NiO film and preparation method thereof

Abstract

The invention belongs to the technical field of functional thin film materials, and discloses a preparation method of a NiO thin film, which comprises the following steps: performing magnetron sputtering deposition and annealing on a substrate in a sputtering cavity by adopting a NiO target material to obtain the NiO thin film, wherein the magnetron sputtering power is 1000-1200 w, the magnetron sputtering atmosphere is a mixed gas of argon and oxygen, and the gas flow ratio of the argon to the oxygen is (80-70): (20-30), and by controlling the magnetron sputtering power and the magnetron sputtering atmosphere, the electrochemical performance of the NiO thin film can be effectively improved, and the stability of the photoelectric property of the thin film in the atmospheric environment is prolonged; in addition, the invention further discloses the NiO thin film which is prepared through the preparation method of the NiO thin film.

Description

Technical Field

[0001] The present application relates to the field of functional thin film materials, and particularly to a NiO thin film and a preparation method thereof. Background Art

[0002] NiO thin film material is a new type of wide-bandgap transparent semiconductor material that has been studied quite popularly in recent years. Its bandgap width at room temperature is 3.6 eV to 4.0 eV, and the material exhibits p-type conductive characteristics. Due to its excellent optical, electrical, magnetic and other properties, it has wide applications in gas sensors, supercapacitors, electrochromic devices, ultraviolet detectors, OLED screens, etc.

[0003] However, when the NiO thin film is placed in the air atmosphere for a long time, its optical and electrical stability is affected by various factors. For example, it may undergo further oxidation in the air to generate nickel oxides with higher valence states (such as Ni2O3), which will change its optical and electrical properties; in addition, the surface of the thin film may react chemically with water vapor, carbon dioxide, etc. in the air to form carbonates or hydroxides, resulting in performance degradation; at the same time, light irradiation may induce a photocatalytic reaction, causing chemical changes on the surface of the thin film and further affecting its optical and electrical properties; finally, the preparation process of the thin film has an important impact on its stability. Thin films with poor crystallization quality or high defect density are more likely to react with oxygen, moisture, etc. in the environment, resulting in performance degradation. Therefore, optimizing the preparation process (such as improving crystallization quality and reducing defects) is the key to improving the stability of the thin film.

[0004] The problem to be solved by this solution: How to improve the long-term stability of the optical and electrical properties of the NiO thin film. Summary of the Invention

[0005] The purpose of the present application is to propose a NiO thin film and a preparation method thereof, and by controlling the power during target sputtering and in a mixed gas atmosphere composed of argon and oxygen in a certain mass ratio, the optical and electrical stability of the prepared NiO thin film is improved.

[0006] To achieve the above purpose, the present application discloses a preparation method of a NiO thin film. The preparation method is: using a NiO target to perform magnetron sputtering deposition and annealing on a substrate in a sputtering chamber to obtain a NiO thin film;

[0007] wherein, the magnetron sputtering power is 1000 - 1200 w;

[0008] The atmosphere of magnetron sputtering is a mixed gas of argon and oxygen, and the gas flow ratio of argon to oxygen is 80 - 70:20 - 30;

[0009] When the sputtering power is too high, it will cause target poisoning, and the film stress will be relatively large, which is not conducive to the bonding between the film and the substrate. If the power is too small, it will affect the film growth rate and the film crystallization quality. At the same time, the content of oxygen in the atmosphere during sputtering also has a relatively large impact on the film. When the oxygen content in the atmosphere is too low, it will cause the band gap of the prepared film to shrink and reduce the visible light transmittance of the film. When the oxygen content in the atmosphere is too high, it will hinder the sputtered particles from reaching the substrate to form a film, and the energy of the sputtered particles reaching the substrate is also small, reducing the coating efficiency.

[0010] Preferably, the background vacuum degree in the sputtering chamber is 5×10 -6 Torr~5×10 -5 Torr, and it is adjusted to 2.5 - 3.5 mTorr by the mixed gas of argon and oxygen during sputtering;

[0011] During sputtering, keeping the air pressure in the chamber within a certain range can effectively make the film surface smooth and have better density. At the same time, if the air pressure is too high, the film crystallization quality will deteriorate, and the film may appear in an amorphous state or an incomplete crystallization state. Further, if the air pressure is too low, gas ionization is difficult, glow discharge is difficult, and the deposition rate is very low, and a continuous film cannot be formed.

[0012] Preferably, the target-substrate distance between the NiO target and the substrate is 115 - 130 mm;

[0013] During the sputtering process, if the target-substrate distance between the NiO target and the substrate is too large, it will cause the deposition rate to decrease. Conversely, if the target-substrate distance is too small, it will affect the uniformity of the film distribution.

[0014] Preferably, the temperature of the substrate is 190 - 210 °C;

[0015] A lower substrate temperature will cause the film to form an amorphous structure and also weaken the adhesion between the film and the substrate. A higher substrate temperature will deteriorate both the surface quality and mechanical properties of the film, and too high a temperature will cause impurities in the substrate to diffuse into the film, reducing the film layer purity. Finally, as the substrate temperature increases, the sputtering deposition rate decreases significantly, and the refractive index of the film also shows an upward trend.

[0016] Preferably, the specific annealing operation is as follows: in an air atmosphere, heat up to 200 - 250 °C at a rate of 10 - 15 °C / min, the annealing time is 50 - 70, and then cool down to 30 °C at a rate of 10 - 15 °C / min;

[0017] After the annealing treatment, the NiO film will release stress and fill internal vacancy defects, thereby improving the film stability and preventing it from cracking or peeling off. At the same time, during annealing, the heating and cooling should be carried out slowly, and rapid heating and rapid cooling should be avoided to prevent cracks in the film caused by sudden changes in thermal stress.

[0018] Preferably, the substrate is a cleaned ordinary quartz glass substrate, and the rotation speed of the ordinary quartz glass substrate is 6-10 rad / min; the specific cleaning operation is: sequentially performing ultrasonic cleaning with ethanol with a concentration of 95% and pure water, and then drying with nitrogen;

[0019] Ordinary quartz glass has good thermal stability and a dense surface, can provide a clean and pollution-free surface, and the lattice matching between the quartz glass and the film is also good, which helps to form a high-quality film layer and makes the combination of the glass and the film more firm.

[0020] Preferably, the purity of the NiO target is ≥99.99%, and the NiO target needs to be cleaned 3 times on the surface by a radio frequency power supply with a sputtering power of 1000 w before use, each cleaning for 8 min, with an interval of 5 min each time.

[0021] Preferably, the thickness of the NiO film is 100-120 nm.

[0022] In addition, a NiO film is also disclosed, which is prepared by the above-mentioned preparation method of the NiO film.

[0023] The beneficial effects of this application are:

[0024] This application provides a NiO film and its preparation method. By controlling the power during target sputtering and the atmosphere composed of argon and oxygen, the electrochemical performance of the NiO film can be effectively improved, and the stability of the optoelectronic properties of the film in the atmospheric environment can be extended; and by adjusting and controlling the sputtering chamber pressure, target-substrate distance, selection of the substrate, temperature of the substrate, annealing process, etc. during the preparation process, the performance and long-term stability of the NiO film are further improved. Detailed Embodiments

[0025] In the description of this application, it should be noted that for those not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0026] Supplier information:

[0027] Ordinary quartz glass substrate: provided by Shanghai Qizhun Optoelectronic Materials Technology Co., Ltd.

[0028] Example 1

[0029] A NiO film is prepared by the following steps:

[0030] (1) Sequentially put the ordinary quartz glass substrate into ethanol with a concentration of 95% and pure water for ultrasonic cleaning, then dry with nitrogen, and put it into the waiting chamber;

[0031] (2) Place the NiO target with a purity of 99.99% into the sputtering chamber, and pump the background vacuum of the sputtering chamber to 5×10 -6 torr. Introduce argon into the sputtering chamber, and adjust the air pressure to make the chamber vacuum degree 3 mtorr. Set the target-substrate distance to 120 mm, set the power to 1000 W, turn on the radio frequency power supply to clean the surface of the target 3 times, each cleaning for 8 min, with an interval of 5 min between each cleaning;

[0032] (3) Place the ordinary quartz glass substrate in the waiting chamber into the sputtering chamber. Introduce argon and oxygen into the sputtering chamber, and the gas flow ratio of argon to oxygen is 78:22. Keep the air pressure in the sputtering chamber at 3 mtorr. Set the target-substrate distance to 120 mm, set the sputtering power to 1100 W, turn on the power supply, and perform magnetron sputtering deposition on the ordinary quartz glass substrate at a temperature of 200 °C and a rotation speed of 8 rad / min. Stop sputtering when the thickness of the deposited film reaches 110 nm, put it into the waiting chamber, and when the temperature of the vacuum environment drops to 30 °C, the ordinary quartz glass substrate deposited with the film can be obtained;

[0033] (4) Place the ordinary quartz glass substrate deposited with the film into a medium-temperature annealing furnace, heat it to 230 °C at a rate of 10 °C / min, anneal for 60 min, and then cool it to 30 °C at a rate of 10 °C / min to obtain the NiO film.

[0034] Example 2

[0035] (1) Place the ordinary quartz glass substrate into 95% ethanol and pure water in sequence for ultrasonic cleaning, then dry it with nitrogen and put it into the waiting chamber;

[0036] (2) Place the NiO target with a purity of 99.99% into the sputtering chamber, and pump the background vacuum of the sputtering chamber to 5×10 -6 torr. Introduce argon into the sputtering chamber, and adjust the air pressure to make the chamber vacuum degree 3 mtorr. Set the target-substrate distance to 120 mm, set the power to 1000 W, turn on the radio frequency power supply to clean the surface of the target 3 times, each cleaning for 8 min, with an interval of 5 min between each cleaning;

[0037] (3) Place the ordinary quartz glass substrate in the waiting chamber into the sputtering chamber. Introduce argon and oxygen into the sputtering chamber, and the gas flow ratio of argon to oxygen is 78:22. Keep the air pressure in the sputtering chamber at 3.5 mtorr. Set the target-substrate distance to 115 mm, set the sputtering power to 1100 W, turn on the power supply, and perform magnetron sputtering deposition on the ordinary quartz glass substrate at a temperature of 190 °C and a rotation speed of 8 rad / min. Stop sputtering when the thickness of the deposited film reaches 110 nm, put it into the waiting chamber, and when the temperature of the vacuum environment drops to 30 °C, the ordinary quartz glass substrate deposited with the film can be obtained;

[0038] (4) Place the ordinary quartz glass substrate deposited with the thin film into a medium-temperature annealing furnace, heat it to 200 °C at a rate of 10 °C / min, anneal for 70 min, and then cool it to 30 °C at a rate of 10 °C / min to obtain the NiO thin film.

[0039] Example 3

[0040] (1) Place the ordinary quartz glass substrate into ethanol with a concentration of 95% and pure water in sequence for ultrasonic cleaning, then dry it with nitrogen and place it in the waiting chamber;

[0041] (2) Place the NiO target with a purity of 99.99% into the sputtering chamber, and pump the background vacuum of the sputtering chamber to 5×10 -6 torr, introduce argon into the sputtering chamber, adjust the air pressure so that the chamber vacuum is 3 mtorr; set the target-substrate distance to 120 mm, set the power to 1000 W, turn on the radio frequency power supply to clean the surface of the target 3 times, each time for 8 min, with an interval of 5 min between each time;

[0042] (3) Place the ordinary quartz glass substrate in the waiting chamber into the sputtering chamber, introduce argon and oxygen into the sputtering chamber, and the gas flow ratio of argon to oxygen is 78:22, and keep the air pressure in the sputtering chamber at 2.5 mtorr, set the target-substrate distance to 130 mm, set the sputtering power to 1100 W, turn on the power supply, and perform magnetron sputtering deposition on the ordinary quartz glass substrate at a temperature of 210 °C and a rotation speed of 8 rad / min. Stop sputtering when the thickness of the deposited thin film reaches 110 nm, place it in the waiting chamber, and let the temperature of the vacuum environment drop to 30 °C to obtain the quartz glass substrate deposited with the thin film;

[0043] (4) Place the ordinary quartz glass substrate deposited with the thin film into a medium-temperature annealing furnace, heat it to 250 °C at a rate of 15 °C / min, anneal for 50 min, and then cool it to 30 °C at a rate of 15 °C / min to obtain the NiO thin film.

[0044] Example 4

[0045] Basically the same as Example 1, the difference is that the sputtering power in step (3) is 1000 w.

[0046] Example 5

[0047] Basically the same as Example 1, the difference is that the sputtering power in step (3) is 1200 w.

[0048] Example 6

[0049] Basically the same as Example 1, the difference is that the gas flow ratio of argon to oxygen in step (3) is 80:20.

[0050] Example 7

[0051] It is basically the same as Example 1, except that in step (3), the gas flow ratio of argon to oxygen is 70:30.

[0052] Example 8

[0053] It is basically the same as Example 1, except that a commercially available ordinary glass substrate is used to replace the ordinary quartz glass substrate.

[0054] Example 9

[0055] It is basically the same as Example 1, except that in step (3), the target-substrate distance is 100 mm.

[0056] Example 10

[0057] It is basically the same as Example 1, except that in step (3), the target-substrate distance is 140 mm.

[0058] Example 11

[0059] It is basically the same as Example 1, except that in step (3), the pressure in the sputtering chamber is 2 mtorr.

[0060] Example 12

[0061] It is basically the same as Example 1, except that in step (3), the pressure in the sputtering chamber is 4 mtorr.

[0062] Example 13

[0063] It is basically the same as Example 1, except that in step (3), the temperature of the ordinary quartz glass substrate during sputtering is 30 °C.

[0064] Example 14

[0065] It is basically the same as Example 1, except that the annealing operation in step (4) is not performed, and it is directly cooled to 30 °C at a rate of 10 °C / min.

[0066] Comparative Example 1

[0067] It is basically the same as Example 1, except that in step (3), the sputtering power is 900 w.

[0068] Comparative Example 2

[0069] It is basically the same as Example 1, except that in step (3), the sputtering power is 1300 w.

[0070] Comparative Example 3

[0071] It is basically the same as Example 1, except that in step (3), the gas flow ratio of argon to oxygen is 90:10.

[0072] Comparative Example 4

[0073] It is basically the same as Example 1, except that in step (3), the gas flow ratio of argon to oxygen is 60:40.

[0074] Performance test:

[0075] Resistivity, carrier concentration, carrier mobility: Measured by using a Hall effect tester on the NiO thin film before aging and the NiO thin film after 18 months of aging, respectively;

[0076] Transmittance: Measured by using an ultraviolet-visible spectrophotometer on the NiO thin film before aging (film 1) and the NiO thin film after 18 months of aging (film 2) for visible light with a wavelength of 400 - 1200 nm;

[0077] After testing, the performance of film 1 is shown in Table 1:

[0078] Table 1

[0079]

[0080]

[0081] The performance of film 2 is shown in Table 2:

[0082] Table 2

[0083]

[0084]

[0085] The performance gap between film 1 and film 2 (i.e., before aging and after 18 months of aging) is shown in Table 3:

[0086] Table 3 (where "-" indicates that the performance data shows a decrease)

[0087]

[0088]

[0089] Conclusion analysis:

[0090] 1. From Examples 1 - 3 and the data in Table 1, it can be seen that when changing process parameters such as the target-substrate distance, substrate temperature, and annealing process during sputtering, the performance of the prepared thin film will also be different, and among them, the thin film prepared under the process conditions of Example 1 has the best performance;

[0091] Meanwhile, combining with Table 1-3, it can be seen that after 18 months of aging of the thin film, the thin film prepared in Example 1 has the smallest changes in electrochemical performance and optical performance. Therefore, it can be known that its long-term stability of the thin film is the best.

[0092] 2. From Example 1 and Examples 4-5 and the data in Table 1, it can be seen that when other process conditions remain unchanged and only the sputtering power during sputtering is changed, the performance of the prepared thin film will decline;

[0093] Similarly, observing Example 1 and Examples 6-7 and the data in Table 1, it can be seen that when only the gas flow ratio of argon to oxygen during sputtering is changed, the performance of the prepared thin film will also decline;

[0094] And combining with Table 1-3, it can be seen that when the sputtering power is 1100w and the gas flow ratio of argon to oxygen during sputtering is 78:22, the performance of the prepared thin film is the best and the long-term stability of the thin film is the best.

[0095] 3. From Example 1, Example 8 and the data in Table 1, it can be seen that when a commercially available ordinary glass substrate is used to replace the quartz glass substrate, compared with Example 1, the thin film prepared with the commercially available ordinary glass substrate has differences in resistivity, carrier concentration, carrier mobility and transmittance of 0.957×10 -4 Ω·cm, -0.690×10 20 cm 3 , -12.669cm 2 / v·s, -13.5% (“-” only indicates that the performance data shows a decline). This is because the lattice match between the quartz glass and the thin film is also good, thus making the combination of the glass and the thin film more firm;

[0096] And from Table 3, it can be seen that among the performance changes of the thin films before and after aging of the two, the performance change of the thin film prepared with the commercially available ordinary glass is also greater. Therefore, it can be known that its long-term stability is poor.

[0097] 4. From Example 1, Examples 9-10 and the data in Table 1, it can be seen that when other process conditions remain unchanged and the distance between the target and the substrate is further changed, the performance of the thin film will further decline due to the decrease in deposition rate or uneven distribution of the thin film;

[0098] Further observing Examples 11-12, it can be seen that similarly when other process conditions remain unchanged and the air pressure in the chamber during sputtering is further changed, the thin film will appear in an amorphous state, an incomplete crystallization state or unable to form a continuous thin film, resulting in a decline in the performance of the thin film;

[0099] And from Table 3, it can be seen that while the performance of the thin film declines, the performance difference between the thin films before and after aging will also become larger, that is, the long-term stability of the thin film declines.

[0100] 5. It can be seen from Example 1, Examples 13 - 14 and the data in Table 1 that when the substrate temperature is 30 °C and annealing is carried out, or when the substrate temperature is maintained at 200 °C but annealing is not carried out, the properties of the prepared thin film will also show a downward trend. This is because the temperature of the substrate and the annealing operation are closely related to the quality and mechanical properties of the thin film. The lack of either of them will lead to a decrease in the performance of the thin film;

[0101] Further observing Table 3, it can be seen that the resistivity, carrier concentration, carrier mobility and transmittance of the thin film prepared in Example 1 differ by 0.108×10 -4 Ω·cm, -0.442×10 20 cm 3 , -4.441 cm 2 / v·s, -4.5% (“-” only indicates that the performance data shows a decrease) before and after aging. For the thin films prepared in Examples 13 - 14, the differences in performance before and after aging, except for the carrier mobility, are more than twice that of Example 1. Thus, it can be seen that the temperature of the substrate and the annealing operation are also quite important for maintaining the long-term stability of the thin film.

[0102] 6. It can be seen from Example 1, Comparative Examples 1 - 2 and the data in Table 1 that compared with Example 1, when other process conditions remain unchanged, the thin film obtained by further changing the sputtering power shows a greater decrease in performance compared with Example 1. This is because too high power will cause target poisoning, large film stress, or too low power will affect the film growth rate and film crystallization quality;

[0103] Similarly, observing Example 1, Comparative Examples 3 - 4 and the data in Table 1, it can be seen that by further changing the atmosphere during target sputtering, due to the change in the oxygen content in the atmosphere, during the sputtering process of the target, it will cause target poisoning of the target or affect the formation of the thin film, thereby leading to a decrease in the performance of the thin film;

[0104] And it can be seen from the data in Table 3 that the thin films obtained by further changing the sputtering power or atmosphere have relatively poor long-term stability.

[0105] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present application shall be equivalent replacement methods and are all included in the protection scope of the present application.

Claims

1. A method for preparing a NiO thin film, characterized in that: The preparation method comprises: using a NiO target material to perform magnetron sputtering deposition and annealing on a substrate in a sputtering chamber to obtain a NiO film; Among them, the magnetron sputtering power is 1000~1200w; The atmosphere of magnetron sputtering is a mixed gas of argon and oxygen, and the gas flow ratio of argon to oxygen is 80-70:20-30.

2. The preparation method according to claim 1, characterized in that: The background vacuum degree in the sputtering chamber is 5×10 -6 ~5×10 -5 torr, and during sputtering, the mixed gas of argon and oxygen is adjusted to 2.5-3.5 mtorr.

3. The preparation method according to claim 1, characterized in that: The target-substrate distance between the NiO target material and the substrate is 115-130 mm.

4. The preparation method according to claim 1, characterized in that: The temperature of the substrate is 190-210°C; The specific operation of the annealing is: in an air atmosphere, the temperature is raised to 200-250° C. at a rate of 10-15° C. / min, the annealing time is 50-70 minutes, and then the temperature is lowered to 30° C. at a rate of 10-15° C. / min.

5. The preparation method according to claim 1, characterized in that: The substrate is a cleaned quartz glass substrate, and the rotation speed of the quartz glass substrate is 6 to 10 rad / min; The specific operation of cleaning is: using 95% ethanol and pure water to perform ultrasonic cleaning in sequence, and then blowing dry with nitrogen.

6. The preparation method according to claim 1, characterized in that: The purity of the NiO target material is ≥99.99%; Before use, the NiO target surface needs to be cleaned three times by a radio frequency power supply with a sputtering power of 1000w, each cleaning lasting 8min with an interval of 5min.

7. The preparation method according to claim 1, characterized in that: The thickness of the NiO film is 100-120 nm.

8. A NiO thin film, characterized in that: The NiO thin film is prepared by the method for preparing the NiO thin film according to any one of claims 1 to 7.

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