Scanning probe instrument

Details Scanning probe instrument Scanning probe instrument

2001-06-25

2003-12-09

Tran, Huan (Department: 2861)

Radiant energy

Inspection of solids or liquids by charged particles

C250S442110

Reexamination Certificate

active

06661006

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scanning probe instrument such as a scanning probe microscope and, more particularly, to a scanning probe instrument capable of making calibrations regarding metrology accuracy easily and accurately.
2. Description of the Related Art
The present applicant has already invented a scanning probe instrument having a zooming function as shown in FIG.
3
and filed an application for patent (Japanese patent application No. 118015/1996). The structure and operation of this scanning probe instrument are briefly described below.
An enclosure
1
has a scanning tube
20
whose main portion consists of a thin tubular portion
14
protruding into a sample chamber and a thick tubular portion
15
continuous with the thin tubular portion
14
. An inner cylinder
13
is supported inside the thick tubular portion
15
via a viscous body
17
. These members, i.e., the thick tubular portion
15
, the inner cylinder
13
, and the thin tubular portion
14
, are made of the same material such that they are identical in thermal conductivity and coefficient of thermal expansion.
A first voice coil motor is mounted on top of the enclosure
1
. This first voice coil motor comprises a magnet
2
having a core rod portion
3
, a movable element
4
a
around which a coil
5
is wound, a movable element part
4
b
fixedly mounted to the movable element
4
a
, a membrane
6
a
, and a firmly holding part
6
b
firmly holding the outer periphery of the membrane
6
a
. A spindle
8
extending in the Z-direction is firmly mounted to the movable element part
4
b
. A detector
9
for detecting the amount of displacement of a probe
10
is mounted to the lower end of the spindle
8
.
The spindle
8
is resiliently held by first and second springs
11
and
12
, respectively, held to the inner cylinder
13
. A heating coil
16
is wound at a position that is outside the thick tubular portion
15
and located opposite to the viscous body
17
. The heating coil
16
is electrically energized to soften the viscous body
17
during coarse Z motion of the probe
10
.
Mounted beside the enclosure
1
is a second voice coil motor comprising a magnet
21
having a core rod portion
22
, a movable element
23
a
around which a coil
24
is wound, a movable element part
23
b
firmly fixed to the movable element
23
a
, a membrane
25
, and a firmly holding part
25
a
firmly holding the outer periphery of the membrane
25
.
Also mounted beside the enclosure
1
is a thin annular leaf spring
23
c
for preventing the movable element
23
a
from touching the core rod portion
22
or the magnet
21
when the thick tubular portion
15
of the scanning tube
20
tilts in the X- or Y-direction. The outer periphery of the thin annular leaf spring
23
c
is held down by both enclosure
1
and membrane firmly holding part
25
a
. The inner surface portion is held down by both the movable element part
23
b
and an annular spring-holding part
23
d
. A spindle
27
extending in the X-direction is mounted to the movable element part
23
b
and to the annular spring-holding part
23
d
. This spindle
27
has a free end rigidly affixed to the protruding portion
15
a
of the thick tubular portion
15
.
A third voice coil motor (not shown) is mounted in a direction differing by 90° from the direction of the second voice coil motor. This third voice coil motor is identical or similar in structure with the second voice coil motor described above. A Y-direction (vertical to the plane of the paper) spindle interconnects a movable element part rigidly mounted to the movable element of the third voice coil motor and the aforementioned thick tubular portion
15
. The probe
10
is scanned in the X- and Y-directions by driving the second and third voice coil motors.
A sample stage (not shown) is placed opposite to the probe
10
. A sample to be inspected or processed is placed on the sample stage. This sample stage is positioned on coarse X-, Y-, and Z-stages (not shown).
An outer tubular portion
71
whose one side is securely mounted to the enclosure
1
is mounted outside the thin tubular portion
14
and extends coaxially with the thin tubular portion
14
in a direction to protrude into the sample chamber described previously. A heat transfer ring
73
is mounted on the outer periphery of the front end of the outer tubular portion
71
. A heating coil
76
is wound around the heat transfer ring
73
via a heat-insulating member
72
made of a ceramic or the like. The ends of the heat transfer ring
73
are inserted in a holder
74
for the heat-insulating member. A low-melting-point metal
75
such as U-alloys is received in the holder
74
.
The energizing current through the heating coil
76
is turned on and off to melt and solidify the low-melting-point alloy
75
to switch the spring rigidity between one given only by the thin tubular portion
14
and one given by both thin tubular portion
14
and outer tubular portion
71
. In this way, the range in which the scanning tube
20
can be driven in the X- and Y-directions by the same driving force of each voice coil motor is changed. Hence, a zooming function can be accomplished.
When a sample is measured, the probe
10
is brought close to the sample at a coarse motion velocity. When its tip comes into contact with the surface of the sample, the temperature of the viscous body
17
is lowered to a preheating temperature by adjusting the energizing current through the heating coil
16
. This increases the viscosity of the viscous body
17
, making stationary the thick tubular portion
15
and the inner cylinder
13
. In consequence, measurement of the sample is enabled.
In the scanning probe instrument of the structure described above, the scan distance of the probe
10
represents a measured value. The scan distance depends on the force that deflects the scanning tube
20
, i.e., the amplitude of the scan signal supplied to each voice coil motor. Accordingly, the relation between the amplitude of the scan signal and the scan distance of the probe
10
needs to be calibrated to maintain a predetermined relation at all times.
FIG. 4
is a diagram showing the structure of a driver circuit for a voice coil motor
24
in the prior art scanning probe instrument. This driver circuit comprises a scan signal generator
40
for producing a triangular wave used as a scan signal, a first operational amplifier
41
for amplifying and supplying the scan signal to the voice coil motor
24
, a second operational amplifier
42
having one input terminal connected with the output side of the voice coil motor
24
, a resistor
43
used for detection of an electric current and connected with the output side of the voice coil motor
24
, and resistors
44
,
45
for determining the gain G of the second operational amplifier
42
. The output of the second operational amplifier
42
is connected with the negative (−) terminal, or inverting input terminal, of the first operational amplifier
41
. The electric current IL flowing through the voice coil motor
24
is given by IL=VL/R. The gain G of the second operational amplifier
42
is given by G=(R
1
+R
2
)/R
1
.
Calibration of measured values is made by comparing each measured value obtained by scanning a reference sample with the calibration value of this reference sample and adjusting the variable resistor R
2
such that they agree, the resistor R
2
being used for voltage adjustment.
The probe instrument equipped with a zooming mechanism has both a wide mode in which the low-melting-point metal
75
is softened, only the thin tubular portion
14
is bent, and a scan is made over a wide range and a zoom mode in which the low-melting-point metal
75
is hardened, both thin tubular portion
14
and outer tubular portion
71
are bent, and a scan is made over a narrow range. The relation between the current value supplied to the voice coil motor
24
and the amount of movement of the probe
10
differs between the wide mode and the zoom mode. Th

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