Details and optimization of titanium nitride magnetron sputtering process
In the implementation of titanium nitride magnetron sputtering technology, the optimization of process details directly affects the performance and application effect of the film. This article will discuss in detail the four key links of target preparation and selection, film growth mechanism, deposition parameter optimization, and film quality and uniformity control, and gradually analyze their role in the entire process and its optimization strategy.
Titanium Nitride Structure
1. Target preparation and selection
1.1 Preparation technology of high-purity Ti target
In the magnetron sputtering process, the purity and quality of the titanium target directly determine the performance of the final titanium nitride film. The preparation of a high-purity titanium target includes multiple steps, mainly including vacuum melting, electron beam melting, cold rolling and annealing. Through these processes, impurities can be effectively removed, and the purity of the titanium target can be improved.
Vacuum melting: Titanium is initially melted in a vacuum environment to remove low-boiling impurities. This step ensures the initial purification of the titanium material.
Electron beam melting: Titanium is melted multiple times using a high-energy electron beam to effectively remove gas impurities such as oxygen, hydrogen, and nitrogen in titanium. This process is usually carried out under high vacuum conditions, which can further improve the purity of titanium to more than 99.9%.
Cold rolling and annealing: The smelted titanium material is cold rolled to form the final shape and size of the target. Subsequently, annealing can reduce the stress inside the material, improve the uniformity of the grains, and provide stable target performance during magnetron sputtering.
The preparation of high-purity titanium targets not only affects the stability of the target during sputtering but also has a direct impact on the chemical purity and structural uniformity of the film. Therefore, when selecting titanium targets, in addition to paying attention to purity, the microstructure and mechanical properties of the target need to be considered to ensure its stability during long-term sputtering.
1.2 Selection of Ti target and different nitrogen mixing ratios and their effects on TiN formation
In the deposition process of titanium nitride film, the interaction between nitrogen flow and titanium target is the key factor in the formation of ideal TiN film. Different nitrogen flow rates affect the stoichiometric ratio of sputtered particles, deposition rate and final structure of the film.
Control of nitrogen flow rate: Nitrogen is used as a reaction gas to react with the sputtered titanium atoms to form TiN. At a low nitrogen flow rate, the reaction between titanium atoms and nitrogen is not sufficient, which may lead to the formation of non-stoichiometric TiNx (x<1) films, which usually exhibit high resistivity and poor mechanical properties. With the increase of nitrogen flow rate, the reaction is more complete, and the generated TiN film gradually tends to the stoichiometric ratio of 1:1, and the conductivity and wear resistance of the film are significantly improved.
Effect of excessive nitrogen: Although increasing the nitrogen flow rate can increase the generation ratio of TiN, excessive nitrogen may cause supersaturation of nitrogen in the film and produce excessive internal stress. Excessive stress not only affects the mechanical properties of the film but may also cause the film to peel or crack. Therefore, in the actual process, the nitrogen flow rate needs to be precisely controlled, and the optimal flow rate ratio is usually found through experimental adjustment to balance the generation of TiN and the internal stress of the film.
By reasonably selecting the purity of the titanium target and the flow ratio of nitrogen, the composition and structure of the TiN film can be effectively controlled, thereby obtaining a film with excellent performance.
TRUNNANO Titanium Nitride
2. Growth mechanism of titanium nitride film
2.1 Mechanism of atoms and molecules in nucleation and growth
The formation of TiN film is a complex physical and chemical process, which mainly includes the sputtering of titanium atoms, the dissociation of nitrogen molecules, and the nucleation and growth of TiN. During the magnetron sputtering process, the sputtered titanium atoms and nitrogen molecules meet and react chemically on the substrate surface to generate the initial crystal nuclei of TiN. Subsequently, these crystal nuclei gradually grow to form a continuous film.
Nucleation process: Titanium atoms migrate on the substrate surface and combine with nitrogen atoms to form crystal nuclei. The efficiency of nucleation depends on the energy of the sputtered particles and the surface state of the substrate. High-energy sputtered particles can produce more active sites on the substrate surface, which helps the rapid formation of crystal nuclei.
Growth process: After the crystal nucleus is formed, the sputtered titanium and nitrogen molecules will attach and expand around the crystal nucleus, causing the crystal nucleus to increase and form a thin film gradually. In the growth process, the substrate temperature plays a key role. Appropriate substrate temperature can promote the surface diffusion of atoms and make the film structure more dense and orderly.
2.2 Formation path of nitride and control of its crystal orien tation during sputtering
The crystal structure of TiN film is usually face-centered cubic (FCC), and its formation path is significantly affected by deposition parameters. During the deposition process, the formation path of TiN can be adjusted by controlling parameters such as nitrogen flow rate, sputtering power and substrate temperature to optimize the crystal orien tation of the film.
(111) and (200) crystal orien tations: In TiN films, (111) and (200) are two common crystal orien tations. Generally, (111)-orien ted TiN films show higher hardness and better wear resistance, while (200)-orien ted films have better conductivity. The formation of a specific crystal orien tation can be promoted by adjusting the substrate temperature and sputtering power. For example, high substrate temperature and high sputtering power are conducive to the formation of the (111) orien tation, while a low nitrogen flow rate may help to enhance the (200) orien tation.
The control mechanism of crystal orien tation: The control of crystal orien tation involves the diffusion and arrangement of atoms during the growth of the film. By precisely controlling the deposition conditions, the atomic arrangement in the TiN film can be ordered, thereby obtaining a film with a specific orien tation. This can not only improve the mechanical properties of the film but also improve its electrical and optical properties.
By understanding and controlling the nucleation and growth mechanism of TiN films, the performance of the film can be customized in different applications to meet specific functional requirements.
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