Nitrogen-polar GaN HEMT devices based on diamond substrates and their fabrication methods

Abstract

This invention discloses a nitrogen-polar GaN HEMT device based on a diamond substrate and its fabrication method. The device includes: a diamond substrate; and SiN... x Layer, located on a diamond substrate; inverted "T" shaped gate electrode, including lateral and longitudinal structures, the lateral structure located on SiN x Inner layer; AlGaN barrier layer, located within SiN x The device comprises a GaN channel layer, with the vertical structure located within the AlGaN barrier layer; an AlN insertion layer, located on the AlGaN barrier layer; a GaN channel layer, located on the AlN insertion layer, wherein the gallium polar facet of the GaN channel layer contacts the AlN insertion layer; and source and drain electrodes, located at both ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer, wherein the nitrogen polar facet of the GaN channel layer is exposed. This invention places the gate electrode on the back side of the nitrogen-polar GaN-based HEMT device, improving gate control capability and further enhancing the device's frequency characteristics.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a nitrogen-polar GaN HEMT device based on a diamond substrate and its fabrication method. Background Technology

[0002] Gallium nitride (GaN), as a third-generation wide-bandgap semiconductor material, possesses advantages such as high breakdown electric field, high electron mobility, and high electron saturation velocity. Thanks to these advantages, gallium nitride high electron mobility transistors (HEMTs) have significant advantages in radio frequency, microwave, and other fields requiring high power and high frequency.

[0003] Compared with traditional gallium-polar GaN-based HEMT devices, nitrogen-polar GaN-based HEMT devices have the following unique advantages: (1) greater ability to scale down device size and potential for radio frequency applications; (2) easier formation of low-resistance ohmic contacts; (3) stronger gate control capability; and (4) effective suppression of short-channel effects. They have great potential for application in high-power microwave transistors, CMOS logic gates, and ultra-high-speed digital signal integrated circuits and systems. However, in nitrogen-polar GaN / AlGaN / GaN heterostructures, due to the opposite polarization direction to gallium polarity, 2DEG is easily formed at the GaN / AlGaN interface. This means that in nitrogen-polar GaN-based HEMT devices, the contact between the electrode metal and the channel layer does not need to pass through the AlGaN barrier layer, which greatly reduces the ohmic contact resistance. However, the gate electrode metal can form a leakage path with the GaN channel, and the ion bombardment during the etching process can damage the nitrogen-polar GaN channel. Therefore, a gate dielectric is usually required to reduce leakage between the GaN channel and the gate electrode, and to reduce damage to the GaN channel during the etching process.

[0004] However, this increases the distance between the gate electrode and the GaN channel, which weakens the gate control capability and thus affects the frequency characteristics of the device. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a nitrogen-polar GaN HEMT device based on a diamond substrate and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] In a first aspect, embodiments of the present invention provide a nitrogen-polar GaN HEMT device based on a diamond substrate, the device comprising:

[0007] Diamond substrate;

[0008] SiNx A layer located on the diamond substrate;

[0009] The inverted "T" shaped gate electrode includes a lateral structure and a longitudinal structure, wherein the lateral structure is located on the SiN x Inside the layer;

[0010] AlGaN barrier layer, located in the SiN x The vertical structure is located on the AlGaN barrier layer;

[0011] An AlN insertion layer is located on the AlGaN barrier layer;

[0012] A GaN channel layer is located on the AlN insertion layer; wherein the gallium polar surface of the GaN channel layer is in contact with the AlN insertion layer;

[0013] The source and drain electrodes are located at both ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer; wherein the nitrogen polarity surface of the GaN channel layer is exposed.

[0014] In one embodiment of the present invention, the lateral structure of the inverted "T"-shaped gate electrode is located in the SiN x The depth within the layer is less than that of the SiN x Half the thickness of the layer.

[0015] In one embodiment of the present invention, the depth of the longitudinal structure of the inverted "T"-shaped gate electrode within the AlGaN barrier layer is greater than half the thickness of the AlGaN barrier layer.

[0016] In one embodiment of the present invention, the SiN x The thickness of the layer is 20nm to 50nm.

[0017] In one embodiment of the present invention, the thickness of the AlGaN barrier layer is 15nm to 50nm.

[0018] In one embodiment of the present invention, the thickness of the GaN channel layer is 100nm to 300nm.

[0019] Secondly, embodiments of the present invention provide a method for fabricating a nitrogen-polar GaN HEMT device based on a diamond substrate, the fabrication method comprising:

[0020] Obtaining Si substrates;

[0021] A GaN buffer layer is grown on the Si substrate;

[0022] A GaN channel layer is grown on the GaN buffer layer; wherein the gallium polarity surface of the GaN channel layer is exposed.

[0023] An AlN insertion layer is grown on the gallium polar surface of the GaN channel layer;

[0024] An AlGaN barrier layer is grown on the AlN insertion layer;

[0025] The middle region of the AlGaN barrier layer is etched to form a gate groove, and gate metal is deposited in the gate groove and on the AlGaN barrier layer on both sides to form a "T"-shaped gate electrode.

[0026] SiN is grown on the "T"-shaped gate electrode and the AlGaN barrier layer. x layer;

[0027] In the SiN x Diamond substrates are grown on the layer;

[0028] The device is flipped, and the Si substrate and the GaN buffer layer are etched away; wherein, after flipping, the "T"-shaped gate electrode becomes an inverted "T"-shaped gate electrode, and after etching, the nitrogen polarity surface of the GaN channel layer is exposed;

[0029] The nitrogen polar surface of the GaN channel layer at both ends of the device is etched, and a source electrode and a drain electrode are formed on the remaining nitrogen polar surface of the GaN channel layer at both ends of the device, wherein the source electrode and the drain electrode are not in contact with the AlN insertion layer.

[0030] In one embodiment of the present invention, a GaN channel layer is grown on the GaN buffer layer, comprising:

[0031] A GaN channel layer with a thickness of 100 nm to 300 nm is grown on the GaN buffer layer.

[0032] In one embodiment of the present invention, the depth of the etched gate groove is greater than half the thickness of the AlGaN barrier layer.

[0033] In one embodiment of the present invention, the thickness of the gate metal deposited on the AlGaN barrier layer is smaller than that of the SiN barrier layer. x Half the thickness of the layer.

[0034] The beneficial effects of this invention are:

[0035] This invention proposes a novel nitrogen-polarized GaN HEMT device based on a diamond substrate. It innovatively places the gate electrode on the back side of the device, avoiding the problem in conventional GaN-based HEMT devices where the gate dielectric is used to reduce leakage between the GaN channel and the gate electrode, which increases the distance between the gate electrode and the GaN channel and weakens gate control capability. Furthermore, by growing the source / drain electrodes and the gate electrode on opposite sides of the heterojunction, ohmic contact resistance is reduced, and contact between the gate electrode metal and the GaN channel layer is avoided. Simultaneously, the gate dielectric layer is eliminated, improving gate control capability and further enhancing the device's frequency characteristics. Moreover, the excellent thermal conductivity and mechanical stability of the diamond substrate effectively reduce the device temperature and provide good thermal management, improving device reliability and robustness and reducing the impact of thermal effects on device performance. In summary, the device structure proposed in this invention has greater application potential in high-power microwave transistors, CMOS logic gates, and ultra-high-speed digital signal integrated circuits and systems.

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the process of a nitrogen-polar GaN HEMT device based on a diamond substrate provided in an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of a fabrication method for a nitrogen-polar GaN HEMT device based on a diamond substrate provided in an embodiment of the present invention;

[0039] Figures 3a to 3g This is a schematic diagram of the fabrication process of the nitrogen-polar GaN HEMT device based on a diamond substrate provided in this embodiment of the invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0041] Due to the inherent properties of GaN HEMTs, severe localized self-heating effects may occur in the conductive channel. This effect increases with the increase of device power density. Currently, most nitride substrates use silicon-based and sapphire materials, which have poor thermal conductivity. This inability to dissipate large amounts of heat in a timely manner limits the performance of gallium nitride devices and further compromises reliability. To address this issue, existing methods provide nitrogen-polar GaN-based HEMT device structures based on diamond substrates. First, diamond has the highest thermal conductivity of all bulk materials, and integrating diamond films with GaN-based HEMT devices as substrates or packages has been shown to enhance heat extraction during device operation, thereby significantly reducing junction temperature and increasing the maximum power density that GaN-based HEMT devices can safely handle. Second, using a method of epitaxial growth of gallium-polar GaN material followed by inversion to form nitrogen polarity avoids many problems associated with directly growing nitrogen-polar GaN, thus improving device performance. However, for nitrogen-polar GaN-based HEMT devices, not only self-heating effects need to be considered, but also gate control capabilities to better improve the device's frequency characteristics. To address the aforementioned needs, this invention proposes a nitrogen-polar GaN HEMT device based on a diamond substrate and its fabrication method.

[0042] Firstly, please see Figure 1 This invention provides a nitrogen-polar GaNHEMT device based on a diamond substrate, the device comprising:

[0043] Diamond substrate;

[0044] SiN x A layer located on a diamond substrate;

[0045] The inverted "T" shaped gate electrode includes a lateral structure and a longitudinal structure, with the lateral structure located in SiN. x Inside the layer;

[0046] AlGaN barrier layer, located on SiN x The vertical structure is located within the AlGaN barrier layer;

[0047] An AlN insertion layer is located on an AlGaN barrier layer;

[0048] A GaN channel layer is located on an AlN insertion layer; wherein the gallium polar facet of the GaN channel layer is in contact with the AlN insertion layer.

[0049] The source and drain electrodes are located at both ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer; the nitrogen polarity surface of the GaN channel layer is exposed.

[0050] In this embodiment of the invention, the thickness of the diamond substrate is 50 μm to 200 μm; SiNx The layer thickness is 20nm to 50nm, SiN x For example, the layer can be Si3N4; the AlGaN barrier layer thickness is 15nm–50nm; the AlN insertion layer thickness is 1nm–2nm; the GaN channel layer thickness is 100nm–300nm; the source and drain electrodes can be made of Ti / Al / Ni / Au, and the source and drain electrodes are made of... Figure 1 Schematic diagram of black filling within the GaN channel layer; the material of the inverted "T" gate electrode can be Ni / Au, and the lateral structure of the inverted "T" gate electrode is within the SiN... x The depth within the layer is less than that of SiN x Half the thickness of the layer, preferably a lateral structure in SiN x The depth within the layer is 5nm to 20nm. The depth of the vertical structure of the inverted "T" gate electrode within the AlGaN barrier layer is greater than half the thickness of the AlGaN barrier layer. Preferably, the depth of the vertical structure within the AlGaN barrier layer is 10nm to 40nm.

[0051] In summary, the nitrogen-polar GaN HEMT device based on a diamond substrate proposed in this invention innovatively places the gate electrode on the back side of the nitrogen-polar GaN-based HEMT device. This avoids the problem in conventional nitrogen-polar GaN-based HEMT devices where reducing leakage between the GaN channel and gate electrode through the gate dielectric increases the distance between the gate electrode and the GaN channel, leading to weakened gate control capability. Furthermore, by growing the source / drain electrodes and the gate electrode on opposite sides of the heterojunction, ohmic contact resistance is reduced, and contact between the gate electrode metal and the GaN channel layer is avoided. Simultaneously, the gate dielectric layer is not required, improving gate control capability and further enhancing the device's frequency characteristics. Moreover, the excellent thermal conductivity and mechanical stability of the diamond substrate effectively reduce the device temperature and provide good thermal management, which improves the device's reliability and durability, reducing the impact of thermal effects on device performance. In conclusion, the device structure proposed in this invention has greater application potential in high-power microwave transistors, CMOS logic gates, and ultra-high-speed digital signal integrated circuits and systems.

[0052] Secondly, please see Figure 2 This invention provides a method for fabricating a nitrogen-polar GaNHEMT device based on a diamond substrate. The fabrication method includes:

[0053] S10, Obtain the Si substrate.

[0054] The embodiments of the present invention are not limited to Si substrates; the obtained substrates can also be sapphire substrates, etc.

[0055] S20. Grow a GaN buffer layer on a Si substrate.

[0056] In this embodiment of the invention, a GaN buffer layer with a thickness of 500 nm to 2000 nm is grown on a Si substrate using MOCVD (Metal-organic Chemical Vapor Deposition) technology.

[0057] S30. A GaN channel layer is grown on the GaN buffer layer; wherein the gallium polarity surface of the GaN channel layer is exposed.

[0058] In this embodiment of the invention, a GaN channel layer with a thickness of 100 nm to 300 nm is grown on a GaN buffer layer using the MOCVD process, at which time the nitrogen polarity surface of the GaN channel layer is exposed.

[0059] S40. An AlN insertion layer is grown on the gallium polar surface of the GaN channel layer.

[0060] In this embodiment of the invention, an AlN insertion layer with a thickness of 1 nm to 2 nm is grown on the gallium polar surface of the GaN channel layer using the MOCVD process.

[0061] S50. An AlGaN barrier layer is grown on the AlN insertion layer.

[0062] In this embodiment of the invention, an AlGaN barrier layer with a thickness of 15 nm to 50 nm is grown on an AlN insertion layer using the MOCVD process.

[0063] Finally, the device structure obtained by S10 to S50 in this embodiment of the invention is as follows: Figure 3a As shown, existing epitaxial structures, such as those shown in 3a, can also be obtained directly.

[0064] S60. The middle region of the AlGaN barrier layer is etched to form a gate groove, and gate metal is deposited in the gate groove and on the AlGaN barrier layer on both sides to form a "T"-shaped gate electrode.

[0065] In this embodiment of the invention, an ICP (Inductively Coupled Plasma) process is used to etch the middle region of the AlGaN barrier layer to form a gate groove. At this time, it is necessary to ensure that the depth of the vertical structure of the inverted "T"-shaped gate electrode within the AlGaN barrier layer is greater than half the thickness of the AlGaN barrier layer, that is, the depth of the etched gate groove is greater than half the thickness of the AlGaN barrier layer. Preferably, the depth of the etched gate groove is 10nm to 40nm, that is, the preferred depth of the vertical structure within the AlGaN barrier layer is 10nm to 40nm. Then, an electron beam evaporation process is used to deposit gate metal, such as Ni / Au, within the gate groove and on the AlGaN barrier layer on both sides, forming a "T"-shaped gate electrode. Figure 3b As shown.

[0066] It should be noted that when etching the AlGaN barrier layers to form gate trenches, the depth of the gate trenches is controllable. This can be used to create conventional depletion-mode GaN-based HEMT devices, or to form deep gate trenches to deplete the two-dimensional electron gas in the GaN channel layer below the gate electrode, thereby realizing enhancement-mode GaN-based HEMT devices and improving switching performance and operating frequency.

[0067] S70. SiN is grown on the "T"-shaped gate electrode and the AlGaN barrier layer. x layer.

[0068] In this embodiment of the invention, SiN with a thickness of 20 nm to 50 nm is grown on a T-shaped gate electrode and an AlGaN barrier layer using PECVD (Plasma Enhanced Chemical Vapor Deposition) technology. x Layers Figure 3c As shown, at this time, it is necessary to ensure that the "T" type gate electrode is in SiN x The depth within the layer is less than that of SiN x Half the thickness of the layer, meaning the thickness of the gate metal deposited on the AlGaN barrier layer is less than that of the SiN layer. x The thickness of the layer is half of the total thickness, preferably 5 nm to 20 nm for the gate metal deposited on the AlGaN barrier layer, which is preferably a "T"-shaped gate electrode on SiN. x The depth within the layer is 5nm to 20nm. This invention relates to SiN... x The purpose of layer growth is to prevent hydrogen ion etching used in subsequent diamond substrate growth from damaging the underlying epitaxial layer.

[0069] S80, in SiN x A diamond substrate is grown on the layer.

[0070] This invention employs MPCVD (Microwave Plasma Chemical Vapor Deposition) technology on SiN x For example, a diamond substrate with a thickness of 50 μm to 200 μm is grown on Si3N4. Figure 3d As shown, diamond substrates can increase the thermal conductivity and mechanical stability of devices, which helps to reduce temperature and improve the power handling capability of devices.

[0071] S90. The device is flipped and the Si substrate and GaN buffer layer are etched away; after the flip, the "T" gate electrode becomes an inverted "T" gate electrode, and the nitrogen polarity surface of the GaN channel layer is exposed after etching.

[0072] In this embodiment of the invention, the device obtained in S80 is first flipped as follows: Figure 3e As shown, the Si substrate and GaN buffer layer are then etched away as follows. Figure 3f As shown, specifically: the Si substrate can be removed using wet etching or dry etching; if a sapphire substrate is used, it can be removed using laser; and the GaN buffer layer can be precisely etched using ICP (Inductively Coupled Plasma) technology. At this point, the "T"-shaped gate electrode becomes an inverted "T"-shaped gate electrode, and the nitrogen polarity surface of the GaN channel layer is exposed.

[0073] S100: Etch the nitrogen polar surface of part of the GaN channel layer at both ends of the device, and form source and drain electrodes on the remaining nitrogen polar surface of the GaN channel layer at both ends of the device, and the source and drain electrodes are not in contact with the AlN insertion layer.

[0074] In this embodiment of the invention, the nitrogen polarity surfaces of a portion of the GaN channel layer at both ends of the device obtained by ICP etching at S90 are used, i.e., the etching depth is less than the thickness of the GaN channel layer. Ohmic metals such as Ti / Al / Ni / Au are deposited on the remaining nitrogen polarity surfaces of the GaN channel layer at both ends of the device to form source and drain electrodes, without contacting the AlN insertion layer. Figure 3g As shown.

[0075] In summary, the fabrication method of the nitrogen-polar GaN HEMT device based on a diamond substrate provided by this invention innovatively places the gate electrode on the back side of the nitrogen-polar GaN-based HEMT device. By first growing the Ga-polar GaN channel layer and then flipping it to form the N-polar GaN channel layer, it is possible to grow the gate electrode first and then form the nitrogen-polar GaN channel layer. This avoids the leakage problem between the GaN channel layer and the gate electrode that conventional nitrogen-polar GaN-based HEMT devices rely on the gate dielectric to reduce leakage, resulting in better gate control capability. By etching a groove gate on the gallium polar side of the GaN channel layer, the damage to the nitrogen polar side of the GaN channel layer by ion bombardment during the etching process is avoided, effectively reducing the on-resistance and leakage current of the device, thereby reducing energy loss and improving switching speed, and thus improving the efficiency of the device. After growing the gallium polar GaN wafer, the diamond substrate is replaced. The diamond substrate has good thermal conductivity and mechanical stability, which can effectively reduce the device temperature and provide good thermal management, which will improve the reliability and durability of the device and reduce the impact of thermal effects on performance.

[0076] As for the second aspect of the preparation method embodiment, since it is basically similar to the first aspect of the device structure embodiment, the description is relatively simple. For relevant details, please refer to the description of the first aspect of the device structure embodiment.

[0077] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0078] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the specification and accompanying drawings, will understand and implement other variations of the disclosed embodiments in carrying out the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. While certain measures are described in different embodiments, this does not mean that these measures cannot be combined to produce good results.

[0079] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A nitrogen-polar GaN HEMT device based on a diamond substrate, characterized in that, The device includes: Diamond substrate; SiN x A layer located on the diamond substrate; The inverted "T" shaped gate electrode includes a lateral structure and a longitudinal structure, wherein the lateral structure is located on the SiN x Inside the layer; AlGaN barrier layer, located in the SiN x The vertical structure is located on the AlGaN barrier layer; An AlN insertion layer is located on the AlGaN barrier layer; A GaN channel layer is located on the AlN insertion layer; wherein the gallium polar surface of the GaN channel layer is in contact with the AlN insertion layer; The source and drain electrodes are located at both ends of the device, embedded in the GaN channel layer and not in contact with the AlN insertion layer; wherein the nitrogen polarity surface of the GaN channel layer is exposed.

2. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that, The lateral structure of the inverted "T" shaped gate electrode in the SiN x The depth within the layer is less than that of the SiN x Half the thickness of the layer.

3. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that, The longitudinal structure of the inverted "T"-shaped gate electrode has a depth greater than half the thickness of the AlGaN barrier layer within the AlGaN barrier layer.

4. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that, The SiN x The thickness of the layer is 20nm to 50nm.

5. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that, The thickness of the AlGaN barrier layer is 15nm to 50nm.

6. The nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 1, characterized in that, The thickness of the GaN channel layer is 100nm to 300nm.

7. A method for fabricating a nitrogen-polar GaN HEMT device based on a diamond substrate, characterized in that, The preparation method includes: Obtaining Si substrates; A GaN buffer layer is grown on the Si substrate; A GaN channel layer is grown on the GaN buffer layer; wherein the gallium polarity surface of the GaN channel layer is exposed. An AlN insertion layer is grown on the gallium polar surface of the GaN channel layer; An AlGaN barrier layer is grown on the AlN insertion layer; The middle region of the AlGaN barrier layer is etched to form a gate groove, and gate metal is deposited in the gate groove and on the AlGaN barrier layer on both sides to form a "T"-shaped gate electrode. SiN is grown on the "T"-shaped gate electrode and the AlGaN barrier layer. x layer; In the SiN x Diamond substrates are grown on the layer; The device is flipped, and the Si substrate and the GaN buffer layer are etched away; wherein, after flipping, the "T"-shaped gate electrode becomes an inverted "T"-shaped gate electrode, and after etching, the nitrogen polarity surface of the GaN channel layer is exposed; The nitrogen polar surface of the GaN channel layer at both ends of the device is etched, and a source electrode and a drain electrode are formed on the remaining nitrogen polar surface of the GaN channel layer at both ends of the device, wherein the source electrode and the drain electrode are not in contact with the AlN insertion layer.

8. The method for fabricating a nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 7, characterized in that, Growing a GaN channel layer on the GaN buffer layer includes: A GaN channel layer with a thickness of 100 nm to 300 nm is grown on the GaN buffer layer.

9. The method for fabricating a nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 7, characterized in that, The depth of the gate groove formed by etching is greater than half the thickness of the AlGaN barrier layer.

10. The method for fabricating a nitrogen-polar GaN HEMT device based on a diamond substrate according to claim 7, characterized in that, The thickness of the gate metal deposited on the AlGaN barrier layer is smaller than that of the SiN layer. x Half the thickness of the layer.

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