Novel epitaxial structure based on embedded barrier layer and semiconductor power device

Abstract

The invention 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 step gradient AlGaN buffer layer arranged below the buffer layer, the embedded barrier layer is composed of an AlN layer and a gradient component back barrier layer, the AlN layer can reduce alloy disordered scattering possibly generated by the back barrier to two-dimensional electron gas, the electron mobility is further improved, and the performance of the epitaxial structure is improved. By adopting the gradient component back barrier layer, the trap of the buffer layer is inhibited, and meanwhile, the generation of a parasitic channel is avoided. The added step gradient AlGaN buffer layer comprises four or more step gradient AlGaN layers growing in sequence, the Al component is gradually reduced from the bottom layer to the top layer, the lowest layer is close to AlN, the uppermost layer is close to GaN, the GaN crystal growing on the AlGaN buffer layer can be better in quality, and traps in the buffer layer can be reduced.

Description

Technical Field

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

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

[0003] In the existing device structure design, such as Figure 7 As shown in the figure, 650V GaN HEMT, which is mainly based on silicon (Si) devices, has been commercialized as a core component of power electronic converters. Among them, electron capture in the buffer layer is the dominant mechanism of 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 barrier between the AlN nucleation layer and the Si substrate through thermal excitation, inject into the buffer layer and be captured by the acceptor trap, thereby affecting the 2DEG conductivity, and the capture of hole traps (or release of acceptor traps) will also alleviate the depletion of 2DEG. At the same time, the charge transfer and redistribution inside the buffer layer will also cause changes in the 2DEG depletion boundary, resulting in dynamic resistance decay.

[0004] GaN is both a buffer layer and a channel layer in a single heterojunction structure, which causes a portion of 2DEG to overflow from the channel to the buffer layer, resulting in reduced flexibility and reliability. The most direct way to enhance the heterojunction 2DEG confinement and suppress the overflow of carriers to the buffer layer is to use a back barrier, which constitutes a double heterojunction structure, but the introduction of a back barrier structure at the same time will produce unnecessary parasitic channels.

[0005] Therefore, it is necessary to propose a new epitaxial structure and a new GaN HEMT device structure to solve the above problems. Summary of the invention

[0006] In view of the above problems, on the one hand, the present 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 graded composition back barrier layer and an AlN layer disposed above the graded composition back barrier layer, and the graded composition in the graded composition back barrier layer increases from 0 to 0.1 in a specific direction.

[0008] Furthermore, the epitaxial structure includes, from bottom to top, a substrate, a nucleation layer, a step-gradient AlGaN buffer layer, a buffer layer, a graded 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 composition in the graded composition back barrier layer increases from 0 to 0.1 from the direction close to the AlN layer to the direction far away from the AlN layer; or,

[0011] The graded composition in the graded composition back barrier layer increases from 0 to 0.1 from the direction close to the upper side of the buffer layer to the direction away from the buffer layer.

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

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

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

[0015] Further, the step-gradient AlGaN buffer layer comprises four or more step-gradient AlGaN layers grown sequentially upward;

[0016] The content of the Al component in the stepped gradient AlGaN layer 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 includes one of silicon carbide, sapphire, silicon and gallium nitride.

[0018] Furthermore, the nucleation layer includes 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, an ohmic contact, a gate and source-drain ohmic metal electrodes, and a cap layer on the novel epitaxial structure based on the embedded barrier layer.

[0021] Further, 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 polysilicon;

[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] Beneficial effects of the present invention:

[0025] The present invention sets an embedded barrier layer between the UID GaN layer and the buffer layer, which can inhibit the capture of 2DEG by the electronic traps in the buffer layer, thereby inhibiting the dynamic resistance decay of the device. The embedded barrier layer of the present invention is composed of an AlN layer and a gradient component back barrier layer, wherein the AlN layer can reduce the alloy disorder scattering that may be generated by the back barrier to the two-dimensional electron gas, thereby improving the electron mobility; and the gradient component back barrier layer is used to replace the fixed component back barrier layer, and the gradient component can be modulated to grow from 0 to 0.1 in a specific direction, while suppressing the buffer layer traps and avoiding the generation of parasitic channels. In addition, the present invention adds a step-gradient AlGaN buffer layer on the nucleation layer, and the step-gradient AlGaN buffer layer includes four or more step-gradient AlGaN layers grown in sequence, and the Al component gradually decreases from the bottom layer to the top layer, the bottom layer is close to AlN, and the top layer is close to GaN. The stepped design can make the GaN crystals grown thereon better quality and reduce the internal traps of the buffer layer.

[0026] The present invention can control carrier distribution and suppress dynamic resistance decay caused by the electron trap capture effect of the buffer layer by adopting the embedded barrier layer technology of the epitaxial layer, thereby improving device performance.

[0027] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A structural diagram showing a novel epitaxial structure based on an embedded barrier layer proposed in an embodiment of the present invention is shown;

[0030] Figure 2 The schematic diagram of the energy bands of the novel epitaxial structure based on the AlGaN embedded barrier layer and the conventional epitaxial layer proposed in the embodiment of the present invention is shown;

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

[0032] Figure 4 A schematic diagram of the layer structure of a GaN HEMT device having only a back barrier layer with a gradual composition change (decreasing from top to bottom) in an embodiment of the present invention is shown;

[0033] Figure 5 A schematic diagram of the layer structure of a GaN HEMT device having only a back barrier layer with a gradual composition change (increasing from top to bottom) in an embodiment of the present invention is shown;

[0034] Figure 6 A schematic diagram of the layer structure of a GaN HEMT device having only a step-gradient AlGaN buffer layer in an embodiment of the present invention is shown;

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

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The present invention proposes a novel epitaxial structure based on an embedded barrier layer, such as Figure 1As shown, the novel epitaxial layer structure includes from bottom to top: a substrate, a nucleation layer, a step-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] Among them, the embedded barrier layer includes a gradient component back barrier layer and an AlN layer from bottom to top, 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 from close to 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 from close to the upper side of the buffer layer to away from the buffer layer.

[0039] The substrate is the support and foundation of 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 a layer or layers of thin film grown between the substrate and the epitaxial layer during the epitaxial growth of the semiconductor, which can improve lattice matching, reduce stress, and provide nucleation centers. The present invention does not impose specific restrictions 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] The AlGaN buffer layer is generally located on the GaN substrate to reduce the electric field strength inside the transistor and improve the reliability and performance of the device. In the present invention, the AlGaN buffer layer is designed in a step gradient form. The step gradient AlGaN buffer layer includes four or more step gradient AlGaN layers grown in sequence, and the Al component decreases continuously from bottom to top, that is, the bottom layer is close to AlN, and the top layer is close to GaN.

[0042] The buffer layer doping element is one or a combination of two or more of silicon, magnesium, carbon, iron, and indium. The setting of the buffer layer can reduce the stress caused by the lattice constant difference between the step gradient AlGaN buffer layer and the embedded AlGaN barrier layer, reduce the formation of dislocations and defects, and provide a smoother interface, which is conducive to the growth of the gradient component back barrier layer, thereby improving the performance of the entire 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 to optimize the performance parameters of the device, such as threshold voltage, transconductance, etc.

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

[0044] It should be noted that the present invention does not limit the growth method of the graded composition back barrier layer, and it can be achieved, for example, by epitaxial techniques such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0045] The AlN layer is disposed on the layer with graded composition as part of the embedded barrier layer and used in combination with the graded composition intentionally doped layer to further improve the performance of the device. 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 not doped, its carrier mobility is relatively high, which is conducive to the high-speed transmission of electrons in the channel.

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

[0048] The structures of the embedded barrier layer and the step-gradient AlGaN buffer layer in the embodiments of the present invention are exemplarily described below with reference to the accompanying drawings.

[0049] Figure 2 The energy band diagram of the epitaxial structure with an embedded AlGaN barrier layer and the traditional epitaxial structure in the embodiment of the present invention is shown, wherein the left side is the energy band diagram of the epitaxial structure with an embedded AlGaN barrier layer, and the right side is the energy band diagram of the traditional GaN epitaxial layer. It can be seen that the embedded AlGaN barrier layer can form an energy barrier, and a higher barrier can reduce the leakage current during reverse bias and improve the blocking ability of the device. At the same time, the presence of the barrier helps to limit the movement of electrons in the buffer layer, thereby suppressing the influence of the non-uniform spatial distribution of donor traps and acceptor traps in the buffer layer on the dynamic resistance decay.

[0050] Figure 3 The layer structure of a GaN HEMT device with a back barrier layer of fixed composition in the prior art is shown, wherein the back barrier layer is Al 0.1 Ga 0.9N barrier layer and fixed-component back barrier layer can improve the conduction band of GaN buffer layer relative to GaN channel, improve carrier confinement, reduce buffer capture effect, and enhance high-frequency performance. However, the introduction of fixed-component back barrier layer will affect the growth quality of GaN and will cause unnecessary parasitic channels to be generated at the AlGaN / GaN buffer interface.

[0051] In an exemplary embodiment of the present invention, Figure 4 The layer structure of the back barrier layer GaN HEMT device with a gradient component Al (decreasing from top to bottom) is used as an example for explanation. The AlN layer is not shown in the figure. The Al component transitions from 0.1 to 0 from top to bottom, where the Al component of the gradient AlGaN back barrier layer close to the GaN main channel (i.e., the UID GaN layer in the figure) is 0.1, and gradually decreases to 0 in the direction away from the GaN main channel. By introducing a back barrier with a gradient component, the electron confinement in the channel can be effectively enhanced, thereby improving the performance of the device. In addition, the polarization gradient in the back barrier can reduce the 2DEG concentration in the parasitic channel and weaken the adverse effects of the channel, which is beneficial to improving the electronic performance of the device.

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

[0053] For example, the graded AlGaN back barrier layer may be Al 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 InGaN 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 an exemplary embodiment of the present invention, Figure 5The layer structure of the back barrier layer GaN HEMT device with a gradient Al component (increasing from top to bottom) is used as an example for explanation. The AlN layer is not shown in the figure. The Al component transitions from 0 to 0.1 from top to bottom, where the Al component of the gradient AlGaN back barrier layer close to the GaN main channel side is 0, and gradually increases to 0.1 in the direction away from the GaN main channel. The addition of the gradient component back barrier structure can enhance the gate control capability of the HEMT device, greatly reduce the leakage current, and further improve the current collapse effect, thereby significantly improving the breakdown voltage and power characteristics of the device. However, the depletion effect of the back barrier layer will cause a slight decrease in the output characteristics of the device, and due to the increase in scattering and parasitic effects, the frequency characteristics of the device will also be reduced.

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

[0056] For example, the gradient AlGaN back barrier layer can be GaN, Al 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 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 step gradient AlGaN buffer layer is as follows: Figure 6As shown, on the nucleation layer, by increasing the composition of Al, 4 stepped AlGaN layers are grown in sequence from the bottom to the top, and the Al component decreases from bottom to top, that is, the bottom layer is close to AlIn, and the top layer is close to GaN, gradually reducing 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, make the GaN crystal grown thereon better in quality, and reduce the internal traps of the buffer layer.

[0058] In an exemplary embodiment of the present invention, a semiconductor power device with high electron mobility comprising the novel epitaxial structure based on an embedded barrier layer is proposed. 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 the novel epitaxial layer structure using a traditional process.

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

[0060] The passivation layer can be formed by growing a high-quality Si3N4, AlN, Al2O3, or SiO2 thin film 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, and SiO2.

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

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

[0063] The gate metal conductive material includes a combination of one or more of platinum, iridium, nickel, gold, molybdenum, palladium, selenium, beryllium, TiN, and polysilicon. For example, in GaN HEMT devices, the gate metal usually uses a metal with a higher work function (such as Ni / Au) to prevent the GaN depletion layer under the gate from expanding.

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

[0065] Compared with conventional enhancement-mode devices, the enhancement-mode GaN MOSHEMT obtained by adopting the novel epitaxial structure can effectively suppress dynamic resistance decay and improve device performance.

[0066] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions 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 includes an embedded barrier layer disposed above the buffer layer and a stepped gradient AlGaN buffer layer disposed below the buffer layer; The embedded barrier layer includes a graded composition back barrier layer and an AlN layer disposed above the graded composition back barrier layer, and the graded composition in the graded composition back barrier layer increases from 0 to 0.1 in a specific direction.

2. The novel epitaxial structure based on the embedded barrier layer according to claim 1, characterized in that: The epitaxial structure comprises, from bottom to top, a substrate, a nucleation layer, a step-gradient AlGaN buffer layer, a buffer layer, a graded composition back barrier layer, an AlN layer, a UID GaN layer, an AlN insertion layer and an intrinsic AlGaN barrier layer.

3. The novel epitaxial structure based on the embedded barrier layer according to claim 2, characterized in that: The gradient component in the gradient component back barrier layer increases from 0 to 0.1 in a specific direction as follows: The graded composition in the graded composition back barrier layer increases from 0 to 0.1 from the direction close to the AlN layer to the direction far away from the AlN layer; or, The graded composition in the graded composition back barrier layer increases from 0 to 0.1 from the direction close to the upper side of the buffer layer to the direction away from the buffer layer.

4. The novel epitaxial structure based on an embedded barrier layer according to any one of claims 1 to 3, characterized in that: The structural formula of the graded composition back barrier layer is Al X Ga 1-X N or In X Ga 1-X N; Wherein, the gradient component is Al or In, and x=0-0.

1.

5. The novel epitaxial structure based on an embedded barrier layer according to any one of claims 1 to 3, characterized in that: The thickness of the AlN layer is 0.7-1 nm.

6. The novel epitaxial structure based on the embedded barrier layer according to claim 1, characterized in that: The step-gradient AlGaN buffer layer comprises four or more step-gradient AlGaN layers grown sequentially upward; The content of the Al component in the stepped gradient AlGaN layer 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.

7. The novel epitaxial structure based on the embedded barrier layer according to claim 2, characterized in that: The substrate includes one of silicon carbide, sapphire, silicon and gallium nitride.

8. The novel epitaxial structure based on the embedded barrier layer according to claim 2, characterized in that: The nucleation layer includes one or more combinations of gallium nitride, aluminum nitride and aluminum gallium nitride.

9. The novel epitaxial structure based on the embedded barrier layer according to claim 2, characterized in that: The buffer layer doping elements include one or more combinations of silicon, magnesium, carbon, iron and indium.

10. 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 a source-drain ohmic metal electrode, and a cap layer on the novel epitaxial structure based on an embedded barrier layer as described in any one of claims 1 to 9.

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