1. Field of the Invention
The present invention relates to the field of evacuation systems used in semiconductor water processing. More specifically, the present invention relates to a method of evacuating HF gas from a process tube.
2. Prior Art
During processing of semiconductor wafers, they are sometimes places on sleds, and processed through a deposition step. These sleds require regular cleaning to remove the material that has been deposited on them. The sleds are placed in a process tube, and exposed to hydrogen fluoride (HF) gas. After the cleaning, it is desired to remove the gas from the process tube. Typically this is done by evacuating the process tube which contains the gas and the sleds. In the prior art this evacuation was done with a vacuum pump having a slow pump line and a high vacuum line. The slow pump line was first utilized to reduce the pressure in the tube to a first threshold level (for example, 200 TORR). Then the high vacuum valve is opened, and the tube is pumped down to a base pressure.
A disadvantage of the old method is the short lifetime of the vacuum pump. Because of the highly corrosive nature of the gas, the vacuum pump fails after a relatively short period of use.
Therefore, it is an object of the present invention to provide a method of evacuating corrosive gas from a process tube which results in a longer lifetime for vacuum pumps than prior art methods.
It is a further object of the present invention to provide a control system for automatically controlling the evacuation system.