Abstract:
In a nondestructive and noncontact analysis system for analyzing and evaluating an object, a light beam generation/modulation apparatus emits a modulated and focused light beam to thereby irradiate the object, and the modulation of the modulated and focused light beam is carried out with a modulation signal synchronized with a reference signal composed of a series of regular pulses. A magnetism detection apparatus detects a magnetic field, which is generated by an electric current induced by irradiating the object with the modulated and focused light beam, to thereby produce a magnetic field signal. A signal extraction circuit extracts a phase difference signal between the reference signal and the magnetic field signal. An image data production system produces phase difference image data based on the phase difference signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a nondestructive and noncontact analysis system for analyzing and evaluating an object, such as a semiconductor wafer, in which an electric current is induced when being irradiated with a light beam having a given wavelength, and more particularly relates to such a nondestructive and noncontact analysis system including a SQUID (Superconducting Quantum Interference Device) photoscanning microscopic method using a SQUID magnetic sensor, for the analysis of the object.  
         [0003]     2. Description of the Related Art  
         [0004]     Presently, nondestructive and noncontact analysis systems having a SQUID magnetic sensor have been researched and developed to be put into practical use for analyzing and evaluating semiconductor wafers.  
         [0005]     Such a prior art nondestructive and noncontact analysis system includes a system control unit having a microcomputer, and a laser beam generation/modulation apparatus operated under control of the system control unit. The laser beam generation/modulation apparatus has a laser beam generator/modulator, and a reference signal generator.  
         [0006]     For example, the laser beam generator/modulator contains a fiber laser device for generating and emitting a laser beam, and an acoustic optical device for modulating the emitted laser beam. The reference signal generator generates a reference signal composed of a series of regular pulses, and the reference signal is output as a modulation signal from the reference signal generator to the acoustic optical device of the laser beam generator/modulator, such that the laser beam is modulated in accordance with the modulation signal.  
         [0007]     The laser beam generation/modulation apparatus also has an optical unit optically connected to laser beam generator/modulator through an optical fiber. Namely, the modulated laser beam is introduced from the laser beam generator/modulator into the optical unit through the optical fiber. The optical unit includes an optical lens system for focusing the modulated laser beam. Namely, the modulated laser beam is focused and emitted from the optical unit as a modulated and focused laser beam.  
         [0008]     The nondestructive and noncontact analysis system further includes an X-Y stage, and an object, such as a silicon wafer, to be analyzed and evaluated, is detachably mounted on the X-Y stage. Note, the silicon wafer has a plurality of semiconductor chips or devices produced thereon.  
         [0009]     The X-Y stage has a central opening formed therein, and the silicon wafer is irradiated with the modulated and focused laser beam, which passes through the central opening of the X-Y stage. The X-Y stage is moved along an X-axis and Y-axis of a rectangular X-Y coordinate defined with respect to the X-Y stage, such that each of the semiconductor devices on the silicon wafer is scanned with the laser beam. During the scanning of the semiconductor device with the laser beam, an electric current or OBIC (Optical Beam Induced Current) is induced at a spot area of the semiconductor device, which is irradiated with the scanning laser beam, and the OBIC generates a magnetic field (magnetic flux).  
         [0010]     To detect the magnetic field, the nondestructive and noncontact analysis system is provided with a magnetism detection apparatus which includes a SQUID (Superconducting Quantum Interference Device) magnetic sensor, and a SQUID controlling/processing circuit containing an FLL (Flux Lock Loop) circuit. The SQUID magnetic sensor is controlled by the SQUID controlling/processing circuit, and detects the magnetic field to thereby produce a SQUID signal in accordance with an intensity of the detected magnetic field. Namely, while the semiconductor device is scanned with the modulated and focused laser beam, a series of SQUID signals are produced and output from the SQUID magnetic sensor to the SQUID controlling/processing circuit, in which the series of SQUID signals are suitably processed to thereby generate a magnetic field signal.  
         [0011]     The nondestructive and noncontact analysis system is also provided with a signal extraction circuit containing a two-phase type lock-in amplifier. While the magnetic field signal is input from the SQUID controlling/processing circuit to the signal extraction circuit, the reference signal is input from the reference signal generator to the signal extraction circuit.  
         [0012]     In the two-phase type lock-in amplifier of the signal extraction circuit, the same frequency components as those of the reference signal are extracted from the magnetic field signal, and are suitably processed and output from the signal extraction circuit as a magnetic field intensity signal.  
         [0013]     The magnetic field intensity signal is fed to the system control unit, and then is successively converted into digital magnetic field intensity image data by an analog-to-digital (A/D) convector included in the system control unit. When the scanning of the semiconductor device concerned is completed, a frame of digital magnetic field intensity image pixel data is produced based on the successively-converted digital magnetic field intensity data, and is stored in a random access memory (RAM) included in the system control unit.  
         [0014]     The nondestructive and noncontact analysis system is further provided with a personal computer associated with a TV monitor. The frame of magnetic field intensity image pixel data is fed from the system control unit to the personal computer, and is suitably processed to thereby produce a magnetic field intensity video signal, whereby a magnetic field intensity image is displayed on the TV monitor in accordance with the magnetic field intensity video signal.  
         [0015]     In general, the magnetic field intensity image, which is obtained by using the SQUID photoscanning microscopic method, is called a SQUID microscopic image, and a spatial resolution power of the SQUID microscopic image depends upon only a spot diameter of the scanning laser beam projected on the object to be analyzed and evaluated, with no relationship to a size of the SQUID magnetic sensor and the distance between the SQUID magnetic sensor and the object. Note, usually, the spatial resolution power of the SQUID microscopic image is on the order of submicrons.  
         [0016]     The SQUID photoscanning microscopic method is used to detect a distribution of impurity density on a bare silicon wafer, as disclosed in literature “SQUID Photoscanning: An Imaging Technique for UDN of Semiconductor Wafers and Devices based on Photomagnetic Detection”, reported in “IEEE Transactions on Applied Superconductivity”, U.S.A., March, 2001, Vol. 1, P. 1162-1167, by Jorn Beyer, Dietmar Drung and Thomas Schuring.  
         [0017]     Also, the SQUID photoscanning microscopic method is used to measure a diffusion length of small carriers in a diffusion layer formed in a silicon wafer, as disclosed in JP-A-2003-197700.  
         [0018]     Further, the SQUID photoscanning microscopic method is used to analyze and evaluate semiconductor chips or devices, produced in a silicon wafer, using SQUID microscopic images, or magnetic field intensity images derived therefrom, as disclosed in JP-A-2002-313859.  
         [0019]     In the above-mentioned prior art nondestructive and noncontact analysis system using the SQUID photoscanning microscopic method, a magnetic field intensity image derived from a semiconductor device is frequently compared with a magnetic field intensity image derived from another semiconductor device, with the two semiconductor devices being identical to each other. In this case, if the two semiconductor devices are good products, the magnetic field intensity images cannot be distinguished from each other. On the other hand, if one of the semiconductor devices has a defect, the magnetic field intensity image derived from the defective semiconductor device is different from the magnetic field intensity image derived from the good semiconductor device at a local area at which the defect exists in the defective semiconductor device.  
         [0020]     Nevertheless, in the prior art nondestructive and noncontact analysis system, it is difficult to distinguish the difference between the defective and good magnetic field intensity images, as stated in detail hereinafter.  
       SUMMARY OF THE INVENTION  
       [0021]     Therefore, an object of the present invention is to provide a nondestructive and noncontact analysis system using a SQUID photoscanning microscopic method, which is constituted such that an analysis and an evaluation of an object, such as a semiconductor wafer, can be more accurately carried out in comparison with the prior art nondestructive and noncontact analysis system.  
         [0022]     Another object of the present invention is to provide a nondestructive and noncontact analysis method performed in the aforesaid nondestructive and noncontact analysis system.  
         [0023]     In accordance with an aspect of the present invention, there is provided a nondestructive and noncontact analysis system for analyzing and evaluating an object. In this nondestructive and noncontact analysis system, a light beam generation/modulation apparatus emits a modulated and focused light beam to thereby irradiate the object, and the modulation of the modulated and focused light beam is carried out with a modulation signal synchronized with a reference signal composed of a series of regular pulses. A a magnetism detection apparatus detects a magnetic field, which is generated by an electric current induced by irradiating the object with the modulated and focused light beam, to thereby produce a magnetic field signal. A signal extraction circuit extracts a phase difference signal between the reference signal and the magnetic field signal. An image data production system produces phase difference image data based on the phase difference signal.  
         [0024]     Preferably, the nondestructive and noncontact analysis system further comprises a scanning system that scans the object with the modulated and focused light beam, to thereby induce a series of electric currents at spot areas of the object, which are irradiated with the modulated and focused light beam.  
         [0025]     The image data production system may include a gradation conversion system for converting gradations of the phase difference image data in accordance with a predetermined gradation characteristic.  
         [0026]     The nondestructive and noncontact analysis system may comprises an image display system for displaying a phase difference image based on the phase difference image data.  
         [0027]     The nondestructive and noncontact analysis system may comprise an image display system for displaying a phase difference image based on the phase difference image data together with a referential phase difference image based on previously-prepared referential phase difference image data, whereby the phase difference image can be compared with the referential phase difference image.  
         [0028]     The nondestructive and noncontact analysis system may comprise an image display system for displaying a phase difference histogram based on phase difference histogram data which is produced from the phase difference image data.  
         [0029]     The nondestructive and noncontact analysis system may further comprise an image display system for displaying a phase difference histogram based on the phase difference histogram data together with a referential phase difference histogram based on previously-prepared referential phase difference histogram data, whereby the phase difference histogram can be compared with the referential phase difference histogram.  
         [0030]     According to the present invention, the signal extraction circuit may extract a magnetic field intensity signal from the magnetic field signal by the signal extraction circuit, and the image data production system may produce a magnetic field intensity image data based on the magnetic field intensity signal.  
         [0031]     The nondestructive and noncontact analysis system may comprise an image display system for displaying a magnetic field intensity image and a phase difference image based on the magnetic field intensity image data and the phase difference image data, respectively.  
         [0032]     The nondestructive and noncontact analysis system may further comprise an image display system for displaying respective magnetic field intensity and phase difference images based on the magnetic field intensity image and phase difference image data together with respective referential magnetic field intensity and phase differential images based on previously-prepared referential magnetic field intensity image and phase difference image data, whereby the respective magnetic field intensity and phase difference images can be compared with the referential magnetic field intensity and phase difference images.  
         [0033]     The nondestructive and noncontact analysis system may further comprise an image display system for displaying respective magnetic field intensity and phase difference histograms based on magnetic field intensity histogram and phase difference histograms which are produced from the magnetic field intensity image and phase difference image data, respectively.  
         [0034]     The nondestructive and noncontact analysis system may further comprise an image display system for displaying respective magnetic field intensity and difference histograms based on magnetic field intensity histogram and phase difference histogram data, which are produced from the magnetic field intensity image and phase difference image data, respectively, together with respective referential magnetic field intensity and phase difference histograms based on previously-prepared referential magnetic field intensity histogram and phase difference histogram data, whereby the magnetic field intensity histogram and the phase difference histogram can be compared with the referential magnetic intensity histogram and the referential phase difference histogram, respectively.  
         [0035]     Preferably, the modulated and focused light beam is emitted as a modulated and focused laser beam from the light beam generation/modulation apparatus, and the magnetism detection apparatus includes a SQUID (Superconducting Quantum Interference Device) magnetic sensor to detect the magnetic fields generated in the object by each of the electric currents.  
         [0036]     In accordance with another aspect of the present invention, there is provided a nondestructive and noncontact analysis method for analyzing and evaluating an object, comprising the steps of: emitting an modulated and focused light beam to thereby irradiate the object, the modulation of the modulated and focused light beam being carried out with a modulation signal synchronized with a reference signal composed of a series of regular pulses; detecting a magnetic field, which is generated by an electric current induced by irradiating the object with the modulated and focused light beam, to thereby produce a magnetic field signal; extracting a phase difference signal between the reference signal and the magnetic field signal; and producing phase difference image data based on the phase difference signal.  
         [0037]     Preferably, the nondestructive and noncontact analysis method further comprises the step of scanning the object with the modulated and focused light beam, to thereby induce a series of electric currents at spot areas of the object, which are irradiated with the modulated and focused light beam.  
         [0038]     The phase difference image data may be subjected to a gradation conversion processing such that gradations of the phase difference image data are converted in accordance with a predetermined gradation characteristic.  
         [0039]     The nondestructive and noncontact analysis method may comprise the step of displaying a phase difference image in an image display system based on the phase difference image data.  
         [0040]     The nondestructive and noncontact analysis method may comprise the step of displaying a phase difference image in an image display system based on the phase difference image data together with a referential phase difference image based on previously-prepared referential phase difference image data, whereby the phase difference image can be compared with the referential phase difference image.  
         [0041]     The nondestructive and noncontact analysis method may comprise the steps of: producing phase difference histogram data from the phase difference image data; and displaying a phase difference histogram in an image display system based on the phase difference histogram data.  
         [0042]     The nondestructive and noncontact analysis method may comprise the steps of: producing phase difference histogram data from the phase difference image data; and displaying a phase difference histogram in an image display system based on the phase difference histogram data together with a referential phase difference histogram based on previously-prepared referential phase difference histogram data, whereby the phase difference histogram can be compared with the referential phase difference histogram.  
         [0043]     The nondestructive and noncontact analysis method may comprise the steps of: extracting a magnetic field intensity signal from the magnetic field signal; and producing magnetic field intensity image data based on the magnetic field intensity signal.  
         [0044]     The nondestructive and noncontact analysis method may comprise the step of displaying a magnetic field intensity image and a phase difference image in an image display system based on the magnetic field intensity image data and the phase difference image data.  
         [0045]     The nondestructive and noncontact analysis method may comprise the step of displaying respective magnetic field intensity and phase difference images based on the magnetic field intensity image and phase difference image data together with respective referential magnetic field intensity and phase difference images based on previously-prepared referential magnetic field intensity image and phase difference image data, whereby the magnetic field intensity image and the phase difference image can be compared with the referential magnetic field intensity image and the referential phase difference image, respectively.  
         [0046]     The nondestructive and noncontact analysis method may comprise the step of producing magnetic field intensity histogram data and phase difference histogram data from the magnetic field intensity image data and the phase difference image data, respectively.  
         [0047]     The nondestructive and noncontact analysis method may comprise the step of displaying respective magnetic field intensity and phase difference histograms based on the magnetic field intensity histogram and phase difference histogram data together with referential magnetic field intensity and phase difference histograms based on previously-prepared magnetic field intensity histogram phase difference histogram data, whereby the magnetic field intensity histogram and the phase difference histogram can be compared with the referential magnetic intensity histogram and the referential phase difference histogram, respectively. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0048]     The above object and other objects will be more clearly understood from the description set forth below, with reference to the accompanying drawings, wherein:  
         [0049]      FIG. 1  is a block diagram of an embodiment of a nondestructive and noncontact analysis system according to the present invention, in which a silicon wafer is analyzed and evaluated;  
         [0050]      FIG. 2  is a block diagram of a system control unit included in the nondestructive and noncontact analysis system shown in  FIG. 1 ;  
         [0051]      FIG. 3  is a view conceptually showing relationships between a reference signal, a modulation signal and a magnetic field intensity signal, which are produced in the nondestructive and noncontact analysis system shown in FIG.  1 ;  
         [0052]      FIG. 4  is a view conceptually showing a scanning manner in which a semiconductor chip on the silicon wafer is scanned with a modulated and focused laser beam which is generated in the nondestructive and noncontact analysis system shown in  FIG. 1 ;  
         [0053]      FIG. 5  is a view conceptually showing a frame of m×n magnetic field intensity image pixel data, which is stored in a random access memory (RAM) included in the system control unit;  
         [0054]      FIG. 6  is a view conceptually showing a frame of m×n phase difference image pixel data, which is stored in the random access memory (RAM) included in the system control unit;  
         [0055]      FIG. 7  is a view conceptually showing a one-dimensional map, which is stored in a read-only memory (ROM) included in the system control unit, and which is used to subject the phase difference image pixel data to a gradation conversion processing;  
         [0056]      FIG. 8  is a block diagram of a personal computer included in the nondestructive and noncontact analysis system shown in  FIG. 1 ;  
         [0057]      FIG. 9A  is a real magnetic field intensity image which is produced based on a frame of magnetic field intensity image pixel data derived from a defective semiconductor device;  
         [0058]      FIG. 9B  is a real magnetic field intensity image which is produced based on a frame of magnetic field intensity image pixel data derived from a good semiconductor device;  
         [0059]      FIG. 10A  is a real phase difference image which is produced based on a frame of phase difference image pixel data derived from the aforesaid defective semiconductor device;  
         [0060]      FIG. 10B  is a real phase difference image which is produced based on a frame of phase difference image pixel data derived from the aforesaid good semiconductor device;  
         [0061]      FIG. 11A  is a real magnetic field intensity histogram which is produced from the frame of magnetic field intensity image pixel data derived from the aforesaid defective semiconductor device;  
         [0062]      FIG. 11B  is a real magnetic field intensity histogram which is produced from the frame of magnetic field intensity image pixel data derived from the good semiconductor device;  
         [0063]      FIG. 12A  is a real phase difference histogram which is produced from the frame of phase difference image pixel data derived from the defective semiconductor device;  
         [0064]      FIG. 12B  is a real phase difference histogram which is produced from the frame of phase difference image pixel data derived from the good semiconductor device;  
         [0065]      FIG. 13  is a flowchart of a main routine executed in the system control circuit of the nondestructive and noncontact analysis system;  
         [0066]      FIG. 14  is a flowchart of an image production routine executed as a subroutine in the main routine of  FIG. 13 ;  
         [0067]      FIG. 15  is a flowchart of a main routine executed in the personal computer of the nondestructive and noncontact analysis system; and  
         [0068]      FIG. 16  is a flowchart of a histogram production routine executed as a subroutine in the main routine of  FIG. 15 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0069]     With reference to FIGS.  1  to  3 , an embodiment of a nondestructive and noncontact analysis system according to the present invention will be now explained below.  
         [0070]     The nondestructive and noncontact analysis system is used to analyze and evaluate an object, such as a silicon wafer, to be analyzed and evaluated, in which an electric current is induced when being irradiated with a laser beam. Note, as already stated hereinbefore, such an electric current is called an OBIC (Optical Beam Induced Current) in this field.  
         [0071]     The nondestructive and noncontact analysis system comprises a system control unit  10 , which is constituted as a microcomputer as shown in  FIG. 2 . Namely, the system control unit  10  includes a central processing unit (CPU)  10 A, a read-only memory (ROM)  10 B for storing various programs and constants, a random-access memory (RAM)  10 C for storing temporary data, an input/output (I/O) interface circuit  10 D, and two analog-to-digital (A/D) converters  10 E and  10 F.  
         [0072]     Also, the nondestructive and noncontact analysis system comprises a laser beam generation/modulation apparatus  12  including a laser beam generator/modulator  12 A, and a reference signal generator  12 B. In this embodiment, for example, the laser beam generator/modulator  12 A contains a fiber laser device for generating and emitting a laser beam, and an acoustic optical device for modulating the emitted laser beam. The reference signal generator  12 B generates a reference signal RE-S composed of a series of regular pulses, and outputs a modulation signal MO-S to the acoustic optical device of the laser beam generator/modulator  12  in synchronization with the reference signal RE-S, to thereby modulate the laser beam in accordance with the modulation signal MD-S.  
         [0073]     Note, the laser beam generator/modulator  12 A and the reference signal generator  12 B are connected to the I/O interface circuit  10 D, and are driven under control of the system control unit  10 .  
         [0074]     The laser beam generation/modulation apparatus  12  further includes an optical unit  12 C optically connected to laser beam generator/modulator  12 A through an optical fiber  12 D, which is symbolically and conceptually illustrated in  FIG. 1 . Namely, the modulated laser beam is introduced from the laser beam generator/modulator  12 A into the optical unit  12 C through the optical fiber  12 D. The optical unit  12 C includes an optical lens system for focusing the modulated laser beam. Namely, the modulated laser beam is focused and emitted from the optical unit  12 D as a modulated and focused laser beam MLB, which is symbolically and conceptually illustrated in  FIG. 1 .  
         [0075]     The nondestructive and noncontact analysis system further comprises an X-Y stage  14 , and an object, such as a silicon wafer, to be analyzed and evaluated, is detachably mounted on the X-Y stage  14 . In  FIG. 1 , the silicon wafer to be analyzed and evaluated is indicated by reference SW. The X-Y stage has a central opening formed therein, and the silicon wafer SW is irradiated with the modulated and focused laser beam MLB, which passes through the central opening of the X-Y stage  14 .  
         [0076]     The X-Y stage  14  is movable along an X-axis and Y-axis of a rectangular X-Y coordinate  16  defined with respect to the X-Y stage  14 , such that the silicon wafer SW is scanned with the laser beam MLB. To this end, the X-Y stage is mechanically associated with a mechanical scanning system  18 , and the mechanical association between the X-Y state  14  and the mechanical scanning system  18  is conceptually represented by a broken arrow BA in  FIG. 1 . The mechanical scanning system contains two respective electric drive motors for moving the X-Y stage  14  along the X-axis and Y-axis of the rectangular X-Y coordinate  16 , and these electric drive motors are driven by a driver circuit  20 , which is operated under control of the system control unit  10 .  
         [0077]     While the silicon wafer SW is scanned with the modulated and focused laser beam ##MLB, a series of electric currents (OBIC) are induced at spot areas of the silicon wafer SW, which are irradiated with the scanning laser beam MLB, and each of the electric currents generates a magnetic field (magnetic flux) MF, which is conceptually represented by an open arrow illustrated by a broken line in  FIG. 1 .  
         [0078]     In order to detect the magnetic field MF, the nondestructive and noncontact analysis system is provided with a magnetism detection apparatus  22  which includes a SQUID (Superconducting Quantum Interference Device) magnetic sensor  22 A of HTS (High Temperature Superconducting) type, and a SQUID controlling/processing circuit  22 B containing an FLL (Flux Lock Loop) circuit. Note, the HTS type SQUID magnetic sensor can detect a very small magnetic field density of less than 1 pT (pico-tesla).  
         [0079]     The SQUID magnetic sensor  22 A is controlled by the SQUID controlling/processing circuit  22 B, and detects the magnetic field MF to thereby produce a SQUID signal SQ-S in accordance with an intensity of the detected magnetic field MF. Namely, while the silicon wafer SW is scanned with the modulated and focused laser beam MLB, a series of SQUID signals SQ-S are produced and output from the SQUID magnetic sensor  22 A to the SQUID controlling/processing circuit  22 B, in which the series of SQUID signals SQ-S are suitably processed to thereby produce a magnetic field signal MF-S.  
         [0080]     Although not illustrated in  FIG. 1 , in reality, the magnetism detection apparatus  22  is covered with a magnetic shield to thereby protect it from an environmental magnetic field. Namely, since a density of the environmental magnetic field is on the order of μT (micro-tesla), it should be reduced to the order of nT (nano-tesla) before the magnetism detection apparatus  22  can be stably operated.  
         [0081]     The nondestructive and noncontact analysis system is also provided with a signal extraction circuit  24  which may contain a two-phase type lock-in amplifier. As is apparent from  FIG. 1 , while the magnetic field signal MF-S is input from the SQUID controlling/processing circuit  22 B to the signal extraction circuit  24 , the reference signal RE-S is input from the reference signal generator  12 B to the signal extraction circuit  24 .  
         [0082]     In the two-phase type lock-in amplifier of the signal extraction circuit  24 , the same frequency components as those of the reference signal RE-S are extracted from the magnetic field signal MF-S, and are suitably processed and output from the signal extraction circuit  24  as a magnetic field intensity signal MFI-S. On the other hand, in the two-phase type lock-in amplifier, respective phase differences between the extracted frequency components of the magnetic field signal MF-S and the corresponding pulses of the reference signal RE-S are detected and output from the signal extraction circuit  24  as a phase difference signal PDF-S.  
         [0083]      FIG. 3  conceptually shows relationships between the reference signal RE-S, the modulation signal MO-S, and the magnetic field intensity signal MFI-S.  
         [0084]     As shown in  FIG. 3 , the magnetic field intensity signal MFI-S is composed of the frequency components which are extracted from the magnetic field signal MF-S in accordance with the reference signal RE-S, and each of the frequency components features a phase difference with respect to a corresponding pulse of the reference signal RE-S. In  FIG. 3 , a phase difference between a frequency component of the magnetic field intensity signal MFI-S and a corresponding pulse of the reference signal RE-S is representatively indicated by reference Δφ. In short, the phase difference signal PDF-S is composed of the consecutive phase differences (Δφ) between the extracted frequency components of the magnetic field signal MF-S and the corresponding pulses of the reference signal RE-S.  
         [0085]     Note, in  FIG. 3 , although the frequency components of the magnetic field intensity signal MFI-S are expediently illustrated as a series of regular rectangular pulses, in reality, the frequency components cannot be represented by regular rectangular pulses. Namely, both the amplitude and the phase difference (Δφ) of the frequency components of the magnetic field intensity signal MFI-S might vary in accordance with the spot areas of the silicon wafer SW, which are irradiated with the scanning laser beam MLB.  
         [0086]     As is apparent from  FIGS. 1 and 2 , the magnetic field intensity signal MFI-S and the phase difference signal PDF-S are input from the signal extraction circuit  24  to the respective A/D converters  10 E and  10 F of the system control unit  10 .  
         [0087]     In this embodiment, the silicon wafer SW has a plurality of semiconductor chip areas defined thereon, and a semiconductor device is produced in each of the chip areas. In order to analyze each of the semiconductor devices, it is scanned with the modulated and focused laser beam MLB, for example, in a scanning manner as conceptually shown in  FIG. 4 . In particular, in  FIG. 4 , one of the chip areas on the silicon wafer SW is representatively indicated by reference CA, and the chip area CA is scanned with the laser beam MLB along a zigzag arrow AW. Note, reference SS indicates a scanning start position, and reference SE indicates a scanning end position. Also, note, reference SD 1  indicates a first scanning direction in which the chip area CA is scanned with the laser beam MLB when moving it in the right direction ( FIG. 4 ), and reference SD 2  a second scanning direction in which the chip area CA is scanned with the laser beam MLB when moving it in the left direction ( FIG. 4 ).  
         [0088]     While the chip area CA is scanned with the laser beam MLB in the scanning manner as shown in  FIG. 4 , the magnetic field intensity signal MFI-S and the phase difference signal PDF are successively converted into 8-bit digital magnetic field intensity data MFI and 8-bit digital phase difference data PDF by the respective A/D convectors  10 E and  10 F.  
         [0089]     When the scanning of the chip area CA is completed, a frame of 8-bit digital magnetic field intensity image pixel data MFI ij  is produced based on the successively-converted 8-bit digital magnetic field intensity data MFI, and is stored in the RAM  10 C of the system control unit  10 , as conceptually shown in  FIG. 5 . As is apparent from this drawing, in this embodiment, the magnetic field intensity image on the chip area CA is composed of a frame of m×n image pixel data MFI ij , and each of these image pixel data MFI ij  is defined as an average value of the consecutive ten digital magnetic field intensity data MFI.  
         [0090]     Similarly, when the scanning of the chip area CA is completed, a frame of 8-bit digital phase difference image pixel data PDF ij  is produced based on the successively-converted 8-bit digital phase difference data PDF, and is stored in the RAM  10 C of the system control unit  10 , as conceptually shown in  FIG. 6 . As is apparent from this drawing, the phase difference image on the chip area CA is also composed of a frame of m×n image pixel data PDF ij , and each of these image pixel data PDF ij  is defined as an average value of the consecutive ten digital phase difference data PDF.  
         [0091]     In this embodiment, before each of the image pixel data PDF ij  is stored in the RAM  10 C of the system control unit  10 , it is subjected to a gradation conversion processing, using a one-dimensional map, as conceptually shown in  FIG. 7  by way of example, which is previously defined and stored in the ROM  10 B of the system control unit  10 . As is apparent from  FIG. 7 , for example, when an image pixel datum PDF ij  represents a phase difference Δφ of −180°, it is converted into an image pixel datum PDF ij  featuring a black level “255”. Also, when an image pixel datum PDF ij  represents a phase difference Δφ of 0°, it is converted into an image pixel datum PDF ij  featuring an intermediate gray level “128”. Further, when an image pixel datum PDF ij  represents a phase difference Δφ of +180°, it is converted into an image pixel datum PDF ij  featuring a white level “000”.  
         [0092]     On the contrary, if necessary, the image pixel datum PDF ij , representing the phase difference Δφ of −180°, may be converted as featuring the white level “000”, and the image pixel datum PDF ij  representing a phase difference Δφ of +180°, is converted as featuring the black level “255”.  
         [0093]     As shown in  FIG. 1 , the nondestructive and noncontact analysis system is further provided with a personal computer  26  associated with a TV monitor  28 . As shown in  FIG. 8 , the personal computer  26  comprises a microprocessor  26 A, a read-only memory (ROM)  26 B for storing various programs and constants, a random-access memory (RAM)  26 C for storing temporary data, and an input/output (I/O) interface circuit  26 D. The TV monitor  28  is connected to the microprocessor  26 A through the I/O interface circuit  26 D.  
         [0094]     The personal computer  26  contains a hard disk drive  26 E for driving a hard disk  26 F. The microprocessor  26 A writes various data on the hard disk  26 F through the hard disk drive  26 E, and also reads the various data from the hard disk  26 F through the hard disk drive  26 E. Further, the personal computer  26  is provided with a keyboard  30  and a mouse  32  which are connected to the microprocessor  26 A through the I/O interface circuit  26 D. The keyboard  30  is used to input various commands and data to the microprocessor  26 A, and a mouse  32  is used to input a command to the microprocessor  26 A by clicking the mouse  32  on any one of the various command items displayed on the TV monitor  28 .  
         [0095]     The frames of m×n image pixel data MFI ij  and PDF ij  are fed from the system control unit  10  to the personal computer  26 , and are temporarily stored in the RAM  26 C of the personal computer  26 . The microprocessor  26 A suitably processes the frames of m×n image pixel data MFI ij  and PDF ij  to thereby produce video signals MFI-VS and PDF-VS, a magnetic field intensity image and a phase difference image are displayed on the TV monitor  28  in accordance with the respective video signals MFI-VS and PDF-VS. Note, the frames of m×n image pixel data MFI ij  and PDF ij  may be stored and reserved in the hard disk  26 F, if necessary.  
         [0096]      FIGS. 9A and 9B  show two real magnetic field intensity images by way of example, which are displayed on the TV monitor  28 . The magnetic field intensity image shown in  FIG. 9A  is derived from a defective semiconductor device produced in a silicon wafer (SF), and the magnetic field intensity image shown in  FIG. 9B  is derived from a good semiconductor device produced in the same silicon wafer (SF) as mentioned above. Note that the defective and good semiconductor devices are identical to each other, and have a size of 6 mm×10 mm. As is apparent from a comparison between  FIGS. 9A and 9B , the respective magnetic field intensity images shown in  FIGS. 9A and 9B  are distinguished from each other at local areas indicated by arrows DT 1  and GD 1 . Namely, it is found that the defective semiconductor device ( FIG. 9A ) has a defect at the local area indicated by the arrow DT 1 .  
         [0097]      FIGS. 10A and 10B  show two real phase difference images by way of example, which are displayed on the TV monitor  28 . The phase difference image shown in  FIG. 10A  is derived from the aforesaid defective semiconductor device, and the phase difference image shown in  FIG. 10B  is derived from the aforesaid good semiconductor device. As is apparent from a comparison between  FIGS. 10A and 10B , the phase difference images shown in  FIGS. 10A and 10B  are also distinguished from each other, at local areas indicated by arrows DT 2  and GD 2 . Namely, the defective semiconductor device ( FIG. 10A ) has the defect at the local area indicated by the arrow DT 2 . Of course, the local area indicated by the arrow DT 2  is the same area as indicated by the arrow DT 1  in  FIG. 9A .  
         [0098]     Note, the four real images shown in  FIGS. 9A and 9B  and  FIGS. 10A and 10B  were obtained under the conditions that a spot diameter of the modulated and focused laser beam MLB is 10 μm, and that a frequency of the modulation signal MO-S is 100 kHz.  
         [0099]     Comparing the magnetic field intensity images shown in  FIGS. 9A and 9B  with the phase difference images shown in  FIGS. 10A and 10B , the existence of the defect in the defective semiconductor device can be more clearly recognized in the phase difference images than in the magnetic field intensity images. Namely, by using the phase difference images as shown in  FIGS. 10A and 10B , it is possible to more accurately analyze and evaluate the semiconductor devices produced in the silicon wafer SW, in comparison with the case where only the magnetic field intensity images are utilized.  
         [0100]     In short, from the inventor&#39;s research, it was found that the respective phase differences between the frequency components of the magnetic field signal MF-S and the corresponding pulses of the reference signal RE-S are influenced by the existence of the defect in the semiconductor device, and more clearly represent the existence of the defect in the semiconductor device in comparison with the magnetic field intensity signal MF-S.  
         [0101]     In this embodiment, if necessary, a magnetic field intensity histogram and a phase difference histogram may be produced based on the respective frames of m×n image pixel data MFI ij  and PDF ij , and may be displayed on the TV monitor  28 . The production of the magnetic field intensity and phase difference histograms may be carried out in the personal computer  26 .  
         [0102]      FIGS. 11A and 11B  show two magnetic field intensity histograms produced based on the magnetic field intensity images shown in  FIGS. 9A and 9B . In these histograms, when 8-bit image pixel data MFI ij  is equivalent to “000”, it represents a white level; when 8-bit image pixel data MFI ij  is equivalent to “128”, it represents an intermediate gray level; and when 8-bit image pixel data MFI ij  is equivalent to “255”, it represents a black level. As is apparent from a comparison between  FIGS. 11A and 11B , the respective magnetic field intensity histograms are distinguished from each other at sections encircled by circles DC 1  and GC 1 .  
         [0103]      FIGS. 12A and 12B  show two phase difference histograms produced based on the phase difference images shown in  FIGS. 10A and 10B . In these histograms, when 8-bit image pixel data PDF ij  is equivalent to “000” (Δφ=−180°), it represents a white level; when 8-bit image pixel data PDF ij  is equivalent to “128” (Δφ=0°), it represents an intermediate gray level; and when 8-bit image pixel data PDF ij  is equivalent to “255” (Δφ=+180°), it represents a black level. As is apparent from a comparison between  FIGS. 12A and 12B , the respective phase difference histograms are distinguished from each other at sections encircled by circles DC 2   1  and DC 2   2 ; and GC 2   1  and GC 2   2 .  
         [0104]     By using the histograms as shown in  FIGS. 11A and 11B  and  FIGS. 12A and 12B , it is possible to more accurately analyze and evaluate the semiconductor devices produced in the silicon wafer SW, in comparison with the case where only the magnetic field intensity and phase difference images as shown in  FIGS. 9A and 9B  and  FIGS. 10A and 10B  are utilized.  
         [0105]      FIG. 13  shows a flowchart of a main routine executed in the CPU  10 A of the system control circuit  10 . Note, the execution of the main routine is started when the nondestructive and noncontact analysis system is powered ON.  
         [0106]     At step  1301 , it is monitored whether a scanning-operation start signal is received from the personal computer  26 . Note, after a silicon wafer (SW) to be analyzed and evaluated is mounted on the X-Y stage  14 , when a command for feeding the scanning operation start signal to the system control unit  10  is input to the personal computer  26  by manipulating either the keyboard  30  or the mouse  32 , the scanning operation start signal is fed from the personal computer  26  to the system control unit  10 .  
         [0107]     When the receipt of the scanning operation start signal is confirmed, the control proceeds from step  1301  to step  1302 , in which a positioning operation for the silicon wafer (SW) is executed by suitably driving the mechanical scanning system  18 . Namely, a chip area (CA) on the silicon wafer (SW) is positioned such that a scanning start position (SS) on the chip area (CA) is irradiated with the modulated and focused laser beam MLB. Then, at step  1303 , it is monitored whether the positioning operation has been completed.  
         [0108]     When the completion of the position operation is confirmed, the control proceeds from step  1303  to step  1304 , in which an image data production routine is executed to thereby produce and store a frame of m×n magnetic field intensity image pixel data MFI ij  and a frame of m×n phase difference image pixel data PDF ij  in the RAM  10 C of the system control unit  10 , as shown in  FIGS. 5 and 6  by way of example. Note, the image data production routine will be explained in detail with reference to  FIG. 14  hereinafter.  
         [0109]     At step  1305 , the produced frames of m×n image pixel data MFI ij  and PDF ij  are fed to the personal computer  26  through the I/ 0  interface circuit  10 D of the system control unit  10 .  
         [0110]     At step  1306 , it is determined whether another chip area (CA) to be scanned remains on the silicon wafer (SW). When there is another chip area (CA) on the silicon wafer (SW), the control returns to step  1302 , and the routine comprising steps  1302  to  1305  is again executed. Namely, the other chip area (CA) on the silicon wafer (SW) is positioned such that a scanning start position (SS) on the chip area (CA) is irradiated with the modulated and focused laser beam MLB (step  1303 ), a frame of m×n magnetic field intensity image pixel data MFI ij  and a frame of m×n phase difference image pixel data PDF ij  on the other chip area (CA) are produced and fed to the personal computer  26  (steps  1304  and  1305 ).  
         [0111]     On the other hand, at step  1306 , when no chip area (CA) to be scanned remains on the silicon wafer (SW), the control returns to step  1301 , in which it is monitored whether a further scanning-operation start signal is received from the personal computer  26  to analyze and evaluate another silicon wafer (SW).  
         [0112]      FIG. 14  shows a flowchart of the image data production routine which is executed as a subroutine in step  1304  of the main routine shown in  FIG. 13 .  
         [0113]     At step  1401 , an initialization is carried out. Namely, counters c, i and j are initialized to “0”, variables SMFI and SPDF are initialized to “0”, and a scanning-direction indicating flag SDF is initialized to “0”.  
         [0114]     Note, as explained with reference to  FIG. 4 , when the chip area (CA) is scanned with the laser beam MLB in the first scanning direction SD 1 , a setting of “0” is given to the flag SDF, and, when the chip area (CA) is scanned with the laser beam MLB in the second scanning direction SD 2 , a setting of “1” is given to the flag SDF.  
         [0115]     At step  1402 , an 8-bit digital magnetic field intensity image datum MFI is fetched from the A/D converter  10 E. Then, at step  1403 , the following calculation is carried out: 
 
SMFI←SMFI+MFI 
 
         [0116]     At step  1404 , an 8-bit digital phase difference image datum PDF is fetched from the A/D converter  10 F. Then, at step  1405 , the fetched datum PDF is subjected to a gradation conversion processing, using the one-dimensional map shown in  FIG. 7 , and, at step  1406 , the following calculation is carried out: 
 
SPDF←SPDF+PDF 
 
         [0117]     At step  1407 , it is monitored whether a count number of the counter c has reached “9”. Since c=0 at the initial stage, the control proceeds from step  1407  to step  1408 , in which the count number of the counter c is incremented by “1”. Then, the control returns to step  1402 , and the routine comprising steps  1402  to  1408  is repeated until the count number of the counter c has reached “9”, i.e. until the respective variables SMFI and SPDF have reached the sums of the consecutive ten magnetic field intensity data MFI and consecutive ten phase difference data PDF.  
         [0118]     At step  1407 , when it is confirmed that the count number of the counter c has reached “9”, the control proceeds from step  1407  to step  1409 , in which the following calculations are carried out: 
 
MFI ij ←SMFI/10 
 
PDF ij ←SPDF/10 
 
 Namely, an image pixel datum MFI ij  is defined as an average value of the consecutive ten digital magnetic field intensity data MFI obtained from the magnetic field intensity signal MFI-S, and an image pixel datum PDF ij  is defined as an average value of the consecutive ten phase difference data PDF obtained from the phase difference signal PDF-S. 
 
         [0119]     At step  1410 , the counter c and the variables SMFI and SPDF are reset to “0”. Then, at step  1411 , it is determined whether the scanning-direction indicating flag SDF is equal to “0” or “1”. Since SDF=0 at the initial stage, the control proceeds from step  1411  to step  1412 , in which it is monitored whether a count number of the counter i has reached “m”. Note, as is apparent from  FIGS. 5 and 6 , “m” represents a number of image pixels included in a horizontal line of each of the frames of magnetic field intensity and phase difference images (MFI ij , PDF ij ).  
         [0120]     Since i=0 at the initial stage, the control proceeds from step  1412  step  1413 , in which the count number of the counter i is incremented by “1”. Then, the control returns to step  1402 , and the routine comprising steps  1402  to  1414  is repeated until the count number of the counter c has reached “m”, i.e. until the respective m image pixel data MFI ij  and PDF ij , included in the horizontal lines of the frames of magnetic field intensity and phase difference images, have been obtained.  
         [0121]     At step  1412 , when it is confirmed that the count number of the counter i has reached “m”, i.e. that respective two first horizontal lines of image pixel data MFI ij  and PDF ij  have been produced, the control proceeds from step  1412  to  1414 , in which the scanning-direction indicating flag SDF is changed from “0” to “1”. Then, at step  1415 , a count number of the counter j is incremented by “1”, and, at step  1416 , it is monitored whether the count number of the counter j has reached “n”. Note, as is apparent from  FIGS. 5 and 6 , “n” represents a number of the horizontal lines included in each of the frames of magnetic field intensity and phase difference images (MFI ij , PDF ij ).  
         [0122]     When the count number of the counter j has not reached “n”, the control proceeds from step  1416  to step  1417 , it is monitored whether the count number (m) of the counter i has been decreased to “0”. If j&gt;0, the control proceeds to step  1418 , in which the count number of the counter i is decremented by “1”. Then, the control returns from step  1418  to step  1402 , to thereby produce two respective second horizontal lines of image pixel data MFI ij  and PDF ij . Note, during the production of the two respective second horizontal lines of image pixel data MFI ij  and PDF ij , the control skips from step  1441  to step  1410 , because of SDF=1.  
         [0123]     At step  1417 , when it is confirmed that the count number of the counter i has been decreased to “0”, i.e. that the two respective second horizontal lines of image pixel data MFI ij  and PDF ij  have been produced, the control proceeds from step  1417  to step  1419 , in which the scanning-direction indicating flag SDF is changed from “ 1 ” to “0”. Then, at step  1420 , the count number of the counter j is incremented by “ 1 ”, and, at step  1421 , it is monitored whether the count number of the counter j has reached “n”.  
         [0124]     When the count number of the counter j has not reached “n”, the control returns from step  1421  to step  1402 , to thereby produce two respective third horizontal lines of image pixel data MFI ij  and PDF ij . Note, during the production of the two respective second horizontal lines of image pixel data MFI ij  and PDF ij , the control proceeds from step  1411  to step  1412 , because of SDF=0.  
         [0125]     At step  1416  or  1421 , it is confirmed that the count number of the counter j has reached “n”, i.e. that the chip area (CA) concerned has been completely scanned with the modulated and focused laser beam MLB, the control returns from  1416  or  1421  to step  1305  of the main routine shown in  FIG. 13 .  
         [0126]      FIG. 15  shows a flowchart of a main routine executed in the microprocessor  26 A of the personal computer  26 .  
         [0127]     At step  1501 , it is monitored whether a signal feeding command for feeding a scanning operation start signal to the system control unit  10  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the signal feeding command is confirmed, the control proceeds from  1501  to step  1502 , in which the scanning operation start signal is fed to the system control unit  10  (see step  1301  of  FIG. 13 ).  
         [0128]     At step  1503 , it is monitored whether the personal computer  26  receives two respective frames of m×n image pixel data MFI ij  and PDF ij  from the system control unit  10  (see step  1305  of  FIG. 13 ). When the receipt of the frames of m×n image pixel data MFI ij  and PDF ij  from the system control unit  10  is confirmed, the control proceeds from step  1504 , in which the frames of image pixel data MFI ij  and PDF ij  are stored in the RAM  26 C of the personal computer  26 .  
         [0129]     At step  1505 , it is monitored whether an image displaying command for displaying respective magnetic field intensity and phase difference images on the TV monitor  28  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the image displaying command is confirmed, the control proceeds from  1505  to step  1506 , in which respective video signals MFI-VS and PDF-VS are produced based on the frames of image pixel data MFI ij  and PDF ij . Then, at step  1507 , a magnetic field intensity image (as shown in  FIG. 9A  or  9 B) and a phase difference image (as shown in  FIG. 10A  or  10 B) are displayed on the TV monitor  28  in accordance with the video signals MFI-VS and PDF-VS. Note, if necessary, only one of the magnetic field intensity image and the phase difference image may be selectively displayed on the TV monitor  28 .  
         [0130]     At step  1508 , it is monitored whether an image data storing command for storing the frames of image pixel data MFI ij  and PDF ij  on the hard disk  26 F is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the image data storing command is confirmed, the control proceeds from  1508  to step  1509 , in which the frames of image pixel data MFI ij  and PDF ij  are stored on the hard disk  26 E through the hard disk driver  26 E.  
         [0131]     At step  1510 , it is monitored whether a referential image displaying command for displaying a referential image on the TV monitor  28  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . Note, the referential image is derived from a good semiconductor device (see  FIG. 9B  or  10 B), and is previously stored as a frame of image pixel data on the hard disk  26 F. When the inputting of the referential image displaying command is confirmed, the control proceeds from  1510  to step  1511 , in which the corresponding frame of image pixel data is read from the hard disk  26 E. Then, at step  1512 , a video signal is produced based on the read frame of image pixel data, and, at step  1513 , an image is displayed as the referential image on the TV monitor  28  in accordance with the produced video signal. For example, when the referential image is a phase difference image, it is possible to compare the phase difference image, displayed at step  1507 , with the referential phase difference image, as shown in  FIGS. 10A and 10B  by way of example.  
         [0132]     At step  1514 , it is monitored whether a histogram producing command for producing respective histogram data from the frames of image pixel data MFI ij  and PDF ij  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the histogram producing command is confirmed, the control proceeds from  1514  to step  1515 , in which a histogram production routine is executed to thereby produce magnetic field intensity histogram data and phase difference histogram data. Note, the image data production routine will be explained in detail with reference to  FIG. 14  hereinafter.  
         [0133]     At step  1516 , it is monitored whether a histogram displaying command for displaying respective magnetic field intensity and phase difference histograms on the TV monitor  28  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the histogram displaying command is confirmed, the control proceeds from  1516  to step  1517 , in which respective video signals for the magnetic field intensity and phase difference histograms are produced based on the aforesaid histogram data. Then, at step  1518 , a magnetic field intensity histogram (as shown in  FIG. 11A  or  11 B) and a phase difference histogram (as shown in  FIG. 12A  or  12 B) are displayed on the TV monitor  28  in accordance with the video signals for the magnetic field intensity and phase difference histograms. Note, only one of the magnetic field intensity histogram and the phase difference histogram may be selectively displayed on the TV monitor  28 , if necessary.  
         [0134]     At step  1519 , it is monitored whether a histogram data storing command for storing the aforesaid histogram data on the hard disk  26 F is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the histogram data storing command is confirmed, the control proceeds from  1519  to step  1520 , in which the histogram data are stored on the hard disk  26 E through the hard disk driver  26 E.  
         [0135]     At step  1521 , it is monitored whether a referential histogram displaying command for displaying a referential histogram on the TV monitor  28  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . Note, the referential histogram is derived from a good semiconductor device (see  FIG. 11B  or  12 B), and is previously stored as histogram data on the hard disk  26 F. When the inputting of the referential histogram displaying command is confirmed, the control proceeds from  1521  to step  1522 , in which the corresponding histogram data is read from the hard disk  26 E. Then, at step  1523 , a video signal is produced based on the read histogram data, and, at step  1524 , a histogram is displayed as the referential histogram on the TV monitor  28  in accordance with the produced video signal for the histogram data. For example, when the referential histogram is a phase difference histogram, it is possible to compare the phase difference histogram, displayed at step  1518 , with the referential phase difference image, as shown in  FIGS. 12A and 12B  by way of example.  
         [0136]     At step  1525 , it is monitored whether an image removing command for removing the displayed images and/or histograms from the TV monitor  28  is input to the microprocessor  26 A by manipulating either the keyboard  30  or the mouse  32 . When the inputting of the image removing command is confirmed, the control proceeds from  1525  to step  1526 , in which the displayed images and/or histograms are removed from the TV monitor  28 .  
         [0137]     Namely, in the personal computer  26 , it is always monitored to determine whether any of the various commands is input to the microprocessor  26 A, and, when the inputting of a command is confirmed, the corresponding processing is carried out.  
         [0138]      FIG. 16  shows a flowchart of the histogram production routine which is executed as a subroutine in step  1515  of the main routine shown in  FIG. 15 . Note, for the production of the respective magnetic field intensity and phase difference histogram data, 256 frequencies MFQ k(000, 001, . . . 254, and 255)  and 256 frequencies PDQ k(000, 001, . . . 254, and 255)  are defined in the RAM  26 C of the personal computer  26 .  
         [0139]     At step  1601 , an initialization is carried out. Namely, counters i and j are initialized to “0”, and the 256 frequencies MFQ k(000, 001, . . . 254, and 255)  are initialized to “0”  
         [0140]     At step  1602 , the pixel datum MFI ij  is read from the RAM  26 C. Then, at step  1603 , a frequency MFQ k , corresponding to a density (gradation) level k of the read pixel datum MFI ij  is read from the RAM  26 C. For example, when the read pixel datum MFI ij  features a density level “122”, the frequency MFQ 122  is read from the RAM  26 C.  
         [0141]     At step  1604 , the following calculation is carried out: 
 
MFQ k ←MFQ k +1 
 
         [0142]     At step  1605 , it is monitored whether a count number of the counter i has reached “m”. Since i=0 at the initial stage, the control proceeds from step  1605  to step  1606 , in which the count number of the counter i is incremented by “ 1 ” Then, the control returns to step  1602 , and the routine comprising steps  1602  to  1606  is repeated until the count number of the counter i has reached “m”, i.e. until the image pixel data MFI ij  included in the first horizontal line (j=0) has been read from the RAM  26 C.  
         [0143]     At step  1605 , when it is confirmed that the count number of the counter i has reached “m”, the control proceeds from  1605  to  1607 , in which the counter i is reset to “0”. Then, at step  1608 , it is monitored whether a count number of the counter j has reached “n”.  
         [0144]     Since j=0 at the initial stage, the control proceeds from step  1608  to step  1609 , in which the count number of the counter j is incremented by “ 1 ”. Then, the control returns to step  1602 , and the routine comprising steps  1602  to  1606  is repeated until the count number of the counter i has reached “m” (step  1605 ), i.e. until the image pixel data MFI ij  included in the second horizontal line (j=1) has been read from the RAM  26 C.  
         [0145]     At step  1605 , when it is confirmed that the count number of the counter i has again reached “m”, i.e. that all the image pixel data MFI ij  included in the second horizontal line (j=1) has been read from the RAM  26 C, the control proceeds from step  1605  to step  1607 . Namely, the routine comprising steps  1602  to  1609  is repeated until the count number of the counter j has reached “n” (step  1608 ), i.e. until the frame of image pixel data MFI ij  has been completely read from the RAM  26 C.  
         [0146]     Note, when the reading of the frame of image pixel data MFI ij  is completed, the 256 frequencies MFQ k  form the aforesaid histogram data for the magnetic field intensity image (MFI ij ).  
         [0147]     At step  1608 , when it is confirmed that the count number of the counter j has reached “n”, the control proceeds from step  1608  to  1610 , in which the counter j is reset to “0”, and the 256 frequencies PDQ k(000, 001, . . . 254, and 255)  are initialized to “0”.  
         [0148]     At step  1611 , the pixel datum PDF ij  is read from the RAM  26 C. Then, at step  1612 , a frequency PDQ k , corresponding to a density (gradation) level k of the read pixel datum PDF ij  is read from the RAM  26 C. For example, when the read pixel datum PDF ij  features a density level “133”, the frequency MFQ 133  is read from the RAM  26 C.  
         [0149]     At step  1613 , the following calculation is carried out: 
 
PDQ k ←PDQ k +1 
 
         [0150]     At step  1614 , it is monitored whether a count number of the counter i has reached “m”. Since i=0 at the initial stage, the control proceeds from step  1614  to step  1615 , in which the count number of the counter i is incremented by “1”. Then, the control returns to step  1611 , and the routine comprising steps  1602  to  1606  is repeated until the count number of the counter i has reached “m”, i.e. until the image pixel data PDF ij  included in the first horizontal line (j=0) has been read from the RAM  26 C.  
         [0151]     At step  1614 , when it is confirmed that the count number of the counter i has reached “m”, the control proceeds from  1614  to  1616 , in which the counter i is reset to “0”. Then, at step  1617 , it is monitored whether the count number of the counter j has reached “n”.  
         [0152]     Since j=0 at the initial stage, the control proceeds from step  1617  to step  1618 , in which the count number of the counter j is incremented by “ 1 ”. Then, the control returns to step  1611 , and the routine comprising steps  1611  to  1615  is repeated until the count number of the counter i has reached “m” (step  1614 ), i.e. until the image pixel data PDF ij  included in the second horizontal line (j=1) has been read from the RAM  26 C.  
         [0153]     At step  1614 , when it is confirmed that the count number of the counter i has again reached “m”, i.e. that all the image pixel data PDF ij  included in the second horizontal line (j=1) has been read from the RAM  26 C, the control proceeds from step  1614  to step  1616 . Namely, the routine comprising steps  1611  to  1618  is repeated until the count number of the counter j has reached “n” (step  1617 ), i.e. until the frame of image pixel data PDF ij  has been completely read from the RAM  26 C.  
         [0154]     Note, when the reading of the frame of image pixel data PDF ij  is completed, the 256 frequencies PDQ k  form the aforesaid histogram data for the phase difference image (PDF ij ).  
         [0155]     At step  1617 , when it is confirmed that the count number of the counter j has reached “n”, the control returns to step  1515  of the main routine shown in  FIG. 15 .  
         [0156]     In the above-mentioned embodiment, although the X-Y stage  14  is moved with respect to the modulated and focused laser beam MLB to thereby scan the silicon wafer SW with the laser beam MLB, the scanning operation may be carried out by either deflecting the laser beam MLB with respect to the silicon wafer SW or a combination of the movement of the X-Y stage and the deflection of the laser beam MLB.  
         [0157]     Also, in the above-mentioned embodiment, although the video signals MFI-VS and PDF-VS are produced in the personal computer  26 , the production of the video signals MFI-VS and PDF-VS may be carried out in the system control unit  10 , if necessary. Similarly, although the magnetic histogram data are produced in the personal computer  26 , the production of the histogram data may be carried out in the system control unit  10 , if necessary.  
         [0158]     Further, in the above-mentioned embodiment, although the silicon wafer SW is mounted on the X-Y stage  14 , a semiconductor device or chip, diced from the silicon wafer SW, may be mounted on the X-Y stage  14 .  
         [0159]     Finally, it will be understood by those skilled in the art that the foregoing description is of preferred embodiments of the system, and that various changes and modifications may be made to the present invention without departing from the spirit and scope thereof.