments of this application, the epitaxial layer includes n-type silicon carbide.

[0009] According to some embodiments of this application, the Schottky metal layer includes titanium nitride.

[0010] According to some embodiments of this application, the thickness of the Schottky metal layer is 200 - 300 nanometers.

[0011] According to some embodiments of this application, the metal composition increases in a direction perpendicular to the Schottky metal layer from the interface with the epitaxial layer.

[0012] According to some embodiments of this application, the Schottky diode further includes a passivation layer covering the exposed area of the Schottky metal layer.

[0013] According to some embodiments of the present application, the back electrode includes: an ohmic contact back electrode formed on the other surface of the substrate relative to the epitaxial layer.

[0014] According to another aspect of the present application, there is also provided a method for manufacturing a Schottky diode, including: preparing a substrate; forming an epitaxial layer on the substrate; forming a back electrode on the substrate; forming a Schottky metal layer with continuously varying metal composition on the epitaxial layer; and forming an electrode layer on the Schottky metal layer.

[0015] According to some embodiments of the present application, forming the epitaxial layer on the substrate includes: performing epitaxial growth on the substrate by CVD method.

[0016] According to some embodiments of the present application, forming the back electrode on the substrate includes: depositing metal nickel to form an ohmic contact back electrode.

[0017] According to some embodiments of the present application, forming the Schottky metal layer with continuously varying metal composition on the epitaxial layer includes: depositing a metal compound on the epitaxial layer by co-sputtering technology using a first target and a second target, and during the deposition process, adjusting the sputtering power of the first target and the second target to form the Schottky metal layer with continuously varying metal composition.

[0018] According to some embodiments of the present application, the first target includes a metal target and the second target includes an alloy target.

[0019] According to some embodiments of the present application, the method further includes: after forming the electrode layer on the Schottky metal layer, forming a passivation layer on the exposed portion of the Schottky metal layer.

[0020] According to yet another aspect of the present application, there is also provided a semiconductor chip including the Schottky diode as described above.

[0021] According to some embodiments of the present application, the Schottky diode provided by the present application has a Schottky metal layer with continuously varying metal composition, which can avoid defects between metal interfaces and improve the stability of the Schottky diode. And by using the method for manufacturing the Schottky diode provided by the present application, the process is simple, has good compatibility with semiconductor processes, and can achieve batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0023] Figure 1 is a schematic cross-sectional view of the Schottky diode according to an exemplary embodiment of the present application;

[0024] Figure 2 Partial cross-sectional TEM image of the Schottky diode according to an exemplary embodiment of the present application;

[0025] Figure 3 Partial interface observation image of the Schottky diode according to an exemplary embodiment of the present application;

[0026] Figure 4 Flowchart of the method for manufacturing the Schottky diode according to an exemplary embodiment of the present application;

[0027] Figures 5A - 5F Manufacturing process diagram of the Schottky diode according to an exemplary embodiment of the present application. Detailed Description of the Invention

[0028] The following, in conjunction with the accompanying drawings and embodiments, further elaborates on the specific implementation of the present application to better understand the solution of the present application and the advantages of its various aspects. However, the specific implementation and embodiments described below are for illustrative purposes only and are not intended to limit the present application.

[0029] The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of the embodiments of the present disclosure. However, those skilled in the art will realize that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or may be implemented in other ways, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0030] The flowchart shown in the accompanying drawings is only an illustrative example and does not necessarily include all the contents and operations / steps, nor is it necessary to be executed in the described order. For example, some operations / steps may be decomposed, while some operations / steps may be combined or partially combined, so the actual execution order may change according to the actual situation.

[0031] The terms "first", "second", "third", "fourth", etc. in the description and claims of the present application and the accompanying drawings are used to distinguish different objects and are not used to describe a specific order. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally further include steps or units not listed, or may optionally further include other steps or units inherent to these processes, methods, products, or devices.

[0032] References to "embodiments" in this specification mean that a particular feature, structure, or characteristic described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] A Schottky diode, also known as a Schottky barrier diode (abbreviated as SBD), is a low-power, ultra-high-speed semiconductor device. Its most significant feature is an extremely short reverse recovery time (which can be as short as a few nanoseconds), and the forward conduction voltage drop is only about 0.4V. It is mostly used as a high-frequency, low-voltage, high-current rectifier diode, freewheeling diode, protection diode, and is also used as a rectifier diode and small-signal detector diode in microwave communication and other circuits. It is relatively common in communication power supplies, frequency converters, etc.

[0034] There are a large number of conductive electrons inside a metal conductor. When a metal contacts a semiconductor (the distance between the two is only on the order of atomic size), the Fermi level of the metal is lower than that of the semiconductor. At the sub-energy level corresponding to the conduction band of the metal and the semiconductor, the electron density is less than that of the conduction band of the semiconductor. Therefore, after the two come into contact, electrons will diffuse from the semiconductor to the metal, causing the metal to carry a negative charge and the semiconductor to carry a positive charge. Since the metal is an ideal conductor, the negative charge is distributed only within a thin layer with an atomic size on the surface. For an N-type semiconductor, the donor impurity atoms that lose electrons become positive ions and are distributed within a relatively large thickness. The result of the diffusion movement of electrons from the semiconductor to the metal forms a space charge region, a built-in electric field, and a potential barrier, and the depletion layer is only on the N-type semiconductor side (the entire potential barrier region falls on the semiconductor side). The direction of the built-in electric field in the potential barrier region points from the N-type region to the metal. As the built-in field increases due to thermionic emission, the drift current in the opposite direction to the diffusion current increases, and finally reaches dynamic equilibrium, forming a contact potential barrier between the metal and the semiconductor, which is the Schottky barrier.

[0035] The internal circuit structure of a typical Schottky rectifier tube is based on an N-type semiconductor substrate. Since silicon carbide material has great advantages under high-power or ultra-high-power conditions, in the structural design, it is very important to minimize the defects of the device. For example, the defects of the single-crystal substrate, the defects of the epitaxial layer, and the interface transition between layers will greatly affect the performance of the device. If the performance is not good, it will cause failure. In the preparation process of silicon carbide Schottky diodes, in order to avoid the diffusion of metals and at the same time achieve good Schottky performance, a double-layer metal is generally used for the metal layer. However, at the interface of the double-layer metal, defects and composition mutations are likely to occur. When subjected to the impact of a large current, the defects may expand. After long-term accumulation, it may affect the stability of the device.

[0036] In view of this, the present application provides a Schottky diode with continuously varying composition and a preparation method thereof.

[0037] The following will describe the present application with reference to specific embodiments.

[0038] Figure 1 It is a schematic cross-sectional view of the Schottky diode according to an exemplary embodiment of the present application.

[0039] Referring to Figure 1 , according to an exemplary embodiment, the Schottky diode provided by the present application includes a substrate 101, an epitaxial layer 103, a Schottky metal layer 105, and an electrode layer. The electrode layer includes an electrode layer 107 formed on the Schottky metal layer and a back electrode layer 104. The metal composition in the Schottky metal layer 105 changes continuously along the vertical direction of the Schottky metal layer from the interface with the epitaxial layer and gradually transitions.

[0040] According to some embodiments, along the vertical direction of the Schottky metal layer from the epitaxial layer interface, the change trend of titanium element in titanium nitride is gradually increasing.

[0041] As Figure 1 shown, according to some embodiments, the substrate 101 includes a silicon carbide single-crystal substrate with a thickness of 300 - 500 microns and a size of 4 - 8 inches. In this embodiment, the substrate 101 is a 4H-SiC single-crystal substrate with a thickness of 300 microns and a size of 4 inches. The aluminum-silicon Schottky diode manufactured by the silicon planar process can not only save precious metals and greatly reduce costs, but also improve the consistency of parameters.

[0042] As Figure 1 shown, according to some embodiments, the epitaxial layer 103 is formed on the substrate 101 and includes n-type silicon carbide with a thickness of 3 - 15 microns and a size of 4 inches. In this embodiment, the silicon carbide epitaxial layer 103 is a 10-micron-thick n-type silicon carbide layer, as Figure 2 shown, the epitaxial layer 103 in the cross-sectional view of the Schottky diode.

[0043] It should be noted here that Figure 2 The partial cross-sectional TEM image of the Schottky diode shown, where the black part of the top layer is introduced during the preparation of the TEM sample and has nothing to do with the device structure.

[0044] As Figure 2 shown, the main function of the epitaxial layer 103 is to reduce the junction capacitance of the Schottky diode, increase the reverse breakdown voltage, and at the same time not make the series resistance too large.

[0045] Refer to Figure 1 , according to the exemplary embodiment, the Schottky metal layer 105 is formed on the epitaxial layer 103, and the metal composition in the Schottky metal layer 105 changes continuously along the vertical direction of the Schottky metal layer from the interface of the epitaxial layer 103. In some embodiments, the Schottky metal layer 105 includes titanium nitride, and the thickness range includes 100 - 300 nanometers, and the titanium content gradually increases along the vertical direction of the Schottky metal layer 105 from the interface of the epitaxial layer 103.

[0046] According to some embodiments, the range of the increase in the titanium content component in titanium nitride includes 0% - 75% (the component is in atomic ratio), preferably 25% - 75%, and more preferably 50% - 75%. In this embodiment, the thickness of the Schottky metal layer is 200 nanometers, and the change range of the titanium element in titanium nitride is 50% - 75%, as Figure 2 shown in the Schottky metal layer 105 in

[0047] Refer to Figure 1 , according to the exemplary embodiment, the Schottky diode includes an electrode layer 107 formed on the Schottky metal layer 105, and a back electrode 104.

[0048] In some embodiments, the metal of the electrode layer 107 includes Au, Ge, Ni, Ti, Cr or their alloys, the thickness range is 1 - 4 microns, and the area is 1.5 - 2 mm 2 . As Figure 2 shown, in this embodiment, the thickness of the electrode layer 107 is 4 microns.

[0049] As Figure 1 shown, according to the exemplary embodiment, the Schottky diode further includes a passivation layer 109 that covers the exposed area of the Schottky metal layer 105. In some embodiments, the passivation layer 109 includes SiO2, Al2O3, SiN x or SiO x N, etc.

[0050] As Figure 2As shown, in this embodiment, the passivation layer 109 is silicon dioxide, covering the edges of the electrode layer and the Schottky metal layer. The function of the passivation layer 109 is to eliminate the electric field in the edge region and improve the breakdown voltage of the diode.

[0051] In addition, according to some embodiments, a back electrode 104 is formed on the other surface of the Schottky diode substrate 101 of the present application relative to the epitaxial layer 103. In some embodiments, the back electrode includes an ohmic contact back electrode, formed on the other surface of the substrate opposite to the epitaxial layer. The back electrode material includes metal nickel, and the thickness range includes 1 - 3 microns.

[0052] According to some embodiments of the present application, as Figure 3 shown in the interface observation diagram, a Schottky metal layer with continuously varying metal composition replaces the layered metal layer in the prior art, thereby avoiding the interface defects between the layered metal layers and preventing problems such as defect expansion in electronic components during high - current operation due to factors such as composition mutation, and thus improving the stability of electronic devices.

[0053] Next, refer to Figure 4 and Figures 5A - 5F to describe the method for manufacturing a Schottky diode according to an exemplary embodiment of the present application.

[0054] In S401, prepare a substrate. According to an exemplary embodiment, such as Figure 5A the substrate 101 shown. In some embodiments, a semiconductor single - crystal substrate can be selected. For example, an n - type silicon carbide substrate, that is, a 4H - SiC single - crystal substrate. However, the present application is not limited thereto, and other suitable substrates can also be used.

[0055] According to some embodiments, the substrate 101 is successively immersed in acetone, ethanol, and deionized water for 10 minutes of ultrasonic cleaning each, taken out and then rinsed with deionized water, and finally dried with dry N2 gas for later use, and then transferred to S403.

[0056] In S403, refer to Figure 5B to form an epitaxial layer 103 on the substrate.

[0057] According to an exemplary embodiment, the substrate is epitaxially grown by CVD method. The gas is supplied to the substrate 101 in the range of C / Si ratio of 0.5 - 1.5 and reacts in the temperature range of 1500°C - 1800°C to deposit the epitaxial layer 103 as shown in Figure 5B .

[0058] In some other embodiments, after obtaining the epitaxial layer 103, a back electrode is formed on the other surface of the substrate 101, and the back electrode is deposited by ion sputtering technology. In this embodiment, the back electrode includes metal nickel with a thickness of 3 microns as an ohmic contact electrode. Then, enter step S405.

[0059] In S405, a back electrode 104 is formed on a substrate, as Figure 5C shown.

[0060] According to some embodiments, forming the back electrode 104 on the substrate includes depositing metallic nickel to form an ohmic contact back electrode. Subsequently, the process proceeds to step S407.

[0061] In S407, referring to Figure 5D , a Schottky metal layer 105 with continuously varying metal composition is formed on the epitaxial layer 103.

[0062] According to some embodiments, the Schottky metal layer 105 is deposited using a co-sputtering technique. During the deposition process, continuous variation of the metal composition is achieved by adjusting the sputtering power of the first target and the second target.

[0063] According to an exemplary embodiment, photoresist is spin-coated on the surface of the epitaxial layer 103, optically exposed through a designed Schottky metal layer mask pattern, and developed to form a first photoresist pattern as a deposition mask.

[0064] Using the first photoresist pattern as a deposition mask, a metal compound is deposited on the exposed area of the epitaxial layer 103 by a co-sputtering technique. During the deposition process, continuous variation of the metal composition can be achieved by adjusting the sputtering power of the first metal target and the second alloy target.

[0065] According to some embodiments, the first target includes a metal target and the second target includes an alloy target. For example, the first target is a titanium metal (titanium content 99.99%) target and the second target is a titanium nitride target.

[0066] In addition, during the deposition process, nitrogen gas can be introduced into the deposition chamber, and the first target, such as a titanium metal target, can be used alone in a nitrogen atmosphere, and a gradient change of titanium nitride can be achieved by adjusting the sputtering power of the first target and / or the nitrogen concentration.

[0067] According to an exemplary embodiment, during the process of achieving continuous variation of the metal content in the Schottky metal layer using a co-sputtering technique, it can be achieved by continuously adjusting the sputtering power of each target. For example, in this embodiment, the ratio of the sputtering frequencies of the first target and the second target is controlled to vary continuously within a certain range.

[0068] Then, the substrate with the Schottky metal layer having continuously varying composition is placed in an organic solvent, such as acetone solvent, to remove the photoresist, and a Schottky metal layer 105 with continuously varying metal composition as shown in Figure 5D is obtained, with a thickness of 300 nm.

[0069] In this embodiment, after obtaining the Schottky metal layer and removing the photoresist, the substrate is placed in a rapid annealing furnace for annealing, and then transferred to step S409.

[0070] In S409, an electrode layer 107 is formed on the Schottky metal layer 105, as Figure 5E shown.

[0071] According to an exemplary embodiment, using magnetron sputtering deposition technology, an electrode layer is formed on the Schottky metal obtained in S407. In some embodiments, photoresist is spin-coated on the surface of the Schottky metal layer 105, optically exposed through a designed electrode layer mask, and developed to form a second photoresist pattern as a mask.

[0072] Using the second photoresist pattern as a deposition mask, it is placed in a magnetron sputtering deposition chamber, and metal aluminum can be selectively deposited to form the electrode layer 107 as shown in Figure 5E the figure.

[0073] The substrate with the electrode layer 107 is placed in an organic solvent, for example, acetone solvent, to remove the photoresist. In this embodiment, the electrode layer 107 with a thickness of 4 microns is obtained.

[0074] According to some other embodiments, in S409, after the electrode layer is formed on the Schottky metal layer, a passivation layer 109 is formed on the exposed portion of the Schottky metal layer, as Figure 5F shown.

[0075] According to an exemplary embodiment, photoresist is spin-coated on the electrode layer, optically exposed with a designed mask, and developed to form a third photoresist pattern substrate.

[0076] The third photoresist pattern substrate is placed in a particle sputtering deposition chamber to form the passivation layer 109 as shown in Figure 5E the figure; the substrate with the passivation layer 109 is placed in an organic solvent, for example, acetone solvent, to remove the photoresist. In this embodiment, the passivation layer is a 1-micron-thick silicon dioxide layer 109.

[0077] The embodiments of the present application have been described and explained in detail above. It should be clearly understood that the present application describes how to form and use specific examples, but the present application is not limited to any details of these examples. On the contrary, based on the teachings of the content disclosed in the present application, these principles can be applied to many other embodiments.

[0078] Through the description of the exemplary embodiments, those skilled in the art can easily understand that the technical solutions according to the embodiments of the present application have at least one or more of the following advantages.

[0079] According to some embodiments, the method for preparing a Schottky diode provided by the present application has a simple process, the raw materials used are easily obtained, has good compatibility with semiconductor processes, and can achieve mass production.

[0080] Obviously, the above embodiments are only examples given for clearly explaining the present application, rather than limiting the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present application.

Claims

1. A Schottky diode, characterized in that, Comprising: A substrate; An epitaxial layer formed on the substrate; A Schottky metal layer formed on the epitaxial layer, wherein the metal composition in the Schottky metal layer continuously changes in the direction perpendicular to the Schottky metal layer from the interface with the epitaxial layer; An electrode layer, comprising: an electrode layer formed on the Schottky metal layer and a back electrode; The Schottky metal layer comprises titanium nitride; The thickness of the Schottky metal layer is 200 - 300 nanometers; The metal composition increases in the direction perpendicular to the Schottky metal layer from the interface with the epitaxial layer.

2. The Schottky diode according to claim 1, characterized in that, The epitaxial layer comprises: N-type silicon carbide with a thickness of 3 - 15 micrometers.

3. The Schottky diode according to claim 1, characterized in that, It further comprises a passivation layer covering the exposed area of the Schottky metal layer.

4. A method for preparing a Schottky diode, characterized in that, Comprising: Preparing a substrate; Forming an epitaxial layer on the substrate; Forming a back electrode on the substrate; Forming a Schottky metal layer with continuously changing metal composition on the epitaxial layer; Forming an electrode layer on the Schottky metal layer; The Schottky metal layer comprises titanium nitride; The thickness of the Schottky metal layer is 200 - 300 nanometers; The metal composition increases in the direction perpendicular to the Schottky metal layer from the interface with the epitaxial layer.

5. The method according to claim 4, wherein The forming of the Schottky metal layer with continuously changing metal composition on the epitaxial layer comprises: Depositing a metal compound on the epitaxial layer by co-sputtering technology using a first target and a second target. During the deposition process, by adjusting the sputtering power of the first target and the second target, the Schottky metal layer with continuously changing metal composition is formed; Wherein, the first target comprises a metal target and the second target comprises an alloy target.

6. The method according to claim 4, characterized in that, It further comprises: After forming the electrode layer on the Schottky metal layer, forming a passivation layer on the exposed part of the Schottky metal layer.

7. A semiconductor chip, characterized in that, Comprising the Schottky diode according to any one of claims 1 - 3.

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