Titanium Dioxide (TiO2)
Titanium Dioxide (TiO2) (sometimes called as titania) is a metal oxide material. This material has wide bangdap and high refractive index. Depending on its crystallographic formation, it is called as anatase, tutile or brookite. These crystallographic conditions influence material properties such as refractive index, and they also differentiate potential applications of this material.
• 2.488 (anatase)
• 2.583 (brookite)
• 2.609 (rutile)
Applications of TiO2
One of the most famous applications of TiO2 is photocatalyst. Water molecules are decomposed when TiO2 is exposed to ultraviolet (UV) light. This effect is called as the the Honda-Fujishima effect, and this photocatalytic decomposition reaction is currently used for various applications of film coating such as self-cleaning roof.
Another interesting application is optical coating. TiO2 film has high refractive index and shows low optical absorption in visible and new-infrared spectrum; therefore, this film is suitable for anti-reflective coating (ARC) of silicon solar cells, sensors and microelectronic devices. In order to enhance anti-reflecting effect in broad band, multi layer stack deposition of TiO2 (high refractive index) and SiO2 (low refractive index) has been investigated by researchers.
Deposition methods of TiO2 films
There are several methods (wet or dry processes) to deposit TiO2 films. One of the popular methods in wet processes is sol-gel method. This deposition method is mainly used for coating of large substrates, and it is less expensive compared to other deposition methods. Dry processes include Chemical Vapor Deposition (CVD), sputtering, Elecron Beam (EB) evaporation, Atomic Layer Deposition (ALD) and Plasma Enhanced Chemical Vapor Deposition (PECVD). These dry processes have advantages over wet processes in film quality control such as grain size. Among these dry processes, PECVD technology shows unique process features such as low-temperature process capabilities (below 300°C). The low-temperature PECVD process can mitigate thermal budget limitation in device fabrication and expand potential applications of TiO2 films.
Refractive Index Control of PECVD TiO2 Films
Samco has provided TiO2 deposition processes using experienced PECVD technologies to various R&D labs for optical device fabrication. A wide range of refractive index control was achieved from 1.49 to 2.27 with adjustment of precursor flow ratio. For this deposition process, several gases were used: Precursor X which provides Ti, Tetraethyl Orthosilicate (TEOS) which provides Si, and a gas which has oxidation effect in deposition process. In this process, deposition rate of TiO2 was also subject to precursor flow ratio.
Precursor Flow Ratio v.s. Refractive Index
Precursor Flow Ratio v.s. Deposition Rate
Stress Control of TiO2 Films Deposited by Low-temperature PECVD
Samco offers process solutions of low-temperature TiO2 PECVD technologies as low as 80°C. This TiO2 film deposition processes show excellent process control for many applications. For example, film stress was controlled to almost zero at state temperature of 80°C with precursor flow ratio adjustment.
Precursor Flow Ratio v.s. Film Stress
For more details of our low-temperature PECVD process capabilities, please visit the page below.
Low-temperature PECVD to Mitigate Thermal Budget Issues