Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-03-15
2003-07-29
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06599666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photolithography techniques used in semiconductor device manufacturing processes. Specifically, the present invention relates to a multi-layer, attenuated phase-shifting mask or reticle that reduces problems associated with side lobe printing in areas including closely-spaced or nested features, while maximizing resolution and depth-of-focus performance for isolated features of a semiconductor device.
2. State of the Art
Photolithography processes are essential to the fabrication of state of the art semiconductor die. Such processes are used to define various semiconductor die features included in semiconductor dice and generally include exposing regions of a resist layer to patterned radiation corresponding to the semiconductor die circuit feature to be defined in a substrate underlying the layer of resist. After exposure, the resist layer is developed to selectively reveal areas of the substrate that will be etched to define the various device features while selectively protecting those areas of the substrate which are not to be exposed to the etching process. In order to properly form a radiation pattern over a resist layer, the radiation is generally passed through a reticle or mask which projects the semiconductor die feature pattern to be formed in the resist layer.
Various types of photolithographic masks are known in the art. For example, known masks often include a transparent plate covered with regions of a radiation blocking material, such as chromium, which define the semiconductor die feature pattern projected by the mask. Such masks are called binary masks since radiation is completely blocked by the radiation blocking material and fully transmitted through the transparent plate in areas not covered by the radiation blocking material. However, binary masks cause significant fabrication problems, particularly where semiconductor die dimensions shrink below 1 &mgr;m.
As the pattern features of a binary mask are defined by boundaries between opaque, radiation blocking material and material which is completely radiation transmissive, radiation passing through a binary mask at the edge of a pattern feature will be diffracted beyond the intended image boundary and into the intended dark regions. Such diffracted radiation prevents formation of a precise image at the feature edge, resulting in semiconductor die features which deviate in shape or size from the intended design. Because the intensity of the diffracted radiation drops off quickly over a fraction of a micron, diffraction effects are not particularly problematic where semiconductor die have dimensions on the order of 1 &mgr;m. However, as feature dimensions of state of the art semiconductor die shrink well below 0.5 &mgr;m, the diffraction effects of binary masks become terribly problematic.
Another type of mask known in the art is an attenuated phase shift mask (APSM). APSM's were developed to address the diffraction problems produced by binary masks and are distinguished from binary masks in that, instead of completely blocking the passage of radiation, the less transmissive regions of the mask are actually partially transmissive. A Importantly, the attenuated radiation passing through the partially transmissive regions of an APSM generally lacks the energy to substantially affect a resist layer exposed by the mask. Moreover, the partially transmissive regions of ASPMs are designed to shift the passing radiation 180° relative to the radiation passing through the completely transmissive regions and, as a consequence, the radiation passing through the partially transmissive regions destructively interferes with radiation diffracting out from the edges of the completely transmissive regions. Thus, the phase shift greatly reduces the detrimental effects of diffraction at the feature edges, thereby increasing the resolution with which sub-micron features may be patterned on a resist layer.
A conventional APSM
4
is illustrated in drawing FIG.
1
. As can be seen, the APSM
4
includes a transparent substrate
6
coated with a partially transmissive material
7
(to ease description, drawing
FIG. 1
provides a greatly simplified APSM). The partially transmissive material
7
has been patterned to form a completely transmissive region
8
and two attenuated regions
10
a,
10
b.
The attenuated regions
10
a,
10
b
of a typical APSM
4
are typically designed to allow the passage of between about 4% (low transmission) and 20% (high transmission) of the incident radiation
12
. The partially transmissive material
7
forming the attenuated regions
10
a,
10
b
is formed to a thickness that shifts the incident radiation
12
one hundred eighty degrees (180°) out of phase.
Also provided in drawing
FIG. 1
is a graph
16
illustrating the electromagnetic intensity (plotted on the vertical axis) of the radiation passing through the APSM
4
relative to the position (plotted on the horizontal axis) on the surface of the exposed resist. As shown, the intensity curve
18
includes a first component
20
located primarily between the edges
22
a
,
22
b
formed between the attenuated regions
10
a
,
10
b
and the completely transmissive region
8
of the APSM
4
. The first component
20
of the intensity curve
18
corresponds to the electromagnetic intensity of the radiation passing through the completely transmissive region
8
of the APSM
4
illustrated in drawing FIG.
1
. As can be seen in the graph
16
, the electromagnetic intensity of the radiation falls to zero at points
24
a
,
24
b
, which are near the edges
22
a
,
22
b
. Points
24
a
,
24
b
correspond to the locations where the magnitudes of the in phase radiation passing through the completely transmissive region
8
and the out of phase radiation passing through the attenuated regions
10
a
,
10
b
are equal. Beyond points
24
a
,
24
b
and moving away from the edges
22
a
,
22
b
, the electromagnetic intensity of the transmitted radiation grows again to a steady value as indicated by the second curve components
26
a
,
26
b
. The second curve components
26
a
,
26
b
represent the electromagnetic intensity of the radiation passing through the attenuated regions
10
a
,
10
b
of the APSM
4
.
The electromagnetic intensity represented by the second curve components
26
a
,
26
b
is also known as “ringing effects,” and one significant disadvantage of APSMs is that such ringing effects become much more severe as feature density of an APSM increases. As device features designed into an APSM are spaced closer and closer together, the ringing effects of adjacent device features begin to overlap, and as the ringing effects overlap, the electromagnetic intensity of such ringing effects becomes additive. These increased ringing effects are known as “additive side lobes”, “additive ringing effects”, or “proximity effects.” In contrast to isolated ringing effects produced by isolated device features, the electromagnetic intensity of additive side lobes created by closely-spaced (i.e., 0.5 &mgr;m) or nested device features often becomes sufficiently intense to cause printing of the resist layer, which is commonly termed “side lobe printing.”
Illustrated in drawing
FIG. 2
is the additive ringing effects associated with conventional APSMs having closely-spaced feature formations. As illustrated in drawing
FIG. 2
, a second APSM
30
includes a transparent substrate
32
coated with a partially transmissive phase-shifting film
34
(again, for ease of description, drawing
FIG. 2
provides a greatly simplified A APSM). The partially transmissive phase-shifting film
34
has been patterned to form four attenuating regions
36
a
-
36
d
and three completely transmissive regions
38
a
-
38
c
, which are closely-spaced. Radiation
39
incident on the APSM
30
passes through the completely transmissive regions
38
a
-
38
c
and the attenuated regions
36
a
-
36
d
and impinges upon the surface of the resist layer to be patterned (not illustrated in drawing FIG.
2
Micro)n Technology, Inc.
Rosasco S.
TraskBritt
LandOfFree
Multi-layer, attenuated phase-shifting mask does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-layer, attenuated phase-shifting mask, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-layer, attenuated phase-shifting mask will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3010667