JP2009053017A - Scanning probe microscope, and local electric characteristic measuring method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning probe microscope capable of measuring a local electric characteristic highly accurately even in the case of a sample having irregularities. <P>SOLUTION: Height information of a sample surface is acquired by vibrating a cantilever 22 provided with a needle-shaped probe 23 of the tip part, and when stopping vibration of the cantilever 22 and scanning, a cantilever 22 position is controlled so as to keep the tip of the probe 23 at a constant distance from the sample surface based on the height information of the sample surface, and the cantilever 22 is bent from the state of keeping the cantilever 22 height, and the tip of the probe 23 is indented into the sample 51. Since the distance between the tip of the probe 23 and the sample surface is kept constant, an indentation depth of the probe 23 can be kept constant even to the sample 51 having irregularities only by bending the cantilever 22 as much as a fixed quantity. Hereby, the local electric characteristic can be measured highly accurately even in the case of the sample 51 having irregularities. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a scanning probe microscope capable of locally measuring electrical characteristics such as conductivity and dielectric constant of a sample, and a local electrical characteristics measuring method using the same.

  In recent years, with the high integration of semiconductor devices such as LSIs, elements such as transistors constituting the semiconductor devices have been miniaturized. Conventionally, in order to evaluate a semiconductor device, an electrode is connected to each element using a prober, and a measurement signal is applied to measure the electrical characteristics of the element. However, with the progress of miniaturization, it is becoming difficult to evaluate the electrical characteristics of the device using a prober.

  In the miniaturization of elements, local impurity distribution has a great influence on the characteristics of the element, so it is required to measure not only the electrical characteristics of the entire element but also the electrical characteristics within the element. Yes. Such measurement of electrical characteristics is important for elucidating the cause of defects as the manufacturing process (manufacturing conditions) becomes more complex and sophisticated with the miniaturization of elements.

As a method for measuring local electrical characteristics of a semiconductor device, there is a measurement method using a probe (probe) such as an AFM (Atomic Force Microscope). In this method, the electrical characteristics of the sample can be locally measured by applying a predetermined voltage between the probe and the sample while scanning the AFM probe while contacting or approaching the sample (for example, Patent Document 1). In order to measure the local electrical characteristics of a sample on which an insulating film such as a natural oxide film is formed, the natural oxide film on the surface of the sample is removed by pushing the tip of the probe into the sample during the scanning of the probe. There is a method of measuring electrical characteristics by penetrating and making electrical contact between the probe and the inside of the sample.
JP 2005-64061 A

  In the measurement of a sample using a conventional scanning probe, the shape of the sample surface is measured in a contact mode in which the probe is in contact with the sample, and the electrical characteristic is measured by measuring the amount of bending of the cantilever by a piezoelectric element, etc. The probe was pressed so that the amount of bending was constant while detecting with. However, in this method, the measurement error may increase depending on the state of the sample surface. 1 and 2 show conventional problems. Here, in FIG. 1, 101 is a semiconductor substrate constituting the sample 105, and 102 is a natural oxide film on its surface. In FIG. 2, reference numeral 104 denotes a cantilever that supports the probe 103.

  For example, when the measurement is performed on the sample 105 having the surface as shown in FIG. 1, the frictional force is different between the portion of the region I where the sample surface is relatively flat and the region II having the inclination, and the cantilever 104. The contact pressure of the probe 103 cannot be kept constant only by keeping the amount of bending constant. Further, when the pushing amount is controlled by the bending amount of the cantilever 104, the pushing amount d1 as shown in FIG. 2A is obtained in the portion (region I) where the friction with the sample surface is small, whereas the sample In the region where the frictional force with the surface is large (region II), the push amount d2 as shown in FIG. 2B is obtained, and the push amount cannot be made uniform on the sample surface. For this reason, the contact area between the probe 103 and the sample 105 changes, and an error due to the shape of the sample surface is included in the measurement result. In a sample with unevenness, the electrical characteristics of the sample itself are high. Measurement could not be performed with accuracy.

  Therefore, in the conventional method, in order to measure the electrical characteristics of the sample with high accuracy, it was necessary to polish the sample before the measurement to make the root mean square roughness (RMS) of the sample surface 0.2 nm or less. . However, there is a problem that it is very time-consuming to prepare a sample having an RMS of 0.2 nm or less. Furthermore, it is impossible to measure local electrical characteristics with high accuracy for a sample having a structure that is not suitable for mirror polishing.

  An object of the present invention is to provide a scanning probe microscope capable of measuring electrical characteristics with high accuracy even for a sample having irregularities and a method for measuring local electrical characteristics using the scanning probe microscope.

  According to one aspect of the present invention, the sample height information acquisition means for acquiring the height information of the sample surface by vibrating a cantilever provided with a needle-like probe at the tip, and the vibration and scanning of the cantilever are stopped. Sometimes, based on the information on the height of the sample surface, a cantilever height control means for controlling the position of the cantilever so as to keep the tip of the probe at a constant distance from the sample surface; By bending the cantilever, a cantilever bending means that pushes the tip of the probe into the sample, and when the probe is pushed into the sample, a measurement signal is applied to the sample and the sample is locally passed through the probe. An electrical property measuring device for measuring the electrical properties, and the probe for measuring height information and local electrical property distribution of the sample. Scanning probe microscope characterized by comprising a probe scanning mechanism for scanning along the serial sample surface is provided.

  According to the above aspect, the height information of the sample is acquired by vibrating (tapping) the cantilever. This improves the followability of the probe to the uneven sample surface as compared with the conventional contact mode. Further, when the cantilever is pushed in, vibration and scanning of the cantilever are stopped, and the height of the cantilever is controlled by the cantilever height control means so that the tip of the probe is at a constant distance from the sample surface. Thereby, the condition immediately before pushing the cantilever can always be made equal without being affected by the sample surface state (inclination or unevenness). Here, the “constant distance” includes a case where the distance between the probe tip and the sample surface is zero, that is, a state where the probe tip is in contact with the sample surface.

  The pushing operation of the probe is performed by pushing the tip of the probe into the sample by bending only the cantilever by the cantilever bending means while keeping the height of the cantilever constant by the cantilever height control means. In this way, the probe is pushed in by bending the cantilever close to the probe, so that the probe can be reliably controlled with high controllability without being affected by the sample surface condition compared to pushing down the entire cantilever and pushing the probe down. Can be pushed into the sample. Therefore, according to the scanning probe microscope of the said viewpoint, even if it is a sample which has an unevenness | corrugation on the sample surface, the pushing amount of a probe can be made constant and a local electrical property can be measured with high precision.

  Furthermore, according to the present invention, there is provided a scanning probe microscope in which the above-mentioned cantilever bending means is constituted by a piezoelectric element provided on the cantilever. By using the piezoelectric element, the free end of the probe can be controlled with high accuracy such as nm order.

  When the cantilever bending means is composed of a piezoelectric element, one end is connected to the upper or lower surface of the cantilever tip side, and the other end is a piezoelectric element fixed to a holder that holds the cantilever, and voltage application Thus, it can be constituted by a piezoelectric element that applies a force in a direction to push down the cantilever. With such a configuration, a stacked type in which a plurality of piezoelectric bodies are stacked can be used. Further, the cantilever bending means is a plurality of piezoelectric films provided on the upper and lower surfaces of the cantilever, and a differential voltage is applied to the piezoelectric films provided on the upper and lower surfaces of the cantilever. You may comprise by the some piezoelectric material film which gives the force of the direction extended to an upper surface side, and gives the force of the direction to shrink | contract to the lower surface side of the said cantilever. In this case, the piezoelectric film and its electrode can be produced using a semiconductor manufacturing process such as a film formation process and etching.

  Furthermore, in the above aspect of the present invention, the height of the cantilever immediately before pushing is maintained such that the probe tip is at a constant distance from the sample surface. For this reason, the pushing depth of the probe can be made constant only by making the amount of bending of the cantilever by the cantilever bending means constant. In this way, the control of the cantilever bending means only allows a certain amount of bending to be performed, and the configuration of the control device can be simplified.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 3 is a block diagram showing a scanning probe microscope according to an embodiment of the present invention. 4A and 4B are side views showing a cantilever used in a scanning probe microscope according to one embodiment of the present invention. In the following description, the XY direction refers to a direction parallel to the surfaces of the sample stage 52 and the sample 51, and the Z direction means a direction perpendicular to the surface of the sample 51.

  In the scanning probe microscope 10 according to the embodiment of the present invention shown in FIG. 3, the sample height information acquisition means is a feedback comprising an optical sensor 62, an amplitude detection circuit 42, an overall control circuit 41, and a Z-direction feed control circuit 44. The cantilever height control means is constituted by a general control circuit 41 and a Z-direction feed control circuit 44, the cantilever bending means is constituted by a cantilever bending member 70, and the electric characteristic measuring device is an electric characteristic measuring circuit 45. And the measurement voltage control circuit 47, and the probe scanning mechanism is composed of an XY direction feeding mechanism 31. Hereinafter, the configuration of each part of the scanning probe microscope 10 according to the present embodiment will be described in more detail.

  The XY direction feeding mechanism 31 is a mechanism for feeding a holder 33 (to be described later) and a probe (probe) 23 attached thereto in the XY direction. Can be scanned parallel to the surface. The XY direction feed mechanism 31 can be configured by a drive element using a piezoelectric material such as PZT (lead zirconate titanate), and the cantilever 22 and the probe 23 formed at the tip thereof can be 1 nm or less. It can be moved in steps.

  The Z-direction feed mechanism 32 is attached to a movable part of the XY-direction feed mechanism 31, and the cantilever 22 and the probe 23 attached to the tip of the Z-direction feed mechanism 32 are, for example, about 0.05 nm (minimum resolution of the optical lever system) in the Z direction. Can be sent in steps. The Z-direction feed mechanism 32 is configured by a drive element using a piezoelectric material such as PZT. The Z-direction feed mechanism 32 can further give the cantilever 22 a vibration in the vicinity of its resonance frequency (for example, 300 kHz) and having an amplitude in the Z direction. The feed amount of the Z-direction feed mechanism 32 is determined by a control output from a Z-direction feed control circuit 44 described later.

  The holder 33 is a member for holding the cantilever 22 and is attached to the movable part of the Z-direction feed mechanism 32. The cantilever 22 is detachably attached to the holder 33.

  One end of the cantilever 22 is fixed to the holder 33, the other end is a free end, and a probe 23 is formed at the free end. The cantilever 22 is, for example, a hollow triangular or rectangular thin plate with a thickness of about 0.1 to 5 μm and a length of about several tens of μm. As the cantilever 22, for example, a thin plate of Si or SiN single crystal can be used. The cantilever 22 is provided with a cantilever bending member 70 driven by a cantilever bending control circuit 46. The cantilever bending member 70 can bend the cantilever 22 in the Z direction independently of the Z-direction feeding mechanism 32, and the probe 23 attached to the free end side of the cantilever 22 can be pressed against the sample surface. The amount of bending of the cantilever 22 can be adjusted by a control voltage applied to the cantilever bending member 70. For example, when the sample 51 performs measurement on a semiconductor device (Si single crystal), the thickness of the natural oxide film is about 1 to 3 nm, and therefore the distance between the probe 23 immediately before the cantilever 22 is bent and the surface of the sample 51. In addition, the cantilever 22 is bent so that the probe push-down amount of 1 to 3 nm necessary for the probe 23 to break through a natural oxide film such as a semiconductor can be obtained.

  The probe 23 is formed to project from one surface of the free end side of the cantilever 22. The probe 23 is formed so as to narrow toward the tip, and the tip has a radius of curvature of about 1 to 50 nm, for example. Since the probe 23 of the present embodiment breaks through a natural oxide film and makes electrical contact with the inside of the sample, it is preferable to use a material having high mechanical strength. For example, the probe 23 has conductivity formed by a CVD method or the like. DLC (Diamond Like Carbon) etc. can be used. Further, in order to improve the conductivity of the probe 23, a metal thin film (for example, PtIr) may be formed on the surface thereof by sputtering or the like. In addition, the probe 23 can be made of PtIr or NiSi having high hardness.

  Hereinafter, a configuration example of the cantilever bending member 70 of the present embodiment will be described with reference to FIGS. 4 (a) and 4 (b).

  As shown in FIG. 4A, the first configuration example of the cantilever bending member 70 of the present embodiment is configured by a piezoelectric element 71 attached to the cantilever 22. One end of the piezoelectric element 71 is attached to the cantilever 22 by a joining member 73, and the other end is fixed to the holder 33 via a structure such as a spacer 74 and a support plate 72. The piezoelectric element 71 can be a stacked piezoelectric element in which a large number of piezoelectric films are stacked to form a rod shape, and expands and contracts in the thickness direction (I direction in the figure) due to a change in voltage. In the cantilever 22 of this configuration example, by applying a voltage to the piezoelectric element 71, the piezoelectric element 71 contracts in the vertical direction (arrow I direction) on the paper surface, and the free end of the cantilever 22 can be pushed down in the arrow A direction. . The piezoelectric element 71 may be attached above the cantilever 22 and the cantilever 22 may be pushed down by extending the piezoelectric element 71.

  FIG. 4B is a second configuration example of the cantilever bending member 70 of the present embodiment, and has a bimorph structure in which piezoelectric elements 75 and 76 are stacked on both upper and lower surfaces of the cantilever 22. For the piezoelectric elements 75 and 76, for example, a PZT film formed on the surface of the cantilever 22 of a Si single crystal thin plate by a sputtering method, a CVD method or the like can be used. The electrodes of the piezoelectric elements 75 and 76 can be manufactured by a known semiconductor manufacturing process. The cantilever bending member 70 of the present configuration example contracts the piezoelectric element 75 in the direction of arrow II by applying a differential (different sign) voltage to the piezoelectric elements 75 and 76, and also causes the piezoelectric element 76 to move in the direction of the arrow. Can be stretched in the III direction. The cantilever 22 is warped by the expansion and contraction of the piezoelectric elements 75 and 76, and the free end side thereof is pushed down in the arrow A direction. In the illustrated example, the piezoelectric elements 75 and 76 are formed only on a part of the surface of the cantilever 22, but these may be formed on the entire surface of the cantilever 22.

  In the above configuration example, a piezoelectric element is provided on the cantilever 22 to cause warpage. However, the present embodiment is not limited to these, and various configurations for displacing the free end side of the cantilever 22 toward the sample 51. For example, a structure in which a bimetal obtained by bonding metals having different coefficients of thermal expansion is attached to the cantilever 22 and the cantilever 22 is bent by applying a force in a direction to push down the cantilever 22 due to heat generated by an electric current, or by magnetic or static electricity. It can be set as the structure using a suction force or a repulsive force.

  In the above embodiment, the cantilever bending member 70 is formed on the cantilever 22 as a member for pressing the probe 23 against the sample 51. As a result, the probe 23 can be pushed into the sample 51 with a stronger force and better controllability than when the Z-direction feed control means is used to push the probe 23.

  Returning to FIG. 3, another configuration of the scanning probe microscope 10 will be described.

  The laser light source 61 and the optical sensor 62 constitute a sensor that detects a change in the Z direction of the cantilever 22. The light from the laser light source 61 is applied to the upper surface near the free end of the cantilever 22, and the reflected laser light is configured to form a predetermined image on the optical sensor 62. The optical sensor 62 can be constituted by, for example, a photodiode divided into four. According to the displacement of the cantilever 22 in the Z direction, the image of the reflected light formed on the optical sensor 62 changes, and the output of each photodiode constituting the optical sensor 62 changes. The output from the optical sensor 62 is sent to the vibration state detection circuit 42.

  As shown in FIG. 8, the sample 51 is obtained by cutting a semiconductor device, for example, and has an electrode 114 for applying a measurement voltage. A measurement signal control circuit 47 is connected to the electrode 114, and a predetermined DC voltage or AC voltage (measurement voltage) is applied to the sample 51 when measuring the electrical characteristics. In FIG. 8, 110 is a gate, 111 and 112 are impurity diffusion regions, and 113 is a silicon substrate. According to the scanning probe microscope 10 of this embodiment, for example, when an element having an extension width of 5000 nm is used as the piezoelectric element constituting the Z-direction feed mechanism 32, a sample having a root mean square roughness (RMS) of up to about 2500 nm. The local electrical properties can be measured. The sample stage 52 holds the sample 51, and is not particularly shown, but is provided with a coarse movement mechanism that gives a rough feed movement to the vicinity of the measurement region.

  Next, the control unit of the scanning probe microscope 10 of the present embodiment will be described. The control unit of the present embodiment includes a vibration state detection circuit 42, an XY direction feed control circuit 43, a Z direction feed control circuit 44, an electrical characteristic measurement circuit 45, a cantilever bending control circuit 46, a measurement signal control circuit 47, and these The overall control circuit 41 controls the entire control circuit.

  The vibration state detection circuit 42 measures the amplitude of vibration of the cantilever 22 based on the detection signal from the optical sensor 62. When the probe 23 approaches or comes into contact with the sample 51 due to the vibration motion of the cantilever 22, an atomic force acts between the atoms on the surface of the sample 51 and the probe 23, and the amplitude of the cantilever 22 changes. When the amplitude value exceeds a predetermined reference value or falls below the predetermined reference value, an error signal having an output corresponding to the difference between the detected amplitude value and the reference value is sent to the overall control circuit 41. Sent out. The overall control circuit 41 sends a control signal to the Z-direction feed control circuit 44 so that the error signal becomes zero, that is, the amplitude of the cantilever 22 is constant while keeping the distance between the probe 23 and the sample 51 constant. Is output. The control output to the Z-direction feed control circuit 44 when the error signal from the vibration state detection circuit 42 becomes zero gives the height information of the sample 51. Thus, in the scanning probe microscope 10 according to the present embodiment, a feedback loop is formed by the vibration state detection circuit 42, the overall control circuit 41, and the Z-direction feed control circuit 44, and the interval between the probe 23 and the sample 51 is as follows. Kept constant.

  The XY direction feed control circuit 43 sends a control output to the XY direction feed mechanism 31 based on a control signal from the overall control circuit 41. Based on this control output, the XY direction feed mechanism 31 scans the probe 23 (cantilever 22) along the surface of the sample 51.

  The Z-direction feed control circuit 44 applies a DC component control voltage to the Z-direction feed control mechanism 32 in order to give the Z-direction feed movement of the cantilever 22 based on the control signal from the overall control circuit 41. Further, the Z-direction feed control circuit 44 applies an AC component control voltage having a constant amplitude to the Z-direction feed control mechanism 32 so as to be superimposed on the above-described DC component control voltage. The frequency of the control voltage of the AC component is a frequency near the resonance frequency of the cantilever 22, thereby causing the cantilever 22 to vibrate in the Z direction near the resonance frequency (for example, 300 kHz). Note that, during the pushing operation of the probe 23 described later, the application of the AC component control voltage is stopped, and only the DC component control voltage is applied to the Z-direction feed mechanism 32.

  The electrical characteristic measurement circuit 45 is electrically connected to the probe 23 and detects the value of the current flowing through the probe 23 and the signal level when a predetermined measurement signal is applied to the sample 51. For example, when the local capacitance C or dC / dV distribution measurement of the sample 51 is performed, a capacitance meter or the like can be used, and the local resistance value R or dI / dV distribution measurement of the sample 51 is performed. In some cases, an ammeter can be used. Further, the electrical characteristic measurement circuit 45 may include both a capacitance meter and an ammeter, and may be used by switching according to the measurement purpose. The measurement result of the electrical characteristic measurement circuit 45 is sent to the overall control circuit 41.

  The cantilever bending control circuit 46 applies a predetermined control voltage to the cantilever bending member 70 based on the control signal from the overall control circuit 41. For example, in the configuration example of FIG. 4A in which a laminated piezoelectric element is used for the cantilever bending member 70, the probe 23 attached to the free end side of the cantilever 22 is fixed by applying a constant control voltage to the piezoelectric element 71. Press down the amount. 4B, when the cantilever bending member 70 has a bimorph structure in which the piezoelectric elements 75 and 76 are stacked, the piezoelectric element 75 and the piezoelectric element 76 are each differential ( Apply a control voltage (different in sign). Since the distance between the probe 23 and the surface of the sample 51 is always controlled to a constant value by the feedback loop described above, the voltage applied from the cantilever curve control circuit 46 to the piezoelectric element 71 or the piezoelectric elements 75 and 76 is set to a constant value. If this is the case, the amount by which the tip of the probe 23 is pushed down (the amount by which the probe 51 is pushed) is always maintained at a constant value regardless of the unevenness of the surface of the sample 51.

  The measurement voltage control circuit 47 is connected to an electrode attached to the sample 51 and applies various measurement signals to the sample 51 based on a control signal from the overall control circuit 41. For example, in the case of measuring the IV characteristic, a constant voltage is applied to the sample 51 from a constant voltage power source. When measuring the dI / dV characteristic, a voltage that changes the applied voltage at a constant speed is applied. In the case of measuring the capacitance C, an AC voltage having a predetermined amplitude is applied to the sample 51 while being superimposed on a predetermined DC voltage as necessary.

  The overall control circuit 41 performs control by transmitting control signals to the various control circuits 42 to 47 described above, and receives detection signals from the vibration state detection circuit 42 and the electrical characteristic measurement circuit 45. In addition, although not particularly shown, measurement data is output and various operation commands are received via an external interface.

  Next, the operation of the scanning probe microscope 10 of the present embodiment will be described with reference to FIGS. Here, FIG. 5 is a flowchart showing an example of a measurement procedure of the scanning probe microscope according to the embodiment of the present invention, and FIG. 6A is a measurement time of the scanning probe microscope according to the embodiment of the present invention. FIG. 6B is a side view showing the state of bending of the cantilever during the pushing-in operation, and FIG. 7 shows the scanning probe microscope according to the embodiment of the present invention. It is a figure which shows an example of the waveform of the control signal at the time of a measurement. FIG. 8 is a perspective view showing a state of measurement of the scanning probe microscope according to one embodiment of the present invention.

  Hereinafter, the operation of the scanning probe microscope 10 according to the present embodiment will be described by taking as an example the case where the local electrical characteristics are measured while scanning the probe 23 along the surface of the sample 51 having irregularities as shown in FIG. To do.

  First, the vicinity of the measurement region is brought close to the vicinity of the probe 23 using a coarse movement mechanism (not shown) of the sample stage 52. Thereafter, the probe 23 is moved closer to the surface of the sample 51 while the cantilever 22 is vibrated near the resonance frequency by the Z-direction feed mechanism 32 (step S10).

Next, the probe 23 is moved by the XY direction feed mechanism 31 while keeping the probe 23 at a constant distance from the surface of the sample 51 by the feedback loop of the vibration state detection circuit 42, the overall control circuit 41 and the Z direction feed control circuit 44. It moves (scans) along the surface of the sample 51 at a constant speed for a certain time (for example, t _{0 to} t ₁ ) (step S20). At this time, the probe 23 moves while vibrating (tapping) the portions indicated by arrows t _{0 to} t ₁ in FIG. Immediately before time t ₁ , the probe 23 vibrates at the positions indicated by the broken lines 23b and 23c. Further, during the time t _{0 to} t ₁ , the control voltage from the Z-direction feed control circuit 44 changes, for example, as shown by the waveform (B) in FIG. Here, in the waveform (B), the horizontal axis represents time, and the vertical axis represents the control voltage. An AC component control voltage is applied to the Z-direction feed mechanism 32 to vibrate the cantilever 22 from t _{0 to} t ₁ . Further, the control voltage of the DC component controlled by the above-described feedback loop is applied so that the amplitude of the cantilever 22 is constant. As shown in FIG. 6A, since the height of the sample 51 is constant in the portion where the probe 23 moves from t ₀ to t ₁ , the DC component control voltage from the Z-direction feed control circuit 44 is also shown in FIG. As shown in the waveform (B) of FIG. On the other hand, the position (height) of the probe 23 in the Z direction changes as shown by the waveform (A) in FIG. Here, the horizontal axis of the waveform (A) indicates time, and the vertical axis indicates the position (height) in the Z direction of the tip portion of the probe 23. As shown in the waveform (A) of FIG. 7, the tip of the probe 23 vibrates with a constant amplitude in the Z direction by the vibration of the cantilever 22 from time t _{0 to} time t ₁ .

Next, the application of the AC component control voltage from the Z-direction feed control circuit 44 is stopped, the vibration of the Z-direction feed mechanism 32 is stopped, the feed movement in the XY directions is stopped, and the probe 23 is scanned. Is stopped (step S30). Accordingly, as indicated by a broken line 23c in FIG. 6A, the sample stops at a position spaced a predetermined distance from the surface of the sample 51. At this time, the control voltage from the Z-direction feed control circuit 44 and the position (height) of the probe 23 in the Z direction take values at time t ₁ in FIG.

Next, from time t _{1 to} t ₂ , the cantilever 22 is bent and the probe 23 is brought into contact with the surface of the sample 51 or pushed into the sample 51 (step S40). For example, when measuring dI / dV (I / V) characteristics of a sample 51 in which a natural oxide film 51b is formed, such as a semiconductor, the tip of the probe 23 is as shown in FIG. Then, it is pushed into the sample 51. When measuring the capacitance C, the cantilever 22 is bent to such an extent that it does not push the probe 23 into the sample but contacts the sample surface.

At this time, the control voltage from the Z-direction feed control circuit 44 is maintained at the DC component control voltage immediately before the application of the AC component control voltage is stopped (time t ₁ ) in the waveform (B) of FIG. On the other hand, the control voltage shown in the waveform (C) of FIG. 7 is applied from the cantilever bending control circuit 46 to the piezoelectric element 71 of the cantilever bending member 70 from time t ₁ to time t ₂ , for example. Here, the horizontal axis of the waveform (C) represents time, and the vertical axis represents the control voltage from the cantilever bending circuit 46. As a result, the cantilever 22 is curved, the free end side is lowered toward the sample surface, and the probe 23 is pushed into the sample. The position of the tip of the probe 23 in the Z direction changes from time t _{1 to} t ₂ as shown by the waveform (A) in FIG.

Further, from time t _{1 to} t ₂ , for example, a measurement voltage as shown in the waveform (D) of FIG. 7 is applied from the measurement voltage control circuit 47 to the sample 51 to measure the local electrical characteristics of the sample 51 ( Step S50). The waveform in FIG. 7 is an example when dI / dV measurement is performed. When only resistance measurement is performed, a DC voltage measurement signal with a voltage value kept constant from t ₁ to t ₂ is applied. In the case of capacitance measurement, a measurement voltage in which an AC signal is superimposed on a DC voltage is applied. The measurement of electrical characteristics from t _{1 to} t ₂ is performed for several milliseconds.

Next, at time t ₂ , the curve of the cantilever 22 is returned, and the tip of the probe 23 is pulled up from the sample surface or inside the sample (step S60). As a result, as indicated by a broken line 23c in FIG. 6A, the probe 23 moves to a predetermined height from the sample surface.

  Next, the cantilever 22 is vibrated (step S70). At the same time, the feedback loop of the vibration state detection circuit 42, the overall control circuit 41, and the Z direction feed control circuit 44 is operated to control the Z direction feed mechanism 32 so as to keep the distance between the probe 23 and the surface of the sample 51 constant. Do.

  Thereafter, the process returns to step S20 described above, and the local electrical characteristics of the sample 51 are measured while repeating the processes from step S20 to S70 until the scanning of the probe 23 is completed. During this time, for example, as shown in FIG. 6A, the probe 23 moves from the right to the left of the paper surface, and pushes the probe 23 into the sample 51 at regular intervals to measure local electrical characteristics. The interval (pitch) between the measurement positions of the local electrical characteristics can be appropriately set from the viewpoint of the measurement range and the measurement time. However, when measuring at the highest spatial resolution, it can be performed at a 1 nm pitch. In such a pushing operation of the probe 23, the interval between the probe 23 and the surface of the sample 51 immediately before the probe 23 is pushed is kept constant without being affected by the height or friction of the sample surface. As a result, as shown in FIG. 6B, the push amount D of the probe 23 with the cantilever 22b immediately before pushing and the bent cantilever 22a during pushing operation is constant regardless of the state (friction and inclination) of the sample surface. It becomes.

  As described above, according to the scanning probe microscope 10 of the present embodiment, the distance between the probe 23 and the surface of the sample 51 is kept constant by the feedback loop, and a constant control voltage is applied to the cantilever bending member of the cantilever 22. The probe 23 can be pushed into the sample by a certain amount regardless of the unevenness of the sample. Thereby, even if it is a sample with an unevenness | corrugation, a local electrical property can be measured with a sufficient precision. For this reason, it is not necessary to perform mirror polishing of the sample, and the number of work steps required to obtain a measurement result can be reduced. In addition, local electrical characteristics can be measured with high accuracy for a sample having a surface structure that is not suitable for polishing.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

  (Appendix 1) Sample height information acquisition means for acquiring the height information of the sample surface by vibrating a cantilever provided with a needle-like probe at the tip, and when the vibration and scanning of the cantilever are stopped, the sample Based on the surface height information, the cantilever height control means for controlling the position of the cantilever so as to keep the tip of the probe at a constant distance from the sample surface, and the cantilever is bent from the state where the constant distance is maintained. Accordingly, a cantilever bending means that pushes the tip of the probe into the sample, and when the probe is pushed into the sample, a measurement signal is applied to the sample, and the local electrical characteristics of the sample are obtained via the probe. An electrical property measuring device for measuring, and measuring the height information and local electrical property distribution of the sample, the probe on the surface of the sample Scanning probe microscope for the probe scanning mechanism which along with scanning, comprising the.

  (Additional remark 2) The said cantilever bending means consists of a piezoelectric element attached to the said cantilever, The scanning probe microscope of Additional remark 1 characterized by the above-mentioned.

  (Supplementary Note 3) The cantilever bending means is a piezoelectric element having one end connected to the upper surface or the lower surface on the tip end side of the cantilever and the other end fixed to a holder that holds the cantilever. 2. The scanning probe microscope according to appendix 1, wherein the scanning probe microscope is composed of a piezoelectric element that applies a force in a direction of pushing down.

  (Supplementary Note 4) The cantilever bending means is composed of a plurality of piezoelectric films provided on the upper surface and the lower surface of the cantilever, and is different between a piezoelectric film provided on the upper surface and a piezoelectric film provided on the lower surface. 2. The scanning probe microscope according to claim 1, wherein a dynamic voltage is applied to provide a force in a direction to extend to the upper surface side of the cantilever and a force to contract to the lower surface side of the cantilever. .

  (Additional remark 5) The said cantilever bending means is comprised by the metal laminated film which laminated | stacked the metal which has a different thermal expansion coefficient provided in the upper surface or lower surface of the said cantilever, and gives the force of the direction pushed down to the said cantilever by the heat_generation | fever by an electric current The scanning probe microscope according to appendix 1, wherein

  (Supplementary note 6) The scanning probe microscope according to supplementary note 1, wherein the electrical characteristic measuring device measures a local current / voltage characteristic of the sample by applying a DC voltage as a measurement signal to the sample. .

  (Supplementary Note 7) The electrical property measuring apparatus applies an AC voltage superimposed on a DC voltage as a measurement signal between the sample and the probe, and the local capacitance / voltage (dC / dV) of the sample. The scanning probe microscope according to appendix 1, wherein the characteristic is measured.

  (Supplementary note 8) The scanning probe microscope according to supplementary note 1, wherein a bending amount of the cantilever by the cantilever bending means is a constant value.

  (Supplementary note 9) The step of acquiring the height information of the sample by vibrating the cantilever having a needle-like probe formed at the tip thereof, stopping the scanning of the probe and stopping the vibration of the cantilever, Controlling the height of the cantilever so that the tip of the probe is kept at a constant distance from the sample surface based on the height information, and curving the cantilever while maintaining the height of the cantilever. A step of pushing into the sample, and a step of measuring a local electrical property of the sample by applying a measurement signal to the sample while the probe is pushed into the sample and detecting the measurement signal from the probe And a method for measuring local electrical characteristics.

  (Supplementary note 10) The method for measuring local electrical characteristics according to supplementary note 9, wherein the probe push-in depth is made constant by making the amount of bending of the cantilever constant.

  (Appendix 11) The step of measuring the electrical characteristics includes applying a direct current voltage as a measurement signal to the sample to measure local current / voltage characteristics of the sample. Of measuring electrical characteristics.

  (Supplementary Note 12) The step of measuring the electrical characteristics includes applying an AC voltage superimposed on a DC voltage to the sample as a measurement signal and measuring a local capacity / voltage (dC / dV) characteristic of the sample. The scanning probe microscope according to appendix 1, characterized by:

FIG. 1 is a schematic diagram showing a problem at the time of local electrical characteristic measurement by a conventional scanning probe microscope (part 1). FIG. 2 is a schematic diagram showing a problem at the time of measuring local electrical characteristics by a conventional scanning probe microscope (part 2). FIG. 3 is a block diagram showing a scanning probe microscope according to an embodiment of the present invention. 4A and 4B are side views showing a cantilever used in a scanning probe microscope according to one embodiment of the present invention. FIG. 5 is a flowchart showing an example of a measurement procedure of the scanning probe microscope according to the embodiment of the present invention. FIG. 6A is a schematic diagram showing the operation of the probe during measurement by the scanning probe microscope according to the embodiment of the present invention. FIG. 6B is a side view showing the state of bending of the cantilever during the pushing operation. FIG. 7 is a diagram illustrating an example of a waveform of a control signal at the time of measurement by the scanning probe microscope according to the embodiment of the present invention. FIG. 8 is a schematic diagram showing an example of a sample used for measurement by a scanning probe microscope according to one embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Scanning probe microscope, 22 ... Cantilever, 23 ... Probe, 31 ... XY direction feeding mechanism, 32 ... Z direction feeding mechanism, 33 ... Holder, 41 ... Overall control circuit, 42 ... Vibration state detection circuit, 43 ... X -Y direction feed control circuit, 44 ... Z direction feed control circuit, 45 ... electric characteristic measurement circuit, 46 ... cantilever bending control circuit, 47 ... measurement voltage control circuit, 51 ... sample, 52 ... sample stage, 61 ... laser light source, 62 ... optical sensor, 70 ... cantilever bending member, 71 ... piezoelectric element, 72 ... support plate, 73 ... bonding member, 74 ... spacer, 75, 76 ... electric element, 101 ... semiconductor substrate, 102 ... natural oxide film, 103 ... Probes 23, 104 ... cantilever, 105 ... sample, 110 ... gate, 111, 112 ... impurity diffusion region, 113 ... silicon substrate, 114 ... electrode.

Claims (6)

Sample height information acquisition means for acquiring the height information of the sample surface by vibrating a cantilever provided with a needle-like probe at the tip,
A cantilever height control means for controlling the position of the cantilever so as to keep the tip of the probe at a constant distance from the sample surface based on the height information of the sample surface when vibration and scanning of the cantilever are stopped;
A cantilever bending means for bending the tip of the probe into the sample by bending the cantilever from a state where the constant distance is maintained;
An electrical property measuring device that applies a measurement signal to the sample when the probe is pushed into the sample and measures a local electrical property of the sample through the probe; and
A scanning probe microscope comprising: a probe scanning mechanism that scans the probe along the sample surface in order to measure the height information of the sample and the distribution of local electrical characteristics.   The scanning probe microscope according to claim 1, wherein the cantilever bending means includes a piezoelectric element attached to the cantilever.   The cantilever bending means is a piezoelectric element having one end connected to an upper surface or a lower surface of the tip end side of the cantilever and the other end fixed to a holder that holds the cantilever, and is configured to push down the cantilever by applying a voltage. The scanning probe microscope according to claim 1, comprising a piezoelectric element that applies force.   The cantilever bending means is composed of a plurality of piezoelectric films provided on the upper surface and the lower surface of the cantilever, and a differential voltage is applied between the piezoelectric film provided on the upper surface and the piezoelectric film provided on the lower surface. 2. The scanning probe microscope according to claim 1, wherein a force in a direction of extending toward the upper surface side of the cantilever and a force in a direction of contracting toward the lower surface side of the cantilever are applied by applying.   The scanning probe microscope according to claim 1, wherein the amount of bending of the cantilever by the cantilever bending means is a constant value. Obtaining a sample height information by vibrating a cantilever having a needle-like probe formed at the tip;
Stopping scanning of the probe and stopping vibration of the cantilever, and controlling the height of the cantilever so as to keep the tip of the probe at a constant distance from the surface of the sample based on the height information of the sample When,
Curving the cantilever while maintaining the height of the cantilever and pushing the probe into the sample;
Measuring a local electrical characteristic of the sample by applying a measurement signal to the sample in a state where the probe is pushed into the sample and detecting the measurement signal from the probe. A method of measuring local electrical characteristics that are characteristic.

Images