JP3103217B2 - Scanning probe microscope and method for observing a sample using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope which obtains an observation image of a sample by utilizing a physical phenomenon (for example, a tunnel or an atomic force) observed when a probe is brought close to the sample, and uses the same. And a method for observing a sample by using the method.

[0002]

2. Description of the Related Art In recent years, a probe and a sample are brought close to each other, and a scanning probe microscope capable of directly observing an electronic structure on a material surface and near the surface by utilizing a tunnel phenomenon which is a physical phenomenon generated at that time, and using the same. (Hereinafter referred to as STM) has been developed [G. Binnig et al., Helvetic
a Physica Acta, 55.726 (1982)], real-space images can be measured with high resolution irrespective of single crystal or amorphous. In addition, STM has the advantage that it can be observed at low power without damaging the medium due to electric current. Furthermore, it can be used not only in ultra-high vacuum but also in air and solutions to be used for various materials. It is expected to be widely applied in academic or research fields. In the industrial field,
For example, JP-A-63-161552 and JP-A-16155
As disclosed in Japanese Unexamined Patent Publication No. 3 (1999), attention is paid to a principle having a spatial resolution of an atomic or molecular size, and application to a recording / reproducing apparatus and practical application thereof are being vigorously promoted.

[0003]

Since the STM has a spatial resolution of a molecular size, in the conventional STM device, the stage and the probe are affected by temperature fluctuation, vibration, and the influence of a driving system such as a piezoelectric actuator. Drift occurs, and the probe scanning area on the sample surface moves, which causes a problem that the observation target moves with time. Such a problem also occurs in other scanning probe microscopes, for example, an atomic force microscope (AFM).

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a scanning probe microscope capable of obtaining a stable observation image of a sample and a method of observing the sample using the same.

[0005]

A scanning probe microscope according to the present invention comprises: a probe arranged opposite to a surface of a sample; scanning means for two-dimensionally scanning the surface of the sample with the probe; In a scanning probe microscope including a detection unit that detects a signal corresponding to a structure of a sample from a probe and an output unit that outputs an observation image of the sample from the signal detected by the detection unit, the output is output from the output unit. Control means for controlling scanning by the scanning means based on a signal detected by the detection means is provided so that an observation image is not shifted.

Further, a method of observing a sample using a scanning probe microscope is such that a surface of the sample is two-dimensionally scanned by a probe arranged opposite to the surface of the sample, and the probe corresponds to the structure of the sample. In the method of observing the sample using a scanning probe microscope that obtains an observation image of the sample from the detected signal by detecting the detected signal, so that the observation image of the sample does not shift, the signal is detected from the probe. The scanning of the probe is controlled based on a signal.

[0007]

A scanning probe microscope having the above-described structure and a method for observing a sample using the same are used to read a change position of a detection signal caused by a structure of an observation target using a signal obtained at the time of scanning, and to use a probe. By correcting the position by feedback control, the scanning area is fixed with respect to the sample surface,
Freeze the STM image.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 shows a block circuit diagram of a first embodiment in which the present invention is applied to an STM. A sample S is fixed on a stage 1 which can be driven in both X and Y directions. It is supported by the driving means 3 so as to be able to move up and down. A predetermined DC voltage is applied between the sample S and the probe 2 by the power supply 4, and a tunnel current flowing by this voltage is converted into a voltage by the amplifier 5, and the A / D
The signal is input to an (analog / digital) converter 6. A / D
The converter 6 converts the magnitude of the tunnel current into a digital value at a predetermined sampling interval, and outputs the data to the data signal generator 7 and the Z-direction control circuit 8.
The data signal generator 7 is a raster, that is, 1 in the scanning direction.
The line portion is transmitted to the data bus 9 as a data packet. The Z-direction control circuit 8 detects the distance between the probe 2 and the sample S based on the magnitude of the tunnel current, and feeds back to the control voltage applied to the piezoelectric actuator of the Z-direction drive means 3 to keep the distance constant. I do.

The data bus 9 includes a CPU (central processing unit) 1
The data packet from the data signal generator 7 is converted into image data by the image data output unit 11 and sent to the image output device 12 including a monitor or the like. Also, the same data packet is sent to the data cutout unit 13,
The data cutout unit 13 outputs only data within the area specified by the area window specifying unit 14. The output of the data cutout unit 13 is input to a calculation unit 15, and the calculation unit 15 performs a calculation described below according to the flowchart of FIG.
The amount of movement of the image with respect to the previous screen in both the X and Y directions is calculated, and based on this, the feedback amount in both the X and Y directions is calculated and output. On the other hand, the CPU 1
The XY scanning control circuit 16 outputs control voltages in both the X and Y directions according to a command transmitted from 0. The outputs of the operation unit 15 are converted into voltages by D / A converters 17x and 17y, respectively, added to the output of the XY scanning control circuit 16, and then amplified by the amplifiers 18x and 18y. Are applied to the respective piezoelectric actuators.

First, a case where an image is stopped in the X direction by using a gold electrode having a groove formed by a semiconductor process as a sample S in such a configuration will be described.
A predetermined voltage is applied between the sample S and the probe 2,
The tunnel current flowing through the two is converted into a digital value by the A / D converter 6 by the voltage. The tunnel current data is collected by the data signal generator 7 as data packets of the tunnel current data for each raster and sent to the data bus 9. In this embodiment, one raster is 51
Two data and one screen are composed of 512 rasters.

The Z-direction control circuit 8 controls the distance between the probe 2 and the sample S by applying a control voltage to the piezoelectric actuator attached to the Z-direction drive means 3. At this time, the Z-direction control circuit 8 takes in the A / D-converted tunnel current data and performs feedback control using the data as information on the distance between the probe 2 and the sample S. The image data output unit 11 generates image data using the data packet received from the data bus 9,
An STM image is output to an image output device 12 such as a monitor. The XY scanning is performed by applying a control voltage output from the XY scanning control circuit 16 to a piezoelectric actuator attached to the stage 1. A series of operations are managed by the CPU 10, and the observation of the sample surface is performed by each operation.

Next, the specific operation of the STM image stationary mechanism will be described. First, a spatially changing position of a tunnel current signal, which is a detection signal, is effectively detected, and a detection area is set in order to perform feedback control. specify. The area window specifying unit 14 determines which part on the screen is to be a detection area, and sends information on the area position to the data extracting unit 13. The data extracting unit 13 extracts only the data in the area from the tunnel current data packet received from the data bus 9 and sends the data to the arithmetic unit 15. Arithmetic unit 15
As shown in the flowchart of FIG. 2, the data in the area are binarized (STEP1), spatial filter processing (STEP2), the signal change position, that is, the edge position is detected from the result (STEP3), and the movement amount is calculated. (STEP
4) and calculating the feedback amount (STEP 5), and finally adding the feedback amount to the output of the XY scanning control circuit 16 to stop the scanning area with respect to the sample surface.

The sample S used in this embodiment has a width of 200 nm as shown in FIG.
A groove T having a depth of 50 nm and an L-shape having a length of 1000 nm in length and width is used. The size of the scanning area SA is 2 μm square (the number of tunnel current data is 512 × 512)
X-direction detection area DAX, Y-direction detection area DAY
Are 250 nm square (tunnel current data number 64 ×
64). The sizes of the detection areas DAX and DAY need to be such that the position detection edges in the X direction and the X direction do not go outside due to drift by the next detection.

The data processing process in the arithmetic unit 15 of FIG. 1 will be described in detail with reference to the control flowchart shown in FIG. 2 and the actual calculation results. FIG. 4 shows image data that has been binarized by the arithmetic circuit, and is obtained by binarizing data in the detection area with a threshold current of 1 nA. The black portion indicates the inside of the groove (bit 0, the portion of observed current <threshold current), and the white portion indicates the outside of the groove (bit 1). The stationary control is performed by determining the boundary between the black and white as a groove edge and fixing the position by feedback control. FIG. 4 shows data of the detection area in the X direction. In this state, there are many isolated small points (noise) and the edge portions are unstable. The accuracy when the static control was performed with this image as it was was 20 to 30 nm.

Next, a two-dimensional filter was used for the purpose of stabilizing the binarized image. FIG. 5 shows data obtained by performing a two-dimensional filter process on the data of FIG. In practice, a method of determining the center bit by taking a spatial average with a data size of 3 × 3 is adopted. As a result, it can be confirmed that the isolated point is removed and the edge is stabilized as shown in FIG. In the static control performed using this filter, the accuracy is increased by several times to 5 to 8 nm.
It was confirmed that the effect of the filter was great.

Next, the method of calculating the amount of movement by the arithmetic unit 15 will be described. In calculating the amount of movement, first, a signal change position, that is, a groove edge position is detected, and the amount of movement is calculated from the difference between the position and a target value. Referring to FIG. 5, there is no white part in the right half black area, but there is a black (small signal) area in the left half white area (outside the groove). Therefore, attention was paid to the horizontal line, how much the black portion continued from the right end was measured, and the average of all horizontal lines at that position was determined as the edge position.

In this embodiment, the P control is used as the feedback control, and the difference between the center of the detection area, which is the target position, and the detection position is directly output as the feedback amount. However, it is also possible to use PID control or fuzzy control for more accurate and flexible control. For example, by using the PID control, the moving speed can be set as a control target for a slow movement having a long cycle such as a temperature drift, and more accurate control can be performed. In addition, by using fuzzy control, if the speed of returning to the deviation amount is controlled,
The time until stabilization can be greatly reduced. Furthermore, by combining them and devising a moving method, a more accurate image can be obtained. For example,
When moving the correction amount for one screen, not only the movement is performed one step at a time, but also the number of correction
By finely moving the moving amount for the screen in steps of several tens to several hundreds, it is possible to suppress the flow and distortion of the image with respect to a certain slow movement such as thermal drift.

In this embodiment, the stationary mechanism in the X direction has been described. However, by using the Y direction detection area DAY shown in FIG. 3, the edge position is detected and the position is controlled in the Y direction in the same manner as in the X direction. Thereby, the Y direction can be stopped.

Next, a second embodiment will be described.
In the first embodiment, it is necessary to artificially create a marker, but in the second embodiment, a part of an image actually observed can be used as a marker. The feedback mechanism is the same as that shown in FIG. 1 in the first embodiment. First, when specifying a detection area, an image of a size that can be completely included in the area or a part of the image is selected as a marker. FIG. 6 shows a process of binarizing the signal in the detection area (S
(STEP 11) and passed through a spatial filter (STEP 1).
2) shows things. As described above, the region (black portion) where the tunnel current is small forms a certain image, and has a size that is included in the detection area.

As shown in the flowchart of FIG. 7, the position of the center of gravity of this figure was obtained (STEP 13). And
The amount of movement is calculated from the change in the position of the center of gravity (STEP 14),
The feedback amount in the X direction is calculated (STEP 15) and the feedback amount in the Y direction is calculated (STEP 16). Then, by superimposing this feedback amount on a control signal input to the stage, the observation image is controlled so as not to move.

The method of calculating the center of gravity is as follows. First, 64 × 64 data shown in FIG. 6 is calculated in the vertical direction, the position GX of the horizontal line where the area is reduced to half is calculated. Find the position GY of the vertical line of. The position of the center of gravity (GX, GY) is obtained from the two positions, and the position is controlled in both the X and Y directions to match the target position, thereby stopping the STM image. When P control was performed with the target position as the center of the detection area, it was possible to simultaneously stop in both the X and Y directions with an accuracy of 2 nm.

According to this method, different from the first embodiment, by specifying one detection area, control can be performed simultaneously in both the X and Y directions. Also, there is no need to artificially create markers using a semiconductor process or the like. Although the detection area is specified by the operator, the power can be saved by automatically specifying the detection area by, for example, the CPU 10 in FIG. 1 such as a computer.

Although the above embodiment relates to an STM, the present invention relates to an apparatus for observing a sample by using another physical quantity between the sample and a probe, for example, an atomic force microscope (AF).
M) can also be applied.

FIG. 8 is a block circuit diagram showing a third embodiment applied to the AFM. In FIG. 8, the same members as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. In this embodiment, the probe 20 is a cantilever 2
1 supports the microscope body so as to be displaceable in the Z direction. A mirror 22 is mounted on the upper surface of the cantilever 21. This mirror 22 has a light source 2
The light beam from the light source 3 is incident thereon, and the reflected light of the light beam by the mirror 22 is received by a photodetector having a divided light receiving surface.

In the above configuration, when the probe 20 is brought very close to the sample S, an interatomic repulsion acts between them. In this state, when the sample S is moved in the X direction and the Y direction by the stage 1, the probe 20 is vertically displaced so as to trace irregularities on the surface of the sample S. The cantilever 21 is deformed with the displacement of the probe 20, and the light source 2
The angle of the mirror 22 with respect to the light beam from No. 3 changes. As a result, the spot of the reflected light moves on the light receiving surface of the photodetector 24. Therefore, the movement of this spot is detected by the photodetector 24.
Thus, the uneven shape of the surface of the sample S can be known. The movement of the spot of the reflected light can be detected by, for example, subtracting the output signals of the divided portions of the light receiving surface.

A signal corresponding to the structure of the sample S detected as described above is converted into a digital signal by the A / D converter 6, and thereafter, the image output and the scanning area are performed in the same manner as in the embodiment of FIG. Is corrected. That is, image data is generated by the image data output unit 11 from the data passed from the data signal generator 7 to the data bus 9, and an observation image is output by an image output device 12 such as a cathode ray tube (CRT). Is done.

On the other hand, of the data output from the data signal generator 7, data corresponding to the area specified by the area window specifying unit 14 is extracted by the data extracting unit 13 and sent to the arithmetic unit 15. The arithmetic unit 15 is shown in FIGS.
A correction signal for correcting the image shift is generated by the method described in the above section, and is fed back to the control signal input from the XY scanning control circuit 16 to the stage 1 through the D / A converters 17x and 17y. You.

As described above, even when the present invention is applied to the AFM, the shift of the observed image is prevented as in the case of the STM.
A stable observation image can be obtained.

[0029]

As described above, the scanning probe microscope according to the present invention and the method of observing a sample using the same are caused by a change in the relative position between the stage and the probe due to temperature change, vibration, piezo creep and the like. Since the drift of the STM image or the like can be eliminated, the same region can be observed for a long time. In particular, there is an advantage that movement of an image due to a temperature change immediately after the start of observation, relaxation of a mechanical system, or the like is suppressed, and observation can be performed in a stable state. Also, by detecting the signal change position by designating the area, if there is only a part of the screen that has little change over time, that part can be designated as the area. It can also be applied to observations with time-dependent changes such as the growth process of a metal thin film by MBE or MBE.

[Brief description of the drawings]

FIG. 1 is a block circuit configuration diagram of a first embodiment.

FIG. 2 is a flowchart of a calculation unit according to the first embodiment.

FIG. 3 is an explanatory diagram of a sample.

FIG. 4 is a pattern diagram of image data of an edge detection area according to the first embodiment.

FIG. 5 is a pattern diagram after passing through a spatial filter.

FIG. 6 is a diagram showing a binarized pattern after passing through a spatial filter according to the second embodiment.

FIG. 7 is a flowchart of a calculation unit according to the second embodiment.

FIG. 8 is a block circuit configuration diagram of a third embodiment.

[Explanation of symbols]

 Reference Signs List 1 stage 2, 20 probe 3 Z-direction driving means 4 power supply 5, 18 amplifier 6 A / D converter 7 data signal generator 8 Z-direction control circuit 10 CPU 13 data cut-out unit 15 arithmetic unit 16 XY scanning control circuit 17 D / A converter 21 Cantilever 23 Light beam 24 Photodetector

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihiko Yamano 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Miya ▲ Saki ▼ Toshihiko 3-30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc. (56) References JP-A-4-238202 (JP, A) JP-A-4-350503 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 21/00-21/32 G01B 7/00-7/34 102 G01N 37/00

Claims (2)

(57) [Claims] 1. A probe arranged opposite to a surface of a sample, scanning means for two-dimensionally scanning the surface of the sample with the probe, and detecting means for detecting a signal corresponding to the structure of the sample from the probe. And an output unit that outputs an observation image of the sample from the signal detected by the detection unit, wherein the observation image output from the output unit is detected by the detection unit so that the observation image output from the output unit does not shift. A scanning probe microscope, further comprising control means for controlling scanning by the scanning means based on a signal. 2. A two-dimensional scanning of the surface of the sample with a probe arranged opposite to the surface of the sample, a signal corresponding to the structure of the sample is detected from the probe, and a sample is detected based on the detected signal. In a method of observing a sample using a scanning probe microscope that obtains an observation image of, the scanning of the probe is controlled based on a signal detected from the probe so that the observation image of the sample does not shift. Observing a sample using a scanning probe microscope.