JPH0475658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a power transistor capable of increasing breakdown resistance during use.

[Technical background of the invention and its problems]

One of the defects in power transistors is the current concentration breakdown phenomenon caused by thermal positive feedback. This phenomenon poses a problem in that the usage conditions of the device are restricted and extra margins are required in the design of the device. For this reason, various methods have been proposed to increase the breakdown resistance of transistors. For example, a balance resistor is interposed in the emitter region of a transistor, and an example thereof will be explained with reference to FIG.

FIG. 1A is a plan view of a power transistor in which a balance resistor is inserted in the emitter region, and FIG. 1B is a sectional view taken along line A-A' of the plan view shown in FIG. 1A. In FIG. 1, 1 is an N-type collector layer, 2 is a P-type base layer, 3 is a plurality of emitter layers formed separately on the base layer 2, 4 is an insulating film, and 5 is an insulating film.
6 is a balance resistor formed of polysilicon, for example, which is in contact with the emitter layer 3 on the insulating film 4, and 6 is each balance resistor 5 on the insulating film 4.
7 is a separate emitter electrode in contact with the emitter layer 3, 8 is a base electrode, and 9 is a collector electrode. In the power transistor shown in FIG. 1, a large number of separately formed emitter layers 3 are commonly connected via a balance resistor 5, so that the emitter current is evenly distributed and current concentration is less likely to occur. As a result, a large amount of destruction resistance can be obtained.

However, from a manufacturing technology perspective, by providing the resistive layer 5, a step is created between the resistive layer 5 and the insulating film 4. Therefore, there is a drawback that wiring breaks are likely to occur during aluminum vapor deposition to form the electrodes 6. Therefore, the balance resistor 5 made of polysilicon cannot be made very thick for the reasons mentioned above. For this reason, there was a problem in that even if the current was divided into many parts, the withstand capacity of the resistance layer was limited by its size.

Furthermore, a power transistor in which the balance resistor 5 shown in FIG. 1 is formed by diffusion has also been considered. Such a transistor will be explained. In FIG. 2, 11 is an N-type collector layer, 12 is a P-type base layer, 13 is a plurality of emitter layers formed separately on the base layer 12, 14 is an insulating film, and 15 is connected to the plurality of emitter layers 13. 16 is the N-type resistance layer formed by the above-mentioned resistance layer 15.
and the emitter electrode commonly connected to the contact, 17
is a base electrode, and 18 is a collector electrode.

The power transistor shown in FIG. 2 is considered to have the same effect as the power transistor shown in FIG. 1. However, in the power transistor shown in FIG. 2, when the transistor is in operation, the resistance layer 15 generates heat due to a large current, and a phenomenon occurs in which the resistance layer 15 itself begins to inject as an emitter. For this reason, there was a drawback that the function as a resistor was reduced by half, and the expected effect could not be obtained.

Furthermore, another way to increase the breakdown resistance of power transistors is to insert a balance resistor into the base.
There is a way to control the base current. FIG. 3 is a sectional view showing a power transistor controlling base current in this manner. In Figure 3,
21 is an N-type collector layer, 22 is a P-type base layer, 2
3 is an emitter layer, 24 is an insulating film, 25 is an N-type base separation layer formed on the base layer 22 and located between the emitter layer 23 and the base electrode 27;
26 is an emitter electrode in contact with the emitter layer 23, 27 is a base electrode, and 28 is a collector electrode. In the transistor shown in FIG. 3, the base layer 22 directly below the N-type isolation layer 25 acts as a base current balancing resistor, and the current can be distributed uniformly over the entire emitter region.

However, in the power transistor shown in FIG. 3, the base layer 22 is directly used as a resistor, so if the resistance of the base layer 22 is increased to further improve the effect, the positive voltage in the base will be increased. Pore concentration decreases. This has the disadvantage of causing conduction modulation quickly and lowering the current gain. Furthermore, reduction in current gain at high currents is often a particular problem in power transistors.

[Purpose of the invention]

This invention was made in view of the above points,
The purpose is to provide a power transistor in which a balance resistor is formed separately in a base layer to uniformly distribute emitter current during transistor operation and increase breakdown resistance.

[Summary of the invention]

A balance resistor is formed separately in the base layer to evenly distribute emitter current during transistor operation and increase breakdown resistance.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. 4 shows a power transistor according to an embodiment of the present invention, FIG. 4A is a plan view, and FIG.
FIG. 3 is a sectional view taken along line A'. In Figure 4,
The case of manufacturing an npn type planar transistor will be explained. First, the N-type semiconductor substrate 31 is oxidized at high temperature in a steam atmosphere to form the SiO ₂ layer 34. Then, holes for selective diffusion are formed in the SiO ₂ layer 34 by photolithography to form a base region, and boron atoms are diffused to form the P-type base layer 32. The diffusion in this case is performed in an oxidizing atmosphere, and at the same time as the boron atoms are diffused, a SiO ₂ layer is again formed on the main surface of the base layer 32. Next, an N-type emitter layer 33 and an n-type resistance layer 35 are formed in the base layer 32 by selective diffusion of phosphorus atoms. The emitter layer 33 and the resistance layer 35 are formed separately,
After opening holes in the SiO ₂ layer again by photolithography, aluminum is vacuum evaporated. Then, the emitter electrode 36, the base electrode 37, and the base contact electrode 371 are formed separately by photolithography. In this way, the emitter layer 33 and the resistance layer 3 are divided.
5 are arranged so as to be commonly connected. Further, the collector electrode 38 is formed by plating or vacuum deposition of nickel metal.

〔Effect of the invention〕

As described in detail above, according to the present invention, the balance resistor is formed separately in the base layer, and the emitter current during transistor operation is uniformly distributed, so that breakdown resistance can be increased.
Furthermore, it is possible to provide a power transistor in which conductivity modulation in the base layer is less likely to occur.

[Brief explanation of the drawing]

FIG. 1A is a plan view of a conventional power transistor, FIG. 1B is a sectional view taken along line A-A' in FIG. 1A, and FIGS. FIG. 4A is a cross-sectional view, and FIG. 4A is a plan view of a power transistor according to an embodiment of the present invention.
Figure B shows A- of the transistor shown in Figure 4A.
It is an A′ cross-sectional view. 31...N-type semiconductor substrate, 32...Base layer, 33
...emitter layer, 34...SiO ₂ layer, 35...resistance layer.

Claims (1)

[Claims] 1. A plurality of emitter regions and a plurality of diffused resistance layers of the same conductivity type as the emitter regions formed separately in a base region facing the emitter regions, and a base electrode is taken out through the diffused resistance layers. A power transistor characterized by: