JPS63177468A - Thyristor - Google Patents

Abstract

PURPOSE:To obtain a thyristor which can prevent a surface leakage current from occurring, whose operation is stable and whose reliability and withstanding voltage are high by a method wherein a first field electrode is formed on a P-N junction which is biased in the forward direction and a second field electrode is formed on another P-N junction which is biased in the reverse direction. CONSTITUTION:A P-N junction, where the impurity concentration in a region 1 is lower than the impurity concentration in a region 2 and which is formed by the region 1 and the region 2, is biased in the reverse direction; another P-N junction which is formed by the region 1 and a region 3 is biased in the forward direction. At this thyristor, a first electrode 6 connected to the region 3 is formed in such a way that it is extended over the region 1 via an insulating film 8; a second electrode 5 connected to a region 9 is formed in such a way that it is extended over the region 1 via the insulating film 8. A depletion layer 4 which is expanded inside the region 1 by said P-N junction biased in the reverse direction is made easy to extend by the second electrode 5; it is blocked by the first electrode 6 that the depletion layer 4 reaches said P-N junction biased in the forward direction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a thyristor, and particularly to a highly reliable and high voltage thyristor.

A unidirectional thyristor or bidirectional thyristor (TRIAC) consists of multiple PN junctions, and the PN junction is biased in the forward direction during device operation.

Adjacent PN junctions that are biased in the opposite direction are often provided. In that case, the layer sandwiched between the two junctions is often diluted. For example, triple diffusion manufactured thyristors and triacs used in high voltage fields are said to have extremely low impurity concentrations. In this state, a type of instability (referred to as Lie theory), which is different from simple PN junction instability (due to ionic contamination or crystal defects) as shown in FIG. 1, is likely to occur. In the same figure, characteristic A
Characteristic B shows the initial state, and characteristic B shows the state after BT processing. This is because the BT process causes a change in the charge distribution in the insulating film or on the insulating surface on the reverse bias junction side, which affects the semiconductor surface and abnormally extends the surface depletion layer of the reverse bias junction, causing the adjacent Surface leakage current is generated when the current reaches the vicinity of the head bias junction.

In order to increase the breakdown voltage of semiconductor devices, this phenomenon lowers the impurity concentration on the low impurity concentration side of the blocking PN junction, and changes the type, formation method, and treatment process of the insulating film that covers the surface so that the surface depletion layer can expand well. It is clear that the more you choose, the more this will occur.

The object of the present invention is to provide an effective thyristor which eliminates the disadvantages of the prior art.

The feature of the present invention is that in a thyristor having a forward biased PN junction and a reversely biased PN junction on the substrate surface, the tenth electric field electrode is provided on the forward biased PN junction, and The 20th electric field on the PN junction biased to 1! This is because a body was established.

Since the 20th electric field electrode makes it easier to extend the υ surface depletion layer, and the 10th electric field electrode prevents it from elongating too much, thereby preventing the generation of surface leakage current, a thyristor with stable operation can be realized.

FIG. 2 shows data comparing the structure according to the present invention and the fluctuation state in BT processing of the conventional structure in the case of a planar thyristor described below, and it can be seen that the structure according to the present invention fully achieves the purpose. In the same figure, the characteristic
is based on the prior art, and characteristic Y is based on the present invention.

The present invention will be explained below based on the drawings. FIG. 3 is a detailed explanation of the present invention.
, an N+ region 9 is provided in the Pi region 2, an electric field electrode 5 conventionally used for extending the depletion layer 4 is provided in the N medium region 3, and an electric field electrode 5 according to the present invention is provided in the P region 3. ,
An electric field electrode 6 for blocking the depletion layer 4 is provided respectively. As is clear from the figure, according to the present invention, the elongated depletion layer 4 is exposed to an electric field! , [6, the current is blocked at the end 7, so the current is much smaller and stable.

Next, an embodiment of the present invention will be explained based on FIG. First, a diffusion layer 12 is formed by selectively thermally diffusing a P-type impurity having an electric groove shape opposite to that of the substrate from both sides of an N-type semiconductor substrate 11 until it selectively penetrates the substrate. Similarly, impurities in the shape of an electric groove opposite to the substrate are selectively diffused into the substrate to form a diffusion layer 13.
m, forming 13b. 13 more layers! N-type impurities, which have the same conductivity type as the substrate, are selectively diffused into L to form one layer 19
form. Further, on the surface of the substrate 110, an insulating film 18 having a thickness of several thousand λ to several μ is formed during or after the diffusion, but in the case of a high voltage semiconductor device, the impurity concentration of the substrate is on the order of 10 − In some cases, the electric field concentration may be reduced to the order of 10 Ω, and in order to increase the radius of curvature at the tip of the depletion layer 14 to alleviate electric field concentration, the insulating film 18 transfers minority carriers in the substrate 110 to the surface as described above. The type, production conditions, and processing conditions that allow accumulation are selected in order to improve the withstand pressure distribution. For example, (1) lead-based or zinc-based glass, some sand (ii) 810□ membrane and kt203
A film in which thin films of equal metal oxides and two materials are laminated, or (iii) sio
2 After fixing the positive mobile ions in the membrane with phosphorus, the membrane is treated with an appropriate surface treatment, or the semiconductor surface is pretreated with hydrogen peroxide or a mixture of hydrogen peroxide and a liquid containing an amine group. After treatment, it is a film that is coated at a low temperature by a chemical reaction. Next, a conventionally used electric field electrode 15 and a semiconductor electric field electrode 16 for preventing the generation of surface leakage current according to the present invention are formed.

First, a predetermined contact hole is made in the absolute M film 18, and then a polycrystalline silicon film with a thickness of several thousand to several micrometers containing nanoparticles is formed using epitaxial technology.
This is achieved by covering and protecting the portion corresponding to 5.16 with a photoresist film and removing the unnecessary portion with an HF-HNO3 etching solution. Next, At or Mo
After forming the myopole 21 with a single layer metal such as Pt-Ti-Au or a multilayer metal such as Pt-Ti-Au, S is heated at low temperature using CV'D technology.
A tO□ film or a PSG film 20 is formed, a predetermined hole is made in the wire ending portion, and an electrode is formed for ohmic contact using an Au vapor-deposited film on the back surface to complete the process.

This is a semiconductor device having such a PNPN structure.

In the iristor, since the impurity concentration of the substrate 110 is the lowest, when a positive voltage is applied to the electrode 22 and a negative voltage is applied to the electrode 21 as shown in the figure, the depletion layer 14 is promoted to expand by the electric field electrode 15 and reaches the region 12, or leakage current However, in the present invention, since the electric field electrode 16 is provided, the surface depletion layer is blocked at the end portion 17, and the leakage current becomes small and stable.

To further explain the electric field electrode 16, its shape may be, for example, a round ring or a square ring, as long as it surrounds a forward bias PN junction. Of course. Further, as shown in the above embodiment, if the polarity of the bias applied to the semiconductor device is sometimes reversed, it is more effective to form the electric field electrodes 16 at both PN junctions. Furthermore, the electric field electrode 16 can also be made of metal. However, an electric field electrode made of a semiconductor such as polycrystalline silicon is more advantageous because it prevents a decrease in breakdown voltage distribution and prevents a decrease in pellet yield per wafer.

Figure 5 shows a second example in which the present invention is applied to a lateral type thyristor.
This is an example. 4 have the same functions as those in FIG. 4, but one end 17 of the depletion layer 14 is prevented from elongating by an electric field electrode 16 made of polycrystalline silicon semiconductor, and at the same time the other end 17' can be prevented by the N+ region 23.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between reverse voltage and leakage current in a thyristor according to the prior art in an initial state and a state after BT processing. FIG. 2 is a graph showing the relationship between the BT waiting time and leakage current in a thyristor for the prior art and the present invention. FIG. 3 is a cross-sectional view illustrating the present invention in detail. FIG. 4 and FIG. 5 are cross-sectional views showing a tenth embodiment and a twentieth embodiment of the present invention, respectively. In the plan view, 1 and 11 are Nu semiconductor substrates, 2°3.1
2, 13.13m, 13b are Pi regions 4, 14 are depletion layers, 5, 6.15.16 are electric field electrodes, 7.7' are the ends of the depletion layers, 8.18 are insulating films, 9, 19 23, the N+ region 20 is a PSG film, and 21, 22, and 24 are electrodes. Figure 3 10° 101102103 Reverse voltage (V) 87 hours (Hr)

Claims (1)

[Claims] A semiconductor substrate includes a first region of one conductivity type, a second region and a third region of the opposite conductivity type adjacent to the tenth region, and a first region of the one conductivity type formed in the twentieth region. 40 regions, the impurity concentration of the first region is lower than the impurity concentration of the 20th region, and the PN junction formed by the first region and the second region is in opposite directions. In the thyristor, the PN junction formed by the first region and the 30th region is biased in the forward direction.
The electrode is provided so as to extend over the first region through an insulating film, and the second electrode connected to the fourth region extends over the tenth region through an insulating film. A PN junction provided and biased in the forward direction facilitates extension of a depletion layer expanding into the first region by the second electrode, and the depletion layer is biased in the forward direction. said first to arrive at the junction.
A thyristor characterized in that the thyristor is blocked by an electrode.