A method for manufacturing a heterojunction bipolar transistor epitaxial wafer

Abstract

The present application belongs to the technical field of heterojunction bipolar transistor, and particularly relates to a preparation method of a heterojunction bipolar transistor epitaxial wafer. The present application provides a preparation method, which is prepared in a MOCVD device, wherein the small-dish supporting gas of the MOCVD device is changed to hydrogen and nitrogen before growth of a base region, and the base region is grown after rapid cooling by 20-30 DEG C; after growth of the base region, the small-dish supporting gas is changed to argon and nitrogen, and the emitter layer is grown after rapid heating by 20-30 DEG C. The present application rapidly changes the temperature of the surface of the epitaxial wafer by changing the small-dish supporting gas, and the surface temperature of the epitaxial wafer is shown in Fig. 2, so that the rapid transformation of the temperature of the collector region and the base region, and the temperature of the base region and the emitter region is well realized, that is, the quality of the base region epitaxial layer is not affected, and the quality of the epitaxial layer interface is not affected.

Description

Technical Field

[0001] This invention belongs to the field of heterojunction bipolar transistor technology, specifically relating to a method for fabricating an epitaxial wafer of a heterojunction bipolar transistor. Background Technology

[0002] A heterojunction bipolar transistor (HBT) is a type of bipolar transistor (BJT) that uses different semiconductor materials to form a heterojunction between the emitter and base. HBTs offer advantages such as high current gain and low base resistance. Furthermore, due to the inherent material properties of the semiconductor layers, HBTs fabricated by epitaxially growing compound semiconductor layers on GaAs substrates (hereinafter referred to as GaAs HBTs) exhibit high electron mobility, which is a significant advantage in high-frequency applications. For example, GaAs HBTs are commonly used in mobile phones, WiFi terminals, and their base stations, such as radio frequency (RF) power amplifiers and other monolithic microwave integrated circuits (MMICs). Bandgap engineering of the base, emitter, and / or collector using strained or graded semiconductor layers can effectively improve the performance of GaAs HBTs. For example, using InGaAs / InGaP, GaAsSb / InGaP, and GaAsPBi / InGaP materials for the base and emitter regions, respectively, can reduce the conduction electron transport time of the HBT, thereby improving its high-frequency performance, such as the high current gain cutoff frequency (f). t ) and maximum oscillation frequency (f max )wait.

[0003] The InGaAs base layer of HBT is generally highly doped, which often requires a relatively low growth temperature to achieve high doping. However, the emitter region requires high-temperature growth to obtain better material quality. Therefore, in the epitaxial growth process of InGaAs / InGaP HBT, how to grow InGaAs material that meets the design requirements is a challenge in the preparation of high-performance HBT epitaxial wafers.

[0004] Chinese patent CN106505100A proposes a heterojunction bipolar transistor (HBT) that divides the InGaAs base region into four segments, with the composition increasing from bottom to top. This reduces the strain of mismatched InGaAs and prevents stress relaxation leading to dislocations when the InGaAs growth thickness exceeds a critical thickness, thereby reducing carrier mobility. While this method yields a high-quality base region, it also reduces the In composition, which to some extent lowers the high-frequency characteristics of the HBT device.

[0005] Chinese patent CN115831743A proposes a molecular beam epitaxy (MBE) method for HBT devices. During the deposition of the base layer on the collector layer, the gallium source furnace employs a piecewise linear heating method. In the epitaxial growth of the base layer with continuously varying composition, by setting the gallium source furnace to a piecewise linear heating method and selecting segmented target temperature values ​​according to a logarithmic function, the piecewise linear heating method approximates the logarithmic heating method. Compared to methods that step-increment the gallium source furnace temperature from a first temperature or directly linearly increase it to a second temperature, this significantly reduces the temperature overshoot that may occur during rapid heating in a short time. This significantly improves the abnormal compositional changes of the InGaAs material in the base layer caused by temperature overshoot, thus enhancing the performance of the HBT device. While this method yields a high-quality base region, the slow growth rate and high cost of MBE limit the widespread use of HBT epitaxial wafers.

[0006] In summary, current GaAs / InGaAs / GaInP HBT transistors suffer from the problem of high base region doping concentration and difficulty in epitaxial growth. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a heterojunction bipolar transistor epitaxial wafer. This invention uses MOCVD epitaxial growth to prepare high-quality InGaAs base material, resulting in HBT epitaxial wafers with high gain and good reliability.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for fabricating a heterojunction bipolar transistor epitaxial wafer in an MOCVD device, comprising the following steps:

[0010] (1) Place the substrate in an MOCVD equipment and grow a buffer layer, a collector ohmic contact layer, a collector region etching barrier layer and a collector region sequentially on the surface of the substrate to obtain the first epitaxial wafer semi-finished product.

[0011] (2) Change the support gas of the small disk of the MOCVD equipment to hydrogen and nitrogen, cool the surface of the first epitaxial wafer semi-finished product and grow the base region. The material of the base region is P-type doped InGaAs. The cooling time is ≤5s and the temperature difference of the cooling is 20~30℃ to obtain the second epitaxial wafer semi-finished product.

[0012] (3) Change the small disk support gas to argon and nitrogen, heat the surface of the second epitaxial wafer semi-finished product and grow an emission layer. The material of the emission layer is N-type doped InGaP. The heating time is ≤5s and the temperature difference is 20~30℃ to obtain the third epitaxial wafer semi-finished product.

[0013] (4) A sub-emitter layer and an emitter ohmic contact layer are grown on the surface of the third epitaxial wafer to obtain a heterojunction bipolar transistor.

[0014] Preferably, in step (2), before changing the type of the small disk support gas, the method further includes: stopping the supply of the current collector growth gas source to the reaction chamber of the MOCVD equipment, and supplying TMAs to the reaction chamber of the MOCVD equipment, wherein the flow rate of the TMAs is 180 sccm.

[0015] Preferably, the flow rate ratio of hydrogen to nitrogen is (2-5):(15-20).

[0016] Preferably, the temperature difference for cooling is 25°C.

[0017] Preferably, the growth method of the base region includes the following steps: maintaining the flow rate of the TMAs and the type and flow rate of the disk support gas unchanged, and introducing TMIn, TMGa and CCl4 into the reaction chamber; the flow rate of TMIn is 60 sccm, and the TMGa is introduced into the reaction chamber through a double dilution pipeline, with a flow rate of 12 sccm.

[0018] Preferably, the doping concentration of the base region is 4E19cm. -3 The thickness is 50nm.

[0019] Preferably, in step (3), before changing the type of gas supporting the small disk, the method further includes: maintaining the flow rate of the TMAs unchanged and stopping the introduction of TMI, TMGa and CCl4 into the reaction chamber.

[0020] Preferably, the flow rate ratio of argon to nitrogen is (17-22):(0.5-2).

[0021] Preferably, the temperature difference during the heating process is 25°C.

[0022] Preferably, the method for growing the emission layer includes the following steps: maintaining the type and flow rate of the supporting gas in the small disk unchanged, stopping the introduction of TMAs into the reaction chamber, introducing PH3 into the reaction chamber at a flow rate of 720 sccm; and introducing TMGa, TMIn, and SiH4 into the reaction chamber.

[0023] This invention provides a method for fabricating a heterojunction bipolar transistor epitaxial wafer in an MOCVD (Multi-Mechanical Vapor Deposition) device, comprising the following steps: (1) placing a substrate in the MOCVD device, and sequentially growing a buffer layer, a collector ohmic contact layer, a collector region etching barrier layer, and a collector region on the substrate surface to obtain a first epitaxial wafer semi-finished product; (2) changing the support gas of the small disk in the MOCVD device to hydrogen and nitrogen, cooling the surface of the first epitaxial wafer semi-finished product, and then growing a base region, wherein the material of the base region is p-type doped InGaAs. The cooling time is ≤5s, the temperature difference of the cooling is 20~30℃, and a second epitaxial wafer semi-finished product is obtained; (3) the small disk support gas is changed to argon and nitrogen, and the surface of the second epitaxial wafer semi-finished product is heated to grow an emitter layer. The material of the emitter layer is N-type doped InGaP. The heating time is ≤5s, the temperature difference of the heating is 20~30℃, and a third epitaxial wafer semi-finished product is obtained; (4) a sub-emitter layer and an emitter region ohmic contact layer are grown on the surface of the third epitaxial wafer semi-finished product to obtain a heterojunction bipolar transistor.

[0024] The HBT epitaxial wafers prepared by the method provided in this invention have high reliability. The reason is:

[0025] (1) In the growth of the base layer of a heterojunction transistor, a relatively low growth temperature is often required to obtain high doping, while the collector and emitter regions require high-temperature growth to obtain better material quality. Therefore, different growth temperatures are used for different layers during epitaxial growth. Traditionally, after the collector region is grown, the temperature of the heating wire is changed to change the surface temperature of the epitaxial wafer. This method is time-consuming and the temperature fluctuates. This invention uses the method of changing the gas supporting the small disk to quickly change the surface temperature of the epitaxial wafer, avoiding interface defects caused by waiting for temperature changes between the collector and base regions, and between the base and emitter regions, thereby improving the reliability of the HBT epitaxial wafer.

[0026] (2) This invention utilizes the different thermal conductivity of different gases to achieve rapid cooling of the epitaxial wafer surface. The thermal conductivity of hydrogen is 1769 μW / cm·K, that of nitrogen is 250 μW / cm·K, and that of argon is 161 μW / cm·K. Under the same dose of thermal radiation, the temperature of the small disk when using a mixture of argon and nitrogen as the supporting gas is 20–30 °C lower than that when using a mixture of hydrogen and nitrogen as the supporting gas.

[0027] The HBT epitaxial wafer prepared by the method provided in this invention has high gain. This is because the invention uses a method of changing the supporting gas in the small disk to rapidly change the temperature of the epitaxial wafer surface, avoiding doping diffusion in the base region while waiting for temperature changes, and preventing the steep PN junction from becoming a gradually changing junction, thus resulting in higher gain.

[0028] In summary, this invention rapidly changes the surface temperature of the epitaxial wafer by altering the gas supporting the small disk. The surface temperature of the epitaxial wafer is as follows: Figure 2 As shown, it effectively achieves rapid temperature transitions between the collector region and the base region, and between the base region and the emitter region, without affecting the quality of the epitaxial layer in the base region or the quality of the epitaxial layer interface. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the HBT epitaxial structure provided by the present invention;

[0030] Figure 1 In the diagram: 01 is the substrate, 02 is the buffer layer, 03 is the collector ohmic contact layer, 04 is the collector region corrosion barrier layer, 05 is the collector region, 06 is the base region, 07 is the emitter layer, 08 is the sub-emitter layer, and 09 is the emitter region ohmic contact layer.

[0031] Figure 2 This is a schematic diagram of the surface temperature of the epitaxial wafer in an embodiment of the present invention;

[0032] Figure 3 This is a performance comparison chart of the HBT obtained in Example 1 of the present invention and the HBT prepared in Comparative Example 1. Detailed Implementation

[0033] This invention provides a method for fabricating a heterojunction bipolar transistor epitaxial wafer in an MOCVD device, comprising the following steps:

[0034] (1) Place the substrate in an MOCVD equipment and grow a buffer layer, a collector ohmic contact layer, a collector region etching barrier layer and a collector region sequentially on the surface of the substrate to obtain the first epitaxial wafer semi-finished product.

[0035] (2) Change the support gas of the small disk of the MOCVD equipment to hydrogen and nitrogen, cool the surface of the first epitaxial wafer semi-finished product and grow the base region. The material of the base region is P-type doped InGaAs. The cooling time is ≤5s and the temperature difference of the cooling is 20~30℃ to obtain the second epitaxial wafer semi-finished product.

[0036] (3) Change the small disk support gas to argon and nitrogen, heat the surface of the second epitaxial wafer semi-finished product and grow an emission layer. The material of the emission layer is N-type doped InGaP. The heating time is ≤5s and the temperature difference is 20~30℃ to obtain the third epitaxial wafer semi-finished product.

[0037] (4) A sub-emitter layer and an emitter ohmic contact layer are grown on the surface of the third epitaxial wafer to obtain a heterojunction bipolar transistor.

[0038] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0039] The method for fabricating heterojunction bipolar transistor epitaxial wafers provided by this invention is performed in an MOCVD device.

[0040] The structural schematic diagram of the heterojunction bipolar transistor provided by this invention is shown below. Figure 1 As shown below, in conjunction with Figure 1 This invention provides a detailed description of the heterojunction bipolar transistor. The heterojunction bipolar transistor includes a substrate, and sequentially disposed on the surface of the substrate are a buffer layer, a collector ohmic contact layer, a collector region etch barrier layer, a collector region, a base region, an emitter layer, a sub-emitter layer, and an emitter region ohmic contact layer. In a specific embodiment of this invention, information about each layer of the heterojunction bipolar transistor is shown in Table 1.

[0041] Table 1 Information on the HBT epitaxial structure provided by this invention

[0042] Serial Number Epitaxial materials thickness wavelength dopant Doping Remark 09 <![CDATA[In 0.5 GaAs]]> 110nm Te <![CDATA[2E19cm -3 ]]> Ohmic contact layer 08 GaAs 140nm / Si <![CDATA[5E18cm -3 ]]> Sub-launching layer 07 GaInP 25nm Si <![CDATA[4E17cm -3 ]]> launch area 06 <![CDATA[In 0.06 GaAs]]> 50nm / C <![CDATA[4E19cm -3 ]]> base area 05 GaAs 1100nm / Si <![CDATA[0.5-5E17cm -3 ]]> Collection area 04 GaInP 80nm Si <![CDATA[5E18cm -3 ]]> Corrosion stop layer 03 GaAs 500nm / Si <![CDATA[5E18cm -3 ]]> Contact layer 02 GaAs 100nm / Si <![CDATA[1E18cm -3 ]]> Buffer layer 01 SI-GaAs 675um / / substrate

[0043] The present invention places a substrate in an MOCVD device and sequentially grows a buffer layer, a collector ohmic contact layer, a collector region etching barrier layer, and a collector region on the substrate surface to obtain a first epitaxial wafer semi-finished product.

[0044] In a specific embodiment of the present invention, the growth of the buffer layer, the ohmic contact layer of the collector region, the corrosion barrier layer of the collector region, and the collector layer is preferably carried out in an MOCVD system (Aixtron). The reaction chamber pressure is 100 mbar, the growth temperature is 680°C, H2 is used as the carrier gas, and one or more of trimethylindium (TMIn), trimethylgallium (TMGa), trimethylaluminum (TMAl), carbon tetrachloride (CCl4), silane (SiH4), trimethylarsine (TMAs), arsine (AsH3), and phosphine (PH3) are used as the reaction source gas. The buffer layer, the ohmic contact layer of the collector region, the corrosion barrier layer of the collector region, and the collector layer are grown sequentially. The present invention does not have special requirements for the specific growth method of the buffer layer, the ohmic contact layer of the collector region, the corrosion barrier layer of the collector region, and the collector layer.

[0045] After obtaining the first epitaxial wafer semi-finished product, the present invention changes the support gas of the small disk of the MOCVD equipment to hydrogen and nitrogen, and grows a base region after cooling the surface of the first epitaxial wafer semi-finished product. The material of the base region is P-type doped InGaAs. The cooling time is ≤5s and the temperature difference of the cooling is 20~30℃, thus obtaining the second epitaxial wafer semi-finished product.

[0046] In this invention, before changing the type of support gas for the small disk, the invention preferably further includes: immediately closing the TMGa, SiH4, and AsH3 valves to stop the supply of the current collector growth gas source to the reaction chamber of the MOCVD equipment; opening the TMA valve to supply TMA to the reaction chamber of the MOCVD equipment; the flow rate of the TMA is preferably 180 sccm. Then, the support gas for the small disk is changed to hydrogen and nitrogen, and the surface temperature of the epitaxial wafer will drop by 20-30°C within 5 seconds. This invention preferably adjusts the actual surface temperature of the epitaxial wafer according to the ratio of hydrogen to nitrogen. The flow rate ratio of hydrogen to nitrogen is preferably (2-5):(15-20), more preferably 3:17. The temperature difference for cooling is preferably 25°C.

[0047] In this invention, after the cooling temperature stabilizes, the growth method of the base region preferably includes the following steps: maintaining the flow rate of the TMAs and the type and flow rate of the small disk support gas unchanged, and introducing TMIn, TMGa and CCl4 into the reaction chamber; the flow rate of TMIn is preferably 60 sccm, and the TMGa is preferably introduced into the reaction chamber through a double dilution pipeline, and the flow rate of TMGa introduced into the reaction chamber is preferably 12 sccm.

[0048] This invention introduces TMIn, TMGa, and CCl4 together into an MOCVD reactor to grow C-doped InGaAs, with the doping concentration detected at 4E19 cm⁻¹. -3 The flow rate of TMIn is set to 60 sccm, and TMGa is introduced into the reaction chamber via a dual dilution pipeline with source / dilute / inject flow rates of 30 / 970 / 400 respectively. The gas concentration introduced into the reaction chamber via the dual dilution pipeline can be calculated using the following formula:

[0049]

[0050] Where S is the actual gas flow rate introduced into the reaction chamber, and F Source F Dilute F Inject These represent the flow rates of Source, Dilute, and Injection, respectively. Therefore, the flow rate of TMGa introduced into the reaction chamber is 12 sccm. The growth rate of the InGaAs epitaxial layer is linearly related to the flow rates of In and Ga, and the calculated growth rate of InGaAs is 0.084 nm / s. After 595 seconds of growth, the thickness of the InGaAs base region is 50 nm.

[0051] After obtaining the second epitaxial wafer semi-finished product, the present invention changes the small disk support gas to argon and nitrogen, and grows an emission layer on the surface of the second epitaxial wafer semi-finished product by heating. The material of the emission layer is N-type doped InGaP. The heating time is ≤5s, and the temperature difference is 20~30℃, thus obtaining the third epitaxial wafer semi-finished product.

[0052] In this invention, before changing the type of gas supporting the small disk, the invention preferably further includes: maintaining the flow rate of the TMAs unchanged, immediately shutting off TMGa, TMIn, and CCl4, and stopping the introduction of TMIn, TMGa, and CCl4 into the reaction chamber. Then, the gas supporting the small disk is changed to argon and nitrogen. The surface temperature of the epitaxial wafer will rise by 20-30°C within 5 seconds. Preferably, the actual surface temperature of the epitaxial wafer is adjusted according to the ratio of argon to nitrogen. The flow rate ratio of argon to nitrogen is preferably (17-22):(0.5-2), more preferably 19:1. The temperature difference during the temperature rise is preferably 25°C.

[0053] In this invention, after the temperature stabilizes, the growth method of the emission layer preferably includes the following steps: maintaining the type and flow rate of the support gas of the small disk unchanged, immediately closing the TMAs valve to stop the flow of TMAs into the reaction chamber, opening the PH3 valve to flow PH3 into the reaction chamber, wherein the flow rate of the PH3 is preferably 720 sccm; and then introducing TMGa, TMIn and SiH4 into the reaction chamber.

[0054] After obtaining the third epitaxial wafer semi-finished product, the present invention grows a sub-emitter layer and an emitter region ohmic contact layer on the surface of the third epitaxial wafer semi-finished product to obtain a heterojunction bipolar transistor. The present invention does not have special requirements for the growth method of the emitter layer and the emitter region ohmic contact layer.

[0055] This invention employs a method of changing the supporting gas in a small disk to rapidly alter the temperature of the epitaxial wafer surface. The epitaxial wafer surface temperature is as follows: Figure 2 As shown, it effectively achieves rapid temperature transitions between the collector region and the base region, and between the base region and the emitter region, without affecting the quality of the epitaxial layer in the base region or the quality of the epitaxial layer interface.

[0056] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] The schematic diagram of the HBT epitaxial structure provided in this embodiment is as follows: Figure 1 As shown. Table 1 is a table showing the information on the materials, thicknesses, doping elements, doping concentrations, and corresponding functions of each layer of the HBT epitaxial structure provided in this embodiment. According to... Figure 1The structure shown is used to fabricate a junction bipolar transistor.

[0059] With a resistivity of 4x10 8 GaAs with a density of Ω·cm was used as the growth substrate and placed in an Aixtron MOCVD system for growth. The reaction chamber pressure was 100 mbar, the growth temperature was 680 °C, H2 was used as the carrier gas, and trimethylindium (TMIn), trimethylgallium (TMGa), trimethylaluminum (TMAl), carbon tetrachloride (CCl4), silane (SiH4), trimethylarsine (TMAs), arsine (AsH3), and phosphine (PH3) were used as the reaction source gases. The small disk support gas was a mixture of nitrogen and argon (preferably in a ratio of 19:1). First, trimethylgallium (TMGa) is introduced as the source gas, and silane (SiH4) is used as the dopant gas. The source flow rate of TMGa is set to 100 sccm to grow an N-GaAs buffer layer and an N-GaAs collector ohmic contact layer. Then, AsH3 is switched to PH3, and then trimethylgallium (TMGa) and trimethylindium (TMIn) are introduced to grow a GaInP etching stop layer. The source flow rate of TMGa is set to 15 sccm, and the source flow rate of TMIn is set to 600 sccm. Then, PH3 is switched to AsH3 to grow a GaAs collector region, and the source flow rate of TMGa is set to 100 sccm.

[0060] After the collector region is grown, immediately close the TMGa, SiH4, and AsH3 valves, and open the TMA valve, introducing a TMA source flow rate of 180 sccm. Then, change the support gas for the small disk to hydrogen and nitrogen. The epitaxial wafer surface temperature will drop by 25°C within 5 seconds. Adjust the actual surface temperature of the epitaxial wafer according to the hydrogen to nitrogen ratio (hydrogen to nitrogen flow rate ratio 3:17). Then, TMIn, TMGa, and CCl4 are introduced together into the MOCVD reaction chamber to grow C-doped InGaAs, with the doping concentration detected at 4E19 cm⁻¹. -3 The flow rate of TMIn is set to 60 sccm, and TMGa is introduced into the reaction chamber via a dual dilution pipeline with source / dilute / inject flow rates of 30 / 970 / 400 respectively. The gas concentration introduced into the reaction chamber via the dual dilution pipeline can be calculated using the following formula:

[0061]

[0062] Where S is the actual gas flow rate introduced into the reaction chamber, and F Source F Dilute F InjectThese represent the flow rates of Source, Dilute, and Injection, respectively. Therefore, the flow rate of TMGa introduced into the reaction chamber is 12 sccm. The growth rate of the InGaAs epitaxial layer is linearly related to the flow rates of In and Ga, and the calculated growth rate of InGaAs is 0.084 nm / s. After 595 seconds of growth, the InGaAs base region reaches a thickness of 50 nm. Then, TMGa, TMIn, and CCl4 are immediately shut off, and the support gas for the small disk is changed to argon and nitrogen. The surface temperature of the epitaxial wafer will rise by 25°C within 5 seconds. The actual surface temperature of the epitaxial wafer can be adjusted according to the ratio of argon to nitrogen (argon to nitrogen flow rate ratio 19:1). After the temperature stabilizes after 5 seconds, the TMA valve is immediately closed, and the PH3 valve is opened. The Source flow rate of PH3 is 720 sccm, followed by the introduction of source gases such as TMGa, TMIn, and SiH4 to grow the InGaP emitter epitaxial layer, and then the GaAs sub-emitter region and the InGaAs ohmic contact layer, thus forming a complete HBT epitaxial structure.

[0063] Comparative Example 1

[0064] Compared to the conventional process, the equipment and substrate used in this invention are the same. The growth processes for the buffer layer, collector ohmic contact layer, collector region etch barrier layer, and collector region on the substrate surface are the same as in Example 1. After the collector region is grown, the TMGa, SiH4, and AsH3 valves are immediately closed, and the TMA valve is opened, with a TMA source flow rate of 180 sccm. Then, the set temperature is lowered to prepare for the growth of the base region. By lowering the set temperature, the surface temperature of the epitaxial wafer drops by 25°C for approximately 55 seconds. Then, TMIn, TMGa, and CCl4 are introduced together into the MOCVD reaction chamber to grow C-doped InGaAs with a doping concentration of 4E19cm⁻¹. -3 The level is the same as in Example 1. After the base region is grown, TMGa, TMI, and CCl4 are immediately shut off, and then the temperature is set to rise to prepare for the growth of the emitter region. By raising the set temperature, the surface temperature of the epitaxial wafer rises by 25°C, and the cooling time lasts for about 55 seconds. Then, the TMAs valve is immediately closed, the PH3 valve is opened, and the source flow rate of PH3 is 720 sccm. Then, source gases such as TMGa, TMI, and SiH4 are introduced to grow the InGaP epitaxial layer of the emitter region (the same as in Example 1). Then, the GaAs sub-emitter region and the InGaAs ohmic contact layer are grown, thus forming a complete HBT epitaxial structure.

[0065] Test case

[0066] The epitaxial wafers obtained in Example 1 and Comparative Example 1 of this invention were used to fabricate transistor devices with an E-region area of ​​75 μm × 75 μm. Their current gain and base region sheet resistance characteristics were tested, and the results are as follows: Figure 3 As shown.

[0067] Depend on Figure 3 It can be seen that the epitaxial wafer grown using the process of this invention increases the current gain amplification factor from 110-130 to 140-150, an increase of more than 10%. This is because the pause time at the interface after the growth of the base region is short, avoiding doping diffusion caused by the base region waiting for temperature changes, and preventing the steep PN junction from becoming a gradual junction, thus resulting in higher gain.

[0068] As can be seen from the above embodiments, the present invention provides a method for preparing epitaxial wafers of heterojunction bipolar transistors. In view of the difficulty of epitaxial growth due to the high doping concentration of the base region of GaAs / InGaAs / GaInP HBT transistors, the present invention provides a MOCVD epitaxial growth method for high-quality InGaAs base region materials, which can obtain HBTs with high gain and good reliability.

[0069] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for fabricating a heterojunction bipolar transistor epitaxial wafer, characterized in that, Preparation in an MOCVD device includes the following steps: (1) Place the substrate in an MOCVD equipment and grow a buffer layer, a collector ohmic contact layer, a collector region etching barrier layer and a collector region sequentially on the surface of the substrate to obtain the first epitaxial wafer semi-finished product; (2) Change the support gas of the small disk of the MOCVD equipment to hydrogen and nitrogen, cool the surface of the first epitaxial wafer semi-finished product and grow the base region. The material of the base region is P-type doped InGaAs. The cooling time is ≤5s and the temperature difference of the cooling is 20~30℃ to obtain the second epitaxial wafer semi-finished product. (3) Change the small disk support gas to argon and nitrogen, heat the surface of the second epitaxial wafer semi-finished product and grow an emission layer. The material of the emission layer is N-type doped InGaP. The heating time is ≤5s and the temperature difference is 20~30℃ to obtain the third epitaxial wafer semi-finished product. (4) A sub-emitter layer and an emitter ohmic contact layer are grown on the surface of the third epitaxial wafer to obtain a heterojunction bipolar transistor.

2. The preparation method according to claim 1, characterized in that, In step (2): before changing the type of support gas for the small disk, the process further includes: stopping the supply of the current collector growth gas source to the reaction chamber of the MOCVD equipment, and supplying TMAs to the reaction chamber of the MOCVD equipment, wherein the flow rate of the TMAs is 180 sccm.

3. The preparation method according to claim 1, characterized in that, The flow rate ratio of hydrogen to nitrogen is (2~5):(15~20).

4. The preparation method according to claim 1 or 3, characterized in that, The temperature difference for the cooling is 25°C.

5. The preparation method according to claim 2, characterized in that, The growth method of the base region includes the following steps: maintaining the flow rate of the TMAs and the type and flow rate of the disk support gas unchanged, and introducing TMIn, TMGa and CCl4 into the reaction chamber; the flow rate of TMIn is 60 sccm, and the TMGa is introduced into the reaction chamber through a double dilution pipeline, with a flow rate of 12 sccm.

6. The preparation method according to claim 5, characterized in that, The doping concentration of the base region is 4E19cm⁻¹ -3 The thickness is 50nm.

7. The preparation method according to claim 5, characterized in that, In step (3): before changing the type of gas supporting the small disk, the process also includes: maintaining the flow rate of the TMAs unchanged and stopping the introduction of TMI, TMGa and CCl4 into the reaction chamber.

8. The preparation method according to claim 1, characterized in that, The flow rate ratio of argon to nitrogen is (17~22):(0.5~2).

9. The preparation method according to claim 1 or 8, characterized in that, The temperature difference for the heating is 25°C.

10. The preparation method according to claim 7, characterized in that, The method for growing the emission layer includes the following steps: maintaining the type and flow rate of the support gas in the small disk unchanged, stopping the introduction of TMAs into the reaction chamber, introducing PH3 into the reaction chamber at a flow rate of 720 sccm; and introducing TMGa, TMIn, and SiH4 into the reaction chamber.

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