Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1999-07-21
2002-07-30
Beck, Shrive P. (Department: 1762)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C250S492100, C250S492200, C430S005000, C428S066600
Reexamination Certificate
active
06426131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to photolithography systems and more particularly, to techniques for designing features of photolithography systems to improve the resolution and focus of an image that is projected onto a semiconductor wafer.
2. Description of the Related Art
Photolithography is an important part of semiconductor technology. Devices made from semiconductor wafers depend greatly on the resolution and focus of images directed onto selected regions of the wafers. Although much improvement has occurred in the development of photolithography systems that enable the fabrication of smaller and smaller features sizes, photolithography engineers continue to battle defects in resolution as geometries continue to decrease.
For example, many of today's photolithography systems are now using deep UV wavelengths (i.e., 248 nm) and deep UV photoresists in efforts to better define the image resolution of patterned photoresist. Unfortunately, it has been observed that many resolution defects occur when feature geometries have angled profiles, with respect to horizontal and vertical features. Consequently, when photoresists are developed after being exposed, only horizontal and vertical feature geometries exhibit good resolution, while angled features are substantially distorted.
An example of a photolithography system
100
is shown in
FIG. 1A
, which includes a scanner system
102
. The scanner system
102
is also known as a stepper apparatus. A light source
104
is commonly positioned near a top region of the scanner system
102
in order to allow produced light waves to be directed toward a first lens system
106
. From the first lens system
106
, the light is projected through a pupil aperture
108
that is used to better direct light onto a second lens system
110
. As is well known, the pupil aperture
108
assists in precisely directing the light source onto the desired location of a reticle
112
.
The reticle
112
being a glass plate, is patterned with exemplary feature geometries typically defined by a chromium material, which blocks light from propagating through the reticle
112
. After the desired light passes through the reticle
112
, it leaves the scanner system
102
and comes into contact with a die region
114
a
of a semiconductor wafer
114
having a photoresist covered surface.
The light then changes the chemical composition of the photoresist so that a developer will allow removal of the exposed regions of photoresist material (i.e., for positive photoresists). In this manner, the feature geometries of the reticle
112
are transferred to the die region
114
a.
For ease of illustration, only one die region
114
a
is shown, but as is well known in the art, many more die regions
114
a
are formed throughout the semiconductor wafer
114
during normal fabrication.
FIG. 1B
is a top view of one example of a conventional pupil aperture
108
a.
The pupil aperture
108
a
(also known as a clean-up aperture) includes an aperture
116
a
with a &sgr; value of about 0.6. The pupil aperture
108
a
is used to more precisely direct light received from the light source
104
onto the reticle
112
. Generally, the aperture
116
a
will define a cone of light that is directed toward the second lens system
110
and then illuminates the reticle
112
. Although this pupil aperture
108
a
assists in more precisely controlling the direction of the light from the light source
104
, as demands for smaller and more defined feature resolution continues to increase, the precision provided by the pupil aperture
108
a
has failed to produce adequate results.
In order to increase resolution of the pattern printed on the die region
114
a,
several different pupil aperture designs have been devised.
FIG. 1C
shows an example of an off-axis pupil aperture
108
b.
The pupil aperture
108
b
includes a number of off-axis apertures
116
b.
For purposes of explanation, a zero order region
118
is shown defined around a center point
119
from which an offset
120
measurement is made to the off axis apertures
116
b.
In the pupil aperture
108
b,
most of the center portion actually blocks the passage of light, thus enabling a focusing of the light that passes through the off-axis apertures
116
b.
Although the added level of focus precision provided by off-axis apertures is well known, many defects in resolution have still been detected when an off-axis pupil aperture, such as the pupil aperture
108
b
is used.
FIG. 1D
shows an example of a quadrupolar off-axis pupil aperture
108
c.
The pupil aperture
108
c
includes a set of four pole apertures
116
c,
each with a &sgr; value of about 0.1. A horizontal axis
117
is defined through the center point
119
of the pupil aperture
108
c.
The distance between the center point
119
and the pole apertures is defined by an offset
120
. The angle between the pole apertures
116
c
and the horizontal axis
117
is defined by &phgr;, which is strongly suggested by photolithography scanner equipment manufactures to be exactly 45° from the horizontal axis
117
.
In fact, scanner equipment manufacturers recommend that when very small feature geometries are being patterned, standard 45° quadrupole pupil apertures be used because light received from the first lens system
106
will be more accurately directed to the second lens system
110
and then to the surface of the reticle
112
(as shown in FIG.
1
A). Consequently, the scanner equipment manufacturers provide users of their photolithography equipment with standard machined pupil apertures having the aforementioned 45° quadrupole design.
In addition, some scanner equipment manufacturers, such as Silicon Valley Group, Inc. (SVG) of Wilton, Conn. provide users of their equipment with guidelines for using the standard 45° quadrupole design pupil apertures. Unfortunately, none of the prior art pupil apertures have been able to supply an adequate level of resolution for very small features having angled geometries.
FIG. 1E
shows an example of a reticle
112
with a number of feature lines
112
b
and a corresponding number of angled feature lines
112
b
′ patterned on the reticle's glass surface. Also shown are a number of inter-feature spaces
112
c
defined between any two of the feature lines
112
b
and its corresponding angled feature lines
112
b′.
For exemplary purposes, the feature lines
112
b
/
112
b
′ are patterned such that line widths and spaces as small as 160 nm are transferred onto a resist covered die region
114
a
as shown in FIG.
1
F.
As shown, the die region
114
a
includes a number of photoresist lines
114
b
and angled photoresist lines
114
b
′ that result after development of the exposed photoresist. As evidenced from numerous experimental trials, the photoresist lines
114
b
′, which have an angled geometric orientation (with respect to a vertical axis), will not produce the ideal pattern shown in the reticle
112
.
In fact, because none of the above-described pupil apertures are able to accurately and precisely direct light onto the surface of the reticle
112
when small geometries are being fabricated, major distortion in the developed photoresist will occur as shown in FIG.
1
F. It should also be noted that when such distortion occurs, the feature geometries will not produce the desired electrical interconnections, thereby producing a malfunctioning integrated circuit device. Of course, when such malfunctions occur, semiconductor devices are scrapped, and corresponding fabrication yield will suffer.
In view of the foregoing, there is a need for photolithography scanner pupil apertures that assist in more accurately directing light onto a reticle when features having very small critical dimensions are being patterned. There is also a need for methods for manufacturing custom pupil apertures to correct resolution distortions when features having small angled geometries are patterned over photoresist covered wafers.
SUMMARY OF THE INVENTION
Garza Mario
Jackson Philip Eric
Neville Christopher
Beck Shrive P.
Beyer Weaver & Thomas LLP
LSI Logic Corporation
Tsoy Elena
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