U.S. patent application number 11/772524 was filed with the patent office on 2007-11-08 for implant optimization scheme.
This patent application is currently assigned to TEXAS INSTRUMENTS INCORPORATED. Invention is credited to James D. Bernstein, Said Ghneim, Nandu Mahalingam, Benjamin Moser, Lance S. Robertson.
Application Number | 20070257211 11/772524 |
Document ID | / |
Family ID | 35309968 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070257211 |
Kind Code |
A1 |
Bernstein; James D. ; et
al. |
November 8, 2007 |
Implant Optimization Scheme
Abstract
The present invention provides a method for implanting ions in a
substrate and a method for manufacturing an integrated circuit. The
method for implanting ions in a substrate, among other steps,
including placing a substrate (410) on an implant platen (405) such
that a predominant axes (430) of the substrate (410) is rotated
about 30 degrees to about 60 degrees or about 120 degrees to about
150 degrees offset from a radial with respect to the implant platen
(405), and further wherein the substrate (410) is not tilted. The
method further includes implanting ions into the substrate (410),
the rotated position of the predominant axes (430) reducing
shadowing.
Inventors: |
Bernstein; James D.; (Plano,
TX) ; Robertson; Lance S.; (Rockwall, TX) ;
Ghneim; Said; (Richardson, TX) ; Mahalingam;
Nandu; (Richardson, TX) ; Moser; Benjamin;
(Dallas, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
TEXAS INSTRUMENTS
INCORPORATED
7839 Churchill Way M.S. 3999
Dallas
TX
75251
|
Family ID: |
35309968 |
Appl. No.: |
11/772524 |
Filed: |
July 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11006257 |
Dec 7, 2004 |
7253072 |
|
|
11772524 |
Jul 2, 2007 |
|
|
|
60571669 |
May 13, 2004 |
|
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|
Current U.S.
Class: |
250/492.21 ;
257/E21.345; 257/E21.427; 257/E21.634 |
Current CPC
Class: |
H01L 21/823814 20130101;
H01L 21/26586 20130101; H01L 29/66659 20130101 |
Class at
Publication: |
250/492.21 |
International
Class: |
H01J 37/08 20060101
H01J037/08 |
Claims
1. A method for implanting ions in a substrate, comprising: placing
a substrate on an implant platen such that predominant axes of the
substrate are chordal with respect to the implant platen and
implanting about 1/4 of a desired amount of ions into the
substrate; rotating the substrate in a direction by about 90
degrees to a second position and implanting about another 1/4 of
the desired amount of ions into the substrate; rotating the
substrate located in the second position in the direction by about
90 degrees to a third position and implanting about another 1/4 of
the desired amount of ions into the substrate; and rotating the
substrate located in the third position in the direction by about
90 degrees to a fourth position and implanting a remaining amount
of ions into the substrate.
2. The method as recited in claim 1 wherein placing a substrate
includes placing a substrate such that one of the predominant axes
is about 30 degrees to about 60 degrees or about 120 degrees to
about 150 degrees offset from a radial with respect to the
platen.
3. The method as recited in claim 1 wherein placing a substrate
includes placing a substrate such that one of the predominant axes
is about 45 degrees or about 135 degrees offset from a radial with
respect to the platen.
4. The method as recited in claim 1 wherein the substrate is not
tilted.
Description
[0001] This application is a divisional of application Ser. No.
11/006,257, filed Dec. 7, 2004, which claims the benefit of
provisional Application No. 60/571,669, filed May 13, 2004.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention is directed, in general, to an implant
optimization scheme and, more specifically, to an implant
optimization scheme wherein predominant axes of an implantable
substrate are chordal with respect to an implant platen.
BACKGROUND OF THE INVENTION
[0003] Advanced integrated circuit design requires precise control
of beam incidence angles. While a number of different types of beam
incidence angle error exist, three of the more common types are
cone angle error, beam steering error and parallelism error across
the wafer. Cone angle error is typically a result of cone angle
effects caused by the geometry of the wafer scanning system. Cone
angle error causes within wafer variation. For example the beam
angle error may be about -x degrees at one edge of the wafer, be
approximately zero degrees as the center of the wafer, and be about
+x degrees at the opposing edge of the wafer.
[0004] Steering error, on the other hand, tends to be a fixed error
across the wafer that is introduced while tuning the beam between
lots, implant batches, or whenever the tuning may occur. The
parallelism error, for whatever reason, leads to random beam
incidence angle errors across the width of the wafer. This error is
particularly difficult to correct as a result of its random
nature.
[0005] Unfortunately, without precise control of beam incidence
angles, various different problems degrade the transistors of the
integrated circuit. As an example, transistor asymmetry, variation,
and depressed MPY often result due to beam incidence angle error.
The beam incidence angle error also typically leads to gate
shadowing and an asymmetric dopant distribution, both of which are
undesirable.
[0006] Turning to FIGS. 1A and 1B, illustrated is an example of an
implant system 100 that could lead to gate shadowing on a
transistor device. The implant system 100 illustrated in FIG. 1A
includes one or more substrates 110 located on or over an implant
platen 105. As is illustrated, a predominant axis of each of the
substrates 110 is radial with respect to the implant platen 105.
The radial nature of the substrates 105 in the example shown is
accomplished by aligning an alignment feature 120 of the implant
platen 105 with alignment features 125 on each of the substrates
110, the alignment features 125 on each of the substrates 110
aligned with a predominant axis of each of the substrates 110. The
alignment features 120, 125, as one would expect, allow the
substrates 110 to be easily positioned and aligned during an
implant process.
[0007] Each of the substrates 110 theoretically have one or more
transistor devices 140 located thereon that are being subjected to
an implant process 130 as the implant platen 105 rotates. The
transistor device 140 illustrated in FIG. 1B includes a gate
structure 150, having a height (h), located over the substrates
110. The transistor device 140 illustrated in FIG. 1B is being
subjected to the implant process 130 to form implant regions 160.
As is illustrated, the combination of the implant beam incidence
angle (.theta.) and gate structure 150 height (h) causes the
implant regions 160 located within the substrates 110 not be placed
equidistance from the gate structure 150. For example, one of the
implant regions 160 is located a distance (d) from the sidewall of
the gate structure 120, where the other implant region 160 is
located adjacent the sidewall of the gate structure 150. While the
distance (d) can be estimated using the equation d=h tan (.theta.),
it nevertheless creates an undoped/underdoped region 170 defined by
the distance (d) that often tends to cause serious operational
problems for the transistor device 140.
[0008] Accordingly, what is needed in the art is a method for
implanting dopants within a substrate that does not experience the
drawbacks of the prior art methods and devices.
SUMMARY OF THE INVENTION
[0009] To address the above-discussed deficiencies of the prior
art, the present invention provides a method for implanting ions in
a substrate and a method for manufacturing an integrated circuit.
The method for implanting ions in a substrate, among other steps,
including placing a substrate on an implant platen such that a
predominant axes of the substrate is rotated about 30 degrees to
about 60 degrees or about 120 degrees to about 150 degrees offset
from a radial with respect to the implant platen, and further
wherein the substrate is not tilted. The method further includes
implanting ions into the substrate, the rotated position of the
predominant axes reducing shadowing. The method for manufacturing
an integrated circuit, on the other hand, additionally includes
forming interconnects within dielectric layers located over
microelectronic device features located over or on the substrate to
form an operational integrated circuit.
[0010] The foregoing has outlined preferred and alternative
features of the present invention so that those skilled in the art
may better understand the detailed description of the invention
that follows. Additional features of the invention will be
described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiment as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention is best understood from the following detailed
description when read with the accompanying FIGUREs. It is
emphasized that in accordance with the standard practice in the
microelectronic industry, various features are not drawn to scale.
In fact, the dimensions of the various features may be arbitrarily
increased or reduced for clarity of discussion. Reference is now
made to the following descriptions taken in conjunction with the
accompanying drawings, in which:
[0012] Prior Art FIGS. 1A and 1B illustrate an example of an
implant system that could lead to gate shadowing on a conventional
transistor device;
[0013] FIGS. 2A and 2B illustrate a cross-sectional view and
top-down view, respectively, of a device illustrating the shadowing
distance (d) and reduced shadowing distance (d=);
[0014] FIG. 3 illustrates an explosion plan view of an embodiment
of a substrate that might be used in an implant system to
accomplish the unique aspects of the present invention;
[0015] FIG. 4 illustrates a plan view of an embodiment of an
implant system that might be used in an exemplary embodiment to
implant ions, such as a dopant, within a substrate in accordance
with the principles of the present invention;
[0016] FIG. 5 illustrates a cross-sectional view of a transistor
device that might be located on one of the substrates illustrated
in FIG. 4; and
[0017] FIG. 6 illustrates a cross-sectional view of a conventional
integrated circuit (IC) incorporating transistor devices
constructed according to the principles of the present
invention.
DETAILED DESCRIPTION
[0018] For the purpose of completeness, a few terms need to be
clarified prior to getting into the details of the present
invention. For example, the term chord or chordal as used herein is
intended to mean a straight line joining any two points on a
perimeter of an implant platen, except for a straight line that
intersects a center point of the implant platen. Where the implant
platen is circular, the term chord or chordal means any straight
line joining any two points on the perimeter of the circular
implant platen that does not intersect a center point of the
circular implant platen, and thereby define the diameter of the
circular implant platen. On the other hand, where the implant
platen is a polygon, the term chord or chordal means any straight
line adjoining any two points on the perimeter of the polygon that
does not intersect the center point of the polygon.
[0019] The term predominant axes, as used herein, may be defined
using the substrates themselves or the features thereon. Often, the
substrates have streets on them delineating different dies on the
wafer. In this instance, the predominant axes could be
substantially defined by the axes created by the orientation of the
majority of the streets, taken through a center point of the
substrate. Other times, streets may or may not exist and the
orientation of the features on the substrate could substantially
define the orientation of the predominant axes of the substrate. In
this instance, the predominant axes could be defined by the axes
created by the orientation of the majority of the features, taken
through a center point of the substrate. Most times, the
predominant axes created by the majority of the streets and the
majority of the features, are substantially the same. Often, the
predominant axes created by either of the streets or the features
are orthogonal to one another, however, this need not always be the
instance.
[0020] The term rotation angle (.omega.), as used herein, means an
angle of rotation of a predominant axis away from a radial with
respect to the implant platen. For instance, if a predominant axis
were pointed directly to a center point of the implant platen, as
it is in the prior art, the rotation angle (.omega.) would be zero,
and thus the predominant axis would be non-chordal, as defined.
[0021] Low energy, as used herein, refers to a beam of charged
particles having an energy of about 20 KeV or less. In an exemplary
embodiment, however, the beam of charged particles has an energy of
about 15 KeV or less, or even more advantageously of about 8 KeV or
less. It goes without saying, however, that other low energy beams
of charged particles could be used without departing from the scope
of the present invention.
[0022] Given the aforementioned definitions, as shown in FIGS. 2A
(cross-sectional view) and 2B (top-down view), the present
invention is based in part on the unique recognition that for a
fixed implant angle error (.theta.), a shadowing distance (d)
created during the implanting of traditional implant regions into a
substrate may be reduced to a distance (d=) by simply rotating the
substrate such that the predominant axes of the substrate are
chordal with respect to the implant platen. Traditional implant
techniques, often using alignment marks on the substrate and the
implant platen, aligned one of the predominant axes of the
substrate to be radial with respect to the implant platen. This
configuration causes the shadowing distance (d), which can be
calculated using the equation d=h*tan(.theta.), where (h) is the
height of the gate structure and (.theta.) is an angle between a
line drawn perpendicular to the implant platen and the incidence
implant source, to be significant. Simply by rotating the substrate
by an angle (.omega.) away from a radial with respect to the
implant platen, such that the predominant axes of the substrate are
chordal with respect to the implant platen, the traditional
shadowing distance (d) can be reduced to a distance (d=). In the
example given, the reduced distance (d=) may be measured using the
equations d==h*tan(.theta.)sin(.omega.) or d==d*sin(.omega.). These
equations assume that all of the angle error (.theta.) is in the
direction of d when .omega.=0 (i.e., there is no component of angle
error into or out of the page). This is a valid approximation since
the beam angle error occurs in the dispersive plane of the magnet,
and that plane is fixed. If the dispersive plane of the magnet is
orthogonal then the same equation would apply to a transistor
oriented orthogonally from the one in FIGS. 2A and 2B. Thus,
depending on the angle of rotation (.omega.), the reduced distance
(d=) can be up to about 29 percent less than the traditional
shadowing distance (d).
[0023] Turning now to FIG. 3, illustrated is an explosion plan view
300 of an embodiment of a substrate 310 that might be used in an
implant system to accomplish the unique aspects of the present
invention. The substrate 310 illustrated in FIG. 3 has a plurality
of both streets 320 and features 330 located thereon. Either one or
both of the plurality of streets 320 or features 330 could be used
to determine the predominant axes of the substrate 310 of FIG. 3.
It goes without saying that certain embodiments may exist where the
substrate 310 illustrated in FIG. 3 contains no streets 320. In
this embodiment, the features 330 alone would be used to determine
the predominant axes of the substrate 310.
[0024] In determining the predominant axes of the substrate 310
using the streets 320, one skilled in the art would look at an
orientation of the majority of the streets 320, and would then
project that orientation through a center point of the substrate
310. The substrate 310 illustrated in FIG. 3 contains a plurality
of streets 320. While a majority of the streets 320 are positioned
in a grid-like manner, a few of the streets 320 are abnormal to the
majority. Nevertheless, the orientation of the majority of the
streets 320 would define the orientation of the predominant axes.
Thus, after determining the orientation of the predominant axes,
that orientation would be projected through a center point of the
substrate 310, thus providing the predominant axes 340.
[0025] On the other hand, in determining the predominant axes using
the features 330, one skilled in the art would look at an
orientation of the majority of the features 330, and would then
project that orientation through a center point of the substrate
310. The substrate 310 illustrated in FIG. 3 contains a plurality
of features 330, many of which have the same orientation, but some
of which are abnormal to the majority. Nevertheless, the
orientation of the majority of the features 330 would define the
orientation of the predominant axes. Thus, after determining the
orientation of the predominant axes, that orientation would be
projected through a center point of the substrate 310, thus
providing the predominant axes 340. [0026] Interestingly, in the
embodiment discussed with respect to FIG. 3, the streets 320 and
features 330 provide substantially the same predominant axes 340.
It is believed that this is often the case, as placement of the
features 330 define the position of the streets 320, or vice-versa.
Nevertheless, certain instances may exist where the streets 320 and
features 330 do not provide the same predominant axes 340. In this
instance, it is believed that the features 330 should define the
predominant axes 340.
[0026] Turning now to FIG. 4, illustrated is a plan view of an
embodiment of an implant system 400 that might be used in an
exemplary embodiment to implant ions, such as a dopant, within a
substrate in accordance with the principles of the present
invention. The implant system 400 illustrated in FIG. 4 includes a
plurality of substrates 410 located on or over an implant platen
405 as they are being subjected to an implant source 420, such as a
low energy beam of charged particles. The substrates 410 may be
similar to the substrate 310 illustrated and discussed with respect
to FIG. 3 above. For clarification, the plan view is a snapshot of
the implant platen 405 and substrates 410 as they rotate about a
center point of the implant platen 405. As those skilled in the art
are aware, the implant platen 405 in the embodiment of FIG. 4
typically rotates in a clockwise or counterclockwise direction at a
high rate of speed as the implant source 420 slowly scans across
the implant platen 405 from side to side. In the embodiment shown,
the substrates 410 are not tilted with respect to the implant
platen 405.
[0027] The embodiment of FIG. 4 illustrates that only four
substrates 410 are located on or over the implant platen 405. In
actuality, any number of substrates 410, for example from one
substrate 410 to an infinite number of substrates 410, could be
located on or over the implant platen 405. Additionally, while the
implant platen 405 is illustrated in FIG. 4 as a disk, those having
skill in the art appreciate that the shape of the implant platen
405, design of the implant platen 405, and for that matter the
design of the implant system 400 itself, may vary widely while
staying within the scope of the present invention. Likewise, the
present invention is applicable with single-wafer implanters that
do not use disks or wheels.
[0028] While each of the substrates 410 in the embodiment of FIG. 4
only have vertical transistors, those skilled in the art understand
that it is within the scope of the present invention for the
substrates 410 to have both vertical (v) and horizontal (h)
transistors. This is often the case in current integrated circuits,
especially in view of the apparent need to save wafer real-estate.
Nevertheless, the inventive aspects of the present invention are
applicable to those situations where only vertical (v), only
horizontal (h), or both vertical (v) and horizontal (h) transistors
exist.
[0029] As required by the present invention, the substrates 410 are
positioned such that their predominant axes 430 are chordal with
respect to the implant platen 405. In the embodiment illustrated in
FIG. 4, one of the predominant axes 430 of the substrates 410 is
offset from a radial with respect to the implant platen 405 by a
rotation angle (.omega.). In reality, the rotation angle (.omega.)
may be almost any angle except for 0 degrees, 90 degrees, 180
degrees or 270 degrees. In one advantageous embodiment the rotation
angle (.omega.) of one of the predominant axes 430 is about 15
degrees to about 75 degrees, about 105 degrees to about 165
degrees, about 195 degrees to about 255 degrees, or about 285
degrees to about 345 degrees from the radial with respect to the
implant platen 405. Assuming the predominant axes 430 of the
substrates 410 are orthogonal to one another, the other of the
predominant axes 430 would be about 105 degrees to about 165
degrees, about 195 degrees to about 255 degrees, about 285 degrees
to about 345 degrees, or about 15 degrees to about 75 degrees,
respectively, from the radial with respect to the implant platen
405. In an exemplary embodiment, one of the predominant axes 430 is
about 45, about 135 degrees, about 225 degrees, or about 315
degrees from the radial with respect to the implant platen 405.
Assuming again that the predominant axes 430 are orthogonal, the
other of the predominant axes 430 would be about 135 degrees, about
225 degrees, about 315 degrees or about 45 degrees, respectively,
from the radial with respect to the implant platen 405. It is
believed that this embodiment provides the best results, thereby
providing the smallest distance (d=) for a given angle error
(.theta.). In the embodiment illustrated in FIG. 4 it is shown that
the substrates 410 are rotated clockwise from a radial position.
Nevertheless, those skilled in the art would appreciate that the
substrates 410 may also easily be rotated counterclockwise and stay
within the scope of the present invention.
[0030] One embodiment of the invention has the substrates 410
having alignment lines thereon to allow the predominant axes 430 to
be easily found. For example, the alignment lines may be placed
such that they are aligned with one of the predominant axes 430,
and thus the alignment lines are also chordal with respect to the
implant platen 405. Another embodiment of the invention has the
alignment lines placed such that they are not aligned with one of
the predominant axes 430. In this embodiment, the alignment lines
might be configured so that they are radial with respect to the
implant platen 405, while the predominant axes 430 are chordal with
respect to the implant platen 405. This embodiment would allow for
easy placement of the substrates 410 such that they are chordal
with respect to the implant platen 405.
[0031] The embodiment of FIG. 4 illustrates that the substrates 410
are implanted with a full implant dose after they have been placed
on the implant platen 405 such that their predominant axes 430 are
chordal with respect to the implant platen 405. This represents but
one embodiment covered by the present invention. Another embodiment
has the substrates 410 positioned in a first position similar to
that illustrated in FIG. 4, but only 1/4 of a total implant dose is
implanted at this time. The substrates 410 would then be rotated in
the same direction by about 90 degrees to a second position and
would be subjected to another 1/4 of the total implant dose. The
substrates 410 would then be rotated in the same direction by about
90 degrees to a third position and would be subjected to another
1/4 of the total implant dose. And finally, the substrates 410
would then be rotated in the same direction by about 90 degrees to
a fourth position and would be subjected to the last 1/4 of the
total implant dose. This embodiment provides exemplary coverage for
the implant dose. A similar situation could occur where only 2 of
the implant dose in implanted in two different steps, as well as
any other conceivable configuration. [0033] Turning finally to FIG.
5, illustrated is a cross-sectional view of a transistor device 500
that might be located on one of the substrates illustrated in FIG.
4. The transistor device 500 illustrated in FIG. 5 includes a gate
structure 520, having a height (h), located over the substrates
510. The transistor device 500 illustrated in FIG. 5 is being
subjected to the implant process 530 to form implant regions 540.
As is illustrated, the combination of the implant beam incidence
angle (.theta.) and gate structure 520 height (h) causes the
implant regions 540 located within the substrates 510 not be placed
equidistance from the gate structure 520. For example, one of the
implant regions 540 is located a distance (d=) from the sidewall of
the gate structure 520, where the other implant region 540 is
located adjacent the sidewall of the gate structure 520.
[0032] Unique to the present invention, the distance (d=) is
significantly less than the distance (d) that would be obtained for
the same incidence angle (.theta.) and gate structure height (h)
for a similar transistor device in prior art structures. The
reduced distance (d=) may be attributed to the positioning of the
substrates such that predominant axes of the substrates are chordal
with respect to the implant platen.
[0033] Advantageously, the reduced distance (d=) provides for
improved transistor symmetry between the source and drain regions
of single transistors. Additionally, the reduced distance (d=)
provides for improved transistor symmetry between horizontal and
vertical transistors in the same region on a wafer. Moreover, it
provides for reduced lot-to-lot variations.
[0034] Referring finally to FIG. 6, illustrated is a
cross-sectional view of a conventional integrated circuit (IC) 600
incorporating transistor devices 610 constructed according to the
principles of the present invention. The IC 600 may include
devices, such as transistors used to form CMOS devices, BiCMOS
devices, Bipolar devices, or other types of devices. The IC 600 may
further include passive devices, such as inductors or resistors, or
it may also include optical devices or optoelectronic devices.
Those skilled in the art are familiar with these various types of
devices and their manufacture. In the particular embodiment
illustrated in FIG. 6, the IC 600 includes transistor devices 610
having dielectric layers 620 located thereover. Additionally,
interconnect structures 630 are located within the dielectric
layers 620 to interconnect various devices, thus, forming the
operational integrated circuit 600.
[0035] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without
departing from the spirit and scope of the invention in its
broadest form.
* * * * *