Structure and method for improving two-dimensional electron gas concentration of HEMT device
By introducing a lithium phosphate cap layer on the AlGaN barrier layer, the tensile stress and polarization charge density at the interface of the AlGaN/GaN heterojunction are improved, and the problems of crystal quality decline and surface state increase caused by the increase of Al component are solved, and the problem of crystal quality reduction and surface state increase is achieved. Dynamic characteristics of high-performance HEMT devices are improved.
Patent Information
- Application Number
- CN202411259328.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-09
- Publication Date
- 2024-12-17
AI Technical Summary
When the prior art increases the two-dimensional electron gas concentration at the AlGaN/AlN/GaN heterojunction interface, as the Al component increases, the crystal quality deteriorates, resulting in a decrease in 2DEG mobility and an increase in ohmic contact resistance, and surface passivation. Technology cannot effectively increase the physical quantity such as tension stress at the interface.
By introducing a lithium phosphate cap layer on the AlGaN barrier layer, tensile stress is introduced to the AlGaN barrier layer, polarization charge density is increased, and the conduction band pull-down effect of the lithium phosphate cap layer is used to reduce the surface state density near the gate, forming a High-performance HEMT devices.
Without affecting crystal quality, the two-dimensional electron gas concentration at the AlGaN/GaN heterojunction interface is improved, the dynamic characteristics of the device are improved, additional etching and ion implantation processes are avoided, and high-performance HEMT devices are obtained .
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Figure CN119153508A_ABST
Abstract
Description
Technical Field
[0001] The present invention particularly relates to a structure and method for improving the two-dimensional electron gas concentration of a HEMT device, belonging to the technical field of semiconductors. Background Art
[0002] The main technologies for increasing the two-dimensional electron gas concentration (2DEG) at the interface of AlGaN / AlN / GaN heterojunctions are: increasing the Al component of the AlGaN barrier layer or increasing the thickness of AlGaN, enhancing the spontaneous polarization intensity, increasing the net positive bound charge concentration at the interface, and thus increasing the 2DEG concentration. Using a passivation layer to reduce surface states, prevent surface states from capturing electrons to form negative charge regions, and compensate for the interface two-dimensional electron gas.
[0003] CN 115842041 A makes the hole injection structure close enough to the gate, so that the surface trap recombination is more complete; at the same time, long-distance surface charge transmission is avoided, thereby bringing about faster surface charge transfer and improving the surface trap recombination efficiency to achieve the best effect of hole injection.
[0004] However, although increasing the Al component is the main method to improve 2DEG, the crystal quality will gradually deteriorate with the increase of Al component, and the increase of defects will lead to the decrease of 2DEG mobility, the increase of ohmic contact resistance and the increase of surface states, which will affect the dynamic characteristics of the device. Surface passivation technology can reduce surface states and improve 2DEG, but it cannot introduce physical quantities such as tensile stress into the heterojunction to improve 2DEG at the AlGaN / GaN heterojunction interface. Summary of the invention
[0005] The main purpose of the present invention is to provide a structure and method for increasing the two-dimensional electron gas concentration of HEMT devices. Under the premise of not affecting the crystal quality, it can not only introduce tensile stress into the AlGaN barrier layer to increase the two-dimensional electron gas concentration, but also play a passivation role to suppress the surface state and improve the dynamic characteristics of the device. For p-gate enhanced HEMT devices, there is no need to etch the non-gate area to reproduce 2DEG, and etching damage will introduce additional surface states to affect device performance. For normally-off AlGaN / GaN HEMT devices, tensile stress can be introduced into the AlGaN barrier layer to increase the polarization charge density at the interface, thereby overcoming the shortcomings of the prior art.
[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:
[0007] A first aspect of the present invention provides a structure for increasing the two-dimensional electron gas concentration of a HEMT device, comprising an epitaxial structure and a source, a drain and a gate matched with the epitaxial structure, the epitaxial structure comprising a stacked channel layer and a barrier layer, a carrier channel being formed at an interface between the channel layer and the barrier layer, and the structure for increasing the two-dimensional electron gas concentration of the HEMT device further comprises: a lithium phosphate cap layer, the lithium phosphate cap layer being covered on the epitaxial structure.
[0008] In a more specific embodiment, the lithium phosphate cap layer is coated on the barrier layer, the conduction band of the barrier layer is pulled down and tilted by the lithium phosphate cap layer, the source, the drain, and the gate are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
[0009] In another more specific embodiment, the epitaxial structure also includes a p-type semiconductor layer, the p-type semiconductor layer is stacked on the barrier layer, the lithium phosphate cap layer is covered on the p-type semiconductor layer, the conduction band of the carrier channel is pulled down to below the Fermi level by the lithium phosphate cap layer, the gate is arranged on the p-type semiconductor layer, the source and the drain are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
[0010] Furthermore, the thickness of the lithium phosphate cap layer is within 100 nm.
[0011] Furthermore, the HEMT device is a normally-off device or an enhancement mode device.
[0012] A second aspect of the present invention provides a method for increasing the two-dimensional electron gas concentration of a HEMT device, comprising fabricating an epitaxial structure and fabricating a source, a drain and a gate matching the epitaxial structure, wherein the epitaxial structure comprises a channel layer and a barrier layer arranged in sequence, a carrier channel is formed at an interface between the channel layer and the barrier layer, and the method further comprises: fabricating a lithium phosphate cap layer on the epitaxial structure.
[0013] In a more specific embodiment, the lithium phosphate cap layer is coated on the barrier layer, the conduction band of the barrier layer is pulled down and tilted by the lithium phosphate cap layer, the source, the drain, and the gate are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
[0014] In another more specific embodiment, the epitaxial structure also includes a p-type semiconductor layer, the p-type semiconductor layer is stacked on the barrier layer, the lithium phosphate cap layer is covered on the p-type semiconductor layer, the conduction band of the carrier channel is pulled down to below the Fermi level by the lithium phosphate cap layer, the gate is arranged on the p-type semiconductor layer, the source and the drain are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
[0015] Furthermore, the thickness of the lithium phosphate cap layer is within 100 nm.
[0016] Furthermore, the HEMT device is a normally-off device or an enhancement mode device.
[0017] Compared with the prior art, the advantages of the present invention include:
[0018] For enhanced HEMT, the present invention avoids additional semiconductor manufacturing processes such as etching and ion implantation near the gate, avoids the introduction of a large number of surface states, and improves the dynamic characteristics of the device;
[0019] For enhanced HEMT, the present invention directly epitaxies lithium phosphate (Li3PO4) on the p-GaN layer, which can directly pull the energy level of the carrier channel down to below the Fermi level, effectively reduce the surface state density near the gate, improve the dynamic characteristics of the device, and obtain a high-performance HEMT device;
[0020] For the normally-off HEMT, the present invention epitaxies lithium phosphate (Li3PO4) on the Al1GaN barrier layer. The lithium phosphate can introduce tensile stress into the Al1GaN barrier layer, increase the polarization electric field strength of the Al1GaN barrier layer, and improve the concentration of net positive bound charges at the Al1GaN / GaN interface. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 is a schematic structural diagram of a normally-off HEMT device provided in Example 1 of the present invention;
[0022] Figure 2a It is a schematic diagram of the conduction band structure of a conventional normally-off HEMT device;
[0023] Figure 2b Schematic diagram of a conduction band of a normally-off HEMT device provided in Example 1 of the present invention;
[0024] Figure 3 It is a schematic diagram of a preparation process of a normally-off HEMT device provided in Example 1 of the present invention;
[0025] Figure 4is a schematic structural diagram of an enhanced HEMT device provided in Example 2 of the present invention;
[0026] Figure 5a It is a schematic diagram of the conduction band structure of a conventional enhancement mode HEMT device;
[0027] Figure 5b is a schematic diagram of a conduction band of an enhanced HEMT device provided in Example 2 of the present invention;
[0028] Figure 6 is a schematic diagram of a preparation process of an enhanced HEMT device provided in Example 2 of the present invention;
[0029] Figure 7 It is a schematic structural diagram of another enhanced HEMT device provided in Example 3 of the present invention. DETAILED DESCRIPTION
[0030] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle, etc. will be further explained in conjunction with the accompanying drawings and specific implementation cases. Unless otherwise specified, the semiconductor manufacturing process and etching, self-alignment process, etc. adopted in the present invention are all known to those skilled in the art.
[0031] Example 1
[0032] See also Figure 1 A normally-off HEMT device comprises: an epitaxial structure and a source, a drain and a gate matched with the epitaxial structure, the epitaxial structure comprises a GaN channel layer, an AlGaN barrier layer and a lithium phosphate cap (Li3P04) layer stacked in sequence on a substrate along a first direction, a carrier channel (such as a two-dimensional electron gas, 2EDG) is provided at an interface between the GaN channel layer and the AlGaN barrier layer, the source, the drain and the gate are arranged on the AlGaN barrier layer, the source and the drain are electrically connected via the carrier channel, the gate and the lithium phosphate cap layer are arranged between the source and the drain along a second direction, the second direction is perpendicular to the first direction, the first direction may be a longitudinal direction of the epitaxial structure, and the second direction may also be a lateral direction of the epitaxial structure.
[0033] Specifically, in the second direction, the lithium phosphate cap layer is arranged between the gate and the source, or the lithium phosphate cap layer is arranged between the gate and the drain, or the lithium phosphate cap layer is arranged between the gate and the source and the drain. More specifically, the thickness of the lithium phosphate cap layer is 100 nm.
[0034] Specifically, for normally-off HEMT devices, the lithium phosphate cap layer can introduce tensile stress into the AlGaN barrier layer, increase the polarization electric field strength of the AlGaN barrier layer, and increase the net positive bound charge at the AlGaN / GaN interface, such as Figure 2a and Figure 2b As shown, under the action of the lithium phosphate cap layer, the conduction band of the AlGaN barrier layer is tilted, and the electron confinement of the carrier channel (i.e., the two-dimensional potential well) is improved, that is, the longitudinal depth of the carrier channel is increased, which can also be understood as increasing the concentration of the carrier channel.
[0035] See also Figure 3 , a method for preparing a normally-off HEMT device, comprising the following steps:
[0036] 1) A GaN channel layer, an AlGaN barrier layer and a lithium phosphate cap layer stacked along a first direction are sequentially epitaxially grown on a substrate to form an epitaxial structure of a HEMT device, wherein the GaN channel layer and the AlGaN barrier layer form a heterojunction, and a carrier channel (e.g., two-dimensional electron gas, 2DEG) is formed at an interface between the GaN channel layer and the AlGaN barrier layer, and the thickness of the lithium phosphate cap layer is 100 nm.
[0037] Specifically, the substrate may be a Si substrate, a SiC substrate, a sapphire substrate, a GaN substrate, or the like.
[0038] 2) The lithium phosphate cap layer located in the source region, the drain region and the gate region is removed by etching to expose the AlGaN barrier layer.
[0039] It should be noted that the specific etching process can be carried out in a manner known to those skilled in the art. Of course, a lithium phosphate cap layer can also be formed between the gate region and the source region and the drain region by a method such as selective epitaxy.
[0040] 3) A source electrode, a drain electrode and a gate electrode are formed in the source region, the drain region and the gate region respectively, the source electrode and the drain electrode are electrically connected via a carrier channel, and in the second direction, the source electrode, the drain electrode and the lithium phosphate cap layer are spaced and matched to form a normally-off HEMT device.
[0041] It should be noted that the source, drain and gate can be formed by a metal deposition process known in the art. The preparation method of the present invention may also include other processes such as annealing activation, which are not specifically limited here.
[0042] Example 2
[0043] See also Figure 4, an enhanced HEMT device, comprising: an epitaxial structure and a source, a drain and a gate matched with the epitaxial structure, the epitaxial structure comprising a GaN channel layer, an AlGaN barrier layer, a p-GaN layer, and a lithium phosphate cap (Li3PO4) layer stacked in sequence on a substrate along a first direction, a carrier channel (such as a two-dimensional electron gas, 2EDG) is provided at an interface between the GaN channel layer and the AlGaN barrier layer, the source, the drain and the gate are arranged on the AlGaN barrier layer, the source and the drain are electrically connected via the carrier channel, the p-GaN layer is arranged between the source and the drain along a second direction, the lithium phosphate cap layer and the gate are arranged on the p-GaN layer, the second direction is perpendicular to the first direction, the first direction can be a longitudinal direction of the epitaxial structure, and the second direction can also be a lateral direction of the epitaxial structure.
[0044] Specifically, in the second direction, the lithium phosphate cap layer is arranged between the gate and the source electrode, or the lithium phosphate cap layer is arranged between the gate and the drain electrode, or the lithium phosphate cap layer is arranged between the gate and the source electrode and the drain electrode. More specifically, the thickness of the lithium phosphate cap layer is 100nm. Because the intrinsic lithium phosphate has good insulation, it can be used as a conventional hemt passivation layer layout and is in close contact with the gate, source, and drain electrodes. However, at present, there are many impurities in the lithium phosphate crystal, which may show a certain conductivity, so the distance between the lithium phosphate cap layer and the gate, source, and drain electrodes is within 20nm.
[0045] Specifically, Figure 5a and Figure 5b As shown, under the action of the lithium phosphate cap layer, the conduction band of the carrier channel is pulled back below the Fermi level, thereby effectively reducing the surface state density in the area near the gate, improving the dynamic characteristics of the device, and thus obtaining a high-performance HEMT device.
[0046] For details, please refer to Figure 6 , a method for preparing an enhanced HEMT device, comprising the following steps:
[0047] 1) A GaN channel layer, an AlGaN barrier layer, a P-GaN layer and a lithium phosphate cap layer are sequentially epitaxially grown on a substrate along a first direction to form an epitaxial structure of a HEMT device. The GaN channel layer and the AlGaN barrier layer form a heterojunction, and a carrier channel (such as a two-dimensional electron gas, 2DEG) is formed at the interface between the GaN channel layer and the AlGaN barrier layer. The thickness of the lithium phosphate cap layer is within 100nm. This epitaxial structure is suitable for reducing the additional surface states introduced during the device preparation process, reproducing 2DEG, and realizing a P-gate enhanced HEMT.
[0048] Specifically, the substrate may be a Si substrate, a SiC substrate, a sapphire substrate, a GaN substrate, or the like.
[0049] 2) The lithium phosphate cap layer in the gate region is removed by etching to expose the P-GaN layer in the gate region, and a gate is formed on the P-GaN layer in the gate region.
[0050] Specifically, the lithium phosphate cap layer in the gate region can be etched using a hard mask, and the mask can be directly deposited using a self-aligned process and can also be used as a surface protection, and then the entire surface is etched to deposit and form a gate to deplete the 2DEG below to form an enhanced type. It should be noted that the specific etching process can be used in a manner known to those skilled in the art, and is not specifically limited here.
[0051] 3) The lithium phosphate cap layer and the P-GaN layer in the source region and the drain region are removed by etching to expose the AlGaN barrier layer in the source region and the drain region, and the source and the drain are formed on the exposed AlGaN barrier layer.
[0052] Specifically, the manufacturing process and specific materials of the source and drain are not specifically limited here.
[0053] It should be noted that the source, drain and gate can be formed by a metal deposition process known in the art. The preparation method of the present invention may also include other processes such as annealing activation, which are not specifically limited here.
[0054] Example 3
[0055] See also Figure 7 The structure of an enhancement mode HEMT device in this embodiment is substantially the same as that in embodiment 2, except that the lithium phosphate cap layer and the p-GaN layer in this embodiment are arranged between the gate and the drain, the lithium phosphate cap layer contacts the gate, the distance between the drain and the lithium phosphate layer / p-GaN is increased, and only the lithium phosphate layer near the gate is retained.
[0056] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.
Claims
1. A structure for improving the two-dimensional electron gas concentration of a HEMT device, comprising an epitaxial structure and a source, a drain and a gate matched with the epitaxial structure, wherein the epitaxial structure comprises a stacked channel layer and a barrier layer, wherein a carrier channel is formed at an interface between the channel layer and the barrier layer, wherein: Also includes: A lithium phosphate capping layer is disposed on the epitaxial structure.
2. The structure for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 1, characterized in that: The lithium phosphate cap layer is covered on the barrier layer, the conduction band of the barrier layer is pulled down and tilted by the lithium phosphate cap layer, the source, the drain and the gate are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
3. The structure for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 1, characterized in that: The epitaxial structure also includes a p-type semiconductor layer, which is stacked on the barrier layer. The lithium phosphate cap layer is covered on the p-type semiconductor layer. The conduction band of the carrier channel is pulled down to below the Fermi level by the lithium phosphate cap layer. The gate is arranged on the p-type semiconductor layer, the source and the drain are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
4. The structure for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 1, 2 or 3, characterized in that: The thickness of the lithium phosphate cap layer is within 100 nm.
5. The method for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 1, characterized in that: The HEMT device is a normally-off device or an enhancement mode device.
6. A method for increasing the two-dimensional electron gas concentration of a HEMT device, comprising fabricating an epitaxial structure and fabricating a source, a drain and a gate matching the epitaxial structure, wherein the epitaxial structure comprises a channel layer and a barrier layer arranged in sequence, and a carrier channel is formed at the interface between the channel layer and the barrier layer, characterized in that: Also includes: A lithium phosphate cap layer is formed on the epitaxial structure.
7. The method for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 6, characterized in that: The lithium phosphate cap layer is covered on the barrier layer, the conduction band of the barrier layer is pulled down and tilted by the lithium phosphate cap layer, the source, the drain and the gate are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
8. The method for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 6, characterized in that: The epitaxial structure also includes a p-type semiconductor layer, which is stacked on the barrier layer. The lithium phosphate cap layer is covered on the p-type semiconductor layer. The conduction band of the carrier channel is pulled down to below the Fermi level by the lithium phosphate cap layer. The gate is arranged on the p-type semiconductor layer, the source and the drain are arranged on the barrier layer, and the lithium phosphate cap layer is arranged between the gate and the source and / or the drain.
9. The method for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 6, characterized in that: The thickness of the lithium phosphate cap layer is within 100 nm.
10. The method for increasing the two-dimensional electron gas concentration of a HEMT device according to claim 6, characterized in that: The HEMT device is a normally-off device or an enhancement mode device.