JPH0110938Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a switching transistor in which a diode is forwardly connected to the collector, and in particular to prevention of parasitic thyristor effects and improvement of switching characteristics.

Generally, some switching transistors have a diode for absorbing reverse surge voltage connected to the collector and formed within one chip.

FIG. 1 is a cross-sectional view showing the structure of a conventional switching transistor with a built-in diode. Reference numeral 1 denotes an N+ type semiconductor substrate in which impurities such as phosphorus are diffused at a high concentration, and a collector region is formed on the semiconductor substrate 1. An N-type epitaxial layer 2 is formed. Further, in the epitaxial layer 2, a base region 3 and a diode region 4 of opposite conductivity type, that is, P type, are formed by diffusion of impurities such as boron, and furthermore, in the base region 3, impurities such as phosphorus are diffused at a high concentration. An N+ type emitter region 5 is formed by the wafer, and electrodes 6, 7, 8 are formed in each region by ohmic contact with aluminum.

The above structure is shown in the circuit of FIG. 2a, and when a reverse surge voltage occurs, in which the collector current flows through the diode 9 due to the base current flowing, it is absorbed by the reverse withstand voltage of the diode 9. This eliminates the application of reverse surge voltage to the external circuit. However, according to the structure shown in FIG. 1, as shown in FIG. 2b, a parasitic transistor 1 is formed in which the diode region 4 is the emitter, the epitaxial layer 2 is the base, and the base region 3 is the collector.
0 is formed and a pulse-like high voltage is applied, the thyristor operates, that is, even when the base current is removed, the base current is supplied from the collector of the parasitic transistor 10, and the transistor 1
This has the drawback that the switching transistor cannot function as a switching transistor.

The present invention has been devised in view of the above-mentioned points, and is intended to provide a switching transistor that completely eliminates the conventional drawbacks. The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a sectional view showing an embodiment of the present invention,
Reference numeral 12 denotes an N+ type semiconductor substrate made of silicon, in which impurities such as phosphorus are diffused at a high concentration. On the semiconductor substrate 12, impurities such as phosphorus are diffused at a low concentration by vapor phase growth, etc., and a collector is formed. N becomes the area
- type epitaxial layer 13 is formed. An impurity such as boron is diffused into the epitaxial layer 13 from its surface to simultaneously form a P-type base region 14 and a diode region 15, and an impurity such as phosphorus is diffused into the base region 14 at a high concentration to form an N+ A mold emitter region 16 is formed.

On the other hand, an N+ buried layer 17 is formed between the base region 14 and the diode region 15 to separate the two at the same time as the emitter region 16 is formed. N
The buried layer 17 blocks a channel induced on the surface of the epitaxial layer 13 and prevents the base region 14 and the diode region 15 from being electrically connected.
The feature of the present invention is that a metal diffusion layer 18 is formed around this N+ buried layer 17. After forming the emitter region 16 and the N+ buried layer 17, the metal diffusion layer 18 is formed by removing the oxide film on the N+ buried layer 17, depositing gold or platinum, etc. on its surface, and heating it in a diffusion furnace at about 1100°C. By heat treatment, N
+ It is formed by diffusing around the buried layer 17 until it reaches the semiconductor substrate 12 inside the epitaxial layer 13.

Electrodes 19, 20, 21 are epitaxial layer 13
a base region 14 of an overlying oxide film 22;
A portion of the emitter region 16 and diode region 15 is removed and an ohmic contact made of aluminum is formed.

According to the above structure, the lifetime of carriers injected from the emitter region 16 and moving in the epitaxial layer 13 is shortened by recombination in the metal diffusion layer 18, and the base current I _B and the collector current are blocked. The time difference between Furthermore, in a parasitic transistor having the epitaxial layer 13 as a base region, carriers injected from the diode region 15 recombine in the metal diffusion layer 18, so that it no longer operates as a transistor.
The supply of base current to the switching transistor is blocked, and so-called thyristor operation is prevented. Furthermore, assuming that the characteristics of the conventional switching transistor are as shown in FIG. 4a, the collector resistance is reduced by providing the metal diffusion layer 18 in the collector region, that is, the epitaxial region 13, as shown in FIG. 4b. Thus, a larger collector current can be caused to flow with the same base current I _B .

Therefore, according to the present invention, by forming a metal diffusion layer in the collector region between the base region and the diode region, the parasitic thyristor effect can be prevented and the switching characteristics can also be improved. It is a big thing.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional example, FIGS. 2a and 2b are equivalent circuits of the semiconductor device shown in FIG. 1, FIG. 3 is a sectional view showing an embodiment of the present invention, and FIGS. b is a characteristic diagram of transistors in the conventional and the present invention. 12...Semiconductor substrate, 13...Epitaxial layer, 14...Base region, 15...Diode region, 16...Emitter region, 17...N+ buried layer, 18...Metal diffusion layer, 19, 20, 21...
Electrode, 22... oxide film.

Claims (1)

[Scope of utility model registration request] a collector region formed on a semiconductor substrate; a base region formed in the collector region by diffusion of impurities of opposite conductivity type; and a base region formed by diffusion of impurities of the same conductivity type as the semiconductor substrate in the base region. and a diode region formed by diffusing impurities of opposite conductivity type into the collector region, the collector region between the base region and the diode region is provided. A semiconductor device characterized in that a high concentration impurity layer of the same conductivity type as the semiconductor substrate and a metal diffusion layer are formed around the high concentration impurity layer in a region.