I'm currently struggling with a foreline trap on a rotary vane pump.
Since I have not received any formal education about vacuum equipment, it did not come to my mind at first that oil mist would diffuse backwards into the vacuum chamber.
After many failures, I realized this by observing the phenomenon, and tried to make my own foreline trap using activated carbon or silica gel, but the plasma quality deteriorated due to the pressure loss.
Currently, I use a trap with a general paper filter, and although I'm getting some improvement, it's still not good enough.

Professional equipment seems to use liquid nitrogen to chill the upstream of the pump to trap the mist, but it is impossible to introduce such a device at home.
This part will be an important theme in the future improvement of the device.