Method for preparing ohmic contact of gan-based device
By employing a combination of low-power dry etching and plasma treatment after dry etching, impurity atoms on the ohmic contact metal surface of GaN-based devices are removed, solving the problem of insufficient ohmic contact characteristics and improving the electrical performance and reliability of the devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA RESOURCES MICROELECTRONICS (CHONGQING) CO LTD
- Filing Date
- 2021-12-28
- Publication Date
- 2026-05-19
AI Technical Summary
The ohmic contact characteristics of GaN-based devices in the present technology need to be further improved. Impurity atoms introduced by the dry etching process during the manufacturing of GaN power electronic devices lead to defects in the device and affect the electrical characteristics.
Low-power dry etching is used to process the ohmic contact metal surface. By combining low bias power and low source power, impurity atoms, such as Cl atoms, are removed from the ohmic contact metal surface, and ohmic contacts are formed through low-damage etching.
It effectively improves the purity of the ohmic contact metal, enhances the electrical performance of the ohmic contact, reduces damage during the etching process, and improves the reliability and electrical characteristics of the device.
Smart Images
Figure CN116364534B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of GaN-based electronic device fabrication technology, and in particular to a method for fabricating ohmic contacts for GaN-based devices. Background Technology
[0002] Gallium nitride (GaN), a third-generation semiconductor material, is an ideal candidate for high-voltage and high-frequency applications due to its wide bandgap and high electron saturation velocity. GaN semiconductors can withstand stronger currents and higher voltages than silicon semiconductors, enabling higher power densities. Therefore, it shows significant market potential in radar, fast charging, and DC-DC transducers, and will become a cost-competitive next-generation consumer power electronics product.
[0003] Dry etching, which uses plasma-enhanced gas atoms to bombard and etch the material, is one of the main processes in the manufacturing of GaN power electronic devices. Dry etching offers advantages such as high selectivity and good anisotropy, providing greater controllability compared to wet etching. However, dry etching also introduces additional problems, such as surface damage and unintentional introduction of impurity atoms. These issues can lead to undesirable defects within the device, affecting its characteristics and increasing reliability and failure risks. In GaN power electronic devices, the ohmic contact characteristics of the electrodes are crucial to the overall electrical properties of the device. Current research mainly focuses on the damage generated during the direct etching of GaN-based epitaxial layers. This is achieved by introducing buffering gases such as C2H4 to reduce the physical bombardment of ions, or by using plasma treatment on the GaN surface, such as N2 plasma, to improve the surface morphology and defects of GaN and thus enhance the ohmic contact characteristics. However, the ohmic contact characteristics formed by these methods still need further improvement. Summary of the Invention
[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for fabricating ohmic contacts for GaN-based devices, in order to solve the problem that the characteristics of ohmic contacts in GaN-based devices need to be further improved in the prior art.
[0005] To achieve the above and other related objectives, the present invention provides a method for fabricating an ohmic contact for a GaN-based device, the method comprising:
[0006] A substrate is provided, and a GaN-based epitaxial structure is formed on the substrate;
[0007] An insulating layer is formed on the GaN-based epitaxial structure and patterned to form an opening in the insulating layer;
[0008] A metal layer is deposited on the insulating layer, and the metal layer fills the opening;
[0009] A photoresist layer is formed on the metal layer and patterned to expose the metal layer above the opening;
[0010] The metal layer not blocked by the photoresist layer is removed by a dry etching process, and the remaining metal layer is formed as an ohmic contact metal.
[0011] Remove the photoresist layer;
[0012] The metal surface is treated with low-power dry etching to remove the ohmic contact metal of a predetermined thickness. The parameters used in the low-power dry etching of the metal surface are as follows: chlorine-containing gas is used; the bias power is between 0W and 25W (excluding 0W); and the source power is between 400W and 750W.
[0013] The ohmic contact metal is annealed to form an ohmic contact.
[0014] Optionally, after removing the ohmic contact metal by low-power dry etching, the process further includes treating the ohmic contact metal with a plasma treatment process, wherein the parameters used in the plasma treatment process are: bias power of 0W; source power between 1200W and 1500W.
[0015] Furthermore, the gas used in the plasma treatment of the metal surface is N2 or H2.
[0016] Optionally, the plasma treatment process for metal surfaces is implemented using an ICP device or an ICP-RIE device.
[0017] Optionally, the chlorine-containing gas in the low-power dry etching process on the metal surface is at least one of Cl2 and BCl3.
[0018] Optionally, the low-power dry etching process is used to remove the metal surface, and the preset thickness of the ohmic contact metal is between 10 nm and 40 nm.
[0019] Optionally, the low-power dry etching process on the metal surface is performed using an ICP device or an ICP-RIE device.
[0020] Optionally, the parameters for removing the metal layer not obscured by the photoresist layer using a dry etching process are as follows: chlorine-containing gas is used; the bias power is between 80W and 200W; and the source power is between 800W and 1400W.
[0021] Optionally, the insulating layer is made of silicon nitride or silicon oxide.
[0022] Optionally, the GaN-based device is a GaN-based HEMT device, and the GaN-based epitaxial structure includes a GaN channel layer and an AlGaN barrier layer, and the formed ohmic contacts include source ohmic contacts and drain ohmic contacts.
[0023] As described above, the method for fabricating ohmic contacts for GaN-based devices of the present invention involves using low-power dry etching to process the surface of the ohmic contact metal after dry etching to form the ohmic contact metal. A low bias power between 0W and 25W is used to reduce the surface bombardment rate, and a relatively low source power between 400W and 750W is used to reduce the plasma activation reaction. This process slowly and with low damage removes the metal surface, allowing a layer of high-concentration impurity atoms, such as Cl atoms, introduced by the dry etching process to be etched away along with the metal surface. This removes the high concentration of impurity atoms and reduces the introduction of new damage, thereby effectively improving the purity of the ohmic contact metal and subsequently improving the electrical performance of the formed ohmic contact after annealing. Attached Figure Description
[0024] Figure 1 The diagram shows a process flow chart of the method for fabricating the ohmic contact of the GaN-based device according to the present invention.
[0025] Figures 2 to 10 The diagram shows a cross-sectional structure of each step in the fabrication method of an ohmic contact for a GaN-based device, as an example of the present invention.
[0026] Component designation explanation
[0027] 100 GaN-based epitaxial structure
[0028] 101 GaN channel layer
[0029] 102 AlGaN barrier layer
[0030] 103 Insulation layer
[0031] 104 Opening
[0032] 105 Metal Layer
[0033] 106 Photoresist Layer
[0034] 107 Ohm Contact Metal
[0035] 108 impurity atoms
[0036] Steps S1 to S8 Detailed Implementation
[0037] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.
[0038] Please see Figures 1 to 10 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be changed according to actual needs, and the layout of the components may also be more complex.
[0039] As described in the background section, current research on factors affecting ohmic contact characteristics mainly focuses on the damage generated during the direct etching of GaN-based epitaxial layer materials. Ohmic contact characteristics are improved by introducing buffering gases such as C2H4 to reduce the physical bombardment of ions, or by using plasma treatment on the GaN surface such as N2 plasma. However, the ohmic contact characteristics formed by this method still need further improvement. Based on this, the inventors discovered through research that in GaN-based devices, dry etching is generally used to form patterned ohmic contact metals. Dry etching typically uses chlorine (Cl)-based gas as the main gas for opening the electrode pattern window and forming the patterned metal. After etching to form the ohmic contact, a large number of Cl atoms were observed in the ohmic contact metal and the GaN-based epitaxial layer, and the peak of the Cl atom content appeared on the surface of the ohmic contact metal. The inventors analyzed that this may be because the photoresist layer failed to effectively block the injection of Cl atoms during the etching process. The dry etching step of the patterned metal introduced a large number of Cl atoms into the metal surface. Subsequently, the diffusion of Cl atoms from the metal surface to the interior of the GaN-based epitaxial layer was aggravated during the annealing process. The Cl atoms that entered the interior of the GaN-based epitaxial layer interacted with defects in the GaN-based epitaxial material to form acceptor-like complexes, which ultimately made it difficult to form ohmic contacts between the GaN-based epitaxial layer and the metal, resulting in a decrease in the electrical properties of the device.
[0040] Based on the above analysis, this invention provides a method for fabricating ohmic contacts for GaN-based devices. This method effectively improves the electrical performance of the subsequently formed ohmic contacts by effectively reducing or even eliminating impurity atoms on the metal surface of the ohmic contact. For example... Figure 1 As shown, the preparation method includes:
[0041] A substrate is provided, and a GaN-based epitaxial structure is formed on the substrate;
[0042] An insulating layer is formed on the GaN-based epitaxial structure and patterned to form an opening in the insulating layer;
[0043] A metal layer is deposited on the insulating layer, and the metal layer fills the opening;
[0044] A photoresist layer is formed on the metal layer and patterned to expose the metal layer above the opening;
[0045] The metal layer not blocked by the photoresist layer is removed by a dry etching process, and the remaining metal layer is formed as an ohmic contact metal.
[0046] Remove the photoresist layer;
[0047] The metal surface is treated with low-power dry etching to remove the ohmic contact metal of a predetermined thickness. The parameters used in the low-power dry etching of the metal surface are as follows: chlorine-containing gas is used; the bias power is between 0W and 25W (excluding 0W); and the source power is between 400W and 750W.
[0048] The ohmic contact metal is annealed to form an ohmic contact.
[0049] Dry etching processes typically employ ICP or ICP-RIE equipment, using chlorine-containing gases such as Cl2 and / or BCl3 as the etching gas. When dry etching parameters are used, with a bias power between 80W and 200W and a source power between 800W and 1400W, wafer SIMS analysis shows that Cl impurity atoms are introduced into the ohmic contact metal surface after dry etching. Furthermore, electrical testing of the TLM pattern on the wafer after annealing reveals poor ohmic contact characteristics.
[0050] The method for fabricating ohmic contacts for GaN-based devices proposed in this embodiment involves using low-power dry etching to treat the surface of the ohmic contact metal after dry etching to form the metal. A low bias power between 0W and 25W is used to reduce the surface bombardment rate, and a relatively low source power between 400W and 750W is used to reduce the plasma activation reaction. This process slowly and with minimal damage removes the metal surface, allowing a layer of high-concentration impurity atoms, such as Cl atoms, introduced by the dry etching process to be etched away along with the metal surface. This removes the high concentration of impurity atoms and reduces the introduction of new damage, thereby effectively improving the purity of the ohmic contact metal. Consequently, the electrical performance of the formed ohmic contact is improved after annealing.
[0051] The following describes in detail the method for fabricating ohmic contacts of GaN-based devices using GaN-based HEMT devices as an example. However, this method should not be considered as a limitation, as the fabrication method of the present invention is suitable for fabricating ohmic contacts of any GaN-based device.
[0052] like Figure 2 As shown, step S1 is performed first, a substrate is provided, and a GaN-based epitaxial structure 100 is formed on the substrate. The GaN-based epitaxial structure 100 includes a GaN channel layer 101 and an AlGaN barrier layer 102 from bottom to top.
[0053] As an example, the substrate can be any suitable semiconductor substrate, such as a Si substrate, a SiC substrate, a gallium nitride substrate, or a sapphire substrate, etc.
[0054] As an example, the GaN channel layer 101 and the AlGaN barrier layer 102 can be grown using epitaxial technology.
[0055] like Figure 2 As shown, step S2 is then performed, in which an insulating layer 103 is formed on the GaN-based epitaxial structure 100 and patterned to form an opening 104 on the insulating layer 103. The opening 104 includes an opening for the subsequent formation of a source ohmic contact and an opening for a drain ohmic contact.
[0056] As an example, the insulating layer 103 can be selected from existing conventional insulating materials, such as silicon nitride, silicon oxide, etc. In this embodiment, silicon nitride is selected as the insulating layer. The opening 104 is formed by photolithography and etching processes.
[0057] like Figure 3 As shown, step S3 is then performed, in which a metal layer 105 is deposited on the insulating layer 103, and the metal layer 105 fills the opening 104. The metal layer 105 can be deposited using existing conventional processes, such as CVD deposition or sputtering deposition, etc.
[0058] like Figure 4 As shown, step S4 is then performed, whereby a photoresist layer 106 is formed on the metal layer 105 and patterned to expose the metal layer 105 above the opening 104.
[0059] like Figure 5 and Figure 6As shown, step S5 is then performed, where a dry etching process is used to remove the metal layer 105 that is not blocked by the photoresist layer 106. The remaining metal layer 105 forms an ohmic contact metal 107. In the HEMT device structure, this ohmic contact metal 107 serves as both the source ohmic contact metal and the drain ohmic contact metal. During this step, the inventors believe that the photoresist layer 106 fails to effectively block atoms in the dry etching gas, allowing them to penetrate the photoresist layer 106 and be injected onto the surface of the ohmic contact metal 107, thereby introducing a large number of impurity atoms 108 onto its surface.
[0060] As an example, the dry etching process uses ICP equipment or ICP-RIE equipment, and the etching gas used is a chlorine-containing gas, such as Cl2 and / or BCl3. The bias power is between 80W and 200W, and the source power is between 800W and 1400W, so that Cl impurity atoms are introduced into the ohmic contact metal surface after dry etching.
[0061] like Figure 7 As shown, step S6 is then performed to remove the photoresist layer 106.
[0062] like Figure 8 As shown, step S7 is then performed, where a low-power dry etching process is used to remove the preset thickness of the ohmic contact metal 107 from the metal surface. The parameters used for the low-power dry etching process are as follows: chlorine-containing gas is used; the bias power is between 0W and 25W (excluding 0W and including 25W); and the source power is between 400W and 750W (including the endpoint value).
[0063] As a preferred example, the preset thickness of the ohmic contact metal 107 to be removed is between 10 nm and 40 nm, in order to completely remove the ohmic contact metal containing impurity atoms. The chlorine-containing gas is typically selected from at least one of Cl2 and BCl3.
[0064] As an example, the equipment used for the low-power dry etching process on the metal surface can be an ICP device or an ICP-RIE device.
[0065] like Figure 9As shown, as a preferred example, an additional step can be applied after this step: treating the ohmic contact metal 107 with a plasma surface treatment process. The parameters used in this plasma surface treatment process are: bias power of 0W; source power between 1200W and 1500W. The high-energy plasma gas generated in this step can cause residual impurity atoms on the metal surface to precipitate, further reducing the number of impurity atoms on the ohmic contact metal surface. Additionally, the high-energy plasma gas can repair damage to the ohmic contact metal surface caused by dry etching gas, reducing defect generation. The gas used in this plasma treatment of the ohmic contact metal 107 is N2 or H2. Furthermore, this step can also be implemented using an ICP device or an ICP-RIE device, so that low-power dry etching treatment of the ohmic contact metal 107 surface and plasma treatment of the ohmic contact metal 107 surface can be performed in the same equipment, eliminating the need for new process equipment and saving the time spent on repeated vacuuming. Etching is as follows... Figure 10 As shown, step S8 is performed to anneal the ohmic contact metal 107 to form the ohmic contact. In the HEMT device structure, the final formed ohmic contact includes source ohmic contacts and drain ohmic contacts, which has high efficiency and feasibility compared to other surface treatment technologies, while also achieving cost savings.
[0066] In this step, the annealing process uses conventional process parameters to achieve ohmic contact between metals, and no further restrictions are imposed here.
[0067] In summary, this invention provides a method for fabricating ohmic contacts for GaN-based devices. After dry etching to form the ohmic contact metal, the metal surface is treated with low-power dry etching. A low bias power (between 0W and 25W) is used to reduce the surface bombardment rate, and a relatively low source power (between 400W and 750W) is used to reduce plasma activation. This allows for slow and low-damage removal of the metal surface, removing a layer of high-concentration impurity atoms, such as Cl atoms, introduced by the dry etching process. This removes the high concentration of impurity atoms while minimizing the introduction of new damage, effectively improving the purity of the ohmic contact metal. Consequently, the electrical performance of the formed ohmic contact is improved after annealing. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.
[0068] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A method for fabricating an ohmic contact in a GaN-based device, characterized in that, The preparation method includes: A substrate is provided, and a GaN-based epitaxial structure is formed on the substrate; An insulating layer is formed on the GaN-based epitaxial structure and patterned to form an opening in the insulating layer; A metal layer is deposited on the insulating layer, and the metal layer fills the opening; A photoresist layer is formed on the metal layer and patterned to expose the metal layer above the opening; The metal layer not blocked by the photoresist layer is removed by a dry etching process, and the remaining metal layer is formed as an ohmic contact metal. Remove the photoresist layer; The metal surface is treated with low-power dry etching to remove the ohmic contact metal of a predetermined thickness. The parameters used in the low-power dry etching of the metal surface are as follows: chlorine-containing gas is used; the bias power is between 0W and 25W (excluding 0W); and the source power is between 400W and 750W. The ohmic contact metal is annealed to form an ohmic contact.
2. The method for fabricating the ohmic contact of a GaN-based device according to claim 1, characterized in that, After removing the ohmic contact metal by low-power dry etching, the process further includes treating the ohmic contact metal with a plasma treatment process, wherein the parameters for the plasma treatment process are: bias power of 0W; source power between 1200W and 1500W.
3. The method for fabricating the ohmic contact of a GaN-based device according to claim 2, characterized in that: The plasma treatment process for metal surfaces uses N2 or H2 as the gas.
4. The method for fabricating the ohmic contact of a GaN-based device according to claim 2, characterized in that: The plasma treatment process for metal surfaces is implemented using ICP equipment or ICP-RIE equipment.
5. The method for fabricating an ohmic contact in a GaN-based device according to claim 1, characterized in that: The chlorine-containing gas in the low-power dry etching process on the metal surface is at least one of Cl2 and BCl3.
6. The method for fabricating an ohmic contact in a GaN-based device according to claim 1, characterized in that: The metal surface is treated by the low-power dry etching method, and the preset thickness of the ohmic contact metal removed is between 10 nm and 40 nm.
7. The method for fabricating an ohmic contact in a GaN-based device according to claim 1, characterized in that: The low-power dry etching process for metal surfaces is achieved using ICP equipment or ICP-RIE equipment.
8. The method for fabricating an ohmic contact for a GaN-based device according to claim 1, characterized in that: The parameters used for removing the metal layer not covered by the photoresist layer using a dry etching process are as follows: chlorine-containing gas is used; the bias power is between 80W and 200W; and the source power is between 800W and 1400W.
9. The method for fabricating an ohmic contact in a GaN-based device according to claim 1, characterized in that: The insulating layer is made of silicon nitride or silicon oxide.
10. The method for fabricating an ohmic contact for a GaN-based device according to claim 1, characterized in that: The GaN-based device is a GaN-based HEMT device. The GaN-based epitaxial structure includes a GaN channel layer and an AlGaN barrier layer, and the formed ohmic contacts include source ohmic contacts and drain ohmic contacts.