Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2002-05-31
2004-11-30
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S005000, C382S144000, C716S030000, C716S030000, C716S030000
Reexamination Certificate
active
06824937
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to fabrication of integrated circuits, and more particularly, to a method and system for determining optimum optical proximity corrections for a mask pattern within a photolithography system.
BACKGROUND OF THE INVENTION
A long-recognized important objective in the constant advancement of monolithic IC (Integrated Circuit) technology is the scaling-down of IC dimensions. Such scaling-down of IC dimensions reduces area capacitance and is critical to obtaining higher speed performance of integrated circuits. Moreover, reducing the area of an IC die leads to higher yield in IC fabrication. Such advantages are a driving force to constantly scale down IC dimensions.
Referring to
FIG. 1
, a photolithograpy system
100
is used for patterning integrated circuit structures on a semiconductor wafer
102
. In the photolithography system
100
, a reticle
104
has a pattern of polygons thereon to be patterned onto the semiconductor wafer
102
. Light from a light source
106
is illuminated through the pattern of polygons on the reticle
104
onto the semiconductor wafer
102
. In addition, a lens system
108
is used within the photolithography system
100
to typically reduce the image of the pattern of polygons on the reticle
104
onto the semiconductor wafer
102
. The pattern of polygons on the reticle
104
are typically opaque to the light from the light source
106
.
A photoresist material on the semiconductor wafer
102
is cured when light from the light source
106
reaches the photoresist material and is not cured otherwise. When the photoresist material is then developed, cured photoresist material may be etched away while the uncured photoresist material remains, and the remaining uncured photoresist material may further act as a mask for etching away exposed material deposited below the photoresist material. Thus, when the light from the light source
106
does not reach the semiconductor wafer
102
for the pattern of opaque polygons on the reticle
104
, the pattern of polygons on the reticle
104
is transferred to the photoresist material on the semiconductor wafer
102
. Such a photolithography system
100
is known to one of ordinary skill in the art of integrated circuit fabrication.
As the dimensions of integrated circuit structures are constantly scaled down such that a desired dimension of an integrated circuit structure is smaller than the wavelength of the light from the light source
106
within the photolithography system
100
, the shape and dimensions of the structure formed on the semiconductor wafer
102
is no longer that expected from the design of the pattern of polygons on the reticle
104
. For example, referring to
FIG. 2
, assume that a polygon
110
is designed on the reticle
104
for a rectangular shape to be patterned on the semiconductor wafer
102
within the photolithography system
100
. When the width of the polygon
110
is smaller than the wavelength of the light from the light source
106
within the photolithography system
100
, the actual polygon
112
patterned onto the semiconductor wafer
102
is different from the expected polygon
110
.
Typically, the polygon
10
on the reticle
104
acts as a low-pass filter when the width of the polygon
110
is smaller than the wavelength of the light from the light source
106
such that the corners of the actual polygon
112
become more rounded than desired and the length of the actual polygon
112
become shorter than desired, as known to one of ordinary skill in the art of integrated circuit fabrication. Such non-linear distortions of the actual polygon
112
results from optical diffraction of the light from the light source
106
and resist effects in pattern transfer when the width of the polygon
110
is smaller than the wavelength of the light from the light source
106
, as known to one of ordinary skill in the art of integrated circuit fabrication. The nature of the non-linear distortions of the actual polygon
112
also depends on the density, size, and location of nearby polygon features, as known to one of ordinary skill in the art of integrated circuit fabrication.
The wavelength of light from the light source
106
is currently approximately 250 nanometers. However, device dimensions are now desired to be below 200 nanometers. Referring to
FIG. 3
, to over-come such non-linear distortions, the patterned polygons of the reticle are perturbed with addition of OPC (optical proximity corrections), as known to one of ordinary skill in the art of integrated circuit fabrication. In the example of
FIG. 3
, such OPC (optical proximity corrections) includes structures that are added to the pattern of polygons of the reticle to negate the non-linear distortions.
Referring to
FIG. 3
, assume that the initial reticle
104
without any OPC (optical proximity corrections) includes a first polygon
122
and a second polygon
124
. Then, OPC (optical proximity corrections) structures are added as perturbations to the polygons
122
and
124
of the initial reticle
104
to result in a perturbed reticle
130
. Example OPC (optical proximity corrections) structures include “dog-ears”
132
(i.e., opaque squares or rectangles) added to outside corners of the polygons, “cut-outs”
134
(i.e., transparent squares or rectangles) added to inside corners of the polygons, and long-line embellishments
136
(i.e., transparent rectangles) added to sides of relatively long polygons. When the perturbed reticle
130
is used within the photolithograpy system
100
, such OPC (optical proximity corrections) structural perturbations added to the polygons
122
and
124
negate the non-linear distortions such that the pattern transferred to the semiconductor wafer
102
is closer to the desired pattern of polygons even when the dimensions of the polygons are smaller than the wavelength of light from the light source
106
, as known to one of ordinary skill in the art of integrated circuit fabrication.
However, different OPC (optical proximity corrections) have different effects on the polygons patterned onto the semiconductor wafer. For example, different shapes, sizes, and locations of the OPC (optical proximity corrections) structures added to perturb the polygons of the reticle have different effects on the polygons patterned onto the semiconductor wafer. Thus, a determination of optimum OPC (optical proximity corrections) is desired for achieving polygons patterned onto the semiconductor wafer that are closest to the desired pattern of polygons.
In the prior art, the optimum OPC (optical proximity corrections) are determined by manual trial and error. Various reticles with different OPC (optical proximity corrections) structures added are used and the resulting polygons patterned onto the semiconductor wafer are visually examined to determine the optimum OPC (optical proximity corrections). However, such a manual determination by trial and error is tedious and prone to human error as such a process is repeated for different integrated circuit processes and different photolithography systems.
Thus, a mechanism is desired for efficiently and accurately determining optimum OPC (optical proximity corrections).
SUMMARY OF THE INVENTION
Accordingly, in a general aspect of the present invention, an array of mask areas are formed on a reticle, and a computer system and a database are used for automatically determining optimum OPC (optical proximity corrections).
In a general aspect of the present invention, in a method and system for determining optimum optical proximity corrections (OPC) for a mask pattern comprised of a plurality of polygons for a photolithography system, an array of a plurality of mask areas are formed on a reticle with each mask area having the mask pattern comprised of the plurality of polygons. The mask pattern comprised of the plurality of polygons is for forming a desired image of the plurality of polygons on a semiconductor wafer within the photolithography system. In addition, the plurality of polygons within each mask area i
Advanced Micro Devices , Inc.
Choi Monica H.
Young Christopher G.
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