Chemical vapor deposition apparatus

A chemical vapor deposition apparatus, for forming a thin film on a substrate, comprising:

• a reaction chamber comprising an inlet port and an exhaust vent, wherein a processing gas flows into the reaction chamber through the inlet port, an exhaust gas is exhausted from the reaction chamber through the exhaust vent, and the processing gas comprises a reaction gas;
• a first pressure detector connected with the reaction chamber to detect a pressure in the reaction chamber and output a first pressure signal;
• a pressure controller electrically connected with the first pressure detector to generate a feedback signal according to the first pressure signal;
• a filter connected with the exhaust vent of the reaction chamber to remove unreacted reaction gas and a byproduct from the exhaust gas;
• a throttle valve disposed at a downstream side of the filter, and an open level of the throttle valve, wherein the open level of the throttle valve is adjustable to adjust the pressure of the chamber;
• a ballast gas source connected to a node between the exhaust vent of the reaction chamber and the filter to provide a ballast-gas flow from the ballast gas source;
• a second pressure detector deposed at the node between the exhaust vent of the reaction chamber and the filter to detect a pressure of the node and output a second pressure signal to the pressure controller;
• and
• a mass flow controller electrically connected with the pressure controller and used to control a ballast-gas flow rate of the ballast-gas flow, wherein the pressure controller control the mass flow controller to decrease the ballast-gas flow rate when the pressure of the node is greater than the pressure in the reaction chamber according to the first pressure signal and the second pressure signal.