Abstract:
A prober for measuring electrical characteristics of a semiconductor device includes a contact device having a contactor with a sharp tip provided at a position close above the position of the semiconductor device at which the electrical characteristics are to be measured, a drive device for driving the contact device in the directions of the x-, y- and z-axes on the nm order, an x- and y-axis drive circuit that supplies drive current to the drive device for driving the contact device in the directions of the x- and y-axes, a signal supply device for supplying a signal between the surface of the semiconductor device and the contact device, a detection device for detecting the signal from the supply device and providing an output signal, a z-axis drive control circuit that supplies drive current to the drive device for driving the contact device in the z-axis direction by using the output signal from the detection device as a feedback input signal, a circuit for providing output to the z-axis drive control circuit of a signal that halts the driving of the contact device in the z-axis direction upon detection of an abnormal signal by the detection device, a switch that connects the contact device to the detection device, a controller that supplies signals for driving the contact device in the x-, y- and z-axis directions, preset tunneling current signals for the z-axis drive control circuit and preset voltage signals for variable DC bias voltage of the detection device, acquires and stores x, y and z positional information for the contact device along with voltage, current and potential information from the detection device, and performs image processing on the information, and a display device that displays the information and image information.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a prober for directly measuring the electrical characteristics of electronic devices and the method of measuring same, and relates particularly to a prober suited to the measurement of the electrical characteristics of semiconductor devices with a fine structure. 
     2. Description of the Prior Art 
     Determining the internal state of operation of a semiconductor device is essential to semiconductor device research and development. The apparatus conventionally used for this kind of determination is a prober for the electrical measurement of semiconductor devices. Such a prober is first positioned and then a certain amount of force is applied with the tips of its probes to make electrical contact between contacts on the semiconductor device and the probes, and thereby the electrical characteristics (current, voltage, etc.) at various locations on the device are measured using two or three probes, or it may be used together with a stage that varies the temperature of the semiconductor device to measure the electron mobility or the like, and thereby determine spatial electrical characteristic information about the interior of the semiconductor device. 
     Since the aforementioned conventional probers for the electrical measurement of semiconductor devices have probe tips of a size on the μm order or greater, the contacts at various locations on a semiconductor device with a fine structure are smaller than the size of the probe tips, so it is not possible to measure the electrical characteristics directly. In addition, even with semiconductor devices having design rules of a size of μm or greater, the probers for electrical measurement do not have drive means for driving the prober in sub-μm order units, so they are inappropriate as a means of directly measuring the potential distribution within a semiconductor device. Moreover they have a problem in that the contact pressure of the probe tip destroys the contact of the semiconductor device. 
     For this reason, the electrical measurement of semiconductor devices was performed instead by packaging the semiconductor device for radio-frequency measurement and then the probes were put into contact with electrode contacts that extended out from the semiconductor device. However, as semiconductor devices reach finer geometries, probers for measuring electrical characteristics that directly measure various locations of the semiconductor device have become necessary. 
     In addition, the effects of the surfaces and interfaces on the internal structure within the semiconductor device are not negligible at the time of measuring the electrical characteristics, but rather the appearance of quantum effects arising from the miniaturization of the semiconductor devices have made the interior electronic structure of the semiconductor devices even more complex. For this reason, parameters such as the potential distribution and the like which are necessary for the design simulation of semiconductor devices cannot be measured with conventional probers, so research and development of fine-geometry semiconductor device technology is in a difficult predicament. 
     In the design of future fine-geometry semiconductor devices, the direct measurement of electrical characteristics at various locations of a semiconductor device with a probe will be essential to find the size of electrodes or other fabrication errors, and the potential distribution or other parameters necessary for simulation, so that by performing comparative studies of these parameters against the simulation, it is possible to increase the operating speed of semiconductor devices, raise their switching ratios, reduce their power consumption and perform various other kinds of optimization. 
     For this reason, there is a need for the development of technology that can directly measure the internal potential distribution within fine-geometry semiconductor devices and semiconductor devices, along with the size of electrodes or other fabrication errors and the like. 
     The present invention came about in consideration of the aforementioned situation and its object is to provide a prober for electrical measurement that is capable of direct measurement of electrical characteristics required for fabrication technologies for fine-geometry semiconductor devices, and also provide a measurement method using said prober. 
     SUMMARY OF THE INVENTION 
     In order to achieve the aforementioned objects, the prober for electrical measurement of the present invention comprises: a probe with a sharp tip, drive means for driving said probe in the direction of the x-, y- and z-axes on the nm order, an x- and y-axis drive circuit that supplies drive current to said drive means for driving in the direction of the x- and y-axes, a first electrical circuit for detecting the tunnel current between said probe and the semiconductor device to be measured, a z-axis drive control circuit that supplies drive current to said drive means for driving said probe in the z-axis direction by using the output from said first electrical circuit as feedback input, a second electrical circuit that applies a variable DC bias voltage between said probe and semiconductor device and detects the current and voltage between said probe and semiconductor device, a circuit for providing output to the z-axis drive control circuit of a signal that halts the driving of said probe in the z-axis direction upon the detection of an abnormal increase in the current flowing in said second electrical circuit, a switch that connects said probe to either said first electrical circuit or said second electrical circuit, a controller that supplies signals for driving said probe in the x-, y- and z-axis directions, setting tunneling current signals for the z-axis drive control circuit and setting voltage signals for the variable DC bias voltage of the second electrical circuit, and acquires x, y and z positional information for said probe along with the voltage, current and potential information from the second electrical circuit, and stores and performs image processing on said information, and a display device that displays said information and image information. 
     As the means of driving the aforementioned probe on the nm order, a piezoelectric element actuator or inchworm drive may be used. 
     The probe can also be driven to the desired position while using interatomic forces, temperature or light instead of the aforementioned tunnel current to detect the state of contact between the probe and the surface of the semiconductor device. 
     In addition, the method of measuring electrical characteristics using the aforementioned prober according to the present invention comprises the steps of: causing a sharp probe to scan over the surface of a semiconductor at a distance at which the tunnel current phenomenon occurs and based on the semiconductor surface approach position data thus obtained, accurately positioning said probe at a semiconductor surface approach position corresponding to the desired position on the semiconductor surface, driving said probe lower in the z-axis direction toward the semiconductor surface until an abnormal increase in current flows through said probe, applying a voltage to said probe, and directly measuring the current and voltage at the desired position on the semiconductor device. 
     The probe can also be driven to the desired position while using interatomic forces, temperature or light instead of the aforementioned tunnel current to detect the state of contact between the probe and the surface of the semiconductor device. 
     As described above, the present invention uses a conductive probe with a tip radius of not more than 0.02 μm or less as the probe, and by using a drive mechanism that drives the sharp probe to approach a position near the semiconductor device with nm order accuracy until an abnormal increase in the current flowing in the sharp probe is detected, thereby detecting the electrical contact between the sharp probe and the semiconductor surface, it is possible to put a sharp probe into electrical contact with the semiconductor surface without destroying the semiconductor device, thereby directly measuring the electrical characteristic of a specific location on a semiconductor device with a sharp probe and an electrical characteristic measurement circuit. 
     The other objects and other characteristics of this invention will be further clarified in the following detailed description based on the appended drawings. 
    
    
     BRIEF EXPLANATION OF THE DRAWING 
     FIG. 1 is a diagram used to explain the position detection mode of the prober according to the present invention. 
     FIG. 2 is a diagram used to explain the measurement mode of the prober of FIG.  1 . 
     FIG. 3 is a flowchart that shows the measurement procedure for the prober of the present invention. 
     FIG. 4 is a diagram showing a three-dimensional image of the approach position plan detected in the position detection mode of FIG.  1 . 
     FIG. 5 is a diagram showing a track of the movement of the probe tip in the measurement ode of FIG.  2 . 
     FIG. 6 is a diagram used to explain the Coulomb blockade of the semiconductor device shown in FIGS. 1 and 2. 
     FIG.  7 ( a ) is a graph showing the current/voltage characteristic of a thin metal wire during the Coulomb blockade phenomenon. 
     FIG.  7 ( b ) is a graph showing the potential distribution of a thin metal wire during the Coulomb blockade phenomenon. 
     FIG. 8 is a diagram used to explain the position detection mode of the prober according to the present invention on another semiconductor device. 
     FIG. 9 is a diagram used to explain the measurement mode of the prober of FIG.  8 . 
     FIG. 10 is a diagram used to explain the Coulomb blockade of the semiconductor device shown in FIGS. 8 and 9. 
     FIG. 11 is a diagram used to explain the principle of the inchworm drive mechanism for the probe. FIG.  11 ( a ) shows the state at the start of operation of the inchworm drive mechanism. FIG.  11 ( b ) shows the state when the drive shaft is clamped with one clamp element. FIG.  11 ( c ) shows the state when the piezoelectric element is extended. FIG.  11 ( d ) shows the state when the drive shaft is clamped with another clamp element. FIG.  11 ( e ) shows the state when the clamping of one clamp element is released. FIG.  11 ( f ) shows the state when the piezoelectric element is compressed and the drive shaft is moved to the left. FIG.  11 ( g ) shows the state when one clamp element is clamped. FIG.  11 ( h ) shows the state when the clamping of the other clamp element is released. 
     FIG. 12 is an explanatory diagram showing the principle of using the tunnel current to detect positions near the surface of a semiconductor device. 
     FIG. 13 is an explanatory diagram showing the track of the needle tip in positions near the surface. 
     FIG. 14 is a diagram used to explain an apparatus that utilizes interatomic forces to measure the electrical characteristics of a semiconductor surface. 
     FIG. 15 is a diagram used to explain the method of utilizing light to detect contact with a seniconductor surface. 
     FIG. 16 is a diagram used to explain the method of utilizing temperature to detect contact with a semiconductor surface. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Here follows a detailed description of the basic structure of the prober according to the present invention based on FIGS. 1-7. 
     FIGS. 1 and 2 show an embodiment of the prober for electrical measurement according to the present invention, using a probe with a tip radius of not more than 0.02 m or less, and utilizing the principle of a scanning tunneling microscope for approach positioning as the drive apparatus for said probe. 
     We will first explain the detection of positions near the surface of a semiconductor device utilizing the principle of the aforementioned scanning tunneling microscope (STM). FIG. 12 is a diagram that illustrates this principle. Reference numeral  31  denotes a conductive probe, numeral  32  a semiconductor substrate disposed in an xy plane, numeral  32   a  schematically shows the atoms on the surface of the semiconductor substrate, numeral  33  the tunneling current flowing between the probe  31  and the semiconductor substrate  32 , numeral  36  a DC bias power supply, numeral  37  a tunneling current detection circuit, numeral  41  a z-axis drive control circuit, numeral  42  an xy-axis drive circuit, numerals  43   x,    43   y  and  43   z  x-axis, y-axis and z-axis piezoelectric element actuators that drive the probe in the x-axis, y-axis and z-axis, respectively, numeral  44  a controller comprising a processor, storage device and the like, numeral  45  is a control panel for entering operation instructions and setpoints, and numeral  46  is a display device. 
     When the probe  31  is in a position near the surface of the semiconductor substrate  32 , a tunneling current  33  that depends on the voltage applied between the tip of the probe and the atoms  32   a  in the surface of the semiconductor substrate  32  flows across the vacuum gap as the barrier. Since the fluctuations in the tunneling current  33  are very sensitive to the distance s between the probe  31  and the surface of the semiconductor substrate  32 , by detecting fluctuations in the tunneling current with the tunneling current detection circuit  37 , fluctuations in the heights above the reference plane of the semiconductor surface can be detected. 
     The piezoelectric element actuators  43   x,    43   y  and  43   z  which drive three spatially independent shafts are used for the fine-motion driving and scanning motion driving of the probe  31 . By applying a voltage to two electrodes provided on each piezoelectric element (piezo element), the probe  31  is subjected to fine-motion displacement scanning in the x-axis and y-axis directions and fine-motion displacement driving in the z direction (e.g., 0.1 nm/V). 
     The z-axis drive control circuit  41  accepts feedback input of the output of the tunneling current detection circuit  37  using the tunneling setting from the controller  44  as its setting, thus serving as a feedback drive control circuit that exerts control such that the tunneling current  33  is maintained at the setting. The setting from the controller  44  (the tunneling current setting) corresponds to the set distances of the probe  31  from the surface of the semiconductor substrate, and the output of the z-axis drive control circuit represents a quantity  31   s  corresponding to the approach position in the z-axis direction to the surface of the semiconductor substrate  32   a.    
     When the probe  31  scans in the direction of the x-axis or y-axis on instruction from the control panel  45 , the probe  31  is driven to scan across the surface of the semiconductor substrate at a height matching the state of the surface on an atomic level, as shown by  31   s  in FIG.  12 . The scanning displacement of the probe tip in the x-axis direction and y-axis direction, and the driving displacement in the z-axis direction are acquired, stored and subjected to three-dimensional image processing by the controller  44 , so the surface state at the approach position is shown in real time as a three-dimensional image on the display device  46 . 
     FIG. 13 shows the approach position track  31   s  in the z-axis direction of the probe  31  under conditions that the tunneling current  33  flowing between the probe and the surface of the semiconductor device is to be constant. In fact, the tunneling current also differs depending on the electronic structure at various locations on the semiconductor device, so the approach position of the probe tip in the z-axis direction also differs depending thereon. Note that in the diagram, reference numeral  32  denotes a semiconductor substrate while numeral  34   a  denotes an electrode provided upon the semiconductor substrate. 
     Returning to FIGS. 1 and 2, FIG. 1 shows the connection state in the position detection mode of the probe, while FIG. 2 shows the connection, state during measurement mode. Reference numeral  1  denotes a sharp probe (hereinafter referred to simply as a “probe”), numeral  2  a semiconductor substrate disposed with its surface in the xy plane, numeral  3  the tunneling current flowing between the probe  1  and the semiconductor device, numeral  4  a thin metal wire (e.g., a Pt wire several hundred nm wide) which is a semiconductor element, numeral  5  a ground electrode, and numeral  5   a  an electrode. The ground electrode  5  may also be an electrode contact that is able to be extended outside. 
     Reference numeral  6  denotes a DC bias power supply, numeral  7  a tunneling current detection circuit, numeral  8  a variable DC bias power supply, numeral  9  is a current detection circuit, numeral  10  a switch where a position detection mode terminal  10   t  is connected to the tunneling current detection circuit  7  when the measurement prober is in position detection mode while a measurement mode terminal  10   m  is connected to the current detection circuit  9  when the measurement prober is in measurement mode, numeral  11  a z-axis drive control circuit, numeral  12  an xy-axis drive circuit, numerals  13   x,    13   y  and  13   z  x-axis, y-axis and z-axis piezoelectric element actuators that drive the probe in the x-axis, y-axis and z-axis, respectively, numeral  14  a controller comprising a processor, storage device and the like, numeral  15  a control panel for entering operation instructions and setpoints, and numeral  16  a display device. (Note that in this Specification, items that are given the same reference number indicate identical or equivalent items.) 
     FIG. 3 is an example of a flowchart of the measurement method by the prober for electrical measurement of the present invention. The measurement method of the present invention comprises two stages, the position detection mode of FIG.  1  and the measurement mode of FIG. 2, with the switching among them performed by the switch  10 . In the position detection mode of FIG. 1, the surface approach positions (x s , y s , z s ) above the semiconductor device is measured by STM scanning under the constant tunneling current conditions (Step S 2 ), stored in the memory device of the controller  14 , and the state of the surface approach position is displayed as a three-dimensional image on the display device  16  (Step S 3 ). Upon the measurement mode settings input from the control panel  15 , the switch  10  switches from the position detection mode terminal  10   t  to the measurement mode terminal  10   m,  and the prober for electrical measurements switches to measurement mode (Step S 4 ). At this time, the feedback input to the z-axis drive control circuit is halted. 
     FIG. 4 is a three-dimensional image from the STM of FIGS. 1 and 2 displayed on the display device  16 . The image of the surface approach positions corresponds to the physical shape and electrical characteristics of the locations on the surface of the semiconductor device. The position (x, y) of the location to be measured is set from the control panel  15  in reference to positions in the image of surface approach positions (e.g., the image of electrode  5   a ) (Step S 5 ), and the probe is moved to an approach position corresponding to the position of the location to be measured (x, y, z s =j) (Step S 6 ). (However, the [positions] are found by (x, y) interpolation of the surface approach positions (x s , y s , z s ) in the vicinity stored in STM scanning.) At the point in time when the probe  1  has moved to the corresponding approach position, the voltage applied to the piezoelectric element actuators  13   x  and  13   y  is fixed, namely the scanning position of the probe in the xy plane is fixed. 
     Next, a voltage is applied to piezoelectric element actuator  13   z  to cause the probe  1  to approach the surface of the semiconductor device. In this state, when the probe  1  makes electrical contact with the semiconductor device, the current flowing through the probe  1  will increase abnormally, and by detecting this with a current change detector, e.g. a differential current detector, within the variable DC bias power supply  8 , the driving of the piezoelectric element actuator  13   z  is halted and the position of the probe in the z direction is fixed (Step S 7 ). The voltage of the variable DC bias power supply  8  is set to constant or variable and applied to probe  1 , while the current and voltage are measured (Step S 8 ). 
     In order to measure the electrical characteristics of another location on the semiconductor device (Step S 10 ), that location is set with the control panel  15  and the probe  1  is moved to the stored approach position (Step S 5 ), and the current and voltage are measured in the same manner as in the previous measurement. In this manner, it is possible to measure the voltage and current at various locations on the semiconductor device. 
     FIG. 5 shows the track of movement of the tip of the probe  1  (solid lines) when moving among measurement points A m , B m , C m , . . . on the semiconductor device. A, B, C . . . are the positions among the surface approach positions of the probe  1  measured during STM scanning that correspond to the measurement points A m , B m , C m , . . . in a plane. The tip of the probe  1  moves via positions in the plane of approach positions corresponding to measurement points and moves to the measurement points. In addition, it is also possible to move from the measurement point A m  to the approach position B corresponding to the next measurement point. Note that the dotted line shows approach positions measured by STM scanning. 
     Moreover, even without performing the STM operation in advance and storing surface approach position information, it is also possible to position the probe at a surface approach position for each measurement point individually and then make electrical contact with the semiconductor surface and repeat the process of measuring electrical characteristics. Namely, this method of switching the mode at each measurement point can also be used. 
     Since the electrode  5   a  is sub-μm in size, the probes of conventional probe apparatus would also make contact with portions other than the electrode  5   a.  The gap between the electrode  5   a  and electrode  5  is also predicted to become sub-μm in size in the future, so the contact region of the current probes would be larger than the gap between electrode  5   a  and electrode  5 . Therefore, it is necessary to use a sharp probe as in the present apparatus, and probes having a tip radius of not more than 0.02 μm can be produced with ordinary electropolishing. With such sharp probes, it is possible to measure the current/voltage characteristic between the electrode  5   a  and the electrode  5  (ground). 
     When the tip of the probe  1  approaches a stipulated surface location on the semiconductor device, the wave function of the stipulated location extends out from the surface, and by making contact with the wave function, free electrons freely move to the tip of the probe  1 . So even if the probe  1  does not make physical contact with the stipulated location on the semiconductor, the probe  1  and the semiconductor achieve continuity. Since there is no mechanical contact, it is possible to measure the current/voltage characteristic of the semiconductor device without damage to the contact locations, electrodes (contacts) or substrate surface of the semiconductor device. In addition, since the abnormal increase in current is detected by a current change detection circuit or differential circuit, the electrical contact of the probe  1  can be detected sensitively on the very outside of the wave function (the position furthest away from the semiconductor device). 
     In the case of FIG. 2, the electrical contact of the probe  1  to electrode  5   a  can be detected by detecting the abnormal increase in current with the current detection circuit  9 . Next, by scanning the voltage of the variable DC bias power supply  8  from zero, the current/voltage characteristic of the electrode  5   a  of the thin metal wire  4  is measured directly with the current detection circuit  9 . 
     The electrode  5  connected to the DC bias  6  and current detection circuit  9  need not be connected directly to the thin metal wire  4  which is the semiconductor device as shown in FIGS. 1 and 2, but rather it may be connected to the substrate  2 . Even if the probe  1  makes electrical contact with locations of insulation on the semiconductor device, the abnormal increase in the current flowing between the probe  1  and electrode  5   a  can still be measured. Therefore, the current/voltage characteristic of any stipulated location on the semiconductor device can be measured directly. 
     In the event that ions or the like are present near the thin metal wire  4  of the semiconductor device, then a known phenomenon called Coulomb blockade locally impedes the flow of current in a portion of the thin metal wire. As the electrodes and the like of the semiconductor device become finer, metallic impurities present in the vicinity are expected to result in this Coulomb blockade. FIG. 6 shows the state wherein the Coulomb blockade phenomenon has appeared due to a metal island  2 I. 
     By artificially inducing a Coulomb blockade based on various metal islands, it is possible to measure electrical characteristics in this embodiment and investigate the effects of the thin metal wire  4  on conductivity. By adsorbing specific metals to the tip of the probe  1  with vapor deposition or the like, putting this metal into contact with the surface of the semiconductor device near the thin metal wire  4  and instantaneously applying a high-voltage bias with the variable DC bias power supply, it is possible to form any metal island  2 I desired. If one examines he effects of metallic impurities on semiconductor devices as described above, it is possible to analyze and evaluate clearly which kinds of metallic impurities should be paid attention to in order to improve the reliability of a semiconductor device. 
     Crystal defects can be formed by using the variable DC bias power supply  8  to apply an instantaneous high-voltage pulse to the probe  1  of this apparatus near the surface of the semiconductor device instead of vapor-depositing specific metals. The effects of crystal defects on the conductivity of thin metal wires can also be examined in the same manner as for the metal islands  2 I. FIG.  7 ( a ) shows the current/voltage characteristic in the case that the Coulomb blockade phenomenon appears in the electrical characteristics of thin metal wire. It is possible to analyze and evaluate semiconductor devices which have thin metal wires  4  based on this characteristic curve. Note that the straight line shows the current/voltage characteristic in the case in which the Coulomb blockade phenomenon is not present. 
     FIGS. 1 and 2 show an example of measuring the electrical characteristics of a semiconductor device provided with an electrode, but FIGS. 8-10 show an example of measuring the electrical characteristics of semiconductor devices without electrodes, with FIG. 8 being an example of the connections in position detection mode and FIG. 9 being an example of connections in measurement mode. This embodiment shows a semiconductor device with one thin metal wire  4 . The embodiment of FIGS. 8-10 is used to describe examining the internal structure of a semiconductor device not only its electrodes. Since the probe  1  can be moved to any location on the surface of a semiconductor device, it is possible to examine the change in current as a function of the distance along the thin metal wire  4  to the probe position, for example. 
     Since the piezoelectric element actuators  13   x,    13   y  and  13   z  can be moved with an accuracy of 0.10 nm, positioning even at the position of the thin metal wire  4  to nm-order accuracy is possible as shown in FIG.  9 . Positioning in the z direction is possible at 0.1 nm precision, so the probe  1  and thin metal wire  4  can be put into electrical contact without damaging the thin metal wire  4 . The fact that the thin metal wire  4  is a so-called quantum thin wire can be confirmed by the functional relationship in that the conductivity which increases exponentially within a coherent distance becomes constant at positions where this distance is exceeded. 
     In this manner, it is possible to measure electrical characteristics that set foot on the internal structure within the semiconductor device. Quantum effects that conventionally were not a problem begin to appear with such fine structures, so when fine metal electrodes are used in simulations used for the fabrication of semiconductor devices, it is possible to determine directly how to change the handling of their conductivity depending on their size. 
     Here follows an explanation of the measurement of the potential and other characteristics other than conductivity. FIG. 10 shows the state wherein the Coulomb blockade phenomenon occurs in the semiconductor device shown in FIGS. 8 and 9, and this figure is nearly identical to that shown in FIG.  6 . The effects of metallic impurities were examined using the current between electrodes in the example of FIG. 6, but in the example of FIG. 10, the effects of impurities are examined using the potential in the vicinity of the metal island  2 I. The means of forming the metal island  2 I is to be identical. While a localized potential distribution is thought to occur in the vicinity of the metal island  2 I, as shown in FIG. 10, by bringing the probe  1  into direct electrical contact with the semiconductor surface although not above the thin metal wire  4 , and varying the voltage of the variable DC bias power supply  8 , the voltage at which the detection current of the current detection circuit  9  becomes zero is found. This voltage is the potential at that position. By mapping the potential in two dimensions, it is possible to examine the potential distribution in the vicinity of the metal island  2 I. FIG.  7 ( b ) shows the potential distribution in the thin metal wire  4  when the Coulomb blockade phenomenon is caused by the metal island  2 I, so the potential is at 100% at the side of the thin metal wire  4 , roughly 50% at the position of the metal island  2 I and 0% at the connected position of the ground electrode  5 . 
     By examining the effects of metallic impurities on semiconductor devices which could not be examined conventionally, it is possible to analyze and evaluate clearly how any kind of metallic impurity can disturb the operating conditions of the semiconductor device. The potential distribution can be also similarly examined on semiconductor devices that are operating normally, so the direct electrical examination of structures in the interior of the device is possible. 
     In addition, by slightly displacing the probe  1  in the x-axis and y-axis directions around point A of FIG. 5, thus performing a fine-scale measurement of measurement points around measurement point A m , the potential of the conductor (electrode) will be markedly different from the potential of the substrate in the vicinity of the electrode, so it is possible to measure the size of the conductor (electrode) from the potential distribution. 
     In this embodiment, piezoelectric element actuators were used to drive the probe  1  but it is also possible to use any means which can perform scanning on an atomic order (nm order), such as an inchworm drive or the like. FIG. 11 shows the drive mechanism of an inchworm (one axial direction only). An inchworm drive is a mechanism combining a piezoelectric element for elongation and contraction with clamping elements, thereby moving the probe  1  in the manner of an inchworm. 
     In FIG. 11, reference numeral  51  denotes a drive shaft for driving the probe in one direction, while numerals  52  and  53  denote clamp elements and numeral  54  denotes a piezoelectric element with a fixed central portion. FIG.  11 ( a ) shows the state prior to the start of operation of the inchworm drive mechanism. FIG.  11 ( b ) shows the state wherein the drive shaft  51  is clamped by one of the clamp elements  52 . FIG.  11 ( c ) shows the state wherein the piezoelectric element  54  is elongated. FIG.  11 ( d ) shows the state wherein the drive shaft  51  is clamped by the other of the clamp elements  53 . FIG.  11 ( e ) shows the state wherein the clamping of clamp element  52  is released. FIG.  11 ( f ) shows the-state wherein the piezoelectric element  54  is compressed, moving the drive shaft  51  to the left. FIG.  11 ( g ) shows the state wherein clamp element  52  is clamped. FIG.  11 ( h ) shows the state wherein the clamping of clamp element  53  is released. When the piezoelectric element  54  is further elongated, the drive shaft  51  moves further to the left. In this manner, the drive shaft can be moved in nm increments. 
     Instead of using the tunnel current to scan along the surface of the semiconductor device and detect and store positions, it is possible to use interatomic forces, temperature or light to detect electrical contact with the surface of the semiconductor device. 
     FIG. 14 illustrates the principle of an embodiment wherein interatomic forces are utilized to detect electrical contact at a semiconductor surface position. A protrusion (probe)  61   a  (0.02 μm or smaller) is present on the tip of a cantilever  61  that is able to detect minute forces, and the cantilever  61  is distorted as shown in the figure by the interatomic forces that act between this protruding portion  61   a  and the surface of the semiconductor surface. This distortion of the cantilever causes the direction of reflection of the light L 0  emitted from a laser source  66  to change from Ls to Lr. The light is received by a photodetector  67 , and the change in the direction of reflection of light is converted to interatomic force by the displacement signal detector  68 . When the cantilever protrusion  61   a  approaches to near contact with the surface of the semiconductor device, first an attraction mode occurs wherein it is pulled to the atoms  2   a  of the semiconductor surface and upon a closer approach a repulsion mode occurs due to the repulsion from the atoms  2   a  of the semiconductor surface. This state is quite similar to the process undergone in the scattering of rigid spheres, so if one considers the instant of scattering to be contact, the surface contact can be detected from the instant when the forces on the cantilever  61  change from attraction to repulsion. The position of surface contact can be measured by scanning with a drive mechanism similar to that of the apparatus of FIG. 1, stored in the storage device of controller  14 , subjected to image processing and displayed on the display device  16 . 
     In measurement mode, the cantilever  61  is positioned at the stipulated position by a controller as in FIG. 1, the switch puts measurement mode terminal  10   m  into the closed state, and the prober measurement circuit is formed by the semiconductor  2  (or electrode), variable DC bias power supply  8 , current detection circuit  9 , measurement mode terminal  10   m  and the conductor layer  61   b  of the cantilever  61 . The voltage of the variable DC bias power supply  8  is applied between the cantilever and semiconductor (or electrode) and the current is detected, so the electrical characteristics of the semiconductor can be directly measured in the same manner as in FIG.  2 . 
     FIG. 15 illustrates the principle of an embodiment wherein temperature is utilized to detect a semiconductor surface. In this case, a sensor made from a bimetal of two different types of metal M 1  and M 2  welded together and given a sharp tip (0.02 m or less) by electropolishing or the like is used as the probe  71 , and compensating conductors LM 1  and LM 2  lead the potentials of the two metals to a temperature signal extractor  78  which measures the difference between the two potentials and converts it to a temperature. When the tip of this sensor  71  contacts the semiconductor surface, the detected temperature will rapidly change to the temperature of the semiconductor surface, so surface contact can be detected in this case also. 
     FIG. 16 illustrates the principle of an embodiment wherein light is utilized to detect contact with a semiconductor surface. An optical fiber with a sharpened tip is used as the sensor  81 . In order to limit the areas where light can pass to only the sharp area at the tip, all other areas are shut off to light with metal or the like. While the resolution of measurement with light is normally determined by the wavelength, in this state it is determined by the shape of the sharp tip of the optical fiber. Evanescent light (near-field light) is sensitive to the dielectric constant of the optical fiber tip. 
     Light that is emitted from a laser source  86  passes through the fiber and becomes evanescent light Le which senses the dielectric field at the tip, becoming reflected light Ler which returns through the fiber and is detected by the detector  87 , so that a signal is detected by the optical signal extractor  88 . Therefore, the dielectric field will change rapidly when the fiber tip Tp comes in contact with the surface of the semiconductor surface, so contact can be detected. 
     The contact position on the semiconductor surface in FIGS. 15 and 16 is measured by scanning with the same kind of drive mechanism as in FIG. 1, acquired and stored by the controller  14  and displayed as a three-dimensional image on the display device  16 . Moreover, in measurement mode, a conductor layer is applied to the sensors  71  and  81  in the same manner as the device of FIG. 14, the conductor (electrode), variable DC bias power supply, current detection circuit and measurement mode switch assumes the closed state, and the connected measurement mode terminal forms an electrical characteristic measurement circuit of the cantilever conductor layer, so the electrical characteristics of the semiconductor device can be measured directly in the same manner as in FIG.  14 . 
     With the prober for electrical measurement and measurement method therefor, positioning is performed using information on the semiconductor device surface based on surface position data for the semiconductor, and a sharp probe can be put in direct contact with the semiconductor surface without damaging the surface of the semiconductor, so the direct measurement of potential in the interior of ultra-fine semiconductor devices and semiconductor devices becomes possible. Thereby the calculation of various parameters required for simulation is possible and it is possible to find optimal parameters as well as evaluate semiconductor devices.