N-polarity enhancement mode HEMT device structure and preparation method thereof

Abstract

The present invention discloses an N-polarity enhanced HEMT device structure and a preparation method thereof, wherein the structure comprises an N-polarity enhanced HEMT device body; a polarity neutralization composite gate structure is arranged between a channel layer and a gate of the N-polarity enhanced HEMT device body, wherein the polarity neutralization composite gate structure comprises a first polarity neutralization layer and a second polarity neutralization layer which are arranged in sequence from the channel layer to the gate and can combine with the channel layer to generate polarization charges, and the first polarity neutralization layer and the second polarity neutralization layer are made of different nitride materials. Thus, not only can the thickness of the polarity neutralization composite gate structure be ensured by the second polarity neutralization layer, the concentration of polarization charges for neutralizing two-dimensional electron gas can be increased, or the threshold voltage of the HEMT device can be increased by combining with the p-type doped polarity neutralization composite gate structure; but also the stress at the device gate can be reduced and the reliability of the device can be improved by adjusting the opposite stress of the first polarity neutralization layer and the second polarity neutralization layer.

Description

Technical Field

[0001] The present invention relates to the technical field of enhancement mode power semiconductor devices, and in particular to an N-polarity enhancement mode HEMT device structure and a preparation method thereof. Background Art

[0002] The third-generation semiconductor materials have a wider bandgap width, and when used in power semiconductor devices, they have higher breakdown voltage and power density compared to traditional Si-based power semiconductor devices. When these third-generation semiconductor materials with a wider bandgap width are used in high electron mobility transistors (HEMTs), the inherent polarization characteristics (spontaneous polarization and piezoelectric polarization) of the third-generation semiconductor materials can be used to generate high-concentration, high-electron-mobility two-dimensional electron gas (2DEG), so that the HEMT has a higher switching frequency and a smaller on-state resistance, thereby making it possible to produce a smaller HEMT, and can meet the needs of high voltage and high frequency fields.

[0003] However, 2DEG will cause the HEMT to still conduct under zero gate bias, and a negative gate bias needs to be applied to turn off the device, which poses a serious safety risk in practical applications. To this end, people have developed enhancement-mode devices (or normally-off devices) that are off under zero gate bias through F ion implantation, recessed gates or p-GaN gates. Among them, enhancement-mode devices made by setting p-GaN gates have become the main technical solution for preparing enhancement-mode devices due to their relatively simple process and high reliability.

[0004] According to the GaN, AlN, AlGaN, InGaN and other materials, which have Ga-polarity and N-polarity along the c-axis direction, HEMT devices can be divided into Ga-polarity HEMT device structure and N-polarity HEMT device structure. Among them, the N-polarity HEMT device structure has a Ga-polarity and N-polarity because its 2DEG is located above the barrier layer, and the source and drain are directly deposited on the channel layer with a narrow bandgap width (such as Figure 1As shown in the figure, compared with the widely used Ga-polar HEMT device structure, it has the advantages of good conduction band continuity, low barrier height and small ohmic contact resistance. Moreover, since the N-polar HEMT device structure has a natural back barrier layer, it can reduce the leakage of the device substrate and improve the breakdown voltage of the device; and there is no need to consider the effect of the thickness of the barrier layer on the gate control ability, so that the barrier layer can be adjusted in a larger range; at the same time, since the thickness of the channel layer can also be thin, the confinement ability and gate control ability of 2DEG can be further improved; in addition, an enhanced device can be realized by depositing an active neutralization layer on the channel layer in the gate region. These advantages of the N-polar HEMT device structure over the G-polar HEMT device structure have made the N-polar HEMT device structure increasingly attract the attention of R&D personnel.

[0005] Since N-polarity HEMT devices are basically normally-on devices, the threshold voltage of the device is less than 0. Existing N-polarity normally-off HEMTs are mainly realized as enhanced devices by depositing AlN or AlGaN polar neutralization layers on the channel layer. However, there is a lattice mismatch between AlN and the materials of the channel layer. Limited by the quality of material growth, the thickness of AlN is generally 1nm-2nm, which limits the concentration of polarization charges used to neutralize 2DEG, resulting in a small threshold voltage of the HEMT device; or in order to achieve a higher threshold voltage, the concentration of 2DEG can only be reduced, resulting in a small saturation current of the device. For polar neutralization materials such as AlGaN, since the channel layer is generally made of GaN material, there is currently no mature and effective AlGaN-GaN selective etching or corrosion method. When selective etching is used, the etching rate of the channel layer is generally higher than that of AlGaN, and AlGaN cannot be effectively etched. Summary of the invention

[0006] In order to solve at least one of the problems of low threshold voltage, low saturation current and ineffective etching when the polarity neutralization layer is set on the N-polarity normally-off HEMT, the inventor sets the polarity neutralization layer into a double-layer polarity neutralization composite gate structure. The double-layer polarity neutralization composite gate structure has two layers of polarity neutralization layers distributed up and down. Both polarity neutralization layers can combine with the channel layer to generate polarization charges, and the two polarity neutralization layers are made of different nitrides. Since the thickness of the lower polarity neutralization layer cannot be very thick due to the material growth quality limit, the threshold voltage of the device can be adjusted by adjusting the thickness or doping of the upper polarity neutralization layer. At the same time, the stress in the upper and lower polarity neutralization layers can be adjusted to reduce the gate region stress of the device to improve the reliability of the device. Therefore, according to one aspect of the present invention, an N-polarity enhancement type HEMT device structure is provided.

[0007] The N-polarity enhancement-type HEMT device structure comprises an N-polarity enhancement-type HEMT device body; wherein a polarity neutralization composite gate structure is arranged between a channel layer and a gate of the N-polarity enhancement-type HEMT device body, the polarity neutralization composite gate structure comprises a first polarity neutralization layer and a second polarity neutralization layer sequentially arranged along a direction from the channel layer to the gate, the first polarity neutralization layer and the second polarity neutralization layer are both made of a nitride that can combine with the channel layer to generate polarization charges, and the materials used to make the two are different.

[0008] The present invention arranges the polarity neutralization layer into a double-layer structure arranged up and down, and arranges the material of the first polarity neutralization layer to be different from the material of the second polarity neutralization layer, so that even if the thickness of the first polarity neutralization layer is limited to less than 2nm due to lattice mismatch with the channel layer, the thickness of the polarity neutralization composite gate structure can be increased by increasing the thickness of the second polarity neutralization layer, thereby increasing the concentration of polarization charges used to neutralize 2DEG and increasing the threshold voltage of the HEMT device.

[0009] In some embodiments, the first polarity neutralization layer is made of a material that can be used as a selective etching barrier layer for the second polarity neutralization layer, and the material can be removed from the channel layer by selective wet etching. Thus, the upper polarity neutralization layer can be selectively etched to remove the unnecessary part; and the lower polarity neutralization layer can be selectively etched to remove the unnecessary part, so as to ensure that the double-layer polarity neutralization composite gate can be etched effectively and with low damage, and avoid damage to the surface of the channel layer caused by etching.

[0010] Based on the fact that materials with higher Al component concentration have lower etching rate than materials with lower Al component concentration, the inventors set the polar neutralization layer located in the upper layer to have lower Al component concentration than the polar neutralization layer located in the lower layer, so that the second polar neutralization layer located in the upper layer can be formed by selective etching.

[0011] In some embodiments, the material of the first polar neutralization layer is Al x In (1-x) N; the material of the second polar neutralization layer is Al y (In,Ga,Sc) (1-y) N; wherein 1≥x>y>0. By setting the Al component concentration of the first polarity neutralization layer to be higher than the Al component concentration of the second polarity neutralization layer, the second polarity neutralization layer outside the gate region can be removed by selective etching; and, using Al x In (1-x)N is used as the material for preparing the first polarity neutralization layer. When removing the first polarity neutralization layer in the gate region, a selective wet etching process can be used to ensure that the surface of the channel layer is not damaged when removing the first polarity neutralization layer.

[0012] In some embodiments, 1≥x>0.5. Since the general channel layer is made of GaN material, the material of the first polarity neutralization layer is Al x In (1-x) The value range of x of N is set to be above 0.5, which can ensure that the corrosion rate of the first polarity neutralization layer during wet etching is much higher than the corrosion rate of the channel layer, thereby avoiding damage to the surface of the channel layer when removing the first polarity neutralization layer.

[0013] In some embodiments, x=0.83. Thus, the lattice mismatch between the first polarity neutralization layer and the channel layer can be reduced to avoid the performance degradation of the HEMT device and ensure the reliability of the HEMT device.

[0014] In some embodiments, at least one of the first polarity neutralization layer and the second polarity neutralization layer is p-doped. Since N-polarity materials are easier to p-dope than G-polarity materials, the threshold voltage of the HEMT device can be further increased by p-doping the polarity neutralization composite gate structure.

[0015] In some embodiments, the first polarity neutralization layer is made of a material that can form one of tensile stress and compressive stress with the channel layer; the second polarity neutralization layer is made of a material that can form the other of tensile stress and compressive stress with the first polarity neutralization layer. Thus, by adjusting the stress between the channel layer and the first polarity neutralization layer, and between the first polarity neutralization layer and the second polarity neutralization layer, the stress in the gate region can be reduced, and the performance and reliability of the HEMT device can be further improved.

[0016] In some embodiments, when the material of the channel layer is GaN and the first polarity neutralization layer is made of AlN, the second polarity neutralization layer is made of AlInN or AlGaN. Since the AlN / GaN interface exhibits tensile stress and the AlN and AlInN or AlGaN interface exhibits compressive stress, the two stresses can partially or completely offset the stress in the gate region to reduce the stress in the gate region.

[0017] According to another aspect of the present invention, a method for preparing the aforementioned N-polarity enhancement mode HEMT device structure is provided.

[0018] The method for preparing the N-polarity enhanced HEMT device structure comprises the following steps:

[0019] S20: in the process of preparing an N-polarity enhancement-mode HEMT device structure, epitaxially growing a first polarity neutralization initial layer and a second polarity neutralization initial layer on the channel layer obtained by epitaxial growth in sequence, wherein the materials used for epitaxially growing the first polarity neutralization initial layer and the second polarity neutralization initial layer are both nitride materials that can combine with the channel layer to generate polarized charges, and the materials used to make the first polarity neutralization initial layer and the second polarity neutralization initial layer are different;

[0020] S30: etching and removing the area other than the gate of the second polarity neutralization initial layer to obtain a second polarity neutralization layer;

[0021] S40: etching the area outside the gate of the first polarity neutralization initial layer to obtain a first polarity neutralization layer;

[0022] S50: preparing a gate electrode on the second polarity neutralization layer, and preparing a source electrode and a drain electrode on the channel layer.

[0023] In some embodiments, in step S30, the process used to etch and remove the area other than the gate of the second polarity neutralization initial layer to obtain the second polarity neutralization layer is a selective etching process.

[0024] In some embodiments, the process of etching the region outside the gate of the first polarity neutralization initial layer to obtain the first polarity neutralization layer is a wet etching process.

[0025] Since the Al component in the material of the first polarity neutralization initial layer is more than that in the material of the second polarity neutralization initial layer, the etching rate of the second polarity neutralization initial layer is much greater than that of the first polarity neutralization initial layer. When the second polarity neutralization layer is prepared by selective etching, the etching end point can be stopped at the surface of the first polarity neutralization initial layer; and since the material of the first polarity neutralization initial layer does not contain Ga component, when the first polarity neutralization layer is prepared, the portion of the first polarity neutralization initial layer other than the gate region can be etched away by a wet etching process, and it is ensured that the surface of the channel layer will not be damaged. Although the material used to prepare the first polarity neutralization layer does not contain Ga component, which will result in the thickness of the first polarity neutralization layer being limited due to the lattice mismatch between the first polarity neutralization layer and the channel layer, the thickness of the total neutralization layer can be ensured by increasing the thickness of the second polarity neutralization layer, thereby increasing the concentration of polarization charges used to neutralize 2DEG and increasing the threshold voltage of the HEMT device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of an N-polar HEMT commonly used in the prior art;

[0027] Figure 2 A schematic structural diagram of an N-polarity enhancement mode HEMT device structure according to an embodiment of the present invention;

[0028] Figure 3 A schematic structural diagram of a polarity neutralization composite gate structure according to an embodiment of the present invention;

[0029] Figure 4 A schematic flow chart of a method for preparing an N-polarity enhancement-mode HEMT device structure according to an embodiment of the present invention;

[0030] Figure 5 Based on Figure 4 A schematic diagram of the structure obtained by preparing a buffer layer on a substrate using the preparation method shown;

[0031] Figure 6 Based on Figure 4 A schematic diagram of the structure obtained by preparing a barrier layer on a buffer layer according to the preparation method shown;

[0032] Figure 7 Based on Figure 4 The schematic diagram of the structure obtained by preparing an insertion layer on a barrier layer according to the preparation method shown;

[0033] Figure 8 Based on Figure 4 A schematic diagram of the structure obtained by preparing a channel layer on a barrier layer using the preparation method shown;

[0034] Fig. 9 Based on Figure 4 The schematic diagram of the structure obtained by sequentially preparing a first polarity neutralization initial layer and a second polarity neutralization initial layer on a channel layer according to the preparation method shown;

[0035] Fig.10 Based on Figure 4 The preparation method shown is a schematic structural diagram of a first polarity neutralization layer prepared on a first polarity neutralization initial layer;

[0036] Fig.11 Based on Figure 4 The schematic structural diagram of the preparation method shown is to prepare a first polarity neutralization layer on a channel layer;

[0037] Fig.12 Based on Figure 4 A schematic diagram of the structure obtained by preparing the source electrode, drain electrode and gate electrode by the preparation method shown;

[0038] Fig.13 A schematic flow chart of a method for preparing an N-polarity enhancement mode HEMT device structure according to another embodiment of the present invention;

[0039] Fig.14 Based on Fig.13 The schematic diagram of the structure obtained by etching away the boundaries of the first polarity neutralization initial layer, the second polarity neutralization initial layer, the channel layer and the barrier layer according to the preparation method shown;

[0040] Fig.15 Based on Fig.13 A schematic structural diagram of an N-polarity enhancement mode HEMT device structure obtained by the preparation method shown;

[0041] Figure numerals: 20, substrate; 30, buffer layer; 31, first buffer sublayer; 32, second buffer sublayer; 301, Ga polarity buffer layer; 302, polarity inversion layer; 303, N polarity buffer layer; 40, barrier layer; 41, first barrier sublayer; 42, second barrier sublayer; 401, insertion layer; 50, 2DEG; 60, channel layer; 70, polarity neutralization composite gate structure; 71, first polarity neutralization layer; 711, polarity neutralization layer 1; 712, polarity neutralization layer 1+m; 701, first polarity neutralization initial layer; 72, second polarity neutralization layer; 721, polarity neutralization layer n; 722, polarity neutralization layer n+z; 702, second polarity neutralization initial layer; 81, source; 82, drain; 83, gate; 90, dielectric passivation layer. DETAILED DESCRIPTION

[0042] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0043] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include" and "comprise" include not only those elements, but also other elements not explicitly listed, or also include elements inherent to such processes, methods, articles or equipment. In the absence of further restrictions, the elements defined by the sentence "include..." do not exclude the existence of other identical elements in the process, method, article or equipment that includes the elements. The terms used in this article are generally those of skill in the art.

[0044] If there is any discrepancy between these terms and the commonly used terms, the terms in this article shall prevail.

[0045] Herein, the term “back barrier layer” refers to a barrier layer disposed on a side of the channel layer facing the substrate, which contacts the channel layer and generates 2DEG at the contact interface.

[0046] Herein, the term "lattice mismatch" refers to the mismatch phenomenon caused by the difference in lattice constants of the substrate and the epitaxial layer.

[0047] 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.

[0048] Figure 2 The structure of an N-polarity enhancement mode HEMT device according to an embodiment of the present invention is schematically shown.

[0049] like Figure 2 As shown, the N-polarity enhancement type HEMT device structure includes an N-polarity enhancement type HEMT device body. The N-polarity enhancement type HEMT device body in the prior art generally includes a substrate, a buffer layer, a barrier layer and a channel layer epitaxially grown in sequence on the substrate, and a source electrode, a drain electrode and a gate electrode prepared on the channel layer. The difference between the N-polarity enhancement type HEMT device body of the present invention and the N-polarity enhancement type HEMT device body in the prior art is mainly that a polarity neutralization composite gate structure is arranged between the channel layer and the gate electrode, and the polarity neutralization composite gate structure includes a first polarity neutralization layer and a second polarity neutralization layer, the first polarity neutralization layer is arranged on the channel layer, the second polarity neutralization layer is arranged on the first polarity neutralization layer, and the gate electrode is arranged on the second polarity neutralization layer, and the first polarity neutralization layer and the second polarity neutralization layer are both made of nitride that can combine with the channel layer to generate polarization charge, and the materials used to make the two are different. Therefore, even if the first polarity neutralization layer is thin due to lattice mismatch with the channel layer, the thickness of the polarity neutralization composite gate structure can be increased by increasing the thickness of the second polarity neutralization layer, thereby increasing the polarization charge concentration used to neutralize 2DEG and increasing the threshold voltage of the HEMT device.

[0050] In a preferred embodiment, the first polarity neutralization layer is made of a material that can serve as a selective etching barrier layer for the second polarity neutralization layer, and the material used to make the first polarity neutralization layer can be removed from the channel layer by selective wet etching. Thus, the portion of the second polarity neutralization layer outside the gate region can be removed by selective etching; the portion of the first polarity neutralization layer outside the gate region can be removed by a selective wet etching process to avoid damage to the surface of the channel layer when removing the portion outside the gate region of the double-layer polarity neutralization composite gate. Based on the fact that materials with higher Al component concentrations have lower etching rates than materials with lower Al component concentrations, the inventors set the second polarity neutralization layer to have a lower Al component concentration than the first polarity neutralization layer, so that the second polarity neutralization layer can be formed by selective etching. Exemplarily, the material of the first polarity neutralization layer is Al x In (1-x) N; the material of the second polar neutralization layer is Al y (In,Ga,Sc) (1-y) N; wherein, 1≥x>y>0.

[0051] Since the first polarity neutralization layer and the second polarity neutralization layer constituting the polarity neutralization composite gate structure are arranged in a bottom-up manner, and the Al component concentration in the material of the first polarity neutralization layer is greater than the Al component concentration in the material of the second polarity neutralization layer, the etching speed of the material with a high Al component concentration is slower than the etching speed of the material with a low Al component concentration, so that the second polarity neutralization layer can be formed by selective etching; at the same time, the first polarity neutralization layer can be formed by wet etching without causing damage to the surface of the channel layer; and although the first polarity neutralization layer There is a lattice mismatch between the first polarity neutralization layer and the channel layer, which results in that in order to ensure the quality of the first polarity neutralization layer, the thickness of the first polarity neutralization layer needs to be limited to less than 2nm, that is, the thickness of the first polarity neutralization layer cannot be too thick. However, since the present invention also provides a second polarity neutralization layer on the first polarity neutralization layer, the deficiency of the thin thickness of the first polarity neutralization layer can be compensated by increasing the thickness of the second polarity neutralization layer, thereby achieving the purpose of increasing the thickness of the polarity neutralization composite gate structure as a whole, so as to increase the polarization charge concentration used to neutralize 2DEG and increase the threshold voltage of the HEMT device.

[0052] In some embodiments, the value range of x is set to 1≥x>0.5. This is to further increase the difference in corrosion rate between the first polarity neutralization layer and the channel layer, and further reduce the damage to the surface of the channel layer when removing the first polarity neutralization layer. Preferably, x=0.83, so as to reduce the lattice mismatch between the first polarity neutralization layer and the channel layer, avoid the performance degradation of the HEMT device, and ensure the reliability of the HEMT device.

[0053] In a preferred embodiment, at least one of the first polarity neutralization layer and the second polarity neutralization layer is p-doped. Since N-polarity materials are easier to p-dope than G-polarity materials, the threshold voltage of the HEMT device can be further increased by p-doping the polarity neutralization composite gate structure.

[0054] In a preferred embodiment, the first polarity neutralization layer is made of a material that can form one of tensile stress and compressive stress with the channel layer; the second polarity neutralization layer is made of a material that can form the other of tensile stress and compressive stress with the first polarity neutralization layer. For example, when the first polarity neutralization layer is made of a material that can form compressive stress with the channel layer, the second polarity neutralization layer is made of a material that can form tensile stress with the first polarity neutralization layer; for another example, when the first polarity neutralization layer is made of a material that can form tensile stress with the channel layer, the second polarity neutralization layer is made of a material that can form compressive stress with the first polarity neutralization layer. Exemplarily, when the material of the channel layer is GaN, the first polarity neutralization layer is made of AlN, and the second polarity neutralization layer is made of AlInN or AlGaN, the AlN / GaN interface is tensile stress, and the AlN and AlInN or AlGaN interface is compressive stress, and the two stresses can achieve partial or complete offset of stress in the gate region to reduce the stress in the gate region and further improve the performance and reliability of the HEMT device.

[0055] In a preferred embodiment, any one of the first polar neutralization layer and the second polar neutralization layer can be configured as a single-layer structure composed of one material, or a multi-layer composite structure composed of two or more materials, or a multi-layer composite structure composed of two or more Al components of one material, such as Figure 3 As shown, the first polarity neutralization layer includes a plurality of polarity neutralization layers arranged up and down, wherein the polarity neutralization layer provided on the channel layer is numbered 1 (polarity neutralization layer 1), the number of the polarity neutralization layer increases with the increase of the distance from the channel layer (the number is an integer), the polarity neutralization layer adjacent to the second polarity neutralization layer in the first polarity neutralization layer is numbered 1+m (m≥1), and the polarity neutralization layers numbered 1 to 1+m together constitute the first polarity neutralization layer. The second polarity neutralization layer also includes a plurality of polarity neutralization layers arranged up and down, wherein the polarity neutralization layer disposed on the first polarity neutralization layer is numbered n (polarity neutralization layer n), n=m+2. The number of the polarity neutralization layer increases with the increase of the distance from the channel layer (the number is an integer), and the polarity neutralization layer adjacent to the gate in the second polarity neutralization layer is numbered n+z (z≥1), and the polarity neutralization layers numbered from n to n+z together constitute the second polarity neutralization layer. Taking the second polarity neutralization layer as an example, it can be implemented as Al2O3 arranged up and down. 0.2 Ga 0.8 N layer and Al0.2 In 0.8 A multi-layer composite structure consisting of N layers.

[0056] Figure 4 The figure schematically shows a method for preparing an N-polarity enhancement mode HEMT device structure according to a first embodiment of the present invention.

[0057] like Figure 4 As shown, the method for preparing the N-polarity enhancement mode HEMT device structure comprises the following steps:

[0058] S20: in the process of preparing an N-polarity enhancement-mode HEMT device structure, epitaxially growing a first polarity neutralization initial layer and a second polarity neutralization initial layer on the channel layer obtained by epitaxial growth in sequence, wherein the materials used for epitaxially growing the first polarity neutralization initial layer and the second polarity neutralization initial layer are both nitride materials that can combine with the channel layer to generate polarized charges, and the materials used to make the first polarity neutralization initial layer and the second polarity neutralization initial layer are different;

[0059] S30: etching and removing the area other than the gate of the second polarity neutralization initial layer to obtain a second polarity neutralization layer;

[0060] S40: etching the area outside the gate of the first polarity neutralization initial layer to obtain a first polarity neutralization layer;

[0061] S50: preparing a gate electrode on the second polarity neutralization layer, and preparing a source electrode and a drain electrode on the channel layer.

[0062] As a first implementation method of step S20, it includes epitaxially growing a buffer layer on a substrate; epitaxially growing a barrier layer on the buffer layer; epitaxially growing a channel layer on the barrier layer; epitaxially growing a first polarity neutralization initial layer on the channel layer; epitaxially growing a second polarity neutralization initial layer on the first polarity neutralization initial layer; wherein the epitaxial growth is achieved by molecular beam epitaxy technology or metal organic vapor phase epitaxy technology.

[0063] Exemplarily, the material of the substrate may be any one of Si, silicon-on-insulator (SOI), sapphire, SiC, GaN and AlN.

[0064] As a functional type, the buffer layer can be realized in various ways. In one of the implementations, the buffer layer is made of a material, and the buffer layer is an N-polar buffer layer. For example, GaN, AlGaN, AlN or AlInN is used as the material for preparing the buffer layer. The obtained structure is as follows: Figure 5As shown in Figure (a) in . In another implementation, the buffer layer is a composite structure composed of at least two materials, or a composite structure composed of at least two identical materials but different components. The composite structure is a multi-layer structure (for example, 2 layers, 3 layers, 5 layers, etc.), the number of layers being equal to the type of material or component of the composite structure, each material or each component constituting one layer of the composite structure, and buffer sublayers composed of different materials or different components are stacked in sequence along the epitaxial growth direction, and all buffer sublayers together constitute a buffer layer having a composite structure. Taking a two-layer composite structure as an example, when the first buffer sublayer grown on the substrate is made of material 1, and the second buffer sublayer grown on the first buffer sublayer is made of material 2 different from material 1, the structure of the buffer layer having a double-layer composite structure is formed as shown in FIG. Figure 5 As shown in Figure (b); Similarly, the composite structure composed of multiple components of materials (on the basis of the same materials) is also applicable to the above structure, the difference is that the material components of all buffer sublayers are different, with material Al z (In,Ga,Sc) (1-z) N is taken as an example, the z values ​​of the materials of all buffer sublayers are different. When the composite structure is three-layer, in addition to sequentially epitaxially growing three buffer sublayers of different materials or different components in the same manner as the composite structure of two layers to form a buffer layer, the buffer sublayers in the composite structure can also be divided by different polarities. For example, a buffer layer of a composite structure with a three-layer structure is formed by sequentially epitaxially growing a Ga polarity buffer layer, a polarity reversal layer and an N polarity buffer layer on a substrate (such as Figure 5 As shown in Figure (c) in the figure, no matter how many layers the composite structure has, it is necessary to ensure that the polarity of the buffer sublayer farthest from the substrate is N polarity.

[0065] The barrier layer is a functional type, and its implementation is similar to that of the buffer layer. In one implementation, the barrier layer is made of a single material, such as Al m (In,Ga,Sc) (1-m) N is used as the material for preparing the barrier layer, and the obtained structure is as follows Figure 6As shown in (a) in FIG. 1 . In another implementation, the barrier layer is a composite structure composed of at least two materials, or a composite structure composed of at least two identical materials but different components. The composite structure is a multi-layer structure (e.g., 2 layers, 3 layers, 8 layers, etc.), the number of layers being equal to the type of material or component of the composite structure, each material or each component constituting one layer of the composite structure, and barrier sublayers composed of different materials or different components are stacked in sequence along the epitaxial growth direction, and all barrier sublayers together constitute a barrier layer having a composite structure. Taking a two-layer composite structure as an example, when the first barrier sublayer grown on the buffer layer is made of material 1, the second barrier sublayer grown on the first barrier sublayer is made of material 2 different from material 1, or is made of a material of material 1 different from the component of the first barrier sublayer, the structure of the barrier layer having a double-layer composite structure is formed as shown in FIG. Figure 6 As shown in Figure (b) in the figure. In particular, when the component that distinguishes different barrier sublayers is the Al component, the Al component of the barrier sublayer is set to: the Al component content of the barrier sublayer closer to the buffer layer is higher than the Al component content of the barrier sublayer farther from the buffer layer. Regardless of the form in which the barrier layer is made, it must be ensured that the barrier layer is of N polarity. Preferably, the density of 2DEG can be increased by doping the barrier layer, and the doping method can be unintentional doping, partial doping or full doping, all doping is N-type doping (such as Si doping), and when the doping is partial doping, the partially doped area is the area of ​​the barrier layer close to the buffer layer.

[0066] The channel layer is obtained by epitaxially growing a material with a bandgap smaller than that of the barrier layer on the barrier layer (e.g. Figure 8 As shown in FIG. 1 , the channel layer is N-polar, and after the channel layer is grown on the barrier layer, a 2DEG is formed between the two. Exemplarily, the channel layer is made of non-doped GaN.

[0067] The first polarity neutralization initial layer and the second polarity neutralization initial layer are epitaxially grown on the channel layer in sequence. The composite structure formed by the first polarity neutralization initial layer and the second polarity neutralization initial layer obtained by epitaxial growth has N polarity, and the composite structure depletes the 2DEG between the channel layer and the barrier layer (such as Fig. 9As shown). The materials used for epitaxial growth of the first polarity neutralization initial layer and the second polarity neutralization initial layer are both nitrides, and the materials used to produce the first polarity neutralization initial layer and the second polarity neutralization initial layer are different. Therefore, even if the thickness of the first polarity neutralization initial layer is limited due to the lattice mismatch between the layer and the channel layer, the thickness of the total neutralization initial layer can be ensured by increasing the thickness of the second polarity neutralization initial layer, thereby increasing the concentration of polarization charges used to neutralize 2DEG and increasing the threshold voltage of the HEMT device. Preferably, the Al component in the material of the first polarity neutralization initial layer is more than the Al component in the material of the second polarity neutralization initial layer, so as to facilitate the subsequent selective etching of the first polarity neutralization initial layer and the second polarity neutralization initial layer. Exemplarily, the material used to prepare the first polarity neutralization initial layer is Al x In (1-x) N, the material used to prepare the second polar neutralization initial layer is Al y (In,Ga,Sc) (1-y) N, and 1≥x>y>0. Preferably, 1≥x>0.5>y. When x=1, the material used to prepare the first polarity neutralization initial layer is AlN. Considering the lattice mismatch between AlN and the material of the channel layer, the thickness of the first polarity neutralization initial layer is in the range of 1nm-2nm. Considering that when the N-polarity enhanced HEMT device is working, the high electric field or high temperature point is mainly distributed in the gate region, and the gate region also includes the first polarity neutralization initial layer and the second polarity neutralization initial layer in the gate region. In order to improve the reliability of the N-polarity enhanced HEMT device, it is more preferred to set the x component of the material for preparing the first polarity neutralization initial layer to 0.83 to reduce the lattice mismatch between the first polarity neutralization initial layer and the channel layer. In one implementation of the second polarity neutralization initial layer, the second polarity neutralization initial layer is made of a material, and the component of the material is single. In another implementation of the second polarity neutralization initial layer, the second polarity neutralization initial layer is a composite structure composed of at least two materials, or a composite structure composed of at least two identical materials but different components. The composite structure is a multilayer structure (e.g., 2 layers, 3 layers, 8 layers, etc.), the number of layers being equal to the type of material or component of the composite structure, each material or each component constituting one layer of the composite structure, the second polarity neutralization initial sublayers composed of different materials or different components being stacked in sequence along the epitaxial growth direction, and all the second polarity neutralization initial sublayers together constituting the second polarity neutralization initial layer having a composite structure, the specific implementation method can refer to the setting method of the buffer layer or the barrier layer, which will not be repeated here.

[0068] As a second implementation of step S20, the difference between the second implementation of step S20 and the first implementation of step S20 is that after the epitaxial growth of the barrier layer is completed and before the epitaxial growth of the channel layer is started, an insertion layer (such as Figure 7 As shown in (a) or (b) in the figure, an insertion layer is grown between the barrier layer and the channel layer, and the material of the insertion layer can be selected from AlN to increase the concentration of the subsequently formed 2DEG.

[0069] As the third implementation of step S20, it is different from the first implementation of step S20 in that: a cladding layer is also epitaxially grown on the second polarity neutral and initial layers, and the cladding layer can be made of GaN or AlGaN, and its thickness ranges from 1nm to 2nm to protect the surface of the material.

[0070] As the fourth implementation of step S20, it is different from the second implementation of step S20 in that: a cladding layer is also epitaxially grown on the second polarity neutral and initial layers, and the cladding layer can be made of GaN or AlGaN, and its thickness ranges from 1nm to 2nm to protect the surface of the material.

[0071] As one of the implementation methods of step S30, since the Al component in the material of the first polarity neutralization initial layer is greater than the Al component in the material of the second polarity neutralization initial layer, the etching rate of the second polarity neutralization initial layer is much greater than the etching rate of the first polarity neutralization initial layer. The photolithography and selective etching process can be used to etch the area outside the gate of the second polarity neutralization initial layer, and the etching is terminated at the surface of the first polarity neutralization initial layer, and finally the second polarity neutralization layer (such as Fig.10 As shown). Exemplarily, the selective etching process may use inductively coupled plasma (ICP) technology.

[0072] As one of the implementation methods of step S40, since the material of the first polarity neutralization initial layer does not contain Ga components, when preparing the first polarity neutralization layer, the first polarity neutralization initial layer can be etched away by a wet etching process except for the gate region to obtain the first polarity neutralization layer, and it is ensured that the surface of the channel layer will not be damaged. With the completion of the etching of the first polarity neutralization initial layer, 2DEG appears at the interface near the barrier layer outside the gate region in the channel layer. The prepared first polarity neutralization layer and the second polarity neutralization layer together constitute a polarity neutralization composite gate structure. By adjusting the material and thickness of the polarity neutralization composite gate structure, the 2DEG below it is depleted (such as Fig.11 shown).

[0073] As one of the implementation methods of step S50, the source and drain are prepared on the channel layer by electron beam evaporation or magnetron sputtering. The source and drain can form an ohmic contact with the channel layer during the preparation process, or form an ohmic contact with the channel layer by rapid thermal annealing. The gate can be a Schottky contact electrode or a metal-insulator-semiconductor (MIS) structure electrode. When the gate is a Schottky contact electrode, the gate can be deposited on the polarity neutralization composite gate structure by electron beam evaporation technology. The gate can form a Schottky contact with the polarity neutralization composite gate structure during the preparation process, or form a Schottky contact with the polarity neutralization composite gate structure by annealing. When the gate is an MIS structure electrode, it is necessary to first deposit one or more dielectric layers on the polarity neutralization composite gate structure by combining LPCVD (Low pressure chemical vapor deposition), PECVD (Plasma Enhanced chemical vapor deposition) or ALD (Atomic layer deposition) and photolithography and etching methods. The material of the dielectric layer can be SiN x 、SiO2、SiON、Al x O y , in order to effectively suppress the gate leakage phenomenon, the obtained structure is as follows Fig.12 shown.

[0074] After the gate, source and drain are prepared, a dielectric passivation layer can be deposited on the surface of the channel layer, source, drain, polarity neutralization composite gate structure and gate by PECVD or other methods, that is, a dielectric passivation layer covering the channel layer, source, drain, polarity neutralization composite gate structure and gate is deposited on the channel layer, and then, the dielectric passivation layer corresponding to the source, drain and gate is removed by photolithography and etching methods to expose the source, drain and gate. The obtained structure is as follows: Figure 2 The material of the dielectric passivation layer can be a commonly used dielectric passivation layer material, for example, SiN x A field plate may also be prepared on the dielectric passivation layer to further improve the breakdown voltage of the N-polarity enhanced HEMT device. The specific field plate preparation process may adopt the process commonly used in the prior art, and the present invention does not limit the specific method for preparing the field plate.

[0075] The following is an exemplary description of the method for preparing an N-polarity enhancement mode HEMT device structure in conjunction with specific embodiments.

[0076] Example 1

[0077] In the first step, a N-polar GaN layer is epitaxially grown on a sapphire substrate using molecular beam epitaxy technology as a buffer layer.

[0078] In the second step, a N-polar AlGaN layer is epitaxially grown on the buffer layer using molecular beam epitaxy technology as a barrier layer.

[0079] The third step is to epitaxially grow an N-polar GaN layer on the barrier layer using molecular beam epitaxy technology as a channel layer.

[0080] In the fourth step, a N-polarity AlN layer is epitaxially grown on the channel layer using a molecular beam epitaxy technique as a first polarity neutralization initial layer, and the thickness of the first polarity neutralization initial layer is 2 nm.

[0081] The fifth step is to use molecular beam epitaxy technology to epitaxially grow a layer of Al on the first polarity neutral and initial layer. 0.2 Ga 0.8 N, as the second polarity neutralization initial layer.

[0082] In the sixth step, a photolithography and ICP selective etching process is used to remove the portion of the second polarity neutralization initial layer outside the gate region, so as to form a second polarity neutralization layer in the gate region.

[0083] In the seventh step, a wet etching technique is used to remove the portion of the first polarity neutralization initial layer outside the gate region, and a first polarity neutralization layer is formed in the gate region. The first polarity neutralization layer and the second polarity neutralization layer constitute a polarity neutralization composite gate structure.

[0084] In the eighth step, the source and drain are respectively deposited on the channel layer by electron beam evaporation technology, and the gate is deposited on the second polarity neutralization layer, and the ohmic contact between the source and drain and the channel layer, as well as the Schottky contact between the gate and the second polarity neutralization layer are improved by annealing treatment.

[0085] In the ninth step, a dielectric passivation layer is prepared by using PECVD technology and photolithography and etching technology, and finally an N-polarity enhancement mode HEMT device structure is obtained, wherein the dielectric passivation layer is located on the surface of the N-polarity enhancement mode HEMT device structure away from the substrate.

[0086] Example 2

[0087] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0088] In the fourth step, a layer of N-polar Al is epitaxially grown on the channel layer using molecular beam epitaxy technology. x In (1-x) The N layer serves as the first polarity neutralization initial layer, wherein x=0.83.

[0089] Example 3

[0090] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0091] In the fourth step, a layer of N-polar Al is epitaxially grown on the channel layer using molecular beam epitaxy technology. x In (1-x) The N layer is used as the first polarity neutralization initial layer, wherein x=0.51.

[0092] Example 4

[0093] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0094] In the fifth step, a layer of Al is epitaxially grown on the first polarity neutral and initial layer using molecular beam epitaxy technology. 0.2 Ga 0.8 The N layer is used as a second polarity neutralization initial layer, and the second polarity neutralization initial layer is p-doped.

[0095] Example 5

[0096] This embodiment is adjusted on the basis of embodiment 4, and the main differences are:

[0097] In the fifth step, a layer of Al is epitaxially grown on the first polarity neutral and initial layer using molecular beam epitaxy technology. 0.2 Ga 0.8 The N layer serves as the second polarity neutralization initial layer.

[0098] Example 6

[0099] This embodiment is adjusted on the basis of embodiment 4, and the main differences are:

[0100] In the fifth step, a layer of AlGaN is epitaxially grown on the first polarity neutralization and initial layer using molecular beam epitaxy technology to serve as the second polarity neutralization and initial layer.

[0101] Example 7

[0102] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0103] In the second step, a layer of N-polar AlGaN layer is epitaxially grown on the buffer layer using molecular beam epitaxy technology as a barrier layer, and then a layer of AlN is epitaxially grown on the barrier layer as an insertion layer.

[0104] In the third step, a N-polar GaN layer is epitaxially grown on the insertion layer using molecular beam epitaxy technology to serve as a channel layer.

[0105] Example 8

[0106] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0107] In the fifth step, a layer of Al is epitaxially grown on the first polarity neutral and initial layer using molecular beam epitaxy technology. 0.2 Ga 0.8 The N layer is used as a second polarity neutralization initial layer. After the second polarity neutralization initial layer is prepared, 2 nm of GaN is epitaxially grown on the second polarity neutralization initial layer as a cladding layer.

[0108] Fig.15 The figure schematically shows a method for preparing an N-polarity enhancement mode HEMT device structure according to a second embodiment of the present invention.

[0109] The preparation method is adjusted based on the preparation method of the first embodiment, such as Fig.15 As shown, the main difference between the preparation method of the first embodiment and the preparation method of the first embodiment is:

[0110] Between step S20 and step S30, step S201 is also included, in which the boundaries of the first polarity neutralization initial layer, the second polarity neutralization initial layer, the channel layer and the barrier layer are removed by etching.

[0111] As one implementation of step S201, photolithography and reactive ion etching (RIE) or ICP process are used to etch away the boundaries of the first polarity neutralization initial layer, the second polarity neutralization initial layer, the channel layer and the barrier layer, and the obtained structure is as follows: Fig.14 shown.

[0112] When a dielectric passivation layer is also prepared when manufacturing the N-polarity enhancement-mode HEMT device structure, the difference between this embodiment and the first embodiment is that, in addition to depositing a dielectric passivation layer covering the channel layer, the source electrode, the drain electrode, the polarity neutralization composite gate structure and the gate electrode on the channel layer, a dielectric passivation layer is also deposited on the boundary between the channel layer and the barrier layer, and on the surface of the buffer layer away from the substrate; when step S201 also removes part of the surface of the buffer layer, that is, when step S201 etches and removes part of the boundary of the buffer layer, the deposited dielectric passivation layer also needs to cover the boundary of the buffer layer, and the obtained N-polarity enhancement-mode HEMT device structure is as follows: Fig.15 shown.

[0113] The following is an exemplary description of the method for preparing an N-polarity enhancement mode HEMT device structure in conjunction with specific embodiments.

[0114] Example 9

[0115] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0116] In the seventh step, after forming the polarity neutralization composite gate structure, an Al2O3 layer is deposited as a dielectric layer in the polarity neutralization composite gate structure region by ALD, or a SiN layer is deposited in the polarity neutralization composite gate structure region by LPCVD. x layer as a dielectric layer.

[0117] In the eighth step, the source and drain are deposited on the channel layer respectively by electron beam evaporation technology, and the gate is deposited on the dielectric layer, and the ohmic contact between the source and drain and the channel layer, and the Schottky contact between the gate and the dielectric layer are improved by annealing.

[0118] Example 10

[0119] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0120] In the eighth step, the source and drain are deposited on the channel layer respectively by electron beam evaporation technology, and the gate is deposited on the second polarity neutralization layer, and the ohmic contact between the source and the channel layer, the Schottky contact between the drain and the channel layer, and the Schottky contact between the gate and the second polarity neutralization layer are improved by annealing treatment, thereby obtaining a unidirectional conducting HEMT device.

[0121] Embodiment 11

[0122] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0123] In the second step, a N-polar AlGaN layer is epitaxially grown on the buffer layer using molecular beam epitaxy technology. When used as a barrier layer, the Al component of the AlGaN barrier layer gradually changes from 10% on the buffer layer side to 30% on the channel layer side.

[0124] Example 12

[0125] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0126] In the fifth step, a layer of Al is epitaxially grown in the first polarity and on the initial layer by molecular beam epitaxy. 0.2 Ga 0.8 N layer and one layer of Al 0.2 In 0.8 N layer, Al 0.2 Ga 0.8 N layer and Al 0.2 In 0.8 The N layers together constitute the second polarity neutralization initial layer.

[0127] Embodiment 13

[0128] This embodiment is adjusted on the basis of embodiment 1, and the main differences are:

[0129] In the sixth step, photolithography and ICP selective etching processes are first used to remove the boundaries of the first polarity neutralization initial layer, the second polarity neutralization initial layer, the channel layer and the barrier layer, and then the portion of the second polarity neutralization initial layer outside the gate area is removed to form a second polarity neutralization layer in the gate area.

[0130] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. N-polarity enhancement mode HEMT device structure, characterized in that: The invention comprises an N-polarity enhancement mode HEMT device body; wherein, A polarity neutralization composite gate structure is arranged between the channel layer and the gate of the N-polarity enhancement mode HEMT device body, and the polarity neutralization composite gate structure comprises a first polarity neutralization layer and a second polarity neutralization layer arranged in sequence from the channel layer to the gate, and the first polarity neutralization layer and the second polarity neutralization layer are both made of nitride that can combine with the channel layer to generate polarization charge, and the materials used to make the two are different; The first polarity neutralization layer is made of a material that is a selective etching barrier layer of the second polarity neutralization layer, and the material is removed from the channel layer by selective wet etching; The material of the first polar neutralization layer is Al x In (1-x) N; The material of the second polar neutralization layer is Al y (In,Ga,Sc) (1-y) N; Among them, 1≥x>y>0.

2. The N-polarity enhancement mode HEMT device structure according to claim 1, characterized in that: 1≥x＞0.5。 3. The N-polarity enhancement mode HEMT device structure according to claim 1, characterized in that: At least one of the first polarity neutralization layer and the second polarity neutralization layer is p-type doped.

4. The N-polarity enhancement mode HEMT device structure according to claim 2, characterized in that: At least one of the first polarity neutralization layer and the second polarity neutralization layer is p-type doped.

5. The N-polarity enhancement mode HEMT device structure according to any one of claims 1 to 4, characterized in that: The first polarity neutralization layer is made of a material capable of forming one of a tensile stress and a compressive stress with the channel layer; The second polarity neutralization layer is made of a material capable of forming the other of a tensile stress and a compressive stress with the first polarity neutralization layer.

6. The N-polarity enhancement mode HEMT device structure according to claim 5, characterized in that: When the material of the channel layer is GaN and the first polarity neutralization layer is made of AlN, the second polarity neutralization layer is made of AlInN or AlGaN.

7. The method for preparing an N-polarity enhancement mode HEMT device structure according to any one of claims 1 to 6, characterized in that: The following steps are involved: S20: in the process of preparing an N-polarity enhancement-mode HEMT device structure, epitaxially growing a first polarity neutralization initial layer and a second polarity neutralization initial layer on the channel layer obtained by epitaxial growth in sequence, wherein the materials used for epitaxially growing the first polarity neutralization initial layer and the second polarity neutralization initial layer are both nitride materials that can combine with the channel layer to generate polarized charges, and the materials used to make the first polarity neutralization initial layer and the second polarity neutralization initial layer are different; S30: etching and removing the area other than the gate of the second polarity neutralization initial layer to obtain a second polarity neutralization layer; S40: etching the area outside the gate of the first polarity neutralization initial layer to obtain a first polarity neutralization layer; S50: preparing a gate electrode on the second polarity neutralization layer, and preparing a source electrode and a drain electrode on the channel layer; In step S40, the region outside the gate of the first polarity neutralization initial layer is etched to obtain the first polarity neutralization layer by a wet etching process.

8. The method for preparing an N-polarity enhancement mode HEMT device structure according to claim 7, characterized in that: In step S30, the area other than the gate electrode of the second polarity neutralization initial layer is removed by etching, and the process adopted to obtain the second polarity neutralization layer is a selective etching process.

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