JP5045325B2 - Transistor inspection method and inspection apparatus - Google Patents

Description

  The present invention relates to a technique for inspecting a transistor.

  Development of power transistors including IGBTs and MOSFETs has been actively conducted. Since these transistors handle a large amount of power, a high degree of reliability is required. In order to ensure a high level of reliability, a technique for appropriately inspecting a manufactured transistor is required.

Various techniques for inspecting the quality of manufactured transistors have been developed.
Patent Document 1 discloses a technique for inspecting the quality of a transistor constituting an inverter in a state where the transistor is incorporated in the inverter.
Patent Document 2 discloses a technique that uses different inspection methods depending on the magnitude of temperature dependency of various electrical characteristics of a transistor.
Patent Document 3 discloses a technique for accurately inspecting the quality of a transistor while suppressing the influence of leakage current when inspecting the transistor.
Patent Document 4 discloses a technique for estimating low-temperature operating characteristics of other transistors having the same structure based on a test result of low-temperature operating characteristics of a certain transistor without performing a test.

JP 7-318608 A JP 2006-349355 A JP 2006-317208 A JP-A-5-283620

  In the case of a power transistor that handles a large amount of power, destruction of the element when a load short circuit occurs becomes a problem. When the load is short-circuited and the power supply voltage is directly applied, an excessive current flows in the transistor, causing destruction of the element. The resistance of the transistor to such a load short circuit is referred to as a short circuit tolerance.

  In order to check the quality of the short-circuit withstand capability of a transistor, usually a part of the transistor manufactured in the same lot is extracted and inspected, a predetermined voltage is applied with the load short-circuited, and the time until the transistor breaks down is checked. This is done by measuring. However, in order to perform a more reliable test, it is preferable to perform a short-circuit withstand test for each transistor. There is a need for an inspection technique that can determine whether a transistor is good or short in terms of short-circuit tolerance without destroying the transistor.

  The present invention solves the above problems. The present invention provides a technique capable of appropriately inspecting the short-circuit tolerance of a transistor.

The present invention is embodied as a method for testing a transistor. The method includes a step of measuring a gate threshold voltage of the transistor before heat generation to determine a first gate threshold voltage, and a predetermined time between a collector / emitter or a source / drain of the transistor over a predetermined time. A step of causing the transistor to generate heat by flowing a current of a magnitude, a step of measuring a gate threshold voltage of the transistor that has generated a high temperature due to heat generation, and specifying a second gate threshold voltage; A step of calculating a gate threshold voltage difference from one gate threshold voltage and the second gate threshold voltage, and a step of determining pass / fail of the transistor based on the gate threshold voltage difference. .

  In this inspection method, after measuring the gate threshold voltage of a transistor to be inspected, a current is passed between the collector / emitter or between the source / drain to cause the transistor to generate heat and reach a high temperature state. Thereafter, the gate threshold voltage of the transistor that has become high temperature due to heat generation is measured, and the amount of change in the gate threshold voltage before and after the heat generation is calculated as the gate threshold voltage difference. Then, the quality of the transistor is determined based on the gate threshold voltage difference.

FIG. 6 shows the temperature dependence of the gate threshold voltage _Vth of a general transistor. The gate threshold voltage V _th is a tendency to decrease as the temperature T _a of the transistor is increased. Therefore, the gate threshold voltage difference ΔV _th before and after heat generation can be used as an index indicating the degree of temperature rise of the transistor due to heat generation.

  In the case where the transistor is a discrete device in which a plurality of IGBTs or MOSFETs are integrated, the degree of temperature rise of the transistor due to heat generation changes according to variations in characteristics of individual IGBTs or MOSFETs. In the case where there are variations in characteristics of individual IGBTs or MOSFETs in the transistor, when a current flows between the collector / emitter or the source / drain, the current flows locally in the transistor. The part where the current flows in a concentrated manner is overheated and becomes hotter than the other parts, and the gate threshold voltage of the transistor after heat generation is significantly lower than the gate threshold voltage before heat generation. When a short circuit of a load occurs in such a transistor, the current is concentrated locally and flows inside the transistor, so that the short circuit resistance is low. Therefore, when the transistor is a discrete device in which a plurality of IGBTs or MOSFETs are integrated, it is possible to appropriately determine whether the short circuit withstand capability is good or not based on the gate threshold voltage difference before and after heat generation.

Note that the difference between the inspection method of the present invention and the technique for determining pass / fail based on the difference in on-voltage before and after the heat generation of the transistor will be described below. FIG. 5 shows the temperature dependence of the relationship between the collector / emitter voltage V _CE and the collector current I _C in a general IGBT. Collector / emitter voltage V _CE is low region, the collector / emitter voltage V _CE for flowing a predetermined collector current I _C decreases with the temperature T _a of the transistor is increased. That is, in the region where the collector / emitter voltage V _CE is low, the on-voltage of the transistor has a negative temperature coefficient. However, the collector / emitter voltage V _CE is a high region, the collector / emitter voltage V _CE for flowing a predetermined collector current I _C, increases with the temperature T _a of the transistor is increased. That is, in the region where the collector-emitter voltage V _CE is high, the on-voltage of the transistor has a positive temperature coefficient. Thus, the temperature dependence of the on-voltage of the transistor shows the opposite tendency between the region where the collector-emitter voltage _VCE is low and the region where it is high. Here, the on-voltage of the IGBT has been described, but the on-voltage of the MOSFET shows a similar tendency. Therefore, when trying to determine whether a transistor is good or bad based on the difference in on-state voltage before and after heating the transistor, it is inspected according to the specifications of the transistor to be inspected and the specifications of the power supply connected to the transistor for inspection. Must be changed each time, and a great deal of labor must be devoted to the inspection.

In contrast, as shown in FIG. 6, the gate threshold voltage V _th of the transistor is a tendency that decreases constantly along with the temperature T _a of the transistor is increased, always negative temperature Has a coefficient. Therefore, as in the inspection method of the present invention, the quality of the transistor is determined based on the difference in the gate threshold voltage _Vth before and after the transistor is heated, so that various inspection standards can be obtained without greatly changing the inspection standard. It is possible to inspect transistors with various specifications with little effort.

  In measuring the on-voltage of the transistor, it is necessary to pass a certain amount of current between the collector / emitter or between the source / drain, and the transistor generates heat and rises in temperature during the on-voltage measurement. . For this reason, it is difficult to accurately evaluate the difference in on-voltage before and after heat generation. On the other hand, when measuring the gate threshold voltage, the current flowing through the transistor is very small, so the transistor hardly generates heat during the measurement of the gate threshold voltage, and almost no temperature. Does not rise. Therefore, it is easy to accurately evaluate the difference in gate threshold voltage before and after heat generation. Therefore, according to the inspection method of the present invention, it is possible to accurately evaluate the change in transistor characteristics before and after heat generation.

The present invention is also embodied as an apparatus. The device of the present invention is a device for inspecting a transistor. The apparatus measures the gate threshold voltage of the transistor before generating heat to determine the first gate threshold voltage, and determines a predetermined value between the collector / emitter or the source / drain of the transistor over a predetermined time. Means for causing the transistor to generate heat by passing a current of a magnitude of, a means for determining a second gate threshold voltage by measuring a gate threshold voltage of the transistor that has been heated to a high temperature, and the first Means for calculating a gate threshold voltage difference from one gate threshold voltage and the second gate threshold voltage, and means for determining the quality of the transistor based on the gate threshold voltage difference .

  According to the inspection method and inspection apparatus of the present invention, it is possible to appropriately inspect the short-circuit tolerance of the transistor.

The main features of the embodiments described below are listed.
(Mode 1) A transistor to be inspected is a discrete device in which a plurality of IGBTs are integrated.
(Mode 2) In the step of generating heat by flowing a current between the collector / emitter or the source / drain of the transistor, the transistor is driven in a saturation region.
(Mode 3) In the step of determining the quality of the transistor based on the gate threshold voltage difference, if the gate threshold voltage difference is lower than a predetermined reference value, the transistor is determined to be defective.

An inspection apparatus 20 embodying the present invention will be described with reference to FIG.
Transistor T _r the inspection device 20 is inspected is a discrete device that integrates a plurality of the IGBT. The transistor _Tr includes a gate terminal G, a collector terminal C, and an emitter terminal E.

The gate terminal G of the transistor T _r is connected to the inspection gate power supply 22 of the inspection apparatus 20. The inspection gate power supply 22 is a voltage source whose output voltage is variable, and can adjust the voltage applied to the gate terminal G. The output voltage of the inspection gate power supply 22 is controlled by the control circuit 28.

The collector terminal C of the transistor T _r is connected to the inspection collector power source 24 of the inspection apparatus 20. The inspection collector power supply 24 is a voltage source whose output voltage is variable, and can adjust the voltage applied to the collector terminal C. The output voltage of the inspection collector power supply 24 is controlled by the control circuit 28.

The emitter terminal E of the transistor T _r is connected to the ground line via the emitter current instrument 26 of the inspection apparatus 20. The emitter current measuring device 26 measures the current value of the emitter current _IE that flows from the emitter terminal E to the ground line. The current value measured by the emitter current measuring instrument 26 is input to the control circuit 28.

The emitter current measuring instrument 26 has very little resistance, and the potential of the emitter terminal E can be regarded as a substantially ground potential. That is, the output voltage of the inspection gate power supply 22 corresponds to the gate / emitter voltage V _GE of the transistor T _r, the output voltage of the inspection collector power supply 22 is equivalent to the collector / emitter voltage V _CE of the transistor T _r To do.

The control circuit 28 is a control computer including a CPU, a ROM, a RAM, and the like. The control circuit 28 controls the inspection gate power supply 22 and the inspection collector power supply 24 according to the program stored in the ROM, determines the quality of the transistor _Tr , and outputs the determination result to an output means (not shown).

With reference to FIG. 2, a method for inspecting a transistor T _r by the test device 20.

In step S202, the inspection apparatus 20 measures the gate threshold voltage of the transistor _Tr at room temperature as the first gate threshold voltage _Vth1 . At the time of step S202, the transistor _{T r} is kept at room temperature. First gate threshold voltage V _th1 of the transistor T _r is the output voltage of the inspection collector power supply 24 in advance fixed to a predetermined value, gradually increases from 0V to the output voltage of the inspection gate power supply 22 The measurement is performed by obtaining the output voltage of the inspection gate power supply 22 when the emitter current _IE measured by the emitter current measuring device 24 reaches a predetermined value. In step S202, since only flow a weak current to the transistor _{T r,} the transistor _{T r} is kept at room temperature. The control circuit 28 stores the measured first gate threshold voltage V _th1 of the transistor _Tr in the RAM.

In step S204, the inspection device 20, heat is generated by flowing a large current between the collector / emitter of the transistor T _r, the transistor T _r in a high temperature state.
3 in a general transistor T _r in a state of applying a predetermined gate / emitter voltage V _GE, illustrates the relationship between the collector / emitter voltage V _CE and the collector current I _C. As shown in FIG. 3, the collector current I _C increases as the collector-emitter voltage V _CE increases. However, the collector current I _C reaches a certain level, and the collector-emitter voltage V _CE further increases _. collector current I _C also increased is kept substantially constant. Thus the scope of the collector current I _C is the collector / emitter voltage V _CE of approximately constant, that the saturation region. The magnitude of the collector current I _C in the saturation region varies depending on the magnitude of the applied to that gate / emitter voltage V _GE. Increasing the gate / emitter voltage V _GE increases the collector current I _C in the saturation region, and decreasing the gate / emitter voltage V _GE decreases the collector current I _C in the saturation region.

In the inspection apparatus 20 of the present embodiment, in step S204, the transistor _Tr is driven in the saturation region for a predetermined time to cause the transistor _Tr to generate heat. The control circuit 28 fixes the output voltage of the inspection collector power supply 24 in the saturation region, adjusts the output voltage of the gate power supply 22 so that the emitter current measured by the emitter current measuring instrument 24 becomes a predetermined value, It continues to drive the transistor T _r during the time. In step S204, the transistor _Tr generates heat and becomes high temperature.

In step S206, the inspection apparatus 20 measures the gate threshold voltage of the transistor _{Tr at} a high temperature as the second gate threshold voltage _Vth2 . At the time of step S206, the transistor _Tr is at a high temperature due to the heat generated in step S204. Control circuit 28, in the same manner as in the measurement of the first gate threshold voltage _{V th1} in step S202, measuring a second gate threshold voltage _{V th2} of the transistor _{T r.} The control circuit 28 stores the measured second gate threshold voltage V _th2 of the transistor _Tr in the RAM.

In step S208, the inspection apparatus 20 calculates the difference between the first gate threshold voltage V _th1 measured in step S202 and the second gate threshold voltage V _th2 measured in step S206, and the transistor _Tr The gate threshold voltage difference ΔV _th = V _th1 −V _th2 is acquired. The control circuit 28 stores the calculated gate threshold voltage difference ΔV _th in the RAM.

In step S210, the inspection apparatus 20, based on the gate threshold voltage difference [Delta] V _th of the transistor _{T r} calculated in step S208, it determines the quality of the transistor _{T r.}
In the inspection apparatus 20 of the present embodiment, the gate threshold voltage difference [Delta] V _th is large transistor T _r is determined to be defective as short-circuit tolerance is low, the gate threshold voltage difference [Delta] V _th small transistor T _r is A non-defective product is determined as having a high short-circuit resistance.

Figure 4 is present inventor has obtained by the test indicates a gate threshold voltage difference [Delta] V _th, the relationship between the short-circuit tolerance S _c. 4 the transistor T _r is the amount of power supplied to the transistor T _r before reaching the fracture after entering the load short-circuit state and short-circuit tolerance S _c. As best seen in FIG. 4, the larger the gate threshold voltage difference [Delta] V _th of the transistor T _r, short-circuit tolerance S _c of the transistor T _r has become low. This is considered due to the following reasons.
The transistor _Tr is composed of a plurality of IGBTs connected in parallel. If the characteristics of the individual IGBTs vary, the collector currents of the individual IGBTs when the transistor _Tr is driven also vary. Therefore, when heat is generated such a transistor T _r in step S204, the variation in calorific value at the IGBT occurs, not uniformly increase the temperature within the transistor T _r, is locally overheated. In locally superheated transistor T _r, the gate threshold voltage V _th2 at high temperature measured in step S206 becomes low, resulting gate threshold voltage difference [Delta] V _th is a large value.
On the other hand, upon entry into such a transistor T _r is the load short-circuit state, also variations occur in the collector current of each IGBT, flows locally concentrated high current in the transistor T _r, as a result the greatest current It is destroyed from the flowing IGBT. Such transistor T _r is no variation in characteristics of the individual IGBT, since the current therein destroyed earlier than the transistor T _r uniformly flows, the short-circuit tolerance is reduced.

In the inspection apparatus 20 of the present embodiment, by focusing on the relationship between the gate threshold voltage difference [Delta] V _th mentioned above and short-circuit tolerance S _c, determine the quality of the transistor T _r based on the gate threshold voltage difference [Delta] V _th To do. In step S210, the inspection apparatus 20 compares the gate threshold voltage difference ΔV _th calculated in step S208 with a predetermined reference value ΔV _thc stored in advance in the RAM of the control circuit 28, and the threshold voltage If the difference [Delta] V _th is larger than the reference value _{[Delta] V thc} determines the transistor _{T r} as defective is determined as non-defective transistors _{T r} when the threshold voltage difference [Delta] V _th is less than the reference value _{[Delta] V thc} . Then, the inspection apparatus 20 outputs the result of the quality determination of the transistor T _r.

By using the inspection apparatus 20 of the present embodiment as described above, it is possible to determine the quality regarding short-circuit capacity of the transistor T _r appropriately. Without destroying the transistor T _r, it is possible to discover a low short-circuit tolerance transistor T _r as a defective product.

In the inspection apparatus 20 of the present embodiment, the measurement of the gate threshold voltage _{V th} at step S202 or step S206, since only flow a small current through the transistor _{T r,} the transistor _{T r} hardly heat. Therefore, although the transistor _{T r} Step S204 to the temperature rise by heat generation, while measuring the gate threshold voltage _{V th} at step S202 or step S206, the temperature rise due to heat generation of the transistor _{T r} is little. Therefore, it is possible to appropriately evaluate the gate threshold voltage difference ΔV _th and accurately determine whether the transistor _Tr is good or bad.

In the inspection apparatus 20 of the present embodiment evaluates the gate threshold voltage difference [Delta] V _th before and after the heating of the transistor T _r, is performed quality determination of the transistor T _r based on the evaluation result. The gate threshold voltage V _th of the transistor T _r, unlike other electrical characteristics, shows a tendency to constantly reduce the temperature of the transistor increases. Therefore, the inspection apparatus 20 of the present embodiment, for the transistor T _r what specification, without significantly altering the criteria for inspection, inspection can be performed with less effort.

Note and specific values of the collector / emitter voltage _{V CE} and the emitter current _{I E} in the measurement of the gate threshold voltage _{V th} at step S202 or step S206, the collector / emitter of the heat generation of the transistor _{T r} in step S204 specific numerical values between the voltage V _CE, the collector current I _C and heating time t may, depending on the size and heat dissipation of the transistor T _r to be inspected, appropriately modified.

Note that this embodiment has been described a case where the transistor T _r and a high temperature state by a predetermined time drives the transistor T _r in the saturation region in step S204, instead of a predetermined time drives the transistor T _r, for example, a transistor T _r keep in preparing a temperature sensor for monitoring the temperature of the transistor T _r to a temperature of the transistor T _r detected by the temperature sensor reaches a predetermined temperature may be driven in a saturation region.

Note that this embodiment has described the case of inspecting a transistor T _r is a discrete device that integrates a plurality of IGBT, transistor to be inspected is not limited thereto. The transistor to be inspected by the inspection apparatus 20 of the present embodiment may be, for example, a discrete device in which a plurality of MOSFETs are integrated.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

Figure 1 shows a circuit diagram of a state in which setting the transistor T _r to be inspected in the inspection apparatus 20. Figure 2 is a diagram showing a test flow of the transistor T _r by the test device 20. Figure 3 is a diagram showing the relationship between the collector / emitter voltage V _CE and the collector current I _C of the transistor T _r. Figure 4 is a diagram showing the relationship between short-circuit tolerance S _c and the gate threshold voltage difference [Delta] V _th. Figure 5 is a graph showing the temperature dependence of the relationship between the transistor T _r the collector / emitter voltage V _CE and the collector current I _C. 6 is a diagram showing the temperature dependence of the gate threshold voltage V _th of the transistor T _r.

Explanation of symbols

20: Inspection device 22: Gate power supply for inspection 24: Collector power supply for inspection 26: Emitter current measuring instrument 28: Control circuit

Claims (2)

A method for inspecting a transistor comprising:
Measuring a gate threshold voltage of the transistor before generating heat to determine a first gate threshold voltage;
Passing a current of a predetermined magnitude between the collector / emitter or the source / drain of the transistor over a predetermined time, and heating the transistor;
Measuring a gate threshold voltage of the transistor that has become high temperature due to heat generation to determine a second gate threshold voltage;
Calculating a gate threshold voltage difference from the first gate threshold voltage and the second gate threshold voltage;
A transistor inspection method comprising a step of determining whether the transistor is good or bad based on the gate threshold voltage difference. A device for inspecting a transistor,
Means for determining a first gate threshold voltage by measuring a gate threshold voltage of the transistor before heat generation ;
Means for causing the transistor to generate heat by flowing a current of a predetermined magnitude between the collector / emitter or the source / drain of the transistor over a predetermined time;
Means for determining a second gate threshold voltage by measuring a gate threshold voltage of the transistor which has been heated to a high temperature;
Means for calculating a gate threshold voltage difference from the first gate threshold voltage and the second gate threshold voltage;
A transistor inspection apparatus comprising means for determining whether or not the transistor is good based on the gate threshold voltage difference.

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