Electrical resistance measuring device, Hall effect measuring device, and semiconductor characteristic measuring device

Abstract

The present invention provides an electrical resistance measuring device capable of shortening the sample preparation process, which has required current formation for the measurement sample by patterning electrodes and alloying by annealing. [Solution] The electrical resistance measuring device is characterized by comprising a DC power supply connected in series with a current limiting resistor to a first terminal on the primary side of a transformer, a switch element connected in series with a second current limiting element to a second terminal on the primary side of the transformer, a surge arrester connected in parallel with current shunt resistors connected to both ends of the secondary side of the transformer, and two metal needles in contact with the thin film to be measured, one connected to one terminal on the secondary side of the transformer and the other connected to the other terminal on the secondary side of the transformer.

Description

Technical Field

[0001] The present invention relates to an apparatus for measuring the sheet resistance of a conductive substrate such as a semiconductor substrate or a conductive layer formed on the surface, the mobility of carriers such as electrons and holes in the conductive layer, the carrier concentration in the conductive layer, and the like.

Background Art

[0002] For GaAs semiconductors and GaN semiconductors having AlGaN in the surface layer, devices are formed on substrates on which an electrically conductive layer is formed by crystal growth using the MOCVD method or the like or ion implantation. Before forming the device, it is necessary to measure the sheet resistance of the electrically conductive layer and the carrier mobility and the like.

[0003] However, when a metal needle is brought into direct contact with the semiconductor surface with respect to a GaN semiconductor or a SiC semiconductor having a large bandgap, a Schottky junction is formed between the metal needle and the semiconductor. Since one of the metal needles has the voltage blocking property of the Schottky junction, current cannot flow. For this reason, a metal having a small work function must be patterned by lithography and alloyed at a high temperature to form an electrically conductive electrical contact.

[0004] This is called an ohmic formation process and requires a great deal of time for preparing the measurement sample. For this reason, it is required to shorten the time required for creating the current-carrying electrodes necessary for measuring electrical characteristics such as sheet resistance measurement, Hall measurement, and capacitance-voltage (CV) measurement, which are common for measuring electrical characteristics of semiconductors and the like.

[0005] The four-terminal probe method is a simple sheet resistance measurement method. This measures the sheet resistance by bringing four metal needles arranged at equal intervals linearly into contact with the semiconductor, connecting a current source to the outer two metal needles, and measuring the voltage generated between the inner two metal needles. However, in semiconductors such as GaN and SiC having a large bandgap, the metal needle and the semiconductor become a Schottky diode and current cannot flow, so the conventional four-terminal probe method cannot be applied.

[0006] As another method, a device for measuring sheet resistance has been put into practical use by measuring the eddy current generated in an electrically conductive layer by applying an alternating magnetic field as impedance. However, when a conductive substrate having a plurality of layers is used as the measurement target, the synthesized sheet resistance is measured, and accurate measurement cannot be performed. In addition, commercially available sheet resistance measuring instruments using non-contact eddy currents have difficulty in measurement because the eddy current becomes small in a high-resistance substrate.

[0007] Also, even when measuring the Hall effect to measure carrier mobility, it is necessary to form an electrically conductive electrical contact. Conventionally, it has been common to partially adhere In solder to the surface of a sample cut out into small pieces and heat it to form electrical conduction. This process of sample preparation takes time.

[0008] To measure carrier concentration, CV measurement (capacitance-voltage measurement) is often performed. This is to measure the capacitance value by applying a reverse voltage to a Schottky diode with a determined area.

[0009] Naturally, an electrically conductive electrical contact is required on the opposite side of the Schottky junction. For this reason, it is necessary to form an electrode pattern different from the Schottky electrode on the semiconductor surface and create electrical conduction and contact by heat treatment, which takes time for sample preparation.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0012] When a metal needle in contact with the semiconductor surface is brought into contact with a wide-bandgap semiconductor such as a GaN semiconductor, two Schottky junctions connected in reverse are formed between the metal needle and the semiconductor. Since the breakdown voltage of the Schottky diode of the wide-bandgap semiconductor sometimes exceeds 1000V, it cannot be energized.

[0013] As a result, it is difficult to directly measure the electrical characteristics of wide-bandgap semiconductors with a metal needle. Therefore, a method has been proposed (Patent Document 2) to break the Schottky junction by applying a high voltage to the metal needle using a piezoelectric element. However, since it is a method of mechanically striking, there is a problem of poor reproducibility.

[0014] There are various circuits that generate a high voltage electrically, but the applied current tends to become excessive. Even when the Schottky junction can be broken, there are problems such as the tip of the metal needle melting due to heat generation and the measurement sample being denatured. When applying a high voltage, a method is required to prevent the melting of the metal needle by reducing the current flowing through the metal needle and not causing denaturation of the measurement sample.

Means for Solving the Problems

[0015] The high-voltage generation circuit according to the present invention includes a DC power supply connected in series with a first current limiting element to a first terminal on the primary side of a transformer, a switch element connected in series with a second current limiting element to a second terminal on the primary side of the transformer, and a surge arrester connected in parallel with a current shunting element connected across both ends of the secondary side of the transformer. One terminal on the secondary side of the transformer is connected to one of two metal needles that contact the thin film to be measured, and the other terminal on the secondary side of the transformer is connected to the other of the two metal needles.

[0016] Further, in the high-voltage generation circuit according to the present invention, it is preferable to provide an intermediate tap on the primary side of the transformer, the first terminal is located at the intermediate tap, and include another switch element connected in series with a third current limiting element to a third terminal on the primary side of the transformer.

[0017] Further, in the high-voltage generation circuit according to the present invention, it is preferable to include an inductor coil having two terminals for detecting a voltage waveform and provided so as to share a core with the transformer.

[0018] The four-terminal sheet resistance measuring device according to the present invention includes the above-described high-voltage generation circuit, four metal needles that are provided at equal intervals and arranged in a row and contact the thin film to be measured, a current source connected to two metal needles located outside the four metal needles, a voltage measurement unit connected to two metal needles located inside the four metal needles to measure voltage, a first switch unit that switches to connect the high-voltage generation circuit and two of the four metal needles, and a second switch unit that switches to connect the current source and the voltage measurement unit to two of the four metal needles, respectively. It is characterized by comprising these components.

[0019] The Hall effect measuring device according to the present invention includes the above-described high-voltage generation circuit, four metal needles that are arranged at the vertices of a quadrilateral and contact the thin film to be measured, a current source connected to two of the four metal needles that are located diagonally, a measurement unit that obtains the Hall electromotive force between the remaining two of the four metal needles that are located diagonally, a first switch unit that switches to connect the high-voltage generation circuit and two of the four metal needles, and a second switch unit that switches to connect the current source and the voltage measurement unit to two of the four metal needles, respectively. It is characterized by comprising these components.

[0020] The Hall effect measuring device according to the present invention includes the above high-voltage generation circuit, four metal needle arrays arranged linearly and at equal intervals, another four metal needle arrays arranged perpendicular to the four metal needle arrays, a current source connected to the outermost two of the four metal needle arrays, a voltage Vs measuring unit for measuring the voltage Vs of the two innermost metal needles of the four metal needle arrays, a voltage VH measuring unit for applying a magnetic field perpendicular to the measured thin film and measuring the voltage VH of the two innermost metal needles of the other four metal needle arrays, a first switch unit for switching to connect the high-voltage generation circuit and two of the four metal needles and two of the other four metal needles, the current source and the voltage measuring unit, and a second switch unit for switching to connect two of the four metal needles and two of the other four metal needles, and is characterized in that a regular quadrilateral is formed by using the two innermost metal needles of the four metal needle arrays and the two innermost metal needles of the other four metal needle arrays, and electrical contacts are formed on all eight metal needles of the four metal needle arrays and the other four metal needle arrays.

[0021] The semiconductor characteristic measuring device according to the present invention includes the above high-voltage generation circuit, a Schottky junction region formed on the measured thin film, four metal needles, one of which contacts the Schottky junction region and the remaining three contact the measured thin film, and a first switch unit for switching to connect the high-voltage generation circuit and two of the four metal needles, and is characterized in that the capacitance-voltage characteristics are measured between the one metal needle contacting the Schottky junction region and the remaining three metal needles.

[0022] Further, in the semiconductor characteristic measuring device according to the present invention, it is preferable that the Schottky junction region is formed using an ionic liquid.

[0023] Further, in the four-terminal sheet resistance measuring device according to the present invention, when forming electrical contacts with the four metal needles, it is preferable that the electrical measurement circuit is grounded during high-voltage generation.

[0024] A surge arrester is a device that protects equipment by generating a discharge between electrode gaps provided inside the element when a high voltage is applied. By enclosing gas in a sealed package and designing the distance between the gaps, it has the feature of being able to control the discharge start voltage.

[0025] Once a discharge occurs, a large current can flow, but there is a problem that a high voltage is applied until the discharge is started. The present invention uses the property that a high voltage is intentionally held for only a short time in response to the drawback of a surge arrester that cannot handle high-speed phenomena. With this configuration, even when a high voltage destroys a Schottky junction, since a large current does not flow through the material to be measured by the surge arrester, there is no worry of damaging the electrode needle.

[0026] Also, when two metal needles are brought into contact with the object to be measured, each becomes a Schottky junction, and a configuration is formed in which two diodes are connected in reverse. For this reason, the metal needles are in the forward and reverse directions respectively, and when a high voltage is applied, the reverse Schottky junction side is destroyed and short-circuited.

[0027] Since the Schottky junctions of the two metal needles cannot be destroyed and short-circuited simultaneously, the polarity must be changed and a high voltage must be applied. In the present invention, an intermediate tap is provided on the primary side of the transformer, and the voltage polarity applied to the electrode needle is switched with a simple configuration in which a DC power supply is connected to the intermediate tap. With this configuration, a stable energization contact can be realized.

[0028] Also, even when a single high-voltage pulse is applied, depending on the material to be measured, an energization contact may not be formed. In that case, it is necessary to repeatedly apply a high-voltage pulse, but there is no method for determining whether the energization contact has been completed. In the present invention, by using the phenomenon that the resistance on the secondary side decreases in a state where the energization state is completed, a third coil is provided in the transformer to detect the amount of decrease in the back electromotive force, and it is possible to determine whether the energization contact has been completed.

Effects of the Invention

[0029] According to the present invention, it is possible to break the Schottky junction without melting the tip of the metal needle due to heat generation.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0031] Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In the following, the same elements in all the drawings are denoted by the same reference numerals, and redundant descriptions are omitted. Also, in the description in the text, the reference numerals described above will be used as necessary.

[0032] The electrical resistance measurement device 1 according to an embodiment of the present invention will be described with reference to FIG. 1. One end of the primary coil L1 of the transformer is connected to a 12V DC power supply (DC1) via resistors R1 and R2 that limit the current, and the other end of the primary coil L1 is grounded via a current limiting element (for example, diode D1) and a switch (for example, power MOS) M1.

[0033] In the electrical resistance measurement device 1, as shown in FIG. 1, the circuit including the resistor R1, the resistor R2, the DC power supply, the capacitor C1, the switch M1, the diode D1, the transformer, the resistor 4, and the surge arrester SA1 is called a high voltage generation circuit 1a (HVG).

[0034] This diode D1 may be other elements as long as it limits the current, for example, a resistor may be used. A capacitor C1 is grounded between the current limiting resistors R1 and R2, forming a low-pass filter that suppresses noise due to surges. When the switch M1 is turned on, current gradually flows through the primary coil L1, and when the switch M1 is turned off, a high voltage is generated in the primary coil L1.

[0035] As a result, a high voltage is also generated in the secondary coil L2 via the transformer, and by connecting it to the metal pins 13 and 14, a high voltage is applied to the contact portion 17 with the semiconductor 18. A resistor R4 and a surge arrester SA1 are connected in parallel on the secondary side. The surge arrester SA1 holds the generated high voltage for several microseconds to several milliseconds and then absorbs the current by discharging (Non-Patent Document 8).

[0036] The resistor R4 functions to shunt the current generated by the back electromotive force. However, in a state where no current flows through the metal pins 13 and 14 (open), if the resistance value is large, a high voltage is generated, and if the resistance value is small, the generated voltage becomes small. That is, the generated voltage can be controlled by adjusting the resistor R4. The Schottky junction is broken during the period when this high voltage is held.

[0037] Various products of surge arresters SA1 have been put into practical use, and in the present invention, such commercially available products can be selected.

[0038] Another electrical resistance measuring device 2 according to an embodiment of the present invention will be described with reference to FIG. 2. Since the voltage polarity of the high voltage generation circuit 1a is unidirectional, among the Schottky junctions formed by the two metal pins 13 and 14, the reverse Schottky junction is broken, but the other one may be in the forward direction and thus may not be broken.

[0039] To switch the polarity of this high voltage, a DC power supply (DC1) is connected to the center tap of the primary coil L1, and high voltage generation circuits 2a and 2b are prepared with two systems of current switching circuits (HVG) at both ends of the primary coil L1, so that the polarity of the high voltage output on the secondary side can be switched. By operating the two systems of current switching circuits alternately, it becomes possible to apply high voltages of both polarities.

[0040] Another electrical resistance measuring device 3 according to an embodiment of the present invention will be described with reference to FIG. 3. When no electrical contact is formed on the secondary side, it is in a high impedance state, so the back electromotive force on the secondary side increases. However, in the state where the energized state is achieved, the resistance on the secondary side decreases, so the induced voltage decreases.

[0041] This back electromotive force on the secondary side can be indirectly detected by a third coil L3 provided on the same transformer core. By performing current switching multiple times, the amount of decrease in the back electromotive force can be measured, and it can be determined whether the energized contact is completed. Hereinafter, a bipolar high voltage application circuit, which is a high voltage generation circuit 3a equipped with a detection coil, is referred to as DHVG.

[0042] The electrical resistance measuring device 3 shortens the sample preparation process that has hitherto required energization formation such as electrode patterning and alloying by annealing on the measurement sample. Electrical contacts can be formed on the wafer by DHVG, and the electrical characteristics can be measured using the metal needles 13, 14.

[0043] By DHVG, four-terminal sheet resistance measurement and Hall measurement of various wide bandgap semiconductors can be easily performed. Also, in Hall measurement where it is difficult to perform accurate measurement depending on the sample shape, by forming minute electrical contacts using eight metal needles, the mobility of the semiconductor layer can be measured in a short sample preparation time without fragmenting the measurement sample.

[0044] Also, when performing capacitance-voltage (CV) measurement in a Schottky electrode or MIS structure, if an electrically conductive contact is formed using the electrical resistance measuring device 3 according to the embodiment of the present invention, the measurement can be performed in a short sample preparation time.

[0045] Further, instead of the method of forming a Schottky junction using a conventional mercury contact (Non-Patent Document 9), by using a Schottky junction in contact with an ionic liquid (Non-Patent Document 10), CV measurement can be safely performed without patterning the Schottky electrode. In the laboratory, it is necessary to measure the carrier concentration immediately after crystal growth. However, the carrier concentration can be easily measured by measuring the capacitance-voltage (CV) characteristics of the electric resistance measuring device 3 according to the embodiment of the present invention.

[0046] Patent Document 2 proposes a method of forming an electrically conductive contact by generating a high-voltage pulse using a piezoelectric body. However, in the high-voltage application circuit 3a of the electric resistance measuring device 3 according to the embodiment of the present invention, a bipolar voltage can be generated, so that polarity switching is unnecessary. Further, by using a surge arrester, the energization current can be made extremely small. Therefore, the electrode needle is not melted, and the damage to the measurement sample can be reduced. In particular, when a metal needle is brought into contact with a wide-bandgap semiconductor such as GaN or SiC, an electrically conductive contact can be easily obtained by easily breaking through the Schottky junction having an extremely high breakdown voltage formed.

[0047] As a result of the experiment, it was found that the present invention can easily measure the sheet resistance and the mobility of the two-dimensional electron gas layer at the hetero-junction interface of the AlGaN / GaN layer. Even for the p-type GaN semiconductor layer, although the Schottky diode polarity becomes back-to-back connection, electrical contact can be made in the same manner.

Example

[0048] A four-terminal sheet resistance measuring device 4 of the first form using the high-voltage application circuit 3a of the electric resistance measuring device 3 according to the embodiment of the present invention will be described with reference to FIG. 4. In this embodiment, the high voltage generated by the bipolar high-voltage application circuit (high-voltage application circuit 3a) is connected to the 2×4 matrix switch 8. The matrix switch 8 is a relay array installed at the contact points (intersections) of the vertical wiring and the horizontal wiring, and has a function of short-circuiting and opening at the intersections.

[0049] As a result, the output destination of the high voltage generated in the bipolar high voltage circuit (high voltage application circuit 3a: DHVG) can be selectively distributed to any of the terminals from A1 to A4. A relay with an insulation breakdown voltage of 1000 V or more was used for the matrix switch 8.

[0050] The single-pole double-throw switch array 9 distributes the directions of the high voltage side and the electrical measurement side with the metal pins 13, 14, 15, and 16 as the poles. A C-contact relay with an insulation breakdown voltage of 1000 V or more was used for the single-pole double-throw switch. The electrical measurement side is connected via a 4×4 matrix switch 10.

[0051] When the metal pins 13 to 16 are brought into contact with the epitaxial growth surface 17 on which an AlGaN / GaN heterojunction is formed on the Si(111) substrate, Schottky diodes represented by D1, D2, D3, and D4 are formed between the metal pins 13 to 16 and the epitaxial growth layer 17. Electrical contact can be realized for all the metal pins 13 to 16 by the above-described procedure.

[0052] For example, when S11 and S24 of the 2×4 matrix switch 8 are short-circuited and the single-pole double-throw switch array 9 is connected to the high voltage generation side in its entirety and the DHVG is operated, a high voltage can be applied to the metal pins 13 and 16, and electrical contact is formed between the metal pins 13 and 16. Sequentially, by selecting the matrix switch 8, electrical contact can be formed for all combinations of the metal pins.

[0053] After the energization formation of each of the metal pins 13 to 16 is completed, the metal pins 13 to 16 are connected to the electrical measurement side by the single-pole double-throw switch array 9. The current source 11 and the voltmeter 12 are connected to arbitrary connection points B1 to B4 by the 4×4 matrix switch 10. For example, by short-circuiting W11 and W42, the current source 11 is connected to the metal pins 13 and 16, and by short-circuiting W23 and W34, the voltmeter 12 is connected to the metal pins 14 and 15.

[0054] From this measured voltage and the set current value, the sheet resistance can be measured. Regarding the sheet resistance measurement, as described in (Non-Patent Documents 2 and 3), when the layer to be measured is thin, the sheet resistance Rs is calculated by the following formula from the current I and the measured voltage V. Rs = (4.5324)V / I ······(1)

Example

[0055] A second-form Hall effect measurement device 5 using the high-voltage application circuit 3a of the electric resistance measurement device 3 according to an embodiment of the present invention will be described with reference to FIG. 5. This is for the purpose of measuring the carrier mobility of a sample using the Hall effect. A general method for obtaining the carrier mobility and carrier concentration by Hall effect measurement is the Van der Pauw method. The measurement sample is a small square piece in which an undoped GaN epitaxial layer 38 and an undoped AlGaN layer 37 are sequentially formed on a silicon (111) plane substrate 39.

[0056] The sample is placed on the N pole of a neodymium magnet 40, and metal needles 33, 34, 35, and 36 arranged at the vertices of a regular square with a side length of 1 mm are in contact with the sample. The configurations of the other matrix relays and single-pole double-throw switch arrays are common to those in the first embodiment. Electrical contact is formed with the measurement sample with respect to the metal needles 33, 34, 35, and 36 using DHVG in the same procedure as in the first embodiment.

[0057] Regarding the metal needles 33 to 36 used in this configuration, when magnetic materials such as Ni or iron are used for the springs for holding and the sleeves for housing them, displacement may occur in a strong magnetic field. Here, those obtained by gold-plating phosphor bronze as a non-magnetic material are used for the metal needles 33 to 36, the springs, and the sleeves. Beryllium copper or tungsten can also be used as the non-magnetic material.

[0058] For the 4×4 matrix switch 10, the Hall electromotive force generated in the following connection order is measured.

[0059] (1) Short-circuit W11 and W42 to pass a current between metal pins 34 and 35 by current source 31, and short-circuit W23 and W34 to measure the Hall electromotive force V36 generated between metal pins 33 and 36 by voltmeter 32. Further, to remove the offset voltage caused by the positional error of the metal pins, the current is passed in the reverse direction and averaged. For this reason, measure again with the following connections.

[0060] (2) Short-circuit W41 and W12 to pass a current in the reverse direction between metal pins 34 and 35 by current source 31, and short-circuit W23 and W34 to measure the Hall electromotive force V63 generated between metal pins 33 and 36 by voltmeter 32. By averaging V63 and V36, the offset voltage due to the displacement of the metal pins can be removed and the accurate Hall electromotive force can be derived. Further, if the current source and the voltmeter are connected so as to be orthogonal to the above example to measure the Hall electromotive force, the measurement accuracy can be further improved. The procedure is as follows.

[0061] (3) Short-circuit W21 and W32 to pass a current between metal pins 33 and 36 by current source 31, and short-circuit W13 and W44 to measure the Hall electromotive force V45 generated between metal pins 34 and 35 by voltmeter 32. Further, to remove the offset voltage, measure again with the following connections.

[0062] (4) Short-circuit W31 and W22 to pass a current between metal pins 34 and 35 by current source 31, and short-circuit W13 and W44 to measure the Hall electromotive force V54 generated between metal pins 34 and 35 by voltmeter 32.

[0063] By averaging the Hall electromotive forces obtained in the above four-step procedure, a more accurate measurement of the Hall effect becomes possible. Also, for the housing such as the metal pins, the springs that push them out, and the sleeves that house them, non-magnetic materials such as phosphor bronze and beryllium copper were used.

[0064] Additionally, by changing the direction of the magnet, the accuracy can be improved. Commercially available neodymium magnets with a magnetic flux density of 0.4 T can be used. However, if the measurement sample is placed on the S pole by inverting the top and bottom, the generated Hall electromotive force will be reversed. By utilizing this and performing averaging again, the accuracy can be enhanced.

[0065] The measured Hall electromotive force varies depending on the shape of the measurement sample. Also, since the magnetic flux density is that of the outermost surface, there is a slight difference from the magnetic flux density at the measurement position of the sample. Regarding the shape dependence of the Hall electromotive force, it has been analyzed in Non-Patent Document 4. In terms of the relationship between the Hall electromotive force and the carrier mobility, it is known that the Hall electromotive force is proportional to the magnetic flux density and the current flowing, and proportional to the mobility. Therefore, if a standard sample is prepared and a calibration coefficient is obtained based on the mobility pre-measured by a standard Hall effect measurement method, measurements with good reproducibility can be performed.

Example

[0066] In the Van der Pauw method of Example 2, since it is necessary to cut the target sample small, sample preparation cannot be done with a large-diameter substrate. In Non-Patent Document 4 (boundaryless Hall measurement method), the substrate can be large, but electromagnetic analysis is required in the process of deriving the Hall coefficient, which makes it complicated. Also, errors are likely to occur depending on the shape inside the energized sample. This example provides a method for simply and easily obtaining the carrier mobility and carrier concentration by newly using two sets of four metal needle arrays arranged orthogonally.

[0067] As shown in Fig. 6, it is equipped with four linear and equally spaced metal needle arrays orthogonal to four similar metal needle arrays arranged orthogonally, and the two innermost metal needles of the metal needle arrays form a square. The measurement substrate is an Si(111) substrate with an AlGaN layer epitaxially grown on a GaN layer. A two-dimensional electron gas is formed at the interface between the AlGaN layer and the GaN layer due to polarization.

[0068] First, according to the methods described in Examples 1 and 2, electrical contacts are formed on all eight metal needles in both columns.

[0069] After connecting a current source to the two outermost metal needles in the metal needle column, the voltage Vs of the two innermost metal needles in the metal needle column is measured, a magnetic field is applied perpendicular to the semiconductor or conductive thin film, and the voltage Vh of the two innermost metal needles in the metal needle column is measured.

[0070] The Hall effect is a state where the force due to the Lorenz force by the magnetic field B and the force from the electric field due to the generated Hall electromotive force are in equilibrium. Therefore, if the carrier velocity Vo, elementary charge q, Hall voltage VH, and the spacing L between the metal needles are considered, each force is as follows. Lorenz force: qVoB ·····(2) Force due to Hall electric field: qVH / L ·····(3)

[0071] If (2) and (3) are made equal, VoB = VH / L ·············(4) Also, the carrier velocity Vo is the product of the carrier mobility μ and the electric field in the direction in which the current flows. Therefore, from the detected sense voltage Vs and the spacing L between the electrode needles, the carrier velocity Vo is expressed by the following equation. Vo = μVs / L ·············(5)

[0072] From (4) and (5), by eliminating L, the carrier mobility μ can be obtained. This becomes very simple and results in the following equation μ = κVH / (VsB)············(4) According to Equation (4), it can be seen that if the magnetic flux density B is measured in advance, the mobility can be derived using only the two voltages Vs and Vh that can be simply measured.

[0073] This is much simpler compared to conventional Hall measurements. In this configuration, since the current source is separated from the measurement location, the current uniformity is relatively high. However, considering the non-uniformity of the magnetic flux at the measurement location and the non-uniformity of the current distribution from the metal needles, a correction coefficient κ is introduced. κ can be determined by measuring a sample whose correct mobility is already known by another method.

[0074] Also, since the sheet resistance Rs is obtained from equation (1) in Example 1, The sheet carrier concentration Ns is obtained by the following equation. Ns = 1 / (qRsμ) ······ (5) In this way, with the configuration of this example, the mobility μ and the sheet carrier density of the measurement sample having a two-dimensional electron gas can be derived.

[0075] Of course, the above measurement method can improve the measurement accuracy by reversing the direction of the current source and averaging. The above has been described for the case where the metal needle array is in the current direction. However, by exchanging the metal needle arrays and performing measurements in the orthogonal direction, or by reversing the direction of the applied magnetic field and performing measurements in the same procedure and then averaging, the error in the position accuracy can be reduced and the measurement accuracy can be further improved.

[0076] In this way, since this example uses the four-terminal method in combination and can know the sheet resistance in advance, it enables the simple measurement of the carrier mobility and the carrier concentration even in the case of a two-dimensional electron gas in a GaN / AlGaN heterojunction.

[0077] Needless to say, it is possible to apply the measurement platform used in Example 5 twice to the orthogonal metal needle arrays and use two voltmeters for implementation.

[0078] A third form of Hall effect measurement device 7 using the high voltage application circuit 3a of the electric resistance measurement device 3 according to an embodiment of the present invention will be described with reference to FIG. 7. This is a device that forms a MIS (Metal Insulator Metal) junction or a Schottky junction on a semiconductor sample, applies a DC voltage to the junction, and measures the capacitance change. A metal electrode 48 for forming a capacitance portion is formed on the measurement sample and is in contact with a metal needle 43, and other metal needles 41, 42, 44 are in contact with the periphery of the metal electrode 46.

[0079] The configurations of other parts are common to those of the first and second embodiments, and a conduction contact can be formed by a bipolar high voltage circuit. A Schottky junction as an example of a measurement sample is formed by forming a metal electrode 48 on an N-type GaN epitaxial layer 45 and an undoped GaN layer 46 sequentially formed on a (111) plane silicon substrate 47.

[0080] When measuring a MIS junction formed by depositing an insulating film on the same substrate, for the metal needles 41, 42, 44, an insulating film can be broken and an electrical contact can be made by applying a high voltage in the same procedure as before. Similarly, CV measurement can be performed on the metal electrode 48 formed on the insulating film.

[0081] For the procedure of forming conduction, tilt the two-way changeover switch 9 to the upper side in the figure, and perform the 2×4 matrix switch 8 in the following setting order. (1) Connect S11 and S22, and form an electrical contact with DHVG. (2) Connect S21 and S12, and form an electrical contact with DHVG. (3) Connect S12 and S24, and form an electrical contact with DHVG. (4) Connect S22 and S14, and form an electrical contact with DHVG.

[0082] By always keeping S13 and S23 open (not in use), a high voltage can be prevented from being applied to the metal electrode 48. In the case of measuring the MIS structure, although the metal needle will contact the insulating film, if the insulating film is 100 nm or less, the breakdown voltage is usually 100 V or less, so an electrical contact can be formed through the insulating film.

[0083] The matrix switch 10-2 represents a state in which W11, W21, W41, and W34 are always short-circuited in the matrix switch 10. By connecting the electrode needles 41, 42, and 44 and connecting them to the terminal E1 and short-circuiting W34, the upper electrode on the Schottky junction or MIS junction side can be connected to the terminal E4.

[0084] E1 and E4 are connected to the capacitance meter 53 via the bias tee 52. The bias tee 52 connected to the E1 and E4 terminals is formed by connecting the variable DC voltage source 49 and the inductor 50 in parallel and the DC cut capacitor 51 in series, preventing the high frequency generated from the capacitance meter 53 from flowing into the variable DC voltage source 49 and preventing the DC voltage 49 from being applied to the capacitance meter.

[0085] If the measurement frequency is low, the inductor 50 and the capacitor 51 need to be increased. The bias tee is a module used when separating DC and RF, and there are also commercially available products with the function built into the capacitance meter 53. For example, when using an E4980ALCR meter manufactured by Agilent, the bias tee is not required.

Example

[0086] A fourth form of semiconductor characteristic measuring device 20 using the high voltage application circuit 3a of the electric resistance measuring device 3 according to the embodiment of the present invention will be described with reference to FIG. 8. Example 4 performs CV measurement on a Schottky connection using an ionic liquid instead of the Schottky electrode in Example 3. By using an ionic liquid, the labor of electrode formation can be saved.

[0087] The portion forming the capacitance section uses the ionic liquid 59 filled in a container 60 having an open bottom. The bottom of the container 60 is configured to be in close contact with an O-ring around the contact surface of the semiconductor substrate, thereby preventing leakage of the liquid and fixing the bonding area. As the ionic liquid used as the gate electrode of the carbon nanotubes employed, an ionic liquid composed of an imidazolium cation and several kinds of inorganic anions was used (Non-Patent Document 6).

[0088] The platinum electrode 58 immersed in the same ionic liquid is used as the upper electrode of an MIS (Metal Insulator Metal) junction or a Schottky junction. The material of the container 60 needs to be corrosion-resistant to the ionic liquid, but it is also possible to use quartz, Teflon (registered trademark), or platinum.

[0089] The metal needles 54, 55, and 57 are installed around the ionic liquid container 60, and the measurement configuration is common to Example 3. The energization and electrode formation for the electrode needles 54, 55, and 57, the two matrix switches, the single-pole double-throw switch, and the procedure for forming an energized junction using the same, and the CV measurement system are also the same as in Example 3.

[0090] The advantage of using the ionic liquid in this example is that by using a liquid electrode for the measurement sample, it is possible to omit the formation of the metal electrode pattern. As a result, the labor required to prepare the sample can be saved. For CV measurement, it is necessary to know the area of the capacitance section, but the area of the capacitance section can be determined by the size of the O-ring. As such a liquid electrode, there is a method of using mercury (Non-Patent Document 5).

[0091] However, mercury has concerns about environmental pollution and has been globally prohibited from use by the Minamata Convention. By using an ionic liquid with a small environmental load as in this example, this problem can be solved. By combining with the energized junction formation method of the present invention, it is not necessary to form a metal electrode, and rapid CV measurement is possible. However, since the measured capacitance value is in series connection with the capacitance depleted on the ionic liquid side, capacitance correction is required when obtaining the carrier concentration on the semiconductor side.

Example

[0092] Although most of the components are shared in Embodiments 1, 2, 3, and 4 of the present invention, since the DHVG is a kind of surge generator, it may cause adverse effects such as malfunction or destruction to precise current sources and voltmeters due to unnecessary radiation into the air. When replacing the single-pole double-throw (SPDT) switch array with a double-pole double-throw (DPDT) switch array and operating the DHVG connected, such adverse effects can be avoided if the electrical measurement side is grounded.

[0093] The fifth form of the four-terminal sheet resistance measuring device 21 using the high voltage application circuit 3a of the electric resistance measuring device 3 according to the embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 shows the configuration of sheet resistance measurement with the electrical measurement side grounded using a DPDT. This configuration is applicable not only to sheet resistance measurement but also to Hall measurement and CV measurement. Although this figure describes the case of a 4-terminal sheet resistance measuring device, it can also be applied to other measurement methods.

[0094] The present invention can provide sheet resistance measurement, Hall effect measurement, and CV measurement on one platform, and by replacing metal needles and pedestals, it is possible to measure a plurality of electrical characteristics with one device.

Explanation of Reference Numerals

[0095] 1 Electrical resistance measuring device, 1a High-voltage generating circuit, 2 Electrical resistance measuring device, 2a, 2b High-voltage generating circuit, 3 Electrical resistance measuring device, 3a High-voltage generating circuit, 4 Four-terminal sheet resistance measuring device, 5 Hall effect measuring device, 7 Hall effect measuring device, 8 Matrix switch, 9 Single-pole double-throw switch array, 9 Two-way changeover switch, 10 Matrix switch, 11 Current source, 12 Voltmeter, 13, 14, 15, 16 Metal needles, 17 Contact part, 18 Semiconductor, 20 Semiconductor characteristic measuring device, 21 Four-terminal sheet resistance measuring device, 31 Current source, 32 Voltmeter, 33, 34, 35, 36 Metal needles, 37 Undoped AlGaN layer, 38 Undoped GaN epi-layer, 39 Silicon (111) plane substrate, 40 Neodymium magnet, 41, 42, 44 Metal needles, 43 Metal needle, 45 N-type GaN epi-layer, 46 Metal electrode, 46 Undoped GaN layer, 48 Metal electrode, 49 DC voltage, 50 Inductor, 51 Capacitance, 52 Bias tee, 53 Capacitance meter, 54, 55, 57 Metal needles, 58 Platinum electrode, 59 Ionic liquid, 60 Container.

Claims

1. a DC power supply connected in series with a first terminal of the primary side of the transformer together with a first current limiting element; a switch element connected in series with a second terminal on the primary side of the transformer together with a second current limiting element; a surge arrester connected in parallel with a current shunt element connected to both ends of the secondary side of the transformer; Equipped with One terminal of the secondary side of the transformer is connected to one of two metal needles that contact the thin film to be measured, A high voltage generating circuit, characterized in that the other terminal of the secondary side of the transformer is connected to the other of the two metal needles.

2. 2. The high voltage generating circuit according to claim 1, A center tap is provided on the primary side of the transformer, and the first terminal is located at the center tap; another switch element connected in series with a third terminal on the primary side of the transformer together with a third current limiting element; A high voltage generating circuit comprising:

3. 3. The high voltage generating circuit according to claim 2, A high voltage generating circuit comprising: an inductor coil having two terminals for detecting a voltage waveform and provided to share a core with the transformer.

4. A high voltage generating circuit according to claim 3; Four metal needles arranged at equal intervals in a row and in contact with the thin film to be measured; A current source connected to two metal needles located outside the four metal needles; a voltage measuring unit connected to two metal needles located inside the four metal needles and configured to measure a voltage; a first switch unit that switches so as to connect the high voltage generating circuit to two of the four metal needles; a second switch unit that switches so as to connect the current source and the voltage measurement unit to two of the four metal needles, respectively; A four-terminal sheet resistance measuring device comprising:

5. A high voltage generating circuit according to claim 3; Four metal needles are arranged at the vertices of a quadrilateral and contact the thin film to be measured; A current source connected to two diagonally positioned metal needles among the four metal needles; a measurement unit for determining a Hall electromotive force between the two remaining metal needles that are diagonally positioned among the four metal needles; a first switch unit that switches so as to connect the high voltage generating circuit to two of the four metal needles; a second switch unit that switches so as to connect the current source and the measurement unit to two of the four metal needles, respectively; A Hall effect measuring device comprising:

6. A high voltage generating circuit according to claim 3; Four metal needle rows arranged linearly and at equal intervals; Another four metal needle rows are arranged perpendicular to the four metal needle rows; a current source connected to the two outermost metal needles of the four metal needle arrays; a voltage Vs measuring unit for measuring a voltage Vs of the two innermost metal needles of the four metal needle rows; a voltage VH measuring unit that applies a magnetic field perpendicular to the thin film to be measured and measures the voltages VH of the two innermost metal needles of the other four metal needle arrays; a first switch unit that switches so as to connect the high voltage generating circuit to two of the four metal needles and two of the other four metal needles; a second switch unit that switches between the current source and the voltage Vs measurement unit and two of the four metal needles and two of the other four metal needles; Equipped with A Hall effect measurement device characterized in that a regular quadrilateral is formed using the two innermost metal needles of the four metal needle rows and the two innermost metal needles of the other four metal needle rows, and electrical contacts are made to all eight metal needles of the four metal needle rows and the other four metal needle rows.

7. A high voltage generating circuit according to claim 3; A Schottky junction region formed on the thin film to be measured; Four metal needles, one of which contacts the Schottky junction region and the remaining three of which contact the thin film to be measured; a first switch unit that switches so as to connect the high voltage generating circuit to two of the four metal needles; Equipped with a metal needle contacting the Schottky junction region and the remaining three metal needles, the metal needles being arranged to contact the Schottky junction region and measure capacitance-voltage characteristics between the metal needles and the remaining three metal needles;

8. 8. The semiconductor characteristic measuring apparatus according to claim 7, 4. A semiconductor characteristic measuring device, comprising: a Schottky junction region formed using an ionic liquid;

9. 5. The four-terminal sheet resistance measuring device according to claim 4, A four-terminal sheet resistance measuring device, characterized in that an electrical measuring circuit is grounded when a high voltage is generated when electrical contact is made with the four metal needles.

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