Ion implantation beam monitor

An ion implantation apparatus comprising:

• an ion beam source for producing an ion beam;
• a substrate holder, downstream of the ion beam source;
• a two-dimensional scanner to mechanically scan the substrate holder relative to the ion beam to perform slow scans in a first, slow scanning, direction at a first, slow scan, rate and multiple fast scans, for each said slow scan, in a second, fast scanning, direction;
• a beam stop, downstream of the substrate holder, for capturing ions in the ion beam missing the substrate holder, to generate a beam stop current therefrom;
• said scanner being arranged to perform said slow scans from a start scan position at which the substrate holder does not intersect the ion beam so that the generated beam stop current is continuously a maximum value during said fast scans,
• a timer responsive to the generated beam stop current during a predetermined said slow scan to determine a first time at which the generated beam stop current first reduces from said maximum value and a second time at which the generated beam stop current first reaches a lowest value for the slow scan, and
• a processor operative to correlate said first and second times with the slow scan motion to determine the ion beam width in said slow scan direction.

An ion implantation apparatus comprising:

• an ion beam source for producing an ion beam;
• a substrate holder, downstream of the ion beam source, the substrate holder including a rotatable wheel having a plurality of spokes arranged radially around the wheel, said spokes carrying circumferentially spaced substrate supports;
• a beam stop, downstream of the substrate holder, for capturing ions in the ion beam missing the substrate holder, and to generate a beam stop current therefrom;
• a two-dimensional scanner to mechanically scan the substrate supports relative to the ion beam to perform slow scans in a first, slow scanning, direction and multiple fast scans, for each said slow scan, in a second, fast scanning, direction at a fast scan rate, the scanner being operative to scan in said second, fast scanning, direction by rotation of said wheel;
• wherein during each said slow scan, the beam stop current includes a series of pulses, each pulse defining a pulse maximum beam stop current, where the ion beam passes between adjacent said substrate holders or spokes, and a lower beam stop current, where the ion beam passes across the substrate holders or spokes;
• and
• a processor responsive to the generated beam stop current to identify in a predetermined slow scan a pulse of said beam stop current which defines a pulse maximum beam stop current of a lowest value in said slow scan, said processor including a timer to determine a duration of said identified pulse and being further operative to correlate said pulse duration with said fast scan rate to determine the ion beam height in said fast scan direction.

A method of monitoring an ion beam in an ion implantation apparatus comprising:

• generating an ion beam;
• mechanically scanning a substrate holder in a first, slow scanning, direction and in a second, fast scanning, direction relative to the ion beam, the substrate holder supporting a plurality of circumferentially spaced substrates;
• capturing, in a beam stop, ions in the ion beam missing the substrate holder;
• generating a beam stop current from the ions captured in the beam stop;
• obtaining samples of the beam stop current generated by beam ions captured by the beam stop which pass between adjacent pairs of the plurality of circumferentially spaced substrates;
• and
• comparing said samples from the beam ions passing between successive said adjacent pairs of substrates to monitor the continuity of the ion beam.