Solid precursor feed system for thin film depositions
A dry powder MOCVD vapor source system is disclosed that utilizes a gravimetric powder feeder, a feed rate measurement and feeder control system, an evaporator and a load lock system for continuous operation for thin film production, particularly of REBCO type high temperature superconductor (HTS) tapes.
1. A precursor feed system for deposition of thin films, the system comprising:
a powder feeder assembly that is maintained under vacuum and comprising a feed screw device and a powder vessel for housing a precursor powder;
a load lock assembly located outside the powder vessel and comprising a pressure isolated chamber for reloading the powder vessel;
a scale coupled to the powder vessel and configured to provide continuous mass data of precursor powder in the powder vessel;
a control system comprising a PID controller with a data processor; and
an evaporator configured to receive the precursor powder from the powder feeder assembly and evaporate the powder,
wherein the load lock assembly further comprises a plurality of gas control valves and a gate valve configured to pressure isolate the load lock assembly from the powder vessel to provide for addition of powder precursor while the feed system operates continuously, and a flow control orifice to equalize pressure between the load lock assembly and powder vessel; and
wherein the control system is configured to convert the continuous mass data from the scale to a feed screw rate to deliver a target precursor powder feed rate to the evaporator.
2. The feed system of claim 1 , wherein the precursor powder is comprised of more than one thin film component.
3. The feed system of claim 1 , further comprising a motor driven agitator located within the powder vessel and configured to provide powder mixing and distribution.
4. The feed system of claim 1 , wherein the evaporator further comprises an outlet screen.
5. A precursor feed system for deposition of thin films, the system comprising:
a powder feeder assembly that is maintained under vacuum and comprising a feed screw device and a powder vessel for housing a precursor powder;
a load lock assembly located outside the powder vessel and comprising a pressure isolated chamber for reloading the powder vessel;
a scale coupled to the powder vessel and configured to provide continuous mass data of precursor powder in the powder vessel;
a spectrometer configured to measure the thickness of a deposited thin film;
a control system comprising a PID controller with a data processor;
an evaporator configured to receive the precursor powder from the powder feeder assembly and evaporate the powder,
wherein the load lock assembly further comprises a plurality of gas control valves and a gate valve configured to pressure isolate the load lock assembly from the powder vessel to provide for addition of powder precursor while the feed system operates continuously, and a flow control orifice to equalize pressure between the load lock assembly and powder vessel; and
wherein the control system is configured to convert the continuous mass data from the scale and the thin film thickness from the spectrometer to a feed screw rate to deliver a target precursor powder feed rate to the evaporator.
6. The feed system of claim 5 , wherein spectrometer is an X-ray fluorescence spectrometer.