Method of forming a trench with a single-sided sloped sidewall and device

Abstract

The present application relates to a kind of trench forming method and device with one side of sidewall inclined.The method comprises: preparing the required trench in the SiC substrate;The trench protection mask is filled in the above-mentioned trench, and the trench protection mask on the front main surface of SiC substrate is selectively masked and etched to obtain the inclined sidewall etching window located at one outer side of trench;The above-mentioned SiC substrate is inclined and placed on the inclined body, and the front main surface of SiC substrate is dry etched using inclined sidewall etching window to obtain the inclined sidewall formed by the trench after etching, and the trench protection mask is removed, wherein, after removing the trench protection mask, the sidewall of the trench protected by the trench protection film is vertical surface, and the other sidewall of the trench is the inclined sidewall.The present application can effectively prepare the trench with one side of sidewall inclined on SiC substrate, improve the channel mobility of SiC device, and is compatible with existing process.

Description

Method and device for forming a groove with unilaterally inclined sidewall Technical Field

[0001] This invention relates to a method and apparatus for forming a trench, and more particularly to a method and apparatus for forming a trench with a single-sided inclined sidewall. Background Technology

[0002] After more than 30 years of development, the performance of power devices using Si substrates has approached the limits of Si materials. With the development of new power electronics applications such as electric vehicles, photovoltaics, wind power, and smart grids, there is an urgent need for power electronic devices to be upgraded in terms of performance. Compared with similar Si devices, wide-bandgap semiconductor SiC power electronic devices have higher turn-off voltage, an order of magnitude lower on-resistance, higher operating frequency, and higher power density.

[0003] Silicon carbide (SiC) is a wide bandgap semiconductor material that can be used to fabricate power devices. SiC power devices are suitable for high-frequency, high-voltage, and high-temperature applications and help improve the efficiency and power density of power electronic systems.

[0004] After SiC MOSFETs are fabricated by direct dry oxidation of silicon carbide, the channel mobility is very low, and even annealing processes offer limited improvement. Furthermore, the channel mobility varies depending on the silicon carbide crystal plane, as the silicon carbide / silicon oxide interface state density differs after oxidation.

[0005] Planar SiC MOSFETs are typically fabricated on the Si {0001} plane, resulting in a channel mobility of around 20. Devices fabricated on the {11-20} plane have a channel mobility of around 80, and those on the {0-33-8} plane have around 90. The {11-20} plane is perpendicular to the {0001} plane, and the {0-33-8} plane forms an angle of approximately 54.7 degrees with the {0001} plane.

[0006] When fabricating trench-type SiC devices, the process is extremely difficult if the sidewalls of the trench fall on the {0-33-8} plane. If only one sidewall of the trench falls on the {0-33-8} plane and the other side is a vertical plane, the process becomes even more difficult. Therefore, how to fabricate trenches with unilaterally tilted sidewalls on SiC substrates is a problem that urgently needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and device for forming trenches with one side inclined on one side. This method can effectively prepare trenches with one side inclined on one side on SiC substrates, improve the channel mobility of SiC devices, and is compatible with existing processes.

[0008] According to the technical solution provided by the present invention, a method for forming a groove with a unilaterally inclined sidewall is provided, the method comprising:

[0009] A SiC substrate is provided, and trench etching is performed on the positive main surface of the SiC substrate to prepare the desired trench within the SiC substrate;

[0010] A trench protection mask is filled in the trench, wherein the trench protection mask filled in the trench also covers the front main surface of the SiC substrate.

[0011] The trench protection mask on the main surface of the SiC substrate is selectively masked and etched to obtain an inclined sidewall etching window located on the outer side of the trench. The inclined sidewall etching window exposes the main surface of the SiC substrate corresponding to the inclined sidewall etching window, and the edge of the inclined sidewall etching window adjacent to the trench corresponds to one sidewall of the adjacent trench.

[0012] The SiC substrate is tilted and placed on an inclined surface. The front main surface of the SiC substrate is dry etched using the inclined sidewall etching window to obtain the inclined sidewall that forms the trench after etching. The inclined sidewall falls on the {0-33-8} surface of the SiC substrate. One end of the inclined sidewall is connected to the bottom of the trench, and the other end of the inclined sidewall is connected to the front main surface of the SiC substrate.

[0013] Remove the aforementioned trench protective mask, wherein, for the trench after removing the trench protective mask, one side wall of the trench protected by the trench protective film is a vertical plane, and the other side wall of the trench is the aforementioned inclined side wall.

[0014] The angle between the inclined sidewall and the main surface of the SiC substrate is β, wherein the angle β is 53°~60°.

[0015] For the inclined plane, the included angle of the inclined plane is . ,in,

[0016] The back face of the SiC substrate is placed on the inclined surface of the inclined body, and the included angle of the inclined surfaces of the inclined body is... It is 90-β.

[0017] When dry etching is performed on the front main surface of a SiC substrate using an inclined sidewall etching window, the dry etching process includes:

[0018] When fabricating trenches within a SiC substrate, the trench fabrication process includes: dry etching using an inductively coupled plasma etching machine, wherein the etching gas comprises SF6 and O2, or CF4 and O2, wherein...

[0019] The etching source power of the inductively coupled plasma etching machine is 1000W~1300W, the bias power is 100W~250W, and the chamber pressure is 0.34Pa~1Pa.

[0020] When SF6 and O2 are used as etching gases, the flow rate of SF6 is 100 sccm~120 sccm and the flow rate of O2 is 5 sccm~15 sccm.

[0021] When CF4 and O2 are used as etching gases, the flow rate of CF4 is 100 sccm to 120 sccm and the flow rate of O2 is 5 sccm to 15 sccm.

[0022] Deposit trench etching masks on the positive main surface of the SiC substrate;

[0023] The trench etching mask is selectively masked and etched to obtain a trench etching window that penetrates the trench etching mask;

[0024] The positive main surface of the SiC substrate is etched using the aforementioned trench etching window to obtain a trench after etching.

[0025] The trench protection mask and the trench etching mask are made of the same material, or the trench protection mask and the trench etching mask are made of the same material with the same removal process.

[0026] Trench etching masks include dielectric thin films or metal thin films, wherein,

[0027] The trench protection mask is deposited and filled within the trench, covering the front main surface of the SiC substrate.

[0028] For dielectric thin films, including silicon oxide thin films or aluminum oxide thin films;

[0029] For metal thin films, including nickel thin films or chromium thin films.

[0030] The depth of the trench is 1.5μm to 3μm.

[0031] The SiC substrate includes a conductive substrate, a buffer layer fabricated on the conductive substrate, and an epitaxial layer fabricated on the buffer layer, wherein,

[0032] The upper surface of the epitaxial layer forms the positive main surface of the SiC substrate, and the deviation angle between the upper surface of the epitaxial layer and the {000-1} surface of the SiC substrate is α, wherein the deviation angle α is not greater than 5°.

[0033] A device having a single-sided inclined groove on the sidewall, the device comprising the single-sided inclined groove on the sidewall, wherein the single-sided inclined groove on the sidewall is prepared by the forming method described above.

[0034] Advantages of the present invention: The trench is elongated and has one side wall that is vertical and the other side wall that is inclined. The inclined side wall is obtained by using a sloping body and dry etching of the SiC substrate. The prepared trench can be used to prepare trench gate SiC MOSFET devices. The devices can obtain high channel mobility and are compatible with existing processes. Attached Figure Description

[0035] Figures 1-9 are cross-sectional views of the process steps for forming a trench according to an embodiment of the present invention, wherein...

[0036] Figure 1 is a cross-sectional view of the SiC substrate of the present invention.

[0037] Figure 2 is a cross-sectional view of the trench etching mask prepared according to the present invention.

[0038] Figure 3 is a cross-sectional view of the trench etching window prepared according to the present invention.

[0039] Figure 4 is a cross-sectional view of the trench obtained by etching using the trench etching window according to the present invention.

[0040] Figure 5 is a cross-sectional view of the trench protective mask prepared according to the present invention.

[0041] Figure 6 is a cross-sectional view of the inclined sidewall etched window prepared according to the present invention.

[0042] Figure 7 is a cross-sectional view of the present invention placed on an inclined plane.

[0043] Figure 8 is a cross-sectional view of the inclined sidewall obtained according to the present invention.

[0044] Figure 9 is a cross-sectional view of the single-sided inclined groove on the sidewall prepared according to the present invention.

[0045] Explanation of reference numerals in the attached figures: 101-conductive substrate, 102-buffer layer, 103-epitaxy layer, 104-trench etching mask, 105-trench etching window, 106-trench, 107-first sidewall of the trench, 108-second sidewall of the trench, 109-bottom wall of the trench, 110-etching window of the inclined sidewall, 111-inclined body, 112-inclined sidewall, 113-trench protective mask. Detailed Implementation

[0046] The present invention will be further described below with reference to specific accompanying drawings and embodiments.

[0047] To effectively fabricate trenches with one side inclined, thereby improving the channel mobility of SiC devices, in one embodiment of the present invention, the trench formation method includes:

[0048] A SiC substrate is provided, and trench etching is performed on the positive main surface of the SiC substrate to prepare the desired trench 106 in the SiC substrate;

[0049] A trench protection mask 113 is filled in the trench 106, wherein the trench protection mask 113 filled in the trench 106 also covers the front main surface of the SiC substrate.

[0050] The trench protection mask 113 on the main surface of the SiC substrate is selectively masked and etched to obtain an inclined sidewall etching window 110 located on the outer side of the trench 106. The inclined sidewall etching window 110 exposes the main surface of the SiC substrate corresponding to the inclined sidewall etching window 110, and the edge of the inclined sidewall etching window 110 adjacent to the trench 106 corresponds to one sidewall of the adjacent trench 106.

[0051] The SiC substrate is tilted and placed on the inclined body 111. The main surface of the SiC substrate is dry etched using the inclined sidewall etching window 110 to obtain the inclined sidewall 112 forming the trench 106 after etching. The inclined sidewall 112 falls on the {0-33-8} surface of the SiC substrate. One end of the inclined sidewall 112 is connected to the bottom of the trench 106, and the other end of the inclined sidewall 112 is connected to the main surface of the SiC substrate.

[0052] Remove the aforementioned trench protective mask 113. For the trench 106 after removing the trench protective mask 113, one side wall of the trench 106 protected by the trench protective mask 113 is vertical, and the other side wall of the trench is the aforementioned inclined side wall 112.

[0053] Specifically, the SiC substrate can adopt commonly used forms. Figure 1 shows an embodiment of the SiC substrate. In Figure 1, the SiC substrate includes a conductive substrate 101, a buffer layer 102 prepared on the conductive substrate, and an epitaxial layer 103 prepared on the buffer layer 102.

[0054] The upper surface of the epitaxial layer 103 forms the positive main surface of the SiC substrate, and the deviation angle between the upper surface of the epitaxial layer 103 and the {000-1} surface of the SiC substrate is α, wherein the deviation angle α is not greater than 5°.

[0055] Generally, the conductive substrate 101, buffer layer 102, and epitaxial layer 103 have the same conductivity type. The SiC substrate generally has two corresponding main surfaces, which are called the front main surface and the back main surface. The front main surface is formed by the surface of the epitaxial layer 103, and the back main surface is formed by the corresponding surface of the conductive substrate 101. The {000-1} surface of the SiC substrate is the surface on which the back main surface of the conductive substrate 101 is formed.

[0056] For the SiC substrate, the trench etching process commonly used in this technical field can be used to prepare all the trenches 106. The trench opening of the trench 106 is located on the positive main surface of the SiC substrate. The depth of the trench 106 is 1.5μm~3μm. The trench 106 is located in the epitaxial layer 103. The trench depth of the trench 106 is generally less than the thickness of the epitaxial layer 103.

[0057] Figures 2-4 illustrate one embodiment of the fabrication of trench 106. Specifically, when fabricating trench 106 in a SiC substrate, the trench 106 fabrication process includes:

[0058] A trench etching mask 104 is deposited on the positive main surface of the SiC substrate;

[0059] The trench etching mask 104 is selectively masked and etched to obtain a trench etching window 105 that penetrates the trench etching mask;

[0060] The positive main surface of the SiC substrate is etched using the aforementioned trench etching window 105 to obtain trench 106 after etching.

[0061] In Figure 2, the trench etching mask 104 is deposited on the epitaxial layer 103, that is, the trench etching mask 104 covers the epitaxial layer 103. The trench etching mask 104 can be deposited on 103 using existing commonly used deposition processes. The specific deposition process can be selected according to actual needs, so as to meet the requirements of preparing the trench etching mask 104.

[0062] In specific implementation, the trench etching mask 104 includes a dielectric thin film or a metal thin film. For dielectric thin films, it includes a silicon oxide thin film or an aluminum oxide thin film; for metal thin films, it includes a nickel thin film or a chromium thin film. The type of trench etching mask 104 can be selected according to actual needs, ensuring that it can be used to perform trench etching on the SiC substrate.

[0063] In Figure 3, photoresist is spin-coated onto the trench etching mask 104 and photolithography is performed. The photoresist is used to selectively mask and etch the trench etching mask 104 to obtain a trench etching window 105 after etching. The trench etching window 105 is used to expose the surface of the epitaxial layer 103 that corresponds to the trench etching window 105.

[0064] In Figure 4, trench etching is performed on the epitaxial layer 103 using the trench etching window 105, thereby obtaining the trench 106. The depth of the trench 106 is h. The trench 106 is an elongated trench. The trench 106 has a first sidewall 107 and a second sidewall 108, wherein both the first sidewall 107 and the second sidewall 108 are vertical surfaces.

[0065] After the trench 106 is fabricated, a trench protection mask 113 is fabricated. The trench protection mask 113 fills the trench 106 and covers the surface of the epitaxial layer 103, as shown in Figure 5. To simplify the process, i.e., to avoid removing the trench etching mask 104 before fabricating the trench mask 113, the trench protection mask 113 and the trench etching mask 104 are made of the same material, or the trench protection mask 113 and the trench etching mask 104 are made of materials with the same removal process. Specifically, choosing materials with the same removal process for the trench protection mask 113 and the trench etching mask 104 means that in subsequent removal processes, both the trench protection mask 113 and the trench etching mask 104 can be removed simultaneously.

[0066] In a specific implementation, the trench protection mask 113 is deposited and filled within the trench 106 and covers the front main surface of the SiC substrate. The trench protection mask 113 can be prepared using existing commonly used deposition processes. The specific type and conditions of the deposition process can be selected as needed, with the aim of successfully preparing the trench protection mask 113.

[0067] In Figure 6, after the trench protection mask 113 is prepared, the trench protection mask 113 on the main surface of the SiC substrate is selectively masked and etched to obtain the inclined sidewall etching window 110 located on the outer side of the trench 106. The method of preparing the inclined sidewall etching window 110 can be referred to the description of the trench etching window 105 above.

[0068] In Figure 6, the inclined sidewall etching window 110 penetrates the trench protective mask 113 directly corresponding to the inclined sidewall etching window 110. At this time, the inclined sidewall etching window 110 exposes the positive main surface of the SiC substrate directly corresponding to the inclined sidewall etching window 110. The inclined sidewall etching window 110 is located only on one side of the trench 106. The edge of the inclined sidewall etching window 110 adjacent to the trench 106 corresponds directly to one sidewall of the adjacent trench 106, that is, the downward projection of the inclined sidewall etching window 110 contacts the sidewall of the trench 106. In Figure 6, the width of the inclined sidewall etching window 110 is x.

[0069] In Figure 7, the SiC substrate is placed at an angle on the inclined surface 111. The inclined surface 111 has an inclined plane, and the conductive substrate 101 of the SiC substrate is in contact with the inclined plane of the inclined surface 111. The included angle between the inclined surfaces of the inclined surface 111 and the inclined surface of the inclined surface 111 is... The included angle of the inclined plane is the angle between the inclined plane of the inclined plane 111 and the bottom surface of the inclined plane 111.

[0070] Dry etching is performed on the front main surface of the SiC substrate using an inclined sidewall etching window 110 to obtain an inclined sidewall 112 forming the trench 106 after etching. The inclined sidewall 112 lies on the {0-33-8} plane of the SiC substrate, with one end connected to the bottom of the trench 106 and the other end connected to the front main surface of the SiC substrate. In a specific implementation, the projection length of the inclined sidewall 112 toward the conductive substrate 101 is x.

[0071] When dry etching is performed on the front main surface of a SiC substrate using the inclined sidewall etching window 110, the dry etching process includes: dry etching using an inductively coupled plasma (ICP) etching machine, wherein the etching gas includes SF6 and O2, or CF4 and O2, wherein...

[0072] The etching source power of the inductively coupled plasma etching machine is 1000W~1300W, the bias power is 100W~250W, and the chamber pressure is 0.34Pa~1Pa.

[0073] When SF6 and O2 are used as etching gases, the flow rate of SF6 is 100 sccm~120 sccm and the flow rate of O2 is 5 sccm~15 sccm.

[0074] When CF4 and O2 are used as etching gases, the flow rate of CF4 is 100 sccm to 120 sccm and the flow rate of O2 is 5 sccm to 15 sccm.

[0075] In practical implementation, the inductively coupled plasma etching (ICP) machine is a commonly used dry etching device, and its specific features are consistent with existing methods. During etching, when SF6 and O2 are used as the etching gases, the preferred flow rate ratio of SF6 to O2 is 16:1. Similarly, when CF4 and O2 are used as the etching gases, the preferred flow rate ratio of CF4 to O2 is 16:1.

[0076] In Figure 8, the angle between the inclined sidewall 112 and the front main surface of the SiC substrate is β, where the angle β is 53°~60°. That is, the angle between the inclined sidewall 112 and the surface of the epitaxial layer 103 is β. For the inclined body 111 supporting the SiC substrate, the back main surface of the SiC substrate is placed on the inclined surface of the inclined body 111, and the angle between the inclined surfaces of the inclined body is... It is 90-β.

[0077] In practical implementation, when it is necessary for the inclined sidewall 112 to fall on the {0-33-8} plane of the SiC substrate, the range of values ​​for the included angle β can be determined. At this time, based on the value of the included angle β, the included angle of the inclined surface 111 can be obtained. .

[0078] In Figure 9, based on the materials of the trench protection mask 113 and the trench etching mask 104, appropriate removal processes are employed to simultaneously remove both the trench protection mask 113 and the trench etching mask 104, thereby forming the desired trench 106 with a single-sided inclined sidewall. The trench protection mask 113 and the trench etching mask 104 are generally removed using a wet process. The specific removal process conditions and procedures can be selected according to actual needs, ensuring that both the trench protection mask 113 and the trench etching mask 104 can be removed simultaneously.

[0079] In Figure 9, the sidewall corresponding to the first sidewall 107 of the above-mentioned trench is protected by the trench protection mask 113 during the above-mentioned etching. At this time, the first sidewall 107 of the trench is still a vertical surface. After the second sidewall 108 of the trench is etched, it forms an inclined sidewall 112.

[0080] Furthermore, a device with a single-sided inclined groove can be obtained, the device including a single-sided inclined groove 106, wherein the single-sided inclined groove 106 is prepared by the forming method described above.

[0081] Specifically, the device can be a common power device such as a SiC MOSFET, and the type of device can be selected according to actual needs. The device includes at least the trench 106 mentioned above. The specific fabrication process of the trench 106 can be found in the above description and will not be repeated here.

Claims

1. A method for forming a groove with a unilaterally inclined sidewall, characterized in that, The trench formation method includes: providing a SiC substrate and performing trench etching on the positive main surface of the SiC substrate to prepare a desired trench within the SiC substrate; filling the trench with a trench protection mask, wherein the trench protection mask filled within the trench also covers the positive main surface of the SiC substrate; selectively masking and etching the trench protection mask on the positive main surface of the SiC substrate to obtain a sloping sidewall etching window located on one outer side of the trench, wherein the sloping sidewall etching window exposes the positive main surface of the SiC substrate corresponding to the sloping sidewall etching window, and the sloping sidewall etching window is adjacent to the edge of the trench. The SiC substrate is tilted and placed on a sloping surface. The main surface of the SiC substrate is dry-etched using the etch window of the tilted sidewall to form the tilted sidewall of the trench. The tilted sidewall falls on the {0-33-8} surface of the SiC substrate. One end of the tilted sidewall is connected to the bottom of the trench, and the other end is connected to the main surface of the SiC substrate. The trench protection mask is removed. After the trench protection mask is removed, the sidewall of the trench protected by the trench protection film is vertical, and the other sidewall of the trench is the tilted sidewall.

2. The method for forming a groove with a unilaterally inclined sidewall according to claim 1, characterized in that: The angle between the inclined sidewall and the main surface of the SiC substrate is β, wherein the angle β is 53°~60°.

3. The method for forming a groove with a unilaterally inclined sidewall according to claim 2, characterized in that: For the inclined plane, the included angle of the inclined plane is . In this case, the back face of the SiC substrate is placed on the inclined surface of the inclined plane, and the included angle of the inclined plane is... It is 90-β.

4. The method for forming a groove with a unilaterally inclined sidewall according to any one of claims 1 to 3, characterized in that, When dry etching is performed on the front main surface of a SiC substrate using an inclined sidewall etching window, the dry etching process includes: dry etching using an inductively coupled plasma etching machine, with etching gases including SF6 and O2, or CF4 and O2. The etching source power of the inductively coupled plasma etching machine is 1000W~1300W, the bias power is 100W~250W, and the chamber pressure is 0.34Pa~1Pa. When SF6 and O2 are used as etching gases, the SF6 flow rate is 100sccm~120sccm, and the O2 flow rate is 5sccm~15sccm; when CF4 and O2 are used as etching gases, the CF4 flow rate is 100sccm~120sccm, and the O2 flow rate is 5sccm~15sccm.

5. The method for forming a groove with a unilaterally inclined sidewall according to any one of claims 1 to 3, characterized in that, When fabricating trenches in a SiC substrate, the trench fabrication process includes: depositing a trench etching mask on the positive main surface of the SiC substrate; selectively masking and etching the trench etching mask to obtain a trench etching window that extends through the trench etching mask; and using the trench etching window to etch the positive main surface of the SiC substrate to obtain a trench after etching.

6. The method for forming a groove with a unilaterally inclined sidewall according to claim 5, characterized in that, The trench protection mask and the trench etching mask are made of the same material, or the trench protection mask and the trench etching mask are made of the same material with the same removal process. The trench etching mask includes a dielectric thin film or a metal thin film, wherein the trench protection mask is deposited and filled in the trench and covers the positive main surface of the SiC substrate.

7. The method for forming a groove with a unilaterally inclined sidewall according to claim 6, characterized in that, For dielectric thin films, including silicon oxide thin films or aluminum oxide thin films; For metal thin films, including nickel thin films or chromium thin films.

8. The method for forming a groove with a unilaterally inclined sidewall according to any one of claims 1 to 3, characterized in that, The depth of the trench is 1.5μm to 3μm.

9. The method for forming a groove with a unilaterally inclined sidewall according to any one of claims 1 to 3, characterized in that, The SiC substrate includes a conductive substrate, a buffer layer prepared on the conductive substrate, and an epitaxial layer prepared on the buffer layer. The upper surface of the epitaxial layer forms the positive main surface of the SiC substrate, and the deviation angle between the upper surface of the epitaxial layer and the {000-1} surface of the SiC substrate is α, wherein the deviation angle α is not greater than 5°.

10. A device having a single-sided inclined groove on its sidewall, characterized in that, The device includes a groove with one side inclined, wherein the groove with one side inclined is prepared by the forming method according to any one of claims 1 to 9.

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