Electric resistance measuring device, hall effect measuring device, and semiconductor characteristic measuring device

Abstract

To provide an electric resistance measuring device that can shorten a sample preparation process that has so far required energization and formation of a measurement sample by patterning of an electrode and alloying by annealing.SOLUTION: An electric resistance measuring device comprises: a DC power supply that is connected to a first terminal on a primary side of a transformer in series with a current restriction resistor; a switch element that is connected to a second terminal on the primary side of the transformer in series with a second current restriction element; a surge arrestor that is connected to both ends of a secondary side of the transformer in parallel with a current shunt resistor; and two metal needles that are in contact with a thin film to be measured, wherein one of the two metal needles is connected to one-side terminal on the secondary side of the transformer, and the other is connected to the other-side terminal on the secondary side of the transformer.SELECTED DRAWING: Figure 1

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, and the carrier concentration in the conductive layer. [Background technology]

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

[0003] However, when a metal needle is placed in direct contact with the surface of a GaN or SiC semiconductor, which have a large band gap, a Schottky junction is formed between the metal needle and the semiconductor, and one side of the metal needle has the voltage blocking properties of a Schottky junction, so no current can pass through. For this reason, a metal with a small work function must be patterned by lithography and alloyed at high temperature to form a conductive electrical contact.

[0004] This is called the ohmic formation process, and it takes a long time to prepare the measurement sample. For this reason, there is a demand to shorten the time it takes to prepare the current-carrying electrodes required for electrical property measurements such as sheet resistance measurements, Hall measurements, and capacitance-voltage (CV) measurements, which are common for measuring the electrical properties of semiconductors, etc.

[0005] The four-terminal probe method is a simple method for measuring sheet resistance. This method involves contacting four metal needles arranged at equal intervals in a straight line with a semiconductor, connecting a current source to the two outer metal needles, and measuring the voltage generated between the two inner metal needles to measure the sheet resistance. However, for semiconductors with large band gaps such as GaN and SiC, the metal needles and the semiconductor act as Schottky diodes, making it impossible to pass current, so the conventional four-terminal probe method cannot be applied.

[0006] As an alternative method, a device has been developed that measures sheet resistance by measuring the eddy current generated in an electrically conductive layer by applying an AC magnetic field as impedance, but when a conductive substrate having multiple layers is used as the measurement target, the composite sheet resistance is measured, making accurate measurement impossible. In addition, commercially available sheet resistance measuring devices that use non-contact eddy currents have difficulty measuring substrates with high resistance because the eddy currents are small.

[0007] Also, when measuring the Hall effect to measure carrier mobility, it is necessary to form a conductive electrical contact. Conventionally, it is common to partially attach In solder to the surface of a small cut sample and heat it to form a conductive contact. This sample preparation process takes time.

[0008] To measure the carrier concentration, a CV measurement (capacitance-voltage measurement) is often used, in which a reverse voltage is applied to a Schottky diode of a fixed area and the capacitance is measured.

[0009] Naturally, a conductive electrical contact is required on the opposite side of the Schottky junction, so a process is required to form an electrode pattern on the semiconductor surface in addition to the Schottky electrode and create a conductive contact by heat treatment, which takes time to prepare the sample. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2014-29946 A [Patent Document 2] JP 2022-99212 A [Non-patent literature]

[0011] [Non-Patent Document 1] Bipolar high voltage application circuit product example: http: / / www.rika.com / product / prod_detail1.php?catalog_no=B10-4500 [Non-Patent Document 2] Explanation of the principle of four-terminal sheet resistance measurement https: / / www.napson.co.jp / technique / [Non-Patent Document 3] Examples of commercially available sheet resistance measuring devices: https: / / www.napson.co.jp / technique / [Non-Patent Document 4] Boundaryless hole measurement https: / / www.mdpi.com / 2224-2708 / 2 / 1 / 85 [Non-Patent Document 5] CV measurement using a mercury probe https: / / gato-docs.its.txstate.edu / jcr:f7fc3908-d50a-462c-aa80-48ef6d7898e9 / CVanalyzer.pdf [Non-Patent Document 6] Example of a device using ionic liquidhttps: / / www.jstage.jst.go.jp / article / jscm1975 / 30 / 1 / 30_1_10 / _pdf [Non-Patent Document 7] Features of surge arresters FIL3035059.PDF (zaikostore.com) Summary of the Invention [Problem to be solved by the invention]

[0012] When a metal needle is placed in contact with a semiconductor surface and then brought into contact with a wide bandgap semiconductor such as a GaN semiconductor, two reverse-connected Schottky junctions are formed between the metal needle and the surface. The breakdown voltage of Schottky diodes in wide bandgap semiconductors sometimes exceeds 1000V, making it impossible to pass current through them.

[0013] As a result, it is difficult to directly measure the electrical properties of wide band gap semiconductors using a metal needle. Therefore, a method has been proposed in which a high voltage is applied to a metal needle using a piezoelectric element to destroy the Schottky junction (Patent Document 2). However, because this is a mechanical impact method, there is a problem that it is poor in reproducibility.

[0014] There are various circuits that generate high voltages electrically, but the applied current can easily become excessive, and even if the Schottky junction is destroyed, there are problems with the tip of the metal needle melting due to heat generation and the measurement sample being degraded. When applying high voltages, a method is required to prevent the metal needle from melting by reducing the current flowing through the metal needle and to prevent the measurement sample from being degraded. [Means for solving the problem]

[0015] The high-voltage generating circuit of the present invention comprises 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 current shunt elements connected to both ends of the secondary side of the transformer, wherein 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] In addition, in the high-voltage generation circuit according to the present invention, it is preferable that an intermediate tap is provided on the primary side of the transformer, the first terminal is located at the intermediate tap, and another switch element is connected in series with a third terminal on the primary side of the transformer together with a third current limiting element.

[0017] Moreover, the high-voltage generating circuit according to the present invention preferably further comprises an inductor coil having two terminals for detecting a voltage waveform and provided in the transformer so as to share a core.

[0018] The four-terminal sheet resistance measuring device of the present invention is characterized by comprising the above-mentioned high voltage generating circuit, 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 the two metal needles located on the outside of the four metal needles, a voltage measuring unit connected to the two metal needles located on the inside of the four metal needles and measuring voltage, a first switch unit that switches to connect the high voltage generating circuit to two of the four metal needles, and a second switch unit that switches to connect the current source and the voltage measuring unit to each of two of the four metal needles.

[0019] The Hall effect measurement device of the present invention is characterized by comprising the above-mentioned high voltage generating circuit, four metal needles arranged at the vertices of a quadrangle and in contact with the thin film to be measured, a current source connected to two of the four metal needles located diagonally, a measurement unit for determining the Hall electromotive force between the remaining two of the four metal needles located diagonally, a first switch unit for switching to connect the high voltage generating circuit to two of the four metal needles, and a second switch unit for switching to connect the current source and the voltage measurement unit to each of the two of the four metal needles.

[0020] The Hall effect measurement device according to the present invention comprises the above-mentioned high voltage generating circuit, an array of four metal needles arranged in a straight line at equal intervals, another array of four metal needles arranged perpendicular to the array of four metal needles, a current source connected to the two outermost metal needles of the array of four metal needles, a voltage Vs measuring unit that measures the voltage Vs of the two innermost metal needles of the array of four metal needles, a voltage VH measuring unit that applies a magnetic field perpendicular to the thin film to be measured and measures the voltage VH of the two innermost metal needles of the other array of four metal needles, and a current source connected to the high voltage generating circuit, two of the four metal needles and the front The device is characterized in that it comprises a first switch unit which switches to connect two of the other four metal needles, and a second switch unit which switches to connect the current source, the voltage measurement unit, and two of the four metal needles and two of the other four metal needles, and that the innermost two metal needles of the row of four metal needles form a regular quadrilateral and electrical contact is formed with all eight metal needles of the row of four metal needles and the other row of four metal needles.

[0021] The semiconductor characteristic measuring device according to the present invention comprises the above-mentioned high voltage generating circuit, a Schottky junction region formed on the thin film to be measured, four metal needles, one of which is in contact with the Schottky junction region and the remaining three are in contact with the thin film to be measured, and a first switch unit that switches between connecting the high voltage generating circuit and two of the four metal needles, and is characterized in that the capacitance-voltage characteristics are measured between the one metal needle in contact with the Schottky junction region and the remaining three metal needles.

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

[0023] In the four-terminal sheet resistance measuring device according to the present invention, it is preferable that an electrical measuring circuit is grounded when a high voltage is generated when electrical contact is made with the four metal needles.

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

[0025] Once a discharge occurs, a large current can flow, but there is a problem that a high voltage is applied until the discharge starts. The present invention uses the property of intentionally maintaining a high voltage for only a short time to address the drawback of surge arresters that they cannot handle high-speed phenomena. With this configuration, even if a Schottky junction is destroyed by a high voltage, the surge arrester does not allow a large current to flow through the material being measured, so there is no need to worry about damaging the electrode needle.

[0026] In addition, when two metal needles are brought into contact with the object to be measured, each of them forms a Schottky junction, resulting in a configuration in which two diodes are reverse-connected. As a result, the metal needles each have a forward and reverse direction, and when a high voltage is applied, the Schottky junction side in the reverse direction is destroyed or shorted.

[0027] Since it is not possible to simultaneously destroy or short the Schottky junctions of the two metal needles, the polarity must be changed when applying a high voltage. In this invention, a center tap is provided on the primary side of the transformer, and the polarity of the voltage applied to the electrode needles is switched with a simple configuration in which a DC power supply is connected to the center tap. This configuration realizes stable conductive contact.

[0028] In addition, even if a single high voltage pulse is applied, there are cases where a conductive contact is not formed depending on the material being measured. In such cases, it is necessary to repeatedly apply a high voltage pulse, but there is no way to determine whether a conductive contact has been formed. In the present invention, by using the phenomenon in which the resistance of the secondary side decreases when a conductive state is completed, a third coil is provided in the transformer and the amount of decrease in the back electromotive force is detected, thereby making it possible to determine whether a conductive contact has been formed. Effect of the Invention

[0029] According to the present invention, the Schottky junction can be destroyed without melting the tip of the metal needle due to heat generation. [Brief description of the drawings]

[0030] [Figure 1] FIG. 2 is a configuration diagram of an electrical resistance measuring device according to an embodiment of the present invention, in which electrical contact is formed by a high voltage application circuit. [Diagram 2] FIG. 2 is a configuration diagram of an electrical resistance measuring device according to an embodiment of the present invention, in which electrical contact is formed by a bipolar high voltage application circuit. [Diagram 3] FIG. 1 is a configuration diagram of an electrical resistance measuring device according to an embodiment of the present invention, which is provided with a function for detecting completion of electrical contact formation by a bipolar high voltage application circuit. [Figure 4] FIG. 13 is a configuration diagram of a four-terminal sheet resistance measurement apparatus according to an embodiment of the present invention, in which a DHVG is connected to a matrix switch to form electrical contacts and four-terminal sheet resistance is measured. [Diagram 5] FIG. 13 is a diagram showing the configuration of a Hall effect measurement device according to an embodiment of the present invention, in which a DHVG is connected to a matrix switch to form electrical contacts in a probe having metal needles at the vertices of a quadrangle, and which performs Hall measurement. [Figure 6] FIG. 1 is a diagram showing the configuration of a Hall effect measurement device according to an embodiment of the present invention, in which electrical contacts are formed with eight metal needles, four of which are perpendicular to each other, using a DHVG, and the voltage of the two inner perpendicular needles is measured. [Figure 7] FIG. 2 is a configuration diagram of a semiconductor characteristic measuring apparatus according to an embodiment of the present invention, which forms electrical contacts with a DHVG and performs capacitance-voltage (CV) measurement. [Figure 8] This is a configuration diagram of a CV measurement device in an embodiment of a semiconductor characteristic measuring device according to the present invention, in which electrical contact is formed with a DHVG and an ionic liquid held in a cylindrical container is brought into contact with the semiconductor surface to form a Schottky barrier. [Figure 9]FIG. 11 is a diagram showing a measurement method for protecting a measurement circuit from grounding via a DPDT switch when a bipolar high voltage is applied in a four-terminal sheet resistance measurement device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, an embodiment of 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 given the same reference numerals, and duplicated explanations will be omitted. In addition, in the explanation in the text, the reference numerals previously described will be used as necessary.

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

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

[0034] This diode D1 may be any other element that limits the current, such as a resistor. A capacitor C1 is grounded between the current limiting resistors R1 and R2, forming a low-pass filter that suppresses noise caused by 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 this to the metal needles 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, and the surge arrester SA1 holds the generated high voltage for several μs to several msec, and then absorbs the current by discharging (Non-Patent Document 8).

[0036] Resistor R4 has the function of shunting the current generated by the back electromotive force, but when no current flows through metal needles 13 and 14 (open state), a high resistance value generates a high voltage, and a low resistance value generates a low voltage. In other words, the generated voltage can be controlled by adjusting resistor R4. The Schottky junction is destroyed during the period when this high voltage is maintained.

[0037] There are various commercially available surge arresters SA1, and the present invention can be selected from such commercially available products.

[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 generating circuit 1a is unidirectional, the Schottky junction formed by the two metal needles 13 and 14 in the reverse direction is destroyed, but the other Schottky junction is in the forward direction and may not be destroyed.

[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 two current switching circuits (HVG) are provided at both ends of the primary coil L1 to form high voltage generating circuits 2a and 2b, which makes it possible to switch the polarity of the high voltage output on the secondary side. By alternately operating the two current switching circuits, it becomes possible to apply high voltages of both polarities.

[0040] Another embodiment of the electrical resistance measuring device 3 according to the present invention will be described with reference to Fig. 3. When no electrical contact is formed on the secondary side, the secondary side is in a high impedance state, and the counter electromotive force on the secondary side is large, but when a current-carrying state is achieved, the resistance on the secondary side decreases, and the induced voltage decreases.

[0041] This secondary back electromotive force can be indirectly detected by a third coil L3 provided in the same transformer core. By measuring the amount of decrease in the back electromotive force while switching the current multiple times, it is possible to determine whether the energized contact has been completed. In the following, the bipolar high voltage application circuit, which is the high voltage generation circuit 3a equipped with a detection coil, is referred to as DHVG.

[0042] The electrical resistance measuring device 3 shortens the process of sample preparation, which previously required the formation of electrical continuity by patterning electrodes on the measurement sample and alloying by annealing, etc. Electrical contacts are formed on the wafer by DHVG, and the electrical characteristics can be measured using the metal needles 13, 14.

[0043] DHVG allows easy four-terminal sheet resistance and Hall measurements of various wide band gap semiconductors. In Hall measurements, which are difficult to measure accurately due to the sample shape, eight metal needles are used to form tiny electrical contacts, making it possible to measure the mobility of the semiconductor layer in a short sample preparation time without cutting the measurement sample into small pieces.

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

[0045] Moreover, by using a Schottky junction in contact with an ionic liquid (Non-Patent Document 10) instead of the conventional method of forming a Schottky junction using a mercury contact (Non-Patent Document 9), CV measurement can be performed safely without patterning the Schottky electrode. In the laboratory, the carrier concentration needs to be measured immediately after crystal growth, but the carrier concentration can be easily measured by measuring the capacitance-voltage (CV) characteristics using the electrical 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, but the high voltage application circuit 3a of the electrical resistance measuring device 3 according to the embodiment of the present invention can generate a bipolar voltage, making polarity switching unnecessary. In addition, the use of a surge arrester can make the current flow extremely small. This prevents the electrode needle from melting, and reduces damage to the measurement sample. In particular, when a metal needle is brought into contact with a wide band gap semiconductor such as GaN or SiC, it is possible to easily break the Schottky junction that is formed and has an extremely high breakdown voltage, thereby obtaining an electrically conductive contact.

[0047] As a result of the experiment, it was found that the present invention can easily measure the sheet resistance and mobility of the two-dimensional electron gas layer at the heterojunction interface of AlGaN and GaN layers. Electrical contact can be made to the p-type GaN semiconductor layer in a similar manner, although the Schottky diode polarity is back-to-back connected. EXAMPLES

[0048] A first embodiment of a four-terminal sheet resistance measurement device 4 using a high-voltage application circuit 3a of an electrical resistance measurement device 3 according to an embodiment of the present invention will be described with reference to Fig. 4. In this embodiment, the high voltage generated in the bipolar high-voltage application circuit (high-voltage application circuit 3a) is connected to a 2x4 matrix switch 8. The matrix switch 8 is a relay array installed at the contact points (intersections) of vertical and horizontal wiring, and has the function of short-circuiting and opening at the intersections.

[0049] This allows the output of the high voltage generated in the bipolar high voltage circuit (high voltage application circuit 3a: DHVG) to be selectively distributed to any terminal from A1 to A4. Note that a relay with a dielectric strength of 1000V or more is used for the matrix switch 8.

[0050] The single-pole double-throw switch array 9 uses metal needles 13, 14, 15, and 16 as poles to separate the high voltage side and the electrical measurement side. Note that the single-pole double-throw switches are C-contact relays with a dielectric strength of 1000 V or more. Note that the electrical measurement side is connected via a 4 × 4 matrix switch 10.

[0051] When the metal needles 13-16 are brought into contact with the epitaxial growth surface 17 that forms an AlGaN / GaN heterojunction on the Si(111) substrate, Schottky diodes represented by D1, D2, D3, and D4 are formed between the metal needles 13-16 and the epitaxial growth layer 17. By using the above procedure, electrical contact can be achieved for all of the metal needles 13-16.

[0052] For example, when S11 and S24 of the 2 × 4 matrix switch 8 are shorted and all of the single-pole double-throw switch array 9 are connected to the high-voltage generating side, operating the DHVG allows a high voltage to be applied to metal needle 13 and metal needle 16, and electrical contact is formed between metal needles 13 and 16. By sequentially selecting the matrix switch 8, electrical contact can be formed for all combinations of metal needles.

[0053] After the current formation of each of the metal needles 13 to 16 is completed, the metal needles 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, the current source 11 is connected to the metal needles 13 and 16 by shorting W11 and W42, and the voltmeter 12 is connected to the metal needles 14 and 15 by shorting W23 and W34.

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

[0055] A second embodiment of the Hall effect measurement device 5 using the high voltage application circuit 3a of the electrical resistance measurement device 3 according to the embodiment of the present invention will be described with reference to FIG. 5. This is intended to measure the carrier mobility of a sample using the Hall effect. The Van der Pauw method is a common method for determining carrier mobility and carrier concentration by Hall effect measurement. The measurement sample is a small square piece in which an undoped GaN epitaxial layer 38 and an undoped AlGaN layer 37 are laminated in this order on a silicon (111) substrate 39.

[0056] The sample is placed on the north pole of a neodymium magnet 40, and metal needles 33, 34, 35, and 36 arranged at the vertices of a regular square with sides of 1 mm are in contact with the sample. The rest of the configuration of the matrix relay and single-pole double-throw switch array is the same as in Example 1. Electrical contact is made between the measurement sample and the metal needles 33, 34, 35, and 36 using DHVG in the same procedure as in Example 1.

[0057] The metal needles 33-36 used in this configuration may become misaligned in a strong magnetic field if magnetic materials such as Ni or iron are used for the springs for holding them or the sleeves that house them. Here, phosphor bronze plated with gold is used as a non-magnetic material for the metal needles 33-36, springs, sleeves, etc. Beryllium copper and wangsten can also be used as non-magnetic materials.

[0058] The Hall voltage generated in the 4 × 4 matrix switch 10 is measured in the following connection order.

[0059] (1) W11 and W42 are shorted and a current is passed between metal needles 34 and 35 by current source 31, and W23 and W34 are shorted and the Hall electromotive force V36 generated between metal needles 33 and 36 is measured by voltmeter 32. Furthermore, in order to remove the offset voltage caused by the positional error of the metal needle, the current is passed in the opposite direction and averaged. For this reason, measurement is performed again with the following connections.

[0060] (2) W41 and W12 are shorted and a current is passed in the reverse direction between metal needles 34 and 35 by current source 31, and W23 and W34 are shorted and the Hall electromotive force V63 generated between metal needles 33 and 36 is measured by voltmeter 32. By averaging V63 and V36 and removing the offset voltage due to the misalignment of the metal needle, an accurate Hall electromotive force can be derived. Furthermore, if the current source and voltmeter are connected orthogonally to the above example and the Hall electromotive force is measured, the measurement accuracy can be further improved. The procedure is as follows.

[0061] (3) W21 and W32 are shorted and a current is passed between metal needles 33 and 36 by current source 31, and W13 and W44 are shorted and the Hall electromotive force V45 generated between metal needles 34 and 35 is measured by voltmeter 32. Furthermore, in order to eliminate the offset voltage, the measurement is performed again with the following connections.

[0062] (4) W31 and W22 are shorted and a current is passed between metal needles 34 and 35 by current source 31. By shorting W13 and W44, the Hall electromotive force V54 generated between metal needles 34 and 35 is measured by voltmeter 32.

[0063] By averaging the Hall electromotive force obtained by the above four steps, it becomes possible to measure the Hall effect with higher accuracy. In addition, non-magnetic materials such as phosphor bronze and beryllium copper were used for the metal needle, the spring that pushes it out, and the sleeve that houses them.

[0064] Additionally, the accuracy can be improved by changing the direction of the magnet. A commercially available neodymium magnet with a magnetic flux density of 0.4 T can be used, but if the magnet is turned upside down and the measurement sample is placed on the south pole, the Hall electromotive force generated will be reversed. Using this, the accuracy can be improved by performing averaging again.

[0065] The measured Hall electromotive force varies depending on the shape of the measurement sample. In addition, 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. The shape dependency of the Hall electromotive force is analyzed in Non-Patent Document 4, and in terms of the relationship between the Hall electromotive force and the mobility of carriers, it is known that the Hall electromotive force is proportional to the magnetic flux density and the amount of current flowing, and is proportional to the mobility. Therefore, if a standard sample is prepared and a calibration coefficient is obtained based on the mobility measured in advance by a standard Hall effect measurement method, measurements with good reproducibility can be performed. EXAMPLES

[0066] In the Van der Pauw method of Example 2, it is necessary to cut the target sample into small pieces, so a sample cannot be prepared using a large-diameter substrate. In Non-Patent Document 4 (boundary-free Hall measurement method), the substrate can be large, but the process of deriving the Hall coefficient requires electromagnetic analysis, which is complicated. In addition, errors are likely to occur depending on the shape of the sample to which electricity is passed. This example provides a method for simply and easily determining carrier mobility and carrier concentration by using two new rows of four orthogonal metal needles.

[0067] As shown in Figure 6, the device used has four metal needle arrays arranged linearly and at equal intervals, and four similar metal needle arrays arranged perpendicular to each other, with the innermost two metal needles forming a regular quadrangle. The measurement substrate is a Si(111) substrate with an AlGaN layer epitaxially grown on a GaN layer. Two-dimensional electron gas is formed at the interface between the AlGaN layer and the GaN layer due to polarization.

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

[0069] After connecting a current source to the two outermost metal needles in the metal needle array, the voltage Vs of the two innermost metal needles in the metal needle array 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 array is measured.

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

[0071] If we set (2) and (3) equal, VoB=VH / L ················(4) In addition, the carrier velocity Vo is the product of the carrier mobility μ and the electric field in the direction of current flow. Therefore, the carrier velocity Vo can be expressed by the following formula based on the detected sense voltage Vs and the electrode needle distance L. Vo=μVs / L ···············(5)

[0072] From (4) and (5), L can be eliminated to obtain the carrier mobility μ. This is very simple and becomes μ=κVH / (VsB) (4) According to equation (4), if the magnetic flux density B is measured in advance, it is possible to derive the mobility using only two voltages Vs and Vh that can be simply measured.

[0073] This is much simpler than conventional Hall measurements. In this configuration, the current source is far from the measurement point, so the uniformity of the current is relatively high, but a correction factor κ is introduced to take into account the non-uniformity of the magnetic flux at the measurement point and the non-uniformity of the current distribution from the metal needle. κ can be determined by measuring a sample whose mobility is already known by another method.

[0074] In addition, since the sheet resistance Rs is calculated from the formula (1) in Example 1, The sheet carrier concentration Ns is calculated by the following formula. Ns = 1 / (qRsμ) (5) In this manner, the configuration of this embodiment makes it possible to derive the mobility μ and sheet carrier density of a measurement sample having a two-dimensional electron gas.

[0075] Of course, the above measurement method can improve the measurement accuracy by reversing the direction of the current source and averaging. The above explanation was given for the case where the metal needle array is in the current direction, but by exchanging the metal needle array and performing measurements in a perpendicular direction, or by reversing the direction of the applied magnetic field and performing measurements in the same procedure, it is possible to reduce errors in positional accuracy and further improve measurement accuracy by averaging.

[0076] In this way, by using the four-terminal method in combination in this embodiment, the sheet resistance can be known in advance, which makes it possible to easily measure the carrier mobility and carrier concentration even in the case of two-dimensional electron gas in a GaN / AlGaN heterojunction.

[0077] Needless to say, the measurement platform used in Example 5 can be applied twice to two orthogonal metal needle rows, and two voltmeters can be used.

[0078] A third embodiment of the Hall effect measurement device 7 using the high voltage application circuit 3a of the electrical resistance measurement device 3 according to the embodiment of the present invention will be described with reference to Fig. 7. In this embodiment, a MIS (Metal Insulator Metal) junction or Schottky junction is formed on a semiconductor sample, and a DC voltage is applied to the junction to measure the capacitance change. A metal electrode 48 forming a capacitance section is formed on the measurement sample, and a metal needle 43 is in contact with the metal electrode 48, and other metal needles 41, 42, 44 are in contact with the periphery of the metal electrode 46.

[0079] The configuration of other parts is the same as in Examples 1 and 2, and a conductive contact can be formed in a bipolar high voltage circuit. The Schottky junction as a measurement sample example is an N-type GaN epitaxial layer 45 and an undoped GaN layer 46, which are successively formed on a (111) silicon substrate 47, on which a metal electrode 48 is formed.

[0080] When measuring an MIS junction with an insulating film formed on the same substrate, the insulating film can be broken down and electrical contact can be established by applying a high voltage to the metal needles 41, 42, and 44 in the same manner as before. In this way, CV measurement can also be performed on the metal electrode 48 formed on the insulating film.

[0081] To form the current, flip the two-way switch 9 to the upper side in the figure, and set the 2 × 4 matrix switch 8 in the following 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 to form an electrical contact with DHVG. (4) Connect S22 and S14 and form an electrical contact with DHVG.

[0082] By always leaving S13 and S23 open (unused), it is possible to prevent a high voltage from being applied to the metal electrode 48. When measuring an MIS structure, the metal needle comes into contact with the insulating film, but if the insulating film is 100 nm or less, the dielectric strength is usually 100 V or less, so that a conductive 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 shorted in the matrix switch 10. By joining the electrode needles 41, 42, and 44 and connecting them to the terminal E1, and shorting 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 a capacitance meter 53 via a bias tee 52. The bias tee 52 connected to the E1 and E4 terminals is a circuit in which a variable DC voltage source 49 and an inductor 50 are connected in parallel, and a DC blocking capacitor 51 is connected in series, and prevents high frequency waves generated from the capacitance meter 53 from flowing into the variable DC voltage source 49, and prevents the DC voltage 49 from being applied to the capacitance meter.

[0085] If the measurement frequency is low, the inductor 50 and the capacitance 51 must be large. A bias tee is a module used to separate DC and RF, but a capacitor meter 53 with this function built in is also available on the market. For example, if you use an Agilent E4980ALCR meter, a bias tee is not necessary. EXAMPLES

[0086] A fourth embodiment of a semiconductor characteristic measuring apparatus 20 using a high voltage application circuit 3a of an electrical resistance measuring apparatus 3 according to an embodiment of the present invention will be described with reference to Fig. 8. Example 4 is a case where CV measurement is performed on a Schottky junction using an ionic liquid instead of the Schottky electrode in Example 3. By using an ionic liquid, it is possible to save the effort of forming electrodes.

[0087] The portion forming the capacitance portion uses an ionic liquid 59 filled in a container 60 with an open bottom. The bottom of the container 60 is fitted tightly around the contact surface of the semiconductor substrate with an O-ring, preventing leakage of the liquid and fixing the contact area. The ionic liquid used is one that has been used as a gate electrode for carbon nanotubes and is composed of imidazolium cations and several types of inorganic anions (Non-Patent Document 6).

[0088] A platinum electrode 58 immersed in the ionic liquid serves as an upper electrode for a MIS (Metal Insulator Metal) junction or a Schottky junction. The material of the container 60 must be resistant to corrosion by the ionic liquid, but it may be quartz, Teflon (registered trademark), or platinum.

[0089] Metal needles 54, 55, and 57 are placed around a container 60 of an ionic liquid, and the measurement configuration is the same as in 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, the procedure for forming an energization junction using them, and the CV measurement system are also the same as in Example 3.

[0090] The advantage of using an ionic liquid in this embodiment is that by using a liquid electrode as the measurement sample, it is possible to omit the pattern formation of a metal electrode. This makes it possible to save the effort required to prepare the sample. The area of ​​the capacitance part needs to be known for CV measurement, but the area of ​​the capacitance part can be determined by the size of the O-ring. There is a method using mercury as such a liquid electrode (Non-Patent Document 5).

[0091] However, there are concerns about environmental pollution caused by mercury, and its use has been banned worldwide by the Minamata Convention. This problem can be solved by using an ionic liquid with a small environmental impact as in this embodiment. By combining this with the current-carrying 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 a series connection with the capacitance depleted on the ionic liquid side, capacitance correction is required when determining the carrier concentration on the semiconductor side. EXAMPLES

[0092] In the present invention, most of the components are common to the first, second, third and fourth embodiments, but since the DHVG is a type of surge generator, unwanted radiation into the air can cause adverse effects such as malfunction or destruction of precision current sources and voltmeters. Such adverse effects can be avoided by replacing the single-pole double-throw (SPDT) switch array with a double-pole double-throw (DPDT) switch array and grounding the electrical measurement side when connecting and operating the DHVG.

[0093] A four-terminal sheet resistance measurement device 21 of a fifth embodiment using a high voltage application circuit 3a of the electrical resistance measurement device 3 of the embodiment of the present invention will be described with reference to Fig. 9. Fig. 9 shows a sheet resistance measurement configuration in which the electrical measurement side is grounded using DPDT. This configuration is applicable not only to sheet resistance measurement, but also to Hall measurement and CV measurement. Note that although the figure shows the case of a four-terminal sheet resistance measurement 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 a single platform, and by replacing the metal needle and base, it is possible to measure multiple electrical properties with a single device. [Explanation of symbols]

[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 switch, 10 Matrix switch, 11 Current source, 12 Voltmeter, 13, 14, 15, 16 Metal needle, 17 Contact, 18 Semiconductor, 20 Semiconductor characteristic measuring device, 21 Four-terminal sheet resistance measuring device, 31 Current source, 32 Voltmeter, 33, 34, 35, 36 Metal needle, 37 Undoped AlGaN layer, 38 Undoped GaN epilayer, 39 Silicon (111) surface substrate, 40 Neodymium magnet, 41, 42, 44 Metal needle, 43 Metal needle, 45 N-type GaN epilayer, 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 needle, 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 voltage 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 so as to connect the current source and the voltage measurement unit to 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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