In the past, oil-sealed vacuum pumps were widely used in various semiconductor processes, with rotary vane and piston vacuum pumps being the most common. However, their performance in many applications was not ideal. As a result, dry vacuum pumps were developed.   Over the years, several types of dry vacuum pumps have been designed and manufactured, differing significantly in mechanical structure. Based on these differences, dry vacuum pumps can be categorized into the following types: circular lobe, claw, hybrid (roots-claw), and screw-type. These designs are now widely used by different manufacturers.   Circular lobe, claw, and hybrid (roots-claw) pumps are known as multi-stage pumps because their working principles are similar—vacuum is created by repeatedly compressing gas through multiple vacuum chambers. During this process, the temperature and pressure of the gas change significantly, making it easier to alter the gas's physical properties.   Screw-type pumps are called single-stage pumps because they generate vacuum using only one vacuum chamber. Depending on the gas compression method, they can be further divided into internally compressed and externally compressed screw pumps. Below are some physical examples of these different pump types for reference.   The twin-lobe design, similar to the Roots pump, is currently the most popular and widely used. In fact, the earliest dry pump designs were based on combining Roots pumps. This multi-stage approach creates a large gas path, requiring a high nitrogen flow rate at each stage for dilution and sealing. At the same time, achieving good vacuum performance demands strict sealing at all stages. While this design results in relatively low power consumption, it also increases the internal compression ratio.   The three-lobe circular design operates on the same principle as the twin-lobe design, except it divides the gas into three parts instead of two. The three-lobe design shares similar advantages and disadvantages with the twin-lobe version. To further reduce power consumption, some manufacturers use two DC motors in the drive section, but this may lead to reduced torque and restart capability. Like the twin-lobe design, the three-lobe circular design also requires a high nitrogen flow rate for effective dilution.