Ion beam lithography

An ion projection lithography apparatus comprising:

• means to provide an ion beam,
• a mask in the path of said ion beam with apertures for producing a desired beam pattern,
• an optical column after said mask,
• said column defined by first and second principal lenses located along said ion path,
• said first lens being arranged to focus said ion beam,
• said second lens positioned after said first lens and being arranged to project a reduced image of said mask,
• a target station after said second lens for supporting a target that receives said image, and a shield of high permeability magnetic material extending about said optical column, said shield being comprised of a series of removable longitudinal segments that define a tubular shield and end plates of high permeability magnetic material in magnetic continuity with said tubular enclosure, said segment being defined by a set of longitudinally extending circumferentially spaced ribs mounted about said optical column, and a set of removable longitudinally extending side plates, each said plate spanning the gap between and in magnetic continuity with adjacent ribs, and electrical conductors positioned inside the shield and arranged to provide adjustment enabling reduction of a stray magnetic field in the region of the ion beam.

An ion projection lithography apparatus comprising:

• means to provide an ion beam,
• a mask in the path of said ion beam with apertures for producing a desired beam pattern,
• an optical column after said mask,
• said column defined by first and second principal lenses located along said ion path,
• said first lens being arranged to focus said ion beam,
• said second lens positioned after said first lens and being arranged to project a reduced image of said mask and
• a target station after said second lens for supporting a target that receives said image,
• said means to provide said ion beam comprises an ion source and a solenoid lens located between said ion source and said mask for selecting the virtual source point along the axis of said optical column,
• said solenoid adapted to contribute to the selection of the desired ion specie from various species of different mass issued from said source by differential deflection of said species according to their mass.

An ion projection lithography apparatus comprising:

• means to provide an ion beam,
• a mask in the path of said ion beam with apertures for producing a desired beam pattern,
• an optical column after said mask,
• said column defined by first and second principal lenses located along said ion path,
• said first lens arranged to focus said ion beam,
• said second lens positioned after said first lens and being arranged to project a reduced image of said mask,
• a target station after said second lens for supporting a target that receives said image, and
• a multipole means located within said second lens or beyond and a voltage control system adapted to apply quadrupole fields to said multipole means to vary the magnification of the image at said target in the X direction relative to the magnification of the image in the Y direction.

A lithographic method of producing features of size of the order of 0.1 micron on a target comprising,

• providing an ion beam projection lithographic apparatus capable of imaging the desired features of a lithographic mask upon a target field, the system having a set of adjustable parameters,
• using a metrology mask having an array of metrology features, empirically determining the effect of each of said parameters across the target field while the other parameters are held constant to provide a set of shim functions,
• initially setting the parameters of said system by linear optimization based upon metrology measurements across said field, exposing targets through a lithographic mask having desired features, periodically interrupting said exposure, substituting for said lithographic mask a metrology mask defining an array of metrology features across said field,
• determining from said measurement a set of error values, and by linear optimization, determining adjustments to said set of parameters to reduce said error values on the basis of said shim functions, making said adjustments, and resuming said exposure of targets.

An ion projection lithography apparatus comprising:

• means to provide an ion beam,
• a mask in the path of said ion beam with apertures for producing a desired beam pattern,
• an optical column after said mask,
• said column defined by first and second principal lenses located along said ion path,
• said first lens being an accelerating Einzel lens arranged to form a crossover within said column,
• said second lens positioned after said crossover and being a gap lens, arranged to project a reduced image of said mask,
• a target station after said gap lens for supporting a target that receives said image, and
• wherein said mask has, in addition to mask structure to define the desired image beam, also a set of reference marks that define reference beams adapted to be imaged by the lens column and probe corresponding reference marks at the target station for generating alignment control signals that are connected to bring the image beam into alignment with the desired position on the wafer, wherein deflection means shielded from said image beam are provided to repeatedly scan said reference beam across respective reference marks at the target station.