Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2001-10-11
2003-09-09
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
Reexamination Certificate
active
06618120
ABSTRACT:
FILED OF THE INVENTION
This invention pertains to microlithography, which involves the transfer of a pattern, usually defined by a reticle or mask, onto a “sensitive” substrate using an energy beam. Microlithography is a key technique used in the manufacture of microelectronic devices such as integrated circuits, displays, thin-film magnetic heads, and micromachines. More specifically, the invention pertains to methods and devices, used in the context of a microlithography method and apparatus, respectively, for compensating for lateral shift accompanying a leveling tilt imparted to a leveling table, such as a wafer table, associated with the wafer stage.
BACKGROUND OF THE INVENTION
As the density and miniaturization of microelectronic devices has continued to increase, the accuracy and resolution demands imposed on microlithographic methods and apparatus also have increased. Currently, most microlithography is performed using, as an energy beam, a light beam (typically deep UV light) produced by a high-pressure mercury lamp or excimer laser, for example. Emerging microlithographic technologies include charged-particle-beam (“CPB”; e.g., electron-beam) microlithography and “soft-X-ray” (or “extreme UV”) microlithography.
All microlithographic technologies involve pattern transfer to a suitable substrate, which can be, for example, a semiconductor wafer (e.g., silicon wafer), glass plate, or the like. So as to be imprintable with the pattern, the substrate typically is coated with a “resist” that is sensitive to exposure, in an image-forming way, by the energy beam in a manner analogous to a photographic exposure. Hence, a substrate prepared for microlithographic exposure is termed a “sensitive” substrate.
Microlithography conventionally is performed using any of various basic approaches including “direct writing,” “contact printing,” and “projection” microlithgraphy. Projection microlithography is the most common.
Basic aspects of a modern microlithography apparatus (“exposure apparatus”)
10
are shown in
FIG. 18
, in the context of a projection-exposure apparatus. A pattern is defined on a reticle (sometimes termed a “mask”)
12
mounted on a reticle stage
14
. The reticle
12
is “illuminated” by an energy beam (e.g., UV light, charged particle beam, X-rays) produced by a source
16
and passed through an illumination-optical system
18
. As the energy beam passes through the reticle
12
, the beam acquires an ability to form an image, of the illuminated portion of the reticle
12
, downstream of the reticle
12
. The beam passes through a projection-optical system
20
that focuses the beam on a sensitive surface of a substrate
22
held on a substrate stage (“wafer stage” or “wafer XY stage”)
24
. As shown in the figure, the source
16
, illumination-optical system
18
, reticle stage
14
, projection-optical system
20
, and wafer stage
24
generally are situated relative to each other along an optical axis AX. The reticle stage
14
is movable at least in the X- and &thgr;
3
-directions via a stage actuator
26
(e.g., linear motor), and the positions of the reticle stage
14
in the X- and Y-directions are detected by respective interferometers
28
. The apparatus
10
is controlled by a controller (computer)
30
.
The substrate
22
(also termed a “wafer”) is mounted on the wafer stage
24
via a wafer chuck
32
and wafer table
34
(also termed a “leveling table”). The wafer stage
24
not only holds the wafer
22
for exposure (with the resist facing in the upstream direction) but also provides for controlled movements of the wafer
22
in the X- and Y-directions as required for exposure and for alignment purposes. The wafer stage
24
is movable by a suitable wafer-stage actuator
23
(e.g., linear motor), and positions of the wafer stage
24
in the X- and Y-directions are determined by respective interferometers
25
. The wafer table
34
is used to perform fine positional adjustments of the wafer chuck
32
(holding the wafer
22
), relative to the wafer stage
24
, in the X-, Y-, and Z-directions. Positions of the wafer table
34
in the X- and Y-directions are determined by respective wafer-stage interferometers
36
.
The wafer chuck
32
is configured to hold the wafer
22
firmly for exposure and to facilitate presentation of a planar sensitive surface of the wafer
22
for exposure. The wafer
22
usually is held to the surface of the wafer chuck
32
by vacuum, although other techniques such as electrostatic attraction can be employed under certain conditions. The wafer chuck
32
also facilitates the conduction of heat away from the wafer
22
that otherwise would accumulate in the wafer during exposure.
Movements of the wafer table
34
in the Z-direction (optical-axis direction) and tilts of the wafer table
34
relative to the Z-axis (optical axis AX) typically are made in order to establish or restore proper focus of the image, formed by the projection-optical system
20
, on the sensitive surface of the wafer
22
. “Focus” relates to the position of the exposed portion of the wafer
22
relative to the projection-optical system
20
. Focus usually is determined automatically, using an auto-focus (AF) device
38
. The AF device
38
produces data that is routed to the controller
30
. If the focus data produced by the AF device
38
indicates existence of an out-of-focus condition, then the controller
30
produces a “leveling command” that is routed to a wafer-table controller
40
connected to individual wafer-table actuators
40
a
. Energization of the wafer-table actuators
40
a
results in movement and/or tilting of the wafer table
34
serving to restore proper focus.
Details of a conventional scheme for tilting of the wafer table
34
are shown in
FIG. 19
, which shows the wafer stage
24
, wafer-stage actuator
23
, wafer table
34
, and interferometer
36
. Relative to the wafer stage
24
, the wafer table
34
is supported by the wafer-table actuators
40
a
. Normally, three wafer-table actuators
40
a
are provided, supporting the wafer table
34
in a tripod manner, relative to the wafer stage
24
, at respective “push points.” The wafer-table actuators
40
a
can be, for example, piezo-electric actuators.
FIG. 19
depicts two closed-loop control systems. A first control system
42
pertains to tilting of the wafer table
34
relative to the wafer stage
24
. A second control system
44
pertains to lateral (X-Y) positioning of the wafer stage
34
. The first control system
42
is diagrammed as including a comparator
45
, a controller
46
, and a converter
47
. A leveling command from the controller
30
responsive to an AF condition detected by the AF device
38
(
FIG. 18
) is routed to the comparator
45
. The comparator
45
also is connected to a feedback loop
48
discussed below. The output signal of the comparator
45
is routed to the controller
46
, which processes the signal according to a respective transfer function G
WT
. The processed signal from the controller
46
is routed to the converter
47
, which converts the processed signal to a torque command (voltage) applied to the wafer-table actuators
40
a
. The resulting energization of the actuators
40
a
causes the wafer table
34
to tilt relative to the wafer stage
24
and relative to a line L
AX
parallel to the optical axis AX. The resulting angular rotation of the wafer table
34
is denoted by &thgr;. Data concerning &thgr; is fed back from leveling-table-tilt sensors (not shown) via the feedback loop
48
to the comparator
45
.
The second control system
44
includes a comparator
50
, a wafer-stage controller
51
, and a converter amplifier
52
. A stage-position command from the controller
30
is routed to the comparator
50
. The comparator
50
is connected to a feedback loop
53
discussed below. The output signal from the comparator
50
is routed to the controller
51
, which processes the signal according to a respective transfer function G
WS
. The processed signal from the controller
51
is routed to the converter amplifier
52
, which conv
Esplin D. Ben
Klarquist & Sparkman, LLP
Nikon Corporation
LandOfFree
Devices and methods for compensating for tilting of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Devices and methods for compensating for tilting of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Devices and methods for compensating for tilting of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3041718