A method for gradient step growth of cubic boron nitride film

Abstract

The application discloses a method for gradient step growth of cubic boron nitride film, and aims at the problem that sp2 to sp3 structure efficient and controllable conversion is difficult to realize at present, and proposes a growth strategy of stage gradient energy regulation, which comprises the following steps: depositing a buffer layer mainly in sp2 hybrid structure under zero bias voltage or low bias voltage; inducing the buffer layer to transform into sp3 hybrid structure by gradually increasing the negative bias voltage of the substrate to-80V to-120V, so as to form a high-density cubic boron nitride nucleation layer; and stably setting the negative bias voltage of the substrate to-110V to-130V for epitaxial growth, so as to obtain a high-phase-purity cubic boron nitride film. By adjusting the ion bombardment energy in stages, the application realizes decoupling control of the phase transformation kinetics process and the internal stress evolution process of the film, significantly improves the phase purity, structure uniformity and interface quality of the c-BN film, and reduces the surface roughness and internal residual stress.

Description

Technical Field

[0001] This application belongs to the field of semiconductor fabrication technology, specifically relating to a method for gradient stepwise growth of cubic boron nitride thin films. Background Technology

[0002] Cubic boron nitride (c-BN) is a high-performance wide-bandgap semiconductor material with extremely high hardness, high thermal conductivity, a wide bandgap (approximately 6.4 eV), high breakdown electric field strength, and excellent chemical and thermal stability. These properties make c-BN a promising candidate material for extreme environment electronic devices and high-reliability power devices, following diamond, and it has broad application prospects in deep ultraviolet optoelectronic devices, high-power high-frequency electronic devices, and other fields.

[0003] However, c-BN is thermodynamically metastable, with its stable phase being hexagonal boron nitride (h-BN). During thin film deposition, boron nitride more readily forms sp² hybridized h-BN structures, while it is difficult to spontaneously form sp³ hybridized c-BN structures. Therefore, achieving the controllable preparation of high-purity c-BN thin films has always been a technical challenge in this field.

[0004] Currently, the preparation of c-BN thin films mainly employs techniques such as ion-assisted deposition, magnetron sputtering, and radio frequency plasma-enhanced chemical vapor deposition. The basic principle of these methods is to introduce high-energy particles to bombard the growth surface, using ion kinetic energy to break the sp² bonds in h-BN, inducing structural reconstruction, thereby achieving the phase transition from h-BN to c-BN. In practical applications, the most commonly used technique is the constant high negative bias direct growth method, which applies a constant high negative bias (typically -100 V to -150 V) throughout the entire film deposition process, promoting sp³ bond formation through continuous high-energy ion bombardment.

[0005] However, existing technologies have the following shortcomings in the preparation of c-BN thin films: First, it is difficult to simultaneously achieve phase purity and structural stability. Ion bombardment energy is highly coupled with the internal stress of the thin film. When the bombardment energy is insufficient, sp² bonds are difficult to break fully, resulting in a large amount of residual h-BN impurities. When the bombardment energy is too high, it easily leads to lattice distortion, enhanced backsputtering, internal stress accumulation, and the phenomenon of sp³ bonds inverting to sp² bonds. Under a single energy window, it is difficult to simultaneously achieve high phase purity and good structural order.

[0006] Second, the problem of interfacial stress concentration is prominent. The direct high-bias growth method applies strong ion bombardment in the early stage of deposition, which causes large stress concentration in the substrate / film interface region. This easily leads to structural defects or non-ideal nucleation states, thereby affecting the overall crystallization quality and interfacial bonding strength of the subsequent film.

[0007] Third, the surface smoothness of the thin film is poor. Due to the continuous high-energy bombardment and enhanced back sputtering effect, c-BN thin films prepared by existing methods often suffer from particle agglomeration, local accumulation, and high surface roughness, which is not conducive to subsequent device integration and interface reliability control.

[0008] Fourth, the stress control capability is limited. The formation process of c-BN is accompanied by significant volume changes and internal stress accumulation. Under constant bias conditions, the ion bombardment intensity and the internal stress of the film increase synchronously. The lack of an effective stress release mechanism leads to large residual stress inside the film, which easily causes cracks or peeling.

[0009] In summary, existing technologies generally lack a design approach for staged energy control during the deposition process, making it impossible to achieve synergistic optimization of phase transformation kinetics and stress evolution, and thus difficult to stably obtain cubic boron nitride thin films with high phase purity, low defects, and uniform structure. Therefore, there is an urgent need to develop a novel preparation method capable of staged control of ion bombardment energy during the deposition process. Summary of the Invention

[0010] To address the aforementioned problems in the prior art, this application provides a method for gradient-step growth of cubic boron nitride thin films. The technical problem to be solved by this application is achieved through the following technical solution: A method for gradient stepwise growth of cubic boron nitride thin films includes the following steps: S100, under zero or low bias conditions, forms a continuous and dense buffer layer on the substrate by gas deposition. S200, on the buffer layer, by gradually increasing the negative bias voltage of the substrate to the first bias voltage range, the buffer layer is induced to transform into an sp³ hybrid structure, and a high-density cubic boron nitride nucleation layer is formed by gas deposition; S300: On the cubic boron nitride nucleation layer, the substrate negative bias is stabilized in the second bias range, and epitaxial growth is performed to obtain a cubic boron nitride thin film with high phase purity.

[0011] Optionally, a substrate pretreatment is included before S100. The substrate pretreatment includes: ultrasonically cleaning the substrate in acetone, anhydrous ethanol and deionized water in sequence, drying it and placing it in a vacuum chamber, and performing plasma etching activation treatment using argon, oxygen or nitrogen-argon mixture for 3 to 10 minutes.

[0012] Optionally, the substrate is a single-crystal silicon wafer, silicon carbide, diamond, a metal substrate, or an oxide substrate; the method achieves decoupled control of the phase transformation kinetics process and the internal stress evolution process of the thin film by adjusting the negative bias voltage of the substrate in stages.

[0013] Optionally, in S100, the zero bias or low bias condition refers to a substrate negative bias of 0V to -50V; the gas deposition uses a mixed atmosphere of nitrogen and argon, wherein the flow ratio of nitrogen to argon is 10:20, and the total gas flow rate is 30 to 40 sccm; the deposition time accounts for 5% to 20% of the total deposition time.

[0014] Optionally, the buffer layer formed in S100 is hexagonal boron nitride or boron nitride containing a metastable transition phase, wherein the proportion of sp³ hybridized boron nitride structure is less than 20%, and no characteristic absorption peak of cubic boron nitride appears in the Fourier transform infrared spectroscopy test.

[0015] Optionally, in S200, the first bias voltage range is -80V to -120V; the method of gradually increasing the substrate negative bias voltage is a step-by-step increase or a continuous gradual increase; the deposition time accounts for 10% to 20% of the total deposition time.

[0016] Optionally, the stepped increase is a gradual increase from 0V to -120V in increments of 20V; the continuous gradual increase is a linear function. Continuous change, rate of change The range is 5 to 15 V / min, with a change time of... The range is 6 to 15 minutes.

[0017] Optionally, the high-density cubic boron nitride nucleation layer formed in S200 has a nucleation point density greater than or equal to 1 × 10¹² cm⁻¹. - ²; The deposition time of the stable growth stage in S300 is adjusted according to the target film thickness: when the target film thickness is 100nm, the deposition time is 40 to 45 min; when the target film thickness is 500nm, the deposition time is 180 to 200 min; when the target film thickness is 1000nm, the deposition time is 380 to 400 min.

[0018] Optionally, in S300, the second bias voltage range is -110V to -130V; the gas deposition uses a mixed atmosphere of nitrogen and argon, wherein the flow ratio of nitrogen to argon is 40:4, and the total gas flow rate is 70 sccm; the deposition time accounts for 60% to 80% of the total deposition time.

[0019] Optionally, the method for gradient stepwise growth of cubic boron nitride thin films is implemented based on a radio frequency magnetron sputtering system, an ion beam assisted deposition system, or a plasma-enhanced chemical vapor deposition system; the substrate temperature during the deposition process is controlled at 300°C to 800°C, the working pressure is controlled at 0.1 Pa to 2 Pa, and the radio frequency power is controlled at 80 W to 150 W.

[0020] Beneficial effects: This application discloses a gradient-step growth method for cubic boron nitride (c-BN) thin films, belonging to the field of semiconductor fabrication technology. Addressing the limitations of existing constant high-bias direct growth methods, such as single ion bombardment energy, limited stress control capabilities, and difficulty in achieving efficient and controllable conversion of sp² to sp³ structures, this application proposes a staged gradient energy-controlled growth strategy. The method includes: depositing a buffer layer dominated by sp² hybrid structures under zero or low bias conditions; inducing the buffer layer to convert to an sp³ hybrid structure by gradually increasing the substrate negative bias to -80V to -120V, forming a high-density cubic boron nitride nucleation layer; and stabilizing the substrate negative bias at -110V to -130V for epitaxial growth to obtain a high-phase-purity cubic boron nitride thin film. By adjusting the ion bombardment energy in stages, this application achieves decoupled control of the phase transformation kinetics and the internal stress evolution of the film, significantly improving the phase purity, structural uniformity, and interface quality of the c-BN thin film, while reducing surface roughness and internal residual stress. This application is applicable to radio frequency magnetron sputtering, ion beam assisted deposition, and plasma-enhanced chemical vapor deposition systems. The high-quality c-BN thin films prepared have important application prospects in extreme environment electronic devices and high-power devices.

[0021] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of a method for gradient stepwise growth of cubic boron nitride thin films provided in this application; Figure 2 This is a schematic diagram of the preparation of the buffer layer provided in this application; Figure 3 This is a schematic diagram of the preparation of the phase transformation induced layer provided in this application; Figure 4 This diagram illustrates the parameters of the cubic boron nitride thin films grown using this application and conventional methods. Detailed Implementation

[0023] The present application will be described in further detail below with reference to specific embodiments, but the implementation of the present application is not limited thereto.

[0024] like Figure 1As shown, this application provides a method for gradient stepwise growth of cubic boron nitride thin films, including steps S100 to S300. Before S100, this application further includes substrate pretreatment, which includes: ultrasonically cleaning the substrate in acetone, anhydrous ethanol and deionized water in sequence, drying it and placing it in a vacuum chamber, and performing plasma etching activation treatment using argon, oxygen or nitrogen-argon mixed gas for a treatment time of 3 to 10 minutes.

[0025] The substrate is a single-crystal silicon wafer, silicon carbide, diamond, metal substrate, or oxide substrate; the method achieves decoupled control of the phase transformation kinetics process and the internal stress evolution process of the thin film by adjusting the negative bias voltage of the substrate in stages.

[0026] In addition to silicon, silicon carbide, or diamond substrates, the substrate material of this application can also be a metal substrate, an oxide substrate, or other high-temperature resistant materials, as long as it can withstand the staged energy-controlled deposition process, the purpose of this application can be achieved.

[0027] The substrate was cleaned sequentially: first, it was placed in acetone and ultrasonically cleaned at 70°C for 10 min; then transferred to anhydrous ethanol and ultrasonically cleaned at 50°C for 5 min; finally, it was ultrasonically cleaned in deionized water for 5 min under heating. The ultrasonic power was controlled at 100W in all cases to thoroughly remove organic contaminants and particulate impurities from the substrate surface. After cleaning, the substrate was dried with high-purity nitrogen and then placed in a deposition vacuum chamber for pre-vacuum treatment. If necessary, the substrate underwent plasma pretreatment. The pretreatment gas used was high-purity Ar, O2, or a N2 / Ar mixture, with a gas flow rate of 10–30 sccm, a plasma power of 70–80 W, and a DC bias voltage. 10~ At 20V and a processing time of 3–10 min, plasma etching and activation enhance the surface energy and interfacial activity of the substrate, providing a reliable foundation for subsequent uniform nucleation and stable growth of thin films.

[0028] S100, under zero-bias or low-bias conditions, a continuous and dense buffer layer is formed on a substrate by gas deposition; the zero-bias or low-bias conditions refer to a substrate negative bias of 0V to -50V; the gas deposition uses a mixed atmosphere of nitrogen and argon, with a nitrogen to argon flow rate ratio of 10:20 and a total gas flow rate of 30 to 40 sccm; the deposition time accounts for 5% to 20% of the total deposition time. The formed buffer layer is hexagonal boron nitride or boron nitride containing a metastable transition phase, with the sp³ hybridization structure of the boron nitride accounting for less than 20%, and no characteristic absorption peak of cubic boron nitride appears in Fourier transform infrared spectroscopy. Figure 2 As shown.

[0029] Understandably, to ensure a mild deposition environment and good film quality, it is necessary to avoid excessive gas flow rate leading to plasma energy enhancement and surface damage. Therefore, in this application, the N2 / Ar flow rate ratio is controlled at 10:20, and the total gas flow rate is 30–40 sccm during the formation of the buffer layer. The deposition time can be controlled within 5%–20% of the total deposition time. This stage mainly forms a continuous and dense h-BN or BN-like transition layer.

[0030] To avoid ambiguity in structural concepts, the "BN-like transition layer" is now clearly defined as follows: It is mainly sp²-BN (h-BN structure), and may contain a small amount of t-BN (metastable transition phase boron nitride). No obvious sp³ main peak (XPS judgment criterion (B 1s): sp²-BN peak position: 190.3 ± 0.2 eV; sp³-BN peak position: 190.9 ± 0.2 eV). Buffer layer requirements: sp³ ratio should be less than 20%; no obvious 1050-1100 cm⁻¹ should appear in the FTIR test. - ¹ c-BN characteristic peaks; continuous substrate coverage, AFM test results RMS < 2nm.

[0031] The physical mechanism of the buffer layer in this application is as follows: 1) Low-energy ion bombardment avoids initial strong stress concentration; 2) Reduces structural mismatch between the substrate and the functional layer; 3) Provides a uniform nucleation interface; 4) Reduces interface defects caused by high-energy bombardment.

[0032] In addition to forming a BN-like transition layer through in-situ growth under low bias, the buffer layer construction method of this application can also pre-grow an h-BN thin layer, an amorphous BN layer, or other nitride transition layer to achieve the purpose of reducing interface stress and optimizing nucleation conditions.

[0033] S200, on the buffer layer, by gradually increasing the substrate negative bias voltage to a first bias voltage range, the buffer layer is induced to transform into an sp³ hybrid structure, and a high-density cubic boron nitride nucleation layer is formed by gas deposition, reference. Figure 3 As shown.

[0034] The first bias voltage range is -80V to -120V; the method of gradually increasing the substrate negative bias voltage is a step-by-step increase or a continuous gradual increase; the deposition time accounts for 10% to 20% of the total deposition time. The step-by-step increase is a gradual increase from 0V to -120V in increments of 20V; the continuous gradual increase is a linear function... Continuous change, rate of change The range is 5 to 15 V / min, and the change time is... The time range is 6 to 15 minutes. A high-density cubic boron nitride nucleation layer is formed, with a nucleation site density greater than or equal to 1 × 10¹² cm⁻¹. - ²; The deposition time of the stable growth stage in S300 is adjusted according to the target film thickness: when the target film thickness is 100nm, the deposition time is 40 to 45 min; when the target film thickness is 500nm, the deposition time is 180 to 200 min; when the target film thickness is 1000nm, the deposition time is 380 to 400 min.

[0035] After the buffer layer deposition is completed, this application gradually increases the substrate negative bias voltage to the range of -80V to -120V. The bias voltage increase can be a step-wise increase or a continuous gradual increase. In the RF magnetron sputtering system, the substrate negative bias voltage is adjusted in stages as follows: Step-by-step elevation method: 0→-80V→-100V→-120V, each step is 20V. The duration of each step should be the same, and the duration of each step should be adjusted according to the proportion of the total deposition time. The deposition time of this step accounts for 10% to 20% of the total deposition time.

[0036] Continuous Gradual Enhancement Implementation Method: The bias voltage changes continuously according to a linear function: Where k = 5–15 V / min, initial V0 = 0 V, and final V e =-120V, change time 6–15min.

[0037] Continuous mode is suitable for substrates that are more sensitive to interfacial stress (such as Si or diamond). The N2 / Ar flow ratio is controlled at 30:20, and the total gas flow rate is 50 sccm.

[0038] In addition to step-by-step segmented increase, the negative bias voltage adjustment method of this application can also adopt continuous linear gradual change, exponential gradual change, pulse modulation or multi-cycle cyclic adjustment. As long as it can realize the staged change of ion energy during the deposition process, it is within the protection scope of this application.

[0039] The physical mechanism of the high-density cubic boron nitride nucleation layer in this application is as follows: 1) providing sufficient ionic kinetic energy to break sp² bonds; 2) inducing the transformation of h-BN to c-BN; 3) forming high-density sp³ nucleation sites under controlled stress conditions; and 4) achieving kinetic activation of the sp²→sp³ transformation. In this stage, ion energy and atomic migration rate reach a synergistic state, and the transformation of the h-BN transition layer into the c-BN nucleation layer using appropriate ion bombardment is a crucial stage in the phase structure evolution.

[0040] S300, on the cubic boron nitride nucleation layer, the substrate negative bias is stabilized within a second bias range for epitaxial growth to obtain a high-phase-purity cubic boron nitride thin film. The second bias range is -110V to -130V; gas deposition uses a mixed atmosphere of nitrogen and argon, with a nitrogen to argon flow rate ratio of 40:4 and a total gas flow rate of 70 sccm; the deposition time accounts for 60% to 80% of the total deposition time.

[0041] After forming a high-density cubic boron nitride nucleation layer, the bias voltage is stabilized within an optimized window (preferably -120V). Then, the main layer thickness is grown. The N2 / Ar flow ratio is controlled at 40:4, and the total gas flow rate is 70 sccm. This stage accounts for 60%–80% of the total deposition time.

[0042] The mechanism of action of this stage in this application is as follows: 1) using the formed sp³ structure as a template to dominate epitaxial growth; 2) suppressing sp³ bond reversal; 3) controlling internal stress within an acceptable range; 4) reducing the back sputtering effect; and 5) improving the orderliness and phase purity of the thin film structure.

[0043] In addition to Ar / N2 mixed gas, the deposition atmosphere of this application may also be pure N2 atmosphere, Ar / N2 / H2 mixed atmosphere, or other inert gas and nitrogen combination system, as long as nitrogen source supply can be achieved and energy regulation can be used to complete the formation of c-BN phase, all of which fall within the scope of protection of this application.

[0044] The gradient stepwise growth method of cubic boron nitride thin films described in this application is implemented based on a radio frequency magnetron sputtering system, an ion beam assisted deposition system, or a plasma enhanced chemical vapor deposition system; the substrate temperature during the deposition process is controlled at 300°C to 800°C, the working pressure is controlled at 0.1 Pa to 2 Pa, and the radio frequency power is controlled at 80 W to 150 W.

[0045] In addition to a fixed ratio, the phased time ratios in this application can also be dynamically adjusted according to the film thickness, deposition rate, or equipment characteristics. As long as the functional separation principle of low-energy interface construction to medium-energy phase conversion and then to optimized energy-stable growth is met, it is considered an equivalent alternative to this application.

[0046] In addition to being used to prepare monolayer c-BN thin films, this application can also be used to construct multilayer composite structures, heterojunction structures, or gradient stress-controlled structures. As long as their core is still based on the staged regulation of ion energy during the deposition process to achieve the formation of high-phase pure c-BN, they all fall within the scope of protection of this application.

[0047] In addition to radio frequency magnetron sputtering systems, the deposition equipment used in this application may also include ion beam assisted deposition systems, DC magnetron sputtering systems, pulsed magnetron sputtering systems, plasma-enhanced chemical vapor deposition systems, or other deposition devices capable of tunable ion energy.

[0048] The thin film deposition in this application is divided into a phase transformation induction stage and a stable growth stage, namely S200 and S300. Specific examples of deposition times for each stage, combined with different target film thicknesses, are as follows: Example 1: When the target film thickness is 100±5nm, the deposition time of the phase transformation induction stage is controlled to be 15-20min. This stage can fully form a transition layer with a thickness of 5-8nm and a density ≥1×10¹²cm. - The sp³ nucleation points are 2; the deposition time during the stable growth stage is controlled at 40-45 min to ensure that the film is deposited to the target thickness and the film thickness uniformity deviation is ≤ ±3 nm.

[0049] Example 2: When the target film thickness is 500±10nm, the deposition time during the phase transformation induction stage is controlled to be 25-30min, forming a transition layer with a thickness of 8-12nm and a density ≥1.2×10¹²cm. - The sp³ nucleation points are 2; the deposition time during the stable growth stage is controlled at 180-200 min to ensure the film density and thickness accuracy, and to meet the target film thickness requirements.

[0050] Example 3: When the target film thickness is 1000±20nm (1μm), the deposition time of the phase transformation induction stage is controlled at 35-40min, the transition layer thickness reaches 12-15nm, and the sp³ nucleation point density is ≥1.5×10¹²cm. - ²; The deposition time during the stable growth stage is controlled at 380–400 min to achieve stable deposition of the target film thickness, while ensuring the interfacial adhesion and surface smoothness of the film.

[0051] In addition to using staged adjustment of substrate negative bias, the gradient energy control method of this application can also achieve staged changes in ion incident energy by adjusting ion beam energy, plasma density, radio frequency power, or pulse bias duty cycle, thereby achieving the same sp²→sp³ conversion control and stress adjustment effect.

[0052] refer to Figure 4 , Figure 4The figures show the parameters of cubic boron nitride thin films grown according to the present application and conventional methods. Figures a to c show the parameters of the cubic boron nitride thin films grown according to the present application method, where a is the XPS full spectrum, b is the peak fitting of the fine spectrum of the B1s binding energy, and c is the peak fitting of the fine spectrum of the N1s binding energy. Figures d to f show the parameters of cubic boron nitride thin films grown according to the conventional method, where d is the XPS full spectrum, e is the peak fitting of the fine spectrum of the B1s binding energy, and f is the peak fitting of the fine spectrum of the N1s binding energy.

[0053] from Figure 4 As can be seen, in the gradient stepwise growth method sample, the B1s fine spectrum is mainly composed of sp³-BN components, with the fitted c-BN phase accounting for as high as 98.04%, and the sp² component accounting for only a very small proportion. The main peak is concentrated and has a narrow half-peak width, indicating that boron atoms are mainly in a stable four-coordinate sp³ bonding environment. In contrast, the sp³-BN proportion in the direct growth method sample is only 72.99%, with a significantly enhanced sp²-BN component and a significantly increased fitted peak area ratio, indicating that there are still many h-BN or graphitized structures in the sample. At the same time, in the gradient stepwise growth method, C and O impurities are significantly reduced, indicating that the film has higher purity and lower impurity content, and the overall stoichiometry is closer to the ideal cubic boron nitride structure. In contrast, the overall spectral background of the direct growth method sample is slightly raised, and the impurity peaks are relatively obvious, reflecting that it is more likely to introduce defects or form non-ideal bonding structures in the early stage of growth.

[0054] It is worth noting that the terms "first" and "second" in this application are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0055] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of this application, and all such modifications or substitutions should be considered within the scope of protection of this application.

Claims

1. A method for gradient stepwise growth of cubic boron nitride thin films, characterized in that, Includes the following steps: S100, under zero or low bias conditions, forms a continuous and dense buffer layer on the substrate by gas deposition. S200, on the buffer layer, by gradually increasing the negative bias voltage of the substrate to the first bias voltage range, the buffer layer is induced to transform into an sp³ hybrid structure, and a high-density cubic boron nitride nucleation layer is formed by gas deposition; S300: On the cubic boron nitride nucleation layer, the substrate negative bias is stabilized in the second bias range, and epitaxial growth is performed to obtain a cubic boron nitride thin film with high phase purity.

2. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, Before S100, a substrate pretreatment is also included, which includes: ultrasonically cleaning the substrate in acetone, anhydrous ethanol and deionized water in sequence, drying it and placing it in a vacuum chamber, and performing plasma etching activation treatment using argon, oxygen or nitrogen-argon mixture for a treatment time of 3 to 10 minutes.

3. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, The substrate is a single-crystal silicon wafer, silicon carbide, diamond, metal substrate, or oxide substrate; the method achieves decoupled control of the phase transformation kinetics process and the internal stress evolution process of the thin film by adjusting the negative bias voltage of the substrate in stages.

4. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, In S100, the zero bias or low bias condition refers to a substrate negative bias of 0V to -50V; the gas deposition uses a mixed atmosphere of nitrogen and argon, wherein the flow ratio of nitrogen to argon is 10:20, and the total gas flow rate is 30 to 40 sccm; the deposition time accounts for 5% to 20% of the total deposition time.

5. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, The buffer layer formed in S100 is hexagonal boron nitride or boron nitride containing a metastable transition phase, with the proportion of sp³ hybridized boron nitride structure being less than 20%, and no characteristic absorption peak of cubic boron nitride appearing in Fourier transform infrared spectroscopy.

6. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, In S200, the first bias voltage range is -80V to -120V; the method of gradually increasing the substrate negative bias voltage is a step-by-step increase or a continuous gradual increase; the deposition time accounts for 10% to 20% of the total deposition time.

7. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 6, characterized in that, The stepped increase is achieved by gradually increasing the voltage from 0V to -120V in increments of 20V; the continuous gradual increase is achieved according to a linear function. Continuous change, rate of change The range is 5 to 15 V / min, with a change time of... The range is 6 to 15 minutes.

8. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, The high-density cubic boron nitride nucleation layer formed in S200 has a nucleation point density greater than or equal to 1 × 10¹² cm⁻¹. - ²; The deposition time of the stable growth stage in S300 is adjusted according to the target film thickness: when the target film thickness is 100nm, the deposition time is 40 to 45 min; when the target film thickness is 500nm, the deposition time is 180 to 200 min; when the target film thickness is 1000nm, the deposition time is 380 to 400 min.

9. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, In S300, the second bias voltage range is -110V to -130V; gas deposition uses a mixed atmosphere of nitrogen and argon, wherein the flow ratio of nitrogen to argon is 40:4 and the total gas flow rate is 70 sccm; the deposition time accounts for 60% to 80% of the total deposition time.

10. The method for gradient stepwise growth of cubic boron nitride thin films according to claim 1, characterized in that, The method for gradient stepwise growth of cubic boron nitride thin films is implemented based on a radio frequency magnetron sputtering system, an ion beam assisted deposition system, or a plasma-enhanced chemical vapor deposition system; the substrate temperature during the deposition process is controlled at 300°C to 800°C, the working pressure is controlled at 0.1 Pa to 2 Pa, and the radio frequency power is controlled at 80 W to 150 W.

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