The key to the quality of the film layer is the stress of the film layer, the uniformity of the film thickness and the reflectivity of the film layer.
Factors Affecting Film Stress
Different materials have different coefficients of thermal expansion. The smaller the difference between the coefficient of thermal expansion of the film material and the coating, the smaller the stress of the film due to temperature changes. The better the toughness of the metal or alloy, the smaller the stress of the deposited film. .
The stress of the film layer decreases with the increase of the vacuum degree. When the partial pressure of argon gas is lower than 0.13Pa during sputtering, the film layer generally does not produce stress.
If the incident angle between the sputtered particles and the coating is less than 15°, stress cracks will not occur. When the incident angle is greater than 15°, the stress cracks of the film will increase with the increase of the angle.
The heating of the plated parts is one of the main reasons for the occurrence of stress cracks. Therefore, the temperature of the plated parts is generally controlled below the critical temperature for cracks.
Factors Affecting Uniformity of Coating Thickness
If the sputtering of the magnetron source on the entire target surface is uneven, it will lead to uneven film thickness. Therefore, when designing the magnetron source, rationally arrange the magnet structure so that the magnetic field strength at the side or at both ends is greater than the magnetic field strength in the middle, and the film can be improved.
thick distribution. The plated parts have various movement modes relative to the magnetron source, which should be determined according to the shape of the magnetron source. The movement mode of the planetary mechanism has uniform film formation, good step coverage performance, and large loading capacity of the plated parts. It is the most commonly used movement mode. Select the relative position between the magnetron source and the plated piece, let the plated piece move, so that the probability of each surface being sputtered is equal.
Factors Affecting the Reflectivity of Coatings
Generally, the larger the sputtering rate, the higher the reflectivity of the obtained film layer, but the relationship between reflectivity and sputtering rate of different metal film layers is different, and a good sputtering rate should be determined through experiments. The lower the surface roughness of the coating, the greater the reflectivity of the coating, and vice versa. The reflectivity of the film layer decreases with the increase of the film thickness, and the degree of influence is not the same for different metal materials. Generally, the reflectivity of the film layer decreases sharply with the increase of argon pressure, so the partial pressure of argon should be controlled within the range of 0.40~0.53Pa.
