In the past, oil-sealed vacuum pumps (with piston vacuum pumps as important representatives) were widely used in various semiconductor processes. However, their performance in practical applications was not ideal.To address the shortcomings of oil-sealed vacuum pumps, dry vacuum pumps came into being.

Different dry vacuum pumps have significant differences in their mechanical structure design, which serves as the basis for classification.

 Specific types

They are mainly divided into four types

Circular lobe type, claw type, combined type (roots-claw type), and screw type. Currently, these types are widely used by different manufacturers.

Circular lobe type, claw type, and combined type (roots-claw type) belong to multi-stage pumps. They generate vacuum by repeatedly compressing gas in multi-stage vacuum chambers. During the compression process, the temperature and pressure of the gas change significantly, which easily alters the physical properties of the gas.

Single-stage pump category

Screw type pumps are single-stage pumps, which can generate vacuum only by relying on one vacuum chamber. According to different gas compression methods, they can be further divided into internal compression screw pumps and external compression screw pumps.

a.It is very similar to the currently popular and widely used Roots pumps. In fact, the earliest dry pump design was developed by combining Roots pumps.

b.It adopts a multi-stage scheme, resulting in a large gas path. Each stage requires a relatively large nitrogen flow to dilute and cut off the gas. To obtain good vacuum, strict sealing requirements are imposed on all stages.

c.Its advantage is relatively low power consumption due to the increased internal compression ratio.

Three-lobe Circular Scheme

a.Its principle is exactly the same as that of the two-lobe split scheme. The only difference is that it divides the gas into three parts (while the two-lobe split scheme uses two circular lobes to divide the gas into two parts).

b.It shares similar advantages and disadvantages with the two-lobe split scheme. To further reduce power consumption, some manufacturers choose to use two DC motors in the transmission part, but this also leads to a decrease in torque and the ability to restart.

c.Like the two-lobe split scheme, each pump with the three-lobe circular scheme requires a large flow of nitrogen to achieve the dilution effect.