Lithographic process for device fabrication using electron...

Details Lithographic process for device fabrication using electron... Lithographic process for device fabrication using electron...

1999-03-15

2001-01-23

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

06177218

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed to a lithographic process for device fabrication in which charged particle energy is used to delineate a pattern in an energy sensitive material. The pattern is delineated by projecting the charged particle energy onto a patterned mask, thereby projecting an image of the mask onto the energy sensitive material.
2. Art Background
In device processing, an energy sensitive material, denominated a resist, is coated on a substrate such as a semiconductor wafer (e.g., a silicon wafer), a ferroelectric wafer, an insulating wafer, (e.g. a sapphire wafer), a chromium layer supported by a substrate, or a substrate having a combination of such materials. An image of a pattern is introduced into the resist by subjecting the resist to patterned radiation. The image is then developed to produce a patterned resist using expedients such as a solution-based developer or a plasma etch to remove one of either the exposed portion or the unexposed portion of the resist. The developed pattern is then used in subsequent processing (e.g. as a mask to process (e.g. etch) the underlying layer). The resist is then removed. For many devices, subsequent layers are formed and the process is repeated to form overlying patterns in the device.
In recent years, lithographic processes in which a charged particle beam is used to delineate a pattern in an energy sensitive resist material have been developed. Such processes provide high resolution and high throughput. One such process is the SCALPEL® (scattering with angular limitation projection electron beam lithography) process. The SCALPEL® process is described in U.S. Pat. No. 5,260,151 which is hereby incorporated by reference.
Referring to
FIG. 1
, in the SCALPEL® process, a mask
10
is used to pattern particle beams
11
and
12
. The entire mask
10
is not illuminated at once. Rather, the mask
10
is illuminated in segments (two adjacent segments
25
and
26
are illustrated in FIG.
1
). Accordingly, segment
25
is first illuminated by means of particle beam
11
and subsequently segment
26
is illuminated by particle beam
12
. Mask
10
, as shown, consists of a membrane
13
, which is transparent to the particle beams incident thereon.
The developed image of the mask pattern is defined by blocking regions
14
, which scatter the particle beams incident thereon. The blocking regions block the particles incident thereon from being transmitted onto the resist-coated wafer
24
. In the illustrated example, the mask
10
also has skirt regions
15
on the periphery of the segments
25
and
26
. Supporting struts
16
are spaced to define a mask segment
25
and
26
. Emerging beams
11
a
and
12
a
are that portion of the radiation incident on the mask that is significantly scattered by either the blocking regions
14
or skirt regions
15
. Skirt regions
15
are provided because it is preferable for the incident beam to fit entirely within the area defined by the segment and not to contact the support struts. Since the diameter of the beam incident on the mask segment may extend beyond the patterned region of the mask segment in at least one dimension, the skirt regions are provided so that the distance between the struts
16
is greater than the diameter of the beam.
Unblocked illumination, consisting, in sequence, primarily of beams
11
a
and
12
a
is caused to converge by means of electromagnetic/electrostatic first projector lens system
17
, thereby producing emerging beams
11
b
and
12
b
to result in cross-over, e.g. of beams
11
c
and
12
c
at position
18
, as depicted on the plane of apertured scatter filter
19
. Filter
19
is on the back focal plane for the instance in which beams
11
a
and
11
b
are parallel to the optical axis.
Second projector lens system
22
is of such configuration and so powered as to bring the beams of each of the bundles (
11
c
and
12
c
) into an approximately parallel relationship. The action of the lens
22
is sufficient to direct the on-axis bundle
11
d
into orthogonal incidence onto wafer
24
. For the off-axis bundle
12
c
, redirection is required in order to avoid imaging the struts
14
and skirts
15
that separate mask segments
25
and
26
. Such redirection is performed by deflectors
20
and
21
. Deflectors
20
are so energized as to redirect off-axis beams such as beams
12
c
to result in positioned beams
12
d
. The function of the deflectors
21
is to bring about final directional control so as to result in beams
12
e
and so as to eliminate images of associated struts and skirts.
Various strategies for blending the images projected from discrete areas of a patterned mask in order to provide a seamless image in the energy sensitive material have been suggested. One such strategy is described in U.S. Pat. No. 5,624,774 to Okino et al. In Okino et al., the mask contains patterned regions separated by border region. The image of a first pattern is transferred into the energy sensitive material. The image of a second pattern is then transferred into the energy sensitive material. Pattern
1
and pattern
2
are separated by a border on the mask. However, the image of the border is not to be transferred into the energy sensitive material, that is, the image of pattern
1
and the image of pattern
2
are to be seamlessly joined (stitched) in the energy sensitive material. In order to accomplish this, Okino et al. have a third pattern on the mask which is an image of the desired seam between patterns one and two (i.e. pattern
3
has a certain portion of the side of pattern
1
adjacent to pattern
2
and comparable portion of pattern two from the side adjacent to pattern
1
. Thus Okino et al. have a separate pattern of the desired seam between all of the main patterns on the mask.
As previously noted, the mask used in SCALPEL® has a plurality of patterned areas separated by struts. In the SCALPEL® process, it is desired to produce a seamless image of the patterned areas on the mask. If the images of the patterned areas are not precisely joined, then the device that is ultimately fabricated may be defective (e.g., if the pattern is a conductive path and the portions of the image are not properly aligned, conductivity can be reduced or destroyed, rendering the device unuseable). Accordingly, an efficient and accurate process for producing a seamless image from a plurality of discrete patterned portions on a strutted mask is desired.
SUMMARY OF THE INVENTION
The present invention is directed to a lithographic process for device fabrication in which a pattern is transferred from a mask into an energy sensitive material by projecting charged particle (e.g. electron beam) radiation onto the mask. The radiation transmitted through the mask and incident on the layer of energy sensitive material transfers an image of the pattern into the energy sensitive material.
An example of a SCALPEL® mask is illustrated in FIG.
2
. The mask
100
has a thin (about 100 nm-thick) membrane
105
made of a low atomic number material; a thin (about 20 nm thick) patterned layer
110
made of a high atomic number material; a supporting grillage
115
and a mounting ring
120
. SCALPEL® masks are described in Liddle, J., et al., “Error budget analysis of the SCALPEL® mask for sub-0.2 &mgr;m lithography,”
J. Vac. Sci. Technol.
B 13(6), pp. 2483-2487 (1995), which is hereby incorporated by reference.
The mask
100
contains a plurality of patterned areas
125
. Referring to
FIG. 3
, a continuous image
200
(
FIG. 3C
) is formed from segmented pattern
205
(FIG.
3
A). The continuous image
200
is formed in a layer of energy sensitive resist material formed on a semiconductor substrate. The image depicted in the figures is not representative of an actual pattern used in device fabrication, but is provided to illustrate the general concept of assembling an image from discrete pattern segments on the mask. A discussion of assembling an image using a mask with a segmented pattern in described in Berger, S. D., et al., “High t

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