JP2006234738A - Substrate for measuring carrier mobility of semiconductor thin film, measuring apparatus and measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate, a device, and a method for measuring carrier mobility, which can measure a semiconductor thin film along in-plane directions in a state similar to an actual usage, easily and accurately at a low cost. <P>SOLUTION: The substrate 10 for measuring the carrier mobility comprises: a board 11 which transmits exciting light; a light blocking layer 12 which is formed on the board 11 and has an aperture 13 in its portion; a first electrode 14 which is disposed so as to be adjacent to the aperture 13 or to cover a portion of the aperture 13; and a second electrode 15 which is formed on the light blocking layer 12 and disposed at a prescribed spacing from the first electrode 14. In the case the light blocking layer 12 is conductive, it is preferable that an insulating layer 16 is disposed in order to prevent the light blocking layer 12 from coming into electric contact with the electrodes 14, 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a carrier mobility measuring substrate for a semiconductor thin film, a carrier mobility measuring device, and a measuring method thereof.

  Semiconductor carrier mobility (also referred to as charge mobility) is an extremely important parameter for fabricating and operating various devices using semiconductors, and measurement is indispensable especially in the design of electronic devices. . A time-of-flight method (hereinafter referred to as TOF method) has been reported as a method for measuring the carrier mobility of semiconductors, particularly organic semiconductors used in light-emitting elements, thin film transistors, and the like (see, for example, Non-Patent Document 1).

  FIG. 11 is a schematic cross-sectional view showing the principle of the TOF method. In the TOF method, a measurement cell 110 having a structure in which a semiconductor 111 is sandwiched between a transparent electrode 112 and an electrode 113 is used. For carrier mobility, a DC power source 114, a load resistor 115, and a digital oscilloscope 116 are connected to the measurement cell 110. Measured with the device. In such a TOF method, pulsed excitation light 117 is irradiated from the transparent electrode 112 side while a voltage is applied to the semiconductor 111, and carriers (electrons or holes) generated by the excitation light 117 are directed toward the electrode 113. This is a method of measuring a temporal change in current when drifting with the digital oscilloscope 116. Here, in order to accurately measure the carrier mobility from the temporal change in current, the carrier generation distribution when the carrier that is the source of the observed transient photocurrent is generated in the sample must be clear. Is desirable. That is, the distribution of carriers generated by the excitation light needs to be sufficiently thin in the thickness direction near the transparent electrode, and the thickness of the semiconductor 111 is about 10 times the penetration length of the excitation light wavelength. It is necessary to provide it. As the thickness of such a semiconductor, about 10 μm is actually required.

  The above is an example of observing charge transport in the film thickness direction of a semiconductor. However, as an attempt to observe transient photocurrent in the film surface, a technique as shown in FIG. 12 is known (for example, see Non-Patent Document 2). In this case, since a wide range of the semiconductor thin film 121 to which a voltage is applied is irradiated with the excitation light 127, photogenerated charges observed as transient photocurrents are widely distributed in the film in the initial state. Therefore, although the total amount of transient photocurrent flowing between the electrodes 122 and 123 can be observed, it is difficult to quantitatively observe the carrier mobility. Reference numeral 128 denotes a substrate that transmits excitation light.

FIG. 13 is a schematic cross-sectional view showing the principle of a conventional modified TOF method in which the TOF method is partially changed. In this modified TOF method, pulsed excitation light is collected by a lens, and the condensed excitation light 137 is irradiated to the semiconductor thin film 131 located in the vicinity of the end of the first electrode 132, and the semiconductor thin film 131 is irradiated by the irradiation. This is a method of measuring a time change of current when carriers generated at a condensing point drift to the second electrode 133 (see, for example, Non-Patent Document 3 and Patent Document 1). In this modified TOF method, the carrier generation region is set near the end of the first electrode 132 in order to facilitate the calculation of mobility while keeping the distance at which each generated carrier drifts to the second electrode 133 constant. Yes. Reference numeral 138 denotes a substrate that transmits excitation light.
RGKepler, Phys. Rev. Vol. 119, p1226 (1960) Masatoshi Kitamura, Tadahiro Imada, Satoshi Kako and Yasuhiko Arakawa, Jpn. J. Appl. Phys. Vol. 43, p2326 (2004) Nikkei Business Daily, December 2, 2003 article JP 2004-315441 A

  In the above TOF method, a semiconductor thin film having a thickness of at least about 10 μm is required. However, in general semiconductor materials, it may be difficult to obtain such a thick film. Depending on the film quality and grain boundaries, the carrier mobility may be different depending on whether it is thick or thin. For this reason, the carrier mobility obtained by the TOF method may not necessarily match the carrier mobility of the semiconductor thin film in the actual usage pattern depending on the semiconductor material used for the measurement. Furthermore, in actual device operation, carrier drift may be in the in-plane direction rather than the thickness direction of the semiconductor thin film, but the conventional TOF method cannot measure the carrier mobility in the in-plane direction of the semiconductor thin film. Even in this respect, depending on the semiconductor material used for the measurement, there is a possibility that the carrier mobility of the semiconductor thin film in the actual usage pattern does not necessarily match.

  On the other hand, in the modified TOF method, since the carrier generation region is in the vicinity of the end of the first electrode, it is necessary to accurately irradiate only the semiconductor thin film in the vicinity of the end of the electrode with excitation light having a small beam diameter. Therefore, there is a problem that a complicated condensing optical system using a plurality of lenses or mirrors and a highly accurate and expensive substrate position control device are required. In the modified TOF method, carriers are generated in a narrow range by irradiation of the condensed excitation light. However, in order to obtain an observable photocurrent signal, it is necessary to increase the intensity of the excitation light. However, when the intensity of the excitation light is increased, a space charge is formed in the irradiation region, which causes a problem that accurate mobility measurement becomes difficult.

  The present invention has been made in order to solve the above-mentioned problems, and its object is to be able to measure a semiconductor thin film close to an actual usage pattern in the in-plane direction, and to measure easily and accurately at a low cost. An object of the present invention is to provide a carrier mobility measurement substrate, a measurement apparatus, and a measurement method.

  In order to solve the above-described problem, a substrate for measuring carrier mobility of a semiconductor thin film according to the first aspect of the present invention includes a substrate that transmits excitation light, and a light shield that is formed on the substrate and has an opening in a part thereof. A layer, a first electrode that is adjacent to the opening or covers a part of the opening, and a second electrode that is formed on the light-shielding layer and provided at a predetermined interval from the first electrode. It is characterized by.

  The measurement substrate according to the present invention is preferably used for measuring the carrier mobility of a semiconductor thin film in which carriers are likely to be generated when irradiated with excitation light. According to the present invention, the first electrode is formed so as to be adjacent to the opening or to cover a part of the opening. Therefore, the semiconductor thin film is formed on the measurement substrate and excited from the substrate side. When light is irradiated, carriers can be generated in the semiconductor thin film over the opening. Since the generated carriers move in the formed semiconductor thin film toward the second electrode, the carrier mobility in the in-plane direction of the semiconductor thin film can be measured, and in the in-plane direction in a form close to the element actually used. Carrier mobility can be measured easily and accurately.

  In the substrate for measuring carrier mobility of a semiconductor thin film according to the present invention, an insulating layer that transmits excitation light is formed between the first electrode and the second electrode, and the light shielding layer and an opening formed in a part thereof. It is characterized by being.

  According to this invention, since the insulating layer that transmits the excitation light is provided between each electrode and the light shielding layer, even when a conductive light shielding layer such as a chromium thin film is formed as the light shielding layer, The conductive light shielding layer and the two electrodes do not contact each other. As a result, the carrier mobility in the in-plane direction of the semiconductor thin film can be measured easily and accurately.

  In order to solve the above-described problem, a substrate for measuring carrier mobility of a semiconductor thin film according to a second aspect of the present invention includes a substrate that transmits excitation light, a first electrode formed on the substrate, and the substrate. A charge generation layer formed between or on the first electrode and a second electrode formed on the substrate and provided at a predetermined interval from the first electrode; The charge generation layer is optically exposed to a side to be irradiated with the excitation light.

  The measurement substrate according to the present invention is preferably used for measuring the carrier mobility of a semiconductor thin film in which carriers are hardly generated even when irradiated with excitation light. According to this invention, since the charge generation layer is formed between the substrate and the first electrode or on the first electrode, if a semiconductor thin film is formed on the measurement substrate and irradiated with excitation light, The carriers can be generated in the charge generation layer. Since the generated carriers move in the formed semiconductor thin film toward the second electrode, the carrier mobility in the in-plane direction of the semiconductor thin film can be measured, and the carrier mobility in the in-plane direction in a form close to the actual one. Can be measured easily and accurately.

  The substrate for measuring carrier mobility of a semiconductor thin film according to the first and second aspects of the present invention is characterized in that the first electrode and the second electrode are arranged to face each other.

  In the substrate for measuring carrier mobility of a semiconductor thin film according to the first and second aspects of the present invention, a plurality of the same unit structures in which the first electrode and the second electrode are arranged to face each other are formed on the substrate. It is characterized by being.

  According to the present invention, a plurality of the same unit structures for measuring the carrier mobility are formed. Therefore, if the excitation light is irradiated after forming the semiconductor thin film on the carrier mobility measurement substrate, the carriers are emitted at a plurality of locations. It can be generated to measure carrier mobility. As a result, the measured current value can be increased, so that data with higher reliability can be obtained.

  In order to solve the above problems, a carrier mobility measuring device for a semiconductor thin film according to the present invention includes a substrate for measuring carrier mobility of a semiconductor thin film according to the first or second aspect, and the carrier mobility measuring substrate. A light irradiation unit for irradiating the substrate with excitation light, a power supply unit connected to a first electrode of the carrier mobility measurement substrate, and a current measurement connected to a second electrode of the carrier mobility measurement substrate And at least a portion.

  In order to solve the above problems, a method for measuring carrier mobility of a semiconductor thin film according to the present invention includes a substrate for measuring carrier mobility of a semiconductor thin film according to the first or second aspect, and the carrier mobility measuring method. A light irradiation unit for irradiating the substrate with excitation light, a power supply unit connected to a first electrode of the carrier mobility measurement substrate, and a current measurement connected to a second electrode of the carrier mobility measurement substrate A method for measuring the carrier mobility of a semiconductor thin film using a carrier mobility measuring device comprising at least a unit, the step of forming a semiconductor thin film as a material to be measured on the carrier mobility measuring substrate, Irradiating the formed carrier mobility measurement substrate with excitation light from the light irradiation unit, and measuring a temporal change in the current obtained by the current measurement unit. To.

  As described above, according to the carrier mobility measurement substrate of the present invention, the carrier generation position of the semiconductor thin film formed on the measurement substrate and the movement distance of the generated carrier are determined. The carrier mobility in the in-plane direction can be accurately measured, and the carrier mobility in the in-plane direction in a form close to the actual can be measured easily and accurately. In addition, since a complicated optical system and an expensive substrate position control device are not required, a simple and low-cost measurement system can be configured.

  According to the carrier mobility measuring apparatus and measuring method of the present invention, since the carrier mobility measuring substrate of the present invention is used, it is possible to accurately measure the carrier mobility in the in-plane direction of the semiconductor thin film and Since a simple optical system and an expensive substrate position control device are unnecessary, a simple and low-cost measuring device can be configured.

  Hereinafter, a substrate for measuring carrier mobility, a measuring apparatus, and a measuring method of a semiconductor thin film of the present invention will be described with reference to the drawings. The following embodiments are given for the purpose of describing the present invention, and the technical scope of the present invention is not limited to the following description and drawings.

(Carrier mobility measurement substrate: first embodiment)
FIG. 1 is a diagram showing an example of a carrier mobility measurement substrate according to the present invention. In FIG. 1, (a) is a plan view of one embodiment, (b) is a sectional view thereof, (c) is a partial plan view of another embodiment, and (d) is a sectional view thereof. . The carrier mobility measurement substrate 10 according to this embodiment is preferably used for measuring the carrier mobility of a semiconductor thin film in which carriers are easily generated by excitation light, and is formed on the substrate 11 that transmits the excitation light. A light shielding layer 12 having an opening 13 in a part thereof, a first electrode 14 adjacent to or covering a part of the opening 13, and formed on the light shielding layer 12 from the first electrode 14. And a second electrode 15 provided at a predetermined interval.

  The substrate 11 is not particularly limited as long as it can transmit excitation light, and examples thereof include a glass substrate, a quartz substrate, and a resin substrate. Note that which substrate is selected is arbitrarily selected according to the wavelength of the excitation light. Although the thickness of the substrate 11 is not particularly limited, a thickness of about 0.7 to 1.1 mm is usually used from the viewpoints of excitation light transmittance, mechanical strength, and the like.

  The light shielding layer 12 is provided on the substrate 11 and is provided in a form having an opening 13 for irradiating a predetermined portion with excitation light irradiated from the substrate 11 side. As a constituent material of the light shielding layer 12, a light-shielding metal such as chromium and tantalum, a resin material for forming a light shielding layer such as acrylic or polyimide, a photoresist material that can be a material for forming the light shielding layer, an inorganic material, or the like. Can be mentioned. Which material is selected is arbitrarily selected depending on the ease of film formation, the wavelength of excitation light, and the like. The thickness of the light shielding layer 12 may be a thickness that can sufficiently shield the excitation light, and the thickness varies depending on various materials and cannot be generally described, but is usually about 0.5 to 2 μm.

  When the light shielding layer 12 is conductive, that is, when the light shielding layer 12 is formed of a metal such as chromium or tantalum, the light shielding layer 12 and the opening 13 formed in a part thereof are covered. In addition, an insulating layer 16 is preferably formed (see FIG. 2 described later, details will be described later). The carrier mobility measurement substrate 10 shown in FIG. 1 shows a configuration in the case where the light shielding layer 12 does not have conductivity.

  The opening 13 is a part capable of transmitting excitation light irradiated from the substrate 11 side when measuring carrier mobility, and is formed in a part of the light shielding layer 12. Although the planar view shape of the opening part 13 is not specifically limited, For example, the slit shape as shown in FIG. 1 etc. can be illustrated. The dimension of the opening 13 having a slit shape can be set to, for example, about 0.5 to 10 mm, preferably about 1 to 4 mm as the slit length A, and the slit width B can be set to about 0.5 to 5 μm, preferably 1 It can be set to about ˜2 μm. Among these, the slit length A is preferably equal to or less than the area of the excitation light irradiation region on the substrate 11 and is set so that the transient photocurrent component due to photoexcitation becomes large. On the other hand, the slit length B is set so that the generation positions of photoexcited carriers are limitedly arranged in an area that is at least 1/10 or less of the distance from the end of the first electrode 14 described later to the second electrode 15. .

  In the measurement substrate of the present invention, the opening 13 composed of the long slit length A and the short slit width B is formed and the end of the first electrode 14 covers the opening 13, so that the transport length is A slit having a finer width than the slit length A can be formed. As a result, the generation position of the carriers generated by photoexcitation is clearly defined, and the time at which the carriers reach the second electrode in the transient photocurrent can be observed with high reliability. Thus, the carrier mobility can be measured with high accuracy.

  For example, the opening 13 is formed by appropriately using the light shielding layer 12 formed on the entire surface by a photolithography process, dry etching using plasma, wet etching using a solution, or the like. Further, the opening 13 can be formed simultaneously with the formation of the light shielding layer 12. For example, a material for forming the light shielding layer 12 is selectively formed by a lift-off method, and the light shielding layer 12 and the opening 13 are formed. Can be formed simultaneously.

  The first electrode 14 is an electrode for applying a voltage in the measurement of carrier mobility, and is formed so as to cover a part of the opening 13 as shown in FIGS. For example, the 1st electrode 14 can be made into the shape which covered a part of slit-like opening part 13 over the longitudinal direction. Moreover, the 1st electrode 14 may be formed adjacent to the opening part 13 so that the opening part 13 may not be covered as shown in FIG.1 (c) (d). For example, the 1st electrode 14 can be made into the shape along the edge (edge of the side which is not the 2nd electrode side) of the slit-shaped opening part 13. As shown in FIG. As a material for forming the first electrode 14, a metal such as gold, aluminum, chromium, and tantalum, an alloy such as an aluminum-neodymium alloy, a conductive polymer such as polyaniline, polyethylenedioxythiophene, and polystyrene sulfonate are used. be able to. The first electrode 14 is a blocking contact between the semiconductor thin film as the material to be measured and the carrier type to be measured in order to avoid difficulty in analysis due to electric field redistribution due to charge injection of the dark current component. Is desirable.

  The second electrode 15 is an electrode for current measurement in the measurement of carrier mobility, and is formed on the light shielding layer 12 at a predetermined interval from the first electrode so as to be electrically independent of the first electrode 14. . As a material for forming the second electrode 15, the same material as that of the first electrode 14 can be used. The second electrode 15 is conveniently formed of the same material as the first electrode, but may be formed independently, and may be opaque or transparent.

  The first electrode 14 and the second electrode 15 are preferably arranged to face each other at a predetermined interval. Specifically, as shown in FIG. 1, the electrode edges on the opposite sides are parallel to each other. It is preferable to be formed. It is convenient to form both electrodes in the same process. For example, after a layer made of an electrode material is formed on the entire surface of the light shielding layer 12 (including the opening 13), a photolithography process or a dry process using plasma is performed. The electrodes 14 and 15 are formed by appropriately using etching, wet etching using a solution, or the like. The first electrode 14 and the second electrode 15 formed by such a process have the same thickness, and are usually formed with a thickness of about 0.1 to 0.3 μm.

  The distance between the first electrode 14 and the second electrode 15 is represented by the distance between the parallel electrode edges on the opposite side, and the distance is not particularly limited, but is formed to be in the range of 5 to 50 μm, for example. The It is desirable to set the distance in consideration of the characteristics of the semiconductor thin film to be used.

  For example, in a semiconductor thin film having a high carrier mobility, the drift time may be shortened and measurement may be difficult. In that case, it is preferable that the distance is set longer. In such a case, in the conventional TOF method, it is necessary to further increase the thickness of the semiconductor formed between the electrodes, and it is difficult to produce a measurement sample. However, in the present invention, if the distance between the electrodes is increased. Well, it is possible to measure the carrier mobility of various types of semiconductor thin films. On the other hand, as the distance between the electrodes is increased, the power supply voltage required for applying a specific electric field to the semiconductor thin film is increased, but an electric field strength of about 10 V / μm can be easily obtained practically. It is preferable to set the distance between the electrodes.

  The semiconductor thin film to be formed is preferably a semiconductor thin film made of an organic semiconductor material used for a light emitting element, a thin film transistor or the like. For example, as the organic semiconductor material, N, N′-bis (3-methylphenyl) is used. -N, N'-diphenylbenzidine (TPD), poly-N-vinylcarbazole (PVK), polythiophene, pentacene, oxadiazole (PBD), triazole derivative (TAZ), electron transport materials, hole transport materials, etc. Can be mentioned. Such a semiconductor thin film is formed by a vacuum deposition method, a spin coating method, or the like, although it varies depending on the material form. The thickness of the semiconductor thin film is not particularly limited, but may be a thickness that can generate a sufficient amount of carriers when irradiated with excitation light, for example, a thickness of about 10 to 500 nm.

(Carrier mobility measurement substrate: second embodiment)
2A and 2B are diagrams showing another example of the carrier mobility measurement substrate of the present invention, in which FIG. 2A is a plan view and FIG. 2B is a cross-sectional view thereof. Similarly to the above, the carrier mobility measuring substrate 20 according to this embodiment is also preferably used for measuring the carrier mobility of a semiconductor thin film that easily generates carriers when irradiated with excitation light, and is a substrate that transmits excitation light. 11, a light shielding layer 12 formed on the substrate 11 and having an opening 13 in a part thereof, a first electrode 14 adjacent to or covering a part of the opening 13, and the light shielding layer 12 And a second electrode 15 formed at a predetermined interval from the first electrode 14. In particular, this embodiment is characterized in that an insulating layer 16 that transmits excitation light is formed between the first electrode and the second electrode, and the light shielding layer 12 and the opening 13 provided in a part thereof. The details of the substrate 11, the light shielding layer 12, the opening 13, the first electrode 14, and the second electrode 15 have been described above, and are omitted here.

The insulating layer 16 is a layer preferably provided to prevent electrical contact between the light shielding layer 13 and the electrode when the light shielding layer 13 has conductivity, but the light shielding layer 13 does not have conductivity. May be provided. As shown in FIG. 2, the insulating layer 16 is formed so as to cover the light shielding layer 12 and the opening 13 formed in a part thereof. The insulating layer 16 is formed of a material that transmits excitation light, such as inorganic oxides such as SiO ₂ and Ta ₂ O ₅ , inorganic fluorides such as LiF and MgF ₂ , cycloolefin polymers, polycarbonate, and polymethyl methacrylate. Organic compounds such as can be selected and used depending on the wavelength of the excitation light.

  As described above, the carrier mobility measuring substrates 10 and 20 of the present invention having the configuration shown in FIGS. 1 and 2 are preferably used for measuring the carrier mobility of a semiconductor thin film in which carriers are easily generated when irradiated with excitation light. It is done. According to the present invention, since the first electrode 14 is formed so as to be adjacent to the opening 13 or to cover a part of the opening 13, a semiconductor thin film is formed on the carrier mobility measuring substrates 10 and 20. When the substrate is formed and irradiated with excitation light from the substrate side, carriers can be generated in the semiconductor thin film on the opening 13. Since the generated carriers move in the formed semiconductor thin film from the first electrode 14 toward the second electrode 15, the carrier mobility in the in-plane direction of the semiconductor thin film can be measured, and an element that actually uses the semiconductor thin film The carrier mobility in the in-plane direction can be measured easily and accurately.

(Carrier mobility measurement substrate: third and fourth embodiments)
3 and 4 are diagrams showing still another example of the carrier mobility measurement substrate of the present invention, wherein (a) is a plan view and (b) is a cross-sectional view thereof. The carrier mobility measurement substrates 30 and 40 according to this embodiment are preferably used for measuring the carrier mobility of a semiconductor thin film that hardly generates carriers even when irradiated with excitation light, and the substrate 11 that transmits excitation light. A first electrode 14 formed on the substrate 11, a charge generation layer 17 formed between or on the substrate 11 and the first electrode 14, and a first electrode formed on the substrate 11. And a second electrode 15 provided at a predetermined interval from one electrode 14, and the charge generation layer 17 is optically exposed to the side to be irradiated with excitation light. is there.

  The measurement substrates 30 and 40 of this embodiment are different from the measurement substrates 10 and 20 shown in FIGS. 1 and 2 in that the light shielding layer 12 and the opening 13 are not formed. That is, the measurement substrates 10 and 20 shown in FIG. 1 and FIG. 2 specify the carrier generation part 18 by the irradiation of excitation light by the light shielding layer 12 and the opening part 13, whereas FIG. 3 and FIG. The measurement substrates 30 and 40 shown in FIG. 1 specify the carrier generation part 18 by irradiation with excitation light by the charge generation layer 17 provided above or below the first electrode 14. The details of the substrate 11, the first electrode 14, and the second electrode 15 have been described above, and are omitted here.

  The charge generation layer 17 is a layer formed of a carrier generation material that only causes a detectable current change when irradiated with excitation light. The charge generation layer 17 may be formed between the substrate 11 and the first electrode 14 (see FIG. 3), or the first electrode 14 may be covered on the first electrode 14. (See FIG. 4). In more detail, it is sufficient that at least a part of the charge generation layer 17 exists between the first electrode 14 and the second electrode 15, and as shown in FIGS. The layer 17 is preferably provided on or below the first electrode 14.

  As a material for forming the charge generation layer 17, for example, phthalocyanine pigments, perylene pigments, and the like are used. After these materials are formed by a vacuum vapor deposition method using a shadow mask, a spin coating method, an electrodeposition method, or the like. After forming, the desired pattern can be formed by a photolithography process or the like.

  The carrier mobility measurement substrates 30 and 40 on which the charge generation layer 17 is formed are preferable for a semiconductor thin film in which it is difficult to observe a transient response of the photocurrent because the current generated by the irradiation of excitation light is weak. Used. Examples of the material for forming such a semiconductor thin film include general fluorescent materials. As the excitation light in such a case, if the charge generation layer 17 that efficiently generates charges at that wavelength is formed by using light having a wavelength that the semiconductor thin film itself as a reference does not absorb, charge transport can be carried out satisfactorily. The characteristics can be observed. Many carriers generated in the charge generation layer 17 move in the semiconductor thin film and are measured as a sufficiently large transient response signal. Thus, the measurement of the carrier mobility of a semiconductor thin film (charge transport layer) that does not absorb excitation light can be performed without providing a light shielding layer.

  As described above, the carrier mobility measuring substrates 30 and 40 of the present invention having the configuration shown in FIGS. 3 and 4 are preferably used for measuring the carrier mobility of a semiconductor thin film in which carriers are not easily generated when irradiated with excitation light. It is done. According to the present invention, since the charge generation layer 17 is formed between the substrate 11 and the first electrode 14 or on the first electrode 14, a semiconductor thin film is formed on the measurement substrate 30. Then, when the excitation light is irradiated, carriers can be generated in the charge generation layer 17. Since the generated carriers move in the formed semiconductor thin film toward the second electrode 15, the carrier mobility in the in-plane direction of the semiconductor thin film can be measured, and the carrier movement in the in-plane direction in a form close to the actual one. The degree can be measured easily and accurately.

(Carrier mobility measurement substrate: fifth embodiment)
FIG. 5 is an example of another embodiment of the substrate for measuring carrier mobility of the present invention, FIG. 5 (a) is a plan view of an opening formation pattern, and FIG. 5 (b) is a plan view of an electrode formation pattern. FIG. 5C is a plan view of a measurement substrate produced by combining comb-shaped electrodes. The carrier mobility measurement substrate 50 is characterized in that a plurality of identical unit structures in which the first electrode 14 and the second electrode 15 are arranged to face each other are formed on the substrate 11.

  In the example shown in FIG. 5, after the light shielding layer 12 is formed on the entire surface of the substrate 11, the opening 13 is formed using the opening forming pattern 51 shown in FIG. Next, after forming a layer made of an electrode material on the entire surface of the light shielding layer 12 and the opening 13 on the substrate, the layer made of a predetermined pattern is removed by the electrode formation pattern 52 shown in FIG. Comb-shaped first electrode 14 and second electrode 15 are formed. At this time, each comb-shaped tooth portion of the first electrode 14 is formed on each opening portion 13 formed at a predetermined interval. In the carrier mobility measurement substrate 50 of this embodiment, the opening 14 that transmits the excitation light is formed with a width C above and below the teeth of the first electrode 14 when viewed in plan in FIG. . Further, the first electrode 15 and the second electrode 15 are formed at a distance L in the vertical direction when the plan view of FIG.

  According to the measurement substrate 50 of this embodiment, since the same unit structure for measuring the carrier mobility is formed in plural, if the excitation light is irradiated after forming the semiconductor thin film on the carrier mobility measurement substrate 50, Carrier mobility can be measured by generating carriers at a plurality of locations. As a result, the measured current value can be increased, so that data with higher reliability can be obtained.

(Carrier generation part)
Here, the carrier generation unit 18 included in the carrier mobility measurement substrate according to each embodiment described above will be described.

  The carrier generation unit 18 is a part that generates carriers when irradiated with excitation light. Specifically, in the measurement substrates 10 and 20 shown in FIGS. 1 and 2, the portion where the semiconductor thin film is irradiated with excitation light and the portion sandwiched between the first electrode 14 and the second electrode 15 generates carriers. It becomes part 18. When the first electrode 14 does not transmit excitation light, the size of the opening 13 other than the portion covered by the first electrode 14 becomes the size of the carrier generating portion 18.

  Further, in the measurement substrates 30 and 40 shown in FIGS. 3 and 4, the portion where the charge generation layer 17 is irradiated with excitation light and the portion sandwiched between the first electrode 14 and the second electrode 15 is the carrier generation portion. 18

(Production method of carrier mobility measurement substrate)
Next, a method for manufacturing each carrier mobility measurement substrate of FIGS. 1 to 4 will be described.

  As an example of a method for manufacturing the carrier mobility measurement substrate 10 shown in FIG. 1, first, a substrate 11 is prepared, and a light shielding layer 12 is formed on the entire surface of the substrate 11 by coating or the like, and then the opening 3 is formed by photolithography. It is formed by a process or the like. Thereafter, a layer (for example, an aluminum layer) made of the material of the first electrode 14 and the second electrode 15 is formed, and the first electrode 14 and the second electrode 15 are formed by a photolithography process or the like. In this way, the carrier mobility measuring substrate 10 shown in FIG. 1 can be manufactured.

  As an example of a method for producing the carrier mobility measuring substrate 20 shown in FIG. 2, first, the substrate 11 is prepared, and the light shielding layer 12 is formed on the entire surface of the substrate 11 by coating or the like, and then the opening 3 is formed by photolithography. It is formed by a process or the like. Next, after forming the insulating layer 16 so as to cover the light shielding layer 12 and the opening 13, a layer (for example, an aluminum layer) made of the material of the first electrode 14 and the second electrode 15 is formed, and the first layer is formed by a photolithography process or the like. A first electrode 14 and a second electrode 15 are formed. In this way, the carrier mobility measuring substrate 20 shown in FIG. 2 can be produced.

  As an example of a method for manufacturing the carrier mobility measurement substrate 30 shown in FIG. 3, first, the substrate 11 is prepared, and the charge generation layer 17 is formed in a desired pattern on the substrate 11 by a photolithography process or the like. Next, a layer made of the material of the first electrode 14 and the second electrode 15 (for example, an aluminum layer) is formed so as to cover the entire surface of the substrate including the charge generation layer 17, and the first electrode 14 is formed by the photolithography process or the like. A second electrode 15 is formed on the substrate 11 and formed on the charge generation layer 17. In this way, the carrier mobility measurement substrate 30 shown in FIG. 3 can be produced.

  As an example of a method for producing the carrier mobility measurement substrate 40 shown in FIG. 4, first, the substrate 11 is prepared, and a layer (for example, an aluminum layer) made of the materials of the first electrode 14 and the second electrode 15 is prepared on the substrate 11. ) And the first electrode 14 and the second electrode 15 are formed by a photolithography process or the like. Next, after a resist film is formed on the entire surface of the substrate including both electrodes, the resist film around the first electrode 14 where the charge generation layer 17 is to be formed is removed by exposure / development and the like, and the charge generation layer is formed at the removed portion. 17 is filled by spin coating. Thereafter, all the remaining resist film is removed. In this way, the carrier mobility measurement substrate 40 shown in FIG. 4 can be produced.

(Carrier mobility measuring device)
FIG. 6 is a diagram showing an example of the carrier mobility measuring apparatus of the present invention. The carrier mobility measuring device 60 of the present invention includes a carrier mobility measuring substrate 61 according to the present invention illustrated in FIGS. 1 to 4 and a light irradiation unit 62 that irradiates the carrier mobility measuring substrate 61 with excitation light 66. And a power supply unit 63 connected to the first electrode 14 of the carrier mobility measurement substrate 61 and a current measurement unit 64 connected to the second electrode 15 of the carrier mobility measurement substrate 61. There is a special feature. Since the carrier mobility measurement substrates 10, 20, 30, and 40 according to the present invention illustrated in FIGS. 1 to 4 have already been described, they are omitted here. FIG. 6 is a diagram showing an example using the carrier mobility measurement substrate 20 shown in FIG.

  The light irradiation unit 62 is a device for irradiating the measurement substrate 61 on which the semiconductor thin film 65 is formed with pulsed excitation light 66. As the light source, for example, a nitrogen gas laser, an Nd: YAG laser, or a xenon flash is used. A lamp or the like is used. The pulsed excitation light 66 has energy larger than the band gap of the semiconductor material that is the material to be measured, the on-time duration is 0.1 ns to 100 ns, and the off-time is negligibly short compared to the on-time. Things are used.

  The power supply unit 63 is a device for applying a DC voltage to the first electrode 14.

  The current measuring unit 64 includes a load resistor 67 and a digital oscilloscope 68 and is connected to the second electrode 15. In the current measuring unit 64, the digital oscilloscope 68 and the second electrode 15 may be connected via a preamplifier (not shown) in order to further increase the measurement accuracy. The pulse of the excitation light 66 and the digital oscilloscope 68 are synchronized using, for example, a function generator (not shown). A change in current flowing between the first electrode 14 and the second electrode 15 is detected by the digital oscilloscope 68 as a voltage change of a voltage drop across the load resistor 67 connected to the second electrode 15.

(Carrier mobility measurement method)
FIG. 7 is a diagram showing an example of the carrier mobility measuring method of the present invention. The carrier mobility measurement method of the present invention includes a semiconductor thin film carrier mobility measurement substrate 61 according to the present invention illustrated in FIGS. 1 to 4 and a light irradiation unit that irradiates the carrier mobility measurement substrate 61 with excitation light. 62, a power supply unit 63 connected to the first electrode 14 included in the carrier mobility measurement substrate 61, and a current measurement unit 64 connected to the second electrode 15 included in the carrier mobility measurement substrate 61. This is a measurement method using a carrier mobility measuring device, a step of forming a semiconductor thin film 65 as a material to be measured on a carrier mobility measuring substrate 61, and a carrier mobility measuring substrate 61 on which the semiconductor thin film 65 is formed. And the step of irradiating the excitation light 66 from the light irradiation unit 62 and the step of measuring the temporal change of the current obtained by the current measurement unit 64. FIG. 7 is a diagram showing an example using the carrier mobility measurement substrate 20 shown in FIG.

  First, a semiconductor thin film 65 that is a material to be measured is formed on a carrier mobility measurement substrate 61. The semiconductor thin film 65 can be formed by various means, for example, can be formed by coating, vacuum deposition, or the like. Since the material for forming the semiconductor thin film has been described in the description of the semiconductor thin film, the description thereof will be omitted.

  Next, the excitation light 66 is irradiated from the light irradiation unit 62 to the carrier mobility measurement substrate 61 on which the semiconductor thin film 65 is formed. The irradiation region of the excitation light 66 only needs to include the carrier generation unit 18. That is, in FIG. 1 and FIG. 2, at least the formation region of the opening 13 may be included, and in FIG. 3 and FIG. 4, the formation region of the charge generation layer 17 may be included.

  In the measurement method using the measurement substrates 10 and 20 shown in FIG. 1 and FIG. 2 among the measurement substrates of the present invention, the carrier generator 18 is specified by the light shielding layer 12 and the opening 13, so that the excitation light It is necessary to irradiate 66 from the substrate 11 side. On the other hand, in the measurement method using the measurement substrates 30 and 40 shown in FIGS. 3 and 4, the carrier generation unit 18 is specified by the charge generation layer 17 provided above or below the first electrode 14. The light 66 may be irradiated from the substrate 11 side or may be irradiated from the upper semiconductor thin film side.

  The semiconductor thin film 66 irradiated with the excitation light 66 absorbs the excitation light 66 and generates carriers. In the semiconductor thin film 65, an electric field is generated by a DC voltage applied to the first electrode 14, and the generated carriers drift to the second electrode 15 side by the electric field. Although the carriers that have reached the second electrode 15 disappear, the current measurement section 64 measures the temporal change of the current flowing through the semiconductor thin film during this time.

  FIG. 8 is a graph showing a typical example of a current change flowing through the second electrode 15 after the excitation light is turned off. The current change is roughly classified into non-dispersion conduction and dispersion conduction. it can. FIG. 8A is a graph showing non-dispersed conduction, FIG. 8B is a graph showing dispersed conduction, and FIG. 8C is a graph showing dispersed conduction when represented by a logarithmic axis. It is.

In non-distributed conduction shown in FIG. 8 (a), it may represent the time at which current starts to decay as transient time t _T. However, since the generated carriers generally have a Gaussian spread in the semiconductor thin film, the current conduction type becomes a graph of distributed conduction as shown in FIG. A clear transition time t _T does not appear. In the case of such non-distributed conduction, as shown in FIG. 8 (c), the graph both axes logarithmic axis, it is possible to obtain the inclination is different bending point of the graph as a transient time t _T.

The transient time t _T obtained as described above represents the time (hereinafter referred to as the drift time) required for the carriers generated in the carrier generation unit 18 to drift toward the second electrode 15. Accordingly, when the distance between the carrier generation unit 18 and the second electrode 15 is L and the voltage applied between the electrodes is V, the mobility μ (cm ² / Vs) is μ = L ² / (V · t _T ) And the mobility μ can be calculated.

  Next, a method for measuring the temperature dependence of the carrier mobility of the semiconductor thin film will be described. In order to obtain detailed information on the charge transport characteristics of the semiconductor thin film to be measured, it is effective to measure the temperature dependence of the charge transport ability.

  As a method for measuring the temperature dependence of carrier mobility, it is preferable to use a method in which a protective layer is provided on a semiconductor thin film to be measured. This protective layer needs to be insulative.

  By forming the protective layer on the semiconductor thin film, the protective layer can be placed on the temperature control stage with the protective layer forming surface facing down (that is, with the substrate 11 surface facing up). By irradiating excitation light from above, the carrier mobility of the temperature-controlled semiconductor thin film can be measured. As a result, the temperature dependence of carrier mobility can be measured. Even when the protective layer is not formed, the carrier mobility of the temperature-adjusted semiconductor thin film can be measured by placing the substrate 11 face down on the temperature adjustment stage. The temperature adjustment stage in this case is desirably provided with a through hole, and the temperature dependence of the carrier mobility can be measured by irradiating excitation light from below the temperature adjustment stage.

  As described above, according to the carrier mobility measuring method of the present invention, the carrier mobility in the in-plane direction of the semiconductor thin film can be measured. Note that the mobility of electrons or the mobility of holes can be measured based on the polarity of a DC power supply applied from the power supply unit.

A glass substrate having a thickness of 0.7 mm was used as the substrate 11, and a light shielding layer 12 having an opening 13 having a slit length of 4 mm and a slit width of 1 μm was formed on the substrate 11. The light shielding layer 12 is a metal chromium layer, and after forming by vacuum deposition, the opening 13 was formed by a photolithography process. Next, an SiO ₂ layer having a thickness of 0.5 μm was formed as an insulating layer 16 on the entire surface of the substrate including the light shielding layer 12 and the opening 13. Next, aluminum having a thickness of 0.3 μm was formed thereon by vacuum deposition, and then the first electrode 14 and the second electrode 15 were formed by a photolithography process.

  The opening formation pattern and the electrode formation pattern are the same as those shown in FIG. 5, and 5000 slit-shaped carrier generation portions 18 are formed in a pattern formation region of about 4 mm × 4 mm. The drift distance L between the carrier generation unit 18 and the second electrode 15 was 9 μm.

  As the measurement sample, N, N′-bis (3-methylphenyl) -N, N′-diphenylbenzidine (TPD) formed into a 200 nm film by vacuum deposition was used. Thus, a sample for measurement was produced.

In the carrier mobility measurement, a nitrogen gas laser having a wavelength of 337 nm and a width of 3 ns is irradiated as pulsed excitation light from the substrate 11 side with an electric field of 2.2 × 10 ⁵ V / cm applied between both electrodes. I went there.

FIG. 9 is a transient photocurrent waveform obtained by measurement. From FIG. 9, typical non-dispersive conduction was observed, and the transition time t _T was 4.9 μs from the inflection point. The hole mobility calculated from this was 8.3 × 10 ⁻⁴ cm ² / Vs. Similarly, the carrier mobility was measured by changing the electric field strength in various ways. FIG. 10 is a graph showing the relationship between various electric field strengths and carrier mobility. FIG. 10 shows the obtained results together with the results obtained by the conventional method (TOF method), which are in good agreement.

It is a figure which shows the example of the board | substrate for carrier mobility measurement of this invention. It is a figure which shows the other example of the board | substrate for carrier mobility measurement of this invention. It is a figure which shows the further another example of the board | substrate for carrier mobility measurement of this invention. It is a figure which shows the further another example of the board | substrate for carrier mobility measurement of this invention. It is an example of the other form of the board | substrate for carrier mobility measurement of this invention. It is a figure which shows an example of the carrier mobility measuring apparatus of this invention. It is a figure which shows an example of the carrier mobility measuring method of this invention. It is a graph which shows the typical example of the current change which flowed into the 2nd electrode, after turning off excitation light. 2 is a transient photocurrent waveform obtained by measurement in Example 1. FIG. It is a graph which shows the relationship between various electric field strengths and carrier mobility. It is the schematic sectional drawing which showed the principle of TOF method. It is the schematic sectional drawing which showed the conventional method of observing the transient photocurrent in a film surface. It is the schematic sectional drawing which showed the principle of the conventional deformation | transformation TOF method.

Explanation of symbols

10, 20, 30, 40, 50, 61 Carrier mobility measurement substrate 11 Substrate 12 Light shielding layer 13 Opening portion 14 First electrode 15 Second electrode 16 Insulating layer 17 Charge generation layer 18 Carrier generation portion 51 Opening formation pattern 52 Electrode formation pattern 60 Carrier mobility measuring device 62 Light irradiation unit 63 Power supply unit 64 Current measurement unit 65 Semiconductor thin film 66 Excitation light 67 Load resistance 68 Digital oscilloscope A Long slit length B Short slit width C Parallel to the electrode edge of the opposing electrode Length in the correct direction D Length in the direction perpendicular to the electrode edge of the opposing electrode

Claims (7)

  A substrate that transmits excitation light; a light shielding layer that is formed on the substrate and has an opening in a part thereof; a first electrode that is adjacent to or covers a part of the opening; and the light shielding layer A substrate for measuring carrier mobility of a semiconductor thin film, comprising: a second electrode formed thereon and provided at a predetermined interval from the first electrode.   2. The semiconductor according to claim 1, wherein an insulating layer that transmits excitation light is formed between the first electrode and the second electrode, and the light shielding layer and an opening provided in a part thereof. Substrate for measuring carrier mobility of thin film.   A substrate that transmits excitation light; a first electrode formed on the substrate; a charge generation layer formed between or on the substrate and the first electrode; and on the substrate And a second electrode provided at a predetermined interval from the first electrode, and the charge generation layer is optically exposed to the side to be irradiated with the excitation light. A substrate for measuring carrier mobility of a semiconductor thin film.   The substrate for measuring carrier mobility of a semiconductor thin film according to any one of claims 1 to 3, wherein the first electrode and the second electrode are disposed to face each other.   4. The semiconductor thin film according to claim 1, wherein a plurality of the same unit structures in which the first electrode and the second electrode are arranged to face each other are formed on the substrate. Carrier mobility measurement board.   A substrate for measuring carrier mobility of a semiconductor thin film according to any one of claims 1 to 5, a light irradiation unit for irradiating the carrier mobility measuring substrate with excitation light, and the substrate for measuring carrier mobility. An apparatus for measuring carrier mobility of a semiconductor thin film, comprising at least a power supply unit connected to the first electrode and a current measurement unit connected to a second electrode of the carrier mobility measurement substrate. A substrate for measuring carrier mobility of a semiconductor thin film according to any one of claims 1 to 5, a light irradiation unit for irradiating the carrier mobility measuring substrate with excitation light, and the substrate for measuring carrier mobility. Carrier mobility measurement of a semiconductor thin film using a carrier mobility measuring apparatus comprising at least a power source connected to the first electrode and a current measuring unit connected to the second electrode of the carrier mobility measuring substrate A method,
Forming a semiconductor thin film as a material to be measured on the carrier mobility measuring substrate; irradiating the carrier mobility measuring substrate on which the semiconductor thin film is formed with excitation light from the light irradiation unit; and the current A method for measuring carrier mobility of a semiconductor thin film, comprising: measuring a temporal change in current obtained by a measurement unit.

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