Gas

Extremely high purity is required of all gases, with bulk gases controlled to seven nines purity (99.99999%) and specialty gases controlled at least to four nines (99.99%). Particulate contamination in gases is controlled to the 0.1 µm range. Other controlled contaminants are oxygen, moisture content, and trace impurities such as metals. Many process gases are toxic, corrosive, reactive, and pyrophoric (they combust or burn when exposed to air). For these reasons, gases are contained in a gas delivery system that delivers the gases in a safe, clean, and accurate manner to the various process stations in the wafer fab.

Gas Purge

A gas purge is a method of flushing undesirable residual gases, atmospheric gases, or water vapor from a process chamber and the gas delivery system. Purging can eliminate stagnation points and contamination in gas lines. It is done with an inert gas such as nitrogen and involves replacing the undesirable gas with the purge gas, either through displacement or by pulling the gas out of the system by vacuum flow. Purging of the system on automated equipment is done automatically through software control of gas line valves before and after situations such as a gas cylinder change or opening a process chamber.

Gas Piping

Gas delivery piping is constructed with electropolished 316L stainless steel tubes to transport the gas (316L is a specific type of stainless steel). There are no plastic parts in a gas piping system, except for some membrane gas filters. Double-walled tubing is often used for hazardous gases . The inner walls of the double-walled tubing are electropolished to minimize contamination. Electropolishing is a chemical process done to remove about 30 microns of the pipe's inner surface, creating a clean, smooth surface that minimizes the possibility of chemical reactions that produce contaminants. An electropolished surface finish brings a thin layer of chromium to the steel's surface, which emits very few particles.

Gas Stick 气体接入系统

The gas line from the local gas distribution system connects into another gas panel at the process tool. The tool panel is made up of a series of gas "sticks," each controlling one type of incoming gas. Each stick will typically have an on/off valve, flow controller, pressure regulator, and filters. The number of incoming gas lines depends on the process, with a typical number being from six to 30 or more lines for multi-chamber process tools.