1. Evaporation rate will effect on properties of evaporated coating
The evaporation rate has a great influence on the deposited film. Because the coating structure formed by low deposition rate is loose and easy to produce large particle deposition, it is very safe to choose a higher evaporation rate to ensure the compactness of the coating structure. When the pressure of residual gas in the vacuum chamber is constant, the bombardment rate of the substrate is a constant value. Therefore, the residual gas contained in the deposited film after selecting a higher deposition rate will be reduced, thus reducing the chemical reaction between the residual gas molecules and the evaporated film particles. Therefore, the purity of the deposited film can be improved. It should be noted that if the deposition rate is too fast, it may increase the internal stress of the film, it will increase of defects in the film, and even lead to the rupture of the film. In particular, in the process of reactive evaporation plating, in order to make the reaction gas fully react with the particles of the evaporation film material, you can select a lower deposition rate. Of course, different materials choose different evaporation rates. As a practical example– the deposition of the reflective film, If the film thickness is 600×10-8cm and the evaporation time is 3s, the reflectivity is 93%. However, if the evaporation rate is slowed down under the same thickness condition, it takes 10 minutes to complete the film deposition. At this time, the film thickness is the same. However, the reflectivity has dropped to 68%.
2. Subtrate temperature will effect on evaporation coating
The substrate temperature has a great influence on the evaporation coating. The residual gas molecules adsorbed on the substrate surface at high substrate temperature are easy to be removed. Especially the elimination of water vapor molecules is more important. Moreover, at higher temperatures, it is not only easy to promote the transformation from physical adsorption to chemical adsorption, thus increasing the binding force between particles. Moreover, it can also reduce the difference between the recrystallization temperature of vapor molecules and the substrate temperature, thus reducing or eliminating the internal stress on the film-based interface. In addition, because the substrate temperature is related to the crystalline state of the film, it is often easy to form amorphous or microcrystalline coatings under the condition of low substrate temperature or no heating. On the contrary, when the temperature is high, it is easy to form crystalline coating. Increasing the substrate temperature is also conducive to improving the mechanical properties of the coating. Of course, the substrate temperature should not be too high to prevent evaporation of the coating.
3. Residual gas pressure in vacuum chamber will effect on film properties
The pressure of residual gas in the vacuum chamber has a great influence on the performance of the membrane. The residual gas molecules with too high pressure are not only easy to collide with the evaporating particles, which will reduce the kinetic energy of the people on the substrate and affect the adhesion of the film. In addition, too high residual gas pressure will seriously affect the purity of the film and reduce the performance of the coating.
4. Evaporation temperature effect on evaporation coating
The effect of evaporation temperature on membrane performance is shown by the change of evaporation rate with temperature. When the evaporation temperature is high, the heat of vaporization will decrease. If the membrane material is evaporated above the evaporation temperature, even a slight change in temperature can cause a sharp change in the evaporation rate of the membrane material. Therefore, it is very important to control the evaporation temperature accurately during the deposition of the film to avoid large temperature gradient when the evaporation source is heated. For the film material that is easy to sublimate, it is also very important to select the material itself as the heater for evaporation and other measures.
5. Cleaning state of substrate and coating chamber will effect on coating performance
The effect of the cleanliness of the substrate and the coating chamber on the performance of the coating can not be ignored. It will not only seriously affect the purity of the deposited film, but also reduce the adhesion of the film. Therefore, the purification of the substrate, the cleaning treatment of the vacuum coating chamber and its related components (such as the substrate frame) and the surface degassing are all indispensable processes in the vacuum coating process.
Post time: Feb-28-2023