A trench type Schottky diode device

Abstract

The present invention relates to the field of semiconductor technology, and in particular to a trench-type Schottky diode device, wherein the active region of the device is formed by connecting a plurality of primitive cells in parallel, wherein a basic primitive cell includes a trench and a p+ layer in an orthogonal arrangement, that is, the direction of the trench and the p+ layer is perpendicular; in a primitive cell, along the depth direction perpendicular to the paper surface, there are structure A and structure B in sequence, wherein the structure A is a pure trench Schottky diode structure, and the structure B is a pn diode structure. For n-type conductive devices, the primitive cell of the device of the present invention forms an orthogonal arrangement of the p+ region and the trench by opposite types of doping, thereby realizing electric field shielding of the trench and the Schottky contact, and reducing the reverse bias leakage current of the device. At the same time, through the Schottky contact with different potential barriers in the trench and on the table, the turn-on voltage and on-resistance of the device are reduced.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a trench type Schottky diode device. Background Art

[0002] Schottky diodes are multi-sub devices. Because they have no reverse recovery charge, they are used in high-frequency switching circuits. They have much lower losses than pn diodes and are widely used. SiC Schottky diodes can achieve the application advantages of high temperature resistance, high voltage and high operating frequency due to the wide bandgap, high critical electric field and high thermal conductivity of SiC materials. In general, the reverse bias leakage current of Schottky diodes is much greater than that of pn diodes, which is its disadvantage. This is mainly determined by the size of the potential barrier and the electric field strength on the Schottky contact surface. Therefore, in order to reduce the reverse bias leakage current of Schottky diodes, the method of setting a reverse doping region is generally used to shield the electric field on the Schottky contact surface, reduce the reverse bias leakage current, and even achieve a reverse bias leakage current close to that of a pn diode. In particular, for trench Schottky diodes, the existing technology is to inject another doped ion at the bottom of the trench in the device cell to form a reverse doping region (structure such as Figure 1 As shown in the figure, the electric field shielding of the Schottky contact on the mesa is realized, and a low reverse bias leakage current is obtained. However, due to the sacrifice of the conductive channel at the bottom of the trench, the further reduction of resistance is limited.

[0003] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0004] The purpose of the present invention is to provide a trench-type Schottky diode device. For n-type conductive devices, the device cell is arranged in an orthogonal form with a p+ region of the opposite type of doping and a trench, so as to achieve electric field shielding of the trench and Schottky contact and reduce the reverse bias leakage current of the device. At the same time, the turn-on voltage and on-resistance of the device are reduced through Schottky contacts with different potential barriers in the trench and on the table.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a trench-type Schottky diode device, wherein the active region of the device is formed by connecting a plurality of primitive cells in parallel, wherein a basic primitive cell comprises a trench and a p+ layer in an orthogonal arrangement, that is, the directions of the trench and the p+ layer are perpendicular; and within a primitive cell, along a depth direction perpendicular to a paper surface, there are structure A and structure B in sequence, wherein structure A is a pure trench Schottky diode structure, and structure B is a pn diode structure.

[0007] As a further technical solution, the structure A comprises, from bottom to top, a cathode, an n+SiC substrate, an n+ buffer layer, an n-drift layer, a trench, a mesa, a Schottky contact and an anode.

[0008] As a further technical solution, the structure B comprises, from bottom to top, a cathode, an n+SiC substrate, an n+ buffer layer, an n-drift layer, a p+ layer, a groove, a mesa, an ohmic contact and an anode.

[0009] As a further technical solution, the groove bottom, groove sidewall and terrace top of the structure A are all Schottky contacts, and Schottky contacts with different barrier heights can be formed in sections;

[0010] As a further technical solution, the Schottky barrier of the Schottky contact on the top of the mesa is S1, the Schottky barrier of the Schottky contact on the sidewall of the trench is S2, and the Schottky barrier of the Schottky contact at the bottom of the trench is S3. <S2<S3。

[0011] As a further technical solution, the segmented Schottky contacts with different barrier heights in the mesas and trenches may be formed using polysilicon with different doping types and concentrations.

[0012] As a further technical solution, the p+ layer is electrically connected to the anode via the ohmic contact in the structure B.

[0013] As a further technical solution, in the structure B, the p+ layer is deeper than the trench, and the distance between the bottom of the p+ layer and the bottom of the trench is greater than 0.5 microns.

[0014] As a further technical solution, the doping concentration in the mesa in the structure A is not less than that in the drift layer.

[0015] By adopting the above technical solution, the present invention has the following beneficial effects:

[0016] For n-type conductive devices, the device of the present invention forms an orthogonal arrangement of the p+ region and the groove by opposite type doping in the primitive cell, realizes electric field shielding of the groove and Schottky contact, and reduces the reverse bias leakage current of the device. At the same time, through the Schottky contact with different potential barriers in the groove and on the table, the turn-on voltage and on-resistance of the device are reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a schematic diagram of the cross-sectional structure of a trench Schottky diode in the prior art;

[0019] Figure 2 A plan view of an active region original cell of a trench Schottky diode device provided by an embodiment of the present invention;

[0020] Figure 3 for Figure 2 Schematic diagram of the cross section at A in the middle;

[0021] Figure 4 for Figure 2 Schematic diagram of the cross section at B;

[0022] Figure 5 A schematic diagram of the circuit structure of structure A provided in an embodiment of the present invention;

[0023] Figure 6 A schematic diagram of the cross-section and device depth structure of structure A provided in an embodiment of the present invention;

[0024] Figure 7 A schematic diagram of the cross-section and device depth structure of structure B provided in an embodiment of the present invention;

[0025] Icon: 1- cathode, 2- n+ SiC substrate, 3- n+ buffer layer, 4- n- drift layer, 401- trench, 402- terrace, 5- p+ layer, 6- ohmic contact, 7- Schottky contact, 701- Schottky contact on top of terrace, 702- Schottky contact on trench sidewall, 703- Schottky contact on trench bottom, 8- anode. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0028] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0030] The n-type doping and p-type doping mentioned in the embodiment of the present invention are relative, and can also be called the first doping and the second doping, that is, the n-type and p-type are interchangeable and applicable to the device. At the same time, the device structure in the embodiment of the present invention is not only applicable to SiC, but also to Si, GaN, Ga 2 O 3 In the embodiment of the present invention, SiC is taken as an example.

[0031] Combination Figure 2-Figure 7 As shown, this embodiment provides a trench Schottky diode device, the active region of the device is formed by multiple cells connected in parallel, in a basic cell, including a trench 401 and a p+ layer 5 in an orthogonal arrangement, that is, the direction of the trench 401 and the p+ layer 5 are perpendicular; in a cell, along the depth direction perpendicular to the paper surface, there are structure A and structure B in sequence, wherein structure A is a pure trench Schottky diode structure, and structure B is a pn diode structure. Compared with a conventional trench Schottky diode (such as a conventional trench Schottky diode in which the trench 401 is parallel to the p+ layer 5) Figure 1 As shown in FIG. 1 , the bottom of the trench of the pure Schottky diode part of the structure of the present invention can also conduct electricity, increasing the area of ​​Schottky conduction. The n+SiC substrate 2 is highly doped, greater than 1E18cm- 3 The doping concentration of n+ buffer layer 3 is about 1E18cm- 3 The thickness is 0.5-5 microns, depending on the thickness of the epitaxial layer. The thickness and concentration of the n-drift layer 4 are determined according to the withstand voltage of the device design. For SiC devices, it is generally 5E14cm- 3 -1E17cm- 3 For devices with a withstand voltage greater than 600V, the thickness is generally greater than 5 microns.

[0032] In this embodiment, as a further technical solution, the structure A from bottom to top is successively a cathode 1, an n+ SiC substrate 2, an n+ buffer layer 3, an n- drift layer 4, a trench 401, a mesa 402, a Schottky contact 7, and an anode 8.

[0033] In this embodiment, as a further technical solution, the structure B from bottom to top is successively a cathode 1, an n+ SiC substrate 2, an n+ buffer layer 3, an n- drift layer 4, a p+ layer 5, a trench 401, a mesa 402, an ohmic contact 6, and an anode 8.

[0034] In this embodiment, as a further technical solution, the bottom of the trench, the sidewall of the trench, and the top of the mesa of the structure A are all Schottky contacts; since the distance from the mesa to the bottom of the p+ region is far, the electric field shielding effect on the mesa is stronger, so a Schottky contact with a lower barrier can be set on the mesa, making the turn-on voltage of the device lower. As the shielding effect gradually weakens from the top of the mesa to the bottom of the trench, the barrier can also increase in a stepped manner. As the distance from the bottom of the trench increases, the barrier gradually decreases, and the barrier at the top of the mesa is the smallest. Even more, the sidewall can be divided into one or several different barrier regions.

[0035] As Figure 5 shown, the Schottky barrier of the Schottky contact 701 at the top of the mesa is S1, the Schottky barrier of the Schottky contact 702 on the sidewall of the trench is S2, and the Schottky barrier of the Schottky contact 703 at the bottom of the trench is S3, where S1 < S2 < S3. The resistance R0 is the resistance of the substrate and the drift region, and R1, R2, and R3 are the on-resistances of the current channels passing through the drift region to the corresponding Schottky contact regions respectively. Since the barrier S1 < S2 < S3, when the forward voltage drop of the anode gradually increases, the Schottky barriers are gradually turned on from S1 to S3, increasing the conduction path and reducing the on-resistance.

[0036] The stepped barrier setting in the structure A of the present invention can be realized by a polysilicon process. After the trench is formed and activated and annealed, the etching defects in the trench are removed by thermal oxidation and then wet etching of SiO 2 The formation of the Schottky contact can first deposit polysilicon to fill the trench and cover the mesa with a certain thickness. Different concentrations of doping are carried out from the bottom up in the trench. Since the Fermi level of polysilicon is related to the doping type and concentration, the barrier height between polysilicon and SiC is related to the doping type and concentration of polysilicon, and the barrier height can be adjusted by adjusting the doping of polysilicon here. For example, different concentrations of doping are implanted at different depths in the trench and on the mesa, and even a nearly continuous Schottky barrier distribution can be formed.

[0037] After the polysilicon Schottky contact is formed, part of the polysilicon in the groove is etched to form a small groove. Anode metal is deposited to fill the groove, and annealing is performed at a temperature of 200-500°C to form an ohmic contact with low contact resistance between the polysilicon and the metal. The anode metal can be Ti / Al, or Ti / W / Al, Ti / TiN / Al, Ti / Cu, Ti / Pt / Au, Ti / Ag, etc. The cathode includes an ohmic contact on the back and a block metal. The ohmic contact is formed by depositing Ni and performing rapid thermal annealing. The block metal can be TiNiAg, TiNiAu, CrNiAg, etc.

[0038] The device consists of an active area, junction terminals and scribe lines. The active area is composed of multiple primitive cells connected in parallel.

[0039] In this embodiment, as a further technical solution, structure A of the present invention is a trench-type pure Schottky diode, with Schottky contacts in the trench (including the bottom and sidewalls of the trench) and on the terrace, and has a larger Schottky contact area. Figure 6 As shown, in the depth direction perpendicular to the paper, the width W of the Schottky contact is the spacing of the pn diode (structure B), and the width is designed based on the size of the reverse bias leakage current of the device and the size of the on-resistance. If the width W is small, the conductive area becomes smaller and the on-resistance increases, but the electric field shielding of the Schottky contact in the trench and on the table by the p+ region is also enhanced, and the reverse bias leakage current is reduced. Generally, W is greater than 0.5 microns.

[0040] In this embodiment, as a further technical solution, the structure B of the present invention is a pn diode with a groove, and both the inside of the groove and the surface of the table are ohmic contacts. Figure 7 As shown. The parallel pn diode not only shields the electric field on the trench and the table at the Schottky diode, but also under large current, when the voltage drop of the pn diode is greater than the built-in potential of the pn junction, minority carriers begin to be injected to modulate the conductivity, and the on-resistance decreases. Therefore, it is beneficial to improve the surge current capability. The metal of the ohmic contact can be TiAl, Ni, TiNi, etc., and is formed by rapid thermal annealing between 900-1100°C. The depth of the trench is less than the depth of the p+ region by d, that is, the distance between the bottom of the p+ region and the bottom of the trench is d. The design of the spacing d is also a compromise effect of the shielding effect of the Schottky contact and the influence on the on-resistance. The design of the spacing d and the width W of the Schottky contact affects each other and requires a comprehensive design. Generally, the spacing d is greater than 0.5 microns.

[0041] In this embodiment, as a further technical solution, the doping concentration in the mesa in the structure A is not less than that in the drift layer. In this way, the resistance of the mesa channel can be reduced.

[0042] The grooves and terraces in structures A and B are the same, and the widths of the grooves and terraces are designed according to the process capability range. Figure 1 As shown, in the prior art, the distribution of the p+ region 5 is located at the entire bottom of the groove, and the width of the mesa directly affects the on-resistance and the shielding effect. In the present invention, the distribution of the p+ region 5 is perpendicular to the groove direction, so the width of the mesa does not affect the shielding effect. The width of the mesa and the groove can be made very small to increase the cell density, such as a width of 0.5 microns.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A trench Schottky diode device, wherein the active region of the device is formed by connecting a plurality of cells in parallel, characterized in that: In a basic primitive cell, a trench and a p+ layer are arranged orthogonally, that is, the directions of the trench and the p+ layer are perpendicular; in a primitive cell, along the direction parallel to the trench, there are structure A and structure B, wherein structure A is a pure trench Schottky diode structure, and structure B is a pn diode structure; The structure A comprises, from bottom to top, a cathode, an n+SiC substrate, an n+ buffer layer, an n-drift layer, a trench, a table, a Schottky contact and an anode; the trench bottom, the trench sidewall and the table top of the structure A are all Schottky contacts; The structure B comprises, from bottom to top, a cathode, an n+SiC substrate, an n+ buffer layer, an n-drift layer, a p+ layer, a groove, a table, an ohmic contact and an anode; the p+ layer is electrically connected to the anode through the ohmic contact in the structure B; the p+ layer in the structure B is deeper than the groove, and the distance between the bottom of the p+ layer and the bottom of the groove is greater than 0.5 microns.

2. The trench Schottky diode device according to claim 1, characterized in that: The Schottky contact is segmented to form Schottky contacts with different barrier heights.

3. The trench Schottky diode device according to claim 2, characterized in that: The Schottky barrier of the Schottky contact at the top of the mesa of the structure A is S1, the Schottky barrier of the Schottky contact at the sidewall of the trench is S2, and the Schottky barrier of the Schottky contact at the bottom of the trench is S3. <S2<S3。 4. The trench Schottky diode device according to claim 2, characterized in that: Polysilicon with different doping types and concentrations is used to form segmented Schottky contacts with different barrier heights on the mesas and in the trenches.

5. The trench Schottky diode device according to claim 1, characterized in that: The doping concentration in the mesa in the structure A is not less than that in the drift layer.

Images