Method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering and the thin films

Abstract

This invention relates to the field of thin film technology, specifically disclosing a method and a thin film for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering. The method includes: placing a substrate into the sputtering chamber of a magnetron sputtering apparatus, evacuating and heating it to 400°C; introducing an activation gas and performing initial magnetron sputtering on a titanium target at a sputtering threshold to form an adhesion-promoting layer on the substrate surface; turning off the activation gas and then introducing a reactive sputtering gas into the sputtering chamber; then performing high-intensity sputtering while simultaneously turning on a bias power supply, wherein the bias power supply is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply; turning off the pulsed DC power supply and the introduction of nitrogen in the reactive sputtering gas, and continuing magnetron sputtering on the substrate; cycling 2-4 times to cool to room temperature to obtain a single-crystal TiN thin film. In this application, the substrate temperature is only 400°C during deposition, thus reducing energy consumption and shortening the time during subsequent cooling. The titanium nitride thin film prepared in this application exhibits a high sputtering deposition rate and high crystal quality.

Description

Technical Field

[0001] This invention relates to the field of thin film technology, and in particular to a method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering and the single-crystal TiN thin films. Background Technology

[0002] In the field of chip manufacturing, titanium nitride (TiN) is a ceramic material with a metallic luster. The ideal titanium-to-nitrogen atomic ratio in TiN thin films is close to 1:1, resulting in a dense face-centered cubic crystal structure. This structure endows it with high chemical stability and hardness, effectively preventing the diffusion of copper (Cu) or aluminum (Al) atoms into the silicon substrate or dielectric layer, thereby preventing metal contamination and electromigration failure, and improving device reliability and lifespan. Experiments show that a typical 10nm thick TiN layer can reduce the copper diffusion effect to a negligible level. If the TiN film has high crystal quality and good density, a 1-5nm thick TiN barrier layer can maintain its anti-diffusion performance. Therefore, TiN thin films serve as a key barrier layer material in chips, memory devices, and integrated circuit interconnect structures, and the quality of its fabrication process directly affects chip performance and yield.

[0003] Existing TiN thin film preparation processes mainly include chemical vapor deposition (CVD), atomic layer deposition (ALD), and magnetron sputtering. CVD requires the decomposition of precursor gases at high temperatures, followed by a reaction with ammonia or nitrogen to generate TiN, producing toxic gases and involving a complex process. AALD grows TiN films layer by layer by alternately introducing titanium and nitrogen source gases; while producing high-quality films, its slow deposition rate limits its efficiency for large-scale production. In contrast, magnetron sputtering offers advantages such as simplicity, environmental friendliness, and high deposition rates, making it a widely adopted technology in industrial production.

[0004] Currently, the publicly available methods for preparing TiN thin films by magnetron sputtering involve high deposition temperatures. For example, in patent CN119710911A, the temperature of the single-crystal substrate is stabilized at 700℃. This results in a significant amount of time required for heating and cooling during the preparation process, and the deposition rate is very slow, greatly limiting production efficiency. Moreover, the extremely high temperature causes significant heat load and potential damage to components such as the vacuum gauge and observation window inside the deposition chamber, limiting the practicality of the process and the lifespan of the equipment.

[0005] In addition, during the preparation of titanium nitride, controlling the atomic ratio of titanium to nitrogen to be 1:1 is the key to ensuring the barrier properties, conductivity, and mechanical properties of titanium nitride. If the atomic ratio of titanium to nitrogen deviates significantly from 1:1, lattice defects will be introduced, leading to a deterioration in the phase magnetic properties of titanium nitride.

[0006] Therefore, how to achieve high-quality crystallization of TiN thin films at relatively low temperatures while maintaining a high deposition rate, and how to make the atomic ratio of titanium and nitrogen close to 1:1, has become a direction that current magnetron sputtering technology urgently needs to break through. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention aims to provide a method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering, and the single-crystal TiN thin film itself. This method prepares single-crystal TiN thin films at relatively low temperatures and ensures that the atomic ratio of titanium to nitrogen is close to 1:1, thereby guaranteeing the barrier properties, conductivity, and mechanical properties of titanium nitride.

[0008] The technical solution of the present invention is as follows:

[0009] The first objective of this invention is to provide a method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering, which includes the following steps:

[0010] S1: The substrate is placed into the sputtering chamber of the magnetron sputtering equipment and a vacuum is drawn; then the substrate is heated to 400°C;

[0011] S2: Introduce activation gas into the sputtering chamber, select the pulsed DC magnetron sputtering mode, turn on the pulsed DC power supply to perform initial magnetron sputtering on the titanium target at the sputtering threshold, thereby forming an adhesion promotion layer on the substrate surface.

[0012] S3: After turning off the activation gas, introduce reactive sputtering gas into the sputtering chamber to make the gas pressure in the sputtering chamber 0.5-1.0 Pa;

[0013] S4: Increase the power of the pulsed DC power supply for high-intensity sputtering; at the same time, turn on the bias power supply connected to the sample stage supporting the substrate to provide bias voltage to the substrate and promote nitrogen reaction sputtering; the bias power supply is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply.

[0014] S5: Turn off the pulsed DC power supply and the nitrogen gas in the reactive sputtering gas, and continue magnetron sputtering on the substrate for 5-10 minutes;

[0015] S6: Repeat steps S4-S5 above 2-4 times;

[0016] S7: After magnetron sputtering, the temperature is cooled to room temperature to obtain a single-crystal TiN thin film.

[0017] In a further embodiment, in step S1, evacuation refers to reducing the background vacuum of the sputtering chamber to 5 × 10⁻⁶. -6 Below Pa.

[0018] In a further embodiment, in step S1, the substrate is a single-sided polished monocrystalline sapphire substrate. Heating the substrate to 400°C means simultaneously heating both sides of the substrate to 400°C and then continuing to heat for at least 10 minutes. The purpose is to use additional heating energy to drive the lateral migration of atoms on the substrate, promoting thin film crystallization; and to ensure uniform heating of the substrate, allowing surface moisture and other impurities to fully evaporate.

[0019] In a further embodiment, in step S2, the activation gas refers to a mixture of argon and nitrogen, wherein the flow rate ratio of argon to nitrogen is 50-80:1.

[0020] The activating gas in this application is mainly argon, with a small amount of nitrogen, and the specific flow ratio of argon to nitrogen is 50-80:1. The flow ratio of argon to nitrogen in the reactive sputtering gas is 2:1.

[0021] In a further embodiment, in step S2, the sputtering threshold refers to a sputtering power of 10-30W and a sputtering time of 20-40s for the initial magnetron sputtering.

[0022] This step uses a low-power pulsed DC power supply (i.e., sputtering threshold) to perform initial magnetron sputtering on the titanium target. At this time, only a very small number of low-energy Ti particles reach the substrate surface, which is insufficient to form a film. However, they can react slightly with oxygen atoms on the substrate surface or fill defect sites to form a "chemically bridged" atomic-level activated transition adhesion promotion layer to promote the adhesion between the TiN film and the substrate without destroying the substrate lattice.

[0023] In a further embodiment, in step S3, the reactive sputtering gas is a mixture of nitrogen and argon, wherein the flow rate ratio of argon to nitrogen is 2:1.

[0024] In a further embodiment, the frequency of the pulsed DC power supply is 70kHz and the duty cycle is 30%; and / or,

[0025] The high-intensity sputtering output power is 160W-200W and the time is 10-15min.

[0026] This application utilizes high power density pulsed DC sputtering (160W-200W) to promote increased N content and deposition rate in TiN films. Furthermore, using a high-output pulsed DC power supply enhances the initial kinetic energy of sputtered Ti atoms, enabling them to migrate laterally on the substrate and thus promoting the crystallization and growth of the film into a single crystal.

[0027] In a further embodiment, the output power of the bias power supply is 45-55W. Lower bias power can prevent damage to the substrate lattice.

[0028] In a further embodiment, the bias power supply in step S4 is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply. That is, when the pulsed DC power supply is in the ON phase for high-intensity sputtering, the bias power supply is in the OFF phase; when the pulsed DC power supply is in the OFF phase, the bias power supply is in the ON phase, which promotes atomic rearrangement and defect repair in the newly deposited film.

[0029] The second objective of this invention is to provide a single-crystal TiN thin film, which is prepared by the above method, wherein the TiN in the single-crystal TiN thin film has a face-centered cubic crystal structure.

[0030] In other words, the atomic ratio of titanium to nitrogen in the single-crystal TiN thin film prepared by this invention is close to 1:1, and the TiN in the single-crystal TiN thin film exhibits a face-centered cubic crystal structure. Therefore, the titanium nitride thin film has high crystal quality, ensuring its barrier properties, electrical conductivity, and mechanical properties.

[0031] In this application, a pulsed DC power supply is used for magnetron sputtering. First, an activation gas (primarily argon with a small amount of nitrogen, at a flow ratio of 50-80:1) and low power (i.e., sputtering threshold) are used to perform initial magnetron sputtering on the titanium target, thereby forming an adhesion-promoting layer on the substrate surface. A very small number of low-energy Ti particles reach the substrate surface, insufficient to form a film, but they can slightly react with oxygen atoms on the substrate surface or fill defect sites, forming a "chemically bridged" atomic-level activated transition adhesion-promoting layer. This promotes the adhesion between the TiN film and the substrate without damaging the substrate lattice. Then, high-intensity sputtering is performed using normal reactive sputtering gas (argon to nitrogen flow rate ratio of 2:1) at low pressure (i.e., sputtering chamber pressure of 0.5-1.0 Pa). The low pressure reduces the number of collisions between Ti atoms, increasing their deposition rate on the thin film. In magnetron sputtering, the average distance between two collisions during particle motion is the mean free path. The lower the pressure, the fewer the gas atoms, the fewer the number of particle collisions, and the larger the mean free path. Therefore, Ti atoms sputtered in a low sputtering pressure environment experience fewer collisions on their journey to the substrate, allowing more target particles to reach the substrate surface, thus increasing the thin film deposition rate. Furthermore, fewer collisions mean less energy loss due to collisions, resulting in sufficient kinetic energy for lateral migration upon reaching the substrate, which also promotes the crystallization and growth of the thin film into a single crystal.

[0032] In the field of magnetron sputtering, although radio frequency (RF) sputtering is commonly used to promote nitriding reactions and avoid target poisoning in the preparation of thin films such as nitrides and oxides, most of the output power of the RF power supply needs to be used to maintain the plasma, resulting in a low sputtering rate. Conventional DC power supply sputtering, after prolonged initiation in a nitrogen-containing atmosphere, is prone to target poisoning, leading to unstable deposition rates and thin film defects. However, this application uses a pulsed DC power supply, which can avoid target poisoning by adjusting the frequency and duty cycle of the pulsed DC power supply, while ensuring a high sputtering rate.

[0033] Since the output power of the DC power supply determines the plasma density, a high power density output promotes the ionization of N2 to generate nitrogen ions, which then react with Ti atoms to form TiN. Therefore, this application employs a high output power of 160W-200W to achieve an average power density of 8.8-10W / cm² on the target surface. 2 This high-power-density pulsed DC sputtering can promote the nitrogen content in TiN films. Simultaneously, the high power density output sputters more Ti atoms, thereby increasing the film deposition rate. Furthermore, using a high-output pulsed DC power supply can increase the initial kinetic energy of the sputtered Ti atoms, leading to higher atomic energy upon reaching the substrate. Sufficient kinetic energy allows for lateral migration, further promoting the crystallization and growth of the film into a single crystal.

[0034] In this application, the bias power supply is a pulsed DC power supply, which is connected to the sample stage supporting the substrate and provides a bias voltage to the substrate. The bias power supply in this application is a synchronous pulsed power supply that is inversely phase to the pulsed DC power supply. That is, this application actively mismatches and functionally complements the timing of substrate bias application with the target sputtering cycle. Its output pulse is inversely phase and synchronized with the output pulse of the sputtering power supply, so that a first bias voltage is applied during the first period of the sputtering pulse cycle, and a second bias voltage higher than the first bias voltage is applied during the second period of the sputtering pulse cycle. Specifically, when the pulsed DC power supply performs high-intensity sputtering during the pulse ON period, the bias power supply is in the OFF period, thus reducing excessive bombardment of the film growth interface and preventing high-energy argon and nitrogen ions from causing lattice damage or hindering the ordered arrangement of atoms during the critical nucleation stage.

[0035] When the pulsed DC power supply is in the OFF period, the bias power supply is in the ON period, meaning a high pulsed bias voltage is applied to perform "in-situ" gentle ion bombardment on the newly deposited film, promoting atomic rearrangement and defect repair in the newly deposited film. This involves using accelerated argon and nitrogen ions to selectively assist the newly deposited film surface with in-situ ionization. This assistance has three benefits: first, it provides energy to promote surface atomic migration, achieving "dynamic annealing" and repairing intrinsic defects; second, it enhances film density and fine-tunes internal stress; and third, it utilizes the nitrogen ion flow under high bias voltage to precisely compensate for nitrogen vacancies in the film, optimizing the stoichiometry.

[0036] This application divides the magnetron sputtering deposition process into 2-4 cycles, each cycle containing two stages: a normal sputtering period and an intermittent relaxation period. During the intermittent relaxation period, the pulsed DC power supply and N2 in the reactive sputtering gas are completely shut off, while only Ar gas, temperature, and bias power are maintained. No new material is deposited during this stage; only bias ion bombardment (from Ar) is utilized. + The energy and high-temperature thermal activation provided by the film drive the rearrangement, diffusion, and defect healing of atoms on the surface of the deposited film.

[0037] In summary, the single-crystal TiN thin film prepared by this invention has advantages such as good crystal quality and high efficiency, as detailed below:

[0038] Regarding crystal quality: This invention employs a double-sided heated substrate to ensure highly uniform and stable deposition interface temperature, providing an ideal thermal environment for ordered crystal growth and effectively suppressing lattice distortion and internal stress accumulation caused by temperature gradients. Simultaneously, high-power pulsed DC sputtering generates high-density, highly reactive plasma, significantly enhancing nitrogen ionization and reactivity, allowing titanium and nitrogen atoms to fully combine and promoting the formation of a TiN phase with a stoichiometric ratio approaching 1:1. Combined with the introduction of a substrate pulsed bias, moderate ion bombardment and energy injection are applied to the film growth surface, further enhancing the surface migration ability of deposited atoms and driving them to the lowest energy lattice sites. Therefore, the synergistic effect of these measures results in significantly improved film crystallinity, highly consistent crystal orientation, clear grain boundaries, and low defect density.

[0039] Regarding coating efficiency: High-power pulsed DC sputtering technology, with its high peak power characteristics, not only effectively avoids target poisoning and maintains long-term stability of the sputtering rate, but also significantly improves the sputtering yield and ionization rate of titanium atoms. Combined with the synergistic effect of argon in the reactive sputtering gas, the flux of film-forming particles reaching the substrate per unit time is significantly increased.

[0040] Furthermore, since the substrate temperature during film deposition in this application is only 400°C, energy consumption is low during subsequent cooling, and the overall process time is significantly reduced. Moreover, the titanium nitride thin film prepared in this application exhibits a high sputtering deposition rate of approximately 0.73-0.83 nm / min, with a titanium to nitrogen atomic ratio close to 1:1. Therefore, the titanium nitride thin film prepared in this application has high crystallinity, ensuring its barrier properties, conductivity, and mechanical properties.

[0041] Therefore, this invention employs a high-power, low-pressure pulsed DC sputtering method to prepare single-crystal TiN thin films. This not only increases the initial kinetic energy of Ti atoms and reduces collision losses during their drift, but also ensures that TiN particles have sufficient energy for lateral migration upon reaching the substrate, promoting crystal growth and ultimately forming a single-crystal thin film. Furthermore, it achieves a significant increase in deposition rate while maintaining excellent crystal quality, shortening the process cycle and demonstrating a balance between high quality and high efficiency. Compared to traditional single-crystal TiN thin film preparation processes, this method eliminates the need to apply temperatures exceeding 700°C to the substrate to provide energy for lateral migration and promote single-crystal growth, while simultaneously increasing the single-crystal thin film growth rate. Attached Figure Description

[0042] Figure 1 X-ray diffraction patterns of single-crystal TiN thin films prepared in Examples 1 and 2 and Comparative Examples 1-3;

[0043] Figure 2 The images show the surface morphology of the substrate after cutting the film layer and substrate of the single-crystal TiN thin film, where a is the surface morphology of the substrate after cutting the film layer and substrate of the single-crystal TiN thin film prepared in Example 1, and b is the surface morphology of the substrate after cutting the film layer and substrate of the single-crystal TiN thin film prepared in Comparative Example 4. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0045] In this implementation, the magnetron sputtering equipment selected is the MS-400 magnetron sputtering equipment manufactured by Hefei Zhizhen Precision, and the substrate is a single crystal sapphire substrate (material is Al2O3).

[0046] In this embodiment, the cathode of the magnetron sputtering equipment is equipped with a high-purity Ti target with a diameter of 2 inches and connected to a pulsed DC power supply. The sample stage used to support the substrate is connected to a bias power supply. The frequency of the pulsed DC power supply in the pulsed DC magnetron sputtering mode is 70kHz and the duty cycle is 30%. The output power of the bias power supply is 50W.

[0047] Example 1:

[0048] A method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering includes the following steps:

[0049] S1: A single-sided polished monocrystalline sapphire substrate is fed into the sputtering chamber of a magnetron sputtering equipment. A vacuum is then drawn to bring the background vacuum of the sputtering chamber to 4.5 × 10⁻⁶. -6 Pa; then the substrate is heated to 400°C on both sides simultaneously, and then heated for another 10 minutes.

[0050] In this embodiment, a dual-temperature zone heating plate can be used to improve the heating uniformity of the substrate, precisely controlling the substrate temperature to 400°C, with a heating temperature uniformity of <3% within a four-inch area of ​​the substrate. The purpose of heating the substrate is to promote the lateral migration of atoms on the substrate through additional heating energy, thereby promoting thin film crystallization. The purpose of continuous heating for at least 10 minutes is to ensure uniform heating of the substrate and sufficient evaporation of surface moisture and other impurities.

[0051] S2: Introduce activation gas into the sputtering chamber. The flow rate of argon in the activation gas is 40 sccm and the flow rate of nitrogen is 0.5 sccm (the flow rate ratio of argon to nitrogen is 80:1). Select the pulsed DC magnetron sputtering mode, turn on the pulsed DC power supply and perform initial magnetron sputtering on the titanium target for 30s at the sputtering threshold (sputtering power of 20W) to form an adhesion promotion layer on the substrate surface.

[0052] S3: After turning off the activation gas, introduce reactive sputtering gas into the sputtering chamber. The flow rate of argon in the reactive sputtering gas is 40 sccm and the flow rate of nitrogen is 20 sccm (the flow rate ratio of argon to nitrogen is 2:1), so that the gas pressure in the sputtering chamber is 0.5 Pa.

[0053] S4: Increase the power of the pulsed DC power supply to 200W and perform high-intensity sputtering for 10 minutes; at the same time, turn on the bias power supply connected to the sample stage carrying the substrate to provide bias voltage to the substrate and promote nitrogen reaction sputtering; the bias power supply is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply.

[0054] Specifically, when the pulsed DC power supply is in the ON phase of high-intensity sputtering, the bias power supply is in the OFF phase; when the pulsed DC power supply is in the OFF phase, the bias power supply is in the ON phase, which promotes atomic rearrangement and defect repair in the newly deposited film.

[0055] S5: Turn off the pulsed DC power supply and the nitrogen gas in the reactive sputtering gas, that is, keep the argon gas in the reactive sputtering gas, the substrate temperature and the bias power supply, and continue to sputter the substrate for 5 minutes.

[0056] S6: Repeat steps S4-S5 twice;

[0057] S8: After magnetron sputtering, the pulsed DC power supply, bias power supply, reactive sputtering gas and heating are turned off in sequence; and the temperature is lowered to room temperature to obtain a single-crystal TiN thin film.

[0058] In this embodiment, the activation gas and reactive sputtering gas are introduced in two ways: one is to connect the activation gas and reactive sputtering gas through different pipes and introduce them into the sputtering chamber of the magnetron sputtering equipment as required. The other is to introduce argon and nitrogen into the sputtering chamber of the magnetron sputtering equipment, and then control the different flow rates of argon and nitrogen to achieve different ratios of activation gas and reactive sputtering gas.

[0059] Both of the above methods are applicable to this invention, and the specific operation can be adapted and selected according to actual conditions.

[0060] In this embodiment, the high-power pulsed DC magnetron sputtering cycle is repeated twice, for a total of 30 minutes.

[0061] According to GB / T 36969-2018, the thickness of the titanium nitride thin film was measured using atomic force microscopy (AFM). The deposition rate (i.e., sputtering deposition rate) was then obtained by dividing the film thickness by the deposition time. In this embodiment, the thickness of the titanium nitride thin film is approximately 25 nm, and the sputtering deposition rate is approximately 0.83 nm / min, indicating a fast deposition rate.

[0062] Furthermore, X-ray diffraction testing of the prepared TiN thin film revealed that the center of its characteristic peak was located near the standard TiN (111) peak; X-ray photoelectron spectroscopy analysis showed that the atomic ratio of titanium to nitrogen was close to 1:1. This indicates that the titanium nitride thin film prepared in this embodiment has high crystallinity, ensuring its barrier properties, conductivity, and mechanical properties.

[0063] Example 2:

[0064] A method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering includes the following steps:

[0065] S1: A single-sided polished monocrystalline sapphire substrate is fed into the sputtering chamber of a magnetron sputtering equipment. A vacuum is then drawn to bring the background vacuum of the sputtering chamber to 4.5 × 10⁻⁶. -6 Pa; then the substrate is heated to 400°C on both sides simultaneously, and then heated for another 10 minutes.

[0066] S2: Introduce activation gas into the sputtering chamber. The flow rate of argon in the activation gas is 40.2 sccm and the flow rate of nitrogen is 0.67 sccm (the flow rate ratio of argon to nitrogen is 60:1). Select the pulsed DC magnetron sputtering mode, turn on the pulsed DC power supply and perform initial magnetron sputtering on the titanium target for 30s at the sputtering threshold (sputtering power is 15W) to form an adhesion promotion layer on the substrate surface.

[0067] S3: After turning off the activation gas, introduce reactive sputtering gas into the sputtering chamber. The flow rate of argon in the reactive sputtering gas is 40 sccm and the flow rate of nitrogen is 20 sccm (the flow rate ratio of argon to nitrogen is 2:1), so that the gas pressure in the sputtering chamber is 0.8 Pa.

[0068] S4: Increase the power of the pulsed DC power supply to 180W and perform high-intensity sputtering for 12 minutes; at the same time, turn on the bias power supply connected to the sample stage supporting the substrate to provide bias voltage to the substrate and promote nitrogen reaction sputtering; the bias power supply is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply.

[0069] Specifically, when the pulsed DC power supply is in the ON phase of high-intensity sputtering, the bias power supply is in the OFF phase; when the pulsed DC power supply is in the OFF phase, the bias power supply is in the ON phase, which promotes atomic rearrangement and defect repair in the newly deposited film.

[0070] S5: Completely turn off the pulsed DC power supply and the nitrogen gas in the reactive sputtering gas, that is, maintain the argon gas in the reactive sputtering gas, the substrate temperature and the bias power supply, and continue to perform magnetron sputtering on the substrate for 10 minutes.

[0071] S6: Repeat steps S4-S5 above 3 times;

[0072] S8: After magnetron sputtering, the pulsed DC power supply, bias power supply, reactive sputtering gas and heating are turned off in sequence; and the temperature is lowered to room temperature to obtain a single-crystal TiN thin film.

[0073] Example 3:

[0074] A method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering includes the following steps:

[0075] S1: A single-sided polished monocrystalline sapphire substrate is fed into the sputtering chamber of a magnetron sputtering equipment. A vacuum is then drawn to bring the background vacuum of the sputtering chamber to 4.5 × 10⁻⁶. -6 Below Pa; then heat both sides of the substrate to 400°C simultaneously, and continue heating for 15 minutes;

[0076] S2: Introduce activation gas into the sputtering chamber. The flow rate of argon in the activation gas is 40 sccm and the flow rate of nitrogen is 0.8 sccm (the flow rate ratio of argon to nitrogen is 50:1). Select the pulsed DC magnetron sputtering mode, turn on the pulsed DC power supply and perform initial magnetron sputtering on the titanium target for 30s at the sputtering threshold (sputtering power is 25W) to form an adhesion promotion layer on the substrate surface.

[0077] S3: After turning off the activation gas, introduce reactive sputtering gas into the sputtering chamber. The flow rate of argon in the reactive sputtering gas is 40 sccm and the flow rate of nitrogen is 20 sccm (the flow rate ratio of argon to nitrogen is 2:1), so that the gas pressure in the sputtering chamber is 1.0 Pa.

[0078] S4: Increase the power of the pulsed DC power supply to 170W and perform high-intensity sputtering for 15 minutes; at the same time, turn on the bias power supply connected to the sample stage supporting the substrate to provide bias voltage to the substrate and promote nitrogen reaction sputtering; the bias power supply is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply.

[0079] Specifically, when the pulsed DC power supply is in the ON phase of high-intensity sputtering, the bias power supply is in the OFF phase; when the pulsed DC power supply is in the OFF phase, the bias power supply is in the ON phase, which promotes atomic rearrangement and defect repair in the newly deposited film.

[0080] S5: Completely turn off the pulsed DC power supply and the nitrogen gas in the reactive sputtering gas, that is, maintain the argon gas in the reactive sputtering gas, the substrate temperature and the bias power supply, and continue to perform magnetron sputtering on the substrate for 8 minutes.

[0081] S6: Repeat steps S4-S5 above, 4 times;

[0082] S8: After magnetron sputtering, the pulsed DC power supply, bias power supply, reactive sputtering gas and heating are turned off in sequence; and the temperature is lowered to room temperature to obtain a single-crystal TiN thin film.

[0083] Example 4:

[0084] Same as Example 1, except that in step S4, the output power of the pulsed DC power supply is 160W.

[0085] Comparative Example 1:

[0086] Same as Example 1, except that in step S4, the output power of the pulsed DC power supply is 120W.

[0087] The titanium nitride thin film prepared in Comparative Example 1 was tested using the same method as in Example 1. Its film thickness was approximately 12.6 nm, and its sputtering deposition rate was approximately 0.42 nm / min, which was much slower than the 0.83 nm / min in Example 1.

[0088] The X-ray diffraction (XRD) patterns of the single-crystal TiN thin films prepared in Examples 1, 2 and Comparative Example 1 are as follows: Figure 1 As shown, where Figure 1 Al2O3 (0006) is the diffraction peak of the sapphire substrate.

[0089] from Figure 1As can be seen, with the increase of pulsed DC sputtering power, the intensity of the characteristic peaks of the TiN film gradually increases, and the center position of the characteristic peaks gradually moves closer to the standard peak TiN(111). Most importantly, when the pulsed DC sputtering power is 200W, oscillating fringe peaks appear on both sides of the diffraction peaks of the TiN film, namely thickness interference fringes (Kiessigfringes). This phenomenon reflects the high-quality crystalline phase and interface smoothness of the film.

[0090] The chemical states of Ti and N atoms in the prepared single-crystal TiN thin film were analyzed by X-ray photoelectron spectroscopy, and the atomic ratio in the single-crystal TiN thin film was determined by scanning electron microscopy and its attached energy dispersive spectrometer. The results are shown in Table 1.

[0091] As can be seen from Table 1, when the pulsed DC power is 120W, 180W and 200W respectively, the proportion of N atoms in the prepared TiN film is 30%, 48% and 53% respectively. This indicates that high power density output pulsed DC sputtering can promote N2 to participate in reactive sputtering and form a TiN film with a titanium to nitrogen atom ratio of close to 1:1.

[0092] Comparative Example 2:

[0093] Same as Example 1, except that there is no bias power supply in step S4.

[0094] X-ray photoelectron spectroscopy and SEM-EDS analysis were performed on the Ti and N atoms in the single-crystal TiN films prepared in Example 1 and Comparative Example 2 (as shown in Table 1). The results showed that the proportion of N atoms in the TiN film prepared in Comparative Example 2 was approximately 43%, significantly lower than that in Example 1 (53%) under the same bias voltage. This indicates that the lack of substrate bias guidance and energy injection resulted in insufficient ionization and activation efficiency of the reactive gas N2, and the low surface migration energy of titanium atoms reaching the substrate led to insufficient reaction and bonding between titanium and nitrogen atoms, making it difficult to form an ideal stoichiometric ratio.

[0095] Its X-ray diffraction pattern (XRD) is as follows Figure 1 As shown, the intensity of the characteristic diffraction peaks of the TiN thin film prepared in Comparative Example 2 is significantly weaker than that in Example 1, and the peak positions are shifted to higher angles, indicating an increase in interplanar spacing. This reflects poor film crystallinity and the possible presence of numerous nitrogen vacancies or lattice distortions. Most importantly, no obvious thickness interference fringes were observed on either side of the diffraction peaks. This phenomenon directly proves that without the assistance of a bias power supply, the interface flatness between the film and the substrate is low, and the internal crystallinity and density of the film are insufficient, making it impossible to form a high-quality, steep interface and a uniform film structure.

[0096] Comparative Example 3:

[0097] Same as Example 1, except that step S6 is omitted.

[0098] X-ray photoelectron spectroscopy and SEM-EDS analysis were performed on the Ti and N atoms in the single-crystal TiN films prepared in Example 1 and Comparative Example 3 (as shown in Table 1). The results showed that the proportion of N atoms in the film of Comparative Example 3 was approximately 46%, which was still lower than that in Example 1 (53%). This is because under continuous high-power sputtering, the target surface temperature increased and the poisoning trend intensified, resulting in a slow drift of the sputtering rate and plasma state, which affected the long-term stability of the reaction process.

[0099] Its X-ray diffraction pattern (XRD) is as follows Figure 1 As shown, the full width at half maximum (FWHM) of the diffraction peaks of the single-crystal TiN film prepared in Comparative Example 3 is significantly wider than that in Example 1, indicating that its grain size is smaller or its microstrain is larger. Although weak interference fringes can be observed, their oscillation amplitude is small and decays rapidly. This indicates that due to the lack of a periodic "relaxation" phase to allow for sufficient atomic rearrangement, defects accumulate continuously during the film deposition process, internal stress increases, leading to decreased crystal integrity and poor quality of the periodic structure at the interface and inside the film.

[0100] Comparative Example 4:

[0101] Same as Example 1, except that step S2 is omitted.

[0102] The single-crystal TiN films prepared in Example 1 and Comparative Example 4 were cut at the junction between the film and the substrate using a diamond pen. The substrate surface was damaged along the edge of the cut, and its surface morphology is as follows. Figure 2 As shown in the figure. It can be seen from the figure that, comparative example 4 (such as...) Figure 2 (as shown in b) Compared to Example 1 (as shown in b) Figure 2 The surface damage shown in Figure a is more severe, indicating that the adhesion between the film and the substrate is poor and there are more defects. However, in Example 1, a very small number of low-energy Ti particles are first deposited onto the substrate to form a "chemically bridged" atomic-level activation transition layer, i.e., an adhesion-promoting layer, which compensates for this.

[0103] Comparative Example 5:

[0104] Same as Example 1, except that the air pressure in the sputtering chamber is 5 Pa in step S3.

[0105] X-ray photoelectron spectroscopy and SEM-EDS analysis were performed on Ti and N atoms in single-crystal TiN films. The results showed that the proportion of N atoms in Comparative Example 5 film was approximately 37%, significantly lower than that in Example 1 (53%). This is because the gas molecule density in the sputtering chamber is too high, causing frequent collisions between Ti atoms and Ar / N2, resulting in rapid energy decay. When Ti atoms reach the substrate, their energy is low (<5 eV), significantly reducing surface diffusion and reactivity. The low-energy Ti atoms cannot effectively "capture" N, and a large amount of Ti exists in an elemental / substoichiometric state (Ti). x In the deposition of N (x>1), N is "displaced"; in addition, the ionization efficiency of N2 decreases, and more N2 exists in molecular state, making it difficult to react with Ti; the high-pressure film is loose, porous, and has many grain boundary defects, making it difficult for N to enter the crystal lattice to form stable TiN, and it exists more in interstitial / adsorbed state, which is easy to desorb, resulting in a lower measured N content.

[0106] Table 1

[0107]

[0108] As can be seen from Table 1, the sputtering deposition rate in the preparation method of this application is high, ranging from 0.73 to 0.83 nm / min, and the atomic ratio of titanium to nitrogen in the single-crystal TiN film is close to 1:1.

[0109] Furthermore, the substrate temperature during coating in this application is only 400°C, significantly lower than the existing 700°C. Therefore, the preparation method of this application consumes less energy and has a faster coating rate, greatly improving production efficiency. At the same time, the titanium nitride thin film prepared by this application has high crystal quality, ensuring its barrier properties, conductivity, and mechanical properties.

[0110] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering, characterized in that: Includes the following steps: S1: The substrate is placed into the sputtering chamber of the magnetron sputtering equipment and a vacuum is drawn; then the substrate is heated to 400°C; S2: Introduce activation gas into the sputtering chamber, select the pulsed DC magnetron sputtering mode, turn on the pulsed DC power supply to perform initial magnetron sputtering on the titanium target at the sputtering threshold, thereby forming an adhesion promotion layer on the substrate surface. S3: After turning off the activation gas, introduce reactive sputtering gas into the sputtering chamber to make the gas pressure in the sputtering chamber 0.5-1.0 Pa; S4: Increase the power of the pulsed DC power supply to perform high-intensity sputtering, the output power of the high-intensity sputtering is 160W-200W; at the same time, turn on the bias power supply connected to the sample stage carrying the substrate to provide bias voltage to the substrate and promote nitrogen reaction sputtering; wherein the bias power supply is a synchronous pulse power supply that is inversely phase to the pulsed DC power supply. S5: Turn off the pulsed DC power supply and the nitrogen gas in the reactive sputtering gas, and continue magnetron sputtering on the substrate for 5-10 minutes; S6: Repeat steps S4-S5 above 2-4 times; S7: After magnetron sputtering, the temperature is cooled to room temperature to obtain a single-crystal TiN thin film.

2. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: In step S1, evacuation refers to reducing the background vacuum of the sputtering chamber to 5 × 10⁻⁶. -6 Below Pa.

3. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: In step S1, the substrate is a single-sided polished monocrystalline sapphire substrate. Heating the substrate to 400°C means heating both sides of the substrate to 400°C simultaneously and then continuing to heat for at least 10 minutes.

4. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: In step S2, the activation gas refers to a mixture of argon and nitrogen, wherein the flow rate ratio of argon to nitrogen is 50-80:

1.

5. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: In step S2, the sputtering threshold refers to a sputtering power of 10-30W and a sputtering time of 20-40s for the initial magnetron sputtering.

6. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: In step S3, the reactive sputtering gas is a mixture of nitrogen and argon, wherein the flow rate ratio of argon to nitrogen is 2:

1.

7. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: The frequency of the pulsed DC power supply is 70kHz and the duty cycle is 30%; and / or, The high-intensity sputtering time is 10-15 minutes.

8. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: The output power of the bias power supply is 45-55W.

9. The method for preparing single-crystal TiN thin films based on pulsed DC magnetron sputtering according to claim 1, characterized in that: In step S4, when the pulsed DC power supply is in the pulse ON period for high-intensity sputtering, the bias power supply is in the OFF period; when the pulsed DC power supply is in the OFF period, the bias power supply is in the ON period, which promotes atomic rearrangement and defect repair in the newly deposited film.

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