Closed loop dose control for ion implantation
A method derives a terminal return current or upstream current to adjust and/or compensate for variations in beam current during ion implantation. One or more individual upstream current measurements are obtained from a region of an ion implantation system. A terminal return current, or composite upstream current, is derived from the one or more current measurements. The terminal return current is then employed to adjust scanning or dose of an ion beam in order to facilitate beam current uniformity at a target wafer.
1. An ion implantation system comprising:
an ion source that generates an ion beam along a beam path;
a mass analysis component downstream of the ion source that performs mass analysis on the ion beam;
a beamline assembly downstream of the mass analysis component;
an endstation positioned downstream of the mass analysis component that receives the ion beam;
a resolving aperture and decel located upstream of the endstation; and
a terminal return current system comprising a measuring device located upstream of the resolving aperture and decal, wherein the terminal return current system obtains a terminal return current and alters one or more parameters according to the terminal return current.
2. The system of claim 1 , wherein the terminal return current system measures the terminal return current upstream of the endstation to obtain the terminal return current.
3. The system of claim 1 , further comprising a terminal aperture positioned downstream of the mass analysis component and upstream of the endstation, wherein the terminal return current system obtains the terminal return current by electrically isolating source and beamline components upstream of the terminal aperture and measuring a current that maintains the source and beamline components at a selected potential or potentials.
4. The system of claim 3 , wherein the terminal aperture is downstream of the mass analysis component.
5. The system of claim 1 , further comprising a beamline assembly positioned along the beam path, downstream of the mass analysis component and upstream of the endstation, wherein the beamline assembly adjusts the ion beam to a selected energy.
6. The system of claim 5 , wherein the beamline assembly comprises accel/decel electrodes, and the terminal return current system measures charge on the accel/decel electrodes resulting from the ion beam passing there through and the measured charge is employed to obtain the terminal return current.
7. The system of claim 1 , wherein the one or more parameters include dose of the ion beam.
8. The system of claim 1 , further comprising a scanning system downstream of the mass analyzer.
9. The system of claim 8 , wherein the one or more parameters include scanning rates of the scanner.
10. The system of claim 1 , wherein the terminal return current system comprises a scaling component that applies scaling values to one or more individual measured currents, a filtering component that filters noise from the one or more individual measured currents, an impedance matching component that compensates for impedance variations in the one or more individual measured currents, and an addition component that combines the one or more individual measured currents into the terminal return current.
11. The system of claim 1 , wherein the beamline assembly comprises accel/decel electrodes located upstream of the resolving aperture, and wherein the terminal return current is obtained from measurements taken at or upstream of the accel/decel electrodes.
12. The system of claim 1 , wherein the measuring device measures an induced charge on one or more integral components of the ion implantation apparatus.
13. The system of claim 1 , wherein the terminal return current is measured from more than one induced currents.
14. An ion implantation system comprising:
an ion source that generates an ion beam along a beam path;
a mass analysis component downstream of the ion source that performs mass analysis on the ion beam;
a beamline assembly downstream of the mass analysis component;
an endstation positioned downstream of the mass analysis component that receives the ion beam;
a terminal return current system that obtains a terminal return current and alters one or more parameters according to the terminal return current; and
a beamline assembly positioned along the beam path, downstream of the mass analysis component and upstream of the endstation, wherein the beamline assembly adjusts the ion beam to a selected energy;
wherein the terminal return current system measures one or more individual currents from housings within the mass analysis component and the beamline assembly to obtain the terminal return current.
15. The system of claim 14 , wherein the terminal return current system assigns weights to the one or more individual currents.
16. A terminal return current system comprising:
an ion source that generates an ion beam that travels along a beam path;
a mass analyzer downstream of the ion source that performs mass analysis on the ion beam;
an end station downstream of the mass analyzer that receives the ion beam;
a faraday cup proximate to the end station that measures beam current of the ion beam;
a resolving aperture and decel located upstream of the endstation; and
a measuring device located upstream of the resolving aperture and decel and configured to measure beam induced charge from one or more elements positioned along the beam path upstream of the end station, wherein the measured beam induced charge is a function of beam current of the ion beam.
17. The system of claim 16 , wherein the one or more elements include extraction electrodes of the ion source.
18. The system of claim 16 , wherein the one or more elements include an aperture of the ion source.
19. The system of claim 16 , wherein the one or more elements include a terminal housing containing the ion source.
20. The system of claim 16 , wherein the one or more elements include a beamline housing containing the mass analyzer.
21. The system of claim 16 , wherein the measured beam induced charge is weighted according to a calibration measurement of the faraday cup.
22. A method of adjusting operation of an ion implantation system, the method comprising:
providing an ion beam along a beam path;
obtaining one or more induced current measurements on elements along the beam path;
scaling the one or more induced current measurements by scaling factors;
filtering the one or more induced current measurements;
adding the one or more induced current measurements to obtain a terminal return current; and
adjusting dose of the ion beam according to the terminal return current.
23. The method of claim 22 , wherein adjusting the dose comprises adjusting a slow scan speed.
24. The method of claim 22 , wherein adjusting the dose comprises adjusting a fast scan speed.
25. The method of claim 22 , wherein adjusting the dose comprises altering an ion source.
26. The method of claim 22 , wherein obtaining the one or more induced current measurements comprises measuring induced charge on a terminal housing.
27. The method of claim 22 , further comprising determining the scaling factors according to a measured calibration value.