Gallium oxide-based heterojunction bipolar transistor with vertical structure and manufacturing method thereof

Abstract

The invention provides a gallium oxide-based heterojunction bipolar transistor with a vertical structure and a manufacturing method of the gallium oxide-based heterojunction bipolar transistor. The transistor comprises a Ga2O3 collector electrode, a NiO base electrode and a Ga2O3 emitter electrode which are sequentially arranged from bottom to top, base electrodes are arranged on two sides of the Ga2O3 emitter on the NiO base; the Ga2O3 collector electrode and the NiO base electrode form an n-p junction, and the NiO base electrode and the Ga2O3 emitter electrode form a p-n junction. The current gain is effectively improved, and the voltage endurance capability of the device is enhanced at the same time. According to the invention, a basis is provided for gallium oxide-based bipolar transistors which are lack of in-depth research at present, and the development of high-voltage and high-power bipolar transistors is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a vertically structured gallium oxide-based heterojunction bipolar transistor and a manufacturing method thereof. Background Art

[0002] Bipolar transistors (BJTs) are one of the most important devices in the semiconductor field and are widely used in high-speed circuits, analog circuits, power amplifiers, etc. Among them, high-voltage and high-power bipolar transistors are ideal for applications such as battery chargers, energy supplies, and photovoltaic inverters. BJTs usually have two configurations, npn and pnp. The pn junction will amplify weak input signals, and the thick and low-doped collector region will act as a voltage-resistant layer to bear high reverse bias. Compared with lateral BJTs, vertical BJTs can operate at higher voltages and adapt to higher current densities, so they have shown great potential in power switches and other uses.

[0003] In the research of high-voltage power bipolar transistors, devices based on wide bandgap SiC have been deeply studied and widely used. Similarly, the vertical structure of gallium nitride (GaN) heterojunction bipolar transistors (HBT) is also considered to be a preferred alternative to existing field effect transistor power switches due to its advantages such as low lithography precision requirements, normally-off state, high current density, strong avalanche breakdown capability and lower specific on-resistance caused by the conductive modulation effect. However, due to the limitations of GaN materials themselves and epitaxial technology, such as epitaxial growth of thicker high-quality collectors, and epitaxial growth of p-type GaN with high carrier lifetime and high hole concentration, GaN bipolar transistors are difficult to achieve high breakdown voltage in the off state, and the current gain in the on state is also difficult to improve due to the large number of minority carrier recombination in p-type GaN. Therefore, it is of practical application value to find ultra-wide bandgap semiconductor materials that can be epitaxially grown with high quality and high breakdown field strength, as well as p-type materials with long minority carrier lifetime and high-quality heterogeneous integration with them. Summary of the invention

[0004] The present invention proposes a vertically structured gallium oxide-based heterojunction bipolar transistor and a manufacturing method thereof, so as to solve the technical problems that the existing bipolar transistor structure is difficult to achieve a high breakdown voltage in a cut-off state and is difficult to improve the current gain in a conduction state.

[0005] In order to solve the above technical problems, the present invention provides a vertically structured gallium oxide-based heterojunction bipolar transistor, the transistor comprising Ga 2 O 3 Collector, NiO base and Ga 2 O 3 emitter; The NiO base is located on the Ga 2 O 3 Base electrodes are provided on both sides of the emitter; The Ga 2 O 3 The collector forms an np junction with the NiO base, and the NiO base forms an np junction with the Ga 2 O 3 The emitter forms a pn junction.

[0006] Preferably, the Ga 2 O 3 The collector is made of Ga 2 O 3 Highly conductive substrate and Ga 2 O 3 The Ga 2 O 3 The Sn doping concentration of the high-conductivity substrate is 5×10 18 cm -3 , the Ga 2 O 3 The Si doping concentration of the epitaxial layer is 1×10 16 cm -3 .

[0007] Preferably, the Ga 2 O 3 The emitter adopts a doping concentration of 5×10 18 cm -3 n-type Ga 2 O 3 .

[0008] Preferably, the Ga 2 O 3 The emitter is arranged between the two base electrodes with a spacing of 2 μm; the Ga 2 O 3 The emitter is a circle with a diameter of 6 μm; the two base electrodes are circular rings with a ring width of 3 μm and an outer diameter of 16 um.

[0009] Preferably, the Li doping concentration of the NiO base is in the range of 5×10 17 cm -3 Up to 1×10 19 cm -3 , with a thickness ranging from 70nm to 200nm.

[0010] Preferably, the Li doping concentration of the NiO base is 3×10 18 cm -3 , thickness is 100nm.

[0011] Preferably, the NiO base has a diameter of 20 μm.

[0012] The present invention also provides a method for manufacturing a vertically structured gallium oxide-based heterojunction bipolar transistor, comprising the following steps: Step S1: In Ga 2 O 3 Metal is deposited beneath the highly conductive substrate to form a collector electrode; Step S2: 2 O 3 A NiO layer is heteroepitaxially grown on the epitaxial layer to form a NiO base; Step S3: Partially epitaxially growing Ga on the NiO base 2 O 3 layer, forming Ga 2 O 3 emitter; Step S4: In the Ga 2 O 3 Depositing metal on the emitter to form an emitter electrode; Step S5: Partially deposit Ga on the NiO base 2 O 3 Metal is deposited on both sides of the emitter to form two base electrodes.

[0013] Preferably, the collector electrode is formed of a Ti / Au metal electrode by electron beam evaporation, and is subjected to rapid thermal annealing to form an ohmic contact.

[0014] Preferably, the emitter electrode is formed by Ti / Au metal deposition and subjected to rapid thermal annealing; and the base electrode is formed by Ni / Au metal deposition.

[0015] The beneficial effects of the present invention include at least: gallium oxide Ga 2 O 3 As an ultra-wide bandgap semiconductor material, it has an ultra-wide bandgap of 4.4-4.9eV and a theoretical breakdown field strength of up to 8MV / cm. The mature crystal melt growth technology can be used to prepare thick low-doped epitaxial voltage-resistant layers, making it an ideal material for high-voltage, high-power bipolar transistors. Currently, a variety of p-type materials have been proven to achieve good heterogeneous integration with it. Among them, the gallium oxide heterojunction diode prepared based on nickel oxide NiO shows excellent reverse breakdown performance and forward conduction characteristics, which is comparable to Ga 2 O 3 The preferred material for heterogeneous integration. The heterojunction bipolar transistor of the present invention combines the ultra-wide bandgap material Ga 2 O 3 npn heterojunction integration with NiO, utilizing Ga 2 O 3The high breakdown field strength and mature thick film epitaxial technology of NiO materials are comparable to other materials that can be used with Ga 2 O 3 Long minority carrier lifetime of heterogeneously integrated p-type materials and their relationship with Ga 2 O 3 High-quality heteroepitaxial growth has been used to design a vertical high-voltage heterojunction bipolar transistor. Ultra-wide bandgap materials as emitters improve the efficiency of electron injection. 2 O 3 The large hole injection barrier caused by the special type II band arrangement of Ga / NiO further reduces the hole diffusion current in the base region, effectively improving the current gain. 2 O 3 The collector epitaxial layer enhances the device's voltage resistance, resulting in high-performance Ga 2 O 3 It provides a foundation for gallium oxide-based bipolar transistors, which are still lacking in-depth research, and is conducive to the development of high-voltage and high-power bipolar transistors. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic structural diagram of a gallium oxide-based heterojunction bipolar transistor according to an embodiment of the present invention; Figure 2 The output characteristic diagram of the bipolar transistor constructed in Example 1 of the present invention and the breakdown characteristic diagram in the off state; Figure 3 A schematic diagram showing the relationship between the base current, the collector current and the base voltage of the bipolar transistor constructed in Example 2 of the present invention; Figure 4 A common emitter current gain diagram of a bipolar transistor constructed according to Embodiment 2 of the present invention; Figure 5 The output characteristic of the common emitter configuration of the bipolar transistor constructed in Example 2 of the present invention, that is, the relationship diagram between the collector current and the collector voltage; Figure 6 The bipolar transistor constructed in Example 2 of the present invention is 2 O 3 Breakdown curves at different epitaxial layer thicknesses. DETAILED DESCRIPTION

[0017] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0018] Example 1 like Figure 1 As shown, an embodiment of the present invention provides a vertically structured gallium oxide-based heterojunction bipolar transistor, the transistor comprising Ga 2 O 3 Collector, NiO base and Ga 2 O 3 Emitter: Ga on NiO base 2 O 3 Base electrodes are provided on both sides of the emitter; Ga 2 O 3 The collector forms an np junction with the NiO base, and the NiO base forms an np junction with the Ga 2 O 3 The emitter forms a pn junction.

[0019] Specifically, n-type Ga 2 O 3 The collector includes Ga 2 O 3 High conductivity substrate and lightly doped gallium oxide epitaxial layer, Ga 2 O 3 The Sn doping concentration of the high-conductivity substrate is 5×10 18 cm -3 The Si doping concentration of the GaO lightly doped epitaxial layer is 1×10 16 cm -3 .

[0020] In the embodiment of the present invention, the NiO base pattern is a circle with a diameter of 20 μm. 2 O 3 The emitter is a circle with a diameter of 6 μm. The base electrode is grown at a distance of 100 m from the Ga 2 O 3 The emitter is 2 μm, a ring with a width of 3 μm and an outer diameter of 16 μm.

[0021] The device output characteristics are as follows: Figure 2 As shown, it has an output current gain of nearly 90, which is close to the current gain of GaN bipolar transistors and has a lower base minority carrier diffusion current. However, its reverse cutoff breakdown voltage can reach nearly 1200V, which is much higher than the hundreds of volts of breakdown voltage that can be achieved by homogeneous GaN bipolar transistors at present, and is close to the simulated ideal breakdown voltage of AlGaN / GaN heterojunction bipolar transistors.

[0022] Example 2 Based on Example 1, in order to further illustrate the beneficial effects that can be achieved by the present invention, this embodiment uses the Atlas two-dimensional device simulation tool of Silvaco TCAD software to illustrate the thickness and concentration of the NiO base, and simulates the corresponding device performance for NiO with different concentrations and thicknesses. In the two-dimensional numerical calculation, based on the above-mentioned actual material parameters, the drift diffusion transport model and several other important physical models are used, such as Fermi-Dirac (Fermi), concentration-dependent mobility (CONMOB), electric field-dependent mobility (FLDMOB), carrier generation recombination (SRH, Auger) model and bipolar model.

[0023] For the Gummel characteristic, the doping concentration is the same, both are 3×10 18 cm -3 Under the condition of , the base thickness is set to 70nm, 100nm, 150nm, and 200nm for simulation. As the thickness increases, the base minority carrier (hole) diffusion current increases slightly. At the same time, the number of majority carriers (electrons) that recombine with minority carriers in the base also increases, so the number of carriers entering the collector region and finally reaching the collector decreases, that is, the collector current decreases, which makes the current gain β (the ratio of collector current to base current) decreases. At the same time, the thickness of the base will also affect the output characteristics. As the base thickness increases, the Early voltage decreases slightly, the output impedance decreases, and it is not easy to punch through in the cut-off state, which is beneficial to the operation of the device in the circuit. But on the other hand, in order to obtain a high current gain, the base thickness needs to be thinner to reduce the recombination and minority carrier diffusion currents, so it is necessary to strike a balance between the Early voltage and the current gain. The NiO thickness was selected as 100nm, and then the simulation of different NiO doping concentrations was carried out. The doping concentration was selected as 5×10 17 cm -3 , 1×10 18 cm -3 , 3×10 18 cm -3 , 5×10 18 cm -3 , 1×10 19 cm -3 The lower the doping concentration, the greater the Early voltage, and the base current's ability to control the output is weakened, which is not conducive to device operation. At the same time, low doping makes it easier for the base to punch through when the collector junction is depleted, thereby reducing the breakdown voltage. However, high doping concentration will increase the base minority carrier diffusion current and reduce the current gain, just like a thick base width. At 5×10 18 cm -3 , 1×10 19 cm -3When the doping concentration is 100 nm, the base current increases while the collector current decreases, and the current gain decreases significantly. Therefore, it is necessary to select a moderate doping concentration. Based on the comprehensive consideration of Gummel characteristics and output characteristics, the NiO parameters are selected as 100 nm, 3×10 18 cm -3 Performance is best when doped.

[0024] For breakdown voltage, the highest electric field where HBT is prone to breakdown is located at the NiO / GaO interface, i.e., the collector junction. The NiO thickness is selected as 100nm, and for different doping concentrations, i.e., 5×10 17 cm -3 , 1×10 18 cm -3 , 3×10 18 cm -3 , 5×10 18 cm -3 , 1×10 19 cm -3 The breakdown curve is simulated. Different NiO concentrations have little effect on the breakdown voltage, but mainly affect the collector leakage current. The higher the doping concentration, the lower the leakage current, and the better the reverse cutoff performance. When the base doping concentration is less than or equal to 5×10 17 cm -3 Due to the low doping concentration and thin base thickness, the collector voltage V CB When it increases to a certain value, the neutral base width drops to 0, the collector junction depletion region is directly connected to the emitter junction depletion region, and punch-through occurs. The collector and emitter are short-circuited, causing the leakage current to increase rapidly and the breakdown voltage to decrease significantly. 18 cm -3 Up to 5×10 18 cm -3 When the doping concentration reaches 1×10 19 cm -3 When the breakdown voltage is 1×10 18 cm -3 Up to 5×10 18 cm -3 The doping of the low-voltage section has little change, but the leakage current of the low-voltage section is relatively 1×10 18 cm -3 Up to 5×10 18 cm -3 Therefore, the doping concentration is selected as 1×10 18 cm -3 Up to 5×10 18 cm -3 Next, the NiO doping concentration was fixed at 3×1018 cm -3 For different NiO thicknesses, simulations were performed at thicknesses of 70nm, 100nm, 150nm and 200nm. Since HBT in the off state mainly relies on the collector region to withstand pressure, the thickness and doping concentration of the collector region have a more significant impact on the breakdown voltage, while the change in NiO thickness from 100nm to 200nm has little effect on the breakdown voltage. However, thinner NiO, such as 70nm, is prone to punch-through under high collector reverse bias, resulting in a decrease in breakdown voltage. Therefore, for the off-state HBT, the preferred NiO condition for improving the breakdown voltage is 100-200nm, 1×10 18 cm -3 Up to 5×10 18 cm -3 of doping concentration.

[0025] Through the above simulation analysis, for the requirements of output characteristics and breakdown characteristics, 100nm is selected and the doping concentration is 3×10 18 cm -3 The NiO base is optimal, which can achieve a large current gain while achieving a high breakdown voltage.

[0026] At a thickness of 100 nm and a doping concentration of 3×10 18 cm -3 When the NiO base is used, the relationship between the collector current, base current and base voltage of the gallium oxide-based heterojunction bipolar transistor of the present invention is shown in the figure below: Figure 3 As shown, the common emitter current gain diagram is as follows Figure 4 shown.

[0027] It can be seen that by designing the appropriate NiO doping concentration and thickness, the device can achieve low base leakage and collector current up to milliamperes. Amplification gain in common emitter configuration β , which is the ratio of collector current to base current. Under 20V collector bias conditions, the base voltage is in the range of 3-3.7V β It can reach 300, which is higher than the simulation results of most current BJTs such as AlGaN / GaN. β About 160.

[0028] Figure 5 The DC output characteristics of the common emitter configuration of the device of the present invention, that is, the relationship between the collector current and the collector voltage, are shown. 2 O 3 The thickness of the collector epitaxial layer can achieve good base control collector current output. The unsaturation of the common emitter output characteristic is due to βThere will be a significant increase with the collector voltage, which is the Early effect.

[0029] Figure 6 The device of the present invention is shown in different Ga 2 O 3 The breakdown curve under the thickness of the epitaxial layer. In the case of common emitter configuration and base open circuit, it can be seen that with the increase of epitaxial layer thickness, the withstand voltage of HBT is significantly enhanced. 2 O 3 The epitaxial layer collector bears most of the reverse bias applied to the collector junction. A 10μm epitaxial layer can achieve a high breakdown voltage of nearly 1600V, and it also has good output characteristics, and is the best choice for the high withstand voltage power HBT design in the present invention.

[0030] Example 3 This embodiment provides a method for manufacturing a gallium oxide-based heterojunction bipolar transistor with a vertical structure, wherein parameters such as doping concentration are not limiting conditions of this embodiment.

[0031] Specifically, when making, first, in Ga 2 O 3 Ti / Au is grown on the back of the substrate by electron beam evaporation technology as the metal electrode of the collector, and then rapidly thermally annealed to form an ohmic contact; pattern transfer is performed based on EUV lithography technology, and the Ga 2 O 3 The surface of the epitaxial layer is deposited using magnetron sputtering technology with Ar:O 2 =60:10 growth ratio 100nm Li doped carrier concentration is about 3×10 18 cm -3 The NiO layer is used as the base, and the photoresist is stripped to obtain the pattern. Then, silicon dioxide is deposited by plasma enhanced chemical vapor deposition (PECVD), and the pattern is etched out by reactive ion etching (RIE) as a mask. PLD technology is used to grow a 200nm doping concentration of about 5×10 18 cm -3 The emitter is obtained by etching away the remaining silicon dioxide. Finally, the pattern is transferred based on EUV lithography technology, Ti / Au is grown on the emitter after lithography, and then the photoresist is stripped off and rapid thermal annealing is performed to complete the preparation of the emitter electrode. The base electrode is then prepared by growing Ni / Au on the base in the same way.

[0032] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. Only the preferred embodiments of the present invention are expressed. The description is more specific and detailed, but it cannot be understood as limiting the scope of the present invention. As long as there is no contradiction in the combination of these technical features, they should be considered as within the scope of this specification.

[0033] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A vertically structured gallium oxide-based heterojunction bipolar transistor, characterized in that: The transistor comprises a Ga2O3 collector, a NiO base and a Ga2O3 emitter arranged in sequence from bottom to top; Base electrodes are arranged on both sides of the Ga2O3 emitter on the NiO base; The Ga2O3 collector and the NiO base form an np junction, and the NiO base and the Ga2O3 emitter form a pn junction.

2. The gallium oxide-based heterojunction bipolar transistor with a vertical structure according to claim 1, characterized in that: The Ga2O3 collector is composed of a Ga2O3 high-conductivity substrate and a Ga2O3 epitaxial layer, and the Sn doping concentration of the Ga2O3 high-conductivity substrate is 5×10 18 cm -3 The Si doping concentration of the Ga2O3 epitaxial layer is 1×10 16 cm -3 .

3. The gallium oxide-based heterojunction bipolar transistor with a vertical structure according to claim 1, characterized in that: The Ga2O3 emitter adopts a doping concentration of 5×10 18 cm -3 of n-type Ga2O3.

4. The gallium oxide-based heterojunction bipolar transistor with a vertical structure according to claim 1, characterized in that: The Ga2O3 emitter is arranged between the two base electrodes with a spacing of 2 μm; the Ga2O3 emitter is a circle with a diameter of 6 μm; the two base electrodes are circular rings with a ring width of 3 μm and an outer diameter of 16 um.

5. The gallium oxide-based heterojunction bipolar transistor with a vertical structure according to claim 4, characterized in that: The Li doping concentration of the NiO base is in the range of 5×10 17 cm -3 Up to 1×10 19 cm -3 , with a thickness ranging from 70nm to 200nm.

6. The gallium oxide-based heterojunction bipolar transistor with a vertical structure according to claim 5, characterized in that: The Li doping concentration of the NiO base is 3×10 18 cm -3 , thickness is 100nm.

7. The gallium oxide-based heterojunction bipolar transistor with a vertical structure according to claim 6, characterized in that: The NiO base has a diameter of 20 μm.

8. A method for manufacturing a vertically structured gallium oxide-based heterojunction bipolar transistor, characterized in that: The following steps are involved: Step S1: depositing metal below the Ga2O3 high-conductivity substrate to form a collector electrode; Step S2: heteroepitaxially growing a NiO layer on the Ga2O3 epitaxial layer to form a NiO base; Step S3: partially epitaxially growing a Ga2O3 layer on the NiO base to form a Ga2O3 emitter; Step S4: depositing metal on the Ga2O3 emitter to form an emitter electrode; Step S5: depositing metal on both sides of the Ga2O3 emitter on the NiO base to form two base electrodes.

9. The method for manufacturing a vertically structured gallium oxide-based heterojunction bipolar transistor according to claim 8, characterized in that: The collector electrode is formed into a Ti / Au metal electrode by electron beam evaporation, and is subjected to rapid thermal annealing to form an ohmic contact.

10. The method for manufacturing a vertically structured gallium oxide-based heterojunction bipolar transistor according to claim 8, characterized in that: The emitter electrode is formed by Ti / Au metal deposition and subjected to rapid thermal annealing treatment; the base electrode is formed by Ni / Au metal deposition.

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