Sputter ion pump with penning-trap current sensor

Abstract

A sputter-ion-pump system includes a sputter ion pump and an electronic drive. The electronic drive supplies a voltage across the ion pump to establish, in cooperation with a magnetic field, a Penning trap within the ion pump. A current sensor measures the Penning-trap current across the Penning trap. The Penning trap is used as an indication of pressure within the ion pump or a vacuum chamber including or in fluid communication with the ion pump. The pressure information can be used to determine flow rates, e.g., due to a load, outgassing, and/or leakage from an ambient.

What is claimed is: 
     
         1 . A sputter ion-pump process comprising:
 applying a voltage differential between a cathode set of at least one cathode and an anode set of at least one anode so as to cooperate with a magnetic field to establish a Penning trap in a sputter ion pump and establish a Penning-trap current through the Penning trap; and   measuring the Penning trap-current; and   determining a pressure at least in part as a function of the voltage differential.   
     
     
         2 . The process of  claim 1  wherein the pressure is a pressure in a vacuum chamber including or in fluid-communication with the sputter ion pump. 
     
     
         3 . The process of  claim 1  wherein the magnitude of the voltage differential is determined by a drive controller of an ion-pump drive, the process further comprising calibrating the drive controller so that the pressure can be expressed in standard units for pressure. 
     
     
         4 . The process of  claim 1  further comprising seeking a differential voltage that achieves an optimal pressure, the seeking including comparing Penning-trap currents or pressures derived from Penning-trap currents at plural differential voltages. 
     
     
         5 . The process of  claim 1  further comprising collecting historical data regarding voltage-differential and current settings that cause a Penning trap to become unstable or collapse. 
     
     
         6 . The process of  claim 5  wherein the historical data also regards voltage-differential, magnetic-field strength, and current settings that cause arcing across the Penning trap. 
     
     
         7 . The process of  claim 5  further comprising seeking a differential voltage that achieves an optimal pressure, the seeking including comparing Penning-trap currents or pressures derived from Penning-trap currents at plural differential voltages, the historical data being used to constrain the differential voltages used in the seeking. 
     
     
         8 . The process of  7  wherein the differential voltages are constrained according to a reward-versus-risk algorithm, the reward being lower pressure and the risk being risk of Penning-trap instability or collapse. 
     
     
         9 . The process of  claim 1  wherein the applying includes:
 establishing the Penning trap a first time and obtaining a first set of current measurements including at least a first current measurement; 
 after the first time, shutting down the Penning trap for a first off duration of least an hour; 
 after the first off duration, establishing the Penning trap a second time and obtaining a second set of current measurements including at least a second current measurement; and 
 determining a flow rate to the sputter ion pump based at least in part on the first and second sets of current measurements. 
 
     
     
         10 . The process of  claim 9  wherein the flow rate includes vacuum chamber leakage, outgassing, or load, or a combination thereof. 
     
     
         11 . A sputter ion-pump system comprising non-transitory media that, when executed using hardware causes a process to be implemented, the process including:
 applying a voltage differential between a cathode set of at least one cathode and an anode set of at least one anode so as to cooperate with a magnetic field to establish a Penning trap in a sputter ion pump and establish a Penning-trap current through the Penning trap; and   measuring the Penning trap current; and   determining a pressure at least in part as a function of the voltage differential.   
     
     
         12 . The system of  claim 11  wherein the pressure is a pressure in a vacuum chamber including or in fluid-communication with the sputter ion pump. 
     
     
         13 . The system of  claim 11  wherein the magnitude of the voltage differential is determined by a drive controller of an ion-pump drive, the process further comprising calibrating the drive controller so that the pressure can be expressed in standard units for pressure. 
     
     
         14 . The system of  claim 11  wherein the process includes seeking a differential voltage that achieves an optimal pressure, the seeking including comparing Penning-trap currents or pressures derived from Penning-trap currents at plural differential voltages. 
     
     
         15 . The system of  claim 11  wherein the process includes collecting historical data regarding voltage-differential and current settings that cause a Penning trap to become unstable or collapse. 
     
     
         16 . The system of  claim 15  wherein the historical data also regards voltage-differential and current settings that cause arcing across the Penning trap. 
     
     
         17 . The system of  claim 15  further comprising seeking a differential voltage that achieves an optimal pressure, the seeking including comparing Penning-trap currents or pressures derived from Penning-trap currents at plural differential voltages, the historical data being used to constrain the differential voltages used in the seeking. 
     
     
         18 . The system of  17  wherein the differential voltages are constrained according to a reward-versus-risk algorithm, the reward being lower pressure and the risk being risk of Penning-trap instability or collapse. 
     
     
         19 . The system of  claim 11  wherein the applying includes:
 establishing the Penning trap a first time and obtaining a first set of current measurements including at least a first current measurement; 
 after the first time, shutting down the Penning trap for a first off duration of least an hour; 
 after the first off duration, establishing the Penning trap a second time and obtaining a second set of current measurements including at least a second current measurement; and 
 determining a flow rate to the sputter ion pump based at least in part on the first and second sets of current measurements. 
 
     
     
         20 . The system of  claim 19  wherein the flow rate includes vacuum chamber leakage, outgassing, or load, or a combination thereof.