U.S. patent application number 10/928571 was filed with the patent office on 2005-02-03 for photolithographic techniques for producing angled lines.
This patent application is currently assigned to Micron Technology, Inc.. Invention is credited to Farrar, Paul A..
Application Number | 20050026086 10/928571 |
Document ID | / |
Family ID | 31494820 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050026086 |
Kind Code |
A1 |
Farrar, Paul A. |
February 3, 2005 |
Photolithographic techniques for producing angled lines
Abstract
The present subject matter allows non-orthogonal lines to be
formed at the same thickness as the orthogonal lines so as to
promote compact designs, to be formed with even line edges, and to
be formed efficiently. One aspect of the present subject matter
relates to a method for forming non-orthogonal images in a
raster-based photolithographic system. According to various
embodiments of the method, a first image corresponding to a first
data set is formed on a reticle when the reticle is at a first
rotational position .theta..sub.1. The reticle is adjusted to a
second rotational position .theta..sub.2. A second image
corresponding to a second data set is formed on the reticle when
the reticle is at the second rotational position .theta..sub.2. The
second image is non-orthogonal with respect to the first image.
Other aspects are provided herein.
Inventors: |
Farrar, Paul A.; (Okatie,
SC) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Micron Technology, Inc.
|
Family ID: |
31494820 |
Appl. No.: |
10/928571 |
Filed: |
August 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10928571 |
Aug 27, 2004 |
|
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10215214 |
Aug 8, 2002 |
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Current U.S.
Class: |
430/311 |
Current CPC
Class: |
H01L 27/222 20130101;
G03F 7/70533 20130101; H01J 2237/30488 20130101; G03F 1/78
20130101; B82Y 10/00 20130101; G03F 7/70383 20130101; H01J 37/3174
20130101; B82Y 40/00 20130101; G03F 1/20 20130101; H01L 27/0207
20130101; Y02P 90/02 20151101; Y02P 90/265 20151101 |
Class at
Publication: |
430/311 |
International
Class: |
G03C 005/00 |
Claims
What is claimed is:
1. A method of forming non-orthogonal lines on a substrate,
comprising: forming a reticle with an non-orthogonal image using a
raster-based photolithographic system, including: adjusting the
reticle to a rotational position .theta. to form non-orthogonal
lines on the reticle with respect to a reference; and forming the
non-orthogonal image on the reticle using the raster-based
photolithographic system; and using the reticle with the
non-orthogonal image to form non-orthogonal lines on the
substrate.
2. The method of claim 1, wherein the method is used to form a word
metallization layer, a bit metallization layer, and a select
metallization layer for a magnetic random access memory (MRAM)
array, wherein at least one of the word metallization layer, the
bit metallization layer, and the select metallization layer is
non-orthogonal with respect to a remaining at least one of the word
metallization layer, the bit metallization layer, and the select
metallization layer.
3. A method of forming non-orthogonal lines on a substrate,
comprising: forming a reticle with an orthogonal image using a
raster-based photolithographic system; registering a rotational
position between the reticle and a substrate to provide a desired
non-orthogonal image on the substrate based on the orthogonal image
on the reticle; and using the reticle with the orthogonal image to
form non-orthogonal lines on the substrate.
4. The method of claim 3, wherein registering a rotational position
between the reticle and a substrate includes rotating the
reticle.
5. The method of claim 3, wherein registering a rotational position
between the reticle and a substrate includes rotating the
substrate.
6. The method of claim 3, wherein the method is used to form a word
metallization layer, a bit metallization layer, and a select
metallization layer for a magnetic random access memory (MRAM)
array, wherein at least one of the word metallization layer, the
bit metallization layer, and the select metallization layer is
non-orthogonal with respect to a remaining at least one of the word
metallization layer, the bit metallization layer, and the select
metallization layer.
7. A method of forming non-orthogonal lines on a substrate,
comprising: registering a rotational position of the substrate to
provide a desired non-orthogonal image on the substrate; and
directly writing a non-orthogonal image on the substrate using a
raster-based system.
8. The method of claim 7, wherein the method is used to form a word
metallization layer, a bit metallization layer, and a select
metallization layer for a magnetic random access memory (MRAM)
array, wherein at least one of the word metallization layer, the
bit metallization layer, and the select metallization layer is
non-orthogonal with respect to a remaining at least one of the word
metallization layer, the bit metallization layer, and the select
metallization layer.
9. A method for forming non-orthogonal images on a wafer in a
raster-based photolithographic system, comprising: directly writing
a first image corresponding to a first data set on the wafer when
the wafer is at a first rotational position .theta..sub.1;
registering the wafer to a second rotational position; and directly
writing a second image corresponding to a second data set on the
wafer when the wafer is at the second rotational position
.theta..sub.2, wherein the second image is non-orthogonal with
respect to the first image.
10. The method of claim 9, further comprising: registering the
wafer to an Nth rotational position O.sub.N; and directly writing
an Nth image corresponding to an Nth data set on the wafer when the
wafer is at the Nth rotational position O.sub.N.
11. The method of claim 9, further comprising: adjusting the wafer
to a third rotational position .theta..sub.3; and directly writing
an image corresponding to a second data set on the wafer, wherein
the first rotational position .theta..sub.1 and the second
rotational position .theta..sub.2 are such that a set of parallel
lines in the first image form an angle of approximately 60.degree.
with respect to a set of parallel lines in the second image, and
the second rotational position .theta..sub.2 is such that a set of
parallel lines in the third image form an angle of approximate
60.degree. with respect to a set of parallel lines in the first
image and with respect to a set of parallel lines in the second
image.
12. The method of claim 9, wherein forming a first image includes
forming a number of alignment markings on the wafer for use in
directly writing the second image.
13. The method of claim 12, further comprising registering the
wafer at the second rotational position .theta..sub.2 using the
number of alignment markings prior to forming the second image on
the reticle.
14. The method of claim 9, further comprising: registering the
wafer at the first rotational position .theta..sub.1 using a number
of alignment markings prior to printing the first image on the
wafer; and registering the wafer to the second rotational position
.theta..sub.2 using the number of alignment markings prior to
printing the second image on the wafer.
15. The method of claim 9, wherein adjusting the wafer to a second
rotational position .theta..sub.2 includes accurately steeping the
wafer through a number of rotational positions between the first
rotational position .theta..sub.1 and the second rotational
position .theta..sub.2.
16. The method of claim 9, wherein both the first image and the
second image are formed on a layer of resist on the wafer.
17. The method of claim 9, wherein the first image is formed on a
first layer of resist on the wafer and the second layer is formed
on a second layer of resist on the wafer.
18. A machine-readable medium with instructions stored thereon, the
instructions when executed operable to cause: a first image to be
formed on a workpiece when the workpiece is at a first rotational
position .theta..sub.1; and a second image to be formed on the
workpiece when the workpiece is at a second rotational position
.theta..sub.2, wherein the second image is non-orthogonal with
respect to the first image.
19. The machine-readable medium of claim 18, wherein the
instructions when executed are further operable to cause the
workpiece to be rotated from the first rotational position
.theta..sub.1 to the second rotation position .theta..sub.2 prior
to forming the second image on the reticle.
20. The machine-readable medium of claim 18, wherein the workpiece
includes one or more reticles.
21. The machine-readable medium of claim 18, wherein the workpiece
includes a substrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional under 37 C.F.R. 1.53(b) of
U.S. application Ser. No. 10/215,214 filed Aug. 8, 2002, which is
incorporated herein by reference.
[0002] This application is also related to the following commonly
assigned U.S. patent applications which are herein incorporated by
reference in its entirety:
[0003] "Three Terminal Magnetic Random Access Memory," Ser. No.
09/940,976, filed on Aug. 28, 2001;
[0004] "Photolithographic Techniques for Producing Angled Lines",
Ser. No. ______, filed on even date herewith (Atty. Docket No.
1303.066US3); and
[0005] "Photolithographic Techniques for Producing Angled Lines",
Ser. No. ______, filed on even date herewith (Atty. Docket No.
1303.066U4).
TECHNICAL FIELD
[0006] This disclosure relates generally to integrated circuits,
and more particularly, to semiconductor photolithographic
processes.
BACKGROUND
[0007] Photolithographic processes in the semiconductor industry
use raster scanning methods to produce masks. FIG. 1 illustrates a
schematic diagram of a known raster-based photolithographic system.
One example of a raster-based photolithographic process is an
electron beam (e-beam) process. In an e-beam system 102, for
example, a reticle 104 is placed on a table 106 which provides a
motion to the reticle along a Y axis using a data set 108 and a
worktable motion control module 110, and an electronic beam 112
sweeps back and forth along an X axis using the data set 108 and an
e-beam control module 114 to provide a raster motion. The system
performs raster-based imaging by sweeping the e-beam back and forth
along the X axis, turning the e-beam on over designated areas and
off until the next designated area, and appropriately stepping the
worktable along the Y axis.
[0008] Raster-based photolithographic processes are limited to
generating only orthogonal line patterns. With respect to an e-beam
system, for example, the size of images is limited to integer
multiples of the e-beam spot size. The e-beam spot size can be
considered to be a pixel of the pattern. A series of stepped images
is used to form lines at non-orthogonal angles with respect to a
base direction.
[0009] FIG. 2 illustrates a stepped angled image formed using the
known raster-based photolithographic system of FIG. 1. In this
figure, parallel non-orthogonal lines are drawn at an angle of
about 45.degree. with respect to the base direction, which
functions as a reference. The pattern is built by writing a spot
203 in the X direction, a spot 205 in the Y direction, a spot 207
in the X direction, and so on.
[0010] One problem associated with forming non-orthogonal lines
using a raster-based photolithographic process is that the
non-orthogonal lines require a larger area than the orthogonal
lines. Although the minimum horizontal or vertical line width is
equal to an e-beam spot size (pixel), the stepped 45.degree. line
(a slope of 1:1) requires two pixels 209 and 211, and the space
between parallel 45.degree. lines also requires two pixels 213 and
215. In an image containing parallel 30.degree. lines, for example,
even more space is required for the lines and the space between the
lines.
[0011] Another problem associated with forming non-orthogonal lines
using a raster-based photolithographic process is that the lines
are formed with uneven edges. Although some smoothing of line edges
occur during the exposure and development of the mask, the line
might not smooth completely depending on the resist sensitivity.
The result is an uneven line edge.
[0012] Other problems associated with forming non-orthogonal lines
using a raster-based photolithographic process involve the use of
more metal to form a stepped diagonal line than a minimum width
diagonal line. Additionally, writing stepped images which requires
a number of e-beam sweeps is less efficient than writing an
orthogonal line that requires only one sweep.
[0013] Most semiconductor chip layouts are successfully designed
using orthogonal lines. When a small number of non-orthogonal lines
are required in a layout, they have been formed using stepped
images. However, the problems associated with using stepped images
to form non-orthogonal lines are exacerbated when a design requires
more non-orthogonal lines to be formed in a smaller space.
[0014] Therefore, there is a need in the art to provide improved
photolithographic techniques to form angled lines.
SUMMARY
[0015] The above mentioned problems are addressed by the present
subject matter and will be understood by reading and studying the
following specification. The present subject mater provides
improved photolithographic techniques to form non-orthogonal
(angled) lines on workpieces such as wafers and reticles. The
present subject matter allows non-orthogonal lines to be formed at
the same thickness as the orthogonal lines (a minimum width
corresponding to a pixel or e-beam spot, for example) so as to
promote higher density designs, to be formed with even line edges,
and to be formed efficiently.
[0016] Various embodiments of the preset subject matter involve
forming non-orthogonal lines on a reticle. The non-orthogonal lines
in the reticle result in non-orthogonal lines in a wafer. Various
embodiments of the present subject matter involve rotating the
relative position between a wafer and a reticle (by rotating the
wafer and/or reticle) to form non-orthogonal lines on the wafer
using orthogonal lines on the reticle. Various embodiments of the
present subject matter involve directly writing non-orthogonal
lines on a rotated wafer.
[0017] One aspect of the present subject matter relates to a method
for forming non-orthogonal images in a raster-based
photolithographic system. According to various embodiments of the
method, a first image corresponding to a first data set is formed
on a reticle when the reticle is at a first rotational position
.theta..sub.1. The reticle is adjusted to a second rotational
position .theta..sub.2. A second image corresponding to a second
data set is formed on the reticle when the reticle is at the second
rotational position .theta..sub.2. The second image is
non-orthogonal with respect to the first image.
[0018] One aspect of the present subject matter relates to a method
for forming an integrated circuit metallization layer using a
damascene process and direct write raster-based photolithographic
system using an electron beam or other similar means. According to
various embodiments of this method, an insulator layer is deposited
on a wafer, and a layer of resist is deposited on the insulator
layer. A first image corresponding to a first data set is formed on
the layer of resist when the wafer is at a first rotational
position .theta..sub.1 with respect to a reference. The wafer is
adjusted to a second rotational position .theta..sub.2 with respect
to the reference. A second image corresponding to a second data set
is formed on the first layer of resist when the reticle is at a
second rotational position .theta..sub.2. The second image is
non-orthogonal with respect to the first image. The first image and
the second image are developed, and the wafer is processed using a
damascene metal fill to form a metallization layer based on the
developed first image and the developed second image.
[0019] One aspect of the present subject matter relates to a method
for forming integrated circuit metallization layers. According to
various embodiments of the method, a first metal layer is deposited
on a wafer, and a first layer of resist is deposited on the first
insulator layer. A first image corresponding to a first data set on
a first reticle is formed on the layer of resist when the wafer is
at a first rotational position .theta..sub.1 with respect to a
reference. The first image is developed, and the wafer is processed
to form a portion of the first metallization layer based on the
developed first image. A second resist layer is deposited over the
first metallization layer. A second reticle is registered to a
second rotational position .theta..sub.2 with respect to the
reference. A second image corresponding to a second data set is
formed on the second layer of resist when the wafer is at the
second rotational position .theta..sub.2. The second image is
non-orthogonal with respect to the first image. The second image is
developed, and the reticle is processed to form a complete
metallization layer based on the developed second image. This may
be accomplished either by rotating the reticle with respect to the
wafer or the wafer with respect to the reticle. One of ordinary
skill in the art will understand, upon reading and comprehending
this disclosure, that non-orthogonal metallization layer can be
formed when the reticle has non-orthogonal images (formed by
rotating the reticle with respect to the raster-based system), can
be formed by rotating the wafer or reticle with respect to the
raster-based system to form non-orthogonal lines when the reticle
is formed with orthogonal images, and can be formed by rotating the
wafer with respect to the raster-based system and directly writing
onto the wafer using the raster-based system.
[0020] One aspect of the present subject matter relates to a method
for forming a magnetic random access memory (MRAM) array. According
to various embodiments of the method, an image of a first wiring
layer of approximately parallel conductors is formed in a first
reticle. An image of a second wiring layer of approximately
parallel conductors is formed in a second reticle such that the
conductors of the second wiring layer would cross with the
conductors of the first wiring layer at a number of intersections.
An image of a third wiring layer of approximately parallel
conductors is formed in a third reticle such that the conductors of
the third wiring layer would cross the conductors of the first
wiring layer and the second wiring layer at the number of
intersections. The three reticles are used to process three
successive metal layers. A layer of magnetic storage elements is
provided such that the storage elements are proximately located to
the intersections and are adapted to be written by a first magnetic
field produced by energized conductors in the first wiring layer, a
second magnetic field produced by energized conductors in the
second wiring layer, and a third magnetic field produced by
energized conductors in the third wiring layer. At least one of the
first wiring layer, the second wiring layer and the third wiring
layer is formed after adjusting an rotational position (.theta.) of
the reticle so as to be non-orthogonal with respect to at least one
of the other wiring layers. One of ordinary skill in the art will
understand, upon reading and comprehending this disclosure, that a
non-orthogonal metallization layer can be formed when the reticle
has non-orthogonal images (formed by rotating the reticle with
respect to the raster-based system), can be formed by rotating the
wafer or reticle with respect to the raster-based system to form
non-orthogonal lines when the reticle is formed with orthogonal
images, and can be formed by rotating the wafer with respect to the
raster-based system and direct writing onto the wafer using the
raster-based system.
[0021] One aspect of the present subject matter relates to a
raster-based photolithographic system for forming orthogonal and
non-orthogonal images on reticles. According to various
embodiments, the system includes an imager and a worktable adapted
to function to orthogonally image a workpiece (such as a reticle or
a wafer) in an X direction and a Y direction using a raster motion.
The imager and the worktable also are adapted to adjust a
rotational position of the workpiece with respect to the raster
motion. The system further includes a database, and an
X-controller, a Y-controller, and a .theta.-controller. The
database includes a first data set for writing an orthogonal image
with respect to the raster motion and a second data set
corresponding for writing a non-orthogonal image with respect to
the raster motion. The X-controller is adapted to control imaging
of reticles or direct writing of wafers in an X direction. The
Y-controller is adapted to control imaging of reticles or direct
writing of wafers in a Y direction. The .theta.-controller is
adapted to control an adjustment of the rotational position of the
workpiece (reticle or wafer) with respect to the raster motion.
[0022] These and other aspects, embodiments, advantages, and
features will become apparent from the following description of the
present subject matter and the referenced drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 illustrates a schematic diagram of a known
raster-based photolithographic system.
[0024] FIG. 2 illustrates a stepped angled image formed using the
known raster-based photolithographic system of FIG. 1.
[0025] FIG. 3 illustrates a schematic diagram of a raster-based
photolithographic system according to various embodiments of the
present subject matter.
[0026] FIG. 4 illustrates an angled image formed according to
various embodiments of the present subject matter using the
raster-based photolithographic system of FIG. 3.
[0027] FIG. 5 illustrates a schematic representation of a first
image formed on a reticle using a first data set in a raster-based
photolithographic system.
[0028] FIG. 6 illustrates a schematic representation of a second
image formed on a rotated reticle (after the first image is formed
in FIG. 5) using a second data set in the raster-based
photolithographic system.
[0029] FIG. 7 illustrates a MRAM according to various embodiments
of the present subject matter with magnetic memory cells or storage
devices located at intersections among bit lines, word lines and
select lines in a cross point array.
[0030] FIG. 8 illustrates an intersection in the cross point array
of FIG. 7 in more detail.
[0031] FIG. 9 illustrates a structure for various embodiments of
the cross point array of FIG. 7.
[0032] FIGS. 10A, 10B and 10C illustrate horizontal word lines,
angled select lines, and angled bit lines, respectively, formed
using the known raster-based photolithographic system of FIG.
1.
[0033] FIGS. 11A, 11B and 11C illustrate horizontal word lines,
non-orthogonal select lines, and non-orthogonal bit lines,
respectively, formed according to various embodiments of the
present subject matter using the raster-based photolithographic
system of FIG. 3.
[0034] FIG. 12 is a simplified block diagram of a high-level
organization of various embodiments of an electronic system
according to the present subject matter.
[0035] FIG. 13 illustrates a method for forming non-orthogonal
images in a raster-based photolithographic system according to
various embodiments of the present subject matter.
[0036] FIG. 14 illustrates a method for aligning the second image
with the first image according to various embodiments of the method
illustrated in FIG. 13.
[0037] FIG. 15 illustrates a method for aligning the first image
and the second image with the reticle according to various
embodiments of the method illustrated in FIG. 13.
[0038] FIG. 16 illustrates a method for forming an integrated
circuit metallization layer according to various embodiments of the
present subject matter.
[0039] FIG. 17 illustrates a method for forming integrated circuit
metallization layers according to various embodiments of the
present subject matter.
[0040] FIG. 18 illustrates a method for forming non-orthogonal
lines on a substrate according to various embodiments of the
present subject matter.
[0041] FIG. 19 illustrates a method for forming non-orthogonal
lines on a substrate according to various embodiments of the
present subject matter.
[0042] FIG. 20 illustrates a method for forming non-orthogonal
lines on a substrate according to various embodiments of the
present subject matter.
DETAILED DESCRIPTION
[0043] The following detailed description refers to the
accompanying drawings which show, by way of illustration, specific
aspects and embodiments in which the present subject matter may be
practiced. These embodiments are described in sufficient detail to
enable those skilled in the art to practice the present subject
matter. Other embodiments may be utilized and structural, logical,
and electrical changes may be made without departing from the scope
of the present subject matter. The following detailed description
is, therefore, not to be taken in a limiting sense, and the scope
of the present subject matter is defined only by the appended
claims, along with the full scope of equivalents to which such
claims are entitled.
[0044] The term "substrate" used in the following description may
include any semiconductor-based structure that has an exposed
surface. The structure may include silicon, silicon-on insulator
(SOI), silicon-on sapphire (SOS), doped and undoped semiconductors,
epitaxial layers of silicon supported by a base semiconductor
foundation, and other semiconductor structures. The semiconductor
need not be silicon-based. The semiconductor could be
silicon-germanium, germanium, or gallium arsenide. A wafer is a
slice of semiconductor material from which chips are made, and thus
form a substrate. When reference is made to a wafer or substrate in
the following description, previous process steps may be utilized
to form regions, junctions, or layers in or on the base
semiconductor or foundation.
[0045] One definition of raster is a scan/write pattern in which an
area is scanned/written from side to side in lines from top to
bottom (or bottom to top). A raster-based photolithographic system,
such as an e-beam system, writes an image on a line along an X
axis, increments to a new line along a Y axis, writes an image on
the new line, and so on to form the overall image. Since the
degrees of motion lie in the X direction and the Y direction, the
raster-based photolithographic system provides orthogonal images.
Orthogonal images are images that, at their smallest pixel level,
involve orthogonal lines along the X axis and the Y axis. As is
known in the art such raster based electron beam systems are used
to produce the reticles used in the modern step and repeat and step
and scan photo tools. They are also used in direct write electron
beam expose tools.
[0046] The present subject matter effectively rotates a workpiece
such that non-orthogonal images are capable of being written on the
workpiece. In various embodiments, the present subject matter
effectively rotates the reticle blank such that non-orthogonal
images are capable of being written on the reticle. In various
embodiments, the reticle is rotated with respect to the orthogonal
directions of motion for the e-beam and the worktable.
[0047] In various embodiments, the present subject matter
effectively rotates a wafer such that non-orthogonal images are
capable of being directly written on the wafer. In various
embodiments, the wafer is rotated with respect to the orthogonal
directions of motion for the e-beam and the worktable.
[0048] In various embodiments, the present subject matter
effectively rotates the mask such that non-orthogonal images are
capable of being written on the wafer. In various embodiments, the
wafer is rotated with respect to the orthogonal directions of the
mask axes.
[0049] FIG. 3 illustrates a schematic diagram of a raster-based
photolithographic system according to various embodiments of the
present subject matter. The illustrated system 302 includes a
worktable 306 which is adapted to receive a reticle 304 and to
provide a linear motion to the reticle along a Y axis using a data
set 308 (such as may be contained in a programmable computer) and a
worktable control module 310. The illustrated system 302 also
includes an electronic beam 312 that sweeps back and forth along an
X axis using the data set 308 and an e-beam control module 314 to
perform the raster scan. One of ordinary skill in the art will
understand the system 302 includes the required technology to
produce and focus the electronic beam 312.
[0050] The worktable 306, or holder, of the reticle 302 is capable
of linear motion (i.e. Y axis motion) and, according to various
embodiments, is capable of having a rotational angle (.theta.)
adjusted. Thus, the worktable 306 is capable of being at a first
predetermined rotational position .theta..sub.1 for imaging
orthogonal lines on the reticle, and is capable of being at a
second predetermined rotational position .theta..sub.2 for imaging
non-orthogonal lines on the reticle. One or ordinary skill in the
art will understand, upon reading and comprehending this
disclosure, that a number of systems are capable of being used to
provide the reticle 302 with a desired rotational position.
[0051] According to various embodiments, the worktable 306 is
capable of being at a number of other rotational positions.
According to various embodiments, the worktable is capable of being
accurately moved or stepped through a number of rotational
positions from rotational position .theta..sub.1 to rotational
position .theta..sub.2. In various embodiments, the worktable
motion control module 310 is adapted to control the rotational
motion and position of the reticle 302. In various embodiments, a
registration sensor system 321 is used to accurately detect the
position of the reticle, and to work with at least one of the
control modules 310 and 314 to adjust the position of the reticle
304 or otherwise register the image on the reticle. For example,
the registration sensor system 321 is capable of finely adjusting
the rotation of the worktable and/or adjusting the deflection of
the e-beam such that a number of images are accurately printed with
respect to each other.
[0052] One of ordinary skill in the art will understand, upon
reading and comprehending this disclosure, that the superimposed
chip image is sized and/or designed to fit in the usable area of
the reticle 302 regardless of the rotational position of the
reticle. The chip image pattern is produced using at least two data
sets 316 and 318. A first data set 316 is used to pattern first
images (e.g. orthogonal images) when the reticle 304 is at a first
rotational position .theta..sub.1. The orthogonal images, for
example, can be viewed as having horizontal and vertical directions
that are consistent with previous chip levels. A second data set
318 is used to pattern second images (non-orthogonal or angled)
when the reticle is at a second rotational position .theta..sub.2.
Additional data sets (N) 320 are capable of being used to pattern
non-orthogonal images when the reticle is at an Nth rotational
position .theta..sub.N. The data sets are operated on by a
programmable computer to provide the image patterns. One of
ordinary skill in the art will understand, upon reading and
comprehending this disclosure, that the superimposed chip image may
be formed either directly on a wafer or other substrate, or on a
reticle which will be used to expose a wafer or other
substrate.
[0053] FIG. 4 illustrates an angled image formed according to
various embodiments of the present subject matter using the
raster-based photolithographic system of FIG. 3. One of ordinary
skill in the art will understand, upon reading and comprehending
this disclosure, that the resulting non-orthogonal image has angled
lines with even edges, and that the lines and the spaces are imaged
to a minimum thickness corresponding to the dimensions of the
e-beam spot. Additionally, each of the lines are capable of being
formed with one e-beam scan motion, and as such are efficiently
formed.
[0054] Raster-based photolithographic systems are capable of
aligning sub-fields to, for example, place two or more chip images
on a single reticle. One of ordinary skill in the art will
understand, upon reading and comprehending this disclosure, how to
register a reticle to accurately image a number of sub-fields with
respect to each other. Thus, one of ordinary skill in the art will
understand, upon reading and comprehending this disclosure, how to
align the first image corresponding to the first data set 316 with
the second image corresponding to the second data set 318.
[0055] FIG. 5 illustrates a schematic representation of a first
image formed on a reticle using a first data set in a raster-based
photolithographic system. In the illustrated embodiment, the area
524 of the first data set (less the alignment markings) corresponds
with the usable area of the reticle.
[0056] According to various embodiments, alignment markings 522 on
the reticle 524 are used to properly position the image produced by
the second data set with the image produced by the first data set.
In various embodiments, for example, the alignment markings are
included in the first data set and are incorporated in the
orthogonal first image. Thus, the markings 522, the vertical lines
526 of the orthogonal first image, and the horizontal lines 528 of
the orthogonal first image are imaged or printed together. These
alignment markings 522 from the first data set are used to align
the second image that corresponds to the second data set.
[0057] In various embodiments, for example, the alignment markings
522 are preprinted or otherwise incorporated on the reticle 524.
These preprinted alignment markings 522 are used to properly
position the image of the first data set and are used to properly
position the image of the second data set.
[0058] In various embodiments, for example, the alignment markings
522 include crosses at each corner of the chip. In various
embodiments, the crosses are positioned on a line that bisects the
corner angle of the reticle/chip. One of ordinary skill in the art
will understand that other alignment markings are able to be used,
and that other methods for registering the position of the reticle
are anticipated. In various embodiments, the registration sensor
system 321 of FIG. 3 is used to accurately detect the position of
the reticle, and to function with at least one of the control
modules 310 and 314 to adjust the position of the reticle 304 or
otherwise register the image on the reticle.
[0059] FIG. 6 illustrates a schematic representation of a second
image formed on a rotated reticle (after the first image is formed
in FIG. 5) using a second data set in the raster-based
photolithographic system. The second data set is rotated with
respect to the first data set so that the angled lines are
vertical/horizontal lines 630 with appropriate alignment markings
632. The alignment markings 632 are coincident with the alignment
markings 522 (shown in FIG. 5) when superimposed on the first data
set.
[0060] The total area of the second data set is shown via line 634.
However, there is no data (i.e. lines) outside of the area 624 of
the rotated first data set, except for the alignment markings 632.
The imaged lines 630 from the second data set are illustrated to
connect the imaged lines from the first data set.
[0061] In the illustrated embodiment, the exposure field of the
e-beam system is as large as area 634 for the second data set,
including the alignment markings. The reticle size needs only be as
big as the first data set, including the alignment markings.
[0062] The actual production of the reticle can be done on a number
of ways, depending upon the type of alignment system used to align
the e-beam fields. In various embodiments, the first data set is
printed upon the resist on the plate, and the plate is removed from
the system and the resist is developed and the plate metallurgy
etched. A new layer of resist is applied, the plate is placed back
in to the system in a rotated position, and data set two is aligned
to the alignment markings. The resist is developed and the plate
metallurgy etched.
[0063] In various embodiments, alignment markings are
pre-positioned on the reticle prior to the first exposure. In this
system, the two data sets are aligned to the pre-positioned
alignment markings. The first data set is used followed by the
required mask rotation and then the second data set is used for the
second exposure.
[0064] One or ordinary skill in the art, upon reading and
comprehending this disclosure, will understand that a process
sequence similar to the sequence used in the illustrated production
of a reticle in FIGS. 5 and 6 can be used in the raster beam direct
write of a wafer or other substrate. Additionally, one of ordinary
skill in the art will understand, upon reading and comprehending
this disclosure, how to rotate the relative position of the wafer
with respect to the reticle to produce non-orthogonal lines on the
wafer when the reticle has an orthogonal image.
[0065] The systems and methods of the present subject matter are
capable of being used to form a magnetic random access memory
(MRAM) array such as that provided by the patent application
entitled "Three Terminal Magnetic Random Access Memory," Ser. No.
09/940,976, filed on Aug. 28, 2001, which was previously
incorporated by reference in its entirety. As discussed therein,
the three terminal MRAM significantly diminishes half-select errors
by energizing three lines (a word line, a bit line and a select
line) rather than two lines to access a selected bit. At least one
of the three lines is non-orthogonal with respect to the other
lines. FIGS. 7-9 illustrate various aspects for forming a three
terminal magnetic random access memory.
[0066] FIG. 7 illustrates a MRAM with magnetic memory cells or
storage devices located at intersections among bit lines, word
lines and select lines in a cross point array. The illustrated MRAM
740 includes Word Line Control Circuitry 742, Bit Line Control
Circuitry 744, and Select Line Control Circuitry 746. These control
circuits control the current direction and magnitude on the
conductors, cooperate with each other to write to a desired
magnetic storage device by providing the appropriate current to a
word line conductor 750, a bit line conductor 752, and a select
line conductor 754 that corresponds to the desired magnetic storage
device 756. The magnetic storage device is capable of being
magnetically coupled to a magnetic field generated by current in
the word line, bit line and select line conductors.
[0067] According to various embodiments, the word line conductors
are oriented at an angle of approximately 60.degree. with the bit
line conductors and the select line conductors, and the bit line
conductors are oriented at an angle of approximately 60.degree.
with the select line conductors. The MRAM 740 is characterized as a
three terminal MRAM, as it includes requires a terminal to control
the word line conductors 750, a terminal to control the bit line
conductors 752, and a terminal to control the select line
conductors 754. All three conductors are energized to write to a
desired memory cell 756.
[0068] FIG. 8 illustrates an intersection in the cross point array
in more detail. This intersection represents a memory cell, and
includes a magnetic storage element 856, a word line conductor 850,
a bit line conductor 852, and a select line conductor 854.
[0069] FIG. 9 illustrates a structure for one embodiment of the
cross point array of FIG. 7. In this embodiment, a properly
insulated magnetic storage element 956 is interposed between a bit
line 952 and a word line 950 at each intersection. A select line
954 also passes operably close to the magnetic storage element 956
at the intersection. According to various embodiments, the array is
fabricated by forming or otherwise providing a word line layer, a
storage element layer on the word line layer, a bit line layer on
the storage element layer, an insulator layer 958 on the bit line
layer, and a select line layer on the insulator layer. The magnetic
storage element is capable of being magnetically coupled by a
magnetic field generated by a current in each of these layers. One
of ordinary skill in the art will understand, upon reading and
comprehending this disclosure, that other structural designs are
capable of being used to magnetically couple the magnetic storage
element 956 with the magnetic fields produced by energizing the
three lines. According to various embodiments, the magnetic storage
element is a magnetoresistance device, and is electrically coupled
to the word line and the bit line.
[0070] FIGS. 10A, 10B and 10C illustrate horizontal word lines,
angled select lines, and angled bit lines, respectively, formed
using the known raster-based photolithographic system of FIG. 1.
FIGS. 10A, 10B and 10C are stacked together to form the array shown
in FIG. 7. The word lines 1050 of FIG. 10A, the select lines 1054
of FIG. 10B, and the bit lines 1052 of FIG. 10C form metallization
layers, and cross each other at intersections such as is
illustrated in FIGS. 7-9.
[0071] The angled select lines 1054 and the angled bit lines 1052
are stepped images, which require more than a minimum feature size
to form the lines and to separate the lines. Since both the angled
select lines 1054 and the angled bit lines 1052 are separated by a
greater distance, the select lines 1054 and the bit lines 1052
cross and form intersections fewer times in a given area. The
horizontal lines 1050 cross the angled select lines 1054 and the
angled bit lines 1052 at the intersections, and thus are separated
by a distance greater than a minimum distance that corresponds to
the pixel width or e-beam spot width. Six word lines, six select
lines and six bit lines fit within the area illustrated in FIGS.
10A-10C.
[0072] FIGS. 11A, 11B and 11C illustrate horizontal word lines,
non-orthogonal select lines, and non-orthogonal bit lines,
respectively, formed according to various embodiments of the
present subject matter using the raster-based photolithographic
system of FIG. 3. The word lines 1150 of FIG. 1A, the select lines
1154 of FIG. 11B, and the bit lines 1152 of FIG. 11C form
metallization layers, and cross each other at intersections such as
is illustrated in FIGS. 7-9.
[0073] The angled select lines 1154 and the angled bit lines 1152
have even edges, and are imaged to a minimum thickness
corresponding to the feature size or e-beam spot. Because the
parallel angled lines are separated by a minimum distance, the
angled select lines 1154 and the angled bit lines 1152 cross and
form intersections more times in a given area. The horizontal lines
1150 cross the angled select lines 1154 and the angled bit lines
1152 at the more densely-packed intersections, and thus are capable
of being closer together. Nine word lines, ten select lines and ten
bit lines fit within the area illustrated in FIGS. 11A-11C, as
compared to the six word lines, six select lines and six bit lines
fit within the area illustrated in FIGS. 10A-10C. Thus, the present
subject matter provides more compact, three-terminal MRAM designs
as compared to using stepped angled images from a conventional,
raster-based photolithographic system.
[0074] System Level
[0075] FIG. 12 is a simplified block diagram of a high-level
organization of various embodiments of an electronic system
according to the present subject matter. In various embodiments,
the system 1200 is a computer system, a process control system or
other system that employs a processor and associated memory. The
electronic system 1200 has functional elements, including a
processor or arithmetic/logic unit (ALU) 1202, a control unit 1204,
a memory device unit 1206 and an input/output (I/O) device 1208.
Generally such an electronic system 1200 will have a native set of
instructions that specify operations to be performed on data by the
processor 1202 and other interactions between the processor 1202,
the memory device unit 1206 and the I/O devices 1208. The control
unit 1204 coordinates all operations of the processor 1202, the
memory device 1206 and the I/O devices 1208 by continuously cycling
through a set of operations that cause instructions to be fetched
from the memory device 1206 and executed. According to various
embodiments, the memory device 1206 includes, but is not limited
to, random access memory (RAM) devices, read-only memory (ROM)
devices, and peripheral devices such as a floppy disk drive and a
compact disk CD-ROM drive. As one of ordinary skill in the art will
understand, upon reading and comprehending this disclosure, any of
the illustrated electrical components are capable of being
fabricated to include a chip produced with non-orthogonal
photolithography in accordance with the present subject matter.
[0076] The illustration of system, as shown in FIG. 12, is intended
to provide a general understanding of one application for the
structure and circuitry of the present subject matter, and is not
intended to serve as a complete description of all the elements and
features of an electronic system that uses non-orthogonal
photolithographic processes according to the present subject
matter. As one of ordinary skill in the art will understand, such
an electronic system can be fabricated in single-package processing
units, or even on a single semiconductor chip, in order to reduce
the communication time between the processor and the memory
device.
[0077] Applications that use non-orthogonal photolithographic
processes as described in this disclosure include electronic
systems for use in memory modules, device drivers, power modules,
communication modems, processor modules, and application-specific
modules, and may include multilayer, multichip modules. Such
circuitry can further be a subcomponent of a variety of electronic
systems, such as a clock, a television, a cell phone, a personal
computer, an automobile, an industrial control system, an aircraft,
and others.
[0078] Method Aspects
[0079] The figures presented and described in detail above are
similarly useful in describing the method aspects of the present
subject matter. The methods described below are nonexclusive as
other methods may be understood from the specification and the
figures described above.
[0080] FIG. 13 illustrates a method for forming non-orthogonal
images in a raster-based photolithographic system according to
various embodiments of the present subject matter. In the
illustrated method 1300, a first image is formed at 1302 when the
reticle is at a first rotational angle .theta..sub.1. The first
image corresponds to a first data set. For example, the first image
may be formed to be orthogonal with respect to other
photolithographic images on the reticle.
[0081] At 1304, the reticle is adjusted to a second rotational
angle .theta..sub.2. At 1306, a second image corresponding to a
second data set is formed when the reticle is at the second
rotational angle .theta..sub.2. According to various embodiments,
the difference between the angles .theta..sub.2-.theta..sub.1 is
not 0.degree., 90.degree., 180.degree. or 270.degree. such that the
second image is non-orthogonal with respect to the first image.
According to various embodiments, the reticle is adjusted by
rotating the worktable from the first rotational angle
.theta..sub.1 to the second rotational angle .theta..sub.2.
According to various embodiments, the reticle is adjusted by
accurately stepping the worktable through a number of rotational
positions from the first rotational angle .theta..sub.1 to the
second rotational angle .theta..sub.2.
[0082] Additional images are formed on the reticle in various
embodiments. For example, the reticle is adjusted to an Nth
rotational position .theta..sub.N at 1308, and at 1310, an Nth
image corresponding to an Nth data set is formed on the reticle
when the reticle is at the rotational position .theta..sub.N.
[0083] One of ordinary skill in the art will understand, upon
reading and comprehending this disclosure, how to substitute a
wafer or other workpiece for the reticle shown in FIG. 13 for a
direct write electron beam or similar direct write system.
[0084] FIG. 14 illustrates a method for aligning the second image
with the first image according to various embodiments of the method
illustrated in FIG. 13. In the illustrated method 1412, a first
image includes alignment markings, and is formed on the reticle at
1414 when the reticle is at a first rotational position
.theta..sub.1. At 1416, the image is positioned at a second
rotational position .theta..sub.2 and is registered to the
alignment markings formed as part of the first image. One of
ordinary skill in the art will know how to register to the reticle
to the alignment markings. According to various embodiments, the
reticle is rotated between the first rotational position
.theta..sub.1 and the second rotation position .theta..sub.2.
According to various embodiments, the reticle is accurately stepped
through a number of rotational positions between the first
rotational position .theta..sub.1 and the second rotation position
.theta..sub.2. At 1418, a second image is formed at
.theta..sub.2.
[0085] FIG. 15 illustrates a method for aligning the first image
and the second image with the reticle according to various
embodiments of the method illustrated in FIG. 13. In the
illustrated method 1520, at 1522, the reticle is positioned at a
first rotational position .theta..sub.1 and is registered to
alignment markings already preprinted or otherwise identified on
the reticle. At 1524, a first image is formed at the first
rotational position .theta..sub.1. At 1526, the reticle is
positioned at a second rotational position .theta..sub.2 and the
image is registered to the alignment markings. One of ordinary
skill in the art will understand, upon reading and comprehending
this disclosure, that in various embodiments, the image used at
1526 is a different image than that used at 1522. At 1528, a second
image is formed at the second rotational position
.theta..sub.2.
[0086] FIG. 16 illustrates a method for forming an integrated
circuit metallization layer according to various embodiments of the
present subject matter. In the illustrated method 1630, an
insulator is deposited on a wafer at 1632, and a resist is
deposited on the insulator at 1634. At 1636, a first image is
formed on the resist when the reticle is at a first rotational
position .theta..sub.1. At 1638, the second reticle is adjusted and
appropriately registered to a second rotational position
.theta..sub.2. At 1640, a second image is formed on the resist when
the reticle is at the second rotational position .theta..sub.2. The
first and second images are developed at 1642, and at 1644, the
wafer is processed to form a metallization layer using the
damascene process based on the developed first and second images.
One of ordinary skill in the art will understand, upon reading and
comprehending this disclosure, that the metallization layer also
can be formed using subtractive etch process. Thus, a single
metallization layer is capable of including both orthogonal and
non-orthogonal lines.
[0087] FIG. 17 illustrates a method for forming integrated circuit
metallization layers according to various embodiments of the
present subject matter. In the illustrated method 1746, a first
insulator is deposited on a wafer at 1748, and a first resist is
deposited on the first insulator at 1750. At 1752, a first image is
formed on the resist when the first reticle is at a first
rotational position .theta..sub.1. The first image is developed at
1754, and at 1756, the wafer is processed to form a first
metallization layer using the damascene process based on the
developed first image. One of ordinary skill in the art will
understand, upon reading and comprehending this disclosure, that
the wafer can be processed to form the metallization layer using a
subtractive etch process. The damascene process and the subtractive
etch process are known. Upon reading and comprehending this
disclosure, those of ordinary skill in the art will understand how
to incorporate the present subject with these processes.
[0088] At 1758, a second insulator is deposited on the wafer, and a
second resist is deposited on the second insulator at 1760. At
1762, the process uses a second reticle which was imaged registered
a second rotational position .theta..sub.2. The reticle is
appropriately registered to the first level. At 1764, a second
image is formed on the resist. The second image is developed at
1766, and at 1768, the wafer is processed to form a metallization
layer based on the developed second image. Thus, as the image on
the second reticle was placed at an angle to the first, one
metallization layer is capable of being non-orthogonal with respect
to another metallization layer.
[0089] FIG. 18 illustrates a method for forming non-orthogonal
lines on a substrate according to various embodiments of the
present subject matter. In the illustrated method, a reticle is
formed with a non-orthogonal image at 1870. According to various
embodiments, the non-orthogonal image is formed on the reticle by
rotating or otherwise adjusting the reticle to a desired rotational
position, and forming the non-orthogonal image on the rotated
reticle using a raster-based photolithographic system. At 1872, the
non-orthogonal lines are formed on the substrate/wafer using the
reticle.
[0090] FIG. 19 illustrates a method for forming non-orthogonal
lines on a substrate according to various embodiments of the
present subject matter. In the illustrated method, at 1974 a
reticle is formed with an orthogonal image using a raster-based
system. The relative position between the reticle and the
substrate/wafer is registered at 1976. In various embodiments, the
reticle is rotated to register the relative position. In various
embodiments, the substrate is rotated to register the relative
position. At 1978, non-orthogonal lines are formed on the
substrate/wafer using the reticle.
[0091] FIG. 20 illustrates a method for forming non-orthogonal
lines on a substrate according to various embodiments of the
present subject matter. In the illustrated method, a rotational
position of the substrate/wafer is registered at 2080. A
non-orthogonal image is directly written on the substrate at
2082.
CONCLUSION
[0092] The present subject mater relates to improved
photolithographic techniques for forming non-orthogonal (angled)
lines. The present subject matter provides a modified raster-based
photolithographic process in which a rotational angle (.theta.) of
a reticle is adjusted to change the reference of the orthogonal,
raster-based system. Thus, orthogonal lines are capable of being
printed using a first data set, and after .theta. is adjusted,
non-orthogonal lines are capable of being printed using a second
data set. The present subject matter allows non-orthogonal lines to
be formed at the same minimum thickness as the orthogonal lines, to
be formed with even line edges, and to be formed efficiently since
each line is capable of being printed in a single scan.
[0093] In various embodiments, the present subject matter is used
to produce reticles with non-orthogonal lines. In various
embodiments, the present subject matter is used to rotate a
relative position between a wafer and a reticle to produce
non-orthogonal lines on the wafer from the orthogonal lines on the
reticle. In various embodiments, the present subject matter is used
to directly write non-orthogonal lines on a wafer.
[0094] This disclosure refers to several figures that resemble flow
diagrams. One of ordinary skill in the art will understand, upon
reading and comprehending this disclosure, that the methods related
to the flow diagrams may occur in the order as illustrated in the
flow diagrams, and may be ordered in another manner. Thus, the
present subject matter is not limited to a particular order or
logical arrangement.
[0095] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that any arrangement which is calculated to achieve the
same purpose may be substituted for the specific embodiments shown.
This application is intended to cover adaptations or variations of
the present subject matter. It is to be understood that the above
description is intended to be illustrative, and not restrictive.
Combinations of the above embodiments, and other embodiments, will
be apparent to those of skill in the art upon reviewing the above
description. The scope of the present subject matter should be
determined with reference to the appended claims, along with the
full scope of equivalents to which such claims are entitled.
* * * * *