JPH0833296B2 - Scanning atomic force tunneling microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is used in semiconductor processes and material development, and is a scanning atomic force tunnel microscope for evaluating minute irregularities and potential distribution on the surface of a conductive substance. It is about.

[Prior Art] Conventionally, fine irregularities on the surface of a conductive material are
enstra et al .; IBM Journal of Research and Develope
ment Vol.30, No.5, p466, September 1986 etc., it was evaluated by a scanning tunneling microscope (hereinafter referred to as STM). Figure 3 shows the STM that was used before
FIG. In this figure, a piezo element composed of piezo elements 2 _X , 2 _Y and 2 _Z in the XYZ directions and driving the probe 3 in the XYZ directions is provided on the sample 1. This piezo element is driven by the XY driver 4 in the XY directions. Then, when a voltage Vs is applied from the power source 5 between the probe 3 and the surface of the sample 1 and the surface of the sample 1 and the probe 3 are brought close to each other by a distance of, for example, 10 Å, both electron clouds are overlapped and the voltage is increased. The tunnel current It flows corresponding to Vs. The probe 3 and the piezo element 2 are moved up and down in the Z direction by the feedback control system 6 so that the distance between the probe 3 and the surface of the sample 1 becomes constant, that is, the tunnel It becomes constant. In this way, the piezo element 2
Among them, the piezo element 2 _{X in} the X direction and the piezo element 2 _{Y in} the Y direction scan the probe 3 two-dimensionally and store a drive signal in the Z direction in the data storage 7, thereby By converting the displacement component into an electric signal, the unevenness information of the sample surface, that is, the equipotential surface such as an electron cloud can be displayed on the image display 8.

[Problems to be Solved by the Invention]

However, when the charges 9 are localized on the surface of the sample 1 as shown in FIG.
Is repelled or sucked, and the vertical piezo element 2 _Z that holds the probe 3 contracts and drives the probe up and down. Therefore, although the actual surface unevenness is flat, it may be displayed as if unevenness exists as shown in FIG. 4, for example.

On the other hand, atomic force microscope (hereinafter AFM)
In principle, there is no electrical influence due to the electric charge on the material surface, and it is possible to simply measure the minute mechanical irregularities on the material surface. However, there is a drawback that electrical information on the surface of the substance cannot be obtained.

The present invention has been made in view of the problems of such conventional scanning tunneling microscopes and atomic force microscopes, and it is possible to identify and recognize irregularities and charge regions existing on a sample surface. Is a technical issue.

[Means for solving the problem]

The present invention has a driving means for driving a sample held on an XY table whose upper surface is parallel to the XY surface in a minute section along the XY direction,
A cantilever whose one end is held by a base adjacent to the XY table, a conductive probe provided at the tip of the cantilever facing the sample, and a Z direction at the tip of the cantilever perpendicular to the XY table. Detecting means for detecting displacement to the sample, voltage applying means for applying a predetermined voltage between the conductive probe and the sample via the cantilever, switch means for connecting and disconnecting the voltage by the voltage applying means, and driving means. Subtract the XY direction secondary image data obtained in the data storage section that holds the displacement by the displacement detection means when the sample moves in the XY directions and the data storage section when the switch of the switch means is opened and closed. And an image display device for displaying the data in the data storage unit, and an image processing device for providing the data to the data storage unit. It is intended to.

[Action]

According to the present invention having such characteristics, the displacement based on the interatomic force between the probe and the sample is detected during the AFM operation to obtain the two-dimensional uneven profile. And STM
A two-dimensional uneven profile is obtained by keeping the tunnel current constant during operation. Then, these two-dimensional image data are subjected to subtraction processing in the image processing device so that the charge region and the minute unevenness on the surface can be distinguished and recognized.

〔Example〕

Next, examples of the present invention will be described. FIG. 1 is a principle diagram showing a configuration of a main part of a scanning atomic force tunnel microscope according to an embodiment of the present invention. In this figure, the base 11
A cantilever 12 whose one end is held is provided on the upper side, and a first conductive probe 13 made of a conductive material is provided on the lower surface thereof. The lower surface of the cantilever 12 is formed of a conductive material 12a, and the metal film 12b is also attached to a part of the upper surface. Also, on the base 11, place the upper surface on the XY table 14.
A sample 15 that is parallel to the XY plane is held. A bias power source (voltage Vs) 16 as a voltage applying means is connected to the conductive probe 13 between the conductive film 12a and the sample 15 via a switch 17.

A metallic second probe 21 is attached to a piezo element 22 which is a Z-axis driving means, right above the cantilever 12 in which the conductive probe 13 is implanted. The piezo element 22 is a probe 21
Is moved in the Z direction, and a bias power source 23, which is a second voltage applying unit for the voltage Vs2, is connected between the probe 21 and the metal film 12b. Then, the tunnel current output is given to the feedback control system 25 via the A / D converter 24, and the control amount corresponding to the manipulated variable is D /
It is given to the piezo element 22 via the A converter 26, and is controlled so that the space between the probe 21 and the tip of the cantilever 12 becomes a predetermined distance. Here, each block from the probe 21 to the D / A converter 26 constitutes one-dimensional displacement detection means for measuring the displacement of the cantilever 12.

The output of the A / D converter 24 is also given to the feedback control system 31. The feedback control system 31 moves the sample 15 in the Z direction by driving the piezo element 33 of the XY table 14 via the D / A converter 32 with this input as a control amount. Further, the XY table 14 is provided with piezo elements 34, 35 for moving the sample in the X and Y directions. The outputs of the XY driver 36 are given to the piezo elements 34 and 35 via the D / A converters 37 and 38, respectively, to move the sample in the XY directions. The output of the XY driver 36 and the output of the feedback control system 31 are also provided to the data storage 40.
The data storage 40 holds this two-dimensional image information, and its output is directly given to the image display 41 and further given to the image processing device 42. Image processing device
Reference numeral 42 is for subtracting two pieces of image data, as will be described later, and displaying the result on the image display 41. Here, the piezo elements 34 and 35, the D / A converters 37 and 38, and the XY driver 36
It constitutes a driving means for driving the sample 15 on the Y table 14 in the XY directions.

Next, the operation of this embodiment will be described. First, at the time of AFM operation, the switch 17 is opened and a voltage is applied to the piezo elements 48 and 35 by the XY driver 36 to scan in the XY directions. When the conductive probe 13 at the tip of the cantilever 12 and the surface of the sample 15 approach up to several Å due to minute unevenness of the sample 15, an atomic force acts between them and stress is applied to the cantilever 12, causing the cantilever 12 to become stressed. 12 bends down. At this time, the probe 21 is also moved downward by extending the piezo element 22 downward along the Z-axis by the feedback control system 25 so that the tunnel current It flowing by the bias power supply 23 becomes constant. The feedback control block 31 controls the voltage applied to the piezo element 33 of the XY table 14 so that the interatomic force applied to the cantilever 12 in response to the change in the electric signal is kept constant. In this way, the profile of the unevenness corresponding to the minute unevenness on the sample surface can be obtained in the data storage 40. At this time, the sample 15 is two-dimensionally moved by the voltage signal applied to each of the XY piezo elements 34 and 35 connected to the XY table 14, so that a two-dimensional uneven profile as shown in FIG. Obtainable. Since this operation detects the interatomic force between substances, the uneven profile is not affected by the electrical characteristics even if the charge localized region due to the trap or the like exists on the surface of the sample 15.

After obtaining the uneven profile by the AFM in this way, the switch 17 is closed and the operation by the STM is performed. In this case, the conductive probe 13 is connected to the bias power source 1 via the conductive material 12a.
Bias voltage from 6 is applied. Therefore sample 15
When the conductive probe 13 during scanning of arrives at the charge localized region,
The conductive probe 13 repels due to the Coulomb force based on the charges in the localized charge region, and the conductive probe 13 moves away from the surface of the sample 15. Therefore, an uneven profile affected by the minute unevenness and the localized charge region can be obtained. Here, by moving the sample two-dimensionally in the XY directions as in the AFM operation, FIG.
It is possible to obtain a two-dimensional uneven profile as shown in. This profile is maintained in data storage 40.

In this way, by obtaining the AFM image shown in FIG. 2 (a) by one scan and then obtaining the STM image shown in FIG. 2 (b) by the second scan, only minute irregularities can be obtained in the same observation field of view. It is possible to obtain data on the distribution of and the localized charge distribution including it. Therefore, the image processing apparatus 42 subtracts the data shown in FIG. 2B from the data shown in FIG.
It is possible to obtain a charge distribution profile based only on the charge localized region shown in FIG.

In this embodiment, the displacement of the cantilever 12 is measured using a one-dimensional tunnel microscope.
It is also possible to detect the displacement amount of the deflection by coating a metal film on the surface of the cantilever and irradiating a laser beam or the like from above to detect it from the position change of the reflected light.

〔The invention's effect〕

As described in detail above, according to the present invention, by electrically switching between the AFM mode and the STM mode for measurement, it is possible to localize the charge region and the surface physics from the image data of both by localizing on the sample surface by a trap or the like. It can be recognized by distinguishing it from the typical unevenness. Therefore, the effect of being able to more accurately measure the evaluation results of the fine unevenness of the material surface by the conventional STM alone can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of a scanning atomic force tunneling microscope according to an embodiment of the present invention, FIG. 2 is a diagram showing the resulting two-dimensional unevenness distribution on the sample surface, and FIG. FIG. 4 is a schematic diagram showing the configuration of the scanning tunneling microscope that performs the STM operation, and FIG. 4 is a diagram showing the charge distribution profile thereof. 12 …… Cantilever, 13 …… Conductive probe, 14 …… XY table, 15 …… Sample, 16,23 …… Bias power supply, 21 …… Probe, 25,31 …… Feedback control system, 33,34 , 35 ... Piezo element, 36 ... XY driver, 40 ... Data storage, 41 ... Image display, 42 ... Image processing device.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/66 7735-4M

Claims (1)

[Claims] 1. A driving means for driving a material, which is held on an XY table, whose upper surface is parallel to the XY surface, in a minute section along the XY direction, and one end is held by a base provided adjacently on the XY table. A cantilever, a conductive probe provided at the tip of the cantilever facing the material, a displacement detecting means for detecting the displacement of the tip of the cantilever in the Z direction perpendicular to the XY table, Voltage applying means for applying a predetermined voltage between the conductive probe and the material via the cantilever, switch means for connecting and disconnecting the voltage by the voltage applying means, and XY direction of the material by the driving means. And a data storage unit for holding the displacement by the displacement detection unit when the switch is moved, and a data storage unit for opening and closing the switch of the switch unit. Scanning type, which comprises: an image processing device that subtracts two-dimensional image data in the XY directions and gives the data to the data storage unit; and an image display that displays the data in the data storage unit. Atomic force tunneling microscope.