The Radio-frequency Plasma Enhanced Chemical Vapor Deposition Of 3D Structure TiO₂ Thin-film By Pulse Modulation

After decades of research by experts and scholars, TiO₂, one kind of metallic oxide, has become an emerging class of material in the field of material applications.TIO₂ has many characteristics, For example, it has a special environment corrosion, good chemical stability, good biocompatibility, cheap and so on. It showed a good application prospect in the field of new energy, new materials, environment, medicine and other fields. TiO₂ can be used in hydrolysis of hydrogen production, air and water purification, photovoltaic energy conversion and so on.This article mainly starts with the pulse modulation technology, use the new plasma discharge characteristics which are discovered by pulse modulation techniques in recent year to generate stable plasma. Then construct the TiO₂ thin film with three dimensional space by the theory of dry etching chemical vapor phase deposition. The purpose of the experiment is manipulate the pulse modulation technology and transform the parameters of different kinds of deposition, then obtain the thin film which are different in optical properties and morphology. The three-dimensional-structure morphology of the thin film of TiO₂ can be obviously observed. The deposition parameters need to be contorlled mainly by include pressure, substrate temperature, upper and lower electrode distance, power, and pulse modulation duty cycle. Find the difference between parameters, compare various morphology difference and performance. Firstly, using the sedimentary system which designed for the industry and generate the plasma successfully. The plasma has the features of good stability, high strength, large scale uniform pulse modulation rf glow discharge.First of all,With the industrial design of the deposition system, the stability, high discharge intensity, large scale uniform pulse modulated RF glow discharge plasma.Next, we discussed the system of Ar/O₂/TiCl4 reactive plasma at 13.56 MHz in different power pressure, duty ratio, and the flow rates of O₂ and TiCl4 by measuring the discharge morphology, I/V curves and optical emission spectroscopy. It has shown that discharge morphology is uniform. The I/V curves show that the discharge current and voltage curve are similar to the sinusoidal curve, and the phase of the discharging current leads to that of the discharge voltage, which indicates the typical atmospheric dielectric barrier discharge characteristics of capacitive coupled glow. The peak value of the peak value of the current voltage curve at different pressure is compared. At the same time, under low pressure, the peak of the current peak is increased with the increase of the discharge power, while the peak value of the voltage is almost constant. Under constant power, the duty cycle of pulse modulation decreases, and the peak value of voltage is almost constant. After addition of TiCl4 gas, the typical OES intensities of Ar I（ 763 nm, 811 nm, 912 nm） and O I（ O 777 nm and O 844 nm） increased with the discharge power and then stabilized. With increasing the O₂ flow rate, the intensities of Ar I（ 763 nm, 811 nm, 912 nm） decreased and O I（ O 777 nm and O 844 nm） firstly increased and then stabilized. With TiCl4 flow increased to 0.2 sccm, the intensities of Ar I（ 763 nm, 811 nm, 912 nm） increased and reached the maximum value and O I（ O 777 nm and O 844 nm） decreased and tends to be stable. Therefore, discharge with higher power and optimized O₂ and TiCl4 flow ratio, is beneficial to the formation of stimulated atom Ar I and O I at high energy states and the chemical vapor deposition and crystallization of TiO₂ film.In the end, The effects of substrate temperature, electrode spacing, power, air pressure and pulse modulation on the morphology and crystallization of TiO₂ thin films were investigated. The formation mechanism of TiO₂ thin films with different morphologies and properties were discussed. The experimental results show that the pulse modulation technique can reduce the thermal accumulation effect caused by RF continuous discharge, and is suitable for the preparation of large area uniform TiO₂ thin films. When the distance between the discharge electrodes is reduced, the structure of the thin film is changed from the mesh structure to the three-dimensional sheet crystal structure. After the film is heated, the adhesion properties and crystallinity of the films are enhanced. Under atmospheric pressure, the RF power is improved, which effectively changes the morphology of TiO₂ thin film, and increases the specific surface area. High power at atmospheric pressure is helpful to the growth of large size crystals, but the uniformity of the crystal is poor, and the structure is loose. Although the TiO₂ crystal particles are small, the growth is even, the crystal rules are orderly and the structure is compact. Under low pressure, with the decrease of the duty ratio of the pulse modulation, the morphology of the thin film is changed, the crystal structure is tight, and the crystallinity is improved. It was found that the temperature of the heated substrate was helpful to the photocatalytic degradation of methylene blue solution.