JP2010016051A - Semiconductor evaluating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor evaluating apparatus capable of highly accurately evaluating the carrier mobility of an organic semiconductor material. <P>SOLUTION: The semiconductor evaluating apparatus 100 irradiates a thin planar device under test 10 to be measured with a laser beam 17, generates a current by moving a carrier generated in the device under test 10 to be measured in the surface direction of the device under test 10 to be measured, and evaluates the carrier mobility of the device under test 10 to be measured from the duration of the current. The semiconductor evaluating apparatus 100 includes a sample-to-be-measured installation part 30 for installing the device under test 10 to be measured, the sample-to-be-measured installation part 30 has two transparent glass substrates, the device under test 10 to be measured is disposed to one transparent glass substrate, and a metal film which is a light shielding film is formed on the other transparent glass substrate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor evaluation apparatus for evaluating carrier mobility of a semiconductor material or the like.

  Since organic semiconductor materials are used for flexible thin film transistors (TFTs) and light-emitting diodes for ubiquitous information terminal applications, the development of such materials has been actively conducted. The carrier mobility of organic semiconductor materials is a characteristic that directly determines device performance, and its evaluation is an important index for developing these materials. Until now, the carrier mobility has been estimated from the time-of-flight measurement method (Time-of-flight: TOF).

  FIG. 4 shows how the carrier mobility is measured by the conventional TOF method. This measuring method is the TOF method in the film thickness direction. As shown in FIG. 4, an organic semiconductor material film is sandwiched between a transparent conductive film substrate 52 and an ITO glass substrate 53 as a sample 51 to be measured, and a film of the sample 51 to be measured is interposed between the two substrates using a voltage source 54. A DC voltage is applied in the thickness direction. When UV light 56 is irradiated as a pulse from the transparent conductive film substrate 52 side, carriers (electrons and holes) are generated on the surface of the sample 51 to be measured on the transparent conductive film substrate 52 side, and electrons or electrons are generated by the Coulomb force of the electric field in the thickness direction. One of the holes moves to the electrode on the ITO glass substrate 53 side. A displacement current flows between the substrates as the carrier moves, and the displacement current signal is detected using the signal detection means 55, thereby measuring the duration Tf of the displacement current. The carrier mobility of the organic semiconductor material that is the sample 51 to be measured can be evaluated from the duration Tf and the thickness of the sample 51 to be measured.

  For example, when the carrier mobility is μ, the electric field strength is E, the carrier flight distance, that is, the film thickness is L, and the carrier speed is v, μ is μ = v / E from the relationship of v = L / Tf. Can be obtained from

  By the way, in the conventional measuring method, the measurement is performed by adjusting the thickness of the sample 51 to be measured so that the duration Tf of the displacement current, that is, the carrier moving time becomes a convenient length for the measurement. . However, it is generally difficult to prepare a uniform and large sample in a high mobility organic semiconductor material such as pentacene or rubrene which has been attracting attention in recent years. That is, in order to increase the film thickness, a large amount of high-purity samples are required, and it is not easy to control the thickness uniformly. Therefore, it is difficult to lengthen the carrier movement time, and there is a problem that the carrier mobility cannot be measured with high accuracy by the conventional TOF method.

For example, when the carrier mobility of the sample 51 to be measured is 1 × 10 ⁻² cm ² / V · sec or more, the sample 51 to be measured having a thickness of 1 mm or more is required. Usually, an electric field strength of 1000 V / cm or more is required to sufficiently run the carrier with the organic semiconductor material. However, if the thickness is smaller than the above film thickness, the duration of the displacement current becomes submicroseconds, and the signal detecting means 55 It is difficult to ensure the S / N ratio in this case, and signal recording becomes difficult. This is because the duration of the detection signal of the displacement current signal is about the same as or less than the duration of the noise.

  Furthermore, since organic semiconductors are used by moving carriers in the in-plane direction of a film such as a thin film transistor, it is required to evaluate the carrier mobility in the in-plane direction rather than the carrier mobility in the film thickness direction of the organic semiconductor. . Many organic semiconductors are crystalline and the crystal structure is three-dimensionally anisotropic. To improve the amplification performance of thin film transistors, the anisotropy of in-plane mobility is evaluated by the TOF method. It is necessary to do. For this purpose, it is difficult to cope with the TOF method in the film thickness direction, which is a conventional technique.

  For example, Non-Patent Document 1 discloses a technique for measuring the mobility in the in-plane direction of an organic semiconductor film so that adjustment of the thickness of a sample to be measured is not necessary. FIG. 5 shows the state of the sample to be measured used for this measurement. As shown in FIG. 5, a slit is formed in the light shielding film 63 on the transparent glass substrate 62, and the pulsed light 68 is incident on the sample 61 to be measured from the transparent glass substrate 62 side through the slit. . The incident light passes through the transparent glass substrate 62 and the silicon oxide film 64 and is irradiated to the sample 61 to be measured. Two electrodes 65 are formed at both ends of the sample 61 to be measured, and a voltage is applied from the power source 66 between the two electrodes 65. The carrier generated due to the incidence of the pulsed light 68 moves between the two electrodes 65, and by detecting the voltage fluctuation between both ends of the resistor 67 due to the displacement current accompanying the movement, the duration of the displacement current can be reduced. Measure.

In the measurement method disclosed in Non-Patent Document 1, since the carrier moving direction is the horizontal direction of the sample to be measured, even when a thin sample to be measured is used, the measured carrier moving time is lengthened. Can do. For this reason, even in an organic semiconductor material that is difficult to increase in thickness, the carrier mobility can be measured.
Atsushi Kuwahara, et al., “Carrier mobility of organic thin films using lateral electrode structure with optical slits”, Applied Physics Letters 89, 2006

  However, in the evaluation method disclosed in Non-Patent Document 1, when the pulsed light 68 is irradiated onto the sample 61, the irradiated region is aligned with the vicinity of the electrode 65, so that the sample 61, the electrode 65, and the light shielding film 63 are measured. It is necessary to adjust the positional relationship. In order to configure these measurement jigs, an assembly operation with lithography or a microscope is required, and the transmissive glass substrate 62, the light-shielding film 63, and the like are laminated to form a manufacturing yield. There was a problem of being bad.

  Further, in the evaluation method of Non-Patent Document 1, in order to exchange and measure the sample 61 to be measured, a laminated structure composed of a transmissive glass substrate 62, a light shielding film 63, a silicon oxide film 64, and an electrode 65 is reproduced. Must. Further, the light shielding film 63 is easily damaged by the laser beam. For this reason, all of these parts must be reconfigured when they are damaged, which increases the labor and cost of parts consumption. Has occurred.

  In view of the above problems, an object of the present invention is to provide a semiconductor evaluation apparatus that can very easily reduce the consumption cost and evaluate the carrier mobility of a semiconductor material with high accuracy.

  In order to achieve the above object, a semiconductor evaluation apparatus according to the present invention irradiates a thin flat plate-like sample to be measured with laser light, and generates carriers generated by the laser light irradiation on the surface of the sample to be measured. A semiconductor evaluation apparatus for generating a current by moving in a direction and evaluating the carrier mobility of the sample to be measured from the duration of the generated current, wherein the sample to be measured is irradiated with the laser light In this way, a measured sample setting part for setting the measured sample is provided, and the measured sample setting part has a first surface and a first permeability having a second surface formed on the opposite side of the first surface. A second transmissive substrate having a substrate, a third surface contacting the second surface of the first transmissive substrate, and a fourth surface formed on the opposite side of the third surface; and the first transmissive substrate. The second surface of the transparent substrate and the third surface of the second transparent substrate are in contact with each other. And a fixing member capable of fixing the first transmissive substrate and the second transmissive substrate, and allows the laser light to pass through a third surface of the second transmissive substrate. A light-shielding film having an opening, wherein the sample to be measured is disposed on a first surface of the first transmissive substrate, and is incident from a fourth surface of the second transmissive substrate; The laser beam that passes through the opening of the light shielding film in the light is irradiated on the sample to be measured.

  In the above semiconductor evaluation apparatus, a current is generated by moving the carrier generated in a thin flat plate-like sample to be measured in the lateral direction of the sample to be measured, and the carrier mobility of the sample to be measured is evaluated from the duration of the current. To do. For this reason, it is not necessary to adjust the thickness of the sample to be measured, and the carrier mobility can be evaluated with high accuracy even when a thin sample to be measured is used.

  Then, the transmissive substrate is a two-layer stack that can be attached and detached, a sample to be measured is placed on the first transmissive substrate, and a light-shielding film is provided on the second transmissive substrate to limit the laser light irradiation site. Then, the two transmissive substrates are fixed to each other by a fixing member. Since the first and second transmissive substrates can be fixed by the fixing member, only the first transmissive substrate is replaced when the sample to be measured is replaced. Only the second transparent substrate needs to be replaced. For this reason, it is possible to realize a semiconductor evaluation apparatus capable of suppressing component consumption.

  Further, by allowing the first transmissive substrate and the second transmissive substrate to be fixed by the fixing member, the position adjustment between the laser light irradiation portion of the sample to be measured and the opening of the light shielding film can be performed. Since the adjustment can be made even after the sample to be measured is attached to the transparent substrate, the configuration of the sample-to-be-measured portion is facilitated.

  Further, a light shielding film is formed on the third surface of the second transmissive substrate, and the first transmissive substrate is bonded after the formation. For this reason, scattering of the light shielding film due to the sputtering effect when the laser beam is irradiated is mechanically pressed, and as a result, damage to the light shielding film is suppressed.

  The total value of the thickness of the first transmissive substrate and the thickness of the second transmissive substrate is preferably 1 mm or less.

  Normally, from the viewpoint of the durability of the transmissive substrate, the thickness of the transmissive substrate also increases with the thickness of the sample to be measured. It is possible to reduce the thickness of the substrate. As a result of intensive studies on the thickness of the transmissive substrate, the present inventors have determined that the laser light incident on the sample to be measured even if the laser light is transmitted if the thickness of the transmissive substrate is 1 mm or less. It has been found that the generation of carriers in the sample to be measured is sufficiently performed by the strength of.

  That is, in the above-described semiconductor evaluation apparatus, the total value of the thickness of the first transmissive substrate and the thickness of the second transmissive substrate is set to 1 mm or less, so that the sample passes through the transmissive substrate and reaches the sample to be measured. Since the decrease in the intensity of the laser beam is suppressed, carriers in the sample to be measured are sufficiently generated, and the detection accuracy of the current accompanying the carrier movement can be improved.

  Therefore, even when it is difficult to prepare a uniform and large sample thickness in a high mobility organic semiconductor material such as pentacene or rubrene, the carrier mobility can be evaluated with high accuracy.

  The light shielding film is preferably a metal film including any one of aluminum, titanium, iron, nickel, and copper.

  In this case, since the sample to be measured is arranged on the laminated structure in which the light shielding film is formed on the transmissive substrate, the durability of the sample to be measured can be improved. Moreover, the durability of the sample to be measured can be further improved by forming the light shielding film from a metal film containing any one of aluminum, titanium, iron, nickel, and copper.

  The sample-to-be-measured portion further includes two opposing electrodes formed on the sample to be measured, and a light irradiating unit that emits a laser beam that irradiates the sample to be measured, and the light irradiating unit. In synchronization with the irradiation of the laser beam, the voltage application means for applying a voltage between the two opposing electrodes and the voltage between both ends of the load resistance unit connected in series to one of the electrodes of the sample to be measured are detected. And a signal detecting means.

  In this case, a voltage is applied between two opposing electrodes provided on the sample to be measured in synchronism with the time when the sample to be measured is irradiated with the laser light, so that the carrier moves within the sample to be measured. The signal detection means can detect the voltage across the load resistor connected in series to one of the electrodes of the sample to be measured. For this reason, the accuracy of voltage detection of the signal detection means can be improved.

  It is preferable that a resistance value of the load resistance unit is 50 to 1000Ω, and the signal detection unit has a preamplifier having an input capacitance of 500 pF or less and amplifying a voltage between both ends of the load resistance unit. Is preferred.

  In this case, even in the case of a sample to be measured having a very high insulating property such as an organic semiconductor material, it is possible to accurately detect a voltage displacement due to a current generated by carrier movement.

  The preamplifier preferably has its own direct-current voltage component and gain, subtracts the direct-current voltage component from the input voltage, and outputs a voltage obtained by multiplying the subtraction result by the gain.

  In this case, since the input voltage is amplified using the DC voltage component and gain of the preamplifier, amplification can be performed efficiently by the preamplifier.

  The preamplifier is preferably located at a distance within 25 cm from the sample to be measured.

  In this case, it is possible to suppress the preamplifier from being affected by noise caused by electromagnetic waves generated from the electric wire connecting the sample to be measured and the preamplifier. This noise is an electromagnetic wave of about 10 to 100 MHz, and the wavelength is about 1 m at the maximum. Usually, if the length of the wire is 1/4 or less of the wavelength, that is, 25 cm or less, the wire does not function as an antenna.

  It is preferable to further include a storage container for storing the sample to be measured and the load resistance portion.

  Preferably, the storage container further stores the preamplifier.

  It is preferable that the storage container has any one of an exhaust device that makes the inside of the container a vacuum state and a gas introduction device that makes the inside of the container a nitrogen atmosphere or an inert gas atmosphere.

  When this evaluation is performed in the atmosphere, discharge is likely to occur around the sample to be measured due to the influence of humidity in the atmosphere, and if the discharge occurs, noise is mixed into the sample to be measured and measurement data is mixed. Occurs. Further, the effect of using the inert gas is effective in suppressing the chemical reaction with the organic semiconductor sample and suppressing the deterioration of the sample.

  A light blocking unit that is disposed on the optical path of the laser beam from the light irradiation unit to the sample to be measured and can block the progress of the laser beam, and processing the detection result of the signal detection unit, thereby Signal processing means for evaluating carrier mobility of the sample, and the signal processing means integrates the detection results of the signal detection means a plurality of times when the laser light is transmitted by the light blocking unit, and averages the transmission time Calculating a value, calculating the average value at the time of interruption by multiplying the detection results of the signal detection means at the time of interruption of the laser light by the light interruption unit, and calculating the average value at the time of transmission and the average value at the time of interruption. It is preferable to evaluate the carrier mobility of the sample to be measured from the difference value.

  In this case, the signal-to-noise ratio of the signal detection means is improved, and the signal processing means processes the signal by integration averaging, so that it is less susceptible to the vibration of the apparatus itself, and no vibration isolator is required. The device can be miniaturized.

  As described above, the semiconductor evaluation apparatus of the present invention includes a measured sample setting unit that sets the measured sample so that the laser beam is irradiated onto the measured sample, and the measured sample setting unit includes: A first transparent substrate having a first surface and a second surface formed on the opposite side of the first surface, a third surface in contact with the second surface of the first transparent substrate, and the third surface The second transmissive substrate having a fourth surface formed on the opposite side of the first transmissive substrate, the second surface of the first transmissive substrate and the third surface of the second transmissive substrate in contact with each other. A fixing member capable of fixing the first transmissive substrate and the second transmissive substrate; and a third surface of the second transmissive substrate having an opening through which the laser light passes. A light-shielding film is formed, the sample to be measured is disposed on the first surface of the first transmissive substrate, and the second transmissive substrate is Wherein the laser beam passing through the opening of the light shielding film of the laser light incident from the surface to be irradiated to the sample.

  Therefore, there is an effect that the consumption cost can be suppressed very simply and the carrier mobility of the semiconductor material can be evaluated with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same part, and what attached the same code | symbol in drawing may abbreviate | omit description.

  FIG. 1 shows a schematic configuration diagram of a semiconductor evaluation apparatus according to an embodiment of the present invention. As shown in FIG. 1, a semiconductor evaluation apparatus 100 according to the present embodiment includes a measured sample setting unit 30 that sets a measured sample 10 and a light irradiation unit that emits pulsed light irradiated to the measured sample 10. 11, voltage applying means 12 for applying a DC voltage to the sample 10 to be measured, signal detecting means 13 for detecting a current signal flowing through the sample 10 to be measured, and signal processing means 22 for processing the detection result of the signal detecting means 13. And a control means 21 for controlling each part in the semiconductor evaluation apparatus 100.

  FIG. 2 shows a schematic cross-sectional view of the measured sample setting part 30. FIG. 2B is a view for explaining the periphery of the sample 10 to be measured shown in FIG. In the measured sample setting section 30 shown in FIG. 2, the measured sample 10 is arranged on the surface (first surface) of a transmissive glass substrate (first transmissive substrate) 31a. A metal film (light-shielding film) 33 is deposited on the surface (third surface) of the transmissive glass substrate 31b (second transmissive substrate).

  Then, as shown in FIG. 2B, the transmissive glass substrate 31a and the transmissive glass substrate 31b are arranged so that the back surface (second surface) of the transmissive glass substrate 31a and the surface of the transmissive glass substrate 31b are in contact with each other. Is fixed by a fixing member 39. The fixing member 39 is detachable from the transmissive glass substrate 31a and the transmissive glass substrate 31b. For example, a metal clamp may be used as the fixing member 39.

  Therefore, by removing the fixing member 39 from the transmissive glass substrate 31a and the transmissive glass substrate 31b, the transmissive glass substrate 31a and the transmissive glass substrate 31b are separated from each other. That is, the step of placing the sample 10 to be measured on the transmissive glass substrate 31a and the step of depositing the metal film 33 on the transmissive glass substrate 31b can be performed independently of each other.

  Examples of the material of the metal film 33 include aluminum, titanium, iron, nickel, and copper. In short, any material that shields the laser beam 17 incident from the back surface (fourth surface) of the transmissive glass substrate 31b may be used.

  An opening 34 is provided in a part of the metal film 33. Examples of the shape of the opening 34 include a slit and a fine hole. Of the laser beam 17 incident on the metal film 33, only the laser beam passing through the opening 34 is irradiated on the sample 10 to be measured through the transparent glass substrate 31a.

  The sample 10 to be measured has a thin flat plate shape and is disposed so as to be in direct contact with the surface of the transmissive glass substrate 31a. The sample 10 to be measured is a measurement sample whose mobility of its own carrier is to be evaluated. The sample 10 to be measured is an organic semiconductor material that is difficult to increase in thickness, such as pentacene or rubrene. Of course, as the sample 10 to be measured, an inorganic semiconductor material such as silicon or germanium that can be evaluated using a conventional TOF method may be used.

  Electrodes 32 are formed on both ends of the sample 10 to be measured, and a voltage is applied between the both ends of the sample 10 to be measured using these electrodes 32. More specifically, of these electrodes 32, one electrode 32 is directly connected to the terminal A, and the other electrode 32 is connected to the terminal B via a load resistance portion 35 having a predetermined resistance value. The terminals A and B are connected to the voltage application unit 12, and a voltage is input from the voltage application unit 12. The distance between the two electrodes 32 corresponds to the flight distance L of the carrier generated in the sample 10 to be measured.

  In addition to the terminal A and the terminal B, the measured sample setting part 30 has a terminal C and a terminal D that are connected to both ends of the load resistor 35. The terminals C and D are connected to the signal detection means 13 and output a voltage across the load resistor 35 to the signal detection means 13.

  The measured sample setting unit 30 further includes a storage container 36 for storing the measured sample 10, the load resistance unit 35, and the like. The storage container 36 is configured so that the inside thereof can be kept in a vacuum state. For example, after the sample 10 to be measured is installed, the inside thereof is exhausted by an exhaust device 38 such as a vacuum pump provided in the storage container 36. Is done.

  Further, the storage container 36 may be configured to be in an atmosphere of an inert gas such as nitrogen or argon instead of maintaining the inside in a vacuum state. In this case, instead of the exhaust device 38, a gas introduction device capable of filling the inside of the storage container 36 with an inert gas such as nitrogen or argon may be provided.

  Moreover, as a material of the storage container 36, it is comprised with metals, such as aluminum, titanium, iron, nickel, copper, for example.

  Further, the storage container 36 has a window 37 through which the laser light 17 can be transmitted in order to introduce the laser light 17 emitted from the light irradiation means 11 into the inside.

  As shown in FIG. 1, the light irradiation means 11 has a laser light source capable of emitting laser light 17 that is visible light or ultraviolet light. The laser light source can emit the laser beam 17 in a pulse shape. As the wavelength of the laser beam 17, it is preferable to select a wavelength that is easily absorbed by the sample 10 to be measured. Here, the light irradiation means 11 is demonstrated as what has a nitrogen pulse laser light source with a wavelength of 337 nm.

  The laser beam 17 emitted from the light irradiation means 11 is reflected by each of the first parabolic mirror 15 and the second parabolic mirror 16, and then is measured on the measured sample setting unit 30. It goes straight toward the sample 10 and is irradiated to the sample 10 to be measured. By irradiation with the laser beam 17, carriers (electrons, holes) are generated at the irradiation position of the sample 10 to be measured.

  On the optical path of the laser beam 17 from the light irradiation means 11 to the sample 10 to be measured, a light blocking unit 14 capable of blocking the progress of the laser beam 17 is disposed. By operating the light blocking unit 14, the irradiation of the laser beam 17 on the sample 10 to be measured can be interrupted without stopping the laser beam emission operation of the light irradiation unit 11. The light blocking unit 14 includes a light detection unit that detects light, and detects whether or not the laser light 17 passes through the light detection unit 14 based on the detection result of the light detection unit.

  The voltage applying means 12 is connected to the terminal A and the terminal B of the measured sample setting section 30 and can apply a DC voltage between the electrodes 32 at both ends of the measured sample 10 via the terminal A and the terminal B. Has a voltage source. The voltage source preferably applies a voltage of 5 kV or less, more preferably 2.5 kV or less. By applying this voltage, an electric field is generated between the two electrodes 32 of the sample 10 to be measured. Carriers generated in the sample 10 to be measured move according to the direction of the electric field.

  The signal detection means 13 has a digital oscilloscope that is connected to the terminals C and D of the measured sample setting section 30 and can detect the voltage across the load resistance section 35 via the terminals C and D. is doing. As described above, the carrier generated in the sample 10 to be measured by the irradiation of the laser beam 17 moves according to the direction of the electric field generated by the voltage application by the voltage application unit 12. During the period in which this movement continues, the voltage across the load resistor 35 is displaced due to the movement of the carrier. The digital oscilloscope detects a voltage displacement between both ends of the load resistance unit 35.

  Further, the signal detecting means 13 may further include a preamplifier (preamplifier) that amplifies and outputs the input voltage when the voltage across the load resistor 35 is input. More specifically, a preamplifier may be connected between the terminal C and terminal D of the measured sample setting unit 30 and the digital oscilloscope. In this case, the voltage between both ends of the load resistance unit 35 is amplified by the preamplifier, and the amplified voltage is input to the digital oscilloscope. For this reason, since the digital oscilloscope can amplify and detect the voltage across the load resistor 35, the voltage across the load resistor 35 can be detected with finer voltage accuracy.

  Also, the preamplifier has its own direct-current voltage component (DC offset component) and gain (gain), and subtracts the direct-current voltage component (DC offset component) from the input voltage, and gain is obtained from the subtracted input voltage. The result of multiplying (Gain) is output. This increases the dynamic range of the preamplifier. By detecting this output voltage, the digital oscilloscope can detect the voltage between both ends of the load resistance unit 35 with finer voltage accuracy.

  The signal processing unit 22 acquires the detection result output from the signal detection unit 13. More specifically, the signal processing unit 22 processes the detection result to calculate a carrier moving time Tf in which the carrier generated in the sample to be measured 10 flies between the two electrodes 32 of the sample to be measured 10. . Then, based on the calculation result, the mobility of carriers generated in the sample 10 to be measured is evaluated.

  The control means 21 controls the operation timing between the above-mentioned parts when evaluating the mobility of the carrier generated in the sample 10 to be measured, and records and processes the signals output from the above-mentioned parts and input to the respective parts. Etc. More specifically, the control unit 21 controls each of the light irradiation unit 11, the voltage application unit 12, and the signal detection unit 13.

  The control means 21 and the signal processing means 22 can be realized by the computer 20, for example. The computer 20 has input means 23 and output means 24. The output unit 24 displays the output result of the signal processing unit. The output means 24 has a display device such as a liquid crystal display panel, and displays the output result so that the user can visually recognize it. The input unit 23 includes a numeric keypad, a keyboard, and the like. For example, the display format of the output unit 24 is input.

  Next, a semiconductor evaluation apparatus according to an embodiment of the present invention will be described using a specific example.

  As a laser light source of the light irradiation means 11, a nitrogen pulse laser light source (wavelength: 337 nm) made by USHO is used. When the light irradiation means 11 receives a signal indicating the start of light irradiation from the control means 21, the light irradiation means 11 drives the laser light source to emit the laser light 17 from the laser light source.

  The laser beam 17 emitted from the laser light source is irradiated to the sample 10 to be measured installed in the sample-to-be-measured installation unit 30 via the first parabolic mirror 15 and the second parabolic mirror 16. . Laser light emitted from the laser light source is detected by a photodetector (light detection unit) in the light blocking unit 14 installed in the middle of the optical path. The light blocking unit 14 outputs the detection result to the control unit 21.

  When the detection result is input, the control means 21 outputs a signal indicating the start of voltage application to the measured sample 10 to the voltage application means 12. When the signal is input, the voltage applying unit 12 drives the voltage source and applies a voltage to the sample 10 to be measured.

  As the sample 10 to be measured, a thin flat-plate thin-film organic semiconductor single crystal is used. As the material, rubrene is used. In order to apply a DC electric field in the in-plane direction of the sample 10 to be measured, electrodes 32 are formed on both ends of the sample 10 to be measured (the distance between both ends is 2 mm). The material of the electrode 32 is silver.

  A metal film 33 having an opening 34 is adhered to the surface of the transmissive glass substrate 31b. The opening 34 is a slit and is formed in the metal film 33 in which aluminum is vapor-deposited through a metal mask. The width of the opening (slit) 34 is 150 μm. The laser beam 17 passes through the opening (slit) 34 and is irradiated to the sample 10 to be measured.

  When the laser beam 17 is irradiated on the sample 10 to be measured, a carrier is generated at the irradiation position of the sample 10 to be measured. This carrier moves according to the electric field direction between the electrodes 32 at both ends of the sample 10 to be measured. The current generated due to the carrier movement flows through the load resistor 35, and as a result, the voltage across the load resistor 35 is displaced.

  The signal detection means 13 amplifies this voltage displacement using a preamplifier, and observes and records it with a digital oscilloscope. In order to measure a high mobility organic material, it is important to ensure a sufficient transmission band of the preamplifier. A preamplifier having a cutoff frequency of 100 MHz and an amplification factor of 40 dB is preferable.

FIG. 3 shows the evaluation result of the sample 10 to be measured. This result is a TOF waveform of rubrene, which is a single crystal material of an organic semiconductor. The distance between the electrodes 32 of the sample 10 to be measured, that is, the flight distance of carriers (electrons, holes) is 1.85 mm. A kink appears on the right side of FIG. 3, which is considered to correspond to the flight time of the generated hole. The hole mobility obtained from this evaluation result is 13 cm ² / V · sec. As a result of performing the same evaluation a plurality of times, the hole mobility is recorded in the range of 10 to 20 cm ² / V · sec.

  As described above, the semiconductor evaluation apparatus according to the present embodiment brings the electrode 32 into contact with two different parts of the thin film or plate-like sample 10 and applies a DC voltage to the two electrodes 32. An electric field is generated between the electrodes 32.

  Then, in the vicinity of one electrode 32, the surface of the sample 10 to be measured is irradiated with visible or ultraviolet laser light 17 through a metal film 33 having openings (slits or fine holes) 34, and the laser light 17 is irradiated. This is an apparatus for evaluating the carrier mobility of the sample 10 to be measured from the duration of the current flowing between the electrodes 32 along with the movement of the carriers generated by.

  In the semiconductor evaluation apparatus 100 of the present embodiment, the sample 10 to be measured is fixed on the transmissive glass substrate 31a, and the metal film 33 to be a light shielding film is fixed on the transmissive glass substrate 31b. The total thickness of the transparent glass substrates 31a and 31b is 1 mm or less, preferably 200 μm or less. This is because, in the present embodiment, since the sample to be measured 10 is turned sideways and the electrode 32 is formed, the traveling distance of the carrier can be freely set even if the sample to be measured 10 is thin. . As a result, the durability of the sample 10 to be measured can be maintained even when the transparent glass substrates 31a and 31b are thin. For this reason, the sample 10 to be measured is attached to the transmissive glass substrate 31a, the metal film 33 is formed on the transmissive glass substrate 31b, and the transmissive glass substrates 31a and 31b are brought into contact with each other. Can be irradiated in the vicinity of the electrode 32, and the simplicity of the semiconductor evaluation apparatus 100 is improved. According to the experiments by the present inventors, when the transmissive glass substrates 31a and 31b are thick, the intensity of the laser light 17 is lowered and the detection sensitivity is deteriorated. According to the results of experiments by the present inventors, the total thickness of the transmissive glass substrates 31a and 31b is preferably 200 μm or less.

  Further, the semiconductor evaluation apparatus 100 of the present embodiment has a three-layer laminated structure of the transmissive glass substrate 31a, the metal film 33, and the transmissive glass substrate 31b. For this reason, damage to the metal film 33 due to laser beam irradiation can be effectively prevented.

  Furthermore, in the semiconductor evaluation apparatus 100 of the present embodiment, the resistance value of the load resistance unit 35 is 50 to 1 kΩ, preferably 50 to 300Ω. The input capacity of the preamplifier that detects the voltage generated in the load resistance unit 35 is preferably 500 pF or less. This is because the sample to be measured 10 has very high insulation, that is, high internal impedance. Therefore, if the voltage is not detected with a low input resistance and with the associated capacitance suppressed as much as possible, it is caused by carrier movement. This is because the voltage displacement due to the generated current cannot be clearly detected.

  Further, in the semiconductor evaluation apparatus 100 of the present embodiment, it is preferable that the preamplifier of the signal detection means 13 is sealed with an insulating solid material, shielded with metal, and brought close to the measured sample 10 within a distance of 25 cm. More preferably, the distance is within 10 cm. This is effective in improving the S / N ratio of the preamplifier. This is because the longer the wire connecting the sample 10 to be measured and the preamplifier, the more likely the preamplifier is affected by noise caused by electromagnetic waves generated from the wire that propagates the signal between the sample 10 to be measured and the preamplifier. It is. This noise is an electromagnetic wave of about 10 to 100 MHz, and the wavelength is about 1 m at the maximum. Usually, if the length of the wire is 1/4 or less of the wavelength, that is, 25 cm or less, the wire does not function as an antenna. Furthermore, if the safety factor is doubled and 10 cm or less, it becomes more effective.

  Furthermore, in the semiconductor evaluation apparatus 100 of the present embodiment, the light blocking unit 14 is provided in the path until the laser beam 17 is irradiated to the sample 10 to be measured. When the laser light 17 is transmitted, the detection results of the signal detection means 13 are integrated multiple times to calculate an average value, and when the laser light 17 is interrupted, the detection results of the signal detection means 13 are integrated multiple times to calculate an average value, The carrier mobility of the sample 10 to be measured may be evaluated from the difference value between the former average value and the latter average value. In this case, the S / N ratio of the preamplifier of the signal detection means 13 is improved, and the signal processing means 22 processes the signal by integration averaging, so that it is less susceptible to mechanical vibrations, and no vibration isolator is required. The device can be downsized.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible in the range shown to the claim. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can also be expressed as follows. That is, the semiconductor evaluation apparatus according to the present invention causes an electrode to contact two different parts of a thin film or a plate-like sample to be measured, and a DC voltage is applied to the two electrodes to generate an electric field between the electrodes. The sample surface near one electrode is irradiated with a pulse of visible light or ultraviolet light through a light-shielding film having slits or fine holes, and measured from the duration of photocurrent flowing through two electrodes after the pulse irradiation is completed. In an apparatus for evaluating the carrier mobility of a sample, a sample to be measured is fixed to one surface of an insulating transparent substrate, and a light shielding film is fixed to the surface opposite to the surface with the sample of the insulating transparent substrate. The thickness of the transparent substrate is 1 mm or less, preferably 200 μm or less.

  The light shielding plate has a two-layer laminated structure of glass and metal film, preferably a three-layer laminated structure of glass, metal film and glass, and the metal film is made of any one of aluminum, titanium, iron, nickel and copper. It is preferable to contain.

  A resistor of 50 to 1 kΩ, preferably a resistor of 50 to 300 Ω, is connected in series between the electrode and the voltage source, and the voltage generated in the resistor is input to a preamplifier of 500 pF or less as an input capacitance. It is preferable to record the output signal and calculate the carrier mobility of the sample to be measured from the record.

  A preamplifier having a function of subtracting a constant DC voltage from the input signal is preferably provided.

  It is preferable to seal the preamplifier with an insulating solid material, shield it with metal, and bring it close to the sample to be measured within a distance of 10 cm.

  It is preferable that the resistor and the sample to be measured are contained in the same metal container.

  It is preferable to house in a resistor, a sample to be measured and a preamplifier.

  In order to create a vacuum, nitrogen, or inert gas atmosphere around the sample to be measured, it is preferable to have a metal vacuum container for storing the sample to be measured and a gas introduction device or a vacuum exhaust device.

  An optical circuit breaker is provided in the path until the sample of visible light or ultraviolet light is irradiated, and the photocurrent signal is integrated several times during transmission of light, the average value is calculated, and the photocurrent signal is output multiple times when light is blocked. It is preferable to integrate and calculate the average value, and to evaluate the carrier mobility of the sample to be measured based on the difference value between the former average value and the latter average value.

  The present invention can be applied to a semiconductor evaluation apparatus for evaluating characteristics such as carrier mobility and carrier life of a semiconductor.

It is a block diagram showing a schematic structure of a semiconductor evaluation device concerning an embodiment of the invention. (A) is sectional drawing which shows schematic structure of the to-be-measured sample installation part of FIG. 1, (b) is a figure for demonstrating the circumference | surroundings of the to-be-measured sample of (a). It is a graph which shows the example of an evaluation result of the semiconductor evaluation apparatus of FIG. It is a figure for demonstrating the conventional TOF method. It is a figure for demonstrating the other conventional TOF method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sample to be measured 11 Light irradiation means 12 Voltage application means 13 Signal detection means 14 Light blocker 15, 16 Parabolic mirror 17 Laser light 18, 36 Storage container 20 Computer 21 Control means 22 Signal processing means 23 Input means 24 Output means 30 Measured Sample Placement Part 31a, 31b Transparent glass substrate (first transparent substrate, second transparent substrate)
32 electrode 33 metal film (light-shielding film)
34 opening 35 load resistance 37 window 38 exhaust device 39 fixing member

Claims (12)

A thin flat plate-like sample to be measured is irradiated with laser light, and a carrier is generated by moving the carrier generated due to the irradiation of the laser beam toward the surface of the sample to be measured. A semiconductor evaluation apparatus for evaluating the carrier mobility of the sample to be measured from the duration,
A sample-to-be-measured portion for installing the sample to be measured so that the laser beam is irradiated on the sample to be measured;
The measured sample setting part is:
A first transmissive substrate having a first surface and a second surface formed on the opposite side of the first surface;
A second transmissive substrate having a third surface in contact with the second surface of the first transmissive substrate and a fourth surface formed on the opposite side of the third surface;
A fixing member capable of fixing the first transmissive substrate and the second transmissive substrate so that the second surface of the first transmissive substrate and the third surface of the second transmissive substrate are in contact with each other. And having
A light-shielding film having an opening through which the laser beam passes is formed on the third surface of the second transparent substrate,
The sample to be measured is arranged on the first surface of the first transparent substrate, and passes through the opening of the light shielding film among the laser light incident from the fourth surface of the second transparent substrate. A semiconductor evaluation apparatus for irradiating the sample to be measured with laser light.   The semiconductor evaluation apparatus according to claim 1, wherein a total value of the thickness of the first transmissive substrate and the thickness of the second transmissive substrate is 1 mm or less.   3. The semiconductor evaluation apparatus according to claim 1, wherein the light shielding film is a metal film containing any one of aluminum, titanium, iron, nickel, and copper. The measured sample setting part further includes two opposing electrodes formed on the measured sample,
A light irradiating means for emitting a laser beam applied to the sample to be measured;
Voltage application means for applying a voltage between the two opposing electrodes in synchronization with the irradiation of the laser beam by the light irradiation means;
The signal detection means which detects the voltage between the both ends of the load resistance part connected in series with one of the electrodes of the said to-be-measured sample is further provided, The one of Claims 1-3 characterized by the above-mentioned. Semiconductor evaluation equipment.   The semiconductor evaluation apparatus according to claim 4, wherein a resistance value of the load resistance unit is 50 to 1000Ω.   The semiconductor evaluation apparatus according to claim 4, wherein the signal detection unit has a preamplifier having an input capacitance of 500 pF or less and amplifying a voltage between both ends of the load resistance unit.   The preamplifier has a DC voltage component and a gain unique to the preamplifier, subtracts the DC voltage component from the input voltage, and outputs a voltage obtained by multiplying the subtraction result by the gain. Semiconductor evaluation equipment.   The semiconductor evaluation apparatus according to claim 6, wherein the preamplifier is located at a distance within 25 cm from the sample to be measured.   The semiconductor evaluation apparatus according to claim 4, further comprising a storage container that stores the sample to be measured and the load resistance unit.   The semiconductor evaluation apparatus according to claim 9, wherein the storage container further stores the preamplifier.   10. The storage container according to claim 9, wherein the storage container includes any one of an exhaust device that makes the inside thereof a vacuum state and a gas introduction device that makes the inside thereof a nitrogen atmosphere or an inert gas atmosphere. 10. The semiconductor evaluation apparatus according to 10. A light blocking part arranged on the optical path of the laser beam from the light irradiation means to the sample to be measured, and capable of blocking the progress of the laser beam;
Signal processing means for evaluating carrier mobility of the sample to be measured by processing the detection result of the signal detection means; and
The signal processing means calculates the average value during transmission by multiplying the detection results of the signal detection means during transmission of the laser light by the light blocking section a plurality of times, and when the laser light is blocked by the light blocking section The detection results of the signal detection means are integrated several times to calculate an average value at the time of blocking, and the carrier mobility of the sample to be measured is evaluated from the difference value between the average value at the time of transmission and the average value at the time of blocking The semiconductor evaluation apparatus according to claim 4, wherein the semiconductor evaluation apparatus is a semiconductor evaluation apparatus.

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