Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2000-10-04
2002-08-27
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S296000, C430S942000
Reexamination Certificate
active
06440620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is generally directed to electron patterning, and more particularly electron patterning using scatter-nonscatter masking and even more particularly electron patterning in accordance with the SCALPEL process described in U.S. Pat. No. 5,079,112, issued Jan. 7, 1992. The present invention is also applicable to ion patterning.
2. Description of the Related Art
An exemplary conventional apparatus
40
depicted in
FIG. 1
includes an electron or other energy source
41
, condenser lens system
42
, mask
43
including blocking regions
44
and transparent regions
45
, objective lens
46
, back focal plane filter
47
shown as provided with on-axis aperture
48
, projector lens system
49
, exposure medium
50
, between lens
51
and stage
52
, which together constitute registration and alignment system
53
. The apparatus
40
is completed by vacuum chamber
54
and air lock
55
, the latter providing the specimen exchange.
Another conventional apparatus shown in
FIG. 2
includes a particle source
30
, illustrated as an electron gun, delivering electron beam
31
. Collimator lens
32
brings the initially diverging rays into parallel relationship at
33
as shown. Scan deflectors
34
and
35
are responsible for electronic scanning, e.g. with continuous x-direction scanning. The second deflector provides for y-direction movement, either continuous or as stepped intermediate x-direction scans. Mask
36
, as depicted again in exemplary terms, is shown as segmented by struts
37
. Upon passing through the mask, the now pattern-containing beam
38
, comes under the influence of dynamic focus and stigmator deflectors
39
and
40
. Deflectors
41
and
42
provide for a precision in placement of adjoining regions during x- and y-electronic scanning/stepping.
Projection lens
43
is provided with variable axis deflector
44
. The multiple aperture filter
45
including apertures
46
produces a focused image on wafer
47
shown atop wafer stage
48
. As discussed, for illustrative purposes, mask
36
is shown as constituted of pattern regions corresponding with strut-separated segments. Following modulation which imparts patterning information on the beam during passage through mask
36
, the beam is converged, finally reaching a crossover (or image inversion) on or near the plane defined by aperture filter
46
. The aperture filter
45
is included for electron imaging for blocking unwanted scattered radiation. It may serve, as well, to block other “noise”—e.g. by blocking unwanted feature-edge scattered radiation. Aperture
46
may define the numerical aperture (or pupil) of the system.
The apparatus of
FIG. 1
has separate condenser and projector lens systems. This may be preferred to facilitate focusing with minimum mechanical adjustment. There may be a further preference for multiple lenses in the projector system. For example, use of three lenses is useful to allow correction for image distortion and other aberrations, and to control image rotation as well.
The exemplary, conventional projector lenses
49
,
43
may include other elements, e.g. may include a doublet of two optically equivalent lenses, in operation oppositely polarized to inherently cancel corresponding aberrations implicit to design or operation common to the two. Consistent with usual practice, the hardware responsible for generation of the functional shaped field is, itself, referred to as the “lens”.
In
FIG. 2
, lenses
39
and
40
perform dynamic correction for aberration as well as for focusing, e.g. correcting for wafer height variation as well as field curvature. Assigning responsibility for dynamic adjustment to these lenses speeds the process by lessening inductive lag time. For example, dynamic aberration correction may entail additional deflectors compensating for errors resulting from equipment/process defects. Lenses
39
and
40
are illustrative and they may include additional elements.
FIGS. 3 and 4
illustrate systems with exemplary optics.
FIGS. 3 and 4
discussed below illustrate schematics serving as a basis for discussing the fundamental principles involved in conventional electron patterning.
The conventional single lens system depicted in
FIG. 3
makes use of beam electrons, or other delineating energy, identified as rays
1
incident on mask
2
which includes blocking regions
3
and transparent regions
4
. Rays transmitted through transparent regions
4
, are identified as rays
1
a
while those transmitted by blocking regions
3
are identified as rays
1
b
. Such rays are refracted by lens
5
with emerging rays made incident on back focal plane filter
6
. As schematically depicted rays
1
a
pass through filter aperture
7
to result in image
9
including replicated illuminated regions
10
and unilluminated regions
11
. Rays
1
b
scattered beyond a critical scattering angle, do not pass through aperture
7
, but instead are absorbed or otherwise blocked by the non-apertured portion
8
of filter
6
.
A conventional system in which scattered energy is selectively used to form the image is illustrated in FIG.
4
. Here, scattered rays
1
b
pass through apertures
17
while transmitted rays
1
a
are now stopped by filter region
18
. Image
19
a negative of image
9
, results from selective illumination of regions
21
. Regions
20
are unilluminated. In this arrangement, the back focal plane filter is absorbing although alternative designs may make use of forms of scattering such as Bragg scattering, etc.
Generally the projection system(s) illustrated in
FIGS. 1-4
perform mask-to-wafer demagnification, on the order of 4:1-5:1. They are equally applicable to 1:1 and other magnification ratios.
Generally, systems illustrated in
FIGS. 1-4
are arranged so that the resulting image on the wafer is focused as well as possible. As illustrated in a simplified system of
FIG. 5
, the goal is to focus the image
60
at the mask
62
on the wafer
64
. Assuming the lens doublet
66
,
68
as illustrated in
FIG. 5
includes no aberrations, the best focused image
70
occurs at the Gaussian plane
72
. However, due to several types of aberration, the most significant being chromatic and spherical aberrations, present in the lens doublet
66
,
68
, the best focused image plane
74
usually does not coincide with the Gaussian plane
72
. Conventional techniques for determining the best focused image plane
74
have concentrated on separately analyzing the effect of chromatic and spherical aberrations on the location of the best focused image plane. These techniques are discussed below.
A conventional technique for estimating beam focus quality is a point spread function (PSF). Typically this includes launching up to 5000 trajectories' from a single point at the center of the mask
62
plane and studying individual trajectories arrival points at the center of the wafer
64
plane.
Typical initial launch conditions included electrons' angular distribution resulting in landing angles up to 12 mrad (up to 10 mrad, or up to 8 mrad), and electrons' actual energy distribution. The latter have been obtained experimentally by analyzing electrons' energy spread before and after passing through a mask
62
(silicon nitride Si
x
N
y
, 0.1 &mgr;m thick). An exemplary electron energy distribution is shown in FIG.
6
.
As one can see from
FIG. 6
, electron passage through the mask
62
introduces an energy spread change: a substantial fraction (up to 20%) of electrons lose energy due to electron-plasmon inelastic collisions. Peak A in
FIG. 6
describes electrons passed through the membrane without losing energy, and its width is defined by the beam source temperature. Peak B in
FIG. 6
describes electrons passed through the membrane with substantial energy losses due to inelastic collisions with the plasmons. The energy distribution shown in
FIG. 6
are characteristic of electron patterning masks, where membrane thickness is smaller than electron mean free path, such as SCALPEL™ mask structures.
The da
Katsap Victor
Munro Eric
Rouse John Andrew
Waskiewicz Warren K.
Zhu Xieqing
Agere Systems Inc.
Harness & Dickey & Pierce P.L.C.
Young Christopher G.
LandOfFree
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