• Conductance of the valve and gas line used for venting
  larger conductance ==> faster pressure rise in chamber
  
  
• Gas source pressure
  larger gas source pressure ==> faster pressure rise in chamber
  
  
• Chamber pressure
  higher chamber pressure ==> faster pressure rise in chamber
  This is because the gas flow rate from the nitrogen venting source to the chamber is porportional to the difference between the gas source pressure and the chamber pressure. Thus, if the gas source pressure is about atmospheric, the pressure in the chamber will rise more slowly as atmospheric pressure is approached. Therefore, the venting process would be unacceptably long with a near-atmospheric-pressure venting source, and so much higher gas source pressures are usually used.
  
  
• Chamber volume
  larger chamber volume ==> slower pressure rise in chamber
  This is because larger chambers require more gas input in order to reach a given pressure.
  
  

Fast venting for manufacturing speed: In general, one would always wnat process steps to be as fast as possible. Venting the reaction chamber doesn't add value to the semiconductor wafer (since no material change is made to the wafer), so we want to shorten the venting cycle to enhance manufacturing speed.

Slow venting to reduce particle generation: However, if gas inlet for venting is too fast, gas flow can become turbulent rather than laminar (smooth), so that particles are displaced from chamber and vacuum system walls. When such particles land on the wafer surface, they can destroy the functaionality of the semiconductor chips, degrading manufacturing yield. As a result, "soft venting" procedures have been developed to minimize particle generation during venting, such that the venting process is slow during the initial venting, and flow rates for venting are increased as the chamber pressure increases.