CVD technology is based on chemical reaction. The reaction in which the reactants are in gaseous state and one of the products is in solid state is usually referred to as CVD reaction, therefore its chemical reaction system must fulfill the following three conditions.
(1) At the deposition temperature, the reactants must have a sufficiently high vapor pressure. If the reactants are all gaseous at room temperature, the deposition device is relatively simple, if the reactants are volatile at room temperature is very small, it needs to be heated to make it volatile, and sometimes need to use the carrier gas to bring it to the reaction chamber.
(2) Of the reaction products, all substances must be in the gaseous state except for the desired deposit, which is in the solid state.
(3) The vapor pressure of the deposited film should be low enough to ensure that the deposited film is firmly attached to a substrate having a certain deposition temperature during the deposition reaction. The vapor pressure of the substrate material at the deposition temperature must also be low enough.
The deposition reactants are divided into the following three main states.
(1) Gaseous state. Source materials that are gaseous at room temperature, such as methane, carbon dioxide, ammonia, chlorine, etc., which are most conducive to chemical vapor deposition, and for which the flow rate is easily regulated.
(2) Liquid. Some reaction substances at room temperature or slightly higher temperature, there is a high vapor pressure, such as TiCI4, SiCl4, CH3SiCl3, etc., can be used to carry the gas (such as H2, N2, Ar) flow through the surface of the liquid or the liquid inside the bubble, and then carry the saturated vapors of the substance into the studio.
(3) Solid state. In the absence of a suitable gaseous or liquid source, only solid-state feedstocks can be used. Some elements or their compounds in hundreds of degrees have considerable vapor pressure, such as TaCl5, Nbcl5, ZrCl4, etc., can be carried into the studio using the carrier gas deposited into the film layer.
The more common situation type through a certain gas and the source material gas-solid or gas-liquid reaction, the formation of appropriate gaseous components to the studio delivery. For example, HCl gas and metal Ga react to form gaseous component GaCl, which is transported to the studio in the form of GaCl.
–This article is released by vacuum coating machine manufacturer Guangdong Zhenhua
Post time: Nov-16-2023