The cryo pump is a vacuum pump that utilizes cryogenic surface condensing gas, also known as a condensing pump. The cryopump can obtain a clean vacuum with the highest pumping rate and the lowest ultimate pressure. It is widely used in the research and production of semiconductors and integrated circuits, as well as molecular beam research, vacuum coating equipment, vacuum surface analysis instruments, ion implanters and space simulation devices.
Cryogenic pumps are divided into injection liquid helium cryopumps and closed-cycle gas helium refrigerator cryopumps.
Injected liquid helium cryopump
It is mainly composed of a liquid helium container, a pump body, and a liquid nitrogen cavity connected to the baffle. In order to reduce the consumption of liquid helium, the outer wall of the liquid helium container uses a double insulation wall and a vacuum is drawn in between. When the pump is pre-pumped to a pressure of -6 Pa, liquid nitrogen and liquid helium are filled, and the gas condenses on a 4.2K working cold plate. The partial pressure of helium and hydrogen is pre-pumped to the order of -12 Pa, so the pump can obtain the ultimate pressure below -11 Pa. If the liquid helium container is evacuated to 6650 Pa and the temperature of the liquid helium can be reduced to 2.3K, a lower ultimate pressure can be obtained.
Closed-cycle gas helium refrigerator cryopump
It is a new type of cryopump that appeared in the 1970s. This pump does not consume helium, is easy to operate, easy to maintain, and is increasingly used. The refrigeration medium of the refrigerator is gas helium. The temperature of the primary cold plate is 50 ~ 100K, and the typical application is 65K, used to condense water vapor and pre-cooling other gases; Gases such as oxygen and argon. The inner surface of the secondary cold plate is coated with activated carbon. Activated carbon has a strong adsorption capacity for helium, neon and hydrogen at low temperatures. The cold plate is made of oxygen-free copper and the surface is polished to a mirror surface to reduce the emissivity. The ultimate pressure of the pump is -8 Pa, the working pressure range is -1 ···· -8 Pa, and the pre-pump pressure is required to be 1 Pa. The pumping rate of the finished product has reached 60,000 liters / second. In addition, the extraction cold plate can be arranged in the container being pumped according to the characteristics of the process, and the extraction rate can reach more than 106 liters per second.