A method for heteroepitaxial growth of single crystal barium titanate thin films on silicon substrates

Abstract

The application provides a method for hetero-epitaxial monocrystalline barium titanate film on a silicon substrate, and belongs to the technical field of thin film material preparation. The method mainly utilizes a pulsed laser deposition technology, effectively inhibits the oxidation of the silicon substrate by maintaining an ultrahigh vacuum environment, and realizes the high-quality epitaxial growth of the monocrystalline barium titanate (00h) film on the silicon (100) substrate by combining the strontium titanate / titanium nitride hetero-buffer layer structure to accurately control the lattice mismatch. The method has the advantages of simple preparation process, controllable process cost, good repeatability and easy realization, and can complete in-situ growth in a single deposition chamber without post-processing operation.

Description

Technical Field

[0001] This invention belongs to the field of thin film material preparation technology, specifically relating to a method for heteroepitaxial production of single-crystal barium titanate thin films on silicon substrates. Background Technology

[0002] Barium titanate (BaTiO3), as a high-performance perovskite ferroelectric material, is an ideal candidate for integrated electro-optic modulators and ferroelectric memories. With the continuous advancement of new material design methods and microstructure control technologies, the innovative potential of two-dimensional barium titanate thin films in emerging technology fields is increasingly prominent. Compared to bulk materials, the performance of barium titanate thin films is not only determined by their intrinsic lattice response but also profoundly influenced by the significant interface effects, strain engineering, and defect states inherent in their low-dimensional morphology.

[0003] To achieve the integration of ferroelectric functionality with silicon (Si)-based semiconductor technology, the industry has long been committed to the epitaxial growth of high-quality single-crystal barium titanate thin films on silicon substrates. However, this process currently faces two fundamental technical bottlenecks. First, there is a significant intrinsic mismatch: the approximately 26.5% lattice mismatch between barium titanate and silicon introduces high-density dislocations and other crystal defects, severely impacting the crystallinity and stability of the film. Second, there are harmful interface reactions: in the high-temperature, oxygen-containing growth environment required for barium titanate thin films, the silicon substrate surface is easily oxidized to form an amorphous silicon oxide layer. This completely destroys the atomically ordered interface required for epitaxy and introduces numerous interface state defects, limiting the performance and reliability of the final device.

[0004] Therefore, there is an urgent need to develop a method that can effectively suppress interfacial reactions while precisely controlling and relaxing the intrinsic mismatch and stress state of barium titanate films, in order to obtain high-quality single-crystal barium titanate films and thus promote their application in high-performance silicon-based optoelectronic integrated devices. Summary of the Invention

[0005] In view of this, the present invention provides a method for heteroepitaxial production of single-crystal barium titanate thin films on silicon substrates. Compared with the prior art, the present invention solves the key problems of interface oxidation and stress accumulation on silicon substrates by heteroepitaxial production of a strontium titanate (SrTiO3) / titanium nitride (TiN) composite buffer layer under high vacuum conditions. The strontium titanate / titanium nitride composite structure can act as a buffer layer between the silicon substrate and the barium titanate thin film, reducing the original lattice mismatch from 26.5% to 2.28%, enabling the controllable fabrication of high-quality, low-defect-density single-crystal barium titanate thin films on silicon substrates.

[0006] To achieve the above objectives, the present invention provides a method for heteroepitaxially producing a single-crystal barium titanate thin film on a silicon substrate, the specific technical solution of which includes the following steps:

[0007] (1) The silicon substrate is acid-washed to remove surface oxides;

[0008] (2) Place the silicon substrate processed in step (1) into the growth chamber of pulsed laser deposition and evacuate the growth chamber to a vacuum state;

[0009] (3) Maintain the vacuum in the growth chamber and heat the silicon substrate from step (2) using a heating wire;

[0010] (4) Maintain the vacuum in the growth chamber and the temperature of the heating wire in step (3) and perform pulsed laser ablation on the titanium nitride and strontium titanate targets respectively;

[0011] (5) Maintain the heating wire temperature of step (4), raise the vacuum of the chamber to 1 Pa, and perform pulsed laser ablation on the barium titanate target;

[0012] (6) After the laser ablation is completed, the sample is cooled to room temperature at a rate of 10 °C per minute, the chamber is opened and the sample is taken out, and the growth of the single crystal barium titanate film is completed.

[0013] Preferably, the silicon substrate in step (1) is a (100) single crystal orientation.

[0014] Preferably, the vacuum state in step (2) is 10. -5 - 10 -4 Pa.

[0015] Preferably, the temperature of the heating wire in step (3) is 800 °C.

[0016] Preferably, the titanium nitride and strontium titanate targets used for ablation in step (4) have a purity of at least 99.99%.

[0017] Preferably, the purity of the barium titanate target used for ablation in step (5) is at least 99.99%.

[0018] Preferably, the barium titanate film in step (6) is a (00h) single crystal orientation.

[0019] The beneficial technical effects of this invention on heteroepitaxial single-crystal barium titanate thin films on silicon substrates are as follows:

[0020] In a pulsed laser deposition system, by maintaining an ultra-high vacuum environment to effectively suppress silicon substrate oxidation and by precisely controlling lattice mismatch using a strontium titanate / titanium nitride heterostructure buffer layer, high-quality epitaxial growth of single-crystal barium titanate (00h) films on silicon (100) substrates was achieved. This method has advantages such as simple preparation process, controllable process cost, good repeatability, and ease of implementation. In-situ growth can be completed in a single deposition chamber without post-processing. Attached Figure Description

[0021] Figure 1This is a schematic diagram of the epitaxial structure of a heteroepitaxial single-crystal barium titanate thin film on a silicon substrate according to the present invention;

[0022] Figure 2 This is the out-of-plane θ-2θ scan pattern of the heteroepitaxial single-crystal barium titanate thin film on a silicon substrate according to the present invention;

[0023] Figure 3 This is the in-plane φ scan pattern of the heteroepitaxial single-crystal barium titanate thin film on a silicon substrate according to the present invention;

[0024] Figure 4 This is an atomic force microscopy (AFM) scan of the surface morphology of a heteroepitaxial single-crystal barium titanate thin film on a silicon substrate according to the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] Example 1

[0027] The steps for preparing the single-crystal barium titanate thin film in this embodiment are as follows:

[0028] (1) The silicon substrate was ultrasonically cleaned with acetone, ethanol and deionized water in sequence to remove surface oil and impurities. The silicon surface oxide was removed by chemical method hydrofluoric acid etching solution to obtain a highly pure silicon substrate with atomic arrangement.

[0029] (2) Transfer the silicon substrate processed in step (1) into the growth chamber of the pulsed laser deposition system, maintaining a distance of 4.1 cm between the target and the silicon substrate, and evacuate the chamber to a base vacuum of 10. -5 - 10 -4The silicon substrate was heated to 800 °C at a rate of 10 °C per minute. A laser energy of 300 mJ was used to ablate the titanium nitride target at a frequency of 4 Hz for 20 minutes, yielding a 60 nm thick titanium nitride film. Next, maintaining the base vacuum and 800 °C, the strontium titanate target was ablated at a laser energy of 200 mJ at a frequency of 4 Hz for 20 minutes, yielding a 90 nm thick strontium titanate film. Subsequently, the chamber vacuum was reduced to 1 Pa, the silicon substrate temperature was maintained at 800 °C, and the barium titanate target was ablated at a laser energy of 200 mJ at a frequency of 5 Hz for 30 minutes, yielding a 200 nm thick barium titanate film. Finally, the chamber was evacuated to base vacuum, the sample was cooled to room temperature at a rate of 10 °C per minute, the chamber was opened, and the sample was removed, completing the growth of the single-crystal barium titanate film.

[0030] The structure of the heteroepitaxial single-crystal barium titanate thin film on a silicon substrate according to the present invention is as follows: Figure 1 As shown, a heteroepitaxial structure is formed by a silicon substrate, a strontium titanate / titanium nitride heterocomposite structure (a domain matching layer of titanium nitride thin film and a buffer layer of strontium titanate thin film), and a barium titanate thin film.

[0031] like Figure 2 As shown, XRD out-of-plane θ-2θ scanning was performed on a heteroepitaxial single-crystal barium titanate film on a silicon substrate to obtain its phase characterization results in the range of 2θ from 10 to 60°. The spectrum shows a single barium titanate (00h) peak with extremely high peak value, which proves the single-crystal nature of the barium titanate film and its high crystal density.

[0032] like Figure 3 As shown, φ-scans were performed on silicon (220) and barium titanate (202) to obtain their in-plane orientation patterns from 0 to 360°. The results show that silicon (220) and barium titanate (202) strictly follow the pattern of generating a peak every 90° within the in-plane range of 360°, and the peak positions correspond one-to-one, proving that the barium titanate (002) thin film achieves good single-crystal epitaxial characteristics on the silicon (200) substrate.

[0033] like Figure 4 As shown, the monocrystalline barium titanate thin film heteroepitaxially grown on a silicon substrate was characterized by AFM. The results show that the barium titanate film exhibits a layered crystalline distribution on its surface, and its root mean square surface roughness is only 1.76 nm, demonstrating that the barium titanate film has good surface smoothness.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for heteroepitaxially producing a single-crystal barium titanate thin film on a silicon substrate, characterized in that, The method includes the following steps: (1) The silicon substrate is acid-washed to remove surface oxides; (2) Place the silicon substrate processed in step (1) into the growth chamber of pulsed laser deposition and evacuate the growth chamber to a vacuum state; (3) Maintain the vacuum in the growth chamber and heat the silicon substrate from step (2) using a heating wire; (4) Maintain the vacuum in the growth chamber and the temperature of the heating wire in step (3) and perform pulsed laser ablation on the titanium nitride and strontium titanate targets respectively; (5) Maintain the heating wire temperature of step (4), raise the vacuum of the chamber to 1 Pa, and perform pulsed laser ablation on the barium titanate target; (6) After the laser ablation is completed, the sample is cooled to room temperature at a rate of 10 °C per minute, the chamber is opened and the sample is taken out, and the growth of the single crystal barium titanate film is completed.

2. The method according to claim 1, characterized in that, The silicon substrate mentioned in step (1) is a (100) single crystal orientation.

3. The method according to claim 1, characterized in that, The vacuum state described in step (2) is 10. -5 - 10 -4 Pa.

4. The method according to claim 1, characterized in that, The temperature of the heating wire in step (3) is 800 °C.

5. The method according to claim 1, characterized in that, The titanium nitride and strontium titanate targets used in step (4) for ablation have a purity of at least 99.99%.

6. The method according to claim 1, characterized in that, The purity of the barium titanate target used for ablation in step (5) is at least 99.99%.

7. The method according to claim 1, characterized in that, The barium titanate film in step (6) is a (00h) single crystal orientation.

Images