JP5759751B2 - Scanning tunneling microscope and nanoscale surface observation method using the same - Google Patents

Description

  The present invention relates to a scanning tunneling microscope and a nanoscale surface observation method using the same.

  The scanning tunneling microscope (hereinafter also referred to as “STM”) is attracting attention as one of the most useful tools in nanoscience. However, this method leaves room for improvement in time resolution. That is, the time resolution is limited by the response speed characteristics of the tunnel current readout circuit.

  As a means for solving this problem, a high-frequency scanning tunneling microscope (hereinafter also referred to as “RF-STM”) using a high-frequency measurement circuit has been proposed by Kemiktarak et al. (See Non-Patent Document 1). According to the high-frequency scanning tunneling microscope, it is expected that the time resolution can be improved by a factor of 100 compared to the state-of-the-art STM by using the relationship between high-frequency impedance matching and reflected wave amplitude in the LCR resonant circuit.

FIG. 1 shows a scanning tunneling microscope 101 proposed by Chemitarak et al. As a reference example. The scanning tunneling microscope 101 according to the reference example includes a tunnel resistance R _t between the sample mounting table 2 on which the sample 5 can be mounted and the probe 5 that is spaced from and opposed to the sample 5. A resonant circuit 100 including a coil L and a capacitor C connected to the probe 3, a directional coupler 12 connected to the resonant circuit 100, and a high-frequency signal is transmitted to the resonant circuit 100 via the directional coupler 12. A high-frequency input / output device 14 and a reflection measurement device 16 that receives a reflection signal from the resonance circuit 100 via the directional coupler 12 are included. Here, the distance between the sample 5 and the probe 3 is represented by n. A bias voltage may be applied to the sample mounting table 2. Although not shown, an actuator is disposed on either the probe 3 side or the sample mounting table 5 side. This actuator can be operated using an electrical signal from the controller 161 to control the relative distance between the probe 3 and the sample 5.

  The scanning tunnel microscope 101 further includes an input device 18 for inputting information to the reflection measuring device 16, and an output display device 20 for displaying the information obtained by the reflection measuring device 16 and the surface of the sample based on the information. . The reflection measuring device 16 includes a controller 161 that keeps the distance between the sample 5 and the probe 3 constant, and a feedback circuit 163 that sends a control signal to the controller 161.

  The principle of the tunnel resistance measurement method by impedance matching will be described with reference to FIG.

  In the system of FIG. 1, the reflection coefficient (amplitude ratio: Γ) at the resonance frequency is given by Equation 1.

Γ = | (Z _RLC -Z _s ) | / | (Z _RLC + Z _s ) | (Formula 1)
(In the formula, Z _RLC represents the impedance of the resonance circuit, and Z _s represents the signal source impedance.)
Power ratio of the logarithm used the reflection coefficient generally (dB units): becomes as follows if expressed in S _11.

S ₁₁ = 20log ₁₀ Γ = 20log ₁₀ (| (Z _RLC -Z _s ) | / | (Z _RLC + Z _s ) |) (Formula 2)
The impedance of the resonant circuit 100 is given by Equation 3.

Z _RLC = (Z _LC ) ² / R (Formula 3) where Z _LC = (L / C) ^1/2 (Formula 4)
If the values of L and C are fixed here, the impedance of the resonance circuit 100 depends on R. The reflection coefficient of the resonant circuit in FIG. 1 also depends on R.

Then treat the R as the tunnel resistance R _t between the probe and the sample in the scanning tunneling microscope.

And let _Rt be a constant value. Specifically, the distance n between the probe 3 and the sample 5 is feedback-controlled so that the reflection coefficient is always constant.

  The sample 5 is scanned while the distance between the sample 5 and the probe 3 is kept constant, and the feedback control output is imaged.

  As described above, the sample surface can be observed with the scanning tunneling microscope using the tunnel resistance instead of the tunnel current.

  However, the method of measuring tunnel resistance by Chemitarac et al. Has the following problems, and it has been difficult to put a high-frequency scanning tunneling microscope using this principle into practical use.

(1) The tunnel resistance was measured with sufficient sensitivity only in a relatively narrow region of several tens of kΩ to several hundreds of kΩ. For this reason, in the tunnel resistance measurement in the region of several MΩ to several hundred MΩ suitable for observation by STM, the amount of change in the reflected wave is small and sufficient sensitivity cannot be obtained. Even if it is applied to STM, the observation as STM is established in a very limited area where the distance between the probe and the sample is small (around 0.1 nm, where the tunnel resistance is several tens to several hundreds kΩ). ).

(2) In relation to (1), the effective dynamic range in tunnel resistance measurement is about one digit, which is very narrow compared with the dynamic range (3 to 4 digits) originally required in STM measurement. Since tunnel resistance varies exponentially with the distance between the probe and the sample, a wide dynamic range is required when applied to STM.

(3) The relationship between the tunnel resistance and the amount of high-frequency reflection was not monotonously increasing (decreasing). When the tunnel resistance is decreased from infinity, the amount of reflection at the resonance frequency decreases until the impedance of the resonance circuit matches perfectly with the signal source impedance. Then, the increase starts at the perfect matching point (= the point at which reflection is minimized). Therefore, when applied to STM observation, there is a problem that the feedback control operation becomes very unstable when the set point of the tunnel resistance (= distance between the probe and the sample) is close to the perfect matching point.

“Kemiktarak et al, Nature”, Volume 450 (November 2007), pp85-89

  The gist of the first object of the present invention is to provide a scanning tunneling microscope using tunnel resistance, which enables measurement of tunnel resistance with high sensitivity and good quantification over a wide dynamic range.

  The second object of the present invention is to enable stable feedback control in a scanning tunneling microscope using tunnel resistance.

  The gist of the third object of the present invention is to provide a nanoscale surface observation method using the above-described scanning tunneling microscope.

According to a first aspect of the present invention, there is provided a resonance circuit including a tunnel resistance between a sample and a probe that is spaced from and opposed to the sample, a matching resistance connected in parallel to the tunnel resistance, and the resonance circuit. A directional coupler, a high-frequency input / output device that transmits a high-frequency signal to the resonant circuit via the directional coupler, and a reflection measurement device that receives the reflected signal from the resonant circuit via the directional coupler, The matching resistor is a resistance value that approximates or matches the impedance of the resonant circuit and the impedance of the high-frequency input / output device, scans the sample while keeping the distance between the sample and the probe constant, and based on the tunnel voltage The gist is a scanning tunneling microscope characterized by observing the surface. Here, the scanning tunneling microscope may further include one of a microammeter and a high impedance voltmeter connected to the resonance circuit.

  The second aspect of the present invention includes a step of preparing a scanning tunnel microscope and placing a sample on a sample mounting table, a step of transmitting a high-frequency signal from a high-frequency input / output device to a resonance circuit via a directional coupler, In the reflection measurement device, it is confirmed whether the impedance of the resonance circuit and the signal source impedance match, and if they do not match, the step of adjusting the matching resistance so that they match, and the reflection measurement device The gist of the present invention is a nanoscale surface observation method having a step of grasping the unevenness state of the surface of the sample in terms of the locus of the tip of the probe.

  According to a third aspect of the present invention, a scanning tunneling microscope having a microammeter or a high impedance voltmeter is prepared, and a sample is placed on a sample mounting table, and a high frequency input / output device resonates via a directional coupler. Check whether the impedance of the resonant circuit and the signal source impedance match in the step of transmitting a high-frequency signal to the circuit and in the reflection measurement device. If they do not match, the matching resistance is set so that they match. A step of adjusting the surface of the sample by converting from the locus of the tip of the probe in the reflection measuring device, and a pseudo point contact diode formed by a tunnel gap between the probe and the sample The process of inputting the minute current generated by the rectifying action of the current into the minute ammeter through the low-pass filter and the value and polarity of the DC current generated by the rectifying action are mapped. A step of graying, and gist nanoscale surface observation method and a step of setting the amplitude of the input high-frequency signal to a sufficient amplitude to DC current.

  According to a fourth aspect of the present invention, there is provided a step of preparing a scanning tunnel microscope having a microammeter or a high impedance voltmeter and placing the sample on the sample mounting table, and the sample so that the entire sample is immersed in the electrolyte solution. The step of injecting the electrolyte solution into the mounting table, the step of transmitting a high-frequency signal from the high-frequency input / output device to the resonant circuit via the directional coupler, and the impedance of the resonant circuit and the signal source impedance in the reflection measuring device match. If the two do not match, adjust the matching resistance so that they match, and the surface roughness of the sample converted from the probe tip trajectory in the reflection measurement device And the step of inputting the electromotive force of the battery formed between the probe and the sample in the electrolyte solution to the high impedance voltmeter through the low-pass filter , The gist nanoscale surface observation method comprising the step of mapping the value and polarity of the DC voltage generated by the electromotive force of the battery.

  ADVANTAGE OF THE INVENTION According to this invention, the scanning tunnel microscope using a tunnel resistance which enables the measurement of a tunnel resistance with high sensitivity and sufficient quantification over a wide dynamic range is provided.

  According to the present invention, it is possible to perform stable feedback control in a scanning tunneling microscope using tunnel resistance.

  According to the present invention, a nanoscale surface observation method using the above-described scanning tunneling microscope is provided.

It is the schematic of the high frequency scanning tunneling microscope concerning a reference example. It is the schematic of the high frequency scanning tunneling microscope concerning embodiment. It is a simulation result of the resonance curve when there is a matching resistance. It is a simulation result of the resonance curve when there is no matching resistance. It is the relationship (simulation) of the logarithm of the tunnel resistance and the reflection coefficient (logarithm of power ratio) at the resonance frequency. It is the surface observation photograph of the graphite image | photographed using the high frequency scanning tunneling microscope concerning embodiment. It is the schematic of the high frequency scanning tunneling microscope concerning the modification 1 of embodiment. It is the schematic of the high frequency scanning tunneling microscope concerning the modification 2 of embodiment.

  Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the following embodiments. In addition, about what has the same function or a similar function in a figure, the same or similar code | symbol is attached | subjected and description is abbreviate | omitted.

[Scanning tunneling microscope]
FIG. 2 is a schematic diagram of the scanning tunneling microscope 1 according to the embodiment. The scanning tunneling microscope 1 according to the embodiment includes a tunnel resistance R _t between a sample mounting table 2 on which a sample 5 can be mounted and a probe 3 that is spaced from and opposed to the sample 5 and the sample 5. transmitting a resonant circuit 10 comprising a matching resistor R _m which is connected in parallel to the tunneling resistance R _t, a directional coupler 12 which is connected to the resonant circuit 10, a high-frequency signal to the resonant circuit 10 via a directional coupler 12 A high-frequency input / output device 14 that receives the reflected signal from the resonance circuit 10 via the directional coupler 12. In the resonance circuit 10, a coil L and a capacitor C are further connected to the probe 3. The distance between the sample 5 and the probe 3 is represented by n. As the matching resistor R _m , for example, a variable resistor or a semi-fixed resistor can be used. A bias voltage may be applied to the sample mounting table 2. Although not shown, an actuator is disposed on either the probe 3 side or the sample mounting table 5 side. The relative distance between the probe 3 and the sample 5 can be controlled by operating this actuator using an electrical signal from the controller 161. As the actuator, for example, an actuator including a piezoelectric element can be used.

The scanning tunnel microscope 1 further includes an input device 18 for inputting information to the reflection measuring device 16 and an output display device 20 for displaying the information obtained by the reflection measuring device 16 and the surface of the sample based on the information. . The reflection measuring device 16 includes a controller 161 that keeps the distance between the sample 5 and the probe 3 constant, and a feedback circuit 163 that sends a control signal to the controller 161. The controller 161 may be configured by an arithmetic device used in a normal computer system such as a CPU or a PLC (programmable controller).

  Examples of the input device 18 include a pointing device such as a keyboard and a mouse, or a TP (touch panel). Examples of the output display device 20 include an image display device such as a liquid crystal display and a monitor, and a printer. The output display device 20 may incorporate a storage device such as a ROM, a RAM, or a magnetic disk.

  First, the principle of the embodiment will be described below.

  In the system of FIG. 2, the reflection coefficient (amplitude ratio: Γ) at the resonance frequency is given by Equation 1.

Γ = | (Z _RLC -Z _s ) | / | (Z _RLC + Z _s ) | (Formula 1)
(In the formula, Z _RLC represents the impedance of the resonance circuit 10, and Z _s represents the impedance of the signal source (high-frequency input / output device 14).)
In a matching state where the value of the impedance Z _RLC of the resonant circuit 10 is very close to the value of the signal source impedance Z _s , the reflection coefficient is very sensitively affected by the impedance of the resonant circuit 10. The effect is very clear especially when attention is paid to the logarithm of the reflection coefficient. Therefore, if the resonant circuit 10 is brought into a matching state, it is possible to detect a very slight impedance change.

Then, treat the R in the resonance circuit 10 of FIG. 2, as a combined value when tunneling resistance R _t and matching resistor R _m are connected in parallel. Then, the value of R is expressed as shown in Equation 5.

R = 1 / (1 / R _t + 1 / R _m ) (Formula 5)
(In the formula, the values of L and C are fixed, and the value of R _t is infinite.)
At this time, the value of R _m is set to a value at which the impedance Z _RLC of the resonance circuit 10 and the signal source impedance Z _s completely match. For example, when L = 5 μH, C = 10 pF, and Z _s = 50Ω, the value of R _m is 10 kΩ.

When the tunnel resistance R _t is infinite (R _t = ∞), the resistance value of the matching resistance R _m is adjusted so that the reflection coefficient at the matching state, that is, the resonance frequency is minimized. Specifically resonance curve of the resonant circuit 10 adjusts the value of the matching resistor R _m as most deeper using a network analyzer or the like. In FIG. 2, a network analyzer having the function of the directional coupler 12 may be used as the directional coupler 12.

In the matching state, even if a very large tunnel resistance R _t is connected in parallel with R _{m and} the value of R slightly changes, the reflection coefficient from the resonant circuit 10 changes sensitively. Therefore, by bringing it into the matching state, it becomes possible to detect the change of the tunnel resistance due to the change of the reflection coefficient with extremely high sensitivity. On the other hand, when measuring changes in the reflection coefficient in a non-matching state as shown in FIG. 1, the change in reflection coefficient due to the change of R _t is much smaller than the matching state of FIG.

[Sample (semiconductor) surface observation method]
As a usage example of the scanning tunnel microscope 1 of FIG. 2, a method for observing the surface of a sample (semiconductor) will be described.

(A) A scanning tunneling microscope 1 having a configuration as shown in FIG. 2 is prepared. Then, a semiconductor is arranged as the sample 5 on the sample mounting table 2. Here, a bias voltage may be applied to the sample mounting table 2.

(B) A high frequency signal is transmitted from the high frequency input / output device 14 to the resonance circuit 10 via the directional coupler 12.

(C) The reflection signal reflected by the resonance circuit 10 is received by the reflection measuring device 16 via the directional coupler 12. Then, in the reflection measuring device 16, it is confirmed whether or not the impedance Z _RLC of the resonance circuit and the signal source impedance Z _s match.

(D) When the impedance Z _{RLC of the} resonance circuit and the signal source impedance Z _s do not match, the matching resistance R _m is adjusted so that they match.

(E) The controller 161 and the feedback circuit 163 are operated to scan the sample 5 while keeping the distance between the sample 5 and the probe 3 constant. At that time, the gain of the feedback circuit 163 is set to a value that does not cause oscillation while the locus of the probe 3 accurately reproduces the surface shape of the sample 5.

(F) In the reflection measuring device 16, the surface roughness of the sample 5 is grasped by converting from the locus of the tip of the probe 3. Then, the result is output to the output display device 20.

  As described above, according to the scanning tunnel microscope 1 according to the embodiment, the surface shape of the sample 5 is changed based on the tunnel resistance by scanning the sample 5 while keeping the distance between the sample 5 and the probe 3 constant. Can be observed.

  When there is no matching resistance as in the scanning tunnel microscope 101 of FIG. 1, the feedback direction (positive or negative sign) is reversed with the perfect matching point as a boundary. It is necessary to set the tunnel resistance set point to a point slightly larger than the matching point, and to set the feedback polarity so that the distance between the probe and the sample increases when the amount of high-frequency reflection decreases. . Consider a case in which the distance between the probe and the sample, that is, the tunnel resistance exceeds the perfect matching point and enters a smaller region due to vibration noise or the like. In this case, in the scanning tunneling microscope 101 of FIG. 1, the feedback direction is reversed as expected, and when the distance between the probe and the sample is reduced, feedback is applied in the direction of further reducing this, and as a result, the probe is attached to the sample. Will collide with. On the other hand, according to the scanning tunnel microscope 1 according to the embodiment, such a problem is solved.

  The procedure from (e) to (f) in the above description is an observation procedure in the tunnel resistance constant mode. Instead of the procedures from (e) to (f), it is also possible to perform observation in the constant height mode by the following procedures from (g) to (h).

(G) The controller 161 and the feedback circuit 163 are operated to scan the sample 5 while keeping the distance between the sample 5 and the probe 3 constant. However, the gain of the feedback circuit 163 is set to a value slightly larger than zero. The feedback gain in the constant height mode is set to a much smaller value than the feedback gain in the tunnel resistance _Rt constant mode. That is, in the constant height mode, the feedback circuit 163 is operated with a small gain so as to keep the average distance between the sample 5 and the probe 3 during scanning substantially constant. Therefore, in the constant height mode, the locus of the probe 3 does not need to accurately reproduce the shape of the sample surface.

(H) the reflection measuring device 16, and outputs the reflection coefficient of the resonant circuit 10 to an output display device 20, for mapping a tunnel resistance R _t.

As described above, according to the scanning tunneling microscope 1 according to the embodiment, by scanning over the sample 5 while maintaining an average distance between the sample 5 and the probe 3 constant, based on the tunnel resistance R _t sample 5 surfaces can be observed. According to the scanning tunneling microscope 1 according to the embodiment, it is possible to highly sensitive and measuring a good tunnel resistance R _t of quantitative over a wide dynamic range.

[Example]
To indicate the effect of the scanning tunneling microscope 1 according to the embodiment was simulated as follows under the conditions without or there is a matching resistor R _m. Figure 3 is a simulation result of the resonance curve of the resonant circuit 10 at the time of changing a tunnel resistance R _t when matching resistor R _m there. Figure 4 is a simulation result of the resonance curve of the resonant circuit 10 at the time of changing a tunnel resistance R _t in the absence of the matching resistor R _m. In all cases, L = 5 μH, C = 10 pF, and the value of R _m giving a matching state was 10 kΩ.

As shown in FIG. 3, if there is a matching resistor R _m, tunnel resistance R _t is the reflection coefficient at the resonance frequency in the range of several MΩ~ several hundred MΩ changes greatly. As shown in FIG. 4, if there is no matching resistor R _m, the change in reflection coefficient due to the change in tunnel resistance R _t was very small as compared with the case where there is a matching resistor.

  From the above, it was found that by inserting a matching resistor, the amount of reflection at the resonance point varies greatly depending on the tunnel resistance value in a wide region from 100 kΩ to 100 MΩ or more, and the detection sensitivity of the tunnel resistance is remarkably improved.

Figure 5 is a graph plotting the logarithm of the tunnel resistance (logarithm of the power ratio) reflection coefficient at the resonance frequency of each of the absence or when matching resistor R _m there. It was found that the tunnel resistance of several tens of kΩ to several hundred MΩ, which is important in actual STM observation, can be measured with high sensitivity in a wide dynamic range of 3 to 4 digits or more by inserting a matching resistor. It was also found that the dependence of the reflection coefficient on the tunnel resistance has a monotonically decreasing relationship with no peak.

  According to the embodiment, the problem of the possibility of collision due to reversal of the feedback direction when applied to the scanning tunnel microscope 1 is solved. In addition, the stability of control is greatly improved.

Furthermore, by inserting the matching resistor R _m , very good quantitativeness can be obtained in a wide range in the relationship between the tunnel resistance and the reflection amount. If those represent (reflected power / incident power) at the logarithmic (dB) units and S _11, S ₁₁ is expressed as follows.

S ₁₁ = -20log ₁₀ (R _t / R _m ) − 20 log ₁₀ (R _m / R _t +2) (Formula 6)
Here, when R _t is sufficiently larger than R _m , Equation 6 takes the form of Equation 7.

S ₁₁ = -20log ₁₀ (R _t / R _m ) -6 (Formula 7)
(It was treated as 20log ₁₀ 2 = 6.02 ≒ 6 in Equation 7.)
When R _t is sufficiently larger than R _m , the slope of the relationship between the reflection coefficient (logarithm) at the resonance frequency and the logarithm of the tunnel resistance is always constant regardless of the values of L, C, and Z _s , and the value of the matching resistance It can be seen that the value of the tunnel resistance is automatically determined if the value of the reflection coefficient is known. That is, the resonance circuit 10 with the matching resistor inserted can be used as it is as a tunnel resistance meter with high dynamic range and high accuracy.

  FIG. 5 shows the result of observing the atomic surface of graphite using the scanning tunneling microscope 1 of FIG. According to FIG. 5, it was shown that it can be observed in one atomic unit of graphite.

As described above, by adding a matching resistor R _m for impedance matching the resonant circuit 100 of FIG. 1, the sensitivity of interest in its application to the scanning tunneling microscope (STM), the dynamic range, the tunnel resistance - the reflection coefficient It was shown that all the dependent properties are resolved. In the practical application of RF-STM using the relationship between the tunnel resistance _Rt and the high-frequency reflection coefficient in the resonance circuit 10, the practical use of the scanning tunneling microscope 101 of FIG. The tunnel microscope 1 is expected to be put to practical use.

  Since RF-STM uses a high-frequency signal to detect the distance between the probe and the sample, scanning is much faster than a conventional scanning tunneling microscope (hereinafter also referred to as “DC-STM”) that measures tunneling current. Is possible. In DC-STM, since a very large feedback resistor is used for a minute current amplifier, the frequency band is limited, so that high-speed scanning is difficult. In DC-STM, only still images could be observed. However, using RF-STM makes it possible to acquire images at a video rate or higher. In addition, the RF-STM does not require a DC bias, which is essential in the conventional DC-STM. Therefore, it can also be used for observing samples that are destroyed, altered, or deteriorated by a DC bias.

  In RF-STM, the observation environment is not limited to the atmosphere, gas atmosphere, or vacuum, and may be in a liquid. Therefore, in addition to observing the surface of a semiconductor or metal (in the air or in a vacuum), it can be used, for example, for analysis of battery electrode materials in an electrolyte solution, analysis of metal corrosion processes, and analysis of electroplating processes.

  It is possible to apply a DC bias between the probe and the sample while performing control between the probe and the sample using a high-frequency reflected signal. The sample surface can be manipulated (manipulated) at the atomic level while observing the surface shape by controlling the polarity and voltage of the DC bias.

[Modification 1 of Embodiment]
The scanning tunneling microscope 1 according to the embodiment can extract a DC voltage or DC current signal from the probe 3 while performing control between the probe 3 and the sample 5 using a high-frequency reflected signal. Therefore, by combining with a high-impedance DC voltmeter, nanoscale surface potential measurement that can be observed simply and at the atomic level can be expected.

  FIG. 7 shows a modification (application example) 1 of the embodiment in which a resonance circuit 10a is connected to a high-pass filter 32 (hereinafter also referred to as “LPF”) 32 for blocking high-frequency components. 1 shows a scanning tunneling microscope 1a further comprising an impedance DC voltmeter or a microammeter 30. FIG.

  The semiconductor dopant distribution evaluation using the scanning tunneling microscope 1a will be described.

(A) A scanning tunneling microscope 1a having a configuration as shown in FIG. 7 is prepared. Then, a semiconductor is arranged as the sample 5 on the sample mounting table 2.

(B) Similar to steps (b) to (f) of the above-described embodiment, the distance between the probe 3 and the sample 5 is made constant so that the tunnel resistance between the probe 3 and the sample 5 is made constant. The surface of the sample 5 is scanned while being controlled.

(C) A micro-ammeter through a low-pass filter (LPF) 32 for a minute (DC) current generated by a rectifying action of a pseudo point contact diode formed by a tunnel resistance R _t between the probe 3 and the sample 5 Enter 30.

(D) Then, the value and polarity of the DC current generated by the rectifying action are mapped.

(E) The amplitude of the input high-frequency signal is set to an amplitude sufficient for generating a DC current.

  As described above, according to the scanning tunneling microscope 1a, non-contact and high-resolution dopant distribution can be evaluated. In the evaluation of the nanoscale dopant distribution on the semiconductor surface, the DC bias is basically set to zero. However, a minute bias voltage may be applied as necessary.

  To date, methods such as a scanning spreading resistance microscope (SSRM), a scanning capacitive microscope (SCaM), and a scanning Kelvin force microscope (KFM) have been used as methods for evaluating nanoscale dopant distribution on a semiconductor surface. However, the conventional method has various problems. For example, in SSRM, there are problems of plastic deformation and surface destruction of the sample because the conductive cantilever is strongly pressed against the sample. In addition, KFM has a problem that the measurement system is very complicated.

  However, according to the modification of the embodiment, the nanoscale dopant distribution on the semiconductor surface can be evaluated with a very simple measurement system.

  In FIG. 7, a high impedance voltmeter may be used instead of the minute ammeter 30. When a high impedance voltmeter is used instead of the microammeter 30, the voltage is input to the high impedance voltmeter. Then, by measuring and mapping the voltage value and polarity, the dopant concentration and type distribution can be visualized.

[Modification 2 of the embodiment]
FIG. 8 shows a scanning tunneling microscope 1b as a modification (application example) 2 of the embodiment.

  In the scanning tunneling microscope 1b, the sample mounting table 2 is replaced with a sample mounting table 2b having a reservoir, and the probe 3 is replaced with a probe 3b in a form in which the surface other than the tip is insulated and only the tip is exposed. Except for, a configuration similar to that of the scanning tunneling microscope 1a of FIG.

  The nanoscale battery electrode material evaluation using the scanning tunneling microscope 1b will be described.

(A) First, a scanning tunneling microscope 1b having a configuration as shown in FIG. 8 is prepared. Then, a battery electrode material is arranged as the sample 5b on the sample mounting table 2b. The electrolyte solution 35 is injected into the sample mounting table 2b so that the entire sample 5b is immersed in the electrolyte solution 35. Further, the tip portion of the probe 3 b is immersed in the electrolyte solution 35. In the electrolyte solution 35, a battery is formed between the probe 3b and the sample 5b.

(B) The surface of the sample 5b is scanned while the distance between the probe 3b and the sample 5b is controlled to be constant so that the tunnel resistance between the probe 3b and the sample 5b is constant in the electrolyte solution 35.

(C) A DC voltage generated by the electromotive force of the battery formed between the probe 3b and the sample 5b is input to the high impedance voltmeter 30b through the low-pass filter (LPF) 32b.

(D) Then, the value and polarity of the DC voltage generated by the electromotive force of the battery are mapped.

As described above, according to the scanning tunneling microscope 1b, the nanoscale electromotive force and the surface shape of the battery electrode material can be simultaneously evaluated.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, it is possible to provide a surface observation system for a sample that includes the scanning tunnel microscopes 1 and 1a described in the embodiments. In addition, it is possible to provide a semiconductor manufacturing method including the steps of the sample surface observation method using the scanning tunneling microscopes 1 and 1a described in the embodiment.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

1, 1a, 1b, 101 scanning tunneling microscope 2,2b specimen table 3,3b probe 5,5b sample L coil C capacitor R _t tunneling resistance R _m matching resistor 10, 10a, 10b resonant circuit 12 the directional coupler 14 High-frequency input / output device 16 Reflection measuring device 30 High impedance voltmeter or microammeter 32 Low-pass filter (LPF)

Claims (8)

A resonant circuit including a tunnel resistance between a sample and a probe disposed oppositely to the sample and a matching resistor connected in parallel to the tunnel resistance;
A directional coupler connected to the resonant circuit;
A high-frequency input / output device that transmits a high-frequency signal to the resonant circuit via the directional coupler;
A reflection measuring device that receives a reflected signal from the resonant circuit via the directional coupler;
The matching resistor is a resistance value that approximates or matches the impedance of the resonant circuit and the impedance of the high-frequency input / output device,
A scanning tunneling microscope characterized by scanning the sample while maintaining a constant distance between the sample and the probe and observing the surface of the sample based on tunnel resistance.   The scanning tunnel microscope according to claim 1, further comprising one of a high impedance voltmeter and a microammeter connected to the resonance circuit.   The scanning tunneling microscope according to claim 1 or 2, wherein the scanning tunneling microscope is used for nanoscale observation of the sample surface.   The scanning tunneling microscope according to claim 1 or 2, wherein the scanning tunneling microscope is used for evaluation of nanoscale electromotive force measurement of a battery material in an electrolyte solution.   The scanning tunneling microscope according to claim 1 or 2, wherein the scanning tunneling microscope is used for observing a dopant distribution on a semiconductor surface. Preparing the scanning tunneling microscope according to claim 1 and arranging the sample on the sample mounting table;
Transmitting a high-frequency signal from the high-frequency input / output device to the resonance circuit via the directional coupler;
Checking whether the impedance of the resonance circuit and the signal source impedance match in the reflection measurement device, and if both do not match, adjusting the matching resistance so that they match,
A method for observing the surface of a sample by converting from the locus of the tip of a probe in a reflection measuring device. Preparing the scanning tunneling microscope according to claim 2 and arranging the sample on the sample mounting table;
Transmitting a high-frequency signal from the high-frequency input / output device to the resonance circuit via the directional coupler;
Checking whether the impedance of the resonance circuit and the signal source impedance match in the reflection measurement device, and if both do not match, adjusting the matching resistance so that they match,
In the reflection measurement device, converting from the tip trajectory of the probe to grasp the surface roughness of the sample,
Inputting a minute current generated by a rectifying action of a pseudo point contact diode formed by a tunnel gap between a probe and a sample to a minute ammeter through a low-pass filter;
Mapping the value and polarity of the DC current generated by the rectifying action;
And a step of setting the amplitude of the input high-frequency signal to an amplitude sufficient for generating a DC current. Preparing the scanning tunneling microscope according to claim 2 and arranging the sample on the sample mounting table;
Injecting the electrolyte solution into the sample mounting table so that the entire sample is immersed in the electrolyte solution;
Transmitting a high-frequency signal from the high-frequency input / output device to the resonance circuit via the directional coupler;
Checking whether the impedance of the resonance circuit and the signal source impedance match in the reflection measurement device, and if both do not match, adjusting the matching resistance so that they match,
In the reflection measurement device, converting from the tip trajectory of the probe to grasp the surface roughness of the sample,
Inputting the electromotive force of the battery formed between the probe and the sample in the electrolyte solution to a high impedance voltmeter via a low-pass filter;
A nanoscale surface observation method characterized by mapping a value and polarity of a DC voltage generated by an electromotive force of a battery.