Preparation method of p-type GaN film and p-type GaN film

Abstract

The invention provides a preparation method of a p-type GaN film and the p-type GaN film, and relates to the technical field of semiconductor materials. The preparation method of the p-type GaN film comprises the following steps: depositing and growing a p-type GaN layer by adopting an MOCVD (Metal Organic Chemical Vapor Deposition) method, and then carrying out pulse activation treatment on the p-type GaN layer to obtain the p-type GaN film, the pulse activation treatment sequentially comprises thermal annealing treatment and reinforcement treatment, and the number of times of the pulse activation treatment is not less than 2; the temperature of the thermal annealing treatment is T1 DEG C, the pressure is Y1mbar, the temperature of the reinforcing treatment is T2 DEG C, the pressure is Y2mbar, T1 is greater than T2, and Y1 is less than Y2. The hole concentration and the surface appearance of the p-type GaN film prepared through the preparation method are excellent, and the use performance of a device can be improved.

Description

Technical Field

[0001] This application relates to the technical field of semiconductor materials, and particularly relates to a method for preparing a p-type GaN film and a p-type GaN film. Background Art

[0002] The third-generation semiconductors represented by group-III nitrides have excellent properties such as high bandgap width, high breakdown electric field, high saturated electron drift velocity, and strong polarization, and are widely used in the fields of power electronics, radio frequency electronics, and optoelectronics. When preparing the third-generation semiconductors, vapor deposition methods such as Metal-organic Chemical Vapor Deposition (MOCVD) can be used. Taking p-type gallium nitride (GaN) as an example (p is the abbreviation of positive, and p-type GaN is hole-type gallium nitride, which can be abbreviated as p-GaN), its p-type effect is mainly achieved by doping Mg in GaN.

[0003] However, when growing p-type GaN by the MOCVD method, the internal Mg is easily passivated. Therefore, in-situ thermal annealing is usually performed on the grown p-GaN in the MOCVD chamber to "activate" the p-GaN so that the p-GaN can have a certain concentration of holes. However, the surface morphology of p-GaN is prone to degradation after annealing, with voids appearing on the surface and the roughness increasing significantly, which will have an adverse effect on the device performance. If we want to avoid the deterioration of the p-GaN surface morphology, we often need to reduce the in-situ annealing temperature, but this will lead to a decrease in the activation efficiency of Mg impurities in p-GaN and a decrease in the hole concentration, which is also not conducive to the device performance. Summary of the Invention

[0004] This application provides a method for preparing a p-type GaN film and a p-type GaN film, which can improve the hole concentration of the p-type GaN film and at the same time enable the p-type GaN to still maintain a good surface morphology, thereby improving the performance of the device.

[0005] In a first aspect, this application provides a method for preparing a p-type GaN film, which includes the following steps: depositing and growing a p-type GaN layer by the MOCVD method, and then performing a pulse activation treatment on the p-type GaN layer to obtain a p-type GaN film. The pulse activation treatment sequentially includes a thermal annealing treatment and a strengthening treatment, and the number of times of the pulse activation treatment is not less than 2 times. The temperature of the thermal annealing treatment is T1 °C, the pressure is Y1 mbar, the temperature of the strengthening treatment is T2 °C, the pressure is Y2 mbar, and T1 > T2 and Y1 < Y2.

[0006] In the above technical solution, during the pulse activation treatment of the grown p-type GaN layer, due to the high temperature and low pressure during the thermal annealing treatment, magnesium in the p-type GaN can be activated, thus having a certain concentration of holes; after the thermal annealing treatment, a strengthening treatment is carried out. The temperature during the strengthening treatment is low and the pressure is high, which can strengthen and repair the surface morphology of the p-type GaN, so as to avoid significant degradation of the surface of the p-type GaN in a long-term high-temperature environment, and avoid phenomena such as the formation of holes on the surface and an increase in roughness. Alternating the thermal annealing treatment and the strengthening treatment is regarded as one cycle (i.e., one pulse activation treatment). Performing at least 2 cycles can significantly increase the hole concentration of the p-type GaN, and at the same time can still maintain a good surface morphology of the p-type GaN, thereby improving the performance of the device.

[0007] In a possible implementation manner, the thickness of the p-type GaN layer is 20 nm to 3000 nm.

[0008] In the above technical solution, the pulse activation treatment is particularly obvious for improving the p-type GaN layer with a thickness of 20 nm to 3000 nm.

[0009] In a possible implementation manner, 750 ≤ T1 ≤ 900, 50 ≤ Y1 ≤ 300.

[0010] In a possible implementation manner, 0 < T2 < 750, 300 ≤ Y2 ≤ 600.

[0011] In a possible implementation manner, the number of times of the pulse activation treatment is 2 to 20 times.

[0012] In the above technical solution, the number of times of the pulse activation treatment is 2 to 20 times, which is beneficial to improving the hole concentration and surface morphology of the p-type GaN layer, and at the same time can save the preparation cost.

[0013] In a possible implementation manner, the time of the thermal annealing treatment is 0.5 min to 3 min; and / or, the time of the strengthening treatment is 0.5 min to 3 min.

[0014] In a possible implementation manner, the pulse activation treatment is carried out in an inert gas atmosphere, and the inert gas includes nitrogen.

[0015] In a possible implementation manner, the steps of depositing and growing the p-type GaN layer by the MOCVD method include: first growing a transition layer on the surface of the substrate, and then growing a p-type GaN layer on the surface of the transition layer.

[0016] In a possible implementation manner, the material of the substrate includes at least one of silicon, silicon carbide, sapphire, gallium nitride or aluminum nitride, and the material of the transition layer includes at least one of gallium nitride, aluminum nitride or aluminum gallium nitride.

[0017] In the above technical solution, the material of the transition layer is beneficial to reducing the internal stress of the p-type GaN layer and improving the crystal quality.

[0018] In a second aspect, the present application provides a p-type GaN film, which is prepared by the preparation method of the above-mentioned p-type GaN film.

[0019] In the above technical solution, the prepared p-type GaN film has a high hole concentration and a good surface morphology, which can well improve the performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0021] Figure 1 It is a schematic structural diagram when preparing the p-type GaN layer.

[0022] Figure 2 It is a schematic diagram showing the change of temperature and pressure with time in the pulse activation step of the present application.

[0023] Figure 3 It is an AFM diagram of the p-type GaN film in Embodiment 1 of the present application.

[0024] Figure 4 It is an AFM diagram of the p-type GaN film in Comparative Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to make the purpose, technical solution and advantages of the present application more clear, the following will further describe the present application in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0026] p-type GaN is mainly achieved by doping Mg in GaN. However, since Mg is easily passivated, annealing is carried out after obtaining p-type GaN to activate Mg. However, the annealing process will cause the surface morphology of p-type GaN to deteriorate. In order to avoid the deterioration of the morphology of p-type GaN during annealing, there is currently a method of reducing the annealing temperature, but this will lead to a decrease in the hole concentration of p-type GaN, which is not conducive to improving the device performance. For example, in an enhancement-mode GaN-based HEMT (High electron mobility transistor) power device implemented with a p-GaN gate structure, this deteriorated surface morphology easily leads to a poor contact quality between p-GaN and the gate metal in subsequent device processes, resulting in adverse effects such as an increase in device gate leakage. If methods such as low-temperature activation are used to avoid the deterioration of the surface morphology of p-GaN, it will lead to a decrease in the device threshold voltage and even become negative, turning it into a depletion-type device, affecting the practicality of the device.

[0027] To solve the above technical problems, the present application proposes a preparation method of a p-type GaN film. The p-type GaN film prepared by the preparation method of the present application has a good hole concentration and an excellent surface morphology, which can improve the use performance of the device.

[0028] The preparation method of the p-type GaN film of the present application specifically includes the following steps:

[0029] S100. Prepare a p-type GaN layer.

[0030] When preparing the p-type GaN layer, the MOCVD method is generally used to deposit and grow the p-type GaN layer. When using MOCVD to prepare the p-type GaN layer, a transition layer is usually grown on the surface of the substrate first, and then the p-type GaN layer is grown on the surface of the transition layer. Its specific structure can be referred to Figure 1 . During the preparation process, the material of the substrate includes at least one of silicon, silicon carbide, sapphire, gallium nitride or aluminum nitride, and the material of the transition layer includes at least one of gallium nitride, aluminum nitride or aluminum gallium nitride. Since the lattice energy of the transition layer is relatively close to that of the p-type GaN layer, the p-type GaN layer deposited and grown on the surface of the transition layer has small internal stress and high crystal quality.

[0031] This application has no specific requirements for the temperature, pressure, and V / III ratio (i.e., the molar ratio of Group VA elements to Group IIIA elements) in the preparation of the p-type GaN layer by the MOCVD method, as long as the purpose of this application can be satisfied. For example, when growing the p-type GaN layer on the transition layer using the MOCVD method, the growth temperature can be 900°C to 1200°C, the pressure can be 40 mbar to 500 mbar, the V / III ratio can be 200 to 20000, and the carrier gas can be hydrogen. Since this step is to prepare the p-type GaN layer, the Group V source is a nitride, and the Group III source is a gallium organic compound; moreover, since it is a p-type GaN layer, a small amount of magnesium element is also doped. In addition, the carrier gas introduced into the reaction chamber can create a corresponding gas environment in the reaction chamber. For example, when growing the p-type GaN layer using the MOCVD method in this step, the gas environment of hydrogen formed in the reaction chamber can ensure that the reaction and process can proceed normally. In some other embodiments and subsequent steps, the reaction chamber atmosphere can be not only hydrogen, but also nitrogen, or a mixture of nitrogen and hydrogen. Since the process of preparing semiconductor films by MOCVD is already relatively mature, the specific preparation process will not be elaborated in detail in this application.

[0032] The thickness of the p-type GaN layer obtained through this step is preferably 20 nm to 3000 nm, so that the modification effect on the p-type GaN layer in the subsequent steps is more obvious.

[0033] S200. Perform at least two pulse activation treatments on the p-type GaN layer to obtain a p-type GaN film.

[0034] After growing the p-type GaN layer, the p-type GaN layer is usually not moved, but directly subjected to pulse activation treatment in the MOCVD chamber, which can reduce the operation difficulty and process cost.

[0035] This step sequentially includes a thermal annealing treatment and a strengthening treatment. The temperature during the thermal annealing treatment is T1°C, the pressure is Y1 mbar, the temperature of the strengthening treatment is T2°C, and the pressure is Y2 mbar, where T1 > T2 and Y1 < Y2.

[0036] During the thermal annealing treatment, due to its high temperature and low pressure, the atmosphere at this time is relatively active. Therefore, the magnesium in the p-type GaN layer will be activated, thus having a certain concentration of holes, ensuring that it can be used as a donor. During the thermal annealing treatment process, the temperature is usually 750°C to 900°C, the pressure is usually 50 mbar to 300 mbar, and the treatment time is usually 0.5 min to 3 min, so as to better activate the magnesium in the p-type GaN layer and make its hole concentration higher.

[0037] During the strengthening treatment, due to the relatively low temperature and relatively high pressure during the strengthening treatment, the surface morphology of p-type GaN can be strengthened and repaired. During the strengthening treatment, the temperature is usually greater than 0°C and less than 750°C, the pressure is usually 300 mbar to 600 mbar, and the treatment time is usually 0.5 min to 3 min, which can better repair the morphology.

[0038] After each thermal annealing treatment, a strengthening treatment is performed, which is one pulse activation treatment operation; after at least 2 pulse activation treatments, the hole concentration and surface morphology of the p-type GaN layer can be significantly improved. The obtained p-type GaN film not only has a good hole concentration but also has a good surface morphology, which can improve the performance of, for example, enhancement-mode HEMT devices.

[0039] In addition, the pulse activation treatment is usually carried out under the atmosphere of an inert gas, and the inert gas includes nitrogen.

[0040] In addition, the inventors also found that as the thickness of the p-type GaN layer increases, in order to significantly improve the hole concentration and surface morphology of the thicker p-type GaN layer, the number of pulse activation treatments can also be correspondingly increased. However, as the number of pulse activation treatments increases, the improvement of the hole concentration and surface morphology of the prepared p-type GaN film becomes less and less obvious; considering the actual use requirements and production costs, the number of pulse activation treatments usually does not exceed 20 times.

[0041] The following further describes in detail the preparation method of the p-type GaN film of the present application in conjunction with the embodiments. For those not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0042] Example 1

[0043] This example provides a method for preparing a p-type GaN film, which includes the following steps:

[0044] (1) Select a sapphire substrate, and use the MOCVD method to grow a transition layer on the sapphire substrate. The material of the transition layer is gallium nitride, and then a p-type GaN layer with a thickness of 100 nm is deposited and grown on the surface of the transition layer. When depositing and growing the p-type GaN layer, the temperature is 960°C, the pressure is 300 mbar, and the V / III ratio is 10,000.

[0045] (2) Stop growing the p-type GaN layer, and then perform a pulse activation treatment on the p-type GaN layer, and repeat the steps of the pulse activation treatment 10 times.

[0046] Each pulse activation process sequentially includes a thermal annealing process and a strengthening process. During the thermal annealing process, the temperature T1 is 800 °C, the pressure Y1 is 100 mbar, the time is 1 min, and the inert gas atmosphere is nitrogen; during the strengthening process, the temperature T2 is 600 °C, the pressure Y1 is 400 mbar, the time is 1 min, and the inert gas atmosphere is nitrogen.

[0047] Example 2

[0048] This example provides a method for preparing a GaN film, and its preparation steps are as follows:

[0049] (1) Select a sapphire substrate. Using the MOCVD method, first grow a transition layer on the sapphire substrate. The material of the transition layer is gallium nitride, and then deposit and grow a p-type GaN layer with a thickness of 20 nm on the surface of the transition layer. When depositing and growing the p-type GaN layer, the temperature is 960 °C, the pressure is 300 mbar, and the V / III ratio is 10,000.

[0050] (2) Stop growing the p-type GaN layer, and then perform a pulse activation process on the p-type GaN layer, and repeat the steps of the pulse activation process 5 times.

[0051] Each pulse activation process sequentially includes a thermal annealing process and a strengthening process. During the thermal annealing process, the temperature T1 is 750 °C, the pressure Y1 is 300 mbar, the time is 1 min, and the inert gas atmosphere is nitrogen; during the strengthening process, the temperature T2 is 550 °C, the pressure Y1 is 600 mbar, the time is 1 min, and the inert gas atmosphere is nitrogen.

[0052] Example 3

[0053] This example provides a method for preparing a GaN film, and its preparation steps are as follows:

[0054] (1) Select a sapphire substrate. Using the MOCVD method, first grow a transition layer on the sapphire substrate. The material of the transition layer is gallium nitride, and then deposit and grow a p-type GaN layer with a thickness of 3000 nm on the surface of the transition layer. When depositing and growing the p-type GaN layer, the temperature is 960 °C, the pressure is 300 mbar, and the V / III ratio is 10,000.

[0055] (2) Stop growing the p-type GaN layer, and then perform a pulse activation process on the p-type GaN layer, and repeat the steps of the pulse activation process 20 times.

[0056] Each pulse activation treatment sequentially includes a thermal annealing treatment and a strengthening treatment. During the thermal annealing treatment, the temperature T1 is 850 °C, the pressure Y1 is 50 mbar, the time is 3 min, and the inert gas atmosphere is nitrogen; during the strengthening treatment, the temperature T2 is 650 °C, the pressure Y1 is 300 mbar, the time is 3 min, and the inert gas atmosphere is nitrogen.

[0057] Example 4

[0058] This example provides a method for preparing a p-type GaN film. Compared with Example 1, the main difference is that in step (2), the number of pulse activation treatments is 2 times.

[0059] Comparative Example 1

[0060] This comparative example provides a method for preparing a p-type GaN film, which includes the following steps:

[0061] (1) Select a sapphire substrate. Using the MOCVD method, first grow a transition layer on the sapphire substrate. The material of the transition layer is gallium nitride, and then deposit and grow a p-type GaN layer with a thickness of 100 nm on the surface of the transition layer. When depositing and growing the p-type GaN layer, the temperature is 960 °C, the pressure is 300 mbar, and the V / III ratio is 10,000.

[0062] (2) Stop growing the p-type GaN layer, and then perform a thermal annealing treatment on the p-type GaN layer. During the thermal annealing treatment, the temperature T1 is 800 °C, the pressure Y1 is 100 mbar, the time is 10 min, and the inert gas atmosphere is nitrogen.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing a p-type GaN film. Compared with Example 1, the main difference is that in step (2), the pressure Y1 during the thermal annealing treatment is 400 mbar, and the pressure Y2 during the strengthening treatment is 100 mbar.

[0065] Performance test

[0066] Use AFM (Atomic Force Microscope) to test the surface morphology and surface roughness of the p-type GaN films of each example and comparative example. The surface roughness parameters are shown in Table 1; in addition, the AFM images of Example 1 and Comparative Example 1 are as Figure 3 and Figure 4 shown.

[0067] From Figure 3 、 Figure 4As can be seen from the test results in Table 1, the surface roughness of the p-type GaN film in Example 1 is less than 0.4 nm, and the surface roughness of the p-type GaN film in Comparative Example 1 is greater than 1 nm. Therefore, the surface morphology of the p-type GaN film in Example 1 is significantly better than that in Comparative Example 1. This shows that the surface morphology of p-GaN after pulse activation treatment is more excellent.

[0068] The hole concentration of the p-type GaN film in each example and comparative example was measured using a Hall effect tester, and the results are shown in Table 1:

[0069] Table 1

[0070] Group <![CDATA[Hole concentration (×10 18 / cm 3 )]]> Surface roughness (nm) Example 1 1.00 0.4 Example 2 0.95 0.38 Example 3 1.10 0.41 Example 4 0.93 0.39 Comparative Example 1 1.02 1.53 Comparative Example 2 0.99 1.23

[0071] As can be seen from Table 1, the p-type GaN films in the examples all have good hole concentrations after pulse activation treatment. In Comparative Example 2, the pressure during thermal annealing treatment is higher than that during strengthening treatment, resulting in a poor surface morphology and high roughness.

[0072] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a p-type GaN film, characterized in that, It includes the following steps: Deposit and grow a p-type GaN layer by MOCVD method, and then perform a pulse activation treatment on the p-type GaN layer to obtain a p-type GaN film, and the number of times of the pulse activation treatment is not less than 2 times; The pulse activation treatment sequentially includes a thermal annealing treatment and a strengthening treatment; The temperature of the thermal annealing treatment is T1 °C, and the pressure is Y1 mbar. The temperature of the strengthening treatment is T2 °C, and the pressure is Y2 mbar, where T1 > T2 and Y1 < Y2.

2. The preparation method of the p-type GaN film according to claim 1, wherein The thickness of the p-type GaN layer is 20 nm to 3000 nm.

3. The preparation method of the p-type GaN film according to claim 1, characterized in that, 750 ≤ T1 ≤ 900, 50 ≤ Y1 ≤ 300.

4. The preparation method of the p-type GaN film according to claim 1, characterized in that, 0 < T2 < 750, 300 ≤ Y2 ≤ 600.

5. The preparation method of the p-type GaN film according to claim 1, characterized in that, The number of times of the pulse activation treatment is 2 to 20 times.

6. The method for preparing the p-type GaN film according to claim 1, characterized in that, The time of the thermal annealing treatment is 0.5 min to 3 min; and / or The time of the strengthening treatment is 0.5 min to 3 min.

7. The method for preparing a p-type GaN film according to claim 1, characterized in that, The pulse activation treatment is carried out in an atmosphere of an inert gas, and the inert gas includes nitrogen.

8. The method for preparing the p-type GaN film according to claim 1, characterized in that, The step of depositing and growing a p-type GaN layer by MOCVD method includes: first growing a transition layer on the surface of the substrate, and then growing the p-type GaN layer on the surface of the transition layer.

9. The method for preparing a p-type GaN film according to claim 8, characterized in that, The material of the substrate includes at least one of silicon, silicon carbide, sapphire, gallium nitride or aluminum nitride, and the material of the transition layer includes at least one of gallium nitride, aluminum nitride or aluminum gallium nitride.

10. A p-type GaN film, characterized in that, It is obtained by the preparation method of the p-type GaN film according to any one of claims 1 to 9.

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