CN111403479A - HEMT device with multi-metal gate structure and preparation method thereof - Google Patents

Abstract

The invention discloses a HEMT device with a multi-metal gate structure and a preparation method thereof. The device comprises AlGaN/GaN epitaxy, wherein two ends of the upper surface of the AlGaN/GaN epitaxy are respectively connected with a source drain electrode, a gate electrode is arranged on the source drain electrode close to the source side, a first layer of metal X of the gate electrode is deposited in an electron beam evaporation mode, a second layer of metal Y of the gate electrode is deposited in a magnetron sputtering mode, the work function of the second layer of metal Y of the gate electrode is higher than that of the first layer of metal X, photoetching is not needed, and the metal structure which is formed after the gate electrode is stripped and is in contact with (Al) GaN is Y/X/Y. The (Al) GaN is contacted with a multi-metal gate structure, so that an electric field is redistributed, the electric field peak value close to the edge of a grid electrode of a drain electrode is reduced, and the breakdown voltage of a device is improved; meanwhile, the lower electric field peak value at the edge of the grid electrode weakens the injection of electrons into the grid electrode to form a virtual grid effect, reduces the current collapse of the device and improves the dynamic performance of the device.

Description

HEMT device with multi-metal gate structure and preparation method thereof

technical field

The present invention relates to the field of semiconductors, in particular to a HEMT device with a multi-metal gate structure and a preparation method thereof.

Background technique

GaN materials are widely used in high-frequency power amplifiers and high-voltage power switches due to their high electron mobility, low on-resistance, excellent heat dissipation, and high breakdown. At present, the breakdown voltage of GaN-based HEMT devices is far from the theoretical limit of GaN materials (3.4 MV/cm), and the device is often prone to breakdown between the gate and drain. How to reduce the high voltage at the gate edge near the drain side? The electric field peak will be beneficial to increase the breakdown voltage of the device. The most common method at present is to use a gate field plate or a source field plate to adjust the electric field distribution, thereby reducing the high electric field peaks at the gate edge near the drain side. On the other hand, the virtual gate effect caused by electron injection into the gate exacerbates the influence on the current collapse of the device, which makes the device show poor performance under stress conditions. At present, the passivation process is generally used to reduce the surface state on the barrier layer and suppress the current collapse (R. Hao, et al, IEEE Electron Device Lett., 2017, 38(11)); the field plate process is used to modulate the electric field, There are also reports about reducing the surface state (H. Hanawa, et al, IEEE International Reliability Physics Symposium Proceedings., 2013). Some scholars (A. K.Visvkarma, et al, Semicond. Sci. Technol., 2019, 34(10)) realized the double-layer gate metal process by changing the angle of electron beam deposition, forming Ni/(Al)GaN and Ti/ The (Al)GaN gate double-contact interface changes the electric field distribution at the gate fringe and improves the breakdown voltage and dynamic performance of the device.

The current equipment for depositing metals is generally electron beam evaporation or magnetron sputtering. The magnetron sputtering equipment mainly relies on argon ions to bombard the target material and sputter the atoms of the material to the surface of the wafer; while the electron beam evaporation equipment mainly relies on heating to melt the material. After reaching the boiling point, the particles of the material are separated one by one. off the material surface to the wafer surface. For magnetron sputtering equipment, the sputtering distance is short, which mainly involves collisions between particles. There is a mean free path of particle motion to consider. Similar to a point light source, the angle between each particle is large, so sputtering The area of material on the wafer surface will be larger than the defined lithography window; while the e-beam evaporation cavity is long, similar to a parallel light source, the metal material will evaporate vertically on the wafer surface.

In conclusion, the double-layer gate metal process helps to improve the breakdown voltage and dynamic performance of the device. However, the above-mentioned method of changing the angle of electron beam deposition is difficult to precisely control and has poor repeatability.

SUMMARY OF THE INVENTION

The present invention proposes a HEMT device with a multi-metal grid structure. The second layer of metal Y prepared by magnetron sputtering completely wraps the first layer of metal X prepared by electron beams, forming a YXY metal grid structure and adjusting the electric field. distribution, which reduces the electric field peak at the gate edge near the drain and increases the breakdown voltage of the device; at the same time, the lower electric field peak at the gate edge weakens the gate injection of electrons to form a virtual gate for the device current The collapse effect improves the dynamic performance of the device.

The object of the present invention is achieved by at least one of the following technical solutions.

The invention provides a HEMT device with a multi-metal gate structure, the device comprises AlGaN/GaN epitaxy, two ends of the upper surface of the AlGaN/GaN epitaxy are respectively connected to source and drain electrodes, and the source and drain electrodes are provided with gate electrodes close to the source side, The first layer of metal X of the gate electrode is deposited by electron beam evaporation, the second layer of metal Y of the gate electrode is deposited by magnetron sputtering, and the work function of the second layer of metal Y of the gate electrode is higher than that of the first layer The work function of metal X does not require additional photolithography steps, and the metal structure formed after the gate electrode is lifted off and in contact with (Al)GaN is Y/X/Y.

The invention adopts the method of combining electron beam and magnetron sputtering, and realizes multi-metal gate structure Y/X/Y after metal stripping. This method does not need to change the angle of electron beam deposition, and only needs to The traditional deposition method has repeatability, and compared with the above-mentioned double-layer gate metal process, the method based on the present invention realizes a three-layer gate metal process.

The HEMT device with a multi-metal gate structure provided by the present invention includes: AlGaN/GaN epitaxy, source-drain electrodes and gate electrodes; both ends of the upper surface of the AlGaN/GaN epitaxy are respectively connected to the source-drain electrodes; the gate electrode is connected to the AlGaN /GaN epitaxial upper surface connection; the gate electrode includes a first layer of metal X and a second layer of metal Y; the metal structure formed after the gate electrode is peeled off and in contact with (Al)GaN is Y/X/Y.

The HEMT device with the multi-metal gate structure provided by the present invention is an AlGaN/GaN HEMT device.

Further, the length of the second layer of metal Y on both sides of the first layer of metal X is 0.5-1 μm.

Further, the second-layer metal Y completely wraps the first-layer metal X.

Further, the distance from the gate electrode to the source electrode is smaller than the distance from the gate electrode to the drain electrode, that is, the source-drain electrode is provided with a gate electrode close to the source side.

The present invention provides a method for preparing the HEMT device with a multi-metal gate structure, comprising the following steps:

(1) Define source-drain electrode windows on AlGaN/GaN epitaxy, prepare source-drain electrodes and anneal them to form ohmic contacts;

(2) Defining a gate electrode lithography window, preparing a multi-metal gate structure Y/X/Y, and obtaining the HEMT device having the multi-metal gate structure.

Further, the lithography window of the gate electrode in step (2) is designed to be 1-2 μm.

Further, in the multi-metal gate structure Y/X/Y of step (2), the first layer of metal X is deposited by electron beam evaporation, and the second layer of metal Y is deposited by magnetron sputtering; and the second layer of metal Y is deposited by magnetron sputtering; The thickness of Y is greater than the thickness of the first layer of metal X.

Further, in the multi-metal gate structure Y/X/Y in step (2), the first layer of metal X is one of Ni, Ti, TiN, etc., and the second layer of metal Y is one of Cu, W, Ni, etc. a kind of.

Compared with the prior art, the present invention has the following beneficial effects and advantages:

The present invention utilizes the multi-metal gate prepared by electron beam and magnetron sputtering, without additional photolithography steps, the second layer of metal Y prepared by magnetron sputtering completely wraps the first layer of metal X prepared by electron beam, forming The multi-metal gate structure Y/X/Y is adjusted; the electric field distribution is adjusted, the electric field peak value at the gate edge near the drain is reduced, and the breakdown voltage of the device is improved; at the same time, the lower electric field peak value at the gate edge The virtual gate effect formed by electron injection into the gate is weakened. By testing the C-V characteristics, the saturation capacitance (158pF) of the corresponding W/TiN/W structure device at a test frequency of 10KHz is compared with that of the TiN structure device ( 136pF) decreased by 13.9%, improving the dynamic performance of the device.

Description of drawings

1 is a schematic diagram of an epitaxial layer of a GaN-based HEMT device before preparing source-drain contact electrodes according to an embodiment;

2 is a schematic diagram of the device structure of the embodiment after the source-drain contact electrodes are prepared and annealed to form ohmic contacts;

3 is a schematic diagram of a device structure after forming a gate electrode according to an embodiment;

4 is a graph of capacitance data of a HEMT device with a multi-metal gate structure and a device with a TiN structure prepared in Example 2;

In the figure, AlGaN/GaN epitaxy 1 , source-drain electrodes 2 , and gate electrodes 3 .

Detailed ways

The specific implementation of the present invention will be further described below with reference to examples, but the implementation and protection of the present invention are not limited thereto. It should be pointed out that, if there are any processes that are not described in detail below, those skilled in the art can realize or understand them with reference to the prior art.

Example 1

This embodiment provides a HEMT device with a multi-metal gate structure. As shown in FIG. 3 , the device includes an AlGaN/GaN epitaxy 1 , and two ends of the upper surface of the AlGaN/GaN epitaxy are connected to source and drain electrodes 2 respectively. A gate electrode 3 is arranged on the side of the pole 2 close to the source. The first layer of metal Ti of the gate electrode 3 is deposited by electron beam evaporation, and the second layer of metal Ni of the gate electrode 3 is deposited by magnetron sputtering, without additional light. In the etching step, the metal structure formed after the gate electrode 3 is peeled off and in contact with (Al)GaN is Ni/Ti/Ni. G-1 in FIG. 3 represents the first layer of metal, and G-2 represents the second layer of metal.

This embodiment also provides a method for preparing a HEMT device with a multi-metal gate structure, including the following steps:

(1) Define the source-drain electrode window on AlGaN/GaN epitaxy (the epitaxial layer before preparing the source-drain contact electrode is shown in Figure 1), prepare the source-drain electrode 2 and anneal it to form an ohmic contact, as shown in Figure 2;

(2) Define the gate electrode 3 lithography window to prepare a multi-metal gate structure Ni/Ti/Ni, as shown in Figure 3; the gate lithography window of the HEMT device is designed to be 1 μm, and the metal structure Ni/Ti formed after the gate electrode is stripped off In /Ni, the length of the second layer of metal Ni on both sides of the first layer of metal Ti is 0.7 μm, the thickness of the first layer of metal Ti is 50 nm, the thickness of the second layer of metal Ni is 250 nm, and the thickness of the second layer of metal Ti is 250 nm. Ni completely wraps the first layer of metal Ti to obtain the HEMT device with the multi-metal gate structure.

The HEMT device with the multi-metal gate structure prepared in Example 1 has good dynamic performance and low saturation capacitance, as shown in FIG. 4 .

Example 2

This embodiment provides a HEMT device with a multi-metal gate structure. As shown in FIG. 3 , the device includes an AlGaN/GaN epitaxy 1 , and two ends of the upper surface of the AlGaN/GaN epitaxy are connected to source and drain electrodes 2 respectively. A gate electrode 3 is arranged on the side of the pole 2 close to the source, the first layer of metal TiN of the gate electrode 3 is deposited by electron beam evaporation, and the second layer of metal W of the gate electrode 3 is deposited by magnetron sputtering, without additional light In the etching step, the metal structure formed after the gate electrode 3 is peeled off and in contact with (Al)GaN is W/TiN/W.

This embodiment also provides a method for preparing a HEMT device with a multi-metal gate structure, including the following steps:

(1) Define source-drain electrode windows on AlGaN/GaN epitaxy 1, prepare source-drain electrodes 2 and anneal them to form ohmic contacts, as shown in Figure 2;

(2) Define the gate electrode 3 lithography window, and prepare a multi-metal gate structure W/TiN/W, as shown in Figure 3; the gate lithography window of the HEMT device is designed to be 1 μm, and the metal structure W/TiN formed after the gate electrode is stripped off In /W, the length of the second layer of metal W on both sides of the first layer of metal TiN is 0.5 μm, the thickness of the first layer of metal TiN is 50 nm, the thickness of the second layer of metal W is 200 nm, and the second layer of metal W is completely The first layer of metal TiN is wrapped to obtain the HEMT device with the multi-metal gate structure.

FIG. 4 is a C-V characteristic comparison diagram of the HEMT device (W/TiN/W) with a multi-metal gate structure prepared in Example 2, only showing the corresponding capacitance data when the test frequency is 10KHz, it can be seen that with W/TiN/W The devices with TiN/W structure have lower saturation capacitance values than those with TiN structure.

The above examples are only preferred embodiments of the present invention, and are only used to explain the present invention, but not to limit the present invention. Changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention shall belong to the present invention. the scope of protection of the invention.

Claims (8)

1. The HEMT device with a multi-metal gate structure is characterized in that, comprising: AlGaN/GaN epitaxy, source-drain electrode and gate electrode; both ends of the upper surface of the AlGaN/GaN epitaxy are respectively connected to source-drain electrodes; the gate electrode It is connected to the upper surface of AlGaN/GaN epitaxy; the gate electrode includes a first layer of metal X and a second layer of metal Y; the metal structure formed after the gate electrode is peeled off and in contact with (Al)GaN is Y/X/Y. 2 . The HEMT device with a multi-metal gate structure according to claim 1 , wherein the length of the second layer of metal Y on both sides of the first layer of metal X is 0.5-1 μm. 3 . 3 . The HEMT device with a multi-metal gate structure according to claim 1 , wherein the two-layer metal Y completely wraps the first-layer metal X. 4 . 4 . The HEMT device with a multi-metal gate structure according to claim 1 , wherein the distance from the gate electrode to the source electrode is smaller than the distance from the gate electrode to the drain electrode. 5 . 5. A method for preparing the HEMT device with a multi-metal gate structure according to any one of claims 1-4, characterized in that, comprising the steps: (1) Define source-drain electrode windows on AlGaN/GaN epitaxy, prepare source-drain electrodes and anneal them to form ohmic contacts; (2) Defining a gate electrode lithography window, preparing a multi-metal gate structure Y/X/Y, and obtaining the HEMT device having the multi-metal gate structure. 6 . The method for preparing a HEMT device with a multi-metal gate structure according to claim 5 , wherein the lithography window of the gate electrode in step (2) is designed to be 1-2 μm. 7 . 7 . The method for preparing a HEMT device with a multi-metal gate structure according to claim 5 , wherein in the multi-metal gate structure Y/X/Y in step (2), the first layer of metal X adopts electron beams. 8 . Evaporation deposition, the second layer of metal Y is deposited by magnetron sputtering; and the thickness of the second layer of metal Y is greater than the thickness of the first layer of metal X. 8 . The method for preparing a HEMT device with a multi-metal gate structure according to claim 5 , wherein, in the multi-metal gate structure Y/X/Y in step (2), the first layer of metal X is Ni, One of Ti and TiN, and the metal Y of the second layer is one of Cu, W, and Ni.

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