JPH0494572A - Lateral type thyristor - Google Patents

Abstract

PURPOSE:To enhance breakdown strength of a thyristor by providing a diffused layer having a high resistance lower than those of anode and gate diffused layers and of the same degree or more as that of a substrate on the substrate between the anode diffused layer and the gate diffused layer. CONSTITUTION:A P-type diffused layer 9 is formed separately from an anode P-type diffused layer 2 and a gate P-type diffused layer 3 on an N-type substrate 1. The impurity concentration of the layer 9 is lower than those of the layers 2 and 3 and the layer 9 has a high resistance of the same degree as that of the substrate 1. When a depleted layer 8 reaches the layer 2, a current slightly starts to flow, but since the layer 9 of the high resistance exists, a flowing current is microscopic, and not abruptly increased, and a further voltage can be applied. Thus, a breakdown strength can be enhanced without increasing a distance between the layers 2 and 3.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a lateral thyristor.

[Prior Art] Fig. 2 shows a conventional lateral type silicon risk. In the figure, l denotes an N-type substrate, 2 denotes a P-type diffusion layer constituting an anode, 3 denotes a P-type diffusion layer constituting a gate, 4 is an N-type diffusion layer constituting a cathode; 5 is a cathode electrode ohmically connected to the cathode N-type diffusion layer 4; 6 is an anode electrode ohmically connected to the anode P-type diffusion layer 2; 7 is an insulating film; 8 indicates a depletion layer, respectively. In addition, the same figure (a) shows the depletion layer 8 generated in the forward direction blocking state, that is, the state where the potential of the anode electrode 6 is higher than the potential of the cathode electrode 5, and the same figure (b) shows the reverse direction blocking state, that is, The figure shows a depletion layer 8 that occurs when the potential of the anode electrode 6 is lower than the potential of the cathode electrode 5. The dimension in the figure is the distance between the anode P-type diffusion layer 2 and the anode P-type diffusion layer 3. shows.

In such a conventional lateral type thyristor, as shown in FIG.
As shown in the figure, in the forward blocking state, the breakdown voltage (forward blocking voltage) is determined by the fact that the depletion layer 8 spreads from the gate P-type diffusion layer 3 toward the N-type substrate 1 and reaches the anode P-type diffusion layer 2. This is the applied voltage when current suddenly begins to flow between the anode and cathode.

In addition, as shown in FIG. 2(b), in the reverse blocking state, the withstand voltage (reverse blocking voltage) is increased by the depletion layer 8 expanding from the anode P-type diffusion layer 2 toward the N-type substrate 1, This is the applied voltage when the current reaches the P-type diffusion layer 3 and suddenly begins to flow between the anode and cathode.

[Problem B to be solved by the invention] By the way, as mentioned above, the withstand voltage of the thyristor is
Both in the reverse direction depend on the distance between the anode P-type diffusion layer 2 and the gate P-type diffusion layer 3, so it is necessary to increase the distance in order to obtain a higher voltage resistance. Therefore, there was a problem in that the chip area increased, leading to a decrease in yield and an increase in cost.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a lateral type silicon risk that can obtain a high withstand voltage without increasing the chip area.

[1! ! Means for Solving the Problems] In order to solve the above problems, the present invention forms an anode diffusion layer and a gate diffusion layer of the opposite conductivity type on the surface of a semiconductor substrate, separated from each other, and also separates the gate diffusion layer from the semiconductor substrate. In a lateral type thyristor in which a cathode diffusion layer of the same conductivity type as the substrate is formed on a surface thereof, a cathode diffusion layer is formed on the substrate surface between the anode diffusion layer and the gate diffusion layer, and spaced apart from the anode and gate diffusion layers, respectively. The method is characterized in that a diffusion layer of a conductivity type opposite to that of the substrate is formed, which has an impurity concentration lower than that of the anode and gate diffusion layers and approximately equal to or higher than that of the substrate.

[Example] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, which differs from the conventional example described above in that it is between the anode P-type diffusion layer 2 and the gate electrode P-type diffusion layer 3 and is located on the surface of the N-type substrate 1. By forming the P-type diffusion layer 9 apart from the anode and gate diffusion layers 2.3, the impurity concentration of the P-type diffusion layer 9 is lower than that of the anode P-type diffusion layer 2 and the gate diffusion layer 2.3. It is low, and is comparable to or higher than that of the N-type substrate 1. Therefore, this P type diffusion layer 9
becomes a high resistance layer. Note that the other configurations are the same as those of the conventional example, so the description will be omitted by assigning the same reference numerals to the equivalent configurations.

In the lateral type thyristor configured in this way,
As shown in FIG. 1(a), in the forward blocking state, that is, when the potential of the anode electrode 6 is higher than the potential of the cathode electrode 5, as the voltage applied between the anode and cathode increases, the depletion layer 8 From P type diffusion layer 3 to N type substrate 1
It spreads in the direction of and reaches the P-type diffusion layer 9. When the applied voltage is further increased, the depletion layer 8 further expands from the anode side end of the P-type diffusion layer 9 and reaches the anode P-type diffusion layer 2.

In the case where there is no P-type diffusion layer 9, that is, in the case of the conventional example, when the depletion layer 8 reaches the anode P-type diffusion layer 2, a current flows rapidly, so the applied voltage at that time becomes the withstand voltage of the thyristor. However, in the present invention, since the P-type diffusion layer 9 with low impurity concentration, that is, high resistance, exists, when the depletion layer 8 reaches the anode P-type diffusion layer 2, a slight amount of 1t21iL starts to flow.

The applied voltage at this time is between the anode P type diffusion layer 2 and the gate P.
When the distance 11L to the type diffusion layer 3 is equal to that of the conventional example,
This is slightly lower than the applied voltage in the conventional example.

However, in the case of the conventional example, 2. A strong current flows and it cannot be used at a higher voltage, but in the case of the present invention, the current flowing is minute because of the presence of the high resistance P-type diffusion layer 9, and there is no problem in actual use, and further applied voltage is applied. be able to. Therefore, in the case of the present invention, it is possible to use the applied voltage higher than that of the conventional example. The withstand voltage (in this case, forward blocking voltage) of the thyristor according to the present invention is the voltage applied when the voltage flowing between the anode and cathode reaches a specified current (current amount that is a problem in practical use).

In addition, as shown in FIG. 1 Φ), in the case of the reverse blocking state, the potential between the anode and the cathode is opposite to that in the forward direction, and the spread of the depletion layer 8 is also opposite to the anode P-type diffusion layer 2 side. However, as in the case of the forward direction, due to the presence of the high-resistance P-type diffusion layer 9, a higher withstand voltage can be obtained than in the conventional example.

[Effect of the Invention 1] As described above, the present invention provides a high resistance diffusion layer on the substrate surface between the anode diffusion layer and the gate diffusion layer, which has an impurity concentration lower than that of the anode and gate diffusion layers and approximately equal to or higher than that of the substrate. By providing this, a high breakdown voltage can be achieved without increasing the distance between the anode diffusion layer and the gate diffusion layer. That is, since there is no need to increase the chip area, a lateral type thyristor with high breakdown voltage can be obtained without reducing yield or increasing cost.

In other words, in order to achieve the desired breakdown voltage, according to the present invention, the distance between the anode and cathode can be reduced, so the chip area can be reduced.
It is possible to improve yield and reduce costs.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, in which (a) shows a forward direction blocking state, and (-) shows a reverse direction blocking state. FIG. 2 is a sectional view showing a conventional example, in which (a) shows a forward direction blocking state and (b) shows a reverse direction blocking state. 1... Semiconductor substrate, 2... Anode diffusion layer, 3...
・Gate diffusion layer, 4... Cathode diffusion layer, 2... Cathode electrode, 6... Anode electrode, 7... Insulating film, 8
... Depletion layer, 9... High resistance diffusion layer.

Claims (1)

[Claims] (1) On the surface of a semiconductor substrate, an anode diffusion layer and a gate diffusion layer of the conductivity type opposite to that of the substrate are formed at a distance, and a cathode diffusion layer of the same conductivity type as the substrate is formed on the surface of the gate diffusion layer. In the lateral type thyristor, between the anode diffusion layer and the gate diffusion layer, on the substrate surface, spaced apart from the anode and gate diffusion layer, respectively, and lower than the anode and gate diffusion layer;
A lateral type thyristor further comprising a diffusion layer of a conductivity type opposite to that of the substrate and having an impurity concentration comparable to or higher than that of the substrate.