A method for in-situ growth of SiN passivation film on surface of nitride heterojunction material

Abstract

The application provides a method for in-situ growth of SiN passivation film on the surface of nitride heterojunction material, comprising the following steps: S1. selecting a single crystal substrate, placing the single crystal substrate on a graphite base in a MOCVD reaction chamber, and sequentially epitaxially growing a nucleation layer, a buffer layer and a nitride heterojunction in a hydrogen and ammonia atmosphere; S2. closing the metal organic source, keeping the ammonia flow unchanged, converting the hydrogen in the reaction chamber into nitrogen, and reducing the temperature of the reaction chamber; S3. introducing a higher flow of silane to in-situ grow a first SiN passivation layer on the nitride heterojunction; S4. closing the silane, keeping the pressure and atmosphere unchanged, and increasing the temperature of the reaction chamber; S5. introducing a lower flow of silane to in-situ grow a second SiN passivation layer on the first SiN passivation layer; and S6. closing the silane, keeping the ammonia and nitrogen atmosphere, and reducing the temperature to a wafer taking temperature. The application has a wide range of applications and can in-situ grow SiN passivation film on the surface of various heterojunctions such as AlN / GaN, AlGaN / GaN, InAlN / GaN and InAlGaN / GaN.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials and devices technology, and specifically refers to a method for in-situ growth of SiN passivation films on the surface of nitride heterojunction materials. Background Technology

[0002] Surface states caused by crystal defects on the surface of nitride heterojunction materials can lead to current collapse in high-frequency, high-power applications, significantly reducing the device's output power. Surface passivation can effectively suppress current collapse, and growing a passivation layer can also mitigate the influence of the environmental atmosphere on the device's electrical characteristics.

[0003] SiN is the most commonly used material for surface passivation of nitride heterojunctions, and common methods include in-situ PECVD and LPCVD techniques. PECVD can form SiN films at relatively low temperatures through sputtering, but it may damage the nitride semiconductor surface. LPCVD, through chemical vapor deposition, can form a SiN passivation layer well, but it can only be done in-situ. The nitride heterojunction surface is easily oxidized and contaminated by air, introducing deep-level defects to the heterojunction-SiN interface. Furthermore, LPCVD temperatures are relatively low, only 500~700℃, resulting in insufficient SiN film density. When fabricating metal gates, Ni metal tends to sink, causing a decrease in gate control capability and an increase in leakage current.

[0004] Compared to PECVD and LPCVD technologies, MOCVD technology for in-situ SiN growth prevents oxidation and process contamination of the barrier layer surface due to contact with air and cleaning solutions, thus avoiding deterioration of material surface quality and electrical properties. Furthermore, the high-temperature environment of MOCVD allows for the formation of a denser, more insulating SiN passivation layer, effectively improving passivation quality, suppressing surface states, enhancing the high-temperature resistance of the material surface, improving the stability of electrical parameters, and mitigating reliability issues such as current collapse and gate leakage. However, Si in silanes is an n-type impurity in nitrides, and at high temperatures, silanes have an etching effect on the barrier layer, allowing Si impurities to easily diffuse into the barrier layer and form a surface leakage layer. Therefore, the MOCVD in-situ passivation method for SiN needs optimization. Summary of the Invention

[0005] To address the technical challenges of Si impurities easily diffusing into the barrier layer and forming a surface leakage layer under high-temperature growth conditions, and SiN not being dense enough under low-temperature growth conditions, this invention proposes a method for in-situ SiN growth using MOCVD technology. Specifically, after heterojunction epitaxy, hydrogen gas in the reaction chamber is converted to nitrogen gas, and the temperature is rapidly lowered to suppress surface decomposition of the heterojunction material. A first SiN passivation layer is epitaxially grown under low-temperature, high-silane flow conditions. The low temperature reduces Si impurity diffusion into the barrier layer, preventing the formation of leakage interlayers, while the high silane flow rate increases the growth rate, allowing SiN to quickly cover the heterojunction surface. Subsequently, a second SiN passivation layer is epitaxially grown under high-temperature, low-silane flow conditions. The low silane flow rate at high temperature enables slow epitaxy, improving the density and uniformity of the SiN film. After passivation, cooling is performed in a nitrogen and ammonia atmosphere to suppress SiN decomposition, optimize surface quality, and improve the stability and reliability of the material during the process.

[0006] The present invention adopts the following technical solution:

[0007] A method for in-situ growth of SiN passivation film on the surface of a nitride heterojunction material includes the following steps:

[0008] S1. Select a single crystal substrate and place it on a graphite base in the MOCVD reaction chamber. In the atmosphere of hydrogen and ammonia, epitaxially grow a core layer, a buffer layer and a nitride heterojunction in sequence.

[0009] S2. Keep the ammonia flow rate constant, convert the hydrogen in the reaction chamber to nitrogen, and lower the temperature of the reaction chamber;

[0010] S3. Introduce silane to grow the first SiN passivation layer in situ on the nitride heterojunction;

[0011] S4. Turn off the silane, keep the pressure and atmosphere constant, and increase the temperature of the reaction chamber;

[0012] S5. Introduce silane to grow a second SiN passivation layer in situ on the first SiN passivation layer, wherein the silane flow rate during the growth of the second SiN passivation layer is less than the silane flow rate during the growth of the first SiN passivation layer in step S3.

[0013] S6. Turn off the silane, maintain the ammonia and nitrogen atmosphere, and cool down to the wafer removal temperature.

[0014] Furthermore, the nitride heterojunction described in step S1 includes, but is not limited to, AlN / GaN, AlGaN / GaN, InAlN / GaN, or InAlGaN / GaN.

[0015] Furthermore, in step S2, after converting hydrogen to nitrogen in the reaction chamber, the pressure in the reaction chamber is 50~100 torr, and the temperature adjustment rate of the reaction chamber is 50~80℃ / min.

[0016] Furthermore, the temperature for growing the first SiN passivation layer is 600~850℃, and the flow ratio of silane to ammonia is 1:100~1000.

[0017] Furthermore, the temperature for growing the second SiN passivation layer is 900~1100℃, and the flow ratio of silane to ammonia is 1:1500~10000.

[0018] Furthermore, the thickness of the first SiN passivation layer is 3~30nm.

[0019] Furthermore, the thickness of the second SiN passivation layer is 5~30nm.

[0020] The beneficial effects of this invention are:

[0021] (1) The present invention has a wide range of applications, including but not limited to MOCVD methods and commonly used single crystal substrates such as SiC, Si, and sapphire, as well as nitride heterojunction microelectronic and optoelectronic materials;

[0022] (2) After the growth of the nitride heterojunction material is completed, the hydrogen in the reaction chamber is converted into nitrogen and the temperature is rapidly reduced to protect the surface of the barrier layer. At this time, a high flow rate of silane is introduced to grow the first layer of SiN, which can effectively protect the surface of the heterojunction and prevent Si impurities from diffusing into the surface of the nitride heterojunction to form a conductive interlayer. Then, the temperature is raised to a higher temperature and a lower flow rate of silane is introduced to grow the second layer of SiN, which can effectively block process contamination and metal diffusion into the barrier during device fabrication, which helps to reduce device leakage and improve reliability. Finally, the SiN surface is decomposed in the atmosphere of ammonia and nitrogen. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the extensional structure of the present invention;

[0024] Figure 2 This is a schematic diagram of the growth process of the present invention.

[0025] Explanation of reference numerals in the attached figures: 1. Single crystal substrate; 2. Nucleation layer; 3. Buffer layer; 4. Nitride heterojunction; 5. First SiN passivation layer; 6. Second SiN passivation layer. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments. The embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of the claims. Other alternative means that can be conceived by those skilled in the art are all within the scope of the claims of the present invention.

[0027] This invention proposes a method for in-situ growth of SiN passivation films on the surface of nitride heterojunction materials, such as... Figure 2 As shown, it includes the following steps:

[0028] S1. Select a single crystal substrate and place it on a graphite substrate in the MOCVD reaction chamber. In the atmosphere of hydrogen and ammonia, epitaxially grow a core layer, a buffer layer and a nitride heterojunction in sequence. The nitride heterojunction includes, but is not limited to, AlN / GaN, AlGaN / GaN, InAlN / GaN or InAlGaN / GaN.

[0029] S2. Keep the ammonia flow rate constant, convert the hydrogen in the reaction chamber to nitrogen, and rapidly reduce the temperature of the reaction chamber to 600~850℃ to suppress the surface decomposition of the heterojunction material.

[0030] S3. Introduce silane to grow the first SiN passivation layer in situ on the nitride heterojunction. In this step, a high silane flow rate is used to epitaxially grow the first SiN layer under low temperature and high silane flow rate conditions. The low temperature can reduce the diffusion of Si impurities into the barrier layer to form a leakage interlayer, while the high silane flow rate can increase the growth rate and enable SiN to quickly cover the surface of the heterojunction.

[0031] S4. Turn off the silane, keep the pressure and atmosphere constant, and raise the temperature of the reaction chamber to 900~1100℃;

[0032] S5. Introduce silane to grow a second SiN passivation layer in situ on the first SiN passivation layer. When introducing silane in this step, the silane flow rate is less than that in step S3. The second SiN layer is epitaxially grown at high temperature and low silane flow rate. The slow epitaxy is achieved at high temperature by using low silane flow rate, which improves the density and uniformity of the SiN film.

[0033] S6. Turn off silane, maintain ammonia and nitrogen atmosphere, and cool to the wafer removal temperature. After passivation, continue cooling in a nitrogen and ammonia atmosphere to suppress SiN decomposition, optimize surface quality, and improve the stability and reliability of the material during the process. The resulting epitaxial structure is as follows: Figure 1 As shown, from bottom to top, the structure consists of a single crystal substrate 1, a nucleation layer 2, a buffer layer 3, a nitride heterojunction 4, a first SiN passivation layer 5, and a second SiN passivation layer 6.

[0034] Example 1

[0035] A method for in-situ growth of SiN passivation film on the surface of a nitride heterojunction material includes the following steps:

[0036] S1. Select high-purity semi-insulating SiC as the substrate, place it on a graphite base in the MOCVD reaction chamber, heat it to 1050℃, and bake it in a hydrogen atmosphere for 5 minutes; then heat it to 1100℃, introduce trimethylaluminum, and introduce ammonia to epitaxially grow a 100nm aluminum nitride nucleation layer on the substrate; then turn off the trimethylaluminum, cool it to 1050℃, introduce trimethylgallium, and grow a 1~2um thick gallium nitride buffer layer; continue to grow a 100~200nm gallium nitride channel; turn on the trimethylaluminum and grow a 20nm aluminum gallium nitride barrier layer;

[0037] S2. Keeping the ammonia gas constant, convert the hydrogen gas in the reaction chamber to nitrogen gas, with the pressure in the reaction chamber being 100 torr, and adjust the temperature of the reaction chamber to 850℃ at a cooling rate of 50℃ / min.

[0038] S3. Introduce silane, with a silane to ammonia flow ratio of 1:500, and grow a first SiN passivation layer with a thickness of 10 nm in situ on the nitride heterojunction.

[0039] S4. Turn off the silane, keep the pressure and atmosphere constant, and raise the temperature of the reaction chamber to 1100℃ at a heating rate of 80℃ / min;

[0040] S5. Introduce silane, with a flow rate ratio of silane to ammonia of 1:5000, and grow a second SiN passivation layer with a thickness of 15nm in situ on the first SiN passivation layer.

[0041] S6. Turn off the silane, maintain the ammonia and nitrogen atmosphere, and cool down to the wafer removal temperature.

[0042] Example 2

[0043] A method for in-situ growth of SiN passivation film on the surface of a nitride heterojunction material includes the following steps:

[0044] S1. Sapphire was selected as the substrate and placed on a graphite base in the MOCVD reaction chamber. The temperature was raised to 1050℃ and baked in a hydrogen atmosphere for 5 minutes. Then the temperature was lowered to 550℃, trimethylgallium was introduced, and ammonia was introduced to grow a 200nm gallium nitride nucleation layer on the substrate. The temperature was raised to 1070℃, trimethylgallium was introduced, and a 1~2um thick gallium nitride buffer layer was grown. A 100~200nm gallium nitride channel was grown, and trimethylgallium was turned off. Trimethylaluminum was turned on, and a 4nm aluminum nitride barrier layer was grown. Trimethylaluminum was turned off, and trimethylgallium was introduced to grow a 2nm gallium nitride cap layer.

[0045] S2. Keeping the ammonia gas constant, convert the hydrogen gas in the reaction chamber to nitrogen gas, set the pressure in the reaction chamber to 50 torr, and adjust the temperature of the reaction chamber to 700℃ at a cooling rate of 80℃ / min.

[0046] S3. Introduce silane, with a silane to ammonia flow rate ratio of 1:100, and grow a first SiN passivation layer with a thickness of 3 nm in situ on the nitride heterojunction.

[0047] S4. Turn off the silane, keep the pressure and atmosphere constant, and raise the temperature of the reaction chamber to 900°C at a heating rate of 60°C / min;

[0048] S5. Introduce silane, with a flow rate ratio of silane to ammonia of 1:1500, and grow a second SiN passivation layer with a thickness of 30 nm in situ on the first SiN passivation layer.

[0049] S6. Turn off the silane, maintain the ammonia and nitrogen atmosphere, and cool down to the wafer removal temperature.

[0050] Example 3

[0051] A method for in-situ growth of SiN passivation film on the surface of a nitride heterojunction material includes the following steps:

[0052] S1. Select silicon as the substrate and place it on a graphite base in the MOCVD reaction chamber. Heat the substrate to 1050℃ and bake it in a hydrogen atmosphere for 5 minutes. Introduce trimethylaluminum and pre-lay it for 30 seconds. Then introduce ammonia to grow a 100nm aluminum nitride nucleation layer. Introduce trimethylgallium to grow a 1~3µm aluminum gallium nitride transition layer. Turn off trimethylaluminum and grow a 100~200nm gallium nitride channel layer. Turn off trimethylgallium and cool down to 800℃. Turn on trimethylindium, trimethylaluminum, and trimethylgallium to grow a 30nm indium aluminum nitride barrier layer.

[0053] S2. Keeping the ammonia gas constant, convert the hydrogen gas in the reaction chamber to nitrogen gas, set the pressure in the reaction chamber to 80 torr, and adjust the temperature of the reaction chamber to 600℃ at a cooling rate of 80℃ / min.

[0054] S3. Introduce silane, with a silane to ammonia flow rate ratio of 1:1000, and grow a first SiN passivation layer with a thickness of 30 nm in situ on the nitride heterojunction.

[0055] S4. Turn off the silane, keep the pressure and atmosphere constant, and raise the temperature of the reaction chamber to 1000℃ at a heating rate of 80℃ / min to anneal the SiN.

[0056] S5. Introduce silane, with a flow rate ratio of silane to ammonia of 1:10000, and grow a second SiN passivation layer with a thickness of 5nm in situ on the first SiN passivation layer.

[0057] S6. Turn off the silane, maintain the ammonia and nitrogen atmosphere, and cool down to the wafer removal temperature.

[0058] As can be seen from the above, this invention proposes a stepwise method for growing SiN passivation films. After the growth of the nitride heterojunction material is completed, the hydrogen gas in the reaction chamber is converted to nitrogen gas, and the temperature is rapidly reduced to 600-850°C to protect the surface of the barrier layer. A high flow rate of silane is then introduced to grow the first SiN layer. The temperature is then raised to 900-1100°C, and a lower flow rate of silane is introduced to grow the second SiN layer. Afterwards, the temperature is lowered to room temperature in an atmosphere of ammonia and nitrogen to prevent SiN surface decomposition. This invention is simple and easy to implement, and is compatible with existing MOCVD methods for growing nitride heterojunction materials.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for in-situ growth of SiN passivation film on a surface of a nitride heterojunction material, the method comprising: The method comprises the following steps: ​ S1. Selecting a single crystal substrate, placing it on a graphite susceptor in a MOCVD reaction chamber, and epitaxially growing a nucleation layer, a buffer layer and a nitride heterojunction in sequence under a hydrogen and ammonia atmosphere; S2. Keeping the ammonia flow constant, converting the hydrogen in the reaction chamber to nitrogen, the pressure in the reaction chamber being 50-100 torr, reducing the temperature of the reaction chamber, and the adjustment rate of the temperature of the reaction chamber being 50-80 ℃ / min; S3. Introducing silane to in-situ grow a first SiN passivation layer on the nitride heterojunction, the temperature during growth of the first SiN passivation layer being 600-850 ℃, and the flow ratio of silane to ammonia being 1:100-1000; S4. Turning off the silane, keeping the pressure and atmosphere unchanged, and increasing the temperature of the reaction chamber; S5. Introducing silane to in-situ grow a second SiN passivation layer on the first SiN passivation layer, wherein the silane flow during growth of the second SiN passivation layer is less than that during growth of the first SiN passivation layer in step S3, the temperature during growth of the second SiN passivation layer being 900-1100 ℃, and the flow ratio of silane to ammonia being 1:1500-10000; S6. Turning off the silane, keeping the ammonia and nitrogen atmosphere, and cooling to a wafer removal temperature.

2. The method of claim 1, wherein the SiN passivation film is grown in situ on the surface of the nitride heterojunction material. The nitride heterojunction in step S1 includes but is not limited to AlN / GaN, AlGaN / GaN, InAlN / GaN and InAlGaN / GaN.

3. The method of claim 1, wherein the SiN passivation film is grown in situ on the surface of the nitride heterojunction material. The thickness of the first SiN passivation layer is 3-30 nm.

4. The method of claim 1, wherein the SiN passivation film is grown in situ on the surface of the nitride heterojunction material. The thickness of the second SiN passivation layer is 5-30 nm.

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