JPH0224022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and more particularly to a power element having an emitter short-circuit structure.

FIG. 1 shows an equivalent circuit of a general Darlington transistor, in which resistors 3 and 4 are connected between the emitters and bases of the NPN transistor 1 at the front stage and the NPN transistor 2 at the rear stage, respectively. These resistors 3, 4 are transistors 1,
This is to prevent an increase in leakage current between the collector and emitter, an increase in switching speed, and oscillation of the transistors 1 and 2 at high temperatures.
FIG. 2 is a sectional view showing the semiconductor chip 5 of this Darlington transistor sealed in an envelope (ceramic case) 6.

Further, FIG. 3 is a sectional view showing a specific element structure of the Darlington transistor. In the figure, 11 is an N ⁺ layer, 12 is an N ^- layer formed on this N ⁺ layer 11, and 13 is a P layer forming a base formed on this N ^- layer 12. This P layer 13 is provided with a step. Front stage transistor 1
An N ⁺ layer 14 serving as an emitter is formed within the P layer 13 , and the N ⁺ layer 14 and the P layer 13 are short-circuited by an Al (aluminum) electrode wiring layer 15 .
16 is a base electrode. On the other hand, in the transistor 2 in the latter stage, the five N ⁺ layers 18 ₁ , 18 ₂ , 18 ₃ , 18 ₄ , 18 ₅ serving as emitters are each P
It is formed protrudingly on the layer 13. Among these, between the N ⁺ layer 18 ₄ and the N ⁺ layer 18 ₅ is the base P ⁺ layer 13.
are provided protrudingly, and these N ⁺ layers 18 ₄ , 18 ₅
and P ⁺ layer 13 are short-circuited by Al electrode wiring layer 19. Emitter electrodes 20 ₁ to 20 ₃ are formed on the N ⁺ layers 18 ₁ to 18 ₃ , respectively, and the N ⁺ layers 1
8 ₁ to 18 ₃ and each adjacent P of the N ⁺ layer 18 ₅
Base electrodes 21 ₁ to 21 ₄ are formed on the layer 13 . An emitter electrode body 23 is commonly press-connected to the emitter electrodes 20 ₁ to 20 ₃ and the Al electrode wiring layer 19 via a buffer plate 22 . 24 is an insulating film (SiO ₂ ). On the other hand, a collector electrode body 27 is connected and fixed to the back surface of the N ⁺ layer 11 via an Al layer 25 and a buffer plate 26. The buffer plates 22 and 26 are both made of Mo (molybdenum) or W (tungsten), and the emitter electrode body 2
3 and the collector electrode body 27 are both made of Cu (copper).

In this Darlington transistor, the emitter-base resistors 3 and 4 of the transistors 1 and 2 respectively utilize the lateral sheet resistance of the P layer 13 serving as the base. Therefore, on the transistor 2 side, the emitter N ⁺ layer 18 ₄
A P layer 13 serving as a base is provided protrudingly between and N ⁺ layer 18 ₅ , and these are short-circuited at the surface by an Al electrode wiring layer 19 , forming a so-called emitter short-circuit structure. Similarly, on the transistor 1 side, the base P
Layer 13 and emitter N ⁺ layer 14 are Al electrode wiring layer 1
It has an emitter short-circuit structure in which the emitter is short-circuited by 5.

By the way, in this Darlington transistor, in the subsequent transistor 2, in addition to the resistor 4 between the base and emitter, the base region (P layer 13) is an anode and the collector region (N ^- layer 12 and N A parasitic diode d having the ⁺ layer 11) as its cathode is equivalently connected with its cathode facing the collector side, as shown by the broken line in FIG.

Conventionally, when using a Darlington transistor with the above structure, there are two options: to focus only on the resistance value of the resistor 4 and ignore its existence as a diode, or to actively utilize this diode d. There are two methods, and one method that actively utilizes the diode d is to use the diode d as a high-speed freewheeling diode with a wide area.

FIG. 4 shows a motor drive circuit for driving a DC motor using four Darlington transistors shown in FIG. 1 above. In the figure,
_Q1 to _Q4 are each Darlington transistors,
d ₁ to _{d 4} are each of these Darlington transistors Q ₁
~ Parasitic diode connected equivalently between the collector and emitter of the subsequent transistor of Q ₄ , D ₁ ~
_D4 is an external high-speed freewheeling diode connected in parallel to each of these parasitic diodes _d1 to _d4 , M is a DC motor, L is an excitation winding, and E
is the power source. The rotation of this DC motor M is controlled by adjusting each switching period and each phase of Darlington transistors _Q1 to _Q4 . For example, in the forward rotation state, both Darlington transistors Q ₁ and Q ₄ are turned on, and the current I ₁ is transferred to the transistor Q ₁ → excitation winding L → motor M → transistor
Q ₄ flows in the direction shown by the solid arrow in the figure, and as a result, energy is stored in the excitation winding L, and then when either transistor Q ₁ or Q ₄ is turned off, energy is stored in the excitation winding L. The energy generated causes currents I ₂ and I ₃ to flow through the excitation winding L → motor M → transistor
They flow in the directions of the dotted arrows in the figure, as shown in Q ₃ → Power supply E → Transistor Q ₂ . Here, first, both transistors Q ₁ and Q ₄ are on, and the DC motor M
Suppose that it is rotating in the positive direction. Then when transistor Q ₁ turns off and transistor Q ₄ turns off,
The current that has been flowing until now flows through the parasitic diode d ₃ and the high-speed freewheeling diode D ₃ -> the parasitic diode d ₂ and the high-speed freewheeling diode D ₂ . Next, when transistor _Q1 is turned on again,
Immediately after that, the current that begins to flow through the transistor Q ₁ does not flow toward the excitation winding L, but instead flows as a reverse recovery current of the diodes d ₂ and D ₂ . For this reason, these diodes
Until d ₂ and D ₂ recover, most of the voltage of the DC power supply E is applied to the transistor Q ₁ and a large current is generated, so these diodes d ₂ and D ₂
A long recovery time causes transistor Q ₁ to operate outside of its safe operating area, resulting in transistor Q ₁ being destroyed.

By the way, high-speed diodes are generally used as the external high-speed freewheeling diodes _D1 to _D4 , and the recovery time of the diodes is extremely short. However, each transistor Q ₁ ~
The parasitic diodes d ₁ to _{d 4} in Q ₄ are designed to have a long lifetime in order to improve the collector saturation voltage V _CE (sat) of the transistor and to obtain a high current amplification factor per pellet area. Compared to the fast freewheeling diodes _D1 to _D4 , the recovery time is longer under the conditions of the same area and the same reverse current value. For this reason, when a reverse recovery current flows through the diodes d ₂ and D ₂ , the diode D ₂ recovers first, and then the reverse recovery current flows only through the diode d ₂ . This reverse recovery current operates in the same way as the base current when the transistor is turned on, and becomes an excessive reverse recovery current that is current amplified, and the collector current Ic
As a result, the current flows into the emitter regions 18 ₄ and 18 ₅ , causing current concentration in the emitters and destroying the transistor Q ₁ .

This invention was made in view of the above circumstances.
The purpose is to provide a highly reliable semiconductor device that can prevent destruction of the emitter short circuit due to concentration of reverse recovery current flowing through the parasitic diode.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a plan view of the Darlington transistor, FIG. 6 is a sectional view taken along line A-A' in FIG. 5, and FIG. 7 is an equivalent circuit diagram of the Darlington transistor. In Figures 5 and 6, 4
1 is an N ⁺ layer, and 42 is formed on this N ⁺ layer 41.
The N ^- layer 43 is a P layer formed on the N ^- layer 42 and serving as a base. This P layer 43 is provided with a step. The N ⁺ layer 44 which becomes the emitter of the transistor 61 in FIG. 7 is formed within the P layer 43,
The N ⁺ layer 44 and the P layer 43 are short-circuited by an Al electrode wiring layer 45 at the stepped portion. 46 is a base electrode. On the other hand, four N ⁺ layers 48 ₁ , 48 ₂ , 48 which become the emitter of the transistor 62 in FIG.
₃ and 48 ₄ are formed protrudingly on the P layer 43, respectively. Emitter electrodes 49 ₁ to 49 ₄ are formed on each of these N ⁺ layers 48 ₁ to 48 ₄ , and base electrodes 50 ₁ to 50 ₃ are formed on the P layer 43 between these emitter electrodes 49 ₁ to 49 ₄ . are formed respectively. The rightmost N ⁺ layer 484 among the N ⁺ layers ₄₈₁ to ₄₈₄ has _an emitter electrode ₄₉₄ .
A part of the area other than the area connected to the Al wiring layer 5
1 to the P layer 43 serving as the base. An emitter electrode body 53 is commonly press-connected to the emitter electrodes 49 ₁ to 49 ₄ via a buffer plate 52 . On the other hand, a collector electrode body 56 is connected and fixed to the back surface of the N ⁺ layer 41 via an Al layer 54 and a buffer plate 55. 57 is an insulating film (SiO ₂ ). The above buffer plates 52 and 55 are both
The emitter electrode body 5 is made of Mo or W.
3 and the collector electrode body 56 are both made of Cu. In FIG. 5, reference numeral 70 indicates wiring including the Al wiring layer 51 and base electrodes 50 ₁ to 50 ₃ .

In this Darlington transistor, the resistance 63 between the emitter and base of the transistor 61 is
As in the conventional case, the sheet resistance of the P layer 43 shown in FIG. 6 is utilized. On the other hand, the resistance 64 between the base and emitter of the transistor 62 is caused by _the ^N Sheet resistance is used.
That is, between the collector and emitter of the transistor 62 , there is a P layer 43 and an N ^- layer 42 as described above.
A resistor 65 (that is, a resistor 64) is connected in series with the parasitic diode d and the N ⁺ layer 41. Therefore, the collector-emitter is biased in the opposite direction, and the parasitic diode d
Even if the resistor 6 becomes forward biased,
5 limits the reverse recovery current, thereby preventing destruction of the emitter short circuit.

In the above embodiment, a Darlington transistor consisting of NPN transistors 61 and 62 has been described, but the present invention is not limited to this, and it is also possible to apply the present invention to a PNP Darlington transistor. Moreover, the emitter electrode 49 ₁ ~
Of course, the connection between ₄₉₄ and the emitter electrode body 53 is not limited to press-contact connection, but may also be soldering.

As described above, according to the present invention, the emitter electrode body commonly connected to a plurality of emitter electrodes is not connected to the short circuit part of the emitter base, but the sheet resistance of the emitter layer is used.
A large reverse recovery current generated by a parasitic diode can be limited, and breakdown at the emitter-base short circuit can be prevented.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a Darlington transistor, FIG. 2 is a sectional view showing the semiconductor chip of the transistor sealed in an envelope, and FIG. 3 is a sectional view showing the element structure of a conventional Darlington transistor. FIG. 4 is a block diagram of a motor drive circuit using a Darlington transistor, FIG. 5 is a plan view showing the element structure of a Darlington transistor according to an embodiment of the present invention, and FIG.
FIG. 7, a sectional view taken along line A', is an equivalent circuit diagram of the Darlington transistor. 42...N ^- layer, 43...P layer, 48 ₁ to 48 ₄
...N ⁺ layer (emitter), 49 ₁ to 49 ₄ ... emitter electrode, 51 ... Al wiring layer, 53 ... emitter electrode body, 61 , 62 ... NPN transistor, 6
3, 64, 65...resistance, d...parasitic diode.

Claims (1)

[Claims] 1. In a semiconductor device in which a diode and a resistor are connected in series between the emitter and the collector of the second transistor in the latter stage among the first and second transistors connected in Darlington, A semiconductor body formed by forming a plurality of mesa-type second conductivity type layers, a metal electrode layer formed on each of the second conductivity type layers, and at least one of the plurality of second conductivity type layers. A metal wiring layer in which a part of the conductive type layer other than the area connected to the metal electrode layer is used as the resistor, and connects only the first conductive type layer constituting one end of the diode to the resistor; A semiconductor device comprising: a metal electrode body commonly connected to the plurality of metal electrode layers.