JP3996855B2 - Bi-directional photothyristor test apparatus, bi-directional photothyristor test method, and tester - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional photothyristor test apparatus, a bidirectional photothyristor test method, and a tester, and more particularly, a screening test apparatus, tester, and screening test method for a bidirectional photothyristor with a zero-cross function incorporating a MOSFET (MOS field effect transistor) About.
[0002]
[Prior art]
Conventionally, a screening test of a gate oxide film in the MOSFET is performed as follows for a bidirectional photothyristor with a built-in MOSFET for the purpose of adding a zero-cross function. That is, screening is performed by directly applying a DC voltage having a predetermined value that is equal to or lower than the breakdown voltage of the normal gate oxide film to the gate electrode of the MOSFET to destroy the abnormal gate oxide film having scratches or pinholes. It is.
[0003]
As another screening test method, there is also known a method of instantaneously applying a voltage to the gate electrode of the MOSFET (see Patent Document 1).
[0004]
On the other hand, as shown in FIGS. 3 and 4, there are bidirectional photothyristors including a photodiode or a phototransistor for controlling the gate voltage of a MOSFET for adding a zero cross function. FIG. 3 is a circuit diagram, and FIG. 4 is a partial sectional schematic view. However, the element for optically controlling the gate of the MOSFET is a phototransistor.
[0005]
This bidirectional photothyristor operates as follows. That is, in FIG. 3, an alternating voltage is applied between the terminals A and K. In that case, it is assumed that the terminal A side is more positive than the terminal K side. When light is incident on the chip surface in this state, first, the phototransistor Q3 on the CH (channel) 1 side is turned on by the contribution of the photocurrent generated in the base diffusion region 1 of the phototransistor Q3. Then, the base current of the PNP transistor Q1 on the CH1 side is drawn, and this PNP transistor Q1 is turned on. Subsequently, the base current is supplied to the NPN transistor Q2 constituted by the N-type substrate 2, the P gate diffusion region 3 and the cathode diffusion region 4 on the CH1 side by the collector current of the PNP transistor Q1. At that time, in the vicinity of the zero cross point of the AC voltage biased between the terminal A and the terminal K, the base voltage of the N-type MOSFET 5 from the phototransistor Q3 is low and the N-type MOSFET 5 is turned off. A base-emitter voltage corresponding to the resistance value of the gate resistor 6 is applied. Therefore, the NPN transistor Q2 is turned on. Then, the base current is supplied to the PNP transistor Q1, the PNPN portion on the CH1 side is turned on by positive feedback, and an on-current according to the load of the AC circuit flows from the terminal A to the terminal K.
[0006]
In this case, on the CH2 side opposite to the CH1 side, the direction of bias application is opposite, so that the positive feedback of the PNPN portion does not occur and only the primary photocurrent flows.
[0007]
On the other hand, in the time away from the zero cross point of the AC voltage, the N-type FET 5 is turned on, so that the base and emitter of the NPN transistor Q2 are short-circuited, and the base current is applied to the NPN transistor Q2 by the collector current of the PNP transistor Q1. Even if a current is supplied, the NPN transistor Q2 cannot be turned on.
[0008]
In this way, a zero cross function for turning on the photothyristor only in the vicinity of the zero cross point of the AC voltage biased between the terminal A and the terminal K is realized.
[0009]
On the other hand, when the terminal K side is at a more positive potential than the terminal A side, the PNPN section on the CH2 side is turned on by positive feedback operation in the same manner near the zero cross point, and only the primary photocurrent flows on the CH1 side. It is.
[0010]
By the way, the structure of the bidirectional photothyristor including the phototransistors Q3 and Q3 ′ for optically controlling the gate voltages of the MOSFETs 5 and 5 ′ improves the lightning surge resistance and electrostatic breakdown resistance of the gate breakdown of the MOSFETs 5 and 5 ′. It is designed for the purpose. That is, even when a high voltage (rated 800 V) is applied between the terminal A and the terminal K, a voltage higher than the on-voltage of the phototransistors Q3 and Q3 ′ is not applied between the gate and source of the MOSFETs 5 and 5 ′. It is a mechanism to clamp the voltage.
[0011]
[Patent Document 1]
JP-A-6-302663 [0012]
[Problems to be solved by the invention]
However, the conventional screening methods disclosed in Patent Document 1 and Patent Document 2 have the following problems. That is, in any of the above screening methods, a DC voltage having a predetermined value not more than the breakdown voltage of a normal gate oxide film is directly applied to the gate electrode of the MOSFET.
[0013]
However, the above-described conventional screening method is applied to a bidirectional photothyristor incorporating phototransistors Q3 and Q3 ′ for optically controlling the gate voltages of MOSFETs 5 and 5 ′ for adding a zero cross function as shown in FIGS. In the case of application, as shown in FIGS. 3 and 4, a test voltage is applied between the gates and sources of the MOSFETs 5 and 5 ′ from the terminals T1 and K and the terminals T2 and A.
[0014]
Then, a punch-through phenomenon (FIG. 3 and FIG. 3) occurs between the emitter diffusion region (N type) 7 in the phototransistors Q3 and Q3 ′ and the well diffusion region (P type) 8 of the MOSFETs 5 and 5 ′ having the GND potential. In FIG. 4, the zener diodes 10 and 10 ′ are represented. Therefore, the voltage directly applied to the gate electrodes 9 and 9 ′ of the MOSFETs 5 and 5 ′ is limited, and a voltage higher than the punch-through voltage cannot be applied to the gate electrodes 9 and 9 ′.
[0015]
Therefore, in actual use, when a voltage having a steep rise is applied to the gate electrodes 9, 9 ′, a voltage higher than the punch-through voltage may be instantaneously applied to the gate electrodes 9, 9 ′. Nevertheless, a test for screening defective products of the gate oxide film 11 in a wafer state has not been performed.
[0016]
Accordingly, an object of the present invention is a bidirectional photothyristor chip including a MOSFET for adding a zero-cross function and a photodiode or a phototransistor for optically controlling the gate voltage of the MOSFET, and the gate oxide film of the MOSFET is damaged. A bidirectional photothyristor test device, a bidirectional photothyristor test method, and a tester that can eliminate defective chips that cause dielectric breakdown when a voltage with a steep rise due to the presence of a pinhole is present There is to do.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a bidirectional photothyristor test apparatus for conducting a screening test of a bidirectional photothyristor having a MOSFET that provides a zero-cross function and a photodiode or phototransistor that optically controls the gate voltage of the MOSFET. The photodiode or phototransistor has a peak voltage higher than the punchthrough voltage that is a voltage that reaches the punch-through with respect to the diffusion portion at the ground potential, and more than the time until the punch-through passes. Voltage application means for applying a voltage having a waveform that is lower than the punch-through voltage to the gate electrode of the MOSFET is provided.
[0018]
According to the above configuration, the voltage applied to the gate electrode of the MOSFET by the voltage applying unit is greater than the punch-through voltage before the time until the photodiode or phototransistor reaches the punch-through elapses. Has also dropped to a lower voltage. Therefore, the photodiode or phototransistor does not reach the punch-through, and a voltage higher than the punch-through voltage is applied to the gate electrode.
[0019]
That is, by setting the peak voltage to a voltage that is equal to or lower than the withstand voltage of the oxide film of the MOSFET and can destroy the abnormal gate oxide film, the gate oxide film has scratches and pinholes. A bi-directional photothyristor chip with an abnormal quality that causes dielectric breakdown when a voltage is applied is reliably removed.
[0020]
In the bidirectional photothyristor test apparatus of one embodiment, the voltage application means includes a DC power source, a capacitor charged by the DC power source, a switch for switching charging and discharging of the capacitor, and discharging by the capacitor. In this case, a resistor for overcurrent protection for limiting the current flowing into the gate electrode of the MOS field effect transistor is included.
[0021]
According to this embodiment, first, the switch is operated and the capacitor is charged by the DC power supply, and then the switch is switched and the voltage charged in the capacitor is instantaneously applied to the gate electrode of the MOSFET. To be applied. Therefore, a voltage capable of destroying the abnormal gate oxide film is applied to the oxide film of the MOSFET by optimally setting the voltage value of the DC power supply, the capacitance value of the capacitor, and the resistance value of the resistor.
[0022]
In the bidirectional photothyristor test apparatus of one embodiment, the capacitance value of the capacitor is 0.1 μF or more and 0.5 μF or less, and the resistance value of the resistor is 100 kΩ or more and 200 kΩ or less.
[0023]
According to this embodiment, for example, by setting the voltage value of the DC power source to 200 V or more and 300 V or less, the peak voltage is higher than the punch-through voltage and can break the abnormal gate oxide film. A voltage having a waveform that becomes a voltage lower than the punch-through voltage is applied to the oxide film of the MOSFET before the time to reach the time elapses.
[0024]
Further, the bidirectional photothyristor test apparatus of one embodiment includes test voltage recording means for recording a peak voltage applied to the gate electrode of the MOSFET by the voltage applying means as a test voltage.
[0025]
According to this embodiment, during the screening test, the peak voltage actually applied to the gate electrode of the MOSFET is recorded as the test voltage by the test voltage recording means. Therefore, it becomes easy to determine the optimum screening test method and to develop a bidirectional photothyristor having the above structure.
[0026]
The present invention also relates to a screening test method for a bidirectional photothyristor having a MOSFET giving a zero-crossing function and a photodiode or a phototransistor for optically controlling the gate voltage of the MOSFET. A peak voltage that is higher than the punch-through voltage and capable of destroying the abnormal gate oxide film, and has a waveform that is lower than the punch-through voltage before the time to reach the punch-through elapses. After a voltage is applied to the gate electrode of the MOSFET, the threshold voltage of the MOSFET is measured to determine the quality of the gate oxide film of the MOSFET.
[0027]
According to the above configuration, a peak voltage capable of destroying the abnormal gate oxide film is applied to the gate electrode of the MOSFET without causing the photodiode or the phototransistor to punch through. Therefore, by measuring the threshold voltage of the MOSFET after the peak voltage is applied, the quality of the gate oxide film of the MOSFET is accurately determined.
[0028]
In the bidirectional photothyristor screening test method of one embodiment, the screening test method is performed on a wafer on which a plurality of the bidirectional photothyristors are repeatedly formed.
[0029]
According to this embodiment, the screening test of the gate oxide film for the MOSFET for giving the zero cross function in the bidirectional photothyristor is efficiently performed in a short time in the wafer state.
[0030]
The tester according to the present invention is equipped with the bidirectional photothyristor test apparatus.
[0031]
According to the above configuration, the bidirectional photothyristor test apparatus is mounted on a tester used when testing the wafer. Therefore, this tester efficiently performs a screening test of the gate oxide film on the MOSFET of the bidirectional photothyristor in a short time in a wafer state.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a circuit diagram of a bidirectional photothyristor test apparatus for realizing the bidirectional photothyristor test method of the present embodiment.
[0033]
In FIG. 1, reference numeral 22 denotes an N-type MOSFET for adding a zero-cross function in a bidirectional photothyristor to be subjected to a screening test by the bidirectional photothyristor test apparatus 21. Reference numeral 23 denotes a photodiode or phototransistor (hereinafter represented by a phototransistor) that optically controls the gate voltage of the MOSFET 22. The configuration other than the MOSFET 22 and the phototransistor 23 is the same as that in FIG. 3 and is not directly related to the description in the present embodiment, so that the description is omitted. Note that the Zener diode 24 has a punch-through phenomenon that occurs between the emitter diffusion region of the phototransistor 23 and the well diffusion region of the MOSFET 22 having the GND potential when a voltage is applied between the gate and the source of the MOSFET 22. It is shown explicitly.
[0034]
The bidirectional photothyristor test apparatus 21 has the following configuration. That is, the first switch SW1, the resistor R and the second switch SW2 are connected in series, and the second switch SW2 is connected to the first connection terminal 26, while the first switch SW1 is connected to the second switch via the power source V. The connection terminal 27 is connected. Further, a capacitor C is interposed between the node 25 between the first switch SW 1 and the resistor R and the second connection terminal 27. During the test, the gate electrode G of the N-type MOSFET 22 for adding the zero cross function of the bidirectional photothyristor to be tested is connected to the first connection terminal 26, while the source S of the MOSFET 22 is connected to the second connection terminal 27. To do.
[0035]
In the above configuration, in the screening test, first, the first switch SW1 is turned on, while the second switch SW2 is turned off, and the capacitor C is charged by the power supply V. Note that the voltage of the power source V is sufficiently higher than the voltage to be applied to the gate electrode G of the MOSFET 22.
[0036]
Thus, after charging the capacitor C, the first switch SW1 is turned off while the second switch SW2 is turned on, whereby the capacitor C is discharged and a high voltage is instantaneously applied to the gate electrode G of the MOSFET 22. In that case, the punch-through voltage of the phototransistor 23 (that is, the Zener voltage of the Zener diode 24) is set by optimally setting the voltage (V) of the power supply V, the resistance (R) of the resistor R, and the capacitance (C) of the capacitor C. A voltage higher than (50V)) can be applied.
[0037]
The resistor R is an overcurrent protection resistor that limits the current flowing into the gate electrode G of the MOSFET 22. In the present embodiment, the current limit is set to 500 μA. The capacitor C is variable in capacity and has an overvoltage protection function that limits the voltage applied to the gate electrode G of the MOSFET 22 so that the gate oxide film of the MOSFET 22 of the normal chip is not destroyed. In the present embodiment, the voltage limit is set to 250 V (normally, the breakdown voltage of a normal gate oxide film is about 300 V).
[0038]
Thus, after instantaneously applying a voltage higher than the punch-through voltage (zener voltage) to the gate electrode G of the MOSFET 22, the electrical characteristics such as the threshold voltage Vth of the MOSFET 22 (normally, the normal product has a threshold voltage Vth of 30 V). By measuring the above, it is possible to determine a chip that has been damaged due to an abnormality in the gate oxide film as a characteristic defect. In that case, by controlling the application time so that the applied voltage becomes lower than the punch-through voltage (zener voltage) before the phototransistor 23 reaches the punch-through state, a voltage higher than the punch-through voltage is applied to the gate electrode G. It can be applied.
[0039]
In the above description, the channel on one side (CH1 in FIG. 1) in the bidirectional photothyristor is described. Similarly, the first connection terminal of the bidirectional photothyristor test device 21 is also applied to the other channel. 26 may be connected to the gate electrode of the MOSFET while the second connection terminal 27 is connected to the source. In that case, one bidirectional photothyristor test device 21 may be replaced with a photothyristor of one channel and a photothyristor of the other channel, or a bidirectional photothyristor test device is separately provided for each channel photothyristor. You may connect.
[0040]
Incidentally, the test voltage applied to the gate electrode G of the MOSFET 22 during the screening test is arbitrarily set, and a high voltage with a sharp rise is applied between the terminals corresponding to the terminals A and K in FIG. In this case, it differs depending on the actual value of the voltage applied to the gate electrode G of the MOSFET 22. Therefore, when a voltage having a steep rise is applied between the two terminals of the good bidirectional photothyristor chip, it is necessary to measure the peak voltage actually applied to the gate electrode G of the MOSFET 22 in advance. Further, it has a peak voltage Vp ′ that is lower than the normal gate withstand voltage of 300 V and higher than the peak voltage Vp and can break the abnormal gate oxide film, and the punchthrough before the time to reach the punchthrough state elapses. A screening test can be reliably performed by instantaneously applying a high voltage with a sharp rise to a voltage lower than the voltage (Zener voltage) to the gate electrode G.
[0041]
As an example, when a voltage having a rising slope of 3300 V / μs is applied between the two terminals, the peak voltage Vp applied to the gate electrode G of the MOSFET 22 is about 80 V as shown in FIG. In the case of the bidirectional photothyristor, as shown in FIG. 2A, the power supply voltage of the bidirectional photothyristor test device 21 is set so that the peak voltage Vp ′ applied to the gate electrode G of the MOSFET 22 during the screening test is about 150V. V is set to about 300 V and the RC constant is adjusted. In this case, the margin of about 70 V with respect to the peak voltage Vp ′ is set from the breakdown characteristics (TDDB characteristics) of the oxide film in the MOSFET 22 and the guaranteed lifetime.
[0042]
First, the first switch SW1 is turned on, while the second switch SW2 is turned off to charge the capacitor C. Next, the first switch SW1 is turned off while the second switch SW2 is turned on to discharge the capacitor C. Then, as shown in FIG. 2 (a), the peak voltage Vp (Vp = about 80V) applied to the gate electrode G when a voltage having a rising slope of 3300V / μs is applied between the two terminals is normally exceeded. About 150 V is instantaneously applied to the gate electrode G of the MOSFET 22. When the time to reach the punch-through state (about 50 nm) elapses, the applied voltage drops below the punch-through voltage (= Zener voltage: about 50 V). At that time, in the case of a poor quality product in which the gate oxide film of the MOSFET 22 has scratches or pinholes, it is destroyed by an applied voltage of about 150V.
[0043]
As a result of the above, according to the present embodiment, it is possible to surely remove the bidirectional photothyristor chip having a defective MOSFET gate oxide film that has not been removed by the conventional direct application screening test but has flowed to the subsequent process. It can be done.
[0044]
The range of the power supply voltage V is about 200V to 300V. In this case, the capacitance C of the capacitor C is 0.1 μF to 0.5 μF, and the resistance R of the overcurrent limiting resistor R is suitably 100 kΩ to 200 kΩ. is there. For example, when V = 300 V, R = 150 kΩ, and C = 0.2 μF, the peak voltage Vp = 105 V applied to the gate electrode G is obtained.
[0045]
As described above, in the present embodiment, the bidirectional photothyristor test apparatus 21 is connected in series between the power supply V and the gate electrode G of the N-type MOSFET 22 on the bidirectional photothyristor side. The first switch SW1, the resistor R, the second switch SW2, and the capacitor C that is interposed between the source S of the MOSFET 22 and the node 25 and charges the voltage applied to the gate electrode G.
[0046]
When a voltage that is lower than the breakdown voltage of the gate oxide film of the MOSFET 22 and has a steep rise between the terminals of a good bidirectional photothyristor chip (corresponding to between the terminals A and K in FIG. 3) is applied. The peak voltage Vp ′ is higher than the peak voltage Vp applied to the gate electrode G and can destroy the abnormal gate oxide film, and the applied voltage becomes lower than the punchthrough voltage before reaching the punchthrough state. Thus, the power supply voltage V, the capacitance of the capacitor C, and the resistance of the resistor R are set.
[0047]
Therefore, after the capacitor C is charged by the power source V, the capacitor C is discharged, whereby an abnormal gate oxide film higher than the punch-through voltage is applied to the gate electrode G of the MOSFET 22 of the bidirectional photothyristor to be tested. A high voltage that can be destroyed can be instantaneously applied.
[0048]
That is, by using the bidirectional photothyristor test device 21 in the present embodiment and performing the test method as described above, the gate oxide film of the MOSFET for adding the zero-cross function has scratches and pinholes, so that However, it is possible to reliably remove defective chips that cause dielectric breakdown when a steep voltage is applied.
[0049]
In the above embodiment, the case where the phototransistor 23 is used as an element for optically controlling the gate voltage of the MOSFET for adding the zero-cross function in the bidirectional photothyristor has been described. Even when used, the same effect can be obtained.
[0050]
Although not described in detail, the bidirectional photothyristor test apparatus 21 is provided with a test voltage recording means to test the maximum voltage (peak voltage Vp ′) actually applied to the gate electrode G of the MOSFET 22 during the screening test. It is also possible to record it as a voltage.
[0051]
The bidirectional photothyristor test apparatus 21 can be incorporated in a conventional DC (direct current) tester. In such a case, the screening test of the gate oxide film in the MOSFET can be efficiently performed in a short time in the wafer state by using the DC tester.
[0052]
【The invention's effect】
As apparent from the above, the bidirectional photothyristor test apparatus of the present invention has a peak voltage higher than the punch-through voltage at the gate electrode of the MOSFET for giving the zero-cross function by the voltage applying means, Since a voltage having a waveform lower than the punch-through voltage is applied before reaching the gate electrode, a voltage higher than the punch-through voltage can be applied to the gate electrode.
[0053]
Therefore, by setting the peak voltage to a voltage that can destroy the abnormal gate oxide film of the MOSFET, since there are scratches and pinholes in the gate oxide film, dielectric breakdown is caused when a voltage with a sharp rise is applied. The bi-directional photothyristor chip with abnormal quality that is caused can be surely removed.
[0054]
That is, according to the present invention, it is possible to prevent the outflow of the abnormal quality bidirectional photothyristor chip to the subsequent process.
[0055]
Further, the bidirectional photothyristor screening test method of the present invention uses the bidirectional photothyristor test device to apply a voltage having a peak voltage capable of destroying the abnormal gate oxide film of the MOSFET for providing the zero cross function to the gate of the MOSFET. After the application to the electrodes, the threshold voltage of the MOSFET is measured to determine the quality of the gate oxide film of the MOSFET. Therefore, the quality of the gate oxide film can be determined by reliably destroying the abnormal gate oxide film of the MOSFET. It can be judged accurately.
[0056]
In addition, since the tester of the present invention is equipped with the bidirectional photothyristor test apparatus, the tester can efficiently perform a screening test of a gate oxide film on the MOSFET of the bidirectional photothyristor in a wafer state in a short time. It can be carried out.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a bidirectional photothyristor test apparatus according to the present invention.
FIG. 2 is a diagram showing a voltage waveform applied to a gate electrode of a MOSFET in FIG.
FIG. 3 is a circuit diagram of a conventional bidirectional photothyristor including a phototransistor that optically controls the gate voltage of a MOSFET for adding a zero-cross function.
4 is a partial cross-sectional view of the conventional bidirectional photothyristor shown in FIG.
[Explanation of symbols]
21. Bidirectional photothyristor test device,
22: N-type MOSFET,
23 ... Phototransistor,
24 ... Zener diode,
26: first connection terminal,
27. Second connection terminal,
V ... Power supply
SW1 ... 1st switch,
R ... resistance,
SW2 ... second switch,
C: Capacitor.

Claims (7)

A bidirectional photothyristor test apparatus for performing a screening test of a MOS field effect transistor imparting a zero-cross function and a bidirectional photothyristor having a photodiode or phototransistor that optically controls the gate voltage of the MOS field effect transistor,
The photodiode or phototransistor has a peak voltage higher than a punch-through voltage that is a voltage that reaches the punch-through with respect to the diffusion portion at the ground potential, and the punch-through is performed before the time until the punch-through elapses. A bidirectional photothyristor test apparatus comprising voltage application means for applying a voltage having a waveform lower than a through voltage to the gate electrode of the MOS field effect transistor. The bidirectional photothyristor test apparatus according to claim 1,
The voltage application means includes a DC power supply, a capacitor charged by the DC power supply, a switch for switching charging and discharging of the capacitor, and a current flowing into the gate electrode of the MOS field effect transistor upon discharging by the capacitor A bidirectional photothyristor test device comprising a resistor for overcurrent protection that limits the current. The bidirectional photothyristor test apparatus according to claim 2,
The capacitance value of the capacitor is 0.1 μF or more and 0.5 μF or less,
The bidirectional photothyristor test device, wherein the resistance value of the resistor is 100 kΩ or more and 200 kΩ or less. The bidirectional photothyristor test apparatus according to claim 1,
A bidirectional photothyristor test apparatus comprising test voltage recording means for recording a peak voltage applied to the gate electrode of the MOS field effect transistor by the voltage application means as a test voltage. A screening test method for a bidirectional photothyristor having a MOS field effect transistor imparting a zero-crossing function and a photodiode or phototransistor for optically controlling the gate voltage of the MOS field effect transistor
The bidirectional photothyristor test apparatus according to claim 1 has a peak voltage higher than the punch-through voltage and capable of destroying the abnormal gate oxide film, and before the time until the punch-through elapses. After applying a voltage having a waveform lower than the through voltage to the gate electrode of the MOS field effect transistor,
A screening test method for a bidirectional photothyristor, wherein the threshold voltage of the MOS field effect transistor is measured to determine whether the gate oxide film of the MOS field effect transistor is good or bad. In the bidirectional photothyristor screening test method according to claim 5,
A screening test method for a bidirectional photothyristor, wherein the screening test method is performed on a wafer on which a plurality of the bidirectional photothyristors are repeatedly formed. A tester comprising the bidirectional photothyristor test device according to claim 1.

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