A novel epitaxial structure based on embedded barrier layer and semiconductor power device

Abstract

The application provides a novel epitaxial structure based on an embedded barrier layer and a semiconductor power device, and belongs to the field of semiconductor power device manufacturing. The epitaxial structure comprises an embedded barrier layer arranged above a buffer layer and a stepped gradient AlGaN buffer layer arranged below the buffer layer, the embedded barrier layer is composed of an AlN layer and a graded component back barrier layer, the AlN layer can reduce alloy disorder scattering of a two-dimensional electron gas possibly caused by the back barrier, and then improve electron mobility, and the adoption of the graded component back barrier layer can inhibit the buffer layer traps and avoid the generation of a parasitic channel. The added stepped gradient AlGaN buffer layer comprises four or more stepped gradient AlGaN layers which are sequentially grown, the Al component gradually decreases from the bottom layer to the top layer, the lowermost layer is close to AlN, and the uppermost layer is close to GaN, so that the GaN crystal quality grown thereon is better, and the internal traps of the buffer layer can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor power device manufacturing, and specifically relates to a novel epitaxial structure and semiconductor power device based on an embedded barrier layer. Background Technology

[0002] With the development of global power electronics technology, high-frequency, high-power power electronic devices have become a research and application hotspot. Gallium nitride (GaN), as a typical representative of third-generation wide-bandgap semiconductor materials, possesses excellent electrical properties and is an ideal material for manufacturing high-frequency, high-power devices. Especially in the field of power electronic converters, GaN-based high electron mobility transistors (HEMTs) are considered one of the most promising devices due to their low on-resistance, high switching speed, and good thermal stability.

[0003] In existing device structure designs, such as Figure 7 As shown, 650V GaN HEMTs, primarily based on silicon (Si) devices, have been commercialized as core components of power electronic converters. Electron trapping in the buffer layer is the dominant mechanism for 2DEG (two-dimensional electron gas) depletion and current degradation. When the GaN HEMT is turned off, the high electric field in the vertical direction causes electrons to overcome the potential barrier between the AlN nucleation layer and the Si substrate through thermal excitation, injecting into the buffer layer and being trapped by acceptor traps, thus affecting the 2DEG conductivity. The trapping process of hole traps (or the release of acceptor traps) also alleviates 2DEG depletion. Simultaneously, charge transport and redistribution within the buffer layer also cause changes in the 2DEG depletion boundary, leading to dynamic resistance degradation.

[0004] In a single heterojunction structure, GaN acts as both a buffer layer and a channel layer, which can cause some 2DEGs to overflow from the channel into the buffer layer, resulting in reduced flexibility and reliability. The most direct way to enhance the confinement of 2DEGs in the heterojunction and suppress carrier overflow into the buffer layer is to use a back barrier, which constitutes a double heterojunction structure. However, introducing a back barrier structure at the same time can generate unnecessary parasitic channels.

[0005] Therefore, a novel epitaxial structure and a novel GaN HEMT device structure are needed to solve the above problems. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a novel epitaxial structure based on an embedded barrier layer, wherein the epitaxial structure comprises an embedded barrier layer disposed above a buffer layer and a stepped gradient AlGaN buffer layer disposed below the buffer layer.

[0007] The embedded barrier layer includes a gradient component back barrier layer and an AlN layer disposed above the gradient component back barrier layer, wherein the gradient component in the gradient component back barrier layer grows from 0 to 0.1 in a specific direction.

[0008] Furthermore, the epitaxial structure, from bottom to top, includes a substrate, a nucleation layer, a stepped gradient AlGaN buffer layer, a buffer layer, a gradient composition back barrier layer, an AlN layer, a UID GaN layer, an AlN insertion layer, and an intrinsic AlGaN barrier layer.

[0009] Furthermore, the gradient component in the gradient component back barrier layer increases from 0 to 0.1 in a specific direction as follows:

[0010] The graded component in the back barrier layer increases from 0 to 0.1 from near the AlN layer to far away from the AlN layer; or,

[0011] The gradient component in the back barrier layer increases from 0 to 0.1 in the direction from near the upper side of the buffer layer to away from the buffer layer.

[0012] Furthermore, the structural formula of the gradient component back barrier layer is Al. X Ga 1-X N or In X Ga 1-X N;

[0013] The gradient component is either Al or In, and x = 0-0.1.

[0014] Furthermore, the thickness of the AlN layer is 0.7-1 nm.

[0015] Furthermore, the stepped gradient AlGaN buffer layer comprises four or more stepped gradient AlGaN layers grown sequentially upwards.

[0016] In the stepped gradient AlGaN layer, the content of Al component decreases from the bottom layer to the top layer, with the bottom layer being close to AlN and the top layer being close to GaN.

[0017] Furthermore, the substrate comprises one of silicon carbide, sapphire, silicon, and gallium nitride.

[0018] Furthermore, the nucleation layer comprises one or more combinations of gallium nitride, aluminum nitride, and aluminum gallium nitride.

[0019] Furthermore, the buffer layer doping elements include one or more combinations of silicon, magnesium, carbon, iron, and indium.

[0020] On the other hand, the present invention proposes a semiconductor power device with high electron mobility, which is obtained by forming a passivation layer, ohmic contacts, gate and source / drain ohmic metal electrodes, and a cap layer on the novel epitaxial structure based on the embedded barrier layer.

[0021] Furthermore, the material of the passivation layer includes any one of Si3N4, AlN, Al2O3, and SiO2;

[0022] The metal conductive material of the gate includes one or more combinations of platinum, iridium, nickel, gold, molybdenum, palladium, selenium, beryllium, TiN, and polycrystalline silicon;

[0023] The source and drain ohmic metal electrodes include one or more combinations of titanium, aluminum, nickel, gold, platinum, iridium, molybdenum, tantalum, niobium, cobalt, zirconium, and tungsten.

[0024] The beneficial effects of this invention are:

[0025] This invention incorporates an embedded barrier layer between the UID GaN layer and the buffer layer to suppress the trapping of 2DEG by electron traps in the buffer layer, thereby inhibiting the dynamic resistance degradation of the device. The embedded barrier layer consists of an AlN layer and a gradient-component back barrier layer. The AlN layer reduces the alloy disorder scattering that may occur in the two-dimensional electron gas due to the back barrier, thus improving electron mobility. Replacing the fixed-component back barrier layer with a gradient-component back barrier layer allows for modulation of the gradient composition from 0 to 0.1 in a specific direction, suppressing buffer layer traps while avoiding the formation of parasitic channels. Furthermore, this invention adds a stepped-gradient AlGaN buffer layer above the nucleation layer. This stepped-gradient AlGaN buffer layer comprises four or more sequentially grown stepped-gradient AlGaN layers, with the Al composition gradually decreasing from the bottom to the top, the bottom layer approaching AlN, and the top layer approaching GaN. This stepped design results in better GaN crystal quality and reduces traps within the buffer layer.

[0026] This invention employs an embedded barrier layer technique in the epitaxial layer to control carrier distribution and suppress the dynamic resistance decay caused by the electron trapping effect of the buffer layer, thereby improving device performance.

[0027] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The diagram shows the structure of the novel epitaxial structure based on an embedded barrier layer proposed in this embodiment of the invention.

[0030] Figure 2 This invention illustrates the energy band diagrams of a novel epitaxial structure based on an AlGaN embedded barrier layer and a conventional epitaxial layer, as proposed in this embodiment of the invention.

[0031] Figure 3 A schematic diagram of the layer structure of a GaN HEMT device with a fixed back barrier layer in the prior art is shown.

[0032] Figure 4 A schematic diagram of the layer structure of a GaNHEMT device with only a gradient (decreasing from top to bottom) back barrier layer in an embodiment of the present invention is shown.

[0033] Figure 5 This diagram illustrates the layer structure of a GaN HEMT device with only a gradient (from top to bottom) back barrier layer, as shown in an embodiment of the present invention.

[0034] Figure 6 This diagram illustrates the layer structure of a GaN HEMT device with only a stepped AlGaN buffer layer in an embodiment of the present invention.

[0035] Figure 7 A schematic diagram of the structure of 650V GaN-on-Si in the prior art is shown. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention proposes a novel epitaxial structure based on an embedded barrier layer, such as... Figure 1As shown, the novel epitaxial layer structure comprises, from bottom to top: a substrate, a nucleation layer, a stepped gradient AlGaN buffer layer, a buffer layer, an embedded barrier layer, a UID GaN layer, an AlN insertion layer, and an intrinsic AlGaN barrier layer.

[0038] The embedded barrier layer comprises, from bottom to top, a gradient component back barrier layer and an AlN layer. The gradient component in the gradient component back barrier layer is Al or In, and the gradient component in the gradient component back barrier layer increases from 0 to 0.1 in the direction from near the AlN layer to away from the AlN layer; or, the gradient component in the gradient component back barrier layer increases from 0 to 0.1 in the direction from near the upper side of the buffer layer to away from the buffer layer.

[0039] The substrate serves as the support and foundation for the entire device and can provide a stable crystal structure. The substrate material includes, but is not limited to, any one of silicon carbide, sapphire, silicon, and gallium nitride.

[0040] The nucleation layer is one or more thin films grown between the substrate and the epitaxial layer during the epitaxial growth process of the semiconductor. It can improve lattice matching, reduce stress, and provide nucleation centers. This invention does not impose specific limitations on the nucleation layer material. For example, due to the good lattice matching and excellent thermal conductivity between AlN and GaN, the nucleation layer material can be selected from one or a combination of two or more of aluminum nitride, gallium nitride, and aluminum gallium nitride.

[0041] AlGaN buffer layers are typically located on GaN substrates to reduce the electric field intensity inside transistors, thereby improving device reliability and performance. In this invention, the AlGaN buffer layer is designed in a stepped gradient form. The stepped gradient AlGaN buffer layer comprises four or more stepped gradient AlGaN layers grown sequentially, with the Al composition decreasing from bottom to top, i.e., the bottom layer is close to AlN and the top layer is close to GaN.

[0042] The buffer layer is doped with one or more of silicon, magnesium, carbon, iron, and indium. The buffer layer reduces the stress caused by the lattice constant difference between the stepped AlGaN buffer layer and the embedded AlGaN barrier layer, reduces the formation of dislocations and defects, and provides a smoother interface, which is beneficial for the growth of the gradient-component back barrier layer, thereby improving the overall performance of the heterojunction structure. By adjusting the material composition and thickness of the buffer layer, the band structure of the heterojunction structure can be further fine-tuned, optimizing device performance parameters such as threshold voltage and transconductance.

[0043] The gradient composition back barrier layer consists of a lower gradient composition back barrier layer and an upper AlN layer; the AlN layer can reduce the possible alloy disorder scattering of the two-dimensional electron gas by the back barrier, thereby improving electron mobility. In an exemplary embodiment of the present invention, the general structural formula of the gradient composition back barrier layer is Alx Ga 1-x N or In x Ga 1-x N(x=0-0.1), the gradient components Al and In in the back barrier layer near the AlN layer and near the upper side of the buffer layer are 0 (i.e., X). min =0), gradually increasing to 0.1 (i.e., X) away from the AlN thin layer and the upper side of the buffer layer. max =0.1), this setting can suppress buffer layer traps while avoiding the generation of parasitic channels.

[0044] It should be noted that the growth method of the gradient component back barrier layer is not limited in this invention. For example, it can be achieved by epitaxial techniques such as metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0045] The AlN layer is disposed above the layer with the gradient composition, serving as part of the embedded barrier layer. Combined with the intentionally doped layer with the gradient composition, it can further improve device performance. In this embodiment, the thickness of the AlN layer is 0.7-1 nm.

[0046] The UID GaN layer can be used as a channel layer. Since it is undoped, it has a high carrier mobility, which is beneficial for the high-speed transport of electrons in the channel.

[0047] The intrinsic AlGaN barrier layer is used to form a two-dimensional electron gas: In HEMT devices, the heterojunction interface formed between the AlGaN barrier layer and the GaN channel layer can induce a high concentration of two-dimensional electron gas.

[0048] The following description, in conjunction with the accompanying drawings, provides an exemplary illustration of the structure of the embedded barrier layer and the stepped gradient AlGaN buffer layer in an embodiment of the present invention.

[0049] Figure 2 The diagram illustrates the energy band structure of the epitaxial structure with an embedded AlGaN barrier layer and a conventional epitaxial structure according to an embodiment of the present invention. The left side shows the energy band diagram of the epitaxial structure with the embedded AlGaN barrier layer, and the right side shows the energy band diagram of the conventional GaN epitaxial layer. It can be seen that the embedded AlGaN barrier layer can form an energy barrier. A higher barrier can reduce leakage current under reverse bias and improve the blocking capability of the device. Simultaneously, the presence of the barrier helps restrict the movement of electrons in the buffer layer, thereby suppressing the influence of non-uniformly distributed donor and acceptor traps in the buffer layer on the dynamic resistance decay.

[0050] Figure 3 This illustrates the layer structure of a GaN HEMT device with a fixed back barrier layer in the prior art, wherein the back barrier layer is Al. 0.1 Ga 0.9While a fixed-composition back barrier layer can improve the conduction band of the GaN buffer layer relative to the GaN channel, enhance carrier confinement, reduce buffer trapping effects, and improve high-frequency performance, the introduced fixed-composition back barrier layer can affect the growth quality of GaN and lead to the generation of unnecessary parasitic channels at the AlGaN / GaN buffer interface.

[0051] In one exemplary embodiment of the present invention, Figure 4 The following diagram illustrates the layer structure of a GaN HEMT device with a gradient Al composition (decreasing from top to bottom) back barrier layer. The AlN layer is not shown in the diagram. The Al composition transitions from 0.1 to 0 from top to bottom. Specifically, the Al composition of the gradient AlGaN back barrier layer near the GaN main channel (i.e., the UID GaN layer in the diagram) is 0.1, gradually decreasing to 0 towards the direction away from the GaN main channel. By introducing a gradient composition back barrier, the electron confinement in the channel can be effectively enhanced, thereby improving the device performance. Furthermore, the polarization gradient in the back barrier can reduce the 2DEG concentration in the parasitic channel and mitigate the adverse effects of the channel, which is beneficial for improving the electronic performance of the device.

[0052] In other embodiments of the present invention, the gradient AlGaN back barrier layer may also be a gradient InGaN back barrier layer.

[0053] For example, the gradient AlGaN back barrier layer can be Al from top to bottom. 0.1 Ga 0.9 N, Al 0.08 Ga 0.92 N, Al 0.05 Ga 0.95 N, GaN; Al 0.1 Ga 0.9 N, Al 0.07 Ga 0.93 N, Al 0.06 Ga 0.94 N, Al 0.08 Ga 0.92 N, GaN; the gradient InGaN back barrier layer can be In from top to bottom. 0.1 Ga 0.9 N、In 0.08 Ga 0.92 N、In 0.05 Ga 0.95 N, GaN.

[0054] In one exemplary embodiment of the present invention, Figure 5The following diagram illustrates the layer structure of a GaN HEMT device with a gradient Al composition (increasing from top to bottom) back barrier layer. The AlN layer is not shown in the figure. The Al composition transitions from 0 to 0.1 from top to bottom. The Al composition of the gradient AlGaN back barrier layer is 0 near the GaN main channel side, gradually increasing to 0.1 towards the direction away from the GaN main channel. The addition of the gradient composition back barrier structure enhances the gate control capability of the HEMT device, significantly reduces leakage current, and further improves the current collapse effect, thereby significantly improving the device's breakdown voltage and power characteristics. However, the depletion effect of the back barrier layer causes a slight decrease in the device's output characteristics, and the frequency characteristics of the device also decrease due to increased scattering and parasitic effects.

[0055] In other embodiments of the present invention, the gradient AlGaN back barrier layer may also be a gradient InGaN back barrier layer.

[0056] For example, the gradient AlGaN back barrier layer can be GaN, Al, or Al from top to bottom. 0.01 Ga 0.99 N, Al 0.05 Ga 0.95 N, Al 0.06 Ga 0.94 N, Al 0.1 Ga 0.9 N; GaN, Al 0.02 Ga 0.98 N, Al 0.04 Ga 0.96 N, Al 0.08 Ga 0.92 N, Al 0.1 Ga 0.9 N; the gradient InGaN back barrier layer can be GaN, In, or other materials from top to bottom. 0.01 Ga 0.99 N、In 0.05 Ga 0.95 N、In 0.06 Ga 0.94 N、In 0.1 Ga 0.9 N.

[0057] In an exemplary embodiment of the present invention, the structure of the stepped gradient AlGaN buffer layer is as follows: Figure 6As shown, by increasing the Al composition on the nucleation layer, four stepped AlGaN layers are grown sequentially from the bottom to the top. The Al composition decreases continuously from bottom to top, with the bottom layer approaching AlN and the top layer approaching GaN. This gradually reduces the stress and strain in the epitaxial layer, which can effectively improve the surface morphology and crystal quality of the GaN buffer layer, reduce the leakage current of the buffer layer, and make the GaN crystal grown on it of better quality, while reducing the number of traps inside the buffer layer.

[0058] In an exemplary embodiment of the present invention, a semiconductor power device with high electron mobility based on a novel epitaxial structure with an embedded barrier layer is proposed. The device is obtained by forming a passivation layer, ohmic contacts, gate and source / drain ohmic metal electrodes, and a cap layer on the novel epitaxial structure using conventional processes.

[0059] The semiconductor power device can be a transistor, diode, or thyristor.

[0060] The passivation layer can be a high-quality Si3N4, AlN, Al2O3, or SiO2 thin film grown on the surface of the novel epitaxial structure using chemical vapor deposition (CVD) technology. The material of the passivation layer is any one of Si3N4, AlN, Al2O3, or SiO2.

[0061] Ohmic contacts can be formed using techniques such as electron beam evaporation (E-beam evaporation) and physical vapor deposition (PVD). Multiple layers of metal thin films are deposited on the semiconductor surface, and these metal layers react with each other through processes such as annealing to form low-resistance ohmic contacts. For example, in GaN HEMT devices, a commonly used ohmic contact metal combination is Ti / Al / Ni / Au, where Ti reacts with GaN to form TiN, creating a tunneling contact.

[0062] The gate and source / drain ohmic electrode cap layers can also be formed by depositing multilayer metals. The specific metal combination and process parameters may vary depending on the device type and performance requirements.

[0063] Gate metal conductive materials include one or more combinations of platinum, iridium, nickel, gold, molybdenum, palladium, selenium, beryllium, TiN, and polysilicon. For example, in GaN HEMT devices, the gate metal is usually a metal with a high work function (such as Ni / Au) to prevent the GaN depletion layer under the gate from spreading.

[0064] The source and drain ohmic metal electrodes include one or more alloys of titanium, aluminum, nickel, gold, platinum, iridium, molybdenum, tantalum, niobium, cobalt, zirconium, and tungsten.

[0065] Compared to conventional enhancement-mode devices, the enhanced GaN MOSHEMT obtained using the novel epitaxial structure can effectively suppress dynamic resistance degradation and improve device performance.

[0066] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A novel epitaxial structure based on an embedded barrier layer, characterized in that, The epitaxial structure, from bottom to top, includes a substrate, a nucleation layer, a stepped gradient AlGaN buffer layer, a buffer layer, a gradient composition back barrier layer, an AlN layer, a UID GaN layer, an AlN insertion layer, and an intrinsic AlGaN barrier layer. The general structural formula of the gradient component back barrier layer is Al. x Ga 1-x N or In x Ga 1-x N; x=0-0.1, the gradient components Al and In in the back barrier layer near the AlN layer and near the top of the buffer layer are 0, and gradually increase to 0.1 away from the AlN thin layer and the top of the buffer layer.

2. The novel epitaxial structure based on an embedded barrier layer according to claim 1, characterized in that, The thickness of the AlN layer is 0.7-1 nm.

3. The novel epitaxial structure based on an embedded barrier layer according to claim 1, characterized in that, The stepped gradient AlGaN buffer layer comprises four or more stepped gradient AlGaN layers grown sequentially upwards. In the stepped gradient AlGaN layer, the content of Al component decreases sequentially from the bottom layer to the top layer, with the bottom layer being close to AlN and the top layer being close to GaN.

4. The novel epitaxial structure based on an embedded barrier layer according to claim 1, characterized in that, The substrate includes one of silicon carbide, sapphire, silicon, and gallium nitride.

5. The novel epitaxial structure based on an embedded barrier layer according to claim 1, characterized in that, The nucleation layer includes one or more combinations of gallium nitride, aluminum nitride, and aluminum gallium nitride.

6. The novel epitaxial structure based on an embedded barrier layer according to claim 1, characterized in that, The buffer layer doping elements include one or more combinations of silicon, magnesium, carbon, iron, and indium.

7. A semiconductor power device with high electron mobility, characterized in that, The device is obtained by forming a passivation layer, an ohmic contact, a gate and source / drain ohmic metal electrodes, and a cap layer on a novel epitaxial structure based on an embedded barrier layer as described in any one of claims 1-6.

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