Preparation method of novel gallium oxide thin film for phototransistor

Abstract

The invention designs a preparation method of a novel gallium oxide thin film for a phototransistor. A large amount of plasmas are generated to bombard gallium metal by using reaction plasma deposition equipment, so that the gallium metal is melted and evaporated and reacts with ionized oxygen ions at the substrate to generate gallium oxide. On the premise that the growth rate and the film quality are guaranteed, due to the fact that only gas and gallium metal participate in the material growth process, the material growth cost is low, toxic and harmful by-products are not generated, and industrial large-scale production is facilitated. The gallium oxide thin film prepared by the novel preparation method provided by the invention is used for a photoelectric transistor channel layer, the device has obvious transistor characteristics, the current is increased by 1 * 105 times after ultraviolet irradiation in a solar-blind ultraviolet band, and the gallium oxide thin film is suitable for ultraviolet solar-blind light detection.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and particularly to a novel method for preparing gallium oxide thin films for optoelectronic transistors.

[0002] Gallium oxide (Ga 2 O 3 ) as a wide-bandgap semiconductor material has a bandgap width of ~4.9 eV, and its optical response is exactly in the solar-blind band. It can achieve solar-blind ultraviolet detection without any doping and alloying processes, and is a natural and low-cost solar-blind ultraviolet detection material. In addition, the gallium oxide material has high thermal stability and chemical stability, and a breakdown voltage as high as 8 MV / cm, and can be applied to high-voltage and high-power electronic devices. Due to these excellent properties, the gallium oxide material has attracted more and more attention in the scientific community.

[0003] The growth of gallium oxide thin films is crucial for the performance of devices. Currently, researchers have developed a series of material preparation processes, such as magnetron sputtering (MS), atomic layer deposition (ALD), molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), etc. However, among the above methods, magnetron sputtering has a simple process but poor film quality; atomic layer deposition has good uniformity and step coverage, but the film grown in each cycle is very thin and the growth rate is slow; the film grown by molecular beam epitaxy has high quality, but the growth rate is also slow, and at the same time the process is complex and the cost is high; metal-organic chemical vapor deposition has a relatively fast growth rate while ensuring the film quality, but the equipment cost is high, and the precursors and by-products are toxic and difficult to handle; hydride vapor phase epitaxy has a high growth rate but poor film quality, and at the same time the corrosiveness of hydrogen and chlorides is strong, and the equipment maintenance cost is high.

[0004] Reactive plasma deposition (RPD) enables the metal to sublime and react with the gas through the participation of plasma, and prepares metal oxide thin films on the premise of ensuring the growth rate and film quality. At the same time, due to the participation of only gas and metal in reactive plasma deposition, the material growth cost is low and no toxic and harmful by-products are generated, which is conducive to large-scale industrial production.

[0005] Therefore, it is necessary to design a novel method for preparing gallium oxide thin films using a reactive plasma deposition device. Summary of the Invention

[0006] The present invention provides a novel method for preparing gallium oxide thin films for phototransistors. By using a reactive plasma deposition device, on the premise of ensuring the growth rate and film quality, gallium oxide thin film materials for phototransistors are grown at low cost and in an environmentally friendly manner, providing new ideas and methods for growing gallium oxide thin films.

[0007] To achieve the above objectives, the present technical solution provides a novel method for preparing gallium oxide thin films for phototransistors, including the following steps: S1: Clean the substrate and fix the substrate on the substrate holder. S2: Place the substrate holder in the rotating rack and use a baffle to block the substrate. S3: Place a graphite crucible containing gallium metal in a cold crucible. S4: Close the chamber door and wait for the chamber to be pumped to vacuum. S5: Turn on the rotating motor to rotate the substrate, introduce argon gas at the cathode, turn on the power supply to initiate arc discharge at the cathode to generate a large amount of plasma, and the plasma is directed to bombard the gallium metal in the graphite crucible under the deflection magnetic field generated by the deflection coil. S6: A large amount of heat is generated during the bombardment process, the gallium metal melts and rotates rapidly, and the heat causes the liquid gallium to evaporate. S7: Introduce oxygen gas. After the oxygen gas contacts the plasma, it is ionized to form oxygen ions, and the oxygen ions combine with the evaporated gallium to form gallium oxide. S8: Open the baffle, control the film thickness according to the opening time of the baffle. When the film reaches the required thickness, close the baffle, and the film deposition is completed. S9: Turn off the power supply, turn off the argon gas, turn off the oxygen gas, and turn off the rotating motor. S10: Introduce air, take out the substrate, and obtain the required gallium oxide thin film.

[0008] The present invention has the following beneficial effects compared with the prior art: 1. Compared with the traditional gallium oxide growth method, only gallium metal, oxygen, and argon are involved in the method of the present invention, which has the advantages of low cost and simple process and is suitable for large-scale industrial production.

[0009] 2. Compared with the traditional gallium oxide growth method, the highest temperature at the substrate does not exceed 200 °C in the method of the present invention, which belongs to a low-temperature process.

[0010] 3. Compared with the ceramic target of magnetron sputtering, the method of the present invention has a cost advantage, and the grown gallium oxide thin film has higher crystallinity and is closer to the single crystal state, which is beneficial to improving the response speed of the phototransistor.

[0011] 4. Compared with metal-organic chemical vapor deposition, the method of the present invention avoids the participation of organic gases and the generation of toxic and harmful substances, is more environmentally friendly and safe, and compared with molecular beam epitaxy, the growth rate is greatly increased, and the production time is greatly reduced.

[0012] 5. The method of the present invention can add other materials during the growth process, such as tin (Sn), silicon (Si), or introduce other gases, such as nitrogen (N 2 ) to achieve doping. The carrier concentration and bandgap width of the material can be regulated through a simple process. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic structural diagram of the reaction plasma deposition device described in the present invention.

[0014] Figure 2 It is the transmittance curve of gallium oxide prepared on quartz glass in Example 1.

[0015] Figure 3 It is the full X-ray photoelectron spectroscopy spectrum of gallium oxide prepared on a silicon dioxide wafer in Example 2.

[0016] Figure 4 It is a schematic structural diagram of a phototransistor with gallium oxide as the channel layer in Example 3.

[0017] Figure 5 It is a top view of the optical microscope of the phototransistor with gallium oxide as the channel layer in Example 3.

[0018] Figure 6 In, 1 is the argon gas vent, 2 is the ion gun, 3 is the cathode of the deflection coil, 4 is the baffle, 5 is the substrate, 6 is the rotating motor, 7 is the air outlet, 8 is the ion gun power supply, 9 is the reaction gas vent, 10 is the reaction metal, 11 is the anode of the deflection coil, and 12 is the vacuum chamber. gs -I ds relationship curve.

[0019] Figure 1 In, 1 is the metal electrode, 2 is the gallium oxide channel layer, 3 is the silicon dioxide, and 4 is the N-type heavily doped silicon.

[0020] Figure 4 In, 1 is the metal electrode, 2 is the gallium oxide channel layer, 3 is the silicon dioxide, and 4 is the N-type heavily doped silicon. DETAILED IMPLEMENTATION METHOD

[0021] To make the above objects, features, and advantages of the present application more apparent and understandable, the following provides a detailed description of the specific implementation manners of the present application in conjunction with the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0022] In the description of the present application, it should be understood that if terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or positional relationship indicated by these terms is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0023] In the present application, unless otherwise clearly specified and limited, if a first feature is described as "above" or "below" a second feature or the like, its meaning can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over", and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or simply indicates that the first feature has a higher horizontal height than the second feature. The first feature being "below", "beneath", and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or simply indicates that the first feature has a lower horizontal height than the second feature.

[0024] The present invention provides a novel method for preparing a gallium oxide thin film for a phototransistor, comprising the following steps: S1: Clean the substrate (including quartz glass, silicon, silicon dioxide, sapphire, single crystal gallium oxide), and fix the cleaned substrate on the substrate holder. S2: Place the substrate holder in the rotating rack and use a baffle to block the substrate. S3: Put solid gallium with a purity of 99.99 wt% into a graphite crucible and fill it to 2 / 3 of the volume of the graphite crucible. Place a copper sheet in the cold water crucible and place the graphite crucible containing gallium metal in the cold water crucible. S4: Close the chamber door, evacuate the chamber, and wait until the chamber vacuum reaches a pressure below 3×10 5 Pa. S5: Turn on the rotary motor to rotate the substrate, introduce argon gas at the cathode, and the argon gas flow rate is 160 - 200 sccm. Turn on the power supply, with a current of 30 - 45 A, to initiate arc discharge at the cathode, generating a large amount of plasma. After successful ignition, reduce the argon gas flux to 70 sccm and the current to 25 - 35 A. The plasma is directed to bombard the gallium metal in the graphite crucible under the deflection magnetic field generated by the deflection coil; S6: A large amount of heat is generated during the bombardment process, melting the gallium metal and making it rotate rapidly, and the heat causes the liquid gallium to evaporate; S7: Introduce oxygen, with an oxygen flux of 40 - 100 sccm, reduce the argon gas flux to 50 sccm. After the oxygen contacts the plasma, it is ionized to form oxygen ions, and the oxygen ions combine with the evaporated gallium at the substrate to form gallium oxide; S8: Open the baffle, control the film thickness according to the opening time of the baffle. When the film reaches the required thickness, close the baffle, and the film deposition ends; S9: Turn off the power supply, turn off the argon gas, turn off the oxygen, and turn off the rotary motor; S10: Introduce air, take out the substrate, and obtain the required gallium oxide film.

[0025] The structure of the reactive plasma deposition equipment is as Figure 1 shown. The specific structures, connection methods, working principles, and processes of the reactive plasma deposition equipment and its internal components are well-known technologies and will not be elaborated here.

[0026] The technical solutions and effects of the present invention will be described below through specific embodiments. Example 1

[0027] To calculate the band gap of the gallium oxide film grown by the present invention, according to the preparation method of the gallium oxide film described in this patent, quartz glass is selected as the substrate, and a gallium oxide film is prepared thereon, including the following steps: S1: Clean the quartz glass substrate on which the gallium oxide film is to be deposited. Soak it successively in a detergent, concentrated sulfuric acid solution, acetone, ethanol, and deionized water, and ultrasonically clean each for 15 min using an ultrasonic cleaner. After cleaning, dry it with a nitrogen gun; S2: Fix the cleaned quartz glass substrate on the substrate holder, place it in the chamber of the reactive plasma deposition device, and block the substrate holder with a baffle; S3: Put solid gallium with a purity of 99.99 wt% into the graphite crucible, filling it to about two-thirds of its position. Place a copper sheet in the cold water crucible and place the graphite crucible on the cold water crucible; S4: Close the chamber door of the reactive plasma deposition device and wait for the mechanical pump and molecular pump to evacuate to a pressure below 3×10 5 Pa; S5: Turn on the rotating motor to rotate the quartz glass, and introduce argon with a flux of 180 sccm at the cathode. Set the ion gun current to 35 A, turn on the ion gun power supply, and arc discharge occurs at the cathode to generate a large amount of plasma. After successful ignition, reduce the current to 30 A and the argon to 70 sccm; S6: A large amount of plasma is directed to bombard gallium metal under the guidance of the coil. When the gallium metal melts and rotates rapidly, turn on the oxygen, set the flux to 50 sccm, and reduce the argon flux to 50 sccm. The liquid gallium evaporates under a large amount of heat, the oxygen contacts the plasma to form oxygen ions, and the evaporated gallium contacts the oxygen ions to form gallium oxide; S7: After waiting for the pressure in the cavity to stabilize, open the baffle, and close the baffle after 250 s. The deposition of gallium oxide material is completed; S8: Turn off the power supply, increase the argon flux to 180 sccm, wait for the metallic color of the ion gun to fade, turn off the argon, turn off the oxygen, and turn off the rotating motor. Wait for 30 min to cool down the cavity, introduce air into the cavity, take out the substrate, and realize the deposition of gallium oxide on the quartz glass.

[0028] The thickness of the gallium oxide thin film prepared in this example is measured to be about 24 nm. Use a UV-visible spectrophotometer to test its transmittance curve, and the results are as attached Figure 2 shown. According to the Tauc model, the band gap is calculated to be 4.83 eV, which conforms to the wide band gap characteristics of gallium oxide materials. Example Two

[0029] In order to verify the composition and material quality of the gallium oxide thin film grown by the present invention, according to the preparation method of the gallium oxide thin film described in this patent, a silicon wafer is selected as the substrate, and a gallium oxide thin film is prepared on it, including the following steps: S1: Clean the silicon wafer on which the gallium oxide thin film is to be deposited, soak it in acetone, isopropanol, and deionized water in sequence and use an ultrasonic cleaner to ultrasonically clean for 15 min. After cleaning, blow it dry with a nitrogen gun; S2: Fix the cleaned silicon wafer substrate on the substrate, place it in the cavity of the reactive plasma deposition device, and block the substrate with a baffle; S3: Put solid gallium with a purity of 99.99 wt% into the graphite crucible, about two-thirds full. Place a copper sheet in the cold water crucible and place the graphite crucible on the cold water crucible; S4: Close the chamber door of the reactive plasma deposition device and wait for the mechanical pump and molecular pump to evacuate to a pressure below 3×10 5 Pa; S5: Turn on the rotating motor to rotate the silicon wafer, and introduce argon gas with a flux of 180 sccm at the cathode. Set the ion gun current to 35 A, turn on the ion gun power supply, and arc discharge occurs at the cathode to generate a large amount of plasma. After successful ignition, reduce the current to 30 A and the argon gas to 70 sccm; S6: A large amount of plasma bombards gallium metal directionally under the guidance of the coil. Wait until the gallium metal melts and rotates rapidly, then turn on the oxygen, set the flux to 50 sccm, and reduce the argon gas flux to 50 sccm. The liquid gallium evaporates under a large amount of heat, the oxygen contacts the plasma to form oxygen ions, and the evaporated gallium contacts the oxygen ions to form gallium oxide; S7: After waiting for the air pressure in the cavity to stabilize, open the baffle, and close the baffle after 300 s. The deposition of gallium oxide material is completed; S8: Turn off the power supply, increase the argon gas flux to 180 sccm, wait until the metal color of the ion gun fades, turn off the argon gas, turn off the oxygen, and turn off the rotating motor. Wait for 30 min to cool down the cavity, introduce air into the cavity, take out the substrate, and realize the deposition of gallium oxide on the silicon wafer.

[0030] It is measured that the thickness of the gallium oxide thin film prepared in this example is about 30 nm. Use an X-ray photoelectron spectroscopy device to scan the full spectrum. As Figure 3 shown, the characteristic peaks of the gallium 2p and oxygen 1s orbits are obvious, which are the same as the typical spectral lines of the gallium oxide material. Use a scanning electron microscope to take a top view of the silicon wafer on which gallium oxide grows. At a resolution of 500 nm, the surface of the material is smooth. Example 3

[0031] According to the method for preparing a gallium oxide thin film described in this patent, prepare a phototransistor with gallium oxide as the channel layer, including the following steps: S1: Soak the silicon oxide substrate (the upper layer is 100 nm of silicon oxide, the middle layer is N-type heavily doped silicon, and the lower layer is 100 nm of silicon oxide) in acetone, isopropyl acetone, and deionized water in turn and use an ultrasonic cleaner for 15 min, and then blow dry with a nitrogen gun; S2: Put the silicon dioxide substrate in step S1 into a reactive plasma deposition device, put a graphite crucible containing gallium metal, close the chamber door and wait for the vacuum degree to reach below 3×10 5 Pa; S3: Turn on the rotating motor to rotate the silicon dioxide substrate, and introduce argon gas with a flux of 180 sccm at the cathode. Set the ion gun current to 35 A, turn on the ion gun power supply, and after successful ignition, reduce the current to 30 A and the argon gas to 70 sccm; S4: Observe the gallium metal in the crucible through the observation window. Wait until the gallium metal melts and rotates rapidly, then turn on the oxygen, set the flux to 50 sccm, and reduce the argon gas flux to 50 sccm; S5: After waiting for the air pressure to stabilize, open the baffle, and close the baffle after 300 s. The deposition of gallium oxide material is completed. S6: Turn off the power supply, increase the argon flux to 180 sccm, wait for the ion gun to fade in metallic color, then turn off the argon, turn off the oxygen, and turn off the rotating motor. After waiting for 30 min, ventilate and take out the silicon dioxide substrate with gallium oxide grown on it. S7: Put the substrate in step S6 into a spin coater, and spin coat AZ5214 photoresist evenly. The initial spin speed is 500 rpm, the spin time is 5 s, then the spin speed is increased to 3000 rp, and the spin time is 20 s. After spin coating, put the substrate on a constant temperature heating table for pre-baking for 60 s at a temperature of 100 °C. S8: Put the substrate in step S7 into a maskless lithography machine, select the designed interdigital electrode pattern, focus, set the exposure intensity to 0.8, and the exposure time to 180 ms. Wait for the lithography to complete and then take out the substrate. S9: Immerse the substrate in step S8 in a tetramethylammonium hydroxide solution for development for 40 s. Then put it into deionized water for 30 s and dry it with a nitrogen gun. S10: Use an electron beam evaporation device to evaporate 20 nm of titanium and 80 nm of gold on the substrate in step S9 in sequence. Immerse the substrate in an acetone solution to remove the photoresist attached to the surface for 60 s. If necessary, use an ultrasonic cleaner for ultrasonic treatment, soak it in deionized water for 30 s, and dry the substrate with a nitrogen gun.

[0032] The novel phototransistor structure obtained in this example is as shown in the appendix Figure 4 and the top view under an optical microscope is as shown in the appendix Figure 5 .

[0033] To verify the performance of the phototransistor, the novel phototransistor obtained in this example is used to test its performance curve through a Keithley 4200 source meter. The V ds -I ds relationship shows that the device saturates at high source-drain voltages, and the source-drain current increases with the increase of the gate voltage. The V ds -I gs relationship curve measured at ds = 10 V is as shown in Figure 6 . The gate voltage can realize the regulation of the transistor, with a large on-off ratio. Both the output characteristic curve and the transfer characteristic curve meet the standard functions of the transistor. The I ds of the device is measured at V gs = 5 V and V ds = 5 V. Using a xenon lamp with a wavelength of 254 nm as the light source, the magnitude of the device current increases by one order of magnitude of 1×10 5 before and after illumination, showing a large light-dark ratio, which proves that the device has the ability to detect in the solar-blind ultraviolet band.

Claims

1. A novel method for preparing a gallium oxide thin film for a phototransistor, characterized in that: The following steps are involved: S1: cleaning the substrate and fixing the substrate on the base plate; S2: Place the substrate into the rotating rack and use a baffle to block the substrate; S3: placing the graphite crucible containing gallium metal in a cold water crucible; S4: Close the chamber door and wait until the chamber is evacuated to a vacuum; S5: Turn on the rotary motor to rotate the substrate, introduce argon gas at the cathode, turn on the power to make the cathode arc discharge and generate a large amount of plasma, and the plasma bombards the gallium metal in the graphite crucible in a direction under the deflection magnetic field generated by the deflection coil; S6: The bombardment process generates a lot of heat, waiting for the gallium metal to melt and rotate rapidly, and the heat evaporates the liquid gallium; S7: oxygen is introduced, and the oxygen is ionized to form oxygen ions after contacting the plasma, and the oxygen ions combine with the evaporated gallium to form gallium oxide; S8: Open the baffle, control the film thickness according to the baffle opening time, and when the film reaches the desired thickness, close the baffle, and the film deposition ends; S9: Turn off the power, argon, oxygen, and rotating motor; S10: introducing air, taking out the substrate, and obtaining the desired gallium oxide thin film.

2. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: The substrate includes quartz glass, silicon, silicon dioxide, sapphire, single crystal gallium oxide, etc.

3. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: The gallium metal used is solid gallium with a purity of 99.99 wt %, and the solid gallium is filled to 2 / 3 of the volume of the graphite crucible.

4. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: A round copper sheet is placed at the contact point between the cold water crucible and the graphite crucible.

5. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: The vacuum in the cavity is to use a molecular pump to evacuate the cavity to 3×10 5 Pressure below Pa.

6. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: In step S5, before the cathode ignition, the argon gas flux is 160-200 sccm, preferably 180 sccm.

7. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: In step S5, the current of the power supply is 30-45A, preferably 35A.

8. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: In step S5, after the cathode is ignited, the argon gas flux is reduced to 70 sccm.

9. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: In step S5, after the cathode is ignited, the power supply current is reduced to 25-35A, preferably 30A.

10. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: In step S7, the oxygen flux is 40-100 sccm, preferably 50 sccm.

11. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: In step S7, after the oxygen is introduced, the argon flux is reduced to 50 sccm.

12. A novel gallium oxide thin film preparation method for phototransistors according to claim 1, characterized in that: The phototransistor structure is, from top to bottom, metal electrode, gallium oxide channel layer, silicon dioxide, and heavily doped N-type silicon.

13. A novel gallium oxide thin film preparation method for phototransistors according to claim 8, characterized in that: The metal electrode is one metal selected from Au, Ag and Ti or a stack of multiple metals.

14. A novel gallium oxide thin film preparation method for phototransistors according to claim 8, characterized in that: The thickness of the gallium oxide channel layer is 30-100 nm.

15. A novel gallium oxide thin film preparation method for phototransistors according to claim 8, characterized in that: The thickness of the silicon oxide layer is 100 nm.

16. A novel method for preparing a gallium oxide thin film for a phototransistor, characterized in that: The method is prepared by any one of claims 1 to 15.

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