JP2001050934A - Scanning squid microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection accuracy by preventing as much as possible unwanted pseudo-signals from being superposed on a magnetic distribution. SOLUTION: A scanning squid microscope is provided with a laser light application means 20 for applying a laser beam to an observation target W retained at a stage 10, and supplying an excitation energy to the observation target W, a laser light application position traveling means 40 for relatively moving the position of the observation target W for an application point P on the observation target W of the laser beam, a squid magnetic field detection means 50 for detecting the change in a weak magnetic field being induced from the observation target W by the applied laser beam, while being equipped with a superconducting pickup coil 51 and a squid 52, and a control part 60 with an imaging means 62 for displaying the state of the observation target W as an image based on a detection result from the squid magnetic field detection means 50, thus fixing the relative positions of the application point P of the laser beam being applied from the laser beam application means 20 and the pickup coil 51 of the squid magnetic field detection means 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning squid microscope as a magnetic microscope, and more particularly, to irradiating a converged laser beam onto a surface of an object to be observed to detect a change in a magnetic field induced thereby. SQUID: Superco
nducting Quantum Interferer
ence device (superconducting quantum interference device) to measure and image the induced magnetic field distribution, which reflects various physical characteristics of the observation target, in a non-contact, high spatial resolution, and high sensitivity manner, and image it. About.

[0002]

2. Description of the Related Art A scanning squid microscope of this type is a scanning microscope which irradiates an object to be observed with a laser beam and measures a physical state attributable to a magnetic change in the irradiated area with the squid. . This is considered as an improved type of low-temperature SEM, and is considered to be applied to the study of physical properties by imaging changes in magnetization characteristics of superconducting materials and magnetic materials due to temperature changes. Conventionally, this type of scanning squid microscope has been disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 5-24920.
No. 9 is known. As shown in FIG. 15, the scanning squid microscope
Is held on the stage 1, and the observation object W is irradiated with laser light from the laser light irradiation unit 2 to supply excitation energy to the observation object W. The stage 1 is moved by the stage moving means 3 in the Ma direction in FIG. Object W
The upper irradiation point P (focal point) is moved, and is induced from the observation target W by the pickup coil 4 wound around the stage 1 and the squid magnetic field detecting means 5 having the squid (not shown) in this movement path. A weak change in the magnetic field is detected, and the state of the observation target W is displayed as an image on the display unit 7 by the control unit 6 based on the detection result from the squid magnetic field detection unit 5. In the above-mentioned Japanese Patent Application Laid-Open No. 5-249209, laser light is applied as shown in FIG.
There is also disclosed a technique of moving the irradiation point P on the observation target W relatively by moving the irradiation point P in the middle Mb direction.

[0003]

By the way, in the conventional scanning squid microscope, the pickup coil 4 connected to the squid is arranged in a simple direction arranged so as to surround the whole object W to be observed. The surface of the observation object W, which is a wound coil and is inside the pickup coil 4 having a large area, is scanned and imaged by laser light by moving the stage 1 together with the pickup coil 4 by the stage moving means 3. Therefore, the positional relationship between the pickup coil 4 and the beam irradiation point P is relatively moved by scanning, and the relative movement between the pickup coil 4 and the beam irradiation point P adversely affects the detection accuracy. There was a problem that it had. The reason is that when the irradiation point P moves in the coil 4 having a finite cross-sectional area, the magnetic flux crossing the pickup coil 4 changes depending on the observation position. That is, the magnetic field is generated around the irradiation point P and continuously distributed to infinity, whereas the coil 4 having a finite area cannot collect all the magnetic flux. Further, even when the laser light itself is moved, there is a similar problem because the relative movement between the pickup coil 4 and the irradiation point P occurs.

That is, an unnecessary pseudo signal resulting from scanning is superimposed on the magnetic field distribution reflecting the physical characteristics of the observation object W. To minimize this effect, even if a very large pickup coil is used and a relatively small area is scanned near the center of the pickup coil, the size of the pickup coil increases, External magnetic noise other than the object W becomes easy to be picked up, and in addition, the volume required for cooling in order to maintain the pickup coil in the superconducting state is increased, resulting in an increase in the size of the apparatus and deterioration in cooling efficiency. . In particular, when a high-temperature superconducting squid is used, the connection of the high-temperature superconductor is very difficult. Was hindered. In addition, the conventional type uses a simple primary coil, does not perform spatial filtering of signal and noise, and can be pointed out that it is vulnerable to disturbance noise. In some cases, only the scalar measurement of the magnetic field in the direction was possible, and the vector and the direction and strength of the magnetic field could not be measured.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a scanning squid microscope which improves detection accuracy by preventing unnecessary pseudo signals from being superimposed on magnetic distribution as much as possible. And If necessary, the pickup coil can be reduced in size, the cooling efficiency can be improved, it can be applied to high-temperature superconducting squid, it is resistant to disturbance noise, and the vector of the magnetic field from the observation target can be detected. Issues were also addressed.

[0006]

In order to achieve the above object, a scanning squid microscope according to the present invention comprises, as shown in FIG. 1, a stage 10 for holding an observation object W, and a stage 10 for holding the observation object W. A laser light irradiating means 20 for irradiating the observation object W with laser light and supplying excitation energy to the observation object W, and an irradiation point on the observation object W of the laser light emitted from the laser light irradiating means 20 A laser light irradiation position moving means 40 for relatively moving the position of the observation object W with respect to P; a superconducting pickup coil 51 and a squid 52;
The object W to be observed by the laser light
Magnetic field detecting means 50 for detecting a small change in the magnetic field induced from the image, and an imaging means for displaying the state of the observation target W as an image on the display unit 61 based on the detection result from the squid magnetic field detecting means 50 Control unit 6 having 62
In the scanning type squid microscope provided with 0, the relative position between the irradiation point P of the laser light irradiated from the laser light irradiation means 20 and the pickup coil 51 of the squid magnetic field detection means 50 is fixed.

First, the basic principle of the scanning squid microscope having such a configuration will be described. FIG.
As shown in (1), first, a laser beam is focused and irradiated on an observation target (sample). As the observation target, those that absorb laser light are suitable, for example, semiconductors, ceramics,
Efficiency is high because a magnetic material or the like has good laser light absorption.
Observation of organic substances (living organisms) can be made by reducing the laser power, and observation of metals can be made by increasing the laser power. When an object to be observed is irradiated with laser light, energy conversion occurs within the penetration length of the laser light. Many observation objects are converted into thermal energy and the focal point temperature rises. In the case of a semiconductor or the like, a charge may be generated by photoelectric conversion and a diffusion current may be generated due to a concentration gradient, or a drift current may be generated in a depletion layer having an internal electric field and directly converted to a current. In this way, light is converted into heat or electric energy,
As a result, a change in magnetic spin and generation of current occur. As a result, the magnetic flux generated from the observation target,
A subtle change is caused in the magnetic flux passing through the observation target, and the change is measured by a squid, and a magnetic signal reflecting the physical characteristics of the surface of the observation target is obtained. And
By sequentially scanning the laser irradiation position, a magnetic signal is imaged.

The laser light irradiation means 20 supplies excitation energy to the observation object W by temporally modulating the intensity of the laser light, which is not directly induced by the magnetic field as the observation physical quantity, and irradiating the observation object. . In this state, when the laser light irradiation position moving means 40 scans by moving the observation target W relatively to the irradiation point P of the laser light, the squid magnetic field detection means 50 causes the observation target W to be irradiated with the laser light. A small change in the magnetic field induced by W is detected with high sensitivity. In this case, since the position of the superconducting pickup coil 51 is fixed at a fixed position from the irradiation point P of the laser beam, a pseudo signal due to scanning is not generated. Then, the state of the observation target object W is displayed as an image on the display unit 61 by the imaging unit 62 of the control unit 60 based on the detection result from the squid magnetic field detection unit 50.

Here, the process of inducing a change in magnetic flux due to laser irradiation and its imaging process will be described with some examples. First, the case where heat is interposed will be described. As a first example, a case where the observation target is a magnetic material will be described with reference to FIG. When the laser light is focused on the surface of the observation target, the temperature rises. Accompanying this, the disturbance of the spin of the magnetic material increases and the magnetization decreases. In the case of an observation object having a large coercive force and having spontaneous magnetization, observation is possible without a bias magnetic field. On the other hand, in the case of a soft magnetic material having a small coercive force, by applying a bias magnetic field, it becomes possible to observe a change in magnetic permeability due to a temperature rise. As a second example, there is a gradient of the charge density due to the temperature gradient, which causes a current to flow (Seebeck effect) (not shown). By observing the magnetic flux induced by the current with a squid, it becomes possible to image the distribution of the Seebeck coefficient. It is effective for inspection of semiconductors and ceramics.

A third example is imaging of the thermal conductivity, specific heat, and specific gravity of an object to be observed. For example, as shown in FIG. 4, if there are minute cracks, crystal grain boundaries, etc., the thermal conductivity is reduced, so that the portion becomes unique, and a magnetic image reflecting these is obtained. In the case of the above three examples, the position where the magnetic flux changes can be limited if the signal source is within the thermal diffusion length slightly larger than the laser diffraction limit, so that the spatial resolution is higher than that of the conventional SQUID microscope. Can be greatly improved. As an effect of the method caused by heat, an elastic wave may be further interposed. As a fourth example, a mechanism for inducing a change in a subsurface magnetic field as shown in FIG. 5 will be described. When the laser beam is irradiated, the temperature rises and the volume expands locally. The change in volume generates an elastic wave (sound wave). When a local mechanical stress is applied, a change in magnetization or a change in magnetic permeability occurs. FIG.
(A) is a case where there is no portion having a different acoustic impedance, and the elastic wave propagates symmetrically. On the other hand, in FIG. 5B, since there are portions having different acoustic impedances, the wavefront of the elastic wave is distorted. Accordingly, the distribution of the magnetic flux changes. This makes it possible to inspect not only the extreme surface but also the state below the surface.

Next, a case where no heat is interposed will be described. For example, in the case where a laser beam is directly converted into a current, such as a semiconductor junction, the magnetic flux generated by the current can be observed with a squid. Further, even when the current is relaxed inside and it is difficult to make the carriers reach the external electrodes, the scanning type SQUID microscope of the present invention can measure the local change in the magnetic flux of the internal current. Typical examples of such an observation target include a thin-film solar cell and a semiconductor integrated circuit shown in FIG. 6, which are effective for inspection thereof. For example, in a portion where the photoelectric conversion efficiency is reduced due to a defect, the amount of generated electron-hole pairs is small, so that the current is small and the observed magnetic field is small. By observing the magnetic field generated locally, the dispersion of the internal resistance and the influence of the contact resistance of the electrode are hardly affected, and the original characteristics can be observed as compared with the evaluation by the external current. Although an external voltage is applied in FIG. 6, it is not always necessary, and the inspection can be performed by a magnetic field generated by an internal diffusion current.

In the scanning squid microscope according to the present invention, the laser beam irradiation position moving means is constituted by a function of moving the stage as required.
Further, if necessary, the squid magnetic field detecting means is provided with a heat insulating case which covers the pickup coil and the squid and isolates the temperature transmission between the pickup coil and the squid and the object to be observed. The insulating case can keep the squid and the pickup coil at a cryogenic temperature that is in a superconducting state by isolating the temperature of the squid magnetic field detecting means and the temperature of the observation target, and maintain the temperature of the observation target at an arbitrary temperature. And acts to minimize cooling energy.

[0013] Further, if necessary, the control unit may control the timing of temporally modulating the intensity of the laser beam from the laser beam irradiating unit, the timing of extracting the output signal from the squid magnetic field detecting unit, The laser light irradiation position moving means is provided with a synchronous control means for synchronously controlling the timing at which the position of the observation object is relatively moved. Synchronously control the three timings,
The noise and the signal are separated in the time domain to improve the S / N ratio, and also act to detect a signal generated at a desired place of the observation target. Furthermore, the imaging means of the control unit is induced by the laser irradiation in such a manner that the moving distance of the observation target corresponds to the pixel position and the output of the squid magnetic field detecting means at the pixel position corresponds to the pixel density or color tone. It has a function of imaging as a weak magnetic field distribution.

If necessary, the pickup coil of the squid magnetic field detecting means may be of a differential type having a plurality of coil bodies having a neutral axis from which no detection signal is output, and the pickup coil having the neutral axis of the laser. It is arranged at a position deviated from the light irradiation point, so that the differential balance is changed by the change of the magnetic flux induced by the laser light. The differential type pickup coil cancels magnetic signals coming from afar,
It becomes sensitive only to the magnetic signal coming from the vicinity which is the irradiation point (focal point) of the laser light, works as a spatial filter, and improves the S / N ratio. Further, if necessary, the above-mentioned squid magnetic field detecting means is constituted by providing three or more pairs of pickup coils and squids, and each of the pickup coils has a detection axis perpendicular to its coil surface orthogonal to one intersection, and , The intersection of the detection axis of each pickup coil is symmetrically arranged so as to coincide with the irradiation point of the laser beam, and the squid magnetic field detection means can simultaneously detect both the intensity and the direction of the magnetic flux as vectors. . The squid magnetic field detecting means can vector-detect the intensity and direction of the magnetic field generated from the irradiation point of the laser beam at a point where the detection axis of the pickup coil is orthogonal.

Further, if necessary, a replaceable transparent plate for intercepting the scattered object from the observation object is interposed in the irradiation path of the laser light from the laser light irradiation means. The transparent plate prevents scattered objects and the like from the surface of the observation object due to laser light irradiation from reaching the surface of the objective lens, and prevents laser energy loss and increase in aberration due to contamination of the lens surface. Also, if necessary,
The control unit includes a bias magnetic field generating unit that applies a bias magnetic field to the observation target from outside.
The bias magnetic field generating means applies a weak bias magnetic field to the object to be observed, and makes it possible to observe a change in magnetic permeability due to laser beam irradiation. Further, if necessary, the control unit includes signal processing means for performing signal processing in the time domain by time differentiation and / or time integration of the output of the squid magnetic field detection means. The signal processing means in the time domain works to convert the measured data into data reflecting the physical state of the observation target object by integration or differentiation processing. Furthermore, if necessary, the control unit is configured to include signal processing means for performing signal processing in the frequency domain on the output of the squid magnetic field detection means by Fourier transform. The signal processing means in the frequency domain uses a signal that matches the laser irradiation frequency as measurement data and separates the signal from other noise.
Further, if necessary, the control unit may repeatedly irradiate the observation target with laser light with an output in a range in which the state of the observation target by the laser irradiation is reversible, and use the irradiation timing as a reference signal to set the It is provided with lock-in detecting means or box car detecting means for detecting an output signal of the detecting means. The lock-in detecting means or the box car detecting means separates a signal component and a noise component in a time domain to improve an S / N ratio.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning squid microscope according to an embodiment of the present invention will be described below in detail with reference to the accompanying drawings. Note that the same components as described above are denoted by the same reference numerals and described. 1 and 7 show a scanning squid microscope according to an embodiment of the present invention. In this scanning squid microscope, reference numeral 10 denotes a stage for holding the observation target W, which is made of, for example, a non-magnetic material made of ceramics and moves the observation target W. Reference numeral 20 denotes a laser light irradiation unit that irradiates the observation target W held on the stage 10 with laser light from below and supplies excitation energy to the observation target W. In the laser light irradiating means 20, reference numeral 21 denotes a laser light generation source capable of generating a laser light in a pulse shape, reference numeral 22 denotes an ND filter for adjusting the light intensity of the laser light generated from the laser light generation source 21, and reference numeral 23 denotes an intensity of the laser light. An acousto-optic device that modulates and is driven by an acousto-optic device driver 24. Reference numeral 25 denotes a half mirror that transmits laser light from the acousto-optic element 23 and reflects reflected light from the observation target object W toward a half mirror described later.
A mirror that reflects the laser light that has passed through the mirror 27 is an objective lens that collects the laser light. Reference numeral 28 denotes a bias magnetic field coil, and 29 denotes a bias current control circuit, which applies a weak bias magnetic field or a fluctuating magnetic field. Reference numeral 30 denotes an irradiation path of laser light from the laser light irradiation means 20, which is interposed between the stage 10 and the objective lens 27, and is a replaceable transparent plate that blocks flying objects from the observation object W. .

In the scanning squid microscope according to the embodiment, reference numeral 40 designates a position of the observation object W relative to an irradiation point P on the observation object W of the laser light irradiated from the laser light irradiation means 20. This is a laser beam irradiation position moving means for moving. Specifically, the laser beam irradiation position moving means 40 has a function of moving the stage 10 and drives the non-magnetic XY stage 10, for example,
The ultrasonic motor (not shown) using the piezo effect and an XY stage controller 41 that controls the ultrasonic motor control the nonmagnetic XY stage 10 on which the observation target W is mounted.

Reference numeral 50 is provided above the stage 10, that is, provided opposite the objective lens 27 that condenses the laser light of the laser light irradiation means 20 with the stage 10 interposed therebetween.
SQUID magnetic field detection means for detecting a weak magnetic field change induced from the observation target object W by the laser light irradiated by the laser light irradiation means 20. The squid magnetic field detecting means 50 includes a superconducting pickup coil 51 and a squid 52 (S
QUID; superconducting quantum interference device). Also,
The squid magnetic field detecting means 50 includes a pickup coil 51.
And a heat insulating case 53 (also referred to as a “dur”) that covers the squid 52 and isolates the temperature transmission between the pickup coil 51 and the squid 52 and the observation target W. That is, the heat insulating case 53 insulates the arbitrary temperature at which the observation target object W is placed and the low temperature (for example, -196 ° C to -269 ° C) at which the squid 52 operates. The greatest feature is that the irradiation point P of the laser light irradiated from the laser light irradiation means 20 and the squid magnetic field detection means 5
The point is that the relative position with respect to the pickup coil 51 is fixed. More specifically, as shown in FIG. 8, the pickup coil 51 of the squid magnetic field detecting means 50 includes a plurality of (two in the embodiment) symmetric coil bodies having a neutral axis Q from which no detection signal is output. Differential type,
The pickup coil 51 is arranged at a position where its neutral axis Q is deviated from the irradiation point P of the laser light, and is configured such that the differential balance changes due to a change in magnetic flux induced by the laser light.

Reference numeral 60 denotes a control unit having an imaging unit 62 for displaying the state of the observation target W as an image on the display unit 61 based on the detection result from the squid magnetic field detection unit 50. The imaging unit 62 associates the moving distance of the observation target W with the pixel position, sets the output of the squid magnetic field detection unit 50 at the pixel position corresponding to the pixel density or color tone, and distributes the weak magnetic field induced by the laser irradiation. It is configured to have a function of forming an image. Further, the control unit 60 includes a laser beam irradiation unit 20, a laser beam irradiation position moving unit 40, and a squid magnetic field detection unit 50.
Is also controlled. Specifically, as shown in FIG. 1, the control unit 60 includes a timing for temporally modulating the intensity of the laser beam from the laser beam irradiation unit 20, a timing for extracting an output signal from the squid magnetic field detection unit 50, The laser light irradiation position moving means 40 is provided with a synchronous control means 63 for synchronously controlling the timing at which the position of the observation target W is relatively moved. Further, the control unit 60 includes signal processing means for performing signal processing in the time domain by time differentiation and / or time integration of the output of the squid magnetic field detection means 50, and outputs the output of the squid magnetic field detection means 50 in the frequency domain by Fourier transform. The signal processing means for performing signal processing in the, the state of the observation target W by laser light irradiation repeatedly irradiates the laser light to the observation target W with an output of a reversible range, the irradiation timing as a reference signal, It is provided with lock-in detecting means or box car detecting means for detecting the output signal of the squid magnetic field detecting means 50.

In order to realize such a function of the control unit 60, as shown in FIG. 7, the control unit 60 has the following configuration. In the control unit 60, reference numeral 64 denotes a magnetic flux lock loop circuit (FLL), which linearizes the signal from the squid 52, which is a quantized magnetic flux passing through the Josephson junction, so as to be proportional to the output signal. Reference numeral 65 denotes a squid controller, which includes a bias operating point of the squid 52 and FLL.
Control. The SQUID controller 65 outputs a signal S proportional to the amount of change in magnetic flux. Reference numeral 66 denotes a lock-in amplifier.
And a signal G obtained by phase detection with the intensity modulation signal R of the laser light.
Is output. When the signal frequency is high, the same can be realized by using a box car device instead of the lock-in amplifier 66. Reference numeral 70 denotes a control / data collection device realized by the functions of a personal computer or the like, which collects the signal G from the lock-in amplifier 66 and, via the XY stage controller 41, mounts the nonmagnetic XY on which the observation target W is mounted.
The stage 10 is controlled. Control / data collection device 70
Is also configured as an imaging means 62, which images the two-dimensional surface distribution of the change in magnetic flux density by moving the observation target W in XY and scanning the position irradiated with the laser light. The image is displayed on a monitor display as the display unit 61. Further, a confirmation means for confirming the focus and irradiation position of the laser beam and the observation position is provided. This checking means includes the observation light source 71.
A lens 72 through which the light output from the observation light source 71 passes, and a half mirror 2
And a half mirror 73 which guides the reflected light returning to the observation object W via the half mirror 25, the mirror 26, and the objective lens 27 to the opposite side to the half mirror 25 while passing the reflected light through the reverse path. And a CCD camera 74 that receives the light guided to the opposite side by the half mirror 73 and displays the light on the monitor display 61.

Therefore, according to the scanning squid microscope according to this embodiment, first, the light intensity of the laser light generated from the laser light source 21 is adjusted by the ND filter 22. Next, the acousto-optic device 23 is driven by the acousto-optic device driver 24 to modulate the intensity of the laser beam. The modulated laser light is condensed by the objective lens 27 via the mirror 26 and is incident on the surface of the observation target W. The energy given by the laser beam is photothermally converted or photoelectrically converted in the vicinity of the surface of the object W, and finally induces a slight change in magnetic flux through various processes. The change of the magnetic flux is observed by the squid 52. The squid 52 is linearized in a flux lock loop circuit (FLL) 64 so that the output signal is proportional to the quantized magnetic flux passing through the Josephson junction.
, And the bias operating point and FLL are controlled. The SQUID controller 65 outputs a signal S proportional to the amount of change in magnetic flux. The lock-in amplifier 66 outputs an output signal S of the squid controller 65 and a signal G obtained by phase detection with the laser intensity modulation signal R.

In this case, since the relative position between the irradiation point P of the laser light irradiated from the laser light irradiation means 20 and the pickup coil 51 of the squid magnetic field detection means 50 is fixed, the physical position of the observation object W is fixed. Unnecessary pseudo signals due to scanning are not superimposed on the magnetic field distribution reflecting the characteristics, so that the detection accuracy is high. Also,
Since the pickup coil 51 is also a small one accommodated in the heat insulating case 53, it is difficult to pick up extraneous magnetic noise other than the object W to be observed, and in addition, the volume required for cooling to maintain the pickup coil 51 in the superconducting state is small. The size of the device can be reduced and the cooling efficiency can be improved. In particular,
This is effective when a high-temperature superconducting squid is used. Further, the squid magnetic field detecting means 50 is a differential type in which the pickup coil 51 has a symmetrical coil body having a neutral axis Q, and the neutral axis Q of the pickup coil 51 is relative to the irradiation point P of the laser light. The differential balance changes due to the change in the magnetic flux induced by the laser light, and the differential type pickup coil 51
Cancels the magnetic signal coming from a distant place and responds only to the magnetic signal coming from the vicinity which is the irradiation point P (focus) of the laser beam, works as a spatial filter, and therefore improves the S / N ratio Let me do. That is, as shown in FIG. 8, the pickup coil 51 has an eight-shaped shape, and the irradiation point P (focal point) of the laser beam is adjusted to a position shifted from the neutral axis Q of the pickup coil 51. The magnetic flux A crosses the left coil body, and the magnetic flux B passes through the right coil body. Because the coil is of the differential type, AB
Is input to the squid 52. here,
With respect to the noise magnetic flux C other than the change in the magnetic flux generated due to the laser beam irradiation, the noise flux C arriving from a distant place is automatically canceled because it passes equally through the left and right coil bodies. This improves the S / N ratio and eliminates the need for a magnetic shield. In addition, the number of laser pulse repetitions can be reduced, and high-speed inspection can be performed.

The control / data collection device 70
While collecting the signal G, the non-magnetic XY stage 10 on which the observation target W is mounted is controlled via the XY stage controller 41 to move the observation target W to XY,
By scanning the position irradiated with the laser light, a two-dimensional distribution of magnetic flux density change is imaged. The image is displayed on the monitor display 61. The focus of the laser light, the irradiation position, and the observation position are confirmed by using the light output from the observation light source 71 by the lens 72,
The reflected light is guided to the observation target W via the half mirror 73, the half mirror 25, the mirror 26, and the objective lens 27, and the reflected light returning along the reverse path is received by the CCD camera 74 and displayed on the monitor display 61. .

Next, a scanning squid microscope according to another embodiment of the present invention will be described. The scanning squid microscope according to this embodiment is different from the above in the configuration of the squid magnetic field detecting means 50. As shown in FIG. 9, the squid magnetic field detecting means 50 includes a pickup coil 51.
And three or more pairs of squid 52 are provided (three in the embodiment), and each pickup coil 51 has a detection axis H perpendicular to its coil surface orthogonal to one intersection F, and
The intersection F of the detection axes H of the pickup coils 51 is symmetrically arranged so as to coincide with the irradiation point P of the laser beam, and the squid magnetic field detection means 50 enables simultaneous vector detection of both the intensity and direction of the magnetic flux. It has a configuration. Therefore, according to the scanning squid microscope according to this embodiment, the pickup coils 51 are arranged at equal distances from the irradiation point P (focal point) of the laser beam so that the positions of the pickup coils 51 are orthogonal to each other. The coil 51 detects signals in the X, Y, and Z directions, and combines them by signal processing, thereby enabling magnetic flux vector detection. That is, the squid magnetic field detecting means 50 can vector-detect the intensity and direction of the magnetic field generated from the irradiation point P of the laser beam at the point where the detection axis H of the pickup coil 51 is orthogonal.

Next, a scanning squid microscope according to another embodiment of the present invention will be described. The scanning squid microscope according to this embodiment is different from the above in the configuration of the squid magnetic field detecting means 50. As shown in FIG. 10, the scanning squid microscope according to this embodiment is different from the squid magnetic field detection unit 50 according to the other embodiment described above.
Is developed to the differential type described first. That is, the combination of the pickup coil 51 and the squid 52 is
Or more (three in the embodiment), and each pickup coil 51 has one detection axis H perpendicular to its coil surface.
Orthogonal to each other at the intersections F and each of the pickup coils 5
1 are arranged symmetrically so that the intersection point F of the detection axis H coincides with the irradiation point P of the laser light.
Is a differential type having a symmetric coil body having a neutral axis Q, and the pickup coil 51 is disposed at a position where the neutral axis Q is deviated with respect to the irradiation point P of the laser light. The differential balance is configured to be changed by a change in the induced magnetic flux. Therefore, according to the scanning squid microscope according to the other embodiment, the coil on the reference side of the differential pickup coil 51 is arranged at a position distant by an equal distance from the irradiation point P (focal point) of the laser beam. I have. In this case, assuming that the average environmental magnetic flux near the reference side coil is R, the detected signal is XR, Y-
R and ZR signals are obtained. With this configuration, S / N
Good ratio makes vector detection possible.

FIG. 11 shows a scanning squid microscope according to another embodiment. In the scanning squid microscope according to this embodiment, the laser light irradiation point P and the squid 52 are on the same side with respect to the observation target W. That is, the heat insulating case 53 is formed in a hollow cylindrical shape, and three sets of the same pickup coil 51 and squid 52 as shown in FIG. It is configured to introduce. Therefore, according to the scanning squid microscope according to this embodiment, it is possible to irradiate the laser from the front side while keeping the distance between the signal source and the squid 52 to a minimum even in the case of the thick observation target W. it can. This simplifies the mounting of the observation object W, facilitates handling of the apparatus, and increases sensitivity.

When a vector is detected by the scanning squid microscope shown in FIGS. 9, 10 and 11, for example, the result is as shown in FIG. That is, since the strength and direction of the magnetic field at each location are known, if the strength is represented by the length of the arrow and the direction is represented by the direction of the arrow, a magnetic vector distribution image can be obtained. For example, when there is a grain boundary or a crack, inversion or discontinuity of the vector appears.

[0028]

Next, an embodiment will be described. This is an example in the case of the magnetic material observation target W, and the timing of stage movement, laser beam irradiation, and squid measurement is
This was observed according to the timing chart shown in FIG. More specifically, the stage 10 is controlled to move the observation target W to a desired observation position, and then emit a laser light pulse whose output has been adjusted. Here, a rectangular pulse will be described as the simplest example. After the start of pulse irradiation, after a specific delay time, the temperature of the observation target W starts to rise with a specific time constant. Then, when the supply heat energy from the laser beam and the loss heat energy due to the heat outflow from the observation target W are balanced, the temperature rise is saturated and reaches a certain maximum temperature. When the laser beam irradiation is stopped, the temperature falls with a specific time constant after a specific delay time. Observation target W
Is a soft magnetic material, for example, when the ultimate temperature exceeds the Curie temperature, the magnetic permeability sharply decreases. When an appropriate bias magnetic field is applied, the magnetic resistance at the portion where the temperature has increased increases, and the output of the squid 52 decreases. When the laser beam irradiation is stopped, the magnetic permeability rises with the temperature drop, and the output of the squid 52 rises and recovers. Although noise is superimposed on the output of the squid 52 due to various factors, the S / N ratio can be increased by extracting only the signal portion corresponding to the laser light irradiation time and repeatedly integrating the extracted signal portion. Here, various physical states can be estimated by comparing output waveforms of the squid 52 and by differentiating / integrating the waveform.
Specific heat and thermal conductivity affect all time parameters,
Part Td1, T due to the rising edge of the laser pulse
c1 has a strong correlation with the light absorption coefficient (light reflection coefficient) and Curie temperature, while the falling portions Td2 and Tc2 have a strong correlation with the thermal conductivity. The amplitude indicates the magnitude of the magnetic permeability. The deviation of the rising and falling waveforms from the exponential function reflects the nonlinearity of the temperature characteristic of the magnetic permeability.

Next, another embodiment will be described.
This is a scanning type SQUID microscope configured with three sets of the pickup coil 51 and the SQUID 52.
This is an example in which a semiconductor such as a solar cell is selected as the observation target W, and the timing of stage movement, laser beam irradiation, and squid measurement is observed according to the timing chart shown in FIG. Since the squid 52 has three orthogonal channels, waveforms corresponding to the respective magnetic flux components in the XYZ directions generated by the current generated by the photoelectric effect appear. The vector measurement of the magnetic flux generated from the laser focus is performed by synthesizing the signal strength of each component. For example, when the signal strength after synchronous detection is measured at (4: 2: 1) in the XYZ directions, the generated magnetic field vector matches (4: 2: 1).

In the above embodiment, the observation object W
If necessary, a weak bias magnetic field or a fluctuating magnetic field can be applied by the bias magnetic field coil 28 and the bias current control circuit 29. Further, in the present embodiment, the method of externally modulating the laser light that emits continuous light with the acousto-optic element 23 has been described. However, it is sufficient that the laser pulse can be controlled from the outside. For example, a method using an external trigger of a Q-switch laser is used. Alternatively, a method of directly modulating a semiconductor laser may be used. In addition, there is no problem in the transmission of laser light because there is no interaction with magnetism even if an optical fiber is used, and it can be freely bent and arranged, and there is no problem of fluctuation due to air. This is particularly effective when the distance between the squid 52 and the laser transmitter is set to avoid radiation noise. Also, the number of laser pulses per observation point may be at least once, but if the signal is weak and buried in external noise,
By irradiating a large number of pulse trains and performing phase detection in synchronization with the intensity modulation signal R of the laser beam, S
Measurement with a high / N ratio becomes possible. The bias magnetic field is not essential in the present apparatus, but is convenient for measuring a change in magnetic permeability. Further, by synchronizing the bias magnetic field and the laser modulation signal, it is possible to cope with more complicated modulation.

[0031]

As described above, according to the scanning squid microscope of the present invention, the relative position between the irradiation point of the laser light irradiated from the laser light irradiation means and the pickup coil of the squid magnetic field detection means is fixed. Therefore, a pseudo signal due to scanning does not occur. That is, unnecessary pseudo signals are prevented from being superimposed on the magnetic distribution as much as possible, so that the detection accuracy can be greatly improved.

Further, when the laser beam irradiation position moving means is configured with a function of moving the stage, the object to be observed can be easily moved. Further, when the squid magnetic field detecting means is configured to include the pickup coil and the heat insulating case for covering the squid and isolating the temperature between the pickup coil and the squid and the object to be observed, the squid and the pickup coil are brought into a superconductive state. The temperature can be kept extremely low, the temperature of the observation target can be kept at an arbitrary temperature, and the cooling energy can be minimized.

Furthermore, the control unit may control the timing of temporally modulating the intensity of the laser beam from the laser beam irradiating unit, the timing of extracting the output signal from the squid magnetic field detecting unit, and the timing of the laser beam irradiating position moving unit. In the case where the apparatus is provided with a synchronous control means for synchronously controlling the timing at which the position of the observation target is relatively moved, since the three timings are controlled synchronously, noise and signals are separated in the time domain. As a result, the S / N ratio can be improved, and at the same time, it can be made to act so as to detect a signal generated at a desired place of the observation target. Also, the imaging unit of the control unit may be configured to make the moving distance of the observation target correspond to the pixel position, and to make the output of the squid magnetic field detection unit at the pixel position correspond to the pixel density or the color tone so that the weak magnetic field induced by the laser irradiation When a configuration is provided with a function of imaging as a distribution of the magnetic field, the distribution of the magnetic field can be reliably visualized.

The pickup coil of the squid magnetic field detecting means has a plurality of coil bodies having a neutral axis, and the neutral axis is disposed at a position deviated from the irradiation point of the laser light, and is induced by the laser light. If the configuration is such that the differential balance is changed by the change in the applied magnetic flux, the pickup becomes a differential type, so the pickup coil cancels the magnetic signal coming from a distant place, and the pickup coil cancels the magnetic signal coming from a distance. This makes it possible to respond only to a magnetic signal coming from the device and to act as a spatial filter, so that the S / N ratio can be greatly improved.

Further, the squid magnetic field detecting means is constituted by providing three or more sets of pickup coils and squids,
If each pickup coil is symmetrically arranged so that the detection axis perpendicular to the coil surface is orthogonal at one intersection and the intersection of the detection axes of each pickup coil coincides with the irradiation point of the laser light, By magnetic field detection means
Vector detection of both the intensity and direction of the magnetic flux can be performed simultaneously, and the detection accuracy is extremely high. Further, in the case of a configuration in which a replaceable transparent plate for intercepting the scattered object from the observation target is interposed on the irradiation path of the laser light from the laser light irradiation unit, the transparent plate Since scattered objects and the like from the surface of the observation object are prevented from reaching the surface of the objective lens, laser energy loss and an increase in aberration due to contamination of the lens surface can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a scanning squid microscope of the present invention.

FIG. 2 is a diagram showing the principle of the scanning squid microscope of the present invention.

FIG. 3 is a diagram illustrating an example of an observation state of an observation target of a scanning squid microscope according to the present invention, and illustrating a state of demagnetization of a magnetic body caused by laser light irradiation.

FIG. 4 is a view showing an example of an observation state of an observation object by the scanning squid microscope of the present invention, showing a state of thermal conductivity and current bias due to crystal grain boundaries and cracks caused by laser light irradiation.

FIG. 5 is a diagram showing an example of an observation state of an observation target of the scanning squid microscope of the present invention, and showing a state of an elastic wave effect by laser light irradiation.

FIG. 6 is a diagram showing an example of an observation state of an observation target by the scanning squid microscope of the present invention, and showing evaluation of a semiconductor PN junction by laser light irradiation.

FIG. 7 is a block diagram showing a configuration of a scanning squid microscope according to the embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a squid magnetic field detecting means of the scanning squid microscope according to the embodiment of the present invention, the squid magnetic field detecting means using a differential squid.

FIG. 9 shows a configuration of a squid magnetic field detecting unit of a scanning squid microscope according to another embodiment of the present invention,
It is a figure which shows the squid magnetic field detection means using a channel type squid.

FIG. 10 is a diagram showing a configuration of a squid magnetic field detecting means of a scanning squid microscope according to another embodiment of the present invention, which shows a squid magnetic field detecting means using a differential orthogonal three-channel squid.

FIG. 11 shows a configuration of a squid magnetic field detecting means of a scanning squid microscope according to still another embodiment of the present invention,
It is a figure which shows the squid magnetic field detection means which arrange | positioned the laser beam irradiation point and the squid on the same side above an observation object.

FIG. 12 is a diagram showing an example in which a vector magnetic field is imaged by the scanning squid microscope according to the embodiment of the present invention.

FIG. 13 is a diagram illustrating an observation example of the scanning squid microscope according to the example of the present invention, and is a diagram illustrating a one-channel timing chart in the case of a soft magnetic material observation target.

FIG. 14 is a diagram illustrating an observation example of a scanning squid microscope according to an example of the present invention, and illustrates a case of a semiconductor observation target;
It is a figure showing a channel timing chart.

FIG. 15 is a diagram showing an example of a conventional scanning squid microscope.

[Explanation of symbols]

 W Observation target 10 Stage 20 Laser light irradiation means 21 Laser light source 22 ND filter 23 Acousto-optic element 24 Acousto-optic element driver 25 Half mirror 26 Mirror 27 Objective lens 28 Bias magnetic field coil 29 Bias current control circuit 30 Transparent plate P irradiation Point 40 Laser light irradiation position moving means 41 XY stage controller 50 Squid magnetic field detecting means 51 Pickup coil 52 Squid 53 Thermal insulation case Q Neutral axis 60 Control unit 61 Display unit 62 Imaging means 63 Synchronous control means 64 Magnetic flux lock loop circuit 65 Squid Controller 66 Lock-in amplifier 70 Control / data collection device 71 Light source for observation 72 Lens 73 Half mirror 74 CCD camera H Detection axis F Intersection

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G017 AA05 AA08 AD32 AD33 BA15 BA18 2G053 AB01 AB14 BA15 BB03 BB05 CA03 CA10 CB16 CB29

Claims (12)

[Claims] 1. A stage for holding an observation target, a laser irradiation unit for irradiating the observation target held on the stage with laser light and supplying excitation energy to the observation target, and the laser irradiation. A laser light irradiation position moving means for relatively moving the position of the observation object with respect to an irradiation point on the observation object of the laser light irradiated from the means; and a pickup coil and a squid which are irradiated by the laser light irradiation means. Squid magnetic field detection means for detecting a weak magnetic field change induced from the observation target by the laser light, and displaying the state of the observation target as an image on the display unit based on the detection result from the squid magnetic field detection means. A scanning squid microscope provided with a control unit having an imaging means; Scanning SQUID microscope, characterized in that to fix the relative positions of the pickup coils of the irradiation point and the SQUID magnetic detecting means Heather light. 2. The scanning squid microscope according to claim 1, wherein said laser beam irradiation position moving means has a function of moving said stage. 3. The apparatus according to claim 1, wherein said squid magnetic field detecting means comprises a heat insulating case which covers said pickup coil and squid and isolates temperature transfer between said pickup coil and squid and an object to be observed. Or the scanning squid microscope according to 2. 4. The controller according to claim 1, wherein the controller is configured to control a timing of temporally modulating the intensity of the laser beam from the laser beam irradiating unit, a timing of extracting an output signal from the squid magnetic field detecting unit, and a position of the laser beam irradiating position. 4. The scanning squid microscope according to claim 1, wherein said scanning squid microscope is provided with a synchronization control means for controlling a timing of moving said observation target relative to said movement means in a synchronized manner. 5. The imaging unit of the control unit controls the moving distance of the observation target to correspond to a pixel position, and the output of the squid magnetic field detection unit at the pixel position corresponds to a pixel density or a color tone by the laser irradiation. 5. The scanning squid microscope according to claim 4, wherein the scanning squid microscope is provided with a function of imaging as a distribution of the induced weak magnetic field. 6. A pickup coil of said squid magnetic field detecting means is of a differential type having a plurality of coil bodies having a neutral axis which does not output a detection signal, and said pickup coil has a neutral axis whose irradiation point of said laser beam is 6. The scanning device according to claim 1, wherein the differential balance is changed by a change in magnetic flux induced by the laser light, wherein the differential balance is changed. Type SQUID microscope. 7. The squid magnetic field detecting means is provided by providing three or more sets of a pickup coil and a squid,
The pickup coils are symmetrically arranged such that the detection axis perpendicular to the coil surface is orthogonal at one intersection and the intersection of the detection axes of the pickup coils coincides with the irradiation point of the laser light. 7. The scanning squid microscope according to claim 1, wherein both the intensity and direction of the magnetic flux can be simultaneously detected by the magnetic field detecting means. 8. A replaceable transparent plate for intercepting scattered objects from the object to be observed is provided on the irradiation path of the laser light from the laser light irradiation means. The scanning squid microscope according to 3, 4, 5, 6 or 7. 9. A system according to claim 1, further comprising a bias magnetic field generating means for applying a bias magnetic field to said object from outside.
A scanning squid microscope as described. 10. The control unit includes signal processing means for performing signal processing in the time domain by time differentiation and / or time integration of the output of the squid magnetic field detection means. , 2,3,4,5,6,
10. The scanning squid microscope according to 7, 8, or 9. 11. The control unit according to claim 1, further comprising signal processing means for performing signal processing in the frequency domain by Fourier transform of the output of said squid magnetic field detection means. The scanning squid microscope according to 4, 5, 6, 7, 8, or 9. 12. The method according to claim 1, wherein the control section repeatedly irradiates the observation target with laser light with an output in a range in which the state of the observation target by the laser irradiation is reversible, and uses the irradiation timing as a reference signal to detect a squid magnetic field. And a lock-in detecting means or a box car detecting means for detecting an output signal of the means.
The scanning squid microscope according to 3, 4, 5, 6, 7, 8, 9, 10, or 11.