Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-04-28
2002-08-13
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C361S234000
Reexamination Certificate
active
06433346
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to reticle (mask) holders (i.e., “chucks”) as used in microlithography apparatus and methods employed in the manufacture of semiconductor devices, displays, and the like. More particularly, the invention pertains to reticle chucks useful in a low-pressure atmosphere as encountered in charged-particle-beam microlithography.
BACKGROUND OF THE INVENTION
Microlithography is a key technology used in the fabrication of semiconductor integrated circuits, displays, and the like. In microlithography, an image of a circuit pattern, defined by a mask or reticle, is projected onto the surface of a “sensitized” substrate such as a semiconductor wafer coated with a suitable “resist.”
In view of the resolution limits of optical microlithography, a large amount of effort currently is being devoted to the development of microlithography systems that use a charged particle beam (e.g., electron beam or ion beam) to transfer a pattern, defined on a mask or reticle, to a sensitized substrate (e.g., semiconductor wafer). Charged-particle-beam (CPB) microlithography offers prospects of improved resolution compared to optical microlithography.
FIG. 3
shows a CPB microlithography system for projection-exposing a reticle pattern. An electron beam EB emitted from an electron gun
31
propagates along an axis AX and is collimated by a condenser lens
32
. The electron beam is deflected within an XY plane by a field-selection deflector
33
to direct the beam to a “subfield” or other exposure unit of a reticle
50
. A “subfield” is a region of the reticle
50
hat is illuminated by the electron beam at any given instant of time, and normally defines a small respective portion of the overall pattern defined by the reticle. The electron beam propagating from the electron gun
31
to the reticle
50
is termed the “illumination beam.” As the illumination beam passes through the reticle
50
, the beam acquires an ability to form an image of the illuminated subfield, and hence is termed a “patterned beam.” The patterned beam experiences a prescribed magnitude and direction of lateral deflection imparted to the beam by a deflector
34
that causes the patterned beam to be incident on a prescribed region of the substrate (“wafer”)
9
. The illuminated region of the wafer
9
corresponds to the particular subfield of the reticle
50
actually being illuminated by the illumination beam. As the patterned beam propagates to the wafer
9
, the patterned beam passes through first and second projection lenses
35
,
36
, respectively, (collectively comprising a “projection-lens system”) to form an image of the respective pattern portion on the surface of the wafer
9
. The size of the image as formed on the wafer
9
is “reduced” (demagnified) according to a prescribed demagnification ratio of the projection-lens system.
The reticle
50
is mounted on a reticle stage
37
so as to extend parallel to an X-Y plane (in
FIG. 3
, the X-axis extends perpendicularly to the plane of the page). During microlithographic exposure of the wafer
9
, the reticle stage
37
is driven continuously in the X-axis direction and stepwise in the Y-axis direction by a stage driver
38
. The position of the reticle stage
37
in the X-Y plane is sensed by a respective laser interferometer
39
that produces respective output signals routed to a controller
24
.
The wafer
9
is mounted on a wafer stage
12
and extends in an X-Y plane parallel to the reticle
50
. During exposure, the wafer stage
12
is driven continuously in the X-axis direction and stepwise in the Y-axis direction by a stage driver
40
. Because the image is inverted by the projection lenses
35
,
36
, the direction of travel of the wafer stage
12
in both the continuous-motion direction and the stepwise-motion direction during exposure are opposite the corresponding motions of the reticle stage
37
. The position in the X-Y plane of the wafer stage
12
is sensed by a respective laser interferometer
41
that produces output signals routed to controller
24
.
Deflector power supplies
42
,
43
provide electrical power to the deflectors
33
,
34
, respectively, under control of the controller
24
.
FIG. 4
illustrates various relationships extant between the reticle
50
and the wafer
9
. The areas
60
shown on the wafer
9
are “dies.” (A die is a separate area on the wafer
9
into which an entire pattern from the reticle
50
is to be transferred.) For use in a microlithography apparatus such as that shown in
FIG. 3
(in which projection-exposure is performed by dividing the reticle pattern into subfields sized for the particular optical field of the projection-lens system), the pattern
51
of the reticle
50
is divided into multiple regions
51
a
,
51
b
,
51
c
termed “stripes.” Each stripe has a length dimension that extends in the direction (X-direction) of continuous motion of the reticle
50
. Each stripe
51
a
,
51
b
,
51
c
is further divided into multiple subfields
52
arranged by rows in each stripe. In a similar manner, each of the dies
60
on the wafer
9
can be represented as multiple “stripes”
61
a
,
61
b
,
61
c
, wherein each stripe is further divided into multiple “transfer subfields”
62
.
During exposure of a pattern image onto a die
60
, as the reticle
50
and wafer
9
complete one cycle of continuous motion, the respective pattern portions contained in each of the subfields
52
of a stripe
51
a
,
51
b
,
51
c
are projection-exposed, one after the other, into corresponding transfer subfields
62
of a respective stripe
61
a
,
61
b
,
61
c
. For example, in
FIG. 4
, as the reticle
50
moves continuously in the −X-direction (arrow B
1
) and the wafer
9
moves continuously in the +X-direction (arrow C
1
), the electron beam EB is deflected back and forth along the Y-axis (arrow D) to thus scan, in sequence, each of the subfields
52
of the stripe
51
a
. After completing exposure of the stripe
51
a
in this manner, the reticle
50
is stepped in the −Y-direction (arrow B
2
) and the wafer
9
is stepped in the +Y-direction (arrow C
2
). Next, as the reticle
50
and the wafer
9
are moved continuously in the +X- and −X-directions (arrows B
3
and C
3
), respectively, the electron beam EB is deflected so as to illuminate, in sequence, the subfields
52
of the stripe
51
b
. After completing exposure of the stripe
51
b
, the reticle
50
is stepped in the −Y-direction (arrow B
4
) and the wafer
9
is stepped in the +Y-direction (arrow C
4
). Then the reticle
50
and wafer
9
are moved continuously in the −X- and +X-directions (arrows B
5
and C
5
), respectively, to expose the stripe
51
c
. This sequence of exposure steps is repeated until the reticle pattern has been exposed in each of the dies
60
of the wafer
9
.
FIG. 5
shows a conventional reticle holder (“reticle chuck”)
500
suitable for mounting to the reticle stage
37
(
FIG. 3
) and configured to hold a reticle substrate
101
. The reticle substrate
101
is placed on the reticle chuck
500
which holds the reticle by electrostatic attraction. The reticle chuck
500
comprises electrodes
503
,
503
′ situated depthwise in the reticle chuck
500
. The electrodes
503
,
503
′ are connected to an electrode controller
502
. Whenever the electrode controller
102
applies a voltage to the electrodes
503
,
503
′, an electrostatic force is created that attracts and thus urges the reticle substrate
101
against the surface of the reticle chuck
500
. In a region
504
of the reticle, as indicated in the figure, the reticle pattern can be defined, and an area
505
within the region
504
is where the pattern actually is defined.
An apparatus including an electrostatic chuck is disclosed, for example, in Japanese Kôkai Patent Document No.
Hei
10-050584. Additional examples of electrostatic wafer chucks for use in other semiconductor manufacturing processes are disclosed in Japanese Kôkai Patent Document Nos.
Hei
5-063062 and
Berman Jack
Klarquist & Sparkman, LLP
Nikon Corporation
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