JPH10267942A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scanning probe microscope advantageous in measuring a sample mixed with a conductive part and an insulating part by a method wherein there is provided control switching means for switching from control of making constant a measured value of a physical amount of either one of an interatomic force and a tunnel current to control of making constant the other. SOLUTION: This scanning probe microscope has a function of measuring an interatomic force and a tunnel current between a probe 1 and a sample, respectively. A distance between the probe 1 and a sample is controlled so that the measured value of one physical amount is made constant, while in the state that the probe 1 and a sample are relatively scanned, the other physical amount is measured. If the physical amount exceeds a predetermined set value, the control switching means switches from control of making constant the measured value of one physical amount to control of making constant the other physical amount. Namely, a switch 12 switches a z-directional control signal to a feedback signal from either one of servo circuits 4, and 8 by a signal from a control switching circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning probe microscope, and more particularly, to a scanning probe microscope having the functions of a scanning tunnel microscope and an atomic force microscope.

[0002]

2. Description of the Related Art In a scanning tunneling microscope (hereinafter referred to as "STM"), generally, when a predetermined potential difference is applied between a conductive probe and a sample, these two are relatively moved.
While scanning in a dimension, the tunnel current flowing between the probe and the sample is measured, and the distance between the probe and the sample (z direction) by the servo system so that the measured value of the tunnel current becomes constant.
(Hereinafter, referred to as STM scanning), and an unevenness image (STM image) related to the conductivity of the sample surface is obtained from the instantaneous movement amount of the probe in the z direction.

On the other hand, in an atomic force microscope (hereinafter, referred to as AFM), a cantilever-shaped probe is generally brought into contact with the surface of a sample, and these are relatively two-dimensionally scanned. Is measured based on the displacement of the probe based on the displacement of the probe, and the servo system controls the distance (z direction) between the probe and the sample so that the measured value of the force becomes constant (hereinafter, referred to as "the force"). , AFM scanning), and an unevenness image (AFM image) of the sample surface is obtained from the amount of movement of the probe in the z-direction every time.

Conventionally, a cantilever-shaped probe is used, and a potential difference is applied between the probe and the sample so that STM scanning and AFM scanning can be selected. There is known an apparatus in which an STM image and an AFM image are selectively obtained by an apparatus.

[0005]

The STM scanning is possible for a sample having good conductivity, and the AFM scanning does not require the conductivity of the sample, and is based on various forces such as pressing force and frictional force. However, conductive information cannot be imaged like STM.

When an electronic device such as a VLSI is evaluated by STM or AFM, since a conductive part and an insulating part are mixed, when the conductive part reaches the insulating part during STM scanning, a certain amount is determined by the servo system. Depending on the tunnel current value set so as to keep the current, the probe may be pressed too much against the sample in order to flow the tunnel current, and the probe and the sample may be damaged.

An object of the present invention is to provide a scanning probe microscope which is advantageous for measurement of a sample in which a conductive portion and an insulating portion such as a super LSI are mixed.

[0008]

In order to achieve the above object, a scanning probe microscope according to the present invention has a function of measuring an atomic force and a tunnel current between a probe and a sample, respectively. In, while controlling the distance between the probe and the sample so that the measured value of one physical quantity is constant, while the probe and the sample are relatively scanning, measure the other physical quantity, Determining means for determining that the measured value exceeds a preset value; and control switching means for switching from control for keeping the measured value of one physical quantity constant to control for keeping the other physical quantity constant, based on the determination. Characterized by having.

The present invention is intended to automate the switching between the STM scan and the AFM scan so as to obtain a high-contrast image in a single scan even for a sample in which conductive portions and insulating portions are mixed.

That is, a state in which scanning is performed while controlling one physical quantity of the physical quantity acting between the probe and the sample, for example, the tunnel current to be constant (STM scanning).
In the state where the other physical quantity, that is, the atomic force, is measured, and when the measured value exceeds a predetermined value, scanning is performed while automatically controlling the other physical quantity, that is, the atomic force, to be constant. (AFM scanning). Conversely, when the tunnel current value exceeds a predetermined value during AFM scanning, it is also possible to automatically switch to STM scanning.

By automating the switching of the STM scan → AFM scan or the AFM scan → STM scan, even if the probe reaches the boundary between the conductive part and the insulating part during one scan, STM by one scan
A high-contrast image composed of a combination of an image and an AFM image can be obtained over the entire area, and the sample and the probe are not damaged.

Here, in the present invention, when the conductive portion and the insulating portion are mixed in one probe scanning area as described above, an image in which the STM image and the AFM image are mixed is obtained. In this image, the area of the STM image and the AF
It is preferable to superimpose a display such that the region of the M image can be identified.

[0013]

FIG. 1 is a block diagram showing an embodiment of the present invention, in which a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration are shown together.

The probe 1 is formed integrally with a tip of a cantilever 1b having a base fixed to the fixing portion 1a, and is entirely made of a conductive material. This probe 1 and sample W
, A predetermined potential difference is given by the tunnel voltage power supply 2. Further, the probe 1 and the sample W
Is amplified by the tunnel current amplifier circuit 3 and then introduced into the STM servo circuit 4 and the control switching circuit 5.

The displacement of the probe 1 in the z-direction (direction approaching / separating from the surface of the sample W) is detected by a non-contact displacement detector 6 such as a light wave interferometer, and the detection result is obtained. Is an AFM servo circuit 8 via a displacement amplification circuit 7
And the control switching circuit 5.

The sample stage 9 on which the sample W is placed is displaced in x, y and z directions orthogonal to each other by an xyz drive unit 10 having, for example, three piezoelectric elements. The xyz driving unit 10 is driven and controlled by a scanning signal from an xy scanning circuit 11 for causing the probe 1 to scan the sample W in the xy directions, and a z-direction control signal supplied via a switch 12. . The z-direction control signal is supplied to the image memory 13 together with the xy scanning signal from the xy scanning circuit 11.
And imaged by the CRT 14. A signal from the image addition circuit 15 is also supplied to the CRT 14, and the signal from the image addition circuit 15 causes a signal to be displayed on the display image of the CRT 14 as described later.
A boundary between the STM image and the AFM image and a mark or the like for visually recognizing in which display area these images are located are additionally displayed.

The above-mentioned switch 12 is connected to the control switching circuit 5
, And switches the z-direction control signal to be supplied to the xyz drive unit 10 to either the feedback signal from the STM servo circuit 4 or the feedback signal from the AFM servo circuit 8.

As shown in the flowchart of FIG. 2 for the measurement operation of the embodiment of the present invention, the control switching circuit 5 operates in the state where the feedback signal from the STM servo circuit 4 is selected as the z-direction control signal. That is, STM
In the scanning state, when the output signal from the displacement amplifier circuit 7 exceeds a preset value, the switch 12 is driven to switch the z-direction control signal to the feedback signal from the AFM servo circuit 8. In the state where the feedback signal from the AFM servo circuit 8 is selected as the z-direction control signal, that is, in the AFM scanning state, when the output signal from the tunnel current amplifier circuit 3 exceeds a preset value. Drive switch 12,
The z-direction control signal is switched to a feedback signal from the STM servo circuit 4.

The image adding circuit 15 takes in the switching signal of the switch 12 from the control switching circuit 5 and the xy scanning signal from the xy scanning circuit 11, and sets each pixel on the image of the CRT 14 to the STM scanning state or the AFM scanning state. ST so that it is possible to visually recognize which state
A boundary between the M image and the AFM image and a mark or the like for notifying whether each area partitioned by the boundary is an STM image or an AFM image are added on the screen of the CRT 14.

In the above embodiment, when observing a sample in which conductive portions and insulating portions are mixed, at the beginning of the observation, for example, a feedback signal from the STM servo circuit 4 is used as a z-direction control signal. Select and STM
Perform a scan. Thus, when the probe 1 is scanning over the conductive portion, the tunnel current can be maintained at a constant value without bringing the probe 1 extremely close to the sample W. Stores image data relating to the STM image. When the probe 1 approaches the insulating portion, the STM servo circuit 4 starts an operation to bring the probe 1 extremely close to the sample W in order to keep the tunnel current constant. On the way, the output from the displacement amplifier circuit 7 exceeds a preset value,
The control switching circuit 5 drives the switch 12 to switch the z-direction control signal to the feedback signal from the AFM servo circuit 8, and starts AFM scanning. Thus, the image data relating to the AFM image is stored in the image memory 13 thereafter. Also, in this AFM scanning state, when the probe 1 reaches the conductive portion, the tunnel current exceeds a preset value, and the control switching circuit 5 drives the switch 12 to send the z-direction control signal to the STM servo circuit. The signal is switched to the feedback signal from No. 4, and the STM scanning is started again. Thereafter, the image memory 13 stores image data relating to the STM image.

Therefore, after one scan is completed, the image data in which the STM image and the AFM image are mixed is stored in the image memory 13, and the mixed image is displayed on the CRT 14. During the above operation, the image addition circuit 15
Now, the switching signal of STM scanning → AFM scanning and AF
Since the switching signal of M scanning → STM scanning is introduced together with the xy scanning signal, it is possible to identify whether each pixel in the image memory 13 is an STM image or an AFM image. The boundary between the image and the AFM image and each region surrounded by the boundary are the STM image and the AF
A mark or the like indicating which of the M images is added is added.

In the above-described embodiment, an example has been described in which, when the displacement of the probe 1 in the direction of the sample W during the STM scan exceeds a predetermined value, the scan is immediately switched to the AFM scan.
When the displacement of the probe 1 exceeds a predetermined value during M scanning, ST
The STM scan may be continued by changing (decreasing) the tunnel current value set by the servo circuit 4 for M to keep the tunnel current constant. In this case, the set tunnel current value is set to a predetermined minimum value. If the displacement of the probe 1 still exceeds the predetermined value even after reaching the value, it may be configured to switch to the AFM scanning.

[0023]

As described above, according to the present invention, the STM scanning for scanning the probe while controlling the position of the probe in the z direction so that the tunnel current maintains a constant value, and the displacement of the probe ( In a probe microscope having both functions of AFM scanning in which the probe is scanned while controlling the position of the probe in the z direction so that the atomic force keeps a constant value, while scanning using one function, the other is used. Since the physical quantity used to control the function of (1) is monitored, and when the physical quantity exceeds a predetermined value, switching to scanning using the other function is performed. In the surface observation, an image in which the STM image and the AFM image are mixed can be obtained by one scan, and the surface state of the sample can be analyzed in a short time. At the same time, for example, even if the probe approaches the insulating part in the STM scanning state, it automatically switches to AFM scanning, eliminating the problem of pressing the probe against the sample more than necessary and reducing damage to the sample and the probe. can do.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, showing both a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration.

FIG. 2 is a flowchart showing a measurement operation according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Probe 2 Tunnel voltage power supply 3 Tunnel current amplifier circuit 4 STM servo circuit 5 Control switching circuit 6 Displacement detector 7 Displacement amplifier circuit 8 AFM servo circuit 9 Sample table 10 xyz drive unit 11 xy scanning circuit 12 switch 13 Image memory 14 CRT 15 Image addition circuit

Claims (1)

[Claims] 1. A scanning probe microscope having a function of measuring an atomic force and a tunnel current between a probe and a sample, respectively, wherein the probe and the sample are measured so that a measured value of one physical quantity is constant. While controlling the distance, while relatively scanning the probe and the sample, the other physical quantity is measured, and a determination means for determining that the measured value exceeds a preset value, A scanning probe microscope, comprising: a control switching unit configured to switch from control for keeping the measured value of one physical quantity constant to control for keeping the other physical quantity constant according to the determination.