Brief introduction of vacuum coating and its requirement for the material of steam source

 Technology for producing thin film materials by vacuum coating. In the vacuum chamber material atoms from the heating source by separating the hit objects on the surface to be plated. The technology is used for producing aluminum coating on laser disc (CD) and coating metal film on printed circuit board.

Vacuum coating in the source of the material requirements of the steam?

The material and shape of evaporation source should be taken into account in general, and the requirement for the material of steam source is:

(1) high melting point. Because the evaporation temperature (the temperature of the vapor pressure of 1.3Pa) is mostly between 1000~2000 and C, the melting point of the evaporation source material should be higher than that of the temperature.

(2) equilibrium vapor pressure. This is mainly to prevent or reduce the high temperature evaporation of the source material with the evaporation of the material evaporated and become impurities, into the vapor deposition layer. Only in the steamed source material balance pressure is low enough to ensure with minimal self evaporation, not only affect the system vacuum degree and the pollution layer, in order to make steamed vaporized by the source material in very small amounts, in the evaporation temperature, evaporation source material, should make less than the vapor source material in air pressure balance for 1.3 x 10-6Pa the evaporation temperature of the material of the preparation of high quality films can be with 1.3 * 10-3pa corresponding to the temperature during evaporation.

(3) the chemical properties are stable, and the chemical reaction should not be occurred at high temperature. The reaction and diffusion between the material and the evaporating material at high temperature can produce the reaction and diffusion between the material and the alloy. In particular, the formation of low melting point alloy evaporation source is easy to burn off. For example, when the coating machine at high temperature, tantalum and gold will form alloy, aluminum, iron, nickel, cobalt and tungsten, molybdenum, tantalum and other evaporation source material forming alloy. Tungsten can react with water or oxygen to form volatile oxides such as WO2, WO or WO3; molybdenum can react with water or oxygen to form a volatile MoO3, etc.. Therefore, it should be chosen not to react with the coating material or to form an alloy material.

As the source of evaporation, the material must have high melting point, low volatility, high temperature cooling after the brittleness of small and so on. The usual linear evaporation source should be able to be wetted with the evaporating metal. The melting point is much larger than the evaporation temperature of the metal to be deposited, and the alloy is not formed with the reaction of the metal to be plated.