CN113013245A

CN113013245A - Silicon carbide semiconductor device

Info

Publication number: CN113013245A
Application number: CN201911330163.5A
Authority: CN
Inventors: 田意; 徐大伟
Original assignee: Shanghai Industrial Utechnology Research Institute
Current assignee: Shanghai Industrial Utechnology Research Institute
Priority date: 2019-12-20
Filing date: 2019-12-20
Publication date: 2021-06-22

Abstract

The present invention provides a silicon carbide semiconductor device, comprising: an N-type substrate; the N-type drift layer is positioned on the N-type substrate; the P-type well region is positioned in the N-type drift layer; the N-type source region is positioned in the P-type well region; the gate dielectric layer at least spans between the N-type source region and the N-type drift layer; the gate layer is positioned on the gate dielectric layer; the isolation dielectric layer is coated on the gate layer; and the source metal layer is contacted with the N-type source region and extends to cover the isolation dielectric layer, and the source metal layer positioned on the isolation dielectric layer is provided with a through hole array penetrating through the source metal layer so as to reduce the overlapping area of the source metal layer and the grid layer. According to the invention, the through hole array penetrating through the source metal layer is formed in the source metal layer so as to reduce the overlapping area of the source metal layer and the grid layer, thereby reducing the area of an input capacitor between the source metal layer and the grid layer, reducing the input capacitor, improving the switching speed of a device and reducing the conduction loss.

Description

Silicon carbide semiconductor device

Technical Field

The invention belongs to the field of semiconductor design and manufacture, and particularly relates to a silicon carbide semiconductor device.

Background

The silicon carbide material has excellent physical and electrical properties, has the unique advantages of wide forbidden band width, high thermal conductivity, large saturation drift velocity, high critical breakdown electric field and the like, becomes an ideal semiconductor material for manufacturing high-power, high-frequency, high-voltage, high-temperature-resistant and radiation-resistant devices, and has wide application prospect in military and civil fields. The silicon carbide MOSFET device has the advantages of high switching speed, small on-resistance and the like, can realize higher breakdown voltage level in a smaller drift layer thickness, reduces the size of a power switch module, reduces energy consumption, and has obvious advantages in the application fields of power switches, converters and the like. Power mosfets (sic mosfets) based on silicon carbide materials are more suitable for applications in high frequency and high temperature applications. And the SiC MOSFET can form a surface gate oxide layer through a thermal oxidation process and can be basically compatible with the traditional silicon process.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present invention is directed to a silicon carbide semiconductor device, which is used to solve the problems of the prior art that the switching speed of the SiC MOSFET is reduced and the conduction loss is increased due to the introduction of a large input capacitance into the overlapping region of the source metal and the gate layer.

To achieve the above and other related objects, the present invention provides a silicon carbide semiconductor device comprising: an N-type substrate; the N-type drift layer is positioned on the N-type substrate; the P-type well region is positioned in the N-type drift layer; the N-type source region is positioned in the P-type well region; the gate dielectric layer at least spans between the N-type source region and the N-type drift layer; the gate layer is positioned on the gate dielectric layer; the isolation dielectric layer is coated on the grid layer; and the source metal layer is in contact with the N-type source region and extends to cover the isolation dielectric layer, and the source metal layer positioned on the isolation dielectric layer is provided with a through hole array penetrating through the source metal layer so as to reduce the overlapping area of the source metal layer and the grid layer.

Optionally, the thickness of the isolation dielectric layer is between 500 nm and 1500 nm.

Optionally, the array of through holes comprises one of a rectangular array of holes and a circular array of holes.

Optionally, the thickness of the source metal layer is between 5 microns and 10 microns.

Optionally, the source metal layer includes a first Ti layer, an Al layer, a second Ti layer, a Ni layer, and an Ag layer, which are sequentially stacked, where a thickness of the first Ti layer is 100 to 300 nanometers, a thickness of the Al layer is 3 to 6 micrometers, a thickness of the second Ti layer is 100 to 300 nanometers, a thickness of the Ni layer is 1 to 3 micrometers, and a thickness of the Ag layer is 300 to 1000 nanometers.

Optionally, the material of the gate dielectric layer includes silicon dioxide, and the thickness of the silicon dioxide is between 40 nanometers and 100 nanometers.

Optionally, the semiconductor device further includes a P-type contact region, the P-type contact region is connected to the N-type source region, and the source metal layer is in contact with the P-type contact region and the N-type source region.

As described above, the silicon carbide semiconductor device of the present invention has the following advantageous effects:

1) according to the invention, the through hole array penetrating through the source metal layer is formed in the source metal layer so as to reduce the overlapping area of the source metal layer and the grid layer, thereby reducing the area of an input capacitor between the source metal layer and the grid layer, reducing the input capacitor, improving the switching speed of a device and reducing the conduction loss.

2) In order to make up for the defect that the current conduction capability of the source metal layer is reduced by the through hole array, the invention adopts a stacked thick metal process (such as Ti/Al/Ti/Ni/Ag) to increase the deposition thickness of the source metal layer to 5-10 microns, thereby ensuring the capability of the source metal layer for conducting large current.

Drawings

Fig. 1 is a schematic view showing the structure of a silicon carbide semiconductor device as an embodiment of the present invention.

Fig. 2 is an enlarged schematic structural view of a gate layer, an isolation dielectric layer and a source metal layer of a silicon carbide semiconductor device according to an embodiment of the present invention.

Fig. 3 is a schematic top view of a source metal layer of a silicon carbide semiconductor device according to an embodiment of the present invention.

Fig. 4 is a schematic diagram showing another top-view pattern of the source metal layer of the silicon carbide semiconductor device according to the embodiment of the present invention.

Fig. 5 is a schematic flow chart showing the steps of the method for manufacturing a silicon carbide semiconductor device according to the present invention.

Description of the element reference numerals

101N type substrate

102N type drift layer

103P type well region

104N type source region

105 gate dielectric layer

106 gate layer

107 isolation dielectric layer

108 source metal layer

109 via array

110P type contact region

111 drain metal layer

S11-S16

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

As in the detailed description of the embodiments of the present invention, the cross-sectional views illustrating the device structures are not partially enlarged in general scale for convenience of illustration, and the schematic views are only examples, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.

For convenience in description, spatial relational terms such as "below," "beneath," "below," "under," "over," "upper," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that these terms of spatial relationship are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the figures. Further, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

In the context of this application, a structure described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed in between the first and second features, such that the first and second features may not be in direct contact.

It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.

The input capacitance of a silicon carbide field effect transistor (SiC MOSFET) affects its switching speed and thus its conduction loss. In the SiC MOSFET structure, in order to reduce the voltage drop effect caused by the lead resistance, a structure in which a source metal is covered over the gate layer 106 is usually adopted to ensure the current conduction capability of the source metal, but the source metal of such a structure introduces an input capacitance in the overlapping region of the source metal and the gate layer 106, thereby causing the switching speed of the SiC MOSFET to be reduced and increasing the conduction loss.

As shown in fig. 1 to 4, the present embodiment provides a silicon carbide semiconductor device including: the transistor comprises an N-type substrate 101, an N-type drift layer 102, a P-type well region 103, an N-type source region 104, a gate dielectric layer 105, a gate layer 106, an isolation dielectric layer 107 and a source metal layer 108.

The above-mentionedThe N-type substrate 101 is an N-type heavily doped silicon carbide (SiC) substrate, and the doping concentration of the N-type substrate 101 can be between 1e19/cm³～9e20/cm³In the meantime. The back surface of the N-type substrate 101 may further include a drain metal layer 111, the drain metal layer 111 forms an ohmic contact with the N-type substrate 101 to reduce a contact resistance, the drain metal layer 111 may be made of Ni or the like, and a thickness of the drain metal layer may be 1 micrometer to 2 micrometers.

The N-type drift layer 102 is located on the N-type substrate 101, and may be an N-type lightly doped silicon carbide (SiC) layer, and the doping concentration of the N-type drift layer 102 may be between 1e14/cm³～1e15/cm³In the meantime.

The P-well 103 is located in the N-drift layer 102. For example, the doping concentration of the P-type well region 103 may be between 1e15/cm³～1e16/cm³In the meantime.

The N-type source region 104 is located in the P-type well region 103 and is wrapped by the P-type well region 103, and the doping concentration of the N-type source region 104 may be between 1e18/cm³～1e19/cm³In the meantime.

The gate dielectric layer 105 at least spans between the N-type source region 104 and the N-type drift layer 102. The gate dielectric layer 105 may be silicon dioxide, and the thickness thereof is between 40 nanometers and 100 nanometers. For example, the gate dielectric layer 105 may have a thickness of 50 nm.

The gate layer 106 is located on the gate dielectric layer 105, and the material of the gate layer 106 may be polysilicon.

The isolation dielectric layer 107 is coated on the gate layer 106, the dielectric constant of the isolation dielectric layer 107 is between 1 and 3, and the thickness of the isolation dielectric layer 107 is between 500 nanometers and 1500 nanometers, so that the insulating property between the source metal layer 108 and the gate layer 106 is ensured. Preferably, the dielectric constant of the isolation dielectric layer 107 is between 1 and 2.5. The isolation dielectric layer 107 may be made of one of fluorine-doped silicon oxide SiOF, carbon-doped silicon oxide SiOC, fluorocarbon FOx, hydrogen silsesquioxane HSQ, methyl silsesquioxane MSQ, a porous dielectric material and a silicon-containing organic material SiLK. Of course, in other embodiments, the thickness and material of the isolation dielectric layer 107 may also be selectively changed according to actual requirements, and are not limited to the examples listed herein. In the invention, a low-k dielectric with a dielectric constant between 1 and 3 is adopted as the isolation dielectric layer 107 between the source metal layer 108 and the gate layer 106, and compared with the case of adopting a dielectric material such as silicon dioxide and the like as the isolation dielectric layer 107, the input capacitance between the source metal layer 108 and the gate layer 106 can be greatly reduced under the condition of the same dielectric thickness, the switching speed of the device is improved, and the conduction loss is reduced.

The source metal layer 108 is in contact with the N-type source region 104 and extends to cover the isolation dielectric layer 107. In this embodiment, the sic semiconductor device further includes a P-type contact region 110, the P-type contact region 110 is connected to the N-type source region 104, and the source metal layer 108 is in contact with the P-type contact region 110 and the N-type source region 104.

Fig. 2 is an enlarged schematic structural diagram of the gate layer 106, the isolation dielectric layer 107 and the source metal layer 108. in the embodiment, the source metal layer 108 on the isolation dielectric layer 107 has a via array 109 penetrating through the source metal layer 108 to reduce the overlapping area between the source metal layer 108 and the gate layer 106. In one embodiment, the via array 109 may be a rectangular hole array to reduce process difficulty and manufacturing cost, as shown in fig. 3, and in another embodiment, the via array 109 may also be a circular hole array to reduce adverse effects caused by metal tip power concentration and improve current conduction stability of the source metal layer 108, as shown in fig. 4. For example, in other embodiments, the via array 109 penetrating the source metal layer 108 is formed in the source metal layer 108 to reduce an overlapping area between the source metal layer 108 and the gate layer 106, so as to reduce an area of an input capacitor between the source metal layer 108 and the gate layer 106, reduce the input capacitor, further improve a switching speed of the device, and reduce conduction loss.

In order to make up for the defect that the through hole array 109 reduces the current conduction capability of the source metal layer 108, the thickness of the source metal layer 108 is set to be between 5 micrometers and 10 micrometers, so that the capability of conducting large current by the source metal layer 108 is ensured. Preferably, the source metal layer 108 includes a first Ti layer, an Al layer, a second Ti layer, a Ni layer, and an Ag layer stacked in sequence, where the first Ti layer has a thickness of 100-300 nm, the Al layer has a thickness of 3-6 microns, the second Ti layer has a thickness of 100-300 nm, the Ni layer has a thickness of 1-3 microns, and the Ag layer has a thickness of 300-1000 nm. For example, in one embodiment, the thickness of the first Ti layer is selected to be 200 nm, the thickness of the Al layer is selected to be 4 μm, the thickness of the second Ti layer is selected to be 200 nm, the thickness of the Ni layer is selected to be 1.5 μm, and the thickness of the Ag layer is selected to be 500 nm.

As shown in fig. 1 to 5, the present embodiment also provides a method for manufacturing a silicon carbide semiconductor device, including the steps of:

as shown in fig. 1 and fig. 5, step 1) is performed to provide an N-type substrate 101 and an N-type drift layer 102 on the N-type substrate 101.

The N-type substrate 101 is an N-type heavily doped silicon carbide (SiC) substrate, and the doping concentration of the N-type substrate 101 can be between 1e19/cm³～9e20/cm³In the meantime.

As shown in fig. 1 and fig. 5, step 2) is performed, and an ion implantation process and an annealing process are performed to form a P-type well region 103 in the N-type drift layer 102. The P-well 103 is located in the N-drift layer 102. For example, the doping concentration of the P-type well region 103 may be between 1e15/cm³～1e16/cm³In the meantime.

As shown in fig. 1 and 5, step 3) is performed to perform an ion implantation process and an annealing process in the P-well 103Forming an N-type source region 104, and forming a P-type contact region 110 in the P-type well region 103, wherein the P-type contact region 110 is connected to the N-type source region 104. The N-type source region 104 is located in the P-type well region 103 and is wrapped by the P-type well region 103, and the doping concentration of the N-type source region 104 may be between 1e18/cm³～1e19/cm³In the meantime.

As shown in fig. 1 and fig. 5, step 4) is then performed to sequentially form a gate dielectric layer 105 and a gate electrode layer 106 on the N-type drift layer 102, and the gate dielectric layer 105 and the gate electrode layer 106 are etched to form the gate dielectric layer 105 and the gate electrode layer 106 at least crossing between the N-type source region 104 and the N-type drift layer 102.

For example, the gate dielectric layer 105 may be formed by a thermal oxidation method, and the material of the gate dielectric layer 105 includes silicon dioxide, and the thickness of the silicon dioxide is between 40 nanometers and 100 nanometers.

For example, the gate layer 106 may be formed by a PECVD or LPCVD process, and the material of the gate layer 106 may be polysilicon.

As shown in fig. 1 and fig. 5, step 5) is then performed to form an isolation dielectric layer 107, where the isolation dielectric layer 107 covers the N-type source region 104 and the gate layer 106, and a dielectric constant of the isolation dielectric layer 107 is between 1 and 3. The thickness of the isolation dielectric layer 107 is between 500 nm and 1500 nm to ensure the insulating property between the source metal layer 108 and the gate layer 106. Preferably, the dielectric constant of the isolation dielectric layer 107 is between 1 and 2.5. The isolation dielectric layer 107 may be made of one of fluorine-doped silicon oxide SiOF, carbon-doped silicon oxide SiOC, fluorocarbon FOx, hydrogen silsesquioxane HSQ, methyl silsesquioxane MSQ, a porous dielectric material and a silicon-containing organic material SiLK. Of course, in other embodiments, the thickness and material of the isolation dielectric layer 107 may also be selectively changed according to actual requirements, and are not limited to the examples listed herein. In the invention, a low-k dielectric with a dielectric constant between 1 and 3 is adopted as the isolation dielectric layer 107 between the source metal layer 108 and the gate layer 106, and compared with the case of adopting a dielectric material such as silicon dioxide and the like as the isolation dielectric layer 107, the input capacitance between the source metal layer 108 and the gate layer 106 can be greatly reduced under the condition of the same dielectric thickness, the switching speed of the device is improved, and the conduction loss is reduced.

As shown in fig. 1 and 5, step 6) is then performed to etch a source via hole in the isolation dielectric layer 107, where the source via hole exposes the N-type source region 104 and the P-type contact region 110, and a source metal layer 108 is deposited on the source via hole and the isolation dielectric layer 107, where the source metal contacts the P-type contact region 110 and the N-type source region 104 and extends to cover the isolation dielectric layer 107.

As shown in fig. 1 to 5, finally, in step 7) S17, the source metal layer 108 on the isolation dielectric layer 107 is etched to form a via array 109 penetrating through the source metal layer 108 in the source metal layer 108, so as to reduce an overlapping area between the source metal layer 108 and the gate layer 106.

Finally, the method also comprises the following steps: a drain metal layer 111 is formed on the back surface of the N-type substrate 101, the drain metal layer 111 forms ohmic contact with the N-type substrate 101 to reduce contact resistance, and the drain metal layer 111 may be made of Ni or the like and may have a thickness of 1 to 2 micrometers.

As described above, the method for manufacturing a silicon carbide semiconductor device according to the present invention has the following advantageous effects:

Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. A silicon carbide semiconductor device, wherein the silicon carbide semiconductor device comprises:

N-type substrate;

An N-type drift layer, located on the N-type substrate;

A P-type well region located in the N-type drift layer;

N-type source region, located in the P-type well region;

a gate dielectric layer, spanning at least between the N-type source region and the N-type drift layer;

a gate layer, located on the gate dielectric layer;

an isolation dielectric layer, covering the gate layer;

A source metal layer, in contact with the N-type source region, and extending over the isolation dielectric layer, the source metal layer on the isolation dielectric layer has a through hole penetrating the source metal layer array to reduce the overlapping area of the source metal layer and the gate layer.

2 . The silicon carbide semiconductor device according to claim 1 , wherein the thickness of the isolation dielectric layer is between 500 nanometers and 1500 nanometers. 3 .

3 . The silicon carbide semiconductor device of claim 1 , wherein the through hole array comprises one of a rectangular hole array and a circular hole array. 4 .

4 . The silicon carbide semiconductor device according to claim 1 , wherein the thickness of the source metal layer is between 5 μm and 10 μm. 5 .

5 . The silicon carbide semiconductor device according to claim 4 , wherein the source metal layer comprises a first Ti layer, an Al layer, a second Ti layer, a Ni layer and an Ag layer stacked in sequence, wherein the The thickness of the first Ti layer is between 100 and 300 nanometers, the thickness of the Al layer is between 3 micrometers and 6 micrometers, the thickness of the second Ti layer is between 100 nanometers and 300 nanometers, and the thickness of the Ni layer is between 100 nanometers and 300 nanometers. The thickness of the Ag layer is between 300 nanometers and 1000 nanometers.

6 . The silicon carbide semiconductor device according to claim 1 , wherein the material of the gate dielectric layer comprises silicon dioxide, and the thickness thereof is between 40 nanometers and 100 nanometers. 7 .

7 . The silicon carbide semiconductor device according to claim 1 , further comprising a P-type contact region, the P-type contact region is connected to the N-type source region, and the source metal layer is connected to the N-type source region. 8 . The P-type contact region and the N-type source region are in contact.