JP3764076B2 - Probe control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a probe control apparatus for controlling the distance between a probe tip of a tunnel emission microscope and a sample.
[0002]
[Prior art]
With the miniaturization of semiconductor devices and the development of technology that utilizes the characteristics of molecules, there is an increasing demand for characteristics evaluation of nanometer-size microscopic regions of semiconductors and measurement of characteristics of individual molecules of nanometer size. For this reason, a tunnel emission microscope that measures the electrical and optical characteristics in the nanometer size region by injecting current from the sharpened tip of the probe to generate light is used. In recent years, in order to improve the light collection efficiency, a probe with light transmissivity and conductivity (conductive condensing probe) that injects current from the tip of the probe and simultaneously collects light from the tip of the same probe has been developed. It is effective in evaluating the characteristics of nanometer-sized microscopic areas.
[0003]
By the way, in an apparatus for measuring a sample using such a probe, the tunnel current attenuates exponentially with the distance between the probe and the sample surface (hereinafter referred to as a gap), and the change in the gap is extremely difficult. because it is sensitive to, control of the gap is Ru Oh extremely important.
[0004]
Conventionally, the gap is controlled by detecting a tunnel current flowing between the probe and the sample.
[0005]
[Problems to be solved by the invention]
However, since such a conventional control method is limited to the case of measuring a conductive sample, an insulating sample or a sample having a high electric resistance, or an insulating region and a high electric resistance region There is a problem that it is difficult to apply to a sample in which a mixture is mixed.
[0006]
Actually, the measurement target for which the characteristic evaluation of a nanometer-sized minute region is desired includes not only a conductive sample but also a sample in which an insulating region and a high electrical resistance region are mixed. Therefore, a probe control device that can be applied to a sample in which an insulating region and a high electrical resistance region are mixed and that controls a gap without using a tunnel current has been desired.
[0007]
As a method for controlling the gap without using the tunnel current, there is a method using an atomic force such as an attractive force or a repulsive force acting between the tip of the probe and the sample. In this method, when the tip of the flow is very close to the sample surface, the atomic force generated between the two is detected, and the gap is controlled so that the detected value becomes constant.
[0008]
As a method of detecting an atomic force and feeding back the detected value for gap control, there is a method of using an optical lever and a cantilever-shaped soft probe.
[0009]
In this case, laser light is used to detect minute displacements of the probe, but this laser light is much stronger than the detection signal light for measuring the sample, so weak light emission due to the tunnel current There was a problem that the SN ratio at the time of measuring was reduced.
[0010]
Further, in order to suppress the optical transmission loss in the probe, it is desirable to use a probe formed of a linear optical fiber having a diameter of about 100 μm, but such a probe has a cantilever shape necessary for an optical lever. There is a problem that it is difficult to use as a soft probe.
[0011]
Furthermore, there is a method for detecting an atomic force by exciting a rod-shaped probe perpendicular to the surface of the sample in a direction perpendicular to the central axis of the probe and measuring a change in the amplitude of the probe at a specific frequency. However, if a voltage is applied between the tip of the probe and the sample to generate light by injecting current from the tip of the probe, the current flows through the sensing transducer that detects the amplitude, disturbing the detection signal, and the gap Since this control becomes unstable, there is a problem that a voltage cannot be applied to the probe.
[0012]
The present invention solves the above problem and is applicable to a sample in which an insulating region and a high electrical resistance region coexist, and a laser beam that reduces the SN ratio when measuring weak light emission due to a tunnel current is provided. A probe suitable for use as a conductive condensing probe can be used, and a voltage is applied between the probe tip and the sample to inject current from the probe tip to generate light. An object of the present invention is to provide a probe control device capable of
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the probe control apparatus of the present invention includes a rod-shaped probe perpendicular to the surface of a sample, an exciter that excites the probe in a direction perpendicular to the central axis of the probe, and the amplitude of the probe. And a distance control means for controlling the distance between the tip of the probe and the sample by controlling the amplitude of the probe at a specific frequency to a predetermined amplitude. in the control apparatus, the probe collects light from the tip at the same time the same probe when current is injected from the tip of the probe, and an optical transparency and conductivity, between the tip and the sample of the probe to provide a voltage application mechanism for applying a voltage, the amplitude detection means and are electrically insulated between the probe, the voltage application mechanism, the vibration of the probe Wherein a pulse voltage synchronized to the phase, the probe tip, while in the measurement target range is reduced than the horizontal amplitude of the probe tip, that you applied between the probe tip and the sample And
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a configuration of a probe control apparatus according to the present invention.
As shown in the figure, the probe control apparatus according to the present invention includes a probe 1, an excitation vibrator 7, an excitation power source 9, a sensing vibrator 10, a sensing signal processing circuit 11, and a sample position driving mechanism. 12, a sample position drive mechanism control circuit 13, a probe bias power supply 14, a conductive fixing plate 15, and a support structure 16.
[0016]
The rod-like probe 1 provided perpendicular to the surface of the sample 3 is made of a linear optical fiber having a diameter of about 100 μm, which is sharpened by tapering the tip, and imparts conductivity. Therefore, a conductive film is applied to the side surface and the tapered portion. In particular, the tapered portion is coated with a transparent conductive film 2 which is a conductive film having transparency in order to secure a light collecting function. A portion separated from the tip of the probe 1 by about 1 to 2 cm is fixed to the support structure 16 via the conductive fixing plate 15.
[0017]
The conductive fixing plate 15 is connected to one end of the probe bias power supply 14, and supplies a current supplied from the probe bias power supply 14 to the probe 1 through the conductive fixing plate 15. The other end of the probe bias power supply 14 is connected to the sample 3 and constitutes a voltage application mechanism for applying a voltage between the tip of the probe 1 and the sample 3.
[0018]
On the support structure 16, an excitation vibrator 7 which is an exciter that vibrates in a direction orthogonal to the central axis of the probe is provided. The excitation vibrator 7 is connected to an excitation power source 9 and vibrates a point several mm away from the tip of the probe 1 via a sensing vibrator 10 which is an amplitude detection means for detecting the amplitude of vibration. Then, the probe 1 is vibrated in a direction parallel to the surface of the sample 3.
[0019]
The sensing vibrator 10 detects the amplitude of vibration of the probe 1 by outputting a voltage proportional to the amount of displacement (amplitude). The output of the sensing vibrator 10 is transmitted to the sample position driving mechanism 12 via the sensing signal processing circuit 11 and the sample position driving mechanism control circuit 13.
[0020]
The sample position driving mechanism 12 receives the output of the sample position driving mechanism control circuit 13 and moves the sample 3.
[0021]
The sensing signal processing circuit 11, the sample position drive mechanism control circuit 13, and the sample position drive mechanism 12 constitute distance control means for controlling the distance (gap 4) between the tip of the probe 1 and the sample 3. The
[0022]
The insulating vibrator 81 and the probe 1 and the exciting vibrator 7 and the sensing vibrator 10 are electrically insulated by an insulating material 81 and an insulating material 82, respectively.
[0023]
The operation of the probe control apparatus according to the present invention is as follows.
The probe 1 is mounted on the sensing vibrator 10, and the sensing vibrator 10 vibrates at a resonance frequency in a direction orthogonal to the central axis of the probe 1. A voltage corresponding to the vibration of the probe 1 is output from the sensing vibrator 10. In the vicinity of the resonance frequency, when the frequency changes slightly, the amplitude of the probe 1 changes greatly. Therefore, the amplitude of the probe 1 is monitored by the sensing vibrator 10 at a specific frequency slightly away from the resonance frequency. In this state, the tip of the probe 1 is brought close to the surface of the sample 3. (Hereinafter, the operation of bringing the probe 1 close to the surface of the sample 3 is called an approach.)
Even if the approach is started, the probe 1 continues to vibrate at a constant resonance frequency and amplitude while the gap 4 is large and the atomic force acting between the probe 1 and the sample can be ignored. Therefore, the amplitude of the voltage output from the sensing vibrator 10 corresponding to this vibration is also constant.
[0024]
Next, when the probe 1 further approaches the surface of the sample 3 and the interatomic force acting between the two becomes large, this interatomic force acts as a resistance force (shearing force) against the vibration motion of the probe 1 to resonate. The frequency changes. For this reason, the amplitude of the probe 1 at the frequency monitored by the sensing vibrator 10 changes. When the amplitude of the probe 1 changes, the output voltage of the sensing vibrator 10 changes in the same manner. When the amplitude of the output voltage reaches a predetermined value, the probe approach is stopped. Thereafter, feedback control is performed on the gap 4 between the probe 1 and the surface of the sample 3 so that the amplitude of the probe 1 at a monitored frequency becomes constant.
[0025]
When a voltage is applied to the probe 1 in order to inject current from the tip of the probe 1, the current of the probe 1 flows to the sensing transducer 10, thereby disturbing the detection signal from the sensing transducer 10 and causing a gap. In order to prevent the control of 4 from becoming unstable, an insulating material 81 is inserted into a portion where the probe 1 and the sensing vibrator 10 are in contact to be electrically insulated.
[0026]
Since the atomic force is generated regardless of whether the sample 3 is conductive or insulating, even if the sample 3 is a sample in which a conductive region and an insulating or high electrical resistance region are mixed, the probe 1 and the sample 3 It is possible to control the gap 4 between the surface and the surface. For example, when the probe 1 is positioned on the insulating region of the sample 3, no probe current flows, but the control of the gap 4 between the probe 1 and the surface of the sample 3 is normally performed by atomic force. . Further, when the probe 1 is positioned on the conductive region of the sample 3, the gap 4 is similarly controlled by the atomic force and the probe current flows. Therefore, it is possible to detect light emission due to the probe current or the probe current. it can.
[0027]
That is, the tunnel current and the light emission associated therewith can be measured even for a sample having a mixed insulating or high electrical resistance region in which it is difficult to control the gap 4 by the tunnel current. In addition, since the gap 4 is detected by the sensing vibrator 10 and laser light is not used, the SN ratio of the detection signal light is not lowered when measuring weak light emission due to the tunnel current, and a high SN ratio is obtained. Can be measured.
In addition, since it is not necessary to use a cantilevered soft probe, a probe made of a linear optical fiber having a diameter of about 100 μm suitable for use as a conductive condensing probe can be used.
[0028]
Furthermore, since the insulating material 81 is inserted into the portion where the probe 1 and the sensing vibrator 10 are in contact with each other to electrically insulate, the current of the probe 1 to the sensing vibrator 10 even when a voltage is applied to the probe 1. Does not disturb the detection signal from the sensing vibrator 10 and cause the control of the gap 4 to become unstable.
[0029]
FIG. 2 is a diagram showing the relationship between the horizontal amplitude BB ′ at the tip of the probe 1 and the measurement target range AA ′ of the sample 3 in the probe control apparatus according to the present invention. (B) shows the state in which the tip of the probe 1 is displaced in a sine wave shape with respect to the time axis.
[0030]
In the probe control apparatus according to the present invention, since the gap 4 is controlled using the atomic force acting between the probe 1 and the sample 3, the shear force due to the atomic force needs to sufficiently act on the probe 1. There is. For this reason, it is difficult to make the horizontal amplitude BB ′ at the tip of the probe 1 smaller than about several tens of nm. For this reason, the spatial resolution of the measurement is limited by the horizontal vibration amplitude BB ′.
[0031]
In order to remove this restriction, the current injected from the probe 1 to the sample 3 is injected in a pulse manner in synchronization with the phase of the horizontal vibration at the tip of the probe 1. The timing of injecting the current can be synchronized with an arbitrary phase. For example, as shown in the figure, while the tip of the probe 1 is in the measurement target range A-A ′ that is in the vicinity of the center O of the amplitude, A pulse voltage is applied from the probe bias power supply 14 to inject current in a pulsed manner. As a result, even if the horizontal amplitude B-B 'at the tip of the probe 1 required for controlling the gap 4 is large, the spatial resolution of the measurement of light emission by the tunnel current and the tunnel current is within the measurement target range A-A'. It becomes possible to reduce.
[0032]
【The invention's effect】
As described above, the probe control device according to the present invention can be applied to a sample in which an insulating region and a high electrical resistance region are mixed, and the SN ratio when measuring weak light emission due to a tunnel current. A probe suitable for use as a conductive condensing probe can be used without using a laser beam that reduces the flow rate, and a current is injected from the tip of the probe to generate light. There is an effect that it is possible to provide a probe control device that can apply a voltage to the probe.
[0033]
In addition, since the voltage application mechanism applies a pulse voltage synchronized with the probe vibration phase between the probe tip and the sample, even if the horizontal amplitude of the probe tip required for controlling the gap is large. There is an effect that the spatial resolution of the measurement of light emission by the tunnel current and the tunnel current can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a probe control apparatus according to the present invention.
FIG. 2 is a diagram illustrating a relationship between a horizontal amplitude of a probe tip and a measurement target range of a sample in the probe control device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Probe 2 ... Transparent electrically conductive film 3 ... Sample 4 ... Gap 5 ... Electron 6 ... Light 7 ... Excitation vibrators 81 and 82 ... Insulating material 9 ... Excitation power supply 10 ... Sensing vibrator 11 ... Sensing signal processing circuit 12 Sample position driving mechanism 13 Sample position driving mechanism control circuit 14 Probe bias power supply 15 Conductive fixing plate 16 Support structure O Center of amplitude AA ′ Measurement range BB ′ Amplitude

Claims (1)

A rod-like probe perpendicular to the surface of the sample, an exciter for exciting the probe in a direction perpendicular to the central axis of the probe, an amplitude detecting means for detecting the amplitude of the probe, and the probe at a specific frequency And a distance control means for controlling the distance between the tip of the probe and the sample by controlling the amplitude of the probe to a predetermined amplitude, wherein the probe receives a current from the tip of the probe. The amplitude detecting means is provided with a voltage application mechanism for condensing light from the tip of the same probe at the same time as injection and having a light transmission property and conductivity and applying a voltage between the tip of the probe and the sample. and between the probe is electrically insulated, the voltage application mechanism, a pulse voltage synchronized to the phase of the vibration of the probe, the probe tip, the While in the measurement target range is reduced than the horizontal amplitude lobe tip, the probe control device, characterized that you applied between the probe tip and the sample.

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