Method for growing nickel oxide film based on asymmetric cyclopentadienyl nickel ALD

Abstract

The invention discloses a method for growing a nickel oxide film based on asymmetric cyclopentadienyl nickel ALD (atomic layer deposition), which comprises the following steps: introducing asymmetric cyclopentadienyl nickel into a reaction cavity of atomic layer deposition equipment, and carrying out chemical adsorption on the asymmetric cyclopentadienyl nickel on the surface of a substrate in the reaction cavity until adsorption is saturated; introducing protective gas into the reaction cavity for purging, then introducing an oxygen source for reaction to generate atomic layer nickel oxide, and introducing protective gas for purging after the reaction is completed; and repeating the growth cycle, and growing the nickel oxide film on the substrate. According to the method, the asymmetric cyclopentadienyl nickel serves as a nickel source precursor, water, ozone and the like serve as an oxygen source, the nickel oxide film is prepared through the ALD technology, needed reactants are easy to produce and low in cost, the process is simple, conditions are easy to control, the preparation process is good in leakproofness and free of potential safety hazards, and meanwhile the prepared nickel oxide film is high in purity and good in uniformity.

Description

Technical Field

[0001] This invention relates to the field of nickel oxide thin film preparation technology, and specifically to a method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienyl alcohol (ALD). Background Technology

[0002] Nickel oxide (NiO) x Thin films have a wide range of applications in thin-film transistors, photovoltaic solar cells, and other fields. Especially in perovskite solar cell applications, nickel oxide thin films, acting as hole transport layers or functional layers, can achieve charge-selective transport and significantly improve the work function between the nickel oxide film and the light-absorbing layer. Currently, the perovskite industry has an increasingly urgent need for low-temperature crystalline nickel oxide thin films.

[0003] However, the crystallinity of nickel oxide films currently on the market is poor, and the process temperature for ALD (atomic layer deposition) nickel oxide films in the industry is very high, which cannot meet the process requirements of the perovskite industry. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienyl etherification (ALD). Using asymmetric nickel cyclopentadienyl ether as the nickel source, nickel oxide thin films are grown by ALD, resulting in nickel oxide thin films with excellent crystallinity. At the same time, the ALD process temperature is relatively low, enabling the preparation of crystalline nickel oxide thin films under low-temperature conditions.

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienyl alloy (ALD), comprising the following steps:

[0006] S1. Asymmetric nickel cyclopentadienylene is introduced into the reaction chamber of the atomic layer deposition equipment, and the asymmetric nickel cyclopentadienylene is chemically adsorbed on the substrate surface in the reaction chamber until adsorption saturation is achieved.

[0007] S2. Purge the reaction chamber with protective gas, then introduce an oxygen source to react and generate atomic layer nickel oxide. After the reaction is complete, purge with protective gas.

[0008] S3. Repeat steps S1-S2 to grow a nickel oxide thin film on the substrate.

[0009] This invention uses asymmetric nickel cyclopentadienylene as the nickel source to grow nickel oxide thin films via ALD, resulting in nickel oxide thin films with excellent crystallinity. At the same time, the ALD process temperature is relatively low, enabling the preparation of crystalline nickel oxide thin films under low-temperature conditions, which provides possibilities for the application of nickel oxide thin films in the photovoltaic and microelectronics fields.

[0010] Further, the asymmetric cyclopentadienyl nickel is Ni(R1Cp)(R2Cp), where R1 and R2 are independent and distinct, selected from C0-Cx alkyl groups, where x is an integer between 1 and 5. Preferably, the asymmetric cyclopentadienyl nickel is one or more of Ni(MeCp)Cp ((methylcyclopentadienyl)cyclopentadienyl nickel), Ni(EtCp)Cp ((ethylcyclopentadienyl)(cyclopentadienyl nickel)), and Ni(MeCp)(EtCp)((methylcyclopentadienyl)(ethylcyclopentadienyl) nickel).

[0011] Furthermore, the oxygen source is water or ozone (O3).

[0012] Taking Ni(EtCp)Cp as a nickel precursor as an example, the reaction formula is as follows:

[0013] Ni(EtCp)Cp+O3→NiO+HEtCp+HCp+CO2+H2O+etc

[0014] This invention uses asymmetric nickel-cadmium (NiCr) as the nickel source precursor. The asymmetric nickel source precursor possesses a certain polarity, and compared to symmetrical NiCr, its overall configuration is closer to a sphere, resulting in a lower melting point. Furthermore, the spacing effect of the peripheral groups weakens the intermolecular interactions, leading to a higher vapor pressure for the asymmetric NiCr. By reacting the asymmetric NiCr with oxygen sources such as water or ozone, sufficient reaction energy can be obtained at relatively low temperatures, promoting rapid migration and diffusion on the substrate to find the most energy-stable lattice sites and facilitate crystallization. By increasing the number of cycles, stable atomic layer deposition is achieved, growing a nickel oxide thin film. Moreover, after the nickel source precursor used in this invention reacts with the oxygen source, only nickel oxide, a solid product, is produced in the reaction chamber; the remaining reactants and products are gaseous and can be carried away by the subsequent purging gas, ensuring product purity.

[0015] Furthermore, in S1, the reaction chamber and the asymmetric nickel pyrocenyl group are heated before the asymmetric nickel pyrocenyl group is introduced. The heating temperature of the reaction chamber is 100-350°C, and the heating temperature of the asymmetric nickel pyrocenyl group is 60-150°C. Heating the reaction chamber promotes the chemical adsorption of the nickel source precursor and its reaction with the oxygen source, thereby increasing the film deposition rate. Heating the nickel source precursor increases the saturated vapor pressure of the precursor source in the source bottle, increasing the amount of nickel source precursor carried by the carrier gas, and thus improving the deposition rate.

[0016] Furthermore, the substrate is made of one of the following materials: silicon, silicon dioxide, silicon nitride, silicon carbide, glass, sapphire, gallium nitride, and stainless steel.

[0017] Furthermore, the substrate may be planar or non-planar.

[0018] Furthermore, before S1, the process includes: cleaning the substrate with one or more of methanol, acetone, isopropanol, and water, and etching the cleaned substrate with hydrofluoric acid to remove the oxide layer on the substrate surface. Through cleaning and etching, the surface roughness of the substrate can be effectively reduced, surface contaminants removed, impurities and defects reduced, nucleation conditions improved, and thin film deposition facilitated, resulting in a smooth and flat thin film.

[0019] Furthermore, the asymmetric nickel-cadmium and oxygen source are introduced into the reaction chamber in a pulsed manner under the transport of a carrier gas.

[0020] Furthermore, the protective gas and the carrier gas are independently selected from Ar, N2, or He, with a purity greater than or equal to 99.999%.

[0021] The second aspect of the present invention provides a nickel oxide thin film prepared by the preparation method described in the first aspect.

[0022] The third aspect of this invention provides the application of the nickel oxide thin film described in the second aspect in the fields of photovoltaics and microelectronics.

[0023] The beneficial effects of this invention are:

[0024] This invention uses asymmetric nickel cyclopentadienylene as the nickel source precursor and water, ozone, etc., as the oxygen source to prepare nickel oxide thin films via ALD technology. The required reactants are easy to produce and low in cost, and the process is simple, the conditions are easy to control, the preparation process has good sealing performance and no safety hazards, and the prepared nickel oxide thin films have high purity and good uniformity. Specifically:

[0025] First, asymmetric nickel-cadmium (NiCr) was selected as the nickel source precursor. Asymmetric NiCr possesses a certain degree of polarity, and compared to symmetrical NiCr, its overall configuration is closer to a sphere, resulting in a lower melting point. Furthermore, the spacing effect of the peripheral groups weakens the intermolecular interactions, leading to a higher vapor pressure for asymmetric NiCr. By reacting asymmetric NiCr with an oxygen source, sufficient reaction energy can be obtained at a relatively low temperature, promoting rapid migration and diffusion on the substrate to find the most energy-stable lattice sites and facilitate crystallization. By increasing the number of cycles, stable atomic layer deposition was achieved, resulting in the growth of a nickel oxide thin film.

[0026] Secondly, after the nickel source precursor reacts with the oxygen source, only nickel oxide, a solid product, is produced in the reaction chamber. The remaining reactants and products are all in a gaseous state and can be carried out by the subsequent purging gas, ensuring the purity of the product. Attached Figure Description

[0027] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a thickness curve of nickel oxide thin films obtained from the nickel source at different heating temperatures in Example 1 of the present invention;

[0029] Figure 2 This is a thickness curve of the nickel oxide film obtained in the reaction chamber of Example 2 of the present invention at different heating temperatures;

[0030] Figure 3 These are XRD patterns of the nickel oxide films obtained in Examples 2 and 3 of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This embodiment relates to a method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienyl alcohol (ALD), comprising the following steps:

[0033] S1. Asymmetric nickel cyclopentadienylene is introduced into the reaction chamber of the atomic layer deposition equipment, and the asymmetric nickel cyclopentadienylene is chemically adsorbed on the substrate surface in the reaction chamber until adsorption saturation is achieved.

[0034] S2. Purge the reaction chamber with protective gas, then introduce an oxygen source to react and generate atomic layer nickel oxide. After the reaction is complete, purge with protective gas.

[0035] S3. Repeat steps S1-S2 to grow a nickel oxide thin film on the substrate.

[0036] This embodiment uses asymmetric nickel cyclopentadienylene as the nickel source to grow nickel oxide thin films via ALD. The resulting nickel oxide thin films exhibit excellent crystallinity. At the same time, the ALD process temperature is relatively low, enabling the preparation of crystalline nickel oxide thin films under low-temperature conditions, which provides possibilities for the application of nickel oxide thin films in the photovoltaic and microelectronics fields.

[0037] Specifically, the asymmetric cyclopentadienyl nickel is Ni(R1Cp)(R2Cp), where R1 and R2 are independent and distinct, selected from C0-Cx alkyl groups, where x is an integer between 1 and 5. Preferably, the asymmetric cyclopentadienyl nickel is one or more of Ni(MeCp)Cp ((methylcyclopentadienyl)cyclopentadienyl nickel), Ni(EtCp)Cp ((ethylcyclopentadienyl)(cyclopentadienyl nickel)), and Ni(MeCp)(EtCp)((methylcyclopentadienyl)(ethylcyclopentadienyl) nickel). The oxygen source is water or ozone (O3). Taking Ni(EtCp)Cp as a nickel precursor as an example, the reaction formula is as follows:

[0038] Ni(EtCp)Cp+O3→NiO+HEtCp+HCp+CO2+H2O+etc

[0039] This embodiment uses asymmetric nickel-cadmium as the nickel source precursor. The asymmetric nickel source precursor has a certain polarity, and compared to symmetrical nickel-cadmium, its overall configuration is closer to a sphere, resulting in a lower melting point. Furthermore, the spacing effect of the peripheral groups weakens the intermolecular interactions, leading to a higher vapor pressure for the asymmetric nickel-cadmium. By reacting the asymmetric nickel-cadmium with oxygen sources such as water or ozone, sufficient reaction energy can be obtained at relatively low temperatures, promoting rapid migration and diffusion on the substrate to find the most energy-stable lattice sites and facilitate crystallization. By increasing the number of cycles, stable atomic layer deposition is achieved, growing a nickel oxide film. Moreover, after the nickel source precursor used in this invention reacts with the oxygen source, only nickel oxide, a solid product, is produced in the reaction chamber; the remaining reactants and products are gaseous and can be carried away by the subsequent purging gas, ensuring product purity.

[0040] In a preferred embodiment, in S1, the reaction chamber and the asymmetric nickel pyrocenyl group are heated before the asymmetric nickel pyrocenyl group is introduced. The heating temperature of the reaction chamber is 100-350°C, preferably 150-300°C, and the heating temperature of the asymmetric nickel pyrocenyl group is 60-150°C, preferably 80-120°C. Heating the reaction chamber promotes the chemical adsorption of the nickel source precursor and its reaction with the oxygen source, thereby increasing the film deposition rate. Heating the nickel source precursor increases the saturated vapor pressure of the precursor source in the source bottle, increasing the amount of nickel source precursor carried by the carrier gas, and thus improving the deposition rate.

[0041] In a preferred embodiment, the substrate is made of one of the following materials: silicon, silicon dioxide, silicon nitride, silicon carbide, glass, sapphire, gallium nitride, and stainless steel. The substrate may be planar or non-planar.

[0042] In a preferred embodiment, before S1, the process further includes: cleaning the substrate with one or more of methanol, acetone, isopropanol, and water, and etching the cleaned substrate with hydrofluoric acid to remove the oxide layer on the substrate surface. Through cleaning and etching, the surface roughness of the substrate can be effectively reduced, surface contaminants can be removed, impurities and defects can be reduced, nucleation conditions can be improved, and thin film deposition can be facilitated, resulting in a smooth and flat thin film.

[0043] In a preferred embodiment, the asymmetric nickel-cadmium and oxygen source are introduced into the reaction chamber in a pulsed manner, carried by a carrier gas. The protective gas and carrier gas are independently selected from Ar, N2, or He, with a purity greater than or equal to 99.999%.

[0044] Another embodiment provides a nickel oxide thin film prepared by the preparation method described in the above embodiments.

[0045] Another embodiment provides the application of the nickel oxide thin film described in the above embodiments in the fields of photovoltaics and microelectronics.

[0046] Example 1

[0047] This embodiment relates to a method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienyl alcohol (ALD), comprising the following steps:

[0048] (1) Use acetone, methanol, isopropanol and pure water to immerse and clean the silicon wafer surface for 5 minutes in sequence to remove surface organic matter. Then, immerse the treated silicon wafer in HF solution for 30 seconds to etch away the oxide layer on the silicon wafer surface. Place the treated silicon wafer into the reaction chamber of the ALD device within 1 minute and evacuate it to below 1 Torr.

[0049] (2) Using Ni(MeCp)Cp as the nickel source precursor, water as the oxygen source, and high-purity nitrogen as the carrier gas and purge gas; input the deposition working parameters: the heating temperature of the nickel source precursor is set to 60℃, 70℃, 80℃, 100℃, and 120℃ respectively, the water is at room temperature, the heating temperature of the reaction chamber is 150℃, the carrier gas flow rate is 20sccm, and the reaction chamber and nickel source precursor are heated for 1h before the coating begins;

[0050] (3) To begin the coating process, Ni(MeCp)Cp is introduced into the reaction chamber using high-purity nitrogen gas, which adsorbs onto the substrate surface. The pulse duration is 3 seconds. Then, 20 sccm of high-purity nitrogen gas is introduced for 20 seconds of purging.

[0051] (4) Water is introduced into the reaction chamber through high-purity nitrogen gas to react with Ni(MeCp)Cp adsorbed on the substrate to form an atomic layer nickel oxide film. Then, 20 sccm of high-purity nitrogen gas is introduced for 20 s purging to complete a single growth cycle.

[0052] (5) Repeat steps (3)-(4) for 200 cycles to obtain a nickel oxide film.

[0053] In this embodiment, the heating temperatures of Ni(MeCp)Cp were set to 60℃, 70℃, 80℃, 100℃, and 120℃, respectively, to study the effect of Ni(MeCp)Cp on the growth rate of nickel oxide thin films at different heating temperatures. The results are as follows: Figure 1 As shown, when the heating temperature of Ni(MeCp)Cp is 60℃, a thin film can be grown, but the thickness is relatively thin; when the heating temperature is greater than 70℃, the film growth rate increases; when the heating temperature is 80-120℃, the difference in film thickness is small, indicating that the nickel oxide film grown by the saturated adsorption of the precursor within this temperature range is better.

[0054] Example 2

[0055] This embodiment relates to a method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienyl alcohol (ALD), comprising the following steps:

[0056] (1) Use acetone, methanol, isopropanol and pure water to immerse and clean the silicon wafer surface for 5 minutes in sequence to remove surface organic matter. Then, immerse the treated silicon wafer in HF solution for 30 seconds to etch away the oxide layer on the silicon wafer surface. Place the treated silicon wafer into the reaction chamber of the ALD device within 1 minute and evacuate it to below 1 Torr.

[0057] (2) Using Ni(EtCp)Cp as the nickel source precursor, ozone as the oxygen source, and high-purity nitrogen as the carrier gas and purge gas; input the deposition working parameters: the heating temperature of the nickel source precursor is set to 90℃, the ozone is set to room temperature, the heating temperature of the reaction chamber is set to 100℃, 150℃, 200℃, 250℃, 300℃, and 350℃, the carrier gas flow rate is 20 sccm, and the reaction chamber and nickel source precursor are heated for 1 hour before the coating begins;

[0058] (3) To begin the coating process, Ni(EtCp)Cp is introduced into the reaction chamber using high-purity nitrogen gas, which adsorbs onto the substrate surface. The pulse duration is 3 seconds. Then, 20 sccm of high-purity nitrogen gas is introduced for 20 seconds of purging.

[0059] (4) Ozone is introduced into the reaction chamber through high-purity nitrogen gas to react with Ni(EtCp)Cp adsorbed on the substrate to form an atomic layer nickel oxide film. Then, 20 sccm of high-purity nitrogen gas is introduced for 20 s purging to complete a single growth cycle.

[0060] (5) Repeat steps (3)-(4) for 400 cycles to obtain a nickel oxide film.

[0061] In this embodiment, the heating temperature of the reaction chamber was set to 100℃, 150℃, 200℃, 250℃, 300℃, and 350℃, respectively, to study the effect of the reaction chamber temperature on the growth of nickel oxide thin films. The results are as follows: Figure 2 The results show that when the reaction chamber temperature is 100℃, the reaction rate is slow. When the reaction chamber temperature is 150-300℃, the thickness of the deposited film tends to stabilize, with a rate of 0.035-0.042 nm / cycle, and the non-uniformity of the film prepared in this temperature range is <4%. When the reaction chamber temperature is higher than 350℃, the thickness of the deposited film increases, and the rate increases to 0.052 nm / cycle, but the excessive speed may result in poor crystallinity.

[0062] The thin film prepared at a reaction chamber temperature of 150°C in this embodiment was characterized by X-ray diffraction (XRD), and the results are as follows: Figure 3 As shown, diffraction peaks belonging to the (1 1 1), (2 0 0), (2 2 0), and (31 1) crystal planes of nickel oxide can be observed, further demonstrating that a thin film with excellent crystallinity was successfully prepared by combining the above-mentioned precursor source with ALD technology.

[0063] To further confirm the uniformity and repeatability of the nickel oxide film grown in this embodiment, the process of 200°C reaction chamber temperature was repeated three times, and the uniformity of the obtained films 1, 2, and 3 was tested. The test method is as follows: Five sites were taken on the prepared nickel oxide film, the thickness value of each point was measured, and the non-uniformity of each film was calculated (non-uniformity = variance / film thickness). The test results are shown in Table 1 below.

[0064] Table 1

[0065]

[0066]

[0067] As can be seen, the nickel oxide film obtained by this embodiment has excellent uniformity, with a non-uniformity of <4%.

[0068] Example 3

[0069] The difference between this embodiment and Embodiment 2 is that the oxygen source is replaced with water, the heating temperature of the reaction chamber is 150°C, and other steps and parameters remain unchanged.

[0070] The thin film prepared in this embodiment was characterized by X-ray diffraction (XRD), and the results are as follows: Figure 3 As shown in Example 2, diffraction peaks belonging to the (1 1 1), (2 0 0), (2 2 0), and (3 1 1) crystal planes of nickel oxide can be observed, further demonstrating that nickel oxide thin films were successfully prepared by combining the above-mentioned precursor source with ALD technology.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 2 is that Ni(acac)2 is used as the nickel source precursor, the reaction chamber heating temperature is set to 150°C, and other steps and parameters remain unchanged. The resulting nickel oxide film has poor uniformity and is amorphous.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 2 is that NiCp2 was used as the nickel source precursor, the reaction chamber heating temperature was set to 150°C, and other steps and parameters remained unchanged. The uniformity and crystallinity of the obtained nickel oxide film were both poor.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 2 is that NiCp2 was used as the nickel source precursor, water was used as the oxygen source, the reaction chamber heating temperature was set to 150°C, and other steps and parameters remained unchanged. No obvious film growth was observed.

[0077] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for growing nickel oxide thin films based on asymmetric nickel pyroxene (ALD) film, characterized in that, Includes the following steps: S1. Asymmetric nickel cyclopentadienylene is introduced into the reaction chamber of the atomic layer deposition equipment, and the asymmetric nickel cyclopentadienylene is chemically adsorbed on the substrate surface in the reaction chamber until adsorption saturation is achieved. S2. Purge the reaction chamber with protective gas, then introduce an oxygen source to react and generate atomic layer nickel oxide. After the reaction is complete, purge with protective gas. S3. Repeat steps S1-S2 to grow a nickel oxide thin film on the substrate.

2. The method for growing nickel oxide thin films based on asymmetric nickel pyroxene ALD as described in claim 1, characterized in that, The asymmetric cyclopentadienyl nickel is Ni(R1Cp)(R2Cp), wherein R1 and R2 are independent and distinct and selected from C0-Cx alkyl groups, where x is an integer between 1 and 5.

3. The method for growing nickel oxide thin films based on asymmetric nickel pyroxene ALD as described in claim 2, characterized in that, The asymmetric cyclopentadienyl nickel is one or more of Ni(MeCp)Cp, Ni(EtCp)Cp, and Ni(MeCp)(EtCp).

4. The method for growing nickel oxide thin films based on asymmetric nickel pyroxene ALD as described in claim 1, characterized in that, In S1, the reaction chamber and the asymmetric nickel are heated before the asymmetric nickel is introduced. The heating temperature of the reaction chamber is 100-350°C, and the heating temperature of the asymmetric nickel is 60-150°C.

5. The method for growing nickel oxide thin films based on asymmetric nickel pyroxene ALD as described in claim 1, characterized in that, The substrate is made of one of the following materials: silicon, silicon dioxide, silicon nitride, silicon carbide, glass, sapphire, gallium nitride, and stainless steel.

6. The method for growing nickel oxide thin films based on asymmetric nickel pyroxene ALD as described in claim 1, characterized in that, Before S1, the process also includes: cleaning the substrate with one or more of methanol, acetone, isopropanol, and water, and etching the cleaned substrate with hydrofluoric acid.

7. The method for growing nickel oxide thin films based on asymmetric nickel pyroxene ALD as described in claim 1, characterized in that, The asymmetric cyclopentadienyl nickel and oxygen source are introduced into the reaction chamber in a pulsed manner under the transport of a carrier gas.

8. The method for growing nickel oxide thin films based on asymmetric nickel cyclopentadienylene (ALD) as described in claim 7, characterized in that, The protective gas and the carrier gas are independently selected from Ar, N2, or He.

9. A nickel oxide thin film prepared by the preparation method according to any one of claims 1-8.

10. The application of the nickel oxide thin film according to claim 9 in the fields of photovoltaics and microelectronics.

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