WO2002023159A1

WO2002023159A1 - Scanning probe microscope, method for measuring band structure of substance by using the microscope, and microscopic spectroscopy

Info

Publication number: WO2002023159A1
Application number: PCT/JP2001/007935
Authority: WO
Inventors: Koji Maeda; Akira Hida
Original assignee: Center For Advanced Science And Technology Incubation,Ltd.
Priority date: 2000-09-13
Filing date: 2001-09-13
Publication date: 2002-03-21
Also published as: JPWO2002023159A1; AU2001286215A1

Abstract

A novel apparatus/method for directly detecting a light-absorbing substance on the order of nanometers by using a scanning tunnel microscope (STM) probe. When the surface of a semiconductor where band bending (BB) occurs for some cause is irradiated with light of energy more than the bandgap width, generated photocarriers drift because of the electric field produced by the BB, thereby causing charge separation that lowers the BB. The decrease of the BB is called a surface photovoltage (SPV). If an SPV is produced in a specimen being observed by an STM, the PPV is effectively added to the bias voltage applied between the probe and the specimen, varying the tunneling current. If a modulator (12) modulates the surface electric field by modulating the bias voltage, this modulates the band structure. During the modulation, if light causing interband transition is continuously applied, the SPV produced by the light application varies synchronously with the electric field modulation. Therefore, if the amplitude of a tunneling current modulation signal as a function of the wavelength of continuous light is measured, a spectrum equivalent to that obtained by the ER (electro-reflectance) method widely used as means for examining the electronic structure of the band deep part.

Description

TECHNICAL FIELD Scanning probe microscope, method for measuring band structure of substance using the same, and microspectroscopy method

The present invention relates to a scanning probe microscope (SPM), a method for measuring a band structure of a substance using the same, and a microspectroscopy method. Instead of this, it relates to a new STM-EFMS (STM-Electric-Field Modulation Spectroscopy) that measures the tunnel current and significantly improves the spatial resolution. Background art

2. Description of the Related Art An apparatus for observing a sample surface using a tunnel current flowing between a probe and a sample (Scanning Tuning Microscopy, hereinafter referred to as "STM") is known.

The STM is a device that can detect information about the shape and electronic state of the sample surface using the electron tunneling phenomenon with a spatial resolution on the order of atoms, and in addition to its use as a microscope, a microfabrication device and information recording / playback Application to similar devices such as devices is possible.

The STM scans the sample surface with a pointed tip while controlling the distance by using the tunnel current generated when the distance between the tip and the sample is several nm or less as a servo signal to control the distance. Detected.

The conventional technology of STM will be described. FIG. 8 is a functional block diagram of the STM disclosed in Japanese Patent Application Laid-Open No. Hei 6-137810.

In FIG. 8, reference numeral 51 denotes a probe having a sharp tip, and reference numeral 52 denotes a sample arranged to face the probe 51. Numeral 53 denotes a probe control function, which scans the probe 51 in the XY-axis direction and moves it in the Z-axis direction by an XY scanning signal generating circuit (not shown). 54 is a bias circuit that applies a voltage between the probe and the sample, and 55 is a current-to-voltage converter that detects a tunnel current generated when the probe 51 and the sample 52 approach each other in a biased state and converts it into a voltage. Circuit, a logarithmic conversion circuit for further converting the converted voltage into a logarithm, and outputting the converted voltage; 57, a difference circuit for setting a desired tunnel current value as a set value and detecting a difference signal from an input; 59, a difference circuit A mouth-to-pass filter that removes the high-frequency component of the signal and outputs the top signal is a probe Z control signal generation circuit that forms a servo signal from the output of the LPF 59, and is used to control the probe control. Output to 53 to control the distance between the probe samples. Reference numeral 61 denotes a topo (Tbpograph image) signal output from a low-pass filter 59, 62 denotes a current signal output from a logarithmic conversion circuit 56, and a screen information signal. Used as a number.

When a bias is applied between the pointed probe 51 and the sample 52 by the bias circuit 54 and the probe 51 approaches the sample surface to near 1 nm, the tunnel current flows between the probe and the sample. Start flowing. This tunnel current is converted into a voltage by a current-to-voltage conversion circuit 55, and a difference signal from a desired set tunnel current value is detected by a difference circuit 57 through a logarithmic conversion circuit 56, and a low-pass filter 59, a probe A servo signal is formed through the Z control signal generation circuit 58. The servo signal is input to a probe control device 53 composed of a piezoelectric element or the like to control the distance, and at the same time, an XY scanning signal is input by an XY scanning signal generation circuit (not shown), and the XY scanning signal is input along the in-plane direction of the sample. By monitoring the top signal 61 formed through the difference circuit 57 and the low-pass filter 59 or the power signal 62 output from the current-voltage conversion circuit 55 while scanning, and performing image processing. Observed images reflecting the shape of the sample surface and the electronic state can be obtained.

By the way, it is known that when an electric field is applied to a crystal, the band tilts as shown in Fig. 9 and light absorption occurs even for photons with lower energy than the absorption edge due to the leaching of the wave function from the band edge (Franz -Keldish effect). Such deformation of the apparent band structure occurs at other than the absorption edge, and the electric field induces a vibrational change in the light absorption coefficient a as shown in Fig. 10 (a). By irradiating the electric field modulated surface with continuous light and measuring the modulated component of the light reflectance (light absorption coefficient) as a function of the sweep wavelength, the singular point of the band structure corresponding to the singular point as shown in Fig. 10 (b) was obtained. A sharp spectrum structure appears. I used this

The Electro-Reflectance = ER method and the Photo-Reflectance = PR method [DE Aspnes, Handbook on Semiconductors vol., Ed. By T, S. Moss (North-Holland, Amsterdam, 1980) p.109.] It is widely used as a means to study the electronic structure from to deep band.

Now, based on the same principle, it may seem that a method of locally modulating the electric field using the STM tip and performing microscopic ER measurement is possible. However, it is almost impossible to detect very small changes in macro reflected light in terms of S / N ratio. Disclosure of the invention

Therefore, an object of the present invention is to provide an apparatus / method capable of obtaining an extremely high spatial resolution by measuring the tunnel current instead of the intensity of the reflected light and increasing the S / N ratio by orders of magnitude. And This is the new STM-Electric-Field Modulation Spectroscopy (STM-EFMS) or SPM-EFMS (applicable to the type that can measure tunneling current even with a scanning probe microscope, for example, those with a conductive probe. is there). This device / method, for example, measures the band structure of a semiconductor at the nanoscale. It is used to detect changes in band structure due to defects in semiconductors directly at the nanoscale, and more generally to detect light-absorbing substances at the nanoscale.

As semiconductor devices become more complex and finer, foreign substances mixed in the device are detected with a resolution of less than 100 nm.- Identify and identify the desired composition.Whether or not the band structure is realized, and unexpected structures such as defects. The necessity of evaluating semiconductors in the manufacturing process, such as whether or not they exist locally, or the need to inspect semiconductors after manufacturing to find structural defects has increased.

The need for local band structure measurement includes, for example, measurement of the forbidden band width of each layer in semiconductor well structures and superlattices, evaluation of the blur of layer boundaries due to diffusion, and evaluation of distortion due to crystal defects.

Conventionally, there is a force luminescence method as a means for measuring such a local band structure, but the resolution is determined by the diffusion length of a small number of carriers, and is generally not as high as about 1 micron.

Conventionally, there is scanning tunneling spectroscopy (STS) as a means for measuring such a local band structure, and it is possible to measure nanoscale. However, the spectral shape of the STS depends sensitively on the state of the probe, and there is uncertainty in the interpretation of the measurement results, such as the energy position deviating from the true value. Also has the disadvantage that it is often difficult.

The present invention has been made in order to solve the above problems, and has a scanning probe microscope capable of measuring a semiconductor band structure on a nanoscale and directly detecting a foreign substance in a semiconductor on a nanoscale, and a substance using the same. It is an object of the present invention to provide a method for measuring the band structure of the above. Another object is to provide a novel nano-resolution microspectroscopy method.

A scanning probe microscope according to the present invention is configured such that a tip provided near a sample and a tunnel current generated when the tip approaches the surface of the sample are maintained at a constant level. A negative feedback controller that controls a distance between the probe and the sample; a light source; a spectroscope that extracts light of a predetermined wavelength from light emitted from the light source; and an output light of the spectroscope to the sample. Irradiating means for irradiating, surface electric field modulating means for modulating an electric field on the surface of the sample, and an amplifier for detecting and outputting the amplitude of the tunnel current by synchronizing with a modulation signal of the modulating means. Prepare.

The method for measuring the band structure of a substance according to the present invention comprises:

Irradiating the sample with light of a predetermined wavelength having energy equal to or greater than the forbidden band width,

Modulating the electric field on the surface of the sample;

Bringing a probe close to the sample, detecting and outputting the amplitude of the tunnel current by synchronizing the tunnel current with the modulation signal when the probe approaches the surface of the sample,

Detecting a band structure of a substance in the sample based on an amplitude of the tunnel current. I can.

The microspectroscopy method according to the present invention,

Modulating the electric field on the surface of the sample;

A step of repeating the above steps while scanning the wavelength of the light within a predetermined range; and a step of obtaining characteristics of amplitude and wavelength of the tunnel current. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a functional block diagram of the device according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart of the observation method according to the first embodiment of the present invention.

FIG. 3 is a functional block diagram of the device according to Embodiment 2 of the present invention.

FIG. 4 is a flowchart of the observation method according to the second embodiment of the present invention.

5, _c 6 is an example of EFMS spectrum measured by the apparatus / method according to the second embodiment of the invention, in EFMS scan Bae spectrum measured by the apparatus Z method according to the second embodiment of the present invention is there. Fig. 7 shows an EFMS image obtained by scanning the probe while fixing the wavelength to the band edge near the interface between the epi film and the substrate (Fig. 7 (a)), and an STM image recorded simultaneously (Fig. 7 (b)).

FIG. 8 is a functional block diagram of a conventional scanning probe microscope.

FIG. 9 is an explanatory diagram of the Franz-Keldish effect.

FIG. 10 is an explanatory diagram of the principle of electric field modulation spectroscopy (ER). BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the light-absorbing substance is referred to as “foreign substance” for convenience and used in the description.

FIG. 1 is a configuration diagram of an STM-EFMS (STM-Electric-Field Modulation Spectroscopy) according to an embodiment of the present invention.

Reference numeral 1 denotes an ultra-high vacuum scanning tunneling microscope (UHV-STM). The embodiments of the present invention can be applied to other than UHV-STM. For example, inert surfaces such as graphite can be measured in air and do not require high vacuum. Reference numeral 2 is a feedback circuit. The UHV-STM1 is the probe 51, probe control actuator 53 shown in FIG. 8 and the bias circuit 54 shown in FIG. It has a substantial part of them. The feedback circuit 2 includes the current-voltage conversion circuit 55, the logarithmic conversion circuit 56, the difference circuit 57, the probe Z control signal generation circuit 58, and the LPF 59 shown in FIG.

When the probe approaches the sample surface near 1 nm, a tunnel current starts to flow between the probe tf and the sample, and this tunnel current is controlled by the current-voltage converter, logarithmic converter, difference circuit, and LPF. Generates a feedback signal from the signal generation circuit and controls the position of the probe in the Z direction. An XY scanning signal is input by an XY scanning signal generation circuit (not shown), and a top signal, which is an output signal of the feedback circuit 2, is monitored while scanning along the in-plane direction of the sample, and the shape of the sample surface is obtained by performing image processing. Observed images reflecting the electronic state can be obtained.

Reference numeral 11 denotes a DC power supply for applying a bias voltage between the probe and the sample, and reference numeral 12 denotes a modulator for modulating the bias voltage with an appropriate amplitude and frequency.

Reference numeral 3 is a lock-in amplifier, reference numeral 4 is a white lamp as a light source, reference numeral 5 is a lens, reference numeral 7 is a monochromator for separating light of a specific narrow wavelength band from light of the white lamp 4, Reference numeral 8 denotes an optical fiber for guiding the light from the monochromator 7, and reference numeral 9 denotes a condenser lens for condensing the light emitted from the optical fiber 8 onto the sample 10. The lock-in amplifier 3 is an amplifier for performing synchronous detection with an external reference signal, and can detect and measure a signal modulated at the reference frequency from a very high noise level. The lock-in amplifier 3 takes in the tunnel current signal 1 using the modulated bias voltage as a reference signal and outputs it as a current amplitude signal.

The optical fiber 8 and the lens 9 in FIG. 1 may be replaced by an appropriate optical system for guiding light from the light source to the sample.

The device shown in Fig. 1 has a condensing optical system that condenses light of a specific wavelength on the sample 10, and takes in the tunnel current signal It as a reference signal using the modulated bias voltage and outputs it as an amplitude image signal. It differs from the conventional STM in that it has a lock-in amplifier 3. By providing a condensing optical system consisting of a halogen lamp 4, a lens 5, a monochromator 7, an optical fiber 8, and a condensing lens 9, a modulator 12 for modulating a bias voltage, and a lock-in amplifier 3, a sample ( Band structures in semiconductors, for example, can be detected directly at the nanoscale.

Next, the operation of the device in FIG. 1 will be described.

When a semiconductor surface that is band-bending (BB) for some reason is irradiated with light with energy greater than the forbidden band width, the generated photocarriers drift due to the electric field caused by the BB, causing charge separation that lowers the BB. . This decrease in BB is called surface photovoltage (Surface Photo Voltage = SPV). When an SPV occurs in the sample observed by the STM, the SPV is effectively added to the bias voltage applied between the probe and the sample, and the tunnel current changes. On the other hand, modulating the surface electric field in a suitable manner (for example, by modulating the bias voltage with a modulator 12 as shown in FIG. 1) will modulate the band structure. At this time, when the 起こす that causes transition between bands is continuously irradiated, the SPV generated by continuous light irradiation changes synchronously with the electric field modulation. Therefore, measuring the amplitude of the tunneling current modulation signal as a function of the wavelength of the continuous light yields a spectrum similar to ER (Electric Field Modulation = EFMS spectrum).

The procedure is shown in the flowchart of FIG.

S1: For example, in order to artificially induce surface band bending required for generation of surface photovoltaic force, a DC bias voltage having appropriate polarity and magnitude is applied between the probe and the sample.

S 2: Modulate the bias voltage. As a result, the sample surface electric field is synchronized with the bias, and thus the band structure changes in synchronization with the bias.

5 3: Continuously irradiate light causing inter-band transition. The generated SPV (Surface PhotoVoltage) changes in synchronization with the bias modulation.

5 4: Measure the amplitude of the tunneling current modulation signal as a function of the wavelength of the continuous light. More specifically, a current amplitude △ I obtained by lock-in detection of the modulated tunnel current waveform with a bias voltage is obtained.

S 5: Obtain a spectrum similar to ER (Electro-Reflectance) where a sharp spectrum structure appears corresponding to the singular point of the band structure.

S 6: Judgment of foreign substances

In the absence of foreign substances, the spectrum is uniform regardless of location. If there is a foreign substance, the spectrum is different from that around it. An actual measurement example will be described in the following second embodiment of the present invention.

Further, a two-dimensional distribution image of the current amplitude ΔΙ may be obtained. The process of step S3 is repeated while scanning the surface of the sample 10 to obtain a two-dimensional distribution image of the current amplitude ΔΙ. The presence or absence of foreign substances and their positions are determined by measuring the two-dimensional distribution image while fixing the wavelength to a certain appropriate wavelength.

As described above, according to the apparatus / method of Embodiment 1 of the present invention, the band structure (or foreign substance or structural irregularity 'defect) in a semiconductor can be directly detected on a nanoscale by using an STM tip. Can be. The conventional device / method has only a spatial resolution of about several Aims, but according to the first embodiment of the present invention, it is possible to detect with a much higher spatial resolution of 10 nm or less.

Further, according to the apparatus / method of the first embodiment of the present invention, a sample in which modulation band spectroscopy cannot be applied because surface band banding does not occur as in the case of a GaAs cleavage surface and SPV does not occur as it is. Surface band bending (Tip-induced) caused by tip-sample bias (Band Bending = TIBB) makes modulation spectroscopy possible. Embodiment 2 of the invention 2.

In the first embodiment of the present invention, the bias voltage of the probe is modulated in order to modulate the band structure. Instead, the sample is irradiated with monochromatic light (for example, laser light) having a gap energy or more and SPV ( (Not to be confused with continuous light-induced SPV, which plays an essential role in the embodiment of the present invention). This monochromatic light is intermittently irradiated to cause surface electric field modulation. This is the same as the Photo-Reflectance = PR method, in which the electric field modulation is uniform and the spatial resolution is achieved only by the detection system = tunnel current probe.

FIG. 3 shows a configuration example of the device according to the second embodiment of the present invention. The apparatus of FIG. 3 includes a second irradiation optical system including a chopper 6 instead of the modulator 12 of the bias power supply 11 of the apparatus of FIG.

In FIG. 3, reference numeral 4a is a white lamp as a first light source, reference numeral 5a is a lens, reference numeral 6a is a chopper for intermittently intermitting light beams, and reference numeral 7a is light from a white lamp 4a. 8a is a monochromator for separating light of a specific wavelength band from the light. Reference numeral 8a is an optical fiber that guides light from the monochromator 7a. Reference numeral 9a is the light emitted from the optical fiber 8a. This is a focusing lens for focusing light on the top. The lock-in amplifier 3 takes in the tunnel current signal 11 using the intermittent frequency signal f of the chopper 6 as a reference signal, and outputs it as a current amplitude signal.

The intermittent frequency of the illuminating light is set sufficiently higher than the response frequency of the feedback circuit that keeps the tunnel current constant, so that the modulation signal accompanying the light irradiation appears in the tunnel current.

The intermittent frequency of the irradiation light is set high enough to reduce the change in tunnel current due to thermal expansion and contraction of the probe caused by light irradiation.

According to the apparatus / method of the second embodiment of the present invention, there is an advantage that optical modulation spectrometry can be performed by artificially causing surface band bending (TIBB) by a probe-sample bias. In the embodiment of the present invention, an SPV is generated by irradiating a sample with monochromatic light having a gap energy or more, and the monochromatic light is chopped to cause surface electric field modulation. Further, the sample is irradiated with the separated continuous light, and the tunnel current modulation component ΔΙ is measured as a function of the irradiation light wavelength. For the sample, for example, a (110) cross section obtained by cleaving a homoepitaxial film grown on an n-GaAs substrate at a low temperature by ultra-high vacuum was used, and the sample bias voltage V _s > 0 was set to generate SPV. Measure at room temperature with TIBB induced. The procedure is shown in the flowchart of FIG.

S11: For example, a sample is irradiated with laser light to generate SPV (Surface Photo Voltage). The laser light is chopped to cause surface electric field modulation.

Note that monochromatic light obtained through the monochromator shown in FIG. 3 may be used instead of the laser light. Generally, any light having an energy greater than the band gap of the sample, including the laser, can be used here. However, it is desirable that the light be somewhat strong. On the other hand, too repeated strong and probe with the Chiyotsubi ring is the thermal expansion and contraction, in order to suppress this _c background of the scan Bae spectrum rises, the response of the thermal expansion of the modulation frequency as described above The frequency should be higher than the frequency (about 1 kHz).

S 12: Continuous irradiation with light that causes inter-band transition. As a result, the SPV additionally generated depending on the irradiation wavelength changes in synchronization with the electric field modulation.

S13: Measure the amplitude of the tunneling current modulation signal as a function of the wavelength of the continuous light. Specifically, a current amplitude ΔI obtained by performing a lock-in detection of the modulated tunnel current waveform with a bias voltage is obtained.

S14: Obtain a spectrum similar to PR (Photo-Reflectance) where a sharp spectrum structure appears corresponding to the singular point of the band structure.

S15: Determination of foreign substances

FIG. 5 shows an example of the EFMS spectrum measured with the probe fixed to the substrate. The background independent of photon energy is due to the intermittently irradiated laser light. Figure 5 clearly shows the band edge structure of GaAs split by spin orbit interaction. 6 is a EFMS scan Bae spectrum was measured by changing the sample bias voltage V _s. Signal with the increase in V _s becomes stronger, but the position of the band edge is not changed. Vibrational structures are also observed in the sub-band gap.

Fig. 7 shows a modulated signal image obtained by scanning the probe near the interface between the epi film and the substrate while fixing the wavelength to the band edge (referred to as EFMS image for convenience) (Fig. 7 (a)) And STM topographic images recorded simultaneously (Fig. 7 (b)). It can be seen that the contrast of the EFMS image is different due to the very disordered interface layer present at the interface. In Fig. 7 (a), contrast unevenness is observed in the interface layer. Part of the cause is that there is a place where the band gap E (measured by EFMS spectrum) is different from that of the substrate. It can be seen that the size of each unevenness is on the nanometer scale, and the spatial resolution of the EFMS image is extremely high.

In Fig. 6, the reason why the signal becomes stronger with an increase in V _s is as follows: increase in TIBB → increase in SPV modulation induced by intermittent light → increase in modulation of band structure → increase in current modulation width. Can understand well. The dynamic structure of the subband gear is similar to that often observed in the Hepi-epi film, but is usually attributed to the interference effect of the light reflected on the front and back of the film [N. Kallergi, B. Roughani , J. Aubel and S. Sundaram, J. Appl. Phys. 68, 04656 (1990)]. Whether the same explanation can be made by cross-section observation as in the embodiment of the present invention It is a future task including the cause of Red Shift.

STM-EFMS can be expected as a new method that has a wide range of applications, such as microscopic analysis of materials, in the sense that bandgap can be measured on a nanoscale.

This technique makes it possible to analyze the light energy absorption of various substances, and provides an unprecedented nano-resolution microspectroscopy.

In the above description, the case where the difference in the band structure due to the difference in the atomic arrangement structure is detected has been described as an example, but the first and second embodiments of the present invention are not limited to such an example. . For example, it is possible to identify biomolecules, chemical molecules, impurity atoms, etc. based on the light absorption wavelength. In addition, the bonding state and electronic state of atomic molecules can be measured on an atomic scale from the fine structure of the absorption spectrum. These features give STM, which has extremely high spatial resolution, an elemental analysis function that has never existed before.

The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the invention described in the claims, which are also included in the scope of the present invention. Needless to say,

Further, in this specification, means does not necessarily mean physical means, but also includes a case where the function of each means is realized by software. Further, the function of one means may be realized by two or more physical means, or the functions of two or more means may be realized by one physical means.

As described above, according to the novel STM-EFMS (STM-Electric-Field Modulation Spectroscopy) according to the present invention, the band structure of a semiconductor can be measured at a high resolution on the order of nm using an STM needle. The present invention, unlike so-called scanning tunneling spectroscopy (STS), can measure the deep structure of a band with high energy resolution and reliability and reproducibility. The present invention can be widely applied to, for example, semiconductor analysis. The present invention does not create the interpretive ambiguity of STS. Industrial applicability

This apparatus / method is applied to, for example, a semiconductor inspection apparatus.

Claims

The scope of the claims

1. A probe provided close to a sample, and a tunnel current generated when the probe approaches the surface of the sample is received between the probe and the sample so as to maintain the tunnel current constant. A negative feedback controller that controls the distance between the light source, a light source, a spectroscope that extracts light of a predetermined wavelength from the light emitted from the light source, an irradiation unit that irradiates the sample with the light emitted from the spectroscope, and the sample. Surface electric field modulation means for modulating the electric field of the surface of the sample, and an amplifier for detecting and outputting the amplitude of the tunnel current by synchronizing with a modulation signal of the modulation means. Light is a scanning professional with energy greater than the forbidden bandwidth.

—Microscope

2. The scanning probe microscope according to claim 1, wherein the irradiating means includes a condensing optical system for condensing light of a predetermined wavelength.

3. The scanning probe microscope according to claim 1, wherein the surface electric field modulation means includes a bias power supply for applying a bias voltage to the sample, and a modulator for modulating the bias voltage.

4. The surface electric field modulating means comprises: a second light source; an optical modulator for transmitting light emitted from the second light source at predetermined time intervals; and light having a predetermined wavelength from the light emitted from the second light source. 2. The scanning probe microscope according to claim 1, further comprising: a second spectroscope for extracting the light; and second irradiation means for irradiating the sample with light emitted from the second spectroscope.

5. The surface electric field modulating means includes: a laser that emits light having energy equal to or greater than the band gap of the sample; an optical modulator that transmits light emitted from the laser at predetermined time intervals; 2. The scanning probe microscope according to claim 1, further comprising: a second irradiating unit that irradiates the sample with the emitted light.

6. The surface electric field modulating means includes: a laser that emits light having energy equal to or greater than the forbidden band width of the sample; a power source that intermittently oscillates the laser at predetermined time intervals; 2. The scanning probe microscope according to claim 1, further comprising a second irradiating means for irradiating.

7. It is characterized by comprising a detecting unit for detecting a light absorbing substance in the sample based on the output of the amplifier. The scanning probe microscope according to claim 1, wherein

8. The scanning probe microscope according to claim 7, wherein the detection unit determines that the light absorption coefficient is subjected to electric field modulation when the tunnel current amplitude is larger than a normal tunnel current amplitude.

9. An image processing unit that generates a two-dimensional distribution image based on the output of the amplifier, wherein the detection unit determines that a light absorption coefficient of a high contrast portion in the two-dimensional distribution image is subjected to electric field modulation. The scanning probe microscope according to claim 7, wherein:

10. The scanning probe microscope according to claim 1, wherein the spectroscope scans the wavelength in a predetermined range.

11. irradiating the sample with light of a predetermined wavelength having energy equal to or greater than the forbidden band width; and modulating an electric field on the surface of the sample,

Detecting the band structure of the substance in the sample based on the amplitude of the tunnel current.

12. irradiating the sample with light of a predetermined wavelength having energy equal to or greater than the forbidden band width; and modulating an electric field on the surface of the sample,

A microspectroscopy method comprising: repeating the above steps while scanning the wavelength of the light within a predetermined range; and obtaining characteristics of the amplitude and wavelength of the tunnel current.