Methods for determining thermal resistance

Abstract

To realize a thermal resistance measurement method that can accurately determine the thermal resistance of semiconductor devices. [Solution] The method for measuring the thermal resistance of a semiconductor element comprises a temperature characteristic acquisition step (step S200), a voltage measurement step (step S300), a temperature conversion step (step S400), a temperature correction step (step S500), and a thermal resistance calculation step (step S600). The temperature correction step corrects the amount of temperature change of the semiconductor element during the temperature measurement period calculated in the temperature conversion step, based on a temperature correction characteristic for the temperature characteristic previously acquired using a reference semiconductor element having the same structure as the semiconductor element. The thermal resistance calculation step calculates the thermal resistance of the semiconductor element based on the amount of temperature change of the semiconductor element corrected in the temperature correction step.

Description

Technical Field

[0001] The present invention relates to a method for measuring the thermal resistance of a semiconductor device.

Background Art

[0002] Regarding the measurement of the thermal resistance of a semiconductor device, the technique of Patent Document 1 is known. In Patent Document 1, a first step of supplying a minute current in the forward direction to a test semiconductor device and measuring the temperature characteristics of the forward voltage drop of the test semiconductor device, a test current having a value sufficiently larger than the minute current and the minute current are supplied to the test semiconductor device in the forward direction, and a second step of measuring the change characteristics of the forward voltage drop of the test semiconductor device immediately after the supply of the test current is stopped, a third step of supplying the minute current and the test current to a dummy device having an inductance component substantially equivalent to the test semiconductor device and measuring the voltage characteristics between both ends of the dummy device, a fourth step of correcting the error of the measurement result of the second step from the result of the third step, and a fifth step of obtaining the thermal resistance of the test semiconductor device from the measurement results of the first step and the fourth step are described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The thermal resistance measurement method described in Patent Document 1 corrects the forward voltage drop change characteristics of the semiconductor element under test using the measurement results of the voltage characteristics across the ends of a dummy element, and then determines the thermal resistance of the semiconductor element under test based on the corrected result. However, depending on the type of semiconductor element, even if the inductance components are the same, the forward voltage drop change characteristics do not necessarily match. In such cases, the thermal resistance measurement method described in Patent Document 1 has the problem that it is not possible to correctly determine the value of the thermal resistance.

[0005] This invention has been made in view of the above-mentioned problems, and its main objective is to realize a thermal resistance measurement method that can accurately determine the thermal resistance of a semiconductor device. [Means for solving the problem]

[0006] The thermal resistance measurement method according to the present invention is a method for measuring the thermal resistance of a semiconductor element having a gate terminal, a source terminal, and a drain terminal, wherein a current flows between the source terminal and the drain terminal in accordance with a control voltage applied to the gate terminal, and comprises: a temperature characteristic acquisition step of acquiring a temperature characteristic of the semiconductor element that represents the relationship between the temperature of the semiconductor element and the voltage generated between the drain terminal and the source terminal in the semiconductor element; a heating period of heating the semiconductor element by flowing a current from the drain terminal toward the source terminal; and a temperature measurement period of flowing a current from the source terminal toward the drain terminal, wherein the half- The system includes a voltage measurement step for measuring the amount of change in the voltage of a conductor element; a temperature conversion step for calculating the amount of temperature change of the semiconductor element during the temperature measurement period based on the temperature characteristics obtained in the temperature characteristics acquisition step and the amount of change in the voltage measured in the voltage measurement step; a temperature correction step for correcting the amount of temperature change calculated in the temperature conversion step; and a thermal resistance calculation step for calculating the thermal resistance of the semiconductor element based on the amount of temperature change corrected in the temperature correction step, wherein the temperature correction step corrects the amount of temperature change based on a temperature correction characteristic for the temperature characteristics obtained in advance using a reference semiconductor element having the same structure as the semiconductor element. [Effects of the Invention]

[0007] According to the present invention, a thermal resistance measurement method capable of accurately determining the thermal resistance of a semiconductor device can be realized.

[0008] Furthermore, issues, configurations, and effects other than those mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a system configuration for implementing a thermal resistance measurement method according to one embodiment of the present invention. [Figure 2] This is a flowchart of a thermal resistance measurement method according to the first embodiment of the present invention. [Figure 3] This is a flowchart of the temperature compensation characteristic acquisition process according to the first embodiment of the present invention. [Figure 4] This figure shows an example of the temperature characteristics of a semiconductor device. [Figure 5] This figure shows an example of the time evolution of the current flowing through a semiconductor element and the junction temperature when measuring the change in the drain-source voltage. [Figure 6] This diagram illustrates the current paths flowing through the semiconductor element during the heating period and temperature measurement period in MOS-sat mode. [Figure 7] This figure shows an example of the subthreshold characteristics of a SiC-MOSFET. [Figure 8] This diagram illustrates the current path flowing through the semiconductor element during the heating period and temperature measurement period in Diode mode. [Figure 9] This figure shows an example of voltage change measured in MOS-sat mode and diode mode, respectively, using the same SiC-MOSFET. [Figure 10] This is a schematic diagram of electron and hole trapping / detrapping during MOS-sat mode measurement in semiconductor devices. [Figure 11] This figure shows an example of the temperature compensation characteristics of a semiconductor device according to the first embodiment of the present invention. [Figure 12] This is a flowchart of a thermal resistance measurement method according to a second embodiment of the present invention. [Figure 13] This is a flowchart of the temperature compensation characteristic acquisition process according to the second embodiment of the present invention. [Figure 14] This figure shows an example of the temperature compensation characteristics of a semiconductor device according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0010] (First embodiment) FIG. 1 is a diagram showing a system configuration for implementing a thermal resistance measurement method according to an embodiment of the present invention. The system shown in FIG. 1 is configured by connecting a measurement power supply 2 to a semiconductor element 1 which is an object of thermal resistance measurement, and further connecting a thermal resistance measurement device 10 to the semiconductor element 1.

[0011] In this embodiment, for example, a silicon carbide MOSFET (SiC-MOSFET) is used as the semiconductor element 1, and the thermal resistance of this semiconductor element 1 is measured. The measurement power supply 2 is a power supply device capable of applying an arbitrary control voltage to the gate terminal of the semiconductor element 1 and an arbitrary voltage between the drain terminal and the source terminal of the semiconductor element 1.

[0012] The thermal resistance measurement device 10 measures the current flowing between the drain terminal and the source terminal of the semiconductor element 1 and the voltage between the drain terminal and the source terminal in a state where an arbitrary voltage is applied to the semiconductor element 1 by the measurement power supply 2. Using these measurement results, the thermal resistance measurement device 10 can obtain the thermal resistance of the semiconductor element 1.

[0013] FIG. 2 is a flowchart of a thermal resistance measurement method according to the first embodiment of the present invention. In the thermal resistance measurement device 10 of FIG. 1, the thermal resistance measurement method of this embodiment is realized by executing the processing shown in the flowchart of FIG. 2.

[0014] In step S100, a temperature correction characteristic acquisition process for acquiring the temperature correction characteristic of the semiconductor element 1 is performed. Here, a reference semiconductor element having the same structure as the semiconductor element 1 is used to acquire a temperature correction characteristic which is information for correcting the temperature change amount of the semiconductor element 1 calculated in step S400 described later. Note that the details of the processing content of step S100 will be described later with reference to FIG. 3.

[0015] In step S200, the temperature characteristics of the semiconductor element 1, which is the measurement target of the thermal resistance, are acquired. Here, as the temperature characteristics of the semiconductor element 1, the relationship between the temperature of the semiconductor element 1 and the voltage (drain-source voltage) that occurs between them when a current is passed from the drain terminal to the source terminal in the semiconductor element 1 is acquired. For example, the semiconductor element 1 is installed in a thermostatic chamber (not shown), the temperature in the thermostatic chamber is set to a predetermined temperature, and waiting is performed until the inside of the semiconductor element 1 becomes substantially the same as the set temperature of the thermostatic chamber. Then, a current that is negligible for the temperature rise of the semiconductor element 1 is passed from the drain terminal to the source terminal of the semiconductor element 1, and the drain-source voltage at this time is measured. By repeating such measurements while changing the temperature of the thermostatic chamber, the slope of the drain-source voltage with respect to the temperature change of the semiconductor element 1, that is, how much the drain-source voltage changes when the temperature of the semiconductor element 1 changes by 1 °C, can be obtained, and this can be used as the temperature characteristics of the semiconductor element 1. Thereby, for the semiconductor element 1, temperature characteristics as shown in, for example, FIG. 4 described later can be acquired. Note that the temperature characteristics of the semiconductor element 1 obtained in this way are also called the K factor.

[0016] In step S300, the amount of change in the drain-source voltage after heating of the semiconductor element 1, which is the measurement target of the thermal resistance, is measured. Here, by a measurement method using the MOS-sat mode of the semiconductor element 1, the amount of change in the drain-source voltage after heating the semiconductor element 1 by passing a current through it is measured. The amount of change in the drain-source voltage thus acquired is used as a value for calculating the thermal resistance of the semiconductor element 1. Note that the details of the measurement method using the MOS-sat mode used in step S300 will be described later with reference to FIGS. 5, 6, and 7.

[0017] In step S400, the temperature change of the semiconductor element 1, which is the object of thermal resistance measurement, is calculated based on the temperature characteristics of the semiconductor element 1 acquired in step S200 and the change in the drain-source voltage acquired in step S300. Here, the temperature change when the semiconductor element 1 is heated by passing a current through it in step S300 is determined by using the temperature characteristics of the semiconductor element 1 acquired in step S200 and converting the change in the drain-source voltage measured in step S300 into a temperature change.

[0018] In step S500, the temperature change of semiconductor element 1 calculated in step S400 is corrected using the temperature correction characteristics acquired in step S100. Here, for example, a correction value for the temperature change of semiconductor element 1 is determined based on the temperature correction characteristics acquired in step S100 and the temperature characteristics (K factor) of semiconductor element 1 acquired in step S200. By adding the correction value thus determined to the temperature change calculated in step S400, the temperature change of semiconductor element 1 can be corrected.

[0019] In step S600, the thermal resistance of semiconductor element 1 is calculated based on the temperature change of semiconductor element 1 corrected in step S500. Here, the thermal resistance of semiconductor element 1 can be calculated from the relationship between the input loss measured when heating semiconductor element 1 in step S300 and the temperature change of semiconductor element corrected in step S500.

[0020] Once the thermal resistance of the semiconductor element 1 has been calculated in step S600, the thermal resistance measuring device 10 terminates the process shown in the flowchart of Figure 2.

[0021] Next, we will describe in detail the temperature compensation characteristic acquisition process performed in step S100 of Figure 2. Figure 3 is a flowchart of the temperature compensation characteristic acquisition process according to the first embodiment of the present invention.

[0022] In step S110, the temperature of the reference semiconductor element before heating by passing an electric current through it is set. Here, for example, the temperature before heating can be set according to the temperature environment in which the semiconductor element 1 will actually be operated.

[0023] In step S120, the drain-source voltage is measured before heating the reference semiconductor device.

[0024] In step S130, the change in the drain-source voltage after heating the reference semiconductor element from the temperature set in step S110 is measured. Here, similar to step S300 in Figure 2, the change in the drain-source voltage after heating the reference semiconductor element by passing a current through it is measured using a measurement method that utilizes the MOS-sat mode of the reference semiconductor element.

[0025] In step S140, the change in drain-source voltage after heating the reference semiconductor element from the temperature set in step S110 is measured using a different measurement method than in step S130. Specifically, the change in drain-source voltage after heating the reference semiconductor element by passing a current through it is measured using a measurement method that utilizes the diode mode of the reference semiconductor element. Details of the measurement method using the diode mode used here will be described later with reference to Figure 8.

[0026] The reference semiconductor element has the characteristic that, even if the heating temperature is the same, different measurement methods will yield different measurement results in terms of the change in drain-source voltage. Semiconductor element 1, which has the same structure as the reference semiconductor element, also has the same characteristic. This characteristic is due to the structure of semiconductor element 1 and the reference semiconductor element, which will be explained in detail later.

[0027] In step S150, the difference in the amount of change in the drain-source voltage measured in steps S130 and S140 is calculated.

[0028] In step S160, it is determined whether or not to terminate the measurement of the change in drain-source voltage using the reference semiconductor element. This determination in step S160 can be made using any determination condition. For example, it may be determined that the measurement should be terminated when the number of measurements reaches a predetermined number, or it may be determined whether or not to terminate the measurement according to the user's instructions. If the process in step S160 determines that the measurement of the change in drain-source voltage using the reference semiconductor element should be terminated, the process proceeds to step S170; otherwise, it returns to step S110. If the process returns to step S110, the process from step S120 onward is repeated using a reference semiconductor element with different temperature characteristics than the previous one.

[0029] In step S170, the temperature compensation characteristics of semiconductor element 1 are calculated based on the difference between the drain-source voltage before heating and the change in the drain-source voltage after heating, which were obtained for the reference semiconductor element in the previous processing. Here, the temperature characteristics (K factor) of the reference semiconductor element are determined from the relationship between the temperature before heating set in step S110 and the drain-source voltage before heating measured in step S120, similar to step S200 in Figure 2. Then, based on the determined temperature characteristics, the difference in the change in the drain-source voltage calculated in step S150 is converted into a temperature difference, and the relationship between these is determined. This determines the relationship between the slope of the drain-source voltage with respect to the temperature change of the reference semiconductor element and the difference in the measurement results with respect to the temperature change after heating due to differences in measurement methods, and this is taken as the temperature compensation characteristics of semiconductor element 1. The temperature compensation characteristics calculated in this way represent the temperature compensation value for each temperature characteristic (K factor) of semiconductor element 1, and can be used to determine the compensation value for the temperature change of semiconductor element 1 used in step S500 in Figure 2.

[0030] Once the temperature compensation characteristics of the semiconductor element 1 have been calculated in step S170, the thermal resistance measuring device 10 completes the temperature compensation characteristic acquisition process and proceeds to step S200 in Figure 2.

[0031] Next, the temperature characteristics of semiconductor device 1 obtained in step S200 of Figure 2 will be described below.

[0032] Figure 4 shows an example of the temperature characteristics of the semiconductor device 1 obtained in step S200. As mentioned above, in step S200, the drain-source voltage Vds is measured for various temperatures of the semiconductor device 1 when a measurement current is passed while a constant control voltage is applied to the gate terminal of the semiconductor device 1. In Figure 4, the temperature of the semiconductor device 1 (junction temperature Tj) is set on the horizontal axis and the drain-source voltage Vds is set on the vertical axis, and the obtained measurement results are shown at each plot point 45.

[0033] The temperature characteristics of semiconductor device 1 can be determined, for example, by linearly approximating each plotted point 45 in Figure 4 as a linear straight line 46. However, the line representing the temperature characteristics of semiconductor device 1 is not limited to a straight line like the linear straight line 46. For example, each plotted point 45 may be approximated by a quadratic curve, and this may be used as the temperature characteristics of semiconductor device 1.

[0034] Next, the details of the measurement method using the MOS-sat mode, which is used in step S300 of Figure 2, will be explained below.

[0035] Figure 5 shows an example of the time evolution of the current flowing through semiconductor element 1 and the junction temperature Tj when measuring the change in drain-source voltage in step S300. As shown in Figure 5, the period for measuring the change in drain-source voltage is divided into a heating period in the first half and a temperature measurement period in the second half.

[0036] During the heating period from time t0 to time t1, the semiconductor element 1 is heated by passing a predetermined heating current through it, as shown in Graph 41. As a result, the junction temperature Tj of the semiconductor element 1 rises from the minimum value Tjmin to the maximum value Tjmax, as shown in Graph 42.

[0037] During the temperature measurement period from time t1 to time t2, a temperature measurement current lower than the heating current is passed through the semiconductor element 1, as shown in Graph 41. It is preferable that the magnitude of this temperature measurement current is such that the temperature of the semiconductor element 1 does not rise, or the temperature rise is negligible. At this time, as shown in Graph 42, the junction temperature Tj of the semiconductor element 1 gradually decreases from its maximum value Tjmax at time t1. In step S300, the change in the drain-source voltage corresponding to this change in junction temperature Tj is measured.

[0038] In Figure 5, a method (Static method) is shown in which the change in drain-source voltage is measured until the junction temperature Tj decreases to the minimum value Tjmin, which is the temperature before the start of measurement. However, other measurement methods may also be used, such as a method (Dynamic method) that measures only the drain-source voltage at a certain time immediately after the end of the heating period. Once the voltage value for calculating the thermal resistance of semiconductor element 1 is obtained, any measurement method can be used in step S300.

[0039] Figure 6 illustrates the current path flowing through the semiconductor device 1 during the heating period and the temperature measurement period in MOS-sat mode. Figure 6(a) shows the current path during the heating period, and Figure 6(b) shows the current path during the temperature measurement period. As shown in these figures, the semiconductor device 1 is composed of a MOS channel 1a having a gate electrode, a drain electrode, and a source electrode, as well as a body diode 1b with an anode connected to the source electrode side of the MOS channel 1a and a cathode connected to the drain electrode side of the MOS channel 1a.

[0040] As shown in Figure 6(a), during the heating period in MOS-sat mode, a positive control voltage Vgs is applied to the gate terminal of the semiconductor element 1 from the measurement power supply 2, and a predetermined voltage is applied between the drain terminal and the source terminal so that the potential on the drain terminal side is higher. This causes current to flow from the drain electrode to the source electrode in the MOS channel 1a of the semiconductor element 1, so that a predetermined heating current flows from the drain terminal to the source terminal of the semiconductor element 1. At this time, the magnitude of the heating current is set so that sufficient losses occur to heat the semiconductor element 1.

[0041] As shown in Figure 6(b), during the temperature measurement period in MOS-sat mode, a negative control voltage Vgs is applied to the gate terminal of the semiconductor element 1 from the measurement power supply 2, and a predetermined voltage is applied between the drain terminal and the source terminal so that the potential on the source side is higher. This causes current to flow from the anode to the cathode in the body diode 1b of the semiconductor element 1, so that a predetermined temperature measurement current flows from the source terminal to the drain terminal of the semiconductor element 1. At this time, the magnitude of the temperature measurement current is set so that the temperature of the semiconductor element 1 does not rise substantially and the measured value does not become unstable due to noise, etc. The magnitude of the temperature measurement current set in this way is smaller than the heating current.

[0042] Furthermore, when the aforementioned SiC-MOSFET is used as the semiconductor element 1, it is preferable that the temperature measurement current flows through the body diode 1b, as described above. The reason for this is that if the temperature measurement current flows through the MOS channel 1a, it may be difficult to accurately convert the detected voltage to temperature according to the temperature measurement current due to the hysteresis characteristics originating from the gate insulating film of the SiC-MOSFET.

[0043] Figure 7 shows an example of the subthreshold characteristics of a typical SiC-MOSFET. In a typical SiC-MOSFET, when a predetermined drain-source voltage is applied between the source and drain terminals and the control voltage Vgs applied to the gate electrode is changed, the drain current Id rises sharply when the control voltage Vgs exceeds a predetermined value. At this time, the value of the control voltage Vgs at which the change in drain current Id occurs differs depending on whether the control voltage Vgs is gradually increased (upsweep) or gradually decreased (downsweep), as shown in graphs 51 and 52 in Figure 7, respectively. Thus, it is known that the subthreshold characteristics of a SiC-MOSFET have hysteresis.

[0044] When a SiC-MOSFET is used as semiconductor element 1, the hysteresis in the subthreshold characteristics described above must be taken into consideration when measuring the change in drain-source voltage in step S300. In other words, the control voltage Vgs applied to semiconductor element 1 during the temperature measurement period must be set to a sufficiently low value so that the hysteresis of the subthreshold characteristics does not have an effect.

[0045] Next, the details of the measurement method using the diode mode used in step S130 of Figure 3 will be explained below.

[0046] As mentioned above, in step S130 of Figure 3, the change in the drain-source voltage after heating the reference semiconductor element is measured using a measurement method that utilizes the same MOS-sat mode as in step S300 of Figure 2. On the other hand, in step S140, the change in the drain-source voltage after heating the reference semiconductor element is measured using a measurement method that utilizes a different diode mode.

[0047] Figure 8 illustrates the current path through the reference semiconductor element during the heating period and temperature measurement period in the diode mode. Figure 8(a) shows the current path during the heating period, and Figure 8(b) shows the current path during the temperature measurement period. In Figure 8, the structure of semiconductor element 1 in Figure 6, which is the same as the reference semiconductor element, is used to illustrate the current path of the reference semiconductor element in the diode mode.

[0048] As shown in Figure 8(a), during the heating period in diode mode, a negative control voltage Vgs is applied to the gate terminal of the reference semiconductor element (semiconductor element 1) from the measurement power supply 2, and a predetermined voltage is applied between the drain terminal and the source terminal so that the potential on the source side is higher. As a result, similar to Figure 6(b) above, current flows from the anode to the cathode in the body diode 1b of the reference semiconductor element, causing a predetermined heating current to flow from the source terminal to the drain terminal of the reference semiconductor element. At this time, the magnitude of the heating current is set so that sufficient losses occur to heat the reference semiconductor element.

[0049] As shown in Figure 8(b), during the temperature measurement period in diode mode, a negative control voltage Vgs is applied to the gate terminal of the reference semiconductor element (semiconductor element 1) from the measurement power supply 2, similar to the heating period, and a predetermined voltage is applied between the drain terminal and the source terminal so that the potential on the source side is higher. As a result, similar to Figures 6(b) and 8(a) above, current flows from the anode to the cathode in the body diode 1b of the reference semiconductor element, causing a predetermined temperature measurement current to flow from the source terminal to the drain terminal of the reference semiconductor element. At this time, the magnitude of the temperature measurement current is set so that the temperature of the reference semiconductor element does not rise substantially and the measured value does not become unstable due to noise, etc. The magnitude of the temperature measurement current set in this way is smaller than the heating current.

[0050] As explained above, unlike the MOS-sat mode described earlier, in Diode mode, a predetermined heating current is passed through the body diode 1b during the heating period to heat the reference semiconductor element. In this way, in Diode mode, a large current for heating flows through the body diode 1b for a certain period of time, which can cause defects in the reference semiconductor element to expand and potentially increase the resistance of the reference semiconductor element. This phenomenon is called current-conducting degradation. In other words, performing measurements in Diode mode on semiconductor element 1 or the reference semiconductor element may result in current-conducting degradation. For this reason, Diode mode is generally not recommended for semiconductor element 1 used in products.

[0051] Figure 9 shows an example of voltage change measured in MOS-sat mode and diode mode using the same SiC-MOSFET. In Figure 9, graph 61 shows the change in drain-source voltage Vds over time measured in MOS-sat mode, and graph 62 shows the change in drain-source voltage Vds over time measured in diode mode. In graphs 61 and 62, the losses due to the heating current flowing through the SiC-MOSFET during the heating period are assumed to be equal.

[0052] Depending on the SiC-MOSFET used, the measured drain-source voltage Vds may differ between MOS-sat mode and diode mode, even though the input losses are the same, as shown in graphs 61 and 62 of Figure 9. That is, due to the difference in the direction of the heating current flow, the drain-source voltage Vds is measured higher in MOS-sat mode than in diode mode by a difference of 63. This difference 63 is largest immediately after the start of measurement and gradually decreases over time.

[0053] As explained above, when measuring the drain-source voltage Vds in SiC-MOSFETs using MOS-sat mode, the obtained measurement may be higher than it should be. Therefore, if the junction temperature Tj is calculated using the change in drain-source voltage measured in MOS-sat mode, the junction temperature Tj will be calculated at a higher value than it should be, and as a result, the thermal resistance will be calculated to be higher than it should be. To prevent this, the drain-source voltage Vds should be measured in diode mode, but if diode mode measurement is performed on semiconductor element 1, which is the target of thermal resistance measurement, there is a possibility of current degradation in semiconductor element 1, as mentioned above.

[0054] Therefore, in this embodiment, prior to measuring the semiconductor element 1, a measurement is performed in diode mode using a reference semiconductor element having the same structure as the semiconductor element 1, and a temperature correction characteristic is obtained from the measurement result. Then, without performing a measurement in diode mode on the semiconductor element 1, which is the target of thermal resistance measurement, the temperature change amount obtained from the change in drain-source voltage measured in MOS-sat mode is corrected using the temperature correction characteristic obtained from the measurement result of the reference semiconductor element. Based on the corrected temperature change amount obtained in this way, the thermal resistance of the semiconductor element 1 is calculated. This makes it possible to accurately calculate the thermal resistance of the semiconductor element 1 without causing current degradation in the semiconductor element 1.

[0055] Figure 10 is a schematic diagram of electron and hole trapping / detrapping during MOS-sat mode measurement in semiconductor device 1. Figure 10 shows an example of the cross-sectional structure of semiconductor device 1, which is a SiC-MOSFET. As shown in Figure 10, semiconductor device 1 has a source electrode 71 and a gate electrode 72 on one side and a drain electrode 73 on the other side, with P-type SiC 75, N-type SiC 76, and a SiC epitaxial layer 77 stacked between them. A gate insulating film 74 is also placed between the gate electrode 72 and the P-type SiC 75, N-type SiC 76, and SiC epitaxial layer 77. Although not shown, a reference semiconductor device has a similar structure.

[0056] When measuring the drain-source voltage Vds in MOS-sat mode, as explained in Figure 6, the path of the heating current and the temperature measurement current changes when the polarity of the control voltage Vgs applied to the gate terminal switches when transitioning from the heating period to the temperature measurement period. At this time, electron and hole trapping / detrapping occurs in semiconductor element 1 and the reference semiconductor element, respectively, as shown in Figure 10. That is, during the heating period, electrons 81 and holes 82 are trapped near the interface between the gate insulating film 74 and the P-type SiC 75, and near the PN junction formed between the P-type SiC 75 and the N-type SiC 76, respectively, by following the paths shown by arrows 83 and 84. On the other hand, during the temperature measurement period after the heating period, in response to the switching of the control voltage Vgs, electrons 81 that were trapped near the interface between the gate insulating film 74 and the P-type SiC 75 move towards the source electrode 71, and holes 82 that were trapped near the PN junction move in the direction shown by arrow 85, and are detrapped. As a result, the drain-source voltage Vds changes transiently, making it impossible to accurately measure the temperature in MOS-sat mode based on the change in the drain-source voltage Vds.

[0057] In this embodiment, as described above, a reference semiconductor element having the same structure as semiconductor element 1 is used to perform measurements in diode mode, and the temperature correction characteristics obtained from these measurements are used to correct the change in the drain-source voltage of semiconductor element 1 obtained by the MOS-sat mode measurement. As a result, even if the value of the drain-source voltage Vds changes transiently during the MOS-sat mode measurement as described above, the temperature change of semiconductor element 1 can be accurately determined and the thermal resistance can be calculated.

[0058] Next, the temperature compensation characteristics of semiconductor element 1, calculated in step S170 of Figure 3, will be explained below.

[0059] Figure 11 shows an example of the temperature compensation characteristics of a semiconductor element 1 according to the first embodiment of the present invention. In Figure 11, for each slope (K factor) of the drain-source voltage with respect to the temperature change of the semiconductor element 1, the value of the compensation temperature ΔTc corresponding to the difference in the amount of voltage change calculated in step S150 is shown at each plot point 90. In step S170, for example, a linear straight line 91 is obtained by linearly approximating each plot point 90 in Figure 11, and this can be used as the temperature compensation characteristics of the semiconductor element 1. Note that the line representing the temperature compensation characteristics of the semiconductor element 1 is not limited to a straight line such as the linear straight line 91.

[0060] According to the first embodiment of the present invention described above, the following effects are achieved.

[0061] (1) The thermal resistance measuring device 10 has a gate terminal, a source terminal, and a drain terminal, and measures the thermal resistance of a semiconductor element 1 through which current flows between the source terminal and the drain terminal according to a control voltage Vgs applied to the gate terminal. The method for measuring the thermal resistance of the semiconductor element 1 using this thermal resistance measuring device 10 comprises a temperature characteristic acquisition step (step S200), a voltage measurement step (step S300), a temperature conversion step (step S400), a temperature correction step (step S500), and a thermal resistance calculation step (step S600). The temperature characteristic acquisition step acquires the temperature characteristics of the semiconductor element 1, which represent the relationship between the temperature of the semiconductor element 1 and the drain-source voltage generated between the drain terminal and the source terminal in the semiconductor element 1. The voltage measurement step has a heating period in which the semiconductor element 1 is heated by flowing current from the drain terminal to the source terminal, and a temperature measurement period in which current is flowed from the source terminal to the drain terminal, and measures the amount of change in the drain-source voltage of the semiconductor element 1 during the temperature measurement period after the heating period. The temperature conversion step calculates the temperature change of the semiconductor element 1 during the temperature measurement period based on the temperature characteristics of the semiconductor element 1 acquired in the temperature characteristics acquisition step and the change in the drain-source voltage measured in the voltage measurement step. The temperature correction step corrects the temperature change calculated in the temperature conversion step. The thermal resistance calculation step calculates the thermal resistance of the semiconductor element 1 based on the temperature change corrected in the temperature correction step. In the temperature correction step, the temperature change of the semiconductor element 1 is corrected based on the temperature correction characteristics for the temperature characteristics acquired in advance using a reference semiconductor element having the same structure as the semiconductor element 1. In this way, the thermal resistance of the semiconductor element can be accurately determined.

[0062] (2) The semiconductor element 1 can be a silicon carbide MOSFET (SiC-MOSFET). In this case, the semiconductor element 1 has different characteristics when the change in drain-source voltage is measured using the diode mode measurement method, that is, when the semiconductor element 1 is heated by passing a current from the source terminal to the drain terminal and then a current is passed from the source terminal to the drain terminal, and when the change in drain-source voltage is measured using the MOS-sat mode measurement method, that is, when the change in drain-source voltage is measured in the voltage measurement step. Even if the semiconductor element 1 has such characteristics, the thermal resistance of the semiconductor element can be accurately determined using the thermal resistance measurement method of the semiconductor element 1 with the thermal resistance measuring device 10 as described above.

[0063] (3) The semiconductor element 1 incorporates a body diode 1b. In the voltage measurement step, current is passed through the body diode 1b during the temperature measurement period, causing current to flow from the source terminal to the drain terminal. In this way, when measuring the change in the drain-source voltage in the voltage measurement step, the influence of hysteresis characteristics originating from the gate insulating film of the semiconductor element 1 can be avoided, and accurate measurement values ​​can be obtained.

[0064] (4) The method for measuring the thermal resistance of the semiconductor element 1 using the thermal resistance measuring device 10 includes a temperature compensation characteristic acquisition process (step S100). In this temperature compensation characteristic acquisition process, a measurement method using MOS-sat mode is used to heat the reference semiconductor element by passing a heating current from the drain terminal to the source terminal of the reference semiconductor element, and then the change in voltage between the drain terminal and source terminal of the reference semiconductor element is measured when a temperature measurement current is passed from the source terminal to the drain terminal of the reference semiconductor element (step S130). Alternatively, a measurement method using diode mode is used to heat the reference semiconductor element by passing a heating current from the source terminal to the drain terminal of the reference semiconductor element, and then the change in voltage between the drain terminal and source terminal of the reference semiconductor element is measured when a temperature measurement current is passed from the source terminal to the drain terminal of the reference semiconductor element (step S140). The difference between these is then calculated (step S150), and the temperature compensation characteristic of the semiconductor element 1 is acquired based on the calculated difference (step S170). In this way, for semiconductor elements 1, such as SiC-MOSFETs, which have the characteristic that the measured value changes transiently when the drain-source voltage is measured in MOS-sat mode, a temperature compensation characteristic that can accurately compensate for the temperature can be obtained.

[0065] (Second embodiment) Next, a second embodiment of the present invention will be described. This embodiment describes a method for measuring the thermal resistance of a semiconductor element more simply than the thermal resistance measurement method described in the first embodiment. The system configuration for implementing the thermal resistance measurement method according to this embodiment is the same as that shown in Figure 1 in the first embodiment, so this embodiment will be described below using the configuration shown in Figure 1.

[0066] Figure 12 is a flowchart of a thermal resistance measurement method according to a second embodiment of the present invention. The thermal resistance measurement method of this embodiment is realized by executing the processes shown in the flowchart of Figure 12 in the thermal resistance measuring device 10 of Figure 1. In the flowchart of Figure 12, the same step numbers as in the flowchart of Figure 2 described in the first embodiment are used for parts that perform the same processing as in the flowchart of Figure 2. Unless otherwise necessary, the explanation of parts with the same step numbers as in Figure 2 will be omitted below.

[0067] In step S101, a temperature correction characteristic acquisition process is performed to obtain the temperature correction characteristics of the semiconductor element 1. Here, similar to the first embodiment, a reference semiconductor element having the same structure as the semiconductor element 1 is used to acquire the temperature correction characteristics, which are information for correcting the amount of temperature change of the semiconductor element 1 calculated in step S400. However, in this embodiment, in order to simplify the measurement, a temperature correction characteristic representing the temperature correction value at a predetermined temperature is acquired, rather than the temperature correction value for each temperature characteristic (K factor) of the semiconductor element 1. This temperature is preferably determined according to a temperature environment that makes it easy to acquire the characteristics of the semiconductor element 1, such as room temperature. Details of the processing content in step S101 will be described later with reference to Figure 13.

[0068] In steps S200 to S400, the same processes as those described in Figure 2 in the first embodiment are performed.

[0069] In step S501, the temperature change amount of the semiconductor element 1 calculated in step S400 is corrected using the temperature correction characteristics at a predetermined temperature obtained in step S101. Here, for example, a correction value for the temperature change amount of the semiconductor element 1 at a predetermined temperature is determined based on the temperature correction characteristics obtained in step S101. By adding the correction value thus determined to the temperature change amount calculated in step S400, the temperature change amount of the semiconductor element 1 can be corrected.

[0070] In step S600, similar to the first embodiment, the thermal resistance of the semiconductor element 1 is calculated based on the temperature change amount of the semiconductor element 1 corrected in step S501. After that, the process shown in the flowchart of Figure 12 is completed.

[0071] Next, we will describe in detail the temperature compensation characteristic acquisition process performed in step S101 of Figure 12. Figure 13 is a flowchart of the temperature compensation characteristic acquisition process according to the second embodiment of the present invention.

[0072] In steps S110 to S150, the same processes as those described in Figure 3 of the first embodiment are performed. However, it is preferable that the temperature before heating set in step S110 is the same as, or close to, the temperature at which the change in the drain-source voltage after heating of the semiconductor element 1 is measured in step S300 of Figure 12.

[0073] In step S171, which follows step S150, the temperature correction characteristics of the semiconductor element 1 at the temperature set in step S110 are calculated based on the difference between the drain-source voltage before heating measured in step S120 and the change in the drain-source voltage after heating calculated in step S150. Here, the difference in the change in the drain-source voltage calculated in step S150 based on the drain-source voltage before heating measured in step S120 is converted into a temperature difference, and the relationship between these is determined. This determines the relationship between the drain-source voltage of the reference semiconductor element at a predetermined temperature and the difference in the measurement results for the change in temperature after heating due to differences in measurement methods, and this is taken as the temperature correction characteristics of the semiconductor element 1 at the predetermined temperature. The temperature correction characteristics thus calculated represent the temperature correction value of the semiconductor element 1 at that temperature and can be used to determine the correction value for the change in temperature of the semiconductor element 1 used in step S501 in Figure 12.

[0074] Once the temperature correction characteristics of the semiconductor element 1 at a predetermined temperature have been calculated in step S171, the thermal resistance measuring device 10 terminates the temperature correction characteristic acquisition process and proceeds to step S200 in Figure 12.

[0075] Figure 14 shows an example of the temperature compensation characteristics of a semiconductor element 1 according to a second embodiment of the present invention. In Figure 14, for each drain-source voltage Vds of the semiconductor element 1 at a predetermined temperature, the value of the compensation temperature ΔTc corresponding to the difference in the voltage change amount calculated in step S150 is shown at each plot point 95. In step S171, for example, a linear straight line 96 is obtained by linearly approximating each plot point 95 in Figure 14, and this can be used as the temperature compensation characteristics of the semiconductor element 1 at a predetermined temperature. Note that the line representing the temperature compensation characteristics of the semiconductor element 1 is not limited to a straight line such as the linear straight line 96.

[0076] According to the second embodiment of the present invention described above, the method for measuring the thermal resistance of a semiconductor element 1 using a thermal resistance measuring device 10 comprises a temperature characteristic acquisition step (step S200), a voltage measurement step (step S300), a temperature conversion step (step S400), a temperature correction step (step S501), and a thermal resistance calculation step (step S600). In the temperature correction step, the amount of temperature change of the semiconductor element 1 calculated in the temperature conversion step is corrected based on the temperature correction characteristics acquired in advance at a predetermined temperature. In this way, the time required to measure the thermal resistance can be shortened while maintaining the accuracy of the thermal resistance of the semiconductor element obtained for a predetermined temperature.

[0077] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0078] 1. Semiconductor element 2...Measurement power supply 10. Thermal resistance measuring device S100, S101... Steps for acquiring temperature compensation characteristics S200...Temperature characteristic acquisition step S300...Voltage measurement step S400... Temperature conversion step S500, S501... Temperature compensation step S600... Thermal resistance calculation step

Claims

1. A method for measuring the thermal resistance of a semiconductor element having a gate terminal, a source terminal, and a drain terminal, wherein a current flows between the source terminal and the drain terminal in accordance with a control voltage applied to the gate terminal, A temperature characteristic acquisition step to acquire the temperature characteristics of the semiconductor element, which represent the relationship between the temperature of the semiconductor element and the voltage generated between the drain terminal and the source terminal of the semiconductor element. A heating period is defined as a period during which the semiconductor element is heated by passing a current from the drain terminal to the source terminal, and a temperature measurement period is defined as a period during which the current is passed from the source terminal to the drain terminal, wherein a voltage measurement step is defined as measuring the amount of change in the voltage of the semiconductor element during the temperature measurement period after the heating period. A temperature conversion step that calculates the amount of temperature change of the semiconductor element during the temperature measurement period based on the temperature characteristics obtained in the temperature characteristics acquisition step and the amount of change of the voltage measured in the voltage measurement step, A temperature correction step for correcting the amount of temperature change calculated in the temperature conversion step, The system includes a thermal resistance calculation step which calculates the thermal resistance of the semiconductor element based on the temperature change amount corrected in the temperature correction step, In the temperature correction step, the amount of temperature change is corrected based on a temperature correction characteristic for the temperature characteristics obtained in advance using a reference semiconductor element having the same structure as the semiconductor element. Thermal resistance measurement method.

2. In the thermal resistance measurement method described in claim 1, The aforementioned semiconductor device is a silicon carbide MOSFET, The semiconductor element has a characteristic in which the change in voltage of the semiconductor element measured when current is passed from the source terminal to the drain terminal after heating the semiconductor element by passing current from the source terminal to the drain terminal, and the change in voltage measured in the voltage measurement step, are different. Thermal resistance measurement method.

3. In the thermal resistance measurement method described in claim 1, In the temperature correction step, the amount of temperature change is corrected based on the temperature correction characteristics previously acquired at a predetermined temperature. Thermal resistance measurement method.

4. In the thermal resistance measurement method described in claim 1, The aforementioned semiconductor element incorporates a body diode, In the voltage measurement step, current is passed through the body diode during the temperature measurement period, thereby causing current to flow from the source terminal to the drain terminal. Thermal resistance measurement method.

5. In the thermal resistance measurement method described in claim 1, The aforementioned temperature compensation characteristics are After heating the reference semiconductor element by passing a current from its drain terminal to its source terminal, the change in voltage between the drain terminal and the source terminal of the reference semiconductor element, measured when a current is passed from the source terminal to the drain terminal of the reference semiconductor element, After heating the reference semiconductor element by passing a current from the source terminal to the drain terminal of the reference semiconductor element, the change in voltage between the drain terminal and the source terminal of the reference semiconductor element, measured when the current is passed from the source terminal to the drain terminal of the reference semiconductor element, Obtained based on the difference, Thermal resistance measurement method.

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