Pressure control system

#1. Field of the Invention

#This invention relates generally to semiconductor processing and, more particularly, to pressure control systems for process chambers.

#2. Description of the Related Art

#The invention will be better understood from the Detailed Description of the Preferred Embodiments and from the appended drawings, which are meant to illustrate and not to limit the invention, and wherein:

#FIG. 1 is a schematic view of a prior art system for pumping down a process chamber in which the chamber pressure is utilized to control the pump-down; and

#FIG. 2 is schematic view of a system selectively utilizing pump pressure and chamber pressure to control pump-down of a process chamber, in accordance with preferred embodiments of the invention.

#As noted above, the evacuation, or pump-down, of a process chamber involves balancing the conflicting requirements of minimizing gas flow turbulence and particle agitation while maximizing process chamber utilization for substrate processing. It has been found that an optimal solution for reconciling these conflicting goals can be balanced by using a system capable of achieving a controlled mass flow rate during evacuation of the chamber. By having gas exit the process chamber at a roughly steady rate, turbulence and particle agitation caused by sudden changes in gas flow rates can be reduced. Moreover, the constant mass flow allows a set volume of gas to be consistently withdrawn, allowing the chamber to be pumped down more quickly than if the mass flow were allowed to decrease as the pressure in a process chamber decreases. It will be appreciated that such a mass flow decrease can occur where a valve allowing gas to flow out of a chamber has a constant sized opening.

#Pressure control systems according to preferred embodiments of the invention provide an advantageously simple system, relative to, e.g., systems using mass flow controllers, for maintaining a substantially constant mass flow during pump-down. Preferably, a process chamber is connected to a pump using a gas line, or piping systems, that has a valve with a controllable, variable sized opening. A pump pressure sensor is configured to measure the pressure of gas at the pump's inlet. Preferably, the pump pressure sensor is located in the gas line between the vacuum pump and the variable opening. In this location, the pump pressure sensor can measure the gas pressure in the gas line between the vacuum pump and the variable opening, which pressure is equal to gas pressure at the pump inlet. The pressure sensor is also connected to the valve; the pressure measured by the sensor is used to determine the size of the variable opening. The pump preferably withdraws a constant volume of gas at a constant rate to minimize the affects that variable volume displacements and rates may have on the gas line pressure.

#In preferred embodiments of the invention, the pressure sensor is configured to maintain the pressure in the gas line at a constant level during process chamber pump-down. The pressure in the gas line is proportional to the quantity of gas in the gas line. Assuming a constant volumetric displacement of the vacuum pump, maintaining the pressure at the pump inlet at a constant level during evacuation results in a substantially constant displacement of gas into the pump. Thus, a substantially constant mass flow of gas during process chamber evacuation can be achieved.