A Schottky diode and its preparation method

Abstract

The present invention provides a Schottky diode comprising: an N+ substrate and an N-epitaxial layer located on the N+ substrate; a Schottky metal layer unit, wherein the Schottky metal layer unit covers the surface of the N-epitaxial layer, the Schottky metal layer unit comprising a plurality of Schottky metal layers, and the metals of two adjacent Schottky metal layers are different; an anode metal located on the Schottky metal layer unit; and a cathode metal located on the other surface of the N+ substrate. The present invention also provides a method for preparing a Schottky diode, which can relatively flexibly adjust the Schottky barrier to obtain an ideal forward voltage drop and an acceptable reverse leakage current.

Description

Technical Field

[0001] The invention relates to a Schottky diode and a preparation method thereof. Background Art

[0002] At present, the limitations of the physical properties of traditional power electronic devices based on silicon materials are becoming increasingly obvious, which seriously restricts the performance improvement and development of devices. As a representative material of the third generation of semiconductors, silicon carbide materials have the advantages of high bandgap, high breakdown electric field, high thermal conductivity, etc. Silicon carbide Schottky diodes have the advantages of low forward voltage drop and almost no reverse recovery current, such as Figure 1 As shown, it is a diode structure of the prior art, in which the Schottky barrier formed between the Schottky metal 104 and the epitaxial layer 102 directly affects the forward voltage drop and reverse characteristics of the Schottky diode. is the metal work function qΦ m and silicon carbide electron affinity qχ s In order to control the reverse leakage of the diode and obtain a high breakdown voltage, a high Schottky barrier is usually used, but this will also lead to a large forward voltage drop, resulting in large conduction losses. In a silicon carbide diode, since the physical parameters of the epitaxial layer 102 are constant, the work function of the Schottky metal 104 is The size of the work function plays a decisive role, and the metal work function is the inherent value of the metal. Therefore, how to correctly select and design the Schottky metal 104 is an important step in the design of silicon carbide Schottky diodes. In the existing technology, the Schottky metal 104 is usually a single layer of metal directly in contact with the epitaxial layer 102, such as Ti, W and Mo. The problem with this result is that The size can only be determined by the work function of the single-layer metal, which has single characteristics and limitations, and it is difficult to obtain the ideal Schottky barrier height. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a Schottky diode and a preparation method thereof, which can relatively flexibly adjust the Schottky barrier to obtain an ideal forward voltage drop and an acceptable reverse leakage current.

[0004] One of the present inventions is achieved as follows: a Schottky diode comprising:

[0005] An N+ substrate and an N- epitaxial layer located on the N+ substrate;

[0006] a Schottky metal layer unit, the Schottky metal layer unit covering the surface of the N-epitaxial layer, the Schottky metal layer unit comprising a plurality of Schottky metal layers;

[0007] an anode metal located on the Schottky metal layer unit;

[0008] and a cathode metal located on the other surface of the N+ substrate.

[0009] Furthermore, a plurality of p+ implantation regions are spaced apart on the N-epitaxial layer.

[0010] Furthermore, the metal work functions of the two adjacent Schottky metal layers are different.

[0011] The second aspect of the present invention is achieved as follows: a method for preparing a Schottky diode, specifically comprising the following steps:

[0012] Step 1: forming an N- epitaxial layer on an N+ substrate;

[0013] Step 2: making a p+ implantation region on the N-epitaxial layer;

[0014] Step 3: depositing a Schottky metal unit onto the N-epitaxial layer by sputtering, and then performing a heat treatment to cause the Schottky metal unit to alloy with the N-epitaxial layer to form an alloy layer, and forming a Schottky junction with the N-epitaxial layer;

[0015] Step 4: Precipitate cathode metal and anode metal.

[0016] Furthermore, the step 3 is further specified as follows: depositing the first metal layer in the Schottky metal unit to the N-epitaxial layer by sputtering, then depositing the second metal layer on the first metal layer, and so on, completing the deposition, and then forming a Schottky junction by annealing.

[0017] Furthermore, the Schottky metal layer unit includes a plurality of Schottky metal layers, and the metal work functions of two adjacent Schottky metal layers are different.

[0018] The advantage of the present invention is that the Schottky barrier can be adjusted relatively flexibly to obtain an ideal forward voltage drop and an acceptable reverse leakage current. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 It is a schematic diagram of the diode structure of the prior art.

[0021] Figure 2 It is a schematic diagram of a specific embodiment of the present invention.

[0022] Figure 3 It is a schematic diagram of a second specific embodiment of the present invention. DETAILED DESCRIPTION

[0023] Specific implementation method of the present invention:

[0024] like Figure 2 As shown in FIG, the Schottky diode of the present invention includes an N+ substrate 201, an N-epitaxial layer 202, p+ implantation regions 205 arranged at regular intervals in the N-epitaxial layer 202, a Schottky metal unit 203 (including a first Schottky metal layer 203-1 and a second Schottky metal layer 203-2), an anode metal 204, and a cathode metal 206. The first Schottky metal 203-1 is in direct contact with the upper surface of the silicon carbide epitaxial layer 202 and the p+ implantation region 205. The second Schottky metal 203-2 is directly deposited on the surface of the first Schottky metal 203-1. After the deposition of 203-1 and 203-2, rapid annealing is simultaneously performed at a temperature range of 400-600°C for 5 minutes. After annealing, the first Schottky metal 203-1 (e.g., Al metal) and the second Schottky metal 203-2 (e.g., Mo metal) react with the silicon carbide to form a multi-element phase in which the two metal elements are directly in contact with the epitaxial layer. At an annealing temperature of 400-600°C, the metal forms a Schottky contact with the undoped region of the epitaxial layer 202 and an ohmic contact with the p+ injection region 205. During forward conduction, electrons mainly flow through the Schottky contact region, that is, the Schottky contact region where the metal contacts the silicon carbide epitaxial layer is conductive. According to the forward voltage drop formula after considering the recombination current:

[0025]

[0026] Where V F is the forward voltage drop, is the Schottky barrier. When the Schottky barrier at the semiconductor-metal interface is lowered, V F The Schottky barrier is the difference between the metal work function and the semiconductor affinity. When the semiconductor material is fixed, the Schottky barrier can be changed by changing the metal type. In order to obtain a lower Schottky barrier, A metal with a smaller work function can be used as the first Schottky metal in direct contact with the semiconductor. As we all know, forward voltage drop and reverse leakage are a pair of physical quantities that show a restrictive relationship. A too low Schottky barrier also means an increase in reverse leakage current, which is an undesirable thing. R The main component of is the thermionic emission current, which is given by:

[0027]

[0028] With reverse bias V RAs the image force increases, the image force reduction effect will further lower the Schottky barrier, increasing the reverse leakage current. This requires a metal with a larger work function to adjust the Schottky barrier to an appropriate size, acting as the second Schottky metal. After annealing, the high-barrier metal and the low-barrier metal alloy with the semiconductor, forming an alloy metal immediately adjacent to the epitaxial layer. The Schottky barrier at this point is a compromise height, between the range of the Schottky barrier obtained by alloying a single metal layer with the semiconductor. This allows for relatively flexible adjustment of the Schottky barrier to achieve an ideal forward voltage drop and an acceptable reverse leakage current.

[0029] Specific implementation method 2 of the present invention:

[0030] like Figure 3 As shown, based on the first embodiment, a third metal layer 203 - 3 and a fourth metal layer 203 - 4 are added;

[0031] The N-epitaxial layer 202 includes at least two layers of Schottky contact metals with different work functions. A first metal layer 203-1, directly contacting the silicon carbide epitaxial layer, is a low-work-function metal. Above this metal layer is a second metal layer 203-2, which has a higher work function than the first metal layer 203-1. Odd-numbered layers are composed of the same low-work-function metal as the first metal layer 203-1, such as Al or Ti. Even-numbered layers are composed of the same high-work-function metal as the second metal layer 203-2, such as Mo or Au. Regardless of the number of layers, the total thickness of the Schottky metal layer remains constant, preferably at 200 nm. After annealing, all of these metal layers form Schottky junctions with the surface of the silicon carbide epitaxial layer.

[0032] Preparation method: A layer of low-work-function metal, such as Al or Ti, is deposited on the surface of a silicon carbide epitaxial layer using sputtering. A second metal layer with a higher work function, such as Mo or Au, is then deposited on top of this metal layer. A third and fourth metal layers are deposited on top of the second metal layer as needed, with the total Schottky metal thickness controlled to be between 150 and 250 nm. After the metal layer deposition is complete, an annealing treatment is performed on the epitaxial layer surface to generate an alloying reaction, forming a Schottky junction. The annealing temperature is between 400 and 600°C; the thickness of the Schottky metal layer is determined based on the heat treatment conditions to ensure that a Schottky junction is formed after the heat treatment.

[0033] Specific implementation method three of the present invention:

[0034] The method for preparing a Schottky diode of the present invention specifically comprises the following steps:

[0035] Step 1: forming an N- epitaxial layer 202 on an N+ substrate 201;

[0036] Step 2: forming a p+ implantation region 205 on the N-epitaxial layer 202;

[0037] Step 3: Depositing the first metal layer in the Schottky metal unit 203 onto the N-epitaxial layer 202 by sputtering, then depositing the second metal layer on the first metal layer, and so on, completing the deposition, and then forming a Schottky junction by annealing, wherein the Schottky metal layer unit 203 includes a plurality of Schottky metal layers (203-1, 203-2, 203-3, 203-4), and the metal work functions of two adjacent Schottky metal layers are different;

[0038] Step 4: Deposit cathode metal 206 and anode metal 204.

[0039] Specific embodiment four of the present invention:

[0040] like Figure 2 and Figure 3 As shown, the Schottky diode of the present invention comprises:

[0041] An N+ substrate 201 and an N- epitaxial layer 202 located on the N+ substrate 201;

[0042] a Schottky metal layer unit 203 covering the surface of the N-epitaxial layer 202, the Schottky metal layer unit 203 including a plurality of Schottky metal layers (203-1, 203-2, 203-3, 203-4), a plurality of p+ implantation regions 205 spaced apart on the N-epitaxial layer 202, and the metal work functions of two adjacent Schottky metal layers being different;

[0043] an anode metal 204 located on the Schottky metal layer unit 203;

[0044] and a cathode metal 206 located on the other surface of the N+ substrate 201 .

[0045] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A Schottky diode, characterized in that: include: An N+ substrate and an N-epitaxial layer located on the N+ substrate, wherein a plurality of p+ implantation regions are spaced apart on the N-epitaxial layer; a Schottky metal layer unit, the Schottky metal layer unit covering the surface of the N-epitaxial layer, the Schottky metal layer unit including multiple Schottky metal layers, the metal work functions of two adjacent Schottky metal layers being different, the multiple layers being greater than two layers; wherein the metal work function of the Schottky metal in the odd-numbered layers is smaller than the metal work function of the Schottky metal in the even-numbered layers; When forward conducting, electrons flow through the Schottky contact area, which is the area where the metal contacts the silicon carbide epitaxial layer, and the forward voltage drop is V F formula: ; in V F is the forward voltage drop, φ B is the Schottky barrier; when the Schottky barrier at the semiconductor-metal interface is lowered, V F The Schottky barrier is the difference between the metal work function and the semiconductor affinity. When the semiconductor material is determined, the Schottky barrier is changed by changing the metal type. In order to obtain a lower Schottky barrier, φ B , using a metal with a small work function as the first Schottky metal in direct contact with the semiconductor; Forward voltage drop and reverse leakage are a pair of physical quantities that show a restrictive relationship. A too low Schottky barrier also means an increase in reverse leakage current. I R formula: ; With reverse bias V R As the mirror force decreases, the effect of image force reduction will further reduce the Schottky barrier, causing the reverse leakage current to increase. At this time, a metal with a large work function is needed to adjust the Schottky barrier to a suitable size as the second Schottky metal. According to the demand and forward voltage drop, V F Formula and reverse leakage current I R Formula, selecting the required first Schottky metal and second Schottky metal; the thickness of the Schottky metal layer unit is 150~250nm; an anode metal located on the Schottky metal layer unit; and a cathode metal located on the other surface of the N+ substrate.

2. A method for preparing a Schottky diode, characterized in that: The specific steps include: Step 1: forming an N- epitaxial layer on an N+ substrate; Step 2: making a p+ implantation region on the N-epitaxial layer; Step 3: Depositing the first metal layer in the Schottky metal unit onto the N-epitaxial layer by sputtering, and then depositing the second metal layer on the first metal layer, and so on, completing the deposition, and then causing the Schottky metal layer unit to undergo an alloying reaction with the N-epitaxial layer by heat treatment to form an alloy layer, and forming a Schottky junction with the N-epitaxial layer, wherein the Schottky metal layer unit includes multiple Schottky metal layers, and the metal work functions of two adjacent Schottky metal layers are different, and the multiple layers are greater than two layers; wherein the metal work function of the first metal layer is less than the metal work function of the second metal layer; and the metal work function of the Schottky metal of the odd-numbered layers is less than the metal work function of the Schottky metal of the even-numbered layers; When forward conducting, electrons flow through the Schottky contact area, which is the area where the metal contacts the silicon carbide epitaxial layer, and the forward voltage drop is V F formula: ; in V F is the forward voltage drop, φ B is the Schottky barrier; when the Schottky barrier at the semiconductor-metal interface is lowered, V F The Schottky barrier is the difference between the metal work function and the semiconductor affinity. When the semiconductor material is determined, the Schottky barrier is changed by changing the metal type. In order to obtain a lower Schottky barrier, φ B , using a metal with a small work function as the first Schottky metal in direct contact with the semiconductor; Forward voltage drop and reverse leakage are a pair of physical quantities that show a restrictive relationship. A too low Schottky barrier also means an increase in reverse leakage current. I R formula: ; With reverse bias V R As the mirror force decreases, the effect of image force reduction will further reduce the Schottky barrier, causing the reverse leakage current to increase. At this time, a metal with a large work function is needed to adjust the Schottky barrier to a suitable size as the second Schottky metal. According to the demand and forward voltage drop, V F Formula and reverse leakage current I R Formula, selecting the required first Schottky metal and second Schottky metal; the thickness of the Schottky metal layer unit is 150~250nm; Step 4: Precipitate cathode metal and anode metal.

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