Baking and degassing in ultra-high vacuum system (2)

    In addition to the high temperature baking required in the vacuum chamber, commonly used ultra-high vacuum pumps, such as turbomolecular pumps, sputter ion pumps, titanium sublimation pumps, cryogenic pumps, etc., should also bake the pump itself at the allowable temperature. After the ultra-high vacuum gauge is baked, the measurement can be more accurate, otherwise the outgassing of the material in the gauge will cause a large error in the measurement. In surface research and certain production processes, it is required to thoroughly bake the test piece (workpiece) and the support to obtain a "clean and fresh" substrate surface.

    The baking temperature is usually determined according to factors such as the maximum temperature allowed by the baked material and the ultimate pressure of the system. Electronic tubes, bulbs and various static systems must be thoroughly baked before being sealed off. The baking temperature is generally not lower than the maximum temperature of the tube during normal operation.

    The baking temperature range of the dynamic metal ultra-high system is 150~450℃ (the highest baking temperature is about 800℃), which can be selected according to the maximum baking temperature allowed by the system materials. When using a lower baking temperature of 150°C, it is necessary to extend the baking time appropriately to make up for the lack of baking temperature. The baking should be carried out under a pressure of 10^-3~10^-4Pa. The main component of the gas out of the baking is water, and the final gas component is hydrogen. The actual situation may be much more complicated.

    In addition to the outgassing of materials, the leakage of the atmosphere is an important factor that cannot be ignored. After repeated baking, contaminants on the surface of the metal gasket and temperature changes may increase the unevenness of the metal seal, and many small leaks will appear. If the container is connected with a thin-walled corrugated pipe, the leakage of nitrogen during high-temperature baking will also affect the residual gas composition of the ultra-high vacuum system.

(Huiputech)