Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2002-04-01
2003-04-08
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
Reexamination Certificate
active
06545470
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cantilever of a scanning probe microscope.
2. Description of the Background Art
A scanning probe microscope (SPM) can analyze and estimate a surface of a sample in an nm scale.
The SPM is roughly divided into two portions. One of the SPMs is a scanning tunneling microscope (STM) for operating the inside of a two-dimensional plane while measuring a tunnel current flowing between a surface of a sample having a conductivity and a stylus of a metal (which will be hereinafter referred to as a “probe”), thereby three-dimensionally displaying information about the surface of the sample. The other SPM is an atomic force microscope (AFM) for measuring interatomic force acting between a tip of a probe and a surface of a sample from a displacement of a very small leaf spring (hereinafter referred to as a “cantilever”) and operating the inside of a two-dimensional plane, thereby three-dimensionally displaying information about concavo-convex portions formed on the surface of the sample.
The AFM is different from the STM in that it can also estimate an insulating material and does not place restrictions on a sample in principle. A measuring method and an operation principle will be described below by taking the AFM as an example.
FIG. 10
is a diagram illustrating a device structure of the AFM. As shown in
FIG. 10
, a probe
2
is fabricated in the vicinity of a tip of a cantilever
1
and a tip of the probe
2
is provided close to a surface of a sample
4
. The sample
4
is mounted on a stage
5
.
A laser beam
3
is irradiated on a rear face of the cantilever
1
and reflected light thereof is received by a photodiode
6
, and an amount of detection obtained by the photodiode
6
(an amount of warpage of the cantilever
1
) is given to a feedback loop section
7
. The feedback loop section
7
sends a control signal (a signal indicative of an amount of change in a vertical direction of a piezo
8
) to the piezo
8
based on the amount of detection such that the amount of detection is always constant. Upon receipt of the control signal of the feedback loop section
7
, the piezo
8
brings the cantilever
1
up and down in the vertical direction based on the control signal. Moreover, the piezo
8
includes a piezo for moving the cantilever
1
in X and Y directions as well as the vertical direction.
With such a structure, the AFM first moves the sample
4
such that the probe
2
fabricated in the tip of the cantilever
1
comes to a portion just above a measuring point. Next, when the cantilever
1
is brought down and the probe
2
is caused to approach the surface of the sample
4
, interatomic force is generated between the surface of the sample
4
and the probe
2
. Basically, the amount of change in the interatomic force on each measuring point in the sample
4
is measured by the laser beam
3
, the photodiode
6
and the feedback loop section
7
, thereby detecting concavo-convex portions formed on the surface of the sample
4
.
The AFM has three kinds of measuring modes, for example, a contact mode, a tapping mode and a non-contact mode.
In the contact mode, the probe
2
is caused to come in contact with the surface of the sample
4
and the concavo-convex portions formed on the surface of the sample
4
are measured from a displacement of the cantilever
1
(the amount of warpage of the cantilever
1
).
In the tapping mode, the cantilever
1
is oscillated to cause the probe
2
to periodically come in contact with the surface of the sample
4
, thereby measuring the concavo-convex portions formed on the surface of the sample
4
with a change in an oscillation amplitude which is caused by a variation in the interatomic force generated between the cantilever
1
and the surface of the sample
4
.
In the non-contact mode, the probe
2
is not caused to come in contact with the surface of the sample
4
and the concavo-convex portions formed on the surface of the sample
4
are measured with the change in the oscillation amplitude which is caused by the variation in the interatomic force generated on the cantilever
1
and the surface of the sample
4
.
The photodiode
6
detects the displacement of the cantilever
1
and the change in the oscillation amplitude as a change in an angle of the laser beam
3
reflected by the rear face of the cantilever
1
. The feedback loop section
7
gives a control signal to the piezo
8
to carry out feedback control such that the amount of warpage of the cantilever
1
is always constant in the contact mode and the oscillation amplitude of the cantilever
1
is maintained to be constant in the tapping and non-contact modes.
An amount of movement in a vertical direction on each measuring point in the sample
4
(the control signal of the feedback loop section
7
) can be stored in an external computer and the computer can three-dimensionally display the concavo-convex portions formed on the surface of the sample
4
based on the stored data.
Moreover, the AFM can measure the concavo-convex portions formed on the surface of the sample
4
, and furthermore, can measure various electrical characteristics of the sample
4
, for example, the resistance, magnetic force and surface potential of the sample
4
and the like simultaneously with the measurement of the concavo-convex portions. In this case, it is necessary to change the cantilever
1
and the measuring mode corresponding to a measuring item.
An operation will be described by taking a measurement of a current of the sample
4
as an example.
FIG. 11
is a diagram illustrating the device structure of the AFM in the case in which the current of the sample is to be measured.
FIG. 11
is a diagram illustrating the device structure of the AFM in which a resistance can also be measured. As compared with
FIG. 10
, the cantilever
1
is replaced with a conductive cantilever
1
C and the probe
2
is replaced with a conductive probe
2
C. A signal cable
9
is provided for sending an electrical characteristic signal of a sample such as a current measured by the conductive probe
2
C to a signal processor
10
. The signal processor
10
performs a signal processing such as signal amplification for the electrical characteristic signal of the sample measured by the conductive probe
2
C. There is provided a DC voltage
11
to be applied to the sample for measuring a resistance.
As shown in
FIG. 11
, a substance formed of a conductive material is used for the conductive cantilever
1
C and, for example, a substance obtained by implanting an impurity into Si (silicon), a substance formed by depositing a conductive film over a Si cantilever or the like is used. The conductive cantilever
1
C and the conductive probe
2
C are used in place of the probe when the electrical characteristic is to be measured by a tester. In order to measure the current of the sample
4
, it is necessary to cause the conductive probe
2
C to come in contact with the surface of the sample
4
. The measurement is carried out in the contact mode.
A voltage is applied between the sample
4
and the probe (conductive probe
2
C) while measuring the concavo-convex portions formed on the surface of the sample
4
by the measuring method in the contact mode, and a current flowing between the sample, the probe and the cantilever is measured as the electrical characteristic signal. The electrical characteristic signal obtained by the conductive probe
2
C is sent from the conductive cantilever
1
C to the signal processor
10
through the signal cable
9
and data subjected to a signal processing based on the electrical characteristic signal by the signal processor
10
are stored in a computer, and the computer can three-dimensionally display measurement data such as a resistance value of the sample which is calculated based on the stored data.
In the case in which the electrical characteristic of the sample other than the concavo-convex portions formed on the surface of the sample, for example, the resistance, the surface potential and the
Imai Yukari
Maeda Hitoshi
Mashiko Yoji
Tsugami Mari
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patidar Jay
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