Method for forming ohmic contacts in GaN-based electronic devices and ohmic contacts of GaN-based electronic devices manufactured thereby

Abstract

The present invention relates to a method for forming ohmic contacts of a GaN-based electronic element, the method including the steps of: (A) irradiating a GaN-based electronic element with an ion beam to form an ion region in a part of the interior of the GaN-based electronic element; (B) forming an electrode layer on a part of the surface of the GaN-based electronic element corresponding to the ion region; and (C) heat-treating the GaN-based electronic element on which the electrode layer has been formed. The present invention also relates to an ohmic contact of a GaN-based electronic element manufactured by the method for forming ohmic contacts of a GaN-based electronic element.

Description

Technical Field

[0001] The present invention relates to a method for forming an ohmic contact of a GaN-based electronic device and an ohmic contact of a GaN-based electronic device manufactured thereby.

Background Art

[0002] An electronic device based on a gallium nitride (GaN) substrate can form a two-dimensional electron gas (2DEG) having a high electron concentration and a high electron mobility and is thus used in high-frequency electronic devices.

[0003] In order for an electronic device based on a gallium nitride substrate as described above to ensure excellent high-frequency characteristics, it is important to reduce the on-resistance of the device. An electronic device based on a gallium nitride substrate can have a low channel resistance using 2DEG, whereas it is difficult to obtain an ohmic contact having a low resistance value in source and drain regions due to the wide bandgap of gallium nitride.

[0004] To solve such problems, conventionally, titanium (Ti) is deposited and a high-temperature heat treatment (annealing) process at 800°C or higher is performed. In such a heat treatment process, nitrogen derived from the already deposited titanium and gallium nitride reacts with each other to form titanium nitride (TiN), whereby an ohmic contact can be obtained. However, in the existing process for forming an ohmic contact, the heat treatment process has to be advanced at a considerably high temperature, which damages the device surface and additional surface passivation layer has to be deposited before proceeding.

[0005] Furthermore, the high-temperature heat treatment process for forming the source / drain region results in the gate being formed after the source / drain is formed, which imposes constraints on the changes in the device manufacturing process that must be carried out to improve the device's performance. Above all, there are limits to how much the ohmic contact resistance can be reduced by the high-temperature heat treatment process alone, so continuous efforts are being made to improve this from the perspectives of process simplification, stability, and performance. [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to solve the aforementioned problems by overcoming the limitations of ohmic contact resistance that are difficult to reduce by heat treatment processes alone, and by providing a method for forming ohmic contacts that can obtain the resistance value required for high-frequency electronic elements even at low heat treatment temperatures, and by providing ohmic contacts manufactured thereby. [Means for solving the problem]

[0007] One embodiment of the present invention includes the steps of (A) irradiating a GaN-based electronic element with an ion beam to form an ion region in a part of the interior of the GaN-based electronic element; (B) forming an electrode layer on a part of the surface of the GaN-based electronic element corresponding to the ion region; and (C) heat-treating the GaN-based electronic element on which the electrode layer is formed. A method for forming a mic contact is provided.

[0008] Another embodiment of the present invention provides an ohmic contact for a GaN-based electronic element manufactured by the ohmic contact formation method for GaN-based electronic elements described above. [Effects of the Invention]

[0009] The present invention provides a method for forming ohmic contacts in GaN-based electronic devices. This method involves pre-injecting a metal or metalloid into the region where the ohmic contacts are to be formed, and then forming nitrides during the heat treatment process, which are generated from the injected metal or metalloid and nitrogen derived from the GaN-based material. This method reduces the resistance of the ohmic contacts. In particular, the nitrides are easy to form, and unlike conventional methods, ohmic contacts can be formed even at low temperatures. Despite the low-temperature heat treatment, the device can achieve the resistance values ​​required for high-frequency electronic devices.

[0010] This makes it possible to manufacture ohmic contacts for GaN-based electronic devices that are optimized to reduce ohmic contact resistance while preventing a decrease in drop voltage. Furthermore, it reduces surface damage that significantly affects GaN-based electronic devices, simplifies the process, and has the potential to enable development with a variety of electronic device structures. [Brief explanation of the drawing]

[0011] [Figure 1] This figure schematically illustrates a method for forming ohmic contacts in a GaN-based electronic device according to one embodiment of the present invention. [Figure 2] This figure shows the distribution of Ti ions injected into the electronic device of Example 1 according to Experimental Example 1 of the present invention. [Figure 3] This figure, based on Experimental Example 1 of the present invention, shows the amount of Ti ions implanted in the electronic device of Example 1 depending on the Ti ion implantation depth. [Modes for carrying out the invention]

[0012] While the present invention can be modified in various ways and may have many different embodiments, specific embodiments will be illustrated and described in detail with reference to the drawings. However, this should not be understood as limiting the present invention to specific embodiments, but rather as including all modifications, equivalents, or substitutes that fall within the spirit and technical scope of the present invention.

[0013] The terms used herein are used solely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0014] In this specification, the expression "~above" may mean that two members are directly joined and attached to each other, or it may mean that two members are located adjacent to each other.

[0015] Therefore, the configurations illustrated in the embodiments described herein are merely preferred embodiments of the present invention and do not represent the entire technical concept of the present invention; as of the time of filing, there may be a variety of equivalents and modifications that can substitute for them.

[0016] The present invention will be described in detail below.

[0017] This invention provides a method for forming ohmic contacts in GaN-based electronic devices.

[0018] The method for forming ohmic contacts in the GaN-based electronic element is (A) ion The procedure may include: (B) irradiating the GaN-based electronic element with a beam to form an ion region in a part of the interior of the GaN-based electronic element; (A) forming an electrode layer on the surface of the GaN-based electronic element corresponding to the ion region; and (C) heat-treating the GaN-based electronic element on which the electrode layer has been formed.

[0019] The aforementioned electronic elements refer to electronic components that utilize the conduction of electrons within a solid, and may include, but are not limited to, diodes, transistors, power semiconductor elements, high-frequency elements, sensors, light-emitting elements (LEDs), and solar cells.

[0020] The above-mentioned GaN-based electronic device means an electronic device containing a GaN-based material. For example, the GaN-based electronic device may be an electronic device containing a wafer containing a GaN-based material. Specifically, the GaN-based material can include, but is not limited to, GaN, or AlGaN, etc.

[0021] The above-mentioned GaN (gallium nitride) is a wide-bandgap (WBG) material with a higher breakdown voltage and higher thermal conductivity than existing silicon (Si). When using a GaN-based electronic device, especially an AlGaN / GaN-based heterojunction structure, it utilizes a two-dimensional electron gas (2DEG) layer with a high electron concentration and mobility. Due to its excellent current characteristics and fast signal conversion speed, it is suitable for high-frequency and / or high-power electronic devices.

[0022] The above-mentioned GaN-based electronic device may include an AlGaN / GaN-based heterojunction electronic device. That is, the GaN-based electronic device may include a wafer having an AlGaN / GaN-based heterojunction.

[0023] In addition, the above-mentioned GaN-based electronic device may further include a substrate. That is, the GaN-based electronic device may include a structure laminated in the order of substrate / GaN / AlGaN.

[0024] The substrate may include, for example, sapphire (Al2O3), silicon (Si), or silicon carbide (SiC).

[0025] The GaN-based electronic device may be manufactured using known thin-film deposition growth techniques, such as molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), or hydride vapor phase epitaxy (HVPE), but is not limited thereto. In particular, due to the crystal structure and growth direction characteristics of hexagonal zinc crystalline GaN (gallium nitride), using metal-organic chemical vapor deposition (MOCVD) for depositing GaN-based materials is advantageous in that it can produce thin films of superior quality and allows for simultaneous deposition on multiple substrates, but is not limited thereto.

[0026] The aforementioned metal-organic chemical vapor deposition (MOCVD) method is a method for growing compound crystals by supplying organometallic compounds (organometallic raw material gases) into a reactor and thermally decomposing them on a heated substrate. It has the advantage that the thickness of the heterojunction can be adjusted to the nanoscale by adjusting the flow rate of the highly purified organometallic compound and the temperature and pressure of the reactor.

[0027] The ion beam in step (A) above includes an ion beam derived from a metal or metalloid. That's fine.

[0028] The aforementioned ion beam is a charged particle beam consisting of ions, also called a particle beam or electron beam. The irradiation technique of such an ion beam utilizes the phenomenon in which the kinetic energy of high-energy ion beam particles (ions) is transferred to the surface of an electronic element and converted into kinetic energy. Ions incident on the surface of an electronic element irradiated with an ion beam cause a chain collision (collision cascade) of atoms in the electronic element, and the properties of the material can be deformed by elastic or inelastic collisions. In this case, if the ion beam energy is higher than the bonding energy of the surface atoms, a sputtering phenomenon occurs in which ions break the atomic bonds on the surface and release atoms to the outside. Conversely, if the ion beam energy is lower than the bonding energy of the surface atoms, ion implantation occurs in which the surface of the ions remains while undergoing chain collisions with the surface atoms.

[0029] Immediately after ion implantation, collisions cause defects to form within the crystal structure. For the implanted ions to act as dopants, they must be in substitution positions within the crystal structure. However, due to the defects, they cannot maintain the original crystal structure and therefore cannot be electrically activated. Consequently, the defective crystal structure must be recrystallized through a heat treatment (annealing) process to restore it to a normal state, allowing the implanted ions to move to substitution positions within the crystal structure and act as dopants, thereby electrically activating the crystal. Heat treatment methods include furnace annealing, rapid thermal annealing, laser annealing, and electron beam annealing.

[0030] The aforementioned metal may include at least one selected from the group consisting of titanium (Ti), aluminum (Al), and tantalum (Ta).

[0031] The aforementioned metalloid may contain silicon (Si).

[0032] The aforementioned metal or metalloid can form low resistance through bonding with nitrogen atoms (N) contained within the GaN-based electronic device, and among these, using an ion beam derived from titanium (Ti) is preferred in terms of low resistance.

[0033] The ion beam in step (A) above may be irradiated with an energy of 15 to 20 keV. If the ion implantation energy is less than 15 keV, there is a problem that ions are implanted above the AlGaN / GaN interface, making it difficult to achieve low resistance. If it is greater than 20 keV, there is a problem that ions are implanted even deeper than the AlGaN / GaN interface, making it difficult to achieve low resistance.

[0034] When the GaN-based electronic element includes an AlGaN / GaN heterojunction electronic element, the thickness of the AlGaN layer may be between 100 Å and 400 Å. If the thickness of the AlGaN layer does not meet the above range, the 2DEG characteristics may deteriorate.

[0035] Since the 2DEG is located within 100 Å in the direction of gravity from the AlGaN / GaN interface, the formation depth of the ion region can be adjusted by considering the position of the 2DEG. The depth at which the ion region is formed in step (A) may be a point between 100 Å and 500 Å in the direction of gravity (perpendicular to the surface) from the surface of the GaN-based electronic element corresponding to the ion region. When the depth at which the ion region is formed satisfies the above range, a nitride layer of ions and nitrogen originating in the GaN-based electronic element is formed at the AlGaN / GaN interface, resulting in low contact resistance.

[0036] In step (A) above, the average ion implantation amount of the ion beam implanted into the GaN-based electronic device is 1 × 10⁻⁶ 14 From 1 x 10 16 ions / cm 2This may be the case. When the average ion implantation amount of the ion beam satisfies the above range, the ions of the ion beam combine with nitrogen atoms (N) inside the GaN-based electronic element to form nitrides, resulting in a low ohmic contact resistance.

[0037] In step (A) above, the step of patterning the portion of the GaN-based electronic device that will be irradiated with the ion beam before irradiating it with the ion beam may be included.

[0038] The patterning step may include masking the remaining surface portion of the GaN-based electronic device, excluding the surface portion into which ions are implanted via the ion beam. That is, ions originating from the ion beam may be selectively implanted into the GaN-based electronic device through the unmasked portion of the surface.

[0039] The aforementioned patterning step may, but is not limited to, a photolithography method.

[0040] If the patterning step is photolithography, a known photolithography method can be used, and generally, it may be carried out in the order of wafer cleaning / photoresist coating / masking / exposure / phenone / photoresist removal, but is not limited thereto, and in the present invention, some of the listed steps may be omitted or additional steps may be added depending on the process conditions.

[0041] In other words, as mentioned above, the patterned region formed before step (A) may not be removed immediately after step (A), but rather after the electrode layer is formed in step (B) and before the heat treatment step (C).

[0042] For example, if the patterning step is photolithography, the step of removing the patterned area may mean the step of removing the coated photoresist.

[0043] In other words, the electrode layer may be formed only on a portion of the surface of the GaN-based electronic element corresponding to the ion region.

[0044] The electrode layer may represent a concept that includes a source and / or drain.

[0045] The electrode layer may contain an electrode material having a work function even smaller than that of a GaN-based material.

[0046] The electrode layer can be manufactured using known thin-film deposition growth techniques, and may be formed using thin-film growth techniques including, for example, electron beam evaporation, thermal evaporation, sputtering, or electroless plating, but is not limited thereto.

[0047] The electrode material may include at least one selected from the group consisting of titanium (Ti), aluminum (Al), nickel (Ni), gold (Au), silicon (Si), tantalum (Ta), and alloys thereof.

[0048] The electrode layer may be a single layer, or it may be a plurality of layers formed by depositing many electrode materials.

[0049] Finally, the GaN-based electronic element on which the electrode layer is formed can be heat-treated. This heat-treatment step can be performed using a known method for heat-treating electronic elements.

[0050] In this case, the heat treatment step (C) may include the formation of nitrides in the ionic region due to nitrogen atoms (N) contained inside the GaN-based electronic element. For example, if titanium (Ti) ions are contained in the ionic region, the nitrides may include titanium nitride (TiN).

[0051] The nitride affects the mobility of electrons flowing in and out during ohmic contact, thus reducing the ohmic contact resistance.

[0052] The process may include bringing the nitride formed by the heat treatment in step (C) into contact with the electrode layer.

[0053] The present invention provides a method for forming ohmic contacts in GaN-based electronic devices. Compared to conventional techniques that involve depositing titanium onto the device surface, this method uses an ion beam to form ion regions even inside the GaN-based electronic device. Furthermore, the thickness and / or depth of these regions can be easily adjusted, facilitating the formation of nitrides in which ions from the ion beam bond with nitrogen atoms (N). This, in turn, reduces the ohmic contact resistance of the GaN-based electronic device.

[0054] The heat treatment in step (C) may be performed at a temperature of less than 800°C. That is, unlike conventional techniques that require high-temperature heat treatment at 800°C or higher, the ohmic contact formation method for GaN-based electronic elements of the present invention can realize ohmic contact that simultaneously satisfies the characteristics of contact resistance and drop voltage even at low heat treatment temperatures. The heat treatment in step (C) may be performed at a temperature of 600°C or higher but less than 800°C.

[0055] The process may further include a step of removing the patterned region before the heat treatment step in step (C) described above.

[0056] For example, in the present invention, after forming an ionic region in step (A), a lift-off step can be performed after forming an electrode layer on the surface portion of the GaN-based electronic element corresponding to the ionic region in step (B). In the present invention, the lift-off step may mean a method of patterning the electrode layer using a material such as a photoresist, or, if the patterning step is photolithography as described above, it may mean removing the photoresist.

[0057] Another embodiment of the present invention provides an ohmic contact for a GaN-based electronic element manufactured by the ohmic contact formation method for GaN-based electronic elements described above.

[0058] The ohmic contact of the aforementioned GaN-based electronic device exhibits low contact resistance despite being manufactured at low heat treatment temperatures, and simultaneously improves voltage drop, enabling the realization of superior high-frequency electronic devices.

[0059] Therefore, such high-frequency electronic devices can be applied to a variety of high-frequency application fields, such as 5G, autonomous vehicles, and military laser modules.

[0060] The present invention will be described in more detail below with reference to preferred embodiments.

[0061] However, these embodiments are provided to illustrate the present invention in more detail and do not limit the scope of the invention.

[0062] <Example 1> As shown in (1) of Figure 1, an AlGaN / GaN heterojunction structure stacked on a substrate (not shown in the drawing) was used as a wafer. (2) After patterning the source / drain region using a photolithography process, (3) a 20 keV titanium (Ti) ion beam was irradiated, and (4) a Ti / Al / Ni / Au electrode layer was deposited on the patterned portion by electron beam evaporation, followed by a lift-off process to remove the photoresist. Then, (5) an ohmic contact was formed by heat treatment at a temperature of less than 800°C.

[0063] <Experimental Example 1> In Example 1, Figure 2 shows the distribution of titanium (Ti) ions implanted when irradiated with a 20 keV titanium (Ti) ion beam, and Figure 3 shows the amount of titanium (Ti) ions implanted depending on the titanium (Ti) ion implantation depth.

Claims

1. (A) A step of irradiating a GaN-based electronic element with a titanium (Ti)-derived ion beam to form an ionic region in a part of the interior of the GaN-based electronic element; (B) The step of forming an electrode layer on the surface portion of the GaN-based electronic element corresponding to the ionic region; and (C) A step of heat-treating the GaN-based electronic element on which the electrode layer is formed; Includes, The average ion implantation rate of the ion beam is 1 × 10⁻⁶ １４ from 1 x 10 １６ ions / cm ２ And, The ion beam in step (A) above is irradiated with an energy of 15 to 20 keV, The heat treatment step in step (C) above includes the formation of nitrides in the ionic region due to nitrogen atoms (N) contained inside the GaN-based electronic element, A method for forming ohmic contacts in a GaN-based electronic element, wherein the heat treatment in step (C) is performed at a temperature of 600°C or higher and less than 800°C.

2. The method for forming an ohmic contact of a GaN-based electronic element according to claim 1, wherein the GaN-based electronic element includes an AlGaN / GaN heterojunction electronic element.

3. The method for forming an ohmic contact of a GaN-based electronic element according to claim 1, wherein the step in (A) above includes a step of patterning the portion of the GaN-based electronic element that will be irradiated with the ion beam before irradiating it with the ion beam.

4. The method for forming ohmic contacts of a GaN-based electronic element according to claim 3, wherein the patterning step is performed by a photolithography method.

5. The method for forming an ohmic contact in a GaN-based electronic device according to claim 1, wherein the electrode layer includes an electrode material having a work function even smaller than that of a GaN-based material.

6. The method for forming an ohmic contact in a GaN-based electronic device according to claim 5, wherein the electrode material comprises at least one selected from the group consisting of titanium (Ti), aluminum (Al), nickel (Ni), gold (Au), silicon (Si), tantalum (Ta), and alloys thereof.

7. The method for forming an ohmic contact in a GaN-based electronic element according to claim 1, comprising bringing the nitride formed by the heat treatment in step (C) into contact with the electrode layer.

8. The method for forming an ohmic contact of a GaN-based electronic element according to claim 3, further comprising the step of removing the patterned region before the heat treatment step of step (C).

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