JPH0715992B2 - Bidirectional 2-terminal thyristor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a PNPNP (NPNPN) type bidirectional two-terminal thyristor, and relates to improvement in lightning surge current withstanding and improvement in manufacturing yield. .

(Prior Art and Problems to be Solved) P ₁ such as a cross-sectional view shown in FIGS. 1 (a) and 1 (b) and a plan view in which the upper metal electrode is omitted, which is formed by a usual method such as impurity diffusion Two-terminal thyristors with N ₁ PN ₂ P ₂ type structure are widely used. (Note in the figure M _1, M ₂ is a metal electrode, I _n is an insulating film such as SiO ₂ film, d is P ₁ and showing the overlapping width of the P ₂ layer) surge current withstand a small inexpensive in addition recently It is widely used for protection against lightning surges in communication lines and the like because it is large and has two terminals, so it is easy to use.

However, in the current thyristor, it is impossible to improve the withstand capability against current surge of steep rising, such as surge, especially lightning surge, due to its structure. Moreover, variations in the surge current withstand capacity are greatly affected by variations in the vertical structure of the thyristor, the impurity concentration and thickness of each layer, and the geometrical position of each structure. For this reason, by applying highly accurate process technology and the like, the above-mentioned influence is eliminated as much as possible. However, there is a limit in improving the precision of the process technology, so it is difficult to mass-produce with a small variation in surge current withstand.
Therefore, depending on the conventional structure, it is difficult to manufacture a bidirectional two-terminal thyristor having excellent withstand lightning surge current with good yield.

The reason will be described below with reference to FIG. 2 for a general bidirectional two-terminal thyristor relating to the present invention shown in FIG.

In FIG. 2 (a) showing a cross-sectional view of the main part of the bidirectional two-terminal thyristor of FIG. 1, when a voltage is applied in the directions of (+) and (−) in the figure, most of the applied voltage is the junction J ₃ Take a
The current I hardly flows as in step 1 of FIG. 2 (b) showing the voltage-current characteristic. When the voltage reaches and exceeds the breakover voltage V _BO of the junction J ₃ , the current I increases as in step 2 of FIG. 2 (b) which is the turn-on transition region. Then as indicated by the broken line arrows in FIG. 2 (a) N ₁
The injection amount of electrons is increased from the layer. Therefore, the current amplification factor α _N of the N ₁ , P, N ₂ transistors increases due to its current dependence.

Meanwhile a voltage drop occurs due to the lateral resistance of N ₂ layer by a current distribution flowing through the N ₂ layer in the lateral direction, which is forward biased junction J _4. As a result, holes are injected as shown by the solid arrows in FIG. 2 (a), and the current based on this causes the current amplification rate α _{P of the} transistors P ₂ , N ₂ , and _P to increase. As a result, α _N + α _P = 1 and the junction J ₃ cannot hold the reverse breakdown voltage, so that the step 3 which is the turn-on transition area in FIG. However, in this case, the on-state is initially performed at one point, and then spreads over the entire surface of the element by the diffusion of carriers, and is turned on.

As described above, the thyristor of FIG. 1 performs the turn-on operation. Here, the withstand capability against a current surge of a steep rising such as a lightning surge is determined by the steps 2, 3 in the turn-on transition region of FIG. It depends on the power loss that occurs at turn-on and the speed at which the initial ignition at one point spreads over the entire turn-on area, especially due to the former. Therefore, the operation in steps 2 and 3 showing the turn-on transition region of FIG. 2B will be described in more detail with reference to FIG.

That is, in step 2 of FIG. 2 (b), the density of the current flowing across the junction J ₃ and, hence, the density of the current I ₁ flowing across the junction J ₂ is P ₁ , P ₂ shown in FIG. 2 (c). The relationship between the distance x from the center of the overlapping portion d of the layers and the current-voltage, as indicated by the curve (I) in the figure, the center O of the element due to the lateral resistance of each layer.
It becomes the largest at the point A (the portion close to the short-circuited portion). (Note that when negative resistance is shown in step 2 of FIG. 2B, this tendency of current concentration is further strengthened.) As a result, the current flowing through the N ₂ layer is the curve ( I
I) and the voltage drop caused by this current,
That is, the forward bias of the junction J _{4 in} FIG. 2 (a) rapidly increases up to the vicinity of point A as shown by the curve (III) in FIG. 2 (c), and thereafter the increase becomes gentle. Therefore, due to this forward bias voltage, a forward current flows out through the junction J _4, and the density of the current I ₂ is shown by the curve (I
As shown in V), it becomes maximum at the point B away from the center O of the element.

Here, the current amplification factors α _N and α _P related to the turn-on condition α _N + α _P = 1 depend on the current distribution of the currents I ₁ and I ₂ based on the short-circuited emitter structure of the bidirectional thyristor, The degree of dependence greatly changes depending on the vertical structure, the impurity concentration, the thickness, the lifetime of the N ₁ P ₁ N ₂ P layer, and the positional nonuniformity of each structure. Therefore, the current amplification factor α _N
Corresponding to the degree of dependence, becomes maximum at point A and decreases with distance from point A, as shown in the relationship diagram of distance x and current amplification factor shown in FIG. 2 (d). On the other hand, corresponding to the dependency of the current amplification factor α _P , it becomes maximum at point B as shown in FIG. 2 (d), and decreases with increasing distance from it. Therefore,
The maximum points of the current amplification factors α _N and α _P have a positional shift, and this positional shift fluctuates. This is qualitatively that the base widths W _N and W _P are changed as shown in FIG. The base widths W _N and W _P are increased as the point B moves away from the point A, and the current amplification factors α _N and α _P at the turn-on condition α _N + α _P = 1 are effectively It corresponds to the decrease. Therefore, considering the time transition of the turn-on phenomenon, the turn-on time is increased, and the power loss at the time of transition to the turn-on is increased. That is, it is not possible to expect further improvement in the surge current withstanding capability by the conventional thyristor structure.

In addition, the degree of decrease of the effective current amplification factors α _N and α _P and the increase of the turn-on time are influenced by the variation of the vertical structure in manufacturing, and the initial firing position is also varied accordingly. , It spreads to the turn-on area after turn-on and the speed can be varied. Therefore, depending on the conventional structure, it is difficult to manufacture a bidirectional two-terminal thyristor having a current surge withstanding capability of a steep rise higher than that of the present structure with a high yield.

(Object of the Invention) It is another object of the present invention to provide a means for stably mass-producing a bidirectional two-terminal thyristor having an excellent surge current withstanding capability by using a conventional ordinary manufacturing means such as impurity diffusion. Is.

(Means of the Present Invention for Solving Problems) The above elucidation results show that the cause of the decrease and variation in the surge current withstand is due to the relative displacement between the current amplification factors α _N and α _P. , which if such maximum point of the current amplification factor alpha _P occurs at the maximum point or near the current amplification factor alpha _N, it is possible to reduce power loss in the turn-on region, yet this respect the initial firing position It shows that the variation can be reduced by limiting to. On the other hand, the current amplification factors α _N and α _P depend on the current distribution in the device, and as is well known, the current distribution changes depending on the impurity concentration and thickness of the P ₁ N ₁ P ₂ N ₂ layer, the lifetime, etc. The current distribution can be controlled by the structure control means such as.

The present invention can solve the above-mentioned problems of the prior art by providing a region where the current amplification factor α _P is large in the corresponding portion at the position where the current amplification factor α _N is maximized by the structure control means such as the impurity concentration. The idea was made. Next, the present invention will be described with reference to examples.

In the present specification, mainly the first semiconductor layer is a P layer with the first conductivity type, the second semiconductor layer is an N layer with the second conductivity type, and the third semiconductor layer is a P layer with the first conductivity type. , The fourth semiconductor layer is a second conductivity type N layer and the fifth semiconductor layer is a first conductivity type P layer, but the first semiconductor layer is a second conductivity type and the second semiconductor layer is a first conductivity type. Conductivity type, third
The semiconductor layer may have the second conductivity type, the fourth semiconductor layer may have the first conductivity type, and the fifth semiconductor layer may have the second conductivity type.

(Embodiment) FIGS. 4 (a), (b), and (c) are cross-sectional views of an embodiment of the present invention in which the object is achieved by utilizing the control of the impurity concentration distribution as a structure control means, an upper metal electrode, A plan view in which the insulating film is omitted, and a distribution diagram of the impurity concentration in the AA 'section and the BB' section of FIG. 9A are characteristic features thereof are as follows. That is, by selective diffusion or other commonly used means, the P ₁ and P ₂ layers having the width d are
The point is that a partial C region portion in which the impurity concentration is locally increased is provided in the P ₁ and P ₂ layers, respectively, as shown in the concentration distributions of FIGS. 4 (c) and 4 (d).

By doing so, when a voltage is applied with the polarities (+) and (-) shown in FIG. 4 (a), the current in step 2, which is the turn-on region in FIG. 2 (a), is N ₁ , P , The lateral resistance of the N ₂ layer does not change, so its distribution is the same as that shown in FIG. 2 (c), but since the impurity concentration of the P ₂ layer is large, P ₂ for the same current is increased. , the current amplification factor of N _2, P transistor also becomes large. Therefore, the position distribution of the current amplification factor α _P is as shown by the solid line in FIG. 5 (the broken line curve in the figure is C
The curve of the current amplification factor of the portion other than the region is shown) α _N + α _P showing the turn-on condition is forcibly confined to the vicinity of the C region and becomes maximum, and equivalently, the base W described with reference to FIG. _{Reduce N} and W _P.

Therefore, the power loss in the turn-on region is reduced,
The lightning surge current withstand capability can be improved. The initial firing position is also C
It is forcibly confined to the region and acts as an ignition pole.

On the other hand, the above-described operation of the present invention is similarly obtained when a current flows in the opposite direction because the structure is symmetrical.

Therefore, according to the present invention, it is possible to manufacture a bidirectional two-terminal thyristor having a large withstand capability against a surge current having a steep rise such as a lightning surge with a high yield by using manufacturing means which are the same as those of the conventional method.

(Other Embodiments) One embodiment of the present invention has been described above. As a structure control means for increasing the current amplification factor α _P relatively to other portions in the C region, the C region is used.
The base width of the N ₁ and N ₂ layers is made small, and in the C area part
The current amplification factor α _N , by increasing the surface concentration of the P ₁ and P ₂ layers, further introducing a lifetime killer, or shortening the lifetime by using a known technique such as a lifetime killer getter, The same effect can be obtained by setting the relationship of α _P as shown in FIG. 5, and the above methods can be applied in an appropriate combination.

Further, as described above, as shown in FIG. 4, an example in which the C region in which the impurity concentration is locally increased is provided only in the central portion of the overlapping portion of the P ₁ and P ₂ layers has been described. It may be provided over almost the entire width of the element as shown in FIG. 6. In order to make the description easier to understand, the description has been made with reference to a schematic structural diagram in which parts not directly related to the present invention are omitted. It goes without saying that it is possible to apply a channel stopper that is normally used to secure the degree, various surface shapes for coping with other characteristics, and the like.

In the above, the PNPNP conductivity type element was explained.
The same effect can be obtained by applying it to an NPNP conductive type element and further to a composite thyristor having a PNPNP (NPNPN) structure in a part thereof.

(Effects of the Invention) As is apparent from the above description, according to the present invention, a bidirectional two-terminal thyristor having a large surge current withstanding steep rise is manufactured with a high yield by using exactly the same manufacturing means as the conventional one, such as impurity diffusion. It has an excellent effect.

[Brief description of drawings]

1, 2 and 3 are explanatory views of a conventional element, and FIG.
5 and 5 are explanatory views of one embodiment of the present invention, and FIG. 6 is an explanatory view of another embodiment of the present invention.

Claims (2)

[Claims] 1. A first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, a third semiconductor layer of a first conductivity type, a fourth semiconductor layer of a second conductivity type, and a fourth semiconductor layer of a second conductivity type. A fifth semiconductor layer of one conductivity type is composed of five layers arranged in this order, the second semiconductor layer exposed on one surface is the first semiconductor layer, and the fourth semiconductor exposed on the other surface. In a bidirectional two-terminal thyristor in which each layer is short-circuited to the fifth semiconductor layer to form one electrode, the first semiconductor layer and the fifth semiconductor layer have a central portion when viewed from the surface of the thyristor. And a region in which the impurity concentration is locally increased is provided in the central portion of the first semiconductor layer and the fifth semiconductor layer including the overlapping portion. 2-directional thyristor. 2. A first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, a third semiconductor layer of a first conductivity type, a fourth semiconductor layer of a second conductivity type, and a fourth semiconductor layer of a second conductivity type. A fifth semiconductor layer of one conductivity type is composed of five layers arranged in this order, the second semiconductor layer exposed on one surface is the first semiconductor layer, and the fourth semiconductor exposed on the other surface. In a bidirectional two-terminal thyristor in which each layer is short-circuited to the fifth semiconductor layer to form one electrode, the first semiconductor layer and the fifth semiconductor layer have a central portion when viewed from the surface of the thyristor. And a region where the impurity concentration is increased in a strip shape in the entire width direction of the first semiconductor layer and the fifth semiconductor layer including the overlapping portion of the entire width direction region is provided. Bidirectional two-terminal siri Data.