JP2006133100A - Apparatus for measuring anisotropy of semiconductor film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for measuring anisotropy of a semiconductor film, which can measure carrier mobility values in two directions, i.e., vertical and horizontal directions of an organic thin film. <P>SOLUTION: The apparatus 10 for measuring the anisotropy of the semiconductor film is equipped with a measurement object setting means 12 which has a probe contactable with an electrode disposed at an object to be measured; a light irradiation means 14 which irradiates the object to be measured with light; a voltage applying means 16 which applies a voltage to the electrode through the probe; a signal detecting means 18 which detects a current signal flowing in the object to be measured; and a signal processing means 20 for processing a detected signal. The measurement object setting means 12 includes three probes which can be positioned independently, and the voltage applying means 16 is made up such that the class of the voltage applied to each probe can be varied, and the measurement can be carried out in two kinds of measurement modes, i.e., a TOF method measurement mode and an FET method measurement mode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor film anisotropy measuring apparatus for measuring anisotropy based on a molecular structure of a semiconductor thin film from carrier mobility.

Organic thin films are attracting attention for application to next-generation semiconductor materials. Semiconductor performance largely depends on carrier mobility, which is a basic physical property, and several methods for measuring carrier mobility are known, but the following two methods, abbreviated as TOF method and FET method, are better. It is used.
In the TOF method, a measurement object to which a drift voltage is applied is irradiated with pulsed light to generate carriers, and the carrier flow due to the drift voltage is measured to determine mobility (see, for example, Patent Document 1). ). That is, as shown in FIG. 1, one of the objects to be measured is sandwiched between a transparent electrode and the other is sandwiched between metal electrodes, a drift voltage is applied between these electrodes in a pulse shape, and at the same time, pulsed light is irradiated from the transparent electrode side, A carrier mass is generated near the surface of the object to be measured. Then, by detecting the current signal flowing through the sample, the time during which the carrier mass generated by the pulsed light drifts from the generation side to the counter electrode due to the drift voltage, that is, the carrier movement time, is measured. Then, the carrier mobility is obtained.
On the other hand, in the FET method, an FET transistor element using a measurement object as a semiconductor material is produced, and the carrier mobility is obtained by measuring transistor characteristics. As shown in FIG. 2, an FET transistor element that constitutes a channel is manufactured using a measurement object, a drain current is measured while changing a source-drain voltage under a constant gate voltage, and a gate voltage is changed. Repeat the measurement to determine the relationship between the measured gate voltage and drain current. From this relationship, the carrier mobility of the measurement object can be obtained.
JP-A-6-186280

It is known that the mobility of organic molecular crystals varies greatly in the direction of the crystal axis, and the performance of the semiconductor varies greatly depending on the direction of the axis. The organic thin film is not completely amorphous but often has a certain degree of crystallinity. In this case, depending on the arrangement of the crystals, that is, the arrangement of the molecules, the performance as an electronic device in the direction parallel to and perpendicular to the thin film Come different. However, until now, when measuring the mobility of an organic thin film, the mobility in two different directions has not been measured. This is because an apparatus for measuring the carrier mobility of one organic thin film sample due to the difference in the axial direction has not been developed. Therefore, development of a method for measuring the difference in carrier mobility based on the anisotropy of the organic thin film on the substrate and the performance in different directions as an electronic device has been demanded.
The present invention has been made in view of the above problems, and an object of the present invention is to measure the semiconductor film anisotropy capable of measuring the carrier mobility in the vertical direction and the carrier mobility in the horizontal direction with respect to the organic thin film. To provide an apparatus.

Until now, the carrier mobility of organic thin films has not been measured in two different directions. This is because an apparatus for measuring carrier mobility for one organic thin film sample has not been developed. In the present invention, the TOF method obtains the vertical mobility of the thin film, while the FET method can measure the horizontal mobility of the thin film. We have developed a device that can measure the vertical and horizontal mobility of organic thin films.
In order to achieve the above object, a semiconductor film anisotropy measuring apparatus according to the present invention irradiates a measuring object with pulsed light, and a measuring object setting means having a probe capable of contacting an electrode provided on the measuring object. Light irradiation means, voltage application means for applying a voltage to the electrode via the probe, signal detection means for detecting a current signal flowing through the measurement object via the probe, and detection by the signal detection means Signal processing means for processing the processed signal, the measurement object installation means includes three probes that can be positioned independently, and the voltage application means determines the type of voltage applied to each probe. It is configured to be changeable, and can be measured in two types of measurement modes: a TOF method measurement mode and an FET method measurement mode.

Here, in the TOF method measurement mode, two of the three probes of the measurement object placing means are positioned so as to contact two opposed electrodes provided on the measurement sample, respectively, and between the contacting probes A pulse voltage is applied by the voltage applying means, and pulsed light is emitted from the light irradiating means to the measurement object in synchronism therewith, and a current signal generated by the generated carrier is detected by the signal detecting means. On the other hand, in the FET method measurement mode, the three probes are positioned so as to be in contact with the source electrode, the drain electrode, and the gate electrode of the measurement object, respectively, and a constant voltage is applied to the probe in contact with the gate electrode by the voltage application means. The current flowing between the source and drain is measured by the signal detection means while changing the voltage between the probes in contact with the source electrode and the drain electrode, and the measurement is repeated by changing the voltage applied to the gate electrode.
The semiconductor film anisotropy measurement apparatus includes a control unit that controls operations of the light irradiation unit and the voltage application unit. The control unit allows light to be emitted in the TOF method measurement mode and in the FET method measurement mode. It is preferable that the operation of the irradiation means and the voltage application means can be changed.

  According to the semiconductor film anisotropy measuring apparatus of the present invention, the installation means for installing the measurement object includes three probes that can come into contact with the electrodes provided on the measurement object, and the voltage application means includes each of the probes. Since the type of the voltage to be applied to can be changed, it is possible to perform measurement on the same measurement object by two different measurement methods, the TOF method and the FET method. Therefore, deeper knowledge about the structure of the measurement object can be obtained by comparing the measurement results obtained by the two measurement methods.

Next, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 3 is a schematic configuration diagram of a semiconductor film anisotropy measuring apparatus according to an embodiment of the present invention. The semiconductor film anisotropy measuring apparatus 10 of the present embodiment includes a measurement object installation unit 12 that installs a measurement object, a light irradiation unit 14 that irradiates the measurement object with pulsed light, and a voltage applied to the measurement object. Voltage applying means 16, a signal detecting means 18 for detecting a current signal flowing through the measurement object, and a signal processing means 20 for processing the detection signal.
The measurement object installation means 12 has three probes (see FIGS. 4 and 5), and through this probe, voltage is applied to the measurement object by the voltage application means 16 and measurement is performed by the signal detection means 18. Detection of current flowing through the object. At the time of TOF measurement, two of the three probes are used to apply a pulse voltage between the opposing electrodes installed on the measurement object. On the other hand, at the time of FET method measurement, the three probes are brought into contact with the source electrode, drain electrode, and base electrode of the measurement object, respectively, and the transistor characteristics of the measurement object are measured. Furthermore, the voltage application means 16 is configured to be able to change the type of voltage to be applied so as to be compatible with the above two types of measurement methods.

  4 and 5 are a top view and a side view, respectively, of the measurement object setting means 12 in the present embodiment. As shown in FIG. 4, the three probes 22 a to 22 c are respectively held by movable arm portions A to C, and each arm portion is configured to be movable as indicated by a dotted line in the drawing. Therefore, the tip portions of the probes 22a to 22c can be brought into contact with predetermined electrode portions of the measurement object. In the present embodiment, the three probes 22a and 22b are connected to the voltage applying means 16, and the probe 22c is connected to the signal detecting means 18, and the application of voltage to the electrodes of the measurement object via the probes 22a to 22c, Current measurement is performed. Further, as shown in FIG. 5, in the present embodiment, a hole is provided in the lower part of the installation location of the measurement object, and pulsed light is irradiated from here to the measurement object during the TOF method measurement.

The voltage application means 16 is configured to be able to change the type of voltage applied to each probe. For example, a pulse voltage is applied between the probes 22a and 22c in the TOF method measurement mode, a gate voltage is applied to the probe 22b, and a source / drain voltage is applied between the probes 22a and 22c in the FET method measurement mode. Specifically, for example, a two-channel power supply device may be prepared and controlled independently. However, since at least one of the channels is used for the FET measurement mode, it is necessary to sweep the voltage.
In the TOF method measurement mode, of the three probes 22a to 22c, two probes 22a and 22c are positioned so as to be in contact with two opposing electrodes provided on the measurement sample, and the remaining probes 22b are separated from the measurement sample. Keep it. Then, a pulse voltage from the voltage application unit 16 is applied between the electrodes through the probes 22a and 22c, and the measurement sample is irradiated with the pulsed light from the light irradiation unit 14 in synchronization therewith. The generated current signal by the carrier is detected by the signal detection means 18 through the probe 22c.

  On the other hand, in the FET method measurement mode, the three probes 22a, 22b, and 22c are positioned so as to be in contact with the source electrode, the gate electrode, and the drain electrode of the measurement object, respectively. The voltage application means 16 applies a constant voltage to the probe 22b in contact with the gate electrode, and changes the voltage applied to the probes 22a and 22c in contact with the source electrode and the drain electrode while changing the voltage applied between the source and drain. Is measured by the signal detection means 18 through the probe 22c. Further, the transistor characteristics of the measurement object are measured by repeating the measurement while changing the voltage applied to the gate electrode. Here, it is preferable that one (preferably the gate electrode) of the gate electrode, the source electrode, and the drain electrode of the FET transistor element made of the measurement object is a transparent electrode.

The detection signal detected by the signal detection means 18 is sent to the signal processing means 20, where data processing is performed. The control unit 24 controls the operation of the voltage application unit 16 and the light irradiation unit 14, and changes the operation of the light irradiation unit 14 and the voltage application unit 16 between the TOF method measurement mode and the FET method measurement mode. To do. The control means 24 and the signal processing means 20 are configured by a computer or the like, and control the operation of the constituent elements, control the timing between the constituent elements at the time of measurement, and record / process signals. Setting to the control means 24, display of data, and the like are performed via an input unit 38 and a display unit 36 connected to a computer. As described above, in the semiconductor characteristic device of this embodiment, measurement can be performed in two types of measurement modes of the TOF method and the FET method with a single device.
As described above, according to the semiconductor film anisotropy measurement apparatus of the present embodiment, the installation means for installing the measurement object includes three probes that can contact the electrode provided on the measurement object, and the voltage Since the application means is configured to be able to change the type of voltage applied to each probe, it becomes possible to measure the mobility in two different directions, the vertical direction and the horizontal direction, with respect to the same organic thin film. It was. By comparing the measurement results of the mobility in the two different directions, knowledge about the anisotropy of the thin film can be obtained.

The above is the schematic configuration of the semiconductor film anisotropy measuring apparatus according to the present embodiment, and each component will be described in detail below with reference to FIG.
In the apparatus of the present embodiment, it is preferable to provide a noise reduction mechanism during the TOF measurement. Conventionally, in the measurement by the TOF method, when the measurement object is thin or the measurement object has a high mobility, the duration of the signal including the carrier mobility information is very short, and noise existing in this region In some cases, the signal is hidden and analysis becomes impossible. Therefore, in another application, the present inventors have proposed a method capable of measuring the carrier mobility of an organic thin film having a high mobility even by the TOF method, and the noise reduction mechanism will be described.

As a noise reduction mechanism at the time of TOF measurement, the apparatus according to the present embodiment electrically insulates the light irradiation means 14 from the other means, thereby reducing the mixing of noise generated in the light irradiation means 14. Noise reduction means, and noise removal means for removing noise from the light irradiation means 14 mixed in the detection signal of the TOF method measurement.
That is, the signal processing unit 20 includes a digital filter (noise removal unit) as a noise removal unit, and the digital filter removes noise caused by the light irradiation unit 14 included in the detection signal. Since this noise has a frequency component of 18 to 22 MHz and its high frequency component, it can be suitably removed by a digital filter, more preferably an FFT filter.
Further, as the noise reduction means, the light irradiation means 14 and other components are electrically separated and insulated. The noise reduction means of the present embodiment is such that the control signal lines between the light irradiation means 14 and the voltage application means 16 and between the light irradiation means 14 and the signal detection means 18 are not electrically connected but optically connected. It consists of

Specifically, as shown in FIG. 3, the signal line 26 for synchronizing the voltage applying means 16 and the light irradiation means 14 is connected via a photocoupler 28, and the light irradiation means 14 and the signal detection are detected. Synchronization with the means 18 is performed using an optical signal.
Further, as shown in the embodiment of FIG. 3, the timing control between the signal detection means 18 and the light irradiation means 14 is performed by installing a beam splitter 30 in the preceding stage of the measurement object setting means 12, and by applying the light irradiation means. The light from 14 is divided into two light beams, one is used as a light beam for irradiating the measurement object, and the other is used as a light beam for a synchronization signal. That is, when the light detection means 32 composed of a PIN diode or the like detects a light beam for a synchronization signal, it sends a trigger signal to the signal detection means 18 to synchronize the light irradiation means 14 and the signal detection means 18. ing. Thus, it is only necessary that at least a part of the path connecting the light irradiation means 14 and the signal detection means 18 and the light irradiation means 14 and the voltage application means 16 is optically connected.

At the time of the TOF method measurement, a trigger signal is first applied from the computer to the voltage application unit 16, and the voltage application unit 16 applies a bias voltage to the measurement object. Then, a trigger signal is sent to the light irradiation means 14 through the signal line 26 connected via the photocoupler 28. The light irradiation means 14 that has detected the trigger signal irradiates the measurement object and the light detection means 32 with a pulse laser beam. The light detection means 32 that has received the laser light sends a trigger signal to the signal detection means 18. Upon receiving the trigger signal, the signal detection means 18 converts the current signal from the measurement object into a voltage signal and detects it, and sends the detection signal to the signal processing means 20 in the computer. The detection signal sent to the signal processing means 20 is subjected to noise removal processing or the like in the signal processing means 20.
As a result of the above configuration, in the semiconductor film anisotropy measuring apparatus of this embodiment, the measurement range of mobility by the TOF method can be greatly expanded. In particular, measurement is possible even when the movement time, which is difficult to measure by the conventional TOF method, is short, that is, when the high carrier mobility region or the film thickness to be measured is thin. Specifically, the TOF measurement can be suitably performed even on a sample whose duration of a signal including carrier mobility information is 800 nsec or less. Further, since the S / N ratio is improved, measurement is possible even on a measurement object with a small amount of carrier generation that is hidden by noise.

The light irradiation means 14 needs to generate carrier soot in the object to be measured in synchronization with the voltage application means 16, and for example, a pulse laser is used. The pulse laser beam is absorbed by the surface layer of the measurement object, and is converted into a carrier by the photoelectric conversion function of the measurement object. Since the width of the carrier ridge depends on the width of the pulse laser, the width of the pulse laser is preferably as short as possible, preferably 1 nsec or less, more preferably 0.3 nsec or less. Since the intensity of the carrier light depends on the intensity of the pulse laser and the light absorption rate or photoelectric conversion function of the measurement object or the carrier generation layer, the intensity of the pulse laser light is 10 ⁻⁹ to 10 ⁻¹² joule / pulse. Preferably, if it is too strong, the object to be measured is damaged, and the generated carrier soot modifies the electric field in the object to be measured, so that an accurate mobility cannot be obtained. On the other hand, if it is too weak, sufficient carrier soot will not be generated. The wavelength of the pulse laser is preferably variable so as to be matched with the maximum light absorption wavelength of the measurement object. Preferable examples of the pulse laser include a nitrogen laser and a dye laser equipped with a dye solution.

The voltage application means 16 is prepared for applying a bias voltage to the measurement object, and in order to avoid polarization of the measurement object due to dark current at the time of TOF measurement, a pulse voltage having a duration slightly longer than the drift movement time is provided. Must be able to generate The voltage application means 16 used in the present embodiment is a bipolar power supply, preferably a voltage of −500 to +500 V, more preferably −1000 to +1000 V, and a pulse width that is variable about 1 sec.
Further, as the power supply device as the voltage applying unit 16, a device capable of measuring a current as the signal detecting unit at the same time as the voltage application may be used. As a result, the power supply device can be used as a drift voltage applying means at the time of TOF measurement, or as a source-drain voltage sweeping means (voltage applying means) and a current measuring means (signal detection means) at the time of FET method measurement. Become.
The signal detection means 18 is constituted by a digital oscilloscope or the like in order to detect a signal generated from the measurement object. In the TOF method, the current needs to be converted into a voltage for measurement, and the current due to carrier movement is detected by converting it into a voltage with a load resistance. When the source / drain current is measured by the FET method, if a resistor is inserted, a measurement error occurs as an offset at the time of current measurement. Therefore, it is necessary to short-circuit.

Illustration of carrier mobility measurement by TOF method Illustration of carrier mobility measurement by FET method 1 is a schematic configuration diagram of a semiconductor film anisotropy measuring apparatus according to an embodiment of the present invention. The figure which looked at the measuring object installation means concerning the embodiment of the present invention from the top The figure which looked at the measuring object installation means concerning the embodiment of the present invention from the side

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor film anisotropy measuring apparatus 12 Measuring object installation means 14 Light irradiation means 16 Voltage application means 18 Signal detection means 20 Signal processing means

Claims (2)

A measuring object installation means having a probe capable of contacting an electrode provided on the measuring object;
A light irradiation means for irradiating the measurement object with pulsed light;
Voltage applying means for applying a voltage to the electrode via the probe;
Signal detection means for detecting a current signal flowing through the measurement object via the probe;
Signal processing means for processing the signal detected by the signal detection means,
The measurement object placing means includes at least three probes that can be independently positioned;
The voltage application means is configured to be able to change the type of voltage applied to each probe,
Two of the three probes of the measurement object placing means are positioned so as to contact two opposing electrodes provided on the measurement sample, and a pulse voltage is applied between the contacting probes by the voltage applying means. A TOF method measurement mode in which a pulsed light is irradiated from the light irradiation means to the object to be measured in synchronization therewith, and a current signal from the generated carrier is detected by the signal detection means;
The three probes are positioned so as to be in contact with the source electrode, the drain electrode, and the gate electrode of the measurement object, respectively, and a constant voltage is applied to the probes that are in contact with the gate electrode by the voltage applying unit. The FET method measurement mode in which the current flowing between the source and drain is measured by the signal detection means while changing the voltage between the probes in contact with the electrode and the measurement is repeated by changing the voltage applied to the gate electrode. A semiconductor film anisotropy measuring apparatus capable of measuring in a mode. The semiconductor film anisotropy measuring apparatus according to claim 1,
Control means for controlling the operation of the light irradiation means and voltage application means, and the control means can change the operation of the light irradiation means and voltage application means between the TOF method measurement mode and the FET method measurement mode. A semiconductor film anisotropy measuring apparatus characterized by the above.

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