Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-04-08
2002-08-27
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492220
Reexamination Certificate
active
06441384
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to microlithography apparatus for transferring a pattern (e.g., a circuit pattern), defined by a reticle, onto a sensitive substrate (e.g., semiconductor wafer) using a charged particle beam (e.g., electron beam or ion beam), as used in the manufacture of, e.g., semiconductor integrated circuits and displays.
BACKGROUND OF THE INVENTION
Increases in the level of integration of semiconductor devices have so far kept pace with demand for increasingly more intricate integrated circuits. To meet this demand, it has been necessary that microlithographic exposure apparatus used in the manufacture of such devices be capable of resolving circuit features having increasingly smaller critical dimensions so as to produce such increasingly intricate circuits. In view of the resolution limits of optical microlithography, microlithographic apparatus employing a charged particle beam (e.g., an electron beam) are the subject of much interest as the candidate pattern-transfer technology for achieving resolution of pattern features that are substantially smaller than resolvable by optical microlithography.
In charged-particle-beam (CPB) microlithography, the pattern is usually defined by a reticle. The reticle is illuminated by the charged particle beam; charged particles in the beam passing through the illuminated portion of the reticle carry downstream of the reticle an image of the illuminated portion. The image-carrying beam is focused onto a corresponding region of the substrate which is coated with a suitable “resist” that imprints the pattern. Thus, the reticle pattern is “transferred” to the substrate.
Due to various reasons, the entire reticle pattern is typically not illuminated at any one instant by the charged particle beam. Hence, the reticle field is typically divided (“segmented”) into multiple exposure units such as “stripes,” “subfields,” or other regions (each defining a respective portion of the pattern) that are individually and sequentially exposed by the charged particle beam onto corresponding regions of the substrate. Projection of individual images on the surface of the substrate is accurately controlled to ensure that the images are contiguous with each other to form an image of the complete pattern without overlaps or intervening spaces between projected portions of the pattern. The resulting image of a complete reticle pattern on the substrate surface is termed a “die” which is typically coextensive with one of multiple “chips” typically exposed on the surface of a wafer. For details of this process, reference is made to Japanese Kôkai Patent Publication No. HEI 8-64522.
A schematic diagram of a conventional CPB microlithography apparatus is schematically illustrated in
FIG. 1
, depicting a charged particle beam (e.g., an electron beam), a crossover aperture
2
a,
a scattering aperture
2
b,
projection lenses
3
a
-
3
b,
a substrate
5
, an optical axis
6
, a reticle
7
, a CPB source
8
, and condenser lenses
9
a
-
9
c.
The reticle
7
is irradiated by the charged particle beam
1
emitted from the CPB source
8
via the condenser lenses
9
a
-
9
c.
The charged particle beam
1
illuminates a selected region of the reticle
7
; the beam passing through the illuminated region of the reticle
7
passes through the projection lenses
3
a
-
3
b
and the scattering aperture
2
b
to form an image of the illuminated portion of the reticle on the upstream-facing surface of the substrate
5
.
The combination of the condenser lenses
9
a
-
9
c
(and the beam-shaping aperture
2
a
if present) is termed herein an “illumination-optical system.” Similarly, the combination of the projection lenses
3
a
-
3
b
(and the scattering aperture
2
b
if present) is termed herein a “projection-optical system.” Each of the lenses
9
a
-
9
c,
and each of the lenses
3
a
-
3
b,
can be either an electromagnetic lens or an electrostatic lens as known in the art.
In conventional CPB microlithographic exposure, the charged particle beam is focused by the CPB projection-optical system comprising the projection lenses
3
a
-
3
b.
Depending upon the specific type of projection-optical system used to make the exposure, if the projection lenses
3
a,
3
b
are radially symmetrical about the optical axis
6
(as they typically are), then significant spherical aberrations are usually generated. Spherical aberrations tend to cause blurring of the image as projected onto the substrate.
Whenever edges of features of the pattern as projected are blurred, the resulting pattern has poorly transferred features with, for example, dimensions that are outside specification. Such exposure problems can result in unacceptable deviations in electrical performance of the circuit during use of the semiconductor device, such as breaks, shorts, high-resistance loci, poor gate performance, and the like, which ultimately result in failure of the semiconductor device to meet specification. Consequently, it is necessary to reduce spherical aberration as much as possible.
Spherical aberration is proportional to the cube of the “beam semi-angle” &agr;. The beam semi-angle can be measured at the substrate or at any of various other locations, especially where the beam is convergent or divergent, such as at stop locations. The beam semi-angle is the angular divergence of the charged particle beam from the optical axis at the measurement location. Denoting C
sph
as a spherical-aberration coefficient, C
sph
&agr;
3
expresses the magnitude of the corresponding spherical aberration. Consequently, reducing the beam semi-angle at the image plane provides a way in which to decrease spherical aberration.
According to one proposed approach, multi-pole projection lenses are used. However, whereas aberration-correction methods that utilize multi-pole lenses are theoretically appealing, such methods exhibit considerable problems because manufacturing multi-pole lenses is extremely difficult. Furthermore, aligning the optical axes of multi-pole lenses is very difficult.
Aberration correction using multi-pole lenses has not yet become practical also because actual lens-field distributions exhibit considerable deviation from design specifications as a result of manufacturing errors and alignment errors in such lenses. Such deviations typically result in additional aberrations that degrade image fidelity and resolution. Okayama,
Electron Microscope
25(3):159-166, 1990. Another practical problem is that operation of multi-pole lens systems requires extremely complex electrical control systems.
Besides lens aberrations, blurring of the charged particle beam can result from a “Coulomb effect” which is a Coulombic repulsion occurring between charged particles propagating near each other in the beam, especially at points of convergence and divergence. As the beam semi-angle is reduced, the particles in the beam tend to propagate closer together, thereby increasing the Coulomb effect. By increasing the beam semi-angle, the diameter of the electron beam is increased at points of convergence and divergence (e.g., stop locations), which results in an increased spacing between charged particles at such locations. This increased spacing weakens Coulombic repulsion in inverse proportion to the square of the distance between the particles, thereby resulting in less image blurring. Such a situation is illustrated in
FIG. 2
, in which the abscissa is the beam semi-angle and the ordinate is the magnitude of blurring.
Unfortunately, geometric aberrations (including spherical aberration) exhibited by lenses and deflectors used to focus and deflect the charged particle beam tend to increase as the beam semi-angle increases. Such increases in geometric aberrations tend to increase beam blurring, as also shown in FIG.
2
.
With a multi-pole lens system, the interaction time between adjacent charged particles propagating in a beam increases because the distance from the object plane to the image plane is correspondingly increased. Such increased interaction time also increases beam blurring due to th
Berman Jack
Klarquist & Sparkman, LLP
Nikon Corporation
LandOfFree
Charged particle beam exposure device exhibiting reduced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Charged particle beam exposure device exhibiting reduced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charged particle beam exposure device exhibiting reduced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2908109