Method and apparatus for image alignment in ion lithography
First Claim
1. In an ion projection lithography system, an apparatus for positioning on a substrate or wafer at a target station an ion image of structures provided on a mask, said image produced by an ion beam projected along an axis upon said mask, wherein said mask includes reference marks to provide ion reference beams about the image field, the target station includes marks and the beam of the system is controlled to establish a coincidence of the marks on the mask with the corresponding marks at said target station, said ion projection system including in its optical path an electrostatic multipole, which is adapted to be controlled by a control device, means for rotational adjustment of said image relative to said substrate, and means for correcting the scale of the image, wherein at least some of the marks at said target station are carried on a reference block, said block being disposed in a predetermined position relative to the substrate and having an aperture corresponding in size to the mask image to be formed on the substrate so that the marks on said block are disposed outside the optical path used to generate the image on the substrate, said marks being on the side of said block opposite to the side on which the wafer lies and being in position to coincide with respective reference beams while said ion image is projected along the optical path toward said target station,detectors provided for secondary radiation emitted by the marks on the reference block as a result of the ion reference beams passing through said marks on said mask, said detectors and reference block arranged along said beam path such that said reference block can shield said detectors from any secondary radiation emitted as a result of said beam striking a surface after passing through said apertureand the signals from the detectors adapted to be delivered to the control device for the multipole, the means for relative rotational adjustment of said image on said substrate and to the means for scale correction.
2 Assignments
0 Petitions
Accused Products
Abstract
In an ion projection lithography system, apparatus and methods for positioning on a substrate or wafer at a target station an image of structures provided on a mask, wherein the mask includes reference marks to provide ion reference beams about the image field, the target station includes marks and the beam of the system is controlled to establish a coincidence of the marks on the mask with the corresponding marks at the target station. The ion projection system shown includes in this optical path an electrostatic multipole, means for rotational adjustment of the image relative to the substrate, and means for correcting the scale of the image. Embodiments are shown in which the marks at the target station are carried on the wafer or on a reference block which is positionally related to the wafer, e.g., by an interferometer. In the case of the reference block, it has an aperture corresponding in size to the mask image to be formed on the substrate so that the marks are disposed outside the optical path used to generate the image on the substrate. Detectors provided for secondary radiation emitted by the marks at the target station as a result of the ion reference beams passing through the marks on the mask produce signals that control the multipole, the means for relative rotational adjustment of the image on the substrate and the means for scale correction. Special masks are provided that enable the reference beams to reach their respective marks at the target station during blanking and unblanking of the mask, permitting operation of the alignment system at both times. The reference beams are shielded from the image beam and are scanned repeatedly over their respective marks at the target station.
112 Citations
49 Claims
-
1. In an ion projection lithography system, an apparatus for positioning on a substrate or wafer at a target station an ion image of structures provided on a mask, said image produced by an ion beam projected along an axis upon said mask, wherein said mask includes reference marks to provide ion reference beams about the image field, the target station includes marks and the beam of the system is controlled to establish a coincidence of the marks on the mask with the corresponding marks at said target station, said ion projection system including in its optical path an electrostatic multipole, which is adapted to be controlled by a control device, means for rotational adjustment of said image relative to said substrate, and means for correcting the scale of the image, wherein at least some of the marks at said target station are carried on a reference block, said block being disposed in a predetermined position relative to the substrate and having an aperture corresponding in size to the mask image to be formed on the substrate so that the marks on said block are disposed outside the optical path used to generate the image on the substrate, said marks being on the side of said block opposite to the side on which the wafer lies and being in position to coincide with respective reference beams while said ion image is projected along the optical path toward said target station,
detectors provided for secondary radiation emitted by the marks on the reference block as a result of the ion reference beams passing through said marks on said mask, said detectors and reference block arranged along said beam path such that said reference block can shield said detectors from any secondary radiation emitted as a result of said beam striking a surface after passing through said aperture and the signals from the detectors adapted to be delivered to the control device for the multipole, the means for relative rotational adjustment of said image on said substrate and to the means for scale correction.
-
11. In an ion-lithography projection system, an apparatus for controlling the positioning of an ion image of the structure of a mask on a substrate at a target station in which the mask and a surface at the target station to which the substrate is related are provided with respective marks for mutually corresponding locations, and an image of the marks of the mask is cast onto the surface at the target station and brought into coincidence with the corresponding marks thereon, said ion-lithography projection system having:
-
an electrostatic multipole disposed in an ion-beam path between said mask and said substrate, means for rotating the image of the mask structure and a scale variation means disposed in the ion-beam path controllable to vary the image-reproduction scale of the image of the mask structure projected onto said substrate, the improvement which comprises; detectors provided for secondary radiation emitted by the marks at the target station as a result of the ion reference beams passing through said marks on said mask, and the signals from the detectors adapted to be delivered to a control means to control the multipole, the means for relative rotational adjustment of said image on said substrate and to the means for scale variation, and a shutter insertable in said path, in one position said shutter being traversable only by ions passing through said marks on said mask, and in at least one other position said shutter being traversable by ions passing through said marks on said mask and by ions forming an image of said structure, said shutter being movable across the ion path so that in the first mentioned position the target station is exposed to the ion beam only through said marks, to enable coarse alignment of said system, and in the second mentioned position of said shutter said substrate is exposed to said image of said structure simultaneously while said surface at said target station is exposed to ions passing through said marks on said mask to control alignment during exposure of said substrate, said control means including means operative simultaneously while exposure of the substrate to the ion image proceeds, for fine adjustment of the position of said ion image on said substrate in dependence upon said signals from said detectors whereby real time control of the position of the ion beam image on the substrate can be obtained during exposure of the substrate. - View Dependent Claims (12, 13, 14)
-
- 21. In a method of controlling the positioning of an ion image of the structure of a mask on a substrate in an ion-projection lithography system in which the mask and a surface at the target station positionally related to the substrate are provided with respective marks for mutually corresponding locations, and an image of the marks of the mask is cast onto said surface at the target station and brought into coincidence with the corresponding marks thereon, the improvement which comprises the step of simultaneously with exposure of said substrate to said ion beam image for reproduction of said mask structure therein, detecting said marks at said surface and bringing an image of the marks on said mask into coincidence therewith, and in dependence thereupon adjusting the position of the ion beam image to a desired position upon said substrate, thereby providing real-time control of the position of the ion beam image on the substrate during exposure of the substrate.
- 27. In an ion projection lithography system for exposing a wafer to a desired image beam comprising an ion source, a mask, a shutter, a lens column and an exposure or target station, wherein the 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 applied to a control means to bring the image beam into alignment with the desired position on the wafer, wherein the shutter is movable between one position in which the shutter is shaped to blank the image beam but allow a set of the reference beams to reach the target station for accomplishing relatively coarse alignment and at least one other position in which both the image beam and a set of the reference beams are allowed to simultaneously reach the target station, said control means including means operative similtaneously while the exposure of the substrate to the ion image proceeds for fine adjustment of the position of said ion beam image on said wafer in dependence upon said alignment control signals, whereby real time control of the position of the ion beam image on the wafer can be obtained during exposure of the wafer.
-
28. In an ion projection lithography system for exposing a wafer to a desired image beam comprising an ion source, a mask, a shutter, a lens column and an exposure or target station, wherein the 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 applied to a control means to bring the image beam into alignment with the desired position on the wafer, wherein the shutter is movable to blank and unblank the image beam said shutter being constructed to allow a set of the reference beams to reach the target station simultaneously with said image beam during unblanking of the beam, said control means including means operative simultaneously while exposure of the substrate to the ion image proceeds for fine adjustment of the position of said ion beam on said wafer in dependence upon said alignment control signals whereby real time control of the position of the ion beam image on the wafer can be obtained during the exposure of the wafer.
-
41. In an ion projection lithography system for exposing a wafer to a desired image beam comprising an ion source, a mask, a shutter, a lens column and an exposure or target station, wherein the 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.
- 42. A shutter for use in a lithographic system, the shutter being movable across a beam which exposes a mask, and comprising a pair of elongate openings which extend in the direction of movement of the shutter and are spaced apart transversely to that direction, each opening of said pair of openings being disposed adjacent to an optical path which is associated with an alignment mark on the mask in the manner that the alignment marks may be exposed as the shutter moves and an opening is disposed between the elongate openings of said pair over a portion of the extent of said elongate openings so that the mask can selectively be exposed in one position of the movable shutter and covered in another position of the movable shutter while the alignment mark can be exposed in both positions of the shutter.
- 47. A shutter for use in a lithographic system, the shutter being movable across a beam which exposes a mask, said shutter is formed with openings which succeed each other in the direction of movement of the shutter and have parallel edges extending in the direction of movement of the shutter and consecutive openings are separated from each other by a land which has a widened central portion for covering the optical path which is associated with the design area of the mask.
Specification