Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
2002-03-01
2004-08-17
Epps, Georgia (Department: 2873)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S322000, C430S005000, C430S022000, C250S492220
Reexamination Certificate
active
06777166
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a particle-optical lens arrangement, in particular for the particle-optical imaging of an object, to be imaged and positionable in an object area, into an image area, as well as a method employing such a lens arrangement, in particular, a method for device manufacture comprising a photolithographic step. In particular, the lens arrangement is provided for use in an electron beam projection lithographic system as well as for use in a method for device manufacture by means of electron beam projection lithography.
BACKGROUND OF THE INVENTION
The SCALPEL method (Scattering with Angular Limitation in Projection Electron-beam Lithography) is known as a method which employs a beam of electrons for imaging and exposing a radiation sensitive layer. This process is described in the white book “SCALPEL: A Projection Electron-Beam Approach to Sub-Optical Lithography”, Technology Review, December 1999, by J. A. Liddle, Lloyd R. Harriott, A. E. Novembre and W. K. Waskiewicz, Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, N.J. 07974, USA. The entire disclosure of said document is incorporated herein by reference. Furthermore, U.S. Pat. Nos. 5,079,112, 5,130,213, 5,260,151, 5,376,505, 5,258,246, 5,316,879 as well as European patent applications nos. 0,953,876 A2 and 0,969,326 A2 relate to the SCALPEL process. The entire disclosures of the above-mentioned patent documents are likewise incorporated herein by reference.
A conventional imaging lens arrangement with two focusing lenses which can be employed for this purpose is described herein below with reference to FIG.
1
.
FIG. 1
schematically shows a mask support
1
carrying an object, namely structures
3
which are provided in the form of a mask and are to be imaged, such that said structures are disposed in a focal plane of a focusing magnetic lens
5
, i.e., they are spaced apart from the magnetic lens by a distance corresponding to the focal length of the magnetic lens.
The lens
5
images the object plane with the pattern
3
to be imaged to infinity, and a further magnetic lens
7
is provided for imaging the pattern imaged by the lens
5
onto a substrate surface
9
which is spaced apart from the lens
7
by a distance corresponding to the focal length thereof. Between the two lenses
5
and
7
, there is provided an aperture stop
11
which is spaced apart from the lens
5
by a distance corresponding to the focal length thereof and from the lens
7
by a distance corresponding to the focal length of the lens
7
. Particle beams
12
,
13
traversing the mask outside of the structures
3
to be imaged traverse the mask substantially straightly such that they pass through a so-called “crossover point” disposed in the center of the aperture stop
11
, so that these beams are imaged onto the substrate surface
9
. The structures
3
to be imaged are defined by a material on the mask support
1
, which material scatters the electrons comparatively strongly, so that beams impinging on such a stronger scattering structure
3
are deflected from their original direction, as it is shown in
FIG. 1
for a beam
14
. Accordingly, this beam cannot be deflected by the lens
5
to the crossover point in the aperture stop
11
, so that it is absorbed by the aperture stop
11
and thus not imaged onto the substrate
9
either.
In order for the mask
3
to be imaged onto the substrate
9
, it is not necessary to particle-optically illuminate the entire mask at once. Rather, it is also possible to illuminate at any time merely a subfield of the mask and to move said subfield over the mask area in scanning fashion. A subfield is outlined in
FIG. 1
by central and peripheral beams
12
, said subfield being positioned centrally on an optical axis
15
of the lenses
5
and
7
. A subfield which is offset in the mask plane in respect of the optical axis
15
by a distance M is outlined by central and peripheral beams designated by reference numeral
13
.
SUMMARY OF THE INVENTION
It has been found that, in the above-described lens arrangement, imaging characteristics satisfying higher demands are not achievable, in particular for subfields which are deflected from the optical axis.
It is an object of the present invention to propose a particle-optical imaging lens arrangement which enables a reduction of aberrations.
In particular, it is an object of the invention to propose a lens arrangement which enables the reduction of aberrations for particle beams which extend outside of an optical axis of components of the lens arrangement.
Moreover, it is an object of the invention to propose a method for manufacturing miniaturized devices which enables the device to be manufactured with increased precision.
According to a first aspect of the invention, a lens arrangement is provided for the particle-optical imaging of an object, to be imaged and positionable in an object area, into an image area, the lens arrangement comprising a first focusing lens device and a second focusing lens device as well as a deflection lens device. Here, the object area and the image area may at first be of any shape given by the image. However, in practice, an approximation of at least one of the areas to a planar shape is strived at in order to enable, first, a simple configuration of the object or/and the image area and, second, to reduce aberrations which result, among others, from the fact that the object is not exactly positioned in the intended object area or a substrate to be exposed is not exactly positioned in the intended object area.
The first focusing lens device provides a field which has a focusing effect on the imaging particles, so that at least a subfield of the object area is imaged into a subfield of an intermediate image area of the lens arrangement. The second focusing lens device, too, provides a field having a focusing effect, namely for imaging at least the subfield of the intermediate image area into a subfield of the image area.
In order to reduce aberrations of the first and/or the second focusing lens device, the lens arrangement comprises a deflection lens device for providing a field having a deflecting effect on the imaging particles in the region of the intermediate image area. The field of the deflection lens device having a deflecting effect causes the intermediate image to tilt before it is imaged by the second focusing lens device into the image area. Accordingly, aberrations which result into a tilt of the image area relative to a nominal image area can be compensated for. In particular, these aberrations are such which are referred to as image field curvature.
A field having a focusing effect is to be understood in this connection as a field which substantially does not deflect a suitably selected central beam and which deflects decentral beams extending with increasing distance from the central beam and parallel thereto towards the central beam, the angle at which the decentral beams are deflected towards the central beam also increasing with increasing distance of the diffracted beam from the central beam. This focusing effect need not be produced, at a given point in time, in the entire effective range of the fields of the first and the second focusing lens devices, respectively. Rather, it suffices if a partial section of the fields of the focusing lens device has such a focusing effect on the particles traversing said partial section. The effect which the focusing lens device has on the imaging particles is thus comparable to that which a convex lens has in light optics.
Preferably, the first or/and the second focusing lens device provides a field which comprises a magnetic or/and electric field which is substantially axially symmetric in respect of such a central beam of a bundle of beams. As an alternative or in addition thereto, the first or/and the second focusing lens device may comprise two or three axially spaced apart field arrangements in order to achieve the focusing effect, wherein the two field arrangements may comprise dipole or/and quadrupole field
Carl Zeiss SMT AG
Dinh Jack
Epps Georgia
Osha Novak & May L.L.P.
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