阅读说明：本技术 GaN基HEMT无金欧姆接触电极及其热氮化形成方法 (GaN-based HEMT gold-free ohmic contact electrode and thermal nitridation forming method thereof ) 是由 王洪 李先辉 周泉斌 高升 于 2019-08-13 设计创作，主要内容包括：本发明公开了一种GaN基HEMT无金欧姆接触电极及其热氮化形成方法,所述电极为在GaN基HEMT的外延层上表面的两侧从下到上依次排布的第一金属层Ti、第二金属层Al、第三金属层X、第四金属层Ti和帽层金属层TiN,其中X为Ni、Ni/Ti/Ni或Ni/Ti/Ni/Ti/Ni多层金属中的一种以上。本发明避免了高温制备帽层金属层TiN过程,降低了工艺温度和工艺复杂程度,简化了工艺流程,同时低温提升了工艺的兼容性,有助于降低GaN基HEMT器件的制造成本。(The invention discloses a GaN-based HEMT gold-free ohmic contact electrode and a thermal nitridation forming method thereof, wherein the electrode is a first metal layer Ti, a second metal layer Al, a third metal layer X, a fourth metal layer Ti and a cap layer metal layer TiN which are sequentially arranged on two sides of the upper surface of an epitaxial layer of the GaN-based HEMT from bottom to top, wherein X is more than one of Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni multilayer metals. The method avoids the process of preparing the metal layer TiN of the cap layer at high temperature, reduces the process temperature and the process complexity, simplifies the process flow, simultaneously improves the compatibility of the process at low temperature, and is beneficial to reducing the manufacturing cost of the GaN-based HEMT device.)

The gold-free ohmic contact electrode of the GaN-based HEMT is characterized by being a first metal layer Ti, a second metal layer Al, a third metal layer X, a fourth metal layer Ti and a cap layer metal layer TiN which are sequentially arranged on two sides of the upper surface of an epitaxial layer of the GaN-based HEMT from bottom to top, wherein X is more than one of Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni multilayer metals.

2. The GaN-based HEMT gold-free ohmic contact electrode according to claim 1, wherein the thickness of the first metal layer Ti is 1 ~ 30nm, and the thickness of the second metal layer Al is 40 ~ 200 nm.

3. The GaN-based HEMT gold-free ohmic contact electrode according to claim 1, wherein the thickness of the third metal layer X is 5 ~ 30nm, and the thickness of the fourth metal layer Ti is 60 ~ 120 nm.

4. the GaN-based HEMT gold-free ohmic contact electrode according to claim 1, wherein the thickness of the capping layer metal layer TiN is 10 ~ 40 nm.

5. A method of forming a GaN-based HEMT gold-free ohmic contact electrode according to any one of claims 1 to 4 by a thermal nitridation reaction, comprising the steps of:

(1) defining a source-drain electrode pattern area: defining source and drain electrode pattern areas on two sides of the upper surface of the GaN-based HEMT epitaxial layer by utilizing a photoetching technology, and covering areas except the source and drain electrode patterns on the GaN-based HEMT epitaxial layer by a photoetching mask;

(2) Surface treatment: cleaning a source-drain electrode pattern area by using an acid-base solution;

(3) Depositing an electrode metal layer, namely sequentially depositing a first metal layer Ti, a second metal layer Al, a third metal layer X and a fourth metal layer Ti on a source-drain electrode pattern area and a photoetching mask on the GaN-based HEMT epitaxial layer, wherein the first metal layer Ti, the second metal layer Al, the third metal layer X and the fourth metal layer Ti of the source-drain electrode are prepared at low temperature, the temperature of a substrate is 25 ~ 50 ℃, and the substrate is the GaN-based HEMT epitaxial layer processed in the step (2);

(4) Stripping: removing the photoetching mask and the first metal layer Ti, the second metal layer Al, the third metal layer X and the fourth metal layer Ti on the photoetching mask through a stripping process in the step (3), and leaving the first metal layer Ti, the second metal layer Al, the third metal layer X and the fourth metal layer Ti in the source and drain electrode pattern area to form a source and drain electrode;

(5) Annealing: and (4) annealing the source and drain electrodes obtained in the step (4), combining the thermal nitridation reaction with the solid-phase reaction of ohmic contact, carrying out the thermal nitridation reaction on the surface part of the fourth metal layer Ti to form a cap layer metal layer TiN with good chemical stability, carrying out the solid-phase reaction between the multiple layers of metals of the source and drain electrodes, and forming good ohmic contact with the GaN-based HEMT epitaxial layer.

6. The method for forming a GaN-based HEMT gold-free ohmic contact electrode according to claim 5, wherein the deposition method of the electrode metal layer in step (3) is electron beam evaporation or magnetron sputtering deposition.

7. The method of forming a GaN-based HEMT gold-free ohmic contact electrode according to claim 5, wherein the fourth metal layer Ti is evaporated by electron beam at an evaporation rate of 0.4 ~ 0.8.8 nm/sec.

8. The method for forming a GaN-based HEMT gold-free ohmic contact electrode according to claim 5, wherein the deposition method of the electrode metal layer in the step (3) is magnetron sputtering deposition, and the magnetron sputtering is selected from a direct current magnetron sputtering mode.

9. the method for forming a GaN-based HEMT gold-free ohmic contact electrode according to claim 5, wherein the fourth metal layer Ti is deposited in step (3) by magnetron sputtering, and the degree of vacuum in the vacuum chamber is 4E-04Pa or less before the fourth metal layer Ti is deposited.

10. The method of claim 5, wherein the annealing temperature in step (5) is 500 ~ 900 ℃, the annealing time is 15s ~ 10min, and the atmosphere is high purity nitrogen.

Technical Field

The invention relates to a semiconductor device, in particular to a GaN-based HEMT gold-free ohmic contact electrode and a thermal nitridation forming method thereof.

background

the GaN-based High Electron Mobility Transistor (HEMT) has wide application prospect in the fields of high-voltage, high-frequency and high-power semiconductor laser devices, high-performance ultraviolet detectors and the like. However, the production line technology special for the compound semiconductor is relatively lagged behind, the process updating and operation maintenance cost is higher, and the production cost of the GaN-based HEMT device is increased. The HEMT device is produced by adopting a mature and advanced Si-CMOS process line, so that the preparation difficulty of the HEMT device can be effectively reduced, and the manufacturing cost is reduced. Heavy metal Au adopted in the ohmic and Schottky contact processes of the conventional HEMT device can form deep-level impurities in Si to pollute a CMOS process line. Therefore, the HEMT gold-free ohmic contact technology is key to improving HEMT device reliability and enabling large-scale manufacturing of Si-CMOS process lines.

The quality of ohmic contact performance of the GaN-based HEMT device directly influences the performance of key devices such as saturated output current, on-resistance, breakdown voltage and the like. High quality ohmic contacts require mainly the following: (1) low contact resistivity (2), good thermal stability (3), small electrode surface roughness (4), and strong corrosion resistance.

The annealing windows for forming ohmic contact on the GaN-based HEMT mainly comprise 1, a low-temperature annealing window and a nitrogen atmosphere, wherein the annealing temperature is 500 ~ 650 ℃ and the annealing time is 2 ~ 10min, and 2, a high-temperature annealing window and the nitrogen atmosphere, wherein the annealing temperature is 800 ~ 1000 ℃ and the annealing time is 15 ~ 60 sec.

in the high-temperature annealing process, the conventional gold ohmic contact electrode and the non-gold ohmic contact electrodes of W, Mo, Cu and the like reported in the literature are poor in repeatability, and are not beneficial to large-scale industrial production, because the metal Al layer generally requires more than 100nm (the thickness of Al is far greater than that of bottom layer Ti), a large amount of unreacted Al is not fused with Ti-Al alloy which is agglomerated to form an island structure, so that the surface appearance and the edge appearance of the electrode are extremely poor.

At present, the high-performance TiN film is generally deposited by a direct-current reaction magnetron sputtering mode at a higher substrate temperature (300 ~ 700 ℃), however, the deposited ohmic metal is not compatible with the traditional metal stripping process under a high-temperature environment, only an electrode pattern can be formed by metal etching, special mask design and other methods, the complexity of an electrode preparation process is increased, and adverse effects such as etching damage, solid-phase reaction between metal and a semiconductor at a high temperature and the like can be caused.

Disclosure of Invention

In order to overcome the defects and shortcomings in the prior art, the invention aims to provide a gold-free ohmic contact electrode of a GaN-based HEMT and a thermal nitridation forming method thereof.

the TiN metal layer of the cap layer formed by adopting the thermal nitridation reaction can effectively solve the series problems caused by directly depositing the TiN film at high temperature.

the GaN-based HEMT gold-free ohmic contact electrode formed by adopting the thermal nitridation reaction can effectively solve the problem of poor surface appearance of the electrode under high-temperature annealing.

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

the invention provides a GaN-based HEMT gold-free ohmic contact electrode which is a first metal layer Ti, a second metal layer Al, a third metal layer X, a fourth metal layer Ti and a cap layer metal layer TiN which are sequentially arranged on two sides of the upper surface of an epitaxial layer of a GaN-based HEMT from bottom to top, wherein X is more than one of Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni multilayer metals.

Preferably, the thickness of the first metal layer Ti is 1 ~ 30nm, the thickness of the second metal layer Al is 40 ~ 200nm, the thickness of the third metal layer X is 5 ~ 30nm, the thickness of the fourth metal layer Ti is 60 ~ 120nm, and the thickness of the capping layer metal layer TiN is 10 ~ 40 nm.

The invention also provides a method for forming the GaN-based HEMT gold-free ohmic contact electrode by the thermal nitridation reaction, which comprises the following steps:

(1) Defining a source-drain electrode pattern area: defining source and drain electrode pattern areas on two sides of the upper surface of the GaN-based HEMT epitaxial layer by utilizing a photoetching technology, and covering areas except the source and drain electrode patterns on the GaN-based HEMT epitaxial layer by a photoetching mask;

(2) Surface treatment: cleaning a source-drain electrode pattern area by using an acid-base solution;

(3) Depositing an electrode metal layer, namely sequentially depositing a first metal layer Ti, a second metal layer Al, a third metal layer X and a fourth metal layer Ti on a source-drain electrode pattern area and a photoetching mask on the GaN-based HEMT epitaxial layer, wherein the first metal layer Ti, the second metal layer Al, the third metal layer X and the fourth metal layer Ti of the source-drain electrode are prepared at low temperature, the temperature of a substrate is 25 ~ 50 ℃, and the substrate is the GaN-based HEMT epitaxial layer processed in the step (2);

(4) Stripping: removing the photoetching mask and the first metal layer Ti, the second metal layer Al, the third metal layer X and the fourth metal layer Ti on the photoetching mask through a stripping process in the step (3), and leaving the first metal layer Ti, the second metal layer Al, the third metal layer X and the fourth metal layer Ti in the source and drain electrode pattern area to form a source and drain electrode;

(5) Annealing: and (4) annealing the source and drain electrodes obtained in the step (4), combining the thermal nitridation reaction with the solid-phase reaction of ohmic contact, carrying out the thermal nitridation reaction on the surface part of the fourth metal layer Ti to form a cap layer metal layer TiN with good chemical stability, carrying out the solid-phase reaction between the multiple layers of metals of the source and drain electrodes, and forming good ohmic contact with the GaN-based HEMT epitaxial layer.

preferably, the method for depositing the electrode metal layer in the step (3) is electron beam evaporation or magnetron sputtering deposition.

Preferably, the fourth metal layer Ti is evaporated using an electron beam at an evaporation rate of 0.4 ~ 0.8.8 nm/sec.

Preferably, the method for depositing the electrode metal layer in the step (3) is magnetron sputtering deposition, and the magnetron sputtering mode is a direct-current magnetron sputtering mode.

Preferably, magnetron sputtering is adopted for depositing the fourth metal layer Ti in the step (3), and the vacuum degree in the vacuum cavity is below 4E-04Pa before depositing the fourth metal layer Ti.

Preferably, the annealing temperature in the step (5) is 500 ~ 900 ℃, the annealing time is 15s ~ 10min, and the atmosphere is high-purity nitrogen.

the gold-free source drain electrode sequentially comprises a first metal layer Ti, a second metal layer Al, a third metal layer X and a fourth metal layer Ti, wherein the third metal layer X is a multilayer metal of Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni to form a multilayer source drain electrode metal system of Ti/Al/Ni/Ti, Ti/Al/Ni/Ti/Ni/Ti and the like. Through an annealing process in a high-purity nitrogen atmosphere, a thermal nitridation reaction and a solid-phase reaction between multiple layers of metals are combined, a part of the surface of a fourth metal Ti layer is subjected to a thermal nitridation reaction to form a metal TiN with a good chemical stability cap layer, so that a multilayer source/drain electrode metal system and an AlGaN or InAlN intrinsic barrier layer form ohmic contact, and ohmic contact electrodes Ti/Al/Ni/Ti/TiN, Ti/Al/Ni/Ti/Ni/TiN with good contact are formed.

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

(1) Preparing a fourth metal layer Ti at a low temperature, and performing post annealing treatment to enable a part of the surface of the fourth metal Ti layer to generate a thermal nitridation reaction to form a stable cap layer metal TiN which generates a solid-phase reaction with other electrode metals to form good ohmic contact with a GaN-based HEMT epitaxial layer; the capping layer metal layer TiN is formed by the thermal nitridation reaction of the fourth metal layer Ti instead of being directly deposited, thereby avoiding the high-temperature (100-.

(2) The GaN-based HEMT gold-free ohmic contact electrode formed by the thermal nitridation reaction can effectively solve the problem of poor surface appearance of the electrode under high-temperature annealing;

(3) The method avoids the process of preparing the metal layer TiN of the cap layer at high temperature, reduces the process temperature and the process complexity, simplifies the process flow, simultaneously improves the compatibility of the process at low temperature, and is beneficial to reducing the manufacturing cost of the GaN-based HEMT device.

Drawings

Fig. 1 is a schematic view of a GaN-based HEMT epitaxial layer when forming a source-drain electrode pattern in embodiments 1 to 3;

Fig. 2 is a schematic view of the GaN-based HEMT epitaxial layer after a first metal layer Ti, a second metal layer Al, a third metal layer X, and a fourth metal layer Ti are sequentially deposited on the source-drain electrode pattern region and the photolithographic mask in embodiments 1 to 3;

fig. 3 is a schematic view of the structure of the epitaxial layer of the GaN-based HEMT after the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti on the photomask are stripped in embodiments 1 to 3;

FIG. 4 is a schematic view of the structure of the GaN-based HEMT gold-free ohmic contact electrode formed by the thermal nitridation reaction of examples 1 to 3;

FIG. 5 is an I-V curve of the test of forming a GaN-based HEMT gold-free ohmic contact electrode by the thermal nitridation reaction in example 1;

The figures show that: 1-GaN-based HEMT epitaxial layer; 2-a first metal layer Ti; 3-a second metal layer Al; 4-a third metal layer X; 5-a fourth metal layer Ti; 6-capping layer metal layer TiN; 7-source drain electrode pattern area; 8-lithography mask.

Detailed Description

The present invention is further described with reference to the following drawings and examples, but the embodiments of the present invention are not limited thereto; it is to be understood that the following processes and process parameters, if not specified in particular detail, are all within the skill of the art by reference to the prior art.