Radio frequency device, silicon carbide homoepitaxial substrate and method of making same

Abstract

The application provides a radio frequency device, a silicon carbide homoepitaxial substrate and a manufacturing method of the silicon carbide homoepitaxial substrate. The manufacturing method of the silicon carbide homoepitaxial substrate comprises the following steps: providing an N-type silicon carbide substrate, forming a plurality of first grooves in the N-type silicon carbide substrate; forming a defect healing layer on the inner wall of the first grooves and outside the first grooves, the defect healing layer forms second grooves at the positions corresponding to the first grooves; forming an unintentionally doped silicon carbide layer on the defect healing layer, the unintentionally doped silicon carbide layer fills the second grooves. According to the embodiment of the application, the step of the first grooves can make the defect healing layer nucleate and grow, so that the defects in the N-type silicon carbide substrate are healed therein; the step of the second grooves can make the unintentionally doped silicon carbide layer nucleate and grow, and since the defects are terminated in the defect healing layer, the quality of the unintentionally doped silicon carbide layer is improved, and high-quality GaN epitaxial material can be subsequently epitaxially grown thereon, thereby improving the performance of the radio frequency device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a radio frequency device, a silicon carbide homoepitaxial substrate, and a method for fabricating the same. Background Technology

[0002] Third-generation semiconductors, represented by group III nitrides, possess excellent properties such as large bandgap, high breakdown electric field, high saturation electron drift velocity, and strong polarization. In particular, high mobility transistors (HEMTs) based on aluminum gallium nitride / gallium nitride (AlGaN / GaN) heterostructures on silicon (Si) and silicon carbide (SiC) substrates have excellent characteristics such as fast switching speed, low on-resistance, small device size, high temperature resistance, and energy saving, and are expected to be widely used in the field of next-generation microwave RF power devices.

[0003] Currently, gallium nitride-based microwave and radio frequency electronic devices generally employ epitaxial gallium nitride (GaN) on silicon carbide (SiC) substrates, primarily due to the excellent heat dissipation and radio frequency performance of SiC substrates. To improve radio frequency performance, non-conductive SiC substrates are required; however, commercially available SiC substrates are generally N-type.

[0004] In view of this, it is necessary to provide a radio frequency device, a silicon carbide homoepitaxial substrate, and a method for fabricating the same, in order to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a radio frequency device, a silicon carbide homoepitaxial substrate, and a method for fabricating the same, so as to epitaxially grow a high-quality unintentionally doped silicon carbide layer on a low-cost N-type silicon carbide substrate to improve the performance of the radio frequency device.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for fabricating a silicon carbide homoepitaxial substrate, comprising:

[0007] An N-type silicon carbide substrate is provided, and a plurality of first grooves are formed within the N-type silicon carbide substrate;

[0008] A defect-repairing layer is formed on the inner wall of the first groove and outside the first groove, and the defect-repairing layer forms a second groove at the location corresponding to the first groove;

[0009] An unintentionally doped silicon carbide layer is formed on the defect-bridging layer, and the unintentionally doped silicon carbide layer fills the second groove.

[0010] Optionally, the defect-bridging layer is a P-type silicon carbide layer.

[0011] Optionally, in the thickness direction, the P-type ion doping mode in the P-type silicon carbide layer is uniform doping, modulation doping, or Delta doping.

[0012] Optionally, the P-type silicon carbide layer is multilayered, and in the thickness direction, the P-type ion doping concentration in the multilayer P-type silicon carbide layer is modulated as a Delta distribution.

[0013] Optionally, the defect-bridging layer is an alloy layer with a gradually varying AlN:SiC ratio or a superlattice structure layer with a gradually varying AlN:SiC ratio.

[0014] Optionally, when the defect-bridging layer is an alloy layer with a gradually changing AlN:SiC ratio, the proportion of SiC in the alloy layer with the gradually changing AlN:SiC ratio gradually increases in the direction away from the N-type silicon carbide substrate; when the defect-bridging layer is a superlattice structure layer with a gradually changing AlN:SiC ratio, the proportion of SiC is greater the further away from the N-type silicon carbide substrate.

[0015] Optionally, the defect-bridging layer and / or the unintentionally doped silicon carbide layer are formed by metal-organic chemical vapor deposition.

[0016] Optionally, the upper surface of the unintentionally doped silicon carbide layer is flat, or the unintentionally doped silicon carbide layer has a third groove, the position of which corresponds to the position of the second groove.

[0017] Optionally, the N-type silicon carbide substrate may or may not have an off-angle.

[0018] Optionally, the cross-section of the first groove is polygonal in a plane perpendicular to the thickness direction of the N-type silicon carbide substrate.

[0019] Optionally, the formation of multiple first grooves in the N-type silicon carbide substrate is achieved by using a patterned AlN layer as a mask and etching the N-type silicon carbide substrate to form multiple first grooves.

[0020] A second aspect of the present invention provides a silicon carbide homoepitaxial substrate, comprising:

[0021] An N-type silicon carbide substrate having a plurality of first grooves therein;

[0022] A defect-repairing layer located on the inner wall of the first groove and outside the first groove, the defect-repairing layer having a second groove corresponding to the first groove; and

[0023] An unintentionally doped silicon carbide layer is located on the defect-bridging layer, and the unintentionally doped silicon carbide layer fills the second groove.

[0024] Optionally, the defect-bridging layer is a P-type silicon carbide layer.

[0025] Optionally, in the thickness direction, the P-type ion doping mode in the P-type silicon carbide layer is uniform doping, modulation doping, or Delta doping.

[0026] Optionally, the P-type silicon carbide layer is multilayered, and the P-type ion doping concentration in the multilayer P-type silicon carbide layer has an overall Delta distribution in the thickness direction.

[0027] Optionally, the defect-bridging layer is an alloy layer with a gradually varying AlN:SiC ratio or a superlattice structure layer with a gradually varying AlN:SiC ratio.

[0028] Optionally, the upper surface of the unintentionally doped silicon carbide layer is flat, or the unintentionally doped silicon carbide layer has a third groove, the position of which corresponds to the position of the second groove.

[0029] Optionally, the N-type silicon carbide substrate may or may not have an off-angle.

[0030] Optionally, the cross-section of the first groove is polygonal in a plane perpendicular to the thickness direction of the N-type silicon carbide substrate.

[0031] A third aspect of the present invention provides a radio frequency device comprising the silicon carbide homoepitaxial substrate described in any of the preceding claims.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1) The step of the first groove allows the defect-bridging layer to nucleate and grow, so that the defects in the N-type silicon carbide substrate can be bridged within it; the step of the second groove allows the unintentionally doped silicon carbide layer to nucleate and grow. Since the defects terminate in the defect-bridging layer, the quality of the unintentionally doped silicon carbide layer is improved, and high-quality GaN epitaxial material can be epitaxially grown on it subsequently.

[0034] 2) In the optional scheme, the defect-bridging layer is a P-type silicon carbide layer. Holes in the P-type silicon carbide layer can be compensated by electrons in the unintentionally doped silicon carbide layer to form a depletion layer, which meets the requirements of HEMT devices and other devices with high substrate leakage current.

[0035] 3) In the optional scheme, the defect-bridging layer is an alloy layer with a graded AlN:SiC ratio or a superlattice structure layer with a graded AlN:SiC ratio. The alloy layer with a graded AlN:SiC ratio or the superlattice structure layer with a graded AlN:SiC ratio can serve as a barrier layer for impurities and defects, meeting the requirements of radio frequency devices and other devices that have high requirements for low substrate conductivity. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method for fabricating a silicon carbide homoepitaxial substrate according to the first embodiment of the present invention;

[0037] Figure 2 and Figure 3 yes Figure 1 A schematic diagram of the intermediate structure corresponding to the process in the document;

[0038] Figure 4 This is a schematic cross-sectional view of the silicon carbide homoepitaxial substrate according to the first embodiment of the present invention;

[0039] Figure 5 This is a schematic cross-sectional view of the silicon carbide homoepitaxial substrate according to the second embodiment of the present invention;

[0040] Figure 6 This is a schematic cross-sectional view of the silicon carbide homoepitaxial substrate according to the third embodiment of the present invention;

[0041] Figure 7 This is a schematic diagram of the cross-sectional structure of a silicon carbide homoepitaxial substrate according to the fourth embodiment of the present invention.

[0042] To facilitate understanding of this invention, all reference numerals appearing in the accompanying drawings are listed below:

[0043] N-type silicon carbide substrate 10 First groove 101

[0044] Defect repair layer 11 Second groove 111

[0045] P-type silicon carbide layer 11a Unintentionally doped silicon carbide layer 12

[0046] AlN: SiC ratio gradient alloy layer 11b Third groove 121

[0047] Silicon carbide homoepitaxial substrates 1, 2, 3, 4 Detailed Implementation

[0048] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0049] Figure 1 This is a flowchart of a method for fabricating a silicon carbide homoepitaxial substrate according to the first embodiment of the present invention; Figure 2 and Figure 3 yes Figure 1 The diagram shows the intermediate structure corresponding to the process flow. Figure 4 This is a schematic diagram of the cross-sectional structure of a silicon carbide homoepitaxial substrate according to the first embodiment of the present invention.

[0050] First, refer to Figure 1 Step S1 and Figure 2 As shown, an N-type silicon carbide substrate 10 is provided, and a plurality of first grooves 101 are formed in the N-type silicon carbide substrate 10.

[0051] The N-type silicon carbide substrate 10 can have a large number of defects. In addition, the N-type silicon carbide substrate 10 can be a silicon carbide substrate with an off-angle or a silicon carbide substrate without an off-angle.

[0052] The N-type ions in the N-type silicon carbide substrate 10 can be Al ions.

[0053] The first groove 101 can be formed using dry etching, wet etching, or laser grooving. In dry or wet etching processes, a patterned AlN layer can be used as a mask. On a plane perpendicular to the thickness direction of the N-type silicon carbide substrate 10, the cross-section of the first groove 101 can be polygonal, such as triangular, rectangular, pentagonal, or hexagonal. Compared to circular or elliptical shapes, polygonal first grooves 101 have more steps.

[0054] Next, refer to Figure 1 Step S2 and Figure 3 As shown, a defect-repairing layer 11 is formed on the inner wall of the first groove 101 and the outer wall of the first groove 101, and the defect-repairing layer 11 forms a second groove 111 at the corresponding location of the first groove 101.

[0055] In this embodiment, the defect-bridging layer 11 is a P-type silicon carbide layer 11a. The formation process of the P-type silicon carbide layer 11a may include: atomic layer deposition (ALD), chemical vapor deposition (CVD), molecular beam epitaxy (MBE), plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD), metal-organic chemical vapor deposition (MOCVD), or a combination thereof. The P-type dopant ions in the P-type silicon carbide layer 11a can be P ions, which can be in-situ doped or implanted after the silicon carbide layer has been epitaxially grown.

[0056] In this embodiment, the P-type silicon carbide layer 11a is a single layer. In the thickness direction, the P-type ion doping concentration of the P-type silicon carbide layer 11a can be uniform, modulated, or Delta-doped.

[0057] Compared to a planar surface, the P-type silicon carbide layer 11a is more likely to nucleate and grow at the step, and defects within the N-type silicon carbide substrate 10 can be eliminated therein. In other words, the P-type silicon carbide layer 11a can terminate defects within the N-type silicon carbide substrate 10.

[0058] In this embodiment, the defect-repairing layer 11 does not completely fill the first groove 101.

[0059] Then, refer to Figure 1 Step S3 and Figure 4 As shown, an unintentionally doped silicon carbide layer 12 is formed on the defect-bridging layer 11, and the unintentionally doped silicon carbide layer 12 fills the second groove 111.

[0060] The formation process of the unintentionally doped silicon carbide layer 12 can refer to the formation process of the defect-bridging layer 11. Compared to a planar surface, the unintentionally doped silicon carbide layer 12 is also more likely to nucleate and grow at steps.

[0061] Since the defects terminate in the defect-bridging layer 11, the quality of the unintentionally doped silicon carbide layer 12 can be improved. The conductivity of the unintentionally doped silicon carbide layer 12 is much lower than that of the N-type silicon carbide substrate 10.

[0062] In this embodiment, the upper surface of the unintentionally doped silicon carbide layer 12 is flat.

[0063] Reference Figure 4 As shown, the silicon carbide homoepitaxial substrate 1 in this embodiment includes:

[0064] N-type silicon carbide substrate 10, the N-type silicon carbide substrate 10 having a plurality of first grooves 101;

[0065] A defect-repairing layer 11 is located on the inner wall of the first groove 101 and outside the first groove 101, the defect-repairing layer 11 having a second groove 111 corresponding to the first groove 101; and

[0066] An unintentionally doped silicon carbide layer 12 is located on the defect-bridging layer 11, and the unintentionally doped silicon carbide layer 12 fills the second groove 111.

[0067] In this embodiment, the defect-bridging layer 11 is a P-type silicon carbide layer 11a. Holes in the P-type silicon carbide layer 11a can be compensated by electrons in the unintentionally doped silicon carbide layer 12 to form a depletion layer. The aforementioned depletion layer can reduce substrate leakage current, meeting the high requirements for substrate leakage current in HEMT devices and the like.

[0068] Experimental results show that, in the thickness direction, compared with the uniformly doped P-type silicon carbide layer 11a, the P-type silicon carbide layer 11a with Delta doping concentration of P-type ions can form a thicker depletion layer, which has a better effect on reducing substrate leakage current.

[0069] In other embodiments, in addition to Delta doping, the P-type ion doping concentration in the P-type silicon carbide layer 11a can also be modulated to other distributions.

[0070] Furthermore, the quality of the unintentionally doped silicon carbide layer 12 is improved, thus enabling the epitaxial growth of high-quality GaN epitaxial materials on it to form GaN devices, such as radio frequency devices.

[0071] Figure 5 This is a schematic cross-sectional view of a silicon carbide homoepitaxial substrate according to a second embodiment of the present invention. (Refer to...) Figure 5 As shown, the difference between the silicon carbide homoepitaxial substrate 2 in Embodiment 2 and the silicon carbide homoepitaxial substrate 1 in Embodiment 1 is only that the P-type silicon carbide layer 11a is multilayered, and the P-type ion doping concentration in the multilayer P-type silicon carbide layer 11a exhibits a Delta distribution overall in the thickness direction. In other words, the P-type ion doping concentration is lower in the top and bottom layers of the multilayer P-type silicon carbide layer 11a, and higher in the middle layers.

[0072] The advantage is that it can further increase the thickness of the depletion layer formed between the P-type silicon carbide layer 11a and the unintentionally doped silicon carbide layer 12, thereby reducing leakage current.

[0073] Apart from the differences mentioned above, the other structures of the silicon carbide homoepitaxial substrate 2 in this embodiment 2 can refer to the corresponding structures of the silicon carbide homoepitaxial substrate 1 in embodiment 1.

[0074] Accordingly, the difference between the fabrication method of the silicon carbide homoepitaxial substrate 2 in Embodiment 2 and the fabrication method of the silicon carbide homoepitaxial substrate 1 in Embodiment 1 lies only in that: in step S2, the P-type silicon carbide layer 11a is multilayered, and in the thickness direction, the P-type ion doping concentration in the multilayer P-type silicon carbide layer 11a is modulated as a Delta distribution. The modulation of the P-type ion doping concentration can be controlled by in-situ growth or by controlling different concentrations at different depths during ion implantation.

[0075] Apart from the differences mentioned above, the other steps of the method for fabricating the silicon carbide homoepitaxial substrate 2 in this embodiment 2 can refer to the corresponding steps of the method for fabricating the silicon carbide homoepitaxial substrate 1 in embodiment 1.

[0076] Figure 6 This is a schematic cross-sectional view of a silicon carbide homoepitaxial substrate according to a third embodiment of the present invention. (Refer to...) Figure 6As shown, the only difference between the silicon carbide homoepitaxial substrate 3 in this embodiment and the silicon carbide homoepitaxial substrate 1 in embodiment 1 is that the defect-bridging layer 11 is an alloy layer 11b with a gradually changing AlN:SiC ratio. The AlN:SiC gradually changing alloy layer 11b can act as a dense barrier layer, preventing the upward diffusion of N impurities from the N-type silicon carbide substrate 10. In other words, the AlN:SiC gradually changing alloy layer 11b can reduce the conductivity of the silicon carbide homoepitaxial substrate 3. This is because the silicon carbide substrate 10 naturally contains N impurities, and even the unintentionally doped silicon carbide layer 12 contains N impurities. Since subsequent fabrication of radio frequency devices requires the substrate to have the lowest possible conductivity, the AlN:SiC gradually changing alloy layer 11b can prevent the diffusion of N impurities from the lower N-type silicon carbide substrate 10 to the unintentionally doped silicon carbide layer 12.

[0077] In one alternative, in the direction away from the N-type silicon carbide substrate 10, the proportion of SiC in the AlN:SiC ratio-gradient alloy layer 11b gradually increases and the proportion of AlN gradually decreases. The advantage is that it allows for the epitaxial growth of the unintentionally doped silicon carbide layer 12 on a homogeneous substrate, improving the quality of the unintentionally doped silicon carbide layer 12.

[0078] In other embodiments, the defect-bridging layer 11 can also be a superlattice structure layer with a gradually changing AlN:SiC ratio. Such superlattice structure layers generally cause defect orientation deflection, further reducing defect density.

[0079] In one alternative, in a superlattice structure layer with a gradually varying AlN:SiC ratio, the SiC proportion increases and the AlN proportion decreases the further away from the N-type silicon carbide substrate 10. The advantage is that it allows for the epitaxial growth of the unintentionally doped silicon carbide layer 12 on a homogeneous substrate, improving the quality of the unintentionally doped silicon carbide layer 12.

[0080] Apart from the differences mentioned above, the other structures of the silicon carbide homoepitaxial substrate 3 in this embodiment can refer to the corresponding structures of the silicon carbide homoepitaxial substrate 1 in embodiment 1.

[0081] Accordingly, the difference between the fabrication method of the silicon carbide homoepitaxial substrate 3 in Embodiment 3 and the fabrication method of the silicon carbide homoepitaxial substrate 1 in Embodiment 1 is only that: in step S2, a defect-bridging layer 11 is formed on the inner wall and outside of the first groove 101 as an alloy layer 11b with a gradually changing AlN:SiC ratio. The formation process of the alloy layer 11b with a gradually changing AlN:SiC ratio can refer to the formation process of the P-type silicon carbide layer 11a.

[0082] Apart from the differences mentioned above, the other steps of the method for fabricating the silicon carbide homoepitaxial substrate 3 in this embodiment can refer to the corresponding steps of the method for fabricating the silicon carbide homoepitaxial substrate 1 in embodiment 1.

[0083] Figure 7 This is a schematic cross-sectional view of a silicon carbide homoepitaxial substrate according to the fourth embodiment of the present invention. (Refer to...) Figure 7 As shown, the silicon carbide homoepitaxial substrate 4 in this embodiment 4 differs from the silicon carbide homoepitaxial substrates 1, 2, and 3 in embodiments 1, 2, and 3 only in that the unintentionally doped silicon carbide layer 12 has a third groove 121, the position of which corresponds to the position of the second groove 111.

[0084] The advantage is that GaN epitaxial materials are easy to nucleate and grow at the step.

[0085] Apart from the differences mentioned above, the other structures of the silicon carbide homoepitaxial substrate 4 in this embodiment four can refer to the corresponding structures of the silicon carbide homoepitaxial substrates 1, 2, and 3 in embodiments one, two, and three.

[0086] Accordingly, the difference between the method of fabricating the silicon carbide homoepitaxial substrate 2 in this embodiment 2 and the method of fabricating the silicon carbide homoepitaxial substrate 1 in embodiment 1 is only that: in step S3, the unintentionally doped silicon carbide layer 12 formed on the defect-bridging layer 11 has a third groove 121, and the position of the third groove 121 corresponds to the position of the second groove 111.

[0087] Apart from the differences mentioned above, the other steps of the method for fabricating the silicon carbide homoepitaxial substrate 4 in this embodiment four can refer to the corresponding steps of the methods for fabricating silicon carbide homoepitaxial substrates 1, 2, and 3 in embodiments one, two, and three.

[0088] The fifth embodiment of the present invention also provides a radio frequency device, including any of the above-mentioned silicon carbide homoepitaxial substrates 1, 2, 3, and 4.

[0089] High-quality GaN epitaxial materials can be epitaxially grown on silicon carbide homoepitaxial substrates 1, 2, 3, and 4, thereby improving the performance of radio frequency devices.

[0090] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for fabricating a silicon carbide homoepitaxial substrate, characterized in that, include: An N-type silicon carbide substrate (10) is provided, in which a plurality of first grooves (101) are formed. A defect-repairing layer (11) is formed on the inner wall of the first groove (101) and outside the first groove (101), and the defect-repairing layer (11) forms a second groove (111) at the corresponding first groove (101). An unintentionally doped silicon carbide layer (12) is formed on the defect-bridging layer (11), the unintentionally doped silicon carbide layer (12) fills the second groove (111), wherein the defect-bridging layer (11) is a P-type silicon carbide layer (11a), the holes in the P-type silicon carbide layer (11a) and the electrons in the unintentionally doped silicon carbide layer (12) compensate to form a depletion layer; in the thickness direction, the P-type ion doping mode in the P-type silicon carbide layer (11a) is Delta doping.

2. The method for fabricating a silicon carbide homoepitaxial substrate according to claim 1, characterized in that, The P-type silicon carbide layer (11a) is multilayered. In the thickness direction, the P-type ion doping concentration in the multilayer P-type silicon carbide layer (11a) is modulated as a whole, with the doping concentration of the middle layer being higher than that of the top and bottom layers.

3. The method for fabricating a silicon carbide homoepitaxial substrate according to claim 1, characterized in that, The upper surface of the unintentionally doped silicon carbide layer (12) is flat or the unintentionally doped silicon carbide layer (12) has a third groove (121), the position of which corresponds to the position of the second groove (111).

4. The method for fabricating a silicon carbide homoepitaxial substrate according to claim 1, characterized in that, On a plane perpendicular to the thickness direction of the N-type silicon carbide substrate (10), the cross-section of the first groove (101) is polygonal.

5. A silicon carbide homoepitaxial substrate, characterized in that, include: An N-type silicon carbide substrate (10) has a plurality of first grooves (101) therein. A defect-repairing layer (11) is located on the inner wall of the first groove (101) and outside the first groove (101), the defect-repairing layer (11) having a second groove (111) corresponding to the first groove (101). as well as An unintentionally doped silicon carbide layer (12) is located on the defect-bridging layer (11), the unintentionally doped silicon carbide layer (12) fills the second groove (111), wherein the defect-bridging layer (11) is a P-type silicon carbide layer (11a), the holes in the P-type silicon carbide layer (11a) and the electrons in the unintentionally doped silicon carbide layer (12) compensate to form a depletion layer, and in the thickness direction, the P-type ion doping mode in the P-type silicon carbide layer (11a) is Delta doping.

6. The silicon carbide homoepitaxial substrate according to claim 5, characterized in that, The P-type silicon carbide layer (11a) is multilayered. In the thickness direction, the doping concentration of P-type ions in the multilayer P-type silicon carbide layer (11a) is generally higher in the middle layer than in the top and bottom layers.

7. The silicon carbide homoepitaxial substrate according to claim 5, characterized in that, The upper surface of the unintentionally doped silicon carbide layer (12) is flat or the unintentionally doped silicon carbide layer (12) has a third groove (121), the position of which corresponds to the position of the second groove (111).

8. The silicon carbide homoepitaxial substrate according to claim 5, characterized in that, On a plane perpendicular to the thickness direction of the N-type silicon carbide substrate (10), the cross-section of the first groove (101) is polygonal.

9. A radio frequency device, characterized in that, Includes the silicon carbide homoepitaxial substrate as described in any one of claims 5 to 8.

Images