Patent Application
20100075510
1. Field of Invention
The present invention relates to a method for pulsed plasma deposition of titanium dioxide film, especially to a method for deposition of titanium dioxide film by means of pulsed plasma that is applied to various fields such as microelectronic materials and photocatalytic materials.
2. Description of Related Art
Generally, titanium dioxide (TiO2) film is used as optical multi-layer film due to its high refractive index within visible light range. The refractive index is over 2.3. Moreover, the TiO2 features on high dielectric constant, chemical stability, thermal stability and semiconductor characteristic so that it is applied to microelectronic and photocatalytic materials. A common way for deposition of titanium dioxide film is Physical Vapor Deposition (PVD), such as electron-beam evaporation and magnetron sputtering. In the PVD method, the average energy per deposited atom is quite low so that additional energy is required while depositing. For example, an-ion beam for Ion Beam Assisted Deposition is applied, the temperature of the substrate is increased, or post-deposition annealing is employed. However, these ways can not be applied to plastic substrate.
Plasma Enhanced Chemical Vapor Deposition (PECVD) uses electrical energy to create a glow discharge in which gas molecules are ionized into reactive free radicals and high energy ions so that temperature for depositing thin films is effectively reduced. While depositing TiO2 films by PECVD, a common precursor is titanium tetraisopropoxide (TTIP) that is an organic compound containing titanium and is liquid at room temperature. In use, the TTIP is heated to form vapor and set in an oxygen atmosphere. The mixture of TTIP and oxygen is introduced into a vacuum chamber. The plasma is generated by direct current (DC) discharge or radio frequency (RF) and is deposited on a substrate. For example, refer to Nakamura etc., J. Mater. Res., 16(2), 621-626(2001), oxygen gas is introduced into a Multi-jet plasma source to create oxygen plasma reacting with TTIP for forming a titanium dioxide film on a substrate surface. In order to make oxygen ions react completely with TTIP, the substrate temperature is as high as 300 degrees Celsius. As a prior art disclosed in Cruz etc., Surf. Coat. Technol., 126(2-3): 123-130(2000), plasma of TTIP and oxygen/argon is created by RF(13.56 MHz). A substrate is set beside grounded electrodes and ions are directed into the substrate by DC (direct current) bias voltage. Due to applying of the bias voltage, the substrate should be a conductor.
Refer to conventional techniques available, there is no one related to pulsed plasma deposition of TiO2 film. Moreover, the substrate used in traditional techniques requires heat resistance and conductivity. Thus there is a need to provide a method for pulsed plasma deposition of titanium dioxide film in which the TiO2 film is deposited on a substrate such as plastic substrate at low temperature for removal of the heat-resistant and conductive requirements of the substrate.
Therefore it is a primary object of the present invention to provide a method for pulsed plasma deposition of titanium dioxide film in which the TiO2 film is deposited on a substrate such as plastic substrate at low temperature so that the heat-resistant and conductive requirements of the substrate are removed.
It is another object of the present invention to provide a method for pulsed plasma deposition of titanium dioxide film that deposits the TiO2 film on a substrate by pulsed plasma. This is a novel deposition way of titanium dioxide film.
In order to achieve above objects, the present invention provide a method for pulsed plasma deposition of titanium dioxide film formed by following steps. Firstly, set a substrate into a chamber and the chamber is pumped down to a certain vacuum level. Then introduce titanium tetraisopropoxide gas and gas containing oxygen into the chamber and a RF (radio frequency) pulse power supply is turned on to create a glow discharge for generating pulsed plasma. Thus a layer of titanium dioxide film is deposited on the substrate by the pulsed plasma.
The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed descriptions of the preferred embodiments and the accompanying drawings, wherein
Refer to
A method for pulsed plasma deposition of titanium dioxide film according to the present invention includes the following steps, as shown in
The vacuum is under 10−3 torr. The substrate holder 12 and the negative electrode 13 are cooled down by introduction of cooling water for absorbing heat energy from plasma discharge. Thus the temperature of the substrate 2 (can be a plastic substrate) is decreased. The titanium tetraisopropoxide gas mixed with argon gas and the gas containing oxygen can be introduced into the chamber 11 respectively by the gas pipeline 18 and the gas pipeline 19, or mixed with each other outside the chamber 11 and then being introduced into the chamber 11. As to the pneumatic control valve 16, it is used to maintain air pressure at 10−3˜10−1 torr. Then the RF (radio frequency) pulse power supply 15 is turned on for providing alternating current. Through impedance modification of the impedance-matcher 14, a pulsed plasma is generated. Working frequency of the RF pulse power supply 15 ranges from 1 MHz-100 MHz, pulse frequency is from 1 Hz to 3 K Hz, and pulse duty cycle is 1%-60%. By means of the pulsed plasma, the TiO2 film is deposited on surface of the substrate. The power supply is not turned off until the required thickness of the film is achieved. The gas containing oxygen is selected from one of the followings: oxygen (O2), nitrous oxide (N2O) and carbon dioxide (CO2). The substrate 2 is set inside a plasma glow region or an afterglow region of the pulsed plasma. The TTIP is introduced into the plasma glow region or the afterglow region.
Refer to
The plasma source in this embodiment is permanent magnet helicon plasma source, referred to F. F. Chen and H. Torreblanca, Plasma Phys. Control. Fusion. 49, A81-A93 (2007) for related details. As shown in
The process in this embodiment includes following steps:
Set a silicon wafer 2b on a stage 12b of the diffusion chamber 11b and the diffusion chamber 11b is pumped down to vacuum. The stage 12b is introduced with cold water for cooling down. After achieving the required vacuum level (<10−3 torr), N2O of 80 sccm is introduced through a pipeline 18b into the quartz glass tube 111b of the diffusion chamber 11b. Then turn on the RF pulse power supply 15b to generated oxygen pulsed plasma diffused into the diffusion chamber 11b. The mixture of TTIP and carrier gas Ar is introduced into a gas distribution ring 4b in the diffusion chamber 11b through a pipeline 19b and is reacting with oxygen pulsed plasma to generate pulsed plasma for depositing TiO2 film on the silicon wafer 2b. The operation parameters in this embodiment are shown in table 2. After the film achieving required thickness, the power supply is turned off. The silicon wafer 2 is taken out and optical parameters of the deposited TiO2 film are measured. The results are shown in table 2.
In summary, the present invention provides a method for pulsed plasma deposition of titanium dioxide film in which the TiO2 film is deposited on a substrate such as plastic substrate at low temperature so that the substrate doesn't require have heat-resistance and conductivity.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative apparatus shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
