The reaction chamber can be pumped down using just the mechanical pump and a bypass line which connects the pump to the chamber.

Pressure gauges
A pressure indicator is shown centered on the reaction chamber, which gives the current pressure in the chamber in torr units. As you operate the simulator, this and other pressures will change in time, which you witness through the prefactor and exponential values describing the pressure, and/or through watching the motion of the triangular slider (for the prefactor) and bar (for the exponential). For example, if the number next to the triangle is 7.6 and the number next to the bar is E 02, the pressure is 7.6E 02, i.e., 760 torr (or 1 atm). The color of the gauge indicates the pressure range (the color and values of the ranges can be adjusted in the Display Options control panel).

Mechanical pump
A mechanical pump (sometimes called a mech pump) is shown near the bottom of the simulator window. Mechanical pumps utilize variations of rotating fan or turbine blades to push gas from their inlet ports (on top) to their exhaust ports (shown on the side). If a sealed vacuum system is attached to the inlet, mechanical pumps can evacuate the vacuum system to a base pressure of around 10^-2-10^-3 torr, sending the gas out the exhaust pipe at atmospheric pressure. Once the base pressure has been reached, the gas from the exhaust sides slips through the blades as fast as the gas remaining in the chamber is evacuated, establishing a steady pressure state. The pressure gauge on the vacuum pump indicates the pressure at the inlet side of the pump (the outlet is at atmospheric pressure). Left-click on the switch at the left of the pump to turn its power on (green) and off (red).

While the mechanical pump does not alone achieve the low pressures (10^-3-10^-6 torr) needed to assure a chemically clean process chamber, it offers a major advantage in handling the job of pumping from atmospheric pressure.

Bypass line and cutoff valve
In the simulator, a vacuum line on the right connects the mechanical pump to the reaction chamber, so that the mechanical pump can evacuate the reaction chamber. The bypass line is intersected by a  cutoff valve , which opens or closes the bypass line, effectively enabling or disabling the ability of the mechanical pump to pump down the reaction chamber. Left-click on the cutoff valve in the bypass line (the "bypass valve") to change its state from closed (an X shape) to open (an arrow shape). The speed of chamber pumpdown depends not only on the speed of the mechanical pump and the volume of the chamber, but also on the conductance or speed of the bypass line: a wide, short line offers little resistance to pumping, so pumpdown speed depends only on pump capacity and chamber volume, while a thin, long bypass line impedes pumping and can be used to slow the pumpdown speed substantially.

Exercises

Exercise 1: Pump down vacuum lines to the two cutoff valves.  Knowing the basic functions of the reaction chamber, mechanical pump, and bypass line with its cutoff valve, it is now possible to operate the pump and to pump down the chamber. To pump down the vacuum lines:  Start/restart the simulator (stop if already running).  Turn on the mechanical pump .  Observation: Notice that the mechanical pump pressure decreases.  The pressure gauge at the mech pump measures inlet pressure. Since the inlet of the mech pump connects to two lines which are both terminated at closed cutoff valves, the pump inlet sees a sealed volume, so that the mech pump can evacuate the inlet region down to the base pressure of the mech pump.    Questions   What base pressure does the mech pump achieve?  Roughly how long does it take to reach approximate base pressure?  Answers

Exercise 2: Pump down (evacuate) the reaction chamber.  Now that we have pumped down the vacuum lines to the two cutoff valves, let's use the mech pump to pump down (evacuate) the reaction chamber. To do this:  Open the cutoff valve in the bypass line.  Observation: Notice that the volume of the chamber, and therefore the amount of gas to be removed, is much larger than when we only pumped down the lines from the mech pump to the cutoff valves.  What changes do you expect (if any)?   Observation: Notice that the mechanical pump pressure first increases, then decreases. At the same time, the chamber pressure decreases smoothly.  This is because the gas from the chamber expands immediately into the evacuated gas lines as soon as the cutoff valve is opened. In contrast, the chamber pressure started at atmospheric pressure and can only decrease.    Questions   What base pressures do the mech pump and chamber achieve?  Roughly how long does it take to reach approximate base pressure?  For semiconductor manufacturing, do we want fast or slow pumpdown?  Answers

 

Summary
The mech pump evacuates whatever sealed volume it is connected to down to a base pressure of about 10^-2 torr (10 millitorr).

Pumpdown speed is longer when the chamber volume is larger.

While fast pumpdown is desired for manufacturing speed, slow pumpdown is required when evacuating condensible gases like water vapor (or air) to prevent particle formation.