Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2002-04-04
2004-06-29
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492220, C250S492210, C250S492230, C250S3960ML
Reexamination Certificate
active
06756599
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a particle-optical apparatus for changing trajectories of charged particles of a beam of particles. Furthermore, the invention relates to an illumination apparatus and a projection system comprising such a particle-optical apparatus as well as a method for device manufacture. Such method comprises a photolithographic step in which the particle-optical apparatus is employed. In particular, the particle-optical apparatus is provided for use in an projection electron-beam lithographic system as well as for use in a method for device manufacture by means of projection electron-beam lithography.
BACKGROUND OF THE INVENTION
The so-called 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 method 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 in this description 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 method. The entire disclosures of the above-mentioned patent documents are likewise incorporated in this description by reference.
A conventional projection lithographic system is used, for example, for the manufacture of a semiconductor device. Here, the structures to be formed on a semiconductor wafer are defined in a mask, the mask is illuminated by a beam of electrons and the structures defined on the mask are imaged onto the semiconductor wafer. The semiconductor wafer is provided with a radiation sensitive layer. After having been exposed by the electron beam, the radiation sensitive layer as well as the semiconductor wafer are subjected to further steps for forming the structures in the wafer material.
FIG. 1
schematically shows an illumination apparatus for illuminating a mask
3
with charged particles. The charged particles are electrons which are emitted by an electron source
5
in a beam direction
7
. The particle beam emitted by the source
5
exhibits little divergence which, for reasons of illustration, is, however, shown in
FIG. 1
enlarged in size. A maximum angle &agr; of the electrons with respect to the beam direction
7
is about 5 mrad.
The source is imaged by a first electron-optical focusing lens
9
into a front focal plane
11
of a second electron-optical focusing lens
13
. The focusing lens
13
acts to shape the electrons divergently traversing the focal plane
11
such that a substantially parallel particle beam
15
with extended beam cross-section is formed in order to illuminate a field
17
on the mask
3
of a size of about 1 mm transverse to the beam direction
7
.
The maximum illumination aperture which is attainable with this type of illumination is determined by the spatial dimension h of the source
5
transverse to the beam direction
7
as well as by the focal length f
1
of the lens
13
. The maximum angle &bgr; of the particles with respect to the beam direction
7
, when the same impinge on the mask
3
, is determined by
β
=
h
2
·
f
1
.
For small dimensions of the source
3
(
FIG. 1
shows a dot-shaped source), the illumination aperture is thus low. However, a high illumination aperture is desirable in order to be able to transfer also small structures defined on the mask to the wafer with precision.
It is conceivable to increase the spatial dimension of the source transverse to the beam direction in order to increase the illumination aperture. However, it is problematic for sources of charged particles to increase the source dimension if the field illuminated on the mask is to be uniformly illuminated as well.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a particle-optical apparatus which contributes to the increase of an illumination aperture in a particle-optical illumination system.
Moreover, it is an object of the present invention to propose a particle-optical apparatus for changing trajectories of charged particles of a particle beam. In this respect, it is, in particular, an object of the invention to propose a particle-optical apparatus which selectively changes the trajectories of the charged particle, i.e., which acts only on trajectories of specific charged particles and not uniformly on the trajectories of all particles of a particle beam.
Furthermore, it is an object of the present invention to propose an illumination apparatus for illuminating a field which is to be illuminated and is spatially extended transverse to the beam direction with a comparatively high illumination aperture or/and comparatively uniformly.
Moreover, it is an object to propose a projection system, the illumination apparatus of which exhibits the above-mentioned advantages. It is a still further object of the invention to propose a method for manufacturing in particular miniaturized devices which enables the devices to be manufactured with increased precision.
To this end, the invention is based on the following consideration:
In an imaging illumination system, as it has been described above with reference to
FIG. 1
by way of example, the light-transmitting value or emittance is a conservative quantity. This quantity is defined as the product of the square root of the illuminated area and the illumination divergence (numerical aperture). In an imaging illumination system, an increase of the illumination divergence is thus not achievable without decreasing the illuminated area. Therefore, the invention is based on the idea to develop a particle-optical apparatus which does not act as an imaging system but changes the trajectories of the charged particles traversing the particle-optical apparatus in a different way. The trajectories of different groups of particles are to be changed differently such that, all in all, an increase of the light transmitting value or emittance of the beam passing through the apparatus is achieved.
In particular, the invention proposes a particle-optical apparatus comprising two cylindrical electrode arrangements which are fitted into one another, said electrode arrangements being disposed relative to a particle beam entering the apparatus such that the beam direction is oriented approximately parallel to the direction of extension of at least one of the cylindrical electrodes. Moreover, an inner one of the two electrode arrangements is of such a length and has such a diameter that trajectories of at least those particles which enter the apparatus at an angle with respect to the beam axis which is larger than a minimum angle traverse the inner electrode arrangement radially with respect to the beam direction. To this end, the inner electrode arrangement is at least partially transparent for the charged particles. There is an electric potential difference between the inner electrode arrangement and the outer electrode arrangement such that a kinetic component of the particles traversing the inner electrode arrangement is reversed, said kinetic component being oriented transversely to the beam direction.
The inner and outer electrode arrangements together act like a cylindrical, internally mirrored tube which encloses the particle beam and reflects particles which want to escape from the interior of the cylinder back into the same.
For a group of particles of the particle beam which enter the apparatus with little divergence, the apparatus is preferably not effective, that is, this group of particles traverses the apparatus straightly, so that an observer positioned at the exit side of the apparatus perceives these particles as emerging from the particle source.
For another group of particles with increased di
Carl Zeiss SMT AG
Gill Erin-Michael
Lee John R.
Rosenthal & Osha L.L.P.
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