JPS6123668B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION With the recent progress in variable voltage variable frequency control technology, the capacity of control devices thereof has increased and the range of application is expanding to include vehicle drive induction motors. Along with this, the capacity of semiconductor elements used in variable voltage/variable frequency control devices has also increased, and elements with special ratings have become necessary. For example, in a semiconductor device used in a variable voltage/variable frequency control device for a vehicle drive induction motor, the commutation thyristor of the device has a reverse blocking capacity of 2.5KV and its turn-off time is 30μ.
A special thyristor is required that has an average on-current of 200A in seconds, a pulse current of 2000A, and a conduction period of 60μsec di/dt of 300A/μsec. If the thyristor is implemented as a thyristor with a normal structure, the ignition characteristics of the thyristor will deteriorate and it will not be suitable for practical use.

The present invention has been made to fulfill the above-mentioned requirements. The characteristics of the thyristor portion (reverse conduction type thyristor) of the reverse conduction thyristor currently used in vehicle armature choppers are as follows:
Since it has the forward characteristic of the thyristor mentioned above, this part can be used to supplement the reverse blocking ability of the 2.5KV high speed reverse conduction type thyristor.
By integrating a 2.5KV high-speed diode in series, it becomes possible to realize the above-required element that has a 2.5KV reverse blocking ability and has excellent firing characteristics as a thyristor.

A feature of the present invention is that when diode wafers are fixedly integrated in series in a direction that compensates for the reverse blocking ability of the reverse conduction type thyristaulic wafer, a negative bevel is given to the voltage blocking junction of the wafer. . One of the reasons for this is improved mechanical reliability due to the element structure, and the other is 2.5KV
This is based on the experimental fact that leakage current at high temperatures is smaller with a negative bevel than with a positive bevel in class high-speed diodes, in order to improve device reliability.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view of one embodiment of a semiconductor device according to the present invention.
A diode wafer 3 having a junction, an anode electrode 24 and a cathode electrode 24' are integrated. Thyristauer Fura 2 uses high resistivity N-type silicon as a base material, and P-type and N-type silicon is used as the base material.
By selectively diffusing each type of impurity, five layers as shown are formed. That is, 5 is an N-type base layer with a high resistivity, 6 is an N-type base layer with a lower resistivity than the N-type base layer, 7 is a P-type emitter layer with a lower resistivity than the N-type base layer 6, and 8 is a P-type emitter layer with a lower resistivity than the N-type base layer. 9 is an N-type emitter layer having a lower resistivity than the P-type base layer 8;
0 is an anode emitter junction formed by the N type base layer 6 and the P type emitter layer 7, and 11 is the center formed by the N type base material layer 5 and the P type base layer 8.
A PN junction 12 is a cathode emitter junction formed by a P type base layer 8 and an N type emitter layer 9. The thyristor air 2 is a P-type emitter layer 7
Gold is diffused from the surface of the low resistivity N base layer 6 in accordance with the purpose of use in order to shorten the turn-off time of the thyristor air 2. The surfaces of the P-type emitter layer 7 and the low-resistivity N-type base layer 6 are in low-resistance contact with the central support plate 22 via the metal solder layer 23', and are further in contact with the metal solder layer 2.
It is firmly fixed to the diode wafer 3 via 3. A cathode electrode 24' and a gate electrode 21 are provided on the surfaces of the N-type emitter layer 9 and the low-resistivity P-type base layer 8 in low-resistance contact. The diode wafer 3 is formed with a PN junction 18 having a reverse breakdown voltage equal to or higher than the forward blocking ability of the thyristor wafer 2 in order to supplement its reverse blocking ability. Phosphorus, an N-type impurity, is diffused from one side of the silicon wafer to form an N ⁺ type layer 17, which has a lower resistivity than the N-type base material layer 15, and boron, a P-type impurity, is diffused from the other side to form an N-type base material. layer 1
5, a P-type layer 16 having a lower resistivity is formed. In order to make the reverse recovery charge of the diode wafer 3 smaller than the low resistivity P-type layer 16 of the diode wafer 3, gold diffusion is performed depending on the purpose of use. The surface of the N ⁺ type layer 17 is fixed to the intermediate support plate 22 by a metal solder layer 23 in low resistance contact. The intermediate support plate 22 is preferably a thin P-type low resistivity silicon plate.
The metal solder 23, 23' is preferably a thin foil mainly composed of aluminum.

The thyristaulic wafer 2, the intermediate support plate 22, and the diode wafer 3 are made of metal solder 23,
23' are stacked in the illustrated order described in detail above and heated to adhere and integrate them. Thereafter, the cathode electrode 24' and gate electrode 21 of the thyristor wafer 2 are formed by aluminum evaporation using a metal mask, and the anode electrode 24 of the diode wafer 3 is also formed by aluminum evaporation.

Thereafter, end face shaping (bevel) is performed to diagonally cut each PN junction at the peripheral edge of each of the thyristor wafer fabric 2 and the diode wafer fabric 3. The bevel 19 of the thyristor air 2 is provided with respect to its central PN junction (forward blocking junction) 11 in order to reduce the surface electric field strength. As shown in the figure, the inclination angle of the bevel 19 is obtuse with respect to the central PN junction 11 in the direction from the P-type base layer 8 with a high impurity concentration to the N-type base material layer 5, so it becomes a negative bevel. ing. The bevel 20 of the diode wafer 3 is connected to its PN junction 18,
Provided to reduce surface electric field strength. As shown in the figure, the inclination angle of the bevel 20 is a negative bevel that forms an obtuse angle with respect to the PN junction 18 in the direction from the P-type layer 16 with a high impurity concentration to the N-type base material layer 15.

The features of the semiconductor device of the present invention thus formed are listed below.

(1) Since there is no need for any reinforcing members to protect the end face shaping portions on both the outer surfaces of the anode and cathode, the structure is simple and reliability is improved.

(2) Since there is no need for reinforcing members to protect the end face shaping portions of both the anode and cathode outer surfaces, there is no residual stress on the element wafer that occurs when the reinforcing members are fixed, and the pressure resistance is stable. .

(3) Since the components are only silicon and a thin aluminum layer, it is stable in terms of thermal stress and has high reliability.

(4) Since the component parts are only silicon and aluminum, the surface treatment by chemical polishing is stable, so it can be manufactured at a high yield.

(5) By using thin P-type low resistivity silicon for the intermediate support plate, aluminum can be fixed to the N ⁺ type layer of the diode wafer near the eutectic temperature of aluminum and silicon (577°C).
Good ohmic contact can be obtained.

(6) Since both the diode wafer and the thyristor wafer form a negative bevel, a semiconductor device with low leakage current at high temperatures can be easily realized. A specific example of the difference in leakage current at high temperatures for negative and positive bevels is as follows.

In order to realize the special commutation thyristor that is the object of the present invention, a wafer with a diameter of 50 mm is required. The thickness of the thyristor and diode wafer used is because it is a high-speed thyristor.
It needs to be as thin as possible within the range that can provide a withstand voltage of 2.5 KV, specifically about 350 μm.
The thickness of the high resistivity N-type base material layer of both wafers is approximately 250 μm at most.

In order to reduce leakage current at high temperatures in a device designed with a thin N-type base material layer, for example, in the case of a diode wafer, it is necessary to increase the surface path length from the PN junction 18 to the N ⁺ layer 17. We have experimentally discovered that it is extremely effective to do so. In order to increase this surface path length, it is better to use a negative bevel (generally, the shaping angle of the PN junction 18 is 3 to 5 degrees) rather than a positive bevel (generally, the shaping angle of the PN junction 18 is 50 to 60 degrees). is extremely advantageous.

To compare with a specific example, it is 25KV at a temperature of 125℃.
The leakage current during application was 40 to 60 mA for the element shaped with a negative bevel, and 60 to 90 mA for the element shaped with a positive bevel.

(7) Since this thyristor is controlled by inserting a gate signal between the reverse conductivity type thyristor air and the N emitter, the response speed to the gate signal is faster than that of a remote gate type thyristor.

To explain the difference in response speed to gate signals using a specific example, in this semiconductor device with a non-remote gate, the applied voltage of the element
When a gate signal is applied at 1.25KV and a turn-on operation is performed, the turn-on is completed in 2 to 3 μsec. As a result, the di/dt capacity is 300A/
It is possible to realize a special commutation thyristor with a turn-off time of 30 μsec and a pulse current of 2000 A at 400 Hz using a 2.5 KV element having reverse blocking ability, which is the object of the present invention.

On the other hand, according to an experimental example using a remote gate, when turn-on operation is performed under the same test conditions as mentioned above, it takes 7 to 15μ to complete turn-on.
It took sec. As a result, the di/dt withstand capacity could only be secured at 100 to 60 A/μsec, making it impossible to experiment with the special commutation thyristor that is the object of the present invention.

As explained in detail above, the present invention makes it possible to provide a semiconductor device with excellent characteristics in a 2.5KV class high-speed thyristor having reverse blocking capability.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of one embodiment of the semiconductor device of the present invention. DESCRIPTION OF SYMBOLS 1...Semiconductor device, 2...Thyrist wafer, 3...Diode wafer, 24...Anode electrode, 24'...Cathode electrode, 23, 23'...
...Metal brazing layer, 21...Gate electrode, 22...Intermediate support plate.

Claims (1)

[Claims] 1. When connecting and integrating diode wafers in series in a direction that complements the reverse blocking ability of the reverse conductivity type thyristorue fabric, the distance between the diode wafers and the intermediate support plate for fixing and integrating both wafers increases. The wafers have a trapezoidal structure in which the outer diameters of both wafers are reduced, and the voltage blocking junction of the reverse conductivity type thyristor wafer and the voltage blocking junction of the diode wafer are changed from a high resistivity layer to a low resistivity layer. 1. A semiconductor device characterized in that both wafers are shaped to have a negative bevel so that the outer diameter of the wafer decreases in the direction of the wafer. 2. Claim 1, in which a thin P-type low resistivity silicon is used as a central support plate between both wafers when the diode wafers are fixedly integrated in a direction that supplements the reverse blocking ability of the reverse conductivity type thyristaulic wafers. 1. Semiconductor device described in Section 1.