High current ribbon beam ion implanter

In a method of implanting a target with an ion beam, the steps of

• generating an ion beam containing ions of a desired species which diverges in at least one direction,
• passing said beam through a dipole magnet so as to
• i) form ions of the desired species into an output beam of ribbon shape, with a major transverse dimension greater than two hundred millimeters and with a minor dimension, and
• ii) render ions of the output beam parallel within about one degree
• measuring current density profile of said ion beam along its major transverse dimension
• adjusting a plurality of multipole elements arranged to extend substantially across the ion beam to modify aberrations and fit current density profile of said output beam to a desired profile, and
• scanning a workpiece to be treated through said output ion beam at a velocity in relation to said profile effective to accurately implant a uniform dose of ions into the workpiece.

A method of adjusting a multipole lens to achieve a desired one-dimensional current density profile in a ribbon-shaped ion beam used to implant targets with ions, such method comprising the steps of

• setting up a computer model of the ion optical system through which the ion beam is transported, in which the ion beam is represented by an array of rays which are initially uniformly spaced, and in which resulting current density on the target is proportional to current represented by each ray, and is inversely proportional to spacing between rays
• measuring the profile of the current density along a major transverse dimension of the real ion beam and storing this measurement as an array of points in computer memory
• calibrating the model so that its output matches observed ion beam current density profile
• comparing said measured profile with a desired reference profile and calculating an error function, said error function indicating discrepancy between the desired profile and the measured profile in a target implant region
• iteratively adjusting settings of the multipole lens elements, calculating a resulting profile according to a model, calculating a new error function, and saving a setting which reduces error, and
• setting the multipole elements according to a setting obtained in a previous step in order to accurately obtain said output beam with the desired profile.

Apparatus for uniformly implanting targets with an ion beam, such apparatus comprising

• an ion source which produces an ion beam containing ions of a desired species and which diverges in at least one direction along a beam path
• a first dipole magnet in the beam path which forms the desired species into an output beam of ribbon shape, with a major transverse dimension larger than a face of a workpiece to be implanted, and with a minor dimension small relative to said workpiece, said magnet rendering ions of the output beam parallel within about one degree
• profiling means for measuring current density of said ion beam along its major transverse dimension
• at least one multipole ion lens in said beam path adjustable over a range of aberration for controlling current density profile to a desired profile and
• means for traversing a workpiece or batch of workpieces through said ion beam at a velocity effective to implant a substantially uniform dose of ions into the workpiece.

Apparatus for ion implantation, such apparatus comprising

• a first dipole magnet effective to receive a divergent source beam, bend the beam through an angle and bring it to a focus
• a resolving aperture at said focus
• a first dipole magnet effective to receive ions of a desired species from the aperture and form the ions into an output beam having a major transverse dimension over two hundred millimeters with ions of the output beam being substantially parallel within about one degree, and
• a multipole element extending substantially entirely across said beam and having plural adjustable pole elements effective to provide aberrations which accurately fit output beam current density profile to a desire non-constant profile.

In a method of implanting a workpiece with an ion beam, the steps of:

• generating a divergent ion beam including a desired ion species, and passing it through a first magnet which focuses the desired species through a resolving slit, thereby rejecting unwanted species and forming a beam of said desired species,
• passing said beam of said desired species through a second magnet whose ion-optical properties form said beam of desired species into an output beam of ribbon shape, with a major transverse dimension larger than a face of the workpiece to be implanted, and with a minor dimension small relative to said workpiece, ions of the output beam being rendered parallel within about one degree, and matching a non-uniform current profile along said major dimension across the width of the workpiece,
• mounting the workpiece on a scanning mechanism at a selected angle and orientation relative to the direction of said ion beam,
• adjusting a plurality of multipole elements extending entirely across the beam to accurately fit said non-uniform current to a desired non-uniform profile, and
• scanning said workpiece through said ion beam one or more times at a velocity in relation to ion beam current, effective to implant a dose of ions into the workpiece which is substantially uniform in angle, orientation and dose per unit area.