JPH11133038A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning probe microscope which can automatically adjust a servo-gain. SOLUTION: A Z fine adjustment signal of a probe 3 is input to a band pass filter 31 and an error amplifier 8 through a preamplifier 7. The band pass filter 31 extracts an oscillation frequency from the Z fine adjustment signal. The extracted oscillation frequency is smoothed at a square average detection circuit 32, converted to a digital signal and input to a D.S.P 14. The D.S.P 14 gradually increases a gain of a Z servo system from a default value and judges from a size of the digital signal whether or not the Z servo system oscillates. When the D.S.P judges that the Z servo system oscillates, the gain of the Z servo system is determined on the basis of a servo gain at the time. When an output of the error amplifier 8 exceeds a threshold value, the D.S.P 14 outputs a signal temporarily stopping an xy scan to an xy-scan circuit 16.

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, and more particularly, to automatically setting a servo constant (hereinafter referred to as "servo gain") of a Z servo system to a predetermined size that does not cause oscillation of the Z servo system. It relates to a scanning probe microscope that can be set.

[0002]

2. Description of the Related Art An example of a conventional Z servo system of a scanning probe microscope will be described with reference to a block diagram of FIG. A sample 2 to be observed is placed on a cylindrical piezo scanner 1. A cantilever 3 is provided above the sample 2. The amount of warpage of the cantilever 3 is output from a laser generator 4 and reflected by a laser beam 5 reflected from the back surface of the cantilever 3.
Is detected by detecting the incident position of The position detector 6 is composed of four divided photodetecting electrodes. For example, when the amount of warpage of the cantilever 3 is zero, the position of the laser beam 5 is aligned so as to be at the center of the four divided electrodes. ing. For this reason, when warpage occurs in the cantilever 3, the spot of the laser beam 5 becomes 4
Moving on the divided electrodes, a difference occurs in the voltage output from the four divided electrodes.

The output signal of the position detector 6 indicating the warp of the cantilever 3 is amplified by a preamplifier 7 and is output by an error amplifier 8
To one of the input terminals. At the other input terminal of the error amplifier 8, a reference value for the amount of warpage of the cantilever from a digital signal processor (hereinafter abbreviated as DSP) 14 is set. At times, the output of the error amplifier 8 is set to 0. The output of the error amplifier 8 is input to a proportional / integral circuit 9.

The proportional / integral circuit 9 is composed of a proportional circuit and an integral circuit connected in parallel.
The proportional circuit extracts the high frequency component of the output of the error amplifier 8 according to the servo gain (gain) set by
The integrating circuit averages the output. Then, after these outputs are combined, the output is converted into a drive voltage by the z high voltage driver 10 and applied to the z electrode of the piezo scanner.
The synthesized signal is A / D as an observation image signal.
Input to the converter 18. The signal converted into a digital signal by the A / D converter 18 is temporarily stored in a memory 19.
The CPU 20 reads out the data stored in the memory 19 at a predetermined timing, converts the data into image display data, and sends it to the image display 21. The image display 21 displays the surface shape of the sample 2.

The user manually sets the response speed of the servo system, the scan speed of the sample 2, and the like from the input / output device 22. The response speed of the servo system set by the input / output device 22 passes through the CPU 20 to the D.E. S. P14. S. At P14, the data is converted into specific response speed data, that is, servo gain. The servo gain is set in the gain setting device 15, and the proportional / integral circuit 9 operates according to the gain set in the gain setting device 15.

In addition, the input / output device 22 sets:
The scan speed such as “slow, slightly slow, normal, slightly fast, fast” is transmitted via the CPU 20 to the D. S. P14. S. At P14, the data is converted into specific x, y direction scanning time data. The xy scanning time data is sent to the xy scanning circuit 16 to generate an xy scanning signal. The xy scanning signal is converted into an xy driving signal by the xy high voltage driver 17 and applied to the xy electrodes of the piezo scanner.

[0007]

As is well known, the servo gain determines the response speed of the probe (cantilever 3). If the servo gain is too low, the probe cannot follow the surface of the sample 2 accurately, and data obtained by accurately tracing the surface shape of the sample 2 cannot be obtained. On the other hand, if the servo gain is too high, the servo system oscillates and the probe strongly hits the surface of the sample 2 to damage the probe. Therefore, it is necessary to set the servo gain high enough that the servo system does not oscillate.

Conventionally, the user gradually increases the servo gain from the input / output device 22 while looking at the screen of the image display, and when the sign of oscillation appears on the screen, lowers the servo gain somewhat to set the servo gain. I was trying to do it. As described above, conventionally, since the adjustment of the servo gain is performed manually, the adjustment is complicated, and there is a problem that the skill and skill of the user are required for the adjustment. When signs of the oscillation appear, vertical stripes are observed on the screen.

Conventionally, when a sample having a high height suddenly appears on the surface of a sample during xy scanning of the sample with a set servo gain, the probe may hit the projecting portion and be damaged. There was a problem that there is. SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning probe microscope which can eliminate the above-mentioned problems of the prior art and can automatically adjust servo gain. Another object is to provide a scanning probe microscope capable of achieving harmony between the servo gain and the scanning speed.

[0010]

In order to achieve the above object, the present invention relates to a scanning probe microscope having a Z servo system for controlling the operation of a probe for detecting a physical quantity on a sample surface. The first point is that oscillation detection means for detecting oscillation of the system and servo gain automatic setting means for automatically setting the servo gain of the Z servo system to a predetermined magnitude based on the output of the oscillation detection means are provided. There is a feature.

The present invention also provides means for detecting the amount of movement of the probe in a direction perpendicular to the surface of the sample, and means for detecting the amount of movement of the probe parallel to the surface of the sample when the amount of movement of the probe exceeds a predetermined threshold. A second feature is that a means for outputting a stop signal for xy scanning to the xy scanning means and a means for canceling the stop signal when the amount of movement of the probe becomes equal to or less than the threshold value are provided.

According to the first aspect of the present invention, since the servo gain is automatically set to a predetermined value, it is not necessary for the user to manually set the servo gain, and the operability of the apparatus can be improved. become able to. Also,
According to the second feature, when a large convex portion appears on the sample surface, xy scanning parallel to the sample surface can be temporarily stopped so that the probe does not hit the convex portion of the sample, Harmonization between the servo gain and the scanning speed can be achieved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. FIG. 1 differs from the configuration of FIG. 7 in that a bandpass filter 31, a root-mean-square detection circuit 32, and A / D conversion circuits 33 and 34 are added to the configuration of FIG. In addition, the code | symbol other than the above in FIG. 1 shows the same or the same thing as the thing of the same code | symbol in FIG.

FIG. 2 shows the output signal A of the preamplifier 7 of FIG.
FIG. In the figure, the horizontal axis indicates frequency, and the vertical axis indicates amplitude. The solid curve in the figure shows the signal spectrum when the servo system does not oscillate, and the dotted curve shows the signal spectrum when the servo system oscillates. In this figure, the frequency band of 0 to 1 kHz represents an image signal, and when the servo system oscillates, the frequency fr of several kHz increases as shown by the curve. The oscillation frequency fr depends on the size of the piezo scanner 1 and the like.

Therefore, the frequency pass band of the band-pass filter 31 shown in FIG. 1 is (fr ± α). Here, α is about 10% of fr. Next, the operation of the main part of the present embodiment will be described with reference to FIG. First, a gain setting circuit system, that is, a band-pass filter 31 → a root mean square detection circuit 32 → an A / D conversion circuit 33 →
D. S. P14 → gain setting device 15 → proportional / integral circuit 9
Will be described with reference to the flowchart of FIG.
FIG. S. It is a flowchart which shows the gain setting operation of P14.

First, from the input / output device 22, the CPU 20,
D. S. The default value of the servo gain of the servo system is set in the gain setting unit 15 via P14 (step S1). Then, D. S. P14 is the gain setting device 15
The servo gain S is gradually increased by ΔS at a time (step S2). At this time, the output signal of the preamplifier 7 is input to the band pass filter 31 and the error amplifier 8. The band-pass filter 31 extracts an oscillating signal in a frequency band of (fr ± α) from the output signal of the preamplifier 7 and sends the oscillating signal to a root-mean-square detection circuit 32. Mean square detection circuit 3
2 smoothes the oscillation signal and sends it to the A / D converter 33. The A / D converter 33 converts the smoothed magnitude of the oscillation signal into a digital signal. S. Send to P14.

Next, D. S. P14 determines whether or not a flag described later is set (step S3). If the determination is negative, it is determined whether or not oscillation has been recognized (step S4). This determination is made by the A / D converter 33
If the level of the signal from is higher than the initial value, it can be recognized that oscillation has occurred. When the determination in step S4 is negative, the process returns to step S2, and the operation of increasing the servo gain S by ΔS is performed.

The operations in steps S2 to S4 are repeated, and if the determination in step S4 is affirmative, D.D. S. P
14 stores the level L0 of the oscillation waveform (step S
5). Next, a flag is set (step S6), and the process returns to step S2. In step S2, after the servo gain S has been increased by ΔS and the process proceeds to step S3, this determination is affirmative, and it is determined whether or not the level L of the oscillation waveform is, for example, twice or more the level L0 immediately after the oscillation. Is performed (step S7). If the determination is negative, the process returns to step S2, and the servo gain S is increased by ΔS.

As a result of repeating the above operation, if the judgment in step S7 becomes affirmative, a value of, for example, 70% of the servo gain S at this time is obtained (step S8). Next, the 70% servo gain is applied to the gain setting unit 1.
5 is set (step S9). Finally, the flag is lowered (step S10). As described above, according to the present embodiment, the servo gain can be set high enough to prevent the servo system from oscillating.

Next, the scanning speed variable circuit system, that is, the error amplifier 8 → A / D converter 34 → D. S. P14 → xy
The operation of the scanning circuit 16 → xy high voltage driver 17 is shown in FIG.
This will be described with reference to FIG. FIG. S. A flowchart showing the operation of P14, and FIG. 5 shows the x scan voltage.
The adjustment of the scanning speed variable circuit is performed after the adjustment of the gain setting circuit is completed.

First, D. S. P14 instructs the xy scanning circuit 16 to perform xy scanning at the scanning speed input from the input / output device 22 (step S11). Next, A
It is determined whether the output of the error amplifier 8 digitized by the / D converter 34 has exceeded a certain threshold (step S12). If this determination is negative, step S1
Returning to step 1, the xy scanning is continued at the scanning speed input from the input / output device 22.

If the determination in step S12 is affirmative during the xy scanning, a scan stop signal is sent to the xy scanning circuit 16 (step S13). Next, it is determined whether or not the error output has become equal to or less than the threshold (step S14). If the determination is negative, step S13 is performed.
And continues to send a scanning stop signal to the xy scanning circuit 16. This corresponds to time t1 in FIG.

During the xy scanning stop period, step S14
When the determination is affirmative, the process returns to step S11 to perform xy scanning again at the scanning speed input from the input / output device 22. According to the control of the variable scanning speed circuit system, for example, as shown in FIG.
If the cantilever 3 performs x-scanning at the scanning speed input from the input / output device 22 in the case where there is a, the cantilever 3 collides with the convex portion 2a of the sample 2.
S. By performing the operation of step S13 in FIG. 4 by P14, it is possible to prevent the cantilever 3 from colliding with the convex portion 2a of the sample 2, and it is possible to obtain a high-precision observation image and to obtain a cantilever. 3 can be prevented from being damaged.

[0024]

As is apparent from the above description, according to the present invention, the servo gain of the Z servo system can be automatically set, and the operability of the apparatus is improved. Further, it becomes possible to set a servo gain of the Z servo system adapted to the apparatus, and it is possible to improve the accuracy of sample observation.

Further, according to the present invention, even if the sample has a large convex portion, the probe can accurately detect the shape of the convex portion. Further, the probe is prevented from being damaged by hitting the projection.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a drive circuit according to an embodiment of the present invention.

FIG. 2 is a spectrum diagram showing oscillation of a Z servo system.

FIG. 3 is a flowchart illustrating an operation of a gain setting circuit system according to the embodiment.

FIG. 4 is a flowchart illustrating an operation of the scanning speed variable circuit system according to the embodiment.

FIG. 5 is a diagram showing an x scan voltage obtained according to the present embodiment.

FIG. 6 is a conceptual diagram of x-scanning movement of a probe obtained according to the present embodiment.

FIG. 7 is a block diagram illustrating a configuration of a conventional driving circuit.

[Explanation of symbols]

 1 Piezo scanner 2 Sample 3 Cantilever 6 Position detector 7 Preamplifier 8 Error amplifier 9 Proportional / integral circuit 10 z High voltage driver 14 D. S. P (digital signal processor) 16 xy scanning circuit 17 xy high voltage driver 22 input / output device 31 band pass filter 32 root mean square detector 33, 34 A / D converter.

Claims (4)

[Claims] 1. A scanning probe microscope having a Z servo system for controlling an operation of a probe for detecting a physical quantity on a sample surface, wherein: an oscillation detecting means for detecting oscillation of the Z servo system; A scanning probe microscope comprising: servo gain automatic setting means for automatically setting a servo gain of the Z servo system to a predetermined value based on an output. 2. The scanning probe microscope according to claim 1, wherein said oscillation detecting means includes a band-pass filter for extracting an oscillation frequency of said Z servo system, and a smoothing means for smoothing an output of said band-pass filter. A scanning probe microscope comprising: 3. The scanning probe microscope according to claim 1, wherein the servo gain automatic setting means changes the servo gain of the Z servo system by a predetermined amount, and outputs the servo gain in response to the change in the servo gain. Means for confirming the oscillation of the Z servo system from the data of the oscillation detecting means, and means for determining the servo gain of the Z servo system based on the servo gain when the oscillation of the Z servo system is confirmed. Scanning probe microscope. 4. A scanning probe microscope having a Z servo system for controlling an operation of a probe for detecting a physical quantity of a sample surface, a means for detecting a movement amount of the probe in a direction perpendicular to the sample surface, Means for outputting a stop signal for xy scanning parallel to the sample surface to the xy scanning means when the amount of movement of the probe exceeds a predetermined threshold; and the amount of movement of the probe has become less than or equal to the threshold. Means for releasing the stop signal at times.