U.S. patent application number 12/640416 was filed with the patent office on 2010-04-15 for method of determining angle misalignment in beam line ion implanters.
This patent application is currently assigned to VARIAN SEMICONDUCTOR EQUIPMENT ASSOCIATES, INC.. Invention is credited to Atul GUPTA, Joseph C. Olson.
Application Number | 20100090131 12/640416 |
Document ID | / |
Family ID | 39318443 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100090131 |
Kind Code |
A1 |
GUPTA; Atul ; et
al. |
April 15, 2010 |
METHOD OF DETERMINING ANGLE MISALIGNMENT IN BEAM LINE ION
IMPLANTERS
Abstract
A method includes directing an ion beam at a plurality of
differing incident angles with respect to a target surface of a
substrate by tilting the substrate as the ion beam is distributed
across the target surface to implant ions into a plurality of
portions of the substrate, wherein each one of the plurality of
differing incident angles is associated with a different one of the
plurality of portions, measuring angle sensitive data from each of
the plurality of portions of to the substrate, and determining an
angle misalignment between the target surface and the ion beam
incident on the target surface from the angle sensitive data.
Inventors: |
GUPTA; Atul; (Beverly,
MA) ; Olson; Joseph C.; (Beverly, MA) |
Correspondence
Address: |
VARIAN SEMICONDUCTOR EQUIPMENT ASSC., INC.
35 DORY RD.
GLOUCESTER
MA
01930-2297
US
|
Assignee: |
VARIAN SEMICONDUCTOR EQUIPMENT
ASSOCIATES, INC.
Gloucester
MA
|
Family ID: |
39318443 |
Appl. No.: |
12/640416 |
Filed: |
December 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11541373 |
Sep 29, 2006 |
7642529 |
|
|
12640416 |
|
|
|
|
Current U.S.
Class: |
250/492.3 |
Current CPC
Class: |
H01J 2237/1501 20130101;
H01J 2237/24528 20130101; H01J 2237/3045 20130101; H01J 2237/31703
20130101; H01J 37/3171 20130101; H01L 22/14 20130101; H01J 37/1471
20130101; H01J 2237/24535 20130101; H01J 2237/24578 20130101 |
Class at
Publication: |
250/492.3 |
International
Class: |
H01J 37/317 20060101
H01J037/317; G21K 5/00 20060101 G21K005/00 |
Claims
1. A method comprising: directing an ion beam at a plurality of
differing incident angles with respect to a target surface of a
substrate by tilting said substrate as said ion beam is distributed
across the target surface to implant ions into a plurality of
portions of said substrate, wherein each one of said plurality of
differing incident angles is associated with a different one of
said plurality of portions; measuring angle sensitive data from
each of said plurality of portions of said substrate; and
determining an angle misalignment between said target surface and
said ion beam incident on said target surface from said angle
sensitive data.
2. The method of claim 1, wherein said plurality of portions
comprise is nine portions and said plurality of differing incident
angles comprise nine differing incident angles, wherein each one of
said nine differing incident angles is associated with a differing
one of said nine portions.
3. The method of claim 1, wherein said substrate has a crystalline
structure and wherein said angle sensitive data is representative
of damage to said crystalline structure.
4. The method of claim 1, wherein said angle sensitive data is
representative of a change in conductivity of said substrate.
5. The method of claim 1, wherein said angle sensitive data is
representative of a dopant profile of a concentration of said ions
implanted in said substrate versus a depth from said target surface
of said substrate.
6. The method of claim 1, wherein said plurality of incident angles
comprises substantially continuous ion beam incident angles.
7. The method of claim 1, wherein said plurality of incident angles
comprises incrementally varied ion beam incident angles.
8. The method of claim 1, wherein said angle misalignment comprises
a horizontal angle misalignment in a horizontal plane, and said
method further comprises determining an offset tilt angle to tilt
said substrate about a vertical axis to compensate for said
horizontal angle misalignment.
9. The method of claim 1, wherein said misalignment comprises a
vertical angle misalignment in a vertical plane, and said method
further is comprises determining an offset tilt angle to said
substrate about a horizontal axis to compensate for said vertical
angle misalignment.
10. The method of claim 1, further comprising determining a
substrate miscut angle in a first direction between a desired
crystalline plane and an actual plane of said target surface of
said substrate from said angle sensitive data.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of prior application Ser.
No. 11/541,373, filed Sep. 29, 2006, the contents of which are
incorporated herein by reference.
FIELD
[0002] This disclosure relates to beam line ion implanters and,
more particularly, to a method of determining angle misalignment in
beam line ion implanters.
BACKGROUND
[0003] A beam line ion implanter generates a well defined ion beam
and directs the ion beam at a target surface of a substrate. The
ion beam may strike the target surface of the substrate at any
incident angle of the ion beam relative to the target surface to
implant energetic ions of the ion beam into the substrate. A
desired incident angle may be specified before an implant and any
deviation from the desired incident angle can significantly impact
the results of the implant.
[0004] An angle misalignment between the target surface of the
substrate and the incident ion beam may be caused by several
mechanisms and may lead to deviation from the desired incident
angle. For example, the angle misalignment may be caused by a
variation of the actual path of the incident ion beam from a
desired path and/or a variation of the actual position of the
substrate from a desired position of the substrate. Hence, it is
desirable to determine any angle misalignment during an alignment
check procedure before an implant. If there is an angle
misalignment, the substrate may then be re-positioned relative to
the incident ion beam to compensate for any angle misalignment.
Measurement and correction of any angle misalignment is crucial to
ensure accurate and repeatable angle performance of the
implanter.
[0005] One method of determining angle misalignment between the
incident ion beam and the target surface of the substrate requires
a plurality of substrates during an alignment check procedure. Each
of the plurality substrates is positioned at a different known
offset angle by positioning the substrate relative to the ion beam
and the entirety of each substrate is then implanted with ions from
the incident ion beam. In a typical implementation of this
procedure, nine separate substrates are implanted at nine different
incident angles. Angle sensitive data from each substrate is then
measured and the average value of the angle sensitive data from
each is used to determine the angle misalignment. The angle
misalignment may then be accounted for with an offset in the home
position of the substrate.
[0006] This conventional method suffers from several drawbacks.
First, material and processing costs increase with each substrate
utilized. Second, it is difficult to ensure that each of the
plurality of substrates has a similar surface orientation. This can
then lead to inconsistency when measuring angle sensitive data from
different substrates with slightly different surface orientations.
Third, this method takes time that can adversely affect machine
availability of the beam line ion implanter due to increased
downtime. Fourth, variations in a substrate positioning apparatus
may result in variations in substrate positioning for each
substrate further degrading the quality of the results.
[0007] In semiconductor device manufacturing, the substrates may be
cut from a crystalline semiconducting material that is grown into a
cylindrical ingot. The substrates may therefore have a disk shape
and may also be referred to as a wafer. These substrates may be
sliced to obtain a desired crystalline plane at the target surface
of the substrate and polished to ensure a flat target surface.
However, the resulting target surface of the substrate may be
formed from a miscut of the cylindrical ingot relative to the
desired crystalline plane. This may sometimes be referred to in the
art as "substrate miscut". A conventional ion implanter assumes
that there is either no substrate miscut or that the substrate
miscut stays the same for all substrates to be processed in the
implanter, and this assumption may lead to angle misalignment of
the substrate relative to the incident ion beam. The substrate
miscut may vary depending on the particular source of the
particular substrate and how it was sliced relative to the desired
crystalline plane.
[0008] Accordingly, there is a need for an improved method to
determine an angle misalignment between a target surface of a
substrate and an incident ion beam in beam line ion implanters.
There is also a need for a method to determine any crystal miscut
in the substrate.
SUMMARY
[0009] According to a first aspect of the invention, a method is
provided. The method includes directing an ion beam at a plurality
of differing incident angles with respect to a target surface of a
substrate by tilting the substrate as the ion beam is distributed
across the target surface to implant ions into a plurality of
portions of the substrate, wherein each one of the plurality of
differing incident angles is associated with a different one of the
plurality of portions, measuring angle sensitive data from each of
the plurality of portions of the substrate, and determining an
angle misalignment between the target surface and the ion beam
incident on the target surface from the angle sensitive data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a better understanding of the present disclosure,
reference is made to the accompanying drawings, in which:
[0011] FIG. 1 is a top view of a block diagram of a beam line ion
implanter;
[0012] FIG. 2 is a perspective view of the substrate of FIG. 1;
[0013] FIG. 3 is a flow chart of operations consistent with an
embodiment;
[0014] FIG. 4 is a partial schematic top view of a portion of the
beam line implanter of FIG. 1 illustrating horizontal incident
angles;
[0015] FIG. 5 is a partial schematic side view of a portion of the
beam line implanter of FIG. 1 illustrating vertical incident
angles;
[0016] FIG. 6A is a partial schematic side view of one embodiment
of a drive mechanism for tilting the substrate and FIG. 6B is a top
view of the same;
[0017] FIG. 7A is a side view of a substrate having different
tilting positions to achieve different incident angles on the
substrate;
[0018] FIG. 7B is a view of the target surface of the substrate of
FIG. 7A;
[0019] FIG. 8 is a block diagram of a beam line ion implanter;
[0020] FIG. 9A is a side view of a substrate having different
incident angles on different portions of the substrate by
controlling the trajectory of the ion beam;
[0021] FIG. 9B is a view of the target surface of the substrate of
FIG. 9A;
[0022] FIG. 10A is a plot of angle sensitive data to determine a
vertical offset tilt angle to compensate for horizontal angle
misalignment;
[0023] FIG. 10B is a plot of angle sensitive data to determine a
horizontal offset tilt angle to compensate for vertical angle
misalignment;
[0024] FIG. 11A is a perspective view of a cylindrical ingot to be
sliced to fabricate a plurality of substrates;
[0025] FIG. 11B is a cross sectional view of substrate having a
substrate miscut in the X direction of FIG. 11A, and FIG. 11C is a
cross sectional view of the same having a substrate miscut in the Y
direction of FIG. 11A;
[0026] FIG. 12A is a front view of a substrate;
[0027] FIGS. 12B and 12C are plots to illustrate how the implant
pattern of the substrate of FIG. 12A can determine both angle
misalignment and substrate miscut from one wafer; and
[0028] FIGS. 13A-13D are front views of four different substrates
rotated 90.degree. from each other in order to determine substrate
miscut angles.
DETAILED DESCRIPTION
[0029] Turning to FIG. 1, a top view of a block diagram of a beam
line ion implanter 100 is illustrated. The beam line ion implanter
100 may include an ion beam generator 102, an end station 170, a
controller 120, and a user interface system 122. The ion beam
generator 102 is configured to generate a well defined ion beam 104
and direct the ion beam toward a target surface 108 of a substrate
110 positioned in the end station 170. The ion beam 104 may be
distributed over the target surface 108 of the substrate 110 by
beam movement, substrate movement, or by any combination
thereof.
[0030] The ion beam generator 102 can include various types of
components and systems to generate the ion beam 104 having desired
characteristics. The ion beam 104 may be a spot beam or a ribbon
beam. The spot beam may have an irregular cross-sectional shape
that may be approximately circular in one instance. The spot beam
may be a fixed or stationary spot beam without a scanner.
Alternatively, the spot beam may be scanned by a scanner for
providing a scanned ion beam. The ribbon beam may have a large
width/height aspect ratio and may be at least as wide as the
substrate 110. The ion beam 104 can be any type of charged particle
beam, such as an energetic ion beam used to implant the substrate
110.
[0031] The end station 170 may support one or more substrates in
the path of the ion beam 104 such that ions of the desired species
are implanted into the substrate 110. The substrate 110 may be
supported by the platen 112 and clamped to the platen 112 by known
techniques such as electrostatic substrate clamping. The target
surface 108 of a properly cut substrate 110 in an implant position
may define a substrate plane 114. The substrate 110 can take
various physical shapes such as a common disk shape. The substrate
110 can be a semiconductor substrate fabricated from any type of
semiconductor material such as silicon or any other material that
is to be implanted using the ion beam 104.
[0032] The end station 170 may include a substrate drive system
(not illustrated) to physically move the substrate 110 to and from
the platen 112 from holding areas. The end station 170 may also
include a drive mechanism 116 to drive the platen 112 and hence the
substrate 110 clamped to the platen 112 in a desired way. The drive
mechanism 116 may include servo drive motors, screw drive
mechanisms, mechanical linkages, and any other components as are
known in the art to drive the substrate 110 when clamped to the
platen 112.
[0033] The controller 120 may receive input data and instructions
from any variety of systems and components of the beam line ion
implanter 100 and provide output signals to control the same. The
controller 120 can be or include a general-purpose computer or
network of general-purpose computers that may be programmed to
perform desired input/output functions. The controller 120 may
include a processor 130 and a machine readable medium 132. The
processor 130 may include one or more processors known in the art
such as those commercially available from Intel Corporation. The
machine readable medium 132 may include on or more machine readable
storage media such as random-access memory (RAM), dynamic RAM
(DRAM), magnetic disk (e.g., floppy disk and hard drive), optical
disk (e.g., CD-ROM), and/or any other device that can store
instructions for execution. The controller 120 can also include
other electronic circuitry or components, such as application
specific integrated circuits, other hardwired or programmable
electronic devices, discrete element circuits, etc.
[0034] The user interface system 122 may include, but not be
limited to, devices such as touch screens, keyboards, user pointing
devices, displays, printers, etc. to allow a user to input commands
and/or data and/or to monitor the beam line ion implanter 100 via
the controller 120.
[0035] FIG. 2 is a perspective view of the substrate 110 of FIG. 1
to illustrate a coordinate system defined relative to the substrate
plane 114 defined by the target surface of the substrate 110. The
origin of the coordinate system is at the center of the substrate
110 properly positioned for implantation in the substrate plane
114. The X axis is horizontal and in the substrate plane 114, the Y
axis is vertical and in the substrate plane 114, and the Z axis is
perpendicular to the substrate plane 114 in the general direction
of travel of the ion beam 104.
[0036] During implantation, the ion beam 104 strikes the substrate
at a particular incident angle of the ion beam relative to the
target surface 108 of the substrate 110. The actual incident angle
may deviate from a desired incident angle if there is an angle
misalignment between the target surface of the substrate 110 and
the ion beam 104 incident on the target surface. Therefore, it is
desirable to is determine if there is any angle misalignment during
an alignment check procedure and position the substrate 110 at a
particular offset in the home position of the substrate to
compensate for any angle misalignment.
[0037] FIG. 3 is a flow chart of operations 300 consistent with an
embodiment to determine an angle misalignment between the target
surface of the substrate and the ion beam incident on the target
surface. The operations include directing an ion beam at a
plurality of differing incident angles with respect to a target
surface of a substrate to implant ions into a plurality of portions
of the substrate, wherein each one of the plurality of differing
incident angles is associated with a different one of the plurality
of portions. The operations further include measuring angle
sensitive data from each of the plurality of portions of the
substrate 304, and determining an angle misalignment between the
target surface of the substrate and the ion beam incident on the
target surface from the angle sensitive data 306.
[0038] There are several ways to achieve differing incident angles
on different portions of the substrate. These include tilting the
substrate, deflecting the ion beam, or some combination of the two.
The incident angle could be a horizontal angle in a horizontal
plane, a vertical angle in a vertical plane, or some combination of
the two.
[0039] FIG. 4 is a top view of a portion of the beam line implanter
100 of FIG. 1 illustrating a horizontal incident angle
.theta..sub.h in a horizontal (X-Z) plane. In the example of FIG.
4, the ion beam 104 is positioned relative to the target surface
108 of the substrate 110 such that the path 306 of the ion beam
striking the target surface is at a horizontal incident angle
.theta..sub.h. The horizontal angle .theta..sub.h is the angle
measured with respect to a normal direction (Z axis) to the target
surface 108 of the substrate 110 in the horizontal (X-Z) plane.
[0040] FIG. 5 is a side view of a portion of the beam line
implanter 100 of FIG. 1 illustrating a vertical incident angle
.theta..sub.v in a vertical (Y-Z) plane. In the example of FIG. 5,
the ion beam 104 is positioned relative to the substrate 110 such
that the path 506 of the ion beam striking target surface of the
substrate 110 is at a vertical incident angle .theta..sub.v The
vertical angle .theta..sub.v is the angle measured with respect to
a normal direction (Z axis) to the target surface of the substrate
110 in the vertical (Y-Z) plane. An actual incident angle could
have both a horizontal angle component as illustrated in FIG. 4 and
a vertical angle component as illustrated in FIG. 5.
[0041] One way to achieve differing incident angles on different
portions of a single substrate includes tilting the substrate as
the ion beam is distributed across the target surface of the
substrate. Tilting of the substrate may be accomplished by the
drive mechanism 116 of FIG. 1 tilting the platen 112 and hence a
substrate secured thereto in a desired fashion.
[0042] FIG. 6A is a side view of one embodiment of a drive
mechanism 602 for tiling the substrate 110, while FIG. 6B is a top
view of the same. The drive mechanism 602 is configured to tilt the
substrate 110 about two axes 603 and 604. The drive mechanism 602
may tilt the substrate 110 up and down about a first axis 603
parallel with the X axis (FIG. 6A) and/or tilt the substrate 110
side to side about a second axis 604 parallel with the Y axis (FIG.
6B).
[0043] Tilting the substrate up and down about the first axis 603
changes the vertical incident angle and tilting the substrate side
to side about the second axis 604 changes the horizontal incident
angle. For example, assume the ion beam 606 is initially coincident
with the Z axis so that the ion beam has a normal incident angle on
the target surface of the substrate 110 in both the horizontal
(X-Z) plane and the vertical (Y-Z) plane. If the substrate 110 is
tilted up by an angle .theta..sub.x as illustrated in FIG. 6A, the
vertical incident angle of the ion beam 606 will also be at that
angle .theta..sub.x with respect to the normal incidence of the
substrate 110. The angle .theta..sub.x may also be referred to an
X-tilt angle since the substrate 110 is tilted about the first axis
603 that is parallel with X axis. Alternatively, if the substrate
110 is tilted to one side by an angle .theta..sub.y as illustrated
in FIG. 6B, the horizontal incident angle of the ion beam 606 will
also be at that angle .theta..sub.y with respect to the normal
incidence of the substrate 110. The angle .theta..sub.y may also be
referred to a Y-tilt angle since the substrate is tilted about the
second axis 604 that is parallel with the Y axis.
[0044] Turning to FIG. 7A, one example of tilting a substrate 110
to achieve different incident angles on different portions of the
substrate 110 is illustrated. In the embodiment of FIG. 7A, the
substrate 110 is mechanically driven in the Y direction as
indicated by arrow 702. As the substrate is driven in the Y
direction, it may be tilted at differing X tilt positions resulting
in differing vertical incident angles. In one embodiment, the
tilting of the substrate may be accomplished by the drive mechanism
602 tilting the substrate about the axis 603 as it is driven in the
Y direction. Although FIG. 7A illustrates tilting only in differing
X tilt positions, the substrate may also be tilted in differing Y
tilt positions as well as it is mechanically driven in the Y
direction.
[0045] FIG. 7B is a view of the target surface of the substrate 110
of FIG. 7A illustrating a plurality of differing portions 722, 724,
726, 728, 730, 732, 734, 736, 738 of the substrate where an
incident ion beam has a different incident angle on each portion.
The incident angles may be varied either incrementally or
continuously. For example, if the incident angle is varied
incrementally the substrate 110 may be driven in the Y direction a
particular distance at the same first X tilt angle to implant a
first portion 722 of the substrate. The substrate may continue to
be driven in the Y direction another distance at a different X tilt
angle to implant a second portion 724 of the substrate and so on.
The tilting of the substrate 110 may also be varied continuously in
the X or Y direction as the substrate is driven in the Y
direction.
[0046] Another way to achieve differing incident angles on
different portions of a single substrate includes deflecting the
ion beam to desired beam angles. This may be accomplished by one or
more active beam elements in the beam path of a beam line ion
implanter. The deflection of the ion beam may be achieved by
changing one or more magnetic fields, electric fields, or a
combination thereof.
[0047] FIG. 8 is a block diagram of one beam line ion implanter 800
having one or more active beam elements in the beam path to deflect
the ion beam to desired beam angles. Many other beam line ion
implanters will be known to those skilled in the art and the
embodiment of FIG. 8 is provided by way of example only and is not
intended to be limiting.
[0048] The beam line ion implanter 800 may include an ion source
820, an extraction electrode 822, a mass analyzer 824, a resolving
aperture 826, a scanner 828, and an angle corrector magnet 830. For
clarity of illustration, the controller 120 is illustrated in
isolation. Those skilled in the art will recognize that the
controller 120 may provide output signals to each component of the
beam line ion implanter 800 and receive input signals from at least
the same.
[0049] The ion source 820 may generate ions and may include an ion
chamber and a gas box. The gas may be supplied from the gas box to
the ion chamber where it is to be ionized. The ions thus formed may
be extracted from the ion source 820. The extraction electrode 822
and an extraction power supply may accelerate ions from the ion
source. The mass analyzer 824 may include a resolving magnet that
deflects ions so that ions of a desired species pass through the
resolving aperture 826 and undesired species do not pass through
the resolving aperture 826. A scanner 828 positioned downstream
from the resolving aperture 826 may include an electrostatic
scanner or a magnetic scanner for deflecting the ion beam back and
forth. The scanner 828 is not required for other ion implanters
using a ribbon beam. The angle corrector magnet 830 deflects ions
of the desired ion species to normally convert a diverging ion beam
to a nearly collimated ion beam having substantial parallel ion
trajectories.
[0050] One beam element to deflect the ion beam may be the
extraction electrode 822 as electrostatic fields may be varied to
tailor the ion beam angles. Another beam element is the scanner
828. The shape or geometry of scan plates of the scanner may be
varied to achieve different ion beam angles. Yet another beam
element to deflect the ion beam is the angle corrector magnet 830.
The magnetic field provided by the angle corrector magnet 830 may
be varied to cause the ion beam 804 to deflect from its nominal
incident angle. For example, a varying current may be supplied to
the multi-poles (not illustrated) in the corrector magnet 830 to
control the local magnetic fields that change the incident angles
of the ion beam. Similarly, the positions of one or more steel rods
(not illustrated) that shape the magnetic field inside the
corrector magnet 830 may be changed to control the ion beam angles.
The magnetic field of the corrector magnet 830 is typically tuned
to an optimum strength to provide for a nearly collimated ion beam
804 having substantially parallel ion trajectories. However, if the
corrector magnet 830 is detuned below this optimum strength,
diverging ion beam trajectories will result. On the other hand, if
the corrector magnet 830 is detuned above this optimum strength,
converging ion beam trajectories will result.
[0051] Yet another beam element to deflect the ion beam is a
parallelizing lens (not illustrated). The parallelizing lens may
take the place of the angle corrector magnet 830 in some ion
implanter embodiments and serve the same general function by
deflecting a diverging ion beam from the scanner 828 to normally a
near collimated ion beam having substantial parallel ion
trajectories. The parallelizing lens may include a set of
electrodes that are differentially biased as is known in the art to
focus the diverging ion beam with an electric field. Adjusting the
strength of the electric field can change the ion beam trajectories
similarly as adjusting the magnetic field strength for the angle
corrector magnet 830.
[0052] Yet another beam element to deflect the ion beam may be at
least one magnetic dipole element (not illustrated). A magnetic
dipole element may be located before and/or after the angle
corrector magnet 830. By perturbing at least one magnetic dipole
element, the ion beam may be deflected to desired angles. Yet
another beam element to deflect the ion beam may be a deceleration
lens 857. In one embodiment, the deceleration lens may be
positioned downstream from the angle corrector magnet 830 and
adjusting the deceleration lens 857 can adjust the spatial angle
distributions in the ion beam.
[0053] FIG. 9A is an example of ion beam 804 having diverging ion
trajectories to result in different incident angles (.theta..sub.1,
.theta..sub.2, .theta..sub.3, etc.) on different portions of the
substrate 910. This diverging ion beam 804 may be a scanned spot
ion beam, e.g., scanned by scanner 828, where the angle corrector
magnet is detuned to provide the diverging ion trajectories. The
diverging ion beam 804 may also be a ribbon beam having a large
width/height aspect ratio with a width at least as wide as the
substrate 110, where the angle corrector magnet is also detuned to
provide the diverging ion trajectories.
[0054] FIG. 9B is a front view of the target surface of the
substrate of FIG. 9A illustrating nine different regions or bands
902, 904, 906, 908, 910, 912, 914, 916, 918 each having a range of
incident angles from the diverging ion beam 804.
[0055] By either tilting the substrate, deflecting the ion beam, or
a combination of the two, a desired distribution of both horizontal
and vertical incident angles may be achieved on differing portions
of the substrate. Once a substrate is implanted with this desired
distribution of incident angles, angle sensitive data of the
substrate can be measured. One example of a desired distribution of
both effective horizontal and vertical angles is given in Table 1.
In the example of Table 1, nine different portions of the substrate
may be implanted at nine different effective Y and X-tilt angles.
An effective Y-tilt angle (.theta..sub.y of FIG. 6B) results in a
corresponding horizontal incident angle (.theta..sub.h of FIG. 4).
An effective X-tilt angle (.theta..sub.x of FIG. 6A) results in a
corresponding vertical incident angle (.theta..sub.v of FIG.
5).
TABLE-US-00001 TABLE 1 Effective Effective Substrate Portion Y-tilt
angle X-tilt angle 1 -1.0.degree..sup. 0.degree. 2
-0.5.degree..sup. 0.degree. 3 0.degree. 0.degree. 4
+0.5.degree..sup. 0.degree. 5 +1.0.degree..sup. 0.degree. 6
0.degree. -1.0.degree..sup. 7 0.degree. -0.5.degree..sup. 8
0.degree. +0.5.degree..sup. 9 0.degree. +1.0.degree..sup.
[0056] In one embodiment, the angle sensitive data is
representative of damage to the crystalline structure of the
substrate. This damage is proportional to the depth of the
implanted ions as well as the relative incident angle of the ion
beam with respect to the crystal orientation and hence the incident
angle. One way to measure such damage is with a metrology tool such
as a Therma-Probe.RTM. tool manufactured by Therma-Wave Inc. of
Fremont, Calif. Therma-Probe.RTM. is a registered trademark of
Therma-Wave Inc. of Fremont, Calif. The Therma-Probe.RTM. tool
estimates the damage to the crystal lattice through a measured
change in the refractive index of the substrate due to the implant.
Hence, the amount of damage can be correlated to the actual
incident angle to determine a misalignment between the substrate
and the incident ion beam. An offset position of one or both of the
X and Y tilt angles can then be determined to compensate for the
angle misalignment.
[0057] For example, one substrate may be implanted with a
distribution of differing effective Y and X tilt angles given in
Table 1. As illustrated in FIG. 10A, a plot 1002 damage to the
substrate versus effective Y tilt incident angles with no effective
X tilt for portions 1-5 of the substrate as detailed in Table 1 may
then be plotted. The damage units to the substrate may be
Therma-Wave infinity units obtained using the Therma-Probe.RTM.. As
illustrated in FIG. 10B, another plot 1004 of damage to the
substrate versus effective X tilt incident angles with no effective
Y tilt may also be plotted for portions 3, and 6-9 of the substrate
as detailed in Table 1. Each plot may have a general "V" shape and
may therefore be referred to in the art as a "V-curve." The
effective Y-tilt or X-tilt angle when the V-curve is at a minimum
represents the particular Y or X offset tilt angle to set the
substrate in its home position before an implant to compensate for
the angle misalignment. For example, the V-curve 1002 is at a
minimum at an effective Y tilt angle of 0.25.degree. resulting in a
vertical offset tilt angle (Y-tilt) or adjustment of the same and
the V-curve 1004 is at a minimum at an effective X-tilt angle of
0.5.degree. resulting in a horizontal offset tilt angle (X-tilt) or
adjustment of the same.
[0058] In other embodiments, the angle sensitive data may be
representative of a change in conductivity of the substrate. The
change in conductivity may be measured for each of the plurality of
portions of the substrate where a differing incident angle of the
ion beam struck the target surface of the substrate. The change in
conductivity may be determined by measuring the sheet resistance of
the substrate in each of the plurality of portions. As is known in
the art, a four point probe which inputs a test current at one
point and measures a return current at another point may be
utilized to determine sheet resistance which is usually expressed
in units of .OMEGA./square. The sheet resistance measured at each
of the plurality of portions of the substrate can be correlated to
the incident angle of the ion beam to determine a proper X-tilt and
or Y-tilt offset for positioning the substrate in its home
position.
In yet a further embodiment, the angle sensitive data may be
representative of a dopant profile of a concentration of ions
implanted in the substrate versus a depth from a target surface of
the substrate. Known techniques such as a Secondary Ion Mass
Spectrometry (SIMS) technique may be utilized to measure such
dopant profiles and may be referred to in the art as a SIMS
profile. A SIMS profile may be obtained for each of the plurality
of portions of the substrate where a differing incident angle of
the ion beam struck the target surface of the substrate. A dopant
profile with a comparatively larger concentration of dopant at a
greater depth indicates some channeling of the dopant through the
crystalline lattice of the substrate. The comparative dopant
profiles can therefore be correlated to the incident angle of the
ion beam.
[0059] In yet another embodiment, the angle sensitive data may be a
measured backscattering value when the substrate is bombarded with
test source. For example, a Rutherford Backscattering Spectroscopy
(RBS) technique may be utilized and the monitored value of
backscattering may be correlated to the incident angle at that
particular location on the substrate. The angle sensitive data may
also be obtained from other techniques such as infrared (IR)
absorption, photoreflectance, and emissivity techniques.
[0060] Turning to FIG. 11A, a plurality of substrates may be sliced
from of a source. One source may be a material that is grown into a
cylindrical ingot 1100. In one embodiment, the cylindrical ingot
1100 may be made out of pure silicon that is grown up to 300
millimeters in diameter. The cylindrical ingot 1100 is then sliced
into individual substrates 1102, 1104, 1106, 1108, etc. about 0.75
mm thick in some instances. A Cartesian coordinate system
consistent with that of FIG. 2 is also illustrated in FIG. 11A.
[0061] The cylindrical ingot 1100 should be sliced to form a
desired crystalline plane having a desired crystalline orientation.
However, the resulting target surface of the substrate may be
formed from an inadvertent cut of the cylindrical is ingot relative
to the desired crystalline plane which is referred to herein as a
"substrate miscut". FIG. 11B is a cross sectional view of a
substrate 1110 along the X axis of FIG. 11A illustrating a
horizontal substrate miscut angle .theta..sub.x of a target surface
of the substrate 1110 in the X direction. The horizontal substrate
miscut angle .theta..sub.x in the X direction is the angle between
a desired crystalline plane 1130 having a desired crystalline
structure and the actual target surface 1132 in the same X
direction. FIG. 11C is a cross sectional view of the same substrate
1110 along the Y axis of FIG. 11A illustrating a vertical substrate
miscut angle .theta..sub.y of a target surface of the substrate
1110 in the Y direction. The vertical substrate miscut angle
.theta..sub.y in the Y direction is the angle between a desired
crystalline plane 1130 having a desired crystalline structure and
the actual target surface 1132 in the same Y direction. Some
substrates may have no substrate miscut angle, only one substrate
miscut angle in one of the X and Y direction, or both substrate
miscut angles in both X and Y directions which may be similar or
different from each other.
[0062] Turning to FIGS. 12A-12C, a front view of a substrate 1200
and resulting plots are shown to illustrate how both angle
misalignment and substrate miscut can be determined from a single
substrate 1200. The substrate 1200 may be disk shaped. A first
quadrant (I) of the substrate 1200 may first be implanted with ions
from an ion beam at a plurality of different incident angles. In
one instance, the different angles may be effective Y tilt angles
as achieved by the drive mechanism 602 illustrated in FIG. 6B. For
example, the portion 1202 may correspond to an effective Y tilt
angle of -1.0.degree., portion 1204 to -0.5.degree., portion 1206
to 0.0.degree., portion 1208 to +0.5.degree., and portion 1210 to
+1.0.degree.. Differing Y-tilt angles (e.g., .theta..sub.y of FIG.
6B) result in corresponding horizontal incident angles (e.g.,
.theta..sub.h of FIG. 4). In order to restrict the implant of ions
to the first quadrant (I), a shield having an aperture consistent
with the quadrant may is be utilized upstream of the substrate. The
shield or mask may block the ion beam from portions of the
substrate while the aperture permits the ion beam to pass.
Alternatively, a scan distance of a scanner, e.g., scanner 828 of
FIG. 8, as well as a mechanical drive system for driving the
substrate may be controlled to only implant ions in the first
quadrant (I).
[0063] Once the implant of ions in the first quadrant is
accomplished, the substrate 1200 may be rotated 180.degree. from
its first position so that the second quadrant (II) is now
similarly positioned for implant. The ion beam at a similar
plurality of incident angles may be implanted into similar portions
of the second quadrant (II). For example, the five portions 1212,
1214, 1216, 1218, 1220 may be implanted at the same effective Y
tilt angles of -1.0.degree., -0.5.degree., 0.0.degree.,
+0.5.degree., and +1.0.degree. as were portions 1202, 1204, 1206,
1208, 1210 of the first quadrant (I).
[0064] The substrate 1200 may then be rotated 90.degree. clockwise
from its previous position so that the third quadrant (III) is now
similarly positioned for implant. The ion beam may be directed at a
plurality of different X-tilt angles. For example, five different
portions of the third quadrant (III) may be implanted with five
different X-tilt angles of -1.0.degree., -0.5.degree., 0.0.degree.,
+0.5.degree., and +1.0.degree.. Differing X-tilt angles (e.g.,
.theta..sub.x of FIG. 6A) result in corresponding vertical incident
angles (e.g., .theta..sub.v of FIG. 5).
[0065] The substrate 1200 may then be rotated 180.degree. from its
previous position so that the fourth quadrant (IV) is now similarly
positioned for implant. The ion beam at a similar plurality of
X-tilt incident angles as the third quadrant (III) may then be
implanted into similar portions of the fourth quadrant (IV).
[0066] FIG. 12B illustrates results of measuring angle sensitive
data from different portions of the substrate 1200 to determine a
substrate miscut angle and also to determine any angle
misalignment. The results of FIG. 12B illustrate no angle
misalignment, but a substrate miscut. In contrast, the results of
FIG. 12C illustrate both an angle misalignment and a substrate
miscut. The two plots 1250 and 1252 of FIG. 12B plot damage to the
substrate 1200 versus effective Y tilt angles in degrees to
illustrate a vertical substrate miscut angle .theta..sub.y in the Y
direction. The damage units may by Therma-Wave infinity units
obtained using a Therma-Probe.RTM.. The plot 1250 corresponds to
the measured damage to portions 1202, 1204, 1206, 1208, 1210 of the
first quadrant (I) while plot 1252 corresponds to the measured
damage to similar portions 1212, 1214, 1216, 1218, 1220 of the
third quadrant (III). Since both plots 1250, 1252 are symmetrical
about 0.0.degree., there is no angle misalignment. The plots 1250,
1252 do reveal a vertical substrate miscut angle .theta..sub.y in
the Y direction of about 0.25.degree. as illustrated by line
1270.
[0067] FIG. 12C, in contrast to FIG. 12B, illustrates both angle
misalignment and a vertical substrate miscut angle .theta..sub.y.
The angle misalignment is about of about 0.5.degree. as illustrated
by line 1276. The vertical substrate miscut angle .theta..sub.y is
about 0.25.degree. as illustrated by line 1278. Similarly to that
illustrated in FIG. 12B and 12C, the measurements of angle
sensitive data for the third (III) and fourth (IV) quadrants can be
used to determine any angle misalignment and a horizontal substrate
miscut angle .theta..sub.x. Once the substrate miscut angles
.theta..sub.x, .theta..sub.y and/or angle misalignments are
determined, offset angles can be set to compensate for the same.
For instance, the drive mechanism 602 of FIGS. 6A and 6B may set
the substrate to a particular X and Y offset tilt angle home
position to compensate.
[0068] In another embodiment, substrate miscut may be ascertained
using a plurality of substrates. For instance, turning to FIGS.
13A-13D, front views of four substrates 1102, 1104, 1106, 1108 cut
from the same cylindrical ingot 1100 and having identical surface
orientations may be utilized to determine a substrate miscut angle
.theta..sub.x in the X direction and a substrate miscut angle
.theta..sub.y in the Y direction. A plurality of portions of the
first substrate 1102 may be implanted at different incident angles
associated with each of the plurality of portions consistent with
earlier described embodiments. The incident angles may be achieved
by tilting the substrate, deflecting the ion beam, or some
combination of the two. The second, third, and fourth substrates
1104, 1106, 1108 may also be similarly implanted except that each
substrate 1104, 1106, 1108 is rotated about the Z axis with respect
to the implant position of the first substrate 1102.
[0069] The second substrate 1104 is implanted at a rotation
position 90.degree. from the implant position of the first
substrate 1102. The third substrate 1106 is implanted at a rotation
position 180.degree. from the implant position of the first
substrate 1102, and finally the fourth substrate 1108 is implanted
at a rotation position 270.degree. from the implant position of the
first substrate 1102. Phantom line are illustrated in FIGS. 13A-D
from the center of each substrate to a notch in each substrate for
clarity of illustration to show the different rotation positions of
the substrates relative to one another during implant.
[0070] The difference between the measured angle sensitive data for
the first substrate 1102 and the third substrate 1106 rotated
180.degree. relative to the first substrate 1102 gives the
substrate miscut angle .theta..sub.x in the X direction. Meanwhile,
the difference between the measured angle sensitive data for the
second substrate 1104 rotated 90.degree. from the first substrate
1102 and the fourth substrate rotated 270.degree. from the first
substrate 1102 gives the substrate miscut angle .theta..sub.y in
the Y direction. Once the substrate miscut angles .theta..sub.x,
.theta..sub.y are determined, offset angles for each can be set to
compensate for the miscut angles. For instance, the drive mechanism
602 of FIGS. 6A and 6B may set the substrate to a particular X and
Y offset tilt angles to properly compensate for the miscut
angles.
[0071] Accordingly, there is provided a method of determining an
angle misalignment between a target surface of a substrate and an
incident ion beam using one substrate. Hence, additional costs for
additional substrates used in a is conventional method are saved.
Since the same substrate is used, a consistent crystalline
structure of the substrate is ensured which leads to consistency
when measuring angle sensitive data from that substrate.
Furthermore, the method is fast compared to a conventional method
utilizing a plurality of substrates since only one substrate needs
to be measured for angle sensitive data and only one substrate
needs to be implanted. For example, a conventional method using
nine substrates may take about 45 minutes to measure angle
sensitive data from the nine different substrates compared to only
about 5 minutes for a method consistent with the present
invention.
[0072] There is also provided a method of determining a substrate
miscut angle of a substrate. This allows precise control of
incident angles. This information can also improve ion implant
performance from batch to batch. This information can also be
useful in transferring processes between different manufacturing
facilities or recipes suited for substrates for different end users
in a substrate foundry where several batches of substrates with
different crystal orientations may need to be processed for
different end users. In one embodiment, both angle misalignment and
substrate miscut may be determined from the same substrate.
[0073] The terms and expressions which have been employed herein
are used as terms of description and not of limitation, and there
is no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described (or
portions thereof), and it is recognized that various modifications
are possible within the scope of the claims. Other modifications,
variations, and alternatives are also possible. Accordingly, the
foregoing description is by way of example only and is not intended
as limiting.
* * * * *