Indium gallium zinc oxide thin film, preparation method thereof and TFT device

Abstract

The application discloses an indium gallium zinc oxide thin film and a preparation method and a TFT device thereof, and the preparation method is based on a high-power pulse magnetron sputtering technology, and the mole ratio of a target material used for sputtering is In2O3:Ga2O3:ZnO=1.8±0.2:1.4±0.2:1±0.2. The application increases the proportion of indium elements in the target material to improve the thin film mobility, and increases the proportion of gallium elements to inhibit oxygen vacancies, so as to reduce the carrier concentration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor, more particularly, to an indium gallium zinc oxide thin film, a preparation method thereof and a TFT device. BACKGROUND

[0002] Amorphous oxide semiconductors, represented by indium gallium zinc oxide, are used as channel materials for thin film transistors due to their high electron mobility and good electrical uniformity. For example, amorphous indium gallium zinc oxide (α-IGZO) is widely used as a material in the new generation of thin film transistor technology. At present, α-IGZO thin films are generally prepared by direct current (DC) or radio frequency (RF) magnetron sputtering in the industry, which has high flux and good uniformity, and is conducive to mass production.

[0003] However, the thin films prepared by the above-mentioned magnetron sputtering method generally have problems such as loose structure, high density of defects and poor performance. In recent years, high power impulse magnetron sputtering (HiPIMS) is emerging as a method for preparing oxide semiconductor thin films. In the HiPIMS process, the plasma gas and sputtering material are highly excited / ionized, which has more advantages than traditional magnetron sputtering. First, they have high activity, which is beneficial to the synthesis of composite thin films, especially at low substrate temperature. Second, they generally have enough energy to migrate along the substrate surface and grow in order thereon. Therefore, there are fewer defects in the thin film. Finally, the ions excited by the HiPIMS power have higher activity, which makes the thin film better cover the substrate. Therefore, it can deposit thin films on substrates with high aspect ratio, and is more advantageous in small-size TFT device applications.

[0004] Currently, the main IGZO adopts a target material ratio of In2O3: Ga2O3: ZnO (1:1:1). However, this target material ratio is only suitable for RF and DC power supplies. The oxide film prepared by the HiPIMS power supply usually has high oxygen vacancy defects and carrier density, and the excessively high carrier density will cause the TFT device to be unable to turn off, the device On / Off time is long, which is not conducive to the application in semiconductor channel materials. SUMMARY

[0005] The present application provides an indium gallium zinc oxide thin film, a preparation method thereof and a TFT device, which overcome the above problems or at least partially solve the above problems.

[0006] The present application provides an indium gallium zinc oxide thin film preparation method based on high power pulse magnetron sputtering technology, wherein the molar ratio of the target material used for sputtering is In2O3: Ga2O3: ZnO = 1.8±0.2: 1.4±0.2: 1±0.2.

[0007] Preferably, it further comprises:

[0008] The pre-processed substrate is placed in the loading chamber of the HiPIMS device, and then the loading chamber is closed, the pneumatic valve is opened to draw the gas pressure in the loading chamber to a vacuum state below 5×10 -2 torr;

[0009] The pneumatic valve at the connection between the loading chamber and the process chamber is opened, the substrate-loaded carrier plate is parked under the heating furnace tube by the conveying device, and then the pneumatic valve is closed;

[0010] After the substrate is in the process chamber, the Ar gas switch is opened after waiting for the gas pressure to be drawn to below 10 -7 torr, the flow rate of the Ar gas is set by the flow controller, and then the angle of the exhaust valve at the connection between the molecular pump and the process chamber is adjusted to control the gas pressure in the process chamber to reach the required process pressure by adjusting the angle of the valve;

[0011] The power supply of the HiPIMS device is turned on, the working parameters of the HiPIMS power supply are set, the power supply is turned on to pre-sputter the target material to make the surface of the target material clean; wherein the molar ratio of the target material is In2O3: Ga2O3: ZnO = 1.8: 1.4: 1;

[0012] After the pre-sputtering of the target material is completed, the speed of the reciprocating movement of the carrier plate is set, the substrate-loaded carrier plate is conveyed to the lower side of the sputtering target material by the conveying device, and the reciprocating movement mode is started to make the thin film deposited on the substrate uniform;

[0013] The gas pressure in the unloading chamber is drawn to below 5×10 2 torr, then the pneumatic valve at the connection between the process chamber and the unloading chamber is opened, the carrier plate is sent to the unloading chamber by the conveying device, the pneumatic valve at the connection is closed, liquid nitrogen is filled into the unloading chamber to make the gas pressure in the chamber reach atmospheric pressure, and then the carrier plate in the unloading chamber is taken out to obtain the indium gallium zinc oxide thin film on the carrier plate.

[0014] Preferably, before the first mechanical pump connected with the process chamber and the second mechanical pump connected with the pipeline of the HiPIMS device are turned on, it further comprises:

[0015] The total power supply of the HiPIMS device is turned on, the device switch, the cooling water total switch are turned on in sequence, the air pressure control knob is rotated to control the gas pressure to be between 0.6-0.8 MPa;

[0016] The cooling water valves corresponding to each target seat, molecular pump and total power supply are adjusted;

[0017] Turning on a first mechanical pump connected with the process cavity and a second mechanical pump connected with the pipeline of the HiPIMS device to pump the pressure in the process cavity and the pipeline to a vacuum state below 5x10 2 torr.

[0018] Turning off the first mechanical pump and turning on a molecular pump to wait for the molecular pump to pump the pressure in the process cavity to a high vacuum state below 10 -7 torr.

[0019] Preferably, the flow rate of the Ar gas is set to 40 sccm.

[0020] Preferably, the time for pre-sputtering is 15 minutes.

[0021] Preferably, the process pressure is 3x10 2 torr.

[0022] Preferably, after opening a pneumatic valve at the connection between the loading cavity and the process cavity, parking the substrate-loaded carrier plate under the heating furnace tube by the conveying device, and then closing the pneumatic valve, the method further comprises:

[0023] According to whether the temperature of the substrate reaches a preset working temperature, determining whether to heat the substrate.

[0024] Preferably, the working temperature is 25 degrees.

[0025] Preferably, the target-substrate distance between the sputtering target and the substrate is 56 mm.

[0026] The embodiment of the present application further provides an indium gallium zinc oxide thin film prepared by the preparation method.

[0027] The embodiment of the present application further provides a TFT device comprising the indium gallium zinc oxide thin film.

[0028] In one of the above embodiments, the target material has a molar ratio of In2O3:Ga2O3:ZnO = 1.8±0.2:1.4±0.2:1±0.2. Compared with the existing target material, the proportion of indium elements is increased to improve the mobility of the thin film, and the proportion of gallium elements is increased to inhibit oxygen vacancies, thereby reducing the carrier concentration, and thus improving the working performance of the TFT device. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 FIG. 1 is a flowchart of a method for preparing an indium gallium zinc oxide thin film according to a first embodiment of the present application.

[0030] Figure 2A working principle diagram of an indium gallium zinc oxide thin film preparation method provided by an embodiment of the present application.

[0031] Figure 3 A transfer characteristic curve diagram of TFT devices prepared by different proportions of target materials. DETAILED DESCRIPTION

[0032] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present application, but are not used to limit the scope of the present application.

[0033] The first embodiment of the present application provides an indium gallium zinc oxide thin film preparation method, which is based on high-power pulsed magnetron sputtering technology, and the molar ratio of the target material used for sputtering is In2O3: Ga2O3: ZnO = 1.8 ± 0.2: 1.4 ± 0.2: 1 ± 0.2.

[0034] In this embodiment, the principle of high-power pulsed magnetron sputtering (HiPIMS) technology is a kind of magnetron sputtering technology that uses relatively high pulse peak power and lower pulse duty cycle to produce high sputtering metal ionization rate. The peak power of HiPIMS can reach MW level, but due to the short pulse action time, its average power is the same as that of ordinary magnetron sputtering, so the cathode will not overheat due to increased target cooling. The ionization rate of HiPIMS up to 70% can deposit highly dense, uniform, and strong bonding thin films, and can control their phase composition, microstructure, and mechanical and optical properties. In addition, HiPIMS improves the adhesion of the thin film, can deposit a uniform thin film on a complex-shaped substrate, and reduces the deposition temperature.

[0035] In this embodiment, the HiPIMS device can use a device of model LJUHV SP-122I, but is not limited thereto.

[0036] The complete preparation process of the indium gallium zinc oxide thin film of this embodiment is described below. Specifically, please refer to Figure 1 , including:

[0037] S101, place the pretreated substrate in the loading cavity of the HiPIMS device, then close the loading cavity and open the pneumatic valve to draw the gas pressure in the loading cavity to a vacuum state lower than 5 × 10 -2 torr.

[0038] In this embodiment, the substrate can be a silicon substrate or a sapphire substrate, which is not specifically limited by the present application.

[0039] In this embodiment, preparation work needs to be done before work, including:

[0040] Turn on the total power supply of the HiPIMS device, turn on the device switch and the cooling water total switch in turn, rotate the air pressure control knob, control the air pressure between 0.6-0.8 MPa, so as to facilitate the normal opening and closing of the pneumatic valve.

[0041] Adjust the cooling water valves corresponding to each target holder, molecular pump and HiPIMS power supply to ensure that the device will not trigger an alarm due to excessive temperature during HiPIMS deposition, causing the machine to shut down.

[0042] Turn on the first mechanical pump connected to the process chamber and the second mechanical pump connected to the pipeline of the HiPIMS device to pump the process chamber pressure and pipeline pressure to a vacuum state of 5×10 2 torr or below.

[0043] Turn off the first mechanical pump and turn on the molecular pump, and wait for the molecular pump to pump the process chamber pressure to a high vacuum state of less than 10 -7 torr.

[0044] S102, open the pneumatic valve at the connection between the loading chamber and the process chamber, and park the substrate-loaded carrier plate under the heating furnace tube through the conveying device, and then close the pneumatic valve.

[0045] In this embodiment, when the substrate-loaded carrier plate is parked under the heating furnace tube, whether to heat the substrate can be selected according to the experimental conditions. For example, when it is judged that the temperature of the substrate does not reach the required working temperature, the substrate is heated. The working temperature here is set according to actual needs, for example, it can be set to 25 degrees.

[0046] S103, when the substrate is in the process chamber, wait for the gas pressure to be pumped to less than 10 -7 torr, open the Ar gas switch, set the flow rate of Ar gas through the flow controller, and then adjust the angle of the gas extraction valve at the connection between the molecular pump and the process chamber to control the gas pressure in the process chamber by adjusting the valve angle, so that the process chamber reaches the required process pressure.

[0047] In particular, the flow rate of Ar gas is set to 40 sccm, but is not limited thereto, and can be set according to actual needs.

[0048] In particular, the process pressure is set to 3×10 2 torr, but is not limited thereto, and can be set according to actual needs.

[0049] S104, turn on the power supply of the HiPIMS device, set the working parameters of the HiPIMS power supply, turn on the power supply to pre-sputter the target material, so that the surface of the target material is clean.

[0050] The working parameters include voltage, current, pulse average power, pulse width, pulse frequency, etc.

[0051] In particular, the pre-sputtering time is 15 minutes, but is not limited thereto, and can be set according to actual needs.

[0052] S105, after the target pre-sputtering is completed, the speed of the reciprocating movement of the carrier plate is set, the carrier plate carrying the substrate is conveyed to the lower side of the sputtering target through the conveying device, the reciprocating movement mode is started, and the thin film deposited on the substrate is kept uniform.

[0053] The specific working principle can be referred to Figure 2 In operation, the target-substrate distance between the sputtering target and the substrate is 56 mm, but is not limited thereto, and can be set according to actual needs.

[0054] S106, the gas pressure in the loading-out cavity is extracted to 5*10 2 torr, then the pneumatic valve at the connection between the process cavity and the loading-out cavity is opened, the carrier plate is conveyed to the loading-out cavity through the conveying device, the pneumatic valve at the connection is closed, liquid nitrogen is filled into the loading-out cavity, so that the gas pressure in the cavity reaches atmospheric pressure, and then the carrier plate in the loading-out cavity is taken out, and the indium gallium zinc oxide thin film on the carrier plate is obtained.

[0055] After the indium gallium zinc oxide thin film is obtained, it needs to be placed in a vacuum drying cabinet for storage.

[0056] The second embodiment of the present application also provides an indium gallium zinc oxide thin film prepared by the preparation method of any one of the above embodiments.

[0057] The third embodiment of the present application also provides a TFT device comprising the indium gallium zinc oxide thin film as described above.

[0058] In the above embodiments, the molar ratio of the target material is In2O3: Ga2O3: ZnO = 1.8±0.2: 1.4±0.2: 1±0.2, compared with the existing target material, the proportion of indium element is increased to improve the mobility of the thin film, and the proportion of gallium element is increased to suppress oxygen vacancies, thereby reducing the carrier concentration.

[0059] The technical effects of the present application will be described below with an actual experimental result.

[0060] In the experiment, the Hall tester is used to measure the carrier concentration and mobility of the indium gallium zinc oxide thin film, to observe the changes of the carrier concentration and mobility of the indium gallium zinc oxide thin film sputtered by using different proportions of target materials under the same conditions, as shown in Table 2.

[0061] From Table 2, it can be seen that after the adjustment of the target material, the oxygen vacancies of the thin film are reduced, the carrier concentration is reduced by 2 orders of magnitude, and the mobility of the thin film is increased, which represents that the quality of the thin film is improved.

[0062] Table 2, comparison of thin film and device characteristics prepared by different proportion IGZO target materials

[0063]

[0064] Further, the indium gallium zinc oxide thin film is prepared into an IGZO TFT device, and a semiconductor analyzer is used to test the characteristic curve of the TFT device under the condition of VGS =-10 ~ 40V and VDS = 15V, as shown in FIG. 6. Figure 3

[0065] From Figure 3 it can be seen that after being applied to the TFT device, the field effect mobility of the TFT device is increased to 6.9 cm 2 V -1 s -1 , the sub-threshold swing (a performance index for measuring the mutual conversion rate between the on and off states of the transistor) is also reduced, which represents that the On / Off conversion is faster, and the on / off ratio is also improved.

[0066] The above embodiments are only suitable for illustrating the present application, but not limiting the present application, and the ordinary skilled in the technical field can also make various changes and modifications without departing from the spirit and scope of the present application, therefore all equivalent technical solutions also belong to the scope of the present application, and the patent protection scope of the present application should be defined by the claims.​

Claims

1. A method for preparing an indium gallium zinc oxide thin film based on high power pulsed magnetron sputtering technology, characterized in that, the molar ratio of the target material for sputtering is In2O3: Ga2O3: ZnO = 1.8: 1.4:

1.

2. The method of claim 1, wherein the method further comprises the step of: Further comprising: ​ The pre-processed substrate is placed in the load lock chamber of the HiPIMS apparatus, which is then closed and the pneumatic valve is opened to pump the load lock chamber to a vacuum state of less than 5x10 -2 Torr; opening the pneumatic valve at the connection between the loading chamber and the process chamber, parking the substrate-loaded carrier plate under the heating furnace tube through the conveying device, and then closing the pneumatic valve; When the substrate is in the process chamber, the gas pressure is extracted to below 10 -7 After that, the Ar gas switch is opened, the flow rate of Ar gas is set by the flow controller, and then the angle of the pumping valve connected between the molecular pump and the process chamber is adjusted to control the gas pressure in the process chamber by adjusting the angle of the valve, so that the process pressure is reached. turning on the power supply of the HiPIMS device, setting the working parameters of the HiPIMS power supply, and pre-sputtering the target material to make the target material surface clean; after the pre-sputtering of the target material is completed, setting the speed of the reciprocating movement of the carrier plate, conveying the substrate-loaded carrier plate to the lower side of the target material through the conveying device, and starting the sputtering in the reciprocating mode to make the thin film deposited on the substrate uniform; The air pressure of the loading-out cavity is drawn to 5x10 -2 Torr, then the pneumatic valve at the joint between the process cavity and the loading-out cavity is opened, the carrier plate is sent into the loading-out cavity by the transmission device, the pneumatic valve at the joint is closed, liquid nitrogen is filled into the loading-out cavity, so that the air pressure in the cavity reaches atmospheric pressure, and then the carrier plate in the loading-out cavity is taken out, and the indium gallium zinc oxide film on the carrier plate is obtained.

3. The method for preparing indium gallium zinc oxide thin films according to claim 1, characterized in that, before turning on the first mechanical pump connected to the process chamber and the second mechanical pump connected to the pipeline of the HiPIMS device, further comprising: turning on the total power supply of the HiPIMS device, sequentially turning on the device switch and the cooling water total switch, rotating the air pressure control knob, and controlling the air pressure to be between 0.6-0.8 MPa; adjusting the cooling water valves corresponding to each target holder, molecular pump and total power supply; Turning on the first mechanical pump connected to the process chamber and the second mechanical pump connected to the piping of the HiPIMS apparatus to pump down the process chamber and the piping to a vacuum state of 5x10 -2 Torr or below. Turning off the first mechanical pump and turning on the molecular pump, waiting for the molecular pump to pump the process chamber pressure to a high vacuum state of less than 10 -7 Torr.

4. The method for preparing indium gallium zinc oxide thin films according to claim 1, characterized in that, the flow rate of Ar gas is set to 40 sccm.

5. The method for preparing indium gallium zinc oxide thin films according to claim 1, characterized in that, The pre-sputtering time was 15 minutes at a process pressure of 3 x 10 -2 Torr.

6. The method for preparing indium gallium zinc oxide thin films according to claim 2, characterized in that, after opening the pneumatic valve at the connection between the loading chamber and the process chamber, parking the substrate-loaded carrier plate under the heating furnace tube through the conveying device, and then closing the pneumatic valve, further comprising: selecting whether to heat the substrate according to whether the temperature of the substrate reaches the preset working temperature.

7. The method of claim 6, wherein the method further comprises the step of: The working temperature is 25 degrees. ​ 8. The method for preparing indium gallium zinc oxide thin films according to claim 1, characterized in that, The target-substrate distance between the sputtering target material and the substrate is 56 mm.

9. An indium gallium zinc oxide thin film, characterized by, Prepared by the preparation method of any one of claims 1-8.

10. A TFT device, characterized by, The indium gallium zinc oxide thin film of claim 9. The indium gallium zinc oxide thin film of claim 9.

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