U.S. patent application number 14/694115 was filed with the patent office on 2016-02-04 for conductive atomic force microscope and method of operating the same.
The applicant listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Chung-sam JUN, Hyun-woo KIM, Jeong-hoi KIM, Young-hwan KIM, Woo-seok KO, Sang-kil LEE, Chae-ho SHIN, Hyung-su SON, Baek-man SUNG, Jae-youn WI, Yu-sin YANG.
Application Number | 20160033550 14/694115 |
Document ID | / |
Family ID | 55179780 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160033550 |
Kind Code |
A1 |
KIM; Hyun-woo ; et
al. |
February 4, 2016 |
CONDUCTIVE ATOMIC FORCE MICROSCOPE AND METHOD OF OPERATING THE
SAME
Abstract
A conductive atomic force microscope including a plurality of
probe structures each including a probe and a cantilever connected
thereto, a power supplier applying a bias voltage, a current
detector detecting a first current flowing between a sample object
and each of the probes and a second current flowing between a
measurement object and each of the probes, and calculating
representative currents for the sample and measurement objects
based on the first and second currents, respectively, and a
controller calculating a ratio between representative currents of
the sample object measured by each of the probe structures,
calculating a scaling factor for scaling the representative current
with respect to the measurement object measured by each of the
probes, and determine a reproducible current measurement value
based on the second measurement current and the scaling factor may
be provided.
Inventors: |
KIM; Hyun-woo; (Chungju-si,
KR) ; KO; Woo-seok; (Seoul, KR) ; KIM;
Young-hwan; (Seoul, KR) ; KIM; Jeong-hoi;
(Suwon-si, KR) ; SUNG; Baek-man; (Seoul, KR)
; SON; Hyung-su; (Hwaseong-si, KR) ; SHIN;
Chae-ho; (Hwaseong-si, KR) ; YANG; Yu-sin;
(Seoul, KR) ; WI; Jae-youn; (Suwon-si, KR)
; LEE; Sang-kil; (Yongin-si, KR) ; JUN;
Chung-sam; (Suwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Suwon-si |
|
KR |
|
|
Family ID: |
55179780 |
Appl. No.: |
14/694115 |
Filed: |
April 23, 2015 |
Current U.S.
Class: |
850/41 |
Current CPC
Class: |
G01Q 70/06 20130101;
G01Q 60/40 20130101 |
International
Class: |
G01Q 60/40 20060101
G01Q060/40 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2014 |
KR |
10-2014-0098636 |
Claims
1. A conductive atomic force microscope comprising: a plurality of
probe structures, each of which including a probe and a cantilever
connected thereto; a power supply unit configured to apply a bias
voltage to each of a sample object and a measurement object; a
current detecting unit configured to detect a first current flowing
between the sample object and each of the plurality of probe
structures, detect a second current flowing between the measurement
object and each of the plurality of probe structures, and calculate
representative currents with respect to the sample object and the
measurement object based on the first and second currents,
respectively; and a control unit configured to calculate a ratio
between representative currents of the sample object measured by
each of the plurality of probe structures, calculate a scaling
factor for scaling the representative current with respect to the
measurement object measured by each of the plurality of probe
structures, and determine a reproducible current measurement value
based on the second current and the scaling factor.
2. The conductive atomic force microscope of claim 1, wherein when
a resistance of the sample object is equal to a resistance of the
measurement object, the control unit is configured to calculate the
scaling factor as the ratio between the representative currents of
the sample object.
3. The conductive atomic force microscope of claim 1, further
comprising: a scanning unit configured to raster-scan at least one
of the sample object and the measurement object on a pixel-by-pixel
basis.
4. The conductive atomic force microscope of claim 3, wherein the
scanning unit comprises an actuator configured to move, on a
pixel-by-pixel basis, the probe in a first direction and a second
direction perpendicular to the first direction.
5. The conductive atomic force microscope of claim 2, wherein the
current detecting unit is configured to calculate the
representative current by (1) adding up currents measured by the
probe on a pixel-by-pixel basis and (2) dividing the resulting sum
by a number of pixels.
6. The conductive atomic force microscope of claim 1, further
comprising: a display unit configured to display the representative
current of any one of the sample object and the measurement
object.
7. The conductive atomic force microscope of claim 1, wherein the
current detecting unit comprises a current monitoring unit
configured to check whether representative currents measured at the
measurement object are uniform.
8. The conductive atomic force microscope of claim 1, wherein the
control unit comprises a memory unit configured to store the
representative current of each of the sample object and the
measurement object measured by each of the plurality of probe
structures.
9. A method of operating a conductive atomic force microscope, the
method comprising: selecting a first probe as a measurement probe;
applying a bias voltage to a sample object and measuring a first
current image using the first probe; calculating a first
representative current based on the first current image using a
current detecting unit; applying a bias voltage to a measurement
object and measuring a first measured current using the first
probe; selecting a second probe as a measurement probe; applying a
bias voltage to the sample object and measuring a second current
image using the second probe; calculating a second representative
current based on the second current image of the sample object
using the current detecting unit; applying a bias voltage to the
measurement object and measuring a second measured current using
the second probe; calculating a scaling factor by feeding back the
first representative current and the applied first and second bias
voltages and dividing the second representative current by the
first representative current; and determining a reproducible
current measurement value based on the first and second measured
currents and the scaling factor.
10. The method of claim 9, further comprising: measuring the
conductance and resistance of the measurement object based on the
scaling factor.
11. The method of claim 9, wherein the calculating a scaling factor
is performed for a range, in which the current measured by each of
the first probe and the second probe is linear with respect to the
bias voltages.
12. The method of claim 9, further comprising: calculating a
resistance of the sample object by dividing the bias voltage
applied to the sample object by the second representative current;
and calculating a resistance of the measurement object by dividing
the bias voltage applied to the measurement object by the second
measured current, wherein when the resistance of the sample object
is different from a resistance of the measurement object, the
calculating a scaling factor is performed by adding a value, which
is obtained by dividing the bias voltage applied to the sample
object by the first representative current, to a difference between
the resistance of the measurement object and the resistance of the
sample object, and dividing the resulting sum by a value obtained
by adding a value, which is obtained by dividing the bias voltage
applied to the sample object by the second representative current,
to the difference between the resistance of the measurement object
and the resistance of the sample object.
13. The method of claim 9, further comprising: displaying the first
measured current and the second measured current on a display
unit.
14. The method of claim 9, wherein the calculating the first
current image and the calculating the second current image are
performed by scanning the sample object on a pixel-by-pixel basis
using the first probe and the second probe, respectively.
15. The method of claim 12, wherein the calculating each of the
first representative current and the second representative current
is performed by adding up current image values measured by scanning
the sample object on a pixel-by-pixel basis and dividing the
resulting sum by a number of pixels.
16. A conductive atomic force microscope comprising: a power supply
configured to apply a first bias voltage to a sample object and a
second bias voltage to a measurement object; a plurality of probe
structures configured to measure a first sample current flowing
through the sample object and one of the plurality of probe
structures, measure a second sample current flowing through the
sample object and another of the plurality of probe structure,
measure a first measurement current flowing between a measurement
object and one of the plurality of probe structures, and measure a
second measurement current flowing between a measurement object and
another of the plurality of probe structures; a current detector
configured to calculate a first representative current and a second
representative current based on the first sample current and the
second sample current, respectively; and a controller configured to
calculate a scaling factor for the second measured current, and
determine a reproducible current measurement value based on the
second measurement current and the scaling factor.
17. The conductive atomic force microscope of claim 16, wherein
when a resistance of the sample object is equal to a resistance of
the measurement object, the controller is configured to calculate
the scaling factor for the second measurement current as a ratio
between the first and second representative currents of the sample
object.
18. The conductive atomic force microscope of claim 16, wherein
when a resistance of the sample object and a resistance of the
measurement object are different from each other, the controller is
configured to calculate the scaling factor for the second
measurement current based on the first and second bias voltages,
the first representative current, the second representative
current, and the second measured current.
19. The conductive atomic force microscope of claim 16, wherein the
current detector is further configured to track a change trend of
the first and second representative currents according to states of
the plurality of probes by checking whether the first and second
representative currents are uniform.
20. The conductive atomic force microscope of claim 16, further
comprising: a scanner configured to raster-scan the sample object
and the measurement object on a pixel-by-pixel basis, wherein the
current detector is configured to calculate the first
representative current and the second representative current by (1)
adding up currents measured on the pixel-by-pixel basis by one of
the plurality of probes and (2) dividing the resulting sum by a
number of pixels.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn.119
to Korean Patent Application No. 10-2014-0098636, filed on Jul. 31,
2014, in the Korean Intellectual Property Office, the disclosure of
which is incorporated herein in its entirety by reference.
BACKGROUND
[0002] The inventive concepts relate to a conductive atomic force
microscopes and methods of operating the same, and more
particularly, to systems for scaling measured currents of an object
measured by different probes of a conductive atomic force
microscope including probes and/or methods of operating the
same.
[0003] A conductive atomic force microscope (c-AFM) is a microscope
that is configured to measure conductance and resistance of an
object (hereinafter, referred to as measurement object) at a
spatial resolution of tens of nanometers by applying a bias voltage
to the measurement object and measuring a current flowing between a
probe and the measurement object. In order to measure a current by
using a conductive atomic force microscope, a probe coated with a
conductive material may contact with the measurement object to form
a current path therebetween. The resistance and conductance
distribution of the measurement object may be measured by measuring
a current flowing through the probe at each position by moving the
measurement object and/or the probe.
[0004] In the conductive atomic force microscope using the probe,
the contact resistance between the probe and the measurement object
may affect the measurement result. To ensure the reliable and
reproducible measurements, uniform maintenance of the contact
resistance between the probe and the measurement object is
desired.
SUMMARY
[0005] Some of the inventive concepts provide conductive atomic
force microscopes and methods of operating the same, which monitors
a current of a measurement object using a probe and, when different
currents are measured by probes, scales the different currents.
[0006] According to an example embodiment, a conductive atomic
force microscope includes a plurality of probe structures, each of
which including a probe and a cantilever connected thereto, a power
supply unit configured to apply a bias voltage to each of a sample
object and a measurement object, a current detecting unit
configured to detect a first current flowing between the sample
object and each of the plurality of probe structures, detect a
second current flowing between the measurement object and each of
the plurality of probe structures, and calculate representative
currents with respect to the sample object and the measurement
object based on the first and second currents, respectively, and a
control unit configured to calculate a ratio between representative
currents of the sample object measured by each of the plurality of
probe structures, calculate a scaling factor for scaling a
representative current of the measurement object measured by each
of the plurality of probe structures, and determine a reproducible
current measurement value based on the second current and the
scaling factor.
[0007] According to some example embodiments, when a resistance of
the sample object is equal to a resistance of the measurement
object, the control unit may be configured to calculate the scaling
factor as the ratio between the representative currents of the
sample object.
[0008] According to some example embodiments, the conductive atomic
force microscope may further include a scanning unit configured to
raster-scan at least one of the sample object and the measurement
object on a pixel-by-pixel basis.
[0009] According to some example embodiments, the scanning unit may
include an actuator configured to move, on a pixel-by-pixel basis,
the probe in a first direction and a second direction perpendicular
to the first direction.
[0010] According to some example embodiments, the current detecting
unit may be configured to calculate the representative current by
(1) adding up currents measured by the probe on a pixel-by-pixel
basis and (2) dividing the resulting sum by a number of pixels.
[0011] According to some example embodiments, the conductive atomic
force microscope may further include a display unit configured to
display the representative current of any one of the sample object
and the measurement object.
[0012] According to some example embodiments, the current detecting
unit may include a current monitoring unit configured to check
whether representative currents measured at the measurement object
are uniform.
[0013] According to some example embodiments, the control unit may
include a memory unit configured to store the representative
current of each of the sample object and the measurement object
measured by each of the plurality of probe structures.
[0014] According to an example embodiment, a method of operating a
conductive atomic force microscope includes selecting a first probe
as a measurement probe, applying a bias voltage to a sample object
and measuring a first current image using the first probe,
calculating a first representative current based on the first
current image using a current detecting unit, applying a bias
voltage to a measurement object and measuring a first measured
current using the first probe, selecting a second probe as a
measurement probe, applying a bias voltage to the sample object and
measuring a second current image using the second probe,
calculating a second representative current based on the second
current image of the sample object using the current detecting
unit, applying a bias voltage to the measurement object and
measuring a second measured current using the second probe,
calculating a scaling factor by feeding back the first
representative current and the applied first and second bias
voltages and dividing the second representative current by the
first representative current, and determining a reproducible
current measurement value based on the first and second measured
currents and the scaling factor.
[0015] According to some example embodiments, the method may
further include measuring the conductance and resistance of the
measurement object based on the scaling factor.
[0016] According to some example embodiments, the calculating a
scaling factor may be performed for a range, in which the current
measured by each of the first probe and the second probe is linear
with respect to the bias voltages.
[0017] According to some example embodiments, the method may
further include calculating a resistance of the sample object by
dividing the bias voltage applied to the sample object by the
second representative current, and calculating a resistance of the
measurement object by dividing the bias voltage applied to the
measurement object by the second measured current, wherein when the
resistance of the sample object is different from a resistance of
the measurement object, the calculating a scaling factor is
performed by adding a value, which is obtained by dividing the bias
voltage applied to the sample object by the first representative
current, to a difference between the resistance of the measurement
object and the resistance of the sample object, and dividing the
resulting sum by a value obtained by adding a value, which is
obtained by dividing the bias voltage applied to the sample object
by the second representative current, to the difference between the
resistance of the measurement object and the resistance of the
sample object.
[0018] According to some example embodiments, the method of claim
may further include displaying the first measured current and the
second measured current on a display unit.
[0019] According to some example embodiments, the calculating the
first current image and the second current image may be performed
by scanning the sample object on a pixel-by-pixel basis using the
first probe and the second probe.
[0020] According to some example embodiments, the calculating each
of the first representative current and the second representative
current may be performed by adding up current image values measured
by scanning the sample object on a pixel-by-pixel basis and
dividing the resulting sum by a number of pixels.
[0021] According to an example embodiment, a conductive atomic
force microscope includes a power supply configured to apply a
first bias voltage to a sample object and a second bias voltage to
a measurement object, a plurality of probe structures configured to
measure a first sample current flowing through the sample object
and one of the plurality of probe structures, measure a second
sample current flowing through the sample object and another of the
plurality of probe structure, measure a first measurement current
flowing between a measurement object and one of the plurality of
probe structures, and measure a second measurement current flowing
between a measurement object and another of the plurality of probe
structures, a current detector configured to calculate a first
representative current and a second representative current based on
the first sample current and the second sample current,
respectively, and a controller configured to calculate a scaling
factor for the second measured current, and determine a
reproducible current measurement value based on the second
measurement current and the scaling factor.
[0022] According to some example embodiments, when a resistance of
the sample object is equal to a resistance of the measurement
object, the controller may be configured to calculate the scaling
factor for the second measurement current as a ratio between the
first and second representative currents of the sample object.
[0023] According to some example embodiments, when a resistance of
the sample object and a resistance of the measurement object are
different from each other, the controller may be configured to
calculate the scaling factor for the second measurement current
based on the first and second bias voltages, the first
representative current, the second representative current, and the
second measured current.
[0024] According to some example embodiments, the current detector
may be further configured to track a change trend of the first and
second representative currents according to states of the plurality
of probes by checking whether the first and second representative
currents are uniform.
[0025] According to some example embodiments, the conductive atomic
force microscope may further include a scanner configured to
raster-scan the sample object and the measurement object on a
pixel-by-pixel basis, wherein the current detector is configured to
calculate the first representative current and the second
representative current by (1) adding up currents measured on the
pixel-by-pixel basis by one of the plurality of probes and (2)
dividing the resulting sum by a number of pixels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Example embodiments of the inventive concepts will be more
clearly understood from the following detailed description taken in
conjunction with the accompanying drawings in which:
[0027] FIG. 1 is a schematic diagram of a conductive atomic force
microscope according to an example embodiment of the inventive
concepts;
[0028] FIG. 2 is a block diagram illustrating a configuration of a
conductive atomic force microscope according to an example
embodiment of the inventive concepts;
[0029] FIG. 3 is a flowchart of an operation algorithm of a
conductive atomic force microscope according to an example
embodiment of the inventive concepts;
[0030] FIG. 4 is a graph illustrating a bias voltage applied by a
power supply unit of a conductive atomic force microscope according
to an example embodiment of the inventive concepts and currents
flowing between an object and probes;
[0031] FIG. 5 is a schematic diagram illustrating a probe structure
and a power supply unit of a conductive atomic force microscope
according to an example embodiment of the inventive concepts;
[0032] FIG. 6 is a flowchart of an operation algorithm of a
conductive atomic force microscope according to an example
embodiment of the inventive concepts;
[0033] FIG. 7 is a graph illustrating contact resistances depending
on the structures and states of probes of a conductive atomic force
microscope according to an example embodiment of the inventive
concepts; and
[0034] FIG. 8 is a graph illustrating measured currents of an
object depending on the types of probes of a conductive atomic
force microscope according to an example embodiment of the
inventive concepts.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0035] As used herein, expressions such as "at least one of," when
preceding a list of elements, modify the entire list of elements
and do not modify the individual elements of the list.
[0036] Hereinafter, various example embodiments of the inventive
concepts will be described in detail with reference to the
accompanying drawings. However, the inventive concepts may be
embodied in many different forms and should not be construed as
being limited to the example embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
inventive concepts to those of ordinary skill in the art. In the
accompanying drawings, the sizes of elements or components may be
exaggerated for clarity and convenience of description.
[0037] It will be understood that when an element is referred to as
being "on" another element, it may be directly on the other element
or intervening elements may be present. In contrast, when an
element is referred to as being "directly on" another element,
there are no intervening elements present. Other terms, such as
"between", describing a relation between elements may also be
interpreted in the same way.
[0038] Although terms such as "first" and "second" may be used
herein to describe various elements or components, these elements
or components should not be limited by these terms. These terms are
only used to distinguish one element or component from another
element or component. For example, a first element may be termed a
second element, and, similarly, a second element may be termed a
first element, without departing from the scope of the inventive
concepts.
[0039] As used herein, the singular forms "a", "an", and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. It will be understood that terms such
as "comprise", "include", and "have", when used herein, specify the
presence of stated features, integers, steps, operations, elements,
components, or combinations thereof, but do not preclude the
presence or addition of one or more other features, integers,
steps, operations, elements, components, or combinations
thereof.
[0040] It will be understood that when an element or layer is
referred to as being "on," "connected to" or "coupled to" another
element or layer, it can be directly on, connected or coupled to
the other element or layer or intervening elements or layers may be
present. In contrast, when an element is referred to as being
"directly on," "directly connected to" or "directly coupled to"
another element or layer, there are no intervening elements or
layers present. As used herein, the term "and/or" includes any and
all combinations of one or more of the associated listed items.
Expressions such as "at least one of," when preceding a list of
elements, modify the entire list of elements and do not modify the
individual elements of the list.
[0041] Spatially relative terms, such as "beneath," "below,"
"lower," "above," "upper" and the like, may be used herein for ease
of description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, the
example term "below" can encompass both an orientation of above and
below. The device may be otherwise oriented (rotated 90 degrees or
at other orientations) and the spatially relative descriptors used
herein interpreted accordingly.
[0042] Unless otherwise defined, all terms used herein may have the
same meaning as commonly understood by those of ordinary skill in
the art.
[0043] Hereinafter, example embodiments of the inventive concepts
will be described in detail with reference to the accompanying
drawings.
[0044] FIG. 1 is a schematic diagram illustrating components of a
conductive atomic force microscope 1000 according to an example
embodiment of the inventive concepts.
[0045] Referring to FIG. 1, the conductive atomic force microscope
1000 may include a probe structure 100, a scanning unit 200, a
current detecting unit 300, a control unit 400, and a display unit
500. The conductive atomic force microscope 1000 may further
include a power supply unit.
[0046] The probe structure 100 may include a probe 110 and a
cantilever 120. The probe 110 may be formed of a conductive
material. The probe 110 may be a conductive probe, a surface of
which is coated with a conductive material. In an example
embodiment, the probe 110 may be formed of one selected from the
group consisting of platinum (Pt), iridium (Ir), aurum (Au),
ruthenium (Ru), argentum (Ag), and any alloy thereof. The probe 110
may have a size of about 100 nm or less. The cantilever 120 may be
connected to the scanning unit 200 and may be vibrated at a
predetermined frequency by an oscillator. When the cantilever 120
vibrates, the probe 110 may approach the surface of an object S and
thus vibration amplitude or phase change may occur due to an atomic
force between the two. The probe 110 may contact the surface of the
object S to measure a current flowing between the object S and the
probe 110. A vibration amplitude or phase change of the cantilever
120 may be measured and controlled by a position detecting unit
using, for example, laser beams. Thus, the probe 110 may also
measure a surface image of the object S. A bias voltage applied to
the object S and detection of a current flowing between the probe
110 and the object S will be described later in detail with
reference to FIG. 5.
[0047] The scanning unit 200 may move the cantilever 120 in a first
direction X and a second direction Y that is perpendicular to the
first direction X, according to a position signal for controlling
the distance between the probe 110 and the surface of the object S
mounted on a test board 230. When the cantilever 120 moves in the
first direction X and the second direction Y, the probe 110 may
move on the surface of the object S on a pixel-by-pixel basis and
contact the surface of the object S to cause a current to flow. The
scanning unit 200 may measure a current image by scanning a current
flowing between the surface of the object S and the probe 110 on a
pixel-by-pixel basis. The scanning unit 200 may raster-scan the
surface of the object S on a pixel-by-pixel basis.
[0048] The current detecting unit 300 may measure a current flowing
between the probe 110 and the surface of the object S. The current
detecting unit 300 may calculate a representative current by
measuring a current that is generated between the surface of the
object S and the probe 110 by a bias voltage applied from the power
supply unit to the object S. The current detecting unit 300 may
perform an algorithm for adding up pixel-by-pixel current image
values measured by the scanning unit 200 and dividing the resulting
sum by the total number of pixels of the object S. The current
flowing between the probe and the surface of the object S may be
measured several times. Based on the measurement results, the
current detecting unit 300 may calculate a representative current
several times. The current detecting unit 300 may determine whether
the calculated representative currents are uniform. The current
detecting unit 300 may track a change trend of the representative
current according to the states of the probe 110, for example,
abrasion of the probe 110 and impurities deposited on the surface
of the probe 110. The current detecting unit 300 will be described
later in detail with reference to FIGS. 6 to 8.
[0049] The control unit 400 may include, for example, measurement
equipment or an independent workstation. The control unit 400 may
perform an algorithm for storing the representative current
calculated by the current detecting unit 300 in a memory unit and
scaling currents measured by different probe structures, based on,
for example, the representative current of a sample object, the
current of a measurement object, and the bias voltage. The control
unit 400 may transmit information about the representative current
of the sample object, the current of the measurement object, and
the bias voltage to the display unit 500 in order to display the
information on the display unit 500.
[0050] The control unit 400 may include a memory unit 410 (see FIG.
2). The memory unit 410 is a medium that store data from
measurement equipment or a computer. The memory unit 410 may
include, for example, any one of a computer random-access memory
(RAM), a hard disk, a network storage device, a flash drive, and a
compact disk read-only memory (CD-ROM), but is not limited thereto.
The control unit 400 may include a semiconductor chip that may
perform a logical operation such as scaling of the representative
current of the measurement object. For example, the control unit
400 may include at least one of a central processing unit (CPU), a
controller, an application specific integrated circuit (ASIC), and
an application processor (AP).
[0051] The display unit 500 may be connected to the current
detecting unit 300 and/or the control unit 400 to display pieces of
information that are received from the current detecting unit 300
and/or the control unit 400. The display unit 500 may include a
general display device. The display unit 500 may display
information about, for example, the representative current of the
sample object, the current of the measurement object, and the bias
voltage. The information displayed on the display unit 500 may be
displayed such that values measured by different probes are
classified according to the respective probes. In an example
embodiment, the display unit 500 may be integrated with the control
unit 400.
[0052] FIG. 2 is a block diagram illustrating components of a
conductive atomic force microscope 1000 according to an example
embodiment of the inventive concepts.
[0053] Referring to FIG. 2, the conductive atomic force microscope
1000 may include a first probe structure 100-1, a second probe
structure 100-2, a scanning unit 200, a current detecting unit 300,
a control unit 400, a display unit 500, and a power supply unit
600.
[0054] The first probe structure 100-1 and the second probe
structure 100-2 may be selectively connected to the scanning unit
200. The first probe structure 100-1 may include a first probe
110-1 that contacts an object S to measure a current flowing
between the surface of the object S and the first probe structure
100-1, and a first cantilever 120-1 that is connected to the first
probe 110-1. Like the first probe structure 100-1, the second probe
structure 100-2 may include a second probe 110-2 and a second
cantilever 120-2. The first probe structure 100-1 and the second
probe structure 100-2 may contact the surface of the object S and
measure a current flowing on the surface of the object S. For
example, when the power supply unit 600 applies a bias voltage V to
the object S, a current may flow between the surface of the object
S and the first probe structure 100-1. Likewise, the second probe
structure 100-2 may measure a current flowing between the surface
of the object S and the second probe structure 100-2. The first
probe 110-1 and the second probe 110-2 may have different
resistances. Thus, the current flowing between the first probe
110-1 and the surface of the object S and the current flowing
between the second probe 110-2 and the surface of the object S may
be different.
[0055] The scanning unit 200 may include a scanner 210 and an
actuator 220. The actuator 220 may move the first or second
cantilever 120-1 or 120-2 in a first direction X and a second
direction Y, which is perpendicular to the first direction X,
according to position signals for controlling distances between the
surface of the object S and the first or second probe 110-1 or
110-2, respectively. The scanner 210 may raster-scan a current
flowing between the surface of the object S and the probe
110-1/110-2 on a pixel-by-pixel basis.
[0056] The current detecting unit 300 may include a current
measuring unit 310 and a current monitoring unit 320. The current
measuring unit 310 may calculate a representative current by using
currents of the object S measured by the scanner 210. In an example
embodiment, the current measuring unit 310 may calculate a
representative current by performing an algorithm for adding up
currents, which are measured by scanning the surface of the object
S on a pixel-by-pixel basis, and dividing the resulting sum by the
number of pixels of the object S. The current flowing between the
first probe 110-1 and the surface of the object S and the current
flowing between the second probe 110-2 and the surface of the
object S may be measured several times. Based on the measurement
results, the current measuring unit 320 may calculate the
representative current several times. The current monitoring unit
320 may determine whether the measured representative currents are
uniform. The current monitoring unit 320 may check a change trend
of the representative current to determine whether the selected
probe 110-1/110-2 is defective or whether the contact resistance of
the selected probe 110-1/110-2 changes. The current detecting unit
300 will be described later in detail with reference to FIG. 5.
[0057] The control unit 400 may include the memory unit 410 and a
scaling control unit 420. The memory unit 410 may be connected to
the current detecting unit 300 to store a first representative
current that is calculated by measuring a current image of the
object S by the first probe structure 100-1 and a second
representative current that is calculated by measuring a current
image of the object S by the second probe structure 100-2. The
scaling control unit 420 may calculate a scaling factor as the
ratio between the first representative current and the second
representative current. In an example embodiment, the scaling
control unit 420 may also calculate a scaling factor as the
relative ratio between a bias voltage applied from the power supply
unit 600 to the object S and the first representative current and
the bias voltage and the second representative current. An
algorithm for calculating the scaling factor will be described
later in detail with reference to FIG. 3.
[0058] The display unit 500 may be connected to the control unit
400 to display the first representative current that is calculated
by measuring the object S by the first probe structure 100-1 and
the second representative current that is calculated by measuring
the object S by the second probe structure 100-2. The display unit
500 may display a change trend of any one of the first
representative current and the second representative current.
[0059] The power supply unit 600 may apply the bias voltage V to
the object S. Thus, a current may flow between the surface of the
object S and the probe 110-1/110-2, and the probe structure
100-1/100-2 may measure the current.
[0060] FIG. 3 is a flowchart of an operation algorithm of a
conductive atomic force microscope 1000 according to an example
embodiment of the inventive concepts.
[0061] Referring to FIG. 3, a method of operating the conductive
atomic force microscope 1000 according to an example embodiment of
the inventive concepts may include operation S1001 of moving a
sample object to a test board and mounting the sample object on the
test board, operation S1002 of measuring a current image of the
sample object by an (n)th probe, operation S1003 of calculating an
(n)th representative current of the sample object by a control
unit, operation S1004 of storing the (n)th representative current
in a memory unit, operation S1005 of moving a measurement object to
the test board and mounting the measurement object on the test
board, operation S1006 of measuring an (n)th measured current of
the measurement object by scanning a current image of the
measurement object by the (n)th probe, operation S1007 of
determining whether to select another probe, and operation S1008 of
calculating a scaling factor of the (n)th measured current as a
ratio between the (n)th representative current and an (n-1)th
representative current. If a different probe than the (n)th probe
is selected (YES) in operation S1007 of determining whether to
select another probe, (n+1) may be substituted for n to repeat from
operation S1001 of moving the sample object to the test board and
mounting the sample object on the test board to operation S1006 of
measuring the (n)th measured current of the measurement object by
the (n)th probe.
[0062] In an example embodiment, the sample object may have the
same surface state as the measurement object. Also, the resistance
distribution of the sample object may be uniformly maintained, and
the sample object may have the same resistance level as the
measurement object.
[0063] Operation S1002 of measuring the current image of the sample
object may be performed by scanning the surface of the sample
object on a pixel-by-pixel basis by a scanning unit 200 (see FIG.
1) connected to the (n)th probe. In an example embodiment, the
scanning unit 200 may raster-scan the surface of the sample
object.
[0064] After operation S1002 of measuring the current image of the
sample object, operation S1003 of calculating the (n)th
representative current of the sample object may be performed.
Operation S1003 may be performed by a current detecting unit 300
(see FIGS. 1 and 2). The current detecting unit 300 may calculate a
first representative current by adding up current image values
measured by scanning the surface of the sample object on a
pixel-by-pixel basis and dividing the resulting sum by the total
number of pixels. For example, a reference current I.sub.0 may be
calculated by the following equation. In the following equation, p
denotes the total number of pixels of the object S.
I 0 = k = 1 p I k / p ##EQU00001##
[0065] The (n)th representative current may be stored in the memory
unit 410 of the control unit 400 (see FIGS. 1 and 2) (S1004).
[0066] After operation S1004 of storing the nth representative
current, the measurement object may be moved to and mounted on the
test board (S1005), and the (n)th measured current may be measured
by scanning the current image of the measurement object (S1006).
Like the sample object, the (n)th measured current of the
measurement object may be calculated by scanning the surface of the
measurement object on a pixel-by-pixel basis, adding up
pixel-by-pixel current image values, and dividing the resulting sum
by the total number of pixels.
[0067] In an example embodiment, the (n)th representative current
and the (n)th measured current measured by the (n)th probe may be
displayed by the display unit 500 (see FIGS. 1 and 2).
[0068] If a different probe than the (n)th probe is selected (YES)
in operation S1007 of determining whether to select another probe,
(n+1) may be substituted for n to repeat from operation S1001 of
moving the sample object to the test board and mounting the sample
object on the test board to operation S1006 of measuring the (n)th
measured current of the measurement object by the (n)th probe. For
example, if n=1, when a first probe is used to calculate a first
representative current and a first measured current and another
probe (e.g., a second probe) is selected in operation S1007 of
determining whether to select another probe, a second
representative current and a second measured current may be
calculated. When another probe is not selected any more, an (n-1)th
representative current and an (n-1)th measured current may be fed
back to calculate a scaling factor of the (n)th measured current.
That is, in the above example, the first representative current and
the first measured current, which are respectively the (n-1)th
representative current and the (n-1)th measured current, may be fed
back to calculate a scaling factor of the second measured
current.
[0069] In the above example, the value of n is limited to 2, and
the first probe and the second probe are described as two
measurement probes. However, this is merely for convenience of
description, and the inventive concepts are not limited
thereto.
[0070] In the above example, a scaling factor I.sub.2'/I.sub.1' may
be calculated by the scaling control unit 420 (see FIGS. 1 and 2).
When a resistance R.sub.0 of the sample object and a resistance
R.sub.x of the measurement object are equal to each other, the
scaling factor I.sub.2'/I.sub.1' may be equal to a ratio between
the second representative current and the first representative
current.
I 2 ' I 1 ' = I 2 I 1 for ( R x = R 0 ) ( 1 ) ##EQU00002##
[0071] However, when the resistance R.sub.0 of the sample object
and the resistance R.sub.x of the measurement object are different
from each other, the scaling factor I.sub.2'/I.sub.1' may be
calculated by adding a ratio between the bias voltage V.sub.0
applied to the sample object and the first representative current
I.sub.1 to a difference between the resistance R.sub.x of the
measurement object and the resistance R.sub.0 of the sample object
and dividing the resulting sum by a value obtained by adding a
ratio between the bias voltage V.sub.0 applied to the sample object
and the second representative current I.sub.2 to the difference
between the resistance R.sub.x of the measurement object and the
resistance R.sub.0 of the sample object.
I 2 ' I 1 ' = R x - R 0 + V 0 / I 1 R x - R o + V 0 / I 2 for ( R x
.noteq. R 0 ) ( 2 ) ##EQU00003##
[0072] Equation (2) above may be derived from the following
relational equations.
V.sub.0=(R.sub.0.+-.r.sub.1)I.sub.1 (3-1)
V.sub.x=(R.sub.x+r.sub.1)I.sub.1' (3-2)
V.sub.0=(R.sub.0+r.sub.2)I.sub.2 (4-1)
V.sub.x=(R.sub.x+r.sub.2)I.sub.2' (4-2)
[0073] Referring to Equations (3-1) and (3-2), the first
representative current I.sub.1 is equal to a value obtained by
dividing the bias voltage V.sub.0 applied to the sample object by
the sum of the resistance R.sub.0 of the sample object and an
internal resistance r.sub.1 of the first probe, and the first
measured current I.sub.1' is equal to a value obtained by dividing
the bias voltage V.sub.x applied to the measurement object by the
sum of the resistance R.sub.x of the measurement object and the
internal resistance r.sub.1 of the first probe. Referring to
Equations (4-1) and (4-2), the second representative current
I.sub.2 is equal to a value obtained by dividing the bias voltage
V.sub.0 applied to the sample object by the sum of the resistance
R.sub.0 of the sample object and an internal resistance r.sub.2 of
the second probe, and the second measured current I.sub.2' is equal
to a value obtained by dividing the bias voltage V.sub.x applied to
the measurement object by the sum of the resistance R.sub.x of the
measurement object and the internal resistance r.sub.2 of the
second probe.
[0074] Equation (2) may be derived by offsetting the internal
resistance r.sub.1 of the first probe and the internal resistance
r.sub.2 of the second probe by combining Equations (3-1) to (4-2).
Because the internal resistance r.sub.1 of the first probe and the
internal resistance r.sub.2 of the second probe are negligibly
smaller than the resistance R.sub.0 of the sample object and the
resistance R.sub.x of the measurement object, when substitutions of
R.sub.0=V.sub.0/I.sub.2 and R.sub.x=V.sub.x/I.sub.2' are made in
Equation (2), Equation (5) below may be obtained.
I 2 ' I 1 ' = V x / I 2 ' - V 0 / I 2 + V 0 / I 1 V x / I 2 ' for (
R x .noteq. R 0 ) ( 5 ) ##EQU00004##
[0075] Referring to Equation (5), when the resistance R.sub.0 of
the sample object is different from the resistance R.sub.x of the
measurement object (R.sub.x R.sub.0), the scaling factor of the
second measured current I.sub.2' and the first measured current
I.sub.1' may be calculated by adding a value obtained by dividing
the bias voltage V.sub.0 applied to the sample object by the first
representative current I.sub.1 to a difference between a value
obtained by dividing the bias voltage V.sub.x applied to the
measurement object by the second measured current I.sub.2' and a
value obtained by dividing the bias voltage V.sub.0 applied to the
sample object by the second reference current I.sub.2 and dividing
the resulting sum by a ratio between the bias voltage V.sub.x
applied to the measurement object and the second measured current
I.sub.2'. In this case, because the applied bias voltages V.sub.0
and V.sub.x, the first representative current I.sub.1, the second
representative current I.sub.2, and the second measured current
I.sub.2' are known values, the scaling factor may be
calculated.
[0076] In a process of manufacturing a semiconductor device, when
the conductance of the semiconductor device is to be measured or
when the flow of a constant current is to be checked, a conductive
atomic force microscope may be used. When a probe is replaced or a
state of the probe of the conductive atomic force microscope
changes, different currents may be measured through the probe. For
example, even when the current of the same measurement object is
measured by the first probe and the second probe, a current
measured from the first probe and a current measured from the
second probe may not be the same due to variables such as the bias
voltage applied to the measurement object and the internal
resistances of the probes. Because a conductive atomic force
microscope 1000 according to an example embodiment includes the
scaling control unit 420 (see FIG. 2) that scales the current
values measured by different probes as described above, the
conductive atomic force microscope 1000 may correct or calibrate
current values measured by various probe types and/or states of the
probe and produce reproducible current measurement values
regardless of probe types and/or states of the probe. Thus, a more
reliable current measurement is possible.
[0077] FIG. 4 is a graph illustrating a bias voltage V applied by
the power supply unit 600 (see FIG. 1) of the conductive atomic
force microscope 1000 according to an example embodiment of the
inventive concepts and currents flowing between the object S (see
FIG. 1) and the different probes 100-1 and 100-2.
[0078] Referring to FIG. 4, a relational graph of the applied bias
voltage V and the current flowing between the object S and the
probe 100-1/100-2 may be divided into three sections. The first
section I is a reverse bias section in which the bias voltage
applied from the power supply unit 600 to the object S is negative.
The second section II is a nonlinear section in which a negative
bias voltage is applied from the power supply unit 600 to the
object S but currents flowing between the object and the probes
100-1 and 100-2 are uniform. The third section III is a linear
section in which the currents flowing between the object and the
probes 100-1 and 100-2 are proportional to the bias voltage V
applied from the power supply unit 600 to the object S.
[0079] Operation S1008 (see FIG. 3) of calculating a scaling factor
for scaling the current of the measurement object measured by the
second probe structure 100-2 by feeding back the current of the
measurement object measured by the first probe structure 100-1 may
be performed with regard to, for example, the third section III. In
an example embodiment, operation S1008 of calculating the scaling
factor may be performed when the bias voltage applied to the object
S is about 0.5 V or more.
[0080] FIG. 5 is a schematic diagram illustrating a probe structure
100, a current detecting unit 300, and a power supply unit 600 of a
conductive atomic force microscope 1000 according to an example
embodiment of the inventive concepts.
[0081] Referring to FIG. 5, in order to measure a representative
current of a sample object S in the conductive atomic force
microscope 1000, the power supply unit 600 may apply a bias voltage
V to the object S. The bias voltage applied from the power supply
unit 600 may cause a current to flow between the object S and a
probe 110 of the probe structure 100. The current detecting unit
300 may detect a current flowing between the probe 110 and the
object S through a cantilever 120 connected to the probe 110.
[0082] In an example embodiment, the current detecting unit 300 may
include a filter 330, an amplifier 340, and a current measuring
unit 310. A current flowing between the object S and the probe 110
may be transmitted through the cantilever 120 to the current
detecting unit 300 and be detected by the current detecting unit
300. The detected current may include a noise. The filter 330 may
adjust a current below a cut-off level among the detected currents
to 0 A. Accordingly, it is possible to prevent or minimize an
offset effect that may be caused by a noise in the measured current
when the probe 110 has a size of about 100 nm or less. The
amplifier 340 may amplify the current filtered by the filter 330
and transmit the amplified current to the current measuring unit
310.
[0083] FIG. 6 is a flowchart of an operation algorithm of the
conductive atomic force microscope 1000 according to an example
embodiment of the inventive concepts, for calculating a
representative current and monitoring the representative current by
the current monitoring unit 320.
[0084] Referring to FIG. 6, the operation algorithm may include
operation S2001 of applying a bias voltage to a sample object by a
power supply unit 600 (see FIG. 5), operation S2002 of scanning a
current image of the sample object by using a measurement probe,
operation S2003 of calculating an (i)th representative current of
the sample object by a current detecting unit 300 (see FIG. 5),
operation S2004 of storing the (i)th representative current in a
memory unit 410 (see FIG. 2), operation S2005 of determining
whether the (i)th representative current is equal to an (i-1)th
representative current, operation S2006 of storing a change trend
of the (i)th representative current in the memory unit 410, and
operation S2007 of displaying the change trend of the (i)th
representative current on a display unit. If the (i)th
representative current is equal to the (i-1)th representative
current in operation S2005 of determining whether the (i)th
representative current is equal to the (i-1)th representative
current (YES), (i+1) may be substituted for i to repeat from
operation S2001 of applying the bias voltage to the sample object.
For example, when i=3, a third representative current is calculated
(S2003) and the third representative current is stored in the
memory unit (S2004); and when the third representative current is
compared with a second representative current (S2005) and is
determined to be equal to the second representative current (YES),
4 is substituted for i to calculate a fourth representative current
(S2003). In the above example, if the fourth representative current
is different from the third representative current (NO in S2005), a
change trend of the fourth representative current may be stored in
the memory unit 410 (S2006) and may be displayed on a display unit
500 (see FIGS. 1 and 2) (S2007).
[0085] Operation S2002 of scanning the current image of the sample
object by using the measurement probe may include an operation of
raster-scanning the surface of the sample object on a
pixel-by-pixel basis. Operation S2003 of calculating the
representative current of the sample object by using the current
detecting unit 300 (see FIG. 5) may include an operation of adding
up currents measured by scanning the surface of the sample object
on a pixel-by-pixel basis, and dividing the resulting sum by the
total number of pixels of the sample object.
[0086] A current monitoring unit 320 (see FIG. 2) may perform
operation S2005 of determining whether the (i)th representative
current measured at the sample object is equal to the (i-1)th
representative current. If the (i)th representative current is
equal to the (i-1)th representative current, that is, when the
representative currents measured several times are uniform, then
the measurement may be normally performed. In such cases, the
operation of measuring the representative current of the sample
object may be repeated (i.rarw.i+1) in order to obtain a change
trend with regard to the representative current. If the
representative currents are not uniform (NO in S2005), the changed
(i)th representative current may be stored in the memory unit 410
(see FIG. 2) (S2006) and the change trend of the (i)th
representative current may be displayed on the display unit 500
(see FIGS. 1 and 2) (S2007). In a conductive atomic force
microscope 1000 according to an example embodiment of the inventive
concepts, because a probe 110 (see FIG. 5) contacts the surface of
an object in order to measure the conductance or resistance of the
object, the measured representative current may vary due to, for
example, the abrasion of the probe 110. The conductive atomic force
microscope 1000 may detect a state change of the probe 110 and a
contact resistance change point of the probe 110 by performing the
algorithm for calculating and monitoring the representative current
as illustrated in FIG. 6. Thus, the probe 110 may be easily
managed, and highly reproducible measurement results about the
conductance or resistance of the object may be obtained.
[0087] FIGS. 7A and 7B are graphs illustrating contact resistances
depending on the structures and states of probes of a conductive
atomic force microscope according to an example embodiment of the
inventive concepts.
[0088] As illustrated in FIG. 7A, a probe 110a connected to a
cantilever 120 is deformed due to the physical abrasion of an
object contact portion 110a'. In the conductive atomic force
microscope 1000 according to an example embodiment of the inventive
concepts, because the probe 110a contacts the surface of an object,
the object contact portion 110a' may be abraded and thus the
contact resistance of the probe 110a may change. Referring to the
graph of FIG. 7A, the contact resistance of the probe 110a changes
irregularly. When the object contact portion 110a' is abraded, the
contact resistance of the probe 110a may be reduced. Thus, the
representative current measured by the probe 110a may be measured
to be greater than the original value.
[0089] An oxide layer 130 may be formed on the surface of a probe
110b illustrated in FIG. 7B. The oxide layer 130 may be deposited
due to an electric field generated between an object and a lower
end portion of the probe 110b. In an example embodiment, the probe
110 may be formed of a conductive metal selected from the group
consisting of Pt, Ir, Au, Ru, Ag, and any alloy thereof, and the
oxide layer 130 may be formed of an oxide layer of, for example, a
conductive metal. Because the oxide layer 130 is a nonconductor,
the contact resistance of the probe 110b may be increased. Thus,
the current flowing between the probe 110b and the object may be
reduced.
[0090] FIG. 8 is a graph illustrating measured currents of an
object depending on the types of probes of first to third probe
structures 100-1 to 100-3 of a conductive atomic force microscope
according to an example embodiment of the inventive concepts.
[0091] Referring to FIG. 8, by performing operation S2003 of
calculating the (i)th representative current of the sample object
and the monitoring operation (S2005 and S2006) of determining
whether the (i)th representative current is equal to the (i-1)th
representative current, the representative current of the sample
object may be displayed on the display unit (S2007 in FIG. 6). FIG.
8 illustrates three representative currents, including a
representative current measured by the first probe structure 100-1,
a representative current measured by the second probe structure
100-2, and a representative current measured by the third probe
structure 100-3. However, this is merely for convenience of
description, and the inventive concepts are not limited thereto.
The representative current measured by the first probe structure
100-1 is uniformly maintained at a level of about 4.60E.sup.-3 [A],
and the representative current measured by the second probe
structure 100-2 is uniformly maintained at a level of about
3.70E.sup.-3 [A]. However, the representative current measured by
the third probe structure 100-3 decreases from a level of about
2.90E.sup.-3 [A] to a level of about 1.70E.sup.-3 [A]. Because a
conductive atomic force microscope 1000 according to an example
embodiment of the inventive concepts detects a current by bringing
a probe 110 of a probe structure 100 into contact with the surface
of an object, an object contact portion of the probe 110 may be
physically abraded or an oxide layer may be deposited on the
surface of the probe 110. The third probe 100-3 may be physically
changed like the probes 110a and 110b illustrated in FIGS. 7A and
7B. According to the inventive concepts, a state change of the
probe 110 may be detected by detecting a change trend of the
representative current by using the current monitoring unit 320
(see FIGS. 2 and 6), storing the change trend of the representative
current in the memory unit 410 (see FIGS. 2 and 6), and displaying
the change trend of the representative current on the display unit
500 (see FIGS. 2 and 6). Further, by monitoring the current
measured according to the state change of the probe 110 and scaling
the representative current taking into account the change trend
thereof, more highly reproducible measurement results about the
conductance or resistance of the object may be obtained, thereby
reducing the probe dependency for current measurement.
[0092] While the inventive concepts have been particularly shown
and described with reference to example embodiments thereof, it
will be understood that various changes in form and details may be
made therein without departing from the spirit and scope of the
following claims.
* * * * *