Method for inspecting semiconductor device

Abstract

To provide a method for inspecting a semiconductor device, capable of determining whether or not a failure cause is surface discharge without increasing the number of steps other than the DS voltage resistance inspection of a semiconductor device including a MOS transistor when a failure occurs in the DS voltage resistance inspection.SOLUTION: A method for inspecting a semiconductor device comprises: continuously performing the same voltage application step when an applied voltage is reduced to a voltage value lower than a rated voltage in a DS voltage resistance inspection for applying voltage to a drain electrode of a MOS transistor in an off state to boost the applied voltage to the rated voltage; and determining whether or not a failure cause is surface discharge, on the basis of voltage values when the applied voltage is reduced in the middle of voltage application steps when setting the voltage values in the first, second, and third voltage application steps to Vds1, Vds2, and Vds3, respectively.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a method for testing a semiconductor device. [Background technology]

[0002] Conventionally, a method for inspecting the electrical characteristics of a semiconductor device having a MOS transistor such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) has been proposed, for example, as described in Patent Document 1. The inspection method described in Patent Document 1 measures the collector current generated when a gate voltage is applied, and calculates the slope of the collector current with respect to the gate voltage. In this inspection method, the slope of the collector current with respect to the gate voltage is calculated by a factor of 10 -7 The low current section and 10 -5 ~10 -3 If the difference does not coincide with the intermediate current section of the level, it is determined that a switching failure has occurred. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-23964 A Summary of the Invention [Problem to be solved by the invention]

[0004] In addition to the switching characteristics described above, this type of semiconductor device is also subjected to a test of the withstand voltage between the source and drain (hereinafter referred to as a "DS withstand voltage test"). In a DS withstand voltage test, a voltage is applied to the drain electrode of a MOS transistor in an off state, the applied voltage is increased toward the rated voltage of the semiconductor device, and it is measured whether or not the applied voltage exceeds the rated voltage. In a DS withstand voltage test, if the MOS transistor of the semiconductor device is normal, the voltage applied to the drain electrode exceeds the rated voltage, whereas if a defect occurs, the applied voltage is reduced to a voltage below the rated voltage during the test.

[0005] In order to improve the quality of semiconductor devices and the yield in manufacturing, it is important to determine the cause and location of defects when defects occur in DS voltage test. Specifically, when defects occur in DS voltage test, the causes are roughly divided into two categories: short circuit or unstable voltage between source and drain, and creeping discharge on the surface of the drain electrode. In the former case, some abnormality is thought to have occurred in the transistor area, and in the latter case, some abnormality is thought to have occurred in the voltage holding area or the drain electrode surface. Since the measures that can be taken from the viewpoint of improving the quality of semiconductor devices are different, it is important to distinguish between these two.

[0006] Conventional methods for determining whether creeping discharge has occurred during a DS withstand voltage test include visually checking whether there are discharge marks on the surface of the drain electrode after the test, or using an optical sensor to check whether the surface of the drain electrode emits light during the test.

[0007] However, the former method requires an additional inspection process of visually checking the appearance of the semiconductor device after the DS voltage test, and the manufacturing cost of the semiconductor device increases due to the increased man-hours. Also, visual appearance inspection may lead to oversights. The latter method requires a shielding member such as an outer wall to block external light during the DS voltage test, and a light sensor to detect light caused by creeping discharge must be placed near the semiconductor device, which increases the inspection cost.

[0008] In view of the above, an object of the present invention is to make it possible, when a defect occurs in a DS withstand voltage test of a semiconductor device having a MOS transistor, to determine whether or not the cause of the defect is creeping discharge at low cost, without increasing the number of steps other than the DS withstand voltage test. [Means for solving the problem]

[0009] In order to achieve the above object, the method for inspecting a semiconductor device according to claim 1 is a method for inspecting a semiconductor device (1) having a MOS transistor, comprising: performing a first voltage application step of applying a voltage to a drain electrode (12) of the MOS transistor in an off state and raising the applied voltage toward a rated voltage of the MOS transistor; and during the first voltage application step, increasing the applied voltage to a first voltage value (V ds1 ), a second voltage application step is performed in which the applied voltage is continuously increased toward the rated voltage, and during the second voltage application step, the applied voltage is increased to a second voltage value (V ds2 ), a third voltage application step is performed in which the applied voltage is continuously increased toward the rated voltage, and during the third voltage application step, the applied voltage is increased to a third voltage value (V ds3 ), determining whether or not the cause of the defect is creeping discharge based on the first voltage value, the second voltage value, and the third voltage value.

[0010] In the semiconductor device inspection method, if the applied voltage drops to a first voltage value smaller than the rated voltage during the first voltage application process to raise the voltage toward the rated voltage of the MOS transistor, the drain voltage is applied a second time. If the applied voltage drops to a second voltage value smaller than the rated voltage during the second voltage application process, the drain voltage is applied a third time. In other words, if a defect occurs in the first voltage application process where the voltage drops to a value smaller than the rated voltage, the second voltage application process is continued, and if a similar defect occurs in the second voltage application process, the third voltage application process is continued. In other words, if a defect occurs during voltage application, at least three voltage application processes are performed, the voltage value that dropped during each voltage application process is obtained, and based on these voltage values, it is determined whether the cause of the defect is creeping discharge. As a result, even if a defect occurs in the drain voltage application process, it is possible to determine whether the cause of the defect is creeping discharge at low cost without substantially increasing the number of inspection processes other than the application process.

[0013] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram showing an overview of a semiconductor device inspection method according to an embodiment; [Diagram 2] FIG. 2 is a top view layout diagram showing an example of a semiconductor chip. [Diagram 3] FIG. 2 is a diagram showing a circuit configuration in testing a semiconductor device according to an embodiment; [Figure 4] FIG. 13 is a diagram showing an example of a Vds-Ids characteristic in a normal state in a DS withstand voltage test. [Diagram 5] FIG. 13 is a diagram showing an example of a Vds-Ids characteristic when an abnormality occurs in a DS withstand voltage test and a short circuit occurs. [Figure 6]FIG. 13 is a diagram showing an example of a Vds-Ids characteristic when an abnormality occurs in a DS withstand voltage test and the withstand voltage is unstable. [Figure 7] FIG. 13 is a diagram showing another example of the Vds-Ids characteristics when an abnormality occurs in the DS withstand voltage test and the withstand voltage is unstable. [Figure 8] FIG. 13 is a diagram showing an example of a Vds-Ids characteristic when an abnormality occurs in a DS withstand voltage test and a creeping discharge occurs. [Figure 9] 4 is a flowchart showing processing steps in a semiconductor device inspection method according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0016] (Embodiment) The semiconductor device 1 and the method for inspecting electrical characteristics according to the embodiment will be described.

[0017] [Semiconductor Device] First, the semiconductor device 1 will be described with reference to FIGS.

[0018] The semiconductor device 1 is, for example, a vertical MOSFET, and is a semiconductor chip manufactured by processing a single semiconductor wafer whose main material is Si (silicon) or SiC (silicon carbide) by a known semiconductor process. As shown in Fig. 1, for example, the semiconductor device 1 has a structure in which a first electrode 12 is formed on one surface of a substrate 11 mainly made of Si or SiC, and a second electrode 13, a third electrode 14, and a plurality of small signal terminals 15 are formed on the opposite surface. The first electrode 12, the second electrode 13, and the third electrode 14 are a drain electrode, a source electrode, and a gate electrode, respectively.

[0019] 2, the semiconductor device 1 has a second electrode 13, a third electrode 14, and a plurality of small signal terminals 15 formed on the other surface of the substrate 11 in a top view, and a first electrode 12 formed on the entire surface of the opposite side (not shown). In the semiconductor device 1, for example, the second electrode 13 forms a transistor region that serves as a current path, and the third electrode 14 and the plurality of small signal terminals 15 form a small signal region through which a current signal smaller than that of the second electrode 13 is transmitted. In the semiconductor device 1, for example, a withstand voltage holding region such as a guard ring (not shown) is formed on the outer periphery surrounding the second electrode 13 and the third electrode 14. The arrangement of the third electrode 14 and the plurality of small signal terminals 15 and the number of the small signal terminals 15 are not limited to the example of FIG. 2, and may be changed as appropriate.

[0020] [Inspection equipment] Next, an example of an inspection device 3 that inspects the electrical characteristics of the semiconductor device 1 will be described with reference to FIGS.

[0021] The inspection method for the semiconductor device 1 according to the embodiment is a DS withstand voltage inspection, which is performed by setting the semiconductor device 1 having a MOS transistor on a stage 2 and applying a voltage between a first electrode 12 and a second electrode 13 of the semiconductor device 1. For example, the semiconductor device 1 is placed in a state in which the first electrode 12 is in contact with the conductive stage 2, and a voltage is applied to the first electrode 12 (drain electrode) via the stage 2 by an inspection device 3 having a plurality of terminals 31.

[0022] The stage 2 may be electrically connected to the first electrode 12 of the set semiconductor device 1 and may be configured to apply a voltage to the first electrode 12 via the stage 2, and is not limited to an example in which the entire stage 2 is made of a conductive material. For example, the stage 2 may be configured such that only the portion that contacts the semiconductor device 1 has conductivity, and the configuration may be changed as appropriate. The stage 2 may be a part of the inspection device 3, or may be a component separate and independent from the inspection device 3.

[0023] The inspection device 3 includes, for example, a plurality of terminals 31, a potential fixing section 32, a voltage application section 33, a voltage measurement section , a current measurement section 35, and an inspection control section as shown in FIG.

[0024] The multiple terminals 31 are in contact with the electrodes 12 to 14 of the semiconductor device 1 and are used to apply a voltage, detect a current, or fix a potential. The multiple terminals 31 are, for example, individually fixed to a single support head (not shown) and configured to be movable by a moving mechanism (not shown).

[0025] The potential fixing unit 32 is connected to, for example, the third electrode 14 (gate electrode) of the semiconductor device 1 via the terminal 31. The potential fixing unit 32 is used in a DS withstand voltage test to fix the potential of the gate electrode to a predetermined reference potential such as 0 V, and control the MOS transistor of the semiconductor device 1 to an off state.

[0026] The voltage application unit 33 is connected, for example, to the first electrode 12 (drain electrode) of the semiconductor device 1 via the terminal 31 and the stage 2. The voltage application unit 33 is a power source that applies a voltage in a predetermined range (such as, but not limited to, several hundred to 2000 V) to the drain electrode in, for example, a DS withstand voltage test.

[0027] The voltage measurement unit 34 is, for example, a voltmeter connected to the first electrode 12 (drain electrode) and the second electrode (source electrode) of the semiconductor device 1 via the terminals 31, etc. In the DS withstand voltage test, the voltage measurement unit 34 measures the drain voltage and outputs the measurement result to the test control unit 36.

[0028] The current measurement unit 35 is, for example, an ammeter connected to the second electrode 13 (source electrode) of the semiconductor device 1 via the terminal 31. The current measurement unit 35 measures the drain current in the DS withstand voltage test, and outputs the measurement result to the test control unit 36.

[0029] The inspection control unit 36 ​​controls, for example, the operation of the potential fixing unit 32, the voltage application unit 33, the voltage measurement unit 34, and the current measurement unit 35, and the contact between the multiple terminals 31 and the semiconductor device 1. The inspection control unit 36 ​​is, for example, an electronic control unit in which a CPU, a ROM, a RAM, an I / O, and the like are mounted on a circuit board. The inspection control unit 36 ​​performs a DS withstand voltage test in which, while turning off the MOS transistor of the semiconductor device 1, a voltage is applied to the drain electrode, and the applied voltage is increased to a rated voltage, or a voltage equal to or higher than the rated voltage is applied to the drain electrode. When the voltage measurement unit 34 detects that the applied voltage has dropped to a voltage value lower than the rated voltage during the voltage application process in the DS withstand voltage test, the inspection control unit 36 ​​performs the same voltage application process again while continuing the voltage application to the drain electrode. Then, when the inspection control unit 36 ​​detects, for example, a drop in the applied voltage, it determines whether or not the cause of the defect is creeping discharge based on the voltage value at the time of the drop. This will be described in detail later.

[0030] That is, the inspection device 3 has, for example, a circuit configuration as shown in FIG. 3, and the inspection control unit 36 ​​controls the voltage application to the drain electrode by the voltage application unit 33, which is a power source, based on the measurement results of the voltage measurement unit 34 connected between the drain and source.

[0031] The basic configuration of the inspection device 3 that performs the DS withstand voltage test on the semiconductor device 1 has been described above.

[0032] [Electrical characteristics of semiconductor device] Next, examples of the electrical characteristics of the semiconductor device 1 in a DS withstand voltage test, both in a normal state and in a defective state, will be described with reference to FIGS.

[0033] First, when the semiconductor device 1 is normal in the DS withstand voltage test, for example, as shown in FIG. ds1 is the rated voltage V r is larger than the prescribed drain current I ds (For example, several hundred μA to several mA) occurs.

[0034] In the conventional DS withstand voltage test, the rated voltage V r If the above drain voltage can be applied, it is judged as normal, and if not, it is judged as defective and the process ends. Causes of defects in the semiconductor device 1 include, for example, a withstand voltage defect such as a short circuit between the drain and source, or the occurrence of creeping discharge on the surface of the drain electrode. When the defect is caused by a withstand voltage defect, some abnormality has occurred in the transistor region of the semiconductor device 1, and when the defect is caused by creeping discharge, some abnormality has occurred in the withstand voltage holding region of the semiconductor device 1, or contamination of the electrode surface has occurred. In order to improve the quality of the semiconductor device 1 and the yield in manufacturing, it is important to determine the cause of a defect when a defect occurs in the DS withstand voltage test.

[0035] Conventionally, methods for determining whether or not a defect in a DS voltage test is caused by creepage discharge include performing a visual inspection of the drain electrode after the DS voltage test to check for discharge marks, or using an optical sensor to detect light emission near the drain electrode during the test.

[0036] However, the former method requires an additional visual inspection after the DS withstand voltage test, which increases the number of steps and the manufacturing cost, and there is a risk of overlooking something by visual inspection. The latter method requires that the DS withstand voltage test be performed in a state where it is not exposed to external light, which requires a shielding member such as an external wall that blocks external light, and the optical sensor must be placed near the drain electrode of the semiconductor device 1. For this reason, the latter method increases the cost of the DS withstand voltage test itself.

[0037] As a result of intensive research, the inventors have found that the DS withstand voltage test can easily determine the cause of a defect. Specifically, in the past, the DS withstand voltage test was terminated when a defect occurred, but in the present invention, the DS withstand voltage test is continued even if a defect occurs, and the applied voltage is increased to the rated voltage V rWhen the voltage drops to a value smaller than Vr, the voltage value is recorded and this process is repeated at least twice. At this time, the voltage application to the drain electrode is continued without being stopped, and the process of increasing the voltage toward the rated voltage Vr is executed again. Note that since the voltage application process in this DS withstand voltage test is performed in a short time of less than one second, for example, 10 milliseconds, even if the voltage application process is repeated twice in succession, i.e., a total of three times, the test time does not increase significantly.

[0038] The first voltage application process to the drain electrode is the first, the same voltage application process that is continued when a defect occurs in the first voltage application process is the second voltage application process, and the same voltage application process that is continued when a defect occurs in the first voltage application process is the third voltage application process. If the applied voltage exceeds the rated voltage V r When the drain voltage drops to a value smaller than V ds1 , V ds2 , V ds3 As a result of intensive research by the present inventors, it was found that the cause of the defect was the V ds1 , V ds2 , V ds3 The trends were found to be different.

[0039] When the cause of the failure in the DS withstand voltage test is a short circuit between the drain and source, the semiconductor device 1 is, for example, as shown in FIG. ds1 , V ds2 , V ds3 V becomes almost constant ds -I ds The characteristics were shown.

[0040] When the cause of the failure in the DS withstand voltage test is instability of the withstand voltage between the drain and the source, the semiconductor device 1 is, for example, V ds1 , V ds2 , V ds3 Gradually decreases or increases V ds -I ds The characteristics were shown.

[0041] When the cause of the defect in the DS withstand voltage test is creeping discharge, the semiconductor device 1 is, for example, as shown by the arrow in FIG. ds2 V ds1 Larger than V ds3 V ds2 V becomes smaller than ds -I ds In other words, if creeping discharge occurs during a DS withstand voltage test, V ds2 >V ds1 , V ds2 >V ds3 In order to satisfy the condition, V ds There was a tendency for the value to increase or decrease.

[0042] In other words, if a defect occurs in the DS withstand voltage test, voltage is continuously applied and the V ds By utilizing the difference in tendency between the two, it becomes possible to determine whether the cause of the defect is creeping discharge or not. This determination of the cause of the defect in the DS withstand voltage test is particularly effective when the semiconductor device 1 is mainly made of SiC, because its temperature characteristics are lower than when it is mainly made of Si. This is because SiC has an extremely small temperature dependency compared to Si, and the V ds The change in V when voltage is applied is small. ds This is because it allows for a more accurate understanding of fluctuations in the

[0043] [Testing method] Next, an example of a control flow in the method for inspecting the semiconductor device 1 according to the embodiment will be described with reference to FIG.

[0044] In this inspection method, for example, after the semiconductor device 1 is set on the stage 2, multiple terminals 31 of the inspection device 3 are brought into contact with the electrodes 12-14 of the semiconductor device 1, and application of a drain voltage is started (step S1). In step S1, the gate electrode is fixed to a predetermined potential, such as 0V, by the potential fixing unit 32, and while the MOS transistor of the semiconductor device 1 is maintained in an off state, voltage application to the drain electrode is started. The process of applying the drain voltage in step S1 corresponds to the above-mentioned "first voltage application process."

[0045] In the next step S2, for example, the inspection control unit 36 ​​applies the applied voltage V ds1 is the rated voltage V r If the determination is affirmative, the process proceeds to step S4. On the other hand, if the determination is negative in step S2, that is, if the applied voltage V ds1 is the rated voltage V r If it exceeds this limit, for example, the inspection control unit 36 ​​determines in step S3 that the semiconductor device 1 is normal, and ends the process.

[0046] In step S4, for example, the inspection control unit 36 ​​continues the drain voltage application process of step S1 and executes the second voltage application process. In step S4, the inspection control unit 36 ​​determines whether the drain voltage is equal to or higher than the rated voltage V r Even if the voltage value drops to a value smaller than the first voltage application step, the second voltage application step is continued and the third voltage application step is executed.

[0047] In step S5, the inspection control unit 36 ​​calculates, for example, V ds1 , V ds2 , V ds3 But, V ds2 >V ds1 , and V ds2 >V ds3If the result of the determination in step S5 is affirmative, the inspection control unit 36 ​​determines in step S6 that the cause of the defect in the DS withstand voltage test is creeping discharge, and ends the process. On the other hand, if the result of the determination in step S5 is negative, the inspection control unit 36 ​​determines in step S7 that the cause of the defect in the DS withstand voltage test is defective withstand voltage, and ends the process.

[0048] In the above, in step S5, V ds2 >V ds1 , and V ds2 >V ds3 However, the present invention is not limited to this. For example, in step S5, it is sufficient to determine whether Vds in the first to third voltage application steps tends to increase or decrease. ds2 -V ds1 >0 and V ds2 -V ds3 It may be a determination as to whether the condition of >0 is satisfied, or other condition settings may be used.

[0049] In this way, according to the method for testing the semiconductor device 1 according to the embodiment, in the DS withstand voltage test, a voltage is applied to the drain electrode while the MOS transistor of the semiconductor device 1 is maintained in an off state, and the rated voltage V r Check whether a voltage equal to or greater than the rated voltage V can be applied. r When a defect occurs in which the voltage drops to a value smaller than the first voltage value V, the second voltage application step is similarly performed, and when a similar defect occurs in the second voltage application step, the third voltage application step is similarly performed. After the third voltage application step is completed, the voltage at the time of the drop in each voltage application step is set to the first voltage value V. ds1 , a second voltage value V ds2 , the third voltage value V ds3 Based on the magnitude relationship between these, it is determined whether the cause of the defect is a creeping discharge or a voltage resistance defect.

[0050] As a result, if a defect occurs during a DS withstand voltage test, no additional steps are required other than the step of applying the drain voltage, resulting in an inexpensive method of testing electrical characteristics that can determine whether or not the cause of the defect is surface discharge.

[0051] (Other embodiments) The semiconductor device inspection method shown in the above embodiment is an example of the present invention, and is not limited to the above embodiments, but may be modified as appropriate within the scope of the claims. [Explanation of symbols]

[0053] 1 Semiconductor device 12 Drain electrode V ds1 First Voltage Value V ds2 Second Voltage Value V ds3 The third voltage value

Claims

1. A method for testing a semiconductor device (1) having a MOS transistor, comprising the steps of: A first voltage application step is performed in which a voltage is applied to the drain electrode (12) of the MOS transistor in an off state, and the applied voltage is increased toward a rated voltage of the MOS transistor; During the first voltage application step, the applied voltage is changed to a first voltage value (V ｄｓ１ ), performing a second voltage application step of continuously increasing the applied voltage toward the rated voltage; During the second voltage application step, the applied voltage is changed to a second voltage value (V ｄｓ２ ), performing a third voltage application step of continuously increasing the applied voltage toward the rated voltage; During the third voltage application step, the applied voltage is changed to a third voltage value (V ｄｓ３ ), determining whether or not the cause of the defect is creeping discharge based on the first voltage value, the second voltage value, and the third voltage value.

2. 2. The semiconductor device inspection method according to claim 1, wherein, in determining the cause of the defect, when the second voltage value is greater than the first voltage value and the third voltage value is smaller than the second voltage value, it is determined that the cause of the defect is creeping discharge.

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