Watlow’s gas line heaters are designed to regulate temperatures in gas lines in order to prevent condensation in the gas line.
Tetraethyl orthosilicate (TEOS), boron trichloride (BCl3), aluminum chloride (AlCl3), chlorine trifluoride (ClF3) and dichlorosilane (DCS) are gases that condense or liquefy due to a phase shift at low temperatures. In semiconductor processes, the condensation occurs in the gas line and puddles in the shower head before being injected into the vacuum chamber. A substantial number of wafer defects will occur if liquefied gases are injected into the vacuum chamber. Uniform heating of the lines with gas line heaters will prevent condensation. TEOS lines are typically heated above 194°F (90°C) and BCl3 above 86°F (30°C), depending on pressure and flow rate. The optimum line temperature will vary depending on the process parameters.