Ion beam lithography

Claim 2

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 and a target station after said gap lens for supporting a target that receives said image.

Claim 3

The apparatus of claim 1 wherein said mask is located substantially at the first focal plane of said first lens and said target station is located substantially at the second focal plane of said second lens.

Claim 4

The apparatus of claim 2 wherein said means to provide said ion beam comprises an ion source and means to provide to said lens column a virtual image of said ion source more distant from said column than said ion source and the distances (1) between the second focal plane of said first lens and the first focal plane of said second lens, and (2) between said mask and a point defining the virtual image of said source and said mask, being selected to produce said image of said mask at said target with chromatic blurring and geometric distortion arising from said lenses simultaneously substantially minimized.

Claim 5

The apparatus of claim 3 in which.said lenses are Positioned to locate said crossover of said first lens substantially at the first focal plane of said second lens to produce a substantially telecentric beam following said second lens.

Claim 6

The apparatus of claim 1 wherein said lens system simultaneously satisfies substantially the following conditions whereby the beam emerging from the second lens is substantially telecentric and when it reaches the image plane is substantially free of chromatic blurring and geometric distortion: qp=f.sub.1 f.sub.2 (1) ##EQU23## where q is the distance between the second focal plane of the first lens and the first focal plane of the second lens, p is the distance between a point defining the virtual image of said source and said mask, f 1 is the first focal length of said first lens, f 1 ' is the first focal length of said second lens, f 2 is the second focal length of said first lens, δ 1 and δ 1 ' are the changes in the first focal length of said first and said second lenses, respectively, due to a change in the energy of said ions in said beam, G(p)=ap.sup.3 +bp.sup.2 +cp+d where a, b, c and d are lens constants related to the transfer function from the first focal plane to the second focal plane of the first lens, in the presence of third order aberrations, said transfer function being of the form: δ.sub.2 =-r.sub.1 /f.sub.2 +ar.sub.1.sup.3 +br.sub.1.sup.2 δ.sub.1 +cr.sub.1 δ.sub.1.sup.2 +dδ.sub.1.sup.3 where δ 2 is the transformed transverse angular coordinate of a given ion ray at the second focal plane of said first lens, r 1 , δ 1 are said transverse coordinates at the first focal plane of said first lens at said mask and D' is a coefficient in the transformation from the first focal plane to the second focal plane of the second said lens: r.sub.2 '≃f.sub.1 'δ.sub.2 +D'δ.sub.2.sup.3 where r 2 ' is the radial coordinate of the ray at the second focal plane of the second lens.

Claim 8

The apparatus of claim 6 adapted to provide ions in said ion beam at the mask at energy between about 1 and 10 kV.

Claim 13

The apparatus of claim 11 wherein said lens is a solenoid, 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.

Claim 14

The apparatus of claim 12 further comprising an aperture located between said first and second lenses to Prevent passage of ions differing in mass from the desired specie.

Claim 16

The apparatus of claim 14 wherein said multipole means is located after said second lens in a region substantially free of electrical fields.

Claim 18

The apparatus of claim 16 wherein said multipole means is further adapted to produce superposed higher order fields for control of distortion and blurring in said image.

Claim 19

The apparatus of claim 16 wherein said multipole means is a pair of successive sixteen pole circular arrays of arc-form electrodes adapted to introduce a parallel offset to said beam.

Claim 21

The apparatus of claim 19 wherein said voltage adjustment device is further capable of disproportionate adjustment of said lens voltages for tuning said magnification of said image at said target.

Claim 25

The apparatus of claim 23 wherien a tubular shield of high permeability magnetic material extends about and is supported by said rigid metal shell.

Claim 26

The apparatus of claim 24 wherein said tubular shield is comprised of a series of removable longitudinal segments.

Claim 27

The apparatus of claim 24 wherein end plates of high permeability magnetic material are mounted at each end of said tubular shield in a manner to provide magnetic continuity with said tubular shield.

Claim 28

The apparatus of claim 24 wherein an array of longitudinally extending electrically conductive loops is associated with said shield, said loops being arranged to establish magnetic flux in the circumferential direction in said tubular shield.

Claim 29

The apparatus of claim 27 including means to apply an alternating electrical current to the loops to demagnetize the shield and means to apply a momentary small bias current to the loops to increase the magnetic permeability of the shield.

Claim 30

The apparatus of claim 27 wherein each of said conductive loops comprises longitudinally extendign conductive segments extending along the interior and the exterior of said tubular shield.

Claim 32

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.

Claim 33

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.

Claim 36

The apparatus of claim 31 wherein an array of longitudinally extending electrically conductive loops is associated with said shield, said loops being arranged to establish magnetic flux in the circumferential direction in said tubular sheidl.

Claim 37

The apparatus of claim 33 including means to apply an alternating electrical current to the loops to demagnetize the shield and means to apply a momentary small bias current to the loops to increase the magnetic permeability of the shield.

Claim 38

The apparatus of claim 33 wherein each of said conductive loops comprises longitudinally extending conductive segments extending along the interior and the exterior of said tubular shield.

Claim 40

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.

Claim 41

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.

Claim 42

The apparatus of claim 37 wherein said solenoid is a counterwound double solenoid adapted to prevent rotation of said ion beam during passage through said solenoid.

Claim 43

The apparatus of claim 37 or 38 further comprising an aperture located between said first and second lenses sized to prevent passage of ions differing in mass from the desired specie.

Claim 44

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.

Claim 45

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.

Claim 46

The apparatus of claim 40 wherein said multipole means is located after said second lens in a region substantially free of electrical fields.

Claim 47

The apparatus of claim 40 wherein said multipole means is a sixteen pole circular array of arc-form electrodes.

Claim 48

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.

Claim 49

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.

Claim 50

The lithographic method of claim 43 wherein said metrology mask defines an array of pairs of orthogonal slits for producing corresponding pairs of metrology ion beamlets that proceed to said target and said step of empirically determining the effect of each of said parameters across the target field while the other parameters are held constant comprises measuring the width and determining the centroid position of said beamlets at said target.

Claim 51

The method of claim 44 wherein said detector is associated with a pair of orthogonal slits arranged to intercept said metrology beamlets in the manner that only one beamlet of an orthogonal pair falls upon a corresponding slit at one time.

Claim 52

An ion beam projection lithography system having a set of adjustable parameters, said system adapted to project an image of a lithography mask upon a target mounted on an X, Y stage, said X, Y stage adapted to index across a number of exposure positions, a metrology mask adapted to be substituted for said lithography mask, a precision metrology stage mounted on said X, Y stage, a detector mounted on said metrology stage adapted to be indexed across the ion beam field while said metrology mask is in position to determine error values based upon detected blurring and geometric distortion at points distributed across said field, said error values being useful to generate, by linear optimization techniques, correction to said set of parameters to reduce blurring and geometric distortion of said system.

Claim 53

An ion beam projection lithography system having a set of adjustable parameters, said system adapted to project an image of a lithography mask upon a target mounted on an X, Y stage, said X, Y stage adapted to index across a number of exposure positions, a metrology mask adapted to be substituted for said lithography mask, a precision metrology stage mounted on said X, Y stage, a detector mounted on said metrology stage adapted to be indexed across the ion beam field while said metrology mask is in position to determine error values based upon detected blurring and geometric distortion at points distributed across said field, said error values being useful to generate, by linear optimization techniques, correction to said set of parameters to reduce blurring and geometric distortion of said system.

Claim 54

The lithographic apparatus of claim 46 wherein said metrology mask defines an array of pairs of orthogonal slits for producing corresponding pairs of metrology ion beamlets that proceed to said target and said detector mounted on said precision metrology stage is adapted to measure the width and determine the centroid position of said beamlets at said detector.

Claim 55

The apparatus of claim 46 wherein said detector is associated with a pair of orthogonal slits arranged to intercept said metrology beamlets in the manner that only one beamlet of an orthogronal pair falls upon a corresponding slit at one time.

Claim 56

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.

Claim 57

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.

Claim 58

The ion projection lithography system of claim 49 wherein a separate deflection means is associated with each reference beam.

Claim 59

The system of claim 50 wherein said deflection means comprise electrostatic deflectors and wherein said image beam passes through a hollow shield while the reference beams pass outside said shield, the shield protecting the image beam from the electric fields of the deflectors.