A growth method and application for reducing non-uniformity of a GaN heterojunction material square resistance sheet

Abstract

The application discloses a growth method for reducing non-uniformity of GaN heterojunction material square resistance sheet and application. The method adopts zero ammonia supply process when growing an AlN insertion layer, enhances aluminum atom migration through an aluminum-rich atmosphere, and improves thickness uniformity of the insertion layer; before growing an AlGaN barrier layer, N2+H2 mixed carrier gas is adopted and pretreatment is carried out, flow field stability is optimized, and therefore, consistency of aluminum component and thickness of the barrier layer is improved. Through the above-mentioned synergistic process, two core structural parameters affecting square resistance are controlled from the source, the non-uniformity of the square resistance sheet of the epitaxial material can be significantly reduced to below 1%, and the uniformity of the electrical performance of the material is greatly improved, and reliable raw material guarantee is provided for batch manufacturing of high-performance and high-consistency GaN microwave power devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor epitaxial materials technology, specifically relating to a growth method and application for reducing the inhomogeneity of GaN heterojunction material sheet resistance. Background Technology

[0002] Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) have become core devices in next-generation microwave RF and power electronic systems due to their excellent frequency and power characteristics. Their superior performance primarily stems from the high-concentration, high-mobility two-dimensional electron gas (2DEG) induced by strong polarization at the AlGaN / GaN heterojunction interface. The electrical properties of this 2DEG, especially its areal density and mobility, directly determine the device's on-resistance, transconductance, saturated output power, and frequency characteristics.

[0003] With the increasing demands for power capacity and efficiency in wireless communication, micro base stations, and other systems, the demand for GaN microwave devices is growing, driving the mainstream size of epitaxial materials from 4-6 inches to 8 inches to achieve higher production efficiency and cost-effectiveness. However, controlling the uniformity of the temperature field and reactant gas flow field within the reaction cavity during epitaxial growth on large-size substrates presents a significant challenge. These hardware and process limitations directly lead to non-uniformity of key parameters of epitaxial materials within the wafer, with the intra-wafer non-uniformity of sheet resistance (Rsh) being particularly prominent.

[0004] Sheet resistance is a key comprehensive parameter for evaluating the two-dimensional electron gas transport characteristics of heterojunctions, and it is directly related to the DC and microwave performance of devices. Its intra-wafer inhomogeneity mainly stems from quality fluctuations in several nanoscale thin layers within the heterojunction structure: First, the inhomogeneity of the AlN insertion layer thickness. The ultrathin AlN insertion layer (typically 1-2 nm), introduced to improve the two-dimensional electron gas mobility, is extremely sensitive to growth conditions. Even small fluctuations in its thickness within the wafer can significantly alter the distribution of interfacial polarization charges and scattering centers, thus affecting electron mobility and concentration. Second, the inhomogeneity of the aluminum composition and thickness of the AlGaN barrier layer. The aluminum composition and thickness of the barrier layer directly determine the polarization intensity, band shift, and two-dimensional electron gas concentration. The non-uniform distribution of these two parameters on the wafer is another major factor leading to intra-wafer differences in sheet resistance.

[0005] Currently, the industry has explored various approaches to improve uniformity. One common approach is to improve the temperature and flow fields by optimizing hardware design or adjusting global process conditions. Another technical route focuses on material system innovation, such as using ternary or quaternary alloys with smaller lattice mismatch with GaN (e.g., InAlGaN used in Chinese patent application CN115719758A) as intercalation layers to relax the stringent requirements for thickness control precision. However, hardware modifications are costly, and changes to the material system may introduce new process complexities, or require a trade-off between material properties and process tolerance.

[0006] Therefore, within the framework of mainstream AlGaN / GaN heterojunction materials, especially under the premise of using high-performance but difficult-to-grow ultrathin AlN insertion layers, how to fundamentally improve the thickness and compositional uniformity of AlN insertion layers and AlGaN barrier layers at the nanoscale through innovative epitaxial growth processes, thereby effectively reducing the inhomogeneity within the sheet resistance of large-size GaN heterojunction epitaxial materials, has become a key technical bottleneck for improving device performance consistency, yield, and batch production efficiency, and has significant research value and industrial significance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a growth method and application for reducing the intra-chip inhomogeneity of GaN heterojunction material sheet resistance. The AlN insertion layer employs a zero-ammonia supply process, which improves the uniform film formation of the AlN insertion layer by increasing the surface migration length of adsorbed aluminum atoms, thereby improving the intra-chip consistency of the insertion layer thickness. The AlGaN barrier layer uses a mixed N2 and H2 carrier gas atmosphere and introduces pretreatment technology to enhance the intra-chip consistency of the aluminum alloy composition and thickness of the barrier layer.

[0008] This invention is achieved through the following technical solution:

[0009] A growth method for reducing intra-chip inhomogeneities in the sheet resistance of GaN heterojunction materials includes the following steps:

[0010] Step 1) Provide a single-crystal substrate, and sequentially grow an AlN nucleation layer and a GaN buffer layer on the single-crystal substrate;

[0011] Step 2) On the GaN buffer layer, at a temperature of 950~1100℃ and a pressure of 30~150 torr, an aluminum source is introduced while NH3 is stopped to grow an AlN insertion layer with a thickness of 0.5~2 nm.

[0012] Step 3) After growing the AlN insertion layer, the carrier gas is switched to a mixed atmosphere of N2 and H2, and a process pretreatment is performed without growing an epitaxial layer to stabilize the flow field in the reaction chamber.

[0013] Step 4) After the process pretreatment described in Step 3), keep the temperature, pressure and mixed carrier gas atmosphere of N2 and H2 constant, and introduce gallium source, aluminum source and NH3 to grow AlGaN barrier layer on AlN insertion layer.

[0014] Preferably, in step 1), the conditions for growing the AlN nucleation layer include: in an H2 atmosphere, at a temperature of 950~1250℃, a pressure of 30~150 torr, NH3 and an aluminum source are introduced, and the growth thickness is 15~100 nm.

[0015] Preferably, in step 1), the conditions for growing the GaN buffer layer include: in an NH3 atmosphere, setting the temperature to 900~1100℃, raising the pressure to 150~500 torr, introducing a gallium source, and growing a thickness of 0.2~3.0 μm.

[0016] Preferably, in the N2 and H2 mixed atmosphere described in step 3), the flow molar ratio of N2 to H2 is 0.25 to 4.

[0017] Preferably, the duration of the pretreatment in step 3) is 2 to 5 minutes.

[0018] Preferably, the growth method employs metal-organic chemical vapor deposition (MOCVD).

[0019] A GaN heterojunction material, said material being prepared by the growth method described above.

[0020] A semiconductor device comprising the GaN heterojunction material described above.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) Through innovative process combinations, this invention improves the two core structural parameters affecting sheet resistance from the source—the thickness of the AlN insertion layer and the aluminum composition and thickness of the AlGaN barrier layer. Compared with conventional processes, this invention can effectively reduce the intra-chip inhomogeneity of sheet resistance, thereby obtaining high-quality GaN heterojunction epitaxial materials with more consistent and stable electrical properties.

[0023] (2) The “zero ammonia supply” growth process used in this invention creates an aluminum-rich growth environment by interrupting the ammonia supply at a specific stage. This condition significantly increases the migration length of Al adsorbed atoms on the growth surface, giving them more time and opportunity to move to more energy-stable lattice sites, thereby achieving an atomically flat and highly uniform AlN intercalation layer film. This solves the key technical problem of difficulty in controlling the intra-wafer consistency of ultrathin AlN layers (0.5~2 nm) due to process sensitivity.

[0024] (3) This invention uses a mixed carrier gas of N2 and H2 (molar ratio 0.25~4), which combines the characteristics of strong fluidity of metal-organic source under H2 carrier gas and weak diffusion under N2 carrier gas, promoting the formation of a stable and uniform flow field distribution of the reaction precursor in the reaction chamber. This fundamentally suppresses the macroscopic fluctuations in aluminum composition and thickness of AlGaN barrier layer caused by local enrichment or depletion of source material. At the same time, the pretreatment step introduced in this invention before the growth of barrier layer ensures that after process switching (from insertion layer growth to barrier layer growth), the temperature, pressure and mixed carrier gas flow field in the reaction chamber have sufficient time (2~5 min) to reach and maintain dynamic equilibrium. This measure eliminates the transient instability period in the early stage of growth, ensuring that the barrier layer is epitaxially grown under uniform and stable conditions from the first atomic layer, greatly improving the intra-sheet consistency of the entire barrier layer structure.

[0025] (4) The process improvement of this invention focuses on optimizing the gas atmosphere and growth sequence, without requiring fundamental changes to the material system or relying on special or expensive hardware modifications. This solution is highly compatible with mainstream metal-organic chemical vapor deposition (MOCVD) technology platforms, has a clear process window, good repeatability, and is particularly suitable for the mass production of 4-inch and larger wafers with extremely high uniformity requirements, and has good prospects for industrialization and promotion.

[0026] (5) The improved sheet resistance uniformity of the epitaxial material prepared by this invention directly means that HEMT devices prepared based on this material have better consistency in key electrical parameters such as threshold voltage, saturation current, and on-resistance. This not only significantly improves the overall yield of device manufacturing, but also ensures the stable and reliable performance of microwave power devices under complex operating conditions, meeting the stringent requirements for device consistency and reliability in modern communication, micro base stations and other fields. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the GaN heterojunction material in Example 1;

[0028] Figure 1 In the middle: 1. Substrate; 2. Nucleation layer; 3. Buffer layer; 4. Insertion layer; 5. Barrier layer;

[0029] Figure 2 For the comparison of the uniformity of AlN insertion layer thickness in each group in Test Example 1: (a) is the intra-chip distribution of photoluminescence peak intensity of GaN heterojunction material grown in Example 1; (b) is the intra-chip distribution of photoluminescence peak intensity of GaN heterojunction material grown in Comparative Example 1.

[0030] Figure 3For the comparison of AlGaN barrier layer composition and thickness uniformity in each group of test example 1: (a) is the aluminum composition distribution at 7 points in the radial direction within the AlGaN barrier layer grown in Example 1 and Comparative Examples 1 and 2; (b) is the thickness distribution at 7 points in the radial direction within the AlGaN barrier layer grown in Example 1 and Comparative Examples 1 and 2; the horizontal axis of each figure represents the measurement position along the wafer diameter, 0 is the center point, and negative and positive values ​​represent points symmetrical on both sides of the center, respectively;

[0031] Figure 4 For the comparison of sheet resistance uniformity in Test Example 1: (a) is the sheet resistance distribution diagram of the GaN heterojunction material grown in Example 1; (b) is the sheet resistance distribution diagram of the GaN heterojunction material grown in Comparative Example 1; (c) is the sheet resistance distribution diagram of the GaN heterojunction material grown in Comparative Example 2. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art, and the experimental methods without specific conditions are all conventional methods in the art.

[0034] Unless otherwise specified, the equipment and materials used in the following embodiments are commercially available.

[0035] Example 1

[0036] A growth method for reducing inhomogeneities within the sheet resistance of GaN heterojunction materials, such as... Figure 1 As shown, the specific steps are as follows:

[0037] (1) Substrate 1 preparation and pretreatment

[0038] A 6-inch silicon carbide (SiC) single crystal substrate 1 was selected and placed on the base inside the reaction chamber of the MOCVD equipment after cleaning. The reaction chamber pressure was set to 100 Torr, hydrogen gas (H2) was introduced, and the temperature was raised to 1070℃ and held for 10 min to bake away impurities and oxides adsorbed on the substrate surface.

[0039] (2) Growth of AlN nucleation layer 2

[0040] Maintain an H2 atmosphere, setting the reaction chamber temperature to 1150℃ and the pressure to 100 Torr. Introduce ammonia (NH3) at a flow rate of 10 slm and trimethylaluminum (TMAl) at a flow rate of 300 sccm into the reaction chamber to grow an AlN nucleation layer 2 with a thickness of approximately 50 nm, providing a good lattice-matched template for subsequent epitaxy. After growth is complete, turn off the TMAl source.

[0041] (3) Growth of GaN buffer layer 3

[0042] In an atmosphere continuously purging NH3, the reaction chamber temperature was lowered to 1000℃ while the pressure was increased to 250 Torr. Trimethylgallium (TMGa) was introduced to grow a GaN buffer layer 3 with a thickness of approximately 2.0 μm. This layer was used to release the lattice mismatch stress between the substrate and the epitaxial layer, and to obtain a high-quality GaN crystal with a low dislocation density. After growth was completed, the TMGa source was turned off.

[0043] (4) Growth of AlN insertion layer 4 (using zero ammonia supply process)

[0044] The reaction chamber conditions were adjusted to a temperature of 1050℃ and a pressure of 100 Torr, with NH3 continuously supplied to stabilize the atmosphere. Once the gas flow stabilized, the NH3 supply was stopped, creating a temporary aluminum-rich growth environment. Immediately afterwards, TMAl was introduced, utilizing the significant increase in migration length of surface-adsorbed Al atoms in the absence of NH3, to grow an ultrathin AlN intercalation layer with a thickness of approximately 1 nm. This process aims to achieve atomically flat intercalation layers and highly uniform thickness within the wafer. Furthermore, the thickness of the intercalation layer can be controlled by adjusting the intercalation layer growth time and the aluminum source flow rate. After growth was complete, the TMAl source was shut off.

[0045] (5) Pretreatment before growth of AlGaN barrier layer 5

[0046] Maintain the temperature (1050°C) and pressure (100 Torr) at the end of step (4), and resume the NH3 flow. Switch the carrier gas from pure H2 to a mixed atmosphere of N2 and H2, with the N2 to H2 flow rate molar ratio set to 0.7. Under this mixed carrier gas atmosphere, do not introduce any Group III sources, and maintain stable flow for 3 min. This pretreatment step aims to ensure that the temperature field, pressure field, and mixed carrier gas flow field in the reaction chamber reach sufficient equilibrium and stability after the process switch.

[0047] The principle behind the N2+H2 mixed carrier gas atmosphere process is as follows: Because the metal-organic source has strong fluidity in an H2 atmosphere, it is difficult for it to form a stable and uniform distribution in a pure H2 carrier gas atmosphere. Conversely, its fluidity is relatively weak in an N2 atmosphere, making it prone to local enrichment. Both of these factors lead to degradation of the aluminum composition and thickness uniformity of the AlGaN barrier layer alloy. In this invention, the AlGaN barrier layer employs a N2 and H2 mixed carrier gas atmosphere process, with the molar ratio N of N2 and H2 flow rates within a suitable range (0.25~4). This promotes a stable and uniform distribution of the metal-organic source within the reaction chamber, thereby improving the aluminum composition and thickness uniformity of the AlGaN barrier layer alloy.

[0048] The principle behind introducing pretreatment technology before AlGaN barrier layer growth is as follows: Due to the significant difference in process windows between the AlGaN barrier layer and the GaN channel layer, the airflow fluctuations are substantial during the process switching between the barrier layer and the channel layer. In the early stages of barrier layer growth, the unstable flow field leads to significant intra-wafer deviations in the aluminum alloy composition and thickness of the barrier layer. This invention introduces a pretreatment technology, which maintains a constant and stable flow field in the reaction chamber for 2-5 minutes after the AlN insertion layer growth and before the AlGaN barrier layer growth. This improves the stability of the flow field in the reaction chamber and enhances the intra-wafer consistency of the aluminum alloy composition and thickness of the barrier layer in the early stages of barrier layer growth. Furthermore, because the Al-N bond energy is very strong, meaning the AlN insertion layer performance is stable, the pretreatment process will not induce insertion layer decomposition, thus preventing degradation of the heterojunction performance.

[0049] (6) Growth of AlGaN barrier layer 5 (using mixed carrier gas)

[0050] The temperature, pressure, and N2+H2 mixed carrier gas atmosphere were kept constant after the pretreatment. TMGa and TMAl were simultaneously introduced to grow an Al layer with an Al composition of 0.25 and a thickness of approximately 20 nm. 0.25 Ga 0.75 N-barrier layer 5. The mixed carrier gas promoted the uniform distribution of the metal-organic source within the reaction chamber. After growth was complete, all group III sources were shut off.

[0051] (7) Cooling and removing the tablets

[0052] Under the protective atmosphere of NH3, the temperature of the reaction chamber is slowly reduced to room temperature, and the prepared GaN heterojunction epitaxial wafer is taken out.

[0053] Comparative Example 1 (Prior Technology H2 Carrier Gas)

[0054] A method for growing GaN heterojunction materials, the specific steps of which are the same as in Example 1, except that:

[0055] In step (4), NH3 is continuously introduced during the growth of the AlN insertion layer;

[0056] No preprocessing is performed in step (5);

[0057] In step (6), pure H2 carrier gas is used when growing the AlGaN barrier layer.

[0058] Comparative Example 2 (Prior technology N2 carrier gas)

[0059] A method for growing GaN heterojunction materials, with the same specific steps as Comparative Example 1, but with the following differences:

[0060] In step (4), NH3 is continuously introduced during the growth of the AlN insertion layer;

[0061] No preprocessing is performed in step (5);

[0062] In step (6), pure N2 carrier gas is used when growing the AlGaN barrier layer.

[0063] Test Example 1

[0064] The epitaxial wafers prepared in Example 1 and Comparative Examples 1 and 2 were systematically characterized, and the key results are compared as follows:

[0065] 1. Uniformity of AlN insertion layer thickness

[0066] The peak intensity of the GaN heterojunction signal was measured by photoluminescence (PL) spectroscopy. The intra-wafer inhomogeneity of the peak intensity directly reflects the fluctuation of the AlN insertion layer thickness. The results are as follows: Figure 2 As shown.

[0067] like Figure 2 As shown in (a), the heterojunction signal peak intensity inhomogeneity of Embodiment 1 of the present invention is 2.48%, while as... Figure 2 As shown in Figure (b), the non-uniformity of Comparative Example 1, which uses a conventional ammonia supply process, is 5.89%.

[0068] This fully demonstrates that the "zero ammonia supply" process significantly improves the thickness uniformity of the ultrathin AlN insertion layer by enhancing the surface migration of Al atoms.

[0069] 2. AlGaN barrier layer composition and thickness uniformity

[0070] The radial distribution of Al composition and thickness of the barrier layer was measured using X-ray diffraction (XRD) (using 7 feature points on the wafer). The results are as follows: Figure 3 As shown.

[0071] like Figure 3 As shown in (a) and (b), the AlGaN barrier layer of Example 1 of the present invention has a relative standard deviation (RSD) of 0.60% for Al composition and 1.16% for thickness, exhibiting excellent uniformity. In contrast, the RSDs for Al composition and thickness of Comparative Example 1 (pure H2 carrier gas) are 1.75% and 2.63%, respectively; and the RSDs for Al composition and thickness of Comparative Example 2 (pure N2 carrier gas) are 1.91% and 2.25%, respectively.

[0072] Data shows that using a N2+H2 mixed carrier gas combined with pretreatment technology effectively optimizes the reaction flow field and significantly improves the intra-sheet consistency of the barrier layer alloy composition and thickness.

[0073] 3. Sheet resistance (Rsh) uniformity

[0074] The sheet resistance distribution of the entire wafer was measured using a non-contact eddy current method, and the results are as follows: Figure 4 As shown.

[0075] like Figure 4 As shown in Figure (a), the non-uniformity within the sheet resistor sheet of this embodiment is only 0.49%, exhibiting excellent uniformity. Figure 4 As shown in (b) and (c), the sheet resistance non-uniformity of Comparative Example 1 and Comparative Example 2 is 2.79% and 2.13%, respectively. The comparative data clearly demonstrate that the present invention, through systematic process innovation (zero ammonia supply AlN insertion layer + mixed carrier gas and pretreated AlGaN barrier layer), effectively controls the non-uniformity within the sheet resistance, reducing it by an order of magnitude.

[0076] The experimental results of this test case demonstrate that the present invention provides an efficient, stable growth method that is highly compatible with existing MOCVD platforms, and offers a practical and feasible process solution for solving the uniformity bottleneck problem in the mass production of large-size, high-performance GaN heterojunction epitaxial materials.

[0077] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. The scope of protection of the present invention is determined by the scope claimed in the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A growth method for reducing intra-sheet inhomogeneities in GaN heterojunction materials, characterized in that, Includes the following steps: Step 1) Provide a single-crystal substrate, and sequentially grow an AlN nucleation layer and a GaN buffer layer on the single-crystal substrate; Step 2) On the GaN buffer layer, at a temperature of 950~1100℃ and a pressure of 30~150 torr, an aluminum source is introduced while NH3 is stopped to grow an AlN insertion layer with a thickness of 0.5~2 nm. Step 3) After growing the AlN insertion layer, the carrier gas is switched to a mixed atmosphere of N2 and H2, and a process pretreatment is performed without growing an epitaxial layer to stabilize the flow field in the reaction chamber. Step 4) After the process pretreatment described in Step 3), keep the temperature, pressure and mixed carrier gas atmosphere of N2 and H2 constant, and introduce gallium source, aluminum source and NH3 to grow AlGaN barrier layer on AlN insertion layer.

2. The growth method for reducing intra-sheet non-uniformity of GaN heterojunction material according to claim 1, characterized in that, In step 1), the conditions for growing the AlN nucleation layer include: in an H2 atmosphere, at a temperature of 950~1250℃, a pressure of 30~150 torr, NH3 and an aluminum source are introduced, and the growth thickness is 15~100 nm.

3. The growth method for reducing intra-sheet non-uniformity of GaN heterojunction material according to claim 2, characterized in that, In step 1), the conditions for growing the GaN buffer layer include: in an NH3 atmosphere, setting the temperature to 900~1100℃, raising the pressure to 150~500 torr, introducing a gallium source, and growing a thickness of 0.2~3.0 μm.

4. The growth method for reducing intra-sheet non-uniformity of GaN heterojunction material according to claim 1, characterized in that, In step 3), the molar ratio of N2 to H2 flow rate in the N2 and H2 mixed atmosphere is 0.25 to 4.

5. The growth method for reducing intra-sheet non-uniformity of GaN heterojunction material according to claim 1, characterized in that, Step 3) The duration of the pretreatment process is 2-5 minutes.

6. A growth method for reducing intra-sheet non-uniformity of GaN heterojunction material according to any one of claims 1-5, characterized in that, The growth method employs organometallic chemical vapor deposition (MCVD).

7. A GaN heterojunction material, characterized in that, The material is prepared by the growth method as described in any one of claims 1-6.

8. A semiconductor device, characterized in that, The semiconductor device comprises the GaN heterojunction material as described in claim 7.

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