CN107104046B - Preparation method of gallium nitride Schottky diode - Google Patents

Abstract

The present invention provides a method for preparing a gallium nitride Schottky diode, which comprises depositing a passivation layer on the surface of a gallium nitride epitaxial wafer; preparing a cathode of a gallium nitride Schottky diode; dry etching to form a Schottky contact hole; in the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; photolithography is performed on the ohmic metal layer, Etching and annealing are performed to form an ohmic metal structure with a grid structure; an anode of a gallium nitride Schottky diode is prepared; wherein, the ohmic metal structure is a grid structure and is wrapped by the anode. Therefore, the Schottky junction area can be reduced without affecting the output performance of the gallium nitride Schottky diode, thereby reducing the Schottky contact resistance, and improving the device performance and life of the gallium nitride Schottky diode.

Description

Preparation method of gallium nitride Schottky diode

technical field

The invention relates to the technical field of semiconductors, in particular to a method for preparing a gallium nitride Schottky diode.

Background technique

A Schottky diode is a semiconductor device made with metal contacting a semiconductor layer. Compared with semiconductor diodes in the traditional sense, it has the characteristics of extremely short reverse recovery time. Therefore, Schottky diodes are widely used in switching power supplies, frequency converters, drivers and other circuits. Gallium nitride material is the third-generation wide bandgap semiconductor material. Because of its large band gap, high electron saturation rate, high breakdown electric field, high thermal conductivity, corrosion resistance and radiation resistance, it has become a popular choice for the preparation of short-wave optoelectronics. The best material for devices and high-voltage high-frequency high-power devices. In conclusion, the Schottky diode made of gallium nitride material combines the advantages of the above-mentioned strip trick diode and gallium nitride material, has the characteristics of high frequency and low loss, and has good application prospects in switching power systems.

In the preparation of the existing gallium nitride Schottky diode, the anode metal contacts the gallium nitride material to form a Schottky contact, and the cathode metal contacts the gallium nitride material to form an ohmic contact. However, due to the difference in the metal materials and preparation processes of the anode metal and cathode metal used for preparation, the Schottky contact resistance will be much greater than the ohmic contact resistance, which leads to the use of gallium nitride Schottky diodes. The Schottky contact resistance produces a large amount of energy consumption, which in turn generates a large amount of heat and reduces the life of the diode.

SUMMARY OF THE INVENTION

The invention provides a preparation method of a gallium nitride Schottky diode, which is used to solve the problem that the Schottky contact resistance generated during the preparation process of the existing gallium nitride Schottky diode will be far greater than the ohmic contact resistance , to achieve the beneficial effects of reducing the Schottky contact resistance and improving the life of the gallium nitride Schottky diode.

The preparation method of the gallium nitride Schottky diode provided by the present invention includes:

Deposit a passivation layer on the surface of the GaN epitaxial wafer;

preparing the cathode of the gallium nitride Schottky diode;

dry etching is performed in the center of the passivation layer to form a Schottky contact hole;

In the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; photolithography, etching and annealing are performed on the ohmic metal layer to form a ohmic metal layer. Ohmic metal structure with grid structure;

preparing the anode of the gallium nitride Schottky diode;

Wherein, the ohmic metal structure is a grid structure and is wrapped by the anode.

Further, in the above preparation method, the preparation of the cathode of the gallium nitride Schottky diode includes:

dry etching the passivation layer to form two ohmic contact holes;

depositing a first metal in the two ohmic contact holes and on the surface of the passivation layer to form a first metal layer;

Photolithography, etching and annealing are performed on the first metal layer to form the cathode.

Further, in the above preparation method, the first metal is deposited in the two ohmic contact holes and on the surface of the passivation layer to form the first metal layer, comprising:

Using an electron beam evaporation process, metal titanium, metal aluminum, metal nickel and metal copper are sequentially deposited in the two ohmic contact holes and on the surface of the passivation layer to form the first metal layer.

Further, in the above preparation method, the preparation of the anode of the gallium nitride Schottky diode includes:

In the Schottky contact hole, a second metal is deposited on the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure to form a second metal layer;

Photolithography and etching are performed on the second metal layer to form the anode.

Further, in the above preparation method, the second metal is deposited on the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure in the Schottky contact hole to form a second metal. Metal layers, including:

Using the electron beam evaporation process, in the Schottky contact hole, the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure are sequentially deposited metal nickel and metal copper to form the second metal layer.

Further, in the above preparation method, the annealing process is an annealing process with an annealing time of 30 s at an annealing temperature of 840° C. under nitrogen conditions.

Further, in the above preparation method, the deposition of the passivation layer on the surface of the gallium nitride epitaxial wafer includes:

The passivation layer is formed by depositing silicon nitride on the surface of the gallium nitride epitaxial wafer by using a low pressure chemical vapor deposition method.

Further, in the above preparation method, the number of grid bars of the ohmic metal structure includes three.

Further, in the above preparation method, the thickness of the ohmic metal structure is 30 nanometers.

Further, in the above preparation method, before the passivation layer is deposited on the surface of the gallium nitride epitaxial wafer, the method further includes:

The substrate of the gallium nitride epitaxial wafer, the buffer layer and the barrier layer are sequentially prepared.

The present invention provides a method for preparing a gallium nitride Schottky diode, which comprises depositing a passivation layer on the surface of a gallium nitride epitaxial wafer; preparing a cathode of a gallium nitride Schottky diode; dry etching to form a Schottky contact hole; in the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; photolithography is performed on the ohmic metal layer, Etching and annealing are performed to form an ohmic metal structure with a grid structure; an anode of a gallium nitride Schottky diode is prepared; wherein, the ohmic metal structure is a grid structure and is wrapped by the anode. According to the preparation method provided by the present invention, before preparing the anode, an ohmic metal structure with a grid structure is prepared in the Schottky contact hole, and the ohmic metal structure is wrapped by the anode, so as to realize the gallium nitride Schottky without affecting the In the case of the output performance of the base diode, the Schottky junction area is reduced, thereby reducing the Schottky contact resistance, and improving the device performance and life of the gallium nitride Schottky diode.

Description of drawings

FIG. 1 is a schematic flowchart of a method for manufacturing a gallium nitride Schottky diode according to Embodiment 1 of the present invention;

FIG. 2 is a schematic flowchart of a method for preparing a Nitrided Schottky diode according to Embodiment 2 of the present invention;

FIG. 3 is a schematic cross-sectional structural diagram of a gallium nitride Schottky diode after performing step 200 of the second embodiment;

FIG. 4 is a schematic cross-sectional structural diagram of a gallium nitride Schottky diode after step 201 of the second embodiment;

FIG. 5 is a schematic cross-sectional structure diagram of the GaN Schottky diode after step 202 of the second embodiment;

6 is a schematic cross-sectional structural diagram of a GaN Schottky diode after step 203 of the second embodiment;

FIG. 7 is a schematic cross-sectional structural diagram of the GaN Schottky diode after step 204 of the second embodiment;

FIG. 8 is a schematic cross-sectional structural diagram of a gallium nitride Schottky diode after step 205 of the second embodiment;

FIG. 9 is a schematic cross-sectional structural diagram of a gallium nitride Schottky diode after step 206 of the second embodiment;

FIG. 10 is a schematic cross-sectional structural diagram of the GaN Schottky diode after step 207 of the second embodiment;

FIG. 11 is a schematic cross-sectional structure diagram of the gallium nitride Schottky diode after step 208 of the second embodiment is performed.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

FIG. 1 is a schematic flowchart of a method for preparing a gallium nitride Schottky diode according to Embodiment 1 of the present invention. As shown in FIG. 1, the preparation method includes the following steps:

Step 101, depositing a passivation layer on the surface of the gallium nitride epitaxial wafer.

Step 102, preparing the cathode of the gallium nitride Schottky diode.

Specifically, a passivation layer is first deposited on the surface of the gallium nitride epitaxial wafer. For example, a low pressure chemical vapor deposition method can be used to deposit silicon nitride on the surface of the gallium nitride epitaxial wafer to form a passivation layer; wherein the passivation layer is The thickness of the layer may be 30 nanometers. For the preparation process of the cathode of the gallium nitride Schottky diode, the current mature preparation process can be adopted, and those skilled in the art can choose according to the actual situation, which is not limited in the present invention.

Step 103 , dry etching is performed in the center of the passivation layer to form a Schottky contact hole.

Step 104: In the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; photolithography, etching and annealing are performed on the ohmic metal layer to form an ohmic gate-like structure. Metal structure.

Specifically, after the preparation of the cathode is completed, dry etching is performed on the passivation layer at the center of the passivation layer to form a Schottky contact hole deep to the surface of the gallium nitride epitaxial wafer. In the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; the ohmic metal layer is subjected to photolithography, etching and annealing treatment to form an ohmic gate-like structure. Metal structure. The annealing treatment may specifically be an annealing process with an annealing time of 30s at an annealing temperature of 840° C. under the condition of nitrogen. The number of gate bars of the ohmic metal structure includes 3, and the thickness of the ohmic metal structure is 30 nanometers.

Step 105, preparing the anode of the gallium nitride Schottky diode, so that the ohmic metal structure is wrapped by the anode.

In the Schottky contact hole, the anode of the gallium nitride Schottky diode is prepared along the surface of the ohmic metal structure, so that the ohmic metal structure is wrapped by the anode. For the preparation process of the anode of the gallium nitride Schottky diode, the current mature preparation process can be adopted, and those skilled in the art can choose according to the actual situation, which is not limited in the present invention.

Embodiment 1 of the present invention provides a method for preparing a gallium nitride Schottky diode, which includes depositing a passivation layer on the surface of a gallium nitride epitaxial wafer; preparing a cathode of a gallium nitride Schottky diode; The center is dry-etched to form a Schottky contact hole; in the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; Etching, etching and annealing treatments are used to form an ohmic metal structure in a grid structure; an anode for a gallium nitride Schottky diode is prepared; wherein, the ohmic metal structure is a grid structure and is wrapped by the anode. According to the preparation method provided by the present invention, before preparing the anode, an ohmic metal structure with a grid structure is prepared in the Schottky contact hole, and the ohmic metal structure is wrapped by the anode, so as to realize the gallium nitride Schottky without affecting the In the case of the output performance of the base diode, the Schottky junction area is reduced, thereby reducing the Schottky contact resistance, and improving the device performance and life of the gallium nitride Schottky diode.

In order to further illustrate the preparation method of the gallium nitride Schottky diode provided by the present invention, on the basis of the preparation method shown in FIG. 1 , FIG. 2 is the preparation of a gallium nitride Schottky diode provided in the second embodiment of the present invention A schematic flowchart of the method, the second embodiment shown in FIG. 2 describes the preparation method of the gallium nitride Schottky diode in detail.

Step 200 , prepare the substrate of the gallium nitride epitaxial wafer, the buffer layer and the barrier layer in sequence.

Before step 101 in the method shown in FIG. 1 , step 200 may also be included. Specifically, FIG. 3 is a schematic cross-sectional structure diagram of a gallium nitride Schottky diode after performing step 200 of the second embodiment. As shown in FIG. 3 , the substrate 11 in the gallium nitride epitaxial wafer is sequentially prepared by using a deposition process. The buffer layer 12 and the barrier layer 13, wherein the material of the substrate 11 is made of silicon element, and its thickness can be 625 microns; the material of the buffer layer 12 is made of compound gallium nitride, and its thickness can be 3 microns; the barrier layer The material of 13 is made of compound aluminum gallium nitride, and its thickness can be 25 microns. Through step 200, a gallium nitride epitaxial wafer is prepared, which lays a foundation for the preparation of other components of the subsequent device.

Step 201 , depositing a passivation layer on the surface of the barrier layer in the gallium nitride epitaxial wafer.

Specifically, FIG. 4 is a schematic cross-sectional structure diagram of a gallium nitride Schottky diode after performing step 201 of the second embodiment. As shown in FIG. 4 , a passivation layer is deposited on the surface of the barrier layer 13 in the gallium nitride epitaxial wafer. 14. The execution method of step 201 is the same as that of step 101 in FIG. 1 , and details are not described here.

Step 202 , dry etching the passivation layer to form two ohmic contact holes.

Step 203 , depositing a first metal in the two ohmic contact holes and on the surface of the passivation layer to form a first metal layer.

Step 204 , performing photolithography, etching and annealing on the first metal layer to form a cathode.

Step 102 in the above method shown in FIG. 1 may specifically include steps 202-204. Specifically, FIG. 5 is a schematic cross-sectional structure diagram of the gallium nitride Schottky diode after step 202 of the second embodiment. As shown in FIG. 5 , by using a dry etching process, the gallium nitride Schottky diode At the edge of the passivation layer 14, the passivation layer 14 is etched to form two center-symmetric ohmic contact holes 15, and the diameter of each ohmic contact hole 15 can be 5 microns.

FIG. 6 is a schematic cross-sectional structure diagram of a gallium nitride Schottky diode after step 203 of Embodiment 2 is performed. As shown in FIG. 6 , first metal is deposited in the two ohmic contact holes 15 and on the surface of the passivation layer 14 , The first metal layer 16 is formed. Further, an electron beam evaporation process may be used to sequentially deposit metal titanium, metal aluminum, metal nickel and metal copper in the two ohmic contact holes 15 and on the surface of the passivation layer 14 to form the first metal layer 16 . The thickness of the metal layer 16 may be 300 nm.

FIG. 7 is a schematic cross-sectional structure diagram of the gallium nitride Schottky diode after step 204 of the second embodiment is performed. As shown in FIG. 7 , after the first metal layer 16 is formed, the first metal layer 16 is subjected to photolithography and etching. and an annealing process to form the cathode 17 . Specifically, by performing photolithography and etching on the first metal layer 16, only the first metal layer 16 in the ohmic contact hole 15 and its edge portion is retained, and then annealing is performed to form titanium, aluminum, An alloy of nickel and copper, and the first metal layer 16 reacts with the aluminum gallium nitride in the barrier layer 13 to form an alloy on its contact surface, thereby obtaining a cathode 17 with lower ohmic contact resistance. Among them, the photolithography procedure includes glue coating, exposure and development, and the annealing process can be specifically performed under the condition of nitrogen gas, and an annealing process with an annealing time of 30s at an annealing temperature of 840° C. can be used.

Step 205 , dry etching is performed in the center of the passivation layer to form a Schottky contact hole.

Step 206: In the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; photolithography, etching and annealing are performed on the ohmic metal layer to form an ohmic gate-like structure. Metal structure.

FIG. 8 is a schematic cross-sectional structure diagram of the GaN Schottky diode after performing step 205 of the second embodiment, and FIG. 9 is a cross-sectional structure schematic diagram of the GaN Schottky diode after performing the step 206 of the second embodiment. As shown in FIG. 8 , dry etching is performed in the center of the passivation layer 14 to form a Schottky contact hole 18 ; in the Schottky contact hole 18 , metal titanium is deposited on the surface of the passivation layer 14 and the surface of the cathode 17 , to form an ohmic metal layer; as shown in FIG. 9 , photolithography, etching and annealing are performed on the ohmic metal layer to form an ohmic metal structure 19 having a grid-like structure. The number of gate bars in the ohmic metal structure 19 includes three, and the thickness of the ohmic metal structure 19 can be 30 nanometers. The execution methods of step 205 and step 206 are respectively the same as that of step 103 and step 104 in FIG. 1 , and will not be repeated here.

Step 207: In the Schottky contact hole, a second metal is deposited on the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure to form a second metal layer.

Step 208 , performing photolithography and etching on the second metal layer to form an anode.

Step 105 in the above method shown in FIG. 1 may specifically include step 207 and step 208 . FIG. 10 is a schematic cross-sectional structure diagram of the gallium nitride Schottky diode after step 207 of the second embodiment. As shown in FIG. 10 , after the ohmic metal structure 19 is prepared, in the Schottky contact hole 18 , a passivation layer is formed. A second metal is deposited on the surface of the cathode 14 , the surface of the cathode 17 and the surface of the ohmic metal structure 19 to form the second metal layer 20 . Specifically, an electron beam evaporation process can be used to sequentially deposit metallic nickel and metallic copper on the surface of the passivation layer 14 , the surface of the cathode 17 and the surface of the ohmic metal structure 19 in the Schottky contact hole 18 to form the second metal layer 20, wherein the thickness of the second metal layer 20 can be 300 nanometers.

FIG. 11 is a schematic cross-sectional structure diagram of the gallium nitride Schottky diode after step 208 of the second embodiment. As shown in FIG. 11 , after the second metal layer 20 is formed, photolithography and etching are used for the second metal layer 20 . In the etching process, only the second metal layer 20 located at the Schottky contact hole 18 and its edges is retained, and an anode 21 is formed. The photolithography process includes glue coating, exposure and development. The thickness of the anode 21 can be adopted 300 nm. It should be noted that the formed anode 21 is in contact with the barrier layer 13 in the gallium nitride epitaxial wafer to form a Schottky contact, and at the same time, the ohmic metal structure 19 is completely covered to isolate the ohmic metal structure 19 from the air to reduce Small Schottky contact resistance improves device performance and lifetime of GaN Schottky diodes.

The second embodiment of the present invention provides a preparation method of a gallium nitride Schottky diode, by sequentially preparing a substrate, a buffer layer and a barrier layer of a gallium nitride epitaxial wafer; depositing passivation on the surface of the gallium nitride epitaxial wafer dry etching the passivation layer to form two ohmic contact holes; depositing a first metal in the two ohmic contact holes and on the surface of the passivation layer to form a first metal layer; Etching, etching and annealing treatment to form a cathode; dry etching is performed in the center of the passivation layer to form a Schottky contact hole; in the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode , form an ohmic metal layer; perform photolithography, etching and annealing on the ohmic metal layer to form an ohmic metal structure with a grid-like structure; in the Schottky contact hole, the surface of the passivation layer, the surface of the cathode and the ohmic metal A second metal is deposited on the surface of the structure to form a second metal layer; photolithography and etching are performed on the second metal layer to form an anode, so that the ohmic metal structure is wrapped by the anode, so as to achieve a Schottky diode without affecting the gallium nitride. In the case of output performance, the Schottky junction area is reduced, thereby reducing the Schottky contact resistance, and improving the device performance and life of the gallium nitride Schottky diode.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (8)

1. a preparation method of gallium nitride Schottky diode, is characterized in that, comprises: Deposit a passivation layer on the surface of the GaN epitaxial wafer; preparing the cathode of the gallium nitride Schottky diode; dry etching is performed in the center of the passivation layer to form a Schottky contact hole; In the Schottky contact hole, metal titanium is deposited on the surface of the passivation layer and the surface of the cathode to form an ohmic metal layer; photolithography, etching and annealing are performed on the ohmic metal layer to form a ohmic metal layer. Ohmic metal structure with grid structure; preparing the anode of the gallium nitride Schottky diode; Wherein, the ohmic metal structure is a grid structure and is wrapped by the anode; The preparation of the cathode of the gallium nitride Schottky diode includes: performing dry etching on the passivation layer to form two ohmic contact holes; depositing a first metal in the two ohmic contact holes and on the surface of the passivation layer to form a first metal layer; The first metal layer is subjected to photolithography, etching and annealing treatment to form the cathode; The preparation of the anode of the gallium nitride Schottky diode includes: In the Schottky contact hole, a second metal is deposited on the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure to form a second metal layer; Photolithography and etching to form the anode. 2 . The preparation method according to claim 1 , wherein the depositing a first metal in the two ohmic contact holes and on the surface of the passivation layer to form the first metal layer comprises: 3 . Using an electron beam evaporation process, metal titanium, metal aluminum, metal nickel and metal copper are sequentially deposited in the two ohmic contact holes and on the surface of the passivation layer to form the first metal layer. 3 . The preparation method according to claim 2 , wherein in the Schottky contact hole, the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure are deposited. 4 . The second metal, forming the second metal layer, includes: Using the electron beam evaporation process, in the Schottky contact hole, the surface of the passivation layer, the surface of the cathode and the surface of the ohmic metal structure are sequentially deposited metal nickel and metal copper to form the second metal layer. 4 . The preparation method according to claim 1 , wherein the annealing treatment is an annealing process with an annealing time of 30 s at an annealing temperature of 840° C. under nitrogen conditions. 5 . 5. The preparation method according to any one of claims 1-3, wherein the deposition of a passivation layer on the surface of the gallium nitride epitaxial wafer comprises: The passivation layer is formed by depositing silicon nitride on the surface of the gallium nitride epitaxial wafer by using a low pressure chemical vapor deposition method. 6 . The preparation method according to claim 1 , wherein the number of grid bars of the ohmic metal structure includes three. 7 . 7 . The preparation method according to claim 1 , wherein the thickness of the ohmic metal structure is 30 nanometers. 8 . 8. The preparation method according to any one of claims 1-3, characterized in that, before said depositing a passivation layer on the surface of the gallium nitride epitaxial wafer, further comprising: The substrate of the gallium nitride epitaxial wafer, the buffer layer and the barrier layer are sequentially prepared.

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