Vacuum deposition system with improved mass flow control

摘要

A system and method for forming a uniform layer of a material from a vapor phase onto the surface of an object at a high rate of deposition includes a heated reservoir for vaporizing the material to be deposited, a reactor containing the objects to be coated, and a vacuum device for flowing the gaseous material from the reservoir to the reactor. The mass flow rate of the gas from the reservoir is held constant by precisely controlling the pressure at the outlet of the reservoir and at the inlet of the reactor. In one embodiment the upstream pressure is controlled by a valve responsive to a pressure sensor at the reservoir outlet, and the downstream pressure is controlled by adjusting the vacuum in the reactor as measured by a pressure sensor at the reactor inlet. A vacuum bypass line around the reactor is provided to stabilize the upstream pressure prior to admitting the gas to the reactor when a deposition cycle is commenced, and the connection between the reservoir and the reactor, and the flow control valves and pressure sensors in the flow path are maintained at a temperature sufficient to prevent condensation of the vapor downstream of the reservoir.