Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-08-21
2001-04-24
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492230, C250S492200, C250S491100, C250S3960ML
Reexamination Certificate
active
06222197
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to aberration compensation for charged-particle-beam pattern-transfer apparatus.
BACKGROUND OF THE INVENTION
High resolution pattern-transfer apparatus are required for the production of small-geometry integrated circuits. While pattern-transfer apparatus using optical radiation are widely used, charged-particle-beam (“CPB”) apparatus using electron beams have also been used. CPB apparatus generally provide a higher resolution than that available with apparatus using optical radiation.
Integrated circuits are generally formed on a semiconductor wafer by forming a series of circuit patterns on a surface of the wafer. The circuit patterns are formed by transferring a sequence of circuit patterns sequentially onto the wafer surface. The resulting integrated circuit is a multi-layered structure in which planar circuits are layered parallel to the surface of the wafer.
In order to produce small-geometry integrated circuits, circuit patterns must be transferred with a high resolution and the various circuit patterns must precisely align on the wafer. Therefore, the individual circuit patterns must be correctly focused on the surface of the wafer and must be precisely registered with other circuit patterns. Registration errors must be kept within an acceptable tolerance.
In CPB pattern transfer, the mask defining the circuit pattern to be transferred to the wafer is usually divided into a plurality of smaller regions referred to as subfields; the pattern portion in a subfield is transferred to the wafer in a single exposure. The subfields are transferred so that they are accurately joined or “stitched” together on the wafer. One CPB system that stitches together subfield patterns is described in Japanese Kokai patent document No. HEI 8-64522.
In CPB pattern-transfer apparatus, aberration correction systems such as deflectors or dynamic compensators are provided to reduce image blurring and distortion in the subfield images caused by aberrations in the CPB optical system. The CPB optical systems use either electromagnetic or electrostatic lenses and high resolution is obtained by designing the deflectors and dynamic compensators to compensate the aberrations of the lenses.
Some pattern-transfer errors arise from variations in wafer thickness or rotational errors of the wafer with respect to the mask during exposure. These errors show up as rotational misalignments of a subfield image, magnification errors of the subfield image, and focus errors. With reference to
FIG. 19A
, illustrative subfield images a
1
, a
2
are shown with respect to ideal subfield images b
1
, b
2
, respectively. The subfield images a
1
, a
2
are tilted by an angle &thgr; with respect to the ideal subfield images b
1
, b
2
and are thus rotationally misaligned with respect to the ideal subfield images b
1
, b
2
. With reference to
FIG. 19B
, illustrative subfield images a
1
, a
2
are shown with respect to ideal images b
1
, b
2
. The subfield images a
1
, a
2
exhibit a magnification error, i.e., the subfield images a
1
, a
2
are too large. In addition, the subfield images a
1
, a
2
overlap along a seam c. With reference to
FIG. 19C
, subfield images are focused at a focal plane f that is a distance &Dgr;z above a wafer surface W. Thus,
FIG. 19C
illustrates a focus error. To correct the types of errors shown in
FIGS. 19A-19C
, the lens currents (or voltages if electrostatic lenses are used) are adjusted. Alternatively, one or more correcting lenses can be provided.
With reference to
FIG. 20
, a conventional electron-beam pattern-transfer apparatus includes an electron gun
901
that produces an electron beam EB. The electron beam EB propagates along an axis AX and is shaped into a desired transverse profile (e.g., a square) by an aperture
903
. A condenser lens
902
then directs the electron beam EB to a selected subfield
951
of a reticle (mask)
905
with a subfield-selection deflector
904
. The electron beam EB transmitted by the reticle
905
is then deflected by a deflector
908
and imaged with a predetermined demagnification onto the wafer
911
with projection lenses
909
,
910
. Deflector controllers
917
,
918
control the magnitude and direction of the deflection produced by the deflectors
904
and
908
, respectively.
The reticle
905
and wafer
911
are mounted on a reticle stage
906
and a wafer stage
912
, respectively, that provide translations in an xy-plane as directed by respective stage controllers
907
,
913
. The locations of the stages
906
,
912
are detected with corresponding position detectors
914
,
915
, typically, laser interferometers. A main controller
916
controls positioning so that the deflectors
904
,
908
and stages
906
,
912
are controlled based on the positions measured by the position detectors
914
,
915
.
With reference to
FIG. 22
, the mask
905
is divided into a plurality of subfields
951
1
-
951
n
, separated from each other by boundary regions
952
that either block or scatter the electron beam EB. The electron beam EB transmitted by a subfield such as the exemplary subfield
951
1
, that is displaced from the axis AX is imaged onto the wafer
911
at a corresponding transfer subfield
9111
1
, that is also displaced from the axis AX. The remaining subfields
951
2
-
951
n
are similarly projected onto corresponding transfer subfields
9111
2
-
9111
n
so that the circuit pattern is defined by the mask
905
transferred to a wafer field
9110
.
The mask subfields
951
are separated by boundary regions
952
that are not transferred to the wafer
911
. To prevent such transfer, appropriate deflection of the electron beam EB is controlled by the deflector
908
. The mask subfields
951
are projected onto the wafer
911
such that the corresponding transfer subfields
9111
contact each other along their respective edges.
Unfortunately, aberration-correcting deflectors and dynamic compensators that correct CPB optical-system aberrations introduce additional aberrations. With reference to
FIG. 21A
, a portion of a circuit pattern that extends across transfer subfields
9111
a
and
9111
b
ideally joins accurately along a seam
9111
c
located between adjacent transfer subfields. Thus, conductors P extending from the subfield
9111
a
to the subfield
9111
b
extend cleanly and contiguously across the seam
9111
c
. Referring to
FIG. 21B
, if there is distortion in the CPB optical system, then subfield images Q
1
, Q
2
are distorted, creating a gap Q
3
between the subfield images Q
1
, Q
2
and a corresponding break in the conductors P. With reference to
FIG. 21C
, distortion can also cause subfield images Q
1
, Q
2
to overlap each other.
A CPB optical system comprises a series of electromagnetic or electrostatic lenses, each of which can exhibit manufacturing errors. In addition, these lenses also exhibit mounting errors so that the electromagnetic fields that focus and deflect the electron beam deviate from design values. The aberrations in CPB images are a function of the CPB path and the electromagnetic fields along the path. See, e.g., Chu and Munro,
Optik
61:121-145 (1982). If the CPB optical system exhibits such manufacturing errors, aberrations such as defocus and distortion are introduced.
Dynamic correction of deflection aberrations has been achieved using astigmatism compensators comprising focus-correction coils or octopoles to reduce deflection image-plane distortions and deflection astigmatism. For example, X. Zhu et al.,
SPIE Proceedings,
2522:66-77 (1995) proposed using focus-correction coils and astigmatism compensators as an astigmatism corrector for 3rd-order deflection distortion and hybrid distortion aberrations. The apparatus of X. Zhu et al. uses two focus-correction coils and two astigmatism compensators and requires precise positioning. In some cases, to correct manufacturing errors, the positions of focus correctors and astigmatism compensators are recalculated and adjusted to reduce the aberrations. However, such readjustment is difficult and impracti
Berman Jack
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Nikon Corporation
LandOfFree
Charged-particle-beam pattern-transfer methods and apparatus 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 pattern-transfer methods and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charged-particle-beam pattern-transfer methods and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2451888