JP2009074850A - Inspection method of semiconductor integrated circuit and semiconductor integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method of a semiconductor integrated circuit for inspecting a circuit having various constitutions without increasing terminals required for implementing an inspection. <P>SOLUTION: Switch circuits 4, 6 and a constant current source 7 are provided in an operational amplifier 1. A constant current source 5 for supplying a constant current during a normal operation is switched by a signal from an external apparatus through a control signal terminal 8. When a power supply voltage of the operational amplifier 1 is set to a normal voltage level VB, a slew rate is measured in a state that a micro constant current is supplied. When the power supply voltage is set to an inspection voltage VT, the constant current during the normal operation is supplied in a state that a voltage corresponding to the inspection voltage VT is applied across a phase compensation capacitor 14. The slew rate is measured again on the same condition as the initial measurement. The measured results before and after an application of the inspection voltage VT are compared, and the quality is determined. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for inspecting a semiconductor integrated circuit including a constant current source for supplying a constant current for normal operation to an internal circuit, and a semiconductor integrated circuit having a configuration corresponding to the method.

A semiconductor integrated circuit is subjected to an inspection for determining a defective product after completion, so-called screening, and only those that are determined to be non-defective products are shipped. For example, since an operational amplifier generally includes a capacitor for phase compensation, it is inspected whether or not a leak current is detected after applying a voltage higher than a power supply voltage during normal operation to both ends of the capacitor.
In order to perform such inspection, it is necessary to prepare inspection terminals connected to both ends of the device to be inspected, such as the capacitor, in the semiconductor integrated circuit, and there is a problem that the number of terminals increases. Further, Patent Document 1 discloses a method of measuring a leakage current by applying a high voltage for inspection to a phase compensation capacitor via an output terminal of an operational amplifier.
JP 2006-214976 A

  However, in the method disclosed in Patent Document 1, when the operational amplifier forms a part of a large-scale circuit, if the operational amplifier is not arranged at the final output stage of the circuit, a high voltage for inspection is applied. It cannot be applied. Moreover, it is a premise that one end of the device to be inspected such as the capacitor is connected in a state where a voltage can be directly applied from the output terminal, and a circuit configuration that can be inspected is limited.

  The present invention has been made in view of the above circumstances, and its purpose is to inspect a semiconductor integrated circuit capable of inspecting circuits having various configurations without increasing the number of terminals necessary for carrying out the inspection as much as possible. A method and a semiconductor integrated circuit provided with a configuration corresponding to the method.

  According to the inspection method of the first aspect, the semiconductor integrated circuit is configured to be settable from the outside to supply a minute constant current instead of the constant current for normal operation supplied to the internal circuit. Then, when the power supply voltage for operation of the semiconductor integrated circuit is set to a normal voltage level and the characteristic inspection is performed in a state where a small constant current is supplied (first step), the power supply voltage for operation is then set to a high voltage for inspection. When the voltage is set, a state corresponding to the voltage for inspection is applied to both ends of the inspection target portion in the internal circuit, and a constant current for normal operation is supplied (second step). Then, the characteristic inspection is performed again under the same conditions as the first step (third step), and the pass / fail judgment is made by comparing the inspection result of the first step with the inspection result of the third step (fourth step).

  That is, in order to inspect a circuit, it is necessary to determine whether characteristics have changed before and after applying a high voltage to a part to be inspected by supplying a minute current and measuring it. Therefore, in the present invention, the semiconductor integrated circuit is configured in advance so as to supply a minute current for inspection. Further, the high voltage for inspection is supplied by setting the power supply voltage to a level higher than normal, and at that time, a voltage corresponding to the inspection voltage is applied to the internal inspection target portion ( This setting is easy because the power supply voltage itself is at the inspection level).

  Then, (1) characteristic inspection with normal voltage and minute constant current, (2) application of inspection voltage, operation state with constant current for normal operation, and (3) characteristic inspection again with normal voltage and minute constant current. By comparing the inspection results of (1) and (3), it can be determined whether or not the characteristics have changed due to the application of the inspection voltage of (2). Therefore, it is only necessary to add a terminal for switching the internal constant current value as an inspection terminal, and a small constant current for inspection by connecting an inspection circuit or device outside the semiconductor integrated circuit. As compared with the case of supplying the above, the influence on the property inspection can be eliminated. In addition, since the power supply voltage is set to a voltage level for inspection, there are less restrictions when a high voltage is applied to the inspection target portion.

  According to another aspect of the semiconductor integrated circuit of the present invention, in the case where the constant current source for supplying a constant current for normal operation to the internal circuit is built in, the characteristics of the internal circuit are inspected instead of the constant current for normal operation. The setting for supplying a small constant current is made possible from the outside. Therefore, it is possible to provide a semiconductor integrated circuit having a necessary configuration as a premise for carrying out the inspection method of claim 1.

(First embodiment)
A first embodiment in which the present invention is applied to an operational amplifier will be described below with reference to FIG. FIG. 1 shows a configuration of an operational amplifier (semiconductor integrated circuit) 1. Emitters of PNP transistors 3a to 3e are connected to the power supply line 2 of the operational amplifier 1, and the transistor 3a and the transistors 3b to 3e constitute a mirror pair. The collectors of the transistors 3a to which these bases are connected in common are connected to the ground via the switch circuit 4 and the normal constant current source 5. A parallel circuit of the switch circuit 6 and the constant current source for inspection 7 is connected to the switch circuit 4 and the constant current source 5 for normal use.

  The normal constant current source 5 supplies a constant current (bias current) for normal operation to each part of the operational amplifier 1, and the inspection constant current source 7 is used for inspection when performing a characteristic inspection on the operational amplifier 1. Supply a small constant current. The minute constant current is set, for example, to be smaller by one digit or more than the constant current for normal operation. The two switch circuits 4 and 6 are controlled so that one of them is turned on according to the level (high, low) of the control signal given from the outside via the control signal terminal 8.

A differential amplifier circuit comprising PNP transistors 8a and 8b and NPN transistors 9a and 9b is connected between the collector of the transistor 3b and the ground, and the bases of the transistors 8a and 8b are connected to the inverting input terminal Vin of the operational amplifier 1. -, Non-inverting input terminal Vin +.
The collector of the transistor 3c is connected to the emitter of the PNP transistor 10, the collector of the transistor 10 is connected to the ground, and the base is connected to the collector of the transistor 9b. The collector of the transistor 3d is connected to the collector of the NPN transistor 11. The emitter of the transistor 11 is connected to the ground via the resistance element 12, and the base is connected to the emitter of the transistor 10. These constitute the intermediate amplification stage of the operational amplifier 1.

  The collector of the transistor 3e is connected to the collector of the NPN transistor 13. The emitter of the transistor 13 is connected to the ground, and the base is connected to the emitter of the transistor 12. These constitute the output amplification stage of the operational amplifier 1, and the collector of the transistor 13 is the output terminal Vout of the operational amplifier 1. A phase compensation capacitor 14 is connected between the output terminal Vout and the collector of the transistor 8b.

Next, the operation of this embodiment will be described. In the following, a procedure for performing a leakage current test of the phase compensation capacitor (test target part, test target element) 14, which is a kind of screening performed before shipping the circuit including the completed operational amplifier 1 or the operational amplifier 1, will be described. .
<First step>
The power supply voltage of the operational amplifier 1 is a voltage during normal operation (for example, VB = 14 V). For example, a low level signal is given to the control signal terminal 8 to turn on the switch circuit 6 as shown in FIG. 1A and supply a small constant current for inspection to the internal circuit of the operational amplifier 1. In this state, for example, the electrical characteristics of the operational amplifier 1 such as slew rate, transmission delay time between input / output signals, and settling time are measured.

<Second step>
Next, the power supply voltage of the operational amplifier 1 is set to a high voltage for inspection (screening voltage, for example, VT = 35V), a high level signal is given to the control signal terminal 8, and as shown in FIG. The switch circuit 4 side is turned ON, and a constant current during normal operation is supplied to the internal circuit of the operational amplifier 1. Then, the potential of the non-inverting input terminal Vin + of the operational amplifier 1 is set to be higher than the potential of the inverting input terminal Vin−, so that the level of the output terminal Vout is fixed to a high level. In this case, it is desirable that the potential of the inverting input terminal is close to the GND level. By setting the potential in this way, a voltage corresponding to the screening voltage VT is applied to both ends of the capacitor 14.

<Third step>
Then, as in the first step, the power supply voltage of the operational amplifier 1 is set to VB = 14 V, a small constant current for inspection is supplied to the internal circuit, and the same electrical characteristics as in the first step are measured.
<4th step>
The measurement result of the first step is compared with the measurement result of the third step. As a result of the comparison, if there is a change in characteristics, it can be determined that a leakage current has occurred in the capacitor 14 as a result of applying the screening voltage VT (defect determination).

Here, an example of determining a minute constant current value is shown. The minute constant current value is determined in consideration of, for example, the measurement accuracy of electrical characteristics and the leak current value to be rejected as a defective product by inspection. For example, when the capacitance of the capacitor 14 is 20 pF and the leak current threshold value (standard) is 0.1 μA, when the minute current value for inspection is 0.5 μA, the slew rate Sr is
Sr = I / C × A
(I is the current flowing through the differential pair, C is the capacitance of the capacitor 14, and A is a constant specific to the operational amplifier 1). If the leakage current of the capacitor 14 is “0” (A = 1),
Sr = (0.5 μA) / (20 pF) = 0.025 V / μS
It becomes. On the other hand, if a leak current of 0.1 μA is generated in the capacitor 14, the slew rate Sr is reduced by 20%. That is,
Sr = (0.4 μA) / (20 pF) = 0.02 V / μS
It becomes. Such fluctuation of the slew rate can be sufficiently measured by a very general inspection device (such as an oscilloscope).

  If there are other circuits that can be similarly inspected, the control signal supplied to the control signal terminal 8 may be supplied to them. In the case where the transmission delay time or settling time of the operational amplifier 1 is measured and inspected, the occurrence of leak may be determined when the transmission delay time or settling time becomes longer than a predetermined time after application of the screening voltage VT. .

  As described above, according to the present embodiment, the switching circuits 4 and 6 and the constant current source for inspection 7 are provided in the operational amplifier 1, and switching to the normal constant current source 5 that supplies a constant current during normal operation is performed. It was configured to be possible from the outside via the control signal terminal 8. Then, the power supply voltage of the operational amplifier 1 is set to the normal voltage level VB, the slew rate is measured in a state where a minute constant current is supplied, and then the power supply voltage is set to the inspection voltage VT. A constant current for normal operation is supplied in a state in which a voltage corresponding to the inspection voltage VT is applied to both ends of. Then, the slew rate was measured again under the same conditions as the first, and the measurement results before and after application of the test voltage VT were compared to determine whether the operational amplifier 1 was good or bad.

That is, in order to perform a leakage current inspection (good / bad determination) of the operational amplifier 1, a high voltage is applied to both ends of the internal capacitor 14, and a small current is supplied to determine whether the electrical characteristics have changed before and after the application. Need to be measured and judged. In this embodiment, a constant current source for inspection 7 is provided in the operational amplifier 1 and the switching circuits 4 and 6 are switched from the outside so that a small constant current for inspection can be supplied. Therefore, a control signal terminal is used as an external terminal for inspection. Just add 8.
Further, compared to the case where an inspection circuit or device is connected outside the operational amplifier 1 to supply a small constant current for inspection, the influence of these on the characteristic inspection can be eliminated. In addition, since the power supply voltage of the operational amplifier 1 is set to the inspection voltage VT at the time of inspection, restrictions on applying a high voltage to a portion to be inspected such as the internal capacitor 14 become smaller.

(Second embodiment)
FIG. 2 shows a second embodiment of the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals and the description thereof will be omitted. In the second embodiment, for example, in a semiconductor integrated circuit 22 on which a plurality of operational amplifiers 21a to 21c are mounted, the same inspection method as that of the first embodiment is executed on the operational amplifiers 21a to 21c. A configuration with shared use is shown.

That is, the constant current source circuit 23 switches and supplies both the constant current for normal operation and the minute constant current for inspection to the operational amplifiers 21a to 21c simultaneously. A series circuit of a PNP transistor 24 and resistance elements 25 and 26 is connected between the power supply and the ground, and an emitter and a collector of a PNP transistor 27 are connected between the base of the transistor 24 and the ground. The base of the transistor 27 is connected to the collector of the transistor 24. An N channel MOSFET 28 is connected in parallel to the resistance element 26, and the gate of the FET 28 is connected to a control signal terminal 29 corresponding to the control signal terminal 8 of the first embodiment.
The base of the transistor 24 is wired to each of the operational amplifiers 21a to 21c, and is connected to the base of a PNP transistor (corresponding to the transistors 3b to 3e in FIG. Has been.

  Next, the operation of the second embodiment will be described. When each of the operational amplifiers 21a to 21c is normally operated, a high level signal is given to the control signal terminal 29 to turn on the FET 28, and the resistance element 26 is short-circuited. Then, since the collector resistance of the transistor 24 is substantially in the low resistance state of only the resistance element 25, the base current of the transistor 24 is increased, and a constant current corresponding to the normal operation is supplied to the internal circuits of the operational amplifiers 21a to 21c. The

  On the other hand, when performing a leakage current inspection, a low level signal is given to the control signal terminal 29 to turn off the FET 28. Then, the collector resistance of the transistor 24 becomes a series resistance of the resistance elements 25 and 26 and increases, so that the base current of the transistor 24 becomes a minute constant current level corresponding to the inspection.

  According to the second embodiment configured as described above, when a plurality of operational amplifiers 21a to 21c are mounted on the semiconductor integrated circuit 22, a constant current for normal operation and a minute constant current for inspection are supplied to them. Since the constant current source circuit 23 is made common, an increase in circuit scale can be suppressed when an internal circuit for inspection is added.

(Third embodiment)
FIG. 3 shows a third embodiment of the present invention, and different portions from the second embodiment will be described. In the third embodiment, when the semiconductor integrated circuit 31 includes more operational amplifiers 21a to 21f than the second embodiment, the configuration for supplying a constant current during normal operation to them is divided into two groups. It is divided and shared. That is, a constant current source circuit 32A is arranged for the group of operational amplifiers 21a to 21c, and a constant current source circuit 32B is arranged for the group of operational amplifiers 21d to 21f. The two constant current source circuits 32A and 32B share a common circuit for switching and supplying a small constant current for inspection.

The constant current source circuit 32A is configured by connecting a series circuit of a resistance element 33 and an N-channel MOSFET 34 between the collector of the transistor 24 and the ground in addition to the transistors 24 and 27 similar to those of the second embodiment. . The constant current source circuit 32B is basically symmetric with the constant current source circuit 32A, and includes PNP transistors 35 and 36, a resistance element 37, and an N-channel MOSFET 38.
An inspection current supply control unit 39 is added to the constant current source circuits 32A and 32B, and the control unit 39 includes a P-channel MOSFET 40, a resistance element 41, and NPN transistors 42 to 44. The power source is connected to the source of the FET 40, and the drain of the FET 40 is connected to the base and collector of the transistor 42 via the resistance element 41.

  The transistor 42 and the transistors 43 and 44 constitute a mirror pair, their bases are connected in common, the emitters are all connected to the ground, and the collectors of the transistors 43 and 44 are the collectors of the transistors 24 and 35, respectively. It is connected to the. The gates of the FETs 34, 38, and 40 are all connected to the control signal terminal 45. The resistance values of the resistance elements 33 and 37 are set according to the constant current values during normal operation in each group of the operational amplifiers 21a to 21c and the operational amplifiers 21d to 21f. The resistance value of the resistance element 41 is set higher than the resistance values of the resistance elements 33 and 37 in order to define a minute constant current for inspection.

  Next, the operation of the third embodiment will be described. When the operational amplifiers 21a to 21f are normally operated, a high level signal is given to the control signal terminal 45 to turn on the FETs 34 and 38 and turn off the FET 45. At this time, the mirror pair of the transistors 42 to 44 is turned off. Then, the collector currents of the transistors 24 and 35 flow as defined by the resistance values of the resistance elements 33 and 37, and the base currents of the transistors 24 and 35 become values corresponding to those during normal operation, and the operational amplifiers 21a to 21c and 21d to 21f.

  On the other hand, when the leakage current inspection is performed, a low level signal is given to the control signal terminal 45 to turn off the FETs 34 and 38 and turn on the FET 40. At this time, the mirror pair of the transistors 42 to 44 is turned on. Then, since the collector currents of the transistors 24 and 35 are defined by the collector currents (mirror currents) of the transistors 43 and 44 determined by the current value flowing through the resistance element 41, they become a minute constant current level corresponding to the inspection, It is supplied to each operational amplifier 21a-21c, 21d-21f.

  As described above, according to the third embodiment, when the semiconductor integrated circuit 31 includes a plurality of operational amplifiers 21a to 21f, the configuration for supplying a constant current during normal operation to them is divided into two groups. Separately, the constant current source circuits 32A and 32B share the circuit, and the two constant current source circuits 32A and 32B switch and supply a small constant current for inspection to be shared by the inspection current supply control unit 39. The configuration. Therefore, when a plurality of operational amplifiers 21 are used, it is possible to cope with the case where the constant current value during normal operation differs depending on the function.

(Fourth embodiment)
FIG. 4 shows a fourth embodiment of the present invention. In the fourth embodiment, the inspection target is not the internal circuit of the operational amplifier, but the gate oxide film of the N-channel MOSFET 52 arranged at the output stage of the semiconductor integrated circuit 51, and the pass / fail judgment is performed on the gate oxide film. Show. The power source is connected to the emitters of PNP transistors 53a to 53c forming a mirror pair, and these bases are commonly connected to the collector of the transistor 53a. The collector of the transistor 53a is connected to the ground via resistance elements 54 and 55. As in the second embodiment, an N-channel MOSFET 56 is connected in parallel to the resistance element 55, and a normal operation and an inspection time are determined by a control signal applied to the gate of the FET 56 via the control signal terminal 57. The constant current value is switched.

  The collectors of the transistors 53b and 53c are connected to the collectors of NPN transistors 58a and 58b constituting a mirror pair on the ground side, respectively, and the collector of the transistor 53c is connected to the gate of the output stage FET 52. ing. The drain of the FET 52 is connected to the output terminal 59, and the source is connected to the ground. An N-channel MOSFET 60 is connected in parallel to the transistor 58a, and a drive signal for the output stage FET 52 is applied to the gate of the FET 60. That is, when the drive signal is at a low level, the mirror pair of the transistor 58 is turned on to turn off the FET 52, and when the drive signal is at a high level, the mirror pair of the transistor 58 is turned off to turn on the FET 52. .

Next, the operation of the fourth embodiment will be described. The inspection method is basically the same as in the first embodiment, etc.
(1) The FET 52 is driven with the power supply voltage set to VB at the normal operation level and the constant current set to a minute constant current for inspection, and the slew rate is measured for the gate voltage.
(2) Connect the output terminal 59 to the ground, switch the power supply voltage to the screening voltage VT, and switch the constant current during normal operation.
(3) In the same state as (1), measure the slew rate again.
(4) Compare the measurement results of (1) and (3).
It becomes a process. When there is a defect in the gate oxide film of the FET 52, the leakage current from the gate increases by applying the screening voltage VT, so that the slew rate changes as in the first embodiment.
As described above, according to the fourth embodiment, screening can be similarly performed on the gate oxide film of the FET 52 constituting the semiconductor integrated circuit 51.

(5th Example)
FIG. 5 shows a fifth embodiment of the present invention. The operational amplifier (semiconductor integrated circuit) 61 of the fifth embodiment shows a case where the same configuration as the operational amplifier 1 of the first embodiment is replaced with a MOSFET. That is, the NPN transistor is replaced with an N-channel MOSFET, and the PNP transistor is replaced with a P-channel MOSFET. Further, the switch circuits 4 and 6, the constant current sources 5 and 7, and the control signal terminal 8, which are unique to the present invention, are connected in the same manner as in the first embodiment.
The present invention can also be applied to the operational amplifier 61 configured as described above in exactly the same manner as the operational amplifier 1 of the first embodiment.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
Also in the first embodiment, the constant current value output from one constant current source may be changed between normal operation and inspection as in the second embodiment.
For example, when the operational amplifier 1 is incorporated as a part of the product together with other circuits, and the electrical characteristics of the operational amplifier 1 itself cannot be directly measured, it may be determined whether or not the function of the entire product is normal. For example, if the standard of the leakage current determined to be defective for a product is 0.1 μA, the minute constant current for inspection is also set to 0.1 μA. Then, when a leak current of 0.1 μA or more occurs, an abnormality should appear in the function of the product (corresponding to one kind of electrical characteristics), and therefore, determination may be made based on whether or not an abnormality appears.

When it is difficult to set the input signal level appropriately as in the first embodiment and make the voltage applied to both ends of the internal capacitor 14 equivalent to the screening voltage, a changeover switch for applying the inspection voltage, etc. May be arranged.
The configuration of the operational amplifier is not limited to that shown in the first embodiment.
What is necessary is just to change the specific numerical value etc. for performing determination suitably according to an individual design.

The figure which shows 1st Example at the time of applying this invention to an operational amplifier The figure which shows 2nd Example at the time of applying this invention to several operational amplifier. FIG. 2 equivalent view showing a third embodiment of the present invention. The figure which shows 4th Example at the time of applying this invention to FET arrange | positioned in the output stage of an integrated circuit FIG. 1 equivalent view showing a fifth embodiment of the present invention.

Explanation of symbols

  In the drawings, 1 is an operational amplifier (semiconductor integrated circuit), 5 is a constant current source for normal use, 7 is a constant current source for inspection, 14 is a capacitor for phase compensation (part to be inspected), 22 is a semiconductor integrated circuit, and 23 is a constant current. Reference numeral 31 denotes a semiconductor integrated circuit, 32 denotes a constant current source circuit, 51 denotes a semiconductor integrated circuit, 52 denotes an N-channel MOSFET (part to be inspected), and 61 denotes an operational amplifier (semiconductor integrated circuit).

Claims (2)

Built-in constant current source that supplies a constant current for normal operation to the internal circuit, and a semiconductor integrated circuit that can be set from the outside so as to supply a small constant current instead of the constant current for normal operation A method for inspecting a circuit,
A first step of performing a characteristic test in a state in which the operation power supply voltage of the semiconductor integrated circuit is set to a normal voltage level and the minute constant current is supplied; and a power supply voltage for testing the operation power supply voltage of the semiconductor integrated circuit A second step of applying a voltage corresponding to the inspection voltage to both ends of the inspection target portion in the internal circuit and supplying the constant current for normal operation;
A third step of performing the characteristic inspection again under the same conditions as in the first step;
A method of testing a semiconductor integrated circuit, comprising: a fourth step of performing pass / fail judgment by comparing a test result in the first step and a test result in the third step. In a semiconductor integrated circuit incorporating a constant current source for supplying a constant current for normal operation to an internal circuit,
A semiconductor integrated circuit characterized in that a setting for supplying a small constant current for inspecting the characteristics of the internal circuit in place of the constant current for normal operation is made possible from the outside.

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