Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-05-15
2002-10-29
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S005000, C430S312000, C430S322000, C430S394000
Reexamination Certificate
active
06472123
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the fabrication of photolithography devices such as reticles and semiconductor masks. More particularly, the present invention relates to a method of forming clear fields on a reticle and to reticles formed by electron-beam processing.
BACKGROUND OF THE INVENTION
In the manufacture of integrated circuits (ICs), microlithography is used to pattern various layers on a wafer. A layer of resist is deposited on the wafer and exposed using an exposure tool and a template, such as a reticle. During the exposure process, radiant energy, such as ultraviolet light, is directed through the reticle to selectively expose the resist in a desired pattern. The resist is then developed to remove either the exposed portions for a positive resist or the unexposed portions for a negative resist, thereby forming a resist mask on the wafer. The resist mask can then be used to protect underlying areas of the wafer during subsequent fabrication processes, such as deposition, etching, or ion implantation processes.
The manufacture of ICs generally requires the use of numerous reticles or masks. Each individual reticle is expensive and time-consuming to manufacture. Mask production likewise involves substantial time and expense. The complete circuit patterning for a typical IC may require 10 to 20 or more reticles. Thus, accurate formation of reticles may yield savings in IC production costs.
Reticles and masks typically include an opaque thin film of a metal, such as chromium or molybdenum silicide, deposited in a pattern on a transparent substrate of quartz or glass. Defects in the pattern of chromium or molybdenum silicide may occur as a result of electrostatic charge added to the reticle preform during manufacture of the reticle. In conventional reticle patterning methodologies, a photoresist material overlays the layer of chromium. An electron beam exposes a portion of the photoresist material based upon a predetermined pattern. The exposed portion of the photoresist material is removed leaving uncovered a portion of the chromium. The unexposed photoresist material is then used to block the etch and leave the desired pattern in the metal to create the reticle.
Referring to
FIGS. 1-3
, a reticle preform
10
is shown in various stages of manufacture. The reticle preform
10
includes a substrate
12
located on a base
24
. The substrate
12
is formed from a transparent material, such as quartz or glass. A layer of metal
13
, such as, for example, chromium or molybdenum silicide, overlays the substrate
12
and is located beneath a layer of a photoresist material
14
. The photoresist material
14
is formed of a material which is suitable for exposure by electrons.
An electron beam apparatus
16
is schematically shown (
FIGS. 1
,
2
) in a position to direct electrons toward the photoresist material
14
. The apparatus
16
includes an electron beam device
18
, such as an electron beam gun, in mechanical and electrical connection with a controller
22
. An actual electron beam gun, such as one manufactured by ETEC systems, is illustrated in FIG.
10
. The electron beam device
18
directs a stream of electrons
26
toward the photoresist material
14
in a predetermined writing pattern
28
, shown by the dashed lines on the photoresist material
14
. The stream of electrons
26
preferably is controlled electrostatically.
Conventionally, a single predetermined writing pattern
28
is programmed into the controller
22
, which controls the actions of the electron beam device
18
through the appendage
20
. The writing pattern
28
is followed such that predetermined portions of the photoresist material
14
are exposed by the stream of electrons
26
. The exposed portions of the photoresist material
14
are then removed. The remaining unexposed portions of the photoresist material
14
are used as a mask for etching the now exposed portions of the metal
13
to create a reticle
100
(
FIG. 3
) having the desired pattern of metal
13
.
Specifically, and with reference to
FIGS. 1 and 2
, the writing pattern
28
separates the photoresist material
14
into a first strip
30
, a second strip
32
, a third strip
34
, a first portion
36
, a second portion
40
, a third portion
70
, and an interlayer portion
68
. In
FIG. 1
, the writing pattern
28
is shown in dashed lines to indicate that the exposure process has only just started. In
FIG. 2
, the writing pattern
28
is shown in solid lines to indicate that the exposure process has been completed.
In the known process, the stream of electrons
26
exposes the portions
36
,
40
,
70
, and
68
allowing for the subsequent removal of the photoresist material
14
resident in the exposed areas. One problem encountered through the conventional methodology is that using an electron beam to expose large photoresist areas, such as the second and third portions
40
,
70
, sometimes causes a localized build up of electrostatic energy in the reticle preform
10
. The presence of electrostatic energy is detrimental to the accuracy of the stream of electrons
26
, causing the stream
26
to be displaced, or to skew away, from the path intended by the writing pattern
28
(FIG.
2
), thus altering the pattern of exposed photoresist material
14
from the desired writing pattern
28
.
Applicant has determined that where electrostatic energy has caused a displacement of the electron stream
26
the photoresist material
14
exposed may not be consistent with the amount intended to be exposed according to the writing pattern
28
. Instead, the exposed photoresist material
14
which is subsequently removed will leave first, second, third, and fourth uncovered areas of metal
56
,
42
,
71
, and
69
which respectively were beneath the portions
36
,
40
,
70
, and
68
. Since the exposed portions
36
,
40
,
70
, and
68
did not exactly correspond with the writing pattern
28
, the underlying metal areas
56
,
42
,
71
, and
69
also will not match the desired metal areas according to the writing pattern
28
. In addition, the remaining unexposed portions of photoresist material
14
, namely a first strip
50
, a second strip
52
and a third strip
72
do not match with the unexposed strips that were to be formed according to the intended writing pattern
28
.
After removing the exposed photoresist material
14
(as described above), the exposed areas of metal, namely the first, second, third and fourth uncovered areas of metal
56
,
42
,
71
,
69
are etched. The remaining unexposed portions of photoresist, namely the first, second, and third strips
50
,
52
,
72
are washed away by a known method to form the reticle
100
(FIG.
3
), including metal strips
62
,
64
,
66
positioned on the substrate
12
.
Since the exposed and unexposed portions of the photoresist material
14
did not match the writing pattern
28
, the metal strips
62
,
64
,
66
will likewise differ from the desired strips. The discrepancy between the actual metal strips
62
,
64
,
66
and the desired strips may be substantial enough to cause the reticlc
100
to form defective semiconductor devices. Alternatively, additional measures may be required to compensate for the discrepancy.
SUMMARY OF THE INVENTION
The present invention provides a method of forming a reticle including exposing a first portion of the photoresist layer in accordance with a first writing pattern and exposing a second portion of the photoresist layer in accordance with a second writing pattern.
The present invention also provides a photolithography device for forming a semiconductor device that has a transparent substrate and a pattern of conductive material overlaying the substrate. The conductive material pattern is formed utilizing multiple write passes of electron beam energy.
The present invention also provides an apparatus for forming a photolithography device. The apparatus includes a device for projecting electrons at a layer of photoresist material and a controller for controlling the device such that a multiple of
Baxter Janet
Dickstein , Shapiro, Morin & Oshinsky, LLP
Micro)n Technology, Inc.
Walke Amanda C.
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