A HEMT device with Schottky / Ohmic drain structure and a method for preparing the same

Abstract

The present invention discloses a HEMT device with a Schottky / Ohmic drain structure and a preparation method thereof. The HEMT device with a Schottky / Ohmic drain structure comprises, from bottom to top, a silicon substrate, an AlN nucleation layer, an AlGaN buffer layer, a GaN channel layer, an AlN insertion layer and an AlGaN barrier layer; a gate electrode, a source electrode and a drain electrode are arranged above the AlGaN barrier layer, and the gate electrode is located between the source electrode and the drain electrode. From bottom to top, the device comprises a silicon substrate, an AlN nucleation layer, an AlGaN buffer layer, a GaN channel layer, an AlN insertion layer and an AlGaN barrier layer; a gate electrode, a source electrode and a drain electrode are arranged above the AlGaN barrier layer, and the gate electrode is located between the source electrode and the drain electrode. The source and drain electrodes prepared by the present invention form a double-layer contact interface with the cap layer, and a Schottky / Ohmic drain structure is formed after annealing, which optimizes the electric field distribution on the drain side and improves the breakdown voltage and its distribution stability.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and in particular to a HEMT device with a Schottky / Ohmic drain structure and a preparation method thereof. Background Art

[0002] Thanks to the excellent material properties of gallium nitride (GaN), GaN-based high electron mobility transistors (HEMTs) have been widely used in power electronics and radio frequency. With the upgrading of power electronics application requirements, it is particularly important to further improve the breakdown voltage of the device and improve its stability. Among them, the source-drain contact is one of the key factors affecting the breakdown voltage and reliability of the device. Early studies have shown that the morphology of ohmic metal, especially the drain metal morphology close to the gate, has an important influence on the breakdown voltage of the device (Y. Lian, et al, IEEE Electron Device Letters, 33 (7), 2012). After high-temperature annealing, the metal morphology will become rough, which is easy to introduce additional metal spikes, causing the leakage current of the device to increase and break down prematurely.

[0003] At present, the main method to improve the above problems is to use low-temperature annealing or other optimized ohmic electrode structures. Low-temperature annealing generally refers to 600°C and below. Low-temperature annealing can improve the metal morphology very well. Its research is mainly for gold-free metal systems, and generally requires partial etching of the AlGaN barrier layer. This step has very high requirements for etching accuracy. Usually, the remaining barrier layer thickness under the source and drain electrodes is about 1nm. In addition, there are still many uncertainties in the degradation of the ohmic contact formed by low-temperature annealing under high temperature and high stress, and its long-term reliability remains to be verified. The ohmic contact process formed by high-temperature annealing is relatively more mature and is still the mainstream choice for electrode annealing in the industry. Based on this, relevant personnel have proposed structures such as Schottky drain and Schottky / ohmic drain to improve this phenomenon. The Schottky drain structure can produce a more uniform electric field distribution, so the breakdown voltage of the device is higher. Although the Schottky drain can improve the electrode morphology and increase the device breakdown voltage, its on-resistance also increases, which increases the device loss (Y. Lian, et al, IEEE Transactions on Electron Devices, 62 (2), 2015). The Schottky / Ohmic drain structure can well balance the breakdown voltage and on-resistance (W. Zhang, et al, IEEE Journal of the Electron Devices Society, 6 (99), 2018). From the perspective of device characteristics, the Schottky / Ohmic drain structure is more suitable. In addition, the metal surface roughness of the gold-free metal system under high temperature annealing is lower than that of the gold-containing metal system, and its effect on improving the device breakdown voltage is also very significant.

[0004] Conventional Schottky / Ohm drain structures are realized by two-step photolithography process, which has many process steps and many problems such as small photolithography registration window. Realizing Schottky / Ohm drain structure by single-step process will help simplify the process steps and eliminate the problem of secondary registration, which makes the process more feasible. Summary of the invention

[0005] Based on this, in order to solve the problems existing in the prior art, the present invention proposes a HEMT device with a Schottky / Ohmic drain structure and a preparation method thereof. Thanks to different electron beam evaporation angles, through one-time photolithography, the source-drain electrode prepared by the present invention forms a double-layer contact interface with the AlGaN barrier layer, and forms a Schottky / Ohmic drain structure after annealing, which optimizes the electric field distribution on the drain side and improves the breakdown voltage and its distribution stability.

[0006] The object of the present invention is achieved by at least one of the prior art solutions.

[0007] A HEMT device with a Schottky / Ohmic drain structure comprises, from bottom to top, a silicon substrate, an AlN nucleation layer, an AlGaN buffer layer, a GaN channel layer, an AlN insertion layer and an AlGaN barrier layer; a gate electrode, a source electrode and a drain electrode are arranged above the AlGaN barrier layer, and the gate electrode is located between the source electrode and the drain electrode.

[0008] Furthermore, the source electrode and the drain electrode are both obtained by one-step photolithography and two-step variable-angle electron beam evaporation of metal; the source electrode and the drain electrode both include a first-step metal and a second-step metal, wherein the first-step metal is obtained by oblique-angle incidence evaporation, and the second-step metal is obtained by vertical-incidence evaporation.

[0009] Furthermore, the first step metal is located at an obliquely lower side of the second step metal, and both the first step metal and the second step metal are in contact with the AlGaN barrier layer.

[0010] Furthermore, after the source electrode and the drain electrode are annealed, the first-step metal in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer, and the second-step metal forms a Schottky contact with the AlGaN barrier layer.

[0011] Furthermore, the first step metal is an X / Y double-layer metal system, wherein the first metal X includes Ta or Ti, and the second metal Y includes Al.

[0012] Furthermore, the second-step metal is a Z / W double-layer metal system, wherein the third metal Z includes Ni, and the fourth metal W includes Ti, TiN or TiW.

[0013] Further, the work function of the first metal X is smaller than the work function of the third metal Z.

[0014] A method for preparing a HEMT device with a Schottky / Ohmic drain structure comprises the following steps:

[0015] S1, construct silicon substrate, AlN nucleation layer, AlGaN buffer layer, GaN channel layer, AlN insertion layer and AlGaN barrier layer from bottom to top, use photoresist to define source and drain lithography areas on the AlGaN barrier layer, and deposit the first step metal at an oblique angle based on electron beam evaporation equipment;

[0016] S2, after the first step of metal deposition is completed, the second step of metal is deposited by vertical incidence to complete the deposition of the entire source electrode and drain electrode;

[0017] S3, after the stripping of the source electrode and the drain electrode is completed, an annealing treatment is performed, so that the first step metal in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer, and the second step metal forms a Schottky contact with the AlGaN barrier layer;

[0018] S4. Prepare a gate electrode on the AlGaN barrier layer to obtain a HEMT device with a Schottky / Ohmic drain structure.

[0019] Furthermore, when the first step metal is deposited at an oblique angle, the oblique angle ranges from 5° to 20°.

[0020] Furthermore, in the first step of metal, the thickness of the first metal X is 5-20 nm, the thickness of the second metal Y is 60-120 nm; the thickness of the third metal Z is 10-20 nm, and the thickness of the fourth metal W is 60-100 nm.

[0021] Compared with the prior art, the present invention has the following beneficial effects and advantages:

[0022] 1. The present invention utilizes electron beam evaporation at different angles and adopts one-step photolithography to obtain different contact interfaces, and forms a Schottky / Ohm hybrid contact drain after annealing. The process steps are simple and there is no need to consider additional photolithography alignment issues.

[0023] 2. The process proposed by the present invention has good repeatability. The breakdown voltage of the HEMT device using the Schottky / Ohmic drain structure is significantly improved and the distribution is more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the Schottky / Ohmic drain structure of a HEMT device with a Schottky / Ohmic drain structure in Example 1 of the present invention.

[0025] Figure 2 This is a cross-sectional view of a finished product of a HEMT device with a Schottky / Ohmic drain structure in Example 1 of the present invention.

[0026] Figure 3 This is the IV curve of the second step of Example 1 of the present invention, metal Ni / TiN (20 / 100 nm) with an electrode spacing of 10 μm after high temperature annealing.

[0027] Figure 4 The figure is a transfer characteristic curve diagram of a HEMT device with Schottky / Ohmic drain structure in Example 1 and the control group.

[0028] Figure 5a This is the electric field distribution diagram of the device drain side of the Schottky / Ohmic drain structure prepared based on the first step metal Ti / Al and the second step metal Ni / TiN in Example 1; Figure 5b This is the electric field distribution diagram of the drain side of the Ti / Al / Ni / Au ohmic contact device with conventional electron beam evaporation in the control group.

[0029] Figure 6 This is a breakdown voltage distribution diagram of the Schottky / ohmic drain structure device prepared based on the first step metal Ti / Al and the second step metal Ni / TiN in Example 1 and the Ti / Al / Ni / Au ohmic contact device prepared by conventional electron beam evaporation in the control group, wherein the number of devices tested in each group is 50. DETAILED DESCRIPTION

[0030] The following description combines specific illustrations to explain the technical solution so as to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and similar generalized embodiments made by ordinary technicians in the field without creative work are all within the scope of protection of the present invention.

[0031] The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this specification. The singular forms of "a", "the" and "the" used in one or more embodiments of this specification and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0032] It should be understood that although the terms first, second, etc. may be used to describe various information in one or more embodiments of this specification, this information should not be limited to these terms. These terms are only used to distinguish similar objects and are not necessarily used to describe the order or sequence of features described in one or more embodiments of this specification. In addition, the terms "having" and "including" are similarly expressed to indicate a non-exclusive scope. For example, a process, method, system, product or device that includes a series of steps or modules is not necessarily limited to the contents listed in detail, but may include inherent contents related to these steps or modules that are not listed.

[0033] The specific implementation of the present invention is further described below in conjunction with examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art.

[0034] Embodiment 1:

[0035] A HEMT device with Schottky / Ohmic drain structure, such as Figure 2 As shown, from bottom to top, it includes a silicon substrate 101, an AlN nucleation layer 102, an AlGaN buffer layer 103, a GaN channel layer 104, an AlN insertion layer 105 and an AlGaN barrier layer 106; a gate electrode 110, a source electrode and a drain electrode are arranged above the AlGaN barrier layer 106, and the gate electrode 110 is located between the source electrode and the drain electrode.

[0036] The source electrode and the drain electrode are both obtained by one-step photolithography and two-step variable-angle electron beam evaporation of metal; the source electrode and the drain electrode both include a first-step metal 108 and a second-step metal 109, wherein the first-step metal 108 is obtained by oblique-angle incident evaporation, and the second-step metal 109 is obtained by vertical-incidence evaporation; the first-step metal 108 is located at the oblique lower side of the second-step metal 109, and the first-step metal 108 and the second-step metal 109 are both in contact with the AlGaN barrier layer 106.

[0037] After the source electrode and the drain electrode are annealed, the first-step metal 108 in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer 106 , and the second-step metal 109 forms a Schottky contact with the AlGaN barrier layer 106 .

[0038] In this embodiment, the first step metal 108 is Ti / Al; the second step metal 109 is Ni / TiN.

[0039] A method for preparing a HEMT device with a Schottky / Ohmic drain structure, such as Figure 1 As shown, the following steps are included:

[0040] S1, constructing a silicon substrate 101, an AlN nucleation layer 102, an AlGaN buffer layer 103, a GaN channel layer 104, an AlN insertion layer 105 and an AlGaN barrier layer 106 from the bottom up, defining a source and drain photolithography region on the AlGaN barrier layer 106 using a photoresist 107, and depositing a first step metal 108 at an oblique angle based on an electron beam evaporation device;

[0041] S2, after the first step metal 108 is deposited, the second step metal 109 is deposited by vertical incidence to complete the deposition of the entire source electrode and drain electrode;

[0042] S3, after the stripping of the source electrode and the drain electrode is completed, an annealing treatment is performed. In this embodiment, the annealing temperature is 830° C., the annealing time is 1 min, and the annealing atmosphere is nitrogen, so that the first step metal 108 in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer 106, and the second step metal 109 forms a Schottky contact with the AlGaN barrier layer 106;

[0043] S4. Prepare a gate electrode 110 on the AlGaN barrier layer 106 to obtain a HEMT device with a Schottky / Ohmic drain structure.

[0044] In this embodiment, the oblique angle incident range of the first step of depositing the metal 108Ti / Al is 10°.

[0045] In this embodiment, the thickness of the first-step metal 108 Ti / Al is 10 / 100 nm, and the thickness of the second-step metal 109 Ni / TiN is 20 / 100 nm.

[0046] In this embodiment, the control group uses a Ti / Al / Ni / Au10 / 100 / 20 / 100nm gold metal system, the annealing conditions are the same as those in Example 1, and the other device preparation processes are also the same as those in Example 1. After high-temperature annealing, the drain edge of the control group becomes abnormally rough, while the metal of Example 1 is divided into two parts, the side close to the gate is the second layer of metal 109Ni / TiN, which still has a relatively smooth morphology after high-temperature annealing.

[0047] Figure 3 The IV curve of the second-step metal 109 Ni / TiN20 / 100nm with an electrode spacing of 10μm after high-temperature annealing. It can be seen that even under the high-temperature annealing process, the second-step metal 109 and the AlGaN barrier layer still exhibit Schottky characteristics.

[0048] Figure 4 2 is a transfer characteristic curve diagram of Example 1 and the control group. It can be seen that the transfer characteristics of the two are basically the same, so Example 1 is equivalent to the control group in terms of static characteristics.

[0049] Figure 5a Graph showing the electric field distribution on the drain side of Example 1 and the control group. Figure 5b This is the electric field distribution diagram of the drain side of the Ti / Al / Ni / Au ohmic contact device with conventional electron beam evaporation in the control group. It can be seen that the Schottky / ohmic drain will introduce an additional electric field peak on the drain side, thereby lowering the electric field peak of the single ohmic drain and redistributing the electric field.

[0050] Figure 6 The breakdown voltage distribution diagram of Example 1 and the control group, wherein the number of devices tested in each group is 50. The test data of both groups conform to the normal distribution, and the breakdown voltage corresponding to Example 1 is generally higher, with an average breakdown voltage of 1150V, which is 28.5% higher than the 895V of the control group. The process proposed by the present invention has good repeatability, and the HEMT device using the Schottky / Ohmic drain structure has a significantly improved breakdown voltage and a more uniform distribution.

[0051] Embodiment 2:

[0052] A HEMT device with Schottky / Ohmic drain structure, such as Figure 2 As shown, from bottom to top, it includes a silicon substrate 101, an AlN nucleation layer 102, an AlGaN buffer layer 103, a GaN channel layer 104, an AlN insertion layer 105 and an AlGaN barrier layer 106; a gate electrode 110, a source electrode and a drain electrode are arranged above the AlGaN barrier layer 106, and the gate electrode 110 is located between the source electrode and the drain electrode.

[0053] The source electrode and the drain electrode are both obtained by one-step photolithography and two-step variable-angle electron beam evaporation of metal; the source electrode and the drain electrode both include a first-step metal 108 and a second-step metal 109, wherein the first-step metal 108 is obtained by oblique-angle incident evaporation, and the second-step metal 109 is obtained by vertical-incidence evaporation; the first-step metal 108 is located at the oblique lower side of the second-step metal 109, and the first-step metal 108 and the second-step metal 109 are both in contact with the AlGaN barrier layer 106.

[0054] After the source electrode and the drain electrode are annealed, the first-step metal 108 in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer 106 , and the second-step metal 109 forms a Schottky contact with the AlGaN barrier layer 106 .

[0055] In Example 2, the thickness of the first step metal 108 Ti / Al is 10 / 100 nm, and the thickness of the second step metal 109 Ni / Ti is 20 / 100 nm. The other conditions are the same as those in Example 1.

[0056] The IV curve, transfer characteristic curve, electric field distribution diagram and breakdown voltage distribution diagram of a Schottky / Ohmic drain structure HEMT device provided in Example 2 are similar to those in Example 1. For specific performance, please refer to the attached diagram in Example 1. Figure 3 , Attachment Figure 4 , Attachment Figure 5a , Attachment Figure 5b and attached Figure 6 .

[0057] Embodiment 3:

[0058] A HEMT device with Schottky / Ohmic drain structure, such as Figure 2 As shown, from bottom to top, it includes a silicon substrate 101, an AlN nucleation layer 102, an AlGaN buffer layer 103, a GaN channel layer 104, an AlN insertion layer 105 and an AlGaN barrier layer 106; a gate electrode 110, a source electrode and a drain electrode are arranged above the AlGaN barrier layer 106, and the gate electrode 110 is located between the source electrode and the drain electrode.

[0059] The source electrode and the drain electrode are both obtained by one-step photolithography and two-step variable-angle electron beam evaporation of metal; the source electrode and the drain electrode both include a first-step metal 108 and a second-step metal 109, wherein the first-step metal 108 is obtained by oblique-angle incident evaporation, and the second-step metal 109 is obtained by vertical-incidence evaporation; the first-step metal 108 is located at the oblique lower side of the second-step metal 109, and the first-step metal 108 and the second-step metal 109 are both in contact with the AlGaN barrier layer 106.

[0060] After the source electrode and the drain electrode are annealed, the first-step metal 108 in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer 106 , and the second-step metal 109 forms a Schottky contact with the AlGaN barrier layer 106 .

[0061] In Example 3, the thickness of the first step metal 108Ti / Al is 10 / 100nm, and the thickness of the second step metal 109Ni / TiW is 20 / 100nm. The oblique angle incident range of the first step metal 108Ti / Al deposition is 15°. The other conditions are set the same as in Example 1.

[0062] The IV curve, transfer characteristic curve, electric field distribution diagram and breakdown voltage distribution diagram of a Schottky / Ohmic drain structure HEMT device provided in Example 3 are similar to those in Example 1. For specific performance, please refer to the attached diagram in Example 1. Figure 3 , Attachment Figure 4 , Attachment Figure 5a , Attachment Figure 5b and attached Figure 6 .

[0063] The present invention uses electron beam evaporation at different angles and one-step photolithography to obtain different contact interfaces, and forms a Schottky / Ohm mixed contact drain after annealing. The process steps are simple and no additional photolithography alignment issues need to be considered. In addition, the process proposed by the present invention has good repeatability. The HEMT device using the Schottky / Ohm drain structure has a breakdown voltage that is 28.5% higher than that of the control group Ti / Al / Ni / Au gold metal system device, and when the test sample is 50, the breakdown voltage distribution is more uniform and concentrated, such as Figure 6 shown.

[0064] The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. Therefore, changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention should all fall within the scope of protection of the present invention.

Claims

1. A HEMT device with Schottky / Ohmic drain structure, characterized in that: From bottom to top, it comprises a silicon substrate (101), an AlN nucleation layer (102), an AlGaN buffer layer (103), a GaN channel layer (104), an AlN insertion layer (105) and an AlGaN barrier layer (106); a gate electrode (110), a source electrode and a drain electrode are arranged above the AlGaN barrier layer (106), and the gate electrode (110) is located between the source electrode and the drain electrode; the source electrode and the drain electrode are both obtained by one-step photolithography and two-step variable-angle electron beam evaporation of metal; the source electrode and the drain electrode both comprise a first-step metal (108) and a second-step metal (109), wherein the first-step metal (108) is obtained by oblique-angle incident evaporation, and the second-step metal (109) is obtained by vertical-incidence evaporation; the second-step metal (109) forms a Schottky contact with the AlGaN barrier layer (106); and the first-step metal (108) in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer (106).

2. A HEMT device with Schottky / Ohmic drain structure according to claim 1, characterized in that: The first step metal (108) is located at the oblique lower side of the second step metal (109), and both the first step metal (108) and the second step metal (109) are in contact with the AlGaN barrier layer (106).

3. A HEMT device with Schottky / Ohmic drain structure according to claim 1, characterized in that: The first step metal (108) is an X / Y double-layer metal system, wherein the first metal X includes Ta or Ti, and the second metal Y includes Al.

4. A HEMT device with Schottky / Ohmic drain structure according to claim 1, characterized in that: The second-step metal (109) is a Z / W double-layer metal system, wherein the third metal Z comprises Ni, and the fourth metal W comprises Ti, TiN or TiW.

5. A HEMT device with Schottky / Ohmic drain structure according to any one of claims 1 to 4, characterized in that: The first step metal (108) is an X / Y double-layer metal system; the second step metal (109) is a Z / W double-layer metal system; the work function of the first metal X is smaller than the work function of the third metal Z.

6. The method for preparing a HEMT device with a Schottky / Ohmic drain structure according to claim 5, characterized in that: The following steps are involved: S1, constructing a silicon substrate (101), an AlN nucleation layer (102), an AlGaN buffer layer (103), a GaN channel layer (104), an AlN insertion layer (105), and an AlGaN barrier layer (106) from the bottom up, defining a source-drain photolithography region on the AlGaN barrier layer (106) using a photoresist (107), and depositing a first step metal (108) at an oblique angle based on an electron beam evaporation device; S2, after the first step metal (108) is deposited, the second step metal (109) is deposited by vertical incidence to complete the deposition of the entire source electrode and drain electrode; S3, after the stripping of the source electrode and the drain electrode is completed, an annealing treatment is performed, so that the first step metal (108) in the source electrode and the drain electrode forms an ohmic contact with the AlGaN barrier layer (106), and the second step metal (109) forms a Schottky contact with the AlGaN barrier layer (106); S4. Prepare a gate electrode (110) on the AlGaN barrier layer (106) to obtain a HEMT device with a Schottky / Ohmic drain structure.

7. The method for preparing a HEMT device with a Schottky / Ohmic drain structure according to claim 6, characterized in that: When the first step metal (108) is deposited at an oblique angle, the oblique angle ranges from 5° to 20°.

8. The method for preparing a HEMT device with a Schottky / Ohmic drain structure according to claim 6, characterized in that: In the first step metal (108), the thickness of the first metal X is 5-20 nm, the thickness of the second metal Y is 60-120 nm; the thickness of the third metal Z is 10-20 nm, and the thickness of the fourth metal W is 60-100 nm.

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